United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Proceedings

RMRS-P-11

September1999

Proceedings:

Shrubland Ecotones

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Rocky Mountain Research Station

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Abstract

McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999. Proceedings: shrubland ecotones; 1998 August 12–14;

Ephraim, UT. Proc. RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

299 p.

The 51 papers in this proceedings include an introductory keynote paper on ecotones and hybrid zones and a final paper describing

the mid-symposium field trip as well as collections of papers on ecotones and hybrid zones (15), population biology (6), community

ecology (19), and community rehabilitation and restoration (9). All of the papers focus on wildland shrub ecosystems; 14 of the papers

deal with one aspect or another of sagebrush (subgenus Tridentatae of Artemisia) ecosystems. The field trip consisted of descriptions

of biology, ecology, and geology of a big sagebrush (Artemisia tridentata) hybrid zone between two subspecies (A. tridentata ssp.

tridentata and A. t. ssp. vaseyana) in Salt Creek Canyon, Wasatch Mountains, Uinta National Forest, Utah, and the ecotonal or clinal

vegetation gradient of the Great Basin Experimental Range, Manti-La Sal National Forest, Utah, together with its historical

significance. The papers were presented at the 10th Wildland Shrub Symposium: Shrubland Ecotones, at Snow College, Ephraim,

UT, August 12–14, 1998.

Keywords: wildland shrubs, ecotone, hybrid zone, population biology, community ecology, restoration, rehabilitation.

The use of trade or firm names in this publication is for reader information and does not

imply endorsement by the U.S. Department of Agriculture or any product or service

Acknowledgments

The symposium, field trip, and subsequent publication of these proceedings were facilitated by many people and

organizations. We thank all who helped. In particular we extend thanks to Dave Lanier and his staff of the Great Basin

Experimental Education Center of Snow College for providing publicity, facilities, and all around support; President

Gerald Day and Vice President Rick White of Snow College, Forest Supervisor Janette Kaiser and Ranger Tom Shore

of the Manti-La Sal National Forest, and Forest Ecologist Dea Nelson and Ranger Tom Tidwell of the Uinta National

Forest for hosting various aspects of the symposium and field trip; Scott Walker of the Utah Division of Wildlife

Resources, Great Basin Research Center, Gary Jorgensen and Dick Tennent the Rocky Mountain Research Station

Great Basin Experimental Range, and Kelly Memmott of the Rocky Mountain Research Station Shrub Sciences

Laboratory for logistical support; and Sallie Wolsey of the Shrub Sciences Laboratory and volunteer Chris Kitchen for

clerical and general support. Technical sessions were chaired ably by Kent Ostler, Barbara Wachocki, Eugene Schupp,

and Carl Wambolt. Field trip leaders were Durant McArthur, Steve Monsen, and Richard Stevens. We thank the Rocky

Mountain Research Station Publishing Services for preparing the final publication.

E. Durant McArthur

W. Kent Ostler

Carl L. Wambolt

Compilers

Publisher’s note: Papers in this report were reviewed by the compilers. Rocky

Mountain Research Station Publishing Services reviewed papers for format and style.

Authors are responsible for content.
Compilers

E. Durant McArthur, U.S. Department of Agriculture, Forest Service, Rocky Mountin Research Station,

Shrub Sciences Laboratory, Provo, UT

W. Kent Ostler, Bechtel Nevada, Las Vegas, NV

Carl L. Wambolt, Department of Animal and Range Sciences, Montana State University, Bozeman, MT

Proceedings: Shrubland Ecotones

Ephraim, UT, August 12–14, 1998
Shrub Research Consortium

USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory*, Provo, Utah,

E. Durant McArthur (chair)

Brigham Young University*, Provo, Utah, Daniel J. Fairbanks

USDA Agricultural Research Service, Renewable Resource Center*, Reno, Nevada, James A. Young

Utah State University*, Logan, Eugene W. Schupp

State of Utah, Department of Natural Resources, Division of Wildlife Resources*, Ephraim, Scott C. Walker

University of California, Los Angeles, Philip W. Rundel

Colorado State University, Ft. Collins, William K. Lauenroth

University of Idaho, Moscow, Steven J. Brunsfeld

University of Montana, Missoula, Donald J. Bedunah

Montana State University, Bozeman, Carl L. Wambolt

University of Nevada, Reno, Paul T. Tueller

University of Nevada, Las Vegas, Stanley D. Smith

Oregon State University, Corvallis, Lee E. Eddleman

New Mexico State University, Las Cruces, Kelly W. Allred

Texas A & M System, Texas Agricultural Experiment Station, San Angelo, Darrell N. Ueckert

Texas Tech University, Lubbock, Ronald E. Sosebee

USDA Agricultural Research Service, High Plains Grassland Research Station, Cheyenne, Wyoming,

D. Terrance Booth

USDA Agricultural Research Service, Jornada Experimental Range, Las Cruces, New Mexico, Jerry R. Barrow;

USDA Forest Service, Rocky Mountain Research Service, Great Basin Ecology Laboratory, Reno, Nevada,

Robin J. Tausch

University of Utah, Salt Lake City, James R. Ehleringer

Weber State University, Ogden, Utah, Barbara A. Wachocki

Washington State University, Pullman, Benjamin A. Zamora

University of Wyoming, Laramie, Stephen E. Williams

Battelle Pacific Northwest Laboratories, Richland, Washington, Janelle L. Downs

Bechtel Nevada, Las Vegas, Nevada, W. Kent Ostler

*Charter members

The Shrub Research Consortium was formed in 1983 with five charter members (see list). Over time SRC has grown to its present

size of 25 institutional members. The SRC had three principal objectives in its charter: (1) developing plant materials for shrubland

rehabilitation; (2) developing methods of establishing, renewing, and managing shrublands in natural settings; and (3) assisting with

publication and dissemination of research results. These objectives have been met by a series of symposia sponsored by the

Consortium and partners. This publication is the 10th in the series; the previous nine are listed on the next page. Proceedings of all

publications to date have been published by the U.S. Department of Agriculture, Forest Service Intermountain Research Station and

Rocky Mountain Research Station. The executive committee has plans for two more symposia: (1) in Provo, UT, in the year 2000

with a shrubland ecosystem genetics and biodiversity theme in conjunction with the 25th anniversary celebration of the establishment

of the Rocky Mountain Research Station’s Shrub Sciences Laboratory; and (2) in Laramie, WY in 2002 with a shrubland ecosystem

seeds and soil theme. Each symposium has had a theme but the executive committee has encouraged attendance and participation

by shrubland ecosystem biologists and managers with wider interests than any particular symposium theme—the heart of the

Consortium’s programs are wildland shrub ecosystem biology, research, and management.
Availability of Previous Wildland Shrub Symposia Proceedings

First: Tiedemann, A. R.; Johnson, K. L., compilers. 1983. Proceedings—research and management of bitterbrush and cliffrose

in western North America; 1982 April 13-15; Salt Lake City, UT. General Technical Report INT-152. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 279 p. Out of print—

available from National Technical Information Service as document PB83-261537 A13.

Second: Tiedemann, A. R.; McArthur, E. D.; Stutz, H. C.; Stevens, R.; Johnson, K. L., compilers. 1984. Proceedings—symposium

on the biology of Atriplex and related chenopods; 1983 May 2-6; Provo, UT. General Technical Report INT-172. Ogden,

UT: U. S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 309 p. Out

of print—available from National Technical Information Service as document PB85-116358 A14.

Third: McArthur, E. D.; Welch, B. L., compilers. 1986. Proceedings—symposium on the biology and management of Artemisia

and Chrysothamnus; 1984 July 9-13; Provo, UT. General Technical Report INT-200. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station. 398 p. Out of print—available from National Technical

Information Service as document PB86-182318 A18.

Fourth: Provenza, F. D.; Flinders, J. T.; McArthur, E. D., compilers. 1987. Proceedings—symposium on plant herbivore

interactions; 1985 August 7-9; Snowbird, UT. General Technical Report INT-222. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station. 398 p. A few copies are available from the Rocky Mountain

Research Station; otherwise available from National Technical Information Service as document PB90-228578 A09.

Fifth: Wallace, A.; McArthur, E. D.; Haferkamp, M. R., compilers. 1989. Proceedings—symposium on shrub ecophysiology

and biotechnology; 1987 June 30-July 2; Logan, UT. General Technical Report INT-256. Ogden, UT: U.S. Department

of Agriculture, Forest Service, Intermountain Research Station 183 p. Available from the Rocky Mountain Research

Station.

Sixth: McArthur, E. D.; Romney, E. M.; Smith S. D.; Tueller, P. T., compilers. 1990. Proceedings—symposium on cheatgrass

invasion, shrub die-off, and other aspects of shrub biology and management; 1989 April 5-7; Las Vegas, NV. General

Technical Report INT-276. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station.

351 p. Out of print—available from National Technical Information Service as document PB91-117275 A16.

Seventh: Clary, W. P.; McArthur, E. D.; Bedunah, D.; Wambolt, C. L., compilers. 1992. Proceedings—symposium on ecology and

management of riparian shrub communities; 1991 May 29-31; Sun Valley, ID. General Technical Report INT-289.

Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 232 p. Out of print—

available from National Technical Information Service as document PB92-227784 A11.

.

Eighth: Roundy, B. A.; McArthur, E. D.; Haley, J. S.; Mann, D. K., compilers. 1995. Proceedings: wildland shrub and arid land

restoration symposium; 1993 October 19-21; Las Vegas, NV. General Technical Report INT-GTR-315. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Research Station. 384 p. Available from the Rocky Mountain

Research Station.

Ninth: Barrow, J. R.; McArthur, E. D.; Sosebee, R. E.; Tausch, R. J., compilers. 1996. Proceedings: shrubland ecosystem

dynamics in a changing environment; 1995 May 23-25; Las Cruces, NM. General Technical Report INT-GTR-338.

Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 275 p. Available from the

Rocky Mountain Research Station.

Contents

Introduction and Keynote Address .................................................................................................................. 1

E. Durant McArthur Ecotones: Introduction, Scale, and Big Sagebrush Example.......................................... 3

Stewart C. Sanderson

Ecotones and Hybrid Zones ...............................................................................................................................9

John H. Graham Ecological Analysis of the Big Sagebrush Hybrid Zone ................................................11

D. Carl Freeman

Han Wang

E. Durant McArthur

D. Carl Freeman Narrow Hybrid Zone Between Two Subspecies of

Kathleen J. Miglia Big Sagebrush (Artemisia tridentata: Asteraceae):

E. Durant McArthur X. Performance in Reciprocal Transplant Gardens ......................................................15

John H. Graham

Han Wang

Bruce N. Smith Differences in Temperature Dependence of Respiration

Susan Eldredge Distinguish Subspecies and Hybrid Populations of Big Sagebrush:

David L. Moulton Nature Versus Nurture ..................................................................................................25

Thomas A. Monaco

Angela R. Jones

Lee D. Hansen

E. Durant McArthur

D. Carl Freeman

James A. Young Ecotones Between Artemisia nova and A. tridentata Plant

Charlie D. Clements Communities in the Buckskin Mountains of Western Nevada ......................................29

Scott C. Walker Characteristics of Mountain Mahogany (Cercocarpus) Species and

Deborah Turley Hybrids in Utah Hybrid Zone .........................................................................................32

Merrill Webb Occurrence of Birds on a Great Basin-Mohave Desert Ecotone in

Southwestern Utah .......................................................................................................35

Jack D. Brotherson Measured and Inferred Moisture Gradient Relationships Across

Ecotone Boundaries in Shrub-Dominated Foothill Communities ..................................40

Warren P. Clary Riparian Zones—The Ultimate Ecotones?....................................................................49

Dean E. Medin

Thomas A. Eddy Ecotonal Dynamics of the Invasion of Woody Plants into the Tallgrass Prairie ............56

Stanley G. Kitchen Species Richness and Community Structure Along a Great Basin

E. Durant McArthur Elevational Gradient......................................................................................................59

Gary L. Jorgensen

Eugene W. Schupp Piñon and Juniper Seed Dispersal and Seedling Recruitment at

Jeanne C. Chambers Woodland Ecotones ......................................................................................................66

Stephen B. Vander Wall

José María Gómez

Marcelino Fuentes
Robin J. Tausch Fifty Years of Ecotone Change Between Shrub and Tree Dominance

Robert S. Nowak in the Jack Springs Pinyon Research Natural Area ...................................................... 71

Paul T. Tueller Approaches to Mapping Ecotone Boundaries Using Emerging

Remote Sensing Technology ........................................................................................78

R. F. Beck Mesquite-Grassland Ecotones in the Chihuahuan Desert ............................................84

R. P. McNeely

R. P. Gibbens

Sherel Goodrich Sagebrush Ecotones and Average Annual Precipitation .............................................. 88

E. Durant McArthur

Alma H. Winward

Population Biology .............................................................................................................................................95

D. Terrance Booth Freezing Tolerance of Imbibed Winterfat Seeds: Possible

Yuguang Bai Mechanisms and Ecotypic Differences ......................................................................... 97

James T. Romo

Inés Ibáñez Successional History of a Curleaf Mountain Mahogany Stand:

Eugene W. Schupp a Hypothesis ...............................................................................................................102

Janis L. Boettinger

J. L. Downs Leaf Surface Characteristics and Gas Exchange in

R. A. Black Artemisia tridentata subspecies wyomingensis and tridentata ...................................108

Simon A. Lei Phenological Events and Litterfall Dynamics of Blackbrush in

Southern Nevada ........................................................................................................113

Jasleen Kaur Biodiversity in the Management of the Shrub Zizyphus nummularia

K. M. M. Dakshini with Special Reference to Semiarid Regions in India .................................................119

Bilquees Gul Population Dynamics of a Perennial Halophyte Allenrolfea occidentalis ....................124

Darrell J. Weber

M. Ajmal Khan

Community Ecology .........................................................................................................................................131

James A. Young Native Perennial Grass Communities of the Carson Desert of

Charlie D. Clements Northwestern Nevada .................................................................................................133

W. K. Ostler The Classification of Shrublands on the Nevada Test Site ......................................... 137

D. J. Hansen

D. B. Hall

D. J. Hansen The Transition from Mojave Desert to Great Basin Desert on the

W. K. Ostler Nevada Test Site ........................................................................................................148

D.B. Hall

Sherel Goodrich Some Features of Wyoming Big Sagebrush Communities on Gravel

Dwain Nelson Pediments of the Green River in Daggett County, Utah .............................................159

Natalie Gale
Deborah Turley Twig Demography of True Mountain Mahogany

Bruce A. Roundy (Cercocarpus montanus Scop.) ..................................................................................168

Scott C. Walker

Bruce L. Welch Add Three More to the List of Big Sagebrush Eaters .................................................171

Stanley G. Kitchen Annualization of Rodent Burrow Clusters and Winterfat Decline

Gary L. Jorgensen in a Salt-Desert Community ........................................................................................175

Allen Huber Big Sagebrush, Crested Wheatgrass, and Grazing on Gravel-Cobble

Sherel Goodrich Pediments of the Duchesne River Formation and Quaternary

Deposits in Uintah County, Utah .................................................................................181

Andrés F. Cibils Shrub-Grass Interactions in Relation to Cattle Grazing in

Richard H. Hart Atriplex canescens ......................................................................................................186

David M. Swift

Rex G. Cates Predisposition of Willows to Elk Browsing Due to Willow Interactions

Jiping Zou with Abiotic Factors .....................................................................................................191

Stuart C. Wooley

Francis J. Singer

Lauryl C. Mack

Linda Zeigenfuss

Sherel Goodrich Ungulate Browsing of Two Populations of Rubber Rabbitbrush .................................196

E. Durant McArthur

Allen Huber

Jeffrey E. Ott

C. J. Murray Fusing Vegetation Data Sets to Provide a Spatial Analysis of

L. L. Cadwell Sage Grouse Habitat on the Army’s Yakima Training Center.....................................200

J. L. Downs

M. A. Simmons

Steven A. Lei Ecological Leaf Anatomy of Seven Xerophytic Shrub Species

Simon A. Lei in Southern Nevada ....................................................................................................206

Leslie J. Thomas

Steven A. Lei Ecology of Psammophytic Plants in the Mojave, Sonoran, and

Simon A. Lei Great Basin Deserts....................................................................................................212

Simon A. Lei Effects of Severe Drought on Biodiversity and Productivity in a

Creosote Bush-Blackbrush Ecotone of Southern Nevada .......................................... 217

J. H. Kaltenecker Biological Soil Crusts in Three Sagebrush Communities

M. C. Wicklow-Howard Recovering from a Century of Livestock Trampling ...................................................222

R. Rosentreter

M. Ajmal Khan Seed Bank Strategies of Coastal Populations at the Arabian Sea Coast ...................227

Bilquees Gul

Sara J. Manning The Effects of Water Table Decline on Groundwater-Dependent

Great Basin Plant Communities in the Owens Valley, California ................................231
Carl L. Wambolt Response of Shrubs in Big Sagebrush Habitats to Fire on the

Trista L. Hoffman Northern Yellowstone Winter Range...........................................................................238

Chris A. Mehus

Community Rehabilitation and Restoration ...............................................................................................243

Rosemary L. Pendleton Response of Blackbrush (Coleogyne ramosissima) Seedlings to

Burton K. Pendleton Inoculation with Arbuscular Mycorrhizal Fungi............................................................245

Steven D. Warren

J. R. Barrow The Role of Endophytic Fungi in the Survival and Establishment of

I. Feder Fourwing Saltbush (Atriplex canescens [Pursh] Nutt.) in an Arid Environment ..........252

H. C. Monger

Donald J. Bedunah Antelope Bitterbrush and Scouler’s Willow Response to a

Michael G. Harrington Forest Restoration Project ..........................................................................................256

Dayna M. Ayers

Derek B. Hall Reclaiming Disturbed Land Using Supplemental Irrigation in the

David C. Anderson Great Basin/Mojave Desert Transition Region After Contaminated

Soils Remediation: the Double Tracks Project............................................................260

Mary Dudley Volunteers and Planting Techniques for Restoring Southwestern Idaho

Riparian Habitats ........................................................................................................266

Alison Stewart ‘Immigrant’ Forage Kochia (Kochia prostrata) Seed Germination as

Val Jo Anderson Affected by Storage Conditions ..................................................................................274

Stanley G. Kitchen

Chad S. Horman Effects of Utah Juniper (Juniperus osteosperma [Torr.] Little) Litter

Val Jo Anderson Leachate on Germination of Several Range Plant Species ........................................280

Paul R. Jones Restoration of the Moss (Musci) Component of the Microbiotic Crust

Marcia Wicklow-Howard to the Western Snake River Plain, Idaho: Inoculation of Fragmented

Mike Pellant Arid-Land Moss Tissue to Three Rangeland Soil Surface Treatments .......................283

A. L. Hild Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis)

B. Christensen Seedling Growth and Maternal Plant Stand Position ..................................................287

A. Maier

Field Trip .............................................................................................................................................................291

E. Durant McArthur Field Trip Report: Shrubland Ecotones .......................................................................293

Stephen B. Monsen

Richard Stevens
USDA Forest Service Proceedings RMRS-P-11. 1999 1

Introduction and

Keynote Address

Ecotones and

Hybrid Zones

Population Biology

Community Ecology

Community Rehabilitation

and Restoration

Field Trip

USDA Forest Service Proceedings RMRS-P-11. 1999 12

Introduction and

Keynote Address

USDA Forest Service Proceedings RMRS-P-11. 1999 3

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

 E. Durant McArthur is Project Leader and Research Geneticist, and

Stewart C. Sanderson is Research Geneticist (Professional), Shrub Sciences

Laboratory, Rocky Mountain Research Station, Provo, UT 84606.

Ecotones: Introduction, Scale, and

Big Sagebrush Example

E. Durant McArthur

Stewart C. Sanderson

Abstract—Ecotones and other boundary concepts are important in

biological processes. The scale of biological boundaries is enormous

(from molecular and cellular to landscape and biome). Boundaries

offer the opportunity for interaction at these many different scales.

Traditionally, ecotones have been considered junction zones between two or more communities where the processes of exchange or

competition between neighboring communities or subunits of communities occur. Depending on scale, climate, topography, soil characteristics, species interactions, physiological parameters, and population genetics are important considerations at ecotonal boundaries.

Hybridization between compatible taxa often occurs at ecotones.

Members of the big sagebrush (Artemisia tridentata) species complex (subgenus Tridentatae of Artemisia) often meet at ecotones

affording opportunities for hybridization. Some taxa form hybrid

zones at such sites and others do not. Data from sagebrush hybrid

zones favor the bounded superiority hybrid zone model. Stable

hybrid zones with their array of genetic recombinants afford the

opportunity for evolutionary radiation when dynamic climatic processes change habitats and should be considered for management

purposes.

Ecotones and other boundary concepts are important in

biological processes and systems. Many fundamental processes and functions occur at biological boundaries of various scales. Whereas ecotones are generally considered to be

tied to plant community boundaries, the scale of biological

boundaries is enormous, from molecular and cellular to

landscapes and biomes. Boundaries offer the opportunity for

interaction between and among cells and cellular components, organs, organisms, populations of organisms, communities, groups of communities or landscapes, and biomes

(large landscapes with a characteristic late seral dominant

vegetation type, for example, grasslands). The interactions

may be in the nature of exchange of organisms through

migration or invasion or of exchange of organismic characteristics by hybridization or introgression, or of displacement of organisms and modification of habitats by invasion

or competition from other organisms. This paper presents an

introduction to the symposium by examining ecotonal concept history, ecotone definition, the general properties of

ecotones, and other biological boundaries in smaller and

larger scale than traditional community ecotones. Special

attention will be paid to hybridization in sagebrush (subgenus Tridentatae of Artemisia) and hybrid zones between

subspecies of big sagebrush (A. tridentata).

Ecotones ______________________

Ecotone Definition

Pioneering American plant ecologist Frederic Clements

(1905) defined an ecotone as a “junction zone between two

communities, where the processes of exchange or competition between neighboring formations might be readily observed.” Clements (1905) further described ecotones as tension zones where principal species from adjacent communities

meet their limits. Eugene Odum, perhaps the pre-eminent

American ecologist of the last half-century, described an

ecotone as “a transition between two or more diverse communities.... The ecotonal community commonly contains

many of the organisms of each of the overlapping

communities...and organisms characteristic (or) restricted

to the ecotone” (Odum 1971).

A more recent and formal definition is that of the SCOPE/

MAB working group (Holland (1988): “zone of transition

between adjacent ecological systems, having a set of characteristics uniquely defined by space and time scales and by

the strength of the interactions between adjacent ecological

systems.” In this definition the term “ecological system”

includes such commonly described hierarchical entities such

as demes, populations, communities, ecosystems, landscapes,

and biomes (Gosz 1991; Holland 1988). In this definition

ecotones are interpreted as biological boundaries of various

scales. It is important to remember that boundaries are

identifiable and meaningful only relative to specific questions and points of reference. An ecotone at one spacial scale

may be seen as a collection of patches on a finer scale (Gosz

1991).

Scale of Ecotones

Gosz (1993) presented ecotonal hierarchies (table 1). In

the table, ecotones and their possible constraints are listed

from the biome to population levels. Biological boundaries at

smaller scales have analogous properties to the classically

understood organismic and community ecotones (Wiens and

others 1985). The analogy is that boundaries between elements in a community or landscape function at a different

scale or level than those in organismal or physical systems.

Like cellular membranes, ecotonal boundaries vary in their

permeability or resistance to flows. The currency of flow is

contrasting, that is, from organisms to genes to chemicals.

The variation is a consequence of characteristics of the
4 USDA Forest Service Proceedings RMRS-P-11. 1999

boundary, for example, its thickness, the degrees to which

the separated patches, organisms, cells, and cellular component differ and their responses of different materials, organisms, or abiotic factors to the boundary (Gosz 1991).

We conclude this brief discussion on scale by citing some

cellular ecotone examples that demonstrate boundary exchange phenomena:

• Chloroplasts are more homologous to blue-green algae

RNA (47 percent) than they are to cytoplasmic RNA

from their same cells (~1 percent) (Schwemmler 1989).

• Mitochondrial ribosomes are more similar to bacteria

than they are to cytoplasmic ribosomes (Schwemmler

1989).

• The sagebrush (Artemisia subgenus Tridentatae) chloroplast genome has been captured by sand sage (Artemisia filifolia of subgenus Dracunculus) (Kornkven 1997).

Traditional Views of Ecotones

After Clements’ (1905) clarion call about ecotones being a

junction zone between plant communities, scientists and

resource managers began to study ecotones. By the 1930’s

three spacial scales of ecotones with attendant scientific and

management implications had developed (Risser 1995). These

were:

• Wildlife biologists awareness of the value of local edges

or margins for habitat, cover, and food for many game

and nongame species.

• Scientists began studying conspicuous transitional areas at mountain and tundra tree lines including exploring adaptations that enable plants to survive in those

locations.

• Scientists were interested in the broad transitional

areas between continental-scale biomes, for example,

Arctic tundra and boreal forest, North American deciduous forest, and central plains grassland.

Currently, ecotones are studied over broader scales than

these traditional areas, but these areas remain topical

(Holland and others 1991; Levin 1995; Risser 1995; Unwin

and Watson 1997). Risser (1995) in his review of the study of

ecotones suggests that the most important current ecotonal

studies are the dynamic impact of ecotones on an active

landscape, ecotones significant roles in supporting a high

level of biological diversity, ecotones role as a source of high

levels of primary and secondary productivity (ecotones frequently intensify or concentrate the flows of water, nutrients, and other materials, as well as the movement of

organisms across the landscape), ecotones provision of important components of wildlife habitat, and ecotones acting

as sensitive indicators of global change. As an example of

shifting ecotonal boundaries, one of Risser’s (1995) important areas of current ecotonal study, Walker and others

(1996) presented data showing changes in the principal

cover types on the Great Basin Experimental Range (see

field trip report—McArthur and others, this proceedings)

from 1937 to 1991, wherein quaking aspen (Populus tremuloides) cover types declined from 40 percent to 22 percent,

Gambel oak (Quercus gambelii) cover types increased from

16 to 27 percent, and spruce-fir (Picea spp.–Abies ssp.)

increased from 13 to 22 percent). We also comment briefly on

another of Risser’s (1995) important areas of current study,

that of the importance of ecotones to biological diversity. Not

only do ecotones function as an area of concentration of

higher numbers of species through the accommodation of a

higher number of species (~– species diversity) than the

adjacent more traditional communities, but they may also

be areas of greater genetic diversity of individual species or

serve as bridges of gene flow between species populations

(Levin 1995; McArthur 1989). Ecotones in time can be

considered not only as species and community migration in

response to changing conditions but also on a particular site

as succession occurs.

Two conditions favor the formation of traditional community ecotones (Gosz 1992; Risser 1995): (1) Steep gradients in

physical environmental variables, for example, topography

and climate, that directly affect key ecological processes and

the distribution of organisms; (2) Threshold or nonlinear

responses to gradual gradients in the physical environment

that cause large changes in ecosystem dynamics and the

distributions of dominant species. Population ecotones

(table 1) are facilitated by the traditional community ecotones because it is often at the traditional community ecotones that interspecific and intraspecific contact occurs so

that interactions can occur.

Hybridization and Hybrid Zones ___

For the balance of this paper we discuss population ecotones or plant patterns (table 1) using the sagebrush (subgenus Tridentatae of Artemisia) example.

Introgression and Hybridization in

Sagebrush

Big sagebrush (Artemisia tridentata) in particular and

sagebrush (subgenus Tridentatae) in general have apparently gained their landscape-dominant, broad-niche-filling

status through a reticulate, hybridizing, evolutionary pathway (McArthur and others 1981, 1988; Ward 1953; Winward

and McArthur 1995). Several extant taxa are thought to

be the product of hybridization events, some involving

Table 1—Ecotone hierarchy for biome transition area. The range of

constraints and interactions at each level in the ecotone

hierarchy is given; x symbolizes interactions between

constraints (from Gosz 1993).

Ecotone hierarchy Probable constraints

Biome ecotone Climate (weather) x topography

Landscape ecotone Weather x topography x soil characteristics

(mosaic pattern)

Patch ecotone Soil characteristics x biological vectors x

species interactions x microtopography x

microclimatology

Population ecotone Interspecies interactions x intraspecies

(plant pattern) interactions x physiological controls x

population genetics x microtopography x

microclimatology
USDA Forest Service Proceedings RMRS-P-11. 1999 5

polyploidization as well (table 2). We believe that ecotonal

boundaries created as sagebrush and other plant species

moved across the landscape in response to past climatic and

geological changes facilitated contact between sagebrush

taxa (McArthur and Plummer 1978; McArthur and others

1981; Thompson 1991). Given the opportunity, sagebrush

taxa will hybridize. Such opportunities are documented in

table 3 where tightly parapatric or sympatric populations of

several sagebrush taxa are listed. Hybrids resulting from

populations of different taxa in close proximity are probably

incidental and not significant in the long run (Beetle 1970).

However, some have resulted in new adaptative forms,

formally described or otherwise (table 2). We believe that

hybrid zones (see next section) form a stable reservoir of

adapted plants available to migrate into areas that become

available with changing environmental conditions, for example, climate and geology.

Sagebrush Hybrid Zones

Several papers in this proceedings, that is Graham and

others, Freeman and others, Smith and others, Young and

Clements, and Goodrich and others, report the results of

research in sagebrush hybrid zones or ecotones. Hybrid zone

theory is an area of considerable current interest by evolutionary ecologists (Arnold 1997; Harrison 1993). Why is this

so? It is because of the dilemma posed by the number and

stability of hybrid zones despite the dogma of the biological

species concept that hybrids inherently have a reduced

fitness in respect to their parents (Arnold 1997; Freeman

and others, this proceedings; Graham and others, this proceedings; Harrison 1993; and references cited therein).

There are three principal hypotheses that address the

stability of hybrid zones. Two of these accept the reduced

fitness of hybrids: (1) the dynamic equilibrium model is built

on the premise that stability is maintained by a counterbalance of gene flow across the hybrid zone offset by reduced

hybrid fitness (Barton and Hewitt 1985)—with this model

the hybrid zone is independent of the environment and

would not necessarily occur at a ecotone; (2) the mosaic

hybrid zone model is built on the premise that hybrid zones

occur in ecotones that are a mosaic of two habitats with each

parental type adapted to different elements of the mosaics

and with unfit hybrids not adapted to either mosaic element

(Harrison and Rand 1989). The third model, the bounded

hybrid superiority model (Moore 1977), is built on the premise

that hybrids are of superior fitness but only in the hybrid

zone that occupies an ecotone between parental habitats.

Table 2—Described and undescribed hybrid taxa or populations in sagebrush (subgenus Tridentatae of Artemisia).

Taxon or population Putative parents References

A. arbuscula ssp. longicaulis A. arbuscula ssp. arbuscula x Winward and McArthur 1995; McArthur

A. tridentata ssp. wyomingenis and Sanderson, in press

A. argillosa A. cana ssp. visicidula x Beetle 1959

A. longiloba

A. tridentata ssp. spiciformis A. tridentata ssp. vaseyana x Beetle 1959; Goodrich and others 1985;

A. cana ssp. visicidula McArthur and Goodrich 1986; Gunawardena 1994

A. tridentata ssp. xericensis A. tridentata ssp. tridentata x Winward 1970; Rosentretter and Kelsey 1991;

A. tridentata ssp. vaseyana McArthur and Sanderson, in press

A. tridentata ssp. wyomingensis A. tridentata ssp. tridentata x Beetle and Young 1965; Winward 1975;

A. tridentata ssp. vaseyana with McArthur 1983; McArthur and others 1998b,c

perhaps some involvement with

A. nova as well

“Introgressed Wyoming big sagebrush” A. tridentata ssp. wyomingenis x Winward, personal communication; McArthur and

A. tridentata ssp. vaseyana Sanderson, in press; discussion, this paper

“Dubois sagebrush” A. tripartita x Winward, personal communication;

A. tridentata ssp. wyomingenis discussion, this paper

“Gosiute sagebrush” A. tridentata ssp. wyomingenis x Winward, personal communication;

A. longiloba discussion, this paper

“Big sagebrush hybrid zone” A. tridentata ssp. tridentata x Hybrid zone papers in table 4, those footnoteda

A. tridentata ssp. vaseyana

Table 3—Sympatric and tightly parapatric distributions of sagebrush

(subgenus Tridentatae of Artemisia) taxa (data from

McArthur and Sanderson, in press).

A. tridentata ssp. tridentata and A. tridentata ssp. vaseyana

A. tridentata ssp. tridentata and A. tridentata ssp. wyomingensis

A. arbuscula ssp. arbuscula and A. tridentata ssp. wyomingensis

A. tridentata ssp. vaseyana and A. cana ssp. viscidula

A. tridentata ssp. vaseyana and A. tridentata ssp. spiciformis

A. arbuscula ssp. arbuscula and A. tridentata ssp. vaseyana

A. cana ssp. cana and A. tridentata ssp. wyomingensis

A. tridentata ssp. wyomingensis and A. tripartita ssp. tripartita

A. tridentata ssp. wyomingensis and A. nova

A. nova and A. arbuscula ssp. arbuscula
6 USDA Forest Service Proceedings RMRS-P-11. 1999

A series of studies in natural hybrid zones and in gardens

comprised of parental and natural and synthesized hybrids

have led us and our colleagues (principally Carl Freeman,

John Graham, and Han Wang) to support the validity of the

bounded superiority hybrid zone model for the sagebrush

system (table 4). These studies have involved plant morphology, growth rates, plant chemistry, selection gradients and

fitness, developmental instability, insect relationships, soils,

mineral uptake, plant community dynamics, and respiration and water potential. Whereas each study may not

clearly distinguish among the validity of the three principal

hybrid zone models, taken in toto, the studies strongly

support the bounded hybrid superiority model.

Consequences of Sagebrush

Hybridization and Hybrid Zones

We believe that there are important evolutionary and

management considerations for fit hybrids in a stable hybrid

zone. Such zones may be narrow as in the case of the Salt

Creek Hybrid Zone (see Field Trip report—McArthur and

others, this proceedings, and the narrow hybrid zone papers

of table 4) but also broad. Our colleague, Alma Winward

(personal communication, August 1998, and on other occasions), has suggested that at least three sagebrush forms,

which have not been formally described, may be stabilized

hybrids (see table 2 for summary of described and nondescribed hybrid taxa or populations). The first is a plant

that has intermediate characteristics between mountain

(Artemisia tridentata ssp. vaseyana) and Wyoming (A. t. ssp.

wyomingensis) big sagebrush. It is widespread in a broad

ecotone, generally just below or within the pinyon-juniper

(Pinus edulis-Juniperus osteosperma) belt, in Utah and

neighboring States (see Goodrich and others, this proceedings for many locations) above typical Wyoming big sagebrush habitat and below typical mountain big sagebrush

habitat. This plant is most like Wyoming big sagebrush but

occurs in more mesic habitats than typical Wyoming big

sagebrush and shares its habitats with some other shrub

species that are not usual for Wyoming big sagebrush, for

example, bitterbrush (Purshiatridentata), Gambel oak (Quercus gambelii), and Martin ceanothus (Ceanothus martinii).

Its stands also have a richer forb and grass understory than

do typical Wyoming big sagebrush stands. It is tetraploid

like Wyoming big sagebrush but shares some distinctive

chemical characteristics with Wyoming big sagebrush (the

bitter methacrolein smell) and mountain big sagebrush

(some of the water soluble, ultraviolet light visible coumarins). We suspect that it is best treated, until more

definitive studies are conducted, as Wyoming big sagebrush

that has been introgressed by tetraploid mountain big sagebrush or by unreduced pollen from diploid mountain big

sagebrush (McArthur and Sanderson, in press).

The second plant may also best be considered as a variant

of Wyoming big sagebrush until definitive studies are performed. It occurs in the area of ancient Tertiary Lake

Gosiute in the Upper Green River drainage of Sublette

County, WY. Dr. Winward believes that it may be a stabilized hybrid between Wyoming big sagebrush and alkali

sagebrush (A. longiloba). It has a tendency to layer, a trait

absent in typical Wyoming big sagebrush but present in

alkali sagebrush; otherwise it is much like Wyoming big

sagebrush (Winward, personal communication, February

1996 and August 1998). Large stands of typical Wyoming big

sagebrush, typical alkali sagebrush, and the undescribed

plant occur in the area. This suggests that an adapted,

stabilized hybrid may have developed at a ecotone in the

distant past. Its history may be somewhat analogous to

Lahontan low sagebrush (A. arbuscula ssp. longicaulis).

Winward and McArthur (1995) formally described this taxon

and suggested that it is a stabilized hybrid between low

sagebrush (A. arbuscula ssp. arbuscula) and Wyoming big

sagebrush. It occurs in the area of Pleistocene Lake

Lahontan. It shares traits inherent in both low sagebrush

and Wyoming big sagebrush. Lahontan low sagebrush is a

hexaploid. Neighboring populations of low sagebrush are

diploid, and Wyoming big sagebrush are tetraploid (McArthur

and Sanderson, in press).

The third undescribed plant occurs in the upper Snake

River Plain centered near Dubois, ID. Like the previous

examples, it involves Wyoming big sagebrush. In this case

the new plant is quite similar to three-tip sagebrush (A.

tripartita) but also has some similarities to Wyoming big

sagebrush (Winward, personal communication, August 1998).

The undescribed plant incorporates the drought tolerance of

Wyoming big sagebrush and has less dramatic leaf indentations than does typical three-tip sagebrush. In the general

area of its occurrence, both putative parental taxa are

tetraploid (McArthur and others 1998b; McArthur and

Sanderson, in press). Until the definitive taxonomic work is

performed, we suggest that this plant be referred to as

three-tip sagebrush.

We believe that stable hybrid zones serve as a reservoir of

fit hybrid plants that are available for exploitation of new

habitats. In the past, we believe, this has led to differentiation and new taxa formation. It is a dynamic process;

incipient new forms are available for niches as they develop.

The tools of molecular genetics allow for the testing of the

hypotheses that we have suggested. We believe the results

of such research would be interesting.

Table 4—Publications on sagebrush hybrid zones or parental and

hybrid plants grown in common gardens.

Noller and McArthur 1986

McArthur and others 1988

Freeman and others 1991a

Weber and others 1994

Freeman and others 1995a

Graham and others 1995a

Messina and others 1996

Wang and others 1997a

McArthur and others 1998aa

McArthur and others 1998b

Wang and others 1998a

Byrd and others 1999a

Freeman an others in 1999a

Wang and others, in pressa

Graham and others, in reviewa

Freeman and others, this proceedingsa

Graham and others, this proceedings

Smith and others, this proceedings

a

These papers are part of the series “Narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata: Asteraceae).”
USDA Forest Service Proceedings RMRS-P-11. 1999 7

Acknowledgments ______________

We thank our colleague Alma Winward for sharing his

insights on sagebrush hybridizations. Some of our discussion was made possible by his “fill-in” unscheduled presentation on sagebrush hybrid variants at the symposium and

other stimulating discussions on this subject. We also appreciate the opportunity that we have had for ongoing research

and discussions with our colleagues Carl Freeman, John

Graham, Bruce Smith, Han Wang, and others on the big

sagebrush hybrid zone. We thank Clyde Blauer, Sherel

Goodrich, and Alma Winward for constructive comments on

an earlier version of this manuscript.

References _____________________

Arnold, M. L. 1997. Natural hybridization and evolution. New York,

NY: Oxford University Press. 215 p.

Barton, N. H.; Hewitt, G. M. 1985. Analysis of hybrid zones. Annual

Review of Systematics and Ecology. 16: 113-148.

Beetle, A. A. 1959. New names within the section Tridentatae of

Artemisia. Rhodora. 61: 82-85.

Beetle, A. A. 1970. An ecological contribution to the taxonomy of

Artemisia. Madroño. 20: 385-386.

Beetle, A. A.; Young, A. 1965. A third subspecies in the Artemisia

tridentata complex. Rhodora. 67: 405-406.

Byrd, D. W.; McArthur, E. D.; Wang, H.; Graham, J. H.; Freeman,

D. C. 1999. Narrow hybrid zone between two subspecies of big

sagebrush, Artemisia tridentata (Asteraceae). VIII. spatial and

temporal pattern of terpenes. Biochemical Systematics and Ecology. 27: 11-25.

Clements, F. E. 1905. Research methods in ecology. Lincoln, NB:

University Publishing Company. 334 p.

Freeman, D. C.; Graham, J. H.; Byrd, D. W.; McArthur, E. D.;

Turner, W. A. 1995. Narrow hybrid zone between two subspecies

of big sagebrush, Artemisia tridentata (Asteraceae): III. developmental instability. American Journal of Botany. 82: 1144-1152.

Freeman, D. C.; Miglia, K. J.; McArthur, E. D.; Graham, J. H.;

Wang, H. This proceedings. Narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata: Asteraceae).

X. performance in reciprocal transplant gardens.

Freeman, D. C.; Turner, W. A.; McArthur, E. D.; Graham, J. H. 1991.

The characterization of a narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata). American Journal of Botany. 78: 805-815.

Freeman, D. C.; Wang, H.; Sanderson, S. C.; McArthur, E. D. 1999.

Narrow hybrid zone between two subspecies of big sagebrush

(Artemisia tridentata: Asteraceae): VII. community and demographic analyses. Evolutionary Ecology Research. 1: 487-502.

Goodrich, S.; McArthur, E. D.; Winward, A. H. 1985. A new combination and a new variety in Artemisia tridentata. Great Basin

Naturalist. 45: 100-104.

Goodrich, S.; McArthur, E. D.; Winward, A. H. This proceedings.

Sagebrush ecotones and mean annual precipitation.

Gosz, J. R. 1991. Fundamental ecological characteristics of landscape boundaries. In: Holland, M. M.; Risser, P. G.; Naiman, R. J.,

eds. Ecotones, role of landscape boundaries in the management

and restoration of changing environments. New York, NY:

Chapman and Hall: 8-30.

Gosz, J. R. 1992. Ecological functions in biome transition zones:

translating local responses to broad-scale dynamics. In: Hansen,

A. J.; di Castri, F., eds. Landscape boundaries: consequences for

biotic diversity and landscape flows, ecological studies 92. New

York, NY: Springer Verlag: 55-75.

Gosz, J. R. 1993. Ecotone hierarchies. Ecological Applications.

3: 369-376.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. 1995. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae): II. selection gradients and hybrid fitness.

American Journal of Botany 82: 709-716.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. [In review]. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae): XI. insect-plant interactions.

Graham, J. H.; Freeman, D. C.; Wang, H.; McArthur, E. D. This

proceedings. Ecological analysis of the big sagebrush hybrid zone.

Gunawardena, G. U. 1994. Synthesis and chemistry of 4-hydroxy2-cyclopentenones. Salt Lake City, UT: University of Utah. 185 p.

Dissertation.

Harrison, R. G., ed. 1993. Hybrid zones and the evolutionary

process. New York, NY: Oxford University Press. 364 p.

Harrison, R. G.; Rand, D. M. 1989. Mosaic hybrid zones and the

nature of species boundaries. In: Otte, D.; Endler, J., eds. Speciation and its consequences. Sunderland, MA: Sinauer Associates:

111-133.

Holland, M. M. 1988. SCOPE/MAB technical consultations on

landscape boundaries report of a SCOPE/MAB workshop on

ecotones. Biology International, Special Issue. 17: 47-106.

Holland, M. M.; Risser, P. G.; Naiman, R. J., eds. 1991. Ecotones, the

role of landscape boundaries in the management and restoration

of changing environments. New York, NY: Chapman and Hall.

142 p.

Kornkven, A. B. 1997. Molecular systematics of Artemisia sect.

Tridentatae (Asteraceae). Norman, OK: University of Oklahoma.

114 p. Dissertation.

Levin, D. A. 1995. Plant outliers: an ecogenetic perspective. American Naturalist. 145: 109-118.

McArthur, E. D. 1983. Taxonomy, origin, and distribution of big

sagebrush (Artemisia tridentata) and allies (subgenus Tridentatae). In: Johnson K. L., ed. Utah Ecology Workshop I; 1981

September 9-10; Ephraim, UT. Logan, UT: Utah State University

College of Natural Resources: 3-13.

McArthur, E. D. 1989. Breeding systems in shrubs. In: McKell, C.

M., ed. The biology and utilization of shrubs. San Diego, CA:

Academic Press, Inc.: 341-361.

McArthur, E. D.; Freeman, D. C.; Graham, J. H.; Wang, H.;

Sanderson, S. C.; Monaco, T. A.; Smith, B. N. 1998a. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae): VI. respiration and water potential.

Canadian Journal of Botany. 76: 567- 674.

McArthur, E. D.; Goodrich, S. 1986. Artemisia tridentata ssp.

spiciformis: distribution and taxonomic placement. In: McArthur

E. D.; Welch, B. L., comps. Proceedings of symposium on the

biology of Artemisia and Chrysothamnus; 1984 July 9-13; Provo,

UT. Gen. Tech. Rep. INT-200. Ogden, UT: U. S. Department of

Agriculture, Forest Service, Intermountain Research Station:

55-57.

McArthur, E. D.; Monsen, S. B.; Stevens, R. This proceedings. Field

trip report.

McArthur, E. D.; Mudge, J.; Van Buren, R.; Andersen, W. R.;

Sanderson, S. C.; Babbel, D. G. 1998b. Randomly amplified

polymorphic DNA analysis (RAPD) of Artemisia subgenus Tridentatae species and hybrids. Great Basin Naturalist. 58: 12-27.

McArthur, E. D.; Plummer, A. P. 1978. Biogeography and management of native Western shrubs: a case study, section Tridentatae

of Artemisia. Great Basin Naturalist Memoirs. 2: 229-243.

McArthur, E. D.; Pope, C. L.; Freeman, D. C. 1981. Chromosome

studies of subgenus Tridentatae of Artemisia: evidence for autopolyploidy. American Journal of Botany. 68: 589-605.

McArthur, E. D.; Sanderson, S. C. [In press]. Cytogeography and

chromosome evolution of subgenus Tridentatae of Artemisia

(Asteraceae). American Journal of Botany.

McArthur, E. D.; Van Buren, R.; Sanderson, S. C.; Harper, K. T.

1998c. Taxonomy of Sphaeromeria, Artemisia, and Tanacetum

(Compositae, Anthemideae) based on randomly amplified polymorphic DNA (RAPD). Great Basin Naturalist. 58: 1-11.

McArthur, E. D.; Welch, B. L.; Sanderson, S. C. 1988. Natural and

artificial hybridization between big sagebrush (Artemisia

tridentata) subspecies. Journal of Heredity. 79: 268-276.

Messina, F. J.; Richards, J. H.; McArthur, E. D. 1996. Variable

responses of insects to hybrid versus parental sagebrush in a

common garden. Oecologia. 107: 513-521.

Moore, W. S. 1977. An evaluation of narrow hybrid zones in vertebrates. Quarterly Review of Biology. 52: 263-277.
8 USDA Forest Service Proceedings RMRS-P-11. 1999

Noller, G. L.; McArthur, E. D. 1986. Establishment and initial

results from a sagebrush (Artemisia tridentata) mass selection

garden. In: McArthur E. D.; Welch, B. L., comps. Proceedings of

symposium on the biology of Artemisia and Chrysothamnus;

1984 July 9-13; Provo, UT. Gen. Tech. Rep. INT-200. Ogden, UT:

U. S. Department of Agriculture, Forest Service, Intermountain

Research Station: 104-107.

Odum, E. P. 1971. Fundamentals of ecology, 3rd edition. Philadelphia, PA: W. B. Saunders Company. 574 p.

Risser, P. G. 1995. The status of the science examining ecotones.

BioScience. 45: 318-325.

Rosentreter, R.; Kelsey, R. G. 1991. Xeric big sagebrush, a new

subspecies in the Artemisia tridentata complex. Journal of Range

Management. 44: 330-335.

Schwemmler, W. 1989. Symbiogenesis, a macro-mechanism of evolution. Berlin, Germany: Water de Gruyter. 226 p.

Smith, B. N.; Eldredge, S.; Moulton, D. L.; Monaco, T. A.; Jones, A.

R.; Hansen, L. D.; McArthur, E. D.; Freeman, D. C. This proceedings. Differences in temperature dependence of respiration distinguish subspecies and hybrid populations of big sagebrush:

nature vs. nuture.

Thompson, R. S. 1991. Pliocene environments and climates in the

Western United States. Quaternary Science Review. 10: 115-132.

Unwin, M.; Watson, L. E. 1997. The role of ecotypes in the speciation

process: a molecular re-examination of the Clausen, Keck, and

Heisey studies on Achillea. American Journal of Botany. 84(6)

supplement: 238 (abstract 694).

Walker, S. C.; Mann, D. K.; McArthur, E. D. 1996. Plant community

changes over 54 years within the Great Basin Experimental

Range, Manti-La Sal National Forest. In: Barrow, J. R; McArthur

E. D.; Sosebee, R. E.; Tausch, R. J., comps. Proceedings: shrubland ecosystem dynamics in a changing environment; 1995 May

23-25; Las Cruces, NM. Gen. Tech. Rep. INT-GTR-338. Ogden,

UT: U. S. Department of Agriculture, Forest Service, Intermountain Research Station: 66-68.

Wang, H.; Byrd, D. W.; Howard, J. L.; McArthur, E. D.; Graham, J.

H.; Freeman, D. C. 1998. Narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata: Asteraceae):

V. soil properties. International Journal of Plant Science. 159:

139-147.

Wang, H.; McArthur, E. D.; Freeman, D. C. [In press]. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae): IX. elemental uptake and niche separation. American Journal of Botany.

Wang, H.; McArthur, E. D.; Sanderson, S. C.; Graham, J. H.;

Freeman, D. C. 1997. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae): IV.

reciprocal transplant experiments. Evolution. 51: 95-102.

Ward, G. H. 1953. Artemisia, section Serphidium, in North America:

a cytotaxonomic study. Contributions from the Dudley Herbarium. 4: 155-205.

Weber, D. J.; Gang, D. R.; Hall, S. C.; Smith, B. N.; McArthur, E. D.

1994. Inheritance of hydrocarbons in subspecific big sagebrush

(Artemisia tridentata) hybrids. Biochemical Systematics and

Ecology. 22: 689-697.

Wiens, J. A.; Crawford, C. S.; Gosz, J. R. 1985. Boundary dynamics:

a conceptual framework for studying landscape ecosystems. Oikos.

45: 421-427.

Winward, A. H. 1970. Taxonomic and ecological relationships of the

big sagebrush complex in Idaho. Moscow, ID: University of Idaho.

80 p. Dissertation.

Winward, A. H. 1975. Evolutionary development of Artemisia tridentata taxa. In: H. C. Stutz, ed. Proceedings, symposium and

workshop, wildland shrubs; 1975 November 6; Provo, UT. Provo,

UT: Brigham Young University: 163.

Winward, A. H.; McArthur, E. D. 1995. Lahontan sagebrush (Artemisia arbuscula ssp. longicaulis): a new taxon. Great Basin

Naturalist. 55: 151-157.

Young, J. A.; Clements, C. D. This proceedings. Ecotones between

Artemisia nova and A. tridentata communities in the Buckskin

Mountains of western Nevada.
USDA Forest Service Proceedings RMRS-P-11. 1999 93

Ecotones and

Hybrid Zones

USDA Forest Service Proceedings RMRS-P-11. 1999 11

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

John H. Graham is Associate Professor of Biology, Department of Biology,

Berry College, Mount Berry, GA 30149-0446; D. Carl Freeman is Professor of

Biology, Department of Biological Sciences, Wayne State University, Detroit,

MI 48202; Han Wang is Research Associate, Institute of Neuroscience,

University of Oregon, Eugene, OR 97403; and E. Durant McArthur is

Supervisory Research Geneticist, Shrub Sciences Laboratory, Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture, Provo,

UT 84606.

Ecological Analysis of the Big Sagebrush

Hybrid Zone

John H. Graham

D. Carl Freeman

Han Wang

E. Durant McArthur

Abstract—The big sagebrush hybrid zone at Salt Creek, Utah,

occupies an ecotone between two plant communities on the lower

slopes of Mount Nebo. Nevertheless, the ecotone containing the

hybrid zone is not simply intermediate to that of the parental zones.

Soils in the hybrid zone are distinct, and exhibit more spatial

heterogeneity than do soils in the parental zones. Moreover, transplanted hybrids in the hybrid zone have higher fitness than do

transplanted parental taxa. What is the ecological mechanism of

this hybrid superiority? Hybrids in the hybrid garden do not have

significantly greater respiration rates, lower water potential, greater

developmental stability, or lesser gall and herbivore loads. Only

nutrient uptake exhibits a significant genotype by environment

interaction that could account for the hybrid superiority in the

hybrid zone. It is likely that the genetically variable hybrids are able

to adapt to the distinct and heterogeneous soils in the hybrid zone.

Hybrid zones are windows on the evolutionary process

(Harrison 1990; Hewitt 1988). For many years, it was believed that they represented populations in the process of

evolving reproductive isolation. But many hybrid zones are

stable, in clear violation of classic speciation theory, which

predicts that hybridizing taxa should either evolve reproductive isolation or fuse together. Moreover, there is little or

no evidence that reproductive isolation is reinforced in

hybrid zones (Howard 1993). The unexpected stability of

hybrid zones has been attributed to both hybrid inferiority

(Barton and Hewitt 1985; Harrison and Rand 1989) and

hybrid superiority (Moore 1977). Although most authors

have assumed hybrids to be less fit than their parents, very

few studies have rigorously tested predictions of hybrid zone

theory. Using reciprocal transplant gardens that span the

big sagebrush hybrid zone, we have previously examined

hybrid viability and fertility and have shown that hybrid big

sagebrush (Artemisia tridentata ssp. tridentata x ssp.

vaseyana) are more fit than either parental taxon in the

hybrid zone (Wang and others 1997). Here, we review the

studies of hybrid big sagebrush at Salt Creek, Utah, and

suggest that the superiority of hybrids appears to be due to

more successful uptake of nutrients by hybrids in a heterogeneous ecotone.

Big sagebrush (Artemisia tridentata Nutt.) is a widespread species complex (McArthur and others 1988), composed of at least five subspecies. The two most widespread

subspecies are basin big sagebrush (A.t. ssp. tridentata) and

mountain big sagebrush (A. t. ssp. vaseyana), which differ in

habitat, height, root length, branching pattern, leaf morphology and arrangement, flowers per head, coumarin and

monoterpenoid composition, and DNA markers (Byrd and

others 1999; Freeman and others 1991; McArthur and others 1979, 1988, 1998b; Welch and Jacobson 1988).

Hybrid Zone Theory _____________

Three hypotheses have been proposed to explain the

apparent stability of hybrid zones. Two of these hypotheses

accept the inferiority of hybrids. The dynamic equilibrium

model (Barton and Hewitt 1985) suggests that hybrid zones

are stabilized by a combination of hybrid inferiority and

gene flow across the hybrid zone. Accordingly, one expects

such hybrid zones to be independent of the environment, and

not necessarily associated with ecotones. The mosaic hybrid

zone model (Harrison and Rand 1989) suggests that hybrid

zones occur in ecotones that are a mosaic of two habitats.

According to this model, each parental taxon is adapted to a

different element of the mosaic. Because there are only two

elements in the mosaic, the hybrids are not adapted to either

habitat, and so are inferior with respect to fitness. Only one

hypothesis accepts the superiority of hybrids. According to

the bounded hybrid superiority model (Moore 1977), hybrids

have superior fitness, but only in the hybrid zone, which

occupies an ecotone between the parental habitats.

The different models make different predictions regarding hybrid fitness and the relationship between the hybrid

zone and environment. The dynamic equilibrium and mosaic models predict that hybrids are less fit than parental

taxa in all environments. The dynamic equilibrium model

alone predicts that the hybrid zone is independent of environmental variation. The mosaic and bounded hybrid superiority models predict that the hybrid zone is dependent on

environmental variation. The bounded hybrid superiority

model alone predicts that hybrids have superior fitness in

the hybrid zone.
12 USDA Forest Service Proceedings RMRS-P-11. 1999

The Big Sagebrush Hybrid Zone ___

Basin and mountain big sagebrush hybridize throughout

Western North America. Both subspecies co-occur in the

Great Basin and Rocky Mountains of the United States and

Canada (Shultz 1986). In central Utah, basin big sagebrush

is at elevations less than 1,780 m, while mountain big sagebrush is at elevations greater than 1,660 m. They hybridize at

intermediate elevations, where the two subspecies overlap

(McArthur and others 1988). We have studied hybrid big

sagebrush at four locations in Utah: Diamond Fork Canyon

(McArthur and others 1988), Orem (Freeman and others 1991;

Graham and others 1995), Salt Creek (Byrd and others 1998;

Freeman and others 1991, 1995, 1999a; Graham and others

1995; McArthur and others 1998a; Wang and others 1997,

1998, in press), and Clear Creek (Freeman and others 1999b;

Wang 1996; Wang and others 1998).

At Diamond Fork, Salt Creek, and Clear Creek, basin big

sagebrush are on alluvial benches 1 to 2 m above the floodplain of the nearby streams. At Orem, the population of big

sagebrush is on an alluvial fan at the base of Mt. Timpanogas;

this population is not near a stream. In all four locations,

mountain big sagebrush is at higher elevations on the slopes

of the mountains, and hybrids are at intermediate elevations, which range from flat to moderate slope. The widths of

the four hybrid zones range from 80 to 3,000 m.

We have built reciprocal transplant gardens spanning the

hybrid zone at Salt Creek. The basin garden is along Salt

Creek at an elevation of 1,776 m. The mountain garden is on

the lower slopes of Mt. Nebo at an elevation of 1,870 m. The

hybrid garden is between the basin and mountain gardens

at an elevation of 1,800 m. Into each garden, we have planted

seedlings of the parental taxa (basin and mountain) and

three classes of hybrids, designated near basin, middle

hybrid, and near mountain (Wang and others 1997).

The Hybrid Zone as an Ecotone ___

Big sagebrush hybridize in regions that may best be

described as ecotonal. And yet the ecotones have their own

properties and are not simply a mixture of two contiguous

habitats. For example, the sites of hybridization have distinct soils. At Diamond Fork, the hybrids are on xerochrept

colluvium, while basin big sagebrush is on xerofluvent

alluvium and mountain big sagebrush is on haploxeroll

residuum (McArthur and others 1988). At Salt Creek, the

soils in the hybrid zone are distinct in their elemental

composition (Wang and others 1998). Moreover, the soils in

the hybrid zone exhibit more spatial heterogeneity (Wang

and others 1998).

A study of plant communities also supports the notion that

the hybrid zone is in an ecotone. Freeman and others (1999b)

found that only four of 62 species of plants span the entire

hybrid zone at Clear Creek. The hybrid zone straddles an

abrupt discontinuity and has a distinct plant community

associated with distinct soils. At Salt Creek, Orem, and

Diamond Fork, the basin zone is dominated by big sagebrush

and rabbitbrush (Chrysothamnus nauseosus), while the

mountain zone is a mosaic of big sagebrush and oak (Quercus

gambelli) woodlands. The hybrid zone begins where oak

gives way to grasses. At both Salt Creek and Orem, the

hybrids are in a zone of increased grass density.

Hybrid Fitness __________________

Wang and others (1997) estimated the fitness of sagebrush in the reciprocal transplant gardens at Salt Creek.

According to Gavrilets and Cruzan (1998), decreased fertility is more important than decreased viability in restricting

gene flow across hybrid zones. The fitness estimates for the

big sagebrush were based upon both viability (survival) and

fertility (flowering, fruiting, and seed production). Previously, Graham and others (1995) examined seed production

in controlled crosses. These crosses involved artificial pollination of maternal parents (basin, near basin, middle hybrid, near mountain, mountain) by all possible paternal

parents. The only aspect of fitness that has not been examined for the big sagebrush hybrid zone is pollen migration

and pollen tube competition.

Hybrids at Salt Creek have higher fitness than either

basin or mountain big sagebrush, but only in the hybrid

zone. Basin big sagebrush has highest fitness in the basin

garden, and mountain big sagebrush has highest fitness in

the mountain garden (Wang and others 1997). This, together with the zone being in an ecotone, is clear support for

the bounded hybrid superiority model (Moore 1977). But

why do hybrids have the highest fitness in this hybrid zone?

Lewontin and Birch (1966) and Arnold (1997) have proposed that the increased genetic variability of hybrids allows

them to quickly adapt to novel habitats. And ecotones, such

as the one discussed here, offer novel habitats. Moreover,

hybridization is probably the easiest way for a population to

adapt to an ecotone.

It seems unlikely that a population of subspecific or

specific status would develop in an ecotone. Ecotones account for such a small part of the overall landscape that it

becomes difficult for a population to avoid genetic swamping

of adaptative genetic variation. But given their greater

genetic variation, and the presence of intense selection,

hybrids might still stay ahead of the parental taxa in an

ecotone. Wang and others (1997) estimate that within the

hybrid zone, the selection coefficients operating against the

parental taxa exceed 0.60. How have the hybrids at Salt

Creek adapted to the novel aspects of the hybrid zone?

Respiration and Water Potential ___

Hybrids in the gardens at Salt Creek do not have a

physiological advantage that involves respiration rate or

water uptake (McArthur and others 1998a). Dark respiration rate is an indicator of a plant’s potential for growth.

Water potential is an indicator of water stress. If hybrids

were superior in either respect, one would expect a significant genotype by environment interaction in which the

hybrids had greater respiration or lower water potential in

the hybrid zone.

Basin and near basin plants had the highest dark respiration rates, as measured by a LI-COR 6250 infrared gas

analyzer. Mountain plants had the lowest respiration rates.

Middle hybrid and near mountain plants had intermediate

respiration rates. Respiration rates were highest in the

hybrid garden, and lowest in the mountain garden. Respiration rate also decreased seasonally from July through August and September.
USDA Forest Service Proceedings RMRS-P-11. 1999 13

Mountain and near mountain plants were less stressed

with respect to water potential than were basin, near basin,

and hybrid plants, as measured by a Scholander Pressure

Bomb. The plants in the hybrid garden were less water

stressed than were plants in the mountain and basin gardens. Water stress also increased from pre-dawn to mid-day,

and from July through September.

Finally, McArthur and colleagues did not observe the

genotype by environment interactions that one would expect

if hybrid superiority involved either respiration or water

potential.

Developmental Stability __________

Hybrids often exhibit decreased developmental stability

(Graham 1992), presumably because of the breakup of coadapted genes. Developmental instability is estimated by

examining the asymmetry of normally symmetrical characters, such as leaves and flowers. This asymmetry, which is

called fluctuating asymmetry, increases under either genetic or environmental stress (Graham and others 1993). If

hybrids show some developmental advantage in the hybrid

zone, one would expect their developmental stability to be

greater there. Although there are many instances in which

hybrids have lower developmental stability, there is only a

single case in which hybrids have greater developmental

stability than the parental taxa. Alibert and others (1994)

found that hybrid house mice (Mus musculus) have greater

developmental stability than their parents in the hybrid

zone in Denmark.

Freeman and others (1995) did not find consistent differences in fluctuating asymmetry between hybrid and parental populations of big sagebrush at Salt Creek. This study,

however, was done before the reciprocal transplant gardens,

and so it is impossible to say whether or not hybrids differ

from parental taxa in the hybrid zone. But a preliminary

analysis of leaves from the three gardens and five source

populations also revealed no significant effects of genotype

or environment on leaf asymmetry (unpublished data). So it

appears that the hybrid advantage does not involve developmental stability.

Herbivory ______________________

Plant-herbivore interactions play an important role in the

adaptation of plants to their environment. Defense against

herbivores involves plant secondary compounds. Because

basin and mountain big sagebrush show such great differences in their coumarins and terpenes (Byrd and others

1998; McArthur and others 1988), and because coumarins

and terpenes appear to show additive genetic inheritance

(Weber and others 1994), one would expect that hybrids

might show intermediate or lessened ability to defend themselves, depending on the extent of dominance. One certainly

would not expect the hybrids to show superior defensive

ability in the hybrid zone, unless other factors are involved

in defense.

A census of herbivores in the hybrid zone (Graham and

others 1995) and within the transplant gardens (Graham

and others, unpublished data) showed no evidence for hybrid superiority (or inferiority) in the hybrid garden. In the

transplant garden experiment (Graham and others, unpublished data), gall-formers, leaf chewers, and phloem suckers

showed very little preference for any of the five genotypes.

The greatest differences were among gardens, which usually

showed a significant interaction with genotype. But the

genotype by environment interactions were not of the sort

that would reveal why hybrids have superior fitness in the

hybrid zone. The most notable interaction involved severely

stressed basin big sagebrush in the mountain garden. These

plants were infested with Rhopalomyia ampullaria leaf

galls to a greater extent than one would expect given the

performance of basin plants in the other two gardens.

One major herbivore was excluded from the transplant

experiment—mule deer (Odocoileus hemionus), so it may

still be possible that hybrids have some advantage against

browsing by mule deer in the hybrid zone. But mule deer

browsing was much more intense in the mountain garden

(Graham and others 1995). Moreover, insect herbivores

often show great year-to-year variation in numbers, so we

may have missed a significant herbivore in the one year we

censused plants.

Nutrient Uptake _________________

The ability of plants to take up and concentrate essential

elements is an important part of adapting to a particular

environment. Because the soils of the hybrid zone are so

novel in their chemical composition (Wang and others 1998),

it is clearly important that plants be able to adapt to these

soils. Wang and others (in press) have found a significant

genotype by environment interaction in the ability of sagebrush to accumulate several important elements (notably

Fe and Na). Moreover, there were significant genotype and

environmental effects for nearly all elements. This suggests

that the two subspecies differ in their ability to take up

nutrients.

While we haven’t conclusively demonstrated that nutrient uptake influences fitness of the hybrids in the hybrid

zone, these results are consistent with that hypothesis.

Conclusion_____________________

Hybrids in the big sagebrush hybrid zone show superior

fitness, but only in the hybrid zone. The basis for this

superior fitness is probably the ability of some hybrids to

accumulate nutrients in the novel, and heterogeneous, soils

of the hybrid zone. We have found no evidence that hybrids

show elevated respiration rates, lower water potential,

greater developmental stability, or lessened herbivore or

gall loads in the hybrid zone. Nevertheless, it is still not clear

how significant genotype by environment interactions involving nutrient uptake contribute to hybrid fitness. Additional experiments will be required to identify limiting

nutrients.

The big sagebrush hybrid zones at Salt Creek, Clear

Creek, Orem, and Diamond Fork lie in ecotones between

plant communities. The position of these ecotones is related

to elevation, slope, soil, and water availability. In the big

sagebrush hybrid zone, an ecotone is a place where genetically diverse hybrids explore an adaptive landscape of novel

habitats.
14 USDA Forest Service Proceedings RMRS-P-11. 1999

References _____________________

Alibert, P. S.; Renaud, S.; Dod, B.; Bonhomme, F.; Auffray, J. C.

1994. Fluctuating asymmetry in the Mus musculus hybrid zone:

a heterotic effect in disrupted co-adapted genomes. Proceedings

of the Royal Society of London. 258: 53-59.

Arnold, M. L. 1997. Natural hybridization and evolution. New York,

NY: Oxford University Press. 215 p.

 Barton, N. H.; Hewitt, G. M. 1985. Analysis of hybrid zones. Annual

Review of Ecology and Systematics. 16: 113-148.

Byrd, D. W.; McArthur, E. D.; Wang, H.; Graham, J. H.; Freeman,

D. C. 1999. Narrow hybrid zone between two subspecies of big

sagebrush, Artemisia tridentata (Asteraceae). VIII. Spatial and

temporal pattern of terpenes. Biochemical Systematics and Ecology. 27(1): 11-25.

Freeman, D. C.; Turner, W. A.; McArthur, E. D.; Graham, J. H. 1991.

Characterization of a narrow hybrid zone between two subspecies

of big sagebrush (Artemisia tridentata: Asteraceae). American

Journal of Botany. 78: 805-815.

Freeman, D. C.; Graham, J. H.; Byrd, D. W.; McArthur, E. D.;

Turner, W. A. 1995. Narrow hybrid zone between two subspecies

of big sagebrush, Artemisia tridentata (Asteraceae). III. Developmental instability. American Journal of Botany. 82: 1144-1152.

Freeman, D. C.; McArthur, E. D.; Graham, J. H.; Miglia, K. J.;

Wang, H.; Sanderson, S. C. 1999a. [This proceedings] Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). IX. Growth.

Freeman, D. C.; Wang, H.; McArthur, E. D. 1999b. Characterization

of a narrow hybrid zone between two subspecies of big sagebrush

(Artemisia tridentata: Asteraceae). VII. Community and demographic analyses. Evolutionary Ecology Research. 1: 487-502.

Gavrilets, S.; Cruzan, M. B. 1998. Neutral gene flow across single

locus clines. Evolution. 52: 1277-1284.

Graham, J. H. 1992. Genomic coadaptation and developmental

stability in hybrid zones. Acta Zoologica Fennica. 191: 121-131.

Graham, J. H.; Freeman, D. C.; Emlen, J. M. 1993. Developmental

stability: a sensitive indicator of populations under stress. In:

Landis, W. G.; Hughes, J. S.; Lewis, M. A., eds. Environmental

toxicology and risk assessment. ASTM STP 1179. Philadelphia,

PA: American Society for Testing and Materials: 136-158.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. 1995. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). II. Selection gradients and hybrid fitness. American Journal of Botany. 82: 709-716.

Harrison, R. G. 1990. Hybrid zones: windows on the evolutionary

process. Oxford Surveys in Evolutionary Biology. 7: 69-128.

Harrison, R. G.; Rand, D. M. 1989. Mosaic hybrid zones and the

nature of species boundaries. In: Otte, D.; Endler, J. A., eds.

Speciation and its consequences. Sunderland, MA: Sinauer:

111-133.

Hewitt, G. M. 1988. Hybrid zones—natural laboratories for evolutionary studies. Trends in Ecology and Evolution. 3: 158-167.

Howard, D. J. 1993. Reinforcement: the origin, dynamics, and fate

of an evolutionary hypothesis. In: Harrison, R. G., ed. Hybrid

zones and the evolutionary process. Oxford: Oxford University

Press: 46-69.

Lewontin, R. C.; Birch, L. C. 1966. Hybridization as a source of

variation for adaptation to new environments. Evolution. 20:

315-336.

McArthur, E. D.; Blauer, A. C.; Plummer, A. P.; Stevens, R. 1979.

Characteristics and hybridization of important intermountain

shrubs. III. Sunflower family. Res. Pap. INT-220. Ogden, Utah:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 82 p.

McArthur, E. D.; Freeman, D. C.; Graham, J. H.; Wang, H.;

Sanderson, S. C.; Monoco, T. A.; Smith, B. N. 1998a. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). VI. Respiration and water potential.

Canadian Journal of Botany. 76: 567-574.

McArthur, E. D.; Mudge, J.; Van Buren, R.; Andersen, W. R.;

Sanderson, S. C.; Babbel, D. G. 1998b. Randomly amplified

polymorphic DNA analysis (RAPD) of Artemisia subgenus Tridentatae species and hybrids. Great Basin Naturalist. 58: 12-27.

McArthur, E. D.; Welch, B. L.; Sanderson, S. C. 1988. Natural and

artificial hybridization between big sagebrush (Artemisia tridentata) subspecies. Journal of Heredity. 79: 268-276.

Moore, W. S. 1977. An evaluation of narrow hybrid zones in vertebrates. Quarterly Review of Biology. 52: 263-277.

Shultz, L. 1986. Taxonomic and geographic limits of Artemisia

subgenus Tridentatae (Beetle) McArthur (Asteraceae: Anthemidae). In: McArthur, E. D.; Welch, B. L., comps. Proceedings—

symposium on the biology of Artemisia and Chrysothamnus. Gen.

Tech. Rep. INT-200. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Research Station: 20-28.

Wang, H.; Byrd, D. W.; Howard, J. L.; McArthur, E. D.; Graham,

J. H.; Freeman, D. C. 1998. Narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata: Asteraceae).

V. Soil properties. International Journal of Plant Sciences 159:

139-147.

Wang, H.; McArthur, E. D.; Sanderson, S. C.; Graham, J. H.;

Freeman, D. C. 1997. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). IV.

Reciprocal transplant experiments. Evolution. 51: 95-102.

Wang, H.; McArthur, E. D.; Freeman, D. C. [In press]. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). IX. Elemental uptake and niche separation. American Journal of Botany.

Wang, Z. 1996. Ecological analysis of a stable hybrid zone between

two big sagebrush subspecies (Artemisia tridentata ssp. tridentata and A. t. ssp. vaseyana) in Utah. Detroit, MI: Wayne State

University. Dissertation.

Weber, D. J.; Gang, D. R.; Halls, S. C.; Smith, B. N.; McArthur,

E. D. 1994. Inheritance of hydrocarbons in subspecific big sagebrush (Artemisia tridentata) hybrids. Biochemical Systematics

and Ecology. 22: 689-697.

Welch, B. L.; Jacobson, T. L. C. 1988. Root growth of Artemisia

tridentata. Journal of Range Management. 41: 332-334.
USDA Forest Service Proceedings RMRS-P-11. 1999 15

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

D. Carl Freeman is Professor and Kathleen Miglia is a Graduate Student,

Department of Biological Sciences, Wayne State University, Detroil, MI

48202. E. Durant McArthur is Project Leader, Rocky Mountain Research

Station, Provo, UT 84606; John H. Graham is Associate Professor, Department of Biology, Berry College, Mt. Berry, GA 30149; Han Wang is Research

Associate, Institute of Neuroscience, University of Oregon, Eugene, OR

97403.

Narrow Hybrid Zone Between Two

Subspecies of Big Sagebrush (Artemisia

tridentata: Asteraceae): X. Performance in

Reciprocal Transplant Gardens

D. Carl Freeman

Kathleen J. Miglia

E. Durant McArthur

John H. Graham

Han Wang

Abstract—According to the biological species concept, the reinforcement of premating reproductive isolating mechanisms is due to

reduced fitness of hybrids, thus hybridization may play a central

role in speciation. On the other hand, hybridization is also a potent

source of genetic variation that can be passed from one taxon to

another, provided that hybrids survive and reproduce. The importance of introgressive hybridization in evolution is, of course, contingent upon the performance of hybrids relative to that of the parental

taxa in nature. The growth and reproductive potential of Artemisia

tridentata ssp. tridentata x A. t. ssp. vaseyana hybrids and the

parental taxa in reciprocal transplant experiments were examined

over five years. The garden in which the plants were raised significantly influenced vegetative growth (height and crown diameter);

however, it did not influence total inflorescence length. The performance of plants depended upon the population from which the

plants originated (that is, source population), and there were significant source-by-garden interactions for height and crown diameter. Vegetative growth varied significantly among the years. Furthermore, year-by-garden and year-by-source interactions were

significant for both height and crown. In general, the performance

of site-indigenous taxa was superior. This was particularly true of

hybrids in the hybrid zone. This result notably contrasts with the

traditional view of evolutionary biologists that hybrids are universally unfit.

Hybridization has long been considered important in

plant evolution (Anderson, 1949; Stebbins, 1950; see reviews in Arnold, 1997 and Grant, 1971), but has played little

role in the thinking of animal evolutionists (Arnold, 1997;

Endler, 1998; Grant, 1971; Mayr, 1942, 1963;), partly because it violates the assumptions of cladistic analyses and

many species concepts, thereby confounding both taxonomy

and systematics. This, in turn, makes the work of conservationists and others dependent upon the classification of

organisms more difficult (Endler, 1998). As noted by Endler,

many species definitions seek to discount hybridization,

particularly among species, by simply characterizing hybridizing taxa as not “good” species. Yet, field botanists have

long known that hybridization occurs even among representatives of different genera. Cowania stansburiana, for example, can hybridize with Purshia tridentata (Stutz and

Thomas, 1964). Moreover, natural hybrids between these

two genera are displacing the parental taxa over much of

their range; a strong indication that the hybrids are not

necessarily unfit, as presumed by many zoologists (see, for

example, Barton and Hewitt, 1985). It is becoming clear

from the work of McArthur, Stutz, and other Great Basin

botanists (McArthur, 1989; McArthur and Tausch, 1995;

McArthur and others, 1998; Nowak and others, 1994; Stutz,

1987), that there are often genetically well differentiated

populations inhabiting the different mountains and valleys

of the Great Basin. These populations hybridize when their

ranges expand and come into contact. One consequence of

hybridization is that neutral genes can move between adjacent populations of different subspecies or species. Thus,

introgressive hybridization can further differentiate populations within a subspecies or species as different sets of

genes are incorporated, as a result of different hybridization

events. Such species, therefore, are not necessarily “true and

uniform in character” (Darwin, 1859). Another consequence

of hybridization is that genetic variability is often enhanced

at the margins of species ranges via hybridization, rather

than decreasing, as is often believed to occur (McArthur,

1989; Nevo and Beiles, 1989; Wayne and Bazzaz, 1991). This

enhanced variability then becomes the grist for a new round

of local evolution and adaptation. It is probably not accidental that families containing plant taxa prone to hybridize,

generally contain more species than those which don’t hybridize (Ellstrand and others, 1996). The evolutionary picture that is emerging, at least for plants, is one of reticulate

evolution rather than the bifurcation events postulated by

classical cladistics (Rieseberg, 1991).

 There is probably no better example of reticulate evolution than the big sagebrush complex. Big sagebrush (Artemisia tridentata tridentata Nutt.) is composed of five subspecies: A. t. ssp. tridentata (basin), A. t. ssp. vaseyana (Rydb.)

(mountain), A. t. ssp. wyomingensis (Beetle and Young 1965)

(Wyoming), A. t. ssp. spiciformis, and A. t. ssp. xericensis

(Beetle and Young, 1965; Goodrich and others, 1985;
16 USDA Forest Service Proceedings RMRS-P-11. 1999

McArthur, 1983, 1994); each is distinct in pure stands. The

big sagebrush complex (subgenus Tridentatae) has been

prominent in the Great Basin since the late Tertiary or early

Quaternary (Axelrod, 1950; McArthur and others, 1981).

The taxa have repeatedly undergone periods of contact and

isolation as their ranges expanded and contracted in response to changing climatic regimes (McArthur and Plummer,

1978; McArthur and others, 1981). The present geographical

distribution of mountain and basin big sagebrush, the subjects of this study, probably dates to the end of the last

glaciation (approximately 10,000 years ago at the end of the

Pleistocene epoch). Pack rat midden data show that big

sagebrush has occurred across a broad elevational range in

the Great Basin for at least 30,000 years (Nowak and others,

1994). However, it is not possible, at this time, to characterize particular subspecies using midden data. The reticulate

evolution seen in the big sagebrush complex leads to local

differentiation, allowing this group to exploit a landscape

that varies in both space and time (McArthur and others,

1981, 1988; Ward, 1953; Winward and McArthur, 1995).

Hybrid zones have been the subject of intense scrutiny for

the past two decades (see Arnold, 1997; Harrison, 1993;

Hewitt, 1988, for reviews). Stable hybrid zones are important because they appear to violate adaptive speciation

theory (that is, gene flow does not result in the fusion of the

two hybridizing taxa, nor is there the evolution of mechanisms that reinforce premating reproductive isolation). Indeed, the zone in which hybridization occurs neither widens

nor narrows as adaptive speciation theory predicts. While

once viewed as windows on the speciation process (Harrison,

1993; Hewitt, 1988), some hybrid zones are now viewed less

as areas where the process of speciation is being completed,

and more as areas of intense evolution and local adaptation

(Arnold, 1997; Wang and others, 1997, 1998).

Three different models have been proposed to account for

the persistence and stability of hybrid zones. The dynamic

equilibrium model (Barton and Hewitt, 1985) assumes that

hybrids are universally unfit. This unfitness is believed to

result from the breakup of parental coadapted gene complexes. Hybridization is seen as disrupting development by

the destruction of well established gene complexes. Selection against hybrids then balances gene flow. It is this

balance that is believed to determine the width of the hybrid

zone (Barton and Hewitt, 1985; Hewitt 1988). However,

such selection by itself does not account for the position of the

hybrid zone. Indeed, asymmetrical gene flow can push the

position of the zone towards the parent contributing fewer

genes. Barton and Hewitt (1985) and Hewitt (1988) argue

that the hybrid zone will move until it encounters areas of

low population density where it becomes trapped. It is

precisely in areas of low population density that gene flow

will be the least. This model has been overwhelmingly

popular among zoologists and is clearly the model of choice

(Arnold, 1997; Endler, 1998; Hewitt, 1988). However, the

bulk of evidence for this model is correlative (Hewitt, 1988).

There have been remarkably few direct experimental tests

of this model or its assumptions, and all of these to date have

involved plants (see below).

The bounded hybrid superiority model (Moore, 1977), in

contrast, assumes that the parental taxa have not diverged

to the point where coadapted gene complexes are disrupted,

and that genotype-by-environment interactions determine

fitness. Hybrids are assumed to be more fit than the parental

taxa within the hybrid zone but less fit than the parental

taxa outside the hybrid zone. Ecological selection determines both the position and width of the hybrid zone.

The mosaic hybrid zone model (Harrison, 1986; Howard,

1982, 1986) assumes that each parental taxon is adapted to

its native habitat, and that the hybrid zone is merely a

patchwork of the two parental habitats. Because the hybrids

are intermediate for some traits, and coadaptation among

other traits may have been disrupted, this model posits

hybrid unfitness. The width of the zone is believed to result

from a balance between gene flow and endogenous selection,

but the positions of the parental taxa are due to exogenous

selection.

This difference in the presumption of hybrid fitness is

critical to the evolutionary potential of hybrids. If hybrids

are profoundly unfit, then hybrids may have little evolutionary potential. On the other hand, if hybrids have relatively

high fitness, then introgressive hybridization may profoundly

impact the evolutionary potential and trajectory of both

parental taxa involved.

We use a narrow hybrid zone between mountain and basin

big sagebrush to explore the three models outlined above,

and some of the presumptions they make about hybrids.

Specifically, we examined the growth and reproductive potential of hybrids and their parental taxa in reciprocal

transplant gardens over a five-year period. The hybrid zone

studied is located in northern Utah, where mountain and

basin big sagebrush are parapatrically distributed, segregating along strong environmental and topographic gradients.

Materials and Methods ___________

Study area

The study area is located in Salt Creek Canyon near

Nephi, Juab County, Utah. At this site, basin big sagebrush

occurs below 1,770 m in elevation, while mountain big

sagebrush occurs above 1,870 m. The hybrid zone occupies the

narrow elevational belt between the parental taxa (fig. 1).

Three common gardens were established at this site in 1994.

One garden was located in each parental stand and one in

the center of the hybrid zone. (See Freeman and others 1991

and Graham and others 1995, for a more complete description of the study area.) Seeds were collected from five plants

in each native site, germinated in a greenhouse where the

resulting seedlings were raised for a year before being

transplanted into the common gardens (see Wang and others 1997 for a more complete description of the reciprocal

transplant experiments). Height, crown diameter and total

inflorescence length have been measured (± 0.5 cm) in each

of the 5 study years in August.

Data Analysis ___________________

The data were analyzed using a repeated measures analysis of variance (Winer and others, 1991) and post hoc Student-Newman-Keuls multiple range tests (Zar, 1984). Contrasts were used to examine the differences among years.

This procedure analyzes the data from only those plants that

survived the entire 5 years. We have also examined the data
USDA Forest Service Proceedings RMRS-P-11. 1999 17

Figure 1—Hybrid zone between basin and mountain

big sagebrush at Diamond Fork Canyon, Utah.

for each year separately. Because the results only show a

minor difference in the degree of significance, we will only

report the results for the repeated measures design.

Results ________________________

Height

Height differed significantly among the years

(F4,480 = 378.6, P < 0.001), as one would expect for growing

plants. Indeed the linear contrasts show that, on average,

the plants became successively taller (F1,120 = 636.16, P <

0.001). Plants were significantly taller in the hybrid garden

than in the other two gardens (fig. 2). Plants in the mountain

garden were significantly shorter than those in the basin

garden. Across all gardens, mountain plants were significantly shorter than plants from the other source populations

(F4,120 = 51.57, P < 0.001) (fig. 3). Basin-source plants did not

differ in height from plants originating from any of the

hybrid source populations. There was a significant gardenby-source interaction (F8,120 = 2.15, P < 0.05) (fig. 4). Over all

the years, basin-source plants were tallest in the basin

garden, while the middle-hybrid-source plants were tallest

in the hybrid garden and near-mountain-source plants were

Figure 2—Height as a function of garden. Note that,

on average, all taxa grow best in the hybrid garden.

Figure 3—Height as a function of source population. Note that mountain plants, on average, are significantly shorter than all other taxa.

Figure 4—Mean height of each source population in

each garden. Note that basin plants are, on average,

taller than the other taxa in the basin garden, but

shorter than the middle hybrid plants in the hybrid

garden. Also note that the difference between the

height of mountain plants and the other taxa is least in

the mountain garden.
18 USDA Forest Service Proceedings RMRS-P-11. 1999

tallest in the mountain garden. In the mountain garden,

mountain-source plants exceeded the height of basin-source

plants. There was a significant year-by-garden interaction

(F8,480 = 29.17, P < 0.001) (fig. 5). This interaction is due to

two factors. First, plants in the hybrid garden were the

shortest in 1994, but by 1995 and throughout the rest of the

study period, they were the tallest. Second, the difference

between plants in the mountain garden versus those in the

other two gardens increased over the years. There was also

a significant year-by-source interaction (F16,480 = 2.94, P <

0.001 fig. 6). In 1994, plants from the three hybrid sources

were slightly taller than plants from both parental sources.

In that same year, parental-source plants were virtually the

same height across all the gardens. However, by 1996, basinsource plants had become the tallest and mountain-source

plants the shortest. This difference continued to increase

thereafter. The three-way interaction (years*garden*source)

was also significant (F32,480 = 3.091, P < 0.001) (fig. 7). This

interaction was due to several factors. First, hybrid-source

plants exceeded the height of both parental-source plants

early on. Over time, however, basin-source plants became

the tallest. This occurred first in the basin garden, then two

years later in the hybrid garden, and finally in 1998, in the

mountain garden. While, overall, mountain-source plants

were the shortest, in the mountain garden they were as tall

or taller than the basin-source plants for several years, but

in 1998, they did not grow as tall as the basin-source plants.

Crown diameter

Crown diameter differed significantly among the years

(F4,468 = 702.88, P < 0.001). Again, the plants grew broader

with each successive year (F1,117 = 1223.26, P < 0.001). The

garden within which a plant was raised profoundly affected

crown diameter (F2,117 = 104.65, P < 0.001) (fig. 8). Plants in

the basin garden had significantly larger crown diameters

than those in the hybrid garden, which, in turn, had significantly larger crown diameters than those in the mountain

garden. There was also a significant source effect (F4,117 =

3.78, P < 0.006) (fig. 9). Basin-source plants had significantly

smaller crown diameters than plants from the other sources,

while mountain- and near-basin-source plants had smaller

crown diameters than plants from the near-mountain source.

The significant year-by-garden interaction (F8, 468 = 16.20, P

< 0.001) is primarily due to the increase in difference among

the gardens over time. There was also a significant year-bysource interaction (F16,468 = 2.58, P < 0.001) that was largely

due to the increasing difference between the mountain- and

basin-source plants over time. The garden-by-source interaction was also significant (F8,117 = 3.16, P < 0.005) (fig. 10).

Mountain-source plants had only slightly smaller crown

diameters in the mountain garden, compared to the other

two gardens. However, basin- and hybrid-source plants had

considerably smaller crown diameters in the mountain garden, compared to the other two gardens. While the diameters of the basin-source plants were somewhat smaller in

the hybrid garden, compared to the basin garden, the reduction in size was greater for hybrid-source plants. The three

Figure 5—Height as a function of year and source.

Note how the basin plants grow relatively taller than

the other taxa over time, while the mountain plants do

the opposite.

Figure 6—Height as a function of both year and garden. Note that the

plants in the basin garden are more closely approaching the height of

those in the hybrid garden as time passes. Also note that the difference

between the plants in the mountain gardens and the other gardens

increases over time.
USDA Forest Service Proceedings RMRS-P-11. 1999 19

Figure 7—In this figure, we examine the three-way

interaction of garden, source, and year on height.

Clearly, the response of a given taxon depended upon

the garden within which it was raised, as well as the

climate it experienced during a given year.
20 USDA Forest Service Proceedings RMRS-P-11. 1999

in the basin garden. Third, mountain-source plants in the

mountain garden had the largest crown diameters in 1994,

the second largest in 1995, 1996, and 1997, but the smallest

crown diameters in 1998.

Total inflorescence length

Total inflorescence length differed significantly among

the years (F4,92 = 5.22, P < 0.001), increasing with time (F1,23

= 6.39, P < 0.02). The garden in which a plant was raised

profoundly influenced total inflorescence length (F2,23 =

5.90, P < 0.01) (fig. 12). Total inflorescence length was

significantly greater in the basin than hybrid garden, and

significantly less in the mountain than hybrid garden. The

year-by-garden interaction was also significant (F8,92 = 4.96,

P < 0.001). Plants failed to reproduce in the mountain garden

in 1996. The difference in total inflorescence length among

the gardens generally increased over time. The source population did not impact inflorescence length overall, or in any

one year, when the repeated measures design (this design

only examines plants that produced inflorescence every

year) was used. However, when we examined the full data

set, there was a significant source effect (F4,129 = 2.52,

P < 0.05) (fig. 13) and a significant garden-by-source interaction (F8,129 = 2.13, P <0.05) (fig. 14) in 1998. In the same

year, basin-source plants produced significantly less total

inflorescence length than did middle-hybrid-, near-mountain-, and mountain-source plants. The interaction term

was due to the fact that middle-hybrid-source plants produced the greatest total inflorescence length in the basin

garden in 1998, while mountain-source plants produced the

greatest total inflorescence length in the hybrid garden in

the same year.

Figure 8—Crown diameter as a function of the garden plants were raised in. Note the significant decline

in size going from the basin to the mountain garden.

Figure 9—Crown diameter as a function of source

population. Note the smaller crown diameter of basin

plants, and large crown diameters of plants from the

three hybrid populations.

Figure 10—Crown diameter as a function of garden

and source. Note the sharp decline in the size of basin

plants in the hybrid and mountain gardens. Clearly the

hybrids are not inferior to the parental taxa. Note, also,

the lack response of mountain plants to the different

gardens.

way interaction (year*garden* source) was also significant

(F32,468 = 3.01, P <0.001) (fig. 11). This was due to several

factors. First, in 1994, plants in the hybrid garden had the

smallest crown diameters, but by 1995, these plants had

surpassed those in the mountain garden. Second, middlehybrid-source plants had the largest crown diameters in the

basin garden in 1994, but in 1995 and 1996, these plants

were surpassed in crown diameter by the near-basin- and

near-mountain-source plants. By 1997, however, middle

hybrid-source plants had again the largest crown diameters
USDA Forest Service Proceedings RMRS-P-11. 1999 21

Figure 11—Crown diameter as a function of garden,

source, and year.
22 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 12—The effect of garden on the sum of

the lengths of all inflorescences produced by a

plant. Reproductive potential is clearly least in

the mountain and greatest in the basin garden.

Figure 13—The influence of source population

on the total inflorescence length. Basin plants

produced the least amount, while hybrids

tended to produce the most.

Figure 14—In 1998, the source population a plant

came from and the garden in which it was raised both

influenced the total inflorescence length. Obviously,

all sources did best in the basin garden and worst in

the mountain garden. However, the total inflorescence length from one hybrid population exceeded

that of plants from at least one parental population in

each garden.

Discussion _____________________

This common-garden experiment shows that the differences

in the stature of mountain and basin big sagebrush are

genetic, because the differences were maintained when the

plants were raised in common gardens. Moreover, the performance of a plant depended not only upon its genetics, but

also on the garden within which the plant was raised, as well

as the climate it experienced in a given year. From a hybridzone-theory perspective, the salient issue is whether the

parental taxa respond differentially to the different environments of the three common gardens. The dynamic equilibrium model presumes no difference between the parental

taxa. Our findings clearly contrast with this assumption.

Both the mosaic and bounded hybrid superiority models

assume that the parental taxa are adapted to different

environments. Our findings are consistent with this assumption. However, both the mosaic and dynamic equilibrium models assume that the hybrids are unfit because

hybridization disrupts development. We have no indication

of hybrid unfitness, particularly in the hybrid zone. However, we hasten to note that we did not directly measure

fitness. Even total inflorescence length need be only loosely

correlated with fitness. Nevertheless, our data do address

the issue of performance. The hybrids grow at least as

vigorously as the alien parent in the parental sites, and in

the hybrid site, surpass both parental taxa. Moreover, we

have elsewhere (Wang and others, 1997) examined the

major life history components of fitness and found that the
USDA Forest Service Proceedings RMRS-P-11. 1999 23

native parent was more fit than the alien parental taxon,

and that within the hybrid zone, the hybrids were many

times more fit than either parent. We have also previously

examined developmental instability (Freeman and others,

1995) and found that the hybrids are not more developmentally unstable than either parental taxon. Thus, our data are

completely consistent with the bounded hybrid superiority

model, but conflict with both the mosaic and dynamic equilibrium models.

Our findings are consistent with the notion that ecological

selection is structuring the big sagebrush hybrid zone.

However, we do not yet understand the mechanism(s) of this

adaptation (see Graham and others, this proceedings); thus,

we cannot yet explain why the parental taxa are unable to

expand their ranges. These are serious issues because sagebrush is long lived. The mountain plants do survive, grow,

and reproduce in the basin garden and vice versa. Even if the

alien parental taxa are less fit, they can persist and reproduce for years; therefore, they could potentially cause introgression. Worse, yet, the hybrids also survive and reproduce

in the parental environments. Thus, the potential exists to

form a large, unstructured hybrid swarm. That the big

sagebrush hybrid zone is not structured as a hybrid swarm,

but rather forms a sharp cline for many characters (Byrd and

others, 1999; Freeman and others, 1991; Graham and others, 1995; McArthur and Welch, 1982), is a testament to the

strength of the exogenous selection being applied. The existence of sharp clines, and the results of the data presented

here, also suggest that this zone may be quite old and stable.

Byrd and others (1999) found a lack of parental and putative

F1 plants in the hybrid zone. This also suggests that multiple

generations of hybrids have been formed and that natural

selection has had time to sift through the variants creating

the sharp clines we now observe. However, not all linkage

groups of genes are subject to natural selection (Futuyma,

1979) and, thus, there is the potential for neutral alleles (and

blocks thereof) to move from one parental taxon to the other.

Because selection is exogenous, the nature of that selection

and, thus, which alleles can and cannot move through the

hybrid zone, may well differ from one population to the

other. Thus, it is quite likely that the genetic makeup of the

big sagebrush taxa will differ markedly among populations

and that evolution will follow a reticulate pattern (Ward,

1953; McArthur and others, 1981, 1998) rather than a

bifurcation model.

Conclusion_____________________

The performance of basin and mountain big sagebrush

and their hybrids was examined over 5 years in three

common gardens. A garden was located within the native

stand of each parental taxon and in the center of the hybrid

zone. The performance of a plant depended upon the garden

in which it was raised and the source population from which

it was derived. Different years seemed to favor different

taxa. These results are consistent with the bounded hybrid

superiority model and conflict with the dynamic equilibrium

model.

References _____________________

Anderson, E. 1949. Introgressive hybridization. John Wiley & Sons,

Inc. New York, NY.

Arnold, M. L. 1997. Natural hybridization and evolution. New York,

NY: Oxford University Press.

Axelrod, D. I. 1950. The evolution of desert vegetation in western

North America. Publication of the Carnegie Institute Vol. 590:

215-306. Washington, D.C.

Barton, N. H.; Hewitt G. M. 1985. Analysis of hybrid zones. Annual

Review of Ecology and Systematics 16: 113-148.

Beetle, A. A.; Young, A. 1965. A third subspecies in the Artemisia

tridentata complex. Rhodora 67: 405-406.

Byrd, D. W.; McArthur, E. D.; Wang, H.; Graham, J. H.; Freeman,

D. C. 1999. Narrow hybrid zone between two subspecies of big

sagebrush (Artemisia tridentata: Asteraceae) VIII. Spatial and

temporal patterns of terpenes. Biochemical Systematics and

Ecology 27: 11-25.

Darwin, C. 1859. On the origin of species by means of natural

selection or the preservation of favored races in the struggle for

life. John Murray, London. (1964 facsimile ed. Harvard University Press, Cambridge, MA).

Ellstrand, N. C.; Whitkus, R.; Rieseberg, L. H. 1996. Distribution of

spontaneous plant hybrids. Proceedings of the National Academy

of Sciences, U. S. A. 93: 5090-5093.

Endler, J. A. 1998, The place of hybridization in evolution.

Evolution 52: 640-644.

Freeman, D. C.; Turner, W. A.; McArthur, E. D.; Graham, J. H. 1991.

Characterization of a narrow hybrid zone between two subspecies

of big sagebrush (Artemisia tridentata Asteraceae). American

Journal of Botany 78: 805-815.

Freeman, D. C.; Graham, J. H.; Byrd, D. W.; McArthur, E. D.;

Turner, W. A. 1995. Narrow hybrid zone between two subspecies

of big sagebrush (Artemisia tridentata: Asteraceae). III. Developmental instability. American Journal of Botany 82: 1144-1152.

Futuyma, D. J. 1979. Evolutionary ecology. Sunderland, MA:

Sinauer Associates. 565p.

Goodrich, S.; McArthur, E. D.; Winward, A. H. 1985. A new combination and a new variety in Artemisia tridentata. Great Basin

Naturalist 45: 99-104.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. 1995. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). II. Selection and dispersal. American

Journal of Botany 82: 709-716.

Graham, J. H.; Freeman, D. C.; Wang, H.; McArthur, E. D. [This

proceedings]. Ecological analysis of the big sagebrush hybrid

zone.

Grant, V. 1971. Plant speciation. Columbia University Press,

New York.

Harrison, R. G. 1986. Pattern and process in a narrow hybrid zone.

Heredity 56: 337-349.

Harrison, R. G. 1993. Hybrids and hybrid zones: historical perspective. In: Harrison, R. G., ed. Hybrid zones and the evolutionary

process. Oxford University Press, Oxford: 3-12.

Hewitt, G. M. 1988. Hybrid zones—natural laboratories for evolutionary studies. Trends in Ecology and Evolution 3: 158-167.

Howard, D. J. 1982. Speciation and coexistence in a group of closely

related ground crickets. Yale University, New Haven. Dissertation.

Howard, D. J. 1986. A zone of overlap and hybridization between

two ground cricket species. Evolution 40: 34-43.

Mayr, E. 1942. Systematics and the origin of species. Columbia

University Press, New York, NY.

Mayr, E. 1963. Animal species and evolution. Belknap Press,

Cambridge, MA.

McArthur, E. D. 1983. Taxonomy, origin and distribution of big

sagebrush (Artemisia tridentata) and allies (subgenus Tridentatae). In: Johnson, K. L., ed. Utah shrub ecology workshop 1, Utah

State University, Logan: 3-13.

McArthur, E. D. 1989. Breeding systems in shrubs. In: McKell, C.

M., ed. The biology and utilization of shrubs. San Diego, CA:

Academic Press, Inc.: 341-361.
24 USDA Forest Service Proceedings RMRS-P-11. 1999

McArthur, E. D. 1994. Ecology, distribution, and values of sagebrush within the Intermountain Region. In: Monsen, S. B.;

Kitchen, S. G., compilers. Proceedings – ecology and management

of annual rangelands; 1992 May 18-21; Boise, ID. Gen. Tech. Rep.

INT-GTR-313. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 347-351.

McArthur, E. D.; Plummer, A. P. 1978. Biogeography and management of native western shrubs: a case study, section Tridentatae

of Artemisia. Great Basin Naturalist Memoirs 2: 119-243.

McArthur, E. D.; Welch, B. L. 1982. Growth rate differences among

big sagebrush (Artemisia tridentata) subspecies and accessions.

Journal of Range Management 35: 396-401.

McArthur, E. D.; Tausch, R. J. 1995. Genetic aspects of biodiversity

of rangeland plants. In: West, N. F., ed. Biodiversity on rangelands, proceedings of the symposium; 1993 February 16; Albuquerque, NM. Logan, UT; College of Natural Resources, Utah

State University, Natural Resources and Environmental Issues

Volume IV: 5-20.

McArthur, E. D.; Pope, C. L.; Freeman, D. C. 1981. Chromosomal

studies of subgenus Tridentatae of Artemisia: evidence for autopolyploidy. American Journal of Botany 68: 589-605.

McArthur, E. D.; Welch, B. L.; Sanderson, S. C. 1988. Natural and

artificial hybridization between big sagebrush (Artemisia tridentata) subspecies. Journal of Heredity 79: 268-276.

McArthur, E. D.; Mudge, J.; Van Buren, R.; Anderson, W. R.;

Sanderson, S. C.; Babbel, D. G. 1998. Randomly amplified polymorphic DNA analysis (RAPD) of Artemisia subgenus Tridentatae species and hybrids. Great Basin Naturalist 58: 12-27.

Moore, W. S. 1977. An evaluation of narrow hybrid zones in vertebrates. Quarterly Review of Biology 52: 263-267.

Nevo, E.; Beiles, A. 1989. Genetic diversity in the desert: patterns and

testable hypotheses. Journal of Arid Environments 17: 241-244.

Nowak, C. L.; Nowak, R. S.; Tausch R. J.; Wigand, P. E. 1994. Tree

and shrub dynamics in northwestern Great Basin woodland and

shrub steppe during the late Pleistocene and Holocene. American

Journal of Botany 81: 265-277.

Rieseberg, L. H. 1991. Homoploid reticulate evolution in Helianthus:

evidence from ribosomal genes. American Journal of Botany 78:

1218-1257.

Stebbins, G. L. 1950. Variation and evolution in plants. Columbia

University Press, New York, NY.

Stutz, H. C. 1989. Evolution of shrubs. In: McKell, C. M., ed. The

biology and utilization of shrubs. San Diego, CA: Academic

Press, Inc.: 323-340.

Stutz, H. C.; Thomas, L. K. 1964. Hybridization and introgression

in Cowania and Purshia. Evolution 18: 183-195.

Wang, H.; McArthur, E. D.; Freeman, D. C. [In press]. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). IX. Elemental uptake and niche separation. American Journal of Botany.

Wang, H.; McArthur, E.D.; Sanderson, S. C.; Graham, J. H.;

Freeman, D. C. 1997. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). IV.

Reciprocal transplant experiments. Evolution 51: 95-102.

Wang, H.; Byrd, D. W.; Howard, J. L.; McArthur, E. D.; Freeman, D.

C. 1998. Narrow hybrid zone between two subspecies of big

sagebrush (Artemisia tridentata: Asteraceae). V. Soil properties.

International Journal of Plant Sciences 159: 139-147.

Ward, G. H. 1953. Artemisia tridentata, section Serphidium, in

North America, a cytotaxonomic study. Contributions of the

Dudley Herbarium 4: 155-205.

Wayne, D. J.; Bazzaz, F. A. 1991. Assessing biodiversity in plant

communities: the importance of within species variation. Trends

in Ecology and Evolution 6: 400-404.

Winer, B. J.; Brown, Donald R.; Michels, Kenneth M. 1991. Statistical principles in experimental design. McGraw-Hill, Inc. 1057 p.

Winward, A. H.; McArthur, E. D. 1995. Lahontan sagebrush (Artemisia tridentata arbuscula ssp. longicaulis): a new taxon. Great

Basin Naturalist 55: 151-157.

Zar, Jerrold H. 1984. Biostatistical analysis. Englewood Cliffs, NJ:

Prentice Hall. 718 p.
USDA Forest Service Proceedings RMRS-P-11. 1999 25

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Bruce N. Smith is a Professor; Susan Eldredge and David L. Moulton are

undergraduate students; Thomas A. Monaco and Angela R. Jones are graduate students in the Department of Botany and Range Science; Lee D. Hansen

is a Professor in the Department of Chemistry and Biochemistry, Brigham

Young University, Provo, UT 84602. E. Durant McArthur is a Project Leader

and Research Geneticist at the Shrub Sciences Laboratory, Rocky Mountain

Research Station, USDA Forest Service, 735 North 500 East, Provo, UT

84606. D. Carl Freeman is a Professor in the Department of Biological

Sciences, Wayne State University, Detroit, MI 48202.

Differences in Temperature Dependence of

Respiration Distinguish Subspecies and

Hybrid Populations of Big Sagebrush:

Nature Versus Nurture

Bruce N. Smith

Susan Eldredge

David L. Moulton

Thomas A. Monaco

Angela R. Jones

Lee D. Hansen

E. Durant McArthur

D. Carl Freeman

Abstract—Artemisia tridentata ssp. vaseyana grows at slightly

higher, cooler, and drier sites than does A.t. ssp. tridentata. Natural

hybrids between the two subspecies are found in Salt Creek Canyon

near Nephi, Utah where the parent populations are separated by

85 m in elevation and 1.1 km along the transect. In 1993, three

gardens were established with seedlings from five populations

along the transect planted in each garden. From 1995 to 1998,

physiological measurements were made using carbon isotope ratios,

chlorophyll a fluorescence and microcalorimetry. Significant differences were observed among the gardens whatever the source of

origin and among the plant sources in whichever garden they were

grown. Both nature and nurture have an influence. Microcalorimetry has the power to predict optimal growth for a given population

even within this narrow range of environments as the temperature

dependence of heat rate and carbon dioxide evolution differed for

each population. Sagebrush grows slowly at cool temperatures. The

plants are stressed and growth ceases at temperatures much above

30°C.

Artemisia tridentata Nutt. or big sagebrush is one of the

most widespread and economically important shrubs in

western North America. The species ranges from western

Nebraska to eastern California and from British Columbia

to northern New Mexico (USDA 1937, 1988). Big sagebrush

and its subspecies have been prominent since the late

Tertiary or early Quaternary (Axelrod 1950). The present

distribution of the subspecies and contact zones between

them were probably established at the end of the last

glaciation (Freeman and others 1991). Basin big sagebrush

grows at lower elevations than mountain big sagebrush.

Differences in volatile compounds between the subspecies

have also been noted (Weber and others 1994). Natural

hybrids between the subspecies often occur when parent

populations are in close proximity. Hybrids may also be

produced by controlled pollination (Graham and others

1995).

Success of parental subspecies and hybrids between them

in the face of environmental stresses is often assessed by

growth measurements and changes in morphology. A more

sensitive assessment could be made using physiological

parameters. Stem water potential and gas-exchange respiration have been measured in parental and hybrid big

sagebrush grown in common gardens (McArthur and others

1998). Significant differences were found among habitats

and source populations.

Carbon isotopic fractionation associated with degree of

stomatal closure in some circumstances has been correlated

with productivity (Condon and others 1987). Chlorophyll

fluorescence has proven to be a sensitive indicator of plant

stress (Guidi and others 1997, Loik and Harte 1996). Calorimetric measurements of the respiratory heat rates of plant

tissues, made simultaneously with measurements of gas

exchange rates, allow calculation of plant growth rates as a

function of temperature (Hansen and others 1998, Criddle

and others 1997). The purpose of this paper is to demonstrate, using these techniques, adaptation of parental and

hybrid plants to environmental stresses in common gardens

on a single hillside.

Materials and Methods ___________

Mountain sagebrush (Artemisia tridentata ssp. vaseyana

grows at slightly higher, cooler and drier sites than does

valley sagebrush (A. tridentata ssp. tridentata). Natural

hybrids between the two subspecies are often found in

locations such as Salt Creek Canyon, located 10 km east of

Nephi, Utah where the parent populations are separated
26 USDA Forest Service Proceedings RMRS-P-11. 1999

85 meters in elevation and 1.1 km in distance on the eastfacing slope of the canyon. Previous studies (Freeman and

others 1991, Graham and others 1995, McArthur and others

1998) have shown that much of the hillside between the

parent populations is occupied by hybrids. Common gardens

were established at the mountain and valley locations and

about halfway between the two. Seed was collected from the

parent locations and from three areas in the hybrid population zone. The seed was germinated and grown in containers

in the greenhouse. In the spring of 1993, 60 seedlings were

randomly planted in each of the three fenced common

gardens, 12 from each of the five populations (mountain,

high-elevation hybrid, mid-elevation hybrid, low-elevation

hybrid, and valley).

Plant tissues were collected on: July 6, 1995 at air temperatures in the shade ranging from 24 to 30°C; August 8,

1995 at 18 to 24.5°C; and on September 28, 1995, at 18 to

24°C. From 1996 through 1998 plant tissues were collected

at several times. Samples were kept refrigerated for analysis in a Hart model 7707 microcalorimeter.

Metabolic heat rate (q) and respiration rate (RCO2) were

measured for each sample at 15 and 25°C (1995 samples).

Metabolic measurements in subsequent years were made at

nine temperatures: 0, 5, 10, 15, 20, 25, 30, 35, and 40°C.

Using a mathematical model developed by Hansen and

others (1994) metabolic response to temperature was calculated for each individual plant over the entire range of

growth temperatures for sagebrush.

Knowing the heat rate (q) and the respiration rate (RCO2),

the relative specific growth rate (RSG) can be predicted:

 RSGΔHB = (455RCO2 – q) (1)

where RSG is the specific growth rate in terms of moles of

carbon incorporated per gram of biomass, q is the specific

heat rate in μW/mg, RCO2 is the rate of CO2 evolution in the

dark at pmol mg–1 sec–1, and Δ HB is the enthalpy change for

structural biomass formation (as kJ/mol carbon). If photosynthate is stored as starch or sugars (which have chemical

 oxidation states of zero), and assuming that ΔHB is constant

with temperature and among sagebrush plants, Thornton’s

constant (–455 kJ mole–1) may be introduced.

Since the method measures energy changes (q) as well as

gas exchange rates (RCO2), equation (1) can also be expressed

as:

RSG = RCO2[ε/(1–ε)] (2)

where ε is the substrate carbon conversion efficiency. Thus

growth rate is directly proportional to both respiration rate

and efficiency.

Clamps to darken shoot tips and leaves were placed on

sagebrush plants in the gardens on August 30, 1996, with an

air temperature of 28°C. After equilibration in the dark for

10 minutes, a pulse of 655 nm light was given from the

Morgan Scientific CF-1000 Chlorophyll Fluorescence Measurement System and the quantum yield of photosytem II

was measured as fluorescence at 695 nm and expressed as

the ratio of variable to maximal fluorescence (Fv/Fm). A

decrease in the quantum yield (lower Fv/Fm ratio) indicates

greater environmental stress on the plant.

Pooled samples of sagebrush shoot tips collected on each

of the three dates in 1995 were dried overnight at 65°C and

analyzed for carbon isotopes at the Stable Isotope Ratio

Facility for Environmental Research at the University of

Utah.

Results ________________________

As shown in figure 1, both relative specific growth rate (A)

and efficiency (B) were predicted to be high at low temperatures and inhibited at higher temperatures. Growth rate

indicated stress at about 30°C while efficiency was decreased at 25°C. Differences between populations were noted.

Calorimetric data for all of the sagebrush plants (fig. 1)

indicate that sagebrush grows best at low temperatures and

always grows slowly. Plants that grow best at low temperatures generally do poorly at warm temperatures while those

plants that grow better at warmer temperatures do less well

than others at cooler temperatures. They never seem to have

it both ways.

Pooled metabolic and isotopic data from all dates, sites,

and sources (table 1) indicated a decline in heat rate and

respiration rate from early May until late September. An

approximation of efficiency is q/RCO2, predicting best growth

during June and July and in the basin garden. Transplantation itself may have been a slight problem for vaseyana but

differences between source populations were small. Carbon

isotopic values showed only small differences but indicated

stress in warmer weather and in vaseyana. Plant tissue

collected on the warmest date (July 6, 1995) was more

negative than that collected in August or September. This

confirms that sagebrush grows best in cool weather and is

Figure 1—Calorimetric measurements at 15 and

25°C extrapolated through the growth range of temperatures expressed as (A) relative specific growth

rates (RSGΔ HB) and (B) efficiency [(ε/1-ε)Δ HB] for

each of the three gardens and populations. Please

see text for details.

RSG

Δ

HB (ε/1-ε)Δ

HB

15

10

5

0

–5

–10

–15

–20

0.5

0.25

0

–0.25

–0.5

0 10 20 30

Temperature (°C)

0 10 20 30

Temperature (°C)
USDA Forest Service Proceedings RMRS-P-11. 1999 27

Table 1—Pooled metabolic and isotopic data from all dates, sites, and

sources in 1995 and 1996. The values are averages from

36 plants in each case.

Date Qave@15°C RCO2@15°C Qave/RCO2 δ 13C

Data pooled by date:

May 10, 1996 4.596 16.14 322.7

June 6, 1996 4.270 12.90 293.2

July 6, 1995 3.554 13.43 292.1 –29.0

Aug. 8, 1995 2.114 7.77 302.5 –28.3

Sept. 28, 1995 2.097 7.12 337.0 –27.9

Data pooled by site (garden):

Basin 3.646 13.35 254.3 –28.3

Hybrid 3.362 10.54 347.0 –28.7

Mountain 2.853 9.55 349.5 –28.1

Data pooled by source (origin of plants):

Basin 3.596 11.61 324.9 –28.0

Hybrid 3.341 11.66 323.4 –28.0

Mountain 3.046 10.65 299.9 –29.2

stressed at moderately warm temperatures. Subspecies tridentata seems to withstand stress better than ssp. vaseyana

or hybrids between them.

Recent measurements of metabolic heat rates and respiration are expressed as predicted growth rate (RSG) plotted

against temperature (figure 2). Growth of hybrid plants was

slow but not inhibited at cool temperatures in all three

gardens but was inhibited at 30°C in the mountain garden,

at 35°C in the basin garden, and at 40°C in the hybrid

garden. This seems to indicate that hybrid plants are best

adapted to warm temperature extremes at their place of

origin.

Chlorophyll fluorescence measurements (table 2) indicated stress as a reduction in quantum yield only for vaseyana plants grown in the basin garden. Pooled carbon

isotopic ratios for all plants in each garden became more

negative with increased elevation, indicating greater stress

at the higher, cooler, drier sites (table 2). If one pools all the

plants from a common site of origin, no matter where they

were grown, isotopic ratios for A.t. ssp. tridentata were more

positive than hybrid plants, while ssp. vaseyana had the

most negative values at all sites (table 1).

Discussion _____________________

Perhaps our most surprising finding is that sagebrush

grows slowly in cold weather but is not stressed by cool

temperatures. On the other hand, warmer temperatures

produced evidence of stress and reduced growth. Sagebrush

is well-adapted to living in the Great Basin which has cold,

wet winters and hot dry summers. The winters are not

extremely cold and it is rare to find the ground frozen as a

blanket of snow usually insulates the ground surface. Nelson

Figure 2— Calorimetric measurements made at nine

temperatures for each garden and the central hybrid

population expressed as relative specific growth rates

(RSGΔHB).
28 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 2—Sagebrush chlorophyll fluorescence (Fv/Fm) on August 30, 1996

and carbon isotope ratios on September 28, 1995.

Garden Population Fv/Fm δ 13C vs. PDB, o/oo

Basin Basin 0.805 –26.0

Hybrid Basin 0.680 –28.5

Mountain Basin 0.777 –29.1

Basin Low elev. hybrid 0.772

Hybrid Low elev. hybrid 0.793

Mountain Low elev. hybrid 0.784

Basin Hybrid 0.768 –24.5

Hybrid Hybrid 0.729 –27.3

Mountain Hybrid 0.724 –28.5

Basin High elev. hybrid 0.781

Hybrid High elev. hybrid 0.820

Mountain High elev. hybrid 0.779

Basin Mountain 0.543 –26.5

Hybrid Mountain 0.773 –29.5

Mountain Mountain 0.788 –31.1

and Tiernan (1973) found extensive winter injury to big

sagebrush in years with low snow cover and consequent

exposure to extreme cold. Sagebrush apparently can become

dormant and withstand high summer temperatures, but

may have no mechanism for slowing growth during very cold

conditions.

Since sagebrush retains leaves all year, Pearson (1975)

determined hourly and daily photosynthesis rates on six

Artemisiatridentata plants grown outside in Rexburg, Idaho.

He found the highest rates of photosynthesis to be in December, January, and February, while the lowest rates of photosynthesis occurred in July and August when the soil was

very dry. Summer drought and high temperatures coincide

in the Great Basin and the relative contribution of both

stresses must be addressed. In a controlled greenhouse

experiment, Booth and others (1990) concluded that for

three subspecies of big sagebrush, even under the most

severe conditions employed, water was not sufficiently limited to retard seedling growth. These results were supported

by work of Matzner and Richards (1996) who found that

sagebrush roots could maintain nutrient capacity even under water stress.

More negative carbon isotopic ratios may indicate increased discrimination against the heavy isotope during

diffusion through partially closed stomates (Condon and

others 1987). Greater water availability, more extensive

root systems, and cooler temperatures allow more open

stomates and less isotopic fractionation. Data from tables 1

and 2 support that hypothesis.

References _____________________

Axelrod, D. I. 1950. The evolution of desert vegetation in western

North America. Publ. Carnegie Institute, v. 590. Washington DC:

215-306.

Booth, G. D.; Welch, B. L.; Jacobson, T. L. C. 1990. Seedling growth

rate of 3 subspecies of big sagebrush. J. Range Management 43:

432-436.

Condon, A. G.; Richards, R. A.; Farquhar, G. D. 1987. Carbon isotope

discrimination is positively correlated with grain yield and dry

matter production in field-grown wheat. Crop Science 27: 996-

1001.

Criddle, R. S.; Smith, B. N.; Hansen, L. D. 1997. A respiration based

description of plant growth rate responses to temperature. Planta

201: 441-445.

Freeman, D. C.; Turner, W. A.; McArthur, E. D.; Graham, J. H. 1991.

Characterization of a narrow hybrid zone between two subspecies

of big sagebrush (Artemisia tridentata: Asteraceae). Amer. J.

Botany 78: 805-815.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. 1995. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). II. Selection gradients and hybrid fitness. Amer. J. Botany 82: 709-716.

Guidi, L.; Nali, C.; Ciompi, S.; Lorenzini, G.; Soldatini, G. F. 1997.

The use of chlorophyll fluorescence and leaf gas exchange as

methods for studying the different responses to ozone of two bean

cultivars. J. Exp. Botany 48: 173-179.

Hansen, L. D.; Hopkin, M. S.; Rank, D. R.; Anekonda, T. S.;

Breidenbach, R. W.; Criddle, R. S. 1994. The relation between

plant growth and respiration: a thermodynamic model. Planta

194: 77-85.

Loik, M. E.; Harte, J. 1996. High-temperature tolereance of Artemisia tridentata and Potentilla gracilis under a climate change

manipulation. Oecologia 108: 224-231.

Matzner, S. L.; Richards, J. H. 1996. Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water

stress. J. Experimental Botany 47: 1045-1056.

McArthur, E. D.; Freeman, D. C.; Graham, J. H.; Wang, H.;

Sanderson, S. C.; Monaco, T. A.; Smith, B. N. 1998. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae). VI. Respiration and water potential.

Canadian J. Botany 76: 567-574.

Nelson, D. L.; Tiernan, C. F. 1983. Winter injury of sagebrush and

other wildland shrubs in the Western United States. Res. Pap.

INT-314. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station;

17 p.

Pearson, L. C. 1975. Daily and seasonal patterns of photosynthesis

in Artemisia tridentata. J. Idaho Acad. Sci. 11: 11-19.

United States Department of Agriculture. 1937. Range Plant Handbook. Reprinted by Dover Publ., N. Y., 1988: 603-606.

Weber, D. J.; Gang, D. R.; Halls, S. C.; Smith, B. N.; McArthur, E.

D. 1994. Inheritance of hydrocarbons in subspecific big sagebrush

(Artemisia tridentata) hybrids. Biochem. Systematics and Ecology 22: 689-697.
USDA Forest Service Proceedings RMRS-P-11. 1999 29

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

James A. Young is a range scientist and Charlie D. Clements a wildlife

biologist for U.S. Department of Agriculture, Agricultural Research ServIce,

920 Valley Road, Reno, NV 89512.

Ecotones Between Artemisia nova and

A. tridentata Plant Communities in the

Buckskin Mountains of Western Nevada

James A. Young

Charlie C. Clements

Abstract—The habitat restrictions between the larger woody sagebrush (Artemisia) species and the lower growing species have long

intrigued ecologists in the Great Basin. In the Buckskin Mountains

of west-central Nevada, ecotones between big sagebrush (A. tridentata) and black sagebrush (A. nova) communities are extremely

abrupt and distinct, with no intermixing of the two types. These

differences are conditioned by different soils and are reversible with

changing edaphic development through erosion or deposition.

The relative distribution of the taller, woody sagebrush

(Artemisia) species in comparison to the shorter or dwarf

woody species has long intrigued plant ecologists. As typified by big sagebrush (A. tridentata), the taller woody species

of sagebrush are often landscape characterizing in their

distribution. The shorter or dwarf woody species usually

have more limited distribution and are often associated with

specific edaphic situations (Zamora and Tueller 1973). It

was proposed by the soil scientist Harry Summerfield, that

the dwarf sagebrush species low (A. arbuscula) and black

sagebrush (A. nova) often occupied sites where the surface

soil horizons had been removed by erosion on a recent

geologic time scale (Young and others 1996). The woody

sagebrush species occupy such a variety of habitats over

such a large and climatically diverse geographical area,

there are many exceptions to this hypothesis, but it provides

an innovative approach for considering the ecotones between black and big sagebrush communities.

Our purpose was to investigate ecotones between big and

black sagebrush to provide insight into the distribution of

the two species in the Buckskin Mountains of west-central

Nevada.

Study Area _____________________

The Buckskin Mountains are located 100 km southeast of

Reno, Nevada in the rain shadow of the Sierra Nevada and

the Pine Nut Mountains (Morrison 1964). This is the portion

of the Carson Desert in which Billings (1945) suggested that

shadscale (Atriplex confertifolia)-dominated salt desert

shrub communities occurred because of atmospheric

drought rather than the concentration of soluble salts in the

soil.

The Buckskin Mountains are a very structurally complex

fault-block mountain range typical of the Great Basin

(Hudson and Oriel 1979). The bulk of the range is composed

of repeated flows of volcanic tephra. The incandescent volcanic ash flows moved across the landscape like water as they

were deposited. The heat from each new flow converted the

surface of previous landscapes to an indurate tuff (Proffett

and Proffett 1976). These hardened strata tend to form a

series of cliffs above eroding talus slopes.

The landscape of the Buckskin Mountains has existed for

a sufficient period of time for considerable soil development

to have occurred (Blank and others 1996). On north facing

slopes, clay-textured soils occur at the soil surface. Apparently, previously existing surface horizons have eroded over

geologic time. This same relationship is apparent on many

older alluvial fans that spill from the mountain slopes and

canyons. The areas with clay-textured surface soils support

black sagebrush plant communities (Young and Palmquist

1992).

South facing slopes have soils with no horizonation or only

color changes indicating weak horizonation. Shadscalehorsebrush (Tetradymia glabrata)/desert needlegrass

(Achnatherum speciosum) plant communities form the vegetation on the south slopes. Big sagebrush communities do

not occur on the residual soils of the Buckskin Mountains.

Erosion and Deposition __________

Degrading System

On the north end of the Buckskin Mountains, a fairly

substantial drainage has eroded into the stony clay-textured

soils of an alluvial fan complex. Under current climatic

conditions, the drainage would only have running surface

flow for brief periods immediately after exceptional high

intensity short-duration summer thunderstorms. Sometime

in the recent geologic past, there was sufficient flow to erode

a flat bottomed arroyo 3 m deep into the clay. The width of

the arroyo averages 15 m. The erosion surface is partially

filled with irregularly stratified erosional products reflecting the mixed volcanic make up of the watershed. The fill

ranges in texture from sand to substantially sized boulders.

There is no evidence of soil development.

The ecotone between the black sagebrush communities of

the clay textured fans and the big sagebrush community of

the arroyo fill is very striking because of the difference in

stature of the two sagebrush species. The ecotone between
30 USDA Forest Service Proceedings RMRS-P-11. 1999

the two communities is absolutely abrupt, reflecting the

soils change. Most of the shrub species in the arroyo community are at least as tall as big sagebrush. Antelope bitterbrush (Purshia tridentata), gray rabbitbrush (Chrysothamnus nauseosus), and true sage (Salvia dorrii) occur

with big sagebrush in the arroyo.

It is obvious from the ecotone between the two communities that black sagebrush in the Buckskin Mountains is

exclusively adapted to the clay-textured soils where it is the

only woody species except for a diminutive form of green

rabbitbrush (Chrysothamnus viscidiflorus), occasional plants

of Nevada ephedra (Ephedra nevadennsis), and horsebrush

(Young and Palmquist 1992).

Extensive excavation, with mechanical equipment to the

bottom of the arroyo fill, failed to provide any evidence of

prolonged subsurface flow of moisture in the fill. The sandtextured nature of the fine material in the fill certainly offers

contrasting moisture retention characteristics compared to

the predominantly clay-textured soils of the older fans.

Agrading System

The bulk of the Buckskin Mountain range is tilting to the

west (Hudson and Oriel 1979). The mouths of the canyons on

the east side of the range (long axis running north and south)

spill alluvium on the top of old fans rather than eroding

incised arroyos into the old surfaces. The broad basin on the

eastern flank of the range, known as Lincoln Flat, supports

both big and black sagebrush plant communities. The black

sagebrush communities occur on the erosional surfaces with

clay-textured surface horizons. The big sagebrush communities, without antelope bitterbrush or true sage, occur on

the recent alluvial surfaces.

Fulstone Canyon spills on to Lincoln Flat along the northeastern portion of the Buckskin Range. It has a very large

watershed, made larger by the capture of several adjoining

canyons along a fault strike that parallels the main axis of

the range. At the mouth of the canyon, there is an area of

several hectares where coarse-textured recent alluvium has

buried older erosional surfaces with black sagebrush communities. There is a succession of big sagebrush communities from seedling dominance to maturing plants on this

deposition area. There are no black sagebrush plants, seedling or adult, in these recent deposition areas despite the

clay-textured horizon being present under moderately or

thinly bedded recent erosional products.

Lack of Hybridization ____________

Artemisia and Chrysothamnus are the two woody genera

with species common to both communities across the abrupt

ecotonal boundary. They occur exclusively as distinct species with no evidence of hybrid swarms. Perhaps the environmental gradient is so abrupt and occurs over such a short

distance there is no environmental potential suitable for

intermediate forms even if the genetic make up and breeding

system of the species permitted hybridization.

Mutual Exclusion of Artemisia _____

Big sagebrush plants thrive on the clay-textured soils as

long as there is a surface horizon of coarser-textured material. This suggests that seedbed quality may be the factor

excluding big sagebrush from the black sagebrush communities. In the Buckskin Mountains we know very little about

the seedling ecology of black sagebrush plants, because

seedlings are very rare in natural communities (Young and

Palmquist 1992). The black sagebrush plants grow on

mounds, which is a common feature for many shrubs in the

Great Basin (Charley and West 1975) . Young and Palmquist

(1992) suggested, based on a very small sample, that in the

Buckskin Mountains black sagebrush seedlings establish in

the interspace between mounds and new mounds build

around the seedlings. Obviously, because of litter deposition

and nutrient cycling, the old mounds would appear to be the

most desirable seedbed in the black sagebrush communities,

but when black sagebrush plants become senescent and die

the mound becomes densely colonized by the native perennial grass squirreltail (Elymus elymoides) and by the exotic

annual cheatgrass (Bromus tectorum). These herbaceous

species preempt the environmental potential released by the

death of the shrub, making it very difficult for black sagebrush to become established on the mound. Eventually the

herbaceous species exhaust the nitrogen-enriched soils of

the old mound and the mound erodes.

Considering the great linear extent of the ecotones between big and black sagebrush it would seem logical that

occasionally plants of one species would establish in the

community dominated by the other species. This seems

never to happen in the Buckskin Mountains. Big sagebrush

plants would be highly visible in black sagebrush communities. This near total lack of the dominant species crossing of

the soils ecotones suggests the seedbed potential of the

contrasting soils and the inherent potential of the seeds of

the species must be mutually exclusive. The environmental

parameters that control establishment and persistence of

woody sagebrush species on an extensive array of environmental potentials is an intriguing subject for further study

in the Intermountain Area.

In the case of the sagebrush communities in the Buckskin

Mountains, the hypothesis that erosion of surface soil horizons is related to dominance of dwarf species of sagebrush

may have merit and deserves investigation in other areas of

the Great Basin.

References _____________________

Billings, W. D. 1945. The plant associations of the Carson desert

region, western Nevada, BuIter Univer. Botanical Studies. 7:

89-123.

Blank, R. R.; Young, J. A.; Lugaski, T. 1996. Podogenesis on talus

slopes, the Buckskin Range, Nevada, USA. Eeoderma. 71:

121-142.

Charley, J. L.; West, N. E. 1975. Plant-induced soil chemical

patterns in some shrub-dominated semi-desert ecosystems of

Utah. J. Plant Ecology. 63: 945-964.
USDA Forest Service Proceedings RMRS-P-11. 1999 31

Hudson, D. M.; Oriel, W. M. 1979. Geologic map of the Buckskin

Mountain Range, Nevada. Map 64. Nevada Bureau of Mines,

Reno,NV.

Morrison, R. B. 1964. Lake Lahonton: Geology of southern Carson

desert, Nevada. Prof. Paper 401. Geological Survey, Washington,

DC. 477 p.

Proffett, J. M., Jr.; Proffett, B. H. 1976. Stratigraphy of the Tertiary

ash flow tuffs in the Yerington district, Nevada. Report 27.

Nevada Bureau of Mines, Reno, NV. 64 p.

Young, J. A.; Palmquist, D. E. 1992. Plant age/size distribution in

black sagebrush (Artemisia nova): effects on community structure. Great Basin Naturalist. 52:313-320.

Young, J. A., Longland, W. S.; Blank, R. R. 1996. Management of

woody species of Artemisia in western North America. In: Caligari,

P. D. S.; Hind, D. J. N. (eds.) Compositae: Biology and Utilization.

Proc. International Compositae Conference, Kew. Kew, UK.

Royal Botanical Gardens: 277-290.

Zamora, B. T.; Tueller, P. T. 1973. Artemisia arbuscula, A. longiloba,

and A. nova habitat types in northern Nevada. Great Basin

Naturalist. 33: 225-242
32 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Scott C. Walker and Deborah Turley are Research Biologists, Utah Division of Wildlife Resources, Great Basin Research Center, 540 N. Main 32-7,

Ephraim, UT 84627.

Characteristics of Mountain Mahogany

(Cercocarpus) Species and Hybrids in Utah

Hybrid Zone

Scott C. Walker

Deborah Turley

Abstract—Species within the genus Cercocarpus, commonly called

mountain mahogany, are valuable browse species for wildlife and

livestock. Utah is the primary zone of overlap of the three species

common to the Intermountain area. Hybridization occurs between

curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.), true

mountain mahogany (C. montanus Raf.), and little-leaf mountain

mahogany (C. intricatus Wats.) throughout central and northern

Utah where the species come in contact. Hybrid frequency and

characteristics are dependant upon parental varieties of each

species.

Cercocarpus species are vital components in native ecosystems. They increase diversity, maintain soil stability,

and provide good quality habitat for many species of wildlife

and domestic livestock. Three species of Cercocarpus are

common in the Intermountain area of the Western United

States: Cercocarpus montanus Raf. (true mountain mahogany), C. intricatus Wats. (little-leaf mountain mahogany),

and C. ledifolius Nutt. (curlleaf mountain mahogany) represented by two distinct subspecies; var ledifolius and var

intermontanus N. Holmgren. As shown in figure 1, Utah is

the primary zone of overlap for these shrubs (Pyrah 1964;

Davis 1990). The highest concentration of C. intricatus lies

directly and almost entirely within the zone of overlap.

Cercocarpus species are associated with desert shrub, sagebrush, pinyon-juniper, mountain brush, ponderosa pine,

and mixed aspen-conifer zones (Davis 1990).

Where the species of Cercocarpus come in contact with

each other hybridization nearly always occurs. This report is

not intended to be a comprehensive review of the hybridization of species within the genus Cercocarpus. It is more an

overview of the occurrence of hybridization, a brief review of

the literature, and a report of observations recorded by the

authors.

Discussion _____________________

Throughout their range of overlap each of the three species occupy rather distinct habitats. The more xeric C.

intricatus occurs on harsh sites that are exposed to high

temperature and drought (Blauer and others 1975). This

shrub is evergreen, intricately branched, and usually less

than 1 m but can grow up to 2.5 m in height (Blauer and

others 1975). Stutz (1974) suggests that C. intricatus is a

dry, harsh site segregant of curlleaf. C. intricatus is distinguished from C. ledifolius solely on the basis of leaf size and

plant stature. This morphology is not environmentally induced, but rather a genetic assimilation of adaptive characteristics from C. ledifolius var ledifolius. This becomes

apparent when the two species are growing in a common

garden and maintain their individuality, suggesting that

these two taxa are genetically distinct (Pyrah 1964).

C. ledifolius is an erect evergreen shrub that often grows

into small trees, 2 to 8 m tall, with stiff sharp branches. C.

ledifolius occurs on mountain slopes, often in pure stands as

groves surrounded by open sagebrush slopes or mixed with

mountain brush, pinyon-juniper, ponderosa pine, Douglasfir, or white fir. The best developed stands are routinely

Figure 1—Distribution of curlleaf mountain mahogany,

true mountain mahogany, and little-leaf mountain

mahogany (from Davis 1990).
USDA Forest Service Proceedings RMRS-P-11. 1999 33

found on all exposures of warm dry slopes, typically growing

in shallow soils or rocky ridges on slopes averaging around

50 percent (Davis 1990; Blauer and others 1975; Holmgren

1987). The most distinguishing characteristic between C.

ledifolius var ledifolius and C. ledifolius var intermontanus

is leaf size and degree of pubescence on the leaf. C. ledifolius

var intermontanus leaves are (ob)lanceolate or elliptic-lanceolate, 5 to 8 (10) mm wide, sparsely hairy, the midrib and

lateral veins conspicuously visible. C. ledifolius var ledifolius leaves are narrowly lanceolate to linear, 1.5 to 4 (6.5)

mm wide, densely white-hairy beneath, the pubescence

sometimes obscuring the midrib and certainly the lateral

veins (Holmgren 1987). C. montanus grows 1 to 2 m in

height, less commonly, a small tree up to 4 m. C. montanus

communities can usually be found at lower elevations than

C. Ledifolius, occurring on similar slopes but usually with

deeper soils (Davis 1990). Leaves are deciduous, short petiolate, the blade obovate to (ob)lanceolate or orbicular, 6 to 44

mm long, 5 to 23 mm wide, crenate-serrate (Welsh and

others 1987; Blauer and others 1975).

The flowering period for these species of Cercocarpus is

from mid May to late June. Flowering periods for C. ledifolius and C. intricatus tend to overlap in areas of common

occurrence. While C. montanus flowers nearly 2 weeks later

than the evergreen types. The flowering period may overlap

for plants on contrasting canyon slopes where aspect may

affect plant distribution and flowering phenology. Hybrid

plants generally begin flowering 2 weeks after the later

flowering C. montanus (Pyrah 1964).

Hybridization between the species is not a rare occurrence, suggesting genetic reproductive barriers between the

taxa are weak. Though hybrids form upon contact between

all of the taxa, frequency of F1 hybrids varies depending on

parental species combinations. Only those that involve C.

ledifolius var ledifolius as one of the parents produce hybrids

with significant segregant progeny (table 1) (Stutz 1990).

The duration of pollen viability is an important factor in

species isolation in nature. As shown in table 2, a portion of

the pollen of C. ledifolius and C. montanus remains viable for

more than 10 days. Abnormal pollen tubes become increasingly abundant during this period of time (Stutz 1990; Pyrah

1964). This extended pollen viability allows for the cross

pollination among these species.

Hybridization of species within the genus Cercocarpus

offers a unique perspective. At the ecotones where species of

Cercocarpus meet, the distribution of each population is

controlled by precipitation and soil characteristics. There is

often some overlap of the two populations at the ecotone.

Where hybridization occurs, there is generally not a distinct

band or zone that these hybrids occupy. For example, where

C. ledifolius and C. montanus come in contact, C. ledifolius

is generally growing upslope of C. montanus. When hybrids

form between the two, they occur almost without exception

within the bounds of the C. montanus population rather

than where the two populations interface. This suggests

that C. montanus is the maternal parent supported by what

has been observed for flowering dates and pollen durability

(Pyrah 1964). Since pollen from the earlier flowering C.

ledifolius can remain viable for more than 10 days, crosspollination onto C. montanus is possible. However, before

pollen is shed from C. montanus, the stigmas of C. ledifolius

have withered, and as a result reciprocal pollination is

usually not permitted. Generally it appears that pollination

is most common from C. ledifolius to C. montanus.

Noting that the flowering periods are similar for C. ledifolius and C. intricatus, one would expect similar trends for

both species in hybridization with C. montanus. Observations were made that demonstrated exceptions to this pattern for hybrids between C. intricatus and C. montanus. One

example occurs on the Chippean Rocks formation in the

Abajo mountains of southeastern Utah (elevation 2,500 m).

The spires of this weathered sandstone deposit extend up

from a forest of ponderosa pine with a dense shrub understory. The formation is only a few hundred meters in height.

C. montanus is scattered in the understory on lower slopes

of the formation, while C. intricatus is distributed across

upper slopes and on top. Hybrid plants are also located at the

top of the formation within the C. intricatus stand. This

representation of C. montanus not being the probable maternal parent suggests the possibility that reciprocal crossing

can occur.

Another site of interest is found near the Wind Caves

(elevation 2,100 m) located in Logan Canyon in northern

Utah. There is a variety of intermediate phenotypes between

C. ledifolius var intermontanus and C. intricatus, all growing among a C. montanus population. The variety of intermediate phenotypes of the individuals within the populations may be a result of the hybridization of C. intricatus X

C. ledifolius. Also present were hybrid products of C. ledifolius X C. montanus and plants suspected of being C.intricatus

X C. montanus hybrids.

Most of the dozen mahogany sites that were inspected for

this project contained hybrid plants within the population.

The Wind Cave site was unique in which hybrids occurred

where all three species were growing within close proximity,

Table 1—Summary of natural hybridization in Cercocarpus (from Stutz

1990).

Opportunity Abundance of

Parentsa for F1 hybrids in Progeny

from F1 hybridization contact zones hybrids

led led x led interm low high abundant

led led x intricatus high high abundant

led led x montanus low high abundant

led interm x intricatus moderate moderate moderate

led interm x montanus moderate high few

intricatus x montanus moderate low none

a

led led = C. ledifolius var ledifolius; led interm = C. ledifolius var

intermontanus.

and where there were hybrids derived from each combination of species. As this study was by no means a

comprehensive inventory, other sites that may exhibit

similar population dynamics are likely in the Intermountain area.

When C. ledifolius is in contact with C. intricatus and

C. montanus, hybridization nearly always occurs. However, each population, and progeny within populations,

display a different pattern of hybrid products. Plants

may show traits or characteristic of either parent. For

example, a single hybrid plant might be more upright,

have a tendency for evergreen leaves characteristics

associated with C. ledifolius, and have multiple stems,

a characteristic of C. montanus. One of the most telling
34 USDA Forest Service Proceedings RMRS-P-11. 1999

and variable characteristics of hybrids is leaf morphology.

Variability is high, both within species as well as among

hybrids. Leaves taken from adjacent hybrid plants can

demonstrate varying parental traits. For example, leaves

may display strong C. ledifolius traits with more linear

slightly toothed, and strongly enrolled margins, while leaves

from other hybrids maintain stronger C. montanus traits

with a more spatulate shape, stronger toothed and slightly

enrolled margins.

The seeds of hybrids are usually highly inviable, which

suggests the presence of chromosomal or genetic sterility

within the hybrid. Such sterility is probably due to differences in parental chromosomes or to incompatible gene

interaction (Stutz 1990).

For the three mahogany species, seed production always

occurs on second-year branches or from second-year buds.

The flowering phenology of a plant is synchronized and seed

is produced in a single flush. However, C. montanus plants

have been observed to demonstrate a unique partitioning of

resources. One branch will put energy into copious seed

production and will produce very little or no annual leader

growth, while an adjacent branch, on that same plant, will

produce very little or no seed, but instead will produce large

amounts of annual growth. The trigger mechanisms for

seed-versus-growth production within this genera are poorly

understood. Among hybrid plants a unique flowering phenology also occurs. The triggering mechanism for bud and

seed production in hybrids seems to be confused. Hybrid

plants produce maturing seed, new flowers, and developing

buds concurrently on the same branch of current-year’s

growth, as compared to the synchronized flowering on second-year’s growth of nonhybrids. These branches may continue to produce buds and flowers well beyond the normal

flowering period of both parent species.

Hybridization or genetic assimilation is often the key to

long-term survival, adaptation, or evolution of a species. The

unique traits demonstrated by Cercocarpus hybrids include

adaptation of parental characteristics. Hybrids exhibit characteristics that demonstrate a unique relationship to either

parent. When hybrids become established in adaptive habitats, individuals tend to be larger than either parent. This is

probably an expression of hybrid vigor and can be accounted

for by the wide genetic diversity between these two species.

Hybridization among the three species of mountain mahogany is a common occurrence. This leaves one to surmise

that the possibility that a stable hybrid could be produced;

one that will produce viable seed, have desirable characteristics of both parents (such as being evergreen, and have the

ability to resprout), and would be of benefit to the rangelands

they occupied.

Each parental species can produce unique products or

perform different functions. Hybrids may have the ability to

produce all products produced by both parents or perform

both functions. This could explain the continual flowering

process that occurs on hybrids and the ability to produce

seed on current years’ growth. An interesting point is the

idea that these hybrids may be able to synthesize new

products not found in either parent. Gas chromatographic

work done by Pyrah (1964) showed there are indeed unique

compounds produced by the hybrids that are not present in

either parent. Though not identified, these compounds may

have additional value not yet understood.

References _____________________

Blauer, A. C.; Plummer, A. P.; McArthur, E. D.; Stevens, R.; Guinta,

B. C. 1975. Characteristics and hybridization of important Intermountain shrubs. I. Rose family. Res. Pap. INT-169. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 35 p.

Davis, J. N. 1990. General ecology, wildlife use, and management of

the mountain mahoganies in the Intermountain West. In: Johnson,

Kendall L., ed. Proceedings of the fifth Utah Shrub Ecology

Workshop; 1988 July 13-14; Logan, UT. Logan, UT: Utah State

University: 1-13.

Holmgren, N. H. 1987. Cercocarpus ledifolius var intermontanus

(Rosaceae), a new varietal name for the Intermountain curlleaf

mountain-mahogany. Brittonia. 39: 423-427.

Pyrah, G. L. 1964. Cytogenetic studies of Cercocarpus in Utah.

Provo, UT: Brigham Young University. 44 p. Thesis.

Stutz, H. C. 1974. Rapid evolution in Western shrubs. Utah Sci. 35:

16-20, 33.

Stutz, H. C. 1990. Taxonomy and evolution of Cercocarpus in the

Western United States. In: Johnson, Kendall L., ed. Proceedings

of the fifth Utah Shrub Ecology Workshop; 1989 July 13-14;

Logan, UT. Logan, UT: Utah State University: 15-25.

Welsh, S. L.; Atwood, N. D.; Goodrich, S.; Higgins, L. C. 1987. A

Utah flora. Great Basin Natur. Mem. 9. 894 p.

Table 2—Duration of pollen viabilitya for Cercocarpus montanus and C. Ledifolius var intermontanus

(modified from Pyrah 1964).

Age montanus germination var intermontanus germination

days Nb #c % N #%

1 362 278 76.8 374 152 40.7

2 331 91 27.5 —— —— ——

5 305 65 21.3 222 42 18.9

10 332 82 24.7 308 38 12.3

14 381 81 21.2 228 20 8.8

aPollen was germinated on sterile nutrient agar.

b

Number in sample.

c

Number germinated.
USDA Forest Service Proceedings RMRS-P-11. 1999 35

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Merrill Webb is a Science Teacher, Provo High School, Provo, UT 84604.

Occurrence of Birds on a Great BasinMohave Desert Ecotone in Southwestern

Utah

Merrill Webb

Abstract—During four 1998 breeding season visits to a Great

Basin-Mohave Desert ecotone in southwestern Utah, a total of 29

different bird species were observed. Five species were determined

to be migratory, and two additional species were foraging as they

flew over the transects, reducing the number of meaningful resident

species to 22. Ash-throated Flycatcher, House Finch, and Common

Raven were the three species with highest numbers in the ecotonal

area. Transects through the Mohave Desert and the Great Basin

Desert to the south and north, respectively, provided species numbers for comparison.

The zone where two or more different communities meet

and integrate is an ecotone. This zone of intergradation may

be narrow or wide, local or regional. Three types of ecotones

are recognizable. One is an abrupt transition, the result of a

dramatic change in such environmental conditions as soil

type or soil drainage. The second is a sharp transition

brought about by plant interactions such as competition.

The third type is a blending of two or more adjacent vegetational types. In the second and third types the superior plant

competitors on one side of the ecotone extend as far out as

their ability to maintain themselves allows. The ecotone

contains not only species common to the communities on

both sides; it also may include a number of highly adaptable

species that tend to colonize such transitional areas. Because of this the variety and density of life is often the

greatest in such areas. This phenomenon has been called the

edge effect (Smith 1974).

Juniper-pinyon (Juniperis-Pinus) woodlands dominate

almost 30 percent of Utah’s land area, and are estimated to

cover from 43 to 80.2 million acres of the Western United

States. In Utah, this type occurs primarily between 5,000

and 7,000 feet in elevation, but it is not uncommon for these

limits to be transgressed. For example, the woodlands occur

as low as 3,200 feet near St. George (Davis and Harper 1990).

Basically, the North American desert can be divided into

two parts, the northern cool desert—the Great Basin—and

the hot deserts of the Southwest—the Mohave, the Sonoran,

and the Chihuahuan. The cool and warm deserts, however,

grade one into the other at ecotonal sites like the one I

examine here.

Sagebrush (Artemisia) is the dominant plant of the cool

desert. Other important shrubs include saltbushes (Atriplex

spp.), hopsage (Grayia), winterfat (Ceratoides), and greasewood (Sarcobatus). The plant communities of the Great

Basin are simple, often consisting of similar uniform gray

and gray-green shrub stands over large areas (Smith 1974;

Mozingo 1987). I followed Welsh and others (1993) for

taxonomic treatment of plant species.

Hot deserts are dominated mostly by creosote bush (Larrea

tridentata) accompanied by bursage (Ambrosia dumosa) or

burrobush (Hymenoclea salsola). Of the hot deserts, the

Mohave, transitional between the Great Basin and the

Sonoran, is the poorest in species, has the simplest vegetational composition, and contains some species in common

with the Great Basin. Mostly it is a rolling plain covered with

creosote bush and sagebrush, its monotony broken by volcanic mountains and the curious Joshua trees (Yucca brevifolia), a Mohave Desert endemic (Smith 1974).

The purpose of this study was to determine bird species

composition and numbers in the Mohave Desert-Great Basin Desert ecotonal area, and to compare these numbers

with bird species in the Mohave Desert to the south and the

Great Basin Desert to the north. The hypothesis was that the

highest number of bird species should occur at the junction

of the two Deserts. Common and scientific bird names are

listed in the appendix (American Ornithologists’ Union

1997).

Location, Materials, and

Methods _______________________

A transect was selected in southwestern Utah’s Washington County where the vegetation of the Great Basin Desert

merges with that of the Mohave Desert. This transect was

selected on the basis of (1) being as representative of an

ecotonal community as was accessibly possible by car, and

(2) having a limited amount of vehicular traffic noise, which

would affect the ability to adequately hear the birds. Using

the same criteria as mentioned above, two other transects

were selected for comparative purposes, one in the Mohave

Desert to the south and one in the Great Basin Desert to the

north.

The Mohave Desert transect veered south on a road

toward Beaver Dam Wells from the Eardly Road on the

Beaver Dam Slope at an elevation of 3,833 feet. This road

traversed typical Mohave Desert vegetation dominated by

creosote bush, Joshua tree, black brush, blue yucca (Yucca

baccata), and cholla cactus (Opuntia sp.).

The ecotonal transect was 20 miles to the north of the

Eardly Road just off the Motoqua Road at an elevation of

3,835 feet (transect ran north-south bisecting the Motoqua

Road). The vegetation was characterized by both single-leaf
36 USDA Forest Service Proceedings RMRS-P-11. 1999

and two-leaf pinyon pine (Pinus edulis and P. monophylla),

Utah and western juniper (Juniperus osteosperma and J.

scopulorum), Joshua trees, black brush (Coleogyne

ramossima), blue yucca, and big sagebrush (Artemisia tridentata).

The Great Basin transect was approximately 30 miles to

the north of the Motoqua road. This transect started approximately 15 miles west of the town of Enterprise where

it entered the Dixie National Forest at the southernmost

edge of the Great Basin (transect ran east-west). Vegetation

was pinyon pine, juniper, big sagebrush, and scattered

patches of rabbitbrush (Chrysothamnus ssp.) and bitterbrush (Prushia tridentata).

Four sampling trips to coincide with optimal songbird

breeding were conducted through the ecotonal transect—

two in April, one in May, and one in June. One sampling

attempt in March was aborted due to rain, snow, and muddy

road conditions. The Mohave Desert was sampled in May

and the Great Basin Desert was sampled in June.

Each transect was 2 miles long and consisted of 10 stops,

each 0.2 miles apart. Observations at each stop lasted for

10 minutes and consisted of listening for bird calls within

hearing range and watching for bird activity using

8 x 30 binoculars. All counts were started at 7:00 a.m. (Webb,

in press). Identification of bird species was made by using

the “Field Guide to the Birds of North America” (National

Geographic Society 1983).

Plant species numbers were determined through the ecotone study area with help from students in my Provo High

School Zoology Class during my second trip on April 24,

1998. Each of the 10 quadrats was 0.2 miles apart and

corresponded with the location of the birding stop. Each

rectangular quadrat (100 x 30 m) paralleled the road, ordinarily on the right hand (or passenger’s side of the car)

situated 30 m out from the edge of the road.

Results and Discussion __________

Blackbrush was the most abundant species in the ecotonal

study area (table 1). It occurred on all 10 transects, most of

the time with large numbers of individual plants. Juniper

trees were present on nine of the transects, but pinyon pine

occurred on only one transect. Big sagebrush, the main

indicator of the Great Basin Desert, was present on only four

of the transects. Joshua trees and desert peach (Prunus

fasciculata), indicator species of the Mohave Desert, were

each present on seven transects though not in large numbers.

The Mohave Desert transect was conducted May 27, 1998.

Thirteen species of birds were identified with the Blackthroated Sparrow being the most abundant. This sparrow

and the Ash-throated Flycatcher occurred on eight of the 10

stops (table 2).

The Great Basin Desert transect west of Enterprise was

conducted June 17, 1998. Twenty species of birds were

identified, with the Juniper (Plain) Titmouse being the most

abundant in terms of numbers (table 3). The Common Raven

was the only species present at all 10 stops.

The transect through the Mohave Desert-Great Basin

ecotone was sampled four times during 1998: April 11, April

24, May 28, and June 16. A total of 29 species were identified

during the four visits covering the three month period

(table 4). However, 11 bird species were recorded only once,

either as flyovers or probable migrants, and all were initially

eliminated from consideration as permanent ecotonal inhabitants. Subsequently, upon further examination only

five of the 11 bird species were eliminated as probable

migrants. Three species probably moved into the area as a

result of post-breeding dispersal. The remaining two species

(Red-tailed Hawk and Violet-green Swallow) were probably

just foraging as they passed over the ecotonal area. So, in

terms of breeding purposes I believe the ecotone was important to a total of 22 different species of birds.

Of the 29 bird species recorded on the transect through the

ecotone, 10 species were present during all four visits.

These were Ladder-backed Woodpecker, Ash-throated Flycatcher, Common Raven, Juniper Titmouse, Bushtit,

Bewick’s Wren, Blue-gray Gnatcatcher, Chipping Sparrow,

Black-throated Sparrow, and House Finch. Seven species

occurred three of the four times.

Five bird species (Mourning Dove, Ash-throated Flycatcher,

Common Raven, Bewick’s Wren, and House Finch) occurred

on all three transects. These five species could be regarded

as generalists (table 5). Three species, Mourning Dove,

Bewick’s Wren, and House Finch, were more common on the

ecotonal transect than in either of the other two transects.

Four species occurred only in the ecotonal area: Common

Bushtit, Brewer’s Sparrow, Black-chinned Sparrow, and

Brown-headed Cowbird. Comments about each of these four

species is warranted here. The Common Bushtit occurs over

a wide range of habitats. My observations do not imply

specificity, only one breeding pair and scattered individuals

Table 1—Woody plants of a Mohave Desert-Great Basin Desert ecotone.

