United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Proceedings RMRS-P-30

September 2003

Santa Rita Experimental

Range: 100 Years (1903 to 2003)

of Accomplishments and

Contributions

Conference Proceedings

October 30–November 1, 2003

Tucson, AZ

1902 2003
Rocky Mountain Research Station

324 25th Street

Ogden, UT 84401

Cover photographs: Top pair are looking east into Box Canyon from photo station PS 222, June 1902 and May 2003. Bottom pair are looking west

at Huerfano Butte from photo station 233, 1902 (month unknown) and May 2003.

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NOTE: Papers were edited to a uniform style; however, authors are responsible for the content and accuracy of their papers.

Abstract

McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. 2003. Santa Rita Experimental

Range: 100 years (1903 to 2003) of accomplishments and contributions; conference proceedings; 2003

October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station. 197 p.

The purpose of this conference was to celebrate the 100 years of accomplishments and contributions of the Santa

Rita Experimental Range, the longest continuously operating research area dedicated to the sustainable

management of North American rangelands. The conference consisted of one-and-a-half days of invited synthesis

papers and contributed poster presentations and a 1-day field trip to research sites at the Santa Rita Experimental

Range. A forecast of the future contributions of this historical site were also considered. This conference provided

a forum for people to share their knowledge, experiences, and opinions about the contributions that the Santa Rita

Experimental Range has made to rangeland management.

Keywords: long-term research, livestock grazing, vegetation, soils, erosion, cultural resources
Santa Rita Experimental Range:

100 Years (1903 to 2003) of

Accomplishments and Contributions

Conference Proceedings

October 30–November 1, 2003

Tucson, AZ

Technical Coordinators _____________________________

Mitchel P. McClaran is Professor of Range Management, School of Renewable Natural Resources, 325 Biological Sciences East, University of

Arizona, Tucson, AZ 85721.

Peter F. Ffolliott is Professor, School of Renewable Natural Resources,

325 Biological Sciences East, University of Arizona, Tucson, AZ 85721.

Carleton B. Edminster is Project Manager with the USDA Forest Service,

Rocky Mountain Research Station, Flagstaff Lab, 2500 South Pine Knoll,

Flagstaff, AZ 86011.

Sponsors _________________________________________

Rocky Mountain Research Station, USDA Forest Service

USDA Natural Resources Conservation Service

USDA Agricultural Research Service

School of Renewable Natural Resources, University of Arizona

College of Agriculture and Life Sciences, University of Arizona

International Arid lands Consortium

Arizona State Land Department

Society for Range Management

These peer-reviewed proceedings represent a permanent record of this conference, celebrating the accomplishments and contributions of the Santa Rita

Experimental Range, the longest continuously operating research area dedicated to the sustainable management of North American rangelands, and forecasts

the future contributions of this historical site. The

conference consisted of the presentation of a series of

synthesis papers by invited speakers who reviewed

significant research findings on the Santa Rita Experimental Range and, where appropriate, forecast

future research opportunities. Contributed poster papers supplemented and expanded on the synthesis

papers by reporting on recently completed or ongoing

research on the Santa Rita. The conference concluded

with a 1-day field trip to research sites on the Santa

Rita Experimental Range.

This conference provided a forum for researchers,

managers and practitioners, decisionmakers, and other

interested people to share their knowledge, experiences,

and opinions about the contributions that the Santa

Rita Experimental Range has made to rangeland management in the Southwestern United States. The conference and these proceedings also represent a starting

point for planning and implementing research activities, leading to improved, ecosystem-based, multipleuse rangeland management in the future.

The technical coordinators of these proceedings acknowledge the collective efforts of the technical reviewers of these papers. We also acknowledge Louise

Kingsbury, Group Leader, and the Publishing Services

staff, Rocky Mountain Research Station, USDA Forest

Service, Ogden, UT, for their invaluable editorial assistance. Major funding for the preparation of these

proceedings was provided by the Southwestern Borderlands Project (FS-RMRS-4651), Rocky Mountain

Research Station, USDA Forest Service, Flagstaff,

AZ. Additional support was furnished by the other

sponsors of the conference.

Preface

iii

Mitchel P. McClaran

Peter F. Ffolliott

Carleton B. Edminster

Contents

Page

Invited Papers

Nathan F. Sayre Recognizing History in Range Ecology: 100 Years of Science and Management

 on the Santa Rita Experimental Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Mitchel P. McClaran A Century of Vegetation Change on the Santa Rita Experimental Range . . . . . . . . . 16

George B. Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability

 on the Santa Rita Experimental Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Peter F. Ffolliott Vegetation Management Practices: Past and Present . . . . . . . . . . . . . . . . . . . . . . . . 48

Gerald J. Gottfried

William H. Kruse

Paul R. Krausman Wildlife Ecology and Management, Santa Rita . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Michael L. Morrison Experimental Range (1903 to 2002)

John H. Madsen Cultural Resources of the Santa Rita Experimental Range . . . . . . . . . . . . . . . . . . . . 68

Bruce D. Munda Revegetation Practices on the Santa Rita Experimental Range . . . . . . . . . . . . . . . . 80

Mark J. Pater

Leonard J. Lane Hydrology and Soil Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Mary R. Kidwell

Thomas E. Sheridan Archive and Laboratory Embedded in the Landscape:

 Future of the Santa Rita Experimental Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Poster Papers

Michael A. Crimmins Climate Variability and Plant Response at the Santa Rita Experimental

Theresa M. Mau-Crimmins Range, Arizona . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Erika Geiger Spread of a Nonnative Grass Across Southern Arizona:

Theresa Mau-Crimmins Multiple Data Sources to Monitor Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Heather Schussman

Jorry Z. U. Kaurivi Multitemporal MODIS-EVI Relationships With Precipitation and

Alfredo R. Huete Temperature at the Santa Rita Experimental Range . . . . . . . . . . . . . . . . . . . . . . . 121

Kamel Didan

Alessandra Fravolini Role of Soil Texture on Mesquite Water Relations and Response to

Kevin R. Hultine Summer Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Dan F. Koepke

David G. Williams

Stacy Pease Mesquite Removal and Mulching Treatment Impacts on Herbage

Peter F. Ffolliott Production and Selected Soil Chemical Properties . . . . . . . . . . . . . . . . . . . . . . . . 130

Leonard F. DeBano

Gerald J. Gottfried

Alvin L. Medina Gambel and Scaled Quail Diets on the Santa Rita Experimental Range . . . . . . . . . 133

Alvin L. Medina Historical and Recent Flora of the Santa Rita Experimental Range . . . . . . . . . . . . 141

Sharon H. Biedenbender Effects of Neighbor Species and Distance on 2- and 4-Year Survival of

Mitchel P. McClaran Lehmann Lovegrass and Native Grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Bruce A. Roundy

v
vi

Peter F. Ffolliott International Arid Lands Consortium: A Synopsis of Accomplishments . . . . . . . . . . 154

Jeffrey O. Dawson

James T. Fisher

Itshack Moshe

Timothy E. Fulbright

W. Carter Johnson

Paul Verburg

Muhammad Shatanawi

Jim P. M. Chamie

Donald J. Breckenfeld Soil and Ecological Sites of the Santa Rita Experimental Range . . . . . . . . . . . . . . 157

Daniel Robinett

Gerald J. Gottfried Assessment of Fire-Damaged Mesquite Trees 8 Years

Peter F. Ffolliott Following an Illegal Burn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

Pablo Garcia

Diego Valdez-Zamudio

Akram Al-Khouri

Larry D. Howery Sweet Resin Bush on the Santa Rita Experimental Range:

Bruce D. Munda An Eradication Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Dan G. Robinett

Harry H. Buck

A. Karim Batchily Spectral Reflectance and Soil Morphology Characteristics of

Donald F. Post Santa Rita Experimental Range Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

R. B. Bryant

Donald J. Breckenfeld

Phil R. Ogden Cow Weights and Calf Production for Pasture 12-C Lehmann Lovegrass

E. Lamar Smith Grazing Trials, 1982 to 1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Nathan B. English Soil Temperature and Moisure Dynamics After Experimental Irrigation on

David G. Williams Two Contrasting Soils on the Santa Rita Experimental Range:

Jake F. Weltzin Implications for Mesquite Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

Craig Wissler New Data Sources and Derived Products for the SRER

Deborah Angell Digital Spatial Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
USDA Forest Service Proceedings RMRS-P-30. 2003 1

Nathan F. Sayre

Recognizing History in Range Ecology:

100 Years of Science and Management on

the Santa Rita Experimental Range

Introduction _____________________________________________________

The Santa Rita Experimental Range is 100 years old this year, providing an occasion to celebrate and to reflect. The first

of many experimental ranges in the United States, the Santa Rita was founded at a time when both range science and plant

ecology were in their infancy. The purpose was to conduct research that would aid in the management of Southwestern

rangelands by public agencies and private ranchers, in the belief that science, coordinated by public agencies and conducted

on a suitably large scale, would produce methods of restoring and conserving the vast and severely degraded rangelands of

the region more quickly and effectively than a private, trial-and-error approach could. Confidence in the ability of government

science to solve pressing public problems was characteristic of the era, giving birth not only to the Santa Rita but also to range

science more generally and to an array of Federal agencies.

To assess a century of work on the Santa Rita, at least two questions must be answered: (1) What happened on the

experimental range itself, in terms of research and recommendations for management? And (2) what effects did this work

have on rangelands in the region? The historical record is abundant regarding the first question, but comparatively thin

as to the second. I begin by reviewing the circumstances surrounding the creation of the Santa Rita Experimental Range.

Then I use the more than 400 publications produced from the Santa Rita to define four major periods of research from 1901

Nathan F. Sayre is Postdoctoral Research Associate with the Jornada Experimental Range in Las Cruces, NM. Phone: 520-327-5567; e-mail: Nfsayre@aol.com.

He earned a B.A. degree in philosophy from Yale University and a Ph.D. degree in anthropology from the University of Chicago. His research focuses on the history

of range science and management in the Southwest, and the implications of that history for current management.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B. tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: At the centennial of the Santa Rita Experimental Range, historical analysis is called

for on two levels. First, as a major site in the history of range ecology, the Santa Rita illuminates

past successes and failures in science and management and the ways in which larger social,

economic, and political factors have shaped scientific research. Second, with the turn away from

equilibrium-based models in range science—a turn prompted in part by research at the Santa

Rita—there is a growing need for history in range ecology itself. I discuss the needs, premises, and

events underlying establishment of the Santa Rita in 1903. Then I examine the evolution of

research and management recommendations through four major periods from 1901 to 1988, and

I discuss the land swap that transferred the Santa Rita to State ownership in 1988 to 1991. Finally,

I consider what effects the Santa Rita has had on rangelands and range management in the region.

I argue that a static conception of the carrying capacity of Southwestern rangelands was imposed

for economic and political reasons, over the objections or reservations of early range scientists at

the Santa Rita, and that this may have contributed both to range depletion and to rancorous

relations between public agencies and private ranchers in the twentieth century. To meet society’s

current demands on rangelands, the long-term, large-scale data assembled from the Santa Rita

will be critically important.

Keywords: range science, range ecology, history, carrying capacity, mesquite, Frederic

Clements, semiarid rangelands

Acknowledgments: The author gratefully acknowledges Joel Brown, Kris Havstad, Mitchel P.

McClaran, Guy McPherson, and especially Phil Ogden for helpful comments and other assistance

in the preparation of the manuscript. Thanks also to Barbara Gibson for help with the figures.

I remain wholly responsible for the contents.
2 USDA Forest Service Proceedings RMRS-P-30. 2003

Sayre Recognizing History in Range Ecology: 100 Years of Science and Management...

to 1988. Within each period, I examine selected documents—some published, some unpublished—to trace the

evolution of research questions and management recommendations. Then I briefly discuss the period since 1988,

when ownership of the range changed from Federal to Sate.

Finally, I examine the evidence regarding actual management and range conditions over the past 100 years. Although the degree of influence of the Santa Rita is difficult

to determine in detail, several themes and possible lessons

for the future emerge nevertheless.

The overarching thesis of my argument is that a century

of research at the Santa Rita indicates the need for historical

analysis both of and in range ecology. Understanding the

history of range ecology is important for the same reasons as

in any discipline: to learn from past failures and successes,

to recognize intellectual antecedents, and to enable critical

reflection on our own ideas and practices. The history of the

Santa Rita reveals that while the methods and emphases of

research changed to reflect accumulating knowledge, the

central questions and many management recommendations

remained surprisingly consistent until very recently; it also

suggests that institutional and political factors have been as

important as scientific or ecological ones in shaping the

knowledge that researchers produce. The importance of

history in range ecology emerges from what has been learned

in the past century, both at the Santa Rita and in other arid

and semiarid settings. Whereas equilibrium-based ecological theory allowed most past researchers to neglect historical questions, current theories emphasize the potential of

nonstationary climate and discrete events, interacting at

various spatial and temporal scales, to cause significant and

lasting ecological change. Today, with the larger social,

political, and economic contexts of range management dramatically different from a century ago, there is a need both

to recognize and to re-cognize history, so that the changes of

the past can be properly understood and the challenges of

the present and future effectively confronted.

Beginnings: Founding a Range

Research Reserve ______________

Nineteen hundred and three was the fifth year of a 6-year

drought in southern Arizona. The boom and bust cycles of

markets and rainfall were already painfully familiar to both

ranchers and public officials in the area. Just 10 years

before, the drought of 1891 to 1893 had killed scores of

thousands of cattle and wiped out countless ranchers. That

drought, more than the one from 1898 to 1904, helped to set

in motion the factors that would eventuate in the Santa Rita

Experimental Range. But it was not the only, or the first,

factor.

The Hatch Act of 1887 authorized State and territorial

governments to receive Federal funding for agricultural

experiment stations. Lacking other resources, the University of Arizona took advantage of Hatch Act funds beginning in 1890, using them to cover operating expenses and

salaries as well as agricultural research (Webb 2002: 80). A

year later the Arizona Agricultural Experiment Station

published its Bulletin number 2, comprising two short

articles by J. W. Toumey (1890): “Arizona Range Grasses in

General” and “Overstocking the Range.” The latter article

contained a prescient warning. In the open range, Toumey

wrote (1890: 7):

...even the hardiest grasses when continually eaten close to

the ground will, as a rule, in a few years become extinct...

[W]here drought and overstocking both combine, and the

grass that does not burn out from the effects of the hot sun, is

continually eaten close to the ground by hungry cattle, the

range is in poor condition to produce feed for the following

season. The repetition of this process year after year cannot

help but decrease the supply of grasses on the range.

By the time the drought broke in late summer 1893, an

estimated 50 to 75 percent of southern Arizona’s cattle had

perished from lack of feed or water. Photographs from the

time bear out Toumey’s most dire scenario (fig. 1).

The undeniable ecological and economic damage of the

drought helped get the attention of Congress, which in

1895 appropriated the first Federal funding expressly for

range research. In the Texas high plains, Jared Smith and

H. L. Bentley arranged to fence two sections of rangeland

Figure 1—Photograph taken by George Roskruge,

surveyor for the General Land Office, at an unidentified southeastern Arizona location in the

summer of 1891. Heavy, unconrolled grazing combined with drought produced widespread denudation of rangelands previously dominated by

perennial bunchgrasses, eventually prompting

Congressional action to regulate grazing on the

public domain and to create experimental ranges

such as the Santa Rita (courtesy of Arizona Historical Society, Tucson, AHS #45866).
USDA Forest Service Proceedings RMRS-P-30. 2003 3

Recognizing History in Range Ecology: 100 Years of Science and Management... Sayre

for experiments funded by these monies. It was not until 5

years later, however, that the Federal government took the

decisive step of reserving land from the public domain

specifically for range research. President McKinley signed

the order withdrawing four sections southeast of Tucson on

October 10, 1900.

David Griffiths of the Arizona Agricultural Experiment

Station had spent “the greater part of a week” scouting the

Tucson basin for this tract of land (Griffiths 1901: 23). That

it was bisected by the Southern Pacific Railroad was an

advantage in his eyes, because it meant that one side of his

research plot was already fenced. He enclosed 52 acres,

divided it into 60 plots, and began a series of experiments.

But the “small inclosure” [sic], as it came to be called, soon

showed serious limitations. Even including the unfenced

portion, it was too small and too uniform to represent the

varied rangelands of the region. It was also lower and drier

than the prime grasslands south and east of the Tucson

basin. Griffiths tried to assert that the area was “a typical

mesa region in every respect” (1901: 24), but it contained

more creosote and cacti than perennial grasses and little

topographical, climatic, or edaphic variation. “The production of forage is so small here, at best, that one is obliged to

measure his pasture by square miles rather than by acres,”

he noted, “and the operations in range improvement must

be on a correspondingly large scale” (1901: 29). Even if

Griffiths’ experiments in establishing forage plants had

succeeded, the need for a larger research range would have

remained.

In 1902, Alfred Potter—who would shortly become Gifford

Pinchot’s first Chief of Grazing—drafted a report for the

proposed Santa Rita Forest Reserve, from which the experimental range would subsequently be carved (Potter

1902). In its earliest conception, the reserve was to extend

from the Santa Cruz River east to Cienega Creek, and from

the Southern Pacific Railroad south to Sonoita Creek, an

area of 592 square miles or 379,000 acres. Potter acknowledged that only 45,000 acres of this area was “well forested,” and that nearly four-fifths of it was mesa and

foothills land. Most of the lower elevation, nontimber land

was eventually excluded from the reserve, but on the

northwest flank of the Santa Rita Mountains parts of four

townships were withdrawn, giving birth to the Santa Rita

Experimental Range; Griffiths termed it “the large inclosure” [sic]. President Theodore Roosevelt signed the proclamation on April 11, 1902. The boundaries expanded

under subsequent executive orders, by Roosevelt in 1907,

Taft in 1910, and by Coolidge twice, in 1925 and 1927.

Taft’s order also recognized the Santa Rita as distinct from

the adjacent Forest Reserve, which had been consolidated

into the Coronado National Forest 2 years before; in consequence, title to the experimental range remained with the

Interior Department, rather than transferring to the Department of Agriculture. Ultimately, the Santa Rita encompassed over 53,000 acres, or more than 1,000 times the

size of Griffiths’ first enclosure (which was converted to

military uses in 1925 and today is part of Davis-Monthan

Air Force Base).

Two of Potter’s observations about the Santa Rita Forest

Reserve are worth noting here. First, he wrote that before

the 1891 to 1893 drought, the area had “carried fully 25,000

head of cattle and horses and 5,000 sheep,” and that as of

1902 these numbers had dropped to “between 7,000 and

8,000 cattle, from 1,000 to 2,000 horses, and about 4,000

sheep.” These figures translate to roughly 44 head per

section before 1891, and 15 to 18 head per section in 1902.

Potter also described a seasonal pattern of movement within

the proposed reserve, with herds concentrating in the mountains in the fall and winter and the foothills in the spring and

summer.

Second, Potter reported that “the mesa lands are all

covered with mesquite, to a certain extent; although over the

greater part of the area the growth is very scattering and

shrubby in character. The only good solid mesquite area is

along close to the river bottom and in the draws coming down

from the mountains.” He described mesquite as “the most

universally useful tree in this section,” providing almost all

the firewood and fence posts used in the vicinity. Since many

wells at this period relied on steam pumps fueled with wood

(Griffiths 1904: 35), it is possible that mesquite harvesting

may have invisibly skewed later perceptions of the area’s

“original” vegetation.

Between March and June 1903, 27.3 miles of fence were

constructed around the experimental range, at a cost of $105

per mile. For the next 12 years, no livestock would graze on

some 49 sections of land, while Griffiths and his successors

studied its recovery. Spanning more than 2,600 ft of elevation, the new reserve encompassed significant gradients of

rainfall, temperature, soils, and vegetation. At the highest,

most productive edge of the reserve, another nine sections of

land were included in the experimental range but were

allowed to remain in the management of settlers already

established there: McCleary, MacBeath, Proctor, and Ruelas.

Their pastures, ranging in size from 194 to 1,695 acres, were

fenced by 1908 and served comparative purposes for the

researchers, suggesting how recovery proceeded under controlled grazing.

That the founding management act of the Santa Rita

Experimental Range was fencing its perimeter is emblematic of circumstances at the time. There had been livestock

in the Santa Cruz Valley for 200 years, and for most of that

time they had not constituted a problem, as far as we know.

Limited transportation and markets, along with notorious

insecurity, had largely isolated the region from outside

sources of livestock, and herd growth had been determined

mainly by local conditions of forage, water, disease, and

predation. Only in the last quarter-century had the cattle

boom flooded the region with livestock from elsewhere,

brought in on foot or by railroad and financed from afar. In

1903, leases and fences were not yet in place to regulate

competition for forage on Federal lands, but there was

finally a political consensus that access to the range had to

be controlled, and that fencing was the only practicable way

to do this. Many early reports implied that fencing, in and of

itself, would cause range conditions to improve; fences went

up on forest lands after 1905, on State Trust lands after

1912, and on the remaining public domain after 1934. The

expanded scale of the livestock industry, from local to international, entailed a contraction of the scale of the individual

herd—from entire valleys or mountain ranges to defined and

fenced pastures. Almost without exception, research on the

Santa Rita would take this geographical innovation for

granted.
4 USDA Forest Service Proceedings RMRS-P-30. 2003

Sayre Recognizing History in Range Ecology: 100 Years of Science and Management...

Periods of Santa Rita

Research _____________________

With the range fenced, David Griffiths could begin his

research, initiating the stream of publications by which the

Santa Rita’s scientific production can be appraised. Al

Medina’s (1996) bibliography of Santa Rita research publications lists 452 articles spanning the period 1901 to 1988.

This figure includes 18 undated leaflets and several duplicate entries; excluding these and adding one important

reference omitted by Medina (see below), we have a data set

of 427 articles. If we organize these chronologically, and

depict the results graphically (fig. 2), several periods of

research activity can be identified. This periodization is

intended as a heuristic device only; there have always been

multiple threads of inquiry, administration, and funding in

the fabric of the Santa Rita, and the variable lag between

defining, funding, conducting, and publishing research defies neat temporal separation.

It is immediately clear from the graph that wildlife has

been an important focus of research on the Santa Rita since

the 1920s, increasingly so in recent decades. But it has

rarely constituted a majority of publications, and its very

consistency makes it poorly suited as a means of distinguishing periods of research effort. I defer to Krausman (this

proceedings) to illuminate the place of wildlife research in

the history of the Santa Rita. The history of research on

Lehmann lovegrass is not as long, but otherwise similar to

wildlife—recurrent but minor from the 1940s through the

1980s. I will touch upon it along the way.

1901 to 1931: Institutional Consolidation,

Revegetation, and Carrying Capacity

In the first 30 years of the Santa Rita, only 19 articles

were published, never more than two in any one year. This

was a period of minimal funding and staffing of the range,

while the larger institutional basis for range research was

slowly being consolidated. Major events in this consolidation process included the transfer of the Forest Reserves to

the U.S. Department of Agriculture and the formation of

the Forest Service in 1905; the creation of the Office of

Grazing Studies within the Forest Service in 1910, followed

a year later by the subdivision of forest administration into

Figure 2—Annual output of publications from Santa Rita research, 1901 to 1988, organized topically. Halfunits reflect publications that expressly covered two topics together (for example, mesquite and fire) (adapted

from Medina 1996).

0

5

10

15

20

25

190119041907

19101913

1916

191919221925

192819311934

1937

1940

1943

194619491952

195519581961

196419671970

197319761979

198219851988

Number of publications

Other

Fire

Wildlife

Mesquite
USDA Forest Service Proceedings RMRS-P-30. 2003 5

Recognizing History in Range Ecology: 100 Years of Science and Management... Sayre

regional offices; the transfer of range research outside

National Forests—including the Santa Rita Experimental

Range—from the Bureau of Plant Industry to the Forest

Service in 1915; the transfer of the Office of Grazing

Studies from the Branch of Grazing to the Branch of

Research in 1926; and finally, the creation of regional

forest and range experiment stations under the McSweeneyMcNary Forest Research Act of 1928 (Chapline 1944). It

was this last event that created the Southwestern Forest

and Range Experiment Station (SWFRES), based in Tucson, which brought increased Federal funding for range

research and triggered the rise in Santa Rita publications

from 1932 on.

Two pressing issues dominated the research of this period:

(1) how to restore forage plants decimated by the cattle

boom, and (2) how to measure range resources for management and administration. Griffiths (1901, 1904, 1907) and

J. J. Thornber (1910) tested hundreds of native and nonnative plant species in hopes of finding economical ways of

artificially establishing cover and forage on bare or nearly

bare ground. Most failed altogether, and even those that

showed some success were failures in economical terms.

Building up berms of soil to slow runoff and capture seed was

also attempted at the small enclosure, but the structures

often blew out in floods and did not result in enough grass to

justify the costs. “Much more satisfactory results have thus

far been obtained by husbanding the native vegetation and

grazing well within the capacity of the land to maintain

stock” than by any other methods, Griffiths (1910: 13)

concluded. This recommendation against overgrazing has

been a consistent refrain from Santa Rita researchers ever

since, although far less simple than it appears.

Determining carrying capacities was central to the research of this period because it linked environmental and

ecological factors to political and economic imperatives. It

was of “the utmost importance,” according to Griffiths’

boss, because “This knowledge determines the rental and

sale value of range lands and should also determine the size

of the minimum lease or homestead for range purposes...”

(W. J. Spillman, in the preface to Griffiths 1904). If fencing

and leasing were to work as planned, carrying capacity had

to be a coherent concept that public officials could apply,

measure, and enforce. Furthermore, the capacity of any

given piece of range had to be more or less static, both for

administrative efficiency and so that ranchers and their

financial backers could build leases into their business

plans and credit instruments. Griffiths recognized these

constraints, and he delivered carrying capacity estimates

as best he could, as did Wooton (1916). Following Smith’s

(1899) example from Texas, both were inclined to define

carrying capacity by reference to forage production in poor

(in other words, drought) years. In 1904, Griffiths recommended 37 acres per animal unit (AU) (or about 17 AU per

section) for the Santa Rita generally, and 50 to 100 acres

per AU (about 6 to 13 AU per section) for lower or more

degraded ranges; in 1910 he revised the Santa Rita estimate to 32 AU per section. Wooton concurred with the

latter, higher figure.

Griffiths’ reports contain numerous remarks, however,

that suggest he had doubts about the concept of carrying

capacity when applied “in a region where the seasons, the

altitude, the slope, and the rainfall are so variable” (1904:

32). Not only did productivity vary across space and time, it

was also “exceedingly difficult to decide which species are

and which are not forage plants,” because, if necessary,

cattle would eat almost everything (1904: 25). Even in the

absence of grazing, the composition of vegetation did not

display stability:

...differences in vegetation, comparing one year with another,

are very striking... In the large field, even with similar

rainfall, there occurs an ascendency [sic] of one plant one year

and another plant another year... So far as known, no one has

ever offered an explanation for these yearly variations of

annual vegetation (1910: 15).

Griffiths also discerned longer term vegetation changes

taking place, specifically an increase in mesquite and other

shrubs, and he attributed these changes to fire suppression,

not grazing. There is no evidence that his doubts diminished

over time; indeed, his 1910 carrying capacity estimates were

even more cautiously expressed than those of 1904. Likewise, his assertion that 3 years of complete rest would

restore degraded Southwestern rangelands “approximately

to their original productivity” (1910: 13) seems forced, because it conflicts with many of his other observations. He

noted, for instance, that 2 consecutive years of good summer

rainfall were needed for significant establishment of perennial grasses—something that occurred only once in his 10

years of research in the area.

Griffiths appears to have arrived in Arizona with few

preconceptions about the desert and no scientific theories to

attack or defend, allowing his curiosity wide latitude. He

conducted surveys of ranchers, traveled and photographed

extensively in the region, and generally let his observations

lead him where they would. In these respects he stands in

sharp contrast to the other major figure of this period,

Frederic Clements, who arrived in Tucson in 1917 to work at

the Carnegie’s Institution’s Desert Lab on Tumamoc Hill

(also founded in 1903). Clements came with a heavy investment in a powerful theory—his own—and a determination

to make it work in the Southwest and, indeed, everywhere.

Clements installed vegetation plots on the Santa Rita

(Bowers 1990: 40), and he also drew on the work of Griffiths

and other Santa Rita researchers for his 1920 book, Plant

Indicators, which included numerous photographs from the

range. The aim of the book was to demonstrate the practical

uses of his famous theory—published as Plant Succession

4 years earlier (Clements 1916)—in managing the rangelands of the American West. The profound influence of

“Clementsian” theory on range science is widely acknowledged to this day (National Research Council 1994; Society for

Range Management 1995). But both Plant Indicators and

Clements’ role in Santa Rita history have virtually disappeared from memory, as evidenced by omission from Medina’s

bibliography. His practical recommendations for managing

livestock in the Southwest have also been largely forgotten,

even though they anticipated many future developments in

semiarid range management. The debates about Clements’

role in range science and ecology have focused on the theory

of plant communities and succession, but I would argue that

the central practical issue was, again, carrying capacity.

Clements suffered from none of Griffiths’ doubts about the

theoretical coherence of carrying capacity, but he defined it

differently and was perhaps more naive than Griffiths about

how it would be used in practice. Specifically, he did not
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construe carrying capacities as static, and apparently he

didn’t see why anyone would.

No other factor produces such rapid and striking changes

in carrying capacity as does rainfall. The difference in the

total yield of the same range in two successive years of

dissimilar rainfall may be greater than 100 per cent, and in

the wet and dry phase of the same cycle it may be even greater

(1920: 292).

Clements believed that some longer “cycle” existed, probably

linked to sun spot activity, which might eventually render

this variability tractable for science and management. But

his practical recommendation was unequivocal:

It is evident that the maximum production can not have a

fixed or average value... A degree of grazing which would be

disastrous in a drought period would fall far short of adequate

utilization during a wet one (1920: 296).

His book exhaustively classified and described Western

rangelands, but he nowhere offered numerical estimates of

acres per animal or animals per section.

It is imperative that the ranchman be prepared to reduce

the pressure upon his range as the dry phase of the climatic

cycle approaches and that he be ready to take full advantage

of the excess carrying capacity of the wet phase. In fact, the

whole system of improvement must be focused upon the

destructive effect of overgrazing in dry years and the possibility of greater utilization and of successful sowing and planting during wet years (1920: 311).

Clements also suggested that carrying capacity was a

function not just of a given range and its condition but also

of management. He criticized both overstocking and stocking year around (1920: 297). Making reference to wild

herbivores such as bison, he linked secondary succession to

long periods of rest following heavy grazing (1920: 307), and

he recommended rotation of grazing pressure to imitate this

natural process (1920: 310). Like Griffiths, Thornber, and

Wooton before him, Clements called strenuously for fencing:

It is immaterial whether control is secured through ownership or leasing, provided it permits fencing. However, leasing

has the indirect advantage that it enables the State to exact

certain conditions as to utilization (1920: 311).

Although Clements’ theory of succession dominated twentieth century range science, as is well known, his practical

recommendations did not dominate actual management.

There is some evidence that southern Arizona ranchers

practiced summer season rest and variable stocking in the

1920s (Sayre 2002), but whether they took their cues from

scientists is unknown—I would guess they did not, in view

of the fact that continuous yearlong grazing became the

norm when ranchers shifted from stocker to cow-calf operations in the 1930s and 1940s. Even among range scientists,

Clements’ theory did not catch on quickly, if we may judge

from the Santa Rita archive. In the minutes of the Forest

Service’s District 3 Grazing Studies Conference of December 1921, for example, there is no mention of the work of

Clements (or Sampson), nor of succession or climax communities. With one exception (Wooton 1916), Clements’

influence does not appear in Santa Rita publications until

the late 1930s.

Although the number of publications from this period was

small, their importance to subsequent research and range

administration was great. Griffiths and Clements were

pioneers of range science both at the Santa Rita and for the

nation. That both of them expressed reservations, tacitly or

explicitly, about the central premise of the system of rangeland administration institutionalized over the following

decades sheds new light on current debates about range

ecology and management in the United States and elsewhere (Illius and O’Connor 1999).

1932 to 1945: Growth and the Shrub

Problem

The second period extended from 1932 to the end of World

War II, which imposed severe budget restrictions and brought

publications nearly to zero by 1945. With a newly enlarged

staff, the Southwestern Forest and Range Experiment Station supported more focused studies of particular forage

species such as tanglehead, black grama, blue grama, and

vine mesquite, as well as of noxious or invasive plants,

particularly burroweed. Numerous studies sought more

accurate and efficient methods of measuring vegetation and

utilization—an outgrowth of the Forest Service’s need to

define and enforce carrying capacities. These new methods

were both scientifically rigorous and practical for agencies,

but they did not really address the question of static versus

dynamic carry capacities on Southwestern rangelands.

Revegetation remained a major focus, but with more attention on underlying ecological factors such as litter cover and

soil moisture. Research on wildlife expanded as well to

include kangaroo and pack rats, wood rats, quail, jackrabbits, and rattlesnakes. Finally, there was a more specialized

attention to practical management issues as viewed from

the perspective of private ranchers. Matt Culley (1937)

produced a detailed study of the economics of one of the

Santa Rita’s cooperating ranches, and he and Kenneth

Parker placed numerous articles in livestock journals on

range and management issues such as poisonous plants,

drought, and proper stocking.

Perhaps the most important study performed during this

period, historically speaking, was one that was not published. “Occurrence of Shrubs on Range Areas in Southeastern Arizona” (Upson and others 1937) was a cooperative survey conducted in 1936 and 1937 by the Southwestern

Forest and Range Experiment Station, the Arizona Agricultural Experiment Station, the Agricultural Adjustment

Administration, and the Bureau of Agricultural Economics. It involved vegetation measurements at 450 sites coupled

with ocular surveys of nearly 12 million acres, resulting in

maps of the dominant vegetation covering all of southeastern Arizona (figs. 3 and 4). Nearly a third of the area was

dominated by grasses, and another quarter by creosote;

cactus and burroweed dominated just over 9 percent each,

and mesquite dominated another 7 percent; wolfberry,

saltbush, and snakeweed dominated the remaining 10

percent. The mesquite, snakeweed, and burroweed areas

were singled out as having expanded in recent memory,

usually at the expense of grasses, and therefore as having

the greatest potential for restoration. Up to this point,

burroweed had received far more attention from Santa Rita

researchers than the other two species, but the survey

found mesquite to be the most widespread of the three,
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present on more than 9 million acres—three-quarters of

the region. Understanding, explaining and remedying this

shift would be the dominant research priority of Santa Rita

range scientists for decades to come.

As mentioned above, Griffiths had noted the spread of

mesquite nearly 30 years earlier and had attributed it

primarily to fire suppression, not grazing. Curiously, “Occurrence of Shrubs” did not discuss fire at all, aside from a

brief mention under “Artificial Means of Control” of

burroweed (p. 26). The report’s explanation of shrub expansion was that grazing—and only grazing—had shifted the

competitive balance between grasses and shrubs, and that

heavily grazed areas around water sources had provided

sites for establishment and subsequent spread of shrubs into

the surrounding range (p. 12–15). This argument was framed,

moreover, in explicitly Clementsian terms: grasslands “represent, of course, the climax type” for the region, and evidence of former grass dominance in areas of shrubs was

Figure 3—Map of “principal plant cover of range areas in southeastern Arizona,” 1936 to 1937. The report containing

this map drew attention to shrub encroachment in areas formerly dominated by grasslands, and helped shift attention

from burroweed to mesquite (Upson and others 1937).

taken to indicate that such areas “may also be considered,

ecologically, a climax grassland type” (p. 12). The authors

argued that reducing or eliminating grazing would retard or

prevent shrub encroachment, although they also acknowledged documented cases where this had not worked, suggesting the possibility that “there are other factors than

grazing which favor the spread of shrubs” (p. 24).

Researchers initiated studies of mesquite immediately

following completion of the report, but they did not focus on

adjusting stocking rates. Instead, techniques of killing the

trees outright were tested (Parker 1943). In 1940, a study

was launched in which mesquite and/or burroweed were

killed on 1-acre plots; it was followed in 1945 by another,

which used prisoner-of-war labor to thin mesquite to various densities on 2-acre plots. Also in 1940, the Carnegie

Institution ceased its support of the Desert Lab and turned

its facilities on Tumamoc Hill over to the Forest Service.

The SWFRES had its headquarters there until 1953, when

ARIZONA

KEY MAP

AREA SURVEYED

FIG-1

CREOSOTEBUSH BALANCE SNAKEWEED, MESQUITE,

CACTUS, & MINORSPECIES, TRACE OFGRASS

BLACKBRUSH BALANCE CREOSOTEBUSH, MESQUITE, 

SNAKEWEED, BURROWEED, & MINOR SPECIES, SOME GRASS

CACTUS BALANCE MIXED COMPOSITIONOF MANY 

SPECIES, SOME GRASS

SALTBUSH TRACES OF MESQUITE, 

CREOSOTEBUSH, AND GRASS

WOODLAND-TIMBER BROWSE & GRASS BENEATH

MESQUITE BALANCE BURROWEED,

SNAKEWEED, & MINORSPECIES, SOME GRASS

BURROWEED BALANCE MESQUITE, 

SNAKEWEED, CACTUS, & MINORSPECIES, SOME 

GRASS

SNAKEWEED BALANCE MESQUITE, 

BURROWEED, BLACKBRUSH, & MINORSPECIES, 

SOME GRASS

GRASSLAND THREE-QUARTERS GRASS, BALANCE 

MESQUITE, BURROWEED, SNAKEWEED, & MINOR SPECIES

BOUNDARIES OF CROOK AND CORONADO NATIONAL FOREST

PRINCIPAL PLANT COVER OF RANGE AREAS

 IN

 SOUTHEASTERN ARIZONA
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Figure 4—Map of “occurrence of mesquite on range areas in southeastern Arizona,” 1936 to 1937. The

ubiquity of mesquite, present on roughly 75 percent of the region, led to intense research efforts on the

Santa Rita for four decades, and especially from 1946 to 1966. At the time this map was made, however,

mesquites exceeded 30 plants per acre on only 15 percent of the region; heavy stands (>80 plants per

acre) were confined almost entirely to major drainages (Upson and others 1937).

it was merged into the Rocky Mountain Forest and Range

Experiment Station (RMFRES), headquartered in Fort

Collins, CO.

1946 to 1965: Age of Mesquite

The pace of research rebounded quickly with the end of the

war, and the focus turned decisively to mesquite. The overall

goal was the same as in Griffiths’ day: restoration of perennial forage grasses. But now shrubs, rather than just bare

ground, stood in the way. The postwar period was a prosperous one for both ranchers and agencies, and practices previously deemed uneconomical might now pencil out. Beginning in the late 1940s, the Hope-Flannagan Research and

Marketing Act made funds available for research on noxious

range plants.

In 1948, with cooperative agreements up for renewal on

both the Santa Rita and the Jornada Experimental Range,

Kenneth Parker composed “An analysis of range problems

in the Southwest,” another internal document. He cited the

1937 shrub survey in support of the claim that “mesquite

constitutes a problem on some 8 million acres” in southern

Arizona (p. 57)—this appears to have been an exaggeration, as the survey had found medium and high densities of

mesquite on less than 2 million acres (fig. 4). Parker

rejected the earlier study’s Clementsian expectation that

reduced grazing would reverse the trend toward shrub

domination, however. Meter-square quadrats going back to

1916 indicated no consistent relation of vegetation with

either climate or grazing pressure (p. 73); herbage productivity had declined substantially, even with steadily reduced stocking rates (p. 77–79). Parker concluded that “no

degree of moderation in grazing use will eliminate these

 FIG.-4

OCCURRENCE OF MESQUITE ON RANGE AREAS

 IN

 SOUTHEASTERN ARIZONA

 (NUMBER OF PLANTS PER ACE)

LIGHT STAND UNDER 30 PLANTS

MEDIUM STAND 30 TO 50 PLANTS

HEAVY STAND OVER 80 PLANTS

BOUNDARIES OF CROOK & CORONADO NATIONAL 

FORESTS

SCALE IN MILES
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low value plants. The meaning, in unmistakable terms, is

that if we are to continue grazing use by domestic livestock

some positive, drastic treatment which will eliminate these

plants will be necessary to achieve conservation of the

grazing resource” (p. 71). Because shrub encroachment

also threatened watershed function and, therefore, agricultural and municipal water supplies, Parker argued that

“[t]he future welfare of the Southwest is dependent on how

well and in what manner the range resource is used” (p. 7).

During the severe drought of the early 1950s, a sense of

emergency pervaded the ranching industry, and the “war

on mesquite” played well in local newspapers (Sayre 2002).

In all but 3 years from 1947 through 1965, no less than

one-third and often as many as two-thirds of Santa Rita

publications focused on velvet mesquite (49 out of 109 papers

altogether). Studies ranged from basic questions of life

history and reproduction, to demographic analyses, to effects on soils and competition. Herbicidal approaches to

mesquite control using diesel oil or chemicals were increasingly prevalent in the publications of this period. As in

Griffiths’ day, efforts were launched to find (or create by

hybridization) a perennial grass capable of establishment on

degraded semiarid rangelands, and this time several were

found among South African lovegrasses, although the full

implications of this success would not be evident until the

late 1960s. Work on small mammals also continued, and

whereas many earlier rodent studies had emphasized negative impacts on grasses, now some researchers focused on

rodents’ role in helping to propagate shrubs. Other wildlife

research in this period included studies of javelina, cactus

wren, Gambel quail, and deer.

This body of research has been of major and lasting

significance to scientific understanding of semiarid grassshrub rangelands, even though it fell short of its own

goals for practical management. From a theoretical perspective, the decisive turn was from the Clementsianism

of the 1937 shrub report to Parker’s observation in 1948

that reducing or eliminating grazing would not by itself

cause a reassertion of grasses. This opened up research

questions that extended well beyond issues of livestock

production, laying the foundation for subsequent investigations into water cycling and erosion, the spatial and

temporal distribution of moisture and nutrients as it

affects plant growth and competition (fig. 5), and the role

of small mammals and invertebrates in semiarid ecosystem processes. These issues would emerge to dominate

Santa Rita research in the following period. At the time,

however, the concerns of range managers still focused

primarily on producing livestock, and from this perspective the research fell somewhat short. The methods

developed for controlling mesquite were effective only if

the larger economics of ranching were very favorable—

cheap diesel and high prices for calves—and only on

fairly short time scales of 10 to 20 years, as mesquite

steadily reclaimed treated lands. Although vast acreages would be cleared over the 30 years from 1950 to

1980, the goal of restoring native perennial grass domination once again proved elusive.

Today, we think we know the reason for this shortcoming:

the near-total absence of fire from Southwestern semidesert grasslands. Fire was likewise missing from most

Santa Rita research and publications of the period. In his

Figure 5—The temporal distribution of effective

rainfall, 1916 to 1948. Shaded areas on the graph

represent periods when rain fell on successive days

or were preceded or followed by storms of 0.4 inch

or greater during the summer growing season. The

graph reflects growing understanding of the ecology

of major forage plants on the Santa Rita, which were

predominantly C4-pathway perennial grasses limited by the distribution of moisture in space and time,

rather than by gross annual or seasonal rainfall

(USDA 1952).

1948 internal analysis, Parker alluded to Griffiths’ comments on fire suppression, but he did not elaborate on them

or recommend research on the subject. Similarly, “The

Santa Rita Experimental Range” booklet of 1952 (USDA

1952) devoted one-sixth of its text and numerous photos to

noxious plant control, without a single mention of fire.

Somewhat of a maverick, Robert Humphrey—who had originally hired on with the Desert Lab—published numerous

papers making the case that fire suppression was the fundamental cause of woody plant encroachment, and that restoring fire could economically control the problem. But his

argument was based more in natural history than in experimentation, and the idea did not go far, producing only two

Masters theses, one technical bulletin, and two peer-reviewed publications other than Humphrey’s own articles

during this period. Ranchers, agencies, and the general

public were all accustomed to vigorous fire suppression, and

the real-world risks were obviously high. Moreover, in Parker

and Martin’s (1952: 14) words, “[t]he effect of fire or lack of
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fire on the occurrence of mesquite stands is a moot question.”

Whether from grazing, drought, shrub encroachment, or a

combination of the three, much of the region’s rangelands

simply didn’t have enough herbaceous fuels to carry a fire.

Lehmann lovegrass had the potential to change this, however, and Humphrey stood alone on this subject, too, calling

attention to the possible downsides of Eragrostis

lehmanniana a decade before anyone else (Humphrey 1959).

The attention placed on chemical and mechanical mesquite control cast a long shadow, obscuring less exciting

topics such as grazing management. Recommended practices were not much changed from earlier periods: stock

conservatively, distribute grazing pressure evenly, defer or

minimize grazing pressure during the summer growing

season (USDA 1952). Echoing Clements, the 1952 Santa

Rita booklet documented the wide variability of rainfall and

forage production, and it cautioned “that the practice of

building up numbers in the occasional good years removes

the only chance that the range might have to improve”

following drought (USDA 1952: 14). But it sought, nevertheless, to establish atemporal guidelines for stocking rates and

utilization (fig. 6).

Figure 6—Graph of forage yield and rainfall on an

annual basis, 1925 to 1933. Dashed horizontal lines

indicate average rainfall (top) and average forage

production (bottom); the solid horizontal line signifies the—“proper basis of use,” defined as roughly

20 percent below average forage production. Intended to prevent overgrazing during recurrent dry

years, this guideline nevertheless perpetuated the

conception of carrying capacity as a static attribute

of Southwestern rangelands (USDA 1952).

Meanwhile, postwar prosperity allowed greater capitalization of many ranch operations, and mesquite control was

only one of a long list of investments ranchers were making:

in improved breeding, more fencing and water development,

and new technologies for handling cattle (for example, holding corrals, squeeze chutes, calf tables, pickup trucks, and

trailers). The “old ways of doing things on the range... were

romantic, and led to a simpler and more friendly way of life,”

according to the booklet. “However, they cannot compete

with the modern way of doing business,” which involved

replacing labor costs with fixed costs (USDA 1952: 9). By

this time, cow-calf operations were the norm, and the

booklet recommended dividing one’s herd into groups of 50

to 100 animals, each group with its own fenced pasture, to

allow closer supervision and control of breeding. This

amounted to continuous yearlong grazing, which became

the norm in the region during this period.

1966 to 1988: Ecology and the Santa Rita

Grazing System

Research on mesquite continued through the 1970s, but

its dominance waned. The period 1966 to 1988 was the most

prolific in the Santa Rita’s history, and the proportion of

publications devoted to mesquite declined to only 10 percent of the total, compared to 45 percent in the previous

period. A wide array of new research foci emerged, reflecting new interests and methods both in range science and in

ecology more generally. In the late 1960s, animal scientists

used fistulated steers to study cattle diets, nutrition, and

weight gain, and the idea of frequent, automated weighing

of livestock was pursued. In the early 1970s, the International Biological Program’s Desert Biome project produced

a small mountain of research on soil nutrient flows, soil

moisture, termites, and ants. Other research also looked

below the surface of the ground to examine root systems of

grasses in grazed and protected sites, competition among

plants for soil moisture, variations in soil temperature,

factors affecting runoff and infiltration, fungi, and the

penetration and breakdown of various chemicals, especially insecticides. Wildlife research picked up considerably in the late 1970s, comprising more than a third (22 of

63) of all publications from 1976 to 1981. Different research

activities fed off one another, symbiotically or parasitically

depending on your perspective: mesquite removal for range

restoration experiments raised the question of wildlife

habitat effects; the discovery that termites consume large

quantities of biomass provoked attempts to control them,

just as had happened in earlier decades with rabbits and

rodents.

The problem of mesquite had not gone away. Rather,

confidence and funding had dissipated relative to other

interests. Herbicidal methods had largely failed, and from

the oil crisis of the early 1970s on, the cost of mechanical

treatment could not be justified given stagnant real returns to livestock and the likelihood that retreatment

would be necessary down the road. Where large-scale

mesquite clearing continued, it was underwritten by real

estate appreciation and other nonranching investments,

and it was motivated at least partially by tax policies that

incentivized losses (Sayre 2002). Meanwhile, opposition to
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mesquite control, especially using chemicals, emerged

among nonranchers as part of the larger social concern for

the environment.

The turn to a broader ecological orientation was reflected in range science research by Clark Martin’s work

on grazing systems. Building on earlier Santa Rita findings about the timing of forage growth, Martin had initiated studies of various grazing/rest schedules on small

plots beginning in 1957, and in the early 1970s he concluded that spring-summer rest 2 years out of 3 produced

significant improvement in perennial grasses compared

to continuous yearlong grazing (Martin 1973). He anticipated that these improvements would be concentrated in

areas of poor range condition (Martin 1978), a prediction

later confirmed in a 10-year study (Martin and Severson

1988). Perhaps the most intriguing discovery of Martin’s

research, and of related work by Dwight Cable (1971,

1975), was that grazing and drought had interactive,

lagged effects extending over 24 to 36 months: significant

improvement resulted from 2 successive years of good

summer rains, and grazing could retard recovery during

the first postdrought summer. These findings echoed the

views of Griffiths, Clements, and the 1952 Santa Rita

booklet, supporting them with hard data.

Rest-rotation grazing was not new, of course. It had

antecedents in the work of Clements, among others, and the

idea of deferring grazing until late in or after the growing

season had been promoted in the 1910s by Jardine and Hurtt

(1917) and Sampson (1914). What was new, it appears, was

a commitment within the Forest Service to encourage the

implementation of rotational systems on allotments throughout the Southwest. Hormay and Talbot (1961) had revived

and systematized rest-rotation in the early 1960s, pointing

out that under yearlong systems selective grazing would

disproportionately impact palatable species, even at conservative stocking rates. Only periodic rest could prevent this,

and fairly heavy grazing could be beneficial if it reduced

selectivity. Hormay and Talbot even claimed that “grazing is

eliminated as an environmental factor under rest-rotation

grazing” (p. 40). Whether true or not, their claim completed

a paradoxical evolution in range science. The discipline had

long embraced Clements’ theory of succession while neglecting his practical management ideas. Now it embraced one of

his management ideas (without crediting him), and used it

to renounce one of the central tenets associated with his

theory: the primacy of grazing in determining vegetation.

Cable’s (1975) research indirectly supported this view by

documenting the overriding importance of summer rainfall.

1988 to Present: Land Swap and

Reorientation

Medina’s bibliography extends only to 1988, and without

knowing his methods and criteria I am reluctant to attempt

to update it. The date would be an arbitrary endpoint for

historical analysis, except that it was also a pivotal year in

the administration and ownership of the Santa Rita Experimental Range. Funding for Santa Rita range science research had been stagnant or declining since 1975, when the

Tucson-based Southwestern Station of the Rocky Mountain

Forest and Range Experiment Station had been merged into

the Experiment Station at Tempe. Relative to the Southwest’s

booming urban and suburban economic sectors, livestock

grazing had begun to appear less significant, and by the late

1980s the Santa Rita was in danger of becoming an expensive anachronism. That the title to the range still resided in

the Interior Department—a fact that many people had

overlooked, it seems—now became significant. It meant that

the Rocky Mountain Station, and the USDA as a whole,

could simply walk away from the range in response to

shifting priorities and limited budgetary resources. This

would leave it in the hands of the BLM, inheritor of all

undisposed General Land Office holdings. But the BLM did

not have resources or reason to manage an experimental

range either.

Resolution came rather hastily and from an unexpected

direction (Sayre 2002). Some 50 miles southwest of the

range, in the Altar Valley, another branch of the Interior

Department faced a difficulty. The Fish and Wildlife Service

(FWS) had purchased the Buenos Aires Ranch in 1985,

mainly for the purpose of restoring the endangered masked

bobwhite quail. The ranch included leasehold to nearly

90,000 acres of State Trust lands, intermixed with 21,000

acres of deeded land. The FWS had removed all livestock

from the new Buenos Aires National Wildlife Refuge, and it

had no intention of grazing there. This meant, by policy, that

the State Land Department had to reclassify the leases as

commercial and charge the FWS commercial rates: 10 percent of fair market value of the land, or more than half a

million dollars a year. Several small land exchanges were

formulated, which would have enabled the refuge to consolidate its ownership of the prime masked bobwhite habitat.

But the vast majority of the Buenos Aires lease lands would

have remained subject to reclassification, or to reassignment to livestock operators.

Following a change in the governor’s office in 1987, the

Land Department began to press its case and the Buenos

Aires lease fees started to increase, forcing regional FWS

officials to scramble to cover the payments. Early in 1988,

Regional Director Michael Spear and Arizona BLM Director Dean Bibles came up with a solution, which passed into

law with the Idaho-Arizona Conservation Act that November. Nearly two and a half years later, in April 1991, the

transaction was executed: The Interior Department got the

Buenos Aires lease lands, and the State Land Department

took possession of the Santa Rita. Under a special designation passed by the Arizona legislature, the experimental

range was rededicated to research and education. It was

also assigned as its beneficiary the University of Arizona,

which administers the range and collects lease payments

directly from cooperating graziers. In this way, the Santa

Rita conforms to the constitutional mandate of the State

Trust to generate revenue for beneficiaries, but it is outside

of the ordinary policies and procedures of the Land Department. The designation remains in place indefinitely, until

and unless superseded by legislative action (Mitch

McClaran, personal communication).

Under its new ownership, the Santa Rita has continued to

host research projects and to work with its cooperating

grazing lessees. The larger social, economic, political, and

scientific context has shifted dramatically since 1903, however, and the orientation of research on the experimental

range is changing to reflect new interests, opportunities,
12 USDA Forest Service Proceedings RMRS-P-30. 2003

Sayre Recognizing History in Range Ecology: 100 Years of Science and Management...

and constraints. Issues of forage and livestock production

are receding relative to those of climate change, ecological

restoration, watersheds and wildlife. I will return to this

reorientation in a moment, after considering the second

question with which I began.

Effects on the Range ___________

What difference did Santa Rita research make on Southwestern rangelands? The question is surprisingly difficult to

answer.

Many innovations developed or recommended by Santa

Rita researchers have been widely adopted: the installation

of water sources every 2 to 3 miles across the range and the

careful placement of mineral supplements to distribute

grazing pressure evenly; the use of improved breeds and

livestock handling techniques; various methods of brush

control and revegetation with grasses; the construction of

interior fences to control both breeding and grazing; rigorous

culling of underperforming animals; and myriad variations

on rotational grazing. Exactly where and when these practices have been implemented, however, and to what effect on

range conditions, are difficult to determine. Grazing impacts

have probably been made more homogeneous and less severe over the landscape, with differential effects depending

on the scale and organism of concern. Lehmann lovegrass is

established in most of the areas suited to it; whether it is

choking out native grasses or otherwise causing harm is still

a matter of debate, but it has unquestionably succeeded in

reducing erosion compared to former conditions of shrub

dominance. Many ranchers now understand the historical

role of fire in these landscapes, and some are working

diligently to restore it; how widely this will succeed, it is too

early to tell.

One core message—avoid overgrazing—has been a constant of Santa Rita management recommendations, along

with the goal of restoring perennial, warm-season grasses.

Beginning early in the twentieth century, these came together in policies focused on proper stocking of National

Forest allotments; later, a similar approach was applied to

BLM and State lands. Clearly, proper stocking was, and

remains, central to good range management. But what did

it mean in practice, and what role did research play in actual

stocking decisions?

It is generally known that forage production and stocking

rates, as well as carrying capacity figures, have declined

significantly in the past 125 years. The stocking rates

recommended by Clark Martin in 1975, for example, ranged

from less than 4 to 18 to 25 AU per section, depending on

condition and elevation (Martin 1975: 10); these are all lower

than the rates recommended by Griffiths in 1910 and Wooton

in 1916, and less than half of actual rates described by Potter

for the area pre-1891. Actual stocking of the Altar Valley

before 1920 was three to fives times greater than at present

(Sayre 2000). As with the West as a whole, assessments of

regional range conditions have been sporadic and hampered

by inconsistent or disputed methodologies (National Research Council 1994).

Excessive grazing is usually viewed as the major cause of

these declines. The agencies were expected to enforce stocking rates, but on the expansive range compliance had to be

largely voluntary, and there is evidence that overstocking

was widespread in the past. Using sales data and interviews

for 160 ranches that changed ownership from 1957 to 1963,

Martin and Jefferies (1966) found that actual stocking of

BLM and State Trust allotments was, on average, twice the

official rates. Stocking decisions on State lands were largely

at ranchers’ discretion until the early 1980s, and it seems

that every old timer has stories to tell of permittees who

chronically overstocked their Federal or State allotments.

For obvious reasons, however, more comprehensive data on

the extent and severity of overstocking are extremely difficult to find.

Any assertion of causality between overstocking and

range depletion must be qualified, however. A recent analysis of regional vegetation change argues that the drought of

the 1890s might well have resulted in widespread arroyo

formation even if unaccompanied by overgrazing (Turner

and others 2003). Likewise, the drought of the 1950s

appears to have pushed some Southwestern rangelands—

with and without livestock grazing—across thresholds from

which a return to climax has not occurred (Herbel and

Gibbons 1996). Studies such as these suggest that grazing

impacts may have been significant during periods of severe

drought and much weaker, or even nil, during wetter

periods. When summer rains were good, conditions could

improve in the direction of the “climax” of perennial bunchgrass dominance, even under rates of stocking that we now

characterize as excessive. This occurred, for example, in

the upper end of the Altar Valley in the 1930s (Sayre 2002).

Depletion appears to have been concentrated in drought

periods, when herbaceous vegetation could decline significantly even without livestock present.

It can plausibly be argued—although not proven—that

the changes in vegetation observed during the twentieth

century would have occurred even if actual stocking had

adhered to official carrying capacity estimates. Very likely,

those estimates were unnecessarily restrictive during wet

years and too permissive during severe droughts. In spite of

the great natural variability in forage production, ranchers

had obvious economic incentives to maintain their herds,

even at the risk of overgrazing. “The general practice of

stockmen takes no account of the great variation in yield

between the dry and wet phases,” complained Clements

(1920: 297); this sentiment recurs in reports and bulletins

throughout much of the century. Of course, actual stocking

was never completely static, and carrying capacity estimates continued to be debated, studied, and revised throughout the century. But the expectation that some correct

number of livestock should exist for each allotment, independent of time, was a misconception perfectly suited to strain

relations between agencies and lessees. How could the

agencies ever demand reductions below official capacities,

even in severe drought, if the figures were supposed to

account for poor years? Conversely, how could lessees take

official capacities seriously in wet periods, when forage was

many times greater than permitted numbers of animals

could consume? Range scientists generated carrying capacity estimates that aspired to be independent of fluctuating

rainfall, and economic and political constraints compelled

ranchers and agencies to interpret proper stocking in terms

of static carrying capacities—Griffiths’ muted doubts and

Clements’ explicit admonitions notwithstanding.
USDA Forest Service Proceedings RMRS-P-30. 2003 13

Recognizing History in Range Ecology: 100 Years of Science and Management... Sayre

In summary, the effects of Santa Rita research on

regional rangelands are uncertain. Many management

practices have been adopted, although we do not know

how directly to attribute adoption to research findings. In

some cases, such as the shift from stocker to cow-calf

operations, the science may have reflected, rather than

prompted, the actions of producers responding to market

incentives. Santa Rita research did provide a relatively

independent and objective point of reference for agencies

and ranchers as they endeavored to control the number of

livestock grazing on the region’s Federal and State lands.

This appears to have worked reasonably well provided

that moisture was close to normal—although the norm

may itself have been little more than a statistical artifact.

Wet periods probably undermined ranchers’ respect for

agency guidelines (and perhaps the science behind them

as well); dry periods probably undermined agencies’ confidence in ranchers’ judgment and intentions.

Whether observed changes in vegetation are reversible

depends on whether twentieth century erosion has permanently altered the capacity of a given site to support the

earlier vegetation (Turner and others 2003: 261). Where

the answer is yes, overgrazing may have been responsible,

and the threshold was probably crossed during a major

drought. The static conception of carrying capacity—which

Southwestern range scientists did not expressly denounce

until the 1960s (Paulsen and Ares 1961), and which in

practice remains pervasive to this day—may in turn be

viewed as a contributing factor. In view of the writings of

Griffiths and Clements, however, blame should fall not so

much on the science produced from the Santa Rita and

other experimental ranges as on the translation of research

findings into policy and administration. Had Clements’

dynamic notion of carrying capacity been more widely

embraced, it is possible that the shortcomings of his theory

would not be so obvious today: Agencies and ranchers

might have adjusted stocking rates more aggressively, and

the lasting damage of heavy grazing during drought might

have been avoided. Then again, highly variable carrying

capacities might have made Clements’ theory economically

and administratively impractical and precluded its adoption in the first place. Ironically, Clements himself feared

that his theory might serve as “an excuse for overgrazing”

(1920: 310), but whether any ranchers or agency officials

rationalized heavy stocking in this way is unknown.

Conclusions___________________

The decision to create the Santa Rita Experimental Range

in 1903 rested on at least two interlocking premises. The

first was that it was biogeographically representative of a

large swath of Southwestern rangelands. Within its boundaries could be found conditions of vegetation, topography,

soils, and climate similar to those of some 20 million acres in

Arizona, New Mexico, and Texas (USDA 1952; fig. 7). The

second was that it was a representative management unit,

similar in size to the larger ranches that dominated the

region. Both premises reflected the judgment that the highest economic use of Southwestern rangelands was grazing,

such that research aimed at the needs of ranchers and range

managers could benefit the entire area. A century later this

judgment no longer holds, and both premises therefore

warrant reconsideration.

The highest uses of rangelands today, economically speaking, are housing development and recreation. Livestock

grazing in and of itself is relatively insignificant from this

perspective, although in combination with other demands—

for open space, wildlife habitat, and watershed function, for

example—the overall value of ranching remains high. Without getting into whether social demands on rangelands

complement or compete with one another, one can safely say

that the “highest and best” use is no longer uniform. Rather,

it varies depending on factors such as proximity to urban

areas, transportation corridors, or recreational hotspots; the

distribution of wildlife species and their habitats; amenity

values such as scenery and fine weather; and the threats

posed by wildfire, floods, and drought to urban and exurban

settlements.

The landscape is further differentiated by the history of

management. Under equilibrial assumptions this was a

secondary matter because the essential features of the range

were fixed by soils and climate and would reassert themselves if given a chance. In theory, once scientists figured out

how things worked on the experimental range, their knowledge could be taken and applied elsewhere. Now things don’t

look so simple, because we understand—at least in theory—

that discrete events or combinations of events may have

shifted conditions in different ways at different places or

times. Some drainages are cut by arroyos, while others are

not. In some valleys Lehmann lovegrass was planted on

large areas and has spread, while in others it is limited to

roadways or absent altogether. Fields cleared for crops in the

early 1900s still show the effects, decades after abandonment. In some places landscape-scale fires have happened in

living memory, although in most they have not. All these

factors are superimposed on the natural variability of rainfall across space and time as well as the complex patterns of

slope, aspect, soils, and vegetation.

There is still a near consensus that native perennial

grasslands are the most desirable state for the region’s

semiarid rangelands, but the goals of restoration are no

longer rooted in livestock production nor measurable in

terms of carrying capacity. Consequently, how to achieve

restoration, and at what cost, are far from clear. New goals

include wildlife conservation, watershed function, open space

for recreation or for scenery, and ecological restoration. Most

of these generate revenues only indirectly, if at all, and they

are often pursued in the absence of long-term, site-specific

data. Where were various wildlife species present at what

points in the past? How many livestock did each watershed

support during the drought of the 1950s? Which arroyos

have grown in recent decades, which have aggraded, and

what factors are responsible? In summary, a map of the

areas to which knowledge from the Santa Rita might be

applied today would look quite different from the one shown

in figure 7.

The second premise is still true, but less universally so,

and its significance is different from before. Fifty-six thousand acres remains a good size for addressing practical

management problems on Southwestern ranches and on

ranches converted to preserves (if not ranches that have

subdivided). The nature of those problems has changed in

fundamental ways, however, keyed to both spatial and
14 USDA Forest Service Proceedings RMRS-P-30. 2003

Sayre Recognizing History in Range Ecology: 100 Years of Science and Management...

Figure 7—Map depicting the geographical areas deemed comparable to the Santa Rita Experimental

Range, 1952. Although based primarily on biogeographical criteria, this judgment of the range of

applicability of Santa Rita research also contained social and economic assumptions, many of which must

be reconsidered in light of dramatic changes in the region’s economy and demography (USDA 1952).

temporal scale. Although the Santa Rita is large, the vast

majority of experiments conducted there have been relatively small (<100 acres, certainly); this reflected both practical constraints and the overriding interest in maximizing

forage production and optimizing utilization. It was generally assumed that findings would extrapolate to larger areas

unproblematically. More recent empirical and theoretical

work casts doubt on this assumption, and today scientists

aspire to landscape-scale observations and experiments.

A parallel change has occurred along the temporal axis.

Most experiments have been less than 5 years in duration,

but longer term data sets have had the most enduring value,

even when they did not lead to publications. Perhaps the

most valuable information derived from the Santa Rita in

the past century, given today’s needs and concerns, is the

long-term series of matched photographs. The power of the

photos is greater than just visual—it derives from their

ability to capture change on a temporal scale unavailable to

the mortal eye and impractical for more sophisticated techniques of data collection. With knowledge and concern about

climate change growing, data reaching back a century are

increasingly important. That more research has not been

conducted over periods of about 50 years is regrettable, but

it appears that it took that long for us to recognize the need.

Stewarding and sustaining the Santa Rita is essential for

the continuation of past research and for crafting further

long-term studies designed to answer today’s questions.

Finally, it is worth reconsidering the assumption that

knowledge about rangelands must originate from experiments performed in places such as the Santa Rita. In 1903,

few ranchers had more than 30 years’ experience managing

their lands, and it made sense to aspire to teach them what

could be learned by careful scientific investigation. Today,

there is a significant, albeit shrinking, number of ranchers

whose families carry 100 or more years’ experience in

one place. Their history, and their knowledge, ought now

be understood as a storehouse of genuine and valuable

knowledge for the second century of range science in the

Southwest.
USDA Forest Service Proceedings RMRS-P-30. 2003 15

Recognizing History in Range Ecology: 100 Years of Science and Management... Sayre

References ____________________

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Chapline, William R.; Campbell, Robert S.; Price, Raymond; Stewart,

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16 USDA Forest Service Proceedings RMRS-P-30. 2003

Mitchel P. McClaran

A Century of Vegetation Change on the

Santa Rita Experimental Range

Mitchel P. McClaran is Professor of Range Management, School of Renewable Natural Resources, 325 Biological Sciences East, University of Arizona, Tucson,

AZ 85721; telephone (520) 621-1673; e-mail: mcclaran@u.arizona.edu

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

A century of detailed observation, repeat photography, and systematic remeasurement provide an unparalleled opportunity

to reckon the past, evaluate the present, and predict the future vegetation changes on the Santa Rita Experimental Range.

The long and rich history of experiments and manipulations provide valuable information for interpreting these changes. This

legacy reveals that future vegetation changes will likely be contingent on the elevation and soils, future precipitation patterns,

and the current condition of the vegetation.

In general, the century of vegetation change on the Santa Rita included (1) an increase in mesquite trees; (2) several cycles

of burroweed and cholla cactus that persisted for several decades; (3) an initial increase in native perennial grasses following

livestock removal in 1903 and subsequent seasonal and annual fluctuations; and (4) increased dominance of the nonnative

Lehmann lovegrass since 1975 and the coincident decline of native grasses. However, these dynamics have not been uniformly

expressed in space or time. In some cases these inconsistencies are clearly associated with unique geomorphic features such

as washes and soil differences or distinct precipitation patterns, but other inconsistencies are not as easily explained.

Abstract: We know more about vegetation change on the Santa Rita Experimental Range since

1903 than is known about any other 20,000-ha area in the world. This record is only possible

because important techniques of measuring vegetation changes were developed on the Santa Rita,

such as repeat photography and the line intercept transect method, and because they were applied

often and broadly. A 100-year record of experiments and systematic observations nourishes the

interpretation of these changes. Together, they describe a steady increase of mesquite trees, four

cycles of burroweed eruption and decline, one cholla cactus cycle, interannual and interdecadal

variation in native grass composition, and the recent dominance of the nonnative Lehmann

lovegrass. The most conspicuous change is the increase of mesquite, which began before 1903

when the spread of seed by livestock and cessation of fire led to the establishment of mesquite in

the open grasslands. The growth of these plants and subsequent recruits transformed the

grasslands into a mesquite-grass savanna, and neither the elimination of livestock grazing nor the

occasional fire has reversed this change. Burroweed cycles appear to be more closely related to

winter precipitation patterns and maximum plant longevity than land management activities.

Similarly, the increase of Lehmann lovegrass is largely independent of livestock grazing management.

Keywords: mesquite, burroweed, cacti, perennial grasses, Lehmann lovegrass, cover, density,

repeat photography

Acknowledgments: Steve Archer, James Bartolome, Susan Jorstad, and Chad McMurtry

provided excellent comments on an earlier version of this paper. Dawn Browning assisted with

figure 1. This effort is dedicated to all the scientists who contributed to the 100-year legacy of

knowledge generated on the Santa Rita, and especially Dwight Cable and S. Clark Martin for their

extensive and systematic measurements of vegetation. The Santa Rita Experimental Range

digital database at http://ag.arizona.edu/SRER provided some of the data sets used in this paper.

The U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, and the

University of Arizona provided funding for the digitization of these data.
USDA Forest Service Proceedings RMRS-P-30. 2003 17

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

This paper describes the patterns of vegetation change on

the Santa Rita since 1903 and reviews the research attempting to interpret the mechanisms contributing to these patterns. The information is confined to work performed on the

Santa Rita in order to celebrate the richness of that legacy.

The physical setting and administrative history are described first, followed by a review of the methods used to

measure vegetation that were developed on the Santa Rita.

The patterns and interpretations of changes in mesquite,

burroweed, cactus, and perennial grasses are then reviewed.

The concluding section begins by stressing that we are

obliged to continue remeasuring and rephotographing these

areas in order to continue this legacy. A brief description of

interpretative research opportunities follows. Finally, suggestions are made for applying these data to evaluate theoretical issues of vegetation change and for developing practical management tools that are based on a large empirical

body of work.

The Santa Rita __________________

Located about 80 km south of Tucson, AZ, the 21,000-ha

Santa Rita Experimental Range stretches across the western alluvial skirt of the Santa Rita Mountains. Elevation

increases from about 900 to 1,400 m, and average annual

precipitation increases along this gradient from 275 to 450

mm (fig. 1). Between 1,100- and 1,200-m elevation, the mean

(1922 to 2003) summer and winter precipitation have been

213 and 158 mm since 1922 (fig. 2). There is striking

evidence of significant interannual (CV winter = 44.7 percent and CV summer = 31.4 percent) and interdecadal

variation in precipitation at these elevations, and similar

patterns occur at other elevations. Noteworthy features of

the precipitation record are distinct summer and winter

patterns; very wet summers in 1931 and 1984; a prolonged

dry period from 1932 to the late 1950s; wet conditions in the

mid 1980s; and since 1988 to 1989, high interannual variability (CV winter = 51.0 percent and CV summer = 37.6

percent).

The current vegetation is a mixture of short trees, shrubs,

cacti and other succulents, perennial grasses, and other

herbaceous species (table 1). The physiognomy ranges from

a desert scrub at the lowest elevations to savanna woodlands

at the highest. The most extensive vegetation is a mesquitegrass savanna, but Desert Grassland has become a popular

moniker (McClaran 1995).

Established in 1903, the Santa Rita is the oldest continuously operating rangeland research facility in the United

States (McClaran and others 2002). Until 1988, it was

operated by the U.S. Department of Agriculture, first by the

Bureau of Plant Industry (1903 to 1915) and later by the

Forest Service (1915 to 1988). It was then transferred to the

to the Arizona State Land Department (Medina 1996). The

38thArizona Legislature (1987) dedicated the area for rangeland research and education, and assigned administration

to the University of Arizona, College of Agriculture and Life

Sciences (Arizona Senate Bill 1249).

Beginning around 1880, overgrazing of vegetation and

livestock dieoff were widespread because severe droughts

were common and open access to rangeland prevented control of livestock numbers (Bahre and Shelton 1996; Griffiths

1904). Fires were probably frequent prior to the intensification of livestock grazing (Humphrey 1958), and based on the

survival rates of different sized plants, the average time

between fires appears to have been 5 to 10 years. Since 1903,

fire has been very rare. However, three arson-caused fires in

June 1994 covered about 10,000 ha.

Between 1903 and 1915, livestock were excluded from all

areas below about 1,200-m elevation to allow the vegetation

to recover from overgrazing and to ascertain its productive

potential. Since reinstatement of grazing in 1915, hundreds

of experiments and manipulations have been performed to

evaluate livestock grazing practices, rodent influences, methods of vegetation control, and seeding of plants (Medina

1996). A portion of this original data is available in digital

form (McClaran and others 2002), but most of it resides in

the paper archive at the College of Agriculture and Life

Sciences, University of Arizona.

A Legacy of Documenting

Vegetation Dynamics ____________

Our well-founded understanding of vegetation change

during this century is only possible because of the long

record of observations, photographs, and systematic

remeasurement. No other research facility has a longer and

more detailed record of vegetation change. The duration and

detail of vegetation change documentation at the Santa Rita

is unrivaled thanks to the foresight, innovation, and initiative of early scientists. Records of their measurements and

observations have been published or otherwise preserved,

and there are many cases where succeeding scientists have

continued these measurements. Although initial vegetation Figure 1—Elevation and annual precipitation

gradients on the Santa Rita Experimental Range.

325 mm

400 mm

012 4 Kilometers

450 mm

425 mm

425 mm

400 mm

375 mm

350 mm

325 mm

300 mm

275 mm

275 mm

300 mm

1300 m

1200 m

1100 m

1000 m

900 m
18 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

Figure 2—Seasonal and standardized difference for precipitation on the Santa Rita Experimental

Range, 1901–1902 to 2002–2003. Values are from 1902–1903 to 1913–1914 for McLeary Ranch,

1,200-m elevation (Thornber 1910; Wooten 1916); values since 1922 are the average of four rain

gauges, Box, Eriopoda, Road, and Rodent between 1,100- and 1,200-m elevation (McClaran and

others 2002). Summer months are June through September. Standardized difference is the yearly

value minus the long-term average, which is divided by the standard deviation. Mean and standard

deviation for McCleary Ranch were calculated separately from other rain gauges.

0

100

200

300

400

500

600

700

800

1900-011905-061910-111915-161920-211925-261930-311935-361940-411945-461950-511955-561960-611965-661970-711975-761980-811985-861990-911995-962000-01

Year (June-May)

Precipitation (mm)

Winter

Summer

-3

-2

-1

0

1

2

3

4

5

6

1900-011905-061910-111915-161920-211925-261930-311935-361940-411945-461950-511955-561960-611965-661970-711975-761980-811985-861990-911995-962000-01

Year (June-May)

Standardized difference

Winter

Summer
USDA Forest Service Proceedings RMRS-P-30. 2003 19

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

Griffiths’s (1904, 1910) photographs in 1902 and 1903

provided the basis for the first use of repeat photography to

document vegetation change in arid grasslands when Wooten

(1916) used repeat photography to assess changes in

burroweed abundance between 1903 and 1913. These efforts

fostered the continuation of repeat photography on the

Santa Rita that includes the first use to document changes

in mesquite abundance (Parker and Martin 1952) and growth

rates of chainfruit cholla (Tschirley and Wagley 1964). The

repeat photography collection (McClaran and others 2002)

is one of the largest and most accessible in the world.

Systematic and repeated mapping of individual grass

plant basal area was performed on hundreds of permanent

1-m2 quadrats on the Santa Rita from the late 1910s into the

1930s (Canfield 1957; Hill 1920). Although scientists at the

Santa Rita developed modifications to improve the efficiency

and accuracy of mapping (for example, the pantograph [Hill

1920] and the densimeter [Culley 1938]), the method was

abandoned because it was too time consuming, and it did not

measure the trees, shrubs, and cacti. The measurement of

those nongrass species gained urgency when their abundance began to increase in the 1930s.

The line intercept transect method used to measure plant

cover was developed by Canfield (1942) while working on the

Santa Rita. It replaced the quadrat mapping method because it was more efficient and measured both grass and

nongrass plant cover. This continues to be one of the most

widely used methods of estimating plant cover in the world.

Martin and Cable (1974) and Cable and Martin (1975)

measured cover from 1957 to 1966 on about 200 permanent

transects. By adding a width dimension to the line transect,

Martin and Severson (1988) combined the measures of plant

cover and density at 150 permanent located transects every

3 years from 1972 to 1984. My colleagues and I have completed the remeasurement of about 130 of those transects

every 3 years between 1991 and 2003 (McClaran and others

2002). About half of those transects have a measurement

history that started in 1957. This 46-year record of repeated

measurement provides a unique opportunity to document

long-term changes of individual species and vegetation.

Double-sampling methods of estimating herbaceous production were conducted adjacent to the permanent line

intercept transects beginning in the 1950s (Cable and Martin 1975; Martin and Cable 1974). Unfortunately, the comprehensive measurement of herbaceous production was last

performed on the Santa Rita in 1984 (Martin and Severson

1988).

Changes in Mesquite

Abundance_____________________

Mesquite is a long-lived (greater than 200 years), leguminous tree that can grow greater than 5 m tall. The roots are

both shallow and deep (0.25 to greater than 3.0 m), and some

shallow roots may extend far (15 m) from the trunk (Cable

1977). Growth begins in April after a winter deciduous period

(Cable 1977). Seeds can remain viable for 20 years in the soil

(Martin 1970), and plants as small as 1-cm basal diameter will

generally resprout from basal meristems after aboveground

mass is removed (Glendening and Paulsen 1955).

Table 1—Common and scientific names for common shrubs and trees,

cacti and succulents, and grass species on the Santa Rita

Experimental Range.

 Common name Scientific name

Shrubs and trees

Blue palo verde Cercidium floridum Benth.

Burroweed Isocoma tenuisecta Greene

Catclaw acacia Acacia greggii Gray

Creosote bush Larrea tridentata (Sesse & Moc.) Cov.

Desert hackberry Celtis pallida Torr.

Velvet mesquite Prosopis velutina (Woot.)

Cacti and succulents

Cane cholla Opuntia spinisior (Engelm.) Toumey

Chainfruit cholla Opuntia fulgida Engelm.

Fishhook barrel Ferocactus wislizenii (Engelm.) Britt. &

 Rose

Prickly pear Opuntia engelmanni Salm-Dyck

Saguaro Carnegiea gigantea (Engelm.) Britt. &

 Rose

Soaptree yucca Yucca elata Engelm.

Grasses

Black grama Bouteloua eriopoda (Torr.) Torr.

Bush muhly Muhlenbergia porteri Scribn.

Cottontop Digitaria californica (Benth.) Henrard

Curly mesquite Hilaria belangeri (Steud.) Nash

Fluff grass Erioneuron pulchellum (Kunth) Tateoka

Hairy grama Bouteloua hirsuta Lag.

Lehmann lovegrass Eragrostis lehmanniana (Nees)

Needle grama Bouteloua barbata Lag.

Pappus grass Pappophorum macronulatum Nes

Rothrock grama Bouteloua rothrockii (Vasey)

Santa Rita threeawn Aristida glabrata (Vasey) Hitchc.

Sideoats grama Bouteloua curtipendula (Michx.) Torr.

Six weeks grama Bouteloua aristidoides (Kunth) Griseb.

Slender grama Bouteloua filiformis (E. Fourn.) Griffiths

Spidergrass Aristida ternipes Cav.

Sprucetop grama Bouteloua chrondrosoides (Kunth) Benth.

Tall threeawn Aristida hamulosa Henr.

Tanglehead Heteropogon contortus (L.) P. Beauv.

descriptions were largely based on qualitative observations,

some important systematic and quantitative measures were

developed and repeatedly applied on the Santa Rita beginning in 1902.

The qualitative descriptions of the Santa Rita and nearby

areas by Griffiths (1904, 1910), Thornber (1910), and Wooten

(1916) are among the first systematic, professional accounts

of vegetation composition and conditions in the North American arid Southwest. They provide the baseline from which to

judge all subsequent vegetation changes. For example, based

on Griffiths’ initial descriptions (1904), Wooten (1916) was

able to make the first estimates of rates of recovery for arid

grasslands following exclusion of livestock grazing.

Between 1903 and 1908, Griffiths (1904, 1910) performed

the first systematic and repeated measures of herbaceous

biomass production in arid grasslands by clipping, drying

and weighing plants in twenty-eight 0.9 by 2.1 m (3 by 7 ft)

plots in the same locations. Wooten (1916) repeated those

measurements between 1912 and 1914.
20 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

Pattern

Based on observations and photographs between 1902

and 1915, mesquite trees and other woody plants such as

catclaw acacia, blue palo verde, and creosote bush were most

common below 1,000 m and confined to the larger washes

and arroyos above that elevation (figs. 3 and 4; Griffiths

1904, 1910; Thornber 1910; Wooten 1916). However, as

early as 1902, small mesquite plants (less than 1 m tall) were

scattered in the grassland areas between the washes above

1,000 m, and their increase by 1915 was noted by these

observers.

Since 1930, the increase of mesquite density and cover was

greatest between 1,000 and 1,150 m, the same elevations

where the incipient trees mentioned earlier had been noted.

Between 1934 and 1954, there was a 33-percent increase in

1948

1905 1941

1990 2003

 1962

Figure 3—Repeat photography (1905 to 2003) looking east from Photo Station 231, on deep, sandy loam

soil, at 1,080-m elevation (McClaran and others 2002). April 1905 shows Santa Rita boundary and

ungrazed condition of vegetation, and the dark patches are probably poppy flowers in bloom. From

September 1941 to June 1948 and March 1962 shows duration of cholla eruption, and seasonal variation

in grass biomass. March 1990 to March 2003 shows increased size of blue palo verde, mesquite, and

prickly pear cactus. The nonnative Lehmann lovegrass is not present.
USDA Forest Service Proceedings RMRS-P-30. 2003 21

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

elevation (900 to 1,250 m), density fluctuated between 200

and 450 trees per ha (fig. 5).

Mesquite canopy cover also increased after 1930, but it

has not reached the maximum of 30 percent that Glendening

(1952) predicted from stand-level expansion rates between

1932 and 1949. In the early 1940s, Canfield (1948) roughly

estimated mesquite cover to be 4 to 8 percent throughout the

Santa Rita using simple visual observations. At elevations

Figure 4—Repeat photography (1902 to 2003) looking east from Photo Station 222 into Box Canyon arroyo,

at 1,150-m elevation (McClaran and others 2002). In 1902 mesquite are abundant in the arroyo, and a few

trees are scattered on the flat grasslands above the drainage. Since 1902, there are slightly more trees in

the arroyo but many new trees in the grasslands, and they appear as a dark, horizontal line above drainage.

Figure 5—Change in mesquite cover and density on 74 permanent

transects between 950- and 1,250-m elevation (McClaran and

others 2002). No mesquite or burroweed removal treatments were

applied to these transects. Dashed lines indicate periods of greater

than 5 years between remeasurements.

the areal extent of the Santa Rita where mesquite density

exceeded 198 plants per ha, and the occurrence of those

densities spread from lower elevations to above 1,050 m

(Humphrey and Mehrhoff 1958; Mehrhoff 1955). Since 1972,

this density class has become the norm. Between 1972 and

1984, the average density remained about 300 plants per ha

at 900 to 1,350 m elevations (Martin and Severson 1988).

Over a longer time period (1972 to 2000) and slightly lower

Mesquite

0

5

10

15

20

25

1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Cover (percent)

0

100

200

300

400

500

600

Density (#/ha)

density

cover

1902 1951

2003
22 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

between 900 and 1,250 m, mesquite cover has increased

according to systematic remeasurements of permanent line

intercept transects: from 1957 to 1966, Martin and Cable

(1974) estimated cover at 9.5 percent, and from 1960 to 2000,

cover increased from 7 percent to a peak of 20 percent in

1991, but declined to 15 percent by 2000 (fig. 5).

Repeat photography illustrates this increase of mesquite

in the grasslands (figs. 3 and 6), where increases in density

have generally slowed since the 1970s, but tree cover has

generally increased with the growth of individual trees. The

exceptions are the washes and arroyos (for example, fig. 4)

where trees were already abundant in 1902, and in areas

with rocky, clay-rich soils where mesquite remains largely

absent (fig. 7).

Interpretations

Numerous scientists performed experiments and controlled

observations to interpret how livestock grazing, rodents, fire, and

perennial grasses may have influenced mesquite dynamics.

From the early 1930s to late 1940s, the exclusion of

rodents and/or cattle did not stop the increase of mesquite at

elevations between 1,050 and 1,100 m. Mesquite increased

from about 140 to 380 plants per ha between 1932 and 1949

(Glendening 1952) and from about 280 to 380 plants per ha

(Brown 1950) across all exclusion treatments. A similar

pattern emerged when yearlong and seasonally grazed pastures were compared from 1972 to 1984: the average 300

plants per ha did not differ between treatments (Martin and

Severson 1988).

The likely role of cattle and rodents in dispersing mesquite

seed, and the optimum burial depth by rodents for germination were revealed in the mid-1950s. Some seeds remain

viable after cattle digestion, but estimates of viability vary

from 58 to 73 percent (Glendening and Paulsen 1955) to only

3 percent (Cox and others 1993). Reynolds (1954) reported

that kangaroo rats buried mesquite seed 1 to 3 cm, a depth

optimal for germination, but they later consumed 98 percent

of these seeds. He also estimated that they dispersed seeds

a maximum of 32 m. Based on this, he suggested that if

kangaroo rats were the sole vector of dispersal, mesquite

would spread 1.6 km in 500 years, assuming a 20-year period

before the newly established mesquite would produce seed.

By 1950, it was apparent that even small (1-cm basal

diameter) mesquite were able to sprout from basal meristems after the aboveground portions of the plant were

killed by a fire. Glendening and Paulsen (1955) and Cable

(1965) reported only 11 to 60 percent mortality for 1 cm basal

diameter plants, and that rate decreased to about 5 percent

for plants greater than 15 cm diameter. Survival was much

less likely for younger and smaller (less than 1 cm basal

diameter): only one-third of 1-year mesquite survived to

resprout after a fire (Cable 1961). Womack (2000) confirmed

results that plants greater than 15 cm basal diameter have

less than 5-percent mortality, and he noted that mortality

declined as size and number of basal stems (trunks) increased. Not surprisingly, by 1965 there were no differences

in the density of mesquite on unburned areas, areas burned

once (1952), and areas burned twice (1952 and 1955) (Cable

1967). Similarly, 3 years after a 1975 fire, mesquite cover did

not differ between burned and unburned areas (Martin

1983).

Glendening and Paulsen (1955) reported that mesquite

seed germination and establishment were 16 times greater

in the absence of grass than when seeds were sown within

dense stands of cottontop, black grama, and bush muhly.

However, they acknowledged that while grass may interfere

with mesquite establishment, bare patches between grass

plants were ubiquitous even in areas ungrazed by cattle.

Focusing on the seed and seedling stages of mesquite life

history is helpful in understanding how the increase of

mesquite has not been influenced by the manipulations of

livestock, rodents, and fire. The establishment of mesquite

plants in the grasslands started with the livestock dispersing undigested seeds that were produced by plants growing

in the arroyos. Some of the seed in the cattle dung may have

germinated and established. Kangaroo rats may have collected other seeds from the dung and buried them at optimum depths for germination. This series of events would

account for the abundance of scattered small mesquite in the

grasslands by 1902. The cattle vector provided the long

distance dispersal that was not possible by kangaroo rats

alone. By 1930, when small mesquite and caches of mesquite

seed were present, the removal of rodents and/or livestock

did not limit their continued recruitment or growth.

The general absence of fires between the 1880s and 1903

followed after heavy livestock grazing had reduced the mass

and continuity of the grass fuel source. Consequently, the

scattered, recently established seedlings in the open grasslands did not experience fires when they were most susceptible to damage (less than 5 years and less than 1 cm

diameter). Griffiths (1910) and Wooten (1916) applied this

scenario to interpret the increase of small mesquites in the

grassy plains of the Santa Rita observed between 1903 and

1915. Although they were unfamiliar with the details of seed

germination and dispersal, and seedling response to fire,

they recognized that these early life history stages were key

to the understanding the incipient transformation of treeless grasslands into mesquite savannas.

Changes in Burroweed

Abundance_____________________

Burroweed is a short-lived (less than 40 years) shrub that

can grow up to 1.3 m tall (Humphrey 1937). Roots are

common at depths greater than 1 m deep but are relatively

scarce at shallower (5- to 30-cm) depths (Cable 1969). The

greatest period of growth occurs in spring, but some expansion of the canopy occurs in summer (Cable 1969). Seeds

germinate in winter and spring (Humphrey 1937). They are

toxic and not commonly eaten by livestock (Tschirley and

Martin 1961).

Pattern

Four cycles of burroweed increase and decline have been

reported since 1903. Their duration was about 15 to 20 years,

but they have not been perfectly synchronous across the

Santa Rita. Changes in abundance were a function of changes

in both density (recruitment and death of plants) and cover

(growth and shrinkage of plants).

The first reported cycle ended in 1914 (Wooten 1916). The

beginning is harder to determine, but Griffiths (1904, 1910)
USDA Forest Service Proceedings RMRS-P-30. 2003 23

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

Figure 6—Repeat photography (1922 to 2003) looking west from Photo Station 111 at 1,100-m elevation

(McClaran and others 2002). Area beyond fence has been excluded from livestock since 1916. December

1922 shows sparse tree presence and no shrubs in foreground. From September 1935 to October 1947 and

August 1958 shows eruptions of burroweed and cholla, a general decline of grass, and establishment of new

mesquite on both sides of the exclosure fence. From March 1969 to July 1970 shows rapid death of

burroweed. March 1990 to April 2003 shows dominance of nonnative Lehmann lovegrass, and decline of

burroweed.

1935

1958

1970

2003

1947

1969

1990

1922
24 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

first noted increases at low elevations in the northwestern

portion of the Santa Rita that spread upslope to 1,100-m

elevation by 1910.

The second cycle occurred in the 1930s. In 1935, Humphrey

(1937) observed that large plants were conspicuous everywhere below 1,350-m elevation, and in the early 1940s,

Canfield (1948) estimated cover between 4 and 9 percent

below 1,250 m. The timing and extent of the subsequent

decline is not clear. The extent of the highest density class

(greater than 36 plants per m2

) increased only slightly from

about 50 to 55 percent of the Santa Rita between 1934 and

1954 (Humphrey and Mehrhoff 1958; Mehrhoff 1955), but

significant declines in burroweed by the 1950s are documented in several repeat photography comparisons (for

example, fig. 6).

A third cycle peaked in the late 1960s, followed by a decline

beginning in 1970 (figs. 6 and 8) over large areas of the Santa

Rita. Cover on 120 permanent line intercept transects increased from 2.4 percent in 1957 to 13.5 percent in 1966,

then declined to 2.5 percent in 1970 (Martin and Cable

1974). The magnitude of the increase was less on a subset of

Figure 7—Repeat photography (1936 to 2003) looking east from Photo Station 45 across Madera Canyon

alluvial fan at 1,100-m elevation (McClaran and others 2002). In June 1936, there is very sparse grass cover,

scattered ocotillo, and three mesquite trees. From 1936 to October 1984, nonnative Lehmann lovegrass arrives

and abundance reflects the wet summer in 1984. From 1984 to April 2003 there is a reduction of lovegrass, a

continued ocotillo presence, a new catclaw acacia (bottom left), and the persistence of the three mesquite that

were present in 1936.

these transects without mesquite control, but the timing

was identical (fig. 8).

The most recent cycle occurred between the late 1970s and

1990s on large areas of the Santa Rita (figs. 6 and 8). Density

increased from 0.6 plants per m2 in 1972 to 2.7 plants per m2

in 1975, then declined to 1.1 plants per m2 in 1984 (Martin

and Severson 1988). In general, the density above 1,000-m

elevation was about double that below, but the timing of the

cycle was synchronous. Comparing density and cover values

from 1972 to 2000 (fig. 8) reveals the character of these

cycles. Increases in density precedes increases in cover by

about 8 to 10 years. Maximum cover mostly occurs when selfthinning reduces density and surviving plants grow larger.

Near the end of the cycle, there are declines in both density

and cover.

There are some locations where these cycles never materialized, and other locations where some cycles were not

expressed. The cycles have not occurred in areas with rocky,

clay-rich soils (fig. 7), and there is no evidence that the latest

cycle occurred on deep, sandy soils (fig. 3).

1936 1984

2003
USDA Forest Service Proceedings RMRS-P-30. 2003 25

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

Interpretations

The timing of the burroweed cycles appears to be independent of manipulations to livestock grazing, fire, and grass

neighbors. If burroweed responded to a manipulation, it was

expressed as a short-lived change in abundance that lasted

only until the current cycle ended or the next cycle began. An

anecdotal consensus has emerged that variation in winter

precipitation is driving these cycles because of this relative

indifference to livestock grazing, rodents, and fire treatments. This relationship remains anecdotal because the

mechanisms have not been documented, and only one correlation analysis has been performed. Similar to mesquite,

frequent fires may have limited the distribution of burroweed

to lower elevations where fuels did not accumulate.

Cable (1967) placed the emphasis on winter precipitation

when the immediate reduction of burroweed density following fires in 1952 and 1955 was undetectable 10 and 13 years

later (fig. 9). He found a strong correlation (r2 = 0.91)

between burroweed density and winter precipitation between 1952 and 1958 to support his interpretation. Later,

Martin (1983) applied this same interpretation (consecutive

wet winters in 1977–1978 and 1978–1979) to the short-lived

decline of burroweed following a fire in 1975.

The earliest assessments of livestock grazing effects on

burroweed occurred near the start of the 1930s cycle. Without the benefit of replications in his study from 1931 to 1948,

Brown (1950) concluded that exclusion of livestock may slow

a burroweed increase, but it would not prevent one. By the

time of the fourth cycle, the winter precipitation explanation

was used to account for the indifference to yearlong and

rotation of summer grazing from 1972 to 1984 (Martin and

Severson 1988).

Between 1961 and 1964, as the third burroweed cycle

began, Cable (1969) found that burroweed cover increased

slightly less when growing with cottontop grass neighbors

(8- to 20-percent increase) than without cottontop neighbors

(8- to 27-percent increase). He applied the winter precipitation explanation to this pattern, specifically its relative

importance to the two species. Cottontop was largely unresponsive to winter precipitation and, therefore, did not affect

Figure 9—Changes in perennial grass cover and

burroweed density in relation to two, one, and no

prescribed fires (data from Cable 1967).

Perennial Grass

0.0

0.5

1.0

1.5

2.0

1952 1953 1954 1955 1956 1957 1958 1965

Year

Basal cover (percent)

No Burn

Burn 1952

Burn 1952 & 1955

Burroweed

0.0

0.5

1.0

1.5

2.0

1952 1953 1954 1955 1956 1957 1958 1965

Year

No Burn

Burn 1952

Burn 1952 & 1955

Density (#/m2) burroweed during the time of its greatest growth. By contrast, the slight depression in burroweed growth was a

function of competition for soil moisture in the summer,

when cottontop is most actively growing.

There are some additional compelling coincidences of wet

winters (fig. 2) and the timing of burroweed cycles. Three

consecutive wet winters from 1929–1930 to 1931–1932 coincide with the beginning of the 1930s cycle. The wet winter of

1957–1958 may have initiated seedling establishment for

the third cycle, and the very wet 1965–1966 and 1967–1968

winters may have contributed to an increase in plant size.

Figure 8—Change in burroweed cover and density on 74 permanent

transects between 950- and 1,250-m elevation (McClaran and others

2002). No mesquite or burroweed removal treatments were applied to

these transects. Dashed lines indicate periods of greater than 5 years

between remeasurements.

Burroweed

0

5

10

15

1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Cover (percent)

0.0

0.5

1.0

1.5

2.0

2.5

Density (#/m2)

density

cover
26 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

Finally, a similar lag between seedling establishment and

increases in plant size may have contributed to the most

recent cycle following consecutive wet winters in 1977–1978

and 1978–1979. The growth of plants established during

this time would likely have been fostered by the extraordinary string of 13 consecutive wet winters from 1982–1983 to

1994–1995.

Changes in Cactus Abundance ____

The primary cacti are prickly pear, chainfruit cholla, and

cane cholla, which are relatively short lived (less than 50

years). The chollas have cylindrical sections, and a growth

form that is taller (less than or equal to 2 m) than broad (less

than or equal to 1 m); whereas the prickly pear has flat,

circular sections with a growth form that is broader (less

than or equal to 2 m) than tall (less than or equal to 1 m).

Both can establish new plants from seed and from fallen

sections that can develop a root system when the aereoles

are in contact with the soil. However, vegetative reproduction is more common in the chollas than prickly pear.

Pattern

In 1903, cacti were most common below 1,000-m elevation

(Griffiths 1904). An eruption of cholla at higher elevations

occurred by the mid-1930s and lasted into the 1970s. Prickly

pear has been the dominant cactus since 1970.

Many repeat photography series record an eruption of

cholla by 1935 (for example, figs. 3 and 6). Between 1934 and

1954, the proportion of the Santa Rita supporting greater

than 840 plants per ha doubled from 19 to 38 percent

(Humphrey and Mehrhoff 1958; Mehrhoff 1955). The greatest increase occurred between 1,000- and 1,200-m elevation.

The eruption faded by 1960, when both cholla cover and

density declined (figs. 3, 6, and 10). A similar trend was

recorded between 1972 and 1984 at slightly higher elevations (Martin and Severson 1988). In contrast, prickly pear

cover and density have increased since 1970 (figs. 3 and 10),

and density of 800 plants per ha at elevations below 1,200 m

was greater than the 200 to 400 plants per ha at higher

elevations (Martin and Severson 1988).

These patterns have not materialized in all locations.

Neither cholla nor prickly pear abundance changed markedly

on rocky, clay-rich soils (fig. 7), nor did the prickly pear

increase materialize everywhere (for example, fig. 6).

Interpretations

Similar to burroweed, the eruption of cholla and recent

increases of prickly pear appear to be largely independent of

livestock grazing and fire manipulations. The stimuli for the

increases are not clear, but the rate and duration of the

increases may be a function of plant growth rate, longevity,

and the occurrence of a bacterium.

