Proceedings:

Shrubland Dynamics—Fire and Water

Lubbock, TX, August 10-12, 2004

United States Department of Agriculture

Forest Service

Rocky Mountain Research Station

Proceedings RMRS-P-47

July 2007
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Sosebee, Ronald E.; Wester, David B.; Britton, Carlton M.; McArthur, E. Durant; Kitchen, Stanley G., comps. 

2007. Proceedings: Shrubland dynamics—fire and water; 2004 August 10-12; Lubbock, TX. Proceedings 

RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station. 173 p.

Abstract

The 26 papers in these proceedings are divided into five sections. The first two sections are an introduction 

and a plenary session that introduce the principles and role of the shrub life-form in the High Plains, including 

the changing dynamics of shrublands and grasslands during the last four plus centuries. The remaining three 

sections are devoted to: fire, both prescribed fire and wildfire, in shrublands and grassland-shrubland interfaces; water and ecophysiology shrubland ecosystems; and the ecology and population biology of several shrub 

species.

Keywords: wildland shrubs, fire, water, ecophysiology, ecology

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.

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. 
Proceedings: 

Shrubland Dynamics—Fire and Water

Lubbock, TX, August 10-12, 2004

Wyoming Big Sagebrush, Sweetwater County, Wyoming

Photo by E. Durant McArthur

Compilers

Ronald E. Sosebee, Department of Range, Wildlife and Fisheries Management, Texas Tech University, 

Lubbock, TX

David B. Wester, Department of Range, Wildlife and Fisheries Management, Texas Tech University, 

Lubbock, TX

Carlton M. Britton, Department of Range, Wildlife and Fisheries Management, Texas Tech University, 

Lubbock, TX

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

Shrub Sciences Laboratory, Provo, UT

Stanley G. Kitchen, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 

Shrub Sciences Laboratory, Provo, UT
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, Jason L. Vernon

University of California, Los Angeles, Philip W. Rundel

Colorado State University, Fort 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, Barry L. Perryman

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, Vernon, R. J. (Jim) Ansley

Texas Tech University, Lubbock, David B. Wester

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

D. Terrance Booth

USDA Agricultural Research Service, Jordana Experimental Range, Las Cruces, New Mexico, Mary E. Lucero

USDA Agricultural Research Service, Forage and Range Laboratory, Logan, Utah, Thomas A. Monaco

USDA Forest Service, Rocky Mountain Research Station, Forestry Sciences Laboratory, Albuquerque, 

New Mexico, Rosemary L. Pendleton

USDA Forest Service, Rocky Mountain Research Station, 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. Wachochki

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

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

University of Wyoming, Laramie, Ann L. Hild

*Charter members

The Shrub Research Consortium (SRC) 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 charter had three principal objectives: 

(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 13th in the series. The 12 previous symposia 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. 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.

ii
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 Servcie, 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 Servcie 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. 179 p. A few 

copies are available from the Rocky Mountain Research Station; otherwise available from National 

Technical Information Service as document PB 90-228578 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 INT256. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 

183 p. Available from 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.

Tenth: McArthur, E. D.; Ostler, W. K.; Wambolt, C. L., compilers. 1999. Proceedings: shrubland ecosystem 

ecotones; 1998 August 12-14; Ephraim, UT. Proceedings RMRS-P-11. Ogden, UT: U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research Station. 299 p. Available from the Rocky 

Mountain Research Station. 

Eleventh: McArthur, E. D.; Fairbanks, D. J, compilers. 2001. Shrubland ecosystem genetics and biodiversity: 

proceedings; 2000 June 13-15; Provo, UT. Proceedings RMRS-P-21. Ogden, UT: U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research Station. 365 p. Available from the Rocky 

Mountain Research Station.

Twelfth: Hild, A. L.; Shaw, N. L.; Meyer, S. E.; Booth, D. T.; McArthur, E. D., compilers. 2004. Seed and soil 

dynamics in shrubland ecosystems: proceedings; 2002 August 12-16; Laramie, WY. Proceedings 

RMRS-P-31. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 216 p. Available from the Rocky Mountain Research Station.

iii
iv

Contents

Introduction..........................................................................................................1

Plenary Session...................................................................................................3

Shrubland Ecosystems: Importance, Distinguishing Characteristics, and Dynamics ... 3

E. Durant McArthur and Stanley G. Kitchen

Grassland Ecosystems of the Llano Estacado .................................................................. 11

Eileen Johnson

The Southern High Plains: A History of Vegetation, 1540 to Present ............................ 24

David B. Wester

Prescribed Fire to Restore Shrublands to Grasslands..................................................... 48

Carlton M. Britton, David B. Wester and Brent J. Racher

Role of Summer Prescribed Fire to Manage Shrub-invaded Grasslands...................... 52

Charles A. Taylor

Fire Session

Management of South Texas Shrublands with Prescribed Fire...................................... 57

C. Wayne Hanselka, D. Lynn Drawe, and D.C. Ruthven, III

Hydrology, Erosion, Plant, and Soil Relationships after Rangeland Wildfire............... 62

Kenneth E. Spaeth, Frederick B. Pierson, Peter R. Robichaud and Corey A. Moffet

Using Relative Humidity to Predict Spotfire Probability on Prescribed Burns............ 69

John R. Weir

Mesquite Cover Responses in Rotational Grazing/Prescribed Fire Management 

Systems: Landscape Assessment Using Aerial Images .................................................... 73

R. J. Ansley, W. E. Pinchak and W. R. Teague

Modeling Erosion on Steep Sagebrush Rangeland Before and After Prescribed Fire . 79

Corey A. Moffet, Frederick B. Pierson and Kenneth E. Spaeth

Water and Ecophysiology Session

Germination Responses to Temperature and Soil Moisture in Three Species of the 

Subfamily Caragana and Their Implications Toward Restoration in Loess-gully 

Region, China ...................................................................................................................... 85

Zhao Xiaoying and Ren Jizhou

Saltcedar Control and Water Salvage on the Pecos River, Texas, 1999 to 2003 ............ 89

Charles R. Hart, Larry D. White, Alyson McDonald and Zhuping Sheng

Mesquite Root Distribution and Water Use Efficiency in Response to Long-term 

Soil Moisture Manipulations.............................................................................................. 96

R. J. Ansley, T. W. Boutton and P. W. Jacoby

Response of Seedlings of Two Hypogeal Brush Species to CO2 Enrichment............... 104

Charles R. Tischler, Justin D. Derner, H. Wayne Polley and Hyrum B. Johnson

Shrub Biomass Production Following Simulated Herbivory: A Test of the 

Compensatory Growth Hypothesis.................................................................................. 107

Terri B. Teaschner and Timothy E. Fulbright

Soil Responses to Human Recreational Activities in a Blackbrush (Coleogyne 

ramosissima Torr.) Shrubland .......................................................................................... 112

Simon A. Lei

Influence of Shrubs on Soil Chemical Properties in Alxa Desert Steppe, China......... 117

Hua Fu, Shifang Pei, Yaming Chen and Changgui Wan
v

Fungal Genomes that Influence Basic Physiological Processes of Black Grama 

and Fourwing Saltbush in Arid Southwestern Rangelands .......................................... 123

J.R. Barrow, M. Lucero, P. Osuna-Avila, I. Reyes-Vera and R.E. Aaltonen

Ecology and Population Biology Session

Estimating Aboveground Biomass of Mariola (Parthenium incanum) from 

Plant Dimensions............................................................................................................... 132

Carlos Villalobos

Shrub Establishment in the Presence of Cheatgrass: The Effect of 

Soil Microorganisms ......................................................................................................... 136

Rosemary L. Pendleton, Burton K. Pendleton, Steven D. Warren, Jeffrey R. Johansen and Larry L. St. Clair

Differences in Volatile Profiles Between Populations of Ceratoides lanata var. 

subspinosa (Rydb.) J.T. Howell ........................................................................................ 142

Mary Lucero, Rick Estell, Dean Anderson, Ed Fredrickson and Marta Remmenga

Emergence and Growth of Four Winterfat Accessions in the Presence of the 

Exotic Annual Cheatgrass ................................................................................................ 147

Ann L. Hild, Jennifer M. Muscha and Nancy L. Shaw

Seed Germination Biology of Intermountain Populations of Fourwing Saltbush 

(Atriplex canescens: Chenopodiaceae)............................................................................. 153

Susan E. Meyer and Stephanie L. Carlson

Efficacy of Exclosures in Conserving Local Shrub Biodiversity in Xeric Sandy 

Grassland, Inner Mongolia, China .................................................................................. 163

Feng-Rui Li, Zhi-Yu Zhou, Li-Ya Zhao, Ai-Sheng Zhang and Ling-Fen Kang

Intraspecific Variation in Leaf Anatomy of Blackbrush (Coleogyne 

ramosissima Torr.) ............................................................................................................. 170

Simon A. Lei
USDA Forest Service RMRS-P-47. 2007 1

The Southern High Plains of Texas (also known as the 

Llano Estacado) are in the southernmost subdivision of 

the High Plains section of the Great Plains Physiographic 

Province. Most of the Southern Great Plains is comprised of 

upland sites that were once grasslands dominated mostly by 

shortgrass plains that supported large herds of native buffalo. 

However, topographic diversity on the Southern High Plains 

is subtle and important: sandy soils were characterized by tall 

grass prairie or sand shinnery oak; major drainages (or draws) 

that cross the Southern High Plains from the northwest to 

the southeast provide the setting for plant communities that 

support considerable shrub diversity; and the escarpments that 

border the Southern High Plains historically have supported a 

rich complex of woody species.

Following European settlement in the 1500s, the grasslands 

of the Southern High Plains underwent vegetation change 

characterized by invasion by shrubs and trees. Invasion of 

woody plants cannot be attributed to any single environmental 

factor, although overgrazing by domestic livestock is often 

cited as the reason shrubs and trees have become dominant 

in the grasslands. Weather cycles and changing fire regimes 

have been perhaps as important as any other factor in contributing to the increase in woody plants. Woody plants are now a 

dominant species that must be reckoned with if the Southern 

Great Plains is ever again to become grassland.

The C3

, warm-season shrubs and trees, mostly Juniperus

sp. and honey mesquite (Prosopis glandulosa), are commonly 

thought of as “using” large quantities of water that would 

otherwise be available for grass production if the woody 

plants were not present. Certainly, woody plants must have 

water to live just as does any other plant. However, the amount 

of water that is consumed by invasive woody plants is often 

misunderstood and/or misrepresented. Although many of the 

invasive woody plants have been referred to as “extravagant” 

water “users” or water “thieves,” these plants growing on 

dry sites (for example, shallow soils, upland sites, sloping 

hillsides) usually do not have access to large quantities of 

soil water. Therefore, like their grass counterparts, they are 

adapted to the semi-arid conditions under which they have 

evolved.

Fire is a natural part of the environmental conditions of 

the southern Great Plains. However, man has changed the fire 

regime and vegetation changes that this area has experienced 

are also a consequence of changes in the historical fire regime. 

Some ecologists have suggested that there is no such thing as 

a grassland climax. In this view, fire played an important role 

either in eliminating woody species within the grasslands or in 

keeping woody plants suppressed, allowing grasses to dominate.

The theme of the Thirteenth Wildland Shrub Symposium 

was developed to examine the “pristine” vegetation of the 

Southern High Plains of Texas and the use of controlled fire, 

or prescribed burns, to manipulate the woody vegetation and 

return the grasslands to the more desirable grasses that once 

dominated the region. We also included a review of water use 

by woody vegetation from a scientific rather than an emotional 

viewpoint that is often found in popular opinion. As always, a 

wider array of topics was encouraged to broaden one’s knowledge of shrub dominated rangelands.

In addition to both oral and poster presentations of scientific data on shrublands, a field trip provided an opportunity 

to view shrub invasion of some of the formerly- dominated 

grasslands of the Southern High Plains and Panhandle of 

Texas. The field trip included stops with presentations at a 

saltcedar (Tamarix gallica)-infested riparian site, a sand shinnery oak (Quercus havardii)-dominated rangeland, and a 

mesquite-dominated grassland. The final stop of the field tour 

provided an opportunity to view native shrub communities on 

an escarpment along tributaries of the Red River in Texas at 

Caprock Canyons State Park.

The symposium provided an excellent opportunity for 

presentations of scientific changes in vegetation throughout 

geologic and recorded history of the Southern High Plains and 

an opportunity to see some of these changes in the field. It also 

provided an opportunity to broaden our knowledge concerning 

shrub ecology and general shrub biology. It was an excellent 

educational experience.

We would like to extend our thanks to the landowners who 

graciously allowed us to visit their properties. Special thanks 

go to the staff at Caprock Canyons State Park for hosting our 

final stop and for providing a pleasant site for a delightful 

meal at the end of our trip. We would also like to thank the 

presenters and moderators whose participation in this symposium made it a success.

Ronald E. Sosebee and David B. Wester

Introduction
2 USDA Forest Service RMRS-P-47. 2007
USDA Forest Service RMRS-P-47. 2007 3

Plenary Session

Introduction

Shrubs and shrubland ecosystems are valued differently by 

natural resource professionals and pastoralists depending on 

their backgrounds, experience, geographical location, and the 

economic impact of those shrublands on their livelihood. The 

contrasting values or points of views about shrubs were stated 

by Everist (1972) in the context of Australian shrublands, 

which could be extrapolated generally: “wildland shrubs have 

greatest importance on ... grazing lands, mostly as useful 

species but sometimes as invaders of and competitors with 

plants (more useful) ... for animal ... survival or productivity.” In North America, shrubs have been referred to as a 

neglected resource (McKell 1975; 1989) or contrastingly as 

an impediment to productive land use practice (Herbel 1979). 

In Africa and Asia, their value has long been appreciated and 

often over-exploited (Badresa and Moore 1982; CloudsleyThompson 1974). In Australia, shrubs have been recognized 

alternately as valuable, sustainable forage and as a system that 

is more productive when it is converted to a disclimax herbaceous state (Williams and Oxley 1979).

The importance of shrub species and shrubland ecosystems gained considerable impetus about 30 years ago with 

the establishment of the U.S. Forest Service Shrub Sciences 

Laboratory and a series of workshops and symposia that 

preceded and accompanied the establishment of the Laboratory 

(McKell and others 1972, Stutz 1976). Since its charter in 

1983 (McArthur 2001; Tiedemann 1984), the Shrub Research 

Consortium (SRC), lead by the project leaders of the Shrub 

Sciences Laboratory, has sponsored a series of symposia on 

the biology and management of shrubland ecosystems. The 

SRC symposia have generally focused on the positive values 

of shrubs in shrubland ecosystems but have also addressed 

management issues where shrubs were considered as 

Shrubland Ecosystems: Importance, Distinguishing 

Characteristics, and Dynamics

Abstract: The importance of shrub species and shrubland ecosystems gained considerable 

impetus about 30 years ago with the establishment of the USDA Forest Service Shrub 

Sciences Laboratory and a series of workshops and symposia that preceded and accompanied 

the establishment of the Laboratory. Since that time, the Shrub Research Consortium and 

other forums have addressed various aspects of wildland shrub ecosystem biology and 

management. Shrubs occur in most vegetation types but are dominants only in those 

habitats that place plants under considerable stress. Three primary, often interacting factors, 

that promote shrubby habitats are drought or aridity, nutrient-poor soils, and fire. Other stress 

factors that may also be interactive that contribute to the shrubby habitat are shade, poor soil 

aeration, winter cold, short growing season, and wind. Most of these conditions frequently 

occur in semi-arid, temperate, continental climates. The principal shrubland ecosystems 

of the western United States are sagebrush, chaparral, mountain brush, coastal sage, 

blackbrush, salt desert, creosote bush, palo verde-cactus, mesquite, ceniza shrub, shinnery, 

and sand-sage prairie. Similar as well as distinctively different shrubland ecosystems occur 

at other locations around the world. Shrubland ecosystems have different human and wildlife 

values and have, and are, subject to changing environmental conditions including different 

fire regimes. Fragmentations of these ecosystems, for example the sagebrush ecosystems, 

are of concern since some ecosystem components are at critical risk. Shrubland ecosystem 

changes have become more apparent in recent decades posing significant ecological and 

management problems. The challenge for land managers and ecologists is to understand 

the fluidity of the ecosystems and to be proactive and sensitive to the needs of healthy, 

productive landscapes.

E. Durant McArthur1

Stanley G. Kitchen2

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
4 USDA Forest Service RMRS-P-47. 2007

ecological or management problems (table 1). The two 

symposia that focused more on shrub control management 

issues rather than positive values were numbers 9 and 13 in 

the series which were held in the Southwest where shrubs 

have displaced grasses in historic time over large acreages 

(Barrow and others 1996; Herbal 1979, Sosebee and others—

this proceedings). A series of wildland shrub workshops, 

each emphasizing various shrub taxa and communities (especially for land management professionals), were held in both 

Wyoming (1972-1988) and Utah (1981-1991)—see Fisser 

(1990), Johnson (1990), and McArthur (2001) for lists of these 

proceeding publications and more details on the process.

Although shrubs are an important and widespread life 

form, they are difficult to circumscribe. Individual species 

may be shrubs in some circumstances and trees in other 

circumstances. Other species may alternatively be shrubs or 

herbaceous plants depending on certain circumstances, for 

example, climate or soil fertility (Francis 2004). Shrubs do 

not comprise a cohesive phylogenetic unit, but derive from 

many lineages (McArthur 1989; Stebbins 1972; 1976). The 

shrub habit is more of a growth form than a phylogenetic unit. 

However, some taxonomic lines are wholly shrubby as might 

be expected depending upon the point of establishment of the 

shrub growth habit (table 2). Simmonds (1976) identified 168 

principal crop plants of which 12 are shrubs. These 12 crop 

shrubs (tea, hazel, blueberries, cassava, currants and gooseberries, wattles, roselle, guava, pomegranate, raspberries and 

blackberries, coffees, and peppers) represent 12 different families (McArthur 1989). Francis (2004) analyzed the Natural 

Resources Conservation Service (USDA 2003) “Plants” 

database and determined that there were 5,281 species in 

the United States and territories that carry the growth habit 

designations “shrub” or “sub-shrub.” These species represent 166 families (table 3). Note that the West (especially 

the Southwest), Southeast, Hawaii, Puerto Rico, and Virgin 

Islands are more species-rich than other areas, such as Alaska, 

the North Central States, and New England.

Shrubs occur in many vegetation types. Shrubs ordinarily 

have more than one main stem caused by branching below or 

above ground level, are perennial, and are lignified (Francis 

2004). Often shrubs are thought of as midway between a tree 

and herb with adaptive advantages of both life forms that 

sustain the shrub habit in some unique situations (Stutz 1989). 

Shrubs have near relatives that are herbs and/or trees (table 2). 

Shrubs are dominant, but for the most part, only in habitats 

that place plants under considerable stress such as drought 

or aridity, nutrient-poor soils, fire, shade, poor soil aeration, 

winter cold, short growing seasons, and wind (McArthur 1989; 

Stebbins 1972; 1975). Many of these conditions are met in 

semi-arid continental climates (McArthur 1989; McKell and 

others 1972). For example, shrubs are widely distributed in the 

United States (fig. 1), but are dominants from a continentalscale perspective in the semiarid west (McArthur 1984). 

Table 4 is an analysis of shrub importance as determined from 

Küchler’s (1964) map and manual. Significant dominance of 

shrubs is manifest only in the western shrublands and western 

shrub and grasslands. Shrubs as subdominants are important to a greater or lesser degree in nearly all vegetative types 

(table 4). The same general patterns of shrubs rising to dominance are evident in other semiarid and arid climatic regimes 

on other continents (Le Honérou 2000; McKell 1989; McKell 

and others 1972; Walter and Box 1976; West 1983; Wilson 

and Graetz 1979).

We conclude this section with a few comments about some 

shrub species that characterize the western North American 

landscapes. Whereas shrubs are widely distributed and are 

components of many ecosystems and community types, they 

give landscapes their primary character in areas that they 

dominate, such as the interior North American West (Francis 

2004; McArthur 1984; 1989). McArthur (1989) identified 12 

Table 1—Shrub Research Consortium Wildland Shrub Symposia series.

Number Date held Title and location Proceedings publication

1 1982 Research and Management of Bitterbrush and Cliffrose in Western North America Tiedemann and Johnson 1983

 —Salt Lake City, Utah

2 1983 The Biology of Atriplex and related Chenopods—Provo, Utah Tiedemann and others 1984

3 1984 The Biology and Management of Artemisia and Chrysothamnus—Provo, Utah McArthur and Welch 1986

4 1985 Plant—Herbivore Interactions—Snowbird, Utah Provenza and others 1987

5 1987 Shrub Ecophysiology and Biotechnology—Logan, Utah Wallace and others, 1989

6 1989 Cheatgrass Invasion, Shrub Die-off, and other Aspects of Shrub Biology and McArthur and others 1990

 Management—Las Vegas, Nevada

7 1991 Ecology and Management of Riparian Shrub Communities—Sun Valley, Idaho Clary and others 1992

8 1993 Wildland Shrub and Arid Land Restoration— Las Vegas, Nevada Roundy and others 1995

9 1995 Shrubland Ecosystem Dynamics in a Changing Environment—Las Cruces, Barrow and others 1996

 New Mexico

10 1998 Shrubland Ecosystem Ecotones—Ephraim, Utah McArthur and others 1999

11 2000 Shrubland Ecosystem Genetics and Biodiversity—Provo, Utah McArthur and Fairbanks 2001

12 2002 Seed and Soil Dynamics in Shrubland Ecosystems—Laramie, Wyoming Hild and others 2004

13 2004 Shrub Dynamics: Fire and Water—Lubbock, Texas Sosebee and others—this 

 proceedings
USDA Forest Service RMRS-P-47. 2007 5

successful Western North American shrub species complexes 

(table 5). These species complexes demonstrate the variety 

of important entities in widespread and dominant shrubs 

inasmuch as they represent 8 families, a mix of polyploid 

systems versus diploid only chromosome numbers, a mix of 

wind and insect pollination, different degrees of dominance 

in their respective plant communities (table 5). The group is 

primarily outcrossing. The principal shrubland ecosystems of 

the western United States are sagebrush, chaparral, mountain 

brush, coastal sage, blackbrush, salt desert, creosote bush, palo 

verde-cactus, mesquite, ceniza shrub, shinnery, and sand-sage 

prairie (Küchler 1964, McArthur and Ott 1996). As an example 

of these important shrublands, we briefly discuss some of the 

characteristics of sagebrush, an American West icon (fig. 2). 

Sagebrush (the subgenus Tridentatae of Artemisia) occupies 

vast tracts of land west of the 100th meridian west longitude (McArthur and Sanderson 1999). As such, it gives the 

land its character, serves as habitat for resident wildlife, and 

Table 2—Numbers of genera and species including example species and growth forms of selected families (after McArthur 1984 and McArthur 

and Tausch 1995).

Number of species 

from Western Number of species 

Representative Number of shrub United States (World total, all

Familya Genera Generab (all growth forms)c growth forms) Growth habitsd

Anacardiaceae Rhus 1 9 150 S, T

Asteraceae Artemisia

Baccharis

Brickella

Chrysothamnus

Happlopappus

Tetradymia 18 126 2546 H, S

Caprifoliaceae Lonicera

Sambucus

Symporicarpos 5 28 317 S

Chenopodiaceae Atriplex 8 29 441 H, S

Ericaceae Arctostaphylos

Vaccinium 14 82 1211 S, T

Ephedraceae Ephredra 1 10 40 S

Fabaceae Acacia

Dalea

Mimosa 19 70 3276 H, S, T

Fagaceae Quercus 3 20 700 S, T

Fouquieriaceae Fouquieria 1 1 9 S, T

Lamiaceae Salvia 5 24 1175 H, S

Polygonaceae Eriogonum 1 20 250 H, S

Rhamnaceae Ceanothus 6 68 295 S

Rosaceae Amelanchier

Prunus

Rosa

Rubus 23 81 760 H, S, T

Scrophulariaceae Mimulus

Penstemon 4 22 454 H, S

Zygophyllaceae Larrea 2 2 22 S

a

 Families selected on the basis of at least one species included by a dominant by Küchler 1964.

b

 Number of shrub genera in the United States west of 100° W longitude.

c

 Total number of species in the United States west of 100° W longitude.

d

 Growth habits of congeneric relatives: H = herbs, S = shrubs, T = trees.

Table 3—Most important families with shrub representatives in the 

United States and its territories (after Francis 2004).a

Family Number of shrub species

Asteraceae 618

Rosaceae 510

Fabaceae 342

Cactaceae 193

Ericaceae 189

Scrophularaceae 182

Rubiaceae 165

Malvaceae 148

Euphorbiaceae 128

Lamiaceae 124

Polygonaceae 123

Companulaceae 112

Boraginaceae 106

Ramnaceae 103

a There are 152 additional families with from one to 82 species each.
6 USDA Forest Service RMRS-P-47. 2007

contributes to livestock ranges (McArthur and Stevens 2004; 

Welch in press). Other Artemisia species of other subgenera 

are important landscape dominants in Eurasia (Vallès and 

McArthur 2001; West 1983). For additional details on western 

North American dominant shrub species complexes we 

recommend the first three wildand shrub symposium proceedings—McArthur and Welch (1986), Tiedeman and Johnson 

(1983), and Tiedemann and others (1984) (table 1); Francis 

(2004); and chapters on shrub species in Monsen and others 

(2004a)—McArthur and Monsen (2004), McArthur and 

Stevens (2004), Monsen and others (2004b), and Shaw and 

others (2004).

Dynamics

Like all plant species, communities, and ecosystems, shrub 

species and their attendant plant communities or ecosystems 

are not static. Evolutionary forces and environmental change 

have been active over geological time in leading to present day 

species, communities, and ecosystems. Two recent wildland 

Figure 1. Numbers of shrub species in the States and Territories of the United States (Francis 2004).

Table 4—Dominant and subdominant shrub species occurrence in the principal vegetative types of the conterminous United States (after 

McArthur 1989).

Dominant species Subdominant species

All species Shrubs All species Shrubs All shrubs

Vegetative type N + se % + se % ( + se)

Western needleleaf forests 24 2.3 + 0.2 0.04 1.7 10.0 + 1.1 3.9 39.0 3.9 + 0.6

Western broadleaf forests 3 1.3 + 0.3 0 0 10.0 + 2.3 3.7 37.0 3.7 + 1.8

Western broadleaf and needleleaf forests 5 5.6 + 0.7 0.2 3.6 16.4 + 3.0 7.6 46.3 7.8 + 2.1

Western shrublands 13 2.7 + 0.6 1.9 70.4 13.6 + 1.9 8.7 63.9 10.6 + 1.7

Western grasslands 8 3.6 + 0.8 0 0 11.6 + 2.0 1.6 13.8 1.6 + 0.6

Western shrubs and grasslands 6 3.2 + 0.4 1.3 40.6 17.0 + 2.5 3.8 22.4 5.2 + 1.0

Central and eastern grasslands 17 2.9 + 0.3 0 0 14.2 + 1.4 1.4 9.8 1.4 + 0.4

Central and eastern grasslands and forests 15 3.4 + 0.5 0 0 17.2 + 2.5 1.7 9.9 1.7 + 0.3

Eastern needleleaf forests 5 2.4 + 0.2 0 0 6.8 + 0.8 2.0 29.4 2.0 + 0.7

Eastern broadleaf forests 8 3.1 + 0.7 0 0 14.9 + 2.1 1.1 7.4 1.1 + 0.7

Eastern broadleaf and needleleaf forests 11 4.0 + 0.5 0.09 2.2 13.4 + 2.3 1.9 14.2 2.0 + 0.4

Total 115 — — — — — — —

3.1 + 0.5 0.3 9.7 13.2 + 1.9 3.4 25.8 3.7 + 0.9
USDA Forest Service RMRS-P-47. 2007 7

Figure 2. Wyoming big sagebrush, Sweetwater County, Wyoming (photo by E. Durant McArthur).

Table 5—Twelve successful Western North American shrub complexes (McArthur 1989)a.

Shrub complex Polyploidy Breeding system Dominance characteristics

Manzinata—Artostaphylos spp. (Ericaceae) yes Outcrossing, insect Many dominant species in communities

Sagebrushes—subgenus Tridentatae of Artemisia yes Outcrossing (limited Dominant by itself with occasional 

(Asteraceae) self), wind subordinate co-dominants

Saltbushes—Atriplex spp. (Chenopodiaceae) yes Outcrossing, wind Usually dominant by self or with other congeners

 and chenopodsb

Buckbrushes—Ceanothus spp. (Rhamnaceae) no Outcrossing (limited Many dominant species in communities

 self in some 

 species), insect

Mountain mahoganies—Cercocarpos spp. no Outcrossing (limited Few dominant species aside from Cercocarpus

(Rosaceae) amount of self), 

 wind

Rabbitbrushes—Chrysothamnus spp. (Asteraceae)c no Self (limited Usually a sub or co-dominant

 outcrossing), insect

Blackbrush—Coleogyne (Rosaceae) no Outcrossing, windd Usually dominant by self

Cliffrose and bitterbrush—Purshia spp.e (Rosaceae) no Outcrossing, insect Usually a sub or co-dominant

Mormon tea or joint fir—Ephreda spp. (Ephredaceae) no Outcrossing, wind Usually a co-dominant

Bursage—Ambrosia (Asteraceae) yes Outcrossing, wind Usually a co-dominant

Creosote bush—Larrea (Zygophyllaceae) yes Outcrossing, insect Usually a co-dominant

Oakbrush—Quercus spp. (Fagaceae) no Outcrossing, wind Usually a co-dominant

a Documenting references in McArthur (1989) except as noted in additional footnotes.

b Including greasewood (Sarcobatus spp.) which has been recently segregated into its own family (Sanderson and others 1999). c Taxonomy in the rabbitbrushes is under scrunity; some or all are alternately treated as Ericameria (Anderson 1995). d Confirmed by Pendleton and Pendleton (1998).

e The former independent generic standing of cliffrose (Cowania) has been submerged into Purshia (Hendrickson 1986; Reichenbacher 1994)
8 USDA Forest Service RMRS-P-47. 2007

shrub symposia addressed these issues: McArthur and Fairbanks 

(2001), Shrubland Ecosystem Genetics and Biodiversity and 

Barrow and others (1996), Shrubland Ecosystem Dynamics in 

a Changing Environment. Johnson (this proceeding) addressed 

these issues for the Southern High Plains. These changes in 

shrub communities (in other words, community structure and 

species evolution) are on distinct time scales. Both time scales 

are ordinarily very long in terms of the human lifespan perspective. Species evolution is ordinarily the longer of the two 

phenomena. Betancourt (1996) and Tausch and others (1993) 

reviewed climatic influences that have lead to current vegetation 

communities. Since settlement of the American West by EuroAmericans, especially in recent decades, shrubland vegetation 

communities have changed rapidly. Consensus is that these 

changes have been driven not only by global warming, but also 

by management activities, especially livestock grazing, and by 

a change in the frequency of wildfires mediated by the higher 

fine fuel loads of exotic annual grasses such as cheatgrass. Two 

contrasting examples of changed communities are the fragmentation of sagebrush communities in the Intermountain West as 

a result of agricultural conversions, brush control projects, and 

increased fire frequency (Knick 1999; Welch 2005; Whisenant 

1990) and the expansion of woody shrubs (principally 

mesquite—Prosopis spp., tarbush—Flourensia cernua, and 

creosote bush—Larrea tridentata) into warm desert grasslands 

in the Southwest as a result of overgrazing and climate change 

(Havstad and Schlesinger 1996; Herbel 1979). The likelihood 

is that changes will continue, even accelerate, with climate 

change, industrial activities, and intensive land management 

(Neilson and Drapek 1998). The challenges for land managers 

and ecologists is to understand the fluidity of the system and to 

be proactive and sensitive to the needs of healthy, productive 

landscapes.

Acknowledgments

We thank Ron Sosebee and his Texas Tech University 

colleagues for their tireless efforts to lead in the organization 

and conduct of the symposium and field trip. This paper is the 

result and reflection of our involvement in a series of wildland shrub symposia. We appreciate the participation of many 

colleagues over the course of this symposia series. This paper 

reflects that long involvement. We thank Burton V. Barnes, 

John K. Francis, and Stewart C. Sanderson for constructive 

comments on an earlier version of the manuscript.

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The Authors

1 Program Manager and Research Geneticist, USDA Forest Service, 

Rocky Mountain Research Station, Shrub Sciences Laboratory, 

Provo, UT. dmcarthur@fs.fed.us 2 Research Botanist, USDA Forest Service, Rocky Mountain 

Research Station, Shrub Sciences Laboratory, Provo, UT.
USDA Forest Service RMRS-P-47. 2007 11

The Llano Estacado and 

Distribution of Localities

The last synthesis of the Quaternary vegetation of the 

Llano Estacado, based on pollen data, was more than 40 years 

ago (Wendorf 1961). A hallmark of this seminal study was 

its multidisciplinary research effort to examine the paleoecology. Since then, research has generated several lines of 

evidence leading to an increased database from an expanded 

number of localities representative of the major geomorphic 

landforms across the region. Refinements in pollen processing 

and greater understanding of post-depositional processes have 

led to increased interpretive ability that calls into question the 

validity of the earlier pollen diagrams and interpretation. Other 

lines of evidence, generally concordant with each other, are 

not in agreement with the earlier pollen record and regional 

interpretation. This current synthesis, then, is an update based 

on an expanded record that presents a different perspective on 

the past vegetation and ecosystems of the Llano Estacado.

The Llano Estacado, or Southern High Plains, is a flat, 

expansive plateau in northwestern Texas and eastern New 

Mexico covering 130,000 km2

 (fig. 1). Part of the High Plains, 

a subdivision of the Great Plains province (Fenneman 1931; 

Hunt 1967; Holliday and others 2002), the Llano Estacado is 

in the southern portion of the province. Escarpments define 

the region along the north, west, and east sides. The northern 

escarpment overlooks the Canadian River Valley that separates the Southern High Plains from the rest of the High 

Plains section. The Pecos River Valley section is to the west 

and southwest and includes the Mescalero Plains along with 

the Monahans Dunes and Mescalero Dunes that abut the 

southwestern escarpment. Bordering the eastern escarpment 

is the Osage Plains of the Central Lowland province. To the 

south, the region merges with the Edwards Plateau without an 

obvious break. Superimposed over, but not coincident with all 

of the High Plains, is the short-grass ecosystem or short-grass 

steppe (Lauenroth and Milchunas 1992).

The Southern High Plains (Llano Estacado) of today has a 

continental climate. The region experiences a large temperature range that is not influenced by the ocean or other large 

bodies of water (Johnson 1991). Rainfall occurs throughout 

the year, but highs are in the spring and fall as a result of frontal 

lifting of warm moist air. Summer droughts are common due 

to high pressure that dominates the region during this time. 

Summer rains, then, occur mainly through intense thunderstorms that depend on daytime heating and the weakening 

of the high pressure cell. Winter snowfall is minimal, but 

extended periods of below freezing are normal (Barry 1983; 

Haragan 1983:67; Bomar 1995:10). The Southern High Plains 

is dry and classified as semi-arid. It grades into the deserts 

of the Trans Pecos and southeastern New Mexico, the Rocky 

Mountain foothills of northeastern New Mexico, and the 

savannahs of the southern Central Lowlands (Osage Plains).

The modern vegetation of the Llano Estacado is a shortgrass prairie dominated by blue grama (Bouteloua gracilis) 

and buffalograss (Buchlöe dactyloides) with patches of honey 

mesquite (Prosopis glandulosa). Historically, how one viewed 

and used this vast landscape was a matter of cultural perspective. In 1839, an Anglo trader and explorer returning to the 

East from Santa Fe described the Llano Estacado as “an open 

plain...which was one of the most monotonous I have ever 

seen, there being not a break, not a valley, nor even a shrub to 

obstruct the view. The only thing which served to turn us from 

a direct course pursued by the compass, was the innumerable 

ponds which bespeckled the plain, and which kept us at least 

well supplied with water” (Gregg 1954:252). Despite that 

acknowledgement of water, he also noted the Llano Estacado 

as “that immense desert region,” “dry and lifeless” and 

“sterile” (Gregg 1954:357, 362). In the 1850s, governmentbacked Anglo explorers reported that the area was “the Zahara 

of North America” (Marcy 1850:42) with “no inducements to 

Grassland Ecosystems of the Llano Estacado

Abstract: The Llano Estacado, or Southern High Plains, has been a grassland throughout 

the Quaternary. The character of this grassland has varied through time, alternating between 

open, parkland, and savannah as the climate has changed. Different lines of evidence are 

used to reconstruct the climatic regimes and ecosystems, consisting of sediments and soils, 

vertebrate and invertebrate remains, phytolith and macrobotanical remains, isotope data, 

and radiocarbon ages. Binding or key indicator species throughout the late Pleistocene 

and Holocene are bison, pronghorn antelope, and prairie dog. Depending on time period, 

hackberry, cottonwood, sumac, honey mesquite, and Texas walnut are among the native 

trees and shrubs growing in the valleys and around upland basins. The middle Pleistocene 

is characterized as a sagebrush grassland whereas that of the late Pleistocene is a coolclimate pooid-panicoid dominated grassland. Focusing on the Holocene, this dynamic period 

experiences climatic changes, the early rise of the short-grass ecosystem, and modulations 

to that ecosystem.

Eileen Johnson1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
12 USDA Forest Service RMRS-P-47. 2007

Figure 1. Localities on the Llano Estacado yielding paleovegetation data (direct evidence).

cultivation” (Pope 1855:9). Yet, 20 years later in the 1870s, 

the Pastores (Hispanic sheepherders from New Mexico and 

the first non-indigenous settlers of the region) saw the territory as a vast, well-watered grassland ideal for expansion first 

through transhumance and then through year-round sedentary 

village pastoralism (Hicks and Johnson 2000). They called 

the western escarpment La ceja de Dios or “God’s eyebrow” 

(Cabeza De Baca 1954). This appellation imparted a much 

different sentiment from that of the Anglo statements.

A synthesis of the development of the late Quaternary grassland ecosystems of the Llano Estacado from the Last Glacial 

Maximum (LGM) to historic times is based on the data from 

more than 20 localities across the region (table 1; fig. 1). These 

localities occur in the principal landforms (valleys, lake basins, 
USDA Forest Service RMRS-P-47. 2007 13

Table 1—Localities on the Llano Estacado yielding paleovegetation data (direct evidence).

Locality Geomorphic setting Stratum/sge Evidence Reference

Bluitt Cemetery Lunette lunette LGM phytoliths Fredlund and others 2003

Bushland Playa upland playa LGM phytoliths, pollen Fredlund and others 2003

White Lake salina LGM phytoliths Fredlund and others 2003

San Jon upland playa stratum 1 phytoliths Fredlund and others 2003

stratum 2 phytoliths Fredlund and others 2003,

8,000 B.P. phytoliths, charcoal Fredlund and others 2003,

Johnson unpublished data

Barnes Playa upland playa stratum 1 phytoliths Fredlund and others 2003

stratum 2 phytoliths Fredlund and others 2003

8,000 B.P. phytoliths Fredlund and others 2003

Lubbock Lake Landmark valley stratum 1 phytoliths, seeds, Fredlund and others 2003,

preserved wood, Thompson 1987, Robinson 1982

stratum 2 phytoliths, pollen, Fredlund and others 2003,

impressions, Hall 1995, Thompson 1987,

seeds Robinson 1982

8,000 B.P. phytoliths Fredlund, unpublished data

stratum 3 seeds Thompson 1987

stratum 4 seeds Thompson 1987

stratum 5 seeds, charcoal Thompson 1987, Johnson unpublished 

data

Yellowhouse systema valley stratum 1 seeds, charcoal Johnson unpublished data

stratum 2 phytoliths, seeds, Johnson unpublished data

charcoal

stratum 3 phytoliths, seeds, Johnson unpublished data

charcoal

stratum 4 phytoliths, seeds, Johnson unpublished data

charcoal

stratum 5 phytoliths, seeds, Johnson unpublished data

charcoal

Mustang Springs valley stratum 1 phytoliths Bozarth 1995

stratum 2 phytoliths Bozarth 1995

stratum 4 phytoliths Bozarth 1995

stratum 5 phytoliths Bozarth 1995

Plainview valley stratum 2 pollen Hall 1995

Edmonson valley 8,000 B.P. phytoliths Bozarth 1995

Gibson valley stratum 3 phytoliths Bozarth 1995

Enochs valley stratum 3 phytoliths Bozarth 1995

Lubbock Landfill valley stratum 4 phytoliths Bozarth 1995

Sundown valley stratum 4 phytoliths Bozarth 1995

Flagg valley stratum 5 phytoliths Bozarth 1995

41LU119 uplands stratum 5 seeds Johnson unpublished data

Tahoka Lake salina stratum 5 seeds, charcoal Johnson unpublished data

a Represents a compilation of more than 10 localities within a 20 km stretch of the Yellowhouse system.

dunes). Some localities are stratified, providing a record for 

several time periods in one place, whereas others represent 

only a single time period. Some provide multiple lines of 

evidence for past plant communities whereas others produced 

only one. Taken together, these localities cover the region and 

the late Quaternary using multiple lines of evidence to view 

these changing ecosystems.

The Llano Estacado has been a grassland since MiocenePliocene times (Fox and Koch 2003). Despite previous 

interpretations of a boreal forest during latest Pleistocene 

times (Hafsten 1961; Wendorf 1961, 1970, 1975; Oldfield 

and Schoenwetter 1975), the Llano Estacado throughout the 

Quaternary has been a grassland (Holliday 1987). Interpretations 

based on pollen data have proven to be untenable (Holliday 

1987; Holliday and others 1985; Hall and Valastro 1995). As the 

climate changed, the character of the Llano Estacado grassland 

has varied through time, alternating between open, parkland, 

and savannah, with isolated to small stands of deciduous trees.
14 USDA Forest Service RMRS-P-47. 2007

Lines of Evidence

The synthesis is based on both direct and indirect lines of 

evidence that form the basis for interpretation. Direct evidence 

is composed of the vestiges of plants themselves represented 

by phytoliths, pollen, or macrobotanical specimens. Phytoliths 

are hydrated silica-bodies produced by grasses and certain 

other monocotyledon and dicotyledon families as well as some 

spore-producing families (Piperno 1988). The phytolith record 

generally is well-preserved on a regional basis (Bozarth 1995; 

Fredlund 2002; Fredlund and others 2003) and is thought to 

indicate what was growing in the local environs.

Based primarily on phytoliths, three major grass subfamilies have been identified in the record. Pooid grasses are C3

plants that are short-day grasses, having limited available 

sunshine for growing and flowering. They generally prefer 

cool to cold climates with a sufficient moisture regime during 

the growing season. Limiting factors are available moisture 

and temperature. Panicoid grasses are composed of both C3

and C4

 plants that are long-day grasses, having maximum 

available sunshine. They generally prefer moist, humid tropic 

to subtropic conditions. They have the same limiting factors as 

pooid grasses. Chloridoid grasses are C4 plants that are longday grasses. They generally prefer warm, dry climates.

The pollen record for the Southern High Plains is generally 

considered unreliable due to the lack of duplication or notably 

dissimilar nature of pollen diagrams within the same locality, 

very low counts, grain corrosion, and other preservation problems (Bryant and Schoenwetter 1987; Hall 1981; Hall and 

Valastro 1995). The few dependable records are included 

in the synthesis. Because of the ease of wind transport and 

dispersal, pollen records may be a mix of the local environs, 

regional vegetation, and extraregional plants.

Macrobotanical remains consist of seeds, charcoal, 

preserved wood, and preserved impressions (fig. 2). Carbonized 

seeds and charcoal are the most pervasive of the four types, 

having been recovered from throughout the late Quaternary 

stratigraphy. Preserved wood and impressions are rare and, to 

date, have been found only in late Pleistocene fluvial (wood) 

and early Holocene lacustrine (impressions) environments.

Indirect evidence providing proxy data on vegetation 

communities includes sediments and soils, radiocarbon 

and stable-carbon isotope data, and vertebrate records. The 

regional sediments and soils reflect the influence of climate, 

environmental factors, and biota (Buol and others 1973; 

Birkland 1999; Holliday 2004). Well over 325 radiocarbon 

dates are available that provide a solid chronology. Many of 

these are assays from organic-rich sediments that also provide 

∂13C values as a result of routine measurement along with 

radiocarbon dating. This isotopic value reflects the C3 and C4

plant biomass. A positive correlation exists between ∂13C and 

the proportions of C3

 and C4 biomass and ∂13C values (Cerling 

1984; Bowen 1991; Nordt 2001). The C3 plants have a lighter 

isotopic composition. This group is comprised of cool season 

grasses, most aquatic plants, and trees. The C4 plants have a 

heavier isotopic composition and are composed of primarily 

warm season grasses. Each per mil change represents a shift 

of about 7 percent in the ratio of C3

 to C4 biomass (Bowen 

1991).

Although less than half the available radiocarbon dates 

with ∂13C values have been analyzed, an initial pattern has 

emerged that indicates both a shift from lighter (C3 plants) to 

heavier (C4 plants) isotopic composition and a time-transgressive nature of the shift across the Southern High Plains from 

Figure 2. Macrobotanical evidence from localities on the Llano 

Estacado: a) preserved impression of musk-grass (Chara); b) 

preserved impression of horsetail (Equisetum); c) fossil net-leaf 

hackberry (Celtis reticulata) seeds; and d) fossil bulrush (Scirpus) 

seeds.
USDA Forest Service RMRS-P-47. 2007 15

ca. 8,800 to 8,200 B.P. (Holliday 1995a). This difference in 

timing could reflect localized conditions or be an artifact of 

sampling.

The best and longest record (Lubbock Lake Landmark; 

Holliday 1995a:57) covers the Holocene and indicates both 

change and stability. Lighter isotopic values dominate from 

ca. 10,000 to 8,200 B.P. An abrupt shift from lighter to heavier 

isotopic composition occurs ca. 8,200 B.P., with ca. 28 percent 

C4 grasses in the earliest Holocene. The C4 grasses dominate 

throughout the middle Holocene between 7,000 to 4,500 B.P., 

with ca. 79 percent C4 grasses. That pattern holds for most 

of the late Holocene between 4,500 to 500 B.P., with ca. 79 

percent C4 grasses. Around 500 B.P., a shift to lighter composition (C3 plants) occurs, with only ca. 19 percent C4

 grasses. 

This high frequency of C3 plants (ca. 81 percent) most likely 

reflects the aquatic plants of the extensive marsh at this time 

in the valley floor. Based on this record, grasses indicative of 

cooler conditions dominate the valleys of the Llano Estacado 

in the earliest Holocene and were replaced by grasses of 

warmer conditions by the end of the early Holocene. These 

warm season grasses continue throughout the middle and late 

Holocene.

Stable-carbon isotope data from lunettes on the uplands of 

the central Llano Estacado provide a regional perspective with 

a lengthier and compatible but incomplete record that indicates broad trends (Holliday 1997:63-64, 66). From 25,000 

to 15,000 B.P., a gradual shift toward lighter isotope values 

indicates an increase in cooler, temperate-climate plants. 

Between 15,000 and 13,000 B.P., both lighter and heavier 

values occur, with a shift to heavier values from 13,000 to 

10,000 B.P. A shift back to lighter values occurs from 10,000 

to 8,000 B.P., with a shift at 8,000 B.P. back to heavier values 

that is maintained throughout the rest of the Holocene. The 

shift to post-LGM warmer conditions is most dramatic from 

13,000 to 10,000 B.P., with a second shift to warmer conditions around 8,000 B.P.

Major physiographic features and indicator plants and 

animals bind the grasslands together over the vast Great 

Plains (Coupland 1992). The regional late Quaternary vertebrate record is known, and is particularly extensive for the 

late Pleistocene and early Holocene (Johnson 1986, 1987). 

A number of forms are environmentally sensitive or characteristic of certain ecosystems or vegetation communities. 

The vertebrate binding or key indicator species for grasslands are bison, pronghorn antelope, and prairie dog. These 

species are common on the Llano Estacado throughout the 

late Quaternary.

Framework

The Ogallala Formation and the Blackwater Draw 

Formation are the principal units responsible for the flat, 

almost featureless, constructional surface of the Llano 

Estacado. The upper Ogallala Formation (Miocene-Pliocene), 

the principle geologic bedrock of the Llano Estacado, was 

a stable land surface for hundreds of thousands of years, 

resulting in a well-developed soil. The ca. 2 m thick highly 

resistant calcrete at the top of the Ogallala Formation is a 

remnant of that soil. This pedogenic calcrete unit primarily 

is responsible for the configuration and size of the Llano 

Estacado, the prominent escarpments around its margin, and 

contributes to the topographic flatness.

The landforms and Quaternary soils and sediments form the 

framework for examining the past ecosystems of the region. 

The Blackwater Draw Formation (Pleistocene) was formed 

by deposition of episodic, thick, and widespread aeolian sediments laid down starting sometime in the early Pleistocene 

up to about 50,000 years ago (Holliday 1989a; Reeves 1976). 

Originating in the Pecos River Valley, these sediments draped 

the region and blanketed all underlying units and geomorphic features (including the drainage system and basins). The 

sediments were altered by soil formation under dry and warm 

conditions. This deposit and its associated soils represent the 

major surficial deposit of the Llano Estacado.

Landforms

Modern geomorphic features have cut into or through, or 

rest upon the Blackwater Draw Formation. The surface of the 

Llano Estacado has been modified by three geomorphic forms. 

Two of these, basins and dunes, occur on the uplands.

About 25,000 small lake basins (locally known as playas) 

and 40 saline depressions (locally known as salinas) cover 

the landscape, occurring primarily on the High Plains surface 

(Sabin and Holliday 1995). Playas are inset into the Blackwater 

Draw Formation and formed primarily through erosional 

processes. They usually are freshwater sources. Most playas 

began forming in the late Pleistocene. Some basins were filled 

completely and no longer have a surface expression. Salinas 

are large, irregularly shaped basins probably formed through 

dissolution and collapse into the Ogallala Formation. They 

appear to be subsidence basins where long-term infiltration 

of ground water has caused point-source dissolution of the 

Permian salts (Reeves 1991). Although freshwater springs are 

associated with some salinas, the basins contain salt deposits 

and lake waters are brackish (Wood and others 2002).

Dune fields and lunettes rest on the Blackwater Draw 

Formation throughout the Llano Estacado. Extensive dune 

fields occur in three areas on the western side of the Southern 

High Plains. They are coincident with three major reentrant 

valleys on the western escarpment that acted as ramps or 

channels for sediments blowing off the Pecos River Valley in 

an incursion onto the Llano Estacado. Elsewhere along the 

western edge, large dune fields built up against the escarpment.

Lunettes are lee side dunes formed on the downwind side 

of drying playa and salina lake basins. Not all playas have 

lunettes, but of those that do, the lunettes generally are on 

the east and southeast side of the playa basin. Lunettes along 

playas form a single dune ridge. Those around the larger 

salinas typically occur as three dune ridges (Holliday 1997; 

Rich and others 1999).

The northwest-southeast trending now-dry river valleys 

(locally known as draws) are tributaries of the Red, Brazos, 
16 USDA Forest Service RMRS-P-47. 2007

and Colorado rivers that flow through the Osage Plains and 

into the Gulf of Mexico or the Mississippi River. Generally, 

these valleys have cut through the Blackwater Draw Formation 

to the Ogallala Formation except where the drainages have 

intercepted late Pliocene (Blanco Formation) or Pleistocene 

lake sediments. Final down cutting that resulted in the modern 

drainage system began sometime after 20,000 years with 

aggrading and infilling of the valleys starting around 12,000 

years ago (Holliday 1995a).

Numerous springs, active since at least the late Pleistocene 

(Holliday 1995a, 1995b), flowed in various reaches of the 

valleys prior to the 1930s, with both ponds and free-flowing 

water available (Brune 1981). These springs were not distributed throughout the draws but rather were concentrated and 

confined to certain reaches of the valley system where the 

aquifer had been breached by valley downcutting. Today, the 

valleys generally are dry due to the dropping water table, and 

the playas and salinas contain the only naturally impounded, 

although generally seasonal, surface water for the region.

Quaternary Stratigraphy

Soil characteristics provide information on the vegetation community or ecosystem under which they developed. 

A boreal forest imparts distinctive pedologic characteristics 

to the soils, all of which are absent in the buried and surficial soils of the Southern High Plains (Holliday 1987, 1989a). 

The Blackwater Draw Formation is the aeolian mantle that 

covers the Southern High Plains and forms the surficial sediment. It contains several buried soils, the oldest of which was 

buried ca. 1.5 million years ago. Sedimentation ceased around 

50,000 years ago and the regional surface began developing 

(Holliday 1989a). All buried soils virtually are identical to 

surface soils. What this means is that the late Quaternary 

vegetation represents that of most of the Quaternary. At no 

time during the Quaternary were boreal forests or coniferous 

woodlands present on the Llano Estacado. Rather, the region 

has been dominated by grassland, albeit varying in grass 

composition.

The late Quaternary stratigraphic record for the Southern 

High Plains is contained in the three landforms, although 

primarily in the valley system. Generally, late Holocene 

aeolian sediments over Blackwater Draw Formation occur 

in the upland areas between playas, salinas, and dune fields. 

Dune formation is a Holocene feature. Deposition of sand 

sheets began in the early Holocene, with episodic development in the middle and late Holocene (Holliday 1995b, 2001a; 

Muhs and Holliday 2001).

Few playas or salinas are stratified. Salinas contain discontinuous stratigraphic records. Early and middle Pleistocene 

playas occur below some of the recent playas (Gustavson and 

others 1995; Holliday and others 1996). Playas can contain 

thick (average 3 to 5 m) fills of lake mud and some aeolian sediments that span the late Pleistocene and Holocene and provide 

a lengthy record of shifting waters in the basin through time 

(Hill and others 1995; Holliday and others 1996). Lunettes, 

a late Pleistocene to Holocene feature, are stratified and 

typically contain buried soils indicative of episodic accretion 

(Holliday 1997). Lunettes around salinas occur in three bands 

representing different time periods (late Pleistocene, middle 

Holocene, late Holocene) and wind directions (Holliday 1997; 

Sabin and Holliday 1995).

Valley fills provide the most extensive regional record 

(Holliday 1995a). The valley fill stratigraphy is composed 

of five major stratigraphic units within which a number of 

buried soils are contained. Subunits are defined within the 

major units as well as facies. Although the five major units are 

well-represented throughout the valley system, no one location contains the entire record of units, subunits, and facies. 

The most complete record is at Lubbock Lake (Holliday 1985; 

Holliday and Allen 1987) in Yellowhouse Draw. Although 

local subunit and facies designations have been maintained, 

they are correlated with the regional terminology (table 1). 

Although some boundaries regionally are time-transgressive 

(Holliday 1995a), Lubbock Lake’s geochronology provides a 

general framework in which to view the hydrologic and landscape changes through time.

The lowest stratum of valley fill is stratum 1 consisting of 

a basal sand and gravel unit (substratum 1A), cross-bedded 

sand (substratum 1B), and locally, an overlying clay drape 

(substratum 1C). Stratum 1 is interpreted as a meandering 

stream deposit with point bar sediments and overbank deposits. 

Deposition of stratum 1 generally ended about 11,000 B.P., 

although in some reaches flowing water continued as late as 

10,000 years ago. The climate was cool and humid (maritime conditions) with enhanced rainfall in the winter (Johnson 

1987, 1991).

Stratum 2 is primarily a lacustrine and marsh deposit found 

along the valley axis. Substratum 2A contains beds of pure 

diatomite that represent periods of standing water with interbedded peaty muds indicating marshy conditions. Substratum 

2B overlies 2A and contains a homogeneous layer of organic-rich silt and clay representing a slowly aggrading marsh. A 

sandy shore facies is found in a narrow zone along the valley 

margin while a sandy, aeolian facies with some slopewash and 

interbedded marsh sediments is found along the outer valley 

margin. Deposition of stratum 2 began about 11,000 B.P. and 

the 2A-2B transition occurred about 10,000 B.P. Aggradation 

of 2B ceased about 8,500 B.P. and the Firstview Soil formed 

on a stable surface from about 8,500 to 6,400 B.P. Elsewhere 

in the valley system, the Firstview Soil was buried earlier than 

at Lubbock Lake (Holliday 1995a) and at one locality, stratum 

2 started accumulating as early as 11,300 B.P. (Holliday 

1995a:13). The climate was warming with a shift in rainfall 

pattern. Rainfall levels and a lower evaporation rate led to 

more effective moisture reflective of continuing wet conditions (Johnson 1987). Nevertheless, the first signs of Holocene 

drought (less available moisture) occurred during the period 

10,900 to 10,200 B.P. (Holliday 2000).

Stratum 3 lies conformably on top of stratum 2 and is 

composed of a moderately calcareous, sandy aeolian deposit 

along the western valley margin and a highly calcareous, silty 

lacustrine unit found along the valley axis. Stratum 3 represents 

an alkaline lake or marsh along the valley floor with considerable aeolian additions along the valley margin. Stratum 3 
USDA Forest Service RMRS-P-47. 2007 17

deposition and formation of the Yellowhouse Soil occurred 

between about 6,400 to as late as 5,000 B.P. Elsewhere in the 

valley system, stratum 3 deposition occurred perhaps as early 

as 10,000 B.P. and internal buried A-horizons locally occur 

within stratum 3 (Holliday 1995a). Stratum 3 denotes a time 

of increasing temperatures, decreasing rainfall, and lower 

humidity (Johnson 1987).

Stratum 4 is composed of alluvial and marsh deposits found 

only along the valley axis (4A), and a sandy aeolian deposit 

that blankets the valley (4B) with a clayey marsh facies (4m) 

found along the valley axis. The Lubbock Lake Soil formed in 

substratum 4B under well-drained conditions and is well-developed with prominent A and B horizons and often multiple 

calcic horizons. Deposition of 4A occurred between 5,500 and 

5,000 B.P. and 4B between 5,000 and 4,500 B.P. The Lubbock 

Lake Soil began forming around 4,500 to around 1,000 

B.P. when it locally was covered by stratum 5. Elsewhere 

in the valley system, stratum 4 is buried as early as 3,900 

B.P. (Holliday 1995a). Where not buried by stratum 5 sediments, soil formation continues today. Stratum 4 represents 

the culmination of the warming trend, with increasingly hot, 

dry, and dusty conditions known as the Altithermal (Holliday 

1989b). The climate is very xeric. By 4,500 B.P., the modern 

continental climate emerges with a return to cooler and mesic 

conditions (Johnson 1987; Holliday 1989b).

Stratum 5, the uppermost stratum, is represented by marsh 

deposits and upslope, valley margin facies composed of 

layers of aeolian sand and slopewash sand and gravel, burying 

stratum 4. Buried soils occur locally. Deposition of lower 5 

began around 750 to 600 B.P. and continued to about 450 B.P. 

when a soil began to form locally. Deposition of upper 5 began 

about 300 B.P. A weakly developed soil began to form locally 

about 100 B.P. and is exposed locally at the surface today. 

Elsewhere in the valley system, deposition of stratum 5 valley 

margin sands begins as early as 3,900 B.P. and valley axis 

marsh muds by 3,200 B.P. (Holliday 1995a). By 2,000 B.P., 

an episodic drought cycle begins that continues today as part 

of the modern climatic pattern. The intensity and frequency of 

droughts varies through time, alternating between more mesic 

and less mesic conditions (Johnson 1987; Holliday 1995a).

The Record

The various localities across the Southern High Plains 

(fig. 1) provide a composite of the floral and faunal communities from the Last Glacial Maximum (LGM) to the latest 

Holocene. That composite is segmented by time and stratigraphy, with any one time period represented by three to six 

localities. Each locality, as well as stratigraphic units within 

a locality, varies in terms of the type of direct and indirect 

evidence available (table 2). The data come from two primary 

sources—those that are published (Bozart 1995; Hall 1995; 

Hall and Valastro 1995; Holliday 1995a; Johnson 1986, 1987b; 

Thompson 1987) and those that are unpublished. Unpublished 

data either have been presented at professional meetings 

(Fredlund 2002; Fredlund and others 2003) or are those of 

the author’s. Nevertheless, the overall record is robust with a 

clear dominance of grasslands and grassland vertebrate forms 

throughout.

The late Quaternary period is subdivided into late 

Pleistocene and Holocene epochs. Discussion of the late 

Pleistocene begins with the LGM, ca. 20,000 to 18,000 B.P., 

and continues through post-glacial time to the PleistoceneHolocene boundary at 11,000 B.P. Climatic changes and 

large-scale extinctions occurring at the end of the Pleistocene 

and around 11,000 B.P. mark the biotic and ecosystemic end 

of Wisconsinian conditions on the Southern High Plains. This 

time period is used as the boundary between the Pleistocene 

and Holocene rather than the geologic convention of using 

an arbitrary 10,000 B.P. as the boundary (Hageman 1972; 

Holliday 2001b).

Table 2—Correlation of valley fill stratigraphic terminology for the 

Lubbock Lake Landmark with the regional stratigraphy.

Lubbock Lake stratigraphya Regional stratigraphyb

stratum 5 stratum 5

substratum 5B stratum 5s2 and 5gs

substratum 5Bm stratum 5m

substratum 5A stratum 5s1 and 5g1

substratum 5Am stratum 5m

substratum 5m stratum 5m

stratum 4 stratum 4

substratum 4B (upper/A-horizon) stratum 4s

substratum 4B stratum 4s

substratum 4A stratum 4m

substratum 4m stratum 4m

stratum 3 stratum 3

substratum 3c (upper/A-horizon) stratum 3c

substratum 3c stratum 3c

substratum 3m stratum 3m

substratum 3e stratum 3s

stratum 2 stratum 2

substratum 2s stratum 2s

 2s local bed c stratum 2s

 2s local bed b stratum 2s

 2s local bed a stratum 2s

substratum 2e stratum 2s

substratum 2B (upper/A-horizon) stratum 2m

substratum 2B stratum 2m

 2B cienega stratum 2m

substratum 2A stratum 2d

 2A local bed 5 stratum 2d

 2A local bed 4 stratum 2d

 2A local bed 3 stratum 2d

 2A local bed 2 stratum 2d

 2A local bed 1 stratum 2d

stratum 1 stratum 1

substratum 1C stratum 1

substratum 1B stratum 1

substratum 1A stratum 1

a Based on Holliday (1985), Holliday and Allen (1987), and field notes on 

file at the Museum of Texas Tech University. b Based on Holliday (1995a).
18 USDA Forest Service RMRS-P-47. 2007

Late Pleistocene Background

The LGM is represented by three localities dating from 

21,865 to 17,710 B.P. (table 1) that are associated with playas 

or salinas on the uplands. Data indicate a grassland composed 

of sagebrush (Artemisia), grasses (Poaceae), ragweed 

(Ambrosia), daisy-sunflower-aster family (Asteraceae), 

ChenoAms (chenopods and amaranth), and juniper (Juniperus). 

A rare component of the flora consists of hackberry (Celtis), 

Liguliflorae (herbs such as wild lettuce [Lactuca]), wild buckwheat (Eriogonum), carrot or parsley family (Apiaceae), 

greasewood (Sarcobatus; a chenopod shrub), amaranth family 

(Amaranthaceae), evening primrose family (Onagraceae), 

yucca (Yucca), cactus family (Cactaceae), and bluebell-lobelia 

family (Campanulaceae). Aquatic plants indicative of wet 

ground to open water are the sedge family (Cyperaceae), ditch 

grass (Ruppi; submersed vegetation in alkaline lakes), common 

cattail (Typha latifolia; emergent vegetation), and colonies of 

the freshwater algae (Botryococcus and Pediastrum). Ditch 

grass is known only from White Lake, reflecting the brackish 

waters of that salina.

Little is know of the fauna at this time. The presence of 

mammoth (Mammuthus spp.), ancient horse (Equus spp.), 

and ancient bison (Bison antiquus) (Evans and Meade, 1945) 

is indicative of grasslands. The records denote a sagebrush 

grassland with high amounts of composites. This grassland is 

an herbaceous prairie community under an equitable, cooler, 

and humid climate with no modern analog (Hall and Valastro 

1995:244).

Late Pleistocene stratum 1 times are represented by five 

localities dating from 12,500 to 11,000 B.P. (table 1) that 

are associated with upland playas and the valley system. 

Pooid grasses, including needlegrass or wintergrass (Stipa; 

cool-moist season), dominate with a very low component of 

panicoid grasses and chloridoid grasses. Almost no C4

 grasses 

are present and sagebrush is absent. Other floral elements 

reflecting the valley system are seepweed (Suaeda), gromwell 

(Lithospermum), devil’s claw (Proboscidea louisianica), and 

net-leaf hackberry (Celtis reticulata). Aquatic plants indicative 

of wet ground to open water are bulrush (Scirpus; emergent 

vegetation) and spikerush (Eleocharis; emergent vegetation).

A highly diverse herd herbivore fauna, indicative of 

grasslands, is complimented by an equally diverse carnivore guild (table 3). The larger carnivores are dependent 

upon these herbivores and preyed upon and scavenged their 

carcasses (Matheus 1995, 2003; Matheus and others 2003). 

Other grassland forms are as varied (table 3). The tiger salamander and meadow vole, in particular, reflect the riparian 

habitat along the streams. Sedge beds, reflected in the macrobotanical remains, are the preferred habitat of meadow voles 

(Findley and others 1975; Thompson 1965). Equally of note 

is the prairie dog town community (prairie dog, ground squirrels, grasshopper mouse, burrowing owl, western hognose, 

and ground snakes) reflected in these smaller grassland forms 

and some of the town’s predators (rattlesnake, turkey vulture, 

ferruginous hawk).

Table 3—Late Pleistocene (stratum 1) grassland fauna of the Llano Estacado.

Taxon Common name

Herd herbivores

Mammuthus columbi Columbian mammoth

Bison antiquus ancient bison

Equus mexicanus large, stout-legged horse

Equus francisci small, stilt-legged horse

Camelops hesternus yesterday’s camel

Capromeryx spp. extinct, 4-pronged antelope

Hemiauchenia macrocephala large-headed llama

Odocoileus virginianus white-tailed deer

Antilocapra americana pronghorn antelope

Platygonus compressus flat-headed peccary

Carnivore-guild

Arctodus simus short-faced bear

Smilodon fatalis saber-toothed cat

Canis dirus dire wolf

Canis lupus gray wolf

Canis latrans coyote

Vulpes velox swift fox

Urocyon cineroargenteus gray fox

Other grassland forms

Ambystoma tigrinum tiger salamander

Scaphiopus spp. spade-foot toad

Bufo cognatus Plains toad

Kinosternon flavescens yellow mud turtle

Elaphe guttata corn snake

Gyalopion canum western hook-nosed snake

Heterodon nasicus western hognose snake

Lampropeltis triangulum common king snake

Sonora semiannulata ground snake

Thamnophis cf. sirtalis common garter snake

Tropidoclonion lineatum lined snake

Crotalus atrox western diamondback rattlesnake

Carthartes aura turkey vulture

Buteo regalis ferruginous hawk

Athene cf. cunicularia burrowing owl

cf. Pooecetes gramineus vesper sparrow

Holmesina septentrionalis giant pampathere

Glossotherium (=Paramylodon) harlani Harlan’s ground sloth

Lepus californicus black-tailed jack rabbit

Spermophilus richardsonii Richardson’s ground squirrel

Spermophilus tridecimlineatus 13-lined ground squirrel

Spermophilus mexicanus Mexican ground squirrel

Cynomys ludovicianus black-tailed prairie dog

Geomys bursarius Plains pocket gopher

Reithrodontomys montanus Plains harvest mouse

Onychomys leucogaster Northern grasshopper mouse

Neotoma micropus Southern Plains woodrat

Microtus pennsylvanicus meadow vole

Microtus ochrogaster prairie vole

These prairie dog towns existed within an overall dominant 

pooid grass prairie that was a parkland. Isolated hackberry trees 

to small groves grew along the streams in the valley system, 

continuing the presence of this native tree from the LGM. A 

lower mean annual temperature than today, cooler summers 

and warmer winters that lacked extended freezing conditions, 

more effective moisture, lower evaporation rate, and enhanced 

winter precipitation indicated an equitable, humid, and 
USDA Forest Service RMRS-P-47. 2007 19

maritime-like climate that lacked seasonal extremes (Johnson 

1991). Nevertheless, a major environmental shift at 11,000 

B.P. is represented in the draws by an abrupt hydrologic 

change from flowing to standing water, and on the uplands, 

by the onset of regional dune construction that heralds the 

Holocene.

Holocene Dynamics

Early Holocene stratum 2 times are represented by five 

localities dating from 10,800 to 8,200 B.P. (table 1) that are 

associated with upland playas and the valley system. While 

still dominant, pooid grasses, including needlegrass or wintergrass, are steadily decreasing. Chloridoid grasses show a 

continuing rise with a low but steady component of panicoid grasses including the short-grass threeawn (Aristida; 

warm season). Other floral elements reflecting the valley 

system are goosefoot (Chenopodium), buffalo bur (Solanum 

rostratum), guara (Guara), devil’s claw, ragweed, the daisysunflower-aster family, Liguliflorae, mustards (Brassicaceae), 

and the evening primrose family. A variety of emergent and 

submersed vegetation indicative of wet ground to open water 

include cattail, sedge (Cyperus), bulrush, spikerush, horsetail 

(Equisetum), musk-grass (Chara), and colonies of the freshwater algae (Botryococcus).

Native trees in the valley are net-leaf hackberry, sumac 

(Rhus), and cottonwood (cf. Populus), with juniper (cf. 

Juniperus) and piñon-pine (cf. Pinus edulis) along the High 

Plains escarpment. The latter three are from pollen of questionable reliability (Hall 1995), but plausible. Juniper and an 

occasional piñon-pine grow along the western High Plains 

escarpment today and occasional cottonwoods grow in the 

lower reaches of the valley system. Sumac, like hackberry, is 

a shrub to small tree. Isolated, disjunct populations of littleleaf 

sumac (R. microphylla) occur today on the Llano Estacado, 

with a similarly isolated population of prairie sumac (R. 

lanceolata) just to the north of the region (Petrides and 

Petrides 1992:134, 137).

The diversity of herd herbivores, along with the carnivore 

guild, decreased considerably (table 4) due to the changes 

occurring around 11,000 B.P. and the collapse of the Pleistocene 

food web (Matheus and others 2003). Ancient bison became 

the dominant herd herbivore. Although some reduction in 

diversity occurred with the smaller grassland forms, variety 

was still maintained with some new taxa appearing (table 4). 

Both plant and animal forms indicated sedge beds around the 

marshy edges of the ponded waters in the valleys and later 

with the aggrading marshes, along with submersed vegetation 

in the ponds. A prairie dog town community continued along 

with the badger as its predators.

These prairie dog towns existed within an overall mixed 

grassland with an increase in C4

 grasses without sagebrush. 

The setting was that of a savanna. Low numbers of hackberry, sumac, and possibly cottonwood trees grew along the 

valley margins in the valley system. Equitable climatic conditions gave way to the onset of winters with at least occasional 

Table 4—Early Holocene (stratum 2) grassland fauna of the Llano 

Estacado.

Taxon Common name

Herd herbivores

Bison antiquus ancient bison

Capromeryx spp. extinct 4-pronged antelope

Odocoileus spp. deer

Antilocapra americana pronghorn antelope

Carnivore-guild

Canis lupus gray wolf

Canis latrans coyote

Taxidea taxus badger

Other grassland forms

Ambystoma tigrinum tiger salamander

Kinosternon flavescens yellow mud turtle

Terrapene ornata western box turtle

Phrynosoma cornutum Texas horned lizard

Eumeces obsoletus Great Plains skink

Coluber constrictor racer

Sonora semiannulata ground snake

Thamnophis cf. sirtalis common garter snake

Tropidoclonion lineatum lined snake

Circus cyaneus harrier

cf. Eremophila alpestris horned lark

Mimus polyglottis mockingbird

Tympanuchus cupido prairie chicken

Notiosorex crawfordi desert shrew

Lepus californicus black-tailed jack rabbit

Spermophilus tridecimlineatus 13-lined ground squirrel

Spermophilus mexicanus Mexican ground squirrel

Cynomys ludovicianus black-tailed prairie dog

Geomys bursarius Plains pocket gopher

Chaetodipus hispidus hispid pocket mouse

Dipodomys ordii Ord’s kangaroo rat

Reithrodontomys montanus Plains harvest mouse

Onychomys leucogaster Northern grasshopper mouse

Sigmodon hispidus cotton rat

Neotoma cf. micropus Southern Plains woodrat

Microtus pennsylvanicus meadow vole

Microtus ochrogaster prairie vole

periods of freezing temperatures. Summers were warming 

and occasional droughts (less effective moisture) occurred 

(Holliday 2000). While conditions still were humid, rainfall 

pattern was shifting with an eventual decrease in rainfall, and 

mean annual temperature was rising (Johnson 1986, 1987b).

By around 8,000 B.P., the dynamics between climate, 

vegetation, and fauna were such that the character of the 

landscape is changing. Chloridoid grasses are dominant, 

most likely produced by a grama-buffalograss (BoutelouaBüchloe) prairie. A low level of pooid and panicoid grasses 

that included short-grass threeawn continues. Based on phytolith data, the short-grass ecosystem emerges around 8,000 to 

8,200 B.P., with modulations in that ecosystem into modern 

times (Fredlund and others 2003). The phytolith and stablecarbon isotope data, then, are in general agreement.

In tandem with this change but somewhat later, modern 

bison (Bison bison) emerged, not as a replacement species, 

but as the transformation of the ancient form into the modern 

form due to the plasticity of the bison genome (Lewis 2003; 
20 USDA Forest Service RMRS-P-47. 2007

Lewis and others 2001). Bison underwent a rapid decrease 

in body size during the period post-8,000 B.P. and before 

6,500 B.P., most likely with fully modern bison emerging by 

7,000 B.P. This decrease in size appeared correlated with the 

rise and spread of the short-grass ecosystem and the greater 

productivity, but less nutritive value of C4 grasses.

Early middle Holocene stratum 3 times are represented by 

four localities dating from 7,000 to 5,500 B.P. (table 1) that are 

associated with the valley system. Chloridoid grasses, most 

likely produced by a grama-buffalograss prairie, are dominant, 

but some pooid and panicoid grasses continue. Wet ground 

to open water plants include emergent bulrush, submerged 

musk-grass, and the water lily family (Nymphaea). The native 

trees net-leaf hackberry and sumac persist.

In comparison to the faunal diversity in late Pleistocene to 

early Holocene times, the known Middle Holocene faunas in 

general are depauperate. Herd herbivores are modern bison 

and pronghorn antelope (Antilocapra americana), with the 

carnivore guild represented by gray wolf (Canis lupus) and 

coyote (Canis latrans). Other grassland forms include tiger 

salamander (Ambystoma tigrinum), Couchi’s spadefoot toad

(Scaphiopus couchi), yellow mud turtle (Kinosternon flavescens), western box turtle (Terrapene ornata), Texas horned 

lizard (Phrynosoma cornutum), bull snake (Pituophis melanoleucus), black-tailed jackrabbit (Lepus californicus), 

black-tailed prairie dog (Cynomys ludovicianus), Plains 

pocket gopher (Geomys bursarius), yellow-faced pocket 

gopher (Cratogeomys castanops), and cotton rat (Sigmodon 

hispidus). Despite the reduction in diversity, elements occur 

indicating the continuance of a prairie dog town community.

This prairie dog town community, as well as the other 

animals, represents basically a modern fauna adapted to an 

open short-grass prairie with some brushland. The occasional 

hackberry and sumac may have been more like shrubs than 

trees at this time. Warming and drying conditions occurr, with 

a decrease in available moisture and humidity levels, greater 

seasonality, and aeolian sedimentation accumulation that indicates the beginning of a reduction in vegetation cover.

Middle and early Late Holocene stratum 4 times are represented by five localities that date from 5,500 to 2,000 B.P. 

(table 1) and are associated with the valley system. Chloridoid 

grasses increase in frequency and dominance throughout 

this time, most likely produced by a grama-buffalograss 

prairie. Some pooid grasses persist, including needlegrass or 

wintergrass, and panicoid grasses, including the short-grass 

threeawn.

In lower stratum 4, dating to the middle Holocene (5,500 to 

4,500 B.P.), other floral elements are pigweed (Amaranthus), 

knotweed (Polygonum), buffalo bur, and the spurge family 

(Euphorbiaceae). Wet ground to open water plants include 

emergent bulrush and the water lily family. Native trees are 

net-leaf hackberry and honey mesquite.

Modern bison dominate the grassland fauna at this time as 

the herd herbivore. The carnivore guild is represented only by 

the coyote. Other grassland forms include long-nosed snake 

(Rhinocheilus lecontei), black-tailed prairie dog, yellow-faced 

pocket gopher, Ord’s kangaroo rat (Dipodomys ordii), cotton 

rat, and white-throated woodrat (Neotoma albigula).

