Status and Trends of Land Change in the 

Western United States—1973 to 2000

U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1794–A

Status and Trends of Land Change in the 

Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo

Professional Paper 1794–A

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:

Sleeter, B.M., Wilson, T.S., and Acevedo, W., eds., 2012, Status and trends of land change in the 

Western United States—1973 to 2000: U.S. Geological Survey Professional Paper 1794–A, 324 p. 

(Available at http://pubs.usgs.gov/pp/1794/a/.)

Cover:

Farm in Little Lost River Valley near Howe, Idaho, with Lemhi Range in background. Photograph by Benjamin M. 

Sleeter, 2008.

Inside cover:

Grasslands of Antelope Flats, in Grand Teton National Park near Jackson, Wyoming, with Teton Range in background. 

Photograph by Benjamin M. Sleeter, 2008.
iii

Foreword

This Professional Paper is the first multitemporal assessment of late-20th-century land change in 

the conterminous United States across all regions and all land-use and land-cover sectors. The work is the 

culmination of nearly 10 years of research and development by the U.S. Geological Survey, with support from 

the U.S. Environmental Protection Agency and the National Aeronautics and Space Administration, as well 

as university collaborators. It represents the most complete and comprehensive analysis of the rates, types, 

distribution, and drivers of recent changes in land use and land cover. The study bridges the gap between 

coarse-scale continental and global assessments and fine-scale local and regional case studies. 

Land-change studies attempt to explain the “what, where, when, how, and why” of changes to the 

vegetation and to the use of the land. Land-change research is aimed specifically at measuring where 

change is occurring (and where it is not occurring); which land-use and land-cover classes are changing (and 

what they are changing to); how much land is changing (and how fast); and what drivers are responsible 

for the measured changes. The goal is not only to understand the scope of change but also to provide the 

information base necessary to evaluate, predict, and manage the consequences of change.

Like many key issues in climate change and ecosystem functioning, land use and land cover are 

both drivers and indicators of environmental quality. The National Research Council has identified the 

understanding of land-use dynamics as one of the grand challenges for environmental research—no other 

global-change parameter is so tightly intertwined with issues of past, present, and future land-use practices, 

weather patterns, soil and carbon dynamics, ecosystem health and diversity, economic development and 

policy, technology issues, human population size and distribution, and overall human health. People and their 

use of the land are interrelated in complex ways, and the effects of land-use and land-cover change can have 

a huge impact on their quality of life, on the goods and services that they can expect from the land, and on the 

hazards that they may face. Despite these profound consequences, the Intergovernmental Panel on Climate 

Change’s Third Assessment Report has cited the lack of scientific understanding about the timing, magnitude, 

and direction of response of ecological, social, and economic systems to the combined effects of climate 

change and land-use and land-cover change as a key uncertainty in determining societal vulnerabilities and 

predicting both regional and global impacts of climate change.

Prior to this study, only sectorally specific or spatially limited assessments and inventories had been 

conducted to categorize land change in the United States. These efforts often included only certain land-use 

and land-cover classes or ownership categories, or they were conducted over short time intervals only, 

and integrating these various assessments into a comprehensive and consistent national synthesis of land 

change was not possible. The research presented in this Professional Paper has been specifically designed to 

provide the first comprehensive measurement of land-cover change in the conterminous United States. 

Relying on Landsat satellite imagery—the longest continuous and consistent dataset of synoptic Earth 

observations—the authors characterize changes across 11 primary land-use and land-cover classes spanning 

four time periods between 1973 and 2000. For each of these time periods and classes, estimates of change are 

developed for each of 84 distinct ecological regions—or ecoregions—across the conterminous United States.

The results provide useful, if not essential, information for understanding climate change, biodiversity, 

resource management and planning, resource security, and disaster planning. A significant conclusion is 

that no single profile of land-use and land-cover change exists. Numerous different, and often complex, 

interactions between an ecoregion’s socioeconomic drivers and its biological and physical characteristics 

have produced widespread regional and temporal variability in the rates, types, and total extent of land 

change. Among the scientific findings presented are estimates of overall forest decline in response to 

increased rates of disturbance, urbanization, and agricultural intensification. 

This research provides a critical ecoregional to national perspective of land change in the 

conterminous United States. With the completion of the 1973–2000 assessment, this study lays a 

foundation for understanding the Nation’s land-change dynamics and makes possible a new era for 

analyzing the consequences of land change, as well as for modeling future land changes.

Marcia K. McNutt

Director, USGS
iv

Preface

U.S. Geological Survey (USGS) Professional Paper 1794–A is the first in a four-volume series on the status 

and trends of the Nation’s land use and land cover, providing an assessment of the rates and causes of land-use 

and land-cover change in the Western United States between 1973 and 2000. Volumes B, C, and D provide 

similar analyses for the Great Plains, the Midwest–South Central United States, and the Eastern United States, 

respectively. The assessments of land-use and land-cover trends are conducted on an ecoregion-by-ecoregion 

basis, and each ecoregion assessment is guided by a nationally consistent study design that includes mapping, 

statistical methods, field studies, and analysis. Individual assessments provide a picture of the characteristics 

of land change occurring in a given ecoregion; in combination, they provide a framework for understanding the 

complex national mosaic of change and also the causes and consequences of change. Thus, each volume in this 

series provides a regional assessment of how (and how fast) land use and land cover are changing, and why. The 

four volumes together form the first comprehensive picture of land change across the Nation.

Geographic understanding of land-use and land-cover change is directly relevant to a wide variety of 

stakeholders, including land and resource managers, policymakers, and scientists. The chapters that follow 

present brief summaries of the patterns and rates of land change observed in each ecoregion in the Western 

United States, together with field photographs, statistics, and comparisons with other assessments. In addition, 

a synthesis chapter summarizes the scope of land change observed across the entire Western United States. 

The studies provide a way of integrating information across the landscape, and they form a critical component in 

the efforts to understand how land use and land cover affect important issues such as the provision of ecological 

goods and services and also the determination of risks to, and vulnerabilities of, human communities. Results 

from this project also are published in peer-reviewed journals, and they are further used to produce maps of 

change and other tools for land management, as well as to provide inputs for carbon-cycle modeling and other 

climate change research.

This report is only one of the products produced by USGS on land-use and land-cover change in the United 

States. Other reports and land-cover statistics are available online at http://landcovertrends.usgs.gov. 

Acknowledgments

The U.S. Environmental Protection Agency’s Office of Research and Development and the National 

Aeronautics and Space Administration provided initial funding to support this project. 

The U.S. Geological Survey’s (USGS) Geographic Analysis and Monitoring Program and Climate and 

Land Use Change Research and Development Program provided long-term support for this research.

Adam Davis (USGS) provided extensive support in the production of figures and tables.

All photographs contained within this Professional Paper were taken by various members of the 

USGS Land Cover Trends research project while conducting field investigations between 1999 and 2010.

Author Affiliations

William Acevedo 

Mark S. Brooks 

James P. Calzia 

Mark A. Drummond 

Leila Gass 

Todd J. Hawbaker 

Barry Middleton

Darrell E. Napton 

Christian G. Raumann 

Jana Ruhlman

Benjamin M. Sleeter

Terry L. Sohl

Daniel G. Sorenson

Christopher E. Soulard

Michael P. Stier

Janis L. Taylor

Tamara S. Wilson

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

Stinger Ghaffarian Technologies

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

U.S. Geological Survey

South Dakota State University

U.S. Geological Survey
v

Contents

Foreword ........................................................................................................................................................iii

Preface ...........................................................................................................................................................iv

Acknowledgments........................................................................................................................................iv

Author Affiliations.........................................................................................................................................iv

Regional Synthesis

Land-Cover Trends in the Western United States—1973 to 2000..................................................3

 By Benjamin M. Sleeter, Christopher E. Soulard, Tamara S. Wilson, 

 and Daniel G. Sorenson

Marine West Coast Forests Ecoregions

1. Coast Range Ecoregion ..................................................................................................................33

 By Terry L. Sohl

2. Puget Lowland Ecoregion ..............................................................................................................43

 By Daniel G. Sorenson

3. Willamette Valley Ecoregion..........................................................................................................51

 By Tamara S. Wilson and Daniel G. Sorenson

Rocky Mountains Ecoregions

4. Canadian Rockies Ecoregion.........................................................................................................61

 By Janis L. Taylor

5. Middle Rockies Ecoregion .............................................................................................................69

 By Janis L. Taylor

6. Montana Valley and Foothill Prairies Ecoregion ........................................................................77

 By Janis L. Taylor

7. Northern Rockies Ecoregion..........................................................................................................85

 By Janis L. Taylor

8. Southern Rockies Ecoregion .........................................................................................................95

 By Mark A. Drummond

9. Wasatch and Uinta Mountains Ecoregion.................................................................................105

 By Mark S. Brooks

10. Arizona/New Mexico Mountains Ecoregion...........................................................................113

 By Jana Ruhlman, Leila Gass, and Barry Middleton

Western Mountain Ranges Ecoregions

11. Cascades Ecoregion ...................................................................................................................123

 By Daniel G. Sorenson

12. Eastern Cascades Slopes and Foothills Ecoregion................................................................133

 By Daniel G. Sorenson

13. Klamath Mountains Ecoregion ..................................................................................................141

 By Benjamin M. Sleeter and James P. Calzia
vi

14. North Cascades Ecoregion ........................................................................................................151

 By Tamara S. Wilson

15. Sierra Nevada Ecoregion ...........................................................................................................159

 By Christian G. Raumann and Christopher E. Soulard

16. Blue Mountains Ecoregion.........................................................................................................169

 By Christopher E. Soulard

Mediterranean California Ecoregions

17. Central California Valley Ecoregion..........................................................................................181

 By Benjamin M. Sleeter

18. Southern California Mountains Ecoregion ..............................................................................191

 By Christopher E. Soulard, Christian G. Raumann, and Tamara S. Wilson

19. Southern and Central California Chaparral and Oak Woodlands Ecoregion.....................199

 By Darrell E. Napton

Cold Deserts Ecoregions

20. Central Basin and Range Ecoregion.........................................................................................209

 By Christopher E. Soulard

21. Colorado Plateaus Ecoregion ....................................................................................................219

 By Michael P. Stier

22. Columbia Plateau Ecoregion......................................................................................................229

 By Benjamin M. Sleeter

23. Northern Basin and Range Ecoregion .....................................................................................237

 By Christopher E. Soulard

24. Snake River Basin Ecoregion ....................................................................................................245

 By Benjamin M. Sleeter

25. Wyoming Basin Ecoregion.........................................................................................................255

 By Todd J. Hawbaker

26. Arizona/New Mexico Plateau Ecoregion ................................................................................263

 By Jana Ruhlman, Leila Gass, and Barry Middleton

Warm Deserts Ecoregions

27. Chihuahuan Deserts Ecoregion.................................................................................................275

 By Jana Ruhlman, Leila Gass, and Barry Middleton

28. Madrean Archipelago Ecoregion..............................................................................................285

 By Jana Ruhlman, Leila Gass, and Barry Middleton

29. Mojave Basin and Range Ecoregion ........................................................................................293

 By Benjamin M. Sleeter and Christian G. Raumann

30. Sonoran Basin and Range Ecoregion ......................................................................................303

 By James P. Calzia and Tamara S. Wilson

Appendix 1. Map of Ecoregions in Conterminous United States.......................................................313

Appendix 2. Abbreviations for Western United States Ecoregions...................................................316

Appendix 3. Land-Cover Classification System Used in “Status and Trends of 

 Land Change” Study ...........................................................................................................317

Appendix 4. Methodology Used in “Status and Trends of Land Change” Study.............................318
vii

Conversion Factors

Inch/Pound to SI Multiply by To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.004047 square kilometer (km2

)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

barrel (bbl), (petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3

) 

cubic foot (ft3

) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Mass

ton, short (2,000 lb) 0.9072 megagram (Mg) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C=(°F-32)/1.8
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Regional Synthesis

Land-Cover Trends in the 

Western United States—1973 to 2000

By Benjamin M. Sleeter, Christopher E. Soulard, Tamara S. Wilson, and Daniel G. Sorenson

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Introduction

Land-cover change is a pervasive phenomenon, 

brought about by both human and natural alteration of 

landscapes. Studying land-cover change is important because 

it helps explain (1) the types of changes that are occurring, 

(2) the rates at which they are occurring, and (3) the places 

where specific land-cover changes are occurring on the 

landscape. Understanding the spatial, temporal, and thematic dynamics of land-cover change facilitates research 

and development of hypotheses about the major drivers 

and consequences of change, helps define future scenarios, 

and is useful in understanding impacts on other ecosystem 

resources.

Land-cover change in the western United States is an 

important part of the overall story of the West. Humans 

have been using and altering the landscape for centuries 

to take advantage of resources provided by nature. For 

example, Native Americans in the Klamath Mountains in 

northern California regularly set fires for specific landmanagement purposes such as improving hunting conditions or promoting growth of certain species that are useful 

for food and cordage materials (Lewis, 1993). In general, 

Native American practices are believed to have been an 

important component of historical fire regimes and vegetation dynamics (Anderson, 2005; Fry and Stephens, 2006). 

Today (2012), fire management continues to be a major 

component and driver of land-cover change in the western 

United States. 

From the dense redwood forests of the Coast Ranges in 

Washington, Oregon, and California, to the lava fields and 

sagebrush-steppe communities of the Snake River Plain in 

Idaho, to the “Sky Islands” in Arizona and New Mexico, 

land cover in the West is as diverse as in any other part 

of the country. A complex mosaic of landscapes, characterized by abrupt changes in geology, topography, soils, 

and climate, and also their associated floral and faunal 

communities, results in a collection of ecoregions that 

exhibit dramatic variability in land-cover characteristics. 

Ecoregions—that is, areas that are similar in their biotic-, 

abiotic-, terrestrial-, and aquatic-ecosystem components, 

with humans considered as part of the biota (McMahon and 

others, 2001)—serve as useful entities for studying regional 

land-use/land-cover change, as they can encapsulate both 

the similarities and differences in the range of potential 

land-use/land-cover changes that are likely to occur regionally (Gallant and others, 2004). 

To provide estimates of change on an ecoregionby-ecoregion basis, a temporal- and spatial-sampling framework was employed, using U.S. Environmental Protection Agency’s Level III Ecoregions for the United States 

(Omernik, 1987; U.S. Environmental Protection Agency, 

1997) as the spatial stratification. A random sample of 

10 × 10 km sample blocks was selected for most ecoregions 

(20 × 20 km sample blocks were employed for two ecoregions). Within each sample block, land use/land cover was 

mapped for five study dates—1973, 1980, 1986, 1992, and 

2000—using Landsat Multispectral Scanner, Thematic 

Mapper, and Enhanced Thematic Mapper Plus imagery, in 

addition to aerial photographs obtained from the National 

Aerial Photography Program and National High Altitude 

Program. The minimum mapping unit for all study dates 

was a 60 × 60 m pixel.

After the data from the 1992 National Land Cover 

Dataset (Vogelmann and others, 2001) was reviewed and, 

if necessary, modified, areas of land-use/land-cover change 

were identified manually. Upon completion of the mapping, 

results were compiled and statistical estimates, with corresponding standard errors, were derived (see appendix 4 for 

a full description of project methodology; see also, Loveland and others [2002] and Stehman and others [2003]).

Regional Synthesis

The U.S. Geological Survey completed an assessment 

of 30 ecoregions in the western United States (fig. 1A). The 

30 ecoregions, which span approximately 2,707,515 km2

(1,045,373 mi2), extend from the Rocky Mountains to the 

Pacific Coast and from the Canadian to the Mexican border. The ecoregions vary greatly in size, the largest being 

the Central Basin and Range Ecoregion (approximate area, 

343,169km2) and the smallest being the Willamette Valley 

Ecoregion (approximate area, 14,458 km2). 
4 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 1. A, Map of all 30 Western United States ecoregions, showing land-use/land-cover classes from 2001 

National Land-Cover Database (Homer and others, 2004); note that, for this “Status and Trends of Land Change” 

study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed 

classes. B, Map showing six main Western United States ecoregion groups, modified from U.S. Environmental 

Protection Agency’s (1997) Level II Ecoregions for western United States. Within each ecoregion group, individual 

ecoregions share many similar physical and biological characteristics. C, List of six main Western United States 

ecoregion groups depicted in figure 1B; also listed are individual ecoregions included in each ecoregion group, as 

well as ecoregion abbreviations used in figure 1A.

0 75 150 225 300 MILES

0 100 200 300 400 KILOMETERS

MBR

SBR

CD

MA

ANMM

ANMP

CLRP

CBR

SRK

WUM

WB

MRK SRB

NBR ECSF

BM

NRK

CLMP

CRK

MVFP

NC

C

WV

PL

CR

KM

SCCCOW

CCV

SN

SCM

Ecoregion boundary

State boundary

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

MEXICO

CANADA

125° 120° 115° 110° 105°

50°

45°

40°

35°

30°

A

P a c i f i c

O

c

e

a

n

100°
Land-Cover Trends in the Western United States—1973 to 2000 5

Figure 1.—Continued

For purposes of discussion, the 30 Western United States 

ecoregions have been divided into six main groups,1 within 

which the ecoregions share many similar physical and biological 

characteristics: the Marine West Coast Forests Ecoregions, the 

Rocky Mountains Ecoregions, the Western Mountain Ranges 

Ecoregions, the Mediterranean California Ecoregions, the Cold 

Deserts Ecoregions, and the Warm Deserts Ecoregions (fig. 1B). 

1

 These six main groups of ecoregions are based on the U.S. Environmental Protection Agency’s Level II Ecoregions for the western United States 

(Omernik, J.M., 1987; Commission for Environmental Cooperation, 1997; 

U.S. Environmental Protection Agency, 1997), with the following exceptions: 

(1) the Level II Western Cordillera Ecoregion was subdivided into the Rocky 

Mountains Ecoregions and the Western Mountains Ranges Ecoregions, (2) the 

Arizona/New Mexico Mountains Ecoregion was included in the Rocky Mountains Ecoregions, and (3) the Madrean Archipelago Ecoregion was included in 

the Warm Deserts Ecoregions. 

The Western United States ecoregions consist primarily of five land-use/land-cover classes (grassland/shrubland, 

forest, agriculture, developed, and barren); six other land-use/

land-cover classes (water, wetland, mining, mechanically 

disturbed, nonmechanically disturbed, and ice/snow) are also 

present but in smaller amounts. Grassland/shrubland and barren land are most common in the arid-southwest and interiordesert ecoregions, whereas forest dominates ecoregions in 

the Pacific Northwest and Rocky Mountains. Agriculture and 

developed are found to some degree in nearly all ecoregions 

but are concentrated mainly in a relatively few high-density 

ecoregions (fig. 1A).

Studying the 30 Western United States ecoregions has 

revealed several unique land-cover-change histories. The 

dominant patterns and trajectories of change have been 

associated with urbanization, wildfire, forest cutting for 

Marine West Coast Forests Ecoregions

CR – Coast Range Ecoregion

PL – Puget Lowland Ecoregion

WV – Willamette Valley Ecoregion

Rocky Mountains Ecoregions

ANMM – Arizona/New Mexico Mountains Ecoregion

CRK – Canadian Rockies Ecoregion

MRK – Middle Rockies Ecoregion

MVFP – Montana Valley and Foothill Prairies Ecoregion

NRK – Northern Rockies Ecoregion

SRK – Southern Rockies Ecoregion

WUM – Wasatch and Uinta Mountains Ecoregion

Western Mountain Ranges Ecoregions

BM – Blue Mountains Ecoregion

C – Cascades Ecoregion

ECSF – East Cascades Slopes and Foothills Ecoregion

KM – Klamath Mountains Ecoregion

NC – North Cascades Ecoregion

SN – Sierra Nevada Ecoregion

Mediterranean California Ecoregions

CCV – Central California Valley Ecoregion

SCCCOW – Southern and Central California Chaparral 

 and Oak Woodlands Ecoregion

SCM – Southern California Mountains Ecoregion

Cold Deserts Ecoregions

ANMP – Arizona/New Mexico Plateau Ecoregion

CBR – Central Basin and Range Ecoregion

CLMP – Columbia Plateau Ecoregion

CLRP – Colorado Plateaus Ecoregion

NBR – Northern Basin and Range Ecoregion

SRB – Snake River Basin Ecoregion

WB – Wyoming Basin Ecoregion

Warm Deserts Ecoregions

CD – Chihuahuan Deserts Ecoregion

MA – Madrean Archipelago Ecoregion

MBR – Mojave Basin and Range Ecoregion

SBR – Sonoran Basin and Range Ecoregion

EXPLANATION

B C

Warm Deserts

Cold Deserts

Rocky Mountains

Western

Mountain

Ranges

Mediterranean

California

Marine

West

Coast

Forests
6 Status and Trends of Land Change in the Western United States—1973 to 2000

timber production, and shifts in agricultural production. 

However, these land-cover-change histories are expressed 

uniquely from ecoregion to ecoregion. For example, rates of 

forest cutting varied dramatically between the Coast Range, 

Klamath Mountains, and Sierra Nevada Ecoregions, owing 

to their local (and regional) biological and physical characteristics, as well as their land-management practices (Sleeter 

and others, 2010). Likewise, the rates of land-cover change 

in developed land were similar across such dramatically 

different ecoregions as the Mojave Basin and Range, Puget 

Lowland, and Central California Valley Ecoregions. Thus, 

behind each ecoregion emerges a unique story of change that 

can be related to each land-cover class and which is largely 

associated with each ecoregion’s distinct resource base and 

socioeconomic conditions.

The overall spatial change—that is, the amount of 

land area that changed at least one time over the 27-year 

study period—in the western United States was 5.8 percent. Whereas land-cover change across the entire western 

United States was relatively low, considerable ecoregional 

variability exists in the estimates of change (table 1). The 

highest changing ecoregion in terms of overall spatial change 

(as percent of ecoregion area) was the Puget Lowland 

Ecoregion, where an estimated 28.0 percent of the ecoregion underwent some form of change. The lowest changing 

ecoregion was the Chihuahuan Deserts Ecoregion, with an 

estimated 0.5 percent change. 

In general, ecoregions where timber harvesting is common experienced the highest rates of land-cover change, 

whereas ecoregions that have the lowest rates of change 

were generally associated with deserts in the arid Southwest. 

In ecoregions where urbanization and agricultural land use 

were most common, the rates of change tended to be more 

modest. The Marine West Coast Forests Ecoregions had the 

highest average amount of change, at 24.2 percent, largely 

a result of intensive timber harvesting (table 1). The Rocky 

Mountains Ecoregions and the Western Mountain Ranges 

Ecoregions had an estimated 6.9 percent and 10.8 percent 

change, respectively. The Mediterranean California Ecoregions had an estimated 10.1 percent change, mainly a result 

of a mix of urbanization, shifts in the locations of agricultural production, and disturbances from fire. Land-cover 

change in the western desert ecoregions was lowest, with 3.2 

percent change in the Cold Deserts Ecoregions and 1.7 percent change in the Warm Deserts Ecoregions (table 1). And 

yet, even within these groups of ecoregions, considerable 

geographic variability of change exists (fig. 2).

Change in forested ecoregions in the western United 

States was due largely to a mix of timber harvesting and 

disturbances from wildfire, and both of these processes were 

influenced by land-ownership and -management practices 

(fig. 3). The fact that a large proportion of land in forested 

ecoregions consisted of publicly managed, protected areas, 

which include conservation as a primary management objective, resulted in reduced levels of ecosystem disturbance 

caused by timber harvesting. However, because public lands 

were harvested less frequently than private lands, they also 

were prone to large, crown-disturbing fires made larger by the 

buildup of fuels. Changes in grassland/shrubland, agriculture, 

and developed land-cover classes were the other primary 

types of changes. Although agricultural land use intensified in 

some regions, resulting in the conversion of grassland/shrubland to cropland, it deintensified in other regions, primarily 

as a result of implementation of federal policies.

Figure 2. Maps showing (A) overall spatial change as percent of ecoregion area, (B) standard error as percent of ecoregion area, and 

(C) relative error as percent of change, for all 30 Western United States ecoregions over entire study period (1973–2000). 

Area changed,

as percent 

of ecoregion

Standard error,

as percent 

of ecoregion

Relative error,

as percent 

of change

15.1– 30.0

10.1–15.0

5.1 –10.0

2.1– 5.0

0 – 2.0

4.1– 5.0

3.1 – 4.0

2.1– 3.0

1.1– 2.0

0 –1.0

50.1– 70.0

40.1– 50.0

30.1– 40.0

20.1– 30.0

0 – 20.0

A B C
Land-Cover Trends in the Western United States—1973 to 2000 7

Table 1. Overall spatial change in each Western United States ecoregion (in square kilometers and as percent of ecoregion) 

for entire study period (1973 to 2000) and corresponding margin-of-error values for 85-percent confidence interval (in brackets).

Ecoregion

Ecoregion 

area

(km2

)

Overall spatial change

[margin of error]

(km2

) (% of ecoregion)

Marine West Coast Forests Ecoregions

Coast Range Ecoregion 57,338 14,641 [2,226] 25.5 [3.9]

Puget Lowland Ecoregion 18,009 5,041 [553] 28.0 [3.1]

Willamette Valley Ecoregion 14,458 2,090 [428] 14.5 [3.0]

Totals 89,805 21,772 [1,626] 24.2 [1.8]

Rocky Mountains Ecoregions

Northern Rockies Ecoregion 162,746 22,539 [6,373] 13.8 [3.9]

Middle Rockies Ecoregion 90,160 7,974 [3,097] 8.8 [3.4]

Canadian Rockies Ecoregion 18,494 1,397 [449] 7.6 [2.4]

Southern Rockies Ecoregion 138,854 1,444 [431] 1.0 [0.3]

Wasatch and Uinta Mountains Ecoregion 44,176 888 [345] 2.0 [0.8]

Montana Valley and Foothill Prairies Ecoregion 64,658 5,252 [2,619] 8.1 [4.1]

Arizona/New Mexico Mountains Ecoregion 108,432 3,806 [1,586] 3.5 [1.5]

Totals 627,520 43,300 [6,937] 6.9 [1.1]

Western Mountain Ranges Ecoregions

Cascades Ecoregion 46,787 11,520 [1,730] 24.6 [3.7]

North Cascades Ecoregion 30,421 3,200 [1,190] 10.5 [3.9]

Blue Mountains Ecoregion 65,461 4,275 [1,453] 6.5 [2.2]

Eastern Cascades Slopes and Foothills Ecoregion 57,329 6,943 [2,010] 12.1 [3.5]

Klamath Mountains Ecoregion 47,791 4,081 [1,079] 8.5 [2.3]

Sierra Nevada Ecoregion 53,413 2,645 [1,359] 5.0 [2.5]

Totals 301,201 32,664 [2,910] 10.8 [1.0]

Mediterranean California Ecoregions

Southern and Central California Chaparral and Oak Woodlands Ecoregion 102,110 9,872 [3,009] 9.7 [3.0]

Central California Valley Ecoregion 45,983 5,910 [1,434] 12.9 [3.1]

Southern California Mountains Ecoregion 17,871 906 [439] 5.1 [2.5]

Totals 165,965 16,688 [3,057] 10.1 [1.8]

Cold Deserts Ecoregions

Columbia Plateau Ecoregion 90,059 8,270 [2,416] 9.2 [2.7]

Northern Basin and Range Ecoregion 110,039 6,430 [4,254] 5.8 [3.9]

Snake River Basin Ecoregion 66,063 5,618 [2,011] 8.5 [3.0]

Wyoming Basin Ecoregion 128,914 2,372 [1,124] 1.8 [0.9]

Central Basin and Range Ecoregion 343,169 4,979 [2,505] 1.5 [0.7]

Colorado Plateaus Ecoregion 129,617 3,426 [2,694] 2.6 [2.1]

Arizona/New Mexico Plateau Ecoregion 192,869 2,380 [1,298] 1.2 [0.7]

Totals 1,060,730 33,475 [6,269] 3.2 [0.6]

Warm Deserts Ecoregions

Mojave Basin and Range Ecoregion 130,922 3,474 [1,864] 2.7 [1.4]

Sonoran Basin and Range Ecoregion 116,364 2,992 [1,600] 2.6 [1.4]

Madrean Archipelago Ecoregion 40,536 575 [305] 1.4 [0.8]

Chihuahuan Deserts Ecoregion 174,472 822 [389] 0.5 [0.2]

Totals 462,294 7,863 [2,196] 1.7 [0.5]

All Western United States ecoregions 2,707,515 155,762 [11,584] 5.8 [0.4]
8 Status and Trends of Land Change in the Western United States—1973 to 2000

The western United States is covered predominately 

by grassland/shrubland, which made up 59.0 percent of 

the ecoregions’ land cover in 2000 (table 2). Furthermore, 

the amount of grassland/shrubland in the West remained 

relatively stable over the 27-year study period. Forest, the 

second most common land-cover class in the western United 

States, experienced the largest net change, declining from 

29.4 percent of the ecoregions’ area in 1973 to 28.1 percent 

in 2000 (table 2). Agriculture remained relatively stable, 

whereas developed land increased. Water, wetland, mining, 

barren, and ice/snow land-cover classes all remained stable. 

Table 2 presents the total areal percentages of all land-cover 

classes in the Western United States ecoregions for each of 

the five study years.

Net change is the total amount of losses in a land-cover 

class subtracted from the total amount of gains. Although net 

change provides information on how much land converted 

from one land-cover class to another, it can mask the total 

amount of land touched by change. To better understand 

change, gross spatial change also was measured for each 

land-cover class. Gross spatial change is simply the addition 

of gains and losses relating to a land-cover class, accounting 

for areas that changed in multiple time periods (fig. 4). For 

example, net change in forest land cover can be relatively 

small, even in ecoregions where timber harvest is common, 

because a near-equal amount of land could be regrowing 

into forest as is being cut for timber. Therefore, estimates 

of gross spatial change can have important environmental 

Figure 3. Maps showing (A) federal land ownership (National Atlas of the United States, 2006) and (B) protected areas (Conservation 

Biology Institute, 2010), in all 30 Western United States ecoregions. Bureau of Land Management lands offshore of California are part of 

California Coastal National Monument. Protected areas are based on International Union for Conservation of Nature (1994) guidelines 

for protected-area-management categories (see also, DellaSala and others, 2001). 

110°

100° 100°

120°

45°

40°

35°

30°

0 200 400 MILES

0 250 500 KILOMETERS

Bureau of Land Management

Forest Service

National Park Service

Department of Defense

U.S. Fish and Wildlife Service

Bureau of Reclamation

Other Federal lands

Ecoregion boundary

State boundary

Federal land ownership

EXPLANATION

A

MEXICO

CANADA

Other lands

120° 110°

45°

50° 50°

40°

35°

30°

Protected areas (Levels of Protection)

Ecoregion boundary

State boundary

Wilderness Area (I)

National Park (II)

Natural Monument (III)

Habitat/Species Management Area (IV)

Protected Landscape (V)

Managed Resource Protected Area (VI)

EXPLANATION

B

MEXICO

CANADA

Other lands
Land-Cover Trends in the Western United States—1973 to 2000 9

-30

-20

-10

0

10

20

30

Area changed, in thousands of square kilometers

Grassland/Shrubland Agriculture

1973–19801980–19861986–19921992– 2000

1973–19801980–19861986–1992

1992– 2000

1973–19801980–1986

1986–1992

1992– 2000

Forest

Time period

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 4. Gross changes (areas gained from, and lost to, other land-cover classes) in forest, grassland/shrubland, and agriculture 

land-cover classes, in all 30 Western United States ecoregions over entire study period (1973–2000). For each of these three classes, 

colored bars above zero axis indicate land-cover classes that lost area to that class and amounts of area lost, whereas colored bars 

below zero axis indicate land-cover classes that gained area from that class and amounts of area gained.

Table 2. Areal percentages of land-use/land-cover classes in all 30 Western United States ecoregions for each of five study years 

(1973, 1980, 1986, 1992, 2000) and corresponding margin-of-error values for 85-percent confidence interval (in brackets).

[Percentages are of total area in all Western United States ecoregions. See appendix 3 for definitions of land-use/land-cover classifications]

Land-use/land-cover class

1973

[margin of error]

(% of area)

1980

[margin of error]

(% of area)

1986

[margin of error]

(% of area)

1992

[margin of error]

(% of area)

2000

[margin of error]

(% of area)

Water 0.8 [0.2] 0.9 [0.2] 0.9 [0.2] 0.8 [0.2] 0.8 [0.2]

Developed 1.0 [0.2] 1.1 [0.2] 1.2 [0.2] 1.3 [0.2] 1.5 [0.2]

Mechanically disturbed 0.4 [0.1] 0.4 [<0.1] 0.4 [0.1] 0.6 [0.1] 0.5 [0.1]

Mining 0.2 [0.1] 0.2 [0.1] 0.2 [0.1] 0.2 [0.1] 0.2 [0.1]

Barren 1.9 [0.5] 1.9 [0.5] 1.9 [0.5] 1.9 [0.5] 1.9 [0.5]

Forest 29.4 [1.1] 29.2 [1.1] 29.0 [1.1] 28.6 [1.1] 28.1 [1.1]

Grassland/Shrubland 59.0 [1.2] 59.1 [1.2] 58.9 [1.2] 59.0 [1.2] 59.0 [1.2]

Agriculture 6.5 [0.5] 6.6 [0.5] 6.6 [0.5] 6.3 [0.5] 6.3 [0.5]

Wetland 0.7 [0.1] 0.7 [0.1] 0.7 [0.1] 0.7 [0.1] 0.7 [0.1]

Nonmechanically disturbed 0.1 [<0.1] 0.1 [0.1] 0.1 [0.1] 0.4 [0.1] 0.9 [0.3]

Ice/Snow 0.1 [<0.1] 0.1 [<0.1] 0.1 [<0.1] 0.1 [<0.1] 0.1 [<0.1]
10 Status and Trends of Land Change in the Western United States—1973 to 2000

considerations. Table 3 provides estimates of gross spatial 

change and net areal change for each land-cover class.