Combinations of cattle and rodent exclusions established

as the cholla eruption commenced failed to produce any

differences in cacti densities (Brown 1950; Glendening 1952).

Under all treatments, densities increased from tens to hundreds of plants per ha. Similarly, the subsequent decline of

cholla and increase of prickly pear between 1972 and 1984

were no different in areas with yearlong versus seasonal

rotation of grazing (Martin and Severson 1988). Fire produced only a short-lived decline of cactus density, but within

10 to 13 years after fire, the cactus density exceeded that

which existed prior to the fires (Cable 1965).

Tschirley and Wagle (1964) suggested that eruptions are

a function of rapid growth by young plants, and that declines

result from a combination of plants reaching their maximum

age and the increase of bacterial infection that prevents

fallen sections from establishing roots. They used repeat

photography to estimate the curvilinear vertical growth rate

of cholla: the rate is fastest in young plants, then slows

considerably at about 15 years, and then becomes negative

at about 45 years as plants disarticulate (for example, figs.

3 and 6). They suggested that recruitment of new plants

from fallen sections is limited when they are infected by

increasing levels of the bacteria Erwinea carnegiea that

cause the sections to desiccate before roots can be produced.

Changes in Perennial Grass

Abundance_____________________

The common perennial grass species use the C4 photosynthetic pathway. Their seed germinates, and plants grow

most vigorously in July and August after the summer rains

commence. Absolute productivity is a function of both current and previous summer precipitation (Cable 1975), and

there is considerable interannual and spatial variation in

productivity because rainfall amounts differ greatly between

years and with elevation (figs. 1, 2, 11, and 12). Productivity

is about 1.6 times greater on clay-rich versus loamy soils

(Subirge 1983). Plants are relatively short lived, with averages around 5 to 10 years (Cable 1979; Canfield 1957). Roots

are most dense in the upper 15 cm of the soil, but some extend

greater than 60 cm deep (Blydenstein 1966; Cable 1969).

Several species, including cottontop and bush muhly, are

Figure 10—Cover and density changes for cholla

and prickly pear cactus on 74 permanent

transects between 950- and 1,250-m elevation

(McClaran and others 2002). No mesquite or

burroweed removal treatments were applied to

these transects. Dashed lines indicate periods of

greater than 5 years between remeasurements.

Cactus Cover

0.0

1.0

2.0

3.0

1960 1965 1970 1975 1980 1985 1990 1995 2000

Cover (percent)

Cholla

Prickly pear

Cactus Density

0

600

1200

1800

1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Density (#/ha)

Cholla

Prickly pear
USDA Forest Service Proceedings RMRS-P-30. 2003 27

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

more common under mesquite trees, but others, including

threeawns and Rothrock grama, are more common in open

areas (Livingston and others 1997; Van Deren 1993; Yavitt

and Smith 1983).

Pattern

In 1903, perennial grasses were largely absent below

1,350-m elevation except along arroyos where tanglehead,

sideoats grama, and hairy grama were found (Griffiths

1904). The annual grass, six weeks grama, was dominant at

lower elevations. Above 1,100 m, Rothrock grama, black

grama, and bush muhly were only occasionally present, the

latter primarily under shrubs. By 1909, perennial grass

abundance had increased above 1,075 m: Rothrock, black,

and slender gramas between 1,075 and 1,250 m, and

threeawns, sprucetop, black, and sideoats gramas above

1,250 m (Griffiths 1910; Thornber 1910).

Six years later, in 1915, perennial grasses were more

common between 1,000 and 1,250 m, and under shrubs at

the lower elevations when Wooten (1916) estimated the

extent of different types of grass species. The annual, six

weeks grama, continued as the most common grass on about

12 percent of the Santa Rita, all below 1,000 m. Bush muhly

was most common on an equivalent area at those low

elevations, but was largely confined beneath shrubs. Rothrock

grama was the dominant grass on about 50 percent of the

area, mainly between 1,000 and 1,250 m, and the common

associates were threeawns, tanglehead, and slender grama.

Threeawns were the dominants above 1,250-m elevation,

which accounted for 17 percent of the Santa Rita.

Griffiths, and later Wooten, estimated productivity by

clipping twenty-eight 0.9- by 2.1-m (3- by 7-ft) plots in the

same general locations throughout the Santa Rita between

1903 and 1908, and 1912 and 1914. The average for all

elevations was 845 kg per ha from 1903 to 1908 (Griffiths

1910). Wooten (1916) reported productivity by elevation

between 1912 and 1914: 775 kg per ha below 1,000 m, 830 kg

per ha between 1,000 and 1,250 m, and 965 kg per ha above

1,250 m.

Between 1915 and the early 1980s, similar patterns of

perennial species abundance were reported in relation to

elevation, and more systematic measures of plant cover,

density, and productivity provided greater insights to

interannual dynamics. From the 1960s to early 1980s, dominant species by elevation were similar to those reported in

earlier accounts, but cottontop was more common at all

elevations (Cable 1979; Martin 1966; Martin and Severson

1988). The ephemeral nature and slight stature of Rothrock

grama is illustrated by its inconsistent membership in the

top 5 ranking for density and consistently low ranking for

cover (tables 2 and 3). Interannual variability of productivity was greater at lower elevations between 1954 and 1964

(compare figs. 11 and 12; Martin 1966). Interestingly, these

estimates are about one-third to one-half the amounts reported by Griffiths (1910) and Wooten (1916). Their objective

of estimating the potential productivity may have biased the

location of sample areas toward the more productive sites. A

decrease in grass production by 1950 is apparent at some

repeat photography locations (fig. 4), but not at others (fig. 3).

The nonnative Lehmann lovegrass became the most abundant perennial grass by 1981 and 1984, based on density and

basal cover, respectively (tables 2 and 3). By 1991, it was

more common than all native grasses combined for both

measures of abundance (fig. 13). Above about 1,100-m elevation, perennial grass productivity has more than doubled

since the lovegrass gained dominance (fig. 13; Anable and

others 1992; Cox and others 1990), and exceeded estimates

made between 1903 and 1914 (Griffiths 1910; Wooten 1916).

This was a very rapid ascent to dominance from a relatively

limited area of introduction. Between about 1945 and 1975,

seed was sown on about 50 areas, totaling 200 ha (less than

1 percent of the Santa Rita), but the areas were widely

dispersed making the maximum distance between them less

than or equal to 7 km (Anable and others 1992). This

lovegrass invasion is obvious at most repeat photography

Figure 11—Interannual changes in grass production between 900- and 1,000-m elevation

(data from Martin 1966).

Figure 12—Interannual changes in grass production and density of nonnative Lehmann

lovegrass at 1,100-m elevation (data from Cable

and Martin 1975, and Martin and Severson 1988).

0

50

100

150

200

250

1954 1956 1958 1960 1962 1964

Year

Grass Production (kg/ha)

Annual

Perennial

0

250

500

750

1000

1250

1500

1954195819621966197419781982

Year

Perennial Grass (kg/ha)

0

5

10

15

20

25

30

Lovegrass Density (#/m

2)

Grass biomass

Lovegrass density
28 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

Table 2—Changes in the five most common perennial grass species based on density on the Santa Rita Experimental Range, 1934 to 2000. Source

for 1934 and 1954 is Mehrhoff (1955). Source for other dates is from 74 permanent transects, between 950- and 1,250-m elevation, where

no mesquite or burroweed removal treatments were applied (McClaran and others 2002).

Year

Species rank 1934 1954 1972 1981 1991 2000

1 Rothrock grama Fluff grass Threeawns Lehmann Lehmann Lehmann

 lovegrass lovegrass lovegrass

2 Threeawns Black grama Rothrock grama Threeawns Rothrock grama Rothrock grama

3 Fluff grass Threeawns Cottontop Rothrock grama Cottontop Threeawns

4 Slender grama Slender grama Black grama Cottontop Fluff grass Bush muhly

5 Black grama Cottontop Sprucetop grama Bush muhly Threeawns Cottontop

Table 3—Changes in the five most common perennial grass species based on basal cover on the Santa Rita Experimental

Range, 1960 to 2000. Source is from 74 permanent transects, between 950- and 1,250-m elevation, where no

mesquite or burroweed removal treatments were applied (McClaran and others 2002).

Year

Species rank 1960 1970 1984 1991 2000

1 Threeawns Threeawns Lehmann Lehmann Lehmann

 lovegrass lovegrass lovegrass

2 Cottontop Sprucetop grama Threeawns Cottontop Bush muhly

3 Black grama Cottontop Cottontop Bush muhly Threeawns

4 Bush muhly Rothrock grama Rothrock grama Threeawns Rothrock grama

5 Sideoats grama Sideoats grama Black grama Rothrock grama Cottontop

Figure 13—Cover and density changes for nonnative Lehmann lovegrass and native

perennial grasses on 74 permanent transects between 950- and 1,250-m elevation

(McClaran and others 2002). No mesquite or burroweed removal treatments were applied

to these transects. Dashed lines indicate periods of greater than 5 years between

remeasurements.

Perennial Grass Cover

0.0

1.0

2.0

3.0

1960 1965 1970 1975 1980 1985 1990 1995 2000

Cover (percent)

Native

Lovegrass

Perennial Grass Density

0

5

10

15

20

1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Density (#/m

2)

Native

Lovegrass
USDA Forest Service Proceedings RMRS-P-30. 2003 29

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

locations (for example, figs. 6 and 7), except at the lowest

elevations and on deep, sandy soils (fig. 3).

Between 1984 and 1991, cover increased for both the

lovegrass and native grasses, but both have declined from

that maximum. In contrast, native grass density declined

since 1972, whereas lovegrass density steadily increased

until 1991 and then began to decline (fig. 13). These patterns

suggest that the recruitment of native grasses has declined

and the size of surviving plants has increased since the

lovegrass gained dominance.

Interpretations

Livestock grazing, fire, neighboring mesquite and burroweed plants, and the increase of the nonnative Lehmann

lovegrass have been the focus of efforts to interpret perennial grass dynamics. The results from a number of studies

illustrate the important and often overriding influence of

precipitation on these patterns. However, grass dynamics

appear to be more sensitive to varying intensities of livestock grazing and neighboring plants than the dynamics

expressed by mesquite, burroweed, and cactus.

Attention to livestock grazing has a longer and more

detailed history than any other influence. It grew directly

from the objectives of establishing the Santa Rita, which

were to determine the potential of forage production for

livestock and to develop a sustainable approach to livestock grazing. Initial efforts focused on rates of grass

recovery following grazing removal, while subsequent studies

addressed responses to different grazing intensities and the

seasonal rotation of pastures to prevent grazing in two of

three summer growing seasons.

Livestock Exclusion—The exclusion of livestock from

1903 to 1915 on all areas below 1,250-m elevation allowed

Wooten (1916) to speculate on the rate of recovery to full

productive potential from the degraded conditions caused by

nearly two decades of overgrazing. He estimated a 3-year

recovery rate for areas dominated by Rothrock grama between 1,000 to 1,250 m, and a 7- to 8-year recovery for bush

muhly in areas below 1,000 m. However, subsequent comparisons with livestock exclusion are more equivocal. Total

grass cover declined from about 2.0 to 0.1 percent on grazed

areas as well as all combinations of rodent and/or cattle

exclusion from 1932 to 1949 (Glendening 1952). Compared

to adjacent grazed areas, native grass density was less and

nonnative lovegrass was no different in areas that were

ungrazed from 1918 to 1990 (McClaran and Anable 1992).

These contrasting results suggest that the perennial grass

response to the exclusion of livestock is contingent on the

condition of grass at the time of exclusion, precipitation

patterns before the comparisons, and the grazing intensity

outside the exclosure. Wooten may have proposed very

optimistic recovery rates because the general absence of

perennials in 1903 provided a degraded baseline, and the

relatively verdant conditions during his observations in 1915

following six consecutive summers with above average precipitation (fig. 2). In contrast, the decline of grass cover

between 1932 and 1949, which was independent of livestock

exclusion, began with relatively large cover values that

followed the wet summer in 1931 and declined during the

subsequent, prolonged dry period (figs. 2 and 6). Finally,

grazing intensity outside exclosures is not uniform across the

Santa Rita, and has changed over time since grazing was reestablished in 1915. Therefore, unequivocal conclusions about

grass response to livestock exclusion are not possible unless

the grazing intensity outside the exclosure is documented.

Livestock Grazing Intensity—In general, grazing intensity on the Santa Rita has declined since 1915. Until

1941, the stocking rate was about 0.13 animals per ha per

year. Between 1941 and 1956, it was reduced to about 0.06,

which translated to a 47- to 60-percent utilization of grass

production. Since 1957, stocking rates have been reduced to

about 50-percent utilization (Cable and Martin 1975). A

utilization rate of 40 percent was suggested in the early

1940s to prevent damage to individual plants (Parker and

Glendening 1942; Reynolds and Martin 1968). However,

despite repeated attempts to reduce utilization, this goal of

40 percent was never achieved (Cable and Martin 1975;

Martin and Severson 1988). Across the Santa Rita, utilization varies inversely with distance from drinking water

sources (Angell and McClaran 2001; Martin and Cable

1974).

Canfield (1948) made the first estimate of grass response

to grazing intensity. He compared the relative cover of grass

species among areas heavily grazed for 20 years, conservatively grazed for 5 years, and ungrazed for 5 and 25 years. He

concluded that conservative grazing for 5 years would facilitate recovery from overgrazing to the same degree as grazing

exclusion, and that dominance by cottontop indicated proper

grazing intensity. Unfortunately, he provided neither descriptions of stocking rates in overgrazed and conservatively

grazed areas nor estimates of absolute cover of grasses.

However, his list of dominant grass species in these settings

is historically significant because it provided the first quantitative approach using relative cover to identify species that

indicated proper grazing and overgrazing. His work preceded

by 1 year, Dyksterhuis’ (1949) more widely used proposal for

this approach.

Martin and Cable (1974) clearly documented the influence

of grazing intensity on grass production by comparing sites

where utilization decreased with increasing distance from

drinking water sources. From 1954 to 1966, and between

900- and 1,250-m elevation, production of cottontop, black

grama, and threeawns at 0.4 to 1 km from water was 50

percent less than at 1.6 km from water sources. Utilization

decreased from around 48 to 43 percent at these increasing

distances from water.

Between 1,200 and 1,300 m, Cable and Martin (1975)

suggested that the recovery of grass production from drought

stress would be delayed when utilization levels exceeded 50

percent. Based on responses during dry conditions (1957,

1960, and 1962) and wetter conditions (1958, 1959, and

1961), plant recovery was delayed from 1 to 2 years if

utilization exceeded 50 percent.

However, differences in the response of native grass and

nonnative Lehmann lovegrass density to increasing grazing

intensity are less clear. Using a similar approach of increasing distance from water, McClaran and Anable (1992) reported a greater decline of native grass density from 1972 to

1990 with increasing grazing intensity, but Angell and

McClaran (2001) reported no relationship with intensity

from 1972 to 2000. In both studies, increased density of the
30 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

nonnative Lehmann lovegrass was unrelated to grazing

intensity. These results for grazing impacts may differ

because the two measures of response (biomass and density)

may differ in their sensitivity to grazing. Density represents

the number of plants, whereas biomass reflects their total

weight. The earliest studies (Cable and Martin 1975; Martin

and Cable 1974) measured biomass, while the more recent

studies (Angell and McClaran 2001; McClaran and Anable

1992) measured density. In addition, McClaran and Anable

(1992) relied on only a single water source.

More importantly, the intensity levels for the later studies

were greater (60 percent at 0.1 km and 48 percent at 0.5 km)

than the earlier studies (48 percent at 0.4 km and 43 percent

at 1.6 km). There may be little difference in grass response

between 50- and 60-percent utilization, but those responses

will be more severe than where utilization is less than 45

percent. This observation is supported by suggestions that a

40-percent utilization rate will not damage these grasses

(Parker and Glendening 1942; Reynolds and Martin 1968).

Seasonal Rotation of Grazing—Between 1972 and

1984, neither grass density nor production differed between

areas experiencing yearround grazing and those where the

rotation of livestock excluded summer grazing in 2 of 3 years

(Martin and Severson 1988). Three pastures were used to

achieve this rotation, and all animals from those pastures

were confined to a single pasture for 4 to 8 consecutive

months, followed by a period of 8 to 12 months of no grazing.

During the study, utilization levels were 47 to 51 percent.

Contrary to expectations, the provision of summer rest did

not improve grass abundance. The authors suggested that at

the beginning of the study, grass abundance was near

maximum, and therefore was unresponsive to this treatment. Additional considerations must include the increase

of lovegrass through the period, the very wet conditions

through the 1980s (fig. 2), and utilization levels above the

40- to 45-percent threshold.

Effects of Fire—In general, grass abundance decreases

following fire, and the recovery is dependent on subsequent

growing conditions. However, seed germination of the nonnative lovegrass increases after fire.

In 1952, following the first of two prescribed fires, grass

cover declined from 1.7 to 1.1 percent, but cover had already

declined to 0.5 percent on both burned and unburned areas

prior to the second fire in 1955 (Cable 1967). Cover declined

to 0.3 percent on all three treatments in 1957, and the

unburned site reached 0.8 percent cover by 1965 (fig. 9).

These dynamics reflect the overriding influence of dry conditions between 1952 and 1957 (fig. 2). Cable (1965) found

only lovegrass seedlings following a wildfire in June 1963,

and later research revealed that lovegrass seed germination

increases equally after fire and the simple removal of plant

cover (Sumrall and others 1991). In both instances, seed

germination is stimulated by a phytochrome response to

increased red light rather than heat from the fire (Roundy

and others 1992).

Effects of Mesquite—The influence of neighboring mesquite trees on perennial grass appears to be contingent on

elevation, amount of mesquite, and the species of grass.

Beginning in the 1940s, observations of coincident declines

in grass and increases in mesquite stimulated several treeremoval studies. Fortunately, some of them had repeated

measurements performed over the following 40 years. Based

on these observations, increased grass production following

tree removal is most persistent at higher elevations, and is

related to the tree density before removal. For example, tree

removal in 1945 increased grass production during the first

5 years at all four sites, which ranged from 950- to 1,250-m

elevation, but increases were greatest at 1,250 m and where

initial tree density was greater than 300 plants per ha

(Parker and Martin 1952). After 13 years, native grass

production was greater in mesquite-cleared areas above 950 m

and where initial tree density was greater than 100 plants

per ha (Cable 1971). After 23 years, production was greater

for native grasses only at 1,250 m and where initial tree

density was greater than 300 plants per ha (Cable 1971).

After 29 years, grass production was greater only at 1,250 m,

but the nonnative lovegrass dominated the grass composition by that time (Williams 1976).

The relatively brief increase of grass production is probably a function of both the recruitment of new mesquite trees

and the depletion of soil fertility after their removal. Tree

recruitment prompted Parker and Martin (1952) to suggest

that tree removal would be required every 25 years to

maintain grass production. An island of soil fertility develops under mesquite. About three times more organic matter

and nitrogen exists in the top 7.5 cm of soil compared to open

grassland, and 13 years after tree removal there is a 30

percent decline of organic matter and nitrogen (Klemmedson

and Tiedemann 1986; Tiedemann and Klemmedson 1986).

This greater soil fertility under mesquite trees may contribute to the greater likelihood of some grasses to occur

under the trees. Several species, including cottontop and

bush muhly are more common under mesquite than if they

were randomly distributed (Livingston and others 1997;

Van Deren 1993; Yavitt and Smith 1983). Tiedemann and

others (1971) suggested that the greater soil fertility under

mesquite might compensate for the lower light intensity for

those species that are shade tolerant.

It is important to note that increases of native and nonnative lovegrass have occurred without mesquite removal, and

can occur while mesquite is increasing. From 1960 to 1991,

at elevations between 900 and 1,250 m, native and nonnative grass cover more than doubled, while mesquite cover

increased from 7 to 20 percent (figs. 5 and 13).

The rate that Lehmann lovegrass spreads from seeded

areas is not related to the abundance of mesquite. Lovegrass

was seeded on the margins of the areas where mesquite trees

were thinned and removed in 1945 (Parker and Martin

1952). After 13 years, it had spread 75 to 125 m regardless

of mesquite treatment, and its density increased with elevation (Kincaid and others 1959). After 25 years, lovegrass

productivity did not differ among mesquite treatments, but

it did increase with elevation (Cable 1971). This is consistent

with Van Deren’s (1993) finding that the proportion of

lovegrass plants under mesquite is only slightly less than

would be expected randomly.

Effects of Burroweed—The response of perennial grass

to burroweed neighbors appears to be contingent on amounts

of winter and summer precipitation. In 1961, Cable (1969)

removed some existing burroweed plants to create cottontop

plants without burroweed neighbors. Cottontop production

did not differ between treatments, but cover differed in the

last 2 years of the study. In the very dry summer of 1962,
USDA Forest Service Proceedings RMRS-P-30. 2003 31

A Century of Vegetation Change on the Santa Rita Experimental Range McClaran

cottontop cover was no different between treatments, but in

the following summers that had greater precipitation, cover

was greater for cottontop plants without burroweed. Cable

(1969) demonstrated that basal cover was reduced because

burroweed used soil moisture during the winter when grass

tillers were enlarging, rather than preemptive use of water

by burroweed in the summer. This relationship may explain

why total grass cover did not respond to burroweed removal

at 1,100-m elevation in the generally dry periods between

1940 and 1946 (Parker and Martin 1952).

Native and Nonnative Grass Relationships—The

inverse relationship between the increasing abundance of

the nonnative Lehmann lovegrass and declining native

grasses appears to be more closely related to events during

seedling establishment than to interactions among adult

plants. Initially, the lovegrass invasion appears to occur

between existing native grasses, thus increasing total grass

density and productivity, but eventually native grasses are

replaced (fig. 13; Anable and others 1992; Angell and

McClaran 2001; Kincaid and others 1959). The timing and

magnitude of the native grass decline between 1972 and 2000

did not differ in relation to the length of time that lovegrass

had been present in an area (Angell and McClaran 2001). In

addition, all evidence suggests that the increase of lovegrass

is as indifferent to the abundance of native grasses (Angell

and McClaran 2001; McClaran and Anable 1992) as it is to

the abundance of mesquite (Kincaid and others 1959). The

unique response of lovegrass seed to the first summer rains

may be a more important key to its highly successful recruitment. Abbott and Roundy (2003) reported that native grasses

were more likely to germinate with the first summer rains

than lovegrass, and therefore would suffer from the rapid

soil desiccation that follows these sporadic first rains. In

contrast, lovegrass germination was more likely to be delayed and follow the more regularly occurring later rains,

when prolonged soil moisture and survival were more likely.

Opportunities___________________

Continuing the systematic remeasurement and repeat

photography efforts on the Santa Rita presents the greatest

opportunity for improving our understanding of vegetation

change because they will record the pattern and variation of

future changes. The most incontestable conclusion from this

century of vegetation change is that future changes can not

be perceived and understood if there are no records of

previous conditions. An equally important conclusion is that

the response of vegetation to management practices will be

contingent on past and future precipitation patterns, elevation and soils at the location, and the current mix and vigor

of plant species. For example, when the next burroweed

eruption occurs, we will respond with much less anxiety

than our predecessors had in the 1930s and 1950s because

we understand that it is likely to be a short-lived rather than

permanent change. We will not expect the eruption to occur

at all locations, nor will the control of that eruption prevent

future eruptions. Given the importance of this observation

legacy, its continuation should be considered both an opportunity and an obligation.

In addition to continuing the ongoing remeasurements,

there are several opportunities to further the documentation

and understanding of both past and future vegetation

changes. Most of the areas that experienced experimental

manipulations were measured for less than 5 years.

Remeasuring vegetation in those areas can provide insights

into the longevity of responses and the variation expressed

in recent changes such as the spread of Lehmann lovegrass.

A re-evaluation of these old data sets may reveal patterns

and suggest processes that were not originally apparent.

These re-evaluations will certainly benefit from the application of new methods of statistical analysis such as repeated

measures and mixed-effects models of analysis of variance,

classification, and regression tree analysis. In addition,

spatial analyses of these data sets have been facilitated by

the creation of a digital archive that is available on the World

Wide Web (McClaran and others 2002).

The establishment of any new experimental manipulations is given invaluable direction by these long-term records.

In return, these new manipulations should be located where

they will not conflict with ongoing remeasurements or opportunities to remeasure past manipulations. Finally, all

efforts should be made to foster the long-term remeasurement

of these new manipulations beyond the common 3 to 5 years.

No message is clearer from this century of change than the

certainty that the initial response to manipulations will not

persist with time.

There are specific research questions that are stimulated

by this legacy of observation. Given the initial focus on grass

dynamics, efforts focused on the current grassland dominated by Lehmann lovegrass deserve attention. How long

will the dominance persist, and will the absolute abundance

(cover, density, and biomass) stabilize, increase, or decline?

Will lovegrass dominance directly alter the expected patterns of mesquite seedling recruitment, and future eruptions of burroweed and cactus? Will these patterns be altered indirectly by the lovegrass because its abundant

biomass will facilitate and support more frequent fire? Does

the proposed grazing intensity threshold of 45-percent utilization apply equally to lovegrass and native grasses?

Regarding mesquite, what are the maximum cover, density, and productivity per area for the species? Glendening

(1952) predicted a maximum of 30-percent cover, but that

mark has not been reached on the majority of the Santa Rita.

The development of a soil fertility island beneath mesquite

trees has been documented (Klemmedson and Tiedemann

1986; Tiedemann and Klemmedson 1986). What are the

limits to this accumulation, how deep in the soil will fertility

eventually increase, and how long will it last after trees are

removed? These patterns are important to neighbor plants,

and they are globally important because they address interests in the sequestration of atmospheric CO2 through vegetation management.

Consulting past records, maintaining ongoing remeasurements and initiating new manipulations can advance the

prediction of future burroweed and cactus eruptions. The

timing and duration of past eruptions were not entirely

synchronized. The degree and spatial pattern of their

asynchrony should be possible with repeat photography and

the network of 30 rain gauges (McClaran and others 2002).

Further investigation of the potential role of bacterial infection on cactus populations should also occur.

Finally, this accumulation of information should prove

useful in evaluating both theoretical and practical issues of
32 USDA Forest Service Proceedings RMRS-P-30. 2003

McClaran A Century of Vegetation Change on the Santa Rita Experimental Range

rangeland vegetation ecology and management. For example, the gradients of livestock use intensity and precipitation records could be used to evaluate the theoretical

propositions of equilibrium versus nonequilibrium controls

on vegetation change (Illius and O’Connor 1999). Practically, the rich empirical information and documentation of

contingencies such as soils, precipitation patterns, and preexisting species composition could be used to construct a

catalog of vegetation states and the events that led to

transitions between those states (Westoby and others 1989).

It is obvious that the vast opportunities for future research into the patterns, mechanisms, and implications of

vegetation changes are built on the rich legacy of a century

of observation and research. In addition to opportunities,

there are obligations to maintain and add to this legacy.

Therefore, one of our goals should be that during the bicentennial celebration, our future efforts should ensure a second century of research on the Santa Rita.

References _____________________

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Glendening, G. E.; Paulsen, H. A. 1955. Reproduction and establishment of velvet mesquite as related to invasion of semidesert

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American Midland Naturalist. 109: 89–93.
34 USDA Forest Service Proceedings RMRS-P-30. 2003

George B. Ruyle

Rangeland Livestock Production:

Developing the Concept of Sustainability

on the Santa Rita Experimental Range

George B. Ruyle is Professor and Extension Specialist, Range Management, in the School of Renewable Resources, University of Arizona; e-mail:

gruyle@ag.arizona.edu. He holds a B.S. degree from Arizona State University, an M.S. degree from the University of California, Berkeley, and a Ph.D. from Utah

State University. He is a Fellow in the Society for Range Management.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B. tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: The Santa Rita Experimental Range (SRER) was established in 1903 at the behest of

concerned stockmen and researchers as the first facility in the United States set aside to study

range livestock production. At the time, severe overgrazing of the public domain had seriously

reduced carrying capacities of Southwestern rangelands. Researchers on the SRER developed and

demonstrated the concepts that became the foundation for the art and science of range management. These included improved livestock husbandry methods and an initial understanding of how

grazing behavior influenced patterns of vegetation response. The emphasis for range livestock

production research, however, quickly focused on stocking levels and adjusting grazing and rest

periods in order to maintain or improve the abundance and production of forage grasses.

Subsequent research developed and demonstrated methods to achieve sustainable range livestock

production based on limited herd flexibility and controlled forage utilization levels determined by

stocking and monitoring histories. These concepts, conceived and tested on the SRER, contributed

greatly to the foundation of modern range management.

Acknowledgments: Some of the following data sets were accessed via the Santa Rita Experimental Range Digital Database. Funding for the digitization of these data was provided by the USDA

Forest Service, Rocky Mountain Research Station, and the University of Arizona. Additionally,

much material from the Santa Rita Experimental Range archives was reviewed in the preparation

of this manuscript. The effort of those involved in the archiving process is greatly appreciated. The

author gratefully acknowledges Don Dwyer, Larry Howery, Barbara Hutchinson, and Phil Ogden

for their thoughtful reviews.

Introduction ______________________________________________________

The Santa Rita Experimental Range (SRER) was established in 1903 when it was fenced out of the public domain.

Establishment of the SRER was a direct result of pressure from the livestock industry and concern by university and agency

researchers of the time that range productivity, in terms of livestock carrying capacity, had declined considerably. In the

preface to Griffiths (1901), agrostologist F. Lawson-Scribner wrote that the “free-range system has led to the ruthless

destruction of the native grasses” and stressed the “urgent needs of the stockmen for better range conditions.” Griffiths (1901)

recognized that “ranchers and those interested in stock growing are beginning to realize more and more the importance of

placing the range management in the hands of some one having authority and an interest in its preservation.” This authority,

whether at the State or Federal level, also required scientifically accepted criteria for range management, criteria that needed

to be developed and tested. Thus began the application of the art and science of range management to Southwestern

rangelands.

The SRER was specifically established to conduct “ecological research related principally to the range livestock industry”

(Martin and Reynolds 1973). This research program was developed to provide the science on which to base modern range

livestock production. Principle audiences for the research were ranchers and Federal agency field personnel (Roach 1950),

particularly the USDA Forest Service, which was assigned to conduct range research in 1915. For nearly eight decades the

Forest Service directed the research program on the SRER. Livestock grazing has continued on the SRER, but by the early
USDA Forest Service Proceedings RMRS-P-30. 2003 35

Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

1970s, research emphasis had shifted to studies on the

“impacts of grazing on the ecosystem” and more basic ecological aspects of “semidesert ecosystems” (Martin and

Reynolds 1973). A broader audience of “working ecologists”

and the “urban public” had also emerged.

The emphasis for research may have been livestock production, but from the beginning, the SRER was a range

manager’s place and the range vegetation was their primary

focus. Range livestock grazing research on the SRER developed and promoted the concept of conservative use and

sustainability. In 1975, Martin wrote that “Research and

experience indicate that ranges can be grazed at any time of

year without serious detriment if the intensity of grazing is

not too severe, and if periods of grazing alternate with

suitable periods of rest” (Martin 1975a). The objectives of

this paper are to examine the body of knowledge generated

on the SRER related to range livestock production systems

that led to these beliefs; discuss the concepts, methods, and

tools developed to apply them; and present stocking histories that indicate the sustainability of conservative stocking.

I provide this manuscript as a tribute to all of the early

researchers, but especially to S. Clark Martin who spent

much of his long and distinguished career on the Santa Rita.

Grazing History ________________

Early records well document the overstocking and deterioration of southern Arizona rangelands. Livestock were first

introduced into southern Arizona in the late 1600s by Father

Kino and early Spanish explorers (Allen 1989; Sheridan

1995), but Spanish ranching did not begin in earnest until

the beginning of the next century (Sheridan 1995). It is easy

to assume that ranges, where adequate water was available,

were fully stocked by Spanish and Mexican ranches in the

early 1800s. These early ranches were abandoned around

1840, but wild cattle in unknown numbers remained on the

ranges. Anglo ranchers began their influx soon after the

Civil War (Sheridan 1995). Range cattle, as well as sheep

and goat, numbers increased after about 1870 and skyrocketed by the mid-1880s. It was commonly reported that the

number of cattle in the Arizona Territory was about 5,000 in

1870, 230,000 in 1880, 650,000 in 1885, and over one million

in 1890. Dieoffs followed due to the combined effects of

overstocking and drought (Griffiths 1901). Severe summer

drought in 1891 and 1892 resulted in cattle losses of up to 75

percent by late spring of 1893 (Martin 1975a). Nonetheless,

stocking on Arizona ranges continued to exceed carrying

capacities well into the 1900s. Stockmen and government

agency researchers alike attributed overstocking to open

range policy. It was a direct result of these conditions and the

importance of finding ways to stabilize the range livestock

industry that led to the establishment of the Santa Rita

Experimental Range. The SRER was fenced in 1903,

destocked, and allowed ungrazed “recovery” until 1914 (Martin and Reynolds 1973). After 1915 most of the area was

continuously grazed until 1957 when various schedules of

rest were implemented in study pastures.

Sustainable Grazing ____________

At the beginning of Anglo settlement it was thought that

the primary economic resources of the Arizona Territory

would come from minerals, but it was soon determined that

rangeland vegetation, especially the Bouteloua (grama)

grasses in the south, provided a vast forage resource for

livestock production. For the range livestock industry to

become a stable, long-term, economic base, however, the art

and science of range management had to be developed and

applied. This became a reality with the establishment of the

SRER.

The theory and philosophy of the sustainability of range

livestock production was pioneered on the SRER. The concept was variously referred to from the earliest writings as

“the amount of stock that these lands will carry profitably

year after year” (Griffiths 1904), “keeping utilization in

harmony with forage supply” (Roach 1950), “sustained use

without deterioration of rangelands” (Reynolds 1954), and

providing “relatively stable livestock production without

seriously impairing other important resource values” (Martin and Reynolds 1973). Overgrazing was recognized early

as the primary deterrent to sustainable range livestock

production and characterized by observations such as “the

tops are continually eaten to the ground” causing the roots

to “gradually become extinct” (Griffiths 1901). The sustained production of perennial grass forage for range livestock production “requires grazing the desirable plants to

the proper degree at appropriate times and the optimum

distribution of livestock” (Reynolds and Martin 1968). These

concepts were developed and applied on the SRER.

Range livestock production was a primary livelihood in

Arizona when the SRER was established. While decreasing

in economic importance over the years, grazing has continued on Southwestern semidesert ranges. Martin (1975b)

stated that these rangelands produced enough beef for

nearly 3 million people using only a third of the energy

required of other food production systems. The harvesting of

range forage, produced almost totally from solar energy,

remains the most basic way to convert sunshine to food.

Rangeland livestock production remains the most widespread use of Arizona rangelands (Ruyle and others 2000).

Range management practices developed on the SRER have

allowed ranges to improve and maintain productivity over

time, and have led to the continued production of range

livestock.

The following describes the primary literature and basic

findings that supported the development and application of

sustainable range livestock production practices.

Range Management and Livestock

Production ____________________

Most of the researchers connected with the SRER equated

range management with range livestock production. That is,

their range management practices were focused on increasing

forage for livestock on semidesert ranges. The categories

below represent the primary literature related to range

livestock production on the SRER. Much of the literature has

been reviewed in earlier publications, albeit with a different

time reference.

By far the majority of research on the SRER did not focus

on livestock per se, although animal weights, especially of

weaned calves, were often recorded. Instead, the emphasis

was on the range vegetation for the purpose of managing
36 USDA Forest Service Proceedings RMRS-P-30. 2003

Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability ...

grazing to improve and/or maintain the amount and distribution of perennial grasses.

Effects of Grazing on Plant Communities

General impacts of open range grazing and unrestricted

livestock numbers were well documented at the turn of the

century. These included loss of forage productivity and

increases in plant species less palatable to livestock, bare

ground, and soil erosion. The fact that semidesert ranges

were vegetated by bunchgrasses rather than sod-forming

grasses increased the susceptibility of the soil surface to

“injury by trampling” (Griffiths 1901), which seemed to

surprise early observers (Toumey 1891). While overgrazing

was known and described, the ecological processes involved

were only beginning to be studied in an experimental fashion when the SRER was established.

Grazing can influence all vegetation of the range, primarily through selective herbivory on plant species over time

and space. Plants vary greatly in palatability to livestock,

and the preferred species tend to get grazed heavily, especially when animals are allowed to graze yearlong (Reynolds

and Martin 1968). Selective grazing can change the composition of the plant community and reduce the productivity of

the primary forage species. These now well-known processes

were demonstrated in descriptive studies and then experimentally in small plot and pasture studies on the SRER.

In addition to the many early comparisons of ungrazed

versus heavy, continuous, yearlong grazing, vegetation differences associated with distance from water were demonstrated on a pasture with a single permanent water source,

and grazed yearlong for a 38-year period (1930 to 1968)

(Martin 1972). Heavy, moderate, and light use zones, moving

away from water, were associated with about 70-, 50-, and

25-percent utilization, respectively. Differences in grazing

use zones manifested species composition shifts among the

palatable perennial grasses. Heavy use (usually over 70

percent by weight) reduced the percent composition of

Bouteloua eriopoda Torr. (black grama), Tridens muticus

(Torr.) Nash (slim tridens), and Muhlenbergia porteri Scribn.

Ex Beal (bush muhly), and favored Aristida californica

Thurber var. glabrata Vasey (Santa Rita threeawn) and

Bouteloua rothrockii Vasey (Rothrock grama). More moderate stocking was shown to improve composition of the aforementioned midgrasses in later studies. Recovery potential of

overgrazed rangeland, although limited by increases in

mesquite, had been demonstrated early on the SRER and,

along with determining proper stocking levels, were research themes for many years (Wooton 1916).

Early range researchers commonly used various clipping

intensities on range grasses to simulate grazing, although

the limitations of extrapolating data from clipped plots to

pasture level grazing processes were recognized (Culley and

others 1933). Clipping studies on the SRER compared intensity and frequency of defoliation on several perennial grasses.

Findings demonstrated aboveground production was reduced by 50 percent on plants clipped weekly during the

growing season to 1-inch stubble compared to plants clipped

to that level only once at the end of the growing season

(Reynolds and Martin 1968).

Research also demonstrated plant community differences

by comparing protected areas with adjacent areas grazed

continuously (Griffiths 1910). Species most abundant under

continuous yearlong grazing were Hilaria belangeri (Steud.)

Nash (curley mesquite), Rothrock grama, and Bouteloua

filiformis (Fourn.) (slender grama), and species favored by

protection were Digitaria californica (Benth.) Henr. (Arizona cottontop), bush muhly, black grama, Bouteloua

curtipendula (Michx.) Torr. (sideoats grama), Aristida species (threeawns), Eragrostis intermedia Hitchc. (plains

lovegrass), and Leptochloa dubia (H.B.K.) Nees (green

sprangletop) (Canfield 1948; Reynolds and Martin 1968).

Grazing pressure resulted in about 50-percent utilization on

the group of species most abundant where grazing was

continuous and was “much heavier” on the grasses that

responded most to protection from grazing. Other studies

failed to demonstrate such benefits to the more palatable

midgrasses with protection from grazing, especially under

moderate use levels (approximately 40 to 60 percent averaged over species and years) (Canfield 1948) or when shrub

cover (primarily Prosopis juliflora var. velutina (Woot.)

Sarg. (mesquite)) was dominant (Caraher 1970; Glendening

1952).

General Range Animal Husbandry

Many changes were seen in the principles and methods of

raising cattle in the Southwest during the first several

decades after establishment of the SRER. The Superintendent of the SRER from 1921 to 1950, Matt Culley, recognized that modern business and range management methods were necessary for ranching success. Most ranches were

“run as breeding operations” with the chief source of income

being calves sold in the fall or as yearlings the following year

(Culley 1946a). Therefore, the percentage of calves produced

was of extreme importance. Research on the SRER suggested several factors that increased herd production and

earnings (Culley 1937a, 1946a,b,c, 1947, 1948). These included “stocking the range on the basis of sustained yield,”

reducing pasture size, increasing watering places, regulating the breeding season, and reducing death loss. Improving

general management practices with mechanical livestock

handling aids was also suggested. Marketing strategies

were also evaluated, but as Parker (1943) wrote, “the condition of the range should always be considered first” in

deciding when to sell the animals. Such a strategy required

a flexible approach to fall weaning and culling. In good years

calves could be held over, and in drought conditions even

breeding cows might need to be sold.

Although influenced by grazing pressure and the impact

of droughts on forage production, calf crop and calf weights

increased remarkably on the SRER after the 1920s, due to

general improvements in animal genetics and handling

methods (Reynolds 1954) as well as reductions in grazing

pressure (Martin 1943). For example, in the 1943 Hereford

Journal, Martin reported increased average annual calf

production per cow was 192 pounds to 368 pounds, depending on stocking rates that ranged from 30 to 70 acres per cow.

The average cow produced 44 pounds more in calf weight

with each additional 10 acres of range she was allowed to
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Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

graze. Improvements in the kind of cattle, in terms of

breeding, nutrition, and culling practices, also contributed

to these gains. Hereford cattle predominated on the SRER

for much of its history, but after the mid-1960s they were

gradually being replaced with crossbred herds (Culley 1946b;

Martin 1975a).

Grazing Behavior

Grazing Habits—An important aspect of effective range

management is the study of grazing behavior of cattle on the

range (Culley 1937b, 1938a). Culley was interested in the

relative preference by cattle for different forage plants as

well as the general grazing behavior of cattle. He determined

that some forage species were grazed “indiscriminately”

year round while others were primarily selected seasonally.

Culley also described cattle grazing patterns and activity

budgets on a seasonal basis. He reported summer and winter

grazing periods of 7 and 8 hours a day, and spring grazing

averaged 9 hours daily. Fall and early summer grazing was

confined to grasses along washes. Mesquite and Acacia

greggii A. Gray (catclaw) were used during the winter and

late spring, and other shrubs were browsed throughout most

of the year. Zemo and Klemmedson (1970) further quantified

activity budgets using fistulated steers and concluded that

their experimental animals responded in a similar fashion to

intact animals as reported in other studies. However, they

did record a higher amount of night grazing than most other

observations.

Gamougoun (1987) related cattle activity budgets to characteristics of available forage. He found that cattle grazed

longer during the summer than in winter and walked more

in heavily grazed pastures than in more moderately grazed

areas. Gomes (1983) compared behavioral activities of Hereford and Barzona cows and recorded almost identical daily

activities.

Ruyle and Rice (1996) described more recent and detailed

cattle feeding behavior studies conducted in pastures on the

SRER that primarily supported Eragrostis lehmanniana

Nees (Lehmann lovegrass) stands. Cattle grazing utilization patterns on these pastures resulted in heavily grazed

patches interspersed throughout ungrazed or lightly grazed

areas (Ruyle and others 1988). Cattle spent approximately

80 percent of their grazing time feeding in previously grazed

patches and only slightly altered this ratio with increasing

stocking rates (Abu-Zanat 1986; Nascimento 1988; Ruyle

and Rice 1996). Cow biting rates were higher and bite sizes

usually smaller when feeding in heavily grazed patches

versus lightly grazed areas (Ruyle and others 1987; Ruyle

and Rice 1996). Higher nutrient densities and a reduced

presence of residual stems in grazed patches were thought to

be the primary factors influencing cattle grazing strategies

in pastures dominated by Lehmann lovegrass.

Diet Selection—Plant species vary in palatability seasonally and among life forms, and cattle prefer new green

forage, shifting their diets in several ways to accommodate

this preference (Lister 1938a,b, 1939). Santa Rita researchers

observed these differences empirically and experimentally

and attempted to use them to control grazing distribution

and use on the various classes of forage (Canfield 1942a;

Lister and Canfield 1934; Reynolds and Martin 1968). Most

perennial forage grasses were grazed throughout the year.

Arizona cottontop was more heavily grazed in the summer,

and black grama and bush muhly were grazed most heavily

in the winter. Cable and Bohning (1959) were first to demonstrate that the exotic Lehmann lovegrass, introduced

from South Africa, was primarily grazed during the spring

when it occurred in mixed stands with native perennial

grasses.

More exact methods to quantify range cattle diet selection

were employed beginning in the early 1960s on the SRER.

However, these researchers usually estimated only the crude

protein content of diets (Shumway and others 1963). A

method to estimate botanical composition of diets from

fistulated animals was tested and diet selection results

reported in later studies (Galt and others 1968, 1969, 1982).

These studies verified earlier results demonstrating that

certain species were preferred throughout the year while

others were selected seasonally. Summer preference for

Arizona cottontop and Setaria macrostachya H.B.K. (plains

bristlegrass), winter and spring consumption of black grama

and Lehmann lovegrass, summer use of slender grama,

spring use of Rothrock grama, and winter and summer

selection of mesquite and Calliandra eriophylla Benth.

(false mesquite) were again demonstrated.

Nutrition

Early studies indicated that the primary forage grasses on

the SRER did not provide adequate crude protein or phosphorous during the driest times of the year, usually December to February and May and June (Hubber and Cable 1961).

These findings were substantiated by later work. Using

fistulated animals, researchers demonstrated that steers

selected diets much higher in crude protein than handclipped samples, although the forage consumed only provided adequate crude protein year around if green, herbaceous growth was available or shrubs made up large portions

of the diet (Cable and Shumway 1966; Galt and others 1969;

Hayer 1963). While cattle could meet their protein requirements over most of the year by selective grazing, seasonal

animal weight changes were caused by seasonal changes in

animal requirements (primarily associated with reproduction) and seasonal changes in the quantity and quality of

forage (Ward 1975).

Later nutritional studies focused on Lehman lovegrass as

it greatly increased in abundance on much of the SRER

(Anable and others 1991). Nutritive values were reported

from samples clipped seasonally and from heavily and lightly

grazed patches (Abu-Zanat 1989; Osman 1980; Renken

1995). Both crude protein and in vitro dry matter digestibility were higher in Lehmann lovegrass samples from heavily

grazed patches than from the adjacent lightly grazed areas

(Renken 1995). Diet quality of cows grazing Lehmann

lovegrass was also estimated (Ruyle and Rice 1996). Although standing biomass of Lehmann lovegrass is often

nutritionally marginal, cattle were able to select green

material with adequate crude protein and phosphorous to

meet their needs throughout most of the year.
38 USDA Forest Service Proceedings RMRS-P-30. 2003

Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability ...

Grazing Distribution

Achieving adequate grazing distribution became an issue

as stocking rates were slowly reduced on the SRER. Freeranging livestock tend to concentrate grazing use near

permanent water, resting areas, ridges, bottoms, and areas

near trails. Forage utilization levels decrease with increasing distances from these sites (Reynolds and Martin 1968).

Range management practices such as watering, salting,

supplemental feeding, and fencing were all used on the

SRER to improve grazing distribution.

Adding watering places was an early method to promote

uniformity of forage use (Culley 1938b). Water hauling was

also effective in improving grazing distribution, especially

during drought conditions; however, under some situations

this practice proved too costly (Bohning 1958a; Reynolds and

Martin 1968). Controlling access to water within individual

pastures was also used to rotate grazing. Martin and Ward

(1970) demonstrated that utilization of perennial grasses

near water could be reduced and herbage production increased using this technique.

Providing salt or salt meal was another common method

to improve distribution of grazing (Bohning 1958b) albeit

with mixed results (Culley 1938b). Placing salt or salt meal

on remote parts of the range was found to increase utilization of perennial grasses in those locations, but did not

significantly reduce use on areas closer to permanent water

(Martin and Ward 1973).

Fencing to improve grazing distribution was also implemented on the SRER, and subdividing large pastures improved livestock handling and forage use patterns, resulting

in increased calf crops (Reynolds and Martin 1968).

Stocking Strategies

Conceptual Considerations—From the earliest writings, researchers recognized that if overstocking was the

problem, proper stocking was, at least in large part, the

solution. As early as 1891, Toumey wrote, “Overfeeding a

range has a tendency to kill out better grasses.” He recognized that there were ecological and economic limits to

which the range should be stocked and “beyond this limit...

will be a detriment to the permanency of the range.” Reducing stocking rates in order to get cattle numbers more in line

with forage production was one of the first orders of business

on the SRER (Culley 1937c).

As previously stated, the SRER was destocked from 1903

until about 1914 to allow for some degree of recovery from

the extreme overuse suffered under the open range grazing

policy for public lands. The SRER was grazed yearlong from

1915 until 1957 when seasonal grazing and grazing system

research began.

Over the years a variety of stocking rates have been

suggested for semidesert grassland ranges (table 1). Santa

Rita researchers and managers recognized declining productivity coupled with a series of drought years and gradually reduced livestock numbers (table 2). Additionally, perceptions of conservative stocking and resulting moderate

utilization changed over the years, desired levels of utilization being reduced from about 70 percent (derived from

stubble height recommendations found in the archives) to

the 40 percent recommended in various publications by

Reynolds, Martin, and Cable during the 1960s and 1970s.

Stocking rates on the SRER averaged about 19 acres per

Animal Unit Year (AUY) during 1915 until 1925, when they

were reduced to about 44 acres per AUY due to historic

overuse and declining forage productivity (Cable and Martin

1964). Utilization levels, however, remained high until, in

1956, stocking rates were reduced again in at least four

pastures in an attempt to achieve an average 40-percent

utilization over species and pastures, which was the stocking objective of the Cable and Martin study (table 2).

Stocking strategies became especially critical during frequent droughts. Experience indicated that each 10-year

period brought at least 3 years of critically dry conditions

(Canfield 1939). How best to provide continuous yearlong

forage for a constant number of livestock became a stocking

rate problem. On black grama ranges at the Jornado Experimental Range in southern New Mexico, Canfield (1939)

reported that stocking rates of 22 acres per AUY, even

though reduced from higher levels at the beginning of the

study, were still too high to be maintained in drought years.

Conservative stocking levels were recommended that would

leave an additional 25 percent of the “useable grass of the

average forage crop...ungrazed at the beginning of the new

growing season.” Presumably, this adjustment further reduced stocking rates to approximately 29 acres per AUY.

Table 1—Recommended stocking rates for native semidesert grassland in the Southwest.

Stocking

rate acres per AUYa Approximate location Source

37 Semidesert grassland Griffiths (1904)

50 Santa Rita foothills (approximately 4,000 ft) Griffiths (1904)

20 Good pasture on Santa Rita Range Reserve Wooton (1916)

25 to 45 General estimate for semidesert grassland Ware 1939 (AWP)b

22 Black grama range on the Joranada Canfield (1939)

20 Areas over 4,000 ft on the SRER Bohning and Martin (1954)

25 to 50 High-elevation pastures on the SRER Reynolds and Martin (1968)

50 to 100 Mid-elevation pastures on the SRER Reynolds and Martin (1968)

60 to 160 Low-elevation pastures on the SRER Reynolds and Martin (1968)

a

 Acres per Animal Unit Year.

b

 Unpublished document from the Arizona WPA Writer’s Project.
USDA Forest Service Proceedings RMRS-P-30. 2003 39

Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

Reynolds (1954) applied this conservative philosophy in

his classic discussion of drought and range management

based mostly on data from the SRER, collected and organized by Matt Culley. Reynolds compared forage production

and stocking rates during three 10-year periods (1922 to

1931, 1932 to 1941, and 1942 to 1951). He characterized

drought severity during these periods, respectively, as slight,

moderate, and severe. The stocking level was considered

conservative during the entire 30-year period, and “was

maintained about 20 percent below that which would have

been possible based upon average forage production.” Based

on a review of records, this stocking strategy probably

resulted in an average utilization level of around 60 percent

over the 30 years, a little higher during the early years, and

a little lower later in the study. This variance was likely due

to the diligence with which the stocking levels were actually

adjusted. Relying on these long-term records, Reynolds

recommended stocking rates that would “use about 40 percent of the average long-term forage production,” but also

determined that stocking should be 40 percent below this

average about 35 percent of the time “when droughts reach

moderate and severe intensity.” In other words, during

drought years, reduced production levels would provide less

forage for consumption than 40 percent of the long-term

average, even at relatively heavy utilization levels. He

recognized that livestock operations needed to cull heavily in

bad forage years while holding over yearling animals and

perhaps purchasing other growing animals during good

forage years. The basis of his stocking strategy appears to be

aimed at the ability to maintain a base cow herd at a level

that reduces the need to heavily destock in drought years.

For their 8-year grazing study in pastures 1, 7, 8, and 10,

Cable and Martin (1964) carefully set stocking rates every

October based on forage production during the previous

summer in an attempt to achieve a 40-percent utilization

objective. These calculations, based on Reid and others

(1963), resulted in average stocking of 49 acres per AUY in

range units 8 and 10, and 63 acres per AUY in units 1 and 7.

The Reid and others regression approach to stocking requires a history of intensive data on herbage production and

utilization, and was developed for stocking experimental

pastures. However, in the Cable and Martin (1964) study,

utilization varied yearly from about 30 percent to 65 percent,

and use on individual species varied even more widely, even

though animal numbers were adjusted annually. Arizona

cottontop, plains bristlegrass and, surprisingly, Lehmann

lovegrass were used most heavily, while one of the least

utilized species was black grama. The high use levels for

Lehmann lovegrass likely have less to do with palatability

than relative forage abundance; the less abundant species

were grazed the most. Overall, utilization levels achieved

during this study allowed increases in grass cover over prior

years when use was much heavier.

Other records also indicate that species composition of

perennial grasses on the SRER has changed since about

1942 as stocking rates were reduced (Reynolds 1956; Rivers

and Martin 1980). In 1942, a utilization objective of 50

percent of all the perennial grass herbage was considered

conservative. However, actual utilization averaged higher

than that between 1942 and 1957 (52, 54, and 58 percent on

low-, middle-, and high-elevation pastures). From 1957 until

1966, the utilization objective was lowered to 40 percent of

all of the perennial grass herbage, and the Reid and others

(1963) basis for adjusting numbers was employed. Utilization “varied markedly” from year to year even though cattle

numbers were adjusted each fall (Rivers and Martin 1980).

However, over years and all perennial grass species, use at

the upper elevation averaged 42 percent, well below the

previous years, while use in the middle and lower elevation

pastures averaged 49 percent. The more palatable midgrasses

increased in composition up to 72 percent during this period.

Practical Considerations—Estimating grazing capacity for a range and making stocking rate adjustments to

achieve utilization objectives are largely of conceptual interest; however, developing practical strategies to increase or

reduce stocking from one year to the next can have tremendous logistic and economic consequences. Martin (1975c)

clearly recognized these practical implications to range

management recommendations and, using a plethora of

data collected on the SRER, designed a simulation study to

analyze “several strategies for coping with year-to-year

changes in forage production” focused on ranch income.

Records of forage production, utilization, and stocking rates

for eight pastures over 29 years were used to compute

Table 2—Actual stocking rates applied to various locations on the Santa Rita Experimental Range (SRER) in southern Arizona.

 Stocking rate

acres per AUYa Years Approximate location Source

13.3 1908 to 1914 Averages for Ruelas, Proctor, and MacBeath, early ranchers on the SRER Wooton 1916

19 1915 to 1925 Average stocking for pastures 1, 7, 8, and 10 Cable and Martin 1964

63 1926 to 1937 Average stocking for entire SRER Culley 1937?

19 1922 to 1931 Average stocking for “a foothills pasture” Reynolds 1950

30 1932 to 1941 Average stocking for “a foothills pasture” Reynolds 1950

44 1941 to 1956 Average stocking for pastures 1, 7, 8, and 10 Cable and Martin 1964

23 to 63 1957 to 1966 Range of stocking for pastures 1, 7, 8, and 10 Cable and Martin 1964

20 to 43 1957 to 1966 Average stocking for pastures 1, 7, 8, and 10 Cable and Martin 1975

120 1957 to 1967 Average stocking for pastures 12B, 3, 2N, 5S, 5N, and 6B Martin and Cable 1974

45 1972 to 1984 High-elevation, Block 1 Martin and Severson 1988

62 1972 to 1984 Mid-elevation, Block 2 Martin and Severson 1988

141 1972 to 1984 Low-elevation, Block 3 Martin and Severson 1988

a

 Acres per Animal Unit Year.
40 USDA Forest Service Proceedings RMRS-P-30. 2003

Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability ...

“average proper stocking” (based on 40-percent utilization)

and to determine the effect of various stocking strategies on

cattle sales income at these levels. Stocking rate strategies

included constant stocking at 100, 90, and 80 percent of

average proper stocking. “Flexible stocking” allowed the

number of animal units to fluctuate from 60 to 140 percent

of the average proper stocking in accordance with forage

production, and “limited flexible stocking” allowed fluctuations of 70 to 110 percent of average.

Under flexible stocking, two plans to reduce stocking were

tested for culling in years when forage production was less

than the year before. In the first strategy, these management scenarios sold, in order: (1) weaner calves normally held

until yearlings, (2) replacement weaner heifers, (3) replacement heifers, and (4) older breeding cows. In the second

strategy, old cows were sold first and replacement heifers

last. To increase stocking, the scenarios held cows normally

culled if the total number of bred cows was low, also held

calves normally sold as weaners, and “purchased” additional

stocker calves. The highest simulated average net sales

resulted from constant stocking at 100 percent of the average level of proper stocking (the highest constant stocking

rate tested) followed by net sales under flexible stocking (the

flexible rate that allowed increases up to 140 percent of the

average). However, Martin understood that the “hazards

and high costs of overstocking” also should be considered.

The risk of overstocking was evidenced by the fact that these

two stocking levels, constant average and the flexible rate

with the highest stocking, would result in overstocking

almost half the time. The well-documented results of overstocking were manifest in future reduced productivity of

perennial forage grasses, facts well known to Martin!

In Martin’s analysis, the relative economic advantage of

stocking cows and calves over yearlings depended largely on

differences in weight and price per pound between calves

and yearlings. Simulations showed that cow-calf units produced more income per animal unit of stocking than cowyearling units at calf crops of 60 percent or better. Yearlings

needed to be held over a full year to ensure they would weigh

enough to justify keeping them. However, net sales per 100

animal units in flexible stocking of 120, 130, or 140 percent

of average in the best forage years were only $100 to $200

greater than for constant stocking at 90 percent of the

average proper stocking. Martin was “almost certain that

stocking at 90 percent of the average will be more profitable

in the long run” than stocking at any higher levels. This

stocking rate, 90 percent of the long-term “average proper

stocking” (which was calculated at 40-percent utilization)

continues to be recommended for semidesert ranges today

(Holechek and others 2003). Yet, actual stocking rates higher

than these have maintained or improved forage grass stands

on the Santa Rita.

Even though SRER researchers attempted to set stocking

to achieve specific utilization standards each year, their

efforts were surprisingly unsuccessful. Utilization levels

varied yearly and by pasture in every long-term grazing

study conducted on the SRER. As Martin wrote in 1975a,

“stocking rates assume that utilization of perennial grasses

over a period of years averages around 40 percent, but may

range from as low as 20 percent to as high as 60 percent in

individual years.” He went on to say that “the carrying

capacity of a range cannot be measured precisely.” Grazing

capacity estimates should be determined “by pasture tests

under actual grazing use” (Talbot 1937). As Reynolds and

Martin (1968) wrote, “each range should be stocked on its

own merits.” Only by stocking and monitoring utilization

and plant community responses over time can actual grazing capacities be estimated and adjusted as environmental

conditions dictate.

Estimating Utilization

“The key indicator of proper stocking is the intensity of

use” (Martin 1975a), so methods to help adjust stocking

rates accordingly needed to be developed and tested. The

primary expression of stocking levels on range vegetation is

“utilization,” defined in 1944 as the degree to which animals

have removed the current growth of herbage, expressed in

percentage of growth within reach of livestock (Society of

American Foresters 1944, as cited in Heady 1945). Measuring and interpreting utilization is “one of the most important

phases of range management.”

Humphrey stated in 1938 that during the 22 years (at that

time) of regulated grazing on the SRER, “the aim has been

to determine proper utilization.” But to do this, the SRER

researchers needed a way to improve the accuracy and

meaning of utilization estimates. If not conceived on the

SRER, the concept of utilization was certainly refined, and

field methods were developed and applied as a major research effort there. In this way utilization levels on perennial grasses were estimated to determine stocking pressure.

Specifically, early SRER managers and researchers recognized certain fundamental concepts of utilization. The concepts of proper use, using key species as indicators of utilization on the range as a whole, and the variation in “proper

use for a given key species” by range type, soils, and class of

stock were summarized by Crafts and Wall in 1938. They

clearly realized that “In order that the standards may be

properly interpreted and applied, certain fundamental concepts of utilization must be recognized.” They specified that

utilization “should be determined at the end of the grazing

season,” in other words, fall on seasonal summer ranges and

spring on yearlong or seasonal winter ranges.

Parker and Glendening (1942a) defined proper use as “the

degree of grazing that will allow the more palatable forage

plants to maintain density and vigor, prevent undue runoff

and erosion,” and proper use factors, recognized to be “an

average for the type” were assigned to individual grass

species. Proper use guides varied by range condition with

higher levels permissible on ranges in better condition

(Crafts 1938b; Parker and Glendening 1942a). Utilization

was clearly to be determined “at the end of the grazing year

or season” (emphasis in original Parker and Glendening

manuscript).

Commonly, the very early observers merely recorded

utilization in relation to 100-percent use, and ranges were

not considered fully used until “all vegetation was grazed to

the ground” (quote from unpublished field notes in SRER

archive). However, later researchers soon developed progressively quantitative methods to estimate utilization. In

Lister (1938a), “utilization figures represent the percentages grazed of the total plant height” for perennial grasses.

Crafts (1938b) recognized that height and volume were not
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Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

analogous and developed height-weight relationships for

the various forage grasses as “a possible method for measuring volume utilization in the field.” This method was adapted

to field procedures using step or line transects by Parker and

Glendening (1942b). A utilization gauge was developed to

compute the percent of plant volume removed (Lommasson

and Jenson 1943; Parker and Glendening 1942b). Pastures

were divided into at least two utilization zones for sampling

(Parker and Glendening 1942b), and the number of transects

required was determined by the relative size of the zone.

Utilization was estimated by species, and a weighted average based on the number of plants (called percent composition) was calculated for each zone. Then the percent of

proper use was determined by “dividing actual percent use

by the calculated percent proper” that was based on proper

use factors assigned to each important, grazed species.

Canfield (1942a) proposed the line interception method to

estimate utilization (and other “forage-plant inventory” attributes) as a field technique to “insure uniformly good

results.” Stubble heights and basal intercepts were recorded

on the line, and each stubble height measurement was

placed in a stubble height class adapted from Culley (1939)

(SRER archives, unpublished data). Measurements were

then converted to a weighted average height for each species

(Canfield 1944a). A “short-cut” way to apply stubble height

estimates was also described by Canfield (1942b, 1944b) for

“the field man who has much work to do and little time to do

it in.” This procedure estimated only the amount of a grass

stand grazed to a stubble height of 2 inches or less. Canfield

suggested that a proper utilization level was reached when

about 60 percent of the forage grasses had been grazed to a

height of 2 inches.

Methods to estimate forage use on the SRER changed over

time reflecting more conservative stocking levels and more

intensive analysis (table 3). From 1920 to 1938, use was

mapped during a general range reconnaissance by “percent

of proper use” in seven percentage classes (SRER archives,

unpublished field notes): (1) 0 to 30 percent, (2) 35 to 50

percent, (3) 55 to 65 percent, (4) 70 to 80 percent, (5) 85 to 90

percent, (6) 100 percent, (7) greater than 100 percent.

In the 1939 “Utilization survey report on the Santa Rita

Experimental Range,” Culley provided nine stubble height

classes (table 3) that were combined with a line intercept

method to estimate degree of use on individual grass species.

This method was used until 1949, differing only slightly the

last 3 years of use by locating transects at varying distances

from water. In 1950, the method of basing utilization on the

percentage of ungrazed plants (Roach 1950) was initiated.

This then became the method of choice for most subsequent

utilization surveys, including all pasture level grazing studies up to and including Martin and Severson (1988).

Grazing Management and Grazing

Systems

Early range scientists commonly recommended some sort

of seasonal rest (for example see Sampson 1919), and this

was not lost on the Santa Rita researchers. Early research on

the SRER, however, focused on reducing stocking rates and

the effects of yearlong grazing. Lister and Canfield (1934)

studied seasonal differences in cattle selection of grass

species and found that different species were preferred in

different seasons. Lister (1938b) noted that cattle preferred

sideoats grama and Arizona cottontop during the summer,

and curly mesquite, black grama, bush muhly, Bouteloua

chondrosioides (H.B.K.) Benth. Ex S. Wats. (sprucetop

grama), and slender grama were preferred during the fall

and winter. Bouteloua hirsute Lag. (hairy grama) and Lycurus

setosus (Nutt.) C. Reeder (wolftail) were chosen primarily in

the spring. Lister and Canfield concluded, “Seasonal, selective grazing is the natural grazing system.”

To properly stock a range grazed yearlong, this seasonal

preference was to be coupled with seasonal production of

forage species. Canfield (1938) applied this concept to black

grama ranges on the Jornada Experimental Range in a

system of grazing he called “semi-deferred.” Semideferred

Table 3—Methods used to estimate utilization of perennial grasses on the Santa Rita Experimental Range in southern Arizona.

Years Method used Reference

1920 to 1938 General reconnaissance; use was mapped Unpublished field notes from archives

 as percent of “proper use”

1939 to 1946 Line transects to estimate stubble height; Canfield 1942a and b, Culley’s unpublished field

 these were placed into stubble height classesa notes from archives

1947 to 1949 Same as above except line transects were located Parker and Glendening 1942b, unpublished field

 at several distances from permanent water notes from archives

1950 to 1984 Pace transects to estimate the percent of Roach 1951

 ungrazed plants

a

 Stubble height classes from Culley (1939) (unpublished document in SRER archives).

Class Stubble height Comments

1 1

/2 inch or less Very closely used

2 1

/2 to 1 inch Closely used

3 1 to 2 inches Light overuse

4 2 to 4 inches Generally conservative use

5 4 to 6 inches Moderate use

6 6 to 8 inches Light use

7 8 to 10+ inches Light to no use

8 Ungrazed
42 USDA Forest Service Proceedings RMRS-P-30. 2003

Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability ...

grazing provided yearlong use but applied “relatively light

stocking during the summer grazing season and heavier

stocking during fall, winter and spring months.” By regulating stocking in this manner, Canfield concluded, “both

summer and winter forage plants receive their just proportions of use.”

Continuous yearlong grazing, however, especially at heavy

stocking levels, was well known to alter native grass species

composition and reduce forage production on Southwestern

ranges (Canfield 1948; Martin 1972). This was especially

true near waters with long histories of heavy use. Reducing

stocking levels only partly solved this problem because

heavy use persisted near permanent water sources. Rotating access to water on the SRER somewhat altered the

pattern of heavy use if stocking rates were moderate and the

“closed period” included the summer growing season (Martin and Ward 1970).

Under yearlong grazing, proper stocking rates should

allow roughly 70 to 80 percent of the current year’s forage to

remain after summer use (Lister and Canfield 1934; Talbot

1937). These levels were not the norm on southern Arizona

ranges during the first half of the twentieth Century. Utilization surveys on the Santa Rita routinely reported average

use well in excess of 70 percent until the 1940s when levels

were reduced somewhat (SRER archives, unpublished documents). By this time, experience and empirical evidence

conspired to cause reductions in recommended use levels on

the SRER. Utilization levels of around 40 to 45 percent on

perennial grasses were a common recommendation by mid1950, however, surveys continued to document average use

of over 50 percent on the SRER (SRER archives, unpublished documents). While stocking rates had received considerable attention by mid-century, the effects of grazing at

different seasons had not yet been extensively studied in the

Southwest.

Data from studies presented at the 1927 Annual Ranger

Meeting (SRER archives, unpublished document) indicated

that researchers were considering various timings of grazing early in the history of the SRER. Small pasture divisions

were protected from grazing during various seasons, and

these were compared with “yearlong overgrazing” and “conservative grazing.” It is evident that stocking was to achieve

100-percent use of “average forage production” except under

conservative grazing where about 15 percent of the production was left ungrazed (85-percent utilization). Only under

conservative yearlong stocking, even at this high level of

utilization, did the “palatable forage grasses” make gains in

plant density. Thus, level of stocking rather than seasonal

rest was believed to be the primary factor preventing loss of

forage species.

In later studies, Reynolds (1956) demonstrated similar, if

not increased, recovery of cottontop on conservatively stocked

pastures grazed yearlong compared to summer-deferred

pastures. However, season of use continued to be investigated as a potential grazing management strategy. For example, Cable (1979) found that, over a 15 year period, dormant season grazing, even at high intensities (over 70 percent),

had no detrimental influence on Arizona cottontop.

The comparison of seasonal grazing with yearlong grazing

on a pasture scale began in earnest in July 1957 with the two

10-year studies, described fully by Martin and Cable (1974)

and Cable and Martin (1975). The grazing treatments in the

two studies were the same, November to April, May to

October, and yearlong, but stocking was much heavier as

described by Martin and Cable (table 2). The intent was to

stock the seasonally grazed pastures at the same rate as the

yearlong pastures, hence the number of animals were doubled

in the seasonal units. As has proved the norm in large-scale

grazing studies, weather was a dominant influence on vegetation responses. Additionally, initial plant community

differences (perennial grass basal cover) among pastures

persisted throughout the study. Although Cable and Martin

(1964) concluded “moderate utilization of the perennial

grasses combined with alternate-summer deferment of grazing resulted in marked range improvement,” and Reynolds

and Martin (1968) reported seasonal deferment benefits

were “evident in the preliminary results,” the 1974 analyses

stated that such deferment “had no apparent beneficial

effect,” and the 1975 paper stated “alternate-year summer

deferment did not improve perennial grass production.”

Seasonal grazing did not result in improved animal or

vegetation conditions when compared to yearlong grazing,

perhaps partly due to more concentrated use limiting diet

selection and somewhat higher utilization levels in the

seasonally grazed pastures. Calf weights reported by Martin

and Cable (1974) averaged somewhat higher from pastures

grazed yearlong (415 poounds versus 396 pounds) and were

significantly higher from the higher elevation pastures (446

pounds versus 365 pounds). These researchers continued to

ponder the importance of seasonal rest, however, and several important hypotheses came from this study.

Martin and Cable determined that the November to April

grazing treatment was not entirely a dormant season of

grazing, but included a critical period of spring growth

(February to April). Even though perennial semidesert

grasses produce little growth during that period, it is the

time when basal buds “break dormancy to initiate the culms

that produce forage the following summer” (Cable 1975;

Martin and Cable 1974). These researchers suspected that

spring grazing was detrimental to forage production in the

following summer, and this became the basis for further

clipping studies (Martin 1973a) and, eventually, the foundation for the Santa Rita Grazing System (Martin 1973b;

Martin and Severson 1988).

To more fully test this hypothesis, Martin (1973a) designed a series of small plot (20-ft square) grazing treatments to simulate 15 “rest-grazing schedules.” He accomplished these treatments during an 8-year study by rotating

a series of panels to exclude grazing during certain periods

at locations on “overgrazed range near permanent water”

(Martin and Ward 1976). Due to such a location, average

utilization was heavy, as high as 70 percent on plots that had

been grazed continuously for the preceding 12 months or

that had been rested in winter only. Of all the treatments

tested, March through October rest, two years in three,

resulted in greatest total perennial grass production. Grass

densities were also highest in these plots, but not significantly greater than those with other combinations of rest.

Several of these alternate year seasonal rest treatments

were compared in three different pastures in the Martin and

Ward (1976) study. Seasons of rest were spring (March

through June), summer (July through October), and winter

(November through February), and were applied in various

combinations using similar 20-ft-square exclosures as the
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Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

earlier study. Perennial grass production was the measure

of effectiveness and varied greatly among sites and years

during the 7-year study. This variability masked any effects

of the rest schedules on perennial grass production; however, March through October rest in alternate years was the

best of the six treatments at two of the three sites in the

experiment. This gave the researchers some hope that these

results supported the earlier study, but they also suggested

that perennial grass production might be too variable an

attribute to test trends in “short term grazing studies”

(Martin and Ward 1976).

From these studies and others, Martin (1973b, 1978b)

proposed the three-pasture grazing system that became

known as the Santa Rita Grazing System (table 4). The

system was tested experimentally on the SRER at a pasture

scale from 1972 to 1984 (Martin and Severson 1988). Study

treatments included both a continuous yearlong treatment

and the Santa Rita Grazing System, and were blocked by

elevation roughly corresponding to the foothill, mesa, and

transition units recognized by Canfield (1948) and Reynolds

(1954). Utilization and densities of perennial grasses and

canopy cover of shrubs were measured at two distances from

water. Standing crop estimates were also determined

each fall. Utilization was estimated by the ungrazed plant

method (Roach 1950) and averaged about 50 percent for

all treatments.

Plant densities and production varied in response to

precipitation and elevation each year, but did not show

measured positive responses to the grazing treatments. The

pasture level study failed to duplicate the results of the

previous small plot studies. Again, the researchers justified

this nonresponse by citing site-specific variability in overall

range conditions at the beginning of the study (higher

densities of perennial grasses than the earlier study), relatively low grazing intensity, and climatic variability. Undaunted, Clark continued to fully believe and was not hesitant to write that 2 consecutive years of March through

October rest should be included in semidesert grassland

grazing systems (Martin 1975a).

In the early 1980s, a short-duration grazing system was

briefly implemented, with a radial spoke fence design, where

pasture fences radiate from a common water source. The

demonstration never received the management attention

necessary and was soon abandoned as a project.

Data Contingencies and Research

Gaps _________________________

The Santa Rita researchers recognized there were limitations to their research imposed by the range itself.

System-level influences were manifested in the results from

most grazing studies on the SRER and continue to cloud the

interpretation of these studies today. Soils and precipitation

regimes were known to influence the potential for recovery

from overgrazing and the ability of the vegetation to withstand grazing, concepts that became known as resilience

and resistance. Researchers discovered early on that the

elevational position on the SRER was directly related to

precipitation and vegetation potential. Canfield (1948) and

Reynolds (1954) organized this gradient into three units,

the foothill unit (4,000 to 5,000 ft), the mesa unit (3,000 to

4,000 ft), and the transition unit (below 3,000 ft). Most

subsequent grazing studies used similar distinctions as

blocks in experimental designs.

The amount of precipitation received during a particular

study was often the overriding influence on vegetation

responses. Additionally, they learned that the plant community present at the beginning of a study also influenced the

effects of the grazing treatments imposed. The Martin and

Cable study (1974) began after the extremely dry seasons in

1956–1957, which undoubtedly influenced vegetation at the

beginning of the study and, later, the subsequent treatment

effects. Conservative stocking and seasonal grazing treatments were more likely to improve degraded plant communities, which were near water or in other areas of historically

heavy grazing, than those communities less impacted by

grazing. Species such as Rothrock grama and various threeawn grasses consistently increased in density and productivity in response to seasonal rest, while other grasses did

not. The current shift to Lehmann lovegrass as the dominant

grass in some pastures has no doubt changed potential

ecosystem responses to grazing. Such factors continue to

confound landscape-level grazing studies, even those designed as experiments with replicated pastures. Smaller

plot, controlled studies have become the standard for rangeland research. The value of large studies should not be

disregarded, however, and the SRER approach of combining

small plots and pasture-level treatments is relevant today.

There are four areas of grazing effects that were not

studied at the SRER and continue to be gaps in knowledge

that limit science-based management of Southwestern rangelands. These are (1) riparian grazing, (2) combined prescribed burning and grazing, (3) the impacts of grazing on

soils, and (4) grazing effects on endangered species. There is

little or no riparian vegetation on the SRER, hence there was

no opportunity to investigate this area. The impact of livestock grazing on endangered species has only recently

achieved recognition as an important research topic. The

SRER offers a particularly unique opportunity to investigate the influences of grazing on the Corypantha scherri var.

Table 4—Suggested grazing and rest schedules for the three-pasture Santa Rita grazing system (Martin 1973a).

Year 1 Year 2 Year 3

November to March to July to November to March to July to November to March to July to

February June October February June October February June October

Pasture 1 Rest Graze Graze Rest Rest Rest Graze Rest Rest

Pasture 2 Graze Rest Rest Rest Graze Graze Rest Rest Rest

Pasture 3 Rest Rest Rest Graze Rest Rest Rest Graze Graze
44 USDA Forest Service Proceedings RMRS-P-30. 2003

Ruyle Rangeland Livestock Production: Developing the Concept of Sustainability ...

robustinspina (Schott & Engelmenn) L. Benson (Pima pineapple cactus), listed as an endangered plant species.

Fire and grazing regimes were discussed for years, but

never actually applied to research designs due to logistic and

other practical reasons. In addition, the limited amount of

soils research is unusual. As described previously, the early

observers recognized that the native bunchgrasses formed

no sod, leaving the soil subject to trampling damage. Similarly, the presence of “washed soils” was recognized (Griffiths

1901). These conditions presumably resulted in reduced

recovery and productive capacities compared to intact or

undisturbed soils, but such research was not forthcoming.

Future Research Direction _______

Over 25 years ago, Martin (1975a) recommended shifting

research emphasis from livestock production to using livestock as a tool to manage the range for stated objectives. He

also recognized the emerging importance of open space and

recreational opportunities and resource use demands from

an increasingly urban population. These research shifts

have never really occurred, yet the need for such information

remains critical.

The past has certainly set the stage for future range

livestock grazing research on the SRER. Existing, long-term

data sets are available for careful analysis of grazing pressure gradients, including information from protected areas.

Large, pasture-scale grazing treatments should be continued, but with a more integrated approach to range livestock

production that considers vegetation and soil response,

ranch management requirements and economics, and the

role of ranching in planning and regulating urban growth.

Reductions in the number of treatments and herds to consolidate resources, a re-examination of stocking rates, as

well as the reinstitution of some of the traditional management practices should be considered, including adjusting

animal numbers each fall, estimating annual utilization,

and keeping a record of individual animal production. The

potential for producing and marketing natural beef should

also be investigated. In addition, landscape-level analyses to

address questions about the sustainability of range livestock

grazing in terms of nutrient flows, site potential, and watershed processes remain a priority.

Summary and Major

Contributions__________________

Research on the Santa Rita developed the concepts, methods, and tools to manage range livestock conservatively and

therefore sustainably. The studies conducted and experience gained on the SRER provided the philosophy and

working foundation for the Federal regulation of range

livestock management in the Southwest, especially by the

Forest Service. The research demonstrated that, if weather

conditions are at all favorable and mesquite overstory is not

a constraint, rangelands could recover from the effects of

overgrazing and even improve while being conservatively

grazed. Measurements of recovery included densities and

productivity of palatable, native perennial grasses. In addition to precipitation and site potential, heavy stocking rates

were identified as drivers of ecological range condition and

livestock performance.

Seasonal rest, while considered important, actually proved

to be of secondary value. However, spring through summer

rest, for two years out of three was a deferred grazing system

that was recommended and demonstrated, most convincingly in small plots, to improve overgrazed vegetation. Using

this strategy in larger pastures, the most improvement that

was measured was in species such as Rothrock grama and

three-awn grasses rather than such midgrasses as Arizona

cottontop and sideoats grama. Empirical observations, however, indicate that these plants also benefit from seasonal

rest.

Recommended stocking rates for semidesert grasslands

developed from SRER research were approximately 90 percent of average proper stocking based on 40-percent utilization, calculated from a running 10-year average forage

production. It is interesting that, based on utilization surveys in the SRER archives, these recommended use levels

never seemed to be achieved. Such conservative stocking

recommendations appear to be made in order to reduce

extremely heavy grazing in low forage production years and

allow the maintenance of a relatively stable base cow herd

over the long term. Of course, where Lehmann lovegrass

now dominates the herbaceous plant community, higher

stocking rates appear to be possible.

Utilization guidelines were shown to be just that, guidelines, and were never achieved every year. Many processes

combined to produce variability in utilization estimates.

Diet preference influenced degree of use on individual plant

species, and grazing pressure varied over time and space

resulting in uneven utilization patterns. Utilization levels

were consistently inversely proportional to forage production even when livestock numbers were reduced to compensate for years with low precipitation. To provide some uniformity to the concept, utilization was estimated after the

grazing season or in June on yearlong ranges, at several

distances from water, and averaged over species, pasture,

and year.

After grazing resumed in 1914, the SRER was never

completely destocked, even during times of drought or in

periods of drought recovery. In fact it was thought by some

that ranges recovered more quickly under conservative

grazing than when completely protected from grazing.

SRER researchers recognized drought as a stocking rate

problem and adjusted livestock numbers as necessary to

accommodate reduced forage and to protect against ecological deterioration.

In conclusion, the concepts, principles, and practices developed on the SRER continue to be applied by range managers today. Much more is now known, of course, about plant

physiological responses to grazing, animal behavior, and

vegetation dynamics. However, it still behooves current

range managers to integrate the lessons of the past with the

knowledge of today as they continue the quest for sustainable rangeland livestock production that began on the Santa

Rita Experimental Range.
USDA Forest Service Proceedings RMRS-P-30. 2003 45

Rangeland Livestock Production: Developing the Concept of Sustainability ... Ruyle

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48 USDA Forest Service Proceedings RMRS-P-30. 2003

Peter F. Ffolliott

Gerald J. Gottfried

William H. Kruse

Vegetation Management Practices:

Past and Present

Peter F. Ffolliott is Professor, School of Renewable Natural Resources, 325 Biological Sciences East, University of Arizona, Tucson, AZ 85721; e-mail:

ffolpete@ag.arizona.edu. Gerald J. Gottfried is Research Forester, Rocky Mountain Research Station, USDA Forest Service, Phoenix, AZ. William H. Kruse is

Range Scientist, Rocky Mountain Research Station, USDA Forest Service (retired), Flagstaff, AZ.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: Improving management practices have been at the core of most research conducted in

the semidesert grass-shrub vegetation on the Santa Rita Experimental Range. Much of this

research has been directed to sustaining forage resources through proper livestock grazing and

controlling the invasion of competing woody plants, primarily mesquite. Both research orientations require an understanding of the basic ecological requirements and dynamics of the plant

species on the Experimental Range. Cattle grazing system based on seasonal grazing and periodic

rest periods have been able to improve the production and diversity of native perennial grasses.

Several methods have been successful in controlling the occurrence of mesquite and improving

forage production, although there is a growing acknowledgment that mesquite has a place on the

landscape. Research emphasis on the Santa Rita Experimental Range in the future is likely to be

placed more on evaluating the effectiveness of ecosystem-based, multiple-use vegetation management practices that are ecologically sustainable and environmentally sound.

Keywords: semidesert rangelands, grass-shrub vegetation

Acknowledgments: The authors gratefully acknowledge the reviews of this paper by Warren P.

Clary, Project Leader, USDA Forest Service (retired), Boise, ID, and Alejandro Castellanos,

Professor, University of Sonora, Hermosillo, Sonora, Mexico.

Introduction ______________________________________________________

Semidesert grass-shrub vegetation is the characteristic plant cover of the Santa Rita Experimental Range. This vegetation

is similar to that occupying extensive acreage in the Southwestern United States, although its actual coverage is difficult to

quantify because of the historical and, to some extent, continuing invasion of woody vegetation onto adjacent grasslands. Semidesert grass-shrub vegetation is found between 3,000 and 5,000 ft (900 and 1,500 m) elevation within a strip 50 to 100 miles

(80 to 160 km) wide along the southern boundaries of Arizona, New Mexico, and western Texas (Martin 1975). The vegetation

below 3,000 ft (900 m) consists mainly of desert shrubs, while the vegetation above 5,000 ft (1,500 m) is chaparral, pinyonjuniper or oak woodlands, or (on occasion) grassland. Vegetation on the Santa Rita Experimental Range is largely a microcosm

of that found on semidesert grass-shrub rangelands throughout the Southwestern United States.

Forage components on Southwestern semidesert grass-shrub vegetation have supported a livestock industry in the

Southwest since 1850 (Herbel 1979; Martin 1975; McPherson 1997; Sayre 1999), while the small trees have historically been

cut by local people for firewood, poles, posts, and corral rails (Conner and others 1990; Ffolliott 1999; Martin 1986,). However,

the primary land-use concern on these rangelands is no longer to simply graze livestock or occasionally cut trees for local use.

The emphasis in the future will likely be placed more on evaluating the effectiveness of ecosystem-based, multiple-use

management practices that are ecologically sustainable and environmentally sound.

A review of past and present vegetation management practices on the Santa Rita Experimental Range and other semidesert

grass-shrub rangelands in the Southwestern United States is presented in this paper to show how the management emphasis

has changed through time and is likely to continue to change into the future. The literature forming the basis of this review

is not intended to be all inclusive, but rather it is representative of the historical knowledge base obtained on the Santa Rita

Experimental Range and other Southwestern semidesert grass-shrub rangelands.
USDA Forest Service Proceedings RMRS-P-30. 2003 49

Vegetation Management Practices: Past and Present Ffolliott, Gottfried, and Kruse

Vegetation Resources____________

The diversity of vegetation that is characteristic of semidesert grass-shrub rangelands is also found on the Santa

Rita Experimental Range (Humphrey 1953; Humphrey and

Mehrhoff 1958; Martin 1966, 1975, 1986a; Medina 1996;

Severson and Medina 1981). Herbaceous plants include a

variety of perennial grasses, forbs, and succulents. Annual

plants spring forth following rainfall events that are favorable to their germination. Woody vegetation on these rangelands is dominated by small trees and medium to large

shrubs that are often a detriment to sustaining vigorous

stands of forage plants but can have value in themselves.

Herbaceous Vegetation

The composition and relative abundance of perennial

grasses on the Santa Rita Experimental Range change with

elevation and, therefore, temperature regimes and precipitation amounts. Tall threeawns (Aristida hamulosa and A.

ternipes) are commonly found at all elevations. Santa Rita

threeawn (A. glabrata) and Rothrock grama (Bouteloua

rothrockii) are the major species in the middle and lower

elevations but are comparatively minor species above 4,000

ft (1,200 m). Other species of grama including black (B.

eriopoda), side oats (B. curtipendula), slender (B. filiformis),

sprucetop (B. chondrosioides), and hairy (B. hirsuta) comprise about two-thirds of the perennial grass stands at the

upper elevations. However, these latter species are comparatively scarce at the middle and lower elevations. Arizona cottontop (Trichachne californica) is a common grass

throughout all of the elevations on the Experimental Range.

Other species include, but are not limited to, tanglehead

(Heteropogon contortus), bullgrass (Muhlenbergia emersleyi)

and bush muhly (M. porteri), slim tridens (Tridens muticus)

and fluffgrass (T. pulchellus), and curlymesquite (Hilaria

belangeri).

Lehmann lovegrass (Eragrostis lehmanniana), an aggressive species that was introduced into the Southwestern

United States from South Africa in 1913, is the dominant

grass on about 40 percent of the Santa Rita Experimental

Range. This plant is especially well adapted to the climatic

patterns and edaphic conditions of southeastern Arizona

(Cable 1971; Cox and Roundy 1986; Elmi 1981; GinerMendoza 1986; Martin 1986a; Nascimento 1988). It thrives

at elevations where annual rainfall amounts vary from 10 to

15 inches (250 to 380 mm) and on sites with a dominance

of sandy to sandy-loam soils (Ruyle and Cox 1985). Factors that have contributed to the spread of Lehmann

lovegrass include fire, excessive livestock grazing, and

drought conditions.

Among the forbs commonly found on the Santa Rita

Experimental Range are alfileria (Erodium cicutarium),

pink penstemon (Penstemon parryi), lupine (Lupinus spp.),

bladderpod (Lesquerella gordonii), and goldpoppy (Eschscholtzia spp.). Succulents on the Experimental Range include

cholla (Opuntia fulgida, O. spinosior, and O. versicolor) and

prickly pear cactus (O. engelmannii).

Annual plants become most abundant on sites with light

to moderate densities of perennial grasses and where native

grasses are able to persist within a cover of Lehmann

lovegrass (Medina 1988). Spring annuals dominated largely

by a variety of legumes, crucifers, and borages are found in

years when the cool-season rainfall is high. The most common summer annual grasses are needle grama (B.

aristidoides) and six-week threeawn (A. adscensionis).

Woody Vegetation

Woody vegetation on the Santa Rita Experimental Range

and other semidesert grass-shrub rangelands is dominated

by stands of mesquite (Prosopis velutina). (While the taxonomy of Prosopis undergoes almost constant revision

[Burkart 1976; Ffolliott and Thames 1983; Martin 1986b;

Hocking 1993], it is not a purpose of this paper to clarify or

update the classification on Prosopis species.) Mesquite

occupies two general types of habitat in the Southwestern

region (Conner and others 1990; Martin 1980, 1986b). Tree

forms of mesquite tend to grow along riparian (streamside)

corridors, while shrub forms typically occupy dry upland

sites. Other frequently encountered woody species include

acacia (Acacia greggii and A. angustissima), mimosa (Mimosa biuncifera and M. dysocarpa), false mesquite

(Calliandra eriophylla), burroweed (Haplopappus tenuisectus),creosote bush (Larrea tridentata), and ocotillo (Fouquieria

splendens). Scattered paloverde (Cercidium microphyllum)

trees are found along drainages.

More complete listings of the herbaceous and woody plant

species on the Santa Rita Experimental Range and other

semidesert grass-shrub rangelands of the Southwestern

region are found in Little (1962), Martin (1966, 1975),

Kearney and Peebles (1969), Eyre (1980), Severson and

Medina (1981), and Medina (1996).

Vegetation Site Complexes

Major vegetation site complexes on the Santa Rita Experimental Range are listed in table 1. The Prosopis-OpuntiaHaplopappus complex is the most extensive. It is known that

changes in vegetative structure have occurred since the

Experimental Range was established (Cable 1976; Humphrey

and Mehrhoff 1958; Martin 1970, 1975, 1986a; Martin and

Turner 1977; Medina 1996). For example, mesquite has

invaded nearly 30,000 acres (12,150 ha) of previously shrubfree grassland on the Experimental Range in the past 100

years. However, while the information presented in table 1

represents a “snapshot” of the conditions 30 years ago, it is

assumed to reflect the present situation largely because of

the curtailment in large-scale mesquite removals.

Management of Herbaceous

Vegetation _____________________

Depending on the inherent site conditions and prevailing

rainfall patterns, annual herbage production (standing biomass) on semidesert grass-shrub rangelands, such as found

on the Santa Rita Experimental Range can vary from less

than 1,000 to over 1,500 pounds per acre (1,125 to over 1,675

kg per ha). However, the herbage production on a site can be

reduced to significantly lesser amounts by overstories of

woody plants that compete with the herbage for the often
50 USDA Forest Service Proceedings RMRS-P-30. 2003

Ffolliott, Gottfried, and Kruse Vegetation Management Practices: Past and Present

limiting soil water and essential nutrients. Competitive

relationships between herbaceous and woody vegetation are

generally characteristics of forest, woodland, and shrubland

ecosystems (Bartlett and Betters 1983; Ffolliott and Clary

1982). That is, as one form of vegetation (woody plants)

increases in its occurrence, the other form of vegetation

(herbage) decreases. Such competitive relationships occur

on the Santa Rita Experimental Range and other semidesert

grass-shrub rangelands (Cable 1969; Cable and Martin

1964; Kincaid and others 1959; Martin 1963, 1970; Martin

and Cable 1962; Parker and Martin 1952; Patten 1978;

Reynolds and Tschirley 1963, 1975; Tiedemann and

Klemmedson 1971, 1977). Knowledge of these relationships

is necessary in estimating the amount of forage that might

be available for livestock production on rangelands with

woody vegetation.

Proper management of herbaceous (forage) vegetation is a

crucial factor for sustaining livestock production on semidesert grass-shrub rangelands, which is often a primary

management goal in the Southwestern region. Among the

issues that a manager must confront in meeting this goal are

selecting the type of livestock that are suitable to the conditions encountered, designating the proper stocking rates for

the rangeland, and implementing the livestock grazing

systems that will sustain the forage resources at the desired

level of production while maintaining a “healthy” rangeland

condition. Forage management practices that are often

implemented to sustain or, where feasible, increase this

limiting resource include the control of competing woody

vegetation, elimination of undesirable herbaceous plants,

and seeding of selected forage species. Other management

activities that can lead to sustaining or enhancing forage

resources (but will not be addressed in this paper) are

fencing to control livestock movements, constructing stock

tanks and developing other water sources, and placing salt

or salt-meal blocks at strategic locations to attain better

distributions of livestock on the rangeland (Heitschmidt and

Stuth 1991; Holechek and others 2001; Jemison and Raish

2000; Stoddart and others 1975; Vallentine 2001).

Sustaining Forage Resources

Through Livestock Grazing _______

Cattle are better suited to graze on semidesert grassshrub rangelands than sheep or goats because they require

less managerial effort (herding) than other kinds of livestock, and they compete less directly with indigenous wildlife for forage resources (Bohning and Martin 1956; Culley

1947; Gamougoun 1987; Herbel 1979; Martin 1966, 1975).

Therefore, cattle have been and continue to be the primary

type of livestock that graze on the Santa Rita Experimental

Range.

A “rule of thumb” for specifying the stocking rate of cattle

for a semidesert grass-shrub rangeland to maintain or,

where possible, improve the rangeland condition is the

number of cattle that will utilize about 40 percent of the

perennial grasses produced in an “average” year. This stocking rate varies with the rangeland condition and must be

adjusted up or down depending on the trend in rangeland

condition. The estimated average yearlong stocking rates for

cattle on the Santa Rita Experimental Range are shown in

table 2. According to Martin (1975), the stocking rates that

are presented in this table also apply to the entire spectrum

of semidesert grass-shrub rangelands in the Southwestern

region and the rangeland conditions encountered.

Yearlong grazing has historically been the most common

grazing system on semidesert grass-shrub rangelands. Unfortunately, this grazing system can result in “excessive”

forage consumption in areas where cattle concentrate, and

Table 1—Major vegetation-site complexes on the Santa Rita Experimental Rangea.

Dominant shrubs Annual rainfall Elevation Major grass genera Major soil groups Slope

inches feet percent

None (Prosopis has been killed) 15 to 17 4,100 to 4,500 Bouteloua, Whitehouse 5 to 15

Aristida, Caralampi 10 to 40

Trichachne Comoro 0 to 10

Prosopis, 10 to 13 2,900 to 3,500 Aristida, Anthony 0 to 5

Haplopappus, Bouteloua, Sonoita 1 to 8

Opuntia Trichachne

14 to 17 3,500 to 4,200 Bouteloua, Comoro 0 to 3

Aristida, Sonoita 1 to 8

Trichachne, Whitehouse 10 to 35

Heteropogon

Fouquieria, 12 to 15 3,400 to 3,800 Bouteloua, Whitehouse 5 to 10

Calliandra Aristida,

Heteropogon

Larrea 12 3,100 to 3,300 Muhlenbergia, Anthony 0 to 5

Tridens

Acacia, 12 to 14 3,100 to 3,800 Bouteloua, Bernadina 2 to 30

Opuntia, Hilaria, Hathaway 2 to 30

Fouquieria Aristida,

Trindens

a

Source: Martin and Reynolds (1973).
USDA Forest Service Proceedings RMRS-P-30. 2003 51

Vegetation Management Practices: Past and Present Ffolliott, Gottfried, and Kruse

“wasted” forage resources on sites where cattle seldom

graze (Cable and Martin 1975; Herbel 1979; Martin 1972,

1975; Martin and Ward 1976; Reynolds 1959). Yearlong

grazing can also lead to the inequitable use of forage species

among the available forage species, with “favorite species”

grazed more closely and more often than those species that

are less palatable. Because of these and other drawbacks,

the sustainability of the forage resources is difficult to attain

on many semidesert, grass-shrub rangelands when yearlong

grazing is practiced. As a consequence, several alternatives

to yearlong grazing have been proposed, tested, and implemented in attempting to better sustain the forage resources

on these rangelands. These alternatives include seasonal

(spring) grazing systems, rest-rotational systems, high-intensity short-duration grazing systems, and variations and

combinations of these systems.

The so-called “Santa Rita three-pasture” system of cattle

grazing has evolved on the Experimental Range. Each unit

of the three-pasture system is rested from March through

October (spring-summer) in 2 out of 3 years (Martin 1973,

1975, 1978; Martin and Severson 1988; Rivers and Martin

1980). Winter grazing (November to February) takes place

between two successive March-to-October rest periods. Trampling by cattle in the winter helps to plant seeds in the soil,

and grazing of the older forage allows seedlings of intolerant

forage species a better chance of becoming established. The

system’s grazing schedule provides 12 months of rest immediately before each period of spring-summer grazing and, as

a consequence, the system is planned to reduce the intensity

of grazing and regrazing of “favorite forage plants” in the

spring. The Santa Rita three-pasture system is more flexible

in its implementation and management than other grazing

systems tested on the Experimental Range because departures from the pre-established livestock grazing schedule

are permitted if it becomes necessary to sustain the forage

resource. Cattle are normally moved twice (November 1 and

March 1), although they can be moved to the next pasture

ahead of the scheduled time if the forage resource on the

grazed pasture is inadequate. Therefore, a forage shortage

tends to speed up the grazing cycle, although the “normal

schedule” is resumed as soon as possible thereafter. A forage

surplus can allow an extra rest period to be scheduled.

A comprehensive paper on grazing systems and livestock

production on the Santa Rita Experimental Range and other

semidesert grass-shrub rangelands in the Southwestern

United States is found elsewhere in these proceedings.

Control of Competing Woody Vegetation

Several factors have been identified by researchers as

being responsible for the invasion of mesquite and other

unwanted woody vegetation onto the Santa Rita Experimental Range and other semidesert grass-shrub rangelands in

the past 100 years (Fisher and others 1973; Herbel 1979;

Martin 1975; McPherson 1997). The consensus of these

researchers is that grazing cattle have likely been the most

dominant of these factors. Grazing cattle can spread the

seeds of these woody plants by consuming them with many

seeds, and then passing them through their digestive tract

and depositing them on the ground as they graze. Cattle

have further contributed to this invasion by “weakening”

stands of native grasses by their past overgrazing patterns,

which in turn fostered the spread of woody vegetation.

Excessive overgrazing practices of the past also contributed

to the invasion of woody plants by reducing the buildup of

fuels necessary for the occurrence of rangeland fires that

helped to control this invasion.