The grassland fauna was adapted to dry to desert conditions. Conditions had been warming since the early Holocene 

and this period is the height of the Altithermal (Holliday 

1989b, 1995a, 1995b), a climatic episode of greatly reduced 

precipitation and available water, increased temperatures, 

and blowing dust. The setting most likely was a desert grassland with an occasional hackberry or mesquite shrub. Prairie 

dog towns persisted, although most likely reduced in size and 

scope. The short grass, herbaceous prairie dominated within a 

dry landscape of reduced vegetation.

In upper stratum 4, dating to the early part of the late 

Holocene (4,500 to 2,000 B.P.), floral elements in the shortgrass prairie are buffalo bur and the spurge family. Net-leaf 

hackberry and honey mesquite are the native trees.

Herd herbivores are modern bison and pronghorn antelope, 

with the carnivore guild represented by gray wolf and coyote. 

Other grassland forms include tiger salamander, western 

box turtle, Texas horned lizard, 13-lined ground squirrel 

(Spermophilus tridecemlineatus), black-tailed prairie dog, 

and Plains pocket gopher.

By 4,500 B.P., the climate ameliorated, the landscape stabilized, and mesic and cooler conditions returned. Landscape 

stability heralded the establishment of basically modern 

conditions. Only the open prairie was reflected in the fauna 

and prairie dog towns existed in a short-grass, herbaceous 

prairie under essentially a continental climate.

Late Holocene stratum 5 times are represented by five localities dating from 2,000 to 200 B.P. (table 1) that are associated 

with both an upland salina and the valley system. Chloridoid 

grasses, most likely produced by grama-buffalograss prairies, 

continue to dominate. A low frequency of pooid grasses persist, 

including needlegrass or wintergrass, and panicoid grasses, 

including the short-grass threeawn. Crown grass (Paspalum; 

C4

 warm-season grass) joins the grass roster. Other floral 

elements are devil’s claw, prickly poppy (Argemone), and 

buffalo bur. Only emergent bulrush represents wet ground to 

open water plants. Native trees are net-leaf hackberry, honey 

mesquite, and Texas walnut (Juglans microcarpa), another 

small tree to shrub. Isolated populations of the Texas walnut 

occur today on the Llano Estacado in the lower reaches of the 

canyons (Petrides and Petrides 1992:124; Cox and Leslie 

1995).

The late Holocene fauna was more diverse than the middle 

Holocene fauna. The mainstay herd herbivores were modern 

bison and pronghorn antelope. The carnivore guild expanded 

to include gray wolf, coyote, badger (Taxidea taxus), and 

striped skunk (Mephitis mephitis). Other grassland forms 

were tiger salamander, Plains toad, yellow mud turtle, western 

box turtle, Texas horned lizard, ground snake (Sonora semiannulata), checkered garter snake (Thamnophis cf. marcianus), 

western diamondback rattlesnake (Crotalus atrox), hawks 

(Buteo spp.), Say’s phoebe (cf. Sayornis saya), northern mockingbird (Mimus polyglottis), Audubon cottontail (Sylvilagus 

audubonii), black-tailed jackrabbit, 13-lined ground squirrel, 

hispid pocket mouse (Chaetodipus cf. hispidus), black-tailed 

prairie dog, Plains pocket gopher, and cotton rat. A prairie dog 

town community continued, along with hawk and badger as 

its predators.
USDA Forest Service RMRS-P-47. 2007 21

This prairie dog town community existed within a shortgrass, herbaceous prairie in a savanna setting of occasional 

deciduous trees in the valley and mesquite along the upland 

lake basins. Despite the greater availability of moisture and 

less arid conditions than those of the middle Holocene, a 

cyclical drought pattern began around 2,000 B.P. that continues 

today. Periods of some aridity occurred through increased 

temperatures and decreased effective moisture. The droughts 

appeared not to have been severe enough to alter either the 

faunal community or the short-grass prairie significantly. 

Surface erosion from periodic denuding of the vegetation led 

to deposition and altered landscapes (Holliday 2001a; Muhs 

and Holliday 2001).

Summary Statement

Throughout the Quaternary, the Llano Estacado has always 

been a grassland, albeit the character of this grassland has 

changed through time. During the late Quaternary, it remains 

an herbaceous grassland. By the LGM, the region is a grassland 

steppe that was a sagebrush grassland in a cool-dry climate. 

During the latest Pleistocene (stratum 1), the grassland is a tall 

grass prairie in a cool-humid climate with a parkland setting in 

the valleys. By the beginning of the early Holocene (stratum 

2), the grassland is a mixed prairie experiencing an increasing 

rise in C4 grasses in a warming, less humid, and more seasonal 

climate with a savanna setting in the valleys. The emergence 

of the short-grass ecosystem occurs between 8,200 to 8,000 

B.P. and is the dominant vegetation throughout the rest of 

the Holocene. Middle to late Holocene (strata 3 to 5) grasslands are short-grass prairies within a fluctuating climate that 

affected the ecosystem from a mesic to xerix to mesic grassland setting with a continued savanna setting in the valleys.

Various trees are native to the Llano Estacado, and most 

are deciduous. All but one of the deciduous trees can occur 

in a small tree to shrub form, making them more flexible in 

response to changing climatic conditions. Occurring primarily 

in the valley system, an occasional hackberry and mesquite 

were on the uplands around the lake basins depending on the 

period. Net-leaf hackberry is the most consistent tree, having 

persisted in the region since the LGM. Conifers are restricted 

to juniper and the occasional piñon-pine that grew along the 

western escarpment, primarily in the late Pleistocene and 

earliest Holocene. Today, junipers are thick along the western 

escarpment with again the occasional piñon-pine.

Key transformations take place that appear to involve 

climate and vegetation response. An early Holocene warming 

trend with greater seasonality and probable decrease in winter 

precipitation is coupled with a shift from the tall grass prairie 

to the mixed grass prairie. By 8,000 B.P., humid conditions 

have declined with a probable shift in rainfall pattern and 

increasing seasonality leading to less effective moisture than 

proceeding periods. This situation is coupled with the rise of 

the short-grass ecosystem that maintains dominance through 

an increasingly arid period. Heat and drought tolerance are 

key characteristics of the short-grass prairie that maintained 

this dominance then, and throughout the rest of the Holocene. 

The emergence of the continental climate around 4,500 B.P. 

provides more mesic but still semi-arid conditions and that 

climatic regime is modernized by the modification of a cyclical 

drought pattern starting around 2,000 B.P.

Bison, pronghorn antelope, and prairie dog are the binding 

grassland species. The transformation of ancient bison into 

modern bison appears to be in response to the rise of the 

short-grass ecosystem and its greater productivity but less 

nutritional value. The rapid size change reflects both a coping 

mechanism with the changing grassland composition and the 

flexibility of the bison genome. Pronghorn antelope browse 

on forbs and other herbaceous vegetation. Their presence 

throughout the late Quaternary underscores the continuance 

of the herbaceous aspect regardless of the character of the 

grassland. Prairie dogs also are adaptable and resilient, with 

a continuing prairie dog town community throughout, regardless of the character of the grassland.

The various lines of evidence are for the most part concordant and provide a solid foundation for examining the late 

Quaternary ecosystems of the region. Phytolith and macrobotanical remains have proven more informative and reliable 

than pollen. These lines of evidence are more reflective of 

local conditions and generally not influenced by extraregional 

factors. Explorations are on-going to expand the record and 

fill in the details. Of specific interest are the expansion of the 

upland record, an increased knowledge of the herbaceous 

nature of the grassland through time, and the relationship 

between prairie dog town communities (and, in particular, the 

prairie dog) and the health and status of a grassland.

Acknowledgments

Thanks are due to Dr. Ron Sosebee (Department of Range, 

Wildlife, and Fisheries Management, Texas Tech University) 

for his gracious invitation to participate in the opening plenary 

session of the 13th Wildland Shrub Symposium of the Shrub 

Research Consortium; Dr. Vance T. Holliday (Departments 

of Geoscience and Anthropology, University of Arizona) for 

sharing data and critical review of the manuscript; Dr. Glenn 

Fredlund (Department of Geography, University of Wisconsin 

– Milwaukee) for sharing data; and to Tara Backhouse 

(Museum of Texas Tech University) for the figures. This manuscript represents part of the ongoing Lubbock Lake Landmark 

regional research program (under the auspices of the Museum 

of Texas Tech University) into late Quaternary climatic and 

environmental change on the Southern High Plains.

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The Author

1

 Quaternary Scientist and museum curator, Museum of Texas Tech 

University, Lubbock, TX. eileen.johnson@ttu.edu
24 USDA Forest Service RMRS-P-47. 2007

Introduction

The Southern High Plains (SHP) are a 130,000-km2 plateau 

in Texas and eastern New Mexico (Holliday 1990). Also 

known as the Llano Estacado, this southernmost subdivision 

of the High Plains section of the Great Plains Physiographic 

Province is “essentially an isolated remnant of the Rocky 

Mountain piedmont alluvial plain” (Reeves 1965:182). The 

SHP are bordered on the east by the Caprock Escarpment and 

the upper Colorado, Brazos and Red Rivers in Texas, and on 

the west by the Pecos River Valley. The northern border of 

the SHP, abruptly delimited by the Canadian River Valley, 

contrasts with the gradual merging of its southern boundary 

with the Edwards Plateau (fig. 1).

The SHP are both extensive and remarkably flat, which 

has led many authors to rather expressive descriptions. For 

example, Carroll and others (1986:186) wrote that the SHP are 

“almost absolutely flat and represent one of the largest tracts of 

level land in the world.” Morris (1997:2) described the Llano 

Estacado as “perhaps the largest isolated, non-mountainous 

area in North America” and elsewhere (p. 20) as “one of the 

world’s largest and flattest plains.” Hunt (1967:225) wrote 

that “...the Llano Estacado [is] one of the most nearly level 

parts of the United States.” A USGS web site states that the 

“Llano Estacado [is] one the largest expanses of near-featureless terrain” (http://tapestry.usgs. gov /features/features/html). 

Whereas slopes on the SHP average only 3 m per mile (Reeves 

1965), several physiographic provinces in North American 

(for example, the Gulf Coastal Plains and the Atlantic Coastal 

Plains) are also relatively flat as well as larger in areal extent 

than the SHP, occupying about 10 percent of the land area of 

the U.S. (Hunt 1967).

The Southern High Plains: A History of Vegetation, 

1540 to Present

Abstract: Considerable documentary evidence is available about the historic vegetation 

of the Southern High Plains (SHP). Accounts spanning about 350 years (from the earliest 

European explorers in the 1540s to scientists working in the later 19th and early 20th

centuries), however, lead to vague and sometimes contradictory conclusions about the 

nature of this vegetation. The earliest documents describe the SHP as vast grassland. The 

fact that native soils were Paleustolls supports this description. The earliest accounts also 

suggest considerable vegetation diversity in certain topographic settings (for example, in 

sandy soils and major draws that cross the SHP). It is also certain that the SHP supported 

vast populations of native herbivores (which were quickly replaced by large populations 

of domestic livestock); were subject to climatic variability; and were frequently burned. All 

of these factors interact with each other at several spatial and temporal scales to affect 

vegetation. Based on historic documentary evidence, it is difficult to describe the precise 

nature of the vegetation of the SHP when it was first encountered by European explorers. 

Although the dominant aspect of the vegetation was that of a grassland, woody species 

(primarily mesquite, Prosopis glandulosa) were either historically present but unrecorded 

by early explorers in upland sites because they had limited experience in these sites and/or 

because recurrent fires maintained populations; or mesquite was introduced in a novel way 

by domestic livestock beginning in the late 1870s and 1880s. In either of these scenarios, 

subsequent increases in woody vegetation during the 20th century likely involved changes in 

fire frequency, grazing history, and climate.

“Too Grande and Too Sublime to be Imagined”

(Pike 1832, in Haley 1968:23)

“The monotonous level or billowy swells of a sea of grass unrelieved by the presence of 

taller plants like a shrub or tree... could fasten upon the senses a conception of the power 

of a victorious vegetation...” (Bray 1906:92)

“If you w’d remain in ignorance of this region of the world read descriptions of it...if you 

would wish to appreciate the scale of its sublimity, on which all Nature is here arranged, 

come and see it.” (Gilpin 1836)

David B. Wester1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 25

Geological History

Characterized by a semi-arid continental climate, this “virtually featureless, constructional surface” (Holliday 1989:74) is 

the most recent of as many as six well-developed but buried 

soils that comprise the Blackwater Draw Formation formed 

by multiple episodes of eolian sheet deposition separated by 

long periods of relative landscape stability over the past 1.4 

million years (Holliday 1990). In fact, similarities between the 

Quaternary Blackwater Draw Formation and the underlying 

Miocene-Pliocene Ogallala Formation suggest that the SHP 

“has probably been a grassland or savanna grassland varying 

from perhaps an arid to a semi-arid or sub-humid environment 

for about 11 million years” (Holliday 1990:510). The topographic monotony of the SHP is relieved only by Holocene 

dune fields (formed during droughts of the Altithermal period) 

along its southwestern and western borders (Holliday 1989), 

thousands of playas scattered over its surface (Bolen and 

others 1989), over two dozen larger saline lakes, and several 

dry tributaries (or “draws”) of the Colorado, Brazos, and Red 

Rivers (Holliday 1990).

Grazing History

As part of the extensive grasslands of the North American 

Great Plains, the SHP have a long history of herbivory. 

Reviewing global patterns, Coughenour (1985:853) concluded 

that “extensive grasslands, grazers, and semiarid climates 

appeared almost simultaneously,” and suggested that many of 

the characteristics of grasses that are advantageous in semiarid environments (for example, presence of basal meristems, 

small stature, high shoot density, deciduous shoots, belowground storage of nutrients, and rapid growth) are also 

beneficial under grazing. In an influential paper, Stebbins 

(1981:84) concluded that “Coevolution of grasses and herbivores has progressed continuously on the North American 

grasslands ever since they first appeared as savannalike openings in the forest during the early part of the Tertiary period.” 

MacGinitie (1962:99, from Axelrod 1985:168) also suggested 

that “the regular association of grazing and browsing 

mammals on the High Plains from the Middle Miocene into 

the Pliocene supports the idea of a savanna-type vegetation.” Early fossil evidence in the Great Plains suggests that 

Figure 1. The Southern 

High Plains (from 

Morris 1997).
26 USDA Forest Service RMRS-P-47. 2007

cool season caespitose species (for example, Stipa, Nassella, 

Piptochaetium, and the extinct Berrichloa) were associated 

with horses and pronghorn antelope during Pliocene times. 

However, current dominant genera of the Great Plains (for 

example, Andropogon, Schizachyrium, Bouteloua, Buchlöe, 

and Panicum) belong to different tribes than the Pliocene 

flora. Although it is uncertain when this transition occurred, 

Stebbins (1981) believed that the current dominant flora was 

absent or uncommon at the beginning of the Pleistocene 

glaciations. Further, he suggested that the current flora is of 

post-Pleistocene origin. After an extensive literature review, 

Axelrod (1985) agreed with MacGinitie (1962) that “most 

of the current formations of western North America, except 

possibly in the area south of Latitude 35°, are less that 10,000 

years old” (MacGinitie 1962:99, from Axelrod 1985:168). The 

change from long-leaved caespitose species to stoloniferous 

shortgrasses reflects adaptations related to changes both in 

environment (increasing aridity) and in dominant grazers. In 

particular, grazers during the Pliocene were horses and pronghorn. However, Bison latrifrons, a browser/grazer adapted to 

forest openings or woodlands, appeared between 500,000 and 

125,000 years ago, peaked in abundance about 100,000 years 

ago during the Sangamon interglacial, survived until at least 

30,000 to 20,000 years ago, and disappeared in late Wisconsin 

(10,000 years ago). Bison antiquus, a grazer/browser adapted 

to savanna or wooded steppe, probably appeared during the 

Sangamon interglacial and peaked during the late Wisconsin 

(10,000 years ago). Bison bison, primarily a grazer adapted 

to open grassland environments, appeared during the late 

Wisconsin and early Holocene; the southern subspecies (B. 

bison bison) reached maximum numbers about 2,500 years 

ago (McDonald 1981). Although about 75 percent of the 

megafauna of North American disappeared with the closing 

of the last ice age, bison numbers followed a different trend, 

reaching peak numbers from 9,000 to 6,000 years ago (Alford 

1973).

It has been estimated that 100 million buffalo existed on the 

Great Plains. Buffalo hunting began in the Texas Panhandle in 

1874. The southern buffalo herd was exterminated between 

1874 and 1878, the northern herd was slaughtered by 1884, 

and by 1878, only 1,091 animals were left (McComb 1989:82-

83). Almost simultaneous with the extermination of the buffalo 

was the removal of native Americans from the Panhandle of 

Texas with the battle of the Red River in 1874-1875. Carlson 

(1974:15) wrote that “More than most campaigns the Red 

River War made the immense northern border of the Llano 

Estacado safe for an advancing civilization.” Mexican sheep 

ranchers were the first graziers in the SHP (Taylor 1997). 

They were followed, however, and soon outnumbered by 

cattle ranchers. One of the first ranchers in this area, Charles 

Goodnight, brought 1,600 head of cattle to the Palo Duro 

Canyon area in 1876. By 1880, more than 100 other ranchers 

brought 100,000 cattle as well as 100,000 sheep into northwest Texas (Nall 1972). Thus, the native herbivores were 

exterminated and quickly replaced by domestic animals.

There were fewer than 500,000 cattle in Texas in 1830 

(Fisher 1977:183). Cattle numbers increased thereafter 

throughout the state, and by 1888 there were more than 9 

million head of cattle (Brooks and Emel 2000:54). Cattle were 

not grazed on the SHP, however, until the 1880s (Carlson 

1974). Further, the “boom” years of the SHP cattle industry did 

not last long. Two factors combined to lead to a collapse in the 

cattle industry. First, weather conditions in the years around 

1870 were equable (following widespread drought conditions 

throughout much of the Great Plains in the early 1860s; Meko 

1995:322-323; fig. 6 in Woodhouse and Overpeck 1998). 

Second, high livestock numbers led to overgrazing: before 

the worst overgrazing, 5 acres could support one steer, but 

by 1880, 50 acres were needed (White 1991, from Brooks 

and Emel 2000:55). With these two factors as background, 

an extremely harsh winter in 1885, and another in 1888, with 

“freezing temperatures and high winds...combined with loss 

of range due to overgrazing, [and] brought heavy losses...The 

cattle ranching that remained on the plains was just a remnant 

of the flourishing cattle trade of the late 1870s and early 1880s, 

never to recover the teeming numbers of that era” (Brooks and 

Emel 2000:55-56; also see Nall 1972; Taylor 1997). Britten 

(1993) indicated that millions of cattle perished following the 

droughts and blizzards of 1885 to 1887.

Today, the SHP are one of the most intensively-farmed 

areas in the United States, with 90 percent of its area in rowcrop agriculture (on 11,880 farms; farm acreage is based on 

the following Texas counties: Deaf Smith, Randall, Parmer, 

Castro, Swisher, Bailey, Lamb, Hale, Floyd, Cochran, 

Hockley, Lubbock, Crosby, Yoakum, Terry, Lynn, Gaines, 

Dawson, Andrews, Martin; www.nass.usda.gov/census/

census02 /volume1 /tx/st48 _2_001.pdf, and www.census.

gov/prod/2002pubs/00ccdb/dd00_tabB1.pdf.). Cotton is 

the largest crop produced on the Llano Estacado. In fact, 15 

percent of the cotton grown in the U.S. and 3.5 percent of 

the cotton grown world-wide is produced on the SHP (Brooks 

and Emel 2000:111). Texas produces more cattle (13.7 million 

head; Texas Farm Bureau) than any other state. The 26 counties surrounding Amarillo, Texas, have 25 to 30 percent of all 

cattle on feed in the U.S. (Evett 2003).

Human History

The SHP are also remarkable for the records of human 

history they reveal. The earliest evidence of European people 

in southwestern North America (Chipman 1992:11) can be 

found in the descriptions of Alvar Núñez Cabeza de Vaca in 

the 1530s. The area is also among the earliest occupied by 

Native Americans – there are abundant archeological artifacts 

of human habitation 12,000 years ago at the Lubbock Lake 

Landmark site (Johnson 1987). The Paleo-Indian period on the 

SHP can be recognized in the following subdivisions: Clovis 

(11,500 to 10,000 years B.P.); Folsom (10,500 to 10,000 years 

B.P.); Plainview (around 10,000 years B.P.); and Firstview 

(from Plainview to about 8,000 years B.P.). Additional 

native American cultures of the Archaic Period (6,000 to 

2,000 years B.P.), Woodland tradition (2,000 years B.P.), and 

Plains Village Culture (1,350 to 1,450 A.D.) existed on the 
USDA Forest Service RMRS-P-47. 2007 27

SHP. Early Spanish explorers encountered Apaches on the 

SHP. These native Americans were replaced by Comanches 

by 1775 (Brooks and Emel 2000:26-27, 30).

The SHP were one of the last regions settled by Texans 

after fighting with Native Americans ended with the Red 

River War in 1874-1875 (for example, Carlson 1974). Early 

farming settlements were simultaneous with the establishment of cattle ranches on the SHP (Nall 1972). The southern 

parts of the SHP were generally established earlier than the 

northern parts.

Several railroads (for example, the Denver & Fort Worth 

Railroad and the Southern Kansas Railway Company) were 

operating on the SHP by 1888 (Nall 1972). Big Spring began 

to develop around 1880 when rail service began in Howard 

County. Likewise, Miami began around 1887 with rail service, 

and Sutton and Floyd counties and the city of Lubbock were 

established in 1890. Although Deaf Smith County was established in 1879, it had no permanent settlers until 1887 (Burnett 

1990:4). Census returns in 1880 showed a population of 5,388 

residents in the 50 counties of the Llano Estacado. By 1910, the 

population had grown to 140,749 residents (Burnett 1990:4). 

In the Texas Panhandle, the population increased from 1,607 

to 9,542 from 1880 to 1890 (Nall 1972). The first farm was 

established in 1879 in the town of Estacado (Crosby County, 

Texas). In 1886, Estacado became the county seat for Crosby 

County and Central Plains Academy, the first college on the 

SHP, was established in 1890 (http://www.tsha.utexas.edu/

handbook/online/articles/view/EE/hne27.html). In 1900, 803 

farms existed on the SHP. By 1910, this number swelled to 

2001 farms. Continued growth was evident, with 4089 farms in 

1920 and 6,161 farms in 1925 (Brooks and Emel 2000:69-70). 

As early as 1925, farm acreage occupied nearly 49 percent of 

the area of a 10-county region on the SHP (Bailey, Cochran, 

Crosby, Floyd, Hale, Hockley, Lamb, Lubbock, Parmer, and 

Potter counties; Brooks and Emel 2000:84).

In several respects, therefore, the SHP have a remarkably long history: first, with regard to relative geologic and 

climatic stability punctuated by periodic and sometimes 

devastating droughts; second, with regard to the presence of 

herbivores, both native and domestic; and third, with regard 

to interaction with human cultures. All of these factors, whose 

combined influence has shaped the vegetation of the SHP, must 

be considered to more fully understand its dynamic history.

Environmental Characterization

Climate

Elevations on the SHP range from 823 m on the eastern 

border to 1,463 m on the west (Reeves 1965). A semi-arid 

or dry steppe climate with mild winters results from the 

combined influence of relatively high elevation, frequent 

intrusions of dry polar air masses, and distance from sources 

of moisture (NOAA 1982). Annual precipitation increases 

from 300 mm in the west to 500 mm in the east (Holliday 

1990). The continental nature of the SHP climate, however, 

leads to considerable intra-annual (NOAA 1982) and interannual (Holliday 1990) variability in precipitation. The 

months of May and September typically have the highest rainfall, and the period from October to April is generally dry. 

In the northern SHP (Hereford, Randall County), annual rainfall averages 474 mm; May (54 mm), June (74 mm), August 

(82 mm) and September (57 mm) are the wettest months. In 

the central portion of the SHP (Lubbock, Lubbock County), 

annual precipitation averages 475 mm; May (59 mm), June 

(76 mm), August (60 mm) and September (65 mm) are the 

wettest months. In the southern portion of the SHP (Andrews, 

Andrews County), annual precipitation averages 384 mm; 

June (54 cm), July (57 mm), and September (56 mm) are the 

wettest months.

Annual precipitation also varies interannually (fig. 2). 

Droughts are recurring features of the climate of the SHP (for 

example, Woodhouse and Overpeck 1998; fig. 3). Holliday 

(1989) indicated that the warmer, drier conditions during 

the Altithermal, which initiated eolian sedimentation locally 

throughout the SHP between 8000 and 7000 BC, and affected 

all areas of the SHP between 3500 and 2500 BC, resulted 

in “more geomorphic change ... than any other equivalent period of time for which data are available” (Holliday 

Figure 2. Annual rainfall, Lubbock, Texas 

(NOAA).
28 USDA Forest Service RMRS-P-47. 2007

1989:80). In more recent times, droughts have been observed 

in at least some parts of the Great Plains in the last quarter 

of the 13th century (Woodhouse and Overpeck 1998); in the 

second half of the 16th century (Woodhouse and Overpeck 

1998; Stahle and others 2000); and in the 1750s, early 1800s, 

1820s, early 1850s to early 1860s, late 1880s to early 1900s, 

1930s, and 1950s (Meko 1995; Woodhouse and Overpeck 

1998) (fig. 3). It is interesting to note that (1) droughts in the 

16th century evidently lasted longer than the drought of the 

20th century; (2) there is little evidence of drought between 

the severe drought of the latter half of the 16th century and 

the latter half of the 18th century; and (3) despite the severity 

of the droughts of the 20th century, these periods were not 

drastic enough to cause regional mobilization of sand dunes 

(Woodhouse and Overpeck 2000:2696 and references therein; 

also see Muhs and Holliday 1995; Forman and others 2001). 

Periodic droughts have had significant effects of flora, fauna, 

and human activities.

Soils

The Blackwater Draw Formation, with a thickness that 

varies from a “feather-edge” in the southwest to “at least 27 

m” in the northeast (Reeves 1976:217, in Holliday 1990:494) 

forms the surface of the SHP. This “sheet-like body of eolian 

sediment” (Holliday 1990:493), with the Pecos River Valley 

as its source, is comprised of sands to very fine sands in the 

southwest and finer sediments (silts and clays) toward the 

northeast (Holliday 1990). This pattern of textural variability 

is “apparently the result of downwind sorting” (Holliday 

1990:493). Additionally, the thickening of the Blackwater 

Draw Formation from the southwest to the northeast “is 

probably due to the sandy texture of the sediments in the 

southwest, which would be much more susceptible to wind 

deflation than the silty and clayey sediments in the northeast” 

(Holliday 1990:494). It is also likely that vegetative cover in 

the southwest was sparser than in the northeast because of 

drier conditions. This would render the southwestern portion 

more prone to wind deflation (Holliday 1990).

Surface soils of the SHP are very well developed. 

Paleustalfs are common in the central and southwestern SHP, 

and Paleustolls are common in the central and northeastern 

SHP. The Paleustolls of the central SHP are similar to the 

Paleustalfs of the southwestern SHP except for the presence 

of a mollic epipedon. The Paleustolls of the northeastern SHP 

additionally possess a clay to clay loam argillic horizon with 

prismatic structure (Holliday 1990). The complex pattern of 

Paleustalfs and Paleustolls in the central SHP is most likely 

the result of wind erosion. The “native soils were most likely 

Paleustolls, given the native vegetation of the region. Eolian 

erosion could very effectively remove much of the mollic 

epipedon, resulting in a soil with an ochric epipedon, but 

otherwise not affecting the subsurface horizons...it is possible 

that the soil pattern is a historic feature, resulting from many 

periods of dust storm activity” during recent times or the 

middle Holocene (Holliday 1990:498). The Paleustolls of the 

northeastern SHP differ from those of the central SHP because 

of the presence of a darker color in the upper solum and finer 

Figure 3. Palmer Drought Severity 

Index for the Southern High 

Plains, Texas (from www.ncdc.

noaa.gov).
USDA Forest Service RMRS-P-47. 2007 29

textures. The finer textures are due to downwind fining. One 

explanation for the darker solum is that it is a “pachic epipedon, 

the result of slow aggradation of the surface.” As the original 

A horizon became buried, it was converted to a Bt horizon 

(Holliday 1990:501). The darker color also may have resulted 

in part from more vegetation biomass as a consequence of 

higher effective precipitation and cooler temperatures in the 

northeastern SHP (Holliday 1990).

Another noteworthy feature of the landscape and soils of 

the SHP is the relative lack of evidence of erosion compared 

with other parts of the High Plains. No streams have deeply 

incised the SHP (Loomis 1938), leaving its surface “almost 

untouched by erosion” (Fenneman 1931:14). Mead and Brown 

(1970:47) described the Llano Estacado as “the best preserved 

of the [Great] plains, for they have been little dissected....”

Vegetation

Early Descriptions (1540s to 1850s)

Any description of the historic southwest must begin with 

Álvar Núñez Cabeza de Vaca and his celebrated journey in 

the 1530s. Historians disagree (for example, Chipman 1987) 

about the exact route that de Vaca and his three companions followed. Some authors place his route as far north as 

Big Spring (Hallenbeck 1940, from Olson and others 1997), 

Midland, Texas (Terrell 1962), or Lubbock, Texas (Bryan 

1956). Others suggest a more southerly route (for example, 

Chipman 1987, 1992; Olson and others 1997; Krieger 2002).

In Chapter 30 of his Relacíon de los Naufragios (“Account 

of the Disasters”), de Vaca described meeting a group of 

Native Americans whom he called “the cow nation:”

“...They are people with the best bodies that we saw and 

the greatest liveliness and ability and who understood us 

best and responded to what we asked them. We call them 

those of the cows, because most of them [the bison] die 

[are killed?] near here. And up that river more than 30 

leagues they go killing many of them” (Krieger 2002:86, 

bracketed text supplied by Krieger).

Morris (1997:14-15) places this encounter on the southern 

margins of the SHP, perhaps near the Pecos River that flows 

parallel to the SHP, or alternatively near the Rio Grande River. 

Others, notably Davenport and Wells (1918, 1919) and Krieger 

(2002) located “the people of the cows” near the confluence 

of the Rio Concho and Rio Grande rivers near present-day 

Presidio, Texas and Ojinaga, Mexico. Despite these differences in location, many authors (for example, Terrell 1962; 

Morris 1997; Krieger 2002) have suggested that de Vaca and 

his companions nevertheless encountered the “Llano culture.” 

It was in this general area that their native guides told the travelers that:

“...there were no people that way [either] (that is, to 

the north), except very far away, and nothing to eat, 

nor water to be found... (Krieger 2002:80; text in 

parentheses added).

Morris (1997:14) observed that this may well have been 

a description of the SHP: “it is vast; it is arid; it is low in 

traditional foods; and it has no permanent settlements.” In 

the quotation above describing the “cow nation,” Hodge 

(1907:103, footnote 4) suggested that the phrase “near here” 

probably did not refer to the “immediate” vicinity of the 

encounter between de Vaca and the so-named native peoples, 

because de Vaca and his companions:

“...decided to go in search of the maize and we did not 

want to follow the way to the cows because this was 

to the North. And this was for us a great detour...” 

(Krieger 2002:99).

Morris (1997:15) likewise concluded that de Vaca avoided 

the Llano Estacado proper. Nevertheless, the encounter with 

the cow nation was significant. Terrell (1962:207) provided an 

evocative image:

“They listened to talk and tales about things of which 

they had never heard. To the north were endless plains, 

plains so unchanging, so flat and treeless, that not a 

mound, not a stick or bush rose to disfigure their smooth 

flow to the horizons. Where they ended, no one could 

say. They ended in the sky. On them the herds of cattle 

roamed in countless numbers, herds so immense that 

they took several suns to pass, herds that covered the 

earth like ragged blankets as far as a man could see and 

crawled like the shadows of the clouds that journeyed 

to nowhere.”

The description of the SHP that we can draw from de Vaca’s 

travels is noteworthy in two respects. First, the Llano Estacado 

was an extensive, featureless plain with no trees or shrubs to 

relieve the dreary monotony of its level landscape. Second, 

the SHP was the home of immense herds of native grazers. 

Thus, our first description of the SHP is that of a grassland, 

and one that was, at least at times, heavily grazed.

The impressions about the SHP that can be gathered from 

de Vaca’s Relacíon are important, but are unfortunately vicarious. Most historians agree that de Vaca did not observe 

first-hand the Llano Estacado proper. His experiences nevertheless stimulated additional interest in the southwest: Don 

Francisco Vasquez de Coronado’s exploration of the SHP was 

organized partly in response to the stories told by de Vaca and 

his companions about the mysteries of the New World. Prior to 

leading his entire expedition to the SHP, Coronado dispatched 

Captain Hernando de Alvarado and 20 soldiers as an advance 

party to explore the “buffalo plains” (Winship 1964:77). Their 

journey took them past present-day Pecos, New Mexico, and 

then east southeast to present-day Santa Rosa, New Mexico, 

where they crossed the Pecos River (Morris 1997:20):

“After Alvarado had sent an account of this river to 

Francisco Vasquez, he proceeded forward to these 

plains, and at the borders of these he found a little river 

which flows to the southwest [perhaps a tributary of 

the Canadian (Bolton 1964:188)], and after four day’s 
30 USDA Forest Service RMRS-P-47. 2007

march he found the cows, which are the most monstrous 

in the way of the animals which has ever been seen or 

read about...There is such a quantity of them that I do 

not know what to compare them with, except with the 

fish in the sea, because in this journey, as also on that 

which the whole army afterwards made when it was 

going to Quivira, there were so many of them that many 

times when we started to pass through the midst of them 

and wanted to go to the other side of them, we were not 

able to, because the country was covered with them” 

(Winship 1964:355-356; bracketed text added).

The description of the geography of this expedition does not 

explicitly indicate that this advance party actually ascended 

the SHP proper. It seems reasonable, however, from the abundance of bison sighted that they may well have been on the 

Llano Estacado. Although the accounts of this journey do not 

contain a description of the vegetation of the SHP, chroniclers 

of Coronado’s main expedition to the SHP were fulsome in 

their descriptions.

Coronado and his vast expedition departed from near 

present-day Bernanillo, New Mexico, in April, 1541 for 

the distant “buffalo plains.” Morris (1997:26-28) suggested 

that his party may have crossed the Pecos River somewhere between present-day Tecolotito (San Miguel County) 

and Colinia (Guadalupe County), New Mexico. Meyers 

(2003:147) suggested that they reached and crossed the Pecos 

River at Anton Chico (San Miguel County). The expedition 

then traveled east with the escarpment of the Llano Estacado 

to their south. Morris (1997:28) suggested that they ascended 

the caprock onto the Llano Estacado proper between present-day Ragland and San Jon (Quay County), New Mexico 

(also see Chipman 1992:38). Meyers (2003:148) suggested 

that the army ascended the Llano Estacado possibly at Puerto 

del Arroyo (in southeastern Quay County, New Mexico) or at 

Agua del Piedro (near Adrian, Texas).

Pedro Castañeda, “the historian of the Coronado expedition” (Winship 1964:13), provided vivid images of the SHP. 

He described “such great numbers of cows [that is, bison] that 

it already seemed something incredible” (Winship 1964:235). 

He recounted how a Spaniard “got lost who went off hunting 

so far that he was unable to return to camp, because the country 

is very level” (Winship 1964:235). He told how, searching for 

an errant advance party, “it was impossible to find tracks in 

this country, because the grass straightened up again as soon 

as it was trodden down” (Winship 1964:235). Coronado “sent 

some of his companions to guide the army to that place, so 

that they should not get lost, although he had been making 

piles of stones and cow dung for the army to follow. This was 

the way in which the army was guided by the advance guard” 

(Winship 1964:235). Elsewhere, Castañeda wrote:

“Who could believe that 1,000 horses and 500 of our 

cows and more than 5,000 rams and ewes and more 

than 1,500 friendly Indians and servants, in traveling 

over those plains, would leave no more trace where they 

passed than if nothing had been there—nothing—so that 

it was necessary to make a pile of bones and cow dung 

now and then, so that the rear guard could follow the 

army. The grass never failed to become erect after it had 

been trodden down, and, although it was short, it was 

fresh and straight as before” (Winship 1964:302).

Coronado himself described the SHP to King Charles V 

of Spain:

“I traveled...until I reached some plains, with no more 

landmarks than as if we had been swallowed up in the 

sea, when they strayed about, because there was not a 

stone, nor a bit of rising ground, nor a tree, nor a shrub, 

nor anything to go by. There is much very fine pasture 

land, with good grass...[we went] many days without 

water, and cooking food with cow dung, because there 

is not any kind of wood in all these plains, away from 

the gullies and rivers, which are very few” (Winship 

1964:367-368).

Even the native guides who directed the return route of 

Coronado’s army back to New Mexico needed help navigating across this featureless landscape. Castañeda wrote:

“... these people [that is, native American guides] are 

always roaming over this country in pursuit of animals 

and so know it thoroughly. They keep their road this 

way: In the morning, they notice where the sun rises 

and observe the direction they are going to take, and 

then shoot an arrow in its direction. Before reaching 

this they shoot another over it, and in this way they go 

all day toward the water where they are to end the day” 

(Winship 1964:241).

The writings of Coronado and his chroniclers leave an 

unmistakable image of the Llano Estacado. It was a treeless, 

shrubless sea of grass, and the monotony of this featureless 

landscape was not relieved by any structural vegetation diversity at all.

Spanish exploration of the SHP continued after Coronado’s 

first historic journey, and later descriptions corroborated 

the images that Castañeda painted. In 1599, Vincente del 

Zaldivar, sent out by Don Juan Pérez Oñate, an early colonizer 

of New Mexico, explored the northern portion of the SHP in 

the vicinity of the Canadian River. Along the margins of the 

northern SHP timber was found in abundance. Describing 

the Llano Estacado, however, Zaldivar wrote, “These cattle 

have their haunts on some very level mesas which extend 

over many leagues...The mesas have neither mountain, nor 

tree, nor shrub, and when on them they were guided solely 

by the sun” (Bolton 1946:230). The last major expedition in 

the 1600s (Morris 1997:147) was made by Juan Dominguez 

de Mendoza who, in the company of two Franciscan priests, 

found the southern part of the SHP between the Pecos River 

and the Middle Concho River, “all...a plain” (Bolton 1946: 

330). In some locations, the country was so destitute of “suitable timber” that a cross could not be erected, although there 

was nevertheless an abundance of mesquite (for example, 

Bolton 1946:328-329, 333). In the 1780s, Jóse Mares entered 
USDA Forest Service RMRS-P-47. 2007 31

the Llano Estacado on its northwestern borders. He wrote, “I 

traveled very rapidly this day across a very wide plain which 

contains no landmarks other than an arroyo which runs to the 

east and which has two clumps of chinaberry trees” (Loomis 

and Nasatir 1967:291). Loomis and Nasatir (1967:291) and 

Morris (1997:173) suggested that Mares and his companions 

were following Tierra Blanca Creek, and eventually encountered Tule Creek, near present-day Tulia, where permanent 

water allowed cottonwoods and reeds to grow.

The Llano Estacado was explored by Spanish, French, 

and American adventurers from the mid 1500s well into the 

1800s. In fact, by 1800, “generations of New Mexican buffalo 

hunters...had traversed [the Llano Estacado] thoroughly” 

(Morris 1997:153-154). Chipman (1992) and Morris (1997) 

provided a thorough and insightful summary of accounts of 

the SHP written throughout this period. It is remarkable that 

the basic description of the landscape and the vegetation of 

the Llano Estacado, as seen through the eyes of explorers 

from 1541 well into the 1800s, remains essentially the same. 

Quotations presented earlier from the writings of Castañeda, 

for example, can be compared to what Albert Pike, a lawyer 

and author, wrote in 1832:

“Imagine yourself, kind reader, standing in a plain to 

which your eye can see no bounds. Not a tree, not a 

bush, not a shrub, not a tall weed lifts its head above 

the barren grandeur of the desert; not a stone is to 

be seen on its hard beaten surface; no undulation, no 

abruptness, no break to relieve the monotony...Imagine 

then countless herds of buffalo” (Haley 1968:21-22).

Similarly, George Kendall, a newspaperman who accompanied the “Texas-Santa Fe Expedition” of 1841 (Morris 

1997:229-230), wrote in 1856:

“Here we were again gratified by finding spread out 

before us a perfectly level prairie, extending as far 

as the eye could reach, and without a tree to break 

its monotony” (p. 216)...We were going forward at a 

rapid pace, the prairies before us presenting no other 

appearance than a slightly undulating but smooth 

appearance (p. 221)...Not a tree or bush, and hardly a 

weed could be seen in any direction. A green carpet of 

short grass, which even at this season was studded with 

innumerable strange flowers, was spread over the vast 

expanse, with naught else to relieve the eye” (Kendall 

1856:225).

Thomas Falconer, who accompanied the expedition, 

wrote:

“We commenced the ascent to the grand prairie—the 

Llano Estacado of New Mexico. This was the great 

plain spoken of at San Antonio as too extensive to travel 

over, where we should be without timber, without water, 

and where many of our horses would perish...we found 

before us an extensive flat table-land stretching as far 

as the eye could reach...Proceeding over this great 

prairie ...[we] were out of sight of every tree and shrub. 

The grass was fresh and green...Though we had no 

wood, there was an abundance of dried buffalo chips 

(p. 443)...[as they approached the boundary of the 

Llano Estacado] below us we saw a wooded country” 

(Kendall 1856:445; bracketed text added).

A diary by Gallagher and Hoyle, also written in 1841, 

describes the Llano Estacado as “a vast level prairie as far 

as the eye could reach without a tree or a shrub” (Morris 

1997:238). In 1844 Josiah Gregg wrote, “The high plains 

seem too dry and lifeless to produce timber” (Moorhead 

1954:362). In one of the most famous descriptions of the SHP 

(near Adrain, Texas), Captain R.B. Marcy, a military explorer, 

wrote on June 14, 1849:

“When we were upon the high table land, a view 

presented itself as boundless as the ocean. Not a tree, 

shrub, or any other object, either animate or inanimate, 

relieved the dreary monotony of the prospect; it is a 

vast illimitable expanse of desert prairie—the dreaded 

‘Llano Estacado’ of New Mexico; or in other words, the 

great Zahara of North America. It is a region almost as 

vast and trackless as the ocean...it spreads forth into 

a treeless, desolate waste of uninhabitable solitude” 

(Marcy 1850:42).

Many of the descriptions of the SHP emphasize its vastness, its absence of woody vegetation, and its dominance by 

short grasses. These descriptions led to an image of the SHP 

as the “Great Zahara of North America” (Marcy 1850:42), a 

perception that has been thoughtfully analyzed by a number 

of authors (for example, Lewis 1966; Fenton 1990; Morris 

1997). The concept of the “Great American Desert” was introduced to the American public by Z. Pike in 1810: “Beyond the 

meridian 96° 30’ west Pike distinguished between the valley 

floors, which would prove to be cultivable, and the extensive upland plains, poor in soil, treeless, and desiccated for 

eight months of the year, which he predicted might in time 

become ‘as celebrated as the sandy deserts of Africa’ ” (Lewis 

1966:35). Major S.H. Long, however, is often credited with 

introducing this idea after his 1820 exploration to the Rocky 

Mountains. The official map produced from this expedition, 

published in 1823, labeled the region that included the Texas 

Panhandle as well as Oklahoma and parts of Colorado as 

“Great American Desert” (Lewis 1966:35). Many historians 

and geographers have since suggested that Long’s assessment 

of the central and southern Great Plains (from the South Platte 

to the Canadian River) was culturally biased, or even a product 

of a vivid imagination (for example, Blackmar 1906, from 

Lawson and Stockton 1981). However, Lawson and Stockton 

(1981), on the basis of reconstructed climatic data, concluded 

that: “These years of abnormally low moisture culminated in 

extreme drought throughout the lower portion of the western 

interior. Long’s route passed through the core of this moisture 

deficiency. In relative terms, the region identified by Long as 
32 USDA Forest Service RMRS-P-47. 2007

the Great American Desert was experiencing drought stress 

exceeding that of the 1930s. Only one other period, that of 

the late 1720s, surpassed the intensity or extent of the drought 

witnessed by Major Stephen H. Long. When one considers the 

magnitude of this moisture anomaly, augmented by the pressures of overgrazing by buffalo, perhaps it is less reasonable 

to refer to the desert as an illusion. For Long and his scientific 

cadre, the ‘impress of geographic conditions’ represented a 

reality never since experienced by this cis-Rocky Mountain 

west” (Lawson and Stockton 1981:535).

It is also true, however, that early explorers described woody 

vegetation in draws, riverbeds, and ravines, most obvious 

around the periphery of the SHP (on all sides), but also evident 

in some of the more conspicuous canyons that penetrated the 

SHP from the eastern escarpment of the Llano Estacado. For 

example, Coronado’s army constructed a bridge to cross the 

Pecos River on the way to the SHP, clearly indicating that 

woody vegetation was abundant along waterways peripheral 

to the SHP along its northwest margin. After they had crossed 

the SHP, Coronado encountered the eastern escarpment of the 

Llano Estacado, perhaps in Tule Canyon (Chipman 1992:38; 

Morris 1997:56), where “colorful canyons...descended 

hundreds of feet to rough, scrubby flats and timbered headwater creeks far below...Where these streams poured into 

larger drainages...the combination of wood, water, and food 

were particularly pleasant. These fringing woods were cool 

and shady...” (Morris 1997:55-56). Morris (1997, Chapter 

6) also suggested that Coronado’s army stopped at Blanco 

Canyon in Crosby County, where timber, water, and food 

were abundant, including plums, wild grapes, mulberries, and 

possibly hickories.

In addition, the country that lay “below” the SHP (on 

all sides) supported abundant woody vegetation including 

mesquite. In fact, it was in Union County, New Mexico, along 

a stream usually identified as “Major Long’s Creek” (which 

flows into the Canadian River near the Texas state line; 

McKelvey 1955:229; Thwaites 1966, Vol. XVI:85) that Edwin 

James, a botanist traveling with Major S. Long in his exploration of the headwaters of the Red River in 1820, provided an 

early written record of mesquite in the area of the SHP:

“...we found ourselves once more entering a vast 

unvaried plain of sand...Among the few scattered and 

shrubby trees met with in this district, are oaks, willows, 

and the cottonwood; also a most interesting shrub or 

small tree, rising sometimes to a height of twelve or 

fourteen feet. It has dioecious flowers, and produces a 

leguminous fruit, making in several particulars a near 

approach to gladetschia...The leaves are pinnated, 

and the trunk beset with spines, somewhat like a honey 

locust, but the spines are single” (Thwaites 1966, Vol. 

XVI:91-93).

Several military explorers provided valuable descriptions of 

vegetation on the periphery of the SHP. Lt. James Abert traveled eastward along the Canadian River in 1846. Throughout 

his report, he remarked on the abundance of mesquite as he 

traveled across the Texas Panhandle. For example, in the 

general vicinity of Logan, New Mexico, Abert (1846) wrote:

“[The Canadian River]...has increased to 70 or 80 

feet in width, with a deep and very rapid current, so 

that we could scarcely keep our feet whilst bathing...

the [river] bottom in which we encamped is everywhere 

covered with various species of cactus, the sharp spines 

of which penetrated our moccasins, making it painful 

to walk about. There is a plant still more annoying, 

commonly called “Sand-bur.” This is a diminutive 

plant, lying close to the sandy surface, loaded with a 

profusion of little burs, which attach themselves to 

our clothes and blankets by their sharp prickles, and 

adhere with great tenacity. Amongst the sylva, the 

hackberry, “Celtis crassifolia,” is quite common, and 

we observed, for the first time, an extensive grove of the 

pride of India, “Melia azederach”—a tree gifted with a 

beautiful form and dense foliage...The trees were every 

where loaded with heavy masses of grape vines, “Nitis 

aestivalis”...It was now the fruit season of the broadleafed cactus, “C. opuntia,” and they were every where 

in great abundance...We saw to-day great quantities of 

the “musquit,” or muskeet, covered with its long-sabreformed legumes. The creek is well-timbered...” (Abert 

1846:29-30).

In 1849, Marcy traveled from Fort Smith, Arkansas, to 

Santa Fe, New Mexico, along the Canadian River, and then 

returned along the southern boundary of the SHP. Marcy 

generally corroborated Abert’s general vegetation description 

of the Canadian River (also see Marcy 1853, for example, 

Chapter 5). For example, he remarked on June 10 that: “We 

have passed over a high rolling prairie for the last three days, 

destitute of wood, except a narrow fringe of trees upon the 

borders of the ravines” (Marcy 1850:40). However, the 

following day, Marcy wrote: “We started this morning, our 

road continuing over the elevated plateau, destitute of water, 

until we reached here, where there is a fine spring creek, with 

a great abundance of wood and grass” (Marcy 1850:40). On 

June 13, he wrote: “We passed a great deal of small mesquite 

and numberless plants of the jointed cactus today” (Marcy 

1850:41). It should be noted that despite using terms such as 

“high rolling prairie” and “elevated plateau,” Marcy was in 

fact traveling below the SHP. He did not ascend to the Llano 

Estacado proper until June 14 (quoted above).

Marcy (1850) returned to Fort Smith via a route across the 

southern boundary of the SHP. From Santa Fe, he traveled 

south along the Pecos River, and then turned east, crossed 

through the Monahans area (Ward and Winkler Counties, 

Texas), and reached the eastern escarpment of the Llano 

Estacado at Big Spring, Texas (Howard County, Texas). Along 

the Pecos River, Marcy wrote:

“After marching six miles further, we encamped again 

on the west bank of the river. Here we found the finest 

and most luxuriant grama grass we had seen, with 
USDA Forest Service RMRS-P-47. 2007 33

mezquite wood. Keeping down the right bank of the 

river, we found the valley covered in many places with a 

growth of small mezquite trees...” (Marcy 1850:60).

After crossing the Pecos River, Marcy wrote:

“There has been a chain of sand hills in sight to-day, 

running from north to south across our course, about 

twenty miles to the east of us, (upon the Llano Estacado,) 

in which our guide informs us that there is water, but that 

we are obliged to pass over the sandy road from some 

fifteen miles to get through them” (Marcy 1850:61).

Marcy crossed through the sandy country, now known 

as the Monahans Sand Dunes, and was surprised to find 

water, which his guide informed him was permanent. Having 

passed through the sand dunes, Marcy again encountered 

“hard prairie...There is good grass near the hills, and sufficient wood for fuel” (Marcy 1850:62). Although the species 

is not identified, it is likely that Marcy encountered mesquite 

to the northeast of the Monohans sand dunes. Marcy then 

“pushed out upon the high plain of the Llano Estacado” 

(Marcy 1850:62-63). He encountered Mustang Pond and 

then Laguna, or Salt Lake. Marcy wrote: “We marched twenty-three miles today...which brought us to the Laguna, or 

Salt Lake. The country has been similar to that of yesterday, 

over the high rolling table lands of the Mesa, with no wood 

except the small mezquite brush” (Marcy 1850:64). In another 

eight miles bearing northeast, Marcy encountered the eastern 

escarpment of the Llano Estacado near Big Spring. He wrote: 

“The mezquite trees are becoming larger as we descend from 

the high plain” (Marcy 1850:64). As Marcy moved east off 

the Llano Estacado and started towards Fort Smith, Arkansas, 

he described “...a perfectly level grassy glade, and covered 

with a growth of large mesquite trees at uniform distances, 

standing with great regularity, and presenting more the appearance of an immense peach orchard than a wilderness” (Marcy 

1850:68).

Lt. A. Whipple explored the possibility of a railroad route 

along the northern SHP in 1853. He wrote:

“Ascending about two hundred and fifty feet, in about a 

mile from camp we reached the top of the Llano. Here, 

for the first time, we saw what one might call a prairie 

ocean; so smooth, level and boundless does it appear. 

It is covered with a carpet of closely cropped buffalograss, and no other green thing is to be seen (p. 87)...

to the top of the Llano...towards the south, appears 

smooth, level, and of unlimited extent. It is covered with 

short buffalo-grass, but contains neither shrub nor tree 

to vary the landscape” (Whipple 1853:119-120).

Marcy explored the sources of the Big Witchita and Brazos 

Rivers in 1854, accompanied by W.B. Parker. Both men left 

descriptions of their travels. Parker (1854:160-161) described 

the vegetation of a spur of the Llano Estacado along the Brazos 

River as follows: “...and finally ascending over a steep and 

dangerous road, came to a broad level plain, a spur of the 

Llano Estacado, covered with buffalo grass and mesquite, and 

extending as far as the eye could reach in a perfect level towards 

the dim, cloud-like mountains at the head of the Brazos.” This 

description clearly mentions mesquite on the east-central 

Llano Estacado. Two additional observations, however, are 

pertinent: Marcy’s description of this area (Marcy 1854:14) 

fails to mention mesquite on the Llano Estacado and Parker’s 

description is accompanied by a footnote which states, in part, 

that the Llano Estacado “is...without a tree...throughout its 

entire surface” (Parker 1854:161). Thus, the conclusion that 

mesquite was dominant in this area remains ambiguous.

J. R. Bartlett traveled westward from Fredericksburg, 

Texas, to El Paso in October, 1850. He frequently described 

woody vegetation including live oak and mesquite along his 

route through the northern Edwards Plateau. In October, he 

described the vegetation near Antelope Creek, which he identified as on the tributaries of the Concho River. At this time, 

Bartlett was still on the Edwards Plateau:

“Our route today had been over a level prairie country, 

deficient of wood, save a few scattering mezquit trees 

of diminutive size, and light grass, indicating a poorer 

soil. We have noticed as we advanced westward, and 

ascended the high tableland of Texas [he was not on 

the Llano Estacado at this time], an inferior soil, and, 

as a necessary consequence, a more scanty herbage. 

The beautiful live-oak, which abounds in eastern Texas, 

and which grows luxuriantly in the valleys as far as the 

north fork of Brady’s Creek, has not disappeared, save 

on the immediate banks of water courses. The mezquit, 

too, which grew large and thrifty on good soil, had not 

either disappeared or dwindles into a diminutive tree or 

mere shrub” (Bartlett 1854:74; bracketed text added).

As he approached the southern margins of the SHP near 

Mustang Pond, he wrote:

“The desert was not, as I supposed, a level surface, but 

a succession of slight elevations. Everything bore the 

appearance of extreme barrenness; not a tree could be 

seen. Mezquit chapporal, or bushes from three to five feet 

in height, were thinly scattered over the plain. The wild 

sage and Larrea Mexicana, the prickly pear and other 

kinds of cactus, constituted the vegetation of this desert 

region. Grama grass (Chrondosium) [Chondrosum?] 

grew in some spots, and, though completely dried 

up, was eaten with avidity by our animals” (Bartlett 

1854:87; bracketed text added).

And at Mustang Pond, he wrote: “Finding a spot where 

there was plenty of dry grass, the train was stopped and the 

animals turned out to graze...they ate the withered grass and 

browsed on the twigs of mezquit bushes with eagerness” 

(Bartlett 1854:88).

There are, therefore, many descriptions of woody vegetation in the lower country surrounding the SHP. And despite 
34 USDA Forest Service RMRS-P-47. 2007

the poignancy of many of the early descriptions of the SHP 

proper as vast and featureless, it is important to appreciate 

that there was some relief to the dreariness of the Llano 

Estacado even between its western and eastern escarpments. Morris (1997:52ff; also see Bryan 1956:87) provided 

convincing evidence that before reaching the eastern escarpment, Coronado’s expedition encountered Running Water 

Draw, which crosses the SHP in a southeasterly direction. 

While on the SHP probably in lower Hale County, Texas 

(Morris 1997:51), Coronado sent Captain Diego López on 

a reconnaissance trip along a bearing toward the sunrise, 

and along this path, Morris suggests that they encountered 

Running Water Draw, which provided fresh, running water. 

When the reconnaissance party reunited with the main army, 

López reported that “they had seen nothing but cows and the 

sky” (Winship 1964:235), clearly indicating they were on the 

SHP. Significantly, though, in the same area where López saw 

only “cows and sky,” Castañeda writes that the two native 

Indians who had found López’s party and led them back 

to the main army were in fact looking for fruit when they 

encountered López. Clearly, this part of the Llano Estacado 

was crossed by a draw that supported woody vegetation with 

fruits (Morris 1997:54). Coronado himself provided an interesting and important corroborating clue to vegetation patterns 

on the Llano Estacado when he wrote to King Charles V: “...

[we were] going many days without water, and cooking the 

food with cow dung, because there is not any kind of wood in 

all these plains, away from the gullies and rivers, which are 

few” (Winship 1964:368). Similarly, Jóse Mares, dispatched 

by Governor Cabello to reconnoiter a route across the Llano 

Estacado in the 1780s, encountered chinaberry trees along 

an arroyo that Loomis and Nashatir (1967:291) and Morris 

(1997:173) identify as upper Tierra Blanca Creek, which 

soon joined with running water near present-day Friona and 

Hereford, Texas; Mares also encountered Tule Creek, near 

present-day Tulia, which he described as “...permanent [with] 

cottonwood trees and many reeds [tules]” (Morris 1997:173). 

Additionally, mesquite occurred in certain edaphic settings. 

For example, Havard (1884:455) remarked that: “The most 

desolate parts of the Staked plains are the Sand hills—

barren heaps of shifting sand. Between these are sometimes 

found large, vigorous mezquit shrubs.” In 1901, Oberholser 

(Smithsonian Institution Archives, Record Unit 7176, Box 

95, Folder 14) described Rhus aromatica and Celtis occidentalis on the sand dunes 45 miles south of Hereford. Finally, as 

indicated above, Marcy (1850) and Bartlett (1854) reported 

mesquite in the southern part of the Llano Estacado, northeast of the Monahans Sand Hills and near Big Spring.

Summary of Early Descriptions

For a period of about 300 years, a description of the vegetation of the SHP can be drawn, from many sources, that shares 

the same essential features. First, the escarpment itself, as 

well as the country “below” the Llano Estacado, supported 

abundant woody vegetation. The fact that Coronado could 

build a bridge across the Pecos River suggests perhaps 

abundant cottonwood. In addition, Castañeda described a 

number of woody species (for example, Prunus, Morus, and 

probable Carya illinoiensis; Morris 1997:80-81) in what 

Morris suggested was Blanco Canyon, which penetrates the 

SHP from the eastern escarpment in Crosby County. Finally, 

both the first record of mesquite (by James), as well as abundant references to the plant (by, for example, Abert and 

Marcy), provide ample evidence that this country supported 

abundant woody vegetation.

Second, the SHP proper was characterized by grassland 

vegetation over most of its vast, changeless expanse. Further, 

this grassland evidently supported no woody vegetation (but 

see below). Numerous quotations have been cited describing 

a landscape devoid of shrubs and trees, a topographic 

vacuum that demanded travelers to mark their routes with 

piles of buffalo dung to avoid disorientation and swallowed 

up those who strayed beyond the boundaries of the known. 

Third, despite the apparent monotony of the Llano Estacado, 

it is noteworthy that it was interrupted by vegetation diversity including woody species in and along major draws that 

crossed the SHP as well as in sandy soils. Coronado’s telling 

phrase that there is not any kind of wood in all these plains, 

away from the gullies and rivers, which are few (Winship, 

1964, p. 368), implies that the “gullies and rivers” in fact had 

woody species. Further, Coronado’s Indian guides who found 

Captain Lopez were actually looking for fruit at the time, 

suggesting woody species in Running Water Draw in the 

northcentral part of the Llano Estacado. Finally, Jóse Mares 

noted chinaberry trees along upper Tierra Blanca Creek (see 

earlier text).

Later 1800s to Early 1900s

Beginning in the late 1880s, with the “settling” of Texas, 

scientific interest in its natural resources spurred the commission of a biological survey of the state, including the SHP. The 

general descriptions of the vegetation of the SHP that have 

been gathered from the literature between 1541 and the 1850s 

are largely corroborated by Bailey’s (1905) biological survey 

of Texas. Bailey’s map of the distribution of mesquite in Texas 

and New Mexico (Bailey 1905, Plate III; see fig. 4) clearly 

showed that mesquite was absent from most of the SHP. In 

fact, Bailey defined the “plains” portion of the “Upper Austral 

Zone, Upper Sonoran Division” (Bailey 1905:33) (which 

included the SHP, see figure 3a in Schmidly 2002:43) by the 

“absence of mesquite and other shrubs of the surrounding 

Lower Sonoran Zone” (Bailey 1905:33; the “other shrubs” 

included species of Acacia, Mimosa, Ziziphus, Condalia, 

and Lycium; see Schmidly 2002:79). It is also significant 

that Bailey’s map shows that mesquite was present along the 

southeastern portion of the Llano Estacado in the general area 

of Big Spring, which supports Marcy’s (1850) and Bartlett’s 

(1854) observations.

Bailey and his team of scientists left a wealth of valuable 

descriptions of the SHP and its surroundings. For example, 

Merritt Cary provided the following description of the 

Monahans area (Ward and Winkler Counties, Texas) in 1902:
USDA Forest Service RMRS-P-47. 2007 35

“Monahans is situated in a mesquite basin which is 

rimmed in on the southeast, south, southwest, and 

west sides by hard, limy ridges and on the northwest, 

north, northeast, and east by a range of high sandhills. 

A large portion of the basin is sandy, and supports a 

heavy growth of Ziziphus obtusifolia in addition to the 

mesquite. These are the only two shrubs occurring in 

the basin. Among smaller plants growing in the sandy 

soil are Mentzelia sp., Baccharis sp., and Artemisia

sp. as well as Yucca stricta. The hard ridges support a 

heavy growth of range grasses, in addition to Larrea, 

Lycium berlandieria, Ziziphus, and a few mesquites...

These sand hills are quite steep in some places, and 

are clothed with a more or less dense growth of “shin 

oak,” except where the wind has formed “blow outs” 

(Smithsonian Institution Archives, Record Unit 7176, 

Box 93, Folder 13).

In 1892 B.H. Dutcher described the area around Stanton 

(southeast Martin County, Texas) as follows:

“Stanton is situated on the edge of the plateau top of 

the Llano Estacado or Staked Plains. Only a few miles 

east of the town the plain “breaks” down to the shelf 

that extends to the Colorado River. The surface of 

the country is gently undulating, is well-covered with 

grass and weeds, and supports a scattering growth of 

mesquite trees, catclaws, etc. The trees and bushes seem 

to grow in groves, which are interspersed with excluded 

barren reaches...I was informed that the country lying 

to the north over the plains does not differ essentially 

in character from the country at Stanton” (Smithsonian 

Institution Archives, Record Unit 7176, Box 93, Folder 

18).

Dutcher also reported:

“Mesquite. Common though not entirely covering the 

plains. Does not attain a height of over six or eight feet 

in the open. Juniperus virginiana. Common in groves 

along the edges of the plain overlooking the shelf below, 

on the red-soil mesquite plain” (Smithsonian Institution 

Archives, Record Unit 7176, Box 93, Folder 19).

Clay indicated that in the area of Stanton:

“Odessa, Warfield, and Stanton are situated alike on a 

high, grassy mesquite plain...In the vicinity of Stanton, 

however, there are very few mesquites, and large areas 

of open, grassy plain are frequent...The botany of the 

three localities is very similar. The principal shrubby 

plants noted were as follows: Ziziphus obtusifolia, 

Prosopis juliflora, Acacia sp., Opuntia arborescens 

(not noted east of Stanton), Cereus sp., Yucca stricta, 

Figure 4. Distribution of mesquite in 

Texas in 1905 (from Bailey 1905).
36 USDA Forest Service RMRS-P-47. 2007

Ephedra nevadensis, Baccharis sp., Grindelia. A rank 

growth of range grasses obtains throughout the region” 

(Smithsonian Institution Archives, Record Unit 7176, 

Box 93, Folder 13).

In the northern half of the SHP, Bailey described the landscape surrounding Washburn, Texas (northeast corner of 

Armstrong County), in 1892 as:

“Washburn is on the Staked Plains...There is nothing 

to break the smooth, even monotony of almost level 

prairie, meeting the horizon on all sides...A low, thick 

growth of grass covers the country, giving an almost 

velvety smoothness of surface. Here and there a thistle, 

an Aesclepias, or Euphorbia rises a foot or so, but so 

scarce as to be hardly noticed. An occasional house, with 

windmill and fences, or cattle and horses grazing are 

all that break the monotony” (Smithsonian Institution 

Archives, Record Unit 7176, Box 92, Folder 13).

And describing a portion of Palo Duro Canyon (Armstrong 

County, Texas), Bailey wrote:

“Thirteen miles south of Washburn the Prairie Dog 

Fork of the Red River flows through an abrupt cañon of 

about 1,000 in depth...The top of the canyon is about a 

mile wide...The bottom is sandy and smooth. The river 

bed is small and now almost dry. The whole canon is 

lined with trees, brush and plants not found outside in 

the surrounding country, and furnishes the only timber 

for a long distance. Junipers are the most abundant 

and useful tree, being used for fence posts and fuel, and 

are very common along the sides of the cañon. A few 

cottonwoods grow along the bottom, also Celtis and 

chinaberry. Prosopis fills the canon and runs over the 

edge of prairie as also a little oak. Lyssium [Lycium?] 

is common, several species of Rhus, Ptelia, Circocarpos

[Cercocarpos?], Atriplex canescens, five species of 

cactus, Yucca angustifolia, Artemisia and others entirely 

new to me” (Smithsonian Institution Archives, Record 

Unit 7176, Box 92, Folder 13; bracketed text added).

Bailey added the following important note in a plant list 

of the area:

“Prosopis glandulosa, abundant in cañon, extending out 

along the top and a few small plants (rarely over two 

feet high) here and there over the prairie (Smithsonian 

Institution Archives, Record Unit 7176, Box 92, Folder 

14).

Henry Oberholser described the landscape around Hereford 

in 1901 as follows:

“Hereford is located on the Staked Plains at an altitude 

of about 3,800 feet...For long distances in any direction 

from the town the country is a level or slightly rolling 

grassy plain, at intervals interrupted by wide, scarcely 

abrupt and usually not very deep grassy valleys, or 

‘draws’ as they are known in local parlance, which 

lead to the headwaters of the Red River, but contain 

water only after heavy rains. Close to the south side 

of Hereford there is, however, a spring-fed creek, 

the Tierra Blanca, which for some fifteen miles is a 

running though sluggish stream. Along the miles of 

its grassy valley there are frequent outcrops of friable 

white limestone appearing in low isolated cliffs usually 

close to the present stream bed. The margins of this 

creek are overgrown with a dense mass of cattails and 

rushes, while on the cliffs occurs the nearest approach 

to a natural growth tree [sic] anywhere to be found—a 

few scrubby bushes of Celtis occidentalis...Some 45 

miles to the south of Hereford the general evenness 

of the country is broken by an extensive area of low 

sand hills. Here the soil changes from the dark colored 

loam of the environs of Hereford to the fine sand which 

supports a much less dense growth of grass. The 

highest of these hills probably is not much over 30 feet 

above the plain; and all are usually covered with a 

growth of rank weeds and bushes of Rhus aromatica, 

with sometimes a few low trees of Celtis occidentalis...

after crossing them to the southeast the country more 

resembles that immediately about Hereford...The 

portion about Hereford is characterized by the absence 

of shrubby vegetation which begins to appear about 40 

miles to the southward in the shape of scattered bushes 

of Mimosa biuncifera, this increasing in amount to the 

southwest until it forms in many places a low chaparral. 

About 50 miles south of Hereford scattered shrubby 

bushes of Prosopis juliflora begin to be observable, and 

continue to occur along the road leading southwest...” 

(Smithsonian Institution Archives, Record Unit 7176, 

Box 95, Folder 14).

Both Bailey and William Bray traveled from Gail, Texas, 

north to Amarillo in 1899. Bailey wrote:

“From Colorado [River] to 15 miles north of Gail the 

country is Colorado River valley and is characterized 

by an uneven, eroded surface of red beds and sand 

cover by a scattered growth of cactus, mesquite, etc. 

The escarpment of the real[?] Llano Estacado begins 

just west of Gail but our road does not rise onto it for 

about 15 miles farther north. The escarpment here is 

about 400 feet. To the north the country rises slowly 

but steadily to Lubbock, Hail [sic] Center, Canyon and 

Amarillo but appears as a flat plain, covered with short 

grass, free of bushes or trees...Most of the mesquites, 

thorn bushes, and cactus are left below the escarpment 

and soon disappear from the higher levels. Short 

grasses and low prairie, or plains, plants cover the top 

of the plains and give the characteristic smooth carpet 

appearance of the region. A few northern plants are 

met with that may be typical Upper Sonoran species 
USDA Forest Service RMRS-P-47. 2007 37

but the Upper Sonoran Zone of the top of the plains is 

marked rather by the absence of surrounding Lower 

Sonoran species than by a change from one set of 

plants to another...The country is mostly fenced up in 

pastures of enormous extent, often containing several 

hundred square miles, and cattle are scattered over the 

whole region. Except on areas where there has been 

no rain for a long time the range is not overstocked 

and the grass is abundant” (Smithsonian Institution 

Archives, Record Unit 7176, Box 92, Folder 16; 

bracketed text added).

Describing the area from the Colorado River to Gail, Bray 

wrote:

“...the characteristic “red beds” formation continues. 

This is a country left rolling by erosion where 

stream ways occupy broad flat valleys which rise to 

picturesquely carved bluffs no where precipitous but 

for some areas of exposed rock. The gentler swells are 

covered with sandy loam and the valleys with more 

compact silt. On these flats the excellent range grass 

Hilaria jamesii was so abundant as to suggest a field 

of timothy hay. Prosopis julifora is abundant over the 

flatland often covering the ground continuously with 

a large growth...On the flat stretch of some ten miles 

north of Gail before reaching the escarpment of the 

plains Prosopis is very abundant and still of large size. 

[About] ten miles north of Gail the road passes upon 

the Plains...Almost at once the biological character of 

the mesa indicates its individuality...The predominant 

botanical characteristic of the Staked Plains is this: A 

vast stretch of solid grass floor in which is an admixture 

of herbaceous vegetation from the south and another 

equally marked from the north” (Smithsonian Institution 

Archives, Record Unit 7176, Box 93, Folder 8).

Bray continued in description of the “timber or shrubby 

vegetation of the Staked Plains:”

“Prosopis julifora. This is a small tree of approximately 

normal size on the flat north of Gail. Never after 

ascending the escarpment ± 12 miles north of Gail does 

it exceed five feet in height, and is always a cluster of 

sprouts or very small trunks. In many places it is wholly 

absent for miles. At Lubbock there is still considerable 

mesquite one to two feet tall and the merest switches 

of stems. At Hale Center there is an occasional sprout 

of mesquite, but beyond this it disappears entirely. 

Going southeastward from Amarillo on the Denver 

City and Fort Worth line, short mesquite first appears 

at Goodnight station [between present-day Claude and 

Clarendon, Texas], sprouts two to three feet tall. Below 

the eastern escarpment a fairly large tree growth sets in. 

In general to the south and east mesquite stops at 3,500 

ft... .” (Smithsonian Institution Archives, Record Unit 

7176, Box 93, Folder 9; bracketed text added).

It is interesting to compare these comments (written in 

1899) with Bray’s description of mesquite in a 1904 publication:

“[Mesquite’s] spread northward and eastward from the 

Rio Grande country during the past 50 years has been 

a marked phenomenon. By its invasion mile after mile 

of treeless plain and prairie have been won and reduced 

to the characteristic orchard-like landscape...It has 

pushed northward over the Staked Plains, covering half 

their area” (Bray 1904:34).

And in 1906, Bray provided the following poetical description of the vegetation of the Staked Plains:

“It is on these high grass plains that the complete 

masterfulness of the grass-land type of vegetation 

impresses one. The monotonous level or billowy swells 

of a sea of grass unrelieved by the presence of taller 

plants like a shrub or tree, such as the ungrazed plains 

presented, could fasten upon the senses a conception of 

the power of a victorious vegetation such as one might 

get in the depths of a virgin pine forest, or in the sunbeat chaparral jungle which are also the expression of 

dominant vegetation types” (Bray 1906:92).

It seems that Bray’s descriptions of the woody vegetation of the SHP, gathered from his notes written in 1899 in 

conjunction with his work on the biological survey and 

his publications of 1904 and 1906, lack some consistency. 

Also, Bray’s map (fig. 5), in contrast with Bailey’s (fig. 4), 

shows that mesquite was present (although not abundant) in 

several counties along the southeastern border of the SHP (for 

example, Gaines, Dawson, Borden, Andrews, Martin, and 

portions of Lynn Counties).

Several vegetation descriptions in the early 20th century 

indicate that mesquite was present on the SHP. For example, 

in Clements’ (1920:139-144) description of the Short-Grass 

Plains that extended into the Texas Panhandle, characterized by the Buchlöe-Bouteloua association (which he later 

“down-graded” to the Buchlöe-Bouteloua associes, a shortgrass disclimax that resulted from overgrazing; Weaver and 

Clements 1936:524), Clements made no mention of mesquite. 

In his description of the Desert Plains in the grasslands of the 

southwest including New Mexico, Arizona, and Texas, characterized by the Aristida-Bouteloua association, Clements 

(1920:145) remarked that “Indeed, Larrea or Prosopis is 

scattered over so much [of this association] that it has often 

been regarded as mesquite rather than grassland.” Clements 

explained that: “The desert plains are in close contact with 

but one other association of the grassland formation, namely, 

the short grass plains...The contact...is from Synder and Big 

Spring in the Staked Plains of Texas to Roswell and Socorro 

in New Mexico...” (Clements 1920:144-145). It is with this 

background that the following comment by Clements should 

be appreciated. He remarked: “Mesquite savannah lies typically in the desert plains, though the mesquite itself extends 
38 USDA Forest Service RMRS-P-47. 2007

northward into the short-grass association of the Stakes Plains” 

(Clements 1920:278).

In a description of vegetation types in the semiarid portion 

of the U.S., Aldous and Shantz (1924:103) included:

“Grama-Buffalo, and Mesquite.—This is a very common 

type in the southern Great Plains of western Texas 

and eastern New Mexico, growing on hard lands. It is 

composed of an open sod of grama grass and buffalo 

grass, over which are scattered bunches of mesquite.”

However, Shantz and Zon (1924) mapped the Llano 

Estacado as short grass plains (“Grama-Buffalo grass”), with 

tall grass prairie characterizing the sandy soils in the western 

portion of the SHP. “Mesquite and the desert grass savanna” 

was mapped in the Rolling Plains and Edwards Plateau 

regions to the east and south of the SHP. This latter description 

was also followed by Shantz (1938), where “Mesquite-Desert 

Grass Savanna (Desert Savanna)” was distinguished from the 

“Short Grass (Plains grassland)” “in that trees are scattered 

over a short-grass cover” (Shantz 1938:848).

Not all authors, however, recorded mesquite on the SHP. 

For example, in 1917 the Texas state forester, J.H. Foster 

wrote: “[Mesquite] is found in the Breaks of the Plains, but 

has gained no foothold on the high, level plains themselves, 

apparently being killed back by frosts” (Foster 1917:445). 

This is one of the few descriptions of the SHP that specifically 

mentions an absence of mesquite, and it stands in contrast to 

other quotations in this regard.

Interpretation

From the foregoing survey of the literature, an initial 

conclusion can be reached: although the landscape immediately surrounding the SHP was characterized by a mixture 

of grassland and woody species, the Llano Estacado proper 

supported a vast shortgrass plains grassland interrupted 

by woody species only in certain topographic settings (for 

example, in draws or on very sandy soils). This conclusion 

is based on the writings of Spanish explorers as well as later 

military explorers and naturalists, covers a period of approximately 300 years (1540s to 1850s), and is corroborated by 

vegetation maps of Bray (1896) and Bailey (1905).

It is also true, however, that this conclusion is contradicted by other evidence also recorded in the mid to latter 19th

century. Marcy’s summary statement about mesquite, written 

in 1854, is important:

“...In the journeys I have made before upon the plains I 

had observed the mesquite tree extending over vast tracts 

of country...What the exact geographical range of the 

tree is we are as yet (with a great portion of our territory 

unexplored) unable to define; my own observations, 

however, warrant me in asserting confidently that it 

is only indigenous to the great plains of the west and 

south...Between the twenty-sixth and thirty-six parallels 

of north latitude, with the ninety-seventh and one 

hundred and third meridian of longitude, it is found 

abundantly, often constituting vast tracts of wood land, 

and is, indeed, almost the only siloa [sic; silva?] of the 

section...In going north from the parallel of thirty-three 

degrees, (in the direction I have traveled,) the trees 

gradually become smaller and smaller, until at least 

they are mere bushes; and, finally, on arriving near the 

latitude of thirty-six degrees, they disappear entirely...It 

is a tree of short, shrubby growth, with stock averaging 

from four to fifteen inches in diameter, and seldom 

attaining a height, including its top, of more than twenty 

feet...[it] is often found upon the most elevated and arid 

prairies, far from water courses...” (Marcy 1854:25-

26; bracketed text added).