The five land-cover classes that had the highest gross spatial 

change over the entire study period (1973–2000) are as follows:

• Grassland/shrubland, 99,285 km2

 (margin of error, 

9,082 km2) 

• Forest, 88,707 km2

 (margin of error, 7,929 km2)

• Mechanically disturbed, 60,253 km2 (margin of error, 

5,759 km2)

• Nonmechanically disturbed, 40,571 km2

 (margin of 

error, 8,342 km2)

• Agriculture, 33,910 km2

 (margin of error, 4,987 km2)

The five land-cover classes that had the largest net areal 

change over the entire study period (1973–2000) are as follows: 

• Forest, −33,197 km2

 (margin of error, 6,657 km2)

• Nonmechanically disturbed, 22,473 km2

 (margin of 

error, 7,110 km2)

• Developed, 12,785 km2

 (margin of error, 3,000 km2)

• Agriculture, −4,414 km2

 (margin of error, 4,283 km2)

• Mining, 2,233 km2

 (margin of error, 622 km2)

Another important characteristic of land-cover change is 

that it can vary across time in response to changing drivers of 

change. Overall areal change was the highest between 1992 

and 2000, at 3.0 percent, and the lowest was between 1973 

and 1980, at 1.6 percent. Table 4 shows estimates of net areal 

change in each land-cover class for each time period.

Grassland/Shrubland Land-Cover Class

Although grassland/shrubland was the most common 

land-cover class across the West (fig. 5), very little net change 

(−1,106 km2) occurred between 1973 and 2000 (table 3). This 

amounts to a loss of 0.1 percent of the grassland/shrubland 

in the western United States. However, the relatively small 

amount of net change masks substantial fluctuations involving 

the conversion of lands into, and out of, grassland/shrubland. 

Conversions from grassland/shrubland to other classes totaled 

an estimated 65,341 km2, whereas conversions to grassland/

shrubland accounted for an estimated 64,235 km2. The amount 

of total land area that changed to or from grassland/shrubland 

was 99,285 km2 (table 3), meaning that 3.7 percent of the 

western United States experienced conversion into, or out of, 

grassland/shrubland during the 27-year study period. Table 5 

shows Western United States ecoregions that had greater than 

2.5 percent net change in grassland/shrubland.

Changes in grassland/shrubland are associated with 

several land-change processes. A large amount of the gross 

areal change in grassland/shrubland was the result of capturing the intermediate stage (usually grassland/shrubland) of 

forest regrowth after disturbance events such as clearcutting or wildfire. Following such events, forests typically 

take several years before emerging as areas that can be 

once again classified as forest land-cover class. The largest 

grassland/shrubland conversion was associated with regeneration of forest after clearcutting. An estimated 29,949 km2

of land changed from mechanically disturbed to grassland/

shrubland, whereas 21,312 km2 changed from grassland/

shrubland directly back to forest. 

Natural disturbances, specifically wildfire, also have a 

direct impact on grassland/shrubland. Several areas in the 

Table 3. Gross spatial changes and net areal changes in land-use/land-cover classes in all 30 

Western United States ecoregions for entire study period (1973 to 2000) and corresponding 

margin-of-error values for 85-percent confidence interval (in brackets).

[Percentages are of total area in all Western United States ecoregions. See appendix 3 for definitions of 

land-use/land-cover classifications]

Land-use/land-cover class

Gross spatial change (1973–2000)

[margin of error]

Net areal change (1973–2000)

[margin of error]

(km2

) (% of area) (km2) (% change)

Water 5,755 [1,954] 0.2 [0.1] 259 [1,069] 1.1

Developed 12,760 [2,472] 0.5 [0.1] 12,785 [3,000] 48.0

Mechanically disturbed 60,253 [5,759] 2.2 [0.2] 1,195 [2,128] 10.0

Mining 2,834 [704] 0.1 [<0.1] 2,233 [622] 53.4

Barren 1,016 [231] <0.1 [<0.1] 81 [167] 0.2

Forest 88,707 [7,929] 3.3 [0.3] −33,197 [6,657] −4.2

Grassland/Shrubland 99,285 [9,082] 3.7 [0.3] −1,106 [6,883] −0.1

Agriculture 33,910 [4,987] 1.2 [0.2] −4,414 [4,283] −2.5

Wetland 4,006 [1,449] 0.1 [<0.1] 

 −243 [711] −1.3

Nonmechanically disturbed 40,571 [8,342] 1.5 [0.3] 22,473 [7,110] 1,124.3

Ice/Snow 77 [45] <0.1 [<0.1] −66 [43] −3.4
Land-Cover Trends in the Western United States—1973 to 2000 11

West that are dominated by grassland/shrubland experienced 

high rates of fire. This was especially common in the Northern 

Basin and Range, Southern and Central California Chaparral 

and Oak Woodlands, Snake River Basin, and Middle Rockies 

Ecoregions. These ecoregions accounted for 75 percent of firerelated disturbance on grassland/shrubland. 

Changes in grassland/shrubland also were frequently associated with conversions to and from agriculture. Changes associated with agriculture were common in the Columbia Plateau, 

Snake River Basin, Central California Valley, Southern and 

Central California Chaparral and Oak Woodlands, and Montana 

Valley and Foothill Prairies Ecoregions. An estimated 16,662 

km2

 converted from grassland/shrubland to agriculture, whereas 

16,116 km2 converted from agriculture to grassland/shrubland. 

Some areas experienced conversions in both directions as 

marginal lands rotated into and out of production in response to 

regional climate variability and federal farm policy, such as the 

Conservation Reserve Program.

Urbanization was the primary cause of change from 

grassland/shrubland to developed. These conversions were 

most common in the Mojave Basin and Range, Southern 

and Central California Chaparral and Oak Woodlands, and 

Colorado Plateaus Ecoregions. In total, an estimated 5,496 

km2 of grassland/shrubland converted to developed between 

1973 and 2000.

Forest Land-Cover Class

In 2000, forest accounted for 28.1 percent of the 

western United States (table 2). Western forests are highly 

diverse, from oak-studded (Quercus sp.) valleys and pinyon 

pine–juniper (Pinus sp. and Juniperus sp., respectively) 

Table 4. Net areal changes in land-use/land-cover classes in all 30 Western United States ecoregions 

during each of four time periods and corresponding margin-of-error values for 85-percent confidence 

interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Land-use/land-cover class Net change [margin of error] (km2

)

1973–1980 1980–1986 1986–1992 1992–2000

Water 820 [1,110] 178 [1,772] −1,481 [842] 742 [603]

Developed 3,204 [1,138] 2,432 [621] 3,677 [1,129] 3,472 [815]

Mechanically disturbed −2,396 [1,376] 2,572 [1,267] 4,881 [1,513] −3,862 [1,608]

Mining 548 [193] 500 [200] 528 [218] 657 [301]

Barren 3 [54] 6 [110] −59 [99] 131 [79]

Forest −5,328 [1,574] −3,984 [2,275] −11,105 [2,783] −12,779 [5,582]

Grassland/Shrubland 165 [2,611] −2,731 [2331] 2,357 [4,085] −897 [4,694]

Agriculture 2,958 [1,640] 616 [894] −6,673 [2,144] −1,314 [1,799]

Wetland −367 [455] −167 [1,021] 307 [387] −16 [293]

Nonmechanically disturbed 409 [1,957] 584 [2,166] 7,572 [3,981] 13,907 [7,166]

Ice/Snow −15 [9] −6 [6] −4 [8] −41 [27]

Table 5. Net areal changes and gross spatial changes in grassland/shrubland land-cover class for Western 

United States ecoregions that had greater than 2.5 percent net change in grassland/shrubland class for entire 

study period (1973 to 2000) and corresponding margin-of-error values for 85-percent confidence interval (in 

brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Net areal change (1973–2000) 

[margin of error]

Gross spatial change (1973–2000) 

[margin of error]

(% of ecoregion) (km2

) (% of ecoregion) (km2)

Middle Rockies Ecoregion 4.6 [2.6] 4,146 [2,348] 6.6 [2.9] 5,950 [2,626]

Central California Valley Ecoregion −3.9 [1.9] −1,782 [860] 9.9 [2.1] 4,552 [962]

Northern Basin and Range Ecoregion −2.6 [3.3] −2,841 [3,589] 5.5 [3.9] 6,060 [4,249]

Southern and Central California Chaparral 

and Oak Woodlands Ecoregion −2.7 [1.3] −2,746 [1,326] 5.6 [1.0] 5,732 [1,058]

Eastern Cascades Slopes and 

Foothills Ecoregion 2.7 [1.7] 1,531 [986] 7.1 [2.7] 4,095 [1,559]
12 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 5. Areas of grassland/shrubland in western United States. A, Shrubland in northeastern Inyo County, east-central California, in 

Central Basin and Range Ecoregion. In distance to east are White Mountains, along California–Nevada border. B, Grassland in Gilliam 

County, northern Oregon, in southern part of Columbia Plateau Ecoregion. C, Grassy hills east of Porterville, located in Tulare County, 

central California, in Southern and Central California Chaparral and Oak Woodlands Ecoregion. D, Mixed grasses and shrubs north of 

Glenns Ferry, located in Elmore County, southwestern Idaho, in Snake River Basin Ecoregion.

woodlands in drier climates and at lower elevations, to the 

coniferous forests in the Sierra Nevada, the Cascade Range, 

and the Rocky Mountains (fig. 6). Each forest type supports 

a unique suite of habitat, resources, and land-use potential. 

Although forest is not the most common land cover in the 

West, changes in the forest class dominate land-cover change 

in the region.

Between 1973 and 2000, an estimated net decline of 4.2 

percent (33,197 km2) occurred in western United States forest 

land cover (table 3), with losses totaling 73,677 km2 and gains 

totaling 40,480 km2. However, net change masks the overall 

forest land-use/land-cover dynamics; gross spatial change is 

a better indicator of just how much the forest land-cover class 

changed over the 27-year study period. Gross spatial changes 

in forest land affected 3.3 percent of the total area in the 

western United States (table 3), whereas 11.1 percent of all 

western United States forests were touched by change at least 

once during the study period. Table 6 shows Western United 

States ecoregions that had at least 10 percent of their land 

area impacted by forest change.

Changes in forest land cover, which were concentrated in 

the ecoregions of the Pacific Northwest, can occur for many 

reasons. In the West, forest change consisted of forest cutting 

and regrowth for timber production, disturbance and regrowth 

following wildfire, conversion of forest land for urban and 

agricultural uses, and conversion from agriculture back to 

forest. Timber production and wildfire were the most common 

drivers of land-cover change in the forest class. 

High rates of forest land-cover change in Western 

United States ecoregions were linked primarily to forestry, 

also known as silviculture, which is characterized by the 

cutting and regrowth of trees for lumber and other woodrelated products. In this study’s classification scheme, forest 

harvesting was mapped as a change from the forest class to 

the mechanically disturbed class. In rare cases, a mechanically disturbed state associated with the removal of wooded 

vegetation for rangeland improvement (for example, the 

chaining of pinyon pine–juniper woodland for grazing) was 

also captured. Between 1973 and 2000, an estimated 46,745 

km2

 of forest were mechanically disturbed. 

Forest harvest was the top-ranked land-cover conversion across the West in each of the first three time periods 

(1973–1980, 1980–1986, and 1986–1992), and it ranked as the 

second leading land-cover conversion (11,895 km2) between 

1992 and 2000. Regrowth back to forest resulted either in 

the direct conversion from mechanically disturbed to forest 

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 13

Figure 6. Forested areas in western United States. A, Forest along Trinity River, northwestern California, in Klamath Mountains Ecoregion. B, Dense forest and forest understory outside of Olympia, western Washington, in Puget Lowland Ecoregion. C, Low-density oak 

woodland in Southern and Central California Chaparral and Oak Woodlands Ecoregion. D, Forest regrowth in Gifford Pinchot National 

Forest, southwestern Washington, in Cascades Ecoregion.

or in an intermediate stage in which mechanically disturbed 

conversion to grassland/shrubland before reverting to forest. 

The most rapid postharvest forest-recovery rates occurred in 

ecoregions that have favorable climates and other biological 

and physical factors, including the Coast Range and Puget 

Lowland Ecoregions, whereas longer successional periods 

were more common in drier, less productive regions.

The primary drivers of change to western United States 

forests were complex and included several interrelated factors. 

For years, countries in the Pacific Rim have imported logs 

from the Pacific Northwest (PNW), Japan being the largest 

importer. Old-growth logs are highly sought after, owing to 

their high ring count. Japanese mills also have been more 

efficient than PNW mills, capturing as much as 70 percent of 

the raw material, which enabled them to absorb the increased 

costs of import (Daniels, 2005). In the early 1990s, prices for 

PNW soft wood peaked, and importers began looking to other 

global markets, namely Canada, to fill demand. At the same 

time, Canada became a major exporter of wood products to the 

A

C

B

D

Table 6. Gross spatial changes in forest land-cover class for 

Western United States ecoregions that had at least 10 percent 

change to and from forest class for entire study period (1973 to 

2000) and corresponding margin-of-error values for 85-percent 

confidence interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Gross spatial change (1973–2000) 

[margin of error] 

(% of 

ecoregion) (km2

)

Puget Lowland Ecoregion 26.6 [3.1] 4,665 [544]

Coast Range Ecoregion 24.9 [4.5] 14,289 [2,568]

Cascades Ecoregion 23.9 [3.3] 11,172 [1,561]

Northern Rockies Ecoregion 11.8 [3.5] 19,274 [5,638]

Willamette Valley Ecoregion 11.5 [3.0] 1,657 [440]

North Cascades Ecoregion 10.2 [3.9] 3,101 [1,189]

Eastern Cascades Slopes and 

Foothills Ecoregion 10.0 [3.5] 5,738 [2,023]
14 Status and Trends of Land Change in the Western United States—1973 to 2000

United States. In the 1990s, tightened supplies of high-quality 

PNW logs resulted in soaring prices, ultimately prompting overseas importers to experiment with other tree species 

and their wood products. Markets in Russia, New Zealand, 

Canada, Chile, and Europe were developed, along with the 

increased use of new products such as glue-laminated beams. 

The Asian economic crisis of the late 1990s further reduced 

the demand for PNW logs as demand for new housing construction was dramatically reduced (Daniels, 2005).

The United States has passed several pieces of legislation that restrict the amount of logs that can be exported from 

federally owned lands. In 1974, Congress attached a rider 

to the U.S. Department of Interior Appropriation Act that 

initiated a near-total ban on unprocessed timber exports from 

federal lands west of the 100th meridian (Daniels, 2005). 

The Forest Resources Conservation and Shortage Relief Act 

of 1990 was passed to alleviate the effects of the reduced 

timber supply resulting from restrictions caused by the listing of the Northern Spotted Owl (Strix occidentalis caurina) 

on the endangered species list. The goal of the relief act was 

threefold, (1) to promote conservation of forest resources, 

(2) to ensure that United States forest resources were not 

exhausted, and (3) to guarantee a constant and available supply of forest resources to meet domestic needs. As a result, 

the only timber available for export from the PNW was from 

private landowners.

Domestic environmental policy also has had a profound 

impact on the PNW log-export market. In 1990 the Northern 

Spotted Owl was listed as threatened, and it was later joined 

by the Marbled Murrelet (Brachyramphus marmoratus). The 

Endangered Species Act also afforded protection to species 

of salmon (family Salmonidae) in riparian areas. These listings, which have impacted federal, state, and private lands 

alike, have resulted in significant timber harvest restrictions. 

In 1991, virtually all harvest on federal lands stopped in 

response to the Northern Spotted Owl controversy, and the 

issue was not resolved until 1993 when the Northwest Forest 

Plan was adopted. Between 1965 and 1988, timber sold from 

PNW national forests fluctuated between 3 and 4 billion 

board feet annually. In 1991, sales dropped to less than 1 

billion board feet, a level maintained throughout the 1990s 

(Daniels, 2005). Douglas-fir (Pseudotsuga menziesii) exports 

to Japan dropped by 30 percent between 1989 and 1991, and, 

by 1992, 75 percent of PNW log exports were from private 

Figure 7. Agricultural areas in western United States. A, Wheatfield harvest along border between Walla Walla and Columbia Counties, southeastern Washington, in Columbia Plateau Ecoregion. B, Cows in maintained pasture south of Westcliffe, located in Custer 

County, south-central Colorado, in Southern Rockies Ecoregion. C, Grapes near Paso Robles, located in San Luis Obispo County, central 

California, in Southern and Central California Chaparral and Oak Woodlands Ecoregion. D, Wheat field just south of Columbia River in 

Sherman County, northern Oregon, in Columbia Plateau Ecoregion.

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 15

lands (Daniels, 2005). By this time, old growth, which had 

all but disappeared from these areas, was only available on 

protected federal lands (fig. 3).

Forest change in the western United States also was 

strongly associated with natural disturbances caused by wildfire. In this study’s classification scheme, areas affected by 

forest fires were mapped as a change from the forest class to 

the nonmechanically disturbed class. In rare cases, a nonmechanically disturbed state associated with disease from insect 

infestations also was mapped. Between 1973 and 2000, an 

estimated 22,827 km2 of forest converted to nonmechanically 

disturbed, 24 percent (5,448 km2) of which occurred between 

1986 and 1992 and 66 percent (14,994 km2) of which occurred 

between 1992 and 2000. The vast majority of mapped forest 

fires and infestations in the West occurred in the Rocky Mountains Ecoregions, 33 percent of which occurred in the Northern 

Rockies Ecoregion alone. In this ecoregion, land-use histories 

appear to have had relatively little effect on fire risk; rather, 

fires are more strongly associated with increased spring and 

summer temperatures and an earlier spring snowmelt (Westerling and others, 2006).

Agriculture Land-Cover Class

Agriculture was the third most common land-cover class 

in the western United States, accounting for an estimated 6.3 

percent of the total land area in 2000 (table 2; fig. 7). Like grassland/shrubland, agriculture was relatively stable, declining only 

2.5 percent (-4,414 km2) between 1973 and 2000 (table 3). This 

loss in agriculture land cover corresponds to the U.S. Department of Agriculture’s (2004) Census of Agriculture, which 

estimated a loss of approximately 12,000 km2 of total cropland 

in the western United States between 1969 and 1997 (fig. 8). 

However, differences between study years, as well as classification characteristics, make a one-to-one comparison between 

agricultural census and estimates presented here difficult. In 

addition, net change can mask temporal and spatial variability 

in the rates of change in the agriculture class. For example, 

between 1973 and 1986, agriculture increased from 6.5 percent 

to 6.6 percent of the total land area, whereas, between 1986 

and 1992, agriculture declined by 4.5 percent to 6.3 percent 

regionwide. The total area that converted to or from agriculture 

between 1973 and 2000 was 33,910 km2

, approximately 1.2 

percent of the western United States (table 3). 

The most common conversion associated with agriculture was between agriculture and grassland/shrubland, which 

accounted for 83 percent of all agriculture gains and losses 

and, when gains and losses were combined, totaled 32,778 

km2. An additional 4,623 km2 of agriculture land converted to 

developed land, an area roughly equivalent to 2.5 percent of 

the total agriculture land. 

The following five ecoregions accounted for nearly twothirds of all gross agriculture change:

• Columbia Plateau Ecoregion, 7,633 km2

 (margin of 

error, 2,360 km2

)

• Central California Valley Ecoregion, 5,148 km2

 (margin of error, 916 km2

)

• Montana Valley and Foothill Prairies Ecoregion,

4,170 km2 (margin of error, 3,202 km2)

• Southern and Central California Chaparral and Oak 

Woodlands Ecoregion, 2,711 km2 (margin of error, 

596 km2)

• Snake River Basin Ecoregion, 2,407 km2

 (margin of 

error, 1,064 km2)

The Conservation Reserve Program (CRP) was a strong 

driver of agriculture change in the western United States, 

although the effects of the program were limited to a few 

ecoregions. The CRP, which was enacted in 1985 (U.S. 

Congress, 1985), instituted the largest and most rapid conversion of cropland to grassland in United States history (Park 

and Egbert, 2008). The objectives of the CRP were to reduce 

soil erosion, improve water quality, create wildlife habitat, 

implement controls on commodity production, and provide 

financial support to agricultural producers (Park and Egbert, 

2008). By 1992, an area equivalent to approximately 8 percent 

of United States farmland had been enrolled in the CRP 

program (Margheim, 1994). The CRP had the biggest impact 

in the Columbia Plateau and the Montana Valley and Foothill 

Prairies Ecoregions, with lesser impacts in the Snake River 

Basin Ecoregion. The CRP program had minimal impact in the 

Central California Valley and the Southern and Central California Chaparral and Oak Woodlands Ecoregions, accounting 

for less than one percent of total United States enrollments 

(U.S. Department of Agriculture, 2011). 

Conversion of agriculture land to developed land 

accounted for an estimated 4,623 km2

 between 1973 and 2000. 

Five ecoregions accounted for 76 percent of all of the agriculture-to-developed conversion (table 7): the Southern and 

Central California Chaparral and Oak Woodlands Ecoregion 

(1,230 km2), Colorado Plateaus Ecoregion (756 km2), Central 

California Valley Ecoregion (684 km2), Willamette Valley 

Ecoregion (347 km2

), and Northern Rockies Ecoregion (262 

km2). The period between 1973 and 1980 experienced the largest average annual conversion from agriculture to developed, 

at 203 km2 per year. The other three time periods averaged 146 

to 192 km2 per year. Population growth and the demand for 

new developed land resulted in the direct conversion of agriculture to developed, as well as the conversion of grassland/

shrubland to agriculture as displaced farmers sought out new 

areas to farm (Sleeter, 2009).

Developed Land-Cover Class

Developed land cover includes areas of intensive use, 

within which much of the land is covered with either structures or other impermeable surfaces of anthropogenic origin, or less intensive use, within which the land is covered 

with both vegetation and structures, including land that is 
16 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 8. Map of counties that intersect Western United States ecoregions, showing counties whose land changed 

either into (positive values) or out of (negative values) cropland between 1969 and 1997. County data are based on 

U.S. Department of Agriculture’s (2004) Census of Agriculture estimates.

0 75 150 225 300 MILES

0 100 200 300 400 KILOMETERS

−5.0 –−2.1

−10.0 –−5.1

−51.0 –−10.1

Cropland change, as percent of county area

10.1 –51.0

5.1 –10.0

2.1 –5.0

−2.0 –2.0

EXPLANATION

Ecoregion boundary

State boundary

MEXICO

CANADA

125° 120° 115° 110° 105°

50°

45°

40°

35°

30°

P a c i f i c

O

c

e

a

n

100°

MBR

SBR

CD

MA

ANMM

ANMP

CLRP

CBR

SRK

WUM

WB

MRK SRB

NBR ECSF

BM

NRK

CLMP

CRK

MVFP

NC

C

WV

PL

CR

KM

SCCCOW

CCV

SN

SCM
Land-Cover Trends in the Western United States—1973 to 2000 17

functionally related to urban or built-up environments (for 

example, parks and golf courses) (fig. 9). Developed land 

cover increased by 48.0 percent over the study period, a net 

increase of 12,785 km2 (table 3). Developed land accounted 

for 1.0 percent of the western United States in 1973 and 1.5 

percent in 2000 (table 2). Owing to the unidirectional nature of 

change associated with development and urbanization, gross 

change was similar to that of net change. Developed land 

spanned 26,608 km2 in 1973 but, by 2000, had expanded to 

cover 39,393 km2. Between 1970 and 2000, population of the 

western United States experienced similar growth, increasing 

62.6 percent from 72.6 to 118.1 million people (U.S. Census 

Bureau, 2001). Of the 392 counties that intersect the Western 

United States ecoregions, only 40 realized a net decline in 

population between 1970 and 2000 (fig. 10). Table 8 shows the 

ecoregions that experienced the largest increase in developed 

land (defined as the percentage of the ecoregion that converted 

to the developed land-cover class) between 1973 and 2000, 

the largest areal change, and the corresponding areal changes 

relative to their land-cover class in 1973. 

Conversions to developed land were associated primarily 

with agriculture, forest, grassland/shrubland, and mechanically 

disturbed land. However, considerable spatial variability exists 

in the origin of new developed land. The Pacific Northwest 

region (that is, the Marine West Coast Forests Ecoregions and 

parts of the Western Mountain Ranges Ecoregions), which 

is dominated by dense evergreen forests, accounted for the 

majority of forest conversion to developed land, whereas 

the Mediterranean California Ecoregions, as well as the 

Warm Deserts Ecoregions and the Cold Deserts Ecoregions, 

accounted for the majority of change from grassland/shrubland 

to developed land. The loss of agriculture to developed land 

occurred in a more diverse set of ecoregions, namely the 

Mediterranean California Ecoregions, the Warm Deserts 

Ecoregions, the Cold Deserts Ecoregions, and the Marine West 

Coast Forests Ecoregions. Conversion to developed land from 

mechanically disturbed land was most common in ecoregions 

that already contained large areas of development.

Nearly 80 percent of all new developed land came from one 

of two land-cover classes, either grassland/shrubland or agriculture. However, great variability of change exists among the 

ecoregions. For example, in the Southern and Central California 

Chaparral and Oak Woodlands Ecoregion, more developed 

land was converted from agriculture by a 2:1 margin than from 

grassland/shrubland, whereas in the Colorado Plateaus Ecoregion, the margin was close to even, and in the Mojave Basin and 

Range Ecoregion, the margin was 35:1 in favor of grassland/

shrubland. In ecoregions in which agriculture was a dominant 

land use, loss of agriculture to developed land was generally the 

most common conversion. For example, in the Central California 

Valley Ecoregion, conversion from agriculture to developed land 

occurred by a 2:1 margin over conversion of grassland/shrubland 

to developed land, whereas the same conversion occurred by a 

3.5:1 margin in the Columbia Plateau Ecoregion and by a 6:1 

margin in the Snake River Basin Ecoregion.

Conversions from grassland/shrubland to developed 

land accounted for 43.6 percent of all change in developed 

land cover, and six ecoregions accounted for approximately 

70 percent of this specific conversion. Conversions from 

agriculture to developed land were the second most common 

form of change, accounting for an estimated 4,623 km2

 over 

the 27-year study period (table 7). The Southern and Central 

Table 7. Sizes of new areas of developed land-cover class that converted from grassland/shrubland, agriculture, and forest 

classes for the 10 Western United States ecoregions that had largest net change for entire study period (1973 to 2000), as well as for 

all 30 Western United States ecoregions, and corresponding margin-of-error values for 85-percent confidence interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Converted from 

grassland/shrubland 

class [margin of error] 

(km2

)

Converted from 

agriculture class 

[margin of error] 

(km2)

Converted from 

forest class 

[margin of error] 

(km2)

Net change in 

developed class 

[margin of error] 

(km2)

Southern and Central California Chaparral 

and Oak Woodlands Ecoregion 646 [326] 1,230 [931] 31 [30] 2,234 [1,381]

Mojave Basin and Range Ecoregion 1,426 [1,191] 45 [49] 4 [6] 1,680 [1,329]

Colorado Plateaus Ecoregion 644 [711] 756 [1,085] 3 [4] 1,408 [1,795]

Puget Lowland Ecoregion 30 [10] 153 [70] 871 [186] 1,186 [231]

Central California Valley Ecoregion 366 [181] 684 [289] 1 [1] 1,129 [455]

Arizona/New Mexico Plateau Ecoregion 533 [598] 201 [293] 5 [5] 753 [900]

Northern Rockies Ecoregion 241 [337] 262 [361] 205 [238] 717 [938]

Central Basin and Range Ecoregion 538 [386] 50 [73] 0 [0] 649 [484]

Sonoran Basin and Range Ecoregion 355 [228] 84 [115] 2 [2] 481 [310]

Willamette Valley Ecoregion 0 [0] 347 [164] 81 [41] 454 [205]

All Western United States ecoregions 5,496 [1,628] 4,623 [1,549] 1,717 [333] 12,785 [3,000]
18 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 9. Developed areas in western United States. A, New home construction in Palmdale, located in far-northern Los Angeles 

County, southern California, in Mojave Basin and Range Ecoregion. B, Industrial activity along Willamette River in Oregon City, located in 

Clackamas County, northwestern Oregon, in Willamette Valley Ecoregion. C, Oracle campus in Redwood Shores, located in San Mateo 

County, north-central California, in Southern and Central California Chaparral and Oak Woodlands Ecoregion. D, View overlooking 

Banning, located in Riverside County, southern California, in Southern California Mountains Ecoregion.

A

C

B

D

Table 8. Net areal changes in developed land-cover class (as percent of ecoregion area, as 

area in square kilometers, and as percent of developed land-cover class area in 1973) for the 

six Western United States ecoregions that had largest increase in developed class for entire 

study period (1973 to 2000) and corresponding margin-of-error values for 85-percent confidence 

interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Net areal change

[margin of error]

Net areal 

change

(% of developed 

class in 1973) (% of ecoregion) (km2

)

Puget Lowland Ecoregion 6.6 [1.3] 1,186 [231] 53.8 

Willamette Valley Ecoregion 3.1 [1.4] 454 [205] 33.4 

Central California Valley Ecoregion 2.5 [1.0] 1,129 [455] 37.7 

Southern and Central California 

 Chaparral and Oak Woodlands Ecoregion 2.2 [1.4] 2,234 [1,381] 33.1 

Mojave Basin and Range Ecoregion 1.3 [0.6] 1,680 [1,329] 85.8 

Colorado Plateaus Ecoregion 1.1 [1.4] 1,408 [1,795] 431.9 
Land-Cover Trends in the Western United States—1973 to 2000 19

Figure 10. Map of counties that intersect Western United States ecoregions, showing counties that either gained 

(positive values) or lost (negative values) population between 1970 and 2000. Gains and losses expressed as 

percentage of change from 1970 population levels (U.S. Census Bureau, 2001).

0 75 150 225 300 MILES

0 100 200 300 400 KILOMETERS

MBR

SBR

CD

MA

ANMM

ANMP

CLRP

CBR

SRK

WUM

WB

MRK SRB

NBR ECSF

BM

NRK

CLMP

CRK

MVFP

NC

C

WV

PL

CR

KM

SCCCOW

CCV

SN

SCM

MEXICO

CANADA

125° 120° 115° 110° 105°

50°

45°

40°

35°

30°

P a c i f i c

O

c

e

a

n

100°

5.1 –20.0

−5.1 –5.0

−59.0 –−5.1

Population change as percent of county area

300.1 –2,000.0

100.1 –300.0

50.1 –100.0

20.1 –50.0

EXPLANATION

Ecoregion boundary

State boundary
20 Status and Trends of Land Change in the Western United States—1973 to 2000

California Chaparral and Oak Woodlands Ecoregion experienced the highest amount of conversion from agriculture 

to developed land, at 1,230 km2, followed by the Colorado 

Plateaus, Central California Valley, Willamette Valley, and 

Northern Rockies Ecoregions (table 7). Conversion from 

forest to developed accounted for 13.7 percent of all new 

developed land. Approximately 87 percent of all change 

from forest to developed occurred in five Pacific Northwest 

ecoregions, the highest being the Puget Lowland Ecoregion 

(871 km2), followed by the Coast Range (236 km2), Northern 

Rockies (205 km2), Cascades (98 km2), and Willamette Valley (81 km2

) Ecoregions. The 10 ecoregions in the West that 

experienced the greatest net change in developed are shown 

in table 7.

Conversion from mechanically disturbed to developed 

often represents the capture of a intermediate land-cover 

stage, typically consisting of the scraping and leveling of a 

site and other preparations in advance of construction. The 

most common occurrences were in the Southern and Central 

California Chaparral and Oak Woodlands (301 km2), Mojave 

Basin and Range (205 km2), Puget Lowland (135 km2), 

Central California Valley (77 km2), and Central Basin and 

Range (61 km2) Ecoregions. These five ecoregions accounted 

for 82 percent of all conversions from mechanically disturbed to developed.

Transitional Land-Cover Classes

Mechanically disturbed and nonmechanically disturbed 

lands, referred to herein as transitional land-cover classes, 

played a prominent role in the story of change throughout the 

western United States in the 27-year study period. A mechanically disturbed state is mapped when land is in an altered and 

often unvegetated state, owing to disturbances by mechanical 

means, and, thus, is in transition from one land-cover class to 

another (fig. 11). For example, postharvest forest, which varied 

significantly throughout the West, manifested either as a rapid 

reestablishment of, and conversion back to, forest or as an 

intermediate, mechanically disturbed–grassland/shrubland state 

in which succession to forest occurred more slowly. Mechanical disturbances were not solely associated with forest clearing 

in the West. Urbanization, reservoir drawdown, infrastructure 

Figure 11. Mechanically disturbed areas in western United States. A, Newly clearcut hillside in Bighorn Mountains, north-central 

Wyoming, in Middle Rockies Ecoregion. B, Clearcut area undergoing regeneration in Okanogan County, north-central Washington, in 

North Cascades Ecoregion. C, Clearcut area in Douglas County, southwestern Oregon, in Cascades Ecoregion. D, Mountaintop clearcut 

area on private land in Siskiyou County, northern California, in Klamath Mountains Ecoregion.

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 21

construction, and reoccurring vehicular disturbance of vegetation also were associated with the mechanically disturbed classification, although less frequently.