Semidesert grass-shrub rangelands infested with mesquite and other woody plants can often be restored to a

comparatively high level of forage productivity if the competing woody overstory is removed. Among the methods that

have been tested and, on occasional, operationally implemented for this purpose are controlled burning treatments

(Cable 1967; Reynolds and Bohning 1956); applications of

herbicides (Cable 1971, 1972b, 1976; Cable and Martin

1975; Cable and Tschirley 1961; Martin 1968; Martin and

Cable 1974); hand grubbing, root plowing, cabling or chaining, or other mechanical treatments (Martin 1975; Reynolds

and Tschirley 1963); and varying applications of fire, herbicides, and mechanical control methods in combination (Martin 1975; Martin and others 1974; Medina 1996). The environmental concerns of the public and regulations of rangeland

management agencies are restricting or, in some case, prohibiting the use of some of these control methods, especially

those involving applications of herbicides.

Followup treatments have often been necessary with

some of these control methods to sustain the observed

increase in production of forage vegetation. For example, the

removal of mesquite trees with a power saw with control of

post-treatment sprouting by handsawing has recently been

attempted with some success (Pease and others 2000).

Table 2—Estimated average yearlong stocking rates of cattle by rangeland condition class for the Santa Rita Experimental Range and other

semidesert grass-shrub rangelands in the Southwestern Regiona

.

Rangeland condition class

Elevation Precipitation Very poor Poor to fair Good to excellent

animals acres per animals acres per animals acres per

feet inches per mi2 animal per mi2 animal per mi2 animal

4,000 to 5,000 16+ <12 >50 15 to 18 35 to 45 28 to 25 25 to 35

3,300 to 4,000 12 to 16 <6 >100 6 to 12 50 to 100 12 to 16 40 to 50

<3,300 <12 <4 >160 4 to 6 100 to 160 6 to 10 60 to 100

a

Source: Reynolds and Martin (1968).
52 USDA Forest Service Proceedings RMRS-P-30. 2003

Ffolliott, Gottfried, and Kruse Vegetation Management Practices: Past and Present

Elimination of Undesirable Herbaceous

Plants

There have been a few “exploratory investigations” of

methods that can lead to the elimination of undesirable

(noxious) herbaceous plants to favor the establishment and

increase the production of “more favored” forage plants.

Artificial shade has been shown to favor the development of

Arizona cottontop, bush muhly, plains bristlegrass (Setaria

macrostachya), and other forage species that are adapted to

shade (Tiedemann and others 1971). Limited tests have

indicated that pre-emergence winter applications of herbicides (dicamba, glyphosate, and picloram) to eliminate undesirable annual plants are largely ineffective. On the other

hand, summer herbicidal treatments (atrazine, dicamba,

and tebuthiuron) can be effective in eliminating some species of competing annuals (Al-Mashhdany 1978). The removal of competing herbaceous plants by clipping their

previous summer’s biomass has resulted in increased production of sideoats grama (de Andrade 1979). However, most

of the methods that might eliminate undesirable or competing herbaceous plants have not been applied on a large-scale

basis because of economic and environmental considerations.

Seeding of Forage Species

Forage production has been improved on the Santa Rita

Experimental Range by the seeding of selected forage species, with the seeding of perennial grasses preferred to

seeding of other plants in most instances. The results of

early, often small-scale investigations of seeding experiments were summarized by Glendening (1937a,b,c, 1939a,b,

1942) and other researchers. Later studies considered the

respective roles of site quality, rainfall amount and timing,

and other factors that might affect seeding success in more

detail (Anderson and others 1957; Medina 1996). Level sites

with deep, fertile, medium-textured soils that are able to

maintain moisture levels conducive to plant survival have

been determined to be the best candidates for seeding. Other

research efforts examined the relative successes of alternative seeding methods (Cox and Martin-R 1984; Cox and

others 1986), varying site preparation techniques (Slayback

and Cable 1970), and applications of fertilizers to alleviate

nutrient deficiencies (Holt and Wilson 1961; Martin 1975).

It has been generally concluded that successful seeding of

forage species requires continual control of the competing

vegetation and that cattle grazing be closely controlled or

excluded from the seeded rangeland.

A more detailed paper on seeding techniques and their

comparative successes and other revegetation practices that

have been tested on the Santa Rita Experimental Range to

improve forage production is presented elsewhere in these

proceedings.

Impacts of Fire

The historical impact of fire on the vegetation of semidesert grass-shrub rangelands is unclear. Early photographs

of the Santa Rita Experimental Range show extensive grassland communities free of trees and shrubs that are currently

dominated by woody overstories with perennial grasses and

other herbaceous plants in the understories. According to

researchers, this change has likely come about because of a

lack of naturally occurring wildfire to burn freely in the more

recent years. Wright (1980, 1990) and others believe that

occasional fires in combination with cycles of drought played

a significant role in controlling the establishment of small

trees and shrubs and, therefore, kept the rangelands as

predominately grassland ecosystems. This situation changed

with enforcement of the fire suppression policies established

by the Southwestern Region’s management agencies in the

1900s. The wildfire frequencies of 5 to 10 years that were

commonly encountered before 1900 have lengthened to 25

years and longer (Kaib and others 1999; Swetnam and

Baisan 1996), with this change attributed largely to the

implementation of these fire suppression policies and changes

in land-use practices in the region.

Much of the controlled burning that has occurred on the

Santa Rita Experimental Range since its establishment had

been prescribed to kill or control the woody vegetation that

was competing with forage vegetation for the limited soil

moisture available for plant growth. Both early-season and

late-season burning treatments have been tested for this

purpose with varying results. Small trees and shrubs appear

to be susceptible to early-season burning. Herbaceous species such as Lehmann lovegrass and Santa Rita threeawn

seem to survive early-season burning very well; Arizona

cottontop, Rothrock grama, and tanglehead survives intermediately well; and black grama and tall threeawns are

easily damaged by fire (Cable 1965, 1967, 1972a; Glendening

and Paulsen 1955; Martin, 1975; Reynolds and Bohning

1956; White 1969). Late-season burning has also resulted in

the killing of smaller mesquite trees, many other woody

plant species, and cacti. Lehmann lovegrass often eventually increases following a late-season fire with most of the

other perennial grass species not greatly affected (Humphrey

and Everson 1951; Martin 1983; Humphrey 1963, 1969).

The “immediate effects” of prescribed burning treatments

on herbaceous (forage) vegetation of semidesert grass-shrub

rangelands can be relatively short lived. The postfire status

of perennial grasses often lasts 1 or 2 years, while small trees

and shrubs might be easily topkilled by burning but come

back quickly unless they are also rootkilled by the fire (Cable

1967; Cave and Patten 1984; Martin 1975; McLaughlin and

Bowers 1982; Robinett 1994; Robinett and Barker 1996;

Rogers and Vint 1987; Ruyle and others 1988; Sumrall and

others 1990). Most burning treatments favor plant species

that can survive the fire or quickly reproduce themselves

from seed or sprouts after the fire. Selective prescribed

burning treatments at specified intensities and suitable

intervals that are scheduled in combination with other

rangeland improvement methods are generally necessary to

achieve the desired results (Wright 1980, 1990).

The effects of fire on the vegetation of semidesert grassshrub rangelands are species specific, season specific, and

site specific. Many fire-adapted species, both herbaceous

and woody, have achieved dominance on these rangelands

because of mechanisms that enable them to survive burning

(table 3). However, the traits that might enhance a plant’s

success for survival in the presence of fire can also enhance

the plant’s success in the presence of other stressful environmental factors (McPherson 1995). Therefore, caution must

be exercised in interpreting the stimulus for these adaptive
USDA Forest Service Proceedings RMRS-P-30. 2003 53

Vegetation Management Practices: Past and Present Ffolliott, Gottfried, and Kruse

traits. Plant species are usually most susceptible to fire

damage when they are actively growing and tolerant of fire

when they are dormant.

Management of Woody

Vegetation _____________________

This discussion centers largely on the management (or

lack thereof) of mesquite trees and shrubs because of the

dominance of this species in the woody overstory on the

Santa Rita Experiment Range. Mesquite is a plant of often

conflicting values. Mesquite is often associated with nitrogen-fixing Rhizobia bacteria, which results in higher nitrogen levels in the soil beneath the tree canopies (Geesing and

others 2000; Wilson and others 2001). It has been and

continues to be a source of wood, chemicals and, on occasion,

feed for ruminants. It also provides shade for people and

their livestock on sites where there is little other shade

available. But, as already mentioned in this paper, many

ranchers view mesquite as a threat to livestock production

because of its aggressive spreading onto otherwise productive semidesert grass-shrub rangelands (Glendening 1952;

Herbel 1979; Martin 1975, 1986a; McPherson 1997; Parker

and Martin 1952; Tschirley 1959). In spite of the efforts

made to control this spread, the invasion of mesquite remains a problem of significant proportions on some rangelands. Compounding this problem is the need to also accommodate other benefits of semidesert grass-shrub rangelands

in the Southwestern Region, including watershed protection, wildlife habitats, and recreation, in planning for mesquite control or harvesting activities.

Stand, Stocking, and Growth

Characteristics

Mesquite trees up to diameters of 12 to 30 inches (30 to 76

cm) and heights of 20 to 50 ft (6 to 15 m) can form nearly pure

even- or uneven-aged stands in habitats of favorable soil

moisture conditions. Although mesquite is designated a

“forest type” by the Society of American Foresters (Martin

1980), per-acre values of stand, stocking, and growth characteristics that are commonly used to characterize a forest or

woodland type have little meaning because of the high

variability in these characteristics in stands of mesquite

trees. Investigators in one study on the Santa Rita Experimental Range reported an average of about 85 mesquite

trees per acre (about 200 mesquite per ha), but only about 60

percent of the sample plots in the study were stocked with

mesquite trees (DeBano and others 1996).

Most of the volume of mesquite trees is contained in the

large and mostly scattered single-stem trees along drainages, with less volume in the smaller mesquite trees and

shrubs occupying the upland sites. Growth of mesquite trees

is slow, with annual growth rates averaging less than 0.5

percent of the standing volume in most stands (Chojnacky

1991; Ffolliott 1999). Assuming that the dominant woody

plants are mesquite trees, and using this species as a “proxy”

for all of the trees growing on a site, the annual growth rate

of the assemblage of trees found on semidesert grass-shrub

rangelands can vary from less than 0.5 to 1.5 ft3 per acre

(0.35 to 1 m3 per ha). Natural mortality of these trees prior

to their decadence is also comparatively low.

Wood Production

The wood of mesquite trees has been historically used for

a variety of purposes by people of the Southwest. Many of

these uses originated with the American Indian, passed onto

the Mexican, and then the American pioneers from the

Eastern United States. Exploring the potentials of mesquite

trees as a wood source for future uses continue. Mesquite

wood inherently has a high calorific value (Ffolliott 1999;

Hocking 1993; National Academy of Science 1980), making

it a valuable firewood resource. It also makes excellent

charcoal. Wood of mesquite is physically strong and durable

and, as a consequence, has been and continues to be utilized

locally for poles, posts, and corral rails (Ffolliott 1999).

Mesquite wood is hard and has a beauty of grain and color

that also makes it suitable for processing into furniture,

parquet flooring, and miscellaneous novelties.

Efficiently harvesting mesquite trees is one of the main

problems that has limited its more widespread use for

timber, firewood, and chemical products. The type of harvesting equipment that is available for felling, grappling,

and hauling larger trees of more “commercial value” is not

Table 3—Mechanism of plants at different life stages that enable them to survive firea.

Life stage General response Mechanisms

Seeds Avoidance Burial

Resistance Insulative seed coat; protective tissue around fruit

Stimulus Increased germination; mortality of established neighbors

Juveniles Avoidance Rapid growth to resistance (protected) size

Resistance Aboveground buds protected by insulative plant tissue; belowground buds protected by soil

Stimulus Rapid growth of resprouts

Adults Avoidance Life cycle shorter than fire-return interval; flowing and fruiting phenology out of phase with

 fire season; suppression of understory fine fuel production

Resistance Thick, platy, corky, fissured bark; aboveground buds protected by insulative plant tissue;

 belowground buds protected by soil

Stimulus Rapid growth of resprouts; fire-obligate flowering; increase flowering (?)

a

Source: Steuter and McPherson (1995).
54 USDA Forest Service Proceedings RMRS-P-30. 2003

Ffolliott, Gottfried, and Kruse Vegetation Management Practices: Past and Present

always economically or environmentally suitable for harvesting the relatively small and characteristically multi- and

crooked-stemmed mesquite trees. Nevertheless, there are a

few small wood processing industries in the Southwestern

United States that are dependent on harvesting mesquite

trees as a primary wood source in their operations.

Management Practices

Management of mesquite trees for sustainable wood production has not been a main focus of the past or present

management activities on the Santa Rita Experimental

Range or other semidesert grass-shrub rangelands in the

Southwestern Region. However, mesquite trees continue to

gain attention for crafting woodworking and a product for

grilling gourmet food, and, therefore, could represent a

valuable resource in the future. As a consequence, there is a

need to better “manage” rather than “mine” the mesquite

resources in the region. Appropriate management guidelines for this purpose have been generally lacking in the

past, although this situation is changing.

More accurate estimates of the volume of mesquite trees

that are potentially available for wood products are being

obtained (Andrews 1988; Chojnacky 1988; O’Brien 2002) to

provide a better basis to prescribe management practices

and, where appropriate, harvesting schedules to balance

volume removals and growing-stock levels. Whole-stand

growth and volume simulation (prediction) models depicting

the difference of stand volumes at two selected points in time

to estimate growth are also available (Chojnacky 1991).

While regeneration and other ingrowth components of mesquite stands are still largely missing in these models, simulations of mesquite growth rates for alternative management practices can be made for selected 10-year planning

periods. Culmination of mean (average) annual growth

increments of mesquite trees on the Santa Rita Experimental Range suggests a “biological” rotation age of about 45 to

50 years. However, the profits (returns less costs) obtained

from harvesting mesquite trees for primary wood products

are likely to be maximized earlier.

Silvicultural Prescriptions

Silvicultural prescriptions for mesquite stands are incomplete. But, because of its ability to regrow (sprout) following

cutting, silvicultural treatments based on coppicing (which

is the regeneration of stump sprouts or root suckers) might

be feasible on sites supporting mesquite stands such as those

on the Santa Rita Experimental Range. Therefore, the

reproduction of mesquite trees based on vegetative strategies could be possible (Ffolliott 1999; Ffolliott and others

1995). Artificial propagation depending on seeding or seedling establishment is more difficult and probably not economically or environmentally feasible for mesquite on most

semidesert grass-shrub rangelands.

Felker (1998) recommended that mesquite trees on Southwestern rangelands be managed for the production of high

quality wood within a silvopastorial (trees and livestock)

agroforestry system that retains a number of selected crop

trees within a pasture. A spacing of 30 to 35 ft (10 to 10.5 m)

between the crop trees should result in optimal yields

(Felker and others 1990).

Impacts of Fire

Fire has played a historical role in determining the status

of mesquite trees and shrubs on the Santa Rita Experimental Range and other semidesert grass-shrub rangelands

(Blydenstein 1957; Cable 1965; McLaughlin and Bowers

1982; McPherson 1997; Reynolds and Bohning 1956; Rogers

and Steele 1980; Womack 2000; Wright and others 1976).

The mostly lightning-ignited and often uncontrolled fire of

the past helped to slow the invasion of mesquite onto semidesert, grass-shrub rangelands. However, the slowing of

mesquite invasion by occurrences of wildfire largely ended

with the initiation of aggressive fire suppression policies by

management agencies in the early 1900s. Many of these

policies remain in effect, although there is increasing interest by managers, ranchers, and other stakeholders in reintroducing fire into Southwestern ecosystems.

Mesquite can also be adapted to fire depending on the

fire’s intensity. For example, it was found that an illegally

set fire (of unknown burning intensity) on the Santa Rita

Experimental Range only killed 30 percent of the mature

mesquite trees and reduced residual stocking by only 10

percent because over 70 percent of the trees initially damaged by the fire resprouted by 18 months after the fire

(DeBano and others 1996).

Prescribed burning treatments that are planned to be low

in intensity and limited in extent are rarely successful in

effectively controlling the establishment of dense stands of

mesquite on semidesert grass-shrub rangelands because of

the frequent lack of sufficient fuel loads to carry the fire

(Ffolliott 1999; Martin 1973, 1975). Furthermore, a fire that

is “hot” enough to kill mesquite is likely to also kill the

understory grasses and other forage species.

Other Woody Species

The use of other tree species on the Santa Rita Experimental

Range and other semidesert grass-shrub rangelands for

wood production has not often been a planned management

activity. One occasional exception to this situation has been

when the trees have been mechanically uprooted or killed by

herbicides in conversion treatments to improve forage production and are then “salvaged” for firewood by local people

(Ffolliott and others 1979, 1980).

Vegetation Management for Other

Purposes ______________________

The vegetation on the Santa Rita Experimental Range

and other semidesert grass-shrub rangelands in the

Southwestern region has values other than livestock forage

or wood production (Ffolliott 1999; Germano and others

1983; Martin 1986b; McPherson 1997). This vegetation

furnishes needed food and protective cover for a variety of

mammals, avifauna, and herpetofauna. Many of these wildlife species are indigenous to semidesert grass-shrub rangelands, others are transitory, and some are threatened, endangered, or sensitive.

Ethnobotanists are continually locating indigenous plant

species that had been used by historic peoples, which are

then studied, developed, and when they have proven value,
USDA Forest Service Proceedings RMRS-P-30. 2003 55

Vegetation Management Practices: Past and Present Ffolliott, Gottfried, and Kruse

incorporated into “modern” food and fiber products of value

to people. Organic agriculture enterprises often develop

with these native plants furnishing a basis.

Overland flows of surface runoff, when they occur, are

lower in velocity and, therefore, are less erosive when these

rangelands have a “good protective cover” of perennial grasses

and other herbaceous plants than on rangelands with a

sparse vegetative cover. As a result, maintaining a protective cover of vegetation helps to mitigate the losses of soil to

the erosive actions of water and wind on sites susceptible to

these losses. Therefore, good rangeland management is also

good watershed management.

Semi-desert grass-shrub rangelands are important to

hunters, hikers, and birdwatchers. They possess unique

landscapes of vegetation and topography that appeal to local

residents and visitors alike.

Summary ______________________

Southwestern semidesert grass-shrub rangeland vegetation has historically supported a livestock industry and been

a source of limited wood for a variety of mostly local uses.

However, the review of past and present vegetation management practices tested on the Santa Rita Experimental Range

and implemented on other semidesert grass-shrub rangelands presented in this paper suggests that the diversity of

vegetation on these rangelands has values other than only

forage or wood production. This vegetation furnishes food

and protective cover for a variety of desert-dwelling wildlife

species; provides a protective cover to mitigate the losses of

soil resources; and is a valuable backdrop to hikers, campers,

and other recreationists. Future management emphasis for

this vegetation, therefore, is likely to be placed more on

evaluating the effectiveness of ecosystem-based, multipleuse management practices that are ecologically sustainable

and environmentally sound. A presentation on the future of

the Santa Rita Experimental Range and other semidesert

grass-shrub rangelands in the Southwestern United States

is found elsewhere in these proceedings.

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USDA Forest Service Proceedings RMRS-P-30. 2003 59

Paul R. Krausman

Michael L. Morrison

Wildlife Ecology and Management, Santa

Rita Experimental Range (1903 to 2002)

Paul R. Krausman is Professor and Research Scientist of Wildlife and Fisheries Science in the School of Renewable Natural Resources, University of Arizona,

Tucson. He also serves as Associate Director of Arizona’s Agricultural Experiment Station, and Adjunct Professor at Texas Tech University, Lubbock. He has

worked with large mammals in arid environments related to habitat ecology, restoration, and mitigation throughout the Southwest, and in Asia and Africa.

He is also heavily involved in wildlife education and administration and is the current editor of Wildlife Monographs. Paul completed a B.S. degree in zoology

at Ohio State University, an M.S. degree in wildlife science at New Mexico State University, and a Ph.D. degree in wildlife science at the University of Idaho.

Michael L. Morrison holds affiliated positions with the Desert Research Institute, Reno, NV, and the University of California. His interests include wildlife

ecology, habitat restoration, and environmental education. He received his B.S. degree in zoology from Northern Arizona University, an M.S. degree in wildlife

from Texas A & M University, and a Ph.D. degree in wildlife from Oregon State University.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

The Santa Rita Experimental Range (SRER) was established in 1903 as a natural laboratory to better understand arid

rangelands. It is the oldest research area maintained by the USDA Forest Service. Although it was established as a research

site for range improvement in the Southwestern United States, only limited research has been directed toward wildlife. The

history of SRER, location, and mission are outlined by Medina (1996). The purpose of our paper is to summarize the work that

has been conducted at SRER on wild vertebrates, indicate the role those studies have on a better understanding of wildlife

ecology and management, and make recommendations for the future.

We obtained information from the University of Arizona’s digital archive (ag.arizona.edu/SRER), Medina’s bibliography

(1996), and literature searches conducted at the Science Library, University of Arizona. Most of the archival data supported

the published material and was not referenced again.

Although the SRER was established in 1903, it was nearly 2 decades before the first manuscript related to wildlife was

published (Vorhies and Taylor 1922). In the subsequent 5 decades there were approximately 10 publications per decade. In

the eighth decade of SRER (1973 to 1982), the number of publications peaked at 25. Since 1983, only five publications have

been produced and more than 5 are in press or in preparation. We are unaware of ongoing research on wildlife at SRER.

Although wildlife research has been limited (about 0.8 publications per year) at SRER over the past 100 years, much of the

work published are landmark studies that created a framework for future studies, were classical works that are still used as

Abstract: The Santa Rita Experimental Range (SRER), established in 1903, is a natural

laboratory used to better understand desert grasslands. We reviewed the literature to summarize

studies that have been conducted on wildlife at SRER from 1903 to 2002 and to provide

recommendations on expanding contemporary research at SRER. Research related to wild

vertebrates has been limited to a few studies of reptiles, avifauna, and mammals. Mammalian

studies were dominated by rodent research. Peer-reviewed publications dominated the references

(n = 45), followed by technical bulletins (n = 12), theses (n = 9) and dissertations (n = 9), conference

proceedings (n= 3), reports (n= 3), and other (n= 3). Although research on wildlife has been limited

(about 0.8 publications per year) from 1903 to 2002, several works were landmark studies that led

the way for future work (for example, water requirement studies, life history studies of small

mammals, studies of coyotes, and disease studies). There has not been a concentrated effort to

continue wildlife research at SRER, and since 1983, only five manuscripts have been published.

We recommend that land managers and administrators initiate inventory and monitoring of all

vertebrates on SRER to gather new knowledge, to quantify abundance trends, and to assist with

resource research and management.

Acknowledgments: Y. Petryszyn and J. A. Bissonette reviewed this manuscript. Funding to

conduct the review was provided by the School of Renewable Natural Resources and the Arizona

Agricultural Experiment Station, University of Arizona, Tucson.
60 USDA Forest Service Proceedings RMRS-P-30. 2003

Krausman and Morrison Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002)

reference sources, provided data that are applicable to

wildlife in arid regions worldwide, or were part of larger

studies to examine disease in desert mammals. Each of these

appeared to be initiated by individuals who were aware of

the SRER instead of any unified effort by SRER administrators to direct wildlife research. For example, the early life

history studies were conducted by U.S. Biological Survey

biologists; the water-balance work, most coyote and rodent

studies, and disease studies were directed by scientists

affiliated with universities. Because of the location of SRER

to the University of Arizona, it would be valuable to begin a

research program with more direction in the next 100 years

to maximize our ability to learn and provide more and better

information related to how wildlife influences grasslands

grazed by livestock and vice versa. The wildlife research

conducted over the past 100 years has been limited to a few

studies of reptiles, avifauna, and mammals (dominated by

rodents). Peer-reviewed publications dominated the references (n = 45), followed by technical bulletins (n = 12), theses

(n = 9), dissertations (n = 9), conference proceedings (n = 3),

reports (n= 3), and other (references in books, popularpapers,

and mimeographs) (n = 3). In addition, projects were conducted by mammalogy students from the University of

Arizona as part of class requirements (Mammal Museum,

University of Arizona, Tucson). The wildlife research is

categorized as related to reptiles, avifauna, and mammals.

Reptiles ______________________

Reptiles received the least amount of attention by ecologists at SRER. A distribution of rattlesnakes was based on

40 records of diamondbacks (Crotalus atrox Baird and

Girard), six records of tiger rattlesnakes (C. tigris Kennicott),

seven records of Mohave rattlesnakes (C. scutulatus

Kennicott), and nine records of blacktailed rattlesnakes (C.

molossus Baird and Girard). Diamondbacks ranged from

an elevation of 854 to 1,220 m. Mohave rattlesnakes ranged

from an elevation of 854 to 1,373 m, and blacktails were

found in canyons from 1,281 to 1,464 m. The distribution of

tiger rattlesnakes overlapped the distribution of all the

other rattlesnakes (Humphrey 1936).

As mesquite was cleared from SRER in various treatments, the Sonora spotted whiptail (Cnemidophorus sonorae

Lowe and Wright) was more abundant than in areas that

contained undisturbed mesquite and mesquite with irregularly shaped clearings (Germano 1978; Germano and

Hungerford 1981). The studies of Germano (1978) and

Germano and Hungerford (1981) were pioneer studies in

considering reptiles in landscape management plans in the

Southwest.

Avifauna ______________________

Studies of birds at SRER were limited, and seven of the 13

published works were related to quail. The other six articles

included short notes on the first record of the pectoral

sandpiper (Calidris melanotos Vieillot) for Arizona (Vorhies

1932), the life history and diurnal activity of the roadrunner

(Geococcyx californianus Lesson) (Calder 1968a,b), and diet

and nesting data for 20 to 55 Sonoran Desert birds (Russell

and Gould 1974; Russell and others1972, 1973) on a 20.3-ha

study plot in SRER.

Studies of quail included water requirements, productivity, diets, and life history traits (Gorsuch 1934). Whether or

not water supplied for wildlife influences populations has

been debated for years (Grinnell 1927; Rosenstock and

others 1999; Vorhies 1928). The controversy began over 50

years ago when biologists in Western States began to supply

water for game birds (MacGregor 1953). The first studies to

examine the response of Gambel’s quail (Callipepla gambelii

gambelii Gambel) to water sources provided as management

activities were, in part, studied at SRER (Hungerford

1960a,b).

Water supplied by humans was not important, as quail

maintained body moisture from succulent plants. Vitamin A

was an important part of the life history, and during dry

years quail did not store enough vitamin A in their liver for

successful breeding. Rainfall, as it influenced vegetation,

was the driving force for quail reproduction in southern

Arizona, not water provided by humans (Hungerford 1960a,b,

1964). The importance of vitamin A was first proposed by

Vorhies (1928) more than 30 years earlier based on his

studies of lagomorphs on SRER. Diet and physiological

studies (Hungerford 1960a,b, 1962, 1964) of quail supported

Vorhies’ observations.

Diets of scaled quail (Callipepla squamata Vigors) were

studied at SRER (Medina 1988). The scaled quail also selected

succulent food during dry seasons. Unfortunately, additional

studies of avifauna have not been conducted at SRER.

Mammals _____________________

Scientists have concentrated mammalian studies at SRER

on lagomorphs, rodents, coyotes (Canis latrans Say), collared peccaries (Pecari tajacu Linnaeus), and deer (Odocoileus spp). However, there are only limited data for each

group, and no central theme prevails. Because SRER is

primarily grassland, several studies examined influences

of range management practices (for example, mesquite

[Prosopis spp.] control) on wildlife. For example, the control of mesquite (15 to 100 trees per 0.41 ha) caused a

subsequent reduction of use by mourning doves (Zenaida

macroura Linnaeus), white-winged doves (Zenaida asiatica

Linnaeus), Gambel’s quail, scaled quail, and desert cottontails (Sylvilagus audubonii Baird). The abundance of antelope jackrabbits (Lepus alleni Mearns) and blacktailed

jackrabbits (L. californicus Gray) did not change with

mesquite removal (McCormick 1975). Other studies were

very general and simply presented anecdotal sightings of

animals (Martin 1966).

Lagomorphs

Some of the earliest studies of lagomorphs were conducted at SRER (Vorhies and Taylor 1933) with the use of

treatment and control areas. These early wildlife biologists

recognized the importance of examining species in their

habitat and understanding their value and relationships

with humans. The importance of considering human dimensions as a critical component of wildlife management

was raised by Leopold (1933), and Vorhies and Taylor
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Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002) Krausman and Morrison

(1933). Human dimensions have been a central aspect of

wildlife management ever since. As stated by Vorhies and

Taylor (1933: 579), “This is wild life management.” Their

publication came out the same year Leopold (1933) published Game Management, and the monograph serves as a

model for the scientific management Leopold (1933) advocated. Through their studies of lagomorphs, Vorhies and

Taylor (1933) determined life history traits, distribution,

interactions with livestock, forage consumption, diseases

and parasites, censusing techniques, habitat relationships,

predation, and management of antelope and blacktailed

jackrabbits. Their monograph was one of the first in-depth

studies of a game species conducted in the United States.

Taylor and others (1935) also documented and demonstrated ways that jackrabbits influenced vegetation, and

argued that wild animals should be considered in maintaining balanced rangelands.

Two studies followed Vorhies and Taylor (1933) that

expanded on their work. Forage consumed by jackrabbits

was determined from experimental trials (Arnold 1942:

46–69); jackrabbits consume as much as a 454-kg range

cow consumes. Arnold and others (1943) also explored ways

to estimate lagomorph numbers with counts of fecal pellets.

The second study examined the growth, development, and

forage requirements of young California jackrabbits (Haskell

and Reynolds 1947). These studies were conducted in a

scientific manner, and the data are still useful today (Brown

and Krausman 2003), primarily due to the scientific approach adopted by early wildlife biologists. Lagomorphs on

SRER were also used as a model to study water balance and

water requirements.

Early observations correlated moist diets as one mechanism to reduce dependency on free-standing water for the

kangaroo rat (Dipodomys spectabilis Merriam), wood rat

(Neotama albigula Hartley), round-tailed ground squirrel

(Spermophilus tereticaudus Baird), and jackrabbits (Vorhies

1945). Later, more detailed studies of the physiology of

jackrabbits were conducted, which determined that jackrabbits reduced their dependency on free water in other ways:

seeking shade, the insulation properties of their fur, use of

a clear sky as a radiation heat sink during midafternoon

(when solar and reflected radiation are reduced), high blood

flow in the ears to permit heat loss, and development of a

high lethal body temperature (45.4 ∞C) (Schmidt-Nielsen

and others 1966). The survival techniques described by

Schmidt-Nielsen and others (1966) were further applied to

and studied for cottontails and jackrabbits (Hinds 1970).

The study by Hinds (1970) only used animals captured at

SRER; experimentation was conducted at the University of

Arizona, Tucson.

Rodents

More work has been conducted on rodents at SRER than

any other group of mammals. The studies ranged from notes

to studies on ecology and life history traits.

Notes—The note (Taylor and Vorhies 1923) that was

published described the capture of a pair of kangaroo rats.

This was a time in the evolution of natural history writing

where unusual observations were published regularly.

Abundance Indices—The Standard Minimum Method

was a reliable technique to estimate small, nocturnal rodents at SRER, except it required large, homogeneous

sample areas (7.3 ha) and large grids in addition to the

assumptions that accommodate the technique. These drawbacks are time consuming (Olding 1976; Olding and

Cockrum 1977), which preclude the method as a rapid

technique suitable for estimating small rodents.

Breeding population density (per 2.6 km2

) was tabulated

for SRER for selected species by Leopold (1933: 233). Data

for rodents were from Taylor (1930), but estimates for other

species were subjectively estimated.

Physiology—Most of the physiological studies of rodents

on SRER were related to water. Some heteromyid rodents

conserve water through excretion of concentrated urine.

Their maximum excretory ability (1,200 mN for electrolytes

and 900 mN for chlorides) exceeds the limits for other

mammals (K. Schmidt-Nielsen and others 1948). Other

rodents such as white-throated woodrats cannot survive on

dry food only, but solved the water problem by consuming

succulent plants (B. Schmidt-Nielsen and others 1948).

Further studies demonstrated the importance of the humidity in rodent burrows to survival. The humidity in

burrows of kangaroo rats was higher than outside humidity

and significant for their water balance (Schmidt-Nielsen

and Schmidt-Nielsen 1950a,b, 1951). These studies were

some of the first that examined the water balance of desert

mammals and are still widely cited.

More recent studies have examined the survival of small

mammals from which blood was collected (Swann and others

1997). The survival of most rodents was not influenced due

to anesthetization and bleeding through the orbital sinus.

Pocket mice (Chaetodipus spp.) were the exception, and

those that were bled had significantly lower survival rates

compared to controls (Swann and others 1997).

Range Relations—Because of the economic value of

SRER and its representation of desert grasslands in general, managers were interested in animals that competed

with livestock for forage. One of the earliest studies was to

determine how much forage kangaroo rats consumed

(Vorhies and Taylor 1922). Unfortunately, they miscalculated and later revised their figures (Vorhies and Taylor

1924). Kangaroo rats consumed forage equivalent to 28

steers per year. However, because resources are often

limited prior to summer rains, the forage destroyed by

kangaroo rats would support 336 cattle in one month

during this critical period (Vorhies and Taylor 1924). Because rodents have such an impact on range resources, it is

important for managers to know how much they consume

before establishing carrying capacity for livestock. Numerous methods to determine rodent pressure on rangelands

were established, but how rodents interact with other

aspects of rangeland ecology are unknown and need further

research (for example, pressure on soil, relationship between rodents and insects) (Taylor 1930). Only limited

research occurred in the past.

Merriam kangaroo rats were identified as an agent of

mesquite propagation. When harvested, many seeds were

buried that germinated and developed away from the parent

tree. The result was an increase of mesquite at the expense

of grasslands (Reynolds and Glendening 1949).
62 USDA Forest Service Proceedings RMRS-P-30. 2003

Krausman and Morrison Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002)

Some researchers recommended a reduction in kangaroo

rats, along with livestock management to manage forage

(Reynolds 1950; Reynolds and Glendening 1949). Merriam

kangaroo rats consume large-seeded perennial grasses and

other large seeds. When rangelands are in poor condition,

rodents eat most seeds, which prevents rangeland restoration (Reynolds 1950). However, because other mammals

also perpetuate an increase in mesquite and a decrease in

grassland, removing kangaroo rats only would not increase

grassland landscapes (Reynolds 1954). Additional forage

studies of heteromyid rodents were conducted by Price

(1977), and effects of woody removal on nocturnal rodents

was examined by Vaughan (1976). Overall, as woody vegetation was removed, rodents were not effected, with few

exceptions: kangaroo rats decreased and silky pocket mice

(Perognathus flavus Baird) increased, as did others. Manipulation of vegetation for any reason needs to address how

it will influence overall biodiversity.

The early studies on rodents were directed at basic traits

and interactions with the grasslands. However, they also

served to guide future research questions.

Ecology and Natural History—There was not a constant theme identified for the broad area of ecology and

natural history. Studies conducted ranged from soils to

disease and included abundance related to rainfall, dispersal and movements, behavior, life history, and habitat.

Despite the importance of rainfall to rodent populations,

only two studies examined rodent abundance in relation to

rainfall. Rainfall from 1942 to 1972 was correlated to the

density of 10 rodents. Rodent fluctuation was predicted

based on the amount of rainfall during the previous year

(Turkowski and Vahle 1977). Petryszyn (1982) was able to

correlate extreme rodent population fluctuations at SRER

with certain El Niño events. Heteromyid rodent numbers

increased over sixfold in just a few months in 1973. This

pattern was repeated in 1979. Biomass of the Arizona

pocket mouse (Perognathus amplus Benson) increased from

less than 100 g per ha in May 1973 to over 1,100 g per ha

by September 1973. The timing and amplitude of these

increases varied among the rodent species. Petryszyn (University of Arizona, unpublished data) continued monitoring rodent populations at SRER until 1994, thus providing

a 24-year record of rodent population fluctuations.

Rodent movements were contrasted in a control area and

areas cleared of woody vegetation. Shifts in home range from

clearing vegetation were made by adults primarily. However, the difference in movements or numbers of individual

rodents (kangaroo rats, Perognathus penicillatus, southern

grasshopper mouse [Onychomys torridus Coves]) on disturbed and undisturbed areas was minor (Vaughan 1972). A

short removal study (to determine how trapping affected

rodents) most frequently captured the same three rodent

species. Results were inconclusive (Courtney 1971). Additional removal studies were conducted (Courtney 1983), but

removal did not influence home range size or physiology of

kangaroo rats.

Studies on behavior were also limited. One dissertation

was conducted on predatory behavior of the southern grasshopper mouse (Langley 1978). The southern grasshopper

mouse learned how to kill different prey (for example,

crickets, stink beetles, scorpions) based on their defenses

(Langley 1981).

Because so little was known about the life history of many

rodents, some of the earlier studies at SRER concentrated on

establishing a basis of knowledge for several rodents. Early

researchers were also interested in how rodents influenced

rangelands.

Classical life history accounts (for example, status, taxonomy, range, periods of activity, breeding, habitat, diet,

predation, economics, management) were provided for

woodrats (Vorhies and Taylor 1940), Sonoran Desert pocket

mouse (Chaetodipuspenicillatus priceiAllen), Bailey’s pocket

mouse (C. baileye baileyi Merriam), and Merriam’s kangaroo rats (Reynolds 1958, 1960). There was no impact to

rangelands from pocket mice or woodrats. Merriam’s kangaroo rats were more abundant on rangelands grazed by

livestock, and they are likely beneficial by burying seeds.

However, they also bury mesquite and cactus seeds, which

is not always favorable to range management objectives

(Reynolds 1958).

Studies of habitat have been limited. Competition was

examined as a mechanism for rodents to use different

microhabitats for foraging (Price 1976, 1978). Similar results (for example, habitat selection as an important factor

in species coexistence) were reported by Wondolleck (1975,

1978). Price and others (1984) also demonstrated that

rodents spent less time in open areas on moonlit nights

than on dark nights. Langley (1980) described habitat (such

as burroweed, a few grasses, and bare soil) for southern

grasshopper mice at SRER. More recently, the habitat use

and abundance of rodents at SRER was documented. These

data revealed temporal and age-related differences in habitat

use by rodents, which are of use in fine-scale planning for

restoration of desert plant communities (Morrison and others

2002). Gottesman (2002) studied the habitat use and movement patterns of rodents in riparian vegetation and concluded that most animals made only short-distance movements. Although the papers on habitat were limited, they

ranged from basic habitat requirements to brief discussions of

habitat alteration and restoration.

Three studies addressed the response of soils to animal

activity at SRER: Greene and Murphy (1932); Greene and

Reynard (1932); and Taylor (1935). All were very general but

pointed to the importance of physical and chemical changes

animals caused in the soil. No other studies were found that

addressed the influence of wildlife on soil.

Some of the more recent work with rodents at SRER has

examined Sin Nombre virus prevalence. Thirteen species

were captured and examined, but only mice in the genus

Peromyscus were seropositive for the virus. There was a

suggested correlation between population size and

hantavirus-antibody prevalence (Kuenzi and others 1999).

Predators

In the 1970s and early 1980s a series of studies on coyotes

was conducted at SRER. Home ranges (54 to 77 km2 for

juveniles), abundance, and behavior were documented

(Danner 1976; Danner and Smith 1980). During these studies Danner and Fisher (1977) were the first to document

homing by a marked coyote.

More detailed studies of coyotes were conducted at SRER

by Drewek (1980) and Fisher (1980). Drewek (1980) examined home ranges, activity patterns, and age distribution.

~
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Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002) Krausman and Morrison

Fisher (1980) examined how an abundant food source (such

as carrion) influenced density, age distribution, weights,

ovulation rates, and litter sizes of coyotes in three study

areas (no differences). Other diet studies were also conducted (Short 1979).

Ungulates

Collared peccaries and deer received some attention at

SRER. Collared peccary diets were examined and were

found not to be competitive for forage with livestock (Eddy

1959, 1961). General life history data were also presented

(Knipe 1957). Home ranges and movements of five mule

deer were examined (Rodgers 1977; Rodgers and others

1978). These researchers concluded that disturbances by

humans influenced breeding activity and normal movement patterns.

Feeding trials for Coues white-tailed deer (Odocoileus

virginianus Coues) were conducted at SRER (Nichol 1936,

1938). Nichol (1938) also examined parasites, disease, water

and salt consumption, reproductive patterns, and hybridization of mule deer and white-tailed deer. The study was

initiated because the U.S. Forest Service was interested in

appropriate allocation for livestock and wildlife, a controversy that still continues in Arizona. This was one of the first

studies addressing these topics in Arizona, and the work is

still used as a reference.

Despite the importance of deer to Arizona, including

hunting, no studies were found that examined harvests in

SRER. Some summary data were provided in a memo

(Yeager and Martin 1965; not seen, cited in Medina (1996)

(hunt success) for the 1964 deer season.

This array of research has been instrumental in establishing SRER as the natural laboratory it was designed to be.

However, scientists and administrators could be more efficient with a directed approach for long-term research that

include inventory and monitoring. To our knowledge, the

U.S. Department of Agriculture’s Forest Service or the

University of Arizona administrators have not allocated

funds or a central mission in which continuous studies of

wildlife could be conducted. Unless a central theme or

funding level is established, wildlife research at SRER will

continue to be based on individual efforts.

Inventory and Monitoring ________

Inventory and monitoring are the most frequently conducted type of wildlife studies (Morrison and others 2002).

They are done to gather new knowledge about an area,

quantify trends in some animal or resource of interest, and

to assist with resource management. The goal of an inventory is to quantify the current composition, distribution, and

perhaps abundance of a species of interest in an area.

Monitoring is simply conducting repeated inventories to

quantify changes in composition, distribution, and abundance over time. In addition to the general pursuit of knowledge, inventory and especially monitoring are often mandated by legislation, such as by the National Forest

Management Act (1976) and the Endangered Species Act

(1973). Unfortunately, both initial inventories and followup

monitoring are seldom conducted with sufficient rigor to

precisely estimate the parameters of interest (Morrison and

Marcot 1995; Morrison and others 2002).

There are numerous reasons why establishing an organized and rigorous inventory and monitoring program would

benefit an education and research mission at SRER. First,

resource managers need to have reliable data upon which

decisions can be based. Only a comprehensive monitoring

program that involves all taxa can hope to provide an

understanding of the interactions between management

decisions and wildlife responses. Second, there is the need to

provide students and potential researchers with a complete

list of species composition, relative abundances, and distribution to assist with teaching and research planning. Third,

the University of Arizona and the Forest Service should have

an interest in monitoring the influence of local, regional, and

global changes in climate, air quality, human population

impacts, and other factors on wildlife populations over time.

Simply establishing a series of repeated sampling locations (regardless of the specific methodologies used) is insufficient, however, to address any questions regarding wildlife

at SRER in a meaningful way. Specific and quantifiable

objectives must be established before successful monitoring

can be accomplished; these objectives then drive the sampling design, intensity of sampling, and statistical analyses.

A typical goal of monitoring is to identify trends in a resource

of interest. Trends represent the sustained patterns in count

data that occur independently of cycles, seasonal variations,

and irregular fluctuations in counts. A common problem in

trend detection, however, is that sources of “noise” in counts

obscure the “signal” associated with ongoing trends. The

probability that a monitoring program will detect a trend in

sample counts when the trend is occurring, despite the

“noise” in the count data, represents its statistical power.

Although statistical power is central to every monitoring

effort, it is rarely assessed. Consequences of ignoring it

include collection of count data insufficient to make reliable

inferences about population trends, and collection of data in

excess of what is needed (Gibbs 1995).

The statistical power of population monitoring programs

must be estimated relative to (1) the number of plots monitored, (2) the magnitude of counts per plot, (3) count variation, (4) plot weighting schemes, (5) the duration of monitoring, (6) the interval of monitoring, (7) the magnitude and

nature of ongoing population trends, and (8) the significance

level associated with trend detection (Gibbs 1995). Because

these factors interact in complex ways to determine the

capacity of a monitoring program to detect trends in populations, such basic questions of “how many plots should I

monitor” or “how often should I conduct surveys” rarely have

intuitive answers. Programs such as MONITOR (Gibbs

1995) are designed to explore interactions among the many

components of monitoring programs and to evaluate how

each component influences the monitoring program’s power

to detect trends.

In general and certainly applicable to SRER, broad objectives for conducting monitoring are (Spellerberg 1991) to:

1. Provide guidance to wildlife management and

conservation.

2. Better integrate wildlife conservation and management with other land uses.

3. Advance basic knowledge in addition to applied

knowledge.
64 USDA Forest Service Proceedings RMRS-P-30. 2003

Krausman and Morrison Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002)

4. Track potential problems before they become real

problems.

These objectives are often addressed by conducting monitoring studies (Gray and others 1996; Miller 1996) to:

1. Determine wildlife use of a particular resources or

area.

2. Evaluate effects of land use on populations or habitats.

3. Measure changes in population parameters.

4. Evaluate success of predictive models.

5. Assess faunal changes over time.

Monitoring Elements

Key components of a monitoring program at SRER should

include the:

1. Ability to link past, current, and any future research

activities with a systematic grid system (in other words, to

be able to locate relative to base monitoring sampling frame).

2. Sampling frame developed around an attribute-based

GIS vegetation system.

3. Sampling protocol for rare species, such as adaptive

cluster sampling, to be instituted in addition to the basic

sampling frame.

For example, a 500- by 500-m grid coordinate system

could be established across SRER. This spacing would be

applicable for implementing a standard point-count methodology for birds because most counting protocols require

an interpoint spacing of greater than or equal to 300 m. The

actual spacing of grid points is actually irrelevant because

the system would only exist as coordinates in a GIS layer

and not physically exist on the ground. Using the 500- by

500-m spacing and beginning at a random starting point in

one corner of SRER, points would be systematically spread

across the area. Additional points would also be randomly

placed within each currently recognized vegetation type,

while ensuring that adequate sampling occurred in rare

types. For example, additional (nongrid) points would need

to be established in linear (for example, riparian) and

relatively small (for example, hackberry [Celtis reticulata]

woodland) types. A systematic placement of grid points is

recommended because there is no assurance that a currently recognized classification of vegetation would be of

adequate refinement for many applications, or that the

classification would be stable into the future. It is likely,

however, that certain vegetation classifications (for example, riparian, the major plant associations currently

recognized) will remain adequate upon which to base the

general allocation of points. The value of points is that they

are readily locatable using GPS, even if they serve as the

starting point of a transect.

The number of points to be sampled should be based on

power analysis using the best available estimates of variance associated with each parameter of interest. It is important to recognize that power analysis only provides an initial

estimate of sample size. The final sampling effort must be

based on an iterative process that updates the number of

required samples as data are gathered. Power analysis

requires that a magnitude of biological effect be established.

That is, what magnitude of change must be quantified with

what level of certainty? For example, is it sufficient for SRER

resource managers to be able to identify a 5 percent annual

change in abundance of a species in 3 years, or can they wait

to identify this change over 5 years? The answer will vary

depending on the species in question. Note that allowing for

a 5 percent decline in abundance over 5 years results in a

cumulative loss of 29 percent—a substantial decline for any

species.

Unfortunately, very little general guidance is in the literature regarding appropriate initial sample sizes for a largescale, multispecies monitoring program. This is due, in part,

to the rather recent general interest in statistical rigor being

shown among many wildlife professionals. However, many

computer statistical packages are now available that allow

easy access to power analyses. Because there are so many

potential criteria that can appropriately be used for establishing monitoring parameters, and because the rarer species will require specialized sampling efforts, we cannot

provide a cookbook answer for necessary sample sizes. Some

studies on monitoring relatively common bird species have

shown, however, that 30 to 50 points (usually counted 3

times each per season, most often in the breeding season) are

adequate to detect a 5 percent annual change in abundance

within a 5-year period. At SRER, however, it will not be

possible to place that many points within relatively rare

vegetative types or plant associations. In such situations, it

becomes necessary to increase sampling intensity, and conduct a more intensive type of monitoring, to rigorously

quantify change. With birds, for example, researchers often

supplement point counts with more intensive spot mapping

procedures.

Rare Species

Management recommendations are sometimes made for

rare species based on data from common species, although

rare species are excluded from analyses due to small sample

sizes. In many cases, threatened or endangered species are

“rare.” If a species only occurs in a very specialized habitat,

it would be rare in that its only detections occur within

spatially clumped areas. Alternatively, if a species has a

large geographic range it may be considered rare because it

is only detected during a community assessment as it wanders through a study area. Lastly, species are considered

rare when local populations are composed of a few individuals per unit area, as is the case with most threatened and

endangered species (Queheillalt and others 2002).

Due to the great number of “rare” species in plant and

animal communities, these communities are known to adhere to lognormal species abundance distributions, in which

a small number of species are common, only a few species

reside in intermediate to low numbers, and most are uncommon (Harte and others 1999; Maina and Howe 2000;

Rosenberg and others 1995; Van Auken 1997). Frequently

used sampling designs, such as simple random sampling,

stratified random sampling, and systematic random sampling, are ineffective when applied to infrequently encountered species, and such sampling designs return numerous

zero counts and decrease the accuracy of the studies using

these designs (Thompson 1992; Thompson and others 1998).

The exclusion of species due to low detection rates leads to

the erroneous inflation of relative abundance and density

calculations of included species. In instances of special
USDA Forest Service Proceedings RMRS-P-30. 2003 65

Wildlife Ecology and Management, Santa Rita Experimental Range (1903 to 2002) Krausman and Morrison

status species (for example, legally threatened or endangered), elevated density estimates may lead to the biological

notion that a species is prevalent in sufficient numbers when

in fact its actual density is low. Also, if the object of the study

is to compare relative abundances over successive years,

trends may appear for a species, which are due to the

number of species excluded from abundance calculations

rather than true biological trends.

Because rare species are often spatially clumped, we

recommend using one of the forms of adaptive sampling

methods—adaptive cluster sampling design, strip adaptive

cluster sampling, or stratified adaptive cluster sampling—

as described by Thompson (1992) to supplement the systematic arrangement of sampling points described above. Adaptive cluster sampling is a two-stage sampling design in

which initial sampling plots are randomly selected and

monitored. Any of the initial plots containing animals are

selected to have all adjacent plots monitored as well. This

process continues until adjacent plots no longer contain

animals of interest (Krebs 1999; Morrison and others 2001;

Thompson 1992). This method increases the probability of

encountering clumped species, and thus often increases

sample sizes.

Statistical analyses with small sample sizes can be problematic. When samples are from highly variable populations, statistical analyses often have low power. Although

beyond the scope of this paper, there are options for statistical analyses with small sample sizes. Contingent upon the

specific situation and type of data being used, nonparametric tests can be employed or data transformed to allow the

use of parametric tests when working with small sample

sizes.

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68 USDA Forest Service Proceedings RMRS-P-30. 2003

John H. Madsen

Cultural Resources of the Santa Rita

Experimental Range

John H. Madsen is an Associate Curator of Archaeology at the Arizona State Museum, P.O. Box 210026, University of Arizona,Tucson, AZ 85721; e-mail:

jmadsen@u.arizona.edu. He has a B.S. degree in environmental studies and an M.A. degree in archaeology from California State University, Sacramento.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

This paper will address the history of cultural resource management on the Santa Rita Experimental Range (SRER or the

Range) and will provide a summary of how the land was used by American Indians prior to European contact in the late 1690s.

The paper will conclude with a summary of potential strategies to protect and preserve cultural resources on the Range and a

view of how we might blend the environmental information found in prehistoric sites with more traditional range-oriented

research themes.

Historic Preservation Policy Applicable to Santa Rita ___________________

Two Federal laws set the stage for cultural resource management on the Santa Rita Experimental Range. The Archaeological

and Historic Preservation Act of 1960 (AHPA) (Public Law 86-523, 16 U.S.C. 468–469c-2) was adopted to further improve the

intent of the Historic Sites Act of 1935 (16 USC 461–467). The intent of AHPA is to preserve historic American sites, buildings,

objects, and antiquities of national significance. The Act provides for the protection of historical and archaeological data

(including relics and specimens), which might be irreparably lost or destroyed as a result of alterations to the land caused by

a Federal agency or a Federally licensed construction project.

The second law of importance was the National Historic Preservation Act (16 USC 470 et seq.). Enacted in 1966, this Act

provides for a National Register of Historic Places, and has broad authority over national, State, and local historic preservation

programs. Section 110 of the Act has had the most significant impact on the Range.

Section 110 directs the heads of Federal agencies to assume responsibility for the preservation of National Register listed

or eligible historic properties owned or controlled by their agency. Agencies are directed to locate, inventory, and nominate

properties to the National Register, to exercise caution to protect such properties, and to use such properties to the maximum

extent feasible. Other major provisions of Section 110 include documentation of properties adversely affected by Federal

undertakings and the establishment of trained Federal preservation officers in each agency.

After the passage of the National Historic Preservation Act, Federal agencies with land managing responsibilities began to

fill their ranks with cultural resource managers. The Santa Rita Experimental Forest, as it was called in the 1960s, fell into

a unique Federal land category. Because the land was not within the boundaries of a National Forest, it was identified as “other

Federal lands” and was administered by the Bureau of Land Management (BLM). The USDA Forest Service Rocky Mountain

Forest and Range Experiment Station managed the surface of the land through an interagency agreement with the BLM.

Management of cultural resources on the experimental range was shared between the Coronado National Forest and the

Rocky Mountain Forest and Range Experiment Station. Little was known about the cultural resources before 1974. The

Coronado National Forest employed its first Forest Archaeologist by 1975. Personnel at the Station, in cooperation with the

Abstract: The Santa Rita Experimental Range is a vast open space with few signs of houses or

human habitation, but at one time it was quite the opposite scene. Archaeological surface

inspections reveal heavy use of the Range dating back hundreds of years. This paper will review

the history of cultural resource management on the Range and provide a timeline of local cultural

history pertinent to understanding the cultural landscape on the west flank of the Santa Rita

Mountains. An archaeological site inventory done by Cynthia Buttery in 1985 and 1986 will be the

central focus of this paper. Buttery’s work provides an important picture of land use on the Range

over 800 years ago by Hohokam farmers. The paper will conclude with comments on cultural

resource management and research opportunities on the Santa Rita Experimental Range.
USDA Forest Service Proceedings RMRS-P-30. 2003 69

Cultural Resources of the Santa Rita Experimental Range Madsen

Forest Archaeologist, conducted cultural resource inspection on SRER in advance of ground alterations related to

fence installations, buried pipelines to livestock water supplies, and road maintenance.

In the 1980s opportunities arose to place large blocks of

sensitive habitat in south-central Pima County under the

jurisdiction of the U.S. Fish and Wildlife Service. In an

elaborate exchange that involved land from several agencies

including the U.S. Forest Service, BLM, and U.S. Fish and

Wildlife Service, the Range was transferred to the State of

Arizona in 1990. Today the Santa Rita Experimental Range

is administered by the Arizona State Land Department and

leased to the University of Arizona for ecological and ranch

lands research.

Land management responsibilities for SRER now fall to

the Arizona State Land Department and their lessee, the

University of Arizona. National historic preservation policy

applies to SRER when Federally funded or licensed projects

or Federally funded grants are used in a way that might

impact cultural resources. In such instances the Arizona

State Historic Preservation Office in consultation with the

funding or licensing agencies, the recipient of the funds or

license, and other interested parties, such as Arizona Tribes,

assure compliance with Federal legislation.

Two State laws now serve to protect and preserve the

prehistoric, historic, and paleontological resources within

the boundaries of the Experimental Range during the normal course of daily operations and management, and during

State and privately financed research. The first of these laws

is the Arizona State Historic Preservation Act of 1982 (Title

41, Chapter 4.2 Historic Preservation, Article 4, General

Provisions, A.R.S. Sec. 41-861 through 864). This State law

and its associated policies are administered in part by the

Arizona State Historic Preservation Office and guide landmanaging agencies and institutions like the University of

Arizona through their responsibilities to protect and preserve cultural resources on lands they own or control.

The second State law pertaining to SRER is often referred

to as the Arizona Antiquities Act, but in actuality is Title 41,

Chapter 4.1 Article 4, Archaeological Discoveries (A.R.S.

Sec. 41–841 et seq.). The University of Arizona has a long and

honored role in the implementation of this law. In 1927, the

Arizona Eight Legislature enacted the first law to regulate

excavation of prehistoric ruins on State and Federal lands in

Arizona through a permit system. The legislature assigned

the task of administering this statute to the University of

Arizona, Department of Anthropology. The Department

administered the Act until 1960 when amendments placed

administration of the law under the Arizona Board of Regents and the Director of the Arizona State Museum, University of Arizona (ASM).

The intent of the Arizona Antiquities Act is to protect the

information contained in historic and prehistoric ruins, and

paleontological deposits by controlling access to sites on State

lands through a permit program administered by the ASM.

The Act has been amended six times to keep pace with

national and State historic preservation policy and is one of

the strongest preservation and grave protection laws in the

nation.

The University of Arizona has a consistent record of

compliance with the State Historic Preservation Act and the

Arizona Antiquities Act. New information about the cultural

resources on SRER is slowly but steadily gathered as archaeological surveys required by State law are conducted in

advance of range management and range research projects.

Previous Archaeological

Investigations __________________

In the northeast corner of SRER lies Huerfano Butte. This

rocky outcrop contains many archaeological features and

will be described later on in this paper. In 1958 William

Lindsay reported a bedrock seed-processing location on the

Butte, and the ASM gave it a State site number. In 1965 the

Butte gained public notoriety when a young girl discovered

a prehistoric jewelry cache while on a picnic. This discovery

resulted in the first and only scientific journal article about

the archaeology of SRER (Bahti 1970).

In 1974 the U.S. Forest Service began to require surveys

on the range in response to the passage of the National

Historic Preservation Act. The Forest Service recorded eight

small sites between 1974 and 1985.

Cynthia Buttery (1987) accomplished the first systematic

archaeological inventory on the Range. Over a 2-year period

from 1985 to 1986, Buttery recorded 46 Hohokam sites. This

research was accomplished in partial fulfillment of her

master’s degree in anthropology at Texas Tech University

and provided information for U.S. Forest Service and Research Station personnel to better manage and protect the

cultural resources under their care.

From 1987 to present, five compliance surveys have been

completed on the Santa Rita Experimental Range and were

related to the placement of water pipelines, soil testing, and

road improvement projects (Lange 1999; Lascaux 2000;

Madsen 1991; Stone 2001; Swartz 2002). The most recent

work by Swartz (2002) was in response to proposed carbon

sequestration studies funded in part by NASA. The School of

Natural Resources, University of Arizona contracted for

archaeological assistance from Desert Archaeology, Inc., to

meet Federal requirements for funding. Swartz examined

the surface of six parcels prior to the excavation of trenches

related to this study. The archaeological inspection resulted

in the discovery, recordation, and avoidance of one small

prehistoric site. Swartz also found historic features related

to early research on the range. Swartz (2002: 17) found it

interesting that: “Taken as a whole, across the entire 53,000-

acre Range, ... markers and other remains from studies

[conducted] in the first half of the twentieth century may

meet eligibility requirements for inclusion in the National

Register of Historic Places.” These artifacts of past research

on the Range may contribute to our understanding of the

history of range research in the Unites States beyond the

written record. By virtue of being an experimental station

with 100 years of continuous operation and contributing

significantly to range research, SRER today may warrant

national recognition as an historic landmark.

Southern Arizona Prehistory ______

A short summary of southern Arizona prehistory is provided so that the reader can better understand the prehistoric

cultural resources of the SRER. Some findings, particularly
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Madsen Cultural Resources of the Santa Rita Experimental Range

those from Buttery (1987), are incorporated into the body of

this summary, but most of the detailed information from her

work on Hohokam resources will follow this summary.

Big Game Hunters

From archaeological and paleontological investigations a

picture has emerged regarding life in the Western Hemisphere from 10,000 to 8,500 B.C. The term “Paleoindian” is

used to identify the earliest inhabitants of North America.

The origin and ethnicity of these people continues to be

debated, but it is sufficient to say they moved about in small

groups, lived in temporary camps, and hunted megafauna.

Butchering sites with stone tools found in association with

the remains of mammoth have characterized these people as

big game hunters. In southern Arizona, known butchering

sites are located in the San Pedro River Valley and Sulphur

Spring Valley. A spear point type referred to as the Clovis

Point (first discovered near Clovis, NM) has been found

embedded in the bone of mammoth at the site of Naco, AZ

(Haury 1953), and at the nearby sites of Lehner (Haury and

others 1959), and Murray Springs (Hemmings 1970).

Mammoth remains have been found in the Santa Cruz

River watershed. Within the boundaries of SRER a mammoth tusk was found in an eroding arroyo bank (Buttery

1987: 12). The discovery of Clovis points (Agenbroad 1967;

Ayers 1970; Doelle 1985; Huckell 1982) and a later style of

point called the Plainview Point (Agenbroad 1970; Hewitt

and Stephen 1981; Huckell 1984a) indicate a presence of big

game hunters in the Santa Cruz River Valley before 8500

B.C. However, archaeological sites with mammoth remains

and Clovis or Plainview points have yet to be discovered in

the Tucson Basin.

Archaic Hunter Gatherers

Mass extinction of mammoths, mastodons, camels, horses,

giant ground sloths, and other large Pleistocene mammals is

attributed to climatic change and excessive hunting. By

8500 B.C. the door closed on the big game hunter era, and for

the next 7,000 years American Indians adapted to changing

environments and landscapes. People focused on mixed

subsistence strategies of hunting smaller game, fishing, and

eating wild plant resources. Data on social organization,

economy, and ritual behavior are severely limited, but there

is evidence to show increased sedentism between the early

and late periods. Across North America this period of 7,000

years has been separated into the Early, Middle, and Late

Archaic periods. These periods are not chronologically similar from region to region. In Arizona, Archaic hunter-gatherer sites are assigned to one of three periods within the

Southwest Archaic Tradition: the Early Archaic (ca.7500 to

5000 B.C.), the Middle Archaic (ca. 5000 to 1700 B.C.), and

Late Archaic (ca.1700 B.C. to A.D. 150). The term Late

Archaic is also synonymous with Huckell’s Early Agricultural Period (Huckell and others 1995).

Transition to Agriculture

The term Early Agricultural best reflects the cultural

setting between 1700 B.C. and A.D. 150. During this period

farmers irrigated fields of maize on the flood plain of the

Santa Cruz River and farmed at the mouths of watered

canyons. They supplemented their diet with deer and other

small game and wild plant foods (Diehl 1997; Ezzo and

Deaver 1998; Gregory 1999; Huckell and Huckell 1984;

Huckell and others 1995; Mabry 1998; Roth 1989). Sedentism

is expressed in the archaeological record by discoveries in

recent years that include dozens of houses per village,

irrigation ditches, and the byproducts of food processing

such as carbonized or burned maize and animal bone. With

people spending more time in one location, trash accumulated, as objects were discarded or cached away. The resulting material culture of the early agriculture period includes

diverse flaked stone and ground stone tool assemblages,

carved stone pipes, clay figurines, and crude pottery vessels.

Seashell and other nonlocal resources indicate involvement

in trade. Data on social organization and ritual behavior are

speculative. Larger than normal oval structures found in

village settings might be social or ritual places or perhaps

the homes of influential people.

Huckell (1984b) excavated 10 sites at Rosemont on the

eastern slopes of the Santa Rita Mountains immediately

east of SRER; these sites span the later portion of the

Southwest Archaic Tradition through the Early Agricultural Period. No such sites are recorded yet on SRER, but 10

diagnostic arrow points of Archaic and Early Agricultural

origin have been found on the Range.

Early Ceramic Period

The Early Ceramic Period (A.D. 150 to 650) is a relatively

new concept within the Tucson Basin (Heidke and Ferg

2001; Heidke and others 1998). Although ceramic artifacts,

including clay figurines and crude plain pottery, were made

during the Early Agricultural period, pottery containers

revolutionized life after A.D. 150. Over this 500-year period,

pottery was refined into nicely made plain ware and red

ware vessels. A variety of new pit house styles are found—

basically shallow rectangular pits protected by a framework

of posts and beams supporting a coat of matted grass, brush,

and mud. Overall a less homogenous culture is seen. As

people become less mobile, more time is available to experiment and to adopt ideas from distant lands to make life

easier. It is not known if these changes are a step in the

evolution of the local sedentary population or reflect the

influence of new people. Cultigens, including maize, beans,

squash, and cotton, wild plants, and hunting were important

parts of the subsistence economy. Greater quantities of

imported materials such as turquoise, obsidian, and shell

suggest a greater investment in a sedentary life. Data on social

organization and ritual behavior remain speculative. The

cultural setting by A.D. 650 sets the stage for the emerging

Hohokam tradition.

Hohokam

Hohokam is the English pronunciation of Hu Hu Kam, a

word used in the Piman language to mean “those who are

gone.” O’odham ancestral roots are deeply embedded in the

ancient cultures of the Sonoran Desert.

The geographic extent of the Hohokam tradition coincides

closely with the basic and persistent patterns of settlement
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Cultural Resources of the Santa Rita Experimental Range Madsen

and subsistence seen in the Sonoran Desert before the sixth

century A.D. By A.D. 650 new cultural traits such as pottery

with red decoration, public architecture, and extensive irrigation systems are identifying characteristics of the

Hohokam. These new cultural elements were so innovative

that renowned archaeologists Harold Gladwin (1948) and

Emil Haury (1976) postulated a Mesoamerican migration

into the fertile Salt River and Gila River valleys. In recent

years new archaeological data suggest that the traits that

uniquely identify the Hohokam are products of internal

experimentation as well as the external influences of the

Anasazi and Mogollon cultures and the northern cultures of

Mesoamerica.

Hohokam Community—For purposes of this discussion, Hohokam history is divided into the Preclassic period

(A.D. 650 to 1150) and the Classic period (A.D. 1150 to 1450).

The Hohokam aggregated into cohesive agricultural communities that occupied every hospitable niche within the

Sonoran Desert. The term “community” refers to clusters of

sites dominated by villages of different size and social

complexity that maintained farmsteads, multifaceted agricultural systems, and smaller sites located strategically to

acquire natural resources (Fish and others 1992).

Each community had a central village supporting one or

more forms of public architecture. In the Preclassic period,

clay-capped ceremonial mounds and ball courts identified

the religious, economic, and social centers of a community

(Gladwin and others 1937; Wilcox and others 1981; Wilcox

and Sternberg 1983). A shift in Hohokam ideology eventually caused the decline and eventual abandonment of ball

court centers and the rise of Classic-period platform mound

communities reflecting the emergence of new positions of

authority. O’odham oral history suggests that platform

mounds may have been built for the Hohokam elite (Teague

1993).

Hohokam community organization speaks to a high order

of cooperation and social interaction that reaches beyond

community boundaries. These same organizational skills

are also seen at the village level with remarkable consistency through time. During the Preclassic period, families

organized into cohesive courtyard groups. Each courtyard

group contained clusters of rectangular pit houses, cooking

ovens, cemeteries, and trash disposal areas positioned around

the edge of a common open space (or courtyard). In some

larger villages, multiple courtyard groups were positioned

around larger central plazas (Doyel 1991).

By the Classic period the courtyard group takes on a

pueblo design because of innovations in architectural materials, particularly adobe block construction. Villages contain

from one to as many as 20 compounds, each defining the

living and working space of a related social group. Within

compound walls, groupings of houses and ramadas face

common yards containing workspace and cemeteries. Trash

mounds and large cooking ovens lie on the exteriors of

compound walls.

Hohokam Farming—By the sixth century A.D., the

people of the Sonoran Desert had had nearly 2,000 years to

hone their agricultural strategies. In the broadest river

valleys like the Phoenix Basin, Preclassic and Classic-period

Hohokam communities were organized to maintain one or

more river-fed irrigation systems. Villages and farms were

strategically positioned along miles of arterial aqueducts,

canals, and ditches that provided water to croplands.

In narrow river basins like the Santa Cruz and San Pedro,

mountains squeeze the flood plains into narrow stripes of

fertile land. During the Preclassic and Classic period,

Hohokam communities organized along the edges of these

flood plains and successfully used river water to irrigate

crops. The narrowness of valleys also offered the same

communities an opportunity to diversify their agricultural

strategies by farming the alluvial fans of nearby mountains.

Here the Hohokam planted the lower limits of fans where a

combination of direct rainfall and the construction of diversion dams directed water from swollen washes to adjacent

fields.

In basins with no perennial waters alluvial-fan farming

was supplemented with other faming techniques including

diverting rainwater into deeply excavated storage reservoirs for domestic use and pot irrigation, blocking gullies

with rock terraces to capture flowing water and sediments,

and planting crops in gardens bordered on all sides by rock

walls that captured rainwater, prevented runoff, and caused

soil saturation. Specialized crops like agave were grown in

piles of soil and rock that caused a mulching effect and

minimized evaporation.

Hohokam Craft Specialization—Part of the diverse

material culture of the Hohokam—craft specialization—

emerges from the early ceramic period and takes on a strong

Mesoamerican orientation. Seashell, minerals and rock,

animal bone, plant fiber, and clay were transformed into

utilitarian, status, and ritual objects with diverse form and

function. The common person possessed the skill to make

plain ware pottery and flaked stone tools for hunting, harvesting, and processing food, but skilled craft specialists

were spread throughout communities and were actively

involved in repetitive manufacture of products and their

subsequent trade. People specialized in making jewelry,

ritual objects of stone and clay, textiles, and decorative

pottery.

Pottery such as bowls, jars, ladles, and effigy forms, with

painted red designs was the signature of the Hohokam

people. The earliest decorated pottery was a gray ware with

simple incised exterior lines and red painted designs. By

A.D. 800 brown pottery with red designs dominated southeastern Arizona while buff-colored pottery with red designs

dominated the central basins of the Salt and Gila Rivers. By

A.D. 1300 the introduction of distinctive red, black, and

white polychrome pottery provides intriguing questions

about cultural influences, suggesting, perhaps, the acceptance of outside ideology and/or religion (Crown 1994).

The momentum of the Hohokam culture wanes by A.D.

1350, and their descendants reorganize themselves over the

landscape. Pima oral histories tell of social and political

upheaval and of environmental factors that profoundly alter

the cultural landscape of the Sonoran Desert (Teague 1993).

Reorganization Period

By A.D. 1450 warfare, drought, floods, disease, or some

combination of these factors caused change in the structure

of Hohokam society. Desert people did not vanish from the

landscape—they simply reorganized. In 1697, Captain Juan
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Madsen Cultural Resources of the Santa Rita Experimental Range

Mateo Manje and Father Eusebio Kino explored the valleys

of the San Pedro, Gila, and Santa Cruz Rivers. In the Gila

River Valley these explorers noted the abandoned Casa

Grande Ruin and other burned out Hohokam towns. Yet the

Spanish encountered fertile irrigated croplands and many

villages, where often hundreds of people would come out to

welcome them. People were still living a sedentary lifestyle,

but it was seemingly on a different scale than 250 years prior

and analogous to that of people living a thousand years

earlier. Villages were nothing more than clusters of small oval

huts built of sticks and mats (Burrus 1971; Karns 1954). The

people encountered by Kino were the descendants of the

Hohokam and are the ancestors of the O’odham-Piman people.

Southern Arizona History

Hispanic Arizona—Hispanic Arizona is separated into

the Spanish Colonial period (1536 to 1821) and the era of

Mexican Independence (1821 to 1856). Most of the major

river valleys of present-day Arizona were explored, and a

pattern of European settlement was established over this

320-year span. Life on the northern frontier of New Spain

was dangerous, and for the Spanish, and for the later

Mexican citizen, being able to safely and permanently settle

in any one location was never easy.

Franciscan priests attempted a permanent secular presence with the Hopi Tribe from 1629 to 1730 but met with

little success. In southern Arizona the Jesuits similarly

placed priests at the Indian settlements of Guevavi and Bac

on the upper Santa Cruz River between 1701 and 1732. It

was not until 1736, when silver was discovered south of

present-day Nogales, that miners and ranchers hurried to

the borderland of New Spain. The stage was now set for a

permanent Hispanic presence in what is now Arizona, and

the Santa Cruz River drainage attracted the highest density

of Hispanic people. Thereafter, conflict with Indian communities, particularly the conflict between the Apache and

Spanish colonists, impeded permanent political and social

stability. Even the stationing of garrisoned troops and the

building of four presidios, including one at Tubac (established 1751) and one at Tucson (established 1776), did little

to protect missionaries, miners, ranchers, and Indian allies.

A brief negotiated peace between the Apache Indians and

the Spaniards brought calm to the region around 1790, but

the success of the Mexican Independence Movement culminated in the end of Spanish rule in 1821, bringing new

political problems and instability between the Hispanic

population and American Indian.

During the Mexican period (1821 to 1854), conflict with

the Apache people intensified in the borderlands, and settlers again retreated to the safety of the presidio forts. Only

the courageous dared to face the isolation of the mining

camps and ranches of the hinterlands. The instability of the

period is exemplified by the failure of land grants. The San

Ignacio De La Canoa Land Grant is of particular interest

because of its proximity to SRER. In 1821 brothers Tomás

and Ignacio Ortiz gained title to 42,000 ha (17,000 acres)

along the Santa Cruz River, extending from the western

edge of SRER south to present-day Amado. The southern

boundary of the land grant was just a few miles north of the

presidio of Tubac, yet by 1835 repeated Apache raids forced

the brothers to abandon their ranch and to tend their herds

from the safety of the Tubac Presidio.

United States Annexation—Mexico’s refusal to sell

lands to the United States or to resolve land disputes in

Texas resulted in the Mexican War of 1846. The Treaty of

Guadalupe Hidalgo in 1847 ended Mexican control over a

vast region, including Texas, as well as portions of New

Mexico, northern Sonora, and upper California. Under the

Compromise of 1850, the U.S. Congress created the New

Mexico Territory, including present-day Arizona north of

the Gila River, Southwest Colorado, southern Utah, and

Southern Nevada. The Treaty of La Mesilla, also known as

the Gadsden Purchase, finally clarified international boundaries in 1854 when the United States purchased 30,000

square miles south of the Gila River.

The period of annexation was a time of transition in the

Santa Cruz River Valley. To paraphrase Sheridan (1995),

most Anglo Americans viewed southern Arizona as an obstacle and a wasteland on their way to better lands. In 1846

the Mormon Battalion passed through Tucson while mapping a route to California. On their heels came scores of

miners, merchants, and stockmen lured west by the discovery of gold in California in 1848. Through the 1850s and

1860s, Anglo attempts at ranching and mining in the Santa

Cruz River Basin were marginal and paid few dividends.

The Civil War created new problems as Union forces left the

region, opening it to Apache reprisals. For example, between

1855 and 1862 cattle ranching continued on the San Ignacio

De La Canoa Land Grant; by 1859 a lumber mill, hotel, and

tavern were build just southwest of SRER at La Canoa.

Apache raiders burned the newly constructed buildings in

1861 (Willey 1979). In 1862 the Civil War reached Tucson

when a brief tug-of-war over occupation ended with Union

Troops in possession and Confederate Troops retreating to

Texas.

The U.S. military, like their Spanish and Mexican predecessors, could do little to calm old and new ethic conflicts

throughout the period of annexation. During this period,

however, Mexican and Mexican-American residents established the foundation of later successes in southern Arizona.

Arizona Territory (1863 to 1912)—In 1863 the Arizona

Territory was carved out of the Territory of New Mexico. The

land once considered an obstacle to westward expansion was

rediscovered. From 1863 forward, Arizona’s gold, silver, and

copper resources lured an aggressive rush of miners to the

territory, and with each new discovery mercantile centers

thrived. The cattle boom of the 1880s paralleled the growth

of mining; and, finally, the arrival of the railroad through

southern and northern Arizona culminated in the end of the

frontier. Throughout the entire era, a growing U.S. military

presence broadened warfare, leading to suppression and

confinement of Arizona’s Indian tribes.

Santa Cruz River Valley—In the 1860s and 1870s,

Tucson thrived as a center of commerce and was the territorial capital from 1867 to 1877. Mexican and Mexican-American businessmen dominated the economic markets and

provided the majority of services to settlers, ranches, mines,

farms, and above all military posts. Networks of freight

wagons delivered produce from Mexico, as well as hardware

and other goods from the east and west coasts. By 1881 the
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Cultural Resources of the Santa Rita Experimental Range Madsen

Southern Pacific Rail Road offset the balance of power in

Hispanic Arizona. Easterners rolled into the region and

successfully outbid the established frontier merchants for

local markets.

South of present-day Tucson, SRER was in the shadow of

the ranching and mining booms. Frederick Maish and

Thomas Driscoll ran cattle on the San Ignacio De La Canoa

Land Grant in the late 1860s and purchased the land from

founder Tomás Ortiz in 1879. By 1899 they had acquired

title to the Grant from the U.S. Government. Copper was

discovered at the north end of SRER in 1875. Here the

mining town of Helvetia had ups and downs with some

mining successes until it was abandoned in 1911. The Narragansett Copper Mine was established on the eastern edge of SRER

in 1879. Thereafter, a community of 150 people worked the

Rosemont Copper Mill and Smelter from 1894 to 1910.

Buttery (1987) notes the presence of at least three historicperiod ruins on SRER, and Swartz (2001) notes evidence of

past range experimental plots that may date to the Territorial and Statehood periods. Little information exists to fully

describe these historic resources. Nathan Sayre (this proceeding) provides an overview of the history of the SRER,

and his data will provide a glimpse of what historic resources

may lie untapped and awaiting anthropological/archaeological study.

At this point I return to a more indepth look at the

Hohokam culture and the patterns of Hohokam use of land

within the Santa Rita Experimental Range.

Cultural Resources

on the Range ___________________

The work by Buttery (1987) provides the primary source

of information about Range cultural resources. The principal reason for Buttery’s research was to examine how specific environmental factors such as landform, soil, hydrology, and to a broader extent vegetation, influenced how

people organized themselves over the landscape in the

prehistoric past.

Buttery conducted a systematic surface inspection of the

Range with a crew of two to three people spaced 20 m apart.

This team walked north-south transects along U.S. Geological Survey (USGS) topographic section lines and half-section lines. These parallel transects at half-mile intervals

were chosen to give an evenly spaced, systematic sample

covering of all biotic zones on the Range. Based on transect

width and length, Buttery indicates that approximately

19,700 ha (8,000 acres), or a 15-percent sample of the

146,000-ha (53,000-acre) range was inspected for archaeological resources. Buttery found 46 prehistoric sites during

her study (fig. 1). Sites were plotted on USGS 7.5-minute

topographic maps and on to MylarTM sheets covering

1:24,000-scale aerial photographs. The surface characteristics of each site were recorded on U.S. Forest Service site

forms, and sketch maps were made. All site forms are on file

at the Supervisor’s Office of the Coronado National Forest in

Tucson, AZ. Site information is now available to qualified

researchers through the State AZSITE Geographic Information System.

Criteria for designating sites were based on the standards

of the Coronado National Forest in 1985. Archaeological

sites were defined by the U.S. Forest Service as the presence

of six or more artifacts in proximity to each other on the

surface, or by the presence of obvious prehistoric features on

the landscape, such as seed-processing sites with mortar

holes in bedrock outcrops.

In 1985 considerable data were available from adjacent

regions to seriate Hohokam sites by time periods, and to

classify sites into functional groups based on surface artifact

assemblages and visible surface features. Borrowing from a

site classification system used during Phase B of the Central

Arizona Project (Czaplicki and Mayberry 1983: 27–29), Buttery sorted SRER sites into five categories: (1) Lithic Scatters,

(2) Garden Sites, (3) Limited Activity Sites, (4) Habitation

Sites, and (5) Specialized Activity Sites.

Lithic Scatters (Places Where Stone Tools

Were Made)

The Hohokam and their predecessors were expedient

toolmakers. If a task required the use of cutting, scraping, or

piercing tools, the nearest source of fine-grained rock was

used to make the needed implement. The import of exotic

stone tools and raw material from outside southern Arizona

occurred but was not in any way necessary or extensive.

The Santa Rita Mountains provide a wide range of rock

types suitable for making stone tools. On the Range, finegrained black to gray porphyritic andesite is found in abundant quantities on cobble terraces overlooking the Santa

Cruz Floodplain (Jones and others 1998). The same material

is plentiful in streambeds on the upper bajada.

Buttery identified six lithic scatters where someone split

porphyritic andesite cobbles to make tools. Lithic scatters

are characterized by the presence of cores, flakes, and waste

debris. Stone cores are cobbles with flakes removed; the

resulting flakes are sharp and can be used for cutting, or can

be flaked further into other tools. Debris is the byproduct of

toolmaking. Three lithic scatters were found in the upper

reaches of Sawmill Canyon, and three others at the lower

reaches of this drainage. These sites range from 80 to 270 m2

in size.

Garden Sites

Prehistoric agricultural fields marked by rock piles and

low stone alignments cover hundreds of hectares along the

edge of the flood plain of the Santa Cruz River from the

international border to locations 80 miles downstream at

Marana (Fish and others 1992). Interdisciplinary study of

these prehistoric agricultural complexes has detailed the

nature and extent of agave cultivation during the later

portion of the Hohokam sequence. Rock piles and stone

terraces enhance the planting environment of the agave

plant. The uneven, porous surface of a rock pile allows

penetration of rainfall, and the rock acts as mulch, slowing

evaporation of soil moisture. Agave pups gathered from a

high-elevation habitat in the Santa Rita Mountains were

transplanted into rock piles at lower elevation. Agave (or

century plant) has been a source of food and fiber for most

aboriginal groups of North America living within the

distributional range of these drought-adapted perennial

succulents.
74 USDA Forest Service Proceedings RMRS-P-30. 2003

Madsen Cultural Resources of the Santa Rita Experimental Range

Figure 1—Archaeological site locations on the Santa Rita Experimental Range.

Cultural Resources by Site Type

Class I & II Artifact Scatters

Compound & Trash Mound Sites

Garden Site

Limited Activity Sites

Lithic Scatter

Specialized Activity Site

0 3.5 7

Kilometers

N
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Cultural Resources of the Santa Rita Experimental Range Madsen

Four agave fields were recorded on the lower bajada of

SRER below 945 m (3,100 ft) elevation. Fields range from

391 to 10,000 m2 in size with four to 18 rock piles per site.

One agricultural site has a 60-m-long rock terrace. Buttery

found no habitation sites near these fields and postulated

that people living on or near the flood plain maintained them.

Recent work on the western periphery of SRER (Jones and

others 1998) shows that villages dating to the late preClassic and early Classic periods are within a mile of Buttery’s

agave fields.

Limited Activity Sites

Seven Hohokam sites, each with fewer then 25 artifacts,

were scattered between the upper and lower bajada. These

sites range from 12 m2 to 6,360 m2 in size and contain plain

ware pottery and flaked stone artifacts. One of the sites has

three unidentified decorated pot sherds. From this limited

information no particular function can be assigned to these

sites.

Habitation Sites

Over half of the sites recorded by Buttery on SRER (25 of

the 46 sites) are identified as habitation sites. As the word

implies, these are places where people built houses and lived

seasonally or year round. To determine seasonal versus

year-round habitation requires a multidisciplinary approach

to many lines of excavated archaeological data, but habitation in the broadest sense is easily recognized without

excavation from specific indices of artifacts and features

seen on the surface. Buttery separated habitation sites into

four categories based on the types of artifacts and feature

exposed on the surface.

Compound Sites—By A.D. 1150 the Hohokam were building their houses within walled compounds. Compounds were

made from solid adobe blocks or from upright posts intertwined with sticks and brush and bound together with adobe

mud. Evidence of both construction methods are expressed

archaeologically by remnant stone footings on the surface.

Two habitation sites on the upper bajada of SRER are

classified as compound sites. One site has two small rock

compounds with interior spaces of 48 m2 and 108 m2

. Thirteen other segments of wall footing were also recorded

including one footing 25 m long. The larger compound site

has a rock footing nearly 40 m long with three attached

perpendicular walls about 10 m long each. Two rectangular

rooms are attached to the interior of this enclosure.

Besides hundreds of broken pieces of plain utilitarian

pottery and a few decorated pieces, the artifacts on the

surface of both sites include food-grinding tools and flakedstone cutting, scraping, and piercing tools. The dates of

occupation are tentatively placed after A.D. 1150 based on

the Classic period compound architecture. A few pieces of

Rincon Red-on-brown pottery, dated to between A.D. 950

and 1150, were found on both sites. Another pottery type

called Tanque Verde Red-on-brown dated between A.D.

1150 and 1300 was found on one of the sites. Site area is

based on the distribution of artifacts on the surface. The first

site covers an area of 14,000 m2

, and the second, larger site

covers an area of 105,340 m2

. The potential for buried cultural

features on both sites is certain.

Trash Mound Sites—Villages occupied year round or

seasonally over many years have locations set aside for trash

disposal. After repeated dumping episodes in one location,

trash accumulates into mounds, and if conditions are favorable, these mounds remain visible for centuries. On the

upper bajada of SRER four villages were occupied for extended periods of times as suggested by the presence of trash

mounds. Two villages have four trash mounds, and the two

others each have one mound. Most of the mounds are only a

few centimeters high and are identified by the presence of

artifact concentrations, but the largest known trash mound

on SRER covers 72 m2

 and is mounded 50 cm high.

Based on the distribution of surface artifacts, the four

villages range from 70,000 to 200,000 m2 in size. Artifacts

scattered across these sites include plain utilitarian pottery,

flaked-stone cutting, scraping, and piercing tools, and waste

flakes and debris from toolmaking. Seed-grinding tools

(manos and metates) and jewelry made from seashells are

present. Three of the four villages have datable decorated

pottery including Rincon Red, and Rincon Red-on-brown, as

well as Sacaton Red-on-buff, indicating occupation between

A.D. 900 and 1150. The earliest of the four sites has one trash

mound with Santa Cruz Red-on-buff pottery placing its

occupation between A.D. 875 and 950. With little doubt,

these sites have archaeological deposits that include many

buried houses and features.

Class I Artifact Scatters—Buttery used the term “Class I

Artifact Scatter” to describe sites with three or more types of

artifacts. These sites have no surface evidence of trash

mounds, but a few have heavy concentrations of artifacts

that may represent locations of trash disposal. The absence

of trash mounds may have to do with the length of occupation, the intensity and type of use, or the rate of deflation. It

is certain that some of these sites represent permanent

villages with several houses, while others in this group may

be small seasonal farmsteads with a few houses or ramadas.

The surface areas of these sites range from 8,000 m2 to as

large as 306,000 m2.

Plain utilitarian pottery, flaked-stone cutting, scraping,

and piercing tools, waste flakes, and debris from toolmaking

are present on most of these sites. Twelve sites have foodgrinding implements (manos and metates). Dispersed unevenly among the 14 sites are seashell artifacts, carved stone

jewelry, tabular agave knives, a stone axe, pottery spindle

whorls, a quartz crystal, evidence of a cemetery, and rock

pile clusters protruding through the surface.

Five of the 14 sites have datable decorated pottery. Rincon

Red-on-brown dating from A.D. 900 to 1150 is dominant,

followed by Rillito Red-on-brown (A.D. 875 to 950), and

unidentified buff ware sherds.

Class II Artifact Scatters—Buttery grouped these four

sites together because the artifact assemblages are limited

to broken pottery and flaked stone. Plain ware (utilitarian

brown ware) is the dominant pottery type on the surface of

these sites. Rincon Red-on-brown on three sites suggests an

occupation between A.D. 900 and 1150. Flaked stone is

limited to flakes and cores (cobbles with flakes removed),

hammer stones (tools for removing flakes from cobbles), and
76 USDA Forest Service Proceedings RMRS-P-30. 2003

Madsen Cultural Resources of the Santa Rita Experimental Range

cutting tools. One site has a single small rock pile of indeterminate function. These sites range from 14,000 to 95,000 m2

in size, and although they are large sites, the surface artifact

assemblages lack the variety usually found at permanent

habitation sites. The proximity of Class II sites to washes

and fans may indicate they were seasonal habitation sites

that functioned as farmsteads.

Special Activity Sites

These four sites are diverse in function. The first is a plantprocessing site where four mortar holes and four grinding

slicks (bedrock metates) were created on exposed bedrock

near the mountain pediment. In these locations, food products like mesquite pods were milled or ground into flour with

stone pestles and manos. Buttery notes that the largest

mortar hole is 15 cm in diameter and 9 cm deep. The four

nearby bedrock grinding slicks each measure about 70 cm

long, 30 cm wide, and 18 cm deep.

The second special activity site is located at Huerfano

Butte, a small rocky hill in the northeast quadrant of the

Range. Buttery notes that shallow bedrock forces ground

water to the surface in a wash on the south side of the Butte.

Exposed outcrops of granite on either side of the wash have

50 bedrock mortar holes and numerous smaller cupules,

further suggesting that the location may have been a reliable water source at times. Along the same wash is a vertical

stone surface with pictographs painted in red hematite. The

paintings include human and animal life forms as well as

concentric circles. A few plain ware and unidentified decorated pottery sherds and flaked-stone artifacts were noted in

the area. As mentioned earlier, Huerfano Butte gained

notoriety in 1965 when a young girl discovered an extensive

prehistoric jewelry cache while on a picnic. While exploring

cracks and crevices on the butte the young girl discovered a

prehistoric bowl filled with turquoise and shell beads, as

wells as carved bird and frog pendants. This discovery

resulted in the first and only scientific journal article about

the archaeology of SRER (Bahti 1970). The cached offerings,

the red paintings, and the numerous food-processing features may or may not be related, but one can imagine that a

reliable water source near, or on the surface, is an element

that could bind all of the site’s features together.

The third special activity site is associated with food

processing. It is located on the lower bajada in an area

experiencing deflation. The site is 98,400 m2 in size, and

within its boundaries are 34 rock piles, most of which are

check dams. Some of the other rock features are hearths and

roasting pits filled with broken and fire-charred grinding

implements. Buttery recorded 70 manos, 5 metates, and

observed several pestles. The pottery at this site is dominated by mostly broken plain ware, but four broken decorated sherds were noted, including Snaketown Red-on-buff

(A.D. 650 to 900), Rincon Red-on-brown (A.D. 900 to 1150),

and Tanque Verde Red-on-brown (A.D. 1150 and 1300).

Buttery noted a dozen modified sherds, some ground round

into spindle whorls. Buttery noted that the flaked-stone

tools made from black porphyritic rhyolite were abundant

and include flakes, scraping and cutting tools, and cores.

The fourth special activity site is located in Florida Canyon and was identified as a source of black porphyritic

cobbles. These cobbles were broken to test the quality of the

stone for toolmaking. Some material was used on the spot to

make tools, but it is also likely that cobbles were collected

and taken elsewhere for use (see “Lithic Scatter” above).

This site covers 70,000 m2 of land. The discovery of an

Archaic triangular biface tool along with plain ware Hohokam

pottery suggest a long history of use. Every habitation site

on SRER contains stone artifacts made from black porphyritic igneous rock, and as indicated earlier, Florida Canyon

is not the only source for this material. Other drainages

certainly have similar deposits of stone as do the lower

bajada Holocene fans and ridges (Jones and others 1998).

Settlement Pattern

The pattern of Hohokam settlement on the northern

slopes of the Santa Rita Mountains reflects both environmental risks and opportunities. Settlement will be examined in its relationship to the availability of resources on the

upper bajada, middle bajada, and lower bajada of the Range.

Upper Bajada—Finding large numbers of Hohokam

sites in upper bajada locations is a common pattern in the

basin-range country of the Sonoran Desert, particularly

where mountains rise above 1,219 m (4,000 ft) in elevation.

The Santa Rita Mountains rise just over 2,881 m in elevation

(9,453 ft), and the bajada slopes around the entire base

provide many opportunities conducive to human settlement.

Buttery indicates that 63 percent of the Hohokam sites on

the Range are located on the upper bajada between 1,097 m

(3,600 ft) and 1,341 m (4,400 ft) above sea level. Here, there

is enhanced precipitation from orographic rainfall, sufficient elevation to lessen frost from cold air drainage, surface

water, and bedrock water catchments. The bajada itself

offers plant foods like mesquite pods and cacti fruit, and

proximity to the mountain provides access to a rapid succession of plants and animals used for a variety of purposes,

including food, clothing, and shelter.

The Hohokam living on the northern side of the Santa Rita

Mountains depended on the relatively abundant local precipitation for domestic and agricultural use. The uplift of

moisture-laden air passing over the Santa Rita Mountains

delivers predictable precipitation to the mountain peaks,

provides perennial surface water in canyons, and heightened chances for direct rainfall on the upper bajada in the

winter and summer months, probably more so than on the

valley floor. At the mountain front, Holocene sediments over

bedrock are typically no deeper than a few meters; accessible

water tables at the mouth of Box Canyon and Sawmill

Canyon and in nearby ephemeral drainages were important

factors in settlement location.

Upper bajada agriculture—Bottomlands with high agricultural potential are not evenly distributed along Box and

Sawmill Canyons but vary with factors such as width and

morphology of the flood plain, water-table depth, watershed

size, and drainage gradient. The importance of such acreage

for supporting relatively dense populations is indicated by

the locations of large habitation sites along those stretches

of Box Canyon and Sawmill Canyon suitable for flood plain

fields. Buttery suggests that the water may have flowed in

these canyons continuously in the prehistoric period.
USDA Forest Service Proceedings RMRS-P-30. 2003 77

Cultural Resources of the Santa Rita Experimental Range Madsen

The Holocene soils on the broad upper bajada terraces

between major washes are also suitable for agriculture.

The surface runoff would have easily infiltrated the sandy

Holocene soils and remained close to the surface because of

the underlying Pleistocene clay soil. When the water reaches

the clay soil, it would begin to move laterally. At the point

where the sandy soil becomes shallow or pinched out, it is

likely that there would have been free water on or near the

surface, thus creating temporary seeps following above average winter precipitation.... (Buttery 1987: 92).

Between 1,097 m (3,600 ft) and the mountain pediment,

Buttery noted locations where moist conditions near the

surface caused lush growing condition for local gasses.

Middle Bajada—The middle reach of the Range’s bajada

was not a place of settlement because drinking water was

inconveniently distant at either the Santa Cruz River below

or at the mountain edge above. As Box Canyon and Sawmill

Canyon drain downhill and cross into the mid-bajada, surface flow tends to diminish or disappear in channels through

infiltration into increasingly deep valley fill. The lower limit

of habitation sites on Box Canyon and Sawmill Canyon

probably mark the downslope extent of significant surface

flow from all but the largest precipitation events following

major storms.

Many small drainages with bajada catchments are sufficiently shallow that farmers from upper and lower bajada

settlements could have successfully farmed the middle bajada

by diverting storm water into fields. However, water would

have been available only in cases of storms directly over the

watershed, a relatively unpredictable event compared to

higher elevation precipitation triggered by uplift of air over

the mountains. At this time there is no archaeological

evidence suggesting agricultural use of this zone.

The vegetation regimes seen on the Range today probably

mimic to some extent the Range around A.D. 1150, when the

prehistoric population was at its highest. If there were any

differences, it is in the frequency of native trees and plants

seen today as opposed to the presence or absence of these

species in the past. Within the Tucson Basin, analysis of

charcoal from 21 roasting pits dating from A.D. 1150 to 1300

(Fish and others 1992) and from a single roasting pit dating

from A.D. 894 and 1148 (Van Buren and others 1992) shows

abundant fuel woods of mesquite, ironwood, and palo verde,

all consistent with the vegetation seen in the same locations

today. It is likely that exploitation of annual and perennial

plants in the middle bajada was frequent and shared by the

people living above and below this zone.

Lower Bajada—Buttery indicated that 37 percent of the

sites on the Range are below 945 m (3,100 ft) and include

small agave gardens, lithic scatters, a plant-processing site,

and five habitation sites. Lower bajada habitation sites are

linked to the flood-plain community. Here water in the

Santa Cruz River, and at springs like those at Canoa, provides

domestic water sources. Like elsewhere, mesquite, cactus,

and other annual and perennial plants provided food resources. Hardy upland agave plants also were transplanted

to lower elevation gardens, cultivated, and successfully

propagated for food and fiber on the gravel ridges overlooking the flood plain.

Low bajada agriculture—Alluvial fans, composed of

outwash sediments from the uplands, coalesce on the lower

bajada north of Box Canyon. Gentle slopes provide an active

depositional environment and controllable water flow. In

these situations flood waters following storms provided both

moisture and simultaneous enrichment for crops in the form

of suspended nutrients and organic detritus. The clustering

of habitation sites at the lower limits of alluvial fans on the

Range mirrors similar patterns throughout the Santa Cruz

watershed.

Hohokam Community

The archaeological survey conducted by Buttery covered

approximately 19,700 ha (8,000 acres), or a 15-percent

sample of the 146,000 ha (53,159 acres). Of the 46 archaeological sites recorded, 25 are habitation sites representing

places of permanent or seasonal habitation by the Hohokam

people. This sample of area and sites provides sufficient

information to predict with some confidence that many more

Hohokam sites are present on the Range. The majority of the

recorded Hohokam habitation sites were occupied between

A.D. 900 and 1150, and at least two were occupied until A.D.

1300. As indicated in the cultural history section of this

paper, the Hohokam organized into communities with central sites with public architecture at their core. There is little

doubt that the dense Preclassic population on the Range is

part of one or more communities. This suggests that a

central site with a ball court, a form of Hohokam public

architecture associated with Preclassic communities, should

be found somewhere on the Range probably in an upper

bajada location. There is insufficient information on

Hohokam Classic period sites, with only two recorded at this

time, to understand their place and relationship to other sites.

Concluding Comments ___________

Cultural Resource Management

on the Range

Preservation of archaeological resources for scientific investigation outside the Range is not possible except in rare

instances. Since 1987, over 29,600 ha (12,000 acres) of land

has been inspected for archaeological sites on the western

and northern periphery of the Range, mostly as the result of

enforcement of the Pima County Cultural Resource Ordinance (Sec. 18.81.060,B.10). These inspections resulted in

the recordation of over 400 archaeological sites, but unfortunately only a small portion of these sites will be set aside for

preservation in perpetuity. Those sites not fully protected

will be subjected to compliance-related archaeological investigations. Unfortunately, the cost of scientific study is very

expensive, and all work is more often than not geared to

collecting samples that never capture the full breadth and

understanding of how people lived and survived in these arid

lands.