Number of plants occurring in each transect

Plant species 1 2 3 4 5 6 7 8 9 10

Blackbrush (Coleogyne ramosissima) 13 3 149 141 88 198 103 34 62 85

Big sagebrush (Artemisia tridentata) 49 50 0 0 2 0 0 7 0 0

Juniper (Juniperus spp.) 6 4 0 1 5 2 11 17 5 7

Pinyon pine (Pinus spp.) 0 0 0 0 0 0 0 0 0 2

Brigham tea (Ephedra spp.) 4 0 3 0 0 7 1 0 6 0

Desert peach (Prunus fasciculata) 3 0 0 12 6 0 0 0 2 4

Joshua tree (Yucca brevifolia) 0420121065

Cholla cactus (Opuntia spp.) 0 2 2 6 0 0 0 0 1 0

Cliffrose (Cowania stansburiana) 0004000000
USDA Forest Service Proceedings RMRS-P-11. 1999 37

were observed and they could have been in any of my studied

habitats. I was surprised that Brewer’s Sparrows were only

observed in the ecotonal area; ordinarily this species is

common in the sagebrush habitats of the Great Basin. In

Utah, the Black-chinned Sparrow is usually found in the

chaparral community (Rising 1996). A chaparral community occurs southeast of the transect in the nearby Beaver

Dam Mountains. I believe that these two birds were in the

study area as a result of post-breeding dispersal from their

usual chaparral habitat. The Brown-headed Cowbird occurrence on only the ecotonal transect is probably an anomaly

of later sampling dates rather than being absent from the

other two desert communities, especially the Great Basin

Desert where it is a known nest parasite.

I detected Cactus Wren, Spotted Towhee, and Blackchinned Sparrow on the ecotone transect on June 16, the last

date of my four visits. This could be due to post-breeding

dispersal where the Cactus Wren moved in from the Mohave

Desert to the south, and the Spotted Towhee and Blackchinned Sparrow (see previous paragraph) came in from the

chaparral plant community to the east.

Table 2—Birds of the Mohave Desert Transect (Beaver Dam Well

Road).

Number of stops

out of 10 transects

Speciesa Number bird occurred on

1 Gambel’s Quail 7 5

2 Mourning Dove 2 2

3 Ladder-backed Woodpecker 1 1

4 Ash-throated Flycatcher 12 8

5 Common Raven 3 2

6 Cactus Wren 11 7

7 Rock Wren 3 3

8 Bewick’s Wren 2 2

9 Northern Mockingbird 8 6

10 Loggerhead Shrike 5 4

11 Black-throated Sparrow 22 8

12 Scott’s Oriole 5 4

13 House Finch 3 3

Total Species 13

a

Common names given, see appendix for scientific names.

Table 3—Birds of the Great Basin Transect (Dixie National Forest,

west of Enterprise, Utah).

Number of stops

out of 10 transects

Speciesa Number bird occurred on

1 Mourning Dove 2 2

2 Northern Flicker 8 6

3 Gray Flycatcher 10 8

4 Ash-throated Flycatcher 5 5

5 Western Scrub Jay 9 7

6 Common Raven 11 10

7 Juniper (Plain) Titmouse 16 6

8 Bewick’s Wren 7 7

9 Blue-gray Gnatcatcher 3 3

10 Western Bluebird 1 1

11 Mountain Bluebird 2 2

12 Gray Vireo 15 9

13 Black-throated Gray Warbler 5 3

14 Western Tanager 1 1

15 Black-headed Grosbeak 1 1

16 Spotted (Rufous-sided) Towhee 11 6

17 Chipping Sparrow 11 8

18 Lark Sparrow 5 3

19 House Finch 1 1

20 Lesser Goldfinch 2 1

Total Number of Species 20

a

Common names given, see appendix for scientific names.

Table 4—Number of bird species by date at the ecotone study site.

1998

Speciesa 04-11 04-24 05-28 06-16

1 Red-tailed Hawk 1

2 Mourning Dove 1 14 3

3 Black-chinned Hummingbird 1

 4 Broad-tailed Hummingbird 3

5 Ladder-backed Woodpecker 3121

 6 Gray Flycatcher 1 3 1

7 Ash-throated Flycatcher 3 7 12 15

8 No. Rough-winged Swallow 2

9 Western Scrub Jay 2 3 1

10 Pinyon Jay 9 5

11 Common Raven 4634

12 Juniper (Plain) Titmouse 11 4 4 9

13 Bushtit 2215

14 Cactus Wren 3

15 Rock Wren 1 1 6

16 Bewick’s Wren 9 11 8 11

17 Ruby-crowned Kinglet 1

18 Blue-gray Gnatcatcher 1333

19 Gray Vireo 10 13 20

20 Black-throated Gray Warbler 2

21 Green-tailed Towhee 1

22 Spotted (Rufous-sided) Towhee 1

23 Chipping Sparrow 3 29 2 1

24 Brewer’s Sparrow 2 6 1

25 Black-chinned Sparrow 2

26 Lark Sparrow 3

27 Black-throated Sparrow 3 10 16 16

28 Brown-headed Cowbird 1 2

29 House Finch 11 12 10 15

Total Species Each Visit 16 20 17 20

aCommon names given, see appendix for scientific names.

Table 5—Number of birds observed for the five most common species

in all communities.

Speciesa Mohave Ecotone Great Basin

Mourning Dove 2 4 2

Ash-throated Flycatcher 12 9 5

Common Raven 3 11 2

Bewick’s Wren 2 10 7

House Finch 3 12 1

aCommon names given, see appendix for scientific names.
38 USDA Forest Service Proceedings RMRS-P-11. 1999

The most abundant birds in the ecotonal transect were the

House Finch (48 birds), Black-throated Sparrow (45), Gray

Vireo (43), Bewick’s Wren (39), and Ash-throated Flycatcher

(37) (table 4). These species are widespread throughout

western habitats, so it is not surprising that they were

abundantly represented in the ecotone. The Gray Vireo was

absent from the first sampling date in April because, based

on my experience with breeding birds in that area, it had not

yet arrived on the breeding grounds. It is likely that numbers increased for the Ash-throated Flycatcher, Gray Vireo,

and Black-throated Sparrow, with each succeeding visit due

to recruitment into the population of young of the year birds.

I observed sparrow and vireo fledglings exhibiting begging

behaviors on my last trip on June 16.

Four species associated with the Mohave Desert that were

also present in the ecotonal area were Ladderback Woodpecker, Cactus Wren, Rock Wren, and Black-throated Sparrow. Even though the Ladderback Woodpecker occurred in

both the Mohave Desert and on the ecotone, I never observed

it on a pinyon tree or on a juniper tree in the ecotone. It was

always foraging or perched on a Joshua tree.

Nine species from the Great Basin Desert were also

recorded in the ecotone. These included: Gray Flycatcher,

Scrub Jay, Juniper Titmouse, Blue-gray Gnatcatcher, Gray

Vireo, Black-throated Gray Warbler, Spotted (Rufous-sided)

Towhee, and Chipping Sparrow.

The unusually high numbers of Chipping Sparrows observed on April 24 was due to a mixed flock of sparrows,

including Lark Sparrows, migrating through the area on

that particular date (table 4).

Conclusion_____________________

In conclusion, an ecotone is an area between two or more

different kinds of plant communities that contains some of

the vegetation and animal life (in this study, bird life)

present in the surrounding communities. Ecotones generally have more species than that of the surrounding areas.

Ecotones are not only places that species from neighboring

habitats may find attractive, but species from places other

than the immediate surroundings may consider ecotones

more suitable than the habitats that combined to create it.

This seems to be the case for the Bushtit which was present

on all four sampling dates and only in the ecotone on this

particular study. The House Finch was the most abundant

species on the ecotone during the transect followed by the

Ash-throated Flycatcher, Black-throated Sparrow, and Gray

Vireo.

The higher biodiversity present in ecotones is important

for many reasons. Ecotones may serve as places for species

preservation. Many wildlife managers purposefully create

edges in order to provide habitat for many species (Yoakum

and Dasmann 1971). Ecotones may also serve as sources or

sinks for species. A source for a species is a place where

individuals can live and reproduce while individuals in other

locations are dying or are stressed to the point where they

are unable to reproduce. Species may expand into sinks after

reaching the carrying capacity of the original environment

(Pulliam 1988).

Acknowledgment _______________

I would like to express thanks to students in my zoology

class at Provo High School for helping me on one of the

survey dates. I would also like to thank Durant McArthur of

the Shrubland Biology and Restoration Research Work Unit

for providing financial assistance to cover travel expenses to

and from the study sites and for providing valuable technical

assistance.

References _____________________

American Ornithologists’ Union. 1997. Forty-first supplement to

the American Ornithologists’ Union checklist of North American

birds. Auk. 114: 542-552.

Davis, J. N.; Harper, K. T. 1990. Weedy annuals and establishment

of seeded species on a chained juniper-pinyon woodland in central

Utah. In: McArthur, E. D.; Romney, E. M.; Smith, S. D.; Tueller,

P. T., comps. Proceedings—symposium on cheatgrass invasion,

shrub die-off and other aspects of shrub biology and management;

1989 April 5-7; Las Vegas, NV. Gen. Tech. Rep. INT-276. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 72-79.

Mozingo, H. N. 1987. Shrubs of the Great Basin. Reno, NV: University of Nevada Press. 342 p.

National Geographic Society. 1983. Field guide to the birds of North

America. Washington, DC: National Geographic Society. 464 p.

Pulliam, H. R. 1988. Sources, sinks, and population regulation.

American Naturalist. 132: 652-661.

Rising, J. D.; Beadle, D. D. 1996. The sparrows of the United States

and Canada. San Diego, CA: Harcourt Brace and Company. 365 p.

Smith, R. L. 1974. Ecology and field biology, 2nd edition. New York

City, NY: Harper and Row Publishers. 850 p.

Webb, M. 1999. Importance of pinyon-juniper habitats to birds. In:

Monsen, S. B.; Stevens, R.; Tausch, R. J.; Miller, R.; Goodrich, S.,

comps. Proceedings: ecology and management of pinyon-juniper

communities within the Interior West; 1997 September 15-18;

Provo, UT. Proc. RMRS-P-9. Ogden, UT: U. S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station.

244-248.

Welsh, S. L.; Atwood, N. D.; Goodrich, S.; Higgins, L. C. 1993. A Utah

flora, 2nd edition. Provo, UT: Brigham Young University Print

Services. 986 p.

Yoakum J.; Dasmann, W. 1971. Habitat manipulation practices. In:

Giles, R., ed. Wildlife Management Techniques, 3rd ed. Washington, DC: The Wildlife Society: 173-231.
USDA Forest Service Proceedings RMRS-P-11. 1999 39

Appendix ______________________

Common name Scientific name

1. Red-tailed Hawk Buteo jamaicensis

2. Gambel’s Quail Callipepla gambelii

3. Mourning Dove Zenaida macroura

3. Black-chinned Hummingbird Archilochus alexandri

4. Broad-tailed Hummingbird Selasphorus platycercus

5. Ladder-backed Woodpecker Picoides scalaris

6. Northern Flicker Colaptes auratus

7. Gray Flycatcher Empidonax wrightii

8. Ash-throated Flycatcher Myiarchus cinerascens

9. Loggerhead Shrike Lanius ludovicianus

10. Gray Vireo Vireo vicinior

11. Western Scrub Jay Aphelocoma californica

12. Pinyon Jay Gymnorhinus cyanocephalus

13. Common Raven Corvus corax

14. Northern Rough-winged Stelgidopteryx serripennis

Swallow

15. Juniper Titmouse Baeolophus griseus

16. Bushtit Psaltriparus minimus

17. Cactus Wren Campylorhynchus

brunneicapillus

18. Rock Wren Salpinctes obsoletus

19. Bewick’s Wren Thryomanes bewickii

20. Ruby-crowned Kinglet Regulus calendula

21. Blue-gray Gnatcatcher Polioptila caerulea

22. Western Bluebird Sialia mexicana

23. Mountain Bluebird Sialia currucoides

24. Northern Mockingbird Mimus polyglottos

25. Black-throated Gray Warbler Dendroica nigrescens

26. Western Tanager Piranga ludoviciana

28. Green-tailed Towhee Pipilo chlorurus

29. Spotted Towhee Pipilo maculatus

30. Chipping Sparrow Spizella passerina

31. Brewer’s Sparrow Spizella breweri

32. Black-chinned Sparrow Spizella atrogularis

33. Lark Sparrow Chondestes grammacus

34. Black-throated Sparrow Amphispiza bilineata

35. Black-headed Grosbeak Pheucticus melanocephalus

36. Brown-headed Cowbird Molothrus ater

37. Scott’s Oriole Icterus parisorum

38. House Finch Carpodacus mexicanus

39. Lesser Goldfinch Carduelis psaltria
40 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Jack D. Brotherson is Professor, Department of Botany and Range Science,

Brigham Young University, Provo, UT 84602.

Measured and Inferred Moisture Gradient

Relationships Across Ecotone Boundaries

in Shrub-Dominated Foothill Communities

Jack D. Brotherson

Abstract—Vegetation patterns across ecotone boundaries on foothill slopes on the Island of Hawaii, the Castle Cliffs area of southern

Utah, the Strawberry Valley, and Provo Canyon areas of central

Utah were studied. Study plots were established at the following

slope positions: ridge tops, midslopes, and slope base. Plant life form

varied with respect to slope position. Species distribution was

distinct and correlated to slope position. Vegetation was distinct at

the ridge top and slope base and graded towards the midslope from

both ends. Plant species were selected as indicator species and

assigned synthetic moisture index values based on a species’ relative abundance along an inferred moisture gradient of topographic

position (ridge tops being considered xeric and the slope base being

considered mesic). Synthetic moisture index values were computed

for stands at each slope position. Environmental factors, plant

moisture stress (leaf water potential), and the relative amounts of

the stable isotope 13C in leaf tissue were measured at all slope

positions. Correlations between slope position, the synthetic moisture index values (inferred moisture gradient), environmental factors, plant moisture stress, and concentrations of the isotope 13C in

leaf tissue were found to be significant.

Vegetation composition across ecotones has been the subject of much research interest. Such reported research has

generally been conducted in areas with moderate climates

and annual precipitation exceeding 38 cm. Plant species

composition and abundance with respect to ecotones were

early recognized to be correlated to the abiotic factors of the

environments of those sites where they grow (Gleason 1926;

Clements 1936). Microclimate patterns (soil and moisture

differences) associated with the topographical variation of

foothill knolls have also been linked with differences in plant

species distribution (Moretti and Brotherson 1982).

Anderson and others (1976), in a study of vegetation on

windswept ridges in south central Wyoming, found that

mat-forming plants were more predominant on ridge top

areas subjected to strong winds. Less windy areas were

occupied by sagebrush-grass communities. Moretti and

Brotherson (1982) examined vegetation and soil factors in

relation to slope position on foothill knolls in the Uintah

Basin of Utah. They reported that differences in plant lifeform composition, plant cover, and wind-adapted growth

forms were significant between the ridge top and slope base.

Plant diversity was also found to vary with slope position.

Further, the foothill knolls in the Castle Cliffs area of

southern Utah were studied (Brotherson and Masslich 1985)

and similar relationships in that more arid and extreme

climate were also apparent. Patterns were evident in the

distribution of individual species and in differences in the

morphological attributes of the cacti.

England (1979) also found that vegetation patterns varied

with slope position in the montane steppes of Strawberry

Valley in central Utah. Both life form and species composition changed from the ridge top to the slope base, with

grasses dominating the base of the slope and shrubs dominating the ridge top. Plant moisture stress was also found to

vary with slope position.

Ordering vegetative samples along associated gradients

of environmental factors such as temperature, moisture, soil

characteristics, etc., as well as measuring the variation of

plant populations across such gradients has contributed to

an understanding of the biology of the species and vegetative

communities associated with the underlying gradients. Various techniques of gradient analysis have been developed.

Whittaker (1967) discusses two basic approaches. First, a

direct approach where an obvious though usually inferred

gradient is recognized in nature and then the population

responses of various species of that community are measured. In this regard, Curtis and McIntosh (1951) used a

continuum approach with respect to an inferred moisture

gradient to determine if the upland hardwood forest communities associated with the prairie-forest border region of

Wisconsin were discrete or continuously varying. Second, an

indirect approach where an obvious gradient is not readily

apparent and is arrived at by sampling numerous stands of

vegetation and then using ordination techniques to group

similar vegetative stands into graphic one-, two-, or threedimensional arrays, the axes of which are considered to

correspond to environmental gradients (Whittaker 1967).

Variations in vegetative stands as related to underlying

environmental gradients have been utilized in a number of

studies to construct inferred moisture gradients which then

help to explain variations of associated plant species

(Christensen 1963; Curtis 1955; Dix and Butler 1960; Loucks

1962; Waring and Major 1964; Whittaker 1956, 1960). Variations in vegetation factors along underlying environmental

gradients are equally apparent in native (Christensen 1963)

and non-native plant communities (Brotherson 1996).

On foothill knolls of the islands of Hawaii and Lanai, for

example, introduced species have impacted land areas below 1,280 m elevation and have almost totally replaced the

native plant communities. There, introduced species have

partitioned the available niches along a changing elevationalmoisture gradient. The areas of colonization stretch across

the lower slopes of three shield volcanoes from sea level to
USDA Forest Service Proceedings RMRS-P-11. 1999 41

914 m in elevation and range from 25 to 150 cm of precipitation. An assessment of introduced woody species colonization and distribution patterns on these islands indicates the

invading species to have entered the island environments

preadapted to moisture regimes and are now distributed in

almost perfect bell-shaped curves along the entire elevationmoisture gradient. The distribution patterns of the introduced woody species studied are strongly correlated to

elevation and precipitation patterns (Brotherson 1996).

Variation in species composition with respect to landforms has been explained in a number of studies using

inferred moisture gradients related to slope position or

exposure (Whittaker 1967; Waring and Major 1964;

Whittaker and Niering 1965; Wickum and Wali 1974). Such

variation in plant species populations illustrates ecotonal

characteristics often across rather short distances either up

or downslope. With the advent and use of pressure chambers

(Scholander and others 1965) and refined techniques for

their use (Boyer 1967; Slayter 1967; Waring and Cleary

1967), moisture gradients have been directly measured and

used in much the same way as inferred gradients to explain

community variation between sites (Ehleringer and Miller

1975; Zobel and others 1976).

Water tensions (moisture stress) in the plant and water

use efficiency are important parameters for plants of both

native and non-native communities. Plant community composition has long been recognized to be influenced by the

amount of available moisture associated with the environments they occupy (Whittaker 1975). An understanding of

plant species responses across the natural moisture gradients they associate with should permit managers to more

efficiently manipulate plant resources.

Here reported is the correlation of: (1) slope position to

water tension (moisture stress) in the plant; (2) slope position and water tension to vegetational composition; (3) slope

position to synthetic moisture index values (inferred moisture gradient); and (4) slope position to variation in the stable

isotope 13C ratios in the leaves of plant species. Additionally,

it is suggested that there exists a correlation between inferred and real moisture gradients and isotope ratios of 13C

in plant tissues along the slope.

Study Site Descriptions __________

Islands of Hawaii

The study area was located below 1,280 m on the lower

slopes of the shield volcano Mauna Loa on the island of

Hawaii. Study area placement was at South Point in the arid

areas on the volcano’s leeward side where the climate tends

to be sunny and dry. Sampling sites were positioned on the

volcano's lower slopes where little or no erosion had taken

place and where the precipitation gradient mimics the elevation gradient, increasing gradually as elevation increases.

Study site transects began at sea level and extended

upslope some 35 km on Mauna Loa. Elevation ranged from

sea level at South Point to 579 m on the transect’s upper end.

The steepness of the elevational gradient averaged between

8 and 10% along the transect. Precipitation patterns varied

ranging from 256 mm at sea level to 1,282 mm at the

elevational gradient’s upper end. Average annual temperatures range between 23 to 27 °C.

The parent materials along the transect are basalts of

volcanic origin, some of rather recent (200 years) deposition.

The soils are shallow, well drained, and are derived from

weathered volcanic basalts. These Entisol soils are weakly

developed and conspicuously red in color due to an abundance of ferric oxides (Armstrong 1980). Associated vegetation is all of introduced plant species and is dominated by

shrubs and grasses.

Castle Cliffs, Utah

Four slopes of southwest exposure on foothill knolls adjacent to Castle Cliffs Wash 16 km north of the Utah-Arizona

State line along U.S. Highway 91 were selected for study.

Elevation differences from slope crest to slope base varied

from 30 to 50 m. Soils are shallow, well drained, and occur on

slopes of 10 to 20%. Parent materials are mixed limestone,

gneiss, schist, sandstone, and basalt (Bowns 1973). Altitude

of the study area is about 1,420 m. The area average annual

precipitation is 29.6 cm (Hodges and Riechelderfer 1962)

and the annual temperatures range from 47 to –23 °C

(Eubank and Brough 1979). The area lies in a transition zone

between the hot Mojave and the cold Great Basin deserts.

The associated vegetation is of native species dominated by

creosote, yucca, and various other species of shrubs and

cacti.

Strawberry Valley, Utah

Strawberry Valley is located in Wasatch County, Utah, on

the East slopes of the Wasatch Mountains of central Utah at

an elevation of 2,325 m. Topographically the study site is

within an area of low rounded hills (20 to 100 m high)

weathered from fluvial and lacustrine sediments of the

Eocene Uinta formation.

Soils were formed in place from weathered sedimentary

rocks (mostly sandstone and siltstone). Soils are of three

great groups (USDA-SCS 1975): (1) Lithic cryorthents; (2)

Typic cryoborolls; and (3) Lithic cryoborolls. Six of the 12

soils of midslope stands and four of the 12 soils of hill crest

stands were extensively reworked by ground squirrels and

badgers.

The area’s climate is characterized by cool summers and

frigid winters with heavy snow cover. An 8 year average

(1969-1976) of precipitation taken at East Portal (elevation

2,300 m) 3 km south of the study area was 610 mm of which

60% fell as winter snow.

The study area’s vegetation is a montane sagebrush steppe.

The plant life forms represented in the vegetation include

low shrubs, graminoids (grasses and sedges), and forbs

(herbaceous non-graminoids). The relative proportion of these

various life forms vary from crest to base of the knolls.
42 USDA Forest Service Proceedings RMRS-P-11. 1999

Provo Canyon, Utah

The study area is located on two foothill knolls approximately 2.1 km up the Squaw Peak Road in Provo Canyon in

the Wasatch Mountains east of Provo, Utah County, Utah.

The sites lie at 1,615 m elevation and collectively cover an

area of approximately 2.0 ha. Limestone bedrock of Paleozoic

origin underlies Quaternary colluvial and alluvial surface

layers on the sites where loamy soils have formed over clayey

subsurface material. The study site soils resemble the

Henefer-Manila-Dry Creek association as described in the

Utah County Soil Survey (USDA-SCS 1972).

Precipitation in the area averages 406-635 mm per year

with the majority falling as snow during the winter months.

January, the coldest month, exhibits a mean temperature of

–5.6 °C, while July, the hottest month, has a mean temperature of 20 °C. The area has a potential annual evapotranspiration of 533-610 mm (Utah Planning Commission 1981).

The vegetation of the area includes grasses, forbs, and low

growing shrubs. Grasses dominate the ridge crests and

shrubs the slope bases.

Methods _______________________

Island of Hawaii

Transects and study sites were positioned at increments of

30 m on the shield volcano's lower slopes along the elevational gradient. Data collection was accomplished using two

100 m transects at each study site, one placed perpendicular

and the other parallel to the elevation gradient. The two

transects intersected at their 50 m midpoints. Each site was

subsampled with 20, one m2

 quadrats placed every 10 m

along the transects. Canopy coverage by species was estimated according to Daubenmire (1959). Abundance of each

species was ocularly estimated at each study site along a

400 m walking transect, set parallel to the slope and centered on the study site, using abundance classes (Brotherson

1996). Average cover was computed for each species encountered by site and then compared with the abundance estimates of the same site as a check of that species’ importance

at the site. Elevation was determined at each site using a

Thommen TX mechanical/barometer altimeter. Precipitation was estimated for each site from island maps with

isohyetal estimation lines.

Castle Cliffs, Utah

Each of four slopes was sampled with four 10 x 10 m (0.01 ha)

study plots. The plots were established at four different

slope positions: ridge crest, upper slope, lower slope, and

slope base. Each plot was randomly subsampled with 10

0.25 m2 quadrats. Canopy coverage was estimated by species (Daubenmire 1959) at each quadrat. In addition, cover

contributed by rock, litter, and cryptogamic crusts was

estimated. Soil depth was measured with a penetrometer

within five of the ten 0.25 m2

 quadrats (Greenwood and

Brotherson 1978). Total living plant cover, plant cover by life

form (i.e., trees, shrubs, perennial forbs, perennial grasses,

annuals, cryptogams, and succulents) were ocularly estimated from each quadrat following a procedure suggested by

Ostler (1980).

Strawberry Valley, Utah

Each of 12 slopes was sampled with three study plots

placed one stand each at the crest, middle, and base of each

slope. The slopes were located on hills selected for their

proximity to each other, ease of accessibility, lack of disturbance and domination by shrub-steppe vegetation. All exposures were represented, and slopes were selected to insure

that no barriers to overland water movement existed between slope crest and slope base. Plot size equaled 0.01 ha in

size and was selected for intra plot homogeneity. Twentyfive 0.25 m2

 quadrats were used to subsample each vegetative plot. Canopy coverage by species was estimated at each

quadrat (Daubenmire 1959). Vegetation data was measured

during August, the period of maximum vegetative

development.

Exposure and slope were measured at each stand using a

Brunton compass. Soil depth was measured in ten quadrats

of each stand using a one-meter long, sharpened 3⁄8 inch steel

rod marked in decimeter units. Measurements to the nearest decimeter were recorded and the values for each stand

averaged. A composite soil sample of the surface 3 dm was

taken from quadrat one of each stand and analyzed for soil

texture using the hydrometer method (Bouyoucos 1951).

Hydrogen ion concentration (pH) was measured using a

Beckman pH meter and soluble salts were measured using

a Whetstone conductivity bridge.

Provo Canyon, Utah

Two north facing slopes were chosen for study. Both slopes

were on rounded foothill knolls similar in elevation, slope

gradient, aspect, soil parent material, and soil texture. A

total of fifteen (20 x 20 m) 0.04 ha study plots were established on the two slopes. Plots were located along transects

placed at right angles to the contour. Plots were established

along each transect in groups of three on the first slope and

groups of two on the second slope, one transect at each of

three topographic positions: ridge crest, midslope, and slope

base. Plots were subsampled with 16 0.25 m2

 quadrats

placed systematically across each plot in a 4 x 4 grid. Canopy

cover was estimated for each species in each quadrat

(Daubenmire 1959). One additional cover class

(0.0 – 0.5%) was recognized.

Soil samples were taken from the top 20-25 cm of the

profile. Samples were taken from the four corners and the

center of each sample plot, air dried, and bulked together for

analysis. Samples were analyzed for texture (Bouyoucous

1951), pH, organic matter, cation exchange capacity, and

soil mineral nutrient concentrations. Hydrogen ion concentration (pH) was determined with a glass electrode pH meter

on a 1:1 soil:water paste (Russel 1948). Percent organic

matter was determined using the method of Walkley and

Black (Nelson and Sommers 1982). Cation Exchange Capacity (CEC) was determined by extracting soils with ammonium
USDA Forest Service Proceedings RMRS-P-11. 1999 43

acetate, washing thoroughly, and distilling off the adsorbed

NH4

+ in a Kjeldahl device (Rhoades 1982). Exchangeable

quantities of sodium, potassium, calcium, and magnesium

were quantified from the extracts with a Perkin-Elmer

Model 403 atomic absorption spectrophotometer (Isaac and

Kerber 1971). “Available” phosphorous was extracted with

sodium bicarbonate (Olsen and others 1954).

Moisture Gradient Methodology

An inferred moisture gradient was established with respect to slope position. The slope crests were considered the

most xeric and the slope bases the most mesic. In Hawaii this

relationship was reversed with the upper slope being mesic

and the slope base being xeric. It was assumed that the

effective precipitation at a slope crest would be less than the

effective precipitation at the slope base due to water runoff.

Midslope stands were considered to be somewhere in-between the two. These relationships would vary with respect

to the steepness of the slope and the slope’s exposure to the

angle of incoming solar radiation, soil texture, soil depth,

etc.

Indicator species used to delineate the inferred moisture

gradient were selected by comparing average cover of each

species found in the slope crest stands and slope base stands.

A one-tailed t-statistic was performed on the difference

between the mean (X) cover values from the slope crest and

slope base stands for each species. Those species whose cover

values were significantly different (p ≤ 0.01) between the

crest and base stands were considered as possible index

species. If those same species were among the eighteen

prevalent species with the greatest average cover in the top

slope stands (the average number of species per stand at the

top slope position) and the 30 prevalent species with the

greatest average cover in the bottom slope stands (the

average number of species per stand at the bottom slope

position) they were selected as index species. A total of 30

index species were selected.

Synthetic moisture index values for the indicator species

were calculated using the following formula:

Species Synthetic Moisture Index Value = Si = 

 

20x Xb

Xb Xt +

where Xb = average cover of each selected species in bottom

slope stands and Xt = average cover of that same species in

top slope stands.

The constant 20 in the formula was used to give the index

species and consequent stand synthetic moisture index

values a range from 0 to 20, which approximates the expected range in values of measured moisture stress in

atmospheres.

A weighted stand index value (Goff and Cottam 1967)

incorporating the species synthetic moisture index (Si) was

calculated for each stand by use of the following formula:

Stand Synthetic Moisture Index Value (SSMIV) =

 

i

n

Wi Si

i

n

Wi

=

=

∑

∑

1

1

[( )( )]

where Wi = the percent cover of each index species “i” in that

stand, Si = the species synthetic moisture index value of the

species “i” as described above, and n = the total number of

index species present in the measured stand (England 1979).

Moisture stress measurements on the plants were made

during pre-dawn hours (Slayter 1967; Brown and McDonough

1977) at 2 to 3 week intervals starting in June and ending in

September at the Strawberry and Provo Canyon sites. Measurements at the Strawberry site were made on Artemisia

tridentata using a PMS pressure chamber with compressed

nitrogen gas. Although Artemisia tridentata was not the

dominant shrub on the study site, it was the most frequent

woody plant encountered and was the only species present

with sufficient numbers for each stand to be sampled adequately. Five twigs were taken from each of five plants in

each stand. The twigs were cut with a razor at a 45 degree

angle to the axis of the stem and placed in the pressure

chamber with the cut end exposed to the outside atmosphere. Recordings in atmospheres (ATM) of pressure were

made for each twig. The total elapsed time between cutting

the twig from the plant and measuring the moisture stress

was less than thirty seconds (cf. Scholander and others

1965).

Leaf moisture potentials at the Provo Canyon site were

measured using a Campbell Scientific leaf press (Cox and

Hughes 1982). Leaf moistures were measured on three

leaves taken from individuals of Agropyron spicatum and

Artemisia tridentata spp. vaseyana at three separate locations within each plot. Thus, a total of nine measurements

per species per plot were collected. The moisture stress

values were averaged for the plants sampled in each stand

for each recording date.

Leaf tissue from each of four species (Agropyron spicatum,

Astragalus utahensis, Artemisia tridentata spp. vaseyana,

and Balsamorhiza hookeri) was also collected at the Provo

Canyon site. These species represent three life forms (shrubs,

forbs, and grasses) and several rooting depths. Leaf collections were also made from three locations within each plot.

Subsamples were oven dried, combined, and subsequently

analyzed for 13C content. Analysis followed procedures described by Boutton and others (1983).

Statistical analyses consisted of employing descriptive

statistics to obtain means and standard deviations for all

biotic and abiotic parameters sampled. Analysis of variance

(ANOVA) tests were conducted on a stratified random design and used in combination with Fisher’s LSD mean

separation tests to determine if parameters differed significantly among slope positions. Linear regression and correlation analyses were used to describe relationships between

measured plant moisture stress (water tension in the plants)

and stand synthetic moisture index values, and between 13C

values in the plant tissues (Ott 1984).

Results and Discussion __________

Ecologically, ecotones are defined as transition zones

between adjacent community types. Ecotones may be broad,

extending across several hundred miles, as in the transition

between the short and tall grass prairies of North America

(Weaver 1968). They may also be narrow, as in the
44 USDA Forest Service Proceedings RMRS-P-11. 1999

transriparian gradients along our Western streams where

species and vegetation patterns vary quickly over rather

short distances (Webb and Brotherson 1988). Plant species

tend to partition available geographical space across ecotones showing restricted distribution patterns. Different

species tend to peak in importance at specific points in the

landscape and then decline, becoming less important as one

moves away from these peaks. Some species appear highly

restricted in their distribution while others are more broadly

distributed. Plant distribution patterns are generally restricted by their evolutionary history, presence of other

species, and by the nature of the underlying environmental

gradients. As species sort across the landscape they often

depict nearly perfect “bell-shaped” curves relative to their

distribution (Curtis and McIntosh 1957). Such patterns are

well illustrated on the lower slopes of the Mauna Loa volcano

on the island of Hawaii. The species grow along an elevation/

precipitation gradient where they have partitioned the landscape from sea level to 570 m and the corresponding precipitation gradient of 256 mm to 1,282 mm, showing highly

predictable patterns with respect to the landscape and to

other species (fig. 1). Plant species placement along this

elevation/precipitation gradient illustrate distribution patterns in the vegetation highly reflective of an ecotone

(Brotherson 1996).

Where ecotones are broad, as is the case on the slopes of

Mauna Loa, change in associated biotic and abiotic factors

are generally gradual. Conversely, where ecotones are sharp

and change rapidly over short distances, as on foothill

knolls, associated biotic and abiotic changes are often rapid.

The biotic and abiotic factors discussed in this study characterize ecotones associated with foothill knolls in shrubdominated communities in three different Utah locations.

The intent here is to describe the ecotones and underlying

gradients with respect to variations in moisture on foothill

knolls and the effects of these variations on vegetative

patterns.

Following precipitation, water flows downslope, establishing a moisture gradient with respect to slope position

(England 1979). For example, Sturges (1977) in studying

mountain big sagebrush found this species growing mainly

on midslope and slope bottom sites. He suggested that the

species was adapted to these areas because these sites were

more mesic and had better-developed soils. On one site, he

established the over-winter precipitation to be 102 mm on

the ridge crest, 378 mm at midslope and 511 mm at slope

base. The midslope and slope base soils were recharged from

three to five times. The slope crest, then, is somewhat xeric

with respect to downslope positions. Conversely, the slope

base, which receives significant runoff or recharge from

above, would have greater effective precipitation for plant

growth. Midslope positions would tend to be intermediate to

the slope crest and slope base (England 1979).

Plant species and other site characteristics also change

with slope position (tables 1 and 2). As shown in table 1, the

selected examples of plant species tend to peak in importance at one of the three slope positions and then decline

either up or downslope. The distribution of the different

plant species growing along the slope is generally distinct

with respect to all other species and to slope position. For

example, Chrysothamnus viscidiflorus, Eriogonum heracleoides, and Agropyron spicatum were of greatest importance at the ridge crest, while Quercus gambelii, Artemisia

cana, and Festuca idahoensis were generally absent from

Table 1—Plant species distribution patterns across slope ecotones.

Values represent percent cover of individual species at the

slope crest, midslope and slope base topographic positions.

Data follow England 1979, Black 1987, and Moretti and

Brotherson 1982.

Slope postion

Species Crest Midslope Base

Chrysothamnus viscidiflorus 1 25.1a 23.2a 1.6b

Artemisia tridentata1 14.0a 4.4b 2.4b

Eriogonum heracleoides1 10.0a 4.6b 2.2b

Stipa lettermanii1 9.9a 3.0b 3.6b

Agropyron spicatum2 21.2a 15.1a 4.3b

Phlox bryoides3 10.3a 1.7b 3.4b

Lupinus argenteus1 5.9a 4.9a 4.7a

Balsamorhiza hookeri2 0.8a 2.0b 0.5a

Geranium fremontii1 0.9a 4.1b 0.9a

Symphoricarpos oreophilus1 1.1a 3.4b 0.2a

Artemisia tridentata

spp. vaseyana2 14.1a 13.0a 16.3a

Stipa columbiana1 1.6a 3.6b 3.9b

Poa secunda2 0.1a 0.1a 3.6b

Aster chilensis1 0.04a 0.6a 3.4b

Elymus ambiguus3 0.0a 0.0a 4.2b

Artemisia cana1 0.7a 6.1b 10.9b

Festuca idahoensis1 0.2a 1.2a 17.2b

Quercus gambelii2 0.0a 16.8b 28.4c

Artemisia tridentata3 0.0a 13.6b 18.3b

1

,

2, and 3 signify plants studied by England, Black, and Moretti and Brotherson,

respectively.

a,b, and c indicate those species that are significantly different based on

ANOVA results.

Figure 1—Relationship of plant species to elevation/

moisture gradient at South Point, Island of Hawaii.

CHNI = Chamaecrista nictitans; INSU = Indigofera

suffruticosa; LACA = Lantana camara; LELE =

Leucaena leucocephala; PRPA = Prosopic pallida;

PSGU = Psidium guajava; SCTE = Schinus

terebenthifolia; SIFA = Sida falax; SOLI = Solanum

linnaeanum; WAIN = Waltheria indica.
USDA Forest Service Proceedings RMRS-P-11. 1999 45

the crest and were dominant at the slope base. A few species

(Geranium fremontii, Symphoricarpus oreophilus, etc.) actually become most important at the midslope position.

Artemisia tridentata showed importance at each slope position based on study site location (table 1). This variation in

distribution patterns with respect to Artemisia tridentata

would most likely result from variations from site to site in

the underlying moisture or soil gradient, competition from

other species, or because the Artemisia populations encountered represent different genetic strains adapted to localized

conditions.

The vegetation at the base of most knolls is dense, with

the midslope vegetation being moderately dense, and the

vegetation of the knoll crests being the least dense. The total

number of plant species observed in sampled vegetative

stands in Strawberry Valley increased from 41 in the slope

crest vegetation to 65 in the midslope vegetation to 88 in the

slope base vegetation. Accordingly, the average number of

plant species per sampling unit also increased from 18.3 in

the slope crest stands, to 21.8 in midslope stands, and 30.2

in slope base stands. Measured diversity (1/Σpi2

) in Provo

Canyon decreased downslope (table 2).

Among the three slope positions, the crest differed significantly from the midslope and base with respect to total cover

(table 2). The values for the midslope position were higher

than either crest or base, but differed significantly from only

the crest with respect to percent cover (England 1979). Grass

cover mimicked total cover in pattern. Cover of annuals,

forbs, and wind-adapted plants all decreased downslope

while shrubs were generally most important at the slope

base.

Soil textures from the slope crest subplots showed significantly lower clay content and significantly higher percent

sand and exposed rock than samples from midslope and

slope base positions. Significant differences were also found

for soil organic matter, pH, bare ground, litter cover, total

soluble salts, and concentrations of sodium and potassium

when comparisons were made among the three slope positions (table 2). Soil depth increased downslope and was

significantly higher at slope base. Potassium increased

downslope. This may possibly be due to the weakness with

which potassium is adsorbed in soil. It is easily leached from

sites where considerable water flows over and through a soil

to accumulate on slope base sites where water accumulates.

These facts indicate that as water moves downslope it takes

the smaller textured particles and dissolved nutrients along

with it.

Regression analyses were performed to determine if any

correlation existed between measured soil factors of each

stand (i.e., soil depth, soil texture, and soluble salts, etc.),

stand topographic features (slope position, exposure, and

percent slope), stand synthetic moisture index values, and

measured plant moisture stress. The soil parameters, including texture and soluble salts, showed little or no correlation with all other factors due to their homogeneity between stands (all had r2

 values of less than 0.10). The

regression between soil depth and slope position was significant, however, and resulted in a correlation and r2

 = 0.59.

The inferred moisture gradient, which has been suggested

with respect to slope position (i.e. the slope crests being the

most xeric and the slope base being the most mesic), corresponds nicely with the patterns in the biotic and abiotic

factors as discussed above. Annuals, for example, are generally considered to be quite xeric in their habitat requirements. Total cover, on the other hand, would be expected to

increase as soil depth and affective moisture increases. The

correlations become much tighter when the ecology of the

individual species are taken into account. For example,

Agropyron spicatum and Stipa lettermanii are known xeric

species, while Festuca idahoensis and Artemisia cana occupy more mesic habitats.

Indicator species used to establish the inferred moisture

gradient were selected by comparing the mean cover of

species restricted to the slope crest or to slope base stands.

Those species that showed cover values to be significantly

different between the crest and slope base positions were

used in computing the stand synthetic moisture indices.

These computed stand indices allow the individual stands to

then be placed in somewhat linear relationships to each

other with respect to moisture. Once these relationships are

established, then individual species as well as individual

biotic and abiotic factors can be compared to the inferred

moisture gradient. In the past this method has been criticized and it has been suggested that such data may or may

not reflect actual conditions in reality (Whittaker 1967).

Pre-dawn leaf water potential measurements taken in

Strawberry Valley and Provo Canyon showed plant species

at the hill crest position to be under higher moisture tensions

than those at the basal and midslope positions (England

1979; Black 1987). The midslope values fell between those of

the crest and base sites. Leaf moisture potential data taken

Table 2—Patterns of biotic and abiotic factors across slope ecotones.

Values represent factor importance at the slope crest,

midslope, and slope base topographic positions. Data follow

England 1979, Black 1987, and Moretti and Brotherson

1982.

Slope postion

Factor Crest Midslope Base

Biotic factors

Annual cover2 29.4a 14.1b 11.8b

Grass cover2 53.1a 57.7b 36.2c

Shrub cover2 96.3a 87.3a 123.9b

Forb cover2 40.9a 38.4a 22.8b

Total living cover2 40.0a 79.1b 58.6b

Wind adapted plant cover3 15.6a 3.6b 3.7b

Diversity (1/Σ pi2)

3 6.9a 4.4b 3.9b

Abiotic factors

Soil depth (cm)3 20.0a 34.0b 65.0c

Percent bare ground1 20.1a 40.0b 41.0b

Percent exposed rock1 61.9a 38.3b 13.2c

Percent litter1 27.3a 30.5a 46.0b

Soluble salts (ppm)1 181.0a 432.0b 357.0b

Potassium (ppm)2 232.0a 241.0a 381.0b

Sodium (ppm)2 14.0a 11.0a 31.0b

Sand (%)2 42.9a 32.2b 35.5b

Clay (%)2 36.8a 44.8b 42.8b

1,2, and 3

 signify plants studied by England, Black, and Morettiand Brotherson,

respectively.

a,b, and c indicate those species that are significantly different based on

ANOVA results.
46 USDA Forest Service Proceedings RMRS-P-11. 1999

with respect to slope position correlated significantly with

the inferred moisture gradient, a pattern that held constant

throughout the spring and summer months (England 1979)

(fig. 2).

Plant moisture stress as measured on plant twigs and

leaves increased through the growing season as soil moisture was depleted through the heat of summer. The most

marked increases in measured moisture stress occurred at

the slope crest and were followed closely on midslope stands

during the month of August. Variation between stands of the

same slope position also increased with summer’s progression, becoming most pronounced in midslope and slope base

stands (England 1979).

The stand synthetic moisture index, when correlated with

measured plant moisture stress data taken on four different

dates throughout the growing season, resulted in linear and

exponential r2

 values of 0.75 and 0.95 (England 1979). Early

season correlations were linear, while the late season correlations were exponential. Linear regressions between measured plant moisture stress of late summer (September 20)

and the abiotic factors of slope position and soil depth were

significant and showed correlation values of r2

 = 0.75 and

r2 = 0.78, respectively (England 1979).

The high degree of correlation between moisture gradients measured by instrumentation and inferred gradients

established by variations in plant species composition (fig. 2)

is useful in verifying the validity of the synthetic index

approach to gradient analysis. It is important to point out

that the strongest correlation between the two was in the

late growing season when moisture stress in plants is at its

greatest. At that season the relationship is exponential.

The stand synthetic moisture index values discussed in

this paper and similar synthetic moisture indices in other

reports are based upon assumptions mentioned previously

in this paper. Use of inferred synthetic gradients to

demonstrate variations in actual species distribution and

habitat preference employs a circularity of reasoning in and

of itself when variations in plant species abundance are

themselves used in establishing and quantifying that inferred gradient. The strong correlation between the measured and inferred moisture gradients reported in this paper

gives strong evidence that the synthetic gradient approach,

while having flaws, is nevertheless useful and does closely

approximate a directly measured moisture gradient especially late in the growing season. Indications are that an

inferred gradient will yield information closely approximating that of a measured gradient and yet allow greater

flexibility as to time of day and season for sampling of

vegetation in the field.

With the vegetative patterns along the slope being so

highly evident and with slope position being shown to be

strongly correlated with leaf water potentials, one can conclude that these vegetative patterns are correlated with a

moisture gradient. Following ideas suggested by Farquhar

and others (1982), Black (1987) collected tissue from species

in the vegetation of specific slope positions and analyzed

them for 13C content to see if concentrations in this stable

isotope showed any patterns with respect to drought

conditions.

His data show that the 13C content had statistically higher

tissue concentrations (p ≤ 0.05) of the isotope (smaller

negative numbers) at the hill crest than at the slope base.

Although not significantly different from either ridge crest

or slope base samples, midslope values for δ13C followed

similar trends to the leaf water potential measurements

with midslope values being intermediate to those for ridge

crest or slope base (Black 1987).

Leaf water potentials were also found to be negatively

correlated with 13C content of leaf tissue (r = 0.88) (fig. 3).

This observation supports the findings of Ehleringer and

Figure 3—Pre-dawn water stress data plotted

against δ 13C values. The r value = –0.88 and the

equation for the regression line is: y = –11.3 x

–3235.4. Values on the x- and y-axis represent

negative numbers.

Figure 2—Late season relationships observed between measured plant moisture stress (water tension I the plant) in atmospheric pressure (ATM) and

synthetic stand moisture indices.
USDA Forest Service Proceedings RMRS-P-11. 1999 47

others (1985) that efficiency of daily water use was correlated with carbon isotope ratios in leaf tissue of mistletoe

parasites and host trees.

The high degree of correlation between carbon 13C isotope

content of leaf tissue and leaf water potentials should be

useful to researchers in helping to establish relative moisture stress relationships between stands of vegetation. The

method may also have value for estimation of stresses of

plants due to other factors such as nutrient deficiency,

salinity (induced moisture stress), and high and low temperature effects.

References _____________________

Anderson, D. L.; Ostler, W. K.; Freeman, C.; Harper, K. T. 1976.

Vegetation of the proposed Chine Butte coal strip mine. Rocky

Mountain Energy Corporate Report. 1976: 4-23.

Armstrong, R. W. 1980. Atlas of Hawaii. Department of Geography,

University of Hawaii. The University of Hawaii Press, Honolulu.

222 p.

Black, D. R. 1987. Correlation of leaf matrix potential, the stable

isotope 13C and plant vegetation patterns to moisture gradients

in sagebrush-grass communities of the Wasatch Mountains,

Utah, U.S.A. Unpublished thesis. Brigham Young University,

Provo, Utah. 41 p.

Boutton, T. W.; Wong, W. W.; Hachey, D. L.; Lee, L. S.; Cabrera, M. P.;

Dlein, P. D. 1983. Comparison of quartz and pyrex tubes for

combustion of organic samples for stable carbon isotope analysis.

American Chemical Society. 55: 1832-1833.

Bouyouchous, G. J. 1951. A recalibration of the hydrometer method

for making mechanical analysis of soils. Journal of Agronomy. 43:

434-438.

Bowns, J. E. 1973. An autecological study of blackbrush (Coleogyne

ramosissima Torr.) in southwestern Utah. Unpublished dissertation. Utah State University, Logan. 115 p.

Boyer, J. S. 1967. Leaf water potentials measured with a pressure

chamber. Plant Physiology. 42: 133-137.

Brotherson, J. D. 1996. Elevational relationships of introduced

woody species on the Islands of Lanai and Hawaii. In: Barrow,

S. R., McArthur, E. D.; Sosebee, R. E.; Tausch, R. J.; comps. 1996.

Proceedings: shrubland ecosystem dynamics in a changing environment; 1995 May 23-25; Las Cruces, New Mexico. Gen. Tech.

Rep. INT-GTR-338. Ogden, Utah: U.S. Department of Agriculture, Forest Service, Intermountain Research Station.

Brotherson, J. D.; Masslich, W. J. 1985. Vegetation patterns in

relation to slope position in the Castle Cliffs area of southern

Utah. Great Basin Naturalist. 45: 535-541.

Brown, R. W.; McDonough, W. T. 1977. Thermocouple psychrometer

for in situ leaf water potential determinations. Plant and Soil. 48:

5-10.

Christensen, E. M. 1963. The foothill bunchgrass vegetation of

central Utah. Ecology. 44: 156-158.

Clements, F. E. 1936. Nature and structure of the climax. Journal

of Ecology. 24: 252-254.

Cox, J. R.; Hughes, H. G. 1982. Leaf water potentials of perennial

grasses-leafpress and pressure chamber evaluation. Journal of

Range Management. 35: 5-6.

Curtis, J. T. 1955. A prairie continuum in Wisconsin. Ecology. 36:

550-566.

Curtis, J. T.; McIntosh, R. P. 1951. An upland forest continuum in the

prairie-forest border region of Wisconsin. Ecology. 32: 476-496.

Daubenmire, R. 1959. A canopy-coverage method of vegetational

analysis. Northwest Science. 33: 46-66.

Dix, R. L.; Butler, J. E. 1960. A phytosociological study of a small

prairie in Wisconsin. Ecology. 41: 316-327.

Ehleringer, J. R.; Miller, P. C. 1975. Water relations of selected plant

species in the alpine tundra, Colorado. Ecology. 56: 370-380.

Ehleringer, J. R.; Schulze, E. D.; Ziegler, M.; Lnage, O. L.; Farquhar,

G. D.; Cowar, I. R. 1985. Xylem-tapping mistletoes; water or

nutrient parasites? Science. 227: 1479-1481.

England, J. L. 1979. Measured and inferred moisture gradient

relationships: a study of a montane steppe in central Utah.

Unpublished thesis. Brigham Young University, Provo, Utah.

284 p.

Eubank, M. E.; Brough, R. C. 1979. Utah weather. Horizon Publishers. Bountiful, Utah. 284 p.

Farquhar, G. D.; O’Leary, M. H.; Berry, J. A. 1982. On the relationship between carbon isotope discrimination and the intercellular

carbon dioxide concentration in leaves. Australian Journal of

Plant Physiology. 9: 121-137.

Gleason, H. A. 1926. The individualistic concept of the plant association. Bulletin of the Torrey Botanical Club. 53: 7-26.

Goff, F. F.; Cottam, G. 1967. Gradient analysis: the use of species

and synthetic indices. Ecology. 48: 793-806.

Greenwood, L. C.; Brotherson, J. D. 1978. Some ecological relationships between pinyon-juniper and birchleaf mountain mahogany

stands. Journal of Range Management. 31(3): 164-168.

Hodges, L. H.; Reichelderfer, F. W. 1962. Climatography of the

United States. No. 81-37 (Utah) Decennial census of the United

States climate. U.S. Department of Commerce. 2 p.

Isaac, R. A.; Kerber, J. D. 1971. Atomic absorption and flame

photometry: technique and uses in soil, plant and water analysis.

In: L. M. Walsh (ed.), Instrumental methods for analysis of soils

and plant tissue. Soil Science Society of America. Wisconsin.

 17-38.

Loucks, O. L. 1962. Ordinating forest communities by means of

environmental scalars and phytosociological indices. Ecological

Monographs. 32: 137-166.

Moretti, M. O.; Brotherson, J. D. 1982. Vegetation and soil factors

in relation to slope position on foothill knolls in the Uinta Basin

of Utah. Great Basin Naturalist. 42: 81-90.

Nelson, D. W.; Sommers, L. E. 1982. Carbon and organic matter. In:

Methods of soil analysis, part 2; chemical and microbiological

properties. Second edition. American Society of Agronomy, Inc.;

Soil Science Society of America, Inc., Madison, Wisconsin.

539-579.

Olsen, S. R.; Cole, C. V.; Watanabe, F. S.; Dean, D. A. 1954.

Estimation of available phosphorous in soils by extraction with

sodium bicarbonate. U.S. Department of Agriculture Circular

No. 939.

Ostler, W. K. 1980. Evaluating plant community monitoring designs: an example from the Uinta Mountains, Utah. Unpublished

dissertation. Brigham Young University, Provo, Utah. 76 p.

Ott, L. 1984. An introduction to statistical methods and data

analysis, second edition. Duxbury Press, Boston. 775 p.

Rhoades, J. D. 1982. Cation exchange capacity. In: Methods of soil

analysis, part 2; Chemical and microbiological properties. Second

edition. American Society of Agronomy, Inc.; Soil Science Society

of America, Inc., Madison, Wisconsin. 149-157.

Russel, D. A. 1948. A laboratory manual for soil fertility students,

Third edition. Wm. Brown Co., Dubuque, Iowa. 56 p.

Scholander, P. F.; Hammel, H. T.; Bradstreet, E. D.; Hemmingsen,

E. A. 1965. Sap pressure in vascular plants. Science. 148: 339-346.

Slayter, R. O. 1967. Plant-water relationships. Academic Press:

London and New York. 366 p.

Sturges, D. L. 1977. Soil water withdrawal and root characteristics

of big sagebrush. American Midland Naturalist. 98: 257-274.

USDA-SCS in cooperation with Utah Agricultural Experimental

Station. 1972. Utah County Soil Survey.

USDA-SCS. 1975. Soil taxonomy. Agricultural Handbook 436. 754 p.

Utah Planning Commission. 1981. Atlas of Utah County, Utah.

Provo, Utah.

Waring, R. H.; Cleary, B. D. 1967. Plant moisture stress; evaluation

by pressure bomb. Science. 155: 1248-1254.

Waring, R. H.; Major, J. 1964. Some vegetation of the California

coastal redwood region in relation to gradients of moisture,

nutrients, light and temperature. Ecological Monographs. 34:

167-215.

Weaver, J. E. 1968. Prairie plants and their environment. University of Nebraska Press, Lincoln, Nebraska. 276 p.

Webb, G. M.; Brotherson, J. D. 1988. Elevational changes in woody

vegetation along three streams in Washington County, Utah. The

Great Basin Naturalist. 48: 512-529.

Whittaker, R. H. 1956. Vegetation of the Great Smoky Mountains.

Ecological Monographs. 26: 1-80.

Whittaker, R. H. 1960. Vegetation of the Siskiyou Mountains,

Oregon and California. Ecological Monographs. 30: 279-338.
48 USDA Forest Service Proceedings RMRS-P-11. 1999

Whittaker, R. H. 1967. Gradient analysis of vegetation. Biological

Review. 42: 207-264.

Whittaker, R. H. 1975. Communities and Ecosystems, second edition. Macmillan Publishing Co., Inc., New York. 385 p.

Whittaker, R. H.; Niering, W. A. 1965. Vegetation of the Santa

Catalina Mountains, Arizona: a gradient analysis of the south

slope. Ecology. 46: 429-452.

Wickum, D. A.; Wali, M. K. 1974. Analysis of a North Dakota galler

forest: vegetation in relation to topographic and soil gradients.

Ecological Monographs. 44: 441-464.

Zobel, D. B.; McKee, A.; Hawk, G. M.; Dyrness, C. T. 1976. Relationships of environment to composition, structure, and diversity of

forest communities of the Central Cascades of Oregon. Ecological

Monographs. 46: 135-156.
USDA Forest Service Proceedings RMRS-P-11. 1999 49

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

W. P. Clary is Project Leader and D. E. Medin (deceased) was Research

Wildlife Biologist, Forestry Sciences Laboratory, Rocky Mountain Research

Station, 316 E. Myrtle Street, Boise, ID 83702.

Riparian Zones—The Ultimate Ecotones?

Warren P. Clary

Dean E. Medin

Abstract—Riparian zones are important landscape features with

elongate shapes and high edge-to-area ratios. They are open

ecosystems with large energy, nutrient, and biotic interchange

with adjacent aquatic and terrestrial ecosystems. In the arid and

semiarid West, riparian zones typically occur as islands of mesophytic and hydrophytic vegetation that support diverse fauna and

flora that are often quite different from those in the adjacent

terrestrial and aquatic systems. Riparian zones are arguably the

ultimate expression of the ecotonal concept.

A comparison of three high elevation sagebrush areas illustrates a few of the differences that occur in vegetation structure

and bird communities at the riparian-upland interface. Vegetation and bird community measures in the riparian zone varied

from 200 to 1,098 percent of the values present in adjacent upland

areas.

Ecotones

An edge is the place where ecological systems meet, or

where types of vegetation or vegetation conditions within

plant communities come together. The area influenced by

the transition between systems, communities, or stages is

called an ecotone (Leopold 1933; Thomas and others 1979a).

Study of the concept began over a half century ago (Risser

1995). Initially it was viewed in three different contexts: (1)

local edges or margins for habitat, cover, and food for

wildlife species (Leopold 1933); (2) timberline transitions

(Griggs 1938); and (3) broad transitions between continental-scale biomes (Weaver and Albertson 1956). Later, ecotone concepts were expanded. The classifications included

inherent, induced, wide, narrow, high constrast, low

constrast, simple, mosaic, stable, and dynamic ecotones

(Thomas and others 1979a). The different settings and

concepts have led to fragmented understandings and conflicting viewpoints. Often ecotones were excluded from field

sampling in the effort to define relatively homogeneous

populations for study (Risser 1995).

A modern definition of ecotone refers to areas of steep

vegetation gradients between the more homogeneous vegetation associations. These gradients usually occur in response to abrupt physical environmental gradients that

affect ecological processes and distribution of organisms,

although they occasionally occur as threshold or nonlinear

responses to gradual gradients in the physical environments (Gosz 1992). Such transitions between different

ecosystems contain characteristics of adjacent habitats as

well as distinctive microhabitats found only in the intermediate ecotonal area (Thomas and others 1979a; Risser 1995).

The flows of water, nutrients, organisms, and other

materials across the landscape frequently are intensified in

ecotones. Fluxes of water and materials vary with changes

in energy of wind and water (Johnston 1993; Risser 1995).

Ecotones may serve as conduits through which organisms

concentrate, move, and migrate (De’Camps 1993; Risser 1995).

Many species occur at their physiological limits of distribution at ecotones. If species are at the margin of their

environmental tolerance, they could (or perhaps are likely)

to be sensitive and reactive to change (Gosz and Sharpe

1989). There is no paleontological evidence suggesting that

ecotones confer stability (Delcourt and Delcourt 1992),

even though some investigators assume that the diversity

within ecotones provides an inherent element of biological

perseverance (Thomas and others 1979b).

Riparian Zones as Ecotones

Riparian zones are elongate with very high edge-to-area

ratios and provide a classic example of edge effect and the

ecological principle of ecotones. Riparian zones have large

energy, nutrient, and biotic interchanges with aquatic

systems on one boundary and terrestrial systems on the

other boundary (Gregory and others 1991; Odum 1978).

Chemical, biological, and physical processes including denitrification, trapping of suspended particulate material, and

plant uptake of nutrients function to improve the quality of

water as it moves through a wetland from uplands to a

stream or other body of water (Johnston 1993; Risser 1995).

The upland-riparian-aquatic combination also presents

a striking platform for a biotic medley. the mosiac nature of

riparian areas with their high productivity and variability

tends to support a highly diverse biota represented by

species from adjacent upland and aquatic types as well as

species unique to the riparian area itself (Fitch and Adams

1998; Larson 1993; Odum 1978; Thomas and others 1979b).

Riparian zones (ecotones) typically exhibit characteristics quite different from the adjacent “parent” vegetation

types. Shrublands of the Intermountain West are often

defined by a sagebrush-grass vegetation type, wherein the

adjacent riparian zones vary from wetland graminoid types

to tree-dominated communities with multiple strata and

sub-ecotonal zones (fig. 1). This layering and the vegetation

differences within and between communities create numerous niche possibilities (fig. 2). We report some results

from a study of three exclosures to illustrate a few of the

differences between typical riparian zones and the adjacent

upland sites.
50 USDA Forest Service Proceedings RMRS-P-11. 1999

An Example of Vegetation and Small

Bird Comparisons at the Riparian/

Upland Interface ________________

Study Areas

Numerous riparian grazing exclosures on USDA Forest

Service and USDI Bureau of Land Management lands were

examined as potential study areas in central and eastern

Oregon, northern Nevada, and central and southern Idaho.

Three riparian study areas met the following criteria:

1. Protection from grazing for at least 10 years.

2. A minimum size of 1,200 by 150 m.

3. Elevation of 1,850 to 2,000 m, sagebrush (Artemisia

spp.) ecological zone, and average annual precipitation of

approximately 240 to 250 mm.

4. Within the Snake River Basin/High Desert Ecoregion

(Omernik 1995).

Vegetation structural aspects within the riparian zones

of the selected areas varied from herbaceous plants to tall

trees, while the upland sites all had a shrubby aspect. This

provided an opportunity to assess the approximate range of

biological characteristics occurring on ungrazed upland

and riparian sites within this general ecological zone.

Deer Creek is located in northeastern Nevada in a narrow, V-shaped canyon. The stream was closely bordered by

clumped stands of aspen (Populus tremuloides), willow

(Salix boothii and S. geyeriana), and other deciduous shrubs

including currant (Ribes spp.) and Woods rose (Rosa

woodsii). The herbaceous component was dominated by

Kentucky bluegrass (Poa pratensis) and various sedges

(Carex spp.). The upland was dominated big sagebrush

(Artemisia tridentata) and bluebunch wheatgrass (Agropyron spicatum).

Wet Creek is located in central Idaho in a meandering

flood plain located below an upper bench level of a broader

valley configuration. The riparian vegetation included those

species at Deer Creek plus bush cinquefoil (Potentilla

fruticosa), some water birch (Betula occidentalis), redtop

(Agrostis stolonifera), Baltic rush (Juncus balticus), aster

(Aster spp.), Rocky Mountain iris (Iris missouriensis), and

longleaf phlox (Phlox longifolia). Upland species included

those listed for Deer Creek plus rabbitbrushes (Chrysothamnus spp.), crested wheatgrass (Agropyron cristatum), and aster.

Summit Creek is also located in central Idaho in a broad

basin-like valley. Riparian vegetation was dominated by

mat muhly (Muhlenbergia richardsonis), thickspike wheatgrass (Agropyron dasystachyum), Kentucky bluegrass,

beaked sedge (Carex rostrata), and Baltic rush. The dominant shrubs on the adjoining uplands were low sagebrush

(Artemisia arbuscula) and threetip sagebrush (A. tripartita).

Big sagebrush occurred as a minor species. Sandberg’s bluegrass (Poa secunda), bluebunch wheatgrass, aster, and longleaf

phlox were the most apparent herbaceous upland species.

Figure 1—Illustration of the typical Western U.S.

“sandwich” of sagebrush upland-riparian zoneaquatic systems (source unknown).

Figure 2—Illustration of the strata and edges that

often occur within a riparian zone (from Thomas and

others 1979b).
USDA Forest Service Proceedings RMRS-P-11. 1999 51

Methods

Individual study sites were sampled in different years

during a drought period; annual precipitation had been

below average for a minimum of 2 years prior to sampling.

In each year of sampling, precipitation at the nearest

reporting stations was 67 to 85 percent of the respective

long-term means (USDC-NOAA 1986- 1991). Streamflow

at all three sites appeared to be at approximately normal

levels during the course of the study.

Vegetation—On each study area a 600- by 150-m (9-ha)

grid was sampled for vegetation characteristics in August

1988 for Deer Creek, in 1989 for Summit Creek, and in 1991

for Wet Creek. The riparian complex within each grid area

contained 40 to 60 sample locations. A 50 x 50 cm (0.25 m2

)

quadrat was located at each of the systematically positioned sample locations. Height, exclusive of reproductive

structures, of the graminoid, forb, and shrub nearest the

center of each quadrat was recorded. Biomass of each plant

life form was determined by clipping vegetation at ground

level in the 0.25-m2

 quadrats. A 3- by 3-m (9-m2) plot,

concentric to each 0.25-m2

 quadrat, was used to sample

biomass of large shrubs. Basal diameter, maximum height,

and species were recorded for large shrub stems rooted

within the plot. Biomass of large shrubs were estimated

from locally derived equations using stem basal diameter,

stem height, or both as predicting variables. Height and

diameter at breast height were recorded for each aspen

stem rooted within 10- by 10-m (100-m2

) plots concentric to

each 0.25-m2

 quadrat. Biomass of aspen was estimated

from equations developed by Bartos and Johnston (1978).

Breeding Birds—The sites were censused for breeding

birds using the spot-map method (International Bird Census Committee 1970). Census grids 600- by 150-m (9-ha)

were oriented lengthwise along the creek and straddled the

stream channel. Grid points were staked at 25-m intervals.

Eleven to 13 census visits were made to each site from midMay to mid-June during 1 year at each site. Most of the

spot-mapping was done from sunrise to early afternoon

when birds were most active. To ensure complete coverage,

sites were censused by walking within 25 m of all points on

the vegetation sample grid. Wide-ranging raptors and transient bird species were excluded from the comparisons. The

birds reported had established nesting territories within

the sampled plots.

Results

Vegetation Structure—Riparian vegetation structure

was quite different among the study areas. The vegetation

of Deer Creek was organized into three tiers or vertical

strata (in the sense of Whittaker 1975): tree, large shrub,

and small shrub/herbaceous. Wet Creek had a two-tiered

aspect with large shrub and small shrub/herbaceous components. Vegetation on the Summit Creek study area was

a single-tiered herbaceous community. Biomass components and total live biomass were positively associated with

the number of vegetation tiers (table 1). Biomass was

dominated by trees (aspen) at Deer Creek, by large shrubs

(mostly willows) on Wet Creek, and by herbaceous plants on

Summit Creek. Differences in riparian biomass were primarily due to the woody component of the plant community

(table 1). In the riparian area total plant live biomass

values differed by 2,082 g/m2

 between the one-tiered area

and the three-tiered area. Upland vegetation structure was

similar among the three areas in that all had a small shrub/

herbaceous aspect. The biomass did vary (465 g/m2

), but not

to the extent of that on the riparian areas (table 1).

Breeding Birds—We recorded 24 species of birds nesting in the riparian areas and nine species nesting in the

upland areas. The bird community composition was noticeably different among the three study areas. Species richness varied from 3 to 18 in the riparian areas and 2 to 5 in

the upland areas (tables 2 and 3).

In the riparian areas Deer Creek had the most species

and Summit Creek the least. No overlap of bird species

occurred between these two areas. Wet Creek shared four

species with Deer Creek, shared no species with Summit

Creek, and had three unique species. The most abundant

species was different on each area—Dusky Flycatcher (Scientific names in tables 2 and 3) for Deer Creek, Yellow

Warbler for Wet Creek, and Savannah Sparrow for Summit

Creek. The abundance of these species within each study

area reflects the dominant habitat features of the respective study areas (DeGraaf and others 1991). Dusky Flycatchers typically nested in aspen at Deer Creek, Yellow

Warblers in willows at Wet Creek, and Savannah Sparrows

in herbaceous vegetation at Summit Creek. The total density of nesting birds followed the trends for numbers of bird

species (table 2). Both species richness and bird densities

were associated with the average vegetation stand height

(fig. 3). An increase in vegetation stand height was linked

to plant biomass, structural layers or tiers and, by inference, habitat niches.

As with the riparian areas, the upland areas differed in

the most abundant bird species—Green-tailed Towhee at

Deer Creek, Brewer’s Sparrow at Wet Creek, and Vesper

Sparrow at Summit Creek. These differences among upland areas may have reflected the trend (from Deer Creek

to Summit Creek) toward wider and more open canyon

bottoms, and less upland and adjacent riparian plant biomass. Surrounding landscapes have been shown to strongly

Table 1—Plant live biomass in adjacent riparian and upland areas.

Deer Creek Wet Creek Summit Creek

Life form Riparian Upland Riparian Upland Riparian Upland

- - - - - - - - - - - - - - - - - - - - - - - - - - - - (g/m2 ) - - - - - - - - - - - - - - - - - - - - - - - - - - 

Herbage 145.0 52.0 159.2 27.2 279.2 61.6

Shrub 589.8 577.0 1097.5 566.4 0.0 102.2

Tree 1626.3 0.0 0.0 0.0 0.0 0.0

Total 2361.1 629.0 1256.7 593.6 279.2 163.8
52 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 2—Riparian breeding bird foraging guilds, nesting guilds, and breeding pair density per 10 ha.

Density

Foraging Nesting Deer Wet Summit

Species guild1 guild2 Creek Creek Creek

American kestrel GHC SCN 2.7

(Falco sparverius)

Spotted sandpiper SGI GRN 5.0

(Actitis macularia)

Broad-tailed hummingbird FHO BTN 12.9

(Selasphorus platycercus)

Lewis’ woodpecker ASI PCN 1.8

(Melanerpes lewis)

Red-naped sapsucker BEO PCN 2.7

(Sphyrapicus nuchalis)

Downy woodpecker BGI PCN 3.6

(Picoides pubescens)

Northern flicker GGI PCN 3.6

(Colaptes auratus)

Dusky flycatcher ASI BTN 45.3 15.5

(Empidonax oberholseri)

Tree swallow AFI SCN 1.8

(Tachycineta bicolor)

House wren CGI SCN 11.1

(Troglodytes aedon)

American robin GGV BTN 19.6 16.1

(Turdus migratorius)

European starling GFO SCN 0.4

(Sturnus vulgaris)

Warbling vireo CGI BTN 8.9

(Vireo gilvus)

Yellow warbler CGI BTN 16.0 34.5

(Dendroica petechia)

MacGillivray’s warbler CGI BTN 4.4

(Oporornis tolmiei)

Chipping sparrow GFO BTN 5.5

(Spizella passerina)

Savannah sparrow GFO GRN 18.4

(Passerculus sandwichensis)

Song sparrow CFO GRN 5.3

(Melospiza melodia)

White-crowned sparrow GFO BTN 9.3 16.6

(Zonotrichia leucophrys)

Red-winged blackbird GFO CRN 5.6

(Agelaius phoeniceus)

Western meadowlark GGI GRN 3.7

(Sturnella neglecta)

Brewer’s blackbird GFO GBN 2.8

(Euphagus cyanocephalus)

Bullock’s oriole CFO DTN 5.8

(Icterus bullockii)

Cassin’s finch GFO CDN 1.8

(Carpodacus cassinii)

Total density (pairs per 157.0 96.0 27.7

10 ha riparian habitat)

Species richness (n) 18 7 3

1

 After DeGraff et al. (1985). AFI = air feeding insectivore, ASI = air sallier insectivore, BEO = bark excavator omnivore, BGI = bark

gleaning insectivore, CFO = canopy foraging omnivore, CGI = canopy gleaning insectivore, FHO = floral hover-gleaning omnivore,

GFO = ground foraging omnivore, GHC = ground hawker carnivore, GGI = ground gleaning insectivore, GGV = ground gleaning

vermivore, SGI = shoreline gleaning insectivore. 2 After Harrison (1979). BTN = bush and small tree nester, CDN = conifer-deciduous tree nester, CRN = cattail, rush, sedge, reed,

grass, and bush nester, DTN = deciduous tree nester, GBN = ground and bush nester, GRN = ground nester, PCN = primary cavity

nester, SCN = secondary cavity nester.
USDA Forest Service Proceedings RMRS-P-11. 1999 53

Table 3—Upland riparian breeding bird foraging guilds, nesting guilds, and breeding pair density per 10 ha.

Density

Foraging Nesting Deer Wet Summit

Species guild1 guild2 Creek Creek Creek

 Mourning dove GGG GRN 0.3

(Zenaida macroura)

Black-billed magpie GGI BTN 0.4

(Pica pica)

Rock wren GGI CCN 4.6

(Salpinctes obsoletus)

Mountain bluebird GGI SCN 1.0

(Sialia currucoides)

Sage thrasher GGI GBN 0.6

(Oreoscoptes montanus)

Green-tailed towhee GGO BTN 8.0

(Pipilo chlorurus)

Vesper sparrow GGO GRN 3.4 4.4

(Pooecetes gramineus)

Brewer’s sparrow GGI BTN 1.4 4.4

(Spizella breweri)

Western meadowlark GGI GRN 0.5

(Sturnella neglecta)

Total density (pairs per 14.3 9.8 4.9

10 ha upland habitat)

Species richness (n) 4 5 2

1 After DeGraff et al. (1985). GGI = ground gleaning insectivore, GGG = ground gleaning granivore, GGO = ground gleaning

omnivore. 2

 After Harrison (1979). BTN = bush and small tree nester, CCN = cliff, cave, rock, or talus nester, GBN = ground and bush nester,

GRN = ground nester, SCN = secondary cavity nester.

Figure 4—Association of upland bird attributes

with vegetation height.

Figure 3—Association of riparian bird attributes

with vegetation height.

affect avian composition (Saab 1999). Total nesting bird

densities followed the relatively low species numbers in the

upland areas where the vegetation stand heights averaged

less than one-half meter (fig. 4).

The number of foraging guilds represented in the bird

communities again reflected the different habitat diversities provided by these riparian habitats. Summit Creek

with its single-tiered plant community had only the ground

foraging-gleaning guild group represented for a total of

3 guilds, whereas Deer Creek and Wet Creek with more

habitat variety also had the shore-line gleaning (WC only),

canopy foraging-gleaning, timber drilling (DC only), and

air sallying-feeding foraging guild groups represented for a

total of 10 and four foraging guilds, respectively. The number

of nesting guilds were different as well—six at Deer Creek,

three at Wet Creek, and two at Summit Creek (fig. 3).
54 USDA Forest Service Proceedings RMRS-P-11. 1999

Upland areas, characterized by less complex vegetation

structures than the riparian areas on Deer and Wet Creeks,

had smaller differences in number of nesting bird species

and bird densities, and in number of foraging and nesting

guilds represented (the ground foraging-gleaning guild

group with two to four specific guilds, and one to four nesting

guilds). The upland areas did have somewhat variable bird

characteristics because of their different configurations of

herbaceous and small shrub vegetation (fig. 4).

Discussion of Example

Although the comparison of the three areas in the current

study did not allow a statistical compartmentalization of

annual growing condition effects (logistics required data to

be collected in different years), the values presented are

assumed representative for the years of study (1988-1991)

encompassed by a drouth period.

These results illustrate once again the substantial biological differences that can be present among areas in

similar regional environmental settings, but with different

microhabitat conditions—such as occurs in riparian ecotonal settings. The riparian-upland study areas were alike

in elevation, broad ecological zone, and both current and

long-term precipitation, yet differed substantially in vegetation structure and in small bird community characteristics. As the difference in vegetation structure increased

between adjacent riparian and upland sites (Summit

Creek<Wet Creek<Deer Creek), the differences in bird

communities increased. Greater bird densities and diversities typically occur in response to more complex vegetation

structure and habitat mosaics (Bull and Skovlin 1982;

Whittaker 1975; Williams and Williams 1989), although

Knopf (1985) found little correlation.

General Summary _______________

The land-water ecotone, called the riparian zone, is normally the most ecologically productive and diverse of all

terrestrial habitats. This results from a variety of physical

environments arising from moisture gradients, margins of

often highly contrasting vegetation components, and a general mosaic of habitats created by dynamic stream changes

(Naiman and others 1993). The interaction of components in

this ecotone is so compelling that any management action

should always consider both the effects of the physical

environment on the biological community and the effects of

the biological community upon the physical attributes, notably on stream channel characteristics (Fitch and Adams 1998).

Riparian ecotonal habitats are particularly important in

the arid West where the presence of water and relatively

cool, often shaded conditions provide an ecological importance and diversity far beyond their aerial extent (Kondolf

and others 1996). A large portion of both the flora and fauna

in the riparian zones exists nowhere else. Our brief example

from the High Desert Ecoregion suggests riparian plant

biomass was up to 375 percent, plant stand height up to 983

percent, nesting bird species up to 450 percent, nesting bird

density up to 1,098 percent, bird foraging guilds up to 250

percent, and bird nesting guilds up to 200 percent of the

values present in the immediately adjacent uplands.

References _____________________

Bartos, Dale L.; Johnston, Robert S. 1978. Biomass and nutrient

content of quaking aspen at two sites in the Western United

States. Forest Science. 24(2): 273-280.

Bull, Evelyn L; Skovlin, Jon M. 1982. Relationships between

avifauna and streamside vegetation. Transactions North American Wildlife and Natural Resources Conference. 47: 496-506.

De’Camps, Henri. 1993. River margins and environmental change.

Ecological Applications. 3(3): 441-445.

DeGraaf, Richard M.; Scott, Virgil E.; Hamre, R. H.; Ernst, Liz;

Anderson, Stanley H. 1991. Forest and rangeland birds of the

United States: natural history and habitat use. Agric. Handb.

688. Washington, DC: U.S. Department of Agriculture, Forest

Service. 625 p.

DeGraaf, Richard M.; Tilghman, Nancy G.; Anderson, Stanley H.

1985. Foraging guilds of North American birds. Environmental

Management. 9(6): 493-536.

Delcourt, Paul A.; Delcourt, Hazel R. 1992. Ecotone dynamics in

space and time. In: Hansen, A. J.; di Castri, F., eds. Landscape

boundaries: consequences for biotic diversity and landscape

flows. Ecological Studies 92. New York: Springer Verlag: 19-54.

Fitch, L.; Adams, B. W. 1998. Can cows and fish co-exist? Canadian

Journal of Plant Science. 78(2): 191-198.

Gosz, James R. 1992. Ecological functions in a biome transition

zone: translating local responses to broad-scale dynamics. In:

Hansen, A. J.; di Castri, F., eds. Landscape boundaries: consequences for biotic diversity and landscape flows. Ecological

Studies 92. New York: Springer Verlag: 55-75.

Gosz, James R.; Sharpe, Peter J. H. 1989. Broad-scale concepts for

interactions of climate, topography, and biota at biome transitions. Landscape Ecology. 3(3/4): 229-243.

Gregory, Stanley V.; Swanson, Frederick J.; McKee, W. Arthur;

Cummins, Kenneth W. 1991. An ecosystem perspective of riparian zones. BioScience. 41(8): 540-551.

Griggs, Robert. F. 1938. Timberlines in the Northern Rocky Mountains. Ecology. 19(4): 548-564.

Harrison, Hal H. 1979. A field guide to western birds’ nests.

Boston: Houghton Mifflin Co. 279 p.

International Bird Census Committee. 1970. An international

standard for a mapping method in bird census work. Audubon

Field Notes. 24(6): 722-726.

Johnston, Carol A. 1993. Material fluxes across wetland ecotones

in Northern landscapes. Ecological Applications. 3(3): 424-440.

Knopf, Fritz L. 1985. Significance of riparian vegetation to breeding birds across an altitudinal cline. In: Johnson, R. Roy; Ziebell,

Charles D.; Patton, David R.; Ffolliott, Peter F.; Hamre, R. H.,

tech. coords. Riparian ecosystems and their management: reconciling conflicting uses: First North American riparian conference; 1985 April 16-18; Tucson, AZ. Gen. Tech. Rep. RM-120.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station:

105-111.

Kondolf, G. Mathias; Kattelmann, Richard; Embury, Michael;

Erman, Don C. 1996. In: Nevada Ecosystem Project: final report

to Congress: vol. II. Davis: University of California, Centers for

Water and Wildland Resources: 1009-1030.

Larson, Gary E. 1993. Aquatic and wetland vascular plants of the

northern Great Plains. Gen. Tech. Rep. RM-238. Fort Collins,

CO: U.S. Department of Agriculture, Forest Service, Rocky

Mountain Forest and Range Experiment Station. 681 p.

Leopold, Aldo. 1933. Game management. New York: Charles

Scribner’s Sons. 481 p.

Naiman, Robert J.; DeCamps, Henri; Pollock, Michael. 1993. The

role of riparian corridors in maintaining regional biodiversity.

Ecological Applications. 3(2): 209-212.

Odum, Eugene P. 1978. Opening address: ecological importance of

the riparian zone. In: Johnson, R. R.; McCormick, J. F., tech.

coords. In: Strategies for protection and management of floodplain wetlands and other riparian ecosystems: proceedings of

the symposium; 1978 December 11-13; Callaway Gardens, GA.

Gen. Tech. Rep. WO-12. Washington, DC: U.S. Department of

Agriculture, Forest Service: 2-4.

Omernik, J. M. 1995. Ecoregions: a framework for environmental

management. In: Davis, W.; Simon, T., eds. Biological assessment
USDA Forest Service Proceedings RMRS-P-11. 1999 55

and criteria: tools for water resources planning and decision

making. Boca Raton, FL: Lewis Publishers: 49-62.

Risser, Paul G. 1995. The status of the science examining ecotones.

BioScience. 45(5): 318-325.

Saab, V. A. 1999. Importance of spatial scale to habitat use by

breeding birds in riparian forests: a hierarchical analysis. Ecological Applications. 9(1): 135-151.

Thomas, Jack Ward; Maser, Chris; Rodiek, Jon E. 1979a. Edges.

In: Thomas, Jack Ward, tech. ed. Wildlife habitats in managed

forests: the Blue Mountains of Oregon and Washington. Agric.

Handb. 553. Washington, DC: U.S. Department of Agriculture,

Forest Service: 48-59.

Thomas, Jack Ward; Maser, Chris; Rodiek, Jon E. 1979b. Riparian

zones. In: Thomas, Jack Ward, tech. ed. Wildlife habitats in

managed forests: the Blue Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. Department of

Agriculture, Forest Service: 40-47.

United States Department of Commerce, National Oceanic and

Atmospheric Administration. 1986-1991. Climatological data,

Idaho and Nevada. Vols. 92-97. Ashville, NC: National Climatic

Data Center. [n.p.].

Weaver, J. E.; Albertson, F. W. 1956. Grasslands of the Great

Plains: their nature and use. Lincoln, NE: Johnsen Publishing

Co. 395 p.

Whittaker, Robert H. 1975. Communities and ecosystems. New

York: MacMillan Publishing Co. 385 p.

Williams, Molly; Williams, John G. 1989. Avifauna and riparian

vegetation in Carmel Valley, Monterey County, California. In:

Abell, Dana L., tech. coord. Proceedings of the California riparian systems conference: protection, management, and restoration for the 1990’s; 1988 September 22-24; Davis, CA. Gen. Tech.

Rep. PSW-110. Berkeley, CA: U.S. Department of Agriculture,

Forest Service, Pacific Southwest Forest and Range Experiment

Station: 314-318.
56 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Thomas A. Eddy is Professor, Division of Biological Sciences, Emporia

State University, Emporia, KS 66801.

Ecotonal Dynamics of the Invasion of

Woody Plants into the Tallgrass Prairie

Thomas A. Eddy

Abstract—Invasion of woody plants into eastern Kansas has resulted in the loss of thousands of acres of productive tallgrass

prairie. Historical and ecological events related to the decline of the

prairie in a four-county area were assessed. Woody plants invaded

all unburned sites on the study areas, while only 5% of the burned

area was infested. Five woody species were primary invaders.

Frequency of occurrence of trees and shrubs on burned sites was

one-third that of unburned sites, and percent foliar cover on burned

sites was one-fifth that of unburned sites. Economic losses to the

ranching industry in the area was estimated at $317,000 annually.

Good range management practices and selected control strategies

can reduce woody plant populations.

This study traced land use, vegetation, and related ecological changes that have caused the widening of the ecotone

between the tallgrass prairie and the adjacent deciduous

forest in eastern Kansas. The study examined: (1) the

historic and cultural events associated with the conversion

of grassland to shrubland/woodland; (2) the composition and

foliar cover of the woody plants in burned and unburned

prairie; (3) the influence of slope on the occurrence of shrub

and trees in burned and unburned prairie; (4) reduction of

livestock forage by invading woody plants and the resulting

economic losses to the ranching industry; and (5) management techniques useful in reducing the invasion of woody

plants into the area grasslands.

Study Areas ____________________

The four-county study area is located in east central

Kansas, with Morris and Chase counties in the interior

upland of the Flint Hills and Lyon and Greenwood counties

on the eastern edge of the region (fig. 1). The two latter

counties are within the extreme eastern border of the continental forest-tallgrass prairie transition.

Methods _______________________

This study was accomplished in four parts. The preliminary phase examined early settlement newspapers to trace

changes in agricultural and cultural events in the rural

communities of the study area. Journals of military expeditions and diaries by early residents gave insights into the

vegetation of the mid to late 1900’s. Interviews with a

Figure 1—Location of Flint Hills Region Four County Study Area.
USDA Forest Service Proceedings RMRS-P-11. 1999 57

Table 1—Tree and shrub invasion of burned and

unburned prairie sites in the central Flint

Hills study areas in Kansas, 1860-1998.

Average percent sites/woody plants

Year Burned Unburned

1860 0 1

1900 0 2

1940 1 24

1960 2 40

1980 3 64

1998 5 100

Table 2—Effects of slope on occurrence of woody

plants on burned and unburned sites in

the central Flint Hills study areas in

Kansas, 1998.

Average percent sites/woody plants

Slope Burned Unburned

Hill top 1 0

Upper slope 4 2

Mid slope 7 3

Lower slope 12 82

Bottom slope 20 100

ranching family whose great grandfather had homesteaded

in the area was valuable in understanding early land use

philosophy and practice.

Secondly, the history of the occurrence of woody vegetation in the area was assembled by examining section line

surveys by the Federal Land Office in 1856 and 1857, aerial

photographs taken in 1937-1939 and later in 1950, 1956,

1969, and current aerial photographs and soil maps. Fifty

sites (200 m sq) were selected in each of the four counties as

sites to compare the vegetation changes over the past 15

decades. Woody vegetation composition and foliar cover

(Daubenmire method) was determined for each 200 m sq

site. The burning history of 157 sites was collected from

ecological records and interviews of land owners and managers. A comparison was made of the woody vegetation on

slopes (hill top to bottom slope) on burned and unburned

sites on the study area in Chase county.

The third aspect of the study evaluated the economic

impact of the loss of the forage to invading woody plants and

the subsequent loss of income to the ranching industry.

Analysis of vegetation in the transects of the study sites and

1⁄2 cm overlay grids on early and recent aerial photographs

were used to calculate the extent of the woody invasion into

the four-county study area and to estimate the percent

closure of the canopy of woody plants over the grass and

forbs. Each acre lost to grazing was assigned the current

rental value of $18.00/acre/year.

The fourth objective was to develop management strategies to reduce losses in livestock forage from weedy plant

invasions and maintain the productive herbaceous species.

This was accomplished by examination of the scientific

literature, interviews with range management specialists,

and observations based on my field experiences in the study

areas.

Results ________________________

Woody plants have invaded all unburned prairie sites in

the study area. Burned pasture sites (where burning has

occurred in at least once every 4 years) showed a slow

increase in woody plants from 0 to 5% through the period

(150 years) (table 1). Distribution of woody plants on slopes

that burned regularly was linear from hill top (1%) to bottom

slope (20%) (table 2). On unburned areas woody plant infestations occurred on 3% of the hill top sites to 100% of the

slower slope sites.

Five primary woody species were identified on the study

areas of both burned and unburned sites. Frequency of

occurrence on burned sites was one-third that of unburned

sites, and percent foliar density of burned sites was one-fifth

that of unburned sites (table 3).

The invasion of woody plants into prairie may be attributed to events in the history of the region since the Homestead Act of 1857 (table 4).

Economic losses to the ranching industry in the fourcounty study area from forage destroyed by invading shrubs

was estimated to be $317,000 annually (table 5).

Control of woody species must be based on careful balance

of range forage with numbers of livestock on the pastures

(carrying capacity), selective use of woody plant herbicides,

burning practices that maximize woody plant damage by

allowing for adequate accumulation of fuel, and mowing of

vulnerable plants.

Discussion _____________________

Penetration of woody plants into the remaining tallgrass

prairie in the study area in east central Kansas has resulted

from reduction of the intensity and frequency of prairie fires.

The role of fire in maintaining the integrity of the tallgrass

ecosystem has been described by plant ecologists (Weaver

and Rowland 1952; Bragg and Hulbert 1976; Steinauer and

Collins 1996). Several aspects of the ecology of fire and its

effect on the grassland flora were addressed by this study.

Trees and shrubs successfully invaded all unburned prairie sites examined in the four-county study area. This

infestation of woody plants has degraded the value of the

prairie for forage for livestock and has altered the composition of the native tallgrass communities. On sites burned

regularly there has been a gradual increase in woody plant

invasion over the past 15 decades. Invasion has occurred in

various locations in the prairie where overgrazing by livestock has reduced the fuel (previous years’ dead plant

remains) to levels inadequate to carry fire hot enough to

destroy woody plants establishing on the site. Eventually

the tree and shrub-infested site will convert to a shaded

woodland environment where further growth of prairie

vegetation is suppressed. Entry and establishment of woody

plants occurred most frequently in lower and bottom slopes

because of the deeper, fertile, moist soils near woodland

borders or brushy ravines where sources of woody species

occur.
58 USDA Forest Service Proceedings RMRS-P-11. 1999

The history of the decline of acreage and quality of the

tallgrass prairie in the four-county area was attributed to six

periods of human activity during the past 150 years. Each of

these brought unique demands on the prairie landscape. The

Homestead Act (1857) opened the prairie for settlement with

the accompanying need to suppress and break native sod for

crops. Small farms (1860-1900) with associated roads, small

fields, orchards, and home sites brought an end to prairie

burning in many areas. Farm failures during the 1930’s

resulted in abandonment of many prairies, where in the

absence of management, pastures and old crop fields were

invaded by woody species. World War II (1940’s) accelerated

the loss of prairie acres to more intensive agriculture as the

nation’s demand for food increased. Large farms and modern

machines (1960’s to present) caused the remaining loss of

acres suited to cropland agriculture. As small farms were

replaced by large farming operations, small pastures and

isolated old crop fields were left to woody plant invasion.

Table 4—Historical influences on increase of woody plants on unburned

prairie sites in the central Flint Hills study areas in Kansas,

1998.

Beginning % Sites

Historical event of period with woody plants

Homestead Act 1857 1

Small farms on prairie 1875 18

WWI 1918 28

Depression 1930 55

Large farms 1960 78

Modern farming 1980 100

Table 5—Estimated annual costs of tree and shrub invaded prairie to

ranching interests in the central Flint Hills study areas,

Kansas. 1998.

Acres lost

Grazed acres of woody Annual cost of

County (non federal) plant invasion invaded acresa

Chase 404,900 4,700 $85,000

Greenwood 612,900 6,100 $110,000

Lyon 262,900 3,300 $60,000

Morris 262,500 3,400 $62,000

Total 1,543,200 17,500 $317,000

a$18.00/acre/yr

Table 3—Composition and foliar density of woody plants on burned and unburned sites in

the central Flint Hills study areas in Kansas, 1998.

Burned Unburned

Species % occurrence % foliar cover % occurrence % foliar cover

Cornus drummondii 10 2 35 18

Maclura pomifera 4 3 15 24

Rhus glabra 8 3 13 12

Symphoricarpos 6 5 10 11

orbiculatus

Ulmus pumila 2 1 7 10

Other species 8 1 4 9

Economic losses due to reduction in forage caused by

woody plant invasion indicates the effect on the families in

the region who depend on ranching for their income. Many

acres of prairie can be returned to productivity if aggressive

control of woody species is practiced.

References _____________________

Bragg, T. B.; Hulbert, L. C. 1976. Woody plant invasion of unburned

Kansas bluestem prairie. Journal of Range Management. 29:

19-23.

Steinauer, E. M.; Collins, S. L. 1996. Prairie ecology: the tallgrass

prairie. In: Prairie Conservation. Sampson, F. B., Knopf, F. L.,

editors. Island Press. Washington DC.

Weaver, J. E.; Rowland, N. W. 1952. Effects of excess natural mulch

on development, yield, and structure of native grassland. Botanical Gazette. 114: 1-19.
F 

I 

I Species Richness and Community Structure 

Along a Great Basin Elevational Gradient 

Stanley G. Kitchen 

E. Durant McArthur 

Gary L. Jorgensen 

Abstract-Benchmarks for preservation of biological richness can 

be established by surveying representative reference areas at multiple spatial and temporal scales. In this study, vascular plant 

species richness was sampled using nested frequency plots (0.25-

64 m2

) at 14 sites along a southeastern Great Basin elevational 

gradient (1,550-2,675 m). Salt-desert shrubland, pinyon/juniper 

woodland, and mixed coniferous forest communities were represented. Species area curves revealed contrasting distribution patterns for perennial grasses, shrubs, and forbs. Multi-scale nested 

frequency plots provided an efficient method for surveying species 

richness in these communities. 

Whether speaking of individual species or whole ecosystems, the global biota is faced with great challenges as a 

result of high-speed global changes in climate, atmospheric 

CO2, species migrations, habitat loss and fragmentation, 

toxic pollutants, etc. (Gates 1980; Bazzaz 1996). Biological 

diversity, or simply biodiversity, at whatever scale one 

chooses to measure it, has been, and will continue to be an 

unavoidable casualty. Consequently, we are forced to consider the value of, or benefits derived from, conserving 

biodiversity, as well as what aspects deserve our greatest 

attention given limited resources. Equally important will be 

the task of identifying efficient methods for measuring key 

diversity indicators and applying those methods to evaluate 

biodiversity on both at-risk and benchmark reference 

geographies. 

Reasons for maintaining biodiversity may be grouped into 

four categories (West 1993). First, many feel a moral obligation to protect and preserve a place for all life forms. The 

relative importance of this value is rooted in one's core 

beliefs, often religious in nature, regarding our relationship 

with the natural world. A second purpose for protecting 

diversity is rooted in aesthetics, here interpreted as the 

human drive to observe, interact with, and recreate in a 

natural world that seems infinitely unique and fresh. Thirdly, 

the sum economic value of products derived from nature is 

immense and the potential for marketable products is directly linked to biodiversity. Finally, possibly the most 

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L.~ comps. 1999. 

Proceedings: shrubland ecotones; 1998 August 12-14; EphraIm, UT. Proc. 

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. . . 

Stanley G. Kitchen is Botanist; E. Durant McArthur IS Research GenetIcist, Project Leader; and Gary L. Jorgensen is Range ~echnician, U.S. 

Department of Agriculture, Forest Service, Rocky Mountam Research Station, Shrub Sciences Laboratory, Provo, UT 84606. 

USDA Forest Service Proceedings RMRS-P-11. 1999 

important reason to value biodiversity may be manifest by 

the wide spectrum of ecological services provided by natural 

systems. These services include: watershed protection, soil 

development and stability, waste assimilation, nutrient 

cycling, control of pathogens and parasites, etc. Arguably, a 

loss of biodiversity can have a negative impact on the 

capacity for natural systems to deliver those services and 

that this, in turn, often results in negative economic consequences. However, we caution that, although it might be 

intuitive to expect a positive correlation between biodiversity and community stability, evidence is lacking (West 

1993). On the contrary, Harper (1977) suggests that increased complexity might actually be destabilizing and that 

community resilience occurs in spite of high biodiversity. 

An appreciation of the difficulty encountered in deciding 

what aspect of biodiversity to measure is founded in the 

complexity of what is or ought to be included in this "catchall" term. Biodiversity occurs at genetic, population, community, ecosystem, landscape, and regional levels (West 1993). 

Perhaps biological descriptions of diversity that consider the 

ways in which plants sense their environment, and include 

such aspects as within-plant polymorphism and age class 

variability, are more interesting, ifnot more easily quantified, than geographical descriptions (Harper 1977). In addition, species level descriptions generally underestimate biodiversity inasmuch as taxonomic boundaries are artificial and 

inclusive in nature (McArthur and Tausch 1995). Finally, 

the effects oftemporal scale on the measurement ofbiodiversity are as important as those of spacial scale. Ultimately, 

the purpose for estimating biodiversity should drive the 

selection of the most appropriate measure(s) for the task 

(West 1993). 

Numerous methods have been developed for measuring 

diversity at the community or stand level. These methods 

generally incorporate means for determining richness (the 

number of taxa in a given area) and evenness (the relative 

importance or abundance of each taxon) on a relatively 

uniform site. Heterogeneity is an expression of the probability that any two organisms from a single community will be 

of the same taxon, and thus is affected both by richness and 

evenness. Numerous equations have been developed to express heterogeneity as a single compound expression or 

index. A thorough discussion of the relative merits of the 

various indices is not central to this study and will not be 

included here. Suffice it to say that each incorporates biases 

and that they differ in how they weigh the relative importance of richness and evenness. 

Survey methods incorporating multi-scale plots are effective in developing estimates of total taxa, including rare and 

uncommon species, when compared to more traditional 

59 
I 

!I 

I 

I sampling methods (Stohlgren and others 1995; 1998). The 

efficiency of these methods is found in ease of use and 

maximization of information. While small subplots enable 

the observer to characterize vegetation within somewhat 

homogeneous patches, large plots are better suited for including the full variety encountered on heterogeneous landscapes. Frequency data taken from multi-scale plots arranged in nested configurations are useful in evaluating 

community structure and through summation, provide a 

sensitive measurement of community change (Smith and 

others 1987). 

Species richness of vascular plants for the Great Basin 

province of North America is low, given the geography 

involved. Forexample,inasurveyofpinyon/junipercommunities on 66 mountain ranges found throughout the Great 

Basin, only 367 species were identified in 464, 20 by 50 m 

plots (West and others 1998). Shrubland and shrub/grass 

steppe communities found at lower elevations are generally 

more species poor than the more upland woodland communities. High genetic variability is often observed within taxa 

compensating for low species richness (Harper 1977). This is 

apparently the case for the Great Basin where the repeated 

environmental fluctuations of the Pleistocene favored the 

most genetically variable taxa (Tausch and others 1993; 

McArthur and Tausch 1995; West and others 1998). However, one should not assume that these shrubland and 

woodland communities are lacking diversity in structure or 

floristic assemblages. For example, in developing a classification scheme for Great Basin pinyon/juniper woodlands, 

West and others (1998) identified 326 vegetative understory 

associations. Elsewhere, a list of 28 community types was 

described as "far from complete" as a basis for classifying 

salt-desert shrublands (Blaisdell and Holmgren 1984). In 

other words, what Great Basin communities appear to lack 

in species richness, they apparently make up for, at least in 

part, with great within-taxon variability and by the variety 

of ways in which these communities are assembled. 

Our objective was to sample vascular plant species richness across a southeastern Great Basin elevational gradient 

using nested frequency plots. We attempt to use these data 

to explore relationships between species richness, overall 

and by functional groups, and structural complexity. Finally, we evaluate the effectiveness of our method for estimating species richness and structural diversity on a landscape scale. 

Methods --------------------------------- We selected 14 study sites, lIon the USDA Forest Service, 

Desert Experimental Range (DER) and three on the USDI 

Bureau of Land Management, Wah Wah Mountain Research Natural Area in Millard County, Utah. Site elevations range from 1,550 m near the Pine Valley playa (DER) 

to 2,675 m near the northern Summit of Wah Wah Mountain, approximately 10 km east of the DER (table 1). All sites 

were either located inside long-term exclosures (DER) or in 

rugged portions of Wah Wah Mountain kept essentially free 

of livestock by terrain and lack of water. Soils from valley 

sites are composed of mixed alluvium derived from dolomite, 

limestone, quartzite, and igneous parent materials and 

some windblown sands (Tew and others 1997). Soil depth on 

upland sites is variable but generally moderate to shallow in 

60 

depth with dolomite, limestone, or quartzite outcrops being 

common. Sites were located in various combinations of 

mixed salt-desert shrublands (nine sites), pinyon/juniper 

woodlands (four sites), and mixed coniferous forest (one site) 

community types. Mean annual precipitation at the DER 

headquarters (1,600 m) is 165 mm (Alzerreca-Angelo and 

others 1998) with approximately half falling during the 

May-September growing season. We estimate that valley 

floor sites receive slightly less and that upland sites receive 

200-400 mm depending upon elevation, aspect, and local 

orographic effects (from map in: Ashcroft and others 1992). 

Valley sites were 1.6 ha in size and relatively uniform in 

topography. Upland site boundaries were not precisely defined, however, these sites were also selected for uniformity. 

Paired woodland sites were located on Wah Wah Mountain 

(Sites 10 and 11) and on Tunnel Spring Mountain (Sites 12 

and 13) at the north end of the DER. Sites 10 and 12 were 

located on old, but clearly identifiable, burn scars with 

obviously lower mature tree densities (seedlings and small 

juveniles <150 cm in height were generally common). Mature tree density for Sites 11 and 13 was much greater than 

for Sites 10 and 12 but not so much as to produce a "closed" 

canopy as is sometimes observed for this community type 

(West and others 1998). 

Eight (Sites 10, 11, and 14) or 12 (Sites 1-9, 12, and 13) 

64-m2 circular plots were located at 10-30 m intervals on 

permanent transects at each site. Transect ends and plot 

centers were marked with 60-cm longrebar. Nested subplots 

of 0.25 and 1.0 m2 were identified using a square frame 

centered on the rebar. Boundaries for 4, 16, and 64 m2 plots 

were determined by rotating a marked, stretch-resistant 

rope 360 degrees around the plot center. Marks on the rope 

at 1.13, 2.26, and 4.16 m from center passed over boundaries 

for each respective plot size. Using this method, frequency 

data for all vascular plant species were quickly collected 

using a three-person team. Species presence was recorded 

for the smallest plot in which it was observed rooted and for 

each larger plot in the configuration. Each plot size had 

4 times the area of the next smaller plot size. All plots were 

read during June and July 1997. 

Mean number of species for perennial grasses, shrubs, 

native forbs (including cacti), trees, and introduced annuals 

were determined for each plot size at each site using Goodrich 

(1986) and Welsh and others (1987) as taxonomic standards. 

A few distinct subspecies were treated separately. Individual species were subjectively classified as dominant, codominant, abundant, common, etc., based upon frequency of 

encounter and relative dominance of vegetative cover. Results were statistically analyzed using the GLM procedure 

with each plot serving as a replication (SAS 1998). Significant differences among sites were determined using the 

Student-Neuman-Keul (SNK) method (p <0.05). 

Results and Discussion 

Perennial Grasses 

Of the 138 species we observed across all sites, 14 were 

perennial grasses representing 10 genera. We encountered 

no native annual grasses. Cool-season perennial grasses 

(10 species) were observed across all sites with species 

richness somewhat greater for woodland and forest sites, 

USDA Forest Service Proceedings RMRS-P-11. 1999 

I 

I 

, 

I 

I 

I 
Table 1-Elevation, dominant plant species, and number of species sampled in 1997 for 14 ungrazed sites at the Desert 

Experimental Range and Wah Wah Mountain Research Natural Area, Millard County, Utah. PG = perennial 

grasses, S = shrubs, F = native forbs and cacti, T = trees, and IA = introduced annuals. 

Site Elev. 

no. (m) Community co-dominants 

Salt-desert shrublands 

1 1,550 Winterfatlgray molly 

Indian ricegrass 

2 1,575 Winterfatllndian ricegrass 

Greenes rabbitbrush 

3 1,610 Purple three-awn/Indian 

ricegrass/winterfatlbud sagebrush 

shadscale/Greenes rabbitbrush 

4 1,640 Winterfatlshadscale 

Indian ricegrass 

5 1,660 Shadscale/sand dropseed 

Indian ricegrass 

6 1,675 Nevada ephedra/winterfat 

Indian ricegrasslblue grama/Galleta 

7 1,830 Blue grama/shadscale/ 

black sagebrush 

8 1,880 Black sagebrush/winterfat 

squirreltail 

9 1,900 Black sagebrush/Greenes 

rabbitbrush/needle-and-thread/ 

Indian ricegrass/squirreltail 

Pinyon/juniper woodlands 

10 2,200 Pinyon/juniper/bluebunch 

wheatgrass/black sagebrush 

Sandberg bluegrass/muttongrass 

11 2,200 Pinyon/juniper/bluebunch 

wheatgrass/black sagebrush/ 

Sandberg bluegrass/muttongrass 

12 2,215 Pinyon/juniper/bluebunch 

wheatgrass/black sagebrush/ 

shadscale/Sandberg bluegrass/ 

green ephedra!low rabbitbrush 

13 2,215 Pinyonfjuniper/bluebunch 

wheatgrass/ bullgrass/ 

low rabbitbrush 

Mixed coniferous forest 

14 2,675 White fir/pinyon/juniper/ 

ponderosa/bristlecone/ 

black sagebrush/muttongrass 

while warm season grasses (four species) were essentially 

confined to lower elevation shrubland sites. Squirreltail 

(Sitanion hystrix) and Indian ricegrass (Oryzopsis 

hymenoides) were the most widely dispersed species. Although usually not dominant, squirrel tail was observed on 

12 of 14 sites across the full elevational range, while Indian 

ricegrass was abundant to co-dominant on six of nine shrubland sites (table 1) and absent only from the forest community type (Site 14). Sandberg bluegrass (Poa secunda) and 

muttongrass (P.fendleriana) were common in woodland and 

forest communities. Conversely, purple three-awn (Aristida 

purpurea), sand dropseed (Sporobolus cryptandrus), blue 

grama (Boutelouagracilis), bluebunch wheatgrass (Agropyron spicatum), needle-and-thread (Stipa comata), and 

bullgrass (Elymus salinus) are examples of perennial grasses 

co-dominant on at least one site but distributed within a 

more or less narrow elevational range, at least for our sites. 

Galleta (Hilaria jamesii) was the most widely distributed 

USDA Forest Service Proceedings RMRS-P-11. 1999 

Number of species sampled on site 

PG S F T IA Total 

3 3 2 0 2 10 

3 5 13 0 2 23 

5 4 10 0 2 21 

5 3 10 0 2 20 

6 6 19 0 32 

7 10 18 0 2 37 

6 7 19 0 33 

3 5 6 0 3 17 

4 8 7 21 

5 7 18 2 33 

6 7 28 2 44 

8 12 38 2 61 

8 9 34 2 54 

7 3 23 5 o 38 

warm-season grass and was sampled at eight valley and low 

alluvial fan sites. Mean number of perennial grass species 

per 64-m2 plot was highly consistent among sites with no 

significant differences for 11 of 14 sites (table 2). It is 

apparent that, although the suite of species varied with soils 

and elevation, species richness for perennial grasses was 

relatively constant and low with means of5.4 species per site 

and 3.2 species per 64-m2 plot across the full elevational 

gradient. 

Shrubs 

The 27 shrub species we encountered represent nine 

families and 16 genera. Eleven species belong to the 

Asteraceae withArtemisia, Chrysothamnus, and Tetradymia 

as major genera. Six species belonged to the Chenopodiaceae, 

three of which were Atriplex. Shadscale (Atriplex 

confertifolia), winterfat (Ceratoides lanata), and black 

61 

:1 
Table 2-Mean number of perennial grass, shrub, and native forb 

species encountered per 64-m2 plot on 14 southern Great 

Basin sites arranged across an elevational gradient. Within 

columns, means followed by the same letter are not 

significantly different at the p <O.OS level (SNK). 

Number of species per 64-m2 plot 

Sites Perennial grasses Shrubs Forbs 

Shrublands 

1 1.7b 2.2de 0.2e 

2 1.7b 2.6cde S.4c 

3 3.4a 3.8abc 2.3de 

4 3.Sa 2.7cde 2.8de 

S 3.3a 2.8bcde 8.7b 

6 4.3a 4.2ab S.8c 

7 3.Sa 3.4bcd 4.Scd 

8 1.9b 2.3de 1.4e 

9 3.2a 2.9bcde 1.0e 

Woodlands 

10 3.4a 3.4bcd 6.3c 

11 4.1a 3.0bcde 10.6ab 

12 3.4a 4.9a 9.7b 

13 4.1a 4.0abc 12.4a 

Forest 

14 3.Sa 1.6e 11.1ab 

sagebrush (Artemisia nova) were the most widely distributed shrubs. Shadscale and winterfat were abundant to 

dominant on most of the nine shrubland sites (table 1). Both 

maintained a reduced presence on woodland sites and neither was encountered at the forest site. Black sagebrush was 

dominant on three upper elevation, shrubland sites (Sites 

7 -9) and an understory co-dominant for all woodland and 

forest sites. Big sagebrush (A. tridentata), the most widely 

adapted woody Artemisia native to North America, was 

conspicuously absent from our study sites. Budsage (A. 

spinescens), Greenes rabbitbrush (Chrysothamnus greenei), 

low rabbitbrush (C. viscidiflorus), Gray molly (Kochia 

americana), Nevada ephedra (Ephedra nevadensis), and 

green ephedra (E. viridis) were common to dominant with 

somewhat narrower elevational distributions. As with perennial grasses, shrub species richness was relatively constant and low with 6.4 species per site and 3.2 species per 

64-m2 plot across all sites (table 2). 

Forbs 

We observed 86 species of native forbs, including cacti, 

representing 21 families and 45 genera. These included 

annuals, biennials, and short- and long-lived perennials. In 

general, species distributions were elevationally and ecologically restricted indicating narrow niche requirements. 

Gooseberry-leaved globe mallow (Sphraeralcea grossulariifolia), desert phlox (Phlox austromontana), and rock goldenrod (Petradoria pumila) were frequently sampled shrubland, woodland, and forest examples offorbs with somewhat 

broader distributions. A few genera, taken as a whole, were 

broadly represented. For example, we sampled multiple 

species of Eriogonum (7), Gilia (5), Astragulus (5), and 

Penstemon (4) from a broad range of sites. We also sampled 

62 

dolomite spring parsley (Cymenopterus basaltic us ), Goodrich 

bladderpod (Lesquorella goodrichii), desert range beardtongue (Penstemon concinnus), and tufted globemallow 

(Sphraeralcea caespitosa), all narrow endemics (Goodrich 

1986). 

Forb species richness was more variable among shrubland 

sites than among woodland sites (tables 1 and 2). Sites 1, 8, 

and 9 were lowest for species number of all sites with means 

of 0.2, 1.4, and 1.0 species per 64-m2 plot, respectively. Site 1 

is located below the ancient shoreline ofthe Pleistocene Lake 

that once occupied the floor of Pine Valley, and subsequently, the soil is fine textured and rather uniform with 

high levels of exchangeable sodium in subsurface horizons 

(Tew and others 1997). Few species, especially native forbs, 

are adapted to conditions found at this site. On the other 

hand, the soil at Site 2, located only 1.6 km from Site 1, is a 

deep loamy sand. On this site, the mean of 5.4 forb species 

per 64-m 2 plot was equal to or greater than that observed for 

all but one of all other shrubland sites. Sites 8 and 9 are 

dominated by black sagebrush and have low species diversity for perennial grasses as well as forbs, possibly due to 

competitive exclusion. 

Forb species richness (as measured by number of species 

per 64-m2 plot) was significantly higher for three of four 

woodland sites and for the forest site than for all but one 

shrubland site (table 2 ). This is expected given the higher 

precipitation and greater structural complexity of woodland 

sites. Significant differences were also observed between 

members of paired woodland sites. In each case, native forb 

species richness per 64-m2 plot was significantly higher for 

the late seral sites with greater canopy cover (11 and 13) 

than for the early seral sites (10 and 12). Being more 

structurally complex, sites 11 and 13 provide a greater 

variety of micro-environments for species to colonize. Although the mean number of native forb species per 64-m2 

plot was not significantly different for the forest site than for 

the highest values observed for woodland sites, the percent 

contribution offorbs was somewhat greater on the forest site 

(61 %) than on the woodland sites (43-55%). 

Overall, there were fewer perennial grass and shrub 

species than forb species although grasses and shrubs dominated shrubland sites and woodland understories. Some 

grass and shrub species are broadly distributed geographically and elevationally. This suggests that these species are 

quite plastic in response to environmental parameters and! 

or that they possess greater within-population genetic variability than the more narrowly distributed forbs. Either 

condition could make these species more resilient in a 

changing environment. 

Trees 

All six tree species known in the study area were sampled. 

Utah juniper (Juniperus osteosperma) found in the lower 

portions of the woodland zone and on our woodland sites is 

replaced at higher elevation woodland communities and on 

our forest site by Rocky Mountain juniper (J. scopulorum). 

Singleleaf pinyon (Pinus monophylla) occurs in conjuction 

with Utah juniper at our woodland sites and as one of five 

species at the forest site. Other trees species at the forest site 

incl uded: ponderosa pine (P. ponderosa), Great Basin bristlecone pine (P. longaeva), and white fir (Abies concolor). The 

USDA Forest Service Proceedings RMRS-P-11. 1999 
ponderosa pine population was almost entirely composed of 

somewhat widely dispersed mature trees and only once 

occurred within our plots. The other four species, being 

much shorter in stature, occurred in various combinations 

forming a much denser, second-level canopy that often 

descended to ground level. We did not observe an increased 

level in total plant species richness over that observed on 

woodland sites in response to this increased structural 

complexity (tables 1 and 2). 

Introduced Annuals 

Although we observed few species of introduced annuals 

(five total), various combinations of three taxa, cheatgrass 

(Bromus tectorum), halogeton (Halogeton glomeratus), and 

Russian thistle (Salsola species), were common on most 

shrubland sites and locally abundant in conjunction with 

disturbance. Cheatgrass was also locally common on woodland sites and present in some openings ofthe forest community although we did not observe it in any of our plots. The 

aggressive nature of these species is destabilizing to native 

communities in Great Basin ecosystems and often leads to 

site degradation and loss of biodiversity (Tausch and others 

1993; Cronk and Fuller 1995; Harper and others 1996; Kitchen 

and Hall 1996; Kitchen and Jorgensen, these proceedings). 

Species-Area Curves 

The relationship between species richness and sample 

area (plot) size is easily illustrated using species-area curves. 

When the relative difference in sample area sizes remains 

constant (four-fold for our plots) and distribution patterns 

are random, then the predicted curve relating species number to area is a straight line until a hypothetical "leveling off' 

point is approached. The slope or steepness of the line 

reflects the probability of compositional similarity between 

two different-sized sample areas located within the same 

realm. When sample areas or plots are nested the slope 

becomes a measure of patchiness at a spatial scale defined by 

the sizes of the two plots in question. Thus a steep slope 

indicates greater between-plot variability or patchiness, 

while a more shallow incline is indicative of uniformity or 

weak patchiness. An abrupt change in the steepness of the 

slope suggests a change in the degree of patchiness at two 

adjacent spatial scales, which in turn is related to mean 

patch size. 

We examined species-area curves for perennial grasses, 

shrubs, and forbs on shrubland, woodland, and forest sites. 

The slopes for grasses and shrubs on shrubland sites are 

quite straight and flat indicating that we were able to detect 

relatively few new species by increasing plot size (fig. 1). This 

trend can be extended by considering the relatively small 

difference between mean number of species per 64-m2 plot 

(2.9 grasses and 3.0 shrubs) and mean number observed in 

all plots in a site (4.7 grasses and 5.7 shrubs). Overall, 

steepness of the forb slope for shrubland sites is similar to 

that of grasses and shrubs. However, the difference between 

the mean number offorb species per 64-m2 plot (3.6) and the 

mean number observed on all plots in a site (11.6) is greater 

than that observed for perennial grasses and shrubs, suggesting that the increase in slope for the forb curve between 

the 16- and 64-m2 plot sizes might in fact be real. 

USDA Forest Service Proceedings RMRS-P-11. 1999 

12 

11 

10 -+- Forb 

.Q Shrub 

I/) 9 -.- Perennial Grass 

.~ Q) 8 0-

W 7 '0 

.8 6 

E 5 :J 

Z 

c: 4 IV 

Q) 

3 :! 

2 

0 

1/4 4 16 

Plot Size (meters square) 

Figure 1-Species-area curves for forbs, shrubs, and 

perennial grasses for nine salt-desert shrubland sites 

at the Desert Experimental Range (1997). 

64 

This pattern of a relatively flat, straight shrub and grass 

curves and upward bending forb curve is amplified for 

woodland sites (fig. 2). In this case the change in forb 

patchiness occurred between the 4- and 16-m2 plot sizes. 

Again, the upward extension of the pattern is roughly 

confirmed by comparing the relative differences in mean 

number of species for 64-m2 plots (3.8 grasses, 3.8 shrubs, 

and 9.8 forbs) with the mean number observed for a site (6.8 

grasses, 8.8 shrubs, and 29.5 forbs). The basic nature of the 

pattern is maintained for the forest site (fig. 3) with the slope 

ofthe curve, and therefore patchiness, greater for forbs than 

for grasses or shrubs through all spacial scales represented 

by our plots. A small separation between grass and shrub 

curves suggests slightly greater spatial diversity for grasses 

than for shrubs on this site. This is not surprising given the 

12 

10 -+- Forb 

.Q Shrub 

I/) -.- Perennial Grass 

Q) 

·0 

Q) 8 0-

W 

'0 

Q) 6 ..c 

E 

:::I 

Z 

c: 4 

Q) 

IV 

-- --.~ .. :! ...,,- . __ -- .0·· 

2 _-.rr." " .. 

.... 0 

0 

1/4 4 16 

Plot Size (meters square) 

Figure 2-Species-area curves for forbs, shrubs, and 

perennial grasses for four pinyonf]uniper woodland 

sites at the Desert Experimental Range and Wah Wah 

Mountain Research Natural Area (1997). 

64 

63 
II> 

.~ 

8-

CIJ 

'0 

CD 

.J:J 

E 

~ 

z 

c: 

al 

Q) 

:i! 

12 

10 

8 

6 

4 

~Forb 

·0 Shrub 

-...- Perennial Grass 

",....."""" 

-., ;r--

2 ~ __ --r .... 0 

r-- .. 0 ·0" 

0 

o . . ·0' .' • 

1/4 4 

Plot Size (meter square) 

Figure 3-Species-area curves for forbs, shrubs, 

and perennial grasses for a Wah Wah Mountain 

Research Natural Area mixed coniferous forest 

site (1997). 

16 64 

low number of shrub species encountered in plots at this site. 

The 3.5 grass, 1.6 shrub, and 11.1 forb species we sampled 

per 64-m2 plot and 7 grass, 3 shrub, and 23 forb species we 

observed for the whole site support the suggestion that these 

trends will continue on larger spatial scales. 

An examination of the location on forb species-area curves 

where changes in slope, or upward bends, occur suggests 

that, for our sites, mean forb patch size decreases with 

increase in elevation. General observations support this 

notion. For example, shrubland patches are primarily determined by soils and soil disturbance. Three to 15-m diameter 

vegetative patches associated with permanent rodent burrow clusters, representing 10 to 15% of the landscape, are 

obvious and notable examples (Kitchen and Jorgensen, this 

proceedings). These patches are found throughout deep 

alluvial soils above ancient lake shorelines. Forb patchiness 

in woodlands appears to be driven by soil depth and proximity to overs tory individuals. Because variability in these 

factors occurs on a smaller spatial scale than do major 

vegetation patches on shrublands, we might predict that 

mean woodland patch size should also be smaller. The fact 

that the forb curve steepens between the 16- and 64-m2 sized 

plots for shrublands (fig. 1) and between the 4- and 16-m2 

sized plots for woodlands (fig. 2) supports this expectation. 

The slope for the forb curve corresponding to the forest site 

is rather straight and consistently steep (fig. 3). We could 

interpret this to mean that mean patch size is quite small 

compared to that of shrubland and woodland sites. This in 

turn could be a reflection of greater complexity in the 

overs tory (when compared to woodland sites) interacting 

with a highly variable soil profile. We recognize that patchiness exists on spatial scales beyond the reach of our plot 

sizes. We are also aware that we have not addressed the 

relative sensitivity of this method to subtle patch variation. 

Additional studies employing other measures of patchiness 

as comparisons are needed to address this issue. 

64 

Conclusions _________ _ 

Because we made no direct comparisons between our 

methods and other approaches to censusing species richness, care must be taken in weighing the value of our 

particular approach. However, Stohlgren and others (1998) 

demonstrated that multi-scale nested plots are more effective in capturing rare species and less likely to miss small 

species-rich or unique patches than are traditional transect 

methods. In addition, multiple-scale plots are also particularly well suited for sampling communities where member 

species are distributed at different spatial scales. 

Sampling efficiency is the product of the quantity and 

quality of the information gathered and the time and resources required to gather it. Flexibility ensures efficiency 

under variable circumstances. Besides the advantages already listed, we suggest that the approach taken in this 

study is both efficient and flexible for the following reasons: 

1. Plots can be read quickly by a small team familiar with 

the species of the area. 

2. Analyses of summed frequency data from permanentlymarked, nested plots taken overtime has been shown to 

be more sensitive to community change than more 

traditional methods (Smith and others 1987). 

3. Cover, density, and age class data can be added to the 

sampling procedures with relatively little additional 

time investment. 

4. Plot sizes can be adjusted according to need. 

We would improve our method for surveying species 

richness by conducting walk-through searches for species on 

larger macroplots (perhaps 20 x 50 m) as recommended by 

Stohlgren and others (1998). Special attention should be 

given to those habitats that are obviously unique from the 

general landscape. This uniqueness may be due to soil 

characteristics, disturbance history, or location in relation 

to neighboring community types (ecotones). For example, 

had we directed such an effort to washes, rock outcrops, and 

talus slopes in the general areas surrounding our sites we 

would have encountered numerous species not encountered 

in the plots (Goodrich 1986). 

Acknowledgments 

This research was funded in part by a matching grant from 

the USDA Forest Service, Research Natural Areas Program. 

Thanks to Dr. Stewart Sanderson for help in species identification and Neil Roberts and J. L. Kitchen for enthusiastic 

technical assistance in the field. 

References _________________ _ 

Alzerreca-Angelo, H; Schupp, E. W.; Kitchen, S. G. 1998. Sheep 

grazing and plant cover dynamics of s shadscale community. J. 

Range Manage. 51:214-222. 

Ashcroft, G. L.; Jensen, D. T.; Brown, J. L. 1992. Utah climate. 

Logan, UT: Utah Climate Center, Utah State University. 127 p. 

Bazzaz, F. A. 1996. Plants in changing environments. Cambridge 

University Press, Cambridge, UK. 320 p. 

USDA Forest Service Proceedings RMRS-P-11. 1999 
l 

Blaisdell, J. P.; Holmgren, R. C. 1984. Managing Intermountain 

rangelands: salt-desert shrub ranges. Gen Tech. Rep. INT-163. 

Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Intermountain Research Station. 52 p. 

Cronk, Q. C. B.; Fuller, J. L. 1995. Plant invaders. Chapman and 

Hall. London, UK 241 p. 

Gates, D. M.1980. Biophysical ecology. Springer-Verlag, New York, 

NY. 611 p. 

Goodrich, S. 1986. Vascular plants of the Desert Experimental 

Range, Millard County, Utah. Gen. Tech. Rep. INT-209. Ogden 

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 72 p. 

Harper, J. L. 1977. Population biology of plants. Academic Press, 

New York. 892 p. 

Harper, K T.; Van Buren, R.; Kitchen, S. G. 1996. Invasion of alien 

annuals and ecological consequences in salt-desert shrublands of 

western Utah. In: Barrow, J. R; McArthur, E. D.; Sosebee, R E.; 

Tausch, J. R, comps. Proceedings-symposium on shrubland 

ecosystem dynamics in a changing environment; 1995 May 23-25; 

Las Cruces, NM. Gen. Tech. Rep. INT -GTR-338. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Intermountain Research Station: 58-65. 

Kitchen, S. K; Hall, D. B.1996. Community stability in a salt-desert 

shrub land grazed by sheep: the Desert Experimental Range 

story. In: Barrow, J. R; McArthur, E. D.; Sosebee, R E.; Tausch, 

J. R, comps. Proceedings-symposium on shrub land ecosystem 

dynamics in a changing environment; 1995 May 23-25; Las 

Cruces, NM. Gen. Tech. Rep. INT-GTR-338. Ogden, UT: U.S. 

Department of Agriculture, Forest Service, Intermountain Research Station: 102-107. 

Kitchen, S. G.; Jorgensen, G. L. [These proceedings]. Annualization 

of rodent burrow clusters and winterfat decline in a salt-desert 

community. 

USDA Forest Service Proceedings RMRS-P-11. 1999 

McArthur, E. D.; Tausch, R J. 1995. Genetic aspects of the biodiversity ofrangeland plants. In: West, N. E., ed. Proceedings: biodiversity on rangelands; 1993 February 16; Albuquerque, NM. 

Natural Resources and Environmental Issues (Vol. IV); Utah 

State University, Logan, UT: 5-20. 

SAS. 1998. SAS user's guide. SAS Institute, Cary, NC. 

Smith, S. D.; Bunting, S. C.; Hironaka, M. 1987. Evaluation of the 

improvement in sensitivity of nested frequency plots to vegetational change by summation. Great Basin Naturalist. 47: 

299-307. 

Stohlgren, T. J.; Falkner, M. B.; Shell, L. D. 1995. A ModifiedWhittaker nested vegetation sampling method. Vegetatio. 117: 

113-121. 

Stohlgren, T. J.; Bull, K A.; Otsuki, Y. 1998. Comparison of rangeland vegetation sampling techniques in the Central Grasslands. 

J. Range Manage. 51:164-172. 

Tausch, R J.; Wigand, P. E.; Burkhardt, J. W. 1993. Viewpoint: 

plant community thresholds, multiple steady states, and multiple successional pathways: legacy of the Quaternary? J. Range 

Manage. 46:439-447. 

Tew, R K; Kitchen, S. G.; Holmgren, R. C.1997. Soil survey-Desert 

Experimental Range, Utah. Gen. Tech. Rep. INT-GTR-347. Ogden, 

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 22 p. 

Welsh,S. L.;Atwood,N. D.; Higgins,L. C.; Goodrich,S. 1987. A Utah 

flora. Brigham Young University Print Services, Provo, UT. 

894 p. 

West, N. E. 1993. Biodiversity of rangelands. J. Range Manage. 46: 

2-13. 

West, N. E.; Tausch, R J.; Tueller, P. T. 1998. A managementoriented classification of pinyon-juniper woodlands of the Great 

Basin. Gen. Tech. Rep. RMRS-GTR-12. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station. 42 p. 

65 
66 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Eugene W. Schupp is an Associate Professor of Plant Ecology, Department

of Rangeland Resources, Utah State University, Logan, UT 84322. Jeanne C.

Chambers is a Research Ecologist, USDA Forest Service, Rocky Mountain

Research Station, 920 Valley Road, Reno, NV 89512. Stephen B. Vander Wall

is an Assistant Professor of Biology, Department of Biology, University of

Nevada, Reno, NV 89557. José María Gómez is an Assistant Professor of

Ecology, Departamento Biología Animal y Ecología, Universidad de Granada,

E-18071 Granada, Spain. Marcelino Fuentes is an Assistant Professor of

Ecology, Facultade de Ciencias, Universidade da Coruña, E-15071 A Coruña,

Spain.

Piñon and Juniper Seed Dispersal and

Seedling Recruitment at Woodland Ecotones

Eugene W. Schupp

Jeanne C. Chambers

Stephen B. Vander Wall

José María Gómez

Marcelino Fuentes

Abstract—Invasion of grasslands and shrublands by piñon-juniper woodlands is driven by seed dispersal and seedling establishment at woodland ecotones, yet we know little about these processes. We present a preliminary overview of tree seed dispersal

and seedling recruitment at ecotones. Dispersal out of woodlands

depends on the type of seed disperser and their habitat use,

movement patterns, and post-foraging behavior, and on the physical structure of the adjacent community. Seedling establishment

depends on the biotic and abiotic environment of seed deposition

sites, and thus is also affected by the physical structure of the

adjacent community as well as by the overall climate. We conclude

with examples of the value to scientists and land managers of

understanding seed and seedling ecology.

Although not a universal feeling (e.g., Lanner 1977),

there is concern among many land managers over the

apparent conversion of grasslands and shrublands to piñon

and/or juniper woodlands (Johnsen 1962; Tausch and others 1981; Miller and Rose 1995). This conversion is generally attributed to livestock overgrazing, a greatly reduced

fire frequency, and climate change (West and Van Pelt

1987; Miller and others 1994). However, there is little

understanding of the proximal mechanisms driving the

conversion—the dispersal of tree seeds out of woodlands

into adjacent grasslands/shrublands and the successful

establishment of seedlings (Chambers and others 1998;

1999). In particular, there are two related problems impeding development of an understanding of woodland invasion.

First, we have little knowledge of the seed and seedling

ecology of either piñon or juniper species because of a

virtual lack of research on these critical life stages. Second,

most of the information we do have on seed and seedling

ecology concerns processes occurring within existing woodlands, not at the ecotones.

In this paper we first give a brief and somewhat simplified overview of the processes of seed dispersal and plant

establishment of piñon and juniper at woodland ecotones;

it is simplified at this point primarily because of the preliminary nature of our understanding. We then demonstrate why a better knowledge of seed and seedling ecology

may be useful to land managers as well as scientists by

giving examples of how this information may help explain

historical patterns of invasion and predict consequences of

management decisions.

Types of Woodland Ecotones _____

Woodland ecotones are extremely heterogeneous, and

both seed dispersal and seedling establishment will depend

on the physical structure of the ecotone. Ecotones may be

very abrupt, sharp boundaries between woodland and the

adjacent community as is seen following fires or chaining,

or the transition may be gradual, from thick woodland to an

open savanna-like woodland before giving way to the adjacent community. In addition, the adjacent community may

be grassland, shrubland, or filled with snags, or dead trees,

again following a fire or, to a lesser degree, chaining.

Although we do not consider all possible types of ecotones,

it should become clear that the characteristics of the

ecotone will have a large impact on both dispersal and plant

establishment.

Seed Dispersal _________________

Junipers have generally been viewed as having a fairly

simple dispersal system where fruits are fed on and seeds

dispersed by a wide variety of animals, the most important

of which are birds (Phillips 1910; Maser and Gashwiler

1978; Balda 1987). As is generally the case, however, it is

not quite that simple. In reality, it appears that juniper

species vary widely in their assemblages of dispersers

(Chambers and others 1999). A wide variety of frugivorous

animals that eat the pulp and regurgitate or defecate viable

seeds can serve as dispersers, but the importance of different types of frugivores varies with juniper species. Some,

such as western juniper (Juniperus occidentalis), are dispersed predominantly by birds, (Gabrielson and Jewett

1940; Maser and Gashwiler 1978; Schupp and others 1997a).

Others, including Ashe juniper (J. ashei), are dispersed

extensively by birds and by coyotes (Canis latrans), blacktailed jackrabbits (Lepus californicus), and other mammals
USDA Forest Service Proceedings RMRS-P-11. 1999 67

(Smith 1948; Chavez-Ramirez and Slack 1993; 1994). Still

others, such as Utah juniper (J. osteosperma), are apparently dispersed largely by jackrabbits (Schupp and others

1996; 1997b). Additionally, although quantitative data are

few, it is becoming increasingly clear that seed-caching

rodents may be very important dispersers of at least some

species of juniper (Vander Wall, personal observation;

Schupp and Gómez, personal observation).

Frugivorous birds generally regurgitate and defecate

while perched and thus deposit seeds beneath woody vegetation (McDonnell and Stiles 1983; Holthuijzen and Sharik

1985a; b; Holthuijzen and others 1987; Schupp 1993; ChavezRamirez and Slack 1994). Consequently, they are expected

to be responsible for extensive dispersal within woodlands,

mostly depositing seeds beneath trees where they alight to

process fruit (Salomonson 1978). For example, ChavezRamirez and Slack (1994) found >22,000 Ashe juniper

seeds/m2

 beneath known cedar waxwing (Bombycilla

cedrorum) perches, 30 seeds/m2

 beneath known American

robin (Turdus migratorius) perches, and 5 seeds/m2

 in the

open in Texas. Frugivorous birds may also be important for

dispersal out of woodlands into adjacent communities,

however, if perches are abundant as when snags are left

following fire.

Frugivorous mammals differ from birds in that they

frequently defecate while active. This has consequences for

both habitat and microhabitat patterns of seed dispersal.

Since they are not dependent on perches, mammals are

likely responsible for extensive seed dispersal both within

woodlands and across ecotonal boundaries. Although the

exact pattern will depend on habitat preferences of the

dispersing species, mammals are likely much more important than birds for juniper dispersal into grasslands. Utah

juniper seeds dispersed by lagomorphs at a juniper woodland-cheatgrass (Bromus tectorum) ecotone in Utah were

deposited in highest densities within the woodland itself,

but there was detectable movement of seeds out into the

grassland, at least as far as 50 m (fig. 1). Although none

were found 100 m from the woodland border in our sample,

lagomorphs can disperse juniper seeds ≥1.6 km from woodlands (Smith 1948; Frischknecht 1975). Data are lacking,

but mammals may be even more important for dispersal

into shrublands because the shrubs provide protective

cover that may facilitate greater animal movement

(Longland 1991).

Mammals mostly deposit seeds in open interspaces where

they are travelling rather than beneath woody vegetation

(Bustamante and others 1992; Chavez-Ramirez and Slack

1993; Schupp 1993; Schupp and Fuentes 1995; Schupp and

others 1997a; b). In a 2 ha Utah juniper woodland plot in

Tintic Valley, west-central UT, 57 percent of the surface

area was open interspace, but 75 percent of lagomorphdispersed seeds were deposited in the open and none were

deposited beneath shrubs (fig. 2).

In contrast to juniper, piñon seed dispersal is by seedcaching jays, nutcrackers, and rodents. Seed-caching birds

can provide local dispersal within and near woodlands,

which is the dispersal relevant to woodland expansion, and

long-distance dispersal, which is more relevant to founding

new populations (Chambers and others 1998; 1999).

Figure 1—Utah juniper seed dispersal by lagomorphs at a juniper woodland-cheatgrass grassland ecotone at Dugway, UT, based on complete

collections of pellets in 100 x 2 m transects parallel

to the ecotone. The 0 m transect was in the

grassland, but at the border of the woodland. The

figure is adapted from data in a table in Schupp

and others (1997b).

Figure 2—Data from the 2 ha Tintic Valley, UT,

juniper woodland plot in west-central UT (Schupp,

Fuentes, and Gómez, personal observation). The

figure shows for each microhabitat the relative

cover, the proportion of total lagomorph-dispersed

seeds deposited in that microhabitat, and the

proportion of total natural recruits found in that

microhabitat.
68 USDA Forest Service Proceedings RMRS-P-11. 1999

Seed-caching birds are probably responsible for extensive seed dispersal both within woodlands and across ecotonal boundaries, and they appear to mostly cache seeds in

more open sites; i.e., not under dense shrubs (Chambers

and others 1998; 1999). Consequently, they are likely important for dispersal into open interspaces of shrublands

and sparsely-covered grasslands, but not into dense

grasslands.

Although few data are available on the role of seedcaching rodents, they are expected to provide extensive

dispersal for both junipers (Schupp and Gómez, personal

observation) and, at least in years with heavy cone crops,

piñons (Vander Wall 1997). Many rodent species are abundant in ecotonal areas (Mason 1981; Severson 1986;

Sedgewick and Ryder 1987; Albert and others 1994; Kruse

1994; Chambers and others 1998; 1999), and dispersal by

rodents may be especially important at these boundaries.

Species differ in habitat preferences, but because many use

both sides of the boundary, dispersal is expected to both

redistribute seeds within woodlands as well as move seeds

from woodlands into grasslands and shrublands.

Many species of rodents preferentially cache seeds beneath shrubs rather than in the open. Rodents placed 61

percent of singleleaf piñon (Pinus monophylla) seed caches

either under or at the crown edge of shrubs in western

Nevada (Vander Wall 1997). In the Tintic Valley, UT, plot

described above, rodents harvesting Utah juniper seeds

placed 43 percent of 28 caches beneath live shrubs, 32

percent beneath dead shrubs, 18 percent in open interspaces

at the bases of grass clumps, and 7 percent beneath juniper

(Schupp and Gómez, personal observation).

Work with chipmunks (Tamias spp.) dispersing Jeffrey

pine (Pinus jeffreyi) and antelope bitterbrush (Purshia

tridentata) seeds in western Nevada shows what may be a

common pattern of seed dispersal that may help explain the

dispersal of junipers and piñons by rodents (Vander Wall

1992; 1993; 1994). Chipmunks disproportionately moved

pine seeds out of the pine forest into adjacent shrubland,

and within the shrubland they disproportionately cached

seeds beneath shrubs, which is apparently the most suitable microhabitat for Jeffrey pine establishment.

This overview has shown that potential dispersal agents

differ in the likelihood of carrying seeds out of a woodland

into an adjacent community, and differ in what structural

characteristics of the adjacent community promote movement out of the woodland. This gives us the beginnings of

a foundation for making predictions about woodland invasion for different tree species under different conditions.

But because potential dispersal agents also differ in the

type of microhabitat to which they disperse seeds, and

because successful seedling establishment is sensitive to

environmental conditions, we also have to understand

emergence and seedling survival.

Emergence and Seedling

Survival _______________________

It is generally assumed that juniper and piñon need

shrub or tree “nurse plants” for successful establishment,

and most literature supports the idea that seedlings

and saplings are most abundant beneath nurse plants,

especially sagebrush (Johnsen 1962; Jameson 1965;

Burkhardt and Tisdale 1976; Everett and others 1986;

Eddleman 1987; Miller and Rose 1995; Callaway and others 1996; Chambers and others 1998; 1999). For example,

in the Tintic Valley, UT, plot described above, natural Utah

juniper recruits ≤2.0 m tall and 10.0 cm basal diameter

were disproportionately abundant beneath shrubs and rare

in the open (fig. 2).

Such data have been used to suggest greater emergence

and/or survival under shrubs than in other microhabitats.

There are always potential problems with such static distributional data, however, so experiments are crucial. Experimental singleleaf piñon seedling emergence in the Pine

Nuts of western Nevada in 1994 was most rapid in open

interspaces, but final emergence was greatest beneath

shrubs and least beneath piñon and juniper trees (Chambers, personal observation). In 1995, open interspaces not

only had the most rapid emergence, but had the greatest

emergence overall. Differences in patterns probably are

related to 1995 being a cool, wet spring resulting in the soil

of vegetated microhabitats being too cool to promote good

germination. There is little evidence in either year that

nurse plants greatly enhance piñon emergence. Results

from both years, however, but most clearly the drier year,

suggest piñon seedlings are very unlikely to survive the

first summer in open interspaces and that they generally do

need nurse plants as generally assumed (Chambers, personal observation).

It is less certain, however, that juniper require nurse

plants. We have data on emergence and early survival for

four cohorts (three year’s emergence from 1994 planting,

one from 1995 planting) of Utah juniper in the Tintic

Valley, UT, plot described above (Schupp and Gómez,

personal observation). Every year shows a slightly different pattern, but overall emergence was greatest beneath

juniper and more or less equal beneath shrubs and in open

interspaces. As with emergence, each cohort differed somewhat in survival as well, but evidence that survival is

greater beneath nurse plants than in the open is weak at

best. Some cohorts showed equal survival in all microhabitats, while others showed a hint of lower survival in open

interspaces. Although juniper probably benefit from nurse

plants under some circumstances, they do not require

them. We suggest that the disproportionate abundance of

seedlings beneath shrubs may be due at least partly to

patterns of seed caching by rodents, not just to differential

emergence and survival.

The available data indicate that nurse plant requirements vary with species and environmental conditions.

Nurse plants are more important for piñon than juniper,

and their importance may also vary among species within

these genera. Also, some evidence suggests that nurse

plant requirements vary with environmental conditions.

For example, nurse plants are probably most important in

regions without significant summer precipitation, such as

those areas north of the monsoons in the Great Basin

(Chambers and others 1999).

Mechanisms Driving Invasion _____

To summarize, we suggest that woodland expansion, or

invasion, is a complex function of:
USDA Forest Service Proceedings RMRS-P-11. 1999 69

1. The animal species that are dispersing the seeds. For

example, is it frugivorous birds, jackrabbits, or seed-caching rodents?

2. The physical structure of the community adjacent to

the woodland. Are there perches for birds? Are there

shrubs to provide cover for mammals and potential nurse

plants for seedlings?

3. The nurse plant requirements of the tree species. It

appears that piñon always benefit more from nurse plants

than do juniper.

4. Environmental conditions. Nurse plants are probably

more important in regions with dry summers. Additionally,

the benefit of nurse plants may vary with soil physicalchemical properties, aspect, elevation, etc.

Why Care About Seed and Seedling

Ecology? ______________________

By understanding seed dispersal and seedling establishment, we can better explain historical patterns and better

predict what might happen in the future given a particular

set of conditions. Here, we first give an example demonstrating that knowledge of seed and seedling ecology can

help explain historical patterns of invasion. We then present

as examples two preliminary predictions based on seed and

seedling ecology that could guide management decisions if

the goal is to prevent or slow invasion.

Historical Explanation

At a juniper woodland-grassland ecotone in northern

Arizona, Miller (1921) reported that Utah juniper was very

successfully invading the grassland, while one-seed juniper

(J. monosperma) recruitment was occurring only within

the existing woodland. How can we explain this difference?

The patterns are probably unrelated to environmental

tolerances; we believe both species are capable of invading

the grassland because of the climate, which is characterized by summer monsoons. Dispersal ecology, however, can

easily explain the patterns. As Miller noted, Utah juniper

was invading the grassland because it was widely dispersed

by mammals, including sheep, that frequented the grassland. In contrast, one-seed juniper was dispersed almost

exclusively by birds that used juniper trees as perches and

thus failed to carry seeds out into the grassland.

Predictive Ability

Although much remains to be learned about piñon and

juniper seed and seedling ecology, we venture two preliminary predictions in order to demonstrate the utility of this

kind of knowledge.

Prediction 1—Shrub control in the adjacent community

is expected to inhibit piñon invasion more than juniper

invasion because of piñon’s greater need for nurse plants. It

is also expected to inhibit juniper invasion more in the

northern Great Basin where nurse plants are likely more

beneficial than in the southwest where monsoons allow

abundant juniper establishment in open grasslands.

Prediction 2—Snag removal following a fire or chaining

will slow invasion of juniper species that are dispersed

primarily by birds, such as western juniper, but may have

relatively little effect on invasion of juniper species dispersed predominantly by mammals, such as Utah juniper.

In conclusion, understanding seed dispersal and seedling

establishment allows us to better predict the outcomes of

various management scenarios. As such, this knowledge

may be a powerful tool for land managers. The limitation at

this point is data; what we have discussed is based on only

a limited understanding of the processes and on only a few

species. In order to fully realize the potential we need to

know much more.

References _____________________

Albert, S. K.; Luna, N.; Chopito, A. L. 1994. Deer, small mammal,

and songbird use of thinned piñon-juniper plots. In: Shaw, D.

W.; Aldon, E. F.; LoSapio, C., eds. Proceedings—desired future

conditions for piñon-juniper ecosystems. Gen. Tech. Rep. RM258. Ft. Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Forest and Range Experiment Station: 54-64.

Balda, R. P. 1987. Avian impacts on pinyon-juniper woodlands. In:

Everett, R. L., ed. Proceedings—pinyon juniper conference.

Gen. Tech. Rep. INT-215. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station:

525-533.

Burkhardt, J. W.; Tisdale, E. W. 1976. Causes of juniper invasion

in southwestern Idaho. Ecology. 76: 472-484.

Bustamante, R. O.; Simonetti, J. A.; Mella, J. E. 1992. Are foxes

legitimate and efficient dispersers? Acta Oecologica. 13: 203-208.

Callaway, R. M.; DeLucia, E. H.; Moore, D.; Nowak, R.; Schlesinger,

W. H. 1996. Competition and facilitation: contrasting effects of

Artemisia tridentata on desert vs. montane pines. Ecology. 77:

2130-2141.

Chambers, J. C.; Schupp, E. W.; Vander Wall, S. B. 1999. Seed

dispersal and seedling establishment of piñon and juniper

species within the piñon-juniper woodland. In: Monsen, S. B.;

Stevens, R.; Tausch, R. J.; Miller, R.; Goodrich, S., eds. Proceedings: Ecology and management of pinyon-juniper communities

within the Interior West; Proceedings RMRS-P-9. Fort Collins,

CO: U.S. Department of Agriculture, Forest Service, Rocky

Mountain Research Station: 29-34.

Chambers, J. C.; Vander Wall, S. B.; Schupp, E. W. [In press]. Seed

and seedling ecology of piñon and juniper species in the pygmy

woodlands of Western North America. Botanical Reviews. 65.

Chavez-Ramirez, F.; Slack, R. D. 1993. Carnivore fruit use and

seed dispersal of two selected plant species of the Edwards

Plateau, Texas. Southwestern Naturalist. 38: 141-145.

Chavez-Ramirez, F.; Slack, R. D. 1994. Effects of avian foraging

and post-foraging behavior on seed dispersal patterns of Ashe

juniper. Oikos. 71: 40-46.

Eddleman, L. E. 1987. Establishment and stand development of

western juniper in central Oregon. In: Everett, R. L., ed.

Proceedings—pinyon juniper conference. Gen. Tech. Rep. INT215. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 255-259.

Everett, R. S.; Koniak, S.; Budy, J. D. 1986. Pinyon seedling

distribution among soil surface microsites. Res. Pap. INT-363.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station. 3 p.

Frischknecht, N. C. 1975. Native faunal relationships within the

pinyon-juniper ecosystem. In: Gifford, G. F.; Busby, F. E., eds.

The pinyon-juniper ecosystem: a symposium. Logan, UT: Utah

State University: 55-65.

Gabrielson, I. N.; Jewett, S. G. 1940. Birds of Oregon. Corvallis,

OR: Oregon State University.

Holthuijzen, A. M.; Sharik, T. L. 1985a. The avian seed dispersal

system of eastern red cedar (Juniperus virginiana). Canadian

Journal of Botany. 63: 1508-1515.
70 USDA Forest Service Proceedings RMRS-P-11. 1999

Holthuijzen, A. M.; Sharik, T. L. 1985b. The red cedar (Juniperus

virginiana L.) seed shadow along a fenceline. American Midland

Naturalist. 113: 200-202.

Holthuijzen, A. M.; Sharik, T. L.; Fraser, J. D. 1987. Dispersal of

eastern red cedar (Juniperus virginiana) into pastures: An

overview. Canadian Journal of Botany. 65: 1092-1095.

Jameson, D. A. 1965. Arrangement and growth of pinyon and oneseed juniper trees. Plateau. 37: 121-127.

Johnsen, T. N. 1962. One-seed juniper invasion of northern Arizona grasslands. Ecological Monographs. 32: 187-207.

Kruse, W. H. 1994. Effects of fuelwood harvesting on small mammal populations in a piñon-juniper woodland. In: Shaw, D. W.;

Aldon, E. F.; LoSapio, C., eds. Proceedings—desired future

conditions for piñon-juniper ecosystems. Gen. Tech. Rep. RM258. Ft. Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Forest and Range Experiment Station: 91-96.

Lanner, R. M. 1977. The eradication of pinyon-juniper woodland.

Has the program a legitimate purpose? Western Wildlands. 3:

12-17.

Longland, W. S. 1991. Risk of predation and food consumption by

black-tailed jackrabbits. Journal of Range Management. 44:

447-450.

Mason, R. B. 1981. Response of birds and rodents to controlled

burning in pinyon-juniper woodlands. M.S. Thesis, University

of Nevada, Reno.

Maser, C.; Gashwiler, J. S. 1978. Interrelationships of wildlife and

western juniper. In: Proceedings of the western juniper ecology

and management workshop. Gen. Tech. Rep. PNW-4. Portland,

OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station: 37-82.

McDonnell, M. J.; Stiles, E. W. 1983. The structural complexity of

old field vegetation and the recruitment of bird-dispersed plant

species. Oecologia. 56: 109-116.

Miller, F. H. 1921. Reclamation of grasslands by Utah juniper on

the Tusayan National Forest, Arizona. Journal of Forestry. 19:

647-651.

Miller, R. F.; Rose, J. A. 1995. Historic expansion of Juniperus

occidentalis (western juniper) in southeastern Oregon. Great

Basin Naturalist. 55: 37-45.

Miller, R. F.; Svejcar, T. J.; West, N. E. 1994. Implications of

livestock grazing in the Intermountain region: plant composition. In: Vavra, M.; Laycock, W. A.; Pieper, R. D., eds. Ecological

implications of herbivory in the West; Denver, CO: Society for

Range Management: 101-146.

Phillips, F. J. 1910. The dissemination of junipers by birds. Forestry Quarterly. 8: 60-73.

Salomonson, M. G. 1978. Adaptations for animal dispersal of oneseed juniper seeds. Oecologia. 32: 333-339.

Schupp, E. W. 1993. Quantity, quality and the effectiveness of seed

dispersal by animals. Vegetatio. 107/108: 15-29.

Schupp, E. W.; Fuentes, M. 1995. Spatial patterns of seed dispersal and the unification of plant population ecology. Écoscience.

2: 267-275.

Schupp, E. W.; Fuentes, M.; Gómez, J. M. 1996. Dispersal of Utah

juniper (Juniperus osteosperma) seeds by lagomorphs. In: West,

N. E., ed. Proceedings of the Fifth International Rangeland

Congress, Vol. 1. Denver, CO: Society for Range Management:

496-497.

Schupp, E. W.; Gómez, J. M.; Jimenez, J. E.; Fuentes, M. 1997a.

Dispersal of Juniperus occidentalis (western juniper) seeds by

frugivorous mammals on Juniper Mountain, southeastern Oregon. Great Basin Naturalist. 57: 74-78.

Schupp, E. W.; Heaton, H. J.; Gómez, J. M. 1997b. Lagomorphs and

the dispersal of seeds into communities dominated by exotic

annual weeds. Great Basin Naturalist. 57: 253-258.

Sedgewick, J. A.; Ryder, R. A. 1987. Effects of chaining pinyon on

nongame wildlife. In: Everett, R. L., ed. Proceedings—pinyon

juniper conference. Gen. Tech. Rep. INT-215. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Research Station: 541-551.

Severson, K. E. 1986. Small mammals in modified pinyon-juniper

woodlands, New Mexico. Journal of Range Management. 39:

31-34.

Tausch, R. J.; West, N. E.; Nabi, A. A. 1981. Tree age and

dominance patterns in Great Basin pinyon-juniper woodlands.

Journal of Range Management. 34: 259-264.

Smith, H. N. 1948. Rabbits spread cedar menace. Cattleman. 35:

97-98.

Vander Wall, S. B. 1992. Establishment of Jeffrey pine seedlings

from animal caches. Western Journal of Applied Forestry. 7:

14-20.

Vander Wall, S. B. 1993. Cache site selection by chipmunks

(Tamias spp.) and its influence on the effectiveness of seed

dispersal in Jeffrey pine (Pinus jeffreyi). Oecologia. 96: 246-252.

Vander Wall, S. B. 1994. Fate of Purshia tridentata seeds dispersed by seed-caching chipmunks. Ecology. 1911-1926.

Vander Wall, S. B. 1997. Dispersal of singleleaf piñon pine (Pinus

monophylla) by seed caching rodents. Journal of Mammalogy.

78: 181-191.

West, N. E.; Van Pelt, N. S. 1987. Successional patterns in pinyonjuniper woodlands. In: Everett, R. L., ed. Proceedings—pinyon

juniper conference; Gen. Tech. Rep. INT-215. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Research Station: 43-52.
USDA Forest Service Proceedings RMRS-P-11. 1999 71

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Robin J. Tausch is Supervisory Range Scientist, USDA Forest Service,

Rocky Mountain Research Station, 920 Valley Road, Reno, NV 89512. Robert

S. Nowak is Professor, Department of Environmental and Resource Sciences,

University of Nevada, Reno 89512.

Fifty Years of Ecotone Change Between

Shrub and Tree Dominance in the Jack

Springs Pinyon Research Natural Area

Robin J. Tausch

Robert S. Nowak

Abstract—A pinyon Research Natural Area (RNA) has been established on the edge of west-central Nevada near Mono Lake. Woodlands in this RNA are comparable to areas dominated by singleleaf

pinyon over much of the western and central Great Basin. Total

vegetal cover on 17 sampled macroplots from the site ranged from

21 to about 70 percent. These plots had a total of 95 plant species.

Patterns of understory suppression with increasing tree dominance

were similar to those measured on other sites. Comparison of aerial

photographs of the RNA from 1940 and from 1993 made it possible

to document the increases in the area dominated by pinyon over the

53 years. In 1940 nearly 60 percent of the site was dominated by

mature trees and was 30 percent shrub dominated. By 1993 nearly

70 percent was dominated by mature trees and only 12 percent was

shrub dominated. The remainder in both cases were areas with

invading young trees intermixed with old-growth woodland.

Pinyon-juniper (Pinus monophylla Torr. And Frem, Juniperus osteosperma [Torr] Little) woodlands cover about 7.1

million ha (17.6 million ac) in the Great Basin (Tueller and

others 1979), or about 17 percent of the area. Because of their

wide distribution in the Great Basin, these woodlands represent a wide range of community types. West and others

(1998), as part of a woodland classification, have divided the

Great Basin into nine geographic regions based upon similar

environment and community structure. Management of

each of these regions requires understanding of their particular dynamics. Monitoring of the vegetation in Research

Natural Areas (RNA) representative of each of these regions

can provide important ecological and management information. Because of their rarity, studying stands that escaped

disturbance during the settlement of the region are particularly important for the understanding of pinyon-juniper

woodland dynamics.

Establishment of the new Jack Springs Pinyon RNA is

nearing completion. This RNA is located on the southwestern corner of the Bridgeport District of the HumboldtToiyabe National Forest in Nevada. It is east of Mono Lake

about 10 kilometers (5 miles) east of the California State line

(fig. 1). This RNA is representative of one of the pinyon/

juniper geographic regions located on the western edge of

the Great Basin (Mono-Walker-Owens Basin) (West and

others 1998). This region comprises the western edge of

Nevada and adjacent southeastern California, and has large

areas of pure pinyon woodlands. This new RNA was established to replace a previous RNA established many years ago

that was destroyed by trespass wood cutting and ORV use.