Mechanical disturbances are significant anthropogenic 

land-use-change events that are primarily a result of logging 

and, to a lesser extent, urbanization. Biological and physical 

factors combine to create conditions that dictate forest growth 

and reestablishment rates throughout the West: soil composition, geology, climate, vegetation age and diversity, and 

several other environmental parameters collectively determine 

which ecoregions are best suited to sustain a viable forestresource base (Ryan and others, 1996; Powers, 1999). 

Mechanical disturbances affected 2.2 percent (60,253 

km2) of the western United States over the 27-year study 

period. The rate of mechanical disturbance across the West 

escalated in each of the first three time periods, from 1,231 

km2 per year between 1973 and 1980 to 2,469 km2 per year 

between 1986 and 1992, then it declined to 1,487 km2 per year 

between 1992 and 2000. Some level of mechanical disturbance 

was mapped in nearly all the Western United States ecoregions 

between 1973 and 2000, yet the mechanical removal of forest 

was significantly more pervasive in certain ecoregions. The 

ecoregions that experienced the most logging were among the 

Marine West Coast Forests Ecoregions (in the Coast Range, 

Puget Lowland, and Willamette Valley Ecoregions), followed 

by the Western Mountain Ranges Ecoregions (in the Cascades, 

North Cascades, Eastern Cascades Slopes and Foothills, and 

Klamath Mountains Ecoregions) and the Rocky Mountains 

Ecoregions (in the Northern Rockies Ecoregion) (table 9).

Nonmechanically disturbed land reflects changes associated with wildfires, insect infestations, storms, and other natural events (fig. 12); however, the majority of nonmechanical 

disturbance captured in the West was associated with wildfire, 

with only a few cases attributed to insect- and disease-driven 

forest dieback. Fire has a long-established history in the West, 

with its abundance of fuels and its low-to-moderate levels 

of precipitation throughout many ecoregions (Skinner and 

Chang, 1996; Keeley and Fotheringham, 2001; Schoennagel 

and others, 2004). The vast majority of fire occurred in the 

Mediterranean California Ecoregions, the Western Mountain 

Ranges Ecoregions, and the Rocky Mountains Ecoregions, 

although fire has also played a role in the ecology of the Cold 

Deserts Ecoregions (fig. 13).

Nonmechanical disturbances affected 1.5 percent (40,571 

km2) of the western United States over the 27-year study 

period. Fifty-six percent (22,867 km2) of the nonmechanical 

disturbances were in forest, and 38 percent (15,600 km2) were 

in grassland/shrubland. The rate of nonmechanical disturbance 

across the West was 211 km2 per year between 1973 and 1980 

and 151 km2 per year between 1980 and 1986, accelerating to 

908 km2 per year between 1986 and 1992 and to 1,874 km2

per year between 1992 and 2000. Although nonmechanical 

disturbances contributed to land-cover changes in 26 of the 30 

Western United States ecoregions, the Middle Rockies, Northern Rockies, Southern and Central California Chaparral and 

Oak Woodlands, and Northern Basin and Range Ecoregions 

had the largest percentages of gross change, followed by the 

Snake River Basin, Southern California Mountains, and Sierra 

Nevada Ecoregions (table 10).

Nonmechanical disturbances (fires) are usually natural 

events that have been and will continue to be an integral part 

of ecological community vitality across much of the western 

United States. However, the fire cycles under which native 

flora and fauna species have evolved naturally in the past 

Table 9. Gross spatial changes in mechanically disturbed landcover class for the eight Western United States ecoregions that 

had highest amount of gross change to and from mechanically 

disturbed class for entire study period (1973 to 2000) and 

corresponding margin-of-error values for 85-percent confidence 

interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Gross spatial change (1973–2000) 

[margin of error] 

(% of 

ecoregion) (km2

)

Coast Range Ecoregion 22.5 [4.3] 12,887 [2,480]

Cascades Ecoregion 21.1 [3.1] 9,895 [1,471]

Puget Lowland Ecoregion 20.0 [3.4] 3,514 [590]

Willamette Valley Ecoregion 10.0 [2.9] 1,440 [420]

North Cascades Ecoregion 9.8 [3.8] 2,993 [1,171]

Eastern Cascades Slopes and 

Foothills Ecoregion 9.3 [3.5] 5,358 [2,026]

Northern Rockies Ecoregion 6.7 [2.5] 10,829 [3.991]

Klamath Mountains Ecoregion 6.5 [2.1] 3,124 [1,010]

Table 10. Gross spatial changes in nonmechanically 

disturbed land-cover class for the seven Western United States 

ecoregions that had highest amount of gross change to and from 

nonmechanically disturbed class for entire study period (1973 to 

2000) and corresponding margin-of-error values for 85-percent 

confidence interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Gross spatial change (1973–2000) 

[margin of error] 

(% of 

ecoregion) (km2

)

Middle Rockies Ecoregion 6.8 [3.3] 6,165 [3,009]

Northern Rockies Ecoregion 5.9 [3.3] 9,588 [5,290]

Southern and Central California Chaparral and Oak 

Woodlands Ecoregion

5.7 [2.3] 5,837 [2,338]

Northern Basin and Range 

Ecoregion 4.7 [3.9] 5,216 [4,278]

Snake River Basin Ecoregion 3.9 [2.8] 2,580 [1,819]

Southern California Mountains Ecoregion 3.7 [2.3] 659 [415]

Sierra Nevada Ecoregion 3.0 [0.8] 1,625 [410]
22 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 12. Nonmechanically disturbed areas in western United States. A, Fire scar in Douglas County, southwestern Oregon, in 

Cascades Ecoregion. B, Dead trees on mountainside in Valley County, central Idaho, in Northern Rockies Ecoregion. C, Wildfire east of 

Cody, located in Park County, northwestern Wyoming, in Middle Rockies Ecoregion. D, Dead trees resulting from insect infestation in 

Bighorn Mountains, north-central Wyoming, in Middle Rockies Ecoregion.

have changed with rapidly growing human populations and 

the implementation of fire-suppression efforts in the 20th

century. For instance, the introduction of nonnative annual 

grasses since Eurasian settlement of the West in the 1800s

has increased fire frequency because these annual species 

burn more frequently than the native grass and shrub species 

(Keeley and others, 2003; Pellant and others, 2004; Brooks 

and others, 2004). Grassland/shrubland fires were pervasive 

in the Southern and Central California Chaparral and Oak 

Woodlands Ecoregion and the Southern California Mountains Ecoregion, as well as in the Basin and Range ecoregions (Northern Basin and Range, Central Basin and Range, 

Mojave Basin and Range, and Sonoran Basin and Range 

Ecoregions). State- and federally mandated fire-suppression 

activities in the early 20th century have caused a shift 

towards less frequent, yet more severe, fires (Skinner and 

Chang, 1996). Increased forest density not only has increased 

the abundance of fuel sources but also has contributed to 

higher insect and disease attacks in many of the forested 

Western United States ecoregions (Oliver and others, 1996; 

Parker and others, 2006). Dense forests and the presence of 

diseased trees increase the overall fire-hazard risk, as well as 

the likelihood of high-severity fire events (Manley and others, 2000).

Climate has also played a role in fire regimes across the 

West. For instance, the effect of the El Niño/La Niña–Southern Oscillation on fire regimes is well established for the 

southwestern United States. El Niño events bring higher than 

normal winter rainfall caused by the southward displacement 

of the jet stream, whereas La Niña events are associated with 

anomalously dry winters. Available fuel load increases following higher than normal rainfall during an El Niño winter, and 

subsequent dry years and persistent drought deplete vegetation 

fuel moisture; thus, the prevalence of dry fuels creates optimal 

fire conditions. Ultimately, these El Niño/La Niña cycles have 

been shown to increase fire occurrence in the southwestern 

ecoregions (Swetnam and Betancourt, 1990; Swetnam and 

others, 1999). 

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 23

Figure 13. Areas of large fires in western United States between 1984 and 2008. Fire data captured by Monitoring 

Trends in Burn Severity project (Eidenshink and others, 2007).

0 75 150 225 300 MILES

0 100 200 300 400 KILOMETERS

MBR

SBR

CD

MA

ANMM

ANMP

CLRP

CBR

SRK

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WB

MRK SRB

NBR

ECSF

BM

NRK

CLMP

CRK

MVFP

NC

C

WV

PL

CR

KM

SCCCOW

CCV

SN

SCM

Fire year

2001–2008

1993–2000

1987–1992

1984–1986

EXPLANATION

Ecoregion boundary

State boundary

MEXICO

CANADA

105°

100°

125° 120° 115° 110°

50°

45°

40°

35°

30°

P a c i f i c

O

c

e

a

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24 Status and Trends of Land Change in the Western United States—1973 to 2000

Water and Wetland Land-Cover Classes

The water and wetland land-cover classes remained 

relatively stable throughout the 27-year study period. In 2000, 

water accounted for approximately 0.8 percent of the Western United States ecoregions, and wetlands accounted for 

0.7 percent (table 2; fig. 14). Net change in both land-cover 

classes was less than 0.1 percent. Overall, water increased by 

an estimated 259 km2

 between 1973 and 2000, whereas wetlands decreased by 243 km2 over the same time period. Water 

increased in three of the four time periods by an average of 86 

km2 per year; however, water declined at a rate of 247 km2 per 

year between 1986 and 1992, a time period that coincides with 

an extended period of drought across the West. Although rare, 

changes in the water and wetland land-cover classes did occur 

in a few ecoregions; however, more than 60 percent of gross 

change associated with water and wetland classes occurred in 

only five ecoregions (Sonoran Basin and Range, Central Basin 

and Range, Wyoming Basin, Northern Basin and Range, and 

Central California Valley Ecoregions) (table 11).

Mining Land-Cover Class

The amount of land devoted to mining increased by 53.4 

percent over the 27-year study period; however, the total area 

in mining remained relatively small at 0.2 percent of the Western United States ecoregions (table 2). An estimated increase 

of 2,233 km2

 in mining occurred between 1973 and 2000 

(table 3), with more than 60 percent of the gross change occurring in the Central Basin and Range, Mojave Basin and Range, 

Colorado Plateaus, Chihuahuan Deserts, and Arizona/New 

Mexico Mountains Ecoregions. New mining areas, as well as 

the expansion of existing mines, were, in general, related to 

the increased need for construction materials and the demand 

for precious metals (fig. 15). 

Other Land-Cover Classes

Barren areas—that is, areas having less than 10 percent 

vegetated cover (fig. 16)—accounted for 1.9 percent of the 

Western United States ecoregions, whereas areas of ice and 

Figure 14. Water and wetland areas in western United States. A, View to northeast across Emerald Bay toward Lake Tahoe, northern 

California, in Sierra Nevada Ecoregion. B, View to northwest across Crater Lake, southwestern Oregon, in Cascades Ecoregion. C, 

Coastal wetland near Coos Bay, southwestern Oregon, in Coast Range Ecoregion. D, Topock Marsh along Colorado River, eastern 

Arizona, in Mojave Basin and Range Ecoregion.

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 25

Figure 15. Mining activities in western United States. A, Oil field near Coalinga, located in Fresno County, central California, in 

Southern and Central California Chaparral and Oak Woodlands Ecoregion. B, Mountaintop mining in west-central Utah, in Central Basin 

and Range Ecoregion. C, Gas well in Colorado Plateaus Ecoregion. D, Tailings pile in Central Basin and Range Ecoregion.

A

C

B

D

Table 11. Gross spatial changes in water and wetland land-cover classes for the five Western United 

States ecoregions that had highest amount of gross change to and from water and wetland classes for 

entire study period (1973 to 2000) and corresponding margin-of-error values for 85-percent confidence 

interval (in brackets).

[See appendix 3 for definitions of land-use/land-cover classifications]

Ecoregion

Water class Wetland class

Gross spatial change

[margin of error]

Gross spatial change

[margin of error]

(% of ecoregion) (km2

) (% of ecoregion) (km2)

Sonoran Basin and Range Ecoregion 1.1 [1.1] 1,290 [1,313] 0.5 [0.7] 548 [779]

Central Basin and Range Ecoregion 0.3 [0.4] 970 [1,204] 0.2 [0.3] 748 [1,088]

Wyoming Basin Ecoregion 0.4 [0.4] 500 [553] 0.4 [0.2] 471 [305]

Northern Basin and Range Ecoregion 0.4 [0.3] 414 [353] 0.3 [0.3] 318 [313]

Central California Valley Ecoregion 0.6 [0.2] 288 [91] 0.7 [0.5] 326 [231]
26 Status and Trends of Land Change in the Western United States—1973 to 2000

perennial snow accounted for only an estimated 0.1 percent. 

The barren land-cover class most commonly consists of rocky 

outcrops, desert playas, and dry lakebeds. Ice and perennial 

snow (ice/snow land-cover class) is usually found in at the 

highest elevations where glaciers are common. Both of these 

land-cover classes remained stable over the 27-year study 

period (table 2).

Summary

Taken as an aggregate of 30 individual ecoregions, landcover change in the Western United States ecoregions was 

modest, with only 5.8 percent of the land cover changing at 

least one time between 1973 and 2000. Change was highest 

between 1986 and 1992 and between 1992 and 2000, with an 

estimated 0.4 percent change per year. The largest net change 

was a decline of 33,197 km2 of forest land cover, which 

included losses to logging, fire, urbanization, and other land 

uses. In addition, agriculture and grassland/shrubland experienced net declines of 4,414 km2

 and 1,106 km2, respectively, 

whereas developed land increased by an estimated 12,785 

km2

. It is important to note that not all land-use/land-cover 

Figure 16. Barren areas in western United States. A, Mount Hood, northwestern Oregon, in Cascades Ecoregion. B, Lake Mead, southern 

Nevada, in Mojave Basin and Range Ecoregion. C, Stream bed along Nisqually River, in Lewis County, southwestern Washington, in 

Cascades Ecoregion. D, Lakebed near Lake Abert, along Highway 395 in south-central Oregon, in Northern Basin and Range Ecoregion.

change was captured by the methodology applied for this 

study. For example, within-class conversions such as grassland 

to shrubland are not captured given the thematic resolution of 

the classification scheme. 

Land-use/land-cover changes in the western United States 

are centered primarily on ecosystem disturbances resulting 

from logging and fire. These disturbances combined to affect 

3.7 percent (100,824 km2

) of the Western United States ecoregions over the 27-year study period. Forest cutting for timber 

production was most common in the highly productive forested ecoregions of the Pacific Northwest, and it was highest 

during the 1980s, largely owing to favorable global economic 

conditions. The 1990s saw a reduction in forest cutting owing 

to domestic trade and environmental policy changes and a 

downturn in economic conditions in Asia. Although the rate of 

forest cutting declined, disturbances from wildfire increased 

substantially in the 1980s and 1990s, impacting ecoregions 

dominated by both forest and grassland/shrubland. 

Urbanization—and the resultant expansion of developed 

land—was common in several Western United States ecoregions, most notably among the coastal ecoregions. The most 

populous ecoregion in the entire United States—the Southern and Central California Chaparral and Oak Woodlands 

A

C

B

D
Land-Cover Trends in the Western United States—1973 to 2000 27

Ecoregion—gained the largest amount of new developed land, 

with an estimated 2,234 km2 converting over the 27-year study 

period. Other ecoregions that experienced significant growth 

were the Central California Valley and the Mojave Basin 

and Range Ecoregions, where spillover from rapid growth 

in the neighboring Southern and Central California Chaparral and Oak Woodlands Ecoregion influenced their rates of 

land-cover conversions. The other ecoregion that experienced 

large increases in new developed land was the Puget Lowland 

Ecoregion, which contains the Seattle-Tacoma, Washington, 

metropolitan area. Urbanization also acted as a driver of 

change in the agriculture land-cover class. As agricultural land 

was converted to urban uses, farmers relocated to peripheral 

areas where livestock grazing was common, such as the foothills of California. Many of these areas have become popular 

for cultivation of nut crops, citrus, and grapes, and relocations 

to these areas have resulted in substantial changes to the agricultural landscape (Sleeter, 2009). 

Although certain stories of land-use/land-cover change 

emerge for the Western United States ecoregions when viewed 

as a whole, the aggregate masks the temporal and ecoregional 

variability of change. The remaining chapters in this report, 

which contain summaries for each of the 30 individual Western United States ecoregions, document the rates, types, and 

drivers of late-20th century land-use/land-cover change in the 

western United States. 

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Land-Cover Trends in the Western United States—1973 to 2000 29

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Marine West Coast Forests Ecoregions Land-Cover Trends in the Western United States—1973 to 2000 31

Chapter 1

Coast Range Ecoregion

By Terry L. Sohl

Ecoregion Description

The Coast Range Ecoregion, which covers approximately 

57,338 km2 (22,138 mi2), is a thin, linear ecoregion along the 

Pacific Coast, stretching roughly 1,300 km from the Olympic 

Peninsula, in northwest Washington, to an area south of San 

Francisco, California (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). It is bounded on the east 

by the Puget Lowland, the Willamette Valley, the Klamath 

Mountains, and the Southern and Central California Chaparral 

and Oak Woodlands Ecoregions.

Almost the entire Coast Range Ecoregion lies within 

100 km of the coast. Topography is highly variable, with 

coastal mountain ranges and valleys ranging from sea level 

to over 1,000 m in elevation (fig. 2). A maritime climate, 

along with high topographic relief, results in substantial, but 

regionally variable, amounts of rainfall, ranging from 130 cm 

to more than 350 cm per year. The favorable climate of the 

Coast Range Ecoregion has supported forests of Sitka spruce 

(Picea sitchensis) along its northern coast and coast redwoods 

(Sequoia sempervirens) along its southern coast, as well as 

Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja 

plicata), and western hemlock (Tsuga heterophylla) inland 

(Omernik, 1987). Today, however, much of the forest is heavily managed for logging (fig. 3), although the ecoregion still 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Coast Range Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted on 

map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map 

shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. 

See appendix 3 for definitions of land-use/land-cover classifications. 

Cascades

Cascades

C

WV

Sierra

Nevada

Klamath

Mountains

Northern Basin

and Range

Eastern

Cascades 

Slopes

and

Foothills

North

Cascades

NC

Columbia

Plateau

CCV

SCCCOW

SCCCOW

PL

C

BLM

Blue

Mountains

PL

PL

PACIFIC

OCEAN

122°

126° 124°

120°

46°

48°

44°

42°

40° 

38°

CBR

NBR

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

WASH. 

OREGON

CALIFORNIA

P A C I F I C 

O C E A N

San Francisco

Coos Bay

Clatskanie

Eureka

Aberdeen

OLYMPIC

PENINSULA

Willamet te R.

Columbia

R.

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
34 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 2. Pacific Coast and forested coastal mountains of Coast 

Range Ecoregion.

supports some of the largest remaining areas of old-growth 

forest in the Pacific Northwest. Agriculture is a minor component of the landscape, present locally in flat lands and valleys near the coast. Urban development is minimal; Eureka, 

California, is the only urban center in the ecoregion, with a 

population of over 26,000 (U.S. Census Bureau, 2000).

Contemporary Land-Cover Change 

(1973 to 2000)

The footprint of change (the percentage of area that 

changed at least one time between 1973 and 2000) in the 

ecoregion was 25.5 percent (table 1), indicating that the Coast 

Range Ecoregion had one of the highest levels of change in 

the western United States (fig. 4). When normalized to account 

for varying lengths of study periods, annual rates of change 

increased through the first three time periods, peaking between 

1986 and 1992, and then they declined slightly in the last 

period, between 1992 and 2000 (table 2; fig. 5).

A statistically significant negative trend was determined 

for forest land, which had a decline of 5.0 percent between 

1973 and 2000 (table 3). Balancing the decline in forest land 

were corresponding statistically significant positive trends 

in the mechanically disturbed (51.3 percent) and grassland/

shrubland (36.9 percent) classes. However, these gains were 

not constant over the four time periods. Both mechanically 

disturbed and grassland/shrubland experienced two periods of 

net gain and two periods of net loss (fig. 6). 

In the Coast Range Ecoregion, the vast majority of 

mechanically disturbed land and grassland/shrubland were associated with the logging and subsequent replanting and regrowth 

of forest (fig. 7). Clearcut forest patches are initially mapped 

as mechanically disturbed. Depending upon local site conditions and the length of time between initial cutting and the next 

mapped time period, these mechanically disturbed patches typically are mapped either as an intermediate grassland/shrubland 

class in subsequent time periods or as forest once regrowth has 

Figure 4. Overall spatial change in Coast Range Ecoregion (CR; 

darker bars) compared with that of all 30 Western United States 

ecoregions (lighter bars). Each horizontal set of bars shows proportions of ecoregion that changed during time periods 1, 2, 3, or 4; 

highest level of spatial change in Coast Range Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods

Figure 3. Clearcut area and subsequent regrowth of planted 

trees in Coast Range Ecoregion.
Chapter 1—Coast Range Ecoregion 35

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Coast Range Ecoregion are represented by red bars in each time period.

Figure 6. Normalized average net change in Coast Range Ecoregion 

by time period for each land-cover class. Bars above zero axis 

represent net gain, whereas bars below zero represent net loss. 

Note that not all land-cover classes shown in explanation may be 

represented in figure. See appendix 3 for definitions of land-use/

land-cover classifications.

three most common changes were related to forest regeneration 

(mechanically disturbed to grassland/shrubland, mechanically 

disturbed to forest, or grassland/shrubland to forest) (table 5). 

For the whole ecoregion, over 95 percent of change was associated with the timber-cutting cycle, with nearly 11,000 km2

 of 

cutting occurring between 1973 and 2000. Large swaths of forest 

land in the Coast Range Ecoregion were cut between 1973 and 

2000, and they now are in a forest-regeneration stage because of 

the coalescence of individual patches of cut forest (fig. 9).

advanced sufficiently. Overall, while per-period trends in forest, mechanically disturbed, and grassland/shrubland land-cover 

classes fluctuated throughout the study period, total forest use 

(defined as the sum of forest land, mechanically disturbed land, 

and grassland/shrubland) remained remarkably constant (table4).

The timber industry’s effect on the landscape dominated the 

story of change in the ecoregion (fig. 8). For every time period, 

forest cutting (forest to mechanically disturbed) was the most 

common type of land-cover change, whereas each of the next 

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−4

−2

0

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 7. Clearcut (mechanically disturbed) forest in Coast Range 

Ecoregion and subsequent regrowth.

Figure 8. Lumberyard in Coast Range Ecoregion. 
36 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 9. Maps of sample block 1-189 (red square on index map) in Coast Range Ecoregion, showing land-use/land-cover data in 1973 (A), 1980 (B), 1986 (C), 1992 (D), and 2000 

(E). Developed (red) area is town of Clatskanie, Oregon. Over 43 percent of sample block 

experienced some form of land-cover change between 1973 and 2000, vast majority of 

which was related to timber industry. F, Map of sample block 1-189, showing areas that 

changed at least once throughout entire 27-year study period.

124°

122° 120°

126°

46°

48°

44°

42°

0 50 100 Miles

0 100 Kilometers 50

1973 1980 1986

1992 2000

Number of changes

Number of changes

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Land-use/land-cover class

EXPLANATION

EXPLANATION

A B C

D E 

F 
Chapter 1—Coast Range Ecoregion 37

From the 1940s through the 1980s, forestry activity in 

the area generally focused on the cutting of natural forests and 

the establishment of Douglas-fir plantations on these lands 

(Swanson and Franklin, 1992). The annual rate of forest cutting steadily rose during the first three time periods, peaking 

between 1986 and 1992, and then declined between 1992 and 

2000 (fig. 10). Although multiple drivers are responsible for 

the declines in forest cutting after 1992, the status and protection of the Northern Spotted Owl (Strix occidentalis caurina)

likely had the biggest influence. In 1990, the Northern Spotted 

Owl was listed as “threatened” under the Endangered Species 

Act. In February 1991, an interagency scientific committee 

published a report addressing conservation of the Northern 

Spotted Owl (Thomas and others, 1990), leading U.S. District 

Court Judge Dwyer to block timber sales in national forest 

lands in the area to protect the species. In December 1994, 

Judge Dwyer accepted the Northwest Forest Plan, a comprehensive document directing coordinated management activities for lands administered by the U.S. Forest Service and the 

Bureau of Land Management. The plan permitted the cutting 

of 1 billion board feet of timber from public lands per year, 

only one-fourth the timber-harvest levels of the 1980s (Espy 

and Babbitt, 1994).

Another contributing factor responsible for the 1990s 

decline in forest cutting was the very high rate of logging in 

the 1980s, which may have been unsustainable over the long 

term given the 40- to 60-year cutting cycle that is typical for 

Douglas-fir in the ecoregion. In addition, Pacific Northwest forestry as a whole has been increasingly outcompeted by forestry 

operations in the southeastern United States and the interior of 

Canada, and the ecoregion has been at a competitive disadvantage for providing wood products to markets in the eastern and 

southern United States. Siberian larch (Larix sibirica) and Norway spruce (Picea abies) from Russian plantations, as well as 

Monterey pine (Pinus radiata) from more recently established 

plantations in New Zealand and Chile, also strongly increased 

their presence in the softwood lumber market in the 1990s 

(Gataulina and Waggener, 1998; Center for International Trade 

in Forest Products, 1993). At the same time, once-strong Pacific 

Northwest exports of wood products to large Asian markets (primarily Japan, South Korea, and China) declined throughout the 

1990s (fig. 11). Changes in the Japanese housing industry, along 

Figure 10. Annual land-cover change related to forest cutting in 

Coast Range Ecoregion, compared to that of total land-use/landcover changes, for each of four time periods. Both change related 

to forest cutting and total change peaked between 1986 and 1992 

and then declined between 1992 and 2000.

Figure 11. Exports of Pacific Northwest logs between 1961 and 2001 (from Daniels, 

2005). Note how exports to all areas fell dramatically during 1990s.

0

200

400

600

800

1,000

1,200

1,400

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Annual change, in square kilometers 

Total change

Forest cutting

South Korea

China

Japan

Other

0.0

1.0

2.0

3.0

4.0

1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000

Year

“Status and Trends of Land Change”

study period (1973–2000)

Log exports, in billions of board feet
38 Status and Trends of Land Change in the Western United States—1973 to 2000

with the Asian economic collapse of the 1990s, were major factors in declining exports (Daniels, 2005).

Land-cover changes in the ecoregion, other than those 

related to logging, were relatively minor. A statistically significant trend occurred in developed lands, which increased 

from 2.5 to 3.1 percent of the ecoregion between 1973 and 

2000 (table 3). Most of the observed development was 

associated with the largest cities in the ecoregion: Eureka, 

California (population over 26,128 in 2000); Aberdeen, 

Washington (population, 16,461 in 2000); and Coos Bay, 

Oregon (population, 15,374) (U.S. Census, 2000). In addition, scattered high-value developments were found in areas 

with recreational amenities.

Table 1. Percentage of Coast Range Ecoregion land cover that 

changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (74.5 percent), whereas 25.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 9.5 1.5 7.9 11.0 1.0 10.9

2 11.6 1.9 9.7 13.5 1.3 11.1

3 4.2 1.1 3.1 5.4 0.8 18.2

4 0.2 0.1 0.1 0.3 0.1 27.5

Overall 

spatial 

change

25.5 3.9 21.7 29.4 2.6 10.3

Table 2. Raw estimates of change in Coast Range Ecoregion land cover, computed for each of four time 

periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 7.6 1.2 6.4 8.8 0.8 10.6 1.1

1980–1986 10.3 2.0 8.2 12.3 1.4 13.4 1.7

1986–1992 13.1 2.3 10.9 15.4 1.5 11.8 2.2

1992–2000 15.2 2.9 12.3 18.1 2.0 13.0 1.9

Estimate of change, in square kilometers

1973–1980 4,380 688 3,692 5,068 465 10.6 626

1980–1986 5,880 1,168 4,712 7,047 789 13.4 980

1986–1992 7,535 1,312 6,223 8,848 887 11.8 1,256

1992–2000 8,700 1,668 7,032 10,369 1,128 13.0 1,088
Chapter 1—Coast Range Ecoregion 39

Table 3. Estimated area (and margin of error) of each land-cover class in Coast Range Ecoregion, calculated five times between 1973 

and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 5.1 3.0 2.5 1.3 3.7 0.9 0.0 0.0 1.2 0.6 76.2 4.1 4.6 1.4 5.7 2.1 1.0 0.7 0.0 0.0

1980 5.1 3.0 2.6 1.3 3.0 0.5 0.0 0.0 1.1 0.6 75.4 4.2 6.0 1.0 5.7 2.1 1.0 0.7 0.0 0.0

1986 5.1 3.0 2.8 1.4 5.0 1.2 0.0 0.0 1.1 0.6 73.5 4.1 5.7 1.1 5.7 2.1 1.0 0.7 0.0 0.0

1992 5.1 3.0 2.9 1.4 6.0 1.2 0.0 0.0 1.1 0.6 71.0 3.9 7.4 1.2 5.4 2.0 1.0 0.7 0.1 0.1

2000 5.1 3.0 3.1 1.5 5.6 1.4 0.0 0.0 1.0 0.5 72.4 4.0 6.3 1.2 5.4 2.0 1.0 0.7 0.0 0.0

Net

change 0.0 0.0 0.6 0.3 1.9 1.5 0.0 0.0 −0.2 0.1 −3.8 1.9 1.8 1.0 −0.3 0.4 0.0 0.0 0.0 0.0

Gross

change 0.1 0.0 0.6 0.3 10.4 2.1 0.0 0.0 0.2 0.1 12.9 2.1 8.2 2.1 0.8 0.5 0.0 0.0 0.1 0.2

Area, in square kilometers

1973 2,941 1,696 1,438 744 2,142 493 18 17 673 364 43,676 2,349 2,627 782 3,245 1,215 562 406 0 0

1980 2,937 1,695 1,516 770 1,723 314 21 17 641 348 43,208 2,382 3,422 595 3,288 1,211 565 407 0 0

1986 2,941 1,699 1,579 789 2,890 698 23 19 633 335 42,165 2,368 3,284 610 3,247 1,181 558 406 0 0

1992 2,940 1,699 1,647 823 3,423 688 25 19 614 329 40,720 2,226 4,270 672 3,087 1,136 557 406 39 56

2000 2,947 1,707 1,772 845 3,227 794 25 20 584 307 41,504 2,270 3,636 680 3,073 1,139 553 398 0 0

Net

change 7 15 334 162 1,085 850 7 6 −89 79 -2,172 1,074 1,009 594 −172 246 -9 10 0 0

Gross

change 38 23 335 162 5,977 1,203 8 6 120 79 7,397 1,177 4,719 1,194 445 287 20 13 77 111

Table 4. Percentages of forest use, 

defined as sum of forest, mechanically 

disturbed, and grassland/shrubland 

land-cover classes, in Coast Range 

Ecoregion, showing that forest use 

remained remarkably constant over 

study period.

Year Forest use

(% of ecoregion)

1973 84.5

1980 84.3

1986 84.3

1992 84.4

2000 84.4
40 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 5. Principal land-cover conversions in Coast Range Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 1,638 282 191 2.9 37.4

Mechanically disturbed Grassland/Shrubland 1,195 309 209 2.1 27.3

Mechanically disturbed Forest 863 288 195 1.5 19.7

Grassland/Shrubland Forest 451 228 154 0.8 10.3

Forest Agriculture 60 63 42 0.1 1.4

Other Other 174 n/a n/a 0.3 4.0

Totals 4,380 7.6 100.0

1980–1986 Forest Mechanically disturbed 2,796 686 464 4.9 47.6

Grassland/Shrubland Forest 1,094 304 206 1.9 18.6

Mechanically disturbed Grassland/Shrubland 920 215 146 1.6 15.6

Mechanically disturbed Forest 734 177 120 1.3 12.5

Agriculture Forest 61 59 40 0.1 1.0

Other Other 274 n/a n/a 0.5 4.7

Totals 5,880 10.3 100.0

1986–1992 Forest Mechanically disturbed 3,362 675 456 5.9 44.6

Mechanically disturbed Grassland/Shrubland 1,801 543 367 3.1 23.9

Mechanically disturbed Forest 1,049 344 232 1.8 13.9

Grassland/Shrubland Forest 911 203 137 1.6 12.1

Agriculture Forest 124 142 96 0.2 1.6

Other Other 288 n/a n/a 0.5 3.8

Totals 7,535 13.1 100.0

1992–2000 Forest Mechanically disturbed 3,147 780 527 5.5 36.2

Mechanically disturbed Forest 2,173 557 376 3.8 25.0

Grassland/Shrubland Forest 1,847 560 378 3.2 21.2

Mechanically disturbed Grassland/Shrubland 1,178 327 221 2.1 13.5

Forest Developed 92 45 31 0.2 1.1

Other Other 263 n/a n/a 0.5 3.0

Totals 8,700 15.2 100.0

1973–2000

(overall)

Forest Mechanically disturbed 10,943 1,973 1,334 19.1 41.3

Mechanically disturbed Grassland/Shrubland 5,093 1,116 755 8.9 19.2

Mechanically disturbed Forest 4,820 975 659 8.4 18.2

Grassland/Shrubland Forest 4,303 926 626 7.5 16.2

Forest Developed 236 117 79 0.4 0.9

Other Other 1,100 n/a n/a 1.9 4.2

Totals 26,495 46.2 100.0
Chapter 1—Coast Range Ecoregion 41

References Cited

Center for International Trade in Forest Products (CINTRAFOR), 1993, Radiata pine—A competitive force in Asian 

markets: Seattle, University of Washington, CINTRAFOR 

Timber Supply and International Resource Competitiveness 

Series Fact Sheet #7, 2 p. (Available at www.cintrafor.org/

publications/factsheets/FS07.pdf.)

Daniels, J.M, 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Forest Service, Pacific Northwest Research Station, General Technical Report PNWGTR-624, 88 p.