This is why cultural resources inside areas like the Santa

Rita Experimental Range are so important to protect. Within

the Range lies important information about the prehistory of

the region and the history of homesteading and ranching.

Equally important is archaeological information about the

history of range experimentation itself, and how early scientific research was carried out. A record of this scientific use
78 USDA Forest Service Proceedings RMRS-P-30. 2003

Madsen Cultural Resources of the Santa Rita Experimental Range

is embedded in the landscape and will not be found in the

written or photographic history of the Range. Beyond the

humanistic elements of archaeology, sites on the range contain vast amounts of information useful to studies of climate,

plant and animal ecology, geology, and geomorphology.

We are rapidly approaching the time when the Santa Rita

Experimental Range finally and forever will be enclosed on

three sides by a dense urban landscape. High-density residential communities will create new challenges for the

Range and will require an increased commitment on the part

of the Arizona State Land Department, the Arizona Game

and Fish Department, the Arizona Department of Agriculture, and the University of Arizona to manage and monitor

the health of the Range.

A complete inventory of SRER cultural resources will

facilitate the implementation of future range projects, to

include improvements to the land needed in the normal

course of use and during the selection of lands for scientific

study related to the principal purposes of the experimental

range. With the inevitable growth around the periphery of

the Range, inventories of cultural resources are necessary

for the sheer purpose of protecting them and for assessing

impact from allowable public use within the current context

of State law and State Trust lands policy.

Cultural resource inventory can coincide with the teaching mission of the University of Arizona. Opportunities for

students to design and implement research on the scale of

the work accomplished by Buttery (1987) and Fish and

others (1992) abound on the Range, and can co-occur and

even complement and contribute important information

useful to the research objectives of the modern day range

ecologist. With that said, the 100th Anniversary of the

Santa Rita Experimental Range also presents an opportunity for constituents with common interests in the survival

of the Range to develop a long range plan that binds public

and scientific interest in this open space.

References _____________________

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80 USDA Forest Service Proceedings RMRS-P-30. 2003

Bruce D. Munda

Mark J. Pater

Revegetation Practices on the Santa Rita

Experimental Range

Bruce D. Munda has worked for the Natural Resources Conservation Service (formerly the Soil Conservation Service) since 1975. He received a B.S. degree

inagriculture (minor in watershed hydrology and range management) and an M.S. degree in agronomy and plant genetics from the University of Arizona. Contact Bruce

at: Natural Resources Conservation Service, Tucson Plant Materials Center, 3241 N. Romero Road, Tucson, AZ 85705-9223; e-mail: Bruce.Munda@az.usda.gov. Mark

J. Pater has worked for the Bureau of Land Management since 2002. Mark formerly worked for the Natural Resources Conservation Service (formerly the Soil

Conservation Service) from 1987 to 2002. Mark received a B.S. degree in environmental resource management from Arizona State University and an M.S. degree

in agronomy and plant genetics from the University of Arizona.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

From the late 1800s through the early 1900s woody plants increased and grasses decreased on rangelands throughout the

Southwestern United States and Northern Mexico (Roundy 1995). Declining forage conditions and increased erosion led

scientists and land users to attempt to develop management practices to improve the vegetation on these rangelands.

Experimental ranges were created to serve as centers for the study of rangelands and development of information and practices

that would protect, restore, and provide for the proper management of these environments. The Santa Rita Experimental

Range (SRER) was established in 1903 to serve as an experimental range for the arid Southwest (Medina 1996). Early

revegetation studies at the SRER and elsewhere in southern Arizona were conducted by D. A. Griffiths and J. J. Thornber.

Griffiths’ work began in southern Arizona in 1904 and utilized both native and introduced perennial forage species. He

incorporated the use of furrows to concentrate and store moisture in an effort to improve plant establishment. Poor results from

these plantings directed Griffiths to conclude that annual plants were better suited for revegetation of desert rangelands

(Glendening and Parker 1948). In 1910 Thornber, based on his work in southern Arizona, reported that introduced forage

plants were not well adapted to the desert rangelands, and that native plants that are ecologically adapted to the desert and

to soils that are subject to flooding gave the best results in his trials (Glendening and Parker 1948). E. O. Wooton’s revegetation

trials in 1916 at the SRER supported Griffiths’ and Thornber’s earlier findings that, with the exception of annual filaree

(Erodium cicutarium (L.) L’He’r. ex Ait.), revegetation with introduced grasses was not likely to be successful. While

revegetation studies began soon after the SRER was established (Martin 1966), a formal range revegetation program did not

Abstract: This paper discusses the revegetation activites on the Santa Rita Experimental Range

since 1903. Revegetation research includes experiments to evaluate adaptation, seedbed preparation, and sowing methods. We also discuss criteria used to determine if a site has the potential

for a successful revegetation. Successful revegetation was initially based on plant emergence and

establishment but not persistence. Plants in successful plantings typically died or the initial stand

declined substantially within about 10 years. Revegetation trials typically used native and

introduced species. However, introduced species such as Lehmann lovegrass (Eragrostis

lehmanniana Nees) more successfully established and spread. Lehmann lovegrass is invading

and reducing the biodiversity of the semidesert grasslands. Scientists and others are now

emphasizing revegetation with native plants. The Santa Rita Experimental Range will continue

to serve as an outdoor laboratory in the search for revegetation methods, combined with the use

of native species, to improve the biodiversity as well as watershed stability of the semidesert

grasslands.

Keywords: Lehmann lovegrass, native plants, reseeding, seedbed, and transplanting

Acknowledgments: We would like to thank our editors, Dr. Steven Smith and Dr. Bruce Roundy,

for reviewing this document and providing comments, suggestions, and collaboration in developing this document. We would also like to thank Dr. Ramona Garner for her comments. Much of

the information presented in this paper was provided by the Santa Rita Experimental Range

Paper Archives.
USDA Forest Service Proceedings RMRS-P-30. 2003 81

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

begin until 1935. Glendening and Parker (1948) stated that

the most successful species to use in rangeland revegetation

within the semidesert grassland, based on revegetation

experiments at the SRER, were Boer lovegrass (Eragrostis

curvula(Schrad.) Nees), Lehmann lovegrass (E. lehmanniana

Nees), and Wilman lovegrass (E. superba Peyr.). However,

most revegetation trials resulted in failure. Most often this

was attributed to a lack of adequate moisture for plant

establishment. This led to the search to find drought-tolerant plant species for use in revegetation. Scientists and

others experimented with innovative methods in seedbed

preparation and evaluating introduced species in search of

methods and species that would successfully revegetate

severely eroding rangelands (Roundy 1995). In southern

Arizona, these “miracle plants” appeared to be primarily the

exotic lovegrasses from Southern Africa. Several lovegrass

species were tested for revegetation use on the SRER. The

most successful was Lehmann lovegrass. The revegetation

program conducted by the Rocky Mountain Forest and

Range Experiment Station ended on the SRER in the mid1950s (Medina 1996).

Since 1939, the U.S. Department of Agriculture, Natural

Resources Conservation Service, Tucson Plant Materials

Center (PMC) has conducted plantings on the SRER. The

SRER has provided the PMC with long-term evaluation

sites for comparison of the potential of native and introduced

species for revegetation on Southwestern rangelands. The

most recent experimental planting was established in 1968.

Eighteen different plantings (12 warm season and 6 cool

season) were conducted at this site from 1968 through 1988.

This site is located in pasture 5N south of Desert Tank on

Road 401 (SW 1⁄4 of the SW 1⁄4 of Section 3, Township 18 south

and Range 14 east). The objective of these plantings was to

determine the production and erosion control potential of

native and introduced species selected from the PMC testing

program for the arid Southwest (USDA 1988).

Revegetation Principles __________

Researchers have attempted to describe factors to consider when determining if revegetation is feasible. The number of factors varies depending on the author but generally

includes (1) site selection, (2) seedbed preparation, (3) species

selection, and (4) seeding method (Anderson and others 1957;

Jordan 1981; Martin 1966; Roundy and Biedenbender 1995).

The following discussion is a review of the many efforts conducted at the SRER to enhance our knowledge of these factors.

Site Selection

Based on revegetation trials on the SRER, Anderson and

others (1957) summarized the many factors to consider

when determining if a revegetation effort is feasible. Site

selection should be based on local climate and soil types.

Sites should have medium textured soils with moderate

infiltration rates, good waterholding capacities, be at least 2

ft deep, and receive 11 inches of average annual precipitation. Sites that receive less precipitation may be expected to

have successful seedings only in above-average rainfall

years. In drought years, even seedings on favorable sites

may result in failure. Existing vegetation can indicate the

area’s forage production potential. Areas with dense cover

may indicate deep soils with good waterholding capacity and

the potential to produce forage. Anderson and others (1957)

suggested that the existing plant community may be used to

determine if revegetation efforts will be successful. Stands of

mesquite (Prosopis velutina Woot.) and burroweed (Isocoma

tenuisecta Greene) are good indicators of sites suitable for

revegetation and supporting grass. Species like saguaro

(Carnegiea gigantea (Engelm.) Britton & Rose), paloverde

(Parkinsoniaspp. L.), triangle leaf bursage (Ambrosia deltoidea

(Torr.) Payne), and ironwood (Olneya tesota Gray) indicate

sites that are arid and droughty and unsuited to revegetation.

Dense stands of woody vegetation must be controlled before

attempting to reseed. Anderson and others’ (1957) research on

the SRER found that if mesquite density exceeded 15 to 25 trees

per acre they had to be controlled prior to revegetation. Also,

if burroweed was a principal component of the plant community

it would have to be removed prior to revegetation. Revegetation

is seldom justified on those areas where desirable grasses

remain and stand recovery can be obtained following proper

grazing management practices. Reynolds (1951), based on his

work at the SRER, suggested that with an appropriate rest

period sandy loam soils in semidesert rangeland that have an

existing 10- to 20-percent stand of Rothrock and black grama

should not be recommended for revegetation with Lehmann

lovegrass. Reynolds suggested that a rest period of 8 to 10

years is needed on these sites for native grass stands to

recover to similar forage production as similar-aged stands of

seeded Lehmann lovegrass. Cox and Jordan (1983), from

their rangeland revegetation work in southeastern Arizona,

suggested that revegetation should be discontinued in the

Chihuahuan Desert if it is based on an expected gain in

livestock numbers. They stated that a successful seeding can

be expected in 1 of 10 years in the Chihuahuan Desert of

southeastern Arizona, and that forage production from a

successful seeding can be expected to decline over a 10-year

period. Sites heavily infested with cholla and pricklypear

cacti (Opuntia spp. P.Mill.) are seldom suitable for revegetation because the physical manipulation required to prepare

the seedbed would aid in dissemination of cactus propagules

and increase their density. Martin (1966) stated that competitors, especially woody plants, should be removed or

controlled prior to revegetation. Livingston and others (1997)

found that Bush muhly (Muhlenbergia porteri Scribn. ex

Beal) had greater density and cover under overstory woody

species compared to open areas on their research plots at the

SRER, suggesting that shade-tolerant species may emerge

and persist if seeded under overstory plants.

Selection of revegetation sites should incorporate proper

management of the site after revegetation. Revegetation sites

should be rested from grazing for at least 1 to 2 growing

seasons to allow young plants to become established. The site

should be managed so that livestock or other grazers are not

allowed to concentrate and overutilize the reseeded area.

When planning a revegetation project, care should be given to

its size so the reseeded area can be incorporated into the

overall management plan and be properly managed. Also,

indigenous fauna (rodents and rabbits) can have a significant impact on the success of a revegetation project (Anderson and others 1957), especially small revegetation projects.

Jordan (1981) summarized that site selection should be

based on climate, soils, and terrain. The site must have the
82 USDA Forest Service Proceedings RMRS-P-30. 2003

Munda and Pater Revegetation Practices on the Santa Rita Experimental Range

potential for successful establishment and ability to support

the proposed revegetation. The terrain and soil types must

be suitable to support the desired vegetation change. Shallow, coarse, rocky, saline, and or alkaline soils should be

avoided, as should terrain with slopes above 30 percent.

In southern Arizona, Jordan (1981) proposed that seeding

sites should ideally receive an average of 5.5 inches of

precipitation in July, August, and September and at least 11

inches of average annual precipitation to be considered for

potential revegetation. In his summary of revegetation activities on the SRER, Martin (1966) indicated that seeding

should take place in May or June prior to the start of the

summer rainy season. Roundy and others (1993) conducted

laboratory germination experiments with regard to seeding

depth and water availability for three grasses used in semidesert revegetation. Their results indicated that these grasses

required frequent rainfall events for establishment. Lack of

frequent rainfall events may be one reason many of the

revegetation activities in the Southwest have poor results.

Research by Abbott and Roundy (1995) on the SRER suggested that native grass seedings should take place the third

week of July to increase the chance of successful establishment. They found that native grasses germinated faster

than Lehmann lovegrass, especially when sown as naked

caryopsis. By waiting to seed until the third week of July

there is a greater opportunity of receiving rainfall events

that are 5 days apart or less.

Seedbed Preparation

Wooton’s revegetation recommendations based on research

conducted between 1913 and 1916 on the SRER were to

broadcast native seed onto bare ground without preparing

the seedbed (Glendening and Parker 1948). Wilson’s work,

conducted from 1927 to 1931 in southern and central New

Mexico, determined that the best revegetation results were

obtained by seeding just prior to summer rains with little or

no seedbed treatment except when a mechanical treatment

was needed to control competition (Glendening and Parker

1948). Bridges work (Glendening and Parker 1948) from

1938 to 1941 in southern New Mexico indicated that seedbed

preparation was necessary to ensure a successful revegetation. The equipment he used was a two-row lister followed by

a 6-ft drill. Glendening and Parker (1948) stated that the

eccentric disk-cultipacker seeder, developed by the Soil

Conservation Service, was the best piece of equipment for

preparing the seedbed and seeding. On sandy soils, successful revegetation has been achieved by broadcasting directly

onto the soil surface (Glendening and Parker 1948).

Range trials in 1951 used a Krause cutaway disc to

prepare the seedbed, tilling to a depth of 2 to 4 inches. This

seedbed preparation implement was commonly used in the

1950s prior to broadcast seeding and cultipacking (Reynolds

1951). Martin (1966) suggested that planting methods should

ensure proper seed placement in the soil surface, 1⁄4 inch for

fine-seeded species and up to 1 inch deep for large-seeded

species, and promote moisture penetration into the soil.

Successful seedbed preparation methods include pitting,

contour furrowing, ripping, and imprinting (Reynolds and

Martin 1968). Slayback and Cable (1970) conducted a 4-year

trial to evaluate the effectiveness of “intermediate pits” and

conventional pits on three different soil types (sandy loam,

loam, and clay loam) on the SRER at the old PMC site that

was north of the intersection between roads 505 and 401.

The conventional pits were constructed using a standard

pitting disc, creating a pit that was 18 to 24 inches long, 12

inches wide, and 6 inches deep. Intermediate pits were

constructed with the basin-forming machine developed by

Frost and Hamilton (1964) (fig. 1), which created broad,

shallow pits 5 ft wide, 5 to 6 ft long, and 6 inches deep. The

intermediate pit was developed to create pits that had a

longer effective life. Conventional pits were effective for

initial plant establishment, but they filled with soil after

intense rainfall events and lost their ability to concentrate

water within the first year or two. The average forage

production over a 4-year period was 21

⁄2 times greater in the

intermediate pit (basins) as in the standard pit (Martin and

Cable 1975). Slayback and Renney (1972) compared bulldozer pits, reportedly similar to the pits made by the Frost

basin-forming machine, to conventional pits or interrupted

contour furrows, and their brand of “intermediate pits” (fig. 2)

at the current PMC site located approximately 1 mile south

of Desert Tank on road 401. Slayback and Renney’s intermediate pits differed from Frost’s intermediate pits primarily

in the type of equipment used to construct them. Slayback

and Renney used a tractor with a three-point hitch-mounted

blade to form pits that were approximately the same size as

the pits formed by Frost’s basin forming machine. A rangeland drill was used to sow the seeds into the pits compared

to Frost’s machine that formed pits and planted the seed in

a single operation. Herbage production and stand counts

were taken over the 4-year planting effort. Their results

indicate that the intermediate pit was more effective with

Figure 1—Frost basin-forming machine (from K. R.

Frost and L. Hamilton, publication date and source

unknown). Reclaiming semidesert land by planting

perennials in basins on uncultivated soils (available

in Paper Archives at U.S. Department of Agriculture,

Natural Resources Conservation Service, Tucson

Plant Materials Center).
USDA Forest Service Proceedings RMRS-P-30. 2003 83

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

regard to stand establishment and forage production than

the conventional pit and the bulldozer pit treatments.

At the current SRER PMC site, one or more seedbed

treatments were incorporated in all experimental plantings

from 1968 to 1988. Treatments included intermediate pits,

disking, or contour furrowing after ripping. Intermediate

pits were created as described by Slayback and Renney

(1972) along a 200-ft row perpendicular to the slope. Intermediate pits were used in 11 of the 18 plantings at the PMC

site, while only three plantings used the disked treatments

and only one used the furrowed following ripping treatment.

Only two planting dates (1983 and 1984) resulted in good

stand establishment and persistence of seeded species using

the intermediate pits. The disked seedbed treatment had

similar results with regard to percent stand and persistence

in most plantings, but in the 1982 planting the stand

persistence was much lower than the intermediate pits.

Cattle trampling has been another method recommended

for preparing a seedbed that would encourage seedling

establishment (Winkel and Roundy 1991). In the Altar

Valley south of Three Points, Winkel and Roundy (1991)

compared seedling emergence using cattle trampling, land

imprinting, and ripping as seedbed preparation treatments.

They found in years where summer precipitation provided

available soil surface water for at least 3 weeks, land imprinting and heavy cattle trampling increased plant emergence for Blue panic (Panicum antidotaleRetz.) and “Cochise”

atherstone lovegrass (Eragrostis trichophoraCoss. and Dur.).

In years where summer precipitation provided available soil

water for 6 to 9 days, they found that seedbed treatments

with the greatest disturbance (heavy trampling, land imprinting, and ripping) produced higher emergence than no

disturbance or light disturbance treatments. In years where

the available soil water was only 2 to 3 days, emergence was

low for all seedbed treatments. Winkel and Roundy (1991)

suggested that seedbed disturbance may be unnecessary in

wet years and provide little benefit for plant establishment

in dry years, depending on soil type and seed size of sown

species (Winkel and others 1991).

Species Selection

Early revegetation work in southern New Mexico by

Bridges, working from 1938 to 1941, determined that the

most successful species for revegetation (of the 118 tried)

were Rothrock grama (Bouteloua rothrockii Vasey), Boer

and Lehmann lovegrass, and fourwing saltbush (Atriplex

canescens (Pursh) Nutt.) (Glendening and Parker 1948). In

the semidesert grassland of southern Arizona the best

adapted species were Boer, Lehmann, and Wilman lovegrass

(Glendening and Parker 1948).

Glendening (1937) conducted and evaluated several revegetation trials at the SRER from 1933 to 1937. These included

irrigation, use of mulch, seedbed cultivation, winter seeding,

seeding with native hay, seeding with annuals, transplanting, and revegetation using transported topsoil. The following is an overview of this work.

All of the trials were initiated in 1935 except as noted. An

irrigated seeding trial used 24 small seedbeds (1 m2

) that

were sown to either mixtures or pure stands of the following

species: black grama (Bouteloua eriopoda (Torr.) Torr.),

hairy grama (B. hirsuta Lag.), slender grama (B. repens

(Kunth) Scribn. & Merr), sprucetop grama (B. chondrosioides

(Kunth) Benth. ex S.Wats), Rothrock grama, sideoats grama

(B. curtipendula (Michx.) Torr.), and parry grama (B. parryi

(Fourn.) Griffiths); bush muhly and Arizona cottongrass

(cottontop) (Digitaria californica(Benth.) Henr.). Plots were

sown in early July and hand irrigated for approximately

2 weeks, or until the start of the summer rains. Excellent

stands of all the grasses were obtained except black grama

and bush muhly. Poor seed quality was the main reason cited

for the performance of black grama. After 2 years the established plants were spreading vegetatively. Glendening indicated that if a source of viable seed could be developed black

grama would be an excellent species for revegetation due to

its ability to persist and spread on poor soils. Glendening

considered bush muhly a very poor species to be used in revegetation due to its poor emergence characteristics.

A mulch trial incorporated four (10 by 10 ft) plots that were

totally protected from grazing. Plots were seeded to different

species after the start of the summer rains. One-half of each

plot was covered with 1 inch of barley (Hordeum vulgare L.)

straw. Grass species used were slender, Rothrock, and

sideoats grama; and tanglehead (Heteropogon contortus (L.)

Beauv. ex Roemer & J.A. Schultes). Seed was applied to the

bare undisturbed soil surface. An excellent stand was obtained for each grass plot with mulch. The plots without mulch

had little to no emergence or plant establishment (fig. 3). A

seedbed cultivation trial was installed in June 1936 prior to

the start of the summer rains. A 500-ft2

 plot was seeded to

a mixture of Rothrock, slender, and sprucetop grama, and

Figure 2—Pit types used on the Santa Rita Experimental Range by NRCS at the Desert Tank planting site

(adapted from Slayback and Cable 1970).

Intermediate pit 

 

Conventional pit 

 

Bulldozer pit 

 

5’ to 6’ 6”

5’

24”

12” 6” 

8’ to 10’ 

6’ 

6” to 8” 
84 USDA Forest Service Proceedings RMRS-P-30. 2003

Munda and Pater Revegetation Practices on the Santa Rita Experimental Range

tanglehead, Arizona cottontop, and bush muhly. The plots

were hand raked to disturb the soil to a depth of 1 inch, and

half of the plot was lightly covered with mulch. Emergence

was good despite poor summer rainfall. The mulch-covered

portion of the plot had the best emergence, but it was not as

dramatic as the previous trial where the seed was sown on

the bare soil without disturbance. This trial indicates that

cultivation may offset the lack of litter on the soil surface. A

similar trial sown in August 1936 compared three treatments: mulch, raked topsoil, and a control. The species from

the previously described planting were used in addition to

sideoats and black grama. Due to late planting and limited

precipitation few plants established. Plots with mulch had

the greatest number of seedlings though. A winter seeding

trial was sown on December 5, 1935, onto a 2,500-ft2 plot.

The seed mixture included Rothrock, slender, sideoats, and

black grama, bush muhly, tanglehead, and Arizona cottontop.

The plot had raked and unraked soil surfaces for seedbed

treatments. The raked treatment involved cultivating to a

depth of about 2 inches, sowing the seed, and then lightly

raking to cover the seed. This trial was apparently a failure

due to temperatures being too low for germination. This trial

was repeated in January 1937 using the same species and

treatments with the inclusion of mulch on one-third of the

plot. The same results were obtained with no germination or

emergence noted.

A native grass hay trial was conducted during the summer

of 1936. During 1935 a native grass stand (sideoats, slender,

and sprucetop grama, cottontop, and feathergrass (Chloris

virgata Sw.) was cut when the seed was reaching maturity.

The hay was stored and then spread over the study area in

1936. Emergence was good, but plant survival was low by the

end of the summer due to below normal summer rainfall.

Glendening felt strongly that the use of mulch or grass hay

was one of the most promising seeding methods for revegetation of desert rangelands. A winter annual trial included:

indianwheat (Plantago ovata Forsk.), California poppy

(Eschscholzia californicaCham.), filaree, fiddleneck (Phacelia

spp. Juss.), mustards (Descurainia spp. Webb & Berth. and

Lepidium spp. L.), and sixweeks fescue (Vulpia octoflora

var. octoflora (Walt.) Rydb.). Two plantings were conducted

(September and October) in 1935 at the Gravelly Ridge site,

which is almost due south of the present Continental Grade

School on the highway 62. Treatments included the application of mulch over seeds that were sown on bare soil, cultivating the soil prior to sowing, and sowing seeds on bare undisturbed ground. Emergence was good for all treatments due to

good November and December rainfall. Rainfall was poor for

the months of January through March. The best growth was

obtained with the cultivated plot, and the poorest was

associated with the bare undisturbed plot.

Glendening’s (1937) observations from these SRER trials

are summarized below:

Native forage grasses

1. Arizona cottontop, and Rothrock, slender, sprucetop,

and hairy grama were the best performers. Black grama,

curly mesquite (Hilaria belangeri (Steud.) Nash), and bush

muhly were typically difficult to establish.

2. Seeding should be conducted at the beginning or just

prior to the summer rainy season.

3. Mulch can improve germination, especially on eroded

soils. Cultivation and seed incorporation into the soil helps

enhance germination but not as much as mulch.

4. Due to erratic precipitation, natural reproduction of

native grasses does not occur except in years of average or

above average precipitation.

Winter annuals

1. Good stands can be expected from sowing annual species common to Arizona.

2. Winter annuals should be fall planted prior to winter

rains.

3. Repeated plantings of annuals should not be required

due to their ability to produce seed even during seasons with

low precipitation.

4. Cultivation appears to increase germination, but it is

not necessary. The application of mulch has no apparent

effect on germination but does help overall plant growth.

5. Annuals are generally easy to establish, even on poor

soils. Although they can provide some forage they add mulch

to the soil that should improve the condition of the soil where

grasses could become established.

Glendening (1935) evaluated the use of grass sod in his

first transplant trials at the SRER. He indicated that transplanting is a feasible method for small areas but not practical for large areas. Species used in his transplant trial

included pearl millet (Pennisetum glaucum (L.) R.Br.), bush

muhly, tanglehead, Arizona cottontop, poverty threeawn

(Aristida divaricata Humb. & Bonpl. ex Wild.), small or

Santa Rita threeawn (Aristida californica Thurb. ex S. Wats

var. glabrata Vasey), and slender, sideoats, black, and

Rothrock grama. Transplants were either dug directly from

the field or grown as potted plants. Field-dug plants were

placed into flats and taken directly to the trial site and

planted (fig. 4). Potted plants were handled the same except

plants were taken from the flats and planted into tar-paper

pots at the nursery. Potted plants were watered until they

were transplanted into the field. It is interesting to note that

the potted plant method was considered more time consuming and costly compared to the field-dug plants. Treatments

included three planting times (spring, summer, and fall)

along with either complete protection from all grazing or

protection from livestock grazing only. In June 1935, about

Figure 3—“Germination upon bare ground and

under artificial litter” (Mulch trial 1935; Glendening

1937).
USDA Forest Service Proceedings RMRS-P-30. 2003 85

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

4,000 field-dug plants were transplanted (spring planting)

at three study sites on the SRER and irrigated for 3 weeks

until the start of the summer rainy season. Transplants

were generally planted the same day and never held for more

than 24 hours. Five months after transplanting 57 percent

of the transplants had established, and 18 months after

planting 46 percent of the plants had persisted (fig. 5). The

summer planting was conducted after the rains started in

mid-July 1935 (fig. 6). This planting incorporated three

planting sites and 8,500 field-dug plants, which were watered only once at the time they were transplanted. Each

planting site had three plots, two with complete grazing

protection and one protected from livestock grazing only. Six

weeks after planting, one plot was fertilized with a mixture

of sodium nitrate and ammonium sulfate. Six months after

planting the overall establishment was 58 percent, and after

14 months survival fell to 28 percent. There was no apparent

difference between the fertilized and unfertilized plots after

4 months, but after 14 months there was higher survival on

the protected unfertilized plots. Plant establishment was

much lower on the control plots due to grazing by rodents

(fig. 7). The species that had the best establishment on the

control plot was tanglehead. Low establishment, for all

planting dates and treatments, was believed to be due to low

summer rainfall in 1936 followed by a lack of spring precipitation in 1937. Fall transplant trials were initiated in August 1936 and December 1936. Species from the previously

described planting were used except the transplants were

nursery potted plants. The initial results for the August

planting were favorable (fig. 8). Persistence was low, however, due to heavy grazing from rodents that eventually

killed the plants. The winter planting met with similar

results in that survival and establishment were very low.

Topsoil transplanting was also evaluated by Glendening

in 1935 and 1936 at the SRER. Topsoil was removed from

well-grassed areas and spread 3 inches deep onto denuded

areas where the topsoil had eroded away. Topsoil applications were conducted in July of 1935 and 1936. In both cases

fair plant growth was observed. Annuals comprised most of

the growth, but a few perennial grasses also germinated and

established.

Glendening (1937) summarized his transplanting results

as follows:

1. Transplanting of native grasses is feasible under proper

weather conditions and can be used to establish perennial

Figure 5—“Percentage of grasses established by

transplanting during the spring, with artificial irrigation” (Glendening 1937). Bouteloua filiformis syn.

Bouteloua repens, Aristida californica syn. Aristida

californicavar. glabrata, and Valota saccharata syn.

Digitaria californica.

Figure 4—“Small plots 1 by 2 m were transplanted to native grasses. The plants were set

out in rows. The rocky nature of the soil made it

necessary to use a heavy pick to dig the furrows”

(Glendening 1937).

Figure 6—“Grasses transplanted during the summer of 1935 made good growth and many of them

set seed during the fall” (Glendening 1937).
86 USDA Forest Service Proceedings RMRS-P-30. 2003

Munda and Pater Revegetation Practices on the Santa Rita Experimental Range

Figure 7—“Percentage of grasses established by transplanting during the summer of

1935” (Glendening 1937). Bouteloua filiformis

syn. Bouteloua repens, Aristida californica

syn. Aristida californica var. glabrata, Valota

saccharata syn. Digitaria californica, and

Chaetochloa grisebachii syn. Setaria

grisebachii (E. Fourn.).

Figure 8—“Percent of grasses established by transplanting during the summer of 1936” (Glendening

1937). Bouteloua filiformis syn. Bouteloua repens,

Aristida californica syn. Aristida californica var.

glabrata, Trichachne californica syn. Digitaria

californica, and Chaetochloa spp. syn. Setaria spp.
USDA Forest Service Proceedings RMRS-P-30. 2003 87

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

grasses on sites where direct seeding cannot be accomplished successfully.

2. Transplanting should be done in July at the start of the

summer rainy season.

3. Direct field transplants have performed as well as

potted nursery stock. Potted nursery stock may have some

advantages when used in low rainfall areas or on poor soils.

4. Transplanting topsoil from well-grassed areas to badly

eroded sites can be successful.

5. Transplanting soil should be done in late spring prior to

summer rains to provide the opportunity for perennial grass

seed present in the topsoil, to germinate with the summer rains.

6. Topsoil should be acquired from areas supporting grass

that naturally reproduce from seed. Sites dominated by

curly mesquite and black grama should be avoided due to a

lack of a viable soil seed bank.

Glendening installed four trials in the Middle Tank Revegetation Plot, Study Area 205 at the SRER from 1940 to 1948.

The four trials were (1) species adaptation, (2) planting

methods (discussed under seeding methods), (3) compatible

mixture, and (4) grazing (not discussed here).

The species adaptation trial used 50 native and introduced species, mostly grasses. Most of the accessions were

acquired from the Tucson Plant Materials Center (table 1).

Three treatments were used in this two-replication trial:

(1) row plantings, (2) contour furrows, and (3) contour

furrows with mulch. The row planting treatment involved

hand planting of each species in three 12-ft rows spaced 1 ft

apart. The contour furrow treatment used furrows that were

3 to 4 inches deep in 12-ft lengths and on 16-inch centers.

Seed was sown and covered by hand. Contour furrows with

mulch were installed in the same manner as the contour

furrow treatment with mulch applied to the soil surface after

seeding. Due to below average rainfall in 1946 and 1947,

replanting was done in 1947 and 1948. The May 1949

evaluation indicated that many of the replants failed, especially buffelgrass (Pennisetum ciliare (L.) Link). Hall’s panic

(Panicum hallii Vasey) was one of the few replanted accessions found growing in 1949, and African lovegrass (Eragrostis

echinochloidea Stapf.) and weeping lovegrass (E. curvula

(Schrad.) Nees) had all but disappeared. Plants survived

better on the contour furrows than on the row plantings.

The only remaining shrub was rough menodora (Menodora

scabra Gray). In general, the best performing species were

Lehmann, Boer, and Wilman lovegrasses, and Arizona

cottontop, and tanglehead (table 2).

A compatible mixture trial evaluated various grasses,

mixed with Lehmann lovegrass at different seeding rates or

seeded as a single species. The seedbed was prepared by

double disking, harrowing to remove plant debris, and

installing contour furrows 4 to 6 inches deep at 2-ft intervals.

A cyclone seeder was used to broadcast the seed. No seed

incorporation treatment was used. Seedings were conducted

in July 1946 and repeated in July 1947 due to poor stand

establishment from the 1946 planting. The 1947 planting

compared Wilman lovegrass, Lehmann lovegrass, and Arizona cottontop at differing seeding rates (table 3a). Comments on the July 1947 planting were that due to below

average rainfall this planting had a very poor stand. A

second July 1947 planting compared six accessions

(Lehmann, Wilman and Boer lovegrasses, and Arizona

Table 1—Species adaptation trials: species list for July 1946 planting.

Middle Tank Reseeding Plot, Study Area 205 (adapted from

Glendening and others 1946).

SCS accession

Species number

Bothriochloa barbinodis A 11495

B. ischaemum A 1407

Dichanthium sericeum (R.Br.)A. Camus A 11812

Astrebla elymoides Bailey & F.Muell. A 1335

 ex F.M. Bailey

A. lapacea (Lindl.) Domin A 8839

Atriplex canescens A 5099

A. nummularia Lindl. A 30

Bouteloua curtipendula A 2969

B. eludens Griffiths A 11563

B. eriopoda A 5066

B. gracilis (Willd. Ex Kunth) Lag. ex Griffiths A 121424

B. hirsuta A 10216

B. radicosa (Fourn.) Griffiths A 11327

Calliandra eriophylla Benth. A 11672

Chloris berroi Arech. A 2086

C. cucullata Bisch. A 2977

Eragrostis bicolor Nees A 11958

E. brigantha (author not found) A 620

E. curvula A 84

E. curvula A 67

E. echinochloides A 11960

E. intermedia A.S. Hitchc. A 8028

E. lehmanniana A 68

E. lehmanniana var. ampla (author not found) A 11961

E. superba A 11965

Krasheninnikovia lanata (Pursh) Commercial

 A.D.J. Meeuse & Smit

Heteropogon contortus Number not given

Hilaria belangeri A 3323

Pleuraphis mutica Buckl. A 8772

Krameria erecta Willd. Ex J.A. Schultes A 2284

Leptochloa dubia A 11695

Lycurus phleoides Kunth A 10217

Medicago lupulina L. Commercial 3460

Menodora scabra A 2408

M. scabra A 2390

M. longiflora Gray A 9126

Muhlenbergia porteri A 2346

Achnatherum hymenoides (B.L. Johnson) A 2691

 Barkworth

Piptatherum miliaceum (L.) Coss. A 1895

Panicum hallii Vasey A 8002

P. prolutum F. Muell. A 2664

Pappophorum vaginatum Buckl. A 8666

Paspalum setaceum Michx. A 149

Pentzia incana (Thunb.) Kuntze A 149

Pennisetum ciliare A 2348

P. orientale (Willd.) L.C. Rich. A 131

Setaria vulpiseta A 9051

Sporobolus airoides (Torr.) Torr. A 920

S. contractus A.S. Hitchc. A 11569

S. cryptandrus (Torr.) Gray A 810

S. fimbriatus (Trin.) Nees A 69 & A 72

S. flexuosus (Thrub. Ex Vasey) Rydb. A 10117

Digitaria californica A 8084

Tridens muticus (Torr.) Nash var. elongatus A 3014

 (Buckl.) Shinners

T. muticus (Torr.) Nash var. muticus A 11321

Erioneuron pilosa (Buckl.) Nash A 9456

Vicia americana Muhl. ex Willd. Commercial

V. villosa Roth Commercial
88 USDA Forest Service Proceedings RMRS-P-30. 2003

Munda and Pater Revegetation Practices on the Santa Rita Experimental Range

Table 4—Yield trial-species list, July 11, 1951. Pasture 140 (adapted

from Glendening and others 1946).

Planting rate

Species Accession (lb per acre)

Bouteloua eriopoda Flagstaff-1949 40

B. repens A10123-2172 10

Eragrostis bicolor A11958-ll26 2

E. lehmanniana A68-2168 1

Heteropogon contortus SRER 1939 5

Muhlenbergia porteri A8368 25

Panicum hallii A8002-2158 3

Sporobolus cryptandrus Mixed lots 40-41 1

Digitaria californica A8084-1718-49 12

In the early 1950s, several plantings were installed in

Pasture 140 by H. G. Reynolds, similar to those planted in

study area 205 (Reynolds 1952). In July 1951 a three-species

mixture trial was sown in Pasture 140. The mixture trial

incorporated combinations of Lehmann, Boer, and Wilman

lovegrass. The site was cleared of mesquite and the seedbed

prepared with the Krause cutaway disc. A hand-held whirlwind seeder was used to broadcast the seed, and all plots

were cultipacked. In July 1951, a yield study was planted

that used nine different species (table 4). This planting was

repeated in July 1952 with minor changes in species used.

All species were broadcast seeded followed by a cultipacking.

The best performing species was plains bristlegrass (Setaria

vulpiseta (Lam.) Roemer & J.A. Schultes) because it had

better overall emergence. Results for these three plantings

were not definitive with comments indicating that all three

trials were considered failures. Lack of rainfall in 1951 and

1952 (60 percent of average) was indicated as the primary

reason for failure.

Martin (1966) states that based on results from experiments conducted on the SRER the best adapted plants for

range revegetation include the introduced species Lehmann,

Boer, and weeping lovegrass, and the native species Arizona

cottontop, black grama, and sideoats grama with Lehmann

and Boer lovegrass considered most reliable. Lehmann

lovegrass is considered easier to establish but not as palatable or as long lived as Boer lovegrass. Arizona cottontop,

black grama, weeping lovegrass, and sideoats grama were

considered viable choices but are more difficult to establish.

Weeping lovegrass and sideoats grama are considered suitable for upland sites that receive more moisture or where

soils stay moist for a longer period of time. For areas where

water accumulates such as swales, blue panic, Johnsongrass

(Sorghum halepense (L.) Pers.), and Boer, and Lehmann

lovegrass are adapted species (Reynolds and Martin 1968).

Wilman lovegrass is another suitable species but only in those

areas where winter temperatures do not fall below 10 ∞F.

Lehmann lovegrass is generally the only species recommended for upland areas that receive less than 14 inches of

precipitation. Martin stated in his 1966 report that adapted

species and successful seeding methods have not been

developed for areas below 11 inches of annual precipitation

(Martin 1966).

Jordan (1981), based on his research conducted in southern Arizona, developed additional criteria to be considered

Table 2—Species adaptation trial and stand rating as of May 1949.

Middle Tank Reseeding Plot, Study Area 205 (adapted from

Glendening and others 1946).

Type of planting

Furrow and

Species Flat or row Furrow mulch

Heteropogon contortus Good Excellent Excellent

Eragrostis curvula None Very good Very good

E. superba Very poor Good Good

E. lehmanniana Fair Good Good

E. lehmanniana-Ampla Poor Fair Fair

Pennisetum ciliare Poor Good Poor

Digitaria californica Fair Fair Good

Bothriochloa ischaemum None Poor Poor

Bouteloua repens None None Poor

Panicum hallii None None Poor

Setaria macrostachya None None Poor

Leptochloa dubia None None Trace

Table 3a—Compatible mixture trial, July 23, 1947. Middle Tank

Reseeding Plot, Study Area 205 (adapted from Glendening

and others 1946).

Seeding rate Subplot

Species (lb per acre) number

Wilman lovegrass 6 1

Lehmann and Arizona cottontop 3 and 8 2

Wilman and Arizona cottontop 2 and 8 3

Lehmann 3 4

Lehmann and Arizona cottontop 1 and 8 5

Wilman and Arizona cottontop 6 and 8 6

Lehmann and Arizona cottontop 1 and 8 7

Lehmann and Arizona cottontop 3 and 8 8

Wilman 6 9

Wilman and Arizona cottontop 6 and 8 10

Lehmann 3 11

Wilman and Arizona cottontop 2 and 8 12

Table 3b—Compatible mixture trial, July 30, 1947 Middle Tank

Reseeding Plot, Study Area 205 (adapted from Glendening

and others 1946).

Seeding rate Subplot

Species (lbs per acre) number

Boer lovegrass Not shown A

Arizona cottontop Not shown B

Lehmann and Boer and sand dropseed 1, 2, 2 C

Lehmann and Slender grama _, 3 D

Wilman lovegrass Not shown E

Lehmann and slender grama 2, 3 F

cottontop, sand dropseed, and slender grama) at different

seeding rates (table 3b). Comments on this July 1947 planting

were that a good stand of Lehmann lovegrass and slender

grama had emerged, but due to low precipitation in 1948 the

established plants for both July 1947 plantings failed to

persist (USDA 1947–1948).
USDA Forest Service Proceedings RMRS-P-30. 2003 89

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

o’clock accessions displayed good initial establishment but

were no longer evident by the fall of 1982. The 1980 fall

seeding exhibited no evidence of emergence or establishment of the seeded species.

In 1983 a total of 18 species of native and introduced

grasses, forbs, and shrubs were sown on the SRER at the

PMC planting site. Seedbed treatments were intermediate

pits and disking. The summer 1983 planting received abundant summer precipitation that resulted in good stands for

most of the grasses on both seedbed treatments. As of 1991,

“SDT” and “A-130” blue panic, plains bristlegrass, cane

bluestem (Bothriochloa barbinodis (Lag.) Herter), and yellow

bluestem were still exhibiting good stand and vigor ratings.

The PMC installed July plantings in 1985 and 1986 at the

SRER site. The 1985 planting consisted of 25 accessions

comprised of seven introduced species and nine native species.

A transplant trial using African thatchgrass (Hyparrhenia

spp. Anderss. ex Fourn.) and saltbush (Atriplex spp. L.) was

installed with this planting. The July 1985 planting exhibited only fair emergence with infrequent establishment of

only a few accessions. It was noted that competition from

Lehmann lovegrass and common buffelgrass quickly crowded

out the established accessions. Rabbits grazed out the saltbush transplants, and only one African thatchgrass accession

exhibited significant survival. The 1986 planting revealed no

emergence or plant establishment. Low precipitation was

considered the reason for this planting failure.

A 1988 planting evaluated the use of “Seco” barley as a

mulch cover crop on one-half of the seeding plot and Mediterranean ricegrass (Piptatherum coerulescens (Desf.) P. Beauv.)

on the other half of the plot. Both accessions were planted

approximately 1⁄2 inch deep in December 1988 using a grain

drill. The barley was planted at a rate of 30 pure live seed

(PLS) pounds per acre and the Mediterranean ricegrass at a

rate of 2 PLS pounds per acre. By the spring of 1989 only a

few barley plants and no Mediterranean ricegrass plants

were observed. Lack of sufficient winter precipitation and

rodent predation on the barley seed was determined as the

primary reasons for this failure.

The USDA Natural Resources Conservation Service, Plant

Materials Program is unique among Federal programs in

that it can “release” accessions that have superior qualities

to commercial growers for public use. The Tucson PMC has

released two species that were originally collected on the

SRER. “Santa Rita” fourwing saltbush was collected by

S. Clark Martin from a native stand on the SRER December

1962. The collection site was T18S, R14E, in section 3 (Tucson

Plant Materials Center 1987). “Loetta” Arizona cottontop

was collected from a native stand on the SRER by Larry

Holzworth in October 1975. The collection site was T18S,

R14E, in the southwest 1⁄4 of Section 3 (Tucson Plant Materials Center 2000).

Seeding Methods

In rangeland revegetation, seed is typically sown by

broadcasting or by drilling. Both methods have varying

degrees of effectiveness depending on condition of the

seedbed and seed size. Drill seeding was initially conducted

using grain drills, evolving into today’s rangeland drills.

Prior to the rangeland drill, scientists had to develop their

when selecting species for rangeland revegetation. Included

among these were (a) germination rate—species that can

germinate in 3 days are better adapted to limited moisture

conditions than those species requiring 5 days; (b) species

should have good seedling vigor; (c) when revegetation

conditions are favorable adapted native species should be

used. However, if the site does not have all the favorable

conditions, an introduced species may be a better choice; and

(d) selected species must be commercially available. A species’ commercial availability is directly related to not only its

field performance but how much seed it yields, seed production requirements, ease of harvest, seed conditioning requirements, and ability to be sown with currently available

equipment. Current research suggests that slower germination, mimicking the conservative germination behavior of

Lehmann lovegrass, may improve the potential for emergence and establishment of native species (Abbott and

Roundy 2003; Biedenbender and Roundy 1996; Roundy

and Biedenbender 1995).

The PMC plantings conducted on the SRER from 1968

through 1970 utilized 12 lovegrass accessions and 2 accessions of buffelgrass and incorporated yellow bluestem

(Bothriochloa ischaemum (L.) Keng) in the 1969 summer

planting. Overall results from these plantings showed that

common buffelgrass, T-4464, had the greatest forage production, but it was not significantly higher than the

lovegrasses A-1739 and A-17340 or Lehmann lovegrass A16651, or yellow bluestem. The final evaluation, conducted

in 1973, found that “Palar” Wilman lovegrass and a commercial strain of Wilman lovegrass were considered the two best

performers in these plantings based on forage production,

basal cover, and plant density.

Small observational trials were planted in the fall of 1968,

1969, and 1971. Species were planted using mechanical

push planters and seeded into intermediate pits. Sixteen

accessions of native and introduced shrubs and forbs were

included in these trials. Results from the 1968 and 1969

plantings indicated fair to good overall emergence, but none

of the species survived due to dry winters. Two accessions

of rough menodora and prostrate kochia (Kochia prostrata

(L.) Schrad) were sown with two accessions of ballonpea

(Sutherlandia frutescens(L.) R.Br.). Galleta grass (Pleuraphis

jamesii Torr.) was included with the above-mentioned species. The final (1979) evaluation indicated that prostrate

kochia—A-18219, and rough mendodora—A-17773, from

Pomerene, AZ, were the better performers. However, established accessions from both plantings were rated as poor

with regard to overall stand, forage production, and erosion

control.

In 1980 the PMC installed a summer and fall planting at

the PMC planting site on the SRER. The 1980 summer

planting included shrubby senna (Senna corymbosa (Lam.)

Irwin & Barneby), Colorado four o’clock (Mirabilis multiflora (Torr.) Gray), spike muhly (Muhlenbergia wrightii

Vasey ex. Coult.)—A-8604 and “El Vado,” green sprangletop

(Leptochloa dubia (Kunth) Nees), and four accessions of blue

panic. Initial emergence and stand were rated as excellent

on disked only plots. Due to droughty, loose soil conditions,

high plant mortality was observed in this treatment. A September 1982 evaluation indicated that the summer planting of

“SDT” blue panic exhibited the highest vigor and stand ratings

of the four blue panic accessions planted. The Colorado four
90 USDA Forest Service Proceedings RMRS-P-30. 2003

Munda and Pater Revegetation Practices on the Santa Rita Experimental Range

own seeding equipment. Jordan used a modified Nisbet

seeder along with modified seed metering plates to plant the

tiny lovegrass seeds at recommended rates (Roundy and

Biedenbender 1995).

Glendening and others (1946) installed a seeding method

trial in 1946 in the Middle Tank Revegetation Plot, Study

Area 205, at the SRER. This trial compared the effectiveness

of various seedbed treatments and seeding methods using

Boer lovegrass. Treatments included two controls (no treatment); mowed, contour-furrowed, and seeded with a twogang cultipacker with seeder attachment; mowed, contourfurrowed, cultipacked with single-gang cultipacker, and

broadcast seeded; and mowed, and cultipacker-seeded only.

Evaluations made in 1947 indicated a good stand of Boer

lovegrass was obtained with the contour furrow and

cultipacker seeder only (USDA 1947–1948). Evaluations

made in 1948 indicated that established plants had died due

to low precipitation in 1948. A new planting was conducted

by Glendening in 1949 that used five seedbed treatments

and three seeding treatments with Lehmann and Boer

lovegrasses. Imposed on these treatments was a mowing

treatment to control burroweed. The five seedbed and seeding treatments were (1) the Krause cutaway disc and

cultipacker seeder, (2) Eccentric disc and drill, (3) interrupted furrow and drill, (4) interrupted furrow and broadcast, and (5) no seedbed preparation and broadcast seeding.

Results for the 1949 planting indicated that Lehmann

lovegrass had better establishment than Boer lovegrass over

all treatments. This occurred in the interrupted furrow with

drill seeding and interrupted furrow with broadcast seeding.

The controlled burroweed plots had twice as many lovegrass

plants as the uncontrolled plots.

In 1964 a field trial at the SRER was conducted to compare

pelleted and nonpelleted Boer and Lehmann lovegrass seed

that was broadcast onto desert rangeland following herbicide application. Pellet size was 1

⁄

4 inch with an average of 10

seeds per pellet, and the pellets were aerially applied at a

rate of 62 pounds per acre. On average, there were 1,400

pellets per pound (Chadwick 1964). Chadwick in 1969 summarized the results of the pelleted program. Chadwick found

that only one seedling had emerged for every six pellets sown

1 month after sowing, and at the end of September no

seedlings were observed, even though the site received over 10

inches of rain during July, August, and September (Chadwick

and others 1969). Sowing nonpelleted seed into a prepared

seedbed was more successful than broadcasting pelleted seed.

Pelleted seeding failed due to lack of good seed soil contact,

and the pelleting process actually reduced germination

(Roundy and Biedenbender 1995).

All PMC plantings were drill seeded either using a small

rangeland drill, push planter (Planet Jr.), or grain drill.

Seeding rates were generally based on 20 to 25 (PLS) per ft

of row for grasses and 10 PLS per ft for shrubs. Seeding depth

was 1

⁄

4 inch for most small-seeded species and up to 1

⁄

2 inch

for large-seeded species. The 1971 planting incorporated the

use of barley straw for mulch. The site was drill seeded, then

the mulch was applied by hand and tucked into the soil using

a Soil Erosion Mulch Tiller. The mulch, as well as receiving

favorable winter precipitation, provided for good emergence

and stand establishment. However, when the final evaluation

was conducted in the fall of 1972, only one species, Australian saltbush (Atriplex semibaccata R. Br), remained alive.

Summary ______________________

The Santa Rita Experimental Range has provided an

extensive outdoor laboratory for long-term rangeland revegetation trials on species adaptation, seedbed preparation

methods, sowing times and rates, and unique cultural treatments such as mulching. These studies have shown promise

with regard to seedbed treatments that enhance plant establishment. Much of the information gained from revegetation

trials on the SRER is used in developing the USDA Natural

Resource Conservation Service (Arizona) standards and

specifications for the Range Planting practice (USDA 2002.)

Seedbed preparation and selection of adapted species are

important factors when planning a range revegetation activity. It is evident that timing and amount of precipitation are

the primary elements that ultimately determine the success

or failure of a planting. Research conducted at the SRER has

clearly shown that successful establishment may not indicate long-term persistence. Long-term evaluations on persistence are needed to improve and refine recommendations

for range revegetation. Due to costs for brush control, future

revegetation activities may leave larger areas of existing

woody vegetation, creating the need for identification of

shade-tolerant species that can be successfully sown under

existing overstory canopies (Livingston and others 1997).

Scientists have expanded research efforts to include seedbed

ecology, seed germination characteristics, and range plant

genetics (Smith 1998; Smith and others 2000). Recent research on the SRER has dealt with germination characteristics and seedbed ecology of Lehmann lovegrass. Results

from this research have provided suggestions for managing

existing Lehmann lovegrass stands and potential methods,

using fire and herbicides, for re-establishing native grasses

in Lehmann’s dominated areas of the semidesert grassland

(Abbott and Roundy 2003; Biedenbender and Roundy 1996;

Livingston and others 1997). This additional information

and direction can only move us closer to achieving revegetation success. It is interesting to note that early revegetation

work used native plants. Unsuccessful plantings with natives led to the search and use of introduced plants such as

Lehmann lovegrass. Lehmann lovegrass proved to be very

successful, spreading aggressively and reducing biodiversity.

Range scientists and others are again working with native

plants in the semidesert grassland. This renewed interest in

native plants will require research on their germination

characteristics, field establishment requirements, and seed

production qualities and requirements. Identification of

successful establishment characteristics will help to identify

native species and or their genotypes for use in revegetation.

These species will be used if they are readily available in

needed quantities and at an affordable price. The SRER will

again provide testing sites for revegetation trials and demonstrations for livestock forage production, erosion control,

and improving the biodiversity of plant communities dominated by invasive species.
USDA Forest Service Proceedings RMRS-P-30. 2003 91

Revegetation Practices on the Santa Rita Experimental Range Munda and Pater

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Plant Materials Center, Tucson, AZ. May 2000. 8 p.

U.S. Department of Agriculture, Natural Resources Conservation

Service. Arizona 2002. Field office technical guide, Section IVpractice standards and specifications, range planting. Phoenix,

AZ: Natural Resources Conservation Service.

U.S. Department of Agriculture, Soil Conservation Service. 1947–

1948. Technical Report of the Tucson Plant Materials Center,

1947–1948. Tucson, AZ: Tucson Plant Materials Center.

U.S. Department of Agriculture, Soil Conservation Service. 1988.

Technical Report of the Tucson Plant Materials Center, 1988.

Tucson, AZ: Tucson Plant Materials Center.

Winkel, V. K.; Roundy, B. A. 1991. Effects of cattle trampling and

mechanical seedbed preparation on grass seedling emergence.

Journal of Range Management. 44: 176–180.

Winkel, V. K.; Roundy, B. A.; Blough, D. K. 1991. Effects of seedbed

preparation and cattle trampling on burial of grass seeds. Journal

of Range Management. 44: 171–175.
92 USDA Forest Service Proceedings RMRS-P-30. 2003

Leonard J. Lane

Mary R. Kidwell

Hydrology and Soil Erosion

Leonard J. Lane is a Research Hydrologist (retired) with the USDA Agricultural Research Service, Southwest Watershed Research Center in Tucson, AZ. He

completed a B.S. degree (honors) in engineering mathematics and an M.S. degree in systems engineering at the University of Arizona, and a Ph.D. degree in civil

engineering (hydrology and water resources) at Colorado State University. Mary R. Kidwell is an Ecologist with the USDA Agricultural Research Service,

Southwest Watershed Research Center in Tucson, AZ. She received a B.A. degree in economics and organizational behavior and management from Brown

University and an M.S. degree in renewable natural resource studies from the University of Arizona.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction _____________________________________________________

Background

Soil, water, air, the plants and animals they support, and human interaction with them are a central focus of natural

resources research and management. In this paper we focus on hydrology (specifically surface water hydrology) and soil erosion

(specifically soil erosion and sediment transport by water). The Santa Rita Experimental Range (the SRER or simply the Range

hereafter) was established in 1903 (see, for example, Medina 1996). Since the end of World War II, several landmark programs

have contributed to our current understanding of hydrology in desert (arid) and semidesert (semiarid) ecosystems. Notable

examples include the following.

At the third General Conference of UNESCO held in Beirut in 1948, an International Institute of Arid Zone was proposed.

In December of 1949 an International Council was approved, and it met in November, 1950. This effort led to the preparation

of a series of reports on arid regions of the earth. In 1951 the Southwestern and Rocky Mountain Division of the AAAS

Abstract: We review research on surface water hydrology and soil erosion at the Santa Rita

Experimental Range (SRER). Almost all of the research was associated with eight small

experimental watersheds established from 1974 to 1975 and operated until the present. Analysis

of climatic features of the SRER supports extending research findings from the SRER to broad

areas of the Southwest with similar climates. Conceptual models for annual water balance and

annual sediment yield at the SRER were developed and supported by data from four very small

experimental watersheds. The impacts of rotation and yearlong grazing activities, and of

mesquite removal were analyzed using data from four small experimental watersheds. The

analyses suggested that mesquite removal reduced runoff and sediment yield, but differences in

hydrologic response from paired watersheds due to soil differences dominated grazing and

vegetation management impacts. The 28 years of monitoring under the same experimental

design on the four pairs of watersheds provides us with a long period of “pretreatment” data on

the paired watersheds. New treatments could now be adapted and designed based on lessons

learned from monitoring over nearly three decades. There is a unique opportunity to institute

long-term adaptive management experiments on these experimental watersheds.

Keywords: water balance, runoff, sediment yield, watersheds

Acknowledgments: We gratefully acknowledge the dedicated technicians and scientists from

the U.S. Department of Agriculture’s Forest Service and Agricultural Research Service, and the

University of Arizona, College of Agriculture, who have steadfastly operated and maintained the

Santa Rita raingage network, and the land use and management metadata, conducted vegetation

and soil surveys and monitoring, and installed and maintained the eight experimental watersheds used for the research described in this paper. Without their efforts, there would be no

studies of hydrology and soil erosion on the Santa Rita Experimental Range. We also appreciate

the reviewers’ timely and helpful comments and suggestions that significantly improved the

paper. We thank all of you.
USDA Forest Service Proceedings RMRS-P-30. 2003 93

Hydrology and Soil Erosion Lane and Kidwell

established the Committee on Desert and Arid Zones Research to assist “study of the factors affecting human occupancy of semiarid and arid regions.” This Committee was

very active and productive for over two decades in a variety

of natural and social science areas.

In 1953 the U.S. Department of Agriculture established

the 150-km2 Walnut Gulch Experimental Watershed near

Tombstone, AZ. Research from this experimental watershed

established an infrastructure and the scientific understanding and apparatus enabling measurement of surface runoff,

soil erosion, and sediment yield from small rangeland watersheds. This nearby infrastructure and understanding led to

the establishment of eight small experimental watersheds

on the SRER in 1974 and 1975.

From 1967 to 1974 the United States participated in the

International Biological Program. The National Science

Foundation funded and supported the Desert Biome Program throughout the West from 1972 through 1977. Beginning in 1971 and continuing to the present the Arizona

Section of the American Water Resources Association and

the Hydrology Section of the Arizona-Nevada Academy of

Science has published “Hydrology and Water Resources in

Arizona and the Southwest.” In 1978, Academic Press, Inc.,

London, started publishing the “Journal of Arid Environments” as a forum for multidisciplinary and interdisciplinary dialogue on problems in the world’s deserts.

Purpose

Although these programs and projects have immeasurably increased our knowledge and understanding of hydrology of deserts areas, none has produced a focused and

indepth synthesis of surface water hydrology and soil erosion in arid and semiarid areas, and especially, on the SRER.

Therefore, we propose to partially fill this gap with this

paper. Toward this end, the paper focuses on surface water

hydrology and soil erosion by water. Emphasis is on hydrology and erosion occurring on the SRER, but regional data

and research findings are used for background information

and as comparative studies to contrast and broaden similar

findings on the SRER.

Scope and Limitations

Our review and analyses are focused on measurements

and modeling of surface water hydrology, upland soil erosion

by water, and yield of water and sediment from very small

experimental watersheds. While major emphasis is on measured data and what we can learn from them, interpretation

and understanding of the measured data require understanding and application of conceptual models of the dominant physical processes, and mathematical models (computer simulation models or simply simulation models)

describing those processes. The inclusion of conceptual and

simulation models is necessary to interpret the measured

data, to add a dimension of predictability, and to help

understand the processes across a continuum of space and

time when measurements are limited to points in space over

short time periods.

Review of Hydrologic and

Soil Erosion Research

at Santa Rita __________________

Overview

Research has been conducted on the 21,500-ha SRER

since 1903. The goal of research at the SRER is to investigate

and understand the ecology and management of semiarid

rangelands. The U.S. Department of Agriculture Bureau of

Plant Industry operated the SRER from 1903 until 1915,

and from 1915 until 1988 the U.S. Department of Agriculture Forest Service assumed responsibility. Since 1988 the

SRER has been under the administration of the Arizona

State Land Department and is managed by the University of

Arizona for the purpose of conducting ecological and rangeland research (McClaran and others 2002).

According to Martin and Reynolds (1973), the SRER is

representative of over 8 million hectares of semiarid (semidesert) grass-shrub ecosystems in southern Arizona, New

Mexico, Texas, and northern Mexico. The extent to which

research findings from the SRER are transferable over these

broad geographical areas depends, in large part, upon how

widespread climatic characteristics of the SRER are represented regionally.

Climate

Although the focus herein is hydrology and soil erosion,

climate plays such a strong role that a brief climatic summary of the SRER is necessary. Green and Martin (1967)

analyzed precipitation data from the Range. A common 26-

year period, 1940 to 1965, for 22 raingages situated across

the SRER was used for statistical analyses. Average annual

precipitation for this period of record varied from about 282

mm at the northwest gage at an elevation of approximately

914 m MSL to 492 mm at an elevation of approximately

1,310 m. This range of 492 – 282 = 210 mm over an elevation

difference of only 1,310 – 914 = 396 m indicates a strong

trend of about 53 mm of precipitation per 100 m difference

in elevation. These two raingages are located about 17.4 km

apart so that the rate of change in mean annual precipitation

is 210 mm per 17.4 km = 12 mm per km of distance.

These statistics of 53 mm of mean annual precipitation

change per 100 m of elevation change and 12 mm of mean

annual precipitation change per km horizontal distance

indicate a strong orographic effect in precipitation. The dry

adiabatic lapse rate is about 9.8 ∞C per km of elevation so

that mean annual temperature also varies with elevation.

Taken together, the changes in mean annual precipitation

and temperature with elevation mean that the Headquarters (Florida location or Santa Rita Experimental Range

station) climate does not represent the average conditions

over the 21,500 ha SRER. Rather, the Florida station represents an extreme in terms of high precipitation and cooler

temperature. In fact, following Trewartha and Horn (1980),

the Florida station is near the boundary between semiarid

and subhumid climates, and the Northwest station is near

the boundary between semiarid and arid climates. The average climate for the SRER is classified as semiarid or steppe.
94 USDA Forest Service Proceedings RMRS-P-30. 2003

Lane and Kidwell Hydrology and Soil Erosion

Annual Water Balance

The term “hydrologic cycle” is the most general way of

describing the cycling or movement of water through the

lands, oceans, and atmosphere. The hydrologic cycle is

usually described and quantified in terms of its components. These components include precipitation, evaporation, transpiration, runoff, ground water, and water temporarily stored such as in soil moisture, lakes, and reservoirs.

The term “water balance” as used in hydrologic studies has

a similar meaning to the term “hydrologic cycle,” but it

connotes a budgeting or balancing of components in the

hydrologic cycle for a given place or area. In this paper, the

area we use to make water balance calculations is the

watershed.

A watershed is described with respect to surface runoff as

being defined by a watershed perimeter (for example, see

Lane and others 1997). This watershed perimeter is the

locus of points where surface runoff produced inside the

perimeter will flow to the watershed outlet. Therefore, water

balance calculations are for a watershed and a specific time

period such as annual, seasonal, daily, or hourly. Our emphasis herein is on an annual water balance and on storm

event or daily values of water balance used to compute an

annual balance on small watersheds in upland areas.

Conceptual Model for Annual Water Balance—In

warm to hot semiarid regions with bimodal annual precipitation, such as the SRER, a conceptual model of an annual

water balance can be described as follows. Precipitation

varies seasonally with the most prominent period of precipitation in the summer (July to September), with a secondary

peak in the winter (late December to March), and with

relatively dry periods in the spring and fall. Mean annual

precipitation varies between about 250 and 500 mm. Mean

annual surface runoff from small upland watersheds (defined herein as small areas ranging in size from a few square

meters up to a few hectares) varies from near zero up to

about 10 percent of annual precipitation or from near zero to

50 mm. Actual mean annual evapotranspiration (the sum of

the actual amount of evaporation from soil and cover material and the actual amount of plant transpiration) ranges

from about 90 to near 100 percent of mean annual precipitation. During extremely high precipitation episodes (for example, heavy summer or fall rainfall from the influx of

moisture from tropical storms and hurricanes and very wet

winters when the winter storm track is over southern Arizona), soil moisture can increase to field capacity (the upper

limit of soil moisture storage when percolation through the

soil profile begins) and deep percolation of soil moisture

below the plant rooting depth can occur (see for example,

Lane and others 1984; Renard and others 1993). These

periods of high soil moisture and deep percolation are relatively rare so that mean annual values derived from them

are highly variable and highly uncertain.

The conceptual model is that there is little and very rare

percolation below the root zone so that most soil moisture

remains in the upper meter or so of the soil, surface runoff is

due to rainfall rates exceeding the infiltration capacity of the

soil, actual annual evapotranspiration is nearly equal to

annual precipitation (minus infrequent surface runoff and

very rare deep percolation), and that soil moisture storage is

recharged and depleted on an annual basis so that the mean

annual change in soil moisture is near zero.

Empirical evidence of the applicability of this conceptual

model for an annual water balance at the SRER includes the

general absence of (1) perennial and intermittent streams,

(2) springs and seeps, and (3) shallow ground water. Exceptions to ephemeral streams may occur when perennial

streams originating in the mountains flow onto the SRER.

However, the conceptual model is for small upland areas on

the SRER and is generally supported by observations and

measurements (see Lawrence 1996, as discussed later).

Mathematical Model for Annual Water Balance—A

mathematical model of annual water balance for upland

watersheds, such as those on the SRER, can be written as

follows. The one-dimensional water balance equation for a

unit area, to plant rooting depth, ignoring runon (runoff

originating out of the unit area and flowing onto it) and

assuming subsurface lateral flow is zero, can be written as

dS/dt = P – Q – AET – L (1)

where dS/dt is the change in soil moisture (mm), P is

precipitation (mm), Q is runoff (mm), AET is actual evapotranspiration (mm), L is percolation or leaching below the

rooting depth (mm), and t is time (years for an annual water

balance although the actual calculations may be made using

a daily time step).

Example Water Balance Calculations Using a

Simple Model—We selected a simple water balance model

that could be operated based on limited available climatic,

soils, vegetation, and land use data. The CREAMS Model

(Knisel 1980) solves equation 1 for a daily time step and

then sums the results for monthly and annual values. The

CREAMS Model has previously been applied at arid and

semiarid sites somewhat similar to the SRER, including

the Walnut Gulch Experimental Watershed near Tombstone, AZ (see Renard and others 1993 and Goodrich and

others 1997 for details on modeling and descriptions of

Walnut Gulch).

The CREAMS Model was applied to Watershed Lucky

Hills 3, a small semiarid watershed on the Walnut Gulch

Experimental Watershed. Rainfall and runoff data were

available for 17 years (1965 to 1981), and were used to

optimize the model parameters for runoff simulation. As P

and Q were measured, the model was calibrated to match

observed values of runoff, Q, and then AET and L were

estimated using a form of equation 1. These calculations are

summarized in table 1. In table 1, column 1 lists the month

or the annual period, column 2 lists measured precipitation

in mm, column 3 lists measured surface runoff in mm,

column 4 lists the estimated actual evapotranspiration in

mm, column 5 lists estimated percolation below the plant

rooting depth in mm, and column 6 lists the estimated

average plant available soil moisture in mm. Notice that the

annual values in Columns 2 to 5 are annual summations,

whereas the annual value for plant available soil water is an

average annual value. Values of Q, AET, and L in table 1 do

not exactly sum to P because dS/dt was not exactly equal to

zero over the simulation period. However, dS/dt was relatively small, about 1.4 mm in the entire soil profile for the

data shown in table 1.
USDA Forest Service Proceedings RMRS-P-30. 2003 95

Hydrology and Soil Erosion Lane and Kidwell

The mean monthly precipitation distribution at Walnut

Gulch is bimodal (table 1) with a strong summer peak from

July through September and a small secondary peak from

December through March. Soil moisture storage (plant available soil water) follows this trend with recharge occurring

July through October and again in December and January.

Rapid soil moisture depletion occurs from February through

June (table 1, last column).

Annual Water Balance for Small Watersheds on the

Santa Rita—In cooperation with the USDA Forest Service

and the University of Arizona, the USDA Agricultural Research Service established and instrumented eight small

experimental watersheds during 1974 to 1975 within the

Santa Rita Experimental Range. These experimental watersheds were established to study the impact of cattle grazing

and vegetation manipulation methods on hydrology and soil

erosion. Four of the watersheds (WS1 to WS4) were located

at an approximate elevation of 976 to 1,040 m, while the

other four watersheds (WS5 to WS8) were located at a higher

elevation of about 1,170 m. The four upper watersheds are

emphasized in this paper and their locations are shown in

figure 1.

These watersheds enable scientists to study the effects of

livestock grazing and vegetation management practices on

runoff and sediment yield in the semiarid regions of the

Southwestern United States (Martin and Morton 1993). In

1974, two of the watersheds (WS6 and WS7) were treated with

basal applications of diesel oil to control the invasion of

mesquite (Prosopis velutina–Woot.), and were subsequently

retreated as needed. Watersheds 5 and 8 remained untreated.

Grazing practices include yearlong grazing on two watersheds (WS7 and WS8) and a rotation system on the other 2

(WS5 and WS6). Treatment and management have remained

constant since the study’s inception. The watersheds are

instrumented to measure precipitation rate and depth, surface runoff, and sediment yield (Lawrence 1996). Channel

cross-sections, using the method described by Osborn and

Simanton (1989), and vegetation characteristics (Martin and

Table 1—Average annual water balance for Watershed 63.103 at Walnut Gulch, Arizona, as calculated

with the CREAMS Model calibrated using 17 years of rainfall and runoff data, 1965 to 1981

(adapted from Renard and others 1993).

Plant available

Month Precipitation Runoff AET Percolation soil water

1 2345 6

 - - - - - - - - - - - - - - - - - - - - - - - - - - - mm - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

January 18.0 0.58 18.6 0.03 22.2

February 14.2 .28 18.0 .17 2.7

March 15.0 .18 21.2 .0 16.1

April 3.8 .0 11.8 .0 6.6

May 5.3 .13 7.4 .0 2.0

June 8.3 .28 8.4 .0 1.3

July 87.9 7.24 62.2 .0 9.8

August 63.3 4.78 63.7 .0 14.9

September 39.1 3.45 34.8 .0 15.7

October 21.0 1.70 16.5 .0 16.0

November 7.7 .05 9.7 .0 16.0

December 19.3 1.02 12.1 .0 18.8

Annual 302.9 19.7 284.4 .20 11.8

Arizona

Phoenix

Tucson

Experimental Watershed

Santa Rita Experimental Range

110° 55' W

N

31° 50' N

Figure 1—The Santa Rita Experimental Range showing

the location of the upper four experimental watersheds.

Morton 1993) have been measured periodically. Although this

is a brief description, more information on the SRER can be

found in Medina (1996) and McClaran and others (2002).

Lawrence (1996) used measured data and experts’ judgment in a multiobjective decision support system to evaluate

management systems on the upper four small watersheds

described above. Available precipitation and runoff data

from these watersheds were compiled for a 16-year period,

1976 to 1994 (Lawrence 1996). Therefore, an annual water

balance could be constructed by estimating actual evapotranspiration and percolation below the root zone. These

estimates are summarized in table 2. The drainage area for

each watershed and its generalized soil texture are shown in

column 1 of table 2. The mean annual values of actual

evapotranspiration (AET) (column 5) and percolation below

the rooting depth (L) (column 6) were estimated based on the

water balance equation (equation 1) and the CREAMS water
96 USDA Forest Service Proceedings RMRS-P-30. 2003

Lane and Kidwell Hydrology and Soil Erosion

Table 2—Summary of estimated annual water balance on the upper four experimental watersheds at the Santa Rita Experimental Range from 1976

to 1991. Precipitation is for a centrally located raingage on Watershed 5. All values are annual means in mm and values in parentheses

are coefficients of variation, in percent, for the measured variables.

Measured Measured Estimated Estimated

Watershed Treatment precipitation runoff AET percolation

1 2 3 45 6

WS5 (4.02 ha) sandy loam Rotation grazing, mesquite retained 440.0 (27.0) 16.7 (102.0) 423.0 0 to 1

WS6 (3.08 ha) loamy sand Rotation grazing, mesquite removed 440.0 (27.0) 1.6 (138.0) 438.0 0 to 1+

WS7 (1.06 ha) sandy loam Continuous grazing, mesquite removed 440.0 (27.0) 25.2 (123.0) 415.0 0 to 1

WS8 (1.12 ha) sandy loam Continuous grazing, mesquite retained 440.0 (27.0) 30.1 (92.0) 410.0 0 to 1

balance model (described earlier as applied at the Walnut

Gulch Experimental Watershed). The coefficient of variation (CV), defined as the standard deviation of the annual

values divided by their mean, was about 27 percent for

measured mean annual precipitation and between about 90

and 140 percent for measured mean annual runoff. Values of

AET, and especially L, are extremely uncertain as they

contain the natural variability of the measured data as well

as all the errors and uncertainty due to modeling. Therefore,

we did not show estimate CVs for AET and L.

Lawrence (1996) interpreted the data summarized in

table 2 as follows. Watersheds with mesquite removed

appeared to produce less runoff than their paired watershed

with mesquite retained (runoff from WS6 < WS5 and runoff

from WS7 < WS8). The observed reductions in runoff from

mesquite removal for both grazing systems are consistent

with the findings from experiments reported in the literature (for example, Carlson and others 1990).

However, Watersheds 5, 7, and 8 have sandy loam soils,

while Watershed 6 has loamy sand soils. Runoff differences

due to differences in soils (WS6 versus WS5) were more

significant than the differences due to grazing system and

mesquite removal. The technique of using paired watersheds and treating one of each pair is based on the assumption that the paired watersheds have similar hydrologic

behavior. This is not the case for Watersheds 5 and 6 where

different soils (sandy loam versus loamy sand) result in

different hydrologic response to precipitation events. One

way to determine if the watersheds are similar in response

is to instrument and monitor them for a sufficient period of

time before the treatments are imposed. Unfortunately, this

was not done on the four pairs of watersheds on the SRER,

rather, treatments were imposed at the same time that

hydrologic monitoring was initiated.

Finally, the computed annual water balance for the

upper four experimental watersheds at the SRER agrees

quite well with the previously described conceptual model

for water balance on small semiarid watersheds. Although

mean annual runoff was relatively small (0.37 percent of

mean annual precipitation on WS6 to 6.84 percent of mean

annual precipitation on WS8), this does not mean that

runoff in not an important part of the water balance. Runoff

amounts, although small when compared with precipitation, are responsible for flooding, soil erosion, sediment

transport and yield, and significant landscape evolution

over time.

Surface Water Hydrology

Although measuring or modeling an annual water balance involves measuring or modeling individual rainfallrunoff events, and thus surface water hydrology for individual storm events, there are other studies at SRER

providing additional insight into the dynamics of rainfallinfiltration-runoff during individual storm events. It should

be noted that the number of such studies on SRER are small

compared with more comprehensive watershed studies in

the region (such as Walnut Gulch in southeast Arizona and

the lower watershed studies on Beaver Creek in northcentral Arizona). Therefore, quantitative determination of

hydrologic processes during individual runoff events is somewhat lacking and almost entirely based on the eight experimental watersheds established on SRER.

Diskin and Lane (1976) studied the applicability of unit

hydrograph concepts at SRER. Unit hydrographs provide a

means of computing runoff hydrographs from a small watershed given rainfall and infiltration data. They analyzed a

number of rainfall and runoff events on one of the lower

small watersheds (Watershed 1). Double triangle unit

hydrographs were fitted to individual storm events. The

differences in the shapes of individual unit hydrographs

were found to be small so that they could be approximated by

a single double-triangle-unit hydrograph.

Significant errors in estimating surface runoff and erosion

rates are possible if a watershed is assumed to contribute

runoff uniformly over the entire area, when actually only a

portion of the entire area may be contributing. Generation of

overland flow on portions of small semiarid watersheds was

analyzed by three methods: (1) an average loss rate procedure, (2) a lumped-linear model, and (3) a distributednonlinear model. These methods suggested that, on the

average, 45, 60, and 50 percent, respectively, of the drainage

area was contributing runoff at the watershed outlet.

Infiltrometer data support the partial area concept and

indicate that the low infiltration zones are the runoff source

areas as simulated with a distributed and nonlinear kinematic cascade model (Lane and others 1978a). A subsequent

herbicide tracer study was conducted to provide empirical

data to test the partial area concept at SRER.

Based on the concept of partial area response, Lane and

others (1978b) conducted a runoff tracer study on two small

watersheds (Watersheds 1 and 2). The watersheds were

partitioned into four geomorphic subzones or hydrologic

response units. Each of the four zones on both watersheds
USDA Forest Service Proceedings RMRS-P-30. 2003 97

Hydrology and Soil Erosion Lane and Kidwell

was treated with about 1 kg per ha of an individual watersoluble herbicide. Runoff volumes and sources estimated

using the tracers were consistent with results from simulation studies and thus supported the partial-area concept of

surface runoff generation at SRER.

The cited studies of surface water hydrology at SRER

provided additional insight into rainfall-runoff processes,

how they are nonuniform over even small watersheds (partial-area response), that unit hydrograph and kinematic

routing methods can be used to develop runoff hydrographs

from small watersheds at SRER, and that concepts of overland flow and ephemeral streamflow in alluvial stream

channels are applicable at SRER. That these findings are

consistent with findings at Walnut Gulch and at other

semiarid watersheds suggests that research findings from

small watersheds at SRER have broader regional applicability and significance.

Soil Erosion and Sediment Transport

Observations and measurements of water erosion at the

SRER suggest that soil erosion by water dominates over

wind erosion. However there are no long-term studies of

wind erosion comparable to the long-term runoff and water

erosion studies on the eight small watersheds. Nonetheless,

we describe a conceptual model for soil erosion, sediment

transport, and sediment yield for small semiarid watersheds

based on water erosion and neglecting wind erosion.

A Conceptual Model for Soil Erosion, Sediment

Transport, and Sediment Yield—Schumm (1977) presented a description of an idealized fluvial system (a conceptual model) as consisting of three zones of sediment source,

transport, and sink. Zone 1 was described as the drainage

basin as a source of runoff and sediment, Zone 2 as the main

river channels as the transfer component, and Zone 3 as the

alluvial channels, fans, and deltas, as sinks or zones of

deposition. This conceptual model of Zone 1 as a sediment

source, Zone 2 as the sediment transport component, and

Zone 3 as a sediment sink has proven useful in generalizing

processes at the mid to large watershed scale (such as rivers

as large as the Missouri-Mississippi system).

Watersheds contain interior or subwatersheds, and there

often exists a similarity of shape and structure across the

range of scales from the watershed to its smaller sub-watersheds. Building on this similarity concept and the three-zones

concept, we can define the basis for a conceptual model of soil

erosion and sediment yield. The basis is that there is a

continuum of “sediment source-transport-and sink zones”

across a range of scales from the watershed down to its

smallest components.

The conceptual model we propose is that within a semiarid

watershed there is a continuum of sediment source-transport-sink zones and that different erosional processes are

dominant at different spatial scales. Further, at the plot to

hillslope to very small watershed scale (about a square

meter up to perhaps a few hectares) hillslope topography,

vegetative canopy cover, surface ground cover, soil and soil

detachment processes are dominant. At the subwatershed

scale (that is, one to perhaps a thousand hectares) geology,

soils, gully and channel processes, vegetation type, and

sediment transport and deposition processes are dominant.

Although beyond the scope of this paper, at the watershed

scale (from about a thousand to greater than 10,000 ha)

partial rainfall coverage of the watershed, infiltration of

streamflow (transmission losses) to the channel bed and

banks, sediment transport capacities, geology, and soils are

dominant. Of course, all processes are important within a

watershed, but we are describing dominance as a function of

watershed scale. In summary, soil erosion, sediment transport

and deposition, and thus sediment yield vary as a function of

spatial scale with identifiable factors and processes dominating them depending upon spatial scale (table 3).

Hillslope Erosion and Sediment Yield From Very

Small Watersheds—At the plot, hillslope scale, and very

small watershed scale (from a square meter up to a few

hectares appropriate for the experimental watersheds at the

SRER) overland flow processes dominate on hillslopes, as

channelization at this scale is at the microtopographic level

and larger channels are usually absent. At the small watershed scale, hillslope processes are important, but flow becomes channelized, and processes of sediment transport and

deposition are also important in determining watershed

sediment yield. This is the spatial scale appropriate for the

eight experimental watersheds on the SRER. The sediment

source-transport-sink concept applies at this scale and is

observable in the field. At the scale of a meter or less, one can

see debris dams caused by accumulation of litter behind a

plant, rock, or other small feature, and that these debris

dams induce sediment deposition and thus trap sediment.

At the hillslope scale, one can see areas of no apparent soil

erosion (unless closely observed with a trained eye), areas of

rill or concentrated flow erosion, and areas of sediment

deposition such as at the toe of a slope. Hillslopes contribute

water and sediment to small ephemeral channels that drain

to the watershed outlet, and in these channels one can observe areas of scour or degradation, areas in which no scour

or deposition is apparent, and areas of sediment deposition.

Sediment passing the watershed outlet (in the case of the

SRER watersheds, the runoff measuring flumes) is called

sediment yield. It is customary to speak in terms of sediment

mass flux per unit time or sediment mass flux per unit time

per unit area (for example t/ha/y).

As part of his analyses, Lawrence (1996) tabulated annual

runoff and sediment yield data measured at the outlets of the

upper four SRER watersheds for the 16-year period 1976 to

1991. The main channel in each watershed was designated

as the channel from the watershed outlet along its course to

its termination in the upper areas of the watershed.

Mean annual sediment yield (along with mean annual

precipitation and runoff for completeness) are summarized

in table 4. The annual means vary from under 0.1 t per ha

from Watershed 6 to over 4 t per ha from Watershed 5. Also

shown in column 5 of table 4 is the mean annual sediment

concentration, Cb, in percent by weight. Values of mean

sediment concentration varied from a low of 0.38 percent

(3,800 mg per L) from Watershed 6 to a high or 2.5 percent

(25,000 mg per L) from Watershed 5. As was the case for

mean annual runoff, the very low sediment yield from

Watershed 6 is more the result of its different soil (loamy

sand on WS6 and sandy loam on WS5, WS7, and WS8) than

as a result of the treatments. Watershed 6 produced significantly less runoff and correspondingly significantly less
98 USDA Forest Service Proceedings RMRS-P-30. 2003

Lane and Kidwell Hydrology and Soil Erosion

Table 3—Summary of dominant processes controlling sediment yield from semiarid watersheds such as those at Walnut Gulch and the SRER. Table

adapted from Lane and others 1997 to illustrate a conceptual model for soil erosion and sediment yield on semiarid watersheds.

Approximate scale (ha) on the sediment source transport sink continuum

Plot to hillslope (10-4 to 100 ha) Subwatershed (100 to 103 ha) Watershed (103 to 104 ha)

 Dominant processes at the indicated scale 

 Range of scales studied at the SRER 

Topography, vegetative canopy cover, Geologic parent material-soils, gully Partial rainfall coverage, transmission

surface ground cover, soil, and soil and channel processes, vegetation losses, channell processes, sediment

detachment type, sediment transport and deposition transport capacities, and soils

 Processes more or less in common across scales 

Rainfall, runoff amounts, and Intensities

Spatial variability and interactions

Table 4—Summary of mean annual sediment yield from the upper four experimental watersheds at the Santa Rita Experimental Range from 1976

to 1991. Precipitation is for a centrally located raingage on Watershed 5. The values are annual means in mm for precipitation and runoff

and in t per ha for sediment yield. The values in parentheses are coefficients of variation, in percent, for the measured variables.

Measured Measured Measured

Watershed Treatment precipitation runoff sediment yield

1 2 34 5

WS5 (4.02 ha) sandy loam Rotation grazing, mesquite retained 440.0 (27.0) 16.7 (102.0) 4.21 (94.0) (Cb = 2.5 percent)a

WS6 (3.08 ha) loamy sand Rotation grazing, mesquite removed 440.0 (27.0) 1.6 (138.0) 0.06 (107.0) (Cb = 0.38 percent)

WS7 (1.06 ha) sandy loam Continuous grazing, mesquite removed 440.0 (27.0) 25.2 (123.0) 1.48 (106.0) (Cb = 0.59 percent)

WS8 (1.12 ha) sandy loam Continuous grazing, mesquite retained 440.0 (27.0) 30.1 (92.0) 3.67 (83.0) (Cb = 1.2 percent)

a

 Cb = Mean sediment concentration in percent by weight. Note: 1-percent sediment concentration = 10,000 mg per L.

sediment yield than the other three watersheds. Again,

there is a suggestion in the data that removing mesquite

reduces runoff and sediment yield, but differences in the

soils dominated the impacts of grazing and mesquite removal on runoff and sediment yield. Given the high variability in sediment yield (CVs of mean annual sediment yield in

table 4 range from 83 to 107 percent), it is instructive to

examine the role of extreme years (years with annual sediment yield significantly larger than the mean) in determining mean annual sediment yield.

Erosion and sediment yield monitoring programs are

often conducted over short time periods, and the resulting

short-term databases are used for a variety of purposes

including estimation of mean annual soil erosion rates,

mean annual sediment yield, and the resulting rates of

landscape evolution. Since by definition large events are

rare, a short monitoring period may or may not sample any

large events. Annual sediment yields for each of the 16 years

from 1976 through 1991 were computed, and from them a

mean annual sediment yield for all 16 years was computed

for each of the small watersheds. Contributions of sediment yield from the individual years (not events) were used

to analyze the relationship between sediment yield in

“large sediment yield years” and the 16-year mean annual

sediment yield. The relation between sediment yield in the

years with the largest annual sediment yields to the 16-

year mean annual sediment yield from the four upper

watersheds on the SRER is illustrated in figure 2.

We interpret the data shown in figure 2 as follows. During

16 years of measurements, the year with the largest sediment

yield (fraction of years = 1/16 = 0.0625) accounted for about 18

to 26 percent of the mean annual sediment yield. The four

years with the largest sediment yield (25 percent of the period

of record of 16 years) accounted for about 54 to 66 percent of

the mean, and the 8 years with the largest sediment yields

accounted for about 80 to 90 percent of the mean annual

sediment yields on the four watersheds. Similar statistics and
USDA Forest Service Proceedings RMRS-P-30. 2003 99

Hydrology and Soil Erosion Lane and Kidwell

graphs could be computed for annual runoff, and they would

show similar results.

The significance of these results is clear. Runoff and

sediment yield estimates from short periods of record on

semiarid watersheds (such as those at SRER) are highly

variable (CVs of mean annual runoff and mean annual

sediment yield are on the order of 100 percent or more), and

thus there is a great deal of uncertainty in the means

estimated from short periods of record. For data such as

these in tables 2 and 4, the natural high levels of variability

and the resulting high levels of uncertainty make it very

difficult to evaluate the impacts of land use and management (in this case, alternative grazing systems and mesquite removal) on runoff and sediment yield. In the face of

such high natural variability in time, relatively longer

periods of record (at least greater than 16 years) are needed

to evaluate the impacts of land use and management practices. In addition, the technique of using paired watersheds

and treating one of each pair loses much of its power if the

watersheds are significantly different in their rainfall-runoff and runoff-sediment yield relationships before imposition of treatments or alternative land management practices. This argues eloquently for pretreatment monitoring

and modeling to ensure that the paired watersheds are as

similar as is possible in their hydrologic and erosional

characteristics.

Discussion ____________________

Summary

We reviewed hydrologic and soil erosion research on the

SRER. Almost all of that research was associated with the

eight small experimental watersheds established in 1974 to

1975 and operated until the present. Analysis of climatic

features of the SRER supports the concept of extending

research findings from the SRER to broad areas of the

Southwest with similar climatic regimes.

Conceptual models for annual water balance and annual

sediment yield at the SRER were developed. Analyses and

Figure 2—Relation between sediment yield in the

years with the largest annual sediment yields to the

16-year mean annual sediment yield on four watersheds at the Santa Rita Experimental Range in

southern Arizona.

interpretation of measured and modeled hydrologic data on

water balance, soil erosion, and sediment yield from four small

experimental watersheds supported these conceptual models

and added specificity to their general scientific content.

Due to its long history and rich databases of vegetation

characterization, grazing, and land management activities,

the SRER is well suited for evaluating the impacts of land use

and management practices upon hydrology, soil erosion processes, and watershed sediment yield. The impacts of cattle

rotation and yearlong grazing activities and mesquite removal

were analyzed using data from four small experimental watersheds. The analyses suggested that mesquite removal reduced

runoff and sediment yield, but differences in hydrologic response from paired watersheds due to soil differences dominated grazing and vegetation management impacts.

High levels of variability in components of the water

balance and in sediment yield suggest that long duration

watershed studies are required to quantify components of

the water balance and sediment yield.

Some Lessons Learned

• Climatic features of the SRER are similar to broad areas

of the American Southwest and Northern Mexico so that

research findings from hydrologic and erosion studies

on the SRER have broad geographical applicability.

• Hydrograph development techniques such as unit

hydrographs and kinematic cascade models can be successfully applied on the SRER.

• Variations in topography, soils, and vegetative cover

within very small watersheds on the SRER result in

what is called a partial area response where only portions of a watershed may be producing surface runoff.

These simulation modeling results were verified by

herbicide tracer studies.

• A conceptual model of annual water balance developed

for semiarid watersheds is applicable on the SRER.

• A conceptual model for annual sediment yield from

semiarid watersheds is applicable on the SRER.

• Paired watershed studies were used to study the impacts of grazing systems and mesquite removal on

runoff and sediment yield, but the results were ambiguous because of significant differences in hydrological

responses resulting from variations in soil properties

between the paired watersheds (WS5 and WS6).

• Paired watershed studies should include a period of

pretreatment monitoring and modeling before treatments are imposed to determine if the paired watersheds are indeed hydrologically similar.

• Extreme natural variability in components of the water

balance and sediment yield from very small watersheds

suggest that long periods of observation and monitoring

are required to evaluate impacts of land use and management practices on runoff, erosion, and sediment yield.

Path Forward for Hydrology and Soil

Erosion Research at Santa Rita

Twenty-eight years of hydrologic data and observations

are now available for the eight paired experimental watersheds at SRER. Treatments (yearlong versus continuous

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Fraction of Years

Fraction of Sediment Yield

WS 8 Mesquite, 3.67 t/ha

WS 7 No Mesquite, 1.48 t/ha

WS 5 Mesquite, 4.21 t/ha

WS 6 No Mesquite, 0.6 t/ha
100 USDA Forest Service Proceedings RMRS-P-30. 2003

Lane and Kidwell Hydrology and Soil Erosion

grazing, and mesquite removal versus mesquite retained)

have been maintained over this entire period of record. This

presents us with unique and invaluable opportunities.

If new treatments were imposed now, these 28 years of

monitoring under the same experimental design on the

four pairs of watersheds would provide a long period of

“pretreatment” monitoring on the paired watersheds (WS1

versus WS2, WS3 versus WS4, WS5 versus WS6, and WS7

versus WS8). New treatments could now be adapted and

designed based on lessons learned from monitoring and

modeling activities over nearly three decades. There is a

unique opportunity to institute long-term adaptive management experiments on these eight experimental watersheds. Institutional control of the watersheds, scientific

databases, modeling expertise, and “corporate knowledge”

of monitoring, modeling, and interpretation exist within

the cooperating organizations. No other experimental range

or watershed program has such a rich background of three

decades of “pretreatment” baseline results on paired watersheds to begin a carefully designed and long-term adaptive management research program.

References ____________________

Carlson, D. H.; Thurow, T. L.; Knight, R. W.; Heitschmidt, R. K.

1990. Effect of honey mesquite on the water balance of Texas

Rolling Plains rangelands. Journal of Range Management. 43(6):

491–496.

Diskin, M. H.; Lane, L. J. 1976. Application of a double triangle unit

hydrograph to a small semiarid watershed. Tucson: University of

Arizona, Office of Arid Land Studies. Hydrology and Water

Resources in Arizona and the Southwest. 6: 125–135.

Goodrich, D. C.; Lane, L. J.; Shillito, R. M.; Miller, S. N.; Syed, K. H.;

Woolhiser, D. A. 1997. Linearity of basin response as a function

of scale in a semiarid watershed. Water Resources Research.

33(12): 2951–2965.

Green, Christine R.; Martin, S. C. 1967. An evaluation of precipitation, vegetation and related factors on the Santa Rita Experimental Range. Meteorology and Climatology of Arid Regions Tech.

Rep. 17. Tucson: University of Arizona, Institute of Atmospheric

Physics. 82 p.

Knisel, W. G., ed. 1980. CREAMS: a field-scale model for chemicals,

runoff and erosion from agricultural management systems. U.S.

Department of Agriculture Conservation Res. Rep. 26. 643 p.

Lane, L. J.; Diskin, M. H.; Wallace, D. E.; Dixon, R. M. 1978a. Partial

area response on small semiarid watersheds. American Water

Resources Association, Water Resources Bulletin. 14(5): 1143–1158.

Lane, L. J.; Morton, H .L.; Wallace, D. E.; Wilson, R. E.; Martin, R. D.

1978b. Nonpoint-source pollutants to determine runoff source

areas. Tucson: University of Arizona, Office of Arid Land Studies.

Hydrology and Water Resources in Arizona and the Southwest. 7:

89–102.

Lane, L. J.; Romney, E. M.; Hakonson, T. E. 1984. Water balance

calculations and net production of perennial vegetation in the

Northern Mojave Desert. Journal of Range Management. 37(1):

12–18.

Lane, L. J.; Hernandez, M.; Nichols, M. 1997. Processes controlling

sediment yield from watersheds as functions of spatial scale.

Environmental Modeling and Software. 12(4): 355–369.

Lawrence, P. A. 1996. The role of data sources and simulation model

complexity in using a prototype decision support system. Tucson:

University of Arizona, School of Renewable Natural Resources.

332 p. Dissertation.

Martin, S. C.; Morton, H. L. 1993. Mesquite control increases grass

density and reduces soil loss in southern Arizona. Journal of

Range Management. 46(2): 170–175.

Martin, S. C.; Reynolds, H. G. 1973. The Santa Rita Experimental

Range: your facility for research on semidesert ecosystems. Tucson: University of Arizona, Office of Arid Land Studies. Journal

of the Arizona Academy of Science. 8: 56-67.

McClaran, M. P.; Angell, D. L.; Wissler, C. 2002. Santa Rita

Experimental Range digital database: user’s guide. Gen. Tech.

Rep. RMRS-GTR-100. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 13 p.

Medina, A. L. 1996. The Santa Rita Experimental Range: history

and annotated bibliography (1903–1988). Gen. Tech. Rep. RMGTR-276. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment

Station, 67 p.

Osborn, H.; Simanton, J. 1989. Gullies and sediment yield. Rangelands. 11(2): 51-56.

Renard, K. G.; Lane, L. J.; Simanton, J. R.; Emmerich, W. E.; Stone,

J. J.; Weltz, M. A.; Goodrich, D. C.; Yakowitz, D. S. 1993.

Agricultural impacts in an arid environment. Hydrological Science and Technology. 9: 145–190.

Schumm, S. A. 1977. The fluvial system. New York: John Wiley &

Sons. 338 p.

Trewartha, G. T.; Horn, L. H. 1980. An introduction to climate. 5th

ed. New York: McGraw-Hill Book Company. 415 p.
USDA Forest Service Proceedings RMRS-P-30. 2003 101

Thomas E. Sheridan

Archive and Laboratory Embedded in the

Landscape: Future of the Santa Rita

Experimental Range

Thomas E. Sheridan is Research Anthropologist in the Southwest Center and Professor of Anthropology at the University of Arizona; e-mail:

tes@email.arizona.edu. He holds a Ph.D. degree in anthropology from the University of Arizona. He is chair of the Ranch Conservation Technical Advisory Team

of Pima County’s Sonoran Desert Conservation Plan. His research focuses on the ethnohistory and political ecology of the Southwest and Northern Mexico.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

The future of the Santa Rita Experimental Range (SRER) can only be comprehended within the context of the dynamic

political ecology of twenty-first-century Arizona. This makes forecasting a risky proposition at best. When SRER was created

in 1903, Arizona was a largely rural territory dominated by extractive industries, particularly copper mining, irrigated

agriculture, and ranching. World War II transformed Arizona’s economy, triggering explosive urban growth. By the end of the

twentieth century, Arizona was an overwhelmingly urban State fueled by the service and industrial sectors of its economy

(Sheridan 1995). I doubt any seer in 1903 would have predicted a metropolitan Phoenix of three million people, an industrial

border zone swelling like a tick on cheap labor and a multibillion dollar illegal drug trade, or a countryside transformed into

a playground for urban dwellers.

Research on SRER has reflected the explosive growth of Arizona and the West. SRER was created “to protect the native

rangeland from grazing and to conduct research on problems associated with livestock production” (Medina 1996: 1). When

D. W. Griffiths initiated research there, Arizona was a lunar landscape in places, its grasslands denuded by more than two

decades of unregulated grazing, and its woodlands decimated by indiscrimate timber and fuelwood cutting and grass

harvesting (Bahre 1991; Humphrey 1987; Sayre 2002). It was a true tragedy of the commons on the open range because there

were no legal mechanisms to regulate grazing or woodcutting on Arizona’s vast public domain (Sheridan 1995).

A century of rangeland reform provided the necessary regulation. The Forest Reserves, which developed into the National

Forest system, first introduced exclusive grazing allotments in the early 1900s. The establishment of State Trust Lands after

Abstract: The Santa Rita Experimental Range (SRER) is both an archive of past ecological

research and a laboratory for continuing research embedded in the southern Arizona landscape.

The scientific questions being asked there have changed over the last 100 years, but SRER with

its monitoring stations and its legacy of repeat photography still offers a unique opportunity to

study environmental change through time. Now that it belongs to the State of Arizona, however,

the Arizona State Land Department (ASLD) could conceivably sell it for commercial development

if the Arizona legislature were to revoke its special status for “ecological and rangeland research

purposes” administered by the University of Arizona. As metro Tucson, Green Valley, and

Sahuarita continue to experience explosive growth, State Trust Lands are being auctioned off to

real estate developers. Pima County’s Sonoran Desert Conservation Plan is attempting to

preserve biodiversity, open space, cultural resources, and working ranches throughout eastern

Pima County. The Santa Rita Experimental Range provides one of the best opportunities to do so

on State Trust Lands in the upper Santa Cruz Valley.