When evaluating this important statement by one of the 

most successful military explorers of the SHP, it must be 

remembered that despite his lengthy expeditions, Marcy actually spent very little time on the SHP proper (which he alluded 

to in the above quotation when he wrote “with a great portion 

of our territory unexplored”). His travels from Fort Smith 

to Santa Fe in 1849 followed the Canadian River valley and 

ascended the Llano Estacado proper for only one day (June 

14, 1849; Marcy 1850:12, 42). His return along the southern 

borders of the SHP likewise involved little time on the Llano 

Estacado proper (from September 28 to October 3, 1849, 

with one day of rest; Marcy 1850). In 1854, Marcy stated that 

“even the Indians do not venture to cross [the Llano Estacado] 

except at two or three points...” (p. 92). Thus, it might be 

suggested that although Marcy’s determination of the limits of 

the latitudinal range of mesquite was both accurate and based 

on extensive experience, it is not clear from his writings that 

he observed mesquite throughout the extent of the SHP.

Settlers in the Lubbock area described mesquite in the late 

1800s. For example, Lou Stubbs arrived in Lubbock in the early 

1890s and, after a wet June, noted a diverse flora of grasses 

and forbs as well as “green mesquite” (Burnett 1990:12). 

Bray’s notes recorded in 1899 described mesquite on the SHP 

at least as far north as Hale Center (Hale County). Slightly 

later, Clements (1920) remarked that mesquite extended into 

the shortgrass plains of the Llano Estacado, and Aldous and 

Shantz (1924) described a “grama-buffalo and mesquite” 

vegetation type as “very common” in the southern Great 

Plains (that is, “eastern New Mexico and western Texas”).

An inspection of a chronological sequence of maps of the 

distribution of mesquite, together with the written descriptions 

quoted above, suggests that whereas mesquite was evidently 

entirely absent from the SHP (figs. 4, 5, 6) or restricted to 

draws in the SHP in the mid and late 19th century (fig. 7), it 

had expanded its range into “upland” sites by the middle of 

the 20th century (figs. 7, 8), and virtually covered the SHP by 

the latter years of the 20th century (figs. 9, 10). (The distribution map in fig. 7 is from Life Magazine and obviously 

lacks the “credibility” of a refereed scientific publication, and 

it certainly fails to document the sources consulted for the 

construction of the map. Notwithstanding, it is curious that 
USDA Forest Service RMRS-P-47. 2007 39

the distribution it shows for 1850 seems to be more consistent 

with the descriptions provided by the early explorers than the 

1896 or 1905 distributions shown by Bray and Bailey, respectively. See Malin (1953:213) for a comment on the “authority” 

underlying this map.)

An Explanation

Some authors have suggested that mesquite has not 

expanded its range since the early 19th century, but rather it 

has increased in density so that plant populations are greater. 

Burkhart (1976:225) described Prosopis as a “primitive” 

genus that possibly originated in north Africa, and wrote: 

“Present distribution patterns of species of Prosopis do not 

exclude the possibility of an ancient desert flora common 

to both Americas which later divided and became widely 

separated into two centers, the Mexican-Texan center and 

the Argentine-Paraguayan-Chilean one...the fact that in both 

centers endemic species exist indicates their antiquity...” 

Axelrod (1937) reported P. pliocenica in the Pliocene flora of 

southern California and observed that “Since the fossil species 

closely resemble their modern representatives, it is believed 

that the habitat implications of the fossil and living species 

are similar” (p. 138). He further described P. pliocenica as 

part of a “desert border element” whose modern equivalent 

is P. juliflora var. glandulosa. Malin (1953) advanced this 

interpretation with respect to the “floristic range” of mesquite 

generally. Johnston (1963) provided considerable supporting 

evidence, but limited his discussion to mesquite’s distribution 

in south Texas and northeastern Mexico (that is, areas “below 

2,000 ft in elevation and south of the 29th parallel”; Johnston 

1963:456). This explanation has been repeated by numerous 

authors (for example, Fisher 1977; Dahl 1982; Brown and 

Archer 1989, 1999; Jacoby and Ansley 1991), who, for the 

most part, discuss it in a general context. For example, “grassland and savanna systems” (for example, Brown and Archer 

1999) or “the semiarid southwestern U.S.” (for example, 

Dahl 1982) are usually described without the distributional 

Figure 5. Distribution of mesquite in Texas in 1896 (from Bray 1896).
40 USDA Forest Service RMRS-P-47. 2007

Figure 6. Probable distribution of mesquite grassland, 

Acacia grassland, and associated communities about 

A.D. 1600. Acacia grassland was believed to be 

present in the Rio Grande floodplain and adjacent 

areas (A) whereas mesquite extended to the line B. 

By 1923, the thorn shrubs had reached line C, and 

mesquite had reached line D (from Shelford 1964).

Figure 7. Distribution of mesquite (from Life Magazine 1952).
USDA Forest Service RMRS-P-47. 2007 41

Figure 8. Distribution of 

mesquite in 1943 (from 

Allred 1949).

Figure 9. Distribution of 

mesquite in 1977 (from 

Fisher 1977).
42 USDA Forest Service RMRS-P-47. 2007

limitations explicit in Johnston’s (1963) paper (even though 

Johnson’s paper is usually cited).

Many factors are probably involved in the population 

increase of mesquite, including changes in fire frequency, 

herbivory by both large mammals and rodents, and climate 

change. One of the most commonly-implicated factors is 

fire. In particular, many authors have suggested that periodic 

fires maintained relatively low mesquite population densities, 

and the reduction of fires allowed for increases in population 

densities. This explanation has a long history. For example, 

Cook (1908) wrote that:

“It is a matter of popular knowledge in south Texas 

that extensive regions which were formerly grassy, 

open prairies are not covered with a dense growth 

of mesquite...It differs locally only in the number of 

years since the bushes began to grow—thirty years, or 

twenty, or ten—subsequent to the establishment of the 

grazing industry on a large scale, the annual burning 

of the grass by cattlemen, and finally the fencing of the 

land for still more intensive grazing...Very often the 

old mesquite pioneers, the scattered trees which made 

the ‘open mesquite country’ of other decades, are still 

conspicuous among their much smaller progeny and 

the crowds of other camp-following species which now 

occupy the land to the almost complete exclusion of 

the grasses upon which the herds of former days were 

pastured. The change has come so gradually that even 

those who have the most intimate acquaintance with the 

facts have not appreciated their significance...Before 

the prairies were grazed by cattle the luxuriant growths 

of grass could accumulate for several years until 

conditions were favorable for accidental fires to spread. 

With these large supplies of fuel the fires which swept 

over these prairies were very besoms of destruction not 

only for man and animals but for all shrubs and trees 

which might have ventured out among the grass...That 

such fires were evidently the cause of the former treeless 

condition of the southwestern prairies is also shown 

by the fact that trees are found in all situations which 

afford protection against fires [pp. 1-2]...Settlers in 

south Texas early adopted the practice of burning over 

the prairies every year; partly to protect their homes 

against the fires, partly to give their cattle readier access 

to the fresh growth of grass...While the grass was still 

abundant these annual burnings were able to keep the 

woody vegetation well in check, though no longer able to 

drive back the forest or even to prevent its slow advance. 

In spots where the grass is thin, seedling mesquites and 

oaks escape the flames and in a year or two begin to 

shade the ground and gain more protection against the 

dangerous proximity of the combustible grass; and even 

though the tops are killed by later fires the roots may 

send up sprouts again and again to improve the chances 

of becoming established [p. 3]...”

Johnston (1963:465) stated that: “It is emphasized that many 

‘grasslands’ were infested with the ubiquitous mesquite...and 

Figure 10. Distribution of mesquite in 1990 (from Johnson and Mayeux 1990).
USDA Forest Service RMRS-P-47. 2007 43

that the rapid takeover of the mesquite brush involved an 

increase in stature of the aerial parts of the plant and in density 

of stand, rather than invasion of previously brush-less areas. 

Most authors feel the control of fires explains the shrinkage 

of the grasslands. Nothing in this study contradicts such an 

explanation.” More recently, Dahl (1982:A-1) wrote: “Had 

fires not periodically swept southwestern grasslands, probably 

the entire area would have supported a woody overstory long 

before the first white men arrived in North America.” Brown 

and Archer (1989:25) wrote that one possible explanation for 

mesquite in southwestern grasslands is that: “Prosopis may 

have always been present in grassland, but recurring fires kept 

plants from developing in stature and producing seed.”

It may be difficult, however, to reconcile this explanation 

with the apparent absence of mesquite over most the SHP 

as depicted by the much of the literature reviewed here. If 

this explanation were true, it seems that some evidence of 

mesquite, perhaps present as small, stunted plants, would 

have been recorded by early explorers in upland sites, particularly in light of the fact that fire generally kills only very small 

mesquite plants (Havard 1884; Wright and Bailey 1982:149 

and references therein). Additionally, it is noteworthy that 

mesquite seedlings are remarkably hardy, being tolerant of 

repeated top removal during the first growing season (Weltzin 

and others 1998) and capable of vegetative reproduction within 

2 weeks of germination (Scifres and Hahn 1971). Although 

there are numerous statements in the literature about fires 

in the SHP (for example, Bolton 1946:330, 333; Hall 1947; 

Morris 1991:147), the only observation linking fire and the 

stature of mesquite discovered in the literature reviewed here 

was made by Bartlett (1854:75), who wrote about mesquite 

as he approached the southern margins of the SHP: “Where 

the prairies are frequently burned over, the tree is reduced to 

a shrubby state, a great number of small branches proceeding 

from one root, which goes on developing and attains a great 

size, though the portion above ground may not be more than 

four or five feet high.” In describing the grasslands of Arizona, 

Griffiths (1904:29) wrote: “A close examination of the broad, 

gentle, grassy slopes between the arroyos in this vicinity 

reveals a very scattering growth of mesquite...which is in 

the form of twigs 2 to 3 feet high with an occasional larger 

shrub in some of the more favorable localities...One cannot 

tell whether this growth indicates that this shrub is spreading 

or not. The present condition rather suggests this possibility” 

(from Turner and others 2003:xiii). The possibility exists 

that the small shrubs noted by Griffiths possibly had been 

held in check by repeated fires. In this connection, an anecdote reported by Kelton (1993:79-83) is noteworthy. Kelton 

recounted that O. Schwartz, who began farming in 1923 east 

of San Angelo, Texas (to the southeast of the SHP, which was 

“mostly open rangeland”, p. 79), would occasionally plow 

up an unseen mesquite stump that invariably had fire scars. 

Areas not broken out into farms later developed into dense 

stands of mesquite. Although this anecdote specifically relates 

to an area southeast of the SHP, it raises the possibility of like 

situations on the SHP, although no such remarks have been 

noted in the literature reviewed here.

A Second Explanation

A second explanation for the difference between the 

current and historical distributions of mesquite involves a 

combination of livestock grazing and fire considerations. 

In particular, it has been suggested that domestic livestock, 

which had consumed mesquite beans from trees growing 

along water courses, distributed these seeds through feces 

(see Fisher 1977 and references therein). [It should be appreciated, however, that mesquite seeds are an important food 

component for numerous small mammals, including kangaroo 

rat (Dipodymys merriami and D. spectabilis), Perognathus

hispidus, hares (Lepus), and packrats (Mares and others 

1977 and references therein). Additionally, Burkhardt (1976) 

and Mooney and others (1977) suggested that mesquite 

fruits evolved “to very effective endozoic diffusion through 

mammals and larger birds (owing to the succulent, edible 

legumes with hard seeds that escape digestion)” (Burkhardt, 

1976, p. 225).] This mechanism of range expansion can then 

be combined with a reduction in intensity and frequency of 

fire, allowing for mesquite to establish populations in sites 

previously unoccupied by the species.

There are, therefore, two approaches to follow in explaining 

the differences between current and historical mesquite distributions over the SHP. The first approach suggests that woody 

vegetation (probably including mesquite) has been present on 

the SHP (at least since Europeans first explored the area, when 

written records begin), but plants went (largely?) unnoticed 

because recurrent fires maintained populations in a suppressed 

state. Further, mesquite’s current dominance, dramatic as it 

is, has not involved a range expansion, but rather a population explosion. The second explanation involves, first, a range 

expansion of woody species into a grassland (via introduction 

of domestic livestock), and second, a woody species population explosion.

It is likely that the factors involved in the population explosion are similar in both these scenarios and include changes 

in fire frequency, grazing history, and extreme climate events. 

Most range scientists have maintained that increases in woody 

plant populations require (1) a vector for seed dispersal (for 

example, herbivores spreading seed via defecation) and (2) 

a reduction in competition from herbaceous species (caused, 

for example, by heavy grazing or drought conditions) that 

provides gaps in an herbaceous stand for woody plant establishment as well as reduced competitive influence that allows 

for woody seedling growth. Additionally, these factors may be 

coupled with climatic events that favor the woody species, for 

example, episodically high rainfall promotes seed production 

and seed germination (for example, Turner and others 2003) 

(but see below).

It seems that an understanding of shrub dynamics on the 

SHP requires that a choice must be made between (i) an 

increase in the density of existing woody populations or (ii) an 

invasion of woody species into previously unoccupied areas, 

followed by an increase in population density. In an effort to 

evaluate these two scenarios, the following observations are 

offered.
44 USDA Forest Service RMRS-P-47. 2007

1. Woody vegetation (which presumably included 

mesquite) was recorded by the earliest explorers in 

the draws and the sandy soils of the SHP as well as 

in the landscape bordering the SHP. Johnson (this 

proceedings) reported that mesquite, sumac (Rhus sp.), 

and hackberry (Celtis sp.) were present and associated 

with the “valley system” of the SHP as early as 4,500 

B.P., with additional records of these species together 

with Texas walnut (Juglans microcarpa) in the valley 

system as well as an upland salina dating from 2,000 

to 200 B.P. Relative to vegetation dynamics throughout 

the Holocene, and with specific regard to native 

trees, Johnson (this proceedings) stated “Occurring 

primarily in the valley system, an occasional hackberry 

and mesquite were on the uplands around lake basins 

depending on the period.”

2. Early explorers probably traveled across the SHP 

along paths of the existing drainages and not in 

haphazard directions that would have brought them 

across “upland” sites (see, for example, Morris 1997:47, 

97; Meyers 2003). Thus, the absence of descriptions of 

woody vegetation on upland sites may be a result of 

lack of experience with upland sites by early explorers, 

rather than the absence of woody plants in these sites.

3. Early explorers remarked that there were trails 

from the (apparently shrub-less) “high plains” of the 

Llano Estacado down into the wooded canyons along 

the margins of the SHP that buffalo used to move from 

the Rolling Plains to the SHP (for example, Kendall 

1856:228; Morris 1997:56).

If domestic grazing animals are to be invoked as being 

responsible for moving seeds from woody plants (including 

mesquite) naturally growing in draws and canyons to upland 

sites through defecation (as in the second explanation, above), 

then it seems reasonable that buffalo, as well as numerous 

other large mammals and rodents, may have also fulfilled this 

role, leading to the possibility that native herbivores, prior 

to domestic livestock, may have distributed, to some extent, 

seeds of woody species from draws and canyons onto the SHP 

proper. However, Brown and Archer (1987) found no mesquite 

seedlings and fewer seeds in an ungrazed area compared to a 

grazed area in south Texas and concluded that domestic livestock were more effective agents of mesquite seed dispersal 

than native fauna in south Texas. These authors suggested 

that effective seed dispersers would be agents that “transplant large numbers of germinable seeds away from parent 

plants harboring host-specific seed predators and deposit them 

in grazed habitats where emergence and survival could be 

high” (Brown and Archer 1989:25). They concluded that “the 

apparently low densities of mesquite in grasslands prior to 

settlement may have been a consequence of limited dispersal or 

germination rather than biotic or abiotic constraints on establishment” (Brown and Archer 1987:79). Brown and Archer’s 

characterization of an effective seed disperser is reasonable, and it is true that cattle fit this description. However, 

an effective seed dispersal agent is one that would deposit a 

germinable seed “in areas where grasses ha[ve] been defoliated” (Brown and Archer 1989:19), and native fauna that do 

this also would be effective dispersal agents. With effective 

seed dispersal by native fauna, the absence of descriptions of 

woody vegetation in the literature reviewed here might then 

be explained by a lack of experience with these sites by early 

explorers, supplemented with the possibility that population 

densities were low and frequently-burned plants existed in a 

state of suppression and were thus not conspicuous to early 

travelers. If this reasoning is sound, then the conclusion is that 

woody vegetation was a natural component of the SHP, but its 

“dominance” as a community component was most apparent 

only in particular landscape settings (for example, the draws 

or valley systems). Further, on uplands where it may have 

been only occasionally present, woody vegetation was “held 

in check” by recurrent fires. Thus, its apparent neglect by early 

explorers may be explained in part by lack of experience and 

low populations in particular landscape settings.

In this regard, the results of Brown and Archer (1989, 1999) 

are pertinent. These authors showed in the Post Oak savanna 

of central Texas that, relative to non-defoliated plots, moderate 

grass defoliation increased mesquite seedling emergence 

by eight-fold. Further, there was no difference in seedling 

emergence between moderately and heavily-defoliated plots 

(Brown and Archer 1989). To the extent that mesquite emergence was enhanced by moderate defoliation, and because 

there was no difference between moderately and heavily-defoliated plots, these authors concluded that the competitive 

suppression that grasses may have on mesquite establishment 

was easily overcome; that is, “long-term and/or heavy grazing 

is [not] requisite for Prosopis encroachment into grasslands” 

(Brown and Archer 1989:19). In contrast, in south Texas, 

these authors showed that herbaceous biomass or density had 

no affect mesquite seedling establishment. Instead, they documented relatively continuous mesquite seedling emergence 

that was also largely unaffected by moisture conditions (Brown 

and Archer 1999). Thus, whereas non-defoliated herbaceous 

vegetation was effective in reducing mesquite seedling emergence in central Texas, they concluded that “Historic grazing 

at [the south Texas] site appears to have altered herbaceous 

composition and reduced above- and belowground biomass 

production below the threshold level required for competitive 

exclusion of woody vegetation...[their] data suggest that rates 

and patterns of seed dispersal may be the primary determinants 

of P. glandulosa encroachment on present-day landscapes 

in semiarid regions” (Brown and Archer 1999:2385). These 

results suggest that (1) depending on past history, native 

vegetation unaltered by grazing may or may not be capable 

of excluding woody vegetation, and (2) seed dispersal is a 

prerequisite for woody plant invasion into grasslands.

The existence of well-developed ecotypes of mesquite 

extending from south Texas to central Oklahoma (Peacock and 

McMillan 1965; however, these authors did not study populations from the SHP proper) is also important in understanding 

the dynamics of this species. Although rates of evolutionary 

changes involved in the differentiation of ecotypes undoubtedly depend on the species and adaptive gradients in question, 
USDA Forest Service RMRS-P-47. 2007 45

Peacock and McMillan (1965:35) concluded that “Ecotypic 

differentiation over the northern part of its range adds weight 

to the historical evidence that mesquite has occupied its 

current distribution for a considerable period of time.”

An appreciation of the effects of (1) landscape setting (for 

example, draws and valley systems, or upland sites) on vegetation composition and structure, (2) both past and current 

grazing history on woody plant establishment, as well woody 

plant demographic phenomena involving both proximity of 

seed source and effectiveness of seed dispersal, and (3) fire, 

lie at the heart of understanding shrub dynamics in the SHP.

Summary

Despite considerable documentary evidence and the efforts 

of many ecologists, it is difficult to determine the precise 

nature of the vegetation of the SHP from the time of the first 

European explorers to the late 1800s. Based on accounts 

written during this time period, conclusions that can be drawn 

about this vegetation are vague and sometimes contradictory. 

For example, Coronado described a landscape with no trees 

or shrubs, and then added except away from the gullies and 

rivers. Marcy similarly described a landscape without trees 

or shrubs and then provided a delineation of the range of 

mesquite that included all of the SHP. Bray, in turn, wrote 

about the Llano Estacado as being unrelieved by the shrubs 

and trees, but also described mesquite as far north as Hale 

Center (Hale County).

There is little question that the earliest descriptions of the 

SHP indicate that it was a grassland interrupted by woody 

species only in certain topographic settings (for example, 

draws and canyons). The fact that “native soils [of the SHP] 

were most likely Paleustolls, given the native vegetation of 

the region” (Holliday 1990:498) suggests long-term landscape 

stability. It is equally clear that woody vegetation (including 

mesquite) was reported throughout most of the SHP by the 

1890s. Finally, woody vegetation, including mesquite, has 

been recorded in the landscapes surrounding the SHP since 

1820, and the presence of ecotypic differentiation suggests 

that mesquite populations surrounding the SHP have been in 

existence for a considerable time period. With specific regard 

to shrubs on upland sites of the SHP, and using mesquite as 

a case species, either mesquite has historically been present 

but went unrecorded prior to the 1890s because upland sites 

had low population densities, were not frequented, and/or 

because recurrent fires maintained populations inconspicuous, 

or mesquite was introduced in a novel way by domestic livestock that had been introduced in the late 1870s and 1880s. In 

either of these scenarios, subsequent increases in woody plant 

densities likely involved changes in fire frequency, grazing 

history, and climate.

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The Author

1 Department of Range, Wildlife, and Fisheries Mgt., Texas Tech 

University, Lubbock, TX. david.wester@ttu.edu
48 USDA Forest Service RMRS-P-47. 2007

Introduction

Historically, periodic fire was the primary force in holding 

shrub populations at low densities on native grasslands west 

of the Mississippi River. Questions arise as to the timing and 

frequency of these fire events. Unfortunately, we will never 

know the exact nature of these events, as no recorders such 

as fire scarred trees are available to help us estimate what 

happened to grasslands in the past.

Frequency of fire occurrence in grasslands has usually been 

estimated in the range of once every 2 to 25 years. There is no 

normal or average fire return interval because the sequence of 

wet years and dry years impacts fuel loads and atmospheric 

condition conducive to fire spread. It would be a good guess 

to assume that widespread natural fires would dominate in dry 

years that followed one or more very wet year(s) (Wright and 

Bailey 1982). We believe that precipitation regimes and dry 

lightning storms produced the fire environments that shaped 

the western grasslands.

We would like to dispel the myth that summer fires are 

the most natural. If we take the human factor out of the equation, then the natural ignition source is lightning. Lightning 

can occur any month of the year throughout the western 

grasslands; thus, the condition of the fuel becomes paramount. Fuel moisture is the major predictor of when natural 

fires occurred. Except in drought years, this would narrow 

the most likely period from late winter to early spring just 

before green-up of grasses. Air temperature is the third most 

important factor in determining the natural fire period. During 

late winter and early spring, there are frequent warm days, 

and in summer, warm days are abundant. Lastly, humidity is 

a prominent factor. Relative humidity is commonly high in 

summer for most western grasslands. More importantly, absolute humidity is extremely high in summer compared to late 

winter and early spring. Absolute humidity is the factor that 

regulates dormant fine fuel moisture. In summary, we can say 

that a natural fire can occur in any month if the fine fuel is dry 

and lightning occurs.

Another myth that should be dispelled is that because 

summer fires were most common, they are the most natural 

and the most beneficial. We are aware of no data to support 

this myth in grasslands or shrublands. The opposite is 

supported by the literature (Wright and Bailey 1982). The 

more correct scenario would be to follow well-established 

rules of defoliation. After all, fire represents a severe defoliation with removal of herbaceous phytomass to near the 

soil surface. The accepted opinion is that in most western 

grasslands, herbaceous removal is least damaging in the 

winter dormant period and most damaging during the period 

of seed-set or mid summer (Holechek and others 2004). 

Sosebee and others (2004) emphasize this fact by stating “The 

most important deferment or rest period for grasses is postreproduction to dormancy. For perennial, warm-season grasses 

in the southern Great Plains, this occurs from late summer to 

early autumn.” This clearly illustrates that fire in this period 

would be damaging to the forage resource.

Using fire in plant communities that have not experienced 

their historic fire regime is equivalent to applying a natural 

tool to an unnatural situation. We have mismanaged our 

plant communities so that the fuel matrix has been radically 

changed. We currently operate on the two extremes. Either 

we have reduced the fuel to such an extent that a fire will 

not spread, or fuel has accumulated to such high loads that 

the resulting fire is catastrophic. By resource mismanagement 

we have eliminated any possibility of a natural fire. Thus, our 

object in fire management is to apply prescribed fire to meet 

well-thought-out objectives relating to healthy, balanced, 

and productive grassland communities. Restoring fire as an 

ecological force in native plant communities is a priority of 

all land managers. Determining how and when to burn to 

achieve the most natural effect requires planning based on 

sound ecological and historical evidence. Natural landscapes 

and their features—geologic, edaphic, and biotic—are the 

manifestations of factors that structure the world around us. 

An important corollary of this principle is that natural landscapes also are indicators of these factors, both historically 

Prescribed Fire to Restore Shrublands to Grasslands

Abstract: Prescribed burning to restore grasslands is more complicated than just setting a 

fire or, worse, letting a fire burn. We will examine how fire may be used to restore a more 

desirable landscape. First, any area that might be considered for prescribed fire should be 

thoroughly evaluated. Soils are paramount as they will indicate what we can expect from a 

given site. Then, we should study the plant community which originally existed on the site. 

Comparing the original plant community to the current plant community will help us construct 

a viable set of objectives. Second, we will determine how prescribed fire might be used in this 

restoration process. Should it be the first and only tool used or must it be preceded by some 

other tool, such as a mechanical or herbicidal treatment? Finally, we will consider a planning 

chart to organize the re-treatment scenario.

Carlton M. Britton1

David B. Wester1

Brent J. Racher

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 49

and currently. For example, geological processes in the distant 

past produce the parent material from which soil is formed 

by edaphic processes. These processes form the abiotic arena 

in which biotic factors operate to assemble the communities 

characterizing every landscape.

This perspective provided the conceptual cornerstone of 

Frederick Clements’ pioneering vision of the climax community: the climax community was considered to be the ultimate 

expression of the stable equilibrium between vegetation and 

its environment. Hans Jenny and Jack Major later formulated 

these ideas into “factors of soil development” and “factors of 

vegetation development,” respectively, frameworks that have 

guided the thinking of several generations of ecologists.

With European settlement of the U.S., the pristine environment, supposedly the climax, was altered in far-reaching 

ways. It was only natural to view these changes as reversible

consequences of disturbance. After nearly a century of land 

management experience, most observers are reconciled with 

the conclusion that many of these changes may not be reversible. This realization motivated the development of multiple 

stable equilibria, whose trajectories depend on the nature of 

the disturbance and the accidents of subsequent vegetational 

development.

Most interpretations of vegetation change have variously 

implicated land use changes (usually in the context of domestic 

herbivory), climate (both short-term weather fluctuations and 

long-term climatic trends), and fire history. Climate change 

is a global issue that may be beyond our control. Land use 

patterns are a local issue best decided in the private sector by 

responsible land owners. Fire history is a regional issue that 

lies within the domain of state and federal agencies charged 

with land management. In this paper, we focus on the importance of fire history in understanding today’s landscapes.

Recreating fire history is difficult even with the best information. In the forest, decisions based on trees with cat-faced 

scars that document past fire are rife with errors. In grassland or pygmy forest, this task becomes virtually impossible. 

However, good descriptions of previous landscapes can be 

reasonably approximated with an understanding of the total 

resource complex.

Old photographs offer good approximations of previous 

landscapes. Numerous examples throughout the western U.S. 

have been published, and many more can be found in private 

collections through diligent searching. These photographs 

must be evaluated with care to understand the complete natural 

resource base. For example, figure 1 illustrates a view on the 

historic Three Block Ranch in south-central New Mexico. 

The top photograph was taken in 1905 from the western peak 

of the Twin Mountains looking west. Erwin Smith took this 

photograph with George Patullo in the foreground. The ridge 

in the background has a sparse stand of juniper with possibly 

a few small pinon trees. The bottom photograph shows the 

identical location as photographed in 1990. Vegetation on the 

ridge has changed dramatically with juniper density and size 

increasing over the interval between photographs. The question is which photograph illustrates the appropriate ecological 

state of this ridge? Contemporary wisdom will say the 1905 

photograph. After all, this rangeland had been stocked with 

cattle for less than 25 years and, although altered, the period 

of time had been short enough that the negative impacts were 

not yet fully manifest. Fire was eliminated from this plant 

community, and thus, no pyric control on woody plants has 

operated for at least 85 years. This resulting landscape is not 

in balance with historic ecological forces that included recurrent fire. Our challenge is to restore these natural forces.

We suggest additional information be found to support the 

evidence seen in the photographs. The first and easiest place 

to seek excellent information is a soil survey. In this case, the 

Soil Survey of Lincoln County Area New Mexico. This ridge 

is mapped as a 14 Deama-Rock outcrop association, very 

steep (fig. 2).

The following description is provided:

This map unit is on hills and breaks. Slope is 15 to 50 

percent. Areas are irregular in shape and are 1,000 

to 5,000 acres in size. The native vegetation is mostly 

short and mid grasses. Elevation is 4,500 to 6,000 feet. 

The average annual precipitation is 12 to 16 inches, the 

average annual air temperature is 45 to 56 degrees F, 

and the average frost-free period is 150 to 190 days,

This unit is 60 percent Deama very cobbly loam, 15 

to 50 percent slopes, and 20 percent Rock outcrop of 

Figure 1. These photographs were taken 

from the same location looking westward 

from atop the Twin Mountains along the 

Cienega del Macho at the headquarters 

of the Three Block Ranch.
50 USDA Forest Service RMRS-P-47. 2007

limestone. The Deama soil is on hills, and the Rock 

outcrop is on breaks.

Included in this unit are areas of other soils that may 

or may not be present in all mapped units. These areas 

are Harvey, Dioxice, and Pena soils on hillsides and 

Pastura soils on summits. Included areas make up about 

20 percent of the total acreage.

The Deama soil is very shallow to shallow and is well 

drained. It formed in material derived dominantly from 

limestone. Typically, the Deama soil is brown, very 

cobbly loam about 7 inches deep over limestone.

Permeability of the Deama soil is moderate. Effective 

rooting depth is 7 to 20 inches. Available water capacity 

is very low. Runoff is rapid, and the hazard of water 

erosion is high. The hazard of soil blowing is slight.

This unit is used for livestock grazing and wildlife 

habitat.

The potential plant community on this unit is mainly 

sideoats grama, New Mexico feathergrass, plains 

lovegrass, and little bluestem. This unit can support 

scattered oneseed juniper. As the plant community 

deteriorates, the desirable forage plants decrease and 

there is an increase in threeawn, curlyleaf muhly, and 

catclaw acacia, which normally occur in small amounts 

in the potential plant community. Grazing management 

should be designed to increase the productivity and 

reproduction of plains lovegrass, sideoats grama, and 

little bluestem. This unit is poorly suited to rangeland 

improvement practices such as fences, pipelines for 

providing stock water, water impoundments facilities, 

and mechanical brush management because of the 

shallow and very shallow depth to bedrock and steepness 

of slope.

The average annual production of air-dry vegetation on 

this unit ranges from 1,100 pounds per acre in favorable 

years to 300 pounds in unfavorable years.

This range site description provides abundant information. 

First, it describes the soils on the range site and several important characteristics of the soils. If we do not understand soils, 

we do not understand the very basic unit of ecological planning. Second, it gives us a brief description of the common 

vegetation we should expect on the site and the most common 

increasers that occur as the plant community moves away 

from the climax. Vegetation description is the second basic 

unit of ecological planning. The herbaceous production also 

gives us a good indication of potential yield for this range site. 

This information clearly agrees with what we see in the 1905 

photograph as it describes the site with “scattered oneseed 

juniper,” not the dense juniper stand shown in the 1990 photograph.

Now that we have an initial impression of what this 

site should look like, we can expand and refine our view. 

Many sources of additional information are easily available. Surveyors’ notes can be a especially useful. Diaries of 

early explorers and settlers may yield helpful information. 

Descriptive ecological research also can be valuable if one is 

careful to read and understand the sampling methodologies. 

Many times, the methodologies are not suitable to yield data 

that are useful. Old aerial photographs are especially useful as 

they illustrate changes in tree and shrub densities over time. 

Vast amounts of information are available to reconstruct our 

vision of past rangeland plant communities.

Reconstruction of past communities from historical sources 

(for example, old photos) and an understanding of current 

potential (for example, from soil survey descriptions) involve 

a number of interpretational issues that must be considered. 

For example, suppose that in the earlier photograph in figure 

1, there was evidence of human habitation (an old ranch 

house, mining structure, or church). In this case, the absence 

of woody vegetation might then be only apparent if, in fact, 

woody vegetation was an important, harvested source of fuel. 

In this case, the presence of woody vegetation in the latter 

photograph in figure 1 might then be attributed to re-growth of 

woody plants that were, in fact, part of the historical community recorded in the earlier photograph and not woody plant 

invasion into a historical grassland because of the absence of 

fire.

Assuming that the apparent absence of woody vegetation 

in the earlier photograph in figure 1 is also a real absence, 

some investigators have attributed increases in woody shrubs 

throughout the Southwest to changes in climate. This interpretation may have merit, but it also is controversial, and 

resolution awaits additional research.

Once we understand the soils, plants, and ecology of 

an area, it is time to organize the planning chart for our 

fire treatment scenario. Our main objective is to ensure we 

have enough fine fuel (grass and forbs) to carry the fire and 

also accomplish our management goals. Redberry juniper 

at canopy covers of even less than 10 percent can greatly 

decrease fine fuel levels (Racher 2000). When juniper 

canopy cover reaches 30 percent, fine fuel is not continuous 

and a broadcast burn becomes extremely difficult and fire 

is not the first treatment. Therefore, we must resort to some 

Figure 2. Section from Lincoln County Soil Survey 

showing the ridge illustrated in Figure 1 and the 

approximate location where the previous photographs were taken.
USDA Forest Service RMRS-P-47. 2007 51

mechanical treatment to reduce juniper canopy cover and 

increase fine fuel. On other rangeland communities herbicides 

may be effective in increasing fine fuel so fire can be returned 

to its natural role. The planning chart illustrated in figure 3 

shows an initial mechanical treatment step. Next, we would 

have to allow the pasture to rest until sufficient herbaceous 

growth occurs to accumulate fine fuel. All these items must be 

flexible, as precipitation will exert a continuous and changing 

influence.

Weather conditions prior to the burn are very important. 

Excessive rainfall in the weeks before a prescribed burn can 

be either beneficial or disastrous. On the beneficial side, it is 

always desirable to have good soil moisture available so desirable plants can have an uninterrupted growth period after the 

fire. On the negative side, prolonged high moisture conditions 

will result in high juniper leaf moisture contents (Mitchell and 

Britton 1998). Leaf moisture concentrations above 70 percent 

reduce the ignition potential for the juniper canopy, and 

when the moisture concentration reaches 80 percent, canopy 

torching is nearly eliminated. Also, on clayey soils, precipitation can cause long intervals when road and firelines are 

impassible.

The reburn phase of the planning chart would also need 

to be flexible. If several above average precipitation years 

followed the burn, large numbers of juniper seed may germinate and establish. Fire should be applied sooner before either 

a high density of small plants reduces fine fuel load or the 

sprouting collar of redberry is buried and the plant becomes 

resistant to fire induced mortality.

Detailed planning and constructing a meaningful planning 

chart will help eliminate the wide variety of oversights that 

cause failure in prescribed burning. Attention to the interactions between environmental and plant responses will help 

increase the benefits of the prescribed burn.

The absence of fire in ecosystems that have historically 

burned must be an integral component in our understanding 

changes in plant communities. Considerable research has 

yielded a thorough understanding of fire’s role in natural plant 

communities (FEIS 2005). With our understanding of how we 

might reintroduce fire into natural plant community dynamics, 

we can begin proactive management to achieve desirable goals. 

Since fire has been absent from our rangeland plant communities for a great number of years, it may not magically take 

us to the point we envision. It is reasonable to believe that fire 

will take us closer to our vision, but it is contrary to ecological 

principles for it to immediately return us to the original condition. Patience must be the guiding factor in our quest to pursue 

more natural plant communities through the process of goals, 

objectives, and strategies.

Literature Cited

FEIS. 2005. Fire effects information system. (Online) U.S.D.A., F.S., 

Mitchell, R. B.; Britton, C. M. 1998. Redberry juniper foliage 

moisture dynamics in the Texas Rolling Plains. Texas J. Agric. 

and Nat. Resc. 11:23-30

Racher, B. J. 1998. Herbaceous production as influenced by juniper 

canopy cover in west Texas. M.S. Thesis. Texas Tech University. 

190 p.

Sprankle, D. G. 1983. Soil Survey of Lincoln County Area, New 

Mexico. USDA Soil Conservation Service. 217 p.

Sosebee, R. E.; Wester, D. B.; Villalobos, J. C.; Britton, C. M.; Wan, 

C.; Nofal, H. 2004. How grasses grow—How plant growth relates 

to grazing management. Second National Conf. Grazing Lands. 

GLCI. Dec. 2003. Nashville, TN.

Wright, H. A.; Bailey. A. W. 1982. Fire ecology: United States 

and Southern Canada. John Wiley and Son, Wiley Interscience. 

501 p.

The Authors

1 Professors, Department of Range, Wildlife and Fisheries 

Management, Texas Tech University, Lubbock, TX. 

carlton.britton@ttu.edu

Figure 3. Planning Chart for a prescribed burn 

on lightly infested juniper rangeland in the 

Rolling Plains of Texas. Complex burn 

implies a volatile fuel involved in the fuel 

matrix.
52 USDA Forest Service RMRS-P-47. 2007

Introduction

When European explorers and settlers first came to the 

Edwards Plateau, they found a different landscape than what 

is present today—especially for the uplands and “divide” 

regions of the Edwards Plateau (Cory 1948; Smeins and others 

1997). The landscape appeared open with stubby thickets of 

liveoak (Quercus virginiana Mill.) and shinoak (Quercus

spp.) and an occasional larger liveoak. On the valleys, slopes, 

and shallow soils, the dominant grasses were little bluestem (Schizachyrium scoparium (Michx.) Nash), sideoats 

grama (Bouteloua curtipendula [Michx.] Torr.), Indian grass 

(Sorghastrum nutans L. Nash), cane bluestem (Bothriochloa 

barbinodis var. barbinodis Lag. Herter), Texas cupgrass 

(Eriochloa sericea [Scheele] Munro), common curlymesquite 

(Hilaria belangeri [Steud.] Nash), Texas wintergrass (Stipa 

leucotricha Trin. & Rupr.), and others. Warm season perennial 

forbs were also abundant with a diverse mixture of desirable 

woody shrubs. Kidneywood (Eysenhardtia texana Scheele), 

littleleaf leadtree (Leucaena retusa Benth. in Gray), Carolina 

buckthorn (Phamus Caroliniana Walt.), Texas mulberry 

(Morus microphylla Buchl.), white honeysuckle (Lonicerna 

albiflora T.&G.), Plum (Prunus spp.), bumelia (Bumelia lanuginose [Michx.] Pers.), sumacs (Rhus spp.), etc., are just a few 

of the more desirable woody shrubs that were abundant.

With the development of the livestock industry, Edwards 

Plateau rangelands were fire-proofed due to excessive numbers 

of livestock and yearlong grazing that grazed out the tall and 

mid grasses. The more productive grasses were replaced 

with short grasses, which were more resistant to grazing and 

provided much less fuel for fires. Reduced fuel loads were also 

followed by fire suppression activities by early settlers. For 

example, in 1848, a state law was passed in Texas that made 

it illegal to fire the prairies between July 1 and February 15. In 

1884, another Texas law was passed that made setting fire to 

grass a felony. It was not until 1999 that a law was passed in 

Texas that unambiguously stated that a landowner had the right 

to conduct a prescribed burn on his or her own property.

The natural and man-made fires kept woody plants in check 

and allowed the higher successional grasses to dominate 

the landscape. It is well documented that prior to European 

settlement, both prescribed and wild fires were disturbances 

that played key roles in shaping the different plant communities across the United States (Baker 1992; Foster 1917). 

Historically, fires occurred during all months of the year 

(Higgins 1986; Komarek 1968), but summer fires were probably more frequent due to dry conditions combined with 

increased lightning frequency during the summer (Komarek 

1968; Taylor 2001). With the reduced fire frequency, redberry 

juniper (Juniper pinchotii), Ashe juniper (J. Ashei), and prickly 

pear (Optunia spp.) began to increase across the landscape.

The Insidious Invasion of Juniper

A common principle in vegetative ecology is given a certain 

set of circumstances (such as weather, soil, herbivory, fire, etc.), 

some plant species will be more competitive and dominate the 

landscape at the expense of other species. Natural competition is the concept that individuals of a species, which survive 

and reproduce better than other species, will have their genes 

proportionally represented in future populations to a greater 

extent because they leave more offspring. Nowhere can this be 

better demonstrated than with the increase of juniper species 

across the “divide” region of the Edwards Plateau.

At the time of European settlement, juniper species were 

not perceived as a problem and for various reasons. Firewood 

Role of Summer Prescribed Fire to Manage 

Shrub-invaded Grasslands

Abstract: Prior to development of the livestock industry, both anthropogenic and natural 

disturbances (such as prescribed and wild fire) played key roles in shaping the different plant 

communities across Texas. Historically, fires occurred during all seasons of the year, but 

summer fires were probably more frequent due to dry conditions combined with increased 

lightning frequency during the summer. When fire was frequent, the upland or western divide 

region of the Edwards Plateau was typical of a savanna ecosystem. The purpose of this 

study was to determine the effects of summer and winter burning and no burning (controls) 

on vegetation. Woody and succulent vegetation species were highly vulnerable to both 

summer and winter fire. Herbaceous response was species dependent; however, overall 

grass production was greater under a summer burning regime compared to control and 

winter burn treatments. Summer burning is recognized and recommended for reclamation 

of rangeland vegetation under appropriate conditions and levels of supervision, experience, 

and training. Once reclaimed with one or two summer fires, management can shift to lower 

risk, cool-season burns for maintenance.

Charles A. Taylor1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 53

and building materials were important commodities to early 

settlers. For example, Ashe juniper was an important source of 

lumber for construction of houses, railroad ties, fences, pens, 

etc. for the early settlers (Smeins and others 1997). It still has 

commercial and ecological value today (Garriga and others 

1997; Rollins and Armstrong 1997).

The increase in juniper density is slow at first and can go 

unnoticed for many years until it becomes a serious problem. 

In the early 1900s, juniper represented a small part of the plant 

composition on many areas of the Edwards Plateau. With 

the reduction in fire frequency and intensity, the process of 

juniper encroachment was initiated on many areas that had 

previously been grasslands. However, some areas, especially 

on the southeastern Edwards Plateau, are not as conducive to 

repeated fires because of the highly variable topography and 

fine fuel discontinuity (Smeins and others 1997). Therefore, 

it is probable that juniper was present in some local areas and 

occurred in association with rocky outcrops, canyon-lands, or 

along streams and rivers where fire frequency was low. A thorough review of the history of juniper in the Edwards Plateau is 

presented by Smeins and others (1997) and Ueckert (1997).

My concern is the encroachment of juniper on areas in the 

Edwards Plateau that were historically grasslands or savannas. 

Also, it is not the author’s intent to suggest that all areas of 

juniper be removed from the Edwards Plateau. In fact, some 

juniper, even some deliberately located dense stands, may 

be desirable. However, for the sake of biodiversity, wildlife 

habitat, domestic livestock production, water availability, 

and management of volatile fuels, juniper has to be managed 

and fire should be a major part of an active integrated juniper 

management program.

Methods

Study Site

The data presented herein were collected from a replicated 

study from the Texas Agricultural Experiment Station located 

45 km south of Sonora, Texas (31oN; 100oW). The landscape 

of the Sonora Station is rolling stony hill topography typical 

of the Edwards Plateau. Soils on the site are Tarrant stony 

clays and Tarrant silty clays of the Lithic Haplustolls family. 

The growing season associated with the Sonora Station is 240 

days. Most of the precipitation results from intense, convective storms of short duration. The average precipitation (1919 

to 2003) recorded at the station is 57.4 cm per year.

In 1993, six study sites of approximately 2.5 ha each were 

established from two adjacent pastures to measure the effects 

of seasonal fire on native perennial vegetation. Summer and 

winter burning treatments were established along with an 

unburned control with two replications per treatment. Each 

treatment was blocked within each of the two pastures. 

Sites were selected to represent similar woody plant cover 

and herbaceous composition. Dominant herbaceous plants 

included common curlymesquite, threeawn, sideoats grama, 

and Texas wintergrass. Dominant woody plants were live oak, 

ashe juniper, and redberry juniper.

Vegetation in all six sites was sampled for species composition and woody canopy cover in July, 1994. Data were 

collected from transect lines that are permanently marked. 

Various vegetation measurements were sampled that included 

percent composition based on frequency and line intercept. 

Standing crop of grasses was measured by hand clipping 

vegetation from 50 quadrats per replicate. Analysis of variance was conduced on standing crop data with the general 

linear model univariate analysis option of SPSS (SPSS 2001). 

Significance levels for the tests were set at α = 0.05.

Two replicates were burned in August, 1994 (growing 

season treatment), two burned in February, 1995 (dormant 

season treatment) and two were left as unburned controls. 

The winter burn treatments were burned for a second time 

in February, 2000, and summer burned treatments in August, 

2000. The emphasis of this study is to measure the long-term 

effects of repeated seasonal fire on the perennial vegetation community. These sites will continue to be periodically 

burned for at least 20 years or longer. Only the major species 

are discussed in this report. Livestock have not grazed these 

pastures since 1993, but white-tailed deer have access to the 

treatments.

Results and Discussion

In 1994, prior to implementation of the burn treatments, 

standing crop of grass was measured on all six treatment sites. 

Standing crop was not different among treatments and averaged 42 g/m2

 per treatment (fig. 1). The first burn had little 

impact among burn and control treatments. It was not until 

after the second burn that treatment differences were first 

measured. The reason for the increased grass production after 

two summer burns is due to the reduced liveoak canopy cover, 

and elimination of juniper growing under the oak canopies, 

and reduction in prickly pear (Opuntia sp.).

Figure 1. Standing crop of grass (g/m2) from control, winter, and 

summer burned pastures. Winter burned replicates were burned 

in February of 1995 and 2000 and the summer burned replicates 

were burned in August of 1994 and 2000.
54 USDA Forest Service RMRS-P-47. 2007

Liveoak is an evergreen that is usually classified as moderately preferred by livestock and wildlife. Liveoak increases 

in the absence of fire and low browsing pressure, but does 

not generally have the potential to dominate a landscape like 

juniper. Liveoak tends to cluster in mottes on soils derived 

from Buda limestone, which is typical for pastures in the 

current research project.

Liveoak trees make good perch sites for robins (Turdus 

migratorius) and cedar wax wings (Bombycilla cedrorum). 

These two bird species, along with other animals that consume 

juniper berries, disperse the seeds over large areas, especially 

under the canopy of liveoak trees.

For example, after two burns, 100 percent of the oak mottes 

in the unburned control pastures had juniper compared to 67 

and 8 percent for the winter and summer burned treatments, 

respectively. Juniper density was similar for all treatments 

prior to the implementation of the burning treatments (approximately 74 plants per ha in 1993). After two prescribed burns, 

average number of juniper plants per motte was larger for the 

control pastures compared to the summer and winter burn 

pastures—46, 4, and .1 plants, respectively.

Summer fire was more effective than winter fire at managing 

juniper in liveoak mottes and was also more damaging to the 

liveoak. Liveoak canopies were reduced 60 percent in the 

summer burned treatments and 20 percent in the winter burns 

treatment.

Juniper density was measured in June, 2001, and averaged 

1,013, 100, and 25 plants per ha for the control, winter burned, 

and summer burned treatments, respectively. Recall, that both 

burn treatments had received two prescribed fires prior to the 

2001 sampling period. Although juniper density was light 

at the beginning of the study, the trees were large and had 

the potential to produce large seed crops. Also, no livestock 

grazing/browsing has occurred since 1993. The rapid recruitment of juniper in the control treatments is a good example 

how quickly juniper density can increase in an area without 

any type of management (such as fire and/or use of goats).

Most ranchers in the Edwards Plateau attempt to manage 

prickly pear because of its competitive nature with herbaceous forages (Mayeux and Johnson 1989; Ueckert and 

others 1988). Prescribed burns conducted in the winter period 

reduced prickly pear density to about half of the control treatments (642 and 370 plants/ha, respectively), whereas summer 

fire reduced prickly pear to less than 4 percent of the controls 

(25 plants/ha).

Grass response

Common curly mesquite grass is an abundant warm-season 

perennial grass that has increased with the advent of excessive livestock grazing in the Edwards Plateau (Merrill and 

Young 1959). Under better management, or complete rest 

from grazing, common curly mesquite is replaced by higher 

successional grasses (Smeins and Merrill 1988).

In this study, frequency of common curly mesquite 

decreased from 60 percent in 1994 to 32 percent in 2003. 

Because the response of common curly mesquite was similar 

across all treatments, including the non-burned control 

treatments, it appears that fire had little influence and indicates 

that this grass may be neutral to fire.

Sideoats grama, a climax warm season perennial grass, has 

two different growth forms for this region (rhizomatous type 

and bunch type). The rhizomatous type (underground stems) 

dominates the pastures in this study. These underground 

rhizomes are a major source of new tillers for the plants and 

would appear to be resistant to fire.

Averaged across all treatments, frequency of sideoats 

grama was the same in 2003 as in 1994 (19 vs. 20 percent, 

respectively). Frequency of sideoats grama was not affected 

by the fire effect (P = 0.717).

Texas wintergrass, a desirable cool seasongrass, responded 

differently than sideoats grama. Averaged across all treatments, frequency of Texas wintergrass increased from 1994 

to 2003 (36 and 44 percent, respectively). Frequency of Texas 

wintergrass increased for all treatments over the course of the 

study and was not affected by either summer or winter fire.

Threeawn species (Aristida spp.) include both annual 

and perennial threeawns. Most threeawns are not considered 

as good forage, although Wright’s threeawn provides early 

grazing prior to the green-up of the more productive grasses. 

Averaged across all treatments, threeawn frequency decreased 

from 1994 to 2003 (33 and 10 percent, respectively). For the 

summer burning treatments, threeawn frequency decreased 

from 30 to .3 percent (P = 0.064) from 1994 to 2003, respectively. Threeawn tends to accumulate dead leaves and stems, 

which may play a part in its response to hot fire.

Management Implications

These data illustrate the importance of a long-term, 

sustainable management program for juniper. Without fires, 

or when their severity is reduced because of low fuel, juniper 

can quickly invade and start to dominate a range site in a few 

years. Warm-season fires are more effective in killing juniper 

than cool-season fires. After two prescribed burns, it is the 

author’s opinion that the summer burn treatments in this study 

would not have to be burned again for up to 30 years, possibly 

longer, to maintain their grassland dominance. The winter burn 

treatments, given their current juniper status, would need to be 

burned within 15 years to maintain their grassland dominance. 

Recruitment of new seedlings is occurring at an accelerated 

rate in the control treatments. Within a few years, juniper will 

start to dominate the control areas and significantly reduce the 

carrying capacity for both livestock and wildlife.

Because of this, landowners are facing a dilemma with 

predictable consequences. One option, to do nothing, has 

major negative ecological consequences. Without intervention with proper management, the ecological system is locked 

indefinitely into an unnatural juniper dominated woodland.

Literature Cited

Baker, W. L. 1992. Effects of settlement and fire suppression on 

landscape structure. Ecology 73:1879-1887.
USDA Forest Service RMRS-P-47. 2007 55

Cory, V. L. 1949. On some grasses, chiefly of the Edwards Plateau of 

Texas. Field & Laboratory 17:41-52.

Foster, J. H. 1917. The spread of timbered areas in central Texas. 

Journal of Forestry 15:442-445.

Garriga, M.; Thurow, A. P.; Thurow, T.; Conner, R.; Brandenberger, 

D. 1997. Commercial value of juniper on the Edwards Plateau, 

Texas. pp. 8.3-8.12. in C. A. Taylor, Jr., ed. Proceedings, 1997 

Juniper Symposium. Texas A&M University Research & 

Extension Center Technical Report. 97-1. San Angelo, Texas.

Higgins, K. F. 1986. Interpretation and compendium of historical fire 

accounts in the Northern Great Plains. U.S. Department of the 

Interior. Resource Publ. 161. USDI, Washington, DC.

Komarek, E. V. 1968. Lightning and lightning fire as ecological 

forces. Proc. Tall Timbers Fire Ecology Conference 7:169-197.

Mayeux, H. S., Jr.; Johnson, H. B. 1989. Absorption and translocation 

of picloram by Lindheimer pricklypear (Opuntia lindheimeri). 

Weed Sci. 37:161-166.

Merrill, L. B.; Young, V. A. 1959. Response of curly mesquite to 

height and frequency of clipping. Texas Agric. Exp. Sta. MP-33.

Rollins, D.; Armstrong, B. 1997. Cedar through the eyes of wildlife, 

pp. 4.23-4.31. in C. A. Taylor, Jr., ed. Proceedings, 1997 Juniper 

Symposium. Texas A&M University Research and Extension 

Center Tech Report 97-1. San Angelo, Texas.

Smeins, F. E.; Merrill, L. B. 1988. Long-term change in a semiarid 

grassland, p. 101-114. In: B. Amos; Gehlbach, F. (eds). Edwards 

Plateau vegetation: plant ecological studies in central Texas. 

Baylor Univ., Press, Waco. 145 p.

Smeins, F.; Fuhlendorf, S. Taylor, Jr, C. A. 1997. Environmental and 

land use changes: a long-term perspective. pp. 1.3-1.21, in C. 

A. Taylor, Jr., ed. Proceedings, 1997 Juniper Symposium. Texas 

A&M University Research and Extension Center Technical 

Report. 97-1. San Angelo, Texas.

Taylor, C. A., Jr. 2001. Summer fire for the Western Region of the 

Edwards Plateau: A case study. Texas Agricultural Experiment 

Station Technical Report 01-2. Sonora, Texas.

Ueckert, D. N.; Peterson, J. L.; Potter, R. L. ; Whipple, J. D.; Wagner, 

M. W. 1988. Managing pricklypear with herbicides and fire. Texas 

Agric. Exp. Sta. Prog. Rep. Pr-4570.

Ueckert, D. N. 1997. Juniper control and management. pp. 5.23-5.34, 

in C.A. Taylor, Jr., ed. Proceedings, 1997 Juniper Symposium. 

Texas A&M University Research and Extension Center Technical 

Report. 97-1. San Angelo, Texas.

The Author

1 Professor and Research Station Superintendent, Texas Agricultural 

Experiment Station—Sonora, Sonora, TX. angora@sonoratx.net
56 USDA Forest Service RMRS-P-47. 2007
USDA Forest Service RMRS-P-47. 2007 57

Fire Session

Introduction

The Rio Grande Plains (RGP) and Coastal Prairie (CP) 

of South Texas is the southernmost extension of the Great 

Plains Grasslands. Fire, along with other climatic variables, 

such as drought, presumably maintained mesquite (Prosopis 

glandulosa Torr.) savannas and interspersed grasslands of preEuropean settlement South Texas. Frequency of fire appeared 

to be highly variable and ranged from 5 to 30 years (Wright 

and Bailey 1982). Following European settlement, the 

change from grassland to woodlands/shrublands was accelerated by introduction of livestock and fencing. Domestic 

animals served as ideal agents of seed dispersal for some 

species, notably mesquite. Removal of biomass by grazing 

also removed the fine fuel necessary to generate the intense, 

hot fires required to kill young woody plants. Where fuel was 

available to carry the fires, people worked to suppress them. 

Through time, woody plants gained a decided competitive 

edge over the grasses and forbs that had characterized the original grasslands, and the “brush country” was formed (Scifres 

and Hamilton 1993). Thus, suppression of fire, combined with 

heavy livestock grazing, led to the current thorn woodlands 

common throughout South Texas (Archer et al. 1988; Archer 

1994).

Beginning in the mid-twentieth century, South Texas landowners began to convert thorn woodlands back to grasslands 

to enhance rangelands for livestock production. Treatments, 

such as root plowing and herbicides, were commonly used 

to achieve this goal. In recent years the size of individual 

landholdings has decreased and revenue from wildlife has 

increased (Wilkins and others 2000). Brush management to 

enhance habitat has evolved into “brush sculpting” where 

brush is manipulated to increase edge, juxtaposition, and 

biodiversity. Mechanical, chemical, and prescribed fire treatments are used in this effort.

Fire provides an economical means of controlling woody 

species and maintaining the life of mechanical and chemical 

brush management treatments. Burning during late winter 

and early spring has been recommended for achieving many 

goals on South Texas rangelands (Scifres and Hamilton 1993), 

however, information on summer burning has been collected 

(Drawe and Kattner 1978; Ruthven and Synatzske 2003) and 

summer burning is now somewhat more acceptable.

Although fire has been used as a management tool for over 

a hundred years, the effects of fire on South Texas rangeland 

have not been studied until relatively recent times. In a thorough review of the literature, the earliest study mentioned 

by Vogl (1974) was that of Box and others (1967). However, 

since 1967, much work has since been conducted in the region. 

Certainly, a landmark publication that documents the state of 

the art of the use of prescribed fire in the region is Scifres 

and Hamilton’s (1993) book titled “Prescribed Burning for 

Brushland Management: The South Texas Example”.

Methods and Materials

Information in this paper was collected mainly from 

three South Texas locations (fig. 1). The Chaparral Wildlife 

Management Area, in the western RGP, is characterized by 

Management of South Texas Shrublands with 

Prescribed Fire

C. Wayne Hanselka1

D. Lynn Drawe2

D.C. Ruthven, III3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
58 USDA Forest Service RMRS-P-47. 2007

hot summers and mild winters. The growing season is 249 

to 365 days, and precipitation patterns is bimodal with peaks 

occurring in late spring (May-June) and early fall (SeptemberOctober). The 11-year (1989-2000) average precipitation 

amount is 54 cm. The second study area was on La Copita 

Demonstration Ranch and Research Area in the eastern RGP. 

Climate is subtropical with mild winters and hot summers. 

Mean annual temperature is 22.4 ̊C and the growing season 

is 289 days. Average annual rainfall is 68 cm, with maxima in 

May and September. The third area was the Rob and Bessie 

Welder Wildlife Foundation Refuge, located on the transitional 

zone between the CP and RGP. Average annual precipitation 

(1956-1985) is 906 mm.

Although generally considered historic grassland, South 

Texas today is a brush-grass complex; a grassland with brush 

of various densities covering almost all sites except the deep 

sands of the Nueces soils. Vegetation at all three locations 

is dominated by honey mesquite with various mixtures of 

broad-leaved evergreen and deciduous shrubs in its understory. Herbaceous vegetation between shrub clusters was 

composed of C4 grasses such as thin paspalum (Paspalum 

setaceum), knotroot bristlegrass (Setaria geniculata), Texas 

grama (Bouteloua rigidiseta), and hooded windmill grass 

(Chloris cucullata), which give way to grasses such as threeawns (Aristida spp), red grama (Bouteloua trifida), grassburs 

(Cenchrus incertus), and windmillgrass (Chloris verticillata) 

under prolonged, heavy grazing by cattle.

The major woody species in mixed brush communities 

are honey mesquite, black brush (Acacia rigidula), agarito

(Berberis trifoliolata), brasil (Condalia obovata), Mexican 

persimmon (Diospyros texana) lime pricklyash (Zanthoxylum 

fagara), spiny hackberry (Celtis pallida), pricklypear (Opuntia 

engelmannii), and lotebrush (Ziziphus obtusifolia), among 

others. Husiache is also a component of these communities.

Management Implications

Historically, fires burned in the summer and early winter in 

the RGP and CP, and, currently, summer fires are more effective in suppressing woody plant growth than are cool season 

burns. Prescribed fire has been used successfully to suppress 

woody plants in the eastern RGP and CP, however, fire does 

not kill brush. Research indicates that fire does reduce brush 

cover (Box and others 1967; Dodd and Holtz 1972), and two or 

more burns are more effective in reducing brush than a single 

fire (Box and White 1969). Gordon and Scifres (1977) found 

that prescribed burning, particularly when combined with 

chemical or mechanical methods, was effective in restoring 

rangeland heavily infested with Macartney rose (Rosa bracteata). Rasmussen and others (1983) found that in a fire 

regime the cool season Texas wintergrass (Stipa leucotricha) 

increased with increasing huisache (Acacia smallii) canopy 

up to approximately 40 percent canopy coverage of the woody 

invader, but that total herbage production declined beyond 40 

percent canopy. Therefore, to promote cool season plants, a 

certain amount of properly spaced woody cover maintained 

by prescribed fire may be desirable for both cattle and wildlife.

To suppress brush, the most effective burns are those used 

in combination with chemical or mechanical treatments. For 

example, huisache can be removed with chemical or mechanical means, but is only temporarily reduced solely by fire. So, 

fires reduce canopy cover and productivity of woody plants 

and enhance herbaceous growth. It can be used to increase the 

wildlife value of the habitat by causing resprouting of woody 

plants and by increasing forb growth. Fire also increases both 

chemical and mechanical defense mechanisms in certain 

woody species.

Since fire suppresses but does not kill most species of 

resprouting brush, this can be used to great benefit in wildlife habitat management. Top growth removal of brush by fire 

stimulates succulent regrowth for consumption by browsing 

wildlife, and it can create habitat diversity. Hot fires may be 

used in a patchwork design, alternated within burned areas. 

Cool fires, burned over a whole range interspersed with brush 

mottes, will burn around mottes and will leave portions of the 

range unburned thus creating greater diversity.

Timing of burning has a strong influence on the composition of the plant community following the fire and has 

profound effects on animal communities through effects on 

habitat. Plant species composition can be altered by timing 

of burning, thus the manager can create a plant community desirable for wildlife (Hansmire and others 1988). Late 

winter burning reduces forb populations and benefits grasses; 

whereas, early winter burning is followed by normal forb 

populations. In addition to reducing forbs, late winter burns 

may reduce the amount of other cool season plants, particularly Texas wintergrass.

Several studies have concentrated on the influence of 

repeated fires on both woody and herbaceous vegetation. More 

recently, summer prescribed fire has been implemented in an 

Figure 1. Location of study sites on the Rio Grande Plain and 

Coastal Prairie.
USDA Forest Service RMRS-P-47. 2007 59

attempt to suppress woody plant encroachment. An area was 

established on the Welder Wildlife Refuge in 1975 to assess 

the effects of repeated cool season fires on CP vegetation. A 

non-burned control was located adjacent to the burned block. 

The area was initially burned in the winter of 1974 and then 

was subsequently reburned in 1977 and 1980.

Repeated burning effectively suppressed woody vegetation. After the 1974 fire there was almost total top removal 

of woody species. The 1977 fire, which was extremely hot, 

burned through most of the smaller chaparral mottes. On the 

windward side of a motte the 1977 fire removed 100% of the 

cover. On the leeward side of a motte, depending upon wind 

speed during the fire, there were protected areas where some 

woody plants avoided topkill. In the larger mottes, i.e., those 

greater than 20 feet in diameter, woody plants survived in the 

center and on the leeward side of the motte. Fine fuel was 

essentially nonexistent within mottes. Only crown fires burned 

completely across a large motte. Whole mottes survived in the 

cooler 1980 burn, even some of the smaller mottes less than 

20 feet in diameter. Individual woody plants between mottes 

were top-killed. Following the third burn, canopy cover was 

reduced from the original 40% to less than 2%. By the summer 

following the third burn, there appeared to be a reduction in 

the amount of cover of all woody species. However, one year 

after the burn, all species were growing vigorously. Weedy 

herbaceous vegetation was abundant in the mottes totally top 

killed by the fire.

Long periods between burns allow brush to regrow to its 

former height and density and possibly increase in density. 

A prescribed fire program to suppress brush in South Texas 

should be designed to be burned every 3 to 4 years. Otherwise, 

brush regrowth is so rapid that any greater time sequence 

between burns will allow the brush to grow to the point that 

fire can no longer be used as an effective tool for suppressing 

regrowth.

Fire is also an effective tool in removing excess mulch 

accumulations that occur during wet cycles under conservative grazing. On the Welder Refuge, fine fuel loads from 

4,500 pounds per acre to 16,000 pounds per acre were burned 

(average 5,500 pounds per acre). Large amounts of fine fuel 

form a mat that may not be penetrated by light and actually 

acts to suppress plant growth. There is an increase in herbage 

production in the year following the initial burn, because more 

light penetrates to the soil surface and nutrients are released to 

the soil from decadent plants.

On the Chaparral Wildlife Management Area, rangeland 

was subjected to two winter prescribed burns and a winter burn 

followed by a summer fire. Prescribed burning can manage 

woody vegetation without dramatic reduction in woody plant 

diversity, which is common with many traditional mechanical 

treatments. However, percent woody plant cover was reduced 

by 50 percent and 41 percent on winter and winter-summer 

combination burned sites, respectively. Woody plant density 

declined by 29 percent and 23 percent on winter and wintersummer combination burned sites, respectively (Ruthven and 

others 2003). Density of guayacan (Guajacum angustifolium), wolfberry (Lycium berlandieri ), and tasajillo (Opuntia 

leptocaulis) was less on all burning treatments. Percent cover 

of spiny hackberry and density of pricklypear declined on 

winter burned sites. Inclusion of summer fire into the burning 

regime did not increase the decline in woody plants. Fire does 

create a post-fire environment, which results in the decline 

of many woody plant species. It is unclear to what degree 

other environmental factors, such as herbivory and competition between woody plants and among woody and herbaceous 

vegetation, may have interacted with fire to produce woody 

plant declines.

Combinations of winter and summer burns can effectively reduce the cover of honey mesquite, twisted acacia, 

Texas persimmon, lotebush, wolfberry, and tasajillo. Canopy 

cover of spiny hackberry and density of pricklypear decline 

following multiple winter burns. Soil moisture at the time of 

fire application may have a greater impact on woody vegetation response than season of burn.

Both summer and winter burning are effective at reducing 

honey mesquite cover, which may promote increases in herbaceous vegetation following fire. Summer burning following 

significant rainfall is effective in managing honey mesquite, 

while maintaining desirable woody species such as spiny 

hackberry. If reducing total woody plant cover is a management goal, burning during winter following periods of little or 

no rainfall is recommended.

Summer and winter prescribed fire produce similar 

responses from herbaceous vegetation (Ruthven and 

Synatzske 2002). Warm season annuals, such as croton 

(Croton spp.), were more prevalent on burned sites. However, 

increases in annuals did not persist into the second growing 

season following burning. Cool season annuals demonstrated 

little response to summer or winter burns. Perennials such as 

erect dayflower (Commelina erecta) and beach goundcherry 

(Physalis cinerascens) increase following summer and winter 

burns, whereas silky evolvulus (Evolvulus alsinoides) and 

hoary blackfoot (Melampodium cinereum) decrease following 

summer fires. Grass density decreased following summer fire; 

yet, productivity was similar among treated and nontreated 

sites one year post burn.

Initial burns on native RGP rangelands should be conducted 

on a 2-year interval until the desired structure of woody vegetation is achieved. Once desired goals are met, as stated 

earlier, maintenance burning on a 3- to 5-year frequency is 

adequate. Grazing strategies that allow for substantial deferment to produce adequate fuels to carry fire are critical to the 

successful application of fire on both CP and RGP rangelands. 

Other considerations to be taken into account are the highly 

unpredictable weather patterns in South Texas. Short-term 

periods of drought are common and rainfall can be highly 

variable between locations. Drought can severely impact 

production of fine fuels necessary to carry fire and may require 

flexibility in burning schedules. One should plan on burning 

as the opportunity arises since, if a critical burn is missed, 

conditions may not allow burning for several more years.

As stated earlier, fire may be integrated with other practices in brush management systems. An evenly-distributed, 

fine fuel load of 2,500 to 3,000 lb/acre is considered adequate 
60 USDA Forest Service RMRS-P-47. 2007

for an effective burn. However, rangelands supporting 

moderate to heavy brush cover are characterized by seriously 

reduced and patchy herbaceous cover (Scifres and others 

1982, 1983), resulting in inadequate fine fuel load. Because 

of the dependence on an adequate load of evenly distributed 

fine fuel, burning of brushy South Texas rangelands usually 

is a treatment subsequent to an initial method that uniformly 

reduces the brush canopy and releases the fine fuel. Moreover, 

prescribed burning often increases the effective life of initial 

treatments and compensates for characteristic weaknesses 

of several of the methods. Because of this utility, fire-based 

Integrated Brush Management Systems (IBMS) can take 

maximum advantage of several methods, including fire, over 

a relatively long time period. (Scifres and others 1985).

Prescribed burning has been evaluated following applications of herbicide sprays and of pellets as broadcast or 

individual plant treatments. It has also been effectively used 

in conjunction with various mechanical methods for brush 

management as both herbicide and mechanical applications 

reduce brush canopies and release fine fuel for prescribed 

burning. Prescribed burning then suppresses surviving woody 

plants, removes rough forage plants, promotes legumes and 

other desirable forbs usually damaged by sprays, promotes 

uniform distribution of livestock grazing, expedites secondary 

succession and improves botanical composition of grass 

stands. South Texas mixed brush is characterized by all of 

the problems and potentials described above. In most cases, 

burning is impossible until the brush canopy is reduced and 

fine fuel is released.

In 1999, an IBMS was installed in a mixed brush community on La Copita Demonstration Ranch and Research area. An 

outline of the State of Texas was superimposed on a DOQQ 

map of a pasture and coordinates around the perimeter of the 

map were recorded. Using a backpack GPS unit these coordinates were located around a 35 acre parcel of rangeland and 

staked. A D-8 Caterpillar tracked tractor then pulled a “rolling 

chopper- aerator” around the perimeter before chopping the 

area within the perimeter.

As expected, brush regrowth after top removal was rapid. 

In September, 2002, the 35 acres was divided into several 

plots and a variety of herbicides and mixes of herbicides were 

applied to each. Efficacy varied dependent upon species and 

herbicides treatment but, overall, canopy was reduced by 90% 

the first year. By the second year plants/acre were reduced 

by 50%. In spite of being part of a grazing program air dried 

forage production in the fall of 2003 was 280 lbs/ac in the 

control—open pasture; 320 lbs/ac in the control—brushy 

pasture; and 1500–2800 lbs/ac. in the chopped and sprayed 

pasture

Brush regrowth of those species not killed by the herbicide 

treatments was rapid. In February, 2004, the “State of Texas” 

was burned with a prescribed fire. The fire further thinned the 

brush stand, the species mix of forbs and grasses was enhanced 

and wildlife, such as bobwhite quail and white-tailed deer, 

prefer this pasture to non-treated pastures. Measurements of 

cattle grazing also indicate a preference for this pasture.

Summary

In summary, fire affects vegetation by suppressing woody 

growth, removing excess buildup of litter, and stimulating 

herbage production. Fire will not kill the majority of South 

Texas woody plants because of their resprouting characteristics, although there is an indication that repeat burns may 

kill a small percentage of plants of certain species. Timing 

of burning is one of the most important factors to consider in 

planning a burn. Fire stimulates growth of forbs following the 

top removal of woody plants in dense mottes of brush.

Literature Cited

Archer, S.; Scifres, C.; Bassham, C. R.; Maggio, R. 1988. Autogenic 

succession in a subtropical savanna: conversion of grassland to 

thorn woodland. Ecol. Monogr. 58:111-127.

Archer, S. 1994. Woody plant encroachment into southwestern 

grasslands and savannas: rates, patterns and proximate causes, 

p. 13-68. In: M. Vavra et al. (eds.) Ecological implications of 

livestock herbivory in the west. Society for Range Management, 

Denver, Colo.

Box, T. W.; Powell, J.; Drawe, D. L. 1967. Influence of fire on south 

Texas chaparral communities. Ecology. 48:955-961.

Box, T. W.; White, R. S. 1969. Fall and winter burning of south Texas 

brush ranges. J. Range Manage. 22:373-376.

Dodd, J. D.; Holtz, S. T. 1972. Integration of burning with mechanical 

manipulation of south Texas grassland. Journal of Range 

Management. 25:130-135.

Drawe, D. L.; Kattner, K. R. 1978. Effect of burning and mowing on 

vegetation of Padre Island. Southwestern Naturalist. 23:273-278.

Gordon, R. A.; Scifres, C. J. 1977. Burning for improvement of 

Macartney rose-infested Coastal Prairie. Bulletin B-1183, Texas 

Agricultural Experiment Station, College Station, TX.

Hansmire, J. A.; Drawe, D. L.; Wester, D. B.; Britton, C. M. 1988. 

Effects of winter burns on forbs and grasses of the Texas Coastal 

Prairie. Southwest. Nat. 33:333-338.

Rasmussen, G. A.; Scifres, C. J.; Drawe, D. L. 1983. Huisache 

growth, browse quality, and use following burning. Journal of 

Range Management. 36:337-342.

Ruthven, D. C.; Braden, A. W; Knutson, H. J.; Gallagher, J. F.; 

Synatzske, D. R. 2003. Woody vegetation response to various 

burning regimes in South Texas. J. Range Manage. 56:159-166.

Ruthven, D. C.; Synatzske, D. R. 2002. Response of herbaceous 

vegetation to summer fire in the western South Texas Plains. Tex. 

J. Sci. 54:195-210.

Scifres, C. J.; Hamilton, H. T. 1993. Prescribed burning for brushland 

management: the south Texas example. Texas A&M University 

Press, College Station, Tex. 246 p.

Scifres, C. J.; Hamilton, H. T; Conner, J. R.; Inglis, J. M.; Rasmussen, 

G. A.; Smith, R. P.; Stuth, J. W.; Welch, T. G. (eds.) 1985. Integrated 

brush management Systems for South Texas: Development and 

implementation. Tex. Ag. Exp. Stat. B-1493. 71 p.

Scifres, C. J.; Mutz, J. L.; Drawe, D. L.; Whitson, R. E. 1983. 

Influence of mixed brush cover on grass production. Weed Sci. 

31:1-4.

Scifres, C. J.; Mutz, J. L.; Whitson, R. E.; Drawe, D. L. 1982. 

Interrelationships of huisache canopy cover with range forage on 

the coastal prairie. J. Range Manage. 35:558-562
USDA Forest Service RMRS-P-47. 2007 61

Vogl, R. J. 1974. Effects of fire on grasslands. Pages 139-194 in 

T. T. Kozlowski and C. E. Ahlgren, (Ed). Fire and ecosystems. 

Academic Press, New York, NY.

Wilkins, N.; Brown, R. D.; Conner, R. J.; Engle, J.; Gilliland, C.; 

Hays, A.; Slack, R. D.; Steinbach, D. W. 2000. Fragmented 

lands: changing land ownership in Texas. Texas A&M Univ, Agr. 

Commun. Pub. MKT-3443, College Station, Tex.

Wright, H. A.; Bailey, A. W. 1982. Fire Ecology. John Wiley and 

Sons, New York, N.Y. 501 p.

The Authors

1

 Texas Cooperative Extension. c-hanselka@tamu.edu 2 Welder Wildlife Foundation.

3 Texas Parks and Wildlife Dept.
62 USDA Forest Service RMRS-P-47. 2007

Introduction

Fire suppression activities during the past century often 

increase the severity of wildfires resulting in increased soil 

erosion and decreased water quality (Pearson and others 

2001, 2002). Increased runoff and erosion can lead to loss of 

soil productivity, flooding, and increased risk to human life 

and property. Many non-fire related infiltration studies on 

rangeland have shown that litter and vegetation cover protect 

the soil and enhance infiltration (Rauzi and others 1968; 

Blackburn and others 1986). Fire removes this protective 

covering, reduces soil surface organic matter, and exposes 

the soil to raindrop impact. After fire, soils can become 

water-repellent (hydrophobic) although this condition is 

also common on unburned rangelands (DeBano 1981) and 

dry soils conditions (Bond and Harris 1964ab; Rutin 1983; 

Jungerius and de Jong 1989). In the unburned setting, the 

partially decomposed organic matter from brush species, 

when intermixed with the soil surface layer, can also produce 

a water-repellent situation (DeBano and Rice 1973; Pierson 

and others 2001).