The new RNA is in an isolated area with difficult access.

The mostly pure pinyon woodlands on this site were largely

undisturbed during European settlement, and the majority

of woodlands on the RNA and surrounding area represent

old growth as defined by Miller and others (1999). Despite

the dominance of old-growth, successional stands representing a full range of tree age classes as well as sagebrushdominated communities are also present. Many square

Figure 1—Map showing the locality of the Jack

Springs Pinyon Research Natural Area within the

Great Basin.
72 USDA Forest Service Proceedings RMRS-P-11. 1999

kilometers of woodland with the same community composition and patterns of tree age and dominance exist in the

vicinity.

Because of limited accessibility and limited access to

water, past grazing was light and ended in the late 1940’s.

With the absence of important mineral resources, no mining

has occurred in the area. For these many reasons, the Jack

Springs RNA represents a unique opportunity to study the

dynamics of old, established woodlands for comparison with

the extensive areas of post-settlement stands that now

comprise about two-thirds of the woodlands in the Great

Basin (Tausch and others 1981, Tausch 1999).

This study was implemented to provide the initial baseline data necessary for the long- term monitoring of successional patterns, stand dynamics, and associated vegetation

changes on the RNA. We established permanent plots from

which full inventories of plant species composition can be

obtained and monitored. An important part of this study will

be descriptions and explanations of the spatial and temporal

dynamics of the woodlands that can be used in the management of other areas with similar vegetation.

Methods _______________________

Aerial photographs that included the Jack Springs RNA

were obtained from the Bridgeport District files. Two photo

dates were located, one for June, 1940, and one for July 1993.

Enlargements of these photos were used in combination

with ground reconnaissance to do a preliminary identification of the major community types and tree age classes

within the area. Representative sites within these identified

communities were then selected for establishment of the

permanent plots. Seventeen plots representing a majority of

the identified communities and successional conditions were

established (fig. 2) and vegetation cover data collected during the summer of 1997.

Field Sampling

Each permanent macroplot established is 20 by 50 m (66

by 165 ft) in size with the long axis running up slope (fig. 3).

This sampling layout is similar to that described in West and

others (1998). The lower end is permanently marked by a 1.8

m (6 ft) fence post and the upper end, 50 meters from the

fence post, is marked with a reinforcing bar approximately

30 cm (1 ft) tall. Physiographic features recorded at each

macroplot location were: elevation, slope, aspect, length of

slope, position on slope, landform, and macro- and microrelief. Each plot was located and mapped on the appropriate

aerial photo.

For vegetation sampling, the 50 m (165 ft) line between

the fence post and the reinforcing bar was used as the center

of the plot. Ten meters (33 ft) were included on either side of

the center-line to obtain the full 20 by 50 m plot (fig. 3). Each

tree rooted within the full plot was measured for the longest

crown diameter, the diameter perpendicular to the longest,

total tree height, the height of the crown with foliage, and the

basal circumference. Crown measurements were to the

nearest decimeter for trees more than a meter tall and to the

nearest centimeter for smaller trees. Basal diameter measurements were in centimeters.

Percent crown cover for the understory shrub, grass, and

forb species was sampled on five transects, each 20 m (66 ft)

long, located perpendicular to, and centered on the 50 m

center-line tape (fig. 3). One 20 meter cross transect was

randomly located within each 10 meter section of the centerline tape. Each transect was sampled using 10 microplots,

Figure 2—Map of the Jack Springs Pinyon Research

Natural Area showing the border, topography, and

locations of the 17 sampled plots.

Figure 3—Schematic diagram of the sampling

design for the sampled macroplots on the Jack

Springs Pinyon Research Natural Area.
USDA Forest Service Proceedings RMRS-P-11. 1999 73

1 by 2 m (3.3 by 6.6 ft) in size, located contiguously along the

transect. Percent cover was estimated by species to the

nearest 0.5 percent using guides representing 0.5, 1.0, and

2.0 percent of the 1 by 2 meter microplot. Following transect

sampling, the entire 20 by 50 meter plot was searched for

any plant species not encountered during the transect sampling, and those found were recorded as a trace amount.

When plant species could not be identified in the field,

samples were collected and placed in a plant press. These

specimens were later identified in the lab.

Data Analysis

Crown diameters measured for the trees were used to

determine their individual crown area (Tausch and Tueller

1990), and these were summed for the total crown area for

the sampled trees and converted to percent crown cover by

species. Percent crown cover values for each understory

species were averaged by transect and for the entire

macroplot. Data were summed by plot across species for total

tree, total shrub, total grass, total forb, total understory, and

total plot vegetal cover. Regression analysis was used to

compare total tree and total understory cover across the

sampled plots.

Aerial photos were interpreted for three levels or categories of tree dominance (table 1) and each category mapped

for both 1940 and 1993. The three levels used were (1) open

or sagebrush dominated with few visible trees, (2) early

successional woodland sites being invaded by young trees,

and (3) woodland sites greater than 2⁄3 dominated by trees.

In the third category, the majority of the trees were generally mature. No attempt was made at this time to separate

the tree-dominated sites by differences in the age classes of

the trees present. It is hoped that it will be possible to add

this level of resolution in the future.

Woodland classification procedures from West and others

(1998) were used with the Jack Springs RNA data. The last

three levels of their Classification, Series, Association, and

Subassociation hierarchical levels were used. The Series

level is based on the relative cover of the two tree species of

singleleaf pinyon and Utah juniper. There are five levels in

the Series classification: pure pinyon, pinyon dominated,

mixed, juniper dominated, and pure juniper. The Association level is based on the dominant shrub species in the

understory that was determined by relative cover among the

shrub species. The Subassociation is based on the dominant

perennial grass present in the understory and was similarly

determined using the grass species present.

Results and Discussion

A total of 95 plant species were identified on the 17 plots

sampled (table 2, fig. 2). Figure 2 also shows the outline of

the Jack Springs Pinyon RNA and the elevational contours.

Table 1—Category definitions for shrub dominated, intermediate, and tree dominated for

interpretation of aerial photos for the Jack Springs Pinyon Research Natural Area.

Understory dominated Tree cover by young trees less than 25% of total cover.

Intermediate Tree cover greater than 25% but less that 67% of total cover.

Tree dominated Tree cover greater than 67% of total cover.

Table 2—Number of tree, shrub, grass, forb, and total species in

17 plots sampled on the Jack Springs Pinyon Research

Natural Area.

Plot Number of species

number Tree Shrub Grass Forb Total

 1 1 6 2 20 29

 2 1 3 7 30 41

 3 1 6 5 10 22

 4 1 4 6 19 30

 5 1 6 7 24 38

 6 1 4 4 22 31

 7 1 4 2 21 28

 8 1 5 3 12 21

 9 1 3 3 7 14

10 1 5 3 25 34

11 1 2 2 15 20

12 1 5 5 14 25

13 1 3 6 21 31

14 2 3 6 26 37

15 1 4 4 11 20

16 1 3 6 15 25

17 1 7 2 7 17

Average 1.06 4.3 4.3 17.6 27.2
74 USDA Forest Service Proceedings RMRS-P-11. 1999

There were a total of two tree, 12 shrub, 14 grass, and 69 forb

species sampled in the macroplots. The total number of plant

species in the macroplots ranged from 14 to 41 with an

average of 27 total species (table 2). There were an average

of 4 shrub species, 4 annual plus perennial grass species, and

18 annual plus perennial forb species in the 17 macroplots.

All but one plot (14) had singleleaf pinyon as the only tree

species present (table 2). The one plot with Utah juniper only

had a single old individual. Juniper is absent over most of the

RNA except in the lower elevation of the northeast corner

where an occasional old tree can be found. Juniper reproduction was present on the lower elevation areas to the northeast outside the RNA, but was not observed within the RNA

during either reconnaissance or sampling.

Crown cover for the trees varied from a trace to over 68

percent and averaged 38 percent (table 3). Shrub crown

cover varied from less than one percent to over 20 percent

and averaged 5.1 percent. Grass cover was generally low,

ranging from less than 0.1 percent to nearly 5 percent and

only averaging 0.5 percent. Cover for forbs was less than one

percent in all but one plot, where it barely exceeded that

value, and averaged 0.3 percent cover. Total plot cover

averaged 45 percent with a range from about 21 to nearly 70

percent (table 3).

Regression analysis comparing total tree cover and total

understory cover (fig. 4) was similar to the results for these

woodlands from other Great Basin locations (Tausch and

others 1981, Tausch and Tueller 1990, Tausch and West

1995). The maximum cover of the understory, relative to the

maximum cover of the trees, was generally lower than found

in the previous studies (Tausch and others 1981, Tausch and

Tueller 1990). For the Jack Springs Pinyon RNA the maximum understory cover in the absence of trees was less than

40 percent of the maximum tree cover sampled (fig. 4).

Table 3—Vegetal cover for total tree, total shrub, total grass, total forb, total understory, and total

plot cover for the Jack Springs Pinyon Research Natural Area for 17 sampled plots.

 Plot Tree Shrub Grass Forb Under Plot

number total total total total total total

- - - - - - - - - - - - - - - - - - - - - Percent cover - - - - - - - - - - - - - - - - - - - - - 

1 27.57 11.75 0.50 1.08 13.33 40.9

2 41.03 6.87 0.24 0.09 7.21 48.24

3 0.001 20.54 0.50 0.13 21.47 21.47

4 57.23 0.99 0.41 0.07 1.47 58.69

5 42.07 1.87 0.34 0.15 2.36 44.43

6 28.31 7.03 0.14 0.10 7.28 35.59

7 18.62 12.43 0.62 0.66 13.71 32.34

8 52.47 1.09 0.024 0.17 1.29 53.76

9 0.001 19.60 4.90 0.16 24.66 24.66

10 27.04 2.51 0.08 0.54 3.13 30.18

11 68.51 0.86 0.04 0.38 1.28 69.79

12 55.79 0.79 0.24 0.36 1.40 57.19

13 55.61 2.58 0.06 0.19 2.83 58.44

14 46.19 2.03 0.27 0.19 2.48 48.67

15 55.53 2.47 0.16 0.31 2.94 58.48

16 53.70 0.54 0.07 0.17 0.79 54.49

17 10.35 16.70 0.006 0.06 16.77 27.12

Average 37.6 5.13 0.51 0.28 6.50 45.00

Mapping of the tree cover classes (table 1) on the 1940 and

1993 aerial photographs for the RNA area revealed strong

differences in the dominance of trees and the abundance of

sagebrush-dominated locations between dates. Large areas

dominated by old-growth pinyon woodland, the majority of

tree dominated sites, are obvious over the RNA for both

photo dates (figs. 5 and 6). In 1940 the sagebrush-dominated

areas were generally higher at higher elevations from the

northeast to the southwest. The sagebrush-dominated areas, those with less than 1⁄4 relative cover by trees, were found

on a total of 176 ha (437 ac), or 34 percent of the 1,280 ha (3,170

ac) in the RNA (table 4, fig. 5). The young tree category, areas

where young trees dominated greater than 1⁄4, but less than 2⁄3, of the relative vegetation cover of the site, were found on

a total of 49 ha (120 ac) or 9 percent of the total. Areas

dominated by generally mature trees covered 293 ha (723 ac)

in 1940, or 57 percent of the area of the RNA (fig. 5).

By 1993 the area in the open category had declined to 64

ha (157 ac), or 12 percent of the total area (table 4, fig. 6). The

area with 1⁄4 or more of the relative vegetation cover dominated by young trees had increased to 102 ha (254 ac), or

about 20 percent of the RNA. Mature trees had increased to

dominate 352 ha (869 ac), or about 68 percent of the total

area of the RNA. A small fire evident in the northeast corner

in 1940 had become fully occupied by trees by 1993. Overall,

the increase in the total area of tree dominance between

1940 and 1993 was equivalent to the area in the intermediate category in 1940. The area in the intermediate category

in 1993 is equivalent to the loss of area in the understorydominated category between 1940 and 1993.

The expansion in the area dominated by trees in the RNA,

and the reduction in the area dominated by sagebrush in 53

years, is consistent with the pattern of tree expansion

observed for the last 150 years throughout the Great Basin
USDA Forest Service Proceedings RMRS-P-11. 1999 75

Figure 4—Regression analysis results between

the total tree vegetal cover and total understory

vegetal cover for 17 plots sampled on the Jack

Springs Reaearch Natural Area.

Figure 5—Diagram of the June, 1940, aerial photograph showing

three categories of vegetation cover of (1) areas that were dominated

by sagebrush, (2) areas that were being invaded by young trees, and

(3) areas that were dominated by mature trees.

(Tausch and others 1981, Tausch and West 1995). The site

shows evidence of scattered areas burned by lightningcaused fires, and small pockets of trees killed by disease or

drought that are intermixed with unburned old-growth

woodland. Fires have been absent for about 100 years. Small

pockets of dead trees are present that appear to have

resulted from the drought in the early 1990’s. For over 100

years there has been the steady invasion by trees into areas

opened up by past disturbance, the growth in size of trees in

areas already invaded, and negligible addition of sagebrushdominated areas by more recent disturbance from disease or

drought. This is a repeat of the pattern observed throughout

most of the woodlands in the Great Basin (Tausch and others

1991, Tausch and Tueller 1990, Tausch and West 1995, West

and others 1998).

During sampling of the Jack Springs RNA, two subspecies

of sagebrush were observed dominating the open areas and

the understory in tree-dominated areas. Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beatle) dominated in the lowest elevation areas in the northeast corner

of the RNA. This amounted to about 25 percent of the total

area of the RNA (area A, fig. 7), and represents approximately the area of the RNA where an occasional old juniper

Understory cover

Understory dominated

Intermediate

Tree dominated

Understory cover
76 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 7—A copy of figure 2 showing the distribution

of the subspecies of big sagebrush that dominated

the nontree vegetation. For the area indicated by ‘A’

the dominant sagebrush subspecies is Artemisia

tridentata ssp. wyomingensis. For the area indicated

by ‘B’ the dominant sagebrush subspecies is Artemisia tridentata ssp. vasyana.

Figure 6—Diagram of the July, 1993, aerial photograph showing three

categories of vegetation cover of (1) areas that were dominated by

sagebrush, (2) areas that were being invaded by young trees, and

(3) areas that were dominated by mature trees.

Table 4—Number of hectares and percent of total for the three

categories of Understory: Dominated, Intermediate, and

Tree dominated for aerial photos from 1940 and 1993.

1940 1993

 ha % ha %

Understory dominated 176 34 49 12

Intermediate 49 9 102 20

Tree dominated 293 57 352 68

can be found. In the remainder of the RNA, the shrub layer

in both tree and nontree-dominated areas was dominated by

mountain big sagebrush (Artemisia tridentata ssp. vaseyana

Rydb.) (area B, fig. 7). Mid-elevation locations were dominated by either Wyoming or mountain big sagebrush, with

basin big sagebrush (Artemisia tridentata ssp. tridentata

Nutt.) occurring as a scattered subdominant on deeper soils.

When the woodland classification procedures from West

and others (1998) were applied to the macroplot data, eight

Subassociations were the result (table 5). These were also

classified into two Series and four Associations. The most

frequent Subassociation, PIMO-AV- Elel, was found in seven

of the plots (41 percent). The second most frequent

Subassociation, PIMO- AW-Elel, was found in four of the

plots (24 percent). The remaining six Subassociations had

Understory dominated

Intermediate

Tree dominated
USDA Forest Service Proceedings RMRS-P-11. 1999 77

only one plot each. Macroplots falling into the two most

frequent Subassociations are similar communities, differing

primarily in the subspecies of sagebrush that is dominant in

the understory (table 5).

Conclusions____________________

During the Little Ice Age ( prior to about 150 years ago, or

pre-settlement) pinyon-juniper woodlands in the Great Basin generally had more open areas. The most important

factor accounting for the openings appears to be a much

higher fire frequency present during this period (Gruell

1999; Tausch 1999). With the combination of climate change

following the Little Ice Age and settlement impacts, expansion of the woodlands has been observed throughout the

Great Basin and adjacent areas (Tausch and others 1981,

West and others 1998). This expansion has more than

tripled the area in the Great Basin dominated by woodlands.

The same changes have been simultaneously occurring on

the Jack Springs Research Natural Area without the presence of the sustained high levels of disturbance that occurred over most of the rest of the Great Basin. This is

another indication that other global change based drivers

(Tausch 1999) need more intensive study.

Literature Cited _________________

Gruell, George E. 1999. Historical and modern roles of fire in

pinyon-juniper. In: Monson, Stephen B.; Stevens, Richard, comps.

Proceedings: ecology and management of pinyon-juniper communities within the Interior West; 1997 Sept. 15-18; Provo, UT. Proc.

RMRS-P-9. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station: 24-28.

Miller, R,; Tausch, R.J.; Waichler, W. 1999. Old-growth juniper and

pinyon woodlands. In: Monson, Stephen B.; Stevens, Richard,

comps. Proceedings: ecology and management of pinyon-juniper

communities within the Interior West; 1997 Sept. 15-18; Provo,

UT. Proc. RMRS-P-9. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 375-384.

Tausch, Robin J. 1999. Historic pinyon and juniper woodland

development. In: Monson, Stephen B.; Stevens, Richard, comps.

Proceedings: ecology and management of pinyon-juniper communities within the Interior West; 1997 Sept. 15-18; Provo, UT.

Proc. RMRS-P-9. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Research Station: 12-19.

Tausch, R.J.; West, N.E.; Nabi, A.A. 1981. Tree age and dominance

patterns in Great Basin pinyon-juniper woodlands. J. Range

Manage. 34: 259-264.

Tausch, R.J.; Tueller, P.T. 1990. Foliage biomass and cover relationships between tree- and shrub-dominated communities in pinyon-juniper woodlands. Great Basin Naturalist. 50: 121-134.

Tausch, R.J.; West, N.E. 1995. Plant species composition patterns

with differences in tree dominance on a southwestern Utah

pinyon-juniper site. In: Shaw, D.W.; Aldon, E.F.; LoSapio, C.

coords. Desired future conditions for pinyon-juniper ecosystems;

1994 August 8-12; Flagstaff, AZ. Gen. Tech. Rep. RM-GTR-258.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station: 16-23.

Tueller, P.T.; Beeson, C.D.; Tausch, R.J.; West, N.E.; Rae, K.H.

1979. Pinyon-juniper woodlands of the Great Basin: distribution,

flora, vegetal cover. Res. Pap. INT-229. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research

Station. 22 p.

West, N.E.; Tausch, R.J.; Tueller, P.T. 1998. A management oriented classification of pinyon-juniper woodlands of the Great

Basin. Gen Tech. Rep. RMRS-GTR-12. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research

Station. 42 p.

Table 5—Classification of the 17 macroplots into two Series, four Associations, and eight

Subassociations based on procedures and notation described by West and others

1998. Plots representing each of the eight classification categories are listed by

plot number.

Series Association Subassociation Plot numbers (fig. 3)

1 PIMO AV Elel 2, 8, 10, 11, 12, 13, 17

2 PIMO AV Achy 15

3 PIMO AV Stoc 3

4 PIMO AV Stth 4

5 PIMO AW Elel 1, 5, 6, 7

6 PIMO Putr Elel 13

7 PIMO Putr Pasm 9

8 PiMo AW Pose 14

Series

PIMO = singleleaf pinyon has 100% relative tree cover.

PiMo = singleleaf pinyon has 80 - 99% relative tree cover.

Associations

AV = Artemisia tridentata ssp. vaseyana is the dominant shrub.

AW = Artemisia tridentata ssp. wyomingensis is the dominant shrub.

Putr = Purshia tridentata is the dominant shrub.

Subassociations

Elel = Elymus elymoides is the dominant perennial grass.

Achy = Achuatherum hymenoides is the dominant perennial grass.

Pasm = Pascopyrum smithii is the dominant perennial grass.

Pose = Poa secunda is the dominant perennial grass.

Stoc = Stipa occidentalis is the dominant perennial grass.

Stth = Stipa thurburiana is the dominant perennial grass.
78 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Paul T. Tueller is Professor of Range Ecology, Department of Environmental and Resource Sciences, University of Nevada, Reno, Reno, NV 89557.

Approaches to Mapping Ecotone

Boundaries Using Emerging Remote

Sensing Technology

Paul T. Tueller

Abstract—Boundaries between vegetation classes must be identified and delineated in order to map vegetation. The vertical view

offered by remotely sensed data presents a valuable perspective in

the mapping process. However, many ecotones are very subtle, and

because of similar spectral response many boundaries are often

diffuse and difficult to describe and map. This paper explores the

potential application of several new remote sensing procedures for

describing ecotones. For many years we have been able to use large

scale, near-earth aerial photography for doing this. The cost of

acquiring such imagery over large land areas is prohibitive, and it

has been difficult to select the required representative subsamples.

In addition to aerial photography other procedures include multispectral airborne videography, microwave data (e.g., radar) and

high spatial resolution satellite data (e.g., IRS 5 m data and the

proposed 1 m IKONOS data). These along with vegetation indices,

digital classifications incorporating digital elevation models (DEMs)

and other parameters, hyperspectral data, multitemporal data,

and spectral unmixing procedures offer the potential to measure

vegetation and soil differences across ecotones.

Many scientists are busy mapping forest and rangeland

vegetation. Numerous techniques are being used. In the

early years of vegetation science these procedures normally involved the drawing of lines on topographic maps

while in the field or the use of black and white aerial

photographs as a base map. Then with various amounts of

ground experience the mappers drew lines around vegetation types with differing levels of homogeneity. The idea

was to draw lines around these types creating polygons that

had some acceptable level of homogeneity that differed

from the surrounding vegetation and that were of interest

to land managers and ecologists.

Mapping was essentially continued this way for over

40 years. With the advent of modern computers there has

been a gradual move to mapping using image processing

techniques coupled with Geographic Information Systems

(GIS). A number of classification algorithms, both supervised and unsupervised, have been developed. These use

the brightness or spectral characteristics of individual

pixels for each of several discrete wave bands of the electromagnetic spectrum in order to create vegetation maps.

These maps have varied in the amount of ground verification

and accuracy. Much of this early computer classification

involved the use of 80 m pixels from the Landsat series of

satellites. This was followed by the use of data from other

systems such as the Landsat Thematic Mapper system

(30 m pixels) and the SPOT image system (20 m multispectral and 10 m panchromatic pixels).

This paper is a consideration of the potential use of new

and emerging remote sensing technology for identifying,

measuring, and monitoring changes in ecotones. The specific objectives are as follows: (1) to briefly review the

concept of the ecotone with special reference to remote

sensing, (2) to evaluate/examine the potential usefulness of

emerging remote sensing technology to better classify/

delineate ecotones, (3) to describe a potential methodology

to do this with remote sensing, and (4) to provide two

examples.

The Ecotone____________________

I suspect that a number of papers in this symposium will

describe and discuss the concept of the ecotone. Here I add

my brief review of this concept and perhaps develop some

ideas that will relate the concept to the use of remote

sensing data to identify and map ecotones. In the simplest

sense an ecotone is the boundary between two plant or

biotic communities (fig.1). Of course one can embellish such

a simple definition by adding some caveats. One would be

that the boundary of an ecotone is characterized by a

change in species composition. Sometimes these changes

are very abrupt and sometimes they are very obscure. A

Figure 1—A diagrammatic depiction of an aerial

analysis of an ecotone between a grassland and a

shrub-dominated plant community.
USDA Forest Service Proceedings RMRS-P-11. 1999 79

more complex, all-inclusive definition is that by

Holland and others (1991) where they define an ecotone “as

a transition between adjacent ecological systems, having a

set of characteristics uniquely defined by space and time

scales and by the strength of the interactions between

adjacent ecological systems.” It is now clear that, because of

our expanded understanding of ecotones in recent years,

the concept must be applied at many spatial scales (Risser

1995). Remote sensing has the capability to rapidly examine landscapes at a number of spatial scales and, therefore,

offers strong potential for any analysis of ecotones.

Since the question of scale becomes important in ecotone

analysis using remote sensing data a number of questions

can be posed. For example, what scale or resolution element

size is required to identify, examine, and measure these

subtle ecotones and their specific characteristics including

plant species composition? What is a subtle ecotone? It is

one that is not characterized by an abrupt change in the

dominant species. A number of species may be involved,

and the change in species composition may be only a

relative one where the density, cover, and frequency of

several species may change only slightly as one moves

across the ecotonal boundary. Can these more obscure

changes be measured using remote sensing technology?

When considering scale there are two meanings that

must be considered. Aerial photogrammetrists work with

representative fraction scales where the scale is expressed

as a ratio. A scale expressed as a ratio of 1:10,000 means

that a measurement of 1 cm on the photograph would be

equivalent to 10,000 cm on the ground. This scale is large

while a scale of 1:100,000 would be small. This routinely

used definition of scale is at odds with the Landscape

Ecology community who speak of large or small scale

meaning just the opposite. Small scale refers to small land

areas while large scale refers to large areas of land. One

must understand this distinction because much of the

literature having to do with scale analysis is found in the

Landscape Ecology literature.

Emerging Remote Sensing

Technology ____________________

A number of data types must be considered as the question of ecotone analysis is explored. First, there are a

number of near-earth, high resolution systems. These include large scale color and color-infrared airborne photography and videography (Tueller 1996). Such systems provide pixels that are submeter and measured in centimeters.

Of greatest value is the use of digital cameras and multispectral video systems where the data is captured as raster

files. These files are immediately available for analysis

using image processing. Likewise, the emerging satellite

systems that should be considered for vegetation mapping

also provide digital data that is generally ready for analysis. The original Landsat MSS data had 80 m resolution

elements and has been useful for vegetation mapping but

only where very course low-resolution data is sufficient to

show ecotones and produce vegetation maps over very large

areas (small scale). Often the mapper was working with

forest/nonforest or desert/riparian edges. Now we are on

the verge of having high-resolution data from space. Thus,

the term “emerging remote sensing technology” in the title

of this paper.

For many years remote sensing scientists and plant

ecologists have been using aerial photographs and satellite

imagery of relatively low resolution for vegetation studies

(Tueller 1989). These include the MSS data mentioned above

as well as the THEMATIC MAPPER and SPOT IMAGE

data. Aerial photographs have been either black and white,

color, or color infrared, and the scales have varied considerably from 1:200 down to 1:150,000 and smaller.

These emerging remote sensing systems can be exemplified by the following list. It must be remembered that the

technology is changing rapidly and changes from year to

year. This list only constitutes a snapshot of it at one point

in time. The reader must remember that this list can

change from year to year and even month to month.

1. IRS (Indian Remote Sensing) 5 m satellite data.

This satellite system is currently operational. The 5 m

band is panchromatic (0.5-0.75 micrometer spectral

resolution) and is presently colorized using several

bands of Landsat TM data.

2. SPOT 5A will have 10 m multispectral and 2.5 m

panchromatic resolution and is scheduled to fly early

in the next century.

3. QuickBird 1 (from EarthWatch Inc., Longmont, CO).

Scheduled for launch in the fourth quarter of 1999.

This system will have a 1-meter panchromatic and 4-

meter multispectral data. Later a QuickBird Launch

will have 3.28 m multispectral resolution (blue, green,

red and near-infrared) and an 0.82 panchromatic

band from space. It will have a 22 km swath width and

revisit times of 1-5 days at 1 meter and 18 hours - 2

days at 1.5 meter (Lawrie 1998).

4. Ikonos 1 (from SpaceImaging/EOSAT, Thorton, CO).

This system was scheduled for launch in late 1998 but

failed to reach orbit in an early 1999 launch. It will

have 1-meter panchromatic and 4-meter multispectral capability. The swath width will be 11 km at nadir

and the revisit time will be 3 days at 1 meter and 1.5

days at 1.5 meter.

5. OrbView-3 (from ORBIMAGE, Dulles, VA). This system will have 1-meter panchromatic and 4-meter

multispectral bands and is scheduled for launch in

1999. It will have a swath width of 8 km at nadir and

revisit time will be less than 3 days.

6. IFSAR 3 m. The Interferometric Synthetic Aperture

Radar program will provide high resolution radar

data and has been developed as a low-cost method for

producing digital terrain elevation data. An IFSAR

system in a Lear jet aircraft has been developed that

meets the program goals of 3 meter height accuracy at

100 square kilometers per minute collection rate.

7. RADARSAT (from the Canadian Space Agency). This

system will have variable look directions and resolution with pixels as small as 10 meters.

8. AVIRIS - in addition to high spatial resolution, work

is steadily going forward on high resolution or

hyperspectral systems. AVIRIS has 224 different detectors with approximately 10 nanometers bands covering the spectrum from 380 nm to 2,500 nm and 20 m

resolution on the ground in 11 km swaths.
80 USDA Forest Service Proceedings RMRS-P-11. 1999

9. Multispectral videography—these systems are improving each year, and images with 3,000 by 2,000

pixels are relatively common although somewhat

expensive.

(a) multi-camera systems (useful for providing false

color images).

(b) single digital cameras with high resolution (cm

resolution).

Although these systems have much promise there are

certain disadvantages to the satellite systems. One is computational complexity. If one had a scene with 20,000 pixels

and 20,000 lines the storage requirement for the 400,000,000

pixels would be 25.6 gigabytes per scene. Then, any computer classification effort or other processing efforts such as

mosaicking would measurably add to this storage requirement. This, of course, indicates a need for large storage

capacities. Another disadvantage is the fact that we currently lack experience using these systems and their multispectral or hyperspectral attributes.

Data Analysis and Interpretation ___

Traditional field vegetation data accumulation procedures have used field sampling techniques such as measurements of plant cover using line intercept or estimations, production estimates or measurements, species

frequency, and other approaches. These procedures are all

time consuming. They provide point samples only and do

little to assist with the process of creating polygons or

patches useful for analysis and management. But remote

sensing techniques have the potential to examine both the

characteristics of change across the ecotone and to create

information on the distribution and landscape ecology of

the vegetation.

An important researchable problem is to determine the

trade-off between area coverage and pixel size. What pixel

size is optimum for different kinds of plant communities?

One approach to this question is to make an orderly examination of the same ecotone using several different pixel

sizes. Such an analysis could be to examine one or more

ecotones using the following data types with their various

pixel sizes: Landsat MSS 80 m pixels), Landsat TM (30 m

pixels), SPOT Image (20 m pixels registered to 10 m panchromatic pixels), IRS 5 m pixels fused to 30 m Landsat TM

pixels), IKONOS 1 m panchromatic), and digital video

images (10-50 cm pixels). Such an effort should look at the

ease of species or guild identification, the ease of measurement including density counts, and the ability to determine

changes over time.

Apart from the spatial scale question we must also

consider spectral resolution requirements. Spectral response is a function of a number of factors: (1) species

greenness/grayness, (2) size/shape of the species/specimens,

(3) bare ground/color, (4) amount of rock/gravel/litter/cryptogam cover; (5) shadow; and (6) the mixture of these in the

pixel (Tueller 1989). Theoretically it is possible to determine a spectral signature that may hold true for a specific

plant community. However, in actual practice the noise due

to the spectral ambiguity among the various scene components can destroy the strength of the signature, making it

useless when moving in space and/or time. A good signature

is one that would always be able to identify the plant

community or species in question. In any remote sensing

analysis the classification effort is a trade-off between

using the spectral data alone and reinterpretation of the

computer-derived data by the computer operator.

Spectral unmixing is a quantitative procedure used to

determine the makeup of individual pixels. Spectral

unmixing has been studied under several different situations. I used a simple approach based on ground radiometer

samples (Wilson and Tueller 1986). Results have been

varied. Some have thought that desert ecosystems and

their ecotones might lend themselves well to spectral

unmixing because the specimens are often widely separated and the spectral characteristics of some of the important surface components can be quite different. This can

lead to end members that differ enough to be separated

using a spectral unmixing algorithm. Wessman and others

(1997) found that spectral mixture analysis could separate

grazing and fire treatments in tall grass prairie and allow

for the identification of five remotely sensed factors affected by the management treatments: vertical structure,

percentage cover or patchiness, greenness, and distribution of soil and litter.

The idea of measuring change for the purpose of monitoring was mentioned above. Change detection of the ecotone

boundary and changes on either side of the boundary are

required for ecotone identification. A number of change

detection algorithms are available and have been tested

and reported in the literature. This seems like a clear cut

application but there are a number of problems. Researchers should provide a quantitative expression of the differences across the ecotone. For example, they should record

the cover percentages for the dominant species, indicate

which species are found on one side of the ecotone but not

the other, determine the amount of bare ground, rock,

gravel, and cryptogams on each side of the ecotone line, and

record the numbers of individual specimens making up the

changes in species cover. Does this indicate a change in the

productivity of the ecosystem? Many parameters can only

be measured indirectly using remote sensing technology.

Mapping after the ecotone has been identified is the next

step. The accuracy of the final map derived from remote

sensing data can be determined in various ways but normally requires ground data of various kinds. On the other

hand, on several occasions we have used high resolution

aerial photography to do field checking for classification

accuracy. Change detection is important in this regard also

because it is important to show when and how the boundaries have moved.

In the future the use of hyperspectral data along with

spectral unmixing procedures may be especially valuable,

although to date there have been some failures and a few

successes. It is not yet known which of the many bands are

useful or can be useful. Correlation of ground data to the

remotely sensed data and the kinds and amount of ground

data that must be obtained to support the data obtained

from the imagery are also unknown. Ground sample requirements and sampling techniques must be developed to

elucidate ecotone relationships.
USDA Forest Service Proceedings RMRS-P-11. 1999 81

Measurement and Sampling of the

Ecotone _______________________

Two important questions must be asked: (1) What procedures would be useful for measuring the vegetation differences across the ecotone using the high resolution video

data? And( 2) What procedures would be useful for using

the ecotone difference information and the spectral signatures that are developed to create vegetation maps? In the

former case there are three different approaches that can

used:

(a) Measurement of the differences using approximately

the same procedures as used in the field, e.g., the use

of a line intercept approach on the photographic images as well as in the field.

(b) Measurement of the differences using an alternative

approach on the images, e.g., density or number of

individuals per unit area for those plants where identifiable directly from the images. The density approach might serve well for shrubs and trees.

(c) Use of an image processing approach, with classification of the large scale images to differentiate the

proportion of dominant shrubs or other dominant

species on either side of the ecotone or within the

ecotone. This approach would require considerable

computer storage space and computation capability

because relatively large raster files are being used.

However, the savings in time and objectivity might

make such an approach quite feasible.

The second question has to do with vegetation mapping

and is a part of the upscaling question. If the large-scale

images can successfully show the boundary of an ecotone

that cannot be identified on the smaller scale imagery, the

question is how do we subsample so that we can extrapolate

the large-scale well-defined ecotone data to the small-scale

imagery over large land areas? In other words how do we

improve the accuracy of the polygons that represent the

plant communities?

Image Processing/GIS Approach

We can assume that each species has a different brightness level in each of several bands that may be expressed as

a spectral signature. If this is true, it will be possible to use

one or more classification algorithms to measure the relative proportions of the different dominant species in the

stand on each side of the ecotone. This might be useful only

for the dominant species. However, changes in the dominant species are usually important from the stand succession point of view. Mast and others (1997) used image

processing and GIS analysis of topographic maps to identify areas of change in tree cover, and quantified locations

and total hectares of tree invasion into grasslands along the

Colorado front range. Baker and others (1995) were able to

use scanned 1:40,000 color infrared photographs along

with GIS and remotely sensed tools to detect and analyze

changes in ecotones that may be related to global climate

change, although errors due to patchiness and spectral

variation were troublesome.

If it can be assumed that the areas of interest represent

homogeneous plant communities on either side of the ecotone, we can use change or difference detection algorithms

to measure the difference across the ecotone. The scale and

associated resolution necessary to identify the ecotone may

be quite large in may instances, requiring a scaling up

procedure of some kind. It is possible to define individual

pixels or small groups of pixels that, at least on the largescale data, define the existence of species level designations. On some of our enlarged images where pixels become

observable we often see individual pixels that define certain species.

Spectral unmixing, as previously mentioned, constitutes

a potential alternative approach. Mixtures occur at all scales

among materials found in a shrubland. Spatial mixing of

materials within the Instantaneous Field of View (IFOV)

of the pixel result in spectrally mixed reflected signals

(fig. 2). Analysis of remotely sensed images that view areas

of ground containing such mixtures must account for the

blend of reflected spectral radiance values that reach the

sensor. Each of the materials in the pixel contribute to the

total reflected signal. By modeling the spectral composite

for individual pixels, the mixed pixel components can be

estimated through standard least-squares techniques. We

assume that the mixing is linear and that there is no

significant interaction between materials, each photon

only “sees” one material and that these signals add in a

linear process. Spectral mixture analysis reduces a

hyperspectral data set of 100 to 200 bands to a sequence of

a few as two, but seldom more than ten. Surface-component

images are called pure endmember images (each with a

unique spectrum) and are defined as an endmember spectra (a matrix ) and by the abundances of the endmembers

(a vector).

We are presently actively researching these measurement questions and have not yet selected the procedure or

procedures that we prefer and that might give the highest

Figure 2—The Instantaneous Field of View of

a single pixel, showing the various kinds of

endmembers or spectral components within.
82 USDA Forest Service Proceedings RMRS-P-11. 1999

accuracy and allow analysis with the greatest ease. One

approach is to use one or more change detection algorithms.

Jensen (1989) described a number of different algorithms

that might be used. The idea is to use an algorithm that will,

with good accuracy, describe the difference across an ecotone and separate the spectral signatures found on both

sides and potentially in an area of overlap between the two

plant communities.

Upscaling

What does a single pixel or a group of pixels represent on

the landscape? A homogeneous group of pixels can represent like pixels across the scene if the area is truly homogeneous. This of course depends upon the classification accuracy, kind of vegetation, and other factors. The goal is to

create a spectral signature (characteristics of the spectral

response in several bands as related to the feature in

question) that represents a group of like pixels and have

this signature be useful over both space (across the scene)

and time (from scene to scene).

The sampling of the ecotone is important. Will it require

samples equal to 10 percent, 20 percent, or more of the

polygon boundary along the obscure ecotone? Accurate

georeferencing will be required to allow the mapper to place

the polygon line in the proper location. Some photo interpretation skills are required. There still is the possibility of

identifying the differences across the ecotone by examining

the spectral signatures in a image processing classification

approach, although further research is required. Presently,

much mapping is done using supervised classification techniques that may not define all of the important information

classes or plant communities of interest, especially on

heterogeneous wild landscapes.

While it seems a relatively simple concept, there are no

good procedures for upscaling with remote sensing data.

We are researching this question. I think that it will be a

continuing question closely related to the ecotone/vegetation mapping question. Hopefully, the new data from space

will eventually lead to a solution.

Some Examples_________________

In this paper, I would like to describe an example in a

Jeffrey Pine/meadow ecotone and a Jeffrey pine burned and

unburned in the eastern Sierra Nevada. The data types

analyzed include Landsat TM, IRS 5 m data, and Kodak

Digital data. As one moves from smaller to larger scales the

amount of information increases while the area coverage

decreases. There is a trade-off going from large to small

scale relative to pixel size and area coverage. The question

of subsampling becomes paramount and is related to the

quality of the spectral signature and upscaling. When, how,

and where do we sample to really assist in the mapping

process using remotely sensed data?

The site in this example shows a change from Jeffrey pine

(Pinus jeffreyi) to mountain meadow. This is a relatively

abrupt ecotone and rather easy to see on several scales of

imagery. Three important shrub species are often associated with the burned Jeffrey pine sites, manzanita (Arctostaphylos patula), buck brush (Ceanothus velutinus), and

squaw carpet (Ceanothus prostratus). This is not an especially subtle ecotone but can serve to describe the process.

The trees are easy to detect and the change of shrub type is

clear. With the TM data it is not possible to measure the

individual trees, but with the IRS data the large trees can

be examined primarily because of the 5 m pixels. With the

Kodak videography it is quite easy to identify and measure

most of the trees and many of the shrubs.

A second example comes from our work at Camp Williams, Utah. Here we have examined an ecotone between a

burned Gambel Oak stand and burned pinyon/juniper woodland vegetation (Table 1). Field data have been obtained

and we can examine both the Kodak Images and the IRS

images. It is difficult to see many of the ecotones using the

IRS 5 m data, while the Kodak data with quite small pixels

(0.17 m) are useful for differentiating these sites. The rootsprouting Gambel oak is quite clearly observed on the

Kodak digital images but not clearly seen on the IRS 5 m

data. This suggests the need to use subsamples of the

Table 1—A vegetation summary for a burnt juniper to burnt Gambel oak

ecotone at Camp Williams, UT.

Camp Williams field data (percent cover)

Plot Burnt juniper Burnt oak

Overstory

Bromus tectorum 11.782 3.828

Artemisia spp. 0.792 0.000

Agropyron spp. 0.330

Gutierezzia sarothrae 0.792 12.185

Achnatherum hymeniodes 1.122 4.884

Eriogonuim sp. 6.997 0.528

Burnt Juniper 16.106 6.733

Elymus elymoides 0.198 0.363

Chrysothamnus nauseosus 6.469 0.000

Purshia tridentata 1.782 0.000

Marrubium vulgare 0.132

Circium spp. 4.818 0.627

Opuntia spp. 0.726 0.000

Stipa comata 0.462 0.000

Chrysothamnus viscidiflorus 0.198 0.000

Quercus gambelli 0.000 28.449

Verbascum thapsus 0.660 2.178

Rock 6.733 6.007

Litter 8.977 15.017

Bareground 0.330 0.000

Total percent overstory 68.944 81.261

Understory

Bromus tectorum 4.257 2.838

Circium spp. 1.452 0.000

Chrysothamnus nauseosus 0.726 0.000

Eriogonuim spp. 0.528 0.000

Achnatherum hymeniodes 0.198 0.990

Stipa comata 0.198 0.000

Verbascum thapsus 0.132 0.990

Agropyron spp. 0.726

Chrysothamnus viscidiflorus 0.330 0.000

Rock 0.561 0.000

Litter 2.112 18.548

Total percent understory 10.495 24.092

Total percent 79.439 105.353
USDA Forest Service Proceedings RMRS-P-11. 1999 83

Kodak data to define where the ecotone goes on the landscape and is a part of the upscaling question.

A Remote Sensing Approach to

Ecotone Analysis _______________

The foregoing suggests that the identification and measurement of ecotones can be done with remote sensing. So

how do we go about doing the job? The following steps

constitute a reasonable approach to accomplishing ecotone

analysis using remote sensing.

1. One must first identify the spatial, spectral, and

measurement requirements for ecotone analysis. This

is followed by difference detection across the ecotone.

The best spatial data for mapping vegetation based on

improved ecotone delineation is selected. This might

be the Kodak digital data or in some cases the IRS 5 m

data or in the future the 1m data from space that has

been promised. This ecotone detection procedure is

used to develop a more accurate map.

2. Acquire the imagery. This is often a difficult step and

sometimes costly. The prices vary and the worker

must determine the resolution, coverage and

georeferencing requirements. Usually a compromise

must be reached between area covered and resolution

required. If only very high resolution is required then

a subsampling scheme must be developed for obtaining adequate statistical representation of differences

across the ecotone.

3. Test the ecotone data and the spectral signatures

derived by developing classifications of the vegetation

using these new parameters.

4. Test the accuracy of the map and the ecotone differences with ground data.

5. Use the images to complete a map with greater accuracy for your area of interest.

Summary and Conclusions _______

1. New high resolution remotely sensed data is being

evaluated for ecotone identification, delineation, and measurement.

2. It is hypothesized that such procedures will allow

more subtle vegetation differences to be detected across

ecotones.

3. This will allow more accurate mapping over large

lands areas, decreasing reliance on site-specific data where

it is difficult to extrapolate such data over entire landscapes.

4. Spectral characteristics are often sufficient to map

these subtle ecotones with image processing techniques.

5. Preliminary results show that the IRS 5 m data can

map less subtle ecotones but that it requires high resolution

data (cm size pixels) to map the more subtle ecotones.

References _____________________

Baker, W.L.; Honaker, J.J.; Weisberg, P.J. 1995. Using aerial

photography and GIS to map the forest-tundra ecotone in Rocky

Mountain National Park, Colorado, for global change research.

Photogrammetric Eng. and Remote Sens. 61: 313-320.

Holland, M.M.; Risser, P.G.; Naiman, R. J. 1991. Ecotones: the role

of landscape boundaries in the management and restoration of

changing environments. New York, NY: Chapman and Hall. 142 p.

Jensen, J. R. 1981. Urban change detection mapping using Landsat

Digital Data. American Cartographer. 8: 127-147.

Jordan, L.E., III. 1999. 1-Meter earth imagery on the horizon.

Imaging Notes. 13.

Mast, J.N.; Veblen, T.T.; Hodgson, M.E. 1997. Tree invasion

within a pine/grassland ecotone: an approach with historic

aerial photography and GIS modeling. Forest Ecology and

Management. 93: 181-194.

Risser, Paul G. 1995. The status of the science of examining

ecosystems. BioScience. 34: 318-325.

Tueller, P.T. 1989. Remote sensing technology for rangeland

management applications. Jour. of Range Manage. 42: 442-453.

Tueller, P.T. 1996. Near-earth monitoring of range condition and

trend. Geocarto. 11: 53-62

Wessman, C.A.; Bateson, C.A.; Benning, T.L. 1997. Detecting fire

and grazing patterns in tallgrass prairie using spectral mixture

analysis. Ecological Applications. 7: 493-511.

Wilson, R.O.; Tueller, P.T. 1987. Aerial and ground spectral

characteristics of rangeland plant communities in Nevada.

Remote Sensing of Environment. 23: 177-191.
84 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

R. F. Beck, Professor, and R. P. McNeely, Senior Research Assistant, are

both based in the Animal and Range Sciences Department, New Mexico State

University, Box 30003, Dept. 3-I, Las Cruces, NM 88001-0003. R. P. Gibbens

is Collaborator (Range Scientist, Retired), USDA-ARS, Las Cruces, NM

88001.

Mesquite-Grassland Ecotones in the

Chihuahuan Desert

R. F. Beck

R. P. McNeely

R. P. Gibbens

Abstract—Many plains and uplands of the Chihuahuan Desert in

southern New Mexico are in transition from a perennial desert

grassland to a mesquite (Prosopis glandulosa) dominated shrubland. On the Chihuahuan Desert Rangeland Research Center

north of Las Cruces, from 1982 to 1996, mesquite aerial cover

increased from 1.9 to 4.5% and density increased from 123 to 176

plants ha–1, with recruitment averaging 3.5 plants ha–1yr–1. Shrubs

encroach into grasslands by individual plants becoming established and, over time, creating patches of mesquite. These patches

expand into islands of mesquite with a greater biodiversity than

the surrounding grasslands. The mesquite islands eventually

coalesce into the mesquite “front” and biodiversity decreases. Thus

the current grass- shrublands may best be considered as ecotones,

both spatially and temporally.

Today the former grasslands on the uplands in the Jornada

Basin in southern new Mexico are in transition to becoming

desert scrublands, dominated by mesquite (Prosopis

glandulosa Torrey). These changes are of such a magnitude

that much of the plant and animal diversity associated with

grasslands will be lost or at least diminished. There have

been many writings and ideas put forth as to why this

change is taking place. Much of the change has occurred

since the start of large-scale ranching in the latter part of

the 19th century (Buffington and Herbel 1965). But, there

is disagreement about the actual effect of livestock grazing

on the spread of shrubs into the grasslands. Overgrazing is

often considered to be the primary culprit (York and DickPeddie 1969, Schlesinger and others 1990). Humphrey

(1950), and Brown and Archer (1987) stated it was not

overgrazing, but rather the encroachment resulted from

livestock consuming the seeds and spreading them through

their fecal droppings. Humphrey (1958) noted that there

were many possible factors responsible for the increase in

woody vegetation, but he proposed that fire was primarily

responsible for maintaining the desert grasslands and

attributed the spread of mesquite to lack of fire resulting

from grazing removing the fine fuels necessary to carry fire.

Reynolds (1950) found that Merriam kangaroo rats

(Dipodomys merriami merriami Mearns) bury mesquite

seed in caches that are not all used in favorable years, and

this helped the mesquite spread into grasslands.

Another idea that has been proposed is climate change.

Hastings and Turner (1965) suggested that the increase in

woody vegetation was because the climate was becoming

warmer and drier. Neilson (1986) proposed that the increase in shrubs was because of more winter moisture

favoring establishment of C3 plants. Mayeaux and others

(1991) suggested that the world-wide increase of atmospheric CO2 in the last 150 years resulting from industrialization, automobile emissions, etc., has given competitive

advantage to plants with C3 photosynthetic pathways

(shrubs) over those plants with C4 photosynthetic pathways (desert grasses). However, Archer and others (1995)

refuted rather convincingly the idea that an increase in

atmospheric CO2 was primarily responsible for woody plants

moving into grasslands.

Clements (1934) considered the grasslands in the Jornada

Basin to be a climax desert plains grassland. Shreve (1917)

in an earlier paper considered the Jornada grasslands to be

a transition between the mixed grasslands to the east and

the Chihuahuan Desert to the south and west. Perhaps

Shreve correctly recognized the changes taking place in the

region by calling the grasslands a transition, a view point

endorsed by Dick-Peddie (1993). The increase of mesquite

and other woody plants in the region may reflect vegetation

changes already set in motion prior to European settlement

and have been hastened by livestock grazing, industrialization, etc. The grasslands may represent environmental

conditions that no longer exist (Selleck 1960).

Whatever the cause, mesquite continues to invade and

establish in the black grama [Boutelooua eriopoda (Torrey)

Torrey] grasslands (Gibbens and others 1992). The purpose

of this paper is to look at the process of the invasions. We

propose that this ecotone between the grassland and mesquite is not a distinct line, but rather individual mesquite

plants becoming established in the grasslands ahead of the

“front,” and often forming “patches,” which allows the

mesquite to spread in leaps and in uneven patterns.

Study Area _____________________

The study was conducted on a 10 km2 area on the

Chihuahuan Desert Rangeland Research Center located

40 km north of Las Cruces, New Mexico. This particular

area was chosen because it represented an ecotone between

dense mesquite and a grassland with little or no mesquite

present. The climate of the region is characteristic of an

arid, continental interior with summer maximum temperatures frequently exceeding 35° C and the daily minimum
USDA Forest Service Proceedings RMRS-P-11. 1999 85

near 20° C. Daily minimum temperatures in winter are

generally below freezing with daytime maximums 15° C

warmer. The frost-free period is about 200 days. Spring is

the driest and windiest season. Wind during the remainder

of the year is generally associated with storms. Long-term

(1931-1996) average annual precipitation is 234 mm (fig. 1).

The primary growing season is from July through September when 125 mm (53%) of precipitation falls. Another

small peak of precipitation occurs, sometimes as snow, in

December-January.

The landscape of the study area is characterized by a

nearly level plain about 1,400 m above sea level with slopes

less than 2%. Scattered across the plain are occasional

shallow depressions, varying in size from 0.5 to 2-3 ha. Soils

on the plain are generally petroargids, which have a thin

layer of sand deposited by wind over a moderately developed argillic horizon. Total depth to a petrocalcic horizon is

less than 1 m. Within the depressions, soils generally have

greater clay content with a greater depth to a petrocalcic

horizon, if one exists.

Potential vegetation for the site is a black grama grassland. The aspect of the plain varies from an open, mixed

grassland with an occasional single mesquite and sometimes clumps of mesquite along with other shrubs (mainly

Ephedra spp. and Atriplex spp.) to dense mesquite stands.

The depressions in the landform tend to support heavier

stands of mesquite and soaptree yuccas (Yucca elata

Engelm.) with a grass-forb understory (fig. 2). The general

area is currently in a lower seral stage dominated by

mesquite, broom snakeweed [Gutierrezia sarothrae (Pursh)

Britton and Rusby] and several perennial grasses, including mesa dropseed [Sporobolus flexuosus (Thurb. Ex Vassey)

Rybd.] and threeawns (Aristida spp.). Many other grasses

and forbs are common in seasons of average or greater

precipitation.

All of the study area is grazed lightly by cattle, 20 - 25%

use on dominant grasses, during the year. Pronghorn antelope (Antilocapra americana) are frequently seen and the

introduced gemsbok (Oryx gazella) are occasionally sighted

on the study area.

Methods _______________________

The data used for this paper were collected from

14 permanent, randomly located transects in 1982, 1988,

1993, and 1996. Each transect was 61 m long. An estimate

of perennial grass production was obtained by clipping 5

linear plots, 6 m by 5 cm, along each transect. Only the

current year’s growth was clipped from plants rooted in the

plots. The plant material was separated by species, oven

dried, and weighed. Each transect was moved to the side a

minimum of 30 cm each year to avoid previously clipped

areas.

Aerial cover and density of mesquite were determined at

each transect in an oval plot, 860 m2 (40.4 by 73.2 m). On

each mesquite plant, the long canopy diameter and the

canopy diameter perpendicular to the long diameter were

measured. From these measurements the percentage aerial

canopy cover was calculated. Correlation analyses were

used to measure relationships among mesquite attributes

and grass production.

Results and Discussion __________

Total annual and growing season precipitation from 1980

to 1993 was near long-term average or greater, except in

1983 and 1989 (fig. 1). Total precipitation measured during

the summer growing season (July through September) was

also generally average or higher. A drought started in late

1993 and continued through 1996.

Total perennial grass production was 324 kg/ha in 1988

(table 1), resulting from above average precipitation in the

late 1980’s, and dropped to 83 kg/ha in 1996 after 3 years of

below average precipitation. Annual plant production indicated no clear pattern in relation to seasonal or annual

precipitation, which is not unexpected because germination

Figure 1—Annual and seasonal (July - September)

precipitation from 1980 to 1996 and long-term annual

and seasonal precipitation from 1931 to 1996 in the

northern Chihuahuan Desert.

Figure 2—Mesquite growing in a shallow depression on the Jornada Basin. Note presence of different

size of shrubs and grass clumps in the interspaces.

Note also the grass aspect and individual mesquite

plants growing on the hillside behind the cattle.
86 USDA Forest Service Proceedings RMRS-P-11. 1999

and growth of annual plants is often related to one or two

critical precipitation events during the year.

Mean mesquite density increased from 123 plants/ha in

1982 to 175 plants/ha in 1996 (table 2). Percent canopy

cover increased from 1.9% in 1982 to 4.6% in 1993. No

change in canopy cover was noted between 1993 and 1996,

indicating drought may have restricted canopy growth,

although, density increased as some new, small plants

became established. Mesquite canopy cover was highly

correlated with density (r = 0.90, df = 12; table 3).

Mesquite canopy cover in 1982 varied from 0 to about

11%. By 1993 the densest sites had increased to over 21%

cover (table 2) and the total area with no mesquite decreased. The changes in mesquite density are not as pronounced as for canopy cover, but mesquite during this time

period encroached into areas with little or no prior mesquite present. Herbaceous plant production was generally

not well correlated with mesquite cover or mesquite density

(table 3). One of the stronger relations (r = –0.64) is between

total perennial grass production and mesquite density.

Figure 3 indicates the general pattern of how mesquite

advances across the landscape with patches of little or no

mesquite being passed by and later becoming filled in with

mesquite through time. Other areas with established mesquite stands become more dense. Most mesquite patches at

the ecotone between the grassland and mesquite stand are

relatively small.

We believe the deposition of the mesquite seeds across

the rangeland away from stands of mesquite is by fecal

deposits of grazing animals, primarily cattle. Brown and

Archer (1989) support this idea and state further that the

deposition of seeds away from parent plants reduces hostspecific seed predators. However, the deposition of feces is

not equal across the site, but rather occurs at preferred

grazing sites and where animals congregate, drink water,

and bed down. One of the preferred sites for grazing is the

small depressions in the plain (fig. 2). These areas are

frequently heavily grazed because of their small size, and

these areas often have forage plants that are different

species, sometimes being green, as compared to the dry or

dormant plants on the surrounding plain.

Once a seed is deposited on the ground, there are many

things (predation, disease, unfavorable site, etc.) that might

happen to it to keep it from germinating (Bahre and Shelton

Table 1—Mean (± SE) production (kg/ha–1) for perennial grasses and annuals (%) for 4 different years in the Jornada Basin.

 1982 1988 1993 1996

Species x SE x SE x SE x SE

Black grama 50 20 133 50 94 38 52 24

Mesa dropseed 80 26 161 19 72 21 29 13

Threeawns 2 1 30 9 7 2 2 1

Total perennial grass 132 33 324 51 174 40 83 24

Annual grasses and forbs 78 22 24 14 26 14 52 16

Table 3—Correlation coefficients (df = 12) for mesquite cover and density with production of perennial grass species and annual plants in the Jornada

Basin in southern New Mexico.

Species/ Perennial grasses Mesquite

attribute Black grama Mesa dropseed Threeawns Total All annuals % Cover Density

Black grama 1.00

Mesa dropseed –0.31 1.00

Threeawns –0.15 –0.04 1.00

Total grass 0.92 0.07 –0.09 1.00

Annuals –0.15 0.38 –0.15 –0.02 1.00

% Mesquite cover –0.42 –0.1 0.07 –0.49 –0.35 1.00

Mesquite density –0.58 –0.1 0.15 –0.64 –0.29 0.90 1.00

Table 2—Percent cover and density for mesquite in a mesquite-grassland ecotone on

the Jornada Basin for 4 different years.

% Cover Density (#/ha)

Year x SE Range x SE Range

1982 1.9 0.8 0.02 - 11 123 32 12 - 465

1988 3.2 1.1 0 - 15 143 35 0 - 418

1993 4.6 1.5 0.2 - 21 161 33 35 - 418

1996 4.5 1.4 0.2 - 21 175 37 58 - 465
USDA Forest Service Proceedings RMRS-P-11. 1999 87

1993). After germination, establishment is uncertain due to

disease, insects, drought, and herbivory. Gibbens and others (1992) reported that 70% of marked mesquite seedlings

in the Jornada Basin were dead a year later, presumably by

lagamorph herbivory. If the mesquite seedling survives

through the first season, then adequate rainfall in subsequent seasons is important for establishment. New mesquite plants are frequently found growing close to established perennial grasses and forbs as well as in areas void

of plants. Brown and Archer (1989) noted that mesquite

seedlings growing near grass tussocks and on bare

interspaces survived equally well after 2 years. Once the

root system is developed, the small mesquite plants appear

to compete successfully with herbaceous plants (Gile and

others 1997). Growth for the mesquite is generally slow,

and these small plants, while growing in and among grass

plants, rarely produce seed.

Establishment of mesquite is a long, slow process. With

occasional drought, the herbaceous plants lose vigor and

basal area, and sometimes die. Mesquite, because of large

established root systems compared to the above ground

part, usually survives the drought and responds to the

occasional rain shower during the drought, while the herbaceous plants may or may not be able to respond. Through

several growing seasons, depending on the length of the

drought, the shrubs slowly start to dominate the site. After

drought, there is often little competition from herbaceous

species. The mesquite responds quickly to the rains, and

seed production becomes important for the continued spread

of the mesquite.

As a result of the individual mesquite plant becoming

established and producing seed that germinates nearby,

patches of mesquite occur in the grasslands. These patches

appear better developed in the small depressions across the

area (fig. 2). Patchiness may also occur when many mesquite seeds in close proximity germinate and establish at

the same time. The result is a mosaic of plants scattered

across the desert grasslands with mesquite being in patches

varying from a few small shrubs to several large plants,

Figure 3—Aerial view (≈ 250 M elevation) of part of

study area on Jornada Basin showing transition between a dense mesquite stand and the grassland. Note

clumping patches of mesquite in grasslands. White

spots are kangaroo rat dens.

each 2 m or so tall, and the patch being 10 - 50 m and sometimes larger in diameter.

The size of the patch influences surrounding plant and

associated animal life. When the plants are few and diminutive, biodiversity of the area is little affected, other

than the presence of mesquite and its associated microbes

and insects. As the mesquite increases in stature, it provides more habitat niches for plants, insects, and small

animals that originally did not occur on the grasslands. As

the patches grow together and become more dense,

interspaces are affected by wind and water erosion, and

herbaceous species become less abundant and some eventually die. As the grasslands are changed from grass dominants to patchiness with shrubs to shrub dominated, biodiversity increases and then declines. These former grassland

dominated areas are best described as ecotones as suggested by Shreve (1917) and supported by Dick-Peddie

(1993) because they possess greater diversity than they

once had or will have in the future.

References _____________________

Archer, Steve; Schimel, David S.; Holland, Elisabeth A. 1995.

Mechanisms of shrubland expansion; land use, climate or CO2?

Climatic Change. 29: 91-99.

Bahre, Conrad J.; Shelton, M. L. 1993. Historic vegetation change,

mesquite increases, and climate in southeastern Arizona. J.

Biogeography. 20: 489-504.

Brown, J. R.; Archer, Steve. 1989. Woody plant invasions of

grasslands: establishment of honey mesquite (Prosopis

glandulosa var. glandulosa) on sites differing in herbaceous

biomass and grazing history. Oecologia. 80: 19-26.

Buffington, Lee C.; Herbel, Carlton H. 1965. Vegetational changes

on a semidesert grassland range. Ecological Monographs. 35:

139-164.

Clements, F. E. 1934. The relict method in dynamic ecology. J.

Ecology. 22: 39-68.

Dick-Peddie, William A. 1993. New Mexico vegetation: past, present

and future. Albuquerque, NM: University of New Mexico Press:

244 p.

Gibbens, R. P.; Beck, R. F.; McNeely, R. P.; Herbel, C. H. 1992.

Recent rates of mesquite establishment in the northern

Chihuahuan Desert. J. Range Management. 45: 585-588.

Gile, L. H.; Gibbens, R. P.; Lenz, J. M. 1997. The near-ubiquitous

pedogenic world of mesquite roots in an arid basin floor. J. Arid

Environments. 35: 39-58.

Hastings, J. R.; Turner, R. M. 1965. The changing mile. Tucson,

AZ: University of Arizona Press. 317 p.

Humphrey, R. R. 1958. The desert grassland: a history of vegetational change and an analysis of causes. Botanical Review. 24:

193-252.

Neilson, Ronald P. 1986. High-resolution climatic analysis and

southwest biogeography. Science. 232: 27-34.

Mayeux, H. S.; Johnson, H. B.; Polley, H.W. 1991. Global change

and vegetation dynamics. In: James, L. F.; Evans, J. O.; Ralphs,

M. H.; Sigler B. J., eds. Noxious Range Weeds. Boulder, CO:

Westview Press: 62-74.

Reynolds, Hudson G. 1950. Relation of Merriam kangaroo rats to

range vegetation in southern Arizona. Ecology. 31: 456-463.

Schlesinger, William H.; Reynolds, James F.; Cunningham, Gary

L.; Huenneke, Laura F.; Jarrell, Wesley M., Virginia, Ross A.;

Whitford, Walter G. 1990. Biological feedbacks in global desertification. Science: 1043-1048.

Selleck, G. W. 1960. The climax concept. Botanical Review. 26:

534-545.

Shreve, F. 1917. A map of the vegetation of the United States. Geol.

Rev. 3: 119-125.

York, John C.; Dick-Peddie, W. A. 1969. Vegetation changes in

southern New Mexico during the past hundred years. In:

McGinnes, W. G.; Goldman, B. J., eds. Arid lands in perspective.

Tucson AZ: University of Arizona Press: 157-166.
88 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Sherel Goodrich is Ecologist, Ashley National Forest, Vernal, UT 84078. E.

Durant McArthur is Project Leader and Supervisory Research Geneticist,

Shrub Sciences Laboratory, Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture, Provo, UT 84606. Alma H. Winward is

Regional Ecologist, U.S. Department of Agriculture, Forest Service,

Intermountian Region, Ogden, UT 84401.

Sagebrush Ecotones and Average Annual

Precipitation

Sherel Goodrich

E. Durant McArthur

Alma H. Winward

Abstract—Comparing precipitation data from numerous climate

stations in Utah with dominant sagebrush communities at or near

the stations indicate the ecotone between desert shrub communities

and Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis)

communities is associated with 18-20 cm (7-8) inches annual precipitation. Large stands of Wyoming big sagebrush are common at

or near stations with 20-30 cm (8-12) inches annual precipitation.

Sagebrush communities at and near stations with about 11-13

inches often include plants with morphological and chemical features that indicate introgression of Wyoming big sagebrush and

mountain big sagebrush (Artemisia tridentata ssp. vaseyana var.

pauciflora). The area of introgression or the ecotone is commonly in

the pinyon-juniper belt within Utah. Communities of typical mountain big sagebrush are associated with climate stations with greater

than 30 cm (12 inches) annual precipitation.

Although mountain big sagebrush (Artemisia tridentata

ssp. vaseyana var. pauciflora) and Wyoming big sagebrush

(Artemisia tridentata ssp. wyomingensis) are highly similar

morphologically and likely intergrade frequently, they form

large stands of uniform plants that are clearly assignable to

subspecific taxa. The ecological differences between areas

supporting pure stands of mountain big sagebrush and

Wyoming big sagebrush are great. Climate, soils, associated

plant species, fire regime, production potential, potential for

ground cover and watershed protection, stocking rates for

livestock, season of use by wild ungulates, and other features are different for areas of these two sagebrush taxa.

Restoration practices suitable to communities of one might

not be appropriate for those of the other. In view of these

differences, recognition of these two taxa can facilitate

management of sagebrush communities.

This paper provides an evaluation of the distribution of

communities of these two taxa in context of climate (more

specifically annual precipitation) and relationship to other

plant communities in Utah, and especially in relation to the

belt formed by pinyon (Pinus edulis and P. monophylla) and

Utah juniper (Juniperus osteosperma). Understanding the

distribution of these communities can greatly facilitate

recognition of communities of the two sagebrush taxa and

management implications for them. Basin big sagebrush

(Artemisia tridentata ssp. tridentata) communities are found

in areas of Wyoming big sagebrush and mountain big sagebrush as well as in the pinyon-juniper ecotone. It does not

demonstrate the degree of sensitivity to annual precipitation that the other two taxa do. It is not included in this

paper.

Methods _______________________

Sagebrush samples were taken from several Utah climate

stations for which there are records of average annual

precipitation (Ashcroft and others 1992; Martin and Corbin

1932). Precipitation values at some stations were taken from

unpublished data collected by the U.S. Department of Agriculture, Natural Resources Conservation Service. Samples

were also taken from some sites not represented by a climate

station, but for which nearby stations provided an approximation of average annual precipitation or for which precipitation was estimated from Richardson and others (1981).

Samples from 82 sites were tested for fluorescence under

long-wave ultraviolet light, which is useful for separation of

mountain big sagebrush (Artemisia tridentata ssp. pauciflora)

from Wyoming big sagebrush (Artemisia tridentata ssp.

wyomingensis) (Winward and Tisdale 1969; Spomer and

Henderson 1988). The test consisted of placing crushed

leaves in beakers of water that were placed under ultra

violet light. Specimens of mountain big sagebrush in water

fluoresce brightly under this light, and those of Wyoming big

sagebrush are not fluorescent or only slightly so (Stevens

and McArthur 1974). However, as might be expected with

closely related and morphologically intergrading taxa, the

fluorescence test shows intergradation. Some samples were

not fluorescent, and others ranged from slightly fluorescent

to brightly fluorescence. A range of scores from 0-5 was

assigned to fluorescence tests, with 0 representing those

samples that did not fluoresce and 5 representing bright

fluorescence. Samples were taken from three different shrubs

at each site, and the values of the three samples were

averaged for fluorescence scores.

Results and Discussion __________

From the 82 sample sites no fluorescence scores were

found from 3.4 to 3.9 (table 1). This range appears to

represent a major break by which to separate intermediate

populations from those of mountain big sagebrush. Scores of
USDA Forest Service Proceedings RMRS-P-11. 1999 89

Table 1—Sample sites, fluorescence scores, annual precipitation, and their relation to the pinyon-juniper belt and other vegetation.

Position in relation to the

Fluorescence score pinyon-juniper belt and

Sample no. Annual other vegetation:

County/site S1 S2 S3 Average Precip. B = below, I = in, A = above

Cm

Beaver

Minersville (S. edge of town) 5 4 5 4.7 31.4 I (lower JUOS, ARTRP)

Carbon

Clear Creek 5 5 5 5.0 58.5 A (ARTRP4, POTR)

Scofield 5 5 5 5.0 43.7 A (ARTRP4, POTR)

Scofield Dam 5 5 5 5.0 35.7 A (ARTRP4, POTR)

Scofield-Skyline Mine 5 5 5 5.0 59.2 A (ARTRPr, POTR)

Hiawatha 3 3 3 3.0 37.1 I (middle p-j)

Hwy 50/Hiawatha jct. 3 2 1 2.0 22.9a B (desert shrub)

Daggett

Allens Ranch 0 0 0 0 21.7 B

Antelope Flat 0 1 1 0.7 26a B (ARTRW)

Dutch John Gap 0 0 0 0 30a I (middle p-j)

Dutch John Gap South 0 0 0 0 30a I (middle p-j)

Greendale 5 5 5 5.0 41a A (PIPO, mtn. brush)

Flaming Gorge 1 1 1 1 31.8 I (middle p-j. ARTRW)

Flaming Gorge (Dutch John Airport) 2 1 1 1.3 32a I (middle p-j, ARTRW)

Flaming Gorge (Dutch John Flat) 2 2 1 1.7 32a I (middle p-j, ARTRW)

Flaming Gorge (Mustang jct. US 191) 1 0 1 0.7 32a I (middle p-j, ARTRW)

Flaming Gorge S (Bootleg CG.) 5 5 5 5 34a A (PIPO, mtn brush)

Hickerson Park 5 5 5 5 61.7 A (PICO)

Manila 0 0 1 0.3 24.6 B (ARTRW, ATCO)

Manila (1 mi S. on U 44) 0 2 2 1.3 24.6 B (desert shrub)

Manila (6 mi S. on U 44 (Sheep Creek) 0 0 3 1 28a I (lower j)

Manila (12 mi S. on 44 (Spring Creek) 5 5 5 5 34a A (mtn. bursh)

Manila (14 mi S. on 44 (Dowd Hole) 5 5 5 5 38a A (ARTRP4, PIPO)

Duchesne

Altamont 0 0 0 0 23.7 B (at lower edge)

Duchesne W. edge of town 0 0 1 0.3 24.3 B (ATCO)

Duchesne Airport 1 0 0 0.3 19.2 B (ARTRW)

Gilsonite Draw 1 1 1 1.0 28a I (ARTRW)

Fruitland 3 5 1 - 31.5 I (upper p-j)

Fruitland 3 4 4 -

Fruitland 3 3 2 -

Fruitland 2 3.0

Indian Canyon 10KI 5 5 5 5.0 43.0a A (POTR, ABLA)

Hwy. 40, 10 mi W. of Duchesne 3 2 2 2.3 28a I (middle p-j)

Hwy. 40, 13 mi W. of Duchesne 4 2 2 2.6 28a I (middle p-j)

Hwy. 40, 15.5 mi W. of Duchesne 4 1 2 2.3 29.2 I (middle p-j)

Hwy. 40, 20 mi W. of Duchesne 5 4 3 4.0 30a I (middle p-j)

Myton 1 0 3 1.3 17.3 B (desert shrub)

Neola (north) 3 3 3 3.0 25a I (middle p-j)

Neola (west) 0 0 3 1.0 22.2 I (lower edge)

Roosevelt (2 mi E.) 1 1 3 1.7 18.0 B (ARTRW, ATCO)

Starvation Dam 4 3 3 3.3 24a I (lower edge p-j)

Emery

Electric Lake 5 5 5 5.0 63.3 A (ARTRP, POTR)

Ferron Golf Course 0 1 1 0.7 24a I (lower edge p-j)

Hunting (5 mi N.) 1 1 1 1.0 21.6

Iron

Beryl 0 0 0 0 25.9 B (ATCO)

Lund 0 3 0 1.0 23a B (ATCO)

Sevier

Emery 15 SW 2 3 3 2.7 37.2 I (middle p-j)

Salina Canyon MP 74 on I-70 4 2 4 3.3 37a I

(con.)
90 USDA Forest Service Proceedings RMRS-P-11. 1999

Juab

Jericho junction of US 6 0 0 1 0.3 23a B (ARTRW, ARTRT)

Levan (mouth of Chicken Creek) 5 5 5 5.0 38.5 Mtn. brush

Millard

Milford (N. edge of town) 1 2 1 1.3 23.8 B (ARTRW)

SanPete

Ephriam (mouth of Ephriam Canyon) 3 3 4 3.3 32a I (QUGA, SYOR)

Ephriam (east) 0 1 2 1.0 30.1 I (middle p-j)

Fountain Green (hillside above) 5 4 4 4.3 32a I (Utah juniper)

Fountani Green (4.2 mi W.) 5 4 5 4.7 34a I (below QUGA)

Gunnison (12 mi N.) 1 0 2 1.0 27a B (ARTRT)

Manti (hill SE. of) 4 4 5 4.3 34.9 I (Utah juniper)

Mayfield 0 1 1 0.7 25a B (ARTRW)

Summit

Hole In The Rock 5 5 5 5.0 40.1 A (POTR, ARTRP)

Tooele

Rush Valley L 0 1 0 0.3 20a B (desert shrub)

Rush Valley M 0 1 0 0.3 26a B (desert shrub)

Rush Valley U 0 1 1 0.7 31a I (lower j)

Uintah

Bonanza 0 0 0 0

Elk Horn 5 5 5 5.0 34.1 I (upper p-j)

Fort Duchesne 0 0 1 0.3 17.2 B (ARTRW, ATCO)

Grouse Creek 5 5 5 5.0 33a A (mtn. brush, ARTRP)

Gusher east 0 1 2 1.0 20a B (ARTRW, ATCO)

Jensen 3 3 3 3.0 20.7 B (desert shrub)

Kings Cabin 5 5 5 5.0 70.3 A (PSME, POTR)

Lapoint 0 0 1 0.3 21.0 B (ARTRW, ATCO)

Lapoint (7 mi N., Deep Cr./Mosby Jct.) 0 0 0 0 25a B (ARTRW)

Lapoint (9 mi N., Little Water) 0 0 1 0.3 29a I (middle j)

Maeser 9 NW 4 4 5 4.3 34.4 A (mtn. brush)

Snake John, Farm Creek 5 4 4 4.3 35a I (upper p-j)

Watson 0 1 0 0.3 30.1 B (ARTRW, ATCO)

Whiterock Bench 0 0 3 1.0 25a B (ARTRW)

Whiterocks Canyon 5 5 5 5.0 40 A (PIPO, POTR)

Utah

Elberta (2.2 mi W. on US6) 0 1 1 29 a B (ARTRW at edge of j)

Eureka (east edge of town at US6) 5 5 5 5.0 43.2 A, I (upper edge p-j)

Santaquin (Exit 248, I-15) 5 5 5 5.0 46.9 A (QUGA, ARTRP)

Wasatch

Current Creek/Hwy 40 jct. 5 5 5 5.0 33a A (QUGA, PSME)

Heber (mouth of Danials Canyon) 5 5 5 5.0 40.7 A (ARTRP4, QUGA)

Soldier Creek 5 5 5 5.0 37.0 A (ARTRP4, POTR)

Strawberry Hwy. Station 5 5 5 5.0 41.8 A (ARTRP4)

Deer Creek Dam 5 5 5 5.0 62.4 A (QUGA, PSME)

Washington

Enterprise (1 mi. S.) 5 4 3 4.0 36 I (middle p-j, PUTR)

Hildale (0.5 mi W. on U 59) 0 0 1 0.3 30a I (lower j; desert shrub)

a

Sites of estimated annual precipitation. Other precipitation values are from climate stations. ABLA = subalpine fir (Abies lasiocarpa), ARTRP4 = mountain big

sagebrush, ATCO = shadscale (Atriplex confertifolia), j = Utah juniper, p-j = pinyon-juniper, PIPO = ponderosa pine (Pinus ponderosa), POTR = aspen (Populus

tremuloides), PSME = Douglas-fir (Pseudotsuga menziesii), QUGA = Gamble oak (Quercus gambelii), SYOR = mountain snowberry (Symphoricarpos oreophilis). Except

for pinyon and juniper, plant symbols used are listed by Soil Conservation Service (1994).

Table 1 (Con.)

Position in relation to the

Fluorescence score pinyon-juniper belt and

Sample no. Annual other vegetation:

County/site S1 S2 S3 Average Precip. B = below, I = in, A = above

Cm
USDA Forest Service Proceedings RMRS-P-11. 1999 91

4.0 or greater were considered to represent mountain big

sagebrush. A break in fluorescence scores between populations of Wyoming big sagebrush and plants of intermediate

populations was less conspicuous. However, only one sample

site scored between 1.8 and 2.2. Fluorescence scores of 2.0

and less were considered to represent populations of Wyoming big sagebrush, and scores of 2.3-3.3 were considered

intermediate.

The tested samples show an apparent strong relationship

to average or normal annual precipitation. Ranges of annual

precipitation for populations of Wyoming big sagebrush,

intermediate plants, and mountain big sagebrush were

17.2-32.0 cm (6.8-12.6 inches), 20.7-37.2 cm (8.1-14.6 inches),

and 30.0-70.3 cm (11.8-27.7 inches), respectively. Average

annual precipitation for populations of these plants in the

same order was 25.3 cm (10.0 inches), 30.0 cm (11.8 inches),

and 43.2 cm (17.0 inches) (table 1). The lower end of the

annual precipitation range for Wyoming big sagebrush is

represented by stations at Fort Duchesne, Myton, and

Roosevelt, with 17.2 cm, 17.3 cm, and 18.0 cm, respectively.

At these stations Wyoming big sagebrush was found in

scattered populations mostly in washes, on eolian sand, and

other specialized habitats where desert shrub communities

were common landscape dominants. The station at Duchesne

Airport with 19.2 cm (7.5 inches) annual precipitation represented one of the lowest precipitation stations where a

large continuous stand of Wyoming big sagebrush was

found. Average annual precipitation for Wyoming big sagebrush sites below the pinyon-juniper belt was about 22.9 cm

(9 inches). This appears to be quite typical for fans, bajadas,

benches, and valley fill below the pinyon-juniper belt of

Utah where Wyoming big sagebrush is a landscape dominant. The data suggests much of the pinyon-juniper belt in

Utah is within a zone of 24-37 cm (9-15 inches) annual

precipitation. This appears consistent with the suggestion of

Payne (1980) that the Intermountain pinyon-juniper belt

generally falls in a zone of 25.4 and 35.6 cm (10-14 inches)

annual precipitation.

In addition to the 82 sites listed in table 1, there are many

other sites at or near climate stations in Utah listed by

Aschroft and others (1992) from which big sagebrush samples

have been tested for fluorescence and/or examined in the

field with positive identification (table 2). Precipitation data

from these stations indicate Wyoming big sagebrush communities with a range of 19.9-31.5 cm (7.8-12.4 inches)

annual precipitation with a mean of 23.9 cm (9.4 inches).

Climate station data also indicate mountain big sagebrush

communities with a range of 30.8-148.5 cm (12-58 inches)

and a mean of 48.3 cm (19.0 inches) annual precipitation

(table 3). The site with 148.5 cm annual precipitation (Alta)

represents an extreme where mountain big sagebrush is

restricted to steep, warm exposures within a belt where it is

more commonly replaced by aspen and coniferous trees.

In addition to the sites listed in table 2, Wyoming big

sagebrush is found near the following stations where desert

shrub communities dominate and Wyoming big sagebrush is

lacking or mostly confined to washes, dunes, and other

specialized habitats: Desert Experimental Range (15.8),

Lund (18.2), Ouray (17.8), Wah Wah Ranch (17.7). These

stations indicate that stands of Wyoming big sagebrush are

mostly found in areas of above 18.2 cm (7.2 inches) annual

precipitation. Information from the 82 sites of table 1 coupled

Table 2—Utah climate stations representing

Wyoming big sagebrush communities.

Community Precipitation

Cm

Arches NP HQ 22.7

Black Rock 23.0

Circleville 22.4

Delta 20.6

Dugway 20.7

Fairfield 31.5

Fremont Indian State Park 28.2

Ibapah 25.6

Koosharem 21.3

Little Sahara Dunes 32.2

Loa 19.9

Lucin 22.0

Marysvale 21.4

Milford 23.8

Modena 26.2

Piute Dam 20.6

Price Game Farm 24.8

Salina 25.2

Thompson 23.3

Woodruff 23.0

Table 3—Utah climate stations representing

mountain big sagebrush communities.

Community Precipitation

Cm

Alpine 44.6

Alta 148.5

Alton 43.0

Bear Lake State Park 35.6

Beaver Can. Powerhouse 52.6

Bingham Canyon 54.4

Birdseye Pines Range 47.0

Bountiful-Val Verda 50.9

Brigham City 49.1

Coalville 41.7

East Canyon 49.7

Echo Dam 37.9

Filmore 40.6

Gunlock Powerhouse 30.8

Hardware Ranch 44.2

Huntsville Monastery 54.5

Johnson Pass 42.8

Kanosh 38.8

Logan Radio 42.1

Logan Utah State University 49.5

Lower American Fork 41.3

Lower Mill Creek 51.3

Monticello 39.3

New Harmony 46.7

Ogden Pioneer Powerhouse 57.5

Olmstead Powerhouse 52.6

Payson 39.7

Santaquin Chlorinator 46.9

Spanish Fork Powerhouse 52.2

Tooele 47.0

Veyo Powerhouse 33.9

Zion National Park 39.2
92 USDA Forest Service Proceedings RMRS-P-11. 1999

with that from other climate stations in Utah indicate the

ecotone between desert shrub and Wyoming big sagebrush

belts generally corresponds with annual precipitation of 18-

20 cm (7-8 inches). Edaphic differences within and near this

range of precipitation are also determining factors.

In addition to the sites listed in table 2, intermediate or

intergrading populations are known from the following

stations: Beaver (29.8), Cove Fort (32.2), Ephriam Sorensons

Field (30.1), Minersville (31.4), Nephi (36.9). The range in

precipitation for these stations of 29.8-36.9 cm (11.7-14.5

inches) and the mean of 32.1 cm (12.6 inches) are similar to

those found for locations of intermediate populations reported in table 1. These stations are mostly in or near the

pinyon-juniper belt. These stations and the sample sites of

table 1 show the pinyon-juniper belt of Utah to be the ecotone

between Wyoming big sagebrush and mountain big sagebrush.

Relationships With Pinyon-Juniper

in Utah ________________________

Of the 26 samples taken below the pinyon-juniper belt, all

but one had fluorescence scores typical of Wyoming big

sagebrush. All but one of the 11 sample sites with intermediate fluorescence scores were in the pinyon-juniper belt.

Fluorescence scores for all 23 sites sampled above the pinyon-juniper belt were above 4.0 and clearly indicative of

mountain big sagebrush.

Wyoming big sagebrush communities were found below

(60%) and in (40%) the pinyon-juniper belt. Sites with

intermediate fluorescence scores were found below (10%)

and in (90%) the pinyon-juniper belt. Sites with mountain

big sagebrush were found in (25%) and above (75%) the

pinyon juniper belt (table 4).

Of 26 composite samples taken from below the pinyonjuniper belt, 25 (96%) were identified as Wyoming big

sagebrush. Of 32 composite samples taken from within the

pinyon-juniper belt, 14 (44%), 10 (31%), and 8 (25%) were

identified as Wyoming big sagebrush, intermediate plants,

and mountain big sagebrush, respectively. Of 23 composite

samples taken from above the pinyon-juniper belt, all were

identified as mountain big sagebrush. The mixing of taxa in

the pinyon-juniper belt and the isolation of Wyoming big

sagebrush below this belt and the isolation of mountain big

sagebrush above this belt all demonstrate the pinyon-juniper

belt to be an ecotone of Wyoming big sagebrush and mountain big sagebrush.

Table 4—Sagebrush communities and their fluorescence scores, annual precipitation, and relationship to

the pinyon-juniper belt (82 sites total).

Fluorescence scores Annual precipation Relation to p-j belt

Community Range Mean Range Mean Below In Above

- - - - - Cm - - - - - - - - Percent - - - - - 

Wyoming big sagebrush 0-2.0 0.8 17.3-32.0 25.7 60 40 0

Intermediate 2.3-3.3 2.9 20.7-37.2 30.0 9 91 0

Mountain big sagebrush 4.0-5.0 4.8 30.0-70.3 43.2 0 25 75

Intermediate Populations (Fruitland

Example)

The Fruitland area (31.5 cm annual precipitation) in

Duchesne County represents the ecotone between Wyoming

big sagebrush and mountain big sagebrush. This area is

located at the upper edge of the pinyon juniper belt. Of 10

samples taken from the Fruitland area, the range of fluorescence scores was 1-5. The samples included one 1, two 2s

, four

3s

, two 4s, and one 5. The scores indicate intermediate specimens dominate the population with influence from both taxa

about equally present. Intermediate populations are apparently common within the pinyon-juniper belt of Utah with

about 28-37 cm (11-14 inches) annual precipitation.

Management Implications

In many areas of Utah the separation of Wyoming big

sagebrush and mountain big sagebrush communities can be

as simple as recognizing their relationship to the pinyonjuniper belt. Where large stands of Wyoming big sagebrush

occur below the pinyon-juniper belt, annual precipitation

can be expected to average about 20-25 cm (8-10 inches). In

the ecotone of the pinyon juniper belt, annual precipitation

can be expected to range from 22-36 cm (9-15 inches) with an

average of 31 cm (12 inches). Where large stands of mountain big sagebrush occur above the pinyon-juniper belt,

annual precipitation can be expected to range from 33-70+

cm (13-28+ inches). These differences indicate different

potentials for production, ground cover, crown cover of

sagebrush, species diversity, fire return intervals, and other

community features.

Production studies on the Ashley National Forest commonly show annual production of 268-446 kg/ha (300-500

lbs/acre) for Wyoming big sagebrush communities below the

pinyon-juniper belt and 624-1070 kg/ha (700-1,200 lbs/acre)

for mountain big sagebrush communities. Peters and Bunting

(1994) indicated less than 400 kg/ha (357 lbs/acre) for Wyoming big sagebrush communities on the Snake River Plain

of Idaho. Potential for ground cover in Wyoming big sagebrush appears to be from about 60-75% (Kindschy 1994;

Winward 1983; Goodrich and others, these proceedings).

Wyoming big sagebrush communities are noted for low plant

species diversity. In Daggett County, Utah, fewer than 15

vascular plant taxa were commonly found in studies that

included 100 plots of 50 by 50 cm. (Goodrich and others, these

proceedings). Several studies in mountain big sagebrush
USDA Forest Service Proceedings RMRS-P-11. 1999 93

communities on the Uinta Mountains (Ashley National

Forest, unpublished study data) show ground cover commonly above 80% and often near 100% for these communities with light and moderate grazing (unpublished data).

These studies also show 30-50 vascular plant species for

these communities where crown cover of mountain big

sagebrush commonly exceeds 20%, and in the absence of fire

or other crown-decreasing disturbance reaches nearly 40%.

Crown cover of sagebrush in Wyoming big sagebrush communities is commonly less than 25% (Winward 1983; Goodrich

and others, these proceedings).

Mountain big sagebrush communities have generally been

found on soils of the Mollisol Order while those of Wyoming

big sagebrush have generally been found on soils of the

Aridisol Order (Swanson and Buckhouse 1984; Barker and

McKell 1983; Jensen 1990; Tart 1996; Goodrich 1981). The

development of mountain big sagebrush communities on

Mollisols and Wyoming big sagebrush communities on

Aridisols is indicative of higher potential for production and

ground cover for mountain big sagebrush communities.

These features are indicated to be major factors of different fire regimes for communities of these two sagebrush

taxa. With lower production, less ground cover, lower crown

cover of shrubs, and less diversity in species and structure,

Wyoming big sagebrush communities are less prone to fire

than are mountain big sagebrush communities (Peters and

Bunting 1994). Fire return intervals of 50-110 years are

common for Wyoming big sagebrush communities (Whisenant

1990; Winward 1983) while this interval is commonly 10-40

years in mountain big sagebrush communities (Winward

1983). These features also indicate lower capacity of Wyoming

big sagebrush communities to support livestock grazing.

Mountain big sagebrush communities are found in areas

where snow cover commonly exceeds 38 cm (15 inches) while

Wyoming big sagebrush communities are found where snow

cover is commonly less than 41 cm (16 inches) (Sturges and

Nelson 1986). With snow cover of less depth and duration,

Wyoming big sagebrush communities provide greater opportunity for wintering ungulates than do many mountain

big sagebrush communities.

Catastrophic change in ecosystem function induced by

cheatgrass (Bromus tectorum) has been widespread in Wyoming big sagebrush communities and within the pinyonjuniper belt. Although mountain big sagebrush communities of warm exposures are also quite vulnerable to cheatgrass,

the total displacement of mountain big sagebrush communities by cheatgrass is not so common as for communities of

Wyoming big sagebrush and pinyon-juniper belts. The need

for seeding following fire to prevent cheatgrass dominance is

indicated to be high for Wyoming big sagebrush and pinyonjuniper communities and low for the mountain big sagebrush belt.

The recognition of Wyoming big sagebrush and mountain

big sagebrush communities can greatly facilitate recognition of capabilities and values of the land. This can also

facilitate developing prescriptions for reclamation and forage improvement projects. However, within the pinyonjuniper belt some communities of either Wyoming big sagebrush or mountain big sagebrush as well as intergrading

populations can be expected to have intermediate features.

Intermediate features within the pinyon-juniper ecotone

need not be taken as a breakdown in the predictive value of

these two sagebrush taxa. Mixed or intermediate populations indicate intermediate capabilities and values. They

indicate intermediate prescriptions for seeding and seed

mixes and other management practices.

Taxonomic implications

While fluorescence scores strongly support the separation of

Wyoming big sagebrush and mountain big sagebrush, they

show an intermediate range that appears to represent intermediate plants. The plants of intermediate fluorescence in

Utah are mostly found at the ecotone (pinyon-juniper belt)

between the two taxa. These intermediate plants appear to

represent numerous introgressive populations of separate

hybrid origin (McArthur and Sanderson, these proceedings).

The high possibility of numerous and ongoing origins of

introgressive populations indicates much difficulty and questionable value for taxonomic separation of the intermediate

plants. These intermediate plants seem to lack unique

morphological features by which they are consistently separated from plants of Wyoming big sagebrush and/or mountain big sagebrush. The propensity of intermediate plants

for the pinyon-juniper belt does lend some geographic integrity. However, this distribution is not unique, for it is shared

by populations of both Wyoming big sagebrush and mountain big sagebrush.

References _____________________

Ashcroft, G. L.; Jensen, D. T.; Brown, J. L. 1992. Utah climate.

Logan, UT: Utah State University, Utah Climate Center. 125 p.

Ashley National Forest. Unpublished study data on file at: U.S.

Department of Agriculture, Forest Service, Intermountian Region, Ashley National Forest, Vernal, UT.

Barker, J. R.; McKell, C. M. 1983. Habitat differences between basin

and Wyoming big sagebrush in contiguous populations. Journal

of Range Management 36: 450-454.

Goodrich, S. 1981. A floristic study of central Nevada. Provo, UT:

Brigham Young University Press. 399 p. Thesis.

Goodrich, S.; Nelson, D.; Gale, N. These proceedings. Some features

of Wyoming big sagebrush communities on gravel pediments of

the Green River in Daggett County, Utah.

 Kindschy, R. R. 1994. Pristine vegetation of the Jordan Crater

Kipukas: 1978-91. In: Monsen, S. B.; Kitchen, S. G., comps.

Proceedings—ecology and management of annual rangelands;

1992 May 18-21; Boise, ID. Gen. Tech. Rep. INT-313. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Research Station: 85-88.

Jensen, M. E. 1990. Interpretation of environmental gradients

which influence sagebrush community distribution in northeastern Nevada. J. Range Management 43: 161-166.

Martin, R. J.; Corbin, E., eds. 1932. Climate summary of the United

States. Washington, DC: U. S. Department of Agriculture, Weather

Bureau. 32 p..

McArthur, E. D.; Sanderson, S. C. These proceedings. Ecotones:

introduction, scale and big sagebrush example.

Payne, J. F. 1980. A multi-site evaluation of pinyon-juniper chaining in Utah. Logan, UT: Utah State University. 77 p. Thesis.

Peters, E. F.; Bunting, S. C. 1994. Fire conditions pre- and post

occurrence of annual grasses on the Snake River Plain. In:

Monsen, S. B.; Kitchen, S. G., comps. Proceedings—ecology and

management of annual rangelands; 1992 May 18-21; Boise, ID.

Gen. Tech. Rep. INT-313. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 31-36.

Richardson, E. A.; Ashcroft, G. L.; Westrocck, J. K. 1981. Precipitation. In: Greer, D. C.; Gurgel, K. D.; Wahlquist, W. L.; Christy,

H. A.; Peterson, G. B., eds. Atlas of Utah. Provo, UT: Brigham

Young University Press: 66-67.
94 USDA Forest Service Proceedings RMRS-P-11. 1999

Soil Conservation Service. 1994. Plants. U.S. Department of Agriculture. Soil Conservation Service. 954 p.

Spomer, G. G.; Henderson, D. M. 1988. Use of UV absorption for

identifying subspecies of Artemisia tridentata. Journal Range

Management 41: 395-398.

Stevens, R.; McArthur, E. D. 1974. A simple field technique for

identification of some sagebrush taxa. Journal Range Management 27:325-326.

Sturges, D. L.; Nelsen, D. L. 1986. Snow depth and incidence of a

snowmold disease on mountain big sagebrush. In: McArthur, E.

D.; Welch, B. L., comps. Proceedings—symposium on the biology

of Artemisia and Chrysothamnus; 1984 July 9-13; Provo, UT.

Gen. Tech. Rep. INT-200. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station:

215-221.

Swanson, S. R.; Buckhouse, J. C. 1984. Soil and nitrogen loss from

Oregon lands occupied by three subspecies of big sagebrush.

Journal of Range Management 37: 298-302.

Tart, D. L. 1996. Big sagebrush plant associations of the Pinedale

Ranger District. Pinedale, WY: U.S. Department of Agriculture,

Forest Service, Bridger-Teton National Forest. 97 p.

 Winward, A. H. 1983. A renewed commitment to management of

sagebrush grasslands. In: Miller, R. F., ed. Management in the

sagebrush steppe. Special Report 880. Corvallis, OR: Oregon

State University Agriculture Experiment Station: 2-7.

Winward, A. H.; Tisdale, E. W. 1969. A simplified chemical method

for sagebrush identification. Note No. 11; Moscow, ID: University

of Idaho Forest, Wildlife, and Range Exp. Station. 2 p.

Winward, A. H.; Tisdale, E. W. 1977. Taxonomy of the Artemisia

tridentata complex in Idaho. Bull. No. 19. Moscow, ID: University

of Idaho Forest, Wildlife, and Range Experiment Station. 15 p.

Whisenant, S. G. 1990. Changing fire frequencies on Idaho’s Snake

River Plains: ecological and management implications. In:

McArthur, E. D.; Romney, E. M.; Smith, S. D.; Tueller, P. T.,

comps. Proceedings—symposium on cheatgrass invasion, shrub

die-off, and other aspects of shrub biology and management; 1989

April 5-7; Las Vegas, NV. Gen. Tech. Rep. INT-276. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Research Station: 4-10.
USDA Forest Service Proceedings RMRS-P-11. 1999 4

Population Biology

95

USDA Forest Service Proceedings RMRS-P-11. 1999 97

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

D. Terrance Booth is with USDA, Agricultural Research Service, High

Plains Grasslands Research Station, Cheyenne, WY 82009, U.S.A.; Yuguang

Bai is with Kamloops Range Research Unit, Agriculture and Agri-food

Canada, 3015 Ord Road, Kamloops, BC V2B 8A9, Canada; and James T. Romo

is with Department of Plant Sciences, University of Saskatchewan,

Saskatoon, Sask. S7N 5A8, Canada.

This paper is adapted from Bai and others 1998a.

Freezing Tolerance of Imbibed Winterfat

Seeds: Possible Mechanisms and Ecotypic

Differences

D. Terrance Booth

Yuguang Bai

James T. Romo

Abstract—We found survival of fully hydrated winterfat seeds

(Eurotia lanata (Pursh) Moq.) in diaspores harvested from two

U.S.A. and one Canadian location, and cooled to –30°C at 2.5°C h–1

was similar to that of uncooled seeds. Seed and diaspore morphology

appeared to contribute to freezing tolerance. The Canadian collection germinated more slowly at low temperatures and was more

sensitive to imbibition temperature x freezing stress interaction,

suggesting habitat correlated differences among the seed collections.

Warm winter and early spring temperatures and melting

snow often saturate the soil and rehydrate seeds capable of

absorbing water. This includes the seed-containing dispersal units (diaspores) of winterfat (Eurotia lanata (Pursh)

Moq.; Krascheninnikova lanata (Pursh) Mueese & Smit;

Ceratoides lanata (Pursh) J. T. Howell), which often begin

germination with snowmelt (Springfield 1972; Hilton 1941;

Woodmansee and Potter 1971; Booth 1987). However, snowmelt is frequently followed by a return to winter-like conditions that can expose fully hydrated, germinating seeds to

–20°C or colder temperatures (Becker and Alyea 1964).

Our knowledge of freezing in hydrated seeds has been

largely limited to studies of lettuce (Lactuca sativa L.)

(Junttila and Stushnoff 1977; Stushnoff and Junttila 1978;

Keefe and Moore 1981, 1983; Roos and Stanwood 1981).

These studies have identified two mechanisms of adaptation

to freezing stress. The first, supercooling, occurs when water

in the seed is cooled below the freezing point without the

formation of ice crystals. This can result from rapid cooling

(20o

C h–1) (Junttila and Stushnoff 1977; Ishikawa and Sakai

1982) or from the absence of nucleators. The second tolerance mechanism is freeze-desiccation of the embryo. This is

a redistribution of water inside the embryo to external ice

crystals that form during slow cooling (1 or 2°C h–1) (Keefe

and Moore 1981; Ishikawa and Sakai 1982). Seed mortality

due to freezing is generally the result of ice forming in the

embryo when the cooling rate exceeds the freeze-desiccation

rate (Junttila and Stushnoff 1977; Stushnoff and Junttila

1978; Keefe and Moore 1981). Winterfat seeds imbibe greater

amounts of water at 0 to 5°C than at warmer temperatures

(Bai and others 1999). Therefore, we wondered if seed

hydration at snowmelt increases winterfat seed mortality

from a freezing event.

Materials and Methods ___________

Seed Sources

Winterfat diaspores were hand collected in October, 1994,

from Matador, Saskatchewan, Canada; Sterling, Colorado,

U.S.A.; and Pine Bluffs, Wyoming, U.S.A. Detailed site descriptions were reported by Bai and others (1998a,b). Harvested diaspores were stored in paper bags at room temperature until used in experiments 4 to 6 months after harvest.

The mean dry weights of threshed seeds from Matador,

Sterling, and Pine Bluffs were 25, 23, and 18 mg per 100

seeds, respectively.

Seed Imbibition and Differential Thermal

Analysis (DTA)

Diaspores were imbibed at 0, 5, 10, and 20°C in darkness

to full hydration. We defined full hydration as the water

content 8 h before germination began. Full hydration required about 24 h at 20°C and ≥ 120 h at 0°C (Bai and others

1999). Ice crystal formation is an exothermic process where

heat is released (heat of fusion) at the rate of 80 cal/g

(Masterton and Slowinski 1978). Differential thermal analysis (DTA) detects the exotherm created by the heat of fusion.

Differential thermal analysis of fully hydrated diaspores

was accomplished by sealing the diaspores in 0.25 ml tin

capsules (LECO Corp., St. Joseph, MI), one diaspore per

capsule, with a thermocouple contacting the diaspore surface and another thermocouple outside the capsule (Bai and

others 1998b). Diaspore and air (outside the capsules) temperatures were recorded with a datalogger at 1 min. intervals. The resolution provided by the equipment was 1.66 nV

or 0.004°C. Exotherms were detected by comparing the

difference in temperatures inside and outside the capsules.

The encapsulated diaspores were held at 0°C for 1 h, then

cooled at 2.5°C h–1 from 0 to –30°C over a 12 h period.

Additionally, a sample of diaspores was cooled to –50°C, and

paired samples of diaspores, seeds, and embryos were cooled

to –30°C. Our experimental design was a randomized complete block with three replications arranged in blocks over

time and 10 diaspores per replicate.
98 USDA Forest Service Proceedings RMRS-P-11. 1999

Seed Germination and Seedling Vigor

Twenty diaspores per experimental unit were imbibed

and cooled as described above, retrieved from the freezer at

0, –6, –10, or –30°C, incubated at 0°C for 24 h, then at 5 or

20°C under 12 h light. Germination was counted at daily

intervals up to 14 d. Diaspores were considered germinated

if the radicle was ≥ 2 mm. Seedling axial lengths after 14 d

were obtained using a digitizing tablet, and the lengths used

as an indicator of seedling vigor (Booth and Griffith 1994). In

this paper we will concentrate on seedling axial length in

response to temperature treatments.

Data Analysis

Data were first analyzed with ANOVA or general linear

model (Snedecor and Cochran 1980) over the three seed

collections, and were also analyzed in each collection where

interactions occurred between seed collection and treatment. Data were further analyzed within each imbibition

temperature or cooling temperature. Statistical significance

was assumed at P≤0.05 and means were separated by using

LSD.

Results and Discussion __________

DTA Results and Freezing Tolerance

Between 0 and –30°C two exotherms were detected, indicating two separate ice-forming events at different temperatures. The first, or warmer, event is called the high temperature exotherm (HTE), and the second, or colder, event is the

low temperature exotherm (LTE). Temperatures at which

HTEs and LTEs occurred in fully hydrated seeds were

similar among collections. They differed by imbibition temperature (P<0.01) with seeds imbibed at 0 or 5°C having

HTEs and LTEs at warmer temperatures than those imbibed at 10 or 20°C (table 1). The average temperature for all

HTEs and LTEs was –4.6 and –17.6°C, respectively. The LTE

range was –3.7 to –26.8°C with 12% of all LTEs occurring

equal to or warmer than –10°C. The pattern of exotherm

occurrence is consistent with imbibition-temperature-based

differences in seed moisture of fully hydrated diaspores that

we have previously observed (Bai and others 1999).

When hydrated diaspores, threshed seeds, and embryos

from the Matador collection were cooled together, we observed both an HTE and an LTE for diaspores, but only one

exotherm for seeds and for embryos. Mean temperatures for

diaspore HTEs and LTEs were –6.2±0.16 and –20.5±0.77°C,

respectively. Mean temperatures for seed and embryo

exotherms were –21.3±0.79 and –14.9±0.82°C, respectively

(data not shown). No diaspores were observed to have more

than two exotherms, including those cooled to –50°C (data

not shown).

Although imbibition temperatures influenced the temperatures at which exotherms occurred, they did not affect

freezing-related seed mortality. This is a significant contrast with lettuce where greater seed water reduced freezing

tolerance (Roos and Stanwood 1981; Keefe and Moore 1983)

and where the formation of embryo ice is a fatal event

(Junttila and Stushnoff 1977; Stushnoff and Junttila 1978;

Keefe and Moore 1981).

To better understand freezing tolerance in hydrated winterfat seeds as compared to that of lettuce seeds, we present

a possible tolerance mechanism, a tentative model, embodying probable reasons why lettuce seeds are killed at –30°C

and winterfat seeds are not. The important points of logic

supporting our model are as follows:

1. Winterfat diaspores supercooled to –4 to –6°C, as indicated by the HTEs. In lettuce the HTE is caused by water

freezing inside the pericarp but outside the seed endosperm

(Junttila and Stushnoff 1977). Both an HTE and an LTE

occurred in winterfat diaspores, but only one exotherm was

observed for threshed seeds or embryos. This implies that ice

crystals forming between the pericarp and the bract wall or

between the testa and the pericarp wall, generate winterfat

HTEs.

2. When an HTE occurs depends on the size of a water

body (among other things) and the duration of cooling (Salt

1961). The winterfat diaspore bract-pericarp interface, with

its abundance of small hairs (Booth 1988), is an area where

a relatively large body of water is likely to exist when the

diaspore is hydrated. An accumulation of water at this hairy

surface is likely to promote the formation of ice crystals at

the relatively warm –4 to –6°C observed for the HTE.

3. The hairy surface of the winterfat pericarp appears to

be a safe (for the embryo) place for ice crystals to form. We

speculate that the ice crystals evident by an HTE initiate

Table 1—Temperatures (mean±SD) at which exotherms occurred for hydrated winterfat diaspores.

Diaspores were collected from Matador, Saskatchewan; Pine Bluffs, Wyoming, and

Sterling, Colorado, and were cooled at 2.5°C h–1. HTE: high temperature exotherm; LTE:

low temperature exotherm.

Imbibition temperature (°C)

Exotherm Collection 0 5 10 20

HTE Matador –4.3±0.6 –4.2±0.5 –5.1±0.7 –5.1±0.5

Sterling –4.1±0.4 –4.1±0.6 –5.0±0.8 –4.8±0.7

Pine Bluffs –4.0±0.4 –4.3±0.5 –4.7±0.6 –5.1±0.8

LTE Matador –15.1±5.4 –18.4±4.3 –19.9±4.6 –18.4±4.4

Sterling –14.6±5.5 –16.8±6.1 –20.0±4.8 –18.7±5.9

Pine Bluffs –14.0±6.5 –17.6±4.7 –17.9±6.1 –19.2±5.6
USDA Forest Service Proceedings RMRS-P-11. 1999 99

freeze-desiccating conditions by creating an osmotic gradient in which liquid water in the embryo moves to extraembryo ice crystals. Freeze desiccation is the means by

which hydrated seeds tolerate cooling below about –15°C

(Keefe and Moore 1981; Ishikawa and Sakai 1982), and we

suggest diaspore morphology promotes freeze desiccation of

the embryo.

4. Membrane permeability is a fundamental aspect of

freeze desiccation (Lyons and others 1979). The winterfat

seed testa is membranous and highly permeable (Booth and

McDonald 1994) and is unlikely to interfere with emigrating

water molecules.

5. The flat, peripheral-linear morphology of winterfat

seeds allows the highly permeable testa to surround critical

tissues—cotyledons, hypocotyl, and radicle and in a manner

that creates greater testa surface area compared to a sphere

or cylinder (fig. 1).

Therefore, we speculate that winterfat’s HTE represents

the initiation of a freeze-desiccation process that reduces the

amount of water in the seed embryo before an LTE occurs

(Ishikawa and Sakai 1982). Thus, it appears that winterfat

diaspore bracts and the peripheral-liner morphology (Atwater

1980) typical of chenopod seeds may contribute to freezing

tolerance in hydrated winterfat seeds. The difference between lettuce and winterfat’s ability to survive an LTE event

may also be in where LTE-producing ice forms. The place of

ice formation in hydrated seeds varies by species (Ishikawa

and Sakai 1982) and extra-organ freezing, as occurs between the cotyledons and endosperm of common privet

(Ligustrum vulgare L.) (Gazeau and Dereuddre 1980), may

cause mortality.

We noted that critical tissues of winterfat seeds are

adjacent to the highly permeable testa. This is not the case

for lettuce and privet that have linear and miniature embryo

morphologies (Atwater 1980) and more cylindrical and spherical gross morphologies. This means that lettuce and privet

embryos may not freeze desiccate as quickly as winterfat,

and that ice in lettuce or privet embryos may form larger

crystals than are formed in winterfat embryos. Winterfat

embryo ice may form between cells or within cells. Evidence

from Differential Scanning Calorimetry studies of pea

(Pisum sativum L.) and soybean (Glycine max Merr.) using

isolated seed tissues indicates that water may freeze in the

cell with no apparent damage to seed tissue (Vertucci 1988,

1989). [In animals, intracellular freezing was also thought

fatal, but an exception was found in an Antarctic nematode

Panagrolaimus davidi (Timm) (Wharton and Ferns 1995).]

Whether winterfat embryo ice forms in cells, between cells,

or between tissues and organs, it is reasonable to expect that

large crystals are more likely to inflict greater damage.

Thus, if winterfat diaspore and seed morphology does promote extra-embryo ice formation, and dehydration of critical

tissues, it would help explain why hydrated winterfat seeds

tolerate –30°C.

Ecotypic Differences

Germination, with some exceptions in the Matador collection, was ≥ 70% for all collections and was not significantly

reduced by cooling to –30°C. For all collections, germination

was not affected by imbibition temperature if diaspores were

Figure 1—Winterfat seed (A), and a transverse cross-section (B) (as indicated by the white line in (A)),

with a scanning electron microscope. The cross-section shows the relationship of surface area and critical

tissues. The testa is thin, transparent, and not visible as a separate entity in dry seeds such as these.

(Photograph (A) is x20. Photograph (B) is x60 and courtesy of Dr. William Wergin, USDA-ARS Electron

Laboratory, Beltsville, Maryland, U.S.A.)
100 USDA Forest Service Proceedings RMRS-P-11. 1999

not cooled below 0°C (data not shown). However, germination of the Matador and Sterling collections decreased at the

higher imbibition temperatures after the diaspores were

cooled to –6, –10, or –30°C when post-cooling incubation was

5°C.

Axial lengths from seeds cooled to –30°C was significantly

less than for other cooling regimes; but, there were several

exceptions (table 2). The U.S.A. collections appear to have

had a wider range of imbibition temperatures within their

ability to tolerate –30°C without reduced growth. Axial

length after incubation at 5°C was similar among seed

collections and imbibition temperatures where seeds were

not cooled below 0°C (table 2). With freezing stress, axial

length was greater for the Matador and Sterling collections

than for the Pine Bluffs collection (Bai and others 1998a).

Under the 20°C incubation temperature where seeds were

cooled below 0°C, seedling axial length was influenced by the

interaction of seed collection and imbibition temperature.

Seeds from the Matador collection had similar axial lengths

among imbibition temperatures (table 2), while the Sterling

collection axial length was greatest for seeds imbibed at

20°C, and lowest when imbibed at 5°C. The Pine Bluffs

collection had no consistent trend among incubation temperatures. Matador seeds were most sensitive of the three

seed collections to imbibition temperature in the presence of

freezing stress. This suggests habitat correlated differences

among seed collections and supports previous work on the

ability of shrub populations to evolve site-specific characteristics (Meyer and others 1989, 1990; Stutz 1982, 1989).

Table 2—Seedling axial lengths (mm) from hydrated winterfat diaspores of the Matador, Pine Bluffs, and Sterling collections

imbibed at four temperatures then exposed to four cooling regimes. Seeds were incubated at 5 or 20oC for 14 days after

cooling.

5°C 20°C

Cooling incubation incubation

regime (°C) Matador P.B. Sterling Matador P.B. Sterling

0°C Imbibition

0 34 b B 36 a A 38 a A 49 a A 47 a A 50 ab AB

–6 38 a A 32 b A 38 a A 56 a A 47 a A 51 b A

–10 40 a A 33 b A 34 b A 56 a A 48 a A 46 b A

–30 32 b A 30 b A 32 c A 36 b B 36 b A 38 c A

5°C Imbibition

0 36 a B 33 a A 33 a A 52 a A 46 a A 41 a C

–6 36 a A 36 a A 37 a A 56 a A 46 a A 49 a A

–10 37 a A 35 a A 39 a A 55 a A 49 a A 47 a A

–30 30 b A 33 a A 34 a A 37 b B 39 b A 40 a A

10°C Imbibition

0 40 a B 34 a A 38 a A 52 a A 39 a B 46 bc BC

–6 37 a A 34 a A 40 a A 54 a A 43 a A 50 a A

–10 35 a A 37 a A 37 a A 55 a A 45 a A 55 a A

–30 28 a A 34 a A 33 a A 43 a A 39 a A 42 c A

20°C Imbibition

0 43 a A 36 a A 39 a A 54 a A 48 a A 53 a A

–6 43 a A 34 a A 38 a A 55 a A 49 a A 50 a A

–10 40 ab A 37 a A 40 a A 53 a A 49 a A 53 a A

–30 34 b A 30 b A 33 a A 33 b B 35 a A 41 a A

1

Means with the same lower case letter are not significantly different at P≤0.05 within a imbibition temperature across cooling regimes (columns);

means with the same capital letter are not significantly different at P≤0.05 within a cooling regime across imbibition temperatures (column intervals).

Summary and Conclusions _______

We accept the hypothesis that fully hydrated winterfat

seeds are tolerant of –30°C events. We found that postfreezing seedling vigor varied by imbibition temperature;

therefore, we conclude that imbibition temperature influences freezing tolerance. We postulate that diaspore structure and the peripheral-linear morphology of the winterfat

seed contribute to freezing tolerance of hydrated seeds. We

have documented habitat-correlated differences among winterfat populations with respect to post-freezing vigor and the

effect of imbibition temperature on that response. Some

winterfat seeds are not negatively affected by a sequence of

melting snow resulting in seed hydration, followed by freezing stress (–30°C), then cool (5°C) temperatures. Other

seeds were found to survive this sequence, but freezing

damage was reflected in reduced germination rates, and

reduced seedling vigor such that these injuries may limit

field establishment or seedling survival.

References _____________________

Atwater, B.R. 1980. Germination, dormancy and morphology of the

seeds of herbaceous ornamental plants. Seed Science and Technology. 8: 523-573.

Bai, Y.; Booth, D. T.; Romo, J. T. 1998a. Winterfat (Eurotia lanata

(Pursh) Moq.) seedbed ecology: low temperature exotherms and

cold hardiness in hydrated seeds as influenced by imbibition

temperature. Annals of Botany. 81: 595-602.
USDA Forest Service Proceedings RMRS-P-11. 1999 101

Bai, Y.; Booth, D. T.; Romo, J. T. 1998b. Developmental stages of

winterfat germinants related to survival after freezing. Journal

of Range Management. 51: 709-713.

Bai, Y.; Booth, D. T.; Romo, J. T. [In press]. Imbibition temperature

affects winterfat (Eurotia lanata [Pursh] Moq.) seed hydration

and cold-hardiness response. Journal of Range Manage. 52.

Becker, C. F.; Alyea, J. D. 1964. Temperature probabilities in

Wyoming. Agricultural Experiment Station Bulletin 415, University of Wyoming, Laramie.

Booth, D. T. 1987. Contributions to the reproductive autecology of

winterfat (Eurotia lanata [Pursh] Moq.) with notes on direct

seeding methods. Ph.D. Dissertation, University of Wyoming,

Laramie.

Booth, D. T. 1988. Winterfat diaspore morphology. Journal of Range

Management. 41: 351-353.

Booth, D. T.; Griffith, L. W. 1994. Technical note: Measuring postgermination growth. Journal of Range Management. 47: 503-504.

Booth, D. T.; McDonald, M. B. 1994. Cation concentration in postimbibed winterfat seeds as influenced by imbibition temperature. Journal of Range Management. 47: 485-488.

Gazeau, C.; Dereuddre, J. 1980. Effects de refroidissement prolonges

sur la teneur en eau et la resistance au froid des tissus de la

Troene (Ligustrum vulgare L. Oleacees). CR Acad. Sci. Paris Ser

D. 290: 1443-1446.

Hilton, J. W. 1941. Effects of certain micro-ecological factors on the

germinability and early development of Eurotia lanata. Northwest Science. 15: 86-92.

Ishikawa, M.; Sakai, A. 1982. Characteristics of freezing avoidance

in comparison with freezing tolerance: a demonstration of extra

organ freezing. In: Li P. H., Sakai A., eds. Plant cold hardiness

and freezing stress Volume 2: proceedings. New York: Academic

Press: 325-340.

Junttila, O.; Stushnoff, C. 1977. Freezing avoidance by deep supercooling in hydrated lettuce seeds. Nature. 269: 325-327.

Keefe, P. D.; Moore, K. G. 1981. Freeze desiccation: a second

mechanism for the survival of hydrated lettuce (Lactuca sativa

L.) seed at sub-zero temperatures. Annals of Botany. 47: 635-645.

Keefe, P. D,; Moore, K. G. 1983. Freeze tolerance in hydrated

Lactuca sativa L. seed: A model to explain observed variation

between seed lots. Annals of Botany. 51: 373-383.

Lyons, J. M.; Raison, J. K.; Steponkus, P. L. 1979. The plant

membrane in response to low temperature; an overview. In: J.M.

Lyons and others (eds.). Low temperature stress in crop plants -

the role of membrane: proceedings. Academic Press, New York:

1-24.

Masterton, W. L.; Slopwinski, E. L. 1978. Chemical principles with

qualitative analysis. W. B. Saunders Company, Philadelphia.

803 p.

Meyer, S. E.; McArthur, E. D.; Jorgensen, G. L. 1989. Variation in

germination response to temperature in rubber rabbit brush

(Chrysothamnus nauseosus: Asteraceae) and its ecological implications. American Journal of Botany. 76: 981-991.

Meyer, S. E.; Monsen, S. B.; McArthur, E. D. 1990. Germination

response of Artemisia tridentata (Asteraceae) to light and chill:

Patterns of between-population variation. Botanical Gazette.

151: 176-183.

Quamme, H. A. 1991. Application of thermal analysis to breeding

fruit crops for increased cold hardiness. HortScience. 26: 513-517.

Roos, E. E.; Stanwood, P. C. 1981. Effect of low temperature, cooling

rate and moisture content on seed germination of lettuce. Journal

of The American Society for Horticultural Science. 106: 30-34.

Salt, R. W. 1961. Principles of insect cold-hardness. Annual Review

of Entomology. 6: 55-74.

Snedecor, G. W.; Cochran, W. C. 1980. Statistical methods. 7th

edition. Ames, Iowa: Iowa State University Press.

Springfield, H. W. 1972. Winterfat seeds undergo after-ripening.

Journal of Range Management. 24: 395-397.

Stushnoff, C.; Junttila, O. 1978. Resistance to low temperature

injury in hydrated lettuce seed by supercooling. In: Li PH, Sakai

A, eds. Plant cold hardiness and freezing stress: proceedings.

New York: Academic Press: 241-247.

Stutz, H. C. 1982. Broad gene pools required for disturbed lands. In:

Aldon, E. F.; Oaks E.F., eds. Symposium reclamation of mined

lands in the Southwest. New Mexico Chapter, Soil Conservation

Society of America, P.O. Box 2142, Albuquerque, New Mexico:

113-118.

Stutz, H. C. 1989. Evolution of shrubs. In: McKell, C. M. ed, The

biology and utilization of shrubs. Academic Press Inc., San Diego,

California: 323-340.

Thompson, P. A. 1981. Ecological aspects of seed germination. In:

Thompson J. R., ed. Advances in research and technology of

seeds: proceedings. Center for Agricultural Publishing and Documentation, Amsterdam: 9-42.

Vertucci, C. W. 1988. Thermal transitions associated with viability

of seeds exposed to subfreezing temperatures. In: Earnest C. M.,

ed. 17th North American Thermal Analysis Society Conference:

Proceedings. Lake Buena Vista, Florida: 229-223.

Vertucci, C. W. 1989. Relationship between thermal transitions and

freezing injury in pea and soybean seeds. Plant Physiology. 90:

1121-1128.

Wharton, D. A.; Ferns, D. J. 1995. Survival of intracellular freezing

by the Antarctic nematode Panagrolaimus davidi. Journal of

Experimental Biology. 198: 1381-1387.

Woodmansee, R. G.; Potter, L. D. 1971. Natural reproduction of

winterfat (Eurotia lanata). Journal of Range Management. 24:

24-30.
102 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Inés Ibáñez is a Ph.D. student in Ecology, Department of Biology, San

Diego State University, San Diego, CA 92182. Eugene W. Schupp is an

Associate Professor of Plant Ecology, Department of Rangeland Resources,

Utah State University, Logan, UT 84322. Janis L. Boettinger is an Associate

Professor of Pedology in the Department of Plants, Soils, and Biometeorology,

Utah State University, Logan, UT 48320.

Successional History of a Curleaf Mountain

Mahogany Stand: a Hypothesis

Inés Ibáñez

Eugene W. Schupp

Janis L. Boettinger

Abstract—Environmental conditions affecting emergence and early

seedling establishment of the tree Cercocarpus ledifolius were

studied. Natural emergence was highest in open interspaces, intermediate under shrubs, and lowest under trees. Experiments showed

litter inhibited seedling emergence, but favored seedling survival.

Drought and herbivory affected seedling survival, but effects varied

between years depending on environmental conditions. This study

shows there is a seed-seedling conflict in this species which probably

extends into later stages. The tree microhabitat inhibits emergence,

but improves first year survival. Later, however, it is probably too

competitive for older juveniles, but because of the soil it may be the

best site for new adult recruitment once the tree dies.

Curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.,

Rosaceae) is an evergreen, montane xerophyte ranging from

2-9 m or more in height. It is widely spread in the mountain

brush zone of the Intermountain West of North America,

where it occurs on soils with low fertility on hot, dry, rocky

ridges and slopes with south to west aspects (Brotherson

1990; Davis and Brotherson 1991). Curlleaf mountain mahogany is a choice winter forage species for big game because

it is evergreen and has high protein levels and digestibility

(Scheldt and Tisdale 1970). Also, because it fixes nitrogen,

Curlleaf mountain mahogany increases nitrogen levels in

the nutrient-poor soils where it grows (Lepper and Fleschner

1977).

A major problem is that most mountain mahogany stands

are dominated by older trees with practically unreachable

crowns (Mitchell 1951) and little recruitment of new individuals (Scheldt and Tisdale 1970; Schultz and others 1991).

In Utah, many of the stands do not have trees <20 years old

(Davis 1976). It is a difficult species to manage; it does not

sprout after burning or chaining and it is hard to establish

from seed (Davis and Brotherson 1991). Factors that may

limit natural seedling establishment include allelopathy of

mountain mahogany litter, competition for water and soil

resources, and seedling herbivory (Davis and Brotherson

1991). What is needed is much more information on critical

seed and seedling stages.

The objective of this study was to determine the roles of

litter, soil surface conditions, microhabitats, water limitation, and herbivory on mountain mahogany seedling recruitment, and to evaluate soil genesis in the community. A

better understanding of the environment and mechanisms

that affect mountain mahogany recruitment may have a

significant relevance when managing these communities.

Promoting and facilitating seedling recruitment of this species may be a key factor for managing recovery of these

stands, and thus browsing habitat.

Study Site______________________

The study was conducted in northeastern Utah, Cache

County, USA in the Cache National Forest at 41° 57′ N,

111° 28′ W at an elevation of 2,350-2,500 m on a 35%

southwest-facing slope. Mountain mahogany is the dominant tree species, and isolated Douglas-fir (Pseudotsuga

menziesii) are present. Mountain big sagebrush (Artemisia

tridentata var. vaseyana) and snowberry (Symphoricarpos

spp.) are the most common shrubs. No established mountain mahogany seedlings and few juveniles have been

observed. The three major microhabitats in the stand are:

“open,” in open interspaces between woody vegetation;

“shrub,” beneath sagebrush canopies; and “tree,” beneath

mountain mahogany canopies.

Soils and Other Environmental

Characteristics _________________

Although all soils were skeletal and deeper than 1 m,

microhabitats differed in many characteristics. Phosphorous, nitrogen, and organic carbon were significantly higher

in upper layers of tree soils than in shrub and open soils,

indicating much greater organic matter input by trees

(fig. 1). In addition, all had the same vertical distribution:

higher in surface horizons, decreasing with depth. Tree soils

also had the lowest near-surface pH, again reflecting higher

organic matter input (table 1). Additionally, relative to open

interspaces, trees had greater shading, lower soil and air

temperatures, more litter, a much deeper and better developed calcic horizon, and, because of litter and organic

matter, higher expected water infiltration rate (table 1). The

shrub microhabitat was generally intermediate, but much

more similar to the open than the tree microhabitat.

The degree of pedogenesis is greatest under trees. Depth

and stage of CaCO3 accumulation and variation in organic

carbon with depth suggest a period of pedogenesis under the

influence of tree canopies on the order of centuries or more.
USDA Forest Service Proceedings RMRS-P-11. 1999 103

From the perspective of tree recruitment in this dry, harsh

site, the tree microhabitat may be most favorable, the open

microhabitat least favorable, but little information exists on

conditions favoring seedling recruitment. In the remainder

of this paper we present an overview of our studies on

seedling emergence and survival.

Litter and Microhabitats __________

Methods

For natural emergence we counted seedlings emerging in

50, 30 x 30 cm-quadrats in each of the major microhabitats

and compared numbers of seedlings (square root-transformed)

with ANOVA (SAS 1994, MIXED procedure) with location as

a random effect and microhabitat as a fixed effect and with a

Tukey-Kramer adjustment to control for Type I error. Results

were compared with previously collected seed accumulation

data from the same site (Russell and Schupp 1998).

To better evaluate the effects of litter, soil surface condition,

and microhabitat, we conducted an experiment with four

seedbed treatments and five microhabitats. Seedbed treatments were: (1) undisturbed soil without litter, (2) undisturbed soil with seeds sown over litter, (3) undisturbed soil

with seeds sown under litter, and (4) manually disturbed soil

surface without litter. Microhabitats were: (1) beneath clumps

of mountain mahogany trees, (2) beneath isolated mountain

mahogany trees, (3) beneath sagebrush canopies, (4) beneath

snowberry canopies, and (5) open interspaces. For each replicate, we sowed 200 seeds in a 30 x 30 cm plot protected by a

1.2-cm mesh hardware-cloth cage with a strip of nylon window

screening at the base to exclude mammals and crawling

insects. Additionally, in order to exclude naturally dispersing

seeds, we placed a screen over each cage.

Caged plots were cleared of litter and surface seeds, then

seed-free litter (mean mass for microhabitat) was added for

litter treatments and soil was disturbed to 2 cm for surface

disturbance. Seeds were sown fall 1995 with 5 replicates/

treatment combinations and seedlings were recorded through

spring 1996. We analyzed square root-transformed values

with ANOVA (SAS 1994, GLM procedure, alpha = 0.1), and

then made three planned contrasts: (1) with versus without

litter, (2) seeds on versus beneath litter, and (3) disturbed

versus undisturbed soil.

We studied the effect of litter on seedling survival beneath

10 mountain mahogany trees using three amounts of litter:

bare soil, mean amount (249 g/900 cm2

), and 2 x mean

amount (498 g/900 cm2

). We planted 10 seedlings in each

litter treatment beneath each replicate tree. We germinated

seeds following Kitchen and Meyer (1990) and transplanted

seedlings into Lännen PaperpotsTM (2.8 cm diameter x 10 cm

length) filled with soil from the stand. After 5 weeks, when

the first leaves had emerged, we transplanted them, and

recorded survival weekly until snowfall. We used survival

analysis (SAS 1994, LIFEREG procedure, likelihood ratio

test, Weibull distribution) to test for differences among

treatments by comparing predicted median survival values;

that is, time to 50% mortality.

Figure 1—Phosphorous (mg/g), nitrogen (%), and organic carbon (%)

content of representative soils in open, shrub, and tree microhabitats by

depth from surface. Soils were analyzed using standard procedures (see

Ibáñez 1998).

Table 1—Summary of other important environmental characteristics of

the three major microhabitats in the study site from Ibáñez

(1998). For litter, values followed by different letters were

significantly different (alpha = 0.05).

Microhabitat

Characteristic Tree Shrub Open

Shading Greatest Intermediate Least

Temperature Lowest Intermediate Highest

Litter (kg/m2) 2.50a 0.27b 0.12c

Calcic horizon Deep, Shallower,

well-developed less well-developed

Expected infiltration High Lower Lower

pH 7.55 7.84 7.73
104 USDA Forest Service Proceedings RMRS-P-11. 1999

Results

Microhabitats did not differ in numbers of seedlings naturally emerging (F = 0.48; df = 2, 8; P = 0.661). In contrast, the

number of seeds that accumulated on the ground, in the

litter, and in the top 5 cm of soil at this site differed

dramatically among microhabitats, with most seeds under

mountain mahogany and least in open interspaces (Russell

and Schupp 1998).

Only seedbed treatment affected seedling emergence

(table 2). The nonsignificant microhabitat x seedbed interaction shows a consistent treatment effect across microhabitats. Treatments without litter had greater emergence

than treatments with litter (table 2, fig. 2). Neither the two

treatments with litter nor the two treatments without litter

differed significantly (table 2, fig. 2).

Seedling survival was significantly greater with than

without litter (both Chi-square ≥ 6.57, df = 1, P ≤ 0.010). The

two litter treatments, however, did not differ from each

other (Chi-square = 0.21, df = 1, P = 0.647).

Water, Herbivory, and

Microhabitats ___________________

Methods

Effects of water limitation, herbivory, and microhabitat

on seedling survival were evaluated in a 2 x 2 x 3 factorial

experiment. Water treatments were: control with natural

precipitation and water supplementation with natural precipitation plus weekly addition of enough water to equal

estimated precipitation during the very wet year of 1983.

Herbivory treatments were: with and without protection

from aboveground insect (synthetic pyrethrin insecticide,

InterCept-H&G® at 2 ml/l water) and vertebrate herbivores

(1-cm mesh hardware cloth cage, 30 x 30 cm) combined.

Microhabitats were open, shrub, and tree.

In early July, 6-week-old seedlings were transplanted

into 10 sites, 10 seedlings/treatment combination/site in a

30 x 30-cm quadrat. For one week we watered all seedlings

every other day and covered them with a light mesh cloth

(Plant Guard®) to facilitate establishment. We then removed the cloth and only watered plants in the water

addition treatment. On these dates we also applied insecticide (2 ml of mixture/quadrat) for herbivory protection,

sprayed herbivory control plants with water, and recorded

survival. The experiment continued through summer and

early fall for a total of 12 weeks until snowfall, and was

replicated in 1996 and 1997.

Statistical analysis of the data for survival was performed

as described in the seedling survival experiment above.

Results

Results differed between years. In 1996, all main effects

and interactions were significant (table 3, fig. 3a). Water

supplementation increased survival, but not equally in all

microhabitats; while watering greatly increased survival

beneath trees it had little effect in the open. Similarly,

herbivory protection enhanced survival, but the increase was

especially evident beneath trees. The significant water x

herbivory interaction was evident in all three microhabitats,

with herbivory protection especially beneficial with water

supplementation. The 3-way interaction was significant

because the strength of the water x herbivory interaction

was very weak in open interspaces and very strong beneath

trees. Overall, 19% of seedlings survived the summer. Although mortality rate was greatest early, mortality continued through the summer.

In 1997, site was significant and microhabitat was marginally significant, and all interactions except water x herbivory were significant or nearly so (table 4, fig. 3b).

Although water supplementation did not increase survival,

the microhabitat x water interaction was highly significant;

open sites had the highest survival with water supplementation but the lowest survival with natural precipitation.

Table 2—ANOVA (SAS GLM procedure, alpha = 0.10), results from

experimental seedling emergence data, including the three

planned contrasts.

Source df SS F P

Site 4 12.13 0.68 0.606

Microhabitat 4 14.65 0.83 0.513

Seedbed treatment 3 34.04 2.56 0.062

No litter vs. litter 1 34.91 7.77 0.007

Seeds on vs. beneath litter 1 0.02 0.01 0.944

Disturbed vs. undisturbed soil 1 0.02 0.00 0.945

Microhabitat*seedbed 12 57.45 1.08 0.390

Error 71 314.88

Figure 2—Back-transformed mean seedling emergence (+1 SE) in the four litter and soil surface

treatments. NL-US = no litter, undisturbed soil; SOLUD = seeds over litter, undisturbed soil; SUL-US =

seeds under litter, undisturbed soil; and NL-DS = no

litter, disturbed soil. Bars marked with different letters are significantly different.
USDA Forest Service Proceedings RMRS-P-11. 1999 105

Similarly, herbivory protection did not increase survival,

but the microhabitat x herbivory interaction was significant.

Overall, 27.5% of the seedlings survived during this wetter

year. Mortality rate was greatest early, but in contrast to

1996, it had virtually ended by the middle of the season.

Considering all treatment combinations, in both years

survival in most combinations was fairly similar with the

exception of a single treatment standing out with exceptionally high survival (fig. 3). In both years, the combination of

water supplementation and herbivory protection was required to yield this high level of survival. Years differed,

however, in which microhabitat this occurred: tree microhabitat in 1996 and open microhabitat in 1997.

Discussion _____________________

The major microhabitats differed in environmental conditions, especially soil characteristics. Tree soils had the

greatest degree of development, while shrub soils differed

little from open soils. Tree soil had much greater nutrient

and organic matter content, lower surface pH, and a much

deeper, better-developed calcic horizon than shrub and open

soils. Trees appear to have greatly modified the soil where

they have grown over long periods of time while shrubs have

had little effect on their soils. This soil microhabitat diversity may play an important role in plant recruitment and

successional dynamics.

Numbers of seedlings naturally emerging were similar

across microhabitats. Comparing these results to patterns of

seed accumulation, however, suggests emergence rates were

highest in open interspaces and lowest beneath trees. Further, experiments demonstrated that litter inhibits emergence of this species. In the field, litter reduced emergence

across all microhabitats, and in the greenhouse (Ibáñez

1998), seeds planted under a thick litter layer (7 cm) produced fewer seedlings than seeds planted at the top or in the

middle of the litter layer, and fewer seedlings than seeds

planted under a thin (3 cm) litter layer or without litter.

Soil surface conditions (disturbed vs. undisturbed soil surface) did not affect emergence rates. Similarly, emergence did

not differ among microhabitats, contrary to expectations from

Figure 3—Predicted median seedling survival during summer 1996 and 1997. Treatment combinations are W+, water

supplementation; W–, no water supplementation; H+, herbivory protection; and H–, no herbivory protection.

Table 3—Survival analysis for seedling survival during the dry summer of 1996. Log Likelihood for

LogLogistic = –1,038.56.

Variable DF Estimate SE Chi-square P

Intercept 1 2.79 0.19 226.67 0.0001

Site 9 79.50 0.0001

Microhabitat 2 74.84 0.0001

Water 1 12.80 0.0003

Herbivory 1 8.36 0.0038

Site*microhabitat 18 68.72 0.0001

Site*herbivory 9 55.00 0.0001

Site*water 9 34.29 0.0001

Microhabitat*water 2 12.72 0.0017

Microhabitat*herbivory 2 16.75 0.0002

Water*herbivory 1 12.25 0.0005

Microhabitat*water*herbivory 2 8.69 0.0130

Scale parameter 1 0.41 0.01
106 USDA Forest Service Proceedings RMRS-P-11. 1999

natural emergence. However, this result may again indicate

lowest percent emergence under trees and highest in the open

if there is a viable seedbank, since seed accumulation was

greatest under trees and least in the open.

In contrast to its negative influence on emergence, litter

beneath trees increased survival. In the dry year of 1996,

water supplementation and herbivory protection also increased survival, and their combination with the tree microhabitat was necessary for high survival. On the other hand,

in the wetter year of 1997, water supplementation and

herbivory protection were not significant as main effects,

although the most successful treatment was again a combination of both, but this time in the open microhabitat.

Implications for Recruitment in

Existing Stands _________________

It appears that the balance between facilitation by and

competition with existing adults varies with life history

stage of the juvenile recruit (Walker and Vitousek 1991).

The best environment for mountain mahogany emergence is

open interspace with sparse litter and adequate light and

temperature for germination. During the next stage, seedling establishment and survival, open interspaces are probably too dry for seedlings in most years. Only in very wet

years and with low herbivory are open interspaces favorable

for establishment; even then, seedlings may be unlikely to

survive the coming drier years. In most years, the tree

canopy and associated soil and litter favor seedling establishment by reducing temperatures, providing adequate

nutrients, capturing and retaining water, and perhaps also

by hiding seedlings from herbivores. Finally, Schultz et al.

(1996) observed that older seedlings and juveniles preferentially grew under sagebrush canopies, suggesting this

microhabitat may be best during these stages. The tree

microhabitat likely becomes too competitive as juveniles

grow larger, and the exposed open interspaces with poorly

developed soils are too dry. Perhaps the light shading and

hydraulic lift (Caldwell et al. 1991) bringing water to surface

soils combined with less competition makes shrubs most

suitable for longer-term juvenile survival. But where and

under what conditions recruitment of new adults occurs is

uncertain (see next section). Our work does, however, support the idea that conflicts between life history stages (Schupp

1995)—e.g., conditions good for emergence are bad for survival—play a crucial role in recruitment.

Preliminary results suggest a possible management strategy. If tree soil is most suitable (but see next section) but

adult trees inhibit recruitment, cutting adults or burning

stands may provide seedlings with desirable sites for recruitment, although burning may deplete seed availability.

Also, planting of nursery-grown seedlings at edges of tree

soil patches may optimize the use of these potentially

favorable sites. It should be cautioned, however, that much

remains to be learned and these are only preliminary

recommendations.

Succession in a Mountain

Mahogany Stand: Speculation

and Questions __________________

When mountain mahogany first colonized the site, conditions may have been more favorable despite being nutrientpoor because it was probably sparsely vegetated and with

little competition. Mountain mahogany could establish in

these conditions because of associations with nitrogen-fixing actinorhizae and nutrient-acquiring mycorrhizae. Initial establishment may have been facilitated by shrubs.

Through time, we suggest that trees, by adding organic

matter and nutrients, may improve soil conditions to the

point that competitively superior species will invade and

replace mountain mahogany. In this regard, healthy 2-3 m

Douglas-fir are presently growing beneath a few mountain

mahogany in this stand.

A major remaining question revolves around the age of

adults in the stand, and thus population processes that have

occurred to this point. We have not aged our trees, but based

on basal diameters and published accounts, our trees may be

as little as 220 years old (Davis and Brotherson 1991) or as

much as 1,800 years old (Schultz et al. 1990). If the younger

age is correct, the degree of tree soil development suggests

recruitment has been occurring repeatedly in the same sites

and not elsewhere—new recruitment occurs only following

death of existing adults. If, however, the older age is correct

Table 4—Survival analysis for seedling survival during the wet summer of 1997. Log Likelihood for

LogLogistic = –1,038.56.

Variable DF Estimate SE Chi-square P

Intercept 1 0.04 0.26 0.03 0.0001

Site 9 66.23 0.0001

Microhabitat 2 4.62 0.0994

Water 1 0.72 0.3956

Herbivory 1 0.30 0.5834

Site*microhabitat 18 56.14 0.0001

Site*herbivory 9 19.01 0.0906

Site*water 9 19.65 0.0202

Microhabitat*water 2 10.03 0.0066

Microhabitat*herbivory 2 7.20 0.0273

Water*herbivory 1 0.19 0.6659

Microhabitat*water*herbivory 2 5.24 0.0730

Scale parameter 1 0.68 0.02
USDA Forest Service Proceedings RMRS-P-11. 1999 107

we may still be witnessing the initial invasion of the site. We

predict the same eventual outcome in either case, succession

to a new community, but implications for mountain mahogany recruitment are very different. In the former scenario, changes in soils due to trees benefit recruitment of

mountain mahogany for at least several generations before

superior competitors invade, while in the later scenario

conditions may shift from favoring mountain mahogany to

favoring superior competitors in only a single generation.

References _____________________

Brotherson, J. D. 1990. Mineral-nutrient relationships of the mountain mahoganies (Cercocarpus). In: Johnson, K. L., ed. Proceedings of the fifth Utah shrub ecology workshop. Logan, UT: Utah

State University: 43-59.

Caldwell, M. M.; Richards, J. H.; Beyschlag, W. 1991. Hydraulic lift:

ecological implications of water efflux from roots. In: Atkinson,

D., ed. Plant root growth: an ecological perspective. British

Ecological Society Special Publication No. 10. Oxford, UK:

423-436.

Davis, J. N. 1976. Ecological investigations in Cercocarpus ledifolius

Nutt. Communities of Utah. M.S. Thesis. Provo, UT: Brigham

Young University.

Davis, J. N.; Brotherson, J. D. 1991. Ecological relationships of

curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.) communities in Utah and implications for management. Great Basin

Naturalist. 51: 153-166.

Ibáñez, I. 1998. Early recruitment in curlleaf mountain mahogany

(Cercocarpus ledifolius Nutt.) M.S. Thesis. Logan, UT: Utah

State University.

Kitchen, S. G.; Meyer, S. E. 1990. Seed dormancy in two species of

mountain mahogany (Cercocarpus ledifolius and Cercocarpus

montanus). In: Johnson, K. L., ed. Proceedings of the fifth Utah

shrub ecology workshop. Logan, UT: Utah State University:

27-41.

Lepper, M. G.; Fleschner, M. 1977. Nitrogen fixation by Cercocarpus

ledifolius (Rosaceae) in pioneer habitats. Oecologia. 27: 333-338.

Mitchell, G. E. 1951. The status of browse on range of eastern

Washington and eastern Oregon. Journal of Range Management.

4: 249-252.

Russell, S. K.; Schupp, E. W. 1998. Effects of microhabitat patchiness

on patterns of seed dispersal and seed predation of Cercocarpus

ledifolius (Rosaceae). Oikos. 81: 434-443.

SAS. 1994. SAS software: changes and enhancements, Release 6.10.

Cary, NC: SAS Institute Inc.

Scheldt, R. S.; Tisdale, E. W. 1970. Ecology and utilization of curlleaf

mountain mahogany in Idaho. Station Note No. 15. Moscow, ID:

University of Idaho.

Schultz, B. W.; Tausch, R. J.; Tueller, P. T. 1991. Size, age and

density relationships in curlleaf mountain mahogany (Cercocarpus

ledifolius) populations in Western and Central Nevada: competitive implications. Great Basin Naturalist. 51: 183-191.

Schultz, B. W.; Tausch, R. J.; Tueller, P. T. 1996. Spatial relationships among Cercocarpus ledifolius (curlleaf mountain mahogany). Great Basin Naturalist. 56: 261-266.

Schultz, B. W.; Tueller, P. T.; Tausch, R. J. 1990. Ecology of curlleaf

mahogany in western and central Nevada: community and population structure. Journal of Range Management. 43: 13-20.

Schupp, E. W. 1995. Seed-seedling conflicts, habitat choice, and

patterns of plant recruitment. American Journal of Botany. 82:

399-409.

Walker, L. R.; Vitousek, P. M. 1991. An invader alters germination

and growth of a native dominant tree in Hawaii. Ecology. 72:

1449-1455.
108 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

J.L. Downs is Research Scientist, Ecology Group, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352. R.A. Black is Professor

of Botany, Department of Botany, Washington State University, Pullman,

WA 99164-4238.

Leaf Surface Characteristics and Gas

Exchange in Artemisia tridentata subspecies

wyomingensis and tridentata

J. L. Downs

R. A. Black

Abstract—Leaf surface and gas exchange characteristics were

examined in 3-year old plants of two subspecies of big sagebrush

(Artemisia tridentata) growing in a common garden in southeastern

Washington. Scanning electron microscopy (SEM) and subsequent

image analysis revealed larger cell size in the tetraploid Wyoming

big sagebrush (subspecies wyomingensis) resulting in larger stomata. In the diploid basin big sagebrush (subspecies tridentata),

epidermal cells are smaller, so a significantly greater number of

trichomes and stomata occur per unit leaf area.

Photosynthetic rates measured in spring and summer months

were not significantly different between subspecies; however, basin

big sagebrush consistently exhibited higher transpiration rates.

Wyoming big sagebrush with fewer stomata and trichomes per unit

leaf may more efficiently regulate gas exchange processes under

high evaporative demand.

Big sagebrush (Artemisia tridentata) is a dominant shrub

species occurring in semi-arid, shrub-steppe ecosystems

across the Intermountain West. A complex interaction of

available soil water, temperature, and soil type and depth

influence how subspecies of this taxon are partitioned across

the landscape. Of the two subspecies considered here, Wyoming big sagebrush (subspecies wyomingensis) occupies

more xeric habitats and is often found on hillsides in shallow

soils (Schultz 1986). Basin big sagebrush (subspecies tridentata) is usually found in more mesic habitats along draws

and on deep well-drained soils. Wyoming big sagebrush (a

tetraploid) (McArthur and others 1981) is usually smaller

(<1 m tall) than the diploid Basin big sagebrush, which may

reach heights of 2-3 m. At the cellular level, however, the

polyploid subspecies follows the gigas syndrome, and exhibits more robust and larger anatomy. These differences in cell

size result in differences in leaf surface characteristics that

may influence gas exchange processes and plant function.

The increased number of chromosomes found in polyploid

plants effectively increases the cell size and such larger cells

often have higher photosynthetic capacity per cell than

smaller cells (within taxa) (Dean and Leech 1982; Warner

and Edwards 1988; Warner and Edwards 1993). Changes in

stomatal density and leaf cell anatomy can affect the physical diffusion rates of CO2 and H2O and thus affect the

photosynthetic rate and conductance per unit leaf area. Our

objectives in this study were to quantify and describe the

differences in leaf surface characteristics between subspecies that may contribute to differences in gas exchange

characteristics. Such differences may be key to segregation

of these subspecies across environmental gradients.

Methods _______________________

Big sagebrush plants examined in this study were grown

from seedlings transplanted to a common garden on the

Fitzner Eberhardt Arid Lands Ecology Reserve on the

Hanford Site in southeastern Washington. The common

garden, which is located at an elevation of 300 m above sea

level in silt-loam soils, lies within the big sagebrush/bluebunch wheatgrass (Pseudoroegnaria spicata) association.

The site receives annual average precipitation of 20 cm, twothirds of which falls during the winter months (Rickard and

others 1988). Winter precipitation was above average at the

study site during the measurement year (from October 1996

through March 1997) and totaled more than 26 cm (Hoitink

and Burk 1998).

Plants used in this study were grown from seeds of Basin

big sagebrush and Wyoming big sagebrush collected at elevations of 120 to 150 m above sea level in the lower Columbia

Basin (Benton County, Washington). Within the garden, big

sagebrush is planted at approximately 3-m spacing. Throughout the duration of this study, a 1-m diameter buffer around

each big sagebrush plant was maintained free of competing

plants.

Leaf Surface Examination

Winter persistent and ephemeral spring leaves were collected from five, 3-year old plants of each subspecies in the

common garden. Because the tomentose trichomes on big

sagebrush leaves occlude any view of the actual leaf surface,

trichomes were removed by appressing the leaf surface to

plastic adhesive tape and subsequently pulling the leaf off

the tape.

The leaves were placed in fixative (FAA, 10% formalin,

85% ehtanol, 5% glacial acetic acid) in the field and stored

until dehydration and processing. Leaf material was dehydrated in sequential dilutions of ethanol and processed

through critical point drying under pressure (Bozzola and

Russell 1992). Intact leaves were mounted on studs and then

sputter-coated with gold for examination using a scanning
USDA Forest Service Proceedings RMRS-P-11. 1999 109

electron microscope. Polaroid photos were taken of SEM

images at 300 to 500x magnification for three separate

sample areas of the epidermis for each leaf examined.

Photographs were scanned and converted to digital images for analysis using NIH-Image (National Institute of

Health). On each image, individual stomata were identified

and digitized to obtain the area of the stomatal complex and

the number of stomata per unit leaf area. In addition, the

base of each glandular or nonglandular trichome, was identified on the image and counted. Mean values for leaf surface

characteristics were tested for statistical differeces between

subspecies using Student’s t-tests (α <0.05).

Gas Exchange Measurements

Plant gas exchange was measured at 2- to 3-week intervals during the spring and summer months of 1997 using a

LiCor 6200 gas exchange system. Measurements were taken

between 0700 hours and 1300 hours on terminal branches to

determine maximal conductance rates and concurrent rates

for photosynthesis and transpiration. Three to five replicate

plants of each subspecies were sampled over 2 to 4 days. At

the end of each sampling interval, leaf material that had

been enclosed in the gas-exchange system cuvette was clipped

and the leaf area for each measurement was determined for

calculation of gas exchange rates.

Predawn and midday xylem water potentials were measured at each sampling interval using standard pressure

bomb techniques (Ritchie and Hinckley 1975) to determine

plant water status for each subspecies.

Gas exchange data were pooled into three measurement

periods during the growing season (May, June-July, and

August). Statistical analyses were accomplished using analysis of variance (ANOVA) techniques conducted for each

measurement period. The ANOVA was set-up as a single

factor design with subsampling (within subspecies, repeated

observations on an individual plant are treated as

subspamples) and measurement period as a covariate (Neter,

Wasserman and Kutner 1990). Differences between subspecies were deemed significant for p <0.05.

Results and Discussion __________

Big sagebrush leaves are covered with a dense, shielding

mat of tomentose trichomes as shown in fig. 1a and 1b. Both

glandular and T-shaped hair trichomes cover the surface.

Schultz (1986) described the two types of trichomes on

sagebrush leaf surfaces: the glandular trichomes occurring

in pits are biseriate, eight-celled and contain the liquids that

give sagebrush its characteristic odor; the leaf hairs are

uniseriate, two-celled and filled with air. When these trichomes are removed, SEM revealed a complex leaf surface

with stomata that are anomocytic (irregular-celled, no

subsidiary cells are present) and amphistomatous leaves

(fig. 2a,b). The epidermal cells are very irregular and the

microrelief of the epidermal layer surface of the leaf appears

almost wrinkled or folded with stomata and hairlike trichomes occurring on the raised areas and evidence of glandular trichomes in low almost crypt-like invaginations or pits.

Guard cell complexes appear slightly raised relative to other

epidermal cells. The distribution of stomata across the leaf

a

Figure 1—Tomentose trichomes covering the leaf

of basin big sagebrush at (a) 20x magnification, and

(b) 130x magnification.

b
110 USDA Forest Service Proceedings RMRS-P-11. 1999

surface is irregular with fewer stomata occurring at the leaf

margins and over major leaf veins.

Analysis of images indicates significant differences in

stomatal densities between big sagebrush subspecies. The

diploid basin big sagebrush has nearly 40% more stomata

per square cm of leaf area than the tetraploid Wyoming big

sagebrush (table 1). Because Wyoming big sagebrush has

larger cells, both the area and volume of the stomata are

greater and thus, there are fewer stomata per square cm of

leaf area. Basin big sagebrush also has more trichomes per

square cm of leaf area than Wyoming big sagebrush because

epidermal cells are smaller in the diploid subspecies.

Within subspecies, no differences were found in the frequency and size of stomata between persistent and ephemeral leaves. In addition, no significant differences were

found in the number and frequency of stomata on the abaxial

versus adaxial leaf surfaces.

The mean number of stomata per unit leaf area for basin

big sagebrush falls within the range reported for desert

shrubs of 15,000 to 30,000 stomata per cm2

 leaf area

(Larcher 1995), whereas Wyoming big sagebrush stomatal

densities are lower.

Mean values for transpiration and photosynthesis rates

were highest for both subspecies in May and declined as the

summer progressed. Although, no significant differences

were found in photosynthetic rates between subspecies for

any of the measurement periods (fig. 3a), transpiration rates

were significantly different between subspecies on all measurement dates (table 2). Basin big sagebrush consistently

exhibited higher transpiration rates than Wyoming big

sagebrush (fig. 3b). Measurements of predawn and midday

xylem potentials reflecting plant water status were not

significantly different between subspecies for any measurement dates.

Water use efficiencies, calculated as the ratio of photosynthesis to transpiration (μmol CO2 m–2s

–1/mmol H2O m–2s–1)

for each measurement period clearly illustrate differences in

gas exchange characteristics between the two subspecies

(fig. 3c). At all measurement periods, Wyoming big sagebrush exhibited higher water use efficiencies than basin big

sagebrush.

The effects of leaf morphology and anatomy on gas exchange processes are difficult to discern from the complex

environmental conditions and physiological processes that

Figure 2—Leaf epidermis after removal of trichomes

(a) basin big sagebrush at 400x magnification and

(b) Wyoming big sagebrush at 400x magnification.

a

b

Table 1—Densities of stomata and trichomes on big sagebrush leaves.

Stomatal Stomatal Trichome

densities area densities

No. /cm2 leaf No. /cm2 leaf

area μm2 area

Wyoming big

sagebrush (n = 32)

Range 11,000-14,000 540-688 32,484-65,529

Mean 12,995 588 49,111

Basin big

sagebrush (n = 26)

Range 16,330-21,355 266-303 88,092-127,593

Mean 18,025 290 106,205
USDA Forest Service Proceedings RMRS-P-11. 1999 111

act to control plant gas exchange. The differences in leaf

surface characteristics noted in this study could be interpreted to influence gas exchange processes in several ways.

Wyoming big sagebrush, which occupies the most xeric

habitats in which the species is found, maintains similar

photosynthetic rates as basin big sagebrush at lower rates of

water loss per leaf area. This may suggest that the polyploid

cells of Wyoming big sagebrush possess greater photosynthetic capacity than the smaller cells found in basin big

sagebrush. Warner and Edwards (1993) report a doubling of

photosynthesis per cell in autopolyploids; however, this is

balanced by a proportional decrease in the number of cells

per unit leaf area such that the rate of photosynthesis does

not change.

Trichome densities may also play a role in affecting rates of

photosynthesis and transpiration for the two subspecies.

Basin big sagebrush has approximately twice as many trichomes as Wyoming big sagebrush, which may affect the

boundary layer, and leaf reflectance and absorbance properties. The thicker mat of trichomes found on basin big sagebrush leaves would be expected to increase both the boundary

layer and reflectance of the leaf. Increasing the boundary

layer effectively decreases boundary layer conductance and

transpirational water loss. The presence of dense silvery leaf

hairs increases reflectance of solar radiation and effectively

reduces leaf temperatures. This does not seem to be the case

for basin big sagebrush which exhibited higher transpiration

rates on all measurement dates. However, an important

potential disadvantage of leaf pubescence is that it also

reduces the light available for photosynthesis (Ehleringer

1980; Mooney and others 1979). The photosynthetic efficiency

of Basin big sagebrush may be limited by greater pubescence

in comparison with Wyoming big sagebrush.