Assuming SRER survives for another century, several research topics suggest themselves:

(1) the ecological dynamics of exotic Lehmann lovegrass and efforts to eradicate or control it;

(2) the impact of urban and exurban development on native wildlife and vegetation; and (3) the

development of grass-fed, hormone-free beef and the networks necessary to market it successfully. But all future research must build upon and respect the integrity of the SRER archive with

its ongoing record of vegetation change, hydrological and nutrient cycles, and human efforts to

manipulate them.
102 USDA Forest Service Proceedings RMRS-P-30. 2003

Sheridan Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range

Statehood in 1912 extended a similar system to more than 10

million acres selected by ranchers, largely in Arizona’s

grassland valleys (Sayre 2002). Finally, in 1934, the Taylor

Grazing Act regulated grazing on the rest of Arizona’s

Federal public domain.

Most of the research on SRER during the twentieth

century focused on how to make grazing lands more productive. Range scientists developed the Santa Rita System

of grazing rotation and struggled to halt the invasion of

woody shrubs, particularly mesquite, onto Arizona grasslands. The needs of ranchers dominated SRER’s research

agenda.

But as Arizona’s cities sprawled outward or leapfrogged

into desert valleys and mountain meadows, urban needs

began to push aside rural concerns. City dwellers wanted

open space where they could hunt, fish, hike, camp, ride, and

shoot. The growth of the environmental movement brought

issues of biological diversity to the forefront, particularly

after the passage of the Endangered Species Act in 1973.

Because ever-declining proportions of the population made

their living off the land, or from industries that processed

timber, beef, milk, wool, cotton, or copper, the struggle to

make a living in the rural West no longer dictated political

debate, even though ranching and mining interests remained disproportionately strong in the Arizona legislature.

New and powerful constituencies that privileged recreation

or biodiversity over resource extraction increasingly challenged ranchers, loggers, and miners over the management

of public lands.

By the beginning of the twenty-first century, researchers

were increasingly turning to SRER to ask questions that

had nothing to do with range management or beef production. Eleven of the 26 current projects (42 percent) on SRER

focus on ecological or geological questions unrelated to

range issues, including termite biology and control, the

behavior of the swallow-tail butterfly, and seismic imaging

of the Santa Rita Fault (Peter Else, personal communication). Even several of the studies that factored in the

impact of grazing did so in order to study rates of carbon

and nitrogen sequestration in the soil. Such research was

driven by climatological, not range management, concerns.

SRER had developed into a landscape laboratory with an

ever-broadening ecological mission.

State Trust Lands ______________

Meanwhile, residential development crept closer and closer

to the boundaries of SRER. The status of SRER itself was not

really threatened for the first 73 years of its existence

because it belonged to the Federal Government. But in 1988,

a convoluted land swap to create Buenos Aires National

Wildlife Refuge in the Altar Valley transferred SRER to the

Arizona State Land Department (ASLD). Arizona Senate

Bill 1249 stipulated that SRER would be utilized by the

University of Arizona for “ecological and rangeland research

purposes...until such time as the legislature determines the

research can be terminated on all or parts of the lands.”

Given the budget cuts imposed on Arizona universities over

the past 15 years, those words are hardly comforting. The

fate of the SRER will depend on how the Arizona Legislature

values the promotion of research and conservation of open

space.

State Trust Lands will be the defining battleground between the forces of development and conservation during

the early twenty-first century. Arizona currently has

9,471,000 acres of State Trust Lands, more than any other

State in the Union (table 1). Nearly 90 percent of this acreage (8,457,000 acres) is grazed under a system of leases,

generally for 10-year periods, unless classified for commercial sale. Until recently, those leases were preferential, but

court cases instigated by environmental and public education advocacy groups have initiated an open bidding process.

One possible unintended consequence of those decisions is a

greater vulnerability to development on State Trust Lands.

Arizona’s State Trust Land system began when the Territory of Arizona was established on February 24, 1863. The

Act of Congress granted the new territory sections 16 and 36

of each township for the benefit of the “Common Schools.”

The State Enabling Act (Section 24) of June 20, 1910,

allotted two more sections of each township (2 and 32). Four

sections of every township in the new State were to be held

in trust for public schools. The Enabling Act (Sec. 25) also

gave Arizona an additional two million acres to benefit other

public institutions including penitentiaries, insane asylums, miners’ hospitals, and normal schools (ASLD Historical Overview 2003).

To administer those lands, Arizona’s first State Legislature established a three-member State Land Commission.

Table 1—Ten States with Trust Lands greater than one million acresa.

State Year of Statehood Acres granted Sections granted Acres in 1995a Percent original

Arizona 1912 8,093,000 6, 16, 32, 36 9,471,000 117

New Mexico 1912 8,711,000 6, 16, 32, 36 9,217,000 106

Montana 1889 5,198,000 16, 36 5,132,000 99

Utah 1896 5,844,000 6, 16, 32, 36 3,739,000 64

Wyoming 1890 3,473,000 16, 36 3,602,000 104

Colorado 1876 3,686,000 16, 36 2,858,000 78

Washington 1889 2,376,000 16, 36 2,812,000 118

Idaho 1890 2,964,000 16, 36 2,404,000 81

Nebraska 1867 2,731,000 16, 36 1,514,000 55

Oregon 1859 3,399,000 16, 36 1,438,000 42

a

Adapted from Souder and Fairfax 1996.
USDA Forest Service Proceedings RMRS-P-30. 2003 103

Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range Sheridan

The Commission wisely decided not to sell State Trust Lands

but to manage them for their “highest and best use.” The

Commission also recommended that a State Land Department be created to oversee such management in order to

maximize revenues for the beneficiaries. The Arizona legislature accepted those recommendations and created a State

Land Code in 1915 (ASLD Historical Overview 2003).

Because homesteaders, miners, Indian reservations, National Forests, and other Federal entities had already withdrawn the designated school sections in many townships,

the Enabling Act (Sec. 24) granted Arizona the right to select

an equal amount of in lieu lands from the Federal public

domain. The Arizona State Selection Board, which consists

of the Governor, Attorney General, and State Land Commissioner, carries out this process. The board selected most

State Trust Lands between 1915 and 1960, through both inlieu selection and land exchanges with the Federal Government. Those exchanges were originally engineered to create

blocks of State Trust Lands rather than isolated sections.

Homesteaders had already preempted most arable land.

Federal law prevented the State from acquiring mineral

lands. Consequently, the State Selection Board concentrated on acquiring the best grazing lands in Arizona (ASLD

Historic Overview 2003). In fact, ranchers often hired brokers in the Arizona State Capitol of Phoenix to make sure the

lands they wanted to lease made it through the selection

process. As a result, State Trust Lands constitute much of

the nonprivate land in Arizona’s grassland valleys, particularly in the central and southeastern parts of the State

(Sayre 2002).

As Arizona’s urban centers have expanded, these lands

have also become the most attractive for residential development, particularly when they are within an hour’s drive of

metropolitan Phoenix, Tucson, Flagstaff, or Prescott. The

relentless expansion of metropolitan Phoenix has chewed up

much of the private ranch lands originating as homesteads

in the Salt River Valley. Moreover, metro Phoenix’s demand

for second homes at higher elevations has fueled the conversion of private ranch lands into subdivisions from Kingman

Table 2—Beneficiaries of Arizona State Trust Landsa.

Beneficiary Acres in FY 2001 Percentage of total

Common Schools (K-12) 8,107,420 87.4

Normal Schools 174,808 1.9

University Land Code 138,125 1.5

Agricultural and Mechanical Colleges 125,234 1.4

School of Mines 123,558 1.3

School for the Deaf and Blind 82,662 0.9

Military Institutes 80,168 0.9

State Charitable, Penal, and Reformatory Institutions 77,753 0.8

Penitentiary 76,333 0.8

State Hospital 71,249 0.8

Legislative, Executive, and Judicial Buildings 64,406 0.7

University of Arizona 54,591 0.6

Miners’ Hospital (1929) 47,843 0.5

Miners’ Hospital 47,771 0.5

Total 9,271,921

a

Adapted from Arizona State Land Department Historic Overview 2003.

to the White Mountains. Metropolitan Tucson, about 25

percent as large as metro Phoenix, has generated the same

relentless demand across much of southeastern Arizona.

As developers run out of private land to subdivide, they

are going to exert ever-greater pressure on ASLD to sell off

State Trust Lands. ASLD can do so under Arizona’s Enabling Act and Constitution, which mandate that State

Trust Lands be managed for their beneficiaries, which now

number 14 (table 2). As trust law evolved from its British

common law origins, both public and private trusts interpreted “highest and best use” to be the maximization of

revenues, not the conservation of natural resources or the

preservation of open space or biological diversity (Souder

and Fairfax 1996).

For much of the twentieth century, ASLD determined

“highest and best use” to be grazing leases. In part, this

reflected the low demand for State Trust Lands outside the

Phoenix and Tucson basins. Ranchers were also the most

powerful constituency of ASLD. The sale or lease of State

Trust Lands had to be advertised and opened to competitive

bidding at public auctions, where they had to be leased or

sold to the “highest and best bidder” (Arizona Enabling Act,

Sec. 28). But Section 28 of the Enabling Act also stipulated,

“Nothing herein contained shall prevent: (1) the leasing of

any of the lands referred to in this section, in such manner

as the Legislature of the State of Arizona may prescribe

(italics mine), for grazing, agricultural, commercial, and

domestic purposes, for a term of five years” (Arizona Enabling

Act 2003). In 1936, the 74th Congress amended the Enabling

Act to extend that period to 10 years. The Arizona Constitution

(Article 10, Sec. 3) states, “Nothing herein, or elsewhere in

article X contained, shall prevent: 1) The leasing of any of the

lands referred to in this article in such manner as the

legislature may prescribe, for grazing, agricultural,

commercial and homesite purposes, for a term of ten years or

less, without advertisement” (Arizona Constitution 2003)

Ten-year grazing leases became preferential, with current

holders able to renew their leases without competition

(Sayre 2002).
104 USDA Forest Service Proceedings RMRS-P-30. 2003

Sheridan Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range

As Phoenix and Tucson grew, however, other constituencies challenged the ranchers. Until 1966, many States permitted their trust lands to be dedicated to transportation

rights-of-way and other uses that did not generate revenue.

But in Lassen v Arizona Highway Department, the U.S.

Supreme Court ruled, “The Enabling Act unequivocally

demands both that the trust receive the full value of any

lands transferred from it and that any funds received be

employed only for the purposes for which the lands were

given” (quoted in Souder and Fairfax 1996). The Arizona

legislature reinforced the intent of that decision when it

passed the Urban Lands Act in 1981. The act allowed ASLD

to include higher land values generated by surrounding

planning and zoning regulations in its assessment of full

value. In the words of ASLD, “Today the Land Department’s

urban lands lease and sale program is the largest revenue

producer for the Trust” (SLD Historical Overview 2003: 3).

The Arizona State Land Department goes on to say,

“Nearly all the most valuable urban Trust land around the

northern border of the Phoenix metropolitan area and north

and west of Tucson are Common Schools Trust lands. The

large block of Trust lands on the south and southeast sides

of the Tucson metropolitan area is divided amongst the

various institutional Trusts” (SLD Historical Overview

2003:3). The ASLD also notes that 1,628,079 acres of State

Trust lands have been sold or exchanged during the 88 years

since Statehood (1912–2000).

That figure will undoubtedly increase during the twentyfirst century. One report of Pima County’s Sonoran Desert

Conservation Plan (SDCP) notes that 53,000 acres of State

Trust Lands have been reclassified for commercial sale or

lease within a 25-mile radius of I-10 and I-19 in Tucson

(SDCP Our Common Ground 2000: 11). A recent article in

the Arizona Daily Star notes that the ASLD is planning to

auction off 1,500 acres on the northeast corner of Houghton

and Valencia in southeastern Tucson. The city of Tucson’s

Comprehensive Planning Task Force allows up to eight

residential units per acre in the area, so more than 10,000

homes could be constructed on those 1,500 acres alone.

Vistoso Partners, LLC, bid $29.1 million for 1,071 acres of

State Trust Lands on the northwest corner of Houghton and

Valencia in 2002, almost twice the appraised value of the

land (Grubbs 2003).

Such reclassifications affect State Trust Lands that directly border on SRER. As land values escalated south of

metropolitan Tucson and along the I-19 corridor, ASLD

imposed 5-year limits on 16 grazing permits in eastern Pima

County. Eight of these Special Land Use Permits (SLUPs)

occur in the Upper Santa Cruz Valley watershed. They

comprise 49,000 acres, encompassing 11 percent of the

entire area. The largest SLUP runs from Los Reales Road on

the north to SRER on the south. Its western boundary is the

Santa Cruz River and its eastern border is Corona de

Tucson. Ranchers grazing SLUPs can be evicted in 30 days

even if their permits are current. Moreover, they will not be

reimbursed for any improvements on the State Trust Lands

in question. In other words, SLUPs are State Trust Lands

reclassified for commercial sale or lease that permit grazing

on an interim basis only (SDCP Our Common Ground 2000:

45). Most of the State Trust Lands surrounding SRER will

most likely be auctioned off and developed during the next 50

years.

Recently, advocacy groups like the Arizona Gamebird

Alliance and Forest Guardians have won several court

challenges to ASLD’s preferential grazing leases. As it

stands now, environmental groups—and developers—can

bid against ranchers who have long incorporated grazing

leases on State Trust Lands into their ranching operations.

Competitive bidding is in its infancy, but it has the potential

to drive ranchers who depend on State Trust Lands out of

business. Say, for example, a developer wanted to build a

subdivision or a resort on a mixture of private and State

Trust Land in eastern Pima County. If that developer has

deep pockets, he/she could cherry pick State Trust Land

grazing leases by outbidding ranchers who have run their

cattle on those leases for a generation or more. The removal

of such leases would destroy the economic viability of the

ranches in question. And because few ranchers can afford to

wait 10 years until the leases come up for bid again, the

ranchers would be forced to sell their private lands to the

developer or subdivide it themselves.

Such cherry picking would accelerate the transition from

ranching to real estate development and fragment a onceopen landscape. Wildlife corridors would be disrupted. Fire

as a natural process or a landscape management tool would

be removed from the toolkit. Both legal and illegal recreational

impact on the surrounding lands would increase. Biological

diversity as well as the ranching economy would suffer

(Sheridan 2001).

There is a growing movement to modify the mandate of

ASLD and allow some State Trust Lands to be managed for

conservation, not maximum economic returns. A broad

coalition of environmental groups including The Nature

Conservancy, Sonoran Institute, Grand Canyon Trust, and

Arizona League of Conservation Voters drafted a proposal to

put an initiative concerning State Trust Land Reform on the

2002 ballot. Before doing so, however, a working group of

stakeholders encompassing educators, ranchers, developers, conservationists, and business representatives held a

series of meetings to see if they could develop an initiative all

could support. The working group failed to reach consensus

in time for the 2002 elections. The group therefore agreed to

continue meeting to hammer out an initiative for 2004. They

also signed a forbearance agreement not to undermine the

dialogue until they had arrived at a consensus or decided to

disband (Arizona League of Conservation Voters 2003).

Despite this delay, the Arizona legislature had already

taken a first step to conserve selected State Trust Lands. In

1996, legislators passed the Arizona Preserve Initiative

(API). Amended several times since then, API strives to

preserve portions of State Trust Lands in and around

urban areas as open space. API defines conservation as

“protection of the natural assets of State Trust Land for the

long-term benefit of the land, the beneficiaries, lessees, the

public and unique resources such as open space, scenic

beauty, protected plants, wildlife, archaeology, and multiple use values” (ASLD Arizona Preserve Initiative Program 2003: 1).

The Arizona Preserve Initiative also created a process to

reclassify State Trust Lands for conservation purposes.

Citizens groups, State and local governments, and State

land lessees can petition the State Land Commissioner to

nominate State Trust Lands for reclassification. After public

hearings and studies of the impact of reclassification on
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current lessees have been carried out, the Commissioner

may reclassify the land in question, enabling it to be leased

for up to 50 years or even purchased for conservation purposes. In 1998, Arizona voters provided a funding mechanism for API when they approved Proposition 303, the socalled Growing Smarter Initiative. Proposition 303 allocated

$20 million per year for 11 years to lease, buy, or purchase

development rights on State Trust Lands “to conserve open

spaces in or near urban areas and other areas experiencing

high growth pressure” (Arizona State Parks 2003: 2). As

metropolitan Tucson moves south, SRER is likely to qualify

for acquisition under those guidelines.

Unfortunately, API has also been challenged. In Tucson,

Pima County planned to purchase Tumamoc Hill in Tucson,

where the century-old Desert Laboratory is located, and

convey it to the University of Arizona. Negotiations have

been suspended until the challenge is resolved. If the challenge is ultimately defeated, however, API may offer a

mechanism, albeit a potentially expensive one, to preserve

SRER in the rapidly developing Santa Cruz Valley. Without

additional protection through API—or through the much

more difficult process of amending the Enabling Act and

Arizona’s constitution to make conservation one of ASLD’s

mandates—the Arizona legislature will be increasingly

tempted to revoke SRER’s protected status and auction it off

to the highest bidder.

Metropolitan Tucson and

Urban Sprawl in the

Santa Cruz Valley ______________

Development is already lapping at the borders of SRER.

Private (156,455 acres; 35 percent) and State Trust Lands

(212,745 acres; 47 percent) compose a whopping 82 percent

of the Upper Santa Cruz River Valley (449,684 acres) where

SRER is located (SDCP Our Common Ground 2000: 40).

Private and State Trust Lands abut most of the northern and

western boundaries of SRER. The expansion of Green Valley

has already spun off several high-end subdivisions including

Rancho Sahuarita and Quail Creek along the northwestern

side of SRER. Because voters in Green Valley have turned

down several attempts to incorporate the community,

however, it is difficult to disaggregate Green Valley growth

trends from eastern Pima County as a whole.

The formerly agrarian community of Sahuarita, on the

other hand, incorporated in 1994, when it had a population

of 2,159 residents. Ironically, it did so to preserve its rural

character from Green Valley encroachment. Since then,

Sahuarita’s population has jumped to 3,242 according to the

2000 census, and its estimated population in July 2002 was

5,455. According to the Pima Association of Governments

(2000: 5), “Dramatic growth is anticipated in Sahuarita,

both in land size through annexation activity, and in

population growth resulting from the development of a 2810

acre master planned residential community. Sahuarita’s

growth rate was 99.02% between 1990 and 2000.” In the last

decade, Sahuarita has embraced, not restricted, growth.

In 1996, the Pima Association of Governments projected

a population of 23,374 in Sahuarita in 2050. That projection is probably low. Sahuarita and other communities in

the Santa Cruz Valley will develop even faster in the next

20 years as the City of Tucson expands south and southeast, where private and State Trust Lands have fewer

endangered species issues to impede development as they

have done in the northwest part of Tucson. Municipal

planners anticipate that both Houghton and Sahuarita

roads will become major corridors of residential development as well as transportation as metro Tucson’s population continues to increase. This will intensify development

north and east of SRER in addition to accelerated development along the I-19 corridor in the Green Valley-Sahuarita

areas.

Even though medium- and high-density developments are

being built in southeastern Tucson and Green Valley, other

residential and commercial development will undoubtedly

mimic long-established patterns in metropolitan Tucson

itself. Ever since the 1960s, Tucson’s growth has been

increasingly land extensive. In 1930, when Tucson’s population was 32,506, there were 4,526.7 persons per square mile

in the city. That density rose slowly through the 1960 census,

and then began to fall: 3,306.0 in 1970; 3,344.1 in 1980;

2,573.3 in 1990; and 2,490.7 in 2000. In 1990, a staggering

35 percent of land within the incorporated limits of the City

of Tucson was undeveloped. Because land is generally cheaper

on the edges of an urban center, demand and the housing

market have provided bigger lots in new subdivisions, not

greater urban densities and infilling within existing municipal boundaries. The result is urban sprawl and exurban

leapfrogging as 13 acres of desert a day—nearly 5,000 acres

a year—are bulldozed.

A consensus seems to be emerging among City of Tucson

and Pima Association of Governments prognosticators that

eastern Pima County will have a population of about 1.7

million people by 2050, twice as many people as live here now

(table 3). Like estimates in the past, those projections may

be too high (Pima County 2002). Regardless of the numbers,

however, growth will be relentless. If Pima County’s

ambitious Sonoran Desert Conservation Plan goes into effect,

much of that growth will be channeled south and southeast

of metro Tucson. That puts SRER on a collision course with

urban sprawl and exurban leapfrogging.

Even if SRER itself escapes development and is preserved as open space devoted to scientific research, the

impacts of development will nonetheless intensify. SRER

has been open to hunting since it came under the jurisdiction

of ASLD. Traffic from drug runners and undocumented

Table 3—Population projections for Pima Countya.

Year Arizona Pima County

1999 4,595,375 836,153

2000 4,961,950 854,329

2010 6,145,125 1,031,623

2020 7,363,625 1,206,244

2030 8,621,050 1,372,319

2040 9,863,625 1,522,615

2050 11,170,975 1,671,182

Change 1999 to 2050 6,575,600 835,029

Percent change 1999 to 2050 143.1 99.8

aAdapted from Pima Association of Governments and Arizona Department of

Economic Security (based on July 1, 1996).
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Sheridan Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range

workers seeking employment also has intensified in the last

decade and shows no signs of abating. As any rancher in

southern Arizona will tell you, more hunters, target shooters, drug runners, and undocumented crossers mean more

open gates, cut fences, punctured water lines, and trash.

Such traffic also jeopardizes the safety of researchers and

the security of research equipment.

Increasing numbers of people living along SRER’s borders

will also increase other legal and illegal activities as well—

poaching, wildcat dumping, pothunting of archaeological

resources, vandalism of research equipment, soil disturbance resulting from ORVs, and depredation of wildlife by

pets or abandoned cats and dogs. To ensure the integrity of

the landscape, not to mention safety and security of personnel and equipment, SRER will have to intensify its onsite

vigilance or risk seeing its research resources seriously

erode.

Sonoran Desert Conservation

Plan__________________________

One glimmer of hope is a rising demand for open space

among residents of eastern Pima County, including people

in Green Valley and other communities of the Upper Santa

Cruz Valley. In 1999, a coalition of environmentalists,

astronomers, and neighborhood associations in Green Valley

and Elephant Buttes persuaded the Pima County Board of

Supervisors to reject a request for rezoning the southern half

of the historic San Ignacio de la Canoa Land Grant comprising

some 6,000 acres by Fairfield Homes. It was the first time the

Board of Supervisors—by a vote of 4 to 1—had denied a

major rezoning in 25 years (Hadley 2000; Sheridan 2000). A

series of occasionally bitter negotiations eventually resulted

in an approved rezoning that allowed Fairfield Homes to

build homes and a golf course west of I-19 and to develop

commercial properties along a strip east of the freeway

around the Canoa Road interchange. Approximately 4,800

acres, or 80 percent of Canoa Ranch, on the other hand, was

not rezoned. Pima County later purchased that portion of

the Canoa land grant as a county preserve.

Similar battles over rezoning and development are being

waged across eastern Pima County. The most comprehensive attempt to control urban growth and to protect biodiversity, cultural resources, working ranches, and open

space is Pima County’s Sonoran Desert Conservation Plan

(SDCP). The listing of the cactus ferruginous pygmy owl as

endangered in 1997 triggered the SDCP. In 1998, the Pima

County Administrator and his staff decided to seek a

Section 10 permit under the Endangered Species Act (ESA)

to avoid site-by-site battles over development and to protect the County from lawsuits brought by environmental

groups such as the Center for Biological Diversity. A Section 10 permit requires a permittee to develop a Habitat

Conservation Plan (HCP). In return for adopting specified

conservation measures and practices designed to minimize

and mitigate impacts on covered species, an HCP protects

the permittee from being sued or prosecuted for incidental

take. HCPs are designed to protect critical habitat while at

the same time offering security to property owners and

municipalities on lands that are not so designated.

Rather than simply applying for a permit covering the

pygmy owl, however, the County decided to develop a

multispecies HCP to avoid expensive and time-consuming

species-by-species mitigation. At the time, eastern Pima

County was home to seven species that already had been

listed as threatened or endangered, and 18 more that had

been proposed or petitioned. The County therefore initiated

a process to identify other “species of concern.” Pima County

wanted an HCP that would channel urban growth and

development into areas of lower biological diversity while

protecting core areas of critical habitat for listed species and

other species that might be listed in the future. In addition,

Pima County sought to update its Comprehensive Land Use

Plan and included conservation of cultural resources, working

ranches, riparian areas, and mountain preserves.

To determine which species needed to be protected, the

County created a Science Technical Advisory Team (TAT)

composed of wildlife biologists and agency personnel who

manage wildlife. It also hired a biological consulting firm—

RECON of San Diego—to prepare an HCP that would serve

as the biologically preferred alternative. “The goal of the

Science TAT and RECON was to identify vulnerable species of concern and their potential critical habitats. The

County attempted to erect a so-called “firewall” to shield

the Science TAT and RECON from political pressure”

(Davis 2001). The two independent peer reviewers of the

Sonoran Desert Conservation Plan—Reed Noss, Ph.D.,

and Laura Hood Watchman, M.S.—praised Pima County’s

“demonstrated commitment to keeping science insulated

from politics....The autonomy of the scientists (including

the STAT, the consultants, and the expert reviewers) in the

Plan allows them to exercise their best scientific judgment

about what it takes to fulfill the primary goal of the

conservation plan—preserving the biodiversity of the region” (Noss and Watchman 2001).

The County also established a Cultural Resources TAT to

identify where vulnerable archaeological and historical sites

were located. Not surprisingly, the greatest densities of such

sites were along riparian corridors, which were the areas of

greatest biological diversity as well.

Thirdly, the County set up a Ranch Conservation TAT.

The County pointed out that working ranches had defined

metropolitan Tucson’s urban boundaries for more than a

century. Despite the objections of some environmentalists, it

also argued that keeping working ranches in business was

the cheapest and most effective way to preserve open space

in eastern Pima County. Despite some later problems, this

recognition encouraged ranchers to participate in the process.

The County assigned staff to the three TATs and charged

them with gathering information to help develop the HCP.

During the first 4 years of the SDCP, however, the Science

TAT and RECON received the lion’s share of the resources

because Federal funding for SDCP was restricted to the

biological elements of the plan. After several years of intense

consultation and review, the Science TAT identified 55

species of concern. RECON then crafted the biologically

preferred alternative, proposing a system of biological core

reserves, which were renamed Biological Core Management

Areas. The criteria for selection were areas where there were

“high potential habitat for five or more vulnerable species,

special elements (e.g. caves, perennial streams, cottonwoodwillow forests), and other unique biological features.” The
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County went on to say, “Land use and management within

these areas will focus on conservation, restoration, and

enhancement of natural communities, with provision for

other land uses that are consistent with improvement of

conditions for ‘vulnerable species,’ soils, and native vegetation” (CLS Map 2/2002). Biological Core Management Areas

encompass more than 800,000 acres—one-third of eastern

Pima County (2,443,141 acres). SDCP therefore became the

largest HCP being proposed in the United States.

The Santa Rita Experimental Range is considered part of

a Biological Core Management Area except for the northwestern corner, which is called a “Scientific Research Management Area.” The County therefore wants SRER—some

53,159 acres—to remain undeveloped and free of any land

uses that would diminish or destroy critical habitat. One of

the major limitations of SDCP, however, has been the

refusal of the State Land Department to participate. Despite

its location within a Biological Core Management Area, the

County could not prevent the State Land Department from

leasing or selling SRER as commercial property if the Arizona

legislature were to revoke its special status as a research

range. Both Tumamoc Hill’s Desert Laboratory and SRER

were established in 1903 to monitor desert and grassland

environments. It is ironic that during their centennial year,

both may be threatened by sale and development.

Archive and Laboratory Embedded

in the Landscape _______________

As the Upper Santa Cruz Valley develops, open space will

become even more precious for ecological as well as aesthetic

reasons. SRER provides the largest bridge in the wildlife

corridor linking the northern Santa Rita Mountains to the

Sierrita and Cerro Colorado Mountains to the west. This

corridor has been fragmented by development in and around

Green Valley and Sahuarita. The I-19 freeway also truncates

the corridor by imposing a perilous obstacle to mammals and

reptiles attempting to move east and west. In the future,

however, animal-friendly underpasses may be constructed.

The conservation of Canoa Ranch was a critical first step in

maintaining this corridor. Keeping SRER development free

would be an essential second step. A third major step—the

preservation of Sopori Ranch, which straddles Pima and

Santa Cruz counties—will require much more mobilization

and money to achieve.

The Santa Rita Experimental Range, however, is far more

than open space or wildlife habitat. As the oldest active

research range in the United States, SRER is both a landscape laboratory and a unique ecological archive with a

century of research embedded in its soil, watersheds, and

vegetation. If scientists are ever going to understand the

complexities of arid and semiarid ecosystems, they have to

be able to conduct long-term studies that preserve, and build

upon, the studies of the past. Synchronic snapshots of a

landscape, like those of a culture ethnographers engender,

are nothing more than stages in the process of investigating

dynamic, ever-changing systems. Taken alone, they may

offer simplistic, distorted, even misleading glimpses of the

system in question. Short-term economic considerations

must not be allowed to obliterate the soils and vegetation

that encode these 100 years of past research in their everchanging physical, chemical, and community structures.

It is impossible to foresee all future research directions

that may arise during the next 100 years. SRER will probably never be dominated by research designed to improve

the livestock industry as it was for much of its first century.

Grazing is a relatively small part of Southwestern economies now, and scientists are responding to other constituencies and other concerns. More to the point, the notion that

SRER—or any other experimental range or biological reserve, for that matter—can serve as an ecological analogue

for an entire region has been undermined, as the limitations

of Clementsian equilibrium models of plant succession and

climax vegetation communities in semiarid regions have

been exposed. Landscapes are ever-changing products of

historical forces, both natural and anthropogenic, not Platonic templates waiting to be restored to their true essences.

Range science—and the accumulating experience of conscientious ranchers—increasingly recognize that range management must be tailored to individual landscapes as they

change from season to season and year to year (Sayre 2001).

That same appreciation for the historical dynamism of

semiarid ecosystems applies to nonrange ecological research

as well. But as the validity of atemporal space is challenged,

a growing appreciation for time has surged. Using repeat

photography, Rodney Hastings and Raymond Turner (1965)

drew attention to the importance of historic climate change

40 years ago in their classic The Changing Mile. Turner and

his colleagues have recently updated that work, carefully

evaluating the “tangle of hypotheses”—both “climatic and

cultural”—advanced to explain vegetation change in the

Sonoran Desert region (Turner and others 2003: 276).

Researchers like David Griffiths (1904, 1910), Wooten (1916),

and Parker and Martin (1952) pioneered the technique on

SRER. As McClaran (this proceedings) notes, “Currently,

the repeat photography collection is one of the largest and

most accessible in the world.”

The Santa Rita Experimental Range also has provided a

laboratory for the systematic remeasurement of precipitation patterns, vegetation, and experimental manipulations

of the landscape. Again, to quote McClaran (this proceedings), “The most incontestable conclusion from this century

of vegetation change is that future changes can not be

perceived and understood if there are no records of previous

conditions.” Such systematic remeasurement has enabled

scientists to understand the cyclic nature of burroweed and

cholla cactus eruptions, to refine estimates of grass response

to grazing intensity, to untangle the hypotheses for the

spread of mesquite across Southwestern grasslands, and to

recognize the temporal limitations of mesquite-eradication

programs. Systematic remeasurement is SRER’s greatest

scientific legacy—the most important reason why the integrity of SRER must be preserved. The preservation of that

integrity must be carried out at the landscape level by

protecting SRER from development or any other impacts

that would compromise it as a research laboratory. At the

same time, however, preservation must extend to the site

level as well. Future experiments must build on the records

of the past, and must not interfere with the records of the

past. SRER is both a laboratory and an archive. Future

experimental manipulations of the landscape, whether of
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Sheridan Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range

vegetation, soils, or watersheds, should be carefully conducted so they do not diminish or destroy past experiments

already embedded in the landscape.

Future Research Directions ______

As I noted at the beginning of this paper, it is impossible

to predict all future directions of research on SRER. Nonetheless, I do have a number of suggestions. Currently,

tremendous emphasis is placed upon the invasion of nonnative exotic species into Southwestern ecosystems and

the need to eradicate them and “restore” those ecosystems

to some sort of preinvasion state (Tellman 2002). The most

widespread exotic invader on SRER in particular and on

southeastern Arizona grasslands in general is Lehmann

lovegrass (Eragrosis lehmanniana). Biological reserves such

as the Buenos Aires Wildlife Refuge have devoted considerable resources of money and manpower to combating this

perceived threat, without much success.

The Santa Rita Experimental Range should serve as a laboratory to better understand the dynamics of Lehmann lovegrass

and to evaluate the effectiveness of manipulations to control

or eradicate it. Is its current dominance on some Southwestern

grasslands a long-term change or a short-term fluctuation?

What sort of systemic changes does its dominance trigger in

grassland ecosystems? Is the genie out of the bottle or can

the genie be shoved back into the bottle and the bottle

corked? And if so, how much time and money is it going to

take to do so?

Another research topic garnering enormous attention is

the role of fire in grassland and forest ecosystems. Both

ranchers and agency land managers alike are re-examining

the fire suppression policies of the past and exploring the

benefits of letting naturally ignited fires burn. Prescribed

fires are also being set to reduce fuel loads, curtail the spread

of woody shrubs like mesquite, and improve the productivity

and abundance of perennial grasses. Greater experimentation with fire on SRER is problematic for several reasons,

however. One has nothing to do with ecology and everything

to do with rising property values. Despite increasing recognition of the ecological benefits of fire, agencies continue to

suppress any fires within a 5-mile radius of existing commercial or residential structures. As the transition from

ranching to real estate development accelerates in the Upper Santa Cruz Valley, the political latitude to let fires burn

or to carry out prescribed burns will continue to shrink.

An additional concern is the need to preserve the integrity

of previous research on SRER. Any decision about whether

to let a natural fire burn or to set a prescribed fire has to be

carefully weighed against the “noise” such a fire might

introduce into research involving ongoing systematic

remeasurements of hydrologic and nutrient cycles, species

composition, and other variables. Moreover, the greater

adaptability of Lehmann lovegrass over native perennial

grasses to fire has to be taken into consideration. Future

research directions on SRER must always recognize and

mitigate their impacts on long-term studies of environmental change.

Rapid urbanization will, on the other hand, provide wildlife

biologists with greater opportunities to investigate the

impacts of development on desert grassland fauna. Wildlife

biologists should be encouraged to set up long-term monitoring systems to measure those impacts in a systematic fashion rather than conducting short-term studies of individual

species. Aside from climatic change, no other factor is going

to influence wildlife dynamics to a greater extent than

urban, suburban, and exurban development in the rural

West.

Those same forces will affect SRER in other ways that

should be studied as well. The spread of exotic plant species

from neighboring subdivisions, shopping centers, and

roads, the ecological effects of legal and illegal recreational activities, the impact of increased lighting and

microclimatological changes brought about by urban heat

islands and air pollution—these are just some of the anthropogenic factors that undoubtedly will modify the environment on as well as around SRER. SRER was created to serve

rural interests at a time when Arizona was a largely rural

society. The balance tipped more than a half-century ago,

and now SRER is poised to explore the urban-rural interface

that is transforming the State.

Future of Public Lands

Ranching _____________________

But what of SRER’s original mission—range research? In

the early 1900s, both scientists and ranchers alike recognized

the degradation of Southwestern ranges because of the

lethal intersection of overstocking and prolonged drought.

At that time, however, livestock grazing was still considered

the highest and best—indeed often the only—use of much of

Arizona’s arid and semiarid terrain. SRER was designed to

demonstrate how ranges could be restored, and how ranching could become a sustainable industry.

Today, many environmentalists call for an end to livestock grazing on Western public lands. Even when ranching is still considered a legitimate use of Forest Service,

Bureau of Land Management, and State Trust lands,

ranchers have to compete with an ever-growing number of

other constituencies—hikers, campers, hunters, birders,

and offroad vehicle users, among others—who demand a

voice in how public lands are managed. At a time when the

costs of inputs continue to rise while cattle prices stagnate,

in the midst of another prolonged drought, ranchers face

increasing government regulations and a volatile political

climate. When you combine these “push” factors with skyrocketing prices for private lands, it is hardly surprising

that many ranchers sell out to developers or subdivide their

private lands themselves (Knight and others 2002; Sayre

2002; Sheridan 2001).

Is there a future for public-lands ranching in the West?

That question is beyond the scope of this paper to answer,

even though many of us believe that sustainable ranching

should be encouraged for a variety of economic, ecological,

and social reasons. One possible strategy to diversify cattle

ranching is the development of niche markets for beef.

Growing numbers of consumers are becoming increasingly

health conscious and environmentally sensitive. The

nonvegetarians provide a growing market for beef that is not

injected with hormones and finished in feedlots. Moreover,

they may prefer to buy locally produced beef because it is so

much more energy efficient. And for those consumers who
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Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range Sheridan

oppose the killing of predators such as mountain lions and

coyotes, and who support the reintroduction of Mexican gray

wolves, beef certified as predator friendly may be attractive.

But as Will and Jan Holder of Ervin’s Beef in eastern

Arizona have discovered, such beef is difficult for individual

producers or even small groups of producers to achieve.

The Santa Rita Experimental Range has a unique opportunity to explore and nurture such alternative strategies.

Experiments in the production of grass-fed, hormone-free,

and predator-friendly beef could be conducted on SRER. And

because SRER is managed by the University of Arizona,

University marketing specialists, agricultural economists,

and anthropologists could identify potential markets and

investigate ways in which to get those products to consumers.

The development of linkages between Arizona producers

and Arizona consumers would reduce energy costs, stimulate

local economies, and serve as a modest counterpoint to the

relentless globalization of the beef industry. This, it seems to

me, would be an eminently reasonable twenty-first-century

application of the University of Arizona’s original landgrant mission.

Conclusions___________________

To ensure that SRER remains intact as a landscape

laboratory and archive, the University scientists and staff

who manage it need to aggressively build a political constituency—within the University, the State Land Department,

the Arizona legislature, and among the public—that will

resist any attempt to reverse its special legislative status.

More quietly, but just as decisively, SRER advocates should

reach out to political allies who will convince the State Land

Department and the Arizona legislature to give it special

conservation status, either under the Arizona Preserve

Initiative or as part of more general State Trust Land

reform. Now that SRER will have a manager for the first

time since it was transferred to the State Land Department,

the manager and the scientists who work with him should

establish contacts with the groups who joined together to

fight the development of Canoa Ranch. These include environmentalist organizations such as the Coalition for Sonoran

Desert Protection, the Smithsonian’s Whipple Observatory,

and neighborhood associations and citizen’s groups in Green

Valley and Elephant Butte. Pima County, the University of

Arizona, and perhaps even Coronado National Forest also

have an interest in keeping SRER as a research range free

of development.

Ironically and paradoxically, the very people who move

into subdivisions creeping closer and closer to the borders of

SRER may become SRER’s most enthusiastic advocates.

The conservation of 56,000 acres of open space and desert

grassland just beyond their back doors should be an attractive

proposition for SRER’s new neighbors. SRER cannot do

much to stem the tide of development around it, so it should

embrace the newcomers and let them know what a unique

scientific and ecological resource they live next to. A “Friends

of SRER” should be formed. Retired professionals should be

invited to become stewards of both archaeological and

research sites to increase on-the-ground vigilance to prevent

vandalism and other illegal activities. Lecture series and

field trips focusing on grasslands research and sustainable

ranching should be offered. As anyone who does much public

speaking in southern Arizona knows, Green Valley audiences are large and appreciative. Rather than waiting until

its status may be threatened, SRER should take positive

steps to increase its public visibility and build constituencies

that support it.

Research on SRER should also embrace the inevitable.

The threats posed by encroaching development can also be

turned into opportunities. As more and more desert and

grassland valleys are fragmented by subdivisions across

Arizona and the West, the need for precise, long-term

ecological studies of landscape fragmentation and population

growth becomes ever more acute. SRER is a biological

reserve in the path of growth, so it is uniquely well positioned

to investigate growth’s impact upon the flora and fauna of

the Upper Santa Cruz Valley.

Finally, SRER should not abandon its first patrons—the

ranchers of the Southwest. As Ruyle (this proceedings)

points out, many of the principles of sustainable ranching in

the semiarid West were tried and tested on SRER. Fundamental monitoring techniques were pioneered there as well.

The Santa Rita Experimental Range helped ranchers reverse the degradation of Southwestern ranges and meet the

economic and ecological challenges of the twentieth century.

It should continue to assist them to meet the very different

challenges the twenty-first century is going to pose.

References ____________________

Arizona Constitution. 2003. [Online]. Available: http://www.azleg.

state.az.us/const/10/1.htm

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state.az.us/const/const.htm

Arizona League of Conservation Voters. 2003. State trust land reform.

[Online]. Available: http://www.aslcvedfund.org/spotlight2.html

Arizona State Parks. 2003. Growing smarter grants. [Online].

Available at: http://www.pr.state.az.us/partnerships/growing

smarter/growing.html

ASLD (Arizona State Land Department) Historical Overview. 2003.

[Online]. Available: http://www.land.state.az.us/history.htm

ASLD Arizona Preserve Initiative Program. 2003. [Online].

Available: http://www.land.state.az.us/programs/operations/

api.htm

Bahre, Conrad Joseph 1991. A Legacy of change: historic human

impact on vegetation of the Arizona borderlands. Tucson:

University of Arizona Press. 231 p.

Davis, Tony. 2001. Desert conservation plan “credible”: Two environmental scientists laud county move “at the cutting edge.”

Arizona Daily Star. October 27.

Else, Peter. 2003. [E-mails to Thomas E. Sheridan]. May 5 and May

14, 2003.

Griffiths, David. 1904. Range investigations in Arizona. Bureau of

Plant Industry Bull. 67. [10 plates]. Washington, DC: U.S.

Department of Agriculture. 62 p.

Griffiths, David. 1910. A protected stock range in Arizona. Bull. 177.

Washington, DC: U.S. Department of Agriculture. 28 p.

Grubbs, Nicole R. 2003. 10,000+ homes envisioned: State to sell

land near Valencia and Houghton. Arizona Daily Star. May 15:

B1, B5.

Hadley, Diana. 2000. San Ignacio de la Canoa land grant and Canoa

Ranch history/timeline. SMRC-Newsletter. 34 (123): 11–15.

Hastings, James Rodney; Turner, Raymond M. 1965. The changing

mile: an ecological study of vegetation change with time in the

lower mile of an arid and semiarid region. Tucson: University of

Arizona Press. 317 p.

Humphrey, Robert R. 1987. 90 years and 535 miles: vegetation

changes along the Mexican border. Albuquerque: University of

New Mexico Press. 448 p.
110 USDA Forest Service Proceedings RMRS-P-30. 2003

Sheridan Archive and Laboratory Embedded in the Landscape: Future of the Santa Rita Experimental Range

Knight, R. L.; Gilgert, W. C.; Marston, E., eds. 2002. Ranching west

of the 100th Meridian: culture, ecology, and economics. Washington, DC: Island Press. 368 p.

Medina, Alvin L. 1996. The Santa Rita Experimental Range: annotated bibliography (1903–1988). Gen. Tech. Rep. RM-GTR-276.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station. 67 p.

Noss, Reed; Watchman, Laura Hood. 2001. Report of independent

peer reviewers: Sonoran Desert Conservation Plan. October 26.

Parker, Kenneth W.; Martin, S. Clark. 1952. The mesquite problem

on southern Arizona ranges. American Hereford Journal. 31(6):

23.

Pima Association of Governments. 2000. PAG Census 2000 Information Page. [Online]. Available: http://www.pagnet.org/

Population

Pima County. 2003. Cost model for Section 10 Endangered Species

Act permit for the unincorporated area of eastern Pima County.

Pima County, AZ: Tucson.

Sayre, Nathan F. 2001. The new ranch handbook: a guide to

restoring Western rangelands. Santa Fe: The Quivira Coalition.

102 p.

Sayre, Nathan F. 2002. Ranching, endangered species, and urbanization in the Southwest: species of capital. Tucson: University of

Arizona Press. 278 p.

Sheridan, Thomas E. 1995. Arizona: a history. Tucson: University

of Arizona Press. 434 p.

Sheridan, Thomas E. 2000. La Canoa: from land grant to political

football. SMRC-Newsletter. 34(123): 2–5.

Sheridan, Thomas E. 2001. Cows, condos, and the contested commons:

the political ecology of ranching on the Arizona-Sonora

borderlands. Human Organization. 60(2): 141–151.

SDCP (Sonoran Desert Conservation Plan). 2000. Our common

ground: ranch lands in Pima County. Tucson, AZ: Pima County.

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management, and sustainable use. Lawrence: University Press

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Tellman, Barbara, ed. 2002. Invasive exotic species in the Sonoran

region. Arizona-Sonora Desert Museum studies in natural history.

Tucson: University of Arizona Press and Arizona-Sonora Desert

Museum. 424 p.

Turner, Raymond M.; Webb, Robert H.; Bowers, Janice E.; Hastings,

James Rodney. 2003. The changing mile revisted: an ecological

study of vegetation change with time in the lower mile of an arid

and semiarid region. Tucson: University of Arizona Press. 334 p.

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Agriculture. 40 p.
USDA Forest Service Proceedings RMRS-P-30. 2003 111

Michael A. Crimmins

Theresa M. Mau-Crimmins

Climate Variability and Plant Response at

the Santa Rita Experimental Range,

Arizona

Michael A. Crimmins is currently a Ph.D. Student in the Department of Geography, Harvill Building, Box 2, University of Arizona, Tucson, AZ 85721; e-mail:

crimmins@u.arizona.edu. He completed a B.S. degree in atmospheric sciences from the University of Michigan and an M.A. degree in geography from Western

Michigan University. Theresa M. Mau-Crimmins is currently pursuing a Ph.D. degree in the School of Renewable Natural Resources at the University of Arizona.

She has completed a B.S. degree in biology and an M.A. degree in geography from Western Michigan University.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

Climatic variability is reflected in differential establishment, persistence, and spread of plant species. Although studies have

investigated these relationships for some species and functional groups (Ibarra and others 1995; Martin and others 1995;

Neilson 2003; Neilson and Wullstein 1983), few have attempted to characterize the specific sequences of climatic conditions

at various temporal scales (subseasonal, seasonal, and interannual) associated with proliferation of particular species.

Research has primarily focused on the climate conditions concurrent with or occurring just prior to a vegetation response.

However, the cumulative effect of antecedent conditions taking place for several consecutive seasons may have a greater

influence on plant growth.

Our objective in this study was to test whether the changes in percent cover of individual plant species can be explained by

climatic conditions at different time scales. We investigated this relationship for native perennial grasses using long-term

monitoring data from the Santa Rita Experimental Range (SRER) located in southeastern Arizona, U.S.A.

Methods _________________________________________________________

Plant cover data for 11 perennial grass species were obtained from the Santa Rita Experimental Range Digital Database.

The species included in the analysis were sprucetop grama (Bouteloua chondrosioides [H.B.K.] Benth.), sideoats grama

Abstract: Climatic variability is reflected in differential establishment, persistence, and spread

of plant species. Although studies have investigated these relationships for some species and

functional groups, few have attempted to characterize the specific sequences of climatic conditions

at various temporal scales (subseasonal, seasonal, and interannual) associated with proliferation

of particular species. Research has primarily focused on the climate conditions concurrent with

or occurring just prior to a vegetation response. However, the cumulative effect of antecedent

conditions taking place for several consecutive seasons may have a greater influence on plant

growth.

In this study, we tested whether the changes in overall cover of plant species can be explained

by antecedent climate conditions. Temperature, precipitation, and Palmer Drought Severity

Index (PDSI) values at various lags were correlated with cover. PDSI had the strongest correlations

for several drought-intolerant species at lags up to six seasons prior to the sampling date. Precipitation, surprisingly, did not correlate with species cover as strongly as PDSI. This is attributed to PDSI

capturing soil moisture conditions, which are important to plant growth, better than raw precipitation measurements. Temperature correlations were weak and possessed little explanatory

power as predictors of species cover.

Acknowledgments: Data sets were provided by the Santa Rita Experimental Range Digital

Database. Funding for the digitization of these data was provided by the USDA Forest Service

Rocky Mountain Research Station and the University of Arizona.
112 USDA Forest Service Proceedings RMRS-P-30. 2003

Crimmins and Mau-Crimmins Climate Variability and Plant Response at the Santa Rita Experimental Range, Arizona

(Bouteloua curtipendula [Michx.] Torr.), black grama

(Bouteloua eripoda Torr.), slender grama (Bouteloua

filiformis [Fourn.] Griffiths), hairy grama (Bouteloua hirsuta

Lag.), Rothrock grama (Bouteloua rothrockii Vasey), Arizona cottontop (Digitaria californica [Benth.] Henr.),

tanglehead (Heteropogon contortus [L.] Beauv.), curly mesquite (Hilaria belangeri[Steud.] Nash), bush muhly (Muhlenbergia porteri Scribn.), and plains bristlegrass (Setaria

macrostachya H.B.K.). Cover measurements, taken on all

transects all sampling years, were aggregated by species for

each sampling year and normalized by dividing the total by

the number of observations. Pastures on the SRER have

been grazed for many decades using various rotations.

However, data for this study were not stratified by grazing

rotation because differences in grass density and grazing

rotations were detected for only one species in this study,

Muhlenbergia porteri (Angell and McClaran 2001; Martin

and Severson 1988).

We primarily focused on the SRER plant cover data for

this study because the period of record (47 years) is much

greater than that for density measurements (28 years). Data

from 1953 to 1984 were analyzed in this study. Changes in

both personnel carrying out the field work and season of the

work (from autumn to spring) reduced the comparability of

data collected throughout the entire period of record, 1953 to

2000. Many species demonstrate marked increases or decreases in cover between the period 1953 to 1984 and the

period 1991 to 2000. There are several candidate explanations for this significant change in cover measurements. In

1991, the sampling was taken over by a different group of

individuals than had performed the previous sampling. It is

possible that observer bias played a role in the differing

measurements. Additionally, samples taken during the

1953 to 1984 period were recorded in late summer or autumn

while the 1990s data were collected in winter. A number of the

grass species in this study exhibit low C:N ratios, leading to

their quick breakdown following the growing period. This

would cause some species to be under-represented when

sampled in winter, and others to be over-represented when

not sampled during the growing season. Finally, the introduced nonnative perennial bunchgrass Eragrostis

lehmanniana heavily invaded the SRER between 1984 and

1990. The presence of E. lehmanniana may be influencing

the cover of other native grasses. Confounding of both

observer and season suggest that the data collected during

the 1991 to 2000 period should be analyzed separately from

the 1953 to 1984 data.

Five climate variables were used in the lagged correlation

analysis. Four of the variables, including daily total precipitation (PPT), minimum temperature (TMIN), maximum

temperature (TMAX), and mean temperature (TMEAN),

were measured at the Santa Rita Experimental Range

through the cooperative observer program of the National

Weather Service on a daily basis. These data were obtained

from the National Climatic Data Center (NCDC). The fifth

variable, the Palmer Drought Severity Index (PDSI), was

obtained for climate division #7, representing five counties

in southeastern Arizona, from NCDC. The PDSI values were

calculated from temperature and precipitation measurements from across southeastern Arizona and represent an

area-wide indication of soil moisture conditions.

Daily data (PPT, TMEAN, TMIN, TMAX) and monthly

data (PDSI) were combined into seasonal averages for the

period from 1950 to 1984. Seasons were defined as winter

(DJFM), spring (AMJ), summer (JAS), and autumn (ON).

These definitions differ from the convention of even 3-month

seasons, but are more appropriate for the unique seasonality

of precipitation and temperature in southern Arizona. Precipitation is bimodal with 30 percent falling in DJFM and 50

percent falling during the monsoon season of JAS (WRCC

2003). The adjusted definitions are more sensitive to these

seasonal variations in precipitation.

For each season in the study period, precipitation amounts

were summed and all other variables averaged. This resulted in four seasonal values for each year for the period

from 1950 to 1984. The time series of seasonal climate

variables was matched to the time series of species cover

measurements sampled at various years between 1950 and

1984. Each climate variable was then lagged one to 12

seasons from each sampling date, creating a lagged climate

sequence for each species cover amount and each variable.

Paired observations were correlated to produce Pearson’s r

values for each species and climate variable at all seasonal

lags.

Results ________________________

The cover of 11 perennial grass species was tested for

correlation with the five climatic variables. Of the 11 grass

species, six grass species exhibited significantly positive (p

< 0.05) correlations with precipitation at one or more seasons (table 1). These species included B. eripoda, B. filiformis,

B. rothrockii, H. contortus, M. porteri, and S. macrostachya.

Four demonstrated significantly positive (p < 0.05) correlations with PDSI at one or more seasons (table 2). These

grasses were B. eripoda, D. californica, H. contortus, and S.

macrostachya. Four species exhibited significantly positive

(p < 0.05) correlations with TMIN at one or more seasons

(table 3). These grasses were B. eripoda, B. rothrockii, H.

contortus, and S. macrostachya. Results for TMAX and

TMEAN were similar to those for TMIN.

Discussion _____________________

The Palmer Drought Severity Index accounts for antecedent precipitation, moisture supply, and moisture demand

(Palmer 1965). By incorporating accumulated moisture deficiencies or surpluses, it is a better measure of plantavailable water. Strong positive relationships between grass

cover and PDSI were found for several species in this study.

Several species showed significantly positive relationships

with PDSI. These species, which include Bouteloua eripoda,

D. californica, H. contortus, and S. macrostachya, are all

drought-susceptible perennial bunchgrasses (Burgess 1995;

Herbel and others 1972; Matthews and others 1999). No

significant relationships were detected between PDSI at any

lag and cover of the perennial bunchgrasses B. curtipendula,

B. filiformis, B. rothrockii, B. chondrosioides, B. hirsuta,

H. belangeri, and M. porteri. These grasses are all considered to be drought tolerant (Judd 1962; Matthews and

others 1999; Ruyle and Young 1997; Stubbendieck and
USDA Forest Service Proceedings RMRS-P-30. 2003 113

Climate Variability and Plant Response at the Santa Rita Experimental Range, Arizona Crimmins and Mau-Crimmins Table 1—Pearson’s r correlation coefficients between grasses and precipitation at the Santa Rita Experimental Range, Arizona. Species n JAS (p) AMJ (p) DJFM (p) ON (p) JAS-1 (p) AMJ-1 (p) DJFM-1 (p) ON-1 (p) Bouteloua chondrosioides 12 –0.156 (0.628) 0.229 (0.474) –0.056 (0.863) –0.399 (0.199) –0.106 (0.742) –0.341 (0.278) –0.123 (0.703) 0.389 (0.211) Bouteloua curtipendula 14 –0.021 (0.944) –0.234 (0.420) –0.039 (0.893) 0.053 (0.857) –0.147 (0.616) 0.311 (0.279) 0.340 (0.235) 0.303 (0.293) Bouteloua eripoda 16 0.250 (0.351) 0.354 (0.179) –0.151 (0.577) 0.702 b (0.002) 0.555 a (0.026) –0.247 (0.357) 0.439 (0.089) –0.187 (0.488) Bouteloua filiformis 16 –0.159 (0.557) –0.004 (0.987) –0.049 (0.856) –0.194 (0.472) –0.286 (0.283) –0.190 (0.482) 0.001 (0.997) 0.338 (0.200) Bouteloua hirsuta 16 –0.027 (0.921) –0.298 (0.262) 0.072 (0.792) –0.235 (0.381) 0.404 (0.121) –0.258 (0.335) 0.068 (0.803) –0.136 (0.614) Bouteloua rothrockii 16 0.287 (0.281) 0.241 (0.369) 0.027 (0.921) 0.484 (0.058) 0.528 a (0.035) –0.369 (0.160) 0.230 (0.392) –0.063 (0.815) Digitaria californica 16 0.074 (0.786) 0.394 (0.131) –0.070 (0.795) 0.336 (0.204) 0.187 (0.488) –0.156 (0.563) 0.416 (0.109) –0.372 (0.156) Heteropogon contortus 16 0.364 (0.166) 0.535 a (0.033) –0.128 (0.637) 0.698 b (0.003) 0.429 (0.098) –0.078 (0.774) 0.517 a (0.040) –0.319 (0.229) Hilaria belangeri 16 –0.368 (0.161) –0.073 (0.787) –0.065 (0.811) 0.151 (0.578) –0.156 (0.565) –0.068 (0.801) 0.096 (0.724) 0.479 (0.061) Muhlenbergia porteri 16 0.108 (0.690) 0.503 a (0.047) –0.119 (0.660) 0.129 (0.634) –0.144 (0.594) –0.063 (0.818) –0.034 (0.900) –0.347 (0.187) Setaria macrostachya 16 0.286 (0.282) 0.465 (0.069) –0.088 (0.746) 0.610 a (0.012) 0.337 (0.202) –0.177 (0.513) 0.592 a (0.016) –0.375 (0.152)

a Correlation significant at p < 0.05.

b Correlation significant at p < 0.01.

Table 2—Pearson’s r correlation coefficients between grasses and Palmer Drought Severity Index at the Santa Rita Experimental Range, Arizona.

Species n JAS (p) AMJ (p) DJFM (p) ON (p) JAS-1 (p) AMJ-1 (p) DJFM-1 (p) ON-1 (p)

Bouteloua chondrosioides 12 –0.306 (0.333) –0.364 (0.245) –0.555 (0.061) –0.430 (0.163) –0.415 (0.180) –0.342 (0.276) –0.540 (0.070) –0.506 (0.094)

Bouteloua curtipendula 14 –0.091 (0.756) –0.053 (0.857) –0.150 (0.609) –0.208 (0.476) –0.181 (0.535) 0.188 (0.519) –0.040 (0.892) –0.193 (0.509)Bouteloua eripoda 16 0.503a (0.047) 0.474 (0.064) 0.667b (0.005) 0.752b (0.001) 0.787b (0.000) 0.644b (0.007) 0.668b (0.005) 0.252 (0.346)

Bouteloua filiformis 16 –0.351 (0.183) –0.305 (0.251) –0.395 (0.130) –0.338 (0.201) –0.224 (0.405) 0.022 (0.935) –0.037 (0.893) –0.160 (0.555)

Bouteloua hirsuta 16 –0.120 (0.657) –0.209 (0.438) –0.195 (0.469) –0.167 (0.536) 0.000 (0.999) –0.307 (0.247) –0.462 (0.072) –0.552a (0.027)

Bouteloua rothrockii 16 0.397 (0.128) 0.452 (0.079) 0.494 (0.052) 0.475 (0.063) 0.493 (0.052) 0.291 (0.275) 0.301 (0.257) –0.035 (0.899)

Digitaria californica 16 0.436 (0.091) 0.522a (0.038) 0.472 (0.065) 0.486 (0.056) 0.296 (0.266) 0.226 (0.400) 0.093 (0.733) –0.237 (0.377)

Heteropogon contortus 16 0.642b (0.007) 0.621b (0.010) 0.706b (0.002) 0.783b (0.000) 0.680b (0.004) 0.585a (0.017) 0.501a (0.048) 0.049 (0.857)

Hilaria belangeri 16 –0.408 (0.116) –0.267 (0.317) –0.263 (0.325) –0.194 (0.471) –0.053 (0.847) 0.251 (0.348) 0.239 (0.373) 0.102 (0.706)

Muhlenbergia porteri 16 0.276 (0.300) 0.312 (0.239) 0.219 (0.415) 0.306 (0.248) –0.043 (0.874) –0.036 (0.896) –0.063 (0.818) –0.136 (0.617)

Setaria macrostachya 16 0.555a (0.026) 0.563a (0.023) 0.599a (0.014) 0.681b (0.004) 0.537a (0.032) 0.446 (0.083) 0.328 (0.214) –0.166 (0.539)

a Correlation significant at p < 0.05.

b Correlation significant at p < 0.01.

Table 3—Pearson’s r correlation coefficients between grasses and minimum temperature at the Santa Rita Experimental Range, Arizona.

Species n JAS (p) AMJ (p) DJFM (p) ON (p) JAS-1 (p) AMJ-1 (p) DJFM-1 (p) ON-1 (p)

Bouteloua chondrosioides 12 0.184 (0.567) –0.285 (0.369) 0.155 (0.631) 0.180 (0.575) 0.413 (0.182) 0.208 (0.516) 0.029 (0.928) –0.134 (0.677)

Bouteloua curtipendula 14 0.131 (0.656) –0.236 (0.416) –0.004 (0.990) 0.284 (0.326) 0.393 (0.164) 0.059 (0.842) –0.136 (0.644) 0.099 (0.735)

Bouteloua eripoda 16 –0.553a (0.026) 0.149 (0.582) –0.109 (0.687) –0.389 (0.136) –0.558a (0.025) –0.534a (0.033) –0.530a (0.035) –0.287 (0.281)Bouteloua filiformis 16 0.327 (0.216) 0.330 (0.213) 0.484 (0.058) 0.279 (0.296) 0.465 (0.069) 0.032 (0.907) 0.014 (0.958) 0.256 (0.339)

Bouteloua hirsute 16 –0.083 (0.760) 0.169 (0.530) –0.022 (0.935) 0.249 (0.352) –0.196 (0.467) –0.038 (0.890) 0.092 (0.734) 0.389 (0.136)

Bouteloua rothrockii 16 –0.635b (0.008) –0.333 (0.207) –0.527a (0.036) –0.631b (0.009) –0.680b (0.004) –0.857b (0.000) –0.702b (0.002) –0.523a (0.038)

Digitaria californica 16 –0.174 (0.519) 0.308 (0.246) 0.026a (0.924) –0.346 (0.190) –0.289 (0.277) –0.303 (0.255) –0.202 (0.453) –0.406 (0.118)

Heteropogon contortus 16 –0.527 (0.036) –0.037a (0.891) –0.176 (0.513) –0.569 (0.021) –0.549 (0.027) –0.644 (0.007) –0.473 (0.064) –0.431 (0.096)

Hilaria belangeri 16 0.419 (0.106) 0.007b (0.979) 0.341 (0.196) 0.130 (0.631) 0.282 (0.290) 0.093 (0.733) –0.227 (0.398) 0.189 (0.482)

Muhlenbergia porteri 16 –0.084 (0.757) 0.138 (0.609) –0.058 (0.830) –0.479 (0.060) –0.059 (0.829) –0.010a (0.970) 0.157 (0.560) –0.523 (0.038)

Setaria macrostachya 16 –0.358 (0.173) 0.098 (0.719) –0.094 (0.728) –0.525 (0.037) –0.491 (0.054) –0.572 (0.021) –0.339 (0.199) –0.366 (0.163)

a Correlation significant at p < 0.05.

b Correlation significant at p < 0.01.
114 USDA Forest Service Proceedings RMRS-P-30. 2003

Crimmins and Mau-Crimmins Climate Variability and Plant Response at the Santa Rita Experimental Range, Arizona

others 1985; Weaver and Albertson 1956). Therefore, PDSI

can be a good indicator of cover for perennial grasses that are

drought susceptible.

Water is the chief abiotic factor affecting the productivity

and distribution of grasslands ecosystems (Sala and others

1988; Stephenson 1990). It is “very likely” that precipitation

has increased over mid- and high latitude Northern Hemisphere continents by 0.5 to 1 percent per decade since 1900

(IPCC 2001). The ecological impacts of these changes have

been documented in ecosystems ranging from tropical marine to polar terrestrial environments (Hughes 2000;

Parmesan and Yohe 2003; Root and others 2003), affecting

reproduction and species ranges of plants and animals alike.

Little work has evaluated the effects of these changing

precipitation patterns on the distribution, structure, or

composition of plant communities, as a step in understanding future vegetation change. Such changes have implications for the seasonality and intensity of fires, the spread of

nonnative species, and the sustainable management of

rangelands.

Aggregating climatic data to the season removes extreme

events that likely exert the greatest amount of influence on

physiological processes such as reproduction and growth.

This reduces the predictive power of directly measured

climatic variables such as monthly average temperature

and monthly total precipitation. Precipitation had a significantly positive correlation with cover of six species at six of

the 12 different seasonal lags (table 1). These correlations

did not seem to reflect any obvious relationships. We expected to find strong relationships between grass cover and

the precipitation of the previous season. Although the grasses

in this study are warm season grasses that are known to

respond to summer precipitation, we did not find a strong

relationship between grass cover and the precipitation of the

previous season. We believe these relationships are lacking

because precipitation is not necessarily representative of

plant-available water. Precipitation is a measure of water

reaching the earth, but depending on the amount and

intensity of the precipitation event, plants may not be able

to use all of the moisture. In addition, plant response to

water is a function of the plant’s condition. Long periods of

drought may stress plants to a point that they do not respond

immediately to precipitation.

For three of the four grasses exhibiting significantly

positive relationships with PDSI, we see consecutive relationships of seasonal PDSI up to winter of the previous year

(six seasons prior). For both B. eripoda and H. contortus, the

first season significantly correlated with cover was winter of

the previous year (DJFM-1). The first season correlated with

S. macrostachya was summer of the previous year (JAS-1).

Digitaria californica was significantly correlated with PDSI

in only one season, winter of the sampling year (DJFM). Two

seasons prior also show a strong but insignificant relationship (p < 0.10) with PDSI.

The correlations between grass cover and PDSI were

assumed to be independent, but PDSI values are dependent

on those of preceding seasons due to the water balance

accounting inherent in its calculation. Our results of several

consecutive seasons significantly correlated with PDSI for

these species may be due to this temporal autocorrelation.

Nonetheless, successive seasons of high positive PDSI values

(wet conditions) seem to favor greater cover values for these

grasses.

A majority of the significant correlations between grass

cover and TMIN, TMEAN, and TMAX were negative, that is,

higher grass cover amounts were correlated with lower

temperatures at various seasonal lags. This counter-intuitive finding is likely due to the inherent relationship between wet periods and cooler temperatures. PDSI captures

this relationship due to the inclusion of temperature in the

calculation of evapotranspiration. Lower temperatures result in lower rates of potential evapotranspiration and

higher soil moisture.

Conclusions____________________

Plant-available water captured in the PDSI explains the

greatest amount of variation in plant cover for perennial

grasses at the Santa Rita Experimental Range. The strength

of the PDSI’s explanatory power is that it accounts for

antecedent precipitation, moisture supply, and moisture

demand. By incorporating accumulated moisture deficiencies or surpluses, it is a better measure of plant-available

water than precipitation. Grasses known to be droughtsusceptible showed the strongest relationships with PDSI,

while drought-resistant grasses demonstrated little or no

relationships. A critical finding of this study is the utility of

PDSI over precipitation in predicting cover changes for

perennial grasses that are drought susceptible.

References _____________________

Angell, D. L.; McClaran, M. P. 2001. Long-term influences of

livestock management and a non-native grass on grass dynamics in the Desert Grassland. Journal of Arid Environments. 49:

507–520.

Burgess, Tony L. 1995. Desert grassland, mixed shrub savanna,

shrub steppe, or semidesert scrub? The dilemma of coexisting

growth forms. In: McClaran, Mitchel P.; Van Devender, Thomas

R., eds. The desert grassland. Tucson: The University of Arizona

Press: 31–67.

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semi-desert grassland range. Ecology. 53: 1084–1093.

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the signal already apparent? Trends in Ecology & Evolution.

15: 56–61.

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Intergovernmental Panel on Climate Change. In: Houghton, J. T.;

Ding, Y.; Griggs, D. J.; Noguer, M.; van der Linden, P. J.; Dai, X.;

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and New York: Cambridge University Press. 881 p.

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Station Pap. 69. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 93 p.

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Santa Rita grazing system. Journal of Range Management. 41:

291–295.

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buffelgrass productivity in the Sonoran Desert. Journal of Range

Management. 48: 60–63.

Matthews, D.; Pater, M.; Robinett, D.; Munda, B.; Egen, K.; Bailey, C.

1999. Grasses of southeastern Arizona. Coronado RC&D Area,
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Inc., and Conservation Districts of Southeastern Arizona, Tucson, AZ. 42 p.

Neilson, R. P.; Wullstein, L. H. 1983. Biogeography of two Southwest American oaks in relation to atmospheric dynamics. Journal

of Biogeography. 10: 275–297.

Neilson, R. P. 2003. The importance of precipitation seasonality in

controlling vegetation distribution. In: Weltzin, J. K.; McPherson,

G. R., eds. Changing precipitation regimes & terrestrial ecosystems. Tucson: University of Arizona Press.

Palmer, W. C. 1965. Meteorological drought. Res. Pap. 45. Washington, DC: U.S. Department of Commerce. 58 p.

Parmesan, C.; Yohe, G. 2003. A globally coherent fingerprint of

climate change impacts across natural systems. Nature. 421:

37–42.

Root, T. L.; Price, J. T.; Hall, K. R.; Schneider, S. H.; Rosenzweig, C.;

Pounds, J. A. 2003. Fingerprints of global warming on wild

animals and plants. Nature. 421: 57–60.

Ruyle, G. B.; Young, D. J. 1997. Arizona range grasses. Tucson:

University of Arizona, College of Agriculture, Cooperative

Extension.

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Primary production of the central grassland region of the United

States. Ecology. 69: 40–45.

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the role of the water balance. American Naturalist. 135: 649–670.

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Lincoln, NE: Johnsen Publishing Company. 395 p.

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116 USDA Forest Service Proceedings RMRS-P-30. 2003

Erika Geiger

Theresa Mau-Crimmins

Heather Schussman

Spread of a Nonnative Grass Across

Southern Arizona: Multiple Data Sources

to Monitor Change

Erika Geiger is a Ph.D. Student in the School of Renewable Natural Resources at the University of Arizona in Tucson. She completed a B.S. degree in biology

from Colorado University in Boulder, CO, and an M.S. degree in range management from the University of Arizona in Tucson. Theresa Mau-Crimmins is a Ph.D.

Student in the School of Renewable Natural Resources at the University of Arizona in Tucson, e-mail: theresam@u.arizona.edu. She completed a B.S. degree in

biology and an M.A. degree in geography at Western Michigan University in Kalamazoo. Heather Schussman is a Fire Scientist Specialist for The Nature

Conservancy, Arizona Chapter. She completed a B.A. degree in biology/anthropology from Whitman College in Washington and an M.S. degree in range

management from the University of Arizona in Tucson.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction _____________________________________________________

Nonnative plant species have the potential to alter species composition (across guilds), change hydrologic and nutrient

cycles, and influence disturbance regimes (Mack and D’Antonio 1998). One particularly invasive species in southern Arizona

is Eragrostis lehmanniana (Lehmann lovegrass). In the 1930s, E. lehmanniana was brought into the Southwestern United

States to control erosion and provide forage for cattle. Numerous researchers have observed a convincing association between

increasing proportion of E. lehmanniana and decreasing species richness in grasslands of southern Arizona (Cable 1971; Bock

and others 1986; Medina 1988). In addition to decreased species richness, E. lehmanniana has been implicated with alteration

of ecosystem processes (Cable 1971; Bock and others 1986; Williams and Baruch 2000), modification of community composition

(Anable and others 1992; Kuvlesky and others 2002), and changes in fire regimes (Biedenbender and Roundy 1996; Burquez

and Quintana 1994; Ruyle and others 1988). In the 50 years following its introduction, this species doubled the area to which

it was originally sown (Cox and Ruyle 1986).

In the mid-1980s, two researchers mapped the then-current distribution of E. lehmanniana (Cox and Ruyle 1986) and

suggested abiotic factors limiting its distribution. In that study, Cox and Ruyle (1986) predicted that E. lehmanniana

had reached the limits of its range in many areas. Recently, several respected field ecologists have noted the spread of

E. lehmanniana to areas well beyond these documented boundaries (D. Robinett 2002, personal communication;

G. Ruyle 2002, personal communication). Its spread is expected to continue under current climate conditions and landmanagement practices (Anable and others 1992; McClaran and Anable 1992).

Abstract: In 1934, Eragrostis lehmanniana was introduced into southeastern Arizona to

control erosion and provide forage for cattle. The earliest of these introductions took place on the

Santa Rita Experimental Range (SRER) in 1937 and continued there until the early 1960s.

Numerous researchers have observed a convincing association between an increased proportion

of E. lehmanniana and decreasing species richness in these grasslands. This grass is both

invasive and persistent: just 50 years after its introduction, the area occupied by E. lehmanniana

had doubled. Published evidence indicates that variables such as elevation, summer precipitation, winter temperatures, and soils impact its abundance and distribution. We used these

variables to generate a map of current predicted distribution of E. lehmanniana. Using over 600

presence/absence points amassed from eight agencies in Arizona, we selected among the

guidelines to create a current distribution map for E. lehmanniana in Arizona. We then modified

this map using two common general circulation models developed by the Hadley Centre for

Climate Prediction and Research and the Canadian Centre for Climate Modeling and Analysis

to predict the potential distribution of E. lehmanniana in Arizona in the year 2030.
USDA Forest Service Proceedings RMRS-P-30. 2003 117

Spread of a Nonnative Grass Across Southern Arizona: Multiple Data Sources... Geiger, Mau-Crimmins, and Schussman

Our objectives for this study were to (1) use the abiotic

factors suggested by Cox and Ruyle (1986) and other researchers to predict the current distribution of E. lehmanniana, and (2) predict areas likely to become invaded by

E. lehmanniana in the region of Arizona, U.S.A., under a

variety of future climate conditions using two popular global

circulation models (GCMs).

Methods ______________________

We gathered 641 data points from The Nature Conservancy, the USDA Natural Resource Conservation Service,

the USDI Bureau of Land Management, Saguaro National

Park, Fort Huachuca Military Reservation, Buenos Aires

National Wildlife Refuge, the Santa Rita Experimental

Range, and the U.S. Forest Service. The data points were

coded as presence or absence of E. lehmanniana, latitude

and longitude, and the date they were recorded.

A descriptive summary statistics analysis was completed

(JMP IN Ver. 4.0.4, SAS Institute, Inc.) to identify relationships between abiotic factors and the presence or absence of

E. lehmanniana. Explanatory variables included average

total precipitation, average total summer precipitation (July

through September), average total winter precipitation (December through February), average maximum and minimum temperature, elevation, aspect, and slope.

Cox and Ruyle (1986) predicted spread of E. lehmanniana

to be limited to areas between 800 and 1,500 m in elevation,

with summer rainfall exceeding 150 mm in 40 days, and

temperatures rarely falling below 0 ∞C. In earlier research,

Crider (1945) suggested a minimum temperature bound for

E. lehmanniana of –3 ∞C. We compared our presence/absence points to the distribution suggested by the abiotic

factors described by Cox and Ruyle (1986) and Crider (1945).

The current distribution of E. lehmanniana was modeled

using grid arithmetic within ArcView GIS software. Spatial

data sets of long-term climatic averages for minimum January temperature (Thornton and others 1997), annual precipitation (Thornton and others 1997), and corresponding

elevation models (GLOBE 1999) were obtained for the study

area at 1-km resolution. Based on the ranges of these abiotic

factors believed to be tolerated by E. lehmanniana (Cox and

Ruyle 1986; Crider 1945), spatial grids were coded as either

appropriate or inappropriate habitat. When intersected,

these grids resulted in a map of the predicted current

distribution of E. lehmanniana (fig. 1).

Figure 1—Potential current distribution of Eragrostis lehmanniana (Lehmann lovegrass) in Arizona, U.S.A.,

using abiotic factors suggested by Cox and Ruyle (1986) and Crider (1945).
118 USDA Forest Service Proceedings RMRS-P-30. 2003

Geiger, Mau-Crimmins, and Schussman Spread of a Nonnative Grass Across Southern Arizona: Multiple Data Sources...

Potential future distributions of E. lehmanniana were

predicted using two common general circulation models

developed by the Hadley Centre for Climate Prediction and

Research and the Canadian Centre for Climate Modeling

and Analysis. The long-term climatic data sets for winter

temperature and annual precipitation were modified to

reflect the changes in winter temperature and annual precipitation predicted for 2030 by each of these models. The

Hadley Centre model predicts an average increase in winter

temperature of 2.5 ∞C and winter precipitation of 1.0 mm per

day by 2030 for the Southwestern United States. Summer

temperature is predicted to increase by 1 ∞C and 0.25 mm per

day, on average, by the Hadley Centre model. The Canadian

Climate Centre model predicts an average increase in winter temperature of 3 ∞C and winter precipitation of 1.5 mm

per day by 2030 for the Southwestern United States. Summer temperature is predicted to increase by 1.5 ∞C and 0 mm

per day, on average, by the Canadian Centre model.

The current climate grids were then coded as appropriate

or inappropriate habitat for E. lehmanniana based on the

ranges provided by Cox and Ruyle (1986) and Crider (1945).

When intersected with the grid of elevations appropriate

Figure 2—Potential future distribution of Eragrostis lehmanniana (Lehmann lovegrass) in Arizona, U.S.A., based

on the Hadley Centre for Climate Prediction and Research and the Canadian Centre for Climate Modeling and

Analysis general circulation models.

for E. lehmanniana, two scenarios of predicted distribution

of E. lehmanniana in 2030 were generated (fig. 2).

Results _______________________

Summary statistics of the 641 data points revealed that

E. lehmanniana was present in 326 and absent in 227. Sites

where E. lehmanniana was present were, on average, 265

m lower than sites where it was absent (table 1). Slopes

averaged 5.5 percent steeper on sites where E. lehmanniana

was absent than where it was present (table 1). Sites where

E. lehmanniana was present received, on average, 6.4 mm

less total precipitation annually than sites where it was

absent (table 1). Average summer precipitation was 10.2

mm higher for sites where E. lehmanniana was absent

than sites where it was present (table 1). Average winter

precipitation was 2.8 mm higher, on average, for sites where

E. lehmanniana was absent than sites where it was present

(table 1).

The predicted current extent of E. lehmanniana using the

abiotic factors suggested by Cox and Ruyle (1986) and Crider

(1945) appears in figure 1. Areas shaded in dark gray depict
USDA Forest Service Proceedings RMRS-P-30. 2003 119

Spread of a Nonnative Grass Across Southern Arizona: Multiple Data Sources... Geiger, Mau-Crimmins, and Schussman

the range of E. lehmanniana using the limits of abiotic

factors suggested by Cox and Ruyle (1986). Areas shaded in

light gray represent areas that also are predicted to be

invaded by E. lehmanniana when the minimum cold temperature is changed from 0 ∞C, as suggested by Cox and

Ruyle (1986), to –3 ∞C, as suggested by Crider (1945). The

dark gray areas encompass 63 percent of the 326 presence

points we collected; the dark gray and light gray areas

together capture 76 percent of the presence points.

Future spread maps, based on the Hadley Centre for

Climate Prediction and Research and the Canadian Centre

for Climate Modeling and Analysis GCM’s are presented in

figure 2. These models show the distribution of E. lehmanniana increasing, mainly by moving up in elevation. The

Canadian Centre model predicts a slightly greater 2030

extent of E. lehmanniana than the Hadley Centre model.

Discussion ____________________

Several studies have pointed out the importance of average total summer precipitation in limiting the spread of E.

lehmanniana (Anable 1990; Anable and others 1992; Cox

and Ruyle 1986). In our analysis using more than 600 points,

we found no meaningful difference between E. lehmanniana

presence or absence and precipitation. However, elevation

and slope substantially affected the presence of E. lehmanniana. Of the points we amassed, E. lehmanniana was

present more often at lower elevations and less steep slopes.

Of particular interest is our finding that the upper elevation

limit suggested by Cox and Ruyle (1986), 1,500 m, appears

to be too low. Of the 327 presence points analyzed in this

study, 10 percent existed above the predicted limitation of

1,500 m.

Crider (1945) documented that E. lehmanniana could be

found in areas with minimum temperature as low as –3 ∞C,

but in these areas, it acted more like an annual plant,

reproducing primarily from seed rather than previous

years’ vegetative growth. This finding may have influenced

Cox and Ruyle (1986) when they selected 0 ∞C as the

minimum temperature boundary for E. lehmanniana. It

appears from the points we collected that E. lehmanniana

is able to persist at these lower temperatures, as changing

the minimum temperature from 0 to –3 ∞C improved our

predictive power of presence points from 63 to 76 percent.

With the model we have constructed using limits of abiotic

factors suggested by Crider (1945) and Cox and Ruyle

(1986), we predict E. lehmanniana to be present in large

areas expected to be absent. The map appearing in figure 1

is a representation of areas where the conditions are appropriate to host E. lehmanniana. However, myriad other

factors play a role in the species’ ability to inhabit an area.

Factors such as competition, land use history, proximity to

seed source, and microsite variability are likely affecting the

presence or absence of E. lehmanniana in these areas.

The future extent maps (fig. 2) predict that E. lehmanniana will move up in elevation as average summer and

winter temperatures increase. In addition, areas predicted

to currently be invaded in the northwestern portion of the

State are no longer predicted to be appropriate for E.

lehmanniana under future climate conditions. The increase

in E. lehmanniana presence in Arizona predicted by these is

not dramatic compared to the extent already predicted in

figure 1. Using the limits suggested by Cox and Ruyle (1986),

E. lehmannianais predicted to inhabit 25,680 km2

; using the

minimum temperature suggested by Crider (1945), this area

increases to 81,504 km2

. Under the Hadley Centre model,

62,314 km2m are predicted to be appropriate for E.

lehmanniana, and under the Canadian Centre scenario,

66,158 km2 are predicted to potentially host this invasive

grass.

The areas predicted to host E. lehmanniana in the future

distribution models assume that viable seed is spread to

these areas. However, whether E. lehmanniana reaches

this area will depend on the spread of seed. It has been

observed that vehicle traffic is a primary source for seed

introductions (D. Robinett 2002, personal communication).

Spread of E. lehmanniana will likely be driven, at least in

part, by development of areas not currently invaded.

Our hope is that the maps we have generated will give a

quick up-to-date reference guide for areas throughout the

State that are currently occupied by E. lehmanniana to aid

in planning efforts such as large-scale fire restoration.

Additionally, land managers can use the maps to identify

where they fall along the current and future distribution of

E. lehmanniana and adjust management practices as necessary to decrease the spread of E. lehmanniana on their

lands.

Table 1—Mean values of variables affecting presence of Eragrostis lehmanniana in southern Arizona.

E. lehmanniana

status Variable n Mean SE

Present Elevation 326 1,241 m 11 m

Absent Elevation 227 1,510 m 31 m

Present Slope 326 2.3 percent 0.13 percent

Absent Slope 227 7.8 percent 0.65 percent

Present Total precipitation 326 505.4 mm 5.5 mm

Absent Total precipitation 227 511.8 mm 6.2 mm

Present Average summer precipitation 326 163.7 mm 3.5 mm

Absent Average summer precipitation 227 173.9 mm 4.8 mm

Present Average winter precipitation 326 134.8 mm 1.5 mm

Absent Average winter precipitation 227 137.6 mm 1.6 mm
120 USDA Forest Service Proceedings RMRS-P-30. 2003

Geiger, Mau-Crimmins, and Schussman Spread of a Nonnative Grass Across Southern Arizona: Multiple Data Sources...

References ____________________

Anable, M. E. 1990. Alien plant invasion in relation to site characteristics and disturbance: Eragrostis lehmannianaon the Santa

Rita Experimental Range, Arizona 1937–1989. Tucson: University of Arizona. Thesis.

Anable, M. E.; McClaran, M. P.; Ruyle, G. B. 1992. Spread of

introduced Lehmann lovegrass Eragrostis lehmanniana Nees. in

southern Arizona, USA. Biological Conservation. 61: 181–188.

Biedenbender, S. H.; Roundy, B.A. 1996. Establishment of native

semidesert grasses into existing stands of Eragrostis lehmanniana

in southeastern Arizona. Restoration Ecology. 4: 155–162.

Bock, C. E.; Bock, J. H.; Jepson, K. L.; Ortega, J. C. 1986. Ecological

effects of planting African lovegrasses in Arizona. National Geographic Research. 2: 456–463.

Burquez, A.; Quintana, M. 1994. Islands of biodiversity: ironwood

ecology and the richness of perennials in a Sonoran Desert

biological reserve. In: Nabhan, G. P.; Carr, J. L., eds. Ironwood:

an ecological and cultural keystone of the Sonoran Desert. Occasional Pap. 1. Washington, DC: Occasional Papers in Conservation Biology: 9–27

Cable, D. R. 1971. Lehmann lovegrass on the Santa Rita experimental range, 1937–1968. Journal of Range Management. 24: 17–21.

Cox, J. R.; Ruyle, G. B. 1986. Influence of climatic and edaphic

factors on the distribution of Eragrostis lehmanniana Nees. in

Arizona, USA. Journal of Grassland Society of South Africa. 3:

25–29.

Crider, F. J. 1945. Three introduced lovegrasses for soil conservation. U.S. Department of Agriculture Circ. 730.

GLOBE Task Team. 1999. The Global Land One-kilometer Base

Elevation (GLOBE) Digital Elevation Model, Version 1.0. National Oceanic and Atmospheric Administration, National Geophysical Data Center, 325 Broadway, Boulder, CO 80303, U.S.A.

Available: http://www.ngdc.noaa.gov/seg/topo/globe.shtml [2003,

February 15].

Kuvlesky, W. P., Jr.; Fulbright, T. E.; Engel-Wilson, R. 2002. The

impact of invasive exotic grasses on quail in the Southwestern

United States. In: DeMaso, S. J; Kuvlesky, W. P., Jr.; Hernandez,

F; Berger, M. E., eds. Quail V: the fifth national quail symposium;

Austin, TX: Texas Parks and Wildlife Department: 118–128.

Mack, M. C.; D’Antonio, C. M. 1998. Impacts of biological invasions

on disturbance regimes. Trends in Ecology and Evolution. 13:

195–198.

McClaran, M. P.; Anable, M. E. 1992. Spread of introduced Lehmann

lovegrass along a grazing intensity gradient. Journal of Applied

Ecology. 29: 92–98.

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Ruyle, G. B.; Roundy, B. A.; Cox, J. R. 1988. Effects of burning on

germinability of Lehmann lovegrass. Journal of Range Management. 41: 404–406.

Thornton, P. E.; Running, S. W.; White, M. A. 1997. Generating

surfaces of daily meteorology variables over large regions of

complex terrain. Journal of Hydrology. 190: 214–251.

Williams, D. G; Baruch, Z. 2000. African grass invasion in the

Americas: ecosystem consequences and the role of ecophysiology.

Biological Invasions. 2: 123–140.
USDA Forest Service Proceedings RMRS-P-30. 2003 121

Jorry Z. U. Kaurivi

Alfredo R. Huete

Kamel Didan

Multitemporal MODIS-EVI Relationships

With Precipitation and Temperature at the

Santa Rita Experimental Range

Jorry Z. U. Kaurivi, Graduate Associate in the Department of Soil, Water and Environmental Science (SWES) of the University of Arizona, Tucson, e-mail:

jkaurivi@a.arizona.edu.. He obtained his B.S. degree at the University of Natal, South Africa, and an M.S. degree in soil and water science at the University of

Arizona. Alfredo R. Huete, Professor, SWES, and Head of the Terrestrial Biophysics and Remote Sensing Laboratory (TBRS). He obtained a B.S. degree in range

ecology in 1977 from the University of Arizona, an M.S. degree in soil and plant biology in 1982 at the University of California-Berkeley, and a Ph.D. degree in

soil and water science in 1984 at the University of Arizona. Kamel Didan is a Research Scientist in the TBRS, SWES. He receivedhis Ph.D. degree at the University

of Arizona in 1999. He is a MODIS Associate Team Member and leads the research and development of the MODIS VI algorithms.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

Accurate measurements of vegetation dynamics (phenology) at regional to global scale are required to improve models and

understanding of interannual variability in terrestrial ecosystem carbon exchange and climate-biosphere interactions (Zang

and others 2002). An obvious and appealing approach is to relate the net primary production (NPP) to the climate in order to

estimate the efficiency of climate variables to the production of vegetation. Knowledge of the efficiency with which vegetation

converts the absorbed photosynthetically active radiation (APAR) into biomass permits an estimate of NPP. Climate

constraints on NPP have been studied and have indicated greater consistency in estimates of biomass if APAR is excluded from

the annual sum when conditions are unfavorable for production (Turner and others 2002).

The role of precipitation seasonality in arid land systems, although recognized as important, is largely unexplored (Neilson

2003). Together with local elevation and temperature, precipitation determines the distribution and location of vegetation

ecotones. With constant competition for water between the grass and shrub communities, the arid Southwest United States

vegetation dynamics will better be understood when remote sensing and ancillary data are combined on a multitemporal scale.

It has been predicted that the increased precipitation with potential future warming will result in greater distribution of shrubs

when winter rains dominate and grass when the summer monsoons are dominant (Neilson 2003).

Perennial grass species have variable net photosynthesis rates as a function of temperature, and this affects the season when

a plant is most susceptible to carbohydrate depletion with repeated clipping to simulate grazing. It was shown that mesquite

Abstract: The Moderate Resolution Imaging Spectroradiometer (MODIS) provides temporal

enhanced vegetation index (EVI) data at 250, 500, and 1,000 m spatial resolutions that can be

compared to daily, weekly, monthly, and annual weather parameters. A study was conducted at

the grassland site (less than 10 percent velvet mesquite [Prosopis juliflora, var. velutina]) and the

mesquite site (approximately 30 to 40 percent mesquite cover) of the Santa Rita Experimental

Range (SRER) to relate MODIS monthly EVI to temperature and rainfall patterns. Preliminary

results show that these two climate attributes altered the shape of the temporal EVI regime,

particularly at the grassland. High temporal variability in the precipitation regime resulted in a

weaker relationship with EVI than the more consistent temperature regime.

Keywords: MODIS, EVI, Santa Rita, mesquite, temperature, precipitation, multitemporal,

Southwest

Acknowledgments: Precipitation data sets were provided by the SRER Digital Database.

Funding for the digitization of these data was provided by the USDA Forest Service Rocky

Mountain Research Station and the University of Arizona. We extend our gratitude to Dr.

Mitchel P. McClaran for his guidance and input.
122 USDA Forest Service Proceedings RMRS-P-30. 2003

Kaurivi, Huete, and Didan Multitemporal MODIS-EVI Relationships With Precipitation and Temperature...

had a higher net photosynthesis rate than galleta grass

(Hilaria jamesii) at 21 and 38 ∞

C. but that galleta grass had

a higher net photosynthesis rate at 5 ∞C (Ogden 1980).

The Moderate Resolution Imaging Spectroradiometer

MODIS, on board the Terra platform, has a temporal resolution of 2 days and acquires data in 36 spectral bands at

250, 500, or 1,000 m spatial resolution. The high temporal

resolution provides the capability of monitoring rangeland

health worldwide (Reeves and others 2001). Because many

land cover changes that are due to the invasion of shrubs

upon grasslands occur at spatial scales near 250 m, MODIS

may be useful in studying rangeland conversions. The VI

product described in this paper is derived from the MODIS250, 16-day level 3 made available to public on request

through the EOS Data Gateway.

The Enhanced Vegetation index (EVI) was developed and

incorporated into the MODIS products (Huete and others

2002; Van Leeuwen and others 1999). The EVI utilizes the

ratio of the reflectance in the near-infrared band (MODIS

841-876 nm) and the red band (MODIS 620-670 nm). It also

employs the blue band (MODIS 459-479 nm) for the atmospheric correction, coefficients (C1 and C2) of aerosol resistance, L for the background stabilization and G, the gain

factor, as follows:

EVI

L CC

G NIR RED

NIR RED BLUE

= ++ -

- ( ) r r

rr r 1 2

where

L = 1, C1 = 6, C2 = 7.5 and G = 2.5

Vegetation indices have been correlated with various

vegetation parameters such as LAI, biomass, canopy cover,

and fraction of APAR (fAPAR) (Huete and others 2002). The

EVI was found to have a more linear relationship with these

parameters than the NDVI. The objective of this study is to

present a temporal trend of the MODIS EVI product and

relate it to the temperature and precipitation of the SRER

mesquite-dominated site (approximated between 30 to 40

percent mesquite cover and located at –110∞54’56.92’’E,

31∞47’3.75’’N) and grass-dominated site (less than 10 percent mesquite cover and located at –110∞53’44.56’’E,

31∞46’54.01’’N).

Site Description ________________

The SRER (21,500 ha) is 40 km south of Tucson, AZ, and

is administered by the University of Arizona. Small areas

of steep, stony foothills and a few isolated buttes characterize the range, but the dominating landscape features are

the long, gently sloping alluvial fans. Elevations range

from 900 m to about 1,300 m in the southwestern part.

Average rainfall increases with elevation, from 250 mm at

900 m to almost 500 mm at 1,300 m (McClaran 1995;

McClaran and others 2002)

Vegetation at the SRER varies with soil, rainfall, and

elevation. Annual vegetation is most abundant in areas with

a moderate to low density of perennial grasses and in areas

where native grasses persist over the invasive Lehmann’s

lovegrass (Erogrostis lehmanniana. Nees). Since the early

1900s, major vegetation changes have occurred. Where

shrub-free grassland once dominated, velvet mesquite

(Prosopis juliflora var. velutina) is now the dominant overstory species (McClarran and others 2002). This site presents a good opportunity for the study of mesquite encroachment into grassland.

Method _______________________

We first selected two sites that represent dense mesquite

(simply called mesquite site) and the grassland site that has

low-density mesquite trees except in the washes. We obtained the temporal vegetation index data from the MODIS250m, 16-day composite product provided by the EDCDAAC. Available data from November 2000 to March 2003

were extracted using the Msphinx software and transferred

to Sigmaplot software for graphics and S-plus for statistical

analysis. The 16-day composite vegetation index was averaged into monthly values for comparison with the monthly

climate data sets.

We also obtained the climate data from local weather

stations. Local temperature from the Tucson International

Airport, which is about 32 km from the study sites, provided

a good sample of continuous desert environment temperature. We downloaded the monthly rainfall data of the Rodent

and the Exclosure 41 rain gauges from the Santa Rita Web

site. The Rodent rain gauge is within the mesquite study

site, while the Exclosure 41 rain gauge is within 200 m

distance from the grassland site. Precipitation data from the

SRER Web site for all the rain gauges until January 2003

was available, and that was the cutoff point for all data sets

considered in this study.

Results _______________________

Figure 1 shows the multitemporal EVI, temperature, and

precipitation profiles from November 2000 to January 2003.

High temperature months coincide with the summer monsoon period. The period of low precipitation also corresponds

to low EVI value. There was a remarkable difference in the

temporal precipitation distribution between the monsoons

of 2001 and 2002. The monsoon of the 2001 was better

distributed throughout the year and, in fact, there was not

a well-defined break between the winter and summer rainy

seasons. The year 2002 had little precipitation during winter (December to February), a dry spring (March to May), but

a wet summer (June to August) and a small amount during

fall (September to November). The temperature profile is

more consistent than the precipitation curves. The highest

temperature appears in June for the 2 years and lowest

during December and January.

The peak EVI appeared in August during 2001 for both the

grassland and the mesquite sites. During 2002 the grassland had a sharp rise then a sharp drop in the EVI curve

during the period of July to December. The EVI of the

mesquite and grassland sites dropped and then rose before

the monsoon arrived during the period of November 2001 to

May 2002, reaching a minimum in March. During the 2002

season, mesquite had an early rise but did not reach the peak

attained by the grassland site after the well-pronounced

monsoon precipitation arrived.
USDA Forest Service Proceedings RMRS-P-30. 2003 123

Multitemporal MODIS-EVI Relationships With Precipitation and Temperature... Kaurivi, Huete, and Didan EVI x 104

500

1000

1500

2000

2500

3000

3500

ND J F MAMJ J A SO J ND F MAMJ J A SO J N D

Months

EVI_grass

EVI_mesquite

a

b

Temperature (deg C) and Precipitation (mm)

0

20

40

60

80

100

120

ND J F MAMJ J A S O J ND F MAMJ J A S O J N D

Months

Precipitation_grass (mm)

Precipitation_mesquite (mm)

Temperature (deg C)

Figure 1—Multitemporal (a) MODIS Enhanced

Vegetation Index (EVI) and (b) climate from the

Santa Rita mesquite and grassland sites. Data was

collected from November 2000 to January 2003.

Monthly maximum temperature (∞C) was recorded

from the Tucson International, and Precipitation at

rain gauges Exclosure-41 and Rodent represent the

grassland site and mesquite site, respectively.

Figure 2 shows correlation coefficients between temperature, rainfall, and vegetation index from the two sites. The

EVI curves of the two sites are predominantly similar,

followed by the precipitation and temperature. The grassland site, however, showed a temporal variation that was

more correlated to climate attributes than the mesquite site.

Discussion ____________________

The EVI, temperature, and precipitation annual sinusoidal curves are out of phase with each other. Temperature is

the most consistent variable throughout, followed by the

EVI. Warmer months and summer monsoon give rise to high

primary production. Low winter temperature reduces the

primary production, even when substantial amount of precipitation occurs. Vegetation phenology therefore appears to

follow a compromise pattern between precipitation and

temperature temporal variations. This vegetation response

confirms the importance of monsoon and warm temperature

to desert grasslands that characterizes the C4 photosynthetic pathway (McClaran 1995). Winter and spring rains

induce an early takeoff in grassland production compared to

the mesquite site. Ogden (1980) reported similar patterns

where carbohydrate flow was higher in stems during November to March and dropped during the summer for sideoats

grama, while the rain peaked during July to September.

The contrasting variations in precipitation between the 2

years observed in this study did not alter the temperature

curves. EVI profiles for the two sites are more separable

during the summer monsoon but tend to converge during the

spring and early summer months. Precipitation plays a

dominant role in evoking these differences. The arrival of

precipitation during the spring, as noticed during the 2001

season, stimulated the growth of both the mesquite and

grass, but the grass site had a closer relation to precipitation

than the mesquite site.

EVI_grass vs EVI_mesq

Correlation coefficient

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Precip_grass vs Precip_mesq

Temperature vs Precip_mesq

Temperature vs Precip_grass

EVI_grass vs Temperature

EVI_mesq vs Temperature

EVI_grass vs Precip_grass

EVI_mesq vs Precip_mesq

Figure 2—Relationships between enhanced Vegetation Index (EVI), Temperature,

and Precipitation for the grassland and mesquite sites of the Santa Rita Experimental

Range. The correlation coefficients are ranked from high to low.
124 USDA Forest Service Proceedings RMRS-P-30. 2003

Kaurivi, Huete, and Didan Multitemporal MODIS-EVI Relationships With Precipitation and Temperature...