The USDA-ARS Northwest Watershed Research Center 

(NWRC) has been investigating wildfire interactions with 

hydrologic processes on steep, coarse textured, sagebrush 

(Artemisia) dominated landscapes in Nevada and Idaho. The 

sagebrush-steppe is an extensive rangeland shrub type in 

North America and occupies about 42.5 million ha2

 in the 11 

western states. The objectives of these studies are to quantify 

the impacts of wildfire on infiltration capacity, runoff, erosion, 

and soil surface characteristics and determine how long fire 

effects persist. The objective of this paper is to summarize 

interactions between vegetation, soil, topographic features, 

hydrologic parameters, and sediment production after a high 

intensity wildfire.

Hydrology, Erosion, Plant, and Soil Relationships after 

Rangeland Wildfire

Abstract: Wildfire is an important ecological process and management issue on western 

rangelands. Fire suppression activities in the past century have increased the number and 

severity of wildfires, resulting in increased soil erosion and decreased water quality. Many 

infiltration studies on rangeland have shown that litter and vegetation cover protect the soil 

and enhance infiltration. After fire, water repellency is typically found on the soil surface or a 

few centimeters below and is also common on unburned rangelands and dry soils conditions. 

However, the causal agents of water repellency are different for burned and burned 

conditions. Rainfall simulation studies were conducted for 3 consecutive years immediately 

following a catastrophic wildfire in Denio, Nevada, in 1999. Study sites were chosen on northfacing hillslopes (35 to 40 percent slope) where the vegetation was dominated by mountain 

big sagebrush (Artemisia tridentata ssp. vaseyana). The objective of this study was to use 

indirect gradient analysis on the 1999 data to evaluate and summarize pertinent relationships 

between vegetation, soil, topographic features, infiltration, runoff, sediment production, and 

microsite distinction (shrub coppice and interspace) on burned and unburned areas. The first 

ordination (strategy 1) used four infiltration parameters and the results were unexpected. In 

the multivariate context, higher infiltration trends were associated with the burned treatment 

compared to the unburned treatment. Water repellency on the burned sites was apparent 

at the soil surface; however, it appears that repellency was also a significant factor on the 

unburned area. Water repellency in the unburned treatment was likely caused by assorted 

litter buildup (up to 11,605 kg/ha) in > 80-year stands (sagebrush duff and grass in the shrub 

coppice areas and grass litter in the interspace). The second ordination (strategy 2) involved 

the same four infiltration parameters, but specifically used plots from the burned treatment. 

More runoff and sediment was associated with the burn shrub coppice plots; in contrast, 

higher infiltration capacity in the burned interspace. The third ordination (strategy 3) was 

based on plant canopy cover by species. Discrete taxa of native grasses, forbs, and shrubs 

were correlated with infiltration, runoff, and sediment loss on burned and unburned sites. 

On the unburned sites, water repellency and higher runoff was correlated with Sandberg 

bluegrass (Poa secunda), bluebunch wheatgrass (Pseudoroegneria spicata), and western 

aster (Symphyotrichum ascendens). Greater infiltration capacity was correlated with 

increasing cover of Idaho fescue (Festuca idahoensis) and mountain big sagebrush. Future 

analysis will evaluate conditions after the first years growing season and beyond.

Kenneth E. Spaeth1

Frederick B. Pierson2

Peter R. Robichaud3

Corey A. Moffet4

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 63

Study Area

This ongoing study is approximately 24 kilometers southwest of Denio, Nevada, in the Pine Forest Range. The Denio Fire 

burned in late July 1999 and consumed approximately 34,400 

ha. Mean elevation of the research area is 2,050 m, average 

annual precipitation of the study area is 350-400 mm. Study 

sites were located on north-facing hillslopes (35 to 40 percent 

slope). The soil is an Ola bouldery sandy loam which consists 

of moderately deep soils formed in residuum from granite on 

mountain sideslopes. The ecological site description is classified as a Granitic slope 14-16” P.Z., mountain big sagebrush/ 

Idaho fescue/bluebunch wheatgrass (USDA-NRCS 1990). 

Other common subdominant grass species include Columbia 

needlegrass (Achnatherum nelsonii), bottlebrush squirreltail (Elymus elymoides), and Sandberg bluegrass. Associated 

shrubs on the site were common snowberry (Symphoricarpos 

albus) and green rabbitbrush (Chrysothamnus viscidiflorus). 

The major forb species were lodgepole lupine (Lupinus 

parviflorus), nettleleaf giant hyssop (Agastache urticifolia), 

longleaf hawksbeard (Crepis acuminata), small bluebells 

(Mertensia longiflora), indian paintbrush (Castilleja spp.), 

alpine lake prairie-dandelion (Nothocalais alpestris), Siskiyou 

Mountain ragwort (Packera macounii), arrowleaf balsamroot 

(Balsamorhiza sagittata), rosy pussytoes (Antennaria rosea), 

common yarrow (Achillea millefolium), western aster, and 

low scorpionweed (Phacelia humilis).

Methods

Rainfall simulator experiments were conducted in 1999 

under antecedent surface soil moisture conditions. The study 

included two treatment effects: microsites (shrub coppice 

and interspace) with 20 plots (0.5m2) and 10 plots each on 

the three burned and unburned areas. A greater number of 

sample plots were sampled on the burned sites in anticipation of greater variability in response variables compared to 

the control sites. Four portable oscillating-arm rainfall simulators (specifications described by Meyer and Harmon [1979]) 

were used to apply rainfall to each runoff plot for 60 minutes. 

A rainfall rate of 85 mm/hr, equal to the rainfall intensity of a 

10-minute thunderstorm with a 10- year return period (Hanson 

and Pierson 2001), was applied to each runoff plot.

Plot frames were installed immediately after the fire in 

September 1999 and were left in place for subsequent rainfall simulation treatments. Rainfall was first applied starting 6 

weeks following the fire before any natural rainfall events had 

occurred. All burned and unburned control plots were sampled 

within 10 days of the start of rainfall simulations. Runoff was 

routed through a collection tray at the bottom of each plot and 

collected at one- or two-minute intervals throughout the entire 

rainfall simulation. Runoff samples were analyzed for runoff 

volume and sediment concentration by weighing, drying at 

105 o

C, and re-weighing each sample. Infiltration capacity for 

each time interval was calculated as the difference between 

measured rainfall and runoff.

Prior to the simulation runs, soil samples were collected 

adjacent to each runoff plot and analyzed for gravimetric 

soil moisture content. Following rainfall simulation, bulk 

density using the core method (Blake and Hartge 1986), 

organic carbon content using the ashing method (Nelson and 

Sommers 1982), and soil texture using the hydrometer method 

(Bouyoucos 1962) were determined from soil samples taken 

immediately adjacent to each plot. Vegetative canopy cover 

for each plant species, standing dead material, basal vegetative 

crowns, ground cover of cryptogams, woody and non-woody 

litter, rock, and bare ground were estimated ocularly to the 

nearest percent for each plot (Elzinga and others 2000). Some 

of the rarer species occupy < 1.0 percent canopy cover; therefore, we split the cover classes into finer units (0.05, 0.025, 

and 0.01 percent). To improve the estimation procedure, each 

0.5 m2

 plot was divided into 4 segments (0.125 m2) and cover 

values were estimated using a nested frame for calibration, 

which contained representative areas of 50, 25, 15, 10, 5, 1, 

0.05, 0.025, and 0.01 percent. Accuracy of the ocular method 

was evaluated from random plots by recording 500 points 

with a point cover frame. Corresponding percent differences 

between ocular and point cover measurements were not more 

than ± 2 percent.

The experimental design of this study is given in Pierson 

and others (2001). In this analysis, indirect gradient analysis using detrended correspondence analysis (DCA) (Hill 

and Gauch 1980) was used to evaluate plant, soil, site, and 

hydrology interactions following the wildfire. The following 

strategies were used: Strategy 1, because all the above ground 

vegetation including woody stems of shrub species were 

entirely consumed in the 1999 fire, a comparative ordination 

(main matrix) using four infiltration parameters was made of 

both the 1999 burn and unburned sites (n = 90). The infiltration parameters were: minimum infiltration rate (mm/hr)—the 

lowest average infiltration rate of all sample intervals from the 

respective rainfall simulation runs; final infiltration rate (mm/

hr) is the average infiltration rate of the 58 to 60 min time 

interval; time to minimum infiltration (min) (equivalent to 

peak runoff); and cumulative infiltration (mm/hr) calculated 

as total amount of rainfall applied less cumulative runoff. 

Secondary matrix environmental variables were correlated 

with axis loadings from the infiltration data. The environmental variables used appear in Table 1. The axes in DCA 

are scaled in units of the average standard deviation (SD) of 

species turnover. A change of 50 percent occurs in about 1 SD. 

Strategy 2 was the same as 1, except that only burned plots 

were used (n = 60). The third strategy consisted of a DCA 

ordination using the 1999 unburned plant species canopy 

cover data as the main matrix, the secondary matrix data were 

the environmental factors (n = 30). The false discovery rate 

(FOR) (Benjamini and Hochberg 1995) was used to test for 

false positives in the correlation data between axis loadings 

and plant and environmental variables.
64 USDA Forest Service RMRS-P-47. 2007

Results

Strategy 1

Figure 1 is an ordination diagram of 1999 infiltration 

parameters for the burned and unburned plots. Examination of 

the burn and unburned treatments shows definitive groupings 

between burned and unburned treatments along DCA axis 1. 

The angle and length of the centroid line shows the delineation 

and degree of correlation of the respective variables. Each line 

can be related to other variable lines to denote possible environmental gradients (groups of variables). Pearson correlation 

cutoff values in the ordination diagrams were set at r = 0.50. 

Table 1 shows correlation coefficients of environmental variables with the first two DCA infiltration axes.

There is a strong infiltration gradient along axis 1 (fig. 1). 

Final and cumulative infiltration were highly negatively 

correlated with axis 1. Cumulative infiltration and final infiltration rate decrease toward the right along axis 1; therefore, 

the burn treatment plots are associated with higher rates for 

these two variables (table 1). Water repellency as calculated 

in Pierson and others (2001), cumulative runoff, silt, litter, 

and runoff-rainfall ratio were positively correlated with axis 1 

(table 1). These variables increase in magnitude from left to 

right. Pierson and others (2001) found that infiltration rate and 

capacity in water repellent soils after fire were reduced during 

the early stages of the infiltration curve. In the latter stages of 

the rainfall simulation, water repellency decreased with time. 

The hydrophobic causative agents deteriorated resulting in 

gradual recovery of infiltration. Bulk density at 2- to 4-cm 

was negatively correlated with axis 1—higher values in the 

burned treatment.

An infiltration gradient also appears along axis 2, where 

minimum infiltration (the lowest average infiltration rate for 

all sample intervals) and cumulative infiltration are negatively 

correlated (table 1). In the lower left region, interspace microsite burn plots predominate. Although minimum infiltration 

is not significant between burned (45.2 mm/hr) and unburned 

treatments (45.9 mm/hr), it was significant between coppice 

(37.8 mm/hr) and interspace (53.6 mm/hr) microsites on the 

burned treatment (Pearson and others 2001). The complementary measurement to cumulative infiltration, cumulative 

runoff, were positively correlated. Also, the runoff-rainfall 

ratio was positively correlated with axis 2 (table 1). 

Strategy 2

Strategy 2 was included in this paper so that microsites in 

the burned area could be compared. Figure 2 shows the 1999 

burned plots and there were definitive groupings between the 

interspace and coppice microsites. For an in depth review 

of the hydrologic data, refer to Pierson and others (2001). 

Minimum infiltration, cumulative infiltration, final infiltration 

rate, and water repellency were negatively correlated with axis 

1, and cumulative runoff was positive along axis 1. The interspace plots are predominantly on the left side of axis 1 where 

Table 1. Pearson correlations (strategies 1, 2, and 3) with the first two detrended correspondence analysis axes for Denio, 

Nevada, Mountain big sagebrush study sites (fire year, 1999).

Strategy 1 Strategy 2 Strategy 3

Variables Axis 1 (r) Axis 2 (r) Axis 1 (r) Axis 2 (r) Axis 1 (r) Axis 2 (r)

Cumulative infiltration (mm) -0.67 -0.53 -0.63 -0.55 -0.54 -0.19

Final infiltration rate (mm/hr) -0.74 -0.45 -0.55 -0.55 -0.55 -0.12

Minimum infiltration (mm/hr) -0.39 -0.80 -0.83 -0.14 -0.48 -0.31

Runoff/Rain ratio (mm mm) 0.69 0.54 0.66 0.53 0.55 0.18

Cumulative runoff (mm) 0.66 0.54 0.65 0.52 0.54 0.16

Time-to-runoff (min) -0.04 -0.41 -0.38 0.18 -0.47 -0.34

Time-to-peak runoff (min) 0.47 0.24 0.31 0.40 -0.02 -0.40

Cumulative sediment (kg/ha) 0.15 0.45 0.50 0.31 0.46 0.17

Sediment/Runoff ratio (kg/ha mm) -0.18 0.19 0.23 0.06 0.23 0.006

Water repellency index 0.83 -0.38 -0.83 0.50 0.66 -0.17

Antecedent moisture 0-2 cm (%) 0.38 -0.10 0.07 0.26 0.01 -0.06

Bulk Density 0-2 cm (g/cm3) -0.44 0.02 -0.08 -0.09 -0.09 -0.14

Bulk Density 2-4 cm (g/cm3) -0.55 0.02 -0.19 -0.39 -0.05 -0.007

Grass cover (%) 0.62 -0.08 -0.34 0.20 0.21 0.23

Forb cover (%) 0.13 -0.15 -0.11 0.02 -0.20 -0.21

Shrub cover (%) 0.19 -0.16 -0.24 0.06 -0.32 -0.67

Litter cover (%) 0.54 -0.13 0.16 0.13 0.09 -0.41

Sand 0-2 cm (%) -0.48 0.10 -0.17 -0.31 0.17 -0.15

Silt 0-2 cm (%) 0.52 -0.08 0.18 0.32 -0.05 0.14

Clay 0-2 cm (%) -0.12 -0.15 -0.01 0.007 -0.38 0.03

Rock (%) -0.22 -0.08 -0.16 -0.14 . .

Slope (%) 0.44 0.19 0.40 0.10 0.10 0.06

Aspect (degrees) 0.27 -0.10 -0.20 -0.44 -0.39 0.21

Microsite (Coppice, Interspace) 0.19 -0.38 -0.60 0.35 0.31 0.69

Microtopography -0.35 -0.08 -0.20 -0.32 . .

Treatment (burn, unburn) 0.52 -0.15 . . . .
USDA Forest Service RMRS-P-47. 2007 65

Figure 1. Detrended correspondence analysis 

of 1999 Denio wildfire hydrology data from 

all rainfall simulation plots (n=90). Plot points 

represent an ordination of four infiltration 

variables [minimum infiltration rate, final infiltration rate, cumulative infiltration rate, and 

time to minimum infiltration (equivalent to 

peak runoff)]. Secondary matrix correlations 

were the remaining variables listed in table 1. 

Pearson correlation coefficients cutoff values 

in the figure were set at r = 0.5. The dotted 

polygon represents the relative grouping of 

the unburned 1999 sites. The points outside 

the polygon are the 1999 burned plots. 

Correlated variables in diagram are: sand, 

Pb_23=bulk density at 2-4cm, f_infil=final infiltration rate, cuminf=cumulative infiltration, 

cumro=cumulative runoff, ro_r_r=runoff/rainfall ratio, t_pk_ro=time to peak runoff, silt, 

litter, totgrass=total grass cover of all species, 

hydphob=water repellency index, and n_

trtcod=treatment (burned and unburned).

Figure 2. Detrended correspondence analysis 

of 1999 Denio wildfire hydrology data from 

rainfall simulation burned plots (n=60). Plot 

points represent an ordination of four infiltration variables [minimum infiltration rate, final 

infiltration rate, cumulative infiltration rate, 

and time to minimum infiltration (equivalent 

to peak runoff)]. Secondary matrix correlations were the variables listed in table 1. 

Pearson correlation coefficients cutoff values 

in the figure were set at r = 0.5. The dotted 

polygon represents the relative grouping of 

the burned interspace 1999 plots. The points 

outside the polygon are the 1999 burned 

shrub coppice plots. Correlated variables 

in diagram are: hydphob=water repellency 

index, mininf=minimum infiltration rate, 

cuminf=cumulative infiltration, f_infil=final 

infiltration rate, n_ctype=microsite cover 

type (interspace, coppice), ro_r_r=runoff/

rainfall ratio, cumro=cumulative runoff, and 

cumsed=cumulative sediment.
66 USDA Forest Service RMRS-P-47. 2007

average final infiltration, cumulative infiltration, minimum 

infiltration, and water repellency were higher compared to the 

shrub coppice to the right on axis 1. As Pierson and others 

(2001) mentioned, there was more fuel on the shrub coppice 

microsites which may have resulted in higher burn temperatures and a greater tendency for water repellent conditions. 

Fire vaporizes some organic compounds on the soil surface 

and distills the rest downward, concentrating the hydrophobic 

substances in the upper soil surface. On the right side of axis 

1 where the coppice plots are grouped, cumulative sediment 

yield was higher coppice = 410 kg/ha; interspace = 210 kg/

ha (fig. 2). The runoff-rainfall ratio was also higher for the 

burned shrub coppice area (0.37 mm mm) compared to the 

burned interspace (0.30 mm mm) (fig. 2).

Strategy 3

Figure 3 is an ordination of plant canopy cover data for 

all species in the unburned area. In figure 3, the unburned 

coppice and interspace microsites are definitively separated. 

The microsite groupings are unique with respect to plant 

species composition. Near plots have more similar plant 

species composition, far plots are more dissimilar. Along axis 

1, final infiltration and cumulative infiltration are associated 

with the shrub coppice microsites. In contrast, cumulative 

runoff, runoff-rainfall ratio, water repellency, and cumulative 

sediment are higher in the unburned interspace. 

In Pierson and others (2001), final infiltration rates were 

about equal between the burned (55.5 mm/hr) and the unburned 

coppice (55.9 mm/hr) plots. After an intense wildfire, we 

expected to see a difference in infiltration rates between the 

coppice microsites; however, infiltration between burned and 

unburned coppice areas immediately after the fire was about 

the same. We propose that the litter buildup in the unburned 

treatment area was responsible. On the unburned plots, litter 

averaged 5 cm deep and averaged 7,275 kg/ha with a high 

value of 11,605 kg/ha. The litter, sagebrush duff, and grass 

on shrub coppice and senescent grass in the interspace apparently have water repellent properties. We observed this during 

the rainfall simulation experiments. In contrast to the coppice 

areas, final infiltration rate in the burned interspace (60.0 mm/

hr) was significantly greater compared to the unburned interspace (40.4 mm/hr). 

In figure 3, Sandberg bluegrass and bluebunch wheatgrass were positively correlated with axis 1 (> canopy cover), 

the zone of unburned interspace plots. Idaho fescue was 

negatively correlated with axis 1—where the unburned shrub 

coppice plots have higher Idaho fescue and Columbia needlegrass canopy cover. Regression analyses of the unburned data 

showed:

Infiltration = f ( + Idaho fescue, + Columbia needlegrass, + 

mountain big sagebrush),

Runoff = f (+ Sandberg bluegrass, + bluebunch wheatgrass 

+ western aster),

Cumulative sediment = f ( + Sandberg bluegrass, + western 

aster),

where f = function of the following independent variables, + 

sign indicates positive association.

Spaeth and others (1996, 2003) proposed that plant species 

appear to have an impact on rangeland hydrology. Therefore, 

Figure 3. Detrended correspondence analysis 

of 1999 Denio wildfire hydrology data from 

rainfall simulation unburned plots (n=30). Plot 

points represent an ordination of plant canopy 

cover for all species. Secondary matrix correlations were the variables listed in table 1. 

Pearson correlation coefficients cutoff values 

in the figure were set at r = 0.5. The dotted 

polygon represents the relative grouping of 

the unburned interspace 1999 plots. The 

points outside the polygon are the 1999 

unburned shrub coppice plots. Correlated 

variables in diagram are f_infil=final infiltration rate, cuminf=cumulative infiltration, 

mininf=minimum infiltration rate, t_to_ro=timeto-runoff, totshrub=total shrub canopy 

cover, n_ctype=microsite cover type (interspace, coppice), ro_r_r=runoff/rainfall ratio, 

cumro=cumulative runoff, cumsed=cumulative 

sediment, l_cumsed=log of cumulative sediment, and hydphob=water repellency index. 

Correlated plant species appear in the 

respective ordination quadrants.
USDA Forest Service RMRS-P-47. 2007 67

we hypothesize that plant species (considering importance 

values such as cover, biomass, and root biomass) can affect 

hydrology.

Discussion

In Pierson and others (2001), we showed that wildfire can 

have a significant hydrologic impact on the hydrology of 

sagebrush dominated rangelands. In Pierson and others (2001) 

we hypothesized that during the burn year, average infiltration rates would be reduced on the burned compared to the 

unburned treatment because of soil water repellency caused 

by the hot fire. This hypothesis was rejected because rainfall 

simulation experiments shortly after the fire did not result in a 

significant effect on average infiltration between the burn and 

unburned treatments.

A second hypothesis was tested: infiltration rates will be 

different between microsites for burned and unburned treatments (based on previous work by Blackburn 1975, Pierson 

and others 1994). Infiltration rates were reduced on burned 

shrub coppices compared to burned interspace. Burned shrub 

coppice microsites were associated with very uniform fire 

induced water repellency with an average infiltration rate 

reduction of 28 percent. On unburned plots, infiltration rates 

were greater on the shrub coppice areas compared to interspace areas. Comparisons between burned and unburned 

treatments showed that infiltration rates were about the same 

on coppice microsites, but different between interspace areas. 

Infiltration was higher, and runoff lower, on the burned interspace compared to the unburned interspace. Pierson and others 

(2001) attributed this unexpected result to the dense mat of 

senescent grass (litter) on the soil surface. The water repellent 

litter in the interspace area intercepted the rainfall and initiated runoff before the water reached the mineral soil surface. 

In this paper, we examined possible relationships between 

individual species composition and hydrology. In mountain 

big sagebrush vegetation, plant composition, and soil physical properties are different in microsite areas (shrub coppice, 

shrub dripline, and varying distances along the interspace). 

Idaho fescue, lupine, mountain big sagebrush, and snowberry 

are more prevalent in the coppice areas; whereas, Sandberg 

bluegrass, bluebunch wheatgrass, rosy pussytoes, common 

yarrow, and western aster occur mostly in the interspace areas. 

The presence or absence and magnitude of canopy cover of 

certain plant species seems to be associated with infiltration 

capacity, runoff, and sediment loss. This preliminary study 

showed certain plant species were associated with higher and 

lower infiltration and runoff. In figure 3, textural differences, 

antecedent moisture, bulk density, total grass cover, and total 

forb cover were not correlated with the infiltration gradient 

(unburned coppice to unburned interspace). However, Idaho 

fescue and Columbia needlegrass canopy cover were correlated with higher infiltration; whereas, Sandberg bluegrass and 

bluebunch wheatgrass were associated with higher runoff. 

Future analysis will incorporate several more years of 

rainfall simulation experiments at Denio, Nevada to determine the impact of these plant species on hydrology in high 

elevation mountain big sagebrush vegetation. In addition to 

the Denio sites, the NWRC is conducting similar rainfall 

simulation experiments at sagebrush sites at Reynolds Creek 

Experimental Watershed in southwest Idaho.

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ASAE 22 :100-103.

Nelson, D. W.; Sommers, L. E. 1982. Total carbon, organic carbon, 

and organic matter. In: Methods of Soil Analysis. Part 2. Chemical 

and Microbiological Properties. Second Edition, Page AL (ed). 

Agronomy Series #9, ASA, SSSA: Madison, Wisconsin.

Pierson, F. B.; Van Vactor, S. S.; Blackburn, W. H; Wood, J. C. 1994. 

Incorporating small scale spatial variability into predictions 

of hydrologic response on sagebrush rangelands. Soil Science 

Society of America Special Publication 38:23-34.

Pierson, F. B.; Carlson, D. H.; Spaeth, K. E. 2002. Impacts of wildfire 

on soil hydrologic properties of steep sagebrush-steppe rangeland. 

International Journal of Wildland Fire 11:145-151.

Pierson, F. B.; Robichaud, P. R.; Spaeth, K. E. 2001. Spatial and 

temporal effects of wildfire on the hydrology of a steep rangeland 

watershed. Hydrological processes 15:2905-2916.
68 USDA Forest Service RMRS-P-47. 2007

Rauzi, F.; Fly, C. L.; Dyksterhuis, E. J. 1968. Water intake on 

midcontinental rangelands as influenced by soil and plant cover. 

USDA Tech. Bull. No. 1390.

Rutin, J. 1983. Erosional processes on a coastal sand dune, DeBlink, 

Noordwijkerhout. Physical Geography and Soils Laboratory 

Publication 35. University of Amsterdam, The Netherlands.

Spaeth, K. E.; Pierson, F. B.; Weltz, M. A.; Awang, J. B. 1996. 

Gradient analysis of infiltration and environmental variables 

related to rangeland vegetation. Transactions of the ASAE 39(1): 

67-77.

Spaeth, K. E.; Pierson, F. B.; Weltz, M. A.; Blackburn, W. H. 2003. 

Evaluation of USLE and RUSLE estimated soil loss on rangeland. 

J. Range Management. 56:234-246.

USDA-NRCS. 1990. Rangeland ecological site description: Granitic 

Slope 14-16” P.Z. (023XY043NV) ARVA/FEID-AGSP. USDANRCS Technical Guide Section IIE, Reno, Nevada.

The Authors

1 Rangeland Hydrologist, USDA-NRCS, Ft. Worth, TX.

2 Research Hydrologist, USDA-ARS, Northwest Watershed Research 

Center, Boise, ID. 3 Research Engineer, USDA-Forest Service, Rocky Mountain 

Research Station, Moscow, ID. 4 Rangeland Scientist, USDA-ARS, Dubois, ID.
USDA Forest Service RMRS-P-47. 2007 69

Introduction

Spotfires have and always will be a problem that burn 

bosses and fire crews will have to contend with on prescribed 

burns. Spotfires can cause mental and physical stress on burn 

bosses and crews if they occur or not. If a spotfire does take 

place it can cause injury to personnel or even loss of life, as 

well as monetary damages and loss of public support for the 

prescribed burning program. From interviewing many private 

and public land managers in Oklahoma, spotfires or risk of 

escape (liability) is the main reason many of them do not 

conduct prescribed fires. Many of these land managers have the 

personnel and equipment needed to conduct prescribed fires, 

but lack the experience or knowledge to deal with spotfires. 

So any type of simple guideline or rule-of-thumb is always 

needed to assist these people with their prescribed fires.

Temperature, wind speed, and relative humidity are the 

most important weather factors that burn bosses can use to 

predict and monitor prescribed fire behavior. Bunting and 

Wright (1974) determined that danger from firebrands was 

lower if the ambient air temperature was below 60oF (15oC) 

when conducting prescribed burns. Burning above 40 percent 

relative humidity has been shown to slow rates of spread significantly (Lindenmuth and Davis 1973) and reduce danger from 

firebrands (Green 1977). Wind speeds of 8 mph (13 km/h) are 

needed to ignite and burn standing fuels (Britton and Wright 

1971), but with winds over 20 mph (32 km/h) firebrands and 

other debris become problems (Wright and Bailey 1982). As 

indicated from the research, there are several weather related 

thresholds that influence the occurrence of spotfires. So if 

spotfire causes can be narrowed down to one key weather 

factor, this will help burn bosses to focus on that single variable, possibly reducing the likelihood of spotfires.

Methods

At the Oklahoma State University Research Range 

(OSURR) prescribed burns are conducted during different 

seasons of the year and in different fuel types all over the state 

of Oklahoma. These burns are conducted in a wide variety 

of fuels: Tallgrass Prairie (NFES fuel models 1, 3), PostoakBlackjack Oak (NFES fuel models 3, 8, 9), Eroded Mixed 

Prairie (NFES fuel models 1, 3), Sandsage Grassland (NFES 

fuel model 4), and Oak-Pine Forest (NFES fuel models 3, 8, 

9, 11) (NFES fuel models from Anderson 1982). Since 1996, 

records have been kept to track spotfires that occur on these 

prescribed burns. For this study, a spotfire is considered any 

fire that occurs outside the burn unit no matter what size it is 

or what caused it. The size of a spotfire is relative to fuel loads 

outside of the burn unit, crew size, crew experience, equipment 

present, equipment dependability, firebreak type and size, and 

weather conditions. The spotfires during this study ranged in 

size from less than 1 ft2

 (.09-m2) to 120 acres (264 ha). Most 

of these spotfires were due to firebrands caused by crowning 

eastern redcedar (Juniperus virginiana), while leaves from 

Using Relative Humidity to Predict Spotfire Probability on 

Prescribed Burns

Abstract: Spotfires have and always will be a problem that burn bosses and fire crews 

will have to contend with on prescribed burns. Weather factors (temperature, wind speed 

and relative humidity) are the main variables burn bosses can use to predict and monitor 

prescribed fire behavior. At the Oklahoma State University Research Range, prescribed 

burns are conducted during different seasons of the year and in different fuel types all over 

the state of Oklahoma. Since 1996 records have been kept to track spotfires that occur on 

these prescribed burns. Most of these spotfires were due to firebrands caused by crowning 

eastern redcedar (Juniperus virginiana). Leaves from oak (Quercus spp.) trees or tallgrasses 

floating or blowing across the fireline and smoke or fire whirls were responsible for most of the 

other spotfires. When burn data were reviewed, one weather variable stood out as the main 

cause of spotfires, low relative humidity. Of the 99 burns conducted there were 21 spotfires. 

From the data, the probability of a spotfire occurring on any prescribed burn with the relative 

humidity between 20 and 80 percent was determined to be 21.2 percent or approximately one 

out of five burns. Looking at the 40 percent relative humidity threshold, there is a probability 

of 41.3 percent for a spotfire occurring below 40 percent and 3.8 percent above 40 percent. 

There also appears to be another threshold at less than 25 percent relative humidity. At this 

point, there is a 100 percent probability of a spotfire occurring. With this information burn 

bosses can determine spotfire potential when considering burn units or burn days. It can also 

assist them when considering crew size and equipment needed. Most of all, inexperienced 

burn bosses can use this to help reduce risk (liability) and increase safety for their crews.

John R. Weir1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
70 USDA Forest Service RMRS-P-47. 2007

oak (Quercus spp.) trees or tallgrasses floating or blowing 

across the fireline and smoke or fire whirls were responsible 

for most of the other spotfires (fig. 1).

When prescribed fires are conducted by the OSURR crew, 

weather is recorded on site before, during and after the burn. 

This weather data consists of dry bulb and wet bulb temperature, wind speed and direction, and relative humidity, which is 

calculated from the dry and wet bulb temperatures. Information 

is also recorded about spotfires, such as if one occurred and 

time it occurred.

Results and Conclusions

When the burn data was reviewed, one weather variable 

stood out as the main cause of spotfires – low relative humidity. 

Of the 99 burns conducted, there were 21 spotfires, with 

19 of the spotfires occurring at or below 40 percent relative 

humidity (fig. 2). Research has shown that below 40 percent 

relative humidity fine fuels ignite and burn easily, while 

above 40 percent ignition slows (Britton and Wright 1971; 

Lindenmuth and Davis 1973; Green 1977). This research validates that the threshold value of 40 percent relative humidity 

is an excellent rule-of-thumb to follow when conducting 

prescribed burns. This does not mean that there should be 

no prescribed burns conducted below 40 percent relative 

humidity. There are many regions of the US and certain burn 

units that require low relative humidity to allow for the goals 

and objectives of that specific burn to be met. But it should 

be imprinted in the burn boss’ mind that there is an excellent probability for a spotfire to occur if the burn is conducted 

below 40 percent relative humidity. In the same instant burn 

bosses should be ready for spotfires on all prescribed burns 

no matter what the relative humidity values are. For example, 

we recorded one spotfire when the relative humidity was at 

73 percent, which was caused by crowning eastern redcedar 

throwing firebrands across the firebreak into heavy fuels. This 

proves spotfires can occur at higher relative humidity values.

Since most spotfires occur at or below 40 percent relative 

humidity, then what is the probability of a spotfire occurring at 

the 40 percent threshold value or any other relative humidity 

value? This information would be important for burn bosses 

to know as they prepare for and conduct prescribed burns to 

help reduce the risk to personnel and property. The information from the 99 prescribed burns was used to develop a set 

of probabilities for a spotfire occurring at a certain relative 

humidity. To determine this probability the following formula 

was used (Steele and Torrie 1980):

P = number of successes (spotfires)

total number of events (successes + failures) (fires)

From the data collected at the OSURR, the probability 

of a spotfire occurring on any prescribed burn with the relative humidity is between 20 and 80 percent was determined 

to be 21.2 percent, so approximately one out of five burns 

could be a spotfire. The data was then tested for the probability of spotfires above and below the 40 percent relative 

humidity threshold. There was a 41.3 percent probability for 

a spotfire occurring when the relative humidity was below 

Figure 1. Fire whirls and ignition by other volatile fuels can cause spotfires on prescribed burns. The probability of a spotfire occurring is considerably less when the burn is conducted when the relative humidity is over 40 percent.
USDA Forest Service RMRS-P-47. 2007 71

40 percent and only a 3.8 percent probability when the relative humidity was above 40 percent. This is a large difference 

and the 40 percent threshold should be considered when inexperienced personnel are conducting prescribed burns or when 

heavy fuel loads are adjacent to the burn unit or if escape 

could bring possible public scrutiny or litigation. Again this 

is not condemning prescribed burning below 40 percent relative humidity.

If burns are conducted under 40 percent relative humidity, 

does the probability of spotfires change at lower relative 

humidity values? As figure 3 shows, there is a difference 

Figure 3. The percent probability of spotfires 

as a function of relative humidity determined 

from 99 prescribed fires conducted across 

Oklahoma from 1996 to 2002.

in probability at each 5 percent drop in humidity below 

40 percent. There also appears to be another threshold at 

less than 25 percent relative humidity. At this point, there is 

a 100 percent probability of a spotfire occurring. So below 

25 percent relative humidity, burn bosses should be prepared 

for a spotfire. The spotfire probability drops to 46.2 percent in 

the 25 to 29 percent relative humidity range, which reduces 

spotfire risk over half with just a couple of percentage point 

increase in relative humidity. When the relative humidity is 

between 30 and 34 percent, only one out of three prescribed 

burns is likely to have a spotfire. So even within the range of 

20 to 40 percent relative humidity there is a large difference in 

the probability of a spotfire occurring.

With this information, burn bosses can determine spotfire potential when considering burn units or burn days. It can 

also assist when considering crew size; equipment needed and 

possibly reduce anxiety when burning below 40 percent relative humidity. Most of all inexperienced burn bosses can use 

this to help reduce risk (liability) and increase safety for their 

crews. The main item to remember is to burn when conditions 

are safest for the crew and surrounding neighbors.

Literature Cited

Anderson, H. E. 1982. Aids to determining fuel models for estimating 

fire behavior. USDA For. Serv. Gen. Tech. Rep. INT-122, 22 p. 

Intermt. For. and Range Exp. Stn., Ogden, Utah 84401.

Britton, C. M.; Wright, H. A. 1971. Correlation of weather and 

fuel variables to mesquite damage by fire. J. of Range Manage. 

23:136-141.

Bunting, S. C.; Wright, H. A. 1974. Ignition capabilities of nonflaming 

firebrands. J. For. 72:646-649.

Green, L. R. 1977. Fuel breaks and other fuel modification for 

wildland fire control. USDA Handbook No. 499. Washington, 

D.C.

Figure 2. Of the 99 prescribed fires conducted from 1996 to 2002, 

21 burns had spotfires. Only two spotfires occurred when relative 

humidity was greater than 40 percent.
72 USDA Forest Service RMRS-P-47. 2007

Lindenmuth, A. W.; Davis, J. R. 1973. Predicting fire spread in 

Arizona oak chaparral. USDA For. Ser. Res. Paper RM-101. 

Rocky Mtn. For. and Range Exp. Stn. Fort Collins, CO.

Steele, R. G. D.; Torrie, J. H. 1980. Principles and Procedures of 

Statistics. Second Edition. McGraw-Hill Book Company, New 

York, NY.

Wright, H. A.; Bailey, A. W. 1982. Fire Ecology: United States and 

Southern Canada. John Wiley and Sons, New York, NY.

The Author

1 Research Station Superintendent, OSU Research Ranch, Oklahoma 

State University, Stillwater, OK. weir@agr.okstate.edu
USDA Forest Service RMRS-P-47. 2007 73

Introduction

Prescribed fire is an attractive option for reducing mesquite 

dominance on grasslands because it is less costly than other 

options and reduces the need for chemical and/or mechanical 

applications (Wright and Bailey 1982; Teague and others 1997; 

Ansley and Jacoby 1998). However, for fire to be an effective 

method for mesquite control, a grazing management strategy 

must be devised to accumulate the herbaceous biomass (otherwise called ‘fine fuel’) that fuels a fire. Moreover, because 

fire kills very few mesquite and only provides a ‘top-killing’ 

suppression effect at best (Ansley and others 1998; Ansley and 

Jacoby 1998), a management system must allow for frequent 

planned burning (at least every 8 to 10 years) to maintain 

sufficient suppression of mesquite regrowth.

It is difficult in continuous-grazed systems to accumulate sufficient herbaceous fine fuel to carry a fire of sufficient 

intensity to suppress woody vegetation. Prescribed burning 

may be more easily incorporated into systems using one-herd 

and multiple-paddocks (Scifres and Hamilton 1993). Using 

such management systems, we hypothesized that fire could be 

applied every 4 to 6 years and that the deferral period required 

to accumulate fuel could be ‘internalized’ within a management system by burning a small percentage of the system each 

year and rotating burning each year to different paddocks. Not 

burning riparian vegetation and burning to create a savanna 

effect in selected areas on a site specific basis allowed for 

maintenance of wildlife habitat and biodiversity that did not 

impact livestock operations (Teague and others 1997).

Our objectives were to (1) evaluate the utility of rotational grazing and deferment as a means of facilitating use of 

prescribed fire for mesquite suppression through the accumulation of herbaceous fine fuel, and (2) determine system-level 

changes in mesquite cover in different rotational grazing and 

fire/herbicide management scenarios. Mesquite aerial cover 

was used as an indicator of level of mesquite dominance in 

the each system.

Methods

Site Description

The investigation was conducted in the Rolling Plains 

in north central Texas on a 14,400 ha portion of the W.T. 

Waggoner Estate termed the “Kite Camp.” The climate is 

continental with an average 220 frost-free growing days. 

Mean annual precipitation is 648 mm, bimodally distributed 

with peaks in May and September. The mean annual temperature is 17o

C and elevation ranges from 335 m to 396 m.

Mesquite Cover Responses in Rotational Grazing/

Prescribed Fire Management Systems: Landscape 

Assessment Using Aerial Images

Abstract: Prescribed fire is used to reduce rate of mesquite (Prosopis glandulosa) 

encroachment and dominance on grassland ecosystems, but is difficult to apply in continuousgrazed systems because of the difficulty in accumulating sufficient herbaceous biomass (that 

is, ‘fine fuel’) that is needed to fuel fire. We evaluated the potential of rotationally grazing 

cattle as a means to defer grazing to provide fine fuel burning. Mesquite cover changes 

from 1995 to 2000 were compared in four systems: continuous grazing, mesquite untreated 

(Cont.), 4 pasture/1 herd with fire (4:1F), 8 pasture/1 herd with fire (8:1F), and 4:1 with fire 

+ herbicide (4:1F+H). There were two replicate systems per treatment, each 1,400-2,100 

ha. The initial goal in the 4:1F and 8:1F systems was to burn 25 percent of the total area 

each year (1 pasture in 4:1F; 2 pastures in 8:1F). Fires were conducted in late winter. 

Mesquite cover was measured using digitized aerial images in 1995 (pre-treatment) and 

2000. Droughts limited burning over this 5-year period to half the intended area of each 

system. Stocking rates, while adjusted in response to droughts, were maintained at similar 

levels in all systems. Net change in mesquite cover, scaled to account for soil types and 

pasture sizes in each system, was +34 percent, +15 percent, +5 percent, and -41 percent in 

the Cont., 4:1F, 8:1F, and 4:1F+H systems, respectively. Cattle performance was similar for 

all systems during the study period. Rotational grazing and fire systems slowed the rate of 

mesquite cover increase but did not reduce it. Fire was easier to apply in the 8:1F than the 

4:1F system during drought because total area burned could be reduced to 1/8 instead of 

1/4 of the system.

R. J. Ansley1

W. E. Pinchak2

W. R. Teague3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
74 USDA Forest Service RMRS-P-47. 2007

Mesquite trees with aerial cover of 15 to 20 percent dominated the vegetation matrix. The herbaceous understory 

consisted of roughly an equal mixture of C4

 and C3 perennial grasses. The major C4

 grasses are shortgrass buffalograss 

(Buchloe dactyloides), and mid-grasses sideoats grama 

(Bouteloua curtipendula), silver bluestem (Bothriochloa 

saccharoides), and meadow dropseed (Sporobolus asper). 

Mid-grass Texas wintergrass (Nassella leucotricha) and the 

annual grass, Japanese brome (Bromus japonicus), are the 

major C3

 grasses. Soils are variable on the Kite Camp with 

approximately 50 percent shallow clays (3 to 8 percent slopes), 

40 percent moderately deep clay-loams (1 to 3 percent slopes), 

and 10 percent deep loamy bottomlands in riparian zones (0 

to 1 percent slopes). The clay-loam areas are where mesquite 

size, density, and cover are greatest and pose the greatest problems for livestock management.

Mesquite Treatments

The experiment consisted of four treatments with two replicate pastures of 1,400 to 2,100 ha each per treatment. Initial 

treatments were (1) continuous grazing with no mesquite 

treatment, (2) a 4-pasture, 3-herd rotation where one pasture 

was burned each year (4:3F), (3) a 4-pasture, 1-herd rotation 

where one pasture was burned each year (4:1F), and (4) an 

8-pasture, 1-herd rotation where two pastures were burned 

each year (8:1F). A total of 34 paddocks were involved in the 

study (2 in continuous, 8 in 4:3s, 8 in 4:1s, 16 in 8:1s). Area 

of paddocks within each system were not exactly the same 

but were roughly 25 percent of the total area in four pasture 

systems and 12.5 percent of the total area in eight pasture 

systems. Paddocks were fenced in 1995 and first burns were 

conducted in January-March 1996. Fires were applied as 

headfires that were burned into pre-burned blacklines (50 m 

wide) according to procedures outlined by Wright and Bailey 

(1982).

In the fire-based systems, the goal was to burn a different 

25 percent of the area of each system each year. Burns were 

conducted in winter months (January to March) and were 

planned as high-intensity mesquite top-killing fires to maximize mesquite suppression. To accumulate herbaceous fuel on 

the 25 percent to be burned, cattle were rotationally grazed 

on the remaining 75 percent of each system for 4 to 6 months 

without a reduction in stocking rate determined for the entire 

system. Thus, costs of deferral were internalized. Fire was to 

be used when average or above-average precipitation resulted 

in sufficient fine fuel (> 1,500 kg ha-1) to suppress mesquite. 

During drought years deferred pastures were not burned but 

grazed as needed.

A severe spring drought following 1996 fires forced us 

to discontinue the 4:3 system and in 1998 these pastures 

were converted to 4:1 systems with herbicide as the method 

of mesquite control. These paddocks had an initial fire in 

one paddock in 1996 and herbicide aerial spray in the other 

paddocks in 1999 (0.28 kg/ha clopyralid+0.28 kg/ha triclopyr; 

see Ansley and others 2003). This treatment was designated as 4:1 fire+herbicide (4:1F+H). Herbicide spray was 

concentrated on the clay loam soils where mesquite cover 

was greatest. Most of the mesquite on shallow soils was not 

sprayed because of light cover and density.

Livestock were managed in each pasture as a cow-calf 

operation (Hereford breed). Cattle stocking rates were maintained at similar levels in all systems throughout the study and 

were initially set at 7 ha per cow in 1995. Rates were reduced 

to 11 ha per cow in 1996 and 14 ha per cow by 2001 following 

several droughts.

Mesquite Cover Quantification

Color infrared (CIR) aerial images of Kite Camp (1:7,000) 

were taken in October 1995 and September 2000. Images 

were scanned and geo-referenced in Arcview GIS using 

ortho-quads available from the USGS (Ansley and others 

2001). Green vegetation appears as varying shades of pink 

or red on CIR images. Normally, on late summer/early fall 

images, mesquite canopies appear as a bright pink color and 

the herbaceous understory is light gray. However, because 

of well-above average precipitation, herbaceous vegetation 

remained green throughout 1995 and it was not possible to 

use the automated color classification system within ArcView 

to digitally separate mesquite cover from understory vegetation because both vegetation types had similar shades of 

pink. We could visually discern individual mesquite canopies 

from the understory, however, because canopy margins cast 

a small shadow. Therefore, mesquite cover was quantified on 

the images using a variation of the line intercept technique 

(Canfield 1941). Two 1 ha (100 x 100 m) plots each were 

randomly located on clay loam and shallow soil types on 

images of each paddock of each system. Ten parallel computer 

generated lines, each scaled at 100 m length, were placed in 

each 1 ha plot and mesquite canopy intercept was measured 

manually along each line using the distance measure feature 

in Arcview (after Ansley and others 2003). Cover values from 

images were verified with field transects (r2

 = 0.94; ŷ = 0.97x 

- 0.98; n = 12). The same process was used for images taken 

in 2000, although color separation between mesquite canopies and understory was very good. Cover was determined on 

1,360 separate 100 m transect lines (34 paddocks x two soil 

types/paddock x two 1-ha plots/soil type x 10 lines/plot); far 

more than would be possible using field measurements.

Plot-level changes in mesquite cover were scaled to the 

system (pasture) level for each system (4:1, 8:1, etc). Scale 

factors were percent area of each soil type (shallow or clay 

loam) in each paddock and percent area of each paddock 

relative to the total area of each system. Riparian areas were 

excluded from the analysis.

Statistical Analysis

Mesquite percent change values relative to pre-treatment levels were analyzed using a completely randomized 

design with treatment (Continuous, 4:1F, 8:1F and 4:1F+H) 

or paddock (1-4 or 1-8) as the main effect (two replicates 

per treatment or paddock) (SAS 1988). Percentage data were 
USDA Forest Service RMRS-P-47. 2007 75

arc-sine transformed prior to analysis. Means were separated 

using LSD (P < 0.05).

Results and Discussion

Precipitation and Fire History

The 1995 growing season (March-October) was much 

wetter than average, followed by an extremely dry period 

from November 1995 through June 1996 (fig. 1). Severe 

growing season droughts were experienced in 1996, 1998, and 

2000. The years 1997 and 1999 had key periods during each 

growing season when precipitation was less than average and, 

with the exception of the July-August period in 1997, there 

was no 2-month period from 1996 through 2000 when precipitation during the growing season was much above average.

A burn ban due to drought during most of February-March 

1996 limited burning to five of the eight paddocks that were 

scheduled to burn. One paddock in the remaining unburned 

pasture was burned in 1997 to equalize replicates so that one 

paddock had been burned in every system. Droughts in 1996 

and 1998 reduced grass production, which limited the number 

of paddocks that were burned to 14 of the original 36 that 

were planned (table 1).

With the exception of the 1996 fires, droughts also limited 

the intensity of fires because of low herbaceous fine fuel 

amounts. In addition, intensity of the 1998 fires was limited 

because a wet and warm January-February 1998 increased C3

Figure 1. Bi-monthly precipitation at the research site from 1995-

2000. Line indicates 30-yr average precipitation for each 2-month 

period.

Table 1. Planned burns vs. completed burns on the Kite Camp study, 1996-

2000.

Paddocks 

planned Paddocks

Burn dates to burn burned Comments

Jan-March 1996 8 5 Burn ban Feb-March

Jan-March 1997 8 1 1996 drought - low fine fuel

Jan-March 1998 8 6 Feb - March very wet, green

Jan-March 1999 6 0 1998 drought - low fine fuel

Jan-March 2000 6 2 High Opuntia; low fuel in one

1996 - 2000 36 14

1

 Planned burns were reduced from eight to six in 1999 because two systems 

were changed from fire to herbicides as the means for mesquite control.

Table 2. Effectiveness of prescribed fires on mesquite topkill, Kite Camp.

Good topkill Moderate topkill Poor topkill

Burn year 60 - 90 % 40 - 60 % 20 - 40 %

1996 4 1 0

1997 0 1 0

1998 1 2 3

2000 1 0 1

1996-2000 6 4 4

grass growth and green tissue content in the fine fuel retarded 

combustion. Of the 14 fires conducted, 6 had high (60 to 

90 percent), 4 had moderate (40 to 60 percent), and 4 had 

poor (10 to 40 percent) levels of mesquite top-kill (table 2). 

As expected, none of the fire treatments killed more than 2 

percent of the mesquite and most plants re-sprouted from 

stem bases following top-killing fires. The herbicide treatments root-killed over 60 percent and top-killed nearly 100 

percent of the mesquite plants. Herbicide results were viewed 

as typical for this mixture (Ansley and others 2003; Mitchell 

and others 2004). Detailed summaries of herbaceous vegetation responses and cattle performance are available elsewhere 

(Teague and others 2001a).

Mesquite Cover Changes Within 

Each Soil Type

In continuous-grazed, untreated systems, mesquite cover 

increased on clay loam soils from 22.3 to 35.6 percent from 

1995 to 2000, an increase of 13.3 percentage units, or 2.7 

percentage units per year. This is a slightly faster rate of 

cover increase than the 2.2 percentage unit per year rate that 

Ansley and others (2001) found over a 20-year period on a 

clay loam site near the current study area. On shallow soils 

in the continuous-grazed, untreated systems, mesquite cover 

increased from 5.8 to 6.9 percent from 1995 to 2000, or 0.2 

percentage units per year. Mesquite cover was not high on 

shallow soils at study initiation and did not increase at a 

rate that was considered a management problem. However, 
76 USDA Forest Service RMRS-P-47. 2007

mesquite did attain a level of dominance on clay loam soils 

over the 5-year period of the study that was of considerable 

management concern. Ansley and others (2004) found on a 

clay loam site near the current study site that mesquite cover 

did not reduce C4 midgrass production until it was greater 

than 25 percent. However, at that point C4 midgrass production declined sharply to levels that were 25 percent of the 

maximum recorded values (50 g m -2 vs 200 g m-2). Thus, an 

increase in mesquite cover on clay loam soils in the present 

study from 22 to 36 percent would be expected to reduce C4

midgrass production to a much greater degree in 2000 than in 

1995, assuming similar climatic conditions.

Increases in mesquite cover in untreated paddocks of the 

4:1F systems followed a similar pattern as that of the continuous-grazed, untreated systems (fig. 2). In untreated paddocks 

3 and 4, cover increased slightly on shallow soils and from 

about 26 percent to 38 percent on clay loam soils. Responses 

were similar on each soil type in untreated paddocks of the 

8:1F systems (data not shown). Thus, the type of grazing 

pattern (continuous, 4:1 or 8:1) did not appear to affect the rate 

of mesquite cover increase on either soil type if mesquite was 

left untreated. Thus, rotational grazing alone (that is, without 

fire or some other mesquite treatment) did not increase the 

competitive ability of the herbaceous community to slow the 

rate of mesquite canopy growth, as measured by aerial cover.

In treated paddocks in each system, mesquite cover changes 

on each soil type varied considerably with treatment type 

and/or intensity. In the 4:1F systems, paddocks 1 and 2 were 

burned in 1996 and 1998, respectively. The 1996 fire, which 

was very intense, initially reduced mesquite cover on clay 

loam soils from 36 percent to less than 10 percent (data not 

shown). However, by 2000, mesquite cover had increased due 

to mesquite regrowth to levels that were only slightly lower 

than in 1995 on both soil types (fig. 2). The 1998 fires were 

much less effective in top-killing mesquite than the 1996 fires. 

As a result, by 2000, mesquite cover had increased on clay 

loam soils to levels that were greater than the initial level of 

27 percent. This was a slower rate of increase than what was 

found in the untreated paddocks 3 and 4, however. Clearly, 

the fires reduced the rate at which mesquite cover increased. 

Averaged over the four paddocks in the 4:1F systems, cover 

increased on clay loam soils from 29 to 35 percent and did 

not change on shallow soils (fig 2). Averaged over the eight 

paddocks in the 8:1F systems, cover increased on clay loam 

soils from 32 to 35 percent and did not change on shallow 

soils (data not shown in a figure).

In the 4:1F+H systems, the 1996 fire in paddock 1 of each 

replicate yielded a similar result as found for paddock 1 in the 

4:1F systems (fig. 2). The other three paddocks were treated 

with herbicides in 1999 that reduced mesquite cover on clay 

loam soils to < 5 percent. Much of the mesquite that occurred 

on shallow soils was not sprayed because of light cover and 

density. When averaged over the four paddocks, mesquite 

cover in the 4:1F+H systems was reduced from 30 percent to 9 

percent on clay loam soils and from 12 to 8 percent on shallow 

soils. These results agree with what other studies have found 

for this clopyralid+triclopyr treatment (Ansley and others 

2003; Mitchell and others 2004). This treatment is not only 

effective at reducing mesquite cover but also reduces mesquite 

density (root-kill is usually 60 to 70 percent) and has a treatment life of > 20 years (Ansley and others 2004). However, 

typical cost for this treatment is $25 per acre compared to $2 

to 3 for fire (Teague and others 2001b).

Scaling Mesquite Cover Responses 

Over Soil Types

Following scaling mesquite cover changes over both soil 

types in each paddock, the 1996 fires (paddock 1) were the 

only treatment in the 4:1F systems that reduced mesquite 

cover from 1995 to 2000 (fig. 3). Cover increased in the 

other three paddocks but at a slower rate in paddock 2 due 

to the 1998 fires. In contrast, the four paddocks that received 

prescribed fire in the 8:1F systems all yielded lower mesquite 

cover in 2000 than 1995. In this treatment, the most recent 

fires were in the year 2000 (paddock 4) just 8 months prior 

to the date of the 2000 CIR images. We were unable to burn 

in the 4:1F systems after 1998 because droughts prevented 

grazing deferral on 25 percent of the system. The remaining 

75 percent of the system simply could not sustain the herd 

for any length of time even though stocking rates had been 

reduced for each system. We were able to burn one paddock 

in each of the 8:1 systems in 2000 because we could defer 

grazing in 1/8 of the area of each system and rotate the herd 

on the remaining 7/8 of the area.

Figure 2. Mesquite cover from 1995 to 2000 within each paddock (P) 

and soil type (clay loam = solid; shallow = open) and the mean of 

all four paddocks in 4:1F (top) and 4:1F+H (bottom) systems (n = 

2). F = fire, H = herbicide, NT = no treatment.
USDA Forest Service RMRS-P-47. 2007 77

In the 4:1F+H systems, mesquite cover decreased from 

1995 to 2000 in all four paddocks (fig. 3) due to the intense 

fire in 1996 (paddock 1) and the herbicide treatments in the 

other three paddocks. The reason mesquite cover reduction 

was greater in paddock 2 than paddocks 3 and 4 was because 

there was more clay loam soil in paddock 2 and therefore more 

area was sprayed. Paddocks 3 and 4 had a high percentage of 

shallow soils.

Scaling Mesquite Cover Changes 

Over Soils and Paddocks

Net change in mesquite cover, when scaled over soil type 

and area of each paddock within each system, was +34 percent, 

+15 percent, +5 percent, and -41 percent in the Continuous, 

4:1F, 8:1F, and 4:1F+H systems, respectively (fig. 4). Mesquite 

cover was reduced only in the fire+herbicide system during 

the period of the study. However, the rate of system-level 

increases in mesquite cover were much lower in the 4:1F and 

8:1F systems compared to the continuous grazed, untreated 

systems. In addition system-level increases in mesquite cover 

were slower in the 8:1F than the 4:1F systems.

Conclusions

Rotational grazing and fire systems (4:1F and 8:1F) slowed 

the rate of increases in mesquite cover but did not reduce 

it within the time-frame of this study. Severe droughts in 

1996, 1998, and 2000 limited burning to only 14 paddocks 

in 5 years compared to the original goal of 36. It should be 

noted, however, that, while we did not conduct the number 

of fires intended over the scheduled time frame, we were able 

to conduct more fires during these periods of severe drought 

than any ranch in the region. This was attributed to the utilization of rotational grazing systems. As a result, increases 

in system-level mesquite cover were lower in both fire-only 

systems compared to the untreated system.

System-level rate of mesquite cover increase was slower in 

the 8:1F than the 4:1F systems. We believe that one of the most 

significant discoveries in this study was that fire was easier 

to apply in the 8:1F than the 4:1F systems during droughts 

because the area deferred and burned could be reduced to 1/8 

(that is, one paddock) instead of 1/4 of the total area of the 

system. Eight paddocks provided more flexibility for burning 

in drought years than did four paddock systems.

Mesquite cover was reduced to a much greater degree in 

the fire+herbicide systems than the two fire-only systems. We 

believe the fire-only systems would have been more effective 

at suppressing mesquite had precipitation been near average. 

One of the advantages of the herbicide option is that, unlike 

prescribed fire, it requires virtually no pre-planning and is not 

as dependent as is a fire plan on long-term weather patterns. 

However, typical cost for this treatment is $25 per acre 

compared to $2-3 for fire (Teague and others 2001b).

Acknowledgments

The authors wish to acknowledge Kelli Barnett and Betty 

Kramp who quantified mesquite cover on the aerial images. 

Figure 4. Percent change in mesquite cover from 1995 to 2000 within 

each management system when scaled over area per paddock 

in each system and area per soil type within each paddock. Error 

bars indicate + 1 S. E. (n = 2). Means with similar letters are not 

significant at P < 0.05.

Figure 3. Percent change in mesquite cover from 1995 to 2000 

within each paddock (P) in 4:1F, 8:1F, and 4:1F+H systems when 

scaled over both soil types. Error bars indicate + 1 S. E. (n = 2). 

Means with similar letters are not significant at P < 0.05.
78 USDA Forest Service RMRS-P-47. 2007

David Jones, Betty Kramp, Gerral Schulz, Steve Dowhower, 

Tim Tunnell, Matt Angerer, Doug Tolleson, Bob Cross, and 

many others assisted with the prescribed fires. This research 

was funded by grants from USDA-NRI Managed Ecosystems, 

Dow AgroSciences, Indianapolis, IN, and the North Texas 

Brush Control Association, Albany, TX. The E. Paul and 

Helen Buck Waggoner Foundation, Vernon, TX, provided 

significant funding, land area, and cattle for the project and 

Waggoner Ranch personnel assisted with all phases of livestock handling.

References

Ansley, R. J.; Jones, D. L.; Tunnell, T. R.; Kramp, B. A.; Jacoby, P. 

W. 1998. Honey mesquite canopy responses to single winter fires: 

relation to fine fuel, weather and fire temperature. International J. 

Wildland Fire. 8: 241-252.

Ansley, R. J.; Jacoby, P. W. 1998. Manipulation of fire intensity to 

achieve mesquite management goals in north Texas. Pages 195-

204. In: Pruden, T. L.; Brennan, L. A. (eds). Fire in Ecosystem 

Management: Shifting the Paradigm from Suppression to 

Prescription. Tall Timbers Fire Ecology Conf. No. 20. Tall 

Timbers Research Station, Tallahassee, FL.

Ansley, R. J.; Wu, X. B.; Kramp, B. A. 2001. Observation: Longterm increases in mesquite canopy cover in a north Texas savanna. 

Journal of Range Management. 54: 171-176.

Ansley, R. J.; Kramp, B. A.; Jones, D. L. 2003. Converting mesquite 

thickets to savanna through foliage modification with clopyralid. 

Journal of Range Management. 56: 72-80.

Ansley, R. J.; Teague, W. R.; Pinchak, W. E.; Kramp, B. A.; Jones, 

D. L. 2004. Long-term grass yields following chemical control of 

honey mesquite. Journal of Range Management. 57: 49-57.

Archer, S.; Schimel, D. S.; Holland, E. A. 1995. Mechanisms of 

shrubland expansion: land use, climate or CO2

? Climatic Change. 

29: 91-99.

Bedunah, D. J.; Sosebee, R. E. 1984. Forage response of a mesquitebuffalograss community following range rehabilitation. Journal 

of Range Management. 37: 483-487.

Blackburn, W. H.; Tueller, P. T. 1970. Pinyon and juniper invasion 

in black sagebrush communities in east-central Nevada. Ecology. 

51: 841-848.

Canfield, R. H. 1941. Application of line interception in sampling 

range vegetation. Journal of Forest. 39: 388-394.

Carlson, D. H.; Thurow, T. L.; Knight, R. W.; Heitschmidt, R. K. 

1991. Effect of honey mesquite on water balance of Texas Rolling 

Plains rangeland. Journal of Range Management. 43: 491-496.

Dahl, B. E.; Sosebee, R. E.; Goen, J. P.; Brumley, C. S. 1978. Will 

mesquite control with 2,4,5-T enhance grass production. Journal 

of Range Management. 31:129-131.

Koos, W. M.; Williams, J. C.; Dixon, M. L. 1962. Soil survey of 

Wilbarger County, Texas. USDA Soil Conservation Service, Soil 

Survey Series 1959 No. 18, Fort Worth, TX.

Kramp, B. A.; Ansley, R. J.; Tunnell, T. R. 1998. Survival of mesquite 

seedlings emerging from cattle and wildlife feces in a semi-arid 

grassland. The Southwestern Naturalist. 43: 300-312.

Mitchell, R.; Whisenant, S.; Sosebee, R. 2004. A paradigm shift. 

Chap. 6, pages 67-75. In: W. T. Hamilton and others (Editors), 

Brush Management—Past, Present and Future. Texas A&M 

University Press, College Station, TX.

SAS. 1988. SAS/STAT User’s Guide Version 6.03, SAS Inst., Inc., 

Cary, N.C.

Scifres, C. J.; Hamilton, W. T. 1993. Prescribed burning for brushland 

management: The south Texas example. Texas A&M Press, 

College Station, Texas.

Teague, R.; Borchart, R.; Ansley, J.; Pinchak, B.; Cox, J.; Foy, 

J.; McGrann, J. 1997. Sustainable management strategies for 

mesquite rangeland: the Waggoner Kite project. Rangelands 19: 

4-8.

Teague, W. R.; Ansley, R. J.; McGrann, J. M.; Pinchak, W. E. 

2001a. Developing sustainable grazing management strategies 

for mesquite rangeland. Pages 493-502. In: Proceedings: First 

National Conference on Grazing Lands—Heightening the 

Awareness of the Economic and Environmental benefits of 

Grazing Lands, Las Vegas, Nevada, 5-8 Dec. 2000.

Teague, W. R.; Ansley, R. J.; Kreuter, U. P.; Pinchak, W. E.; McGrann, 

J. M. 2001b. Economics of managing mesquite in north Texas: a 

sensitivity analysis. J. Range Management 54: 553-560.

Wright, H. A.; Bailey, A. W. 1982. Fire ecology—United States and 

southern Canada. Wiley-Interscience, John Wiley & Sons, New 

York.

The Authors

1 Professor of Rangeland Shrub and Fire Ecology, Texas Agricultural 

Experiment Station, Vernon, TX. r-ansley@tamu.edu 2 Professor of Range Animal Nutrition, Texas Agricultural Experiment 

Station, Vernon, TX. 3 Professor of Rangeland Ecology, Texas Agricultural Experiment 

Station, Vernon, TX.
USDA Forest Service RMRS-P-47. 2007 79

Introduction

Current trends in soil erosion modeling under various 

management scenarios consist of analyzing erosion in probabilistic terms to account for storm variability and provide 

accurate event-based erosion estimates (Elliott and others 

2001). Under this paradigm, it is not sufficient if a model 

significantly underestimates large events or overestimates 

small events, but does well for long-term averages. The physically-based Water Erosion Prediction Project (WEPP) model 

(Flanagan and others 1995) is a model that has been used to 

provide event-level erosion estimates (Robichaud and others 

2003).

Soto and Diaz-Fierros (1998) measured runoff and erosion 

from natural rainfall on burned and non-burned plots with 

similar vegetation, slopes, and soil textures on shrublands 

in northwest Spain over a 4-year period. Total runoff from 

the control was only 59 percent of that from the burned area 

during the 4 years of study. Measured erosion was significantly 

higher from the burned area than from the control during the 

first 2 years after fire.

Soto and Diaz-Fierros (1998) compared measured and 

WEPP estimated soil water content, runoff, and erosion on 

burned and non-burned sites. Their comparisons excluded 

events during May through September when the soil was dry 

and water repellent. They reported that WEPP did reasonably well at predicting runoff and erosion values, although 

they reported that on severely burned areas, erosion estimates 

were consistently underestimated. In one erosion measurement period (6 to 10 months post-burning), WEPP grossly 

underestimated erosion for control and prescribed burn plots 

that they attribute to the fact that the erosion all occurred 

during one large rainfall event (50.3 mm) when water repellency was severe. Soto and Diaz-Fierros (1998, p. 268) 

concluded, “the model shows a clear tendency to underestimate erosion following severe burns.”

The objectives of this paper were to: (1) evaluate differences in runoff and erosion on a steep mountain big sagebrush 

(Artemisia tridentata ssp. vaseyana) community between 

burned and non-burned conditions; (2) test the capability of 

rangeland WEPP for estimating runoff and erosion for burned 

and non-burned conditions; and (3) suggest how improvements in rangeland WEPP might better represent fire impacts 

on rangelands.

WEPP

The WEPP model treats interrill and rill erosion as separate processes (Flanagen and others 1995). Interrill erosion is 

a function of soil interrill erodibility (Ki

, adjusted for canopy 

and ground cover in the interrill area), effective rainfall intensity, interrill runoff rate, interrill sediment delivery ratio 

(computed as a function of random roughness), and runoff 

duration (Foster and others 1995; Foster 1982). Interrill 

erosion on undisturbed rangeland has been well studied and is 

typically low (Pierson and others 2001).

In WEPP, rill erosion is a function of rill detachment 

capacity, sediment load, transport capacity, rill width, runoff 

duration, and rill spacing. Rill detachment capacity is modeled 

Modeling Erosion on Steep Sagebrush Rangeland Before 

and After Prescribed Fire

Abstract: Fire in sagebrush rangelands significantly alters canopy cover, ground cover, 

and soil properties that influence runoff and erosion processes. Runoff is generated more 

quickly and a larger volume of runoff is produced following prescribed fire. The result is 

increased risk of severe erosion and downstream flooding. The Water Erosion Prediction 

Project (WEPP), developed to model erosion on cropland, forest, and rangeland, is a tool 

that has the potential to model erosion and help managers address erosion and runoff risks 

following fire. WEPP views erosion as two processes: interrill and rill. Experimental results 

on a steep (35 to 50 percent slope) sagebrush site suggest that rill erosion is the dominant 

erosion process following fire and must be adequately understood so that models can provide 

reliable predictions. Evaluation of WEPP parameterization equations using data from steep 

burned sagebrush rangelands suggests that critical parameter estimation procedures within 

WEPP need improvement to include fire effects on infiltration and rill erosion processes. In 

particular, rill detachment estimates could be improved by modifying regression-estimated 

values of rill erodibility. In addition, the interactions of rill width and surface roughness on soil 

grain shear estimates may also need to be modified. In this paper we report the effects of 

prescribed fire on runoff and soil erosion and compare WEPP estimated erosion for several 

modeling options with measured erosion.

Corey A. Moffet1

Frederick B. Pierson2

Kenneth E. Spaeth3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
80 USDA Forest Service RMRS-P-47. 2007

as a function of excess soil shear stress (Foster and others 

1995, Foster 1982):

Drc = { Kr (τfe - τc); τfe > τc

0; τfe ≤ τc

[1]

where Drc is the rill detachment capacity (kg m-2 s-1), τfe is the 

soil shear stress due to rill flow at the end of the uniform slope 

(Pa), τc is the critical soil shear stress (Pa) that is required for 

detachment initiation, and Kr is the rill erodibility (s m-1).

The values for Kr and τc are WEPP input parameters. In 

rangeland WEPP, these parameters are determined based on 

soil properties and do not vary with management, but τfe is 

a function of ground cover and soil surface characteristics, 

slope, and rill flow characteristics:

τfe = γ Rh sin(tan-1(S)) ( f

s

f

t

) [2]

where γ is the specific weight of water (N m-3), Rh is the 

hydraulic radius of the rill flow (m), S is the slope of the 

energy gradient (assumed equal to the soil surface slope, fraction m/m), f

s

 is the Darcy-Weisbach roughness coefficient due 

to soil grains (assumed to be 1.11), and f

t

 is the total DarcyWeisbach roughness coefficient due to soil grains, ground 

cover (litter, rock, plant bases, and cryptogams), and random 

roughness. The Darcy-Weisbach roughness coefficient used in 

rangeland WEPP is empirically estimated from ground cover 

and random roughness parameters.

The rill hydraulic radius (Rh) is the ratio of flow cross-sectional area (A = wd) to wetted perimeter (P = 2d + w), both 

are functions of width (w) and depth (d). In WEPP, rills are 

assumed of rectangular shape with width a function of rill 

discharge rate (q, m3 s-1):

w = 1.13q0.303. [3]

Given the rill discharge rate, slope, width, and Darcy-Weisbach 

roughness coefficient, depth is computed by WEPP.

For a given storm, infiltration and therefore runoff volume 

are affected by the effective hydraulic conductivity (Ke) and 

the matric potential gradient across the wetting front, but not 

f

t

. Peak discharge, qpeak (and therefore q), and runoff duration, 

t

RO, however, are sensitive to ft

. As f

t

 increases, qpeak decreases 

and t

RO increases.

For a given discharge rate the excess soil grain shear stress 

computed by WEPP is a function of only one factor affected 

by management—the Darcy-Weisbach roughness coefficient. 

In the current version of WEPP any effect of management on 

estimated rill erosion must be expressed through differences 

in runoff and Darcy-Weisbach roughness coefficients among 

the management scenarios.

Material and Methods

The study area is located in the Reynolds Creek 

Experimental Watershed in southwest Idaho near the divide 

between Reynolds Creek and Dobson Creek watersheds (43° 

6’ 30” N; 116° 46’ 50” W). The elevation of the research site 

is about 1,750 m and mean annual precipitation is approximately 549 mm.

The vegetation was a typical mountain big sagebrush community with subdominant shrubs of rabbitbrush 

(Chrysothamnus viscidiflorus), antelope bitterbrush (Purshia 

tridentata), and widely scattered juniper (Juniperus occidentalis), and dominant grasses were bluebunch wheatgrass 

(Pseudoroegneria spicata) and Idaho fescue (Festuca 

idahoensis). The soils are mapped Kanlee-Ola-Quicksilver 

association, 3 to 50 percent slopes. All plots in the study are 

on the deeper Kanlee and Ola series. The slopes of the study 

area are 35 to 50 percent with an east facing aspect on granite 

bedrock hillslopes. Soil textures are coarse sandy loam in the 

surface 30 cm and loam or coarse sandy loam in the subsoil 

that extends beyond 100-cm depth. Rock fragment (>2 mm 

diameter) content in the surface layer is about 5 to 15 percent 

and ranges between 5 and 50 percent in the subsoil. Soil water 

content during all phases of this research was low (approximately 0.03 kg kg-1).

Sixteen rectangular plots (6.5 m long by 5 m wide) were 

selected within a narrow elevation band near the top of 

the hillslope prior to prescribed fire. Eight plots each were 

assigned to the non-burned and burned treatments. Plots in the 

non-burned treatment were characterized (canopy and ground 

cover, slope, and random roughness) and rainfall simulations were performed in August and early September. The 

prescribed fire was ignited in late September and a head fire 

burned the study area. The burned plots were characterized 

and simulated rainfall was applied in October.

Rainfall was applied on two plots each day with a Colorado 

State University (CSU) type rainfall simulator (Holland 1969) 

at a rate of 61 mm hr-1 for 1 hr; however, observed application 

rates differed from the design due to mechanical difficulties 

and wind. The observed range was 45.3 to 76.1 mm. Several 

samples of rainfall that fell directly in the runoff collection 

trough were collected during the first several minutes of 

each simulation. Timed samples (500 ml to 1,000 ml) were 

collected approximately every minute. The mass of sediment 

and volume of water collected in each sample was determined 

in the laboratory. The mean trough catch that would have been 

collected during the sample time was subtracted from each 

sample volume.

Vegetation cover, ground cover, slope, and surface random 

roughness were sampled in each large plot prior to the rainfall 

simulations with 100 evenly-spaced point samples recorded 

along six horizontal transects (0.5, 1.5, 2.5, 3.5, 4.5, and 5.5 

m from the upslope end of a plot). At each point the relative 

elevation of the ground surface (measured to the nearest mm), 

the ground cover class and the canopy cover class (if present) 

were recorded. Vegetation and litter mass were determined by 

harvesting all standing plant material by functional group and 

collecting litter from 30 small (1 m2

) plots nearby. The vegetation and litter samples were oven-dried and weighed.

Three parameterization schemes were used to explore the 

WEPP rill erosion estimation capabilities. The first scheme 
USDA Forest Service RMRS-P-47. 2007 81

(Option A) used readily available data; infiltration and erosion 

parameters were computed by WEPP from soil and cover 

data. The next scheme (Option B) used optimized effective 

hydraulic conductivity (Ke) values to match total runoff on a 

plot by plot basis. Option C used the (Ke ) values from Option 

B, and optimized rill erodibility (Kr) values and 0.0001 for 

critical shear (τc).

In all scenarios, the soil data were those available in the 

1995 WEPP soils database. Initial saturation was always 

adjusted to 25 percent and Ke and Kr were adjusted as 

described above. The management data were written to run 

WEPP for rangelands in event mode using measured canopy 

cover, ground cover (litter, plant base, cryptogam, and rock), 

and random roughness to parameterize the initial condition 

section for each plot. Precipitation data were based on the 

measured simulated rainfall on each plot. Pattern parameters 

were assumed to be the same on all plots (duration of 1 hr, 

peak intensity of 1.01 times the mean intensity, and time to 

peak intensity at 20 percent of the simulation duration).

One-way analysis of variance was used to test the significance of treatment effects on response variables. Since only 

two treatment levels were studied, a significant F-test indicated that the means were different. Welch’s t-test was used 

within each treatment to compare WEPP estimated responses 

with measured responses.

Results and Discussion

Plot and Simulation Characteristics

Total precipitation applied and plot slope were similar for 

burned and non-burned treatments (table 1). On burned plots, 

almost no standing material remained except occasional bitterbrush shrub skeletons (sagebrush was consumed to within 

5 cm of the soil surface). Average canopy cover of the shrub 

skeletons was 0.2 percent.

The burn treatment significantly reduced total litter, plant 

basal cover, and canopy cover (table 1). Litter cover outside 

the plant canopy (ashy unconsumed litter and wood) was not 

different between the burned and non-burned treatments even 

though the fire reduced total litter cover. This was because the 

total area outside the canopy significantly increased following 

the fire. Random roughness was significantly less in burned 

than in non-burned treatment plots (table 1). This was most 

likely due to much of the root crowns and litter under shrubs 

being consumed during the fire. The burned treatment plots 

had greater rock cover compared to the non-burned treatment 

plots (table 1). However, a 0.5 percent increase in rock cover 

in burned plots probably had little or no effect on hillslope 

hydrologic or erosion responses.

Mass of litter and vegetation were reduced by fire (table 

1). Litter accumulation, including dung, and wood accounted 

for nearly 45 percent of the total mass of above ground 

organic matter. Litter in non-burned treatment plots was not 

uniformly distributed on the ground, but rather occurred as a 

thick almost continuous layer under canopies and patchy thin 

accumulations outside canopies. The litter mass in burned 

treatment plots was 8 percent of that in non-burned plots, but 

total litter cover on the burned treatment was 31 percent of 

that on the non-burned treatment. The effect of fire on litter 

cover reduction was less than its effect on litter mass/volume 

reduction.

Measured Large Plot Runoff and Erosion

Fire significantly increased total runoff volume from burned 

plots (16.6 mm) compared to non-burned plots (3.1 mm, 

fig. 1). All burned plots yielded runoff, whereas three of the 

eight non-burned plots yielded no runoff. This is consistent 

with findings from Soto and Diaz-Fierros (1998) who found 

that wet-season runoff doubled in the first year after fire.

Areas burned by fire generated runoff more quickly than 

non-burned areas. The mean time to initiation of runoff for 

burned and non-burned plots was 3.3 min and 7.1 min, respectively (excluding the three non-burned plots with no runoff). 

Peak runoff rates from burned treatment plots were about 

three times higher than the non-burned treatment plots (all 

non-burned plots) and about two times greater than the five 

non-burned treatment plots with measurable runoff (fig. 1). 