Differences found in leaf surface anatomy and morphology

between the subspecies may contribute to differences in gas

exchange measured through the spring and summer season.

Wyoming big sagebrush appears to maximize carbon gain

while minimizing water loss in comparison to Basin big

sagebrush.

References _____________________

Beetle, A. A. 1960. A study of sagebrush, the section Tridentatae of

Artemisia. University of Wyoming Agricultural Station Bulletin

368. University of Wyoming, Laramie, WY.

Bozzola, John; Russel, Lonnie. 1992. Electron microscopy: principles and techniques for biologists. Jones and Bartlett,

Sudbury, MA.

Dean, C.; Leech R. M. 1982. Genome expression during normal leaf

development. 2. Direct correlation between ribulose bisphosphate

carboxylase content and nuclear ploidy in a polyploid series of

wheat. Plant Physiology. 70:1605-1608.

Table 2—F-test results and p values for analysis of variance of

photosynthesis, transpiration and calculated water use

efficiencies between subspecies.

N F-test P value

Photosynthesis 64 0.02 0.8932

Transpiration 64 10.22 0.002

Water use efficiency 64 13.08 .0001

Figure 3—Photosynthesis (a) transpiration (b) and

calculated instantaneous water use efficiencies (c) for

Basin big sagebrush and Wyoming big sagebrush.
112 USDA Forest Service Proceedings RMRS-P-11. 1999

Ehleringer, J. 1980. Leaf morphology and reflectance in relation to

water and temperature stress. In: Adaptation of plants to water

and high temperature stress. N. C. Turner and P. J. Kramer, eds.

Wiley, New York: 295-308.

Hoitink, D. J.; Burk, K. W. 1998. Hanford site climatological data

summary 1997, with historical data. PNNL-11794, Pacific Northwest National Laboratory, Richland, WA.

Larcher, Walter. 1995. Physiological plant ecology. Springer-Verlag,

Berlin, Germany.

McArthur, E. D.; Pope, C. L.; Freeman, D. C. 1981. Chromosomal

studies of subgenus Tridentatae of Artemisia: evidence for autopolyploidy. American Journal of Botany. 68:589-605.

Mooney, H. A.; Ehleringer, J. A.; Bjorkman, O. 1977. The energy

balance of leaves of the evergreen desert shrub Atriplex

hymenelytra. Oecologia 38:349-357.

Neter, John; Wasserman, William; Kutner, Michael. 1990. Applied

linear statistical models. Irwin, Boston, MA.

Rickard, W. H.; Rogers L. E.; Vaughan, B. E.; Liebetrau, S. F. 1988.

Shrub-steppe: balance and change in a semi-arid terrestrial

ecosystem. Developments in agricultural and managed forest

ecology 20, Elsevier, New York.

Ritchie, G. A.; Hinckley, T. M. 1975. The pressure chamber as an

instrument for ecological research. Advances in Ecological Research. 9:165-254.

Schultz, L. M. 1986. Comparative leaf anatomy of sagebrush:

ecologcial considerations. In: McArthur, D. and Welch, B. L.

comps. Proceedings—symposium on the biology of Artemisia and

Chrysothamnus. 1984 July 9-13; Provo, UT. Gen. Tech. Rep.

INT-200. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station: 20-28.

Warner, Donn; Edwards, Gerald E. 1993. Effects of polyploidy on

photosynthesis. Photosynthesis Research. 35:135-147.

Warner, Donn; Edwards, Gerald E. 1988. C4 photosynthesis and

leaf anatomy in diploid and autotetraploid Pennisetum

americanum (pearl millet). Plant Science. 56:85-92.
USDA Forest Service Proceedings RMRS-P-11. 1999 113

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Simon A. Lei is a Professor of Biology and Ecology, Department of Biology,

Community College of Southern Nevada, 6375 West Charleston Boulevard,

Las Vegas, NV 89146-1139.

Phenological Events and Litterfall Dynamics

of Blackbrush in Southern Nevada

Simon A. Lei

Abstract—Temporal and spatial variations in phenology and

litterfall were quantitatively examined among blackbrush (Coleogyne

ramosissima) populations in Lee Canyon of the Spring Mountains

in southern Nevada. The initiation of blackbrush phenological

events varied significantly among three elevations and varied

yearly within the same elevation. The earliest phenological time

occurred significantly earlier in the lower blackbrush ecotone than

in the upper ecotone and the nearly monospecific blackbrush stand.

Blackbrush at the lower ecotone had the longest flowering period.

Blackbrush at the nearly monospecific stand had significantly

greater percent flower cover per plant compared to the adjacent

ecotones. Total litterfall and litterfall distribution in blackbrush

varied considerably among elevations and between successive years.

Among litter tissues, leaves comprised the most litterfall and

flowers the least regardless of elevational sites. Blackbrush exhibited temporal and spatial variations in the onset of phenological

events, as well as in total litterfall and litterfall distribution in Lee

Canyon of southern Nevada.

Blackbrush (Coleogyne ramosissima Torr.) plants often

occur in mid-elevations throughout the Mojave Desert, and

covers several million hectares in the southwestern United

States. Blackbrush plants occur primarily along the Colorado River drainage and several adjacent enclosed basins of

the Great Basin-Mojave Desert transition (Bowns and West

1976). Large yearly variation in vegetative, floral, and reproductive phenologies in xerophytic plants has been accounted for by specific abiotic factors, such as air temperature, rainfall, and photoperiod in Rock Valley of southern

Nevada (Rundel and Gibson 1996). Lack of abundant flowers in xerophytic plants is primarily attributed to insufficient precipitation and unfavorable air temperatures in

winter and early spring (Ackermann and Bamberg 1974;

Turner and Randall 1987). In some years, shrubs flower but

produce few fruits. Flowering in blackbrush is induced by

moderate to heavy winter precipitation in southern Nevada

(Beatley 1974). Anthesis is not synchronous throughout the

elevations of blackbrush shrublands (Pendleton 1994).

Blackbrush at higher elevations generally has a shorter,

while blackbrush at lower elevations has a longer flowering

period (Lei 1997). Flowering occurs as early as mid-April,

and flowering on individual blackbrush plants is not synchronous, but typically occurs over a period of 1-3 weeks in

southern Utah and Nevada (Bowns and West 1976; Pendleton

and Pendleton 1995).

Unusual favorable climatic conditions for leafing, flowering, and fruiting tend to produce higher litterfall rates than

unfavorable conditions (Rundel 1996). Peak litterfall in

many semi-deciduous plants, such as blackbrush, may occur

during a summer drought period. The timing of phenological

responses and distribution of litter tissues were found to

vary from year to year within the same species in southern

Nevada (Rundel 1996).

Significant contributions in the past by Bowns and West

(1976), West (1983), Callison and Brotherson (1985), Jeffries

and Klopatek (1987), Provenza (1978), Pendleton and Meyer

(1994), Pendleton and others (1995), Lei (1994), Lei and

Walker (1995 and 1997a,b), Lei (1997), and others have

expanded our knowledge regarding the biology and ecology

of blackbrush. However, no extensive studies were conducted to document temporal and spatial variations of phenological patterns and dynamics of litterfall in blackbrush

plants. In this study, temporal and spatial differences in

phenological and litterfall characteristics in blackbrush

plants were quantitatively investigated among blackbrush

populations in Lee Canyon of southern Nevada.

Methods _______________________

Field Surveys and Laboratory Analyses

Field studies were conducted in Lee Canyon (roughly

36°05' N, 115°15' W; fig. 1) of the Spring Mountains in

southern Nevada. Three elevational sites were selected

within a blackbrush shrubland: lower ecotone (1,500 m),

nearly monospecific blackbrush stand (1,750 m), and upper

ecotone (1,800 m). These three elevational sites represent a

climax community of a desert shrubland. Common woody

plants associated with blackbrush at the lower blackbrush

ecotone include creosote bush (Larrea tridentata) and white

bursage (Ambrosia dumosa), while at the upper blackbrush

ecotone include big sagebrush (Artemisia tridentata) and

Utah juniper (Juniperus osteosperma). Many common herbaceous plants are members of the Asteraceae, Brassicaceae,

Fabaceae, and Poaceae families.

Vegetative, floral, and reproductive phenological patterns

of blackbrush plants were examined along this elevational

gradient. At each elevation, the presence of mature (fully

developed) flowers and the percentage of mature flower

cover were registered in 100 randomly chosen blackbrush

plants. The percentage of mature flower cover was visually

estimated on 10% increments. Phenological observations

commenced in late February and continued through the

growing season in June. Initial dates of each phenophase

(leafing, flowering, and fruiting) of blackbrush plants were

observed during the 1992-1997 period. Subsequent periods
114 USDA Forest Service Proceedings RMRS-P-11. 1999

of each phenophase later in the same season were not

evaluated. Initial dates dates of leaf shedding and summer

dormancy were not considered.

At each elevation, 15 mature blackbrush plants were randomly selected to investigate litterfall dynamics in 1996 and

1997. Litter traps, consisting of 0.90 m diameter and 15 cm

tall cylinders with hardware cloth, were placed around the

periphery of individual shrub canopies (approximately 45-

60 cm in canopy diameter). A 2 mm sieve was used to

separate organic litter from inorganic soil and large rocks.

Litter was collected in summers of both years, and was

oven-dried at 60°C for 72 hours. Litter was separated into

categories of leaves, stems, flowers, and fruits to determine

temporal and spatial variations in dry mass, total litterfall,

and litterfall distribution.

Statistical Analyses

Significant differences in mean percent flower cover per

blackbrush plant and in the onset (mean first dates) of

phenological characteristics were tested with one-way analysis of variance (ANOVA), followed by Tukey’s Multiple

Comparison Test (Analytical Software 1994). Julian day

calendar, a calendar system that numbers days consecutively instead of using cycles of days and months, were used

for ease of computation. However, results were converted

back to the standard calendar system for ease of conception

and interpretation. Temporal and spatial litterfall and relative amount (percentages) of litterfall distribution were

computed. Mean values were presented with standard errors, and p-values less than or equal to (≤) 0.05 were reported

as statistically significant.

Results ________________________

Significant temporal and spatial variations in phenological timing were detected among blackbrush populations of

southern Nevada. Mean first dates of leafing, flowering, and

fruiting were significantly different (p < 0.05; table 1) along

an elevational gradient. Blackbrush growing at the lower

ecotone exhibited the earliest time of shoot budding, leafing,

flower budding, flowering, and fruiting, while blackbrush

growing at the upper ecotone exhibited the latest time prior

to summer dormancy (table 1). The mean interval between

first appearance of blackbrush leaves and their first fully

open flowers was approximately 6 to 8 weeks in all three

elevational sites (table 1). The ripe fruits were first observed

about 2 to 3 weeks after flower initiation (table 1). The mean

interval between first flower budding and appearance of

first flowers was approximately 1 week (table 1). Within

each elevation, the onset of each phenophase varied widely

during the 1992-1997 period. Initial dates of phenophases

ranged over periods of more than a month. In general, shoot

budding appeared in late February through early March, a

new set of blackbrush leaves began to grow in March,

flowering budding and flowering periods began in May, fruit

production occurred in late May through June prior to

summer dormancy that began in mid June or July.

Blackbrush had the shortest flowering period (averaging

11 days) at its upper ecotone, and had the longest period at

its lower ecotone (averaging 14 days). Mean percent flower

cover per plant was significantly different (p < 0.001) along

this elevational gradient (fig. 1). Blackbrush establishing at

Figure 1—Mean percent flower cover per blackbrush

plant during the peak flowering period along an

elevational gradient during the 1992-1997 period in

Lee Canyon. Narrow vertical bars denote standard

errors of the means. Different letters at the top of

columns indicate significant differences at p ≤ 0.05

using ANOVA and Tukey’s Multiple Comparison Test.

Table 1—Mean initial dates of each phenophase (shoot budding, leafing, flower

budding, flowering, and fruiting) in blackbrush during the 1992-1997 period

along an elevational gradient in Lee Canyon of southern Nevada. Mean

dates are presented with standard errors, and statistical significance is

determined at p ≤ 0.05 using Tukey’s Multiple Comparison Test.

Phenophase Lower ecotone Pure stand Upper ecotone

Shoot budding February 28 ± 4 a March 5 ± 4 ab March 10 ± 4 b

Leafing March 8 ± 4 a March 14 ± 4 ab March 19 ± 3 b

Flower budding April 22 ± 4 a April 28 ± 5 ab May 5 ± 4 b

Flowering May 1 ± 5 a May 6 ± 5 ab May 13 ± 4 b

Fruiting May 17 ± 5 a May 23 ± 4 ab May 29 ± 4 b

Mean flower cover per plant (%)

100

80

60

40

20

0

Lower eco BB stand Upper eco

Elevational gradient

a

c

b
USDA Forest Service Proceedings RMRS-P-11. 1999 115

the monospecific stand exhibited the highest mean percent

flower cover per plant compared to the upper and lower

ecotones. Flowering period typically reached its peak within

1 week after the initial date of flowering regardless of

elevational sites.

In addition, substantial temporal and spatial variations

in litterfall distribution among blackbrush populations were

observed between successive (1996 and 1997) years (fig. 2).

Official weather data were not available because long-term

weather stations are located beyond the blackbrush vegetation zones in southern Nevada. Among litter tissues, total

leaf litterfall was greater, while total flower litterfall was

lower at the lower ecotone (fig. 3A) compared to the upper

(fig. 3B) ecotone. A similar pattern in the distribution of

litter tissues was detected in the nearly monospecific

blackbrush stands (data not shown). Major peaks of reproductive (flower and fruit) litterfall occurred at the end of

flowering period and maturation of fruits. Major peaks of

vegetative (stem and leaf) litter occurred when older leaves

were dislodged from shrub canopies during intense summer

drought periods. More favorable climatic conditions, especially precipitation, in winter seasons yielded a higher rate

of reproductive litterfall in 1996 than in 1997 despite the

occurrence of drought in spring seasons of both years (tables

2 and 3).

A severe drought in spring 1997 enhanced leaf and stem

dropping, and led to a greater percentage of vegetative and

a lower percentage of reproductive litterfall compared to

spring 1996 in both upper and lower blackbrush ecotones

(fig. 4A and B). Among blackbrush litter tissues, leaves, by

far, contributed the most litterfall, stems were second in

abundance, fruits were third, and flowers generated the

least at the lower and upper ecotones (fig. 4A and B, respectively) in both years. The lower ecotone consistently yielded

a higher percentage of vegetative litterfall and a lower

percentage of reproductive litterfall than the upper ecotone

in both years. Relative amount of litter tissues exhibited a

similar pattern in the nearly monospecific stand (data not

shown).

Discussion _____________________

In this study, a new set of blackbrush shoots began to grow

in March. Flowering of blackbrush plants was initiated

about 4 to 6 weeks after leaf initiation, and ripe fruit was

first observed about 2 weeks after flowering initiation. My

Figure 2—Total litterfall (leaves, stems, flowers, and

fruits) of 15 individual blackbrush plants along an

elevational gradient in Lee Canyon. Litter was collected

from the spring growing season to the initial summer dry

season from March through June 1996 and 1997. Total litterfall in blackbrush (g)

15

10

5

0

Lower eco BB stand Upper eco

Elevational gradient

1996

1997

Figure 3—Distribution of total litterfall of 15 individual blackbrush plants at lower (A) and upper (B) blackbrush ecotones in Lee Canyon.

Litter was collected from the spring growing season to the initial summer dry season from March through June 1996 and 1997.

0

A.

Total litterfall in blackbrush (g)

6

1996 1997

Year

2

4

8

Leaves

Stems

Flowers

Fruits

0

B.

Total litterfall in blackbrush (g)

6

1996 1997

Year

2

4

8

Leaves

Stems

Flowers

Fruits
116 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 2—Mean monthly precipitation from January through August

during the 1992-1997 period. Official weather data were

acquired from the McCarran Airport (elevation 670) in Las

Vegas, near Lee Canyon. Actual weather data throughout

the blackbrush vegetation zone are not available. The letter

“T” indicates trace precipitation, an amount greater than

zero but less than the lowest reportable value.

Month 1992 1993 1994 1995 1996 1997

- - - - - - - - - - - - - - - - - mm - - - - - - - - - - - - - - - - 

January 11.3 40.8 1.0 75.0 3.3 7.5

February 32.5 63.0 12.0 0.8 3.5 T

March 120.0 3.5 3.3 3.3 9.8 0

April 0.5 0.3 T 0.8 0.0 1.0

May 1.3 0.3 0.3 4.0 3.3 0.0

June 2.3 2.0 0.0 0.5 T T

July 0.8 0.0 2.8 T 29.5 15.0

August 5.3 6.5 2.0 1.3 T .3

Table 3—Mean monthly air temperature from January through August

during the 1992-1997 period. Official weather data were

acquired from the McCarran Airport (elevation 670 m) in Las

Vegas, near Lee Canyon. Actual weather data through-out the

blackbrush vegetation zone are not available.

Month 1992 1993 1994 1995 1996 1997

- - - - - - - - - - - - - - - - - °C - - - - - - - - - - - - - - - - 

January 7.7 7.6 9.6 8.6 9.2 9.1

February 12.3 10.1 9.2 14.8 12.7 10.9

March 13.8 16.1 17.1 14.4 15.4 17.1

April 21.4 19.7 19.7 18.2 20.2 18.6

May 25.4 25.0 24.8 21.7 25.2 27.6

June 28.4 28.1 28.1 27.2 30.6 29.1

July 31.5 31.9 34.1 33.6 34.0 31.2

August 32.5 31.4 33.8 33.9 33.3 32.6

data support Rundel and Gibson’s (1996) suggestion because most plant species in Rock Valley of southern Nevada

follow such phenological trends. In this study, leaf and

flower production overlapped during the spring months.

Blackbrush flowered but produced few fruits in extremely

arid years. Although adequate winter precipitation for flower

initiation occurs in successive years, blackbrush does not

always produce abundant fruits and viable seeds in these

successive years (Meyer and Pendleton, unpublished data).

While winter precipitation initiates and induces flowering,

the size of the resulting fruits and seeds is a function of

available stored resources in southern Utah (Pendleton and

Pendleton 1995). At my study sites, anthesis, on the average,

occurred over a period of 14 and 11 days at the lower and

upper ecotones, respectively. Bowns and West (1976) report

anthesis in blackbrush occurs over a period of 2 to 3 weeks

in southern Utah. However, no comparative data are available since shoot and flower budding have not been examined

in blackbrush plants.

Turner and Randall (1987) use climatic data, including

measurements of rainfall and air temperatures, to predict

initial dates of phenologies in the Mojave Desert. In this

study, large yearly variations in phenological timing at the

same elevation were more strongly associated with winter

precipitation than winter air temperatures. Abundant winter rainfall in 1992, 1993, and 1995 would advance the initial

date of phenophases in blackbrush at my study sites, which

concur with Rundel and Gibson’s (1996) study in southern

Nevada. Mean monthly winter air temperatures fluctuated

a few degrees only and showed no strong relationship with

mean winter precipitation in southern Nevada. High winter

precipitation and low winter air temperatures were not

always associated at my study sites. In addition to rainfall

and air temperature variations, other potential factors, such

as photoperiod and resource reserves, may explain observed

variations in vegetative and reproductive phenologies for

0

A.

Relative amount of litter (%)

80

Stems Fruits

Litter tissue

20

60

100

1996

1997

40

Leaves Flowers

0

B.

Relative amount of litter (%)

80

Stems Fruits

Litter tissue

20

60

100

1996

1997

40

Leaves Flowers

Figure 4—Relative amount of litter tissues of 15 individual blackbrush plants at lower (A) and upper (B) blackbrush

ecotones in Lee Canyon. Litter was collected from the spring growing season to the initial summer dry season from March

through June 1996 and 1997.
USDA Forest Service Proceedings RMRS-P-11. 1999 117

blackbrush in southern Nevada. Although not quantitatively examined in this study, photoperiod may affect vegetative and reproductive development in blackbrush plants.

Blackbrush plants appear to have evolved ecotypes at the

phenological level. This adaptive response may partially

explain why blackbrush plants show variations in the onset

of vegetative and reproductive phenologies at different

elevations.

Moreover, temporal and spatial differences in total litterfall

distribution and relative amount of litter tissues in blackbrush

were detected. Such differences may be strongly attributed

to variations in precipitation and air temperature (climatic) patterns in winters between the 1996 and 1997

years. Although southern Nevada is characterized by hot,

dry summers and cool, moist winters, the timing and total

amount of precipitation vary substantially from year to year,

which can influence the litterfall distribution in time and

space. Among blackbrush litter tissues, leaves comprised

most, stems were second in importance, and flowers contributed the least litter, which correspond with Rundel and

Gibson’s (1996) study. Between the 2 years, more older

leaves dislodged from shrub canopies as drought intensified

in 1997.

Flowers exhibited the least amount of litter in this study

because blackbrush plants have no true petals. Blackbrush

is an anemophilous plant. Anemophily may occur in plant

species that occupy open and often arid habitats, and may

occur in monospecific stands (Stebbins 1974; Pendleton and

Pendleton 1995). At my study sites, blackbrush form nearly

monospecific stands. Wind pollination is also evident in

other members of the Rosoideae, the subfamily to which

blackbrush belongs (Pendleton and Pendleton 1995).

Conclusions____________________

The onset of vegetative, floral, and reproductive phenologies was not synchronous throughout the elevations and

from year to year within the same elevation among

blackbrush populations at Lee Canyon of southern Nevada.

The mean first dates of shoot budding leafing, flower budding, flowering, fruiting, and leaf shedding occurred significantly earlier at the lower than upper blackbrush ecotone.

The mean interval between first appearance of blackbrush

leaves and their first flowers was 6 to 8 weeks. On the

average, anthesis occurred over a period of 2 weeks, with

the shortest flowering period in the upper ecotone and the

longest in the lower ecotone. The mean interval between

first appearance of blackbrush flowering and their first

fruits was 2 to 3 weeks. Significantly greater flower cover

per plant was found in the nearly monospecific blackbrush

stands compared to the adjacent ecotones.

Distribution of litter tissues in various parts of blackbrush

were considerably different from year to year and among

three elevational sites. Leaves consistently contributed the

greatest amount of litter, followed by stems, fruits, and

flowers, in descending order of abundance. Flowers contributed the least amount of litter because blackbrush are

anemophilous plants with no true petals. Favorable climatic

conditions, especially precipitation, led to a greater reproductive litterfall, while unfavorable conditions led to a greater

vegetative litterfall. Among the three elevational sites, the

greatest reproductive litterfall consistently occurred at the

upper blackbrush ecotone, while the greatest vegetative

litterfall consistently occurred at the lower ecotone in Lee

Canyon of southern Nevada.

Acknowledgments ______________

I gratefully acknowledge Steven Lei, David Valenzuela,

and Shevaum Valenzuela for observing the onset of vegetative and reproductive phenologies in blackbrush and for

collecting litter under and around the periphery of blackbrush

canopies in the field. I sincerely appreciate Steven Lei for

separating litter into appropriate categories prior to ovendrying and for recording litter dry mass in the laboratory at

the Community College of Southern Nevada (CCSN). Critical

review by David Charlet greatly improved the manuscript.

References _____________________

Analytical Software. 1994. Statistix 4.1, an interactive statistical

program for microcomputers. St. Paul, MN: Analytical Software. 329 p.

Beatley, J. C. 1974. Phenological events and their environmental

triggers in a Mojave desert ecosystem. Ecology 55:856-863.

Bowns, J. E.; West, N. E. 1976. Blackbrush (Coleogyne ramosissima

Torr.) on southwestern Utah rangelands. Department of Range

Science, Utah State University. Utah Agriculatural Experimental Station, Research Report 27.

Callison, J.; Brotherson, J. D. 1985. Habitat relatioships of blackbrush

community (Coleogyne ramosissima) of southwestern Utah. Great

Basin Naturalist 45:321-326.

Jeffries, D. L.; Klopatek, J. M. 1987. Effects of grazing on the

vegetation of the blackbrush association. Journal of Range Management 40:390-392.

Lei, S. A. 1994. Plants of the North American deserts. Las Vegas,

NV: Unpublished research report. 64 p.

Lei, S. A.; Walker, L. R. 1995. Composition and distribution of

blackbrush (Coleogyne ramosissima) communities in southern

Nevada. In: Roundy, B. A.; McArthur, E. Durant; Haley, J. S.;

Mann, D. K., comps. Proceedings: wildland shrub and arid land

restoration symposium; 19-21 October 1993; Las Vegas, NV. U.S.

Department of Agriculture, Forest Service, Intermountain Research Station, Ogden, UT. General Technical Report INT-GTR315: 192-195.

Lei, S. A.; Walker, L. R. 1997a. Classification and ordination of

Coleogyne communities in southern Nevada. Great Basin Naturalist 57: 155-162.

— . 1997b. Biotic and abiotic factors influencing the distribution of

Coleogyne communities in southern Nevada. Great Basin Naturalist 57: 163-171.

Lei, S. A. 1997. Variation in germination response to temperature and

water availability in blackbrush (Coleogyne ramosissima) and its

ecological significance. Great Basin Naturalist 57: 172-177.

Pendleton, B. K.; Meyer, S. E.; Pendleton, R. L. 1995. Blackbrush

biology: insights after three years of a long-term study. In: Roundy,

B. A.; McArthur, E. Durant; Haley, J. S.; Mann, D. K., comps.

Proceedings: wildland shrub and arid land restoration symposium;

19-21 October 1993; Las Vegas, NV. U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Ogden, UT.

General Technical Report INT-GTR-315: 223-227.

Pendleton, B. K.; Meyers, S. E. 1994. Germination biology of Coleogyne

ramosissima (Rosaceae). I. Laboratory studies. Unpublished

manuscript on file at: Shrub Sciences Laboratory, 735 North 500

East, Provo, UT 84606.

Pendleton, B. K.; Pendleton, R. L. 1995. Pollination biology of

Coleogyne ramosissima (Rosaceae). Unpublished manuscript on

file at: Shrub Sciences Laboratory, 735 North 500 East, Provo, UT

84606. 10 p.
118 USDA Forest Service Proceedings RMRS-P-11. 1999

Provenza, F. 1978. Getting the most out of blackbrush. Utah Science

39:144-146.

Rundel, P. W.; Gibson, A. C. 1996. Ecological communities and

processes in a Mojave Desert ecosystem: Rock Valley, Nevada.

Cambridge, MA: University Press. 369 p.

Stebbins, G. L. 1974. Flowering plants—evolution above the species

level. Cambridge, MA: Belknap Press of Harvard University

Press. 399 p.

West, N. E. 1983. Colorado plateau-Mohavian blackbrush semidesert. In: Temperate deserts and semi-deserts. Amsterdam,

Netherland: Elsevier Scientific Publishing Company: 399-411.
USDA Forest Service Proceedings RMRS-P-11. 1999 119

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Jasleen Kaur is Research Fellow and K. M. M. Dakshini is Professor,

Department of Botany, University of Delhi, Delhi 110007 India.

Abstract—Habitat characteristics influence the behavior of plants.

Diverse forms of a species in terms of morphology or behavior

should, therefore, suggest not only the mosaicness of the habitat

factor(s) but also the ecological status of those forms. To test this

hypothesis the shrub Zizyphus nummularia, a conspicuous component of open scrub vegetation cover of semiarid regions of north/

western India, was investigated. The populations sampled were

distinguished on the basis of leaf shape into two types viz. elliptical

and orbicular. The orbicular form was more common in disturbed

habitats, occurred in relatively poor soils, and accumulated lower

concentrations of nutrients as compared to the elliptical. Analysis of

data suggested that this diversity was with reference to mosaicness

in the habitat. Significance of data collected to manage scrub

vegetation and rangelands has been argued.

In contrast to closed vegetational cover, niche occupation

in open, disturbed, or degraded habitats is not complete. In

such a situation, therefore, the vegetational cover is discontinuous and uneven. Also, due to disturbance in the

community equilibrium, homeostasis and stability are affected, and this should cause evolution/selection of adaptive

forms occupying the available niches, supported by different eco-physiological responses. In this respect the degraded,

disturbed, or open habitats are more similar to ecotones in

general. As a corollary to this, diverse forms in terms of

morphology or behavior should, therefore, suggest not only

the mosaicness of the habitat factor(s) but the status of

those forms as well, especially, if they belong to the same

species. To test this hypothesis the shrub Zizyphus

nummularia (Burm. F.) Wight and Arn.(Rhamnaceae), a

conspicuous component of open scrub vegetation cover of

semiarid and arid regions of north/western India, as well as

an important fodder source for sheep and goat, was selected

for investigations.

Study Area _____________________

The study covers the metropolitan city of Delhi and its

adjoining areas between 28° 12'-28° 53' N and 76° 50'-77° 23' E

longitude. Eighteen sampling sites were chosen in this

region that represent a wide range of ecological conditions in

Biodiversity in the Management of the

Shrub Zizyphus nummularia with Special

Reference to Semiarid Regions in India

Jasleen Kaur

K. M. M. Dakshini

the last trail end extension of the Aravalli Range. The

climate is of semiarid nature with marked diurnal differences of temperature, high saturation deficit, and moderately

low rainfall. It is markedly periodic and is characterized by

a dry and increasingly hot season from March to June, a dry

and cold winter from October to February, and a warm

monsoon period from July to September (Maheshwari 1963).

The soils of the area sampled are aridisol, sandy loams

(Inderjit and Dakshini 1996).

Materials and Methods ___________

Three quadrats were laid at each of the 18 sampling sites,

and six-eight plants from each of the three quadrats were

selected. Sampling was carried out during the months of

April-May for 2 years, 1997 and 1998. Plants at this time are

generally at their peak of growth. The leaf samples from

each of the marked shrubs were collected at fixed nodes. The

soil was collected from the surface and at 40-50 cm depth

from four different locations of the quadrat. The height

and spread of each of the shrubs were recorded in the field.

Leaf samples were rinsed with double distilled water and

oven dried at 45 °C for 48h. These were then analyzed for

leaf area (Leaf Area Meter, Delta T Devices LTD UK) and

weight using replicates of 10 leaves each and leaf specific

weight (LSD) calculated in mg cm–2. Leaf samples were

also analyzed for ash content (in a muffle furnace at 550 °C

for 3h), Ca, Mg, Na, K, Zn, Cu (Atomic absorption spectrophotometer, GBC 902, Australia), PO4 (Molybdenum blue

method) and organic N (indophenol blue method) following

Allen (1989). Composite soil samples for each of the quadrat

were air dried and sieved using a 2 mm sieve. These were

analyzed for the pH, electrical conductivity (EC), HCO3,

Cl, and organic carbon (OC) following Piper (1966); for exchangeable Ca, Mg, Na, K, Zn, Cu (Atomic Absorption

Spectrophotometry), and P (Molybdenum blue method) following Allen (1989). All the analyses were carried out in

triplicates.

Data on all these variables from all the sites were pooled

and infraspecific comparisons were carried out using various statistical procedures. One-way analysis of variance

(ANOVA) was used to compare the two different leaf forms,

namely elliptical and orbicular, individually for each of the

variables analyzed. The relative contribution of each variable toward defining the discrimination between the two

forms were assessed using Discriminant Function Analysis

(DFA) separately for leaf and soil variables (Capone and

Kushlan 1991; Inderjit and Dakshini 1994; Sharma and

Dakshini 1998; Williams 1983). Also, an inter-variable correlation matrix was computed for each form to evaluate the
120 USDA Forest Service Proceedings RMRS-P-11. 1999

degree of inter-relatedness of all the variables in the analysis. All the analyses were carried out using SPSS statistical

software (SPSS PC 1986).

HPLC analysis was carried out to study the variation in

phenols of the two diverse forms. Methanolic extracts of

leaves were subjected to HPLC (JASCO 860) analysis. Reverse phase chromatography was carried out using a steel

column (Gasukuro kogyo, Intersil ODS-2, 4.6 x 150 mm).

The wavelength UV detector was set at 275 nm. The flow

rate was 0.5ml/min, and the volume injected was 5 ml.

Results ________________________

Analysis of the data showed that the populations sampled

could be grouped into two types based on the leaf morphology, i.e., elliptical and orbicular (fig. 1). These two leaf types

Figure 1—Shapes of the leaves in the elliptical (top) and orbicular (bottom) forms of Z.

nummularia.

were significantly different (table 1) in many of the variables

analyzed. While leaf K, PO4, area, org N, Cu, and Mg were

higher in the elliptical form, leaf weight, Ca, Na, Zn, LSW,

and plant height and spread showed higher values in the

orbicular form (table 1). Discriminant analysis of the two

forms on the basis of the 14 leaf variables showed that K,

PO4, and LSW contributed most in discriminating the two

forms (table 1).

Significant differences were also seen in the soils associated with the two diverse forms. All the soil variables

(excepting Cl, Cu, and pH) had higher values in the elliptical

form associated soils. DFA showed that EC, Zn, and K were

the most discriminating soil variables between the two

forms associated soils (table 2).

Additionally, the patterns exhibited by the HPLC phenolic profiles were qualitatively and quantitatively very

different in the two forms of Z. nummularia. The elliptic

form had higher phenolic content in comparison to the

orbicular form (fig. 2).

A comparison of the correlation matrices of the elliptical

and orbicular forms based on the leaf and soil characteristics analyzed showed that the orbicular form exhibited a

greater number of significant (p <0.05) leaf-leaf, leaf-soil,

and soil-soil correlations in comparison to the elliptical form

(table 3 and 4). Only very few correlations (positive or

negative) were common to both the forms, thereby exhibiting an entirely different set of leaf-leaf, soil-soil, and leaf-soil

interactions in the two forms.

Of all the leaf variables that discriminated between the

elliptical and orbicular forms, i.e., K, PO4, and LSW, none

was correlated with any other leaf or soil variable in the

former (table 3). In contrast, in the latter form, leaf K was

correlated with leaf Na and plant spread and soil K, Na,

Table 1—Statistical analysis of plant characteristics of two diverse forms of

Zizyphus nummularia.

DFA Mean ± standard deviation ANOVA

Variable DF correlation Elliptical Orbicular p

Ka 0.38295b 3.187 ± 0.373 c 0.833 ± 0.139 ****

P 0.23682b 0.323 ± 0.054 c 0.133 ± 0.015  

LSW –0.17598b 46.38 ± 15.984 g 149.156 ± 20.06 ** **

Area 0.12497 273.86 ± 29.58 f 120.942 ± 41.97  

Org N 0.11797 4.975 ± 1.458 c 1.49 ± 0.862 ** **

Ca –0.07653 1.407 ± 0.589 c 2.358 ± 0.408  

Na 0.07244 0.57 ± 0.136 c 0.407 ± 0.051 ** **

Cu 0.06470 119.88 ± 32.64 d 76.585 ± 18.60 ***

Zn –0.04167 114.37 ± 15.29 d 145.938 ± 26.94 *

Spread –0.03314 0.266 ± 0.278 i 0.701 ± 0.450 *

Weight –0.02974 128.33 ± 51.92 e 177.083 ± 52.29 NS

Mg 0.02359 0.427 ± 0.183 c 0.353 ± 0.072 NS

Height –0.00787 0.878 ± 0.695 h 0.990 ± 0.318 NS

Ash –0.00002 7.021 ± 1.370 c 7.061 ± 1.878 NS

aVariables ordered by size of pooled within-group correlation between discriminating

variables and canonical discriminant function.

bSignificant correlation within the function.

c

%

d

μg g–1

e

mg

f

mm2

g

mg cm–2

hm

i

m2; * p <0.05; ** p <0.01; ***p <0.001;  p <0.0001; NS-not significant.
USDA Forest Service Proceedings RMRS-P-11. 1999 121

Table 2—Statistical analysis of soil characteristics of two diverse forms of Zizyphus

nummularia.

DFA Mean ± standard deviation ANOVA

Variable DF correlation Elliptical Orbicular p

ECa –0.19901b 183.398 ± 3.242f 177.173 ± 2.669 ** **

Zn –0.18126b 5.529 ± 0.153d 3.342 ± 0.390  

K –0.17975b 120.125 ± 25.98c 83.25 ± 5.933 ** **

P –0.16421 6.562 ± 0.057c 1.248 ± 0.153  

OC 0.16062 1.11 ± 0.042e 0.518 ± 0.113 ** **

Cl –0.15232 0.01 ± 0.00e 0.012 ± 0.003 *

Ca 0.14865 314.45 ± 19.163c 260.834 ± 17.05 ****

Mg 0.13728 38.75 ± 1.768c 32.5 ± 2.955  

HCO3 0.10694 0.0519 ± 0.004e 0.0407 ± 0.005 ** **

pH 0.08558 7.07 ± 0.014 7.36 ± 0.055  

Cu –0.07833 1.152 ± 0.008d 1.333 ± 0.117 ** **

Na –0.05078 55.75 ± 10.607c 43.708 ± 1.543 ****

aVariables ordered by size of pooled within-group correlation between discriminating

variables and canonical discriminant function. b

Significant correlation within the function.

c

mg; 100g–1

d μg g–1

e %

f μmhos cm–1; * p <0.05; **** p <0.0001.

Figure 2—HPLC profiles of phenols of methanolic

extracts of orbicular (top) and elliptical (bottom) leaves

of Z. nummularia.

PO4, and Zn positively and with soil EC negatively (table 4).

Similarly, leaf PO4 was correlated with leaf Cu, Na, and Mg,

and soil Na and PO4 positively, and with soil EC negatively

in this form. Also, its LSW was correlated with leaf Mg,

plant spread, and soil Ca, Mg, Na, OC, and pH positively and

with leaf Zn and Ca and soil Cu and EC negatively.

The discriminating soil variables (i.e., EC, Zn, and K) also

did not show any correlations in the elliptical forms

(table 3). On the other hand, in the orbicular form (table 4)

these variables were highly correlated. Soil EC was correlated positively with leaf Ca and Zn and soil Cu, and

negatively with plant height, leaf K, Na, PO4, Mg, weight,

and LSW, and soil Ca, Mg, Na, OC, and pH. Similarly, soil

Zn was correlated positively with leaf Cu, Na, and Zn, and

soil Cu, K, and PO4, and negatively with plant height, soil

Ca, HCO3, Mg, and OC. Also, soil K was correlated positively

with leaf Cu, K, Na, and Zn, and soil Cu, Na, PO4, and Zn,

and negatively with leaf N and soil Ca, HCO3, Mg, and OC.

Discussion _____________________

The data demonstrate infraspecific diversity in Zizyphus

nummularia. These diverse forms can be distinguished into

two groups, viz. one having prominently orbicular leaves

and the other having elliptical leaves. Also, the orbicular

form is associated with rounded fruits and the elliptical form

with the oblong fruits. Interestingly, these two infraspecific

types occupy different habitats with special references to

soil characteristics (table 2). Elliptical-leaved type inhabits

soils with higher concentrations of nutrients and organic

matter, as well as higher electrical conductivity as compared

to orbicular-leaved type.

A correlative assessment of the data based on 14 leaf

and 12 soil variables shows that the orbicular form exhibits

a higher degree of coordination within itself and with the

soil conditions. This would suggest that the orbicular form

is comparatively a physiologically stable system (El Ghonemy

1978) and its response is well modulated according to the

general ecological conditions of the area (Solbrig 1979).

On the other hand, the elliptical form lacks such an integration. Instead, its successful survival is independent of

substratum conditions (Sharma and Dakshini 1998).

Further, the patterns of mineral cycling also vary in the

two forms. The concentrations of Cu, K, Mg, Na, org N, and

PO4 are higher in the leaves of the elliptical form as

Time (min)

Profiles of Phenols
122 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 3—Correlated leaf and soil variables of elliptical form on the basis of pooled data.

Leaf Soil

Positive Negative Positive Negative

Plant Height

Spread Zn Ca

Leaf Area

Ash

Ca

Cu Org. N

K

Mg

Na Cl.HCO3,OC Cu,pH,PO4

Org. N Cu

PO4

LSW

Weight

Zn Spread Ca

Soil Ca Spread Zn

Cl Na HCO3,OC Cu,pH,PO4

Cu Na pH,PO4 Cl, HCO3,OC

EC

HCO3 Na Cl,OC Cu,pH,PO4

K

Mg

Na

OC Na Cl,HCO3 Cu,pH,PO4

pH Na Cu,PO4 Cl,HCO3.OC

PO4 Na Cu,pH Cl,HCO3.OC

Zn

p <0.05

Table 4—Correlated leaf and soil variables of orbicular form on the basis of pooled data.

Leaf Soil

Positive Negative Positive Negative

Plant Height Wt,Spread Na,OC EC,Zn

Spread LSW,Wt,Ht,K Zn,Ca,Mg Ca,HCO3,Mg,Na,OC,pH Cu,EC

Leaf Area Org N,Wt

Ash Mg Cu HCO3,pH

Ca Zn LSW,Spread Cu,EC Ca,HCO3,Mg, OC,pH

Cu Na,PO4,Zn Cu,K,PO4,Zn Ca,HCO3,Mg, OC,pH

K Na,Spread K,Na,pH,PO4,Zn EC

Mg Na,PO4,LSW,Wt,Spread Zn Ca,Mg,Na,OC,pH,PO4 Cu,EC

Na Cu,K,PO4,Mg K,PO4,Na,Zn EC

Org. N Area,Wt K,PO4

PO4 Cu,Na,Mg Na,PO4 EC

LSW Mg,Spread Zn,Ca Ca,Mg,Na.OC,pH Cu,EC

Weight Ht,area,Mg, Spread Ca,Na,OC EC

Zn Cu,Ca LSW,Mg,Spread Cu,EC,K,Zn Ca,HCO3,Mg, OC,pH

Soil Ca LSW,Mg,Wt Cu,Zn,Ca HCO,Mg,OC,pH Cu,K,EC,Zn

Cl

Cu Cu,ash,Zn,Ca LSW,Mg EC,Zn,K Ca,HCO3,Mg, OC,pH

EC Ca,Zn Ht,K,Na,PO4, LSW,Mg,Wt Cu Ca,Mg,Na,OC,pH

HCO3 Cu,Zn,ash,Ca Ca,Mg,OC,pH Cu,K,PO4,Zn

K Cu,K,Na,Zn Org N Cu,Na,PO4,Zn Ca,HCO3,Mg, OC

Mg LSW,Mg Zn,Cu,Ca Ca,HCO3,OC,pH K,PO4,Zn

Na Ht,K,Na,PO4,LSW,Mg,Wt K,pH,PO4 EC

OC Ht,LSW,Mg,Wt Cu,Zn,Ca Ca,HCO3,Mg,pH Cu,EC,Ca.Zn

pH K,LSW,Mg Cu,Zn,ash,Ca Ca,HCO3,Mg,Na,OC Cu,EC

PO4 Cu,K,Na,PO4 Org N K.Na HCO3,Mg,Zn

Zn Cu,K,Na,Zn Ht Cu,K,PO4 Ca,HCO3,Mg, OC

p <0.05
USDA Forest Service Proceedings RMRS-P-11. 1999 123

compared to the orbicular form that has higher Ca and Zn.

However, the values of LSW, leaf weight, height, and spread

are considerably lower in the elliptical form in comparison

to the orbicular form. The higher concentration of leaf

organic N in the elliptical form would suggest that this

form is comparatively more photosynthetically efficient

(Field and Mooney 1986). Furthermore, the data also suggest that, in spite of the higher nutrient uptake, the nutrient

use efficiency is lower in elliptical form as opposed to the

orbicular form (Vitousek 1982). This may also suggest that

the carbon gain per unit of the nutrients taken up from the

substratum is higher in the orbicular form as compared to

the elliptical form (Boerner 1984). The low LSW and leaf

weight values in elliptical leaves would also mean a faster

release of nutrients through mineralization under it

(Chabot and Hicks 1982). This observation is further substantiated by higher HCO3 values (i.e., high microbial activity) and also the higher concentration of the nutrients in the

soils associated with the elliptical form as compared to the

orbicular form. Additionally, the higher phenolic content

of the elliptical leaves suggests reallocation of photosynthates for the production of secondary metabolites (phenols).

This should make an otherwise nutritious forage (Pareek

1983) of this form more bitter and less palatable. Whether or

not the increase in the concentration of phenolic content in

the elliptical form is under the stress of the herbivory

needs to be investigated (Tang and others 1995; Tuomi

and others 1984).

In view of the economic importance (fodder especially for

goat and sheep, medicinal, erosion control) of this naturally

occurring species the data are of applied value for the

management of habitats in the semiarid and arid environments. The ecophysiologically different infraspecific forms

shall provide ways to meet the challenges in the management and improvement of degraded habitats, either through

revegetation or through maintenance of the existing marginal habitats available in harsh environments.

As evident from the data, the elliptical form shall be more

suitable for reclaiming degraded lands (Hansen 1989) because it is relatively less preferred by the grazers (information gathered from local shepherds). Also, through its higher

uptake and release of nutrients it can initiate recovery,

productivity, and stability of the plant-soil complex. On the

other hand, orbicular form can help in improving rangelands

(Omar-Draz 1989) as it provides valuable forage, checks

erosion, and also maintains the stability of the substratum

without altering the physico-chemical balance (l.c.)

Thus whereas one form can be used for reclamation of

marginal lands, the other can be utilized for the maintenance of the unique ecological systems of the arid areas.

The data presented not only support the hypothesis that

species alone is no longer an adequate base for the adaptive

shrubs for revegetation (Plummer and others 1970a) but

also bring out the importance of such studies in the management of range and degraded lands.

Acknowledgments ______________

We are grateful to Professor N. N. Bhandari’s help in

planning and execution of this manuscript. We wish to

thank Dr. Inderjit for helping us in HPLC analysis. We

would also like to thank Dr. Reetu Sharma for her valuable

suggestions in preparation of the manuscript. Financial

assistance form Council of Scientific and Industrial Research (CSIR) and University Grants Commission (UGC),

India, is gratefully acknowledged.

References _____________________

Allen, S. E. 1989. Chemical analysis of ecological materials (2nd

ed.). Blackwell Scientific Publication, Oxford.

Boerner, R. E. J. 1984. Foliar nutrient dynamics and nutrient use

efficiency of four deciduous tree species in relation to soil fertility.

J. Appl. Ecol. 21: 1029-1040.

Capone, T. A.; Kushlan, J. A. 1991. Fish community structure in

dry-season stream pools. Ecology. 72: 983-992.

Chabot, B. F.; Hicks, D. J. 1982. The ecology of leaf life spans. Ann.

Rev. Ecol. Syst. 13: 229-259.

El-Ghonemy, A. A.; Wallace, A.; Romney, E. M. 1978. Nutrient concentrations in the natural vegetation of the Mojave Desert. Soil. Sci.

126: 219-229.

Field, C.; Mooney, H. A. 1986. The photosynthesis-nitrogen relationship in wild plants. In: Givnish, T. J., ed. On the Economy

of Plant Form and Function. Cambridge University Press,

Cambridge: 25-55.

Hansen, D. J. 1989. Reclamation and erosion control using

shrubs. In: McKell, C. M., ed. The Biology and Utilization of

Shrubs. San Diego, CA. Academic Press, Inc.: 441-458.

Inderjit; Dakshini, K. M. M. 1996. Allelopathic potential of Pluchea

lanceolata: Comparative study of cultivated fields. Weed Science.

44: 393-396.

Inderjit; Dakshini, K. M. M. 1994. Allelopathic effect of Pluchea

lanceolata (Asteraceae) on characteristics of four soils and

tomato and mustard growth. Am. J. Bot. 81: 799-804.

Maheshwari, J. K. 1963. The flora of Delhi. C.S.I.R. New Delhi.

Omar-Draz. 1989. Fodder shrubs for range improvement: The

Syrian experience. In: McKell, C. M., ed. The Biology and Utilization of Shrubs. San Diego, CA. Academic Press, Inc.: 425-440.

Pareek, O. P. 1983. The Ber. ICAR, New Delhi.

Piper, C. S. 1966. Soil and plant analysis. Hans Publishers, Bombay.

Plummer, A. P.; Christensen, D. R.; Stevens, R.; Jorgensen, K. R.

1970. Highlights, results and accomplishments of game range

restoration studies, Utah Div. Fish and Game Pub. 70-3: 94 p.

Sharma, R.; Dakshini, K. M. M. 1998. Integration of plant and soil

characteristics and the ecological success of two Prosopis species.

Plant Ecology. 139: 63-69.

Solbrig, O. T. 1979. Life forms and vegetation patterns in desert

regions. In: Goodin, J. R.; Northington, D. K., eds. Arid land plant

resources. International Center for Arid and Semi-Arid Land

Studies, Texas Tech University: 82-95.

SPSS PC 1986. Advanced statistics: SPSS/PC + McGraw-Hill,

Chicago.

Tang, C.; Cai, W.; Kohl, K.; Nishimoto, R. K. 1995. Plant stress and

allelopathy. In: Inderjit; Dakshini, K. M. M.; Einhellig, F. A., eds.

Allelopathy: organisms, processes and applications. ACS Symposium Series 582, Washington, DC: 142-157.

Tuomi, J.; Niemela, P.; Haukioja, A.; Siren, S.; Neuvonen, S. 1984.

Nutrient stress: an explanation for plant-herbivore responses to

defoliation. Oecologia. 61: 208-210.

Vitousek, P. 1982. Nutrient cycling and nutrient use efficiency. Am.

Nat. 119: 553-572.

Williams, B. K. 1983. Some observations on the use of discriminant

analysis in ecology. Ecology. 64: 1283-1291.
124 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Bilquees Gul is a Plant Ecologist, Department of Botany, University of

Karachi, Karachi-75270, Pakistan. Darrell J. Weber is a Professor of Plant

Pathology, Department of Botany and Range Science, Brigham Young University, Provo, UT 84602. M. Ajmal Khan is a Professor of Plant Ecology,

Department of Botany, University of Karachi, Karachi-75270, Pakistan.

Population Dynamics of a Perennial

Halophyte Allenrolfea occidentalis

Bilquees Gul

Darrell J. Weber

M. Ajmal Khan

Abstract—Demography and population biology of a perennial

halophyte, Allenrolfea occidentalis, was studied during the growing

seasons (May to November) of 1996 and 1997. Soil samples were

collected monthly from the playa throughout the growing seasons

for two years and analysed to determine the conductivity, pH, soil

moistures and ions. During the study period, the population was

exposed to wide variations in soil salinity from low to high and soil

moisture ranging from very wet to drought levels. Seasonal changes

in dry weight was directly related to soil salinity stress. When

salinity levels become low, the dry matter production increases. The

population of A. occidentalis suffered heavy mortality in 1996 due to

the high salinity and temperature stress. Plant growth reached its

maximum in July and succulence decreased with aging of plants.

Results indicate that community vegetation respond differently to

the environmental changes in 1996 and in 1997. Salinity, temperature and precipitation have a major effect on the survival and

growth of A. occidentalis under field conditions.

The distribution of plant species in saline environments of

inland western United States is closely associated with soil

water potentials and other factors influencing the level of

salinity stress, including microtopography, precipitation,

and depth of water table (Young and others 1995). There are

certain areas in western Utah, where the salt content is high

enough to form thick salt crusts on the top of the soil making

plant growth of any kind impossible, on such areas some of

the more salt tolerant plants survive with little or no competition and Allenrolfea occidentalis (Wats.) Kuntze is one of

them (Quigley 1956). Allenrolfea occidentalis is a perennial

chenopod, which colonizes extremely saline habitats of the

temperate desert basins. Plant communities dominated by

A. occidentalis offer the extreme in adaptations to survival

and growth under moisture stress (Young and others 1995).

During the growing season A. occidentalis plants are subjected to a great variation in edaphic conditions (Trent and

others 1997). Seasonal variation in soil salinity in saline

habitats is well documented and is directly influenced by the

fluctuations in soil moisture levels (Ungar 1973, 1978a;

Waisel 1972). Young and others (1995) showed that the

A. occidentalis plants have to allow salts to enter through

root membranes and the physiology of the plant changes

from the wet to dry years due to the increase in soil salinity.

Flanagan and Jefferies (1988) reported that as salinity

increased, photosynthesis in Plantago maritima declined

17 to 14 μmol m–2.S–1 while leaf conductance dropped markedly. Transpiration and photosynthesis involve gas exchange

between the plant and atmosphere through the stomata and

are well known to decrease with water stress (Fisher 1976)

or salinity (Khan and others 1976).

Halophytic species commonly exhibit quite high concentrations of several salt ions in various plant organs or the

entire plant. Although the salt accumulating nature of

halophytes has been recognized for many years, now it has

been proven that sodium is essential to the growth of most of

the chenopodiaceae (Brownwell and Wood 1957; Brownwell

1965; Moore and Caldwell 1972; Naidoo and Rughunanan

1990; Khan and others 1998). Terrestrial halophytes utilize

the controlled accumulation and sequestration of inorganic

ions, chiefly Na+

 and K+ balanced by Cl–, as the basic

mechanism by which they adjust the osmotic potential of

their internal tissue to the external salinity (Flowers and

Yeo 1986; Cheeseman 1988).

In this study, the environmental conditions as they affect

growth of a natural population of Allenrolfea occidentalis

during the growing seasons in an inland salt playa of the

Great Basin desert, are reported. The objective of this study

was to study the effect of variation in soil salinity and

temperature on the growth and ecophysiology of A. occidentalis under natural conditions.

Materials and Methods ___________

Study site

The site chosen for this study is a salt playa east of

Goshen, northwestern Utah. It is an area of flat, low-lying

ground in the bottom of a fairly wide valley that spreads out

at the southern end into a vast stretch of flat, salt incrusted

plain. The area contains numerous salt marshes and salt

playas with nearly pure stands of Allenrolfea occidentalis.

The point centered quarter method (Cottam and Curtis

1956) was used to sample the vegetation over 20 random

points and relative frequencies were calculated for each

species in the community. During the spring of 1996, three

transects were established in the salt playa. These transects

ran through the community and were approximately parallel to the marsh. Fifteen permanent quadrats (100 x 100 m2

)

were established on three transects, three replicates on each
USDA Forest Service Proceedings RMRS-P-11. 1999 125

site. The number of plants surviving in each plot and their

cover were counted monthly throughout the growing season

from May to November 1996 and 1997. In order to reduce

disturbance in quadrats, ten equal sized plants were randomly collected from the area in the vicinity of each quadrat

every month of the growing season for two years. Plants were

separated into leaves, stem and root. Allenrolfea occidentalis does not have true leaves but they form jointed, seemingly

leafless stems. The green leafy succulent portion is considered here as leaf while woody portion as stem. Fresh and dry

weight of the plants was recorded before and after drying the

material in an oven at 80°C for 48 h.

For ion measurements 0.5 gram of plant material was

boiled in 25 ml of water for two hours at 100°C using a dry

heat bath. This hot water extract was cooled and filtered

using Whatman no. 2 filter paper. One ml of hot water

extract was diluted with distilled water for ion analysis.

Chloride, nitrate and sulphate ions contents were measured

with a DX-100 ion chromatograph. Cation contents Na+

, K+,

Ca2+ and Mg2+ of the plant organs were analysed using a

Perkin Elmer model 360 atomic absorption spectrophotometer. The net photosynthesis rate of four replicates per

quadrat were taken with an LI-6200 portable photosynthesis system (LI-COR, Inc., Lincoln, NE). The level of stress in

plants growing in field conditions were measured with CF1000 chlorophyll fluorescence measurement system. The

water potential was measured using a Plant Moisture Stress

Instrument (PMS Instrument Co.).

Ten surface soil (to a depth of 15 cm) and 10 subsurface (to

a depth of 30 cm) soil samples were collected monthly from

the A. occidentalis community during the growing season.

Soil moisture was measured by weighing 12 g of samples,

oven drying them at 136°C for 24 h and reweighing them to

determine the water loss. Percent soil moisture was calculated as percentage weight of water in dry soil. Then for the

determination of organic contents of the soil these samples

were dried at 360°C for 24 h.

Five grams of soil mixed with 25 ml of distilled water were

shaken and filtered using Whatman no. 1 filter paper. PH

(pH meter) and soil conductivity (model-10 portable conductivity meter) were measured. The results of growth, ion

contents, net photosynthesis, water potential and stress

were analysed using three way ANOVA. A Bonferroni test

was carried out to determine if significant (P <0.05) differences occurred between individual treatments (SPSS 1996).

Results ________________________

A three way ANOVA showed a significant individual

effect of quadrats F = 28.71, (P <0.0001) and years F = 7.02,

(P <0.001), while months were not significant in affecting

basal area. Interactions between quadrats, years and months

were also significant (P <0.0001). Phytosociological survey

showed that the salt playa community has an almost pure

population of A. occidentalis a few individuals of Salicornia

rubra, Salicornia utahensis and Distichlis spicata were

present. Quantitative data indicated that A. occidentalis

had consistently high cover in the intermediate plots throughout the growing season of 1996 (fig. 1). The overall cover of

the plants in the A. occidentalis community was higher in

1996 than 1997.

A three way ANOVA showed a significant individual effect

of plant parts, years and months and their interactions in

affecting dry weight of A. occidentalis plants. Plants collected from the field were analysed for leaves, stem and root

fresh and dry weights. Allenrolfea occidentalis plants collected on August 1996 had greater dry weights than plants

collected in other months (fig. 1). The fresh and dry weights

of the plants increased gradually from May to September

and then decreased.

A three way ANOVA showed a significant individual effect

of months (P <0.0001) and years (P <0.0001), while soil

layers were not significant in affecting pH (table 2). The

surface soil pH was generally higher and fluctuated more

than the corresponding subsurface pH. The subsurface pH

of the soil changed very little during the growing season

(table 1 and 2). The decrease in pH of the surface soil

appeared to be correlated to the amount of rainfall. A

decrease in the pH of the surface soil occurred in May to July

1997 due to heavy rainfalls, it was generally inversely

proportional to the increase in subsurface pH.

Figure 1—Seasonal pattern of dry weight (g plant–1)

of leaf, stem and root of plants collected from an

Allenrolfea occidentalis community. Bar represents

mean ± S. E.
126 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 1—Seasonal variation in the pH, conductivity (ds/m), moisture content (%) and organic

content (%) of the soil from Allenrolfea occidentalis community during the year of 1996.

Conductivity Moisture Organic

Months Soil layers pH ds/m contents contents

- - - - - - Percent - - - - - -

May Surface 8.0 ± 0.01 135 ± 19 14 ± 1.2 3.8 ± 0.9

Subsurface 8.2 ± 0.09 78 ± 13 19 ± 1.5 2.7 ± 0.9

June Surface 7.5 ± 0.04 132 ± 8.5 11 ± 0.37 2.2 ± 0.22

Subsurface 7.6 ± 0.07 137 ± 22 14 ± 0.64 2.4 ± 0.27

July Surface 8.2 ± 0.02 160 ± 16 12 ± 0.7 1.8 ± 0.34

Subsurface 8.1 ± 0.03 118 ± 9.0 15 ± 1.3 3.0 ± 1.3

August Surface 7.9 ± 0.03 161 ± 6.0 12 ± 1.1 3.0 ± 2.6

Subsurface 7.7 ± 0.05 91 ± 13 14 ± 0.51 1.3 ± 0.71

September Surface 7.9 ± 0.02 99 ± 21 12 ± 1.8 3.1 ± 1.5

Subsurface 7.6 ± 0.06 74 ± 7.0 12 ± 1.9 3.4 ± 0.81

October Surface 8.3 ± 0.08 109 ± 7.0 11.4 ± 0.88 2.1 ± 0.28

Subsurface 8.2 ± 0.08 73 ± 5.0 16 ± 1.2 2.4 ± 0.33

November Surface 8.2 ± 0.02 87 ± 8.0 12 ± 0.61 1.9 ± 0.60

Subsurface 8.1 ± 0.03 78 ± 4.0 16.2 ± 1.1 1.8 ± 0.39

Soil conductivity remained high throughout the growing

season except for the period when it received summer rains

(table 1 and 2). A decrease in soil solution conductivity

occurred in the fall to levels found in early spring (table 1

and 2).

The sub-surface moisture content was higher than the

surface soil moisture throughout the growing season except

for the months of October 1996 and July 1997, when the

Table 2—Seasonal variation in the pH, conductivity (ds/m), moisture content (%) and organic

content (%) of the soil from Allenrolfea occidentalis community during the year of 1997.

Conductivity Moisture Organic

Months Soil layers pH ds/m contents contents

- - - - - - Percent - - - - - -

May Surface 8.0 ± 0.03 109 ± 4.0 9.2 ± 1.3 2.9 ± 0.46

Subsurface 8.1 ± 0.09 88 ± 2.0 15 ± 1.4 2.4 ± 0.08

June Surface 7.8 ± 0.11 147 ± 11 10.2 ± 1.4 3.4 ± 0.18

Subsurface 8.1 ± 0.08 107 ± 12 11.8 ± 1.4 4.1 ± 0.19

July Surface 7.9 ± 0.02 138 ± 11 14 ± 12 2.9 ± 0.19

Subsurface 8.1 ± 0.06 93 ± 9.0 14 ± 0.53 3.7 ± 0.40

August Surface 7.5 ± 0.07 145 ± 12 12.1 ± 0.50 2.9 ± 0.16

Subsurface 7.8 ± 0.08 108 ± 8.0 11 ± 0.36 3.7 ± 0.40

September Surface 7.3 ± 0.02 135 ± 13 13.3 ± 0.95 2.0 ± 0.19

Subsurface 7.3 ± 0.04 68 ± 9.0 14.3 ± 0.76 3.5 ± 0.75

October Surface 7.3 ± 0.02 122 ± 12 10.7 ± 0.65 2.2 ± 0.28

Subsurface 7.4 ± 0.01 96 ± 11 15.4 ± 1.07 2.8 ± 0.33

November Surface 7.5 ± 0.05 106 ± 12 12.9 ± 0.55 1.3 ± 0.60

Subsurface 7.4 ± 0.02 83 ± 9.0 16.1 ± 0.86 2.4 ± 0.20

salt playa had an increase in surface soil moisture due to the

rainfall (table 1 and 2).

A three way ANOVA showed significant individual effects

of plant parts, years, months and their interactions in

affecting the ion contents of A. occidentalis except for the

interactions of Cl–

 ion. The Cl– ion content in A. occidentalis

tissues (leaf, stem and root) remained constant throughout

most of the growing season of 1996 and 1997 (fig. 2). Na ion
USDA Forest Service Proceedings RMRS-P-11. 1999 127

concentration gradually increased from 1,000 mM to

35,000 mM in 1996, and 28,000 mM in 1997 (fig. 2 and 3). K+

ion concentration in leaves was significantly higher in August. However, K+

 concentration was significantly lower in

stem as compared to the leaves and roots. The K+

 ions in

leaves and roots decreased significantly during the months

of low salinity. The major cation macronutrients Ca++ and

Mg++ differed in their availability patterns throughout the

growing seasons (fig. 2 and 3).

Photosynthesis rates was significantly higher in August

than the other months, which did not significantly differ

from each other (table 3). The monthly values of Fv/Fm were

always low and showed high stress in the field plants. Water

relation parameters of the plants were measured to see if

they might be related to the differences in plant growth in

field conditions. Water potential of the A. occidentalis was

significantly greater in July to October (table 3). Water

Figure 2—Monthly variation in ion contents of leaf, stem and root of

Allenrolfea occidentalis during the year of 1996.
128 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 3—Monthly variation in ion contents of leaf, stem and root of

Allenrolfea occidentalis during the year of 1997.

potentials of shoots decreased significantly with increase in

salinity (table 3).

Discussion _____________________

An Allenrolfea occidentalis population in a Great Basin

salt playa was exposed to great variations in environmental

conditions. This exposure to soil salinity varying from

29-146 dS m–1 and soil moisture ranging from drought to

very wet levels affected the growth of A. occidentalis. Young

and others (1995) reported that the A. occidentalis communities of the salt deserts in Great Basin are distributed

continuously, with inclusion of stable sand dunes that rise

5 to 10 m above the lake plain. He also concluded that the

mounds on the playa surface that predominantly support

A. occidentalis plants are successionally dynamics.
USDA Forest Service Proceedings RMRS-P-11. 1999 129

Table 3—Mean ± S. E. for water potential, photosynthesis and stress under field

conditions.

Water potential Stress Net photosynthesis

Months (–Mpa) (Fv/Fm) (μmol m–2 s–1)

May 36.8 ± 1.2 0.50 ± 0.035 3.8 ± 0.43

June 42.6 ± 1.3 0.69 ± 0.037 4.1 ± 0.49

July 70.6 ± 5.4 0.74 ± 0.032 5.1 ± 1.2

August 87.6 ± 4.3 0.75 ± 0.032 9.2 ± 1.2

September 88.8 ± 86 0.58 ± 0.033 5.7 ± 0.57

October 82.4 ± 3.6 0.46 ± 0.046 0.0 ± 0.0

November 34.4 ± 3.6 0.52 ± 0.031 0.0 ± 0.0

Dry matter production under saline conditions increases

with decreases in salinity (Chapman 1974; McGraw and

Ungar 1981; Gul and Khan 1994). Seasonal changes in dry

weight accumulation observed in this investigation appear

to be directly related to soil salinity stress. The greatest

increase in dry matter production in August and September

appear to be related to increased photosynthesis and maintenance of osmotic balance despite high soil salinity.

The salt playa community of A. occidentalis faces stressful conditions throughout the growing season. During drought

conditions the saline soils become dry and were more stressful to the plants. During such conditions the dry mass

production of plants affected by salinity, pH and conductivity increased which shows that dry season promotes salinity

increases and affects the plant growth. There is an adaptive

capability of A. occidentalis to grow better in high salinity

areas (Young and others 1995). Marks (1950) reported that

A. occidentalis in the lower Colorado desert form pure dense

stands on the moist saline soils. It is usually an indicator of

soils which are heavy textured ranging from silt loam to clay.

The high moisture content of the soil and the subsequent

evaporation may have had a cooling effect upon the temperature of the soil. Both lower temperatures and high relative

humidity would have a favorable effect on plant growth. An

increase in moisture stress throughout the season primarily

due to increases in salt from underground sources and slight

decreases in soil moisture.

Many species in the chenopodiaceae accummulate large

amounts of Na and Cl when the external salinity is high

(Albert 1975; Tiku 1975; Ungar 1978b; Flowers and Yeo

1986). Sodium and chloride were the two principal ions

responsible for increases in osmotic potential of soil samples

(Hansen and Weber 1975). They were also responsible for

85 to 95 percent of the osmotic potentials of Salicornia

utahensis. Donovan and others (1997) reported the similarity of high leaf sodium in Sarcobatus vermiculatus from

different sites throughout the growing season. They concluded that high leaf Na+

 similarity throughout the growing

season indicates a dominance of Na+

 nutrition over the

entire gradient, and a possible upper boundry of Na accumulation and tolerance for S. vermiculatus. Na+

 uptake

necessary for osmoregulation in halophytes, can start as

soon as seedlings germinate, allowing the seedlings to maintain water uptake, turgor and growth (Eddleman and Romo

1987; Romo and Haferkamp 1987). Concentration of Na+

was lower in A. occidentalis root and shoot cells in comparison with the external solution. It is possible that the

permeability of A. occidentalis root and shoot to Na+ is low

and that the Na+

 entering the root by passive diffusion is

probably removed by active efflux. This further supports the

idea of root control over the inflow of Na+

 in higher salinity

modalities. In saline and alkaline soils, availability of the

cation macronutrients, K+, Ca++, and Mg++ may also be

limited (Marschner 1995; Vasek and Lund 1980). Leaf K+

,

Ca++, and Mg++ were all consistent in Sarcobatus (Rickard

and Keough 1968; Glenn and O’ Leary 1984; Rickard 1982;

Donovan and others 1997).

Great Basin desert plants establish and persist in an

environment where halomorphic soils induce extreme osmotic stress and atmospheric precipitation is very low and

erratic and occurs largely during the winter when temperatures are too low for growth (Trent and others 1997). The

effect of soil water potential on photosynthesis, stress and

water potential of the shoots from the A. occidentalis community is inconclusive. We suspect that the plant physiological changes in the field can be explained by an increase in soil

salinity. Flanagan and Jefferies (1988) reported that as

salinity increased, photosynthesis in Plantago maritima

declined. Increased soil salinity cannot fully explain the

dramatic decrease in photosynthesis. Pearcy and Ustin

(1984) suggested that increased salinity primarily reduced

photosynthesis within the mesophyll and secondarily as a

result of reduced leaf conductance. Our data showed a larger

reduction in photosynthesis with seasonal changes. The

water potential of A. occidentalis plants was extremely

negative throughout the growing season. Trent and others

(1997) reported that xylem water potential of A. occidentalis

dropped significantly during dry seasons. Changes in Fv/Fm

stress ratio were more evident when plants were exposed to

a high stress. When plants were exposed to high irradiance

(direct sunlight) they were strongly photoinhibited (Jimenez

and others 1997). In our study low Fv/Fm values in A.

occidentalis plants were found even in low temperatures,

although the lowest values logically appeared in the higher

salinity months. This is in accordance with Sharma and Hall

(1998) and Larcher and others (1990) who only found a

decrease in this ratio when stress was added.

In conclusion, an inland salt marsh population of A.

occidentalis has been shown to be highly salt tolerant.

Growth enhancement by salinities was related to an increase in biomass of the plants, presumably due to the

stimulating effect of NaCl on plants of inland salt marsh

populations. Na+

 and Cl– were accumulated in, rather than

excluded from, the tissues; the cellular NaCl tolerance may
130 USDA Forest Service Proceedings RMRS-P-11. 1999

be related to the capacity to accumulate betains as compatible solutes. Reduced growth at high salinity apparently is

due to an insufficient supply of photosynthate to support

growth, or less than favorable water relations in shoots or

differences in ionic relations in different environmental

conditions.

References _____________________

Albert, R. 1975. Salt regulation in halophytes. Oecologia. 21: 57-71.

Brownell, P. F. 1965. Sodium as an essential micronutrient element

for a higher plant (Atriplex vesicaria). Plant Physiology. 40:

460-468.

Brownell, P. F.; Wood, J. G. 1957. Sodium as an essential micronutrient element for Atriplex vesicaria Heward. Nature. 179:

635-636.

Chapman, V. J. 1974. Salt marshes and salt deserts of the world.

eds. V Verlag and J Cramer. Bremerhaven, Fed. Rep. Germany.

494 p.

Cheesman, J. M. 1988. Mechanisms of salinity tolerance in plants.

Plant Physiology. 87: 547-550.

Cottam, G.; Curtis, J. T. 1956. The use of distance measurements in

phytosociology sampling. Ecology. 37: 451-460.

Donovan, L. A.; James, H. R.; Schaber, E. J. 1997. Nutrient relations

of the halophytic shrub, Sarcobatus vermiculatus, along a soil

salinity gradient. Plant and Soil. 190: 105-117.

Eddleman, L. E.; Romo, J. T. 1987. Sodium relations in seeds and

seedlings of Sarcobatus vermiculatus. Soil Science. 114: 143-155.

Flanagan, L. B.; Jefferies, R. L. 1988. Stomatal limitations of

photosynthesis and reduced growth of the halophyte, Plantago

maritima L. at high salinity. Plant Cell Environment. 11:

239-243.

Fisher, R. A. 1976. After effect of water stress on stomatal opening

potential. II. Possible causes. Journal of Experimental Botany.

21: 336-404.

Flowers, T. J.; Yeo, A. R. 1986. Ion relations of plants under drought

and salinity. Australian Journal of Plant Physiology. 13: 75-91.

Glenn, E. P.; O’Leary, J. W. 1984. Relationship between salt accumulation and water content of dicotyledenous halophytes. Plant

Cell Environment. 7: 253-261.

Gul, B.; Khan, M. A. 1994. Growth, osmoregulation and ion accumulation on the coastal halophyte Arthrocnemum indicum under

field conditions. Pakistan Journal of Marine Science. 3: 115-123.

Hansen, D. J.; Weber, D. J. 1975. Environmental factors in relation

to the salt content of Salicornia pacifica var utahensis. Great

Basin Naturalist. 35: 86-96.

Jimenez, M. S.; Gonzalez-Rodriguez, A. M.; Morales, D.; Cid, M. C.;

Socorro, A. R.; Khan, M. I.; Khan, M. A.; Khizar, T. 1997. Plant

growth regulators from species differing in salt tolerance as

affected by soil salinity. Plant and Soil. 45: 267-271.

Khan, M. A.; Ungar, I. A.; Showalter, A. M. 1998. Growth, water,

and ion relationship of a leaf succulent halophyte, Suaedafruticosa

(L.) Forssk. Annals of Botany.

Larcher, W.; Wagner, J.; Thammathaworn, A. 1990. Effects of

superimposed temperature stress on in vivo chlorophyll

fluorescence of Vigna unguiculata under saline stress. Journal of

Plant Physiology. 136: 92-102.

Marks, J. B. 1950. Vegetation and soil relations in the Lower

Colorado desert. Ecology. 31: 176-193.

Marschner, H. 1995. Mineral nutrition of higher plants, Second

Edition. Academic Press Inc., San Diego, CA.

McGraw, D. C.; Ungar, I. A. 1981. Growth and survival of the

halophyte Salicornia europaea L. under saline field conditions.

Ohio Journal of Science. 81: 109-113.

Moore, R. T.; Caldwell, M. M. 1972. Field use of thermocouple

psychrometers in desert soils. In: Brown, R. W.; VanHaveren, B.

P., ed. Psychrometer in water relations research. Utah Agronomy

Experimental Station.

Naidoo, G. R.; Rughunanan, R. 1990. Salt tolerance in the succulent

halophyte, Sarcocornia natalensis. Journal of Experimental

Botany. 41: 497-502.

Pearcy, R. W.; Ustin, S. L. 1984. Effects of salinity on growth and

photosynthesis of three California tidal marsh species. Oecologia.

62: 68-73.

Quigley, B. H. 1956. The interrelation and interaction of Allenrolfea occidentalis and its edaphic environment. Master thesis.

Brigham Young University.

Rickard, W. H. 1982. Cation content of leaves of deserts shrubs and

its relationship to taxonomic and ecological classification. American Midland Naturlist. 108: 311-316.

Rickard, W. H.; Keough, R. F. 1968. Soil-plant relationships of two

steppe desert plants. Plant and Soil. 29: 205-212.

Romo, J. T.; Haferkamp, M. R. 1987. effects of osmotic potential,

potassium chloride, and sodium chloride on germination of greasewood (Sarcobatus vermiculatus). Great Basin Naturalist. 47:

110-116.

SPSS Inc. 1996. SPSS: SPSS 7.0 for Windows 95. SPSS Inc. USA.

Sharma, J. R.; Hall, D. O. 1998. The effect of salinity, photoinhibition

and interaction of both on photosynthesis in barley. In: Barber, J.;

Malkin, R., ed. Techniques and New Development in Photosynthesis Research. Plenum Press, New York, London. 1998:

571-578.

Tiku, B. L. 1975. Exophysiological aspects of halophyte zonation in

saline sloughs. Plant and Soil. 43: 355-369.

Trent, J. D.; Blank, R. R.; Young, J. A. 1997. Ecophysiology of the

temperate desert halophytes: Allenrolfea occidentalis and Sarcobatus vermiculatus. Great Basin Naturalist. 57: 57-65.

Ungar, I. A. 1973. Salinity tolerance of inland halophytic vegetation

of North America. Bulletin Societe Batanik du Francais. 120:

217-222.

Ungar, I. A. 1978a. Halophyte seed germination. Botanical Review.

44: 233-264.

Ungar, I. A. 1978b. The effects of salinity and hormonal treatments

on growth and ion uptake of Salicornia europaea. French Botanical Society, Actualites Botaniques. 125: 95-104.

Vasek, F. C.; Lund, L. J. 1980. Soil characteristics associated with

primary plant succession on a Mojave desert dry lake. Ecology.

61: 1013-1018.

Waisel, Y. 1972. Biology of halophytes. Academic Press, New York.

395 p.

Young, J. A.; Blank, R. R.; Palmquist, D. E.; Trent, J. T. 1995.

Allenrolfea deserts in Western North America. Journal of Arid

Land Studies. 4: 197-205.
USDA Forest Service Proceedings RMRS-P-11. 1999 5

Community

Ecology

131

Native Perennial Grass Communities of the 

Carson Desert of Northwestern Nevada 

James A. Young 

Charlie D. Clements 

Ahstract-A generalized distribution of the perennial grasses in 

the western Great Basin reveals an inter-mixing of species of the 

two grass Tribes Hordeae and Agrostideae (following the nomenclature of Hitchcock 1950). The dominant genera are Agropyron and 

Achnatherum -Hesperostipa. In the Lahontan trough of the Carson 

Desert, a third Tribe of grasses, Zoysieae, is represented by Hilaria 

jamesii. The extreme northwestern distribution of this grass occurs 

in the Carson Desert. The plant communities associated with the 

extreme distributions of Hilaria jamesii provides insight into the 

evolution of Great Basin plant communities under changing climatic conditions. 

The shrub-dominated plant communities of the pluvial 

lake basins and lower mountain ranges ofthe western Great 

Basin often have rather depauperate representations of 

perennial grasses in the understory among the shrubs. 

Squirreltail (Elymus elymoides) is probably the most widely 

distributed species. In areas with sand-textured soils and in 

sand fields and dunes, Indian ricegrass (Achnatherum 

hymenoides) can be the aspect characterizing species. Often 

Indian ricegrass will alternate in dominance or some mix 

with needle-and-thread grass (Hesperostipa comata) on areas of sand. Rhizomatous grasses are very scarce in these 

salt desert type plant communities. On the lake plains with 

very fine-textured soils, desert saltgrass (Distichlis spicata) 

forms extensive, creeping colonies beneath black greasewood (8arcobatus vermiculatus) mounds, but in the upland 

shadscale (Atriplex confertifolia)lBailey greasewood (8. 

baileyi) communities rhizomatous grasses are very scarce. 

In the Carson Desert of western Nevada isolated stands of 

galleta (Hilariajamesii (Torr.) Ben tho are found in shadscalel 

Bailey greasewood communities. Our purpose here is to 

describe the significance of these communities in terms as 

harbingers of expressions of climatic change as expanding, 

retreating, or true relict populations. 

Galleta Grass ________ _ 

Galleta is primarily a warm desert grass rather than a 

Great Basin temperate desert species. Itisfound throughout 

the southwest, occurring in Colorado, Nevada, northern 

Arizona, New Mexico, western Texas, Utah, the panhandle 

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999. 

Proceedings: shrubland ecotones; 1998 August 12-14; Ephraim, UT. Proc. 

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 

James A. Young is a range scientist and Charlie D. Clements a wildlife 

biologist for U.S. Department of Agriculture, Agricultural Research Service, 

920 Valley Road, Reno, NV 89512. 

USDA Forest Service Proceedings RMRS-P-11. 1999 

of Oklahoma, southern Wyoming, extreme southwestern 

Kansas and eastern California. The distribution of galleta 

was summarized by Western Regional Committee W -90 of 

the Agricultural Experiment Stations (West 1972). Their 

publication is widely recognized as the authoritative source 

for this perennial grass. Many of the areas where galleta is 

found have both winter and significant summer precipitation. Very few of the locations where this grass has been 

collected have almost exclusively winter precipitation such 

as occurs in the Carson Desert. Summer thunderstorms 

occur in the Carson Desert and individual storms can produce high intensity, short duration moisture events. However, these storms occur so irregularly and are so scattered 

in distribution they have little biological significance for 

perennial species. 

Taxonomy 

What is now known as Hilariajamesii (Torr.) Benth, was 

first collected by Dr. Edwin James during an expedition of 

Major Long of the Topographical Engineers to the Rocky 

Mountains from 1819-1820 (West 1972). The type collection 

was from "Sources of the Canadian River (Texas or New 

Mexico)." The species was first described by John Torrey as 

a type of a new genus Pleuraphis. George Bentham, long 

time president ofthe Linnaean Society in London, examined 

herbarium material and placed the taxon under Hilaria. 

Recent publications, such as Jepson Manual of California 

Plants (Hickman 1993) have revised the taxon toPleuraphis 

jamesii Torrey. 

Carson Desert 

The Carson Desert lies in western Nevada in one of the 

major sub-basins of Pluvial Lake Lahontan (Russell 1885). 

The vast former lake plain is interrupted by several interior 

mountain ranges that were islands in the pluvial lake. Soils 

in the Carson Desert range from very fine-textured, salt 

influenced sediments deposited in deep water to vast sand 

fields and more limited areas of fixed or active dunes. The 

sand has been driven to the northeast across the desert 

basins and often over interior mountain ranges by the 

combination of prevailing winds. The origin of the sands is 

the deltas of the glacial-fed Susan, Truckee, Carson, and 

Walker rivers, which drain from the Sierra Nevada to Lake 

Lahontan. 

The Carson Desert is in the rain shadow of the Sierra 

Nevada and the higher ranges such as the Pine Nut and 

Virginia Range which parallel the Sierras to the east 

(Houghton and others 1975). Annual precipitation is highly 

133 

:! 

I 

!I 
i 

I, 

il 

II 

variable among years, ranging from occasional years with 

practically no measured precipitation to rare seasons with 

20 to 25 cm. The long term average for recording stations 

within the Carson Desert is usually around 12 cm. Almost all 

of this precipitation occurs as snow during the winter months. 

Distribution of Galleta In The Carson 

Desert 

In the regional publication GALLETA: TAXONOMY, 

ECOLOGY AND MANAGEMENT (West 1972) the distribution of galleta in the far western Great Basin stopped south 

of the Carson River along U.S. Highway 95 Alt in the 

foothills of Adrain Valley. On broad, old alluvial fans with 

soils derived from mixed volcanic rock and tephra, there are 

extensive colonies of galleta in this area. The northern 

distribution of galleta has been generally given as slanting 

to the northeast from the Carson Desert to the corner of 

Idaho and Utah, generally along the northern distribution of 

pinyon (Pinus)/juniper (Juniperus) woodlands. 

Hot Springs Mountains 

The Hot Springs Mountains are a low range, rising to a 

maximum of 600 m above the floor of the Carson Desert 

(Benoit and others 1982). The range is composed of recent 

volcanic flows with inter-bedded sediments. The range is 

located north of Fernly, Nevada, on the east side and running parallel to Interstate 80. The range is broken by sharp 

fault fractures running parallel yE the crest of the mountains. The most striking feature of the Hot Springs Mountains is that they are partially drowned in sand blown from 

the delta of the Truckee River where it enters Lake Lahonton. 

Plant Communities of the Hot Springs MountainsThe uplands of the mountain range barely reach the Artemisia zone. On north facing slopes, about half-way down the 

range, there is a very small patch of black sagebrush (Artemisia nova). A dwarf, woody sagebrush occurs on an outcrop 

of diatomaceous sediment on the north slope of Desert Peak, 

the highest elevation in the range. Perhaps, this is black 

sagebrush, but if so it is a very unusual form. Except for 

isolated individual plants, found in deep fault break canyons, big sagebrush (Artemisia tridentata) does not occur in 

the Hot Springs Mountains. The dominant vegetation on 

residual soils is shadscalelBailey greasewood, and on sand 

Indian ricegrass with various shrub species (Billings 1949). 

The highest portions of Desert Peak, with residual soils from 

volcanic substrates, have desert snowberry (Symphoricarpus 

longi/Zorus)/desert needlegrass (Achnatherum speciosum) 

communities. 

Galleta in the Hot Springs Mountains-Small isolated patches of galleta are found below Desert Peak on a 

broad plateau created by an unbroken volcanic flow. The 

surrounding vegetation is a very depauperate shadscalel 

Bailey greasewood community. The residual soil is very 

shallow without apparent horizon development. 

The patches of galleta are very distinctive because they 

are the only herbaceous dominated plant communities 

present in a landscape otherwise dominated by low shrubs 

and because the plant cover is so much greater than in the 

134 

surrounding shadscaleIBailey greasewood communities. 

Herbage cover in the galleta communities averaged 43% and 

herbaceous cover among the shadscale and Bailey greasewood averaged 4% and was almost entirely composed of 

cheatgrass (Bromus tectorum). 

The spring of 1988, when these communities were sampled, 

was exceptionally favorable for plant growth in the Carson 

Desert. Spring rains extended well into May. Even with the 

very favorable growth conditions, species diversity was low 

in the shadscalelBailey greasewood communities (table 1). 

The obvious difference between the shadscaleIBailey greasewood communities and the galleta community was the lack 

of shrub dominance and the overwhelming perennial grass 

dominance with galleta. The galleta did not extend as even 

an occasional plant into the shadscaleIBailey greasewood 

communities. The galleta communities were highly colorful 

in June 1998 because of the abundant flowers of Indian 

paintbrush (Castilleja chromosa) and prickly pear (Opuntia 

pulchella). Indian paintbrush plants also occurred in the 

shadscalelBailey greasewood communities, but in far more 

Table 1-Species composition based on cover in shadscale/8aiJey 

greasewood and galleta communities in the Hot Springs 

Mountains, Carson Desert, Nevada. 

Composition based on cover 

Species Shadscale/Bailey 

life form greasewood Galleta 

Percent - - - - -

Shrubs 

Atriplex confertifo/ia 27 5 

Sarcobatus vermiculatus 38 1 

Artemisia spinescens 20 0 

Krasch eninniko via 0 1 

lanata 

Total shrubs 85 7 

Perennial forbs 

Castilleja chromosa 1 4 

Astragalus lentiginosus T1 0 

Opuntia pulchella 0 2 

Mirabi/is a/ipes T 0 

Total perennial forbs 2 6 

Annual forbs 

Nama aretiodes T 0 

Camissonia claviformis T 0 

Caenactis stevioides T 0 

Pectocarya setosa T 0 

Total annual forbs 0 

Perennial grasses 

Elymus elymoides 2 0 

Hilaria jamesii 0 83 

Total perennial grasses 2 83 

Annual grass 

Bromus tectorum 10 4 

Total annual grass 10 4 

1T indicates less than 1 percent species composition. 

USDA Forest Service Proceedings RMRS-P-11. 1999 

l 
sparse populations. The Prickly pear was absolutely restricted to the galleta communities and was not found 

elsewhere in the Hot Springs Mountains, although its range 

extends across the Great Basin to Utah (Hickman 1993). 

Cheatgrass is by far the most abundant herbaceous species in the surrounding shadscalelBailey greasewood communities. The plateau is not grazed by domestic animals. 

The volcanic terrace, just below the plateau where the 

galleta occurs, had signs ofinfrequent visits by feral burros 

(Equus asinus). The distance to water is so great and the 

topography is so broken and interspersed with volcanic 

talus, it is doubtful if the plateau was ever grazed by 

domestic livestock. Despite the apparent lack of past grazing, the abundance of squirreltail was very low, even on a 

year with favorable growing conditions. The successful invasion of cheatgrass into ecologically high condition shadscalel 

Bailey greasewood communities in an arid environment 

underscores the invasive nature ofthis exotic species. Cheatgrass has only recently invaded salt desert plant communities in the western Great Basin (Young and Tipton 1990). 

The shrubs that occurred in the isolated patches of galleta 

appeared dwarfed in stature compared to those in the 

surrounding shadscalelBailey greasewood communities. One 

very dwarfed shrub appeared to be winterfat (Krascheninnikovia lanata), although there was a difference of opinion 

among taxonomists who examined vegetative specimens, 

with the alternative being a dwarf form of red molly (Kochia 

americana). The occurrence of an apparent dwarf form of 

winterfat would be interesting because the Hot Springs 

Mountains are a noted location for the occurrence of very tall 

forms of this species. The tall forms are found growing on 

angle-of-repose sand deposits in deep fault line canyons. 

Bud sagebrush (Artemisia spinescens) is often the most 

abundant woody species in shadscalelBailey greasewood 

communities in the Hot Springs Mountains. It did not occur 

in the isolated communities of galleta. 

The isolated galleta populations appeared to be growing 

on raised beds. The relatively dense herbaceous growth of 

the perennial grass has apparently trapped fine sand and 

silt particles, effectively increasing the rooting depth over 

the shallow residual soil. The sand appeared finer in texture 

than the Truckee River delta sands, partially drowning 

portions of the Hot Springs Mountains, but too coarse to 

have been subaerially deposited (personal communications 

from R. R. Blank, USDA, ARS 1998). 

Southern Carson Desert ____ _ 

What Morrison (1964) described as the Southern Carson 

Desert is that portion south of the Carson River and its 

terminal sinks. This is the area where galleta stands have 

been previously recognized and where the grass is found in 

discontinuous populations into the southern Great Basin. 

The closest previously known occurrence of galleta was 

about 80 km south and slightly west of the Hot Springs 

Mountains, as previously mentioned, in Adrain Valley (West 

1972). We conducted a reconnaissance level survey east and 

north from Adrain Valley along the Desert Mountains and 

into the Dead Camel Mountains. All of these areas are 

located south of the Carson River. We also surveyed the 

USDA Forest Service Proceedings RMRS-P-11. 1999 

portion of the Truckee Range east of Highway 95 Alt and 

north of the Carson River. 

We did not find galleta growing north of the Carson River. 

We found extensive areas of the grass south of the river 

growing on a variety of soils and occurring in a variety of 

plant assemblages. None of the edaphic or plant assemblages even roughly matched those ofthe isolated communities in the Hot Springs Mountains. 

The typical galleta communities found in Adrain Valley 

growing on old alluvial fans occur east along the foothills of 

the Desert Mountains. Galleta plants trickle down along dry 

water courses to the pluvial lake plain and form patches 

beneath black greasewood (Sarcobatus vermiculatus) plants 

growing on parma dunes. At the opposite end of the soil 

textural range, a large stand of galleta occurs just east of 

Hooten Well on the Simpson Road-Pony Express Trail. This 

stand is growing on stabilized sand dunes. 

The Dead Camel Range is another range partially drowned 

in sand similar to the Hot Springs Mountains, but in the case 

of the Dead Camel Mountains the sand came from the delta 

of the Carson River. The extensive sand fields of the relatively rolling topography of the Dead Camel Mountains 

support large nearly pure stands of Indian ricegrass or 

needle-and-thread grass and sometimes intermixtures of 

the two species. The residual soils, derived from mixed 

volcanic material, between the sand fields support shad scale! 

Bailey greasewood communities which occasionally have a 

galleta understory. This is strikingly different from the Hot 

Springs Mountains where galleta was excluded from the 

shadscalelBailey greasewood communities. 

Opuntia pulchella, which was such an abundant and 

apparently key species in the galleta communities in the Hot 

Springs Mountains, was not found in the communities south 

of the Carson River although other species ofOpuntia were 

noted. 

One galleta community found growing on the north facing 

slope of sand dunes in the higher portion of the Dead Camel 

Mountains contained Sandberg bluegrass (Poa sandbergii) 

mixed with the rhizomatous perennial. Blue grasses do not 

occur in the Hot Springs Mountains. 

The sum of the differences between the Hot Springs 

Mountains and the galleta communities south of the Carson 

River might indicate that summer precipitation is beginning 

to have biological significance in the Southern Carson Desert. 

Unfortunately, there are so few weather reporting stations 

in this sparsely populated area information does not exist to 

confirm the trend for more frequent summer precipitation. 

Discussion __________ _ 

Galleta is a perennial species that can persist in isolated 

populations through vegetative propagation. Perhaps, 

through careful exploration it would be possible to locate 

other isolated populations of this grass along the northern 

boundary of distribution across the Great Basin. Genetic 

studies of these populations, using the modern tools of 

molecular biology, could provide insight into the evolution of 

the how shrub dominated plant communities of the salt 

desert environments has and will change as climate change 

occurs. 

135 
i 

, ! 

This type of study could be flipped around to the opposite 

environmental extreme from the salt deserts in a study of 

how the perennial grasses ofthe Tribe Hordeae finger down 

the mountain ranges of the Great Basin in association with 

the woody sagebrush species. 

Based on the isolation ofthe galleta populations in the Hot 

Springs Mountains, it would seem logical that these may be 

true relict populations. The southern Carson Desert populations of galleta may be expanding populations reflecting 

climatic change, 

References __________________ ___ 

Benoit, W. R; Hiner, J. E.; Forest, R T. 1982. Discovery and geology 

of the Desert Peak geothermal field: a case history. Bulletin 97, 

Nevada Bureau of Mines, Univer. Nevada, Reno, NV. 

Billings, W. D. 1949. The shadscale vegetation zone of Nevada and 

eastern California in relation to climate and soils. The American 

Midland Naturalist 42:87-107. 

136 

Hickman,J. C. (ed.) 1993. The Jepson Manual, Univer. Calif. Press, 

Berkeley, CA 

Hitchcock, AS. 1950. Manual of the Grasses of the United States. 

USDA, Misc. Publ. No. 200, Washington, DC. Second Edition 

revised by Agnes Chase. 

Houghton, J. G.; Sakamoto, C. M.; Gifford, R O. 1975. Nev~da's 

weather and climate. Special Publ. 2, Nevada Bureau of Mmes, 

Univer. of Nevada, Reno, NV. 

Morrison, R B. 1964. Lake Lahontan-geology of the Southern 

Carson Desert. U. S, Geological Survey, Professional paper 40, 

Washington, DC. 461 p. 

Russell, I. C. 1885. Geological history of Lake Lahontan. Monograph 

No. 11. Geological Survey, Washington, DC. 366 p. 

West, N. E. (ed.) 1972. Galleta: Taxonomy, ecology, and m.anagement of Hilaria jamesii on western rangelands. Bulletm 487, 

Utah Agric. Expt. Sta., Utah State Univ., Logan, UT. 

Young, J. A; Tipton, F. 1990. Invasion of cheatgrass into arid 

environments of the Lahontan Basin. In: McArthur, E. D.; Romney, E. V.; Smith, S. D.; Tueller, P. T. comps. Proceedingssymposium on cheatgrass invasion, shrub dieoff, and other aspects of shrub biology and management; Gen Tech. Rep. INT-176, 

1989 April 5-7; Las Vegas, NV. Ogden, UT: U.S. Departme~t of 

Agriculture, Forest Service, Intermountain Research StatIOn: 

37-41. 

USDA Forest Service Proceedings RMRS-P-11. 1999 
USDA Forest Service Proceedings RMRS-P-11. 1999 137

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

W. K. Ostler, D. J. Hansen, and D. B. Hall are Biologists with Bechtel

Nevada, P.O. Box 98521, Las Vegas, NV 89193-8521.

The Classification of Shrublands on the

Nevada Test Site

W. K. Ostler

D. J. Hansen

D. B. Hall

Abstract—The Nevada Test Site (NTS) located in south-central

Nevada straddles the Mojave and Great Basin Deserts. Transitional areas between the two deserts have been created by gradients

in elevation, precipitation, temperature, and soils. In an effort to

characterize and manage resources, over 1,500 ecological landform

units (ELU) were sampled at the NTS from 1996-1998. ELUs are

small, homogeneous units of land having similar elevation, slope,

soil, geological parent material, and vegetation. ELUs were delineated for the NTS using remote sensing data, and topographic, soils,

and geological maps. ELUs were sampled for biotic and abiotic

factors, photographed, and a Global Positioning System coordinate

taken from the midpoint along the 200 m sampling transect. ELU

boundaries were digitized into a Geographical Information System.

Cluster analysis was used to classify ELUs into groups with similar

relative abundance of shrub species. The vegetation classification

system proposed by the Federal Geographic Data committee was

used to establish the structure and nomenclature of vegetation

types. A vegetation map was developed. This map and accompanying data are an integral part in resource management at the NTS.

The U.S. Department of Energy (DOE) is currently developing a resource management plan, consistent with ecosystem management principles, to preserve viable populations

of native plants and animals on the Nevada Test Site (NTS).

Before resources can be effectively managed and preserved,

they must first be identified and described. Vegetation

mapping and classification is one of the first steps in implementing ecosystem management. The NTS supports various sensitive plant and animal species that are protected by

state and federal laws or are of concern to state and federal

land and natural resource management agencies. While

numerous studies have been conducted on the NTS, there

has not been an attempt to map biological resources in a

systematic manner or to organize information needed for

ecosystem management. Previous mapping of vegetation of

the NTS was incomplete and inadequate for today’s purposes. The goal of this project was to collect essential biological information needed to fulfill the stewardship role accepted

by DOE to manage NTS resources using ecosystem management principles. Specific objectives were to: identify, classify,

and describe plant communities on the NTS consistent with

National Classification Standards (Federal Geographic Data

Committee 1996; Grossman and others 1998); develop a map

showing boundaries of delineated vegetation types; and

develop an ecosystem geographic information system to

organize, spatially display, analyze, and facilitate retrieval

and use of resource data.

Study Area _____________________

The NTS is located in south-central Nevada approximately 105 km northwest of Las Vegas (fig. 1). The NTS

encompasses approximately 3,500 km2 and straddles two

major North American deserts, Mojave and Great Basin.

Despite drastic changes to localized areas of the NTS due to

nuclear testing activities over the past 40 years, biological

resources over much of the NTS remain relatively pristine

and undisturbed. DOE estimates that only 7 percent of the

site has been disturbed.

The southern two-thirds of the NTS is dominated by three

large valleys or basins: Yucca, Frenchman, and Jackass

Flats (fig. 1). Mountain ridges and hills rise above sloping

alluvial fans and enclose these basins. During years of high

precipitation, surface waters collect and form shallow lakes

in the closed basins of Yucca and Frenchman Flats. Jackass

Flats is an open basin and drains to the southwest via

Fortymile Wash. Mercury, Rock, Topopah, and Mid valleys

are smaller basins with off-site drainage. The northern,

northwestern, and west-central sections of the NTS are

dominated by Pahute and Rainier mesas and Timber and

Shoshone mountains. Elevation on the NTS ranges from less

than 1,000 meters (m) above sea level in Frenchman and

Jackass Flats to about 2,340 m on Rainier Mesa.

NTS has a climate characteristic of high deserts with little

precipitation, hot summers, mild winters and large diurnal

temperature ranges. Monthly average temperatures in the

NTS area range from 7 °C in January to 32 °C in July (DOE

1996). The average annual precipitation on the NTS ranges

from 15 cm at the lower elevations to 23 cm at the higher

elevations (DOE 1996). About 60 percent of this precipitation occurs from September through March. Winter precipitation frequently occurs as snow, which persists in northern

Yucca Flat and to the north. Snow seldom persists for more

than a few hours in the southern valleys.

The NTS is located in an area of southern Nevada that

lies between the Great Basin Desert and the Mojave Desert

as defined by Jaeger (1957). Within the site boundaries are

found both of these desert types. Transitional areas between the two deserts are also present, having been created

by gradients in precipitation, temperature, and soils. Unique

combinations of physical site conditions have created
138 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 1—Major topographic features of the Nevada Test Site.
USDA Forest Service Proceedings RMRS-P-11. 1999 139

different vegetation patterns on the NTS that have challenged development of a simple classification system.

Description of Vegetation Types on the

Nevada Test Site

Descriptions of vegetation types of the NTS consist of

three major classification efforts. Two of these efforts were

done between 1958 and 1963. The third was published in

1976 and is the most detailed. In 1957, work was undertaken

by New Mexico Highlands University to appraise the extent

of nuclear effects on vegetation at the NTS. Eight vegetation

zones were defined by Shields (1958) in these initial surveys.

Subsequently, Shields and others (1959) and Shields and

Rickard (1960) redefined these zones as vegetation types.

Ecological surveys of the flora and fauna were initiated in

1959 (Allred and others 1963a,b) to determine the effects of

past nuclear detonations that began at the NTS in 1951.

Principal objectives of the project were to determine the

kinds, population, seasonal occurrence, geographic and ecological distribution, migration, home range, and related

habits of native animals in these areas. Six plant communities were recognized: Larrea-Ambrosia (Franseria), GrayiaLycium, Coleogyne, Atriplex-Kochia, Salsola, and PinyonJuniper, although no community boundaries were delineated,

nor vegetation map produced. Predominant plant species in

each plant community were identified and communities

were described. A listing of some of the more common plants

found in several communities were given in their appendix,

listing vertebrate and invertebrate animals by plant community type. Seasonal occurrence and relative abundance

data of these animals were also presented.

Beatley (1976) provided the most detailed description of

vegetation on the NTS based on field observations recorded

at the time of collection of herbarium specimens, and data

from 68 permanent study sites on the NTS during the period

of 1962 to 1975. Sites were selected as representative of the

major kinds of ecosystems in the region. Vegetation and

environmental data, including percent cover by perennial

plant species, plant density, rainfall, temperature, soil texture, and soil moisture were also collected and summarized.

Beatley (1976) recognized 12 plant associations as occurring

on the NTS. Additionally, descriptions were also provided

for disturbed sites, introduced species, and endangered and

threatened species. Descriptions of plant associations were

provided in a narrative form that makes comparison of similarities and differences between plant associations difficult.

Nevada Test Site Vegetation Maps

There has been no major effort to map the vegetative

resources of the NTS in the past. The only complete vegetation map for the NTS prior to 1997 was a 14 x 18 cm map

produced by Beatley (1976). By contrast, this same area is

covered by 32 United States Geological Survey (USGS) 7.5

minute quadrangle maps. Beatley’s vegetation map, showing location of plant associations and study sites, is only

approximate and the author recognizes that “all boundaries

are generalized and approximate.” The vegetation map was

highly simplified and lacked desirable cartographic qualities such as color, distinguishable type symbols and boundaries, and detail needed for interpretive use. The cartography was not corrected for proper orientation relative to

acceptable coordinate systems such as decimal degrees,

Universal Transverse Mercator, State Plane, or longitude

and latitude. Enhancements to Beatley’s original map were

provided by O’Farrell and Emery (1976) by refining symbol

patterns and correcting legend and symbol ambiguities.

O’Farrell and Emery further described the NTS vegetation;

however, no vegetation classification was made.

Mapping Unit Delineation

Selection of applicable mapping units is critical in developing a vegetation map. Ecological landform units (ELUs)

were utilized as the base for our vegetation map rather than

a standard unit area (Bailey and others 1994). Landforms

are three-dimensional parts of the general land surface that

are distinctive and repeat themselves frequently across the

landscape in fairly consistent positions with respect to

surrounding landforms. Examples of landforms are mountains, piedmont slopes, alluvial fans, stream channels, valley floors, and playas. In desert areas of Nevada, many of

these landforms are composed of distinctive materials and

are highly correlated with soil consociations (Peterson 1981).

Because the landforms can be readily discerned from aerial

photography, their boundaries can be recognized with a high

degree of accuracy. Soils of a particular landform are frequently quite uniform. Landforms provide a means of rapidly identifying boundaries of soil consociations which, in

turn, are highly correlated with plant communities or wildlife habitat.

When the landscape is delineated into small mapping

units (1 to 10 acres in size) using aerial photography and

multispectral satellite imagery, the area is a mosaic of land

features that closely approximate an Order 2 Soil Survey.

This corresponds to the minimum size delineation, which is

approximately 1.6 cm square (about 2.2 hectares (ha) at

1:24,000 scale) (Holdorf 1989). When these landform units

are visited in the field by trained scientists, observations can

be made of the delineated areas to determine if the vegetation is relatively homogeneous over the unit or if a mosaic of

vegetation patterns exists within the mapping unit. When

landform units with mosaics are divided into subunits that

have relatively homogeneous plant communities, these resulting landform units have been referred to as ELUs. The

physical (e.g., soils, slope, geology, and hydrology) and biological (e.g., plant community composition and structure)

parameters also strongly influence the types of animals (e.g.,

insects, birds, mammals, and reptiles) that will be found in

these ELUs. Because the soils, slope, geology, hydrology,

vegetation, and animals are all relatively uniform and homogeneous within these ELUs, they represent a meaningful

mapping unit that can be hierarchically combined with other

similar units into a statistically defensible (e.g., dendrogram

based on cluster analyses) collection of plant community

types for the purpose of mapping plant communities, determining wildlife habitat, and establishing plant species ranges.
140 USDA Forest Service Proceedings RMRS-P-11. 1999

Methods _______________________

The development of our detailed vegetation map and

classification system built upon the efforts of earlier classification efforts; however, the process utilized evolving technologies and new national standards that provide guidance

for terrestrial ecosystem mapping (Federal Geographic Data

Committee 1996; Grossman and others 1998). The classification system used is a community type system as recognized by scientists dealing with habitat delineation (Hironaka

1986; Ferguson and others 1989; Wellner 1989). It is a

combination of physiognomic levels and floristic levels

(Grossman and others 1998). It is based on delineation of

ELUs and quantitative sampling of these areas. A similar

approach was used in mapping wildlife habitat in the East

Mojave Desert (Berry 1979). Spatial and tabular data have

been organized using a Geographic Information System

(GIS) ArcView® 3.1 to facilitate retrieval and use of information. A description of the methods for ELU delineation, field

surveys, data analysis and vegetation classification, and

image analysis follows.

Ecological Landform Unit Delineation

Mapping of ELUs was initiated by first identifying landforms and delineating their boundaries from prints of aerial

photographs (1:24,000 scale). These boundaries were traced

onto clear plastic sheets registered to the underlying digital

prints as published in the Nevada Test Site Grid Map, A Grid

System Photo Locator Map of the Nevada Test Site (DOE

1995). Boundaries of landforms with similar physical and

biological properties were then verified in the field and

modified, if needed, to delineate ELUs.

The area within an ELU has approximately the same

slope, soils, vegetation, and wildlife. The intent was not to

arbitrarily classify the ELU as a particular vegetation type

or subtype, but rather to delineate all of the basic building

blocks or areas that would respond similarly to management

practices, and then describe physical and biological characteristics within these areas. Descriptions of the ELUs were

made by selecting representative areas, visiting the areas,

and recording information about each ELU on data sheets.

While most ELUs were several ha in size, some having

rather unique environmental conditions were sampled and

delineated in areas as small as 1 ha in size.

Field Surveys

Over 1,500 ELUs were sampled from 1996 through 1998.

Information gathered on each ELU included: location; elevation; slope; aspect; geology; landform; surface soil texture;

erosion pavement; dominant species of shrubs/trees, forbs,

grasses, and cacti; percent plant cover; rodent activity; wild

horse signs; productivity of annual species; and presence of

microbiotic crusts. Universal Transverse Mercator coordinates and one or more representative photographs were

taken to document the location and appearance of the

vegetation and landscape at each transect. Vegetation data

were gathered along 200 m long linear transects with an

observation point located every 20 m along the transect

(i.e., 10 points per transect). At each observation point, the

names of the five closest shrubs to the point were recorded.

The relative abundance of forbs, grasses, cacti, and other

important species such as threatened and endangered

plant species were also recorded and ranked (the most

abundant species received a ranking of 1, the second most

abundant species received a ranking of 2, etc.). Animals

observed, as well as physical conditions of the environment, were described.

Not all ELUs delineated on the NTS were sampled. Based

on ground observations, areas that appeared similar in

physical and biological characteristics to an adjacently

sampled area were not sampled if access was too difficult.

These unsampled ELUs were assigned the same characterization values as an adjacent sampled ELU. On long slopes

where species composition of the vegetation changed in

response to environmental gradients like increase in soil

texture or soil moisture, two or more transects were used to

document the species change. Arbitrary boundaries between the two sampling points were drawn on the map

(straight lines half way between the two transects) to suggest that the upper polygon was most closely described by

the transect in the upper reaches of the slope while the lower

polygon was most closely described by the transect in the

lower reaches of the slope.

Plant species nomenclature was checked for accuracy

using voucher specimens and other taxonomic aids. Samples

of uncommon or unique species were collected when encountered and placed in the NTS herbarium. Plant species were

identified using several published floras (Kartesz 1988;

Hickman 1993; Welsh and others 1993; Cronquist and

others 1994). When the phenological stage of the plant was

less than optimal for identification (e.g., before or after

flowering when the plant lacked key taxonomic features), a

species or variety was determined from a combination of the

taxonomic keys and which species was most commonly

reported (e.g., Beatley 1976) to occur in that community

type. Plant nomenclature used on the NTS up to 1997

generally followed Beatley (1976). However, with the taxonomic revision of some phylogenetic relationships and subsequent reassignment of several plants into more appropriate genera, a need arose to reflect current standardized

nomenclature. In 1996, the Biota of North America Program, under the direction of Dr. John Kartesz, published a

revised list of plant names, both scientific and vernacular

(common) for North America (USDA 1996). Alphanumeric

plant symbols were also assigned to each species or subspecies. This list became the standard to be used by all federal

agencies. Starting in 1997, plant nomenclature on the NTS

was changed to reflect those of the National Plant Data

Center (USDA 1996). Synonyms were retained in the database as a crosswalk to earlier nomenclature of Beatley

(1976).

Soil samples were taken from representative portions of

the area being sampled (i.e., the ELU), usually from the

surface soil just under the perimeter of the shrub canopy.

Atypical areas, such as rocky outcrops, rodent diggings,

desert pavement, or disturbances, were avoided. The intent

was to sample soil in an area that represented the most likely

microsite for germinating seeds. Large rocks and plant litter

were carefully removed from the surface exposing the mineral soil. Approximately 100 milliliters (ml) of soil was

scooped into small plastic containers. Samples were labeled

with the number of the site and returned to the laboratory in

Mercury, Nevada, for processing. Soil samples were sieved
USDA Forest Service Proceedings RMRS-P-11. 1999 141

through a 2 mm-sized sieve to remove gravel and plant

debris. Screened samples were then wetted with tap water

to gradually moisten the sample. The palm-sized sample

was kneaded in the hand to mix the soil and water thoroughly. A textural particle-size class was then assigned

based on the ribbon and grit properties of the sample

(Brady 1974).

Data Analysis and Vegetation

Classification

After an initial review of field data sheets for accuracy,

data were entered into custom data forms using

Microsoft®Access software. Field values were subjected to

validation rules to ensure that entries were within given

size ranges and of proper data type (e.g., alphanumeric

versus numeric or logical). The relational database consisted of five main data forms: (1) site data entry form,

(2) shrub and tree data entry form, (3) herb and grass data

entry form, and (4) cacti and other species (e.g., threatened

and endangered plant species) data entry form, and

(5) plant nomenclature data entry form. Data entry items

that were not legible or unclear were marked for review by

the collector (field scientist) and data were entered, corrected, or reentered. Data tables were exported for use in

Excel® and ArcView® software.

Descriptive statistics were used to summarize and describe data. MINITAB® and Systat® 5.0 software were used

to provide statistical analyses such as cluster analysis,

correlation analysis, and regression analysis. Cluster analysis was used to identify similar ELUs for purposes of classifying vegetation, consistent with national vegetation classification standards. The clustering program utilized squared

Euclidean distance and average linkage to separate unique

cluster groups. Clustering was based on the quantitative

characteristics of only shrubs and trees recorded along each

transect. Forbs and grasses were not used in this analysis.

Cluster groups were assigned to a national vegetation classification category based on the dominant shrubs and trees

in each group. ELUs were assigned a number based on the

cluster group in which they occurred. These groups were

used to produce a vegetation map of the NTS. This removed

many of the problems of having to subjectively decide in the

field which classification category the ELU falls into without

having seen all the site, comparing sites, or having field data

to support the classification decision.

Image Analyses

A GIS was developed to manage and display data collected during the mapping and classification efforts. The

resulting system was referred to as the Ecosystem Geographic Information System. It was developed using

ArcView® 3.1. Metadata conformed to proposed Content

Standard for National Biological Information Infrastructure Metadata (National Biological Service 1995).

Landform units were delineated on 32 images corresponding in area to the 32 USGS 7.5 minute quadrangles that

cover the NTS. The digital images were produced by combining 20-m resolution Satellite Pour L’Observation de la Terre

(SPOT) color digital imagery with 10-m resolution SPOT

black and white imagery and printed to the appropriate

scale. Landforms were distinguished on the image by differences in texture and color. Boundaries were drawn onto

clear acetate overlays attached to and registered with the

underlying map image. When available, clear overlays of

USGS topographic maps were inserted between the image

base and the upper overlay to assist in interpreting slope and

aspect.

In addition to the SPOT images, 240 photo maps of the NTS

and surrounding areas were used to provide greater detail for

photo interpretation. The NTS Grid Map collection was obtained by aerial photographic mapping missions that were

flown in August and September of 1994 by DOE's Remote

Sensing Laboratory. The missions were flown at 488 m above

ground level using two photogrammetric cameras with normal color film and infrared color film. The grid map atlas was

printed from the normal color photography at a scale of

roughly 1:24,000. Registration of latitude and longitude

was only approximate with apparent discrepancies observed from sheet to sheet. Maps were considered accurate

to 30(+/–) meters. Prints of selected images (i.e., photo

negatives were made to provide higher resolution for distinguishing textural differences due to differences in shrub

types and cover. These photographic prints were used in

the field to verify ELU boundaries.

After the final corrections were made to the delineated

boundaries of the ELUs based on the field verification and

photo maps, the ELU boundaries were digitized, using

ESRI's® Data Automation KitTM. Boundaries were verified

and then the polygons (ELUs) were labeled with the appropriate ELU number. This coverage was then linked to the

Access® database using Arcview® 3.1 software.

Results ________________________

Vegetation Classification

The result from the cluster analysis is shown in figure 2.

Based on this cluster process, 10 alliances and 20 associations were recognized as occurring on the NTS. Several

ELUs did not cluster as groups but remained as single units

due to their unique vegetation. These ELUs were listed

together in a miscellaneous category on the final map.

Results of the classification are shown in table 1. There are

three alliances within the Mojave Desert, three within a

transition zone, and four within in the Great Basin Desert.

A brief summary description of each association follows.

Relative abundance values for primary and associated species are enclosed in parentheses.

Mojave Desert

Lycium spp. Shrubland Alliance

Lycium shockleyi - Lycium pallidum Shrubland

Primary species: Shockley's desertthorn (Lycium shockleyi)

(47), rabbit thorn (Lycium pallidum) (17)

Associated species: White bursage (Ambrosia dumosa) (12),

fourwing saltbush (Atriplex canescens) (9), and shadscale

saltbush (Atriplex confertifolia) (8)

Species diversity: 11 species total; averaged 8.8 perennial

species/ELU

Number of ELUs/area of NTS: 4/1,484 ha (0.4%)

Landforms: basins, alluvial flats
142 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 2—Cluster groups showing major vegetation associations on the NTS. 1 = Lycium shockleyi-Lyciumpallidum shrubland,

2 = Atriplex confertifolia-Kochia americana shrubland, 3 = Atriplex canescens-Krascheninnikovia lanata shrubland, 4 = Ericameria

nauseosa-Ephedra nevadensis shrubland, 5 = Coleogyne ramosissima-Ephedra nevadensis shrubland, 6 = Hymenoclea salsolaEphedra nevadensis shrubland, 7 = Lycium andersonii-Hymenoclea salsola shrubland, 8 = Ambrosia dumosa-Larrea tridentata

shrubland, 9 = Atriplex confertifolia-Ambrosia dumosa shrubland, 10 = Menodora spinescens-Ephedra nevadensis shrubland,

11 = Eriogonum fasciculatum-Ephedra nevadensis shrubland, 12 = Krascheninnikovia lanata-Ephedra nevadensis shrubland,

13 = Ephreda nevadensis-Grayia spinosa shrubland, 14 = Chrysothamnus viscidiflorus-Ephedra nevadensis shrubland,

15 = Ephedra viridis-Artemisia tridentata shrubland, 16 = Pinus monophylla-Artemisia tridentata woodland, 17 = Artemisia

tridentata-Chrysothamnus viscidiflorus shrubland, 18 = Pinum monophylla-Artemisia nova woodland, 19 = Artemisia novaChrysothamnus viscidiflorus shrubland, 20 = Artemisia nova-Artemisia tridentata shrubland.

Geology: Quaternary alluvium

Elevation: average 941 m, range 940-943 m

Precipitation: 12.8 cm

Slopes: average 0.8°, range 0-1°

Soils: clay-clay loam (L. shockleyi), sand (L. pallidum)

Annuals: very low

Larrea tridentata/Ambrosia dumosa Shrubland Alliance

Larrea tridentata/Ambrosia dumosa Shrubland

Primary species: White bursage (43), Creosote bush (Larrea

tridentata) (12)

Associated species: Nevada jointfir (Ephedra nevadensis)

(7), Range ratany (Krameria erecta) (7), rabbit thorn (6)

Species diversity: 49 species total; averaged 13.2 perennial

species/ELU

Number of ELUs/area of NTS: 287/61,050 ha (18.0%)

Landforms: variable from basin to foothill slopes of mountains, mostly piedmont slopes

Geology: Quaternary alluvium

Elevation: average 1,080 m, range 847-1,628 m

Precipitation: 14.5 cm

Slopes: average 5.7°, range 1-42°

Soils: primarily sand to sandy loam

Annuals: very low to moderate

Atriplex confertifolia—Ambrosia dumosa Shrubland

Alliance

Atriplex confertifolia—Ambrosia dumosa Shrubland

Primary species: Shadscale saltbush (31), White bursage (16)

Associated species: Nevada jointfir (9), Anderson’s wolfberry

(Lycium andersonii) (6), Winterfat (Krascheninnikovia

lanata) (4), Creosote bush (4)

Species diversity: 49 species total; averaged 16.2 perennial

species/ELU

Number of ELUs/area of NTS: 51/11,577 ha (3.4%)

Landforms: mountains

Geology: variable, mostly Quaternary alluvium/colluvium

with some older limestones and Tertiary tuffs

Elevation: average 1,153 m, range 932-1,494 m

Precipitation: 15.4 cm

Slopes: average 13.6°, range 1-53°

Soils: primarily sandy loam to loam

Annuals: very low-moderate
USDA Forest Service Proceedings RMRS-P-11. 1999 143

Table 1—Classification of NTS shrublands.

Mojave Desert

Lycium spp. Shrubland Alliance

Lycium shockleyi—Lycium pallidum Shrubland

Larrea tridentata/Ambrosia dumosa Shrubland Alliance

Larrea tridentata /Ambrosia dumosa Shrubland

Atriplex confertifolia—Ambrosia dumosa Shrubland Alliance

Atriplex confertifolia—Ambrosia dumosa Shrubland

Transition Zone

Hymenoclea-Lycium Shrubland Alliance

Lycium andersonii—Hymenoclea salsola Shrubland

Hymenoclea salsola—Ephedra nevadensis Shrubland

Ephedra nevadensis Shrubland Alliance

Menodora spinescens—Ephedra nevadensis Shrubland

Krascheninnikovia lanata—Ephedra nevadensis Shrubland

Eriogonum fasciculatum—Ephedra nevadensis Shrubland

Ephedra nevadensis—Grayia spinosa Shrubland

Coleogyne ramosissima Shrubland Alliance

Coleogyne ramosissima—Ephedra nevadensis Shrubland

Great Basin Desert

Atriplex spp. Shrubland Alliance

Atriplex confertifolia—Kochia americana Shrubland

Atriplex canescens—Krascheninnikovia lanata Shrubland

Chrysothamnus-Ericameria Shrubland Alliance

Chrysothamnus viscidiflorus—Ephedra nevadensis Shrubland

Ericameria nauseosa—Ephedra nevadensis Shrubland

Artemisia spp. Shrubland Alliance

Ephedra viridis—Artemisia tridentata Shrubland

Artemisia tridentata—Chrysothamnus viscidiflorus Shrubland

Artemisia nova—Chrysothamnus viscidiflorus Shrubland

Artemisia nova—Artemisia tridentata Shrubland

Pinus monophylla/Artemisia spp. Woodland Alliance

Pinus monophylla/Artemisia nova Woodland

Pinus monophylla/Artemisia tridentata Woodland

Transition

Hymenoclea-Lycium Shrubland Alliance

Lycium andersonii—Hymenoclea salsola Shrubland

Primary species: Anderson’s wolfberry (52), White burrobrush

(Hymenoclea salsola) (10)

Associated species: Winterfat (7), Fourwing saltbush (6),

Nevada jointfir (6), Spiny hopsage (Grayia spinosa) (5)

Species diversity: 23 species total; averaged 12.8 perennial

species/ELU

Number of ELUs/area of NTS: 11/1,489 ha (0.4%)

Landforms: mostly lower piedmont slopes, fan piedmont-fan

skirt

Geology: Quaternary alluvium

Elevation: average 1,263 m, range 942-1,408 m

Precipitation: 16.8 cm

Slopes: average 2.3°, range 1-31°

Soils: primarily sand to sandy loam

Annuals: moderate to very high

Hymenoclea salsola—Ephedra nevadensis Shrubland

Primary species: White burrobrush (52), Nevada jointfir (9)

Associated species: Green rabbitbrush (Chrysothamnus

viscidiflorus) (5), Fourwing saltbush (5), Anderson’s wolfberry (5)

Species diversity: 50 species total; averaged 15.2 perennial

species/ELU

Number of ELUs/area of NTS: 44/6,709 ha (2.0%)

Landforms: lower piedmont slopes, fan piedmont-fan skirt

Geology: Quaternary alluvium/colluvium

Elevation: average 1,263 m, range 950-1,530 m

Precipitation: 16.8 cm

Slopes: average 3.8°, range 1-31°

Soils: primarily sand to sandy loam

Annuals: moderate to very high

Ephedra nevadensis Shrubland Alliance

Menodora spinescens—Ephedra nevadensis Shrubland

Primary species: Spiny menodora (Menodora spinescens)

(14), Nevada jointfir (12), White bursage (10)

Associated species: Shadscale saltbush (8), Blackbrush

(Coleogyne ramosissima) (5), Range ratany (5), Anderson’s

wolfberry (5)

Species diversity: 50 species total; averaged 17.6 perennial

species/ELU

Number of ELUs/area of NTS: 42/8,614 ha (2.5%)

Landforms: upper piedmont slopes to mountain foothills

Geology: mostly Quaternary alluvium/colluvium with some

Tertiary tuffs

Elevation: average 1,198 m, range 993-1,548 m

Precipitation: 16.0 cm

Slopes: average 8.0°, range 1-48°

Soils: primarily sandy loam to loam

Annuals: very low to moderate

Krascheninnikovia lanata—Ephedra nevadensis Shrubland

Primary species: Winterfat (29), Nevada jointfir (12)

Associated species: Spiny hopsage (Grayia spinosa) (8),

Budsage (Artemisia spinescens) (5), Shadscale saltbush (5),

White bursage (4)

Species diversity: 34 species total; averaged 17.6 perennial

species/ELU

Number of ELUs/area of NTS: 29/4,046 ha (1.2%)

Landforms: variable, mostly lower piedmont slopes, fan

piedmont-fan skirt

Geology: Quaternary alluvium/colluvium

Elevation: average 1,258 m, range 1,042-1,463 m

Precipitation: 16.7 cm

Slopes: average 3.6°, range 1-14°

Soils: primarily loamy sand to loam

Annuals: moderate

Eriogonum fasciculatum—Ephedra nevadensis Shrubland

Primary species: Eastern Mojave buckwheat (Eriogonum

fasciculatum) (28), Nevada jointfir (16)

Associated species: White bursage (5), Range ratany (5),

Spiny hopsage (4), Winterfat (4)

Species diversity: 36 species total; averaged 20.4 perennial

species/ELU

Number of ELUs/area of NTS: 14/10,176 ha (3.0%)

Landforms: mountains (mostly in southern NTS)

Geology: Tertiary tuffs

Elevation: average 1,292 m, range 1,140-1,579 m

Precipitation: 17.1 cm

Slopes: average 36.3°, 19-70°

Soils: gravel to sandy loam

Annuals: very low to moderate

Ephedra nevadensis—Grayia spinosa Shrubland

Primary species: Nevada jointfir (23), Spiny hopsage (8),

Fourwing saltbush (8), White burrobrush (8)
144 USDA Forest Service Proceedings RMRS-P-11. 1999

Associates species: Anderson’s wolfberry (6), Green rabbitbrush (5), Cooper’s heathgoldenrod (Ericameria cooperi)

(5), Blackbrush (4)

Species diversity: 66 species total; averaged 19.7 perennial

species/ELU

Number of ELUs/area of NTS: 93/20,067 ha (5.9%)

Landforms: highly variable from basin to mountain

Geology: mostly Quaternary alluvium/colluvium with some

Tertiary tuffs

Elevation: average 1,413 m, range 988-1,884 m

Precipitation: 18.7 cm

Slopes: average 8.8°, range 1-70°

Soils: primarily loamy sand to loam

Annuals: moderate to very high

Coleogyne ramosissima Shrubland Alliance

Coleogyne ramosissima—Ephedra nevadensis Shrubland

Primary species: Blackbrush (56), Nevada jointfir (10)

Associated species: Andersonís wolfberry (3), White

burrobrush (3)

Species diversity: 84 species total; averaged 16.9 perennial

species/ELU

Number of ELUs/area of NTS: 325/72,976 ha (21.6%)

Landforms: variable, mostly piedmont slopes to lower slopes

of mountains

Geology: highly variable, mostly Quaternary alluvium/colluvium with both older limestones and some Tertiary tuffs

Elevation: average 1,385 m, range 981-1,865 m

Precipitation: 18.3 cm

Slopes: average 8.5°, range 1-53°

Soils: primarily loamy sand to loam

Annuals: very low to moderate

Great Basin Desert

Atriplex spp. Shrubland Alliance

Atriplex confertifolia—Kochia americana Shrubland

Primary species: Shadscale saltbush (50), Greenmolly (Kochia

americana) (22)

Associated species: Budsage (7), Spiny menodora (6),

Anderson’s wolfberry (5)

Species diversity: 53 species total; averaged 9.2 perennial

species/ELU

Number of ELUs/area of NTS: 17/3,211 ha (0.9%)

Landforms: basin, alluvial flat

Geology: quaternary alluvium

Elevation: average 1,208 m, range 940-1,382 m

Precipitation: 16.1 cm

Slopes: average 2.7°, range 0-20°

Soils: primarily sandy loam to clay loam

Annuals: low to moderate

Atriplex canescens—Krascheninnikovia lanata Shrubland

Primary species: Fourwing saltbush (58), Winterfat (11)

Associated species: Anderson’s wolfberry (5), White

burrobrush (4)

Species diversity: 87 species total; averaged 11.9 perennial

species/ELU

Number of ELUs/area of NTS: 38/7,275 ha (2.2%)

Landforms: basin alluvial flats to lower piedmont slopes-fan

skirt

Geology: mostly Quaternary alluvium/colluvium with some

Tertiary tuffs

Elevation: average 1,237 m, range 940-1,707 m

Precipitation: 16.5 cm

Slopes: average 3.5°, range 0-24°

Soils: sand to sandy loam

Annuals: moderate to very high

Chrysothamnus-Ericameria Shrubland Alliance

Chrysothamnus viscidiflorus—Ephedra nevadensis

Shrubland

Primary species: Green rabbitbrush (37), Nevada jointfir (11)

Associated species: Fourwing saltbush (7), Winterfat (5),

Spiny hopsage (5), Basin big sagebrush (Artemisia tridentata ssp. tridentata) (5), Anderson’s wolfberry (5), Shadscale

saltbush (4)

Species diversity: 61 species total; averaged 21.4 perennial

species/ELU

Number of ELUs/area of NTS: 77/16,114 ha (4.8%)

Landforms: variable, mostly mountains to upper piedmont

slopes

Geology: mostly Quaternary alluvium/colluvium with some

Tertiary tuffs

Elevation: average 1,495 m, range 1,198-2,292 m

Precipitation: 19.7 cm

Slopes: average 7.2°, range 0-38°

Soils: primarily loamy sand to loam

Annuals: low to moderate

Ericameria nauseosa—Ephedra nevadensis Shrubland

Primary species: Rubber rabbitbrush (Ericameria nauseosa)

(52), Nevada jointfir (11)

Associated species: Basin big sagebrush (6), Blackbrush (5),

Fourwing saltbush (5), Green rabbitbrush (4)

Species diversity: 43 species total; averaged 17.1 perennial

species/ELU

Number of ELUs/area of NTS: 21/2,873 ha (0.8%)

Landforms: variable, mostly piedmont slopes to mountains

Geology: mostly Quaternary alluvium/colluvium with some

Tertiary tuffs

Elevation: average 1,563 m, range 1,311-2,018 m

Precipitation: 20.5 cm

Slopes: average 6.9°, range 1-28°

Soils: primarily sand to sandy loam

Annuals: moderate to very high

Artemisia spp. Shrubland Alliance

Ephedra viridis—Artemisia tridentata Shrubland

Primary species: Mormon tea (Ephedra viridis) (21), Basin

big sagebrush (16), Desert bitterbrush (Purshia

glandulosa) (15)

Associated species: Stansbury cliffrose (Purshia

stansburyiana) (9), Eastern Mojave buckwheat (6), Puberulent green rabbitbrush (5)

Species diversity: 42 species total; averaged 27.0 perennial

species/ELU

Number of ELUs/area of NTS: 21/8,585 ha (2.5%)

Landforms: mountains

Geology: mostly Tertiary tuffs

Elevation: average 1,721 m, range 1,402-2,012 m

Precipitation: 22.5 cm

Slopes: average 18.2°, range 4-35°

Soils: primarily sandy loam to silt loam

Annuals: moderate to very high

Artemisia tridentata—Chrysothamnus viscidiflorus

Shrubland
USDA Forest Service Proceedings RMRS-P-11. 1999 145

Primary species: Basin big sagebrush (56), Green rabbitbrush (8)

Associated species: Nevada jointfir (7), Puberulent green

rabbitbrush (Chrysothamnus viscidiflorus ssp. puberulus)

(3), Granite pricklygilia (Leptodactylon pungens) (3)

Species diversity: 73 species total; averaged 20.8 perennial

species/ELU

Number of ELUs/area of NTS: 142/24,703 ha (7.3%)

Landforms: mostly mountains, some upper piedmont slopes

Geology: mostly Tertiary tuffs with some Quaternary alluvium/colluvium

Elevation: average 1,780 m, range 1,298-2,225 m

Precipitation: 23.2 cm

Slopes: average 6.1°, range 0-65°

Soils: primarily loamy sand to loam

Annuals: very low to moderate

Artemisia nova—Chrysothamnus viscidiflorus Shrubland

Primary species: Black sagebrush (68), Green rabbitbrush (5)

Associated species: Nevada jointfir (4), Basin Big Sagebrush

(4), Puberulent green rabbitbrush (3), Spiny hopsage (2)

Species diversity: 56 species total; averaged 24.7 perennial

species/ELU

Number of ELUs/area of NTS: 104/23,478 ha (6.9%)

Landforms: mostly mountains, foothills, and mesas.

Geology: mostly Tertiary tuffs with some Quaternary alluvium/colluvium

Elevation: average 1,811 m, range 1,433-2,120 m

Precipitation: 23.6 cm

Slopes: average 6.6°, range 0-28°

Soils: primarily sandy loam to loam

Annuals: very low to low

Artemisia nova—Artemisia tridentata Shrubland

Primary species: Black sagebrush (Artemisia nova) (34),

Basin big sagebrush (25)

Associated species: Puberulent green rabbitbrush (8), Green

rabbitbrush (5), Granite pricklygilia (4)

Species diversity: 47 species total; averaged 29.1 perennial

species/ELU

Number of ELUs/area of NTS: 32/4,567 ha (1.4%)

Landforms: mountains

Geology: mostly Tertiary tuffs

Elevation: average 1,843 m, range 1,622-2,079 m

Precipitation: 24.0 cm

Slopes: average 8.9°, range 1-38°

Soils: primarily loamy sand to loam

Annuals: very low to moderate

Pinus monophylla/Artemisia spp. Woodland Alliance

Pinus monophylla/Artemisia nova Woodland

Primary species: Black sagebrush (55), Singleleaf pinyon

(Pinus monophylla) (14)

Associated species: Utah juniper (Juniperus osteosperma)

(6), Green rabbitbrush (4), Basin big sagebrush (3), granite

pricklygilia (2), and Mormon tea (2).

Species diversity: 54 species total; averaged 27.0 perennial

species/ELU

Number of ELUs/area of NTS: 76/24,930 ha (7.4%)

Landforms: mountains, mid slopes to mesas

Geology: mostly Tertiary tuffs

Elevation: average 1,982 m, range 1,725-2,201 m

Precipitation: 25.8 cm

Slopes: average 7.7°, range 1-58°

Soils: primarily sandy loam to loam

Annuals: very low to low

Pinus monophylla/Artemisia tridentata Woodland

Primary species: Singleleaf pinyon (28), Basin big sagebrush (23)

Associated species: Antelope bitterbrush (Purshia tridentata) (8), Utah juniper (7), Black sagebrush (5), Granite

pricklygilia (4)

Species diversity: 47 species total; averaged 28.6 perennial

species/ELU

Number of ELUs/area of NTS: 53/19,922 ha (5.9%)

Landforms: mountains, mid slopes to mesas

Geology: mostly Tertiary tuffs

Elevation: average 2,256 m, range 1,682-2,292 m

Precipitation: 26.7 cm

Slopes: average 13.9°, range 1-55°

Soils: primarily loamy sand to loam

Annuals: very low to low

The transition zone alliances make up slightly over 36% of

the total area of the NTS. The largest single vegetation

association is the Coleogyne ramosissima-Ephedra

nevadensis shrubland, which represents over 21% of the

total area of the NTS. This is followed by the Larrea tridentata-Ambrosia dumosa shrubland with 18%. Each of the

other associations is less than 8% of the total area on the

NTS. More detailed analysis of this transitional zone on the

NTS is provided in the companion paper, Hansen and

others, this proceedings.

These 20 associations are similar to those recognized by

Beatley (1976). However, she recognized only 12 associations. Beatley recognized more associations that included

creosote bush as a major component. She did not recognize

Nevada jointfir or White burrobrush as major alliances or

several other transitional associations such as M. spinosa-E.

nevadensis or E. fasciculatum-E. nevadensis.

Vegetation Mapping _____________

The map resulting from the image processing is shown in

figure 3. Only the vegetation alliances are shown on this

map. All 20 vegetation associations could be utilized for

smaller portions of the NTS or more in-depth study of

smaller areas as needed; however, placement of 20 symbols

(associations) would make a small map confusing.

These data, which were placed in a GIS format, allow for

spatial analysis such as identifying areas contained within

each vegetation association/alliance or range and relative

abundance of individual species (see fig. 2 in the companion

paper, Hansen and others, this proceedings). This is very

useful in identifying and managing resources.

Conclusions____________________

The vegetation of the NTS was classified into 20 associations that correspond to national classification standards.

These associations are similar to associations recognized by

Beatley, although only 12 associations were recognized in

her earlier work. Several differences did occur, particularly

in transition areas between the Mojave and Great Basin

Deserts.
146 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 3—Vegetation alliances on the Nevada Test Site. (1 = Pinus monophylla/Artemisia spp. woodland; 2 = Artemisia spp.

shrubland; 3 = Atriplex spp. shrubland; 4 = Chrysothamnus-Ericameria shrubland; 5 = Coleogyne ramosissima shrubland; 6 = Ephedra

nevadensis shrubland; 7 = Lycium spp. shrubland; 8 = Hymenoclea-Lycium shrubland; 9 = Atriplex confertifolia-Ambrosia dumosa

shrubland; 10 = Larrea tridentata/Ambrosia dumosa shrubland; 11 = Miscellaneous; 12 = Playa/Disturbances).
USDA Forest Service Proceedings RMRS-P-11. 1999 147

Aerial color and infrared photography at a scale of 1:10,000

to 1:24,000 are powerful tools in identifying boundaries of

soil consociations and ELUs. Although at a much smaller

scale, satellite imagery with multispectral band wavelengths,

such as the French SPOT is an additional tool in identifying

unit boundaries. Multispectral analysis is an important tool

because interpretation of the band wavelengths helps identify subtle differences in soil moisture, desert pavement

(surface armoring by eroded gravel), and mineral types (e.g.,

iron oxides or calcareous layers) that influence root development and plant growth.

Ecological landform units are a valuable tool in mapping

vegetation and vegetation classification. They represent

natural mapping units that are easily recognized in arid

environments using remotely sensed data. They also represent logical management units because they respond similarly to management techniques.

The use of a GIS can provide a powerful tool for identifying

and managing resources. They can be used to display and

evaluate spatial data. They can also provide a useful method

for comparing temporal data such as changes of vegetation

associations or species ranges over time.

References _____________________

Allred, D. M.; Beck, D. E.; Jorgensen, C. D. 1963a. Biotic communities of the Nevada Test Site. Brigham Young University Science

Bulletin, Biological Series - Volume II, Number 2, February,

1963, 52 p.

Allred, D. M.; Beck, D. E.; Jorgensen, C. D. 1963b. Biotic communities of the Nevada Test Site. Brigham Young University Science

Bulletin, Biological Series - Volume II, Number 4, May, 1963, 15 p.

Bailey, R. G.; Jensen, M. E.; Cleland, D. T.; Bourgeron, P. S. 1994.

Design and use of ecological mapping units. In: Jensen, M. E.;

Bourgeron, P. S., eds. Ecosystem management: principles and

applications. Gen. Tech. Rep. PNW-318. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest

Research Station: 95-106.

Beatley, Janice C. 1976. Vascular plants of the Nevada Test Site and

Central-Southern Nevada: ecological and geographic distributions. Energy Research and Development Administration, Division of Biomedical and Environmental Research. TID-26881.

Berry, Kristin H. 1979. The East Mojave Desert: an example of

inventory design and habitat analysis. In: classification, inventory and analysis of fish and wildlife habitat, the proceedings of

a national symposium held at Phoenix, Arizona on January 24-

27, 1977. U.S. Department of the Interior, Fish and Wildlife

Service, Biological Services Program PB 299240, FWS OBS-78/76.

Brady, Nyle C. 1974. The natural properties of soils. Eighth Edition.

MacMillan Publishers Co., Inc., New York.

Cronquist, A.; Holmgren, A. H.; Holmgren, N. H.; Reveal, J. L.;

Holmgren, P. K. 1994. Intermountain flora, vascular plants of the

Intermountain West, U.S.A. Volumes I-V. The New York Botanical Garden, Bronx, New York.

Federal Geographic Data Committee. 1996. FGDC vegetation classification and information standards, June 3, 1996, vegetation

subcommittee, U.S. Geological Service, Reston, Virginia, http://

www.nbs.gov/~mikez/fgdc-veg.htm#1, Internet retrieval as of

9/05/1996.

Ferguson, D.E.; Morgan, P.; Johnson, F. D., comps. 1989. Proceedings-land classifications based on vegetation: applications for

resource management, Moscow, ID, November 17-19, 1987.

Gen.Tech. Rep. INT-257. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 315.

Grossman, D. H.; Faber-Langendoen, D.; Weakley, A. S.; Anderson,

M.; Bourgeron, P.; Crawford, R.; Goodin, K.; Landaal, R.; Metzler,

K.; Patterson, K. D.; Pyne, M.; Reid, M.; Sneddon, L. 1998.

International classification of ecological communities: terrestrial

vegetation of the United States. Volume I. The national vegetation classification system: development, status, and applications.

The Nature Conservancy, Arlington, Virginia, U.S.A.

Hansen, D. J.; Ostler, W. K.; Hall, D. B. [This proceedings]. The

transition from Mojave Desert to Great Basin on the Nevada Test

Site.

Hickman, James C., ed. 1993. The Jepson manual, higher plants of

California. University of California Press, Berkely, California.

Hironaka, M. 1986. Habitat type, range site, and community type.

In: Proceedings-symposium on the biology of Artemisia and

Chrysothamnus. Provo, Utah, July 9-13, 1984. Gen. Tech. Rep.

INT-200. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station.

Holdorf, Herbert D. 1989. Designing mapping projects. In: Ferguson,

Dennis E.; Morgan, Penelope; Johnson, Frederick D., comps.

Proceedings-land classifications based on vegetation: applications

for resource management, Moscow, ID. November 17-19, 1987.

Gen. Tech. Rep. INT-257. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 87-89.

Jaeger, E. C. 1957. The North American deserts. Stanford University Press, Stanford. 308 p.

Kartesz, John T. 1988. A flora of Nevada. Parts 1-3. University

Microfilms International, Ann Arbor, Michigan.

National Biological Service. 1995. Draft content standard for national biological information infrastructure metadata. December

1995, U.S. Department of the Interior, Washington, DC.

O’Farrell, T. P.; Emery, L. A. 1976. Ecology of the Nevada Test Site:

A narrative summary and annotated bibliography. U.S. Energy

Research and Development Administration, Nevada Operations

Office, NVO-167, National Technical Information Services, Springfield, Virginia.

Peterson, Frederic F. 1981. Landforms of the basin & range province

defined for soil survey. Tech. Bull. 28, Nevada Agricultural

Experimentation, University of Nevada, Reno, January, 1981.

Shields, L. M. 1958. A botanical study of nuclear effects at the

Nevada Test Site, 1957. Annual report of New Mexico Highlands

University to U.S. Atomic Energy Commission. 109 p.

Shields, L. M.; Rickard, W. H. 1960. A botanical study of nuclear

effects at the Nevada Test Site, 1959. Annual report of New Mexico

Highlands University to U.S. Atomic Energy Commission.

Shields, L. M.; Rickard, W. H.; Drouet, F. 1959. A botanical study of

nuclear effects at the Nevada Test Site, 1958. Annual report

of New Mexico Highlands University to U.S. Atomic Energy

Commission. 160 p.

U. S. Department of Agriculture. 1996. The PLANTS database.

National Plant Data Center, Baton Rouge, LA 70874-4490 U.S.A.

(Also available via the Internet: Natural Resource Conservation

Service, Biological Conservation Sciences Division, http://

trident.ftc.nrcs.usda.gov/npdc/30hm-pg.html, Internet retrieval

as of 9/10/1996).

U.S. Department of Energy, 1995. Nevada Test Site grid map, a grid

system photo locator map of the Nevada Test Site. U.S. Department of Energy, Remote Sensing Laboratory, Nellis Air Force

Base.

U.S. Department of Energy, 1996. Final Environmental Impact

Statement for the Nevada Test Site and off-site locations in the

state of Nevada, Volume 1, Chapters 1-9. DOE/EIS 0243, U.S.

Department of Energy/Nevada Operations Office, Las Vegas,

Nevada, August 1996.

Wellner, Charles A. 1989. Classification of habitat types in the

Western United States. In: Ferguson, Dennis E.; Morgan,

Penelope; Johnson, Frederic D., comps. Proceedings-land classifications based on vegetation: applications for resource management, Moscow, ID, November 17-19, 1987. Gen. Tech. Rep. INT257. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station: 87-89.

Welsh, Stanley, L.; Atwood, N. Duane; Goodrich, Sherel; Higgins,

Larry C.; Editors. 1993. A Utah Flora. Brigham Young University

Print Services, Provo, Utah.
148 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

D. J. Hansen, W. K. Ostler, and D. B. Hall are Biologists with Bechtel

Nevada, P.O. Box 98521, M/S NLV-081, Las Vegas, NV 89193-8521.

The Transition from Mojave Desert to Great

Basin Desert on the Nevada Test Site

D. J. Hansen

W. K. Ostler

D.B. Hall

Abstract—Plant species and associations on the Nevada Test Site

are located along elevation and precipitation gradients. Associations in the Great Basin Desert had the highest species diversity.

Rodent sign and productivity of annual plants are least in the lower

and higher elevations and most abundant in the mid-elevations.

Microbiotic crusts are most abundant in fine-textured soils and of

low abundance in soils with active erosional processes. Texture of

surface soils (0 to 5 centimeters [0 to 2 inches]) differs little among

all associations except for a few that are correlated with playas and

steep mountain slopes. However, differences among associations

are observed for deeper substrates comprised of limestone, basalt,

and tuff parent materials.

The Nevada Test Site (NTS) is located about 105 km (65

miles) northwest of Las Vegas in southern Nevada (see fig. 1

of companion paper, Ostler and others, 1999). The site was

created by a series of land withdrawals in the early 1950s for

nuclear weapons testing. It comprises a total land area of

350,000 ha (1,350 square miles). Despite nearly 1,000

atmospheric and below-ground nuclear tests, the area is

relatively undisturbed and offers an excellent location for

biological studies. The area has had limited or no livestock

grazing since the 1950s and is designated as a National

Environmental Research Park.

The NTS consists of three large valleys, Yucca, Frenchman, and Jackass Flats. It has two high mesas, Rainier and

Pahute. It has a rough elevational gradient from south to

north with the lowest point at 829 m (2,688 ft) in Jackass

Flats and the highest point at 2,340 m (7,679 ft) on Rainier

Mesa. The site straddles the Mojave and Great Basin Deserts

and provides an excellent site to observe the transition

between these two deserts. Numerous detailed studies have

been conducted on NTS biota focusing primarily on inventories and evaluating the effects of nuclear testing. Approximately 730 plant species occur on the NTS, of which several

are sensitive or protected.

Methods _______________________

Shrublands of the NTS were classified using methods described in a companion paper presented in these proceedings

(Ostler and others 1999). Approximately 1,500 ecological landform units (ELUs) were delineated using aerial photography

and satellite imagery to distinguish ecological mapping

types. The boundaries of each ELU were field verified.

Landforms were selected because they are highly correlated

with soil types in Nevada (Peterson 1981) and have been

used historically to help classify habitat types in the Mojave

Desert (Berry 1979). Vegetation and other site parameters

were sampled within representative areas of each ELU.

Data were analyzed using cluster analyses and descriptive

statistics to help classify vegetation into 10 alliances and

20 associations.

Results ________________________

Results of the vegetation classification on the NTS are

shown in table 1. About 23 percent and 37 percent of the

ELUs sampled on the NTS were located in the Mojave Desert

and Great Basin Desert, respectively (table 2). The remaining 36 percent of the ELUs were located in a Transition Zone

between these two deserts. About 4 percent of the 1,508

ELUs sampled were classified as “miscellaneous” because

they were unique vegetation types, burned, scraped, or

disturbed by nuclear testing. In the Mojave Desert the

Larrea tridentata/Ambrosia dumosa Shrubland was the

most numerous association representing about 19 percent of

the ELUs on the NTS (18 percent of the total area). No other

association in the Mojave Desert represented more than

4 percent of the total ELUs. In the Great Basin Desert the

Artemisia tridentata-Chrysothamnus viscidiflorus

Shrubland was the most numerous association representing

about 11 percent of the ELUs on the NTS (7.5 percent of the

total area). No other association in the Great Basin Desert

represented more than 7 percent of the total ELUs. In the

Transition Zone between these deserts, the Coleogyne

ramosissima-Ephedra nevadensis Shrubland was the most

numerous association representing about 22 percent of the

ELUs on the NTS (21.6 percent of the total area). No other

association in the Transition Zone represented more than

6 percent of the total ELUs.

Distribution of Plant Alliances on the

Nevada Test Site

Figure 1 shows the distribution of plant alliances on the

NTS. Also shown are the generalized boundaries for the

Mojave Desert, Great Basin Desert, and the Transition Zone

between these deserts. Plant species that dominate associations within the Transition Zone have been historically
USDA Forest Service Proceedings RMRS-P-11. 1999 149

Table 1—Classification of vegetation on the Nevada Test Site.

Mojave Desert

Lycium spp. Shrubland Alliance

Lycium shockleyi-Lycium pallidum Shrubland

Larrea tridentata/Ambrosia dumosa Shrubland Alliance

Larrea tridentata /Ambrosia dumosa -Shrubland

Atriplex confertifolia - Ambrosia dumosa Shrubland Alliance

Atriplex confertifolia - Ambrosia dumosa Shrubland

Transition Zone

Hymenoclea -Lycium Shrubland Alliance

Lycium andersonii - Hymenoclea salsola Shrubland

Hymenoclea salsola - Ephedra nevadensis Shrubland

Ephedra nevadensis Shrubland Alliance

Menodora spinescens - Ephedra nevadensis Shrubland

Krascheninnikovia lanata - Ephedra nevadensis Shrubland

Eriogonum fasciculatum - Ephedra nevadensis Shrubland

Ephedra nevadensis - Grayia spinosa Shrubland

Coleogyne ramosissima Shrubland Alliance

Coleogyne ramosissima - Ephedra nevadensis Shrubland

Great Basin Desert

Atriplex spp. Shrubland Alliance

Atriplex confertifolia - Kochia americana Shrubland

Atriplex canescens - Krascheninnikovia lanata Shrubland

Chrysothamnus-Ericameria Shrubland Alliance

Chrysothamnus viscidiflorus - Ephedra nevadensis Shrubland

Ericameria nauseosa Shrubland Alliance

Ericameria nauseosa - Ephedra nevadensis Shrubland

Artemisia spp. Shrubland Alliance

Ephedra viridis - Artemisia tridentata Shrubland

Artemisia tridentata - Chrysothamnus viscidiflorus Shrubland

Artemisia nova - Chrysothamnus viscidiflorus Shrubland

Artemisia nova - Artemisia tridentata Shrubland

Pinus monophylla/Artemisia spp. Woodland Alliance

Pinus monophylla/Artemisia nova Woodland

Pinus monophylla/Artemisia tridentata Woodland

associated with either desert, and in some cases, listed as a

minor species in both deserts.

Associations that were considered typical or characteristic of the Mojave Desert were those that contained a presence

of Shockley’s desertthorn (Lycium shockleyi), rabbit thorn

(Lycium pallidum), creosote bush (Larrea tridentata), or

white bursage (Ambrosia dumosa), but lacked species characteristic of the Great Basin Desert (table 3). The distribution of creosote bush on the NTS (fig. 2) approximates the

boundaries for the Mojave Desert on the NTS. Associations

that were considered typical of the Great Basin Desert were

those that contained a presence of sagebrush (Artemisia

spp.), singleleaf pinyon (Pinus monophylla), or Utah juniper

(Juniperus osteosperma), but lacked species characteristic

of the Mojave Desert. The distribution of big sagebrush

(Artemisia tridentata) on the NTS (fig. 3) approximates the

boundaries of the Great Basin on the NTS. Associations

within the Transition Zone were considered to be those that

had a mixture of species, many species occurring in both the

Mojave and Great Basin Desert (table 3), such as Ephedra

(Ephedra) spp. and blackbrush, (Coleogyne ramosissima).

The distribution of blackbrush on the NTS (fig. 4) approximates the boundaries of the Transition Zone on the NTS.

Associations that occur in the Transition Zone appear to

be comprised of shrubs that are predominantly drought

deciduous (e.g., blackbrush) or have essentially leafless,

photosynthetic stems (e.g., Ephedra spp.), while the most

abundant dominant shrubs from associations in the Mojave

Desert and Great Basin Desert are evergreen in habit (e.g.,

creosote bush, big sagebrush, singleleaf pinyon, and Utah

juniper). The evolutionary adaptation of leaf reduction or

abscission during drought and stress-induced dormancy

may help maintain the abundance of blackbrush and Mormon tea (Ephedra nevadensis) in these ecotones. While the

abundance of species other than blackbrush are relatively

low in the Coleogyne ramosissima - Ephedra nevadensis

Shrubland, they are frequently present in small numbers

being found in small patches where animals have disturbed

the soil horizons or fire has reduced competition with

blackbrush.

Blackbrush occurs at intermediate elevations. At these

elevations lightning strikes, associated with storms blowing

from the south, are common during the summer and occasionally fuel loading reaches levels high enough to support

wildfires. Once burned these communities reestablish very

slowly; this phenomenon is also reported by Brown (1982).

Species Diversity

Species diversity (richness or the number of species) of

perennial trees and shrubs was greatest in the Great Basin

Desert associations (mean of 56 species) compared to associations in the Transition Zone (mean of 49 species) and the

Mojave Desert (mean of 36 species). Similar species diversity patterns were also observed for all combined perennial

species on the NTS (table 2) (e.g., Great Basin Desert: 21.7

species per ELU, Transition Zone: 17.4 species per ELU, and

Mojave Desert: 12.7 species per ELU).

Elevation and Precipitation

Plant associations within the Mojave Desert and Great

Basin Desert were ordered according to increasing elevation

and precipitation (fig. 5). Mean annual precipitation was

determined to be positively correlated (r

2

 = 0.85) with elevation on the NTS, based on correlation modeling and actual

weather recording data (French 1986; other detailed meteorological data are presented by Fransioli and Ambos 1997).

The importance of elevation, slope, and substrate in accounting for statistical variance in shrub species cover was also

described for the Nellis Air Force Range consisting of

1,228,355 ha (7,432 mi2

) of shrubland adjacent to the NTS

(Pritchett and others 1997).