Conclusion____________________

It is evident that precipitation is the dominant attribute

that controls the growth of grass in arid rangeland. However, initial growth is also possible before summer rain

arrives. Mesquite growth is dependent on precipitation

arrival time and amount, but responds less to precipitation

variability than the grass. The ability of trees to tap into

deeper soil moisture provides them with a competitive advantage and makes them less reliant on surface conditions

than their grass counterparts. Warming up after a cool

winter triggers new growth in rangeland vegetation. Mesquite cover responds better to seasonal temperature regimes

than grass. MODIS is providing an opportunity to study the

temporal dynamics of rangeland vegetation and should

assist in estimating the carbon fluxes over time.

References ____________________

Huete, Alfredo R.; Didan, Kamel; Miura, Tomoaki; Rodriguez, E.

Patricia.; Gao, Xiang; Ferreira, Laerte G. 2002. Overview of the

radiometric and biophysical performance of the MODIS Vegetation Indices. Remote Sensing of Environment. 83: 195–213.

McClaran, Mitchel P. 1995. Desert grasslands and grasses. In:

McClaran, Mitchel, P.; Van Devender, Thomas R., eds. The desert

grassland. Tucson: University of Arizona Press: 1–30.

McClaran, Mitchel P.; Angel, Deborah L.; Wissler, Craig. 2002.

Santa Rita Experimental Range Digital Database: user’s guide.

Gen. Tech. Rep. RMRS-GTR-100. Ogden, UT: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station.

13 p.

Neilson, Ronald, P. 2003. The importance of precipitation seasonality in controlling vegetation distribution. In: Weltzin, Jake, F.;

McPherson, Guy. Changing precipitation regimes and terrestrial

ecosystems: a North American perspective. Tucson: University of

Arizona Press: 45–69.

Ogden, P. R. 1980, Meeting the physiological requirements of a

plant with grazing systems. In: McDaniel, K. C.; Allison, C.

Grazing management systems for Southwest rangelands: a symposium. Las Cruces: New Mexico State University, The Range

Improvement Task Force: 37–48.

Reeves, Matthew C.; Winslow, Jerome. C.; Running, Steven W.

2001. Mapping weekly vegetation productivity using MODIS

algorithms, Journal of Range Management. 54: 90–105.

Van Leeuwen, Willem. J. D.; Huete, Alfredo R.; Liang, Trevor. 1999.

MODIS vegetation index compositing approach: a prototype with

AVHRR data. Remote Sensing of Environment. 69: 264–280.

Turner, David P.; Gower, Stith T.; Cohen Warren B.; Gregory,

Mathew; Maiersperger, Tom K. 2002. Effects of spatial variability in light use efficiency on satellite-based NPP monitoring.

Remote Sensing of Environment. 80: 397–405.

Zhang, Xiaoyang; Friedl, Mark A.; Schaaf, Crystal B.; Stahler, Alan

H.; Hodges, John C. F.; Gao, Feng; Reed, Bradley C.; Huete,

Alfredo. 2003. Monitoring vegetation phenology using MODIS.

Remote Sensing of Environment. 84: 471–475.
USDA Forest Service Proceedings RMRS-P-30. 2003 125

Alessandra Fravolini

Kevin R. Hultine

Dan F. Koepke

David G. Williams

Role of Soil Texture on Mesquite

Water Relations and Response

to Summer Precipitation

Alessandra Fravolini is a Ph.D. Candidate in the Department of Renewable Natural Resources at the University of Arizona, Tucson; e-mail:

alefravo@u.arizona.edu. She completed a Laurea degree in biology with an emphasis in ecology at the University La Sapienza of Rome, Italy. Kevin R. Hultine

is a Ph.D. Candidate in the Department of Renewable Natural Resources at the University of Arizona, Tucson. He completed a B.S. degree in forest resources

at the University of Idaho, and an M.S. degree in the Department of Renewable Natural Resources at the University of Arizona. Dan F. Koepke is a Research

Technician in the Department of Renewable Natural Resources at the University of Arizona, Tucson. He completed a B.S. degreee in watershed management in

the Department of Renewable Natural Resources at the University of Arizona. David G. Williams is an Associate Professor in the Departments of Renewable

Resources and Botany, University of Wyoming, Director of the University of Wyoming Stable Isotope Laboratory, and Adjunct Associate Professor in the School

of Renewable Resources, University of Arizona. He completed a B.A. degree in botany at the University of Texas, Austin, an M.S. degree in range science at Texas

A&M University, and a Ph.D. degree in botany at Washington State University.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

According to the two-layer hypothesis, different plant life forms extract water from varying soil depths, such that deeply

rooted woody plants extract water from winter precipitation that percolates deep into the soil profile while shallowly rooted

grasses and herbaceous plants rely mostly on growing season precipitation (Walter 1974). However, some studies have shown

a consistent overlap in water use between different functional types having different rooting depths (Lin and others 1996;

Reynolds and others 1999; Schulze and others 1996; Yoder and Nowak 1999), suggesting that in a water-limited ecosystem

the two layer hypothesis may be an oversimplification.

Abstract: In the arid Southwest United States, monsoon precipitation plays a key role in

ecosystem water balance and productivity. The sensitivity of deeply rooted plants to pulses of

summer precipitation is, in part, controlled by the interaction between soil texture, precipitation

intensity, and plant rooting depth and activity. In this study we evaluated the water relations of

a leguminous tree species Prosopis velutina Woot. (velvet mesquite) occurring across three

different aged soils varying in soil texture during two consecutive summers that substantially

differed in the amount of monsoonal precipitation (1999 and 2000). We predicted that mesquite

trees occurring on different textured geomorphic surfaces would be exposed to different levels of

premonsoon water deficit and would not respond equally to summer precipitation. During both

years, predawn and midday leaf water potentials were more negative on coarse textured soils than

on medium and fine textured soils before the onset of the monsoon, indicating that plant water

status is less favorable during drought on coarse-textured soils. However, leaf water potentials

recovered rapidly on coarse-textured soils in response to monsoonal precipitation. These results

suggest that mesquite sensitivity to future changes in winter and summer precipitation may not

be uniform across the landscape, and that the interaction between precipitation and soil-plant

hydraulic properties need to be better understood to realistically predict impacts of land cover

change on ecosystem carbon and water balance.

Acknowledgments: The valuable help of Nathan English and Rico Gazal in reviewing this

manuscript is gratefully acknowledged. Precipitation data sets were provided by the Santa

Rita Experimental Range Digital Database. The study was funded by the National Science

Foundation.
126 USDA Forest Service Proceedings RMRS-P-30. 2003

Fravolini, Hultine, Koepke, and Williams Role of Soil Texture on Mesquite Water Relations and Response to Summer Precipitation

Changes in precipitation are likely to be the dominant

factor affecting future shifts in vegetation structure and

ecosystem processes in arid and semiarid regions. In southeastern Arizona, interannual variations, more than longterm variations, are typically the dominant component in

the total variance of summer precipitation and are of greatest importance in terms of increasing pressures on limited

resources such as water and mineral nutrients (Adams and

Comrie 1997). The pattern of summer precipitation in semiarid regions is characterized by the occurrence of numerous

small pulses (approximately 10 to 15 events smaller than 10

mm) and by occasional large pulses (1 to 4 events greater

than 20 mm). In most arid and semiarid regions, only the

large pulses significantly affect the water balance and productivity of deeply rooted plants (Noy-Meir, 1973).

Large (greater than or equal to 20 mm) but not small (less

than or equal to 10 mm) summer rainfall events from two

weather stations adjacent to the Santa Rita Experimental

Range: Tumacacori, 31∞34’N and 111∞03’W (from 1980 to

2000) and Green Valley, 31∞54’N and 111∞00’W (from 1990

to 2000) were correlated with total summer precipitation

(fig. 1). Apparently the occurrence of wet summers is

generated by a few large rainfall events. From these data,

we predict that the response of deeply rooted plants to

summer precipitation is strongly dependent on the occurrence of large rain events (more than 20 mm) that are

sufficient to percolate below the rooting depth of grasses

and annuals herbaceous plants.

Although patterns of precipitation are strongly linked to

primary productivity in arid and semiarid regions (Eamus

2003), they cannot entirely explain vegetation dynamics

without considering the influence of edaphic factors on plant

water availability. Soil texture is a major factor controlling

plant distribution and abundance by affecting moisture

availability to plants (Bristow and others 1984; Smith and

others 1995; Sperry and others 1998). For example, coarse,

sandy soils lose moisture much more easily than fine textured soils because of the weaker capillary forces in the large

pore spaces. Plants therefore growing in sandy soils potentially exhaust their water supplies more rapidly than plants

in a finer textured soil, resulting in greater water stress,

lower productivity, and more allocation of resources to the

roots compared to plants in fine textured soils (Sperry and

others 2002).

In this study we assessed the sensitivity of leaf water

potential, a measure of plant water status, in Prosopis

velutina Woot. (velvet mesquite) to summer precipitation

across a soil texture gradient during the 1999 and 2000

growing seasons on the Santa Rita Experimental Range in

Southeastern Arizona. This investigation was part of a

larger study to assess the extent to which soil morphology

and summer precipitation mediates the water balance and

productivity of mesquite on the Santa Rita Experimental

Range. Information from this study and future studies will

substantially aid our ability to predict spatial and temporal

patterns of woody plant encroachment and establishment in

arid and semiarid rangelands.

Materials and Methods __________

Study Site

The study site was located on the Santa Rita Experimental Range (SRER) 35 km south of Tucson, AZ. Mean annual

precipitation (average of the last 30 years) on the SRER

ranges from about 250 to 500 mm, depending on elevation.

Greater than 50 percent of the mean annual precipitation

occurs during the summer monsoon (July to September)

with high interannual variation. Mean daytime air temperature is 32 ∞C during summer, while mean nighttime

temperature during winter is 5 ∞C. The plant communities

on the SRER have been altered dramatically over the last

100 years by the encroachment of velvet mesquite trees into

former grasslands. The geomorphology on the SRER varies

from mesic sandy uplands that originated during the Holocene to clay rich Pleistocene alluvial fans (Medina 1996).

Experimental Design and Data Collection

Three sites representing young Holocene (4,000 to 8,000

ybp), late Pleistocene (75,000 to 130,000 ybp), and midPleistocene (200,000 to 300,000 ybp) geomorphic surfaces

were selected on the SRER. The percentage of sand, silt, and

clay for each selected surface is reported in table 1. At each

site, a single plot between 0.25 and 0.5 ha was established,

Green Valley 

0

5

10

15

20

25

30

35

R2 = 0.93

Tumamacori

Total Summer Precipitation

50 100 150 200 250 300 350 400 450

Number of Precipitation Events

0

5

10

15

20

25

30

35

smaller than 10 mm 

larger than 20 mm 

R2= 0.815

Figure 1—Correlation between total summer

precipitation and numbers of events smaller

than 10 mm (filled circles) or larger than 20 mm

(open circles) at the Tumacacori and Green

Valley weather stations in southeastern Arizona.
USDA Forest Service Proceedings RMRS-P-30. 2003 127

Role of Soil Texture on Mesquite Water Relations and Response to Summer Precipitation Fravolini, Hultine, Koepke, and Williams

and all mesquite plants were identified and placed within

one of three height classes; less than 1 m, 1 to 2 m, and

greater than 2 m. Three to five individuals of each size class

were randomly selected at each site for leaf water potential

measurement. Leaf water potential measured just before

dawn yields an approximation of the soil water potential in

the rooting zone, given the assumption that during the

evening leaf water comes into equilibrium with soil water

(Davis and Mooney 1986; Donovan and Ehleringer 1994).

Midday leaf water potential is measured to gauge the minimum water potential a plant can tolerate. Predawn leaf

water potential (y pd ) was measured between 2 a.m. and 5

a.m. approximately once every 4 weeks throughout the

growing seasons (May through September) of 1999 and 2000

using a Scholander-type pressure chamber (PMS Instruments, Corvallis, OR, U.S.A.). Midday leaf water potential

( ) y md was measured between 1000 and 1300 hours every

4 weeks throughout the 2000 growing season.

Statistical Analysis

Multivariate analysis for repeated measures (MANOVA)

was performed on untransformed data to test the effect of

geomorphic surface, precipitation, and their interaction on

predawn and midday leaf water potential. In order to identify the specific differences in leaf water potential across

geomorphic surfaces that were statistically meaningful, a

least significant difference (LSD) contrast analysis was

performed within the MANOVA framework. Results are

discussed only at the highest level of significance (P £ 0.05)

and are reported within the result and discussion section.

JMP 4 software for IBM (SAS Institute Inc.) was used to

perform all statistical analysis.

Results and Discussion _________

Total summer precipitation on the Holocene in 1999 was

395 mm, while in 2000, total growing season precipitation

was 302 mm. Precipitation data for the other two sites was

Table 1—Texture fractions of soils collected on Holocene, late and

early Pleistocene geomorphic surfaces in the Santa Rita

Experimental Range.

Soil Sand Silt Clay

Surface origin depth fraction fraction fraction

 - -cm- - - - - - - - - - - -percent- - - - - - - - - - -

Holocene 5 85.1 8.9 6.1

10 85.1 7.9 7.0

30 80.0 10.2 9.8

60 78.7 12.4 8.9

Late Pleistocene 5 81.3 11.1 7.7

10 77.4 12.4 10.2

30 77.4 12.0 10.5

60 77.4 12.4 10.2

Mid-Pleistocene 5 74.8 12.1 13.1

10 76.1 11.2 12.7

30 62.0 12.7 25.3

60 45.6 15.6 38.8

unavailable. Total monthly precipitation at the Holocene

from November 1998 through September 2000 is presented

in fig. 2 Winter and spring precipitation was relatively

light before the 1999 and 2000 growing seasons, likely

resulting in dry soil conditions before the onset of monsoonal precipitation.

There was no relationship between tree height and leaf

water potential at any of the sites for either year, thus, data

for all size classes were pooled. Predawn leaf water potentials differed between the 1999 and 2000 growing seasons

and across geomorphic surfaces (significant year-by-surface

effect F3,666 = 44.44, P < 0.001 from MANOVA), particularly

during the early monsoon and postmonsoon periods (fig. 3a

and b). Seasonal values of y pd were more similar between

years on the mid-Pleistocene surface compared to either of

the other surfaces; mean y pd values on the mid-Pleistocene

surface ranged from near –1 to –2 MPa during both years

(fig. 3a and b). Predawn water potential on the Holocene

surface was lower before the 1999 and 2000 monsoon seasons, and after the 2000 monsoon than on the other two

surfaces, indicating a much greater water deficit on the

Holocene surface during these periods. Conversely, y pd

was significantly higher on the Holocene and late Pleistocene surfaces relative to the mid Pleistocene during the

1999 monsoon. Mean y pd on the Holocene surface ranged

from less than –4 MPa before both monsoon seasons to

greater than –1 MPa during the 1999 monsoon and late

monsoon of 2000. Early monsoon values of mean y pd in

2000 were significantly lower than in 1999 on the Holocene

and late Pleistocene surfaces due to the lower rainfall in

2000 during the early monsoon period.

The seasonal pattern of y md was similar to that of y pd

in 2000. Again, the lowest values at all sites were observed

before the onset of the monsoon. Mean y md was lowest

before and after the monsoon on the Holocene surface,

followed by the late Pleistocene and mid-Pleistocene surfaces, respectively (fig. 4). The mesquite plants on the midPleistocene surface showed little change in y md after the

onset of the monsoon, and differed by less than 1 MPa

throughout the year.

Pulses of monsoon precipitation can be extremely heterogeneous both spatially and temporally. We therefore can not

discount the possibility that there were differences in the

amount of monsoon precipitation among the three sites in a

given year. However, winter precipitation is much less

variable at this spatial scale such that differences in

premonsoon y pd among the sites were likely related to

differences in the hydraulic properties of the three geomorphic surfaces. As soils dry, air spreads through irregular

pore spaces, and soil water potential ( ) y s declines causing

a reduction in soil hydraulic conductivity (ks). The lower that

ks becomes, the ability for plant roots to extract water from

soil pores decreases. The relationship between y s and ks is

not constant across soil textures; coarse soils with large pore

spaces have high saturated ks, but demonstrate a much more

abrupt decline in ks with y sthan finer textured soils (Jury

and others 1991). The relatively sandy soil textures on the

late Pleistocene and particularly on the Holocene surface

suggests that plants at these sites will exhaust their water

supplies much more quickly than plants on the mid-Pleistocene surface, and will become water stressed more rapidly

as soils dry between precipitation pulses compared to plants
128 USDA Forest Service Proceedings RMRS-P-30. 2003

Fravolini, Hultine, Koepke, and Williams Role of Soil Texture on Mesquite Water Relations and Response to Summer Precipitation

on the mid Pleistocene surface (Sperry and others 1998). On

the other hand, the high ks of coarse-textured soils may

explain why y pd was slightly higher on the Holocene and

Late Pleistocene surfaces relative to the mid-Pleistocene

during the 1999 monsoon season. The above average rainfall

during the 1999 monsoon likely included enough large

events to saturate the soils within the rooting zone (fig. 1),

thereby enhancing the water status of mesquite plants on

the coarse-textured surfaces that have higher saturated

hydraulic conductivities (ks) relative to that of the midPleistocene surface. Regional climate change favoring greater

precipitation would disproportionately favor the establishment and productivity of mesquite occurring on coarsetextured than on finer textured soils.

Plants in these regions must be adapted to sufficiently

utilize short and infrequent pulses of growing season precipitation. During large pulse events, saturated ks is quickly

achieved in coarse-textured soils asy s approaches zero.

Month

Monthly precipitation (mm)

0

50

100

150

200

250

Nov-98 Jan-99 Mar-99 May-99 Jul-99 Sep-99 Nov-99 Jan-00 Mar-00 May-00 Jul-00 Sep-00

1999

 Predawn Leaf Water Potential (MPa)

-5

-4

-3

-2

-1

0

Holocene 

late Pleistocene 

mid Pleistocene 

2000

pre-monsoon early-monsoon late-monsoon post-monsoon pre-monsoon early-monsoon late-monsoon post-monsoon

a b

Figure 2—Total monthly precipitation measured at the Santa Rita Experimental Range between November 1998

and September 2000.

Figure 3—The time course of predawn leaf water potentialy pd of mesquite trees across three different

aged soils during the wetter monsoon season 1999 (a) and the drier 2000 (b) on the SRER. Error bars indicate

± one standard error.
USDA Forest Service Proceedings RMRS-P-30. 2003 129

Role of Soil Texture on Mesquite Water Relations and Response to Summer Precipitation Fravolini, Hultine, Koepke, and Williams

However, as stated above, coarse-textured soils show a rapid

decline in ks withy s during periods of drought. Consequently, plants occurring on coarse soils tend to optimize

their utilization of short-duration pulses by increasing their

root area per leaf area ratio, show a greater vertical rooting

distribution, and have a greater xylem hydraulic conductance relative to plants on finer textured soils (Sperry and

others 2002). Having more root area to absorb water relative

to leaf area reduces the rate of water uptake, and subsequent

drop in ks in the rooting zone, thereby delaying severe plantwater deficits that quickly occur in coarse-textured soils

(Hacke and others 2000). Likewise, plants in drought-stressed

environments tend to develop deep root systems to forage for

water in deep soil layers (Cannedell and others 1998; Jackson and others 1996). Indeed, mesquite plants at the SRER

do utilize water from deeper soil layers on the Holocene than

on the mid-Pleistocene surface (Fravolini, unpublished data),

strongly suggesting that this species develops and maintains deeper root systems on coarser textured soils.

Leaf water potential of mesquite on the SRER shows that

soil morphology likely plays a key role in plant water status

and may have important consequences for patterns of growth

and productivity across the SRER. Current and future work

on the SRER will address the impacts of soil texture and

climate on the water status, recruitment, and productivity of

mesquite plants.

References ____________________

Adams, D. K.; Comrie, A. C. 1997. The North American Monsoon.

Bulletin of American Meteorological Society. 10: 2197–2213.

Bristow, K. L.; Campbell, G. S.; Calissendorf, C. 1984. The effects of

texture on the resistance to water movement within the rizosphere.

Journal of Soil Science Society of America. 42: 657–659.

Canadell, J.; Jackson, R. B.; Ehleringer, J. R.; Mooney, H. A.; Sala,

O. E.; Schulze, E. D. 1996. Maximum rooting depth of vegetation

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plant water relations in a Mojave Desert mixed shrub community: a comparison of three geomorphic surfaces. Journal of Arid

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Midday 2000

Water Potential (MPa)

-7

-6

-5

-4

-3

-2

Holocene 

late Pleistocene 

mid Pleistocene 

pre-monsoon early-monsoon late-monsoon post-monsoon

Figure 4—The time course of midday leaf water

potential ( ) y md of mesquite trees measured

during the 2000 (drier) monsoon season across

three different aged soils in the SRER. Error bars

indicate ± one standard error.
130 USDA Forest Service Proceedings RMRS-P-30. 2003

Stacy Pease

Peter F. Ffolliott

Leonard F. DeBano

Gerald J. Gottfried

Mesquite Removal and Mulching

Treatment Impacts on Herbage Production

and Selected Soil Chemical Properties

Stacy Pease, Peter F. Ffolliott, and Leonard F. DeBano are Research Assistant and Professors, University of Arizona, Tucson. Gerald J. Gottfried is Research

Forester, Rocky Mountain Research Station, USDA Forest Service, Phoenix, AZ.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

Increases in woody plants such as mesquite have been a long-time concern of rangeland managers and livestock producers

in the Southwestern United States because this encroachment has often reduced herbage production and, therefore, livestock

production (Heitschmidt and Dowhower 1991; Herbel and others 1983; Laxson and others 1997; Martin and Morton 1993). The

encroachment of mesquite onto otherwise productive rangelands has been attributed to earlier overgrazing by livestock,

reduced frequency of large-scale wildfire, changes in chemical, biological, and physical properties of the soils, and changes in

climatic patterns (Herbel 1979; Martin 1975; McPherson 1997). One reason for establishment of the Santa Rita Experimental

Range was to study methods of restoring depleted rangeland conditions brought about by earlier heavy livestock grazing.

Among these strategies was improving rangeland conditions by controlling the invasion of mesquite.

The intent of this study was to determine the changes in herbage production (standing biomass) and selected soil chemical

properties that might affect herbage production in response to mesquite removals with and without the control of the

resulting regrowth of stump sprouts, the addition of mulching, or combinations thereof. Information of this kind could be

incorporated into management practices to enhance the productivity of semidesert grass-shrub rangelands in the future.

Preliminary results of the effects of mesquite removal and mulching treatments on herbage production were reported by

Pease and others (2000).

Abstract: Determining the effects of mesquite (Prosopis velutina) overstory removal, posttreatment control of sprouting, and mulching treatments on herbage production (standing

biomass) and selected soil chemical properties on the Santa Rita Experimental Range were the

objectives of this study. Mesquite control consisted of complete overstory removals with and

without the control of the resulting regrowth of stump sprouts. The mulching treatments were

applications of mesquite wood chips, commercial compost, and lopped-and-scattered mesquite

branchwood. Herbage production was estimated in the spring and early fall to determine total

annual production and the production of early growers and late growers. Mesquite removal

resulted in increases in herbage production. Mesquite removal had no effect on the soil chemical

properties considered. The mulching treatments did not have an affect on herbage production,

although a few of the soil chemical properties were affected by some of the mulching treatments.

Keywords: mesquite removal, mulching treatments, herbage production, soil chemical properties

Acknowledgments: The authors gratefully acknowledge the reviews of this paper by William H.

Kruse, USDA Forest Service (retired), Flagstaff, AZ, and George T. Robertson, USDA Forest

Service, Phoenix, AZ.
USDA Forest Service Proceedings RMRS-P-30. 2003 131

Mesquite Removal and Mulching Treatment Impacts on Herbage Production and... Pease, Ffolliott, DeBano, and Gottfried

Description of Study ____________

The study area was located within the Desert Grassland

Enclosure on the Santa Rita Experimental Range, an area

that had not been grazed by livestock for 70 years or more.

Descriptions of the climate, soils and other physiographical

features, and vegetation of the Experimental Range are

presented elsewhere in these proceedings. Within the study

area, mesquite dominates the woody overstory, and Lehmann

lovegrass (Eragrostis lehmanniana), an introduced species

that was initially planted on the Experimental Range in

1937 (Cable 1971; Cox and Roundy 1986; Ruyle and Cox

1985), dominates the herbaceous understory vegetation.

Native herbage species include Eriogonum wrightii, Solanum

elaegnifolium, and Gnaphalium purpureum, while common

annual species are Chenopodium album, Eschscholtzia

mexicana, and Descurainia pinnata. There are two growing

seasons for the herbaceous plants. One season is early

spring when temperatures and antecedent soil moisture are

favorable, while the other is late summer or early autumn in

response to summer rains.

Study Design and Treatments

The study design consisted of 60 5- by 5-m plots containing

a mesquite tree or shrub with a minimum 1-m buffer between the plots. The plots were blocked on the basis of

information from a pretreatment mesquite overstory inventory that indicated the structure and size of the mesquite

tree or shrub in the plot. Treatments were then randomly

assigned to the plots. The treatments, applied in early July

1995, consisted of three overstory treatments and four

mulching treatments within each of the overstory treatments. Each combination of overstory treatment and mulching treatment was replicated five times. The three overstory

treatments were complete removal of the mesquite overstory with and without the control of the resulting regrowth

of stump sprouts by hand cutting in July 1997 and an

untreated control. The mulching treatments included applications of a chip mulch, a commercial compost, lopped-andscattered mesquite branchwood, and a control. The chip

mulch, obtained from chipping the cut mesquite branchwood,

was uniformly distributed on the plots to a depth of 15 to 25

mm. The commercial compost was fir based with 0.5 percent

nitrogen, 0.1 percent iron, and 0.2 percent sulfur. Approximately 0.25 m3 of the compost was applied to the plots. The

lopped-and-scattered mesquite branchwood was spread to

completely cover the plot.

Data Collection and Analysis

Herbage production was estimated biannually (spring

and fall) in May and October from 1995 through 1999 by the

weight-estimate method of sampling described by Pechanec

and Pickford (1937) on 0.89-m2 plots. The herbage samples

were dried, separated by plant species, weighted, and extrapolated to kilograms per hectare. Selected soil chemical

properties were sampled annually from May 1995 through

1998. A composite of 12 subsamples was obtained from the

top 5 cm of the soil on each plot. The soil samples were

collected along a diagonal transect situated across the plots

with 0.3 m between the subsamples. The samples were

analyzed for total nitrogen, nitrate, total organic carbon,

total phosphorus, plant available phosphorus (Olsen phosphorus), and pH at the Soil, Water, Plant Analysis Laboratory of the University of Arizona, Tucson. These chemical

soil properties were selected to provide the basis for a

comparative analysis of a counterpart investigation in northern Israel on controlling shrub cover to increase grass

productivity (Perevolotsky and others 1998).

Precipitation (mostly rainfall) was measured by a standard weighing gage located near the desert grassland enclosure. It was assumed that precipitation affecting early

spring (early) growers fell from November through May,

while the precipitation that fell from June through October

impacted the late summer-early autumn (late) growers.

Analyses of variance were conducted to determine whether

significant differences occurred in herbage production and

the selected soil chemical properties among the overstory

removal and/or mulching treatments. Herbage production of

early growers and late growers was analyzed separately.

Tukey-Kramer HSD was used to determined which

treatment(s) had significantly different effects on herbage

production. All statistical analyses were evaluated at a 0.10

level of significance.

Results and Discussion _________

Herbage Production

Total herbage production averaged 1,896 + 115 kg per ha

per year (mean + standard error) from 1995 to 1999 on the

plots receiving the two mesquite overstory treatments, and

1,554 + 94 kg per ha per year on the control plots. The posttreatment control of resprouting did not significantly affect

total herbage production. Reduced competition between

mesquite and herbaceous plants for soil moisture likely

contributed to the increased total herbage production on the

treated plots. However, the observed increase was less than

that reported in earlier studies of herbage responses to the

removal of mesquite overstories (Herbel and others 1983;

Heitschmidt and Dowhower 1991; Laxson and others 1997;

Martin and Morton 1993.

The mesquite overstory removal treatments had no significant effect on the production of early growers, a finding

that was largely attributed to the (48 percent) below-average precipitation in the period of this growing season.

However, the production of late growers on the plots with

mesquite removal and no post-treatment control of sprouting was greater (1,278 + 89 kg per ha per year) than either

the plots with overstory treatment and post-treatment control of sprouting or the control; the production of late growers

was statistically the same (1,042 + 69 kg per ha per year) on

these latter plots. The shade provided by the resprouting

mesquite might have been a causal factor for this observed

increase (Shreve 1931; Tiedemann 1970).

The mulching treatments had no impact on total annual

herbage production or the production of early or late growers. This result was attributed to the below average amounts

of annual precipitation in the 5-year study period and, to

some extent, the possibility that inadequate levels of mulch

were applied to affect soil moisture availability. Biedenbender
132 USDA Forest Service Proceedings RMRS-P-30. 2003

Pease, Ffolliott, DeBano, and Gottfried Mesquite Removal and Mulching Treatment Impacts on Herbage Production and...

and Roundy (1996) suggested that mulching treatments

might not sufficiently affect soil moisture availability and,

as a consequence, the establishment and growth of herbage

plants in periods of low and infrequent rainfall.

Interaction effects between the overstory and mulching

treatments on total herbage production and the production

of early or late growers were all insignificant.

Soil Chemical Properties

The overstory removal treatments had no effect on the soil

chemical properties evaluated. A decline in nutrient availability 13 years following the removal of mesquite on the

Experimental Range was observed by Klemmedson and

Tiedemann (1986). However, the duration of this current

study might not have been of sufficient length to adequately

reflect the impacts of mesquite removal on the soil chemical

properties evaluated.

The mulching treatments had no significant effects on

nitrate, total organic carbon, or total phosphorus of the soil,

but these treatments did affect total nitrogen, plant available phosphorus, and pH. Total nitrogen was higher on the

lopped-and-scattered plots than the control plots. The plots

receiving the compost and chipped mulch had a higher pH

than the control plots. There was a negative correlation

between pH and plant available phosphorus on the plots

with the compost and chipped mulches. These changes in

soil chemical properties were small in their magnitude,

however, and their impacts on herbaceous plant growth is

unknown.

Conclusions___________________

This study was conducted in a 5-year period of prolonged

drought. The departures of 30 percent or more in average

annual precipitation in the study period might have masked

the treatment effects on annual herbage production and the

selected soil chemical properties. Further investigation of

the effects of mesquite removal and mulching treatments on

herbage production and soil chemical properties is necessary to more completely evaluate the affects observed in this

study. Nevertheless, information such as that presented in

this paper can be useful to managers in attempting to

enhance the productivity and stewardship of semidesert

grass-shrub rangelands.

References ____________________

Biedenbender, S. H.; Roundy, B. A. 1996. Establishment of native

semidesert grasses into existing stands of Eragrostis lehmanniana

in southern Arizona. Restoration Ecology. 2: 155–162.

Cable, D. R. 1971. Lehmann lovegrass on the Santa Rita Experimental Range. Journal of Range Management. 24: 17–21.

Cox, J. R.; Roundy, G. B. 1986. Influence of climatic and edaphic

factors on the distribution of Eragrostis lehmanniana in Arizona,

U.S.A. Journal of the Grassland Society of South Africa. 3: 25–29.

Heitschmidt, R. K.; Dowhower, S. L. 1991. Herbage response following control of honey mesquite within single tree lysimeters.

Journal of Range Management. 44: 144–149.

Herbel, C. H. 1979. Utilization of grass- and shrublands of the

south-western United States. In: Walker, B. H., ed. Management

of semi-arid ecosystems. Amsterdam, The Netherlands: Elsevier

Scientific Publishing Company: 161–203.

Herbel, C. H.; Gould, W. L.; Leifeste, W. F.; Gibbens, R. P. 1983.

Herbicide treatment and vegetation response to treatments of

mesquites in southern New Mexico. Journal of Range Management. 36: 149–151.

Klemmedson, J. O.; Tiedemann, A. R. 1986. Long-term effects of

mesquite removal on soil characteristics. II. Nutrient availability. Soil Science Society of America Journal. 50: 476–480.

Laxson, J. D.; Schacht, W. H.; Owens, M. K. 1997. Above-ground

biomass yields at different densities of honey mesquite. Journal

of Range Management. 50: 550–554.

Martin, S. C. 1975. Ecology and management of Southwestern

semidesert grass-shrub ranges: the status of our knowledge. Res.

Pap. RM-156. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment

Station. 38 p.

Martin, S. C.; Morton, H. L. 1993. Mesquite control increases grass

density and reduces soil loss in southern Arizona. Journal of

Range Management. 46: 170–175.

McPherson, G. R. 1997. Ecology and management of North American savannas. Tucson: University of Arizona Press. 208 p.

Pease, S.; Ffolliott, P. F.; DeBano, L. F.; Gottfried, G. J. 2000.

Effects of mesquite control and mulching treatments on herbage

production on semiarid shrub-grasslands. In: Ffolliott, P. F.;

Baker, M. B., Jr.; Edminster, C. B.; Dillon, M. C.; Mora, K. L.,

tech. coords. Land stewardship in the 21st century: the contributions of watershed management. Proc. RMRS-P-13. Fort Collins,

CO: U.S. Department of Agriculture, Forest Service, Rocky

Mountain Research Station: 265–267.

Pechanec, J. F.; Pickford, G. D. 1937. A weight estimate method for

determination of range or pasture production. Journal of the

American Society of Agronomy. 29: 894–904.

Perevolotsky, A.; Schwartz, R.; Hadar, L.; Yonatan, R. 1998. Controlling shrub cover and increasing grass productivity in semiarid environments. Bet Dagan, Israel: Agricultural Research

Organization. 12 p.

Ruyle, G. B.; Cox, J. 1985. Lehmann lovegrass—a naturalized

citizen. Arizona Farmer Stockman. 51(4): 26.

Shreve, F. 1931. Physical conditions in sun and shade. Ecology. 12:

96–105.

Tiedemann, A. R. 1970. Effect of mesquite (Prosopis juliflora) trees

on herbaceous vegetation and soils in the desert grassland. Tucson:

University of Arizona. 159 p. Dissertation.
USDA Forest Service Proceedings RMRS-P-30. 2003 133

Alvin L. Medina

Gambel and Scaled Quail Diets on the

Santa Rita Experimental Range

Alvin L. Medina is a Research Ecologist with the Rocky Mountain Research Station at the Southwest Forestry Sciences Laboratory in Flagstaff, AZ. He completed

B.S. and M.S. degrees in wildlife management at New Mexico State University. He has extensive field experience in range and wildlife management, having

previously worked for the Colorado Division of Wildlife, Bureau of Land Management, and USDA Forest Service.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

Diets of Gambel (Lophortyx gambelii Gambel) and scaled quail (Callipepla squamata Vigors) have been described for

portions of Texas (Ault and Stormer 1983; Campbell-Kissock and others 1985), Oklahoma (Schemnitz 1961), New Mexico ( Best

and Smartt 1985; Campbell and others 1973; Davis and Banks 1973; Davis and others 1975; Schemnitz and others 1997),

Arizona (Kelso 1937), and the Santa Rita Experimental Range (Hungerford 1960). These studies were seasonal, typically only

fall and winter, or were conducted in habitats different from those available to scaled quail on SRER. Continuous study of quail

diets across seasons and years were first reported by Medina (1988) for scaled quail.

The objective of this research was to compare the amounts and kinds of foods consumed by Gambel and scaled quail in

southern Arizona across seasons for 2 successive years. Additional information on the gonadal cycle and endoparasites was

also collected. The importance of maintaining diverse plant communities as it relates to quail habitats and livestock grazing

is discussed.

Study Area _______________________________________________________

The study was conducted on the Santa Rita Experimental Range (SRER) in Pima County, Arizona. The study area was

described in detail by Martin and Reynolds (1973), but considerable changes in herbaceous vegetation have occurred in the

last 40 years. Lehmann’s lovegrass (Eragrostis lehmanniana Nees) was sown as a reseeding treatment in the 1950s. Spread

by seed, it has become the dominant graminoid in areas of mid to high elevation (Cox and Ruyle 1986; Medina 1986). Vegetation

on the range is dominated by stands of velvet mesquite (Prosopis juliflora), cholla cactus (Opuntia fulgida, O. spinosior, and

O. versicolor), prickly pear cactus (O. engelmanni), burroweed (Haplopappus tenuisectus), acacia (Acacia spp.), and mimosa

(Mimosa spp.). Various native grass species including three-awn (Aristida spp.), grama (Bouteloua spp.), bush muhly

(Muhlenbergia porteri), and Arizona cottontop (Trichachne californica) persist (Medina 1988). Plant nomenclature follow

USDA, NRCS (2002).

Abstract: Diets of Gambel (Lophortyx gambelii Gambel) and scaled quail (Callipepla squamata

Vigors) from 1982 to 1984 were examined on the Santa Rita Experimental Range in southern

Arizona. Quail selected some foods yearlong and others on a seasonal basis, but exhibited a

preference for the seeds and leaves of forbs and insects. Seeds of bristlegrasses were selected

primarily during winter. Gonadal development was strongly associated with the availability of

spring forbs. Forbs were most common in areas frequented by cattle in native range pastures, and

nearly absent from Lehmann lovegrass (Eragrostis lehmanniana Nees) habitats. Gambel quail

exhibited an affinity for desert hackberry (Celtis pallida) as resting cover, while scaled quail were

most often associated with grassland habitats with bunchgrasses. The management implications

of cattle, quail, and Lehmann’s lovegrass interactions are discussed.

Acknowledgments: A debt of gratitude is expressed to Robert Lee Mays, Penny Medina, Scott

Medina, and Joyce Medina for contributing countless hours of volunteer work. Mr. Mays’ technical

expertise in plant identification and collection provided the basis for all the plant work involved

in this study.
134 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Gambel and Scaled Quail Diets on the Santa Rita Experimental Range

The Santa Rita Experimental Rane is situated on a broad

sloping bajada interspersed by numerous dry washes. Elevations range from 885 to 1,370 m. Average rainfall ranges

from 25 cm at 885 m to approximately 51 cm at 1,370 m.

Precipitation for the study period 1982 to 1984 was similar

to the 43-year mean. The frost-free period is approximately

8 months, but growth of herbaceous plants is limited by

drought during May and June. Sixty percent of annual

rainfall occurs between 1 July and 30 September (Medina

1988).

Methods ______________________

Detailed crop analyses were described in Medina (1988).

Quail were collected each month with a shotgun from September 1982 through December 1984. Some quail were collected

by hunters during quail hunting seasons and their attributes

were noted. Individual quail were identified by sex, age, and

species, and their total body weights recorded. Diets (table 1)

were assessed by analysis of crop contents that were ovendried.

Abutilon berlandieri Gray ex S. Wats. ABBE

Acacia angustissima (P. Mill.) Kuntze ACAN

Acacia constricta Benth. ACCO2

Acacia greggii Gray ACGR

Acalypha neomexicana Muell.-Arg. ACLO2

Acleisanthes longiflora Gray ACNE

Amsinckia douglasiana A. DC. AMDO

Argemone pleiacantha Greene ARPL3

Aristolochia watsonii Woot. & Standl. ARWA

Astragalus allochrous Gray var. playanus Isely ASALP

Astragalus nuttallianus DC. ASNU4

Astragalus tephrodes Gray ASTE8

Baileya multiradiata Harvey & Gray ex Gray BAMU

Boerhavia intermedia M.E. Jones BOIN

Boerhavia spicata Choisy BOSP

Calliandra eriophylla Benth. CAER

Carlowrightia arizonica Gray CAAR7

Celtis pallida Torr. CEPA8

Cerastium brachypodum (Engelm. ex Gray)

 B.L. Robins. CEBR

Cerastium glomeratum Thuill. CEGL2

Cerastium nutans Raf. CENU2

Chamaesyce maculata (L.) Small CHMA15

Chamaesyce melanadenia (Torr.) Millsp. CHME5

Chamaesyce prostrata (Ait.) Small CHPR

Chamaesyce serrula (Engelm.) Woot. & Standl. CHSE7

Chenopodium album L. CHAL7

Croton glandulosus L. CRGL

Cryptantha nevadensis A. Nels. & Kennedy CRNE

Dalea aurea Nutt. ex Pursh DAAU

Daucus carota L. DACA6

Daucus pusillus Michx. DAPU3

Descurainia pinnata (Walt.) Britt. DEPI

Digitaria sanguinalis (L.) Scop. DISA

Erodium botrys (Cav.) Bertol. ERBO

Eschscholzia californica Cham. ESCA2

Eschscholzia californica Cham. ssp. mexicana

 (Greene) C. Clark ESCAM

Euphorbia marginata Pursh EUMA8

Ferocactus wislizeni (Engelm.) Britt. & Rose FEWI

Galactia wrightii Gray GAWR

Ipomoea capillacea (Kunth) G. Don IPCA2

Ipomoea coccinea L. IPCO3

Ipomoea eriocarpa R. Br. IPER

Ipomoea plummerae Gray IPPL

Kallstroemia grandiflora Torr. ex Gray KAGR

Lotus humistratus Greene LOHU2

Lotus rigidus (Benth.) Greene LORI3

Lotus salsuginosus Greene LOSA

Lotus strigosus (Nutt.) Greene var. tomentellus

 (Greene) Isely LOST4

Lotus wrightii (Gray) Greene LOWR

Lupinus sparsiflorus Benth. LUSP2

Lygodesmia grandiflora (Nutt.) Torr. & Gray LYGR

Machaeranthera tanacetifolia (Kunth) Nees MATA2

Menodora scabra Gray MESC

Mimosa dysocarpa Benth. MIDY

Mollugo verticillata L. MOVE

Monolepis nuttalliana (J.A. Schultes) Greene MONU

Opuntia engelmannii Salm-Dyck OPEN3

Panicum capillare L. PACA6

Panicum hallii Vasey var. hallii PAHAH

Panicum hirticaule J. Presl PAHI5

Parkinsonia microphylla Torr. PAMI5

Penstemon pseudospectabilis M.E. Jones PEPS

Phaseolus ritensis M.E. Jones PHRI

Physalis crassifolia Benth. PHCR4

Plagiobothrys arizonicus (Gray) Greene ex Gray PLAR

Plagiobothrys pringlei Greene PLPR3

Polanisia dodecandra (L.) DC. ssp. trachysperma

 (Torr. & Gray) Iltis PODOT

Portulaca oleracea L. POOL

Portulaca pilosa L. POPI3

Proboscidea parviflora (Woot.)

 Woot. & Standl. PRPA2

Prosopis juliflora (Sw.) DC. PRJU3

Rumex hymenosepalus Torr. RUHY

Salsola tragus L. SATR12

Salvia columbariae Benth. SACO6

Setaria grisebachii Fourn. SEGR6

Setaria viridis (L.) Beauv. SEVI4

Sida spinosa L. SISP

Silene antirrhina L. SIAN2

Solanum douglasii Dunal SODO

Solanum heterodoxum Dunal var. setigeroides M.D.

 Whalen SOHES

Stephanomeria spinosa (Nutt.) S. Tomb STSP6

Talinum paniculatum (Jacq.) Gaertn. TAPA2

Tetramerium nervosum Nees TENE

Torilis nodosa (L.) Gaertn. TONO

Tragopogon porrifolius L. TRPO

Urochloa arizonica (Scribn. & Merr.) O. Morrone

 & F. Zuloaga URAR

Verbesina encelioides (Cav.) Benth.

 & Hook. f. ex Gray VEEN

Vicia hassei S. Wats. VIHA3

Yeatesia platystegia (Torr.) Hilsenb. YEPL

Ziziphus obtusifolia (Hook. ex Torr. & Gray)

 Gray var. obtusifolia ZIOB

Table 1—List of principal plants comprising the diets of Gambel and scaled quail on the Santa Rita Experimental Range.

Scientific name Plant code Scientific name Plant code
USDA Forest Service Proceedings RMRS-P-30. 2003 135

Gambel and Scaled Quail Diets on the Santa Rita Experimental Range Medina

Individual foods were weighed and measured volumetrically

by water displacement to nearest 0.1 ml. Seed identification

was facilitated by an extensive seed collection (589 species)

from the area, use of manuals (Martin 1946; Martin and

Barkley 1961; Musil 1963; USDA Forest Service 1974), and

identification of plants germinated from seeds found in

samples. Herbage and insect material were treated separately. Data were initially expressed by the aggregate volume

method (Martin and others 1946) and then summarized in

terms of frequency of occurrence (table 2). Results were

summarized on a seasonal basis (winter = December through

February, spring = March through May, summer = June

through August, fall = September through November). Diets

are presented as percent of occurrence across seasons and

years. Simple measures of statistics were used to illustrate

diet selection between quail species. Means and their standard deviations are provided to illustrate diet variability.

Constancy was used as a measure of the relative occurrence

of an individual food across the sample period. Foods selected

in all seasons have high constancy.

Seasonal condition of quail gonads were recorded by

measuring the length, width, and volume of testes. Birds

were refrigerated and processed within 6 hours of collection.

It is well established that testis size is proportional to

testicular activity in birds. In females, the size (volume) of

enlarging follicles was used as a measure of ovarian activity.

Ovary and testis color were also determined. Observations of

general health conditions, for example, endoparasites, were

also noted.

Results _______________________

Over the 2-year period, 512 crops were analyzed: 61 adultscaled females, 15 immature (less than 1-year-old) females,

60 adult males, and 26 immature males; 104 Gambel adult

females, 46 immature, 161 adult males, and 39 immature

males. Seeds of 88 plant taxa (table 1) were identified in the

crops: 18 woody plants, 64 herbaceous plants, and 6 grasses.

Seeds averaged the highest mean frequency of occurrence

(67 percent) of all food categories followed by green herbage

(6.7 percent), insects (5 percent), gravel (3.4 percent), and

miscellaneous.

Forb seeds were selected with 2.7 and 4.5 times greater

frequency than woody and grass seeds, respectively (table 2).

Consumption of forb seeds exceeded woody plant seeds during

most collection periods. Grass seeds were selected with greater

frequency by both quails over forb seeds during the fall

seasons, and Gambel selected them about 3 times more than

scaled (table 3). Gambel quail generally selected seeds of

woody plant more than scaled.

Seeds that averaged high constancy and high mean frequency across seasons included smallflowered milkvetch

(Astragalus nuttallianus), spiny hackberry (Celtis pallida),

spotted sandmat (Chamaesyce maculata), morningglory (Ipomoea eriocarpa), foothill deervetch (Lotus humistratus),

lupine (Lupinus sparsiflorus), spiny sida (Sida spinosa),

velvet mesquite, Grisebach’s bristlegrass (Setaria grisebachii), and green bristlegrass (Setaria viridis) (table 2) .

Other plant seeds that averaged high constancy (greater

than 87 percent) across seasons but with lower mean frequency of occurrence or lower constancy but higher mean

frequency of occurrence included crested pricklypoppy

(Argemone platyceras), spiderling (Boerhaavia intermedia),

lambquarters (Chenopodium album), Arizona carlowrightia

(Carlowrightia arizonica), Strigose bird-foot trefoil (Lotus

strigosus), pinnate tansymustard (Descurainia pinnata),

carpetweed (Mollugo verticillata), desert penstemon (Penstemon pseudospectabilis), sleepy silene (Silene antirrhina),

tetramerium (Tetramerium nervosum), panicum (Panicum

hirticaule), and yellow nightshade groundcherry (Physalis

crassifolia). Mesquite seeds were the dominant woody species selected. Morningglory seeds were selected more than

any other forb. Bristlegrasses were the most important

grasses yearlong.

Seasonal differences in quail diets were highly variable

(table 2) for many species. Seeds of some plants (for example,

Acacia constricta, Tragopogon porrifolius) became important in summer and fall, while others (for example, Baileya

multiradiata, Euphorbia marginata) were more important

in winter or spring. Green herbage and insects were important yearlong, and green herbage was especially important

in late winter. Both green herbage and insects were represented in 67 percent of all crops across all seasons. Ants,

beetles, and grasshoppers composed the bulk of insects

eaten.

Differences in diets between Gambel and scaled quail

were not apparent within or across seasons for individual

plants, but were evident across major food groups (tables 2

and 3). Foods may or may not be selected in any one season.

Individual foods with high constancy across seasons were

used in relatively the similar proportions within seasons.

However, some seasonal differences were evident at the

group level primarily for seeds of forbs and grasses (table 3).

Scaled quail selected seeds of forbs, grasses, and woody

plants 1.5 to 4 times less than Gambel quail in the summer

and fall. These differences were less apparent during the

winter and spring.

Differences in body weights between species, sex, and age

were unremarkable (table 4). Examination of seasonal body

weights also were unremarkable. Differences in body weights

of juveniles during the fall were noted and attributed to

collection times. The body weight of juveniles collected early

in the summer were less than those collected during the first

month of the fall season. This was verified from examination

of body weights across months for this group (table 5).

Male gonadal development initiated in early March with

onset of cool season herbage (primarily Erodium spp.),

peaked in late April to early May, remained active through

mid-July, decreased in September, and slightly increased in

October and November during hunting season (table 6).

Teste size and color ranged from small and white-gray

during periods of low activity to large and black during

developmental periods. Testes began to shrink in August,

attaining a stable volumetric size near 0.1 cc through the

winter. Ovary development in female quail initiated about

1 month earlier than teste development in males. Eggs were

laid primarily in May to June. Hatching of chicks occurred

primarily in June to July, but occasional eggs and chicks were

observed into August.

Nematodes were observed in 8.4 percent of all quail

examined, with a 3.7 percent occurrence in Gambel and 4.7

percent in scaled quail. Tapeworms (Gastrotaenia spp.) were

observed in 9 percent of all quail examined, with a 7 percent

occurrence in Gambel and 2 percent in scaled quail.
136 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Gambel and Scaled Quail Diets on the Santa Rita Experimental Range

Table 2—Frequency of food plants occurring in the diets of Gambel (G) and scaled (S) quail on the Santa Rita Experimental Range by season and

study period. Constancy refers to the occurrence of individual plants across seasons over the study period by quail species; average

is the mean frequency in percent across the period of study for all birds.

Plant Fall Winter Spring Summer Constancy

code G S G S G S G S G S Average

 - - - - - - - percent- - - - - - - - - -

ABBE 0.43 0.88 0.13 50 50 12.86

.60

ACAN .17 0.53 25 25 0.35

ACCO2 .86 .13 .67 50 50 .44

.09

ACGR .52 .88 .18 .40 .40 50 75 .48

ACLO2 .54 0 25 .54

ACNE .27 25 0 .27

AMDO .26 .53 .67 50 25 .49

ARPL3 .35 .29 .18 .36 .40 .40 100 75 .32

.26

ARWA .09 .29 .18 25 50 .20

.26

ASALP .27 0 25 .27

ASNU4 1.81 2.06 2.65 .89 1.25 1.74 .53 100 100 1.51

1.12

ASTE8 .60 25 0 .60

BAMU .29 .18 25 25 .24

BOIN 3.37 .29 3.34 .40 75 50 1.55

.35

BOSP .60 .29 .18 25 50 .33

.26

CAAR7 .09 .36 .89 .13 50 75 .33

.17

CAER .72 .36 .27 50 25 .45

CEPA8 2.59 .88 .54 .54 2.54 1.20 75 100 1.28

.69

CEBR .29 0 25 .29

CENU2 .09 25 25 .09

.09

CEGL2 .09 25 0 .09

CHAL7 1.97 25 0 1.97

CHMA15 2.94 .88 .59 .18 1.25 2.40 .27 100 100 1.16

.78

CHME5 .09 0 25 .09

CHPR .17 . .18 50 25 .32

.60

CHSE7 .09 .18 25 25 .14

CRGL .13 .40 25 25 .26

CRNE .13 25 0 .13

DAAU .29 0 25 .29

DACA6 .29 0 25 .29

DAPU3 .18 .27 25 25 .22

DEPI .09 1.77 2.06 3.58 3.04 25 75 2.11

DISA .09 25 0 .09

ERBO .13 .13 25 25 .13

ESCA2 .18 .40 .40 25 50 .33

ESCAM .17 .18 .54 25 50 .30

EUMA8 .29 .59 .36 .89 50 50 .53

FEWI .69 .29 .29 .36 50 50 .41

GAWR .09 .59 25 25 .34

IPCA2 .09 .13 50 0 .11

IPCO3 .09 .13 50 0 .11

IPER 2.68 2.95 3.54 .54 .54 1.07 100 75 1.85

1.64

IPPL .86 .18 25 25 .83

KAGR .26 .67 .40 50 50 .42

.35

LOHU2 3.71 1.18 2.95 2.33 4.65 2.54 1.47 100 100 2.53

1.38

LORI3 .26 .18 .18 .27 .27 75 75 .24

.26

LOSA .26 .59 .29 .89 1.25 .27 50 75 .59

LOST4 1.38 .88 1.18 1.07 1.79 .80 .27 100 100 .98

LOWR .26 .29 .72 .54 .40 50 75 .44

(Con.)
USDA Forest Service Proceedings RMRS-P-30. 2003 137

Gambel and Scaled Quail Diets on the Santa Rita Experimental Range Medina

Table 2—(Con.)

Plant Fall Winter Spring Summer Constancy

code G S G S G S G S G S Average

 - - - - - - - percent- - - - - - - - - -

LUSP2 2.42 1.47 .88 2.86 3.22 3.20 .67 100 100 1.93

.69

LYGR .95 1.60 .27 50 50 .73

.09

MATA2 .18 25 0 .18

MESC .26 25 0 .26

MIDY .27 25 0 .27

MONU .17 .59 .13 .27 50 50 .29

MOVE .69 .18 1.20 .53 50 50 .65

OPEN3 .09 .27 .27 50 25 .21

PACA6 1.04 2.40 .40 50 50 1.05

.35

PAHAH .18 25 0 .18

PAHI5 1.04 .59 .18 .72 1.34 .80 75 100 .72

.35

PAMI5 .36 1.25 .13 .13 50 50 .47

PEPS .35 2.06 1.18 .18 1.07 .13 75 100 .75

.26

PHCR4 .09 .29 .29 .36 .36 .27 100 75 .27

.26

PHRI .13 25 0 .1

PLAR .36 0 25 .36

PLPR3 .18 .59 .13 50 50 .25

.09

PODOT .18 1.07 50 0 .62

POOL .36 .27 50 0 .32

POPI3 .09 1.47 .53 50 50 .54

.09

PRJU3 4.40 6.78 1.18 3.04 2.86 4.67 1.87 100 100 3.23

1.04

PRPA2 .18 0 25 .18

RUHY .26 0 25 .26

SACO6 .09 .18 .13 50 25 .13

SATR12 .29 25 0 .29

SEGR6 3.63 .59 .59 .54 .36 3.74 .53 100 100 1.37

.95

SEVI4 6.13 1.18 .36 .54 4.81 2.14 75 100 2.36

1.38

SIAN2 .09 .59 .18 1.25 .27 50 75 .48

SISP 4.06 2.06 2.06 1.25 2.33 2.14 1.20 100 100 2.09

1.64

SODO .18 0 25 .18

SOHES .29 25 0 .29

STSP6 .69 25 0 .69

TAPA2 .09 .29 .27 75 0 .22

TENE 2.07 .29 .59 .54 1.07 .67 .67 100 100 .86

.95

TONO .17 .36 1.25 .40 50 50 .55

TRPO .17 .53 1.20 50 50 .58

.43

URAR .13 25 0 .13

VEEN .13 25 0 .13

VIHA3 .43 .13 50 25 .22

.09

YEPL .09 .29 .29 .27 50 50 .24

ZIOB .09 .53 50 0 .31

Bone .51 .88 1.07 .80 .13 100 75 .58

.09

Gravel 5.51 4.13 3.24 3.58 3.04 4.94 1.47 100 100 3.44

1.64

GreenVeg 7.34 14.16 7.56 7.12 6.80 6.01 2.27 100 100 6.7

2.32

Insect 5.11 5.90 5.13 6.03 7.16 5.47 3.34 100 100 5.05

2.25

DryVeg .60 1.18 1.18 1.07 .54 1.34 .80 100 100 .91

.60

Unknown .01 .18 .29 .01 .01 .01 .01 100 100 .07

.01

Total 73.7 55.5 44.5 44.9 55.1 69.2 30.8
138 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Gambel and Scaled Quail Diets on the Santa Rita Experimental Range

Table 4—Comparison of average body weights (g) by species, sex,

and age.

Class Gambel Scaled

Female, juvenile 123.3 + 42.4 123.7 + 51.4

Female, immature 159.4 + 21.1 175.8 + 23.6

Female, mature 169.7 + 17.6 173.4 + 22.4

Male, juvenile 121.0 + 46.8 71.2 + 59.3

Male, immature 164.9 + 18.9 183.0 + 9.8

Male, mature 169.8 + 13.7 186.7 + 13.2

Table 5—Mean body weights (g) with standard deviations indicated of Gambel and scaled quail sampled

on SRER by age class, season, and species. Sample sizes are given within parenthesis.

Season Juvenile Immature Mature

Fall

Gambel 154.9 + 16.8 (37) 168.8 + 11.7 (31) 169.9 + 9.4 (40)

Scaled 152.7 + 43.6 (11) 181.1 + 12.9 (12) 169.2 + 36.2 (15)

Winter

Gambel — 179.0 + 7.1 (2) 172.6 + 14.1 (45)

Scaled — — 178.4 + 14.1 (32)

Spring

Gambel — 165.2 + 23.4 (30) 175.3 + 16.9 (52)

Scaled — 185.3 + 20.0 (20) 185.1 + 9.6 (27)

Summer

Gambel 93.4 + 40.9 (42) 155.8 + 20.4 (38) 155.9 + 13.3 (30)

Scaled 63.4 + 36.3 (14) 170.2 + 13.5 (13) 184.9 + 15.5 (21)

Table 3—Frequency (percent) of seeds selected as foods for quail on the Santa Rita Experimental Range by life form. The total number of

plants selected by individual quail species are indicated by “N.”

Fall Winter Spring Summer

Seeds Gambel Scaled Gambel Scaled Gambel Scaled Gambel Scaled

Foods N 58 47 34 32 39 46 56 46

Forbs total percent 29.39 12.47 18.50 17.35 19.52 29.52 28.28 12.69

Grass total percent 11.84 3.03 0.59 2.36 1.26 1.62 12.42 3.87

Woody total percent 13.39 3.89 10.02 7.35 5.20 6.45 9.88 6.27

Seed total percent 54.19 18.79 29.11 26.18 25.98 37.59 50.45 22.83

Table 6—Monthly progression in teste and ovary

development of Gambel and scaled quail on

the Santa Rita Experimental Range. Values

are volume (cc) determinations.

Month Teste Ovary/egg

January <0.1 0.1

February <0.1 .7

March .7 1.8

April .9 1.7

May .8 6.2

June .5 .6

July .5 .2

August .2 .2

September .1 .2

October .2 .4

November .3 .4

December <0.1 .2
USDA Forest Service Proceedings RMRS-P-30. 2003 139

Gambel and Scaled Quail Diets on the Santa Rita Experimental Range Medina

Discussion and Management

Implications ___________________

Diets of both Gambel and scaled quail were similar to

those described by Campbell and others (1973), Davis and

others (1975), and Schemnitz and others (1997) in southern

New Mexico, Ault and Stormer (1983) in west Texas, and

Campbell-Kissock and others (1985) in southwest Texas.

Similarities included high selection of seeds of forbs, bristle

grass seeds, and woody plants. Selection of these species

over others perhaps resulted from conspicuous size of the

seeds (Davis and others 1975), high protein content (Earle

and Jones 1962; Jones and Earle 1966), and abundance

(Medina 1988). Differences between this study and those

from other states are attributed to differences in vegetation

composition, site influences, and climatic factors. Schemnitz

and others (1997) found Russian thistle and snakeweed seed

were highly preferred by both Gambel and scaled. Medina

(1988) attributed selection of succulent foods during drier

seasons is perhaps an adaptive strategy developed by scaled

quail in arid environments, as was observed by Wilson and

Crawford (1987). Differences in diets were most evident in

the relative greater quantities of forb and woody plant seeds

consumed by quail in Arizona and New Mexico than in some

areas in Texas. Differences in selection of various foods by

quail could also be attributed to methodology of food determination, plant species composition, availability, climatic

factors, individual preferences, sample size, or sampling

period (Medina 1988). Greater similarities in diets of scaled

quail were found between studies with similar methodologies and sampling periods. Seasonal studies tended to amplify the relative importance of individual species or group of

plants (for example, grasses).

Differences in diets between quail species could be attributed to differences in habitat selection. Scaled quail

were most abundant in habitats with low perennial grass

cover but high forb cover. Wash and disturbed habitats had

lowest perennial plant cover, highest annual plant cover,

and low effort ratios. In contrast, Lehmann’s lovegrass

habitats had highest perennial plant cover and lowest

annual plant cover (Medina 1988). Goodwin and Hungerford

(1977), Campbell and others (1973), and Campbell-Kissock

and others (1985) also reported avoidance of densely vegetated habitats by scaled quail and preference for habitats

that exhibited diversity in plant composition, structure,

and density. Apparent differences in selection of individual

foods within a season were attributed to local abundance of

such foods within the home range of respective coveys.

Results of this study revealed that seeds of forb plants

were consumed in higher proportions than any other food

item. This suggests that habitats that exhibit diverse plant

composition are selected by quail. Observations indicated

that scaled quail were most abundant on habitats with low

perennial grass cover and high forb cover (Medina 1988).

Gambel quail were most abundant on mesquite-shrub/grassland habitats. Lehmann’s lovegrass habitats were seemly

the least desirable habitat for both quail, given the high

percent grass cover and low forb cover. Goodwin and

Hungerford (1977), Campbell-Kissock and others (1985),

and Wilson and Crawford (1987) also reported avoidance of

densely vegetated habitats by scaled quail. Campbell and

others (1973), Davis and others (1975), and Campbell-Kissock

and others (1985) concluded that a moderately high degree

of diversity in plant composition and community structure

were conditions required for optimum scaled quail habitat.

The reproductive periods of the gonadal cycle were consistent with studies by Wallmo (1956). The quiescent period of

testicular activity was evident in September through February. Increase in size of testes was coincident with cool-season

herbage (March), which provides vitamins and other nutrients necessary for gonadal development (Hungerford 1964).

The quiescent period for ovarian activity was similar to

testicular activity but marked with a general decline (table

6) as early as July (September in Texas; Wallmo 1956). A

similar increase in testicular activity was noted during the

hunting season (October to November). This increase could

be a hormonal response to nutrient intake from green

herbage produced during late warm-season growth or increased activity due to hunting.

The investigation of endoparasites on SRER’s quail population were incidental to dietary and habitat studies. The

information is presented here to alert managers of their

incidence of occurrence. The prevalence and importance of

parasitic organisms (such as nematodes and tapeworms) in

southwestern quail has not been studied, rather most works

have dealt with bobwhite quail in areas of Southeastern and

Northeastern United States (Kocan and others 1979). Other

studies have also focused on Japanese quail, a species of

commercial significance. Kocan and others (1979) reported

the prevalence of nematodes and cestodes in Oklahoma

bobwhite quail to approximate 27 and 6 percent Statewide,

respectively. Boggs and others (1990) reported an incidence

of physalopterid nematodes in 5 of 64 bobwhite quail examined in Oklahoma. Heavy burdens of tapeworms may reduce

the vigor of the bird, occlude the intestines, and serve as a

predisposing factor for other diseases (Friend and Franson

1999). Nematode infection has been suggested as a factor

that may reduce fecundity within populations as well direct

chick mortality (Friend and Franson 1999).

The management implications of this work for quail populations suggest that rangelands should be managed to produce a diverse vegetative composition. It is also important to

note that key staple foods were those typically known as

weeds, invaders, or generally undesirable species. These

species typically establish on disturbed sites. On SRER

these microsites are mostly sustained by cattle grazing on

upland habitats. Hence, there appears to be a positive

interaction between cattle grazing and good quail habitats.

No evidence exists from cattle dietary studies (Galt and

others 1966; Medina, unpublished data) on SRER that

competition for foods is an issue. Galt and others (1982)

reported cattle diets on SRER as 67 to 97 percent grasses and

0 to 4 percent forbs. Very little dietary overlap was noted for

the principal food group—forbs. Secondly, range management goals have traditionally strived to achieve excellent

range conditions.

This study suggests that attainment of the latter conditions may not be desirable for sustaining quail populations.

Schemnitz and others (1997) concluded that moderate livestock grazing may be beneficial to desert quail by enhancing

the variety and abundance of forb plants. Smith and others

(1996) noted that sightings of scaled quail and other important game species were higher on rangelands classified as
140 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Gambel and Scaled Quail Diets on the Santa Rita Experimental Range

good than on excellent. They also recommend moderate

grazing practices. Livestock grazing on SRER over the past

century has included various grazing designs, including the

Santa Rita Grazing System, continuous, and high intensitylow duration. Here, livestock grazing could be used as a tool

for maintaining low seral plant communities and quail

habitat diversity.

Burning, intensive grazing, and other management practices that could provide a higher proportion of food plants

and perhaps a more diverse environment in lovegrass

stands are alternatives that should benefit scaled quail

populations in the area (Medina 1988). Furthermore, reseeding of native rangelands with Lehmann’s lovegrass

should be re-evaluated with respect to potential long-term

impacts on native flora and fauna. Scaled quail were most

prevalent in areas with early plant successional stages and

open habitats; hence, range management efforts that promote high successional plant communities should include

provisions for wildlife species associated with low seral

habitats. Vegetation treatments (for example, mesquite

removal, fire, grazing) on SRER have demonstrated that

Gambel and scaled quail habitat can be improved (Germano

1978; McCormick 1975).

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Game and Fish Commission Special Rep. W-57-R. Dallas: Texas

Game and Fish. 58 p.

Wilson, M. H.; Crawford, J. A. 1987. Habitat selection by Texas

bobwhites and chestnut-bellied scaled quail in south Texas.

Journal Wildlife Management. 51: 574–582.
USDA Forest Service Proceedings RMRS-P-30. 2003 141

Alvin L. Medina

Historical and Recent Flora of the Santa

Rita Experimental Range

Alvin L. Medina is a Research Ecologist with the Rocky Mountain Research Station at the Southwest Forestry Sciences Laboratory in Flagstaff, AZ; e-mail:

almedina@fs.fed.us. He completed B.S. and M.S. degrees in wildlife management at New Mexico State University. He has extensive field experience in range and

wildlife management, having previously worked for the Colorado Division of Wildlife, Bureau of Land Management, and the USDA Forest Service.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

The Santa Rita Experimental Range (SRER), established in 1903, is the oldest experimental range in the United States.

Much of our knowledge of Southwestern grassland ecosystems was derived from pioneering works on SRER (Medina 1996).

The Santa Rita continues to be an important research facility, with continuance of long-term plant and wildlife studies. Plant

collections from SRER include some of the oldest accessions in herbariums of the Southwest. However, there is no published

listing of the historical flora of SRER.

Early ecologists and range examiners (for example, David Griffiths, John Thornber) working on SRER, made plant

inventories throughout the Santa Rita Mountains, as well as compiled plant lists from individual range studies. John J.

Thornber made several collections throughout the region (Thornber 1909). Griffiths (1901, 1904, 1910) spent considerable time

on the SRER documenting range conditions and noting floristic conditions across seasons. Hence, the historical flora presented

herein is a compilation of floristic data from many plant studies, by many investigators, over the last century. A preliminary

list was initially compiled in 1906, and additions to the list were made periodically until the late 1940s. The master list was

used as a guide in plant studies. This checklist was compiled in tribute to all the scientists, naturalists, and botanists who

conducted research worked on SRER and in recognition of their contributions. Many of the works of these contributors are listed

in Medina (1996). Additions to the historical checklist include plant collections from quail studies (Medina 1988) and new

plants listed in the SRER Web site by the University of Arizona.

The Range _______________________________________________________

The Santa Rita Experimental Range consists of 53,159 acres about 35 miles south of Tucson in Pima County, Arizona. It lies

at the foot of the northwestern edge of the Santa Rita Mountains. It is characterized by small areas of steep, stony foothills

Abstract: The historical flora of the Santa Rita Experimental Range was composed from

historical lists of plants collected by various investigators since 1903. Plant accessions were

verified from lists of plant specimens housed at the Rocky Mountain Research Station herbarium

in Flagstaff, AZ, and the Rocky Mountain National Herbarium in Laramie, WY. Recent additions

(1980 to 1996) to the flora were from plant collections associated with wildlife and plant studies.

This list represents the most comprehensive and current inventory of plants found on the Range.

Acknowledgments: A debt of gratitude is expressed to all scientists who contributed to this

effort. A special appreciation goes to Dr. S. Clark Martin who dedicated most of his professional

career (more than 55 years) and retirement to conducting and organizing research, transferring

technology to ranchers, resource managers, and scientists, securing the integrity of historical

data and photo records, and assisting graduate students with their research. Another special

thanks to Robert Lee Mays who volunteer thousands of hours in assistance to the quail and plant

studies on the Santa Rita Experimental Range. Mr. Mays collected, identified, and indexed

many plant specimens for our herbariums. Additional thanks to Penny Medina, Scott Medina,

and Joyce Medina who provided considerable volunteer time to assist in plant accessions and

field data collection. Plant data from the Santa Rita Experimental Range Digital Database was

also used to make the plant list inclusive. Funding for the digitization of these data was provided

by USDA Forest Service, Rocky Mountain Research Station, and the University of Arizona.
142 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Historical and Recent Flora of the Santa Rita Experimental Range

and a few isolated buttes, but the greater part consists of

long, gently sloping alluvial fans. Upper fans slope rather

steeply and are cut by canyons and arroyos. At lower elevations, the slope diminishes to about 100 ft per mile, and

drainages become relatively shallow. Terraces, breaks, or

low escarpments and numerous gullies characterize some

parts of the lower range. Elevations range from 2,900 ft in

the northwestern corner to about 5,200 ft in the southeastern part. Average annual rainfall increases with elevation,

from 10 inches at 2,900 ft to almost 20 inches at 4,300 ft

(Medina 1996).

The soils are representative of those developed under

southwestern arid conditions. Most consist of, or developed

from, recent alluvial deposits. Three soil orders (Aridisols,

Entisols, and Mollisols) and 21 soil series have been described by Clemmons and Wheeler (1970). The soils present

an interesting range of characteristics due directly or indirectly to differences in elevation and proximity to the Santa

Rita Mountains. With greater elevation and proximity to the

mountains, rainfall increases, temperatures decrease, soils

are darker, soils have a higher content of organic matter, and

soils are more deeply leached of soluble salts. Erosion is most

pronounced in the lower elevations coincident with vegetation density.

Vegetation Changes ____________

Major vegetation changes have occurred since the early

1900s. Velvet mesquite (Prosopis juliflora (Sw.) DC.) is the

dominant overstory species on 20,000 to 30,000 acres where

shrub-free grassland dominated 80 years ago. Mesquite and

prickly pear cactus are major species above 4,000 ft, but

other species including acacia (Acacia greggii Gray var.

greggii, Acacia angustissima (P. Mill.) Kuntze var.

suffrutescens (Rose) Isely), mimosa (Mimosa aculeaticarpa

Ortega var. biuncifera (Benth.) Barneby, Mimosa dysocarpa

Benth.), and falsemesquite (Calliandra eriophylla Benth.)

comprise 65 percent of the cover in this zone compared to 21

percent below 3,000 ft. Mesquite, burroweed (Isocoma

tenuisecta Greene), and cholla cactus (Opuntia fulgida

Engelm., Opuntia spinosior (Engelm.) Toumey, and Opuntia versicolor Engelm. ex Coult.) attain highest densities

between 3,200 and 3,600 ft elevation (Martin and Reynolds

1973). Lower elevations (less than 3,200 ft) are dominated by

creosote bush (Larrea tridentata (Sessé & Moc. ex DC.)

Coville). Lehmann’s lovegrass (Eragrostis lehmanniana

Nees), sown for experimental purposes, has expanded its

distribution across thousands of acres, forming monocultures on some sites (Medina 1996). These changes in grassland types can have serious consequences on quail habitats

and their foods by excluding preferred foods (Medina 1988,

this proceedings).

Martin and Turner (1977) examined vegetational changes

in the Sonoran Desert region and noted that numbers of

some species undergo long-term (low frequency) fluctuations, while others fluctuate with higher frequencies. The

activities of man are considered generally pervasive, but

rodents and other wildlife may also induce and sustain

changes. Pioneer wildlife work on SRER by Vorhies and

Taylor (1933) illustrated that rodents and lagomorphs alone

can keep range sites within a poor or fair condition. Other

factors also contributed to vegetation change on SRER,

including experimentation with grazing systems (Marin

1978), fire (Martin 1983), herbicide and vegetation removal

treatments, rodent and rabbit control, fertilizer applications, and water spreading (Martin 1975). Climate change is

probably the most important natural factor that changed

vegetation dynamics on SRER over the last century. Many

studies throughout the research history of the range document the effects of rainfall and temperature on plant production, mortality, and reproduction (Martin 1975; Martin and

Cable 1974).

Flora _________________________

The vascular flora of SRER contains 468 species, in 283

genera, and 80 families. Since 1984 at least 123 new additions to the flora have been indexed. The three largest

families are Poaceae with 81 species, Asteraceae with 72

species, and Fabaceae with 61 species. These families account for 45 percent of the total flora. Important genera of

the Poaceae family include Bouteloua, Aristida, and

Muhlenbergia. Important genera of the Fabaceae family include

Acacia, Lotus, and Lupinus. Several genera of the Asteraceae

family contain species of unique and common value.

The author has examined all recent and historical collections forming the basis for this checklist. Voucher specimens

are deposited at various herbariums, including the Rocky

Mountain Herbarium and Forest Service National Herbarium in Laramie, WY, Rocky Mountain Research Station

Herbarium in Flagstaff, AZ, Arizona State University Herbarium, and the University of Arizona Herbarium. Nomenclature follows USDA NRCS (2002). This checklist is intended to serve as documentation of historical and recent

additions to the flora of SRER, and as a basis for future plant

studies and reference.

The vascular list (table 1) is intended as documentation of

the historical plants that occurred on SRER. It should serve

as a basis for other comparative floristic studies of the

region. While the list contains many species, many new

species are yet to be indexed. The list is also a valuable guide

to reference species of lesser economic importance but of

ecological significance in regards to invasive plant ecology.

References ____________________

Clemmons, S.; Wheeler, L. D. 1970. Soils report: Santa Rita Experimental Range, Coronado National Forest. Albuquerque, NM:

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

Region. 41 p.

Griffiths, David. 1901. Range improvement in Arizona. Bureau of

Plant Industry Bull. 4. Washington, DC: U.S. Department of

Agriculture. 31 p.

Griffiths, David. 1904. Range investigations in Arizona. Bureau of

Plant Industry Bull. 67 (10 plates). Washington, DC: U.S. Department of Agriculture. 62 p.

Griffiths, David. 1910. A protected stock range in Arizona. Bull. 177.

Washington, DC: U.S. Department of Agriculture. 28 p.

Martin, S. Clark. 1975. Ecology and management of Southwestern

semidesert grass-shrub ranges: the status of our knowledge. Res.

Pap. RM-156. Fort Collins, CO: US Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment

Station. 39 p.

Martin, S. Clark. 1978. The Santa Rita Grazing System. Proceedings of First International Rangeland Congress. 1: 573–575.

Martin, S. Clark. 1983. Responses of semidesert grasses and shrubs

to fall burning. Journal of Range Management. 36(5): 604–610.
USDA Forest Service Proceedings RMRS-P-30. 2003 143

Historical and Recent Flora of the Santa Rita Experimental Range Medina

Acanthaceae

Anisacanthus thurberi (Torr.) Gray

Carlowrightia arizonica Gray

Tetramerium nervosum Nees

Tetramerium hispidum Nees.

Yeatesia platystegia (Torr.) Hilsenb.a

Agavaceae

Agave palmeri Engelm.a

Yucca elata (Engelm.) Engelm.a

Aizoaceae

Trianthema portulacastrum L.a

Amaranthaceae

Amaranthus palmeri S. Wats.

Gomphrena nitida Rothrock

Gomphrena sonorae Torr.

Guilleminea densa (Humb. & Bonpl. ex Willd.) Moq. var. Densa

Tidestromia lanuginosa (Nutt.) Standl.

Anacardiaceae

Rhus trilobata Nutt.

Apiaceae

Bowlesia incana Ruiz & Pavón

Daucus carota L.a

Daucus pusillus Michx.

Spermolepis echinata (Nutt. ex DC.) Heller

Torilis nodosa (L.) Gaertn.a

Yabea microcarpa (Hook. & Arn.) K.-Pol.

Caucalis microcarpa Hook. & Arn.

Apocynaceae

Macrosiphonia brachysiphon (Torr.) Graya

Araliaceae

Aralia racemosa L.

Aristolochiaceae

Aristolochia watsonii Woot. & Standl.

Asclepiadaceae

Asclepias asperula (Dcne.) Woods. ssp. capricornu (Woods.)

Woods.

Asclepias brachystephana Engelm. ex Torr.

Funastrum cynanchoides (Dcne.) Schlechtera

Asteraceae

Agoseris heterophylla (Nutt.) Greene

Ambrosia ambrosioides (Cav.) Payneb

Ambrosia artemisiifolia L.a

Ambrosia dumosa (Gray) Paynea

Artemisia carruthii Wood ex Carruth.a

Baccharis brachyphylla Gray

Baccharis emoryi Gray

Baccharis pteronioides DC.

Baccharis salicifolia (Ruiz & PavÛn) Pers.a

Baccharis sarothroides Gray

Baccharis thesioides Kunth

Baccharis wrightii Gray

Bahia absinthifolia Benth. var.dealbata (Gray) Gray

Baileya multiradiata Harvey & Gray ex Gray

Bidens bigelovii Gray

Carphochaete bigelovii Gray

Chaetopappa ericoides (Torr.) Nesoma

Cirsium arizonicum (Gray) Petrak

Cirsium horridulum Michx.a

Cirsium neomexicanum Graya

Chloracantha spinosa (Benth.) Nesoma

Conyza canadensis (L.) Cronq.

Ericameria laricifolia (Gray) Shinners

Haplopappus laricifolius Gray

Ericameria nauseosa (Pallas ex Pursh) Nesom & Bairda

Ericameria suffruticosa (Nutt.) Nesom

Haplopappus suffruticosus (Nutt.) Gray

Erigeron concinnus (Hook. & Arn.) Torr. & Gray

Erigeron divergens Torr. & Gray

Gutierrezia arizonica (Gray) M.A. Lane

Greenella arizonica Gray

Gutierrezia sarothrae (Pursh) Britt. & Rusbya

Guardiola platyphylla Gray

Heliomeris longifolia (Robins. & Greenm.) Cockerell var. annua

(M.E. Jones) Yates

Viguiera annua (M.E. Jones) Blake

Hymenoclea monogyra Torr. & Gray ex Gray

Hymenothrix wislizeni Gray

Isocoma tenuisecta Greenea

Haplopappus tenuisectus (Greene) Blake

Lasthenia californica DC. ex Lindl.

Lasthenia chrysostoma (Fisch. & C.A. Mey.) Greene

Layia glandulosa (Hook.) Hook. & Arn.

Lygodesmia grandiflora (Nutt.) Torr. & Graya

Machaeranthera canescens (Pursh) Gray ssp. canescens var.

incana (Lindl.) Gray

Machaeranthera tephrodes (Gray) Greene

Machaeranthera gracilis (Nutt.) Shinners

Martin, S. C.; Reynolds, H. G. 1973. The Santa Rita Experimental

Range: your facility for research on semidesert ecosystems. Journal of the Arizona Academy of Science. 8: 56–67.

Martin, S. Clark; Reynolds, H. G. 1974. Managing semidesert grassshrub ranges: vegetation responses to precipitation, grazing, soil

texture, and mesquite control. Tech. Bull. 1480. Washington, DC:

U.S. Department of Agriculture, Forest Service. 45 p.

Martin, S. Clark; Turner, Raymond M. 1977. Vegetation change in

the Sonoran Desert region, Arizona and Sonora. Arizona Academy of Science. 12(2): 59–69.

Medina, Alvin L. 1988. Diets of scaled quail in southern Arizona.

Journal of Wildlife Management. 52: 753–757.

Medina, Alvin L. 1996. The Santa Rita Experimental Range: history

and annotated bibliography (1903–1988). Gen. Tech. Rep. RMGTR-276. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment

Station

Thornber, John J. 1909. Vegetation groups of the Desert Laboratory

domain. In: Spalding, V. M., ed. Distribution and movements of

desert plants. Publ. 113. Washington, DC: Carnegie Institute of

Washington: 103–112.

USDA NRCS. 2002. The PLANTS database, version 3.5 (http://

plants.usda.gov/). Baton Rouge, LA: U.S. Department of Agriculture, Plant Data Center.

Vorhies, Charles T.; Walter P. Taylor, Watler P. 1933. The life

histories and ecology of jackrabbits, Lepus alleni and Lepus

californicus spp., in relation to grazing in Arizona. Tech. Bull. 49.

Tucson: University of Arizona, Agricultural Experiment Station.

117 p.

Table 1—List of the historical and recent flora of the Santa Rita Experimental Range. Family names are in bold. The historical plant name

(nonitalicized) follows the current accepted name (italicized) only when there was a name change.

(Con.)
144 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Historical and Recent Flora of the Santa Rita Experimental Range

Machaeranthera pinnatifida (Hook.) Shinners ssp. pinnatifida var.

pinnatifida

Machaeranthera pinnatifida (Hook) Shinners pinnatifida

 pinnatifida Turner & Hartman

Haplopappus spinulosus (Pursh) DC.

Machaeranthera tagetina Greene

Machaeranthera tanacetifolia (Kunth) Nees

Malacothrix glabrata (Gray ex D.C. Eat.) Gray

Malacothrix californica (DC) glabrata Eaton

Malacothrix fendleri Gray

Oonopsis foliosa (Gray) Greene var. foliosab

Haplopappus fremontii (Gray) Greene

Parthenium incanum Kunth

Pectis longipes Gray

Pectis prostrata Cav.

Porophyllum gracile Benth.

Porophyllum ruderale (Jacq.) Cass. ssp. macrocephalum (DC.) R.R.

Johnson

Pseudognaphalium macounii (Greene) Kartesz, comb. nov. ined.

Gnaphalium decurrens Ives, non L.

Psilactis asteroides Gray

Machaeranthera asteroides (Torr.) Greene

Psilostrophe cooperi (Gray) Greene

Rafinesquia neomexicana Gray

Sanvitalia abertii Gray

Senecio flaccidus Less. var. flaccidusa

Senecio filifolius Nutt., non Berg.b

Senecio longilobus Benth.b

Senecio riddellii Torr. & Gray

Stephanomeria exigua Nutt.

Stephanomeria spinosa (Nutt.) S. Tomba

Stylocline micropoides Gray

Symphyotrichum divaricatum (Nutt.) Nesom

Aster subulatus Michx. var. ligulatus Shinners

Tagetes lemmonii Gray

Tagetes micrantha Cav.

Thelesperma megapotamicum (Spreng.) Kuntze

Thelesperma gracile (Torr.) Gray

Tragopogon porrifolius L.a

Trixis californica Kellogg

Uropappus lindleyi (DC.) Nutt.

Microseris linearifolia (Nutt.) Schultz-Bip.

Verbesina encelioides (Cav.) Benth. & Hook. f. ex Gray

Viguiera dentata (Cav.) Spreng. var. lancifolia Blake

Xanthium strumarium L.a

Zinnia acerosa (DC.) Gray

Zinnia acerosa (DC.) Gray

Zinnia pumila Gray

Zinnia grandiflora Nutt.

Bignoniaceae

Chilopsis linearis (Cav.) Sweet

Bixaceae

Amoreuxia palmatifida Moc. & Sessé ex DC.

Amoreuxia palmatifida M. & S.

Boraginaceae

Amsinckia douglasiana A. DC.a

Amsinckia menziesii (Lehm.) A. Nels. & J.F. Macbr. var. intermedia

(Fisch & C.A. Mey.) Ganders

Amsinckia intermedia F. & M.

Cryptantha angustifolia (Torr.) Greene

Cryptantha barbigera (Gray) Greene

Cryptantha crassisepala (Torr. & Gray) Greene

Cryptantha nevadensis A. Nels. & Kennedya

Pectocarya heterocarpa (I.M. Johnston) I.M. Johnston

Pectocarya recurvata I.M. Johnstona

Plagiobothrys arizonicus (Gray) Greene ex Graya

Plagiobothrys pringlei Greene

Brassicaceae

Arabis perennans S. Wats.

Descurainia pinnata (Walt.) Britt.

Descurainia pinnata(Walt.) Britt. ssp. ochroleuca (Woot.)

 Detling

Guillenia lasiophylla (Hook. & Arn.) Greene

Thelypodium lasiophyllum (Hook. & Arn.) Greene

Lepidium lasiocarpum Nutt.

Lepidium virginicum L. var. medium (Greene) C.L. Hitchc.

Lepidium medium Greene

Lepidium thurberi Woot.

Lesquerella gordonii (Gray) S. Wats.

Streptanthus carinatus C. Wright ex Gray ssp. arizonicus (S. Wats.)

Kruckeberg, Rodman & Worthington

Streptanthus arizonica Wats.

Thelypodium integrifolium (Nutt.) Endl. ex Walp.

Thysanocarpus curvipes Hook.

Thysanocarpus curvipes Hook. Var. elegans (F. & M.) Robins

Thysanocarpus laciniatus Nutt.

Thysanocarpus laciniatus Nutt.var. crenatus (Nutt.) Brewer

Cactaceae

Carnegia gigantea (Engelm.) Britt. & Rosea

Coryphantha scheeri (Muehlenpfordt) L. Bensona

Ferocactus wislizeni (Engelm.) Britt. & Rosea

Mammillaria grahamii Engelm. var. grahamiia

Mammillaria microcarpa Engelm.

Opuntia acanthocarpa Engelm. & Bigelowb

Opuntia arbuscula Engelm.b

Opuntia engelmannii Salm-Dycka

Opuntia fulgida Engelm.a

Opuntia imbricata (Haw.) DC.a

Opuntia leptocaulis DC.b

Opuntia santa-rita (Griffiths & Hare) Rosea

Opuntia spinosior (Engelm.) Toumeya

Opuntia versicolor Engelm. ex Coult.b

Campanulaceae

Triodanis perfoliata (L.) Nieuwl.

Triodanis perfoliata (L.) Nieuwl. var. biflora (Ruiz & PavÛn) Bradley

Triodanis biflora (Ruiz & PavÛn) Greene

Capparaceae

Polanisia dodecandra (L.) DC.a

Polanisia dodecandra (L.) DC. ssp. trachysperma (Torr. & Gray) Iltisa

Caprifoliaceae

Lonicera arizonica Rehd.a

Caryophyllaceae

Cerastium brachypodum (Engelm. ex Gray) B.L. Robins.

Cerastium brachypodium (Engelm.) Ribins

Cerastium glomeratum Thuill.a

Cerastium nutans Raf. var.

obtectum Kearney & Peebles

Silene antirrhina L.

Silene laciniata Cav. ssp. greggii (Gray) C.L. Hitchc. & Maguire

Celastraceae

Mortonia scabrella Gray

Chenopodiaceae

Atriplex canescens (Pursh) Nutt.

Atriplex wrightii S. Wats.

Chenopodium album L.a

Table 1—(Con.)

(Con.)
USDA Forest Service Proceedings RMRS-P-30. 2003 145

Historical and Recent Flora of the Santa Rita Experimental Range Medina

Chenopodium fremontii S. Wats.

Cycloloma atriplicifolium (Spreng.) Coult.a

Kochia scoparia (L.) Schrad.a

Monolepis nuttalliana (J.A. Schultes) Greene

Salsola kali L.a

Salsola tragus L.a

Commelinaceae

Commelina dianthifolia Delile

Tradescantia occidentalis (Britt.) Smyth

Convolvulaceae

Evolvulus arizonicus Gray

Evolvulus nuttallianus J.A. Schultes

Evolvulus pilosus Nutt.

Ipomoea capillacea (Kunth) G. Don

Ipomoea muricata Cav.

Ipomoea coccinea L.

Ipomoea eriocarpa R. Br.a

Ipomoea plummerae Graya

Ipomoea triloba L.

Ipomoea turbinata Lag.a

Cucurbitaceae

Citrullus lanatus (Thunb.) Matsumura & Nakai var. lanatus

Citrullus vulgaris Schrad.

Cucurbita digitata Gray

Cucurbita foetidissima Kuntha

Cyclanthera dissecta (Torr. & Gray) Arn.

Marah gilensis Greene

Cupressaceae

Juniperus deppeana Steud.

Juniperus deppeana Steud. pachyphlaea

Cuscutaceae

Cuscuta cephalanthi Engelm.

Cyperaceae

Cyperus squarrosus L.

Cyperus aristatus Rottb.

Cyperus hermaphroditus (Jacq.) Standl.

Ephedraceae

Ephedra trifurca Torr. ex S. Wats.

Ericaceae

Arbutus arizonica (Gray) Sarg.

Arctostaphylos pungens Kunth

Euphorbiaceae

Acalypha neomexicana Muell.-Arg.

Argythamnia neomexicana Muell.-Arg.a

Ditaxis neomexicana (Muell.-Arg.) Heller

Chamaesyce albomarginata (Torr. & Gray) Small

Euphorbia albomarginata Torr. & Gray

Chamaesyce florida (Engelm.) Millsp.

Euphorbia florida Engelm.

Chamaesyce maculata (L.) Smalla

Chamaesyce melanadenia (Torr.) Millsp.a

Chamaesyce nutans (Lag.) Smalla

Chamaesyce prostrata (Ait.) Smalla

Chamaesyce serrula (Engelm.) Woot. & Standl.

Euphorbia serrula Engelm.

Croton glandulosus L.a

Croton pottsii (Klotzsch) Muell.-Arg. var. pottsii

Croton corymbulosus Engelm.

Euphorbia marginata Pursha

Fabaceae

Acacia angustissima (P. Mill.) Kuntze var. suffrutescens (Rose) Isely

Acacia constricta Benth.

Acacia filiculoides (Cav.) Trelease

Acacia greggii Gray var. greggii

Acacia greggii Grey var. arizonica Isely

Amorpha californica Nutt.

Astragalus allochrous Gray var. playanus Isely

Astragalus wootonii Sheldon

Astragalus arizonicus Gray

Astragalus nothoxys Gray

Astragalus nuttallianus DC.

Astragalus tephrodes Graya

Caesalpinia gilliesii (Hook.) Wallich ex D. Dietr.

Caesalpinia gilliesii Wall.

Calliandra eriophylla Benth.

Calliandra humilis Benth.

Chamaecrista nictitans (L.) Moench ssp. nictitans var. leptadenia

(Greenm.) Gandhi & Hatch

Cassia leptadenia Greenm.

Crotalaria pumila Ortega

Dalea aurea Nutt. ex Pursha

Dalea formosa Torr.

Dalea grayi (Vail) L.O. Williams

Dalea pogonathera Gray

Dalea wrightii Gray

Desmanthus cooleyi (Eat.) Trel.

Desmanthus jamesii Torr. & Gray

Desmanthus virgatus (L.) Willd.a

Desmodium neomexicanum Gray

Desmodium psilocarpum Gray

Eysenhardtia polystachya (Ortega) Sarg.

Galactia wrightii Gray

Hoffmannseggia glauca (Ortega) Eifert

Lathyrus lanszwertii Kellogg var. leucanthus (Rydb.) Dorn

Lathyrus arizonicus Britt.

Lathyrus graminifolius (S. Wats.) White

Lotus greenei Ottley ex Kearney & Peebles

Lotus greenei (Woot. & Standl.) Ottle

Lotus humistratus Greene

Lotus rigidus (Benth.) Greenea

Lotus salsuginosus Greenea

Lotus strigosus (Nutt.) Greene var. tomentellus (Greene) Iselya

Lotus unifoliolatus (Hook.) Benth. var. unifoliolatusa

Lotus wrightii (Gray) Greenea

Lupinus arizonicus (S. Wats.) S. Wats.a

Lupinus concinnus J.G. Agardh

Lupinus neomexicanus Greene

Lupinus palmeri S. Wats.

Lupinus sparsiflorus Benth.

Melilotus indica (L.) All.

Mimosa aculeaticarpa Ortega var. biuncifera (Benth.) Barneby

Mimosa biuncifera (Benth.) Britt. & Rose

Mimosa dysocarpa Benth.

Olneya tesota Graya

Parkinsonia florida (Benth. ex Gray) S. Wats.b

Parkinsonia microphylla Torr.a

Phaseolus acutifolius Gray var. tenuifolius Gray

Phaseolus angustissimus Gray

Phaseolus maculatus Scheele

Phaseolus metcalfei Woot. & Standl.

Phaseolus ritensis M.E. Jonesa

Prosopis juliflora (Sw.) DC.a

Prosopis velutina Woot.

Senna covesii (Gray) Irwin & Barneby

Cassia covesii Gray

Cassia leptadenia Greenm.

Table 1—(Con.)

(Con.)
146 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Historical and Recent Flora of the Santa Rita Experimental Range

 Senna hirsuta (L.) Irwin & Barneby var.

glaberrima (M.E. Jones) Irwin & Barneby

Cassia leptocarpa Benth. var. glaberrima M.E. Jones

Tephrosia leiocarpa Gray

Tephrosia thurberi (Rydb.) C.E. Wood

Vicia hassei S. Wats.a

Vicia leucophaea Greene

Vicia ludoviciana Nutt. ssp. Ludoviciana

Vicia exigua Nutt.

Fagaceae

Quercus emoryi Torr.

Quercus hypoleucoides A. Camus

Quercus oblongifolia Torr.

Quercus _pauciloba Rydb. (pro sp.) [gambelii x turbinella]

Quercus undulata Torr.

Quercus rugosa NÈe

Quercus turbinella Greene

Fouquieriaceae

Fouquieria splendens Engelm.a

Fumariaceae

Corydalis aurea Willd.

Geraniaceae

Erodium botrys (Cav.) Bertol.a

Erodium cicutarium (L.) L’HÈr. ex Ait.

Erodium cicutarium (L.) L’Her.

Erodium texanum Gray

Hydrophyllaceae

Phacelia alba Rydb.

Phacelia arizonica Gray

Phacelia crenulata Torr. ex S. Wats.

Phacelia distans Benth.

Phacelia distans Benth. Var. australis Brand.

Pholistoma auritum (Lindl.) Lilja var. arizonicum (M.E. Jones)

Constance

Juglandaceae

Juglans major (Torr.) Heller

Krameriaceae

Krameria erecta Willd. ex J.A. Schultes

Krameria parvifolia Benth. var. glandulosa (Rose & Painter)

 J.F. Macbr.

Lamiaceae

Agastache wrightii (Greenm.) Woot. & Standl.

Hedeoma dentata Torr.

Hedeoma drummondii Benth.a

Marrubium vulgare L.

Salvia columbariae Benth.

Salvia subincisa Benth.

Stachys coccinea Ortega

Trichostema arizonicum Gray

Liliaceae

Allium cernuum Roth var.

neomexicanum (Rydb.) J.F. Macbr.

Allium kunthii G. Don

Allium scaposum (Benth.)

Calochortus gunnisonii S. Wats.

Dasylirion wheeleri S. Wats.a

Dichelostemma capitatum (Benth.) Wood ssp. pauciflorum (Torr.)

G. Keator

Dichelostemma pulchellum (Salisb.) Heller var. pauciflorum

 (Torr.) Hoover

Linum puberulum (Engelm.) Heller

Milla biflora Cav.

Loasaceae

Mentzelia

rusbyi Woot.

Mentzelia texana Urban & Gilg

Malvaceae

Abutilon berlandieri Gray ex S. Wats.a

Anoda cristata (L.) Schlecht.

Anoda lavaterioides Medik.

Gossypium thurberi Todaro

Hibiscus coulteri Harvey ex Gray

Hibiscus coulteri Harv.

Sida abutifolia P. Mill.

Sida filicaulis Torr. & Gray

Sida procumbens Sw.

Sida spinosa L.a

Sphaeralcea emoryi Torr. ex Gray

Sphaeralcea emoryi Torr.

Sphaeralcea fendleri Gray

Molluginaceae

Mollugo verticillata L.

Moraceae

Morus microphylla Buckl.

Nyctaginaceae

Abronia villosa S. Wats.

Acleisanthes longiflora Graya

Allionia incarnata L.

Boerhavia coulteri (Hook. f.) S. Wats.

Boerhavia erecta L.

Boerhavia intermedia M.E. Jonesa

Boerhavia purpurascens Gray

Boerhavia spicata Choisya

Boerhavia torreyana (S. Wats.) Standl.

Mirabilis coccinea (Torr.) Benth. & Hook. f.

Oxybaphus coccineus Torr.

Mirabilis linearis (Pursh) Heimerl

Oxybaphus linearis (Pursh) B.L. Robins.

Mirabilis longiflora L. var. wrightiana (Gray ex Britt. & Kearney)

Kearney & Peebles

Mirabilis longiflora L. var. wrightiana (Gray) Kearney & Peebles

Oleaceae

Menodora scabra Gray

Menodora scabra Gray var. ramosissima Steyerm.

Onagraceae

Camissonia chamaenerioides (Gray) Raven

Oenothera chamaenerioides Gray

Camissonia scapoidea (Nutt. ex Torr. & Gray) Raven ssp.

Scapoidea

Epilobium canum (Greene) Raven ssp. latifolium (Hook.) Raven

Zauschneria californica K. Presl ssp. latifolia (Hook.) Keck

Oenothera primiveris Gray

Oxalidaceae

Oxalis albicans Kunth

Oxalis drummondii Gray

Oxalis amplifolia (Trel.) Kunth.