Regardless of treatment, runoff rates peaked 10 to 20 minutes 

into the simulated rainfall event and diminished with time 

thereafter (fig. 1). The decrease in runoff rate with time during 

the simulation, for both burned and non-burned treatment 

plots, indicates that the soil in both treatments may have had 

significant water repellent soil properties. Pierson and others 

(2001) found significant water repellency in both burned and 

non-burned plots for similar sites during late summer and early 

Table 1. Comparison of site and simulation characteristics between 

burned and non-burned treatments. Means for a characteristic 

followed by the same letter are not significantly different.

Characteristic Units Burned Non-burned

Precipitation mm 59.1 a 61.4 a

Slope % 41.6 a 40.8 a

Random roughness mm 10.8 b 21.1 a

Ground Cover a

Litter below canopy % 0.1 b 49.6 a

Rock below canopy % 0.0 a 0.1 a

Basal cover below canopy % 0.0 b 1.3 a

Litter outside canopy % 23.3 a 24.7 a

Rock outside canopy % 1.0 a 0.3 b

Basal cover outside canopy % 0.0 b 0.6 a

Canopy cover % 0.2 b 57.0 a

Litter total % 23.4 b 74.3 a

Rock total % 1.0 a 0.5 b

Basal cover total % 0.0 b 1.9 a

Bare ground total % 75.6 a 24.3 b

Ground litter kg ha-1 808b 9517

Vegetation kg ha-1 –c 12125

a

 The sum of litter, rock, and basal cover below canopy and outside 

canopy and total bare ground is equal to 100. b

 Burned treatment litter samples were collected in the spring and early 

summer following the fire. c

 Burned treatments vegetation samples were not collected.
82 USDA Forest Service RMRS-P-47. 2007

fall when the soils were dry. Soto and Diaz-Fierros (1998) 

reported that runoff to precipitation ratios for natural rainfall 

on control and burned plots were significantly greater during 

periods of high water repellency.

The effect of burning on total soil erosion was also significant (α = 0.05, fig. 2). Sediment yield for burned plots was 

significantly greater (10.7 Mg ha-1) than non-burned plots 

(0.1 Mg ha-1). Erosion rates in both burned and non-burned 

treatments were greatest during the first 7 to 20 minutes of 

the simulated rainfall event and steadily decreased thereafter 

(fig. 2). Soto and Diaz-Fierros (1998) reported that erosion 

was higher in burned compared to control plots the first 2 years 

post fire. In one erosion measurement period, when almost all 

erosion occurred from one 50.3 mm storm on dry water repellent soils, erosion was 6.6 times greater from burned plots 

than from control plots (Soto and Diaz-Fierros 1998).

WEPP Estimated Runoff and Erosion

Using WEPP estimated infiltration and erosion parameters 

(Option A), model predicted runoff was significantly greater 

than measure runoff regardless of treatment (fig. 3). Predicted 

runoff was nearly 10 times greater than measured runoff in 

the non-burned treatment and nearly double in the burned. 

Burning caused a large increase in measured runoff while 

model predicted runoff was similar between treatments (fig. 

3). This indicates a lack of model sensitivity to burning.

Model predicted erosion was significantly less than 

measured in burned treatments and significantly greater than 

measured in non-burned treatments. Predicted erosion was 24 

percent less than measured in the burned treatment, but 2.6 

times greater in the non-burned. However, model estimates of 

erosion showed some degree of sensitivity to burning (fig. 4). 

Interpretation of this sensitivity is complicated by errors in 

runoff prediction. Because runoff drives the rill erosion 

process, treatment induced trends in predicted erosion cannot 

be effectively evaluated.

To correct errors in model predicted runoff (Option B) 

we used optimized effective hydraulic conductivity (Ke

) for 

each plot which ranged from 6.7 to 32.3 mm h-1 for burned 

and 26.3 to 77.9 for non-burned. These values are two to four 

times greater than WEPP estimated Ke values used in Option 

A (table 2). Using optimized Ke values, runoff matched 

measured runoff within 0.2 mm on all plots (fig. 3).

Using optimized Ke and WEPP estimated erosion parameters (Option B), predicted erosion was 13 percent of measured 

erosion for the burned treatment and statistically similar for 

the non-burned treatment (fig. 4). WEPP adequately estimated 

low erosion for the non-burned condition and showed an 

increase in erosion due to fire. However, the predicted increase 

was only 1.3 Mg ha-1 compared to a 10.6 Mg ha-1 measured 

Figure 1. Mean hydrographs for 60-minute simulated rainfalls on 

burned and non-burned plots (n = 8). Three non-burned plots 

yielded no runoff and the mean hydrograph for the five plots that 

did generate runoff is also shown (dotted line).

Figure 2. Mean sediment yield for 60-minute simulated rainfalls on 

burned and non-burned plots (n = 8). Three non-burned plots 

yielded no runoff or sediment and the mean sediment yield 

response for the five plots that did generate runoff is also shown 

(dotted line).
USDA Forest Service RMRS-P-47. 2007 83

increase. The increase in WEPP estimated erosion due to fire 

was predominately due to an increase in interrill erosion (fig. 

4). Pierson and others (2003) found that for similar sites rill 

erosion dominated total sediment yield compared to interrill 

erosion. Therefore, it was assumed the majority of error in 

WEPP estimated erosion under Option B was due to error in 

estimated rill erodibility (Kr ) and perhaps critical shear (τc) 

parameters.

Optimized Kr values were greater than WEPP estimated 

values regardless of treatment (table 2). When we optimized Kr values (Option C), WEPP estimated and measured 

erosion converged (within 0.02 Mg ha-1) in only three of 

the eight burned plots. The Kr values for these plots ranged 

from 0.00373 to 0.02470 s m-1 compared to the model estimated value of 0.00063 s m-1. The remaining five burned plots 

had such high measured erosion values that WEPP underpredicted erosion even using the highest allowable value 

for Kr (0.09999). On all eight non-burned plots (only five of 

which produced runoff), good agreement was achieved with 

optimized Kr values (fig. 4). Optimized Kr values for the nonburned plots ranged from 0.00037 to 0.00296 s m-1 compared 

with a model estimated value of 0.00063 s m-1 (table 2) that 

did not vary between burned and non-burned conditions.

Prescribed fire increased Kr values by nearly two orders of 

magnitude (table 2). It seems reasonable that loss of surface 

soil organic matter by fire (Soto and Diaz-Fierros 1998) could 

result in increased rill erodibility. Fire consumes organic matter 

that binds soil particles together making them more difficult 

to detach (Pierson and others 2001). Currently, WEPP has no 

mechanism to incorporate this effect. This paper shows that 

appropriate adjustments to Kr could provide improved erosion 

predictions. However, adjustments in WEPP parameter 

estimation procedures for Darcy-Weisbach roughness coefficients, rill width, and rill depth may also aid in improving rill 

erosion predictions following fire. Future work will explore 

these options.

Figure 4. Mean measured and WEPP estimated erosion for three 

parameterization options. Solid vertical line in the center of each 

bar is the mean WEPP estimated rill erosion. WEPP estimated 

erosion values within a treatment that are marked above the bar 

with an asterisk are significantly different (α = 0.05) from the 

mean measured value.

Table 2. Mean WEPP estimated and optimized runoff and erosion 

parameters for burned and non-burned treatments.

Parameter Units Burned Non-burned

WEPP estimated

Ke mm h-1 8.97 11.31

Kr s m-1 x 103 0.629 0.629

τc Pa 0.939 0.939

Ki,adj

a kg s m-4 x 10-6 0.3470 0.0001

Optimized values

Ke mm h-1 20.66 44.79

Kr s m-1 x 103 67.290 1.132b

τc Pa 0.0001 0.0001

a

 Adjusted interrill erodibility.

b

 Mean of the five non-burned plots with runoff.

Figure 3. Mean measured and WEPP estimated total runoff for 

three parameterization options. WEPP estimated values within 

a treatment that are marked above the bar with an asterisk are 

significantly different (α = 0.05) from the mean measured value.
84 USDA Forest Service RMRS-P-47. 2007

Summary

Runoff and erosion from high intensity storms on steep 

sagebrush rangeland were greatly increased immediately 

after prescribed burning. Runoff was generated more rapidly 

and in larger volume from burned areas compared to nonburned areas. Soil erosion increased 100 times following 

the prescribed fire. The rangeland WEPP model significantly 

underestimated soil erosion after fire. The model was unable 

to achieve agreement with measured erosion values even 

using optimized infiltration (Ke ) and rill erosion parameters 

(Kr and τc ). The WEPP model does not currently provide 

sufficient mechanisms to adequately model the impacts of fire 

on soil erosion. Improvements are needed in estimated adjustments to Ke and Kr to account for changes in surface cover 

and organic matter decreases following burning. In addition, adjustments to other factors such as the hydraulic radius 

and Darcy-Weisbach roughness coefficients need to also be 

considered.

Literature Cited

Elliot, W. J.; Robichaud, P. R.; Hall, D. E.; Cuhaciyan, C. O.; 

Pierson, F. B.; Wohlgemuth, P. M. 2001. A probabilistic approach 

to modeling erosion for spatially-varied conditions. American 

Society of Agricultural Engineers Annual Meeting, Sacramento, 

CA. July 2001. Paper No. 01-8006. 16 p.

Flanagan, D. C.; Ascough II, J. C.; Nicks, A. D.; Nearing, M. A.; 

Laflen, J. M. 1995. Chapter 1. Overview of the WEPP erosion 

prediction model. In: D. C. Flanagan and M. A. Nearing, editors. 

USDA-water erosion prediction project: Technical documentation. 

USDA-ARS National Soil Erosion Research Laboratory, NSERL 

Report No. 10, West Lafayette, IN.

Foster, G. R. 1982. Modeling the erosion process. In: C. T. Haan; 

Johnson, H. P.; Brakensiek, D. L. (Eds). Hydrologic modeling of 

small watersheds. ASAE Monograph No. 5, Saint Joseph, MI.

Foster, G. R.; Flanagan, D. C.; Nearing, M. A.; Lane, L. J.; Risse, L. 

M.; Finker, S. C. 1995. Chapter 11. Hillslope erosion component. 

In. D. C. Flanagan; Nearing, M. A., editors. USDA-water erosion 

prediction project: Technical documentation. USDA-ARS 

National Soil Erosion Research Laboratory, NSERL Report No. 

10, West Lafayette, IN.

Holland, M. E. 1969. Colorado State University experimental rainfallrunoff facility, design and testing of rainfall system. Colorado 

State University experiment station, CER 69-70 MEH 21.

Pierson, F. B.; Robichaud, P. R.; Spaeth, K. E. 2001. Spatial and 

temporal effects of wildfire on the hydrology of a steep rangeland 

watershed. Hydrological Processes 15:2905-2916.

Pierson, F. B.; Robichaud, P. R.; Spaeth, K. E.; Moffet, C. A. 2003. 

Impacts of fire on hydrology and erosion in steep mountain big 

sagebrush communities. p. 625-630. In: Renard, K. G.; McElroy, 

S. A.; Gburek, W. J.; Canfield, H. E; Scott, R. L., (eds.) First 

Interagency Conference on Research in the Watersheds, October 

27-30, 2003. U.S. Department of Agriculture, Agricultural 

Research Service.

Robichaud, P. R.; Elliot, W. J.; Hall, D. E.; Pierson, F. B.; Moffet, C. 

A. 2004. Erosion risk management tool (ERMiT). Available at: 

http://forest.moscowfsl.wsu.edu/cgi-bin/fswepp/ermit/ermit.pl, 

United States Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Moscow, ID.

Soto, B.; Diaz-Fierros, F. 1998. Runoff and soil erosion from areas 

of burnt scrub: comparison of experimental results with those 

predicted by the WEPP model. Catena 31:257-270.

The Authors

1 Rangeland Scientist, USDA-ARS, Dubois, ID. cmoffet@pw.ars.

usda.gov 2 Research Hydrologist, USDA-ARS, Northwest Watershed Research 

Center, Boise, ID. 3 Rangeland Hydrologist, USDA-NRCS, Ft. Worth, TX.
USDA Forest Service RMRS-P-47. 2007 85

Water and Ecophysiology 

Session

Introduction

Semi-arid gully-hill region covers a great many acres 

of China. In this region, vegetation degradation and severe 

soil erosion are obstacles to the sustainable development in the region. Vegetation rehabilitation is essential 

for ecological restoration in the region and sustainable 

development. Selection and use of species adaptation to 

the local environment are directly related to succession of 

vegetation rehabilitation and efficiency of water and soil 

protection.

In the region, water is the limiting factor for the development of the vegetation. Plants have to take maximum 

advantage of the scarce and irregular rainfall, which varies 

between 380 mm annually distributed over a rainy period of 

3 months (June-September). The most common vegetation 

in these regions is desert steppe, but the most common plant 

in south-sloping land is Caragana licentiana. Precipitation 

varies from year to year in theses regions and droughts can 

last up to 5 years. Under these conditions, plants species have 

become adapted to tolerate, evade, and escape drought and 

have developed germination, establishment, growth, and 

reproduction strategies that allow for the perpetuation of the 

species in these conditions. The subfamily Caragana Febr. 

includes major leguminous shrubs in the semi-arid region of 

China. There are 62 species in China (Liu 1987) and 15 species 

in Loess Plateau region (BINC 1992). Caragana species are 

key components of vegetation in the loess-gully region (Wu 

Zhengyi 1995). These species are examples of plants that have 

successfully colonized these semi-arid loess-gully zones and 

they are important for maintaining the dynamic and function 

of the ecosystem. They are also important for restoration of 

degraded ecosystems. In particular, some indigenous Caragana

species have potential value for vegetation establishment, but 

they have attracted little attention from restoration ecologists 

and researchers. Lack of knowledge on their pattern of seed 

Germination Responses to Temperature in Three Caragana

Species in Loess-gully Region, China

Abstract: The leguminous Caragana species are important components of vegetation in the 

semi-arid Loess-gully region, China. These shrub species are important for maintaining the 

dynamics and function of the ecosystem in the region. They are potential plant resources 

for restoration of degraded ecosystems. The germination responses to temperatures in two 

indigenous and one exotic Caragana species were studied under controlled conditions in 

the laboratory. Treatments were nine temperature regimes (constant temperatures of 5, 10, 

15, 20, 25, and 30°C and three alternating day/night temperature regimes of 10/5, 25/15, 

and 30/20°C). Germination response to temperature was different for the three species. For 

C. intermedia, the temperature range for germination was 5 to 30 °C and germination rate 

was quick. Percentage germination was low at all temperature regimes for C. licentiana. 

Germination was inhibited at 30°C for C. opulens and at 5°C for C. licentiana. The average 

incubation period needed for seeds to germinate was longer for C. licentiana than for the 

others. Alternating day/night temperature had no significant effect on germination in the three 

species. Hard-coat seeds existed at different percentages in this plant subfamily. Rate of 

hard-coat seeds was 5.14 percent for C. licentiana and 0.79 percent for C. intermedia, but C. 

opulens had no hard-coat seeds. Germination responses to temperature in the three species 

are related to their ecological distribution and habitat. The different germination patterns in 

the species imply different life cycles. The germination strategies for C. licentiana and C. 

opulens mean that these two endemic species include potential value as good candidates for 

restoration of degraded land in the semi-arid Loess-gully region, China.

Zhao Xiaoying1

Ren Jizhou2

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
86 USDA Forest Service RMRS-P-47. 2007

germination and life cycle is a major factor restricting their 

use in ecological restoration.

The three Caragana species are of particular importance because they are drought resistant and two of them 

are endemic. Caragana licentiana Hand-Mazz is a species 

found in the Dingxi, Lanzhou, and Yongdeng regions in 

Gansu Province, China. It is drought resistant and carries on 

the active phases of its life cycle when soil moisture is abundant. It can survive and grow well in extreme habitats in the 

region. Caragana opulens Kom is distributed in some regions 

of the Loess Plateau. Caragana intermedia Kuang has been 

planted on Gansu Loess Plateau to prevent soil erosion, but it 

is difficult to regenerate by seed in this region for population 

expansion.

Seed germination of mimosa and acacia species, leguminous shrubs, has been reported by several authors 

(Orozco-Almanza 2003; Abulfatih 1995). Studies on temperature range of seed germination of C. intermedia and C. 

korshinskii were reported by BINC (1992). But studies on 

germination patterns of others Caragana species have not 

been carried out, especially regarding comparative studies of 

seed germination in this species.

This study was carried out to answer the following questions: What is the effect of temperature on the seed germination 

of the three species? What are the germination patterns of each 

species and the implications of its restoration? Are the seeds 

dormant after dispersal? Are there differences in dormancy 

among the three species? Are there any moisture or temperature mediated mechanisms preventing germination under 

unfavourable conditions?

Species and Methods

Seed Collection

Seeds of C. licentiana and C. opulens, endemic to Dingxi 

County, were collected from the species of the genus Caragana

growing in natural communities in the Dingxi County Gansu 

province (35°44′14.9′′N, 104°24′17.2′′E) in June 2002 and 

seeds of C. intermedia were collected from the species in 

semi-artificial communities in the county in July 2002. Seeds 

were stored in a laboratory in Dingxi County without heat or 

air condition. Seeds that had been attacked by insects were 

excluded from the test. Dingxi County is considered a typical 

representation of gully-hill region in Loess Plateau, China. 

The plant communities are dominanted by Stipa ungeana

Trin, Stipa breviflora Griseb, Ajania fruticolosa Ledeb, and 

Artemisia frigida Willd. Average annual precipitation and 

temperature (over 10 years) in the region were 380 millimeters and 6.3°C.

Germination under Laboratory Conditions

Trials were carried out in May 2003. Treatments were 

nine temperature regimes: six constant temperatures of 5, 

10, 15, 20, 25, and 30°C and three alternating day/night 

temperature regimes of 10/5, 25/15, and 30/20°C. For each 

thermal treatment, 200 seeds of each species were divided into 

four replicates of 50 seeds each. Each replicate was placed 

in a 9 cm Petri dish (in diameter) on 1 percent 20 ml water 

agar and incubated in a germination chamber at each temperature. The seeds were inspected every day and were considered 

to be germinated when the radical penetrated the seed coat 

and reached about 1mm in length (Teketay 1996). Germinated 

seeds were removed after counting. Trials were run until no 

more seeds germinated for 5 days. Percent germination was 

calculated as the number of seeds germinated divided by the 

number of viable seeds. Dead seeds were excluded. Hard-coat 

seeds were counted.

Statistical Analysis

The results of the germination experiment were analyzed 

for statistical significance with a general linear model analysis 

of variance (ANOVA) from the SPSS package for personal 

computer (version 11.0, SPSS Inc.). Percent germination 

data were arcsine-square-root transformed prior to analysis. 

Arcsine-transformed means and standard errors were back 

transformed for graphic presentation. Multiple comparisons 

of means were made with Tukey tests. A significance level of 

alpha = 0.05 was used for all statistical analyses.

Results

Germination Response

Seed germination of the three Caragana species, tested 

in the laboratory on a constant and alternating temperature 

gradient bar, showed three patterns of response to temperature. 

The pattern of seed germination for C. intermedia was germination over a broad range of temperatures between 5°C and 

30°C. The pattern for C. licentiana was cold-evading germination between 10°C and 30°C. The pattern for C. opulens

was heat-evading germination between 5°C and 25°C. The 

seeds of each species germinated within a specific temperature range (table 1, fig.1).

C. intermedia and C. opulens showed a very high percentage 

of germination at their respective optimum temperatures (100 

percent and 99. percent ±1 percent). The percent germination for C. licentiana was lower at its optimum temperatures 

(89.0 percent ± 2.5) than the other two species. The effect of 

alternating day/night temperature on germination in the three 

species was not significant.

Germination Process

The average incubation period needed for seeds to germinate was longer for C. licentiana than for the other species 

(fig. 2). Seeds began germination after 4 days at 25°C and 

total percent germination reached 25.5 percent ± 6.3 after 

8 days. Few seeds germinated each day for C. licentiana. 

Germination rate was very quick for C. intermedia and
USDA Forest Service RMRS-P-47. 2007 87

C. opulens (fig. 3). C. opulens seeds began germination after 

3 days at optimum temperature and total percent germination 

reached. 67.6 percent ± 6.6 after 4 days. C. intermedia seeds 

began germinating after 2 days and total percent germination 

reached 70.9 percent ± 1.3.

Hard-Coat Seeds

No hard-coat seeds were found for C. opulentce in the 

germination trial. The rate of hard-coat seeds was 0.79 percent 

for C. intermedia and 5.14 percent for C. licentiana.

Figure 3. Percent germination of C. opulens and C. intermedia after 

different time periods of incubation at 25°C.

Table 1. Seed germination percentage of three Caragana species at 

constant and alternate temperatures.

Species

Temperature

(°C) C. licentiana C. opulens C. intermedia

5 0a1 78.5 ± 1.3a 7.0 ± 1.3 a

10 8.7 ± 4.2 a 100 b 66.8 ± 3.9 b

15 64.8 ± 11.7 b 100 b 98.0 ± 0.9 c

20 81.5 ± 2.4 c 100 b 99.0 ± 1.0 c

25 89.0 ± 2.5 c 100 b 99.0 ± 1.0 c

30 65.0 ± 7.7 b 0 d 98.5 ± 1.0 c

0 / 52 1.0 ± 0.6 a 97.9 ± 0.8 c 11.5 ± 4.7 a

25 / 15 90.3 ± 1.9 c 100 b 99.5 ± 0.6 c

30 / 20 93.2 ± 4.0 c 100 b 99.5 ± 0.5 c

1

 Percentage germination with same letter are not significant at P < 0.05. 2

 10h in light and then transfer 14h in dark.

Figure 1. Percent seed germination at constant temperatures in 

three Caragana species after 20 days of incubation.

Figure 2. Percent germination of C. licentiana after different time 

periods of incubation at 25°C.

Discussion

Plants are generally in areas with temperatures that are 

appropriate for their germination and growth (Krebs 1978; 

Bewley and Black 1994). This is true for leguminous shrubs 

(Orozco-Almanza, 2003), as well as others species (Baskin 

and Baskin 1971; Linington 1979; Probert 1985; Abulfatih 

1995). Differences in the temperature requirement for seed 

germination in the three species reflected the distribution and 

habitat of the species. The place of origin for C. intermedia

is sandy desert (Liu 1987) where temperature in the growing 

season is high and temperature fluctuations are great. These 

conditions determine the wide range of temperature within 

which C. intermedia can germinate.

C. opulens is distributed in some regions of higher altitude in the Loess Plateau (Liu 1987). It grows in the northwest 

sloping habitat of the Dingxi County. Therefore, germination was inhibited at 30°C for this species and germination 

percentage at 5°C still reached 78.5 percent ± 1.3. C. licentiana grows mainly in southeast sloping habitat and seeds can 

not germinate at 5°C.

Germination over a wide range of temperatures has important practical implications in the Loess Plateau, where different 

temperature conditions prevail as a result of the topography of 

the region. Furthermore, seeds can artificially propagate the 

species in regions with different temperature conditions. Such 

characteristics make these species good candidates for restoration in semi-arid region of Loess Plateau, China.

Speed of seed germination presents a strategy for species 

survival and development in habitats where precipitation 

is unpredictable such as in semi-arid regions (Gutterman 

1993; Wang 1998). Only a fraction of C. licentiana seeds 

germinated every day under adequate moisture that could 

decrease seedling mortality rate following a drought. 

This germination strategy coincides with the desert plants 

Agriphllum wquarrosum (Wang 1998). Seed-coat imposed 

dormancy is a delaying mechanism that prevents germination 

under conditions that might prove to be unsuitable for establishment, thereby separating germination in both time and 
88 USDA Forest Service RMRS-P-47. 2007

space (Charper 1995). A small percentage (5.14 percent) of 

hard-coat seeds did not germinate under unfavorable conditions and have a lower percentage of predation. This allows 

them to persist in unpredictable environments, and may be 

another strategy that adapts the species to the habitat. This 

strategy suggested that C. licentiana might have a potential 

value in rehabilitation of degraded sloping land, especially 

dry southeastern sloping land.

A majority of seeds germinate and a fraction do not germinate in suitable conditions for C. intermedia. This germination 

response may ensure that a majority of seeds germinate in the 

suitable season to increase seedling survive rate in its original sandy habitat. But in the gully-hill loess habitat of Dingxi 

County, this germination behavior increases the risk of seedling mortality in a following drought. This may be one of 

reasons that little seedlings of C. intermedia were found in an 

artificial community in Dingxi County. Seeds almost synchronously germinated in favorable conditions for C. opulens.

This may increase seedling survival rate in suitable conditions 

and decrease seeds predation by rodents.

Conclusions

Seeds of three Caragana species can germinate in different 

ranges of temperatures in the laboratory. This is directly 

related to their distribution and habitats. Speed of seed germination in the species is different and this may be a strategy 

that ensures the species persist in specific habitats. Seeds in 

the three species were dormant at different percentages and 

this has important ecological significance. These germination 

strategies mean C. licentiana and C. opulens, the endemic 

species, have potential value as good candidates for revegetation of different habitat in Loess Plateau region.

Acknowledgments

The NKBRSF Project G2000D18602 and the project 

“Light for Western China” of Chinese Academy of Sciences 

supported this work. We are grateful to Wang Yan-rong for 

providing experiment equipment and Li Yan-mei, Zhang Jianquan for assistance with germination trial. An earlier draft was 

improved by the comments of Ms. Margaret Cargill and Mr. 

Liu Zhi-ming.

References

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Loess Plateau. Tomus II. Forest Press.

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ecosystem properties. Chichester: JohnWilley and Sons.

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Springer.

Huang, Zhen-ying; Gutterman, Y.; Zheng-hai, H. 2001. Seed 

germination in Artemisia sphaerocephala II. The influence 

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240-246.

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sinarum: Tomus II. Beijing: Science Press.

National Quality Technology Bureau. 2001. Rules for forage seed 

testing. Standards Press of China.

Orozco-Almanza, M. S.; León-Garíca, L. P.; Grether, R. 2003. 

Germination of four species of the genus Mimosa (leguminosae) in 

a semi-arid zone of Central Mexico. Journal of Arid Environments 

55: 75-92.

Proberts, R. J. 2000. The role of temperature in germination 

ecophysiology. In: M. Fenner (Editor), Seeds: The ecology 

of regeneration in Plant Communities. C. A. B. International, 

Wallingford, pp. 285-325.

Probert, R. J.; Smith, R. D.; Berch, P. 1985. Germination responses 

to light and alternating temperatures in European populations of

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Phytologist 99: 305-316.

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eight exotic multipurpose leguminous species from Ethiopia. 

Forest Ecology and Management 80:209-223.

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biology of desert plants. Berlin: Springer-Verlag.

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The Authors

1

 College of Life Sciences and Chemistry, Xinjiang Normal 

University, Urumqi, 830054, China. xyzhao63@hotmail.com 2

 College of Pastoral Agriculture Science and Technology, Lanzhou 

University, Lanzhou 730000, China.
USDA Forest Service RMRS-P-47. 2007 89

Introduction

The Pecos River Ecosystem Project was proposed in 1997 

by the Red Bluff Water and Power Control District to address 

saltcedar issues along the Pecos River. Initial objectives of 

the project were to increase efficiency of water delivery in the 

river to irrigation districts within the Red Bluff District and 

improve the quality of the water by decreasing the salinity. 

After 4 years of herbicide application on saltcedar, the project 

has emerged as the first step to what could be important to 

the overall statewide plan for water conservation along Texas’ 

rivers by managing saltcedar infestations. Success of the 

Pecos River Ecosystem Project can be attributed mainly to 

its cooperative effort and organization. Numerous agencies, 

organizations, and companies, such as Upper Pecos Soil and 

Water Conservation District; Texas Cooperative Extension; 

Texas Department of Agriculture; USDA Natural Resources 

Conservation Service; Red Bluff Water and Power Control 

District; Irrigation Districts in Loving, Reeves, Ward, and 

Pecos Counties; US Environmental Protection Agency; Pecos 

River Compact Commission; International Boundary and 

Water Commission; BASF Co.; North Star Helicopters Inc.; 

and local landowners, were involved in the organizational 

efforts early in the project development.

Saltcedar (Tamarix spp.) is an introduced phreatophyte in 

western North America estimated to occupy well over 600,000 

ha of waterways (Robinson 1965; Kunzmann and others 

1988). It is a vigorous invader of riparian zones and subirrigated pastures. The plant was introduced into the United 

States as an ornamental in the early 1800s. In the early 1900s, 

government agencies and private landowners began planting 

saltcedar to control stream bank erosion along such rivers as 

the Pecos River in New Mexico and Texas (Everitt 1998). The 

plant has spread down river in Texas and occurs along the river 

south of Interstate 10 to the confluence with the Rio Grande. 

Mature plants can reach heights of 6 to 9 m and densities of 

700 to 1,000 plants/ha in this region. More recently, saltcedar 

has become a noxious plant not only along rivers and their 

tributaries, but also along irrigation ditch banks, low-lying 

areas that receive extra runoff accumulation, and areas with 

high water tables.

Saltcedar occupies a near continuous buffer along both 

banks of the Pecos River from Red Bluff Dam southward 

for the entire area (approx. 289 river km) of the Red Bluff 

Irrigation District. This region of Texas is characterized by a 

semi-arid, desert environment receiving 152.5 to 203.2 mm of 

average annual rainfall. This is one of the important reasons 

for controlling saltcedar, which is to conserve water, especially for the semi-arid area experiencing drought most, if not 

all of the time. The width of the saltcedar band varies from 

7.6 to 152.5 m with an average of 45.8 m on each river bank. 

Within this stretch of river, saltcedar occupies about 7.5 to 10 

ha per river kilometer. Additionally, the Pecos River in Texas 

is a meandering stream with a ratio of river kilometers to air 

kilometers of about 3 to 1. Another primary concern of the 

project was to apply the herbicide with minimal contact of 

off-target vegetation. This situation created a real challenge 

for aerial application of herbicides. This paper describes the 

Pecos River saltcedar control program in Texas and its preliminary results.

Saltcedar Control and Water Salvage on the Pecos River, 

Texas, 1999 to 2003

Abstract: A large scale ecosystem restoration program was initiated in 1997 on the Pecos 

River in western Texas. Saltcedar (Tamarix spp.), a non-native invasive tree, had created 

a near monoculture along the banks of the river by replacing most native vegetation. Local 

irrigation districts, private landowners, federal and state agencies, and private industry 

worked together to formulate and implement a restoration plan, with a goal of reducing the 

effects of saltcedar and restoring the native ecosystem of the river. An initial management 

phase utilizing state-of-the-art aerial application of herbicide began in 1999 and continued 

through 2003. Initial mortality of saltcedar averaged 85 to 90 percent. Monitoring efforts were 

initiated at the onset of the project to include evaluating the effects of saltcedar control on 

salinity of the river water, efficiency of water delivery down the river as an irrigation water 

source, and estimates of water salvage. To date, no effect on salinity can be measured 

and irrigation delivery was suspended 2002 through 2003 due to drought conditions. Water 

salvage estimates show a significant reduction in system water loss after saltcedar treatment. 

However, a flow increase in the river is not yet evident. Monitoring efforts will continue in 

subsequent years.

Charles R. Hart1

Larry D. White2

Alyson McDonald1

Zhuping Sheng3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
90 USDA Forest Service RMRS-P-47. 2007

Methods and Procedures

The first step undertaken by the planning group was to 

develop a section 24(C) special use label to use ArsenalTM 

herbicide on saltcedar within rangeland and aquatic areas in 

Texas. The label was prepared by the Pesticide Division of 

the Texas Department of Agriculture and approved for use 

in 1999. The project was designed with two major phases, 

saltcedar treatment phase and debris removal and followup management phase. Also of major concern to the project 

group was the revegetation of the river banks with native 

plants to complete the ecosystem restoration. Once the label 

and funding were secured, the project was ready to begin the 

first phase of herbicide treatments. The Upper Pecos Soil and 

Water Conservation District Board of Directors were selected 

to administer the project.

During the initial meetings to begin planning the process 

of saltcedar removal, several major concerns emerged. First, 

the treatment method selected should provide a high rate of 

saltcedar mortality while minimizing the detrimental effects 

on existing native vegetation. Second, this should be accomplished in the most economical way possible. And finally, 

soil loss from stream banks should be minimized as much 

as possible. Another daunting task was to obtain permission 

from private landowners to treat saltcedar along the river, as 

much of the land is in private ownership. A “spray easement” 

was developed and used as a contract between the Project 

and private landowners, allowing access for treatment and 

follow-up management for a 10-year period. To date, over 

800 easements have been signed by private landowners, with 

a rejection rate of less than 1 percent. Bids were solicited from 

aerial applicators in late summer 1999 with the project ultimately being awarded to North Star Helicopters from Jasper, 

Texas. With funding, landowner permission, and applicator 

contract in hand by August 1999, initial treatments could 

begin in September.

The ecohydrological study was conducted after the application of herbicide to assess impacts of saltcedar control in 

terms of water quality and water quantity. To quantify water 

flow between surface water and ground water, surface water 

flow release and diversions were monitored and groundwater 

level diurnal fluctuations were monitored at both treated and 

untreated sites. The latter were used to estimate the water 

losses by evapotranspiration and water salvage potential from 

the saltcedar control. Details for each component are described 

in this paper.

Herbicide Applications

Applications of 1.12 kg a.i./ha of ArsenalTM herbicide were 

made by helicopter, applied with a specially-designed boom 

that produced large droplets and high total spray volume. The 

helicopter had the advantage of being able to fly at slower air 

speeds compared to fixed-wing aircraft, which made the sharp 

turns of the river much easier to navigate. The helicopter 

application also provided for much higher precision of application by utilizing specialized nozzle and boom technology. 

The herbicide was applied in a total spray volume of 140 L per 

hectare with a 1000 to 1500 μ droplet. Less than 0.5 percent 

of the droplets were “driftable” fines (< 200μ). The boom was 

also sectioned into 3 to 4.5 m sections for an overall width 

of 13.5 m. Combinations of the boom could be turned on to 

allow for a 4.5, 9, or 13.5 m swath width. This further reduced 

the amount of herbicide that came in contact with off-target 

vegetation. Another advantage of the helicopter over fixedwing aircraft was its ability to land on loader trucks that were 

positioned near the river and eliminated the need of ferrying 

to and from a landing strip.

Helicopters were equipped with GPS navigational equipment to aid in application. The use of on-board GPS allowed 

for near elimination of skips between spray swaths and allowed 

pilots to easily return to the point where they finished spraying 

the previous spray load. The system was also connected into 

the sprayers flow control system so that rate of flow through 

the boom was varied to precisely match ground speed, eliminating the need to maintain a constant ground speed. After 

completion of treatments, GPS log files were downloaded to a 

computer to produce maps of the treated area and make calculations about the area treated.

Percent mortality of saltcedar plants was estimated after a 

minimum of 2 years post-treatment. Counts were conducted 

at multiple locations to determine percent mortality of saltcedar by counting live and dead plants along belt transects on 

both sides of the river. If any green plant tissue was evident on 

a plant, it was recorded as live. Plants were counted within a 

2.5-m wide belt transect until 100 plants were recorded as live 

or dead. A minimum of four transects were conducted at each 

sample location, two on each side of the river.

Measuring Water Quantity/Flow

Water quantity is monitored through release and delivery 

data from Red Bluff Water and Power Control District. Water 

released from Red Bluff Reservoir and delivered to seven 

local irrigation districts along the Pecos River is recorded 

daily during the irrigation season in ac-ft. Release and delivery 

data is obtained from weirs located at point of release from 

Red Bluff Reservoir and at each irrigation turnout point on 

the river. Historical release and delivery data have also been 

provided by the Red Bluff Water and Power Control District, 

with pre-treatment averaged from 1988 through 1999 to 

establish a comparative baseline. Flow data is obtained from 

United States Geological Survey (USGS) Gauging Station 

13257 located at Girvin, Texas. This gauging station is located 

at the southern end of the Red Bluff Water and Power Control 

District boundary. Water released from Red Bluff Reservoir 

that is not delivered to upper districts is captured at Imperial 

Reservoir, located upstream from the USGS gauging station.

Estimating Water Salvage

Water loss resulted from evapotranspiration within saltcedar 

stands and water salvage from saltcedar control is estimated by 

monitoring groundwater diurnal fluctuations within saltcedar 
USDA Forest Service RMRS-P-47. 2007 91

sites. Shallow groundwater monitoring wells were installed at 

a study site located on the Pecos River near Mentone, Texas, 

to provide data on the fluctuation of the groundwater table. A 

description of methods used to construct monitoring wells is 

provided in Hays (2003). Water level loggers (Global Water 

Instrumentation, Inc. Model WL14X) were used to measure 

hourly water levels in the wells and the river. The sensor on the 

WL14X is a submersible pressure transducer that is amplified 

and temperature and barometric pressure compensated with 

an accuracy of 0.2 percent. Logger models used in this study 

had a reported accuracy of 0.0091 m and were calibrated prior 

to being placed in the wells. Additionally, wells were cleaned 

and flushed annually to remove silt and root accumulation. 

Loggers were programmed to record water level every hour.

A drawdown-recharge method (fig. 1) of calculation was 

used to estimate water loss from hourly measurements that 

produced diurnal fluctuations in the water table. This method 

assumes little evapotranspiration occurs during the nighttime (21:00 to 08:00 hours) and that the period from the low 

point of the water table during daylight hours to the nighttime 

high can be used to calculate a recharge rate for the drawdown period. This method requires a drawdown and recharge 

diurnal cycle; hence, days when the water table rapidly rises 

or falls through out the diurnal cycle were excluded from the 

calculations. More information on the procedures and calculations used are found in Hays (2003).

A paired-plot design was used, with four monitoring wells 

and a river monitor at each of two plots. Each plot was monitored for an entire growing season (December 1999 through 

September 2001). The relationship between wells across plots 

was established through simple linear regression and reported 

by Hays (2003). In September 2001, one plot was treated with 

ArsenalTM herbicide and the saltcedar killed. When sufficient 

data are available, water loss on untreated plots will be used 

to predict that on untreated plots, and a comparison made 

between predicted and actual. To date, this calculation has 

not been performed due to low water releases for the latest 

2 years.

Results and Discussion

Based on field observation and data analysis over the last 

3 years, the following preliminary results were obtained for 

herbicide application, water quality, water losses by evapotranspiration, and water salvage potential by saltcedar control. 

Additional research is also recommended to gain a better 

understanding of the impacts of saltcedar control and quantifying volume and fate of water salvage by saltcedar control.

Herbicide Applications

The project was funded in 1999 and 2000 by Red Bluff 

Water and Power Control District and irrigation districts along 

the Pecos River. Approximately 106 river kilometers or about 

544 hectares of saltcedar were treated with an actual spray 

cost of $253,555.

During 2001, $1 million was allocated to the Pecos River 

Ecosystem Project by the State of Texas through the Texas 

Department of Agriculture. Eight percent (8 percent) of these 

funds were used for project administration and monitoring 

with the remaining 92 percent used for saltcedar treatments in 

2001 and 2002. Third year (2001) applications treated approximately 92 river kilometers or 583 hectares of saltcedar at a 

cost of $263,000. From 1999 through 2001, 1127 hectares of 

saltcedar were treated at a total cost of $515,635.

Fourth-year applications were completed in September 

2002. Approximately 1,444 ha were treated including segments 

of the river between Red Bluff and Grandfalls, Texas, that were 

not sprayed during the previous years, from the New Mexico/

Texas state line to Red Bluff Reservoir (including areas around 

the lake) and 8 kilometers of Salt Creek, a major tributary of 

Figure 1. Conceptual illustration 

showing diurnal fluctuation in 

groundwater and representation of drawdown-recharge 

method for calculation of 

water loss.

Groundw ater recharge rate

6am 12noon 6pm 12midnight

A

B

Hourly Transpiration Loss (HTL)

Daily water use = HTL X Specific Yield
92 USDA Forest Service RMRS-P-47. 2007

the Pecos River in Reeves County. About $660,000 was spent 

during the 2002 spray season.

Applications in 2003 were funded through a joint effort of 

the USDA-NRCS Environmental Quality Incentives Program 

(EQIP) and Texas State Soil and Water Conservation Board 

Brush Control Program. EQIP is a private landowner based 

program for cost share of environmental practices. This 

program provided 75 percent of the saltcedar treatment costs 

to the landowner. The Texas State Soil and Water Conservation 

Board provided the remaining 25 percent of the cost through 

the Texas Brush Control Program. During 2003, approximately 1,510 hectares of saltcedar were treated within the 

Pecos Basin Watershed in Culberson, Reeves, Ward, Crane, 

Pecos, Crockett, Terrell, and Val Verde counties. Of this area 

treated, approximately 122 kilometers or 1,080 ha were along 

the main river channel. The remaining hectares were treated 

along tributaries and springs within the basin. Treatment cost 

during 2003 was $518.70/ha for a total of $783,300.

To summarize, from 1999 through 2003, 320 kilometers 

of the Pecos River and various tributaries and springs within 

the basin have been treated for saltcedar control in Texas (fig. 

2). Approximately $1.9 million was spent to treat 4,081 ha. 

Debris removal and follow-up management continues to be 

a priority to complete the project and this phase is currently 

being planned.

Percent mortality estimates were made during the summer 

of 2002 at six sites along the river treated in 1999 and 2000. 

Average estimated mortality within a site ranged from a low 

of 84 percent to a high of 90.7 percent after herbicide applications. Across all sample sites, saltcedar mortality averaged 

87.5 ± 0.1 percent 2 years after treatment. These results are 

very close to other studies (Duncan and McDaniel 1998).

Water Quantity/Flow

One priority was to determine if a relationship existed 

between water released at Red Bluff Reservoir and the amount 

of flow measured at Girvin. A coefficient of determination was 

calculated on flow (cfs) measured at Girvin and the volume of 

water (cfs) released from Red Bluff Reservoir, where r2

 = 0.15 

(P < 0.05). A low correlation provides evidence that release 

from Red Bluff Reservoir is at best only weakly related to 

flow through the USGS station at Girvin (Clayton 2002).

After it was determined that losses occurring between 

release and delivery were not highly correlated to the flow at 

Girvin, only release and delivery data were analyzed and the 

Girvin data were not utilized in the analysis. It was observed 

that during certain time periods within a delivery year, percent 

loss changed considerably (fig. 3). This pattern precipitated 

dividing the irrigation delivery year into three categories, 

initial release and delivery (first month), release and delivery 

during the growing season, and later release and delivery 

(later irrigation season). Initial releases did not occur during 

the same month each year but varied between March and 

April. Delivery months were then numbered consecutively 

from the first month of release each year. The three categories allowed for a characterization of changes in percent loss 

occurring during the delivery year.

A monthly average was calculated for each of the three 

delivery categories (table 1). The first month releases 

Figure 2. Areas of the 

Pecos River Basin 

treated for saltcedar 

control during 1999-

2003.
USDA Forest Service RMRS-P-47. 2007 93

averaged 7,862 ac-ft with a delivery of 2,927 ac-ft and 

resulted in an average percent loss of 68 percent. Monthly 

releases increased during the growing season to an average 

of 11,015 ac-ft, but losses decreased to 39 percent. Average 

release for the late season showed to be the lowest, 3,534 

ac-ft, with a loss of 43 percent. It is obvious that much of 

the release during the first month is used to “re-charge” the 

banks that were naturally “drained” during the non-irrigation 

winter months. This initial loss can account for a significant 

amount of the water lost during the irrigation delivery year.

An average pattern of release and percent loss was 

also determined for each month from 1988 through 1999 

during the period of a delivery year. The highest average 

loss occurred during the first month (67 percent) of release. 

Percent loss decreased during the second month of release, 

and for the next 5 months of release, the loss ranged from 

32 percent to 47 percent. However, when the amount of 

water released begins to decrease in month 7, the percent 

loss begins to increase (46 percent) and by month 9, the loss 

increased to 64 percent.

Ultimately, this release and delivery data from pre-treatment years will be compared to post-treatment years to 

determine if control of saltcedar decreases the loss of water 

during the irrigation period thereby increasing the delivery 

efficiency. Only a small portion of the Red Bluff District had 

been treated during 2000-2001 delivery years. During the 

2002 and 2003 delivery season, no water was released from 

Red Bluff Reservoir for delivery to irrigation districts. As 

irrigation delivery resumes, comparisons of pre-treatment to 

post-treatment will be made.

Estimating Water Salvage

Shallow groundwater wells have been monitored during 

the 2001 through 2003 growing seasons. Total water loss is 

calculated for each of the two plots for each year monitored. 

During the 2001 growing season, irrigation water was released 

as normal from Red Bluff Reservoir, but no irrigation water 

was released during the 2002 and 2003 seasons.

Due to the lack of river flow during the 2002 and 2003 

growing seasons, several of the wells were dry during the 

year; hence, only the wells closest to the river are reported 

at this time. Herbicide treatment was applied to plot A at the 

end of the 2001 growing season. Nearly 90 percent control 

of all vegetation was observed at this plot after the 2002 

Table 1. Average monthly release, delivery, and percent loss for three 

release and delivery periods for the Pecos River from 1988 to 

1999.

Average monthly (acre-feet)

Delivery period Release Delivery Percent loss

First month 7,862 2,927 68%

Growing season 11,105 6,648 39%

Late season 3,534 2,074 43%

Average Monthly Release and Percent Loss

for the Pecos River 1988-1999

7,815

11,524

8,200

10,541

11,885

6,241

3,565 3,779

2,064

4,934

4,528

2,735

5,014

4,657

1,841 1,449 2,095

1,404

-

2,000

4,000

6,000

8,000

10,000

12,000

14,000

1 2 3 4 5 6 7 8 9

Month of Release and Delivery

Ac-Ft

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Loss

Red Bluff Release (y1) Water Balance Difference (y1) Percent Loss (y2)

Figure 3. Average monthly release, delivery, and percent loss of Pecos River irrigation water during consecutive delivery months 

from 1988 through 1999, with standard deviations of percent loss illustrated.
94 USDA Forest Service RMRS-P-47. 2007

growing season. Figure 4 shows the diurnal fluctuations in the 

groundwater table during July of each of the years for well 

locations A1 (treated plot) and B1 (untreated plot). Note that 

at well location B1, the diurnal fluctuations are evident for all 

3 years. However, at well location A1, the diurnal fluctuations 

disappear during the 2002 and 2003 growing season. This is 

attributed to the fact that the saltcedar was killed on this plot 

after the 2001 growing season. Total water loss per year was 

calculated at 1.37 m at well location B1 and 0.95 m at well 

location A1 for the 2001 growing season (fig. 5). Water loss 

at well location B1 dropped due to drought to 0.89 and 1.0 m, 

respectively for 2002 and 2003. Water loss at well location 

A1 was reduced to 0.11 and 0.07 m, respectively for 2002 and 

2003, after saltcedar treatment.

Total water loss was greatly reduced following saltcedar control, although actual amount of salvage cannot 

yet be calculated. In addition, native plants take over some 

of the area where the saltcedar has been treated, which will 

further complicate the estimate of water salvage and its fate. 

Research will continue to document actual water loss and estimate amount and fate of salvaged water. Additional, updated 

information on the project can be obtained from the Internet at 

the following web site: http://pecosbasin.tamu.edu

Conclusions

In summary, saltcedar control using the herbicide application described was successful with an average of 85 to 90 

percent apparent mortality of saltcedar 2 years after treatment. 

With long-term monitoring, treatment life of the control strategies should be further evaluated and follow-up management 

alternatives explored.

Preliminary results indicate that there is a great potential 

for water salvage by saltcedar control even though no fixed 

values were obtained for amount of water salvage, nor is the 

fate of the salvaged water identified. It is recommended that 

additional studies on surface water and shallow ground water 

interaction be conducted to have a better understanding of the 

fate of the potentially salvaged water. Additional study is also 

recommended to explore and validate the methodology for 

assessment of water salvage.

Treated Site, July 2001-2003

0

1

2

3

4

5

6

Time

Water Level

2001

2002

2003

Untreated Site, July 2001-2003

0

1

2

3

4

5

6

Time

Water Level

2001

2002

2003

Treated Site, July 2001-2003

0

1

2

3

4

5

6

Time

Water Level

2001

2002

2003

Untreated Site, July 2001-2003

0

1

2

3

4

5

6

Time

Water Level

2001

2002

2003

Figure 4. Shallow groundwater levels at 

sites A1 (Treated) and B1 (Untreated) 

during the month of July for the 2001 

through 2003 growing seasons. Saltcedar 

on the treated site was killed after the 

2001 growing season. Note the absence 

of diurnal fluctuations on the treated 

site during the 2002 and 2003 growing 

season.
USDA Forest Service RMRS-P-47. 2007 95

This paper presents preliminary results of an ongoing 

project. Besides above-mentioned recommendations, the 

authors also identified several other related issues that should 

be addressed in future studies. One of the factors that affect 

assessment of the water salvage is the drought in the region. 

To overcome such an effect, long-term monitoring is recommended to gain a better understanding of the fate of salvaged 

water during the wet period. The second factor is re-vegetation or taking-over of the riparian zone by native plants, which 

could use some of the water salvaged by saltcedar control. 

Therefore, how much water is needed by native plants should 

be considered in estimate of long-term water salvage.

Acknowledgments

Research and monitoring efforts on the Pecos River 

Ecosystem Project were funded by a grant from the Texas 

Department of Agriculture and by the Rio Grande Basin 

Initiative administered by the Texas Water Resources Institute 

of the Texas A&M University System Agriculture Program 

with funds provided through a grant from Cooperative State 

Research, Education, and Extension Service, U.S. Department 

of Agriculture, under Agreement No. 2001-45049-01149.

Literature Cited

Clayton, L. 2002. Saltcedar Management Strategies and Effects 

on Water Quality and Quantity of the Pecos River. Texas A&M 

University, Masters Thesis. 86 p.

Figure 5. Total annual groundwater loss from Site A (Treated) 

and Site B (Untreated) for three 

growing seasons. Site A saltcedar was treated after 2001 

growing season and shows 

dramatic decrease in water 

loss. Site B remains untreated 

through 2003.

1.72

1.94

2.03

2.96

0.17

0.04

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

2001 2002 2003

(Meters)

Site B (Untreated) Site A (Treated)

Duncan, K. W.; McDaniel, K. C. 1998. Saltcedar (Tamarix spp.) 

management with Imazapyr. Weed Technology. Vol.12, Issue 

2:337-334.

Everitt, Benjamin L. 1998. Chronology of the spread of tamarisk in 

the central Rio Grande. Wetlands. 18(4):658-668.

Hays, K. B. 2003. Water Use by saltcedar (Tamarix sp.) and associated 

vegetation on the Canadian, Colorado and Pecos Rivers in Texas. 

Texas A&M University, Masters Thesis. 115 p.

Kunzmann, M. R.; Johnson, R. R.; Bennett, P. S. Technical 

coordinators. 1988. Tamarisk control in southwestern United 

States; 1987 September 2-3; Tucson, AZ. Special Report No. 9. 

Tucson, AZ: National Park Service, Cooperative National Park 

Resources Studies Unit, School of Renewable Natural Resources: 

141 p.

Robinson, T. W. 1965. Introduction, spread, and areal extent of 

saltcedar (Tamarisk) in the western states. U.S. Geol Serv. Prof. 

Paper 491-A. 12 p.

The Authors

1 Texas Cooperative Extension, Fort Stockton, TX. 

cr-hart@tamu.edu 2 Retired, Texas Cooperative Extension, College Station, TX.

3 Texas Agricultural Experiment Station, El Paso, TX.
96 USDA Forest Service RMRS-P-47. 2007

Introduction

Encroachment of woody plants into arid and semi-arid 

grasslands has occurred on a world-wide scale (van Vegten 

1983; Smeins 1983; Ansley and others 2001; Archer and 

others 2001). Causal factors include reduced fire frequency, 

livestock overgrazing, increased seed distribution via livestock consumption and fecal deposition, and possibly 

increased CO2

 levels that favors growth of C3 shrubs over C4

grasses (Archer and others 1995; Kramp and others 1998). 

Success of woody plants is also attributed to an ability to grow 

deeper roots than grasses and thus better withstand droughts 

(Hinckley and others 1983; Hesla and others 1985; Gibbons 

and Lenz 2001).

In the southern Great Plains and southwestern USA, adaptation of honey mesquite (Prosopis glandulosa Torr.) to 

a variety of environments may be related to a plasticity of 

root system distribution (Gile and others 1997). When available, mesquite will exploit sources of deep water by growing 

a taproot (Phillips 1963; Mooney and others 1977; Nilsen 

and others 1981). Mesquite can also persist on sites that 

have little or no ground water by growing lengthy shallow 

lateral roots (Heitschmidt and others 1988; Ansley and others 

1990). Mesquite in north Texas have been termed “facultative 

phreatophytes” that function as phreatophytes if unlimited 

water is available, but are capable of surviving on sites with 

limited soil water (Wan and Sosebee 1991).

Few studies have observed the influence of extended 

droughts or wet periods on water relations and rooting 

behavior of woody perennials such as mesquite, yet prolonged 

climatic trends may confer competitive advantage to woody 

perennials such as mesquite and contribute significantly to 

their encroachment on grasslands (Kummerow 1980; Ansley 

and others 1992; Archer and others 1995). Our objective 

was to determine the effect of chronic drought or wetness 

on distribution and quantity of mesquite roots. A second 

objective was to quantify the isotopic carbon signature of 

mesquite foliage as an indicator of water use efficiency 

response to extended droughts or wet periods. We hypothesized that (1) mesquite exposed to chronic drought would 

grow deeper roots in search of other water sources and (2) 

mesquite exposed to chronic wetness would emphasize root 

growth in shallow layers and possibly sacrifice some deeper 

roots. Finally, because the site where we were conducting 

the study had little or no available soil moisture below about 

2 m depth (from Ansley and others 1990, 1992), we hypothesized that trees exposed to chronic drought would eventually 

die.

Mesquite Root Distribution and Water Use Efficiency in 

Response to Long-term Soil Moisture Manipulations

Abstract: This study quantified honey mesquite (Prosopis glandulosa) root growth and 

water use efficiency following chronic soil drought or wetness on a clay loam site in north 

Texas. Root systems of mature trees were containerized with barriers inserted into the soil. 

Soil moisture within containers was manipulated with irrigation (Irrigated) or rain sheltering 

(Rainout). Other treatments included containerized precipitation-only (Control) and noncontainerized precipitation-only (Natural) with three trees per treatment. After four years of 

treatment, soil cores to 2.7 m depth were obtained beneath each tree canopy. Mesquite and 

grass roots were extracted, separated into size classes, and weighed. Root length density (m 

m-3) was quantified for mesquite roots. Averaged over the entire sample depth, Irrigated trees 

doubled root length density of small (< 2 mm diam.) roots compared to Control trees (232 

vs 105 m m-3). Below 90 cm depth, root length density of large (2 to 10 mm diameter) roots 

was five times greater in Rainout (36 m m-3) than Control trees (7 m m-3). Over all depths, 

root biomass was greatest in Rainout trees and root:shoot (biomass) ratio was three times 

greater in Rainout than Control or Irrigated trees. Mesquite leaf carbon isotope ratio (δ13C) 

was lower (more negative) in Irrigated trees than other treatments, suggesting these trees 

had lower water use efficiency. Leaf δ13C was not different between Rainout and Control 

trees. Mesquite adapted to chronic wet or drought cycles through increased root growth but 

patterns of distribution differed as Irrigated trees emphasized growth of small roots throughout 

the profile and Rainout trees grew large roots into deeper soil layers.

R. J. Ansley1

T. W. Boutton2

P. W. Jacoby3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 97

Materials and Methods

Site Description and Treatments

The study was conducted within a dense stand of mature 

mesquite trees in the northern Rolling Plains ecological area 

of Texas, south of Vernon (33o52’N, 99o17’W; elevation 368 

m). Average annual precipitation is 665 mm. Primary grass 

species are Texas wintergrass (Nassella leucotricha) and 

buffalograss (Buchloe dactyloides). Soils are Typic Paleustolls 

of the Deandale and Kamay series (Koos and others 1962). 

Both series have clay loam surfaces underlain by a sandstone 

and shale parent material beginning at 1 m depth. Soil moisture measurements to 8 m depth indicated that there was little 

available moisture below 2 m depth.

Twelve multi-stemmed mesquite (3.5 ± 0.3 m height; 5.1 ±

0.2 cm diameter, 6.1 ± 0.7 basal stems) were selected for the 

study on the basis of uniform canopy size. All trees occurred 

within a 1.3 ha area. During December 1985 through February 

1986, aerial portions of neighboring woody vegetation occurring within 20 m of each experimental tree were removed and 

remaining stumps killed with diesel oil. A 0.5 m wide and 2.5 

m deep trench was dug and a sheet metal and plastic barrier 

was placed vertically around each of nine trees before re-filling 

the trench (Ansley and others 1988). Each barrier wall was 

hexagon shaped with each point of the hexagon 4.1 m from 

tree center. Trees with root barriers were called “containerized” trees, although bottoms of the containers were unsealed; 

however, soils were dry below 2 m depth. Surface area and soil 

volume within each container was 42.4 m2 and 106 m3 (2.5 m 

x 42.4 m2), respectively. Each container wall extended 10 cm 

above ground to prevent flooding onto the container surface. 

The three non-containerized trees were termed Natural trees.

Three containerized trees, termed Control trees, had no 

manipulations other than the root container. Control and 

Natural trees received rainfall only. Three containerized trees, 

termed Irrigated trees, received precipitation plus periodic 

irrigation at about 35 mm each month during the growing 

season. The irrigation system was supplied via underground 

polyvinyl chloride (PVC) tubing connected to a 23,000 L 

tank and electric pump powered by a generator. Water from 

a municipally approved drinking system was supplied to the 

tank. Three other containerized trees, termed Rainout trees, 

received a reduced soil moisture level after installation of a 

“sub-canopy” rain shelter beneath the foliage of each tree that 

prevented water from falling on the surface of the container 

but allowed foliage to be exposed to sunlight. Rain shelters 

consisted of a wood frame suspended 1 m above ground that 

was covered with wire netting and glasshouse grade 6-mil 

plastic (Jacoby and others 1988). The frame and covering were 

built around the base stems of each tree and extended beyond 

the root container edge with a slight slope away from tree 

center. The shelters did not exclude stem flow. Plastic sheets 

were applied to shelters 29 May 1986. Shelters remained in 

place from May 1986 through July 1989, except for an eight 

month period from September 1986 to April 1987 for repairs. 

Irrigation treatments were also discontinued at the end of July 

1989.

Measurements

Four 5-cm diameter aluminum tubes were installed within 

each root container to 2.2 m depth at 2 m laterally from tree 

center for soil moisture measurement. Volumetric soil moisture was measured every two weeks and at 30 cm increments to 

180 cm depth during each growing season (April-September) 

using a neutron probe (Greacen 1981). Measurements were 

calibrated to field-collected samples.

For root measurements, three 10-cm diameter soil cores 

were taken to 270-m depth near the drip line of each tree 

during the fall 1989 to spring 1990 using a soil coring device 

(Giddings Inc., Ft. Collins, CO). Each core was divided 

into 10-cm segments from 0 to 90 cm, and 30-cm segments 

from 90 to 270 cm. Soil was separated from all roots in each 

segment with a hydro-pneumatic elutriation system (Smucker 

and others 1982). Mesquite roots were separated from roots of 

other species using a dissecting scope and were divided into 

two size classes, small (0 to 2 mm diameter) and large (2 to 

10 mm diameter). Total root length within each soil segment 

and root size class was quantified using an automated image 

analyzer (Harris and Campbell 1989). Values for root length 

were expressed as root length density (RLD; m root length 

m-3 of soil) (Bohm 1979). Following RLD determination root 

samples were oven dried and weighed.

Leaf samples were collected from each tree at two week 

intervals during the 1988 and 1989 growing seasons. Samples 

were oven dried and ground and isotopic carbon ratio (δ13C), 

percent N and percent C was determined using methods 

described by Boutton (1991). Leaf samples were also collected 

in late August and September 1989, one month following 

termination of irrigation July 1989 to determine the effect of 

dry down within root containers following chronic wetness 

on leaf δ13C.

Canopy height of each tree was measured each year. 

Canopy biomass in each treatment was estimated from a 

height-to-mass relationship determined by harvesting over 

20 trees (height range: 2-5 m) near the study site as part of 

another study (Ansley, unpublished data). Root:shoot (R:

S) ratios were calculated for containerized trees using these 

derived canopy mass values and root mass data that were 

scaled to the volume of the root containers.

Statistical Analysis

Root length density and root mass data were analyzed 

within each root size and soil depth segment using a oneway ANOVA with treatment (Irrigated, Rainout, Control, 

Natural) as the main effect (three replicates per treatment) 

(SAS 1988). Non-normal data were square-root transformed 

prior to analysis. Means were separated using LSD (P < 0.05). 

Soil moisture values were pooled over all depths and sample 

dates within each year prior to analysis and analyzed with a 
98 USDA Forest Service RMRS-P-47. 2007

two-way repeated measures GLM with treatment and year as 

main effects.

Results

Precipitation and Soil Moisture

Precipitation was near average for every month in 1986 

except for extremely high amounts in September and October 

(fig. 1). Precipitation was above normal in 1987, below normal 

in 1988 and slightly below normal in 1989 prior to termination of soil manipulations in July 1989.

For the duration of the study (June 1986 through July 1989), 

total incoming water (precipitation or irrigation) was 2,438, 

2,629, 3,455, and 1,021 mm for Natural, Control, Irrigated, 

and Rainout trees, respectively (table 1). Average annual 

incoming moisture was 1,037 mm (41 in.) for Irrigated and 

306 mm (12 in.) for Rainout trees with Control and natural 

trees near the normal 665 mm (26 in.). Small differences in 

incoming water between Control and Natural trees were the 

result of periodic irrigations of Control and/or Rainout trees 

as part of other studies (Ansley and others 1992). The largest 

influx of water to Rainout trees occurred from September 1986 

to April 1987 when rain shelters were removed for repairs and 

rainfall was well above normal.

At study initiation, all containerized trees had similar soil 

moisture when averaged over all depths (fig. 2). Soil moisture was greatest in Irrigated and lowest in Rainout treatments 

throughout the study. Soil moisture in the Control treatment 

was between Irrigated and Rainout trees. Abundant rainfall 

during the fall of 1986 and the 1987 growing season increased 

soil moisture substantially in the Irrigated and Control treatments in 1987. Soil moisture also increased slightly in the 

Rainout treatment due to removal of shelters from September 

1986 to April 1987. Soil moisture near Natural trees was 

Figure 1. Monthly precipitation at the 

research site from 1986 until August 

1989. Line indicates 30-yr average 

precipitation for each month.

Table 1. Incoming water for each treatment during the 40-month period from 29 May 1986 through 05 September 1989. NA = 

Natural, CT = Control, IR = Irrigated, RO = Rainout.

Precip. (mm) Irrigation (mm)1 Precip.+ Irrigation (mm)

NA

CT

Interval IR RO IR CT2 RO2 NA CT IR RO

29 May 86 to 31 Aug 86 193 0 283 73 73 193 266 476 73

01 Sep 86 to 30 Apr 87 731 731 0 0 99 731 731 731 830

01 May 87 to 31 Aug 87 485 0 325 92 92 485 577 810 92

01 Sep 87 to 30 Apr 88 253 0 0 0 0 253 253 253 0

01 May 88 to 05 Sep 89 776 0 409 26 26 776 802 1185 26

Totals (mm) 2438 731 1017 191 290 2438 2629 3455 1021

Average per year (mm) 732 788 1037 306

1

 Irrigation values are precipitation equivalent in mm over the surface area of each root container.

2

 CT and RO trees were irrigated occasionally FROM 1986 to1988 as part of other study objectives not specific to this paper.
USDA Forest Service RMRS-P-47. 2007 99

not measured until 1989 and was similar to the Rainout and 

Control treatments.

Grass cover was > 50 percent in all treatments at study 

initiation and remained at 50 to 80 percent in Natural, Control, 

and Irrigated treatments throughout the study. Grass cover 

declined in the Rainout treatment such that, by 1989, most of 

the area beneath the rain shelters was bare ground.

Root Growth and Distribution

Mesquite root length density (RLD) of small (< 0.2 mm 

diameter) roots, when averaged over all soil segments (0 to 

270 cm depth), was significantly greater in Irrigated trees 

than Natural or Control trees, with Rainout tree RLD intermediate trees in the other treatments (fig. 3). Mesquite RLD 

of large roots (> 0.2 mm diameter) was significantly greater in 

Rainout trees than in all other treatments when averaged over 

all soil segments. Large root RLD was similar among Natural, 

Control, and Irrigated trees.

Small root RLD, when averaged within 10 soil segments, 

was greater in Irrigated trees than Control or Natural trees in 

half of the soil segments (fig. 4). Most of these differences 

occurred within 30 to 180 cm depths. Small root RLD of 

Rainout trees fell between that of Irrigated and Control trees 

in most segments. At 0 to 10 cm, small root RLD showed a 

trend of being greater in Rainout and Irrigated than Control 

or Natural trees, but this was not significant at the 5 percent 

significance level.

Distribution of large root RLD was similar in Natural, 

Control, and Irrigated trees with greatest values between 30 

to 90 cm and a sharp decline below 60 or 90 cm depth (fig. 4). 

In contrast, large root RLD of Rainout trees was three to eight 

Figure 2. Soil moisture when averaged over all depths and dates in 

each growing season. Vertical bars indicate ±1 S. E. (n = 3). Data 

for NA treatment were not available, 1986-88.

Figure 3. Root length density of small and large mesquite roots averaged over all soil depth segments (0-270 cm depth). Error bars 

indicate ± 1 S. E. (n = 3). Means with similar letters are not significant at P < 0.05.

Figure 4. Root length density of small and large mesquite roots 

within 10 soil depth segments. Error bars indicate ± 0.5 S. E. (n = 

3). Means with similar letters are not significant at P < 0.05.
100 USDA Forest Service RMRS-P-47. 2007

times greater than the other treatments in segments below 90 

cm. Averaging the six segments below 90 cm depth, RLD 

of large roots was 36.4, 7.3, 7.1, and 5.8 m m-3 in Rainout, 

Control, Natural, and Irrigated trees, respectively.

Irrigated trees exhibited greater small root mass than trees 

in the other treatments when averaged over all soil segments 

(fig. 5). Rainout trees exhibited greater large root mass than 

trees in other treatments but variability was high. Large root 

mass was similar in Control, Natural, and Irrigated trees.

Carbon Isotope Ratios and Canopy Growth

Leaf δ13C declined in all treatments during each growing 

season (fig. 6). Irrigated trees tended to have lower δ13C values 

than other treatments throughout 1988 and 1989, although 

differences between treatments were greater in 1988. After 

rain sheltering and irrigation treatments were discontinued at 

the end of July 1989, δ13C increased sharply in Irrigated trees. 

Leaf C/N ratio was slightly lower in Irrigated trees (14.6 ±

0.3) than Control (15.4 ± 0.6) or Rainout (15.2 ± 0.5) trees 

throughout 1988, the result of a combination of slightly higher 

N and lower C in these trees than in the other treatments. There 

were no differences in leaf N, C, or C/N ratios between treatments in 1989.

Mesquite canopy height increased in all treatments by 0.5 

m over the course of the study to about 4 m, with no difference 

between treatments (table 2). The root:shoot ratio was 0.3 for 

Control and Irrigated trees and 1.2 for Rainout trees.

Discussion

Survival of mesquite after 4 years of nearly continuous 

rain-sheltering reinforces the suggestion by Gile and others 

(1997) and other studies that root system plasticity affords this 

species a competitive advantage during extended droughts. 

When moisture was not manipulated (Natural and Control 

treatments), most mesquite roots were concentrated at 10 to 

90 cm soil depth (fig. 4). Grass roots in these treatments were 

concentrated in the upper 10 cm (data not shown). Thus, grass 

and mesquite root systems were distributed in the classic “twolayer” pattern proposed by Walter (1954) and Walker and Noy 

Meir (1982) in which grasses occupy the upper soil layer and 

woody plant roots occur beneath the grass roots.

Exposed to chronic soil drought, Rainout mesquite 

explored deeper soil layers by investing energy into growth 

of larger “feeder” roots from which smaller roots extended. 

Caldwell (1976) emphasized that continued root extension 

into regions of soil in which the plant already has a wellestablished root system is a means for evading drought. Other 

studies have shown there can be considerable space between 

roots of woody plants (Chew and Chew 1965; Ludwig 1977), 

including mesquite (Heitschmidt and others 1988), that may 

be exploited during droughts.

We hypothesized that rain-sheltered mesquite would eventually die within a few years because the study site had little or 

no soil moisture below 2 m depth. Because the root containers 

Figure 6. Carbon isotope ratios of mesquite leaf tissue in each treatment during 1988 and 1989. Error bars indicate ± 1 S. E. (n = 3).

Figure 5. Root mass of small and large mesquite roots averaged 

over all soil depth segments (0-270 cm depth). Error bars indicate 

± 1 S. E. (n = 3). Means with similar letters are not significant at P

< 0.05.
USDA Forest Service RMRS-P-47. 2007 101

prevented trees from growing extensive lateral roots that are 

critical to the water use patterns of mesquite on this site (Ansley 

and others 1990), we assumed that the combination of the root 

container and rain sheltering would result in tree mortality. 

However, mesquite not only survived 4 years of nearly continuous drought, but exhibited an aggressive strategy of increased 

root growth and continued canopy growth. Canopy growth 

was maintained levels similar to other less stressed treatments 

possibly because Rainout mesquite found new sources of soil 

moisture through increased root growth. In contrast, the grass 

understory in the Rainout treatment ultimately disappeared. 

These results imply that mesquite responses during drought 

were manifest through increased physiological activity and 

growth rather than by simply surviving drought at some 

reduced metabolic level.

Response to Prolonged Soil Wetness

One reason not often emphasized for the success of mesquite 

may be the ability to exploit wet periods through increased 

root growth. Irrigated mesquite in this study increased growth 

of small roots to a much greater degree than did trees in 

other treatments. This increase in small root growth was not 

concentrated in upper soil layers as we originally hypothesized; rather, it occurred throughout the profile. These smaller 

roots would theoretically be more efficient at absorbing soil 

moisture than would larger roots. High concentrations of 

fine roots would allow exploitation of frequent soil wettings. 

However, this did not translate into greater canopy height or 

biomass in this treatment. Perhaps Irrigated trees increased 

foliage density that we did not measure. Ansley and others 

(1998) found a similar response when intraspecific competition was removed from mesquite.

Lower carbon isotope ratio in Irrigated trees suggests 

a lower water use efficiency (WUE) in this treatment 

(Ehleringer 1988). In indirect support of this conclusion, the 

rapid increase in leaf δ13C in this treatment in the latter part 

of the 1989 growing season when irrigation was terminated 

suggests leaf δ13C values were closely linked to soil moisture 

conditions. We assume trees in this treatment, with their larger 

network of small roots, rapidly absorbed any excess soil moisture in the root containers following termination of irrigation 

and became sufficiently moisture stressed that it affected leaf 

isotopic ratio.

The lack of a difference in leaf δ13C values between Rainout 

and Control trees suggests that Rainout trees were able to 

capture sufficient soil moisture through increased growth of 

large and small roots at least during the period of the study. 

Had the study continued, Rainout trees may have experienced 

sufficient moisture stress to have affected leaf water use efficiency and carbon isotope ratios.

Root:Shoot Ratios

The root:shoot (R:S) biomass ratios estimated for mesquite 

imply that mesquite adjusted root system mass to maintain a 

consistent canopy mass in response to soil drought. However, 

the increase in growth of small roots in Irrigated trees did not 

affect total root mass enough to change R:S ratio compared to 

the Control.

The R:S ratios estimated in this study were likely lower 

than actual R:S ratios because soil cores were obtained closer 

to the canopy dripline of each tree than directly beneath the 

center of the canopy where there was likely greater root mass 

per unit soil volume. The R:S ratio was not calculated for 

Natural trees because the root system in this treatment was 

not contained and roots were likely very extensive (Ludwig 

1977; Heitschmidt and others 1988).

Summary and Implications

Root adaptation to prolonged climatic and edaphic changes 

is an important element for survival of adult mesquite. This 

study demonstrated that mesquite accelerated root growth 

during periods of drought and wetness and that major adjustments to root system architecture occurred within a few years. 

These results imply that mesquite has a natural competitive advantage during both wet and dry cycles. This inherent 

capability, coupled with any management practice, such as 

livestock grazing, that confers even a slight advantage to this 

species over other species during atypical climatic cycles 

will likely accelerate the process of ecosystem domination 

by mesquite. The tendency of managers to increase grazing 

during wet periods to “make up” for grazing losses during 

droughts will likely enhance the natural competitive advantage mesquite possesses via root system adaptation.

Table 2. Root mass (g m-3), root mass within each container, canopy height, projected canopy biomass, and root:

shoot biomass ratios for containerized trees at study end, 1989.

Root mass Root mass/cont. Canopy height Canopy biomass Root:shoot

Treatment (g m-3)1 (kg) (m) (kg)2 ratio

Control 90.5 9.6 4.10 28.4 0.33

Irrigated 85.0 9.0 4.00 26.6 0.34

Rainout 315.3 33.4 4.13 28.9 1.15

1

 Data in left column taken from figure 5 (small + large roots).

2

 Canopy biomass (leaf + wood) was estimated via height-to-mass relationship derived from 23 harvested trees. 

Mass (y) to height (x) relationship was: ŷ = 0.99 - 4.76 x + 2.79 x2; r2 = 0.76.
102 USDA Forest Service RMRS-P-47. 2007

Acknowledgments

The authors wish to acknowledge Keith Lawrence, Cecil 

Meadors (deceased), and Bertha Trevino for assisting in the 

field and laboratory. This research was funded in part by a 

grant from University Lands-Surface Interests, Univ. of Texas 

System, Midland, TX. The research site was provided by the 

E. Paul and Helen Buck Waggoner Foundation, Vernon, TX.

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The Authors

1 Professor of Rangeland Ecology, Texas Agricultural Experiment 

Station, Vernon, TX. r-ansley@tamu.edu 2 Professor of Rangeland Ecology, Dept. Ecosystem Science and 

Management, Texas A&M Univ., College Station, TX. 3 Associate Dean, College of Agriculture, Washington State 

University, Pullman, WA.
104 USDA Forest Service RMRS-P-47. 2007

Introduction

Several studies have demonstrated that seedlings of C3

species demonstrate significant positive growth responses 

to elevated CO2

 concentrations relatively soon after emergence. For example, Tischler and others (2000) found that 

for five herbaceous species, significant responses to doubled 

ambient CO2

 concentration were observed by 3 days after 

emergence. In another study utilizing woody species, significant responses were observed by one week after emergence 

(Tischler and others 2003). All species utilized in these studies 

were epigeal—that is, the cotyledons were elevated above 

soil level by elongation of the hypocotyl. Furthermore, in all 

species utilized in these studies, the cotyledons expanded and 

quickly became photosynthetically active. 

Another grouping of dicots is termed “hypogeal.” In these 

species, the cotyledons remain at planting depth (or often, in 

nature, on the soil surface), as the epicotyl elongates to elevate 

the growing point above the soil surface. In this grouping of 

plants, the cotyledons serve only a storage function and do not 

contribute to the photosynthetic activity of the plant. Numerous 

surveys indicate that hypogeal species have a considerably 

greater seed mass than epigeal species (for example, see Ng 

1985; Bazzaz and Pickett 1980).

Total reproductive output represents a balance between 

seed size and seed number (Smith and Fretwell 1974). For a 

species to allocate a larger proportion of resources to a smaller 

number of seeds, hypogeal germination morphology (and 

greater seed mass) must confer an advantage to the seedling. 

One advantage is resistance to clipping. Adventitious buds in 

the axles of the cotyledons are at or below soil level in hypogeal seedlings, so these seedlings readily survive clipping at 

soil level. In epigeal species, clipping at soil level severs the 

hypocotyl and cotyledons, and thus removes meristematic 

tissue. Another advantage of hypogeal germination (and the 

concomitant abundance of seed reserves) is an innate ability 

to survive stresses, such as low light levels, in the seedling 

stage (Ganade and Westoby 1999). A tradeoff of hypogeal 

germination morphology may be depressed seedling relative 

growth rate (Maranon and Grubb 1993; Stebbins 1976a, b). 