Soils and Parent Materials

Texture of surface soils (0 to 5 centimeters [0 to 2 inches])

appeared to differ little among all associations except for

two that were correlated with playas and steep mountain

slopes. The plant associations associated with playas were

the Lycium shockleyi - Lycium pallidum Shrubland and the

Atriplex confertifolia - Kochia americana Shrubland. Soil

texture of these associations had a greater percentage of

clay than other associations. The most abundant soil textures for surface soils of the associations were comprised of

three textural types: sandy loam (30 percent), loamy sand
150 USDA Forest Service Proceedings RMRS-P-11. 1999 Table 2—Parameters associated with associations in the Mojave and Great Basin Deserts and Transition Zone on the Nevada Test Site. Mojave Desert Transition zone Great Basin Desert Parameters

Lycium shockleyi-Lycium pallidum

Larrea tridentata/Ambrosia dumosa

Atriplex confertifolia-Ambrosia dumosa

Menodora spinescens-Ephedra nevadensis

Krascheninnikovia lanata-Ephedra nevadensis

Lycium andersonii-Hymenoclea salsola

Hymenoclea salsola-Ephedra nevadensis

Eriogonum fasciculatum - Ephedra nevadensis

Ephedra nevadensis-Grayia spinosa

Coleogyne ramosissima-Ephedra nevadensis

Atriplex confertifolia-Kochia americana

Atriplex canescens-Krascheninnikovia lanata

Chrysothamnus viscidiflorus-Ephedra Nevadensis

Number of stands 4 287 51 42 29 11 44 14 93 325 17 38 76

Number of shrub species 11 49 49 50 34 23 50 36 66 84 53 87 61 43 42 73 56 47 54 47

Mean number of perennial species/ELU 8.8 13.2 16.2 19.4 17.6 12.8 15.2 20.4 19.7 16.9 9.2 11.9 21.4 17.1 27 20.8 24.7 29.1 27 28.6

Mean elevation (m) 941 1,080 1,153 1,198 1,258 1,263 1,263 1,292 1,413 1,385 1,208 1,237 1,485 1,563 1,719 1,776 1,805 1,831 1,985 2,054

Mean precipitation (cm) 14.8 16 16.9 17.5 18.2 18.3 18.3 18.7 20.2 19.8 17.6 18 21.1 22.1 24 24.7 25.1 25.4 27.3 28.2

Mean slope (degrees) 0.8 5.7 13.6 8 3.6 2.3 3.8 36.3 8.8 8.5 2.7 3.5 7.1 6.9 18.2 5.9 6.4 8.6 8.1 14.3

Mean rock pavement (percent) 32.5 63.2 57.4 65 58.1 55.5 47.6 17.5 57 68.2 34.1 41.1 57.2 62.8 49.8 52.5 66.7 47.8 53.5 47.8
USDA Forest Service Proceedings RMRS-P-11. 1999 151

Figure 1—Vegetation alliances on the Nevada Test Site. (1 = Pinus monophylla/Artemisia spp. woodland; 2 = Artemisia

spp. shrubland; 3 = Atriplex spp. shrubland; 4 = Chrysothamnus-Ericameria shrubland; 5 = Coleogyne ramosissima

shrubland; 6 = Ephedra nevadensis shrubland; 7 = Lycium spp. shrubland; 8 = Hymenoclea-Lycium shrubland; 9 = Atriplex

confertifolia-Ambrosia dumosa shrubland; 10 = Larrea tridentata/Ambrosia dumosa shrubland; 11 = Miscellaneous;

12 = Playa/Disturbances).
152 USDA Forest Service Proceedings RMRS-P-11. 1999 Table 3—Percent abundance of dominant species found in associations in the Mojave and Great Basin Deserts on the Nevada Test Site. Mojave Desert Transition zone Great Basin Desert Parameters

Lycium shockleyi-Lycium pallidum

Larrea tridentata/Ambrosia dumosa

Atriplex confertifolia-Ambrosia dumosa

Menodora spinescens-Ephedra nevadensis

Krascheninnikovia lanata-Ephedra nevadensis

Lycium andersonii-Hymenoclea salsola

Hymenoclea salsola-Ephedra nevadensis

Eriogonum fasciculatum - Ephedra nevadensis

Ephedra nevadensis-Grayia spinosa

Coleogyne ramosissima-Ephedra nevadensis

Atriplex confertifolia-Kochia americana

Lycium shockleyi 47.5 0.5 0.2 0.0

Lycium pallidum 17.0 5.5 0.4 0.1 1.0 0.1

Ambrosia dumosa 12.5 43.4 15.6 10.3 4.0 1.1 2.2 5.3 3.5 0.5 0.6 0.4 0.6 0.1 0.1

Larrea tridentata 12.4 4.2 3.4 2.4 2.4 1.6 0.3 1.9 0.6 0.1 0.9 0.1 0.0

Krameria erecta 6.6 3.8 4.5 0.8 0.4 0.3 5.0 1.0 0.8 0.0 0.2 0.0 0.1

Menodora spinescens 1.3 1.8 13.9 2.2 0.4 0.0 1.6 0.5 5.8 2.6 0.4 0.0 0.0

Grayia spinosa 2.1 0.6 1.1 8.3 5.3 1.9 3.7 2.1 8.1 0.2 3.2 5.1 0.1 0.8 1.9 2.0 1.9 0.5 0.1

Krascheninnikovia lanata 3.5 3.3 4.4 3.6 28.5 7.3 2.5 3.7 1.4 3.3 2.8 10.8 5.3 0.0 0.1 1.0 0.6 0.5 0.0 0.0

Lycium andersonii 3.0 6.4 4.5 8.0 51.8 4.5 3.4 3.2 5.9 5.4 5.0 4.7 0.5 0.1 0.7 0.6 0.3 0.0

Hymenoclea salsola 0.0 1.7 1.2 2.7 3.7 9.6 51.5 1.3 2.6 7.9 0.2 3.9 1.6 0.2 0.0 0.0

Eriogonum fasciculatum 0.4 0.8 0.5 0.1 0.1 28.1 0.8 1.7 0.1 0.4 6.0 0.4 0.0 0.3 0.0

Coleogyne ramosissima 0.6 3.6 4.7 1.9 2.6 1.6 0.7 56.3 4.1 0.1 1.8 1.8 5.3 1.8 0.5 0.2 1.8 0.1

Ericameria cooperii 0.6 0.2 0.5 1.2 0.4 2.3 0.7 4.9 0.0 0.8 0.7 0.0 0.2 0.1 0.1 0.7

Ephedra nevadensis 7.1 8.9 11.8 12.3 6.4 8.5 16.4 9.6 22.8 0.1 2.9 11.4 11.1 2.1 7.1 4.3 3.1 0.8 1.0

Artemisia spinescens 1.0 0.1 0.7 0.6 5.2 1.5 0.2 0.2 0.9 6.6 0.8 2.6 0.3 0.1 0.1 1.8

Atriplex confertifolia 7.5 2.7 31.3 8.2 4.7 0.5 3.0 1.4 0.7 49.8 3.3 3.9 0.2 0.8 0.0 0.0 0.3

Kochia americana 0.5 0.1 0.0 22.1 0.9 0.3 0.0

Atriplex canescens 9.0 0.4 0.3 0.8 2.5 6.4 4.6 0.4 0.8 8.0 2.4 57.8 6.6 5.2 3.5 1.9 1.4 2.0 0.5 0.0

Chrysothamnus viscidiflorus spp. 0.1 0.5 2.7 2.2 0.6 5.4 2.2 1.5 5.3 0.8 1.0 36.7 4.4 1.9 8.1 5.2 4.8 3.7 2.8

Ericameria nauseosa 0.5 0.3 0.2 0.5 0.3 0.3 51.7 0.2 0.9 0.3 0.8 0.0 0.3

Ephedra viridis 0.0 0.2 0.5 3.0 1.0 1.5 0.9 0.4 1.5 2.3 21.0 2.0 1.7 2.2 2.3 1.1

Purshia stansburiana 0.6 0.6 0.3 0.2 0.4 1.3 8.9 0.8 0.3 0.1 1.1 1.4

Purshia glandulosa 0.1 0.4 0.7 0.2 0.8 15.0 0.6 0.3 0.9 0.8 0.3

Artemisia tridentata 0.0 0.1 0.2 1.3 1.4 0.3 5.0 6.0 15.7 56.1 14.3 25.1 2.6 22.8

Artemisia nova 0.3 0.9 0.0 1.0 0.5 1.9 67.9 33.8 55.4 5.4

Chrysothamnus viscidiflorus spp. 0.0 0.2 0.4 0.2 0.1 4.5 3.3 2.7 7.5 1.7 1.5

Leptodactylon pungens 0.0 0.0 0.0 0.3 0.0 0.0 0.3 1.5 2.9 0.7 3.6 2.3 4.1

Juniperus osteosperma 0.1 0.0 0.0 0.2 0.1 0.6 1.4 0.6 1.2 5.9 7.3

Purshia tridentata 0.0 0.4 0.2 0.6 0.2 0.2 1.7 7.9

Pinus monophylla 0.0 0.2 0.1 0.7 2.2 0.9 1.3 14.1 27.5
USDA Forest Service Proceedings RMRS-P-11. 1999 153

Figure 2—Distribution and percent abundance of creosote bush on the Nevada Test Site.
154 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 3—Distribution and percent abundance of big sagebrush on the Nevada Test Site.
USDA Forest Service Proceedings RMRS-P-11. 1999 155

Figure 4—Distribution and percent abundance of blackbrush on the Nevada Test Site.
156 USDA Forest Service Proceedings RMRS-P-11. 1999Figure 5—Average elevation and precipitation of vegetation associations on the Nevada Test Site.
USDA Forest Service Proceedings RMRS-P-11. 1999 157

(18 percent), and loam (14 percent). Soil samples from the

remaining 38 percent of associations were classified into

more than 30 different textural types. The Eriogonum

fasiculatum - Ephedra nevadensis Shrubland was located on

the steepest slopes (36 degrees) with all other associations

averaging slopes less than 18 degrees, with a mean slope of

7 degrees.

Despite little difference in soil texture near the soil surface, associations were observed to differ in the type of

substrate upon which they most commonly appeared. The

Coleogyne ramosissima - Ephedra nevadensis Shrubland

and Atriplex confertifolia - Ambrosia dumosa Shrubland

appeared frequently on shallow soils of limestone-derived

parent materials, while most of the associations in the Great

Basin Desert occurred in the basalt or tuff formations.

Remaining associations occurred in alluvial soils. Creosote

bush appeared to be limited by shallow soils or the presence

of a caliche layer. Lunt and others (1973) suggest that big

sagebrush and creosote bush have unusually high oxygen

requirements, while roots of white bursage appear to require

less oxygen.

Microbiotic Crusts

The presence of microbiotic crusts on the soil surface (i.e.,

nonvascular microorganisms such as algae, fungi or lichens

that are frequently important for enhancing soil fertility and

surface stabilization) was noted during the field surveys.

Within the NTS 58 percent of the ELUs sampled had no

visual evidence of microbiotic crusts, 28 percent had low

visual evidence of crusts, 11 percent had moderate visual

evidence of crusts, and only 4 percent had high visual

evidence of microbiotic crusts. Visual evidence of crusts were

observed to decrease with increases in elevation. For example, no microbiotic crusts were observed in 31 percent of

sites within the Mojave Desert, 43 percent of sites within the

Transition Zone and 50 percent of sites within the Great

Basin Desert. Associations with high abundance of crusts

also had higher percentages of soil fines (clays or silts). Low

presence of crusts or their absence was associated with

active soil erosional processes (e.g., along washes and steeper

unstable slopes).

Productivity of Annual Vegetation

The presence of annual vegetation and its relative abundance were not randomly distributed across the three areas

(Mojave Desert, Transition Zone, and Great Basin Desert)

based on Chi-square analyses (58.6, P < 0.001, df = 4).

Associations in the Mojave Desert and the Transition Zone

tended to be over-represented in the moderate category (41

and 35 percent respectively) and underrepresented in the

low-very low category (43 and 43 percent respectively)

while associations in the Great Basin Desert tended to be

overrepresented in the low-very low category (60 percent)

and underrepresented in the moderate category (22 percent). Levels within the high-very high category were similar for all three areas. This is consistent with regional floras

which show a greater number of annual species in drier and

hotter deserts of the Southwest compared to the colder

Great Basin Desert.

Rodent Activity

The absence of sign indicating burrowing rodents and the

low abundance of sign (e.g., burrows and excavated soils)

were found to be correlated with increasing elevation. For

example, the Mojave Desert was observed to have 45 percent

of the sites with none to low sign. The Transition Zone was

observed to have 59 percent of the sites with none to low sign,

and the Great Basin Desert was observed to have 80 percent

of the sites with none to low sign Both the moderate rodent

sign and the high to very high rodent sign were inversely

correlated with elevation. For example, the Mojave Desert

had 39 percent moderate sign and 16 percent high to very

high sign. The Transition Zone had 30 percent moderate sign

and 11 percent high to very high sign. The Great Basin

Desert had 14 percent moderate sign and 6 percent high to

very high sign. The Mojave Desert sites may have deeper

soils that are more conducive to burrowing, while the rockier

soils of the Transition Zone have fewer burrows. The Great

Basin Desert sites have shallow soils and more severe

winters that may also reduce burrowing or abundance of

animals likely to burrow.

Species Correlations

Pairwise comparisons of species abundance at a statistical

level of significance of α = 0.05 of the 718 species observed to

occur on the NTS indicate that there were 447 positive

interspecific associations between species and only 271

negative interspecific associations. This general trend is in

agreement with earlier studies conducted using 25 circular

plots of 30.5 m (100 ft) in diameter during the late 1960s at

the NTS (Wallace and Romney 1972). Using Chi-squared

analyses, Wallace and Romney reported a great many more

positive than negative measures of association.

Vegetation and Climate of the Last 45,000

Years

Vegetation patterns in response to changing climatic

conditions have been studied extensively on the NTS and

documented through the analyses of several packrat-midden

sites (Spaulding 1985). Vegetation patterns suggest that

about 45 thousand years before present (k yr BP), the NTS

had cooler and wetter conditions than currently; dominant

plants included littleleaf mountain mahogany (Cercocarpus

ledifolius), Utah juniper, sagebrush, and horsebrush

(Tetradymia spp). By 35 k yr BP, limber pine (Pinus flexilis)

and four-wing saltbush (Atriplex canescens) had established

at the site. By 25 k yr BP, shadscale (Atriplex confertifolia),

snowberry (Symphoricarpos longiflorus), and Utah

Fendlerbush (Fendlerella utahensis) became more common.

By 10 k yr BP, limber pine was no longer found in packratmidden samples and was replaced by the presence of singleleaf

pine and increase in the abundance of Utah Juniper.

Goldenweed (Haplopappus nanus), Dorr’s sage (Salvia

dorii), and grizzlybear pricklypear (Opuntia erinacea) became more prevalent.

During the past 5 k yr BP, creosote bush, white bursage,

and other species characteristic of the Mojave Desert
158 USDA Forest Service Proceedings RMRS-P-11. 1999

established within the NTS area as temperatures increased

and precipitation decreased. It was estimated that many

Great Basin Desert trees and shrubs were displaced about

457 to 610 m (1,500 to 2,000 ft) upward in elevation to what

they historically had been as the climate changed (Spaulding

1985). This climate change opened new niches for colonization by other species such as blackbrush. Ecotonal species

are often adapted to a wide change in climatic conditions

such as freezing temperatures as well as hot, droughty

climate.

Summary and Conclusions _______

Vegetation of the NTS is diverse and relatively protected

from the effects of livestock grazing. Plant communities

appear to respond to moisture and temperature gradients

associated with elevation gradients at the site. Other secondary patterns of plant distribution are associated with

adaptation to unique substrates such as playas, steep rocky

slopes, and novel substrates comprised of limestone, basalt,

tuff, and alluvium. Changes in temporal species patterns on

the NTS have been correlated with changing climate during

the past 45 thousand years. Position of species along the

elevation gradient on the NTS under current climatic conditions creates a Transition Zone characterized by a diverse

mixture of species. This assemblage of species is not recognized as a regional vegetation type, but appears to be shaped

by climatic extremes present in both the Mojave Desert and

Great Basin Desert. The width of this zone is dependent on

the steepness of the elevation gradient, slope aspect, and

moisture retention characteristics of the substrate. Individual species appear to be independently distributed across

the NTS within both deserts and the Transition Zone. This

distribution is based on species growth requirements, although assemblages of species that have similar biological

and physiological needs are found together consistently

enough to be considered as distinct plant communities (i.e.,

alliances and associations). A better knowledge of the vegetation and the environmental conditions within the Mojave

Desert and Great Basin Desert helps us better appreciate

the transition between these deserts with its varying temporal and spatial characteristics.

References _____________________

Berry, K. H. 1979. The East Mojave Desert: An example of Inventory design and habitat analysis. In: Classification, inventory,

and analysis of fish and wildlife habitat—the proceedings of a

national symposium; January 24-27, 1977; Phoenix, AZ; Allan

Marmelstein, General Chairman. Biological Services Program,

PB 299240, FWS/OBS-78/76, U.S. Fish and Wildlife Service,

Washington, D.C.

Brown, D. E. 1982. Biotic communities of the American Southwest—United States and Mexico. Tucson, AZ: The University of

Arizona. Desert Plants. 4(1-4): 151.

French, R. H. 1986. Daily, seasonal, and annual precipitation

at the Nevada Test Site, Nevada. Desert Research Institute

University of Nevada System, Water Resources Center Publication #45042, DOE/NV/10384-01, U.S. Department of Energy,

Nevada Operations, Las Vegas, Nevada.

Fransioli, P. M.; Ambos, D. S. 1997. Engineering design climatology and regional meterological conditions report. TRW

Environmental Safety Systems Inc. B00000000-01717-5707-

00066 REV00, October 2, 1997, U.S. Department of Energy,

Yucca Mountain Site Characterization Office, North Las

Vegas, Nevada.

Lunt, O. R.; Letey, J.; Clark, S. B. 1973. Oxygen requirements for

root growth in three species of desert shrubs. Ecology. 54( 6):

1356-1362.

Ostler, W. Kent; Hansen, D. J.; Hall, D. J. 1999. The classification

of ahrublands on the Nevada Test Site. In: McArthur, E. Durant;

Ostler, W. Kent; Wambolt, Carl L. comps. 1999. Proceedings:

Shrubland Ecotones. 1998 August 12-14, Ephraim, UT. Proceedings RMRS-P-000. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Peterson, F. F. 1981. Landforms of the Basin & Range Province,

defined for soil survey. Technical Bulletin 28. Reno: University

of Nevada, Nevada Agricultural Experiment Station, Max C.

Fleischmann College of Agriculture. 52 pp.

Pritchertt, D.; Knight, T.; Smith, F. 1997. An inventory for rare,

threatened, endangered, and endemic plants and unique communities on Nellis Air Force Bombing and Gunnery Range,

Clark, Lincoln, and Nye Counties, Nevada. The Nature Conservancy, U.S. Department of Defense, Legacy Resource Management Program, Nellis Air Force Base, Nevada.

Spaulding, W. G. 1985. Vegetation and climates of the last 45,000

years in the vicinity of the Nevada Test Site, South-Central

Nevada. U.S. Geological Survey Professional Paper 1329. U.S.

Department of the Interior in cooperation with the U.S. Department of Energy. 83 p.

Wallace, A.; Romney, E. M. 1972. Radioecology and ecophysiology

of desert plants at the Nevada Test Site. TID-25954. United

States Atomic Energy Commission, Office of Information

Services, Library of Congress Catalog Card Number: 72-600110.
USDA Forest Service Proceedings RMRS-P-11. 1999 159

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Sherel Goodrich is Forest Ecologist, Ashley National Forest, Intermountain Region, Forest Service, U.S. Department of Agriculture, Vernal, UT

84078. Dwain Nelson is Rangeland Specialist, Vernal District, Bureau of

Land Management, U.S. Department of the Interior, Vernal, UT 84078.

Natalie Gale is Habitat Project Leader, Utah Division of Wildlife Resources,

Northeastern Region, Vernal, UT 84078.

Some Features of Wyoming Big Sagebrush

Communities on Gravel Pediments of the

Green River in Daggett County, Utah

Sherel Goodrich

Dwain Nelson

Natalie Gale

Abstract—Crown cover of Wyoming big sagebrush (Artemisia

tridentata ssp. wyomingensis) and other shrubs, frequency of understory species, and ground cover were considered in context of

ungulate grazing on Quaternary gravel pediments associated with

the Green River in Daggett County, Utah. Maximum sagebrush

crown cover was found at 22% inside an exclosure that had kept all

ungulates out for about 30 years. The next highest sagebrush crown

cover was found at 15% in an exclosure that had kept all ungulates

out for nine years, and by 13 years crown cover of sagebrush in this

exclosure was 17%. In all cases where pronghorn antelope

(Antilocarpa americana) and/or mule deer (Odocoileus hemionus)

had access to sagebrush, crown cover of sagebrush was lower than

inside these exclosures. Crown cover of sagebrush in areas of high

concentration of deer and antelope in winter without cattle (Bos

tarus) grazing was as low as 4%. Other features including frequency

of understory species and ground cover appear to be strongly

influenced by ungulate grazing and by the influence this grazing has

on sagebrush and perennial grasses. Perennial grasses were more

frequent or more vigorous where mule deer and antelope had access

to sagebrush. High levels of cattle grazing in the spring appeared to

be associated with reduced grass cover, higher percent bare ground,

and increased crown cover of sagebrush.

Study Sites_____________________

Study sites (table 1) were located in Wyoming big sagebrush (Artemisia tridentata var. wyomingensis) communities on Quaternary gravel pediments associated with the

Green River in Daggett County, Utah. The area includes

Lucerne Peninsula (Lucerne Valley), Antelope Flat, Pigeon

Basin, and Browns Park. Annual precipitation for these

sites is indicated by climate stations at Manila, Utah, with

24.6 cm (9.68 inches), Allens Ranch, Utah, with 21.7 cm (8.54

inches) (Ashcroft and others 1992), and at a station on Taylor

Flat in Browns Park with about 23 cm (9 inches) that is

maintained by the U.S. Department of the Interior, Bureau

of Land Management. The Flaming Gorge Climate Station

at Dutch John with 31.75 cm (12.5 inches) annual precipitation (Ashcroft and others 1992) is within the pinyon-juniper

belt at slightly higher elevation and within 2 miles of the

study area. Soils are gravely, sandy loams for the most part.

Gradients typical of the study area are between 1 and 5%.

Needle-and-thread grass (Stipa comata var. comata) is a

dominant grass at all the sites. The dominance of this grass

with Wyoming big sagebrush on sandy soils is indicative of

a habitat type recognized in Idaho by Hironaka and others

(1983) and in Nevada by Tueller and Blackburn (1974).

Sheep (Ovis aries) were grazed in parts of the study area

in early years of settlement, and numbers were highest in

years associated with World Wars I and II. After that sheep

numbers declined. For the past 3 or 4 decades, cattle (Bos

tarus) have been the principal or only species of livestock

grazed in the vicinity of the study sites.

Principal wild ungulates are pronghorn antelope

(Antilocarpa americana), mule deer (Odocoileus hemionus),

and elk (Cervis elaphus). Pronghorn antelope are year-long

residents in parts of the study area, and they often concentrate on parts of the area in winter. Radio telemetry, colored

collar, and ear tag streamer studies of mule deer initiated in

1987 in Browns Park demonstrated a strong pattern of

migration to the Browns Park area for winter. Many of the

deer tagged in Browns Park in winter spent summer on

Diamond Mountain within 32 km (20 miles) of where they

were tagged. However, some deer were monitored as far as

100 km (62 miles) to the west in summer on both the north

slope (China Meadow) and south slope (Uinta Canyon) of the

Uinta Mountains. Most of the tagged deer returned to

Browns Park the following winter (Utah Division of Wildlife

Resources, unpublished report). While in the Browns Park

area, mule deer show strong selectivity for Wyoming big

sagebrush/grass communities. Although tree cover is found

in nearby pinyon-juniper communities, deer highly favor the

open sagebrush/grass communities. Abundance and quality

of forage in these communities are strongly indicated as

principal factors in this selection. An additional potential

factor in this selection is the abundance of favorable cougar

habitat in the rocky, rugged pinyon-juniper zone and relatively poor cougar habitat in the open flats of Wyoming big

sagebrush/grass.

Sage grouse (Centrocercus urophasianus) are also present

in parts of the area. Small birds and mammals expected in

the area include Brewer sparrow (Spizella breweri) and

cottontail rabbits (Sylvilagus spp.).
160 USDA Forest Service Proceedings RMRS-P-11. 1999

Methods _______________________

Data was taken from 12 sites within the study area

between 1985 and 1998. Follow-up readings were made at

some sites after the initial reading. Shrub canopy cover was

determined by line intercept from 152.4 m (500 ft) of transect

at each site (table 2). Nested frequency in 5 by 5, 25 by 25,

25 by 50, and 50 by 50 cm nested plots were determined for

all species at 100 sample points at each site. For initial and

subsequent readings all nested frequency plot sizes were

used to determine nested frequency of each species. Summed

nested frequency scores were based on a potential score of

400 (tables 3 and 4). To achieve a score of 400, a plant must

be rooted in the 5 by 5 cm plot at each of the 100 sample

Table 1—Brief background for study sites.

Study site Study no.

name or symbol Comments

Lucerne 246/150 5-2 Long history of livestock and wild ungulate grazing with near absence of

livestock for about 30 years prior to study, but with continued wild ungulate

(mostly antelope) use.

Lucerne Exclosure I 5-3i Long history of livestock and wild ungulate grazing with fenced absence of

livestock and wild ungulates for about 30 years.

Lucerne Exclosure O 5-3o Long history of livestock and wild ungulate grazing with near absence of

livestock for about 30 years prior to study, but with continued wild ungulate

(mostly antelope) use.

Antelope Flat A 5-27A Long history of livestock and wild ungulate use with partial exclusion of

livestock for 20-30 years with limited use under a rest or deferred rotation

system. Continued heavy use by wild ungulates (mostly antelope and mule

deer).

Antelope Flat B 5-27B Same history as 5-27 but without exclusion of livestock.

Antelope Flat C 5-27C Same grazing history as 5-27B and with sagebrush being cleared manually

in about 1986. Return of sagebrush cover has been slow. At 12 years post

clearing, crown cover of sagebrush was 0.3%. Return of sagebrush crown

cover at this site appears to be paralleling the projection of Winward (1991)

of 40 or more years for Wyoming big sagebrush to return to 20% crown cover

following fire.

Tap Road 5-28 Long history of livestock and wild ungulate (mostly antelope) use with cattle

use managed under rest rotation for past 20-30 years.

Taylor Flat DX DX Moderate to heavy use by livestock since European settlement in the late

1880’s and heavy use in winter by mule deer to the present. The area was

closed to livestock in early 1960’s for a few years followed by spring use by

cattle. It was protected from all ungulates by fenced exclosure in 1985.

Taylor Flat CX CX Same history of use as DX, but with exclusion of livestock (cattle) by fenced

exclosure in 1985 with continued access to wild ungulates.

Taylor Flat OX OX Same history of use as DX, but with continued use by livestock as well as

mule deer without exclosure. Moderate to heavy grazing by cattle in spring

has been practiced for several years to enhance sagebrush for deer winter

range.

Green River S GRS Moderate to heavy use by livestock since European settlement in the late

1880’s with closure to livestock in early 1960’s, which was followed by close

grazing by cattle in spring to enhance sagebrush for deer winter range.

Green River N GRN Same history as GRS but with closure to livestock maintained by a fence

since 1977. Mule deer use in winter has remained heavy through the past

several decades. Sagebrush crown cover has been reduced to 4% and

needle-and-thread grass has become dominant under this grazing regime.

points. The nested frequency method also provided site

consistency and quadrat frequency values (tables 3 and 4).

Values for quadrate frequency are based on the 50 by 50 cm

plots or quadrats. Ground cover (table 5) was determined

from 400 points at each site. Methods used for line intercept,

nested frequency, and ground cover are included in U.S.

Department of Agriculture, Forest Service (1993).

References to vigor are based on ocular observations.

Height and crown spread of plants with respect to seasonal

precipitation were used as principle indicators of vigor.

Annual production of herbage was determined by clipping

and weighing air-dried, above-ground, annual growth. Plant

nomenclature of this paper follows Welsh and others (1993).
USDA Forest Service Proceedings RMRS-P-11. 1999 161

Results and Discussion __________

Wyoming Big Sagebrush

Crown cover for Wyoming big sagebrush varied from 0.3 to

22% (table 2). The two highest values were inside exclosures

that prevented all ungulate access. After about 30 years of

ungulate exclusion, sagebrush cover was 22% inside an

exclosure at Lucerne Peninsula (site 5-3i). Adjacent to the

exclosure (site 5-3o), where pronghorn antelope frequently

use the area, crown cover of sagebrush was found at 11%.

After 9 years of exclusion of wild and domestic ungulates at

the Taylor Flat Game Exclosure (site DX), sagebrush canopy

cover was 15%, and after 13 years it was measured at 17%.

Outside this exclosure, sagebrush canopy cover was 12%

(site CX) where cattle were excluded but wild ungulates

(mostly mule deer) had access. Where both cattle and wild

ungulates had access, this cover was 13% (site OX). Crown

cover measurements were repeated at 13 years post exclosure

construction at the Taylor Flat Exclosure site. In all cases,

these measurements were within 2% of that measured at

9 years. Greater than 13 years protection from wild ungulates may be needed for sagebrush to achieve potential

crown cover. Winward (1991) considered the normal range

for canopy cover for Wyoming big sagebrush communities to

be between 9% and at least 23%. The 22% achieved with

about 30 years of protection at the Lucerne exclosure is

consistent with the upper limit indicated by Winward (1991).

Table 2—Site consistency, average crown cover, and average quadrat frequency of shrubsa.

Crown coverc Average quadrate

Taxon Site consistencyb Range Mean frequencyd

- - - - - - - - - - - - - - - - - - - - - - - - Percent- - - - - - - - - - - - - - - - - - - - - - - - 

Wyoming big sagebrush 100 0.3-22 11 35

Sticky rabbitbrush 58 0.2-1.6 <1 6

Broom snakeweed 67 0.3-4.5 <1 11

Shadscale 17 2.0-4.0 3 19

Plains pricklypear 92 0.1-0.7 <1 9

Winterfat 25 0.2-0.4 <1 5

Slenderbush eriogonum 17 0.2-0.2 <1 1

aBased on 1994 data from DX, CX, and OX and initial readings at each of the other 9 study sites.

b

Site consistency = percent of sites on which the species was represented in sample plots.

c

Crown cover was determined by line intercept method from 152 m (500 ft) of transect.

d

Average quadrate frequency = percent of sample plots in which the species was found (determined from sites at which the plant

was present and not the total number of sites sampled).

Table 3—Site consistency, average quadrat frequency, and summed frequency values for graminoidsa.

Average Summed frequency values

Site quadrat (based on a potential of 400)d

Taxon consistencyb frequencyc Range Mean

- - - - - - - - Percent - - - - - - - 

Needle-and-thread grass 100 95 232-300 270

Junegrass 25 96 0-313 70

Indian ricegrass 92 6 0-29 10

Sandberg bluegrass 58 38 0-228 54

Thickspike wheatgrasse 42 50 0-205 48

Bottlebrush squirreltail 75 13 0-31 15

Galleta 42 14 0-50 12

Sand dropseed 33 3 0-7 1

Blue grama 17 17 0-63 8

Carex stenophylla 25 21 0-100 11

Crested wheatgrass 17 5 0-25 2

Bluebunch wheatgrass 8 1 0-1 0.1

Sixweeks fescue 58 19 0-291 32

Cheatgrass 42 4 0-20 2

aBased on 1994 data from DX, CX, and OX and initial readings at each of the other 9 study sites.

bSite consistency = percent of sites on which the species was represented in sample plots.

c

Average quadrate frequency = percent of sample plots in which the species was found (determined from sites at which

the plant was present and not the total number of sites sampled). dIncludes values from all sites and in all years readings were taken.

e

Plants of both thickspike wheatgrass and western wheatgrass (Elymus smithii) could have been included in the plots.

These plants commonly remain vegetative throughout the growing season. Separation of the two requires flowering

specimens.
162 USDA Forest Service Proceedings RMRS-P-11. 1999

Greater canopy cover might be expected on alluvial soils

and at other more favorable sites. However, for the gravel

pediments of this study area, maximum crown cover of

Wyoming big sagebrush that 20-25 cm (8-10 inches) annual

precipitation will support appears to be about 22%. At this

level of sagebrush crown cover (site 5-3i), frequency of

needle-and-thread grass was significantly less (nested frequency value of 247) than at an adjacent site (5-3o) with 11%

sagebrush crown cover where the nested frequency value for

this grass was 294. However, at lower and mid levels of

canopy cover of sagebrush (5-15%), frequency of understory

species appears to remain about equal.

Although frequency of understory species appears to remain high at moderate levels of sagebrush crown cover,

production and vigor of understory species appears to be

reduced. Production measurements were taken from 10

randomly spaced 0.85 m sq. ( 9.6 ft sq.) plots from site 5-27A

with 8% crown cover of sagebrush and from an adjacent site

(5-27C) with crown cover of sagebrush near zero. These

measurements indicated annual production (air dry weight)

of herbaceous species was 358 and 516 kg/ha (320 and 460

pounds/acre) respectively for these sites. At 8% sagebrush

crown cover, site 5-27A produced 30% less above-ground,

current growth of herbaceous species than did the adjacent

site. This indicates each percent increase of Wyoming big

sagebrush crown cover is associated with a 3.8% loss in

herbaceous understory production. This is within the range

of 3.3-5.2% loss per 1% increase of Wyoming big sagebrush

cover found by Rittenhouse and Sneva (1976) for crested

wheatgrass. However, it is not likely the relationship is

linear. Greater loss of herbaceous production is expected per

unit increase of sagebrush above about 5% crown cover.

Broom Snakeweed

Readings at Taylor Flat sites demonstrated considerable

oscillation in frequency and cover of broom snakeweed

(Gutierrezia sarothrae) within 1 or a few years without

change in management (table 6). This plant increased and

decreased in the absence of deer and cattle grazing within

exclosures. However, some of the variability appears to be

associated with heavy grazing by cattle in spring. Where

cattle grazing was heavy in spring, the amplitude of variation was greater than where livestock were excluded. This

species increased 3-fold in frequency, and its crown cover

increased from 0.3% in 1994 to over 8% in 1998 at site OX.

However, at the same time and in the absence of cattle

grazing, a vigorous stand of needle-and-thread grass at the

nearby GRN site demonstrated high capability to prevent

increase of broom snakeweed. Wide fluctuations in populations of this species over short periods of time have been

documented in other works including Jameson (1970) and

Clary and others (1985). Changes in this species might not

always be associated with grazing patterns. Booms and

Table 4—Site consistency, average quadrat frequency, and summed frequency values for forbsa.

Average Summed frequency values

Site quadrat (based on a potential of 400)

Taxonb consistencyc frequencyd Range Mean

- - - - - - - - Percent - - - - - - - 

Scarlet globemallow 83 13 0-95 23

Hood phlox 75 31 0-116 41

Silver bladderpod 42 38 0-40 6

Plains mustard 45 5 0-32 4

Silvery townsendia 42 6 0-16 4

Cushion buckwheat 42 2 0-10 2

Hoary aster 33 21 0-146 13

Yellow-eye cryptanth 33 3 0-7 2

Cicada milkvetch 25 6 0-25 3

Low pussytoes 25 6 0-40 4

Plains spring-parsley 25 3 0-7 1

Toadflax 25 2 0-10 1

Tansy mustard 75 10 0-170 17

Densecress 50 3 0-12 2

Dwarf gilia 25 3 0-13 2

Western stickseed 25 14 0-55 7

Chenopod 25 2 0-7 1

a

Based on 1994 data from DX, CX, and OX and initial readings at each of the other 9 study sites.

bThere were 13 other forbs recorded with less than 25% site consistency and less than 7% quadrat frequency. These other forbs

also had a mean summed nested frequency score of 1 or less. c

Site consistency = percent of sites on which the species was represented in sample plots.

dAverage quadrate frequency = percent of sample plots in which the species was found (determined from sites at which the plant

was present and not the total number of sites sampled).

Table 5—Number of vascular plant taxa from 12 study sites.

Plant group Range Mean

Graminoids 3-8 6.0

Forbs 4-13 8.5

Shrubs 3-6 4.3

Total taxa 12-27 18.8
USDA Forest Service Proceedings RMRS-P-11. 1999 163

busts of this species seem to be driven by variations in

amounts and timing of precipitation with the booms in wet

years and the busts in dry years.

Other Shrubs

Although six other shrubs or half shrubs were found in

line intercepts, each of these averaged less than 1% canopy

cover, and they were generally of low site consistency (table 2).

Plains pricklypear (Opuntia polyacantha) was present at

11 of the 12 sites, but at none of the sites did it exceed 1%

crown cover. Sticky rabbitbrush (Chrysothamnus viscidiflorus ssp. viscidiflorus) was present at 7 of the 12 sites with

a range of crown cover from 0.2% to 1.6%. Other shrubs of

lower site consistency and lower average crown cover were

shadscale (Atriplex confertifolia), winterfat (Ceratoides

lanata), and slenderbush eriogonum (Eriogonum microthecum). Presence of shadscale and winterfat indicates sites

that grade toward desert shrub communities.

Needle-and-Thread Grass

Frequency data from the 12 sites show needle-and-thread

grass the only graminoid present at all sites and in high

frequency at all sites (table 3). At sites where annual precipitation appears to be about 25 cm (10 inches) (Antelope Flat),

frequency of Junegrass (Koeleria macrantha) was equal to

that of needle-and-thread grass. However, this grass was

lacking at 8 of the 12 sites. Needle-and-thread grass demonstrated highest vigor at the GRN site, which has been

protected from cattle use but subjected to heavy winter

browsing by mule deer for about 21 years. Although vigor of

needle-and-thread grass was greatly reduced by heavy spring

grazing by cattle at the GRS site, frequency of this species

was not significantly decreased. Frequency of needle-andthread grass remained quite stable at most sites over the

13 years of the study (table 5).

Sixweeks fescue

Frequency of sixweeks fescue (Festuca octoflora) was

significantly different each year measurements were taken

at each site (table 6) with and without cattle grazing or wild

ungulate browsing. Vigorous stands of ungrazed needleand-thread grass did not prevent boom populations of this

annual in 1998. High frequency of this plant appears to be

associated with cool, moist or wet springs, and low frequency

appears to be associated with dry springs. The variation was

wide regardless of ungulate use.

Other Graminoids

Other graminoids (table 3) found in the study area included Indian ricegrass (Stipa hymenoides), Sandberg bluegrass (Poa secunda), thickspike wheatgrass (Elymus

lanceolatus), bottlebrush squirreltail (Elymus elymoides),

galleta (Hilaria jamesii), sand dropseed (Sporobolus cryptandrus), blue grama (Bouteloua gracilis), needleleaf sedge

(Carex stenophylla), crested wheatgrass (Agropyron

cristatum), bluebunch wheatgrass (Elymus spicatus), and

cheatgrass (Bromus tectorum).

Table 6—Summed frequency (based on a potential score of 400) for selected species of stable and highly variable

frequency.

Site

Taxon Year DX CX OX GRN GRS

Wyoming big sagebrush 1985 79 69 63 - -

1986 82 71 60 - -

1994 85 76 64 37 69

1998 72 70 64 30 54*

Needle-and-thread grass 1985 235 257 248 - -

1986 247 247 266 - -

1994 232 248 244 291 282

1998 148* 249 242 297 277

Sixweeks fescue 1985 54 101 86 - -

1986 146* 221* 134* - -

1994 20* 13* 34* 4 0

1998 104* 36* 284* 244* 234*

Broom snakeweed 1985 72 55 64 - -

1986 88* 67* 87* - -

1994 36* 21* 78* 0 0

1998 82* 27 235* 4 115*

Hoary aster 1985 34 51 75 - -

1986 36 51 80 - -

1994 0* 0* 146* 0 0

1998 0 9 0* 0 0

*Asterisks indicate values for years that are significantly different from the previous reading at 80% probability (Chi Square = 1.642

with 1 degree of freedom).
164 USDA Forest Service Proceedings RMRS-P-11. 1999

Hoary Aster

At the Taylor Flat sites, hoary aster (Machaeranthera

canescens) was of low to moderate frequency in 1985 and

1986. However, in 1994 it was lacking at all sites except one

(OX) where it showed a high increase. In 1998, it was not

found at site OX, and it was also lacking at all other sites

except CX where it was of very low frequency (table 6). This

species did not respond to the cool, wet spring of 1998.

Reasons for oscillations in frequency of this species are less

obvious than for broom snakeweed and sixweeks fescue.

However, the greatest oscillation was found at a site of heavy

grazing in spring by cattle.

Other Forbs

Frequency data shows none of the forbs had both high site

consistency and high quadrat frequency. Scarlet globemallow

(Sphaeralcea coccinea) and Hood phlox (Phlox hoodii) were

the most consistent forbs. Other forbs found in plots include:

silver bladderpod (Lesquerella ludoviciana), plains mustard

(Schoencrambe linifolia), silvery townsendia (Townsendia

incana), cushion buckwheat (Eriogonum ovalifolium), yellow-eye cryptanth (Cryptantha flavoculata), cicada milkvetch

(Astragalus chamaeleuce), low pussytoes (Antennaria

dimorpha), plains spring-parsley (Cymopterus acaulis), toadflax (Comandra umbellata), tansy mustard (Descurainia

pinnata), densecress (Lepidium densifolium), dwarf gilia

(Gilia pumila), western stickseed (Lappula occidentalis),

and chenopod (Chenopodium spp.).

Diversity of Vascular Plants

Number of vascular plant taxa found in plots (table 5) at

each study site ranged from 12-27 with a mean of 18. This is

low compared to mountain big sagebrush communities.

Studies of the same plot design in mountain big sagebrush

communities with 33-70 cm (13-28 inches) annual precipitation at sites in the nearby Uinta Mountains commonly

include 6-12 graminoids, 20-40 forbs, and 2-6 shrubs and a

total of 30-50 species (Ashley National Forest, unpublished

study data). For mountain big sagebrush communities on

the west flank of the Wind River Mountains, Wyoming, Tart

(1996) found the number of vascular plant taxa per plot

(375 m2

) ranged from 11-39 with a mean of about 27.

 Repeat Monitoring

 Repeat readings at three sites in 1985, 1986, 1994, and

1998 and at two sites in 1994 and 1998 provided an opportunity to evaluate species for variation in summed nested

frequency. The data displayed in table 6 demonstrates

Wyoming big sagebrush and needle-and-thread grass maintained similar frequency over the 13 years of the study. It

also shows wide variations in frequency for sixweeks fescue,

broom snakeweed, and hoary aster. The one exception for

needle-and-thread grass appeared to be related to high

rabbit use in the Taylor Flat DX exclosure where they

apparently found refuge from coyotes and other ground

predators and where larger shrubs of sagebrush provided

more protection from avian predators.

Ground Cover

Ground cover (table 7) at sites protected from livestock

grazing averaged about 55%. Ground cover at sites moderately grazed by livestock under rest or deferred grazing

systems averaged about 59%. However, at sites closely

grazed annually in spring, ground cover averaged 30%.

Persistent cattle grazing in spring has been demonstrated as

a tool to maintain high value browse for wild ungulates.

However, it is highly implied that continued, heavy cattle

grazing in spring caused reduced ground cover.

The greatest difference in ground cover was the amount of

litter or plant residue deposited on the ground. Litter cover

was about two times greater in areas protected from livestock or under moderate intensity grazing than in the area

that was heavily grazed in spring each year. Reduction in

ground cover included not only smaller basal area of perennial grass plants but also lower ability of plants to produce

litter. Actual removal of plant material from the site in

animal tissue is also a factor, but this is expected to be much

less important than the other factors because high percent

ground cover was maintained under moderate intensity,

rest, or deferred rotation grazing.

Influence of Grazing and Browsing by

Ungulates

In absence of all ungulate use, sagebrush achieved high

percent crown cover and demonstrated high capability to

suppress other plant species. Absence of cattle grazing

coupled with high levels of wild ungulate use has reduced

Wyoming big sagebrush to less than 5% crown cover. This

reduction has been associated with high vigor of needle-andthread grass. In this condition, this grass appears to be

highly capable of suppressing other species as does sagebrush when it is at high percent crown cover.

With high levels of cattle grazing in spring, needle-andthread grass was greatly reduced in vigor but not in frequency. In this condition biennials and short-lived perennials such as broom snakeweed and hoary aster demonstrated

boom and bust populations. Where protected or moderately

used with periodic rest from livestock grazing, needle-andthread grass appears to be able to greatly suppress boom

populations of these species. However, sixweeks fescue, an

annual, has expressed high frequency in highly vigorous stands

of needle-and-thread grass in the absence of livestock grazing

(GRN site).

Management Implications ________

Wyoming Big Sagebrush

In the absence of all ungulate grazing, Wyoming big

sagebrush is demonstrated to be the overwhelming dominant on the pediments associated with the Green River

within the study area. For this study area, maximum crown

cover of Wyoming big sagebrush that 20-25 cm (8-10 inches)

annual precipitation will support appears to be about 22%.

High levels of sagebrush crown cover have been associated

with a decrease in frequency of some other species. In the
USDA Forest Service Proceedings RMRS-P-11. 1999 165

Table 7—Ground covera.

Ground cover

Grazing treatment Range Mean

- - - - - Percent - - - - - -

Heavy, annual, spring grazing by cattle (2 sites) 26-33 30

Rest or deferred rotation, moderate intensity grazing by cattle (4 sites) 55-60 59

Protected from livestock for at least 10 years (6 sites) 49-65 55

a

 Basal area of live vegetation, litter, and rock fragments equal to or greater than 2 cm (0.75 inch) were included as ground

cover. Bare soil and pavement (rock fragments less than 2 cm in diameter) were not included in ground cover.

presence of wild ungulate browsing, sagebrush crown cover

has been held between about 5 and 13% crown cover. At this

level of sagebrush cover, needle-and-thread grass and other

species appear to remain with near potential frequency.

Although frequency of understory species remains rather

high, vigor or production appears to be reduced where crown

cover of sagebrush exceeds about 5%. Crown cover of sagebrush at less than 5% was associated with absence of cattle

grazing coupled with high levels of wild ungulate use.

At less than 5% crown cover, sagebrush appears to loose

its capability to drive community dynamics. This indicates

that other shrubs of the study area that have not demonstrated an ability to exceed 5% crown cover have low ability

to drive the system.

Abundance of sagebrush greatly contributes to the value

of the communities of the study area for mule deer and

pronghorn antelope habitat. Sagebrush is a major part of the

pronghorn antelope diet (Ngugi and others 1992; Olsen and

Hansen 1977). It is also used extensively by mule deer

especially in winter (Wambolt 1996; Hansen and Reid 1975;

Willms and McLean 1978; Welch and Wagstaff 1992). Close

hedging of Wyoming big sagebrush is evident across the

study area by its hedged growth form. Wyoming big sagebrush is the principal forage that has sustained mule deer

(Trogsted 1994) and antelope herds through the critical

winter period for many years within the study area.

Wyoming big sagebrush provides structural diversity that

provides habitat for small birds and mammals. It is essential

to sage grouse in winter for forage, and it is highly selected

by these birds for nesting cover (Robertson 19991; Connelly

et al. 1991) . The seeds of sagebrush can also be important

forage for small birds. Actions that drive it to less than 5%

crown cover appear to put it at risk. At less than about 5%

crown cover, it appears to no longer function well in providing structure and ample forage for small and larger species

of wildlife. However, at about 12-15% it becomes highly

oppressive to associated species (Winward 1991; Tueller and

Blackburn 1974).

Perennial Grasses

Where Wyoming big sagebrush is suppressed, needleand-thread grass has been demonstrated to be the most

competitive plant on the study area. It clearly takes command of soil and water resources at such magnitude as to

suppress most other herbaceous species on equal or even

greater scale than does sagebrush. Needle-and-thread grass

was the only grass found at high site consistency and high

frequency at all sites.

Frequency of needle-and-thread grass has remained high

regardless of intensity of livestock grazing. However, the

size of the plants and production appear to have been greatly

reduced by heavy, annual, spring cattle grazing. As suggested by Uresk (1990), a combination of crown cover and

frequency would probably better reflect the status and trend

of vegetation than frequency alone. Although needle-andthread grass has been reduced in vigor by cattle grazing in

spring, its persistence at high frequency indicates potential

for rapid recovery with reduced grazing pressure.

Where needle-and-thread grass has been greatly reduced

in vigor, biennials and short-lived perennials such as broom

snakeweed and hoary aster have demonstrated boom and

bust populations. Where protected or periodically rested

from moderate livestock grazing, needle-and-thread grass

appears to greatly suppress boom populations of these species.

Although Indian ricegrass was found at most sites, frequency of this species was too low for it to play more than a

minor part in plant community dynamics. At Antelope Flat,

Junegrass and Sandberg bluegrass were abundant enough

to be major players in the community. These were about

equally abundant with moderate livestock grazing and where

livestock grazing had been greatly restricted. Bottlebrush

squirreltail was present at most sites at low frequency. It did

not seem to respond differently to different levels of grazing.

This is a major player in some Wyoming big sagebrush/grass

communities. However, on the gravel pediments of this

study area, it does not seem to have much ability to drive

community dynamics. Also it appears to be of limited value

as an indicator of trend as driven by ungulates.

Perennial grasses and the litter they produce function as

major components of soil and watershed protection. They

provide more uniform dispersion of ground cover than does

sagebrush and other shrubs that are more widely spaced.

They are also a major source of forage for ungulates and

probably some small mammals.

Cheatgrass

The recent intrusion of cheatgrass into these communities

indicates a much greater risk to plant community function

and values than livestock or high concentrations of wild

ungulates. Cheatgrass with low frequency was found at 42%

of the sites. However, above normal precipitation in spring

such as in 1998 facilitates a flush of cheatgrass. Data from

1998 indicate it is as capable of increasing in areas of

livestock exclusion as well as where livestock graze. In 1998

it was more abundant at the GRN site (not grazed by cattle)

than at the adjacent GRS site that is grazed by cattle.
166 USDA Forest Service Proceedings RMRS-P-11. 1999

Introduction of fire regimes typical of cheatgrass-driven

systems would be devastating to values of sagebrush/perennial grass communities.

Forbs

Regardless of presence or absence of ungulates, forbs as

individual species were either of low site consistency or low

frequency or both. Individually or collectively they appear to

play no more than a minor role in community dynamics.

Collectively they were not abundant enough or vigorous

enough to produce much forage or cover for wildlife. Observations and limited measurements from the study area

indicate forb production (air dry weight) is often less than

6 kg/ha (5 pound/acre) in areas protected from livestock

grazing. Other than Hood phlox, most of these were of little

value for soil and watershed protection. Although important

as individual agents of diversity, they appear to play a

comparatively minor part in biological functions of other

plants and animals of the area. Low occurrence of perennial

forbs for Wyoming big sagebrush communities has also been

noted by Bunting (1985) and Winward (1983).

In addition to low consistency and low frequency or both,

forbs were not highly succulent. Other than rare occurrence

of Torry malacothrix (Malacothrix torreyi) and dandelion

(Taraxacum officinale), succulent members of the Chicory

Tribe of the Asteraceae Family were not found in these

communities. The nature of forbs indicates low value of

these communities for sage grouse brooding habitat. Where

the study area is adjacent to the Flaming Gorge Reservoir,

greatest sage grouse brooding success appears to be related

to abundance of succulent forbs produced along the highwater line of the reservoir (Perschon 1994). Although of

apparently low value for brooding habitat due to low presence of forbs, the area is valuable winter habitat for sage

grouse due to strong presence of sagebrush.

Plant Community Dynamics and Diversity

In general, plant community dynamics appear to be driven

by Wyoming big sagebrush, needle-and-thread grass, other

perennial grasses at higher precipitation sites, and by ungulates. The high competitive ability of Wyoming big sagebrush and needle-and-thread grass in this area of limited

precipitation greatly limits the number and abundance of

other species. Total plant taxa recorded at the 12 sites of this

study ranged from 12-27 with a mean of 19 (table 5). Only as

far as 1-2 km (1 mile) away where annual precipitation is

about 30 cm (12 inches), plant communities of cool exposures

have been recorded with over 50 vascular plants (Huber and

others 1999). The potential for diversity between 30 cm

annual precipitation on cool exposures and 20-25 cm annual

precipitation on flats appears to be great. Also mountain big

sagebrush communities commonly average twice or more

the number of vascular plant taxa than do Wyoming big

sagebrush communities.

Annual production of plants also provides a measure of

diversity. For many plant communities, greater production

of vegetation seems to indicate greater potential for fauna.

Production studies on the study area and other studies in

Wyoming big sagebrush communities indicate 224-560 kg/

acre (200-500 lbs/acre). Studies from the Uinta Mountains

(Ashley National Forest, unpublished data) indicate 785-

1290 kg/ha (700-1,200 lbs/acre) above-ground, annual production (air dry weight) is common for mountain big sagebrush communities. For the west flank of the Wind River

Mountains, Tart (1996) reported a range of 270-1150 lbs/

acre for mountain big sagebrush communities. The differences in species diversity, production, and other features

demonstrate the need to recognize communities of these two

sagebrush taxa in planning and management.

The wide variation from year to year in frequency of some

plants including sixweeks fescue and hoary aster (table 6),

with no change in management, indicated they have low

value as indicators of trend related to management practices. Although broom snakeweed in a general way has

seemed to reflect intensity of livestock grazing, the frequent

oscillation of this species greatly reduces its value as an

indicator. Ground cover, crown cover of sagebrush, and

frequency and cover of long-lived perennial species are

indicated to be more reliable indicators of trend.

Cattle Grazing

Heavy grazing by cattle annually in spring has been

demonstrated as a tool to maintain high value sagebrush

cover and browse for wildlife. However, this was associated

with reduced ground cover. After a review of literature,

Holecheck and others (1998) concluded:

...various studies of grazing impacts on rangeland soils and

watershed status are highly consistent in showing that

vegetation residue is the primary factor determining degree

of soil erosion and water infiltration into the soil. As residue

is depleted by heavy grazing, soil erosion increases, water

infiltration decreases, and water overland flow increases....

This data from Daggett County is consistent with the summary of Holecheck and others (1998) in that the greatest

difference between areas heavily grazed and those moderately grazed or protected from grazing was the amount of

litter or plant residue found as ground cover. Ground cover

at sites protected from livestock grazing averaged about

55%. Ground cover at sites moderately grazed by livestock

under rest or deferred systems averaged about 59%. However, at sites closely grazed annually in spring, ground cover

averaged 30%.

A need for close monitoring is indicated where livestock

grazing is used as a tool to maintain or increase sagebrush

on winter range for wild ungulates. Wild ungulate values

will ultimately depend on soil values. To avoid long-term

degradation in soil resources, intensity of cattle grazing

needs to be managed at levels that maintain sufficient

ground cover to maintain soil values. Ground cover of about

50% appears to be adequate for soil protection on these low

gradient sites. Ground cover at and above 50% has been

achieved and maintained at sites under moderate intensity

grazing where crown cover of sagebrush has been maintained at greater than 5%.

Desired Condition

Based on inherent capabilities and current values most

apparent for the Wyoming big sagebrush/needle-and-thread

grass communities of the study area, desired condition is
USDA Forest Service Proceedings RMRS-P-11. 1999 167

suggested as follows: Wyoming big sagebrush at 5-15%

crown cover, needle-and-thread grass dominant in the understory, other perennial graminoids rare to abundant depending on local conditions, 4-12 or rarely more forbs present

in a 30.5 m (100 ft) radius plot with most of these of low

frequency, ground cover at 50% or greater.

These conditions have been sustained under livestock and

wild ungulate use over large parts of the study area. The

exception of low percent sagebrush crown cover at the GRN

site represents a comparatively small area. The low percent

ground cover at sites GRS and OX is found on a comparatively small percent of the area. Low percent ground cover

found under annual, spring cattle use of high intensity has

not been found at sites under rest or deferred rotation

grazing of moderate intensity.

Livestock use has been demonstrated to be compatible

with wildlife values in the study area. Wild ungulates

reduced crown cover of sagebrush that facilitates release of

grass and enhances understory diversity and forage for

cattle. Cattle grazing has been associated with maintaining

greater sagebrush cover, which is important to wildlife.

Complementary and not competitive use is demonstrated

for wild ungulates and cattle in this study area. Exclusion of

either or both wild ungulates and moderate intensity cattle

grazing has not resulted in overall higher resource values

than where both are present.

Monitoring and Trend

Capabilities and values of the area indicate monitoring for

resource values and trends should focus on crown cover of

sagebrush, frequency and probably cover of perennial herbaceous species, and ground cover. Crown cover of sagebrush

can provide a measure of wildlife values. Frequency combined with crown cover can provide a measure of diversity

and of forage values. Ground cover can indicate condition

and trend of watershed values and maintenance of productive potential.

Sagebrush crown cover of less than 5% should indicate a

need to consider management actions that would prevent

additional loss of this plant. Reductions in crown cover of

perennial graminoids might provide an advanced warning of

potential loss of ground cover. In retrospect, loss of ground

cover appears to reflect loss of plant vigor. On these low

gradient areas, monitoring for loss of ground cover might

provide adequate warning to respond to loss of plant vigor as

well as to the loss of ground cover. Where ground cover is

found at less than 50% over more than about 10% of a

grazing unit, need for change in management is strongly

indicated in order to maintain overall resource values.

References _____________________

Ashcroft, G. L.; Jensen, D. T.; Brown, J. L. 1992. Utah climate.

Logan, UT: Utah State University, Utah Climate Center. 125 p.

Ashley National Forest. Unpublished study data on file at: U.S.

Department of Agriculture, Forest Service, Intermoutain Region,

Ashley National Forest, Supervisors Office, Vernal, UT.

Bunting, S. C. 1985. Fire in sagebrush-grass ecosystems: successional changes. In: Sanders, K.; Durham, J., eds. Rangeland fire

effects—a symposium, 1984 November 27-29; Boise, ID: U.S.

Department of the Interior, Bureau of Land Management, Idaho

State Office. 7-11.

Clary, W. P.; Goodrich, S.; Smith, B. M. 1985. Response to

Tebuthiuron by Utah juniper and mountain big sagebrush communities. J. Range Manage. 38: 56-60.

Connelly, J. W.; Wakkinen, W. L.; Apa, A. D.; Reese, K. P. 1991. Sage

grouse use of nest sites in southeastern Idaho. Journal of Wildlife

Management 55: 521-524.

Hansen, R. M.; Reid, L. D. 1975. Diet overlap of deer, elk, and cattle

in southern Colorado. J. Range Manage. 28: 43-47.

Hironaka, M.; Fosberg, M. A.; Winward, A. H. 1983. Sagebrushgrass habitat types of southern Idaho. Bulletin number 35.

Moscow, ID: Forest, Wildlife and Range Experiment Station,

Univ. of Idaho. 44 p.

Holechek, J. L.; Gomes, H. dG.; Molinar, F.; Galt, D. 1998. Grazing

intensity: Critique and approach. Rangelands 20: 15-18.

Huber, A.; Goodrich, S.; Anderson, K. 1999. Diversity with successional status in the pinyon-juniper/mountain mahogany/

bluebunch wheatgrass community type near Dutch John, Utah.

In: Monsen, Stephen B.; Stevens, Richard, comps. Proceedings:

ecology and management of pinyon-juniper communities within

the Interior West; 1997 September 15-18; Provo, UT. Proc. RMRSP-9. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station. 114-117.

Jameson, D. A. 1970. Value of broom snakeweed as a range condition indicator. J. Range Manage. 23: 302-304.

Ngugi, K. R.; Powell, J.; Hinds, F. C.; and others. 1992. Range

animal diet composition in southcentral Wyoming. J. Range

Manage. 45: 542-545.

Olsen, F. W.; Hansen, R. M. 1977. Food relations of wild freeroaming horses to livestock and big game, Red Desert, Wyoming.

J. Range Manage. 30:17-20.

Perschon, C. 1994. [Personal communication] March. Vernal, UT:

Utah Division of Wildlife Resources, Northeastern Region.

Rittenhouse, L. R.; Sneva, F. A. 1976. Expressing the competitive

relationship between Wyoming big sagebrush and crested wheatgrass. J. Range Management. 24: 326-327.

Roberston, M. D. 1991. Winter ecology of migratory sage grouse and

associated effects of prescribed fire in southeastern Idaho. Moscow, ID: University of Idaho. 88 p. Thesis.

Tart, D. L. 1996. Big sagebrush plant associations of the Pinedale

Ranger District. Pinedale, WY: U.S. Department of Agriculture,

Forest Service, Bridger-Teton National Forest. 97 p.

Trogsted, Ron. 1994. BLM Utah Spectrum VII (1). Salt Lake City,

UT: U.S. Department of the Interior, Bureau of Land Management. 1-3.

Tueller, P. T.; Blackburn, W. H. 1974. Condition and trend of the big

sagebrush/needle-and-thread habitat type in Nevada. J. Range

Mange. 27: 36-40.

Uresk, D. W. 1990. Using multivariate techniques to quantitatively

estimate ecological stages in a mixed grass prairie. J. Range

Manage. 43: 282-285.

U.S. Department of Agriculture, Forest Service, 1993. Rangeland

ecosystem analysis and management handbook. FSH 2209.21.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Region. 4 ch.

Utah Division of Wildlife Resources. Unpublished report on file at:

Utah Division of Wildlife Resources, North Eastern Region Office, Vernal, UT.

Wambolt, C. L. 1996. Mule deer and elk foraging preference for 4

sagebrush taxa. J. Range Manage. 49: 499-503.

Welch, B. L.; Wagstaff, F. J. 1992. ‘Hobble Creek’ big sagebrush vs.

antelope bitterbrush as a winter forage. J. Range Manage. 45:

140-142.

Welsh, S. L.; Atwood, N. D.; Goodrich, S.; Higgins, L. C. 1993. A Utah

Flora. 2nd edition. Provo, UT: Brigham Young University Print

Services. 986 p.

Willms, W.; McLean, A. 1978. Spring forage selection by tame mule

deer on big sagebrush range, British Columbia, J. Range Manage.

31: 192-198.

Winward, A. H. 1983. Using sagebrush ecology in wildland management. In: Johnson, K. L., ed. Proceedings of the first Utah shrub

ecology workshop; 1981 September 9-11; Ephraim, UT. Logan,

UT: Utah State University, College of Natural Resources: 15-19.

Winward, A. H. 1991. Management in the sagebrush steppe. Special

Report 880. Corvallis, OR: Oregon State University, Agricultural

Experiment Station. 7 p.
168 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Deborah Turley is Graduate Student and Bruce A. Roundy is Professor and

Chair, Department of Botany and Range Science, Brigham Young University,

Provo, UT 84602. Scott C. Walker is Wildlife Biologist and Acting Project

Leader, Great Basin Research Center, Utah Division of Wildlife Resources,

Ephraim, UT 84627.

Twig Demography of True Mountain

Mahogany (Cercocarpus montanus Scop.)

Deborah Turley

Bruce A. Roundy

Scott C. Walker

Abstract—True mountain mahogany (Cercocarpus montanus Scop.)

is a valuable forage species for wild ungulates and livestock in

mountain brush communities of Utah, Wyoming, and Colorado.

Considered good to excellent browse, true mountain mahogany is

utilized heavily. To determine response to browsing, twig demography was studied on shrubs inside and outside an exclosure (approximately 30 m by 30 m), in Gardner Canyon, just northeast of Nephi,

Utah. Long shoot branches were measured, diagrammed, and

monitored in 1996 and 1997 to record the effects of browsing on

seasonal growth. Ratios of annual, second year wood, third year

wood, and seeds to total length of twigs were compared for browsed

and unbrowsed shrubs. Seed ratios were significantly higher in the

exclosure (unbrowsed 0.135, browsed 0.332 seeds/cm), browsing

was moderate to heavy (78.5 ± 6.0% of annual twig growth), and

annual growth ratios were significantly greater outside than inside

the exclosure in 1997. Ratios of 1997 to 1996 total twig length were

0.92 for browsed and 1.12 for unbrowsed shrubs. Increased annual

growth of browsed twigs compensated for twig length removed by

browsing.

True mountain mahogany shrub communities are found

throughout the Great Basin and Rocky Mountains in elevations between 1,070 and 3,050 m (Greenwood and Brotherson

1978). This shrub has the second largest distribution in its

genus, after curlleaf mountain mahogany (Cercocarpos ledifolius), and is centrally located in Utah, Colorado, and

Wyoming with the edges of its range extending to South

Dakota, Nebraska, Oklahoma, New Mexico, Arizona, and

Nevada (Davis 1990; Medin 1960). True mountain mahogany is usually found on foothills and mountain slopes

and grows from 1 to a maximum of 4 m tall (Davis 1990). On

average the plants are 1 m in diameter and 1.5 m tall but can

be much lower and wider when grazed (Stutz 1990). This

species is usually closely associated with other species such

as sagebrush (Artemisia spp.), pinyon-juniper (Pinus spp.

Juniperus spp.), aspen (Populus tremuloides), and mountain brush and mixed conifer communities (Davis 1990).

Brotherson and others (1984) reported that true mountain

mahogany was in greatest abundance on southern exposures at higher elevations but could be found on all aspects.

Physical site factors influencing its growth are soil depth

and stoniness, with greater soil depth increasing growth and

greater stoniness decreasing growth (Medin 1960).

True mountain mahogany is known to have good to excellent palatability and to provide a major amount of winter

forage for mule deer (Odocoileus hemionus). The shrub also

is considered good to excellent for livestock (Range Plant

Handbook 1931) as well as highly valuable for Rocky Mountain elk (Cervus canadensis) as a food source (Kufeld 1973).

Rominger and others (1988) found Cercocarpus montanus

leaves to comprise 56 to 92% of the summer diet of Rocky

Mountain bighorn sheep (Ovis canadensis). Other wildlife

such as antelope (Antilocapra americana), mountain goats

(Oreamnos americanus), and small mammals may use this

shrub as forage (Wasser 1982). This shrub was known to be

hedged between 40 to 60% on one site by deer and elk or

cattle in the Uintah Basin (Applegate 1995). This species

shows good tolerance to winter browsing but may be much

reduced in size and productivity by repeated use during its

growing season.

A study done on bitterbrush (Purshia tridentata) and

sagebrush (Artemisia tridentata) in exclosures showed that

stagnation in the plants occurred after a few years of no

browsing (Tueller and Tower 1979). Waugh (1990) conducted research on a big game exclosure in southeastern

Wyoming. He found no significant difference in biomass

between sagebrush in and outside the exclosures. However,

current year’s production was much less for true mountain

mahogany within the exclosure compared to outside the

exclosure. He suggested that some utilization was necessary

for optimum production of mountain mahogany, and stagnation and decadence would occur if this shrub was not browsed

over time.

Nixon (1977) measured a mountain mahogany growth

after 10 years in Nebraska. Shrubs on the northeast-facing

slope increased 37 cm in height but these shrubs on the

southwest facing slope stayed the same height. There was an

overall decrease in number of base stems on shrubs on both

slopes. Reproduction was found only in one location on the

southwest-facing slope.

Bilbrough and Richards (1993) studied twig demography

to determine growth response to browsing for sagebrush and

bitterbrush. Simulated winter browsing treatments were

applied and responses recorded. The production of the stem

was recorded for short shoots, long shoots, mortality, and

flowering stems. Simulated browsing reduced long-shoot

growth of sagebrush but increased that of bitterbrush. Short

shoots of both species produced long shoots at a similar rate

on both browsed and unbrowsed shrubs. Shoot biomass and

node production in bitterbrush equaled or increased with
USDA Forest Service Proceedings RMRS-P-11. 1999 169

simulated browsing, whereas sagebrush had a greater frequency of long shoots but biomass was the same as the

unclipped plants. Node production of sagebrush also decreased with simulated browsing.

Roundy and Ruyle (1989) studied twig demography to

determine effects of grazing pressure on jojoba (Simmondsia

chinensis). Twigs of heavy, moderate, and ungrazed shrubs

were diagrammed. Regrowth from buds on grazed branches

was sufficient to replace grazed biomass. Lateral buds produced shoots when apical buds were grazed. Both female and

male flowers were less abundant on grazed shrubs.

The objective of this study is to determine response of true

mountain mahogany to winter browsing from deer and elk.

The approach was to compare plant growth responses between browsed and unbrowsed shrubs growing under the

same climatic and ecological conditions. Diagramming

branches allows the determination of growth characteristics

of a shrub and can be done to monitor responses to herbivory

on a specific site. It can determine precisely where shoot

growth occurs, which buds form shoots, what part of the

plant is reproductive, and where second-year and third-year

wood are found. This allows determination of the effects of

browsing, the number of available growing points, and the

amount of growth from those points.

Methods _______________________

An exclosure located in Gardner Canyon a few miles

northeast of Nephi, Utah, was first built in the 1930’s and

then reinforced in 1946. The area of the exclosure supports

a dominant true mountain mahogany community. The portion of the exclosure keeping out wildlife and cattle still

stands presently. Due to the long-term rest from browsing

for shrubs within the exclosure, the site seemed satisfactory

to compare browsed versus nonbrowsed shrubs of mahogany.

The exclosure covers both a south- and north-facing slope

and an area approximately 30 m by 30 m.

A 30 m line transect was set up both inside and outside the

exclosure. Ten mature shrubs were randomly chosen along

the transect line. Four branches on each shrub were then

chosen for diagramming. Three branches contained and

were chosen to measure the amount of long-shoot growth, or

new growth, found on the branch. The fourth branch was

chosen to measure the short-shoot growth. These branches

were then diagrammed with measurements of length of

annual growth, second-year wood, third-year wood, and

locations of buds, flowers, and seeds. The branches were

marked with browse tags and first diagrammed in the fall of

1996 to get a baseline of the branch initially observed. Each

branch was drawn free hand to scale. The drawings were

photocopied and used to diagram new growth in the summer

of 1997. Any missing branches previously drawn but now

absent were recorded so that an accurate diagram of the

branch persisted and browsing effects would be known. The

site was visited in early summer to determine amount of

browsing and number of flowers produced on the branches

diagrammed. Shrubs on this site are mainly browsed during

winter by deer and elk. The site was visited again in late

summer to diagram new growth and number of seeds

produced.

Because each branch varied in size, ratios of seasonal

growth to total branch length were calculated to standardize

the data. Analysis of variance was used to determine significant differences between browsed and unbrowsed shrubs

over time.

Results ________________________

Only results of long-shoot measurements will be presented in this paper. Browsed and unbrowsed shrubs averaged 0.14 and 0.33 seeds/cm of twig length, respectively. The

seed ratios were significantly different (p <0.05). For the

winter of 1996-1997, the percent browsed length of total

twig length was 78.5 ± 6.0 for annual growth, 29.3 ± 5.3 for

second-year wood, 6.8 ± 3.8 for third-year wood, and 41.3 ±

4.0 for total twig length.

There were no significant differences in annual, secondyear wood, and third-year wood between browsed and

unbrowsed shrubs in 1996 (table 1). Annual growth was

significantly higher for browsed than unbrowsed shrubs in

1997. Second-year and third-year growth were both significantly less on browsed than unbrowsed shrubs in 1997.

For unbrowsed shrubs within the exclosure, the annual

growth ratio was significantly lower in 1997 than in 1996.

Second-year wood was also significantly less and third-year

wood was significantly higher in 1997 than in 1996.

Outside the exclosure, annual growth ratios of browsed

shrubs were not significantly different from 1996 to 1997.

Second-year wood was significantly less in 1997 than in

1996. Third-year wood was significantly higher in 1997 than

in 1996. All categories in table 2 were significantly different

from each other comparing browsed to unbrowsed.

Table 2—Ratios of twig length in 1997 to that in 1996 for true mountain

mahogany.

Total twig Annual Second-year

Category length growth wood

Browsed 0.923a 1.379 0.099

Unbrowsed 1.121 0.538 0.522

aAll values within a column differed significantly (p < 0.05).

Table 1—Ratios of specific twig growth of true mountain mahogany to

total twig length.

Annual Second-year Third-year

Category Year growth wood wood

Unbrowsed 1996 0.235aa 0.546a 0.115a

Browsed 1996 0.291a 0.553a 0.103a

Unbrowsed 1997 0.093b 0.209a 0.496a

Browsed 1997 0.342a 0.050b 0.376b

aMeans followed by the same letter within a column and year but between

categories are not significantly different (p <0.05).
170 USDA Forest Service Proceedings RMRS-P-11. 1999

Discussion _____________________

Branches inside and outside the exclosure were similar in

growth parameters in 1996. By 1997, branches outside the

exclosure were significantly different from those inside the

exclosure due to the amount of browsing and regrowth that

had occurred. The ratio for annual growth on the unbrowsed

branches had dropped dramatically, whereas annual growth

on the browsed branches remained similar to that of the year

before. Second-year wood was decreased on browsed branches

indicating the high utilization that had occurred over the

winter.

Seed ratios were much higher for shrubs inside than

outside the exclosure. Seeds of true mountain mahogany are

produced from second-year or older growth. Ratio differences may be a result of greater second- and third-year twig

length on unbrowsed than browsed branches in 1997.

The amount of annual growth diagrammed that was

browsed was high at 78.5%. This, and the fact that 41% of the

total length diagrammed was browsed, indicates moderate

to heavy winter browsing. The ratio of total twig length in

1997 to 1996 is 0.92 for browsed twigs (table 2), indicating

branch length is similar for both years. For the 1996 to 1997

browsing and growing seasons, true mountain mahogany

compensated well with new growth for the amount browsed

even under high utilization on this site.

References _____________________

Applegate, C. K.1995. Allocation of forage among elk and cattle and

vegetative composition of several joint elk-cattle use ranges in

eastern Utah. Provo, UT: Brigham Young University, M. S.

Thesis.

Bilbrough, C. J.; Richards, J. H. 1993. Growth of sagebrush and

bitterbrush following simulated winter browsing: mechanisms

and tolerance. Ecology. 74:481-492.

Brotherson, J. D.; Anderson, D. L.; Szyska, L. A. 1984. Habitat

relations of Cercocarpus montanus (true mountain mahogany) in

Central Utah. Journal of Range Management. 37:321-324.

Davis, J. N. 1990. General ecology, wildlife use, and management of

the mountain mahoganies in the Intermountain West. In: Johnson,

Kendall L., ed. Utah Shrub Ecology Workshop: the genus Cercocarpus: proceedings; 1988 July 13-14; Logan, UT. Logan, UT:

Utah State University: 1-14.

Greenwood, L. R.; Brotherson, J. D. 1978. Ecological relationships

between pinyon-juniper and true mountain mahogany stands

in the Uintah Basin, Utah. Journal of Range Management. 31:

164-167.

Kufeld, R. C. 1973. Foods eaten by the Rocky Mountain elk. Journal

of Range Management. 26:106-113.

Medin, D. E. 1960. Physical site factors influencing annual production of true mountain mahogany, Cercocarpus montanus. Ecology. 41:454-460.

Nixon, E. S. 1977. A mountain Cercocarpus population-revisited.

Great Basin Naturalist. 37:97-99.

Rominger, E. M.; Dale, A. R.; Bailey, J. A. 1988. Shrubs in the

summer diet of Rocky Mountain bighorn sheep. Journal of Wildlife Management. 52:47-50.

Roundy, B. A.; Ruyle, G. B. 1989. Effects of herbivory on twig

dynamics of a sonoran desert shrub Simmondsia chinensis (Link)

Schn. Journal of Applied Ecology. 26:701-710.

Stutz, H. C. 1990. Taxonomy and evolution of Cercocarpus in the

Western United States. In: Johnson, Kendall L., ed. Utah Shrub

Ecology Workshop: The genus Cercocarpus: proceedings; 1988

July 13-14; Logan, UT. Logan, UT: Utah State University:

15-26.

Tueller, P. T.; Tower, J. D. 1979. Vegetation stagnation in threephase big game exclosures. Journal of Range Management. 32:

259-263.

U. S. Department of Agriculture. Forest Service. 1937. Range Plant

Handbook.Washington, DC: U. S. Government Printing Office.

Wasser, C. H. 1982. Ecology and culture of selected species useful in

revegetation disturbed lands in the West. Washington, DC: Fish

and Wildlife Service, U.S. Department of the Interior. FWS/OBS82/56 220-221.

 Waugh, W. J. 1990. Stagnation and decadence of Cercocarpus

montanus in a southeastern Wyoming big game exclosure. In:

Johnson, Kendall L., ed. Utah Shrub Ecology Workshop: the

genus Cercocarpus: proceedings; 1988 July 13-14; Logan, UT.

Logan, UT: Utah State University: 89-96.
USDA Forest Service Proceedings RMRS-P-11. 1999 171

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Bruce L. Welch is Principal Research Plant Physiologist, U.S. Department

of Agriculture, Forest Service, Rocky Mountain Research Station, Shrub

Science Laboratory, 735 N 500 E, Provo, UT 84606.

Add Three More to the List of

Big Sagebrush Eaters

Bruce L. Welch

Abstract—This paper challenges the notion that big sagebrush

(Artemisia tridentata) is a range plant of low value. Present data

that documents the consumption of big sagebrush seeds by darkeyed junco (Junco hyemalis), horned lark (Eremophila alpestris),

and white-crowned sparrow (Zonotrichia leucophrys), and shows

the nutritive value of the consumed seeds to be high in energy, crude

protein, and phosphorus.

A number of years ago I gave a speech to the Utah Section

of The Society for Range Management on the superiority of

big sagebrush (Artemisia tridentata) as a winter forage for

wild ungulates and domestic sheep. Emphasis was given to

its higher digestibility, higher crude protein, higher phosphorus, and higher carotene content than other winter

forages (Welch 1989). The essence of that speech is in table 1.

After I completed the presentation, a seasoned range conservationist of 25-plus years got up and said: “Dr. Welch you

make sagebrush sound real good—too bad nothing eats it.”

A lack of appreciation for big sagebrush as a forage plant is

not uncommon. Big sagebrush is a competitor to grass

(Vallentine 1989). But a statement of such profound

unenlightenment caused me to be speechless for a moment.

Then I enumerated to my range conservationist friend the

animals I have watched eating big sagebrush (table 2).

Where does this lack of appreciation for big sagebrush as

a forage plant come from? I believe I have a partial answer—

Range Management text books (Heady 1975; Heady and

Child 1994; Holechek and others 1989; Stoddart and others

1975; Vallentine 1989, 1990). Sixty-eight percent of comments made concerning big sagebrush in these six text books

are of a negative nature. These comments included: “unpalatable to livestock,” “high levels of volatile oils,” “invader,”

“undesirable,” “reduces the production of better plants,”

“causes rumen disorders,” “uses up water,” “woody,” “noxious,” “poisonous,” “low value,” “little used,” “control,” “eradicate,” “convert,” “suppressed grasses,” and the list goes on.

Only 9% of the comments on big sagebrush were positive.

These comments included: “provide mule deer (Odocoileus

hemionus hemionus), pronghorn antelope (Antilocapra

americana), and domestic sheep (Ovis aries) with winter

feed,” “food for jack rabbits(Lepus californicus),” “food for

sage grouse (Centrocerus urophasianus),” and “nesting sites

for Brewer’s sparrow (Spizella breweri).” Perhaps in his zeal

Table 1—Winter nutritive values of selected range plants (after Welch

1989).a

In vitro Crude

Species digestibility protein Phosphorus

Shrubs

Artemisia tridentata

Big Sagebrush 57.8 11.7 0.18

Cercocarpus montanus

Mountain mahogany 26.5 7.8 0.13

Chrysothamnus nauseosus

Rubber rabbitbrush 44.4 7.8 0.14

Juniperus osteosperma

Utah juniper 44.1 6.6 0.18

Purshia tridentata

Antelope bitterbrush 23.5 7.6 0.14

Grasses

Agropyron desertorum

Crested wheatgrass 43.7 3.5 0.07

Festuca idahoensis

Idaho fescue 46.1 3.8 0.08

Hilaria jamesii

Galleta 48.2 4.6 0.08

Oryzopsis hymenoides

Indian ricegrass 50.5 3.1 0.44

Stipa comata

Needle-and-thread 46.6 3.7 0.07

aNutritive value based on vegetative tissue, not seeds.

Table 2—List of animals that the author has watched eating big

sagebrush (Artemisia tridentata).

Black-tailed jack rabbit Lepus californicus

Dark-eyed junco Junco hyemalis

Domestic sheep Ovis aries

Horned lark Eremophila alpestris

Pronghorn antelope Antilocapra americana

Pygmy rabbit Brachylagus idahoensis

Rocky Mountain cottontail Sylvilagus nuttalli

Rocky Mountain elk Cervus elaphus nelsoni

Mule deer Odocoileus hemionus hemionus

Sage grouse Centrocerus urophasianus

Uinta ground squirrel Spermophilus armatus

White-crowned sparrow Zonotrichia leucophrys

to defend the faith—killing big sagebrush to produce more

grass—my range conservationist friend forgot these few but

positive comments. Unfortunately, he is not alone.

Listed in table 2 are 12 animals I have watched eating big

sagebrush. Three of those animals were new to me and had

not been documented in the literature: Dark-eyed junco
172 USDA Forest Service Proceedings RMRS-P-11. 1999

(Junco hyemalis), horned lark (Eremophila alpestris), and

white-crowned sparrow (Zonotrichia leucophrys). All were

eating the seeds of big sagebrush. The purpose of this report

is to document the consumption of big sagebrush seeds and

to determine the nutritive value of the seeds.

Methods _______________________

I first observed dark-eyed juncos pecking at big sagebrush

inflorescences near Paul Bunyon’s Woodpile, a point of

interest about 56 km northeast of Delta, Utah.

Shortly after that initial observation, four dark-eyed juncos were collected near the site to verify actual consumption

of big sagebrush seeds. Digestive systems were removed

from the esophagus to the gizzard and placed in small plastic

bags. The bags were transported in a cooler filled with ice to

a laboratory freezer. Then the digestive systems were thawed

and the contents removed. Next, the ingesta were placed

inside of a 200-mesh sieve and washed with deionized water.

After the washing, the contents were separated into three

piles: grit, big sagebrush seed, and other foods. Big sagebrush seed piles and other food piles were placed on

preweighed filter paper circles and dried to constant weight

in a convention oven at 100°C. Percent of big sagebrush

seeds on a dry-matter basis was calculated.

Big sagebrush seeds were collected from 30 plants in the

area where the birds were harvested. Seeds were cleaned as

outlined by Booth and others (1997); Welch (1995); Welch

and Nelson (1995). After cleaning, the seeds were ground to

a fine powder inside the mortar of a steel, motorized mortar

and pestle. Liquid nitrogen was used to precool the mortar

and pestle and then more liquid nitrogen was poured over

the seeds and the seeds ground. Next, the powder was placed

in plastic bottles fitted with airtight caps and stored at 0°C.

I analyzed the ground seeds for in vitro digestibility, crude

protein, phosphorus, and crude fat.

Ground seeds were digested using Pearson’s (1970) in

vitro digestibility method, except 1.0 g of fresh weigh was

placed in the digestion tubes. The dry matter content was

determined for the ground seeds. Inoculum was obtained

from a slaughterhouse steer that was fed a ration of alfalfa

and corn. Welch and others (1983) studied the ability of

different rumen inocula to digest range forages. Steers on

fattening ration digested range forages as well as inoculum

from other sources (also Striby and others 1987). The CO2-

injected inoculum was processed 45 minutes after removal

from the rumen (Milchunas and Baker 1982). Data was

expressed as percent of dry matter digested.

Crude protein level was determined by the Kjeldahl method

(Association of Official Analytical Chemists 1980) and expressed as a percent of dry matter. Phosphorus content was

determined by spectrographic means (Association of Official

Analytical Chemists 1980) and expressed as a percent of dry

matter. Crude fat level was determined by the anhydrous

ether method (Association of Official Analytical Chemists

1980) and expressed as a percent of dry matter.

Results ________________________

Results of the four food analyses expressed as a percent of

total food, dry matter basis, were 64, 69, 71, and 76% big

sagebrush seed for a mean of 70. In vitro digestion for four

big sagebrush seed samples were 71.2, 72.7, 73.6, and 74.0%

for a mean of 72.9. Crude fat levels for four samples were

28.2, 28.5, 29.1, and 29.8% for a mean of 28.9%. Crude

protein level (one sample) was 28.8%. Phosphorus level was

0.545%.

Discussion _____________________

The results of this study clearly show that big sagebrush

seeds were eaten by wintering dark-eyed juncos and at that

time constituted about 70% of their diet.

One thing that appeared remarkable to me was, while

searching the ingesta of the four birds, I did not find one seed

bract. Considering the small size of the seed—2 million or

more for 0.454 kg—and the more numerous but equal in size

bracts shows a great amount of dexterity on the part of the

birds, especially when all the birds I watched that day were

swinging up and down and back and forth on the inflorescences. Big sagebrush inflorescences are not stiff enough to

support the weight of the feeding birds without movement.

During this initial observation period, I noticed small

footprints around many of the big sagebrush plants and

trails going from one plant to another (fig. 1). This situation

is very similar to a sage grouse wintering range except in

miniature. In addition, seeds and seed bracts were found on

the snow surface. Birds were walking around pecking in

those areas, presumably, picking up seeds that had fallen.

Since this initial observation, I have watched dark-eyed

juncos eat big sagebrush seeds at 36 different wildland sites.

These sites encompassed an area from The Fort Hall Indian

Reservation, Idaho, in the north, to Salina, Utah, in the

south, from Lynndyl, Utah, in the west, to Helper, Utah, in

the east. In addition, I have observed the eating of big

sagebrush seed by horned larks (7 wildland sites) and whitecrown sparrows (11 wildland sites) (fig. 2). The eating of big

sagebrush seed by dark-eyed juncos and at least two other

birds in the wild appears to be a widespread phenomenon.

 I filled a backyard bird feeder with big sagebrush seeds

and watched not only dark-eyed juncos (fig. 3) feeding on the

seeds, but house finches (Carpodacus mexicanus), blackcapped chickadees (Parus atricapillus), and house sparrows

(Passer domesticus).

In May of 1992, I observed dark-eyed juncos flying in and

out of an open shed that was being used at the time to dry big

sagebrush inflorescences that were collected the previous

winter. Inside the shed, the birds were scratching and

pecking around, among, and through the inflorescences (fig. 4).

The whole scene reminded me of watching domestic chickens feeding in a barn yard. A pile of big sagebrush seeds

(about 50 g) was placed near the layers of drying inflorescences. In less than a day, the entire pile was consumed by

the dark-eyed juncos.
USDA Forest Service Proceedings RMRS-P-11. 1999 173

It is unknown how much of the yearly diet of dark-eyed

juncos, horned larks, and white-crowned sparrows consists

of big sagebrush seeds. Data presented in this study suggest

that at times it may be a substantial amount. Probably more

important than the absolute amount eaten on a yearly basis

is the timing when the birds are eating the seeds. After fresh

snow, big sagebrush seed may be the only food available to

these birds. Perhaps there are times when big sagebrush is

a keystone species (Hunter 1996) to not only these wintering

birds but to others animals as well. Also, evidence was given

in this study that dark-eyed juncos will consume big sagebrush seeds at times other than winter.

Energy, phosphorus, and protein are most limiting in the

winter diet of animals (Dietz 1965). High in vitro digestion

(72.9%) and high crude fat content (28.9%) of big sagebrush

seeds are evidence that this food could furnish high levels of

energy to the consuming animal. Crude protein level at

28.8% and phosphorus level at 0.545% further shows that

big sagebrush seeds are rich in these needed nutrients.

These levels would exceed the levels needed for maintenance

of range birds (grouse, pheasant, quail, turkey) (Welch

1989). Interesting enough, Beck and Braun (1978) reported

that wintering sage grouse gain weight during the winter, a

time when their diet is nearly 100% big sagebrush leaves

Figure 1—Footprints in snow of dark-eyed juncos feeding on big sagebrush seeds. Arrow pointing to

big sagebrush seeds and seed bracts.

Figure 2—White-crown sparrows feeding on big sagebrush seeds. Arrow pointing to a bird feeding on

seeds. All three birds were observed at some time eating seeds.

Figure 3—Dark-eyed junco eating big sagebrush seeds spilled on the roof of a backyard bird feeder.

Arrow pointing to big sagebrush seeds.

Figure 4—Dark-eyed junco feeding on big sagebrush seed among drying big sagebrush inflorescences

in May.
174 USDA Forest Service Proceedings RMRS-P-11. 1999

and short shoots (Klebenow 1970; Patterson 1952; Peterson

1970). Not bad for a plant that nothing eats!

However, negativeness still persists, for example, Baxter

in 1996 states in the publication “Sharing Common Ground

on Western Rangelands: Proceedings of a Livestock/Big

Game Symposium:”

Dr. Alma Winward is a Plant Ecologist for the Intermountain

Region of the U.S. Department of Agriculture, Forest Service,

and a leading authority on the sagebrush-grass ecosystem.

His opinion is that more acres of sagebrush-grass lands in the

Western United States were held in low ecological status the

past decade due to abnormally high sagebrush cover and

density than currently occurring due to livestock grazing. He

notes that when big sagebrush cover reaches 12 to 15 percent,

the understory production of other plants decreases as canopy

increases. This results in increased bare ground and reduction of forage for livestock and wildlife.

It takes big sagebrush cover of 20 to 40 percent to support

sage grouse (Benson and others 1991; Klebenow 1970;

Patterson 1952; Peterson 1970). If the ideas expressed in the

Baxter (1996) statement were fully implemented there would

be no sage grouse habitat and no sage grouse.

Not all Rangeland Management Specialists share this

narrow and biased view. A statement from Heady and Child

(1994-301 p.)—a range management text book—gives hope

that big sagebrush is gaining some respect as a forage plant

“One example, Artemisia spp. in thick stands are generally

undersirable for livestock but furnish food and cover for

wildlife species.”

References _____________________

Association of Official Analytical Chemists. 1980. Official methods

of analysis. W. Horwitz, ed., 13th Ed. Association of Official

Analytical Chemist, Washington, DC. 1018 p.

Baxter, Garth. 1996. Improving rangeland health by thinning

sagebrush stands with Tebuthiuron (spike 20 p). In: Evans,

Keith E., comp. Sharing common ground in western rangelands:

proceedings of livestock/big game symposium; 1996 February 26-

28; Sparks, NV. Gen. Tech. Rep. INT-GTP-343. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Research Station: 60-62.

Beck, Thomas D. I; Braun, Clait E. 1978. Weights of Colorado sage

grouse. Condor. 80:241-243.

Benson, Lee A.; Braun, Clait E.; Leining, Wayne C. 1991. Sage

grouse response to burning in the big sagebrush type. In: Comer,

Robert D.; Davis, Peter R.; Roster, Susan Q.; (and others), eds.

Proceedings national symposium issues and technology in the

management of impacted wildlife; 1991 April 8-10; Snow Mass

Resort, CO. Boulder, CO: Thorne Ecological Institute. 97-104.

Booth, D. Terrance; Bai, Yuguang; Roos, Eric E. 1997. Preparing

sagebrush seed for market: effects of debearder processing. Journal of Range Management. 50:51-54.

Dietz, Donald R. 1965. Deer nutrition research in range management. Transactions North American Wildlife and Natural Resources Conference. 30:275-285.

Heady, Harold F. 1975. Range Management. McGraw-Hill Book

Company, San Francisco. 460 p.

Heady, Harold F.; Child, R. Dennis. 1994. Rangeland ecology and

management. Westview Press, Boulder. 519 p.

Holechek, Jerry L.; Pieper, Rex D.; Herbel, Carlton H. 1989. Range

management principles and practices, 3rd ed. Regents/Prentice

Hall, Englewood Cliffs, NJ. 501 p.

Hunter, Malcolm L., Jr. 1996. Fundaments of conservation biology.

Blackwell Science, Inc. Cambridge, MA. 482 p.

Klebenow, Donald. A. 1970. Sage grouse versus sagebrush control

in Idaho. Journal of Range Management. 23:396-400.

Milchunas, Daniel G.; Baker, Dan L. 1982. In vitro digestion—

sources of within- and between-trial variability. Journal of Range

Management. 35:199-203.

Patterson, Robert L. 1952. The sage grouse in Wyoming. Sage

Books, Inc. Denver, CO. 455 p.

Pearson, Henry A. 1970. Digestibility trials: in vitro techniques. In:

Paulsen, H. A.; Reid, E. H.; Parker, K. W., eds. Range and wildlife

habitat evaluation—a research symposium. Misc. Publ. 1147.

Washington, DC: U.S. Department of Agriculture, Forest Service. 85-92.

Peterson, Joel. 1970. Gone with the sage. Montana Outdoor Newsletter Number 9 September. 3 p.

Stoddart, Laurence A.; Smith, Arthur D.; Box, Thadis W. 1975.

Range management, 3rd edition. San Francisco: McGraw-Hill

Book Company. 532 p.

Striby, Karl D.; Wambolt, Carl L.; Kelsey, Rick G.; Havstad, Kris M.

1987. Crude terpenoid influence on in vitro digestibility of sagebrush. Journal of Range Management. 40:244-248.

Vallentine, John. F. 1989. Range development and improvements,

3rd edition. San Diego: Academic Press, Inc. 524 p.

Vallentine, John F. 1990. Grazing Management. San Diego: Academic Press, Inc. 531 p.

Welch, Bruce L. 1989. Nutritive value of shrubs. In: McKell, C. M.,

editor. The biology and utilizations of shrubs. San Diego: Academic Press, Inc. 405-424.

Welch, Bruce L. 1995. Beyond 12 percent purity. In: Roundy, Bruce

A.; McArthur, E. Durant; Haley, Jennifer, S.; Mann, David K.,

comps. Proceedings: wildland shrub and arid land restoration

symposium. Gen. Tech. Rep. INT-GTR-315. Ogden, Utah: U.S.

Department of Agriculture, Forest Service, Intermountain Research Station: 126-129.

Welch, Bruce L.; Pederson, Jordan C.; Clary, Warren P. 1983.

Ability of different rumen inoculum to digest range forages.

Journal of Wildlife Management. 47:873-877.

Welch, Bruce L. Nelson, David L. 1995. Black stem rust reduces big

sagebrush seed production. Journal of Range Management. 48:

398-401.
USDA Forest Service Proceedings RMRS-P-11. 1999 175

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Stanley G. Kitchen is Botanist and Gary L. Jorgensen is Range Technician,

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research

Station, Shrub Sciences Laboratory, Provo, UT 84606.

Annualization of Rodent Burrow Clusters

and Winterfat Decline in a Salt-Desert

Community

Stanley G. Kitchen

Gary L. Jorgensen

Abstract—Winterfat (Ceratoides lanata) is dominant or codominant on much of the 16 million ha of salt-desert shrublands of

Western North America. This species is in decline in much of the

Great Basin and has been so for 20+ years at the Desert Experimental Range (DER), Pine Valley, UT. Previously, winterfat

dominanted vegetation on rodent burrow clusters (RBCs), landscape features commonly associated with calcareous alluvial soils.

Presently Eurasian annuals dominate most RBCs. In this study,

mean winterfat density was 3.60 plants/m2 on RBC interspaces

and 4.78 plants/m2 on intact RBCs compared to 0.73 plants/m2 on

annualized RBCs. Winterfat seed production (viable seeds/m2) on

intact RBCs was six-fold that of annualized RBCs and three-fold

that of interspaces. To the extent that winterfat stand renewal is

seed limited, RBC annualization appears to contribute disproportionately to population decline.

Salt-desert shrublands comprise an area of approximately 16 million ha in the Western United States, the

majority of which are concentrated in the valleys of the

Great Basin (Blaisdell and Holmgren 1984). These rangelands provide valuable winter forage for livestock and are

critical habitat for numerous wildlife species. Although at

least 28 community types may be described for salt-desert

shrublands, shrubby members of the Chenopodiaceae are

the principal vegetative component of these ecosystems

(Blaisdell and Holmgren 1984). Low shrubs such as

shadscale (Atriplex confertifolia), Gardner saltbush (A.

gardneri), winterfat (Ceratoides lanata), and gray molly

(Kochia americana) and medium-statured shrubs such as

four-wing saltbush (A. canescens), black greasewood (Sarcobatus vermiculatus), and spiny hopsage (Grayia spinosa)

are particularly well adapted to the stressful growing

conditions associated with the combined impacts of high

soil salt content, low effective precipitation, and winter cold

(Comstock and Ehleringer 1992).

Winterfat

Winterfat (also known as whitesage) communities are

second only to shadscale communities in dominance of

salt-desert shrublands (Blaisdell and Holmgren 1984). It

occurs in mixed communities and in nearly pure stands on

deep alluvial soils. This long-lived species (>50 years)

(Chambers and Norton 1993) is highly drought tolerant due

in part to an extensive fibrous root system and taproot

capable of reaching 7 to 8 m in depth (Stevens and others

1977). Fruit structure is composed of two cottony thinwalled bracts enclosing a single seed (Stevens and others

1977). The terms ‘fruit’ and ‘seed’ are commonly used

interchangeably even though significant quantities of immature and/or empty fruits are generally present in most

seed crops. For simplicity’s sake, we use the term ‘seed’

throughout this work. Winterfat seed production is less

consistent than that of most saltbushes (Atriplex spp.)

(Blaisdell and Holmgren 1984), and seeds lack dormancy

mechanisms necessary to preserve a seed bank (Stevens

and others 1977). Seeds are primarily wind dispersed.

When describing successional dynamics of arid and semiarid ecosystems, the ‘Clementsian’ or climax model has

generally been replaced by models incorporating multiple

stable states, successional pathways, and interstate thresholds (Friedel 1991; Laycock 1991). As a principal component of multiple stable states, winterfat is appropriately

described as late seral. Plant longevity, inconsistent seed

production, and a lack of soil seed reserve are winterfat

traits characteristic of late seral strategies (Comstock and

Ehleringer 1992; Tilman 1988). Late seral species are

commonly sensitive to disturbance, and population regeneration is often seed limited (Grime 1977).

Rodent Burrow Clusters

With minimal soil disturbance, desert soils originating

from calcareous parent materials develop a subsurface

calcic horizon. This more or less cemented layer acts as a

barrier to root development and moisture penetration. It

also inhibits animals from constructing deep burrows.

Calcic horizons are common in the Aridisols of the Great

Basin.

A variety of animal inhabitants of salt-desert shrublands

require burrows for nesting, hunting, predator avoidance,

and thermoregulation. Burrowing in soils with shallow

calcic horizons is generally concentrated on landscape

patches or ‘islands’ where burrowing activities preclude

soil horizon development and thus ensure the permanency

of burrow sites. We believe that Great Basin burrow islands

may predate the Pleistocene/Holocene transition (14,000-

10,000 years B.P.). We have observed that burrow sites are

slightly elevated and, on uniform alluvium, somewhat

evenly spaced, 3-15 m in diameter, and comprise approximately 10-15 percent of the total area.
176 USDA Forest Service Proceedings RMRS-P-11. 1999

The Pocket gopher (Thomomys bottae), kangaroo rat

(Dipodomys spp.), and deer mouse (Peromyscus maniculatus) are among the more common rodents to occupy

these salt-desert burrow sites (Blaisdell and Holmgren

1984). Although, for solitary species such as pocket gopher

and kangaroo rat, a burrow site may be occupied by a single

adult at any one time; representatives of different species

generally coexist. For these reasons, and for lack of a more

universally accepted designation, we will refer to these

sites as rodent burrow clusters using the acronym RBC.

Nonrodent species such as badger (Taxidea tabus), kit fox

(Vulpes macrotis), burrowing owl (Speotyto cunicularia),

and a host of reptile and arthropod species also occupy

RBCs, and some of these are also important contributors to

soil disturbance.

Not surprisingly, plant species composition on RBCs is

commonly quite different from that of surrounding

interspaces. In fact, RBCs are usually easily identified,

even from considerable distances (clearly visible in 1:30,000

black and white aerial photographs) because of the contrast

in vegetative composition between RBC and surrounding

landscape. As recently as the middle of this century, RBC

vegetation was dominated by winterfat. The name “silver

dollar” was used by early researchers, an indication of the

contrast in color between the nearly pure stands of bluegray winterfat and surrounding vegetation. Winterfatdominated RBCs can still be found; however, most RBCs in

salt-desert shrublands are dominated by three invasive

annuals from Eurasia: cheatgrass (Bromus tectorum), halogeton (Halogeton glomeratus), and Russian thistle (Salsola

spp.). The mechanisms by which winterfat dominated RBC

vegetation in the past and by which RBCs are converted to

annuals have not received adequate attention.

Desert Experimental Range

The Desert Experimental Range (DER), located in Pine

Valley, Millard County, UT, was set aside to become an

“agricultural range experiment station” by President

Herbert Hoover in 1933 (Clary and Holmgren 1982). The

22,500 ha (87 sections) were subsequently fenced to provide

pasture units for grazing studies and ungrazed exclosures

as reference areas. Most protected areas have not experienced livestock grazing for 64 years.

Approximately 75 percent of the DER is composed of

coalescing alluvial fans, or bajadas, and valley bottom,

including a barren playa, while the remainder is steeper

uplands. Vegetation on alluvial fans is salt-desert shrubland with shadscale, winterfat, low rabbitbrush (Chrysothamnus greenei), bud sagebrush (Artemisia spinescens),

Nevada ephedra (Ephedra nevadensis), and various perennial grasses dominating. Soils are mostly gravelly loams,

sandy loams, and gravelly sandy loams (Aridisols and

Entisols) (Tew and others 1997). Most soil series found on

alluvial fans above ancient shore lines are deep to very deep

and predictably have moderate- to well-developed calcic

horizons starting at depths of 30 to 40 cm (as shallow as 15

cm) and extending to 50 to 65 cm (as deep as 90 cm) (Tew

and others 1997). RBCs are found throughout these alluvial

soils.

Precipitation at the DER is highly variable between and

within years. Mean annual precipitation at the headquarters complex for the period from 1934-1981 was 157 mm,

with approximately half occurring during the months of

October through April, mostly as snow (Clary and Holmgren

1982). Annual precipitation during a recent wet period

(1975-1994) averaged near 200 mm (Alzerreca-Angelo and

others 1998).

Winterfat is found in near solid stands on valley bottom

soils near the playa (below ancient shore lines) and is

subdominant to codominant on soils with calcic horizons.

Most RBCs (both grazed pastures and exclosures) and

much of the once solid stands are now dominated by cheatgrass, halogeton, and/or Russian thistle.

Winterfat Decline

Winterfat is declining over much of the Great Basin, a

phenomenon well documented at the DER. Long-term vegetation studies have been conducted in 16 100-130-ha

winter- and spring-grazed sheep pastures. Each pasture

has two 0.4 ha exclosures. Vegetation on paired, grazed

and ungrazed, permanent plots has been periodically

mapped (1935 to 1994) for various grazing treatments.

Although winterfat plant densities decreased steadily over

time (1935-1977), total cover increased, apparently due to

an increase in mean canopy size for maturing cohorts

(Chambers and Norton 1993). A sudden decrease in density, which occurred between the 1975 and 1989 mappings,

has been linked to a doubling of mortality rates (percent

mortality/year) for the period 1968-1989 compared to those

observed from 1935-1968 (Harper and others 1990). Mortality rate was not found to be correlated with grazing

treatment (including no grazing) or precipitation. Total

winterfat cover for all grazing treatments and ungrazed

exclosures has also decreased sharply since 1975 (AlzerrecaAngelo and others 1998). Low winterfat natality or recruitment rates (Harper and others 1990; Chambers and Norton

1993) in combination with stand aging, negative consequences of above average precipitation, and/or increased

competition from herbaceous species may explain this decrease. Recent evidence (Harper and others 1996) suggests

that winterfat seedling survival is decreased by the presence of invasive annuals, particularly halogeton, by altering soil microbiota. Finally, hand-drawn maps of vegetation mosaics in exclosures and paired grazed areas (Shrub

Sciences Laboratory, unpublished data) reveal that, although winterfat still dominated RBCs in 1967, Russian

thistle and halogeton enjoyed a noticeable presence. Today,

these RBCs are, for the most part, annuals-dominated.

Winterfat decline in the near solid stands of DER valley

bottom soils is presently under investigation, and these

results will be presented elsewhere. Our objective here is to

examine the effect of RBC annualization on the mean

density and reproductive output of winterfat in mixeddesert shrubland communities. To accomplish this, RBCs

were mapped on study sites at the DER. We then sampled

winterfat densities on intact and annualized RBCs and

RBC interspaces. Mean viable seed production estimates

were determined and used to calculate the relative contribution of RBCs to total seed rain across the landscape. The
USDA Forest Service Proceedings RMRS-P-11. 1999 177

impact of RBC annualization on winterfat renewal is then

inferred based on the arguable assumption that recruitment is seed limited.

Methods _______________________

Site Selection and Mapping

In September 1997, we selected three 1.6-ha study sites

for this investigation. Two sites are located approximately

1 km apart within the DER, Research Natural Area (Sites

1 and 2), on Dera gravelly sandy loam with a calcic horizon

at a depth of 33 to 55 cm (Tew and others 1997). A third site

(Site 3) is located on a similar soil in an exclosure approximately 11 km south of the southeast corner of the DER and

13 to 14 km southeast of the other two sites. Shrubby

vegetation for all three sites is dominated by winterfat,

with lesser amounts of shadscale, budsage, and low rabbitbrush. Indian ricegrass (Oryzopsis hymenoides), galleta or

curly grass (Hilaria jamesii), and purple three-awn (Aristida purpurea) are also common. Cheatgrass, halogeton,

and Russian thistle are abundant on disturbances (annualized RBCs). All three sites have been protected from livestock grazing since the 1930’s. Precipitation from October 1,

1996, to September 30, 1997, at the DER headquarters (1-2

km from sites 1 and 2) was 230 mm, with 113 mm occurring

during the months of August and September, resulting in an

above average winterfat seed crop in Pine Valley.

Rodent burrow clusters at Sites 1 and 2 were hand drawn

to scale on site maps (100 x 160 grid; 1:400 scale). Grids

were analyzed to obtain an estimate of relative RBC coverage. The degree of annual dominance was also estimated for

each RBC and recorded as percent annualization. From

these we selected study RBCs corresponding to three arbitrary classes: perennial, transitional, and annualized (<10,

40-60, and >90 percent annualization).

Winterfat Density

Estimates of winterfat density were determined by counting all individuals within 16 16-m2

 circular plots (radius =

2.26 m) at each site. Four plots (replications) were located

within representatives of each RBC class and at random on

RBC interspaces. Living winterfat plants were scored as

immature (seedlings and juveniles) and as mature. Mature

plants were also classified by seed (fruit) production classes

as: mature-0 (no seeds), mature-1 (few stems with seeds

and few seeds per stem), mature-2 (intermediate number of

stems with seeds and/or seeds per stem), and mature-3

(many stems with seeds and many seeds per stem). Attached winterfat skeletons were scored as dead. Total dead

values were viewed as crude indices of mortality rate.

Seed Production and Viability Testing

In October 1997, seeds were hand-stripped from 20+ plants

(replications) of each seed production class (mature-1-3) at

Site 1. We selected this site because it had the best

representation of plants from all seed production classes.

Seeds appeared to be fully ripened, and natural dispersal

was minimal before this time. Half of the plants for each

seed production class were from RBCs and half from RBC

interspaces. Seeds from each plant were carefully collected

and placed in labeled paper sacks.

Each collection was hand cleaned (purity > 95 percent)

and weighed after 5 months storage at room temperature

(20° C). Subsets of 200 seeds (fruits) of each collection (or all

seeds from plants when harvest was less than 200) were

weighed to determine mean seed weight. Seed viability was

estimated using 25 seeds from each collection (plant). Seeds

were placed in plastic petri dishes (100 x 15 mm) on blue

germination blotters moistened with tap water. Petri dishes

were arranged randomly in stacks of 10 and enclosed in

plastic bags to retain moisture and facilitate handling.

Seeds were prechilled for 14 days at 2° C before incubation

for 14 days at 15° C (AOSA 1998). Normal seedlings were

counted on days 7 and 14, and viability of ungerminated

seeds was determined by embryo examination.

Results were statistically analyzed using the GLM procedure (SAS 1998). Significant differences among plant density (all classes), productivity (percent of total live plants

with seed), seed weight, and seed viability means were

determined using the Student-Neuman-Keul (SNK) method

(p < 0.05). Estimates of viable seed production (seeds/m2

) by

plot location were calculated for all three sites by summing

the products of mean density (d) and estimate for number

of viable seeds (s) for each seed production class (mature-1,-

2,-3). For example, to determine viable winterfat seed

production for interspace plots we use:

Viable seeds/m2

int = (dint x sint)mature-1 + (dint x sint)mature-2 +

(dint x sint)mature-3

Mean contribution (m2 basis) to total seed rain by RBC

interspace and by each RBC class was calculated as the

product of the estimates of viable seed production (threesite means) and percent of total area represented by either

interspaces or by RBCs (averaged over Sites 1 and 2). For

example, to determine seed rain contribution for RBCs

(assuming all RBCs are of the perennial class) we used:

Seed rain contributionper = seeds/m2

per (3-site mean) x

(estimated percent cover for all RBCs)

Results ________________________

We mapped 26 RBCs occupying 14.8 percent of the area

at Site 1 and 20 RBCs occupying 10.8 percent of the area at

Site 2. Twenty-four RBCs (both sites combined) were classified as perennial (<10 percent annualized) and nine were

classified as annualized (>90 percent). Transitional RBCs

(40-60 percent annualized) were selected from the remaining 13 RBCs. Although Site 3 was not mapped, total area

occupied by RBCs appeared to be similar to that mapped for

Sites 1 and 2. However, annualization of RBCs was more

advanced at Site 3 than at Sites 1 and 2, with fewer

perennial RBCs available for study. For our calculations of

mean contribution to total seed rain, we assumed 87 percent of all areas was occupied by interspaces and 13 percent

by RBCs.
178 USDA Forest Service Proceedings RMRS-P-11. 1999

Winterfat Stand Density

Winterfat live and dead plant densities by site and plot

location are summarized in table 1. Live plant densities

were highest on perennial RBCs for Sites 1 and 2. Live plant

densities for interspaces, and perennial and transitional

RBCs were not significantly different at Site 3. Significant

and rather steep declines in live winterfat density were

observed in relation to increased annualization on all three

sites. Dead plant densities were lowest for interspaces

across all sites and highest for transitional RBCs on Sites

1 and 2 and annualized RBCs for Site 3. When the results

of all three sites are pooled (table 2), total live plant density

is highest for perennial RBCs followed by interspaces,

transitional RBCs, and annualized RBCs. Although rather

low overall, immature densities are highest for perennial

RBCs and interspaces and lowest for annualized RBCs.

Dead plant densities are highest for transitional RBCs and

lowest for interspaces.

Stand reproductive output, expressed as percent of total

live plants with seeds, was 78 percent at Site 1, 68 percent

at Site 2, and 19 percent at Site 3. Across all sites, the

percent of plants with seeds was significantly higher for all

three classes of RBCs than for interspaces (table 2), and 55

percent of all live plants produced some seeds. Overall,

winterfat density for mature-1 and mature-2 plants was

highest for perennial RBCs followed in order by transitional RBCs, interspaces, and annualized RBCs (table 2).

Mature-3 densities were low for all plot locations.

In summary, total immature, live, and seed-bearing

(mature-1, -2, and -3 combined) plant densities were highest for perennial RBCs (table 2). Interspaces had relatively

high immature and total live plant densities but with fewer

plants bearing seeds (higher percentage of live plants that

were classified as mature-0) and fewer seeds per plant

(lower percentage of seed-bearing plants classified as mature-2 and -3) than did RBC plots. Annualized RBCs had

low immature and total live plant densities, while transitional RBCs were intermediate to perennial and annualized RBCs in these categories. Interspace dead plant densities were significantly lower than RBC dead plant densities

(all classes). Dead plant densities for transitional RBCs

were significantly higher than for perennial or annualized

RBCs.

We calculated an estimate of live winterfat stand density

(averaged across the landscape) using only interspace and

perennial RBC data as 3.75 plants/m2

. Stand density

dropped to 3.47 and 3.22 plants/m2

 when transitional and

annualized RBC data were used. This represents a potential 14 percent loss in winterfat stand density due to RBC

annualization.

Seed Production

Within seed production classes, total seed weight, total

seeds/plant, and total viable seeds/plant did not vary significantly with plot location (table 3). Reproductive output

for mature plants was approximately 10-fold that of mature-1 plants and 2.5 times that of mature-2 plants. Mean

seed weight (223 seed/g) and mean seed viability (50 percent) were not significantly affected by plot location or seed

production class in this study.

Calculated mean viable seed production values (seeds/

m2

) were highest for Site 1 (table 4.) Within sites, seed

production was greatest for perennial RBCs in Sites 1 and

2 and for annualized RBCs on Site 3. Seed production was

consistently greater for all RBCs than for interspaces.

Estimates for seed rain contribution by plot location are

found in table 5. If we assume all RBCs on a site are of the

same class (degree of annualization), then interspaces

would have contributed approximately double the seed of

perennial RBCs, 3.5 times that of transitional RBCs, and

almost 13 times that of annualized RBCs. If the sum of

Table 1—Winterfat live and dead plant density and percent of live

plants producing seeds by site and plot location within sites,

Desert Experimental Range, Utah, 1997. Rodent burrow

clusters (RBCs) are perennial (Per.), transitional (Trans.),

and annualized (Ann.). Mean separation statistics were

calculated by site. Within columns and sites, means followed

by the same letter are not significantly different at the p < 0.05

level (SNK).

Percent of

Plot Winterfat density live plants

location Total live Total dead with seeds

- - - - plants/m2 - - - - 

Site 1 Interspace 3.88b 0.41b 49c

RBC-Per. 5.77a 1.61ab 77b

RBC-Tran. 2.41b 2.61a 92ab

RBC-Ann. 0.25c 0.97b 100a

Site 2 Interspace 2.89b 0.38b 38b

RBC-Per. 4.75a 1.31ab 79a

RBC-Tran. 2.75b 2.34a 78a

RBC-Ann. 0.53c 1.77ab 83a

Site 3 Interspace 4.03a 0.20b 2b

RBC-Per. 3.83a 0.30b 9b

RBC-Tran. 2.72ab 0.45ab 27ab

RBC-Ann. 1.42b 0.69a 41a

Table 2—Mean densities of immature, mature-0, mature-1, mature-2,

and mature-3, total live, and total dead winterfat plants as

affected by plot location for three Desert Experimental Range,

Utah, sites (1997). Plot locations are three classes of rodent

burrow clusters (RBCs), namely, perennial (Per.), transitional

(Trans.), and annualized (Ann.) and RBC interspaces. Within

rows (plant classifications), means followed by the same

letter are not significantly different at the p < 0.05 level (SNK).

Plant Winterfat density

class Interspace RBC-Per. RBC-Trans. RBC-Ann.

- - - - - - - - - - - - - Plants/m2 - - - - - - - - - - - - - - 

Immature 0.21a 0.25a 0.09ab 0.01b

Mature-0 2.41a 1.73a 0.88b 0.30b

Mature-1 0.87c 2.36a 1.39b 0.36d

Mature-2 0.10c 0.40a 0.23b 0.06d

Mature-3 0.01a 0.04a 0.03a 0.01a

Total Live 3.60b 4.78a 2.63c 0.73d

Total Dead 0.33c 1.07b 1.80a 1.14b

- - - - - - - - - - - - - - Percent - - - - - - - - - - - - - - - 

Live Plants 29c 55b 66ab 71a

with Seeds
USDA Forest Service Proceedings RMRS-P-11. 1999 179

Discussion _____________________

Although cheatgrass and Russian thistle introductions

to North America predate DER establishment by several

decades, no mention is made of these species in early plot

maps (1935-1937) (Harper and others 1996). Both species

were found in 1958 (no mapping occurred during the 1937-

58 interval) but were considered uncommon. Halogeton

was first observed on the DER in 1952 and was considered

widespread by 1958, primarily along roads and similar

sites of disturbance, but was not considered a threat to

healthy shrubland communities (Shrub Sciences Lab, unpublished report). Maps of RBCs made in 1967 show pockets of Russian thistle and halogeton annualization. Subsequent increases of cheatgrass were probably associated

with relatively wet conditions experienced during the last

25 years at the DER (Alzerreca-Angelo and others 1998).

We have observed RBCs at the DER since 1992. Clearly,

most RBCs on the DER were fully annualized before that

year. Subsequently, annualization for many, if not most,

RBCs occurred between 1958 and 1992. The actual time

required for RBC conversion is probably 20 years or less.

This time- frame roughly corresponds to the same period in

which winterfat decline was observed in the DER pastures

(Alzerreca-Angelo and others 1998; Harper and others

1990). This decline has been attributed, at least in part, to

stand aging.

Winterfat population dynamics on RBCs, with and without annuals, are clearly different than on RBC interspaces.

This is particularly clear when we consider differences in

mortality rate. Although dead plant density is, at best, a

crude measure of mortality rate, it should be adequate for

the arguments we make. Dead plant densities for RBCs

might even be viewed as conservative indices of mortality

rate given the likelihood that dead plants are more likely to

become detached on RBCs, due to more intensive burrowing, than on interspaces. Therefore, RBC dead plant densities would tend to underrepresent mortality rate for RBCs

when compared to interspace mortality rates.

That said, mature plant mortality rates were higher for

all classes of RBCs when compared to those observed for

interspaces. Higher RBC mortality is probably associated

with root damage and crown burial caused by rodents and

their predators. Notwithstanding, winterfat is apparently

quite well adapted to this level of disturbance in the absence of aggressive annuals such as those observed in this

study and is better adapted than all other perennial species

present on nearby interspaces. Recruitment levels must

therefore be adequate for perpetual regeneration of the

nearly pure stands of winterfat on perennial-dominated

RBCs.

We also observed that dead plant densities for transitional RBCs were higher than for perennial and annualized

RBCs. This suggests that, once annuals take hold, they may

have a direct effect on the survivability of mature winterfat

plants. We have observed this phenomenon on the valley

bottom soils where winterfat is often found in near pure

stands but where halogeton, and to a lesser extent Russian

thistle, now dominate large areas. On these sites, the

Table 3—Estimated seed production for mature-1, mature-2, and

mature-3 winterfat plants as affected by plot location, Desert

Experimental Range, Utah, 1997. Plot locations are rodent

burrow clusters (RBCs) and RBC interspaces. Within

columns, values followed by the same letter are not

significantly different at the p < 0.05 level (SNK).

Plot Seed prod. Total seeds Total Total viable

location class weight/plot seeds/plant seeds/plant

- - g - -

Interspace Mature-1 1.29c 273c 112c

Mature-2 5.26b 1,069b 567b

Mature-3 11.63a 2,634a 1,449a

RBC Mature-1 1.21c 266c 133c

Mature-2 3.96b 922b 479b

Mature-3 11.40a 2,815a 1,464a

Mean Mature-1 1.26c 270c 122c

Mature-2 4.64b 999b 529b

Mature-3 11.52a 2,724a 1,471a

Table 5—Percent of total area occupied by rodent burrow clusters

(RBCs) and RBC interspaces and predicted seed production

assuming all RBCs are of the same level of annualization.

Mean contribution per m2

 assumes even dispersal of all

seeds across the landscape.

Predicted Live Mean

Percent of Seeds Produced Contribution

Seed Source Total Area per m2 per m2

RBC-interspace 87 173 151

RBC 13

perennial 555 72

transitional 334 43

annualized 90 12

Table 4—Estimated 1997 viable seed production for three Desert

Experimental Range, Utah sites for rodent burrow clusters

(RBC’s) with three levels of annualization and RBC

interspaces.

Sample Vegetation

Site Type Site 1 Site 2 Site 3 Mean

- - - - - - - seeds per m2 - - - - - - - 

Interspace Perennial 383 130 6 173

RBC Perennial 981 627 34 555

RBC Transitional 609 337 81 334

RBC Annualized 93 77 89 90

interspace and perennial RBC seed contribution (223 seeds/

m2

) were viewed as the total potential seed production for

the site, then conversion to transitional (194 seeds/m2

) or

annualized RBCs (163 seeds/m2

) would result in a 13 or 27

percent reduction in seed production across the landscape.
180 USDA Forest Service Proceedings RMRS-P-11. 1999

annuals/winterfat ecotone is apparently unstable, resulting in additional losses by the winterfat community (Shrub

Sciences Laboratory, unpublished data). Lower dead plant

densities on annualized RBCs are probably indicative of

the passage of time since mortality rates peaked, allowing

time for skeletal detachment and removal. We have observed that burrowing activity remains high on annualized

RBCs.

Winterfat recruitment on RBCs, as indicated by the

density of immature plants, was inversely related to the

degree of RBC annualization in spite of greatly reduced

levels of competition from remnant perennials. The impact

to winterfat seedlings caused by annual weed competition

for soil moisture is probably important, especially when

cheatgrass is present. Harper and others (1996) suggested

that annuals alter the soil microbiota, creating conditions

unsuitable for winterfat seedling survival. The fact that

mortality and recruitment rates are inversely related suggest that the rate of annualization accelerates once the

threshold that prevents annual dominance is crossed.

Rodent burrow clusters are more favorable for winterfat

growth than are RBC interspaces, as indicated by much

greater RBC-related seed production. This was the case

even when total live plant density, and therefore the potential for intraspecific competition, was greater on perennial

RBCs (Sites 1 and 2) than on interspaces. Although we

acknowledge that competition from other perennial species

on interspaces must have some role, the contrast in soil

physical properties, particularly the absence of a root restricting calcic horizon on RBCs, may be most responsible

for the difference in RBC favorability. Differences in soil

compaction, nutrient levels, and nutrient distribution may

also be important.

We estimated a potential 14 percent loss in winterfat

stand density and 27 percent loss in seed rain as a consequence of complete annualization of RBCs. To what degree

might this disproportionate loss of propogules be sufficient

to cause a decrease of winterfat density on interspace

communities such as has been observed at the DER since

1970? We have suggested, based on its late seral characteristics, that winterfat recruitment is seed limited. However,

we acknowledge that our understanding of winterfat fecundity and seed fate is inadequate for making a strong case

tying population decline (failure to establish adequate

numbers of replacement individuals) to disproportionate

reductions in seed production (due to RBC annualization).

It is probably safe to state that any seed production losses

associated with livestock mis-management could have a

compounding effect. However, we remind the reader that

this study was conducted on sites protected from livestock

for 60+ years and that annualized RBCs are abundant. At

the same time, we had difficulty finding any perennialdominated RBCs on grazed sites regardless of season or

intensity of use.

Our data support the conclusion that annualized RBCs

are not likely to return to perennial dominance, at least not

winterfat, without considerable management intervention.

Because of the low economic importance associated with

salt-desert shrublands, the risky nature of revegetating

salt-desert sites, and the scattered nature of RBCs, such

intervention would not be practical using existing technology. Efforts to develop techniques and plant materials for

restoration of perennial cover to RBCs should include

consideration of ecotypes and/or species that require no site

preparation, can establish from broadcast seeding, are

adapted to a rodent-related disturbance regime, and compete with aggressive annuals.

The picture we paint here is not encouraging. Winterfat

appears to be yet another casualty resulting from the

introduction and naturalization of aggressive Old World

weeds. As such, this study strengthens the argument that

introduced weeds pose one of the greatest threats to the

stability of North American ecosystems.

References _____________________

Alzerreca-Angelo, H.; Schupp, E. W.; Kitchen, S. G. 1998. Sheep

grazing and plant cover dynamics of a shadscale community. J.

Range Manage. 51: 214-222.

Association of Official Seed Analysts (AOSA). 1998. Rules for

testing seeds. Lincoln, NE: Association of Official Seed Analysts. 123 p.

Blaisdell, J. P.; Holmgren, R. C. 1984. Managing Intermountain

rangelands: salt-desert shrub ranges. Gen. Tech. Rep. INT-163.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station. 52 p.

Chambers, J. C.; Norton, B. E. 1993. Effects of grazing and drought

on population dynamics of salt desert shrub species on the

Desert Experimental Range, Utah. J. Arid Environ. 24: 261-275.

Clary, W. P.; Holmgren, R. C.; 1982. Desert Experimental Range:

establishment and research contribution. Rangelands. 4: 261-264.

Comstock, J. P.; Ehleringer, J. R. 1992. Plant adaption in the

Great Basin and Colorado Plateau. Great Basin Naturalist. 52:

195-215.

Friedel, M. H. 1991. Range condition assessment and the concept

of thresholds: a viewpoint. J. Range Manage. 44: 422-426.

Grime, J. P. 1977. Evidence for the existence of three primary

strategies in plants and its relevance to ecological and evolutionary theory. The American Naturalist. 111: 1169-1194.

Harper, K. T.; Van Buren, R.; Kitchen, S. G. 1996. Invasion of alien

annuals and ecological consequences in salt desert shrublands

of western Utah. In: Barrow, J. R.; McArthur, E. D.; Sosebee, R.

E.; Tausch, J. R., comps. Proceedings—symposium on shrubland ecosystem dynamics in a changing environment; 1995 May

23-25; Las Cruces, NM. Gen. Tech. Rep. INT-GTR-338. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 58-65.

Harper, K. T.; Wagstaff, F. J.; Clary, W. P. 1990. Shrub mortality

over a 54-year period in shadscale desert, west-central Utah. In:

McArthur, E. D.; Romney, E. M.; Smith, S. D.; Tueller, P. T.,

comps. 1990. Proceedings, symposium on cheatgrass invasion,

shrub die-off, and other aspects of shrub biology and management; 1989 April 5-7; Las Vegas, NV. Gen Tech. Rep. INT-276.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station. 119-126.

Laycock, W. A. 1991. Stable states and thresholds of range condition on North American rangelands: a viewpoint. J. Range

Manage. 44: 427-433.

SAS. 1998. SAS user’s guide. SAS Institute, Cary, NC.

Shrub Sciences Laboratory. Unpublished data and report on file

at: U.S. Department of Agriculture, Forest Service, Rocky

Mountain Research Station, Shrub Sciences Laboratory,

Provo, UT.

Stevens, R.; Giunta, B. C.; Jorgensen, K. R.; Plummer, A. P. 1977.

Winterfat (Ceratoides lanata). Utah State Div. Wildl. Res. Publ.

No. 77-2. 41 p.

Tilman, D. 1988. Plant strategies and the dynamics and structure

of plant communities. Princeton, NJ: Princeton University Press.

360 p.

Tew, R. K.; Kitchen, S. G.; Holmgren, R. C. 1997. Soil surveyDesert Experimental Range, Utah. Gen. Tech. Rep. INT-GTR347. Ogden, UT: U. S. Department of Agriculture, Forest Service, Intermountain Research Station. 22 p.
USDA Forest Service Proceedings RMRS-P-11. 1999 181

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Allen Huber is Rangeland Manager, Duchesne District, Ashley National

Forest, U.S. Department of Agriculture, Duchesne, UT 84021. Sherel

Goodrich is Forest Ecologist, Ashley National Forest, U.S. Department of

Agriculture, Vernal, UT 84078.

Big Sagebrush, Crested Wheatgrass, and

Grazing on Gravel-Cobble Pediments of the

Duchesne River Formation and Quaternary

Deposits in Uintah County, Utah

Allen Huber

Sherel Goodrich

Abstract—Pediment surfaces of the Duchesne River Formation

near Lapoint and Quaternary deposits at Grouse Creek, Uintah

County, Utah, provide rather uniform habitat conditions on which

to contrast the abundance of crested wheatgrass (Agropyron

cristatum) on seeded areas and adjacent unseeded areas. Although

crested wheatgrass has persisted as a dominant for over 40 years

where it was seeded at one study site, it has spread less than

0.32 km (0.2 mile) into native plant communities from seeded areas

of this study. At 15.25 meters (50 feet) from the plow line, crested

wheatgrass showed over a six-fold decrease in abundance. Where

cattle (Bos taurus) have grazed in winter only, crested wheatgrass

stands have persisted for 33 years with very little Wyoming big

sagebrush recruitment into the seeded area. In nearby crested

wheatgrass seedings, Wyoming big sagebrush has returned to

persistent wheatgrass stands after spring and early summer grazing was initiated. Crested wheatgrass has also demonstrated the

capability to successfully suppress cheatgrass in Wyoming and

mountain big sagebrush communities. Spring and early summer

grazing by cattle is indicate as a tool to achieve sagebrush cover

where it is desired in crested wheatgrass stands.

Over the past several decades, land managers and private

land owners have turned over vast acres of native vegetation

in the Intermountain region and seeded these areas into

crested wheatgrass (Agropyron cristatum). Crested wheatgrass was selected to improve early season forage production

for livestock, for its ease in establishment, tolerance to

drought, and for its ability to adapt to various habitats and

precipitation zones. After seeding, crested wheatgrass has

demonstrated the ability to establish monocultures in sagebrush communities with annual precipitation less than

30.5 cm (12 inches). Land managers have found that sagebrush recruitment in crested wheatgrass seedings is possible when influenced by various grazing techniques (Laycock

and Conrad 1981; Evans and others 1986; Angell 1998).

Time of recovery for sagebrush following treatment and

seeding of crested wheatgrass is apparently variable, but

Winward (1991) found that recovery of sagebrush following

burn treatments vary from 12 years in the mountain big

sagebrush (Artemisia tridentata ssp. vaseyana var.

pauciflora) type to over 40 years in the drier Wyoming big

sagebrush (Artemisia tridentata ssp. wyomingensis) type.

Whisenant (1990) indicated a fire interval of 60 to 110 years

for presettlement Wyoming big sagebrush. Hull and Klomp

(1966) studied the invasive nature of crested wheatgrass

from original seedings into adjacent native sagebrush communities in Idaho. They observed crested wheatgrass plants

growing in the native community as far as 122 m from the

plow line 30 years after mechanical treatment and seeding.

Monsen (1994) found the fire resistant capabilities of crested

wheatgrass could be used to alter fire intervals in cheatgrass

systems.

In Uinta Basin, Utah, numerous communities of Wyoming

and mountain big sagebrush have been mechanically treated

and seeded with crested wheatgrass. Four sagebrush sites

with sharp boundaries between treated and untreated areas

were selected for this study. Objectives of this research were

to determine the invasive nature of crested wheatgrass from

treatment areas into native plant communities, its ability to

suppress cheatgrass (Bromus tectorum) at a common site,

shrub recruitment into seeded areas following treatment, and

the timely use of grazing to influence sagebrush recovery.

Study Sites_____________________

Four sites were included in this study. These sites are

located at Lapoint Bench, Flat Iron Bench, and near Grouse

Creek in Uintah County, Utah. The study sites at Lapoint

Bench (two sites) and Flat Iron Bench (one site) are about

2.4 km east-northeast of Lapoint and 16 km west of Vernal.

The sites are located on relatively flat, uniform stream

pediment surfaces of the Duchesne River Formation. These

pediment surfaces consist of a gravel-cobble layer that

protects these sites from the erosive action that carved

relatively shallow, highly dissected canyons adjacent to the

pediment surfaces. The elevations at these three sites are

approximately 1,760 meters (5,770 ft). Lapoint and Flat Iron

Benches are located between the Lapoint Climate Station

and the Vernal Climate Station. The elevation, latitude, and

vegetation of the study sites and climate stations are similar. Mean annual precipitation at the Lapoint Climate

Station (1948-1961) of 17.7 cm (8.25 inches) and the Vernal

Climate Station (1928-1992) of 17.5 cm (8.16 inches) indicate mean annual precipitation at the study sites are between 17-19 cm (8-9 inches) (Ashcroft and others 1992).
182 USDA Forest Service Proceedings RMRS-P-11. 1999

Sagebrush from these pediments have been identified

with an ultraviolet light test as Wyoming big sagebrush

(Goodrich and others, these proceedings). Wyoming big

sagebrush-grass communities dominate the landscape below the pinyon-juniper belt where these pediment surfaces

occur. Soils of the Aridisol order are typical for these areas.

Soils with a higher content of sand and/or gravel typically

support a understory dominated by needle-and-thread grass

(Stipa comata var. comata). Soils with less sand and/or

gravel typically support more bottlebrush squirreltail (Elymus elymoides). Sites that support needle-and-thread grass

appear to be more resistant to cheatgrass invasion than sites

that support mostly bottlebrush squirreltail.

On Lapoint Bench, the Eakins site was plowed and seeded

with crested wheatgrass in ca. 1970. Wyoming big sagebrush kill due to treatment was nearly 100 percent. Sheep

grazed the Eakins site late winter to early summer from

1970 to ca. 1980. Since 1980, the site has been grazed

annually by cattle during the late spring and early summer

months. Grazing pressure by cattle is generally moderate

(40 to 50% use by weight). The Huber site was plowed and

aerially seeded with crested wheatgrass in fall 1985. The kill

of Wyoming big sagebrush following the plow treatment was

only about 70%. Due to the abundance of cheatgrass, the site

was burned with prescribed fire the following year. After

fire, about 90 percent of Wyoming big sagebrush originally

at the area prior to both treatments was killed. Crested

wheatgrass was reseeded with a drill following the burn and

it replaced cheatgrass as the dominate at the site. Spring

and early summer (May and June) cattle grazing was initiated 3 years following the burn treatment and has been

employed annually for the past 9 years. Forage utilization by

cattle at the Huber site is generally over 60 percent (Huber

1998, personal communication). The site at Flat Iron Bench

was plowed and seeded with crested wheatgrass in 1965 by

the Bureau of Land Management. Wyoming big sagebrush

kill was essentially 100 percent. Approximately 2,400 head

of sheep were permitted to graze the site early spring and

late fall from time of treatment to 1975. The allotment was

converted to cattle in 1975 but was not grazed until 1982.

Since this time, cattle have grazed the area from midNovember to the end of January (Nelson 1998, personal

communication). Antelope and sage grouse utilize these

wyoming big sagebrush sites year round. These areas are

also considered important winter range for deer and elk. At

all three sites, a sharp boundary between treated and

untreated areas in similar habitat exists. These circumstances provided an opportunity to sample the advancement

of crested wheatgrass from treated areas into untreated

areas. Also, the reestablishment of Wyoming big sagebrush

in treated areas under different grazing schemes were

sampled.

The study site at Grouse Creek is approximately 8.8 km

east of Elk Horn Guard Station and 10.1 km north of Tridell.

The site is located on Quaternary stream pediments. Elevation at the Grouse Creek site is 2,164 meters (7,100 ft). The

site is located between the Elk Horn Climate Station and

Maeser 9 NW Climate Station (15 km west). They are about

equal in latitude and position at the base of the Uinta

Mountains to each other and to the study site. Mean annual

precipitation at Elk Horn (1910-1930) of 34.1 cm (13.41

inches) (Martin and Corbin 1930) and Maeser 9 NW of 34.4 cm

(13.55 inches) (Ashcroft and others 1992) indicates mean

annual precipitation at the site is between 34.3 and 35.6 cm

(13.5 and 14.0 inches).

The Grouse Creek site is located above the pinyon-juniper

belt. Sagebrush samples from the area applied to the ultraviolet light test were identified as mountain big sagebrush

(Goodrich and others, these proceedings). Associated plants

at the site include serviceberry (Amelanchier alnifolia),

bitterbrush (Purshia tridentata), yellowbrush (Chrysothamnus viscidiflorus var. lanceolatus), and thickspike wheatgrass (Elymus lanceolatus).

In 1956, the area north of the National Forest boundary

fence, which is administered by the Ashley National Forest,

was mechanically treated to reduce sagebrush and seeded

with a seed mix that included crested wheatgrass and

smooth brome (Bromus inermis). Crested wheatgrass established and persisted as a dominate plant in the seeding.

Forest data indicate that smooth brome was as a minor

component in the community during the 1980’s and 1990’s

(Ashley National Forest, unpublished data). The area south

of the fence, owned by the Ute Indian Tribe, was not treated

and remained in native vegetation. In 1988, both sides of the

fence were burned during the Whiterocks wildfire, which

burned approximately 16,000 acres. The Grouse Creek site

is included in the Mosby Mountain summer cattle allotment.

The grazing season ranges from mid-June to mid-September

under a rest rotation system. Grazing intensity is generally

moderate (40 to 50% utilization). Adjacent Ute Tribal land

receives light grazing intensity (under 40% utilization) from

cattle during most seasons of the year. The Grouse Creek

area is also considered critical late winter and early spring

habitat for elk and deer. The contrast of seeded and nonseeded

range on opposite sides of the fence provided an opportunity

to evaluate the advancement of crested wheatgrass into the

nonseeded area after 42 years following treatment.

Methods & Results ______________

A total of five belt-plots of 0.9 m (3 ft) wide were established parallel to the plow line at each of the four study sites.

Their lengths varied due to topographical limitations. The

length of transects were 137.0 m (450 ft) at the Eakins and

Huber sites, 152.5 m (500 ft) at the Grouse Creek site, and

61.0 m (200 ft) at the Flat Iron site. Of the five transects, four

were established 15.25 m (50 ft), 30.5 m (100 ft), 61.0 m

(200 ft), and 122.0 m (400 ft) from the plow line into the

untreated area, and one transect was established 15.25 m

(50 ft) from the plow line into the area plowed and seeded

with crested wheatgrass. Crested wheatgrass plants were

counted in each belt-plot and standardized to determine

density of crested wheatgrass plants inside treated areas

and outside treated areas of native vegetation at standard

distances from the plow line (table 1). Crown cover for

Wyoming big sagebrush was measured by line intercept

along transect beltlines at the Flat Iron, Eakins, and Huber

study sites. Crown cover for mountain big sagebrush and

other woody plants at Grouse Creek was measured by line

intercept along five 30.5 m (100 ft) beltlines at study 43-16,

which is located ca. 91.5 m (300 ft) north of study site (Ashley

National Forest, unpublished data). A total of one-hundred

50 cm2

 (19.69 inches2) sample plots were established along
USDA Forest Service Proceedings RMRS-P-11. 1999 183

the 15.25 m (50 ft) transects inside and outside of treatment

at the Huber study site. Summed nested frequency was

determined for all grass species as outlined by the U.S.

Department of Agriculture, Forest Service (1993).

The number of crested wheatgrass plants per 1⁄10 hectare

was 6.1 (Grouse Creek), 4.4 (Flat Iron), 4.3 (Eakins), and

54.4 (Huber) times fewer at 15.25 m outside the treatment

than at 15.25 m inside the treatment. The number of plants

per 1⁄10 hectare outside the treatment decreased substantially at further distances from the plow line as indicated in

table 1. No crested wheatgrass plants were observed outside

the treatment 129.5 m (425 ft) from the plow line at the

Eakins and Huber sites, 183.0 m (600 ft) from plow line at

Flat Iron, and 322.0 m (1,056 ft) from plow line at Grouse

Creek. Density of crested wheatgrass plants were greater in

the younger treatment areas and fewer in the older treatment areas. At the Grouse Creek and Huber sites, the

majority of crested wheatgrass plants established outside

the treatment area were found along shallow drainages that

run perpendicular to the transects and plow line. Seed

distribution of crested wheatgrass from the treatment into

the adjacent native community appeared to be primarily a

result of surface water flow. At the Flat Iron and Eakins

sites, seed distribution appears to be more of a function of

wind, especially at the Eakins site where the plow line runs

perpendicular to normal wind patterns and the untreated

area is downwind from the treatment area. Crested wheatgrass plants found in the unseeded areas of the four study

sites did not display highly invasive or otherwise weedy

features, but appeared for the most part as scattered plants

among natives with little indication of initiating a major

shift in plant community function. Cheatgrass, however,

was observed in abundance in the native communities at all

four study sites. At the Huber site, frequency of cheatgrass

was significantly higher (nearly 10 times greater) 15.25 m

outside the treatment than 15.25 m inside the treatment

(table 2).

Outside the treatment area, presence of cheatgrass was

higher on alluvial surfaces where bottlebrush squirreltail is

the most common native grass. On gravel pediment surfaces, where needle-and-thread grass is more abundant,

presence of cheatgrass was much lower. Information from

this study indicates that needle-and-thread grass sites are

less susceptible to cheatgrass than bottlebrush squirreltail

sites in Wyoming big sagebrush communities. In the treatment area at the Huber site, the ability of crested wheatgrass to suppress cheatgrass was much greater than that of

native species. A dense stand of cheatgrass formed at the

Huber site when crested wheatgrass failed to germinate

following the initial plow and seeding. Following the second

treatment, crested wheatgrass at the site germinated and

has been successful in suppressing cheatgrass as indicated

by the frequency data in table 2 above.

At Grouse Creek, cheatgrass was observed in abundance

in the native plant community. Outside the treatment,

cheatgrass formed a nearly continuous, fine, highly flammable fuel within the thickspike wheatgrass-mountain big

sagebrush community. Similar to the Huber site, crested

wheatgrass successfully suppressed cheatgrass in the treatment area. With the potential to increase fire frequency,

cheatgrass presents a major risk to ecological function of the

native plant community. The risk of crested wheatgrass to

ecological function of the native plant community appears to

be low after 42 years. Trend of native shrubs (table 3)

following the 1988 Whiterocks fire demonstrates compatibility of crested wheatgrass with function of native plants at

this site.

Although crested wheatgrass remains the dominant herbaceous species in the treatment area, native shrubs in the

treatment appear to be functioning similar to those outside

Table 1—Number of crested wheatgrass plants per 1⁄10 hectare (10 m2) 15.25 meters inside treatment

areas seeded with crested wheatgrass and 15.25, 30.5, 61.0, and 122.0 meters outside

treatment areas in native vegetation.

Year of 15.25 m 15.25 m 30.5 m 61.0 m 122.0 m

Study site treatment inside outside outside outside outside

Grouse Creek 1956 594 97 77 39 23

Flat Iron 1966 701 160 93 37 3

Eakins 1970 935 216 65 12 1

Huber 1985 1088 20 11 6 0

Table 2—Summed nested frequencya for six grassesb at 15.25 meters inside treatment

area and 15.25 meters outside treatment area at the Huber study site.

Transect AGCR STCO ELEL STHY BRTE HIJA

Inside treatment 303 17 2 7 24 27

Outside treatment 12 94 68 3 236 0

a

Nested frequency scores were derived from 100 nested plots of 5 X 5 cm, 25 X 25 cm, 25 X 50 cm,

and 50 X 50 cm along each 137.0 m transect. Maximum score possible is 400. The treatment area was

plowed and seeded with crested wheatgrass in 1985. b

Agropyron cristatum (AGCR), Stipa comata (STCO), Elymus elymoides (ELEL), Stipa hymenoides

(STHY), Bromus tectorum (BRTE), and Hilaria jamesii (HIJA).
184 USDA Forest Service Proceedings RMRS-P-11. 1999

the treatment (i.e., percent canopy cover and density). Ten

years after fire, bitterbrush, serviceberry, and yellowbrush

are nearly equal to or exceed preburn crown cover percentages. Although slower to return than sprouting shrubs,

mountain big sagebrush appears to be returning at expected

rates following fire. Species richness data indicates that the

total number of species in the treatment area is relatively

high (30 taxa). This value is consistent with Tart (1996). He

found that the number of plant taxa per 375 m2 plot in

mountain big sagebrush communities in central Wyoming

ranged from 11 to 39 taxa with a mean of 27.

Shrub recruitment and species richness values in the

crested wheatgrass treatment at Grouse Creek may be

influenced by livestock grazing, however, cattle grazing at

the site was not addressed in this study. At the Flat Iron,

Eakins, and Huber sites, the return of wyoming big sagebrush in crested wheatgrass treatments appear to be influenced by livestock grazing (table 4).

Crested wheatgrass established and has maintained a

monoculture community at Flat Iron for 32 years in the

absence of spring and summer livestock grazing. Treatment

of Wyoming big sagebrush at the site resulted in essentially

100% kill of the shrub. Information from the site indicates

that recruitment of Wyoming big sagebrush at the margins

of the treatment is currently nonexistent. The Eakins and

Huber sites are grazed by cattle during the boot stage of

phenology. Recruitment of sagebrush at these sites is apparent. Treatment of Wyoming big sagebrush was nearly

100 percent at the Eakins site and about 90 percent at the

Huber site. Although internal as well as external recruitment

of sagebrush at these sites are apparent, spring and summer

grazing appear to initiate or at least accelerate the return of

wyoming big sagebrush into the crested wheatgrass treatments.

Discussion and Management

Implications ____________________

Information from the four study sites indicate that although crested wheatgrass has a high capacity to persist in

original seedings, it has not demonstrated highly invasive or

otherwise weedy features demonstrated by other exotics

such as cheatgrass. Where crested wheatgrass has entered

native plant communities, it appears to have little modifying

influence on community composition and function. Cheatgrass presents a high risk to community composition and

function in big sagebrush communities (Billings 1994;

Peters and Bunting 1994). In the Uinta Basin, crested

wheatgrass has demonstrated a higher capability to suppress cheatgrass in these communities than native species.

Crested wheatgrass can provide a reliable means of altering

high fire frequency and other undesirable features of cheatgrass systems.

Following plowing and seeding, crested wheatgrass established and maintained a monoculture community in the

absence of spring livestock grazing in Wyoming big sagebrush communities with little or no shrub recruitment.

Sagebrush recruitment is apparent in treatments where

livestock grazing in spring and early summer is employed.

Information from the Flat Iron, Eakins, and Huber sites

indicate that timely grazing by cattle can be used as a tool to

promote recruitment of Wyoming big sagebrush in crested

wheatgrass seedings where desired. In the mountain big

sagebrush community at Grouse Creek, crested wheatgrass

did not form a monoculture. Although it remained a

dominante grass, shrub recruitment in the treatment was

apparent and appeared to function similar to shrubs in

adjacent native communities. Species richness in the treatment was relatively high. Summer livestock grazing at

Grouse Creek has probably promoted shrub recruitment.

Coupled with livestock grazing, crested wheatgrass seedings

can be managed for return of sagebrush in communities

altered by cheatgrass invasion.

References _____________________

Angell, R. F. 1998. Crested wheatgrass and shrub response to

continuous or rotational grazing. J. Range Manage. 50:160-164.

Ashcroft, G. L.; Jensen, D. T.; Brown, J. L. 1992. Utah Climate.

Logan, UT: Utah Climate Center, Utah State University. 127 p.

Ashley National Forest. 43-16 Mosby Mountain spike. unpublished

data. Vernal, UT: U.S. Department of Agriculture, Forest Service, Ashley National Forest, Supervisor’s Office.

Billings, W. D. 1994. Ecological impacts of cheatgrass and resultant

fire on ecosystems in the western Great Basin. In: Monsen, S. B.;

Kitchen, S. G., comps. Proceedings—ecology and management of

annual rangelands; 1992 May 18-21; Boise, ID. Gen. Tech. Rep.

INT-313. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station. 22-30.

Evans, R. A.; Eckert, R. E., Jr.; Young, J. A. 1986. High technology

weed control-revegetation systems for establishment and maintenance of crested wheatgrass. In: Johnson, K. L., ed. Symposium

proceedings: crested wheatgrass: its values, problems and myths.

Logan, UT: Utah State University: 91-96.

Table 4—Percent crown covera of Wyoming big sagebrush inside

treatments seeded with crested wheatgrass and outside

treatments at the Flat Iron, Eakins, and Huber study sites.

Year of

Study site treatment Outside Inside

Flat Ironb 1966 12.7 0.00

Eakinsc 1970 21.7 2.40

Huberc 1985 20.2 1.00

a

Crown cover estimates were derived from line intercept data.

bGrazed by cattle during winter only.

c

Grazed by cattle late spring and summer.

Table 3—Percent crown covera for six shrubsb from Grouse Creek

treatment area seeded with crested wheatgrass in 1956.

Year ARTR PUTR AMAL CHVI GUSA CHNA

1987 16.1 12.3 1.4 0.2 0.1 0.0

1988c 0.0 0.0 0.0 0.0 0.0 0.0

1991 0.1 3.9 1.4 1.7 0.3 0.0

1995 0.6 8.9 4.3 2.5 0.1 0.0

1997 1.3 10.3 4.1 2.7 0.0 0.3

1998 1.4 13.0 5.6 2.5 0.0 0.1

a

Crown cover estimates were derived from line intercept data.

bThe six shrubs are: Artemisia tridentata ssp. vaseyana var. pauciflora

(ARTR), Purshia tridentata (PUTR), Amelanchier alnifolia (AMAL), Chrysothamnus viscidiflorus (CHVI), Gutierrezia sarothrae (GUSA), and Chrysothamnus

nauseosus (CHNA). c

area burned during the 1988 Whiterocks wildfire.
USDA Forest Service Proceedings RMRS-P-11. 1999 185

Goodrich, S.; McArthur, E. D.; Winward, A. H. Sagebrush ecotones

and mean annual precipitation. [These proceedings].

Huber, M. 1998. [Personal communication]. November 23. Lapoint,

UT: Land owner.

Hull, A. C., Jr.; Holmgren, R. C. 1964. Seeding southern Idaho

rangelands. Res. Pap. INT-10. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Forest and Range

Experiment Station. 31 p.

Laycock, W. A.; Conrad, P. W. 1981. Responses of vegetation and

cattle to various systems of grazing on seeded and native mountain rangelands in eastern Utah. J. Range Manage. 43:52-56.

Martin, R. J.; Corbin, E., eds. 1930. Climatic summary of the United

States. Washington, DC: U.S. Department of Agriculture, Weather

Bureau. 21-1 through 21-17.

Monsen, S. B. 1994. Selection of plants for fire suppression on

semiarid sites. In: Monsen, S. B.; Kitchen, S. G., comps. 1994.

Ecology and management of annual rangelands: proceedings;

1992 May 18-21; Boise, ID. Gen. Tech. Rep. INT-313. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Research Station: 363-373.

Nelson, D. E. 1998. [Personal communication]. June 19 and November 23. Vernal, UT: U.S. Department of the Interior, Bureau of

Land Management, Vernal Office.

Peters, E. F.; Bunting, S. C. 1994. Fire conditions pre-and post

occurrence of annual grasses on the Snake River Plain. In:

Monsen, S. B.; Kitchen, S. G., comps. Proceedings—ecology and

management of annual rangelands; 1992 May 18-21; Boise, ID.

Gen. Tech. Rep. INT-313. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 31-36.

U.S. Department of Agriculture, Forest Service. 1993. Rangeland

ecosystem analysis and management handbook. FSH 2209-21.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station: 4 ch.

Whisenant, S. G. 1990. Changing fire frequencies on Idaho’s Snake

River Plains: ecological and management implications. In:

McArthur, E. D.; Romney, E. M.; Smith, S. D.; Tueller, P. T.,

comps. Symposium on cheatgrass invasion, shrub die-off, and

other aspects of shrub biology and management: proceedings;

1989 April 5-7; Las Vegas, NV. Gen. Tech. Rep. INT-276. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 4-10.

Winward, A. H. 1991. A renewed commitment to management of

sagebrush grasslands. In: Miller, R. F., ed. Management of

sagebrush steppe. Special Rep. 880. Corvallis, OR: Oregon State

University Agricultural Experiment Station: 2-7.
186 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Andrés F. Cibils is a PhD candidate in the department of Rangeland

Ecosystem Science at Colorado State University, Fort Collins, CO 80523.

Richard H. Hart is a Senior Range Scientist at the High Plains Grasslands

Research Station of the USDA-ARS, Cheyenne, WY 82009. David M. Swift is

an Associate Professor in the Rangeland Ecosystem Science Department and

Senior Scientist at the Natural Resource Ecology Laboratory, both at Colorado State University, Fort Collins, CO 80523.

Shrub-Grass Interactions in Relation to

Cattle Grazing in Atriplex canescens

Andrés F. Cibils

Richard H. Hart

David M. Swift

Abstract—Two related studies conducted at a shrub-dominant site

on the shortgrass steppe in Colorado showed that: (a) relative

numbers of young fourwing saltbush (Atriplex canescens [Pursh]

Nutt.) shrubs decreased significantly with increasing aboveground

biomass of western wheatgrass (Pascopyron smithii Rydb); (b) there

were significant seasonal variations in the levels of cattle utilization

of young shrubs; and (c) utilization of young shrubs was significantly associated with increases in the proportion of C4 grasses in

cattle diets. Herbaceous understory at this site may affect shrub

population dynamics both directly, through shrub-seedling/grass

competition in the absence of grazing, and indirectly, by influencing

cattle foraging behavior.

Fourwing saltbush grows in relatively dense stands on

creek floodplains and terraces of the shortgrass steppe in

northeastern Colorado. Edaphic factors appear to control

the occurrence and distribution of shrub-dominant communities in this grassland ecosystem (Lauenroth and Milchunas

1991). Biotic processes such as grazing can affect shrubgrass interactions and exert a strong influence on the relative abundance of grasses and woody plants at a given point

in time (Archer 1995 and references therein). At our research site, western wheatgrass dominates the shrub

interspaces in ungrazed exclosures. Interactions between

cattle grazing regime and adult fourwing saltbush size and

density are thought to create the necessary conditions for

western wheatgrass proliferation (Hart and others 1997). As

opposed to what occurs with this rhizomatous grass, numbers of juvenile fourwing saltbush shrubs in exclosures are

extremely low relative to surrounding grazed pastures (Cibils

and others 1997). We examined the relation between biomass of western wheatgrass in the shrub understory and

proportion of young shrubs to determine whether these

variables were significantly associated.

Fourwing saltbush is fairly sensitive to defoliation (Buwai

and Trlica 1977; Trlica and others 1997). Adequate periods

of rest are required to maintain viable shrub populations

under grazing (Pieper and Donart 1978; Price and others

1989). At our research site, cattle grazing (winter grazing in

particular) can have a negative impact on shrub longevity

(Cibils and others, submitted), and can apparently cause

population turnover rates to be higher in grazed stands than

in exclosures (Cibils and others 1997). Consequently, young

shrubs account for up to 35% of the population in grazed

shrub stands at our site (Cibils and others 1997). Young

fourwing saltbush shrubs in seeded stands can be severely

damaged by rabbit, grasshopper, and deer herbivory (Springfield 1970). Little is known, however, about the impact of

cattle grazing on juvenile fourwing saltbush shrubs in natural populations and the factors that control it. At our research site we found that the proportion of young shrubs was

greater in winter-grazed stands than in stands that had

been historically grazed in summer (Cibils and others 1997).

We hypothesized that the impact of moderate and heavy

cattle grazing on juvenile shrubs would be greater in summer than in winter. Since young shrubs are intermingled

with the herbaceous understory, we also hypothesized that

the utilization pattern would be related to the seasonal

dynamics of this layer of the plant community.