Espy, M., and Babbitt, B., 1994, Record of decision for 

amendments to Forest Service and Bureau of Land Management planning documents within the range of the Northern 

Spotted Owl: U.S. Department of Agriculture and U.S. 

Department of the Interior Northwest Forest Plan, 74 p. 

(Available at http://www.blm.gov/or/plans/nwfpnepa/

FSEIS-1994/NWFPTitl.htm.)

Gataulina, E., and Waggener, T.R., 1998, The forest sector in 

the Russian Far East—Status and near-term development: 

Seattle, University of Washington, Center for International 

Trade in Forest Products Working Paper 63, 78 p. (Available at http://www.cintrafor.org/publications/workingpapers.

shtml.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Swanson, F.J., and Franklin, J.F., 1992, New forestry principles from ecosystem analysis of Pacific Northwest forests: 

Ecological Applications, v. 2, no. 3, p. 262–274.

Thomas, J.W., Forsman, E.D., Lint, J.B., Meslow, E.C., Noon, 

B.B., and Verner, J., 1990, A conservation strategy for the 

Northern Spotted Owl: Portland, Oregon, Interagency Scientific Committee to Address the Conservation of the Northern Spotted Owl [established under authority of interagency 

agreement between U.S. Department of Agriculture (Forest 

Service) and U.S. Department of the Interior (Bureau of 

Land Management, Fish and Wildlife Service, and National 

Park Service)], U.S. Government Printing Office 1990–

791–171/20026, 427 p. (Available at http://www.fws.gov/

wafwo/species/Fact%20sheets/NSO%20Interagency%20

Conservation%20Strategy.pdf.)

U.S. Census Bureau, 2000, State & county quickfacts: U.S. 

Census Bureau database, accessed March 2012, at http://

quickfacts.census.gov/qfd/index.html.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
This page intentionally left blank
Chapter 2

Puget Lowland Ecoregion

borders the shoreline of the greater Puget Sound, a complex 

bay and saltwater estuary fed by spring freshwater runoff 

from the Olympic Mountains and Cascade Range watersheds. 

The ecoregion is situated in a continental glacial trough that 

has many islands, peninsulas, and bays. Relief is moderate, 

with elevations ranging from sea level to 460 m but averaging 

approximately 150 m (DellaSala and others, 2001). 

Proximity to the Pacific Ocean gives the Puget Lowland 

Ecoregion its mild maritime climate (U.S. Environmental 

Protection Agency, 1999). Mean annual temperature is 10.5°C, 

with an average of 4.1°C in January and 17.7°C in July (Guttman and Quayle, 1996). Average annual precipitation ranges 

from 800 to 900 mm, but some areas in the rain shadow of the 

Olympic Mountains receive as little as 460 mm (DellaSala and 

By Daniel G. Sorenson

Ecoregion Description

The Puget Lowland Ecoregion covers an area of approximately 18,009 km2 (6,953 mi2) within northwestern Washington (fig. 1) (Omernik, 1987; U.S. Environmental Protection 

Agency, 1997). The ecoregion is located between the Coast 

Range Ecoregion to the west, which includes the Olympic 

Mountains, and the North Cascades and the Cascades Ecoregions to the east, which include the Cascade Range. From the 

north, the ecoregion follows the Interstate 5 corridor, from the 

Canadian border south through Bellingham, Seattle, Olympia, and Longview, Washington, to the northern border of the 

Willamette Valley Ecoregion. The Puget Lowland Ecoregion 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Puget Lowland Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in 

appendix 2. See appendix 3 for definitions of land-use/land-cover classifications. 

46° 121°

125° 124° 123° 122°

48°

49°

47°

Coast

Range

Cascades

North

Cascades

NC

Columbia

Plateau

ECSF

WV

CANADA

PACIFIC 

OCEAN

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

OLYMPIC

MOUNTAINS

WASH INGTON

PACIFIC 

OCEAN

Bellingham

Seattle

Olympia

Longview

Tacoma

Bellevue

Everett

Bremerton

C A S C A D E R A N G E

CANADA

OREGON

Puget S o u nd

Strait of Jua n de Fuca

5
44 Status and Trends of Land Change in the Western United States—1973 to 2000

others, 2001). Varying annual average precipitation greatly 

influences vegetation and soil type in the ecoregion. In the 

Puget Lowland Ecoregion, soils are dominated by Inceptisols 

in the north and Ultisols in the south (Jones, 2003). Before 

European settlement, most of the ecoregion was covered by 

coniferous forests, with species composition dependent on 

local climate (U.S. Environmental Protection Agency, 1999). 

The World Wildlife Fund places the Puget Lowland Ecoregion in the Western Hemlock Vegetation Zone. Although this 

vegetation zone is named after the western hemlock (Tsuga 

heterophylla), Douglas-fir (Pseudotsuga menziesii) is the 

dominant tree species. 

Seattle, which had an estimated population of 563,376 

in 2000, is the largest city in the Puget Lowland Ecoregion 

(Puget Sound Regional Council, 2001). The greater Seattle 

metropolitan area, comprising Seattle, Tacoma, Bellevue, and 

Bremerton, had an estimated population of 3.5 million people 

in 2000 (U.S. Census Bureau, 2000). Other sizable cities in 

the ecoregion include the state capital Olympia, as well as 

Tacoma, Bellingham, and Everett, Washington. The center of 

the Puget Lowland Ecoregion is dominated by the Seattle metropolitan area and developed land cover, whereas agriculture 

occurs mainly on river floodplains in the north and south. The 

remainder of the ecoregion area is dominated by forest land 

cover (fig. 1).

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change in the Puget Lowland Ecoregion (that is, the percentage of the land cover that changed 

at least once between 1973 and 2000) was estimated at 28.0 

percent (5,041 km2) (table 1). When compared with other 

ecoregions in the western United States, the Puget Lowland 

Ecoregion had the highest percentage of change in the last 

two of the four time periods analyzed (fig. 2). Between 1992 

and 2000 alone, 16.0 percent of the ecoregion changed from 

one land-cover class to another (table 2). However, when 

the change estimates are normalized to an annual average to 

account for varying lengths of study periods, the normalized 

annual average rate of change was highest in the third time 

period between 1986 and 1992, at 2.3 percent (table 2). Compared to other western ecoregions, Puget Lowland Ecoregion 

experienced the most overall change of any ecoregion in the 

West (fig. 3).

Land-cover estimates in 2000 for the Puget Lowland 

Ecoregion show forest as the most common land-cover class 

(47.1 percent), followed by developed (18.8 percent), water 

(12.9 percent), and agriculture (10.4 percent). All other 

land-cover classes were estimated at less than 5 percent of 

the ecoregion’s land cover (table 3). Land-cover classes with 

the highest estimates of change were the forest, developed, 

mechanically disturbed, and grassland/shrubland. Between 

1973 and 2000, the largest net change in land cover occurred 

in the forest class, with an estimated loss of 17.2 percent 

(1,767 km2). The second largest absolute net change in 

the ecoregion was the 53.8 percent (1,186 km2) increase in 

developed lands. Mechanical disturbance played a large role in 

land-cover change in the Puget Lowland Ecoregion. This transitional land-cover class, attributed primarily to forest cutting 

in this ecoregion, affected an estimated 3,591 km2, with the 

highest estimates recorded between 1986 and 1992 (6 percent 

of ecoregion area; 1,084 km2). Agriculture decreased by 5.4 

percent (107 km2

), with all losses occurring in the last two 

time periods. Grassland/shrubland more than doubled, increasing by 327 km2 during the study period, but still accounted for 

only 3.1 percent of the ecoregion in 2000. All other classes 

increased or decreased less than 50 km2 (table 3; fig. 4).

Figure 2. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Puget Lowland Ecoregion are represented by red bars in each time period.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
Chapter 2—Puget Lowland Ecoregion 45

Four of the top five largest land-cover conversions in 

the ecoregion were associated with timber harvest and forest 

regeneration (table 4; figs. 5,6). Timber harvesting is generally 

accepted as a change from forest to mechanically disturbed, 

with forest regrowth occurring either rapidly (mechanically 

disturbed directly back to forest) or more slowly (mechanically disturbed to grassland/shrubland and then grassland/

shrubland to forest). The only leading land-cover conversion 

not related to timber harvest and forest regeneration was losses 

of forest to developed land. In each time period except the 

last, the conversion from forest to other land-cover classes 

accounted for at least half of all land-cover change.

Regrowth of forest here occurs at a moderate pace, aided 

by mandated replanting efforts (fig. 6). Since 1975, the Washington State Department of Natural Resources (WADNR) has 

required land owners to plant seedlings of desirable species within 3 years of forest harvest to prevent the spread of 

invasive species (Washington State Department of Natural 

Figure 3. Overall spatial change in Puget Lowland Ecoregion (PL; 

darker bars) compared with that of all 30 Western United States 

ecoregions (lighter bars). Each horizontal set of bars shows proportions of ecoregion that changed during one, two, three, or four time 

periods; highest level of spatial change in Puget Lowland Ecoregion 

(four time periods) labeled for clarity. See table 2 for years covered by 

each time period. See appendix 2 for key to ecoregion abbreviations. 

Figure 4. Normalized average net change in Puget Lowland 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

Resources, 2001). This requirement also helps establish steady 

forest regrowth rates after harvest. Logging declines estimated 

in the last time period between 1992 and 2000 coincide with 

notable declines in lumber and wood exports from Washington 

in the 1990s (fig. 7). The export market suffered as a result 

of market downturns in Japan and Asia, reducing demand for 

wood-based products. At the same time, forests in the Pacific 

Northwest also faced increasing competition from other 

wood-producing countries, such as Russia, Canada, and New 

Zealand. 

The 1990s also ushered in an era of federal forest protection in the Pacific Northwest. The Northwest Forest Plan was 

implemented to protect the old-growth forest habitat of the 

threatened Northern Spotted Owl (Strix occidentalis caurina). 

(Daniels, 2005). The Northern Spotted Owl prefers to roost, 

forage, and nest in old growth forests that have moderate to 

high canopy enclosure and many large trees (Tesky, 1992). 

Under the Northwest Forest Plan, timber harvest was banned 

on 10 million of the 17 million acres (40,000 of 69,000 km2) 

of national forest land in the Pacific Northwest. Before the 

Northwest Forest Plan, timber sales from these national forests 

were approximately 4 to 5 billion board feet per year. After 

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods

−6

−4

−2

0

2

4

6

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
46 Status and Trends of Land Change in the Western United States—1973 to 2000

1990, sales dropped to less than a billion board feet per year. 

The WADNR changed its regulatory rules for State forests in 

the 1990s as well, to ensure sustainable logging practices and 

protect critical wildlife habitat. In 1999, the Forests and Fish 

Law was enacted in Washington, protecting critical salmon 

(Oncorhynchus spp.) habitat by requiring tree buffers along 

stream banks, even on private land (Daniels, 2005).

The second most important driver of land-cover change 

in the Puget Lowland Ecoregion was the increase in developed land. Most of the developed land (73.4 percent) was in 

areas that were previously forest land (fig. 8). The largest gain 

in developed land occurred between 1992 and 2000, and the 

slowest growth occurred between 1980 and 1986. During the 

1980s, the Puget Lowland Ecoregion experienced an economic 

downturn. By 1982, the unemployment rate was above 10 

percent. Net migration of people into the ecoregion dropped to 

zero in 1983 but remained above 20,000 per year for the rest 

of the study period (Puget Sound Regional Council, 2007). By 

the 1990s, the economic situation in Puget Lowland Ecoregion 

improved, and the population increased, led by employment 

opportunities and growth in the technology sector, including 

the biotechnology, computer, electronic equipment, software, 

and telecommunications industries. The ecoregion experienced 

a 65.4 percent increase in technology jobs between 1995 

and 2001, adding more than 60,000 jobs at a 7.8 percent rate 

Figure 6. Logging activity and various stages of forest regrowth 

in Puget Lowland Ecoregion, including recently replanted 

seedlings in addition to reestablished forest stand next to older 

growth trees. 

Figure 7. Logging exports at one of many shipping ports along 

Puget Sound. 

Figure 8. Gains in developed land-cover class in Puget Lowland 

Ecoregion. Values are areas in square kilometers that converted 

into developed land. Colors indicate which land-cover class 

converted to developed land.

Figure 5. Transportation of logged trees in Puget Lowland 

Ecoregion. 

0

100

200

300

400

500

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

New developed land, in square kilometers

Water

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 2—Puget Lowland Ecoregion 47

annually (Puget Sound Regional Council, 2006). By 1999, the 

technology sector of manufacturing (excluding transportation 

equipment) and industrial machinery surpassed lumber and 

wood products as Washington’s third leading export commodity (Lin and Schmidt, 2000). 

With a substantial growth in developed land in Puget 

Lowland Ecoregion, one might expect a large decline in 

agricultural land, but this was not the case (table 3; fig. 9). 

Only 12.8 percent of new developed land came at the expense 

of agriculture. Although western Washington makes up only 

5 percent of the state’s farmland, it contributed 23 percent of 

the agricultural earnings in 1992. Small farms tend to grow 

high-value crops such as fruits, vegetables, and greenhouse 

products. To prevent the loss of large amounts of agriculture 

land to developed land, the Washington State legislature 

enacted the Washington State Growth Management Act 

(GMA) in 1990. The GMA requires the fastest growing and 

most populated counties to adopt broad land-use plans. One 

of GMA’s provisions is the protection of agricultural lands 

of long-term commercial significance for the safeguarding of 

food production (Klein and Reganold, 1997). A principal goal 

of the GMA was to reduce the conversion of undeveloped and 

agricultural land into sprawling, low-density developed land. 

The intention was to direct new development to urban growth 

areas (UGA) that are usually located adjacent to existing cities 

and towns. The Puget Sound Regional Council reported that, 

between 1995 and 2000, 87 percent of the population growth 

in the region occurred inside the UGAs. Directing growth 

within UGAs allowed natural resource lands, such as farms 

and forests, to be conserved and to retain their rural character 

(Washington State Department of Community Trade and Economic Development, 2003).

The Puget Lowland Ecoregion experienced some of the 

highest estimates of land-cover change that occurred in the 

western United States over the entire study period (1973–2000). 

The largest proportion of change was attributed to land-cover 

conversions related to forestry and forest regeneration. Clearcut 

areas tend to be large, and the successional regrowth takes many 

years, depending on replanting times and local climate. Along 

with the changes in forests, the Puget Lowland Ecoregion had a 

notable increase in developed land. The aerospace and computer 

technology industries fostered an economic boom in the Puget 

Lowland Ecoregion in the 1990s, with associated population 

expansion and increased housing demand. Agricultural land 

cover remained fairly stable, with a slight net decline. 

Figure 9. New developed land along forest margin in Puget 

Lowland Ecoregion, with agricultural land preserved.

Table 1. Percentage of Puget Lowland Ecoregion that changed 

at least one time during study period (1973–2000) and associated 

statistical error.

[Most sample pixels remained unchanged (72.0 percent), whereas 28.0 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 13.1 1.1 12.2 14.5 0.8 5.7

2 10.7 1.9 8.8 12.6 1.3 12.1

3 3.7 0.9 2.8 4.5 0.6 15.7

4 0.2 0.1 0.2 0.3 0.0 15.2

Overall 

spatial 

change

28.0 3.1 24.9 31.1 2.1 7.4
48 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Puget Lowland Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 13.1 5.3 12.2 2.6 2.9 0.7 0.2 0.1 0.4 0.1 56.9 4.0 1.3 0.4 11.0 2.6 1.9 0.5 0.0 0.1

1980 13.1 5.3 13.6 2.8 2.8 0.7 0.2 0.1 0.5 0.2 54.0 4.0 2.9 0.7 11.0 2.6 1.9 0.5 0.0 0.0

1986 13.2 5.3 14.7 3.0 3.4 0.9 0.3 0.1 0.3 0.1 51.9 3.9 3.2 0.7 11.0 2.6 1.9 0.5 0.0 0.0

1992 13.1 5.3 16.4 3.2 6.0 1.3 0.3 0.1 0.4 0.1 48.1 3.7 3.1 0.7 10.7 2.6 1.8 0.5 0.0 0.0

2000 12.9 5.3 18.8 3.4 4.8 1.0 0.4 0.1 0.6 0.2 47.1 3.9 3.1 0.7 10.4 2.6 1.9 0.5 0.0 0.0

Net

change −0.2 0.1 6.6 1.3 1.9 0.9 0.2 0.1 0.2 0.1 −9.8 1.3 1.8 0.6 −0.6 0.5 0.0 0.1 0.0 0.1

Gross

change 0.8 0.4 6.6 1.3 10.6 2.1 0.2 0.1 0.7 0.4 13.1 1.8 7.2 1.4 1.4 0.5 0.3 0.1 0.0 0.1

Area, in square kilometers

1973 2,367 958 2,204 461 523 125 31 11 71 25 10,254 721 233 79 1,974 466 345 87 8 11

1980 2,352 958 2,457 499 498 120 41 15 88 32 9,733 721 523 130 1,979 471 339 85 0 0

1986 2,373 960 2,653 532 619 159 48 18 61 21 9,345 705 583 123 1,981 473 347 87 0 0

1992 2,361 958 2,954 579 1,084 243 58 21 76 24 8,667 659 550 127 1,929 477 332 84 0 0

2000 2,329 954 3,390 617 867 183 68 27 104 35 8,487 695 561 121 1,867 469 337 84 0 0

Net

change −38 23 1,186 231 344 154 37 17 33 24 −1,767 239 327 115 −107 95 −8 13 −8 11

Gross

change 144 72 1,186 231 1,916 371 43 16 124 69 2,360 328 1,298 255 245 88 58 26 8 11

Table 2. Raw estimates of change in Puget Lowland Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 8.1 1.0 7.1 9.1 0.7 8.1 1.2

1980–1986 9.1 1.5 7.6 10.6 1.0 11.3 1.5

1986–1992 13.6 2.2 11.4 15.8 1.5 10.9 2.3

1992–2000 16.0 2.4 13.6 18.4 1.6 10.2 2.0

Estimate of change, in square kilometers

1973–1980 1,463 175 1,287 1,638 119 8.1 209

1980–1986 1,639 273 1,366 1,911 185 11.3 273

1986–1992 2,454 395 2,058 2,849 268 10.9 409

1992–2000 2,877 433 2,444 3,310 293 10.2 360
Chapter 2—Puget Lowland Ecoregion 49

Table 4. Principal land-cover conversions in Puget Lowland Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 485 120 81 2.7 33.2

Mechanically disturbed Grassland/Shrubland 361 100 68 2.0 24.7

Forest Developed 222 62 42 1.2 15.2

Mechanically disturbed Forest 137 57 38 0.8 9.3

Grassland/Shrubland Forest 76 32 22 0.4 5.2

Other Other 182 n/a n/a 1.0 12.5

Totals 1,463 8.1 100.0

1980–1986 Forest Mechanically disturbed 611 158 107 3.4 37.3

Mechanically disturbed Grassland/Shrubland 315 90 61 1.7 19.2

Grassland/Shrubland Forest 244 61 41 1.4 14.9

Mechanically disturbed Forest 153 48 32 0.8 9.3

Forest Developed 144 56 38 0.8 8.8

Other Other 172 n/a n/a 1.0 10.5

Totals 1,639 9.1 100.0

1986–1992 Forest Mechanically disturbed 1,067 243 165 5.9 43.5

Grassland/Shrubland Forest 363 97 66 2.0 14.8

Mechanically disturbed Grassland/Shrubland 335 93 63 1.9 13.7

Mechanically disturbed Forest 260 90 61 1.4 10.6

Forest Developed 215 52 35 1.2 8.8

Other Other 214 n/a n/a 1.2 8.7

Totals 2,454 13.6 100.0

1992–2000 Forest Mechanically disturbed 851 183 124 4.7 29.6

Mechanically disturbed Forest 559 183 124 3.1 19.4

Mechanically disturbed Grassland/Shrubland 442 112 76 2.5 15.4

Grassland/Shrubland Forest 425 113 76 2.4 14.8

Forest Developed 290 43 29 1.6 10.1

Other Other 310 n/a n/a 1.7 10.8

Totals 2,877 16.0 100.0

1973–2000

(overall)

Forest Mechanically disturbed 3,013 598 405 16.7 35.7

Mechanically disturbed Grassland/Shrubland 1,453 278 189 8.1 17.2

Grassland/Shrubland Forest 1,109 226 153 6.2 13.1

Mechanically disturbed Forest 1,108 314 213 6.2 13.1

Forest Developed 871 186 126 4.8 10.3

Other Other 878 n/a n/a 4.9 10.4

Totals 8,432 46.8 100.0
50 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Daniels, J.M., 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-624.

DellaSala, D., Orians, G., Kavanagh, M., Sims, K., 2001, 

Puget lowland forest (NA0524): World Wildlife Fund, 

Wildfinder Terrestrial Ecoregions, accessed July 2007, at 

http://www.worldwildlife.org/science/wildfinder/profiles/

na0524.html.

Guttman, N.G., and Quayle, R.G., 1996, A historical perspective of U.S. climate divisions: Bulletin of the American 

Meteorological Society, v. 77, no. 2, p. 293–303.

Jones, J.A., 2003, Soils, chap. 11 of Jackson, P.L., and Kimerling, A.J., eds., Atlas of the Pacific Northwest: Corvallis, 

Oregon State University Press, p. 90.

Klein, L.R., and Reganold, J.P., 1997, Agriculture changes and 

farmland protection in western Washington: Journal of Soils 

and Water Conservation, v. 52, no. 1, p. 6–12.

Lin, T.-W., and Schmidt, J., 2000, International trade and 

Washington exports: Washington State Office of Financial 

Management, Research Brief No. 8. (Available at http://

www.ofm.wa.gov/researchbriefs/2000/brief008.pdf.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, p. 118–125.

Puget Sound Regional Council, 2001, Puget Sound trends; 

population change in cities, towns and counties, 1990–2000: 

Puget Sound Regional Council, No. D6. (Available at http://

psrc.org/assets/790/d6jul01.pdf.)

Puget Sound Regional Council, 2006, Puget Sound trends; 

high-tech employment: Puget Sound Regional Council, No. 

E10. (Available at http://psrc.org/assets/798/e10jun06.pdf.)

Puget Sound Regional Council, 2007, Puget Sound trends; 

population change and net migration: Puget Sound Regional 

Council, No. D7. (Available at http://psrc.org/assets/785/

d7feb07.pdf.)

Tesky, J.L., 1992, Strix occidentalis, in Fire Effects Information System: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, Fire Sciences 

Laboratory database, available at http://www.fs.fed.us/

database/feis/animals/bird/stoc/all.html.

U.S. Census Bureau, 2000, U.S. Census, 2000, accessed July 

2007, at http://www.census.gov/prod/www/abs/decennial/

index.htm.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

U.S. Environmental Protection Agency, 1999, Primary distinguishing characteristics of level III ecoregions of the 

continental United States: U.S. Environmental Protection 

Agency database, accessed July, 2007, at http://www.epa.

gov/wed/pages/ecoregions/level_iii.htm.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.

Washington State Department of Community Trade and Economic Development, 2003, Growth management, growth 

management services; overview of the Growth Management 

Act: Washington State Department of Community Trade 

and Economic Development report. (Available at http://

qa.cted.wa.gov/_CTED/documents/ID_892_Publications.

pdf.)

Washington State Department of Natural Resources, 2001, 

Forest practices rules - Title 222-34 WAC, Chapter 222-34 

WAC, Reforestation: Washington State Department of Natural Resources report, p. 34-2. (Available at http://www.dnr.

wa.gov/Publications/fp_rules_ch222-34wac.pdf.)
Chapter 3

Willamette Valley Ecoregion

Klamath Mountains Ecoregion. Topography here is relatively 

flat, with elevations ranging from sea level to 122 m. This even 

terrain, coupled with mild, wet winters, warm, dry summers, 

and nutrient-rich soil, makes the Willamette Valley the most 

important agricultural region in Oregon. Population centers 

are concentrated along the valley floor. According to estimates 

from the Oregon Department of Fish and Wildlife (2006), over 

2.3 million people lived in Willamette Valley in 2000. Portland, 

Oregon, is the largest city, with 529,121 residents (U.S. Census 

Bureau, 2000). Other sizable cities include Eugene, Oregon; 

Salem (Oregon’s state capital); and Vancouver, Washington.

Despite the large urban areas dotting the length of the 

Willamette Valley Ecoregion, agriculture and forestry products are its economic foundation (figs. 2,3). The valley is a 

major producer of grass seed, ornamental plants, fruits, nuts, 

vegetables, and grains, as well as poultry, beef, and dairy

By Tamara S. Wilson and Daniel G. Sorenson

Ecoregion Description

The Willamette Valley Ecoregion (as defined by 

Omernik, 1987; U.S. Environmental Protection Agency, 1997) 

covers approximately 14,458 km2 (5,582 mi2

), making it one 

of the smallest ecoregions in the conterminous United States. 

The long, alluvial Willamette Valley, which stretches north to 

south more than 193 km and ranges from 32 to 64 km wide, 

is nestled between the sedimentary and metamorphic Coast 

Ranges (Coast Range Ecoregion) to the west and the basaltic Cascade Range (Cascades Ecoregion) to the east (fig. 1). 

The Lewis and Columbia Rivers converge at the ecoregion’s 

northern boundary in Washington state; however, the majority 

of the ecoregion falls within northwestern Oregon. Interstate 5 

runs the length of the valley to its southern boundary with the 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Willamette Valley Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in 

appendix 2. See appendix 3 for definitions of land-use/land-cover classifications. 

124° 123°46°

45°

44°

Cascades

Coast Range

KM ECSF

NBR

Puget Lowland

PACIFIC

OCEAN

0 75 MILES

0 75 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

5

WAS H INGTON

OREGON PACIFIC 

OCEAN

Portland

Salem

Vancouver

Eugene C A S C A D E R A N G E

C O A S T R A N G E S

W I L L A M E T T E V A L L E Y

Wil l amett e

River Ri v e r

Lew is Riv er

Colu

mbia
52 Status and Trends of Land Change in the Western United States—1973 to 2000

products. The forestry and logging industries also are primary 

employers of the valley’s rural residents (Rooney, 2008). 

These activities have affected the watershed significantly, 

with forestry and agricultural runoff contributing to river 

sedimentation and decreased water quality in the Willamette 

River and its tributary streams (Oregon Department of Fish 

and Wildlife, 2006). 

Recent years have seen a marked decline in forest health 

related to the increased frequency of multiyear droughts. Insect 

damage and other diseases also are present; however, droughtrelated water stress is the primary factor in coniferous-tree mortality (Oregon Department of Forestry, 2008). Trees most at risk 

include Douglas-fir (Pseudotsuga menziesii), grand fir (Abies 

grandis), and western red cedar (Thuja plicata). Overstocking 

by timber companies and planting on sites with poor conditions 

increase susceptibility. Over time, these problems may lead to 

changes in planting practices and the use of more drought-tolerant species such as ponderosa pine (Pinus ponderosa).

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the footprint (overall areal 

extent) of land-use/land-cover change in the Willamette Valley 

Ecoregion was 14.5 percent, or approximately 2,090 km2 of 

area changed (table 1). This change is high when compared to 

land-cover change in other Western United States ecoregions 

(fig. 4). The footprint of change can be interpreted as the area 

that changed during at least one of the four multiyear periods 

in the 27-year study period. Overall, an estimated 1,240 km2 in 

the ecoregion changed in at least one of the time periods, 594 

km2 changed during two time periods, 195 km2 changed during three periods, and less than 7 km2 changed in all four time 

periods (table 1). 

The average annual rate of change in the Willamette 

Valley Ecoregion between 1973 and 2000 was 0.8 percent 

(table 2). This measurement, which normalizes the results 

for each period to an annual scale, indicates that the region 

averaged an estimated 113.6 km2 of change each year in the 

27-year study period. A closer look at successive time periods 

reveals a steady increase in annual change during the study 

period (fig. 5). Between 1973 and 1980, the annual rate of 

Figure 2. Vineyard adjacent to forested foothills in Willamette 

Valley Ecoregion. Note recovering clearcut hillside (upper left).

Figure 4. Overall spatial change in Willamette Valley Ecoregion 

(WV; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, or 

four time periods; highest level of spatial change in Willamette 

Valley Ecoregion (four time periods) labeled for clarity. See table 2 

for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

Figure 3. Livestock grazing in Willamette Valley Ecoregion.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods
Chapter 3—Willamette Valley Ecoregion 53

change was 0.4 percent (65 km2), increasing to 0.7 percent 

(98 km2) from 1980 to 1986. This rate continued to rise to 1.0 

percent (140 km2) between 1986 and 1992 and again to 1.1 

percent (155 km2) between 1992 and 2000 (table 2). 

Results from 2000 illustrate an estimated dominance of 

four of the ten land-cover classes in the Willamette Valley

Ecoregion: agriculture (45.1 percent), forest (33.5 percent), 

developed (12.5 percent), and mechanically disturbed (4.0 

percent) (table 3). These estimates from the sampled area are 

extraordinarily similar to land-cover percentages reported for 

the entire ecoregion (Oregon Department of Fish and Wildlife, 2006). The remaining six classes together accounted for 

the final 4.8 percent of the classified area in 2000, and each 

of these classes alone represents less than two percent of the 

sampled area (table 3). Between 1973 and 2000, there were 

considerable net losses in the areas of forest land (-11.0 percent) and agricultural land (-4.7 percent), along with net gains 

in developed land (33.4 percent) and mechanically disturbed 

land (236 percent, from 1.2 to 4.0 percent of the total ecoregion area) (fig. 6). 

Net change, however, represents only changes between 

the first and final time periods, or the difference between land 

cover in 1973 and that in 2000. Net change is not the best 

indicator of within-class variability for those classes experiencing spatial and temporal fluctuations. The net-change metric 

does not reveal dynamics of change within and between time 

periods. Analysis of gross change (area gained and lost) by 

individual land-cover classes by time period shows that classes 

have fluctuated throughout the 27-year study period to a greater 

degree than net-change values indicate (Raumann and others, 2007). Classes may experience gains and losses in area 

between time periods. For example, mechanically disturbed 

land experienced a net increase of 2.8 percent between 1973 

and 2000, but variable rates of forest cutting and other disturbances throughout the study period show a gross change of 3.3 

percent. This equates to a net change in mechanically disturbed 

land of 404.7 km2 (area in 2000 minus area in 1973) compared 

with a gross change of 476.3 km2 over the entire study period. 

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change 

for Willamette Valley Ecoregion are 

represented by red bars in each time 

period.

Figure 6. Normalized average net change in Willamette Valley 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
54 Status and Trends of Land Change in the Western United States—1973 to 2000

The “from class–to class” information afforded by a 

postclassification comparison was used to identify land-cover 

class conversions and rank them according to their magnitude. 

Table 4 illustrates the most frequent conversions between 1973 

and 2000. Nearly 80 percent of land-cover class conversions 

were related to timber harvest and successional regrowth. The 

mechanical disturbance of forests accounted for 51.1 percent 

of the changes related to timber harvesting, with 18.2 percent 

recovering directly back to forest and 16.3 percent converting 

to grassland/shrubland. Overall, the cumulative effect of forest clearing represents 1,254 km2

 of disturbed landscape. The 

majority of changes occurred along the ecoregion periphery 

within higher elevation forests. Another important conversion 

somewhat masked by the dominance of forestry is the loss of 

agricultural land to developed land (table 4). In the first change 

period (1973–1980), only 10.3 percent of all changes were from 

agriculture to developed, but between 1980 and 1986, this landcover conversion more than doubled to 22.3 percent (132 km2

). 