Indeed, the literature indicates that seedling growth rates are 

slower in hypogeal than epigeal species. This fact prompted 

us to question if the rapid growth response to elevated CO2

observed in epigeal species might be delayed or less dramatic 

in hypogeal species. If so, CO2

 enrichment might actually be 

a disadvantage for hypogeal species in competitive situations 

where growth rate is important, and thus results from one functional type could not be extrapolated to the other type when 

assessing potential effects of increasing atmospheric CO2

concentrations on ecosystem dynamics. The two hypogeal 

species we chose to study were guajillo (Acacia berlandieri 

Benth) and cat claw acacia (Acacia greggi Gray var. wrightii 

[G. Bentham] D. Isely). Guajillo is a significant brush species 

in south Texas, from west of Corpus Christi to Uvalde. Guajillo 

thrives on chalky limestone (caliche) outcroppings, where it is 

the predominant species, as well as on deeper soils where it is 

Response of Seedlings of Two Hypogeal Brush Species to 

CO2

 Enrichment

Abstract: Previous work has demonstrated that epigeal woody invasive plants (with 

expanding, photosynthetic cotyledons), such as honey mesquite (Prosopis glandulosa L.), 

respond positively to elevated atmospheric CO2 concentrations in as little as 3 days after 

emergence. No research has addressed the behavior of larger seeded, hypogeal invasive 

plants (common in south Texas) exposed to elevated CO2. We studied two such species, 

guajillo (Acacia berlandieri Benth.) and cat claw acacia (Acacia greggii Gray var. wrightii 

(G. Bentham) D. Isley), to quantify growth stimulation at a doubled concentration of CO2. 

Seedlings were grown in glasshouses in 1.5 m tubes at Temple, TX, in the late summer of 

2000. Only seeds within a narrow range of masses were selected for each species, to reduce 

effects of seed mass on seedling size. Plants were harvested 15 days after emergence. Leaf 

area, shoot weight, leaf weight, root weight, and depth of root penetration were determined for 

each plant. Both species exhibited marked root length at sampling, with mean values of about 

75 and 90 cm for guajillo and cat claw acacia, respectively. For both species, all parameters 

demonstrated a positive numerical response to elevated CO2

, although no differences were 

statistically significant. The lack of statistical verification of the observed differences was 

likely caused by the great deal of variability observed within both species. For example, 

values for specific parameters varied by as much as a factor of six within a species and CO2

treatment. These results suggest that seedling growth responses to elevated CO2 may be 

smaller in hypogeal than in co-occurring epigeal species.

Charles R. Tischler1

Justin D. Derner2

H. Wayne Polley3

Hyrum B. Johnson4

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 105

one component of a mixed brush community. Cat claw (called 

Wright acacia in the older literature) is also one component of 

mixed brush stands in south Texas.

Materials and Methods

Seeds of guajillo were harvested from shrubs near Beeville, 

TX, in June of 1999. Cat Claw Acacia seeds were harvested 

from trees near Pearsall, TX, in 1998. Both groups of seeds 

were stored in a seed vault. Because there is considerable variability in seed mass in these species, we weighed individual 

seeds and selected those within a relatively narrow band 

of seed masses. For guajillo, this was from 0.42 to 0.58 g, 

whereas values for cat claw acacia ranged from 0.16 to 0.24 g. 

Obtaining uniform guajillo seed is especially difficult because 

as seed mature, they are rapidly parasitized by weevils of the 

genus Bruchid. Seeds which appear normal often already have 

damage to the embryo, which becomes obvious only after the 

seedling emerges.

Seeds were planted at a 2 cm depth in 1.5 m pvc tubes 

(5-cm diameter) containing Pedernales Fine Sandy loam soil 

wetted with tenth strength Hoagland’s solution. Two seeds 

were planted per tube. In cases when both seed germinated, 

the weaker of the two seedlings was destroyed. Seeds were 

planted on August 1, 2001. Four groups of tubes of each species 

were assigned to four separate greenhouses, two maintained at 

ambient CO2

 concentration and two maintained at 700 ppm 

CO2. Periodic monitoring of light levels indicated that irradiance was very similar among greenhouses. As is common 

in August in central Texas, days were sunny with only occasional scattered clouds, analogous to conditions encountered 

by Tischler and others (2003) in a prior experiment with 

woody epigeal seedlings. Plants were monitored for insect 

infestation, but none was observed. However, several guajillo 

plants were attacked by fungus. These plants were discarded.

Seedlings were watered as needed to maintain soil near drip 

capacity with one-tenth strength Hoagland’s solution for the 

duration of the experiment. At 15 days after emergence, the 

culture tubes were removed from the greenhouse and carefully 

split so that roots could be washed from the soil media. Leaf 

area was determined with a photoelectric leaf area meter, and 

root lengths were measured with a meter stick and recorded. 

Plants were divided into leaves, root, and stem (remnants of 

the seedcoat and hypogeal cotyledons were discarded), dried 

at 70 C for 24 hours, and weighed.

The growth period of 15 days was selected based on earlier 

experimentation, which indicated that no responses to elevated 

CO2

 were observed in these species at earlier harvest dates.

Results

Data presented in tables 1 and 2 indicate no significant 

effect of elevated CO2 by day 15 on any plant parameter for 

either species, although values were numerically higher in 

elevated CO2 for all parameters except root length for guajillo. 

These results, although not unexpected, are in stark contrast 

with data we previously presented for epigeal herbaceous and 

woody species (Tischler and others 2000, 2003), where significant positive effects of CO2

 were observed between 1 and 3 

days after emergence.

The root lengths of the two species were somewhat greater 

than would have been expected, based on behavior of mesquite 

(Prosopis glandulosa L.) in other experiments. The fact that 

root lengths were greater for the smaller-seeded catclaw was 

also unexpected.

Discussion

Several features of these data sets merit further consideration. First, total biomass of the guajillo seedlings, 362 and 

464 mg, respectively, for ambient and elevated CO2, was still 

less than the 420 to 580 mg range of the seed used in the experiment. Of course, a portion of the seed mass was contributed 

by the inert seed coat, but at very best, at 15 days the seedlings 

were barely more massive than the starting seed. The same 

general trends were true for cat claw acacia (249 and 307 mg 

for seedlings at ambient and elevated CO2, with an initial seed 

mass of 160 to 240 mg). A second significant feature of the 

data sets is the somewhat amazing root length of the seedlings 

(approximately 75 cm for guajillo; greater than 90 cm for cat 

claw acacia).

In work with epigeal woody species at ambient and 

elevated CO2, Tischler and others (2003) observed significant 

effects of elevated CO2

 on total biomass for mesquite at day 

Table 2—Plant parameters of 15-day-old Cat Claw Acacia seedlings 

grown at two CO2 concentrations.

CO2 Concentration (ppm)

Parameter 360 (n = 13) 700 (n = 14) P

Leaf area (cm2

) 22.1 26.1 0.3498

Rooting depth (cm) 90.2 92.2 0.7322

Stem wt (mg) 27.4 33.1 0.1805

Root wt (mg)* 98.7 117.39 0.0954

Leaf wt (mg) 122.9 156.0 0.1789

Total biomass (mg) 249.0 306.5 0.1172

*Remnants of seed coat and hypogeal cotyledons not included in mass.

Table 1—Plant parameters of 15-day-old Guajillo seedlings.

CO2 Concentration (ppm)

Parameter 365 (n = 8) 700 (n =12) P

Leaf area (cm2) 37.6 43.7 0.4777

Rooting depth (cm) 77.9 75.9 0.4760

Stem wt (mg) 32.9 43.7 0.0814

Root wt (mg)* 151.2 173.7 0.3498

Leaf wt (mg) 178.2 246.7 0.2290

Total biomass (mg) 362.3 464.2 0.1978

*Remnants of seed coat and hypogeal cotyledons not included in mass.
106 USDA Forest Service RMRS-P-47. 2007

3, and for parkinsonia (Parkinsonia aculeata L.), honey locust 

(Gleditsia triacanthos L.), and huisache (Acacia farnesiana

(L.) Willd.) at day 8. These experiments were conducted in an 

earlier year (1996) in the same greenhouse, with all aspects 

of plant culture being the same, except for the fact that seed 

were planted about August 26, as compared to August 1 in 

this study. Thus, seedlings in this study experienced slightly 

longer day length than those in the 1996 study. Obviously, it is 

hazardous to compare seedlings grown in two separate experiments, but given the similarity of the experimental system, 

it is clear that the hypogeal species’ response was much less 

than would have been expected from woody epigeal species.

Another interesting observation relates to root lengths. 

Admittedly, the root lengths we measured were longer than 

would be expected in a shallow soil or caliche outcropping. 

However, the fact that roots penetrated 3⁄4 to almost one meter 

with no major increase in seedling dry weight suggests that 

these two hypogeal species may reach a developmental stage 

that could be described as “established” with only minimal 

carbon input from photosynthetic activity. This observation argues against any significant role for elevated CO2

 in 

improving seedling establishment or seedling competitive 

ability of guajillo and cat claw acacia, in stark contrast to 

observations of corresponding epigeal species. Thus, blanket 

predictions about effects of elevated CO2 on ecosystem 

processes, especially seedling recruitment, must be tempered 

with an understanding of how seedling morphology can 

modify these responses.

References

Bazzaz, F. A.; Pickett, S. T. A. 1980. Physiological ecolocy of tropical 

succession: A comparative review. Annual Review of Ecology 

and Systematics 11:287-310.

Ganade, G.; Westoby, M. 1999. Seed mass and the evolution of earlyseedling etiolation. American Naturalist 154:469-480.

Maranon, T.; Grubb, P. G. 1993. Physiological basis and ecological 

significance of the seed size and relative growth rate relationship 

in Mediterranean annuals. Functional Ecology 7:591-599.

Ng, F. S. P. 1985. Strategies of establishment in Malayan forest trees. 

Tropical Trees as Living Systems (eds P. B. Tomlinson and M. 

H. Zimmermann), pp. 129-162. Cambridge University Press, 

Cambridge.

Smith, C. C.; Fretwell, S. D. 1974. The optimal balance between size 

and number of offspring. American Naturalist 108:499-506.

Stebbins, G. L. 1976a. Seed and seedling ecology in annual legumes. 

I. A comparison of seed size and seedling development in some 

annual species. Oecologia Plantarum 11:321-331.

Stebbins, G. L. 1976b. Seed and seedling ecology in annual legumes. 

II. Stem growth, seed production and mechanisms for transport. 

Oecologia Plantarum 11:333-344.

Tischler, C. R.; Polley, H. W; Johnson, H. B.; Pennington, R. E. 

2000. Seedling response to elevated CO2 in five epigeal species. 

International Journal of Plant Science 161:779-783.

Tischler, C. R.; Derner, J. D.; Polley, H. W.; Johnson, H. B. 2004. 

Responses of seedlings of five woody species to carbon dioxide 

enrichment. In: Hild, Ann L.; Shaw, Nancy L.; Meyer, Susan E.; 

Booth, D. Terrance; McArthur, E. Durant, comps. 2004. Seed 

and soil dynamics in shrubland ecosystems: proceedings; 2002 

August 12-16; Laramie, WY. Proceedings RMRS-P-31. Ogden, 

UT: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station. 216 p.

The Authors

1

 Plant Physiologist, USDA-ARS Grassland, Soil & Water Research 

Laboratory, Temple, TX. ctischler@spa.ars.usda.gov 2

 Research Leader, USDA-ARS Grassland, Soil & Water Research 

Laboratory, Temple, TX. 3

 Ecologist, USDA-ARS Grassland, Soil & Water Research 

Laboratory, Temple, TX. 4

 Range Scientist, USDA-ARS, High Plains Grasslands Research 

Station, Cheyenne, WY.
USDA Forest Service RMRS-P-47. 2007 107

Introduction

Compensation, over-compensation, and under-compensation were the three original plant responses to biomass removal 

by herbivores (McNaughton 1983). Production of mechanical 

and chemical defenses has been characterized as an induced 

response to biomass loss (Rhoner and Ward 1997). Increased 

thorn length and density may retard browsing (Cooper and 

Owen-Smith 1986). Our goal is to determine plant response to 

various levels of simulated herbivory in two important south 

Texas shrubs. 

Spiny hackberry (Celtis pallida) and blackbrush acacia 

(Acacia rigidula) are important browse species for wildlife in 

southern Texas (Graham 1982, Varner and Blankenship 1987). 

Many wildlife species utilize spiny hackberry and blackbrush 

acacia during dry periods when other available forage has 

been exhausted (Varner and Blankenship 1987). 

Spiny hackberry has spines, but no chemical defensive 

mechanisms against herbivory have been documented and the 

shrub appears to respond to removal of tissue with compensatory growth (Asah and others 1987, Schindler 2000). After 

top growth removal, new spiny hackberry shoots and tissue 

are often higher in nutritive value than previous tissues (Asah 

and others 1987, Schindler and others 2004). Blackbrush 

acacia is more heavily defended with thorns and chemical 

compounds (Clement and others 1998, Schindler and others 

2003). Previous studies have suggested that thorn length and 

density increase on thorn scrub vegetation following mechanical brush clearing (Schindler and others 2004). It is therefore 

important to understand how these two important browse 

plants respond to biomass removal by herbivores.

We hypothesize that 1) simulated herbivory stimulates increased biomass production in spiny hackberry but 

decreases biomass production in blackbrush acacia compared 

to unbrowsed plants and 2) thorn density and length increase 

in blackbrush acacia to a greater extent than in spiny hackberry in response to tissue removal.

Materials and Methods

Study Site

Research was conducted on the Jack R. and Loris J. 

Welhausen Experimental Station in Webb County, about 56 

km northeast of Laredo, Texas (27°40’57N, 98°56’51W ), 

at an elevation of about 137 m. The surface layer soil at the 

site is a sandy clay loam with 0 to 3 percent slopes, with a 

caliche layer underlying the soil at depths of 1 to 5 m (Soil 

Conservation Service 1985). Precipitation, as recorded in 

Laredo (1947-2003), averages about 50 cm a year but varied 

during the 2 years of this study (fig. 1) and deviated from long 

term averages (National Climate Data Center 2004, Asheville, 

NC). Maximum temperatures above 35°C occur from June 

to August and the lowest temperatures, around 8°C, usually 

occur December to January (National Climate Data Center). 

Vegetation at the study site is a mixed shrub community with 

little grass cover (Varner and Blankenship 1987). Cattle and 

wildlife both are present on the ranch under a continuous 

grazing system. However, little use was observed by cattle 

or wildlife of the selected study site area. The area has been 

mechanically cleared of brush in the past, but sufficient time 

Shrub Biomass Production Following Simulated 

Herbivory: A Test of the Compensatory Growth Hypothesis

Abstract: The objective of this experiment was to test the hypotheses that 1) simulated 

herbivory stimulates increased biomass production in spiny hackberry (Celtis pallida), 

but decreases biomass production in blackbrush acacia (Acacia rigidula) compared to 

unbrowsed plants and 2) thorn density and length increase in blackbrush acacia to a greater 

extent than in spiny hackberry in response to tissue removal. Blackbrush acacia shrubs 

defoliated repeatedly at the 75 percent level produced about 66 percent more biomass than 

control shrubs, while shrubs receiving 100 percent repeat defoliation treatments produced 

double the biomass as control shrubs (p < 0.05), suggesting overcompensation. Spiny 

hackberry repeat defoliated shrub biomass production was double control shrub production 

at 25 percent treatment levels and 81 percent higher in repeat defoliated shrubs at 50 percent 

defoliation levels relative to control shrubs (p < 0.05). Biomass production during the third 

and fourth defoliation events was 90 percent lower than (p < 0.05) biomass removed in the 

initial defoliation. New twig and thorn production occurred only in 2003, but only in blackbrush 

acacia. These results suggest that spiny hackberry, a highly palatable shrub, is negatively 

impacted at high defoliation intensity, while the less palatable shrub, blackbrush acacia, 

responds to intense defoliation with increased biomass production.

Terri B. Teaschner1

Timothy E. Fulbright2

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
108 USDA Forest Service RMRS-P-47. 2007

has elapsed for vegetation to recover and form a mature 

shrub community. A representative area was selected in May 

2002 and an exclosure about 60 x 80 m surrounded by a 1.2 

m tall welded wire fence was established to prevent wildlife 

and livestock browsing on shrubs. Chicken wire with a 2.5 

cm diameter mesh was used along the bottom 0.6 m of the 

fence to retard small mammals. A CM20 Campbell Scientific 

Weather Station located on the Welhausen Research Station 

< 1⁄2 km from the study site provided local hourly and daily 

weather conditions (Campbell Scientific Inc., Logan, UT). 

Methods

A randomized, complete-block design was used in this 

experiment. Five blocks per species were used, with each 

treatment randomly assigned to a selected shrub in the block 

(n = 5). Twenty-five plants of each species, blackbrush acacia 

and spiny hackberry, were randomly selected in May 2002 

from plants within the exclosure. Plants had a similar number 

of basal stems and were 1.5 to 2 m tall, which is considered 

the upper limit white-tailed deer (Odocoileus virginianus) 

browse. Plants of each species were randomly chosen and 

were assigned to one of five defoliation treatments on a 

randomly selected stem: 0 percent, 25 percent, 50 percent, 

75 percent, and 100 percent. The 0 percent defoliation was 

the control group and was defoliated at the end of the experiment in October. For the 2003 field season, additional controls 

were added for harvest at the second and third defoliations to 

add a finer degree of resolution for temporal variations that 

might influence biomass production, such as tropical storms 

or insect defoliation. Shrubs were initially defoliated in late 

June and repeat removal of regrowth biomass was conducted 

at 6 week intervals until late October, resulting in one initial 

and three repeat defoliation periods for each year. Leaf tissue 

and new twig material was removed by hand, placed on dry 

ice, weighed, freeze dried for 48 hours, and then reweighed. 

Thorn length and density was measured on new season twig 

growth at the initial defoliation and then only on regrowth 

twig biomass at each repeat defoliation period. Leaf and 

twig biomass production, thorn length, and thorn density 

were analyzed separately by species using ANOVA and Proc 

Mixed commands in SAS version 8 (SAS Institute 1999). 

Independent variables consisted of defoliation intensity, clipping treatment (control or treated), and defoliation event. 

Dependent variables were biomass production, thorn length, 

and thorn density.

Results

Blackbrush acacia

There were no significant (p > 0.05) differences between 

years for blackbrush acacia biomass production. Total 

biomass production by repeat defoliated blackbrush acacia 

shrubs subjected to 25 percent and 50 percent defoliation did 

not differ (p > 0.06) from control shrubs (fig. 2). Blackbrush 

acacia shrubs subjected to 75 percent and 100 percent tissue 

removal produced more (p < 0.01) biomass, double the 

control production for 100 percent removal, than associated 

Figure 1. Precipitation by month as recorded in Laredo (1947-2003) and the Welhausen Research Station 

(2002, 2003), Webb County, TX.

Figure 2. Mean of total blackbrush acacia biomass summed across 

defoliation events for each treatment, no difference between 2002 

and 2003. Control plants were harvested only at end of growing 

season in October; repeat is sum of all biomass removed. Means 

within a defoliation intensity with a different letter are different (p 

< 0.05) at that defoliation level. Research conducted in 2002 and 

2003 at Welhausen Research Station, Webb County, Texas.
USDA Forest Service RMRS-P-47. 2007 109

non-defoliated control shrubs. We reject our hypothesis that 

simulated herbivory decreases biomass production in blackbrush acacia because shrubs defoliated at 25 percent and 50 

percent produced biomass amounts similar to control shrubs 

and shrubs defoliated at 75 percent and 100 percent levels 

overcompensated or produced more biomass than control 

shrubs. 

The change (percent) in blackbrush acacia regrowth 

biomass compared to initial biomass removed demonstrated 

overcompensation during the second defoliation period, but 

a decrease or under-compensation during the third and fourth 

defoliation events (fig. 3). There was no difference (p > 0.05) 

in defoliation intensity (percent removed) or year for each of 

the three repeat defoliation periods. Biomass removed at the 

second defoliation was about 20 percent more than was originally removed. Biomass production 12 and 18 weeks post 

defoliation demonstrated an 80 percent reduction in biomass 

production compared to initial biomass amounts removed. 

Blackbrush acacia did not produce new twig growth after 

defoliation events in 2002. We hypothesize the drought of 

2001, coupled with low rainfall in early 2002, was partially 

responsible for this. In 2003, twig and thorn production 

occurred in treated and control blackbrush acacia shrubs, 

except during the third defoliation period when treated plants 

did not produce any twigs or thorns (figs. 4 and 5). Thorns 

on repeat defoliated plants were twice as long as thorns on 

control shrubs at the second defoliation event and were three 

times longer on treated plants at the final defoliation event 

than control shrubs (p < 0.02, fig. 4). Thorn density in treated 

plants was greater (0.76 thorns/cm) than control plants (0.57 

thorns/cm) (p < 0.02). This appears to support our hypothesis 

that defoliation increased thorn density and length in treated 

shrubs. 

Spiny Hackberry

There was no significant difference (p > 0.05) between 

years for spiny hackberry biomass production. Spiny hackberry shrubs exhibited the opposite compensation pattern than 

blackbrush acacia. Spiny hackberry shrubs repeatedly defoliated at 25 percent produced almost double (p <0 .01) the 

amount of biomass as control shrubs (fig. 6). Biomass production in shrubs subjected to repeat defoliation at 50 percent 

produced approximately 81 percent more (p < 0.01) biomass 

production than associated controls (fig. 6). However, there 

was no difference (p > 0.09) in biomass production in repeatedly defoliated and control shrubs defoliated at 75 percent and 

100 percent levels (fig. 6). This suggests that spiny hackberry 

shrubs compensated for tissue removal at higher defoliation 

intensities and over-compensated for biomass loss at lower 

defoliation intensities, a partial validation of our hypothesis 

that simulated herbivory stimulates increased biomass production in spiny hackberry compared to non-defoliated controls. 

The change (percent) of spiny hackberry regrowth biomass 

compared to biomass removed in the initial defoliation was 

higher in 2002 compared to 2003 (fig. 7). In 2002, repeatedly defoliated shrubs produced more biomass at the second 

defoliation than was originally removed, but less biomass 

was produced relative to the original biomass following the 

second and third defoliation events. In 2003, biomass production following defoliation never exceeded the biomass that 

was originally removed, resulting in under-compensation by 

the plant.

Figure 3. Change (percent) of blackbrush acacia biomass production as a percent of the original biomass removed. Years and 

treatment are not different. Means across defoliation periods with 

a different letter are different (p < 0.05). Research conducted in 

2002 and 2003 at Welhausen Research Station, Webb County, 

Texas.

Figure 4. 2003 Blackbrush acacia thorn length. No thorn production in 2002. No repeat thorn production at 3rd defoliation period. 

Means within a defoliation period with a different letter are 

different (p < 0.02). Research conducted in 2002 and 2003 at 

Welhausen Research Station, Webb County, Texas.

Figure 5. 2003 Blackbrush acacia thorn density (number of thorns 

per cm). No repeat thorn production at 3rd defoliation period. 

Means within a defoliation period with a different letter are 

different (p < 0.02). Research conducted in 2002 and 2003 at 

Welhausen Research Station, Webb County, Texas.
110 USDA Forest Service RMRS-P-47. 2007

Repeatedly defoliated spiny hackberry shrubs did not 

produce new twig browse or thorns following defoliation in 

2002. In 2003, spiny hackberry produced new twigs, but no 

thorn production occurred in repeatedly defoliated shrubs. 

Many possible reasons exist for the lack of twig browse 

production in spiny hackberry. During summer 2001, leaf 

drop was observed in spiny hackberry. In 2002, spiny hackberry had delayed leaf bud until late May, almost 2 months 

past normal leaf bud as reported by Everitt and Drawe (1993). 

We hypothesize the drought of 2001 coupled with low early 

rainfall in 2002, was partially responsible for the lack of twig 

and thorn production.

Conclusions

The shrubs in this experiment demonstrated compensatory 

and over-compensatory biomass growth at different intensities 

of defoliation. In contrast to our original hypothesis, blackbrush acacia responded with overcompensation at high levels 

of tissue defoliation and compensation at lower levels. Spiny 

hackberry demonstrated over-compensation at low defoliation 

levels but not at high defoliation levels where compensation 

occurred. Repeat defoliation resulted in under-compensation in biomass production. This suggests that if defoliation 

occurs frequently, these shrub species may continue to undercompensate, possibly resulting in shrub death (Forbes and 

others 1995). Lack of precipitation appears to intensify the 

influence of tissue removal. 

Implications

The summer months in southern Texas, May to August, 

are characterized by high temperatures and low rainfall. Late 

summer, the third and fourth defoliation periods, are normally 

the driest in southern Texas. The low biomass production 

during this study may reflect the combined influence of 

increased number of defoliations (frequency) and drought. 

The third defoliation of spiny hackberry in 2003 had a 99 

percent reduction in biomass production (fig. 7) and during 

the 6 weeks before the third defoliation in <6 mm of precipitation was received. Forbes and others (1995) reported similar 

results concerning lack of biomass production and stem death 

following repeat defoliations of guajillo (Acacia berlandieri), 

another common south Texas shrub, during a period of low 

precipitation. Our results indicate that biomass removal and 

shrub response may be dependent upon the species of shrub, 

the intensity of biomass removal, the frequency of removal, 

and the amount of precipitation received.

Acknowledgments

This research would not have been possible without help 

from various sources. Field crews including M. Asher, E. 

Dacy, H. McIntyre, and T. Neubauer. Funding and support 

provided by Caesar Kleberg Wildlife Research Institute and 

the Jack R. and Loris J. Welhausen Experimental Station. 

Literature Cited

Asah, H. A.; Fulbright, T. E.; Land, M. L. 1987. Effects of simulated 

browsing on spiny hackberry after top removal. Texas Journal of 

Agriculture and Natural Resources. 1:16-18.

Clement, B. A.; Goff, C. M.; Forbes, T. D. A. 1998. Toxic amines and 

alkaloids from Acacia rigidula. Phytochemistry. 49:1377-1380.

Cooper, S. M.; Owen-Smith, N. 1986. Effects of plant spinescence 

on large mammalian herbivores. Oecologia. 68:446-455.

Everitt, J. H.; Drawe, D. L. 1993. Trees, shrubs, and cacti of south 

Texas. Lubbock, TX: Texas Tech University Press. 213 p.

Forbes, T. D. A.; Pemberton, I. J.; Smith, G. R.; Hensarling, C. 

M. 1995. Seasonal variation of two phenolic amines in Acacia 

berlandieri. Journal of Arid Environments. 30:403-415.

Graham, M. W. 1982. Diets of white-tailed deer and nilgai antelope 

in South Texas. Kingsville: Texas A&M University-Kingsville. 

122 p. Thesis.

McNaughton, S. J. 1983. Compensatory plant growth as a response 

to herbivory. Oikos. 40:329-326.

Figure 7. Change (percent) of spiny hackberry biomass production 

as a percent of the original biomass removed. Treatments not 

different; means across defoliation periods with a different letter 

are different (p < 0.05). Research conducted in 2002 and 2003 at 

Welhausen Research Station, Webb County, Texas.

Figure 6. Mean of total spiny hackberry biomass production summed 

across defoliation events for each treatment, no difference 

between 2002 and 2003. Control plants were harvested only at 

end of growing season in October; repeat is sum of all biomass 

removed. Means within a defoliation intensity with a different 

letter are different (p < 0.05) at that defoliation level. Research 

conducted in 2002 and 2003 at Welhausen Research Station, 

Webb County, Texas.
USDA Forest Service RMRS-P-47. 2007 111

Rohner, C.; Ward, D. 1997. Chemical and mechanical defense against 

herbivory in two sympatric species of desert Acacia. Journal of 

Vegetation Science. 8:717-726.

SAS Institute. 1999. SAS/STAT user’s guide, version 8. Cary, NC: 

SAS Institute Inc. 3089 p.

Schindler, J. 2000. Role of spinescence and secondary compounds in 

white-tailed deer preference of shrubs in burned and mowed areas 

in South Texas. Kingsville: Texas A&M University-Kingsville. 

171 p. Thesis.

Schindler, J. R.; Fulbright, T. E.; Forbes, T. D. A. 2003. Influence of 

thorns and tannins on white-tailed deer browsing after mowing. 

Journal of Arid Environments. 55:361-377.

Schindler, J. R.; Fulbright, T. E.; Forbes, T. D. A. 2004. Shrub 

regrowth, antiherbivore defenses, and nutritional value following 

fire. Journal of Range Management. 57:178-186.

Soil Conservation Service. 1985. Soil survey of Webb County, Texas. 

Temple, TX: U.S. Department of Agriculture, Soil Conservation 

Service.

Varner, L. W.; Blankenship, L. H. 1987. Southern Texas Shrubs—

nutritive value and utilization by herbivores. In: Provenza, F. D.; 

Flinders, J. T.; McArthur, E. D., comps. Proceedings—symposium 

on plant herbivore interactions; 1985 August 7-9; Snowbird, 

UT. Gen. Tech. Rep. INT-222. Ogden, UT: U.S. Department of 

Agriculture, Forest Service, Intermountain Research Station: 

108-112.

The Authors

1 Graduate Student, Caesar Kleberg Wildlife Research Institute, 

Texas A&M University-Kingsville, Kingsville, TX. 2 Meadow’s Professor, Caesar Kleberg Wildlife Research Institute, 

Texas A&M University-Kingsville, Kingsville, TX. 

kftef00@tamuk.edu
112 USDA Forest Service RMRS-P-47. 2007

Introduction

Kyle Canyon of the Spring Mountains is a popular recreational area for nature-loving tourists and local residents in 

southern Nevada (Lei 2004). Due to rapid population growth 

and use of off-road motor vehicles in recent years, there has 

been a considerable increase in anthropogenic (recreational) 

activities, and the landscape disturbance has become increasingly noticeable (Davidson and Fox 1974). A complex network 

of roads and trails, including human foot, bicycle, and motor 

vehicle traffic is evident to casual observers and appears to 

have a long-term adverse effect on soil properties in blackbrush (Coleogyne ramosissima Torr.) shrubland (Lei 2003).

Human activities in Kyle Canyon include hiking and 

biking (bicycles and mountain bikes), while off-road vehicle 

activities include both motor vehicle trails and parking lots. 

These recreational activities are disturbance agents that cause 

soil disturbance through disruption and compaction of surface 

soil (Lei 2004). If disturbed areas were compared to adjacent 

undisturbed areas, an increase in the bulk density or degree of 

compaction of the soil in disturbed areas would be expected 

in the Mojave Desert of southern California (Davidson and 

Fox 1974). The greatest soil disturbance occurs in “pit areas” 

where motor vehicles are parked at the beginning of human 

hiking trails (Davidson and Fox 1974).

Human trampling, biking, and off-road motor vehicle 

traffic adversely affect soil properties by compacting the soil 

(Wilshire and Nakata 1976). Soil compaction can promote 

water (fluvial) erosion at the original site (Nakata and others 

1976) and can reduce soil porosity, infiltration capacity, and 

hydraulic resistance to overland flow (Iverson and others 

1981). Fluvial erosion can cause “head cutting” as erosion 

channels progress into adjacent areas.

Severely compacted soils reduce porosity, which in turn 

decreases water infiltration into the soil in southern Nevada 

(Marble 1985). Compaction through animal, human, or vehicle 

traffic can increase soil bulk density due to applied pressure 

or loading (Iverson and others 1981). Bulk density, which 

increases with compaction, is mainly a function of amount of 

void and the density of soil minerals. The degree of compaction can influence soil erosion dynamics and soil moisture 

status (Marble 1985). Webb and Wilshire (1980) suggest that 

severely compacted soils may require at least a century for 

natural recovery in southern Nevada.

Soil compaction studies have been documented in blackbrush (Coleogyne ramosissima Torr.) shrubland in southern 

Nevada (Lei 2003, 2004). Nevertheless, soil responses to 

various types of compaction and landforms in blackbrush 

shrublands remain poorly understood. From casual observations, extensive recreational activities removed the vegetation 

in trails and parking lots, leaving more soil exposed and 

making it highly susceptible to soil erosion than adjacent 

undisturbed areas. Two hypotheses were formulated prior 

to data collection. First, soil properties would be different 

between disturbed (compacted) and adjacent undisturbed 

(reference) areas, as well as between motor vehicle-compacted 

and human-trampled soils. Second, there would be interactive effects of disturbance type and landform on selected soil 

moisture characteristics. Interactions of disturbance type and 

landform may yield a greater effect than examining disturbance type or landform alone. These two hypotheses were 

tested by a combination of field and laboratory measurements 

Soil Responses to Human Recreational Activities in a 

Blackbrush (Coleogyne ramosissima Torr.) Shrubland

Abstract: Soil responses to human trampling, biking, and off-road motor vehicle traffic 

were quantitatively investigated in a blackbrush (Coleogyne ramosissima Torr.) shrubland 

in Kyle Canyon of the Spring Mountains in southern Nevada. Soil compaction, bulk 

density, and temperature increased significantly, while soil moisture, organic matter, and 

percent pore space (macropore) decreased in disturbed (compacted) areas compared to 

adjacent undisturbed areas. Among disturbed soils, motor vehicle trails and parking lots 

had a significantly greater compaction, higher bulk density, and a lower percent pore space 

compared to human hiking/biking trails. Water infiltration and area of water spread (surface 

water runoff) were an interactive function of disturbance type and landform (terrace and 

slope). When examining disturbance type and landform factors independently, significant 

differences were detected in all of the measured soil moisture characteristics. Results of 

this study revealed that soil compaction led to increased soil bulk density and surface-water 

runoff, along with decreased macropore and water infiltration into the soil in Kyle Canyon of 

southern Nevada.

Simon A. Lei1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 113

of soil properties and soil moisture variables with appropriate 

statistical analyses.

Methods

Study Site

Southern Nevada, within the Basin and Range geological 

province, is a region characterized by annual weather extremes 

and a sparse vegetation cover (Brittingham and Walker 2000). 

The majority of annual precipitation occurs between October 

and April as frontal systems, with the remainder precipitation occurring in the summer as convectional thunderstorms 

(Smith and others 1995). Summer rains occur as brief, intense, 

and localized events that are highly variable in both time and 

space. Prolonged mountain thunderstorms in summer seasons 

can cause flash flooding in canyons and nearby washes. Winter 

rainfalls, on the contrary, are mild and widespread, and can 

last up to several days.

Field studies were conducted during fall 2000 in Kyle 

Canyon (36 °01'N, 115 °09'W), which is located on the eastern 

slope of the Spring Mountains. The blackbrush shrubland, 

ranging from 1,250 to 1,600 m in elevation, is dominated 

by a closely-spaced matrix of blackbrush shrubs with a scattered distribution of other shrub species. Common associated 

woody species that occur in this zone include Joshua tree 

(Yucca brevifolia), Nevada ephedra (Ephedra nevadensis), 

spiny menodora (Menodora spinescens), turpentine bush 

(Thamnosma montana), and Anderson lycium (Lycium andersonii). The herbaceous species present are mostly members 

of the Asteraceae, Brassicaceae, Fabaceae, and Poaceae families.

The terrain is exposed to abundant solid rocks on the soil 

surface. Bajadas, rocky slopes, and alluvial fans are dissected 

by numerous dry wash (intermittent) channels. Soil are calcareous, poorly developed (without distinct soil horizons), and 

composed primarily of weathered granite and limestone 

bedrock. Multiple caliche layers are found in the subsoil. 

Organic decomposition and soil formation are slow due to the 

arid nature of the region.

Field Design and Sampling

Three anthropogenic disturbance areas—human hiking/

biking trails, motor vehicle trails, and parking lots—were 

selected, and were completely interspersed within a single 

area in Kyle Canyon. Within each type of disturbance, 60 soil 

samples from three transects were randomly selected, and 

were excavated 10 cm in diameter to depth of 15 cm. Soil 

samples among three transects in each type of disturbance 

were pooled. Intervals within each transect were randomly 

chosen to avoid biased sampling. Adjacent reference soils 

were sampled, with no clear evidence of compaction or other 

types of soil disturbance. Because of the close proximity 

among the 3 disturbance areas, the same set of reference soils 

was paired with soil samples in each type of disturbance. Soil 

samples were sieved through a 2-mm mesh to remove surface 

litter, plant roots, and rocks > 2 mm in diameter. All tests were 

performed on < 2mm soils oven-dried at 65°C for 72 h. Soil 

samples were measured for bulk density, percent pore space, 

gravimetric moisture, organic matter, and pH.

Fresh soil cores of known volume were carefully removed 

from the field and were oven-dried at 65°C until they reached 

a constant mass. Soil bulk density was obtained by dividing 

mass by volume. Soil compaction was measured in the field 

using a penetrometer, which was inserted into the soil after 

removing stony surface pavements. The penetrometer readings were taken at the point where the cone base reached 

the soil surface (point depth = 3.8 cm). Average pore space 

(macropore) was determined using the equation: pore space 

(%) = 100 - (Db

/Dp * 100), where Db is bulk density of the soil 

and Dp

 is average particle density, usually about 2.65 g cc-1

(Hausenbuiller 1972; Davidson and Fox 1974). Soil moisture 

content was determined gravimetrically by computing differences between fresh and oven-dried mass. Soil temperature 

readings were recorded in the field at 15 cm below the soil 

surface using a metallic soil thermometer. Soil organic matter 

was acquired by mass loss on ignition at 550°C for 4 h. Soil 

pH was determined by preparing a paste consisting of a ratio 

of 1:1 dry soil:distilled water mixture and by measuring with 

an electrode pH meter.

Soil sampling was also stratified by landform, which was 

classified into terrace and slope. Within each type of landform, 

60 plots were randomly selected to determine each of the six 

soil moisture variables. Water infiltration rates were measured 

by using PVC pipes, 5.5 cm in diameter and 9.5 cm tall. These 

pipes were open at both ends and were gently tamped into the 

compacted and reference soils to a depth of 2 cm to prevent 

leakage, and then 50 mL of water was poured into the pipes. 

Time taken for the water to soak into the soil was recorded 

with a stop-watch.

Exactly 1.5 L of water, acting as an artificial rain, was 

manually poured through a perforated 13-cm disk, with perforations evenly spaced on a 0.1-cm grid. The disk was placed 

1.0 m aboveground. Total delivery time was 1 min for the 

water to be dispensed on the soil surface, simulating precipitation at a cloudburst level (Brotherson and Rushford 1983). A 

sudden heavy precipitation is significant due to its impact on 

surface-water runoff and fluvial erosion. Depth of water penetration (water movement through the soil) was measured once 

the water had disappeared completely into the soil surface.

Surface-water runoff was measured by recording the 

downslope and across-slope spread of water that was artificially rained onto study sites (Brotherson and Rushforth 

1983). The area of water spread (surface-water runoff) was 

computed using the formula for the area of an ellipse (πab), 

where a and b are radii of the ellipse (Larson and others 1994). 

Since surface-water runoff was not a perfect elliptical shape, 

measured areas were likely to be an overestimation.

Soil movement was assessed by estimating the amount of 

soil moved through fluvial erosion during a measured (simulated) rain. The following index was used: 1 = no appreciable 

movement; 2 = moderate movement, up to 10 percent of the 
114 USDA Forest Service RMRS-P-47. 2007

soil volume displaced; and 3 = heavy movement, between 

10 percent and 20 percent of the soil volume displaced 

(Brotherson and Rushforth 1983).

Statistical Analyses

One-way analysis of variance (ANOVA; Analytical 

Software 1994), followed by Tukey’s multiple comparison 

test was used to compare differences in soil properties and to 

compare site means when a significant disturbance effect was 

detected, respectively. Two-way ANOVA (Analytical Software 

1994) was computed on soil moisture status, with disturbance 

type (control, human hiking/biking trail, motor vehicle trail 

and parking lot) and landform (terrace and slope) as main 

effects. Statistical significance was tested at P < 0.05.

Results

Soil compaction, bulk density, and soil temperature were 

significantly greater (P < 0.001; table 1) in disturbed areas 

compared to adjacent undisturbed areas. Gravimetric soil 

moisture, organic matter, and macropore were significantly 

lower (P < 0.001; table 1) in disturbed than undisturbed areas. 

Among disturbed areas, motor vehicle-compacted (trails 

and parking lots) soils had a significantly greater compaction, higher bulk density, and lower macropore compared to 

hiking/biking soils (P < 0.01; table 1). In general, parking lots 

were more compacted, but differences were not statistically 

significant (P > 0.05) when compared to motor vehicle trails. 

Nevertheless, soil pH did not differ significantly (P > 0.05; 

table 1) between compacted and non-compacted soils.

In evaluating soil moisture status, significant differences were detected between disturbance type and all of the 

measured soil moisture characteristics, as well as between 

landform and all moisture characteristics (P < 0.05; tables 

2 and 3). Motor vehicle-compacted soils had a significantly 

lower water infiltration and water movement through the soil 

and had a significantly greater downslope and across-slope 

water spread, and surface-water runoff than human-trampled/

biking soils, which in turn differed significantly from adjacent 

reference soils (P < 0.01; tables 2 and 3). Between the two 

types of motor vehicle-compacted soils, water infiltration was 

significantly lower, while downslope and across-slope water 

spread, surface-water runoff, and fluvial erosion were significantly greater on parking lots than on motor vehicle trails (P < 

0.05; tables 2 and 3).

Between the two types of landform, water infiltration and 

water movement through the soil increased, while downslope 

and across-slope water spread, as well as surface-water runoff 

decreased significantly at terrace than at slope sites (P < 0.05; 

tables 2 and 3). Moreover, significant interactions (P < 0.01; 

table 3) were detected between disturbance type and landform 

for water infiltration and area of water spread (surface-water 

runoff).

Discussion

Concentrated use of human hiking/biking trails, along with 

off-road use of all-terrain motor vehicles, severely compacted 

soils and triggered a chain of events that significantly altered a 

number of soil properties in the blackbrush shrubland in Kyle 

Canyon of southern Nevada. With greater compaction from 

off-road motor vehicles, soil particles were pressed closer 

together and the bulk density was increased significantly. Soil 

compaction has been defined as the physical packing together 

of soil particles by instantaneous forces exerted at the soil 

surface (Lei 2004). Soil compaction occurs when the weight 

of humans, bikes, and motor vehicles pushes the soil particles 

together, thus substantially reducing the size of macropores 

(Smith and Smith 2001).

In this study, a combination of increased soil compaction, 

bulk density, and decreased macropore significantly reduced 

soil moisture content, water infiltration, and water movement 

through the soil in disturbed compared to adjacent undisturbed areas. Such combination also reduces soil permeability, 

resulting in a significantly greater surface-water runoff and 

fluvial erosion in compacted than non-compacted (reference) 

soils. The increase in bulk density of disturbed soils, along 

with the resulting decrease in macropore, probably decreases 

the amount of water that the soil can hold and the rate at which 

Table 1. Soil properties (n = 60 per characteristic per disturbance type) of disturbed (human hiking/

biking trails, motor vehicle trails, and parking lots) and adjacent undisturbed (reference) areas in 

the blackbrush shrubland. Pore space, moisture content, and organic matter are expressed in 

percentages. Soil temperatures were measured at 15-cm depth. Mean values in rows followed by 

different letters are significantly different at P < 0.05 using one-way ANOVA and post-hoc Tukey 

multiple comparison test.

Disturbance type

Reference Hiking/biking Motor vehicle trail Parking

Compaction (kg cm-2) 5.9 a 6.6 b 7.0 c 7.2 c

Bulk density (g cm-3) 1.28 a 1.42 b 1.51 c 1.53 c

Pore space (%) 51.7 a 46.4 b 43.0 c 42.3 c

Moisture (%) 2.91 a 1.02 b 0.70 c 0.61 c

Temperature (°C) 24.7 a 27.1 ab 28.7 b 28.8 b

Organic matter (%) 2.45 a 0.81 b 0.30 c 0.20 c

pH 7.7 a 7.6 a 7.6 a 7.6 a
USDA Forest Service RMRS-P-47. 2007 115

water can flow through the soil (Yang and DeJong 1971). 

The increase in bulk density also reduces the permeability of 

the soil so that surface-water runoff is greater (Kubota and 

Williams 1967). Consequently, there is a substantial reduction 

of water stored in the soil and water available for plant growth 

in the Mojave Desert of southern California (Davidson and 

Fox 1974).

On severely compacted soils, water is trapped at the soil 

surface rather than reaching deeper into the subsoil. With less 

moisture content in subsoil due to compaction, temperatures 

of subsoil were expected to be higher in this study. Soil moisture content and temperature are inversely related; drier soils 

tend to be warmer than moist soils. Moisture tends to increase 

the specific heat of the soil. When soils are drier because of 

reduced water infiltration and depth of water penetration, the 

specific heat of the soil would be lower, so that the same insolation rate would cause higher soil temperatures. There would 

be less evaporation from the soil surface, so that the cooling 

caused by the latent heat of evaporation would be less. In this 

study, the lack of shading contributed to increased soil temperature due to the removal of vegetation and plant litter.

Moreover, moisture-holding capacity was also affected by 

organic matter content of the soil. Organic matter decreases 

bulk density of the soil because it is lighter (less dense) than 

a corresponding volume of mineral soil (Barbour and others 

1999). In this study, severely disturbed areas, such as motor 

vehicle trails and parking lots, were completely devoid of vegetation, organic litter, and debris because of the change in soil 

properties and because the vegetation was crushed or smashed. 

Severely compacted soils through extensive recreational activities resembled pavement, thus unable to retain moisture and 

develop new organic layer to sustain any plant growth.

Intensity of disturbance and size of pit area depend on 

number of motor vehicles parked, duration of parking, as 

well as number of times people return during the year and 

from year to year in the Mojave Desert of southern California 

(Davidson and Fox 1974). Anthropogenic activities including 

hiking, biking, and off-road motor vehicle traffic all 

Table 2. Soil moisture characteristics (n = 60 per treatment per characteristic) of disturbed (human hiking/

biking trails, motor vehicle trails, and parking lots) and adjacent undisturbed areas in the blackbrush 

shrubland.

Disturbance type

Reference Hiking/biking Motor vehicle trail Parking

Infiltration (sec.)

Terrace 182.3 365.9 420.8 432.1

Slope 210.2 408.6 492.7 498.5

Depth of water

Penetration (cm)

Terrace 3.8 3.2 2.3 2.4

Slope 3.3 2.5 1.7 1.8

Downslope spread (cm)

Terrace 77.2 129.4 179.8 188.1

Slope 89.8 162.4 213.1 224.9

Across slope spread (cm)

Terrace 60.1 127.2 164.9 189.5

Slope 75.4 157.7 215.4 227.8

Area of spread (cm2)

Terrace 3642.2 11996.5 23274.5 25518.3

Slope 5315.2 17504.5 35627.4 36299.1

Soil movement

Terrace 1.2 1.3 1.3 1.4

Slope 1.3 1.4 1.4 1.5

Table 3. Results of two-way ANOVA showing effects of disturbance type, landform, and their interactions on various 

soil moisture characteristics. df = 1 for landform; df = 3 for disturbance type and for disturbance type * landform 

combination.

Disturbance type x 

Disturbance type Geomorphic surface geomorphic surface

F P F P F P

Water infiltration 2567.69 <0.0001 447.27 <0.0001 637.88 <0.0001

Depth of water penetration 302.55 <0.0001 213.16 <0.0001 1.21 0.3417

Downslope water spread 218.84 <0.0001 47.07 <0.0001 2.61 0.0911

Across slope water spread 139.10 <0.0001 51.88 <0.0001 0.59 0.6385

Area of water spread 207.70 < 0.0001 64.07 < 0.0001 5.77 0.0092

Soil movement 3.67 0.0385 5.51 0.0342 0.34 0.7146
116 USDA Forest Service RMRS-P-47. 2007

contributed to soil compaction, although the degree of 

compaction and disturbance varied significantly in this study. 

Water infiltrability and surface-water runoff were an interactive function of disturbance type and landform. The greatest 

surface-water runoff and the least water infiltrability occurred 

on motor vehicle-compacted soils at slope sites than human 

hiking/biking trails at terrace sites in this study.

Because summer monsoonal thunderstorms are highly 

localized and intense in southern Nevada, much of the rainfall 

cannot be absorbed by the soil, so that the excess running water 

rapidly flows across the compacted soil surface during and 

shortly after major storm events, resulting in fluvial erosion. 

With increased surface-water runoff and decreased water 

infiltration, shallower penetrations of water into compacted 

soils occur at slope than at terrace sites. Substantially greater 

surface-water runoff and fluvial erosion would be expected 

on compacted soils at slope sites compared to non-compacted 

soils at terrace sites if cloudbursts occurred with longer duration, higher frequency, and greater intensity (Lei 2000).

Ecological Implications

A combination of active hiking and biking trails, as well 

as off-road motor vehicle driving and parking have caused 

significant soil property changes in the blackbrush shrubland in Kyle Canyon of southern Nevada. Soil compaction, 

which adversely impacts various soil attributes, is an aspect 

of land degradation. From a distance, a complex network of 

roads and trails is evident. Anthropogenic disturbances, such 

as human foot, bicycle, and motor vehicular traffic can scuff 

away the protective organic layer, halting the development of 

a new organic layer on the soil surface. Impact of raindrops 

increases on compacted soils as organic litter and debris are 

removed. Both terrace and slope sites are vulnerable to catastrophic fluvial erosion during and shortly after major storm 

events. Despite growing evidence that hiking, biking, and 

relentless motor vehicle use is very damaging to fragile desert 

soils, the public continues to use Kyle Canyon and other areas 

of the Mojave Desert for recreational activities.

Acknowledgments

The author gratefully acknowledge Steven Lei, David 

Valenzuela, and Shevaun Valenzuela for valuable field and 

laboratory assistance. Steven Lei assisted with statistical 

analyses. Critical review provided by David Charlet greatly 

improved the manuscript. Department of Biology at the 

Community College of Southern Nevada (CCSN) provided 

logistical support.

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program for microcomputers. St. Paul, MN: Analytical Software. 

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Publishing Company, Inc.

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recruitment by Mojave Desert shrubs. Western North American 

Naturalist. 60: 374-383.

Brotherson, J. D.; Rushforth, S. R. 1983. Influence of cryptogamic 

crusts on moisture relationships of soils in Navajo National 

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compaction and porosity on germination, establishment, and 

yield of barley and globe beet. Journal of Agricultural Science. 

68: 227-233.

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edition. Lexington, MA: D.C., Heath and Company. 1256 p.

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attributes in a Larrea-dominated shrubland. Western North 

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mammal trampling in a blackbrush (Coleogyne ramosissima) 

shrubland. Southern California Academy of Sciences. 102: 

119-129.

Lei, S. A. 2004. Soil Compaction from human trampling, biking 

and off-road motor vehicle activity in a blackbrush (Coleogyne 

ramosissima) shrubland. Western North American Naturalist. 64: 

125-130.

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land damaged by off-road vehicles in the Lake Mead Recreational 

Area. Las Vegas, NV: Cooperative National Park Resources 

Studies Unit, University of Nevada, Las Vegas. 71 p.

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644-648.

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Environments. 29: 339-351.

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edition. San Francisco, CA: The Benjamin/Cummings Publishing 

Company, Inc. 771 p.

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in a Mojave Desert ghost town, Nevada, U.S.A. Journal of Arid 

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211-220.

The Author

1 Statistics and Research Methods Instructor, Department of 

Educational Pyschology, University of Nevada, Las Vegas, NV. 

liesa@unlv.nevada.edu
USDA Forest Service RMRS-P-47. 2007 117

Introduction

Alxa desert steppe is one of the severely degraded rangelands in the arid and semiarid areas in the northwestern China. 

Grazing has been the most common management practice in 

this region. In recent decades, this region has become one of 

the major sources of sandstorms in the northwestern China 

(Wang and others 2004) due to overgrazing and population 

growth (Fu and Chen 2003). Overgrazing may induce dramatic 

changes in vegetation composition and in soil nutrient cycling 

in native rangelands (Fu and Chen 2003). The degree of rangeland degradation can be measured by declines in soil fertility 

(Fang and Peng 1997).

Zygophyllum xanthoxylum and Ammopiptanthus monglicus, the two dominant shrub species belonging to the 

family of Zygophyllaceae and Leguminosae, respectively, 

are widely distributed in the Alxa desert steppe as the main 

forage species for camels, sheep, and goats (Cheng and Zhang 

2001). These shrubs play an important role in protecting this 

area from wind erosion (Charley and West 1975; Garner and 

Steinberger 1989). These shrubs may also affect the distribution and biochemical cycle of soil nutrients (Halvorson and 

others 1995), resulting in the formation of islands of fertility 

around shrubs (Schlesinger 1996).

The development of islands of fertility may be important 

strategies and mechanisms for shrubs to use and recycle soil 

nutrients effectively. Thus, shrubs are important for maintaining the stability of arid ecosystems (Martinez-Meza and 

Whitford 1996). Information about shrub-soil interaction and 

shrub-induced soil chemical changes is vital for a better understanding of the ecological processes in Alxa desert steppe. 

The objective of this study was to investigate the effects of 

two prominent shrub species on soil nutrient accumulation 

and distribution. The study attempted to quantify the magnitudes of element enrichment in SOC, total N, and total P under 

shrub canopy as compared to the inter-shrub space and to test 

if there are any differences in enrichment ratios in SOC, total 

N, and total P between the two shrub communities.

Materials and Methods

Study Site

The study was conducted in a desert steppe of Alxa 

(105°35′ E, 39°08′ N; elevation 1360m), western Inner 

Mongolia, China. The climate is arid with mean annual 

precipitation of 105 mm and nearly 70 percent of rainfall 

occurs between July and September. Mean annual evaporation capacity is 3,000 to 4,100 mm. Mean annual temperature 

is about 8°C. Mean annual wind velocity ranges from 3.44 

to 4.74 ms-1. The brown desert soil in this region is highly 

Influence of Shrubs on Soil Chemical Properties in Alxa 

Desert Steppe, China

Abstract: Alxa desert steppe is one of severely the degraded rangelands in the Northwest 

China. Shrubs, as the dominant life form in the desert steppe, play an important role in 

protecting this region from further desertification. Chemical properties of three soil layers (0 

to 10, 10 to 20 and 20 to 30 cm) at three locations (the clump center [A], in the periphery 

of shrub canopies [B], and the inter-shrub space [C], at least one m away from the edge 

of shrub canopies) were investigated in two prominent shrub communities (Zygophyllum 

xanthoxylum, Ammopiptanthus monglicus) in Alxa desert steppe. The results showed that: 

(1) soils in three layers at the clump center exhibited significantly higher contents of organic 

carbon (SOC), total N, total P, and lower pH value compared to the inter-shrub space. Soils in 

the 0 to 10-cm and 10 to 20-cm depths under periphery of shrub canopy showed significantly 

higher contents of SOC and total N, and slight, but significantly lower, pH value compared to 

the same soil layers in the inter-shrub space. However, there was no significant difference 

in total P in three soil layers between shrub periphery and inter-shrub space; (2) the soil 

enrichment ratios of SOC, total N, and total P at clump center were significantly higher, 

while ratio for pH significantly lower compared to the shrub periphery; and (3) SOC and 

total P contents at all locations around Z. xanthoxylum were higher, while total N and pH 

values lower compared to soils around A. monglicus. The enrichment ratios of SOC, total 

N, and total P at the same location were not significantly different between Z. xanthoxylum

and A. monglicus. The litter-fall seems to influence the soil chemical properties at clump 

center, shrub periphery, and inter-shrub open space, resulting in “fertile island” under shrub 

canopies. This study shows that shrubs play a vital role in accumulating SOC and nutrients 

and maintaining soil fertility in Alxa desert steppe.

Hua Fu1; Shifang Pei1

Yaming Chen2

Changgui Wan3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
118 USDA Forest Service RMRS-P-47. 2007

susceptible to wind erosion due to its coarse texture and loose 

structure characteristics according to the Alxa soil classification system (Plan Committee of Alxa League 1991).

Sampling

Z. xanthoxylum and A. monglicus are two dominant woody 

shrub species in the study area. In August of 2003, six individuals of Z. xanthoxylum and A. monglicus, respectively, 

were randomly selected and the morphological traits of the 

plants were measured (table 1). Soil samples were taken from 

three depths (0 to 10 cm, 10 to 20 cm, 20 to 30 cm) in each 

of the three locations around an individual shrub plant. The 

three locations were: center of the shrub clump (A), under the 

periphery of the shrub canopy (B), and the inter-shrub space 

(at least one meter away from the edge of shrub canopy) (C). 

For each individual plant, four soil samples each at one direction were taken and the samples were then mixed for lab 

analysis.

Laboratory Analyses

Soil samples were air-dried, sieved to pass a 2-mm screen 

to remove plant materials and other debris, and analyzed for 

pH (1:1 distilled water). The samples were ground and then 

sieved to pass a 0.5-mm screen and analyzed for organic 

carbon (oxidization with potassium dichromate in presence 

of H2SO4, heated at 180°C for 5 minutes), total nitrogen 

(Kjeldahl method), and total phosphorus (by spectrophotometer after NaOH digestion) (Institute of Soil Sciences, Chinese 

Academy of Sciences 1978).

Data Analyses

The enrichment ratio (E) was used to evaluate the spatial 

pattern of soil element distribution (Wezel and others 2000), 

where EA = A/C, EB = B/C. The more E differs from 1, the 

more soil elements in A or B deviate from C. E > 1 means a 

higher concentration for the elements analyzed in either A or 

B than in C. An E value less than 1 for pH value means a more 

acid soil environment in either A or B than in C.

Data were analyzed using SPSS 11 package for significance 

at P ≤ 0.05. Significant differences in mean soil properties 

analyzed in the three locations and in the three depths in the 

same sampling location were determined by analyzing replicate means (n = 6) with a one-way analysis variance (ANOVA) 

and least significance difference tests (LSD). The figures of 

results showed as means ± S.E.

Results

General Trends in Soil Chemical 

Properties Around Shrubs

The following data are averages around the two shrub 

communities. SOC, total N, and total P generally showed 

a declining trend from the canopy center to the inter-shrub 

space in the 0 to 10-cm, 10 to 20-cm, and 20 to 30-cm soil 

profiles, respectively (table 2, fig. 1). SOC and total N were 

significantly higher in 0 to 10-cm and 10 to 20-cm soil layers 

under periphery of the shrub canopy compared to the adjacent inter-shrub open space. The means of SOC and total N in 

0 to 10-cm soils under the canopy periphery increased by 58 

and 60 percent respectively, and total P was not significantly 

different (P = 0.345), but pH values decreased 0.30 units 

(P < 0.05) compared to the inter-shrub space. SOC, total N, 

and total P in 0 to 10-cm soils in the clump center were higher 

by 164 percent, 117 percent, and 19 percent respectively, but 

pH values lower by 0.70 units (P < 0.05) than in soils in the 

inter-shrub space. SOC, total N, and total P in 10 to 20-cm 

soil layers at the clump center increased by 103 percent, 

96 percent, and 20 percent respectively, while pH decreased 

0.40 units (P < 0.05) compared to the inter-shrub space. There 

were significant differences in SOC and total N in 20 to 30-cm 

soil layers between clump center and the inter-shrub space. 

However, SOC, total N, and total P in 20 to 30-cm soil layers 

between canopy periphery and the inter-shrub space were not 

different.

The enrichment ratios of soil organic C, total N, and total P 

at the clump center were significantly higher, while pH values 

significantly lower than the canopy periphery with exception 

of total P at 10 to 20-cm soil layers. Our data showed that 

contents and enrichment ratios of SOC and total N decreased 

with the increase of depth.

Soil Chemical Properties as 

Related to Shrub Species

Soil chemical properties were somewhat related to shrub 

species (fig. 1). SOC and total P in the topsoil layers under the 

canopy around Z. xanthoxylum were higher, while total N and 

pH value lower than those around A. monglicus. The enrichment ratios of SOC, total N, and total P at the same soil depths 

were not significantly different between Z. xanthoxylum and 

A. monglicus (table 3).

Table 1. Morphological traits of shrubs (n = 6).

Height Crown diameter Biomass of shrub Height of mound

Item Family cm cm g cm

Z. xanthoxylum Zygophyllaceae, shrub 59~87.5 129~202.5 221.63~594.06 19~25

A. monglicus Leguminosae, shrub 61.05~84 178~280.5 425.35~862.99 31~60
USDA Forest Service RMRS-P-47. 2007 119

Correlation Between Organic C, Total N, and 

Total P at the Various Locations

Contents of elements were linearly correlated between 

clump center and canopy periphery (table 4). The highest 

values of coefficient r were found between A and B for SOC 

(r = 0.705**), total N (r = 0.851**), and total P (r = 0.974**). 

The correlation coefficients between canopy periphery (B) and 

clump center (A) were higher than between canopy periphery 

and the inter-shrub space (C). No significant correlations were 

observed between total N and SOC in inter-shrub space, nor 

were there significant correlations between total N and total P 

in A, B, and C.

Table 2. Soil chemical properties and enrichment ratios for two shrub communities (EA and EB, n = 6). A: clump 

center, B: canopy periphery, C: inter-shrub space.

Value Enrichment ratio t-test 1

Depth Variable Unit Location Mean ± S. E. EA (A/C) EB (B/C) P

0-10 cm Organic C g kg -1 A 4.834±0.27a

B 2.893±0.21b

C 1.831±0.12c 2.74 1.64 <0.001

Total N g kg -1 A 0.496±0.01a

B 0.366±0.02b

C 0.228±0.01c 2.20 1.63 <0.001

Total P mg·kg -1 A 0.266±0.01a

B 0.243±0.01ab

C 0.223±0.02b 1.21 1.10 0.009

pH A 8.68±0.10a

B 9.08±0.08b

C 9.38±0.04c 0.93 0.97 <0.001

10-20 cm Organic C g kg -1 A 3.338±0.17a

B 2.262±0.12b

C 1.727±0.13c 2.03 1.30 0.002

Total N g kg -1 A 0.397±0.02a

B 0.285±0.02b

C 0.202±0.01c 1.96 1.43 <0.001

Total P mg·kg -1 A 0.246±0.01a

B 0.228±0.01a

C 0.209±0.01a 1.20 1.09 0.132

pH A 8.99±0.08a

B 9.25±0.05b

C 9.42±0.06b 0.95 0.99 0.001

20-30 cm Organic C g kg -1 A 2.749±0.23a

B 1.808±0.07b

C 1.660±0.10b 1.67 1.11 0.002

Total N g kg -1 A 0.338±0.01a

B 0.259±0.01b

C 0.184±0.01b 1.85 1.40 <0.001

Total P mg·kg -1 A 0.228±0.01a

B 0.214±0.01a

C 0.202±0.01a 1.14 1.06 0.028

pH A 9.02±0.11a

B 9.26±0.03b 0.96 0.99 0.050

C 9.39±0.04b

1 t-test for paired samples for enrichment ratios.

Means followed by the same letters are not different at P = 0.05 level.

Discussion

The concentrations of nutrients in soils under shrub canopies tend to be greater than in the shrub interspace, thus 

forming “islands of fertility.” This phenomenon has been well 

documented in arid and semiarid ecosystems (Garner and 

Steinbergar 1989; Schlesinger and others 1990; Halvorson 

and others 1995; Whitford and others 1997; Wezel and 

others 2000; Su and others 2004). The increased spatial 

heterogeneity of soil resources may be a useful indicator of 

desertification in arid and semi-arid ecosystems (Schlesinger 

and others 1990). Our results show that fertile islands 

become relatively stable features in this landscape. In these 
120 USDA Forest Service RMRS-P-47. 2007

Figure 1. Soil chemical properties as related to shrub 

species in Alxa desert steppe. A: in the center 

of clump, B: under shrub canopies, C: the intershrub space. Means at the same soil depth within 

a species not followed by the same lowercase 

letters differ (P < 0.05, LSD multiple range tests). 

Means at the same location and same soil depth 

not followed by the same uppercase letters differ 

(between species difference, P < 0.05, t-tests).

Table 3. Enrichment ratios of soil nutrients for two shrub species in Alxa desert steppe.

Z. xanthoxylum A. monglicus t-test for E

 EA EB t-test1/ EA EB t-test1/ P value (between species)

Variable Depth A/C B/C P value A/C B/C p (EA) (EB)

Organic C

0-10 cm 2.81a 1.77a 0.001 2.66a 1.51a 0.010 0.609 0.495

10-20 cm 2.02b 1.18b 0.002 2.03ab 1.44a 0.095 0.954 0.030

20-30 cm 1.68b 0.93b 0.001 1.66b 1.24a 0.097 0.779 0.018

Total N

0-10 cm 2.12a 1.49a 0.001 2.29a 1.77a 0.001 0.528 0.302

10-20 cm 1.90a 1.37a 0.018 2.01b 1.51b 0.001 0.573 0.602

20-30 cm 1.81a 1.30a 0.001 1.87b 1.47b 0.001 0.872 0.212

Total P

0-10 cm 1.19a 1.05a 0.043 1.23a 1.15a 0.147 0.686 0.088

10-20 cm 1.18a 1.10a 0.006 1.23a 1.08a 0.266 0.704 0.788

20-30 cm 1.15a 1.08a 0.330 1.13a 1.05a 0.005 0.561 0.435

pH

0-10 cm 0.92a 0.96a 0.018 0.94a 0.98a 0.002 0.828 0.742

10-20 cm 0.94ab 0.98ab 0.001 0.97b 0.99b 0.064 0.118 0.069

20-30 cm 0.97b 0.99b 0.207 0.96b 0.99b 0.097 0.181 0.723

A: clump center, B: canopy periphery, C: inter-shrub space.

1 t-test for paired samples of enrichment ratios. Means under each category within a column not followed by the same 

letters are different at p = 0.05.
USDA Forest Service RMRS-P-47. 2007 121

ecosystems, shrubs protect topsoil from wind erosion and 

effectively trap wind-blown materials and litters from unprotected areas. Microtopographic mounds ranging from 19- to 

60-cm height were observed around shrub crowns (table 1). 

This suggests that topsoil material mainly accumulated under 

shrub canopies. Such mounds create a landscape that alternates between mounds and inter-shrub open space. The 

mound itself is a soil forming process (Rostagno and others 

1991), because it creates patches with higher concentrations 

of soil resources.

Higher concentrations of total N and total P were linked to 

the higher concentration of SOC under shrub canopies because 

SOC is the most important factor in the storage of nutrients in 

infertile soils (table 4, Wezel and others 2000). It is evident 

from our data that shrubs exert great impacts on nutrient redistribution, with a significant accumulation of growth-limiting 

nutrients such as total N and total P under the shrub canopies. 

This effect was particularly evident in the 0 to 10-cm and 10 

to 20-cm soil layers.

Higher concentration and enrichment ratios of SOC were 

found in soils under Z. xanthoxylum and higher content and 

enrichment ratios of total N were found under A. monglicus. 

This may relate to the fact that A. monglicus is a legume that 

has root nodules to fix nitrogen, thus producing a higher 

concentration of total N in the soil around the shrub (Cheng 

and Zhang 2001).

Nutrient enrichment at the clump center was more 

pronounced than at the shrub periphery (fig. 1, table 2). This 

is because there is much greater litter-fall at the clump center 

than some distance away from the center. In addition, shrub 

plants tend to have more roots at the clump center than near 

the canopy periphery. A larger amount of organic substrates, 

such as exudates, secretions, sloughed cells, and mucilage 

may be released from roots and deposited in the rooting zone 

at the clump center (Lynch and Whipps 1990; Petersen and 

Bottger 1991) leading to higher enrichment ratios.

No significant statistical differences in EA and Eb between 

the two shrub species were found, which may suggest that two 

species were both capable of altering nutrient redistribution in 

the soil. The capacity to accumulate soil nutrients under their 

canopies is similar regardless of whether the shrub is leguminous or not.

Table 4. Pearson linear correlation coefficients (r) between SOC, total N, and total P in soils of the different locations (n =36).

Sampling Organic C Total N Total P

Variable location A B C A B C A B

Organic C B 0.705** 

C 0.418* 0.419** 

Total N A 0.632** 0.552** 0.235 

B 0.431** 0.448** 0.166 0.851** 

C 0.237 0.293 -0.177 0.743** 0.738** 

Total P A 0.781** 0.517** 0.564** 0.197 0.027 -0.158 

B 0.634** 0.437** 0.562** 0.162 0.002 -0.132 0.974** 

C 0.610** 0.513** 0.643** 0.160 0.016 -0.114 0.956** 0.999**

Acknowledgments

This research was supported by the National Natural 

Science Foundation of China (90102011, 30371023).

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The Authors

1 College of Pastoral Agricultural Science and Technology, Lanzhou 

University, Key Laboratory of Grassland Agro-Ecosystem 

Ministry of Agriculture, PR China. fuhua@lzu.edu.cn 2 College of Life Sciences, Lanzhou University, PR China.

3 Department of Range, Wildlife, and Fisheries Mgt., Texas Tech 

University.
USDA Forest Service RMRS-P-47. 2007 123

Introduction

Fungi are unable to synthesize organic carbon, therefore they either assimilate exogenous organic carbon as 

saprophytes or they form associations with photosynthetic 

organisms. Lichens provide the simplest symbiotic model 

where fungi form associations with photosynthetic microorganisms. Evidence supporting similar symbioses between 

fungi and higher plants is increasingly overwhelming. Fungi 

reside in healthy tissues of every native plant examined to 

date and range from destructive pathogens to mutualists that 

profoundly affect ecological fitness (Arnold and others 2000). 

Some endophytic fungi occupy the apoplast of leaves, stems, 

and reproductive organs of many grasses (Clay 1990; Schulz 

and others 2002). Mycorrhizal fungi colonize roots of most 

plant species and have significant, well documented ecological roles in the nutrition and survival of host plants in natural 

ecosystems (Smith and Read 1997). Apparent saprophytic 

fungi also colonize roots with symptomless endophytic or 

biotrophic phases in their life cycles that are not obvious to 

casual observers (Parbery 1996). Most fungal associations 

are localized, while a few inhabit the entire apoplast and are 

vertically transmitted by seed (Clay and Schardl 2002). Not 

surprisingly, fungal endophytes confer multiple benefits to 

their host, such as enhanced tolerance to disease, drought, 

herbivory, and heavy metals and enhanced nutrient uptake 

and photosynthetic efficiency (Arnold 2003; Clay 1990; RuizLozano 2003; Obledo and others 2003).

Recent attention has been given to a diverse group of ascomycetous fungi designated as dark septate endophytes (DSE). 

These fungi have been detected microscopically by their interand intracellular, darkly pigmented (melanized) septate hyphae 

and microsclerotia in the root cortex (Barrow and Aaltonen, 

2001; Jumpponen 2001). They are found extensively in cold, 

nutrient-stressed environments where AM fungi do not proliferate (Kohn and Stasovski 1990). A higher incidence of DSE 

than AM fungi was found in Carex sp. in subarctic alpine 

regions (Haselwandter and Read 1982; Ruotsalainen and 

others 2002). Non-staining hyaline hyphal extensions from 

stained or melanized structures were reported by Barrow and 

Aaltonen (2001), Haselwandter and Read (1982), Newsham 

(1999), and Yu and others (2001) revealing morphological 

variability. DSE are the primary fungal associates of dominant 

native grasses and shrubs in the northern Chihuahuan Desert 

(Barrow and others 1997).

Barrow and Aaltonen (2001) and Barrow (2003) evaluated

Bouteloua eriopoda Torr. (BOER) and Atriplex canescens

(Pursh) Nutt. (ATCA), important forage shrub and grass 

species of the northern Chihuahuan Desert. Histochemical 

staining revealed greater colonization of atypical forms of 

DSE than previously observed using conventional methods. 

Osuna-Avila and Barrow (2004) regenerated plants from 

embryonic shoot meristem cells of naturally produced BOER 

seed and found fungal endophytes to be intrinsically integrated in regenerated plants (Barrow and others 2004).

In this study, naturally colonized roots and leaves of native 

Bouteloua eriopoda Torr. and Atriplex canescens (Pursh) Nutt. 

Fungal Genomes that Influence Basic Physiological 

Processes of Black Grama and Fourwing Saltbush in Arid 

Southwestern Rangelands

Abstract: Symbiotic fungi confer multiple benefits such as enhanced photosynthetic rates and 

drought tolerance in host plants. Shrubs and grasses of southwestern deserts are colonized 

by symbiotic fungi that cannot be removed by conventional sterilization methods. These fungi 

were extensively studied in Bouteloua eriopoda (Torr.) Torr. and Atriplex canescens (Pursh) 

Nutt. over a wide range of locations and environmental conditions. Fungi were intrinsically 

integrated with cells, tissues, and regenerated plant cultures. These composite plantfungus organisms are comprised of more than one fungal species. Fungal association with 

photosynthetic cells and accumulation of lipids provide evidence for carbon management. 

Fungal biofilms that coat cells, tissues, roots, and leaves suggests protection of plants from 

direct exposure to stressed environments. Associations with vascular tissues suggests a 

role in resource transport. Association with stomata indicates an influence in gas exchange, 

photosynthesis, and evapo-transpiration. Transfer of fungal endophytes from native plants to 

non-host plants resulted in substantial modifications in root, shoot morphology and biomass, 

chlorophyll content, and fruiting. Host plants are modified by fungi at the genetic, cellular, and 

physiological level and positively enhance ecological fitness.

J.R. Barrow1

M. Lucero2

P. Osuna-Avila2

I. Reyes-Vera3

R.E. Aaltonen4

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
124 USDA Forest Service RMRS-P-47. 2007

plants are compared with cell cultures, germinating seedlings, 

and micro-propagated plants of both species using scanning 

electron microscopy (SEM) and light microscopy with dualstaining methodology. Endophytic fungal endophytes were 

transferred from BOER and ATCA to non-host plants.

Materials and Methods

Tissue Samples

Root and leaf samples of native and micro-propagated 

plants and germinating seedlings of BOER and ATCA were 

analyzed in this study. Roots were sampled every two weeks, 

from 2001 to the present from native populations of ATCA and 

BOER on the USDA Agricultural Research Service’s Jornada 

Experimental Range in southern New Mexico. Soil moisture 

in the chronically dry collection sites are generally less than 

3 percent. Significant precipitation events are intense, localized rain showers during the summer monsoons that saturate 

the soil for only brief periods. Sampling times included a wide 

range of seasonal, physiological, and climatic conditions. 

Uniform expression of fungal structures was consistent within 

the population at each sampling period. Leaves from native 

plants were sampled over all seasons and included different 

physiological stages ranging from actively growing to drought 

induced dormant plants.

Tissue Preparation and Staining

Staining and mounting methods were modified by Barrow 

and Aaltonen (2001) and Barrow (2003) for optimal fungal 

expression. Tissues were dual stained with trypan blue (TB), 

which targets fungal chitin, and sudan IV (SIV),which targets 

lipid bodies found previously to stain lipids attached to 

fungal structures (Barrow and Aaltonen 2001; Barrow 2003). 

Samples were analyzed with a Zeiss Axiophot microscope 

with both conventional and differential interference contrast 

optics at 1000x. Images were captured with a high resolution 

digital camera and processed using auto-montage 3-D software by SyncroscopyTM to give a focused image.

Tissue Preparation by Liquid Nitrogen

Roots and leaves from native and propagated plants and 

germinated seedlings were also placed in liquid nitrogen and 

dried at 100o

C. Tissues were then ground with a mortar and 

pestle and suspended in a centrifuge vial in 10 ml of 2.5 percent 

KOH and micro-waved for 1.5 min prior to centrifugation at 

3000 rpm until a stable pellet formed. The supernatant was 

removed by pipette and the pellet was re-suspended in 10 ml 

dH2

O and centrifuged again. The pellet was re-suspended in 

10 ml HCL and micro-waved for 1.5 min. The vial was filled 

with dH2

O and the cell pellet was harvested again by centrifugation. Next, the cell pellets were suspended in 5ml trypan 

blue and 5 ml sudan IV and micro-waved for 2 min. The vial 

was rinsed with dH2

O and centrifuged, and the supernatant 

was again removed by pipette.

Stained ground material was suspended in a drop of 

mounting medium on a slide and sealed with a cover slip and 

microscopically examined. This procedure resulted in tissues 

fractured in all possible planes permitting analysis of single 

layers of cells at 1000x magnification. Power settings, time, 

and sample size must be adjusted to prevent over heating in 

the microwave.

Scanning Electron Microscopy

Fresh leaves and roots of native and propagated plants were 

sampled from the field and from micro-propagated plants and 

placed in moist plastic bags and analyzed within 1h by placing 

them in a vacuum chamber of a biological scanning electron 

microscope.

Micro-Propagated BOER Plants

Seeds were manually harvested from native BOER plants; 

caryopses were separated from florets and surface disinfested 

and germinated. Embryonic shoots were excised from roots 

and plated on an auxin supplemented medium to induce callus 

from meristematic shoot cells. Plants were regenerated via 

somatic embryogenesis from callus cells after transferring to 

an auxin-free medium (Osuna and Barrow 2004).