Papaveraceae

Argemone hispida Gray

Argemone platyceras Link & Otto var. hispida (Gray) Prain

Argemone pleiacantha Greenea

Argemone polyanthemos (Fedde) G.B. Ownbey

Argemone intermedia auct. non Sweet

Eschscholzia californica Cham. ssp. mexicana (Greene) C. Clark

Eschscholtzia mexicana Greene

Table 1—(Con.)

(Con.)
USDA Forest Service Proceedings RMRS-P-30. 2003 147

Historical and Recent Flora of the Santa Rita Experimental Range Medina

Pedaliaceae

Proboscidea parviflora (Woot.) Woot. & Standl.

Phytolaccaceae

Rivina humilis L.

Rivina portulacoides Nutt.

Plantaginaceae

Plantago ovata Forsk.a

Plantago insularis Eastw.

Plantago patagonica Jacq.

Plantago purshii R.&S.

Plantago purshii R.&S. picta (Morris) Pilger

Plantago tweedyi Gray

Plantago virginica L.

Poaceae

Achnatherum hymenoides (Roemer & J.A. Schultes) Barkwortha

Aegopogon tenellus (DC.) Trin.

Alopecurus carolinianus Walt.

Bothriochloa saccharoides (Sw.) Rydb.

Andropogon saccharoides Sw.

Aristida adscensionis L.

Aristida californica Thurb. ex S. Wats.

Aristida californica Thurb. ex S. Wats. var. glabrata Vaseya

Aristida glabrata (Vasey) A.S. Hitchc.

Aristida divaricata Humb. & Bonpl. ex Willd.

Aristida purpurea Nutt.

Aristida purpurea Nutt. var. fendleriana (Steud.) Vasey

Aristida fendleriana Steud.

Aristida ternipes Cav.

Aristida hamulosa Henr.

Bothriochloa barbinodis (Lag.) Hertera

Andropogon barbinodis Lag.

Bouteloua aristidoides (Kunth) Griseb.

Bouteloua barbata Lag.

Bouteloua chondrosioides (Kunth) Benth. ex S. Wats.

Bouteloua chondrosioides (H.B.K.) Benth

Bouteloua

curtipendula (Michx.) Torr.

Bouteloua eludens Griffiths

Bouteloua eriopoda (Torr.) Torr.

Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths

Bouteloua hirsuta Lag.

Bouteloua parryi (Fourn.) Griffiths

Bouteloua radicosa (Fourn.) Griffiths

Bouteloua repens (Kunth) Scribn. & Merr.

Bouteloua rothrockii Vasey

Bromus catharticus Vahl

Bromus willdenowii Kunth

Bromus porteri (Coult.) Nash

Cenchrus spinifex Cav.

Cenchrus insertus M.A. Curtis

Chloris virgata Sw.

Cottea pappophoroides Kuntha

Dasyochloa pulchella (Kunth) Willd. ex Rydb.

Tridens pulchellus (Kunth) A.S. Hitchc.

Digitaria californica (Benth.) Henr.

Trichachne californica (Benth.) Chase

Digitaria ciliaris (Retz.) Koel.a

Digitaria cognata (J.A. Schultes) Pilger var. cognatab

Leptoloma cognatum (J.A. Schultes) Chase

Digitaria sanguinalis (L.) Scop.a

Echinochloa acuminata (J. Presl) Kunth var. acuminataa

Eriochloa gracilis (Fourn.) A.S. Hitchc.

Echinochloa crus-galli (L.) Beauv.a

Elionurus barbiculmis Hack.

Elymus elymoides (Raf.) Swezey

Sitanion hystrix (Nutt.) J.G. Sm.

Enneapogon desvauxii Desv. ex Beauv.a

Eragrostis cilianensis (All.) Vign. ex Janchen

Eragrostis cilianensis (All.) Mohser

Eragrostis curvula (Schrad.) Neesa

Eragrostis chloromelas Steud.

Eragrostis curvula (Schrad.) Nees var. conferta Stapfb

Eragrostis intermedia A.S. Hitchc.a

Eragrostis lehmanniana Neesa

Eragrostis superba Peyr.a

Heteropogon contortus (L.) Beauv. ex Roemer & J.A. Schultesa

Hilaria belangeri (Steud.) Nash

Koeleria macrantha (Ledeb.) J.A. Schultes

Koeleria pyramidata auct. p.p. non (Lam.) Beauv.

Leptochloa dubia (Kunth) Nees

Lycurus phleoides Kunth

Muhlenbergia arizonica Scribn.

Muhlenbergia emersleyi Vaseya

Muhlenbergia polycaulis Scribn.

Muhlenbergia porteri Scribn. Ex

Muhlenbergia repens (J. Presl) A.S. Hitchc.

Muhlenbergia rigida (Kunth) Trin.

Muhlenbergia tenuifolia (Kunth) Trin.

Muhlenbergia monticola Buckl.

Panicum bulbosum Kunth

Panicum plenum Hitchc. & Chase

Panicum capillare L.a

Panicum hallii Vasey var. halliia

Panicum hirticaule J. Presl

Panicum obtusum Kunth

Pappophorum vaginatum Buckl.

Piptochaetium fimbriatum (Kunth) A.S. Hitchc.

Poa bigelovii Vasey & Scribn.

Poa fendleriana (Steud.) Vasey

Polypogon viridis (Gouan) Breistr.

Agrostis semiverticillata (Forsk.) C. Chr.

Schizachyrium cirratum (Hack.) Woot. & Standl.

Schizachyrium scoparium (Michx.) Nashb

Setaria grisebachii Fourn.

Setaria viridis (L.) Beauv.a

Setaria vulpiseta (Lam.) Roemer & J.A. Schultes

Setaria macrostachya H.B.K.

Sorghum halepense (L.) Pers.a

Sporobolus airoides (Torr.) Torr.

Sporobolus airoides Torr.

Sporobolus contractus A.S. Hitchc.

Sporobolus cryptandrus (Torr.) Graya

Sporobolus wrightii Munro ex Scribn.

Trachypogon spicatus (L.) Kuntze

Trachypogon secundus (J. Presl) Scribn.

Tragus berteronianus J.A. Schultes

Tridens muticus (Torr.) Nash

Urochloa arizonica (Scribn. & Merr.) O. Morrone & F. Zuloaga

Panicum arizonicum Scribn. & Merr.

Vulpia octoflora (Walt.) Rydb. var. hirtella (Piper) Henr.

Festuca octoflora Walt. ssp. hirtella Piper

Polemoniaceae

Gilia filiformis Parry ex Gray

Gilia filiformis Parry

Gilia leptomeria Gray

Gilia rigidula Benth.a

Gilia sinuata Dougl. ex Benth.

Gilia sinuata Dougl.

Table 1—(Con.)

(Con.)
148 USDA Forest Service Proceedings RMRS-P-30. 2003

Medina Historical and Recent Flora of the Santa Rita Experimental Range

Ipomopsis longiflora (Torr.) V. Grant

Linanthus aureus (Nutt.) Greene

Polygalaceae

Eriogonum abertianum Torr.

Eriogonum thurberi Torr.

Eriogonum wrightii Torr. Ex

Polygala alba Nutt.

Rumex hymenosepalus Torr.

Portulacaceae

Calandrinia ciliata (Ruiz & PavÛn) DC.a

Cistanthe monandra (Nutt.) Hershkovitz

Calyptridium monandrum Nutt.

Portulaca oleracea L.a

Portulaca pilosa L.

Portulaca umbraticola Kunth

Talinum aurantiacum Engelm.

Talinum paniculatum (Jacq.) Gaertn.

Primulaceae

Androsace occidentalis Pursh

Pteridaceae

Astrolepis sinuata (Lag. ex Sw.) Benham & Windham ssp. Sinuate

Notholaena sinuata (Lag. ex Sw.) Kaulfuss

Ranunculaceae

Anemone tuberosa Rydb.

Aquilegia chrysantha Gray

Clematis ligusticifolia Nutt.

Delphinium scaposum Greene

Rhamnaceae

Frangula californica (Eschsch.) Gray ssp. ursina (Greene) Kartesz

& Gandhi

Rhamnus californica Eschsch. ssp. ursina (Greene) C.B. Wolf

Ziziphus obtusifolia (Hook. ex Torr. & Gray) Gray

Zizyphus obtusifolia (Hook. ex Torr. & Gray) var. canescens

 (Gray) M.C. Johnst.

Rosaceae

Cercocarpus montanus Raf. var. glaber (S. Wats.) F.L. Martin

Cercocarpus betuloides Nutt.

Potentilla wheeleri S. Wats.

Potentilla viscidula Rydb.

Prunus serotina Ehrh. var. virens (Woot. & Standl.) McVaugh

Purshia stansburiana (Torr.) Henrickson

Cowania mexicana D. Don var. stansburiana (Torr.) Jepson

Rubiaceae

Bouvardia ternifolia (Cav.) Schlecht.

Bouvardia glabbrima Engelm.

Diodia teres Walt. var. angustata Gray

Galium aparine L.

Galium microphyllum Gray

Houstonia rubra Cav.

Hedyotis rubra (Cav.) Gray

Mitracarpus breviflorus Gray

Sapindaceae

Sapindus saponaria L. var. drummondii (Hook. & Arn.) L. Benson

Saxifragaceae

Heuchera sanguinea Engelm.

Scrophulariaceae

Castilleja exserta (Heller) Chuang & Heckard ssp. exserta

Orthocarpus purpurascens Benth. var. palmeri Gray

Castilleja integra Gray

Castilleja patriotica Fern.

Mimulus guttatus DC.

Nuttallanthus texanus (Scheele) D.A. Sutton

Linaria texana Scheele

Penstemon barbatus (Cav.) Roth

Penstemon linarioides Gray

Penstemon pseudospectabilis M.E. Jonesa

Solanaceae

Chamaesaracha coniodes (Moric. ex Dunal) Britt.a

Datura wrightii Regel

Datura meteloides DC

Lycium torreyi Gray

Margaranthus solanaceus Schlecht.

Nicotiana obtusifolia Mertens & Galeotti var. Obtusifolia

Nicotiana trigonophylla Dunal

Physalis crassifolia Benth.

Physalis hederifolia Gray var. fendleri (Gray) Cronq.a

Solanum adscendens Sendtner

Solanum deflexum Greenm.

Solanum douglasii Dunal

Solanum elaeagnifolium Cav.

Solanum heterodoxum Dunal var. setigeroides M.D. Whalena

Sterculiaceae

Ayenia insulicola Cristobala

Ulmaceae

Celtis laevigata Willd.

Celtis reticulata Torr.

Celtis pallida Torr.

Urticaceae

Parietaria hespera Hinton

Verbenaceae

Aloysia wrightii Heller ex Abrams

Aloysia wrightii (Grey) Heller

Glandularia wrightii (Gray) Umber

Verbena wrightii Gray

Glandularia bipinnatifida (Nutt.) Nutt. var. bipinnatifida

Verbena ambrosiifolia Rydb. ex Small

Tetraclea coulteri Gray

Verbena neomexicana (Gray) Small

Verbena stricta Vent.a

Violaceae

Viola nephrophylla Greene

Viscaceae

Phoradendron californicum Nutt.a

Vitaceae

Vitis arizonica Engelm.

Zygophyllaceae

Kallstroemia grandiflora Torr. ex Gray

Kallstroemia grandiflora Torr.

Larrea tridentata (Sessé & Moc. ex DC.) Coville

Larrea tridentata (DC) Coville

Tribulus terrestris L.

Table 1—(Con.)

aRecent additions (1984 to 1996) by A. Medina and R. Mays.

b

Additions from the University of Arizona Web list.
USDA Forest Service Proceedings RMRS-P-30. 2003 149

Sharon H. Biedenbender

Mitchel P. McClaran

Bruce A. Roundy

Effects of Neighbor Species and Distance

on 2- and 4-Year Survival of Lehmann

Lovegrass and Native Grasses

Sharon H Biedenbender is Rangeland Management Specialist with the USDA Forest Service at the Coronado National Forest Sierra Vista Ranger District

in Hereford, AZ; e-mail: sbiedenbender@fs.fed.us. She completed a B.S. degree in plant sciences and M.S. and Ph.D. degrees in rangeland management at the

University of Arizona. She was a Vegetation Specialist at the USDA Agricultural Research Service, Southwest Watershed Research Center in Tucson, AZ, prior

to transferring to the Forest Service. Mitchel P. McClaran is Professor of Range Management, School of Renewable Natural Resources, University of Arizona,

Tucson, AZ 85721. Telephone: (520) 621-1673; e-mail: mcclaran@u.arizona.edu. Bruce A. Roundy is Professor of Range Science in the Department of Integrative

Biology at Brigham Young University, Provo, UT. He completed an M.S. degree in range management at the University of Nevada, Reno, and a Ph.D. degree in

range management at Utah State University, Logan. He has been Range Scientist, USDA Agricultural Research Service, Reno, NV, and Professor of Range

Science, School of Renewable Natural Resources, University of Arizona.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: The relationship between Lehmann lovegrass, an invasive African grass, and native

Southwestern grasses has not been fully determined. The first purpose of this study was to

compare the survival of Lehmann lovegrass with two native grasses (plains lovegrass and Arizona

cottontop) seeded on the Santa Rita Experimental Range in southeast Arizona in 1994. One year

after establishment, survival was 92 percent for plains lovegrass, 90 percent for Arizona cottontop,

and 92 percent for Lehmann lovegrass. High survival was maintained until the second summer

of the study, when many plants that were alive in June 1996 suffered mortality by September

1996. At that time, survival was 10 percent for plains lovegrass, 30 percent for Arizona cottontop,

and 76 percent for Lehmann lovegrass. Four years after establishment, survival was zero for

plains lovegrass, 16 percent for Arizona cottontop, and 60 percent for Lehmann lovegrass. The

second purpose of the study was to determine if Lehmann lovegrass, as a same-aged neighbor,

affected the two native grasses differently than same-species neighbors. After 2 years, plains

lovegrass mortality was higher with same-species neighbors than no neighbors or Lehmann

lovegrass neighbors; cottontop mortality was highest with Lehmann neighbors; and Lehmann

mortality was highest with plains lovegrass neighbors. By the end of 4 years, all plains lovegrass

seedlings perished regardless of neighbor density (one or two within 40 by 40 cm), spacing (1 to

2 cm or 5 to 6 cm), or species. After 4 years, Arizona cottontop seedlings had 60-percent survival

with no neighbors, 10-percent survival across both densities and spacings with same-species

neighbors, and no survival with Lehmann lovegrass neighbors. Lehmann lovegrass had 80-

percent survival with no neighbors, 60-percent survival with same-species neighbors, and 50-

percent survival with native neighbors. These results suggest that the intensity of competition

between Lehmann lovegrass and the native grasses increased over the first 4 years.

Keywords: plains lovegrass, Arizona cottontop, invasive species, semiarid grassland ecology,

plant competition

Acknowledgments:Funding for planting the research plots in 1994 was provided by the Arizona

Heritage Fund. Bruce Munda and Mark Pater at the Natural Resources Conservation Service

Plant Materials Center, Tucson, AZ, supplied seed, equipment, and expertise. Field monitoring

was assisted by Juan M. Moreno and Carolyn Huntington. Precipitation data sets were provided

by the Santa Rita Experimental Range Digital Database (http://ag.arizona.edu/SRER). Funding

for the digitization of these data was provided by the USDA Forest Service, Rocky Mountain

Research Station, and the University of Arizona.

Introduction _____________________________________________________

Lehmann lovegrass (Eragrostis lehmanniana Nees) is a warm-season, perennial bunchgrass native to South Africa that was

first introduced to Arizona in the 1930s (Cable 1971). Lehmann lovegrass seed was produced at the USDA Natural Resource
150 USDA Forest Service Proceedings RMRS-P-30. 2003

Biedenbender, McClaran, and Roundy Effects of Neighbor Species and Distance on 2- and 4-Year Survival of...

Conservation Service (NRCS, formerly the Soil Conservation Service) Plant Materials Center, Tucson, AZ, and distributed to soil conservationists and scientists within NRCS

for field plantings to stabilize soil and increase forage production in Arizona, New Mexico, and Texas. Areas where

Lehmann lovegrass successfully establishes have sandy to

sandy loam soils to 120 cm deep, mean summer precipitation

greater than 200 mm, and winter temperatures that rarely

fall below 0 ∞C (Cox and Ruyle 1986). Between 1940 and

1950, Lehmann lovegrass began to spread to areas not

intentionally seeded. By the mid-1980s, continued seedings

and natural spread allowed Lehmann lovegrass to become

the most prevalent grass species on approximately 145,000

ha in southeastern Arizona (Cox and Ruyle 1986), and it is

still increasing in land coverage (Anable and others 1992).

Lehmann lovegrass may displace native grasses with

undesirable ecological consequences such as decreased native wildlife species diversity and abundance (Bock and

others 1986), alterations in fire frequency and intensity

(Bock and Bock 1992; Cable 1965), and decreased livestock

forage quality (Cox and others 1990). Although concern

exists regarding the displacement of native grasses by

Lehmann lovegrass, the relationship between Lehmann

lovegrass and native grasses has not been fully understood.

Among the possible mechanisms by which Lehmann lovegrass

may compete successfully against native grasses are greater

seed production, faster growth rate, lower palatability to

herbivores, lower nutrient requirements, and a potential

competitive advantage over native range grasses in procuring soil moisture. Many seedling studies indicate that rapid

growth rate or large size ensure competitive success (Goldberg

1990). Lehmann lovegrass has been shown to recover from

drought more rapidly than native grasses and to spread

after drought into areas previously occupied by native grasses

(Robinett 1992). Angell and McClaran (2001) found that

from 1972 to 2000 native grass species on the Santa Rita

Experimental Range (SRER) in southeastern Arizona declined prior to the arrival of Lehmann lovegrass. Abbott and

Roundy (2002) showed that Lehmann lovegrass, compared

to native grasses, retained a viable seed bank during sporadic early summer precipitation events, hence better ensuring seedling germination and establishment during more

consistent late summer rains.

In June and August 1992, 1993, and 1994, native grasses

were seeded into existing stands of Lehmann lovegrass on

the SRER to determine the effects on native grass establishment of mowing, herbicide application, and burning

treatments applied to the Lehmann lovegrass canopy

(Biedenbender and Roundy 1996). In June 1994 an arson

fire consumed the vegetation in the experimental area,

killing most mature Lehmann lovegrass plants and negating treatment effects. However, massive recruitment of

Lehmann lovegrass seedlings from the seed bank followed

rains occurring in August and September of that year. In

addition, excellent native grass seedling establishment

resulted from the August 1994 planting. To take advantage

of this cohort of same-aged Lehmann lovegrass and native

grasses, an experiment with different numbers, spacings,

and species of neighbors was executed.

The first purpose of this study was to compare the survival

of Lehmann lovegrass and two native grasses (plains

lovegrass, Eragrostis intermedia Hitchc., and Arizona

cottontop, Digitaria californica (Benth.) Henr.). The second

purpose was to determine if Lehmann lovegrass, as a sameaged neighbor, affected the two native grasses differently

than same-species neighbors. Competition is defined as an

interaction between two organisms in which both are negatively affected, whereas an amensal interaction is defined as

one in which one organism is negatively affected and the

other is unaffected by the neighbor (Burkholder 1952).

Competition theory suggests that more closely related individuals compete for resources more intensely than distantly

related individuals (Keddy 1989). Based on this theory,

same-species neighbors would be expected to compete most

intensely, and individuals in the same genus might be

expected to compete more intensely with each other than

with individuals in a different genus. Lehmann lovegrass

and plains lovegrass are in the same genus, whereas Arizona

cottontop is not.

The third purpose was to see if the proximity of neighbors

affected survival. Removal experiments can indicate if a

reduction in the abundance of one species affects the survival and/or production of another (McPherson and DeStefano

2003). If the removal or reduction in number of one species

increases the growth or survival of another, it can be inferred

that the removed species was competing with the survivor.

This study was a removal experiment designed to evaluate

whether, during the early stages of plant establishment,

Lehmann lovegrass competes with plains lovegrass and

Arizona cottontop, and whether the effects of the interaction

increase as the number and proximity of Lehmann lovegrass

neighbors increases.

Methods ______________________

The study site is located in a livestock exclosure containing a Lehmann lovegrass monoculture with scattered mesquite trees. Average annual precipitation is 450 mm, the soil

is a sandy loam, slopes are 2- to 5-percent slope, and elevation is approximately 1,075 m (Biedenbender and Roundy

1996). The precipitation record for 1995 to 1998 was obtained from a SRER rain gage near the study site (fig. 1). The

long-term annual average from 1972 to 2002 for this rain

gage is 388 mm and the long-term average for July through

September is 199 mm.

The treatments were installed in December 1994. Quadrats measuring 40 by 40 cm were placed along seeded rows,

a target seedling was chosen in the center of each quadrat,

and all other vegetation except for the selected neighbors

was removed. Target seedlings of Lehmann lovegrass, plains

lovegrass, and Arizona cottontop were arranged with no

neighbors, one and two same-species neighbors at 1 to 2 and

5 to 6 cm distance, and one and two Lehmann lovegrass

neighbors at 1 to 2 and 5 to 6 cm distance (table 1). In

addition, quadrats with four Lehmann lovegrass neighbors

within 1 to 6 cm were established. Each treatment was

replicated five times for a total of N = 150. When two samespecies seedlings shared a plot, the southern or western

seedling was designated as the target. Every attempt was

made to chose target and neighbor seedlings that were

representative of the range of seedling sizes present on the

site. Also, target and neighbor seedlings of similar size were

selected. These treatments allowed for comparisons among

two densities and two distances of same-species neighbors
USDA Forest Service Proceedings RMRS-P-30. 2003 151

Effects of Neighbor Species and Distance on 2- and 4-Year Survival of... Biedenbender, McClaran, and Roundy

Seasonal and Annual Precipitation

SRER 1995 - 1998 

0

100

200

300

400

500

600

94 - 95 95 - 96 96 - 97 97 - 98 98

Year

Amount (mm)

Jul - Sep Oct - Jun

Figure 1—Seasonal and annual precipitation record

(mm) from the IBP (Pasture 21) rain gage on the

Santa Rita Experimental Range in southeast Arizona, 1995 to 1998; the rain gage is near the

Lehmann lovegrass and native grass survival study;

the long-term annual average from 1972 to 2002

was 388 mm (—); the long term average for July

through September was 199 mm (- - - -).

Table 1—Treatments for a Lehmann lovegrass and native

grass survival study on the Santa Rita Experimental

Range in southeast Arizona, 1995 to 1998; native

grasses were plains lovegrass and Arizona

cottontop; each target seedling had the following

arrangement of neighbors.

Native treatments

1 No neighbors

2 One same species neighbor at 1 to 2 cm

3 Two same species neighbors at 1 to 2 cm

4 One same species neighbor at 5 to 6 cm

5 Two same species neighbors at 5 to 6 cm

6 One Lehmann lovegrass neighbor at 1 to 2 cm

7 One Lehmann lovegrass neighbor at 5 to 6 cm

8 Two Lehmann lovegrass neighbors at 1 to 2 cm

9 Two Lehmann lovegrass neighbors at 5 to 6 cm

10 Four Lehmann lovegrass neighbors at 1 to 6 cm

Lehmann treatments

1 No neighbors

2 One Lehmann lovegrass neighbor at 1 to 2 cm

3 One Lehmann lovegrass neighbor at 5 to 6 cm

4 Two Lehmann lovegrass neighbors at 1 to 2 cm

5 Two Lehmann lovegrass neighbors at 5 to 6 cm

6 Four Lehmann lovegrass neighbors at 1 to 6 cm

7 One Arizona cottontop neighbor at 1 to 2 cm

8 One Arizona cottontop neighbor at 5 to 6 cm

9 One plains lovegrass neighbor at 1 to 2 cm

10 One plains lovegrass neighbor at 5 to 6 cm

for all three species and among three densities and two

distances for Lehmann lovegrass neighbors.

Mortality was determined for target plants in the fall from

1995 through 1998. At the end of the second growing season

in the fall of 1996, all quadrats at the 1 to 2 cm and 1 to 6 cm

spacing were harvested. Mortality was followed on remaining

target plants at the 5 to 6 cm spacing for two more growing

seasons until the fall of 1998. Mortality was calculated for

1995 and 1996 based on 50 total possible survivors for each

species. For 1997 and 1998 mortality calculations were based

on 25 total possible survivors due to the harvest of quadrats

at 1 to 2 and 1 to 6 cm spacings.

Results _______________________

When measured in 1995 the first spring after planting,

there was no mortality of target seedlings. In October 1995,

1 year after establishment, total survival across all treatments was 92 percent for plains lovegrass, 90 percent for

Arizona cottontop, and 92 percent for Lehmann lovegrass

(table 2; fig. 2). High survival was maintained until the

second summer of the study, but many plants had suffered

mortality by September 1996. At that time, plains lovegrass

survival was only 10 percent, Arizona cottontop fared somewhat better with 30 percent, and Lehmann lovegrass survival was an impressive 76 percent. A pattern of winter/

spring growth followed by summer mortality was noted in

1995 and repeated in 1996. Mortality during their second

summer even befell plants among all three species that had

achieved considerable size. Three years after establishment,

survival in November 1997 was zero for plains lovegrass, 24

percent for Arizona cottontop, and remained at 76 percent

for Lehmann lovegrass. Four years after establishment,

survival in November 1998 was 16 percent for Arizona

cottontop and 60 percent for Lehmann lovegrass.

Plains lovegrass mortality was higher with same-species

neighbors than no neighbors or Lehmann lovegrass neighbors (table 2; fig. 3). Cottontop mortality was highest with

Lehmann lovegrass neighbors, and Lehmann mortality was

highest with plains lovegrass neighbors. By the end of 4

years, all plains lovegrass seedlings perished regardless of

neighbor density (one or two within 40 by 40 cm), spacing (1

to 2 cm or 5 to 6 cm), or species. After 4 years, Arizona

cottontop seedlings had 60-percent survival with no neighbors, 10-percent survival across both densities and spacings

with same-species neighbors, and zero survival with

Lehmann lovegrass neighbors. Lehmann lovegrass had 80-

percent survival with no neighbors, 60-percent survival

with same-species neighbors, and 50-percent survival with

native neighbors, 80 percent with cottontop, and only 20

percent with plains lovegrass (table 2).

Discussion ____________________

First-year seedling survival for Arizona cottontop and

plains lovegrass was very high and equal to or only somewhat less than Lehmann lovegrass. However, over the next

3 years, Lehmann lovegrass survival surpassed the natives

for all of the species-spacing treatments. This study suggests

that competitive release activated by the removal of neighbors benefited all three species. Plants with no neighbors

within the 40- by 40-cm quadrats had the best survival both

short and long term. There was little difference in survival

between plants with neighbors at 1 to 2 or 5 to 6 cm. Results

were mixed with respect to evidence for greater competition

from more closely related neighbors. Plains lovegrass seemed

to support the theory, having its lowest survival rate with

same-species neighbors. Cottontop, however, had its lowest
152 USDA Forest Service Proceedings RMRS-P-30. 2003

Biedenbender, McClaran, and Roundy Effects of Neighbor Species and Distance on 2- and 4-Year Survival of...

Table 2—Four-year survival (percent) across all treatments for Lehmann lovegrass and native grasses having

no neighbors, same-species neighbors, or Lehmann lovegrass neighbors on the Santa Rita Experimental

Range in southeast Arizona, 1995 to 1998.

October 1995 September 1996 November 1997 November 1998

Plains lovegrass

No neighbors 100 20 0 0

Plains neighbors 85 5 0 0

Lehmann neighbors 96 12 0 0

Total survival 92 10 0 0

Arizona cottontop

No neighbors 100 100 80 60

Cottontop neighbors 80 40 20 10

Lehmann neighbors 88 12 0 0

Total survival 90 30 24 16

Lehmann lovegrass

No neighbors 100 80 80 80

Lehmann neighbors 100 96 90 60

Plains neighbors 70 40 20 20

Cottontop neighbors 90 60 100 80

Total survival 92 76 76 60

survival rate with neighbors of its most distant relative,

Lehmann lovegrass. Lehmann lovegrass experienced its

lowest survival rate with plains lovegrass neighbors, its

second lowest rate with same-species neighbors, with no

difference between cottontop neighbors and no neighbors.

The timing of the greatest mortality for all three species,

but especially plains lovegrass and cottontop, suggests that

the 2-year-old Lehmann lovegrass plants in this study survived seasonal drought better. The young native and

Lehmann lovegrass plants survived their first dry springearly summer period in 1996, and most were still alive at the

June 1996 census. However, between that census and the

following one in September, most of the plains lovegrass and

cottontop plants perished, whereas many Lehmann lovegrass

plants survived. The precipitation record from a nearby rain

gage (fig. 1) indicates that both 1995 and 1996 were below

average in total annual precipitation (388 mm from 1972 to

2002) and below average in summer precipitation (199 mm

for July through September from 1972 to 2002), but they

differed in their temporal distribution patterns. Summer

moisture was greater in 1996 than 1995, but less for the

remainder of the year. Interestingly, there was high survival

through the June 1996 census followed by abrupt decline in

size or death for most treatments by September. Perhaps a

moisture availability threshold was crossed at which plants

could no longer sustain life; perhaps as the plants grew

larger they required more moisture for survival. In any case,

it appears from this study that Lehmann lovegrass survived

low moisture availability better than plains lovegrass and

Arizona cottontop. It also appears that over the 4 years of

this study, the competitive relationship between Lehmann

lovegrass and the two native species became stronger and

shifted towards amensalism, with Lehmann lovegrass as a

neighbor negatively affecting the two natives to a greater

extent than they were able to affect Lehmann lovegrass.

Abbott and Roundy (2003) recommend seeding native

grasses for revegetation in southeast Arizona in mid to late

summer. Sporadic early summer rains stimulate native

grass germination, but seedlings perish during ensuing dry

periods that precede the more reliable rainfall events that

typically begin in July. Lehmann lovegrass seeds delay

germination until soil moisture reserves are better insured

by later summer rains. This study followed Lehmann

lovegrass and two native grasses from establishment into

adulthood and demonstrated that even successfully established native grasses succumbed to seasonal and annual

drought conditions that Lehmann lovegrass plants of the

same age survived. Because the intensity of competition

between Lehmann lovegrass and the native species increased over time, the sequestration of water resources

between neighboring adults may be more limiting than

between neighboring seedlings.

Alternatively, native grasses may die during drought

regardless of whether Lehmann lovegrass is present, and

Lehmann lovegrass may colonize sites following native

grass decline, as documented on the SRER by Angell and

McClaran (2001). The management implications of these

findings are not encouraging for revegetation with native

grasses in areas where Lehmann lovegrass exists or has

the potential to establish. Without Lehmann lovegrass,

native grass stands would be expected to recover following

drought, but once Lehmann lovegrass is present, it may

prevent native recovery.

References ____________________

Abbott, L. B.; Roundy, B. A. 2003. Available water influences field

germination and recruitment of seeded grasses. Journal of Range

Management. 56: 56–64.

Anable, M. E.; McClaran, M. P.; Ruyle, G. B. 1992. Spread of

introduced Lehmann lovegrass Eragrostis lehmanniana Nees. in

southern Arizona, USA. Biology Conservation. 61: 181–188.

Angell, D. L.; McClaran, M. P. 2001. Long-term influences of livestock management and a non-native grass on grass dynamics in

the Desert Grassland. Journal of Arid Environments. 49: 507–520.
USDA Forest Service Proceedings RMRS-P-30. 2003 153

Effects of Neighbor Species and Distance on 2- and 4-Year Survival of... Biedenbender, McClaran, and Roundy

Figure 2—Two-year fall survival for plains lovegrass,

Arizona cottontop, and Lehmann lovegrass on the

Santa Rita Experimental Range in southeast Arizona, 1995 to 1996; target plants had no neighbors,

one or two same-species neighbors, or Lehmann

lovegrass neighbors at 1 to 2 or 5 to 6 cm spacing.

Figure 3—Four-year fall survival for plains lovegrass,

Arizona cottontop, and Lehmann lovegrass on the

Santa Rita Experimental Range in southeast Arizona, 1995 to 1998; target plants had no neighbors,

one or two same-species neighbors, or Lehmann

lovegrass neighbors at 5 to 6 cm spacing.

Biedenbender, S. H.; Roundy, B. A. 1996. Establishment of native

semidesert grasses into existing stands of Eragrostis lehmanniana

in southeastern Arizona. Restoration Ecology. 4: 155–162.

Bock, C. E.; Bock, J. H.; Jepson, K. L.; Ortega, J. C. 1986. Ecological

effects of planting African lovegrasses in Arizona. Natural Geographic Research. 2: 456–463.

Bock, J. H.; Bock, C. E. 1992. Vegetation response to wildfire in

native versus exotic Arizona grassland. Journal of Vegetation

Science. 3: 439–446.

Burkholder, P. R. 1952. Cooperation and conflict among primitive

organisms. American Scientist. 40: 601–631.

Cable, D. R. 1965. Damage to mesquite, Lehmann lovegrass, and

black grama by a hot June fire. Journal of Range Management.

18: 326–329.

Cable, D. R. 1971. Lehmann lovegrass on the Santa Rita Experimental Range, 1937–1968. Journal of Range Management. 24:

17–21.

Cox, J. R.; Ruyle, G. B. 1986. Influence of climatic and edaphic

factors on the distribution of Eragrostis lehmanniana Nees in

Arizona, USA. Journal of Grassland Society of South Africa. 3:

25–29.

Cox, J. R.; Ruyle, G. B.; Roundy, B. A. 1990. Lehmann lovegrass in

southeastern Arizona: biomass production and disappearance.

Journal of Range Management. 43: 367–372.

Goldberg, D. E. 1990. Components of resource competition in plant

communities. In: Grace J. B.; Tilman, D., eds. Perspectives on

plant competition. San Diego, CA: Academic Press: 27–57.

Keddy, P. A. 1989. Competition. Population and community biology

series. London: Chapman & Hall: 90–97.

McClaran, M. P.; Angell, D. L.; Wissler, C. 2002. Santa Rita

Experimental Range Digital Database: user’s guide. Gen. Tech.

Rep. RMRS-100. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 13 p.

McPherson, G. R.; DeStefano, S. 2003. Applied ecology and natural

resource management. Cambridge University Press: 17–36.

Robinett, D. 1992. Lehmann lovegrass and drought in southern

Arizona. Rangelands 14: 100–103.
154 USDA Forest Service Proceedings RMRS-P-30. 2003

International Arid Lands Consortium:

A Synopsis of Accomplishments

Peter F. Ffolliott is Professor, School of Renewable Natural Resources, University of Arizona, Tucson. Jeffrey O. Dawson is Professor, Department of Natural

Resources and Environmental Sciences, University of Illinois, Urbana. James T. Fisher is Professor and Head, Department of Agronomy and Horticulture, New

Mexico State University, Las Cruces. Itshack Moshe is Deputy Director, Southern Region, Land Development Authority, Gilat DN Negev, Israel. Timothy E.

Fulright is Regents Professor, Caeser Kieberg Wildlife Research Institute, Texas A&M University-Kingsville, Kingville, TX. W. Carter Johnson is Professor,

Department of Horticulture, Forestry, Landscape, and Parks, South Dakota State University, Brookings. Paul Verburg is Assistant Research Professor, Division

of Earth and Ecosystem Systems, Desert Research Institute, Reno, NV. Muhammad Shatanawi is Dean, Faculty of Agriculture, University of Jordan, Amman,

Jordan. Jim P. M. Chamie is Managing Director, International Arid Lands Consortium, Tucson, AZ.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

The International Arid Lands Consortium (IALC) was established to promote research, education, and training activities

related to the development, management, and reclamation of arid and semiarid lands in the Southwestern United States, the

Middle East, and elsewhere in the world. The Consortium supports ecological sustainability and environmentally sound land

stewardship, while addressing the pressures on natural resources associated with shifting demographics and public

expectations and concerns. Areas receiving attention include the reallocation of water from agriculture to urban uses;

protection of endangered, threatened, and sensitive plant and animal species; and mitigation of excessive exploitation and

Peter F. Ffolliott

Jeffrey O. Dawson

James T. Fisher

Itshack Moshe

Timothy E. Fulbright

W. Carter Johnson

Paul Verburg

Muhammad Shatanawi

Jim P. M. Chamie

Abstract: The International Arid Lands Consortium (IALC) was established in 1990 to promote

research, education, and training activities related to the development, management, and

reclamation of arid and semiarid lands in the Southwestern United States, the Middle East, and

elsewhere in the world. The Consortium supports the ecological sustainability and environmentally sound stewardship of these lands in continuing to increase the knowledge base for managers

and land owners. Research and development efforts that relate to the IALC’s mission are

incubated at research centers of its member institutions such as the Santa Rita Experimental

Range. Results from the scientific and technical projects supported by the IALC on soil and water

resources development and conservation, land use and reclamation, processes enhancing ecological management, and inventorying techniques and monitoring are made available to managers

and land owners to improve stewardship of arid and semiarid ecosystems while maintaining the

integrity of the ecological processes.

Keywords: arid lands, semiarid lands, research, development, demonstration projects

Acknowledgments: Preparation of this paper was supported by funds provided to the International Arid Lands Consortium by the USDA Forest Service and Cooperative States Research

Education, and Extension Service. The authors gratefully knowledge the reviews of this paper by

Steven L. Loring, New Mexico Agricultural Station, Las Cruces, NM, and Darrell W. DeBoer,

South Dakota State University, Brookings.
USDA Forest Service Proceedings RMRS-P-30. 2003 155

International Arid Lands Consortium: A Synopsis of Accomplishments Ffolliott, Dawson, Fisher, Moshe, Fulbright, Johnson, Verburg, Shatanawi, and Chamie

development of limited natural resources. The IALC applies

research, development, and demonstration projects, educational and training initiatives, training courses and workshops, and technology transfer activities to the development, management, and reclamation of arid and semiarid

lands in the world. Many of these activities are incubated at

research centers of its member institutions such as the

Santa Rita Experimental Range.

Cooperation and Collaboration ___

The Consortium’s member institutions are the University of Arizona, New Mexico State University, the Jewish

National Fund, South Dakota State University, the University of Illinois, Texas A&M University-Kingsville, the

Desert Research Institute of the University and Community College System of Nevada, Jordan’s Higher Council for

Science and Technology, and Egypt’s Ministry of Agriculture and Land Reclamation. Collaboration with cooperators from other institutions, including the USDA Forest

Service, the USDA Cooperative State Research, Education,

and Extension Service, the U.S. Agency for International

Development, and similar institutions worldwide, is also

fostered. The IALC brings people and programs together in

diverse areas such as water resource development, conservation, and management; soil resource conservation and

management; ecosystem processes; land-use planning and

decisionmaking, and inventory technology.

Accomplishments and

Contributions__________________

Illustrative IALC’s accomplishments and contributions

are presented in this paper through a synopsis of the research, development, and demonstration projects and initiatives grouped into the categories of soil and water resources

development and conservation, land use and reclamation,

processes enhancing ecological management, and inventorying techniques and monitoring. A more detailed review of

the Consortium’s accomplishments and contributions is

presented in a 10-year review of its history by Ffolliott and

others (2001).

Soil and Water Resources Development

and Conservation

The IALC orients its efforts in soil and water resources

development and conservation to help people understand

what causes losses in soil productivity and to synthesize

methods to reclaim degraded soil and water resources.

Results from these efforts provide managers and land owners with ways to overcome existing or anticipated limitations in soil and water resources. For example, while the role

and importance of arid and semiarid land soils in carbon

sequestration are not fully known, management agencies

are being pressed to report management impacts on carbon

flows and strategies potentially useful to offset carbon emissions. The Consortium’s efforts have contributed fresh insights and innovated analytical tools for addressing this

crucial issue in terms of evaluating management impacts

and formulating management strategies for this purpose.

Conserving potable water for critical uses is an important

water supply issue. Managers and land owners must understand the associated agricultural crop and environmental

health risks posed by the water that is locally made available

including treated waste water. IALC research has also

extended people’s knowledge of water and integrated watershed management (Ffolliott and others 2000) and the physical-chemical processes that lead to the contamination of

water systems in arid and semiarid regions.

Land Use and Reclamation

A main thrust of the IALC research and development

projects in land use and reclamation concerns is developing

computer-based systems to improve decisionmaking processes for desert, grassland, and riparian ecosystem management efforts. Managers of these fragile ecosystems generally confront problems that involve several goals and

objectives. One such problem can be minimizing the cost of

a water management practice while maximizing forage

production, with this problem also subject to limited funding, a restricted land base, and a requirement to satisfy the

objectives within a specified period. Managers can effectively analyze this type of resource-allocation problem with

decision-support systems such as those developed by researchers supported by the IALC. While the themes of these

systems have largely centered on plant-water relationships,

optimizing livestock stocking rates, and habitat suitability,

the general structure of the decision-support systems that

have been developed are applicable to a wide spectrum of

management topics.

A database template based on knowledge gained on research centers such as the Santa Rita Experiment Range

has been developed for rangeland managers to build their

own local database systems for planning effective and environmentally sound livestock management practices on public grazing lands in the Southwestern United States. These

databases also help researchers to validate predictive models of forage growth and consumptive patterns, teachers and

students to learn about the ecological processes of livestock

production, and decisionmakers to select the best rangeland

management practice.

Processes Enhancing Ecological

Management

The IALC research and development activities help people

to determine how livestock grazing, invasive shrub control,

reseeding activities, and microphytic soil crust occurrences

influence plant rangeland diversity, nutrient distribution

and productivity, and water capture. The high proportion

of the IALC studies relating to biological diversity and

productivity of plants and animals, and their functional

relationships, reflects the fragility of biodiversity in arid

and semiarid land ecosystems. The Consortium has also

supported research on genetic and physiological determinants of drought hardiness and the productivity of coniferous trees, fruit-producing cacti, and native herbaceous
156 USDA Forest Service Proceedings RMRS-P-30. 2003

Ffolliott, Dawson, Fisher, Moshe, Fulbright, Johnson, Verburg, Shatanawi, and Chamie International Arid Lands Consortium: A Synopsis of Accomplishments

plants. Results from these studies provide a basis for

selecting, breeding, or genetic modification of plants that

tolerate aridity and prolonged heat loads. The improved

understanding of genetic diversity and phenotypic plasticity is helping to predict the effects of global climate change

and habitat destruction on populations of plants and associated organisms.

Efforts supported by the IALC contribute to people’s

understanding of how habitat fragmentation, livestock

grazing patterns, and herbaceous and shrub invasion affects species diversity and the ecology of desert fauna. The

contributing role of small mammals in soil-patch development and maintenance has also been clarified. Studies on

ungulates have centered on anti-nutritional factors in

leguminous shrubs and development of telemetry to track

animals. The effects of landscape-level processes such as

habitat fragmentation and desertification on ungulate and

predator diversity and population dynamics have also been

addressed.

Inventorying Techniques and Monitoring

IALC-supported projects in inventorying and monitoring

have focused on developing improved ways to assess the risk

that humans pose to the fragile ecology of arid and semiarid

environments and, conversely, the hazards that these environments pose to humans (Ffolliott and others 1998, 2001).

Research and development that involve the impact of human activities on the environment largely consider the

response of vegetative systems to traditional land uses

including livestock grazing and agroforestry activities. However, researchers have learned that field-based inventorying and monitoring are often unable to detect subtle changes

in landscape conditions caused by these actions, a situation

necessitating continued study.

Intensive inventorying and monitoring of small areas are

not necessarily representative of the overall condition of the

larger landscape. Therefore, techniques have been developed to provide a wide spatial assessment of land surface

conditions that are compatible with temporal data sets that

represent decades or longer. Geographic information systems play a major role in these research and development

activities.

The Future ____________________

Where technologically based economic development and

urbanization supplants pastoralism and other traditional

land uses of arid and semiarid lands, problems of livestock

overgrazing, ineffective water conservation, excessive recreation impacts, unwise mining operations, and pollution

continue to emerge. Solutions to these problems require

careful research and planning to improve the critical balance between humans and their natural resource systems.

Efforts to restore and preserve natural and cultural heritage, sustain intensive agricultural enterprises, and maintain biological diversity must be increased. The consequences

of overpopulation and resource degradation are dire and, as

a result, will challenge political, economic, and scientific

leaders. Therefore, the future requires the IALC to be

flexible and innovative in meeting its mission. Policies and

approaches that increase collaboration must continue. Member institutions will continue to cooperate, collaborate, and

contribute within a framework of shared interest in, and

concern for, the viability of arid and semiarid ecosystems

worldwide.

References ____________________

Ffolliott, P. F.; Fisher, J. T.; Sachs, M.; DeBoer, D. W.; Dawson,

J. O.; Fulbright, T. E. 1998. Role of demonstration projects in

combating desertification. Journal of Arid Environments. 39:

155–163.

Ffolliott, P. F.; Fisher, J. T.; Sachs, M.; DeBoer, D. W.; Dawson,

J. O.; Fulbright, T. E.; Tracy, J. 2000. International Arid Lands

Consortium: Better land stewardship in water and watershed

management. In: Ffolliott, P. F.; Baker, M. B., Jr.; Edminster,

C. B.; Dillon, M. C.; Mora, K. L., tech. coords. Land stewardship

in the 21st century: the contributions of watershed management. Proc. RMRS-P-13. Fort Collins, CO: U.S. Department of

Agriculture, Forest Service, Rocky Mountain Research Station: 335–338.

Ffolliott, P. F.; Dawson, J. O.; Fisher, J. T.; Moshe, I.; DeBoer, D. W.;

Fulbright, T. E.; Tracy, J.; Al Musa, A.; Johnson, C.; Chamie, J.

P. M. 2001. Arid and semiarid land stewardship: a 10-year review

of accomplishments and contributions of the International Arid

Lands Consortium. Gen. Tech. Pap. RMRS-GTR-89. Fort Collins,

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 74 p.
USDA Forest Service Proceedings RMRS-P-30. 2003 157

Donald J. Breckenfeld

Daniel Robinett

Soil and Ecological Sites of the Santa Rita

Experimental Range

Donald J. Breckenfeld is a Major Land Resource Area Soil Survey Leader with the Natural Resources Conservation Service at the Tucson Soil Survey in Tucson,

AZ; phone: 520-670-6482, ext. 242.. He has a B.S. degree in soil science from the University of Arizona, and he started working with the Soil Conservation Service,

now the Natural Resources Conservation Service, as a Soil Scientist making soil surveys in 1979. Daniel Robinett is currently a Rangeland Management Specialist

with Natural Resources Conservation Service for southern Arizona. He completed a B.S. degree in range management from the University of Arizona and began

working as a Range Conservationist in 1972 with the Soil Conservation Service, now the Natural Resources Conservation Service.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

The soil survey and rangeland resource inventory of the Santa Rita Experimental Range (SRER) were conducted by the

Natural Resources Conservation Service staff, Tucson, AZ. The field work was completed during April and May 1997. This is

an update of an older soil survey completed in 1971 (Richardson 1971). The information contained in this report will be used

by research scientists and range managers for evaluating and utilizing these rangeland resources.

The Cooperative Soil Survey Procedures described and defined in the Soil Survey Manual, Soil Taxonomy, and the National

Soils Handbook (Soil Survey Division Staff 1993, 1999, and 1996) were used to classify and describe the soil morphologic

properties of the Santa Rita Experimental Range (SRER). The Major Land Resource Areas (MLRA) are defined in U.S.

Department of Agriculture (1981), Agricultural Handbook 296, United States Government Printing Office, Washington, DC.

Geomorphic landforms definitions as defined in Peterson (1981) and the Soil Survey Division Staff (1996) National Soil Survey

Handbook were used.

Thirty-two soil series and taxadjuncts were found on the SRER and delineated in 24 different mapping units (table 1).

Taxadjuncts have soil properties that are outside of the recognized soil series by one or more differentiating characteristics

of the series. The three taxadjuncts mapped on the SRER could potentially be new soil series if a significant area is eventually

Abstract: A soil survey and rangeland resource inventory of the Santa Rita Experimental Range

(SRER) was conducted by staff from the Tucson office of the Natural Resources Conservation

Service (NRCS) during April and May of 1997. Thirty-two soils series and taxadjuncts were

mapped on the SRER and delineated in 24 different mapping units. These soils all occur in an

Aridic and Ustic moisture regime and span three precipitation zones, and all soils are in the

thermic soil temperature regime. Soil series and mapping unit descriptions are provided. The

rangeland inventory and the soil map correlate soils into ecological sites and determine the

present day status or condition of the sites by comparing present plant communities with potential

plant communities as described by NRCS in their technical ecological site descriptions. Eighteen

different ecological sites were identified in two Major Land Resource Areas (MLRA 40 and 41) on

the SRER, and eight sites were mapped in the 10- to 13-inch precipitation zone of MLRA 40, the

Upper Sonoran Desert. Eight sites were mapped in the 12- to 16-inch precipitation zone of MLRA

41, the Southern Arizona Grassland. Two ecological sites were mapped in the 16- to 20-inch

precipitation zone of MLRA 41, the Mexican Oak Savanah.

Acknowledgments: GIS data layers for the soils and ecological sites of the SRER were completed

by Debbie Angell and Dr. Mitchel P. McClaran of the University of Arizona, School of Renewable

Natural Resources (SRNR). Additional maps were provided by Dawn Browning, Graduate

Student in SRNR, using the SRNR Advanced Resource Technology (ART) Laboratory facilities.

Field work was conducted by Don Breckenfeld, Dan Robinett, Emilio Carrillo, Rob Wilson, Bill

Svetlick, and Chuck Peacock of the NRCS. They were assisted by Sue Muir of the University of

Arizona SRNR.
158 USDA Forest Service Proceedings RMRS-P-30. 2003

Breckenfeld and Robinett Soil and Ecological Sites of the Santa Rita Experimental Range

recognized. These soils all occur in an Aridic and Ustic soil

moisture regime spanning three precipitation zones, and a

thermic soil temperature regime (mean annual soil temperature at 50-cm depth is 15 to 22 o

C).

Figure 1 presents the soil and ecological map of the SRER.

The approximate boundaries of the MLRA’s are also noted.

Table 2 lists the soil depth, drainage class, and land form for

each of the soil series, and table 3 lists the taxonomic

classification for each soil series. A brief description of the

soil mapping units are included below. The detailed pedon

description and soil interpretations for each soil series are

available online at http://az.nrcs.usda.gov under technical

resources, and a report by Breckenfeld and Robinett (1997)

provide additional information about the SRER soil and

rangeland resources.

Descriptions of Soil Map Unit ____

1 Agustin sandy loam, 0 to 3 percent slopes—Composition of this unit is approximately 80 percent Agustin

and 20 percent inclusions. Typical profile of Agustin has a

yellowish brown sandy loam 0 to 14 cm with 5 to 15 percent

surface gravel (A). (The horizon designations as defined in

Soil Survey Division Staff [1993] are noted in parenthesis

for the major horizons in each soil series. For example an A

horizon is the surface horizon with an enrichment of organic matter, a Bk, Bt, and Bw are subsurface horizons

with an accumulation of carbonates, clay, and minimally

changed horizon, respectively. The C horizons are unconsolidated parent material, and the R horizon is consolidated bedrock.) The subsoil is a pale brown calcareous

sandy loam to coarse sandy loam from 14 to 107 cm (Bw,

Table 1—Soil and ecological map unit legend for the Santa Rita Experimental Range.

Map unit Soil properties

1 Agustin sandy loam, 0 to 3 percent slopes

2 Arizo-Riverwash complex, 0 to 3 percent slopes

3 Baboquivari-Combate complex, 1 to 5 percent slopes

4 Bodecker-Riverwash complex, 1 to 3 percent slope

5 Budlamp-Woodcutter complex, 15 to 60 percent slopes

6 Caralampi sandy loam, 1 to 8 percent slopes

7 Cave-Rillino-Nahda complex, 1 to 10 percent slopes

8 Chiricahua-Lampshire complex, 3 to 18 percent slopes

9 Combate loamy sand, 1 to 8 percent slopes

10 Combate-Diaspar complex, 1 to 5 percent slopes

11 Hayhook-Bucklebar soils complex, 0 to 3 percent slopes

12 Hayhook-Pajarito complex, 0 to 5 percent slopes

13 Keysto-Riverwash complex, 1 to 3 percent slopes

24 Lampshire-Pantak-Rock outcrop complex, 10 to 60 percent slopes

14 Lampshire-Budlamp-Woodcutter complex, 15 to 60 percent slopesa

15 Mabray-Rock outcrop complex, 10 to 60 percent slopes percent slopes

16 Nahda-Rillino complex, 1 to 30 percent slope

17 Oversight fine sandy loam complex, 1 to 3 percent slopes

18 Pinalino-Stagecoach complex, 3 to 15 percent slopes

19 Sasabe-Baboquivari complex, 1 to 8 percent slopes

20 Tombstone complex, 0 to 5 percent slopes

21 Topawa complex, 1 to 8 percent slopes

22 Tubac complex, 0 to 2 percent slopes

23 White House-Eloma complex, 1 to 10 percent slopes

a

Soils in this map unit are taxadjuncts.

Bk). The substratum is a calcareous yellowish brown loam

from 107 to 150 cm (Bk).

2 Arizo-Riverwash complex, 0 to 3 percent slopes—

Composition of this unit is approximately 65 percent Arizo,

25 percent Riverwash and 10 percent inclusions. Typical

profile of Arizo has a yellowish brown gravelly loamy sand 0

to 46 cm with 5 to 15 percent surface gravel and cobbles (A).

The subsoil is a yellowish brown very gravelly loamy sand

from 46 to 150 cm (C). Riverwash consists of unconsolidated

material in the channel of an ephemeral stream, commonly

bordered by steep to vertical banks cut into the alluvium

(Arizo soil). It is usually dry but can be transformed into a

temporary watercourse or a short-lived torrent after a heavy

rain within the watershed.

3 Baboquivari-Combate complex, 1 to 5 percent

slopes—Composition of this unit is approximately 60 percent Baboquivari, 25 percent Combate, and 15 percent

inclusions. Typical profile of Baboquivari has a dark yellowish brown loamy sand 0 to 8 cm with 5 to 10 percent surface

gravel (A). The subsoil is a brown coarse sandy loam to

reddish brown sandy clay loam from 8 to 150 cm (Bt). Typical

profile of Combate has a brown loamy sand 0 to 5 cm with 5

to 15 percent surface gravel (A). The subsoil is a dark brown

coarse sandy loam to sandy loam from 5 to 150 cm (A, C).

4 Bodecker-Riverwash complex, 1 to 3 percent

slopes—Composition of this unit is approximately 65 percent Bodecker, 25 percent Riverwash, and 10 percent inclusions. Typical profile of Bodecker has a brown loamy sand

0 to 8 cm with 5 to 25 percent surface gravel (A). The subsoil

is a brown stratified gravelly sand and very gravelly coarse

sand coarse sandy loam to sandy loam from 8 to 150 cm (C).
USDA Forest Service Proceedings RMRS-P-30. 2003 159

Soil and Ecological Sites of the Santa Rita Experimental Range Breckenfeld and Robinett

Figure 1—Map of soil and ecological site declinations. this map displays the

approximate boundaries of the three MLRAs 40-1, 41-3, and 41-1, and the

major roads on the Santa Rita Experimental Range.

Riverwash consists of unconsolidated material in the channel of an ephemeral stream, commonly bordered by steep to

vertical banks cut into the alluvium (Bodecker soil). It is

usually dry but can be transformed into a temporary water

course or a short-lived torrent after a heavy rain within the

watershed.

5 Budlamp-Woodcutter complex, 15 to 60 percent

slopes—Composition of this unit is approximately 40 percent Budlamp, 30 percent Woodcutter, and 30 percent inclusions. Typical profile of Budlamp has a very dark brown very

gravelly sandy loam 0 to 5 cm with 35 to 45 percent surface

gravel and cobbles (A). The subsoil is a very dark grayish

brown extremely gravelly fine sandy loam dark 5 to 20 cm

(C). The next layer is unweathered bedrock at 20 cm (R).

Typical profile of Woodcutter has a brown very gravelly fine

sandy loam 0 to 5 cm with 35 to 45 percent surface gravel and

cobbles (A). The subsoil is a dark brown to reddish brown

very gravelly loam and very gravelly clay loam 5 to 30 cm

(Bt). The next layer is unweathered bedrock at 30 cm (R).

6 Caralampi sandy loam, 1 to 8 percent slopes—

Composition of this unit is approximately 75 percent

Caralampi and 25 percent inclusions. Typical profile of

Caralampi has a brown gravelly sandy loam 0 to 15 cm with

5 to 20 percent surface gravel (A). The subsoil is a reddish

brown very gravelly sandy clay loam brown coarse sandy

loam to a reddish brown extremely cobbly sandy clay loam

from 15 to 150 cm (Bt).

7 Cave-Rillino-Nahda complex, 1 to 10 percent

slopes—Composition of this unit is approximately 35 percent Cave, 30 percent Rillino, 15 percent Nahda, and 20

percent inclusions. Typical profile of Cave has a brown

calcareous gravelly sandy loam 0 to 13 cm (A, Bk) with 30 to
160 USDA Forest Service Proceedings RMRS-P-30. 2003

Breckenfeld and Robinett Soil and Ecological Sites of the Santa Rita Experimental Range

Table 2—Soil depth, drainage class, and geomorphic land forms of 32 soil series mapped on the Santa Rita Experimental Range.

Soil series Soil depth Drainage class Landform

Agustin Very deep Well Fan terrace

Arizo Very deep Excessively Flood pain, Inset fan

Baboquivari Very deep Well Fan terrace

Bodecker Very deep Excessively Flood pain, Inset fan

Bucklebar Very deep Well Fan terrace

Budlamp Very shallow to shallow Well Hills, mountains

Budlampa Moderately deep Well Hills, mountains

Caralampi Very deep Well Fan terrace

Cave Very shallow to shallow Well Fan terrace

Chiricahua Shallow Well Hills, mountains

Combate Very deep Well Alluvial fans

Diaspar Very deep Well Fan terrace

Eloma Very deep Well Fan terrace

Hayhook Very deep Well Fan terrace

Keysto Very deep Well Inset fans, stream terrace

Lampshire Very shallow to shallow Well Hills, mountains

Lampshire* Moderately deep Well Hills, mountains

Mabray Very shallow to shallow Well Hills, mountains

Nahda Very deep Well Fan terrace

Oversight Very deep Excessively Inset fans, stream terrace

Pajarito Very deep Well Fan terrace

Pantak Very shallow to shallow Well Hills, mountains

Pinalino Very deep Well Fan terrace

Rillino Very deep Well Fan terrace

Sasabe Very deep Well Fan terrace

Stagecoach Very deep Well Fan terrace

Tombstone Very deep Well Fan terrace

Topawa Very deep Well Fan terrace

Tubac Very deep Well Basin floor

White House Very deep Well Fan terrace

Woodcutter Very shallow to shallow Well Hills, mountains

Woodcuttera Moderately deep Well Hills, mountains

a

All three soils are taxadjuncts.

40 percent surface gravel. The next layer is an indurated

calcium carbonate cemented hardpan from 13 to 25 cm thick

(Bkm). Typical profile of Rillino has a pinkish gray sandy

loam 10 cm thick with 35 to 40 percent surface gravel (A).

The subsoil is a brown to light brown calcareous sandy loam

from 10 to 150 cm (Bw, Bk). Typical profile of Nahda has a

reddish brown sandy loam 0 to 8 cm with 45 to 55 percent

surface gravel and cobbles (A). The subsoil is a dark reddish

brown gravelly sandy clay to very gravelly clay from 8 to 61

cm (Bt, Btk). The next layer is a light reddish brown calcareous very gravelly sandy loam from 61 to 87 cm (Bk) and a

calcium carbonate cemented hardpan from 87 to 100 cm

(Bkm).

8 Chiricahua-Lampshire complex, 3 to 18 percent

slopes—Composition of this unit is approximately 60 percent Chiricahua, 20 percent Lampshire, and 20 percent

inclusions. Typical profile of Chiricahua has a dark brown

cobbly sandy loam 0 to 8 cm with 10 to 35 percent surface

gravel, cobbles, and stones (A). The subsoil is a dark reddish

brown very gravelly clay to a gravelly clay loam 8 to 48 cm

(Bt). The next layer is weathered bedrock from 48 to 71 cm

(Cr) and unweathered bedrock at 71 cm (R). Typical profile

of Lampshire has a dark grayish brown very gravelly sandy

loam 0 to 20 cm with 15 to 35 percent surface gravel, cobbles,

and stones (A, C). The next layer is unweathered bedrock at

20 cm (R).

9 Combate loamy sand, 1 to 8 percent slopes—

Composition of this unit is approximately 90 percent Combate

and 10 percent inclusions. Typical profile of Combate has a

brown loamy sand 0 to 5 cm with 5 to 15 percent surface

gravel (A). The subsoil is a dark brown coarse sandy loam to

sandy loam from 5 to 150 cm (A, C).

10 Combate-Diaspar complex, 1 to 5 percent slopes—

Composition of this unit is approximately 65 percent

Combate, 25 percent Diaspar, and 15 percent inclusions.
USDA Forest Service Proceedings RMRS-P-30. 2003 161

Soil and Ecological Sites of the Santa Rita Experimental Range Breckenfeld and Robinett

Table 3—Taxonomic classification of the soil series mapped on the Santa Rita Experimental Range.

Typic Aridica: 10- to 12-inch precipitation zone

Agustin Coarse-loamy, mixed, superactive, thermic Typic Haplocalcids

Arizo Sandy-skeletal, mixed, thermic Typic Torriorthents

Bucklebar Fine-loamy, mixed, superactive, thermic Typic Haplargids

Cave Loamy, mixed, superactive, thermic, shallow Typic Petrocalcids

Hayhook Coarse- loamy, mixed, superactive, thermic Typic Haplocambids

Nahda Clayey-skeletal, mixed, superactive, thermic Typic Petroargids

Pajarito Coarse-loamy, mixed, superactive, thermic Typic Haplocambids

Pinalino Loamy-skeletal, mixed, superactive, thermic Typic Calciargids

Rillino Coarse-loamy, mixed, superactive, thermic Typic Haplocalcids

Stagecoach Loamy-skeletal, mixed, superactive, thermic Typic Haplocalcids

Topawa Loamy-skeletal, mixed, superactive, thermic Typic Haplargids

Tubac Fine, mixed, superactive, thermic, Typic Paleargids

Ustic Aridicb: 12- to 16-inch precipitation zone

Baboquivari Fine-loamy, mixed, superactive, thermic Ustic Haplargids

Bodecker Sandy-skeletal, mixed, thermic, Ustic Torriorthents

Caralampi Loamy-skeletal, mixed, superactive, thermic Ustic Haplargids

Chiricahua Clayey, mixed, superactive, thermic, shallow Ustic Haplargids

Combate Coarse-loamy, mixed, superactive, nonacid, thermic Ustic Torrifluvents

Diaspar Coarse-loamy, mixed, superactive, thermic Ustic Haplarigds

Eloma Clayey-skeletal, mixed, superactive, thermic Ustic Haplargids

Keysto Loamy-skeletal, mixed, superactive, nonacid, thermic Ustic Torriorthents

Lampshire Loamy-skeletal, mixed, superactive, nonacid, thermic Lithic Ustic Torriorthents

Mabray Loamy-skeletal, carbonatic, thermic Lithic Ustic Torriorthents

Pantak Loamy-skeletal, mixed, superactive, thermic Lithic Ustic Haplargids

Sasabe Fine, mixed, superactive, thermic Ustic Paleargids

Tombstone Loamy-skeletal, mixed, superactive, thermic Ustic Haplocalcids

White House Fine, mixed, superactive, thermic Ustic Haplargids

Aridic Usticc

: 16- to 20-inch precipitation zone

Budlamp Loamy-skeletal, mixed, superactive, thermic Lithic Haplustolls

Budlampd Loamy-skeletal, mixed, superactive, thermic Aridic Haplustolls

Lampshired Coarse-loamy, mixed, superactive, thermic Aridic Ustochrepts

Oversight Loamy-skeletal, mixed, superactive, thermic Aridic Ustochrepts

Woodcutter Loamy-skeletal, mixed, superactive, thermic Lithic Argiustolls

Woodcutterd Loamy-skeletal, mixed, superactive, thermic Aridic Argiustoll

aTypic Aridic soils are the soils on the drier end of the aridic moisture regime and are also in thermic temperature regime.

Average annual precipitation is 7 to 12 inches. b

Ustic Aridic soils are the soils on the moist end of the aridic moisture regime and are also in thermic temperature regime.

Average annual precipitation is 12 to 16 inches. c

Aridic Ustic soils are the soils on the drier end of the ustic moisture regime and are also in thermic temperature

regime. Average annual precipitation is 16 to 20 inches. d

Soils are taxadjuncts.

Typical profile of Combate has a brown loamy sand 0 to 5 cm

with 5 to 15 percent surface gravel (A). The subsoil is a dark

brown coarse sandy loam to sandy loam from 5 to 150 cm (A,

C). Typical profile of Diaspar has a brown loamy sand 0 to 13

cm with 5 to 20 percent surface gravel (A). The subsoil is a

brown coarse sandy loam to sandy loam from 13 to 150 cm

(Bt).

11 Hayhook-Bucklebar soils complex, 0 to 3 percent

slopes—Composition of this unit is approximately 50 percent Hayhook, 40 percent Bucklebar (thin and thick surface), and 10 percent inclusions. Typical profile of Hayhook

has a yellowish brown loamy sand 0 to 4 cm with 5 to 15

percent surface gravel (A). The subsoil is a pale brown coarse

sandy loam to gravelly coarse sandy loam from 4 to 150 cm

(Bw, C). Typical profile of Bucklebar (thin surface) has a

brown sandy loam 0 to 8 cm with 5 to 20 percent surface

gravel (A). The subsoil is a brown to yellowish red sandy clay

loam coarse sandy loam from 8 to 150 cm (Bw, Bt). Typical

profile of Bucklebar (thick surface) has a brown sandy loam

0 to 38 cm with 5 to 15 percent surface gravel (A). The subsoil

is a brown to yellowish red sandy clay loam coarse sandy

loam from 38 to 150 cm (Bw, Bt).

12 Hayhook-Pajarito complex, 0 to 5 percent slopes—

Composition of this unit is approximately 50 percent

Hayhook, 30 percent Pajarito, and 20 percent inclusions.

Typical profile of Hayhook has a yellowish brown loamy

sand 0 to 4 cm with 2 to 15 percent surface gravel (A). The

subsoil is a pale brown coarse sandy loam to gravelly coarse

sandy loam from 4 to 150 cm (illuvial calcium carbonate

below 50 cm and noneffervescent above 50 cm) (Bw, Bk).

Typical profile of Pajarito has a brown sandy loam 0 to 11 cm

with 5 to 15 percent surface gravel (A). The subsoil is a brown

to yellowish brown fine sandy loam from 11 to 150 cm

(illuvial calcium carbonate above 50 cm and effervescent)

(Bw, Bk).
162 USDA Forest Service Proceedings RMRS-P-30. 2003

Breckenfeld and Robinett Soil and Ecological Sites of the Santa Rita Experimental Range

13 Keysto-Riverwash complex, 1 to 3 percent slopes—

Composition of this unit is approximately 65 percent Keysto,

25 percent Riverwash, and 10 percent inclusions. Typical

profile of Keysto has a brown sandy loam 0 to 7 cm with 5 to

25 percent surface gravel (A). The subsoil is a brown very

cobbly sandy loam to extremely cobbly loamy sand from 7 to

150 cm (C). Riverwash consists of unconsolidated material

in the channel of an ephemeral stream, commonly bordered

by steep to vertical banks cut into the alluvium (Keysto soil).

It is usually dry but can be transformed into a temporary

watercourse or a short-lived torrent after a heavy rain

within the watershed.

24 Lampshire-Pantak-Rock outcrop complex, 10 to

60 percent slopes—Composition of this unit is approximately 40 percent Lampshire, 30 percent Pantak, and 10

percent inclusions. Typical profile of Lampshire has a very

dark gray cobbly loam 0 to 20 cm with 15 to 35 percent

surface gravel, cobbles, and stones (A). The subsoil is a dark

reddish brown very gravelly clay to a gravelly clay loam 8

to 48 cm (Bt). The next layer is unweathered bedrock at 48

cm (R). Typical profile of Pantak has a very brown very

gravelly to gravelly sandy loam 0 to 10 cm with 35 to 55

percent surface gravel, cobbles, and stones (A). The subsoil

is a brown very gravelly sandy clay loam 10 to 36 cm (Bt).

The next layer is unweathered bedrock at 6 cm (R). Rock

outcrop consists of barren rock that occurs as ledges and

nearly vertical cliffs of tilted and folded formations of

bedrock. Rock outcrop also includes areas where the soil

depth to bedrock is less than 10 cm. The higher percentage

of rock outcrop is in areas near the summit and on steeper

slope areas.

14 Lampshire-Budlamp-Woodcutter complex, 15 to

60 percent slopes—Composition of this unit is approximately 40 percent Lampshire, 20 percent Budlamp, 20

percent Woodcutter, and 20 percent inclusions. All three

soils in this map unit are taxadjuncts. Typical profile of

Lampshire has a brown very cobbly fine sandy loam 0 to 26

cm with 35 to 50 percent surface gravel and cobbles (A). The

subsoil is a brown to reddish brown gravelly fine sandy loam

and loam 26 to 71 cm (Bw). The next layer is weathered

bedrock from 71 to 100 cm (Cr) and unweathered bedrock at

100 cm (R). Typical profile of Budlamp predominately on

north slopes has a dark yellowish brown cobbly fine sandy

loam 0 to 8 cm with 35 to 55 percent surface gravel and

cobbles (A). The subsoil is a dark yellowish brown cobbly

loam 8 to 61 cm (C). The next layer is weathered bedrock

from 61 to 75 cm (Cr) and unweathered bedrock at 75 cm (R).

Typical profile of Woodcutter has a dark brown very gravelly

fine sandy loam 0 to 10 cm with 35 to 45 percent surface

gravel and cobbles (A). The subsoil is a brown to reddish

brown very gravelly sandy clay loam to extremely gravelly

fine sandy loam 10 to 64 cm (Bt, B/C). The next layer is

weathered bedrock from 64 to 71 cm (Cr) and unweathered

bedrock at 71 cm (R).

15 Mabray-Rock outcrop complex, 10 to 60 percent

slopes—Composition of this unit is approximately 60 percent Mabray, 30 percent Rock outcrop, and 10 percent

inclusions. Typical profile of Mabray has a dark gray brown

cobbly to very gravelly calcareous loam 0 to 31 cm with 45 to

55 percent surface gravel, cobbles, and stones (A, Bk). The

next layer is unweathered bedrock at 31 cm (R). Rock

outcrop consists of barren rock that occurs as ledges and

nearly vertical cliffs of tilted and folded formations of bedrock. Rock outcrop also includes areas where the soil depth

to bedrock is less than 10 cm. The higher percentage of rock

outcrop is in areas near the summit and steeper slope areas.

16 Nahda-Rillino complex, 1 to 30 percent slopes—

Composition of this unit is approximately 45 percent Nahda,

35 percent Rillino, and 20 percent inclusions. Typical profile

of Nahda has a reddish brown sandy loam 0 to 8 cm with 45

to 55 percent surface gravel and cobbles (A). The subsoil is a

dark reddish brown gravelly sandy clay to very gravelly clay

from 8 to 61 cm (Bt). The next layer is a light reddish brown

calcareous very gravelly sandy loam from 61 to 87 cm (Btk).

The calcium carbonate cemented hardpan is from 87 to 100

cm (Bkm). Typical profile of Rillino has a pinkish gray

gravelly sandy loam 0 to 10 cm with 35 to 50 percent surface

gravel (A). The subsoil is a brown to light brown calcareous

gravelly sandy loam to very gravelly sandy loam from 10 to

150 cm (Bw, Bk).

17 Oversight fine sandy loam complex, 1 to 3 percent

slopes—Composition of this unit is approximately 75 percent Oversight and 25 percent inclusions. Typical profile of

Oversight has a brown fine sandy loam 0 to 10 cm with 5 to

35 percent surface gravel and cobbles (A). The subsoil is a

brown cobbly fine sandy loam to very cobbly sandy loam from

10 to 150 cm (C).

18 Pinalino-Stagecoach complex, 3 to 15 percent

slopes—Composition of this unit is approximately 45 percent Pinalino, 40 percent Stagecoach, and 15 percent inclusions. Typical profile of Pinalino has a brown gravelly sandy

loam 0 to 5 cm with 45 to 55 percent surface gravel and

cobbles (A). The subsoil is a reddish brown extremely cobbly

sandy clay loam from 5 to 76 cm (Bt, Btk). The next layer is

a calcareous pink extremely gravelly sandy clay loam from

76 to 150 cm (Bk). Typical profile of Stagecoach has a light

brown gravelly sandy loam 0 to 10 cm with 35 to 45 percent

surface gravel (A). The subsoil is a brown light brown

calcareous very gravelly sandy loam to very gravelly loam

from 10 to 150 cm (Bw, Bk).

19 Sasabe-Baboquivari complex, 1 to 8 percent

slopes—Composition of this unit is approximately 55 percent Sasabe, 35 percent Baboquivari, and 10 percent inclusions. Typical profile of Sasabe (thick surface) has a brown

sandy loam 0 to 13 cm with 0 to 10 percent surface gravel (A).

The subsoil is a dusky red clay to sandy clay from 13 to 150

cm (Bt). Sasabe (thin surface) has a brown sandy loam 0 to

5 cm with 5 to 15 percent surface gravel (A). The subsoil is

a dusky red clay to sandy clay from 5 to 150 cm (Bk). Typical

profile of Baboquivari has a dark yellowish brown coarse

sandy loam 0 to 20 cm with 0 to 10 percent surface gravel (A).

The subsoil is a dark brown gravelly sandy clay loam to

sandy clay loam from 20 to 150 cm (Bt).

20 Tombstone complex, 0 to 5 percent slopes—Composition of this unit is approximately 85 percent Tombstone

and 15 percent inclusions. Typical profile of Tombstone has

a brown calcareous gravelly sandy loam 0 to 23 cm with 35

to 45 percent surface gravel (A, Bw). The subsoil is a brown

calcareous very gravelly sandy loam to very gravelly loamy

sand from 23 to 150 cm (Bk).
USDA Forest Service Proceedings RMRS-P-30. 2003 163

Soil and Ecological Sites of the Santa Rita Experimental Range Breckenfeld and Robinett

21 Topawa complex, 1 to 8 percent slopes—Composition of this unit is approximately 40 percent Topawa (thick

surface), 35 percent Topawa (thin surface), and 25 percent

inclusions. Typical profile of Topawa (thick surface) has a

brown coarse sandy loam 0 to 15 cm with 5 to 20 percent

surface gravel (A). The subsoil is a reddish brown gravelly to

very gravelly sandy clay loam from 15 to 150 cm (Bt). Typical

profile of Topawa (thin surface) has a brown coarse sandy

loam 0 to 10 cm with 5 to 20 percent surface gravel (A). The

subsoil is a reddish brown gravelly to very gravelly sandy

clay loam from 10 to 150 cm (Bt).

22 Tubac complex, 0 to 2 percent slopes—Composition of this unit is approximately 40 percent Tubac silt loam,

30 percent Tubac sandy loam, and 20 percent inclusions.

Typical profile of Tubac silt loam has a brown silt loam 0 to

15 cm with 0 to 10 percent surface gravel (A). The subsoil is

a brown to reddish brown clay to sandy clay from 15 to 150

cm (Bt). Typical profile of Tubac sandy loam has a brown

sandy loam 0 to 10 cm with 0 to 15 percent surface gravel (A).

The subsoil is a brown to reddish brown clay to sandy clay

from 15 to 150 cm (Bt).

23 White House-Eloma complex, 1 to 10 percent

slopes—Composition of this unit is approximately 45 percent White House, 35 percent Eloma, and 20 percent inclusions. Typical profile of White House has a brown sandy

loam 0 to 5 cm with 5 to 15 percent surface gravel (A). The

subsoil is a brown to dark reddish brown clay to clay loam

from 5 to 150 cm (Bt, C). Typical profile of Eloma has a brown

sandy loam 0 to 5 cm with 5 to 15 percent surface gravel (A).

The subsoil is a brown to dark reddish brown very gravelly

clay to extremely cobbly clay from 5 to 150 cm (Bt).

Description of the Ecological

Sites _________________________

Eighteen ecological sites were identified in two Major

Land Resource Areas (MLRAs) on the SRER in the 1997

inventory. Table 4 lists the soil series and ecological sites

found in the MLRA. Eight sites were mapped in the 10- to

13-inch precipitation zone (PZ) of MLRA 40, the Upper

Sonoran Desert (D40-1). Soils mapped in this area have

typic aridic moisture regimes and thermic temperature

regimes. This area occurs below 3,200 ft elevation on the

SRER with the exception of the extreme northeast corner

where elevations run to 3,700 ft in this MLRA. Eight sites

were mapped in the 12- to 16-inch PZ of MLRA 41, the

Southeast Arizona Basin and Range (D41-3). Soils mapped

in this zone have an ustic aridic moisture regime and a

thermic temperature regime. This area occurs at elevations ranging from 3,200 ft to 4,400 ft. A few steep southern

aspects carry up as high as 4,900 ft. Two sites were mapped

in the 16- to 20-inch PZ of MLRA 41, the Mexican Oak

Savanah (D41-1). Elevations in this zone range from 4,200

ft on north aspects up to the highest elevations on the SRER

at 5,150 ft. Soils mapped in this zone have an aridic ustic

moisture regime and a thermic temperature regime.

Table 5 shows the ecological sites found on the SRER. The

common plant species of the present day plant community

are shown for each ecological site. The NRCS Field Office

Technical Guide contains more detailed ecological site descriptions with information about climate, soils, potential

plant communities, Major Land Resources Areas, and Official Series Descriptions. It is located online at http://

az.nrcs.usda.gov under technical resources. Several of the

older exclosures (fenced on or before 1937) on the SRER are

used by NRCS as reference areas for ecological sites in these

MLRAs. These include: Exclosure #44, at Gravelly Ridge

Station—Loamy upland and Limy slopes D40-1; Exclosure

#22—Sandy loam, Deep D41-3; Exclosure #96 at Northwest

Station—Sandy loam, Deep D40-1; and Exclosure #8— Sandy

loam upland D41-3.

References ____________________

Breckenfeld, Donald J.; Robinett, Daniel. 1997. Soil and range

resource inventory of the Santa Rita Experimental Range Pima

County, Arizona. Special Report.

Peterson, F. F. 1981. Landforms of the Basin and Range Province

defined for soil survey. Nevada Agricultural Experiment Station

Tech. Bull. 28.

Richardson M. L. 1971. Soil survey of Santa Cruz and parts of

Cochise and Pima Counties, Arizona.

Schoeneberger, P. J.; Wysocki, D. A.; Benham, E. C.; Broderson, W. D.

1998. Field book for describing and sampling soils. U.S. Department

of Agriculture, Natural Resources Conservation Service, National

Soil Survey Center.

Soil Survey Divisions Staff. 1996. National soil survey handbook.

U.S. Department of Agriculture, Natural Resources Conservation Service.

Soil Survey Division Staff. 1993. Soil survey manual. U.S. Department of Agriculture Handb. 18. Soil Conservation Service.

Soil Survey Staff. 1999. Soil taxonomy: a basic system of soil

classification for making and interpreting soil surveys. 2d ed.

United States Department of Agriculture, Soil Conservation Service. 1981. Land resource regions and major land resource areas

of the United States. U.S. Department of Agriculture Handb. 296.
164 USDA Forest Service Proceedings RMRS-P-30. 2003

Breckenfeld and Robinett Soil and Ecological Sites of the Santa Rita Experimental Range

Table 4—Major Land Resource Areas and the soil series and ecological sites in the MLRA.

MLRA 40-1, 10- to 13-inch precipitation zone

1 Agustin sandy loam, 0- to 3-percent slopes

Agustin-Limy Fan, 10- to 13-inch precipitation zone

2 Arizo-Riverwash complex, 0- to 3-percent slopes

Arizo-Sandy Bottom, 10- to 13-inch precipitation zone

7 Cave-Rillino-Nahda complex, 1- to 10-percent slopes

Cave and Rillino-Limy Upland, 10- to 13-inch precipitation zone

Nahda-Loamy Upland, 10- to 13-inch precipitation zone

11 Hayhook-Bucklebar complex, 0- to 3-percent slope

Hayhook-Sandy Loam, Deep, 10- to 13-inch precipitation zone

Bucklebar-Sandy Loam Upland, 10- to 13-inch precipitation zone and Loamy Upland, 10 to 13-inch precipitation zone

12 Hayhook-Pajarito complex, 0- to 5-percent slopes

Hayhook-Sandy Loam, Deep, 10- to 13-inch precipitation zone

Pajarito-Sandy Loam, Deep, 10- to 13-inch precipitation zone and Limy Fan, 10- to 13-inch precipitation zone

16 Nahda-Rillino complex, 1- to 30-percent slopes

Nahda-Loamy Upland, 10- to 13-inch precipitation zone

Rillino-Limy Slopes, 10- to 13-inch precipitation zone

18 Pinalino-Stagecoach complex, 3- to 15-percent slopes

Pinalino-Loamy Upland, 10- to 13-inch precipitation zone

Stagecoach-Limy Slopes, 10- to 13-inch precipitation zone

21 Topawa complex, 1- to 8-percent slopes

Topawa-Sandy Loam Upland, 10- to 13-inch precipitation zone and Loamy Upland, 10- to 13-inch precipitation zone

22 Tubac complex, 0- to 2-percent slopes

Tubac-Clay Loam Upland, 10- to 13-inch precipitation zone and Loamy Upland, 10- to 13-inch precipitation zone

MLRA 41-3, 12- to 16-inch precipitation zone

3 Baboquivari-Combate complex, 1- to 5-percent slopes

Baboquivari-Sandy Loam Upland, 12- to 16-inch precipitation zone

Combate-Sandy Loam, Deep, 12- to 16-inch precipitation zone

4 Bodecker-Riverwash complex, 1- to 3-percent slopes

Bodecker-Sandy Bottom, 12- to 16-inch precipitation zone

6 Caralampi sandy loam, 1- to 8-percent slopes

Caralampi-Sandy Loam Upland, 12- to 16-inch precipitation zone

8 Chiricahua-Lampshire complex, 3- to 18-percent slopes

Chiricahua and Lampshire, Shallow Upland, 12- to 16-precipitation zone

9 Combate loamy sand, 1- to 8-percent slopes

Combate, Sandy Loam, Deep, 12- to 16-inch precipitation zone

10 Combate-Diaspar complex, 1- to 5-percent slopes

Combate-Sandy Loam, Deep, 12- to 16-inch precipitation zone

Diaspar-Sandy Loam Upland, 12- to 16-inch precipitation zone

13 Keysto-Riverwash complex, 1- to 3-percent slope

Keysto-Sandy Bottom, 12- to 16-inch precipitation zone

24 Lampshire-Pantak complex, 10- to 60-percent slope

Lampshire and Pantak-Granitic Hills, 12- to 16-inch precipitation zone

15 Mabray-Rock outcrop complex, 10- to 60-percent slopes

Mabray-Limestone Hills, 12- to 16-inch precipitation zone

19 Sasabe-Baboquivari complex, 1- to 8-percent slopes

Sasabe-Sandy Loam Upland, 12- to 16-inch precipitation zone and Loamy Upland, 12- to 16-inch precipitation zone

Baboquivari-Sandy Loam Upland, 12- to 16-inch precipitation zone

20 Tombstone complex, 0- to 5-percent slopes

Tombstone-Limy Fan, 12- to 16-inch precipitation zone

23 White House-Eloma complex, 1- to 10-percent slopes

White House and Eloma-Loamy Upland, 12- to 16-inch precipitation zone

MLRA 41-1, 16- to 20-inch precipitation zone

5 Budlamp-Woodcutter complex, 15- to 60-percent slopes

Budlamp and Woodcutter-Shallow Hills, 16- to 20-inch precipitation zone

14 Lampshire-Budlamp-Woodcutter complex, 15- to 60-percent slopesa

Lampshire, Budlamp and Woodcutter-Shallow Hills, 16- to 20-inch precipitation zone

17 Oversight fine sandy loam, 1- to 3-percent slopes

Oversight-Sandy Bottom, 16- to 20-inch precipitation zone

aSoils are taxadjuncts.
USDA Forest Service Proceedings RMRS-P-30. 2003 165

Soil and Ecological Sites of the Santa Rita Experimental Range Breckenfeld and Robinett

Table 5—Descriptions of the ecological sites mapped on the Santa Rita Experimental Range.

Ecological sitea MLRAa Site numbera Important plant species

Limy fan 10-13 40-1 040XA108AZ Creosotebush, bush muhly,

pappusgrass, fluffgrass

Sandy Bottom 10-13 40-1 040XA115AZ Mesquite, catclaw, annuals,

paloverdes, dropseed spp.

Limy upland 10-13 40-1 040XA111AZ Creosote, zinnia, ratany,

bush muhly, threeawn spp.

Loamy upland 10-13 40-1 040XA114AZ Ratany, false mesquite,

snakeweed, threeawn spp.

Sandy loam upland 10-13 40-1 040XA118AZ Mesquite, burroweed,

Arizona cottontop, threeawns

Sandy loam, deep 10-13 40-1 040XA117AZ Mesquite, burroweed,

bush muhly, threeawns

Limy slopes 10-13 40-1 040XA110AZ Whitethorn acacia, ocotillo

black grama, bush muhly

Clay loam upland 10-13 40-1 040XA120AZ Tobosa, prickley pear

annual forbs and grasses

Sandy loam upland 12-16 41-3 041XC319AZ Mesquite, Lehmann love,

burroweed, threeawn spp.

Sandy loam, deep 12-16 41-3 041XC318AZ Mesquite, Lehmann love,

burroweed, threeawn spp.

Sandy bottom 12-16 41-3 041XC316AZ Mesquite, catclaw, desert

willow, blue paloverde

Shallow upland 12-16 41-3 041XC322AZ Mesquite, Lehmann love,

prickley pear, grama spp.

Granitic hills 12-16 41-3 041XC306AZ Grama spp., buckwheat,

plains love, mimosa spp.

Limestone hills 12-16 41-3 041XC307AZ Tridens spp., rosewood,

ocotillo, whitethorn

Loamy upland 12-16 41-3 041XC313AZ Mesquite, false mesquite,

Lehmann love, grama spp.

Limy fan 12-16 41-3 041XC325AZ Creosote, bush muhly,

threeawns, pappusgrass

Sandy bottom 16-20 41-1 041XA112AZ Oak spp, catclaw, mesquite

hackberry, sycamore, ash

Shallow hills 16-20 41-1 041XA102AZ Oak spp, grama spp, plains

lovegrass, bluestem spp.

a

Description located online at http://az.nrcs.usda.gov under technical resources.
166 USDA Forest Service Proceedings RMRS-P-30. 2003

Gerald J. Gottfried

Peter F. Ffolliott

Pablo Garcia

Diego Valdez-Zamudio

Akram Al-Khouri

Assessment of Fire-Damaged Mesquite

Trees 8 Years Following an Illegal Burn

Gerald J. Gottfried is Research Forester, Rocky Mountain Research Station, USDA Forest Service, Phoenix, AZ, phone: 602-225-5357. Peter F. Ffolliott and

Pablo Garcia are Professors and Research Assistants, School of Renewable Natural Resources, University of Arizona, Tucson. Diego Valdez-Zamudio is Professor,

Faculty of Agriculture, University of Sonora, Hermosillo, Sonora, Mexico. Akram Al-Khouri is Professor, Faculty of Agriculture, Damascus University, Damascus, Syria.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

An illegal fire burned approximately 80 acres of a mesquite-dominated semidesert grass-shrub rangeland in Sawmill Canyon on the Santa

Rita Experimental Range in the early summer of 1994. The initial effects of this burn on the mesquite component of the burned ecosystem

were assessed in the late fall of 1995, about 18 months after the fire (DeBano and others 1996). This paper reports on a followup assessment

of the effects of the burn on mesquite trees 8 years after the fire. The current assessment was made to determine the extent to which firedamaged mesquite trees have succumbed or recovered from the burn and whether stocking by mesquite has returned to preburn conditions

in the absence of management practices to prevent their return. The information contributes to the earlier literature base (Alonso 1967; Cable

1965; Cox and others 1990; DeBano and others 1996; McLaughlin and Bowers 1982; Reynolds and Bohning 1956; White 1969; and others) on

the effects of fire on mesquite in semidesert grass-shrub ecosystems of the Southwestern United States.

Fire Site _________________________________________________________

The fire burned on a rocky site about 11/2 miles from the Florida Canyon Headquarters near the southern boundary of the

Experimental Range. The site is 3,900 ft in elevation on largely southerly slopes ranging from 5 to 20 percent. Soil information

is not available for the site. The prefire overstory was dominantly mesquite with ocotillo (Fouquieria splendens) scattered

throughout. The prefire herbaceous cover based on similar sites at Santa Rita was dominated by Lehmann lovegrass

(Eragrostis lehmanniana), a species that was introduced onto the Experimental Range in the 1930s (Cox and Roundy 1986),

with black grama (Bouteloua eriopoda) and Arizona cottontop (Digitaria californica) intermixed. Cattle grazed the site in

accordance with research plans prepared by the University of Arizona (Womack 2000). Fuel loadings before the fire are

unknown.

Abstract: Effects of an illegal burn on the Santa Rita Experimental Range on mesquite (Prosopis

velutina) survival in the semidesert grass-shrub ecosystem was initially assessed in terms of firedamage classes 18 months after the fire and again 8 years after the burn. While many of the

mesquite trees on the burned site were damaged by the fire, some of the trees appear to have

recovered to preburn conditions. The effects of the burn on mesquite stocking characteristics and

sprouting mortality were also determined from the latter assessment. Results obtained from the

8-year assessment add to the knowledge about the effects of fire on mesquite trees in semidesert

grass-shrub ecosystems of the Southwestern United States.

Keywords: mesquite trees, fire-damaged, survival, postfire sprouting

Acknowledgments: The authors gratefully acknowledge the reviews of this paper by Malcolm J.

Zwolinski, University of Arizona, Tucson, Carolyn H. Sieg, USDA Forest Service, Flagstaff, AZ,

and Ronald J. Bemis, USDA Natural Resources Conservation Service, Douglas, AZ.
USDA Forest Service Proceedings RMRS-P-30. 2003 167

Assessment of Fire-Damaged Mesquite Trees 8 Years Following an Illegal Burn Gottfried, Ffolliott, Garcia, Valdez-Zamudio, and Al-Khouri

Methods ______________________

Numbers of fire-damaged mesquite trees and mesquite

with no visible fire damage were tallied on 40 1/20-acre

temporary plots spaced at 100-ft intervals along a series of

randomly located transects traversing the burned area. The

tallied mesquite trees were classified in terms of the following fire-damage classes:

• No visible damage

• Partial crown damage (initially classified as scorched

crowns) with and without basal sprouting

• Complete crown kill (initially classified as either shoot

killed or root killed) with and without basal sprouting

Diameter at root collar (d.r.c.) was measured on the singlestemmed trees that were tallied and equivalent diameter at

root collar (e.d.r.c.) was calculated for multiple-stemmed

trees (Chojnacky 1988). Equivalent diameter at root collar is

the square root of the sum of squared d.r.c. values of the

individual stems. These diameter measurements were later

related to the occurrence of mesquite trees in the firedamage classes.

Statistical comparisons of the assessment of fire-damaged

mesquite trees 18 months after the fire with respect to the

assessment made 8 years following the burn were limited

because of the differences in the nature of the two sampling

procedures. Temporary plots were established in both of the

assessments, precluding remeasurements of the same tallied trees. Also, there was a larger number of 1/20-acre plots

(60) in the initial postfire assessment. Although the same

area of the burn was sampled in both assessments, the

placement of transects was another factor. A Fisher’s Exact

Test and a chi-square tests were used to evaluate the

proportion of stocked plots and the distribution of trees

among damage classes. Statistical significance is indicated

by an a = 0.05. General trends and relative comparisons are

reported in this paper. If the sample in each assessment is

assumed to be representative of the burned area, these data

should provide insights into changes over the past 8 years.

Results and Discussion _________

A total of 79 mesquite trees (equivalent to 39.5 trees per

acre) were tallied on 18 (45 percent) of the 40 plots. The

remaining plots were not stocked with mesquite. A total of

257 mesquite trees (equivalent to 85.7 trees per acre) were

tallied on 37 (61.7 percent) of plots traversing the burned site

18 months after the fire (DeBano and others 1996). The

apparent reduction in the stocking of mesquite trees is

attributed largely to the intervening mortality of severely

fire-damaged trees tallied 18 months after the burn. However, the proportion of stocked plots was not significantly

reduced over the 8-year period.

The percent of mesquite trees in the respective fire-damage

classes for the two assessments is shown in figure 1. The

distribution among classes differed significantly between the

two periods. While the number of trees tallied 8 years after the

fire was smaller, the relative proportions of trees with no

visible damage, partial crown damage (scorched crowns), and

complete crown kill with basal sprouting (shoot killed) were

largely similar in the two assessments. There was a decrease

in the relative portions of trees that experienced complete

crown kill with no sprouting (root killed). This finding was

partially due to incorrectly identifying mesquite trees in this

fire-damage class in the initial assessment.

The sampled mesquite trees in 2003 ranged from 0.8 to

16.2 inches in diameter at d.r.c. or e.d.r.c. There were no

relationships between the occurrence of mesquite trees in

the fire-damage classes and their respective diameters (either d.r.c. or e.d.r.c.) or between the occurrence of these trees

and the total number of trees that were tallied on the plots.

This finding was similar to that reported in the initial

assessment of the burn (DeBano and others 1996). Such

relationships (or the lack of these relationships) are mostly

fire specific (Cable 1965; McLaughlin and Bowers 1982;

Reynolds and Bohning 1956; White 1969; Womack 2000)

and probably affected by the interactions of fire intensity

and fire-damaged tree size.

The postfire sprouting characteristics of mesquite 8 years

after the burn were the same as those observed by Cable

(1965), White (1969), and McLaughlin and Bowers (1982).

Basal sprouts originating below the ground surface were the

most commonly observed form of sprouting in the trees with

partial crown damage (initially scorched crowns) in both

postfire assessments. Basal sprouts were also observed in

trees with complete crown kill, which were assumed to be

shoot killed but not root killed 18 months after the fire.

Management Inferences _________

It was postulated that stocking by mesquite trees might

return to preburn conditions in the absence of management

practices to prevent their return in the 18-month assessment (DeBano and others 1996). However, this level of

restocking had not occurred 8 years after the fire, and it is

unlikely that it will be attained in the near future. It is

concluded, therefore, that the Sawmill Canyon fire effectively converted a semidesert grass-shrub rangeland originally stocked (to an unknown level) with mesquite trees to a

rangeland of relatively few mesquite trees. However, the

effects of the reduction in tree density on the herbaceous

cover are unknown. Fire has been reported to be effective in

eliminating mesquite from semidesert grass-shrub rangelands in other studies (Cable 1965, 1967, 1972; Humphrey

1963, 1969; Martin 1975, 1983; Reynolds and Bohning 1956;

Figure 1—Percent of mesquite trees in fire-damage

classes 18 months and 8 years following the Sawmill

Canyon fire on the Santa Rita Experimental Range.
168 USDA Forest Service Proceedings RMRS-P-30. 2003

Gottfried, Ffolliott, Garcia, Valdez-Zamudio, and Al-Khouri Assessment of Fire-Damaged Mesquite Trees 8 Years Following an Illegal Burn

White 1969). These latter studies mostly involved applications of prescribed burning treatments rather than the

occurrence of a wildfire as reported in this paper.

References ____________________

Alonso, R. C. 1967. Desert grassland mesquite and fire. Tucson:

University of Arizona. 164 p. Dissertation.

Cable, D. R. 1965. Damage to mesquite, Lehmann, and black grama

by a hot June fire. Journal of Range Management. 18: 326–329.

Cable, D. R. 1967. Fire effects on semidesert grasses and shrubs.

Journal of Range Management. 20: 170–176.

Cable, D. R. 1972. Fire effects in Southwestern semidesert grassshrub communities. Tall Timbers Fire Ecology Conference. 1972:

150–153.

Chojnacky, D. C. 1988. Juniper, pinyon, oak, and mesquite volume

equations for Arizona. Res. Pap. INT-391. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 11 p.

Cox, J. R.; Roundy, G. B. 1986. Influence of climatic and edaphic

factors on the distribution on Eragrostis lehmannianain Arizona,

U.S.A. Journal of the Grassland Society of South Africa. 3: 25–29.

Cox, J. R.; Ibarra-F., A; Martin-M, M. H. 1990. Fire effects on grasses

in semiarid deserts. In: Krammes, J. S., tech. coord. Effects of fire

of Southwestern natural resources. Gen. Tech. Rep. RM-191. Fort

Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station: 43–49.

DeBano, L. F.; Gottfried, G. J.; Villanueva-Diaz, J.; Ffolliott, P. F.;

Valdez-Zamudio, D. 1996. Initial assessment of fire-damaged

mesquite trees following an illegal burn. In: Ffolliott, P. F.;

DeBano, L. F.; Baker, M. B., Jr.; Gottfried, G. J.; Solis-Garza, G.;

Edminster, C. B.; Neary, D. G.; Allen, L. S., tech. coords. Effects

of fire on Madrean Province ecosystems; a symposium proceedings. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest

and Range Experiment Station: 226–228.

Humphrey, R. R. 1963. The role of fire in the desert grassland areas

of Arizona. Tall Timbers Fire Ecology Conference. 1963: 45–62.

Humphrey, R. R. 1969. The past role of fire in range management

in the Southwest and some future possibilities. In: Wagle, R. F.,

ed. Proceeding of a conference on fire ecology and control and use

of fire in wildland management: 52–56.

Martin, S. C. 1975. Ecology and management of Southwestern

semidesert grass-shrub ranges: The status of our knowledge. Res.

Pap. RM-156. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment

Station. 39 p.

Martin, S. C. 1983. Response of semidesert grasses and shrubs to

fall burning. Journal of Range Management. 36: 604–610.

McLaughlin, S. P.; Bowers, J. E. 1982. Effects of wildfire on a

Sonoran desert plant community. Ecology. 63: 246–248.