Table 1. Percentage of Willamette Valley Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (85.5 percent), whereas 14.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 8.8 1.7 7.1 10.5 1.2 13.4

2 4.2 1.2 3.0 5.5 0.8 20.0

3 1.4 0.5 0.9 1.9 0.3 23.6

4 0.0 0.0 0.0 0.1 0.0 33.5

Overall 

spatial 

change

14.5 3.0 11.5 17.4 2.0 13.9

Table 2. Raw estimates of change in Willamette Valley Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 3.1 0.9 2.2 4.1 0.6 20.4 0.4

1980–1986 4.1 1.0 3.1 5.0 0.6 15.9 0.7

1986–1992 5.8 1.4 4.4 7.2 0.9 16.0 1.0

1992–2000 8.6 2.1 6.5 10.6 1.4 16.2 1.1

Estimate of change, in square kilometers

1973–1980 454 137 317 591 93 20.4 65

1980–1986 590 138 452 728 94 15.9 98

1986–1992 841 198 642 1,039 134 16.0 140

1992–2000 1,238 296 942 1,535 201 16.2 155
Chapter 3—Willamette Valley Ecoregion 55

Table 3. Estimated area (and margin of error) of each land-cover class in Willamette Valley Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.8 0.8 9.4 3.6 1.2 0.5 0.2 0.1 0.0 0.0 37.7 6.0 0.8 0.4 47.3 6.2 1.6 0.9 0.0 0.0

1980 1.8 0.8 9.8 3.8 0.9 0.4 0.2 0.1 0.0 0.0 37.6 6.0 1.1 0.3 47.0 6.3 1.5 0.8 0.0 0.0

1986 1.8 0.8 10.9 4.0 1.4 0.4 0.2 0.1 0.0 0.0 36.6 5.9 1.3 0.4 46.2 6.3 1.5 0.8 0.0 0.0

1992 1.8 0.8 11.6 4.3 2.6 0.8 0.2 0.1 0.0 0.0 34.9 5.6 1.5 0.4 45.9 6.3 1.5 0.8 0.0 0.0

2000 1.8 0.8 12.5 4.5 4.0 1.2 0.2 0.1 0.1 0.0 33.5 5.3 1.2 0.4 45.1 6.3 1.5 0.8 0.0 0.0

Net

change 0.1 0.1 3.1 1.4 2.8 1.0 0.0 0.0 0.0 0.0 −4.1 1.4 0.4 0.6 −2.2 1.2 −0.1 0.1 0.0 0.0

Gross

change 0.2 0.1 3.1 1.4 4.8 1.3 0.1 0.0 0.0 0.0 6.1 1.4 2.6 0.8 3.1 1.1 0.2 0.1 0.0 0.0

Area, in square kilometers

1973 253 116 1,359 524 172 76 29 13 6 4 5,450 870 120 59 6,842 902 226 123 0 0

1980 264 116 1,422 544 136 53 31 15 6 4 5,440 874 153 50 6,790 908 216 118 0 0

1986 260 116 1,574 579 207 60 32 14 6 4 5,298 853 189 55 6,676 904 216 117 0 0

1992 261 115 1,681 615 371 110 30 14 6 4 5,051 813 210 58 6,631 905 216 117 0 0

2000 265 116 1,813 651 578 180 31 14 7 4 4,851 770 174 59 6,521 905 218 117 0 0

Net

change 12 13 454 205 407 142 2 5 1 1 −600 196 54 80 −322 175 −8 15 0 0

Gross

change 25 18 454 205 694 193 12 5 4 4 876 207 376 115 444 161 28 14 0 0
56 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Willamette Valley Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 127 53 36 0.9 28.0

Mechanically disturbed Grassland/Shrubland 85 42 28 0.6 18.8

Mechanically disturbed Forest 85 44 30 0.6 18.6

Grassland/Shrubland Forest 52 38 26 0.4 11.4

Agriculture Developed 45 26 18 0.3 10.0

Other Other 60 n/a n/a 0.4 13.2

Totals 454 3.1 100.0

1980–1986 Forest Mechanically disturbed 201 59 40 1.4 34.1

Agriculture Developed 132 81 55 0.9 22.3

Mechanically disturbed Grassland/Shrubland 94 35 23 0.6 15.9

Grassland/Shrubland Forest 60 30 20 0.4 10.2

Mechanically disturbed Forest 34 23 15 0.2 5.7

Other Other 70 n/a n/a 0.5 11.8

Totals 590 4.1 100.0

1986–1992 Forest Mechanically disturbed 360 110 74 2.5 42.8

Mechanically disturbed Grassland/Shrubland 119 39 27 0.8 14.2

Grassland/Shrubland Forest 102 45 30 0.7 12.1

Agriculture Developed 77 35 24 0.5 9.2

Mechanically disturbed Forest 73 30 20 0.5 8.7

Other Other 109 n/a n/a 0.8 13.0

Totals 841 5.8 100.0

1992–2000 Forest Mechanically disturbed 566 182 123 3.9 45.7

Mechanically disturbed Forest 256 96 65 1.8 20.7

Grassland/Shrubland Forest 138 51 35 1.0 11.1

Mechanically disturbed Grassland/Shrubland 101 37 25 0.7 8.2

Agriculture Developed 93 39 27 0.6 7.5

Other Other 84 n/a n/a 0.6 6.7

Totals 1,238 8.6 100.0

1973–2000

(overall)

Forest Mechanically disturbed 1,255 369 250 8.7 40.2

Mechanically disturbed Forest 447 176 120 3.1 14.3

Mechanically disturbed Grassland/Shrubland 399 126 86 2.8 12.8

Grassland/Shrubland Forest 352 131 89 2.4 11.3

Agriculture Developed 347 164 111 2.4 11.1

Other Other 322 n/a n/a 2.2 10.3

Totals 3,122 21.6 100.0
Chapter 3—Willamette Valley Ecoregion 57

References Cited

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Oregon Department of Fish and Wildlife, 2006, The Oregon 

Conservation Strategy—Willamette Valley Ecoregion: 

Oregon Department of Fish and Wildlife, p. 234–235. 

(Available at http://www.dfw.state.or.us/conservationstrategy/read_the_strategy.asp.)

Oregon Department of Forestry, 2008, Drought and conifer mortality in the Willamette Valley: Oregon Department of Forestry, accessed April 16, 2008, at http://

egov.oregon.gov/ODF/PRIVATE_FORESTS/docs/fh/

DroughtConiferMortalityWV.pdf.

Rooney, Brian, 2008, Oregon’s forestry and logging industry 

is particularly important to rural areas: Oregon Department 

of Employment, accessed May 12, 2008, at http://www.

qualityinfo.org/olmisj/ArticleReader?itemid=00004977.

U.S. Census Bureau, 2000, U.S. Census, 2000, accessed 

April 28, 2008, at http://www.census.gov/prod/www/abs/

decennial/index.htm.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001. Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
This page intentionally left blank
Rocky Mountains Ecoregions

Chapter 4

Canadian Rockies Ecoregion

greater proportion of perennial snow and ice (Omernik, 1987) 

(fig. 2). Over the years, this section of the Rocky Mountains has 

garnered many different names, including “Crown of the Continent” by George Bird Grinnell (Waldt, 2008) and “Backbone of 

the World” by the Blackfeet (Pikuni) Nation. 

Throughout the ecoregion, montane, subalpine, and alpine 

ecosystems have distinct flora and fauna elevation zones. Glaciers, permanent snowfields, and seasonal snowpack are found 

at the highest elevations. Spring and summer runoff fills lakes 

and tarns that form the headwaters of numerous streams and 

rivers, including the Columbia and Missouri Rivers that flow 

west and east, respectively, from the Continental Divide. 

 Many of the vast coniferous forests (fig. 3) throughout the Canadian Rockies Ecoregion lie within four national 

forests (Flathead, Lolo, Lewis and Clark, and Helena), and 

Glacier National Park is located entirely within the ecoregion. 

In 1932, Glacier National Park was combined with Waterton 

Lakes National Park, just across the Canadian border, to form 

By Janis L. Taylor

Ecoregion Description

The Canadian Rockies Ecoregion covers approximately 

18,494 km2

 (7,141 mi2) in northwestern Montana (Omernik, 

1987; U.S. Environmental Protection Agency, 1997). The east 

side of the ecoregion is bordered by the Montana Valley and Foothill Prairies Ecoregion, which also forms a large part of the western border of the ecoregion. In addition, the Northern Rockies 

Ecoregion wraps around the ecoregion to the northwest and south 

(fig. 1). As the name implies, the Canadian Rocky Mountains are 

located mostly in Canada, straddling the border between Alberta 

and British Columbia. However, this ecoregion only includes the 

part of the northern Rocky Mountains that is in the United States. 

This ecoregion is characterized by steep, high-elevation mountain 

ranges similar to most of the rest of the Rocky Mountains. Compared to the Northern Rockies Ecoregion, however, the Canadian 

Rockies Ecoregion reaches higher elevations and contains a 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Canadian Rockies Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in 

appendix 2. Also shown is part of one Great Plains Ecoregion, Northwestern Glaciated Plains (NWGLP). See appendix 3 for definitions of 

land-use/land-cover classifications.

113°

112°

115° 114°

49°

48°

47°

47°

Northern

Rockies

Northern

Rockies

Northern Rockies

MVFP

MVFP

NRK

NWGLP

MVFP

NWGLP

CANADA

MONTANA

Canadian Rockies

Ecoregion

0 50 100 MILES

0 50 100 KILOMETERS

MONTANA N O R T H E R N R O C K Y M T N S Wilderness

areas

Continental

Divide

Marias Pass

GLACIER 

 NATIONAL

 PARK

WATERTON LAKES NP

Missouri R.

Flathead

Lake

Hungry 

Horse

Reservoir

So. Fork

Flathead

R.

Bynum

Flathead R.

Swan R.

Clark Fork

Blackfoot R.

Flathead

Valley

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION
62 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 2. High peaks along east slope of northern Rocky 

Mountains, near Bynum, Montana. State-owned Blackleaf Wildlife 

Management Area lies at lower elevations in this area. Photograph taken in June 2009. 

Figure 3. South Fork Flathead River, with dense forest 

throughout river valley and hillsides.

the world’s first International Peace Park, Waterton-Glacier 

International Peace Park. This area is also designated as a 

World Heritage Site, and it is rich in flora and fauna. 

Throughout the Canadian Rockies Ecoregion, more than 

70 species of mammals, including lynx (Lynx canadensis), 

mountain lions (Puma concolor), wolves (Canis lupus irremotus), black bears (Ursus americanus), moose (Alces alces), 

bighorn sheep (Ovis canadensis), mountain goats (Oreamnos 

americanus), elk (Cervus elaphus), and wolverines (Gulo gulo), 

roam and mate in large tracts of undeveloped land. Designated 

wilderness areas within the national forests and on tribal lands, 

combined with Glacier National Park, make up 68 percent of the 

ecoregion (table 1; fig. 3). Surrounding this large, protected landscape are open lands across the Blackfeet Nation and Flathead 

Reservations and roadless lands in national forests, as well as 

wild and scenic rivers, all of which provide habitat vast enough 

to support large grizzly bear (Ursus arctos horribilis) populations (Waldt, 2008; Mace and Chilton, unpub. data, 2009). 

Native Americans have hunted in and harvested this 

ecoregion for over 5,000 years (Malone and others, 1991). 

Though still sparsely populated, communities are linked 

together by highway corridors that bisect vast areas of undeveloped, roadless landscape. Economies in the small communities 

are closely tied to the natural landscape. Approximately 2 million people visit Glacier National Park annually. Lakes, rivers, 

and winter snow further support a tourism economy through 

recreation, including skiing, hiking, biking, all-terrain-vehicle 

use, snowmobiling, camping, hunting, and fishing. Government 

agencies, the private timber industry, and tourist destinations 

and services provide the bulk of employment in the ecoregion. 

Harvesting of timber and other forest products has continued 

for more than a century (fig. 4). However, harvesting levels 

have varied over time and under different tract ownership. 

Climate within the Canadian Rockies Ecoregion varies 

significantly from west to east. The climate on the west side of 

the Rocky Mountains is moderated by a maritime influence, 

whereas the climate on the east side has a harsher, more continental regime. Throughout the ecoregion, the higher elevations 

force moisture out of the atmosphere to precipitate primarily 

as snow, leaving a drier climate in the surrounding valleys. 

Because of the mountainous terrain, there are many local 

climatic effects, including aspect, exposure to prevailing wind, 

thermal inversions, and dry pockets (Ricketts and others, 1999).

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change—the percentage of land area 

within the Canadian Rockies Ecoregion where land cover 

changed at least once between 1973 and 2000—was 7.6 percent (1,397 km2

). Estimates show that 3.0 percent (555 km2) 

of the ecoregion changed at least one time, and 4.6 percent 

(851 km2) changed two or more times (table 2). Comparing 

the amount of overall change in each of the 30 western United 

Figure 4. Forest logging activity in Swan River valley, Montana.
Chapter 4—Canadian Rockies Ecoregion 63

States ecoregions, the Canadian Rockies Ecoregion’s overall 

change is moderate (fig. 5). 

Total percent change in each of the four time periods in 

this study ranges from a low of 2.2 percent (400 km2) between 

1980 and 1986 to a high of 4.4 percent (809 km2) between 

1992 and 2000. After normalizing the land-cover change in 

each time period to an annual rate of change, the rates range 

from a low of 0.4 percent (67 km2) per year between 1980 and 

1986 to a high of 0.6 percent (110 km2) per year between 1986 

and 1992 (table 3) (fig. 6). 

Forest, the major land-cover class, covered 70.1 percent 

(12,964 km2) of the ecoregion in 1973, and it experienced a 

2.3 percent (293 km2) decrease during the entire study period. 

Grassland/shrubland, which covered 18.5 percent (3,418 km2) 

of the ecoregion in 1973, increased 8.2 percent (277 km2) over 

the study period. The mechanically disturbed class accounted 

for 1.5 percent (281 km2) of the land cover in 1973 and 1.1 

percent (196 km2) in 2000 (table 4). Net change in all landuse/land-cover categories is presented in figure 7. 

The top four land-cover conversions were all components 

of man-made and naturally occurring forest change and regeneration: (1) forest to mechanically disturbed, (2) mechanically 

disturbed to grassland/shrubland, (3) grassland/shrubland 

to forest, and (4) forest to nonmechanically disturbed (table 

5). Forest cuts, which were documented as mechanically 

disturbed, were the most common land-cover conversions 

between 1980 and 1986 and between 1986 and 1992 (table 4). 

Between 1986 and 1992, the second most common conversion 

was forest to nonmechanically disturbed, a result of naturaldisturbance events such as fire and (or) beetle kill. 

Forest products and their rate of harvest have changed 

in the decades between 1970 and 2000, affecting the rates of 

change of forest land cover. As early as 1976, the U.S. Forest 

Service stopped approving the clearcutting of areas larger than 

40 acres (U.S. Department of Agriculture, 1998). In 1989, the 

U.S. Forest Service established and implemented an annual 

forest-management plan that defined a more comprehensive 

Figure 5. Overall spatial change in Canadian Rockies Ecoregion 

(CRK; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that change during one, two, three, or 

four time periods; highest level of spatial change in Canadian 

Rockies Ecoregion (four time periods) labeled for clarity. See table 

3 for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

Figure 6. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Canadian Rockies Ecoregion are 

represented by red bars in each time 

period.
64 Status and Trends of Land Change in the Western United States—1973 to 2000

list of forest uses. After 1992, stringent restrictions were 

applied to clearcutting, and its use continues to decline. The 

most common timber harvested in the 1980s was the largegirth tree for lumber and sheet products, but this is being 

replaced by the harvest of dead or small-diameter trees by 

stewardship projects, which aim to improve wildlife habitat 

and (or) enhance cultural features. Today, overall timber-harvest rates are near 1950 levels (U.S. Department of Agriculture, 1998).

The vast wild and protected landscapes in the Canadian 

Rockies Ecoregion provide a crucial link for the Yellowstone 

to Yukon (“Y2Y”) Initiative. Furthermore, the “Crown of 

the Continent” is a priority area where various conservation 

efforts are underway to protect movement of animals as they 

travel between parks and other forested lands. A goal of the 

Y2Y Initiative is to protect both the wild and human inhabitants so that they remain connected and healthy into the future. 

The grizzly bear is one of the many animals that require large 

amounts of land. The Northern Continental Divide Grizzly 

Bear Project has determined that this area has the largest grizzly bear populations found in the lower 48 states (Kendall and 

others, 2008; Mace and Chilton, unpub. data, 2009). Projects 

Figure 7. Normalized average net change in Canadian Rockies 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation may be represented in figure. See appendix 3 for definitions 

of land-use/land-cover classifications.

Figure 10. Highway 2 over Rocky Mountains at Marias Pass, 

Montana. Highway affects movement of large mammals in region.

Figure 9. Tourists in Glacier National Park.

Figure 8. Glaciers and snowpack in Glacier National Park.

like the Y2Y Initiative may limit future land-use/land-cover 

change if implementation successfully continues. 

 Mountain glaciers, along with annual snowpack and rainfall, support the headwaters of large rivers (fig. 8). Because of 

the quality and quantity of the water, the rivers and streams, 

along with the riparian corridors that they flow through, 

provide habitat for a wide variety of species, as well as critical 

habitat for several fish species. A particularly important factor 

is the input of glacial meltwater that enters the streams during 

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 4—Canadian Rockies Ecoregion 65

the hottest and driest days of late summer, sustaining temperature-sensitive species (Hall and Fagre, 2003). 

The landscape is rich in the ecosystem services that it 

provides, which include forest products, habitat for wildlife, 

fresh water, and recreational opportunities. In the future, these 

services may change along with the forest as the result of both 

human and natural processes.

Natural amenities, such as forests, lakes, and rivers, 

provide outdoor recreation opportunities for numerous visitors, 

making them an economic asset to local communities (fig. 9). 

Towns directly adjacent to the Canadian Rockies Ecoregion, 

Figure 11. Remnants of forest fire above Hungry Horse Reservoir, Montana.

such as those in the Flathead Valley, observed an increase in 

population and housing starts throughout the 1980s and 1990s 

(Baron and others, 2000), and the ecoregion’s developed area 

doubled in size (from 17 to 33 km2) over the course of the study. 

Future change in this forested ecoregion is inevitable. 

Increased human use of the landscape may affect water quality 

(and quantity) and, thus, wildlife habitat, and transportation 

corridors may fragment the landscape (fig. 10). Clean water 

may be especially at risk owing to human activities such 

as mining, as well as human-caused impacts from erosion 

and runoff from landscaping and septic systems (Baron and 

others, 2000). Because humans have actively controlled and 

suppressed fire in this region for decades, forests have grown 

dense with vegetation, and infestations have killed off large 

swaths of trees. Future wildfires may be large and devastating 

in some areas (Arno and Allison-Bunnell, 2002). 

Climate change may also play a strong role in future 

changes. Glaciers are melting in Glacier National Park (Fagre, 

2005); as of 2000, only 37 of the estimated original 150 mountain 

glaciers remained. Summer and winter temperatures are expected 

to rise; models predict that by 2030 all of the glaciers within 

Glacier National Park will have melted (Fagre, 2005; Hall and 

Fagre, 2003; Fagre and others, 2003). Increasing temperatures, 

increasing numbers of frost-free days, and decreasing numbers 

of extended periods of very cold temperatures during winter may 

further influence disturbance regimes in the forests from both 

wildfires (fig. 11) and insect infestations (Carter, 2003). 

Table 1. Sizes of natural areas in Montana, which together 

represent one of the most completely preserved mountain 

ecosystems in the world.

Natural area Acres Square

kilometers

Square

miles

Bob Marshall Wilderness 1,009,356 4,085 1,577

Scapegoat Wilderness 239,936 971 375

Great Bear Wilderness 286,700 1,160 448

Mission Mountains Wilderness 73,877 299 115

Mission Mountains Tribal Wilderness 89,500 362 140

Jewel Basin 15,349 62 24

Hungry Horse Reservoir 23,813 96 37

Glacier National Park 1,400,000 5,665 2,187

Total 3,138,531 12,701 4,904

Table 2. Percentage of Canadian Rockies Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (92.4 percent), whereas 7.6 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.0 1.3 1.8 4.3 0.9 28.2

2 3.8 1.3 2.5 5.1 0.9 23.8

3 0.7 0.4 0.3 1.0 0.2 36.8

4 0.1 0.0 0.0 0.1 0.0 47.6

Overall 

spatial 

change

7.6 2.4 5.1 10.0 1.6 21.7
66 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Raw estimates of change in Canadian Rockies Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 2.7 1.1 1.6 3.9 0.8 27.7 0.4

1980–1986 2.2 0.8 1.4 3.0 0.5 25.0 0.4

1986–1992 3.6 1.3 2.3 4.8 0.8 23.8 0.6

1992–2000 4.4 1.4 2.9 5.8 1.0 22.1 0.5

Estimate of change, in square kilometers

1973–1980 505 207 299 712 140 27.7 72

1980–1986 400 148 252 548 100 25.0 67

1986–1992 659 232 427 891 157 23.8 110

1992–2000 809 264 545 1074 179 22.1 101

Table 4. Estimated area (and margin of error) of each land-cover class in Canadian Rockies Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.7 0.8 0.1 0.1 1.5 0.7 0.0 0.0 6.9 2.6 70.1 4.7 18.5 3.8 0.3 0.3 0.4 0.2 0.0 0.0

1980 1.6 0.8 0.1 0.1 0.9 0.4 0.0 0.0 6.9 2.6 70.2 4.7 19.1 3.7 0.4 0.3 0.4 0.2 0.0 0.0

1986 1.6 0.8 0.1 0.1 0.8 0.4 0.0 0.0 7.0 2.6 70.2 4.7 19.1 3.7 0.4 0.3 0.4 0.2 0.0 0.0

1992 1.7 0.8 0.1 0.1 1.1 0.4 0.0 0.0 6.9 2.6 69.0 4.7 19.0 3.8 0.4 0.3 0.4 0.2 1.0 0.9

2000 1.5 0.7 0.2 0.1 1.1 0.5 0.0 0.0 7.0 2.6 68.5 4.6 20.0 3.7 0.4 0.3 0.4 0.2 0.5 0.5

Net

change −0.2 0.2 0.1 0.1 −0.5 0.5 0.0 0.0 0.1 0.1 −1.6 1.2 1.5 1.1 0.1 0.1 0.0 0.0 0.5 0.5

Gross

change 0.4 0.5 0.1 0.1 3.4 1.2 0.0 0.0 0.1 0.1 4.1 1.2 3.4 1.2 0.1 0.1 0.0 0.0 2.6 1.9

Area, in square kilometers

1973 312 152 17 10 281 124 1 1 1,284 474 12,964 878 3,418 700 64 54 80 29 0 0

1980 288 147 21 13 159 73 1 1 1,284 474 12,988 874 3,536 691 65 55 80 29 0 1

1986 303 149 24 15 144 70 1 1 1,291 477 12,980 873 3,527 691 66 55 80 29 6 8

1992 309 151 27 18 194 82 1 1 1,285 474 12,765 862 3,510 696 67 55 79 28 182 174

2000 277 137 33 23 196 89 2 1 1,294 479 12,671 847 3,699 691 80 60 79 28 98 91

Net

change −35 35 16 13 −85 99 1 1 10 12 −293 213 281 196 16 19 −1 1 98 91

Gross

change 78 88 16 13 622 226 1 1 21 20 751 231 621 216 18 19 2 1 473 353
Chapter 4—Canadian Rockies Ecoregion 67

Table 5. Principal land-cover conversions in Canadian Rockies Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Mechanically disturbed Grassland/Shrubland 174 87 59 0.9 34.3

Forest Mechanically disturbed 137 70 47 0.7 27.1

Mechanically disturbed Forest 107 91 62 0.6 21.2

Grassland/Shrubland Forest 58 66 45 0.3 11.6

Water Mechanically disturbed 21 28 19 0.1 4.1

Other Other 9 n/a n/a 0.0 1.7

Totals 505 2.7 100.0

1980–1986 Forest Mechanically disturbed 141 70 47 0.8 35.3

Grassland/Shrubland Forest 84 44 30 0.5 21.0

Mechanically disturbed Grassland/Shrubland 76 56 38 0.4 19.0

Mechanically disturbed Forest 62 45 30 0.3 15.4

Mechanically disturbed Water 15 20 13 0.1 3.7

Other Other 23 n/a n/a 0.1 5.7

Totals 400 2.2 100.0

1986–1992 Forest Mechanically disturbed 194 81 55 1.1 29.5

Forest Nonmechanically disturbed 182 174 118 1.0 27.6

Grassland/Shrubland Forest 120 69 47 0.6 18.2

Mechanically disturbed Grassland/Shrubland 102 59 40 0.5 15.4

Mechanically disturbed Forest 41 24 16 0.2 6.2

Other Other 21 n/a n/a 0.1 3.1

Totals 659 3.6 100.0

1992–2000 Nonmechanically disturbed Grassland/Shrubland 182 174 118 1.0 22.5

Forest Mechanically disturbed 165 88 59 0.9 20.3

Mechanically disturbed Grassland/Shrubland 123 60 41 0.7 15.2

Grassland/Shrubland Forest 110 75 51 0.6 13.6

Forest Nonmechanically disturbed 86 78 53 0.5 10.6

Other Other 144 n/a n/a 0.8 17.8

Totals 809 4.4 100.0

1973–2000

(overall)

Forest Mechanically disturbed 637 258 174 3.4 26.8

Mechanically disturbed Grassland/Shrubland 474 218 147 2.6 20.0

Grassland/Shrubland Forest 372 213 144 2.0 15.7

Forest Nonmechanically disturbed 275 185 125 1.5 11.6

Mechanically disturbed Forest 272 174 117 1.5 11.4

Other Other 345 n/a n/a 1.9 14.5

Totals 2,374 12.8 100.0
68 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Arno, S.F., and Allison-Bunnell, S., 2002, Flames in our forest—

Disaster or renewal?: Washington, D.C., Island Press, 227 p.

Baron, J.S, Theobald, D.M., and Fagre, D.B, 2000, Management of the land use conflicts in the United States Rocky 

Mountains: Mountain Research and Development, v. 20, 

no. 1, p. 24–27, accessed December 4, 2009, at http://www.

nrmsc.usgs.gov/files/norock/products/GCC/MtnRes-Dev_

Baron_00.pdf.

Carter, L.M., 2003, U.S. national assessment of the potential 

consequences of climate variability and change, Rocky 

Mountain/Great Basin region: U.S. Climate Change Science Program/U.S. Global Change Research Program 

Educational Resources Regional Paper, accessed January 

12, 2009, at http://www.usgcrp.gov/usgcrp/nacc/education/

rockies-greatbasin/rockiesandgreatbasin-edu-2.htm. 

Fagre, D.B., 2005, Adapting to the reality of climate change 

at Glacier National Park, Montana, USA: Proceedings of 

The First International Conference on the Impact of Climate 

Change on High-Mountain Systems, Bogota, Colombia, 

November 21–23, 2005, Instituto de Hidrologia, Meteorologia y Estudios Ambientales IDEAM, p. 221–235, accessed 

at http://www.mtnforum.org/en/content/adapting-realityclimate-change-glacier-national-park-montana-usa.

Fagre, D.B., Peterson, D.L., and Hessl, A.E., 2003, Taking the 

pulse of mountains—Ecosystem responses to climatic variability: Climatic Change, v. 59, no. 1, p. 263–282.

Hall, M.P., and Fagre, D.B., 2003, Modeled climate-induced 

glacier change in Glacier National Park, 1850–2100: BioScience, v. 53, p. 131–140.

Kendall, K.C., Stetz, J.B., Roon, D.A., Boulanger, J.B., and 

Paetkau, D., 2008, Grizzly bear density in Glacier National 

Park, Montana: Journal of Wildlife Management, v. 72, no. 

8, p. 1,693–1,705.

Malone, M.P., Roeder, R.B., and Lang, W.L., 1991, Montana—A history of two centuries (revised ed.): Seattle, 

University of Washington Press, 480 p. (Available at 

http://www.washington.edu/uwpress/search/books/

MALMRC.html.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125. 

Ricketts, T.H., Dinerstein, E., Olson, D.M., Loucks, C.J., 

Eichbaum, W., DellaSala, D., Kavanagh, K., Hedao, 

P., Hurley, P., Carney, K., Abell, R., and Walters, S., 

eds., 1999, Terrestrial ecoregions of North America—A 

conservation assessment: Washington, D.C., World Wildlife 

Fund, Island Press, p. 213–216.

U.S. Department of Agriculture, 1998, National summary, Forest Management Program annual report, fiscal year 1997: 

Washington, D.C., U.S. Department of Agriculture, Forest 

Service, 143 p., accessed at www.fs.fed.us/forestmanagement/documents/tspirs/1997/tspirs97.pdf.

U.S. Environmental Protection Agency, 1997, Descriptions of level III ecological regions for the CEC report on 

ecological regions of North America: U.S. Environmental 

Protection Agency database, accessed April 12, 2006, 

at http://www.epa.gov/wed/pages/ecoregions/na_eco.

htm#Downloads.

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., Wylie, 

B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 67, p. 650–662.

Waldt, R., 2008, Crown of the continent—The last great 

wilderness of the Rocky Mountains: Helena, Montana, 

Riverbend Publishing, 167 p. (Available at http://www.

riverbendpublishing.com/crown.html.)
112° 110° 108° 106° 104°

104°

46°

44°

42°

Northwestern

Great Plains

Wyoming

Basin

Snake

River

Basin

MVFP MVFP

MVFP

NRK NRK

NRK

NRK

MVFP

Central

Basin

and Range

Western

High Plains

NSH

SRK

NRK

NRK

WUM

0 50 100 150 MILES 

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

Yellowstone River

Powder R.

Green R.

Tongue R.

Bighorn R.

Wind R. WYOMING

MONTANA

IDAHO SOUTH

DAKOTA

NV

Gallatin R. 

Madison R.

BLACK

HILLS BIGHORN MTNS

WIND RIVER RA.

Continental Divide

YELLOWSTONE NP

GRAND TETON NP

Jackson

Big Sky

Island Park

Chapter 5

Middle Rockies Ecoregion

to the west, and the Wyoming Basin Ecoregion to the south 

and east. The Bighorn Mountains section lies between the 

Wyoming Basin Ecoregion to the west and the Northwestern 

Great Plains Ecoregion to the east, and it abuts the Montana 

Valleys and Foothill Prairies Ecoregion to the north. The 

Black Hills section is entirely surrounded by the Northwestern 

Great Plains Ecoregion. The Continental Divide crosses 

the ecoregion from the southeast along the Wind River 

Range, through Yellowstone National Park, and west along 

the Montana-Idaho border. On both sides of the divide, 

topographic relief causes local climate variability, particularly 

the effects of aspect, exposure to prevailing wind, thermal 

By Janis L. Taylor

Ecoregion Description

The Middle Rockies Ecoregion—characterized by steep, 

high-elevation mountain ranges and intermountain valleys—is 

a disjunct ecoregion composed of three distinct geographic 

areas: the Greater Yellowstone area in northwest Wyoming, 

southwest Montana, and eastern Idaho; the Bighorn Mountains 

in north-central Wyoming and south-central Montana; and the 

Black Hills in western South Dakota and eastern Wyoming 

(Omernik, 1987; U.S. Environmental Protection Agency, 

1997). The ecoregion covers approximately 90,160km2

(34,881 mi2), and its three distinct geographic sections are 

bordered by several other ecoregions (fig. 1). The Yellowstone 

section abuts the Montana Valley and Foothill Prairies and 

the Northern Rockies Ecoregions to the north, the Snake 

River Basin and the Central Basin and Range Ecoregions 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Middle Rockies Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed 

in appendix 2. Also shown on map are parts of three Great Plains ecoregions: Northwestern Great Plains, Western High Plains, and 

Nebraska Sand Hills (NSH). See appendix 3 for definitions of land-use/land-cover classifications. 
0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in three time periods

70 Status and Trends of Land Change in the Western United States—1973 to 2000

inversions, and rain-shadow effects, that are reflected in the 

wide variety of flora and fauna within the ecoregion (Ricketts 

and others, 1999). 

The three main land uses common to the Middle Rockies 

Ecoregion are logging, recreation, and agriculture. Agricultural 

land use within the intermountain valleys includes managed 

hay fields and pasture lands, irrigated alfalfa, and other 

scattered crops (fig. 2). Grazing of cattle and sheep occurs in 

the valleys year-round and on higher elevation open areas in 

summer. There are ski resorts and destination communities 

such as the towns of Big Sky, Montana; Jackson, Wyoming; 

and Island Park, Idaho. Yellowstone National Park and Grand 

Teton National Park, both in the ecoregion, draw millions 

of visitors each year. There are nine national forests within 

the ecoregion that are managed for multiple uses including 

logging, grazing, and recreation. 

Land cover in the valleys is dominated by grassland/

shrubland (fig.3). Common grass species include grama 

grass (Bouteloua spp.), wheatgrass (Eremopyrum spp.), 

and needlegrass (Nassella spp.). Common shrubs 

include sagebrush (Artemisia tridentata), rabbitbrush 

(Chrysothamnus viscidiflorus), and serviceberry 

(Amelanchier arborea). Hillsides are mostly forested. 

Lodgepole pine (Pinus contorta) is the most common conifer 

throughout the Yellowstone area and the Bighorn Mountains, 

but ponderosa pine (Pinus ponderosa) is more common in 

the Black Hills, which are lower in elevation (Mohlenbrock, 

2002). Perennial streams and rivers run through many of 

the valleys, and riparian vegetation such as cottonwoods 

(Populus spp.) and aspens (Populus tremuloides) line the 

banks. The headwaters for the Yellowstone, Wind, Snake, 

Powder, Tongue, Green, Madison, and Gallatin Rivers are all 

within the ecoregion, making it a major source of water for 

the central United States.

Figure 2. Small alfalfa field and flat to rolling agricultural land at 

base of forested hills in Middle Rockies Ecoregion. Photograph by 

Terry Sohl, 2008. 

Figure 3. Sagebrush (grassland/shrubland) dominates flatter, 

lower elevation areas west of Interstate 15 in Middle Rockies 

Ecoregion. Photograph by Terry Sohl, 2008. 

Figure 4. Overall spatial change in Middle Rockies Ecoregion 

(MRK; darker bars) compared with that of all 30 Western United 

States ecoregions. Each horizontal set of bars shows proportions 

of ecoregion that changed during one, two, three, or four time 

periods; highest level of spatial change in Middle Rockies Ecoregion (three time periods) labeled for clarity. See table 2 for years 

covered by each time period. See appendix 2 for key to ecoregion 

abbreviations.
0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−8

−6

−4

−2

0

4

2

6

8

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Chapter 5—Middle Rockies Ecoregion 71

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change—the percentage of land area 

within the ecoregion where land cover changed at least once 

between 1973 and 2000—was 8.8 percent (7,974 km2) (table 

1). Of that total, 1.7 percent (1,533 km2) changed one time, 

and 7.1 percent (6,401 km2) changed two times. The amount 

of change in this ecoregion is moderate when compared with 

all 30 Western United States ecoregions (fig. 4).

Total change in each of the four time periods selected for 

this study ranged from a low of 0.9 percent (795 km2) between 

1973 and 1980 to a high of 7.5 percent (6,740 km2) between 

1992 and 2000 (table 2). After normalizing to an annual rate of 

change, the rates ranged from a low of 0.1 percent (114km2) 

per year between 1973 and 1980 to a high of 1.1 percent 

(1,012 km2

) per year between 1986 and 1992 (fig. 5).