Saltbushes (Atriplex sp.) are fairly short-lived shrubs

(Stewart and others 1940; Crisp 1978; Norton 1978; West

1979). Recruitment in many saltbush species is a somewhat

continuous process (Eldridge and Westoby 1991), as opposed

to other dryland shrubs that exhibit episodic recruitment

events (Paur 1971). At our research site, recruitment occurs

almost entirely through sexual reproduction. Hence, factors

that affect seed germination, seedling establishment, and

juvenile shrub survival are crucial to the long-term viability

of these populations.

We conducted our research in a fairly homogeneous

fourwing saltbush stand at a site on the shortgrass steppe in

Colorado. We addressed the following research questions:

(a) is the relative abundance of young shrubs related to the

abundance of western wheatgrass in the shrub interspaces?

(b) are there seasonal and stocking-density-related variations

in the level of cattle utilization of young shrubs? and (c) are

seasonal variations in cattle utilization of young shrubs

related to the dynamics of the herbaceous understory?

Materials and Methods ___________

Our study site was located on a floodplain area close to

Owl Creek, within the USDA-ARS Central Plains Experimental Range (40° 49' N 107° 47' W). Soils of this site have

been described as loamy to sandy loams. Fourwing saltbush,

blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud), and

western wheatgrass are the dominant plant species at the
USDA Forest Service Proceedings RMRS-P-11. 1999 187

site (Liang and others 1989). Mean annual precipitation is

320 mm, most of which occurs between April and September.

The first research question (stated above) was addressed

by revisiting data we had collected in a transect study at our

site in the fall of 1995 that we describe elsewhere (Hart and

others 1997; Cibils and others 1997). We performed linear

regression analysis between percent young shrubs (dependent variable) and aboveground biomass of western wheatgrass in the shrub interspaces (independent variable). We

calculated percent young shrubs and mean western wheatgrass biomass for each of six transects: two in historically

winter-grazed pastures; two in historically summer-grazed

pastures; and two in exclosures.

The second research question was addressed by measuring utilization of marked young shrubs in 12 half-hectare

experimental pastures. The pastures were built in two

parallel blocks of seven adjacent units each (one plot was left

as an exclosure in each block) in the general area where we

had previously placed the transects. We conducted a 2-year

(1997 and 1998) browsing experiment that consisted of

browsing four pastures with cattle for a period of 4 days in

winter (January), early spring (April), and late summer

(September). Two pastures were browsed moderately

(4 heifers) and two were browsed heavily (12 heifers). Moderate stocking densities simulated levels of cattle herbivory

historically imposed on fourwing saltbush stands at the

CPER. High stocking densities were three times the historical (moderate) densities. Cattle used in the experiments

were always taken from herds grazing pastures with abundant fourwing saltbush, so as to minimize dietary and social

adjustment times. We used heifers in all experiments, except for September 1997, when heifers were not available,

obliging us to use steers instead. The mean live weights of

the heifers or steers used ranged from about 400 to 520 kg.

Pastures were assigned randomly to each stocking density

treatment. Randomization was performed within each block

of experimental pastures, subject to the constraint that no

two adjacent pastures were grazed on the same date.

Twenty young shrubs were randomly selected and labeled

in each half-hectare grazing plot. Shrubs were labeled in a

manner that would be inconspicuous to cattle. Small (not

taller than 25 cm) non-reproductive individuals were classified as juvenile shrubs. In the weeks prior to each experiment, four primary leaders were marked on each labeled

shrub. Length of marked leaders was measured prior to

introducing the cattle. Once each experiment was over (and

the cattle removed), length of marked leaders were remeasured. Leaders marked on young shrubs were mono

axial stems seldom exhibiting branches and never exhibiting flowers or fruits. We, therefore, assumed a linear length/

weight relation for such leaders, where percent length removed was assumed to be roughly equal to percent biomass

consumed by cattle.

Mean percent utilization of marked leaders on young

shrubs was calculated for each experimental plot. Data were

analyzed using repeated measures analysis of variance

(ANOVAR). The statistical model selected for the analysis

was a mixed effects repeated measures factorial experiment

design. Season (January, April, and September), stocking

density (moderate and heavy), year (1997 and 1998), and

block (1 or 2) were the factors studied. Season, stocking

density, and block were repeated within year. Season,

stocking density, and year were considered fixed effects,

while block was considered a random effect. We included all

possible two-way and three-way interactions between fixed

effects in the final model. We also explored interactions

between fixed and random main effects, and included significant interactions in the final model. Utilization data

were arcsin-transformed in order to meet the assumption of

homogeneity of variances of the ANOVA. The overall level of

significance was set at p = 0.05.

The last research question was addressed by performing

regression analysis between percent C4 grasses in cattle

diets and utilization of marked leaders on young shrubs. In

order to do this we collected fecal material samples (in the

1997 experiments) immediately after removing cattle from

the pastures. These samples were used to determine diet

composition applying microhystological analysis techniques

described by Sparks and Malecheck (1968).

Results ________________________

Biomass of western wheatgrass in the shrub interspaces

explained 80% of the variation in relative numbers of young

shrubs (p = 0.016). Overall, increases in biomass of western

wheatgrass were associated with a significant decrease in

the relative abundance of young shrubs (fig. 1).

Utilization of young shrubs increased significantly as the

growing season progressed and was significantly higher

under heavy stocking densities than under moderate ones

(fig. 2.a,b). Utilization was lowest in January, intermediate

in April, and highest in September, and was always higher

in the high stocking density pastures. This pattern was

consistent across years (table 1). In 1998 overall utilization

of young shrubs was higher than in 1997. A milder winter in

Figure 1—Relationship between aboveground

biomass of western wheatgrass and percent

young shrubs.

Western wheatgrass

Biomass (g/m2

)

0 100 200 300 400

Percent young shrubs

40

30

20

10

0

R2 = 0.80

p = 0.016
188 USDA Forest Service Proceedings RMRS-P-11. 1999

1998 relative to 1997, and less rainfall in the month of July

1998 relative to July 1997 may have contributed to the

significant year effect.

Under moderate stocking density, increases in the content

of C4 grasses in cattle diets were significantly associated

with an increase in utilization of young shrubs (p = 0.011

 [fig. 3.a]). Percent C4 grasses in cattle diets explained 83%

of the variation in utilization of young shrubs. Under high

stocking density the relationship between these variables

was somewhat weaker (R2

 = 0.63) and marginally significant (p = 0.058) (fig.3.b).

Discussion _____________________

The negative association between aboveground biomass

of western wheatgrass and proportion of young fourwing

saltbush shrubs (in relation to the cattle grazing regime) is

consistent with predictions of a conceptual model proposed

by Archer (1995). According to this model, probability of

seedling establishment tends to increase as graminoid shoot

Figure 2—(a) Utilization of marked leaders in high

stocking density (full bars) and moderate stocking

density (empty bars) pastures. (b) Experiment means

for utilization of marked leaders in January, April, and

September.

Figure 3—Relationship between percent C4 grasses

in cattle diets and utilization of marked leaders on

young shrubs under: (a) moderate stoking density

and (b) high stocking density.

Table 1—Anova table for arcsin transformed percent utilization of

marked leaders on young shrubs.

Source df F p

Fixed effects:

Year 1 72.17 <0.001

Stocking density 1 35.24 <0.001

Season 2 12.41 0.002

Year*Stocking density 1 0.57 0.466

Year*Season 2 2.48 0.129

Stocking density*Season 2 0.99 0.403

Stocking density*Year*Season 2 0.57 0.466

Random effect:

Block 1 0.0007 0.980

Percent C4 grasses in the diet

R2 = 0.63

p = 0.058

Percent utilization young shrubs Percent utilization young shrubs

Percent C4 grasses in the diet

R2 = 0.83

p = 0.011

Utilization of marked leaders Utilization of marked leaders
USDA Forest Service Proceedings RMRS-P-11. 1999 189

and root biomass decreases. Increases in grazing pressure

over time are predicted to favor a decrease in graminoid

biomass and allow seedlings of woody plants to establish.

Archer (1995) stated that grazing can promote shrubseedling establishment by releasing water resources otherwise used by grasses. Situations such as those predicted by

Archer’s (1995) model, where grazing is thought to mediate

shrub-seedling establishment, occur in other species of the

genus Atriplex such as shadscale (Atriplex confertifolia)

(Chambers and Norton 1993).

Seed germination and seedling establishment require

adequate windows of opportunity, which are affected by

climate and other species in the plant community (Booth and

Haferkamp 1995). In fourwing saltbush such “windows” are

apparently related to the simultaneous occurrence of cool

temperatures (around 25 °C) and the availability of sufficient water to allow seed imbibition (Springfield 1970).

Temperatures either above or below 25-28 °C depress germination (Springfield 1970). Utricle bracts of fourwing saltbush can have considerable amounts of saponins (Nord and

Van Atta 1960) that can act as germination inhibitors.

Therefore, water is required not only for imbibition but also

to eliminate water-soluble inhibitors prior to the onset of

enzymatic processes leading to seed germination. Optimal

growth temperatures for C3 grasses are within the range of

20-25 °C (Larcher 1980). On the other hand, C4 grasses grow

optimally at temperatures ranging from 32-40 °C (Larcher

1980). Hence, onset of growth in western wheatgrass (using

available water resources) overlaps considerably with the

narrow window of opportunity for fourwing saltbush seed

germination. Conversely, by the time active growth of blue

gramma (dominant in the understory of grazed stands)

occurs, temperatures are far from optimal for fourwing

saltbush seed germination. The taller canopy structure of

western wheatgrass (relative to blue gramma) favors the

interception of larger amounts of rainwater and light, thus,

decreasing still more the probabilities of successful shrub

seed germination and/or seedling survival. Hence, while the

grass/young-shrub relation we measured does not necessarily imply a cause-effect relation, there are a number of

physiologically-based explanations that suggest that the

statistical association we found is biologically meaningful.

Utilization of juvenile shrubs was highest in summer,

intermediate in spring, and lowest in winter, and always

higher under high stocking densities than under moderate

ones. Seasonal patterns of utilization of juvenile shrubs

were the same in both years, and persisted under a threefold increase in stocking density. Heavy defoliation can

promote mortality of adult fourwing saltbush shrubs (Buwai

and Trlica 1977; Trlica and others 1977; Pieper and Donart

1978). Atriplex canescens is more sensitive to heavy defoliation than other species of its genus (Benjamin and others

1995). Fourwing saltbush seedlings can also be affected

negatively by herbivory. Survival in seedling plots exposed

to grasshopper, rabbit, and deer herbivory was only 67% of

protected controls (Springfield 1970). While little is known

about how cattle grazing affects juvenile fourwing saltbush

shrubs, studies conducted with other shrub species suggest

that livestock may increase natural mortality rates of young

shrubs. Cattle grazing promoted grater mortality of juvenile

basin big sagebrush shrubs (Artemisia tridentata Nutt ssp.

tridentata Beetle) compared to adults of the same species

(Owens and Norton 1990). In another set of experiments, big

sagebrush seedlings exhibited higher mortality rates in

shrub interspaces grazed by either sheep or cattle relative to

ungrazed exclosures (Owens and Norton 1992). Revegetated

rangelands grazed by horses and deer suffered greater

mortalities of big sagebrush juveniles relative to the ungrazed

controls (Austin and others 1994). Assuming that shrub

mortality increases with increasing levels of herbivory (as

suggested in the literature), survival of juvenile fourwing

saltbush shrubs at our site would be expected to be lowest

under summer grazing, intermediate under spring grazing

and highest under winter grazing by cattle.

Utilization levels of juvenile fourwing saltbush shrubs at

our site increased significantly with increasing proportion of

warm season grasses in cattle diets both in moderately and

heavily stocked pastures. Cattle are generally roughage

eaters (Hofmann 1989), and can feed more efficiently on the

herbaceous understory than on shrubs (Petersen and others

1994). Anatomical adaptations that enable cattle to harvest

large volumes of forage on a daily basis constrain their

ability to be selective feeders (Van Soest 1994). On the

shortgrass steppe cattle shift from a shrub-grass diet in

winter to a grass-dominant diet in spring and summer

(Schwartz and Ellis 1981; Shoop and others 1985). When

high quality herbaceous forage is available in adequate

amounts, cattle apparently feed predominantly on grasses

and forbs in the herbaceous understory (Cibils, unpublished

data). It is therefore not surprising that juvenile fourwing

saltbush shrubs in our experiments (intermingled in the

herbaceous canopy) were utilized the most at times of the

year when cattle were feeding primarily on grasses. This

implies that seasonal increases in utilization of juvenile

shrubs at our site were a consequence of the phenology of the

herbaceous understory, rather than of the direct dietary

selective behavior of cattle. Young shrubs were possibly

most heavily utilized in summer because cattle could not

help harvesting them together with the bulk of herbaceous

forage they were feeding on.

Grasses may have an important influence on population

dynamics of fourwing saltbush at our site. In the absence of

grazing, asymmetric competition interactions between

grasses and shrub seeds or seedlings may result in reduced

(or no) shrub recruitment. In stands grazed by cattle, grasses

may indirectly affect survival of juvenile individuals by

influencing cattle foraging behavior.

References _____________________

Archer, S. 1995. Herbivore mediation of grass-woody plant interactions. Tropical Grasslands 29:218-235.

Austin, D. D.; Urness, P. J.; Durham, S. L. 1994. Impacts of mule

deer and horse grazing on transplanted shrubs for revegetation.

Journal of Range Management 47:8-11.

Benjamin, R. W.; Lavie, Y.; Forti, M; Barkai, D.; Yonatan, R.; Hefetz,

Y. 1995. Annual regrowth and edible biomass of two species of

Atriplex and of Cassia sturtii after browsing. Journal of Arid

Environments 29:63-84.

Booth, D. T.; Haferkamp, M. R. 1995. Morphology and seedling

establishment. in Bedunah, D. J.; Sosebee, R. E. editors. Wildland plants: Physiological Ecology and Developmental Morphology. Society For Range Management, Denver, CO.
190 USDA Forest Service Proceedings RMRS-P-11. 1999

Buwai, M.; Trlica, M. J. 1977. Multiple defoliation effects on herbage

yield, vigor, and total nonstructural carbohydrates of five range

species. Journal of Range Management 30 :164-171.

Chambers, J. C.; Norton, B. E. 1993. Effects of grazing and drought

on population dynamics of salt desert shrub species on the Desert

Experimental Range, Utah. Journal of Arid Environments 24:

261-275.

Cibils, A. F.; Swift, D. M.; Hart, R. H. 1997. Animal-plant interactions in an Atriplex canescens dominant community browsed by

cattle. Proceedings XVIII International Grassland Congress,

June 8-19; Winnipeg and Saskatoon. Vol.2 Session 21:23-24.

Cibils, A. F.; Swift, D. M.; Hart, R. H. (manuscript submitted).

Shrub gender-related differences in stands of Atriplex canescens

(Pursh) Nutt. with different histories of grazing by cattle.

Cibils, A. F. 1998. Data on file at: Colorado State University,

Department of Rangeland Ecosystem Science, Fort Collins, CO.

Crisp, M. D. 1978. Demography and survival under grazing of three

Australian semi-desert shrubs. Oikos 30:520-528.

Eldridge, D. J.; Westoby, M. 1991. Recruitment and survival in

Atriplex vesicaria populations in semiarid western New South

Wales, 1977-1987. Australian Journal of Ecology 16:309-314.

Hart, R. H.; Cibils, A. F.; Ashby, M. M.; Swift, D. M. 1997. Atriplex

canescens impact on understory vegetation under different seasons of grazing. Proceedings—XVIII International Grassland

Congress, June 8-19; Winnipeg and Saskatoon. Vol. 2 Session

21:25-26.

Hofmann, R. R. 1989. Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of

their digestive system. Oecologia 78:443-457.

Larcher, W. 1980. Physiological plant ecology. Springer Verlag,

New York.

Lauenroth, W. K.; Milchunas, D. G. 1991. Short-grass steppe. Pages

183-226 in Coupland, R. T. editor. Ecosystems of the world, 8A,

Natural grasslands, Introduction and Western Hemisphere.

Elsevier, New York.

Liang, Y. M.; Hazlett, D. L.; Lauenroth, W. K. 1989. Biomass

dynamics and water use efficiencies of five plant communities in

the shortgrass steppe. Oecologia 80:148-153.

Nord, E. C.; Van Atta, G. R. 1960. Saponin—a seed germination

inhibitor. Forest Science 6:350-353.

Norton, B. E. 1978. The impact of sheep grazing on long term

successional trends in salt desert shrub vegetation of southwestern Utah. First International Rangeland Congress, Society for

Range Management, Denver, CO: 610-613.

Owens, M. K.; Norton, B. E. 1990. Survival of juvenile basin big

sagebrush under different grazing regimes. Journal of Range

Management 43:132-135.

Owens, M. K.; Norton, B. E. 1992. Interactions of grazing and plant

protection on basin big sagebrush (Artemisia tridentata ssp.

tridentata) seedling survival. Journal of Range Management

45:257-262.

Paur, L. F. 1971. Establishment patterns of bitterbrush. MS Thesis.

Colorado State University, Fort Collins, CO.

Petersen, J. L.; Lawrence, K.; Ueckert, D. N. 1994. Comparison of

fourwing saltbush and herbaceous forage intake by cattle during

winter. Research Advance Report. The Texas A&M University

System, The Texas Agricultural Experiment Station, San Angelo,

TX. 4 p.

Pieper, R. D.; Donart, G. B. 1978. Response of fourwing saltbush to

periods of protection. Journal of Range Management 31:314-315.

Price, D. L.; Donart, G. B.; Southward, M. 1989. Growth dynamics

of fourwing saltbush as affected by different grazing management systems. Journal of Range Management 42:158-162.

Schwartz, C. C.; Ellis, J. E. 1981. Feeding ecology and niche

separation in some native and domestic ungulates on the shortgrass prairie. Journal of Applied Ecology 18:343-353.

Shoop, M. C.; Clark, R. C.; Laycock, W. A.; Hansen, R. M. 1985.

Cattle diets on shortgrass ranges with different amounts of

fourwing saltbush. Journal of Range Management 38:443-449.

Sparks, D. R.; Malecheck, J. C. 1968. Estimating percentage dry

weight in diets using a microscope technique. Journal of Range

Management 21:264-265.

Springfield, H. W. 1970. Germination and establishment of fourwing

saltbush in the southwest. Research Paper RM-55. Fort Collins,

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO

80521. 48 p.

Stewart, G.; Cottam, W. P.; Hutchings, S. S. 1940. Influence of

unrestricted grazing on northern salt desert plant associations in

western Utah. Journal of Agricultural Research 60:289-317.

Trlica, J.; Buwai, M.; Menke, J. 1977. Effects of rest following

defoliations on the recovery of several range species. Journal of

Range Management 30:21-27.

Van Soest, P., ed. 1994. Nutritional ecology of the ruminant, Second

Edition. Cornell University Press, Ithaca, NY.

West, N. 1979. Survival patterns of major perennials in salt desert

shrub communities of southwestern Utah. Journal of Range

Management 32:442-445.
USDA Forest Service Proceedings RMRS-P-11. 1999 191

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Rex G. Cates and Jiping Zou are the Director and Associate Director,

respectively, of the Chemical Ecology Laboratory, and Stuart C. Wooley,

Research Assistant, Department of Botany, Brigham Young University,

Provo, UT 84602. Francis J. Singer and Linda Zeigenfuss, Research Ecologist

and Ecologist, respectively, Biological Division of the U.S. Geological Survey,

Midcontinent Ecological Center, Natural Resources Ecology Lab, Colorado

State University, Fort Collins, CO 80523. Lauryl C. Mack is a Wildlife

Biologist, P.O. Box 168, Yellowstone National Park, WY 82190.

Predisposition of Willows to Elk Browsing

Due to Willow Interactions with Abiotic

Factors

Rex G. Cates

Jiping Zou

Stuart C. Wooley

Francis J. Singer

Lauryl C. Mack

Linda Zeigenfuss

Abstract—Current literature indicates that the decrease in willow

stature and productivity on the winter range in Yellowstone National Park is due to a complex interaction among abiotic and biotic

factors. Lack of change in soluble carbohydrates, total phenolics and

tannins when willows were mechanically clipped in exclosures in

Yellowstone National Park show that willows were not able to

respond physiologically to these treatments. These data are supportive of the premise that the willow decline is due to unfavorable

growing conditions on the northern winter range. Willow physiology, growth, and recruitment are impacted adversely by ungulate

browsing, but experimental manipulations within exclosures indicate that browsing may not be the only important factor. The trend

toward aridity, lowered water tables, reduced stream flow, lack of

flooding, and absence of beaver are suggested to be important

factors in reduced willow production, reproduction, and lower levels

of primary and defensive chemicals.

Over the last 60 years large decreases in willow (Salix

spp.) populations and stature have occurred in the northern

winter range in Yellowstone National Park (YNP), Wyoming

(Wagner and others 1995a; Chadde and Kay 1991; Houston

1982). Willow declines have been especially dramatic occurring primarily between 1920 and 1940 during an extended

drought (Engstrom and others 1991). Reasons for these

changes in willow dyamics have been heavily debated resulting in several hypotheses. The most common is that elk

(Cervus elaphus) have increased to unnaturally high levels

due to reduced predation including hunting, alterations of

the landscape by modern man, and disruption of migration

routes (Wagner and others 1995b; Boyce 1991; Pengally 1963).

A second set of hypotheses focus on climate and hydrological changes in conjunction with beaver declines. For the

winter range in Yellowstone National Park climates are

warmer and drier this century (Balling and others 1992a,b),

which is suggested to have resulted in lower water tables as

judged by stream downcuts, reduced stream flows, and less

flooding. These changes may foster a habitat that is unfavorable for willow growth and recruitment (Singer and others

1994; Houston 1982). Compounding these adverse effects on

willows is the decline in beaver, which has resulted in almost

no beaver ponds, a change in stream flows, and lower water

tables (Jonas 1955). Most likely, with fewer beaver ponds

reestablishment sites for willow shoots, sprouts, and seedlings are greatly diminished and nutrient dynamics may

have changed significantly (Naiman and others 1986; Naiman

and Melillo 1984). Changes in these climatic and hydrological factors combined with the loss of beaver are purported to

have resulted in willows that are unable to produce sufficient natural defenses against ungulates. As a result, willows become nutritionally more suitable to these large herbivores and are not able to grow beyond the height of

browsing.

Although heavy browsing exacerbates willow physiology

and growth, we suggest that elk browsing may not be the

only cause of willow declines. We posit that changes in water

dynamics due to reduced precipitation, higher temperatures, reduced flooding, lowered water tables, and the absence of beaver may be important factors causing the demise

of willows on the northern winter range. In support of the

climate-hydrological-beaver scenario, tall productive willows growing within the upper reaches of the drainages

where the habitat is more favorable for growth were browsed

seven to nine times more than were suppressed willows at

lower elevations (Singer and Cates 1995).

Willow Chemistry and Ungulate Browsing

Compounds in willows that function as defenses against

herbivores and also affect nutritional quality are tannins

that bind to several primary metabolites (e.g., nitrogencontaining compounds like proteins, amino acids, DNA,

RNAs), and low molecular weight phenolics, which are

suggested to be toxic and/or act as feeding deterrents (Robbins

1993). Of these two, low molecular weight phenolics may
192 USDA Forest Service Proceedings RMRS-P-11. 1999

play the major role in deterring ungulate browsing since

some large animal browsers may render tannins less effective as defenses (Robbins and others 1987). For willows

inhabiting sites favorable for growth, the challenge from

tissue removal by herbivores and infection from pathogens

normally results in an induced increase in phenolics and

tannins in remaining and new leaf and stem tissues (Karban

and Baldwin 1997). Where conditions for willow growth are

unfavorable on the northern winter range, willows will not

be able to respond by increasing their production of defensive chemicals when exposed to heavy ungulate browsing

and mechanical clipping experiments.

Clipping experiments using willows have produced mixed

results regarding changes in nitrogen and soluble carbohydrates in new growth. Clipping Bebb willow (S. bebbiana)

resulted in no significant increase in carbohydrates, total

nitrogen, and phosphorus (Chapin and others 1985), but

clipping S. lanata at 0, 50, and 100% for 2 years resulted in

a significant increase in total nitrogen and phosphorus

(Ouellet and others 1994). In this same study soluble carbohydrates decreased significantly and then returned to control levels. An important contribution of the study reported

here is the determination of carbohydrate concentrations

over a 3 year period in which willows located inside exclosures were clipped at 0, 50, and 100% of their current annual

growth.

Objectives and Hypotheses _______

Our objectives were first to test hypotheses, in the context

of the climate-hydrological-beaver paradigm, regarding the

physiological status of willows on the northern winter range

of Yellowstone National Park. Secondly, we summarize

from the literature the characteristics purported or documented for sites deemed to be unfavorable or favorable to

willow growth, productivity, and recruitment, and a description of willow responses to these site characteristics. Included in this summary are projections as to how ecosystem

processes may change as site conditions change, and the

communities that result from alteration of these processes

(Naiman and others 1988; Cummins and others 1989). The

hypothesis tested is that willows from which the current

annual growth (CAG) was mechanically clipped at the 50

and 100% levels inside exclosures in YNP will not be able to

respond, as compared to the control (0% clip), by increasing

defensive phenolic and tannin compounds. The response in

carbohydrates to these treatments is mixed, but the expectation is that total soluble carbohydrate content will decrease in the presence of mechanical clipping as compared to

the control. Clipping experiments inside 30-35 year old

exclosures should be particularly instructive since the effect

of elk browsing is eliminated, and the experiments were

carried out over a 3-year period.

Study Areas and Methods ________

Study Sites

Study areas, and the indepth analysis of climate, growth,

and physiological data, are detailed in Singer and others

(1998). In summary, the northern winter range in YNP is

about 140,000 hectares located on the northern boundary of

the park. This area is characterized by cold winters (averaging –4.90°C) and short, cool summers (15°C) with mean

annual precipitation averaging about 18-40cm/year

(Houston 1982). At the time of this study, elk population

densities on the YNP winter range were 11-16 elk/km2

.

Beaver, however, are rare or absent on the winter range in

YNP (<1% of stream length with beaver activity).

Primary and Secondary Metabolites

Ten to 15 shoots from each plant were analyzed for total

soluble carbohydrates, phenolics, and tannins, and were

expressed on a dry-weight basis. ANOVA for unequal sample

sizes on log transformed data were performed using clipping

treatment as the independent variable, and total content of

soluble carbohydrates, phenolics, and tannins as the dependent variables.

Results and Discussion __________

Willow Physiology as an Indirect

Indication of Unfavorable Habitat Quality

for Willow Growth

Measurements of primary and secondary metabolites

over a 3 year period indicate that 50 and 100% clipped

willows in exclosures in YNP were not able to respond to

these treatments by increasing phenolic and tannin content

(tables 1,2). Soluble carbohydrates for Bebb willow and false

mountain willow (S. pseudomonticola) did not change or

decrease significantly in the 50 and 100% treatments (e.g.,

false mountain, 1996) (tables 1, 2).

Total phenolic content in Bebb (table 1) and false mountain willows (table 2) followed the pattern of not changing

significantly across treatments within a year, or of decreasing significantly (e.g., Bebb willow summer 1993—100%

decreased compared to 50%; for the winter 1995 collection,

50 and 100% decreased compared to 0%). Bebb willow tannin

content in leaf and twig tissues for the 0 and 50% clipped

plants was not significantly different, but tannin content

decreased significantly in the 100% clipped plants compared

to the other two treatments for 1993 (table 1). For the 1995

winter twig collection, tannin content decreased in the 100%

clip compared to the 0 and 50% treatments (table 1). For

false mountain willow the 1993 and 1996 tannin content in

leaf and twig tissues in the summer was not different among

any treatments, but did significantly increase in the 100%

clip in 1995 (table 2). In the 1993 winter collections tannin

content significantly decreased in the 50% treatment compared to the control and 100% clip (table 2).

These physiological data are consistent with the hypothesis that willows in exclosures that have been protected from

browsing 31-35 years were occupying unfavorable habitats

for growth. An additional clue to the willow decline, as

related to water dynamics and improved habitat quality for

willow growth and physiology, is found in the phenolic data

in the clipping experiments. A trend toward increased moisture and lower temperatures in YNP seems to have occurred

during the late 1990’s (Stohlgren and others 1998). This
USDA Forest Service Proceedings RMRS-P-11. 1999 193

trend is associated with a two to three times increase in

phenolic content in the samples taken from Bebb and false

mountain willows (tables 1, 2).

Climate Change, Beaver Abundance,

Ecosystem Processes, and Riparian

Communities

Several factors noted in recent publications indicate a

trend toward aridity and change in habitat quality on the

winter range toward one less suitable for willow growth and

physiological response (table 3) (and perhaps aspen, Romme

et al. 1995). The summer temperature increase has been

0.87°C, while the average January-June precipitation decreased 61 mm. Beaver and their associated activities are an

additional factor affecting water dynamics and ecosystem

processes (table 3). Beaver were found to be almost

nonexistent on the winter range in YNP. Their activity

results in local water tables being higher near beaver dams

and surrounding areas, in the formation of a mosaic of

braided, meandering, slow-moving water in streams, and

ponds that are rich and efficient in processing nutrients,

carbon, and litter (table 3) (Naiman and others 1988).

Reduced production, leader length and weight, plant

height, and recruitment of unbrowsed and browsed willows

also suggest poor growing conditions for willows (table 3).

Clipping willows over a 4 year period in YNP exclosures

showed a cumulative negative change in production and

height for the 0, 50, and 100% clipped plants (Singer and

others 1998). Noted also were decreases in catkin production. These, combined with the lack of physiological response

in soluble carbohydrates, low molecular weight phenolics,

and tannins in mechanically clipped willows in exclosures,

suggest that browsing may not be the only factor in willow

declines.

Table 1—Effect of mechanical clipping on total phenolic, tannin, and total soluble carbohydrate content of the current year’s growth of Bebb willow

from July 1993 through summer 1996 ( x, sd§

), Yellowstone National Park, Wyoming.

0 50 100

Year/compound+ Summer Winter Summer Winter Summer Winter

1993

Total phenolics 4380 ± 1226 5091 ± 1784 5191 ± 1357a* 4349 ± 427 3634 ± 1200b* 5200 ± 1184

Tannins 76 ± 12a* 57 ± 17 72 ± 8a* 52 ± 7 56 ± 13b* 55 ± 8

Sol. carbo.¤ 44 ± 16 23 ± 1 47 ± 12 22 ± 2 47 ± 13 21 ± 8

1995

Total phenolics 3071 ± 466 6987 ± 1688a* 3133 ± 688 3287 ± 1546b* 3066 ± 749 3873 ± 2246b*

Tannins 66 ± 8 52 ± 12a* 57 ± 14 53 ± 14a* 57 ± 13 30 ± 10b*

Sol. carbo. 32 ± 5 19 ± 6 29 ± 4 20 ± 5 32 ± 14 17 ± 1

1996

Total phenolics 9154 ± 1595 — 9181 ± 2295 — 8953 ± 2950 —

Tannins 62 ± 8 — 64 ± 7 — 59 ± 17 —

Sol. carbo. 26 ± 5 — 32 ± 8 — 28 ± 5—

§

Means followed by different letters significantly different at *p ≤0.05; **p ≤0.10, ANOVA. +Total phenolics expressed as average peak height divided by 100. Tannins and soluble carbohydrates expressed as mg/g dry weight. ¤From S. C. Wooley, M.S. Thesis 1998. Brigham Young University, Provo, UT

Table 2—Effect of mechanical clipping on total phenolic, tannin, and total soluble carbohydrate content of the current year’s growth of false mountain

willow from July 1993 through summer 1996 ( x, sd§), Yellowstone National Park, Wyoming.

0 50 100

Year/compound+ Summer Winter Summer Winter Summer Winter

1993

Total phenolics 7141 ± 668 4532 ± 1423 6061 ± 1639 4593 ± 847 6649 ± 1793 4847 ± 913

Tannins 76 ± 10 48 ± 7a* 75 ± 11 35 ± 10b 77 ± 10 47 ± 10a**

Sol. carbo.¤ 46 ± 11 35 ± 7 40 ± 15 31 ± 3 46 ± 17 23 ± 11

1995

Total phenolics 6745 ± 1721 5069 ± 1534 6888 ± 1474 4771 ± 539 7264 ± 1125 5141 ± 597

Tannins 58 ± 12a 42 ± 12a 59 ± 21a 46 ± 7a 79 ± 13b* 62 ± 10b*

Sol. carbo. 32 ± 6 26 ± 9 30 ± 8 25 ± 7 31 ± 6 25 ± 6

1996

Total phenolics 17,166 ± 3343 — 15,265 ± 4864 — 16,283 ± 3034 —

Tannins 65 ± 9 — 62 ± 14 — 68 ± 12 —

Sol. carbo. 47 ± 9a — 25 ± 4b* — 24 ± 4b*

§Means followed by different letters significantly different at p ≤0.05; p ≤0.10, ANOVA. +Total phenolics expressed as average peak height divided by 100; tannins and soluble carbohydrates expressed as mg/g dry weight. ¤From S.C. Wooley, M.S. Thesis 1998. Brigham Young University, Provo, UT.
194 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 3—Verified and predicted parameters describing sites favorable and unfavorable for willow growth, and willow and habitat responses on these

sites, in the northern winter range of Yellowstone National Park, Wyoming.

Site

Parameter/response Unfavorable Favorable

Parameters

Precipitation1-4, 8 Less, drier winters Higher, wetter

Temperature1-4, 8 Warmer Cooler

Water Tables1-3 Lower Perennially higher

Streambanks1-3 Prevalent downcutting Less downcutting, vegetated

Flooding1-3 Common, extensive Infrequent, reduced intensity

Streams6, 7 Single or few streams, narrow Network of braided, expounded streams, ponds;

streams; increased flow impounded water, high sediment organic matter

Beaver3, 5, 6 Few to none; loss of food supply Common; food supply abundant (aspen, willow)

Willow Response

Production1-3 Reduced; negative gain in CAG Net increase, vigorous gain in CAG

Recruitment1-3 Reduced to nonexistent Seed productivity high, asexual

 Leader Length and Weight1-3 Short, lighter Longer, heavier

Plant Height1-3 Reduced in stature Able to grow beyond reach of elk

Browsing Effect on Growth Form2 Morphological juvenility response; Morphological and physiological

reduced physiological response juvenility

Defense Response Reduced or none Induced response vigorous

Habitat

Nutrients6, 9 Reduced input of N Enhanced N availability

Aquatic Invertebrates6, 7 Shredders, scrapers; biomass less Collectors, predators; greater biomass

Carbon6, 7 Low carbon input High carbon input and processing

Litter More recalcitrant; slower processing More rapidly processed

Plant Community2, 7, 8 Grass, sedges, conifer encroachment, Mosaic of riparian vegetation; willow

dryland shrubs aspen maintained

1Singer and others 1998 4Balling and others 1992a,b 7Naiman and Melillo 1984 2

Singer and others 1994 5Consolo-Murphy and Hanson 1993 8Houston 1982 3Singer and Cates 1995 6Naiman and others 1988 9Jonas 1955

References _____________________

Balling, R. C., Jr.; Meyer, G. A.; Wells, S. G. 1992a. Relation of

surface climate and burned area in Yellowstone National Park.

Agricultural and Forest Meteorology. 60:285-293.

Balling, R. C., Jr.; Meyer, G. A.; Wells, S. G. 1992b. Climate change

in Yellowstone National Park: is the drought-related risk of

wildfires increasing? Climate Change. 22:35-40.

Boyce, M. S. 1991. Natural regulation or control? In: Keiter, R. B.;

Boyce, M. S., eds. The Greater Yellowstone Ecosystem: redefining

America’s wilderness heritage. New Haven, CT: Yale University

Press: 183-208.

Chadde, S.; Kay, C. 1991. Tall willow communities on Yellowstone’s

northern range: a test of the Anatural regulation@ paradigm. In:

Keiter, R. B.; Boyce, M. S., eds. The Greater Yellowstone Ecosystem: redefining America’s wilderness heritage. New Haven, CT:

Yale University Press. 231-262.

Chapin, F. S., III; Bryant, J. P.; Fox, J. F. 1985. Lack of induced

chemical defense in juvenile Alaskan woody plants in response to

simulated browsing. Oecologia. 67:457-459.

Consolo-Murphy, S.; Hanson, D. D. 1993. Distribution of beaver in

Yellowstone National Park, 1988-89. In: Cook, R. S., ed. Ecological issues on reintroducing wolves into Yellowstone National

Park. National Park Service Science Monograph. No. 22. Denver,

CO. 38-48.

Cummins, K.; Wilzbach, M.; Gates, D.; Perry, J.; Taliaferro, W.

1989. Shredders and riparian vegetation. Bioscience. 39:24-30.

Engstrom, D. R.; Whitlock, C.; Fritz, S. C.; Wright, H. E. 1991.

Recent environmental change inferred from the sediments of

small lakes in Yellowstone’s northern range. Journal of

Paleolimnology. 5:139-174.

Houston, D. B. 1982. The Northern Yellowstone elk: ecology and

management. New York, NY: MacMillan Publishing Co. 473 p.

Jonas, R. J. 1955. A population and ecological study of the beaver

(Castor canadensis) of Yellowstone National Park. M.S. Thesis.

Moscow, ID: University of Idaho:

Karban, R.; Baldwin, I. 1997. Induced responses to herbivory.

Chicago, IL: University of Chicago Press: 319 p.

Naiman, R. J.; Johnston, C.; Kelly, J. 1988. Alteration of North

American streams by beaver. Bioscience. 38:753-762.

Naiman, R. J.; Melillo, J. M. 1984. Nitrogen budget of a subarctic

stream altered by beaver (Castor canadensis). Oecologia. 62:

150-155.

Naiman, R. J.; Melillo, J. M.; Hobbie, J. E. 1986. Ecosystem alteration of boreal forest streams by beaver (Castor canadensis).

Ecology. 67:1254-1269.

Ouellet, J. P.; Boutin, S.; Heard, D. C. 1994. Responses to simulated

grazing and browsing of vegetation available to caribou in the

Arctic. Canadian Journal Zoology. 72:1426-35.

Pengelly, W. L. 1963. Thunder on the Yellowstone. Naturalist.

14:18-25.

Robbins, C. T. 1993. Wildlife feeding and nutrition. San Diego, CA:

Academic Press. 351 p.

Robbins, C. T.; Mole, S.; Hagerman, A. E.; Hanley, T. A. 1987. Role

of tannins in defending plants against ruminants: reduction in

dry matter digestion. Ecology. 68:1606-1615.

Romme, W. H.; Turner, M. G.; Wallace, L. L.; Walker, J. S. 1995

Aspen, fire, and elk in northern Yellowstone National Park.

Ecology. 76:2097-2104.

Singer, F. J.; Mack, L.; Cates, R. G. 1994. Ungulate herbivory of

willows on Yellowstone’s northern winter range. Journal of Range

Management. 47:435-443.
USDA Forest Service Proceedings RMRS-P-11. 1999 195

Singer, F. J.; Cates, R. G. 1995. Response to comment: ungulate

herbivory on willows on Yellowstone’s northern winter range.

Journal of Range Management. 48:563-565.

Singer, F. J.; Zeigenfuss, L.; Cates, R. G.; Barnett, D. 1998. Elk,

multiple factors and persistence of willows in national parks.

Wildlife Society Bull. (In press).

Stohlgren, R. J.; Chase, N.; Pielke, R. A.; Kittel, T.; Baron, J. 1998.

Evidence that local land use practices influence regional climate,

vegetation, and stream flow patterns in adjacent natural areas.

Global Change Biology (In press).

Wagner, F. H.; Foresta, R.; Gill, R. B.; McCullough, D. R.; Pelton, M.

R.; Porter, W. F.; Salwasser, H. 1995a. Wildlife policies in the U.S.

National Parks. Washington, DC: Island Press: 242 p.

Wagner, F. H.; Keigley, R.; Wombalt, C. 1995b. Ungulate herbivory

of willows on Yellowstone’s northern winter range: Comment to

Singer et al. (1994). Journal of Range Management. 48:475-477.

 Wooley, S. C., 1998. Carbohydrate concentrations in mechanically

clipped willows on Yellowstone’s northern winter range. M.S.

Thesis. Provo, UT: Brigham Young University: 29 p.
196 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Sherel Goodrich is an Ecologist, Ashley National Forest, Vernal, UT 84078.

Durant McArthur is Project Leader and Supervisory Research Geneticist,

Shrub Sciences Laboratory, Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture, Provo, UT 84606. Allen Huber is a

Range Conservationist, Duchesne District, Ashley National Forest, U.S.

Department of Agriculture, Duchesne, UT 84021. Jeff Ott is a Biological

Technician, Shrub Sciences Laboratory, Rocky Mountain Research Station,

Forest Service, U. S. Department of Agriculture, Provo, UT 84606.

Ungulate Browsing of Two Populations of

Rubber Rabbitbrush

Sherel Goodrich

E. Durant McArthur

Allen Huber

Jeffrey E. Ott

Abstract—Utilization of willow-leaf rubber rabbitbrush (Chrysothamnus nauseosus ssp. salicifolius) was determined by twig measurements in spring and fall at two populations in Duchesne

County, Utah. These measurements indicted ungulates used between 38 and 59% of twig growth in 2 years at two sites. Use was

mostly in winter when mule deer (Odocoileus hemionus) and elk

(Cervus elaphus) were present. Cattle (Bos taurus) were also present

in summer and fall. Most of the cattle use appeared to be in the fall.

Use of two color morphs (white and green) was compared at one site.

There was no significant (P > 0.05) difference between use of marked

twigs of the color morhps. However, the percent branches browsed

did show highly significant seasonal differences between the color

morphs (P < 0.01 for three of the four dates but P > 0.2 for the fourth

date).

Rabbitbrush (Chrysothamnus) is generally considered low

preference and low forage value for ungulates. However,

the genus is far too complex for standard criteria of universal

application. Anderson (1986a) listed five sections, 16 species, and 39 subspecies for the genus, with 22 subspecies for

rubber rabbitbrush (C. nauseosus). Within the great variation of the genus are found some taxa of high forage preference by at least some ungulates. Moderate use and value of

yellowbrush or mountain low rabbitbrush (Chrysothamnus

viscidiflorus ssp. lanceolatus) has been noted by Sampson

(1919), Lommasson and others (1937), and Dayton (1931).

However, decades have passed with this plant still often

considered, by association with its relatives, to be of low or

worthless forage value, and most often studied as an object

of range control (McArthur and Meyer 1987). Although large

stands of some taxa of rubber rabbitbrush show little, if any,

ungulate use, other populations are moderately to heavily

used annually. In general, narrow-leaved plants with green

or yellow stems are less used by herbivores than are wideleaved plants with white stems (Hanks and others 1975;

McArthur and others 1979a). The study reported in this

paper is focused on wide-leaved plants with both green and

white stems. We entered the study assuming these plants

were willow leaf or mountain white rubber rabbitbrush (C.

nauseosus ssp. salicifolius). However, we wondered if the

green-stemmed plants were a different taxon.

Study Locations ________________

Based on previous observations of use of rubber rabbitbrush, two sites were selected in Duchesne County, Utah.

One site is at Bear Gulch, West Tavaputs Plateau, about 32 km

and 232 degrees from Duchesne, Utah, at 2,455 m elevation

(fig.1). This site is on an alluvial bottom with calcareous,

gravelly, loam soils developed from the Uinta Formation.

The shrubs are associated with seeded grasses (mostly

smooth brome) on the canyon bottom. Slopes adjacent to the

bottom support contrasting communities with Douglas-fir

(Pseudotsuga menziesii) on cool (northerly) aspects. Colorado pinyon (Pinus edulis), Utah juniper (Juniperus osteosperma), Alder-leaf mountain-mahogany (Cercocarpus

montanus), and Salina wildrye (Elymus salinus) are common on warmer aspects.

The other site is near Round Grove (Red Rock), Farm

Creek drainage at the south flank of the Uinta Mountains,

about 18 airline kilometers and 358 degrees from Tabiona,

Utah, at 2,350 m elevation (fig. 1). This site is also on an

alluvial bottom where basin big sagebrush (Artemisia

Figure 1—Study site locations.
USDA Forest Service Proceedings RMRS-P-11. 1999 197

tridentata ssp. tridentata), snowberry (Symphoricarpos oreophilus), Kentucky bluegrass (Poa pratensis), and thickspike

wheatgrass (Elymus lanceolatus) are common species. The

adjacent uplands support an abundance of alder-leaf mountain-mahogany and other browse species.

Methods _______________________

At the Bear Gulch site 10 rubber rabbitbrush plants were

selected for study. For each plant, 12 branches were selected for measurements. Only unbrowsed twigs were selected in the fall of each year. Heavy plastic tape was used

to mark a point on each selected twig below the point of

anticipated browsing (fig. 2). Data were collected on four

dates (22 Oct. 1991, 12 May 1992, 13 Oct. 1992, and 20 May

1993) so seasonal patterns of use and growth could be

documented. Primary and secondary twigs were measured

from the tape upward on each of these twigs in the fall after

growth had stopped and in spring before initiation of

growth for 2 years for a total of four readings. We recorded

two primary branch measurements; the first one was total

length of the branch distal to the stem and the second one

(included in the first) was that portion of the branch

between the tape and the first secondary branch. Secondary branches were only recorded if they were longer than

5 cm. Fecal group counts in three 1 by 50 m plots were made

to give an indication of relative ungulate presence at the

site (table 1). Fecal groups were swept from the plots after

they were counted. At the Round Grove site 20 rubber

rabbitbrush plants were selected with 10 plants having

greenish stems and 10 plants having whitish stems. These

plants were paired, e.g., each white-stemmed plant was

paired systematically with a green-stemmed plant of similar size within a 2 meter radius. Branch measurements and

pellet group counts were made as described above. Also 30

additional small branches per plant were observed for

utilization. Branches were recorded as used if they had any

obvious use by ungulates. Those with no obvious use were

recorded as not used. Results are shown in table 2. Mean

values that are followed with + indicate mean + standard

error of the mean. To compare the white and green color

morphs at Round Grove a paired t-test was performed

(Woolf 1968). Percent values were arcsine transformed for

data analysis but are reported herein as percent values.

Table 1—Ungulate fecal groups.

Ungulate fecal groups

Round Grove Bear Gulch

Percent Number Percent Number

 Date Ungulate Total of total per M2 Total of total per M2

05/92 Deer 9 100 0.060

Elk 0 0 0

Cow 0 0 0

10/92 Deer 4 14 0.027 1 2 0.007

Elk 0 0 0 18 34 0.120

Cow 25 86 0.167 34 64 0.227

05/93 Deer 6 23 0.040 0 0 0

Elk 18 69 0.120 29 97 0.123

Cow 2 8 0.013 1 3 0.007

Figure 2—Sampling scheme for branch measurement. The 2nd primary branch (2nd 1°) was included

in the regular primary measurement and is not discussed further in the study.

Results ________________________

Contrast of branch length between fall and spring readings indicated about 55% use at the Bear Gulch site in both

winters. This contrast indicated 59 and 36% use of the whitestemmed morph and 47 and 38% of the green-stemmed

morph at Round Grove in the winters 1991-1992 and 1992-

1993 respectively (tables 1, 2). Use of branches on individual
198 USDA Forest Service Proceedings RMRS-P-11. 1999

shrubs varied from 34 to 72% at Bear Gulch and 18 to 80%

for the white morph and from 6 to 92% for the green color

morph at Round Grove (data not shown). The 30 twig

comparisons of the white and green morphs at Round Grove

were temporally different (table 2). White morphs ranged

from 90-100%; green morphs from 30-90%. Fall readings

showed greater use of the white morph than of the green one.

Spring readings shows less difference in use between the 2

morphs than fall readings. Figure 3 documents the use and

regrowth of primary and secondary branches of willowleaf

rubber rabbitbrush at Bear Gulch and Red Rock (Round

Grove). Note that primary branches are much longer (~2x) at

Red Rock but the secondary branches (per primary branch)

are much longer (~3x) at Bear Gulch.

Discussion _____________________

Cattle were present in summer at the Round Grove site and

in one summer at the Bear Gulch site. Cattle use of this shrub

appeared to be quite limited except in the fall just before they

were removed from the sites. Considerable cattle use of

willow-leaf rubber rabbitbrush was observed in other canyons

of the Tavaputs Plateau in the fall. Pellet group counts

indicated most browsing of these shrubs at the Bear Gulch

site was a function of elk use, and at Round Grove it was

mostly a function of mule deer use in winter of 1991-1992

and elk and deer use in winter of 1992-1993 (table 3). We

suspect the different growth forms at Bear Gulch and Round

Grove are a result of more elk and cattle use on a sustained

basis at Bear Gulch so the plant’s main central stem is

Table 2—Paired t-tests for white and green morphs for ungulate use.

Percent of branches browsed

(n = 30/plant)

Date White Green t P

10/91 90.3 30.3 6.6 <0.01

05/92 98.0 68.0 4.0 <0.01

10/92 99.7 73.6 4.7 <0.01

05/93 100.0 99.0 1.4 >0.20

harvested more frequently than at Round Grove. The mule

deer at Round Grove apparently strip more secondary branches

(fig. 3).

At the Bear Gulch site, use was observed to take place as

soon as wild ungulates moved on the area in late fall or early

winter. Considerable use of this shrub occurred prior to or

concurrent with use of alder-leaf mountain mahogany on

adjacent slopes. Preference or selectivity equal to or greater

than for alder-leaf mountain mahogany is indicated for this

population. We have observed similar use of rubber rabbitbrush early in the winter season at Taylor Flat, Daggett

County, where other browse species are available. This

location in Daggett County was seeded with rubber rabbitbrush seed from a palatable population of C. nauseosus ssp.

hololeucus from Salt Creek, Juab County, Utah.

The two color morphs at Round Grove are apparently both

willow-leaf rubber rabbitbrush. Subspecies of rubber rabbitbrush are often sympatric (McArthur and others 1979b;

Anderson 1986b) but in this case the two morphs behave

quite similarly and are eaten by ungulates much the same.

The stems of the green morph are light green and not as dark

as many rubber rabbitbrush subspecies. The difference in

stem color and temporal difference in twig end browsing

(total stem browsing was not different) may be due to a small

genetic difference within the population. Readings in the fall

showed considerably higher use of twigs of the white morph

than for the green one. However, by spring the difference

was smaller. This indicates preference for the white morph

and acceptance of the green morph as preferred forage had

evened out during the winter. Early use of preferred plants

and delayed acceptance of less preferred plants as winter

progresses seems reasonable. Such a relationship has been

noted by Welch and others (1981) and Hutchings and Stewart

(1953) for ungulates and by Welch and others (1991) for sage

grouse. This relationship is not reflected in our branch

utilization measurements that compare growth with utilization at the end of winter. Had measurements been taken to

compare late fall or early winter use, branch utilization data

might have reflected preference for the white morph.

In addition to rubber rabbitbrush use, we observed use

of yellowbrush at the Bear Gulch and Round Grove sites

where it was moderately to closely hedged after each winter

browsing season.

Table 3—Summary of branch lengths and percent Use.

Date

10/91 5/92 10/92 5/93

BearGulch

Branch length (cm) 16,404 7,522 11,925 5,255

Percent usea — 55.5 ± 4.3 — 54.5 ± 2.8

Red Rock (Round Grove)

White morph

Branch length (cm) 5,604 2,178 5,736 3,240

Percent usea — 59.0 ± 5.4 — 36.4 ± 5.2

Green morph

Branch length (cm) 5,511 2,686 6,007 3,780

Percent usea — 47.4 ± 8.1 — 38.5 ± 2.7

a

Based on individual samples, 10 plants per population and 12 branches per plant.
USDA Forest Service Proceedings RMRS-P-11. 1999 199

Apparently by association with large stands of unpalatable rabbitbrush, all rabbitbrush is sometimes considered of

no forage value or at best of low value. This complex of plants

is far too variable to fit such a simplified standard criteria.

In addition to selectivity demonstrated by some ungulates at

least at some times of the year, nutritional value is indicated

to be high. In a study of seven subspecies of rubber rabbitbrush, Bhat and others (1990) found crude protein levels

about equal to that of other high-protein shrubs such as big

sagebrush and fourwing saltbush. Protein levels found in

this study exceeded protein requirements of wintering mule

deer and sheep of about 7.5-8.9% (Welch 1989). On the

Wyoming Red Desert, crude protein values of 9.7 and 6.8%

were found for summer and winter, respectively (Krysl and

others 1984). Phosphorus levels and in vitro dry matter

digestion also rated high compared to some other winter

browse species (Bhat and others 1990).

Complexity of this group of plants as well as rangelands in

general demonstrate the need to go beyond simplified standard criteria designed for universal application. Observations passed on from one generation to the next without

critical review has greatly suppressed the understanding

and use of valuable resources to be found in the rabbitbrush

complex.

References _____________________

Anderson, L. C. 1986a. An overview of the genus Chrysothamnus

Asteraceae. In: McArthur, E. D.; Welch, B. L., comps. Proceedings—symposium on the biology of Artemisia and Chrysothamnus; 1984 July 9-13; Provo, UT. Gen. Tech. Rep. INT-200. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 29-45.

Anderson, L. C. 1986b. Sympatric subspecies in Chrysothamnus

nauseosus. In: McArthur, E. D.; Welch, B. L., comps. Proceedings—symposium on the biology of Artemisia and Chrysothamnus; 1984 July 9-13; Provo, UT. Gen. Tech. Rep. INT-200. Ogden,

UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 98-103.

Bhat, R. B.; Welsh, B. L.; Weber, D. J.; McArthur, E. D. 1990. Midwinter protein, phosphorus, and digestibility of Chrysothamnus

nauseosus subspecies. Journal of Range Management. 43: 177-179.

Dayton, W. A. 1931. Important western browse plants. Misc. Pub.

101. Washington, DC: U.S. Department of Agriculture. 214 p.

Hanks, D. L.; McArthur, E. D.; Plummer, A. P.; Giunta, B. C.;

Blawer, A. C. 1975. Chromatographic recognition of some palatable and unpalatable subspecies of rubber rabbitbrush in and

around Utah. Journal of Range Management. 28: 144-148.

Hutchings, S. S.; Stewart, G. 1953. Increasing forage yields and

sheep production on Intermountain winter ranges. Circular No.

925. Washington DC: U.S. department of Agriculture, Forest

Service. 63 p.

Krysl, L. J.; Sowell, B. F.; Hubbert, M. E.; Plumb, G. E. et al. 1984.

Horses and cattle grazing in the Wyoming Red Desert, II. dietary

quality. Journal of Range Management. 37: 252-256.

Lommasson, T.; Park, B. C.; Kutzleb, C. A. and others. 1937. Range

plant handbook. Washington, DC: U.S. Department of Agriculture.

McArthur, E. D.; Blauer, A. C.; Plummer, A. P.; Stevens, R. 1979a.

Characteristics and hybridization of important Intermountain

shrubs III. INT-RP-220. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 82 p.

McArthur E. D.; Tiernan, C. F.; Welch, B. L. 1979b. Subspecies

specificity of gall forms on Chrysothamnus nauseosus. Great

Basin Naturalist. 39: 81-87.

McArthur, E. D.; Meyer, S. E. 1987. A review of the taxonomy and

distribution of Chrysothamnus. In: Johnson, K. L. Proceedings

of the Fourth Utah Shrub Ecology Workshop, the genus Chrysothamnus; 1986 September 17-18; Cedar City UT. Logan, UT:

Utah State University, College of Natural Resources: 9-17.

Sampson, A. W. 1919. Plant succession in relation to range management. U.S. Department of Agriculture Bull. 791. Washington,

DC: U. S. Department of Agriculture. 76 p.

Welch, B. L. 1989. Nutritive value of shrubs. In: McKell, C. M., ed.

The biology and utilization of shrubs. San Diego: Academic Press

Inc.: 405-424.

Welch, B. L.; McArthur, E. D.; Davis, J. N. 1981. Differential preference

of wintering mule deer for accessions of big sagebrush and for black

sagebrush. Journal of Range Management. 34: 409-411.

Welch, B. L.; Wagstaff, F. J.; Roberson, J. A. 1991. Preference of

wintering sage grouse for big sagebrush. Journal of Range Management. 44: 462-465.

Woolf, C. M. 1968. Principles of Biometry. Princeton, NJ: D. Van

Nostrant Co., Inc. 359 p.

Figure 3—Branch lengths over the course of the study. Left—Bear

Gulch, Right—Red Rock (Round Grove).
200 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

C. J. Murray, L. L. Cadwell, J. L. Downs, and M. A. Simmons are Research

Scientists in the Applied Geology and Geochemistry Group (CJM) and the

Ecology Group (LLC, JLD, and MAS), Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352.

Fusing Vegetation Data Sets to Provide a

Spatial Analysis of Sage Grouse Habitat on

the Army’s Yakima Training Center

C. J. Murray

L. L. Cadwell

J. L. Downs

M. A. Simmons

Abstract—Resource and land managers need better methods for

deriving detailed spatial environmental data to support resource

management decisions. This paper presents a case study for the

U.S. Army’s Yakima Training Center (YTC) that demonstrates the

fusion of plot-level field data with a detailed land/vegetation cover

map to describe habitat characteristics across cover types. An

advanced geostatistical algorithm, sequential Gaussian simulation

with locally varying means, was used to fuse field data on vegetation

parameters with Geographic Information System (GIS) data on

vegetation cover types present at the study site and provide spatial

interpolation of the data. The resulting vegetation data raster

layers were used to develop a spatial habitat suitability index (HSI)

for the western subspecies of sage grouse on the YTC. Using an HSI

allows ecologists and site managers to examine the spatial distribution of areas that provide suitable habitat for sage grouse.

This paper describes the application of a geostatistical

method used to fuse two different data types, a GIS map of

vegetation cover type and field data collected for five different vegetation variables from across the landscape.

Geostatistics is a specialized form of spatial statistics that

develops quantitative models for the spatial continuity of

variables using variogram analysis, then estimates or simulates the values at unsampled locations using either kriging

or a stochastic simulation technique based on kriging (Isaaks

and Srivastava 1989; Goovaerts 1997). This approach allows

effective estimation of the value of a variable at locations

where field data are not available. The products of the data

fusion are spatially explicit map layers that can then be used

as input to models or for ecosystem management decision

making. In this exercise, the geostatistical estimates were

used to create raster layers for vegetative variables, which

were then used as input to a spatial habitat suitability index

(HSI) model.

We adopted the basic framework of a draft HSI for sage

grouse in Washington State (Ashley 1998). After reviewing

extensive vegetation data sets available for the U.S. Army’s

Yakima Training Center (YTC), and based on our own

habitat-related studies of the species (Eberhardt and

Hofmann 1991; Cadwell and others 1994, 1997; Sveum

1995), we chose a subset of the Ashley variables to represent

current sage grouse nesting habitat for the YTC. The selected variables we used for the modified version of Ashley’s

model were grass cover, forb cover, exotic weed cover, sagebrush height, sagebrush cover, and sagebrush species.

The YTC is an important military training area used to

maintain readiness for wartime and contingency operations. The facility is also home to one of only two small

populations of western sage grouse (Centrocercus

urophasianus phaios) in the state, which the Washington

Department of Fish and Wildlife recently listed as “threatened.” Because of the potential for training activities to

destroy sage grouse habitat, the Army’s Directorate of Environment and Natural Resources identified the need for an

HSI model for sage grouse on the YTC. The HSI model,

displayed as a map layer, will be used to plan and schedule

training so impacts to sage grouse habitat are minimized.

Methods _______________________

Site

The YTC occupies 1,322 km2 in east-central Washington.

It is part of the shrub-steppe ecoregion of Washington State

and part of the big sagebrush (Artemisia tridentata)/

bluebunch wheatgrass (Pseudorgeneria spicata) vegetation

zone. Area climate is characterized by hot, dry summers and

cold, dry winters. Annual precipitation is approximately 20

cm, and temperatures range from –4°C in January to 40°C

in July. A 322 km2 portion of the YTC, which represents

prime sage grouse habitat, was used for this study.

Vegetation Data

A detailed vegetation and land cover map for the sage

grouse protection area on the YTC was reclassified to delineate 13 cover types with respect to sage grouse habitat

requirements (fig. 1A). The level of detail included in the

mapping efforts allowed us to separate cover classes not only

by plant community type or land use, but also to separate

units where shrub cover was sparse (<5%) or patchy, from

areas where shrub cover was continuous.
USDA Forest Service Proceedings RMRS-P-11. 1999 201

Figure 1—Maps of sage grouse protection area at Yakima Training Center: (A) vegetation

cover type; (B) spatial distribution of sagebrush cover at the site from geostatistical

mapping; (C) spatial distribution of habitat suitability index for sage grouse.
202 USDA Forest Service Proceedings RMRS-P-11. 1999

 Several different data sets were used to quantify the

vegetation characteristics within each cover type at a number of points across the modeling landscape (fig. 1A and

table 1). The primary data set used was the Army’s Land

Condition Trend Analysis Data (LCTA) for the site for 1996.

The methodology used for LCTA data collection provided

information on the relative cover of grasses, forbs, exotic

weeds, and sagebrush height. Four other existing data sets

relevant to the sage grouse modeling area were used in

addition to the LCTA data. Two of those data sets included

transect data describing shrub characteristics (100-m lineintercept measurements), while a third data set was composed of data gathered along 100-m transects and quadrats

to describe both shrub and herbaceous vegetation (Canfield

1941; Daubenmire 1970). Ocular estimates of species cover

and height gathered through ground reconnaissance during

vegetation mapping constituted the fourth additional data

set. These five data sets were individually summarized to

provide numerical values for sagebrush cover, sagebrush

height, perennial forb cover, perennial grass cover, and

exotic weed cover at each field sampling point in the sage

grouse protection area. The sixth HSI variable, sagebrush

species, was determined for each cover type by evaluating

both the original mapped cover type and the shrub cover

data for all sampling points within that cover type.

Geostatistical Methods

Geostatistical methods were used to estimate the values of

five of the vegetation variables discussed above (sagebrush

cover, sagebrush height, perennial forb cover, perennial

grass cover, and exotic weed cover) on a 100-m-square grid

across the study area. For each variable, the geostatistical

estimations were conditioned on two different types of data:

the point data measurements of the variable and the vegetation cover map. The vegetation cover map allowed us to

constrain the geostatistical estimates based on the variation

in mean values for the variables among cover types. Sequential Gaussian simulation with a locally varying mean was

applied to fuse the data sets and ultimately generate the

habitat characteristic layers [implemented through the

GSLIB program SGSIM (Deutsch and Journel 1998)].

Several analysis steps were required for each vegetation

variable. Mean values of each variable for each cover type

were determined from the available field data from within

the respective cover types. Most variables had skewed distributions, so the median values for habitat variables, rather

than the means, were normally retained because they were

more representative of the central value of the data. To apply

the Gaussian simulation algorithm used in the study, point

measurements of each variable first were transformed to a

univariate normal distribution using a graphical normal

score transform (Deutsch and Journel 1998). Residuals from

the local means were calculated for each data point by

subtracting the normal score for the mean of all data measured for the relevant cover type from the normal score

transform of the value measured at a data point. The

variogram calculation and modeling (Isaaks and Srivastava

1989) for each variable were performed on the residual

normal scores of the point data using the GSLIB program

GAMV (Deutsch and Journel 1998). The variogram models

for each variable were then used with the locally varying

mean option of SGSIM to generate 100 simulations of the

spatial distribution of each variable. Because each simulation was conditioned on the point measurements and the

cover type present at each grid node, each simulation in the

suite of realization represents an equally probable map of

the variable that honors the conditioning data and the

spatial continuity model captured in the variogram model.

The suite of simulated values at each grid node can be used

as an estimate of the local, conditional-distribution function,

and statistics calculated on the suite of simulated values can

be used to estimate values at each grid node (Goovaerts

1997). For this study, the median simulated value at each

grid node was retained as the estimate for each variable and

used to generate the raster layers defining vegetation characteristics for numerical input to the HSI model.

Habitat Suitability Index

Habitat Suitability Index models are used to assess the

ability of a habitat to support a species. Variables for the

model are developed through an understanding of the biology of the species and characteristics of the habitat. For each

Table 1—Relative area of each cover type and number of samples of each variable by cover type.

Cover type Relative area Sage cover Sage height Perennial grass Exotics Perennial forbs

Percent

(Big sagebrush)/bunchgrass 14.82 50 56 41 41 41

[Big sage-bitterbrush]/bunchgr 8.00 30 35 20 20 20

Big sagebrush/bunchgrass 31.90 99 121 80 80 80

Bunchgrass 4.76 17 17 15 15 15

Cheatgrass 0.08 2 2 2 2 2

Facility 0.27 1 1 1 1 1

Greasewood/grass 0.15 2 2 2 2 2

Lithosol/goldenweed/sand. bluegrass 10.60 30 33 29 29 29

Quarry 0.11 0 0 0 0 0

Rabbitbrush/bunchgrass 7.29 19 22 17 17 17

Sand. bluegrass/Grays desertp 0.16 7 7 6 6 6

Stiff sagebrush/bunchgrass 0.96 5 6 6 6 6

Threetip sage/bunchgrass 20.87 45 54 47 47 47

Total 100.00 307 356 262 262 262
USDA Forest Service Proceedings RMRS-P-11. 1999 203

variable in the model, a relationship is constructed between

the level of the variable and a measure or index of how

different levels of that variable affect the suitability of the

habitat. The index ranges from 0 (for poor habitat) to 1 (for

excellent habitat). The overall HSI is generally calculated as

the geometric mean of all the parameters. The HSI model for

a species or population is represented as an equation of

several variables whose individual value may range between

“0” for the poorest habitats and “1” for the best habitats.

For the six variables in the HSI (grass cover, forb cover,

exotic weed cover, sagebrush height, sagebrush cover, and

sagebrush species), we used the habitat relationships developed by Ashley (1998) for the Washington State sage grouse

population (see appendix A):

(GC * FC * EC)1/3 *[ (SC * SH)1/2 * SS] 1/2

where:

GC = grass cover

FC = forb cover

EC = exotic weed cover

SC = sagebrush cover

SH = sagebrush height

SS = sagebrush species

Geostatistical analysis generated map layers for five of

the six variables needed by the HSI. The sixth map layer,

sagebrush species, was generated as a reclassification of the

vegetative land cover map. The HSI map layer was produced

using the six map layers as input to the model function in the

ERDAS IMAGINE GIS software package. The function

evaluates the model for each grid node in the study area and

produces a map (fig. 1C) showing the distribution of the HSI

across the landscape.

Results and Discussion __________

Analysis of the available plot-level vegetation data by

cover type revealed major differences in mean values for

each of the five variables between the different cover types

(table 2). These differences in mean values for sagebrush

cover and height and bunchgrass cover reflect differences

expected for the different habitat types and help substantiate the accuracy of the cover type map.

The spatial continuity of the five vegetation variables was

examined by calculating the experimental variograms for

the residual normal scores and fitting spherical variogram

models (Isaaks and Srivastava 1989) to the experimental

variograms of all variables. Figure 2 plots an example, the

variogram for the normal score residuals of the sagebrush

cover data. The range of spatial correlation of the variables

varied from 1,200 to 3,500 m (table 3). The relative nugget

effect, which is a measure of the proportion of the variability

in the data that cannot be accounted for by spatial variation

at the scale of the variogram models, ranged from 60 to 75%.

This indicates that a large proportion of the variability in the

normal score residuals occurs at distances less than 160 m,

the shortest lag interval that could be calculated for the

variograms. The magnitude of the relative nugget can be due

to several sources, the most common of which are variability

in the measurement process and spatial variability that

occurs over short distances. Both effects probably contribute

to the relative nugget in this case. No directional difference

in spatial continuity (i.e., anisotropy, see Isaaks and

Srivastava 1989), was identified in the variogram modeling.

The lack of spatial anisotropy and the high relative nugget

effects are both caused in part by transformation of the data

to normal score residuals, which removes some of the largescale trend information inherent in the data. This spatial

information is not “lost” though, because the trend information is recaptured in the simulation process when the cover

type data are fused with the point data using the locally

varying mean simulation algorithm.

Conditional Gaussian simulation with locally varying means

was used to generate raster layers depicting the spatial

distributions of each of the five variables. Figure 1B is an

example showing the spatial distribution of sagebrush cover

at the site. Statistical analysis over the set of cover types in the

map area showed that the median values estimated at each

grid node did an excellent job of reproducing the local means

for the cover types. Shifts in the local mean across cover type

boundaries can be seen by comparison of the sagebrush cover

map (fig. 1B) and the cover type map (fig. 1A).

Table 2—Means of vegetation data by cover type.

Cover type Sage cover Sage height Perennial grass Exotic Perennial forbs

Percent Cm - - - - - - - - - - - - - - - - Percent - - - - - - - - - - - - - - - - 

(Big sagebrush)/bunchgrass 1 36.3 36 4 4

[Big sage-bitterbrush]/bunchgr 3.5 40 20.5 4 12

Big sagebrush/bunchgrass 15.2 47.3 40 2 4

Bunchgrass 0.5 26.2 42.1 4 15

Cheatgrass 0 0 0 100 0

Facility 0 0 0 23 1

Greasewood/grass 5 63 23 23 1.5

Lithosol/goldenweed 1 10 20 1 14

Quarry 0 0 0 00

Rabbitbrush/bunchgrass 0.25 10.2 41.9 5 2

Riparian 0 0 0 00

Sand. bluegrass/Grays desertp 0.1 8.6 20 2 27

Stiff sagebrush/bunchgrass 10 27.5 16.5 3 4

Threetip sage/bunchgrass 12 42 50 1 9

Water 0 0 0 00
204 USDA Forest Service Proceedings RMRS-P-11. 1999

Residual normal scores for the point data exhibited spatial continuity ranging from 1 to 3 km, indicating that a

geostatistical mapping approach was suitable. Statistics

calculated for point measurements of habitat characteristics

by cover type (table 2) at the YTC site showed marked

differences between the different shrubland cover types.

This indicates that the cover type maps capture real differences in habitat characteristics, which can then be reproduced by the geostatistical simulations. The resulting raster

layers of habitat characteristics closely honor the GIS cover

type map and capture detail and information not possible

with other methods of gridding point data (e.g., inverse

distance or spline algorithms).

The HSI values from evaluation of the model (fig. 1C)

ranged from 0 to 1. The values (table 4) were in three

predominant groups, with 20% of the area having a low

range of HSI values (< = 0.2), another 20% having a middle

range (0.5 to 0.6), and 30% having a high range of HSI values

(>0.8).

Conclusions____________________

Many resource management decisions require detailed

habitat or site information that is readily available only

through field inventory or sampling. Such sampling efforts

are often of limited scope because of budget constraints,

time, and personnel. Neither field point data collection nor

vegetation cover mapping alone provide adequate information on which to base management decisions. Using

geostatistical methods allowed us to merge data sets collected at different scales to realistically represent landscape-scale habitat characteristics that could not otherwise

be mapped. Our simulations of spatial variation in habitat

characteristics across the study area were applied to habitat

suitability assessment. This combination of geostatistical

techniques and GIS-based methods of data integration could

also be applied to fuse data sets of different scales such as

remote sensing imagery from satellites or aerial sources

with field inventory data to address a number of other

ecological applications. Digital data sets describing spatial

habitat or vegetation characteristics such as those generated using this methodology are critical to landscape modeling efforts and management of resources.

Acknowledgments ______________

This work was funded by the U.S. Department of the Army

through a Related Services Agreement with the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.

The authors wish to acknowledge Margaret Pounds of the

U.S. Army Directorate of Environment and Natural Resources, Yakima Training Center, whose vision and guidance made this work possible.

References _____________________

Ashley, P. R. 1998. Personal communication of draft sage grouse

HSI model. Spokane, WA: Washington Department of Fish and

Wildlife.

Cade, B. S.; Sousa, P. J. 1985. Habitat suitability index models:

ruffed grouse. Washington DC: Western Energy and Land Use

Team, Division of Biological Services, Research and Development, Fish and Wildlife Service. 42 p.

Cadwell, L. L.; Simmons, M. A.; Downs, J. L.; Sveum, C. M. 1994.

Sage grouse on the Yakima Training Center: a summary of

studies conducted during 1991 and 1992. Richland, WA: Pacific

Northwest Laboratory. 36 p.

Cadwell, L. L.; Simmons, M. A.; Nugent, J. J.; Cullinan, V. I. 1997.

Sage grouse habitat on the Yakima Training Center: Part II

Habitat modeling. Richland, WA: Pacific Northwest Laboratory.

54 p.

Table 3—Parameters of variogram models fit to residual normal

scores of vegetation data.

Variable Range Relative nugget

M Percent

Sagebrush cover 1,200 65

Sagebrush height 1,400 75

Perennial forb cover 3,500 60

Perennial grass cover 1,400 70

Exotic weed cover 3,500 60

Figure 2—Variogram of normal score residuals for

sagebrush cover data. The diamonds represent the

experimental variogram values calculated from the

data and the solid line represents the model fit to the

experimental variogram.

Table 4—Percent of the sage grouse

study area within specified

ranges of HSI values.

HSI range Percent of area

Percent

0 to <=0.1 10

>0.1 to <=0.2 10

>0.2 to <=0.3 5

>0.3 to <=0.4 7

>0.4 to <=0.5 7

>0.5 to <=0.6 19

>0.6 to <=0.7 8

>0.7 to <=0.8 3

>0.8 to <=0.9 12

>0.9 to <=1.0 19

Gamma(h) = 0.65 + .35 Sph. 1,200(h)

0 2,500 5,000 7,500 10,000 12,500
USDA Forest Service Proceedings RMRS-P-11. 1999 205

Canfield, R. 1941. Application of the line interception method in

sampling range vegetation. J. Forestrey 39:388-394.

Deutsch, C. V.; Journel, A. G. 1998. GSLIB: Geostatistical software

library and user’s guide. New York: Oxford University Press.

340 p.

Eberhardt, L. E.; Hofmann, L. A. 1991. Sage grouse on the Yakima

Training Center: a summary of studies conducted during 1989

and 1990. Richland, WA: Pacific Northwest Laboratory. 54 p.

Goovaerts, P. 1997. Geostatistics for natural resources evaluation.

New York: Oxford University Press. 483 p.

Isaaks, E. H.; Srivastava, R. M. 1989. An introduction to applied

geostatistics. New York: Oxford University Press. 561 p.

Appendix A ____________________

Relationships between habitat variables and habitat suitability indices for sage grouse at the Yakima Training

Center from Ashley (1998). The first five variables (A-E)

came from the model for the nesting and brood rearing

Prose, B. L. 1987. Habitat suitability index model. Plains sharptailed grouse. Washington DC: National Ecology Center, Fish

and Wildlife Service. 31 p.

Schroeder, R. L. 1984. Habitat suitability index models: blue grouse.

Washington DC: Western Energy and Land Use Team, Division

of Biological Services, Research and Development, Fish and

Wildlife Service. 19 p.

Sveum, C. M. 1995. Habitat selection by sage grouse hens during the

breeding season in south-central Washington. Master’s Thesis.

Oregon State University, Corvallis, OR. 86 p.

population; the sixth variable was associated with the winter population. The variables are: (A) grass cover; (B) forb

cover; (C) exotic weed cover; (D) sagebrush cover; (E) sagebrush height, and (F) sagebrush species.

1

0.8

0.6

0.4

0.2

0

0 5 10 15 20

Percent

HSI Value

A

1

0.8

0.6

0.4

0.2

0

0 2 4 10 12

Percent

HSI Value

B

1

0.8

0.6

0.4

0.2

0

0 40 100

Percent

HSI Value

C

1

0.8

0.6

0.4

0.2

0

0 20 40 50 70

Percent

HSI Value

D

10 30 60

1

0.8

0.6

0.4

0.2

0

0 30 60 75 105

Height (cm)

HSI Value

E

15 45 90 120 135

1

0.8

0.6

0.4

0.2

0

None, A. rigida

Species

HSI Value

F

A. tridentata

tridentata

A. tripartata A. tridentata

wyomingensis
206 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Steven A. Lei is an Undergraduate Student, Department of Electrical and

Computer Engineering, University of Nevada, Las Vegas, 4505 Maryland

Parkway, Las Vegas, NV 89154-4026. Simon A. Lei is a Professor of Biology

and Ecology and Leslie J. Thomas is an Undergraduate Student, Department

of Biology, Community College of Southern Nevada, 6375 West Charleston

Boulevard, Las Vegas, NV 89146-1139.

Ecological Leaf Anatomy of Seven

Xerophytic Shrub Species in Southern

Nevada

Steven A. Lei

Simon A. Lei

Leslie J. Thomas

Abstract—Variations in leaf anatomical structures of seven xerophytic shrub species were quantitatively examined at a creosote

bush-blackbrush ecotone in the Newberry Mountains of southern

Nevada. Leaves of creosote bush, white bursage, brittle-bush, Anderson wolfberry, thornbush, and turpentine bush were amphistomatic.

More trichomes and a thicker cuticle were observed on the adaxial

relative to abaxial leaf blades in all seven shrub species. Xerophytic

leaves characteristically had uniseriate epidermis, abaxial spongy

parenchyma with little intercellular air spaces, and multiple layers

of isolateral palisade parenchyma. However, thick, fleshy leaves of

Anderson wolfberry contained large intercellular air spaces and

large spongy mesophyll with a weakly developed palisade. Uniseriate

hypodermis was observed in blackbrush, thornbush, and turpentine

bush leaves. Blackbrush leaves were hypostomatic with revolute

leaf margins, and possessed a biseriate epidermis. Multiple layers

of bifacial palisade parenchyma, with fairly large intercellular

space in the abaxial spongy parenchyma were detected in blackbrush

leaves only. Anatomical features of blackbrush leaves were more

typical of chaparral than desert shrubs. Not all plants in deserts

shared typical xerophytic leaf anatomical structures in southern

Nevada.

Deserts cover approximately one-third of the total land on

earth (Goudie and Wilkinson 1988). Aridity is primarily a

function of climatic components, including temperature,

rainfall, and evaporation (Goudie and Wilkinson 1988).

Perennial plants of the North American deserts are generally xerophytes because their leaf anatomical structures

have been largely associated with aridity of habitats

(Oppenheimer 1960; Mauseth 1988). Some xeromorphic leaf

characteristics include dense trichomes, well-developed waxy

cuticle, reduction of leaf size and intercellular air space,

expansion in leaf thickness and palisade mesophyll, as well

as high surface to volume ratio (Culp 1986). Abundant

pubescence, small leaf size, and high internal leaf surface to

outer surface interact to increase water use efficiency in

desert plants. Leaf pubescence is an important regulator of

light absorbance, and small, narrow leaves are more efficient energy dissipators and lose less water per unit leaf area

than large, broad leaves (Barbour and others 1987). The

palisade parenchyma can increase the internal surface area

of a leaf without increasing the external surface area (Culp

1986). The development of elongated palisade parenchyma is

densely packed on both side of leaves at the expense of spongy

parenchyma and intercellular air space is a well-known

xeromorphic phenomenon (Culp 1986). Shedding all or portions of plant leaves in xerophytes, such as white bursage

(Ambrosia dumosa), blackbrush (Coleogyne ramosissima),

and Anderson wolfberry (Lycium andersonii), is also an

ecophysiological response to aridity.

However, not all plants in deserts share a typical xerophytic leaf anatomy. Brittle-bush (Encelia farinosa), a common woody perennial of the Sonoran and Mojave Deserts,

possesses large, broad leaves. Leaves of Anderson wolfberry

have an extremely large spongy parenchyma layer and

intercellular spaces at the expense of poorly developed

palisade parenchyma layer (Gibson 1996). Hypodermis is

observed in thornbush (Menodora spinescens) and turpentine bush (Thamnosma montana) from relatively cool desert

habitats (Gibson 1996). Hypostomatry, hypodermis, and

revolute leaf margins appear in blackbrush plants that

establish at higher elevations in cool climates (Gibson 1996).

Despite its xeromorphic appearance, blackbrush exhibits

sclerophyllous leaves that are more typical of chaparral

plants than desert shrubs (Rundel and Gibson 1996). The

sclerophyll leaf design, a characteristic of Mediterraneantype climate, is generally interpreted as a response to arid

habitats with water deficits and poor soil nutrients (Gibson

1996). Nevertheless, these xerophytic characteristics would

not be an advantage under water-sufficient environments.

Anatomical observations of leaves provide an ecological

tool for delineating the amplitude of plants’ adaptations to

aridity. The objective of this study was to quantitatively

investigate variations in leaf anatomy of seven xerophytic

shrub species in a creosote bush-blackbrush ecotone in the

Newberry Mountains of southern Nevada.

Methods _______________________

Collection Site and Anatomical Studies

Fresh leaves were collected at the creosote bush-blackbrush

ecotone in Christmas Tree Pass of the Newberry Mountains

(roughly 35°20' N, 114°50' W) during Fall 1997. The study

area, located southeast of Searchlight, Nevada, and northwest of Davis Dame, Arizona (fig. 1), is in the jurisdiction of
USDA Forest Service Proceedings RMRS-P-11. 1999 207

the Bureau of Land Management and National Park Service. The weather patterns for southern Nevada is characterized by wide-ranging daily air temperatures, high yearround temperatures, extremely high potential evaporation,

little cloud cover, low relative humidity, low annual precipitation. Southern Nevada resembles the Mediterranean-type

climate characterized by hot, dry summers and cool, wet

winters (table 1). Episodic monsoonal winds and thunderstorms occur during summer seasons. Winter rainfalls,

although varying considerably from year to year, contribute

to most of the total annual precipitation. The terrain is

exposed to abundant solid rocks. The rocky slopes and

alluvial fans are dissected by dry wash channels. Soils of the

Newberry Mountains are poorly developed and are

composed primarily of weathered granite and limestone

bedrock. Organic decomposition and soil formation are slow

due to the arid nature of the region.

The creosote bush-blackbrush ecotone was subdivided

into the upper and lower halves. Three common shrub

species—creosote bush (Larreatridentata), white bursage, and

brittle-bush—dominate the lower half (elevation <1,000 m),

while four shrub species—blackbrush, thornbush, Anderson

wolfberry, and turpentine bush—dominate the upper half

(elevation >1,100 m) of the ecotone. For each of the seven

xerophytic shrub species, ten mature plants were randomly

selected. For anatomical studies, two fresh leaves from each

plant were randomly collected without regard to specific

canopy positions. Tiny pieces of leaf tissues were thinly

sliced. An optical microscope, with a build-in microscopic

(um) measurement in the ocular lens and with a total

magnification of 40x, was used to determine relative tissue

thickness and percentage. Relative tissue percentage of each

shrub species was computed by dividing the tissue thickness

of each compartment by the total laminal thickness.

Statistical Analyses

Significant differences in mean adaxial/abaxial ratio,

upper/lower palisade parenchyma ratio, and percent mesophyll (palisade and spongy) among the seven shrub species

was tested with one-way analysis of variance (ANOVA) and

Tukey’s Multiple Comparison Test (Analytical Software

1994). Mean values for each shrub species were presented

Figure 1—Location of the Newberry Mountains near

the extreme southern tip of Nevada in the southwestern United States. Searchlight of Nevada and Davis

Dam of Arizona are in the vicinity of the Newberry

Mountains.

Table 1—Mean monthly air temperature and precipitation for the region surrounding the

Newberry Mountains. Christmas Tree Pass lies approximately half-way in

elevation between Searchlight and Davis Dam. The length of weather record in

Searchlight of Nevada and Davis Dam of Arizona was 29 and 24 years,

respectively. Weather data were obtained from Holland, 1982.

Searchlight Davis Dam

Month Air temperature Precipitation Air temperature Precipitation

°C mm °C mm

January 6.7 19.0 11.1 14.8

February 8.9 12.8 16.3 8.8

March 11.3 17.3 16.3 13.3

April 15.4 11.3 20.9 7.0

May 20.3 4.0 25.6 3.8

June 25.6 2.5 30.4 0.8

July 29.3 22.5 34.3 5.8

August 28.1 22.0 33.3 14.0

September 24.7 10.0 29.6 6.3

October 18.8 11.8 23.4 6.5

November 11.3 14.8 16.5 10.0

December 7.1 17.8 12.1 14.0
208 USDA Forest Service Proceedings RMRS-P-11. 1999

with standard errors, and p < 0.05 was reported as statistically significant.

Results and Discussion __________

All seven xerophytic shrub species had a few anatomical

structures in common. Their leaves contained trichomes

with dense, waxy cuticles on both sides of blades, although

creosote bush possessed few trichomes. Trichomes are

effective in blocking excess sunlight. The adaxial epidermis

of these xerophytes had more abundant trichomes, a thicker

cuticle, and more waxes than the abaxial epidermis (data

not shown). The adaxial epidermis were thicker than abaxial

epidermis in all seven species (tables 2 and 3). Mean

adaxial/abaxial epidermal ratio was significantly different

(p < 0.001; fig. 2) among the seven shrub species, and the

overall mean epidermal ratio was 1.34. Turpentine bush

revealed the highest, while creosote bush showed the lowest

mean adaxial/abaxial epidermal ratio (table 3). My data

generally concur with Gibson’s (1996) study, indicating that

mean epidermal thickness rarely exceeds 30 um, and mean

adaxial/abaxial epidermal ratio was 1.21. The adaxial dermis characteristically has more dense trichomes, a thicker

cuticle, and more waxes than the abaxial epidermis to

greatly reduce cuticular transpiration losses and to reflect

excessive sunlight (Mauseth 1988). When comparing with

other species, blackbrush leaves exhibited the greatest epidermal thickness, exceeding 30 um (table 3) due to the

presence of biseriate epidermis.

Table 2—Mean tissue thickness and tissue percentage (excluding cuticles, trichomes, and

intercellular spaces) of three xerophytic shrub species at the lower half of the

creosote bush-blackbrush ecotone in the Newberry Mountains, Nevada. Mean

values are expressed with standard errors (n = 20 leaves per shrub species).

Creosote bush White bursage Brittle-bush

Tissue thickness (um)

Lamina 374.8 ± 4.9 473.3 ± 5.1 354.6 ± 6.4

Upper epidermis 22.5 ± 0.7 18.5 ± 1.1 21.3 ± 1.1

Hypodermis Absent Absent Absent

Upper palisade parenchyma 133.1 ± 2.5 117.2 ± 3.6 118.1 ± 3.2

Spongy parenchyma 65.6 ± 2.4 211.9 ± 3.5 106.4 ± 3.4

Lower palisade parenchyma 131.6 ± 3.7 110.1 ± 3.4 94.7 ± 2.7

Lower epidermis 22.0 ± 0.7 15.6 ± 0.4 14.2 ± 0.5

Tissue percentage (%)

Upper epidermis 6.0 ± 0.1 3.9 ± 0.2 6.0 ± 0.2

Hypodermis Absent Absent Absent

Upper palisade parenchyma 35.5 ± 0.5 24.8 ± 0.7 33.3 ± 0.5

Spongy parenchyma 17.5 ± 0.5 44.7 ± 0.7 30.0 ± 0.5

Lower palisade parenchyma 30.9 ± 0.8 23.3 ± 0.07 26.7 ± 0.4

Lower epidermis 5.9 ± 0.1 3.3 ± 0.04 4.0 ± 0.08

Table 3—Mean tissue thickness and tissue percentage (excluding cuticles, trichomes, and intercellular

spaces) of four xerophytic shrub species at the upper half of the creosote bush-blackbrush

ecotone in the Newberry Mountains, Nevada. Mean values are expressed with standard errors

(n = 20 leaves per shrub species).

Blackbrush Anderson wolfberry Turpentine bush Thornbush

Tissue thickness (um)

Lamina 378.7 ± 4.2 617.8 ± 5.2 169.9 ± 4.3 125.6 ± 3.9

Upper epidermis 20.1 ± 1.3 19.2 ± 1.8 8.2 ± 0.5 3.3 ± 0.2

Hypodermis 33.7 ± 1.4 Absent 13.8 ± 0.8 20.9 ± 0.8

Upper palisade 172.4 ± 3.1 45.1 ± 1.9 68.5 ± 2.7 43.6 ± 1.0

Spongy parenchyma 134.4 ± 2.6 539.3 ± 3.5 47.9 ± 2.1 19.9 ± 0.8

Lower palisade Absent Absent 27.2 ± 1.4 35.1 ± 1.1

Lower epidermis 18.2 ± 0.6 14.2 ± 0.7 4.1 ± 0.5 2.8 ± 0.1

Tissue percentage (%)

Upper epidermis 5.3 ± 0.3 3.1 ± 0.3 4.8 ± 0.1 2.6 ± 0.02

Hypodermis 8.9 ± 0.3 Absent 8.1 ± 0.2 16.6 ± 0.2

Upper palisade 45.5 ± 0.7 7.3 ± 0.3 40.3 ± 0.5 34.7 ± 0.3

Spongy parenchyma 35.5 ± 0.6 87.3 ± 0.7 28.2 ± 0.4 15.8 ± 0.2

Lower palisade Absent Absent 16.0 ± 0.3 27.9 ± 0.3

Lower epidermis 4.8 ± 0.1 2.3 ± 0.1 2.4 ± 0.1 2.2 ± 0.03
USDA Forest Service Proceedings RMRS-P-11. 1999 209

Figure 2—Mean adaxial/abaxial epidermal ratio

of seven shrub species at the creosote bushblackbrush ecotone in the Newberry Mountains,

Nevada. Different letters at the top of columns

indicate significant differences at p < 0.05 based

on ANOVA and Tukey’s Multiple Comparison

Test. Symbols: creosote bush (CB); white

bursage (WB); brittle-bush (BR); blackbrush (BB);

anderson wolfberry (AW); turpentine bush (TB);

and thronbush (TH).

Figure 3—Mean upper/lower palisade parenchyma ratio of seven shrub species at the creosote bush-blackbrush ecotone in the Newberry

Mountains, Nevada. Leaves of blackbrush and

Anderson wolfberry do not contain lower palisade layers. Different letters at the top of columns indicate significant differences at p < 0.05

based on ANOVA and Tukey’s Multiple Comparison Test. Symbols of shrub species are

explained in Figure 2.

The upper palisade parenchyma was thicker than the

lower palisade parenchyma in this study. The upper/lower

palisade parenchyma ratio was significantly different (p <

0.001; fig. 3), ranging from 1.05 in creosote bush to 2.50 in

turpentine bush. The overall mean parenchyma ratio was

1.42 among the five species. However, lower palisade layers

were completely absent in blackbrush and Anderson wolfberry leaves. Leaves of all seven xerophytic species possessed

a tremendously thick zone of mesophyll (palisade and spongy

parenchyma), ranging from 74.0% in thornbush to 94.6% in

Anderson wolfberry, excluding trichomes (fig. 4). Mean

percent mesophyll thickness also varied significantly (p <

0.001; fig. 4) among the seven shrub species, and overall

mean mesophyll thickness was 86.3%. A thick zone of

mesophyll is typical of non-succulent upper canopy xerophytic leaves, and mean mesophyll thickness is 84%, ranging from 66 to 94% of the total laminal thickness, excluding

trichomes (Gibson 1996).

At lower elevations of the creosote bush-blackbrush ecotone, creosote bush, white bursage, and brittle-bush plants

shared a similar leaf anatomy. Leaves were amphistomatic

and hypodermis was completely absent. Isolateral (unifacial)

palisade parenchyma was detected, although the adaxial

palisade was consistently thicker by less than 10% than the

abaxial palisade in all three species (table 2). However, on

average, adaxial palisade is approximately 20% thicker

than the abaxial zone in leaves of desert plants (Gibson

1996). Within the mesophyll, the tremendously thick zone of

palisade parenchyma surrounded the spongy parenchyma

Figure 4—Mean percent mesophyll thickness of

seven shrub species at the creosote bushblackbrush ecotone in the Newberry Mountains,

Nevada. Narrow vertical bars denote standard

errors of the means. Different letters at the top of

columns indicate significant differences at p <

0.05 based on ANOVA and Tukey’s Multiple

Comparison Test. Symbols of shrub species are

explained in Figure 2.

0.0

Adaxial/abaxial ratio 1.5

CB

Shrub species

0.5

1.0

2.5

2.0

WB BR BB AW TB TH

a ab a

b

b

ab

c

0

Upper/lower palisade ratio

2

CB

Shrub species

1

3

WB BR TB TH

a a

c

b

b

b

0

Mean mesophyll thickness (%)

CB

Shrub species

30

60

120

90

WB BR BB AW TB TH

a ab a

b

b

ab

c cd c b d a b
210 USDA Forest Service Proceedings RMRS-P-11. 1999

with small intercellular spaces was observed. Leaf transection of white bursage, creosote bush and brittle-bush shows

that large, isolateral palisade parenchyma is separated by

small, central spongy parenchyma (Gibson 1996).

Blackbrush and associated shrub species—thornbush,

turpentine bush, and Anderson wolfberry—were frequently

established at cooler and higher elevations of the creosote

bush-blackbrush ecotone (table 3). Uniseriate hypodermis,

consisting of large, highly vacuolate parenchyma, was

present in blackbrush, thornbush, and turpentine bush

leaves (table 3). Hypodermis is typically absent or weakly

developed among warm-desert representatives, being more

common in green-stemmed species of cool deserts and

semiarid vegetation types (Gibson 1996). Leaves of greenstemmed, such as thornbush and turpentine bush, also

closely fit the anatomical profiles of typical warm, lowland

desert shrubs with amphistomatry, uniseriate epidermis,

and isolateral palisade mesophyll (Gibson 1996). Isolateral

mesophyll in leaves of white bursage, creosote bush, brittlebush, thornbush, and turpentine bush were observed

(tables 2 and 3). However, fleshy leaves of Anderson wolfberry exhibited a poorly developed adaxial palisade parenchyma, but exhibited an extremely thick zone of spongy

parenchyma with large intercellular spaces (table 3). Spongy

mesophyll in desert leaves has been interpreted as water

reservoir or water-storing tissue (Shields 1950). Fleshy

leaves of Anderson wolfberry typically shed during water

stress. Thick leaves of Anderson wolfberry have large

mesophyll parenchyma cells and have seldom exhibited a

well-defined palisade layer (Gibson 1996).

Blackbrush had a completely different internal leaf

design from its associated xerophytic shrub species at the

creosote bush-blackbrush ecotone (tables 2 and 3). Leaves

of thornbush, turpentine bush, and Anderson wolfberry

were amphistomatic, while leaves of blackbrush were

hypostomatic with stomates appearing only at the abaxial

leaf surface. More than 90% of non-succulent woody perennials in warm, inland deserts have amphistomatic leaves

(Gibson 1990). The placement of stomata on both upper and

lower epidermises, instead of limited to one surface such as

in blackbrush, would maximize CO2 uptake per unit area.

Plants showing hypostomatic desert leaves with hypodermis generally do not occur in the most arid sites because

they are probably not successful colonizers of warm, low

elevation desert habitats (Gibson 1996).

The palisade parenchyma, rich in chloroplasts and occurring close together in multiple (two to five) layers, is found

on both sides of the leaves in white bursage, brittle-bush,

thornbush, turpentine bush, and creosote bush. Nevertheless, the palisade parenchyma was present on the adaxial

surface only in blackbrush leaves (table 3), which correspond

with Gibson’s (1996) study.

Additionally, biseriate epidermis (table 3), revolute leaf

margins, and fairly large intercellular spaces in the spongy

parenchyma appeared only in blackbrush leaves (data not

shown). A hypodermis occurs more often in tough and

sclerophyllous leaves; thinner, softer leaves generally do not

have a hypodermis (Mauseth 1988). Leaves of typical

sclerophyllous shrubs, which endure summer drought stress,

are tough because they possess thick cell walls in adaxial

epidermis and a well-cutinized adaxial surface. These leaves

also include revolute leaf margins, hypostomatry, multiple

epidermis, uniseriate hypodermis, and bifacial mesophyll

(Gibson 1996). Xerophytic leaves tend to have a high internal surface-to-volume ratio because there is an increased

contact between mesophyll cells to reduce water loss, and

consequently form small intercellular air spaces (Mauseth

1988). Despite their xeromorphic appearance, transection of

blackbrush leaves was more characteristic of chaparral

plants with a Mediterranean-type climate, as opposed to

typical warm, lowland desert plants. In this study, there are

at least two potential explanations for the sclerophyllous leaf

design in blackbrush plants. First, hypostomatry, uniseriate

hypodermis, and revolute leaf margins are characteristics of

relatively cool and high elevation desert (semiarid) habitats,

corresponding with the nearly monospecific blackbrush

shrublands. Second, the Mojave Desert of southern Nevada

resembles a Mediterranean-type climate, characterized by

hot, dry summers and cool, wet winters.

Conclusions and Implications _____

A variety of leaf anatomy was detected among the seven

xerophytic shrub species in southern Nevada. Amphistomatry and uniseriate epidermis were observed in leaves

of six shrub species other than blackbrush. Hypodermis was

present in blackbrush, thornbush, and turpentine bush

leaves only. Bifacial palisade parenchyma was present in

blackbrush and Anderson wolfberry leaves only. Hypostomatry, biseriate epidermis, revolute leaf margins, and

large intercellular air spaces were present in blackbrush

leaves only. The anatomical profile of blackbrush leaves

was more typical of chaparral than desert leaves. Despite

similar xeromorphic appearance, leaves of seven shrub

species exhibited few anatomical similarities. In all seven

species, the adaxial epidermis was thicker than abaxial

epidermis, and mesophyll (palisade and spongy parenchyma) comprised a large percentage of leaf compartment.

Devising a formal and universal description for xerophytic leaves has been unsuccessful in this study. Variations in leaf anatomy are numerous, ranging from dense to

sparse trichomes, well- to poorly-developed palisade parenchyma, bifacial to unifacial palisade, amphistomatry

to hypostomatry, and large to small intercellular spaces

in the spongy parenchyma. Yet, these shrub species have

leaf anatomical characteristics that are especially adapted

to arid environment where water is frequently scarce.

Discovering anatomical variations among xerophytic

shrub species show the usefulness of plant anatomy in

detecting substantially different internal leaf designs

within the creosote bush-blackbrush ecotone. Hence, not

all plants growing in hot, dry environments share similar

anatomical adaptations to aridity in the Newberry Mountains of southern Nevada.

Acknowledgments ______________

We sincerely thank the Department of Science at the

Community College of Southern Nevada for providing logistical support and thank David Charlet for providing critical

review.
USDA Forest Service Proceedings RMRS-P-11. 1999 211

References _____________________

Analytical Software. 1994. Statistix 4.1, an interactive statistical

program for microcomputers. St. Paul, MN: Analytical Software. 329 p.

Barbour, M. G.; Burk, J. H.; Pitts, W. D. 1987. Terrestrial Plant

Ecology. Menlo Park, CA: The Benjamin/Cummings Publishing

Company, Inc. 634 p.

Culp, M. G. 1986. Anatomical and Morphological Adaptations of

Plants to Aridity in Death Valley National Monument. Las

Vegas, NV: Cooperative National Park Resources Studies Unit. 65 p.

Gibson, A. C. 1996. Structure-function Relations of Warm Desert

Plants. Berlin, Germany: Springer-Verlag. 215 p.

Goudie, A.; Wilkinson, J. 1988. The Warm Desert Environments.

Cambridge, United Kingdom: Cambridge University Press. 87 p.

Holland, J. 1982. A floristic and vegetation analysis of the Newberry

Mountains, Clark County, Nevada. Las Vegas, NV: Cooperative

National Park Resources Studies Unit. 211 p.

Mauseth, J. D. 1988. Plant Anatomy. Menlo Park, CA: The

Benjamin/Cummings Publishing Company, Inc. 560 p.

Oppenheimer, H. R. 1960. Adaptation to drought: Xerophytism.

Plant-water relationships in arid and semiarid conditions.

Reviews of Research, UNESCO. Arid Zone Research 15:105-138.

Rundel, P. W.; Gibson, A. C. 1996. Ecological Communities and

Processes in a Mojave Desert Ecosystem: Rock Valley, Nevada.

Cambridge, MA: Cambridge University Press: 369 p.

Shields, L. M. 1950. Leaf xeromorphy as related to physiological and

structural influences. Botanical Review 16:399-447.
212 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Steven A. Lei is an Undergraduate Student, Department of Electrical and

Computer Engineering, University of Nevada, Las Vegas, 4505 Maryland

Parkway, Las Vegas, NV 89154-4026. Simon A. Lei is a Professor of Biology

and Ecology, Department of Biology, Community College of Southern

Nevada, 6375 West Charleston Boulevard, Las Vegas, NV 89146-1139.

Ecology of Psammophytic Plants in the

Mojave, Sonoran, and Great Basin Deserts

Steven A. Lei

Simon A. Lei

Abstract—A vegetation survey of the 15 selected inland sand

dunes in the Mojave, Sonoran, and Great Basin Deserts was conducted in spring 1997. Plant communities on dunes consisted of a

mixture of dune, marginal dune (ecotone), and adjacent non-dune

habitats. Creosote bush (Larrea tridentata) was a dominant shrub

in all three habitats in the warm deserts, but became fewer and

larger in the dune habitats. Four-wing saltbush (Atriplex canescens)

was found at all dune sites, but was particularly abundant in the

Great Basin dunes. Bugseed (Dicoriacanescens) and Indian ricegrass

(Oryzopsis hymenoides) were widespread in both warm and cold

deserts. Psammophytes require special adaptations for dune environments in addition to the arid desert environments. Although all 15

dunes look similar in general appearance, each dune system was

unique in terms of plant assemblages and environmental conditions.

Active inland sand dunes cover less than 1% of the North

American deserts. The vegetation of desert sand dunes is

floristically and ecologically distinct from the surrounding

habitats. Previous studies have shown that psammophytes

possess a number of adaptations to their environment (Bowers 1982, 1986; Pavlik 1980, 1985, 1989). Endemic species,

long dry seasons, high temperatures, low soil nutrient levels, as well as mobile and abrasive sand with coarse texture

are characteristics of inland desert dunes (Pavlik 1985;

Bowers 1986). Habitat homogeneity, extremely poor edaphic

conditions, and degree of sand movement (accumulation

and excavation) are the most important factors affecting

distribution and species composition of plant communities

in a single dune field (Bowers 1982). Dune habitats are

floristically simple compared to adjacent non-dune habitats

(Lei, personal observation). Low species diversity in sand

dunes is largely due to instability of sand substrates and lack

of habitat diversity (Bowers 1982). Seedlings of herbaceous

plants are abundant after adequate rainfall, but they may

die within a few months and are covered or excavated by

drifting sand (Brown 1972).

Many perennial psammophytes have extensive root systems or rhizome networks that form adventitious roots to

secure water, nutrients, and anchorage in mobile substrates

(Barbour and others 1987). Failure to form adventitious

roots can lead to oxygen deprivation as sand piles higher and

higher on active dunes (Bowers 1986). The main stems of

most plants on active dunes grow rapidly to keep reproductive and photosynthetic organs above the level of accumulating sand (Bowers 1982). Four-wing saltbush (Atriplex

canescens), locoweed (Astragalus spp.), desert willow

(Chilopsis linearis), bugseed (Dicoria canescens), evening

primose (Oenothera avita), Indian ricegrass (Oryzopsis

hymenoides), honey mesquite (Prosopis grandulosa), and

Nevada ephedra (Ephedra torreyana) are some of the plants

with rapid growth adaptations to active sand (Bowers 1982).

Additionally, many plants on the dunes, such as saltbush

(Atriplex spp.) and desert marigold (Baileya pleniradiata),

have a silver, white, or gray coat of hairs to avoid overheating caused by sunlight.

Although inland dunes look similar in general appearance

and in the spacing of vegetation, they differ in overall size,

shape, climate, elevation, and plant assemblage. Size and

composition of sand particles, together with climate, latitude,

and elevation, largely account for differences in vegetation

among inland dunes (Brown 1972). Plant diversity is

strongly and positively correlated with annual rainfall

(Pavlik 1989). Based on geographic locations, the northern

(Great Basin) dunes generally have more rainfall, cooler air

temperature, and greater plant diversity than southern

(Mojave and Sonoran/Colorado Deserts) dunes (Brown 1972;

Pavlik 1989). Creosote bush (Larrea tridentata) is a dominant shrub on the southern dunes, while four-wing saltbush

tends to be the most abundant shrub on the northern dunes

(Brown 1972).

Although sand dune ecosystems in the deserts appear

simple, they are fairly complex and delicately balanced.

Sand dunes are biological islands isolated by their physical

and biological properties and by factors related to the evolution of the landscape through time (Brown 1972). Because

inland dunes have low economic and agricultural values,

they are one of the least studied ecosystems in the southwestern deserts. The objective of this study is to examine

differences in vegetation, with particular regard to plant

assemblages in relation to ecological conditions among the

15 active inland dunes in Utah, Nevada, and California.

Methods _______________________

Study Areas

Common woody and herbaceous plant species were observed

from the 15 active inland dune systems in Utah, Nevada, and

California during spring 1997 (fig. 1). With respect to regional

vegetation, five of the dunes were associated with the Mojave

Desert, three with the Sonoran Desert, and five with the Great
USDA Forest Service Proceedings RMRS-P-11. 1999 213

Basin (table 1). Elevations varied considerably, ranging from

well below sea level in Death Valley of southern California

to approximately 1,850 m in Coral Pink Dunes of southern

Utah (table 1). Geographic locations also varied widely,

ranging from approximately 33°00' to 39°35' N in latitude to

from 110°25' to 119°00' W in longitude (fig. 1 and table 1).

Dunes from the Great Basin were situated at higher latitudes and elevations which, in turn, have lower mean

annual temperature and higher mean annual precipitation

than dunes of the Mojave and Sonoran/Colorado Deserts

(Pavlik 1989). The substrates were deep, unstable, and

coarse-grained on all 15 dunes. Dunes with abundant vegetation are more or less stabilized, and may eventually cause

soil to develop as in Rice Valley of southern California. The

negative impact of past and present off-road vehicles on

vegetation may be significant on some of the dunes, including the Kelso and Algodones Dunes of southern California.

Vegetation Surveys

A vegetation survey of dune, marginal dune (ecotone), and

adjacent non-dune plant communities was conducted in

each of the 15 active dune systems. Woody and herbaceous

plant species were identified. Only plant species that were

commonly established in each of the three habitats were

recorded in this study.

Results and Discussion __________

Among the 15 inland dunes, the transition of vegetation

from the alluvial fans to the sand dune was sharp. Most of

the shrub companions of creosote bush and saltbush disappeared, whereas grasses adapted to sand appeared. Populations of creosote bush were found on all dunes in the Mojave

and Sonoran Deserts (tables 2 and 3), and were generally

taller and larger (up to 3.5 m) than their non-dune counterparts. From casual observations, creosote bush populations

often displayed a circular pattern to form nebkas, indicating

sand accretion and community stabilization through time.

The accretion of sand layers increases the amount of water

penetrating the soil to a depth where it is protected from

direct evaporation. Felger (1980) believes that creosote bush

grows rapidly enough to outstrip sand accumulation and

may also reflect patches of superior moisture conditions on

active dunes. Creosote bush is accompanied by carpets of

showy, colorful annual plants in rainy years (Danin 1996).

Figure 1—Location of 15 inland sand dunes surveyed in

Utah, Nevada, and California. Dune systems are numbered as follows: 1 = Mono, 2 = Cresent, 3 = Eureka Dunes,

4 = Death Valley, 5 = Ash Meadows, 6 = Corn Creek Dunes,

7 = Baker, 8 = Kelso, 9 = Twentynine Palms, 10 = Borrego

Springs, 11 = Algodones, 12 = Rice Valley, 13 = Navajo

Dunes, 14 = Coral Pink, and 15 = Little Sahara.

Table 1—Characteristics of the 15 selected inland sand dunes. Location, type of desert, as well as

approximate elevation (m), latitude (N), and longitude (W) of each dune system are shown.

Dune systems are arranged alphabetically within each desert type.

Dune system County, State Latitude Longitude Elevation Desert

m

Ash Meadows Nye, NV 36°20' 116°15' 670 Mojave

Corn Creek Clark, NV 35°50' 115°35' 910 Mojave

Death Valley Inyo, CA 36°35' 117°05' < 0 Mojave

Eureka Inyo, CA 37°

05' 117°40' 930 Mojave

Baker San Bernardino, CA 35°05' 116°00' 430 Mojave

Kelso San Bernardino, CA 34°55' 115°40' 670 Mojave

Twentynine Palms San Bernardino, CA 34°

00' 115°55' 450 Mojave

Algodones Imperial, CA 33°00' 115°10' 90 Sonoran

Borrego Springs San Diego, CA 33°10' 116°05' 280 Sonoran

Rice Valley Riverside, CA 34°

00' 114°50' 210 Sonoran

Coral Pink Kane, UT 36°50' 112°30' 1,830 Great Basin

Crescent Nye, NV 38°15' 117°20' 1,570 Great Basin

Little Sahara Juab, UT 39°35' 112°25' 1,780 Great Basin

Mono Mono, CA 38°10' 119°00' 1,980 Great Basin

Navajo Navajo, AZ 36°55' 110°25' 1,530 Great Basin
214 USDA Forest Service Proceedings RMRS-P-11. 1999

Table 2—Common woody and herbaceous species occurred in the dune, marginal dune (ecotone), and

adjacent non-dune habitats of the Mojave Desert. Plant species within each dune system are

arranged alphabetically. Saltbush (Atriplex spp.) include both A. canescens and A. confertifolia;

Russian thistle (Salsola spp.) include S. australis and S. paulsenii unless otherwise noted.

Annual and herbaceous perennial species are indicated by the asterisks.

Dune system Dune Marginal dune Non-dune

Ash Meadows Atriplex spp. Atriplex spp. Ambrosia dumosa

Hymenoclea salsola Larrea tridentata Larrea tridentata

Salsola spp.* Salsola spp.*

Baker Allenrolfea occidentalis Atriplex spp. Ambrosia dumosa

Atriplex spp. Dicoria canescens* Larrea tridentata

Dicoria canescens* Hymenoclea salsola

Corn Creek Atriplex canescens Atriplex canecens Ambrosia dumosa

Atriplex confertifolia Hymenoclea salsola Larrea tridentata

Prosopis grandulosa Larrea tridentata

Death Valley Atriplex spp. Atriplex spp. Atiplex spp.

Larrea tridentata Larrea tridentata Larrea tridentata

Salsola tetrabdra* Achnatherum hymenoides Atriplex polycarpa

Eureka Atriplex spp. Atriplex polycarpa Larrea tridentata

Astragalus lentiginosus Dicoria canescens

Dicoria canescens Swallenia alexandrae

Swallenia alexandrae Tiquilia plicata

Kelso Atriplex spp. Atriplex spp. Ambrosia dumosa

Austragalus lentiginosus* Cryptantha micrantha* Cryptantha micrantha

Larrea tridentata Larrea tridentata Larrea tridenta

Stipa hymenoides* Tiquilia plicata* Schismus barbatus*

Twentynine Allenrolfea occidentalis Atriplex spp. Ambrosia dumosa

Palm Atriplex spp. Dicoria canescens* Bromus rubens

Hymenoclea salsola Hymenoclea salsola Larrea tridentata

Larrea tridentata

Table 3—Common woody and herbaceous species occurred in the dune, marginal dune (ecotone),

and adjacent non-dune habitats of the Sonoran Desert. Plant species within each dune

system are arranged alphabetically. Saltbush (Atriplex spp.) include both A. canescens

and A. confertifolia unless otherwise noted. Annual and herbaceous perennial species are

indicated by the asterisks.

Dune system Dune Marginal dune Non-dune

Algodones Atriplex spp. Atriplex spp. Ambrosia dumosa

Dicoria canescens* Cercidium floridum Ephedra nevadensis

Ephedra nevadensis Chilopsis linearis Fouquieria splendens

Larrea tridentata Prosopis grandulosa Larrea tridentata

Borrego Springs Atriplex spp. Atriplex spp. Agave desertii

Larrea tridentata Larrea tridentata Ambrosia dumosa

Prosopis grandulosa Prosopis grandulosa Atriplex spp.

Rice Valley Ambrosia dumosa Atriplex spp. Ambrosia dumosa

Atriplex spp. Cercidium floridum Fouquieria splendens

Ephedra nevadensis Hymenoclea salsola Larrea tridentata

Hilaria rigida* Larrea tridentata

Populations of saltbush were established on all 15 dunes

and marginal dunes (tables 2-4). Stutz and others (1975)

state that on the Little Sahara Dunes in Utah, a diploid

population of the normally tetraploid four-wing saltbush is

well adapted to active sand by abnormally rapid growth.

Seedlings of diploid four-wing saltbush grow twice as fast as

tetraploid seedlings (Bowers 1982). Most of the diploid fourwing saltbush occur on the lee side (slip face) of dunes where

soil moisture is favorable and burial is rapid; thus their

speedy growth is necessary for survival (Bowers 1982).

In the dune sites, creosote bush, white bursage (Ambrosia

dumosa), and ocotillo (Fouquieria splendens) were some of

the plants commonly established in the Sonoran Desert

(table 3), while big sagebrush (Artemisia tridentata), rubber

rabbitbrush (Chrysothamnus nauseosus), and Utah juniper

(Juniperus osteosperma) were found in the Great Basin

Desert (table 4). In the stabilized marginal dunes, creosote

bush, bugseed (Dicoria canescens), cheesebush (Hymenoclea

salsola), Indian ricegrass, and locoweed (Astragalus spp.)

were some of the plants commonly established in the Sonoran
USDA Forest Service Proceedings RMRS-P-11. 1999 215

Desert, whereas saltbush big sagebrush, rubber rabbitbrush, bitterbush (Purshia tridentata), and Indian ricegrass

were found in the Great Basin Desert (tables 2 and 4). Indian

ricegrass was widely scattered throughout the active sand

area in the Mojave and Great Basin Deserts (tables 2 and 4).

Kelso Dunes of the Mojave Desert and many dunes of the

Great Basin consisted of a variety of annual plants (tables 2

and 4). The abundance of annuals offers an advantage in

response to extreme abiotic and edaphic conditions found on

dunes, especially with mobile substrates. Pavlik (1985)

states that physiological features of annuals, including high

rates of carbon assimilation and growth, minimize the time

that vulnerable vegetative tissues are exposed to strong

winds, as well as to burial, deflation, and abrasion of sand.

Annual plants simply escape environmental extremes and

stresses as seeds. Seeds usually germinate where sand

movement is less intense and moisture is closer to the soil

surface. Emergence of seedlings is best at depths of 1-2 cm,

and none emerged from below about 8 cm of sand (Emerson

1935; Bowers 1982).

Most of the plants on desert dune fields are xerophytes

(tables 2-4). Many of the dune perennials occurred on the

marginal dunes, and were more abundant at the adjacent

non-dune habitats where the sand is relatively stable. Creosote bush, white bursage, and big sagebrush commonly established at marginal dunes (tables 2 and 4) and have stabilized

the perimeter of the dune field. None of these plants grew in

the central, active dune field where sand movement was most

intense. In this study, perennials, such as saltbush and

creosote bush, often produced ephemeral shoots and possessed rhizomes or rootstocks that could maintain buds near

the dune surface despite sand accumulation. Perennial plants

growing on active dunes must form adventitious roots,

which can reach a considerable length. However, the root

system of such plants are not as dense as in non-dune plants

Table 4—Common woody and herbaceous species occurred in the dune, marginal dune (ecotone), and

adjacent non-dune habitats of the Great Basin Desert. Plant species within each dune system are

arranged alphabetically. Saltbush (Atriplex spp.) include both A. canescens and A. confertifolia

unless otherwise noted. Annual and herbaceous perennial species are indicated by asterisks.

Dune system Dune Marginal dune Non-dune

Coral Pink Atriplex canescens Artemisia tridentata Artemisia tridentata

Stipa hymenoides* Atriplex canescens Chrysothamnus nauseosus

Chrysothamnus nauseosus Juniperus osteosperma

Crescent Atriplex canescens Artemisia tridentata Artemisia tridentata

Abronia turbinata* Atriplex spp. Juniperus osteosperma

Cleome sparsifolia* Austragalus sabulonum*

Lupinus pusillus* Stipa hymenoides*

Little Sahara Atriplex canescens Atriplex spp.* Artemisia tridentata

Dicoria canescens* Gilia leptomeria* Chrysothamnus nauseosus

Salsola spp.* Lupinus pusillus* Juniperus osteosperma

Mono Atriplex spp. Atriplex spp. Artemisia tridentata

Abronia turbinata* Abronia turbinata* Juniperus osteosperma

Cleome sparsifolia* Distchilis spicata* Purshia tridentata

Lupinus pusillus* Lupinus pusillus* Chrysothamnus nauseosus

Chrysothamnus nauseosus

Navajo Chrysothamnus spp. Artemisia filifolia Artemisia tridentata

Poliomintha incana Artemisia tridentata Bouteloua gracilis

Sporobolus cryptandrus Chrysothamnus spp. Gutierrezia spp.

Poliomintha incana Juniperus osteosperma

(Bowers 1986). Saltbush and creosote bush, widespread

plants at many dune fields, are relatively insensitive to

minor environmental changes. Bowers (1986) suggests that

the gene pool of saltbush and creosote bush is so large and

varied that it could survive any particular environmental

upheaval. However, no such large and varied gene pool

exists for psammophytes with relatively small populations;

they are highly susceptible to extinction through time (Bowers 1986). Significant or subtle changes in climatic and

edaphic conditions can have negative impacts on

psammophytes with small populations, which may not have

enough genetic variability to adjust (Bowers 1986).

The seeds of most perennial pioneer species found on the

active inland dunes are not adapted to long-distance dispersals, but simply fall beside or a short distance away from the

parent plant (Bowers 1982). From casual observations, seeds

from nearby communities landed on the sand, but only a few

germinated and became established. Moreover, halophytic

plants were frequently found on dune sites (tables 2-4),

although they are not psammophytic plants. In this study,

halophytes that grew on inland dunes include saltbush,

pickleweed (Allenrolfea occidentalis), seepweed (Suaeda

torreyana), and sand dropseed (Sporobolus cryptandrus).

These halophytes were observed in Baker and Twentynine

Palms of the Mojave Desert in southern California (table 3).

Honey mesquite was a dominant tree occurring at dune

sites of Death Valley and Algodones in the Mojave and

Sonoran Deserts, respectively (tables 2 and 3). Only a few

trees, such as desert willow of the Kelso Dunes and honey

mesquite of the Death Valley Dunes, are able to outstrip

sand accumulation by producing adventitious roots (Bowers

1982). Deep roots are starved for oxygen unless the plants

can form adventitious roots. Desert willow and honey mesquite, a typical of riparian trees, are not specially adapted

to sand dunes. Bowers (1986) states that formation of
216 USDA Forest Service Proceedings RMRS-P-11. 1999

adventitious roots is an adaptation for survival on floodplains along riparian corridors, where occasional floods deposit silt and sand around the trunks. Desert willow can also

form leafy shoots when submerged in sand and can survive

numerous burials and resurrections (Bowers 1986).

On the contrary, cacti were nonexistent on active dunes in

this study, partially because they grow too slowly to outstrip

accumulating sand and are not well adapted to mobile

substrates. Cacti also have shallow root systems and are

highly vulnerable to excavation of sand by wind. Despite

having a special mode of photosynthesis that enables cacti to

conserve water and manufacture sugars simultaneously,

they pay a heavy price for conserving water; they simply

grow too slowly (Bowers 1986). However, cacti were grown

only at the adjacent non-dune plant communities where

sand substrates were considerably more stable in this study.

Another problem psammophytes must experience is high

air temperatures. Photoinhibition may occur when leaf

temperatures are high. Many plant species, such as winterfat

(Ceratoides lantata), bugseed, and saltbush, have adapted to

excess light and heat by evolving silvery, white, or gray

leaves with abundant trichomes (Bowers 1986). Leaf hairs

help plants regulate the leaf temperatures by blocking out

some of the intense light, and by reducing water loss through

transpiration from the leaf surface.

Although the total number of dune-adapted species known

to form beneficial associations with microorganisms is not

large, only a small fraction of the total flora of western desert

dunes has been investigated for such associations. Saltbush

and big sagebrush form symbiotic associations with vesicular-arbuscular mycorrhiza, which increases absorption of

nutrients, particularly phosphorus from the soil (Bowers

1982; Williams and Aldon 1976). In this study, saltbush and

big sagebrush were dominant species on the Little Sahara

and adjacent non-dune community, respectively. Indian

ricegrass, locoweed, and big sagebrush form symbiotic associations with nitrogen-fixing bacteria (Wullstein and others

1979). Nitrogen fixation by bacteria associated with roots of

vascular plants may largely contribute to their nitrogen

economy in harsh sand dune environments.

Desert sand dunes are one of the least studied ecosystems

in the southwestern United States largely due to their low

economic and agricultural values. Differences in plant assemblages and environmental conditions among the 15 inland

dunes were observed. Despite such differences, dunes are

characterized by unique physical and edaphic conditions and

support limited plant species. Although desert sand dunes

can potentially support additional plant species, not enough

existing species possess the adaptation necessary to colonize

dunes, and not enough speciation events have occurred to

permit new species to fulfill these niches.

Acknowledgments ______________

Brett Riddle and David Charlet provided stimulating

discussion and critical review to greatly improve this manuscript. Jason Alexander assisted with identifying some of the

psammophytes. The Motor Pool of the University of Nevada,

Las Vegas, provided partial logistical support.

References _____________________

Bowers, J. E. 1982. The plant ecology of inland dunes in western

North America. Journal of Arid Environments 5:199-220.

Brown, J. H. 1972. Species diversity of seed-eating desert rodents in

sand dune habitats. Ecology 54:775-787.

Barbour, M. G.; Burk, J. H.; Pitts, W. D. 1987. Terrestrial plant

ecology (2nd ed.). Menlo Park, CA: The Benjamin/Cummings

Publishing Company, Inc. 634 p.

Danin, A. 1996. Plants of desert dunes. Springer-Verlag, Berlin,

Germany. 177 p.

Emerson, F. 1935. An ecological reconnaissance in the White Sands,

New Mexico. Ecology 16:226-233.

Felger, R. S. 1980. Vegetation and flora of the Gran Desierto,

Sonora, Mexico. Desert Plants 2:87-114.

Pavlik, B. M. 1980. Patterns of water potential and photosynthesis

of desert sand dune plants, Eureka Valley, California. Oecologia

46:147-155.

Pavlik, B. M. 1985. Sand dune flora of the Great Basin and Mojave

Deserts of California, Nevada, and Oregon. Madrono 32:197-213.

Pavlik, B. M. 1989. Photogeography of sand dunes in the Great

Basin and Mojave Deserts. Journal of Biogeography 16:227-238.

Stutz, 1975. Evolutionary studies of Atriplex: a relic gigas diploid

population of Atriplex canescens. American Journal of Botany

62:236-245.

Williams, S. T.; Aldon, E. F. 1976. Endomycorrhizal (vesiculararbuscular) associations of some arid zone shrubs. Southwestern

Naturalist 20:437-444.

Wullstein, L. H.; Bruening, M. L.; Bollen, W. B. 1979. Nitrogen

fixation associated with sand grain root sheaths (Rhizosheaths)

of certain xeric grasses. Physiologia Plantarum 46:1-4.
USDA Forest Service Proceedings RMRS-P-11. 1999 217

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Simon A. Lei is a Professor of Biology and Ecology, Department of Biology,

Community College of Southern Nevada, 6375 West Charleston Boulevard,

Las Vegas, NV 89146-1139.

Effects of Severe Drought on Biodiversity

and Productivity in a Creosote BushBlackbrush Ecotone of Southern Nevada

Simon A. Lei

Abstract—Plant responses to severe drought was investigated in a

creosote bush-blackbrush (Larreatridentata-Coleogyne ramosissima)

ecotone in Cold Creek Canyon of the Spring Mountains in southern

Nevada. Initial vegetation data were collected in June 1993, with

data comparably collected on approximately the same dates in 1997.

Species richness, density, frequency, percent vegetation cover, and

above-ground biomass of annuals and biomass of herbaceous perennials were significantly reduced during the 1997 drought compared

to the moist 1993 year. Many annual plants simply escaped drought

as seeds. However, species richness, density, frequency, and percent vegetation cover of woody plants were not significantly different, and were less prone to drought. Xerophytic plants of various

life-forms utilized different adaptive strategies to reduce and cope

with water stress. A severe drought in spring 1997 limited local

biodiversity and productivity, especially the winter ephemerals in

the creosote bush-blackbrush ecotone of southern Nevada.

Drought refers to a period with low precipitation in which

the water content of the soil greatly reduces and the plants

suffer from lack of water. Substantial rainfall variability is

a major factor in the occurrence of drought. Tilman and

Haddi (1992) state that the instability caused by environmental fluctuations may limit species richness, density, and

above-ground biomass (productivity) in Minnesota. Climatically extreme conditions, such as drought, may periodically

lower population densities (Tilman and Haddi 1992). They

(1997) further suggest that rapid local and regional climatic

change may be occurring, and may impact the biodiversity of

otherwise undisturbed environments.

The dominant plant life-form in southern Nevada is the

shrub, although subshrub, herbaceous perennials, and annual (ephemeral) life-forms constitute a significant fraction

of the total vegetation (Lei 1994). In warm, lowland deserts,

large trees are generally absent, except on flood-plains along

riparian corridors. Many shrubs lose all or a portion of their

leaves during droughts (Lei 1994). Herbaceous perennials,

which die back to the ground surface during drought periods,

are also common (Lei, personal observations). Woody species

can be classified into drought-tolerant, drought-deciduous,

and succulent.

Creosote bush (Larrea tridentata), white bursage (Ambrosia dumosa), and blackbrush (Coleogyne ramosissima) are

three dominant shrub species in southern Nevada. Creosote

bush-blackbrush shrublands often form relatively broad

ecotones (Lei and Walker 1997). Species density and diversity are generally higher in ecotonal areas than in the

adjacent creosote bush-white bursage and nearly monospecific blackbrush shrublands. Stable vegetation assemblages,

dominated by creosote bush, white bursage, and blackbrush

occur on the oldest, least disturbed geomorphic surfaces

(Webb and others 1987). West (1983) states that composition

and productivity of annuals vary considerably from year to

year because they rely heavily on the timing and amount of

precipitation.

The droughts in southern Nevada are unpredictable in

terms of their duration and time of initiation. Previous

vegetation studies in southern Nevada have documented

that climatic patterns strongly influence the distribution of

plant communities, and weather patterns influence the

germination of annual plants (Beatley 1966, 1967, 1969,

1974, 1976). The aim of this study was to quantitatively

investigate how plants of various life-forms responded to

severe drought at a creosote bush-blackbrush ecotone in

southern Nevada.

Methods _______________________

Field Surveys

Vegetation analysis was conducted on approximately the

same dates in June of 1993 and 1997 at the creosote bushblackbrush ecotone in Cold Creek Canyon (36°15'

N, 115°15'W;

elevation 1,350-1,550 m; fig. 1) of the Spring Mountains,

located approximately 60 km northwest of Las Vegas, Nevada. Data on species richness, density, frequency, and

percent cover of woody taxa were compared between 1993

and 1997. Density, frequency, percent vegetation cover, and

above-ground biomass of annual and herbaceous perennial

plants were determined and compared between these two

years. Prior to harvesting the herbaceous vegetation, two

sets of 9-month weather data, from October 1992 through

June 1993 and from October 1996 through June 1997, were

included because winter precipitation is an important source

of moisture during the early growing season (table 1). However, weather data after June were excluded because woody

vegetation were surveyed and herbaceous vegetation were

harvested by the end of June, and precipitation after this

month would not influence the results for that year.

Initial vegetation data were collected in 1993, with data

comparably collected in 1997. Fifteen elevational transects at

five elevational sites were established. A total of 75, 100-m2

circular plots were placed across the entire creosote bushblackbrush ecotone. Plots within each transect were placed at
218 USDA Forest Service Proceedings RMRS-P-11. 1999

a fixed elevational interval of 30 m with directions from

evident landmarks, and topographic maps were used to

ensure that plots could be easily found in subsequent years

to facilitate repeated vegetation surveys. Brightly colored

flagging tapes were tagged on shrubs that occurred at the

center of each plot for ease of visualization. Altimeter was

used to detect elevation. Within each plot, all plant species

were identified using Munz (1974). Woody taxa were quantified to determine species richness, densities, and frequencies. Annual and herbaceous perennial taxa were quantified

to determine species richness, densities, frequencies,

percent vegetation cover, and above-ground living plant

biomass. Individuals of annual plants were counted within a

randomly selected 1-m2 in each plot for density measurement before harvesting to determine above-ground biomass.

Percent cover of woody and herbaceous (annuals and perennials) vegetation was visually estimated on 10% increments. Herbaceous perennial plants were harvested within

a randomly selected 16-m2 in each plot. The harvested

annuals and herbaceous perennials was then transported to

a laboratory and oven-dried at 50 °C for 72 h, and weighted

to determine above-ground living plant biomass.

Statistical Analyses

Vegetation data from all five elevations within 1 year

(1993 or 1997) were pooled. One-way analysis of variance

(ANOVA), followed by Tukey’s Multiple Comparison Test

(Analytical Software 1994) were performed to detect significant differences in mean species richness, and to compare

site means when a significant drought effect was detected,

respectively. Student t-tests (Analytical Software 1994) were

used to detect significant differences in woody and herbaceous vegetation between the moist 1993 and arid 1997

years. Mean values are presented with standard errors, and

statistical significance is determined at p < 0.05.

Results ________________________

Winter and spring 1993 were considerably more moist

than the winter and spring 1997 (table 1). Abundant rainfall

occurred in December 1992, and in January and February

1993, with a total amount of 148.8 mm (table 1), which

clearly exceeded the mean monthly rainfall from December

through February (35.6 mm) and mean total annual rainfall

(101.6 mm) in southern Nevada. However, mean monthly

air temperatures did not change considerably between these

two 9-month periods (table 1).

Field surveys revealed a significant reduction in density,

frequency, percent vegetation cover, and above-ground biomass (p < 0.001; table 2) in local annual plants in spring 1997

Figure 1—Sketch map showing the location of Cold

Creek Canyon in the Spring Mountains of southern

Nevada. Las Vegas Valley lies to the southeast of the

Cold Creek Canyon.

Table 1—Mean monthly precipitation and air temperature of Las Vegas Valley in October

1992 through June 1993, and in October 1996 through June 1997. Official

weather data were obtained from McCarran Airport in Las Vegas, near Cold

Creek Canyon. Actual weather data in the creosote bush-blackbrush ecotone

were not available. The letter “T” indicates trace precipitation, an amount

greater than zero but less than the lowest reportable value. Mean values are

based on the 1936-1997 period.

1992-1993 1996-1997

Month Temperature Precipitation Temperature Precipitation

°C mm °C mm

October 21.6 31.0 19.3 2.8

November 11.5 0.0 13.6 2.1

December 6.4 43.4 7.7 4.6

January 7.6 41.4 9.3 7.6

February 10.1 64.0 10.9 T

March 16.1 3.6 17.1 0.0

April 19.7 0.3 18.6 1.0

May 25.0 0.3 27.6 T

June 28.1 2.0 29.1 T
USDA Forest Service Proceedings RMRS-P-11. 1999 219

compared to spring 1993 across the creosote bush-blackbrush

ecotone. Mean annual species richness declined significantly

(p < 0.01; fig. 2) during Spring 1997. Among the annual

species, red brome (Bromus rubens) by far experienced the

greatest decline in 1997 than in 1993. Biomass and density

of desert trumpet (Eriogonum inflatum), desert marigold

(Baileyapleniradiata), and fiddleneck (Amsinckiatessellata)

also showed a significant reduction (p < 0.001). Locally

uncommon annual species, including New Mexico thistle

(Cirsium neomexicanum) and evening primrose (Oenothera

spp.), were nearly absent during the 1997 drought period.

Similarly, local herbaceous perennial vegetation also

exhibited a significant difference (p < 0.05; table 2) in

above-ground biomass between the two years that differed

in timing and total amount of precipitation. Conversely,

species richness (fig. 2), density, frequency, and vegetation cover (table 2) of herbaceous perennials were not

significantly different. Herbaceous vegetation was sparely

distributed in Cold Creek Canyon. In general, many species, such as Indian paintbrush (Castilleja chromosa),

locoweed (Astragalus spp.), speargrass (Stipa speciosa),

and desert globemallow (Sphaeralcea ambigua), largely

died back to the ground surface. Nevertheless, populations

of perennials were more stable than populations of annuals

despite the arid winter 1996 and spring 1997 seasons.

On the contrary, all local woody, subwoody (suffrutescent),

and succulent taxa remained nearly the same in species

density, frequency, and percent vegetation cover in both

1993 and 1997 years (table 3). Percent vegetation cover was

38.7 and 38.1% in 1993 and 1997, respectively. Creosote

bush-white bursage-Mojave yucca (Yucca schidigera) associations were commonly established at the lower half of the

creosote bush-blackbrush ecotone. Joshua-tree (Yucca

brevifolia) and blackbrush were commonly established at

the upper half of the creosote bush-blackbrush ecotone.

Individuals of snakeweed (Gutierrezia sarothrae) were frequently found on disturbed sites despite the occurrence of

severe drought. Among the three major plant life-forms,

woody taxa consistently had the most stable populations,

while annual taxa had the least stable populations at the

creosote bush-blackbrush ecotone.

Discussion _____________________

Extremely low annual species richness, density, frequency,

percent vegetation cover, and above-ground biomass were

detected during the severe drought in spring 1997 in southern Nevada. From casual observations, a number of seeds

were found in the seed bank to avoid such severe drought.

The drought began in 1995, and reached its greatest intensity during the first 6 months of 1997. In this study, exceptionally low precipitation in these years may explain the

major reduction in overall species diversity and productivity

of annual plants.

The life cycle of annual plants rarely experiences water

deficit and other types of environmental stresses. Plants

simply escape the harsh environment as seeds in this study.

After rain, seeds germinate and plants grow, flower, and

produce seeds rapidly before the water supply is exhausted

(Frietas 1997). Annuals have relatively high growth and

photosynthetic rate, and can complete their life cycle before

the advent of environmental stress. The seed bank at my

study site stores some winter ephemeral seeds, which can

germinate and complete their life cycle when soil moisture

is abundant during spring seasons preceded by winter

rainfall. Germination and mortality of desert ephemerals

are largely controlled by a combination of soil moisture and

temperature (Barbour and others 1987). Many winter

ephemerals in the Mojave Desert germinate after fall or

winter rains in excess of 10-15 mm; if falling below this

critical limit, germination is nearly absent (Barbour and

others 1987), which concurs with this study. Exceptionally

low density of annuals was found at my study sites because

rainfall in winter and spring 1997 fell below 15 mm. Beatley

(1967) proposes that density of annuals strongly correlates

with increasing rainfall between 15-45 mm. Beatley (1967)

suggests that winter annuals grow slowly through winter,

Table 2—Frequency, mean density, percent vegetation cover, and

above-ground biomass of annuals (1 m2) and herbaceous

perennials (16 m2) at the creosote bush-blackbrush ecotone

in Cold Creek Canyon of southern Nevada during 1993 and

1997. Mean values are expressed with standard errors, and

mean values in rows followed by different letters are

significantly different at p ≤ 0.05 based on Student t-tests.

Life-form Parameter 1993 1997

Annual Density 140.1 ± 5.7 a 20.3 ± 1.2 b

Frequency 100.0 % 60.0 %

Percent cover 26.3 ± 1.4 a 7.4 ± 0.7 b

Biomass 6.1 ± 0.3 a 1.5 ± 0.05 b

Perennial Density 4.7 ± 0.04 a 4.4 ± 0.02 a

Frequency 68.0 % 65.3 %

Percent cover 3.9 ± 0.001 a 2.1 ± 0.001 a

Biomass 1.9 ± 0.02 a 0.8 ± 0.003 b

Figure 2—Mean species richness of annual, herbaceous (H), and woody (W) perennial plants at the

creosote bush-blackbrush ecotone in Cold Creek

Canyon of southern Nevada. Mean values are expressed with standard errors, and columns within the

same life-form labeled with different letters are significantly different at p < 0.05 based on Tukey’s

Multiple Comparison Test.

a

a a

b

a a

Annuals

H. Perennial

W. Perennial

15

Mean number of species

12

9

6

3

0

1993 1997

Year
220 USDA Forest Service Proceedings RMRS-P-11. 1999

then grow rapidly in spring as temperatures rise. Late

September is the earliest and early April is the latest time

that germination of winter annuals occur; a 7- to 8-month

growing season is the longest, and 6 to 10 weeks is the

shortest that appear possible in southern Nevada. However, even when the growing season is compressed into a

few weeks, and preceded by heavy rains, more than onethird of the seedlings fail to reach maturity (Beatley 1967).

Under the best conditions, density of ephemerals may be

1,000 m2, cover 30%, biomass 60 g/m2, but typically, density

is 100 m2 and biomass 10/g m2 (Barbour and others 1987).

In this study, density, biomass, and percent vegetation

cover of winter ephemerals were significantly reduced

during the 1997 drought compared to the moist spring

1993. Wide variations of germination and mortality exist in

desert annuals from region to region, site to site, and

species to species during each year in southern Nevada

(Beatley 1976).

Red brome was the dominant winter ephemeral at my

study site, and is a common member of many creosote bushblackbrush ecotones, which occur at elevations between

1,220 to 1,310 m in southern Nevada (Beatley 1966). Red

brome was most abundant under the shrubs, especially at

the periphery of shrub canopies in the creosote bush and

blackbrush shrublands. Red brome occupied the same

ecological niche as the native winter annuals in this study.

This grass has the ability to dominate other native winter

ephemerals primarily due to its greater reproductive success, greater ability to survive to maturity and reproduce,

and higher survival percentages during the growing season

(Beatley 1967).

There are several potential explanations for the significant reduction in local annuals, but not woody perennials,

during a severe drought period in this study. First, annuals

usually avoid germination in the drought year, and usually

remain dormant in the seed bank of their original habitats.

Seeds of many annual species may remain dormant for

years, and may not germinate until the advent of next

moisture and nutrient pulse. Second, density, frequency,

biomass, and vegetation cover of annuals are strongly

associated with the timing and amount of precipitation,

which can vary considerably from year to year. Third,

annuals commence their life cycle each year from seeds,

which would experience a greater mortality rate than

established woody perennials. Fourth, established perennial plants may experience a more moist environment than

annuals since roots of perennials can obtain moisture from

deeper soils. Annual plants have a shallow root system, and

root biomass of annuals generally occurs at the upper 15 cm

of the soil (Lei, personal observation). Fifth, annuals in

southern Nevada are generally C3 winter species, and may

be more drought sensitive than native C3 and C4 perennials.

In this study, woody, suffrutescent, and succulent taxa in

the creosote bush-blackbrush ecotone exhibited little change

Table 3—Mean density (plants/100 m2) and frequency (number of plants present) of

woody, subwoody, and succulent taxa at the creosote bush-blackbrush ecotone

in Cold Creek Canyon of southern Nevada during 1993 and 1997. All taxa were

not significantly different (p > 0.05) in mean density and frequency.

1993 1997

Species Density Frequency Density Frequency

Acamptopappus shockleyi 10.7 60 10.2 60

Ambrosia eriocentra 0.05 3 0.03 1

Ambrosia dumosa 24.5 87 24.7 87

Atriplex canescens 0.6 7 0.5 7

Atriplex confertifolia 0.5 5 0.4 5

Coleogyne ramosissima 9.4 53 9.1 53

Echinocactus polycephalus 0.02 3 0.02 3

Encelia virginensis 3.4 16 3.2 16

Ephedra nevadensis 5.5 40 5.4 40

Eriogonum fasciculatum 1.7 13 1.4 13

Eurotia lantata 2.7 27 2.7 27

Gaura coccina 0.01 3 0.01 1

Grayia spinosa 0.01 7 0.01 7

Hymenoclea salsola 0.9 16 1.2 16

Gutierrezia sarothrae 0.7 7 0.9 7

Krameria parvifolia 3.9 52 3.8 52

Larrea tridentata 4.5 73 4.5 73

Menodora spinescens 0.01 5 0.01 5

Opuntia acanthocarpa 0.3 12 0.3 12

Opuntia basilaris 0.2 13 0.2 13

Opuntia echinocarpa 0.3 12 0.3 12

Opuntia ramosissima 0.2 11 0.2 11

Psorothamnus fremontii 0.2 15 0.3 15

Salazaria mexicana 0.7 13 0.7 13

Stephanomeria pauciflora 0.1 3 0.2 1

Yucca brevifolia 0.9 39 1.2 39

Yucca schidigera 1.9 65 2.1 65
USDA Forest Service Proceedings RMRS-P-11. 1999 221

in community composition, with vegetation cover and species

density and frequency remaining nearly the same throughout

the severe drought period. Woody taxa establishing at desert

mountain slopes were characterized as drought-tolerant

(evergreen), drought-deciduous, and succulent plants in this

study. Drought-tolerant plants, such as creosote bush and

saltbush, are true xerophytes because they grow and transpire throughout periods of water stress and have a high

degree of tolerance for desiccation (Frietas 1997). Net photosynthesis and root growth are possible, and transpiration

rates are very low when moisture is limiting (Barbour and

others 1987). The advantage of being evergreen is that when

water becomes available again, no lag exists while new

tissues are produced. This adaptive mode is a more competitive strategy than other life-form strategies in a stressful

environment with limited resource availability. The cost of

maintaining evergreen leaves that can withstand episodic

environmental stress is less than that of producing new

photosynthetic leaves annually. Many evergreen species,

however, shed a fraction of their leaves during severe drought

periods, presumably to reduce surface area and water loss

through transpiration (Barbour and others 1987).

Although the evergreen life-form solves certain environmental problems, it creates others. When water stress intensifies, stomatal control can provide temporal drought-escape

mechanisms (Frietas 1997). Reducing water loss by partial

stomatal closure restricts the C02 influx and lowers the

photosynthetic production. Such water loss also results in

the reduction of evaporative cooling and can overheat the

leaf (Frietas 1997). Drought-tolerant plants respond to seasonal drought by adjusting the amount of leaf area exposed

and by reducing gas exchange via partial stomatal closure

mechanisms (Frietas 1997). Midday stomatal closure may

contribute to drought avoidance, decrease water loss, and

increase water-use efficiency.

However, drought-deciduous species, such as white

bursage, blackbrush, and goldhead (Acamptopappus

shockleyi), avoided water stress by becoming temporarily

dormant and shedding some of the older leaves as stress

intensified during the dry season in this study. Drought can

be so severe in southern Nevada that perennial plants have

to survive for several months without much photosynthetically active lamina. Most drought-deciduous species produce only one crop of leaves a year and enter a long summer

dormancy following leaf drop (Barbour and others 1987).

Their leaves are energetically inexpensive to manufacture

compared to conifer and other evergreen leaves, and their

photosynthetic rates are generally 2-3 times higher than

evergreens (Barbour and others 1987). These plants appear

to exhibit maximum photosynthetic activity in the cool,

moist winter and spring months.

Succulent plants, including cacti, have a very shallow root

system that can absorb water even from light rains. Cacti are

uncommonly distributed in my study area because they

cannot tolerate water stress at the cellular level. Internal

water stress rarely exceeds –0.5 MPa (Barbour and others

1987). In wet periods, water is stored in massive parenchyma cells, swelling the stem; in dry periods, water is used

and the stem shrinks (Barbour and others 1987). Cacti

utilize the CAM photosynthetic pathway, with stomates

open at night when under mild air temperatures and

relative humidity. The assimilated CO2 is stored in the form

of organic acids and later, during daytime, the stored CO2 is

utilized to form carbohydrates while the stomata remain

closed. Among all plant life-forms, cacti clearly exhibit the

highest water use efficiency, even higher than true xerophytes. Yet, cacti have extremely slow growth rates because

they allocate much of their energy in tolerating adverse and

stressful environments.

Plants of various life-forms utilized different adaptive

strategies to reduce and cope with water stress at the

creosote bush-blackbrush ecotone in Cold Creek Canyon of

southern Nevada. The severe drought in 1997 limited the

overall local biodiversity and productivity of local annual

plants because they simply avoided the drought year as

seeds. Hence, a change to a harsher, drier climate in southern Nevada would increase the chance of annual species to

remain dormant in the seed bank of their original habitats.

Acknowledgments ______________

I express my gratitude to Steven Lei, David Valenzuela,

and Shevaum Valenzuela for their valuable field assistance

during the course of study. I sincerely appreciate Wesley

Niles for identifying the unknown plant species, and appreciate David Charlet for critically reviewing the manuscript.

References _____________________

Analytical Software, 1994. Statistix 4.1, an interactive statistical

program for microcomputers. St. Paul, MN: Analytical Software.

329 p.

Barbour, M. G.; Burk, J. H.; Pitts, W. D. 1987. Terrestrial plant

ecology. Menlo Park, CA: The Benjamin/Cummings Publishing

Company, Inc. 634 p.

Beatley, J. C. 1966. Ecological status of introduced brome grass

(Bromus spp.) in desert vegetation of southern Nevada. Ecology

47:548-554.

Beatley, J. C. 1967. Survival of winter annuals in the northern

Mojave Desert. Ecology 48:745-750.

Beatley, J. C. 1969. Biomass of desert winter annual plant populations in southern Nevada. Oikos 20:261-273.

Beatley, J. C. 1974. Effects of rainfall and temperature on the

distribution and behavior of Larrea divaricata (creosote bush) in

the Mojave Desert of Nevada. Ecology 55:245-261.

Beatley, J. C. 1976. Vascular plants of the Nevada Test Site and

central-southern Nevada: ecologic and geographic distributions.

National Technical Information Service, U.S. Dept. of Commerce,

Springfield, VA.

Lei, S. A. 1994. Plants of the North American deserts. Las Vegas,

NV: Unpublished research report. 64 p.

Lei, S. A.; Walker, L. R. 1997. Biotic and abiotic factors influencing

the distribution of Coleogyne communities in southern Nevada.

Great Basin Naturalist 57:163-171.

Munz, P. A. 1974. A flora of Southern California. University of

California Press, Berkeley, CA. 1086 p.

Tilman, D.; Haddi, A. E. 1992. Drought and biodiversity in grasslands. Oecologia 89:257-264.

Webb, R. H.; Steiger, J. W.; Turner, R. M. 1987. Dynamics of Mojave

Desert shrub assemblages in the Panamint Mountains, California. Ecology 68:478-490.

West, N. E. 1983. Colorado Plateau-Mohavian blackbrush semidesert. In: Temperate Deserts and Semideserts. Elsevier Scientific Publishing Company, Amsterdam, Netherlands: 399-411.
222 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

J. H. Kaltenecker is Research Associate, Biology Department, Boise State

University, Boise, ID 83725. M. C. Wicklow-Howard is Professor of Biology,

Boise State University, Boise, ID 83725. R. Rosentreter is Botanist, Bureau

of Land Management, Idaho State Office, Boise, ID 83709.

Biological Soil Crusts in Three Sagebrush

Communities Recovering from a Century of

Livestock Trampling

J. H. Kaltenecker

M. C. Wicklow-Howard

R. Rosentreter

Abstract—Biological soil crusts and their recovery from long-term

livestock impacts were studied in three sagebrush communities in

east-central Idaho. In 1996, biological crust and vascular plant

cover were measured outside and inside of livestock exclosures in

Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis),

mountain big sagebrush (Artemisia tridentata ssp. vaseyana), and

low sagebrush (Artemisia arbuscula) communities. The Wyoming

big sagebrush exclosure had the greatest cover of biological crust

relative to the vascular plant canopy. Biological crust cover was

double inside the Wyoming and mountain big sagebrush exclosures

compared to the areas outside, indicating substantial recovery since

release from livestock use 8 and 11 years previous, respectively. The

low sagebrush site had the least biological crust cover, which did not

differ due to livestock exclusion. A gravelly soil surface and dominance of rhizomatous grasses appear to limit biological crust development on the low sagebrush site.

Biological soil crusts are a conspicuous entity in many arid

and semiarid ecosystems, providing living cover in environments where soil conditions and high evapotranspiration

rates do not support dense vascular plant cover. Biological

crusts (also known as microbiotic, microphytic, cryptogamic,

or cryptobiotic crusts) are composed of lichens, bryophytes,

algae, microfungi, cyanobacteria, and other bacteria. They

reduce soil erodibility (Williams and others 1995a,b; Belnap

and Gillette 1998) and enhance nutrient cycling (Beymer

and Klopatek 1991; Evans and Ehleringer 1993; Belnap

1995) in semiarid and arid plant communities worldwide.

Polysaccharide sheaths associated with cyanobacteria bind

soil particles (Belnap and Gardner 1993), creating a stable

matrix that resists wind erosion (Williams and others 1995b;

Belnap and Gillette 1998). Roughened soil surfaces formed

by biological crusts create catchments for water, reducing

sheet erosion (Williams and others 1995a). Mosses and

lichens provide cover, protecting the soil surface from raindrop impacts. Tissues from vascular plants grown in biologically crusted soils have greater nutrient content compared

to plants grown in uncrusted soils (Belnap and Harper

1995), indicating that they may support the vascular plant

community via mechanisms that enhance nutrient uptake

(e.g., chelating compounds). Organisms associated with biological crusts fix carbon through photosynthesis (Beymer

and Klopatek 1991). Additionally, cyanobacteria and lichens with cyanobacterial photobionts fix atmospheric nitrogen. This contribution of carbon and nitrogen can be

significant in systems where above and below-ground biomass of live vascular plants and litter is low (Skujins 1981;

Beymer and Klopatek 1991; Evans and Ehleringer 1993).

Studies of livestock impacts to biological crusts in the

Great Basin, Colorado Plateau, and Australia have documented reductions in biological crust cover and species

richness due to livestock trampling (Kleiner and Harper

1972; Anderson and others 1982a,b; Brotherson and others

1983; Andrew and Lange 1986; Johansen and St. Clair 1986;

Marble and Harper 1989; Beymer and Klopatek 1992).

Biological crusts in interspaces are most vulnerable since

they are not protected from trampling by a shrub overstory.

The destabilized interspace soil is susceptible to the formation of flow patterns and accelerated erosion (Belnap 1995).

Because crustal components might be responsible for much

of the available nitrogen in some ecosystems, trampling

impacts are likely to modify both the amount of nitrogen

cycling through the system and its spatial distribution

within the community (Evans and Ehleringer 1993). Studies

by Belnap and others (1994) and Belnap (1996) documented

long-term depression of nitrogen fixation in cyanobacterialdominated crusts on the Colorado Plateau due to anthropogenic-related soil disturbances. Disturbance severity ranged

from mild (raking, trampling with smooth-soled shoes) to

severe (off-road vehicles, military tanks). Suppression of

nitrogen fixation persists long after crusts appear to be

recovered in terms of visible cover and biomass (Belnap and

others 1994).

Although biological crusts have received considerable

attention by the scientific community over the last decade,

land management agencies have only recently begun to

consider impacts to biological crusts and the resulting effects on soil health in making land management decisions.

Traditional studies on livestock impacts and vegetation

recovery have focused on vascular plant communities. This

study, initiated by the Bureau of Land Management’s (BLM)

Lemhi Resource Area in east-central Idaho, examined

changes in biological crust and vascular plant cover following exclusion of livestock roughly one decade previous. The

study focused on sites supporting three different sagebrush

taxa to determine how biological crusts recover over a range

of edaphic and biotic conditions. Little published work exists
USDA Forest Service Proceedings RMRS-P-11. 1999 223

on biological crust ecology in the Pacific Northwest, with the

exception of a study by Johansen and others (1993) on postfire recovery in the lower Columbia Basin.

The Study Area _________________

The Lemhi Resource Area contains the north-south oriented valleys of the Lemhi River, Salmon River, and upper

Birch Creek in east-central Idaho. These valleys support

sagebrush-bunchgrass vegetation typical of the Columbia

River drainage (Hironaka 1979). The valleys lie in an area

where the climate is influenced by moist air masses from the

Pacific Ocean and the Gulf of Mexico and dry, continental air

from Canada (Moseley 1992). Average annual precipitation

ranges from 230 to 560 mm, most of which occurs during the

winter and spring in the Lemhi and Salmon valleys (USDI,

BLM, unpublished data). Opposite conditions prevail in the

Birch Creek Valley, with greater than 40% of the annual

precipitation occurring between June and September

(Hauxwell 1977).

Wyoming big sagebrush (Artemisia tridentata Nutt. ssp.

wyomingensis Beetle and Young) dominates the lower, drier

slopes of the valleys. It is replaced by mountain big sagebrush [Artemisia tridentata Nutt. ssp. vaseyana (Rydb.)

Beetle] at mid-elevations where precipitation exceeds

300 mm annually. Windswept ridges and shallow, gravelly

soils of glacial outwash fans are dominated by low sagebrush

(Artemisia arbuscula Nutt.). The predominant bunchgrass

throughout the Lemhi Resource Area is bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love]. Idaho fescue (Festuca idahoensis Elmer) is co-dominant on north

aspects. Presence of these palatable species resulted in

extensive use of the valleys for livestock grazing beginning

in the 1860’s. Records of a late 19th century rancher, G. E.

Shoup, document severe depletion of native vegetation by

the late 1880’s, with “large areas virtually going to dust”

(Shoup 1935).

Methods _______________________

In spring 1996, three study sites were established, each

occurring in a different sagebrush community and containing a livestock exclosure ranging in age from 8 to 11 years

(Table 1). All sites occur on level or gently sloping topography of alluvial terraces. The Wyoming and mountain big

sagebrush sites are located on deep, well-drained silt loams

formed in calcareous alluvium (Cheney 1970). The low

sagebrush site occurs on calcareous, gravelly loams derived

from limestone glacial outwash (Hauxwell 1977). These soils

are shallow, with a petrocalcic layer at approximately 30-40

cm.