Reynolds, H. G.; Bohning, J. W. 1956. Effects of burning on a desert

grass-shrub range in southern Arizona. Ecology. 37: 769–777.

White, L. D. 1969. Effects of a wildfire on several desert grassland

shrub species. Journal of Range Management. 22: 284-285.

Womack, J. D. 2000. Mortality and sprouting vigor of burned and

cut velvet mesquite (Prosopis velutina Wooten): the role of basal

diameter and number of stems. Tucson: University of Arizona.

61 p. Thesis.
USDA Forest Service Proceedings RMRS-P-30. 2003 169

Larry D. Howery

Bruce D. Munda

Dan G. Robinett

Harry H. Buck

Sweet Resin Bush on the Santa Rita

Experimental Range: An Eradication Effort

Larry D. Howery has worked as an Assistant and Associate Professor and Range Extension Specialist with the University of Arizona in Tucson since 1995. Larry

completed B.S. and M.S. degrees in wildlife science at Texas Tech University, and a Ph.D. degree in range science at Utah State University. Contact Larry at:

School of Renewable Natural Resources, 325 Biological Sciences East, University of Arizona, Tucson, AZ 85721; telephone: (520) 621-7277; e-mail: lhowery@ag.

arizona.edu. Bruce D. Munda has worked for the Soil Conservation Service (now the Natural Resource Conservation Service) since 1975. Bruce received a B.S.

degree in agriculture (minor in watershed hydrology and range management) and an M. S. degree in agronomy and plant genetics from the University of Arizona.

Dan G. Robinett has worked for the Soil Conservation Service (now the Natural Resource Conservation Service) for the last 31 years as a Rangeland Management

Specialist in southern Arizona. Dan received a B.S. degree in range management from the University of Arizona. Harry H. Buck worked for the Agriculture

Research Service’s Range section from 1987 to 1992 as a Range Technician. He has worked as Farm Superintendent at the Natural Resource Conservation Service’s

Tucson Plant Materials Center since 1992.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: Sweet resin bush (Euryops subcarnosus DC ssp. vulgaris B. Nord; or, Euryops

multifidis (L. f.) DC.), a South African shrub introduced to Arizona in the 1930s, was discovered

on the Santa Rita Experimental Range (SRER) in 1998. Due to the threat of spread of this invasive

plant and its potential to cause adverse environmental and economic effects, and because it posed

a threat to the Federally listed endangered Pima pineapple cactus (Coryphantha sheeriiMuehlenph.

L.D. Benson var. robustispina L.D. Benson), we initiated a project in early 1999 with the overall

goal of eradicating about 154 acres of the shrub from SRER. Prior to initial treatments in 1999,

permanent monitoring plots were randomly established within grazed and ungrazed areas that

contained heavy, moderate, or no amounts of sweet resin bush. Plant cover (percent) and density

(plants per 15m2) were sampled in January and February for 4 consecutive years (1999 to 2002).

Sweet resin bush was hand grubbed in 1999, 2000, and 2001. Picloram (Tordon 22K) was spot

sprayed via a backpack sprayer in February 1999 to soil areas where sweet resin bush had been

grubbed. Initial eradication treatments in 1999 (mechanical + chemical) greatly reduced sweet

resin bush species composition and density, and apparently released soil moisture and nutrients,

allowing some native plants to re-establish in 2000. Sweet resin bush seedling density increased

substantially in 2001; however, the combined effects of mechanical and herbicidal treatments

along with periodic drought substantially reduced sweet resin bush density and canopy cover by

2002. No new seed production occurred for sweet resin bush on SRER during this 4-year study,

and we detected no encroachment of sweet resin bush into uninfested control plots (grazed or

ungrazed). Although this project greatly reduced sweet resin bush on SRER, total eradication of

the shrub was not accomplished. Surveys and eradication efforts for sweet resin bush are planned

on SRER for at least another 10 years.

Acknowledgments: We appreciate the dedication of AmeriCorps and Boy Scout volunteers who

worked hard to remove sweet resin bush from SRER. We acknowledge Dr. Mitchel McClaran who

contributed ideas regarding project design and data collection procedures, and Dr. Ed Northam

and Doug Parker for their critical review, which greatly improved an earlier draft of this paper.

We thank Beth Jordan and Valerie Oriole for their assistance with field data collection.

Precipitation data presented in this paper were accessed via SRER Database (http://ag.arizona.edu/

SRER/). The USDA Forest Service Rocky Mountain Research Station and the University of

Arizona provided funding for the digitization of these data.

Introduction ______________________________________________________

Sweet resin bush is a low-growing, South African shrub that was introduced into several areas of southern and central

Arizona during the 1930s (Pierson and McAuliffe 1995). The shrub was selected for introduction into the arid southwest
170 USDA Forest Service Proceedings RMRS-P-30. 2003

Howery, Munda, Robinett, and Buck Sweet Resin Bush on the Santa Rita Experimental Range: An Eradication Effort

because it could readily propagate from seed and was extremely drought resistant. Other perceived benefits included the exotic shrub’s ability to control soil erosion and

provide nutritional forage for sheep. Paradoxically, some

areas where sweet resin bush was introduced has experienced reduced ground cover, increased soil erosion, and

decreased forage production. The shrub exhibited a remarkable ability to displace native vegetation and transform

extensive landscapes into monocultures, and unfortunately

proved to be unpalatable to domestic and wild herbivores.

Currently, sweet resin bush infests several thousand acres

in southern and central Arizona (McAuliffe 2000).

In 1998, an employee from the Natural Resource Conservation Service (NRCS) discovered a dense core infestation

and several smaller “satellite” stands of sweet resin bush

scattered across approximately 154 acres in and near the

Gravelly Ridge Exclosure of SRER. Due to the threat of

spread of this invasive plant and its potential to cause

adverse environmental and economic effects, NRCS, the

University of Arizona, Arizona State Lands Department,

and U.S. Fish and Wildlife Service (USFWS) decided to

cooperatively plan and implement a multiyear project to

eradicate SRER sweet resin bush infestation. The USFWS

was consulted because the Federally listed endangered

Pima pineapple cactus was known to occur in the project

area and was threatened by sweet resin bush expansion.

Objectives of this 4-year project were to (1) contain sweet

resin bush expansion on SRER using mechanical and chemical control measures to remove plants around the infestation’s

perimeter, working inward to remove the core infestation;

(2) evaluate effectiveness of combined mechanical and herbicidal control techniques; and (3) monitor changes in species composition and density in grazed and ungrazed plots

that contained heavy, moderate, or no amounts of sweet

resin bush. We monitored infested and uninfested areas,

and grazed and ungrazed areas to evaluate potential influences of sweet resin bush and disturbance associated with

grazing on plant community dynamics.

Methods _______________________

Pima Pineapple Cactus

In compliance with USFWS consultation, conservation

measures were developed and implemented before eradication treatments were executed to locate and protect individual Pima pineapple cactus plants growing in or near

areas infested by sweet resin bush. A detection team, consisting of employees from NRCS, the University of Arizona,

and AmeriCorps volunteers, implemented USFWS sampling protocol. Pima pineapple cactus plant locations were

recorded in a global positioning system (GPS) and flagged

prior to applying treatments in 1999.

Sweet Resin Bush and Other Vegetation

In January 1999, we randomly established a total of 24

15-m2 permanent plots in grazed (outside the Gravelly

Ridge Exclosure) and ungrazed areas (inside the Gravelly

Ridge Exclosure) that were ocularly estimated to contain a

heavy, moderate, or no sweet resin bush cover. We collected

baseline plant cover and density data for grasses, forbs, and

woody plants detected in permanent plots just prior to

applying treatments (table 1). Cover data were collected

using the line intercept technique to determine basal (grasses)

or canopy (forbs, cactus, and woody species) cover along

permanent 15-m transects. Cover data were used to calculate species composition for two life form categories plus

sweet resin bush (herbaceous vegetation, cactus and woody

vegetation other than sweet resin bush, and sweet resin

bush). For density data, we counted individual plant species

rooted within permanent 15-m2 plots. Density data were

tallied by individual plant species and summarized using six

life form categories plus sweet resin bush (annual grass,

annual forb, perennial grass, perennial forb, woodies, cactus, and sweet resin bush).

In February 1999, nine AmeriCorps volunteers spent

2 weeks hand grubbing sweet resin bush using hoes, picks,

shovels, and hand pulling. The sweet resin bush core infestation consisted of about 5 acres that were heavily infested,

and a few satellite infestations that radiated outward from

the core infestation to encompass a total of 154 acres.

AmeriCorps volunteers were instructed to remove all sweet

resin bush plants (mature and seedlings) from satellite and

Table 1—Plant species sampled in permanent sampling plots on Santa

Rita Experimental Range, 1999 to 2002.

 Common name Scientific name

Grasses

Arizona cottontop Digitaria californica (Benth.) Henr.

Bush muhly Muhlenbergia porteri Scribn. ex Beal

Fluffgrass Erioneuron pulchellum (H.B.K.) Tateoka

Lehmann lovegrass Eragrostis lehmanniana Nees

Plains bristlegrass Eragrostis intermedia Hitchc.

Rothrock grama Bouteloua rothrockii Vasey

Six-weeks grama Bouteloua aristidoides (H.B.K.) Griseb.

Slender grama Bouteloua repens (H.B.K) Scribn. & Merr.

Three awn spp. Aristida spp.

Forbs

Ayenia Ayenia insulicol Cristobal

Deerweed Porophyllum gracile Benth.

Desert senna Senna bauhinioides (Gray) Irwin & Barneby

Ditaxis Argythamnia neomexicana Muell. Arg.

Evolvulus Evolvulus arizonicus Gray

Nightshade Solanum spp.

Purple aster Machaeranthera tanacetifolia (Kunth) Nees

Sida Sida abutifolia P. Mill.

Spurge Chamaesyce albomarginata (Torr. & Gray)

Woodies and cactus

Burroweed Isocoma tenuisecta Greene

Cactus spp. Opuntia spp.

Desert zinnia Zinnia acerosa (DC.) Gray

False mesquite Calliandra eriophylla Benth.

Janusia Janusia gracilis Gray

Mesquite Prosopis velutina Woot.

Mormon tea Ephedra spp.

Palo verde Cercidium spp.

Range ratany Krameria grayi Rose & Painter

Sweet resin bush Euryops subcarnosus DC.

 ssp. vulgaris B. Nord

Whitethorn Acacia constricta Benth.

Wolfberry Lycium spp.
USDA Forest Service Proceedings RMRS-P-30. 2003 171

Sweet Resin Bush on the Santa Rita Experimental Range: An Eradication Effort Howery, Munda, Robinett, and Buck

core infestations. As the crew removed individual sweet

resin bush plants, a one-time Picloram (Tordon 22K; 1 qt ai/

acre) treatment was applied via a backpack sprayer to soil

areas where shrubs were grubbed to kill seedlings that

might germinate near parent plants in subsequent years. No

herbicide was applied within 30 m of any Pima pineapple

cactus plant as directed by USFWS. Boy Scout volunteers

also helped to mechanically remove sweet resin bush plants

during the summer and fall of 1999 and 2000. In March of

2001, another AmeriCorps crew spent 1 week scouting the

original 154-acre infestation and mechanically removing

any sweet resin bush plants found growing in the formerly

infested area. We collected post-treatment plant cover, species composition, and density data during January and

February of 2000 to 2002 in the same manner described for

pretreatment baseline data collected in 1999. Precipitation

data for the Gravelly Ridge Exclosure were accessed via

SRER Database.

Results and Discussion __________

Pima Pineapple Cactus

A total of 21 Pima pineapple cactus plants were located

outside the core sweet resin bush infestation, and near

“satellite” infestations. No Pima pineapple cactus plants

were detected within the core infestation itself, or within any

of our permanent monitoring plots.

Species Composition

Prior to treatments in 1999, sweet resin bush respectively

made up 72 and 64 percent of species composition in heavily

infested grazed and ungrazed plots (figs. 1A,B) and 41 and

11 percent in moderately infested grazed and ungrazed plots

(figs. 2A,B). After 1999 treatments, no plot contained more

than10 percent sweet resin bush from 2000 to 2002. Thus,

combined mechanical and herbicidal treatments were effective in initially removing sweet resin bush cover from treated

plots.

Figure 1A—Species composition (percent) in

heavily infested grazed plots before (1999) and

after (2000, 2001, and 2002) eradication efforts

near the Gravelly Ridge Exclosure, SRER (clear

bars = herbaceous vegetation; light gray bars =

cactus and woody vegetation other than sweet resin

bush; darkest bars = sweet resin bush).

Figure 1B—Species composition (percent) in

heavily infested ungrazed plots before (1999) and

after (2000, 2001, and 2002) eradication efforts

near the Gravelly Ridge Exclosure, SRER (clear

bars = herbaceous vegetation; light gray bars =

cactus and woody vegetation other than sweet

resin bush; darkest bars = sweet resin bush).

Figure 2B—Species composition (percent) in moderately infested ungrazed plots before (1999) and

after (2000, 2001, and 2002) eradication efforts

near the Gravelly Ridge Exclosure, SRER (clear

bars = herbaceous vegetation; light gray bars =

cactus and woody vegetation other than sweet

resin bush; darkest bars = sweet resin bush).

Figure 2A—Species composition (percent) in

moderately infested grazed plots before (1999) and

after (2000, 2001, and 2002) eradication efforts near

the Gravelly Ridge Exclosure, SRER (clear bars =

herbaceous vegetation; light gray bars = cactus and

woody vegetation other than sweet resin bush;

darkest bars = sweet resin bush).
172 USDA Forest Service Proceedings RMRS-P-30. 2003

Howery, Munda, Robinett, and Buck Sweet Resin Bush on the Santa Rita Experimental Range: An Eradication Effort

Species composition remained relatively stable in control

plots from 1999 to 2002, although grazed control plots

contained higher relative amounts of herbaceous cover than

ungrazed control plots every year of the study (figs. 3A,B).

No sweet resin bush plants were detected in grazed or

ungrazed control transects or plots in any year of the study.

Density

Prior to treatments in 1999, mean sweet resin bush

density was respectively 167 and 67 sweet resin bush plants

per 15 m2 in heavily infested grazed and ungrazed plots

(tables 2A,B), and 85 and 39 plants per 15 m2 in moderately

infested grazed and ungrazed plots (tables 3A,B). These

same plots contained less than four sweet resin bush plants

in 2000. Little precipitation occurred from January to May

Figure 3B—Species composition (percent) in

ungrazed plots with no sweet resin bush before

(1999) and after (2000, 2001, and 2002) eradication efforts near the Gravelly Ridge Exclosure,

SRER (clear bars = herbaceous vegetation; light

gray bars = cactus and woody vegetation other

than sweet resin bush).

Figure 3A—Species composition (percent) in

grazed plots with no sweet resin bush before

(1999) and after (2000, 2001, and 2002) eradication efforts near the Gravelly Ridge Exclosure,

SRER (clear bars = herbaceous vegetation; light

gray bars = cactus and woody vegetation other

than sweet resin bush).

Table 2B—Mean density (plants per 15 m2, ±6 SE) of sweet resin bush

and other plants by life form in ungrazed plots that were

heavily infested with sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 1 43 40

Annual forb 8 0 312 303

Perennial grass 0 4 23 17

Perennial forb 0 0 8 2

Woodies 17 4 3 4

Cactus 1 0 1 1

Sweet resin bush 67 1 21 3

Table 2A—Mean density (plants per 15 m2

, ± 6 SE) of sweet resin bush

and other plants by life form in grazed plots that were heavily

infested with sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 7 154 0

Annual forb 15 13 165 179

Perennial grass 3 26 87 121

Perennial forb 0 2 10 4

Woodies 21 6 7 6

Cactus 0 0 0 0

Sweet resin bush 167 2 134 17

Table 3B—Mean density (plants per 15 m2

, ± 6 SE) of sweet resin bush

and other plants by life form in ungrazed plots that were

moderately infested with sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 9 153 6

Annual forb 86 22 680 474

Perennial grass 45 119 10 50

Perennial forb 21 9 20 1

Woodies 41 21 29 20

Cactus 5 11 6 5

Sweet resin bush 39 3 64 3

Table 3A—Mean density (plants per 15 m2, ± 6 SE) of sweet resin bush

and other plants by life form in grazed plots that were

moderately infested with sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 3 282 10

Annual forb 120 23 488 410

Perennial grass 28 38 26 24

Perennial forb 3 11 24 11

Woodies 12 12 11 11

Cactus 9 3 5 2

Sweet resin bush 85 2 4 2
USDA Forest Service Proceedings RMRS-P-30. 2003 173

Sweet Resin Bush on the Santa Rita Experimental Range: An Eradication Effort Howery, Munda, Robinett, and Buck

1999 (1.76 inches), which likely hindered sweet resin bush

germination and the ability of Picloram to kill actively

growing sweet resin bush seedlings during the first year of

the study. January to May precipitation in 2000 was even

more limited (1.55 inches), which apparently continued to

limit sweet resin bush germination, and thus, herbicide kill

of shrub seedlings.

In early 2001, sweet resin bush seedling density substantially increased in heavily infested grazed and ungrazed

plots (tables 2A,B), and in moderately infested ungrazed

plots (table 3B). Fall, winter, and spring (October to May)

precipitation was above average in 2000 to 2001 (11.85

inches), which provided a favorable opportunity for sweet

resin bush seedlings to germinate in 2001. Another Americorp

crew mechanically removed these seedlings in 2001 about

1 month after plots were sampled, which helped to reduce

sweet resin bush density by January and February 2002

(less than 18 plants per 15 m2; tables 2A,B, and 3B). Moreover,

data collected in early 2002 fell in the middle of another very dry

fall, winter, and spring (only 1.27 inches of precipitation from

October 2001 to May 2002), which likely inhibited additional

sweet resin bush germination during this dry spell.

Annual grasses and annual forbs showed slight to dramatic increases in density in at least one of the years after

sweet resin bush was initially treated (2000 to 2002), especially in early 2001 following the wettest year of the study

(19.39 inches in 2000). The flush of annuals in early 2001

coincided with the substantial increase of sweet resin bush

seedlings during the same time. Grazed and ungrazed control plots also exhibited dramatic annual plant production in

2001 (tables 4A,B).

Mechanical and herbicidal treatments in the heavily and

moderately infested plots (both grazed and ungrazed) in

1999 apparently reduced competition for soil moisture and

nutrients, allowing an increase in perennial grass density by

2000 (tables 2A,B; 3A,B). Summer rainfall in 1999 (9.6

inches from June to September) was favorable for warm

season perennial grass production, which was detected in

our plots in early 2000.

Woody plant density declined substantially in heavily

infested plots (both grazed and ungrazed) and in moderately

infested plots that were ungrazed after the initial eradication treatment in 1999. Volunteers may have mistaken

native, low-growing shrubs for sweet resin bush because

density reductions occurred in false mesquite (Calliandra

eriophylla Benth.), range ratany (Krameria grayi Rose &

Painter), and desert zinnia (Zinnia acerosa (DC.) Gray).

Picloram applied to grubbed areas could also have injured or

killed native shrubs. Conversely, woody plant density remained remarkably constant in both grazed and ungrazed

control plots where no mechanical or herbicidal treatments

were applied (tables 4A,B).

Summary and Conclusions _______

Combined mechanical and chemical control measures

were effective in initially removing core and satellite sweet

resin bush infestations from the Gravelly Ridge area of

SRER. Sweet resin bush removal in 1999 apparently released soil moisture and nutrients, allowing some components of the native plant community to begin reestablishing

within 1 year. However, timing and amount of precipitation

(or lack thereof) was apparently the major factor driving

plant community dynamics throughout the project. Drought

in early and late 1999 and throughout the first half of 2000

likely kept sweet resin bush seedling production at bay until

late 2000 or early 2001; hence, there was negligible opportunity for Picloram to kill sweet resin bush seedlings during

this dry period.

This field project integrated mechanical and herbicidal

control measures during above and below average precipitation years and was not designed to differentiate sweet resin

bush mortality due to mechanical removal, Picloram, or

drought (for example, no sweet resin bush plants were left

intact to monitor drought-caused mortality). Mechanical

removal of sweet resin bush by volunteers in 1999, 2000, and

2001 certainly played a key role in keeping sweet resin bush

in check throughout the project. In addition, both Picloram

and drought likely impaired sweet resin bush seedling

production during the 4-year project. However, Picloram

could not override the effects of above average precipitation

in late 2000, which stimulated a substantial increase in

sweet resin bush seedling density in most plots by the time

they were measured in early 2001. We speculate that without the one-time Picloram application in 1999, sweet resin

bush seedling density may have been even more pronounced

in 2001. It is noteworthy that the combined effects of mechanical and herbicidal treatments, in addition to periodic

drought, prevented any new seed production by sweet resin

bush for the entirety of our 4-year project.

Grazed plots were located immediately outside of the

grazing exclosure to intentionally select a “worst case scenario” for grazing disturbance because areas near fences are

Table 4B—Mean density (plants per 15 m2, ± 6 SE) of sweet resin bush

and other plants by life form in ungrazed plots that contained

no sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 9 4 4

Annual forb 90 286 1,224 879

Perennial grass 7 9 6 4

Perennial forb 26 120 81 9

Woodies 12 13 13 12

Cactus 0 0 0 0

Sweet resin bush 0 0 0 0

Table 4A—Mean density (plants per 15m2, ± 6 SE) of sweet resin bush

and other plants by life form in grazed plots that contained

no sweet resin bush in 1999.

Year

Life form 1999 2000 2001 2002

Annual grass 0 9 15 1

Annual forb 70 203 670 269

Perennial grass 14 25 13 14

Perennial forb 11 79 40 5

Woodies 7 7 5 5

Cactus 1 1 4 2

Sweet resin bush 0 0 0 0
174 USDA Forest Service Proceedings RMRS-P-30. 2003

Howery, Munda, Robinett, and Buck Sweet Resin Bush on the Santa Rita Experimental Range: An Eradication Effort

typically associated with amplified disturbance associated

with livestock and wildlife trailing. Sweet resin bush species

composition and density were initially higher in grazed

versus ungrazed plots, indicating that disturbance may

have facilitated sweet resin bush establishment in heavily

impacted areas. However, no sweet resin bush plants were

detected in grazed or ungrazed control plots during the entire

study, demonstrating that the shrub had not established and

did not spread approximately 400 m north where control plots

were located. Moreover, no sweet resin bush plants were

detected in grazed areas outside the original 154-acre infestation where grazing disturbance was much lower than in

grazed study plots located immediately outside the exclosure.

Thus, light to moderate grazing apparently did not facilitate

the spread of sweet resin bush on SRER.

Noxious weed invaders often exhibit the potential to

explode after a long period of slow and unapparent growth

(Sheley and Petroff 1999). The 154-acre sweet resin bush

infestation on SRER has not expanded to the degree other

sweet resin bush infestations have in Arizona (for example,

about 3,000 acres on Frye Mesa in east-central Arizona).

Nevertheless, several cooperating agencies and organizations justified eradicating this invasive shrub from SRER for

several reasons. First, the SRER sweet resin bush infestation was small enough to justify eradication as a goal.

Second, SRER sweet resin bush infestation is only 5 km from

the Santa Cruz River where seeds could potentially be

transported hundreds of miles during flood events. Third,

the stand is only 6 km from Green Valley, a rapidly growing

urban area between Tucson and Nogales. This area, with

increasing traffic and large disturbed areas around construction sites, offers ideal conditions for the shrub to spread.

Fourth, Interstate 19 from Tucson to Nogales is an international corridor on which nearly two-thirds of the winter

produce coming into the United States is transported each

year. Hence, seed from SRER could easily become a source of

introduction of sweet resin bush into Mexico. Finally, USFWS

views sweet resin bush as a direct threat to Pima pineapple

cactus survival because SRER is the only large area of prime

cactus habitat currently protected from development.

Although we did not accomplish our main goal of eradicating sweet resin bush from SRER, significant progress was

made during this project. Mechanical and herbicidal treatments along with periodic drought substantially reduced

sweet resin bush density and canopy cover on SRER since

1999. The fact that no new seed production occurred on

SRER during this project is of paramount importance in

depleting the shrub’s residual seed bank, thereby reducing

and eventually eliminating its capacity to reproduce in the

future. Conservation measures developed during this project

to identify and protect individual Pima pineapple cactus

plants were successful. This project has begun to restore

native plants to the previously infested area, thereby facilitating habitat recovery for the cactus, and severely limiting

the potential for additional colonies of sweet resin bush to

establish in uninfested endangered cactus habitat. Nevertheless, the detection of significant numbers of sweet resin

bush seedlings in 2001 indicates the crucial need for followup monitoring when invasive plants are targeted for eradication (Sheley and Petroff 1999). Survey and eradication

efforts are planned on SRER during the next 10 years.

References _____________________

McAuliffe, J. R. 2000. The battle against a harmful alien invader:

sweet resin bush from South Africa. The Sonoran Quarterly. 54:

4–9.

Pierson, E. A.; McAuliffe, J. R. 1995. Characteristics and consequences of invasion by sweet resin bush into the arid Southwestern United States. In: Biodiversity and management of the

Madrean Archipelago: the sky islands of Southwestern United

States and Northwestern Mexico. Gen. Tech. Rep. RM-GTR-264.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station: 291–230

Sheley, R. L.; Petroff, J. K. 1999. Biology and management of

noxious rangeland weeds. Corvallis: Oregon State University

Press. 438 p.
USDA Forest Service Proceedings RMRS-P-30. 2003 175

A. Karim Batchily

Donald F. Post

R. B. Bryant

Donald J. Breckenfeld

Spectral Reflectance and Soil

Morphology Characteristics of

Santa Rita Experimental Range Soils

A. Karim Batchily is a Research Specialist in the Department of Soils, Water and Environmental Science (SWES) at the University of Arizona. He received

a B.S. degree in agronomy from the Agronomic Institute Nicolae Balcescu, Buchurest, Romania, in 1982, and an M.S. degree in soil science from the University

of Arizona in 1991. He has more than 10 years of experience in soils and remote sensing. Donald F. Post is Professor Emeritus of soil science from the Soil, Water

and Environmental Science Department, University of Arizona; e-mail: postdf@ag.arizona.edu. He joined the University of Arizona faculty in 1967 and has taught

classes in basic soils, soil morphology and classification, and soil and water conservation from 1967 until the present. His research has been in soil morphology and

classification, and in using remotely sensed data to map soils and other natural resources. R. B. Bryant is a research specialist employed by the USDA Agricultural

Research Service in Tucson, AZ. He has a B.A. degree in geology from Colorado College, and he completed an M.S. degree in soil and water science from the University

of Arizona in 1990. Donald J. Breckenfeld is a Major Land Resource Area Soil Survey Leader with the USDA Natural Resources Conservation Service at the Tucson

Soil Survey in Tucson, AZ. He has a B.S. degree in soil science from the University of Arizona. He started working with the Soil Conservation Service as a Soil Scientist

making soil surveys in 1979.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: The Santa Rita Experimental Range (SRER) soils are mostly transported alluvial

sediments that occur on the piedmont slope flanking the Santa Rita Mountains in Arizona. The

major geomorphic land forms are alluvial fans or fan terraces, but there are also areas of residual

soils formed on granite and limestone bedrock, basin floor, stream terraces, and flood plains. The

soils range in age from recent depositions to soil material one to two million years of age. We

sampled A and B horizons of soil series from different geomorphic surfaces, and measured the dry

spectral reflectance (0.4 to 2.5 mm wavelength) on the sieved less than 2-mm-size fraction. Soil

color (measured with a Chroma Meter), texture, organic carbon, calcium carbonate content, and

effervescence properties were determined and correlated to spectral reflectance in selected

wavelengths. The Munsell soil color value component was most positively correlated to reflectance. Soil effervescence and calcium carbonate content, percent sand and clay, and the Munsell

soil color hue component and redness rating were also significantly correlated to soil reflectance.

Energy reflected from soil surfaces represents the interaction between many soil properties, and

soil color is an integrated expression of many soil properties. It is the best soil morphology property

to measure to predict the spectral reflectance of soils, particularly in the visible and near infrared

parts of the electromagnetic spectrum.

Acknowledgments: The Soils Map GIS data for the Santa Rita Experimental Range (SRER)

were completed by Debbie Angell and Dr. M. McClaran, and the manipulation of this data to

prepare the geomorphic land form map was prepared by Dawn Browning and Mamadou Niane,

University of Arizona, School of Renewable Natural Resources (SRNR). The SRNR Advanced

Resource Technology (ART) Laboratory facilities were utilized to create the geomorphic land form

map of the SRER. Special thanks are extended to Mary Kay Amistadi and Dr. Jon Chorover,

Department of Soil, Water and Environmental Science, University of Arizona, for determining the

organic carbon and calcium carbonate content of the SRER soils. We also thank Dr. M. S. Moran,

the USDA Agricultural Research Service, Tucson, AZ, for allowing us to use her Analytical

Spectral Device to measure spectral reflectance.

Introduction ______________________________________________________

Jenny (1941, 1980) presents a soil formation equation that states a soil is a product of the interaction of the five “Factors

of Soil Formation,” namely climate, biota, parent material, time, and topography. Within the Santa Rita Experimental Range
176 USDA Forest Service Proceedings RMRS-P-30. 2003

Batchily, Post, Bryant, and Breckenfeld Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ...

(SRER) all factors are important; however, the time and

parent material factors are particularly important. Most

SRER soils are formed in alluvium of mixed origins, derived

from igneous and sedimentary rocks (mostly granite and

limestone), and these materials then experienced different

time periods for soil development to occur. It is particularly

useful to identify what are called “geomorphic surfaces” (Ely

and Baker 1985; McAuliffe 1995 a,b; Peterson 1981), as they

are closely related to soil characteristics.

A “geomorphic surface” is a mappable landscape element

formed during a discrete time period, which has distinctive

geologic materials, topographic features, and soil profiles.

From this definition, it can be inferred that each stable

surface will have a soil developed upon it, which has properties that are in part a function of the time since erosion and/

or deposition has ceased. Quantifying pedogenic properties

of soils on different geomorphic surfaces provides a means to

compare the age of surfaces. On the SRER, soil texture, the

color (amount of reddness) of the soil, presence or absence of

carbonates in the parent material, and soil horizons distinguish the soil series mapped on the SRER

Significant relationships between soil properties and the

spectral reflectance of soils in the visible and near-infrared

portions of the electromagnetic spectrum (Baumgardner

and others 1985; Condit 1970; DaCosta 1979; Shields and

others 1968; Stoner 1979; Stoner and Baumgardner 1981)

show it is possible to use remote sensing techniques to

quantify soil properties. These researchers emphasized how

the soil components of organic carbon, iron oxides, texture,

water, and salts affect spectral reflectance. Correlations

with Munsell hue, value, and chroma were also presented,

but the color measurements were made using only the visual

comparison procedure (Soil Survey Division Staff 1993).

Escadafal and others (1988, 1989) investigated the relationships between Munsell soil colors and Landsat spectral

response, especially on arid landscapes, and reported that

the Munsell color parameters of hue, value, and chroma

were significantly correlated with Landsat data. Post and

others (1994) and Horvath and others (1984) concluded that

the reflectance of radiant energy from sparsely vegetated

arid rangelands is determined by the characteristics of the

soil and geologic material on the land surface. They also

concluded colorimeters to accurately quantify the color of

earth surface features are very important for evaluating

remotely sensed data. Other researchers (Bowers and Hanks

1965; Cipra and others 1980; Huete and Escadafal 1991;

Weismiller and Kaminsky 1978; Westin and Lemme 1978)

report how remotely sensed spectral data can be used to

characterize and map soils.

There is a keen interest in understanding how incoming

solar radiation from the sun is absorbed at the earth’s

surface. The ratio of the energy reflected back to the atmosphere is called the albedo of that surface. When discussing

albedo the spectral wavelength must be identified, and

commonly an integration of the amounts of energy reflected

between 0.3 to 2.8 mm is used. Post and others (2000)

described how albedo of soils can be predicted from soil color

and spectral reflectance and how the albedo of SRER soils

will be evaluated.

The objectives of this paper were to (1) collect samples of

soil series mapped on different geomorphic surfaces with

different kinds of alluvial parent materials and measure

their spectral reflectance, (2) measure the morphological

properties of these soils, and (3) correlate soil reflectance in

selected spectral bands to soil properties. Identification of

basic spectral curves of the soil series found on the SRER

would be useful for improved interpretation of remotely

sensed data acquired by airborne sensors and orbiting

satellites.

Materials and Methods ___________

Thirty soil samples were collected from 16 different locations from six SRER geomorphic surfaces. The A and B

horizons were sampled for mature soils; however, only the A

horizon was collected from the Holocene age soils, except for

one site where a C horizon was also collected. The samples

were selected to encompass the range of soil reflectances

that are found on the SRER. Multiple sample sites were

selected for three soil series because these soils had a wider

range of soil physical properties within these soil series.

All samples were air dried and passed through a 2-mm

sieve, and all analyses were completed with the less than

2-mm soil fraction. Soil color was measured using a Model

200 Chroma Meter (Minolta Company) as follows: the samples

were evenly distributed on a flat surface to provide a thickness of about 2 mm, the measuring head was rested in a

vertical position on the soil surface, and a color reading was

taken. A detailed description of this procedure and how the

hue color notation was converted to a number for statistical

analyses is described by Post and others (1993). The three

Munsell color components were also converted into a redness rating as follows (Torrent and others 1980):

where the chroma and value are numerical values of each,

and the hue is the notation number preceding the YR in the

Munsell color notation system. Organic and inorganic carbon (C) contents were measured using a dry combustion

method (TOC-VCSH, Total Carbon Analyser, made by

Shimadzu Corporation, Columbia, MD). The samples were

heated to 300 and 800 o

C, and the CO2 evolved at these two

temperatures were measured by an infrared detector. The

percent C released was converted to percent Organic Carbon

(O.C.) and percent calcium carbonate (CaCO3) found in each

soil. Soil texture characteristics were determined by the

“Field or Feel Method” (Thien 1978) by two field soil scientists, a mean percent clay and sand was calculated, and then

the textural class was identified. Also, how the soil reacts

when 10 percent HCL is applied to the sample (Soil Survey

Division Staff 1993) was observed and recorded. The amount

of effervescence refers to the amount of bubbles (CO2) released, and terms like “slight,” “strong,” and “violent” are

used to describe the reaction.

The reflectance spectra of these soils were recorded between the 0.4 to 2.5 mm wavelengths region at one nanometer increments using an Analytical Spectral Device full

range hyperspectral system with a 15o field of view. Smooth

soil surfaces were viewed vertically from a height of 0.5 m,

and the reflected energy was referenced to a calibrated

standard reflectance plate. The spectra were measured on a

clear, cloud-free day in Tucson, AZ, between 11:00 and 11:30

a.m. on April 16, 2003. Reflectance data of special interest to

(10 – hue) x chroma

Value Redness =
USDA Forest Service Proceedings RMRS-P-30. 2003 177

Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ... Batchily, Post, Bryant, and Breckenfeld

us were the Landsat Thematic mapper (TM) bands, namely

TM1 (blue, 0.45 to 0.52 mm), TM2 (green, 0.52 to 0.60 mm),

TM3 (red, 0.63 to 0.69 mm), TM 4 and 5 (near infrared [NIR]

0.76 to 0.90 and 1.55 to 1.75 mm), and TM 7 (middle infrared

[MIR], 2.08 to 2.35 mm). A mean reflectance factor for each

band was computed for the following wavelengths: blue =

0.485 mm, green = 0.560 mm, red = 0.660 mm, NIR = 0.830 mm,

near short wave infrared = 1.650 mm, and middle infrared =

2.180 mm. These reflectance factors were correlated with the

soil morphology properties for the 16 A horizons, 13 B

horizons, and one C horizon for a total of 30 samples. The

correlation coefficient (r value) was computed and reported

(Gomez and Gomez 1984).

Results and Discussion __________

The Soil and Ecological Site Map of the SRER prepared by

Breckenfeld and Robinett (these proceedings) was the basic

map used to prepare a general geomorphology map of the

SRER and to determine where soil samples were to be

collected. Figure 1 is a map outlining seven geomorphic

surfaces on the SRER, and table 1 defines the terms that

Figure 1—Geomorphology land form surfaces map and the soil sample location sites

collected on the Santa Rita Experimental

Range.
178 USDA Forest Service Proceedings RMRS-P-30. 2003

Batchily, Post, Bryant, and Breckenfeld Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ...

describe these surfaces. Figures 2 and 3 present the spectral

curves for representative A and B horizons, respectively. Table

2 lists the mean reflectance values for the 30 soils for six of the

Thematic Mapper (TM) wavelength bands, and table 3 lists

the soil morphology characteristics for the 30 soils.

Table 1—Description of the geomorphic land form surfaces and geologic terms to define their age as identified on the SRER listed in alphabetical

order.

Geomorphic surfaces

Alluvial fan A low, outspreading mass of loose soil and rock material, commonly with gentle slopes that are shaped like an

 open fan or a segment of a cone, deposited by water at the place where it issues from mountains.

Basin floor A general term for the nearly level, lower most part of intermontane basins. The floor includes all the alluvial,

 eolian, and erosional land forms below the piedmont slope.

Fan terrace A general term for land forms that are remaining parts of older fan B land forms, such as alluvial fan

 (fan remnant is another term used to describe this land form).

Flood plain The nearly level A plain that borders a stream and is subject to inundation under flood-stage conditions

 (unless it is protected artificially).

Hills and mountains A hill is an area of land surface, rising as much as 300 m above the surrounding lowlands, whereas a mountain

 rises more than 300 m.

Inset fan An ephemeral stream flood plain rather broad in area incised in alluvial fans or fan terraces; a barren channel

 covers a minor portion of its surface, but its breadth is rather extensive.

Piedmont slope The dominant gentle slope at the foot of a mountain that grades to a basin floor or alluvial flood plains.

Stream terraces One of a series of levels in a stream valley that mostly parallels the stream, but it no longer floods.

Geologic terms to define the age of geomorphic surfaces

Holocene The geologic time period extending from the end of the Pleistocene (Ice Age) Epoch from10,000 to 12,000 years

 before present.

Pleistocene The epoch of geologic time referred to as the Quaternary Period with a geologic time from approximately

 2 million to 10,000–12,000 years before present.

Late Pleistocene 10,000–12,000 to 25,000 years before present.

Middle Pleistocene 25,000 to 300,000 or 400,000 years before present.

Early Pleistocene 300,000 or 400,000 to 1,000,000–2,000,000 years before present.

Figure 2—Spectral curves for A horizons of representative Santa Rita

Experimental Range soils.

Stoner (1979) and Stoner and Baumgardner (1981) describe in great detail the spectral characteristics for many

soils. They explain that moisture content, organic matter,

iron content, and presence of minerals such as calcium

carbonate most determine soil color. The SRER soils have a
USDA Forest Service Proceedings RMRS-P-30. 2003 179

Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ... Batchily, Post, Bryant, and Breckenfeld

Figure 3—Spectral curves for B horizons of representative Santa

Rita Experimental Range soils.

Table 2—Percentage of reflected energy in six selected wavelengths corresponding to the Landsat Thematic Mapper (TM) bands.

Soil Soil names Blue Green Red NIR MIR MIR

ID and horizons (0.485 mm) (0.560mm) (0.660mm) (0.830mm) (1.650mm) (2.179mm)

1 Agustin (A) 0.1521 0.2126 0.2823 0.3474 0.4634 0.4814

1 Agustin (Bk) .1678 .2264 .2999 .3888 .5086 .5181

2 Nahda (A) .0912 .1336 .1891 .2441 .3645 .3747

2 Nahda (Btk) .0707 .1027 .1485 .2047 .3203 .3237

3 Sasabe (A) .0803 .1283 .2008 .2650 .4021 .4197

3 Sasabe (Bt) .0619 .0976 .1597 .2247 .3544 .3536

4 Hayhook (A) .1110 .1718 .2565 .3278 .4464 .4611

4 Hayhook (Bw) .0802 .1267 .1999 .2724 .3796 .3782

5 Tubac (A) .0947 .1492 .2303 .3021 .4205 .4288

5 Tubac (Bt) .0681 .1129 .1954 .2633 .3582 .3364

6 Tombstone (A) .1326 .1875 .2549 .3262 .4612 .4734

6 Tombstone (Bk) .1381 .1940 .2658 .3465 .4716 .4792

7 Whitehouse (A) .0950 .1581 .2549 .3246 .4466 .4435

7 Whitehouse (Bt) .0522 .0856 .1592 .2211 .3335 .2962

8 Caralampi (A) .1060 .1572 .2307 .2966 .3760 .3861

8 Caralampi (Bt) .0779 .1204 .1887 .2496 .2927 .2794

9 Combate (A) .0667 .0880 .1187 .1833 .3995 .4017

10 Whitehouse (A) .0625 .1001 .1561 .2089 .3563 .3512

10 Whitehouse (Bt) .0501 .0879 .1730 .2427 .3885 .3156

11 Whitehouse (A) .0620 .1100 .1963 .2625 .3933 .3949

11 Whitehouse (Bt) .0456 .0808 .1617 .2072 .3178 .2524

12 Combate (A) .0832 .1189 .1640 .2326 .4265 .4244

12 Combate (C) .1088 .1541 .2069 .2749 .4502 .4443

13 Combate (A) .0970 .1392 .1955 .2684 .4323 .4416

14 Baboquivari (A) .1023 .1567 .2304 .3131 .4560 .4376

14 Baboquivari (Bt) .0759 .1179 .1815 .2567 .3953 .3620

15 Bucklebar (A) .1053 .1646 .2514 .3301 .4393 .4374

15 Bucklebar (Bt) .0798 .1249 .1962 .2656 .3520 .3429

16 Bucklebar (A) .1027 .1603 .2373 .3167 .4465 .4369

16 Bucklebar (Bt) .0696 .1136 .1778 .2523 .3628 .3465
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Batchily, Post, Bryant, and Breckenfeld Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ...

Table 3—Soil morphology characteristics of the thirty soils sampled on the Santa Rita Exerimental Range.

Soil Geomorphic Soil names Munsell soil color Redness Organic

ID Surfacea and Horizons Hue Hue Value Chroma rating carbon CaCO3 Clay Sand Efferb Albedo

. . . . . . . . . percent . . . . . . . . . . 

1 D Agustin (A) 9.5 YR 4.8 6.1 3.6 0.3 0.49 13.7 10 73 3.2 0.31

1 D Agustin (Bk) 9.0 YR 4.6 6.0 3.2 .5 .59 19.4 18 69 3.8 .30

2 E Nahda (A) 8.7 YR 4.5 4.8 3.4 .9 .71 .0 18 63 .0 .22

2 E Nahda (Btk) 8.2 YR 4.3 4.2 3.2 1.4 .92 .7 32 50 .4 .18

3 G Sasabe (A) 7.2 YR 3.9 4.8 4.4 2.6 .48 .0 13 67 .0 .22

3 G Sasabe (Bt) 6.0 YR 3.4 4.2 4.3 4.0 .46 .0 30 57 .2 .18

4 F Hayhook (A) 8.0 YR 4.2 5.5 4.4 1.6 .34 .0 10 75 .0 .27

4 F Hayhook (Bw) 7.5 YR 4 4.6 4.1 2.3 .32 .0 16 70 .0 .20

5 B Tubac (A) 7.5 YR 4 5.2 4.5 2.2 .29 .0 9 78 .0 .24

5 B Tubac (Bt) 5.5 YR 3.2 4.5 4.9 5.0 .21 .0 42 41 .0 .19

6 D Tombstone (A) 9.7 YR 4.9 5.5 3.4 .2 .80 7.6 12 68 3.8 .27

6 D Tombstone (Bk) 8.7 YR 4.5 5.7 3.5 .8 .52 7.8 15 69 3.8 .28

7 G Whitehouse (A) 7.0 YR 3.8 5.2 4.7 2.7 .52 .0 8 76 .0 .24

7 G Whitehouse (Bt) 4.2 YR 2.7 3.8 4.7 7.2 .94 .0 47 30 .0 .15

8 G Caralampi (A) 8.2 YR 4.3 5.2 3.8 1.3 1.00 .0 9 67 .0 .24

8 G Caralampi (Bt) 6.7 YR 3.7 4.2 3.9 3.0 .71 .0 35 52 .0 .18

9 F Combate (A) 9.7 YR 4.9 3.9 1.9 .1 .89 .0 5 87 .0 .16

10 G Whitehouse (A) 7.2 YR 3.9 4.2 3.9 2.6 .84 .0 17 69 .0 .18

10 G Whitehouse (Bt) 4.0 YR 2.6 4.1 5.3 7.7 .68 .0 48 40 .0 .17

11 G Whitehouse (A) 5.7 YR 3.3 4.4 4.9 4.9 .92 .0 14 58 .0 .19

11 G Whitehouse (Bt) 3.2 YR 2.3 3.9 5.2 9.1 .69 .0 53 25 .0 .16

12 C Combate (A) 10.0 YR 5 4.6 2.7 .0 .62 .0 7 85 .0 .20

12 C Combate (C) 10.0 YR 5 5.1 3.0 .0 .43 .9 5 89 1.5 .23

13 F Combate (A) 9.0 YR 4.6 4.8 3.2 .7 .38 .0 8 85 .0 .22

14 F Baboquivari (A) 9.0 YR 4.6 5.3 3.9 .7 .80 .0 8 76 .0 .25

14 F Baboquivari (Bt) 7.7 YR 4.1 4.6 3.8 1.9 .53 .0 25 64 .0 .20

15 F Bucklebar (A) 7.7 YR 4.1 5.4 4.3 1.8 .49 .0 9 72 .0 .26

15 F Bucklebar (Bt) 7.0 YR 3.8 4.8 4.0 2.5 .32 .0 15 70 .0 .22

16 F Bucklebar (A) 8.7 YR 4.5 5.2 4.0 1.0 .99 .0 12 71 .0 .24

16 F Bucklebar (Bt) 8.0 YR 4.2 4.5 3.9 1.7 .30 .0 25 63 .0 .19

a Refer to figure 1 and table 1 for descriptions of geomorphic surfaces.

b

 Effervescence: 0 = none, 1 = slight, 2 = moderate, 3 = strong, 4 = violent.

low organic matter. Content and the older land surfaces,

particularly the Whitehouse soil series, are very red, indicating the presence of iron oxide in the soil. It also has a clay

texture which occurs as soils get older. Although we did not

measure the iron content of the SRER soils, we did compute

the redness index, which is indicative of the iron content

(particularly Fe20 3 – ferric iron) in a soil.

The spectral curves for the A horizons show that Combate

(9) has the lowest reflectance factor in the 0.4 to 1.0 mm

wavelength range (fig. 2). This soil also has a color value of

3.9, the lowest of all soils. The Agustin (1) soil has the highest

reflectance factor, and it also has the highest Munsell color

value of 6.1. The Agustin soil has about 14 percent CaCO3,

which contributes to the lighter color and higher Munsell

value. Other representative soil curves for the Hayhook,

Whitehouse, Nahda, and a second Combate sample are

shown to illustrate the range in spectral characteristics of

the A horizons mapped on the SRER.

Figure 3 presents the spectral curves for the B horizons.

The Agustin soil is the most reflective, and the Tombstone

soil has the next highest reflectance. Both of these soils are

formed from alluvium derived from limestone parent materials. The Whitehouse Bt horizon is very red (redness rating

of 9.1), and the shape of the spectral curve shows the

presence of iron in this soil. The iron absorption occurs in the

0.5 to 0.9 mm band width. The Bucklebar and Hayhook soils

have intermediate spectral reflectance characteristics. The

Nahda Btk horizon reflectance is similar to the Whitehouse

Bt horizon, but the curve shape is different because the

Nahda soil is less red and likely has a lower iron content.

The spectral curves for both the A and B horizons from 1.0

mm to 2.5 mm show very strong absorptions at about 1.9 mm,

and a less pronounced absorption band at 1.4 mm. There are

striking other differences in reflected energy in the 1.0 to 2.5

mm bands, which are mostly water or hydroxyl absorption

bands. Spectral data in the visible and NIR are commonly

used to classify the reflectance properties of land surfaces

because orbiting satellites collect data in these wavelengths, and this is of most interest to us.

Table 4 lists the linear relationships, expressed as the

correlation coefficient > r value =, for the mean reflectances

of six TM bands and soil morphology properties. The correlations were determined for the A and B horizons, and all 30

samples including one C horizon sample. The significance of

each correlation is noted in the table for P £ 0.05 and P £ 0.01,

with one and two asterisks, respectively.
USDA Forest Service Proceedings RMRS-P-30. 2003 181

Spectral Reflectance and Soil Morphology Characteristics of Santa Rita ... Batchily, Post, Bryant, and Breckenfeld

For all three groups, there was a very significant correlation with Munsell value, and the r values ranged from 0.93

to 0.99 for the visible and NIR bands. For the middle NIR

and the MIR bands the r values were lower, and they

ranged from 0.69 to 0.95, and were lowest for the A horizons.

For the A horizons, the percent CaCO3 and effervescence had

the next strongest correlations to reflectance in the blue and

green bands, but they were less important in the other bands.

Munsell chroma was significantly correlated in the red and

NIR bands.

There were many significant correlations identified for

the B horizons and for all 30 samples. Munsell value, percent

CaCO3, and effervescence were again most strongly correlated, but other soil morphology properties like Munsell hue

and chroma, redness rating, and percent clay and sand were

also significantly correlated. The only soil morphology property that was not correlated to reflectance was percent

organic carbon. Organic carbon is a very important factor in

other soils, but the low percent of organic carbon in SRER

soils showed that it did not significantly affect reflectance.

Post reported that soil albedo in the 0.3 to 2.8 mm can be

computed using the Munsell color value as follows: Soil

Albedo = 0.069 (color value) – 0.114. Using this equation the

albedos of SRER soils (A horizon) would range from 0.155

for the Combate (9) to 0.307 for the Agustin, and are

presented in table 3.

Summary ______________________

The range of spectral characteristics of the SRER soils

were presented, and these data will be useful as researchers

complete remote sensing projects on the SRER. The geomorphology map compiled from the basic soils and ecological site

map helps us to better understand the soil-forming factors

responsible for the formation of the SRER soils. What soil

morphology characteristics determine the reflectance characteristics of SRER soils have been identified, and the

Munsell color value component is the most important, particularly in the 0.4 to 1.0 mm wavelengths. The range of soil

properties for the A and B horizons have been measured, and

these data will be helpful in understanding the biophysical

conditions that exist on the SRER.

References _____________________

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Chroma –0.39a –0.25 0.06 0.03 –0.28 –0.40a

Effervescence 0.79b 0.72b 0.62b 0.60b 0.59b 0.59b

a Correlation significance P £ 0.05. b

 Correlation significance P £ 0.01.
182 USDA Forest Service Proceedings RMRS-P-30. 2003

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USDA Forest Service Proceedings RMRS-P-30. 2003 183

Phil R. Ogden

E. Lamar Smith

Cow Weights and Calf Production for

Pasture 12-C Lehmann Lovegrass Grazing

Trials, 1982 to 1993

Phil R. Ogden is retired; e-mail: pro29@cox.net. At the time of the research reported in this paper, he was Professor of range management and Extension Range

Management Specialist, University of Arizona. He completed B.S. and M.S. degrees in range management at Utah State University and a Ph.D. degree in plant

physiology at Iowa State University. Lamar Smith is a Rancher and Range Management Consultant. At the time of the research reported in this paper, he was

Associate Professor of range management at the University of Arizona. He has B.S. and M.S. degrees in range ranagement and a Ph.D. degree in soil science

from Colorado State University.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Introduction ______________________________________________________

This paper is written as a printed version of a poster presentation. Each section of the paper is written as text associated

with a figure or table, as displayed on a poster. No review of literature is included.

Eragrostis lehmanniana Nees. (Lehmann lovegrass) has become a dominant species on many ecological sites in southern

Arizona, and strategies for management of these sites are not well established. This paper adds livestock production and

utilization pattern data to the management information base.

Water Source and Site Characteristics ________________________________

Implementation of the grazing trials began in the spring of 1982, with the installation of 2 miles of water line from Benson

Wells to a storage tank installed near the center of pasture 12-C. The PVC pipe was bedded in soil free of large rocks (fig. 1)

Abstract: The purpose of the grazing trials described in this paper was to provide information to

aid in the development of grazing management strategies where Lehmann lovegrass has become

a dominant species. Seven pastures were utilized from 1984 to 1987 for a comparison of four

yearlong stocking rates to seasonal grazing rotated through three pastures. A second trial, 1988

to 1993, rotated cows and calves through all pastures at a very low stocking rate. Spot grazing

created patchy grazing patterns that persisted throughout the study period on all treatment

pastures, except the yearlong very heavy stocking and summer-use rotation pastures. Weaned

calf production for all treatments (especially the rotated treatment) tended to decrease in the last

2 years of the 1984 to 1987 trial because cows slipped to later breeding and poorer percentage calf

crops. Cows selected for limited high quality forage, especially in winter and spring, from the

heavily grazed patch areas, and repeated heavy grazing reduced the potential quantity of forage

produced in these patches. A two-pasture, alternate summer use, with both pastures grazed during

winter and spring, is suggested as a possible grazing system to maintain favorable calf production

and a sustainable range resource.

Keywords: Lehmann lovegrass, grazing trial, stocking rate, pasture rotation, cow weight, patch

grazing

Acknowledgments: The research from which the data reported in this paper were obtained was

planned, funded, implemented, and conducted as a cooperative effort among the Department of

Animal Science and School of Renewable Natural Resources, University of Arizona; William A.

McGibbon, Santa Rita Ranch; and USDA Forest Service, Rocky Mountain Forest and Range

Experiment Station.

The precipitation data for Station 41 reported in table 1 were provided by the Santa Rita

Experimental Range Digital Database. Funding for the digitization of these data was provided by

USDA Forest Service, Rocky Mountain Research Station, and the University of Arizona.
184 USDA Forest Service Proceedings RMRS-P-30. 2003

Ogden and Smith Cow Weights and Calf Production for Pasture 12-C Lehmann Lovegrass Grazing Trails, 1982 to 1993

prior to covering by a grader. Figure 1 also provides a view

of the loamy upland ecological site on a Whitehouse soil

series that dominates the study area. Sampling on this site

in 1980 estimated 1,500 pounds per acre standing biomass.

Sampling on monitoring plots in 1984 estimated 2,250 pounds

per acre standing biomass with a vegetation composition of

Lehmann lovegrass, 69 percent; Calliandra eriophylla Benth.

(false mesquite), 25 percent; grama grass group: Bouteloua

chondrosioides (H.B.K.) Benth. (sprucetop), B. hirsuta Lag.

(hairy), and B. repens (H.B.K.) Scribn. & Merr. (slender), 3

percent; and other species, 2 percent. The slopes of the

draws that drain these uplands had 700 pounds per acre

standing biomass and vegetative composition of Lehmann

lovegrass, 9 percent; false mesquite, 16 percent; grama

grass group, 55 percent; and other species, 12 percent.

Precipitation ___________________

Seasonal precipitation for the forage production year

summarized in table 1 includes precipitation in October,

November, and December from the previous calendar year,

as this precipitation is a major factor contributing to this

production. Precipitation in 1983 and 1984 was very favorable, especially in summer. These 2 years of very favorable

precipitation led to optimistic estimates for stocking rates

for this grazing trial. Precipitation was lower over the next

3 years, but no years during the trial period were drought

years. Precipitation Station 41 is located near the center of

the study pastures.

Pasture Layout__________________

Two-wire electric fences for an initial six pastures and

water troughs at the center of the pastures were completed

by fall 1982. At this time, 118 cows were allocated to the

pastures to test three intensities of yearlong grazing and a

seasonal treatment with one herd rotated among three

pastures. Corrals and working facilities to accommodate

scales, calf table, and loading chute were completed in 1983.

After fall roundup in 1983, the grazing trial design was

modified to add a very heavy stocking intensity. Original

pasture 4, which was to be a rotated pasture, was divided to

make pastures 4 and 5 as shown in figure 2. Pasture 3 was

exchanged with pasture 4 to be the summer rotation pasture. The holding pasture was not fenced until the winter of

1986 to 1987.

Figure 1—Bedding water line across a loamy

upland ecological site dominated by Lehmann

lovegrass, spring 1982.

Table 1—Seasonal precipitation (inches), Station 41, Santa Rita

Experimental Range, fall 1980 to summer 1993.

Forage Season

production October to February to June to

year January May September Total

1981a 2.70 3.94 10.71 17.35

1982 2.19 1.82 8.90 12.91

1983 5.79 4.03 12.27 22.09

1984 7.92 1.77 22.65 32.34

1985 8.45 2.56 7.96 18.97

1986 3.54 3.51 8.07 15.12

1987 3.66 4.25 5.39 13.30

1988 5.65 2.52 9.91 18.08

1989 5.76 1.53 6.44 13.73

1990 5.42 1.92 15.56 22.90

1991 3.59 3.92 4.77 12.28

1992 4.46 5.08 11.87 21.41

1993 7.30 4.21 9.65 21.16

Mean 5.11 3.16 10.32 18.59

a October, November, and December precipitation is for previous calendar

year.

Figure 2—Pasture layout for Santa Rita Experimental Range pasture 12-C grazing trial, 1984 to

1993.
USDA Forest Service Proceedings RMRS-P-30. 2003 185

Cow Weights and Calf Production for Pasture 12-C Lehmann Lovegrass Grazing Trails, 1982 to 1993 Ogden and Smith

Data Collection and General

Information ____________________

Cows were weighed, condition estimated, and calves were

worked at the calf table (fig. 3) at spring roundup in mid-May

to early June. At the fall roundup in early November of each

year, cows and calves were weighed, cow condition was

estimated, calves were weaned, and limited culling (to allow

cumulative treatment effects to be expressed) and replacement of the cows was accomplished. Percentage of cows culled

was 1.8 in 1984, 10.1 in 1985, 9.1 in 1986, and 37.5 at the end

of the initial 4-year trial in November 1987. The annual

percentage of cow death losses during the 1984 to 1987 trial

were: 1.8 in 1984, 2.8 in 1985, no death loss in 1986, and 3.1

in 1987.

Stocking Intensity _______________

Planned stocking rates for the 1984 to 1987 trial were

initiated by assigning four cows and 16 bred heifers to

pasture 2 (light use, 16 acres per animal unit year [AUY], 18

cows to pasture 1 (moderate use, 12 acres per AUY), 15 cows

to pasture 5 (heavy use, 10 acres per AUY), 13 cows to

pasture 4 (very heavy use, 7 acres per AUY), and 49 cows to

pastures 3, 6, and 7 (seasonally rotated, 17 acres per AUY for

the total area of the three rotated pastures). Dates of

seasonal pasture moves varied annually, but summer use

was July to mid-November, winter use was mid-November

to March, and spring use was from March to July. Following

the 1984 to 1987 grazing trial, a second trial was initiated.

The stocking rate was reduced to a very light use (31 acres per

AUY), and cows were rotated annually through seven pastures until 1992 when they also grazed the previously ungrazed pasture 8. Calves were weighed at fall roundup.

Implemented stocking rates (fig. 4) varied from the initial

allocation due to culling, death losses, and a few cows not

staying in their assigned treatment pasture. The heavy

stocking level became similar to the moderate stocking level

at the beginning of the trial, as two cows assigned to the

heavy treatment were missed in the initial roundup and

remained in other pastures, and two cows in this treatment

died early in the trial. These two treatments are similar in

stocking rate as implemented, and are referred to as moderate to heavy in the following discussion. Implemented stocking rate data include bulls.

Cow Weights ___________________

Annual spring cow weight treatment means for 1985 to

1987 (cows were not weighed in the spring of 1984) generally

varied between 800 and 900 lb, and coefficients of variation

were near 10 percent (95-percent confidence intervals were

on the order of +/– 50 pounds). Cow weights at the spring

roundup were similar for all treatments. At fall roundup, cows

in the moderate to heavy use treatments were the heaviest,

averaging over 950 pounds (fig. 5). Cows in the very heavy use

treatment and seasonal rotation averaged 900 lb, and the cows

in the light use pasture averaged about 850 lb. The light cow

weights for the light use treatment were due to a high

proportion of first calf heifers assigned to this treatment at

the beginning of the trial. Fall cow weights for all treatments

except the very heavy intensity were higher in 1984 than for

Figure 3—Working calves at the calf table during

spring roundup.

Figure 4—Stocking rate, acres per animal unit year.

Figure 5—Cow weights at fall roundup, pounds per cow. Acres/AUY Pounds/cow
186 USDA Forest Service Proceedings RMRS-P-30. 2003

Ogden and Smith Cow Weights and Calf Production for Pasture 12-C Lehmann Lovegrass Grazing Trails, 1982 to 1993

all other years, and this correlates with the extremely good

summer precipitation in 1984 (table 1).

Weaned Calf Weights ____________

Treatment mean weaned calf weights generally varied

between 350 to 550 lb with coefficients of variation near 20-

percent and 95-percent confidence intervals on the order of

+/– 50 lb among treatments within years. Calves from the

light use pasture weighed over 600 lb in 1984 (fig. 6). This

high weight was a bias in the trial, as a result of the high

proportion of first calf heifers assigned to this treatment.

These heifers had been bred to calve earlier than the cows

that were assigned to the grazing trial. The very heavy use

treatment calf weights were lower in both 1984 and 1985

compared to the other treatments, and there was a trend to

lighter weight calves in the later 2 years of the 1984 to1987

trial for all other treatments.

Calf Production as Pounds Per

Animal Unit Year ________________

Calf pounds per AUY (fig. 7) combine the effects of calf

weight, percentage calf crop, and stocking rate. The low

weaned calf pounds per AUY the second year of the very

heavy use treatment is very evident. Even with the very good

precipitation years of 1983 and 1984, cows bred on the very

heavy use pasture in 1984 had light calves in 1984 (fig. 6)

and a 70-percent calf crop in 1985. Calf crops for the other

treatments ranged from 85 to 100 percent in 1985. Cow

numbers assigned to the very heavy treatment were reduced

to seven cows in the fall of 1985. In 1986 and 1987 when

forage in the very heavy use pasture became limited, these

remaining cows were placed with and contributed to the

calculated stocking rate of the rotated pastures, and the

stocking rate of the heavy use pasture reduced accordingly.

The poorest mean calf pounds per AUY for the 1984 to 1987

trial was for the seasonally rotated treatment. In addition to

the trend to lighter calf weights in the later 2 years of the 1984

to 1987 trial, percentage calf crop in 1987 was 67, 64, and 72

percent for the light, moderate, and rotated treatments,

respectively. Progressively drier years, lack of nutritional

forage to stimulate prompt breeding after calving, and

limited culling during the 1984 to 1987 trial contributed to

these results. Mean calf pounds per AUY for the rotated

treatment with very light stocking from 1988 to 1993 was

slightly higher than the rotated treatment mean for the 1984

to 1987 trial.

Calf Production as Pounds

Per Acre _______________________

The very heavy use treatment yielded high calf production

per acre for 2 years and then was not sustainable (fig. 8).

Weaned calf production for the yearlong moderate to heavy

use treatments averaged near 30 pounds per acre per year,

and the yearlong light use and the 1984 to 1987 light use

rotated herd produced near 20 pounds per acre. Mean

weaned calf production for the very light stocking and rotation through seven or eight pastures from 1988 to 1993 was

10 pounds per acre. Reducing the stocking rate and rotating

through seven or eight pastures as compared to rotating

Figure 6—Calf weaning weights, pounds per calf.

Figure 7—Calf weaning weights, pounds per

animal unit year.

Figure 8—Calf weaning weights, pounds per acre.

Pounds/calf

Pounds/AUY Pounds/acre
USDA Forest Service Proceedings RMRS-P-30. 2003 187

Cow Weights and Calf Production for Pasture 12-C Lehmann Lovegrass Grazing Trails, 1982 to 1993 Ogden and Smith

through three seasonal pastures did improve individual calf

weights (fig. 6), but production per acre was very poor (fig. 8).

Patch Grazing __________________

Forage utilization within pastures was very patchy (areas

of Lehmann lovegrass and other species utilized as much as

80 percent or more, especially under mesquite and on slopes

of draws, dispersed among areas with little or no utilization)

(fig. 9). Lehmann lovegrass produced new growth in these

patch areas from early spring to late fall when moisture was

present. During these grazing trials, cows selectively improved their nutritional intake by grazing in previously

grazed patch areas, as reported by Ruyle in his paper

presented at this symposium. Spot grazing in patches persisted throughout the grazing trials on all treatment pastures, except the yearlong very heavy use treatment and the

summer use seasonal rotation pasture. In 1986, the yearlong

very heavy use pasture (7 acres per AUY) became one large,

heavily grazed patch with little regrowth available for use.

This pasture supported only light stocking rates in 1986 and

1987, indicating that heavy, repeated grazing in patch areas

reduced potential forage production on these patch areas,

even in a short term.

Patch Management ______________

Stocking rates based on acres or average standing perennial grass production for the grazing trials reported in this

paper provide little guidance for management decisions.

Results indicate that the key to management of pastures

dominated by Lehmann lovegrass is management of the

grazed patches.

Cows slipped to later breeding or skipped a breeding

during the later years of the 1984 to 1987 grazing trial for all

treatments, especially the rotated treatment. Nutritional

intake during the breeding season is known to influence cow

breedback time after calving. New tiller growth in grazed

patches provided improved nutrition, but repeated and

heavy utilization of forage in these patches reduced the

potential to produce adequate forage quantity.

The observation of use pattern for the summer use rotated

pasture provides a clue to a possible strategy for management. By 1987 the summer use rotated pasture had become

one large patch (fig. 10), but utilization was less than in the

very heavy use pasture. High intake of green forage by cows

in the summer, growing calves eating the green forage, high

stocking density in a rotated pasture, and 4 consecutive

years of summer grazing combined to account for the utilization pattern developed on this pasture.

A two-pasture rotation may be suitable for improving the

quantity of high quality forage during spring in pastures

that are dominated with Lehmann lovegrass. One pasture is

grazed during the summer and fall season, and the second

pasture is rested. Both pastures are then open for grazing

during the winter and spring seasons. The second pasture is

grazed during the second summer and the first is rested, and

again both are open for use in the winter and spring. The

objective is to increase the area of patches with higher

stocking density in the summer pasture without stressing

the livestock. During winter and spring, livestock have the

opportunity to maximize forage selection for quality from

the patches. The grazed patches are then provided rest every

other summer to maintain plant vigor.

Figure 9—Patch utilization pattern for Lehmann

lovegrass in pasture 2 after 4 years of light yearlong

stocking.

Figure 10—Uniform grazing use pattern for Lehmann

lovegrass in pasture 3 after 4 years of grazing each

summer to late fall.
188 USDA Forest Service Proceedings RMRS-P-30. 2003

Nathan B. English

David G. Williams

Jake F. Weltzin

Soil Temperature and Moisure Dynamics

After Experimental Irrigation on Two

Contrasting Soils on the Santa Rita

Experimental Range: Implications for

Mesquite Establishment

Introduction ______________________________________________________

The demography of woody plants within Southwestern savannas and grasslands is constrained by factors that affect seedling

establishment and survival, and ultimately, recruitment of individuals into the population (Grubb 1977; Harper 1977;

Hochberg and others 1994; McPherson 1997; Scholes and Archer 1997; Weltzin and McPherson 1999). On local scales, biotic

(for example, neighboring individuals, herbivory) and edaphic factors and disturbance (for example, fire) are important

determinants of vegetation patterns (Archer and others 1995; Prentice 1986). However, at larger scales abiotic constraints (for

Nathan B. English is a Research Specialist with the School of Renewable Natural Resources, 325 Biological Sciences East, University of Arizona, Tucson, AZ

85721; e-mail: nenglish@geo.arizona.edu. He completed a B.A. degree in geology at Colorado College and an M.S. degree in geosciences at the University of Arizona.

David G. Williams is an Associate Professor in the Departments of Renewable Resources and Botany, University of Wyoming, Director of the University of

Wyoming Stable Isotope Laboratory, and adjunct Associate Professor in the School of Renewable Natural Resources, University of Arizona. He completed a

B.A. degree in botany at the University of Texas, Austin, an M.S. degree in range science at Texas A&M University, and a Ph.D. degree in botany at Washington

State University. Jake F. Weltzin is an Assistant Professor in the Department of Ecology and Evolutionary Biology at the University of Tennessee, Knoxville. He

completed a B.S. degree in forest and rangeland management at Colorado State University, an M.S. degree in rangeland science at Texas A & M University, and

a Ph.D. degree in renewable natural resource studies at the University of Arizona.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Abstract: We established a large-scale manipulative experiment in a semidesert grassland on the

Santa Rita Experimental Range to determine how the recruitment and physiology of woody plants

(Prosopis velutina Woot.) are affected by invasive grasses, seasonal precipitation regimes, and

underlying soil characteristics. We established 72 2.8-m2 plots beneath six large rainout shelters

divided evenly between a clay-rich and a sandy loam soil less than 1 km apart. Monospecific stands

of the the invasive African grass Eragrostis lehmanniana and the native grass Heteropogon

contortus were established into four plots each, and four plots were left bare under each shelter.

Our watering protocol simulated 50 percent increases and decreases in average summer precipitation. Here we compare soil water content and temperature in Eragrostis and bare plots during

a large, isolated irrigation event that we applied to the plots in June 2002. Daily average and

maximum temperatures near the soil surface declined following the irrigation compared to

nonirrigated, external plots, and were cooler for several days afterwards. Soil moisture contents

declined and maximum soil temperatures increased more rapidly in plots dominated by Eragrostis

than in bare plots. Near-surface soil temperatures are apparently too high for establishment of

Prosopis seedlings in June prior to the onset of summer rains. Eragrostis may further prevent

successful Prosopis establishment by shortening the period over which moisture and soil

temperatures are suitable for germination and survival of Prosopis seedlings following a pulse of

summer rain.

Acknowledgments: This project would not have been possible without the hard labor and

invaluable input from Dayna Burns, Bill Cable, Michael Andregg, Susan Schwinning, Don Post,

Alessandra Fravolini, Liegh Thomas, and many others at the University of Arizona and the

University of Tennessee. I am grateful for the input and thoughtful reviews provided by

Alessandra Fravolini and Kevin Hultine. This project was funded by USDA-CSREES Grant #00-

35101-9308.
USDA Forest Service Proceedings RMRS-P-30. 2003 189

Soil Temperature and Moisure Dynamics After Experimental Irrigation ... English, Williams, and Weltzin

example, regional or global climate change) may be more

important than biotic constraints on woody plant establishment. In sum, woody plant population dynamics within any

given grassland, savanna, or woodland are affected by the

interaction between biotic and abiotic factors operating at a

variety of spatial and temporal scales.

Using large rain-out shelters (fig. 1), we are investigating

many of the factors that may determine the relative abundance and distribution of woody plants within grasslands and

savannas of Western North America. Specifically, we are

examining the effects of geomorphic/edaphic substrates, native versus nonnative grasses, and the seasonality of precipitation on the recruitment and physiology of mesquite (Prosopis

velutinaWoot.) and ecosystem gas exchange (net photosynthesis and transpiration). We anticipate that each of these factors

will influence recruitment rates; however, interactions between these factors, and their relative contributions as constraints on recruitment, are more difficult to predict.

Global temperatures are predicted to increase from 1.4 to

5.8 ∞C during this century and will likely alter patterns of

precipitation over much of the Earth (IPCC 2001). The ecological effects of changing precipitation and temperature

regimes will be particularly dramatic in arid and semiarid

environments, where water availability most limits the

ecosystem productivity and function (Noy-Meir 1973; Weltzin

and McPherson 2003). In the Southwestern United States,

two different regional climate models predict increased

temperatures, but predict very different changes in the amount

and timing of precipitation. The Regional Circulation Model

(RegCM) of Giorgi and others (1998) predicts a decrease in

the amount of winter precipitation and an increase in summer

precipitation. In contrast, the Hadley Circulation Model 2

(HADCM2) developed by the Hadley Centre for Climate

Prediction and Research, UK Meteorological Office (NAST

2000), predicts that by 2030 the Southwest will experience

drier summers and wetter winters.

Soil temperature, and the effect of precipitation on soil

temperature, can influence the germination rate and survival of woody species that grow in semiarid and arid

environments (Scifres and Brock 1969). In southern Arizona, maximum daily, near-surface (0.5 cm) soil temperatures frequently exceed 50 ∞C and have been measured up to

61 ∞C (Cable 1969). After scarification, mesquite seeds require

both moisture and an optimal temperature (29 ∞C) to emerge

and survive on the soil surface (Scifres and Brock 1969).

During the summer monsoon, precipitation increases soil

moisture and decreases soil temperatures at the surface

(Abbot 1999). The soil dries and returns to prerain temperatures very rapidly following a single rain event, leading to

seedling death if the seedling has not had time to establish

roots in deeper soil layers. Therefore, changes in the frequency of precipitation will likely have direct impacts on

recruitment of mesquite by regulating soil temperature and

moisture during the summer months. Here we present data

that suggests a decrease in the frequency of summer precipitation, or the presence of Eragrostis, may lead to longer

periods between rain events over which soil temperature is

above the optimal range for Prosopis seedling recruitment

on the Santa Rita Experimental Range.

Methods and Materials ___________

Site Description

Our rainout shelters are located on two sites 1 km apart

(N 31.78∞, W 110.88∞) on the Santa Rita Experimental Range.

Three shelters each were constructed on middle-Holocene

(4-8 ka) and late-Pleistocene (200-300 ka) alluvial fan surfaces

(McAuliffe 1995). The middle Holocene soil is a loamy coarse

sand, while the Pleistocene soil contains up to 50 percent clay

beneath a shallow (0 to 25 cm) sandy loam surface. Both sites

are on gentle slopes (2 percent) at about 1,100 m elevation.

Figure 1—Shelter (9 by 18 m, 4 m tall) on the Pleistocene site; open sides are 1.5 m off the ground. Tall grasses

visible beneath the shelter are Heteropogon contortus. Note the cables attached to the shelter and steel

fenceposts for greater wind stability, and polypropelene rope holding down the plastic cover.
190 USDA Forest Service Proceedings RMRS-P-30. 2003

English, Williams, and Weltzin Soil Temperature and Moisure Dynamics After Experimental Irrigation ...

Shelter and Plot Installations

In April and May 2001, we established twelve 1.5- by 1.8-m

plots in each of three shelters on Holocene and Pleistocene

surfaces (72 plots total). The 12 plots in each shelter were

randomly assigned to one of three vegetation cover treatments (Heteropogon contortus (L.) Beauv., Eragrostis

lehmanniana Nees., or bare) and one of two precipitation

treatments (50 percent wetter than average in summer, 50

percent drier than average in summer). In June and July of

2001, we carefully removed all aboveground vegetation from

plot surfaces and transferred 56 greenhouse-grown grass

seedlings into the appropriate grass plot (in a regular grid

with about 20 cm spacings, 21 plants per m2). We trenched

each plot to >0.75 m depth (40 cm wide), leaving a pedestal

of soil (2.7 m2, > 2 m3). Time-domain reflectometry probes

(Ledieu and others 1986; Risler and others 1996; TDR) that

measure soil volumetric water content (Qv) of soil were

installed horizontally into the side of each plot at 15, 35, and

55 cm depths. After TDR installation, the trench faces were

lined with black 6-mil PVC film attached to wooden frames

(10 cm tall) that sit at ground level. The plastic and frames

were designed to prevent horizontal subsurface flow out of

the plots and surface runon to and runoff from the plots.

Twenty-gage, copper-constantan thermocouples (0.5 cm long

and epoxy coated) were installed at 2 and 10 cm soil depth to

measure soil temperature in two Eragrostis plots, two bare

plots, and one unwatered and one bare plot outside the

shelters (as controls) on each site. Care was taken to bury the

first 10 cm behind the thermocouple junction at a depth

equal to the desired measurement depth to prevent heat

from direct sunlight on the wire from travelling along the

cable to the thermocouple junction.

Data collection

A datalogger (CR-10X, Campbell Scientific, Logan, UT)

connected to the soil thermocouples was used to measure

temperature every 15 minutes and averaged hourly from

June 10 to June 21, 2002. To account for variations in thermocouple temperatures and reduced radiative load on soils under

the shelters caused by interception of light by the shelters

(less than several degrees Celsius), we cross-calibrated experimental plot thermocouples to thermocouples at the

same depth in the control plots. We cross-calibrated the

thermocouples at a time when we expected soil temperature

in and outside the shelters to be similar (a daily mean

temperature on June 25, 2002). We used a commercially

available cable tester (TDR100, Campbell Scientific) connected to a portable battery and computer to measure Qv

from the TDR probes in the field. We determined the average

bulk-density and the rock-fragment fraction from each site

at the relevant depths to convert Qv to gravimetric water

content (Qg).

Irrigation

Our precipitation protocols were designed to test the

influence of seasonal precipitation amount and pattern on

production, composition, and demography of grasses and, at

a later date, establishment of woody plants. For the soil

temperature and moisture data presented in this paper, we

applied the rainfall equivalent of 39 mm of water to each plot

on the evening of June 10, 2002. Water at 26 ∞C was applied

manually at a rate of about 28 l min-1 and measured with a

digital totalizer (accuracy ± 1.5 percent) connected to a gaspowered water pump.

Results and Discussion __________

While scarification, ample moisture, and a thin layer of

soil are prerequisites for Prosopis seedling establishment,

soil temperature also exerts a strong influence (Scifres and

Brock 1969, 1972). Scifres and Brock (1969) found that the

optimum temperatures for establishment of honey mesquite

(Prosopis glandulosa Torr. var glandulosa) seedlings were

29 ∞C, and that temperatures below 21 ∞C and above 38 ∞C

led to reduced emergence rates and greater sensitivity to soil

moisture stress. Although mesquite may germinate at temperatures greater than 38 ∞C, they will not survive in these

temperatures for more than 10 days at soil water potentials

less than –0.2 MPa (Scifres and Brock 1969). Typically, our

research plots on the Holocene and Pleistocene soils reach

this moisture threshold at Qg values of 5 percent and 9

percent, respectively (Schwinning, unpublished data).

Prior to watering in early June, mean daily soil temperatures on both sites at 2 cm were about 37 ∞C, and maximum

daily temperatures at 2 cm exceeded 42 ∞C and ranged up to

53 ∞C (fig. 2). These temperatures are consistent with temperatures measured on a Holocene site by Cable (1969) and

are well above the optimum seedling establishment temperature for Prosopis. Gravimetric soil moisture content (Qg) at 15

cm was less than 1 percent on the Holocene plots, and was 9

percent and 6 percent on bare and Eragrostis plots, respectively, on the Pliestocene plots prior to irrigation. For all plots,

Qg measured at 15 cm was likely higher than at 2 cm depth.

The watering event reduced soil temperatures and increased Qg on all plots, but soil temperatures and Qg recovered to prewatering values more quickly on Eragrostis plots

(fig. 2) than on bare plots. Mean daily soil temepratures on

both sites remained near the optimum seedling recruitment

temperature (29 ∞C) for less than 2 days. Watering reduced

both maximum and mean daily soil temperatures on the

Holocene and Pleistocene soils at 2 cm by up to 20 and 11 ∞C,

respectively, compared to the control plots. Recovery of

mean temperatures to >30 ∞C occurred within 2 days after

the precipitation event on vegetated and bare plots regardless of site or the presence or absence of Eragrostis. Recovery

of daily maximum temperatures to within 20 percent of that

in the control plot occurred 3 days after the pulse on both

sites. Eragrostis plots returned to higher maximum daily

temperatures more quickly than did bare plots. Reductions

of maximum daily soil temperature in bare plots was observed beyond the 12-day duration of the experiment. Patterns of rewarming at 10 cm depth are similar, but generally occur 1 to 2 days later than at 2 cm.

Gravimetric water content (Qg) varied by vegetative treatment and site. Qg exceeded 5 percent after watering in both

treatments on the Holocene and 9 percent in Pleistocene bare

plots for 2 days (fig. 2). Qg exceeded 9 percent for the duration

of the experiment on Pleistocene bare plots. Although Qg

in the Pleistocene bare plots was higher (9 percent)

than in vegetated plots (6 percent) before the watering
USDA Forest Service Proceedings RMRS-P-30. 2003 191

Soil Temperature and Moisure Dynamics After Experimental Irrigation ... English, Williams, and Weltzin

pulse was applied, both plots had comparable Qg (12 percent)

immediately following the water addition. Two days after

watering, Qg in Eragrostis plots on both sites was lower than

in bare plots at the same site. Six days after watering, Qg in

Eragrostis plots was 1 percent and 3 percent lower than in

bare plots on the Holocene and Pleistocene, respectively.

Soil temperatures in excess of 29 ∞C and very dry soils in

late spring and early summer on the SRER make Prosopis

seedling establishment during this time very difficult. Our

data suggest that (1) infrequent storm events in late spring

and early summer, while triggering seed germination, will

neither wet nor cool the soil at 2 cm or shallower for a long

enough period of time to allow for successful seedling establishment; and (2) Eragrostis appears to rapidly take up soil

moisture and drive maximum daily temperatures up, and

reduce the period of time soils remain at optimal temperatures

Figure 2—Maximum and mean daily soil temperature at 2 cm depth for Holocene and Pleistocene plots (bare,

n = 2; Eragrostis lehmanniana, n = 2; external n = 1) and gravimetric water content (Qg) at 15 cm depth. Arrow

indicates the application of a 39 mm rainfall equivalent water pulse added to the plots between 4 p.m. and 10 p.m.

on June 10, 2002. Vertical lines on Gravimetric Water Content graphs represent ± 1 standard error (n > 9).

60

50

40

30

20

Holocene Surface Pleistocene Surface

Maximum

Temperature (°C)

Bare E. lehmanniana Extreme

50

40

30

20

Mean

Temperature (°C)

38

10

8

6

4

2

Gravimetric Water

Content (%)

0

6/10 6/12 6/14 6/16 6/18 6/20 6/22

Bare E. lehmanniana Extreme

14

12

10

8

6

4

6/10 6/12 6/14 6/16 6/18 6/20 6/22

Date
192 USDA Forest Service Proceedings RMRS-P-30. 2003

English, Williams, and Weltzin Soil Temperature and Moisure Dynamics After Experimental Irrigation ...

for seedling establishment. Our continuing studies will test

the hypothesis that while mean soil temperatures above 21 ∞C

in the upper 2 cm occur between April and October on the

SRER, mean soil temperatures over 35 ∞C coupled with low

soil moisture prevent seedling establishment until the onset

of the monsoon, when frequent rains consistently wet soils

and reduce soil temperatures to the optimum temperature

for seedling establishment.

Conclusions____________________

We instrumented several bare and grass-covered plots,

and a bare external control plot, on two different soil types

with TDR probes and thermocouples at various depths to

measure the effect that a pulse of precipitation would have

on maximum and mean daily soil temperatures. After an

artificially applied precipitation pulse, maximum daily soil

temperatures at 2 cm on both sites were depressed by up to

20 ∞C, and mean temperatures remained near the optimal

temperature range (29 ∞C) for seedling recruitment several

days after the pulse. Within 3 to 4 days, mean daily temperatures of soils on both sites had returned to within 20 percent of

that in the control plots and well beyond the optimal temperature range for seedling recruitment. Average temperatures in

late spring and the premonsoon months are too high for

successful Prosopis establishment, despite infrequent rains.

Eragrostis reduces soil moisture and drives up maximum

daily temperatures compared to that in bare plots.

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Weltzin, J. F.; McPherson, G. R. 1999. Facilitation of conspecific

seedling recruitment and shifts in temperate savanna ecotones.

Ecological Monographs. 69: 513–534.

Weltzin, J. F.; McPherson, G. R. 2003. Changing precipitation

regimes and terrestrial ecosystems: a North American perspective. Tucson: University of Arizona Press.
USDA Forest Service Proceedings RMRS-P-30. 2003 193

Craig Wissler

Deborah Angell

New Data Sources and Derived Products

for the SRER Digital Spatial Database

Craig Wissler is an Assistant Professor of renewable natural resources in the School of Renewable Natural Resources, 325 Biological Sciences East, University

of Arizona, Tucson, AZ 85721; e-mail: craig@srnr.arizona.edu. He is also Director of the Advanced Resource Technology (ART) facility in the College of Agriculture

and Life Sciences. Craig holds a B.S. degree in environmental resources in agriculture from Arizona State University and a Master of Landscape Architecture

degree from the University of Arizona. Deborah Angell is the Data Manager for the National Park Service Sonoran Desert Network Natural Resources Inventory

and Monitoring Program. She is also a part-time Senior Research Specialist in the University of Arizona’s School of Renewable Natural Resources. Deborah

earned a B.S. degree in renewable natural resources and an M.S. degree in range management from the University of Arizona.

In: McClaran, Mitchel P.; Ffolliott, Peter F.; Edminster, Carleton B., tech. coords. Santa Rita Experimental Range: 100 years (1903 to 2003) of accomplishments

and contributions; conference proceedings; 2003 October 30–November 1; Tucson, AZ. Proc. RMRS-P-30. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Santa Rita Experimental Range Digital Database _______________________

Ecological data have been collected at the Santa Rita Experimental Range (SRER) since its establishment in 1903,

distinguishing it as the oldest continuously operating range experiment station in the world with a long-term data record that

is unsurpassed in the Southwestern United States (McClaran and others 2002). The SRER digital database was developed to

preserve these data and to increase their accessibility. The database includes precipitation measurements, vegetation

measurements, plant synonymy tables for taxonomic groups, repeat ground photography, an annotated bibliography, and a

collection of spatial data. The SRER spatial database is developed and maintained at the Advanced Resource Technology (ART)

facility housed in the School of Renewable Natural Resources in the College of Agriculture and Life Sciences. The goal of the

SRER spatial database project is to integrate site-based data with referenced spatial locations and to provide source and

derived spatial data layers to support spatial analyses.

Existing Spatial Data_______________________________________________

The spatial database provides information to create maps of four types: (1) human structures and boundaries, (2) topography

and elevation, (3) soil and ecological sites, and (4) locations of permanent transects established in previous Forest Service

studies and those still being remeasured at 3-year intervals. All currently available spatial data is downloadable in ARC/INFO

export file format (*.e00) (McClaran and others 2002). The digital elevation models (DEMs) now available in the database are

30-m resolution for the four U.S. Geological Survey (USGS) 7.5-minute quadrangles covering the SRER.

Abstract: The Santa Rita Experimental Range (SRER) digital database was developed to

automate and preserve ecological data and increase their accessibility. The digital data holdings

include a spatial database that is used to integrate ecological data in a known reference system

and to support spatial analyses. Recently, the Advanced Resource Technology (ART) facility has

added three new Federal geographic data products to this spatial database. U.S. Geological

Survey (USGS) digital raster graphics (DRG) are scanned images of USGS topographic maps.

Digital orthophoto quarter quads (DOQQ) are computer-generated images of aerial photographs

that have been registered to a coordinate system and ortho-rectified. Digital elevation models

(DEM) are georeferenced arrays of regularly spaced elevation values. A product description,

production methodology discussion, and file format description is provided for each product. The

applications of these products include reference mapping, spatial analysis, and data visualization.

A sample image of each of these products is provided. These data represent an ongoing

commitment to providing researchers with accurate, up-to-date, and relevant data products to

support research on the SRER. Products that will be derived from these sources include slope

aspect, land slope, and hillshade layers. Improved Federal geographic data products will be added

to the database as they become available.

Keywords: digital databases, Federal geographic data products, SRER database
194 USDA Forest Service Proceedings RMRS-P-30. 2003

Wissler and Angell New Data Sources and Derived Products for the SRER Digital Spatial Database

New Spatial Data Products________

Recently, three additional geographic data products for

the SRER study area have become available from the Federal Government for inclusion in the SRER spatial database.

Digital raster graphics (DRGs), digital orthophoto quarter

quads (DOQQs), and higher resolution (10-m) DEMs will be

available for the Corona de Tucson, Green Valley, Helvetia,

and Sahuarita quadrangles. These products are valuable

additions to the database for their potential use in research

applications.

Digital Raster Graphics (DRG)

A DRG is a scanned image of a USGS topographic map,

including all map collar information. Only the portion of the

image inside the neatline is georeferenced to the Earth’s

surface. A standard palette of 13 colors, modeled after the

line-drawing nature of the source map, is used for consistency among all DRGs (U.S. Department of the Interior;

U.S. Geological Survey 2002b). The USGS has produced

DRGs at scales from 1:20,000 to 1:125,000.

A DRG is produced by scanning a printed map at a

minimum of 250 dots per inch (dpi) with a high-resolution

scanner. The digital image is georeferenced to true ground

coordinates and fit to the Universal Transverse Mercator

(UTM) projection, which provides consistency with DOQQs

and digital line graphs (DLGs). DRGs can reference either

the North American Datum of 1927 (NAD 27) or the North

American Datum of 1983 (NAD 83). In most cases, the DRG

is referenced to the same datum as the source map; thus, a

DRG produced from a paper map referenced to NAD 27 will

also be referenced to NAD 27. Colors are standardized, and

the image is compressed to reduce file size. The horizontal

positional accuracy of a DRG is approximately equal to the

accuracy of the source map. For example, a 1:24,000 DRG

scanned at 250 dpi has a ground sample distance of 2.4 m

(U.S. Department of the Interior; U.S. Geological Survey

2002b). The DRGs available in the SRER digital database

are eight-bit palette-color images in the GeoTIFF format.

Figure 1 displays a portion of a DRG zoomed to the area

surrounding Huerfano Butte.

A DRG is perhaps most useful as a backdrop for other

spatial data. For example, an image combining the DRG

Figure 1—A portion of a USGS digital raster graphic from the Helvitia 7.5-minute

quadrangle.
USDA Forest Service Proceedings RMRS-P-30. 2003 195

New Data Sources and Derived Products for the SRER Digital Spatial Database Wissler and Angell

with DOQQs is useful for collecting and revising digital map

data. A shaded relief map created by combining a DRG and

a DEM provides additional details for viewing, extracting,

and revising map information (U.S. Department of the

Interior; U.S. Geological Survey 2002b).

Digital Orthophoto Quarter Quads (DOQQ)

A DOQQ is a computer-generated image of an aerial

photograph with the effects of camera tilt and topographic

relief removed to create a uniform-scale orthophoto. It combines the image characteristics of a photograph with the

geometric qualities of a map. The files include an ASCII

header that contains data for identifying, displaying, and

georeferencing the image. To facilitate the spatial referencing of other spatial data to the DOQQ, both North American

Datum of 1927 (NAD 27) and North American Datum of

1983 (NAD 83) coordinates for the upper left pixel are

contained in the header (U.S. Department of the Interior;

U.S. Geological Survey 2002a). DOQQs are available as

black and white, color, or color infrared images with a 1-m

resolution.

A DOQQ is created by scanning an aerial photograph

transparency at high resolution. The aerial photo should

be a quarter-quadrangle centered image that meets the

standards of the National Aerial Photography Program

(NAPP). The digital image is then ortho rectified using

computerized mathematics to generate an orthophoto. The

orthophoto is put into the Universal Transverse Mercator

(UTM) projection and referenced to NAD 83 (U.S. Department of the Interior; U.S. Geological Survey 2002a).

The source of the DOQQs included in the SRER database

is aerial photography taken by NAPP in 1996. Each DOQQ

is a color infrared (CIR) image with 1-m resolution in the

GeoTIFF format, representing an area of 3.75 minutes longitude by 3.75 minutes latitude with a 50- to 300-m overlap

between adjacent images to facilitate tonal matching and

mosaicking. The CIR images were produced for areas in

southern Arizona, including the SRER. Average file size of a

3.75-minute CIR DOQQ is 11 megabytes (U.S. Department

of the Interior; U.S. Geological Survey 2002a). Figure 2

displays a portion of a DOQQ zoomed to the area surrounding Huerfano Butte.

Any geographic information system (GIS) that can manipulate raster images can incorporate DOQQs. A DOQQ

Figure 2—A portion of a digital orthophoto from the Helvetia 7.5-minute quadrangle

showing Huerfano Butte.
196 USDA Forest Service Proceedings RMRS-P-30. 2003

Wissler and Angell New Data Sources and Derived Products for the SRER Digital Spatial Database

may be used as a base layer for displaying and modifying

associated spatial data, as well as evaluating data for completeness and accuracy, particularly on DLGs (U.S. Department of the Interior; U.S. Geological Survey 2002a). Color

infrared (CIR) DOQQs include the near infrared band and

may be processed to identify actively growing vegetation.

Digital Elevation Models (DEM)

A DEM is a georeferenced array of regularly spaced

elevation values at a 30-m or 10-m resolution. The grid cells

are regularly spaced along south to north profiles ordered

from west to east. The USGS produces five types of DEMs

ranging from 7.5-minute to 1-degree maps (U.S. Department of the Interior; U.S. Geological Survey 2002c).

A 7.5-minute DEM (corresponding to a USGS 7.5-minute

topographic quadrangle map) is created by interpolation

using either photogrammetric sources or vector data DLG

hydrographic (stream channel) and hypsographic (elevations represented as contours) data. The DEM is horizontally referenced to the UTM projection and either the NAD

83 or NAD 27 datum and vertically referenced to the North

American Vertical Datum of 1929 (NAVD 29). The horizontal accuracy of 7.5-minute DEMs derived from vector or DLG

source data must have a root-mean-square error (RMSE) of

one-half of a contour interval or better. For 7.5-minute DEs

derived from a photogrammetric source, 90 percent have a

vertical accuracy of 7-m RMSE or better, and 10 percent are

in the range of 8 to 15 m. For 7.5- and 15-minute DEMs

derived from vector or DLG hypsographic and hydrographic

source data, an RMSE of one-half of a contour interval or

better is required (U.S. Department of the Interior; U.S.

Geological Survey, 2002c).

The DEMs available from the SRER digital base are 10-m

resolution in the Spatial Data Transfer Standard (SDTS)

format. This format allows the transfer of georeferenced

spatial data with potentially no loss of information between

dissimilar computer systems (U.S. Department of the Interior; U.S. Geological Survey 2000). DEM files are approximately 9.9 megabytes for the 7.5-minute coverage. Figure 3

displays a portion of a 10-m DEM with hypsographic shading zoomed to the area surrounding Huerfano Butte.

A variety of products may be derived from DEMs. Maps

displaying slope percent or degrees of slope can be in spatial

analyses. A map displaying aspect could be used to infer

vegetation types in areas where north- and south-facing

slopes are characterized by different plant species. The

accuracy of a vector stream layer could be visually checked

by overlaying it on a hillshade map. DEMs form the basis for

many hydrologic models that are used to predict runoff and

estimate erosion potential. Drainage networks can also be

derived from DEMs.

Figure 3—A portion of a 10-m digital elevation model of the area surrounding

Huerfano Butte displayed as a hillshade with 10-m contour lines.
USDA Forest Service Proceedings RMRS-P-30. 2003 197

New Data Sources and Derived Products for the SRER Digital Spatial Database Wissler and Angell

Future Plans ___________________

The addition of these new Federal geographic data products represents a commitment toward the project goal of

providing spatial data for reference and spatial analyses.

The current project plans for the spatial database include

the update of Federal geographic data products and development of standard products derived from the DEMs and

DOQQs. As funding permits, standard product development

from the DEMs will include land slope data, slope aspect

data, and hillshade images. The land slope and slope aspect

data will add to the utility of the spatial database, as these

themes are commonly used in spatial analyses. The CIR

DOQQs will be processed into false color images using green

color to show actively growing vegetation. These images may

be used as reference themes in cartographic products, or as a

product for input into further image processing applications.

The National Elevation Dataset (NED) is a new raster

product produced by the USGS to provide seamless DEM

data for entire country (U.S. Department of the Interior;

U.S. Geological Survey 2002d). The NED represents an

effort by the USGS to respond to the need for seamless

topographic data that has been processed to remove slivers,

artifacts, and other abnormalities. Although originally developed at a resolution of 1 arc-second (about 30 m), the

USGS is in the process of completing the incorporation of the

10-m DEMs into NED for southern Arizona. As the 10-m

data for the SRER quadrangles becomes available, it will be

added to the spatial database. The 10-m NED will provide

for improved surface modeling for hydrological applications.

References _____________________

McClaran, Mitchel P.; Angell, Deborah L.; Wissler, Craig. 2002.

Santa Rita Experimental Range digital database: user’s guide.

Gen. Tech. Rep. RMRS-GTR-100. Ogden, UT: U.S. Department

of Agriculture, Forest Service, Rocky Mountain Research Station. 13 p.

U.S. Department of the Interior; U.S. Geological Survey. 2002a.

(December 31-last update). USGS, [Online]. Available: http://

mac.usgs.gov/mac/isb/pubs/factsheets/fs05701.html [2002, December 31]. Digital Orthophoto Quadrangles Fact Sheet 057-01

[Online]. (2001, May). USGS Eastern Region Geography (page

maintainer).

U.S. Department of the Interior; U.S. Geological Survey. 2002b.

(December 31-last update). USGS, [Online]. Available: http://

mac.usgs.gov/mac/isb/pubs/factsheets/fs08801.html [2002, December 31]. USGS GeoData Digital Raster Graphics Fact Sheet

088-01 [Online]. (2001, September). USGS Eastern Region Geography (page maintainer).

U.S. Department of the Interior; U.S. Geological Survey. 2002c.

(December 31-last update). USGS, [Online]. Available: http://

mac.usgs.gov/mac/isb/pubs/factsheets/fs04000.html [2002, December 31]. US GeoData Digital Elevation Models Fact Sheet

040-00 [Online]. (2000, April). USGS Eastern Region Geography

(page maintainer).

U.S. Department of the Interior; U.S. Geological Survey. 2002d.

(November 6-last update). USGS, [Online]. Available: http://

gisdata.usgs.net/NED/About.asp [2002, November 6]. National

Elevation Dataset [Online]. (2002, November). USGS (page

maintainer).

U.S. Department of the Interior; U.S. Geological Survey. 2000.

(February 14-last update). USGS, [Online]. Available: http://

mcmcweb.er.usgs.gov/sdts/whatsdts.html [2000, February 14].

What is SDTS? [Online]. sdts@usgs.gov (page maintainer).

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discussed here have been registered. All uses of pesticides must be

registered by appropriate State and/or Federal agencies before they can

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CAUTION: Pesticides can be injurious to humans, domestic animals,

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