In 1973, forest made up 50.4 percent (45,463 km2

) of 

the ecoregion, grassland/shrubland made up 44.4 percent 

(40,061 km2), wetland and agriculture each covered roughly 

1.0 percent of the ecoregion, and barren (for example, 

mountain peaks) covered 2.0 percent (table 3). Forest 

decreased 11.3 percent by 2000, and grassland/shrubland 

increased 10.3 percent. In the first two time periods, 

nonmechanically disturbed land (areas subject to wildfire 

or insect-caused mortality) never accounted for more than 

0.1 percent of the ecoregion, but in the period between 1986 

and 1992, that value jumped to 5.7 percent of the ecoregion 

(5,159 km2), largely as a result of the 1988 Yellowstone fires 

(fig. 6).

Forest to nonmechanically disturbed, nonmechanically 

disturbed to grassland/shrubland, and grassland/shrubland to 

nonmechanically disturbed were three of the four largest landcover conversions (table 4), and all are related to wildfires. Of 

the 30 sample blocks that were interpreted, 6 showed greater 

than 20 percent change, and 5 of these were located within the 

perimeter of the 1988 wildfires (fig. 7). The sixth block with 

greater than 20 percent change was located in the Black Hills, 

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Middle Rockies Ecoregion are represented by red bars in each time period.

Figure 6. Normalized average net change in Middle Rockies 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.
72 Status and Trends of Land Change in the Western United States—1973 to 2000

A

B

Figure 7. In 1988, Yellowstone area fires caused marked 

increase in area of nonmechanically disturbed land. Photographs 

by Terry Sohl, 2008. A, Interpretive sign about “Huck Fire,” one of 

three largest fires to strike Yellowstone area in 1988. In northern 

part of this sample block, forest along road ends abruptly at 

edge of burn. B, Near “Huck Fire” interpretive sign, forest was 

completely burned; now, 20-year-old regenerating trees cover 

much of area. Small marsh area lines stream in foreground. 

where the Jasper fire burned in 2000. The fourth most common 

land-cover change was forest to mechanically disturbed, a 

result of timber harvest.

The 1988 Yellowstone fires represented by far the 

largest changes in this ecoregion. The fires followed a 

prolonged drought and burned more than 3,200 km2 in and 

around Yellowstone National Park (Christensen and others, 

1989). Dry-lightning storms sparked numerous blazes that 

converged to become a single major fire. In the decades 

following the fire, vegetation changes continued, with 

vigorous herbaceous growth and young forests replacing 

burned stands of forest (Knight and Wallace, 1989). 

Lodgepole pines are adapted to fire and produce serotinous 

cones that respond to fire by opening up to release seed, 

facilitating forest regrowth.

Additional ecoregion change came from timber harvest 

in national forests and private forests. One example of such 

activity is 20 years of salvage logging in Targhee National 

Forest near Island Park, Idaho, between 1970 and 1990 

(Wilkinson, 1999). Large areas were clearcut, right up to 

the border of Yellowstone National Park, in order to remove 

beetle-killed lodgepole pine trees. In 1990, the U.S. Forest 

Service changed their management practices and harvest rates 

in the Targhee National Forest and in eight other national 

forests within the ecoregion (Hansen and others, 2002). 

Table 1. Percentage of Middle Rockies Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (91.2 percent), whereas 8.8 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.7 1.0 0.6 2.7 0.7 42.1

2 7.1 3.4 3.7 10.5 2.3 32.2

3 0.0 0.0 0.0 0.1 0.0 50.4

4 0.0 0.0 0.0 0.0 0.0 92.3

Overall 

spatial 

change

8.8 3.4 5.4 12.3 2.3 26.5
Chapter 5—Middle Rockies Ecoregion 73

Table 2. Raw estimates of change in Middle Rockies Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.9 0.4 0.5 1.2 0.2 27.2 0.1

1980–1986 0.9 0.4 0.5 1.4 0.3 31.2 0.2

1986–1992 6.7 3.3 3.4 10.1 2.3 33.9 1.1

1992–2000 7.5 3.3 4.1 10.8 2.3 30.5 0.9

Estimate of change, in square kilometers

1973–1980 795 318 477 1,113 216 27.2 114

1980–1986 856 392 464 1,248 267 31.2 143

1986–1992 6,075 3,019 3,055 9,094 2,057 33.9 1,012

1992–2000 6,740 3,019 3,722 9,759 2,056 30.5 843

Table 3. Estimated area (and margin of error) of each land-cover class in Middle Rockies Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.7 0.5 0.1 0.1 0.2 0.1 0.0 0.0 1.9 0.8 50.4 5.7 44.4 5.7 1.1 0.8 1.0 0.3 0.0 0.0

1980 0.7 0.4 0.2 0.1 0.4 0.3 0.0 0.0 1.9 0.8 50.0 5.7 44.5 5.7 1.0 0.8 1.0 0.3 0.1 0.1

1986 0.5 0.3 0.2 0.1 0.2 0.1 0.0 0.0 2.0 0.8 50.0 5.7 44.9 5.7 1.1 0.8 1.0 0.3 0.0 0.0

1992 0.7 0.5 0.2 0.2 0.4 0.3 0.0 0.0 1.9 0.8 45.0 5.4 43.8 5.7 1.1 0.7 1.0 0.3 5.7 3.3

2000 0.7 0.5 0.2 0.2 0.2 0.2 0.0 0.0 1.9 0.8 44.7 5.2 49.0 5.4 1.0 0.7 1.0 0.3 1.0 1.0

Net

change 0.0 0.0 0.1 0.1 0.0 0.2 0.0 0.0 0.0 0.0 −5.7 2.7 4.6 2.6 0.0 0.1 0.0 0.0 1.0 1.0

Gross

change 0.4 0.6 0.1 0.1 1.5 0.7 0.0 0.0 0.2 0.2 7.6 3.1 7.6 3.9 0.2 0.1 0.1 0.1 12.5 6.7

Area, in square kilometers

1973 648 419 96 74 182 135 17 15 1,721 746 45,463 5,170 40,061 5,168 966 725 897 298 0 0

1980 610 378 158 127 380 252 18 15 1,726 749 45,113 5,142 40,161 5,150 932 679 910 307 46 66

1986 473 255 161 130 193 128 18 16 1,788 751 45,081 5,180 40,462 5,126 955 680 909 306 22 32

1992 671 446 173 147 396 233 20 16 1,728 750 40,606 4,890 39,467 5,152 948 664 899 297 5,159 2,993

2000 674 449 174 147 169 139 21 17 1,739 752 40,327 4,674 44,207 4,854 938 663 901 296 937 930

Net

change 27 33 78 82 −13 144 4 3 17 16 −5,135 2,425 4,146 2,348 −27 80 4 40 937 930

Gross

change 385 505 79 82 1,387 671 4 3 143 162 6,810 2,770 6,865 3,522 165 113 79 73 11,294 6,008
74 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Middle Rockies Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent 

of all 

(km2

) (+/− km2) (km2) changes

1973–1980 Forest Mechanically disturbed 378 252 172 0.4 47.5

Mechanically disturbed Grassland/Shrubland 113 114 77 0.1 14.2

Mechanically disturbed Forest 69 74 51 0.1 8.7

Forest Nonmechanically disturbed 46 66 45 0.1 5.8

Agriculture Developed 36 52 35 0.0 4.5

Other Other 153 n/a n/a 0.2 19.3

Totals 795 0.9 100.0

1980–1986 Mechanically disturbed Grassland/Shrubland 233 210 143 0.3 27.2

Forest Mechanically disturbed 193 128 87 0.2 22.5

Mechanically disturbed Forest 147 149 101 0.2 17.2

Water Grassland/Shrubland 79 110 75 0.1 9.3

Water Barren 60 81 55 0.1 7.0

Other Other 144 n/a n/a 0.2 16.8

Totals 856 0.9 100.0

1986–1992 Forest Nonmechanically disturbed 4,089 2,358 1,606 4.5 67.3

Grassland/Shrubland Nonmechanically disturbed 1,068 1,513 1,030 1.2 17.6

Forest Mechanically disturbed 394 233 159 0.4 6.5

Mechanically disturbed Grassland/Shrubland 174 127 87 0.2 2.9

Grassland/Shrubland Water 106 143 98 0.1 1.7

Other Other 244 n/a n/a 0.3 4.0

Totals 6,075 6.7 100.0

1992–2000 Nonmechanically disturbed Grassland/Shrubland 4,488 2,538 1,729 5.0 66.6

Forest Nonmechanically disturbed 866 861 586 1.0 12.8

Mechanically disturbed Grassland/Shrubland 313 223 152 0.3 4.6

Forest Mechanically disturbed 169 139 95 0.2 2.5

Mechanically disturbed Forest 71 61 41 0.1 1.1

Other Other 834 n/a n/a 0.9 12.4

Totals 6,740 7.5 100.0

1973–2000

(overall)

Forest Nonmechanically disturbed 5,024 2,502 1,705 5.6 34.7

Nonmechanically disturbed Grassland/Shrubland 4,557 2,602 1,772 5.1 31.5

Forest Mechanically disturbed 1,133 610 416 1.3 7.8

Grassland/Shrubland Nonmechanically disturbed 1,116 1,512 1,030 1.2 7.7

Mechanically disturbed Grassland/Shrubland 833 532 362 0.9 5.8

Other Other 1,804 n/a n/a 2.0 12.5

Totals 14,466 16.0 100.0
Chapter 5—Middle Rockies Ecoregion 75

References Cited

Christensen, N.L., Agee, J.K., Brussard, P.F., Hughes, J., 

Knight, D.H., Minshall, G.W., Peek, J.M., Pyne, S.J., 

Swanson, F.J., Thomas, J.W., Wells, S., Williams, S.E., and 

Wright, H.A.. 1989, Interpreting the Yellowstone fires of 

1988—ecosystem responses and management implications: 

Bioscience, v. 39, no. 10, p. 678–685.

Hansen, A.J., Rasker R., Maxwell, B., Rotella, J.J., Johnson, 

J.D., Parmenter, A.W., Langner, U., Cohen, W.B., Lawrence, R.L., and Kraska, M.P.V., 2002, Ecological causes 

and consequences of demographic change in the New West: 

BioScience, v. 52, no. 2, p. 151–162.

Knight, D.H., and Wallace, L.L., 1989, The Yellowstone 

fires—issues in landscape ecology: BioScience, v. 39, no. 

10, p. 700–706.

Mohlenbrock, R.H., 2002, Where forests meet—The Black 

Hills are a crossroads of vegetation: Natural History Magazine Inc., accessed March 12, 2010, at http://findarticles.

com/p/articles/mi_m1134/is_5_111/ai_86684501/.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125. 

Ricketts, T.H., Dinerstein, E., Olson, D.M., Loucks, C.J., 

Eichbaum, W., DellaSala, D., Kavanagh, K., Hedao, P., 

Hurley, P., Carney, K., Abell, R., and Walters, S., eds.. 1999, 

Terrestrial ecoregions of North America—a conservation 

assessment: Washington, D.C., World Wildlife Fund, Island 

Press, p. 213–216.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., Wylie, 

B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 61, p. 650–662.

Wilkinson, T., 1999, The Forest Service sets off into uncharted 

territory: High Country News, November 8, 1999.
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Chapter 6

Montana Valley and Foothill Prairies Ecoregion

cases, the valleys are conduits for some of the largest rivers 

in the state, including Clark Fork and the Missouri, Jefferson, 

Madison, Flathead, Yellowstone, Gallatin, Smith, Big Hole, 

Bitterroot, and Blackfoot Rivers (fig. 2). The Montana Valley 

and Foothill Prairies Ecoregion also includes the “Rocky 

Mountain front,” an area of prairies along the eastern slope 

of the northern Rocky Mountains. Principal land uses within 

the ecoregion include farming, grazing, and mining. The 

valleys serve as major transportation and utility corridors and 

also contain the majority of Montana’s human population.

The Montana Valley and Foothill Prairies Ecoregion 

extends into 17 mostly rural counties throughout western 

Montana. Only three of the counties—Carbon, Yellowstone, 

and Missoula—are part of a metropolitan statistical area with 

By Janis L. Taylor

Ecoregion Description

The Montana Valley and Foothill Prairies Ecoregion 

comprises numerous intermountain valleys and low-elevation 

foothill prairies spread across the western half of Montana, 

on both sides of the Continental Divide (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997). The ecoregion, which covers approximately 64,658 km2

 (24,965 mi2), 

includes the Flathead Valley and the valleys surrounding 

Helena, Missoula, Bozeman, Billings, Anaconda, Dillon, and 

Lewistown (fig. 1). These valleys are generally characterized 

by shortgrass prairie vegetation and are flanked by forested 

mountains (Woods and others, 1999); thus, the valleys’ biotas 

with regards to fish and insects are comparable. In many 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Montana Valley and Foothill Prairies Ecoregion and surrounding ecoregions, showing land-use/land-cover classes 

from 1992 National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was 

subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 20 x 20 km sample blocks 

analyzed in study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. Also shown on map are parts of two Great Plains ecoregions: Northwestern Glaciated Plains (NWGLP) 

and Northwestern Great Plains. See appendix 3 for definitions of land-use/land-cover classifications.

Middle

Rockies

Northwestern

Glaciated Plains

NRK

NRK

NRK

NRK

MRK

Northwestern

Great Plains

Canadian

Rockies

Wyoming

Basin NRK SRB

MRK

MRK

NRK

NRK

NWGLP

SRB

CANADA

110°

108°

114° 112°

48°

46°

44°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

Butte

Virginia City 

Nevada City

Bannack

Dillon

Coolidge

Anaconda

Helena

Missoula

Deer Lodge

Bozeman

Lewistown

Billings

IDAHO

MONTANA

WYOMING

Clark

Fork

Missouri River

N O R T H E R N R O C K Y M T N S

Continental Divide

Flathead Valley

Blackfoot R.

Jefferson R.

Big Hole R.

Madison R.

Flathead R.

Yellow stone Riv er

Gallatin R.

Smit h R.

Bitterroot R.
78 Status and Trends of Land Change in the Western United States—1973 to 2000

contiguous built-up areas tied to an employment center. Nearly 

two-thirds of Montana residents live in nonmetropolitan 

counties (Albrecht, 2008). Ten of the counties within the 

ecoregion had population growth rates greater than national 

averages (9–13 percent) between 1970 and 2000 (table 1). 

Ravalli and Gallatin Counties had the highest growth rates. 

Population growth was largely due to amenity-related inmigration and an economy dependent on tourism, health care, 

and services. Counties that had population declines, such as 

Deer Lodge, Silver Bow, and Meagher Counties, also had 

declines in agriculture and mining activity, and they had 

railroad closures as well. 

Climate varies from north to south and from the east 

side of the Continental Divide to the west side. However, all 

areas are semiarid with long cold winters and short growing 

seasons. In the western part of the ecoregion, Beaverhead, 

Bitterroot, Flathead, and Lolo National Forests provide the 

natural resources, particularly timber, that form the economic 

base for towns within nearby valleys. Mineral resources from 

mines in and around Anaconda, Deer Lodge, and Butte have 

long provided an economic base for these towns (fig. 3). 

Contemporary Land-Cover 

Change (1973 to 2000)

The overall spatial change—the percentage of land area 

within the Montana Valley and Foothill Prairies Ecoregion 

where land cover changed at least once between 1973 and 

2000—was 8.1 percent (5,252 km2). Of that total, 6.5 percent 

(4,203 km2) changed one time, and 1.5 percent (970 km2) 

changed two or more times (table 2). Compared to the 

amount of overall change in each of the 30 western United 

States ecoregions, this ecoregion falls in the middle (fig. 4).

 Total percent change in each of the four time periods 

ranged from a low of 1.6 percent (1,039 km2) between 1973 

and 1980 to a high of 3.4 percent (2,229 km2) between 

1992 and 2000. When annualized, the rates of change 

ranged from a low of 0.2 percent (148 km2) per year 

between 1973 and 1980 to a high of 0.5 percent (317km2) 

per year between 1986 and 1992 (table 3; fig. 5).

Net change by time period for all land-use/land-cover 

classes are presented in figure 6. Grassland/shrubland 

accounted for 63.5 percent (41,030 km2) of the ecoregion 

in 1973. By 2000, an additional 1.7 percent (1,104 km2) 

of the ecoregion had converted into grassland/shrubland. 

Forest covered 18.3 percent (11,861 km2) of the ecoregion 

in 1973 and had a net decrease during the study period 

of 3.5 percent (421 km2). Agriculture covered 11.0 percent (7,115 km2

) of the land cover in 1973 and had a net 

decrease of 12.9 percent (920 km2) during the study period 

(table 4). Net change doesn’t always tell the whole story 

of change. Gross change, the area gained and lost by individual land-cover classes during each period, shows that, 

Figure 2. Headwaters of Missouri River in Montana Valley and 

Foothill Prairies Ecoregion. A, Satellite image showing Jefferson 

and Madison Rivers coming together to form Missouri River. 

Downstream from junction, note Gallatin River also joining 

Missouri River. B, View to west of junction of Jefferson and 

Madison Rivers. Photograph by Terry Sohl, 1999.

Figure 3. View of Trident Mine, Montana. Photograph by Terry 

Sohl, 1999.

N

Jefferson

River

Madison

River

Gallatin

River

Missouri

Rive

0 1 MILE r

0 1 KILOMETER

Junction of Jefferson

and Madison Rivers

© 2012 Google

A

B
Chapter 6—Montana Valley and Foothill Prairies Ecoregion 79

during the entire study period, individual classes fluctuated to a greater degree than net-change values reflect. 

This increased amount of gross change can be further 

explained by the top two land-cover conversions. Overall, the 

top two conversions between 1973 and 2000 were agriculture 

to grassland/shrubland (2,918 km2) and grassland/shrubland to 

agriculture (1,972 km2) (table 5). The mechanical disturbance 

of forest by logging was the third most common conversion 

during the study period (371 km2). The fourth and fifth most 

common conversions were forest to grassland/shrubland 

(344 km2) and grassland/shrubland to forest (301 km2), 

respectively. Grassland/shrubland to agriculture was the 

most common conversion in the first two time periods 

(1973–1980, 1980–1986), but this reversed in the last 

two time periods (1986–1992, 1992–2000) when agriculture to grassland/shrubland was the top conversion. This 

ecoregion has little developed land, and land-cover conversion to developed was very minor in all time periods.

When many of the valleys and prairies throughout the 

Montana Valley and Foothill Prairies Ecoregion were first 

homesteaded, farms and ranches sprang up, and some of them 

are still in existence (Malone, 1996). In the areas around 

Butte, Anaconda, and Deer Lodge, mining once brought 

great wealth to southwestern Montana. Towns like Virginia 

City, Nevada City, Bannack, and Coolidge formed around 

the search for gold, silver, and other minerals mined from the 

area (Malone, 1996). In its heyday, the Anaconda Mine was 

the richest mine on Earth. Many of the mining towns disappeared almost as quickly as they sprang up, whereas others 

stood the test of time and are still small towns today. Today 

(2012), the area around Anaconda, Butte, and the whole 

Upper Clark Fork River District are part of an Environmental 

Protection Agency Superfund site (Diamond, 2005). The 

ranching industry began about the same time as the mining 

industry. Cattle and sheep were raised to feed the miners and 

homesteaders, often replacing herds of buffalo and elk. Today 

(2012), ranching remains an important industry (fig. 7).

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Montana Valley and Foothill Prairies 

Ecoregion are represented by red bars 

in each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

Figure 4. Overall spatial change in Montana Valley and Foothill 

Prairies Ecoregion (MVFP; darker bars) compared with that of all 

30 Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportion of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial change 

in Montana Valley and Foothill Prairies Ecoregion (four time 

periods) labeled for clarity. See table 3 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
80 Status and Trends of Land Change in the Western United States—1973 to 2000

 In the 1970s, global demand for wheat increased greatly, 

and rangeland and other grassland that had not previously been 

broken was planted with wheat. This trend continued into the 

1980s as low-interest bank loans and tax credits for breaking 

new ground—also known as “sodbusting”—provoked speculators and investors to enter into farming (fig. 8). The trend of 

purchase, plow, and resell was also bolstered by National Farm 

Program incentives, such as diversion payments and deficiency payments (Watts and others, 1983). In the mid-1980s, 

the price of wheat plummeted as the world supplies became 

saturated, and farmers, both old and new, wanted out of farming. In 1986, the Conservation Reserve Program was started, 

in which farmers were paid to retire many of the fields broken 

in the 1970s (Leistritz and others, 2002). These national trends 

were seen to some degree in the Montana Valley and Foothill 

Prairies Ecoregion, with increases in agricultural land until 

1986 and then declines in agricultural land as it converted 

back to grassland/shrubland between 1986 and 2000.

Figure 8. Large farm operation with granaries and numerous 

outbuildings in Montana Valley and Foothill Prairies Ecoregion. 

Photograph by Terry Sohl, 1999.

Figure 6. Normalized average net change in Montana Valley 

and Foothill Prairies Ecoregion by time period for each land-cover 

class. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. Note that not all land-cover classes 

shown in explanation may be represented in figure. See appendix 

3 for definitions of land-use/land-cover classifications.

Figure 7. Sheep grazing in Montana Valley and Foothill Prairies 

Ecoregion. Photograph by Terry Sohl, 1999. −2

−1

0

1

2

1973–1980 1980–1986 1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Time period

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 6—Montana Valley and Foothill Prairies Ecoregion 81

Table 2. Percentage of Montana Valley and Foothill Prairies 

Ecoregion land cover that changed at least one time during study 

period (1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (91.9 percent), whereas 8.1 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 6.5 3.6 2.9 10.1 2.3 34.9

2 1.5 0.6 0.9 2.1 0.4 26.1

3 0.1 0.1 0.0 0.1 0.0 37.4

4 0.0 0.0 0.0 0.0 0.0 56.2

Overall 

spatial 

change

8.1 4.1 4.1 12.2 2.6 31.7

Table 1. Population change in 17 Montana counties between 1970 and 2000 (from Forstall, 1995).

County 1970 1980 1990 2000

Total 

change,

# of persons

Change

(Percent)

Metropolitan counties

Carbon County 7,080 8,099 8,080 9,552 2,472 34.9

Yellowstone County 87,367 108,035 113,419 129,352 41,985 48.1

Missoula County 58,263 76,016 78,687 95,802 37,539 64.4

Rural counties

Beaverhead County 8,187 8,186 8,424 9,202 1,015 12.4

Deer Lodge County 15,652 12,518 10,278 9,417 −6,235 −39.8

Fergus County 12,611 13,076 12,083 11,893 −718 −5.7

Flathead County 39,460 51,966 59,218 74,471 35,011 88.7

Gallatin County 32,505 42,865 50,463 67,831 35,326 108.7

Jefferson County 5,238 7,029 7,939 10,049 4,811 91.8

Lake County 14,445 19,056 21,041 26,507 12,062 83.5

Lewis and Clark County 33,281 43,039 47,495 55,716 22,435 67.4

Meagher County 2,122 2,154 1,819 1,932 −190 −9.0

Park County 11,197 12,660 14,562 15,694 4,497 40.2

Powell County 6,660 6,958 6,620 7,180 520 7.8

Ravalli County 14,409 22,493 25,010 36,070 21,661 150.3

Silver Bow County 41,981 38,092 33,941 34,606 −7,375 −17.6

Teton County 6,116 6,491 6,271 6,445 329 5.4
82 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Estimated area (and margin of error) of each land-cover class in Montana Valley and Foothill Prairies Ecoregion, calculated 

five times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 6.1 8.7 0.3 0.2 0.1 0.1 0.0 0.0 0.5 0.4 18.3 6.5 63.5 11.3 11.0 6.3 0.3 0.3 0.0 0.0

1980 6.1 8.7 0.3 0.2 0.0 0.0 0.0 0.0 0.5 0.4 18.3 6.5 63.1 11.2 11.4 6.6 0.3 0.3 0.0 0.0

1986 6.1 8.7 0.4 0.2 0.1 0.1 0.0 0.0 0.5 0.4 17.9 6.3 62.4 11.1 12.4 6.8 0.3 0.3 0.0 0.0

1992 6.1 8.7 0.4 0.2 0.2 0.2 0.0 0.0 0.5 0.4 17.6 6.2 64.0 11.0 11.0 5.3 0.3 0.3 0.0 0.0

2000 6.1 8.7 0.5 0.3 0.3 0.3 0.0 0.0 0.5 0.4 17.7 6.3 65.2 11.4 9.6 3.8 0.3 0.3 0.0 0.0

Net

change 0.0 0.0 0.1 0.1 0.2 0.3 0.0 0.0 0.0 0.0 −0.7 0.4 1.7 3.3 −1.4 3.4 0.0 0.0 0.0 0.0

Gross

change 0.0 0.0 0.1 0.1 0.4 0.4 0.0 0.0 0.0 0.0 1.0 0.5 5.4 3.8 5.1 3.8 0.0 0.0 0.0 0.0

Area, in square kilometers

1973 3,915 5,611 204 142 41 49 21 32 306 287 11,861 4,197 41,030 7,288 7,115 4,094 165 168 0 0

1980 3,915 5,611 221 150 22 26 21 32 306 287 11,834 4,172 40,811 7,261 7,356 4,262 172 178 0 0

1986 3,915 5,611 232 157 59 59 21 32 306 287 11,600 4,062 40,357 7,187 8,001 4,390 167 170 0 0

1992 3,916 5,611 259 159 107 149 21 32 306 287 11,403 4,023 41,379 7,132 7,098 3,426 169 174 0 0

2000 3,917 5,610 298 196 186 222 21 32 303 287 11,441 4,060 42,134 7,345 6,194 2,431 164 167 0 0

Net

change 2 3 93 78 145 175 0 0 −3 5 −421 286 1,104 2,152 −920 2,195 0 0 0 0

Gross

change 4 4 93 78 273 227 0 0 3 5 630 355 3,509 2,446 3,297 2,461 20 30 0 0

Table 3. Raw estimates of change in Montana Valley and Foothill Prairies Ecoregion land cover, 

computed for each of four time periods between 1973 and 2000, and associated error at 85-percent 

confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 1.6 0.5 1.1 2.1 0.3 21.3 0.2

1980–1986 1.8 0.7 1.1 2.6 0.5 24.4 0.3

1986–1992 2.9 1.7 1.2 4.6 1.1 36.6 0.5

1992–2000 3.4 2.6 0.8 6.0 1.7 47.9 0.4

Estimate of change, in square kilometers

1973–1980 1,039 348 691 1,387 221 21.3 148

1980–1986 1,193 459 734 1,652 291 24.4 199

1986–1992 1,903 1,095 808 2,998 696 36.6 317

1992–2000 2,229 1,680 549 3,909 1,067 47.9 279
Chapter 6—Montana Valley and Foothill Prairies Ecoregion 83

Table 5. Principal land-cover conversions in Montana Valley and Foothill Prairies Ecoregion, showing amount of area changed 

(and margin of error, calculated a 85-percent confidence level) for each conversion during each of four time periods and also 

during overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 529 290 184 0.8 50.9

Agriculture Grassland/Shrubland 291 112 71 0.5 28.0

Grassland/Shrubland Forest 46 50 32 0.1 4.5

Mechanically disturbed Grassland/Shrubland 41 48 31 0.1 3.9

Forest Grassland/Shrubland 39 40 26 0.1 3.8

Other Other 93 n/a n/a 0.1 8.9

Totals 1,039 1.6 100.0

1980–1986 Grassland/Shrubland Agriculture 729 359 228 1.1 61.1

Forest Grassland/Shrubland 193 185 118 0.3 16.1

Agriculture Grassland/Shrubland 104 54 34 0.2 8.7

Forest Mechanically disturbed 59 59 37 0.1 5.0

Grassland/Shrubland Forest 31 31 20 0.0 2.6

Other Other 78 n/a n/a 0.1 6.5

Totals 1,193 1.8 100.0

1986–1992 Agriculture Grassland/Shrubland 1,236 1,056 671 1.9 64.9

Grassland/Shrubland Agriculture 334 295 188 0.5 17.6

Forest Mechanically disturbed 106 148 94 0.2 5.6

Forest Grassland/Shrubland 101 115 73 0.2 5.3

Mechanically disturbed Grassland/Shrubland 58 58 37 0.1 3.1

Other Other 68 n/a n/a 0.1 3.6

Totals 1,903 2.9 100.0

1992–2000 Agriculture Grassland/Shrubland 1,288 1,552 986 2.0 57.8

Grassland/Shrubland Agriculture 380 235 149 0.6 17.1

Grassland/Shrubland Forest 198 293 186 0.3 8.9

Forest Mechanically disturbed 184 219 139 0.3 8.3

Mechanically disturbed Grassland/Shrubland 68 91 58 0.1 3.0

Other Other 111 n/a n/a 0.2 5.0

Totals 2,229 3.4 100.0

1973–2000

(overall)

Agriculture Grassland/Shrubland 2,918 2,525 1,604 4.5 45.8

Grassland/Shrubland Agriculture 1,972 817 519 3.1 31.0

Forest Mechanically disturbed 371 417 265 0.6 5.8

Forest Grassland/Shrubland 344 255 162 0.5 5.4

Grassland/Shrubland Forest 301 393 249 0.5 4.7

Other Other 457 n/a n/a 0.7 7.2

Totals 6,364 9.8 100.0
84 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Albrecht, D.E., 2008, Population brief—Trends in the western 

U.S., the State of Montana: Logan, Utah, Western Rural 

Development Center, accessed June 23, 2010, at http://wrdc.

usu.edu/files/publications/publication/pub__8289905.pdf.

Diamond, Jared, 2005, Collapse—How societies choose 

to fail or succeed: New York, Viking Penguin, 575 p.

Forstall, R.L., comp., 1995, Montana—Population of counties by decennial census: 1900 to 1990: U.S. Bureau 

of the Census, accessed March 1, 2011, at http://www.

census.gov/population/cencounts/mt190090.txt.

Leistritz, F.L., Hodur, N.M., and Bangsund, D.A., 2002, 

Socioeconomic impacts of the conservation reserve program 

in North Dakota: Rural America, v. 17, no. 3, p. 57–65. 

Malone, M.P., 1996, Montana—A contemporary profile: Helena, Montana, American & 

World Geographic Publishing, 200 p.

Omernik, J.M., 1987, Ecoregions of the conterminous United States: Annals of the Association of 

American Geographers, v. 77, no. 1, p. 118–125.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of 

the 1990s National Land Cover Data Set for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetric 

Engineering & Remote Sensing, v. 67, p. 650–662.

Watts, M.J., Bender, L.D., and Johnson, J.B., 1983, Economic incentives for converting rangeland to cropland: Bozeman, Montana State University, Cooperative Extension Service Bulletin 1302, 26 p.

Woods, A.J., Omernik, J.M., Nesser, J.A., Shelden, J., 

and Azevedo, S.H., 1999, Ecoregions of Montana: 

U.S. Geological Survey Ecoregion Map Series, scale 

1:1,500,000, available at http://rockyweb.cr.usgs.

gov/outreach/mapcatalog/environmental.html.
Chapter 7

Northern Rockies Ecoregion

Middle Rockies, Northwestern Great Plains, and Northwestern 

Glaciated Plains Ecoregions; also to the east, the Northern 

Rockies Ecoregion interfingers with the Montana Valley and 

Foothill Prairies Ecoregion, each enclosing some isolated 

areas of the other (fig. 1).

The ecoregion is composed of a series of high, rugged 

mountain ranges, mostly oriented northwest-southeast, with 

intermontane valleys between them (fig. 2). The entire ecoregion was glaciated during the Pleistocene (1,800,000 to 11,400 

years ago), and today numerous large lakes occupy basins 

By Janis L. Taylor

Ecoregion Description

The Northern Rockies Ecoregion (Omernik, 1987; U.S. 

Environmental Protection Agency, 1997) covers approximately 162,746 km2

 (63,200 mi2), primarily in Idaho but also 

including areas in western Montana and northeastern Washington (fig. 1). Canada forms the northern border of the ecoregion. To the west it is bordered by the Columbia Plateau and 

Blue Mountains Ecoregions, to the south by the Snake River 

Basin Ecoregion, and to the east by the Canadian Rockies, 

Figure 1. Map of Northern Rockies Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted on map; note 

also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed 

and nonmechanically disturbed classes. Note that all small areas entirely surrounded by Northern Rockies Ecoregion are parts of Montana 

Valley and Foothill Prairies Ecoregion. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map shows locations of 

geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. Also shown are parts of 

two Great Plains ecoregions: Northwestern Glaciated Plains (NWGLP) and Northwestern Great Plains (NWGP). See appendix 3 for definitions 

of land-use/land-cover classifications.

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Columbia

Plateau

Middle Rockies

MVFP

MVFP

MVFP

Snake River Basin

Blue

Mountains

Northern

Basin

and Range

Northwestern

Glaciated Plains

NWGLP

NWGP

WB

Canadian

Rockies

MVFP

MRK

MVFP

MRK

MVFP

MRK

BLM

MRK

NC

CANADA

120° 118° 116° 114° 112° 110°

48°

50°

46°

44°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Boise

Coeur

d’Alene

OREGON

WASHINGTON

IDAHO

MONTANA

WYOMING

Clark

Fork

Spokane R.

Pend Oreille R.

Missouri River

Columbia River

N O R T H E R N R O C K Y M T N S

SALMONCHALLIS NF

Continental Divide

Snake

Rive r

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
86 Status and Trends of Land Change in the Western United States—1973 to 2000

formed by glacial action (Omernik, 1987; Habeck and Mutch, 

1973). Streams draining these mountain ranges provide a 

water source for many western cities and towns (fig. 3). The 

Continental Divide, located at the highest elevations along the 

northern Rocky Mountains, separates rivers that flow westward into the Columbia River watershed from those that flow 

eastward into the Missouri River watershed.