Cover data were collected for biological crust components

(lichen, moss), vascular plant canopy by species, rock and

gravel, litter, and bare mineral soil along four randomly

selected 10-m transects located inside and outside of each

exclosure. All data were collected using a line-intercept

method with the measuring tape placed near the soil surface

to facilitate reading of ground cover. The smallest measurable unit was 5 mm. Sampling occurred between 3 and 6

June 1996. Cover data were analyzed using a two-way

factorial analysis of variance. Interactions between treatment (livestock exclusion) and site effects were evaluated to

assess the reliability of main effects across the study area.

Tukey’s HSD test was used to compare means between sites

if main effects were significant. An alpha level of 0.05 was

used to determine significance for all analyses.

As with many natural experiments (Diamond 1986), this

study lacks replication (in this case, of each sagebrush type),

limiting statistical interpretation. In addition, a “space-fortime” substitution was employed (Michener 1997) due to the

lack of pre-exclosure baseline data. Therefore, the study

should be treated as a case study, with statistical inferences

applicable only to the sites described in this paper.

Voucher specimens representing all lichen and moss taxa

comprising the biological crust at each site were collected,

identified, and deposited at the Snake River Plains Herbarium (SRP), Boise State University, Boise, Idaho.

Results ________________________

Wyoming Big Sagebrush

Biological soil crusts were the dominant living cover in the

Wyoming big sagebrush exclosure (Fig. 1). Crust cover was

significantly higher in this exclosure compared to cover

inside the other exclosures (p ≤0.05). This site has the least

annual precipitation (Table 1), which limits vascular plant

cover (Fig. 1, 2). Biological crusts covered the interspaces,

leaving little bare ground inside the exclosure (Fig. 3). The

crust was comprised of lichens and mosses in nearly equal

proportions. Biological crust cover was significantly greater

(p = 0.0017) and amount of bare mineral soil was significantly less (p = 0.0001) inside the exclosure compared to the

area outside (Fig. 3). Differences in shrub and herbaceous

canopy as well as litter cover were all nonsignificant. Litter

was concentrated under shrubs.

Table 1—Characteristics of study sites located within the Lemhi River and Birch Creek valleys, east-central Idaho.

Year exclosure Average annual Soil textural

Site name established Elevation precipitation class

m mm

Wyoming big sagebrush 1988 1,433 180-250 silt loam

Mountain big sagebrush 1985 1,747 300-410 silt loam

Low sagebrush 1986 2,149 280-330 gravelly loam
224 USDA Forest Service Proceedings RMRS-P-11. 1999

Mountain Big Sagebrush

This site had greater potential for vascular plant and litter

cover compared to the Wyoming big sagebrush site due to

higher annual precipitation (Table 1). Biological crusts accounted for 40% of the soil surface cover inside the mountain

big sagebrush exclosure (Fig. 3). However, they were a less

dominant element inside the exclosure relative to the vascular plant community when compared to the Wyoming big

sagebrush site (Fig. 1). Cover of biological crusts and herbaceous plants were significantly greater inside the exclosure

(p = 0.0044 and p = 0.0002, respectively) and occurred primarily in interspace locations (Fig. 2, 3). Shrub cover was

significantly less inside the exclosure (p = 0.0150). Biological

crust and litter outside the exclosure were found only in

protected areas under the shrub canopy. Cover of bare

mineral soil was significantly less inside the exclosure (p =

0.0028) (Fig. 3).

Low Sagebrush

The low sagebrush site had the least biological crust cover

relative to the cover of vascular vegetation when compared

to the two big sagebrush communities (p ≤0.05) (Fig. 1).

Cover of bare mineral soil and surface rock (gravels) inside

the exclosure was higher compared to the areas inside both

big sagebrush exclosures (Fig. 3). The biological crust was

dominated by lichens; very little moss occurred on this site

(Fig. 3). There was no difference in biological crust cover,

bare mineral soil, or litter inside and outside the exclosure.

Shrub canopy cover was greater inside the exclosure (p =

0.0084) (Fig. 2, 3), while cover of the dominant perennial

grass, western wheatgrass [Pascopyrum smithii (Rydb.) A.

Love], was greater outside the exclosure (p = 0.0037).

Discussion _____________________

Potential for Biological Crust

Development

Soil texture and cover of vascular vegetation appeared to

influence the relative cover of biological crusts in each plant

community. Biological crusts had higher cover on finetextured silt loams supporting the two big sagebrush communities, both of which had negligible cover of surface

gravels when compared to the low sagebrush site. Surface

gravels function as cover and protect the soil surface from

erosion, thereby acting as an ecological replacement for

biological crusts in that role.

The Wyoming big sagebrush site receives the least annual

precipitation of the two big sagebrush sites and thus has less

potential for vascular plant cover. Interspaces inside the

Wyoming big sagebrush exclosure had a continuous cover of

biological crust and very little bare mineral soil, indicating

greater ecological importance of biological crusts as soil

protection on sites where effective precipitation is inadequate to support continuous cover of vascular vegetation

and litter. Crustal organisms require minuscule moisture to

carry out metabolic activity and are highly drought tolerant.

Figure 1—Relative cover of the vascular plant canopy

and biological soil crust inside livestock exclosures in

three sagebrush communities (N = 24).

Figure 3—Mean ground cover outside and inside of livestock exclosures in three sagebrush

communities (N = 24).

Figure 2—Mean canopy cover of vascular vegetation life forms outside and inside of livestock

exclosures in three sagebrush communities (N = 24).
USDA Forest Service Proceedings RMRS-P-11. 1999 225

If undisturbed they can maintain site stability through

prolonged drought periods that vascular plants may not

tolerate (Belnap and Gillette 1998).

The mountain big sagebrush site has adequate moisture

to support relatively high canopy cover (>80%) with a diversity of herbaceous vegetation. Biological crust accounts for

approximately 40% of the soil surface cover. While the crust

is probably not as critical for soil stabilization on this site due

to high cover of vascular plants and litter, mosses and

lichens form a rather bumpy carpet under the canopy and

contribute to both the structural and biological diversity of

the site. Contributions to nitrogen inputs on this site are as

yet unknown, but the presence of nitrogen-fixing lichen

species [Collema coccophorum Tuck., Collema tenax (Sw.)

Ach., Heppia lutosa (Ach.) Nyl.] indicate a potential role.

The low sagebrush site has decreased potential for vascular plant cover due to the droughty nature of the welldrained, gravelly, calcareous soils. Cover of surface gravels

were an obvious limiting factor to biological crust development. Another factor may be the presence of western wheatgrass, a rhizomatous species. Rhizomatous grasses tend to

occur in homogeneous, dense stands, leaving little area

available for occupation by biological crusts (Mack and

Thompson 1982). Although canopy cover values for western

wheatgrass were not high (Fig. 2), the data do not reflect the

effect of tillering on the soil surface, which resulted in more

continuous cover compared to bunchgrasses. Values for bare

mineral soil inside the low sagebrush exclosure were high

compared to the other two sites (Fig. 3); however, bare soil

occurred in small, discontinuous patches broken by gravel

and rhizomatous vegetation.

Recovery from Long-Term Livestock Use

The Wyoming big sagebrush site is stocked at a rate of 17.9

acre/animal unit month (AUM) and is used from 1 May to

1 June or 1 June to 1 July in alternating years. The current

stocking rate has been in effect since 1950. Previous to 1992

the pasture was used only during May. Livestock were

removed from the pasture approximately 2 days prior to the

June 1996 sampling. Small differences in vascular plant

canopy cover (Fig. 2), particularly perennial grasses, indicate that this grazing system may be protecting the vascular

plant community. However, considerable increase in biological crust cover inside compared to outside the exclosure

(Fig. 3) suggests that management on this site has not

allowed biological crust recovery from historical (pre-1950)

heavy livestock use. Biological crusts are most resilient to

livestock use during cool seasons when the soil surface is

frozen or snow-covered (Marble and Harper 1989; Memmott

and others 1998). Crustal organisms need moisture for

metabolic activities (including growth and reproduction),

and livestock use immediately prior to a hot, dry period

provides little opportunity for regrowth. This may be particularly detrimental in areas that receive brief, high intensity summer storms, which can result in soil loss on sites

where the surface has been destabilized by trampling impacts (Marble and Harper 1989). The dramatic increase in

biological crust cover in the 8 years following exclusion from

grazing is remarkable in that visible recovery occurred

much more quickly than the several decades estimated by

Belnap (1993) for soil lichens and mosses in southern Utah.

This indicates that environmental conditions in the Lemhi

Valley are conducive to growth and reproduction of both

lichens and mosses, possibly due to predominance of cool

season moisture and short duration of the hot, dry season.

Fall (October-November), winter (December-February), or

early spring (March-April) livestock use would result in less

damage to the biological soil crust. These regimes would

allow at least 1 month of moist conditions for growth and

reattachment of disturbed crustal organisms prior to the

hot, dry season.

The mountain big sagebrush site was stocked lighter than

the Wyoming big sagebrush site (23.3 acre/AUM). Between

1950 and 1994 this site was used from 15 May to 1 September. Season of use was modified drastically in 1995 and now

extends from 15 May to 6 June. Livestock were removed

immediately prior to the June 1996 sampling. Deep hoof

prints (>5 cm deep) indicated that the soil was very wet while

livestock were using the allotment. These conditions were

probably due to snow melt followed by spring rains. As with

the Wyoming big sagebrush site, visible recovery from livestock impacts was considerable inside the exclosure, both

with regards to the biological crust (Fig. 3) and the herbaceous component of the plant community (Fig. 2). This site

receives higher annual precipitation than the Wyoming big

sagebrush site and thus has the potential for more rapid

regrowth of both biological crust and vascular plants. However, the entire site is undoubtedly recovering from past

season-long summer use, and 2 years of management change

(i.e., shortening of the grazing season) were probably not

adequate to see recovery in either the vascular plant community or the biological crust outside the exclosure. Continued

spring use when the soil surface is extremely wet might

inhibit biological crust recovery by churning the soil surface

and burying the crust. Fall use, when soils are more likely to

be moist but not saturated, would be a better option for this

site and would protect the perennial grasses as well as the

biological crust.

The low sagebrush site was used by sheep from 1950 to

1991 at a rate of 20.1 acre/AUM from 1 May to 15 July and

1 September to 9 September. The site was not grazed

between 1992 and the sampling date in 1996. The data

indicate that there was little change in biological crust cover

regardless of the rest period (10 years since the exclosure

was built vs. four years of rest outside the exclosure).

Western wheatgrass might have increased and replaced

bluebunch wheatgrass on the site due to decades of historical heavy use by sheep (S. Beverlin, BLM, Lemhi Resource

Area, personal communication). Western wheatgrass is less

impacted by grazing due to its rhizomatous nature and

responds quickly to periods of rest. If bluebunch wheatgrass

and other perennial bunchgrasses formerly dominated the

herbaceous component of the community, it is possible that

the site historically had slightly greater cover of biological

crust than is now present. Gravels armor the soil surface and

reduce trampling impacts. Lichens may recover more quickly

on this site where greater elevation results in cooler temperatures and short periods of hot, dry weather.
226 USDA Forest Service Proceedings RMRS-P-11. 1999

Conclusions____________________

An important observation of this study was the relatively

rapid visible recovery of the biological crust, even on the

driest of the three sites. Interspaces in the Wyoming big

sagebrush community had almost complete cover of biological crust after only 8 years of rest. Due to the long history of

livestock use in the study area, and indeed, much of western

North America, it is difficult to determine the precise ecological potential of any given site. The measure of recovery

used here is the increase in biological crust cover and the

lack of bare mineral soil.

The results of this study indicate that a “one size fits all”

approach is not appropriate with regard to biological crust

management. Some biological crust communities may be

more resistant to disturbance due to protection of the soil

surface by rock or gravel. Others may recover more quickly

due to cooler temperatures, higher annual precipitation, or

short duration of the hot, dry season. The most fragile

communities are those with little surface rock and vascular

plant cover. Resistance and resilience of the entire community, i.e., both vascular plants and biological crust, need to be

considered when applying livestock management to large

areas containing multiple vegetation types.

Biological crusts are often a major component of arid and

semiarid landscapes. Soil and nutrient losses resulting from

damage to the crust can impact the vascular plant community and ultimately result in desertification (Belnap 1995).

This study indicated that, in this geographic area, biological

crusts can regrow relatively quickly following release from

disturbance. More work is needed to determine how other

functional aspects of the biological crust (e.g., nutrient

cycling) are affected by management changes.

References _____________________

Anderson, D. C.; Harper, K. T.; Holmgren, R. C. 1982a. Factors

influencing development of cryptogamic soil crusts in Utah deserts.

Journal of Range Management 35: 180-185.

Anderson, D. C.; Harper, K. T.; Rushforth, S. R. 1982b. Recovery of

cryptogamic soil crusts from grazing on Utah winter ranges.

Journal of Range Management 35: 355-359.

Andrew, M. H.; Lange, R. T. 1986. Development of a new biosphere

in arid chenopod shrubland grazed by sheep. 1. Changes to the

soil surface. Australian Journal of Ecology 11: 395-409.

Belnap, J. 1993. Recovery rates of cryptobiotic crusts: inoculant use

and assessment methods. Great Basin Naturalist 53: 89-95.

Belnap, J. 1995. Surface disturbances: their role in accelerating

desertification. Environmental Monitoring and Assessment 37:

39-57.

Belnap, J. 1996. Soil surface disturbances in cold deserts: effects on

nitrogenase activity in cyanobacterial-lichen soil crusts. Biology

and Fertility of Soils 23: 362-367.

Belnap, J; Gardner, J. S. 1993. Soil microstructure in soils of the

Colorado Plateau: the role of the cyanobacterium Microcoleus

vaginatus. Great Basin Naturalist 53: 40-47.

Belnap, J.; Gillette, D. A. 1998. Vulnerability of desert biological soil

crusts to wind erosion: the influences of crust development, soil

texture, and disturbance. Journal of Arid Environments 39:

133-142.

Belnap, J.; Harper, K. T. 1995. Influence of cryptobiotic soil crusts

on elemental content of tissue of two desert seed plants. Arid Soil

Research and Rehabilitation 9: 107-115.

Belnap, J.; Harper, K. T.; Warren, S. D. 1994. Surface disturbance

of cryptobiotic soil crusts: nitrogenase activity, chlorophyll content, and chlorophyll degradation. Arid Soil Research and Rehabilitation 8: 1-8.

Beymer, R. J.; Klopatek, J. M. 1991. Potential contribution of carbon

by microphytic crusts in pinyon-juniper woodlands. Arid Soil

Research and Rehabilitation 5: 187-198.

Beymer, R. J.; Klopatek, J. M. 1992. Effects of grazing on cryptogamic crusts in pinyon-juniper woodlands in Grand Canyon

National Park. The American Midland Naturalist 127: 139-148.

Brotherson, J. D.; Rushforth, S. R.; Johansen, J. R. 1983. Effects of

long-term grazing on cryptogam crust cover in Navajo National

Monument, Ariz. Journal of Range Management 35: 579-581.

Cheney, M. D. 1970. General soil map and interpretations, Lemhi

County, Idaho. St. Anthony, ID: U. S. Department of Agriculture,

Soil Conservation Service.

Diamond, J. 1986. Laboratory experiments, field experiments, and

natural experiments. In: Diamond, J.; Case, T. J., eds. Community ecology. New York: Harper & Row: 3-21.

Evans, R. D.; Ehleringer, J. R. 1993. A break in the nitrogen cycle

in arid lands? Evidence from δ

15N of soils. Oecologia 94: 314-317.

Hauxwell, D. L. 1977. Sagebrush soils study, Birch Creek Valley,

Idaho. Unpublished report. Moscow, ID: University of Idaho.

139 p.

Hironaka, M. 1979. Basic synecological relationships of the Columbia River sagebrush type. In: The sagebrush ecosystem: a symposium; 1978 April; Logan, UT. Logan, UT: Utah State University:

26-32.

Johansen, J. R.; Ashley, J.; Rayburn, W. R. 1993. Effects of rangefire

on soil algal crusts in semiarid shrub-steppe of the Lower Columbia Basin and their subsequent recovery. Great Basin Naturalist

53: 73-88.

Johansen, J. R.; St. Clair, L. L. 1986. Cryptogamic soil crusts:

recovery from grazing near Camp Floyd State Park, Utah, USA.

Great Basin Naturalist 46: 632-640.

Kleiner, E. F.; Harper, K. T. 1972. Environment and community

organization in grasslands on Canyonlands National Park. Ecology 53: 299-309.

Mack, R. N.; Thompson, J. N. 1982. Evolution in steppe with few

large, hooved mammals. The American Naturalist 119: 757-773.

Marble, J. R.; Harper, K. T. 1989. Effect of timing of grazing on soilsurface cryptogamic communities in a Great Basin low-shrub

desert: a preliminary report. Great Basin Naturalist 49: 104-107.

Memmott, K. L.; Anderson, V. J.; Monsen, S. B. 1998. Seasonal

grazing impact on cryptogamic crusts in a cold desert ecosystem.

Journal of Range Management 51: 547-550.

Michener, W. K. 1997. Quantitatively evaluating restoration experiments: research design, statistical analysis, and data management considerations. Restoration Ecology 5: 324-337.

Moseley, R. K. 1992. Ecological and floristic inventory of Birch

Creek Fen, Lemhi and Clark Counties, Idaho. Unpublished

report. Boise, ID: Idaho Department of Fish and Game, Conservation Data Center.

Shoup, G. E. 1935. Ranges of Salmon River 10/22/35. Unpublished

report on file at the Bureau of Land Management, Lemhi Resource Area, Salmon, ID. 2 p.

Skujins, J. 1981. Nitrogen cycling in arid ecosystems. Ecological

Bulletin (Stockholm) 33: 477-491.

Williams, J. D.; Dobrowolski, J. P.; West, N. E. 1995a. Microphytic

crust influence on interrill erosion and infiltration capacity.

Transactions of the ASAE 38: 139-146.

Williams, J. D.; Dobrowolski, J. P.; West, N. E.; Gillette, D. A. 1995b.

Microphytic crust influence on wind erosion. Transactions of the

ASAE 38: 131-137.
USDA Forest Service Proceedings RMRS-P-11. 1999 227

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

M. Ajmal Khan is a Professor of Plant Ecology at the Department of

Botany, University of Karachi, Karachi-75270, Pakistan. Bilquees Gul is a

Plant Ecologist at the Department of Botany, University of Karachi, Pakistan. Corresponding author and address: P.O. Box 8452, University of

Karachi, Karachi-75270, Pakistan, e-mail: ajmal@www.fascom.com

Abstract—Pure populations of halophytic shrubs (Suaedafruticosa,

Cressa cretica, Arthrocnemum macrostachyum, Atriplex griffithii,

etc.) and perennial grasses (Halopyrum mucronatum, Aeluropus

lagopoides, etc.) dominate the vegetation of the Arabian Sea coast

at Karachi, Pakistan. The coastal populations maintained a persistent seed bank. There is a close relationship between seed bank

flora and existing vegetation. The size of the seed bank varies with

the species dominating the population. Arthrocnemum macrostachyum, which dominated the coastal swamps, had the highest

seed density, 940,000 seed m–2, followed by Halopyrummucronatum,

which showed 75,000 seed m–2. For all other species (Suaeda fruticosa, Cressa cretica, Atriplex griffithii, and Aeluropus lagopoides),

seed bank varies from 20,000 to 35,000 seed m–2. Seed bank of all

species substantially reduced a few months after dispersal.

The desert littoral salt marshes near Karachi, Pakistan,

are characterized by a simplicity of structure and composition (Chaudhri 1961). Monospecific patches of vegetation

are common with occasional stands dominated by a single

species with or without minor associates (Khan, unpublished data). The vegetation from seaward to landward is

mangrove (Avicennia marina) followed by muddy coastal

swamp with A. macrostachyum (Karim and Qadir 1979)

and then other communities like Atriplex griffithii Moq.

var. stocksii Boiss. (Chenopodiaceae), Suaeda fruticosa (L.)

Forssk. (Chenopodiaceae), Halopyrum mucronatum (L.) Stapf.

(Poaceae), Aeluropus lagopoides (L.) Trine. Ex Thwarts (Poaceae) and Cressa cretica L. (Convolvulaceae) were present

on adjacent low dunes.

There are few studies on the seed bank of coastal communities and little information is available on the seed bank of

subtropical shrub-dominated coastal communities. The

coastal shrubs and grasses produce a large number of seeds

and most of them disappear a few months after dispersal.

Such marshes maintain a persistent seed bank despite a

significant loss of seed. The size of coastal salt marsh seed

banks varies from a 0 to 140,000 seed m–2 (Jefferies and

others 1981; Jerling 1984; Hartman 1988; Ungar and Woodell

1993, 1996), but are usually small. Similar low densities

have been encountered in several Arabian Sea coastal

communities near Karachi. Seed bank studies from

Seed Bank Strategies of Coastal Populations

at the Arabian Sea Coast

M. Ajmal Khan

Bilquees Gul

Karachi, Pakistan, have demonstrated that dominant

perennial halophytic shrubs and grasses maintain a persistent seed bank (Gulzar and Khan 1994; Aziz and Khan

1996). Six different coastal dune communities showed a

very small seed bank (30-260 seed m–2, Gulzar and Khan

1994), while coastal swamp communities had a larger seed

bank (11,000 seed m–2). The Cressa cretica seed bank at

Karachi showed a persistent seed bank (Aziz and Khan

1996), with the number of seeds reaching its maximum

(2,500 seed m–2) after dispersal and dropping down to 500

seed m–2 a few months later. Gul and Khan (1998) reported

that coastal swamps dominated by Arthrocnemum

macrostachyum showed a great deal of variation from upper

to lower marsh. Upper marsh had the highest number of

seeds with higher species diversity. A number of hypotheses

have been suggested to explain this relatively small number

of seeds. These include: loss of seeds because of coastal

abrasion (Hutching and Russell 1989), environmental extremes beyond the range of tolerance (Ungar 1995a,b), and

composition of aboveground vegetation and its seed production (Milton 1939; Hutchings and Russell 1989). Factors

that contribute to the distribution and maintenance of

seeds in wetland soils include burial, inundation pattern

(depth, duration, and timing of water fluctuation), physical

and chemical characteristics of the substrate, and disturbance (Leck 1989).

The role of the seed banks in coastal salt marsh communities of arid subtropical regions dominated by perennial

halophytic shrubs is poorly understood. Although a large

number of seeds is produced (Gul 1993; Khan and Ungar

1996; Noor and Khan 1994; Aziz and Khan 1996) recruitment from seeds is rare (Gul 1993). The size of the seed bank

varies widely, temporally, and spatially. The role of population characteristics in maintaining this distribution is

largely ignored. We are reporting here the temporal dynamics of seed bank of Arabian Sea coast communities, and their

size and its relationship with vegetation.

Materials and Methods ___________

Study Site

The study site is located in Manora creek, near Sands pit

at the Karachi coast (24° 48' N, 65° 55' E), Pakistan. Mean

ambient summer temperature is 36 °C and mean winter

temperature is 25 °C. Rains are received during monsoon

season extending from June to September. Avicennia marina dominated the area submersed with seawater, and

from the Avicennia marina edge to mean high tide line, the

area (110 meters) is dominated by Arthrocnemum macrostachyum. Toward the landward side there are various
228 USDA Forest Service Proceedings RMRS-P-11. 1999

communities dominated by Atriplex griffithii, Suaeda

fruticosa, Aeluropus lagopoides, Halopyrum mucronatum,

Urochondra setulosa, and Cressa cretica.

The vegetation in each community was sampled 20 times

using the point-centered quarter method (Cottam and Curtis

1956), which places grids randomly. Density, frequency, and

cover were measured and importance value index was calculated. To assess the seed bank, 20 random soil cores were

collected using a 1.5-cm diameter corer to a depth of 15 cm

and placed into plastic bags. Samples were collected at

regular monthly intervals over a period of 12 months from

June 1994 to May 1995. Seeds were manually sorted after

collection with the help of a binocular microscope, identified

from using a reference collection, and counted. Germination

of seed method does not work with perennial sub-tropical

halophytic shrub seed banks (Khan 1991).

Results ________________________

Vegetation analysis showed that there were pure stands

of Arthrocnemum macrostachyum, Aeluropus lagopoides,

Atriplex griffithii, Cressa cretica, Halopyrum mucronatum,

and Suaeda fruticosa. The size of Arthrocnemum macrostachyum seed bank was large. The maximum density of

917,135 seed m–2 of A. macrostachyum seeds occurred after

dispersal (fig. 1). The number declined to 61,136 seed m–2

after 2-3 months.

The seed bank of Suaeda fruticosa reached to about 28,000

seed m–2 after the dispersal (fig. 2) and after 4 months of

dispersal the size of the seed bank was reduced to about

5,000 seed m–2. The seed of Cressa cretica also increased

substantially after dispersal reaching 35,000 seed m–2

(fig. 3) and their number decrease substantially only after

1 month of dispersal to about 4,000 seed m–2.

Seeds of Atriplex griffithii also increased substantially

after the dispersal reaching a size of 20,000 seed m–2 (fig. 4)

and then declined abruptly after a month of dispersal to only

5,000 seed m–2. Seeds of Halopyrum mucronatum gradually decreased and went down to 10,000 seed m–2 from

70,000 seed m–2 after the dispersal (fig. 5). Seeds of Aeluropus lagopoides increased substantially after dispersal and

decreased immediately to less than 5,000 seed m–2 (fig. 6).

Figure 1—Seasonal distribution of Arthrocnemum

macrostachyum seeds in an Arabian seashore .

Figure 2—Seasonal distribution of Suaeda fruticosa

seeds in an Arabian seashore.

Figure 3—Seasonal distribution of Cressa cretica seeds

in an Arabian seashore.

Figure 4—Seasonal distribution of Atriplex griffithii

seeds in an Arabian seashore.
USDA Forest Service Proceedings RMRS-P-11. 1999 229

Figure 5—Seasonal distribution of Halopyrum

mucronatum seeds in an Arabian seashore.

Figure 6—Seasonal distribution of Aeluropus lagopoides

seeds in an Arabian seashore.

which occupied dry elevated sandy areas at the Karachi

coast and is seasonally inundated with seawater. The size of

the seed bank reached its maximum (2,500 seed m–2) after

dispersal. Gulzar and Khan (1994) surveyed various communities at the Karachi coast and reported sizes from 50 to

11,000 seed m–2. In addition, size of the seed bank (in coastal

communities) varied significantly from the time of dispersal

to a few months after dispersal (Aziz and Khan 1996). As

noted by Harper (1977) seed bank composition varied, one

species often making up an overwhelming proportion of the

seed bank. The size of the seed bank in coastal salt marshes

elsewhere varied from 47 seeds m–2 to 130,000 seeds m–2

(Jerling 1984; Hartmann 1988; Ungar and Woodell 1993,

1996). British coastal marshes have no seed bank or only a

small seed bank in the zonal communities (Milton 1939;

Jefferies and others 1991; Hutching and Russell 1989).

Investigations of Pacific coastal marshes indicate that some

communities may have large seed banks, with either temporary or persistent seed banks (Josselyn and Perez 1981;

Hopkins and Parker 1984). In a Pacific zonal community

dominated by Salicornia virginica the seed bank in October contained 700 to 3,174 seed m–2 (Hopkins and Parker

1984). The dominants made up 96.7% of the seed bank and

there was a high correlation between the seed bank and the

species within the plant community. Other Arabian Sea

coast communities also showed a close relationship between

vegetation and seed bank flora (Gulzar and Khan 1994; Aziz

and Khan 1996). The number of seeds in various A.

machrostachyum zones declined substantially 2 months

after the dispersal but they maintained a sizeable seed

bank (≥61,113 seed m–2). Similar results were reported on

H. mucronatum, A. lagopoides, A. griffithii, S. fruticosa,

and C. cretica by (Gulzar and Khan 1994; Aziz and Khan

1996). Our data showed a great deal of spatial and temporal

variation in the size of the seed bank. The number of seed

banks could substantially change with the change in time or

place of the sample taken. A large variation that was reported in the size of the coastal seed banks may not be a real

representation of actual dynamics of the seed banks unless

they are studied for extended periods and include all the

coastal zones.

References _____________________

Aziz, S.; Khan, M.A. 1996. Seed bank dynamics of a semi-arid

coastal shrub community in Pakistan. J. Arid Environ. 34: 81-87.

Chaudhri, I.I. 1961. The vegetation of Karachi. Vegetatio. 10:

229-246.

Chaudhri, I.I.; Qadir, S. A. 1958. Sand dune vegetation of coastal

regions of Karachi. Pak. J. For. 8: 337-341.

Cottam, G.; Curtis, J.T. 1956. The use of distance measurements in

phytosociology sampling. Ecology. 37: 451-460.

Gul, B. 1993. Demography, ecophysiology and seed bank dynamics

of Arthrocnemum indicum. M.Sc. Thesis, University of Karachi,

Karachi. 143 p.

Gul, B.; Khan, M.A. 1994. Growth, osmoregulation, and ion accumulation in the coastal halophyte Arthrocnemum indicum under

saline conditions. Pak. J. Mar. Sci. 3: 115-123.

Gulzar, S.; Khan, M.A. 1994. Seed banks of coastal shrub communities. Ecoprint. 1: 1-6.

Harper, J.L. 1977. Population biology of plants. Academic Press,

New York.

Hartman, J.M. 1988. Recolonization of small disturbance patches in

a New England salt marsh. Am. J. Bot. 75: 1625-1631.

Hopkins, D.R.; Parker, V.T. 1984. A study of the seed bank of a salt

marsh in northern San Francisco Bay. Am. J. Bot. 71: 348-355.

Discussion _____________________

The vegetation of the Arabian Sea coast is characterized

by low diversity and usually found in the form of pure

communities. Seed bank is also characterized by low diversity. The densities of seeds in the seed bank vary from

20,000 seed m–2 to 940,000 seed m–2.

Six different communities from sand dunes to coastal

swamps were studied. Size of the seed bank showed a

great deal of variation ranging from 10,000 seed m–2 to

900,000 seed m–2. Gul and Khan (1998) studied the five

zones of coastal swamps at an Arabian Sea coast marsh and

reported a substantial decrease in seed bank size with a

corresponding increase in inundation frequency. Low species diversity could be attributed to high soil salinity (Aziz

and Khan 1996) and increased degree of inundation (Zahran

1973; Leck 1989), coastal abaration (Hutchings and Russell

1972), environment beyond the range of salt tolerance (Ungar

1995), or composition of vegetation and seed production

(Hutchings and Russell 1989). Coastal communities differ

widely in seed bank size (Gulzar and Khan 1994; Ungar

1995a; Aziz and Khan 1996). Aziz and Khan (1996) studied

the seed bank of a community dominated by Cressa cretica,
230 USDA Forest Service Proceedings RMRS-P-11. 1999

Hutchings, M.J.; Russell, P. J. 1989. The seed regeneration dynamics of an emergent salt marsh. J. Ecol. 77: 615-637.

Jefferies, R.L.; Davy, A. J.; Rudmick, J. 1981. Population biology of

the salt-marsh annual Salicornia europaea agg. J. Ecol. 69: 17-31.

Jerling, L. 1984. Composition and viability of the seed bank along a

successional gradient on a Baltic Sea shore meadow. Holarctic

Ecol. 6: 150-156.

Josselyn, M.N.; Perez, R.J. 1981. Sediment characteristics and

vegetation colonization. In: Niessen. T.; Perez, R.J., eds. The

Hayward regional shoreline marsh restoration: biological

succession during the first year of dike removal. Technical

report 1. Tiburon Center for Environmental Studies, Tiburon:

7-34.

Karim, A.; Qadir, S.A. 1979. Phytosociological studies of the coastal

swamps of Karachi. Bangladesh. J. Bot. 4: 89-98.

Khan, M.A.; Gul, B. 1998. High salinity tolerance of germinating

dimorphic seeds of Arthrocnemum indicum. Int. J. Pl. Sci. 159:

826-832.

Khan, M.A.; Ungar, I.A.; Gul, B. 1998. Action of compatible osmotica

and growth regulators in alleviating the effect of salinity on the

germination of dimorphic seeds of Arthrocnemum indicum L. Int.

J. Pl. Sci. 159: 313-317.

Leck, M.A. 1989. Wetland seed banks. In: Leck, M.A.; Parker, V.T.;

Simpson, R.L., eds. Ecology of soil seed banks. Academic Press,

New York: 283-305.

Milton, W.E.J. 1939. Occurrence of buried viable seeds in soils at

different elevations on a salt marsh. J. Ecol. 27: 149-159.

Ungar, I.A. 1995a. Seed germination and seed-bank ecology in

halophytes. In: Kigel, J.; Galili, G., eds. Seed development and

germination. Marcel and Dekker, Inc. New York: 599-628.

Ungar, I.A. 1995b. Seed bank ecology of halophytes. In: Khan, M.A.;

Ungar, I.A., eds. Biology of salt tolerant plants. University of

Karachi, Pakistan: 65-79.

Ungar, I.A.; Woodell, S.R.J. 1993. The relationship between the

seed bank and species composition of plant communities in two

British salt marshes. J. Veg. Sci. 4: 531-536.

Ungar, I.A.; Woodell, S.R.J. 1996. Similarity of seed bank to the

aboveground vegetation in grazed and ungrazed salt marsh

communities on the Gower Peninsula, South Wales. Int. J. Pl. Sci.

157: 746-749.

Zahran, M.A. 1973. Comparative eco-physiological studies on

Puccinellia maritima and Festuca rubra. Bull. Fac. Sci. Man.

Uni. 1: 43-66.
USDA Forest Service Proceedings RMRS-P-11. 1999 231

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Sara J. Manning is Vegetation Scientist, Inyo County Water Department, 163 May St., Bishop, CA 93514.

Abstract—Groundwater pumping in the Owens Valley, CA, is

managed to prevent adverse changes in vegetation. Preventing

changes over the long term requires an understanding of vegetation

at the plant community scale. A vegetation map and results of

subsequent monitoring were analyzed to discern vegetation patterns and trends. The map showed that phreatophytic communities

consisted of some well-documented and some newly described types.

Median depth to the water table beneath meadow communities was

about 2 m (6.5 ft), and median depth to water beneath phreatophytic

scrub communities ranged from 2.6 to 3.8 m. Floristic comparisons

showed overlap between some communities, revealing potential

successional pathways. Vegetation monitoring results showed that

conversion from Alkali Meadow to Nevada Saltbush Meadow to

Nevada Saltbush Scrub could occur at sites affected by pumping.

Phreatophytic scrub communities, however, may represent successional dead ends where further disturbance results in barren,

weedy land.

The Owens Valley, CA, lies on the western edge of the

Great Basin between the Sierra Nevada and the White/Inyo

ranges (fig. 1). Annual precipitation on the valley floor

averages only 13 cm. Although arid in climate, abundant

runoff from snowmelt recharges the groundwater basin and

supports large areas of phreatophytic vegetation.

Disputes over managing the water resources of the

Owens Valley have a long and well-known history (Kahrl

1982). Recent conflict over groundwater pumping for export

by the City of Los Angeles Department of Water and Power

(LADWP) led to a joint water management agreement between LADWP and Inyo County. In 1997, LADWP and Inyo

County commenced full implementation of the agreement,

which allows pumping to occur as long as Owens Valley

vegetation is not significantly adversely affected. Baseline

vegetation conditions against which future changes would

be gauged were set equal to conditions measured by LADWP

between 1984 and 1987.

The LADWP baseline vegetation data showed that phreatophytic species occupied over 50,000 ha (123,500 acres), over

half of the LADWP-owned land in the valley (91,900 ha).

Plant species occurred in recurring assemblages, which

were mapped by LADWP as parcels containing homogeneous vegetation. It was believed that groundwater withdrawal beneath these assemblages might result in the loss

of some phreatophytic species (Sorenson and others 1991),

but whether the sites would subsequently be colonized by

xeric species was unknown.

Initially, changes in vegetation were to be prevented

by monitoring physical and physiological aspects of the

phreatophytic plants and their environment at 22 permanent monitoring sites located in the Owens Valley wellfields.

By 1991, it was realized that to determine whether pumping

was adversely affecting vegetation, conditions needed to be

evaluated on a scale larger than the permanent monitoring

site. Therefore, a method was adopted to monitor vegetation

conditions within entire LADWP parcels.

The objective of this paper was to evaluate pumpinginduced changes in Owens Valley plant communities. By

applying GIS and statistics to the baseline vegetation data,

scrub and meadow communities were characterized and

relationships among them were identified. These relationships were then used to interpret patterns of change that

were detected in the vegetation monitoring data.

Figure 1—Location of the Owens Valley, CA.

The Effects of Water Table Decline on

Groundwater-Dependent Great Basin Plant

Communities in the Owens Valley, California

Sara J. Manning
232 USDA Forest Service Proceedings RMRS-P-11. 1999

Methods _______________________

Vegetation Classification

During the LADWP 1984-1987 vegetation survey, the

dominant species occurring in the parcels were used to

assign the parcels to a California Department of Fish and

Game “Holland (1986)” plant community. Recently, I analyzed these assignments for the scrub and meadow communities (Manning 1997) to: determine the quantitative characteristics of the plant communities; identify potential

anomalies and outlier parcels; compare Owens Valley plant

communities to those reported in the literature; begin to

update the classification and align it with the currently

accepted statewide vegetation classification system (Sawyer

and Keeler-Wolf 1995); and analyze the parcel cover and

species composition using multivariate techniques.

All LADWP parcel data were screened to remove errors

and redundancies. Percent cover of each species in each

parcel was computed and used for all further analyses.

Diversity indices were calculated using eH' (Hill’s N1) and

1/lambda (Hill’s N2), where H' is Shannon’s index and

lambda is Simpson’s index. Both indices emphasize dominant species, and, in effect, N1 is the number of abundant

species and N2 is the number of very abundant species in the

community (Ludwig and Reynolds 1988). Depth to water

table (DTW) data were obtained from the time of the baseline

vegetation survey from observation wells located throughout the Owens Valley. These data were kriged to develop a

GIS-based grid coverage for DTW (C. Howard, Inyo County

Water Dept. report, in preparation). Mean and median

DTW, obtained by tallying the grid cells underlying each

parcel, were summarized by plant community. Non-metric

multidimensional scaling (MDS) (NTSYS-pc) using species

cover data was applied to explore the relationships among

parcels within a community and to look for overlap between

communities. The latter was achieved by running all parcels in each possible pair; for example, all rabbitbrush scrub

parcels with all Nevada saltbush scrub parcels. Community

“centroids” (single data entries per community containing

the mean cover for each species in each parcel) were also

compared to derive the relationships among all communities. A Bray-Curtis distance matrix served as the input for

MDS. Output was arrayed along three axes, and groupings,

outliers, and possible gradients were identified visually

using the degree to which parcels intermingled in the

output data (Manning 1997).

Effects of Groundwater Pumping

From 1991-1997, a set of parcels was annually inventoried

to monitor the vegetation response to lowered water table.

Of the approximately 95 parcels in the set, about one-half lay

within areas of groundwater withdrawal (wellfield areas)

and half served as controls. All 95 parcels were inventoried

in 1992 and 1996; in other years, a subset was inventoried.

From 1987-1994, pumping had lowered the water table

beneath all wellfield parcels. In 1995, some of the parcels

experienced recovery of the water table due to groundwater

recharge and curtailment of pumping. This trend continued

through 1997, by which time water tables had recovered in

about one-third of the wellfield parcels. The water table

beneath control parcels had been affected solely by natural

fluctuations in discharge and recharge. Drought conditions

prevailed in the Owens Valley from 1987-1992, and 1994

was also a dry year.

Because it had been used originally to inventory the

vegetation, the line-point transect technique was employed

to monitor changes in plant cover and composition. Each

year, 12 to 30 50-m transects were randomly located within

the selected parcels, and the identity of live plants was

recorded at 0.5-m intervals along the transect. Data were

analyzed to assess changes in perennial cover. In addition,

annual changes in species composition were analyzed according to plant life form. The three life form categories used

for analysis included all the common species, and they are

defined as:

Grass—perennial, native grasses, primarily saltgrass

(Distichlis spicata) and alkali sacaton (Sporobolus airoides).

Shrub—native shrubs, primarily Nevada saltbush

(Atriplex lentiformis ssp. torreyi), rabbitbrush (Chrysothamnus nauseosus), greasewood (Sarcobatus vermiculatus) and

other native woody perennials.

Weed—annual and/or exotic species, primarily fivehook

bassia (Bassia hyssopifolia) and Russian thistle (Salsola

tragus).

The data were searched for trends within communities to

see whether or how they differed from overall trends. The

Wilcoxon signed-rank test (SYSTAT 5.0) was used to determine significant changes (p <0.05). Because management

according to plant community had not been envisioned

when monitoring began, there were not always sufficient

numbers of parcels within each community to demonstrate

statistically significant trends. In instances where less

than two parcels defined the group, data were omitted from

these analyses.

Results and Discussion __________

Vegetation Classification

Scrub and meadow plant communities identified by

LADWP during the 1984-1987 survey and pertinent quantitative characteristics are listed in table 1. The predominant

plant community in the Owens Valley was Alkali Meadow.

Great Basin Mixed Scrub, Greasewood Scrub, and Desert

Sink Scrub, and Shadscale Scrub also covered large portions of LADWP land.

Median DTW for the plant communities ranged from 1.6

to 8.5 m (no data were available for areas under Blackbrush Scrub). Previous studies had determined that the

maximum rooting depth of the two dominant grasses in the

Owens Valley, saltgrass and alkali sacaton, was 2 m; for the

dominant shrubs, Nevada saltbush, rabbitbrush, and

greasewood, it was 4 m (Groeneveld 1990). Correspondingly,

the GIS grid of 1984-1987 DTW beneath the plant communities showed meadow communities with median DTW near

2 m and phreatophytic scrub communities with DTW from

2.6 to 3.8 m (table 1). Shadscale scrub, which is not believed

to be a phreatophytic community (Billings 1949), had a DTW

of 2.7 m. Median DTW in all other xeric communities

exceeded 4 m. Therefore, the communities most likely to be
USDA Forest Service Proceedings RMRS-P-11. 1999 233

adversely affected by groundwater pumping were: Alkali

Meadow, Desert Sink Scrub, Rabbitbrush Meadow, Nevada

Saltbush Meadow, Rush/Sedge Meadow, Greasewood

Scrub, Nevada Saltbush Scrub, and Rabbitbrush Scrub.

These are marked with an asterisk in table 1.

Depth to water was not observed to be correlated with

patterns of cover or species diversity among the phreatophytic communities. Average plant cover in these communities ranged from 13.0 percent for Greasewood Scrub to

69.4 percent for Rush/Sedge Meadow. (Rush/Sedge Meadow

is often irrigated in the Owens Valley.) The number of

species recorded in the phreatophytic communities ranged

from 17 for Nevada Saltbush Scrub to 78 for Alkali Meadow.

Rush/Sedge Meadow exhibited the highest diversity indices,

Desert Sink Scrub had the second highest, and Nevada

Saltbush Meadow and Nevada Saltbush Scrub retained

the lowest diversity indices.

Descriptions for most but not all Owens Valley communities matched those of Holland (1986). Nevada Saltbush

Scrub, Nevada Saltbush Meadow, and Rabbitbrush Meadow

were newly described, and others (Sawyer and Keeler-Wolf

1995; Bourgeron and Engelking 1994) do not describe series

or associations that matched these three communities. The

prevalence of the two Nevada saltbush-dominated communities in or near wellfields suggested that lowered water

tables may have influenced their development. Owens Valley Desert Sink Scrub possessed the same name as a previously described community (Holland 1986), but the written

description differed. In the Owens Valley, this community

displayed high diversity with as many as five species serving

as co-dominants. Also, despite being designated “scrub” the

parcels possessed a high proportion of grasses, and median

DTW was 1.9 m.

MDS output for community centroids appears in figure 2.

Although MDS processed data on parcel floristic composition only, the three-dimensional display suggests environmental gradients along which the communities may be

aligned. For example, Shadscale Scrub, Greasewood Scrub,

Desert Sink Scrub, Alkali Meadow, and Rush/Sedge Meadow

are arrayed in increasing order along the x-axis, are nearly

constant along the y-axis, and increase along the z-axis.

Rabbitbrush Scrub and Nevada Saltbush Scrub are lower

along the y-axis than their meadow counterparts.

The pairwise MDS outputs (not presented) revealed

floristic overlap between some plant communities.

By combining the MDS output for community centroids

(x- and y-axes only) with the pairwise results, a simple

model showing relationships among Owens Valley plant

communities was constructed (fig. 3). Figure 3 depicts the

communities with circles proportional to the number of

parcels used for these analyses. Two major groups were

distinguished: xeric and phreatophytic, with the division

occurring between Shadscale and Greasewood Scrubs.

Table 1—Characteristics of Owens Valley plant communities. Phreatophytic communities are denoted

with an asterisk.

Median Average Mapped No. Diversity

Plant community DTW cover area species index

Shrub m percent ha N1 N2

Blackbrush Scrub n.d. 15.7 1,604 16 3.8 2.3

Mojave Mixed Woody Scrub 8.5 19.6 3,694 28 10.5 6.3

Great Basin Mixed Scrub 5.0 15.6 11,193 56 20.1 13.3

Big Sagebrush Scrub 6.8 17.9 4,320 40 5.7 2.4

Desert Saltbush Scrub 4.4 13.7 1,362 21 4.4 2.6

Rabbitbrush Scrub* 3.8 14.8 3,917 33 7.0 3.3

Nevada Saltbush Scrub* 2.8 20.1 3,305 22 5.3 2.8

Shadscale Scrub 2.7 12.7 8,425 33 6.1 2.7

Greasewood Scrub* 2.6 13.0 10,482 27 6.3 3.8

Desert Sink Scrub* 1.9 14.2 9,655 30 8.4 6.1

Meadow

Alkali Meadow* 1.6 37.8 18,140 78 7.9 4.3

Rabbitbrush Meadow* 2.2 31.0 748 20 5.3 3.4

Nevada Saltbush Meadow* 1.9 31.5 1,323 17 4.5 3.3

Rush/Sedge Meadow* 2.0 69.4 1,509 55 18.2 10.9

Figure 2—Three-dimensional MDS output for plant

community centroids.
234 USDA Forest Service Proceedings RMRS-P-11. 1999

It was hypothesized that succession could occur between

communities adjacent to each other in figure 3. For example, alkali sacaton-dominated Alkali Meadow might convert to Desert Sink Scrub or Nevada Saltbush Meadow.

Nevada Saltbush Meadow may tend toward Nevada Saltbush Scrub.

Effects of Groundwater Pumping

Groundwater pumping from 1987-1992 caused measurable declines in the water table beneath wellfields and was

correlated with adverse vegetation changes (Manning 1998).

On average, parcels within the wellfields declined in perennial cover, while control parcels increased (fig. 4). In 1995,

the “recovered wellfield” group was created to account for

the wellfield parcels located in areas where water tables

began returning to the plant root zones. From baseline

years to 1997, changes in plant life form occurred. Generally,

grasses declined in wellfields, and shrubs and weeds increased everywhere (fig. 5).

For the three management categories, annual changes in

total perennial cover and 1997 changes in life form are

discussed below by community. Figures 6a-e show annual

average changes in perennial cover that occurred in five

phreatophytic communities from 1991-1997. Figures 7a-e

show average changes in plant life forms from baseline to

1997.

In control Alkali Meadows, perennial cover had increased

significantly above baseline levels by 1993 and continued to

Figure 3—Diagrammatic model showing floristic overlap between Owens Valley communities.

Figure 4—Annual average change from baseline in

perennial cover for control, wellfield, and recovered

wellfield parcels. Asterisks denote significant change

from baseline (p <0.05).

exceed baseline in subsequent years. For wellfield Alkali

Meadows, cover declined and remained below baseline

levels in all years (fig. 6a). Increased cover in the control

Alkali Meadows was largely due to increases in the shrub

rabbitbrush, and declines in wellfield Alkali Meadows were

due to declines in grass cover (fig. 7a). Recovered Alkali
USDA Forest Service Proceedings RMRS-P-11. 1999 235

Figure 5—Average change in grass, shrub, and weed

cover between baseline year and 1997, in control,

wellfield, and recovered wellfield parcels. Asterisks denote significant change from baseline (p <0.05).

Figure 6—Annual average change from baseline

in perennial cover for control, wellfield, and recovered wellfield parcels grouped according to

plant community: (a) Alkali Meadow; (b) Nevada

Saltbush Meadow; (c) Rabbitbrush Meadow;

(d) Nevada Saltbush Scrub; (e) Rabbitbrush Scrub.

Meadows showed no statistically significant change in

total perennial cover from baseline (fig. 6a, 1995 through

1997), but shrub cover, primarily Nevada saltbush, increased (fig. 7a).

Control Nevada Saltbush and Rabbitbrush Meadows

(fig. 6b, c, respectively) did not show measurable changes in

perennial cover from baseline conditions. Wellfield parcels

for both communities, however, showed declines relative to

baseline, but with one exception, these were not statistically

significant. Declines in wellfield perennial cover for these

two communities was, apparently, caused by declines in

grass and shrub cover (fig. 7b, c). Results in figures 6b and

7b suggest that Nevada Saltbush Meadows react to pumping-induced decline and recovery of the water table by first

dying back, then rapidly increasing in Nevada saltbush

growth. Results of shrub recruitment monitoring further

support this hypothesis (S. Manning, Inyo County Water

Dept., data on file). The continuation of this trend could

result in conversion of this community from Meadow to

Nevada Saltbush Scrub.

From 1995-1997, control Nevada Saltbush Scrub parcels

showed slight increases in perennial cover due to increases

in grass cover (fig. 6d and 7d). This finding and field observations of senescent alkali sacaton tufts beneath shrubs

suggest that these sites were meadows in the past. Wellfield

and recovered wellfield Nevada Saltbush Scrub parcels,

however, showed decreases in shrub cover, suggesting that

pumped Nevada Saltbush Scrub cannot sustain itself. Although the apparent decline in perennial cover relative to

baseline in the recovered wellfields (fig. 6d, 1996-1997) may

represent a longer lag time between water table recovery

and vegetation response, the poor performance of the control

parcels and the observed accumulations of dead, woody

debris at these sites suggest that pumped Nevada Saltbush

Scrub may eventually degenerate beyond the ability to

fully recover with native vegetation.
236 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 7—Average change in grass, shrub, and

weed cover between baseline year and 1997, in

control, wellfield, and recovered wellfield parcels grouped according to plant community as in

figure 6.

Very few Rabbitbrush Scrub parcels have been systematically inventoried. From baseline years to 1997, control

Rabbitbrush Scrub parcels have increased in shrubs, while

recovered wellfield parcels have increased in shrubs and

weeds (fig. 6e and 7e).

Conclusions____________________

Vegetation parcels mapped by LADWP in the 1980’s

generally sorted into distinct communities possessing diagnostic characteristics. MDS revealed overlap between certain communities, suggesting potential directions for community conversion.

Monitoring data from 1991-1997 showed that when affected by groundwater pumping Alkali Meadow may succeed to either Nevada Saltbush Meadow or Rabbitbrush

Meadow, but not Desert Sink Scrub. The conversion to

Nevada Saltbush Meadow may occur relatively quickly

when water tables are altered due to pumping. Conversion

to Rabbitbrush Meadow could be affected by pumping,

grazing, and/or other disturbances. Currently, these are

allowable changes under the water agreement, but improved understanding of this trend may render this change

undesirable.

The species-poor Nevada Saltbush Scrub and Rabbitbrush Scrub communities appear to result from intense

disturbance. The former was shown to be adversely affected

by groundwater pumping. Both communities may be the

last vestiges of native plant communities; if disturbance

continues they may degenerate into barren sites populated

in wet years by annual weeds.

Approaching pumping-induced vegetation changes from

the plant community perspective shows promise that

trends can be correlated with community change. Further

understanding of the characteristics of and the processes

sustaining the plant communities will allow better management, because adverse changes may be identified sooner

and communities with no known successional endpoint

may be managed more conservatively.

Acknowledgments ______________

D. Waterbury, D. Olson, B. Stange, R. Potashin, S. Frei,

A. Parravano, S. Osotoja, and others assisted extensively

with field data collection. C. Howard, Inyo County GIS

Specialist, helped with DTW information and figure 1.

References _____________________

Billings, W. D. 1949. The shadscale vegetation zone of Nevada

and eastern California in relation to climate and soils. American

Midland Naturalist. 42(1): 87-109.

Bourgeron, Patrick S.; Engelking, Lisa D., eds. 1994. A preliminary

vegetation classification of the Western United States. Boulder,

CO: Western Heritage Task Force for the Nature Conservancy.

Groeneveld, David P. 1990. Shrub rooting and water acquisition on

threatened shallow groundwater habitats in the Owens Valley,

California. In: McArthur, E. Durant; Romney, Evan M.; Smith,

Stanley D.; Tueller, Paul T., comps. Proceedings: symposium on

cheatgrass invasion, shrub die-off, and other aspects of shrub
USDA Forest Service Proceedings RMRS-P-11. 1999 237

biology and management; 1989 April 5-7; Las Vegas, NV.

Gen. Tech. Rep. INT-276. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station:

221-237.

Holland, Robert F. 1986. Preliminary descriptions of the terrestrial

natural communities of California. Sacramento: California Department of Fish and Game. 156 p.

Kahrl, William L. 1982. Water and power. Los Angeles: University

of California. 583 p.

Ludwig, John A.; Reynolds, James F. 1988. Statistical ecology.

New York: John Wiley. 337 p.

Manning, Sara J. 1997. Plant communities of LADWP land in the

Owens Valley: an exploratory analysis of baseline conditions.

Bishop, CA: Inyo County Water Department. 160 p.

Manning, S. 1998. Results of 1997 vegetation re-inventory. Bishop,

CA: Inyo County Water Department. 26 p.

Sawyer, John O.; Keeler-Wolf, Todd. 1995. A manual of California

vegetation. Sacramento: California Native Plant Society. 471 p.

Sorenson, Stephen K.; Dileanis, Peter D.; Branson, Farrel A. 1991.

Soil water and vegetation responses to precipitation and

changes in depth to ground water in Owens Valley, California.

U.S. Geological Supply Paper 2370-G. 54 p.
238 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Carl L. Wambolt is Professor of Range Science, Department of Animal

and Range Sciences, Montana State University, Bozeman, MT 59717.

Trista L. Hoffman and Chris A. Mehus are former Research Assistants in

Range Science at Montana State University, Bozeman, MT 59717.

Abstract—A wildfire on the Northern Yellowstone Winter Range

(NYWR) was studied 19 years after burning to compare relative

re-establishment of three big sagebrush (Artemisia tridentata

Nutt.) and three rabbitbrush (Chrysothamnus Nutt.) taxa. Recovery was minimal for all three subspecies of big sagebrush, while

rabbitbrush abundance was much greater after burning. At other

NYWR locations prescribed burned mountain big sagebrush (A.t.

vaseyana [Rydb.] Beetle) characteristics at seven sites were compared with 33 unburned sites to determine the amount of recovery

10 to 14 years after burning. Mountain big sagebrush canopy

coverage on unburned sites averaged 12 times that of burned sites

and densities of established shrubs on unburned sites were 15 times

those of burned sites.

Sagebrush (Artemisia L.) habitat types are important

winter foraging areas for ungulates on the Northern

Yellowstone Winter Range (NYWR) (Wambolt and McNeal

1987; Wambolt 1996; Wambolt 1998; Wambolt and Sherwood

1999). Basin big sagebrush (Artemisia tridentata Nutt. tridentata), Wyoming big sagebrush (A.t. wyomingensis Beetle

and Young), and mountain big sagebrush (A.t. vaseyana

[Rydb.] Beetle) are the dominant taxa. All three are nonsprouting and at least temporarily eliminated by fire. In

addition, browsing on the NYWR is very intense (Kay 1990)

and has been found to reduce sagebrush populations

(Wambolt 1996; Wambolt and Sherwood 1999). The loss of

big sagebrush taxa can impact numerous wildlife populations for which they provide habitat requirements (Welch

1997). Big sagebrush is particularly important for ungulates

during winter as a nutritious forage (Welch and McArthur

1979) and for thermal and security cover. When big sagebrush is reduced, long-term reductions may be expected in

some wildlife populations. Given the importance of big

sagebrush to wildlife, natural resource managers need to

appreciate that these taxa should often be maintained.

Therefore, it is necessary to understand the long-term dynamics of big sagebrush communities following fire on

ranges where browsing is intense like on the NYWR. This

Response of Shrubs in Big Sagebrush

Habitats to Fire on the Northern Yellowstone

Winter Range

Carl L. Wambolt

Trista L. Hoffman

Chris A. Mehus

research was conducted because fire may interact with

browsing to further influence shrubs. Our objective was to

investigate shrub recovery following prescribed and wildfire in big sagebrush communities in the Gardiner Basin of

the NYWR.

Methods _______________________

Study Area

The study was conducted in the Gardiner Basin of the

NYWR adjacent to Yellowstone National Park (YNP) in

southwestern Montana (fig. 1). Along the Yellowstone River

annual precipitation averages 305 mm. The nearby benchlands receive 406 mm of precipitation. Half of the annual

precipitation is in the form of snow and June is the wettest

month. Orographic effects on precipitation of mountain

peaks up to 3,353 m make the benches and adjacent slopes

of the Gardiner Basin a natural winter range for ungulates.

Elk (Cervus elaphus nelsoni) and mule deer (Odocoileus

hemionus hemionus) are the important ungulates on the

sites used in this research.

Glacial scouring and deposition have been strong influences on the soils. Parent materials include granites and

limestones deposited by glaciers as well as basalts and

breccias. The soil regolith in the study area may range from

a few cm in areas scoured by glaciers to over 1.5 m in

depositional areas. Mollisols are the dominant soil order.

Soil textures are most commonly loams and sandy loams

(Wambolt and McNeal 1987).

Four sagebrush taxa, basin big sagebrush, Wyoming big

sagebrush, mountain big sagebrush, and black sagebrush

(Artemisia nova Nels.), occur sympatrically but with varying frequency. Mountain big sagebrush is the dominant on

the majority of the area. Threadleaf rubber rabbitbrush

(Chrysothamnus nauseosus consimilis [Greene] Hall &

Clem.), mountain low rabbitbrush (C. viscidiflorus lanceolatus [Nutt.] Hall & Clem.), narrowleaf low rabbitbrush (C.

v. viscidiflorus var. stenophyllus [Hook.] Nutt.), and gray

horsebrush (Tetradymia canescens D.C.) occur throughout

the sagebrush-dominated portions of the area.

Bluebunch wheatgrass (Agropyron spicatum [Pursh.]

Scribn.) and Idaho fescue (Festuca idahoensis Elmer) are the

principal grasses found as sagebrush understory. Other

common grasses are prairie junegrass (Koeleria macrantha

Ledeb.), needle-and-thread (Stipacomata Trin. & Rupr.), and

Indian ricegrass (Oryzopsis hymenoides [R. & S.] Ricker).
USDA Forest Service Proceedings RMRS-P-11. 1999 239

Figure 1—The Northern Yellowstone Winter Range. This study was conducted north

of Yellowstone National Park in the Gardiner Basin. That area is especially important

for wintering ungulates (National Park Service map).

Sampling and Analysis

A wildfire burned approximately 80 ha in July 1974.

During summer 1993, shrub canopy cover, density, and

production of winter forage were measured within the 1974

wildfire and also in three adjacent, environmentally paired,

unburned sagebrush communities. One-hundred-eighty

30 m transects were located every 10 m over the burned

area. The three adjacent unburned areas were sampled with

30 transects each for comparison with the burned area. Belt

transects of 60 m2

 were established by measuring 1 m on

each side of the line transect. A plumb bob was used to

determine canopy cover to the nearest cm along each 30 m

transect. Plant density was determined by counting all

sagebrush plants rooted within the belt transect. Measurements for determining production of winter forage were

made on 10 large plants per line transect using models

developed on the NYWR (Wambolt and others 1994).

To make comparisons among the shrub taxa, data from

the burned and unburned areas were combined into ratios

(burned/unburned) for each measured parameter. This ratio

represented the extent (percentage) to which each shrub

taxon recovered since the 1974 wildfire. Because both the

numerator and denominator of the ratio have distinct variability values, a combined variance term was calculated for

each ratio (Cochran 1977). The ratios were then compared

using multiple t-tests.

Also during summer 1993, 33 unburned and seven prescribed burned mountain big sagebrush sites were studied

in the Gardiner Basin (fig. 1). Each site was a stand of

mountain big sagebrush that was homogeneous in characteristics of slope, aspect, and elevation. These sites ranged

between 0.25 and 3 ha in area. Plant characteristics measured were percent canopy cover of shrubs, density of large

and small shrubs, and age. Large plants were ≥22 cm across

the widest portion of crown and small plants were <22 cm. At

each site, two line transects, 30 m long and 10 m apart, were

established with the slope of the site. Procedures used to

obtain shrub canopy cover and density followed those

described above for studying the wildfire. Aging was accomplished by counting annual growth rings in crosssection. Production was not a consideration as the sagebrush plants in the burns were too small for the models

minimum size requirements. Student’s t-tests were used to

compare parameters between burned and unburned sites.

Results and Discussion __________

On the portion of the Gardiner basin burned by wildfire in

1974 and studied 19 years later, overall recovery was minimal for three subspecies of big sagebrush (figs. 2-6), while

rabbitbrush abundance was much greater than that of

unburned areas (fig. 7). Wyoming big sagebrush and mountain big sagebrush canopy cover recovery was only 0.6 and

1.6%, respectively, that of unburned paired sites (fig. 6).

Basin big sagebrush canopy cover recovered to 20% of that

of the paired unburned sites. The recoveries of burned

compared to unburned Wyoming, mountain, and basin big

sagebrushes were 2, 12, and 16% for density and 0.1, 14, and

11% for production of winter forage, respectively (fig. 6). All

parameters were significantly greater (P <0.0001) in the

unburned treatment.

Rabbitbrush canopy cover and density for all taxa were

greater in the burned than paired unburned sites. Threadleaf

rubber rabbitbrush, mountain low rabbitbrush, and
240 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 2—Photo following fire in 1974. Compare to scene

20 years later (1994) in Fig. 3.

Figure 3—Photo in 1994. Compare to scene the year of

fire (1974) in Fig. 2. Note lack of sagebrush recovery in

20 years.

Figure 4—Photo following fire in 1974. Compare to scene

20 years later (1994) in Fig. 5.

Figure 5—Photo in 1994. Compare to scene the year of

fire (1974) in Fig. 4. Note lack of sagebrush recovery in

20 years.

narrowleaf low rabbitbrush recovery in canopy cover were

not different (fig. 7). The only difference found in recovery

among the three rabbitbrush taxa was that mountain low

rabbitbrush established to a greater density than either

threadleaf rubber or narrowleaf low rabbitbrush (P ≤0.02).

A large number of seedling and small mountain low rabbitbrush plants collectively did not contribute much to canopy

cover. Because of heavy browsing a large proportion of

seedlings did not reach maturity, thus canopy cover was

probably a better indicator of long-term establishment than

was density.

Logically the sprouting rabbitbrush taxa should have

been benefited by the burn and been plentiful, until successionally replaced by the dominant big sagebrush taxa. Although there was significantly (P <0.01) more canopy cover

and individuals for all three rabbitbrush taxa in the burn,

the canopy cover was still low in the burn at 1.3, 1.6, and

5.6% for mountain low rabbitbrush, narrowleaf low rabbitbrush, and threadleaf rubber rabbitbrush, respectively.

Wambolt and Sherwood (1999) found that even sprouting

rabbitbrushes may decline from the levels of ungulate browsing on the NYWR.

The comparison of the 33 unburned and seven prescribed

burned mountain big sagebrush sites provided results quite

similar to the wildfire above. All seven mountain big sagebrush prescribed burned areas sampled also indicated that

recovery of the taxon following fire is slow (table 1). Although

sites had burned between 9 and 13 years previous to sampling, none had significantly recovered (table 2). Mountain

big sagebrush canopy cover averaged 1.2%, but this value

was highly dependent on a single site (table 1, site 5) that

had 6.7% sagebrush cover. This was the only burned site to

exceed 1% canopy cover. This compared with an average

cover of 14.2% for the 33 unburned sites. Average canopy
USDA Forest Service Proceedings RMRS-P-11. 1999 241

coverage of unburned sagebrush was over 12 times that on

burned sites. Mountain big sagebrush density was also

reduced by burning. The highest density of large plants on a

burned site was 14/transect (0.23 plants/m2

) at site 5. The

average density on unburned sites was 52 plants/transect

(0.86/m2). The density of small plants followed a similar

trend with an average on unburned sites of 11 times that on

burned sites. The differences in canopy cover and densities

of large and small plants between burned and unburned

sites were all significant (table 2).

Table 1—Characteristics of mountain big sagebrush on seven burned

sites in 1993.

Year Canopy Densitya (plants/m2)

 Site burned cover % Large Small Total

1 1982 0.0 0.0 0.0 0.0

2 1979 0.4 0.1 0.0 0.1

3 1978 0.0 0.0 0.0 0.0

4 1979 0.0 0.0 0.1 0.1

5 1984 6.7 0.2 0.3 0.5

6 1984 0.8 0.1 0.1 0.1

7 1982 0.3 0.0 0.1 0.1

Average 1.2 0.1 0.1 0.1

aLarge plants measured ≥22 cm across widest portion of crown and small

plants <22 cm.

Table 2—Student’s t-test comparisons of burned and unburned

mountain big sagebrush sites.

B/Ua n x Prob > t

Percent cover of B 7 1.2 0.0001

 sagebrush U 33 14.2

Density of largeb B 7 0.06 0.0000

 plants/m2 U 33 0.86

Density of smallb B 7 0.08 0.04

 plants/m2 U 33 0.91

aB = Burned site, U = Unburned site.

b

Large plants measure ≥22 cm across the widest portion of crown and small

plants <22 cm.

Figure 7—Canopy cover and density expressed as

ratios (burned/unburned) for three rabbitbrush taxa compared between a 19 year old wildfire and paired unburned sites. Different letters above columns are

significantly different (P ≤0.05) among taxa within each

measured parameter.

Figure 6—Canopy cover, density, and production of winter forage expressed as ratios (burned/unburned) for three

big sagebrush subspecies compared between a 19 year

old wildfire and paired unburned sites. Different letters

above columns are significantly different (P ≤0.05) among

taxa within each measured parameter.

Our results are similar to Blaisdell (1953) who found little

re-establishment of mountain big sagebrush 12 years after

burning. Wambolt and Payne (1986) and Watts and Wambolt

(1996) found that Wyoming big sagebrush exhibited a

similar pattern in southwestern Montana. While plants as

young as 2 years are capable of producing seed (Young

and others 1989), no plants growing in our burned areas,

less than 10 years old, had reproductive stalks. Some of the

aged plants were found to be older than the burns. This

indicated that they had not established after the fire, but

had survived the burn. These residual plants represent the

most important seed source for stand regeneration

(Frischknecht and Bleak 1957).

Big sagebrush taxa are declining from browsing on this

important ungulate winter range (Wambolt 1996; Wambolt

1998; Wambolt and Sherwood 1999) and our data indicate

burning will probably accelerate this decline. In addition,

browsing may substantially reduce seed production in sagebrush. Heavy browsing on Wyoming big sagebrush at lower

elevations of the study area were found to nearly preclude

the growth of reproductive structures (Hoffman and Wambolt

1996). Combined effects, such as browsing with the difficulty

of seed production by a limited number of parent plants that

may survive burning, will logically restrict the ability of

big sagebrush to re-establish after fire. Burning big sagebrush stands that provide cover and forage to ungulates will

likely concentrate ungulates on unburned areas and accelerate the decline in sagebrush.
242 USDA Forest Service Proceedings RMRS-P-11. 1999

References _____________________

Blaisdell, J. P. 1953. Ecological effects of planned burning of sagebrush-grass range on the upper Snake River Plains. U.S. Department of Agriculture Technical Bulletin No. 1075.

Cochran, W. B. 1977. Sampling techniques. John Wiley & Sons, Inc.

Frischknecht, N. C.; Bleak, A. T. 1957. Encroachment of big sagebrush on seeded range in northeastern Nevada. Journal of

Range Management. 10:165-170.

Hoffman, T. L.; Wambolt, C. L. 1996. Growth response of Wyoming

big sagebrush to heavy browsing by wild ungulates. In: Barrow,

J. R.; McArthur, E. D.; Sosebee, R. E.; Rausch, R. E., compilers,

Proceedings, symposium on shrubland ecosystem dynamics in a

changing environment. USDA Forest Service General Technical

Report INT-GTR-338. Ogden, UT: 242-245.

Kay, C. E. 1990. Yellowstone’s northern elk herd: a critical evaluation of the “natural-regulation” paradigm. Ph.D. Dissertation,

Utah State University, Logan, UT.

Wambolt, C. L. 1996. Mule deer and elk foraging preference for 4

sagebrush taxa. Journal of Range Management. 49:499-503.

Wambolt, C. L. 1998. Sagebrush and ungulate relationships on

Yellowstone’s northern range. Wildlife Society Bulletin.

26(3):429-437.

Wambolt, C. L.; Creamer, W. H.; Rossi, R. J. 1994. Predicting big

sagebrush winter forage by subspecies and browse form class.

Journal of Range Management. 47:231-234.

Wambolt, C. L.; McNeal, A. F. 1987. Selection of winter foraging

sites by elk and mule deer. Journal of Environmental Management. 25:285-291.

Wambolt, C. L.; Payne, G. F. 1986. An 18-year comparison of control

methods for Wyoming big sagebrush in southwestern Montana.

Journal of Range Management. 39:314-319.

Wambolt, C. L.; Sherwood, H. W. 1999. Sagebrush response to

ungulate browsing in Yellowstone. Journal of Range Management.

52:363-369.

Watts, M. J.; Wambolt, C. L. 1996. Successional trends of Wyoming

big sagebrush 30 years after four treatments. Journal of Environmental Management. 46:95-102.

Welch, B. L. 1997. Seeded versus containerized big sagebrush

plants for seed-increase gardens. Journal of Range Management. 50:611-614.

Welch, B. L.; McArthur, E. D. 1979. Feasibility of improving big

sagebrush (Artemisia tridentata) for use on mule deer winter

ranges. In: Goodin, J. R.; Northington, D. K., editors. Arid land

plant resources. Texas Tech University, Lubbock, TX: 451-473.

Young, J. A.; Evans, R. A.; Palmquist, D. E. 1989. Big sagebrush

(Artemisia tridentata) seed production. Weed Science. 37:47-53.
USDA Forest Service Proceedings RMRS-P-11. 1999 6

Community Rehabilitation

and Restoration

243

USDA Forest Service Proceedings RMRS-P-11. 1999 245

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Rosemary L. Pendleton and Burton K. Pendleton are Research Ecologists,

USDA Forest Service, Rocky Mountain Research Station, 735 North 500 East,

Provo, UT. At the time of the research, Steven D. Warren was Research

Ecologist, U.S. Army Corps of Engineers, Construction Engineering Research

Laboratory, PO Box 9005, Champaign, IL 61826-9005.

Response of Blackbrush (Coleogyne

ramosissima) Seedlings to Inoculation with

Arbuscular Mycorrhizal Fungi

Rosemary L. Pendleton

Burton K. Pendleton

Steven D. Warren

Abstract—Blackbrush, (Coleogyne ramosissima), occurs as a landscape dominant in the ecotonal region between hot and cold deserts

of the western United States. Revegetation efforts using blackbrush

have met with limited success, prompting speculation on possible

interactions with soil microorganisms, including mycorrhizal fungi.

From 1993 to 1997, we conducted a series of experiments designed

to test the effect of inoculation with arbuscular mycorrhizal fungi on

the growth of young blackbrush seedlings under a variety of soil

nutrient conditions. In all cases, growth of blackbrush seedlings was

enhanced in the presence of mycorrhizal fungi. Inoculation resulted

in increased plant biomass, decreased allocation to root systems in

general and to fine roots in particular, and increased tissue concentrations of both phosphorus and nitrogen. The addition of mycorrhizal fungi also significantly decreased the ability of cheatgrass to

compete with blackbrush seedlings when grown at low soil nutrient

levels. Revegetation of blackbrush areas would likely benefit from

the use of mycorrhizal inoculum. Soil fertilization, however, is detrimental to the establishment of this species and is not recommended.

Blackbrush, or Coleogyne ramosissima, occurs as a landscape dominant on over three million ha in the southwestern

United States, occupying the transition zone between hot

and cold deserts (Bowns and West 1976: Benson and Darrow

1981). It forms a major vegetational component of many

National and State Parks in Utah, Nevada, and California,

including Canyonlands, Arches, Valley of the Gods, Lake

Powell, and Red Rocks. At lower elevations, blackbrush is

bounded by creosote (Larrea tridentata) and Joshua tree

(Yucca brevifolia) communities; at higher elevations by

juniper (Juniperus sp.) and big sagebrush (Artemisia tridentata) communities. Blackbrush provides forage for bighorn

sheep and wintering deer. The seed is used by both rodents

and birds (Pendleton 2000).

Limited attempts at revegetation of blackbrush areas

have generally had poor success (Pendleton and others

1995). Factors that may have been responsible include

timing and amount of precipitation, lack of seed, and weed

competition. A contributing factor is the extremely slow

growth of blackbrush. In a study at Arches National Park,

average height of five-year-old seedlings was less than 6 cm

(S. E. Meyer and B. K. Pendleton, unpublished data). Slowgrowing species such as blackbrush are at a competitive

disadvantage in disturbed sites dominated by exotic weeds.

Another hypothesis, examined in this paper, is that the soil

microflora may play an important part in the successful

establishment of this species (Pendleton and others 1995).

An important but little-studied aspect of arid-zone ecosystems is the role of the soil microflora, including microphytic

soil crust organisms and arbuscular mycorrhizal fungi.

Microphytic soil crusts (also known as cryptobiotic, microbiotic and cryptogamic crusts) contribute significantly to ecosystem stability by means of soil stabilization and improved

growth and establishment of vascular plant species (Harper

and Marble 1988; St. Clair and Johansen 1993). They are

formed initially by blue-green algae that fix nitrogen and

bond soil particles. Mature crusts also contain a variety of

soil lichens and mosses. Arbuscular mycorrhizal fungi are

known to aid plants in nutrient acquisition, primarily of

phosphorus. In desert systems, however, their role is poorly

understood. Root colonization by these fungi can vary widely

with season (Allen 1983), possibly corresponding to changes

in photosynthetic activity (Bethlenfalvay and others 1984).

Disturbance can have a profound effect on soil microorganisms. Disturbance of the soil crust when dry through

trampling or off-road vehicle use causes the crust to collapse,

leading to erosion of the soil surface (Belnap 1993). The

erosion can be significant, exposing six inches or more of the

shrub root zone (personal observation). The ensuing drifting

of the sandy soils buries other areas of undisturbed crust,

resulting in reduced nitrogen fixation or in the death of the

crust. Disturbance also results in decreased numbers of

mycorrhizal propagules in the soil (Moorman and Reeves

1979; Powell 1980). Invasive weeds are generally less dependent on mycorrhizal fungi than are climax species (Miller

1979; Reeves and others 1979; Allen and Allen 1980). Consequently, the lack of mycorrhizal inoculum may increase

the time it takes for vegetation to recover.

The research we report on here has been funded by the

Army Corps of Engineers as part of an effort aimed at

restoration of disturbed lands. The focus of our research has

been an examination of the interaction of arbuscular mycorrhizal fungi with soil crust organisms as it pertains to the

successful establishment of native plant species. In this

paper, we summarize findings from a series of experiments

designed to test the effect of inoculation with arbuscular
246 USDA Forest Service Proceedings RMRS-P-11. 1999

mycorrhizal fungi on the establishment and subsequent

growth of blackbrush plants both in the presence and absence of crust-forming microorganisms.

Methods _______________________

Three experiments evaluating growth of blackbrush under different soil conditions were undertaken in the years

from 1993 to 1997. In the first experiment, we applied three

soil fertility levels using mature microphytic soil crusts

collected near Moab, Utah; blow sand (no crust present),

mixed crust (100% pulverized crust material), and a crustover-sand treatment in which we attempted to mimic natural conditions by placing a circle tz intact crust material over

blow sand. Nitrogen levels varied from 4 ppm in blow sand

to 80 ppm in the mixed crust treatment. Mycorrhizal inoculum of the species Glomus intraradices, obtained from Native Plants, Inc., was introduced to half of the plants. Ten

blackbrush plants, pre-germinated from seed collected in

Washington County, UT, were grown in each of the six soil

fertility/mycorrhizal treatment levels. Plants were randomized and maintained in a greenhouse for 12 weeks.

In the second experiment, we attempted to establish

conditions that would exist in a field restoration attempt. A

low-fertility bank sand was purchased from Western Sand

and Gravel in Spanish Fork, UT. The sand had a pH of 8.5,

conductivity of 0.4 mmhos/cm, and plant-available nutrient

concentrations of 4.7, 2.9, and 22.4 ppm for nitrate-N,

phosphorus, and potassium, respectively. The sand was

steamed for two hours at 77 °C, then amended to one of three

agronomic soil fertility levels using a slow-release 17-7-12

Osmocote fertilizer. The low fertility level had no additional

fertilizer added. Medium and high treatment levels were

amended to low (5 oz. per cubic foot) and medium (9 oz. per

cubic foot) values recommended by the manufacturer. The

mycorrhizal inoculum consisted of spores isolated from

soils near Toquerville, UT, where blackbrush was growing.

Spores were extracted from the soil by wet-sieving and

decanting, followed by sucrose centrifugation (Daniels and

Skipper 1982; Walker and others 1982). The algal inoculum

used was a pelletized blue-green algal inoculum, primarily

containing Schizothrix sp., developed for crust restoration

by Jeff Johansen of John Carroll University and Larry

St. Clair of Brigham Young University. The inoculum was

applied at a rate of 75 g/m2

 or approximately 1.6 g per pot,

sprinkled evenly over the top of the soil at the time of

planting. Half of the pots were also planted with one seed of

cheatgrass (Bromus tectorum) to assess the effects of competition. Total treatment number was 24, with three replications per treatment. Plants were grown for 6 months in a

walk-in growth chamber programmed to simulate early

spring to late summer conditions.

The third experiment was a modification of the second.

Two soil fertility levels, low and medium, were established

as previously described. Competition with cheatgrass was

limited to the low soil fertility level. Ten replicate pots were

used for each treatment combination. Pots were randomized

and grown for five months in a greenhouse that had been

cleaned, sprayed with a biocide, and equipped with new

evaporative cooling pads.

At the end of each experiment, plants were harvested,

dried, and weighed. Shoot biomass was ground and analyzed

for nutrient composition at the Soil and Plant Analysis

Laboratory at Brigham Young University. Total root length

was calculated using a modified line intersect method of

Tennant (1975). Data were entered, stored on disk, and

analyzed using SAS version 6.11 for the personal computer.

Mean separations were accomplished using the StudentNewman-Keuls multiple range test.

Results ________________________

Growth and Allocation Patterns

The addition of mycorrhizal fungi resulted in increased

shoot growth of blackbrush plants across all soil treatments.

In the first experiment, mycorrhizal plants had a significantly higher average shoot weight (p = 0.0100) and total

plant weight (p = 0.0208) than did nonmycorrhizal plants

(fig. 1). They also responded more to the higher nutrient

Figure 1—Mean shoot weights and root/shoot

ratios for mycorrhizal and nonmycorrhizal

blackbrush plants grown in one of three soils;

mixed crust, crust-over-sand, and blow sand

(experiment 1).
USDA Forest Service Proceedings RMRS-P-11. 1999 247

content of the crusted soils than did their nonmycorrhizal

counterparts. Indeed, mycorrhizal plants growing in blow

sand had as much aboveground biomass as did nonmycorrhizal plants growing in the two crusted soils.

Similar results were obtained in the second and third

experiments, although the means were not statistically

different. In experiment 2, shoot weight of mycorrhizal

plants grown at low soil fertility averaged 0.187 g as compared with an average of 0.103 g for nonmycorrhizal plants.

Poor survival at medium and high soil fertility precluded

comparisons for these treatments. In experiment 3, shoots of

mycorrhizal plants averaged 0.785 g at medium fertility and

0.152 g at low fertility as compared with 0.682 g and 0.140 g,

respectively, for nonmycorrhizal plants (fig. 2).

The addition of mycorrhizal fungi also significantly changed

the allocation of plant biomass between shoots and roots.

Mycorrhizal plants consistently invested less in root biomass than did nonmycorrhizal plants. In experiment 1, this

difference was significant across all soil treatments (fig. 1).

In experiment 2, root/shoot ratios averaged 0.574 for mycorrhizal plants and 2.392 for nonmycorrhizal plants. A similar

pattern was seen in experiment 3, root/shoot ratios of mycorrhizal plants averaging 0.222 at medium soil fertility and

1.16 at low soil fertility, whereas ratios for nonmycorrhizal

plants averaged 0.385 and 1.35, respectively (fig. 2). Specific

root lengths (a measure of root architecture) of mycorrhizal

plants were also significantly lower (p = 0.0230), indicating

less allocation to fine feeder roots as opposed to larger

transporting roots. Specific root lengths for mycorrhizal

plants in experiment 1 averaged 4544.3 m/g as compared

with 5452.1 m/g for nonmycorrhizal plants, a 17 percent

decrease.

In general, blackbrush did not respond positively to inoculation with the pelletized algae. In experiment 3, blackbrush

plants grown in soils inoculated with the algae had significantly smaller shoot weights than did the control plants

(p = 0.0086), especially at medium fertility (fig. 3). Plants

with noninoculated soils had a mean shoot weight of 0.893 g

at medium fertility and 0.157 g at low fertility, as compared

with 0.655 g and 0.135 g for inoculated soils. A similar

pattern was seen in experiment 2, plants with noninoculated

soils averaging a shoot weight of 0.119 g compared with

0.110 g for plants with inoculated soils.

Elemental Tissue Analysis

The addition of mycorrhizal inoculum had a notable effect

on the elemental tissue concentrations of various plant

nutrients. Mycorrhizal plants in the first experiment had a

significantly higher concentration of immobile elements,

including Zn, Cu, and P (table 1). The plant-fungal association was particularly beneficial in increasing tissue concentrations of phosphorus under low nutrient conditions typical

of blackbrush habitat (fig. 4). When percent phosphorus is

multiplied by plant biomass to obtain total phosphorus

uptake, highest phosphorus uptake was found in mycorrhizal plants growing in the crust-over-sand treatment,

suggesting that greatest efficiency in nutrient uptake may

occur where mycorrhizae and healthy mature microphytic

crusts co-occur. Mycorrhizal blackbrush plants also tended

to have a higher nitrogen content in their tissues, although

the statistical significance was marginal for this element

(p = 0.1008).

Competitive Ability

Although shoot growth of blackbrush plants was increased

by the addition of fertilizer (fig. 2), the ability of blackbrush

to survive and compete was greatly reduced in the higher

nutrient soils. In the absence of competition from cheatgrass, survival of shrubs was lower under fertilization in

both experiment 2 and 3 (table 2). When grown with cheatgrass, no shrubs survived in fertilized soils (experiment 2).

In experiment 3, four inoculation treatments were applied

to blackbrush plants growing at low soil fertility with and

Figure 2—Mean shoot weights (g) and root/shoot ratios for mycorrhizal

and nonmycorrhizal blackbrush plants grown at low and medium soil

fertilization levels (experiment 3).
248 USDA Forest Service Proceedings RMRS-P-11. 1999

Figure 3—Effect of soil inoculation with crust-forming algae on shoot growth of blackbrush plants

grown at low and medium soil fertilization levels

(experiment 3).

Table 1—Means and attained significance values from ANOVA of leaf

and stem tissue concentrations of mycorrhizal and

nonmycorrhizal plants grown in three soils; mixed crust, crustover-sand, and blow sand. Data are from experiment 1.

P N Zn Cu

- - - Percent - - - - - - - - Ppm - - - - - 

With mycorrhizae 0.21 1.34 32.04 4.82

Without mycorrhizae 0.09 1.23 23.96 3.27

p value 0.0001 0.1008 0.0067 0.0041

Figure 4—Nitrogen and phosphorus content of stem

and leaf tissue of blackbrush plants grown in three

soils; mixed crust, crust-over-sand, and blow sand

(experiment 1). Nitrogen content was determined using the Kjeldahl digestion method. A Technicon Auto

Analyzer (Technicon Instrument Corp., Tarrytown, NY)

was used to determine phosphorus content. Three

composite samples of three plants each were used in

the analysis.

Table 2—Blackbrush survival as affected by soil fertility and competition

with cheatgrass. Entries for experiment 2 are the number of

plants surviving out of an initial 12. Entries for experiment 3

are the number of surviving plants out of an initial 40.

High Medium Low

fertility fertility fertility

Experiment 2

With cheatgrass 0 0 9

Without cheatgrass 4 8 7

Experiment 3

With cheatgrass — — 40

Without cheatgrass — 14 40

without competition from cheatgrass. Inoculation treatment

had a significant effect on blackbrush shoot growth when

grown alone (p = 0.0095), but not when grown in the presence

of cheatgrass (p = 0.9326). Treatment did, however, affect

the growth of the cheatgrass (p = 0.0029). When grown alone,

blackbrush shoots grew significantly better when inoculated

with mycorrhizae only (fig. 5). This difference in shoot

growth disappeared in the presence of cheatgrass. In contrast, cheatgrass grew best when algae were added to the

soil, and least with mycorrhizae. The same pattern was

observed in experiment 2. In the absence of competition,

blackbrush grew better with mycorrhizae only. No treatment differences were observed for the shrub when grown

with cheatgrass, whereas the cheatgrass grew best with

algae and least with mycorrhizae.

One reason for the observed reduction of blackbrush shoot

growth in the presence of both mycorrhizae and cheatgrass

may be found in the biomass allocation patterns. Competition resulted in an altered allocation pattern for the shrub,

but not the grass. In the absence of competition, root/shoot

ratios of mycorrhizal plants were reduced (fig. 1). However,

when competition was introduced, the root/shoot ratio of

blackbrush actually increased (fig. 6). In contrast, root/shoot

ratios for the competing cheatgrass declined with the addition of mycorrhizal fungi.
USDA Forest Service Proceedings RMRS-P-11. 1999 249

Discussion _____________________

Nitrogen and phosphorus availability have been implicated as major determinants of community structure and

successional dynamics (Tilman 1986; Vitousek and White

1981). Arbuscular mycorrhizal fungi and crust-forming bluegreen algae are biological processors of these nutrients.

Arbuscular mycorrhizal fungi have demonstrated the ability to enhance nutrient acquisition of many plant species

through the formation of mutualistic relationships with

plant roots (Allen 1992). The hyphal network essentially

provides an extension of the root surface area, increasing

plant access to certain immobile elements in exchange for

carbon compounds. Beneficial effects are a function of plant

root architecture, plant and fungal species interactions, and

environmental conditions, including soil nutrient levels,

temperature, and moisture.

Blackbrush clearly benefits from a relationship with

arbuscular mycorrhizal fungi, and is partially dependent on

that relationship for optimal growth. This was evidenced in

the first experiment, where blackbrush plants grew larger in

the presence of mycorrhizae and had higher tissue concentrations of many nutrients, including nitrogen and phosphorus. Studies documenting increased growth and phosphorus

content of mycorrhizal plants are numerous and well-reviewed (Mosse 1973). Several studies have reported an

increase in nitrogen uptake as well (Quintero-Ramos and

others 1993; Trent and others 1993). Next to water, nitrogen

is the factor most limiting to plant growth in desert ecosystems (Evans and Belnap 1999).

Allocation to root function was also significantly reduced

in mycorrhizal blackbrush, indicating that proportionately

less root mass was needed to meet the demand for plant

growth. Similar reductions in allocation to root function in

response to mycorrhizal colonization and increased soil

fertility have previously been reported (Chapin 1980; Allen

1991; Redente and others 1992). Root architecture of

blackbrush, as measured by specific root length, further

indicates a shift in allocation of mycorrhizal plants away

from fine feeder roots. Optimal resource utilization and

flexibility in allocation patterns may be particularly important for slow-growing aridland perennials. Plasticity in

allocation and root architecture in response to mycorrhizal

colonization has been proposed as characteristic of mycorrhizal-dependent plant species (Smith and Smith 1996;

Hetrick and others 1991).

Growth and allocation trends in the second and third

experiments were similar to those in the first experiment,

however, in many cases the observed differences were not

statistically significant. One reason for this may lie in the

inoculum used. Mycorrhizal isolates vary in their ability to

increase plant growth (van der Heijden and others 1998;

Trent and others 1993; Bethlenfalvay and others 1989;

Wilson 1988). In the first experiment, the fungal isolate used

was one developed and marketed for its superior growthenhancing capability. In native situations, using a mixture

of fungi, the growth response tends to be lower (Trent and

others 1993). The consistency of the results obtained from

the different experiments does, however, lend credibility to

the hypothesis that blackbrush is partially dependent on

arbuscular mycorrhizal fungi.

 Mycorrhizal fungi may play a part in mediating interspecific plant competition (Francis and Read 1995; Allen 1991;

Miller 1987), including interactions between native species

and exotic annuals (Goodwin 1992). Exotic annuals and

other early seral species are almost always nonmycorrhizal

or facultative in nature (Allen 1991). Many of these show a

reduction of yield and survivorship when grown with mycorrhizal fungi (Francis and Read 1995) Later seral species are

hypothesized to have more of a competitive advantage when

mycorrhizae are present. This has been borne out in limited

studies involving native western grasses and a number of

chenopod- or mustard-family annuals. (Johnson 1998; Allen

and Allen 1986; Allen and Allen 1984).

Figure 6—Root/shoot ratios of mycorrhizal and

nonmycorrhizal blackbrush plants grown at low soil

fertility, alone and in competition with cheatgrass

(experiment 3). Root/shoot ratios of the competing

grass are also given.

Figure 5—Effect of soil inoculation treatment on

shoot growth of blackbrush plants grown at low soil

fertility, alone and in competition with cheatgrass

(experiment 3). Cheatgrass weights shown here

have been divided by 10 so that shrub and grass

weights could be presented on the same graph.
250 USDA Forest Service Proceedings RMRS-P-11. 1999

In our study, blackbrush grew best in the single-inoculation mycorrhizal treatment in the absence of competition. In

competition with cheatgrass, the addition of mycorrhizae

did not increase plant growth and the allocation to root

growth increased, indicating an increase in competitive

intensity. Other studies have found that the addition of

mycorrhizal fungi increased the intensity of intraspecific

competition (Moora and Zobel 1998, and references therein).

The cheatgrass, in contrast, showed a decrease in top growth

in response to mycorrhizal inoculation, suggesting that its

competitive ability declined. These results suggest that, at

low soil nutrient levels, the presence of mycorrhizal fungi

may give slow-growing shrubs more of a competitive edge

against exotic annuals such as cheatgrass. Further study on

this point is needed.

Soil fertility levels may also affect plant interactions. The

initial dominance and persistence of annuals on disturbed

sites may be related to high nutrient availability, particularly that of nitrogen (Allen 1995; McLendon and Redente

1991). Native perennials displace exotic annuals such as

cheatgrass more rapidly on nitrogen deficient soils (Harper

1992). Although a common reclamation practice, fertilization may place slow-growing native species at a competitive

disadvantage. In this study, blackbrush demonstrated reduced competitive ability and survival in fertilized soils

when grown in competition with cheatgrass. The rapid

growth of the cheatgrass in response to fertilization shaded

out the slow-growing blackbrush, resulting in stunted growth

or death of the shrub.

Mycorrhizal fungi and biological soil crusts may work

synergistically to increase plant establishment and growth.

Harper and Pendleton (1993) found greater root colonization

by mycorrhizal fungi in soils where microphytic soil crusts

were intact. Others report that the presence or limited

addition of organic matter can favor the mycorrhizal symbiosis in a way that fertilization does not (Johnson 1998;

Hepper and Warner 1983). In this study, the combination of

mature soil crust and mycorrhizae provided a better growing

environment over that of noncrusted soils. Highest total

phosphorus and nitrogen uptake occurred in the crust-oversand treatment. Harper and Pendleton (1993) reported that

tissue concentrations of phosphorus were increased in the

presence of soil crusts for mycorrhizal Festuca, but not for

the nonmycorrhizae forming Mentzelia. The greatest difference in root/shoot ratios also occurred in the crust-over-sand

treatment.

The decreased growth of blackbrush in the algal-inoculated soils of experiments 2 and 3 suggest that competition

for soil nutrients may occur during the initial establishment

phase of soil-crust formation. Inoculation with the algae also

appeared to benefit the growth of cheatgrass. Although

these results suggest some negative effects of crust inoculation, other research indicates that the long-term benefits of

biological soil crusts to plant establishment and growth are

considerable. Once established, mature soil crusts have

been shown to improve seedling establishment of several

native species, including blackbrush, under field conditions

(Harper and Pendleton 1993; Harper and Marble 1988).

Tissue concentrations of many plant nutrients, including N,

Mg, and Zn, are higher in plants growing on microphytic soil

crusts (Belnap and Harper 1995; Harper and Pendleton

1993). Destruction of the soil crust may disrupt the soil

nitrogen balance, leading to permanent alterations in plant

species composition (Evans and Belnap 1999).

Conclusions____________________

1. Arbuscular mycorrhizal fungi benefit the native

blackbrush community by improving growth, reducing investment in fine roots, and enhancing mineral uptake. They

may also positively influence the competitive ability of the

shrub.

2. Fertilization as a restoration technique may increase

plant growth, but can reduce shrub survival and result in

competitive exclusion of shrubs in the presence of cheatgrass.

3. The presence of a healthy soil crust is essential to soil

stability and proper ecosystem function, however there may

be some competition with plants for nutrient resources

during the initial establishment phase. The effect of crust

inoculation on growth and competitive ability of cheatgrass

needs further examination.

References _____________________

Allen, E. B. 1995. Restoration ecology: limits and possibilities in arid

and semiarid lands. In: Roundy, B. A.; McArthur, E. D.; Haley, J.

S.; Mann, D. K., comps. Proceedings: wildland shrub and arid

land restoration symposium; 1993 October 19-21; Las Vegas, NV.

Gen. Tech. Rep. INT-GTR-315. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station:

7-15.

Allen, E. B.; Allen, M. F. 1986. Water relations of xeric grasses in the

field: interactions of mycorrhizas and competition. The New

Phytologist. 104: 559-571.

Allen, E. B.; Allen, M. F. 1984. Competition between plants of

different successional stages: mycorrhizae as regulators. Canadian Journal of Botany. 62: 2625-2629.

Allen, E. B.; Allen, M. F. 1980. Natural re-establishment of vesicular-arbuscular mycorrhizae following stripmine reclamation in

Wyoming. Journal of Applied Ecology. 17: 139-147.

Allen, M. F. 1983. Formation of vesicular-arbuscular mycorrhizae

in Atriplex gardneri (Chenopodiaceae): seasonal response in a

cold desert. Mycologia. 75: 773-776.

Allen, M. F. 1991. The ecology of mycorrhizae. New York, NY:

Cambridge University Press. 184 p.

Allen, M. F., ed. 1992. Mycorrhizal functioning. New York, NY:

Chapman and Hall. 534 p.

Belnap, J. 1993. Recovery rates of cryptobiotic crusts: inoculant use

and assessment methods. Great Basin Naturalist. 53: 89-95.

Belnap, J.; Harper, K. T. 1995. Influence of cryptobiotic soil crusts

on elemental content of tissue of two desert seed plants. Arid Soil

Research and Rehabilitation. 9: 107-115.

Benson, L.; Darrow, R. A. 1981. Trees and shrubs of the southwestern deserts, 3rd ed. Tucson, AZ: University of Arizona Press.

Bethlenfalvay, G. J.; Brown, M. S.; Franson, R. L.; Mihara, L. K.

1989. The Glycine-Glomus-Bradyrhizobium symbiosis. IX. Nutritional, morphological and physiological responses of nodulated

soybean to geographic isolates of the mycorrhizal fungus Glomus

mosseae. Physiologia Plantarum. 76: 226-232.

Bethlenfalvay, G. J.; Dakessian, S.; Pacovsky, R. S. 1984. Mycorrhizae in a southern California desert: ecological implications.

Canadian Journal of Botany. 62: 519-524.

Bowns, J. E.; West, N. E. 1976. Blackbrush (Coleogyne ramosissima

Torr.) on southwestern Utah rangelands. Utah Agriculture Experiment Station Research Reports. 27: 1-27.

Chapin, F. S., III. 1980. The mineral nutrition of wild plants. Annual

Review of Ecology and Systematics. 11: 233-260.

Daniels, B. A.; Skipper, H. D. 1982. Methods for recovery and

quantitative estimation of propagules from soil. In: Schenck, N.

D., ed. Methods and principles of mycorrhizal research. St. Paul,

MN: American Phytopathological Society: 29-36.
USDA Forest Service Proceedings RMRS-P-11. 1999 251

Evans, R. D.; Belnap, J. 1999. Long-term consequences of disturbance on nitrogen dynamics in an arid ecosystem. Ecology. 80:

150-160.

Francis, R.; Read, D. J. 1995. Mutualism and antagonism in the

mycorrhizal symbiosis, with special reference to impacts on plant

community structure. Canadian Journal of Botany. 73: S1301-

S1309.

Goodwin, J. 1992. The role of mycorrhizal fungi in competitive

interactions among native bunchgrasses and alien weeds: a

review and synthesis. Northwest Science. 66: 251-260.

Harper, K. T. 1992. Accelerated displacement of Bromus tectorum

by native perennials on nutrient deficient soils. In: Monsen, S. B.;

Kitchen, S. G., comps. Abstracts - Symposium on ecology and

management of annual rangelands; 1992 May 16-22; Boise, ID: 21.

Harper, K. T.; Marble, J. R. 1988. A role for nonvascular plants in

management of arid and semiarid rangelands. In: Tueller, P. T.,

ed. Application of plant sciences to rangeland management and

inventory. Boston, MA: Kluwer Academic Publishers: 135-169.

Harper, K. T.; Pendleton, R. L. 1993. Cyanobacteria and cyanolichens:

can they enhance availability of essential minerals for higher

plants? Great Basin Naturalist. 53: 59-72.

Hepper, C. M.; Warner, A. 1983. Role of organic matter in growth of

a vesicular-arbuscular mycorrhizal fungus in soil. Transactions

of the British Mycological Society. 81: 155-156.

Hetrick, B. A. D.; Wilson, G. W. T.; Leslie, J. F. 1991. Root architecture of warm- and cool-season grasses: relationship to mycorrhizal dependence. Canadian Journal of Botany. 69: 112-118.

Johnson, N. C. 1998. Responses of Salsola kali and Panicum

virgatum to mycorrhizal fungi, phosphorus and soil organic

matter: implications for reclamation. Journal of Applied Ecology.

35: 86-94.

McLendon, T.; Redente, E. F. 1991. Nitrogen and phosphorus effects

on secondary succession dynamics on a semi-arid sagebrush site.

Ecology. 72: 2016-2024.

Miller, R. M. 1987. The ecology of vesicular-arbuscular mycorrhizae

in grass- and shrublands. In: Safir, G. R., ed. Ecophysiology of VA

mycorrhizal plants. Boca Raton, FL: CRC Press Inc: 135-170.

Miller, R. M. 1979. Some occurrences of vesicular-arbuscular mycorrhiza in natural and disturbed ecosystems of the Red Desert.

Canadian Journal of Botany. 57: 619-623.

Moora, M.; Zobel, M. 1998. Can arbuscular mycorrhiza change the

effect of root competition between conspecific plants of different

ages? Canadian Journal of Botany. 76: 613-619.

Moorman, T.; Reeves, F. B. 1979. The role of endomycorrhizae in

revegetation practices in the semiarid west. II. A bioassay to

determine the effect of land disturbance on endomycorrhizal

populations. American Journal of Botany. 66: 14-18.

Mosse, B. 1973. Advances in the study of vesicular-arbuscular

mycorrhiza. Annual Review of Phytopathology. 11: 171-196.

Pendleton, B. K. 2000 . Coleogyne ramosissima Torr. In: Bonner, F.;

Krugman, S., tech. coords. Woody plant seed manual. In press.

Pendleton, B. K.; Meyer, S. E.; Pendleton, R. L. 1995. Blackbrush

biology: insights after three years of a long-term study. In:

Roundy, B. A.; McArthur, E. D.; Haley, J. S.; Mann, D. K., comps.

Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech Rep. INTGTR-315. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station: 223-227.

Powell, C. L. 1980. Mycorrhizal infectivity of eroded soils. Soil

Biology and Biochemistry. 12: 247-250.

Quintero-Ramos, M.; Espinoza-Victoria, D.; Ferrera-Cerrato, R.;

Bethlenfalvay, G. J. 1993. Fitting plants to soil through mycorrhizal fungi: mycorrhiza effects on plant growth and soil organic

matter. Biology and Fertility of Soils. 15: 103-106.

Redente, E. F.; Friedlander, J. E.; McLendon, T. 1992. Response of

early and late semiarid seral species to nitrogen and phosphorus

gradients. Plant and Soil. 140: 127-135.

Reeves, F. B.; Wagner, D.; Moorman, T.; Kiel, J. 1979. The role of

endomycorrhizae in revegetation practices in the semi-arid West.

I. A comparison of incidence of mycorrhizae in severely disturbed

vs. natural environments. American Journal of Botany. 66: 6-13.

Smith, F. A.; Smith, S. E. 1996. Mutualism and parasitism: diversity in function and structure in the “arbuscular” (VA) mycorrhizal symbiosis. Advances in Botanical Research. 22: 1-43.

St. Clair, L. L.; Johansen, J. R. 1983. Introduction to the symposium

on soil crust communities. Great Basin Naturalist. 53: 1-4.

Tennant, D. 1975. A test of a modified line intersect method of

estimating root length. Journal of Ecology. 63: 995-1001.

Tilman, G. D. 1986. Nitrogen-limited growth in plants from different successional stages. Ecology. 67: 555-563.

Trent, J. D.; Svejcar, A. J.; Bethlenfalvay, G. J. 1993. Growth and

nutrition of combinations of native and introduced plants and

mycorrhizal fungi in a semiarid range. Agriculture, Ecosystems

and Environment. 45: 13-23.

van der Heijden, M. G. A.; Boller, T.; Wiemken, A.; Sanders, I. R.

1998. Different arbuscular mycorrhizal fungal species are potential determinants of plant community structure. Ecology. 79:

2082-2091.

Vitousek, P. M.; White, P. W. 1981. Process studies in succession. In:

West, D. C.; Shugart, H. H.; Botkin, D. B., eds. Forest succession:

concepts and application. New York, NY: Springer-Verlag: 267-

276.

Walker, C.; Mize, C. W.; McNabb, H. S., Jr. 1982. Populations of

endogonaceous fungi at two locations in central Iowa. Canadian

Journal of Botany. 60: 2518-2529.

Wilson, D. O. 1988. Differential plant response to inoculation with

two VA mycorrhizal fungi isolated from a low-pH soil. Plant and

Soil. 110: 69-75.
252 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

J. R. Barrow and I. Feder are employed by the USDA-ARS Jornada

Experimental Range, P.O. Box 30003, MSC 3JER, NMSU, Las Cruces, NM

88003-8003 U.S.A. H. C. Monger is with the Department of Agronomy and

Horticulture, New Mexico State University, Las Cruces, NM 88003-8003

U.S.A.

The Role of Endophytic Fungi in the Survival

and Establishment of Fourwing Saltbush

(Atriplex canescens [Pursh] Nutt.) in an Arid

Environment

J. R. Barrow

I. Feder

H. C. Monger

Abstract—A seedborne septate fungus (Aspergillus sp.) formed

intimate non-destructive interfaces with seedling radicles of germinating fourwing saltbush, (Atriplex canescens [Pursh] Nutt.) seedlings. When seedlings were separated from insoluble phosphorus

sources with a screen that excluded roots but allowed passage of

extraradicle hyphae, which accessed plant insoluble phosphate and

transported it through the barrier to the plant. The fungi enhanced

phosphorus uptake, biomass production of the host plants and

aggregated sand similar to functions attributed to mycorrhizal

fungi. The importance of symbiotic fungi in the remediation and

stabilization of arid ecosystems is discussed.

In the last century, shrubs have invaded native grasslands in the northern Chihuahuan Desert, resulting in

severe disturbances in the plant and soil structure and

productivity. Little is known about how these disturbances

have affected the structure of soil and below-ground soil

microflora populations.

Mycorrhizal fungi are directly involved in the nutrition

and survival of host plants in all major ecosystems

(Bethlenfalvay 1992). It is expected that mycorrhizal fungi

have a major role in plant nutrition and survival in resourcestressed arid ecosystems. Classical mycorrhizal fungi nondestructively colonize roots of host plants and form interfaces between and within cortical cells for the exchange of

photosynthetic carbon, mineral nutrients, and water. The

fungi also extend from the root surface into the soil increasing access and absorption of nutrients and water. They

indiscriminately colonize roots of widely different species,

forming an underground network that potentially allows for

the exchange of photosynthetic carbon, water, mineral nutrients between plants, and soil microflora (Bethlenfalvay

1992; Read 1997; Simmard and others 1997).

Barrow and others (1997a) found that in addition to

classical mycorrhizal fungi, the roots of fourwing saltbush

(Atriplex canescens [Pursh] Nutt.), and other dominant shrubs

and grasses of the arid Southwestern United States are

constantly and more extensively colonized by non-pathogenic septate fungi. Similary, septate fungi also non-destructively colonize the emerging radicles of fourwing saltbush at germination and enhance seedling growth and

establishment by transferring nutrients in the seed capsule

to the seedling (Barrow and others 1997b).

The objective of our studies is to determine if these septate

fungi function similar to mycorrhizal fungi in arid ecosystems. Our hypothesis was that these fungi access immobile

nutrients and transport them to the host, and that they

function like mycorrhizae in arid environments.

Materials and Methods ___________

The hard fibrous utricle and internal embryonic tissues of

fourwing saltbush are naturally and consistently colonized

by septate fungi that are not eliminated by standard seed

sterilization or heat treatments. Because inoculated and

sterile plants could not be compared, plant containers (fig. 1)

were constructed with a 20 um screen to exclude roots but

allow penetration of endophytic root fungi into the lower

chamber containing phosphorus sources insoluble to plants

but not by fungi. Standard 7.62 cm diameter schedule 40

PVC tubing was cut into 7.62 cm lengths. A 2 mm mesh vinyl

Figure 1—Root exclusion chamber

Polyvinyl screen &

filter paper

7.64 cm schedule

40 PVC tubing

Hyphal chamber

Insoluble phosphorus

20 um screen

7.64 cm coupling

Root excluding

Root chamber
USDA Forest Service Proceedings RMRS-P-11. 1999 253

screen was glued to the bottom of each piece, and filter paper

was cut the same diameter and inserted above the screen to

retain sand and allow drainage. A commercial grade of silica

blasting sand was acid washed to remove all P. The sand was

soaked for 30 minutes in 0.1 N HCl and copiously rinsed with

distilled water before drying at 110 °C for 72 hours.

Four treatments were established: (1) zero P (0P), with no

plant available P, (2) 30 ppm soluble P (SP), adequate for

normal plant growth, (3) rock phosphate (RP), and

(4) tricalcium phosphate (TCP). For treatments OP and SP,

the above and below tube compartments were filled with

acid-washed sand. For Treatments RP and TCP, the lower

tube compartments were filled with acid-washed sand to

1 cm from the screen. The last cm was filled with a mixture

of sand and insoluble P consisting of 1 part RP or TCP to two

parts acid-washed sand. The 20 um root excluding screen

was glued to the top of each tube interfacing firmly with the

sand beneath the screen. A standard 7.62 cm coupling was

lubricated with a light petroleum jelly and placed on the tube

to secure the screen in place. Acid-washed silica sand was

then added to the open end of the coupling providing a plant

root chamber above the screen (7.62 cm d x 4 cm h).

Seeds of fourwing saltbush were germinated on the

surface of moist silica sand. Three germinants with radicles

approximately 1 cm long, naturally colonized by septate

fungi, were transplanted to each tube. Tubes were randomly placed in a growth chamber at 25 °C with a 12 hour

light, 12 hour dark regime. Each treatment had 16 replications, 12 of which were used for root and shoot biomass and

P tissue analysis at the end of the experiment. Remaining

replications were used for microscopic analysis of roots and

subchamber fungal colonization.

Plant containers were saturated just prior to wilting with

their respective nutrient solution, which drained quickly.

This interval gave plants adequate water for growth and

kept tubes as dry as possible. Treatment 0P, RP, and TCP

were all watered with standard Hoagland’s solution with all

essential nutrients except P. The SP treatment plants were

watered with Hoagland’s solution containing 30 ppm of

plant soluble P, not limiting to plant growth. Any P utilized

by seedlings in RP and TCP treatments were obtained from

the insoluble P source. Distilled water was used every third

watering to prevent salt accumulation. Nutrient solutions

were adjusted to pH 5.5 to prevent solubilization of P from

the RP and TCP treatments.

After 12 weeks, plants were carefully removed from the

upper root chamber by submerging and rinsing in water to

remove sand. Shoots and roots were separated, dried and

weighed. Dried shoots and roots were finely ground, digested, and mg of phosphorus per gm of dry plant tissue was

determined with a Jobin Yvon JY Plus Inductively Coupled

Plasma Spectrophotometer.

After natural drying of the containers, feeder roots from

the root chambers were harvested from additional replications, cleared and stained using the method of Brundrett

and others (1984), and analyzed microscopically. One tube

from the TCP treatment was infiltrated with a low viscosity

resin, hardened, and cut into petrographic thin sections to

observe the intact three dimensional structure of roots,

screen, fungi, and sand.

Data were analyzed as a completely randomized design with phosphorus treatment as the main effect. The

dependent variables were shoot, root, and plant biomass

and P tissue concentrations. Mean differences were tested

using a protected LSD (P 0.01).

Results ________________________

Fungi internally colonized the cortex cells of healthy roots,

and considerable extraradical hyphae intimately associated

with the root surface readily penetrated the 20 um screen

and extended into the lower chamber in all treatments. No

roots penetrated the screen. When plants were approximately 25 to 35 cm tall, those treated with SP required

watering every 3 days to prevent wilting while equal sized

plants in both insoluble P treatments would wilt after 5 days

without watering.

Shoot and root biomass of fourwing seedlings in both

insoluble P treatments were equivalent to plants receiving

soluble P and were greater (P <0.01) than control plants

receiving no P (table 1). Shoot biomass of plants grown with

insoluble RP and TCP was equal to those supplemented with

SP, yet P content was one-third less in these tissues compared to shoots of SP-treated plants. Root biomass of seedlings supplemented with RP or TCP was greater (P <0.01)

than those watered with either SP or no 0P. The root/shoot

ratio was greatest (P <0.01) in seedlings in the 0P treatment,

intermediate for the insoluble RP and TCP treatments, and

least with SP.

Screen sections approximately 2 cm in diameter were

carefully cut and observed under a stereo microscope. Substantial quantities of hyphae were observed enmeshing

sand particles in the region 5 mm below the screen in the RP

and TCP treatments. Petrographic thin sections made from

a container with TCP revealed the intact structure of the

roots, screen, and the hyphal interface with the TCP-sand

mixture. An airspace 1 to 3 mm thick separated the P-sand

mix from the screen and the roots due to settling of sand

during the experiment. An amorphous white material observed accumulating on hyphal surfaces increased fungal

hyphal diameters from less than 10 to more than 200 um.

These hyphae formed a fibrous network similar in structure

and dimensions to plant roots, which also physically aggregated a layer of the TCP-sand mixture approximately 5 mm

thick. Additional settling of the sand below this aggregated

layer resulted in another airspace below the aggregate,

illustrating its cohesive nature. The white material on the

hyphal surface did not effervesce in cold dilute HCl, suggesting it was not CaCO3. We suspect this material to be

extracellular polysaccharide secretion by the fungus. An

isolate of the fungus was tentatively identified as Asprilligus

sp. by Dr. Gary Samuels of the USDA-ARS Systematic

Botany and Mycology Laboratory, Beltsville, MD. This isolate developed a typical endophytic, septate association with

alfalfa root organ cultures.

Discussion _____________________

Fungal associations of this type have been classed as dark

septate (DS) fungi, an inconclusive term because internal

hyphae are often hyaline (Haselwandter and Read 1980;

Odell and others 1993; Treu and others 1996). They have

also been considered a part of the mycelium radicis atrovirons
254 USDA Forest Service Proceedings RMRS-P-11. 1999

(MRA) complex (Wang and Wilcox 1985). Generally the

these fungi form extensive symptomless inter- and intracellular hyphal networks and microsclerotia within plant roots.

These data showed that a septate seedborne fungus (Aspergillus sp.) enhanced P uptake and biomass production of

fourwing saltbush seedlings. Fungi intimately colonized

seedling radicles, forming interfaces similar to those observed in the roots of mature grasses and other dominant

shrubs harvested from native sites (Barrow and others

1997a).

These findings are also consistent with those of

Haselwandter and Read (1980, 1982) who found that species

of the Cyperaceae family, Carex firma and C. sempervirens,

were more extensively colonized with dark septate fungi

than by vesicular arbuscular mycorrhizal (VAM) fungi.

They also observed that associated isolates ascribed to the

genus Rhizoctonia differed morphologically from established

mycorrhizal classes and increased yield and shoot phosphorus concentrations, typical of responses of host plants inoculated with VAM. They concluded these fungi were mycorrhizal. Sengupta and others (1989) also induced growth

responses in Cajanas cajan with two dark septate isolates

that accessed P from insoluble tricalcium phosphate under

salinity stress and likewise suggested a mycorrhizal function for these isolates.

Mycorrhizal fungi also modify the size, shape, and anatomy

of plant roots (Berta and others 1993) and alter photosynthetic activity of their hosts (Allen and Boosalis 1983). In

this study, all seedlings in all treatments were colonized.

The increase of plant and root biomass, soil aggregation, and

the solubilization and transport of P would suggest increased photosynthetic rates when the plant fungal component was challenged by different phosphorus sources. The

observed bridging of roots with the insoluble P source by the

fungus provided a physical pathway for P to be transported

to the roots via fungal hyphae, similar to observations of

mycorrhizal fungi.

Equivalent shoot biomass production and greater root

biomass for the insoluble P treatments compared to the SP

treatment (P <0.01) (table 1) with only one-third of the

phosphorus uptake suggests that the fungus not only solubilized P, but increased P use efficiency. This is consistent

with the report of Brown and others (1988), who found that

P use efficiency was significantly greater in VAM-inoculated

plants compared to non-inoculated plants supplemented

with high P. Asprigillus niger and other soil microbes have

previously been shown to effectively solubilize P from rock

phosphate (Azcon and others 1976; Khan and Bhatnagar

1977; Khasawneh and Doll 1978). In this study, an Aspergillus sp. fungus not only solubilized rock phosphate, but

similar to mycorrhizal fungi, formed an intimate interface

with root cells and the insoluble P source.

Another similarity to mycorrhizal fungi and a potentially

important ecological function of these fungi is that they

aggregate and stabilize sand and soil particles, enhancing

nutrient and water retention (Bethlenfalvay 1992). An increase of fungal and root biomass and aggregation of sand in

the chambers could explain the reduced need for watering

observed in the insoluble P treatments. We agree with

Trappe (1989) and Treu and others (1996) that septate fungi

that do not currently fit into accepted mycorrhizal classification systems are ecologically significant and are composed of

a wide assembledge of fungal species. Several of these fungi

isolated from the roots of native plants formed similar nondestructive interfaces with the root cortex cells of native

plants and are tentatively identified as common soil fungi

(Barrow, unpublished). Their known function as pathogens

or as soil saprobes may be a primary reason why their

ecological significance or potential as symbiotic fungi has

been overlooked. The consistent root colonization of desert

plants by both VAM and septate fungi suggests that they

comprise a flexible suite of organisms to meet a variety of

challenges imposed by highly variable arid environments,

including the enhancement of nutrient uptake and plant

survival. Each fungal component may be specifically adapted

to function under a specific environmental condition. Ecological roles of these fungi are varied and require innovative

research approaches and measurements to understand their

ecologically significant and complex multifunctional roles.

We propose that the ecological significance of these fungi

as well a other mycorrhizal fungi found in arid ecosystems is

to provide an underground network that allows the conservation, distribution, and transport of carbon, mineral

nutrients, and water in chronically dry soils that cannot be

achieved by diffusion or by mass flow. The structural integrity of this below-ground network is essential for the nutrition and survival of plant communities. If this structure is

damaged by disturbances to the system, it would need to be

repaired before plant establishment could be successful.

References _____________________

Allen, M. F.; Boosalis, M. G. 1983. Effects of two species of VA

mycorrhizal fungi on drought tolerance of winter wheat. New

Phytology. 93: 67-76.

Table 1—Mean dry weights in mg and phosphorus content of shoots and roots of fourwing saltbush grown on four different

phosphorus treatments.

Root Shoot Plant Root/shoot

P treatment Dry weight Wt P Dry weight Wt P Dry weight Wt P ratio

mg mg mg

Zero phosphorus 103.3ca 0.004b 202.3b 0.028c 305.6c 0.032d 0.820a

30 ppm soluble P 178.4b 0.385a 496.8a 2.744a 675.1b 3.129a 0.360b

Rock phosphate 263.7a 0.121b 500.3a 0.859b 764.0a 0.980c 0.622ab

Tricalcium phosphate 292.1a 0.512a 502.3a 0.967b 794.4a 1.479b 0.598ab

a

Means within a column followed by different letters are significant at P <0.01.
USDA Forest Service Proceedings RMRS-P-11. 1999 255

Azcon, R.; Barea, J. M.; Hayman, D. S. 1976. Utilization of rock

phosphate in alkaline soils by plants inoculated with mycorrhizal

fungi and phosphate-solubilizing bacteria. Soil Biology and Biochemistry. 8: 135-138.

Barrow, J. R.; Havstad, K. M.; McCaslin, B. D. 1997a. Fungal root

endophytes in fourwing saltbush, Atriplex canescens, on arid

rangelands of Southwestern USA. Arid Soil Research and Rehabilitation. 11: 177-185.

Barrow, J. R.; Havstad, K. M.; Hubstenberger, J.; McCaslin, B. D.

1997b. Seed-borne fungal endophytes on fourwing saltbush,

Atriplex canescens. Arid Soil Research and Rehabilitation. 11:

307-314.

Berta, G. A.; Fusconi, A.; Trotta, A. 1993. VA mycorrhizal infection

and the morphology and function of root systems. Environmental

and Experimental Botany. 33: 159-173.

Bethlenfalvay, G. 1992. Mycorrhizae and crop productivity. In:

Bethlenfalvay, G. J.; Linderman, R. G., eds. Mycorrhizae in

sustainable agriculture. Special Publication 54. Madison, WI:

American Society of Agronomy: 1-27.

Brown, M. S.; Thamsurkul, S.; Bethlenfalvay, G. J. 1988. The

Glycine Glomus Bradyrhizobium symbiosis: VIII. Phosphorus

use efficiency of carbon dioxide and nitrogen fixation in mycorrhizal soybean. Physiologia Plantarum. 74: 159-163.

Brundrett, M. C.; Piche, Y.; Peterson, R. L. 1984. A new method for

observing the morphology of vesicular-arbuscular mycorrhizae.

Canadian Journal of Botany. 62: 2128-2134.

Haselwandter, K.; Read, D. J. 1980. Fungal associations of roots of

dominant and sub-dominant plants in high-alpine vegetation

systems with special reference to mycorrhizae. Oecologia. 45:

57-62.

Haselwandter, K.; Read, D. J. 1982. The significance of root-fungus

association in two Carex species of high-alpine plant communities. Oecologia. 53: 352-354.

Khan, J. A.; Bhatnagar, R. M. 1977. Studies on solubilization of

insoluble phosphates by microorganisms. I. Solubilization of

indian phosphate rock by Aspergillus niger and Penicillium sp.

Fertilizer Technology. 14: 329-333.

Khasawneh, F. E.; Doll, E. C. 1978. The use of phosphate rock for

direct application to soils. Advances in Agronomy. 30: 159-206.

Khasawneh, F. E.; Doll, E. C. 1978. The use of phosphate rock for

direct application to soils. Advances in Agronomy. 30: 159-206.

Mosse, B.; Powel, C. L.; Hayman, D. S. 1976. Plant growth responses

to vesicular-arbuscular mycorrhiza, IX. Interactions between VA

mycorrhiza, rock phosphate and symbiotic nitrogen fixation. New

Phytology. 76: 331-342.

Odell, M.; Massicotte, H. B.; Trappe, J. M. 1993. Root colonization

of Lupinus latifolius agardh. and Pinus contorta Dougl. by

Phialocephala Fortinii. New Phytology. 124: 93-10.

Read, D. J. 1997. Ties that bind. Nature. 388: 517-518.

Sengupta, A.; Chakraborty, D. C.; Chaudhuri, S. 1989. Do septate

endophytes also have a mycorrhizal function for plants under

stress? In: Mahadevan, A.; Raman, N.; Natarajan, K., eds. Mycorrhizae of Green Asia: proceedings of the first Asian conference

on mycorrhizae; Madras, India: 169-174.

Simard, S. W.; Perry, D. A.; Jones, M. D.; Myrold, D. D.; Durall, D.

M.; Molina, R. 1997. Net transfer of carbon between

ectomycorrhizal tree species in the field. Nature. 388: 579-582.

Trappe, J. M. 1981. Mycorrhiazae and productivity of arid and

semiarid rangelands. In: Manassah, J. T.; Briskey, E. J., eds.

Advances in food-producing systems for arid and semiarid lands.

Academic Press: New York: 581-599.

Treu, R.; Laursen, G. A.; Stephenson, S. L.; Landolt, J. C.; Densmore,

R. 1996. Mycorrhizae from Denali National Park and Preserve,

Alaska. Mycorrhiza. 6: 21-29.

Wang, C. J. K.; Wilcox, H. E. 1985. New species of ectendomycorrhizal

and pseudomycorrhizal fungi: Phialophora finlandia, Chloridium

paucisporum, and Philaloxephala fortinii. Mycologia. 77: 951-958.
256 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Donald J. Bedunah is Professor, School of Forestry, University of Montana,

Missoula 59812. Michael G. Harrington is Research Forester, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station,

Intermountain Fire Sciences Laboratory, Missoula, MT 59807. Dayna M.

Ayers is Research Assistant, Division of Biological Sciences, University of

Montana.

Antelope Bitterbrush and Scouler’s Willow

Response to a Forest Restoration Project

Donald J. Bedunah

Michael G. Harrington

Dayna M. Ayers

Abstract—Scouler’s willow (Salix scouleriana) and antelope bitterbrush (Purshia tridentata) survival, vigor, and use by ungulates

were monitored following shelterwood cut and prescribed burn

treatments designed to restore pre-European settlement conditions

to a western Montana forest stand. The prescribed burn treatments

resulted in modest willow mortality, substantial bitterbrush mortality, concurrent decreases in canopy cover, but increased plant

vigor in spite of heavy ungulate browsing on treated areas. A no

stand entry option would eliminate mortality of individual shrubs

caused by these restoration treatments, but population fitness may

decline dramatically as overstory density increases, and the threat

of severe wildfire will increase. A wildfire could be highly destructive to bitterbrush specifically, and to the forest in general.

Antelope bitterbrush (Purshia tridentata) and Scouler’s

willow (Salix scouleriana) are two important shrubs occupying grasslands, low-elevation forest and forest ecotones in

the northern Rocky Mountains. In western Montana, these

species are often two of the most preferred browse for wild

ungulates such as mule deer (Odocoileus hemionus) (Wilkins

1957), elk (Cervus elaphus) (Leege 1979), bighorn sheep

(Ovis canadensis) (Welch and others 1982), and moose

(Alces alces) (Pierce 1984), as well as white-tailed deer

(Odocoileus virginianus) and domestic livestock. There is

ample evidence that fires, both natural and human caused,

were a significant ecological component of these forestgrassland ecotones (Gruell and others 1982), and land

management agencies are prescribing fire as an ecological

restoration tool. The ponderosa pine (Pinus ponderosa)

cover type, located on lower elevation areas in western

Montana, is of special interest to land managers because of

the many values of this type. Early photographs provide

evidence that many ponderosa pine stands were more open

and spatially patterned by fire (Gruell and others 1982).

Since the late 1800’s fire suppression and selective logging

in ponderosa pine stands have resulted in forest stands with

dense Douglas-fir (Pseudotsuga menziesii) with largely unknown affects on browse production. The large-scale replacement of ponderosa pine by Douglas-fir may be undesirable because fir are more susceptible to disease and outbreaks of defoliating insects. Fir forests are usually more

“closed” with subsequent reduction in vigor and biomass of

understory vegetation, and these forests are more prone to

stand-replacement fires.

In 1991 the Bitterroot National Forest and Intermountain

Forest Science Fire Laboratory initiated a project to examine the response of a ponderosa pine/Douglas-fir stand to a

combination of prescribed fire and shelterwood cutting as

ecological restoration management tools. Photographs of

the study area in the early 1900’s reveal an open stand of

large ponderosa pine with little shrub understory. Apparently, with the removal of fire and subsequent stand entry

for harvesting trees, the area became dominated by Douglas-fir with an important component of antelope bitterbrush and Scouler’s willow in the understory. Since the

study area is an important winter range for wild ungulates

(deer, elk, and moose), the influence of the treatments on

browse species was considered very critical. Therefore, our

objective was to determine the effects of the restoration

treatments on antelope bitterbrush and Scouler’s willow

survival, vigor, and use by ungulates following treatments

and to determine variables influencing survival and vigor.

Study Area _____________________

The study site was approximately 50 ha (124 acres) of

second-growth Douglas-fir and ponderosa pine at the Lick

Creek Study Area of the Bitterroot National Forest in

Ravalli County, Montana. Elevation is 1,300 to 1,500 m and

precipitation averages 56 cm/yr, approximately 50 percent

occurs as snow (Gruell and others 1982). The soils are

derived from granitic parent materials and are shallow to

moderately deep. Tree basal area averaged 28 m2/ha and

was predominately even-aged Douglas-fir and ponderosa

pine that established after a 1906 clearcut (Gruell and

others 1982). Habitat types varied from Pseudotsuga

mensiezii/Vaccinium caespitosum on the toe slopes and

benches to Pseudotsuga mensiezii/Symphoricarpos albus,

Agropyron spicatum phase (Pfister and others 1977) on the

drier south aspects.

Experimental Approach

The study site was divided into 12 approximately equal

units of 4 ha (10 acres) by personnel from the Intermountain Fire Sciences Laboratory. Each unit was assigned to

one of the following four treatments: (1) a shelterwood cut,

(2) a shelterwood cut and a high-consumption burn, (3) a

shelterwood cut and a low-consumption burn, and
USDA Forest Service Proceedings RMRS-P-11. 1999 257

(4) a control. The shelterwood cut was completed in the fall

of 1992. Tree basal area was reduced by 53 percent to 13.1m2.

Prescribed burns were conducted in May 1993.

Before application of the shelterwood cut, we permanently

recorded the location of all bitterbrush and willow within 36

400-m2 circular plots established in the control, shelterwood

cut, low-consumption burn, and high-consumption burn

treatments. Pretreatment measurements of 1,856 bitterbrush and 871 willow permanently located included height,

stem diameter, and a vitality rating. Immediately after the

shelterwood cut, all bitterbrush and willow were relocated to

determine the degree of mechanical damage (all treatments

except control) and proximate fuel quantity (low consumption and high consumption burn treatments). Following

prescribed burning, all bitterbrush and willow were relocated to determine level of fire damage. Each shrub was then

monitored in the summers of 1993 and 1994 to document

survival and vigor. In each treatment, canopy cover (percent) of willow and bitterbrush was estimated in 36 33-m2

circular quadrats.

Data Analysis ___________________

Differences in pre- and post-treatment canopy cover and

density were evaluated using one-way analysis of variance.

We also grouped bitterbrush and willow into categories of

burned and unburned, since not all plants within the

burned treatments received fire damage, and then used

logistic regression to determine which variables were most

significant in predicting mortality for each group using the

variables of height, diameter, vitality class, mechanical

damage, fuel class, and burn class. These variables were

also correlated with post-treatment vigor using Kendalltau non-parametric correlation analysis (Sokal and Rohlf

1995). Differences in vigor among treatments were compared using an X 2 test. Differences were considered significant at p <0.05 for all analyses. Assumptions of equal

variance and normality were tested and, if necessary,

variables were transformed to meet assumptions.

Results and Discussion __________

The shelterwood cut and prescribed burn treatments

resulted in modest willow mortality, substantial bitterbrush

mortality, concurrent decreases in canopy cover, but increased plant vigor (table 1). Mortality of Scouler’s willow

and bitterbrush was greatest in the burn treatments associated with the combined effects of the harvest and burn. The

combined effects of the stand entry and prescribed burning

is best illustrated using flow diagrams grouping the low and

high consumption burn treatments since there was not a

difference (p >0.05) in mortality between the burn treatments (figs. 1 and 2). Stand entry resulted in 77 percent and

70 percent of the Scouler’s willow and bitterbrush, respectively, receiving plant damage. Only 55 percent of the

bitterbrush plants in the burn treatments exhibited fire

damage; however, of these plants only 28 percent survived

(fig.1). For bitterbrush with mechanical damage, but exhibiting no fire damage, mortality was still high averaging 65

percent (fig. 1). For Scouler’s willow a greater percentage of

plants exhibited fire damage (81 percent) as compared to

bitterbrush, but survival was much greater averaging 82

percent (fig. 2). It is also interesting to note that of the

Scouler’s willow in the burned treatments that received

mechanical damage, but no fire damage, mortality was 50

percent. This relatively high mortality was a result of severe

plant damage associated with skid trails and was not representative of the response of willow to the range of mechanical

damage effects. Scouler’s willow mortality for the shelterwood

cut was only 14 percent compared to 35 percent mortality of

bitterbrush (table 1). This difference in survival between

species is likely associated with differences in plant morphology. The deep root system and multi-stemmed growth of

willow allow for higher tolerance to disturbance than that of

bitterbrush. Willow often resprouts after surface disturbance from a subterranean root crown (Lyon 1966), whereas

bitterbrush can only resprout from a surface caudex (Guinta

and others 1978), which is more easily removed or injured by

disturbance.

Mortality of willow and bitterbrush with burn damage

was best explained by the degree of burn severity (burn

class) (table 2). Bitterbrush was notably impacted by any fire

damage, whereas willow was not markedly affected until it

suffered deep charring of the root crown. Vigorous resprouting

is consistent with other research (Leege and Hickey 1971;

Leege 1979), and willow has been reported to increase in

both biomass and vigor by as much as 100 percent following

a burn (Noste and Bushey 1987; Leege 1969; Mueggler

1965). For willow and bitterbrush without fire damage,

mortality was best explained by the degree of mechanical

damage (table 2). Of the bitterbrush plants receiving any

mechanical damage, almost 70 percent sustained severe

damage and 86 percent of those died. Willow survival was

Table 1—Change in cover, mortality, and plants with high vigor for antelope bitterbrush (Purshia tridentata)

and Scouler’s willow (Salix scouleriana) by treatment in the Lick Creek Demonstration Area, 1994.

Changes are relative to pre-treatment conditions. Average pre-treatment cover was 0.94 percent

for bitterbrush and 0.77 percent for willow.

Antelope bitterbrush Scouler’s willow

Cover High vigor Cover High vigor

Treatment reduction Mortality plants reduction Mortality plants

- - - - - - - - - - - - - - - - - - - - - - - - - - percent - - - - - - - - - - - - - - - - - - - - - - - - - - - 

Control 2 4 28 1 3 15

Harvest-only 75 35 70 33 14 60

Low consumption 83 62 88 62 22 71

High consumption 92 68 78 58 26 69
258 USDA Forest Service Proceedings RMRS-P-11. 1999

greater than 94 percent, except for those plants severely

damaged on skid trails, where survival decreased to 58

percent.

For surviving bitterbrush and willow we found an increase in the proportion with high vigor in the burn and the

harvest-only treatments compared to the control (p <0.05)

(table 1). This increase in vigor apparently increased the

palatability of these plants to browsers. Elk, moose, and

mule deer were observed on the study site throughout the

year. Heavy browsing of willow occurred during summer

immediately after burning; whereas, browse utilization of

bitterbrush was most extensive on the shelterwood cut

treatment, probably associated with higher available bitterbrush on this treatment compared to the burn treatments.

The heavy browsing before initial reference measurements

probably resulted in an underestimation of intensity of

browse use and most likely resulted in loss of new growth

and subsequently lower vigor for these plants. Other research findings have reported an increase in current annual

growth of bitterbrush following logging for up to 7 years after

overstory removal (McConnell and Smith 1970; Stuth and

Winward 1976; Edgerton 1982) and immediately after spring

burning (Demarchi and Lofts 1985; Cook and others 1994).

Management Implications ________

Our results show significant bitterbrush mortality and

modest willow mortality associated with overstory removal

and prescribed burning associated with the restoration

treatments. The restoration treatments were a positive

stimulus to willow productivity with survival greater than

75 percent, and the percentage of high-vigor plants increased from 15 percent pre-treatment to 70 percent posttreatment. The reduction in bitterbrush density by an average of 65 percent for the burn treatments would certainly be

of concern to land managers interested with the maintenance of this important browse species. However, these

treatments also increased vigor of surviving bitterbrush,

and because its regeneration strategy requires almost competition-free, mineral seedbeds for seed germination from

rodent caches (Sherman and Chilcote 1972; Clark and others 1982) long-term effects on this species may still be

positive. Also, the restoration treatments would lower the

risk of a stand-replacement wildfire that would likely be

highly detrimental to the bitterbrush in this stand. By

reducing impacts of harvesting with widely spaced skid

trails using low-impact equipment and prescribing low fuel

consumption burns with variable fire coverage, plant mortality should be minimized, especially for bitterbrush. With

the return of open stand conditions, mineral seedbeds, and

Figure 1—Mechanical damage, fire damage, and

mortality of antelope bitterbrush (Purshia tridentata)

for the low-consumption and high-consumption burn

treatments combined.

Pre-treatment

bitterbrush

N = 1169

Shelterwood cut

No mechanical

damage

N = 352

Prescribed burn

Mechanical

damage

N = 817

Prescribed burn

Without

fire

damage

N = 95

Survival

89%

With

fire

damage

N = 257

Survival

32%

Without

fire

damage

N = 435

Survival

35%

With

fire

damage

N = 382

Survival

26%

Figure 2—Mechanical damage, fire damage, and

mortality of Scouler’s willow (Salix scouleriana) for

the low-consumption and high-consumption burn

treatments combined.

Pre-treatment

willow

N = 401

Shelterwood cut

No mechanical

damage

N = 91

Prescribed burn

Mechanical

damage

N = 310

Prescribed burn

Without

fire

damage

N = 2

Survival

100%

With

fire

damage

N = 89

Survival

82%

Without

fire

damage

N = 62

Survival

50%

With

fire

damage

N = 248

Survival

82%

Table 2—Significant variables in antelope bitterbrush (Purshia

tridentata) and Scouler’s willow (Salix scouleriana) mortality

in Lick Creek Demonstration Area, 1995.

Number Variance

Species Exposure dead (N) Variable explained

percent

Bitterbrush Fire 459 (639) Burn class 72

No fire 425 (1217) Mechanical damage 91

Willow Fire 65 (337) Burn class 84

No fire 68 (534) Mechanical damage 90
USDA Forest Service Proceedings RMRS-P-11. 1999 259

more vigorous plants, the potential for natural regeneration

to replace fire-killed plants should be high (Gruell 1986).

References _____________________

Clark, R. G.; Britton, C. M.; Sneva, F. A. 1982. Mortality of bitterbrush after burning and clipping in eastern Oregon. Journal of

Range Management. 35: 711-714.

Cook, J. G.; Hershey, T. J.; Irwin, L. L. 1994. Vegetative response to

burning on Wyoming mountain-shrub big game ranges. Journal

of Range Management. 47: 296-302.

Demarchi, D. A.; Lofts, S. 1985. The effects of spring burning on the

productivity and nutrient concentration of several shrub species in

the southern Rocky Mountain trench. MOE Technical Report 19.

Victoria, BC: British Columbia Ministry of Environment. 89 p.

Edgerton, P. J. 1982. Response of the bitterbrush understory of a

central Oregon lodgepole pine forest to logging disturbance. In:

Tiedemann, A. R.; Johnson, K. L., comps. Proceedings—research

and management of bitterbrush and cliffrose in Western North

America; 1982 April 13-15; Salt Lake City, UT. Gen. Tech. Rep.

INT-152. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station:

256-265

Gruell, G. E.; Schmidt, W. C.; Arno, S. F.; Reich, W. J. 1982. Seventy

years of vegetative change in a managed ponderosa pine forest in

western Montana—implications for resource management. Gen.

Tech. Rep. INT-130. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Forest and Range Experiment

Station. 42 p.

Gruell, G. E. 1986. Post-1900 mule deer irruptions in the Intermountain West: principle cause and influences. Gen. Tech. Rep.

INT-206. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station. 37 p.

Guinta, B. C.; Stevens, R.; Jorgenson, K. R.; Plummer, A. P. 1978.

Antelope bitterbrush—an important wildland shrub. Publication

78-12. Salt Lake City, UT: Utah State Division of Wildlife

Resources. 48 p.

Leege, T. A. 1969. Burning seral brush ranges for big game in

northern Idaho. North American Wildlife and Natural Resources

Conference Transactions. 34: 429-437.

Leege, T. A.; Hickey, W. O. 1971. Sprouting of northern Idaho

shrubs after prescribed burning. Journal of Wildlife Management. 35: 508-515.

Leege, T. A. 1979. Effects of repeated prescribed burns on northern

Idaho elk browse. Northwest Science. 53: 107-113.

Lyon, L. J. 1966. Initial vegetative development following prescribed burning of Douglas-fir in south-central Idaho. Res. Pap.

INT-29. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station.

17 p.

McConnell, B. R.; Smith, J. G. 1970. Response of understory vegetation to ponderosa pine thinning in eastern Washington. Journal

of Range Management. 23: 208-212.

Mueggler, W. F. 1965. Ecology of seral shrub communities in the

cedar-hemlock zone of northern Idaho. Ecological Monographs.

35: 165-185.

Noste, N. V.; Bushey, C. L. 1987. Fire response of shrubs of dry forest

habitat types in Montana and Idaho. Gen. Tech. Rep. INT-239.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Forest and Range Experiment Station. 21 p.

Pfister, R. D.; Kovalchik, B. L.; Arno, S. F.; Presby, R. C. 1977. Forest

habitat types of Montana. Gen. Tech. Rep. INT-34. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 174 p.

Pierce, J. D. 1984. Shiras moose forage selection in relation to

browse availability in north-central Idaho. Journal of Canadian

Zoology. 62: 2403-2409.

Sherman, R. J.; Chilcote, W. W. 1972. Spatial and chronological

patterns of Purshia tridentata as influenced by ponderosa pine.

Ecology. 53: 294-298.

Sokal, R. R.; Rohlf, F. J. 1995. Biometry. 3rd ed. New York: W. H.

Freeman and Co. 887 p.

Stuth, J. W.; Winward A. H. 1976. Logging impacts on bitterbrush

in the lodgepole pine-pumice region of central Oregon. Journal of

Range Management. 29: 453-456.

Welch, B. L.; Monsen, S. B.; Shaw, N. L. 1982. Nutritive value of

antelope and desert bitterbrush, stansbury cliffrose and apacheplume. In: Tiedemann, A. R.; Johnson, K. L., comps. Proceedings—research and management of bitterbrush and cliffrose in

Western North America; 1982 April 13-15; Salt Lake City, UT.

Gen. Tech. Rep. INT-152. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 173-185.

Wilkins, B. T. 1957. Range use, food habits, and agricultural

relationships of the mule deer, Bridger Mountains, Montana.

Journal of Wildlife Management. 21: 159-169.
260 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Derek B. Hall and David C. Anderson are Scientist and Science Supervisor,

Bechtel Nevada, M/S NLV081, P.O. Box 98521, Las Vegas, NV 89193-8521.

Work was performed by Bechtel Nevada for the U.S. Department of Energy,

Nevada Operations Office, under contract No. DE-AC08-96NV11718.

Reclaiming Disturbed Land Using

Supplemental Irrigation in the Great Basin/

Mojave Desert Transition Region After

Contaminated Soils Remediation: the

Double Tracks Project

Derek B. Hall

David C. Anderson

Abstract—Approximately 3.8 hectares (9.3 acres) were reseeded

following contaminated soil remediation operations at the Double

Tracks site in south-central Nevada during the fall of 1996. Four

irrigation/topsoil treatments, including a nonirrigated control, were

studied to determine plant response to the different treatments.

Seedling emergence and subsequent establishment (one-and-a-half

years later) of seeded species were highest in the spring irrigated

with topsoil treatment. Initial seedling emergence was significantly

lower when no irrigation was used, which suggests the need for

supplemental irrigation for seed germination. Seedling and plant

densities were highest for winterfat (Krascheninnikovia lanata),

Indian ricegrass (Achnatherum hymenoides), squirreltail (Elymus

elymoides), Nevada jointfir (Ephedra nevadensis), and shadscale

(Atriplex confertifolia).

On May 15, 1963, the Double Tracks test, which consisted

of plutonium and depleted uranium, was exploded on the

Nellis Air Force Range (NAFR) to study the dispersal of

radionuclides in the environment (Church 1969; Shreve

1965). As a result of the explosion, approximately 0.98-1.6

kilograms (kg) (2.2-3.5 pounds) of plutonium was scattered

across the Double Tracks site (Shreve 1964).

During the summer and early fall of 1996, remediation of

the Double Tracks site occurred. The remediation process

entailed scraping the top 5 to 15 cm (2 to 6 inches) of

contaminated topsoil, packaging the soil, and transporting

it to a disposal site at the Nevada Test Site. The last phase

of the remediation process was to reclaim the land surface

disturbed by the remediation process. The reclamation objective was to establish a permanent native vegetative cover

on the site to prevent soil erosion and re-establish wildlife

habitat. The purpose of this paper is to describe techniques

used to accomplish the reclamation objective, explain some

of the results to date, and describe a monitoring plan used to

evaluate reclamation success.

Methods _______________________

Site Description

The Double Tracks remediation site is located on the

NAFR, approximately 22 kilometers (14 miles) east of Goldfield, Nevada, located in the south-central part of the State

(fig. 1). The site is on the northwest edge of Stonewall Flat

on an alluvial fan extending off the western slope of the

Cactus Spring Mountains. Elevation at the site ranges from

1,487 to 1,584 m (4,879 to 5,197 feet) above sea level.

Common vascular plant species found on the site include

Figure 1—Location of Double Tracks remediation site.

Nevada

California

Nellis

Air Force

Range Lincoln

County

Clark

County

SCALE

0 30 60 Kilometers

0 20 40 Miles

Double Tracks

Test Site

LEGEND

N

6

6

504

95

160 95



318

375

93

Beatty

Mercury

Pahrump

Nevada

Test

Site

Esmeralda

County

Goldfield

Tonopah

Warm

Springs Nye

County

Tonopah

Test

Range

Range

7N

Double

Tracks

Test Site

Primary highway

State boundary

County boundary

City
USDA Forest Service Proceedings RMRS-P-11. 1999 261

greasewood (Sarcobatus vermiculatus), budsage (Artemisia

spinescens), winterfat (Krascheninnikovia lanata), desert

pepperweed (Lepidium fremontii), and shadscale (Atriplex

confertifolia). Soils are predominantly gravelly sandy loams

and gravelly loams (Leavitt 1978). Average annual precipitation at Goldfield is 118 mm (5.2 inches) (Office of the Nevada

State Climatologist, unpublished).

Figure 2 shows the layout of the remediation site and eight

sections that were reclaimed. Only 1.1 ha (2.7 acres) were

remediated (A and B). Little or no topsoil from the remaining

2.7 ha (6.6 acres) was removed (C - H). These sections were

disturbed in support of the remediation operation but were

not remediated because they were characterized as having

radioactivity levels lower than the specified interim corrective action level or less than or equal to natural background

levels. The eight sections (fig. 2) were categorized into the

following four areas: (1) the remediated area where topsoil

was removed (A and B), (2) the staging area where some

topsoil was removed and later replaced (C), (3) the support

facility area where little or no topsoil was removed (D), and

(4) the remaining area where little or no topsoil was removed

(E, F, G, and H). A total of 3.8 ha (9.3 acres) were reclaimed

at the Double Tracks remediation site.

Site Preparation

During the fall of 1996, all of the areas to be reclaimed

were ripped to a depth commensurate with the degree of

compaction. Areas with large dirt clods were disked to

smooth the seedbed. Additionally, portions of the site were

recontoured to predisturbance conditions with emphasis on

re-establishing natural drainages.

Seeding/Polyacrylamide Gel Application

Native species were used in the seed mix in proportions

similar to what naturally occurs on the site. To determine

species composition, a reference area was located adjacent to

the remediation site, and plant density and cover data were

collected from 15, 50 m (164 ft) transects in July 1995

(Anderson and Hall 1997). A seed mix was then developed

based on the density and cover data from the reference area

(table 1). Galleta (Pleuraphis jamesii), spiny hopsage (Grayia

spinosa), and fourwing saltbush (Atriplex canescens) were

not found in the reference area, but were included in the seed

mix because they do occur in the general vicinity of the

remediation site.

The remediation site was broadcast seeded in November

1996, at a rate of 23.5 pure live seed (PLS) kg/ha (21.0 lb/ac),

using a tractor-drawn seed drill with its disk openers raised

above the ground. An average of 444 seeds PLS/m2

 (41 seeds

PLS/ft2

) were seeded across the site. Several lengths of

chain were attached to the back of the seeder and dragged

along the ground to lightly cover the seed. The seed drill had

three seed bins: a fluffy seed bin, a hard seed bin, and a

small seed bin. The fluffy seed bin contained seed of the

following species: winterfat, white burrobush (Hymenoclea

salsola), rubber rabbitbrush (Ericameria nauseosa), spiny

hopsage, California buckwheat (Eriogonum fasciculatum),

and galleta. The hard seed bin contained seed from the

remaining nine species (table 1). The small seed bin contained polyacrylamide gel crystals. These were applied at a

rate of 22.4 kg/ha (20.0 lb/acres). Gel crystals were used to

increase the moisture-holding capacity of the soil and

enhance germination.

Mulching/Crimping

After seeding was complete, the site was mulched with

wheat straw at a rate of 4,500 kg/ha (4,000 lb/ac). Mulch

protects the soil surface from wind and water erosion, and

also provides a more favorable microenvironment for seedling establishment. After the straw was blown on the site, a

tractor-drawn crimper was used to crimp the straw into the

soil. Crimping holds the straw in place, thus reducing

erosion, and also incorporates a portion of the straw into the

soil, which over time can improve the amount of organic

matter in the soil.

Irrigation

An irrigation system was designed by Harward Irrigation Systems of Spanish Fork, Utah, and set up on-site in

December 1996. Water was stored in two 37,854 liter

(10,000 gallon) storage tanks and pumped through a delivery system using a Berkeley water pump (Model B1-1/

2ZQM-12) attached to a Wisconsin 14 horsepower portable

gasoline engine (Model S-14D). The delivery system had

nine valves that controlled flow into nine separate “zones,” Figure 2—Location of areas reclaimed at the Double

Tracks cleanup site.

Legend

A - Ground zero

B - Plume

C - Staging area

D - Support facilities

E - Unused well pad

F - Topsoil stockpile

G - Staging area for reclamation plots

H - Loading/unloading area

Section to be reclaimed

H

E



G

F

B

C

A

D
262 USDA Forest Service Proceedings RMRS-P-11. 1999

with approximately 25 portable sprinkler stands per “zone.”

The sprinkler stands, spaced at regular intervals, were

placed in the remediated, staging, and support facility areas. The remediated and staging areas were irrigated during

the late fall of 1996 and the spring of 1997. The support

facility area only received irrigation during the spring of

1997, and the remaining area received no irrigation.

The amount of irrigation to be applied was based on

precipitation events favoring good seedling emergence and

plant growth. Those events occurred in fall/winter/spring of

1991-1992, 1992-1993, and 1994-1995. Precipitation records

were obtained from the Goldfield, Nevada, weather reporting station. The average monthly precipitation for the above

years was chosen as a standard. The difference between the

average monthly precipitation and that received in 1996-

1997 was the amount of supplemental irrigation applied for

a given time period.

Irrigation water was obtained from the Roller Coaster

Well on the Tonopah Test Range approximately 22.4 kilometers (14.0 miles) east of the Double Tracks remediation site.

Water from the Roller Coaster Well was analyzed and found

to be suitable for irrigation (Ludwig and others 1976).

Treatments

Four different irrigation/topsoil treatment combinations

were studied: (1) fall/spring irrigation with topsoil removed

(fall/spring-no topsoil), (2) fall/spring irrigation with some

topsoil removed and later replaced (fall/spring-topsoil), (3)

spring irrigation with little or no topsoil removed (springtopsoil), and (4) no irrigation with little or no topsoil removed

(nonirrigated-topsoil).

Seed bags

Small samples of seed from the fluffy and hard seed mixes

were put into small nylon mesh seed bags and placed in the

fall/spring-topsoil, spring-topsoil, and nonirrigated-topsoil

treatments to determine the timing of germination of the

different species in the seed mix and the effects of different

irrigation regimes on seed germination. Seed bags were then

collected periodically from each treatment through the winter and spring of 1997. Germinated seeds were counted by

species and then discarded.

Data Collection and Analysis

A weather station was set up onsite to measure and

automatically record several climatic variables. Precipitation (mm) was collected using a tipping bucket rain gauge.

Electrical resistance (ohms) and maximum and minimum

soil temperature (degrees Celsius) were measured with

thermistor soil cells. Maximum and minimum air temperature (degrees Celsius) were measured with a thermistor

probe. All data were recorded using an electronic datalogger.

Thermistor soil cells were placed at 2 cm (1 inch), 15 cm (16

inch), and 30 cm (12 inch) depths in two undisturbed places

not receiving irrigation, in two places on the staging area

receiving fall/spring irrigation, and in one place near ground

zero in the remediated area that received fall/spring irrigation to measure electrical resistance. Resistance data were

converted to percent soil moisture by volume using a fourthorder polynomial regression equation obtained by calibrating soil samples from the site using a method adapted from

Kelley (1944).

Densities of seeded and nonseeded plants by species were

counted in five randomly placed 4 m2

 (43 ft2) quadrats along

15, 50 m (164 ft) transects in each of the four treatment

combinations during June 1997, and again during June

1998. Densities were converted to a per-meter-square basis. Additionally, data on wildlife use of the site were

documented by noting any animals seen onsite or any

passive animal indicators (e.g., animal scat, ant hills). All

plant density data were square-root transformed before

being analyzed to normalize the data, but means presented

are actual means. Standard analysis-of-variance procedures (Wilkinson and others 1992) were used to analyze the

data, and Tukey’s mean separation procedure was used to

Table 1—Seedmix for the Double Tracks remediation site.

Life form Species Common name Seed mix PLS kg/ha PLS seeds/m2

percent

Shrub Atriplex canescens Fourwing saltbush 4.3 1.0 12

Shrub Atriplex confertifolia Shadscale 19.0 4.5 64

Shrub Ephedra nevadensis Nevada jointfir 11.9 2.8 12

Shrub Ephedra viridis Green ephedra 9.5 2.2 12

Shrub Ericameria nauseosus Rubber rabbitbrush 1.9 0.5 40

Shrub Eriogonum fasciculatum California buckwheat 0.5 0.1 11

Shrub Grayia spinosa Spiny hopsage 1.4 0.3 12

Shrub Hymenoclea salsola White burrobush 7.1 1.7 41

Shrub Krascheninnikovia lanata Winterfat 16.7 3.9 49

Shrub Lycium andersonii Anderson's wolfberry 8.1 1.9 12

Shrub Sarcobatus vermiculatus Greasewood 2.4 0.6 26

Grass Achnatherum hymenoides Indian ricegrass 9.5 2.2 70

Grass Elymus elymoides Squirreltail 1.9 0.5 19

Grass Pleuraphis jamesii Galleta 4.8 1.1 39

Forb Sphaeralcea ambigua Desert globemallow 1.0 0.2 25

Total 100.0 23.5 444
USDA Forest Service Proceedings RMRS-P-11. 1999 263

determine significant differences (α = 0.05) among treatment means.

Results ________________________

Precipitation and Irrigation

Total precipitation was recorded at the Double Tracks

site. However, due to a malfunction in the precipitation

gauge, precipitation data from the Goldfield, Nevada, reporting station was used. Table 2 shows the amount of

natural precipitation received and irrigation applied. The

total amount of precipitation received added to irrigation

applied exceeded the goal by about 8 mm (0.3 inch). Natural

precipitation from September through December was almost equivalent to the goal. However, only 6.6 mm (0.3 inch)

of precipitation was received after seeding. Therefore, irrigation was applied so that the seed would benefit from the

additional moisture. A total of 158.0 mm (6.2 inches) of

natural precipitation was received from October 1, 1996, to

September 30, 1997, compared to the long-term average of

118 mm (5.2 inches). From October 1, 1997, to June 30, 1998,

297.2 mm (11.7 inches) of precipitation was received. This is

more than double the total annual long-term average, so this

was an exceptionally wet winter and spring.