Micro-Propagated ATCA Plants

Seeds of four-wing saltbush, Atriplex canescens, were 

surface disinfested by soaking them in 95 percent ethanol 

for 1 minute, followed by 2.6 percent sodium hypochlorite (50 percent dilution of commercial liquid bleach) for 7 

minutes. Seeds were rinsed three times in sterile distilled 

water then were placed on hormone-free, modified White’s 

media (White 1934) for germination. Germinated seedlings 

of Atriplex canescens were used to initiate shoot cultures by 

transferring them to shoot proliferation media consisting of 

standard Murashige and Skoog (MS) basal salts (Murashige 

and Skoog 1962) supplemented with 11.42 μM Indole-3- 

Acetic Acid (IAA) and18.58 μM 6-Furfurylaminopurine 

(Kinetin). Vitamins were supplemented according to the L2 

formulation of Phillips and Collins (1979), 30 g l-1 sucrose, 

and solidified with 0.8 percent agar. The pH of the medium 

was adjusted to 5.8 ± 0.05 prior to autoclaving at 121°C at 

125 kPa for 35 minutes. Cultures were grown in 100 x 25 

mm polystyrene petri dishes and sealed with Parafilm®. They 

were subcultured to fresh media every 4 weeks. This protocol 

represents the standard control media.

Shoots were originally vitrified and were reverted to normal 

by transferring to shoot proliferation media with the following 

modifications. Ammonium-free MS (NH4

NO3 excluded from 

the original major salts composition) was supplemented with 

4.40 g/L of casein hydrolysate to provide an amount of total 

nitrogen content comparable with the standard MS formulation. Standard MS basal salts served as the control. Vitamin 

supplements were added according to the L2 formulation by 

Phillips and Collins (1979) plus 30 g l-1 sucrose. All experimental 
USDA Forest Service RMRS-P-47. 2007 125

media treatments were solidified with 5.0 g/L of Agargel ® 

(Sigma Chemical Co., St Louis MO, USA), a blend of agar 

and phytagel documented to control vitrification (Pasqualetto 

and others, 1986). Growth regulator composition consisted of 

24.61 μM 6-(γ-γ-Dimethylallylamino) purine (2iP). The pH 

of the medium was adjusted to 5.8 ± 0.05 prior to autoclaving 

at 121oC at 125 kPa for 35 minutes and dispensed in polycarbonate Magenta® GA7 vessels (Magenta Corp., Chicago, 

IL., USA). Culture boxes were closed with either standard 

Magenta ® GA7 vessel covers or vented lids with a 10 mm 

polypropylene membrane (0.22 μm pore size) Magenta® 

(Magenta Corp. Chicago, USA). All cultures were incubated 

at 28 ± 1°C under continuous fluorescent light (14-18 μmol —2 s-1). Normal shoots were removed from culture boxes and 

subcultured on the reversion medium.

Normal shoots of three nodes or longer were rooted by 

culturing on White’s media culture (White, 1934) supplemented with 2.46 μM of indolebutyric acid (IBA), 30 g/l 

of sucrose, and solidified with 2.5 g/L of Phytagel® (Sigma 

Chemical Co., St Louis MO., USA). Pure phytagel facilitated 

easy visual evaluation of root initials. The pH was adjusted 

to 5.5 ± 0.05 prior to autoclaving at 121°C at 125 kPa for 35 

min and dispensed in 107 x 107 x 96 mm high LifeGuard® 

polycarbonate culture boxes closed with vented lids with an 

opening of 22 mm and a 0.3 μm pore size (Osmotek Ltd, 

Israel).

Fungal Transfer

Fungi were transferred from BOER and ATCA by placing 

germinating disinfested tomato seed in contact with callus 

cultures of both species. Tomato plants with fungi were 

compared with control plants without fungi under greenhouse 

conditions.

Ribosomal DNA Analysis

Polymerase chain reactions (PCRs) targeting ribosomal 

DNA (rDNA) and internal spacer regions (ITS) developed for 

identification of fungi (White, 1990) were applied to tomato 

DNA isolated from leaves of control, BOER- and ATCA-inoculated plants. Electrophoresis of PCR products was used to 

identify products that differed between treatment groups.

Some of the fungal endophytes present in BOER and 

ATCA inoculated plants have been previously characterized by sequence analysis of cloned PCR products and/or 

by isolation and morphological identification (Barrow and 

others 2004; Lucero and others 2004). The ATCA callus used 

to inoculate tomato was known to contain Aspegillus ustus, 

Pennicillium olsoni, and Bipolaris spicifera. The BOER callus 

was also associated with A. ustus. In addition, BOER callus 

contained Engyodonitium album and an uncharacterized, telilospore-producing fungus (Lucero and others 2004). Mention 

of trade names or commercial products in this publication is 

solely for the purpose of providing specific information and 

does not imply recommendation or endorsement by the U.S. 

Department of Agriculture.

Results and Discussion

 Symbiotic fungal presence was verified in plant tissues 

by light and electron microscopy and DNA sequence analysis. Fungi were found to be intrinsically integrated with all 

cells tissues and organs of native and aseptically regenerated BOER and ATCA plants. Significant associations with 

specific cell types and potential functions are presented here. 

A key observation was the consistent association of fungal 

tissue, as indicated by positive staining with TB (fig. 1, sf), 

with all root meristem and daughter cells. The transmission of 

fungi to daughter cells explains how fungi become associated 

with all host plant cells. Such an association has significant 

implications regarding how the host plant may perform at the 

genetic, physiological, and ecological levels. Internal fungal 

structures were morphologically variable; many differed from 

classically recognized structures and escape detection using 

conventional analytical methods.

Fungi were previously found to be non-destructively associated with xylem and sieve elements of the vascular cylinder, 

cortical, and epidermis of native BOER and ATCA roots with 

external hyphal extensions into the soil (Barrow and Aaltonen 

2001; Barrow 2003). Such associations suggest the potential 

enhancement of resource transport in the vascular cylinder by 

fungal symbionts. Historically, axenically cultured plants have 

been considered microbe free (Borkowska 2002). However, 

tissue cultured BOER and ATCA plants were found to have 

intrinsically associated fungi that were found to be continuous 

from embryonic shoot meristem cells, to callus and to regenerated BOER plants (Barrow and others 2004). SEM analysis 

of callus tissue induced from embryonic BOER cells (fig. 

2) reveals hyphae (h) enmeshed within the biofilm (bf) that 

completely encapsulates the axenically cultured callus tissue. 

This is consistent with observations of Pirttila and others 

(2002), who also found fungal biofilms on the surface of 

Pinus tissue cultures. Embryos were induced within the callus 

(Barrow and others 2004). SEM analysis of embryonic roots 

of developing plantlets (fig. 3) shows a tightly woven hyphal 

mass (hn) enmeshed within a biofilm (bf). Symbiotic fungal 

endophytes are shown here to totally encapsulate cells, callus, 

and roots and prevent their direct exposure to the external 

environment. Similar fungal layers have been observed to 

completely cover all root and leaf surfaces of native plants in 

the field.

Native plants in the northern Chihuahuan are chronically 

exposed to extreme nutrient and soil water deficits (soil moisture < 3 percent) for long periods, as well as high temperatures, 

dry atmospheric conditions, and high light intensity. Fungi, as 

well as other microbes, synthesize exo-polysaccharides that 

attach to their cell surfaces (Sutherland 1998). Biofilms constitute a protective mode for the microbe (Costerton and others 

1999). They have unique characteristics that may be valuable contributions to host plants in an arid ecosystem. They 

hydrate rapidly on contact with water and assist in the attachment to substrates or to host plants. Biofilms protect against 

invasions from pathogens and changes in the physico-chemical environment and allow microbes to survive in hostile 
126 USDA Forest Service RMRS-P-47. 2007

Figure 1. Meristematic cells of a lateral root initial of Bouteloua eriopoda seedling. Trypan blue stained fungus associated with all 

cells (sf).

Figure 2. An SEM image 

of Bouteloua eriopoda

callus tissue encapsulated 

with fungal hyphae (h) 

enmeshed within a biofilm 

(bf).
USDA Forest Service RMRS-P-47. 2007 127

environments (Costerton and others 1999; Krembs and others 

2002; Wotton 2004). Consistent with findings of Deckert 

and others (2001), we also observed that external hyphae on 

root and leaf surfaces that were embedded within a mucilaginous (polysaccharide) matrix. The fungus with a protective 

biofilm, makes fungi an attractive cohort for native plants that 

enables them to function under extreme stress. This barrier 

would be expected to confer multiple benefits to host plants, 

protecting plant surfaces from dry soil and atmospheric conditions, temperature extremes, intense light, salinity, absorption 

of heavy metals, or infection by pathogens.

Also significant was the association of symbiotic fungi 

with photosynthetic cells and the stomatal complex. Fungal 

associations with all photosynthetic cells of native and regenerated plants of BOER and ATCA were observed. Figure 4 

shows stained fungal structures (sf) associated with photosynthetic bundle sheath cells (bs) and mesophyll cells (mp) of 

BOER. Note that the fungi assume the shape of the respective cells. The interpretation of extensive observations is that 

fungal tissue adheres to the outer plasmalema of most cells 

and is transmitted to new cells at division. Positively stained 

fungal structures (fig. 5, sf) were also observed associated with 

bundle sheath cells of native and regenerated ATCA plants. 

The xylem vessels (st) also stained positively for fungal tissue. 

Fungi bind with and assume the shape of the lignified xylem 

vessels. Fungal association with photosynthetic cells suggests 

a potential site where these biotrophic endophytes may access 

carbon from the host plant. The quantity of exo-polysaccharides produced by these fungi for protective biofilms suggests 

considerable carbon expenditure for protection of the hybrid 

plant-fungus organism. Associations with xylem vessels 

suggest a role of active water transport by fungi and enhancement of drought tolerance.

Fungal association with cells of the stomatal complex with 

both native and regenerated plants further confirmed their 

distribution to all cells and tissues and their existence as a 

composite plant-fungus symbiota. Figure 6 shows stained 

fungal tissue (stf) associated with guard cells of stomata 

(st) in a regenerated ATCA plant. Similar fungal staining 

was consistently observed in cells of the stomatal complex 

of native and regenerated BOER plants (fig. 7). The staining 

pattern in BOER, was a consistent staining of the terminal 

ends of guard cells (gc), while in ATCA, staining of the entire 

guard cells was observed (fig. 6). Staining was also regularly 

observed in the subsidary cells (sc) of the stomatal complex. 

Colonization of stomata of these native plants suggests that 

these endophytes influence stomatal regulation and evapotranspiration. Minimizing water loss in arid ecosystems would 

enhance drought tolerance. A suggested fungal role may be to 

maximize gas exchange and photosynthetic efficiency, while 

reducing water loss by transpiration.

Unexpected, was the intrinsic association of endophytic 

fungi with cell cultures, calluses, and axenically cultured 

plants, previously expected to be microbe free (Barrow and 

Osuna-Avila 2004; Borkowska 2002). Also of interest, was 

that these fungi did not grow on the carbon-mineral rich culture 

medium as long as the plant tissues were healthy. However, 

after the eventual death of plants, A. ustus, Crinipellis and 

Engyodontium album were isolated and grew well on the 

culture medium. This suggested an obligate affinity of these 

species to healthy living tissue compared to their saprophytic 

potential on artificial medium after plant health is impaired.

Attempts to completely separate BOER and ATCA cell 

cultures from fungi have not been successful. Therefore, in 

order to observe the effects that BOER- and ATCA-associated fungi might have on their prospective host plant, callus 

Figure 3. An SEM image of 

an embryonic root developing from a regenerated 

Bouteloua eriopoda

plantlet that is encapsulated with a dense hyphal 

network (hn) and fungal 

biofilm (bf).
128 USDA Forest Service RMRS-P-47. 2007

Figure 4. Trypan blue stained 

fungal tissue (sf) within 

photosynthetic mesophyll 

cells (mp) and bundle 

sheath cells (bs) of native 

Bouteloua eriopoda.

Figure 5. Trypan blue stained fungal tissue (sf) in photosynthetic bundle sheath (bs) cells in leaves of regenerated Atriplex canescens leaves. Lignified xylem vessels (sx) also stain positively for fungal tissue.
USDA Forest Service RMRS-P-47. 2007 129

Figure 6. Trypan blue stained fungal tissue (stf) within guard cells of the stomata 

(st) in leaves of regenerated Atriplex canescens plantlets.

Figure 7. Trypan blue stained fungal tissue (sf) associated with terminal ends of guard cells (gc) and 

subsidary cells (sc) of the stomatal complex of 

native Bouteloua eriopoda leaves.

Figure 8. Control tomato plants, var. Bradley (without fungi). Fungi transferred to 

plants from Atriplex canescens (ATCA) callus. Fungi transferred to plants from 

Bouteloua eriopoda (BOER) callus.
130 USDA Forest Service RMRS-P-47. 2007

Figure 9. PCR products obtained from amplification of rDNA from 

control tomato plants, var. Bradley (without fungi), and from 

tomato plants (var. Bradley) inoculated with Atriplex canescens

(ATCA) callus or Bouteloua eriopoda (BOER) callus. Left to right: 

Lane 1-Molecular Weight Marker, Lane 2- Control tomato, Lane 3- 

Tomato inoculated with BOER callus, Lane 4- Tomato inoculated 

with ATCA callus.

from cell cultures was used to inoculate tomato seedling. 

Evidence for their transfer was a three- to five- fold increase 

in root and shoot biomass. Figure 8 compares standard tomato 

variety, Bradley, control plants (c) to plants with fungi transferred from ATCA callus, and to plants with fungi transferred 

from BOER callus. Transferred fungi immediately take up 

residence in the apoplastic spaces of the non-host tomato. 

Substantial increase in shoot biomass is observed with earlier 

and larger fruit production. Fungi increased root biomass from 

three to five times. Differences in responses were observed, 

suggesting that different fungi may have been transferred with 

ATCA and BOER callus.

When the primers NS1 and NS4 were used with defined 

protocols (White 1990), a band was seen in both BOER and 

ATCA treated samples that was absent from the control (fig. 

9). Curiously, this band has not been seen in PCR products 

that have been amplified from endophytes such as the putative rust, the Crinipellis and the Aspergillus ustus (Lucero and 

others, submitted), which have previously been characterized in ATCA and BOER cultures. This suggests yet another 

fungal endophyte resides in these cell cultures. If the different 

effects observed in the BOER- and ATCA-inoculated treatment groups are indeed due to different fungi, then sequence 

analysis should produce a different sequence for each of the 

bands shown in figure 9. The intrinsic integration of symbiotic fungi with all cells and tissues suggests that fungi modify 

plant behavior at genetic, cellular, physiological, and ecological levels and that fungal genes contribute multiple benefits 

to the host plant. It is unlikely that plants bearing such large 

fungal populations would continue to thrive under any environment unless the fungi contributed benefits to the host plant 

in exchange for substantial quantities of organic carbon they 

consume.

The simplicity with which fungi can be transferred to 

new hosts, combined with the benefits conferred on plants 

by fungi, raises interesting possibilities for native and crop 

plant improvement. Continued research in the identification 

and characterization of fungal endophytes promises to yield 

a complex assortment of species that may serve as tools for 

plant improvement. Clearly, microbial diversity in our arid 

rangelands has been a largely overlooked and underutilized 

resource.

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The Authors

1 Research Scientist, USDA-ARS-Jornada Experimental Range, Las 

Cruces, NM. jbarrow@nmsu.edu 2 Postdoctoral Associate, USDA-ARS-Jornada Experimental Range, 

Las Cruces, NM. 3 Graduate Assistant, USDA-ARS-Jornada Experimental Range, Las 

Cruces, NM. 4 Research Associate, USDA-ARS-Jornada Experimental Range, 

Las Cruces, NM.
132 USDA Forest Service RMRS-P-47. 2007

Ecology and Population Biology 

Session

Introduction

The Chihuahuan desert is the largest of the three creosotebush-dominated deserts in North America. The Chihuahuan 

desert covers 450,000 to 629,000 km2

 (Henrickson and 

Straw 1976; Morafka 1977; Dinerstein and others 2000) 

in eastern Chihuahua, western Coahuila, San Luis, Potosi, 

southern Nuevo Leon, northeast Zacatecas, eastern 

Durango, southwest Texas, and southern New Mexico, as 

well as smaller but equally distinctive areas in southeast 

Arizona and northeast Sonora (Brown 1982). Chihuahuan 

desert grasslands contain a varied flora of herbaceous, 

suffrutescent, and woody species. Vegetation pattern is 

spatially diverse across the landscape and is influenced 

by highly variable patterns of precipitation and subtle 

changes in edaphic factors as well as natural and anthropogenic disturbance regimes (Buffington and Herbel 1965). 

Creosotebush, (Larrea tridentata), is a prominent element 

of the Chihuahuan Desert, often covering large areas. Other 

common shrubs include catclaw (Mimosa biuncifera), 

mesquite (Prosopis glandulosa), mariola (Parthenium 

incanum), fourwing saltbush (Atriplex canescens), tarbush 

(Flourensia cernua), javelinabush (Condalia ericoides), 

goldeneye (Viguiera cordifolia), and ocotillo (Fouquieria 

splendens). Among these shrubs, fourwing saltbush 

(Atriplex canescens) and mariola (Parthenium incanum)

are important components of the diet of grazing animals.

Maynez and others (1984) evaluated the nutritional value 

of mariola by collecting samples during 1 year in a monthly 

period. They found the highest crude protein (CP) values 

during September (20.3 percent) and April (18.3 percent). 

The lowest CP contents were measured during the months 

of October (11.7 percent), November (12.6 percent), and 

January (13.6 percent). The highest percentages of mariola in 

vitro organic matter digestibility (IVOMD) were determined 

during the months of September and April – 65.5 and 63.5 

percent, respectively. In contrast, the lowest IVOMD values 

were found in November with an average of 54.1 percent.

Mariola is one of the most important components of the 

diet of grazing animals on a desert shrublands. Marquez 

and others (1984) used esophageal fistulated steers to determine dietary botanical composition. The most important 

plants were mariola buddleja (Buddleja scordiodes) and 

oreganillo (Aloysia wrightii). Mariola constituted about 31 

percent of their diet for grazing steers. Villalobos and others 

(1984) working in the same vegetation type estimated that on 

Estimating Aboveground Biomass of Mariola (Parthenium 

incanum) from Plant Dimensions

Abstract: The distribution and abundance of plant biomass in space and time are important 

properties of rangeland ecosystem. Land managers and researchers require reliable shrub 

weight estimates to evaluate site productivity, food abundance, treatment effects, and stocking 

rates. Rapid, nondestructive methods are needed to estimate shrub biomass in semi-arid 

ecosystems. Shrub height and crown diameter are useful non-destructive measures of shrub 

size. Mariola (Parthenium incanum) is an important shrub that is widely distributed in the 

Chihuahuan and Sonoran deserts. Mariola is found from the southwest United States to the 

central part of Mexico. Regression analyses were used to examine the relationships between 

aboveground biomass and four plant measurements (shrub height, longest canopy width, 

shortest canopy width, and crown volume) from 45 plants. All variables were related to aerial 

biomass; R values varied from 0.73 to 0.98. Regression equations developed for mariola 

compared favorably to equations in similar species in desert environments, suggesting that 

results might be applicable to other desert regions for rapid and accurate estimation of shrub 

biomass.

Carlos Villalobos1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 133

average, 18 percent the diet with esophageal goats was made 

up of mariola.

The distribution and abundance of plant biomass in space 

and time are important properties of rangeland ecosystem. 

Researchers and natural resources managers require reliable 

estimates of shrub weights to assess site productivity, food 

abundance, treatment effects, and stocking rates. The accurate 

measurement of vegetative biomass by traditional clipping and 

weighing is a time-consuming and labor-intensive process. 

As a result, indirect methods are needed to rapidly determine 

shrub aerial biomass. Considerable research has gone into estimating the biomass of individual shrub species (Tucker 1980; 

Murray and Jacobson 1982; Frandsen 1983; Navar and others, 

2002). However, established techniques, such as harvesting, 

are slow and expensive. Shrub height and crown diameter are 

useful non-destructive measures of shrub growth, but precise 

direct estimates of yields of aerial biomass require destructive methods that are unsatisfactory in studies on perennial 

shrubs.

Uresk and others (1977) estimated that clipping big sagebrush (Artemisia tridentata) phytomass was 120 times more 

expensive than using dimension analysis. Using the weight 

estimate technique (Pechanec and Pickford 1937) requires a 

considerable training and clipping to check estimates. A technique that is rapid, relatively accurate, and requires little training 

is desirable. Tufts (1919) found a high correlation between 

trunk circumference and weight of the top of fruit trees. Since 

this early beginning, many others including Kittredge (1944), 

Attiwill (1962), Baskerville (1965), and Brown (1978) have 

used combinations of trunk diameter, total height, live crown 

length, ratios of live crown length to total height, and crown 

widths to estimate tree biomass. In most cases, very useful 

predictive relationships were developed from these simple 

measurements. Similarly, biomass estimates of various shrub 

species and plant fractions have been developed using stem 

diameters (Telfer 1969; Brown 1976), crown diameter axes 

(Rittenhouse and Sneva 1977), crown volume (Chew and 

Chew 1965; Lyon 1968; Mack 1971; Burk and Dick-Peddie 

1973; Ludwig and others 1975; Rittenhouse and Sneva 1977; 

Wakimoto and Menke 1978), crown cover (Ludwig and others 

1975), and height x circumference (Harniss and Murray 1976) 

as independent variables.

A large number of variables can be used to predict biomass. 

However, variables that express the size of the crown or the 

volume appear to be most useful. The objective of this study 

was to examine the relationships between aboveground 

biomass and four plant measurements (shrub height, longest 

canopy width, shortest canopy width, and crown volume) 

recorded in the field.

Materials and Methods

This study was conducted on a private ranch 50 km east 

of Chihuahua city (28° 46’ N, 65°50’ W) at elevation of 

1,150 m. The climate of the region is semi-arid and warm. 

The average annual precipitation is 250 mm, with about 

65 percent occurring between July and September. The 

vegetation is characterized by perennial, drought resistant 

woody species adapted to conserve water in drought periods; 

perennial grasses; and various types of annual species. 

Dominant shrubs are creosotebush, mariola, tarbush mesquite, 

saltbush, and yucca (Yucca spp.). The study site received 

moderate continuous grazing all year by domestic livestock.

Four morphological variables were used to estimate 

aboveground biomass: plant height, longest canopy width, 

shortest canopy width, and crown volume. Mariola volume 

was computed as if the plant was the upper half of a spheroid 

in shape with the formula: canopy volume = π (4/3) a2 b, 

where a is the average of the longest and shortest radii, and 

b is plant height (Ludwig and others 1975). Plant morphological measurements were recorded in the field on 45 randomly 

selected plants in December. A single estimate of biomass 

during December was considered an adequate basis to estimate shrub production because current year shoots and leaves 

remain attached to the plant and are easily identifiable. We 

did not consider diameter increases of branches but only their 

elongation; thus, our data may have a bias towards underestimation.

After recording morphological measurements, shrubs were 

clipped at ground level with all aboveground parts including 

branches, stems, and leaves collected. All plants were dried 

at 60°C to a constant mass and weighed to the nearest 0.01g. 

Plants chosen for this analysis represent the range of sizes 

encountered in the region based on experience with field work 

that occurred in conjunction with this study involving botanical composition of the diet of grazing animals at the same 

site. All plants collected were judged to be in good condition 

at the time of harvest and were collected from similar range 

sites.

Regression analyses were used to examine the relationships 

between aboveground biomass and four field measurements 

shrub height, longest canopy width, shortest canopy width, 

and crown volume from 45 plants.

Results and Discussion

The range in the height, longest canopy width, shortest 

canopy width, and crown volume of the shrubs was 17 to 77.0 

cm (mean 42.82 cm, standard deviation [SD] 16.06 cm); 18 

to 132 cm (mean 61.29, SD 29.48 cm); 16 to 124 cm (mean 

52.51 cm, SD 25.41 cm); and volume, 0.3845 to 0.9939 cm3

, 

respectively,. Time spent clipping and harvesting each plant, 

averaged 20 to 30 minutes. In contrast, taking all the measurements averaged 4 to 6 minutes/plant.

All independent variables were highly correlated with 

shrub biomass. In general, the relationship among the variables, height, longest canopy width, and shortest canopy 

width, showed an exponential relationship. In contrast, crown 

volume indicated a linear relationship. The linear regression 

modeling results showed that different plant attributes predict 

plant biomass with a high coefficient of correlation (table 1).

Analyzing each independent variable individually showed 

that plant volume had the highest correlation with biomass 

(r = 0.97). Rittenhouse and Sneva (1976) and Bryan and 
134 USDA Forest Service RMRS-P-47. 2007

Kothmann (1979) found similar results between aboveground 

biomass and volume. Longest canopy width (r = 0.86), shortest 

canopy width (r = 0.74), and height (r = 0.73) also were individually significantly related to biomass. Other studies on 

desert shrubs have demonstrated strong relationship between 

biomass and morphological measurements. Felker and others 

(1982) showed that the dry matter weight of Prosopis was 

highly correlated (r2 = 0. 99) with stem diameter. Sosa and 

Perez (1983) and Sosa and Baez (1985) mentioned that height 

was the best predictor of biomass for Mimosa biuncifera and 

Menodora scabra. However, height had the lowest correlation 

with the biomass in the current study. This may be related to 

differences among species in individual growth form and in 

response to site resources. Rittenhouse and Sneva (1977) also 

noted useful results in estimating big sagebrush biomass with 

one variable. Longest canopy width was successfully used 

to estimate biomass of mariola. Therefore, using at least one 

these variables, biomass can be estimated. However, Cook 

(1960) suggested using two or more plant measurements to a 

single measurement.

Although the statistical analysis in this study indicates 

strong relationships between plant attributes and biomass, 

caution should be used in estimating mariola biomass for 

seasons other than the season used in this study. The time of 

year when biomass prediction equations were developed for 

mariola can influence the magnitude of the equations parameters. Plant measurements have potential for predicting mariola 

production in the Chihuahuan and the Sonoran desert, mainly 

due to mariola definite growing pattern. Using prediction 

equations to estimate mariola biomass saves time and is not a 

destructive procedure.

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Variables Coefficients Statistics

Dependent Independent β0 β1 P > F r2 Sx.y n

Biomass Height -412.1 14.23 0.00 .730 0.31 45

Biomass Longest canopy width -317.7 8.406 0.00 .859 0.51 45

Biomass Shortest canopy width -313.5 9.73 0.00 .855 0.60 45

Biomass Volume -13.55 .0012 0.00 .965 0.87 45
USDA Forest Service RMRS-P-47. 2007 135

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The Author

1

 Associate Professor, Department of Range, Wildlife, and 

Fisheries Management, Texas Tech University, Lubbock, TX. 

c.villalobos@ttu.edu
136 USDA Forest Service RMRS-P-47. 2007

Introduction

Restoring disturbed rangelands infested with invasive 

annual grasses is a complex and difficult process. Once established, invasive annual grasses, such as cheatgrass (Bromus 

tectorum), create changes in soil moisture regimes, decomposition cycles, nutrient availability, and soil microorganism 

communities, as well as changes in fire frequency and 

frequency of native plant recruitment (Whisenant 1990; Belnap 

and Phillips 2001; Norton and others 2004). Competition from 

cheatgrass for limiting soil resources severely reduces shrub 

establishment (Stevens and Monsen 2004). Reversing these 

changes and reestablishing a functional native plant community is a difficult and often unsuccessful process. The role that 

soil organisms might play in such restoration efforts has yet 

to be explored.

Biological soil crusts of arid and semiarid lands contribute 

to a variety of ecological functions, including soil stabilization, nitrogen (N) fixation, nutrient availability, and vascular 

plant establishment (Belnap and others 2001). Considerable 

evidence also indicates that mycorrhizal fungi play an important role in plant uptake of N, including atmospheric N fixed 

by soil crust organisms, as well as that of more immobile 

elements such as phosphorus (Ibijbijen and others 1996; 

Hawkes 2003).

This study examines the effects of mass-produced, 

crust-forming soil algae and arbuscular mycorrhizal fungi 

on growth and survival of shrub seedlings grown with and 

without competition from cheatgrass under controlled greenhouse conditions. The ultimate goal of this research is to 

provide information on microorganism interactions that will 

aid revegetation efforts of disturbed arid lands.

Methods

Seeds of five shrub species—Ephedra viridis (EPVI), 

Coleogyne ramosissima (CORA), Artemisia filifolia (ARFI), 

Chrysothamnus nauseosus ssp. hololeucus (CHNA), and 

Artemisia nova (ARNO), representing both cold and mixed 

desert communities—were obtained from native populations 

in Utah. Cheatgrass (BRTE) seed was collected from the 

Whiterocks area in northern Utah.

Algal inoculum of the genus Schizothrix was produced in 

concentrated slurry form, pelletized, dried, and ground to a 

powder according to the procedures described in Buttars and 

others (1998). Mycorrhizal inoculum was produced from soil 

collected from beneath shrubs growing near Toquerville, UT. 

Shrubs growing at this location included Coleogyne ramosissima, Artemisia filifolia, Artemisia tridentata, and one 

species of Ephedra. We assumed that spores collected from 

this site, which had many of the same genera as were used 

in our experiment, would provide a compatible source of 

mycorrhizal inoculum. Spores were extracted from the soil by 

wet-sieving and decanting, followed by sucrose centrifugation 

(Daniels and Skipper 1982; Walker and others 1982). Freshly 

extracted spores were suspended in water and added to pots 

using a pipette. Replicate aliquots were decanted onto filter 

paper and spore counts made. Non-mycorrhizal treatments 

received an equal volume of killed (autoclaved) spore suspension combined with microbial-containing washings that had 

passed a 25-micron sieve.

One-liter Durapots (Hummert Int.) were filled with a 

steam-sterilized bank sand that had a pH of 8.3, conductivity 

of 0.58 mmhos/cm, and plant-available nutrient concentrations of 4.96, 2.48, and 41.6 ppm nitrate-N, phosphorus, 

Shrub Establishment in the Presence of Cheatgrass: 

The Effect of Soil Microorganisms

Abstract: Invasive annual grasses, such as cheatgrass (Bromus tectorum), create changes 

in soil microorganism communities and severely limit shrub establishment, a situation that is 

of considerable inportance to land managers. We examined the effects of biological crustforming algae and arbuscular mycorrhizal fungi on growth and survival of Ephedra viridis

(EPVI), Coleogyne ramosissima (CORA), Artemisia filifolia (ARFI), Chrysothamnus nauseosus

ssp. hololeucus (CHNA), and Artemisia nova (ARNO), with and without competition from 

cheatgrass, in a controlled laboratory pot experiment. Shrub survival declined as soil fertility 

increased. Few shrubs were able to survive in competition with cheatgrass in fertilized growth 

medium. Under low nutrient conditions, the addition of mycorrhizal inoculum intensified 

competition with cheatgrass, reducing shrub shoot biomass over that of the control treatment 

in all species except ARFI. However, shoot growth of cheatgrass in the mycorrhizal treatment 

was reduced to an even greater extent in all cases except when grown with ARNO. Algal 

inoculation increased shrub survival and appeared to beneficially affect the growth of ARFI 

and EPVI at the expense of cheatgrass. Our findings suggest that soil microorganisms can, 

to some extent, improve shrub establishment in the presence of cheatgrass.

Rosemary L. Pendleton1

Burton K. Pendleton1

Steven D. Warren2

Jeffrey R. Johansen3

Larry L. St. Clair4

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 137

and potassium, respectively. Following steaming, approximately one-third of the sand was amended using Osmocote 

17-7-12 NPK (5 oz per cubic foot) formulated for 12 to 14 

months continuous fertilization to produce a medium soil 

fertility level. The low fertility level had no additional fertilizer added.

Plants were grown using one of four inoculation treatments: algal crust inoculum applied to the soil surface at a 

rate of 100 g/m2; arbuscular mycorrhizal inoculum consisting 

of 50 to 100 spores added to pots at a depth of 1 to 2 inches; 

dual inoculation; and a non-inoculated control. Seeds of 

CORA and EPVI were pre-germinated on moistened filter 

paper before planting. All other shrub species were seeded 

into a sterile, sand-filled flat then transplanted to the treatment pots following emergence of the first true leaves. Half 

of the low fertility treatment pots were subsequently planted 

with one seed of BRTE. BRTE was not planted in the medium 

fertility pots because previous trials found that few shrubs 

could survive competition with BRTE in fertilized soils. Ten 

pots were used for each fertility/treatment/competition combination for a total of 120 pots per species.

Plants were grown for 5 months in a greenhouse that 

had been cleaned, sprayed with a biocide, and equipped 

with new evaporative cooling pads. Additional lighting was 

provided for 12 hours per day using mercury vapor lamps. 

Pots were randomized within the greenhouse bench using a 

computer-generated randomization procedure and watered as 

needed using a hose with a fine spray head. Shrub planting/

transplanting was carried out from late November to midDecember 1996. Harvesting was accomplished throughout 

May. At harvest, shoots were excised at ground level, dried 

at 65oC, and weighed. Roots were washed free of sand, dried, 

and weighed.

Statistical analyses were accomplished using SAS version 

6.11 for the personal computer (SAS Institute Inc. 1989). 

Survival data were analyzed using a logistic regression procedure. Growth effects were analyzed separately for each shrub 

species using the GLM procedure, with mycorrhizal inoculation, algal inoculation, and either soil fertility or competition 

with cheatgrass as main effects. These analyses were further 

subdivided depending on significance of the interaction 

terms. Treatment effects were also examined using GLM by 

first coding the four inoculation treatment combinations 1 to 

4. Mean separations were determined using Tukey and GT2 

procedures.

Results

The initial model used in the logistic regression for shrub 

survival included soil fertility level, shrub species, mycorrhizal inoculation, and algal inoculation, along with all 

two-way interactions. Stepwise elimination resulted in a final 

model containing soil fertility (P = 0.0001), shrub species (P 

= 0.0001), and algal inoculation (P = 0.0014) as significant 

effects in predicting shrub survival. There was no significant 

mycorrhizal effect for shrub survival. Survival of the two 

sagebrush species (ARFI and ARNO) was high (> 95 percent 

at both soil fertility levels). Survival of the other three shrub 

species was reduced at the medium fertility level (35 percent 

for CORA, 53 percent for CHNA and EPVI). Algal inoculation increased shrub survival from 95 percent to 99 percent 

at low fertility and from 62 percent to 72 percent at medium 

fertility. Algal inoculation has consistently increased plant 

survival in our other greenhouse experiments (R. Pendleton, 

data on file, Rocky Mountain Research Station, Albuquerque, 

NM). Whether this effect is due to the presence of the algae 

themselves (possible precluding colonization by facultative 

pathogens) or to the alginate carrier is not known.

Soil fertility level significantly affected root and shoot 

biomass of all shrubs (P < 0.0138), except EPVI. Fertilization 

increased shoot biomass of the faster growing species (ARFI, 

ARNO, and CHNA) 20- to 40-fold (fig. 1a). CORA also 

responded to a lesser degree, increasing shoot growth fivefold. Soil fertility significantly altered root/shoot ratios of all 

shrub species (P < 0.0001) indicating proportionately less 

investment in root biomass at higher soil nutrient levels (fig. 

1b). All species invested more actual biomass in roots than 

shoots at low fertility, but at medium fertility, the reverse was 

true.

Statistical differences in growth of individual species due 

to inoculation treatment were few and varied with soil fertility 

level. However, a comprehensive examination at growth 

results by fertility level allows some meaningful generalizations to be made. At medium fertility, the faster growing 

ARFI, ARNO, and CHNA produced the greatest shoot and 

total growth with no microorganism additions (significantly 

so for ARNO and CHNA; fig. 2a). Shoot growth of CORA 

grown at medium fertility was suppressed in the algal inoculation treatment (P = 0.0299), whereas EPVI grew best in 

the presence of the algae (P = 0.0133). Under low nutrient 

conditions, only CORA showed a significant difference with 

inoculation treatment, producing the greatest shoot growth in 

the mycorrhizal treatment (fig. 2b). However, in no case did 

control plants exhibit the greatest growth at low soil fertility, 

and most shrub species appeared to respond positively to one 

or more inoculation treatments: ARNO and CORA to mycorrhizal inoculum, CHNA and EPVI to the algal inoculum.

Competition with BRTE significantly affected all aspects 

of shrub growth (P < 0.0033), reducing biomass production 

of both roots (data not shown) and shoots (fig. 3). The effect 

of inoculation treatment on competitive interactions differed 

among shrubs. ARFI showed no significant treatment differences in shoot growth whether grown alone or in competition 

with BRTE (fig. 2b, 4a). It is interesting to note, however, 

that when ARFI and BRTE were grown together, the control 

treatment had the least average ARFI biomass and the most 

BRTE biomass (fig. 4). The mycorrhizal treatment averaged a 

30 percent higher shoot biomass of ARFI over that of control 

plants, whereas shoot biomass of BRTE in the mycorrhizal 

treatment was 8 percent lower than that of control plants.

CHNA likewise showed no significant treatment differences at low fertility, either with or without competition from 

BRTE. BRTE, however, showed a significant treatment effect 
138 USDA Forest Service RMRS-P-47. 2007

Figure 1. Effect of soil fertility level on (a) shoot 

biomass and (b) root/shoot ratio of five 

Intermountain shrub species. Shrub species 

are indicated by four letter codes. See text for 

an explanation of codes.

Figure 2. Effect of inoculation treatment 

on shoot growth of five Intermountain 

shrub species growing at (a) medium 

and (b) low soil fertility. Letters denote 

significant differences at P < 0.05 using 

the Tukey test for multiple comparisons.
USDA Forest Service RMRS-P-47. 2007 139

for mycorrhizal inoculation (P = 0.0259). Shoot biomass of 

BRTE was reduced 17 percent (fig. 4) and root biomass was 

reduced 22 percent in the presence of mycorrhizae (root data 

not shown).

When grown alone at low soil fertility, CORA grew best 

in the presence of mycorrhizae (fig. 2b.). This difference 

disappeared when grown in competition with BRTE (fig. 4a). 

Shoot biomass of mycorrhizal CORA plants growing with 

BRTE averaged 7 percent lower (nonsignificant) than that 

of controls. Above-ground biomass of BRTE, however, was 

significantly affected by inoculation treatment. Shoot growth 

of BRTE was reduced by 12 percent in the presence of mycorrhizae (P = 0.0112), but increased 24 percent in the presence 

of the algal inoculum (P = 0.0046).

In the absence of competition, EPVI showed a slight, 

though not significant, increase in shoot growth in response 

to algal inoculation (fig. 2b). When grown with BRTE, algal 

inoculation made a much greater difference in EPVI shoot 

growth (P = 0.0161). The two algal treatments averaged a 

58 percent increase in EPVI shoot growth (fig. 4a) and a 75 

percent increase in root growth (data not shown) over that of 

control plants. Mycorrhizae alone did not affect shoot growth 

of the shrub, but significantly decreased shoot biomass of 

BRTE (P = 0.0382; fig. 4b).

ARNO also showed a small, though not significant, increase 

in shoot growth in response to mycorrhizal inoculation when 

growing alone at low soil fertility (fig. 2b). In competition 

with BRTE, however, control treatment shrubs produced the 

Figure 4. Shoot biomass of (a) shrubs and (b) cheatgrass grown together in a low fertility soil. Letters 

denote significant differences at P < 0.05 using 

the Tukey test for multiple comparisons.

Figure 3. Effect of competition with cheatgrass on shoot 

biomass of five Intermountain shrub species. P 

values indicate level of significance when comparing 

shrubs grown alone versus those grown in competition with cheatgrass.
140 USDA Forest Service RMRS-P-47. 2007

greatest shoot growth (P = 0.0115; fig. 4a). Growth of BRTE 

was not significantly affected by treatment (fig. 4b). It therefore appears that, for ARNO, soil microorganisms did not 

provide a benefit for shrubs growing in competition with 

BRTE.

Discussion

Associations with arbuscular mycorrhizal fungi have been 

reported for many aridland plant species, including many 

shrubs (for example, see Bethlenfalvay and others 1984; 

Lindsey 1984). Benefits to the plant include enhanced uptake 

of minerals, improved water relations, and reduced susceptibility to pathogens (Miller and Jastrow 1994; Newsham 

and others 1995; Mathur and Vyas 2000). The presence or 

absence of mycorrhizal fungi can also affect plant community composition and diversity (Grime and others 1987; van 

der Heijden and others 1998; Hartnett and Wilson 1999). The 

role that mycorrhizal fungi might play in regulating competitive interactions between native vegetation and exotic annual 

grasses, such as cheatgrass, is not well understood. In monoculture, cheatgrass shows no positive response to mycorrhizal 

fungi, although colonization levels can be quite high (Allen 

1984; Benjamin and Allen 1987; Schwab and Loomis 1987). 

Goodwin (1992) hypothesized that competition between 

native and exotic grasses would be little changed by mycorrhizal fungi. Experiments between cheatgrass and shrubs, 

however, had not previously been done.

Biological soil crusts have been shown to improve growth 

and establishment of many aridland plant species, including 

CORA (Harper and Pendleton 1993; Belnap and others 

2003; Pendleton and others 2004). Unfortunately, manipulative studies looking at effects of soil crusts on interspecific 

competition have not been done. Larsen (1995) reported that 

density of cheatgrass was lower on intact crusts as compared 

to uncrusted soils, whereas density of native Stipa was unaffected. Biological crust-forming organisms interact with a 

variety of other organisms, including small invertebrates, 

rhizobia, and mycorrhizal fungi (Harper and Pendleton 

1993; Belnap 2003). Furthermore, mycorrhizae may enhance 

a plant’s ability to utilize nitrogen fixed by crust-forming 

cyanobacteria and lichens (Ibijbijen and others 1996; Hawkes 

2003). These studies suggest that soil microorganisms may be 

important regulators of competition in arid shrubland ecosystems.

In this experiment, the addition of mycorrhizae appeared 

to intensify competition between shrub seedlings and cheatgrass. At low fertility, shrubs with mycorrhizal additions were 

equal to or slightly larger than controls. When grown with 

cheatgrass, however, mycorrhizal treatment shrubs tended 

to be smaller than control plants for all shrub species except 

ARFI. However, in four of five cases, shoot growth of cheatgrass growing with shrubs was reduced to a greater extent, 

suggesting that the presence of mycorrhizae may positively 

affect the shrub’s ability to compete with cheatgrass.

Results for the algal inoculation were mixed. Algal inoculation increased growth of EPVI (and possibly ARFI) grown 

in competition with cheatgrass. In contrast, the algal inoculum 

appeared to benefit cheatgrass when grown in competition 

with ARNO and CORA. Competition for soil nutrients likely 

occurs between algae and vascular plants during initial crust 

formation. Results may have been different had the crust been 

allowed to establish for a period, or if mature crusts had been 

used.

The finding that soil microorganisms may affect survival, 

growth, and competitive interactions of native shrubs with 

exotic annuals, such as cheatgrass, is of considerable importance to current land management practices. Shrubs comprise 

the dominant form of plant life throughout much of the 

western United States and are important components of many 

other vegetation types. Shrubs contribute to vegetation structure, biodiversity, and provide food and shelter to a variety 

of wildlife. Reestablishing shrub cover is a priority for many 

management plans; however, seedling establishment in the 

presence of annual grasses is unlikely to succeed without some 

kind of weed control (Stevens and Monsen 2004). Our results 

indicate that soil microorganisms, including crust-forming 

algae and arbuscular mycorrhizal fungi, may enhance seedling establishment in the presence of cheatgrass. Additional 

field studies are warranted.

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Schwab, S. M.; Loomis, P. A. 1987. VAM effects on growth of 

grasses in monocultures and mixtures. In: Sylvia, D. M.; Hung, 

L. L.; Graham, J. H., eds. Proceedings of the 7th North American 

conference on mycorrhizae, Gainesville, FL: University of 

Florida, Institute of Food and Agricultural Sciences: 7.

Stevens, R.; Monsen, S. B. 2004. Guidelines for restoration and 

rehabilitation of principal plant communities. In: Monsen, S. B.; 

Stevens, R.; Shaw, N. L., comps. Restoring western ranges and 

wildlands. Gen. Tech. Rep. RMRS-GTR-136-vol-1. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station: 199-294.

van der Heijden, M. G. A.; Klironomos, J. N.; Ursic, M.; Moutoglis, 

P.; Strietwolf-Engel, R.; Boller T.; Wiekman, A.; Sanders, I. R. 

1998. Mycorrhizal fungal diversity determines plant biodiversity, 

ecosystem variability and productivity. Nature 396: 69-72.

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.

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., 

eds. Proceedings: symposium on cheatgrass invasion, shrub dieoff, and other aspects of shrub biology and management. Gen. 

Tech. Rep. INT-276. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Intermountain Research Station: 4-10.

The Authors

1 Research Ecologists, USDA Forest Service, Rocky Mountain 

Research Station, Albuquerque, NM. rpendleton@fs.fed.us 2 Research Scientist, Center for Environmental Management of 

Military Lands, Colorado State University, Fort Collins, CO. 3 Professor, Department of Biology, John Carroll University, 

University Heights, OH. 4 Professor, Department of Integrative Biology and Curator of 

Lichens, M.L. Bean Museum, Brigham Young University, 

Provo, UT.
142 USDA Forest Service RMRS-P-47. 2007

Introduction

Ceratoides lanata var. lanata (winterfat) is a widespread 

chenopod on western rangelands. The plant is valued for its 

nutrient content, grazing and drought tolerance, palatability to 

large herbivores, and ability to rapidly establish on disturbed 

soils (Stevens and others 1977). The subspecies C. lanata var.

subspinosa (‘subspinosa’), native to the southwestern U.S. 

and northern Mexico, is reputedly unpalatable to livestock 

(Gibbens 1999; Ueckert 2000). Although no controlled studies 

directly evaluating the palatability of ‘subspinosa’ have been 

found, its reputation for unpalatability has been indirectly 

supported in a high density stocking study at the Jornada 

Experimental Range in Southern New Mexico (Anderson 

1990). In the study, cattle, sheep, and goats in mixed paddocks 

were more likely to consume tarbush (Flourensia cernua DC 

than ‘subspinosa’ (table 1). Tarbush is generally described as 

unpalatable, and has been used as a model “unpalatable” plant 

for studies evaluating diet selection by livestock (Estell and 

others 1994, 1996, 1998).

Curiously, observations of heavily grazed ‘subspinosa’ 

north of the Chihuahuan Desert suggest that some phenotypes of ‘subspinosa’ are palatable. Availability of palatable 

and unpalatable phenotypes could make C. lanata var. subspinosa a useful seed source for plant breeders seeking 

drought tolerant varieties and an interesting model plant for 

identification of secondary compounds influencing diet selection. Here we report the identification of 33 volatile compounds 

extracted from ‘subspinosa’ using solid-phase microextraction. Relative amounts of these compounds were examined 

in 106 plants from 13 populations. These compounds were 

subjected to a stepwise discriminate analysis in order to test 

the hypotheses that differences in volatile composition could 

be used to distinguish between heavily grazed and ungrazed 

populations of ‘subspinosa.’

Materials and Methods

‘Subspinosa’ was collected from 12 sites in New Mexico. 

The GPS coordinates for these sites, as determined using a 

Garmin GPS 12 personal navigator, are listed in table 2. 

Additional samples were provided by Darrell Ueckert from 

the Texas Agricultural Experiment Station in San Angelo. 

Each site was characterized as either “heavily grazed” or 

“ungrazed” (table 2). The populations from Carrizozo, 

Magdalena, Willard, Dusty, and Winston were all collected 

from populations that extended into pastures stocked with 

cattle. Plants inside the stocked pastures had been grazed to 

less than 20 cm.

Populations from two sites on the NMSU-Corona ranch 

were in pastures from which livestock grazing had been 

limited. One site was an official grazing exclosure. However, 

Differences in Volatile Profiles Between Populations of 

Ceratoides lanata var. subspinosa (Rydb.) J.T. Howell

Abstract: Ceratoides lanata (Rydb.) J.T. Howell, common winterfat, is valued for its 

nutrient content and palatability to livestock; however, the subspecies Ceratoides lanata 

var. subspinosa (Rydb.) J.T. Howell, (‘subspinosa’) is considered unpalatable. Curiously, 

observations of ‘subspinosa’ revealed several populations in central New Mexico that 

were heavily grazed. Volatile terpene profiles are associated with differences in palatability 

in many plant species. To determine whether differences in volatile profiles between 

‘subspinosa’ populations would correlate with apparent differences in palatability, plants from 

13 populations of ‘subspinosa’ were collected. Volatile analysis of shoot samples identified 

33 compounds. Limonene, myrcene, and 3-carene were the most abundant volatiles in all 

populations, comprising 81 percent and 85 percent of the volatiles detected in heavily grazed 

and ungrazed plants, respectively.

Compounds present in at least half of either the heavily grazed or ungrazed plants were 

subjected to a stepwise discriminate analysis of relative quantities. The analysis identified 

a subset of 14 chromatographic peaks (myrcene, 3-hexenol, 3-carene, AR-curcumene, 

limonene, n-hexanol, p-cymene, a mixture thought to contain alpha-pinene, alpha-thujene, 

and tricyclene, a mixture thought to contain n-decanal, and five unknowns), which may 

distinguish between palatable and unpalatable phenotypes. When a discriminate rule based 

on these chemicals was applied to chemical data from individual plants at all sites, none of 

the plants were misclassified. The possibility that these varied oil profiles may be used to 

distinguish palatable from unpalatable phenotypes is discussed.

Mary Lucero1

Rick Estell2

Dean Anderson2

Ed Fredrickson2

Marta Remmenga3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 143

plants on opposite sides of the fences to both pastures were 

accessible to sheep, and had been heavily grazed. Researchers 

working at the ranch stated that the winterfat populations were 

typically utilized by sheep, especially in the winter and early 

spring, when other forage was limited.

The samples from San Angelo were classified as unpalatable to cattle, sheep, and goats (Ueckert 2000). ‘Subspinosa’ 

populations from the Jornada Experimental Range, historically identified as common winterfat, have all been classified 

as unpalatable. One of these sites was previously utilized for 

the high density feeding study illustrated in table 1.

Two more populations were collected from the Chihuahuan 

Desert Rangeland Research Reserve near Las Cruces, NM. 

These populations were unusual in that they were small, 

both in number of plants (less than twenty plants each) and 

in size (less than 30 cm/plant). Observations of plants in the 

field revealed some evidence of light grazing. Approximately 

5 percent of the shoots had been removed. The sharp edges 

remaining on removed shoots suggested grazing was by 

rabbits rather than livestock. We classified both these populations as “ungrazed.”

All samples were collected in the fall of 2000 after flowering. Samples consisted of 10 ten cm leaders from each plant 

(table 2). When possible, 10 plants were sampled at each 

site. The year 2000 had little summer rainfall, and at some 

sites fewer than 10 plants had flowered. Samples were placed 

under dry ice upon harvesting. After transport, samples were 

Table 2. Site locations, usage classification (heavily grazed or ungrazed, with “ungrazed” defined as populations that exhibited no clear evidence 

of grazing by livestock) of Ceratoides lanata var. subspinosa (Rydb.) J.T. Howell, (‘subspinosa’).

 Elevation Sampling Number Usage

Site Latitude Longitude (m) date of plants classification

Corona Range and Livestock Research Center 34o16.710’ 105o23.612’ 1,905 8/3/2000 10 grazed

Corona Range and Livestock Research Center 34o16.481’ 105o19.862’ 1,864 8/3/2000 10 grazed

Magdalena 33o51.515’ 107o19.511’ 1,912 8/10/2000 10 grazed

Willard 34o 22.992’ 105o

42.985’ 1,972 8/3/2000 10 grazed

Dusty 33o57.297’ 107o39.869’ 2,273 9/29/2000 10 grazed

Winston 33o21.107’ 107o33.382’ 1,838 9/29/2000 10 grazed

Chihuahuan Desert Rangeland Research Reserve 32o35.236’ 106o 55.703’ 1,341 7/27/2000 8 ungrazed

Chihuahuan Desert Rangeland Research Reserve 32o33.823’ 106o 54.269’ 1,341 7/27/2000 2 ungrazed

Jornada Experimental Range 32o 43.295’ 106o46.187’ 1,352 7/25/2000 8 ungrazed

Jornada Experimental Range 32o31.142’ 106o44.630’ 1,325 7/7/2000 1 ungrazed

7/30/2000

Jornada Experimental Range 32o31.933’ 106o41.773’ 1,344 8/9/2000 7 ungrazed

Table 1. Summary of bite-count data resulting from high density feeding trials with cattle, sheep, and 

goats (Anderson, 1990). Initial forage composition was determined, then fixed numbers of livestock 

were placed in paddocks under continuous observation. The number of bites taken from each 

species of plant was recorded. Data reflecting “subspinosa” (Ceratoides lanata var. subspinosa 

[Rydb.] J.T. Howell ) and tarbush (Flourensia cernua DC [comp.]) selection are shown here.

Paddock 1 2

Plant species % composition % of bites % composition % of bites

‘subspinosa’ 4.5 1.6 1.1 0.2

tarbush 30.8 42.4 37.3 50

stored at -20°C prior to volatile extraction. Taxonomic classification was verified at the Range Science Herbarium at New 

Mexico State University and voucher specimens were deposited there.

Preparation for Solid Phase Microextraction (SPME) 

analysis consisted of grinding all leaders from a single 

plant to a coarse powder under liquid nitrogen. SPME was 

performed by placing 0.2 g (fresh weight) of ground plant 

tissue into 4 mL glass screw-cap vials. Vials were sealed 

with pre-baked aluminum foil and ethanol-washed Viton 

septa, then equilibrated for 3.5 h at 50°

C. SPME fibers (100 

uM PDMS, Supelco, Bellefonte, PA) were exposed to vial 

headspace at a depth of 1 cm for 20 min using a manual 

fiber holder (also from Supelco). The fiber was injected into 

a Varian model 3400 GC with a DB-5 column (30 m x 0.25 

mm fused silica capillary column, film thickness 0.25 μm) 

coupled to a Finnigan ion trap mass spectrometer (EI, 70 

eV) and desorbed for 3 min. Blank injections followed each 

sample to verify the absence of residual compounds on the 

SPME fiber.

GC/MS analysis was performed using Helium at approximately 1 mL/min as a carrier gas. Injector and transfer line 

temperatures were set at 220°

C and 260°C, respectively. The 

initial column temperature was 60°C and a linear temperature 

increase of 3°C/min was programmed into each run. Duplicate 

extractions of each sample were examined. Compounds were 

identified by comparing mass spectra and retention indices 
144 USDA Forest Service RMRS-P-47. 2007

with literature data (Adams 1995, 2001) or with authentic 

standards.

Relative amounts of each compound detected were defined 

based on relative peak heights. [Total Ion Chromatogram 

(TIC) peak height]/[TIC peak height of 4 ng 3-carene] X 100. 

Compounds with relative heights greater than 0.01 detected 

in at least half of either the heavily grazed or ungrazed plants 

were subjected to a stepwise discriminate analysis of relative 

heights against palatability. The resulting discriminate rule 

was then applied individually to each plant sampled.

Results

A total of 62 unique volatiles were detected in SPME 

samples from winterfat. Those that comprised greater than 

0.01 percent of the chromatographic peak area in at least 50 

percent of the plants from either the grazed or the ungrazed 

populations are presented in table 3. Amounts shown represent either the relative peak height (RH), which was calculated 

as the peak height relative to the height of 4 ng of the monoterpene standard 3-carene, or the percent height, which 

represents the percent of the chromatogram comprised of that 

particular peak. Derived, rather than actual values were necessary because analytical grade standards were not available for 

all of the compounds found in winterfat.

Of the 33 volatiles listed in table 3, fourteen were positively 

identified by matching spectra and retention indices to library 

values. Several compounds consistently gave non-gaussian 

peaks and spectra that varied at points across the peaks. These 

are identified in the table with question marks indicating that 

the peaks detected were probably co eluting with unknown 

compounds.

Limonene was the dominant peak in all samples, 

comprising nearly 50 percent of the SPME-extractable fraction. Curiously, seven plants from the site at Carrizozo also 

Table 3. Compounds found in at least 50 percent of either the heavily grazed or ungrazed ‘subspinosa’ populations. Values represent the mean 

peak height relative to the height of 4 ng 3-carene (Mean RH), the standard deviation of the Mean RH, the mean peak height expressed as a 

percent of the total chromatogram (Mean pH), and the standard deviation of the Mean pH. Compounds whose spectra did not match anything 

in available reference libraries were designated as CELA (Ceratoides lanata), followed by the retention time at which they eluted from the 

DB-5 column. Retention index values indicated with an asterisk (*) were determined by extrapolation, since they eluted prior to the retention 

time of the earliest hydrocarbon standard. Compounds with identification followed by “_mix?” were not spectrally pure and probably contained 

two or more chemicals.

Heavily grazed shrubs Ungrazed shrubs

Retention

time Compound ID Mean RH Std RH Mean PH Std PH Mean RH Std RH Mean RH Std PH

597* CELA1.482 0.01 0.01 0.39 0.35 0.01 0.01 0.32 0.22

639* CELA1.62 0.10 0.13 1.85 1.32 0.08 0.11 1.42 1.57

669* CELA1.756 0.00 0.01 0.28 0.22 0.01 0.01 0.26 0.22

693* CELA1.884 0.05 0.03 1.05 0.63 0.05 0.04 1.30 1.14

716 CELA1.977 0.01 0.01 0.28 0.17 0.01 0.01 0.28 0.22

782 CELA2.508_mix? 0.00 0.01 0.19 0.08 0.00 0.00 0.16 0.11

806 CELA2.806 0.02 0.02 0.44 0.33 0.02 0.03 0.42 0.32

861 (Z)-3-hexenol 0.09 0.10 1.66 1.14 0.03 0.06 0.83 1.29

872 n-hexanol 0.02 0.03 0.48 0.36 0.01 0.02 0.22 0.15

931 pinene-thujene mix? 0.03 0.04 0.99 0.60 0.02 0.04 0.74 0.48

940 CELA5.25 0.03 0.03 1.06 0.41 0.03 0.03 0.91 0.33

977 sabinene_mix? 0.06 0.05 1.10 0.54 0.06 0.04 0.96 0.23

981 6-methyl-5-hepten-2-one 0.02 0.02 0.46 0.41 0.01 0.01 0.24 0.07

988 CELA6.6 0.01 0.01 0.22 0.09 0.01 0.03 0.26 0.18

992 myrcene 0.87 0.66 16.12 2.37 0.89 0.54 16.13 1.47

1012 CELA7.38 0.01 0.01 0.20 0.11 0.01 0.01 0.20 0.09

1013 3-carene 0.89 0.69 16.56 2.15 1.05 0.56 19.33 2.03

1027 p-cymene 0.03 0.02 0.55 0.47 0.02 0.02 0.31 0.08

1032 limonene 2.47 1.65 48.78 5.29 2.59 1.26 49.60 5.24

1043 1,8-cineole 0.01 0.01 0.31 0.34 0.00 0.00 0.16 0.08

1074 CELA9.38 0.03 0.02 0.67 0.49 0.01 0.01 0.19 0.09

1085 artemisia alcohol 0.01 0.02 0.26 0.15 0.02 0.02 0.45 0.33

1106 n-nonanal_mix? 0.01 0.03 0.70 1.17 0.02 0.04 1.40 1.35

1107 CELA10.71 0.05 0.04 1.29 1.05 0.08 0.07 1.68 1.13

1170 CELA13.2 0.01 0.01 0.34 0.63 0.00 0.00 0.15 0.09

1206 n-decanal_mix? 0.01 0.01 0.22 0.13 0.01 0.01 0.18 0.09

1220 CELA15.47 0.01 0.01 0.19 0.09 0.00 0.01 0.12 0.03

1419 beta-caryophyllene 0.02 0.04 0.78 1.38 0.02 0.03 0.66 0.57

1438 CELA24.6 0.00 0.01 0.18 0.08 0.02 0.03 0.78 0.66

1458 alpha-humulene 0.01 0.01 0.23 0.13 0.01 0.02 0.33 0.17

1485 germacreneD 0.01 0.02 0.38 0.33 0.02 0.03 0.39 0.32

1486 AR-curcumene 0.01 0.02 0.34 0.26 0.03 0.03 0.55 0.50

1512 (E)-beta-ionone 0.01 0.02 0.38 0.37 0.01 0.01 0.31 0.22
USDA Forest Service RMRS-P-47. 2007 145

contained relatively large peaks of a compound thought to be 

sylvestrene. The retention times of limonene and sylvestrene 

vary only by 2s, and the only significant difference in their 

mass spectra is that limonene has a strong 93 peak with a base 

peak of 67, whereas sylvestrene has a strong 67 peak with 

a base peak of 93. Because of the difficulties in separating 

limonene, a major component, from this putative sylvestrene 

peak (PSP), the decision was made to report calculated peak 

heights rather than areas. This would reduce the potential for 

inaccurate calculation of limonene quantities when PSP was 

present. Unfortunately, the point for the maximum height of 

PSP always fell underneath the shoulder of the limonene peak, 

therefore, relative amounts of PSP are not reported.

Two other major peaks, myrcene and 3-carene, were 

present in every sample analyzed. The combination of 

myrcene, 3-carene, and limonene peaks resulted in a distinct 

chromatographic fingerprint, also seen in common winterfat 

(not shown), which may be unique to Ceratoides.

Stepwise multivariate analysis of the compounds identified 

in table 3 identified a subset of 14 chromatographic peaks that 

best distinguished between grazed and ungrazed populations. 

The subset included myrcene, 3-hexenol, 3-carene, AR-curcumene, limonene, n-hexanol, p-cymene, a mixture thought to 

contain alpha-pinene, alpha-thujene, and tricyclene, a mixture 

thought to contain n-decanal, as well as five unknowns (table 

3). When a discriminate rule based on these chemicals was 

applied to chemical data from individual plants at all sites, 

none of the plants were misclassified.

Discussion

The three major compounds present in all volatile profiles 

observed were limonene, myrcene, and 3-carene. These three 

compounds are ubiquitous monoterpenes found in many of the 

plants we have previously analyzed and often serve as precursors to biosynthesis of other terpenoids. Although the large 

percentages of limonene, an industrially important compound, 

seem attractive, the overall yield of oil in ‘subspinosa’ was 

low. Attempts to harvest and quantify oil by steam distillation resulted in less than 5 uL oil per gram dry weight of leaf 

tissue, approximately half of which was limonene. Therefore, 

even though limonene is abundant relative to other volatiles, 

it is not likely that purification for industrial use would be cost 

effective due to the low yield per gram of plant tissue.

Fifteen of the 33 peaks listed in table 3 could not be identified, even though 14 of these were spectrally pure. This 

abundance of previously undescribed compounds is not 

surprising in natural products analysis due to the remarkable 

diversity of plant volatiles.

The identification of 14 compounds that distinguished 

grazed from ungrazed populations in this preliminary study 

may be seen as a starting point for additional research. 

Although some of the observed differences are undoubtedly 

due to differences in environment and grazing intensity at 

the various sites, it is encouraging to note that some of the 

compounds identified, namely limonene, myrcene, p-cymene, 

and alpha-pinene have also been associated with differences in 

livestock herbivory in tarbush [Flourensia cernua DC] (Estell 

and others 1996). Curiously, subsequent studies in which individual terpenes associated with low herbivory in tarbush were 

applied to alfalfa pellets in sheep feeding trials demonstrated 

only minimal reductions in herbivory (Estell and others 

2002). It is possible that the mixture, rather than the individual 

compounds, is necessary for antiherbivory effects. If this is 

the case, a benefit of multivariate techniques is the ability 

to narrow down the possible combinations of compounds, 

permitting identification of groups of compounds, rather than 

individuals, which may act in conjunction to create an effect. 

Tests in which the compounds, combined in proportions 

defined in discriminate rules following multivariate analysis, 

need to be carried out.

Perhaps the most significant findings in this preliminary 

data include the abundance of Ceratoides lanata var. subspinosa (Rydb.) J.T. Howell in New Mexico, where it had not 

been previously described, and the observation that in some 

populations, ‘subspinosa’ showed evidence of heavy grazing. 

C. lanata has long been considered a desirable species on 

grazed lands and considerable effort has been devoted to 

development of germplasm suitable for revegetation in 

various environments. The availability of large and phenotypically diverse populations of ‘subspinosa’ may be useful in the 

development of germplasm for use in arid environments.

References

Adams, R. P. 1995. Identification of essential oil components by 

gas chromatography/mass spectroscopy. Carol Stream, Illinois, 

Allured Publishing Corporation.

Adams, R. P. 2001. Identification of essential oil components by gas 

chromatography/quadrupole mass spectroscopy. Carol Stream, 

Illinois, Allured Publishing Corporation.

Anderson, D. A. 1990. Unpublished Data. Research Animal Scientist, 

USDA-ARS Jornada Experimental Range, Las Cruces, NM.

Estell, R.; Fredrickson, E.; Anderson, D. M.; Havstad, K.; Remmenga, 

M. D. 2002. Effects of four mono- and sesquiterpenes on the 

consumption of alfalfa pellets by sheep. Journal of Animal 

Science. 80(12): 3301-3306.

Estell, R. E; Fredrickson, E. L.; Anderson, D. M.; Havstad, K. M.; 

Remmenga, M. D. 1996. Tarbush leaf surface terpene profile in 

relation to mammalian herbivory. In: Barrow, J. R., McArthur, 

E. D.; Sosebee, R. E.; Tausch, R. J., compilers. 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. 237-241.

Estell, R. E.; Fredrickson, E.; Anderson, D. M.; Havstad, K.; 

Remmenga, M. D. 1998. Relationship of tarbush leaf surface 

terpene profile with livestock herbivory. Journal of Chemical 

Ecology. 24(1): 1-11.

Estell, R. E.; Fredrickson, E.; Anderson, D. M.; Mueller, W. F.; 

Remmenga, M. D. 1994. Relationship of tarbush leaf surface 

secondary chemistry to livestock herbivory. Journal of Range 

Management. 47(6): 424-428.

Gibbens, R. 1999. Personal communication. Range Scientist, USDAARS Jornada Experimental Range, Las Cruces, NM.
146 USDA Forest Service RMRS-P-47. 2007

Stevens, R.; Giunta, B. C.; Jorgensen, K. R.; Plummer, A. P. 1977. 

Winterfat (Ceratoides lanata). Publication 77-2. Salt Lake City, 

UT: Utah Division of Wildlife Resources. 41 p.

Ueckert, D. 2000. Personal communication. Regent Fellow 

and Professor, Range Improvement Rangeland Ecology and 

Management, Texas A & M University San Angelo Research and 

Extension Center, San Angelo, TX.

The Authors

1 Postdoctoral associate, USDA-ARS-Jornada Experimental Range, 

Las Cruces, NM. malucero@nmsu.edu 2 Research scientists, USDA-ARS-Jornada Experimental Range, 

Las Cruces, NM. 3 Associate professor, Department of Economics and International 

Business, New Mexico State University, Las Cruces, NM.
USDA Forest Service RMRS-P-47. 2007 147

Introduction

Widely distributed across the interior western United 

States, winterfat (Krascheninnikovia lanata [Pursh] A. D. J. 

Meeuse & Smit; synonym: Ceratoides lanata [Pursh] J. T. 

Howell) (U.S. Department of Agriculture, Natural Resources 

Conservation Service 2004) is an important subshrub on 

millions of acres of salt desert shrublands, often occurring as 

a landscape-dominating species. Although it is most common 

in valley bottoms and foothills, it is found on sites ranging 

from the Lower Sonoran and Mojave Deserts to mountain 

ridges above 3,050 m in Utah to mixed-grass prairies of the 

Midwest (Carey 1995; Stevens and others 1977). A highly 

variable species morphologically, dwarf forms of winterfat 

are common on desert floors, salty soils, and high mountain 

ridges, while larger, more woody forms, grow on alluvial fans, 

foothills, and mesas in the southern portion of the species’ 

range (McArthur and Monsen 2004).

On the Snake River Birds of Prey National Conservation 

Area (listed hereafter as ‘Birds of Prey’) located southwest of 

Boise, Idaho, extensive loss of winterfat-dominated communities has been linked to shortened fire intervals associated 

with the advance of the annual exotic invasive, cheatgrass 

(Bromus tectorum L.). Winterfat communities at Birds of Prey 

are especially important for supporting high Townsend ground 

squirrel (Spermophilus townsendii Bachman) densities that 

provide a prey base for nesting raptor species (Nydegger and 

Smith 1986; Van Horne and others 1998).

Efforts to reestablish winterfat in the Birds of Prey 

following wildfires are often hampered by the lack of local 

seed supplies and the reportedly poor establishment of the 

indigenous seed source, particularly with competition from 

cheatgrass. Winterfat seeding efforts may be hampered by 

the rapid germination and root growth of cheatgrass seedlings with spring or autumn precipitation that allows them to 

compete successfully for available resources (Harris 1967, 

1977; Harris and Goebel 1976). Concerns for reestablishing 

and maintaining the local winterfat population on the Birds 

of Prey make it essential that we understand the impact of 

cheatgrass competition on its germination and establishment. 

The purpose of this study was to compare germination and 

seedling growth of four native winterfat seed collections with 

cheatgrass competition.

Methods

The winterfat seed sources were: (1) Birds of Prey; (2) 

northeastern New Mexico; (3) Northern Cold Desert Selected 

Germplasm; and (4) Open Range Tested Germplasm. All seed 

was harvested in fall 2003.

The Birds of Prey seed was a composite of three local 

wildland collections made at the Birds of Prey National 

Conservation Area on the Lower Snake River Plain south 

of Boise, Idaho. The area ranges from 850 to 1,000 m in 

elevation and is characterized by dry, hot summers and mild 

Emergence and Growth of Four Winterfat Accessions in 

the Presence of the Exotic Annual Cheatgrass

Abstract: Winterfat (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit; synonym: 

Ceratoides lanata [Pursh] J. T. Howell) is a desired shrub species and an integral component 

of salt desert shrublands in the Intermountain West. On the Snake River Birds of Prey National 

Conservation Area in southwestern Idaho, extensive loss of winterfat-dominated communities 

has been linked to altered fire regimes associated with cheatgrass (Bromus tectorum L.) 

invasions. Post-fire revegetation efforts are often hampered by the quick emergence of 

cheatgrass seedlings with autumn or spring moisture. We compare the establishment of four 

winterfat populations (Birds of Prey; northeastern New Mexico; Northern Cold Desert Select 

Germplasm; and Open Range Tested Germplasm) with and without cheatgrass competition. 

Seed of each accession was planted in 15 cm diameter pots containing four densities of 

cheatgrass (0, 2, 4, and 8 plants per pot) in a greenhouse. Plant measurements were made 

4, 5, 7, 9, 11, 13, 15, 17, 19, and 21 weeks after planting. Measurements included winterfat 

survival, height and two canopy diameters, and cheatgrass height and number of leaves and 

culms per plant. Initial establishment was greatest for the New Mexico winterfat source at all 

cheatgrass levels. Growth of this source exceeded the others in the absence of cheatgrass. 

However, the presence of cheatgrass depressed growth of all sources by at least 90 percent. 

Establishment of winterfat on cheatgrass infested rangelands necessitates seeding on sites 

where cheatgrass densities are low or reduced by site preparation procedures.

Ann L. Hild1

Jennifer M. Muscha2

Nancy L. Shaw3

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
148 USDA Forest Service RMRS-P-47. 2007

winters. Annual precipitation in Boise averages 306 mm (U.S. 

Department of the Interior, U.S. Geological Survey, Biological 

Resource Division 1996). The dwarf, spreading growth form 

of this seed source averages about 0.2 m in height (Nydegger 

and Smith 1986) and is typical of populations found in association with other salt desert species such as shadscale (Atriplex 

confertifolia [Torr. & Frem] S. Wats.), squirreltail (Elymus 

elymoides [Raf.] Swezey), and cheatgrass.

New Mexico seed was collected from native stands near 

Mora in northeastern New Mexico’s Colfax County. The growth 

form is large, upright, and woody. Plants commonly grow 

on rocky foothills and valleys in association with ponderosa 

pine (Pinus ponderosa P. & C. Lawson) and pinyon-juniper 

(Pinus L.- Juniperus L.) communities at elevations from 

1,500 to 2,000 m (Stevens and others 1977). This morphological variant has sometimes been given the subspecific or 

variety epithet subspinosa (see Booth 2005 for discussion).

Annual precipitation in Colfax County ranges from 380 mm at 

lower elevations and increases to 400 mm in higher foothills 

(U.S. Department of Agriculture, Soil Conservation Service 

and Forest Service 1982). Northern Cold Desert Winterfat 

Selected Germplasm (NCD) was released by the U.S. 

Department of Agriculture, Natural Resources Conservation 

Service, Aberdeen Plant Materials Center in 2001 (St. John 

and Blaker 2004). A composite of four eastern and southern 

Utah and one western Colorado population, it was selected for 

cold, drought, and alkalinity tolerance. Plants have an upright 

growth habit, growing to 0.9 m in height. The germplasm is 

recommended for Intermountain sites receiving 180 to 400 

mm of annual precipitation (U.S. Department of Agriculture, 

Natural Resources Conservation Service 2002). The seed used 

in this study was produced in a seed orchard.

The Open Range Tested Germplasm Winterfat is a 

composite of three accessions from eastern and south-central 

Montana and south-central Wyoming, selected for their seedling vigor and forage and seed production. Plants are spreading 

and 0.3 to 0.75 m tall. Recommended area of use includes 

the northern Great Plains, northern Intermountain area, and 

the Snake River Plain (Majerus and Holzworth 2003). Open 

Range seed was harvested from a nursery planting.

Cheatgrass seed and soil for greenhouse competition studies were collected from the Birds of Prey National 

Conservation Area in summer 2003. Soil texture was a silty 

clay loam, organic matter averaged 1.5 percent, and pH was 

7.8. Potting soil was prepared by first sieving the field soil to 

remove large rocks and pieces of organic material. A soil mix 

of two parts of field soil to one part vermiculite by volume 

was prepared to insure water infiltration into the pots. All seed 

was allowed to afterripen for 12 weeks prior to study initiation 

to enhance germination (Springfield 1972) and then cleaned to 

remove debris and small utricles. For each source of winterfat, 

12 pots, each 15 cm in diameter, were prepared for each block. 

Four winterfat seeds were centered in each pot. On the same 

date, cheatgrass seeds were placed around the perimeter of 

three pots for each source to obtain one of four densities: 0, 2, 

4, or 8 seedlings per pot. Three pots containing no winterfat 

were also planted at each grass density to document cheatgrass 

growth without winterfat present. Seeds were covered with a 

0.5 cm layer of washed masonry sand to insure good seed-tosoil contact and to prevent seed movement during watering.

Because we hand selected large seed for both cheatgrass 

and winterfat (Springfield 1973) to optimize germination 

success, we had little problem in obtaining the desired densities. Excess seedlings of either species were thinned as 

necessary to obtain target densities by clipping seedlings at 

the plant base. However, at the time of seeding, we did start 

germination of both winterfat and cheatgrass seeds in additional identical pots to serve as replacement plants in case 

seeds in treatment pots did not germinate. In two cases, we 

transplanted winterfat seedlings into the study pots within 

the first 2 weeks of the study because winterfat seeds did not 

germinate in the center of treated pots. We did no additional 

transplanting or thinning after the second week.

Pots within each block were randomized on greenhouse 

benches and re-randomized weekly. Soils were thoroughly 

wetted at the time of planting. Pots were rewatered every 2 

days for the first 2 weeks after seeding. For the remainder of 

the treatment period, pots were allowed to dry until cheatgrass 

plants in the four plants/pot treatments showed evidence of 

temporary wilt, when all treatments were again watered with 

equal amounts (200 ml) of water using a graduated cylinder. 

Temperatures in the greenhouse ranged from 20o

C at night to 

37oC during the day; day length averaged 12 hours.

Plantings were replicated on five dates (blocks) in 2003. 

We documented winterfat and cheatgrass seedling growth 

for 21 weeks following seeding (at 4, 5, 7, 9, 11, 13, 15, 17, 

19, and 21 weeks). On each evaluation date, winterfat seedling survival, height, and two perpendicular canopy diameter 

measurements were recorded for determination of plant size 

(canopy volume). Cheatgrass seedling height and number of 

leaves and culms per plant were recorded on the two consecutive days prior to the winterfat measurements. At 21 weeks, 

we harvested plants, washed roots, and separated plants into 

above-ground and below-ground biomass for measurements 

of leaf and root area with a leaf area meter. Samples were 

oven-dried at 60oC for 48 hours and weighed.

Data were analyzed using ANOVA appropriate to a factorial arrangement in a randomized complete block design using 

sampling dates as repeated measures. Because winterfat seedling size was much smaller in the presence of cheatgrass plants 

than when grown without cheatgrass competition, we also 

compared the four winterfat seed sources to each other when 

grown only with three densities of cheatgrass (excluding the 

0 cheatgrass treatment). Least significant difference (LSD) 

mean separations were evaluated at the 0.05 alpha level in 

SAS (SAS 2002).