The ecoregion consists of montane, subalpine, and alpine 

ecosystems that have distinct floral and faunal elevation zones, 

with the highest elevations in the southern part of the ecoregion. The lower elevation montane forest provides habitat 

for mule deer (Odocoileus hemionus), elk (Cervus elaphus), 

moose (Alces alces), mountain lions (Puma concolor), bears 

(Ursus spp.), and raptors (for example, bald eagles (Haliaeetus 

leucocephalus), Swainson’s hawks (Buteo swainsoni), and 

American kestrels (Falco sparverius)) (fig. 4). The winter 

snowfall supports a lucrative skiing and tourism economy, and 

ski resorts have been built throughout the midelevation subalpine forest. Alpine ecosystems occupy the highest elevations, 

where harsh climates support trees and shrubs with smaller, 

dwarfed structures and more dense ground cover (Barrera, 

2009). In addition to the vast conifer forests throughout the 

Northern Rockies Ecoregion, there are also many mountain 

meadows, foothill grasslands, and riparian woodlands (fig. 5). 

Climate within the Northern Rockies Ecoregion varies 

extensively from west to east, as well as north to south. The 

climate on the west side of the Rocky Mountains is moderated 

by a maritime influence, whereas the climate on the east side 

is harsher and more continental. Climate likewise varies from 

north to south across latitude. In general, the higher elevations 

receive more precipitation and have lower average temperatures. Orographic lifting of air masses over the mountains 

forces much of the moisture content to precipitate (primarily 

as snow). Because of the mountainous terrain, local microclimates are highly variable as a result of differences in slope 

aspect, exposure to prevailing wind, thermal inversions, and 

dry pockets (Ricketts and others, 1999).

This ecoregion is sparsely populated, but it has been 

occupied for more than 5,000 years by indigenous peoples 

who hunted throughout the foothills and valleys of the 

mountains. In the last two centuries, trappers, traders, and 

explorers led the tide of European settlers into the ecoregion. 

The Lewis and Clark expedition crossed through the northern 

Rocky Mountains twice on their journey to the Pacific Ocean 

and back. Miners and trappers explored every mountain and 

established the first industries in the ecoregion. After railroads 

made the ecoregion more accessible, hard-rock mines for gold, 

silver, lead, molybdenum, zinc, and even garnets were established. Along with mining, logging of the ecoregion’s vast 

conifer forests still provides its economic backbone (fig. 6).

Most land within the Northern Rockies Ecoregion is 

publicly owned, the largest part being under the control of the 

U.S. Forest Service. The first forest reserves in the ecoregion 

were established in the late 1800s. Today there are 15 different national forests and a number of state-owned forests 

in the ecoregion (fig. 7). Within the national forests are 10 

designated wilderness areas, including the 9,300-km2

 Frank 

Church–River of No Return Wilderness, the largest contiguous area of protected wilderness in the conterminous United 

States. There are also four U.S. Fish and Wildlife Service 

National Wildlife Refuges and several major hydroelectric 

dams along the ecoregion’s large rivers, the Clark Fork, the 

Pend Oreille River, and the Spokane River. 

The Coeur d’Alene metropolitan area in northern Idaho 

is the largest concentration of population in the ecoregion; 

in 2000 it had a population of around 100,000. Overall, this 

large ecoregion includes little developed land. The five Indian 

reservations within the ecoregion are the Flathead Reservation 

in Montana (fig. 8), the Colville and the Spokane Reservations in Washington, and the Coeur d’Alene and the Kootenai 

Reservations in Idaho. 

Figure 2. Intermontane valley located between parallel mountain 

ranges in Northern Rockies Ecoregion. Photograph by Janis 

Taylor, 2008. 

Figure 3. Water, in form of runoff and snowmelt from peaks, 

feeds rivers and has helped shape mountains in Northern Rockies 

Ecoregion. These mountain ranges can be considered water 

towers because they provide water source for many western 

cities and towns. Photograph by Janis Taylor, 2008.
Chapter 7—Northern Rockies Ecoregion 87

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change—the percentage of land area 

within the ecoregion where land cover changed at least once 

between 1973 and 2000—was 13.8 percent (22,539 km2). Of 

that total, 7.8 percent (12,769 km2) changed one time, and 5.0 

percent (8,192 km2) changed two or more times (table 1). This 

ecoregion had the fifth highest overall change among all western United States ecoregions (fig. 9). The four ecoregions that 

had higher overall change were the Puget Lowland, the Coast 

Range, the Cascades, and the Willamette Valley Ecoregions.

Total change in each of the four time periods selected 

for this study ranged from a low of 3.7 percent (6,057 km2

) 

between 1973 and 1980 to a high of 8.7 percent (14,242 km2) 

between 1992 and 2000. After normalizing to an annual rate 

of change, these two time periods still provided the extreme 

Figure 4. Lower elevation montane forest in Northern Rockies 

Ecoregion, which provides habitat for mule deer, elk, moose, mountain lions, raptors, and bears. Photograph by Janis Taylor, 2008.

Figure 5. Wet meadow occupying valley flat in Northern Rockies 

Ecoregion, with forested hillsides in distance. Photograph by 

Janis Taylor, 2008.

Figure 6. Effect of logging of vast conifer forests in Northern 

Rockies Ecoregion is seen in large cut area on near slope of this 

hillside. Photograph by Janis Taylor, 2008.

Figure 7. Salmon-Challis National Forest is just one of 15 

national forests within Northern Rockies Ecoregion. Photograph 

by Janis Taylor, 2008.

Figure 8. Flathead Reservation is just one of five reservations within 

Northern Rockies Ecoregion. Photograph by Janis Taylor, 2008.
88 Status and Trends of Land Change in the Western United States—1973 to 2000

values: 0.5 percent (818 km2) per year and 1.1 percent 

(1,801km2) per year, respectively (table 2; fig. 10). 

Between 1973 and 1980, forest and grassland/shrubland 

combined to account for 90 percent (146,557 km2) of the land 

cover in the ecoregion (fig. 11). The amount of forest decreased 

from 72.2 percent (117,534 km2) of the ecoregion in 1973 to 

66.5 percent (108,290 km2) in 2000 (table 3). The amount of 

grassland/shrubland increased from 17.8 percent (29,023 km2) 

of the ecoregion in 1973 to 20.3 percent (32,962 km2) in 2000. 

Net changes in land-use/land-cover classes by period are 

found in figure 12.

The top four land-cover conversions are forest to 

mechanically disturbed, forest to nonmechanically disturbed, mechanically disturbed to grassland/shrubland, and 

grassland/shrubland to forest. These changes are all components of forest change resulting from logging, wildfires, 

and insect-caused mortality, all common occurrences in the 

Rocky Mountains. In the first three time periods (1973–1980, 

1980–1986, and 1986–1992), the most common land-cover 

conversion was the result of timber harvest, in which forest 

is converted to mechanically disturbed land, which regrows 

to grassland/shrubland and eventually back to forest, representing a cyclic pattern of land-cover change (table 4). Large 

wildfires (fig. 13) and (or) increased insect mortality (fig. 14) 

in the last time period (1992–2000) made forest to nonmechanically disturbed the most common land-cover conversion for that time period. 

The continuing pattern of timber harvest is supported 

by the fact that there were areas of mechanically disturbed 

land in all time periods between 1973 and 2000; 1.9 percent 

(3,057 km2

) of land was classified as mechanically disturbed 

in 1973 and 1.1 percent (1,749 km2) in 2000 (table 3). New 

forest areas were logged in each of the time periods, and these 

return to grassland/shrubland and eventually to forest land 

cover in subsequent time periods. 

Figure 9. Overall spatial change in Northern Rockies Ecoregion 

(NRK; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that experienced change during one, 

two, three, or four time periods; highest level of spatial change in 

Northern Rockies Ecoregion (four time periods) labeled for clarity. 

See table 2 for years covered by each time period. See appendix 2 

for key to ecoregion abbreviations.

Figure 10. Estimates of land-cover change per time period, normalized to annual rates 

of change for all 30 Western United States ecoregions (gray bars). Estimates of change 

for Northern Rockies Ecoregion are represented by red bars in each time period.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods
Chapter 7—Northern Rockies Ecoregion 89

The conversion of forest to nonmechanically disturbed 

land—resulting from wildfires and insect-caused mortality—

was not as common in earlier time periods, and the cyclic pattern of land-cover change in forest land was not as prominent. 

The amount of nonmechanically disturbed land cover was only 

0.4 percent (712 km2) in 1973, increasing dramatically in the 

last time period to 4.7 percent (7,624 km2) in 2000, a pattern 

common throughout the western United States.

This ecoregion provides numerous ecosystem services. 

Probably the most important is the large amounts of fresh 

water demanded by rapidly growing urban populations in 

neighboring ecoregions, as well as for agricultural irrigation, 

industry, and power generation. Other ecosystem services 

include wildlife habitat, timber, and snow-based recreation 

such as ski resorts. Local economies promote tourism through 

outdoor recreation opportunities, including hiking, backpacking, hunting, fishing, whitewater rafting, mountain biking, 

skiing, and snowmobiling. 

Even though mining was only a minor land cover identified during the study period, there is a long history of mining 

activity throughout the northern Rocky Mountains. Today, 

there are numerous abandoned mines, as well as associated 

Figure 13. Trees killed during wildfire that burned through previously logged areas in Northern Rockies Ecoregion. Photograph by 

Janis Taylor, 2008.

Figure 14. Trees killed by insects can be seen on hillside in 

Northern Rockies Ecoregion. Photograph by Janis Taylor, 2008.

−6

−4

−2

0

2

4

6

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 11. Grassland/shrubland land cover in Northern Rockies 

Ecoregion. Photograph by Janis Taylor, 2008.

Figure 12. Normalized average net change in Northern Rockies 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.
90 Status and Trends of Land Change in the Western United States—1973 to 2000

mine tailings, contaminated soils and waterways, and erosion. 

Many of these mines have had documented impacts on fisheries and vegetation throughout the northern Rocky Mountains 

(U.S. Environmental Protection Agency, 2001; Montana 

Department of Environmental Quality, 2009) (fig. 15). Some 

abandoned open-pit mines have become small mountain lakes. 

Other mines have reopened with the resurgence in the price 

of metals. The Coeur d’Alene mining district in Shoshone 

County in northern Idaho is still considered one of the richest 

metal mining areas in the world.

Aside from timber harvesting, wildfires and insectcaused mortality are the major disturbance regimes in the 

Northern Rockies Ecoregion. Human control of wildfires, 

notably the fire-suppression efforts between 1930 and 1950, 

have altered the size, incidence, and location of wildfires 

(Gruell, 1983). As a result, by 1950 the size and intensity 

of wildfires had grown significantly (Arno, 1980). In the 

1980s, these suppression tactics ceased; wildfires were again 

allowed to burn, and there were notable fires in the SelwayBitterroot Wilderness and Kootenai National Forest (Arno 

and Allison-Bunnell, 2002). Scientists continue to study the 

role of fire as a natural process and its effects on people, 

wildlife, soil, and water.

Forest recovery has also been studied thoroughly since 

the 1980s; the following are a couple of findings that are 

reflected in the state of land cover through time. Some areas 

that have burned more than one time have the potential to 

stay in a grassland/shrubland state for a longer period of 

time than those burned just once. Disturbances that occur 

near timberline can also expect a slow recovery (Arno and 

Allison-Bunnell, 2002). On the basis of their study, the overall 

increase in the amount of grassland/shrubland may, in part, be 

a result of multiple wildfires at high elevations. 

Current research indicates that climate change will result 

in a higher likelihood of wildfires and insect-caused mortality (Carter, 2003). In this ecoregion, the number of frost-free 

days per year has already increased, and there have been fewer 

extended periods of very cold temperatures during winter. 

Because of these changes, in combination with recurring 

drought, scientists predict an increase in insect infestations 

(Shore and others, 2003), killing more trees and thus adding to 

a higher potential for regional fire events.

Figure 15. Example of impact from numerous abandoned mines 

throughout Northern Rockies Ecoregion, showing mine tailings, 

contaminated soils and waterways, and erosion. Photograph by 

Janis Taylor.

Table 1. Percentage of Northern Rockies Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (86.2 percent), whereas 13.8 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 7.8 2.9 4.9 10.8 2.0 25.5

2 5.0 1.7 3.3 6.8 1.2 23.5

3 0.9 0.6 0.3 1.5 0.4 45.0

4 0.0 0.1 0.0 0.1 0.0 75.4

Overall 

spatial 

change

13.8 3.9 9.9 17.8 2.7 19.2
Chapter 7—Northern Rockies Ecoregion 91

Table 2. Raw estimates of change in Northern Rockies Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 3.7 1.7 2.0 5.4 1.2 31.5 0.5

1980–1986 3.9 1.8 2.1 5.7 1.2 30.9 0.7

1986–1992 4.5 1.5 3.0 6.1 1.0 22.8 0.8

1992–2000 8.7 2.9 5.8 11.6 2.0 22.6 1.1

Estimate of change, in square kilometers

1973–1980 5,990 2,774 3,217 8,764 1,884 31.5 856

1980–1986 6,408 2,912 3,496 9,320 1,978 30.9 1,068

1986–1992 7,394 2,485 4,909 9,879 1,688 22.8 1,232

1992–2000 1,4169 4,710 9,459 18,879 3,200 22.6 1,771

Table 3. Estimated area (and margin of error) of each land-cover class in Northern Rockies Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.8 0.8 0.3 0.3 1.9 1.0 0.0 0.0 3.0 1.6 72.2 5.3 17.8 3.7 3.2 2.7 0.4 0.2 0.4 0.6

1980 0.8 0.8 0.4 0.5 1.0 0.5 0.0 0.0 3.0 1.6 71.5 5.3 19.9 3.5 3.0 2.5 0.4 0.2 0.0 0.0

1986 0.8 0.8 0.5 0.6 1.3 0.6 0.0 0.0 3.0 1.6 71.2 5.4 19.6 3.5 3.0 2.5 0.4 0.2 0.3 0.3

1992 0.8 0.8 0.6 0.8 1.6 0.6 0.0 0.0 3.0 1.6 70.5 5.4 20.1 3.8 2.8 2.2 0.4 0.2 0.2 0.1

2000 0.8 0.8 0.7 0.9 1.1 0.4 0.0 0.0 3.0 1.6 66.5 5.6 20.3 3.7 2.5 2.0 0.4 0.2 4.7 2.9

Net

change 0.0 0.0 0.4 0.6 −0.8 0.9 0.0 0.0 0.0 0.0 −5.7 3.2 2.4 1.3 −0.6 1.0 0.0 0.0 4.2 3.0

Gross

change 0.0 0.0 0.4 0.6 4.2 1.4 0.0 0.0 0.0 0.0 9.3 3.2 5.8 2.3 0.8 1.0 0.0 0.0 6.0 2.9

Area, in square kilometers

1973 1,290 1,280 495 529 3,057 1,584 21 17 4,833 2,540 117,534 8,592 29,023 6,012 5,131 4,348 646 274 712 1,036

1980 1,275 1,277 694 804 1,555 885 37 26 4,842 2,540 116,362 8,611 32,412 5,752 4,920 4,089 629 264 20 20

1986 1,266 1,260 813 947 2,059 964 27 23 4,844 2,542 115,864 8,786 31,834 5,765 4,899 4,026 624 262 515 547

1992 1,274 1,277 1,031 1,246 2,673 976 38 34 4,840 2,540 114,770 8,821 32,725 6,147 4,515 3,610 628 264 248 206

2000 1,274 1,277 1,212 1,466 1,749 678 61 56 4,842 2,541 108,290 9,114 32,962 6,097 4,102 3,231 628 265 7,624 4,666

Net

change −16 24 717 938 −1,308 1,500 40 57 9 9 −9,244 5,237 3,939 2,183 −1,030 1,559 −18 21 6,913 4,847

Gross

change 63 52 717 938 6,865 2,272 61 56 18 16 15,086 5,219 9,364 3,794 1,244 1,555 36 35 9,753 4,707
92 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Northern Rockies Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Mechanically disturbed Grassland/Shrubland 2,697 1,535 1,043 1.7 45.0

Forest Mechanically disturbed 1,543 881 599 0.9 25.8

Nonmechanically disturbed Grassland/Shrubland 707 1,029 699 0.4 11.8

Mechanically disturbed Forest 336 261 177 0.2 5.6

Grassland/Shrubland Forest 162 116 79 0.1 2.7

Other Other 545 n/a n/a 0.3 9.1

Totals 5,990 3.7 100.0

1980–1986 Forest Mechanically disturbed 2,018 949 644 1.2 31.5

Grassland/Shrubland Forest 1,879 1,596 1,084 1.2 29.3

Mechanically disturbed Grassland/Shrubland 1,363 860 584 0.8 21.3

Forest Nonmechanically disturbed 433 495 336 0.3 6.8

Mechanically disturbed Forest 169 138 94 0.1 2.6

Other Other 545 n/a n/a 0.3 8.5

Totals 6,408 3.9 100.0

1986–1992 Forest Mechanically disturbed 2,597 949 644 1.6 35.1

Mechanically disturbed Grassland/Shrubland 1,672 925 628 1.0 22.6

Grassland/Shrubland Forest 1,286 921 625 0.8 17.4

Nonmechanically disturbed Grassland/Shrubland 427 457 310 0.3 5.8

Mechanically disturbed Forest 346 227 154 0.2 4.7

Other Other 1,066 n/a n/a 0.7 14.4

Totals 7,394 4.5 100.0

1992–2000 Forest Nonmechanically disturbed 6,906 4,510 3,064 4.2 48.7

Forest Mechanically disturbed 1,729 673 457 1.1 12.2

Mechanically disturbed Grassland/Shrubland 1,727 713 484 1.1 12.2

Grassland/Shrubland Forest 1,476 700 475 0.9 10.4

Mechanically disturbed Forest 722 500 340 0.4 5.1

Other Other 1,609 n/a n/a 1.0 11.4

Totals 14,169 8.7 100.0

1973–2000

(overall)

Forest Mechanically disturbed 7,888 2,834 1,926 4.8 23.2

Forest Nonmechanically disturbed 7,459 4,494 3,053 4.6 22.0

Mechanically disturbed Grassland/Shrubland 7,458 3,575 2,429 4.6 22.0

Grassland/Shrubland Forest 4,803 2,986 2,028 3.0 14.1

Mechanically disturbed Forest 1,573 867 589 1.0 4.6

Other Other 4,780 n/a n/a 2.9 14.1

Totals 33,962 20.9 100.0
Chapter 7—Northern Rockies Ecoregion 93

References Cited

Arno, S.F., 1980, Forest fire history in the Northern Rockies: 

Journal of Forestry, v. 78, p. 460–465. 

Arno, F.A., and Allison-Bunnell, S., 2002, Flames in our forest—disaster or renewal?: Washington, D.C., Island Press, 

245 p.

Barrera, L., 2009, Portraits of climatic change; the Rocky 

Mountains: World Watch, v. 22, no. 4, p. 8–16. 

Carter, L.M., 2003, US National Assessment of the potential consequences of climate variability and change: U.S. 

Climate Change Science Program / U.S. Global Change 

Research Program, Educational Resources Regional Paper, 

Rocky Mountain / Great Basin Region, accessed on January 

12, 2009, at http://www.usgcrp.gov/usgcrp/nacc/education/

rockies-greatbasin/rockiesandgreatbasin-edu-2.htm. 

Gruell, G.E., 1983, Fire and vegetative trends on the Northern 

Rockies; interpretations from 1871-1982 photographs: U.S. 

Department of Agriculture, Forest Service, Intermountain 

Research Station, General Technical Report INT-GTR-158, 

available at http://www.fs.fed.us/rm/pubs_int/int_gtr158.html.

Habeck, J.R., and Mutch, R.W., 1973, Fire dependent forests 

in the Northern Rocky Mountains: Quaternary Research, 

v. 3, p. 408–424.

Montana Department of Environmental Quality, 2009, Site 

update, January 2009: Montana Department of Environmental Quality, Mike Horse Messenger, available at http://www.

deq.mt.gov/statesuperfund/ubmc/default.mcpx. 

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125. 

Ricketts, T.H., Dinerstein, E., Olson, D.M.. Loucks, C.J., 

Eichbaum, W., DellaSala, D., Kavanagh, K., Hedao, P., 

Hurley, P., Carney, K., Abell, R., and Walters, S. eds.. 1999, 

Terrestrial ecoregions of North America—a conservation 

assessment: Washington, D.C., World Wildlife Fund, Island 

Press, p. 213–216.

Shore, T.L., Brooks, J.E., and Stone J.E, eds., 2003, Mountain Pine Beetle Symposium—challenges and solutions, 

October 30-31, 2003, Kelowna, British Columbia: Natural 

Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, B.C., Information Report BC-X-399, 

298 p., available at http://www.for.gov.bc.ca/hfd/library/

mpb/bib93473.pdf.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

U.S. Environmental Protection Agency, 2001, Part 7, Summary: Coeur d’Alene Basin RI/FS Section 1.0, RAC, U.S. 

Environmental Protection Agency Region 10, Final RI 

Report, September 2001, accessed on October 29, 2009 at 

http://yosemite.epa.gov/R10/CLEANUP.NSF/74e73c4c720

b643888256cdb006958af/427ff0cc21e14b9d88256ce70077

5f48/$FILE/1.0%20Introduction_text%20only.pdf. 

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., Wylie, 

B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 67, p. 650–662.
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Chapter 8

Southern Rockies Ecoregion

the Arizona/New Mexico Plateau Ecoregion on the south, 

and the Northwestern Great Plains, Western High Plains, 

and Southwestern Tablelands Ecoregions on the east (fig. 

1). The ecoregion receives most of its annual precipitation 

(25–100 cm) as snowfall, which provides a significant amount 

of high-elevation snowpack that is an important water source 

for surrounding ecoregions. The Southern Rockies Ecoregion 

has a steep elevation gradient from low foothills to high peaks, 

with several hundred summits higher than 3,660 m (12,000 ft). 

As a southern extension of the larger Rocky 

Mountain system, it is composed primarily 

of seven main north-south trending mountain ranges that are separated by four large 

intermontane basins. A fifth basin, the San 

Luis Valley, is outside the ecoregion, forming a northern finger of the Arizona/New 

Mexico Plateau Ecoregion that lies mostly 

to the south. To the east, late Tertiary sand 

and gravel deposits that were eroded from 

the relatively young Rocky Mountains were 

carried eastward by streams, forming the 

nearby Western High Plains Ecoregion and 

its underlying Ogallala aquifer. 

By Mark A. Drummond

Ecoregion Description

The Southern Rockies Ecoregion is a high-elevation 

mountainous ecoregion that covers approximately 138,854km2 

(53,612 mi2), including much of central Colorado and parts 

of southern Wyoming and northern New Mexico (fig. 1) 

(Omernik, 1987; U.S. Environmental Protection Agency, 

1997). It abuts six other ecoregions: the Wyoming Basin 

and Colorado Plateaus Ecoregions on the north and west, 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Southern Rockies Ecoregion 

and surrounding ecoregions, showing land-use/

land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); 

note that not all land-use/land-cover classes 

shown in explanation may be depicted on map; 

note also that, for this “Status and Trends of Land 

Change” study, transitional land-cover class 

was subdivided into mechanically disturbed and 

nonmechanically disturbed classes. Squares 

indicate locations of 10 x 10 km sample blocks 

analyzed in study. Index map shows locations of 

geographic features mentioned in text. Abbreviations for Western United States ecoregions 

are listed in appendix 2. Also shown on map are 

three Great Plains ecoregions: Northwestern 

Great Plains, Western High Plains, and Southwestern Tablelands. See appendix 3 for definitions of land-use/land-cover classifications.

36°

Wyoming Basin

Colorado

Plateaus

Arizona/

New Mexico

Plateau

Southwestern

Tablelands

Western

High

Plains

Northwestern

Great Plains

MRK

Arizona/

New Mexico

Mountains

ANMP

WUM

106°

104°

108°

42°

40°

38°

36°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

Aspen

Breckenridge Denver

Salida

SUMMITVILLE

MINE

Vail

Cheyenne

Santa Fe

Gunnison

ROUTT NF

R O C K Y M T N S FRONT RANGE

COLORADO

WYOMING

NEW MEXICO

70

San Luis

Valley
96 Status and Trends of Land Change in the Western United States—1973 to 2000

Approximately 56 percent of the ecoregion is forested 

in a heterogeneous pattern, whereas grassland/shrubland 

cover makes up nearly 38 percent of the total area (table 1). 

There are many forest types, including the more prevalent 

spruce-fir (Picea spp. and Abies spp.), ponderosa pine (Pinus 

ponderosa), lodgepole pine (Pinus contorta), aspen (Populus 

tremuloides), and pinyon-juniper (Pinus edulis and Juniperus 

scopulorum, monosperma, and osteosperma) types. Vegetation patterns correspond with the steep elevation gradient. 

In general, grassland and shrubland covers the lower elevation valleys and intermontane basins. Sagebrush (Artemisia 

tridentata), oak (Quercus spp.), pinyon-juniper woodland, and 

blue grama grass (Bouteloua gracilis) are common at lower 

elevations, which range from 1,828 to 2,438 m (Chapman 

and others, 2006). Ponderosa pine, aspen, juniper, and oak are 

common at middle elevations. The higher elevation subalpine 

forests are often dense, consisting of Engelmann spruce (Picea 

engelmannii) and subalpine fir (Abies lasiocarpa). High-elevation alpine zones are above the tree line and support a variety 

of low shrubs, wildflowers, krummholz (stunted trees), and 

other vegetation interspersed with exposed rocks, peaks, and 

permanent snowfields.

Many of the forest systems are heavily influenced by 

disturbances, particularly those caused by fire and insects, but 

high winds, avalanches, and disease are also factors. Forests 

of lodgepole pine, ponderosa pine, and aspen have all been 

affected by frequent low-intensity fires (Buskirk and others 

2000). The low-intensity fire regimes have been altered by 

historical land-management practices of fire exclusion and 

suppression, contributing to higher density, even-aged forest 

stands as well as high-intensity, stand-replacing fires from the 

resulting heavy fuel loads. Substantial areas of western North 

American coniferous forest have been affected since 2000 

by bark beetle (Dendroctonus spp., Ips spp., and Dryocoetes 

confusus) outbreaks related to climate variability and change 

(fig. 2). Drought and warming amplify the effects of insect 

outbreaks and also cause additional tree mortality and forest 

dieback (Breshears and others, 2005; van Mantgem and others, 

2009). Atmospheric warming and precipitation changes may 

have a significant effect on the future elevations of upper and 

lower tree lines. Blowdown events can be substantial—high 

winds downed an 80-km2

 area of spruce trees in the Routt 

National Forest in 1997 (Neely and others, 2001). 

The human population of the Rocky Mountains is growing three times faster than the national rate (Baron and others, 

2000). Despite the high rate of population growth, the Southern Rockies Ecoregion had no towns of more than 15,000 

people during the study period. The permanent populations of 

many of the larger towns range from 3,000 to 6,000 people, 

including the more agriculturally inclined cities of Gunnison 

and Salida in central Colorado, as well as the ski towns of 

Breckenridge, Vail, and Aspen, Colorado. Besides the permanent population, many amenity-rich areas have a significantly 

higher seasonal population. Breckenridge had 2,366 permanent residents in 2000, but of the 4,229 total housing units, 

3,166 were vacant, primarily because of seasonal use patterns 

Figure 2. Example of beetle-killed trees (with brown needles) in 

central Colorado.

Figure 3. Valley development along Interstate 70 corridor near 

Vail, Colorado.

(U.S. Census Bureau, 2000). Several large cities, including 

Denver, Colorado, and other Front Range communities lie just 

outside this ecoregion, and their suburbs and other exurban 

development has spread into the Southern Rockies Ecoregion. 

The Interstate 70 corridor that cuts across Colorado is also a 

central locus of new residential, commercial, and economic 

development, although growth and tourism reach many rural 

communities as well.

The steep elevation gradient is important to land-use 

and land-ownership patterns. Large tracts of high-elevation 

forest and wilderness are publically owned, whereas many 

of the small towns characteristic of the ecoregion are located 

in the valleys and near riparian zones (fig. 3). Approximately 

40 percent of the region is privately owned, and 60 percent is 

managed as public land. More than 80 percent of the public 

land is managed by the U.S. Forest Service. The numerous 

amenity-rich rural areas and recreation opportunities, including national parks and monuments, other public lands, and ski 

resorts, play a role in attracting new development, tourism, 
Chapter 8—Southern Rockies Ecoregion 97

and regional population growth. Land-use changes in the valley bottoms, which are often disproportionately rich in habitat 

diversity, can affect wildlife and habitat connectivity when 

grasslands, shrublands, and riparian areas are lost or fragmented by development (Theobald and others, 1996). Similarly, the subdivision of valley ranches into smaller “ranchette” developments is a concern for biodiversity (Mitchell and 

others, 2002; Theobald and others, 1996). Land-cover changes 

also occur as residential development spreads into nearby forest edges (fig. 4). 

Timber harvesting in the Rocky Mountain region 

accounts for approximately 5 percent of the national total 

(Darr, 1995). In the Southern Rockies Ecoregion, forest 

regeneration after clearcutting is slow compared to many 

other United States ecoregions because of the shorter growing 

season and relatively dry climate. This makes the ecoregion 

less attractive for large-scale industrial silviculture, although 

the recent forest die-off may cause an increase in timber 

clearance. Reservoir construction also affects the ecoregion, 

particularly as agricultural land uses and cities along the drier 

Front Range require an increasing reliable supply of water. 

Agriculture in the Southern Rockies Ecoregion is primarily 

related to livestock grazing (fig. 5), which occurs on both private and public lands, and hay production (fig. 6). Abandoned 

or reclaimed precious metal mines are a relatively common 

feature (fig. 7).

Contemporary Land-Cover Change 

(1973 to 2000)

Land-cover changes between 1973 and 2000 were very 

low (fig. 8), with no net or gross changes greater than 1.0 

percent of ecoregion area for any time period or land-cover 

class (table 1). Net forest land declined by an estimated 0.6 

percent (452 km2), which is the highest amount of net change 

in absolute terms (fig. 9). Forest land also had a relatively 

Figure 4. Exurban development near Colorado’s western slope.

Figure 5. Cattle and maintained pasture in south-central Colorado.

Figure 6. Hay field with aspen and coniferous forest in background in Southern Rockies Ecoregion.

Figure 7. Summitville Mine Superfund Site in southern part of 

Colorado. 
98 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 8. Overall spatial change in Southern Rockies Ecoregion 

(SRK; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Southern 

Rockies Ecoregion (four time periods) labeled for clarity. See table 

4 for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations. 

Figure 9. Estimates of net land-cover change in Southern 

Rockies Ecoregion for each land-cover class between 1973 and 

2000. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. See appendix 3 for definitions of 

land-use/land-cover classifications.

Figure 10. Normalized average net change in Southern Rockies 

Ecoregion by time period for each land cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

high level of gross change (684 km2), in comparison to the 

other land-cover types. Grassland/shrubland and mechanically 

disturbed land had the highest gross changes, at 1,021 km2 and 

848 km2, respectively. 

The declines in forest resulted from mechanical disturbance (table 2), which is caused primarily by clearcutting and 

other timber harvest practices. A smaller amount of forest 

recovered from mechanical disturbance during the study 

period, indicating the slow recovery of those forests. Most 

of the reforestation occurred from an intermediate cover of 

grassland/shrubland that followed mechanical disturbance. 

Additional forest land was lost to mining and developed land. 

The largest extent of forest loss, 299 km2

, occurred between 

1986 and 1992 (fig. 10).

The gross changes in grassland/shrubland were related 

to mechanical disturbance of forest that caused an intermediate stage of vegetated land cover. Switches between 

−0.5

0

0.5

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed,

as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 8—Southern Rockies Ecoregion 99

grassland/shrubland and agriculture also caused gross change, 

but these resulted in only a small amount of agricultural 

expansion (59 km2). Gains in agriculture between 1973 and 

1980 and between 1980 and 1986 were offset somewhat by 

conversion to grassland/shrubland between 1986 and 1992, 

when the Conservation Reserve Program (CRP) may have 

had an impact. The CRP, enacted by Congress in 1985, pays 

farmers to take marginal cropland out of production and return 

it to a seminatural grassland condition. Switches between 

grassland/shrubland and mining, which occur as mining 

areas expand and are eventually able to recover to vegetated 

land cover, resulted in minor losses to mining. Development 

expanded into some grassland/shrubland areas.

The two most common types of land conversion involved 

mechanical disturbance. Forest to mechanically disturbed, 

discussed above, was the most common conversion (518 km2

), 

followed by mechanically disturbed to grassland/shrubland 

(462 km2). Because this a transitional land cover, it experienced little net change and a high rate of gross change, which 

affected 0.6 percent of ecoregion area. 

Developed land increased by only 13 percent during the 

study period but still occupied only 0.6 percent of the ecoregion. The remaining land-cover types had negligible amounts 

of net change.

Overall, only 1.0 percent of the ecoregion’s land 

cover changed between 1973 and 2000 (table 3). The rates 

of change during each time period were consistently low 

(table 4; fig. 11). Compared to other western United States 

Figure 11. Estimates of land-cover change per time period, normalized to annual rates 

of change for all 30 Western United States ecoregions (gray bars). Estimates of change 

for Southern Rockies Ecoregion are represented by red bars in each time period.

ecoregions, change in the Southern Rockies Ecoregion was 

very low (fig. 8). Relatively small amounts of change, combined with some variability in the rates of change between 

the 36 sample sites, resulted in high margins of error. More 

than one-third of the sample blocks had no change or negligible change during all time periods, which is reflective of a 

large amount of relatively stable land use. This contrasts with 

the much smaller area undergoing intense land conversion, 

such as development in valleys and the suburban and exurban 

growth associated with the Front Range urban corridor and 

Interstate 70. 