Percent soil moisture by volume did not differ significantly between irrigated and nonirrigated plots for the

period March 1 to June 30, 1997. This period was chosen for

analysis because this is the period during which most of the

germination took place. Percent soil moisture by volume

averaged 6.0 and 2.1 in the irrigated and nonirrigated areas,

respectively, at the 2.5 cm (1 inch) depth. Although not

statistically significant, the higher soil moisture in the

irrigated areas may help explain why seedling emergence

was higher in irrigated areas than in areas receiving no

irrigation.

Seed Bags

Seed bags were retrieved on March 4, March 17, April 15,

and May 5, 1997. The first retrieval occurred before the

March irrigation began. Therefore, germination to this point

was a result of natural precipitation and the fall irrigation.

Winterfat, greasewood, squirreltail, fourwing saltbush, Nevada jointfir, Indian ricegrass, and rubber rabbitbrush had

germinated by the first retrieval date. By the second retrieval date, shadscale had germinated also, but only in the

fall/spring irrigation regime. Winterfat and greasewood

germinated in all three irrigation regimes by the second

retrieval date. No additional species had germinated by the

third and fourth retrieval dates. Germination of green ephedra (Ephedra viridis), California buckwheat, spiny hopsage,

white burrobush, Anderson’s wolfberry (Lycium andersonii),

galleta, and desert globemallow (Sphaeralcea ambigua) was

not detected. Peak germination across all species was at the

March 17 retrieval date.

Seedling Emergence

A total of 6.7 seeded seedlings/m2 and 6.9 total perennial

seedlings/m2

 (including seeded and nonseeded perennials)

had emerged across all treatments by June 1997. Based on

a seeding rate of 444 pure live seeds/m2

, 1.5 percent of the

seeds emerged. The emergence percentage of individual

species varied. All 15 seeded species emerged. Additionally,

five nonseeded native perennial species emerged; namely,

budsage, Fremont’s milkvetch (Astragalus lentiginosus var.

fremontii), desert pepperweed, low woollygrass (Erioneuron

pulchellum), and desert prince’s plume (Stanleya pinnata).

Significant differences were detected among treatments

for total seeded species as well as all perennials (both seeded

and nonseeded) combined (fig. 3). Seedling densities were

highest in the spring-topsoil treatment and lowest in the

nonirrigated-topsoil treatment. No significant differences

were evident between the fall/spring irrigated with topsoil

and the fall/spring irrigated with no topsoil treatments.

Significant differences were also detected among treatments for several species. Differences are depicted for the

five most abundant species in figure 4. These data reveal

that individual species responded differently to the various

treatments. For instance, shadscale and squirreltail emerged

best in the fall/spring-topsoil treatment, while winterfat and

Indian ricegrass emerged best in the spring-topsoil treatment. A trend for densities to be lowest in the nonirrigatedtopsoil treatment is evident. Winterfat is the only exception

to this trend (fig. 4).

Table 2—Natural precipitation received and irrigation applied at the Double Tracks remediation site.

Natural Supplemental Natural

Month of Goal (assuming precipitation irrigation Total water precipitation

irrigation 90% efficiency) (1996/1997) (1996/1997) (1996/1997) (1997/1998)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - mm - - - - - - - - - - - - - - - - - - - - - - - - 

December 51 48a 37 85 65a

March 79 34b 23 57 82b

April 45 0c 42 42 41c

May 15 1d 13 14 21d

Total 190 83 115 198 209

a

Amount received from September through December.

b

Amount received during January and February.

c

Amount received during March.

d

Amount received during April.
264 USDA Forest Service Proceedings RMRS-P-11. 1999

Plant Establishment

By June 1998, a total of 6.4 seeded plants/m2 and 6.7 total

perennial plants/m2

 were found across all treatments. Therefore, 1.4 percent of the seeded seeds had emerged and/or

established. The establishment percentage of individual

species varied. Again, all 15 seeded species had either

emerged or established. In addition, five native nonseeded

perennial species were found. These included budsage,

Fremont's milkvetch, desert pepperweed, desert prince’s

plume, and low rabbitbrush (Chrysothamnus viscidiflorus).

Total plant density in the reference area was 2.1 plants/m2

in July 1995, as compared to 6.7 plants/m2 in the reclaimed

area in June 1998.

Significant differences were detected among treatments

for total seeded species as well as all perennials combined

(fig. 5). Seedling densities were highest in the spring-topsoil

treatment. Densities in the nonirrigated-topsoil treatment

increased substantially due to the exceptionally wet winter

and spring. No significant differences were evident between

the fall/spring irrigated with topsoil and the fall/spring

irrigated with no topsoil treatments.

Significant differences were also detected among treatments for several species. Differences are depicted for the

five most abundant species in figure 6. Individual species

responded differently to the various treatments. For example, shadscale emerged and/or established best in the fall/

spring-topsoil treatment; whereas, winterfat, Nevada jointfir,

and Indian ricegrass emerged and/or established best in the

spring-topsoil treatment. Densities of Indian ricegrass in the

spring-topsoil and nonirrigated-topsoil treatments increased

by 1.3 and 2.4 plants/m2

, respectively (fig. 6).

Wildlife Use

Several wildlife species have been documented using the

reclaimed area as evidenced by direct animal observations

and presence of sign (e.g., scat, tracks). These data are

entered in a database to document wildlife use on the site.

During plant density sampling in 1997, 72.0 percent of the

quadrats sampled contained black-tailed jackrabbit (Lepus

californicus) pellets and 2.3 percent contained pronghorn

antelope (Antilocapra americana) scat. Also, 36.0 percent of

Figure 4—Seedling response of five species to four

treatments, June 1997.

Figure 5—Total seeded and total perennial plant

response to four treatments, June 1998.

Figure 6—Plant response of five species to four

treatments, June 1998.

Figure 3—Total seeded and total perennial seedling

response to four treatments, June 1997.

2 Seedlings/m 12

10

8

6

4

2

Seeded species All perennials

1997 seedling densities

a

a

b

b

c c

b

b

0

Spring–topsoil

Fall/Spring–no topsoil

Fall/Spring–topsoil

Non-irrigated–topsoil

2 Seedlings/m

3

2.5

2

1.5

1

0.5

ATCO

1997 seedling densities

a

b b

c

0 KRLA EPNE ACHY ELEL

a

b b

b a

b

a a

c

b

a

b

b b

a

c

Spring–topsoil

Fall/Spring–no topsoil

Fall/Spring–topsoil

Non-irrigated–topsoil

2 Plants/m 10

9

7

6

4

2

Seeded species All perennials

1998 plant densities

a

a

b

b b b

b

b

0

8

5

3

1

Spring–topsoil

Fall/Spring–no topsoil

Fall/Spring–topsoil

Non-irrigated–topsoil

4.5

3.5

4

1.5

1

0.5

ATCO

a

b

0

KRLA EPNE ACHY ELEL

a

bc b

a

a

b

a a

b

2 Plants/m

1998 plant densities

2.5

2

3

Spring–topsoil

Fall/Spring–no topsoil

Fall/Spring–topsoil

Non-irrigated–topsoil

b b

c

b b c

c c

a
USDA Forest Service Proceedings RMRS-P-11. 1999 265

the quadrats sampled contained at least one or more plants

that showed signs of herbivory. In 1998, 36.0 percent of the

quadrats sampled contained black-tailed jackrabbit pellets

and 1.3 percent contained pronghorn antelope scat. Only 0.7

percent of the quadrats sampled contained plants that

showed signs of herbivory.

Conclusions and Future

Monitoring _____________________

Results from this study show that irrigation significantly

increases seedling densities during years of average precipitation. Wallace and others (1980) determined that about 2

out of every 6 years are conducive to new seedling establishment on the Nevada Test Site based on precipitation records

in their study. Because it is impossible to predict when the

above-average precipitation years will occur, irrigation

maximizes the potential for reclamation success. Results

also indicate that spring irrigation was adequate for successful seedling emergence, but certain species like shadscale

and squirreltail emerged best when irrigated both in the fall

and spring.

Reclamation Success Criteria and Future

Monitoring

Plans for future monitoring include sampling the reference area and the reclaimed area during the third, fifth, and

tenth years following reclamation and comparing vascular

plant density, cover, and diversity data between the two

areas at each sampling period. If after 10 years vascular

plant density, cover, and diversity of the reclaimed area are

60 percent of that measured on the reference area, reclamation of the Double Tracks site will be considered successful.

Sampling during the third and fifth years allows scientists

to track the progress of the reseeded disturbed remediation

site in comparison to the native vegetation. If after 5 years,

vascular plant density is less than 2.1 plants/m2

 or vascular

plant cover is less than 50 percent of the amount of cover on

the reference area, remedial action such as reseeding or

transplanting may occur to ensure successful reclamation

by the tenth year (Anderson and Hall 1997).

References _____________________

Anderson, D. C.; Hall, D. B. 1997. Double Tracks revegetation and

monitoring plan. DOE/NV/11718-104, UC-708. U.S. Department

of Energy, Nevada Operations Office, Las Vegas, NV.

Church, H. W. 1969. Cloud rise from high-explosives detonations.

SC-RR-68-903. Sandia National Laboratories, Albuquerque, NM.

Kelley, O. J. 1944. A rapid method of calibrating various instruments for measuring soil moisture in situ. Soil Science. 58:

433-440.

Leavitt, V. D. 1978. Soil surveys and profile descriptions of plutonium-contaminated areas on the test range complex in Nevada,

1970-1977. In: White, M. G.; Dunaway, P. B., eds. Selected

environmental plutonium research reports of the NAEG. DOE/

NV Operations Report NVO-192. Las Vegas, NV.

Ludwig, A. E.; Hergert, G. W.; Franklin, W. T. 1976. Irrigation water

quality criteria. Colorado State University Extension Service.

Service in Action Sheet No. 506. 2 p.

Office of the Nevada State Climatologist. 1991-1998. Unpublished

data.

Shreve, J. D., Jr. 1964. Operation Roller Coaster, April 1964 conference data presentation and evaluation. Sandia National Laboratories, Albuquerque, NM.

Shreve, J. D., Jr. 1965. Operation Roller Coaster, scientific director’s

summary report. DASA-1644. Sandia National Laboratories,

Albuquerque, NM.

Wallace, A.; Romney, E. M.; Hunter, R. B. 1980. The challenge of a

desert: revegetation of disturbed desert lands. In: Soil-plantanimal relationships bearing on revegetation and land reclamation in Nevada deserts. Great Basin Naturalist Memoirs, Vol. 4.

Brigham Young University, Provo, UT.

Wilkinson, L.; Hill, M.; Welna, J. P.; Birkenbeuel, G. K. 1992.

Statistics. Evanston, IL: Systat, Inc. 750 p.
266 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Mary Dudley is Volunteer Coordinator, Idaho Department of Fish and

Game, 109 W. 44, Boise, ID 83714.

Volunteers and Planting Techniques for

Restoring Southwestern Idaho Riparian

Habitats

Mary Dudley

Abstract—Restoration of protected riparian areas may be hastened and enhanced by planting native trees and shrubs. There is no

exact science to successful planting due, in part, to the uniqueness

of individual creeks and rivers. There are sound guidelines to follow.

Trying different techniques to fit diverse situations is important.

Obtaining quality plants from a local seed source is best. If cuttings

or poles are planted, harvesting them from a local source, preferably

from along the same stream, is desirable. Another key element in

establishing native riparian species involves selecting the best

possible planting sites for survival. Sometimes there is a need for

replanting, additional plantings, or adding more species as they

become available or as the site stabilizes. Properly trained and

supervised volunteers can make riparian restoration projects feasible. Planting is labor-intensive and requires dedicated people who

plant with care. A highly motivated volunteer crew will accomplish

a tremendous amount of quality work. Volunteers can also assist

with riparian monitoring. Monitoring helps to determine which

methods work at a particular site, thus contributing to the success

of future restoration efforts.

Imagine a creek flowing beneath high, crumbling cutbanks,

sagebrush roots exposed to the elements. Another chunk of

earth is about to fall into the water, taking the gnarled

Artemesia with it and depositing more sediment in the creek.

The water is a sickly green in color; algae covers the creek

bottom. Tumbleweeds several feet deep choke the creek in

places. Dust devils spin up from the parched earth next to

the creek where red band trout once thrived. Is this the scene

of a nuke zone? Now imagine the creek flowing between

lovely green willows that shade and cool the clear water.

Young cottonwood trees, wild rose, hawthorn, and golden

currant grow along the banks. Rushes, sedges, bulrushes,

monkey flowers, and other perennial herbaceous species

thrive. Kingfishers dive for small fish, now abundant in the

deepening water. A brood of mallards swim closely behind

their mother. Song sparrows, killdeer, and spotted sandpipers belt out territorial calls and songs. The heart-shaped

tracks of deer are distinct in the wet earth at the water’s

edge. Is this an oasis in the high desert of southwest Idaho,

a lush piece of paradise, a refuge for wildlife and people?

Places like the nightmarish scene are all too common in

the West. Yet, there is hope. Riparian areas can be restored

by thoughtful planning, protection, careful planting, time,

and with the help of dedicated volunteers (fig. 1).

 My work has been done in southwest Idaho. My crews

consist of volunteers. This paper includes information about

successful planting techniques for willow cuttings, poles and

cottonwood poles, and containerized and bare root shrubs

and trees. I will also tell you how dedicated volunteers can

make successful planting projects a reality.

Figure 1—A. Volunteers planted willow cuttings and

cottonwood poles along Cold Springs Creek, November 1993. B. Cold Springs Creek, June 1997. Willows

and cottonwoods grow thick and lush along the creek,

shading and cooling the water, catching sediment, and

providing wildlife habitat.

A.

B.
USDA Forest Service Proceedings RMRS-P-11. 1999 267

Designing a Plan ________________

Planting sites differ, so plans should be designed based on

ground observation of the area. Factors to consider include:

elevation, length of growing season, size of creek/river,

typical high water levels, duration of spring run-off, existing

riparian species and presence of seed sources for natural

regeneration, severity of active erosion and bank sloughing,

availability of local plant materials and seed for artificial

revegetation, availability of suitable planting sites, accessibility, and long-term plans for protection from livestock.

Willow Cuttings _________________

When to Plant

Autumn is a good time to plant because the cuttings can be

planted at the water’s edge while the water level is low.

Cuttings require sufficient and constant moisture throughout the growing season to produce roots and become firmly

established. Planting at the water’s edge during autumn

will help to ensure adequate water for root growth during the

critical first growing season. An advantage of planting

cuttings in the fall is that they can be harvested and planted

within a day or two.

 There are several problems associated with planting cuttings in the spring. Water levels are usually high well after

willows have broken bud. Planting after high water shortens

the first growing season. If cuttings are planted while still

dormant and during high water, they usually end up being

planted too far up the bank. When water levels drop during

late summer and fall, the cuttings are left high and dry.

Where to Obtain Cuttings

Ideally, cuttings should be harvested from willows growing in the same drainage as the planting site, which could be

1 mile or 10 miles away. The closer, the better, especially in

regard to elevation. Take cuttings from mature, robust

stands of willows. Watch for insects and diseases. Removal

of several cuttings from each clump will not be noticeable

and the plants will be stimulated to produce new growth.

When to Obtain Cuttings

The cuttings should be harvested after the leaves have

started to turn color or have fallen and the willows are

dormant. The planted cuttings will remain dormant until

spring when they will begin to grow. Obtain the cuttings as

soon before planting them as possible, preferably on the same

day or a day before planting them. Cuttings can be harvested

in early spring while dormant, wrapped in wet burlap, and

kept in cold storage until water levels are low enough to plant.

The advantage of planting cuttings in the fall is that they can

be obtained and planted within a day or two.

How to Make the Cuttings

Use sharp loppers for clean cuts and ease of use. Skilled

volunteers can keep the tools sharpened. For plantings

along small streams, cuttings about 18 inches in length and

0.75 to 1.5 diameter work well. Use at least 2 year old growth

and nothing decadent. Cut willow whips from the base of the

mature plant. Often two cuttings can be made from one

willow whip. Trim off all branches and leaves with sharp

loppers or pruning shears. Make a 45 degree cut at the base

of the cutting for ease of planting.

Care of Cuttings Before Planting

After harvesting, place the cuttings, base end down, in

buckets half filled with water to keep the rooting end of the

branch moist (5 gallon plastic buckets with handles work

well). Keep the cuttings in a cool, shady place until planting.

Plant cuttings within a few days of harvesting.

Custom Planting Bars

Willow planting bars patterned after the KBC tree/shrub

planting bar make life bearable for planters struggling to

plant cuttings in rocky and sometimes frozen ground. The

bars are designed with a ‘T’ handle and a bar across the

bottom of the bar on which one or two feet can be placed so

that part, if not all, of the planter’s weight can press down on

the bar to create deep holes. The bars are made from

3⁄4 inch steel. A good welder can make these tools (fig. 2).

Figure 2—Volunteers planting willow cuttings using

custom made planting bars along Cold Springs

Creek, November 1993.
268 USDA Forest Service Proceedings RMRS-P-11. 1999

Rubber Mallets

Planting the cuttings deep enough sometimes requires the

use of an additional tool. Rubber mallets can be used to drive

cuttings into hard, rocky ground. A hole can be made with a

planting bar and a cutting driven into it with a rubber

mallet. A 2+ pound rubber mallet with a 2.75 inch diameter

head works well.

Choose the Best Possible Place for

Survival

Site selection is critical for successful planting of willow

cuttings, as well as for any wildland plantings. When selecting suitable sites, look for bare ground or at least ground with

minimal vegetation. Competition from previously established

plants reduces the willow cutting’s ability to establish.

While steep, raw, actively eroding banks are in dire need

of deep-rooted shrubs and trees for stabilization, these are

poor places to plant willow cuttings or anything else. These

places are too unstable. The chances for survival of newly

planted cuttings or even rooted stock are jeopardized greatly

by forces of stream current and continued chunks of earth

falling into the stream, taking the new plant with them.

It is best to plant in the best sites for survival of the

cuttings. When the plants become well established after a

few years, they will begin to regenerate and spread into the

raw areas on their own. By that time, the planted willows

will be catching sediment and debris and armoring previously unprotected stream banks.

Planting Techniques

 Plant the cuttings at or near the water’s edge or where the

water table stays high season long at a 45 degree angle to the

stream. Planting at this angle may increase the cuttings’

chance of surviving spring run-off. Because root growth is

the priority in establishing plants, cuttings must be planted

as deeply as possible, leaving only a quarter to a third of the

cutting exposed. Unnecessary energy goes into leaf production if too much of the cutting is above ground. Planting

proximity is best determined by availability of suitable

planting sites. The cuttings can be planted closely together,

for instance 12 inches apart.

Plant Establishment

At the beginning of the first growing season, surviving

cuttings will sprout leaves. While leaf sprouting gives reason to be optimistic, remember that root establishment is

critical the first year. If the cuttings have become firmly

rooted, they have a better chance to survive spring run-off

and other high water events . By the second growing season,

branches will begin to sprout as well as leaves. Sometimes a

cutting may appear to be dead, but closer observation may

reveal sprouting from the roots at or near the base of the

cutting. When conditions are favorable (sufficient water,

little or no insect, rodent, rabbit, deer or livestock damage,

no killing frosts early in the growing season, no overwhelming vegetative competition), willow cuttings can grow markedly during the second spring and summer.

At Cold Springs Creek, a degraded stream in Elmore

County, Idaho that flows through a sagebrush zone between

3,500 and 3,000 ft, willow cuttings planted in early November 1993 became established rapidly. By late September

1995, after two growing seasons, some of the willows were 7

feet tall, multiple-branched and robust. By summer 1996,

willows lined the creek and some were sending up shoots.

The 1997 growing season was dramatic. Willows grew thick

and lush and up to 10 to 14 feet tall. The creek has narrowed

and deepened, and the willows shade the water. The willows

have been catching debris and sediment since 1995; they

now are so well established that beavers will be introduced

to the creek in September 1999 to further enhance restoration.

Slower Plant Establishment at High

Elevations and Along Rivers

 Short growing seasons characteristic of high elevations

slow plant establishment. The growing season may be less

than two and a half months in the high mountains. Cuttings

planted along a low (below 4,000 feet) elevation stream will

begin to break bud in mid-April and continue to grow until

October, growing for nearly 6 months. Riparian restoration

at high elevations will take longer.

Usually, plants establish more slowly along rivers and

major tributaries than along small streams and creeks. High

water can last until late June or July during spring run-off,

which shortens the growing period. Flooding during other

Table 1—Survival of cuttings.

Date Date Percent

Planting site planted monitored survival Overall status by 1998

Cold Springs Creek Nov. 1993 Sept. 1995 74 Outstanding; willows regenerating, catching

sediment, shading stream.

Squaw Creek Oct. 1993 Oct. 1995 37 Limited; most planting sites too unstable;

63 percent washed out during high and long

spring run off during 1995.

Brood Creek Oct. 1997 Sept.1998 98 By Sept. 1998, plants were leafy and robust.

North Fork Payette River Oct. 1997 July 1998 10 Most cuttings washed away during prolonged

high spring run-off.

South Fork Payette River Nov. 1997 July 1998 99 By Sept. 1998, plants were leafy and robust (fig. 3).
USDA Forest Service Proceedings RMRS-P-11. 1999 269

be planted as deeply as possible. Unnecessary energy goes

into leaf production if too much of the pole is above the

ground. Make a 3 foot deep hole with the auger, planting the

pole as deeply as possible. Tamp in well. Leave only a quarter

to a third of the pole above ground. Poles should be planted

at least 6 feet apart.

Plant Establishment

When planted in late autumn, willow and cottonwood

poles should sprout leaves the next spring. While sprouting

leaves give reason to be optimistic, remember that root

establishment is critical the first growing season. If the

plants survive the first growing season and the next winter,

the poles will again sprout leaves and small branches at the

beginning of the second growing season. Sometimes the pole

will look dead the second spring, but closer observation may

reveal sprouting from the roots at or near the base of the pole.

When conditions are favorable (sufficient water, little or no

insect damage, minimum nibbling by wild or domestic animals, no killing frost, vegetative competition minimal),

cottonwood and especially willow poles can grow dramatically during the second growing season.

 At Cold Springs Creek, cottonwood poles planted in early

November 1993 grew numerous leaves and appeared to be

establishing during the 1994 growing season. During the

following summer, spring elm caterpillar larvae (Nymphalis

antiopa) attacked the young trees, slowing their growth

markedly. In early June 1996, a severe frost blackened

newly sprouted leaves. Late that same summer, a lone bull

found his way into the otherwise protected riparian area and

favored the young cottonwoods, eating them back drastically. That bull has since become hamburger and the cottonwoods survived. By late June 1997, the cottonwoods suddenly

looked like trees. They were over 7 feet tall, multiplebranched, full and robust. By September, the young cottonwoods had grown another 4 feet (fig. 4).

 It is important to continue to monitor plantings for

several years because sometimes plantings take years to

become fully established and to thrive or they may crash and

burn and partial replanting may be necessary. Restoring

riparian areas that have been degraded over decades often

requires many years.

Bare Root and Containerized

Plants _________________________

 Some streams and rivers will recover well merely by being

protected from factors causing degradation and do not require

additional planting if adequate seed sources already exist.

There are, however, far more rivers and creeks that have only

raw banks and xeric vegetation or weeds lining the water.

Planting willow and cottonwood cuttings and poles is

inexpensive and can be highly successful. However, most

other riparian species do not establish from mere cuttings or

poles. Planting a variety of native riparian species grown as

bare root or containerized stock, will add diversity and

richness to restoration efforts. An aggressive plan involving

fall cutting and pole planting and spring planting of rooted

species can hasten and enhance riparian restoration and

stream bank stabilization.

Figure 3—One year old willow cuttings along the

South Fork of the Payette River.

high water events can also slow plant establishment. Small

creeks and streams respond to plantings more rapidly than

rivers. Water rushes over the plants for a shorter time and

with much less volume and velocity.

Willow and Cottonwood Poles _____

Poles can be planted deeper than cuttings, enabling them

to better withstand the strong forces of deep, fast water

during high water events. Poles may establish more readily

than cuttings along small creeks that become extremely low

or intermittent during late summer and fall. An auger will

be needed to plant poles of this size. The same basic guidelines for cuttings apply to poles.

How to Make Poles

Use sharp loppers or a saw, depending on the size of the

pole. Cut willow poles about 4 feet long and 2 to 3 inches in

diameter. Trim off all branches and leaves. If left on the pole,

the branches and leaves will utilize energy that would

otherwise be used for root growth. During the first year, root

establishment is critical.

Planting Augers

Use an auger with a 3 foot long, 3 inch diameter bit. A

powerful and tuned-up chain saw with an auger bit works

well. A “stinger” run by a tractor can be used to make holes if

the terrain is suitable. However, many streams and rivers

needing restoration need a lighter touch during planting efforts.

Planting Techniques

Willow poles should be planted within a foot or so of water

in sites with little or no vegetative competition. Cottonwood

poles should be planted so that their roots touch the water

table, but not as close to the water’s edge as willows. Because

root growth is the priority in establishing plants, poles must
270 USDA Forest Service Proceedings RMRS-P-11. 1999

Species Selection

Species that are native to the area being restored should

be selected. Ideally, many different species should be planted,

preferably all of the major riparian species that grow in the

local area and that are not likely to re-establish on their own.

Select species that grow at the water’s edge, such as willow,

alder, and dogwood, as well as plants that grow on the banks,

Table 2—Survival of poles.

Date Date Percent

Planting site planted monitored survival Overall status by 1998

Cold Springs Creek Nov. 1993 Sept. 1995 29 Excellent; surviving cottonwoods thriving.

(cottonwoods)

Cascade Reservoir May 1997 June 1998 80 Prospects look good.

(cottonwoods)

North Fork Payette River Oct. 1997 July 1998 75 Success looks promising.

(willows)

Brood Creek Oct. 1997 Oct. 1998 98 Plants are healthy and robust (fig. 5).

(willows)

Figure 4—A. Young cottonwood one year after planted

as a pole, Cold Springs Creek, June 1994. B. Cottonwoods thriving four years later, Cold Springs Creek,

June 1998.

for example, pink spirea, woods rose, black twinberry, and

hawthorn. Planting native sedges, rushes, and bulrushes

may be a good idea if these species are native and scarce in

the area. These water-loving plants often re-establish themselves along even the most degraded streams if seed sources

exist nearby.

Seed Source

Obtaining plants that have been grown from locally collected seeds or plant materials is ideal. Some nurseries

collect seed locally to use for starting plants. Another alternative is to give locally collected seed to the nursery to grow

out into bare root or containerized plants. I have worked

with volunteers collecting seed from rose, hawthorn, pink

spirea, alder, shrubby penstemon, kinickinick, mountain

ash, snowberry, Rocky Mountain Maple, ceanothus, ninebark,

bitterbrush, and sagebrush.

Scheduling Nursery Production

Planning riparian planting projects at least a year in

advance of the proposed planting date will assure acquisition of sufficient quantities of desired species. Nurseries

generally sow seeds for bare root stock in the fall or early

spring. Fall sowings will be ready to transplant the second

spring. Seeds sown in the spring will be ready the next

spring. Containerized plants grown in a hot house are ready

to transplant in less than a year for 10 inch size seedlings.

Gallon-sized plants usually require about 2 years propagation period.

When to Plant

Plant bare root and containerized plants in the spring

after the highest run-off. Many rivers are not ready to plant

until late June or July. In 1998, riparian planting projects

located on three major rivers in SW Idaho had to be postponed until the second and fourth weeks of July. Small creeks

and streams can be low enough to plant in April or May.

Sometimes planting can be accomplished in phases. For

instance, we planted woods rose, golden currant, and clematis on top of a rock dike on the Boise River located in Ada

County, Idaho, at 2,800 foot elevation in late February 1998.

We planted the riparian plants, including dogwood, cottonwood, willow, sedges, and rushes on July 24. Planting species

that grow in or adjacent to water before spring run-off can

A.

B.
USDA Forest Service Proceedings RMRS-P-11. 1999 271

result in the plants being torn from the ground by high and

fast water. Their roots simply would not be well enough

established to withstand the forces of the water.

Problems associated with fall planting rooted stock include frost heaving and frozen ground. If the ground is

frozen, it is difficult to prepare planting holes and to compact

soil around the seedling once it is planted. Because fallplanted species quickly become dormant, root growth is

limited. Frost heaving can push the plants out of the ground,

especially 10 inch containerized seedlings. If not damaged

by frost heaving, these plants are highly vulnerable to high

water the following spring because their roots have not been

firmly established. Poles and cuttings do not seem to be

affected by frost heaving, probably because they are planted

deeper than containerized plants and there is less surface

area to be pushed out of the ground.

Care of Containerized and Bare Root

Plants Before Planting

Seedlings grown in tubes and bare root plants should be

kept dormant in cold storage until planting. After they are

taken out of cold storage, the plants should be kept covered

and protected from the sun until planted or gradually

acclimated to preclude shock. Take care to protect larger,

potted plants from wind and heat en route to planting sites.

If they cannot be transported in an enclosed vehicle, the

plants should be protected by a tarp rigged securely over the

back of a pickup bed. Otherwise high speed travel over long

distances will whip the young plants around, and can damage buds and new, tender leaves.

Choose the Best Possible Site for Survival

 Careful site selection is critical to permit successful

establishment of all riparian plantings. The same guidelines

for selecting the best possible sites for survival for planting

cuttings and poles apply to rooted plants.

Plant species such as alder, willow, and dogwood at the

water’s edge. Species such as woods rose, hawthorn, golden

currant, pink spirea, and black twinberry should be planted

further up the stream bank. Cottonwoods should be planted

in low sites where the roots can reach the water table, but not

at the water’s edge. With experience and a discerning eye,

suitable sites will pop out at the planter and beg to be

planted.

Protection of Plantings ___________

 All plantings must be protected from livestock. Riparian

restoration takes years, so protecting these areas while the

plants become fully established and mature is critical. Riparian areas are sensitive and vulnerable to abuse and can

be degraded slowly but surely by mismanagement. The

tender young shoots of even thorny shrubs such as hawthorn

and rose are delectable to ungulates. If the new growth is

eaten back each year, eventually the “mother” shrub or tree

will die, leaving nothing but a stump, snag, or broken down

log. Adverse impacts to plantings and to riparian areas in

general result from livestock grazing, ORV use, and repetitive camping.

Monitoring and Photo Plots _______

Monitoring survival and growth of plantings will help to

identify successful planting techniques and problems, species, and planting site selection. Plant survival should be

checked toward the end of each growing season while plants

are fully leafed out. In addition to determining whether a

plant is dead or alive, you may want to include: height and

width measurements; the number of stems; damage, if any,

by insects, frost, or grazing by rabbits, rodents, livestock,

deer or elk; flowering/seed production; and overall health

and vigor (fig. 6). Monitoring should be done at the same time

each year within a week before or after the day the plants

were inspected the first time. If the planting is successful

after the first 3 or 4 years the vegetation will become thick

and tall and at this point, photo monitoring is all that is

practical.

Before and after photographs tell the story of riparian

restoration efforts better than anything. The results of

successful plantings is dramatic, especially after just a few

years. Documenting projects with photos is one of the most

valuable aspects of the restoration work. Photo plots should

be established by using a permanent point of reference from

which photos will be taken every year. Each year photos

Figure 5—First-year growth on a willow pole

planted along Brood Creek.
272 USDA Forest Service Proceedings RMRS-P-11. 1999

should be retaken within a week before or after the originals

were taken. Continue to take photographs for at least 5 years

after restoration work began, and preferably for many additional years.

Replanting or Additional

Plantings ______________________

Often there is a need for replanting or making additional

plantings to restore riparian areas. On the Little Salmon

River, located in Adams County, Idaho, elevation 4,500 feet,

we planted 960 native plants of 12 species in late June 1996.

Survival was excellent the first growing season. During the

following winter, extreme flooding plagued this river, as well

as many other rivers in Idaho for several months, followed by

exceptionally high water during spring run-off. Across the

state, mountainsides slid, roads washed out, and rivers

carved new channels. We did not expect to see any surviving

plants from our 1996 planting, especially because most of

the plants were seedlings. Amazingly, some of plants survived, perhaps 10 percent. Species such as rose, hawthorn,

pink spirea, alder, and dogwood miraculously made it through

the ravages of the flooding.

Fortunately, I had planned on continuing the planting

effort in 1997, so I had ordered 3,500 shrubs and trees the

previous fall. In late June 1997, a week later than in 1996,

we planted the 2,100 containerized and potted shrub and

tree seedlings and 1,400 one year old woods rose bare root

seedlings. The rose had been grown from seed volunteers

collected in 1995. We added a few species that were not

available the first year, as well as more 1 gallon potted

plants. Survival of the second year’s planting was nearly

100%. We will evaluate the need for additional plantings in

fall 1998 at the close of the growing season. We will plant

willow poles in suitable sites in late October 1998.

Weeds_________________________

Exotic plants can pose problems. Weeds can grow much

taller than newly planted native seedlings and even 1 or 2

gallon containerized plants. We have often planted sites that

appear devoid of vegetation in the spring only to find a

veritable jungle of weeds by mid-July. The previously established exotics can tower over a young new native plant,

shading it from the sun and competing for growing space.

While weeds may seem overwhelming, the deep-rooted nature of woody shrubs gives them an advantage over exotic

grasses and forbs. Planted shrubs that survive the first

growing season can become firmly established during the

second year in spite of exotics. If weeds are especially

rampant, a volunteer crew can help eliminate many exotics

with shovels and brute force.

Volunteers Make it Happen________

Dedicated volunteers who are willing to work hard and

plant carefully make riparian restoration projects a reality.

People volunteer to plant because they truly want to help

wildlife and to heal the land. Motivation lies not in paychecks, prizes, or required assignments. Rather, motivation

stems from a genuine desire and willingness to do positive

work.

More than 4,161 volunteers contributed 88,962 hours

working on many diverse projects with the Idaho Department of Fish and Game during 1997. If the Department had

been billed for all of the services received, we would have

written a check for at least $1,206,426!

A major focus of the Department’s volunteer program is on

habitat restoration on both public and private lands. In the

Southwest Region alone, over 1,000 volunteers planted over

117,000 plants during 1997 and the first half of 1998.

Projects included big game winter range restoration (92,500

bitterbrush seedlings); wetland plantings (4,650 native

plants); Habitat Improvement Program plantings (12,000

shrubs and trees); and riparian restoration (8,250 native

plants). All but 650 of the 8,250 plants were rooted native

trees and shrubs; the remainder were cuttings and poles.

The work on the 26 projects was accomplished in 53 days

during spring and fall. These habitat restoration projects

simply would not have been possible without the excellent

help of volunteers. The cost of paying contract planters to do

these jobs is prohibitive.

Besides providing the backbone of riparian and other

planting projects, volunteers assist with riparian monitoring. All of the photo plots we have established and most of the

“before and after” photos have been taken by a volunteer

photographer.

The Nuts and Bolts of a Successful

Volunteer Program

Why do people volunteer for the IDFG and keep coming

back for more? Because our projects are fun! Projects are

important and they wouldn’t be accomplished without

Figure 6—Volunteer monitoring plant survival along

the Little Salmon River.
USDA Forest Service Proceedings RMRS-P-11. 1999 273

volunteers. We explain that importance when we recruit and

also when we begin the project work.

Tangible Benefits

Volunteer projects have tangible benefits. We plant willows along an eroded stream bank and the plants grow and

regenerate and catch sediment, and they ultimately benefit

fisheries and wildlife for the future. Riparian planting projects

that involve a private landowner, who, in effect, is also a

volunteer, have a major added benefit in providing a demonstration area for good riparian management to the landowner, his or her neighbors, and the public. The volunteers

who worked on the project become ambassadors to their

friends, associates, and government land management

 agencies.

Project Planning

Projects are well organized and carefully planned far in

advance of the project date. All details are thought out and

addressed, such as tools, materials, transportation, weather

and road conditions, crew leaders, cooperation with landowners and other agencies, and training needed. Nothing is

left to chance.

Training, Supervision, and Quality of

Projects

We plan the best and expect the best. We give volunteers

the best possible training. We have people, whether professionals, or qualified volunteers train and supervise. Volunteers take pride in their accomplishments. Whether we are

planting shrubs, collecting seeds, or establishing photo plots,

we do it as well, if not better, than professional contractors.

Working with Volunteers

We work closely with volunteers. Department personnel

work alongside volunteers so the projects are indeed accomplished as a partnership. When I was hired to initiate the

Volunteer Program in 1990, a couple of bureau office types

asked why I was out planting bitterbrush with volunteers. I

said that if you want a bureaucrat who simply recruits and

tells people what to do, then hire someone else. One of my

keys to success is working with volunteers. Besides, that is

the best part of my job because volunteers are cheerful,

positive, and fun to work with.

Recruiting

We give people lots of advance notice. People plan weeks,

even months in advance. We recruit successfully by making

personal contacts. While we may announce upcoming projects

in the local media and by mailings, personal contact is the

ultimate method by which to recruit and obtain commitments from volunteers.

Figure 7—Hard core volunteers with years of

planting experience at the end of a good day’s

work.

Commitment/Confirmation

With a good rapport with your volunteers, you will get

good commitments. We emphasize the importance of each

individual’s contribution when we recruit them for projects.

We confirm a week or more before a project and again a

couple of days in advance. The result? We know who is

coming and we can plan accordingly.

Conclusion_____________________

Successful restoration of riparian habitats is possible

using volunteer crews and proper planting techniques. Even

if funds were available to pay for contract planting crews, I

am convinced that caring and properly trained volunteers do

a better job (fig. 7).

Acknowledgments ______________

I would like to express my thanks for the review and

valuable input on this paper to Nancy Shaw and Stacy

Gebhards. Nancy has been my main native plant consultant

and has provided support and guidance on all of the restoration planting projects I have done. I am grateful to Stacy and

Nancy for their unwavering faith in me and for their encouragement. I wish to thank all of the volunteers, including

especially my husband, David, for their dedicated, loyal, and

superb help on all phases of the riparian restoration projects.

Photo credits go to Dean Barnard, who has expertly documented most of our projects with his excellent photos; his

photos comprise all figures but 3 and 6. Figures 3 and 6 are

my photos.
274 USDA Forest Service Proceedings RMRS-P-00. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-00. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Alison Stewart was Adjunct Professor, Life Science Department, Utah

Valley State College, Orem, UT; now residing at 320 Pomelo Drive #39,

Vista, CA 92083. Val Jo Anderson is Associate Professor, Botany and Range

Science Department, Brigham Young University, 493 WIDB, Provo, UT

84602. Stanley G. Kitchen is Botanist, Shrub Sciences Laboratory, Rocky

Mountain Research Station, USDA Forest Service, 735 North 500 East,

Provo, UT 84606.

Abstract—‘Immigrant’ forage kochia (Kochia prostrata) is an introduced semi-evergreen subshrub planted as a forage and reclamation plant on western cold deserts. Currently, seed demand is high;

however, effective use of forage kochia seed is complicated by its

short shelf-life. Delaying harvest until seeds are mature, typically

from mid-October to mid-November, should ensure that seeds have

good germination characteristics and will be better able to withstand storage. To preserve maximum dormancy and the delayed

and desynchronized germination rate found in fresh seeds, storage

with a low seed water content (2 to 6%) is critical; low temperature

(2 °C) storage is also important.

Forage kochia (Kochia prostrata) is the only introduced

subshrub species to have a variety released as a forage crop

in the United States (Horton and others 1994). It is native to

arid and semiarid regions of central Eurasia where it is

valuable for forage (Balyan 1972). On native sites, it is often

associated with crested wheatgrass (Agropyron cristatum)

and Eurasian sagebrush species (Artemisia spp.) and grows

on alkaline, stony, and sandy steppes, deserts, plains, and

mountains (McArthur and others 1974). Forage kochia was

first introduced to the United States from Russia during

the early 1960’s (Keller and Bleak 1974).

Many accessions of forage kochia have since been tested

as potential forage and reclamation plants for western

rangelands (Keller and Bleak 1974; Stevens and others 1985).

A named variety of forage kochia, ‘Immigrant’, was released

in 1985 for forage and erosion control on greasewoodshadscale (Sarcobatus vermiculatus-Atriplex confertifolia),

sagebrush-grass, and pinyon-juniper (Pinus spp.-Juniperus

spp.) rangelands of the Intermountain West (Stevens and

others 1985). Most commercially available seed is used in

reclamation, primarily for post-burn seedings on cheatgrassdominated rangelands (Horton and others 1994). Most

seedings currently use the Immigrant variety.

Due to its many uses and unusual range of adaptability,

demand for Immigrant forage kochia seeds is generally

high. Fresh forage kochia seeds should be planted in late

‘Immigrant’ Forage Kochia (Kochia prostrata)

Seed Germination as Affected by Storage

Conditions

Alison Stewart

Val Jo Anderson

Stanley G. Kitchen

fall or winter for best establishment (Haferkamp and others

1990; Monsen and Kitchen 1994). Many times, however,

buyers have planted year-old seeds and have experienced

low seeding success. Haferkamp and others (1990) had poor

stand establishment using year-old seeds and attributed it

to a loss in seed vigor or viability. Their data suggests that

seeds may have experienced changes in germination timing

mechanisms, such as dormancy and germination rate. Several factors may contribute to changes in these mechanisms.

One factor is the short shelf-life of seeds, especially under

uncontrolled storage conditions (Balyan 1972; Jorgensen

and Davis 1984; Keller and Bleak 1974). To maximize

seeding success and return of dollars spent, it is essential to

understand changes in germination characteristics over

time, seed storage requirements, and seed longevity (Stevens

and Jorgensen 1994).

An additional factor that may contribute to changes in

seed germination characteristics is early harvest. Forage

kochia seeds may not ripen until October or November

(Moghaddam 1978). Seed growers may be motivated to

harvest the seeds before snow falls. However, germination

controls may not be in place until later in seed development

(Waller and others 1983). Thus, when seeds are not fully

matured at harvest, they may not have the germination

timing mechanisms that would help them survive, especially after being stored.

Another important consideration is the environment in

which the seeds mature. Environmental conditions, including temperature, length of growing season, photoperiod,

light quality, soil nutrients, soil moisture, and position on

the plant may significantly affect germination characteristics (Baskin and Baskin 1973).

Afterripening ___________________

Two germination timing mechanisms that prevent germination at inappropriate times are dormancy and slow germination rates (Meyer and Monsen 1991). Afterripening, which

occurs over time, results in reduced dormancy and increased

germination rate (Meyer and others 1997). An afterripening

requirement in forage kochia seeds allows for emergence

when better conditions for seedling survival are encountered. Afterripening of forage kochia seeds, when harvested,

may occur in as little as a few weeks at room temperature or

over a longer period in cold storage (Balyan 1972; Kitchen

and Monsen, in press).

Dormancy is a delay mechanism in seeds that prevents

premature germination in conditions that might prove to
USDA Forest Service Proceedings RMRS-P-00. 1999 275

be unsuitable for establishment (Meyer and Monsen 1991).

Seed dormancy is associated with species from unpredictable environments (Meyer and Monsen 1992), which is the

case in arid rangelands where rainfall tends to be highly

variable. A large fraction of fresh Immigrant forage kochia

seeds remain dormant until late winter or early spring

(Balyan 1972). Preserving dormancy in forage kochia

seeds becomes especially important when seeds are stored

for use in years following initial growth season. If fully

afterripened seeds are seeded in the fall or winter, they may

germinate too quickly, leading to poor overall stand establishment (Kitchen and Monsen, in press).

Slow germination rate is also important for seeds of

species from unpredictable environments. Meyer and Monsen

(1991) found that for big sagebrush (Artemisia tridentata)

slow germination rate may have been almost as effective as

dormancy in preventing precocious emergence of seeds.

Overall, fresh forage kochia seeds have a delayed and

desynchronized germination rate, which should allow for

some portion of the seeds to germinate when good conditions

for seedling survival occur (Monsen and Kitchen 1994).

Forage kochia seeds that have afterripened have a more

rapid and synchronized germination rate (Haferkamp and

others 1990; Kitchen and Monsen, in press). This again may

be detrimental when planting year-old seeds in the fall or

winter, as they may germinate under adverse conditions.

Cold temperature (2 °C) germination tests are useful in

studying germination rate and synchronization because

they more closely resemble field conditions when seedling

emergence is likely to occur. Differences in germination rate

are also magnified at lower temperatures (McArthur and

others 1987; Meyer and Monsen 1991).

Objective ______________________

Our objective was to examine the effects of harvest date

(an index of seed maturity), maternal growth environment

(wildland or irrigated), and storage conditions (temperature, seed water content, and duration) on dormancy and

cold temperature germination rate of Immigrant forage

kochia seeds. These factors influence the seeding success of

Immigrant on western rangelands.

Methods _______________________

Seed Collection Sites (Growth

Environments)

Fruits (hereafter referred to as seeds) were collected

from two sites (Romo and Haferkamp 1987). The first was a

USDI Bureau of Land Management wildland site, located

approximately 11 km north of Dugway, Tooele County,

Utah. Soil is a deep, well-drained Timpie silt loam, and

annual precipitation is 13 to 20 cm. Several hundred

mature Immigrant forage kochia plants are present. The

second site was an irrigated field managed by Stevenson

Intermountain Seed Company near Manti, Sanpete County,

Utah, where certified Immigrant forage kochia seed is

grown commercially. The soil is a Sigurd gravely loam (Soil

Conservation Service 1981); the crop is irrigated as needed

to maximize production.

Seed Harvest

Seeds were harvested from both sites in fall 1996 on

October 4, October 18, November 1, and November 15.

Twenty plants were selected at each site to represent withinpopulation variation. Seeds were hand-stripped on each

collection date and air-dried for 3 to 10 days. Empty and

immature fruits, fruit fragments, leaves, and small stems

were removed using Seedburo Equipment Company’s K

(2 /64"), U (4 /64"), and A (12/64") Rounds.

Storage Treatments

A subsample (3-20 g) of each fresh seed lot was dried to 0%

moisture in a drying oven. This sublot was used as a

reference in calculating seed water content to obtain the

desired water contents for storage. The remaining fresh

seeds were then divided evenly into sublots to provide a

complete factorial arrangement of storage treatments [four

seed maturity levels (harvested on Oct. 4, Oct. 18, Nov. 1,

and Nov. 15) x two growth environments (wildland and

irrigated sites) x three storage temperatures (fresh seed

with no storage, cold storage at 2 °C, and warm storage at

25 °C) x three seed water contents during storage (fresh

seed with no storage, low seed water content at 2 to 6%, and

high seed water content at 12 to 16%) x four storage duration

periods (0, 4, 8, and 12 months)]. Each of these sublots was

weighed and stored in a plastic vial. Each group of vials was

placed in a sealed plastic bag and a cardboard box.

Germination Tests

Tests for dormancy and cold temperature germination

rate were performed on each seed lot, when fresh and after

treatments. Each test included four replications of 25

seeds from each seed lot. Seeds were placed in 100 x 15 mm

plastic petri dishes on two 1-mm thick blotters (Anchor

Paper) saturated with tap water. To retain moisture, petri

dishes were randomized, stacked, and placed in plastic bags.

To ensure even light treatment for all dishes, a blank dish

with two blotters was placed on the top of each stack.

Blotters were resaturated as needed during the germination

tests. Petri dishes were randomly arranged in a germination

chamber and rearranged after weekly counts. Germination

was defined as 5+ mm radicle emergence.

Dormancy Test—To determine dormancy of each seed

lot, seeds were incubated in a controlled environment

chamber in a 12 hour diurnal photoperiod at 10 and 20 °C.

Every 7 days, for a period of 4 weeks, the number of seeds in

each dish that had germinated were counted and removed.

After 28 days, firmness of ungerminated seeds in each dish

was determined using a cut test to examine the tissue of the

seeds (Association of Official Seed Analysts 1988). Dormant

seeds were defined as firm seeds that did not germinate

within 28 days.

Cold Temperature Germination Rate Test—To estimate cold temperature germination rate of each seed lot,

seeds were incubated at 2 °C for 16 weeks, during which time

germinated seeds were counted and removed weekly. Following the chilling period, seeds were incubated in a

germination chamber in 12 hour diurnal photoperiods at
276 USDA Forest Service Proceedings RMRS-P-00. 1999

10 and 20 °C for an additional week for a final germination

count. The results of this test confirmed the dormancy

analysis of firm seeds completed in the above test.

Statistical Analysis

Germination percentage (firm seed basis) was calculated

for each replication of the dormancy test. Germination rate

(days to 50% germination) was calculated for each replication of the cold temperature germination test. The germination percentages were arcsine transformed prior to

analysis to normalize the data. A factorial analysis of variance appropriate to the completely randomized experimental design was used to determine significance of treatments

and interactions (SAS 1998). Mean separation was completed using the Student-Newman-Keuls means comparison test.

Results and Discussion __________

Effects of seed maturity, growth environment, and storage conditions on dormancy and cold temperature germination rate of Immigrant forage kochia seeds were highly

significant (p <0.01). Fresh seed viability and treatment

effects on seed viability were also assessed for each seed lot.

Mean viability for fresh seeds from the first harvest was low

(17%). The dormancy and cold temperature germination

rate data from that harvest is suspect because it is based on

few viable seeds of questionable vigor. Viability of fresh

seeds from the last three harvests was high (88%); thus, in

all following results only data from the last three harvest

dates are included.

Dormancy

Means of percent germination (firm seed basis) for harvest

date x seed water content x storage temperature x storage

length are found in table 1. Differences in dormancy associated with storage temperature, seed water content, and

harvest date were highly significant (p <0.01). Fresh seeds

from the last three harvest dates were highly dormant

(12% germination). Low seed water content in storage,

especially when the seeds were stored at a cold temperature, allowed for the greatest preservation of dormancy (67%

germination over all storage periods). Low water content

when seeds were stored at a warm temperature yielded

seeds that were less dormant (79% germination overall).

Seeds stored with a high water content in the cold retained

little dormancy (90% germination overall). Seeds stored

with a high water content at a warm temperature were only

4% viable, so dormancy results were not reliable. None of the

storage conditions used preserved dormancy in forage kochia

seeds at the level observed in fresh seeds. Allen (1985) noted

that no successful method for avoiding afterripening of

forage kochia seeds had been developed; however, other

work suggests that at subzero storage temperatures, dormancy can be preserved (Kitchen, unpublished data).

Dormancy, as previously discussed, may be environmentally cued, and in this study, there were differences in

the dormancy patterns of seeds depending on growth

environment and seed maturity. This resulted in a significant interaction between site and harvest date for percent

germination (p <0.05). Seeds from the irrigated growth

environment and the wildland environment responded similarly to treatments, differing only in magnitude. The irrigated growth environment yielded less dormant seeds than

the wildland site over all harvest dates (67 and 55% germination, respectively). However, an irrigated environment

for commercially growing seeds is able to produce a much

greater volume of seeds, a benefit that greatly outweighs

possible effects on seed dormancy.

The interaction of seed maturity and length of storage was

highly significant for percent germination (p <0.01) (table 1).

Seeds from the first harvest responded differently to storage

than seeds from later harvests; however, as previously

Table 1—Means of percent germination (firm seed basis) for ‘Immigrant’ forage kochia seeds incubated

in a 12 hour diurnal photoperiod at 10 and 20 °C for 28 days. Seeds were collected from a

wildland site and an irrigated site in central Utah on four harvest dates in fall 1996 and tested for

dormancy when fresh and after storage treatments. Due to low viability (13%) of seed from the first

harvest, percent germination is shown only for seed from the last three harvests. High and low

seed water contents were 12 to 16%, and 2 to 6%, respectively. Cold temperature storage was

2 °C, and warm storage temperature was 25 °C. Numbers in parentheses are standard errors.

Storage length

Seed 4 months 8 months 12 months

Harvest water Fresh Storage temperature

 date content seed Cold Warm Cold Warm Cold Warm

- - - - - - - - - - - - - - - - Percent germination - - - - - - - - - - - - - - - - - -

Oct. 18 High 80 (5) 68 (16) 69 (5) 88 (6) 98 (2) 58 (18)

Low 49 (8) 65 (8) 36 (6) 53 (5) 96 (2) 98 (1)

10 (2)

Nov. 1 High 88 (4) — 86 (4) — 99 (1) —

Low 57 (6) 72 (7) 39 (6) 76 (5) 98 (1) 100 (0)

6 (1)

Nov. 15 High 92 (3) — 96 (2) 13 (13) 99 (1) —

Low 73 (5) 81 (6) 46 (4) 70 (7) 96 (1) 100 (0)

20 (3)
USDA Forest Service Proceedings RMRS-P-00. 1999 277

mentioned 83% of the seeds began as nonviable, so differences were viewed with caution. Seeds from the other three

harvests responded to storage in a similar pattern but

differed in magnitude, with seeds from the third and fourth

harvests retaining slightly more of their dormancy (55

and 60% germination, respectively) than seeds from the

second harvest (67% germination). Seeds that mature and

disperse early may be more dormant than later developing

seeds. Germination characteristics are driven by the genetics of each plant but are also influenced by the maternal

environment. Late-ripening seeds may mature under a

different environment than early-ripening seeds. Thus, seeds

retained on the plant that were collected on the fourth

harvest date may have experienced changes that caused

more of them to germinate. Meyer (unpublished data) has

results that indicate this happening with rubber rabbitbrush (Chrysothamnus nauseosus), another fall-ripening

species. The differing environmental conditions each subset

of seeds experienced may explain the differences in their

levels of dormancy or rate of afterripening.

A fivefold increase (from 12 to 60%) in germinating seeds

from the last three harvests occurred after 4 months in

storage, which was the greatest loss of dormancy in any of

the storage periods (table 1). From 4 to 8 months of storage,

no major changes in dormancy occurred; however, by 12

months storage a majority of dormancy had been lost (79%

germination overall), as the seeds were mostly afterripened

by then. Afterripened forage kochia seeds, used for seeding

in late fall or early winter, may experience premature

germination resulting in poor stand establishment. Thus,

any measure, e.g., storage with low seed water content in a

cold temperature, which can delay afterripening may improve seeding success of Immigrant forage kochia.

Cold Temperature Germination Rate

Means of cold temperature germination rates (days to

50% germination) for harvest date x seed water content x

storage temperature x storage length are found in table 2. An

interaction between level of seed water content and length of

storage was highly significant for cold temperature germination rate (p <0.01). All seeds germinated more rapidly

over time in storage as they afterripened; however, seeds

stored with a low water content germinated more slowly

than seeds stored with a high water content (46 and 12 days

to 50% germination overall, respectively) (fig. 1). Low seed

water content in storage resulted in a steady increase in

germination rate (decrease in days to 50% germination) over

time, which may be the result of steady afterripening of the

seeds. However, high seed water content in storage caused

a considerable increase in germination rate after just the

first 4 months of storage, suggesting afterripening was

accelerated with a high seed water content. Storage with a

low seed water content delayed afterripening, which may

again benefit seeding success with stored forage kochia

seeds. Because germination rates for all seeds were greatly

shortened over time in storage, this reaffirms that the

storage methods used were not highly effective in retarding

afterripening of Immigrant forage kochia seeds. However,

seeds stored for more than 3 years at 2 °C have been able to

delay germination sufficiently for successful stand establishment (Kitchen and Monsen, in press).

Differences in cold temperature germination rates resulted in a highly significant interaction between storage

temperature and levels of seed water content (p <0.01).

Fresh seeds overall germinated slowly, taking 110 days to

reach 50% germination (fig. 2). Low seed water content and

Table 2—Means of germination rate (days to 50% germination) for Immigrant forage kochia seeds

incubated at 2 °C for 16 weeks, followed by 1 week incubated in 12 hour diurnal photoperiods at

10 and 20 °C. Seeds were collected from a wildland site and an irrigated site in central Utah on

four harvest dates in fall 1996 and tested for cold temperature germination rate when fresh and

after storage treatments. Germination rates are shown only for seeds from the last three harvests,

due to low viability (13%) of seed from the first harvest. High and low seed water contents were

12 to 16%, and 2 to 6%, respectively. Cold temperature storage was 2 °C, and warm storage

temperature was 25 °C. Numbers in parentheses are standard errors.

Storage length

Seed 4 months 8 months 12 months

Harvest water Fresh Storage temperature

 date content seed Cold Warm Cold Warm Cold Warm

- - - - - - - - - - - - Days to 50% germination at 2 °C - - - - - - - - - - - - -

Oct. 18 High 40 (3) 39 (10) 18 (1) 15 (6) 13 (5) 6 (6)

Low 112 (2) 72 (3) 50 (2) 41 (3) 21 (1) 12 (4)

116 (1)

Nov. 1 High 22 (2) — 10 (3) — 12 (3) —

Low 95 (3) 46 (3) 47 (4) 23 (2) 19 (2) —

115 (1)

Nov. 15 High 24 (3) — 4 (3) — 8 (3) —

Low 85 (2) 60 (3) 63 (4) 35 (2) 42 (4) 11 (4)

98 (3)
278 USDA Forest Service Proceedings RMRS-P-00. 1999

cold temperature storage treatments maintained the slowest germination rate (59 days to 50% germination) compared to other storage treatments. Low seed water content

and warm temperature storage retained the next slowest

germination rate (32 days to 50% germination). High seed

water content for both cold and warm temperature storage

yielded much more rapid germination rates (17 and 3 days

to 50% germination, respectively). Thus, storage with a low

seed water content, along with storage at a cold temperature, will benefit in maintaining a slower, desynchronized

germination rate in stored forage kochia seeds.

Seeds from the two growth environments responded differently in germination rates as seeds matured (p <0.01)

(table 2). The wildland site yielded seeds with a slower

germination rate than the irrigated site (37 and 33 days to

50% germination overall, respectively). This difference, again,

is outweighed by the high volume of seeds generated in a

commercial seed production setting. Also, the germination

rate pattern of seeds from the last three harvests was again

similar and only differed slightly in magnitude. Once more,

differences in afterripening rate of seeds may have resulted

from the differing environmental conditions seeds from

each harvest experienced.

Conclusions____________________

Forage kochia seeds should not be stored in the same

manner as most range plant seeds. Some seed companies

store Immigrant seeds in a breathable polypropylene bag on

a shelf in a warehouse where annual temperatures may fluctuate from 7 to 38 °C. Forage kochia seeds can be expected to

afterripen quickly if stored in that manner, even if only for

a short time. To preserve maximum dormancy and to maintain the most delayed and desynchronized germination rate,

storage with a low seed water content (2 to 6%) is critical;

storing seeds at a low temperature (2 °C) is the next priority.

Aside from ensuring seed viability, seed maturity had little

effect on the rate of afterripening. As the use of forage kochia

increases on western rangelands, these recommendations

will aid in obtaining the best possible seeding success when

using stored Immigrant forage kochia seeds.

References _____________________

Allen, P. S. 1985. Studies on seed performance of five arid landscape

species. Provo, UT: Brigham Young University. 111 p. Thesis.

Association of Official Seed Analysts. 1988. Rules for testing seeds.

Lansing, MI: Stone Printing Company. 6(2): 1-36.

Balyan, G. A. 1972. Prostrate summer cypress and its culture in

Kirghizia. Frunze, USSR: Isdatel’stovo “Kyrgyzstan” (Translated from Russian; U.S. Department of Commerce, TT77-59206,

1979.). 296 p.

Baskin, J. M.; Baskin, C. C. 1973. Plant population differences in

dormancy and germination characteristics of seeds: heredity or

environment?. American Midland Naturalist. 90: 493-498.

Haferkamp, M. R.; Ganskopp, D. C.; Marietta, K. L.; Knapp, B. W.

1990. Environmental influences on germination of utricles and

seedling establishment of ‘Immigrant’ forage kochia. Journal of

Range Management. 43: 518-522.

Horton, H. H.; Monsen, S. B.; Newhall, R. L.; Stevens, R. 1994.

Forage kochia holds ground against cheatgrass, erosion. Utah

Science. 55: 10-11.

Jorgensen, K. R.; Davis, J. N. 1984. A technique for retaining seed

viability in Kochia prostrata (L.) Schrad. In: Tiedemann, A. R.;

McArthur, E. D.; Stutz, H. C.; Stevens, R.; Johnson, K. L., comps.

Figure 2—Cold temperature (2 °C) germination rate

(days to 50% germination) of ‘Immigrant’ forage kochia

seeds with three seed water content levels (fresh seeds

with no storage, high at 12 to 16%, and low at 2 to 6%) and

three storage temperatures (fresh seeds with no storage,

cold at 2 °C, and warm at 25 °C). This two-way interaction

was significant at p <0.01. For means of fresh seeds, n =

32, and for all other means, n = 96.

Figure 1—Cold temperature (2 °C) germination rate

(days to 50% germination) of ‘Immigrant’ forage kochia

seeds with two seed water content levels (high at 12 to

16% and low at 2 to 6%) shown over length of storage

(0, 4, 8, and 12 months). This two-way interaction was

significant at p <0.01. For means at 0 months of

storage, n = 32, and for all other means, n = 64.
USDA Forest Service Proceedings RMRS-P-00. 1999 279

Proceedings: symposium on the biology of Atriplex and related

chenopods; 1983 May 2-6; Provo, UT. Gen. Tech. Rep. INT-172.

Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Forest and Range Experiment Station: 166-167.

Keller,W.; Bleak, A. T. 1974. Kochia prostrata: a shrub for western

ranges?. Utah Science. 35: 24-25.

Kitchen, S. G. Unpublished data on file at: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station,

Shrub Sciences Laboratory, Provo, UT.

Kitchen, S. G.; Monsen, S. B. [In press]. Kochia Roth. In: Seeds of

woody plants of the United States. U.S. Department of Agriculture, Forest Service.

McArthur, E. D.; Guinta, B. C.; Plummer, A. P. 1974. Shrubs for

restoration of depleted ranges and disturbed areas. Utah Science.

35: 28-33.

McArthur, E. D.; Meyer, S. E.; Weber, D. J. 1987. Germination rate

at low temperature: rubber rabbitbrush population differences.

Journal of Range Management. 40: 530-533.

Meyer, S. E. Unpublished data on file at: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station,

Shrub Sciences Laboratory, Provo, UT.

Meyer, S. E.; Allen, P. S.; Beckstead, J. 1997. Seed germination

regulation in Bromus tectorum (Poaceae) and its ecological significance. OIKOS. 78: 475-485.

Meyer, S. E.; Monsen, S. B. 1991. Habitat-correlated variation in

mountain big sagebrush (Artemisia tridentata ssp. vaseyana)

seed germination patterns. Ecology. 72: 739-742.

Meyer, S. E.; Monsen, S. B. 1992. Big sagebrush germination patterns: subspecies and population differences. Journal of Range

Management. 45: 87-93.

Moghaddam, M. R. 1978. Kochia prostrata—a plant material for

range improvement in arid and semiarid regions. Rangeman’s

Journal. 5: 153-154.

Monsen, S. B.; Kitchen, S. G. 1994. Annual report—summary report

of progress related to Interagency Agreement No. ID910 between

USDI, Idaho Bureau of Land Management and USDA, Forest

Service, Intermountain Research Station. Provo, UT: USDA,

Forest Service, Intermountain Research Station, Shrub Sciences

Laboratory. 45 p.

Romo, J. T.; Haferkamp, M. R. 1987. Forage kochia germination

response to temperature, water stress, and specific ions. Agronomy

Journal. 79: 27-30.

SAS.1998. SAS user’s guide. SAS Institute. Cary, NC.

Soil Conservation Service. 1981. Soil survey of Sanpete Valley Area,

Utah. Washington, DC: U.S. Department of Agriculture, Soil

Conservation Service. 179 p.

Stevens, R.; Jorgensen, K. R. 1994. Rangeland species germination through 25 and up to 40 years of warehouse storage. In:

Monsen, S. B.; Kitchen, S. G., comps. Proceedings: ecology and

management of annual rangelands; 1992 May 18-21; Boise, ID.

Gen. Tech. Rep. INT-GTR-313. Odgen, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station:

257-265.

Stevens R.; Jorgensen, K. R.; McArthur, E. D.; Davis, J. N. 1985.

‘Immigrant’ forage kochia. Rangelands. 7: 22-23.

Waller, S. S.; Britton, C. M.; Schmidt, D. K.; Stubbendieck, J.;

Sneva, F. A. 1983. Germination characteristics of two varieties

of Kochia prostrata (L.) Schrad. Journal of Range Management.

36: 242-245.
280 USDA Forest Service Proceedings RMRS-P-11. 1999

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Chad S. Horman is a Restoration Ecologist, Environmental Science and

Research Foundation, Inc., P.O. Box 51838, Idaho Falls, ID 83405-1838. Val

Jo Anderson is an Associate Professor of Range Science, Department of

Botany and Range Science, Brigham Young University, 493 WIDB, P.O. Box

25228, Provo, UT 84602-5228.

Effects of Utah Juniper (Juniperus

osteosperma [Torr.] Little) Litter Leachate

on Germination of Several Range Plant

Species

Chad S. Horman

Val Jo Anderson

Abstract—A growth chamber study was conducted to determine

what allelopathic effects a leachate made from Utah juniper

(Juniperus osteosperma) litter has on seed germination and

germination rate of eight potential understory species. Three

water treatments (distilled water, 1%, and 10% litter leachates)

were tested. Leachates had no negative effect on germination of any

of the eight species. Bluebunch wheatgrass (Pseudoroegneria spicata) and antelope bitterbrush (Purshia tridentata) seeds treated

with leachates had significantly (P <0.05) higher germination

than the control. Leachates initially increased the germination rate

of mountain big sagebrush (Artemisia tridentata ssp. vaseyana),

but later had no effect.

The pinyon (Pinus spp.)-juniper (Juniperus spp.) woodland

is an important ecosystem of the Western United States,

comprising approximately 25 million hectares throughout

Nevada, Utah, Colorado, New Mexico, and Arizona (Hurst

1987). In pre-settlement days, juniper was most abundant

in the southwestern United States, but distinct populations

could be found on rocky mid-elevation foothills of the Great

Basin (Welch and others 1987). Since the mid-1800’s, juniper has slowly encroached into the valleys of the Great

Basin. As juniper has become the dominant species in these

communities, elements of both the biotic and abiotic environments have been modified (Tausch and others 1981).

This has been a serious problem for land managers; when

these trees dominate a site, the herbaceous understory is

severely reduced (Johnsen 1962; Christensen and Johnson

1964; Jameson 1967; Barney and Frischknecht 1974; Tausch

and Tueller 1977; Jeppesen 1978; Young and Evans 1981;

Schott and Pieper 1985). Increased runoff and soil erosion

has been reported as a result of this community shift

(Farmer 1995). Hypotheses to explain how junipers are able

to dominate a site include: (1) increased canopy cover that

creates precipitation interception and shading (Johnsen

1962; Skau 1964; Jameson 1967; Anderson and others 1969;

Gifford 1970; Schott and Pieper 1985; Pieper 1990), (2) deep

litter accumulation (Johnsen 1962; Jameson 1966; Everett

and Koniak 1981; Schott and Pieper 1985), (3) allelopathy

(Jameson 1961; Johnsen 1962; Lavin and others 1968;

Jameson 1970a; Peterson 1972), (4) changes in the soil

nutrient composition (Doescher and others 1987; Klopatek

1987; Tiedemann 1987), and (5) competition for soil moisture (Johnsen 1962; Jameson 1970b; Jeppesen 1978; Young

and Evans 1981; Miller and others 1987; Breshears and

others 1997).

It has been reported that juniper litter may be allelopathic (Jameson 1961; Lavin and others 1968; Jameson

1970a; Peterson 1972). Rice (1984) defined allelopathy “...as

any direct or indirect harmful effect of one plant on another

through production of chemical compounds that escape into

the environment.”

The effects of these compounds may be primary or secondary. Primary effects occur at the cellular level and

include such things as: (1) interference with cell elongation,

(2) interference with membrane function, (3) interference

with hormone interaction, or (4) changes in the ultrastructure of the root tip (Lovett and Ryuntyu 1992).

Secondary effects are a result of primary effects and

are the ones more readily seen in the field. These include:

(1) delayed or inhibited germination, (2) delayed or inhibited

stimulation of root or shoot growth, (3) reduced germination rate, (4) reduced biomass or yield, (5) reduced vigor, or

(6) reduced survivability (Winter 1961).

With respect to junipers, the literature contains conflicting evidence as to whether allelopathy really occurs.

Jameson (1961) showed that extracts from one seed juniper

(J. monsperma), Utah juniper (J. osteosperma), and alligator juniper (J. deppeana) inhibited growth of wheat (Triticum spp.) radicles. Jameson (1970a) later identified two

compounds from Utah juniper that were considered possible

growth inhibitors. Peterson (1972) found that Rocky Mountain juniper (J. scopulorum) produced both water soluble

and volatile inhibitors that reduced germination of several

herbaceous species. Lavin and others (1968) reported that

allelopathy in Utah juniper was species specific. Johnsen

(1962) found one seed juniper extracts did not significantly

reduce blue grama (Bouteloua gracilis) germination.

Much of the work done on allelopathy has focused on

juniper species other than Utah juniper and little has been

done in the foothill environment of central Utah. Thus, this

study was conducted to determine what allelopathic effects

a leachate made from Utah juniper litter would have on

total seed germination and germination rate of eight potential understory species.
USDA Forest Service Proceedings RMRS-P-11. 1999 281

Methodology ___________________

The experiment tested the effects of 1 and 10% leachates

made from Utah juniper litter leachate on total germination and germination rate of eight potential understory

species: bluebunch wheatgrass (Pseudoroegnaria spicata

[Pursh] Love ‘Secar’), bottlebrush squirreltail (Elymus

elymoides [Raf.] Swezey), cheatgrass (Bromus tectorum L.),

orchardgrass (Dactylis glomerata L.’Paiute’), Lewis flax

(Linum lewisii Pursh ‘Appar’), small burnet (Sanguisorba

minor Scop. ‘Delar’), antelope bitterbrush (Purshia tridentata [Pursh] DC.), and mountain big sagebrush (Artemisia

tridentata spp. vaseyana [Rydb.] J. Boivin).

The leachate was made from litter collected beneath Utah

juniper trees in the Tie Fork drainage of Spanish Fork

Canyon, Utah County, Utah. The litter was sifted through

#20 hardware mesh to separate soil from litter.

A 1% leachate solution was prepared by soaking 1 g of

litter in 100 ml of distilled water for 24 hours at 20 °C

(Jobidon 1986). The leachate was then poured through a #60

mesh filter. A 10% leachate was made in the same fashion

except that 10 g of litter per 100 ml of water was used.

The experiment was a completely randomized design with

three treatments: distilled water (control), 1%, and 10%

leachate, replicated four times. Each grass sample contained 50 seeds and each forb or shrub sample contained

25 seeds. In each petri dish, the seeds were placed on two

1-mm thick blotter pads saturated with one of the treatment solutions. Due to their large diameter, small burnet

and antelope bitterbrush seeds were placed between blotter

pads to insure adequate imbibition. The dishes were then

double-sacked in plastic bags. In order to have constant

humidity, a petri dish with two saturated blotter pads was

placed at the bottom and top of each stack in the bags. The

dishes were then placed in cold storage (1 °C) for 8 weeks

to simulate overwintering that normally occurs in the field.

Following the cold storage, the dishes were moved to a

growth chamber with a 20/15 °C temperature regime consisting of 12 hours each. Number of seed germinated were

recorded during the cold treatment and for 21 days following

placement in the growth chamber or until all seeds had

germinated, whichever came first. Germination was defined

as 1 mm of radicle emergence.

Percent germination data were arcsine transformed prior

to analysis. Analysis of variance (ANOVA) was performed

using Minitab (1995) statistical package and a Fisher’s

protected LSD was used for mean separation (Ott 1993).

Differences were deemed significant at P <0.05 unless otherwise noted.

Results ________________________

The results of the two leachate treatments were not

significantly different and were therefore pooled. Leachate

treatments had no negative effects on germination of any

of the eight species (table 1). Germination of bluebunch

wheatgrass and antelope bitterbrush seeds treated with

leachate was significantly higher, 3 and 7%, respectively,

than the control treatment. Mountain big sagebrush was

the only species whose germination rate was affected by

the leachate treatment (table 1). Seeds watered with leachate

reached 25% germination 6 days faster than did those

watered with distilled water. However, by the time 50% of

the mountain big sagebrush seeds had germinated, there

was no difference in germination rate between control and

treated seeds (table 1).

Discussion _____________________

This study indicated leachate from Utah juniper litter

had no allelopathic affect on seed germination. Surprisingly,

the leachate was found to cause a slight, but significant,

increase in percent germination of bluebunch wheatgrass

and antelope bitterbrush over the control. Lavin and others

(1968) reported one seed juniper extract caused a slight

increase in four-wing saltbush (Atriplex canescens) germination. With respect to germination rate, Utah juniper

leachate caused a decrease in the number of days for mountain big sagebrush to reach 25%, but then had no effect by

the time 50% emergence had occurred.

Allelopathy has been reported to occur in some juniper

species. Jameson (1961) reported a 5% water extract made

from fresh foliage of Utah juniper, alligator juniper, and one

seed juniper reduced wheat radicle germination by 85, 83,

and 79%, respectively. Lavin and others (1968) found Utah

juniper leaf and stem extracts decreased germination of

crested wheatgrass (Agropyron cristatum), blue grama, and

side oats grama (B. curtipendula). They reported no effect on

Luna pubescent wheatgrass (Elytrigiaintermedia) and weeping lovegrass (Eragrostis curvula). Peterson (1972) reported foliage extracts of Rocky Mountain juniper negatively affected germination of some herbaceous plants.

Johnsen (1962) reported leachate made from old and fresh

Table 1—Effects of leachate made from Utah juniper litter on seed germination and germination rate.

Germination (%) # of Days to 25% germination # of Days to 50% germination

Species Control Leachate Control Leachate Control Leachate

Bluebunch wheatgrass 91.3 a* 94.6 b 57.0 a 57.0 a 57.0 a 57.0 a

Cheatgrass 84.6 a 85.8 a 41.0 a 42.7 a 48.0 a 46.2 a

Orchardgrass 56.4 a 59.0 a 60.5 a 58.9 a 72.5 a 68.0 a

Bottlebrush squirreltail 69.6 a 81.2 a 56.7 a 55.5 a 57.0 a 57.0 a

Lewis flax 82.2 a 74.5 a 57.0 a 57.0 a 57.0 a 57.6 a

Small burnet 95.3 a 96.4 a 57.0 a 57.0 a 57.0 a 57.1 a

Mountain big sagebrush 99.0 a 98.1 a 57.5 a 51.5 b 55.0 a 54.1 a

Antelope bitterbrush 88.9 a 95.7 b 57.0 a 57.0 a 57.0 a 57.0 a

*Values in rows followed by a different letter were significantly different at P <0.05.
282 USDA Forest Service Proceedings RMRS-P-11. 1999

litter and fresh foliage of one seed juniper had no effect on

blue grama germination.

Differences in the results of this study and those previously reported may be due to methodology. The majority of

studies have been conducted by making the leachate

from fresh foliage. The negative effects observed in those

studies may have been due to allelopathic compounds that

are quickly degraded and lost once the foliage begins to

decompose. Jameson (1970a) identified two potentially allelopathic compounds in Utah juniper foliage and litter that

behaved in just such a manner. The first compound, although allelopathic, degraded quickly enough that it never

reached toxic concentration. The second compound had a

slower decomposition rate and could accumulate to toxic

levels when the right conditions occurred. This same principle may apply to other compounds in Utah juniper litter.

When extracts are made and tested from fresh foliage, they

may contain harmful compounds that decompose or volatilize quickly and never reach toxic levels in a natural setting.

This may explain why no allelopathic effects were observed

in the present study when decomposing leaf litter was used.

Conclusions____________________

In this study, leachate made from Utah juniper litter had

no negative effect on seed germination on any of eight

species tested. The leachate significantly increased germination of bluebunch wheatgrass and antelope bitterbrush.

Germination rates were largely unaffected by the leachate.

Mountain big sagebrush did show an initial increase in

germination rate, but, by the time 50% of the seeds had

germinated, no difference was found between leachate and

control treatments. These findings indicated, with respect to

seed germination, allelopathy of Utah juniper litter is not a

major force in reducing understory vegetation.

References _____________________

Anderson, R. C.; Loucks, O. L.; Swain, A. M. 1969. Herbaceous

response to canopy cover, light intensity, and throughfall precipitation in coniferous forests. Ecology. 50(2): 255-263.

Barney, M. A.; Frischknecht, N. C. 1974. Vegetation changes following fire in the pinyon-juniper type of west-central Utah.

Journal of Range Management. 27(2): 91-96.

Breshears, D. D.; Myers, O. B.; Johnson, S. R.; Meyer, C. W.;

Martens, S. N. 1997. Differential use of spatially heterogeneous

soil moisture by two semiarid woody species: Pinus edulis and

Juniperus monosperma. Journal of Ecology. 85: 289-299.

Christensen, E. M.; Johnson, H. B. 1964. Pre-settlement vegetation

and vegetational changes in three valleys in central Utah. Brigham

Young University Science Bulletin. 4(4): 1-16.

Doescher, P. S.; Eddleman, L. E.; Vaitkus, M. R. 1987. Evaluation

of soil nutrients, pH, and organic matter in rangelands dominated by western juniper. Northwest Science. 61(2): 97-102.

Everett, R. L.; Koniak, S. 1981. Understory vegetation in fully

stocked pinyon-juniper stands. Great Basin Naturalist. 41(4):

467-475.

Farmer, M. E. 1995. The effect of anchor chaining pinyon-juniper

woodland on watershed values and big game animals in central

Utah. M. S. Thesis Brigham Young University, Provo, UT. 48 p.

Gifford, G. F. 1970. Some water movement patterns over and

through pinyon-juniper litter. Journal of Range Management.

23: 365-366.

Hurst, W. D. 1987. Management strategics within the pinyon-juniper

ecosystem. In: Everett, R. L., ed. Proceedings: pinyon-juniper

conference; Jan. 13-16, 1986; Reno, NV. USDA Forest Service,

Intermountain Research Station. Gen. Tech. Rep. INT-215:

187-194.

Jameson, D. A. 1961. Growth inhibitors in native plants of northern Arizona. Fort Collins, CO. USDA Forest Service, Rocky

Montan Forest and Range Experiment Station. 2 p.

Jameson, D. A. 1966. Pinyon-juniper litter reduces growth of blue

grama. Journal of Range Management. 19: 214-217.

Jameson, D. A. 1967. The relationship of tree overstory and herbaceous understory vegetation. Journal of Range Management. 20:

247-249.

Jameson, D. A. 1970a. Degradation and accumulation of inhibitory substances from Juniperus osteosperma (Torr.) Little.

Plant and Soil. 33: 213-224.

Jameson, D. A. 1970b. Juniper root competition reduces basal area

of blue grama. Journal of Range Management. 23: 217-218.

Jeppesen, D. J. 1978. Competitive moisture consumption by western juniper (Juniperus occidentalis). In: Proceedings of the

western juniper ecology and management workshop. USDA Forest Service. Gen. Tech. Rep. PNW-74: 83-89.

Jobidon, R. 1986. Allelopathic potential of coniferous species to oldfield in eastern Quebec. Forest Science. 32(1): 113-118.

Johnsen, T. N., Jr. 1962. One-seed juniper invasion of northern

Arizona grasslands. Ecological Monographs. 32(3): 187-207.

Klopatek, J. M. 1987. Nutrient patterns and succession in pinyonjuniper ecosystems of northern Arizona. In: Everett, R. L., ed.

Proceedings: pinyon-juniper conference; Jan. 13-16, 1986;

Reno, NV. USDA Forest Service, Intermountain Research Station. Gen. Tech. Rep. INT-215: 391-396.

Lavin, F.; Jameson, D. A.; Gomm, F. B. 1968. Juniper extract and

deficient aeration effects on germination of six range species.

Journal of Range Management. 21: 262-263.

Lovett, J.; Ryuntyu, M. 1992. Allelopathy: broadening the context.

In: Rizvi, S. J. H.; Rizvi, V., ed. Allelopathy: basic and applied

aspects. London: Chapman and Hall. 12 p.

Miller, R. F.; Angell, R. F.; Eddleman, L. E. 1987. Water use by western

juniper. In: Everett, R. L., ed. Proceedings: pinyon-juniper conference; Jan. 13-16, 1986; Reno, NV. USDA Forest Service, Intermountain Research Station. Gen. Tech. Rep. INT-215: 418-422.

Minitab 1995. Minitab Inc. State College, PA.

Ott, R. L. 1993. An introduction to statistical methods and data

analysis. Belmont, CA: Wadsworth Publishing Co: 813-814.

Peterson, G. B. 1972. Determination of the presence, location and

allelopathic effects of substances produced by Juniperus

scopulorum Sarg. Dissertation Abstracts B. 32: 3811-3812.

Pieper, R. D. 1990. Overstory-understory relations in pinyon-juniper woodlands in New Mexico. Journal of Range Management.

43(5): 413-415.

Rice, E. L. 1984. Allelopathy. Orlando, FL: Academic Press, Inc. 1:

293-306.

Schott, M. R.; Pieper, R. D. 1985. Influence of canopy characteristics

of one-seed juniper on understory grasses. Journal of Range

Management. 38(4): 328-331.

Skau, C. M. 1964. Interception, throughfall, and stemflow in Utah

and alligator juniper cover types in northern Arizona. Forest

Science. 10(3): 283-287.

Tausch, R. J.; Tueller, P. T. 1977. Plant succession following chaining of pinyon-juniper woodlands in eastern Nevada. Journal of

Range Management. 30(1): 44-49.

Tausch, R. J.; West, N. E.; Nabi, A. A. 1981. Tree age and dominance

patterns in Great Basin pinyon-juniper woodlands. Journal of

Range Management. 34(4): 259-264.

Tiedemann, A. R. 1987. Nutrient accumulations in pinyon-juniper

ecosystems—managing for future site productivity. In: Everett,

R. L., ed. Proceedings: pinyon-juniper conference; Jan. 13-16,

1986; Reno, NV. USDA Forest Service, Intermountain Research

Station. Gen. Tech. Rep. INT-215: 352-359.

Welch, S. L.; Atwood, N. D.; Goodrich, S.; Higgins, L. C. 1987. A

Utah flora. Great Basin Naturalist Memoirs. 9: 27.

Winter, A. G. 1961. New physiological and biological aspects in the

interrelation between higher plants. Society of Experimental

Biology (Cambridge) Symposium. 15: 229-244.

Young, J. A.; Evans, R. A. 1981. Demography and fire history of a

western juniper stand. Journal of Range Management. 34(6):

501-506.
USDA Forest Service Proceedings RMRS-P-11. 1999 283

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

Paul R. Jones, Graduate Research Assistant, and Marcia Wicklow-Howard,

Professor, are from Boise State University, Biology Department, Boise, ID

83706. Mike Pellent is Rangeland Ecologist, U. S. Department of the Interior,

Bureau of Land Management, Idaho State Office, Boise, ID 83709.

Restoration of the Moss (Musci) Component

of the Microbiotic Crust to the Western

Snake River Plain, Idaho: Inoculation of

Fragmented Arid-Land Moss Tissue to Three

Rangeland Soil Surface Treatments

Paul R. Jones

Marcia Wicklow-Howard

Mike Pellant

Abstract—Microbiotic soil crusts occupy an invaluable position in

arid and semiarid ecosystems. They are displaced by the conversion

of native vegetation to annual grasslands. Moss inoculated to

various treatments or disturbances could be an essential step in

restoration of microbiotic crusts. Field experiments were conducted

to determine if the fragmented tissue of three moss species would

exhibit vegetative growth after inoculation to three soil surface

treatments. Significant treatment differences were noted in litter

and annual forb frequency. Moss growth frequency, although low,

exhibited interesting patterns.

Microbiotic soil crusts are assemblages of cyanobacteria,

bacteria, eukaryotic algae, fungi, lichens, and mosses (St.

Clair and Johansen 1993). They are found throughout the

Western United States and are best represented in the arid

steppes of the Colorado Plateau, Great Basin, and Columbia

Plateau (Johansen 1993). Additionally, they are found in

other arid regions of the world such as Australia (Eldridge

and Greene 1994; Eldridge and Tozer 1996; Eldridge 1996)

and the Mediterranean (Martínez-Sánchez and others 1994).

The organisms that comprise microbiotic crusts of the

Western United States vary regionally. For example, on

sandy soils of Utah canyonlands the cyanobacterium Microcoleus vaginatus (Vauch.) Gom. is the predominate organism (Belnap and Gardner 1993). Lichens are predominant in

the Great Basin (St. Clair and others 1993) and are well

represented in microbiotic crusts of southern Idaho

(Kaltenecker and Wicklow-Howard 1994; Rosentreter 1986).

Bryophytes, such as mosses, are also found in microbiotic

crusts (Kaltenecker and Wicklow-Howard 1994; Rosentreter

1986) and tend to dominate in areas that receive a majority

of the annual precipitation during a cool-season (Rincon and

Grime 1989).

Research indicates that microbiotic crusts serve several

roles important to vascular plant establishment in arid and

semiarid rangeland ecosystems, including stabilization of

the soil surface (Williams, and others 1995a,b; Brotherson

and Rushforth 1983) and influence of soil moisture

(Brotherson and Rushforth 1983) and nutrient relationships

(Belnap and Harper 1994; Beymer and Klopatek 1991;

Evans and Ehleringer 1993). St. Clair and others (1984)

observed a trend of higher seedling establishment among

seeded graminoids (Agropyronelongatum = Elymus elongatus

[Host] Runem., E. cinereus Scribn. and Merr., and E.junceus

Fisch.) on soils with intact microbiotic crust. Common constituents of the microbiotic crust, short mosses, form tight

mats (Kaltnecker 1997) that may provide a physical barrier

to cheatgrass (Bromus tectorum L.) establishment (Jaques

1984; Larsen 1995).

Cheatgrass is a cool-weather, exotic annual grass that has

successfully invaded the shrub steppe of Idaho. It produces

a large amount of litter and when it is widespread provides

a contiguous source of fuel prone to violent wildfires that

destroy existing native vegetation and associated microbiotic crust (Peters and Bunting 1994; Whisenant 1995).

Considering the scope of the invasion of cheatgrass and

exotic annual plant species large expanses of the shrub

steppe habitat is threatened with extirpation. Destruction of

the native vegetation to any degree results in an opening for

invasive annual flora. Small patches and vast expanses of

the complex native ecosystem of the western Snake River

Plain (SRP) are converted to simplistic annual grasslands.

Annual grasslands lack native vertebrates and invertebrates typical of the native ecosystem. Additionally, the

microbiota (microbiotic crust and soil organisms) involved in

the operation of the system (energy flow, water cycling, and

nutrient balance) are lost (Billings 1994).

The main goal of this research is to determine if it is

possible to restore the moss component of microbiotic crust

to a site devoid of perennial mosses and composed of exotic

annual grasses. In order to do this the fragmented gametophytic thalli of three arid-land moss species (Bryum

argenteum Hedw., Ceratodon purpureus [Hedw.] Brid., and

Tortula ruralis [Hedw.] Gaertn., Meyer and Scherb.) were

inoculated to three soil surface treatment plots.
284 USDA Forest Service Proceedings RMRS-P-11. 1999

Methods _______________________

Treatment Plot Location

Three treatment plot sites are positioned on an approximate north-south line across the western SRP. This area is

located in what is characterized as the sagebrush steppe

vegetation zone of the northern intermountain region of the

Western United States (West 1988). Site number one is

located at Mountain Home Air Force Base (MHAFB). Treatment site number two is located adjacent to Interstate 84

about 15 air km northwest of Mountain Home, Idaho. This

site was once used to demonstrate rangeland rehabilitation

machinery and technique (M. Pellant, personal conversation). The third site is located on a portion of the western SRP

south of the Snake River. This site is east of the Bruneau

River, within the Exclusive Use Area (EUA) of Saylor Creek

Air Force Range (SCR), about 22 air km southeast of Bruneau,

Idaho (fig. 1).

Statistical Design and Treatments

The experiment utilized a split-plot design with site location as a blocking factor (fig. 1). The main plot factor was soil

surface treatment and the subplot factor was moss fragment

inoculation. Soil surface treatments included burning, herbicide (Oust®) application, and tilling. These treatments

were chosen because of their similarity to conditions likely

associated with large-scale rangeland rehabilitation efforts

or rangeland disturbance. Treatments were performed on a

schedule consistent with natural conditions. Herbicide application took place before the final spring of 1997 (table 1),

allowing the pre-emergent herbicide to contact seeds and

florets at the surface. Tilling took place before the soil had

completely dried and buried some of the existing litter and

living plants. Back burning took place when cheatgrass had

reached maturity in an effort to eliminate litter and destroy

current seed crop. These treatments were replicated three

times and randomly applied to nine 5 x 8 m plots at each site.

Oust® was applied using a backpack, hand-pressurized sprayer

with a 1 m wide hand-held boom. Herbicide was applied at a

rate equivalent to 1 oz acre–1 (70 g hectare–1). Plots were tilled

with a large rear-tine rototiller, and 2 m wide buffer strips

were also tilled around the nine plots to act as fire break.

Each treatment plot was halved and randomly chosen for

inoculation with equal amounts of fragmented tissue of

three moss species. The moss species used for the experiment were chosen because they could be readily collected in

the Boise area. Additionally, they represent morphological

types, short and tall mosses, found comprising microbiotic

crusts associated with native and seeded vegetation in the

area (Kaltenecker 1997). Based on the success of growth

cabinet experiments, an equal mass of moss per unit area

was maintained for the field experiment, that is, 3.0 x 10–4g

moss tissue cm–2 or 19.6 g moss tissue 20 m–2. Subplots were

divided into eight 1 x 2.5 m inoculation strips to get consistent subplot coverage with moss fragments. Each subplot

was inoculated a strip at a time by pushing the contents of

prepackaged moss tissue through a No. 100 (149 μm) standard soil sieve. The soil surface was moistened with demineralized water before and after inoculation to help fragments adhere to the soil surface. Cardboard wind walls (0.5 m

tall) with the dimensions of the inoculation strips were

employed when wind became more than light air (>5 km

hr–1). Inoculation was halted when wind became more than

a gentle breeze (>13 km hr–1).

Sampling Protocol and Statistical

Analysis

Plots were sampled 6 months after subplot inoculation

(table 1). Sampling was accomplished by setting three 4 m

long transects at 1.25 m, 2.5 m, and 3.75 m perpendicular to

and along the 5 m base of each treatment plot. At 1 m, 2 m,

and 3 m of each transect a point frame was randomly placed

on one side or the other of the measuring tape. The point

frame (75 x 30 cm) was read at nine placements per treatment combination. The vegetation present at the soil surface

was recorded (table 2) at each of seventy points per frame

(total n = 34,020).

Data were analyzed using the general linear model procedure for analysis of variance (ANOVA) and Fisher’s exact

test (SAS, 1996).

Results and Discussion __________

Litter, cheatgrass, and bare soil were the variables (fig. 2)

distributed appropriately for ANOVA. Of these, litter reflected a reasonably significant (p = 0.04) treatment difference, based on p <0.05. Litter was most frequent on the

herbicided plots. It was reduced by burning and showed the

greatest reduction on the tilled plots. The removal of litter

and exposure of the soil surface is desirable to allow moss

fragments to reach mineral soil. Leaving some litter to trap

fragments and shelter gametophytes may also be important

to the establishment of mosses.

Burning reduced cheatgrass nearly as effectively as the

herbicide. Effect coded data for annual forbs indicated

a reduction in the relative frequency of this variable in

the herbicided plots using Fisher’s exact test, p = 0.0001.

Figure 1—Schematic diagram of treatment plot

position.
USDA Forest Service Proceedings RMRS-P-11. 1999 285

Moss recovery or initiation was low over the entire experiment (table 2, fig. 3). Since gametophytes and protonema

were occasionally noted outside the point frame placements

under sampling of the moss variables is suspected. However,

some interesting patterns are notable in these relative

frequencies. The preexisting moss Pterygoneurum ovatum

(Hedw.) Dix. responded to back burn as did moss protonema.

This growth may be due to nutrient release and litter

reduction.

Conclusions____________________

Weed control is of primary concern and usually the initial

step in restoration efforts (Youtie 1997). Fire, herbicide

application, and tilling temporarily reduced the massive

potential of the annual grassland seedbank in these plots.

Weed control utilizing the treatments may yield positive

results in the restoration of similar sites.

Using fire to open up the soil surface and reduce water

interception by litter and standing biomass could be useful

restoration strategy in annual grasslands with patches of P.

ovatum. This moss species is desirable because of its ability

to quickly spread into open soil and trap fine soil particles.

Low frequency of moss establishment from inoculated

fragments may have been due to a variety of factors. Six

months may have been too little time to detect any appreciable growth from the fragments of these species. Regardless of precautions to prevent loss of fragments from the

plots, it is possible some deflation of fragments may have

occurred. Variable precipitation patterns may have also

influenced the growth of these species from fragmented

tissue.

Future experimentation with inoculation methodology

should be conducted. Investigation into methods that would

increase the residence time of the fragments at the soil

surface and expedite their delivery would be useful. Information about the growth response of larger fragments and

various application times would also be of value.

Table 1—Time table (month-day) for treatment application, 1997.

Treatment Base Lockman Range

Burning July 8 July 9 July 8

Herbicide application May 21 May 21 May 20

Rototilling June 2 June 2 June 3

Inoculation November 13 and 18 November 15, 21, and 22 November 12

Table 2—Variables encountered in field experiment and count.

Variable Relative frequency

Percent

Litter (annual vascular plant detritus) 60

Bromus tectorum L. 23

Bare soil 12

Annual forbs 2

Rocks 1

Vascular perennial graminoids and forbs 1

Pre-existing moss (Pterygoneurum ovatum [Hedw.] Dix.) 0.2

Woody litter 0.2

Moss protonema 0.2

Charcoal fragments 0.2

Inoculated moss 0.05

Lichen 0.02

Burned Herbicided Tilled 

INOC PTOV PROT

Percent 0.5

0.4

0.3

0.2

0.1

0.0

Figure 2—Relative frequency (%) of ANOVA appropriate variables and vascular annual forbs per

treatment (n = 11,340).

Burned Herbicided Tilled 

Annual forbs Bare soil Cheatgrass Litter

Percent 80

70

60

50

40

30

20

10

0

Figure 3—The relative frequency of the moss categories: Inoculated mosses (INOC), moss protonema

(PROT), and pre-existing moss (PTOV).
286 USDA Forest Service Proceedings RMRS-P-11. 1999

References _____________________

Belnap, J; Gardner, J. S. 1993. Soil microstructure in soils of the

Colorado Plateau: The role of the cyanobacterium Microcoleus

vaginatus. Great Basin Naturalist 53:40-47.

Belnap, J.; Harper, K. T. 1994. Influence of cryptobiotic soil crusts

on elemental content of tissue of two desert seed plants. Arid Soil

Research and Rehabilitation 9:107-115.

Beymer, R. J.; Klopatek, J. M. 1991. Potential contribution of carbon

by microphytic crusts in pinyon-juniper woodlands. Arid Soil

Research and Rehabilitation 5:187-198.

Billings, W. D. 1994. Ecological impacts of cheatgrass and resultant

fire on ecosystems in the western Great Basin. In: Monsen, S. B.;

Kitchen, S. G., comps. Proceedings-ecology and management

of annual rangelands; 1992 May 18-21; Boise, ID. Gen. Tech. Rep.

INT-GTR-313. Ogden, UT: U. S. Department of Agriculture,

Forest Service, Intermountain Research Station: 22-30.

Brotherson, J. D.; Rushforth, S. R. 1983. Influence of cryptobiotic

crusts on moisture relationships of soils in Navajo National

Monument, Arizona. Great Basin Naturalist 43:73-78.

Eldridge, D. J. 1996. Distribution and floristics of tericolous lichens

in soil crusts in arid and semi-arid New South Wales, Australia.

Australian Journal of Botany 44:581-599.

Eldridge, D. J.; Greene, R. S. B. 1994. Microbiotic soil crusts: a

review of their roles in soil and ecological processes in the

rangelands of Australia. Australian Journal of Soil Research

32:389-415.

Eldridge, D. J.; Tozer, M. E. 1996. Distribution and floristics of

bryophytes in soil crusts in semi-arid and arid eastern Australia.

Australian Journal of Botany 44:223-247.

Evans, R. D.; Ehleringer, J. R. 1993. A break in the nitrogen cycle

in aridlands? Evidence from nitrogen 15 of soils. Oecologia 94:

314-317.

Jaques, I. D. 1984. Self-revegetation of a sagebrush-bunchgrass

community after surface blading by bulldozer. M. S. thesis,

Washington State University, Pullman, WA.

Johansen, J. R. 1993. Cryptogamic crusts in semiarid and arid lands

of North America. Journal of Phycology 29:140-147.

Kaltenecker, J. H. 1997. The recovery of microbiotic crusts following

post-fire rehabilitation on rangelands of the western Snake River

Plain. M. S. thesis, Boise State University, Boise, ID.

Kaltenecker, J.; Wicklow-Howard, M. 1994. Microbiotic soil crusts

in sagebrush habitats of southern Idaho. Unpublished report

produced for the U.S. Department of Agriculture, Forest Service,

Eastside Ecosystem Management Project, Walla Walla, WA.

Larsen, K. D. 1995. Effects of microbiotic crusts on the germination

and establishment of three range grasses. Unpublished masters

thesis, Boise State University, Boise, ID.

Martínez-Sánchez, J. J.; Casares-Porcel, M.; Guerra, J.; GutiérrezCarretero, L.; Ros, R. M.; Hernández-Bastida, J.; Cano, J. 1994.

A special habitat for bryophytes and lichens in the arid zones of

Spain. Lindbergia 19:116-121.

Pellant, M. [Personal communication]. Bureau of Land Management, Idaho State Office, Boise, ID.

Peters, E. F.; Bunting, S. C. 1994. Fire conditions pre- and post

occurrence of annual grasses on the Snake River Plain. In:

Monsen, S. B.; Kitchen, S. G., comps. Proceedings-ecology and

management of annual rangelands; 1992 May 18-21; Boise, ID.

Gen. Tech. Rep. INT-GTR-313. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Intermountain Research Station:

31-36.

Rincon, E.; Grime, J. P. 1989. An analysis of seasonal patterns of

bryophyte growth in a natural habitat. Journal of Ecology 77:

447-455,

Rosentreter, R. 1986. Compositional patterns within a rabbitbrush

(Chyrsothamnus) community of the Idaho Snake River Plain. In:

McArthur, E. D.; Welch, B. L., comps. Proceedings-symposium on

the biology of Artemisia and Chrysothamnus. 1984 July 9-13,

Provo, UT. Gen. Tech. Rep. INT-200. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research

Station: 273-277.

St. Clair, L. L.; Johansen, J. R. 1993. Introduction to the symposium

on soil crust communities. Great Basin Naturalist 53:1-4.

St. Clair, L. L.; Johansen, J. R.; Rushforth, S. R. 1993. Lichens of soil

crust communities in the Intermountain Area of the Western

United States. Great Basin Naturalist 53:5-12.

St. Clair, L. L.; Webb, B. L.; Johansen, J. R.; Nebeker, G. T. 1984.

Cryptogamic soil crusts: enhancement of seedling establishment

in disturbed and undisturbed areas. Reclamation and Revegetation Research 3:129-136.

SAS Institute Inc. 1996. Cary, NC.

Williams, J. D.; Dobrowolski, J. P.; West, N. E. 1995a. Microphytic

crust influence on interrill erosion and infiltration capacity.

Transactions of the American Society of Agricultural Engineers

38:139-146.

Williams, J. D.; Dobrowolski, J. P.; West, N. E.; Gillette, D. A. 1995b.

Microphytic crust influence on wind erosion. Transactions of the

American Society of Agricultural Engineers 38:131-137.

Whisenant, S. G. 1995. Landscape dynamics and arid land restoration. In: Roundy, B. A.; McArthur, E. D.; Haley, J. S.; Mann,

D. K., comps.Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech.

Rep. INT-GTR-315. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Research Station: 26-34.

Youtie, B. 1997. Weed control as the first step in protecting and

restoring native plant communities on northeast Oregon natural

areas. In: Kaye, T. N.; Liston, A.; Love, R. M.; Luoma, D. L.;

Meinke, R. J.; Wilson, M. V., eds.Conservation and management

of native plants and fungi. Corvallis, OR: Native Plant Society of

Oregon, Corvalis, Oregon: 78-82.
USDA Forest Service Proceedings RMRS-P-11. 1999 287

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

A. L. Hild is Assistant Professor of Rangeland Ecology and B. Christensen

and A. Maier are Graduate Students in the Department of Renewable

Resources, University of Wyoming, Laramie, WY 82071-3354.

Abstract—Little is known of maternal plant influence upon seedling characteristics of native shrubs. This study examined influence

of maternal Wyoming big sagebrush (Artemisia tridentata ssp.

wyomingensis) stand position on emergence and growth of seedlings. Seedlings from maternal plants in upslope, core, and

downslope positions were grown in a common greenhouse setting.

Percent germination, height, and canopy volume of seedlings

differed among three maternal plant positions. Emergence of

downslope and core-derived seed occurred later than that of

upslope-derived seed. Canopy volume and height of seedlings from

downslope plants were less than that of core- and upslope-derived

plants after 14 weeks of growth. These results indicate that seed

collection from different positions within a stand can produce

seedlings with divergent growth characteristics. Heritable differences that depend on seed source plant position offer potential for

more refined revegetation efforts when using Wyoming big sagebrush seed.

Little is known of the relative influences of genetics and

environment upon seedlings, although maternal plants

may have great impact (Roach and Wulff 1987). Maternal

plants may undergo selective change via environmental

constraints (Lacey 1991). Within-population variation has

been documented for many herbaceous species (Antonovics

and Schmitt 1986; Ducousso and others 1990; Keeler 1978;

Linhart 1988; Plantenkamp and Shaw 1993). Seedling variability may derive from both environmental and genetic

constraints that limit maternal plant individuals. Shrubland ecotones between shrub stands and adjacent grasslands may provide variable environmental constraints that

alter inheritance of propagules. Ecotones may thus become

a source of genetic variability within shrub stands through

differential selection. Levin (1995) has suggested that outlier plants that are distant from conspecifics may offer

variability in the gene pool that can enhance population

viability. Differences in growth form of hybrid sagebrush in

transition zones between subspecies distributions have been

documented (Freeman and others 1999, this proceedings).

Wyoming Big Sagebrush (Artemisia

tridentata ssp. wyomingensis) Seedling

Growth and Maternal Plant Stand Position

A. L. Hild

B. Christensen

A. Maier

Phenotypic display of seedling variability within stand

positions has not been examined for native shrub stands. We

examined the seed crop of three Wyoming big sagebrush

stands with respect to maternal plant positions central or

peripheral to the stand. Seedlings grown in a common

greenhouse setting displayed differential growth depending

on stand position of maternal plants.

Methods _______________________

Study Site

Research sites are located at USDA-ARS Fort Keogh

Livestock and Range Research Labs (LARRL), near Miles

City, Montana, at 46° 22' N latitude and 105° 5' west

longitude. Annual precipitation averages 33.8 cm annually,

with approximately 60% received from mid April to mid

September. Air temperatures range from –10 to 24 °C in

January and July, respectively.

Three stands of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) were selected; each stand lies on

a gentle (<10%) slope with northern aspect. Within each of

these three Wyoming big sagebrush stands, three relative

stand positions were identified as upslope periphery,

downslope periphery, and core positions. Upslope and

downslope positions were recognized as topographic positions at the margins of each stand. Core positions were then

located intermediate to upslope and downslope positions

and at the center of the stand. We sampled soil cores from

each position at two depths (surface 0-10 cm and 10-20 cm)

in each of three stands. All positions in the three stands were

located on clay loam soils deeper than 50 cm with comparable soil moisture content in surface and subsoil samples.

Stands were approximately 3 km apart from one another.

Data Collection

Within each position, 10 mature flowering sagebrush

plants were randomly selected and marked for study.

These plants (maternal plants) were used as seed sources

for 2 consecutive years (1996 and 1997). We measured

height, width of canopy in two perpendicular measures,

basal diameter, and distance to nearest sagebrush neighbor

for each parental plant. In December 1996 and again in

December 1997, inflorescence was removed from each parental plant and transported to the University of Wyoming

for germination studies. Inflorescences were allowed to

air dry, separated into twigs, leaves, and flower portions.
288 USDA Forest Service Proceedings RMRS-P-11. 1999

Biomass of each portion was recorded as well as biomass of

20 randomly selected seeds from each maternal plant for

planting. Following the second year of inflorescence collection, spring 1998, all parental plants were harvested for

aging.

In April 1997 and April 1998, we planted 20 seeds from

each maternal plant in a common greenhouse setting. Seeds

were placed on a commercial germination media (2:1:1 parts

peat moss, vermiculite, and pearlite, respectively), watered

and placed under growth lights. For maternal plants that

produced fewer than 20 seeds, we planted all available

seeds. After planting, we recorded number of seeds planted

from each maternal plant, days to seedling emergence, and

percent emergence. Because our goal was to obtain seedlings

from each parent, we replanted seeds of parent plants that

did not have successful seedlings on May 13-15, 1997, and

June 1-3, 1998, and again recorded days to emergence.

Growth of individual seedlings of each successful maternal plant was documented for 26 weeks after emergence.

Beginning 5 weeks after emergence, we recorded the height

and number of leaves of each seedling. After week nine,

seedlings had sufficient growth to cause leaf counts to be

difficult. Consequently, height, canopy dimensions, and

number of branches were recorded, beginning week 14 after

emergence. Canopy of seedlings was recorded as height, two

perpendicular widths of the crown, and total branch length.

In week 12 seedlings were transplanted from six-pac pots

into plastic-lined PVC tubes (16 cm diameter x 100 cm tall)

containing a soil mix of 2:1 parts potting soil and washed

masonry sand to allow for deep root growth, and monitoring

was continued. After seedlings were 1 year old, they were

removed from PVC containers and planted into a field

setting.

Experimental Design

Data for parental plants were subjected to analysis of

variance (SAS 1997) appropriate to a randomized block

design; with each stand as a block and parental position

(downslope, core, and upslope) treatments. Seedling data

were assessed for treatment (maternal plant stand position)

effects among weeks in a repeated measures analysis

(weeks = 5, 6, 7, and 9 for number of leaves; 5, 6, 7, 9, 14, 18,

22, and 26 for seedling height; 14, 18, 22, and 26 for seedling

canopy width, and branch lengths). Results are reported as

F ratio probabilities and all data were assessed for conformance to assumptions of the analysis of variance.

Results ________________________

Maternal Plants

Maternal plants did not differ in canopy size or basal

diameter by position. Upslope position parental plants

were shorter (P <0.03) than core or down-position plants

(mean heights were 45.5, 55.5, and 53.6 cm for upslope, core,

and downslope parental plants, respectively). Additionally,

as might be expected, distance to nearest neighboring sagebrush plants was least between core plants (P <0.01 mean

distance 46.2 cm), farthest between downslope parental

plants (mean distance 134.4 cm); upslope plants were intermediate in distance (77.4 cm) to nearest neighboring sagebrush and not different than core-position plants.

Biomass of inflorescence, biomass of 20 seeds, and number of seeds planted did not differ between positions in either

year of the study (P >0.66 and 0.25, respectively). Total

inflorescence biomass of maternal plants was greater in

1996 than in 1997 collections (P <0.01) with means of 13.0

and 8.8 g per maternal plant, respectively. Number of

successful parental plants (producing at least one seedling)

was not different by position or year (table 1).

Seedlings

In 1997 and 1998, 130 and 338 seedlings, respectively,

were monitored. Both number and percent emergence of

seedlings differed between years depending on position

(position by year interaction P <0.01 and 0.01 for number

and percent emerged, respectively). Total number of seedlings and percent emergence (table 1) were both greater for

downslope and core positions in 1998 than from upslope

positions. In 1997, number and percent emergence did not

differ between positions, and emergence was less than 25%

for any position in both years.

Core-position seedlings emerged later than did downslopeposition seedlings in both years (P <0.02). Core seedlings

emerged 17.1 days after planting while the mean number of

days to emerge were 13.5 and 14.9 for downslope and

upslope positions, respectively.

In 1997, branch length increased with week (P <0.01)

but did not differ by position (P >0.74). Seedling heights in

1997 differed (P <0.01) by position after week nine.

Seedlings derived from downslope maternal plants were

shorter than seedlings derived from maternal plants in the

other two positions. Additionally, canopy volume of

Table 1—Successful maternal plants and seedling emergence by position in 1997 and 1998.

1997 1998

Downslope Core Upslope Downslope Core Upslope

Successful maternal plants (total) 12 12 7 19 15 6

Percent germination (mean)* 3.6a 7.7a 7.6a 25.4b 24b 6a

Seedlings emerged (total) 23 66 41 155 145 38

*Mean within years with the same letters do not differ, P >0.05, LSD.
USDA Forest Service Proceedings RMRS-P-11. 1999 289

Figure 1—Canopy volume of seedlings derived from maternal plants in three stand positions by

week after emergence. Means within a position with the same lower case letters, or within a week

with the same upper case letters, do not differ, P >0.05, LSD.

downslope-derived seedlings was less (P <0.01) than that of

seedlings from the other two positions by week 18 following

their emergence (fig. 1). Growth of the second cohort of

seedlings continues to be monitored in 1998.

Discussion _____________________

This study is limited by the growth of seedlings in a

controlled greenhouse rather than in a field setting. However, the common growth environment restricts the possibility that seedling growth differences noted here are the

result of environmental conditions. Thus, our study supports the notion that differences noted in seedling growth

may derive from genetic inheritance.

Production of seedlings from core and downslope maternal plants was much greater in 1998 although their success

varied greatly by year. Additionally, reduced canopy of

downslope-derived seedlings relative to seedlings from maternal plants in the other two positions suggests the existence of within-stand variation. Explanations of the differences in growth of seedlings are difficult to tie to biological

constraints on maternal plants, yet the presence of growth

differences by position suggests that growth potential of

seedlings within a stand may provide variety within stand

gene pools. Future genetic studies are needed to verify our

results. However, these growth differences may result in

an array of relative competitive abilities of sagebrush seedlings. Given the possible genetic differences of seed by virtue

of maternal plant locations within sagebrush populations,

seed collection efforts for specific goals may be enhanced. It

remains to be seen, however, whether greenhouse growth

trends are persistent under competitive field conditions.

Acknowledgments ______________

This study was funded by USDA-ARS Cooperative Agreement No. 58-5434-7-103. We thank Dr. Rod Heitschmidt and

the staff of the Fort Keogh Livestock and Range Research

Lab in Miles City, Montana, for providing access to the

research sites and facilitating our sampling efforts. Especially helpful were the many students who assisted with

greenhouse activities.

References _____________________

Antonovics, J.; Schmitt, J. 1986. Parental and maternal effects on

propagule size in Anthoxanthum odoratum. Oecologia 69:277-282.

Ducousso, A.; Petit, D.; Valero, M.; Vernet, P. 1990. Genetic variation between and within populations of a perennial grass:

Arrhenatherum elatius. Heredity 65:179-188.

Freeman, D. C.; Miglia, K. J.; McArthur, E. D.; Graham, J. H.;

Wang, H. 1999. [These proceedings.]

Keeler, K. 1978. Intra-population differentiation in annual plants.

II. Electrophoretic variation in Veronica peregrina. Evolution

32:638-644.

Linhart, Y. B. 1988. Intrapopulation differentiation in annual

plants. III. The contrasting effects of intra- and interspecific

competition. Evolution 42:1047-1064.

Lacey, E. P. 1991. Parental effects on life-history traits in plants. In:

Dudley, E. C., ed. 1991. The unity of evolutionary biology. Proc.

Fourth International Congress of Systematic and Evolutionary

Biology. July 1990. College Park, Maryland, U.S.A.

Levin, Donald A. 1995. Plant outliers: an ecogenetic perspective.

Am. Nat. 145:109-118.

Platenkamp, G. A. J.; Shaw, R. G. 1993. Environmental and genetic

maternal effects on seed characters in Nemophila menziesii.

Evolution 42:540-555.

Roach, D. A.; Wulff, R. 1987. Maternal effects in plants: evidence

and ecological and evolutionary significance. Ann. Rev. Ecol.

Syst. 18:209-235.

SAS Institute Inc. 1997. JMP statistical discovery software version

3.2.2. Cary, NC.

USDA Forest Service Proceedings RMRS-P-11. 1999 7

Field Trip

291

USDA Forest Service Proceedings RMRS-P-11. 1999 293

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.

Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.

RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station.

E. Durant McArthur is Project Leader and Research Geneticist and

Stephen B. Monsen is Research Botanist, Shrub Sciences Laboratory, Rocky

Mountain Research Station, Provo, UT 84606; Richard Stevens was Project

Leader and Wildlife Biologist, Utah Division of Wildlife Resources, Great

Basin Research Center, Ephraim, UT 84627; he is currently with Maple Leaf

Industries, Ephraim, UT 84627.

Field Trip Report: Shrubland Ecotones

E. Durant McArthur

Stephen B. Monsen

Richard Stevens

Abstract—The field trip was held on August 13, 1998, accompanied

by beautiful weather. It featured visits to the Salt Creek big

sagebrush (Artemisia tridentata) hybrid zone on the Uinta National

Forest and the Great Basin Experimental Range on the Manti-La

Sal National Forest. The eight stops afforded opportunities to see

and better understand the structure and dynamics of several plant

communities and ecotones as well as the sagebrush hybrid zone and

to learn about past and ongoing research and management in these

areas. The field trip facilitated discussion on how management

practices affect communities and their interfaces or ecotones. This

report documents the field trip and provides information for those

who may visit the sites in the future.

The field trip was designed to complement the symposium

theme by incorporating visits to community ecotones and a

sagebrush hybrid zone. It was also our intention to showcase

the Great Basin Experimental Range (GBER) with its rich

history of rangeland research and to highlight current research, management practices, and opportunities for future

research. The field trip consisted of eight stops. One of these

stops was on the Nebo Loop Road in Juab County in the Uinta

National Forest; all other stops were along the Ephraim

Canyon Road, on the Great Basin Experimental Range,

Manti-La Sal National Forest, Sanpete County. Our report

briefly summarizes the biological and management issues

addressed at each stop. The geology is treated separately.

Geology _______________________

Dr. Helmut Doelling of the Utah Department of Natural

Resources, Utah Geological Survey, was the discussion leader

and described geological aspects throughout the field trip.

Rather than describe each site, we briefly summarize the

geology. The stop on the Nebo Loop Road (stop 1) was at the

south end of Mt. Nebo and offered some interesting geological vistas. To the south is the Gunnison Plateau (known also

as the San Pitch Mountains), which is composed in part from

Createous conglomerate and sandstone derived from high

Cretaceous mountains that had been formed by the Sevier

orogeny (mountain building event) and from the lacustrine

rock strata that also form the Wasatch Plateau (see figure 1

for the geologic time table and the second, third, and fourth

paragraphs below this one for the treatment of Wasatch

Plateau geology). These Cretaceous Sevier orogeny mountains have long since eroded away, but gravelly alluvial fans

that extended eastward from them remain as conspicuous

parts of the Gunnison Plateau. Salt Creek Canyon slopes

both on the north end of the Gunnison Plateau and the south

end of Mt. Nebo expose the middle Jurassic Arapien Shale.

Arapein shale is rich in gypsum; an active gypsum mine is

located at the mouth of Salt Creek Canyon. It was deposited

in a central Utah basin in a shallow sea that extended

southward from the Arctic Ocean in a semiarid climate.

These evaporitic and muddy deposits were important in the

formation of our modern structural features.

An interesting grey, Bryce Canyon-like erosion surface

lies just above Salt Creek Canyon on the southeast flank of

Figure 1—Geological time (after Chronic 1990). Time

frame presented only for those periods and epochs mentioned in the text.

Era Period Epoch Agea

Cenozoic Quaternary Recent (Holocene) 0.01

Pleistocene 2

Tertiary Pliocene 5

Miocene 24

Oligocene 37

Eocene 58

Paleocene 66

Mesozoic Cretaceous 144

Jurassic 208

Triassic 245

Paleozoic Permian 286

Pennsylvanian 330

.... ...

.... ...

.... ...

505

a Approximate time in millions of years before the present at the beginning

of the geological time frame.
294 USDA Forest Service Proceedings RMRS-P-11. 1999

Mt. Nebo; this is a mid-Tertiary volcaniclastic deposit presently being eroded into badlands. Mount Nebo itself is the

southern most extension of the Wasatch Mountains or central Rocky Mountains and exposes a complicated upthrust of

Pennsylvanian and Permian Oquirrh Formation resting on

Triassic, Jurassic, and Cretaceous rocks (Chronic 1990;

Banks 1991; Biek 1991). The Wasatch Mountains were

formed beginning in Miocene time as previously folded and

thrust-faulted rocks were uplifted along the Wasatch Fault.

The fault is still active, and hence the mountains continue to

rise. The displacement of the Wasatch Fault probably exceeds 30,000 ft (9,150 m) at the present time, but much of the

Wasatch Mountains has already been worn away by erosion.

The stops on the Great Basin Experimental Range showcased the Wasatch Plateau and at stop 3, the Sanpete Valley,

Gunnison Plateau, and Wasatch Mountains. To understand

the geology of the Wasatch Plateau, a brief review of the

geological history of Utah is in order (Spieker 1949; Hintze

1988; Doelling, personal communication, August 1998, January 1999). For most of geological time Utah was near sea

level, nearer the equator, and much of its present area was

covered by marine and fresh water seas or lakes. Subsequently the Sevier and Laramide orogenies and erosion gave

rise to the topographic relief of today. During Miocene time

the entire region encompassing Utah was elevated. Tensile

forces at work beneath the Earth’s crust between the Colorado Plateau and Central Rocky Mountain axis (Wasatch

Plateau and Wasatch Mountains of this field trip) and the

Sierra Nevada have lead to collapses along faults. The entire

Great Basin (basin and range province) consists of a series

of mountain ranges bordered by faults and separated by

grabens (dropped valleys bordered by faults) filled with

alluvium.

The Wasatch Plateau consists mainly of sedimentary

rocks, shales, and weathered materials from marine and

lacustrine strata. During the late Cretaceous thrust faults

pushed slabs of rock from west to east, soling or rafting in the

soft Arapien Shale. One of these thrusts broke through the

then existing sequence of formations by first forming a

north-south trending fold at the present location of Sanpete

Valley. This fold was eroded nearly flat and the upturned

edges of these rocks are visible along the east flank of the

Gunnison Plateau at Chistianburg and at the mouth of

Wales Canyon. The ridges of coal-bearing Cretaceous rocks

in Sixmile Canyon are the remnants of eroded folds on the

west flank of the Wasatch Plateau. A succession of fluvial

and then lacustrine rocks were deposited over the upturned

edges starting in the last stage of the Cretaceous and

extending into the Eocene. Principal among these, in increasing age, are the Crazy Hollow, Colton, Green River,

Flagstaff, and North Horn Formations. The Green River,

Flagstaff, and North Horn are lacustrine deposits from fresh

water Tertiary lakes including Flagstaff Lake and Lake

Uinta (Chronic 1990). The North Horn Formation is a

deposit of alternating mudstone, sandstone, conglomerate,

and thin limestone presently highly conductive to forming

landslides as are the shale units of the Flagstaff and Green

River Formations. Landslides and mudflows of Holocene

(Recent) age are common in the canyons of the Wasatch

Plateau and were pointed out on the field trip. Overlying the

North Horn Formation is the Flagstaff Limestone from

Paleocene Lake Flagstaff. Flagstaff Limestone forms the

hard top of the Wasatch Plateau along Skyline Drive and the

top of the Wasatch monocline. The Wasatch monocline

slopes steeply to the west into the Sanpete Valley where it is

overlain by a thick alluvium. Remnants of the overlying

Crazy Hollow, Colton, and Green River Formations are

found along the west flank of Wasatch Plateau as hogbacks

(narrow sharp-crested ridges of tilted rock or shale strata).

A prominent Green River Formation hogback lies just east

of Ephraim and served as a lookout in pioneer days. A

landslide block, not stable, of Green River and Crazy Hollow

Formations forms Temple Hill north of Manti, upon which

the Manti LDS Temple stands. Oolitic (= composed of small

spheres) limestone of the Green River Formation was used

in construction of the Temple and the Park (Administration)

Building on the University of Utah campus.

The Wasatch Plateau was elevated as was all of the Utah

region beginning in Miocene time. The North Horn Formation is exposed in drainages and is responsible along with the

Flagstaff Formation and Green River Formation shale units

for land slippage when the ground is saturated. Land slides

and mudflows of various ages are common on the Wasatch

Plateau and were pointed out on the field trip. The dramatic

relief of the Wasatch Plateau and its west face, the Wasatch

monocline, is a result of the Miocene uplift of the Utah

region. Relaxation along the old thrust faults soled (footed)

in Arapien shale caused the collapse that formed the Wasatch

monocline and tilted the Flagstaff Formation along the west

margin of the Wasatch Plateau. Because the collapse occurred along a subsurface thrust fault (now moving backward), there are no major faults present along the margins

adjacent to Sanpete Valley (Doelling, personal communication, January 1999). Nevertheless, the collapsed early Tertiary lacustrine deposits are found in the Sanpete Valley

under alluvial cover giving Sanpete Valley the characteristics of a basin and range (Great Basin) graben. Certainly the

minuscule San Pitch River could not have carved the valley.

At stop 3, to the northwest Mt. Nebo and other Wasatch

Mountains and more directly west (south of Mt. Nebo) the

Gunnison Plateau are clearly visible beyond the Sanpete

Valley in the foreground (see first paragraph of section). The

Sanpete Valley floor can be seen with its island-like hogbacks rising above the relatively level Quaternary alluvium

of high clay content derived as out wash from the Wasatch

and Gunnison Plateaus.

Plant Taxonomy_________________

Discussion leaders were Mr. Sherel Goodrich, Dr. Durant

McArthur, Ms. Dea Nelson, Dr. Stewart Sanderson, Mr.

Robert Thompson, and Dr. Alma Winward. Throughout the

tour these group discussion leaders were available and kept

field trip participants apprised of the identity of plants, often

pointing out cryptic differences between closely related taxa.

Salt Creek Canyon ______________

Discussion leaders were Dr. Durant McArthur, Mr. Gary

Jorgensen, Dr. Carl Freeman, Dr. John Graham, Ms. Dea

Nelson, Dr. Bruce Smith, and Mr. Tom Tidwell.
USDA Forest Service Proceedings RMRS-P-11. 1999 295

Stop 1: Salt Cave Hollow

This stop is about 1 mile (1.6 km) up the Nebo Loop road

from its junction with state highway U-132, just past the

Uinta National Forest entry sign. It is the area that McArthur,

Freeman, Graham, Smith, Wang, Sanderson, and others

have been studying a narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata). These

are basin (A. t. ssp. tridentata) and mountain (A. t. ssp.

vaseyana) big sagebrush. The hybrid zone is located in the

Salt Creek drainage ranging in elevation from 5,838 ft (1,780

m) at the basin big sagebrush site to 6,134 ft (1,870 m) at the

mountain big sagebrush site over a 0.7 mile (1.1 km) linear

distance extending from the Salt Creek flood plain up Salt

Cave Hollow in a westerly direction (see Freeman and others

1991; Graham and others 1995; and Wang 1996 for a more

complete description). The soils range from well-drained

dark brown loam at the basin big sagebrush site through

stony loam in the hybridization area to gravelly loam at the

mountain big sagebrush site (Trickler and Hall 1984) and

vary by site in pH, thickness, and mineral concentrations

(Wang 1996). Precipitation is about 22 inches (560 mm)

annually with about 65 percent of that coming from October

to April, much of it as snow (Richardson and others 1981;

Ashcroft and others 1992).

Dea Nelson and Tom Tidwell of the Uinta National Forest

explained some of the principal land uses in the area. The

stop is on the Nebo Management Area administered by the

Spanish Fork Ranger District. The Uinta National Forest

was established in 1897 as the Uintah Forest Reserve in

response to local residents’ concerns that range, timber, and

water resources should be better managed and maintained.

The high peak country above the study site including the

upper elevations of Bald Mountain, North Peak, and Mount

Nebo were established as the Mount Nebo Wilderness Area

in 1984 under the Utah Wilderness Act. The Nebo Management Area is a popular recreational area for camping,

hiking, horseback riding, fishing, and hunting. Recreational

use is high and increasing as the Wasatch Front population

continues to increase. The site is in a cattle allotment and as

such is important for the management of domestic livestock

and the livelihood of several families of livestock owners.

Studies in the hybrid zone have included analyses of

plants and their habitats in five sites within the zone that we

have labeled basin-population (5,840 ft or 1,780 m, “pure”

basin big sagebrush population), near-basin-population

(5,870 ft or 1,790 m, much like basin big sagebrush but with

influence from mountain big sagebrush plants, 850 ft or 260 m

upslope from basin-population), hybrid-population (5,900 ft or

1,800 m, includes substantive elements of both basin and

mountain big sagebrush plants, 650 ft or 200 m upslope from

near-basin-population), near-mountain-population (5,970 ft

or 1,820 m, much like mountain big sagebrush but with

influence from basin big sagebrush plants, 1,180 ft or 360 m

upslope from hybrid-population), and mountain-population

(6,135 ft or 1,870 m, “pure” mountain big sagebrush, 790 ft or

240 m upslope from near-mountain-population). In May of

1993 three reciprocal transplant gardens (ca. 8 x 15 m) were

established: within the basin-population (basin-garden),

within the hybrid-population (hybrid-garden), and within

the mountain-population (mountain-garden). The stock

placed in the transplant gardens was 1 year old plants grown

from seed in a greenhouse including three half-sib families

of four plants each from each of the basin-, near-basin,

hybrid-, near-mountain, and mountain populations. The

genetic makeup of these families is not known except the

maternal (seed-bearing, open-pollinated) parents conformed

to basin, near-basin, hybrid, near-mountain, and mountain

phenotypes on morphological and chemical (coumarin and

terpenoid) criteria (McArthur and others 1988; Freeman

and others 1991). The gardens were fenced, for protection,

with 2.5 m high fences in October 1994. Gardens were

established on sites that appeared to be homogeneous. Gary

Jorgensen and Dick Tennant built a foot bridge across Salt

Creek especially for this field trip for better access to the

basin population and garden.

Demonstrations and explanations were presented at the

near-basin population site. Dr. Hellmut Doelling explained

the site geology; Dr. Durant McArthur reviewed the study

history and site characteristics; Dr. Bruce Smith demonstrated portable physiological equipment used to measure

plant respiration; Mr. Gary Jorgensen demonstrated the

ultraviolet light technique in distinguishing mountain and

basin big sagebrush (Stevens and McArthur 1974); Dr. John

Graham pointed out various galls and insects found on big

sagebrush and commented on their occurrence across the

hybrid zone. Three subgroups then visited in rotational

turns the basin-garden, the hybrid-garden, and the mountain-garden, with respective tour leaders Drs. Durant

McArthur, Carl Freeman, and John Graham, where morphological and growth differences in the five hybrid zone

subpopulations (basin, near-basin, middle-hybrid, nearmountain, and mountain) were examined and a series of

studies involving plant morphology, growth rates, plant

chemistry, selection gradients and fitness, developmental

instability, insect relationships, soils, mineral uptake, plant

community dynamics, and respiration and water potential

as well as the importance and stability of hybrid zones to

population biology were reviewed (see McArthur and

Sanderson, Freeman and others, and Graham and others,

these proceedings, for review and synthesis).

Great Basin Experimental

Range _________________________

Discussion leaders were Dr. Durant McArthur, Mr. Stephen

Monsen, Mr. Richard Stevens, Dr. Dale Bartos, Mr. Robert

Campbell, Ms. Janette Kaiser, Mr. Donald Okerlund, Mr.

Edward Shoppe, Mr. Thomas Shore, Mr. Robert Thompson,

Mr. Scott Walker, and Dr. Alma Winward.

The GBER is an excellent place to study ecotones. In its

4,600 acres (1,860 ha) it ranges from 6,790 ft (2,070 m) to

10,500 ft (3,200 m) over its 5 mile (8 km) length; it varies in

width from about 1 to 2.5 miles (1.5 to 4 km). Within this steep

elevational gradient several life zones are incorporated

(Merriam 1894) from sagebrush and pinyon-juniper through

mountain brush, conifer, and aspen to subalpine herblands

(Keck 1972; McArthur and Monsen 1996). Precipitation

increases from about 18 inches (450 mm) to about 36 inches

(900 mm) through the elevational gradient. At lower elevations about half the precipitation falls as snow during the

November 1 to May 1 winter season with that figure increasing to over three-fourths of the total at higher elevations
296 USDA Forest Service Proceedings RMRS-P-11. 1999

(Price and Evans 1937; G. L. Jorgensen, data on file, Great

Basin Experimental Range, Ephraim, UT).

The GBER has been a focal point for research on the

ecology and management of watersheds, rangelands, and

silviculture since its establishment as the Utah Experiment

Station in 1912. Subsequent names for this research area

have been Great Basin Experiment Station (1918-1930),

Great Basin Branch Experiment Station (1930-1947), Great

Basin Research Center (1947-1970), and Great Basin Experimental Range (1970 to present). It was one of the key

elements that coalesced into the Intermountain Forest and

Range Experiment Station (now part of the Rocky Mountain

Research Station) when the nationwide network of geographical Forest Service Research Stations was established

in 1930.

Stop 2: Dahl’s Exclosure and Major’s Flat

Overlook

This stop (at Dahl’s Exclosure) is about 0.5 miles (0.8 km)

above the forest boundary (Major’s Flat) on the Ephraim

Canyon Road at an elevation of 7,300 ft (2,225 m). Distances

given in this narrative are road distances and therefore are

larger than the straight-line distance for the length of the

GBER. This stop is located in a mountain brush vegetation

community (major species: Gambel oak—Quercus gambelii,

mountain big sagebrush, bitterbrush—Purshia tridentata,

birchleaf mountain mahogany—Cercocarpus montanus,

Martin ceanothus—Ceanothusmartinii) and provides views

of many plant communities, prominent among them PinyonJuniper (Pinus edulis -Juniperus osteospermus), mountain

big sagebrush, Wyoming big sagebrush (A. tridentata ssp.

wyomingensis), and white fir (Abies concolor). The zonation

of plant communities can be seen to be displaced elevationally

higher on the more arid south-facing slopes than the more

mesic north-facing slopes. Landslides and other disturbances are also visible. Both Major’s Flat and Dahl’s Exclosure

are signposted. Major’s Flat is an important species adaptation site used by Perry Plummer and his colleagues as they

evaluated the performance of scores of grasses, shrubs, and

forbs for revegetation and restoration purposes (Plummer

and others 1968). The Dahl’s Exclosure was the site of

pioneering adaptation and experimental hybridization studies in the bitterbrush-cliffrose (Purshia-Cowania) complex

(Blauer and others 1975); some of those plants are still in the

exclosure.

Stop 3: Sanpete Overlook and Snowberry

Exclosure

This stop is signposted as the Sanpete Overlook; the

Snowberry Exclosure is obvious by its 7 foot (2.1 m) fence just

across the Ephraim Canyon Road. It is at an elevation of

about 8,300 ft (2,530 m) about 2 miles (3.2 km) above the

previous stop. This location has a magnificent vista of the

Sanpete Valley as well as proximate and distant mountains

and is an excellent place to better understand the area

geography and geology. Dr. Doelling led a discussion in those

areas. On the way from the last stop ponderosa pine (Pinus

ponderosa) and other conifers were visible above the dominant Gambel oak and other mountain brush species. These

are a legacy of early studies to see if commercial pine

plantations might be feasible (Baker and Korstian 1931).

The conclusion is that they are not due to climatic (light July

and August precipitation followed by early frosts) and heavy

fine-grained soil conditions.

This stop is a good one to see aspect-related plant community displacement and to see distinct communities as well as

the ecotonal areas between them. Quaking aspen (Populus

tremuloides), white fir, and Douglas fir (Pseudotsuga

douglasii) are common tree species here with snowberry

(Symphoricarpos oreophilus), a common understory species.

Also common in openings are mountain big sagebrush and

willow-leaf rubber rabbitbrush (Ericamerica nauseosus ssp.

salicifolius).

The Snowberry Exclosure is an example of many exclosures

on the GBER. It was built in 1923 to use in studies, still

ongoing, to determine the effects that livestock and big game

have on individual species and to investigate natural changes

in species composition as effected by seasonal and long-term

climatic conditions.

Stop 4: The Hole

This stop is about 1.5 miles (2.4 km) above stop 3 and 0.5

miles (0.8 km) below the well-marked entrance to the Great

Basin Environmental Education Center. It is on a small side

road about 0.25 miles (0.4 km) east of the main Ephraim

Canyon Road. The name “The Hole” derives from pioneering

Forest Service Researcher A. W. Sampson becoming stuck in

his buggy in 1918: “Sampson’s Mud Hole” has became

shortened to “The Hole.” This stop features the dynamics of

conifer, mainly firs (Abies concolor and A. lasiocarpa) and

spruces (Picea englemanni and P. pungens), with quaking

aspen. Dr. Dale Bartos, Mr. Robert Campbell, and Mr. Scott

Walker led the discussion. Stands of quaking aspen of

various ages can be seen. These diverse stands are a result

of past disturbances and plant successional dynamics. Some

stands are nearly pure quaking aspen whereas others are

overtopped with conifers. Closed stands of conifers are also

present. In addition to nearby tree stands that are accessible

for close examination, varied mixtures of tree and other

species can be seen in the distance on slopes extending to the

top of the Wasatch Plateau.

The discussion centered on the value of quaking aspen to

ecosystem health. Quaking aspen substantially enhance

stream flow, biodiversity, and understory productivity over

pure stands of conifers. Quaking aspen in the Western

United States are virtually all clonal and have survived for

millennia through regeneration from frequent wildfires

(Bartos and Campbell 1998). Establishment and survival

from seedlings is extremely rare. Since settlement by

Euroamericans, fire suppression and excessive browsing of

young quaking aspen have led to the displacement of 50

percent of the aspen communities in Utah (Bartos and

Campbell 1998); the GBER situation mirrors this general

trend. Walker and others (1996) reported that quaking

aspen cover types declined from 40 to 22 percent from 1937

to 1991 on the GBER.

Ecotones between quaking aspen and conifers on the

GBER and throughout the upper elevations of the Wasatch
USDA Forest Service Proceedings RMRS-P-11. 1999 297

Plateau demonstrate changes in production and biodiversity

between the aspen and conifer general types. These ecotones

shift with succession as conifer replaces aspen and then

return to aspen with disturbance. A recent concern is that

with a long-term absence or suppression of disturbance

coupled with aspen’s lack of reproduction from seed, that

ancient, adapted clones will be and have been lost. Management practices that stimulate aspen regeneration, e.g., prescribed fire and selective cutting and protection of aspen

sprouts from herbivores are being implemented. In the

discussion, Mr. Campbell suggested that with the frequent

fires of the pre-settlement past, aspen may have been small

and shrub-like over much of its range. This situation would

suggest open canopies with diverse understories.

Stop 5: Great Basin Environmental

Education Center

This is the historic headquarters complex of the GBER. It

is located below a scenic glacial cirque in a quaking aspen

grove at an elevation of 8,850 ft (2,700 m) about 0.5 (0.8 km)

above the road leading to the last stop. The center is located

about 100 yards (90 m) southwest of the main Ephraim

Canyon Road on a well marked side road. It consists of

several classic Forest Service white frame buildings with

green roofs. The buildings were constructed during two

main time frames (1912-1914 and 1934-1936). Snow College

has been managing and refurbishing the headquarters complex as the Great Basin Environmental Education Center

(GBEEC) since 1992. The GBEEC serves as environmental

education and research center for a wide range of clients.

This is fitting given the cutting edge science that has been

centered on this place since its selection as a research

administration site in 1911. It was from this headquarters

that Dr. Arthur Sampson formulated and tested many of his

range and watershed ideas that helped him establish the

discipline of range management as the first professor of

range management at the University of California, Berkeley

(Sampson 1919; 1923, 1924); that Drs. Fredrick Baker and

Clarence Korstian gained their early experience in silviculture before they became, respectively, Forestry Deans at the

University of California, Berkeley and Duke University;

that Mr. C. L. Forsling cut his research and administrative

teeth before becoming the Director of Range Research in the

Washington Office of the Forest Service and The Department of the Interior’s Grazing Service (Bureau of Land

Management forerunner); that Dr. Edward McCarty performed his pioneering research on the relationship between

plant nutritive quality and phenology (McCarty and Price

1942); that Dr. Lincoln Ellison studied plant community

composition in subalpine settings and formulated his principal ideas about the relationships between plant succession

and grazing (Ellison 1954; 1960); that Mr. Perry Plummer

developed his ideas about range restoration and plant adaptation (Plummer and others 1968); and that many others

from several generations including the authors gained experience and insights into biological processes.

The group enjoyed both a mid-day lunch and evening

barbecue and program at this beautiful historic and dynamic site. The GBEEC under the direction of David Lanier

has a full slate of diversified environmental education programs; this field trip and symposium among them.

Stop 6: The Dungeon Overlook

This stop is about 1.5 miles (2.4 km) up the Ephraim

Canyon Road from the GBEEC on a sharp curve above

Bluebell Flat with a side road going off to the north at an

elevation of 9,050 ft (2760 m). It has magnificent views. Mr.

Donald Okerlund led a discussion on the uses and values of

the Englemann spruce-Subalpine fir (Picea engelmannii -

Abies lasiocarpa) forest, which is prominently visible on the

mountain slopes to the south and east and the discussion of

conifer-aspen interactions from the last stop was continued.

Englemann spruce is one of the largest and most valuable

timber trees of the high mountain conifers (Alexander and

Shepperd 1990). Patches damaged by the spruce beetle

(Dendroctonus rufipennis) were visible. Mr. Okerlund explained that this is a serious pest in Englemann spruce

stands throughout its range especially in mature and

overmature trees. Forest Service managers including those

on this Forest are seeking proactive ways including timber

harvest and prescribed fires to maintain the health and

vitality of the spruce-fir forests. These activities can also be

useful in maintaining the healthy dynamic between conifers

and earlier seral quaking aspen communities.

This site showcased many community types and ecotones

or transitions between them. At the stopping point grasses

and forbs were the dominant vegetation (see discussion in

stop 7 and 8 sections) but there are aspen clones and stands

of spruce-fir forest all around; these various vegetation types

or communities sometimes have sharp boundaries and sometimes interfinger. Successional patterns and change are

obvious and were discussed by the group.

Sanpete Ranger District Range Conservationist Edward

Shoppe and District Ranger Tom Shore discussed livestock

allotment management on steep gradients typical of this

site. Mr. Shoppe made the point that individual grazing

allotments consist of a diverse array of plant communities

including transitional plant communities (ecotones) and

require careful allotment and livestock management to

maintain plant health. Monitoring of plant phenology or

development is a critical consideration and is dependent, in

part, on aspect, elevation, and other local site factors. Careful allotment and livestock management is obviously complex but is essential to maintain plant health. The District

is committed to maintaining a healthy and beautiful GBER.

Stop 7: Experimental Watersheds

This stop is about 2.5 miles (4 km) above the last one at an

elevation of 10,100 ft (3,080 m) and is signposted with a

designated view area. The historic experimental watersheds

are visible to the northeast (Watershed A) and east (Watershed B); each watershed has a sediment catchment structure (cabin-like appearing buildings) at the lower end of its

drainage basin. Mr. Richard Stevens led a discussion explaining the establishment and manipulation of these watersheds. Dr. Arthur Sampson initiated the study in 1912

when Watershed A was depleted by overgrazing and Watershed B had a good cover of grass. Through time the cover of the

watersheds was manipulated in various ways and the volume

of sediment recorded (Meeuwig 1960). The watersheds are

both now stable, no sediment has been produced for many

years but vegetational dynamics are active, especially in
298 USDA Forest Service Proceedings RMRS-P-11. 1999

Watershed B where the vegetation was most dramatically

modified by seeding exotic grasses, especially smooth brome

(Bromus inermis) (Stevens and others 1992)

Mr. Stephen Monsen and Dr. Alma Winward led a discussion on the ecology, including succession, and recovery of

subalpine herblands. At the time of Euroamerican settlement the top of the Wasatch Plateau was covered, for the

most part, with tall herbaceous vegetation sometimes known

as the “tall forb type” (Ellison 1954). Philadelphia Flat is the

large expanse of level ground off to the west with a log-andblock exclosure visible in its center. Soon after settlement,

grazing livestock and felled logs could not be seen because of

the tall luxuriant herbaceous growth. The relative composition of grasses versus forbs is an issue on which Sampson

and Ellison held differing viewpoints; Sampson favoring the

viewpoint that grasses predominated and Ellison the viewpoint that forbs predominated. This debate of the relative

composition and distribution of late seral cover types continues (Klemmedson and Tiedemann 1998). However, we believe that both forbs and grasses are important components.

The ability of many sites to again support the late seral

mixture of species remains problematical. Heavy grazing by

sheep in the last decades of the 19th century depleted the

vegetation and subsequently much, perhaps all, of the A soil

horizon was lost to erosion (Reynolds 1911; Klemmedson

and Tiedemann 1994). A challenge now is to restore the

native subalpine herblands to protect subalpine watersheds, build soil, and help the systems operate more naturally. Both Mr. Monsen and Dr. Winward think this will be

difficult but envision possibilities perhaps by seeding native

species on the sites with the best soil-moisture relationships

(Lewis 1993; Monsen 1997; Winward 1998). The loss of soils

and subsequent drying out of the remaining soil profile has

lead to irruptions of populations of mountain tarweed (Madia

glomerata). We believe that the best way to combat this

problem is to restore the native herbaceous vegetation;

mountain tarweed is a native plant thought to have been an

innocuous, inconspicuous component of the pristine vegetation. Currently mountain tarweed dominates thousands

of acres on the Wasatch Plateau and other high elevation

Intermountain areas. Prominent species of the Wasatch

Plateau herblands include: Rydberg penstemon (Penstemon rydbergii) and other Penstemenon species, sticky geranium (Geranium viscosissimum), showy daisy (Erigeron

speciosus), Indian paintbrush (Castilleja spp.), silky lupine

(Lupinus sereceus), showy goldeneye (Viguiera multiflora),

American vetch (Vicia americana), Louisiana sagewort

(Artemisia ludoviciana ssp. incompta), cinquefoil (Potentilla ssp.), western yarrow (Achillea millefolium), leafy

jacobsladder (Polemonium folioissimum), Pacific aster (Aster chilensis), Letterman’s needlegrass (Stipa lettermanii),

and many other species (Ellison 1954; Lewis 1993; Monsen

1997; Winward 1998).

Stop 8: Seely Creek Overlook (Wasatch

Plateau Summit)

This stop overlooks vistas into the Basin and Range

country to the west and the Colorado Plateau to the east. It

is about 1 mile (1.6 km) above the last stop at an elevation of

about 10,200 ft (3,110 m). Dr. Alma Winward and Mr. Robert

Thompson continued to lead a discussion on the extent and

importance of the tall forb community. From this site the

large extent of the relatively flat and accessible nature of the

country is visible. It is apparent why the Wasatch Plateau

was so attractive, even inviting to exploitive overgrazing by

the early settlers and by migrant sheep herds that had rail

access at lower elevations from both the north and south.

Intermixed here and there among the herbaceous vegetation

are the wind-sculpted, krumholtz-like spruce-fir-common

juniper (Juniperus communis) clumps bearing witness to

winter winds and blizzards that frequent this high country.

Mr. Thompson has worked in this area for nearly 50 years.

He shared with us his insights on the vegetative complexity

including community interfaces and ecotones. He is in the

process of classifying the many plant communities on the

Wasatch Plateau. Below the site immediately to the east a

system of collection canals or ditches are visible. These

capture snow melt and transfer water via tunnels to the

Sanpete side of the plateau; that project speaks to the

importance of water in the arid landscapes below.

Concluding Statement ___________

The field trip emphasized the dynamic character of vegetation communities in the topographical and geologically

diverse landscapes of the Wasatch Mountains (Salt Creek

Canyon) and the Wasatch Plateau (Great Basin Experimental Range). It also featured past and ongoing research and

management.

Acknowledgments ______________

The success of the field tour was made possible by many

who helped. We thank the discussion leaders at each stop for

their advance preparations and lucid explanations and the

van drivers from Snow College’s GBEEC and the Utah

Division of Wildlife Resources’ Great Basin Research Station. We especially thank Dave Lanier and his staff of

GBEEC, Scott Walker of Utah Division of Wildlife Resources’ Great Basin Research Center, and Gary Jorgensen

of the Rocky Mountain Research Station’s Great Basin

Experimental Range for their timely and pleasant logistical

assistance. Hellmut Doelling helped us substantially with

the geological portion of an earlier draft of the manuscript

and kindly provided a review of that draft as did Gary

Jorgensen, Stan Kitchen, and Ty Robinson.

References _____________________

Alexander, R. R.; Shepperd, W. D. 1990. Picea engelmannii Parry ex

Engelm. Engelmann spruce. In: Burns, R. M.; Honkala, B. H,

tech. coords. Silvics of North America, volume 1, conifers. Agriculture Handbook 654. Washington, DC: U.S. Department of Agriculture, Forest Service:187-203.

Ashcroft, G. L.; Jensen, D. T.; Brown, J. L. 1992. Utah climate.

Logan, UT: Utah Climate Center, Utah State University. 127 p.

Baker, F. S.; Korstian, C. F. 1931. Suitability of brush lands in the

Intermountain region for the growth of natural or planted western yellow pine forests. Tech. Bull. 256. Washington, DC: U.S.

Department of Agriculture, Forest Service. 83 p.

Banks, R. L. 1991. Provisional geologic map of the Fountain Green

North quadrangle, Sanpete and Juab Counties, Utah. Utah

Geological and Mineral Survey Map M-134. Salt Lake City, UT:

Utah Department of Natural Resources, Utah Geological Survey.

21 p., 2 plates, scale 1:24,000.
USDA Forest Service Proceedings RMRS-P-11. 1999 299

Bartos, D. L.; Campbell, R. B., Jr. 1998. Decline of quaking aspen in

the Interior West—examples from Utah. Rangelands. 20: 17-24.

Biek, R. F. 1991. Provisional geologic map of the Nephi quadrangle,

Juab County, Utah. Utah Geological and Mineral Survey Map

M-137. Salt Lake City, UT: Utah Department of Natural Resources, Utah Geological Survey. 21 p., 2 plates, scale 1:24,000.

Blauer, A. C.; Plummer, A. P.; McArthur, E. D.; Stevens, R.; Giunta,

B. C. 1975. Characteristics and hybridization of important Intermountain shrubs. I. rose family. Res. Pap. INT-169. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 36 p.

Chronic, H. 1990. Roadside geology of Utah. Missoula, MT: Mountain Press Publishing Company. 326 p.

Ellison, L. 1954. Subalpine vegetation of the Wasatch Plateau,

Utah. Ecological Monographs. 24: 89-184.

Ellison, L. 1960. Influence of grazing on plant succession on rangelands. Botanical Review. 26: 1-78.

Freeman, D. C.; Miglia, K. J.; McArthur, E. D.; Graham, J. H.;

Wang, H. [These proceedings]. Narrow hybrid zone between two

subspecies of big sagebrush (Artemisia tridentata: Asteraceae).

X. performance in reciprocal transplant gardens.

Freeman, D. C.; Turner, W. A.; McArthur, E. D.; Graham, J. H. 1991.

The characterization of a narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata). American Journal of Botany. 78: 805-815.

Graham, J. H.; Freeman, D. C.; McArthur, E. D. 1995. Narrow

hybrid zone between two subspecies of big sagebrush (Artemisia

tridentata: Asteraceae): II. selection gradients and hybrid fitness.

American Journal of Botany. 82: 709-716.

Graham, J. H.; Freeman, D. C.; Wang, H.; McArthur, E. D. [These

proceedings]. Ecological analysis of the big sagebrush hybrid

zone.

Hintze, L. F. 1988. Geologic history of Utah. Brigham Young

University Geology Studies Special Publication 7. Provo, UT:

Department of Geology, Brigham Young University. 202 p.

Keck, W. M. 1972. Great Basin Station—sixty years of progress in

range and watershed research. Res. Pap. INT-118. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 48 p.

Klemmedson, J. O.; Tiedemann, A. R. 1994. Soil and vegetation

development in an abandoned sheep corral on degraded subalpine rangeland. Great Basin Naturalist. 54: 301-312.

Klemmedson, J. O.; Tiedemann, A. R. 1998. Soil-vegetation relations of recovering subalpine range of the Wasatch Plateau. Great

Basin Naturalist. 58: 352-362.

Lewis, M. E. 1993. Successional changes in the tall forb type—

Wasatch Plateau. Report. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Region. 75 p.

McArthur, E. D.; Monsen, S. B. 1996. Great Basin Experimental

Range. In: Schmidt, W. C.; Friede, J. L., comps. Experimental

forests, ranges, and watersheds in the northern Rocky Mountains: a compendium of outdoor laboratories in Utah, Idaho, and

Montana. Gen. Tech. Rep. INT-GTR-334. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research

Station: 23-30.

McArthur, E. D.; Sanderson, S. C. [These proceedings]. Ecotones:

introduction, scale and big sagebrush example.

McArthur, E. D.; Welch, B. L.; Sanderson, S. C. 1988. Natural and

artificial hybridization between big sagebrush (Artemisia tridentata) subspecies. Journal of Heredity. 79: 268-276.

McCarty, E. C.; Price, R. 1942. Growth and carbohydrate content of

important mountain forage plants in central Utah as affected by

clipping and grazing. Tech. Bull. 818. Washington DC: U.S.

Department of Agriculture, Forest Service. 51 p.

Meeuwig, R. O. 1960. Watersheds A and B—a study of surface runoff

and erosion in the subalpine range of central Utah. Journal of

Forestry. 58: 556-560.

Monsen, S. B. 1997. Patterns of natural succession within subalpine

herblands of the Wasatch Plateau, Great Basin Research Station,

Utah. Abstract 36. In: paper/poster abstracts 24th Annual Natural

Areas Association Conference and Exotic Pest Plant Council

Conference; 1997 August 27-30; Portland, OR. Portland OR:

National Areas Association: 38.

Plummer, A. P.; Christensen, D. R.; Monsen, S. B. 1968. Restoring

big-game ranges in Utah. Publication 68-3. Salt Lake City, UT:

Utah Division of Fish and Game. 183 p.

Price, R.; Evans, R. B. 1937. Climate of the west front of the Wasatch

Plateau in central Utah. Monthly Weather Review. 65: 291-301.

Reynolds, R. V. R. 1911. Grazing and floods: a study of conditions in

the Manti National Forest, Utah. Bulletin 91. Washington DC:

U.S. Department of Agriculture, Forest Service. 16 p.

Richardson, E. A.; Ashcroft, G. L.; Westbrook, J. K. 1981. Precipitation. In: Greer, D. C.; Wahlquist, W. L.; Peterson, G. B., eds. Atlas

of Utah. Provo, UT: Weber State College and Brigham Young

University Press: 66-70.

Sampson, A. W. 1919. Plant succession in relation to range management. Bull. 741. Washington, DC: U.S. Department of Agriculture, Forest Service. 76 p.

Sampson, A. W. 1923. Range and pasture management. New York,

NY: John Wiley and Sons. 421 p.

Sampson, A. W. 1924. Native American forage plants. New York,

NY: John Wiley and Sons. 435 p.

Spieker, E. M. 1949. Guidebook to the geology of Utah, number 4:

the transition between the Colorado Plateaus and the Great

Basin of central Utah. Salt Lake City, UT: Utah Geological

Society. 106 p. + map, scale 1: 39,600.

Stevens, R.; McArthur, E. D. 1974. A simple field technique for

identification of some sagebrush taxa. Journal of Range Management. 27: 325-326.

Stevens, R.: McArthur, E. D.; Davis, J. N. 1992. Reevaluation of

vegetative cover changes, erosion, and sedimentation of two

watersheds, 1912-1983. In: Clary, W. P.; McArthur, E. D.;

Bedunah, D.; Wambolt, C. L., comps. Proceedings—symposium

on ecology and management of riparian shrub communities; 1991

May 29-31; Sun Valley, ID. Gen. Tech. Rep. INT-289. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Research Station: 123-128.

Trickler, D. L.; Hall, D. T. 1984. Soil survey of Fairfield-Nephi area,

Utah; parts of Juab, Sanpete, and Utah Counties. Salt Lake City,

UT: U.S. Department of Agriculture, Soil Conservation Service,

Utah State Office. 361 p. + 130 maps.

Walker, S. C.; Mann, D. K.; McArthur, E. D. 1996. Plant community

changes over 54 years within the Great Basin Experimental

Range, Manti-La Sal National Forest. In: Barrow, J. R; McArthur

E. D.; Sosebee, R. E.; Tausch, R. J., comps. Proceedings: shrubland

ecosystem dynamics in a chainging environment; 1995 May 23-

25; Las Cruces, NM. Gen. Tech. Rep. INT-GTR-338. Odgen, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Research Station: 66-68.

Wang, Z. 1996. Ecological analysis of a stable hybrid zone between

two big sagebrush subspecies (Artemisia tridentata ssp. tridentata and A. t. ssp. vaseyana) in Utah. Detroit, MI: Wayne State

University, Department of Biological Sciences. 132 p. Ph.D.

dissertation.

Winward, A. H. 1998. The tall forb type. Report. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Region. 6 p.

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