Results and Discussion

Two-thirds of winterfat mortality occurred in the first 5 

weeks after planting. After 21 weeks, survival of winterfat 

varied significantly among sources and was greatest for the 

northern New Mexico collection (98.3 percent) followed 
USDA Forest Service RMRS-P-47. 2007 149

by the Open Range (79.7 percent) and Birds of Prey (78.7 

percent) sources, with survival of the Northern Cold Desert 

seed source lowest (56.7 percent) when averaged across all 

four cheatgrass competition levels.

Winterfat leaf area was greatly reduced by the presence of 

cheatgrass at any density (fig. 1) and total biomass followed the 

same trend (data not shown). Leaf area of winterfat from New 

Mexico (2.23 cm2/plant) and Open Range (1.87 cm2/plant) 

sources were significantly greater than the Birds of Prey (1.09 

cm2/plant) and Northern Cold Desert (0.71 cm2/plant) sources 

when grown without cheatgrass. Similar trends were noted 

for total winterfat biomass (data not shown). During weeks 

11 through 21, New Mexico plants produced greater canopy 

volume (fig. 2 a-d) than other sources only in the absence of 

cheatgrass competition. The same differences were significant 

for winterfat leaf area (data not shown).

Growth of cheatgrass (biomass and leaf area) was not 

different among the 2, 4, and 8 plants/pot cheatgrass densities, 

but did differ among the winterfat seed sources (figs. 3 and 4) 

grown with cheatgrass. Cheatgrass biomass was reduced by 

46 percent when grown with the Northern Cold Desert seed 

source and leaf area was reduced by 35 percent when grown 

with the Northern Cold Desert or Birds of Prey seed sources 

relative to the New Mexico source.

Our results indicate that initial emergence and survival 

of the larger-statured New Mexico source with or without 

cheatgrass competition, and 21-week growth (leaf area and 

biomass) of this source in the absence of cheatgrass competition, were greater than for any of the remaining sources. Booth 

(2005) commented that several authors (Booth 1992; Moyer 

and Lang 1976; Springfield 1968) have found differences 

in seed quality and seedling vigor among other accessions 

and suggested that these may result as adaptive responses 

to stressful environments. However, in the presence of 

cheatgrass at any competition level, growth of all four sources 

was reduced by at least 90 percent. Consequently, winterfat 

at the seedling stage appears vulnerable to cheatgrass competition, even when the annual occurs at the lowest densities 

tested. However, it should be noted that as cheatgrass production did not vary among the cheatgrass densities, all of our 

treatments appear to have provided similar levels of competition (in terms of cheatgrass biomass present within a 7.5 cm 

radius of the winterfat seedling). Repeating the experiment 

using the same cheatgrass densities, but larger pots, might 

reveal whether there is a differential in competitive ability of 

the four winterfat sources at lower competition levels.

Both the Northern Cold Desert and Birds of Prey sources 

reduced cheatgrass production, while the more rapidly 

growing New Mexico source had no effect on cheatgrass 

growth. Although cheatgrass is generally considered to be a 

strong competitor with seedlings of other species, Francis and 

Pyke (1996) found that seedlings of ‘Hycrest’ crested wheatgrass (Agropyron desertorum x cristatum), but not those of 

‘Nordan’ crested wheatgrass (Agropyron desertorum), significantly reduced growth of cheatgrass seedlings. Identification 

of the mechanism responsible for differential suppression of 

cheatgrass growth by the winterfat seed sources included in 

this study would aid in understanding the dynamics of competitive interactions between cheatgrass and winterfat.

Although this research was conducted under greenhouse 

conditions, the results clearly indicate that sites where cheatgrass densities are high following wildfires are likely to be 

problematic for winterfat establishment regardless of the seed 

source planted.

Reduction of cheatgrass densities to low levels or seeding 

only in areas where competition is expected to be minimal is 

essential to permit emergence and growth of winterfat seedlings.

Figure 1. Winterfat seedling leaf area by seed 

source and cheatgrass density per pot (2, 4, or 8 

seedlings) after 21 weeks of growth in a greenhouse.

*Number of cheatgrass seedlings per pot.

*
150 USDA Forest Service RMRS-P-47. 2007Figure 2. Canopy volume of winterfat seed sources in response to cheatgrass competition level during the 21-week period following seeding. Cheatgrass density: (a) 0 plants/ pot; (b) 2 plants/pot; (c) 4 plants/pot; and (d) 8 plants/pot. )3 Winterfat Canopy Volume (cm )3 Winterfat Canopy Volume (cm )3 Winterfat Canopy Volume (cm )3 Winterfat Canopy Volume (cm
USDA Forest Service RMRS-P-47. 2007 151

References

Booth, D. T. 2002. Seedbed ecology of winterfat: imbibition 

temperature affects post-germination growth. Journal of Range 

Management. 45: 159-164.

Booth, D. T. 2005. Krascheninnikovia lanata (Pursh) A. D. J. Meeuse 

& Smit. In: Bonner, F. T.; Nisley, R. G., eds. Woody Plant Seed 

Manual. Washington, DC: U.S. Department of Agriculture, Forest 

Service. Online. Available: http://ntsl.fs.fed.us/wpsm/

Carey, J. H. 1995. Krascheninnikovia lanata. In: Fire Effects 

Information System. U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, Fire Sciences 

Laboratory (Producer). : http://www.fs.fed.us/database/ feis

Francis, M.; Pyke, D. A. 1996. Crested wheatgrass-cheatgrass 

seedling competition using a mixed-density design. Journal of 

Range Management. 49:432-438.

Harris, G. A. 1967. Some competitive relationships between 

Agropyron spicatum and Bromus tectorum. Ecological 

Monographs. 37: 89-111.

Harris, G. A. 1977. Root phenology as a factor of competition among 

grass seedlings. Journal of Range Management. 30: 172-177.

Harris, G. A.; Goebel, C. J. 1976. Factors in plant competition in 

seeding Pacific Northwest ranges. Agric. Exp. Sta. Bull. 820. 

Pullman, WA: Washington State University.

Majerus, M.; Holzworth, L. 2003. Open Range Tested Class 

Germplasm Winterfat: a conservation plant for Montana and 

Wyoming. Bridger, MT: U.S. Department of Agriculture, Natural 

Resources Conservation Service: 4 leaves. Brochure.

McArthur, E. D.; Monsen, S. B. 2004. Ch. 20. Chenopod shrubs. In: 

Monsen, S. B.; Stevens, R.; Shaw, N. L., comps. 2004. Restoring 

western ranges and wildlands. Gen. Tech. Rep. RMRS-GTR-136-

vol-2. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station: 467-492.

Moyer, J. L.; Lang, R. L. 1976. Variable germination response to 

temperature for different sources of winterfat seed. Journal of 

Range Management. 29: 320-321.

Nydegger, N. C.; Smith, G. W. 1986. Prey populations in relation to 

Artemisia vegetation types in southwestern Idaho. 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: 

152-156.

Figure 3. Cheatgrass biomass production (g) when planted at three 

densities (2, 4, or 8 seedlings per pot) alone or in the presence of 

winterfat seed sources.

Figure 4. Cheatgrass leaf area (cm2

) when planted at three densities 

(2, 4, or 8 seedlings per pot) alone or in the presence of winterfat 

seed sources.

SAS. 2002. Jmp Statistical Discovery Software. SAS Institute Inc., 

Cary, NC.

Springfield, H. W. 1972. Winterfat seeds undergo after-ripening. 

Journal of Range Management. 25: 479-480.

Springfield, H. W. 1968. Germination of winterfat seeds under 

different moisture stresses and temperatures. Journal of Range 

Management. 21: 314-316.

Springfield, H. W. 1973. Larger seeds of winterfat germinate better. 

Journal of Range Management. 26: 153-154.

St. John, L.; Blaker, P. 2004. New native plant releases from the 

USDA-NRCS, Aberdeen, ID, Plant Materials Center. In: Hild, 

A. L.; Shaw, N. L.; Meyer, S. E.; Booth, D. T.; McArthur, E. 

D., comps. Seed and soil dynamics in shrubland ecosystems: 

proceedings; 2002 August 12-16; Laramie, WY. Proceedings 

RMRS-P-31. Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station: 138-139.

Stevens, R.; Giunta, B. C.; Jorgensen, K. R.; Plummer, A. P. 1977. 

Winterfat (Ceratoides lanata). Pub. 77-2. Salt Lake City: Utah 

State Division of Wildlife Resources. 41 p.

U.S. Department of Agriculture, Natural Resources Conservation 

Service. 2002. Northern Cold Desert Winterfat Selected Class 

Germplasm. Fact Sheet. Aberdeen, ID: U.S. Department of 

Agriculture, Natural Resources Conservation Service, Aberdeen 

Plant Materials Center. USDA, NRCS. 2004. The PLANTS 

Database, Version 3.5 (http://plants.usda.gov). National Plant 

Data Center, Baton Rouge, LA 70874-4490 USA.

U.S. Department of Agriculture, Soil Conservation Service and U.S. 

Department of Agriculture, Forest Service. 1982. Soil Survey of 

Colfax County New Mexico. Washington, DC: U.S. Department 

of Agriculture, Soil Conservation Service and U.S. Department of 

Agriculture, Forest Service. 187 p.

U.S. Department of the Interior, U.S. Geological Survey, Biological 

Resources Division. 1996. Effects of military training and fire in 

the Snake River Birds of Prey National Conservation Area. BLM/

IDARNG Res. Proj. Final Rep. Boise, ID: U.S. Department of the 

Interior, U.S. Geological Survey, Biological Resources Division, 

Snake River Field Station.130 p.

Van Horne, B.; Schooley, R. L.; Sharpe, P. B. 1998. Influence of 

habitat, sex, age and drought on the diet of Townsend’s ground 

squirrels. Journal of Mammalogy. 79: 521-537.
152 USDA Forest Service RMRS-P-47. 2007

The Authors

1 Associate Professor, University of Wyoming, Department of 

Renewable Resources, Laramie, WY. AnnHild@uwyo.edu 2

 Rangeland Scientist III, U.S. Department of Agriculture, 

Agricultural Research Service, Fort Keogh Livestock and Range 

Research Center, Miles City, MT. 3 Research Botanist, U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station, Boise, ID.
USDA Forest Service RMRS-P-47. 2007 153

Introduction

Fourwing saltbush (Atriplex canescens) is one of the shrub 

species most widely seeded for reclamation, revegetation, and 

habitat improvement throughout the semiarid western United 

States (McArthur and Monsen 2004). It has proven to be relatively easy to establish from direct seeding, even on harsh 

disturbances, and it provides valuable forage for all classes 

of livestock as well as wild ungulates. Its seeds are easily 

collected in large quantities and readily cleaned and planted 

with commercial equipment. Perhaps because of this ease of 

use, the species has received relatively little study in terms of 

germination and establishment ecology (reviewed in Meyer 

on line). The classic work of Springfield (1970) remains the 

most detailed study of fourwing saltbush germination biology 

to date. He worked primarily with southwestern collections 

from summer rainfall areas and perhaps for this reason, recognized the role of dry after-ripening, but not moist chilling, in 

alleviating seed dormancy.

Fourwing saltbush is a fall to early winter ripening species, 

with fruits maturing earlier at higher elevations and later at 

lower elevations. The fruits often over-winter on the plants 

and are thus unavailable for germination the first spring after 

production. Whether they germinate soon after dispersal in 

spring, in response to summer rains, in response to winter 

chilling, or in later years depends on post-dispersal dormancy 

status and its interaction with the local environment.

In this study, our goal was to examine variation in the 

dormancy status of freshly harvested fourwing saltbush seed 

collections to determine the relative impact of moist chilling 

and dry after-ripening on dormancy status and to relate any 

differences in primary dormancy and patterns of dormancy 

loss to habitat at the site of seed origin. We also wanted to look 

for differences in initial viability and in patterns of viability 

loss among seed collections. Our collections were made in 

the primarily winter precipitation regions of the Great Basin, 

Snake River Plains, Uinta Basin, Colorado Plateau, and 

Mojave Desert (table 1).

Methods

Seed collections were made in the fall of 1988. A total of 27 

collections were made, but four collections were subsequently 

dropped from the study because of very low fruit fill (< 20 

percent). Seed collections were obtained from four states and 

from the full range of habitat types where fourwing saltbush 

occurs (table 1). Fruits of each collection were de-winged on 

a rubbing board and cleaned by screening and fanning prior 

to the initiation of experiments. As a rough estimate of initial 

viability, we performed a cut test on 200 randomly selected 

fruits from each lot.

Experiments with seeds designated as recently harvested 

were begun in January of 1989, within 3 to 8 weeks of the 

harvest date, depending on individual collection dates. For 

each treatment, eight replications of 25 fruits were included. 

For each replication, fruits were placed in 100 mm plastic 

Petri dishes between two blue germination blotters (Anchor 

Paper, St. Paul MN) and moistened with tap water initially 

and as needed during the course of the experiment. The treatments were: no chilling, 4 weeks of chilling, and 24 weeks of 

chilling. Chilling took place in the dark (in boxes) in a walkin cold room at 2°C, while post-chilling incubation, also in 

the dark, was carried out for 4 wks at 15°C. Germination was 

Seed Germination Biology of Intermountain Populations of 

Fourwing Saltbush (Atriplex canescens: Chenopodiaceae)

Abstract: Fourwing saltbush (Atriplex canescens) is a widely distributed shrub of semiarid 

western North America. We studied viability and germinability of fourwing saltbush seeds over 

10 years for collections from 23 Intermountain populations. Fruit fill averaged 53 percent, and 

96 percent of filled fruits contained viable seeds even after 6 years of laboratory storage. 

Seed collections were generally dormant to some degree at harvest and lost dormancy 

via two processes, moist chilling and after-ripening in dry storage. Prolonged chilling (24 

wks) substituted for dry after-ripening, resulted in germination percentages similar to those 

obtained without chilling after 2 years of storage. Collections from warm desert habitats were 

generally least dormant, while collections from pinyon-juniper and mountain brush habitats 

were highly dormant. But these trends were not very strong. Seeds of the diploid population 

from Jericho Dunes were essentially nondormant at harvest, while those from a population 

near Page, Arizona, were essentially completely dormant. Unchilled seeds did not germinate 

to any degree until tested after 10 years of storage. Patterns of dormancy loss suggest that 

this species is opportunistic and generally able to establish in response to either winter or 

summer precipitation. In addition, its seeds probably form persistent seed banks in the field.

Susan E. Meyer1

Stephanie L. Carlson2

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
154 USDA Forest Service RMRS-P-47. 2007

recorded weekly in the 24-wk chilling treatment and during 

post-chilling incubation for all treatments. Seeds were considered germinated when the radicle visibly protruded from the 

tip of the fruit. At the end of the incubation period, remaining 

fruits in each dish were subjected to a cut test to determine 

their viability. Germination proportion for each treatment and 

replication was calculated based on the total number of viable 

seeds in the dish.

Fruits of each of the 23 collections were stored unsealed 

under laboratory conditions (20 to 22°C, ca. 30 to 35 percent 

relative humidity) for 10 years following the initial germination experiment. Germination tests were carried out after 1, 2, 

6, and 10 years of storage. The experiments at 1 and 2 years 

were similar in design to those for recently harvested seeds, 

except that 4 replications of 50 seeds were included for each 

treatment and collection. After 6 years, the 23 collections were 

subjected to the no chilling treatment only. At the end of the 

incubation treatment, these seeds were evaluated for viability 

using tetrazolium chloride in addition to a 

simple cut test, that is, fruits whose seeds 

appeared filled were stained to determine 

seed viability. After 10 years, four replications of 25 seeds for each collection were 

subjected to the no chilling and 4-week 

chilling treatments. These seeds were not 

subjected to a post-incubation cut test. We 

used initial viability values in the calculation of germination percentages for the 

10-year data.

We analyzed our data using analysis 

of covariance for completely randomized 

designs with seed collection as the class variable and seed 

age (storage period) and chilling duration as continuous variables. Two analyses were performed. The first was a complete 

factorial using the data for recently harvested, 1-year-old, and 

2-year-old seeds. These were the experiments that included all 

three chilling durations. The second analysis was for the no 

chilling treatment only and included data for recently harvested 

seeds and seeds 1, 2, 6, and 10 years old. This approach gave 

two balanced designs. We did not analyze the 4-wk chilling 

data for the 10-year-old seeds beyond calculation of means 

and standard errors because it became apparent that the effects 

of dormancy loss and vigor loss were confounded in this treatment. Germination proportions were arcsine-transformed to 

improve homogeneity of variance prior to analysis.

Simple t-tests were used to compare means obtained from 

different measures of viability, that is, initial cut test, post-germination cut tests at 1 and 6 years, and tetrazolium viability 

evaluation at 6 years.

Principal components analysis (PCA) was performed using 

germination percentages from each of the 12 treatment combinations for each of the 23 seed collections as variables. The 

goal was to detect groups of collections with similar germination responses and to examine whether these groups could be 

interpreted ecologically. Because all the variables were in the 

same units, we performed PCA on the non-standardized correlation matrix. Scores from the first two principal components 

were plotted for each collection, and eigenvector loadings on 

these two principal components were used in the interpretation of the resulting scattergram.

Results

Viability Evaluation

Initial viability as estimated by fruit fill varied from 35 to 

75 percent across collections, with a mean of 52.3 percent 

(table 2). This value was closely matched by the viability estimate based on germinated seeds plus filled seeds remaining 

from experiments with recently harvested seeds (52.0 percent 

mean). Viability percentages based on post-germination cut 

tests from the experiment with 6-year-old seeds were similar 

(54.3 percent mean). More importantly, the viability percentage 

based on tetrazolium staining at 6 years was also very close 

Table 2. Mean percentage of viable seeds for 23 Atriplex canescens collections included 

in the study, as determined by initial cut test to determine fruit fill, post-germination 

cut tests on recently harvested and 6-year-old fruits, and post-germination tetrazolium 

staining for 6-year-old fruits.

Viability percentage

Viability measure Mean Standard error Range

Initial fill estimate 52.3 2.25 35-75

Post-test fill estimate - recently harvested seeds 52.0 2.73 27-72

Post-test fill estimate - 6-year-old seeds 54.3 2.81 31-74

Tetrazolium viability - 6 year old seeds 52.0 2.69 30-72

Tetrazolium viability as percentage of filled fruits 95.8

Table 1. Collection locations and habitat types for 23 Atriplex canescens

seed collections included in the study. Collection locations are 

approximate.

Collection location State Habitat type

Littlefield Arizona Creosote bush shrubland

Glendale Nevada Creosote bush shrubland

Kingman Arizona Creosote bush shrubland

Snow’s Canyon Utah Blackbrush shrubland

Santa Clara Utah Blackbrush shrubland

Page Arizona Blackbrush shrubland

Torrey Utah Salt desert shrubland

Caineville Utah Salt desert shrubland

Roosevelt Utah Salt desert shrubland

Nampa Idaho Sagebrush steppe

Jordan Valley Idaho Sagebrush steppe

Niagra Springs Idaho Sagebrush steppe

Burley Idaho Sagebrush steppe

Ephraim Utah Sagebrush steppe

Wales Utah Sagebrush steppe

Elberta Utah Sagebrush steppe

Jericho Dunes Utah Sagebrush steppe

Cedar Canyon Utah Pinyon-juniper/mountain brush

Beaver Canyon Utah Pinyon-juniper/mountain brush

Starvation Utah Pinyon-juniper/mountain brush

Gay Mine Idaho Pinyon-juniper/mountain brush

Book Cliffs Utah Pinyon-juniper/mountain brush

Winnemucca Nevada Pinyon-juniper/mountain brush
USDA Forest Service RMRS-P-47. 2007 155

to these values (52 percent). The four viability estimates are 

not significantly different from each other. This means that 

the cut test is an excellent estimate of viability for fourwing 

saltbush seeds from 1 to 6 years of age, and that seeds in this 

study did not lose any significant viability overall during this 

period. Tetrazolium viability at 6 years averaged 96 percent of 

viability estimated by cut test.

Viability at 10 years was not explicitly measured, but 

decreases in germination percentage relative to the 6-year data 

suggest that seeds of some lots were beginning to lose vigor. 

This interpretation is supported by the fact that in many of 

these collections, a 4-wk chilling treatment actually resulted 

in a substantial decline in germination percentage relative to 

the no chilling treatment. This effect was rarely seen in earlier 

experiments.

Germination Experiments

Both moist chilling and dry after-ripening resulted in 

increases in germination percentage overall (fig. 1). In the 

factorial experiment with seeds up to 2 years old, both chilling 

and seed age main effects were highly significant, as was their 

interaction (table 3). Longer chilling periods were especially 

effective in breaking the dormancy of recently harvested 

collections. After a year in storage, germination in both the no 

chill and 4-wk chill treatments increased substantially, while 

the increase in response to 24-wk chilling was smaller. After 

an additional year in storage, there was little further change 

in response to no chill and 4-wk chill treatments, while the 

response to a 24-wk chill increased.

There was also a significant increase in the fraction of seeds 

that could germinate without chilling as the storage period 

increased (seed age main effect highly significant; table 4). 

After 6 years of storage, germination of unchilled seeds was 

almost as high as the germination percentage after 24 weeks 

of chilling for 2-year-old seeds (fig. 1). These results show 

that chilling can be an important mechanism of dormancy 

removal for recently dispersed seeds, but that dry after-ripening will eventually render most of these seeds germinable 

without chilling. Chilling thus serves as a substitute for dry 

after-ripening in recently dispersed seeds. The net effect of 

these processes is to ensure a nondormant seed fraction available for germination in response to both winter and summer 

germination-triggering precipitation events. It also ensures 

Figure 1. Mean germination proportions (averaged across 23 

collections of Atriplex canescens) for 12 combinations of 

seed age and chilling duration. For each treatment combination, seeds were incubated for 4 weeks at 15°C following the 

seed storage and chilling treatments. Germination data are 

expressed as proportion of viable seeds. Standard error bars 

are shown for each mean.

Table 3. Analysis of covariance based on a completely randomized design for germination experiments with 23 collections of 

Atriplex canescens in which seeds of each collection were tested when recently harvested and after 1 and 2 years of laboratory 

storage. For each seed age, three chilling durations were included: no chilling, 4 weeks of chilling, and 24 weeks of chilling. 

Source of Variance d.f. Mean square F-value P-value 

Seed collection 22 1.4679 33.23 <0.0001

Seed age 1 9.3949 212.70 <0.0001

Chilling duration 1 10.7489 243.36 <0.0001

Seed collection x seed age 22 0.1943 4.40 <0.0001

Seed collection x chilling duration 22 0.3031 6.86 <0.0001

Seed age x chilling duration 1 0.5075 11.49 0.0007

Seed collection x seed age x chilling duration 22 0.0831 1.88 0.0083

Error 1012 0.0442

Seeds were incubated at 15°C for 4 weeks after each treatment sequence, and germination proportion was scored as a fraction of 

viable seeds. Data were arcsine transformed for analysis. Seed age and chilling duration are treated as continuous independent 

variables in the analysis, while seed collection is considered a class variable.
156 USDA Forest Service RMRS-P-47. 2007

that not all seeds in a cohort will germinate in response to 

the same triggering event. Instead, germination may be spread 

across seasons and probably even across years.

The trend toward increasing germination percentages 

with increasing seed age did not hold for the 10-year data. 

Instead, percentages dropped slightly, and there was a trend 

for decreased germination after chilling. These effects are 

probably an indication of decreasing seed viability and vigor 

in 10-year-old lots.

There was tremendous variation among seed collections in terms of dormancy status at harvest and response 

to dormancy breaking treatments (highly significant seed 

collection main effects and interactions; tables 3, 4). We 

chose to group the collections in terms of their habitat of 

origin, then look for common patterns that could be interpreted ecologically. Such patterns were only sometimes in 

evidence, but examining collection responses by habitat 

enabled us to extract some meaningful generalizations from 

this complex data set.

Fourwing saltbush seed collections made in warm desert 

creosote bush (Larrea tridentata) habitats were relatively 

nondormant at harvest (51 to 77 percent without chilling; 

fig. 2). They generally changed very little in dry storage over 

2 years, but after 6 years achieved germination from 76 to 

95 percent without chilling. They showed little viability loss 

after 10 years.

Fourwing saltbush seed collections made in warm desert 

fringe blackbrush (Coleogyne ramosissima) habitats were 

extremely variable in their germination responses (fig. 3). 

They were generally more dormant at harvest than collections 

from creosote bush habitats, but showed sharply contrasting 

responses to chilling. The Santa Clara collection achieved 

germination of 86 percent after chilling when recently 

harvested, while at the other extreme the collection from 

Page, Arizona, germinated to only 4 percent when recently 

harvested regardless of chilling regime. The Page collection 

did not acquire any substantial ability to germinate without 

chilling until after 10 years of storage, and by that time was 

losing vigor, as indicated by the precipitous drop in germination after a 4-wk chill. The other two collections behaved 

more like collections from the creosote bush habitat, with 

generally small and inconsistent change in dormancy status 

and chilling responsiveness over the first 2 years, then a jump 

Table 4. Analysis of covariance based on a completely randomized design for germination experiments with 23 

collections of Atriplex canescens in which seeds were tested when recently harvested and after 1, 2, 6 , and 10 

years of storage. Seeds were incubated for 4 weeks at 15°C. 

Source of Variance d.f. Mean square F-value P-value

Seed collection 22 0.7771 24.39 <0.0001

Seed age 1 8.6748 272.31 <0.0001

Seed collection x seed age 22 0.0969 3.04 <0.0001

Error 506 0.0319

Germination data are based on viable seed proportion determined at the end of each test with one exception. For the 

10-year data, germination is based on the proportion of fruits initially viable as determined by an a priori cut test 

on recently harvested seeds. Data were arcsine transformed for analysis. Seed age was treated as a continuous 

independent variable in the analysis, while seed collection was considered a class variable.

Figure 2. Germination proportions for three Atriplex canescens

seed collections from the creosote bush shrubland habitat type 

following 12 combinations of seed age and chilling duration. For 

each treatment combination, seeds were incubated for 4 weeks 

at 15°C following the seed storage and chilling treatments. 

Germination data are expressed as proportion of viable seeds. 

Standard error bars are shown for each mean.
USDA Forest Service RMRS-P-47. 2007 157

at 6 years in the fraction able to germinate without chilling. 

Both these collections showed signs of decreasing viability 

after 10 years.

Fourwing saltbush collections made in salt desert habitats 

were generally more dormant at harvest than those from warm 

desert habitats (15 to 36 percent germination without chilling) 

Figure 3. Germination proportions for three Atriplex canescens seed 

collections from the blackbrush shrubland habitat type following 

12 combinations of seed age and chilling duration. For each treatment combination, seeds were incubated for 4 weeks at 15°C 

following the seed storage and chilling treatments. Germination 

data are expressed as proportion of viable seeds. Standard error 

bars are shown for each mean.

and were not very responsive to short chilling (fig. 4). They 

varied in their response to long chilling; the Caineville collection was most responsive and the Roosevelt collection the 

least. Dormancy generally decreased in dry storage through 

6 years, but maximum germination percentages without 

chilling were only moderate (63 to 68 percent) and chilling of 

Figure 4. Germination proportions for three Atriplex canescens seed 

collections from the salt desert shrubland habitat type following 

12 combinations of seed age and chilling duration. For each treatment combination, seeds were incubated for 4 weeks at 15°C 

following the seed storage and chilling treatments. Germination 

data are expressed as proportion of viable seeds. Standard error 

bars are shown for each mean.
158 USDA Forest Service RMRS-P-47. 2007

short duration, as would be expected in this habitat, did little 

to increase total germination beyond these values.

Fourwing saltbush probably achieves its greatest abundance in sagebrush steppe habitats in the Intermountain 

West, a fact reflected in the larger number of collections 

we made in this habitat (table 1). Seven of the eight collections in this group followed a similar pattern (fig. 5). Their 

seeds were moderately dormant at harvest (16 to 50 percent 

germination without chilling) and lost dormancy steadily and 

usually quickly in dry storage (38 to 92 percent germination 

after 2 years). They were generally not very responsive to 

short chilling when recently harvested and showed variable 

response to long chilling. The eighth collection included in 

the sagebrush steppe group, from Jericho Dunes, was actually 

from a sand dune habitat embedded within the sagebrush type, 

and is also unusual in being diploid (Stutz and others 1975). 

It was the least dormant collection in the study, with germination from 85 to 100 percent regardless of seed age or chilling 

treatment (fig. 5).

Fourwing saltbush collections from foothill woodland 

or mountain brush habitats were uniformly dormant when 

recently harvested (germination without chilling 3 to 11 

percent). The fraction germinable without chilling increased 

steadily through time but never achieved high values (54 to 

62 percent). Seeds were moderately chilling-responsive when 

recently harvested (21 to 45 percent maximum germination after chilling). The fraction to germinate in response to 

chilling generally showed incremental increase through time 

over the first 2 years (fig. 6).

Principal Components Analysis

The first principal component from PCA accounted for 77 

percent of the total variance, and the eigenvector loadings for 

all 12 variables were positive and of similar magnitude. PC1 

basically represents a scale of increasing overall germinability 

(decreasing dormancy), with the most dormant collection 

(Page) at the left hand extreme and the least dormant collection (Jericho Dunes) at the right hand extreme (fig. 7). In fact, 

scores on PC1 are highly correlated with mean germination 

percentages (averaged across 12 treatments), with an r-value 

of 0.982 (d.f.=21, p<0.0001). The high eigenvalue (77 percent) 

for PC1 reflects the fact that the germination variables tend to 

be correlated, sometimes highly correlated.

Other than the two anomalous collections (Page and Jericho 

Dunes), collections from different habitats form a reasonably 

orderly progression along PC1, with the more dormant foothill 

collections grouped to the left, the less dormant creosote bush 

shrubland collections grouped to the right, and the intermediate sagebrush steppe, salt desert shrubland, and blackbrush 

shrubland collections in the middle (fig. 7).

PC2 accounts for only an additional 9 percent of the total 

variance, so scores on this PC are less important for interpretation than scores on PC1. They do have a clear interpretation, 

however. The eigenvector loadings for PC2 are all either near 

zero or negative, except for the loadings for the three 24-

week chilling response variables, which are all positive and 

large. This can be interpreted to mean that collections with 

high scores on PC2 responded more to 24-week chilling than 

collections with low scores. All six foothill collections were 

intermediate in this respect, and form a tight group on the 

graph (fig. 7). The remaining collections did not show any 

clear relationship to habitat in terms of their scores on PC2. 

For example, Snow’s Canyon and Santa Clara, both from 

blackbrush shrubland, had similar germination percentages 

overall and similar scores on PC1. But they differed widely 

on PC2, because Santa Clara seeds tended to respond positively to 24 week chilling, while Snow’s Canyon seeds did 

not (fig. 3).

Discussion

We can safely conclude that both moist chilling and dry 

after-ripening play important roles in seed dormancy regulation for Intermountain populations of fourwing saltbush. 

Chilling is especially important as a mechanism of dormancy 

removal for recently dispersed seeds, but most seeds eventually become nondormant through the process of dry 

after-ripening.

Levels of primary dormancy and patterns of change in 

dormancy status as a function of both chilling and dry afterripening varied dramatically among collections. With the 

notable exception of the collections from Page and Jericho 

Dunes, there was a general pattern of increasing primary 

dormancy and decreasing maximum germination percentages 

in the progression from warm desert to foothill habitats. Most 

collections from creosote bush dominated sites seemed to be 

composed of a sizeable fraction able to germinate at the first 

opportunity and a smaller fraction that became germinable after 

short chilling or short-term after-ripening. Seed bank carryover across years seems unlikely in this group, except that in 

this dry environment, wet conditions that last long enough to 

trigger germination of non-dormant seeds may not be encountered in any given year. Particularly in a heterogeneous seed 

bed, many seeds may find themselves in microenvironments 

that dry very rapidly at germination-conducive temperatures. 

A 4-week period of moist chilling may be equally unlikely. 

Thus the seeds may not need elaborate dormancy protections 

in order for a fraction to persist across years.

At the other end of the spectrum, collections from foothill pinyon-juniper and mountain brush habitats were highly 

dormant at dispersal and achieved relatively low germination 

percentages even after prolonged chilling. Chilling continued 

to be incrementally effective as a dormancy-breaking treatment even in seeds stored 2 years. This response pattern 

would tend to limit emergence to the spring in these cold 

winter environments, where the winter chilling period lasts 

much longer than 4 weeks and occasionally even as long 

as 24 weeks, and where frost risk to fall-emerging seedlings is high. Seed bank carryover across years is assured in 

these environments by virtue of the fact that there is always 

a chilling non-responsive fraction, even after a very long 

chilling period.
USDA Forest Service RMRS-P-47. 2007 159

Figure 5. Germination proportions for eight Atriplex canescens seed collections from the sagebrush steppe habitat type following 12 combinations of seed age and chilling duration. For each treatment combination, seeds were incubated for 4 weeks at 15°C following the seed 

storage and chilling treatments. Germination data are expressed as proportion of viable seeds. Standard error bars are shown for each 

mean.
160 USDA Forest Service RMRS-P-47. 2007

Figure 6. Germination proportions for six Atriplex canescens seed collections from the pinyon-juniper woodland/mountain brush habitat type 

following 12 combinations of seed age and chilling duration. For each treatment combination, seeds were incubated for 4 weeks at 15°C 

following the seed storage and chilling treatments. Germination data are expressed as proportion of viable seeds. Standard error bars are 

shown for each mean.
USDA Forest Service RMRS-P-47. 2007 161

Germination patterns for the numerous collections from 

intermediate blackbrush shrubland, salt desert shrubland 

and sagebrush steppe habitats were much more variable 

and difficult to generalize. The seeds tended to be intermediate between the warm desert and foothill groups in primary 

dormancy, to lose dormancy fairly rapidly in dry storage, and 

to reach intermediate to high final germination percentages 

under test conditions. An explicit ecological interpretation of 

these results would require much more detailed knowledge of 

the climate at particular collection sites, as well as additional 

experiments under a broader array of test conditions.

Because of the large number of collections in our study, we 

were limited in terms of the number of treatments we could 

apply, so that extrapolation of our laboratory results to the 

field must be done cautiously. Seeds under field conditions 

experience a changing temperature and moisture environment. For example, the rate at which seeds dry after-ripened 

in our experiment is only an index of the after-ripening speed 

under one uniform condition. While this index is useful in 

making comparisons among collections, it is almost certain 

that temperature will have a strong positive effect on after-ripening rate in fourwing saltbush, as it does in the related species 

shadscale (Atriplex confertifolia; Garvin and Meyer 2003). 

Similarly, temperature and moisture conditions during chilling 

are not uniform under field conditions, and this variation, as 

well as time spent either above or below effective stratification temperatures, undoubtedly has an effect on the pattern of 

change in dormancy status. This limits our ability to interpret 

our results in the absence of a field study to corroborate our 

laboratory findings. However, we were able to successfully 

predict germination timing and seed bank carryover for shadscale seed collections from contrasting habitats placed under 

field conditions, using results of experiments similar to those 

described here (Meyer and others 1998). The predictions were 

verified in a field seed retrieval experiment, an approach that 

would be the logical next step in understanding dormancy loss 

and germination phenology in fourwing saltbush.

Acknowledgments

We gratefully acknowledge the able technical assistance 

of Scott Walker in the early stages of this study. Thanks also 

to Steven Monsen, Stan Kitchen, Richard Stevens, Dale 

Turnipseed, and Mike Pellant for providing seed collections. 

This research was supported in part by a CSREES Rangelands 

Special Grant.

References

Garvin, S. C.; Meyer, S. E. 2003. Multiple mechanisms of seed 

dormancy regulation in shadscale (Atriplex confertifolia: 

Chenopodiaceae). Canadian Journal of Botany 81: 301-310.

McArthur, E. D.; Monsen, S. B. 2004. Chenopod shrubs. p. 467-492. 

In: Monsen, S. B; Stevens, R.; Shaw, N. L. (comps.). Restoring 

Western Ranges and Wildlands, Vol. 2. RMRS-GTR-136. USDA 

Forest Service, Rocky Mountain Research Station, Ft. Collins, 

Colorado.

Meyer, S. E.; Carlson, S. L.; Garvin, S. C. 1998. Seed germination 

regulation and field seed bank carryover in shadscale (Atriplex 

confertifolia: Chenopodiaceae). Journal of Arid Environments. 

38: 255-267.

Meyer, S. E. Atriplex. In: Woody Plant Seed Manual. Published 

online at ntsl.fs.fed.us/wpsm/

Springfield, H. W. 1970. Germination and establishment of fourwing 

saltbush in the southwest. Research Paper RM-55. USDA Forest 

Service, Rocky Mountain Research Station, Ft. Collins, Colorado. 

48 p.

Stutz, H. C.; Melby, J. M.; Livingston, G. K. 1975. Evolutionary 

studies of Atriplex: a relic gigas diploid population of Atriplex 

canescens. American Journal of Botany. 62: 236-245.

Figure 7. Principal components analysis 

based on Atriplex canescens seed germination data. Scores on the first two 

principal components for each of the 

23 populations were used to create the 

plot. These two principal components 

accounted for 86 percent of the total 

variance. Symbols correspond to plant 

communities where the seed collections 

were made. Two unfilled (white) symbols 

correspond to populations with anomalous 

germination responses (see text for explanation).
162 USDA Forest Service RMRS-P-47. 2007

The Authors

1 Research Ecologist, USDA Forest Service, Rocky Mountain 

Research Station, Shrub Sciences Laboratory, Provo, UT. 

smeyer@fs.fed.us 2 Biological Technician, USDA Forest Service, Rocky Mountain 

Research Station, Shrub Sciences Laboratory, Provo, UT.
USDA Forest Service RMRS-P-47. 2007 163

Introduction

Grasslands in the arid, semi-arid and dry semi-humid 

regions of northern China are becoming increasingly 

degraded or lost due to anthropogenic influences (Li 1997; 

Chen 1998; Chen and Wang 2000), such as overgrazing, overcultivation (conversion of grassland to farmland), extensive 

firewood collection, and excessive groundwater withdrawal 

or surface water use for agricultural purposes. This is particularly true for those ecologically fragile ecosystems with a 

low resilience, such as the xeric sandy steppe grassland in the 

Horqin Sandy Land of Inner Mongolia (Liu and others 1996). 

The total area of the Horqin sandy steppe is approximately 

518 × 104

 ha, which constitutes an important part in Inner 

Mongolia’s pasture resources (Jiang and others 2003). Due 

to human activities, however, almost 80 percent of the Horqin 

sandy steppes suffered from desertification (a form of land 

degradation resulting primarily from wind erosion activity 

after destruction of vegetation by overgrazing), of which 

about one third was severely desertified (Zhu and Chen 1994; 

Wang 2000). Thus, the Horqin Sandy Land has been identified as one of the worst examples of desertification in northern 

China (Wang and others 2003). The ecological consequences 

of unchecked desertification in this region are a substantial 

loss of the region’s specific floristic biodiversity, as well as a 

range of negative environmental and socio-economic impacts 

(Chang and Wu 1997; Jiang and others 2003). For example, 

once the vegetation in sandy grasslands has been destroyed 

by overgrazing or other human activities, they become less 

stable and highly erodible during the dry and windy seasons 

(Li and others 2003a), which are most likely to become new 

sources of sand and dust that could contribute to sand-dust 

storms that occur frequently in the arid and semi-arid regions 

of the northern China (Xuan and others 2000). 

Shrubs are an important component in degraded sandy 

grassland vegetation. Previous studies have shown that some 

of shrub species such as Artemisia holodendren is a pioneer 

sand-stabilizing plant and plays a key role in maintaining 

the stability of natural sandy grassland ecosystems (Liu and 

others 1996; Li and others 2002; Zhang and others 2004). 

Moreover, some of shrub species, such as Artemisia frigida, 

are commonly known as an indicator species. Its presence 

or absence in the grassland has been used for establishing 

whether grassland is degraded (Zhao and Zhou 1999; Li and 

others 2002). In the last decade, a number of experiments 

have been carried out in laboratory and experimental garden 

Efficacy of Exclosures in Conserving Local Shrub 

Biodiversity in Xeric Sandy Grassland, Inner Mongolia, 

China

Abstract: This study investigated the abundance and frequency of occurrence of all shrub 

species present in the standing vegetation at four sites, including a 5-year exclosure 

(protected grassland) and three adjacent unprotected grazing sites that had been subjected 

to different levels of degradation (light, moderate and severe), in xeric sandy grassland 

of Inner Mongolia for three growing seasons. Shrub species abundance, richness, and 

diversity in the exclosure were compared with three unprotected sites to determine the 

efficacy of exclosure on shrub biodiversity conservation. Using the data set, the responses 

of individual shrub species to level of grassland degradation were also examined by means 

of detrended correspondence analysis (DCA). Individual shrub species responded differently 

to degradation level. From individual species responses we identified three main response 

types. The first type is represented by Artemisia holodendren showing a positive response 

to degradation level. The second type is represented by Lespedeza davurica, Hedysarum 

fruticosum, and Caragana microphylla indicating a negative response to degradation level. 

The third type included Ceratoides arborescens and Artemisia frigida following a different 

response pattern from the first two response types. Exclosure effects varied remarkably 

with different shrub species. The results suggest that it is generally necessary to apply an 

exclosure to the severely degraded grassland while light to moderate grazing disturbance 

is helpful for the maintenance of shrub species diversity. These findings are important for 

understanding how grassland degradation affected the population demography of shrub 

species and for developing appropriate management strategies for conservation of degraded 

shrub vegetation.

Feng-Rui Li1

Zhi-Yu Zhou2

Li-Ya Zhao1

Zhi-Gang Huang1

Ling-Fen Kang1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
164 USDA Forest Service RMRS-P-47. 2007

plots to explore the ecological and physiological adaptation 

mechanisms of several shrub species, such as A. halodendron, 

A. frigida, Caragana microphylla, and Salix gordejevii, to the 

harsh environmental conditions of sandy grassland ecosystems characterized by frequent drought, high temperature, 

and sand burial (Wang and Zhou 1999; Zhou 1999; Zhou and 

others 1999; Ren and others 2001; Zhou and Zhao 2002). 

However, few studies have examined the efficacy of shortterm exclosure (grazing exclusion) in conserving local shrub 

species diversity and the response of individual shrub species 

to level of grassland degradation. 

To address this deficiency, we carried out an experiment in 

the Horqin sandy grassland to examine how degradation level 

affects shrub species abundance, richness, and diversity and 

to assess the efficacy of short-term exclosure. The objectives 

of this study were to: (i) determine changes in the abundance, 

richness, and diversity of shrub species present in the established vegetation and (ii) determine the specific efficacy of a 

5-year exclosure on the restoration of degraded shrub vegetation and the maintenance of shrub species diversity. Here, two 

specific hypotheses we posed were as follows: (1) Individual 

shrub species respond differently to degradation level due to 

their distinct life-history and plant morphological attributes. 

Some species will be advantaged by the local disturbances 

associated with moderate to heavy grazing, and will thus show 

trends of increasing abundance with increasing disturbance 

intensity (degradation level) and consequently occur more 

frequently in grasslands under moderate to severe degradation. Some species will be disadvantaged and will thus show 

patterns of decreasing abundance with increasing degradation 

level, and consequently disappear or occur less frequently in 

grasslands under moderate and severe degradation and (2) 

The effect of exclosure on the conservation of shrub biodiversity varies with different shrub species.

Materials and Methods

Site Description

The study site is located in Naiman county (42o55’ N, 

120o44’ E; altitude c. 360 m a.s.l.) in the eastern part of 

Inner Mongolia, China, about 500 km northeast of Beijing 

(Li and others 2003b). Naiman is in the southwestern part of 

the Horqin Sandy Land, which represents the most desertification-threatened area in northern China (Jiang and others 

2003). General landscape in this area is characterized by sand 

dunes alternating with gently undulating lowland areas. The 

soils are sandy, light yellow, and loose in structure (Zhu and 

Chen 1994). The main soil type is classified as an Arenosols in 

WRB (ISSS, ISRIC and FAO 1998). The climate is temperate, 

semi-arid and continental, receiving 360 mm annual mean 

rainfall, with 75 percent of the annual rainfall falling in the 

June–September period. The annual mean potential evaporation is 1, 935 mm, and the annual mean temperature is 6.5°C.

The original vegetation of this area was an open, sparse 

forest steppe (Liu and others 1996). Due to human activities, 

however, woody species (mainly elm Ulmus spp.) have almost 

disappeared and most of the grass cover is gone (Andrén 

and others 1994). Degraded sandy grasslands are generally 

classified into three main forms: fixed or stabilized (light 

degradation), semi-fixed or semi-stabilized (moderate degradation), and mobile or least stabilized (severe degradation), 

representing a realistic range of historically grazing impacts. 

Over space, these differently degraded grassland patches 

occur in a complex mosaic (Zhao and others 2003).

Vegetation Survey Design and Sampling

A field survey of the abundance and frequency of occurrence of all shrub species present in the established vegetation 

was conducted in four sites, including a demonstration exclosure (protected grassland) and three adjacent communal 

grazing sites that were selected over an area of 3×3 km. The 

exclosure was established in an open and level grassland area 

of about 10 ha in April 1997. The grassland had been subjected 

to severe degradation due to a history of heavy grazing by livestock prior to fencing the exclosure. Three adjacent communal 

grazing sites differed in degree of vegetation degradation in 

terms of vegetation cover, species richness, and composition. According to the classification criteria of desertification 

degree of Zhu and Chen (1994), one of the three sites was 

identified as light degradation (LDG, lightly degraded grassland), another as moderate degradation (MDG, moderately 

degraded grassland), and the third one as severe degradation 

(SDG, severely degraded grassland). Thus, these three sites 

constitute a gradient of degradation in sandy grasslands. LDG 

was situated on a typical fixed sand dune area (two separated 

fixed dunes were selected for sampling). MDG was situated 

on a typical semi-fixed sand dune area (two separated semifixed dunes were selected for sampling). SDG was located on 

a typical mobile sand dune area (two separated mobile dunes 

were selected for sampling). Three unprotected grazing sites 

were at least 1 km apart from one another while their distances 

from the exclosure were 1.5 to 2 km apart.

A hundred and eighty plots (2 × 2 m) were randomly 

selected along five parallel transects (each 25 m apart) in the 

exclosure and 120 plots were randomly selected in each of the 

three unprotected grazing sites to investigate species composition and density of each shrub species present in each plot in 

the last week of August at the time of peak biomass production and species diversity. For each site, richness of the shrub 

species was assessed by the total number of shrub species per 

site and the mean number of shrub species m-2. Abundance of 

each shrub species was assessed by its number of established 

plants m-2 and its frequency of occurrence that was calculated 

as the percentage of the number of plots occupied by a species 

relative to the total number of plots per site. The sampling 

of the standing vegetation was repeated for three consecutive 

growing seasons (2002–2004).
USDA Forest Service RMRS-P-47. 2007 165

Data Analysis

One-way analysis of variance (ANOVA) was used to test 

for differences in shrub vegetation parameters between sites. 

Significant differences between sites were compared using 

LSD tests. Data for species richness (measured as the mean 

number of shrub species m-2) and abundance (measured as 

the number of established plants m-2) were log-transformed 

to normalize the distributions. To detect any general patterns 

in species abundance relationships with sites, we undertook detrended correspondence analysis (DCA) based on the 

species abundance (density and frequency) data for the four 

sites. Shannon-Wiener diversity index (H ́; Magurran 1988) 

and Pielou’s evenness index (J; Pielou 1975) were used to 

analyse changes in shrub species diversity and evenness across 

sites. H ́ and J were calculated by the following formula:

H ́ = –∑Pi

lnPi

J = H ́/lnS

where Pi is the abundance of the ith species that was measured 

as the importance value (IV) of the ith species in the shrub 

community containing S species. IV was calculated as IV = (Dr

+ Fr

)/200, where Dr is the relative abundance that is calculated 

as the percentage of the observed abundance of a species relative to the cumulative abundance for all species occurring in 

the shrub community; Fr

 is the relative frequency that is calculated as the percentage of the observed frequency of a species 

relative to the cumulative frequency for all species occurring 

in the shrub community. Data were pooled from the 3 years in 

the analyses because the interest in this study is to determine 

differences in shrub vegetation between sites rather than to 

determine inter-annual variability in shrub vegetation within 

sites.

Results

A total of six shrub species were recorded in the established 

vegetation of the four sites sampled and biological characteristics of these shrub species are shown in table 1. Degradation 

level had significant effects on the abundance, richness, and 

diversity of shrub species in the established vegetation. The 

total number of shrub species per site was much lower in 

grassland under severe degradation than in other three sites 

that were similar in this variable (fig. 1a). There were striking 

differences in the mean number of shrub species m-2 among 

sites (F3, 1616 = 142.14, P < 0.0001), with the lightly degraded 

grassland having a significantly higher mean number of 

shrub species m-2 than other sites. At the same time, the mean 

number of shrub species m-2 was also significantly higher in 

the moderately degraded grassland than in both the protected 

and severely degraded grasslands and in the protected grassland than in the severely degraded grassland (fig. 1b). Almost 

the same patterns were observed when comparing the shrub 

species diversity and evenness index values between sites (fig. 

1c, d).

Total shrub abundance was significantly higher in the 

lightly degraded grassland than in other sites, because of high 

densities of established Lespedeza davurica and Hedysarum

fruticosum plants at this site (table 2). Total shrub abundance 

was also significantly higher in the moderately degraded grassland than in the protected and severely degraded grasslands, 

because of high density of established Artemisia halodendron 

plants at this site, and in the protected grassland than in the 

severely degraded grassland (table 2).

Detrended correspondence analysis (DCA) showed tight 

associations between shrub species and particular sites (fig. 2). 

Of the six shrub species occurred at the study site, Ceratoides 

arborescens and Artemisia frigida were restricted to the 

Table 1. Main biological characteristics of shrub species recorded at the study sites.

Family Life form Growth form Root growth form Ecological type of water Palatability

Artemisia halodendron Turcz. ex Bess. Compositae Hemicrypto-geophyte Limb Rhizome Mesoxerophyte Less palatable

Artemisia frigida Willd. Compositae Chamaephyte Stolon Taproot Xerophyte Palatable

Lespedeza davurica (Laxm.) Schindl. Leguminosae Chamaephyte Limb Taproot Mesoxerophyte Palatable

Hedysarum fruticosum Pall. Leguminosae Hemicryptophyte Limb Taproot Mesoxerophyte Palatable

Caragana microphylla Lam. Leguminosae Chamaephyte Limb Taproot Mesoxerophyte Palatable

Ceratoides arborescens (Losinsk.) Tsien et Ma Chenopodiaceae Chamaephyte Turb Taproot Xerophyte Less palatable
166 USDA Forest Service RMRS-P-47. 2007

exclosure, whereas A. halodendron occurred more frequently 

in grasslands under moderate and severe degradation (fig. 2a 

and table 2). Moreover, L. davurica and Caragana microphylla were far more frequent in occurrence in the lightly 

degraded grassland, although the former was present in all 

four sites (fig. 2a and table 2). Similar patterns were observed 

when performing DCA using the species abundance data for 

the four sites (fig. 2b and table 2).

Table 2. Mean (± SE) density of established plants m-2 (% frequency) of shrub species present in the established vegetation of 

the four sites along the degradation gradient. EXC = exclosure (protected grassland), LDG = lightly degraded grassland, 

MDG = moderately degraded grassland, and SDG = severely degraded grassland. Means with different letters within each 

species indicate significant differences between the four sites (ANOVA followed by LSD tests). *P < 0.05, **P < 0.01, ***P

< 0.0001 and ns = not significant.

EXC LDG MDG SDG F (3, 1616)

Artemisia halodendron 0.003 ± 0.001c (1) 0.50 ±0.16b (26) 1.62 ± 0.09a (91) 0.60 ± 0.07b (62) 53.45***

Artemisia frigida 0.01 ± 0.004a (1) 0.00 ±0.00b (0) 0.00 ±0.00b (0) 0.00 ±0.00b (0) 2.01ns

Lespedeza davurica 1.71 ± 0.28b (75) 11.60 ± 1.22a (91) 0.82 ± 0.19bc (41) 0.013 ± 0.003c (6) 91.82***

Hedysarum fruticosum 0.00 ± 0.00b (0) 1.13 ±0.18a (67) 0.05 ± 0.01b (9) 0.00 ± 0.00b (0) 52.63***

Caragana microphylla 0.00 ± 0.00a (0) 0.07 ±0.05a (13) 0.02 ± 0.004a (5) 0.00 ± 0.00a (0) 2.08ns

Ceratoides arborescens 0.05 ± 0.02a (6) 0.00 ±0.00b (0) 0.00 ± 0.00b (0) 0.00 ± 0.00b (0) 5.69**

Total shrub abundance 1.77 ± 0.27c 13.30 ± 1.29a 2.51 ± 0.20b 0.61 ± 0.06d 99.61***

Discussion

Effects of Degradation Level

This study indicates that degradation level strongly affected 

shrub plant diversity and abundance of individual species in 

the xeric sandy grasslands. This is consistent with observations from other studies to have demonstrated that overgrazing 

Figure 1. Changes in (a) total 

number of shrub species per 

site, (b) mean number of shrub 

species m-2, (c) shrub diversity 

index and (d) shrub evenness 

index in the established vegetation of the four sites along 

the degradation gradient. EXC 

= exclosure (protected grassland). LDG = lightly degraded 

grassland. MDG = moderately 

degraded grassland. SDG = 

severely degraded grassland. 

Means with different letters 

indicate significant differences 

at P < 0.05 between the four 

sites (ANOVA followed by LSD 

tests).
USDA Forest Service RMRS-P-47. 2007 167

by herbivores generally has negative impacts on recruitment 

and regeneration of many species in most plant communities (Tiver and Andrew 1997; Li and others 2002; Landsberg 

and others 2003; Zhao and others 2004). However, the influence of degradation level varied with different shrub species, 

providing evidence supporting the hypothesis we originally 

posed, that is, different shrub species are likely to have had 

different responses to level of grassland degradation. From the 

responses of individual shrub species, we were able to identify 

three definite response types relating to degradation level. The 

first type is represented by A. halodendron showing a positive response to degradation level. Its number of established 

plants m-2 and its frequency of occurrence in the vegetation 

increased with increasing degradation level, and maximum 

abundance and frequency were noted in the moderately degraded 

grassland. This indicates that moderate grazing disturbance 

favors the survival and growth of this species. This is in line 

with the study of Chao and others (1999) on the distribution of 

A. halodendron population in differently degraded grassland 

types, reporting that abundance of A. halodendron plants was 

highest on moderately degraded semi-fixed sand dunes, intermediate on severely degraded mobile sand dunes, and lowest 

on lightly degraded fixed sand dunes. In contrast, some shrub 

species such as L. davurica, H. fruticosum and C. microphylla

belonged to the second type demonstrating a negative response 

to degradation level. Their number of established plants and 

their frequency of occurrence in the vegetation decreased 

dramatically with increasing degradation level, and peak 

abundance and frequency occurred in the lightly degraded 

grassland. This suggests that these three shrub species appear 

to be adapted to survive under light grazing pressure. C. arborescens and A. frigida belonged to the third type exhibiting a 

different response pattern from the first two response types. 

Both species had disappeared from the three unprotected sites 

and occurred only in the protected grassland (exclosure), again 

suggesting that they are very sensitive to grazing disturbances. 

Previous studies have shown that the survival and growth 

of A. frigida was strongly affected by defoliation due to its 

low grazing tolerance, and light to moderate grazing is likely 

to result in extinction of this species (Li and others 2002). 

Therefore, presence or absence of A. frigida in the community is usually used as an indicator for establishing whether 

grassland is overgrazed (Zhao and Zhou 1999). The observed 

differences in response patterns of individual shrub species to 

degradation level resulted most probably from the differences 

in their life-history and plant morphological traits, which in 

turn led to the differences in their ecological adaptation abilities to grazing disturbances. Many studies have shown that 

life history and plant morphology are important attributes in 

determining the responses of plant species to grazing intensity (Noy-Meir and others 1989; McIntyre and others 1995; 

Lavorel and others 1997). In the present study, for example, 

an explanation for high grazing tolerance of A. halodendron

is its massive perennating buds on rhizomes that are buried 

near the soil surface (Li and Zhang 1991). Further, persistence 

of A. halodendron may also be associated with its superior 

capacity to produce offspring through vegetative propagation 

under the condition of sand burial (Chao and others 1999). 

This is because vegetative propagation of A. halodendron can 

take place only when its shoots are partially buried by moving 

sand, as the buried shoots can form roots from their nodes 

under favorable moisture conditions and consequently become 

new ramets (Chao 2000). The grasslands under moderate and 

severe degradation are generally characterized by a highly 

erodible environment (Li and others 2003a), providing greater 

opportunities for A. halodendron shoots to be buried by 

moving sand and thus encouraging its vegetative propagation. 

In contrast, both the protected and lightly degraded grassland 

are characterized by a significantly less erodible environment, 

providing less chance for A. halodendron shoots to be buried 

by moving sand and thus limiting A. halodendron‘s vegetative 

Figure 2. Derended correspondence analysis based on (a) 

frequency and (b) abundance of shrub species present in the 

established vegetation of the four sites along the degradation 

gradient. EXC = exclosure (protected grassland), LDG = lightly 

degraded grassland, MDG = moderately degraded grassland, 

and SDG = severely degraded grassland. S1 = Artemisia halodendron, S2 = Lespedeza davurica, S3 = Hedysarum fruticosum, 

S4 = Ceratoides arborescens, S5 = Artemisia frigida, and S6 = 

Caragana microphylla.
168 USDA Forest Service RMRS-P-47. 2007

propagation. For that reason, it is not surprising why A. halodendron had significantly higher abundance and frequency in 

grasslands under moderate and severe degradation in comparison with the protected and lightly degraded grasslands.

Analysis of the associations between shrub species and 

sites sampled also provided further evidence for supporting 

the hypothesis above. In these analyses, we found that most 

of the shrub species were closely associated with particular 

sites relating to different degrees of degradation. Of the six 

shrub species recorded in the study site, A. halodendron and 

L. davurica occurred in all four sites but the former had the 

highest frequency in the moderately degraded grassland and 

the latter had the highest frequency in the lightly degraded 

grassland. H. fruticosum and C. microphylla were restricted to 

the lightly and moderately degraded grasslands and C. arborescens and A. frigida occurred only in the exclosure.

Role of Exclosure Management

Our results indicate that the short-term (5 years) exclosure resulted in an increase in shrub plant diversity through 

conserving species that decreased or disappeared under 

intense grazing conditions. However, exclosure effects were 

found to vary remarkably with the community parameter 

considered (for example, shrub species richness, species 

diversity, or shrub density of buried seeds). For example, 

the total number of shrub species per site was only higher in 

the exclosure than in the severely degraded grassland but no 

differences were found between the exclosure and both the 

lightly and moderately degraded grasslands. Nonetheless, the 

mean number of shrub species m-2 and shrub species diversity index in the exclosure were consistently higher than 

in the severely degraded grassland but were significantly 

lower as compared with the lightly and moderately degraded 

grasslands. These results suggest that exclosure practice is 

generally necessary to the severely degraded grassland while 

light to moderate grazing disturbance is helpful for the maintenance of shrub species diversity. This agrees with findings 

of a 5-year grazing experiment conducted in a sandy grassland 

in the Horqin Sandy Land (Zhao and others 2004), reporting 

that light grazing favors vegetation restoration and community 

stability of the deteriorated grassland. Li and Wang (1999) and 

Li and Li (2000) also reported that light grazing is helpful in 

maintaining plant species diversity and standing crop biomass 

production in sandy grasslands of Inner Mongolia.

The effect of exclosure also changed with shrub species. 

The short-term exclosure only resulted in an increase of 

L. davurica abundance as compared with the moderately 

and severely degraded grasslands and re-colonization of C. 

arborescens and A. frigida that had disappeared from the 

unprotected grassland. However, exclosure had less impact on 

abundances of established H. fruticosum and C. microphylla

plants. This species-specific response to exclosure may reflect 

a major difference in that the short-term exclosure may create 

a new biotic and abiotic environment by allowing only certain 

species to establish and survive but preventing recruitment of 

other species. Further information on the mechanism how the 

survival and growth of individual shrub species is affected 

by interactive effects of a set of biotic and abiotic factors is 

needed to guide the management for conservation of degraded 

shrub plants in the studied sandy grassland ecosystem.

Acknowledgments

We gratefully acknowledge the Naiman Desertification 

Research Station in Chinese Academy of Sciences for permission to work on its experimental grasslands. This work 

was supported financially by the International Partnership 

Project (CXTD-Z2005-2-4), the National Natural Science 

Foundation of China (39730100 and 90102011), and the 

Innovation Research Project from the Cold and Arid Regions 

Environmental and Engineering Research Institute, Chinese 

Academy of Sciences (2004121).

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The Authors

1

 Key Laboratory of Desert and Desertification, the Cold and Arid 

Regions Environmental and Engineering Research Institute, 

Chinese Academy of Sciences, Lanzhou 730000, China. 

lfengrui@vip.163.com 2

 Pastoral Agriculture Science and Technology. Lanzhou University, 

Lanzhou 730000, China.
170 USDA Forest Service RMRS-P-47. 2007

Introduction

The blackbrush (Coleogyne ramosissima Torr.) vegetation 

type occurs at the bioregional transition between the Mojave 

and Great Basin Deserts from California through Nevada, 

Arizona, and Utah (Bowns 1973; Brooks and Matchett 2003). 

In the Mojave Desert, blackbrush occupies mid-elevations, 

with creosote bush-white bursage (Larrea tridentata-Ambrosia 

dumosa) vegetation zones below and pinyon-juniper (Pinus 

monophylla-Juniperus osteosperma) zones above (Bradley 

and Deacon 1967; Lei 1995; Lei and Walker 1997a, b). 

Blackbrush often forms nearly monospecific stands, which 

can comprise 90 to 95 percent of the total plant cover (Shreve 

1942; Brooks and Matchett 2003).

Blackbrush generally grows less than 1 m in height in 

southern Nevada. Blackbrush has relatively small, ashy gray 

leaves from 5 to 15 mm long that turn black when wet (Bowns 

1973). Terminal branches of blackbrush often die back several 

centimeters from the tip and become spinescent, allowing 

lateral growth to form intricate branches, resulting in a dense, 

rounded shrub (Provenza and Urness 1981). Blackbrush 

leaves are simple, sessile, and are semi-deciduous during 

many drought periods.

Blackbrush leaves possess some of the characteristics of 

xerophytic leaves that are typically small with reduced cell 

size, thick cuticle and blades, cylindrical, well-developed 

palisade mesophyll, and dense adaxial pubescence (Rundel 

and Gibson 1996). Such leaf design is generally interpreted 

as a response to arid habitats with water deficits and poor soil 

nutrients (Beadle 1966; Rundel and Gibson 1996). However, 

blackbrush leaves also share some of the features of typical 

sclerophyllous leaves. Plants, such as blackbrush, having 

revolute leaf margins and hypostomatic leaves with hypodermis are common occurrence in some sclerophyllous scrub 

(chaparral) communities of the Mediterranean-type climate or 

cool and high elevation xerophytic plant communities (Gibson 

1996). Blackbrush does not occur in low Mojavean valleys in 

southern Nevada.

Previous studies by Bowns (1973), Bowns and West (1976), 

Callison and Brotherson (1985), Jeffries and Klopatek (1987), 

Provenza (1978), Lei (1995, 1997c, 1999, 2001, 2003), Lei and 

Walker (1997a and 1997b), Pendleton and Pendleton (1995), 

Brooks and Matchett (2003), and others have increased our 

understanding on various aspects of the biology and ecology 

of blackbrush. However, previous research studies did not 

examine ecotypic variation in blackbrush leaf anatomy as 

elevation changes. The objective of this study was to quantify 

ecotypic variation of anatomical characteristics in blackbrush 

leaves along an elevational gradient in a southern Nevada 

blackbrush shrubland.

Methods

Field and Laboratory Studies

Field studies were conducted in Lee Canyon (36°04’ N, 

115°16’ W) of the Spring Mountains in southern Nevada. 

Lee Canyon is located approximately 70 km northwest of 

Las Vegas, Nevada. Within a climax blackbrush shrubland, 

three elevational sites were chosen: a lower ecotone (1,400 

m), a nearly monospecific blackbrush stand (1,625 m), and 

an upper ecotone (1,750 m). Common woody plants present 

at the lower blackbrush ecotone included creosote bush and 

white bursage, while at the upper blackbrush ecotone, woody 

associates included big sagebrush (Artemisia tridentata) and 

Utah juniper. Common herbaceous plants contained members 

of the Asteraceae, Brassicaceae, Fabaceae, and Poaceae families.

Southern Nevada has an arid continental desert climate with 

hot, dry summers and cool, wet winters (table 1). Although 

most precipitation occurs during winter and summer seasons, 

Intraspecific Variation in Leaf Anatomy of Blackbrush 

(Coleogyne ramosissima Torr.)

Abstract: Differences in anatomical characteristics of blackbrush (Coleogyne ramosissima 

Torr.) leaves were quantitatively investigated along an elevational gradient in Lee Canyon 

of the Spring Mountains in southern Nevada. Three elevational sites were selected: a lower 

blackbrush ecotone, a nearly monospecific stand in the middle of the gradient, and an upper 

blackbrush ecotone. Stomatal density was significantly greater and palisade parenchyma was 

significantly shorter in the lower ecotone compared to the upper ecotone. Vessel diameters 

and areas were significantly smaller, while vessel density was higher with increasing aridity. 

Blackbrush shrubs exhibited upper and lower elevational ecotypes at the anatomical level in 

Lee Canyon of southern Nevada.

Simon A. Lei1

In: Sosebee, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comp. 2007. Proceedings: Shrubland dynamics—fire and water; 

2004 August 10-12; Lubbock, TX. Proceedings RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 173 p.
USDA Forest Service RMRS-P-47. 2007 171

the total amount of annual precipitation varies considerably 

from year to year. Summer monsoonal rainfall and storms 

generally occur from July through early September, and 

primarily come from the Gulf of California. Summer storms, 

brief, episodic, and locally intense, are variable in both time 

and space. Winter rainfall, on the contrary, tends to be mild 

and widespread, and come from the Pacific Ocean. Winter 

rainfalls may last up to several days. Snow is frequent in upper 

blackbrush ecotones at relatively high elevations on desert 

mountain slopes. Southern Nevada is an area of temperature 

extremes, ranging from a mean minimum January temperature 

of 1.1°C to a mean July maximum of 41.1°C (Climatological 

Data, Las Vegas) (table 1). In general, precipitation is positively correlated, and air temperature is negatively correlated 

with elevation (Rowlands and others 1977; Lei 1997b).

Blackbrush leaves were collected for anatomical observations in a Community College of Southern Nevada (CCSN) 

biology laboratory. Fifteen (15) different plants were randomly 

selected in each of the three elevational sites. Within each 

blackbrush, a stratified random selection method was used, 

with two leaves being systematically collected—one from the 

upper canopy and one from the lower canopy. Within each 

layer of canopy, leaves were collected in all cardinal directions to avoid biased sampling. A thin coat of clear nail polish 

was applied to the abaxial leaf surfaces, followed by the aid of 

an optical microscope (400X) to determine relative stomatal 

density and dimensions (length and width). Tiny, thin pieces of 

leaf tissues were sliced using two sharp razor blades that were 

compressed tightly. This optical microscope, with an ocular 

micrometer installed in the eyepiece, was also used to quantify vessel diameter and area, as well as to determine relative 

tissue thickness that were seen in the microscopic field. Vessel 

areas were computed using the standard circle formula (π r2). 

A microprojector was used to enlarge the transection so that 

stomatal and vessel characteristics could be quantified.

Statistical Analyses

One-way analysis of variance (ANOVA; Analytical 

Software 1994) were performed to detect elevational ecotype 

variation in anatomical characteristics of blackbrush leaves. 

Tukey and Scheffe multiple mean comparison tests (Analytical 

Software 1994) were conducted to compare means when a 

significant elevation effect was detected. Mean values were 

presented with standard errors, and statistical significance was 

determined at P < 0.05.

Results and Discussion

Blackbrush leaves are hypostomatic. Stomates were deeply 

sunken in the abaxial epidermis only, and were connected to 

large substomatal chambers. Anatomical observations revealed 

that stomatal density of blackbrush decreased significantly (P 

< 0.05; table 1) with ascending elevation. Stomatal densities 

are greater in desert plants compared to mesophytic ecotypes 

(Gibson 1996). My results concur with Gibson’s (1996) study 

since low elevational site had significantly greater stomatal 

densities per mm2 when compared to high elevational site. 

Characteristic stomatal densities of geographically widespread species are 100 or more stomates per mm2

 (Mauseth 

1988), which also corresponds with my data. Nevertheless, 

stomatal size (length and width) of blackbrush leaves did not 

differ significantly among the three elevational sites (P > 0.05; 

table 2), indicating that stomatal dimension was similar irrespective of elevational changes.

At the lower ecotone, vessel diameter and area of blackbrush leaves increased, whereas vessel density decreased 

significantly along a gradient of ascending elevation (P < 0.05; 

table 3). Vessels in desert shrubs would become shorter, 

Table 1. Mean monthly precipitation and mean monthly maximum 

and minimum air temperature in the Las Vegas Valley. The 

climatological data (National Weather Service) were obtained 

collectively from multiple long-term weather stations in Las Vegas 

of southern Nevada.

Temperature (C)

High Low Precipitation (mm)

January 14.4 1.1 12.7

February 17.0 23.9 11.4

March 20.6 6.7 10.2

April 25.6 10.6 5.1

May 31.1 15.6 5.1

June 37.7 20.6 5.1

July 41.1 23.3 11.4

August 39.4 23.3 14.0

September 35.0 18.9 7.6

October 27.8 12.2 6.4

November 19.4 6.1 11.4

December 14.4 1.1 7.6

Table 2. Mean (± se) stomatal density and dimension of blackbrush leaves along an elevational 

gradient in southern Nevada. Adaxial stomata are absent in blackbrush.

Lower ecotone Nearly pure stand Upper ecotone

Stomatal density (stomates mm-1) 90.3 ± 13.2 a 1 86.4 ± 12.6 ab 80.6 ± 10.7 b

Stomatal length (μm) 10.8 ± 0.7 a 11.0 ± 0.8 a 11.8 ± 1.1 a

Stomatal width (μm) 5.4 ± 0.3 a 5.6 ± 0.2 a 5.9 ± 0.2 a

1

 Means within a leaf character followed by the same letter are not significantly different (P > 0.05; n 

= 30).
172 USDA Forest Service RMRS-P-47. 2007

narrower, and more numerous with increasing aridity. This 

phenomenon also occurs in creosote bush, saltbush (Atriplex

hymenelytra), and big sagebrush in Death Valley of southern 

California (Culp 1986). As predicted, conductive tissues in 

desert shrubs respond to greater water stress in lower than 

higher elevations (Culp 1986). Moreover, the range of vessel 

diameters is also of interest. Carlquist (1977) stated that foliar 

modifications can strongly affect a plant’s response to its environment. Leaves exert a strong degree of control over water 

relations within big sagebrush (Scultz 1983) and blackbrush 

populations. Nevertheless, no comparative data are available 

since variations in vessel area and diameter of blackbrush 

leaves have not been measured quantitatively.

Vessel density increased significantly (P < 0.05; table 2) 

with decreasing elevation. The density of leaf vessels is known 

to increase with increasing aridity (Fahn 1982). The density of 

vessels is fewer at the higher elevations compared to the lower 

sites in southern Nevada (Culp 1986).

Below a uniseriate hypodermis, the palisade parenchyma 

was readily distinguished from the spongy parenchyma in 

this study. The palisade parenchyma consisted of continuously elongated (column-like) cells, mainly in the direction 

perpendicular to the leaf surface. The bifacial (abaxial) palisade parenchyma was significantly shorter (P < 0.05; table 4) 

with increasing aridity. The mean thickness of palisade parenchyma ranged from 165.9 um in the lower ecotone to 176.8 um 

in the upper ecotone. No comparative data are available since 

variations in palisade parenchyma of blackbrush have not 

been measured quantitatively. Palisade parenchyma in creosote bush was also shown to increase in length with increasing 

aridity in Death Valley of southern California (Culp 1986).

Water availability during a growth period is an important factor affecting cell elongation. Cells imbibe water and 

exert turgor pressure on the primary cell wall. Therefore, the 

more water available to the cell, the longer it is likely to grow 

(Culp 1986). This possible explanation for differential cell 

elongation along the elevational gradient may be results of 

the greater amount of water available at higher elevations in 

southern California (Culp 1986). Shorter palisade cells allow 

space for an increase in vessel numbers without significantly 

increasing in leaf size (Culp 1986).

Other leaf anatomical structures did not differ significantly 

(P > 0.05; table 4), indicating that tissue thicknesses were 

similar irrespective of elevational changes. These structures 

included length (thickness) of total lamina, upper and lower 

epidermis, hypodermis, and spongy parenchyma.

Ecological Implications and 

Future Directions

Although blackbrush growing at various elevations looked 

similar in general appearance, plants exhibited significant 

differences in certain anatomical structures as elevation 

changes in Lee Canyon of southern Nevada. Discovering 

upper and lower elevational ecotypes within the same species 

reveal the usefulness of plant anatomy in detecting fine-tuned 

variation. However, one must realize that ecotypic variation 

in blackbrush leaves is not strictly a function of elevation. A 

number of environmental attributes vary with changing elevation. Air and soil temperatures increase, whereas precipitation 

and soil moisture decrease with descending elevation. Such 

variation in environmental attributes would cause anatomical 

changes observed in blackbrush leaves. The extent to which 

my results are representative of blackbrush occurring at other 

sites is not completely known. However, this study suggested 

that blackbrush leaves were anatomically adaptable to habitat 

changes in the Spring Mountains of southern Nevada.

Blackbrush also exhibits upper and lower elevational 

ecotypes at the seed germination (Lei 1997c) and imbibition levels (Lei 2007). Blackbrush shrublands are a dominant 

Table 3. Mean (± se) vessel characteristics of blackbrush leaves along an elevational gradient in southern Nevada.

Lower ecotone Nearly pure stand Upper ecotone

Vessel diameter (μm) 5.1 ± a 1.7 a 6.0 ± 1.6 ab 6.9 ± 1.2 b

Vessel area(μm2

) 20.4 ± 0.7 a 28.3 ± 0.8 b 37.4 ± 1.1 c

Vessel density (vessels mm-2) 98.6 ± 5.9 a 91.4 ± 5.5 b 86.1 ± 4.4 c

1

 Means within a leaf character followed by the same letter are not significantly different (P > 0.05; n = 30).

Table 4. Mean (± se) tissue thickness (μm) (excluding cuticles and intercellular spaces) of blackbrush leaves along an 

elevational gradient in southern Nevada. Adaxial stomata are absent in blackbrush.

Lower ecotone Nearly pure stand Upper ecotone

Lamina 374.9 ±13.2 a 376.2 ±6.8 a 380.8 ± 5.6 a

Upper epidermis 16.4 ± 1.8 a 15.9 ± 2.5 a 15.8 ± 2.9 a

Lower epidermis 14.1 ± 1.2 a 14.1 ± 1.4 a 13.7 ± 1.5 a

Hypodermis 34.0 ± 3.1 a 33.1 ± 2.6 a 32.8 ± 1.9 a

Palisade parenchyma 165.9 ± 7.9 a 169.7 ± 7.3 ab 176.8 ± 8.2 b

Spongy parenchyma 140.5 ± 7.2 a 141.5 ± 8.9 a 141.7 ± 6.5 a

1

 Means within a leaf character followed by the same letter are not significantly different (P > 0.05; n = 30).
USDA Forest Service RMRS-P-47. 2007 173

vegetation type in the Mojave Desert. Despite significant 

publications and contributions in the past, the biology of 

blackbrush are still not completely known and should deserve 

further investigations to improve our understanding on various 

aspects of blackbrush shrubs.

Acknowledgments

I gratefully acknowledge Steven Lei, David Valenzuela, and 

Shevaun Valenzuela for collecting fresh blackbrush leaves in 

the field and for meticulously observing anatomical structures 

in the laboratory. I also sincerely appreciate David Charlet for 

critically reviewing an earlier version of this manuscript. The 

Department of Biology at the Community College of Southern 

Nevada (CCSN) provided logistical support.

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The Author

1 Statistics and Research Methods Instructor, Department of 

Educational Psychology, University of Nevada, Las Vegas, NV. 

leisa@unlv.nevada.edu
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