Land use in the West is often cited as undergoing a 

conversion from a resource-extraction economy to one that is 

increasingly based on service and technical industries. This is 

accompanied by population expansion, as technology allows 

telecommuting and a move towards amenity-rich mountain 

areas. The change analysis does not target the specific locations where the much-discussed amenity-driven land conversion occurs. However, it does provide a regional overview of 

land-cover change that reflects the large expanses of land in 

public ownership, whereas other case studies provide an indepth understanding of the intensive local-scale changes.

Since 2000, the Southern Rockies Ecoregion has also 

undergone a substantial amount of forest change. Significant 

areas of forest are affected by insect outbreaks and the amplifying effects of drought and climate warming. This will likely 

have a host of consequences affecting fire regimes, logging, carbon sequestration, hydrology, ecosystem function, and tourism. 

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
100 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 1. Estimated area (and margin of error) of each land-cover class in Southern Rockies Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications. 

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.1 0.1 0.5 0.4 0.1 0.0 0.1 0.0 1.1 0.6 56.3 6.4 37.5 5.4 2.8 1.7 1.4 1.0 0.0 0.0

1980 0.2 0.1 0.6 0.5 0.0 0.0 0.1 0.0 1.1 0.6 56.3 6.4 37.5 5.4 2.8 1.8 1.4 1.0 0.0 0.0

1986 0.2 0.1 0.6 0.5 0.1 0.0 0.1 0.1 1.1 0.6 56.3 6.4 37.4 5.4 2.9 1.8 1.4 1.0 0.0 0.0

1992 0.2 0.1 0.6 0.5 0.2 0.2 0.1 0.1 1.1 0.6 56.1 6.3 37.5 5.4 2.8 1.7 1.4 1.0 0.0 0.0

2000 0.2 0.1 0.6 0.5 0.1 0.0 0.1 0.1 1.1 0.6 56.0 6.3 37.7 5.3 2.8 1.7 1.4 1.0 0.0 0.0

Net

change 0.0 0.0 0.1 0.1 0.0 0.1 0.0 0.0 0.0 0.0 −0.3 0.2 0.2 0.2 0.0 0.1 0.0 0.0 0.0 0.0

Gross

change 0.1 0.1 0.1 0.1 0.6 0.4 0.1 0.1 0.0 0.0 0.5 0.2 0.7 0.3 0.3 0.2 0.1 0.0 0.0 0.0

Area, in square kilometers

1973 197 137 731 599 71 55 77 56 1,528 826 78,228 8,857 52,120 7,490 3,887 2,410 1,983 1,349 0 0

1980 244 161 771 627 28 18 88 66 1,529 826 78,221 8,857 52,046 7,481 3,955 2,487 1,940 1,347 0 0

1986 260 166 791 640 95 60 157 138 1,528 826 78,138 8,840 51,919 7,467 4,005 2,491 1,929 1,347 0 0

1992 241 159 805 642 331 248 169 160 1,529 826 77,839 8,763 52,055 7,464 3,936 2,394 1,917 1,347 0 0

2000 249 162 826 646 89 64 137 121 1,529 826 77,776 8,753 52,350 7,388 3,946 2,375 1,915 1,347 4 5

Net

change 52 50 94 70 18 87 61 69 1 1 −452 286 230 308 59 102 −68 58 4 5

Gross

change 102 80 94 70 848 491 132 149 2 2 684 313 1,021 374 367 249 94 64 4 5
Chapter 8—Southern Rockies Ecoregion 101

Table 2. Principal land-cover conversions in Southern Rockies Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 81 90 61 0.1 24.1

Mechanically disturbed Water 42 45 31 0.0 12.4

Grassland/Shrubland Forest 33 18 12 0.0 9.9

Mechanically disturbed Grassland/Shrubland 29 33 23 0.0 8.6

Forest Mechanically disturbed 28 18 12 0.0 8.2

Other Other 124 n/a n/a 0.1 36.8

Totals 336 0.2 100.0

1980–1986 Forest Mechanically disturbed 90 61 41 0.1 23.5

Grassland/Shrubland Agriculture 77 69 47 0.1 20.3

Grassland/Shrubland Mining 41 42 29 0.0 10.9

Grassland/Shrubland Forest 38 26 18 0.0 10.0

Mechanically disturbed Grassland/Shrubland 28 18 12 0.0 7.2

Other Other 107 n/a n/a 0.1 28.1

Totals 381 0.3 100.0

1986–1992 Forest Mechanically disturbed 319 248 169 0.2 44.9

Mechanically disturbed Grassland/Shrubland 94 60 41 0.1 13.3

Agriculture Grassland/Shrubland 93 116 79 0.1 13.1

Grassland/Shrubland Forest 58 44 30 0.0 8.1

Forest Mining 21 31 21 0.0 3.0

Other Other 125 n/a n/a 0.1 17.7

Totals 711 0.5 100.0

1992–2000 Mechanically disturbed Grassland/Shrubland 311 246 167 0.2 50.0

Forest Mechanically disturbed 82 64 43 0.1 13.1

Grassland/Shrubland Agriculture 46 29 19 0.0 7.5

Agriculture Grassland/Shrubland 39 31 21 0.0 6.3

Mining Grassland/Shrubland 37 40 27 0.0 5.9

Other Other 107 n/a n/a 0.1 17.3

Totals 622 0.4 100.0

1973–2000

(overall)

Forest Mechanically disturbed 518 295 201 0.4 25.3

Mechanically disturbed Grassland/Shrubland 462 285 194 0.3 22.5

Grassland/Shrubland Agriculture 223 133 90 0.2 10.9

Agriculture Grassland/Shrubland 162 148 100 0.1 7.9

Grassland/Shrubland Forest 150 74 50 0.1 7.3

Other Other 536 n/a n/a 0.4 26.1

Totals 2,051 1.5 100.0
102 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Raw estimates of change in Southern Rockies Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.2 0.1 0.1 0.3 0.1 26.2 0.0

1980–1986 0.3 0.1 0.2 0.4 0.1 25.3 0.0

1986–1992 0.5 0.2 0.3 0.7 0.2 29.5 0.1

1992–2000 0.4 0.2 0.3 0.6 0.1 29.1 0.1

Estimate of change, in square kilometers

1973–1980 336 129 207 466 88 26.2 48

1980–1986 381 142 239 523 96 25.3 64

1986–1992 711 309 402 1,019 210 29.5 118

1992–2000 622 267 356 889 181 29.1 78

Table 3. Percentage of Southern Rockies Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (99.0 percent), whereas 1.0 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 0.6 0.2 0.4 0.8 0.1 22.4

2 0.4 0.2 0.2 0.6 0.1 35.2

3 0.0 0.0 0.0 0.0 0.0 62.5

4 0.0 0.0 0.0 0.0 0.0 98.7

Overall 

spatial 

change

1.0 0.3 0.7 1.4 0.2 20.3
Chapter 8—Southern Rockies Ecoregion 103

References Cited

Baron, J.S., Theobald, D.M., and Fagre, D.B., 2000, Management of land use conflicts in the United States Rocky 

Mountains: Mountain Research and Development, v. 20, no. 

1, p. 24–27.

Breshears, D.D., Cobb, N.S., Rich, P.M., Price, K.P., Allen, 

C.D., Balice, R.G., Romme, W.H., Kastens, J.H., Floyd, 

M.L., Belnap, J., Anderson, J.J., Myers, O.B., and Meyer, 

C.W., 2005, Regional vegetation die-off in response to 

global-change-type drought: Proceedings of the National 

Academy of Sciences of the United States of America, v. 

102, no. 42, p. 15,144–15,148.

Buskirk, S.W., Romme, W.H, Smith, F.W., and Knight, R.L., 

2000, An overview of forest fragmentation in the Southern 

Rocky Mountains, in Knight, R.L., Smith, F.W., Buskirk, 

S.W., and Romme, W.H, eds., Forest Fragmentation in the 

Southern Rocky Mountains: Boulder, University Press of 

Colorado, p. 3–14.

Chapman, S.S., Griffith, G.E., Omernik, J.M., Price, A.B., 

Freeouf, J., and Schrupp, D.L., 2006, Ecoregions of Colorado (color poster with map, descriptive text, summary 

tables, and photographs): Reston, Virginia, U.S. Geological 

Survey (map scale 1:1,200,000), available at http://www.

epa.gov/wed/pages/ecoregions/co_eco.htm.

Darr, D.R., 1995, U.S. forest resources, in LaRoe, E.T., ed., 

Our Living Resources: Washington, D.C., U.S. Department 

of the Interior, National Biological Service, p. 214–215.

Mitchell, J.E., Knight, R.L., and Camp, R.J., 2002, Landscape 

attributes of subdivided ranches: Rangelands, v. 24, no. 1, 

p. 3–9.

Neely, B., Comer, P., Moritz, C., Lammert, M., Rondeau, R., 

Pague, C., Bell, G., Copeland, H., Humke, J., Spackman, 

S., Schulz, T., Theobald, D., and Valutis, L., 2001, Southern 

Rocky Mountains; an ecoregional assessment and conservation blueprint: Prepared by The Nature Conservancy with 

support from the U.S. Forest Service, Rocky Mountain 

Region, Colorado Division of Wildlife, and Bureau of Land 

Management, 86 p.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers 

v. 77, no. 1, p. 118–125.

Theobald, D.M., Gosnell, H, and Riebsame, W.E., 1996, Land 

use and landscape change in the Colorado mountains II—a 

case study of the East River Valley: Mountain Research and 

Development, v. 16, no. 4, p. 407–418.

U.S. Census Bureau, 2000, U.S. Census, 2000, accessed at 

http://www.census.gov/prod/www/abs/decennial/index.htm.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

van Mantgem, P.J., Stephenson, N.L., Byrne, J.C., Daniels, 

L.D., Franklin, J.F., Fulé, P.Z., Harmon, M.E., Larson, A.J., 

Smith, J.M., Taylor, A.H., and Veblen, T.T., 2009, Widespread increase of tree mortality rates in the western United 

States: Science, v. 323, p. 521–524.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
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Chapter 9

Wasatch and Uinta Mountains Ecoregion

Central Basin and Range Ecoregion to the west; in addition, 

the Middle Rockies, Snake River Basin, and Northern Basin 

and Range Ecoregions are nearby to the north. Considered the 

western front of the Rocky Mountains, the two major mountain 

ranges that define the Wasatch and Uinta Mountains Ecoregion 

include the north-south-trending Wasatch Range and east-westtrending Uinta Mountains. Both mountain ranges have been 

altered by multiple mountain building and burial cycles since 

the Precambrian era 2.6 billion years ago, and they have been 

shaped by glacial processes as early as 1.6 million years ago. 

The terrain is defined by sharp ridgelines, glacial lakes, and narrow canyons, with elevations ranging from 1,829 m in the lower 

By Mark S. Brooks

Ecoregion Description

The Wasatch and Uinta Mountains Ecoregion covers 

approximately 44,176 km2 (17, 057 mi2) (fig. 1) (Omernik, 

1987; U.S. Environmental Protection Agency, 1997). With 

the exception of a small part of the ecoregion extending into 

southern Wyoming and southern Idaho, the vast majority of 

the ecoregion is located along the eastern mountain ranges of 

Utah. The ecoregion is situated between the Wyoming Basin 

and Colorado Plateaus Ecoregions to the east and south and the 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Wasatch and Uinta Mountains Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 

1992 National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation 

may be depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks

analyzed in study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States 

ecoregions are listed in appendix 2. See appendix 3 for definitions of land-use/land-cover classifications. 

Central

Basin

and Range

Colorado

Plateaus

SRK

Wyoming

Basin

SRB

MRK

Middle

Rockies

NBR

112° 110°

42°

40°

38°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION UINTA MTNS

Kings

Peak W A S A T C H R A N G E

Ogden

Logan

Provo

Midway

Heber City

Cedar

City

Snyderville

Park City Salt Lake City

Great

Salt

Lake

Logan R.

BRYCE CANYON NP ZION NP

TIMPANOGOS CAVE NM

CEDAR

BREAKS

NM 

U T A H

I D A H O

WYOMING

DIXIE NF

CACHE NF
106 Status and Trends of Land Change in the Western United States—1973 to 2000

canyons to 4,123 m at Kings Peak, the highest point in Utah 

(Milligan, 2010).

The climate is a midlatitude highland climate influenced 

by Pacific storms moving in from the west. Average temperature and precipitation vary with elevation and latitude. The 

southern part of the ecoregion is generally 6° to 8°C warmer 

than northern parts at similar elevations. The average annual 

precipitation varies between 457 and 1,016 mm (Utah Center 

for Climate and Weather, 2009).

The ecoregion is largely made up of federally managed 

lands. Approximately 67 percent (30,000 km2) of the ecoregion 

falls within six National Forests (Wasatch-Cache, Ashley, Uinta, 

Manti–La Sal, Fishlake, and Dixie), seven Wilderness Areas 

(Mount Naomi, High Uintas, Twin Peaks, Lone Peak, Mount 

Timpanogos, Box–Death Hollow, and Ashdown Gorge), two 

National Monuments (Timpanogos Cave and Cedar Breaks), 

one National Park (Zion), and a number of Bureau of Land 

Management Public Domain lands. The Uintah and Ouray Reservation is also located within the ecoregion.

The ecoregion’s forest lands, which cover approximately 

61 percent of its area, vary according to elevation, soils, precipitation, and temperature. Gambel’s oak (Quercus gambelii) 

and canyon maple (Acer grandidentatum) live on lower mountain slopes and foothills, giving way to pinyon-juniper forests 

along the drier foothills. The pinyon-juniper forests include 

the singleleaf pinyon pine (Pinus monophylla), Colorado pinyon (Pinus edulis), and two types of juniper, the Utah juniper 

(Juniperus osteosperma) and Rocky Mountain juniper (Juniperus scopulorum). The middle elevations support Douglas-fir 

(Pseudotsuga menziesii), white fir (Abies concolor), ponderosa 

pine (Pinus ponderosa), and lodgepole pine (Pinus contorta). 

The higher elevations support quaking aspen (Populus tremuloides), Engelmann spruce (Picea engelmannii), and balsam 

fir (Abies lasiocarpa) (Utah Department of Natural Resources, 

Division of Forestry, Fire and State Lands, 2003).

Grassland/shrubland land cover accounts for approximately 34 percent of the ecoregion. Similar to forest land 

cover, grassland/shrubland in the ecoregion also varies according to elevation, soils, precipitation, and temperature. Big 

sagebrush (Artemesia tridentata) is commonly found along 

the drier foothills, whereas perennial bunchgrasses and mixed 

forbs can be found at the middle elevations. Herbaceous 

plants, grasses, sedges, and rushes are found in upland meadows (Grahame and Sisk, 2002).

Owing to the steep terrain and rugged landscape of the 

ecoregion, most developed land is located in the fertile valleys and the unincorporated area surrounding Snyderville, 

known informally as “Snyderville Basin,” situated between 

the Wasatch Range and Uinta Mountains just east of Salt Lake 

City, Utah. The Wasatch and Uinta Mountains Ecoregion is 

sparsely populated with only one town of over 20,000 people 

recorded in the 2000 Census (Cedar City, Utah, population 

20,527); the next three largest towns were Park City, Utah 

(population 7,371), Heber City, Utah (population 7,291), and 

Midway, Utah (population 2,121) (U.S. Census Bureau, 2010). 

However, an estimated 1.7 million people live just west of 

the ecoregion boundary along the Wasatch Front (extending 

roughly 129 km from Ogden, Utah, to Provo, Utah) (Economic 

Development Corporation of Utah, 2008). Agriculture, which 

is not a significant land cover within the ecoregion, is limited to 

irrigated pasture and hay in fertile lowland stream valleys. 

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the ecoregion’s overall spatial 

change (the percentage of area undergoing at least one landcover change during the study period) is estimated at approximately 2.0 percent, and an estimated 0.5 percent of the ecoregion area changed in two or more time periods (fig. 2). The 

vast majority of land, approximately 98 percent, did not change 

Figure 2. Overall spatial change in Wasatch and Uinta Mountains Ecoregion (WUM; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial 

change in Wasatch and Uinta Mountains Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods
Chapter 9—Wasatch and Uinta Mountains Ecoregion 107

during the study period (table 1). This level of change is among 

the lowest of the western United States ecoregions (fig. 2). 

The total land-cover change estimated within the four 

time periods varied only slightly between 1973 and 2000. The 

first three time periods showed similar amounts of change, but 

the last time period, between 1992 and 2000, had the greatest 

amount of change at 1.1 percent of the ecoregion (table 2). 

When time periods are normalized to an average annual rate of 

change to adjust for uneven time periods, all four time periods 

had a minimal change rate of approximately 0.1 percent per 

year (table 2; fig. 3). 

The land-use/land-cover composition of the ecoregion 

experienced little change during the study period. In 2000, 

forest was the dominant land cover at approximately 60.8 percent of the ecoregion, followed by grassland/shrubland (33.7 

percent), barren (2.9 percent), and agriculture (0.9 percent); 

the remaining land-cover classes combined for approximately 

1 percent of the ecoregion (table 3). 

The most significant net gain and net loss identified 

between 1973 and 2000 was the net loss of approximately 

1.4 percent (408 km2) of forest and a net gain of approximately 261 km2

 of nonmechanically disturbed lands, which 

did not occupy any area in 1973 (table 3; fig. 4). The association between the loss of forest and the increase in nonmechanical disturbance is likely the result of beetle infestation 

and wildfire (fig. 5). Increased beetle infestation, which is a 

natural process, is believed to be caused by warmer winters, 

extended drought, and the practice of fire suppression over 

several decades. Forest-management activities that include 

prescribed burns and mechanical thinning have been implemented in recent years to improve forest health and reduce 

the likelihood of large-scale natural fires (Utah Department 

of Natural Resources, Division of Forestry and State Lands, 

2003) (fig. 6). 

Figure 3. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Wasatch and Uinta Mountains Ecoregion are represented by red bars in 

each time period.

Figure 4. Normalized average net change in Wasatch and Uinta 

Mountains Ecoregion by time period for each land-cover class. 

Bars above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−1

−0.5

0

0.5

1

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
108 Status and Trends of Land Change in the Western United States—1973 to 2000

The three leading conversions during the 1973 to 2000 

study period involved the disturbance of forest either by 

mechanical means (timber harvesting or mechanical thinning) 

or by nonmechanical means (beetle infestation or fire) and 

the subsequent recovery of disturbed land to grassland/shrubland. An estimated 58 percent of all change is explained by 

this cyclical pattern of land-cover conversion. The fourth and 

fifth leading conversions identified are fluctuations between 

agriculture and grassland/shrubland, with an estimated 92 

km2

 of grassland/shrubland converting to agriculture, and an 

estimated 70 km2 of agriculture converting back to grassland/

shrubland during the study period (table 4). 

The Wasatch and Uinta Mountains Ecoregion experienced 

little change during the study period. The low level of change 

can be largely explained by the remote and rugged terrain 

characterized by its sharp ridgelines and narrow canyons (fig.7). 

In addition, the presence of federal lands may also inhibit 

change within the ecoregion (fig. 8). The change that did occur 

resulted from either natural processes (beetle infestation and 

natural fire) or anthropogenic disturbance (prescribed burns, 

timber harvesting, and mechanical thinning). Combined, these 

processes accounted for an estimated net loss of 408 km2 of 

forest. Given probable increases in temperature and prolonged 

periods of drought, future changes are likely to involve a higher 

incidence of nonmechanical disturbance including natural fires 

and insect infestations (Utah Department of Natural Resources, 

Division of Forestry and State Lands, 2003). 

Figure 6. Mechanical thinning of stand of Engelmann spruce 

devastated by spruce beetle infestation near Cedar Breaks 

National Monument in Dixie National Forest, Utah.

Figure 7. Logan River rushing through steep, narrow canyon in 

Cache National Forest, Utah.

Figure 8. Aspen, pine, spruce, and fir along State Route 39 in 

Cache National Forest, Utah, with towering Wasatch Range in 

distance (elevation, 2,650 m).

Figure 5. Stand of Engelmann spruce showing impact of spruce 

beetle infestation in Dixie National Forest, Utah (elevation, 2,970 m).
Chapter 9—Wasatch and Uinta Mountains Ecoregion 109

Table 1. Percentage of Wasatch and Uinta Mountains Ecoregion 

land cover that changed at least one time during study period 

(1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (98.0 percent), whereas 2.0 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.5 0.6 0.8 2.1 0.4 29.2

2 0.5 0.3 0.2 0.7 0.2 38.4

3 0.0 0.0 0.0 0.1 0.0 35.6

4 0.0 0.0 0.0 0.0 0.0 96.3

Overall 

spatial 

change

2.0 0.8 1.2 2.8 0.5 26.3

Table 2. Raw estimates of change in Wasatch and Uinta Mountains Ecoregion land cover, computed for 

each of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.5 0.4 0.1 0.8 0.2 49.9 0.1

1980–1986 0.4 0.2 0.2 0.6 0.1 34.4 0.1

1986–1992 0.6 0.3 0.3 0.9 0.2 32.4 0.1

1992–2000 1.1 0.5 0.6 1.6 0.4 32.8 0.1

Estimate of change, in square kilometers

1973–1980 216 159 57 375 108 49.9 31

1980–1986 184 93 91 277 63 34.4 31

1986–1992 255 122 133 377 83 32.4 42

1992–2000 485 234 250 719 159 32.8 61
110 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Wasatch and Uinta Mountains Ecoregion, calculated five 

times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.2 0.1 0.1 0.1 0.2 0.2 0.0 0.0 2.9 1.9 61.7 5.2 33.7 5.0 0.9 0.6 0.3 0.2 0.0 0.0

1980 0.2 0.1 0.1 0.1 0.1 0.1 0.0 0.0 2.9 1.9 61.7 5.2 33.7 5.0 0.9 0.6 0.3 0.1 0.0 0.0

1986 0.2 0.1 0.1 0.1 0.2 0.1 0.0 0.0 2.9 1.9 61.5 5.1 33.8 4.9 1.0 0.7 0.3 0.2 0.0 0.0

1992 0.2 0.1 0.1 0.1 0.1 0.1 0.0 0.0 2.9 1.9 61.4 5.1 33.9 4.9 0.9 0.7 0.3 0.2 0.0 0.0

2000 0.2 0.1 0.1 0.1 0.3 0.2 0.0 0.0 2.9 1.9 60.8 5.0 33.7 4.8 0.9 0.7 0.3 0.2 0.6 0.5

Net

change 0.1 0.0 0.0 0.0 0.2 0.3 0.0 0.0 0.0 0.0 −0.9 0.5 0.1 0.6 0.0 0.3 0.0 0.0 0.6 0.5

Gross

change 0.2 0.1 0.0 0.0 0.8 0.4 0.0 0.0 0.0 0.0 1.1 0.5 1.1 0.5 0.3 0.3 0.1 0.1 0.7 0.5

Area, in square kilometers

1973 71 42 47 35 76 86 2 1 1,298 836 27,276 2,286 14,878 2,222 376 257 150 77 0 0

1980 98 50 52 37 53 59 6 5 1,299 836 27,241 2,277 14,895 2,200 401 275 122 62 10 14

1986 92 46 53 38 69 64 6 5 1,299 836 27,182 2,264 14,913 2,184 423 294 136 67 4 5

1992 92 48 54 38 60 43 7 5 1,300 835 27,141 2,256 14,988 2,153 399 302 131 67 6 6

2000 101 52 57 38 144 92 8 6 1,299 836 26,868 2,212 14,903 2,107 398 302 136 71 261 209

Net

change 30 19 10 8 68 121 6 6 1 1 −408 234 25 262 22 114 −14 13 261 209

Gross

change 86 64 10 8 373 188 6 6 3 3 483 234 474 240 120 114 61 59 292 218
Chapter 9—Wasatch and Uinta Mountains Ecoregion 111

Table 4. Principal land-cover conversions in Wasatch and Uinta Mountains Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Mechanically disturbed Grassland/Shrubland 65 82 55 0.1 30.1

Forest Mechanically disturbed 47 59 40 0.1 21.8

Grassland/Shrubland Agriculture 24 30 20 0.1 11.2

Wetland Water 24 32 21 0.1 10.9

Grassland/Shrubland Forest 21 27 18 0.0 9.8

Other Other 35 n/a n/a 0.1 16.2

Totals 216 0.5 100.0

1980–1986 Forest Mechanically disturbed 66 64 43 0.2 36.1

Mechanically disturbed Grassland/Shrubland 47 59 40 0.1 25.6

Grassland/Shrubland Agriculture 22 30 21 0.0 11.8

Water Wetland 12 17 11 0.0 6.5

Nonmechanically disturbed Forest 8 11 7 0.0 4.1

Other Other 29 n/a n/a 0.1 15.8

Totals 184 0.4 100.0

1986–1992 Mechanically disturbed Grassland/Shrubland 60 62 42 0.1 23.6

Agriculture Grassland/Shrubland 57 67 45 0.1 22.3

Forest Mechanically disturbed 50 43 29 0.1 19.7

Grassland/Shrubland Agriculture 34 48 32 0.1 13.4

Grassland/Shrubland Forest 9 9 6 0.0 3.5

Other Other 45 n/a n/a 0.1 17.5

Totals 255 0.6 100.0

1992–2000 Forest Nonmechanically disturbed 193 189 128 0.4 39.9

Forest Mechanically disturbed 91 58 39 0.2 18.7

Grassland/Shrubland Nonmechanically disturbed 67 91 62 0.2 13.8

Grassland/Shrubland Mechanically disturbed 36 50 34 0.1 7.4

Mechanically disturbed Grassland/Shrubland 31 32 21 0.1 6.5

Other Other 67 n/a n/a 0.2 13.8

Totals 485 1.1 100.0

1973–2000

(overall)

Forest Mechanically disturbed 254 148 101 0.6 22.3

Forest Nonmechanically disturbed 211 194 132 0.5 18.5

Mechanically disturbed Grassland/Shrubland 203 185 125 0.5 17.9

Grassland/Shrubland Agriculture 92 123 83 0.2 8.1

Agriculture Grassland/Shrubland 70 74 50 0.2 6.2

Other Other 308 n/a n/a 0.7 27.0

Totals 1,139 2.6 100.0
112 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Economic Development Corporation of Utah, 2008, Wasatch 

Front profile: Salt Lake City, Economic Development 

Corporation of Utah, accessed July 2010, at http://www.

edcutah.org/documents/WasatchFrontProfile_032511.pdf.

Grahame, J.D., and Sisk, T.D., eds., 2002, Canyons, cultures 

and environmental change; An introduction to the land-use 

history of the Colorado Plateau: Land Use History of North 

America database, accessed July 2010, at http://cpluhna.

nau.edu/Biota/mtn_grasslands.htm.

Milligan, Mark R., 2000, How was Utah’s topography 

formed?: Utah Geological Survey Survey Notes, accessed 

July 2010, at http://geology.utah.gov/surveynotes/

gladasked/gladtopoform.htm.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

U.S. Census Bureau, 2010, U.S. Census, 2010: U.S. Census Bureau database, accessed July 2010, at http://www.

census.gov/.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Utah Center for Climate and Weather, 2009: Climate of Utah, 

accessed July 2010, at http://utahweather.org/climatology/

climate-of-utah/.

Utah Department of Natural Resources Division of Forestry, 

Fire and State Lands, 2003, Forest Health in Utah: Utah 

Department of Natural Resources Division of Forestry, Fire 

and State Lands report, accessed July 2010, at http://www.

ffsl.utah.gov/foresthealth/fhgov4a.pdf.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
Chapter 10

Arizona/New Mexico Mountains Ecoregion

Chihuahuan Deserts Ecoregions; to the north, the ecoregion 

is both bounded and surrounded by the Arizona/New Mexico 

Plateau Ecoregion (fig. 1). The ecoregion encompasses the 

largest contiguous ponderosa pine (Pinus ponderosa) forest 

in the United States (Strom and Fulé, 2007), which stretches 

from Williams, Arizona, along the Mogollon Rim, Arizona, 

into southwestern New Mexico, north and west of Silver 

City, New Mexico. 

By Jana Ruhlman, Leila Gass, and Barry Middleton

Ecoregion Description

As the name suggests, the Arizona/New Mexico Mountains Ecoregion includes much of the mountainous regions 

of these two states, plus a very small part in the Guadalupe 

Mountains of northwestern Texas. Several isolated areas of 

higher terrain in Arizona and New Mexico are also included 

in the ecoregion, which occupies approximately 108,432 km2

(41,866 mi2) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). The ecoregion is bounded on the south 

by the Sonoran Basin and Range, Madrean Archipelago, and 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Arizona/New Mexico Mountains Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 

1992 National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation 

may be depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided 

into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed 

in study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions 

are listed in appendix 2. Also shown on map is part of one Great Plains Ecoregion, Southwestern Tablelands (SWT). See appendix 3 for 

definitions of land-use/land-cover classifications.

Arizona/

New Mexico

Plateau

Chihuahuan

Desert

Southern

Rockies

Southern

Rockies

Colorado Plateaus

Madrean

Archipelago

Sonoran Basin

 and Range

SWT

MBR

MEXICO

112° 110° 108° 106°

36°

34°

32°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

ARIZONA

TEXAS

UTAH

COLORADO

NEW MEXICO

Coconino Co.

Williams

Flagstaff

Sedona

Payson

Prescott Prescott Valley

Silver City

Mule Creek

Morenci

Tyrone

Salt River

Rio

Grande

GRAND CANYON NP

GUADALUPE

MTNS

San Francisco Mtn

M O G O L L O N R I M

Gila Riv er

Little C olora do Riv er

Mimbres R.

Verde River

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
114 Status and Trends of Land Change in the Western United States—1973 to 2000

 The mountains of the Arizona/New Mexico Mountains 

Ecoregion are lower in elevation than neighboring mountainous ecoregions and have vegetation indicative of drier, warmer 

climates (U.S. Environmental Protection Agency, 2002). Semiarid grassland, chaparral, and pinyon-juniper (Pinus spp. and

Juniperus spp.) and oak woodlands (Quercus spp.) grow in the 

lower elevations. Ponderosa pines dominate the higher elevations, along with Douglas-fir (Pseudotsuga menziesii), Engelmann spruce (Picea engelmannii), and even alpine tundra atop 

the highest mountain peaks (fig. 2). San Francisco Mountain 

(known locally as the “San Francisco Peaks”), Arizona, is 

the most prominent (and highest) point of the ecoregion, at 

3,851 m (12,633 ft). The wide variety of topography results in 

annual precipitation averages that range from 182 mm (7 in) 

to 1,293 mm (51 in), in the form of both rain and snow (Daly 

and others, 2002). Melting snow and summer monsoonal 

rains feed the headwaters of several river systems within the 

ecoregion, including the Verde, Salt, Gila, and Little Colorado 

Rivers in Arizona and the Mimbres River in New Mexico. 

Average temperatures vary greatly by season and along elevation gradients but range from −18°C during the winter months 

in the highest elevations to more than 38°C during the summer 

months in the lowest elevations. 

Flagstaff, Arizona, is the largest urban area, with a 2000 

population of 52,894. Numerous smaller communities exist 

throughout the ecoregion: Prescott, Prescott Valley, Payson, 

and Sedona, Arizona, are the only communities that have 

greater than 10,000 residents (U.S. Census Bureau, 2000). A 

large part of the conifer forests are on federal (mainly U.S. 

Forest Service) or tribal lands, and they provide a valuable 

resource for timber harvesting and livestock grazing, as well 

as tourism and outdoor recreation. Almost all public land in 

the ecoregion other than forest is leased for grazing (Arizona 

Game and Fish Department, 2006), and all eight national 

forests in the ecoregion sell saw timber and other tree products. Mining is an important contributor to the economy of 

towns along the southern border of the ecoregion, with major 

operating copper mines in Morenci, Arizona, and Tyrone, 

New Mexico. Two sizeable copper mines are also located just 

outside the ecoregion boundary (Freeport-McMoRan Copper 

and Gold, 2009). The popularity of the cool mountain country with easy access to the hotter deserts brings millions of 

visitors to the region to enjoy hiking, camping, skiing, fishing, 

and hunting, and many towns in the ecoregion rely on tourism 

for their local economy. Grand Canyon National Park, located 

in Coconino County, Arizona, in the northwestern part of the 

ecoregion, receives approximately 3.3 million visitors each 

year (U.S. Forest Service, 2008). 

Contemporary Land-Cover Change 

(1973 to 2000)

As measured by the project methodology, the Arizona/

New Mexico Mountains Ecoregion experienced little landcover change during the study period (fig. 3). An estimated 

3.5 percent of the ecoregion (3,806 km2) changed land cover 

during the study period: 2.0 percent of the ecoregion changed 

only once, 1.3 percent changed twice, and 0.2 percent changed 

three times (table 1). Compared to other western United States 

ecoregions, change in the Arizona/New Mexico Mountains 

Ecoregion was low but not as low as the more arid ecoregions 

of the Southwest (figs. 3,4). 

Estimated change in land cover per time period varied from 

0.9 percent (1973–1980) to 2.0 percent (1992–2000). When the 

change estimates were normalized to account for the varying 

lengths of time between satellite imagery dates, the average rate 

Figure 2. Various vegetation zones of Arizona/New Mexico 

Mountains Ecoregion. A, Ponderosa pine forest in Tonto National 

Forest, central Arizona. B, Pinyon-juniper woodland on Fort 

Apache Reservation, eastern Arizona. C, Grassland near Mule 

Creek, New Mexico. 

A

B

C

A
Chapter 10—Arizona/New Mexico Mountains Ecoregion 115

of change per year was 0.1 percent between 1973 and 1980, 0.2 

percent between 1980 and 1986 and between 1986 and 1992, 

and 0.3 percent between 1992 and 2000 (table 2; fig. 4).

The study results showed that forest and grassland/shrubland were the primary land-cover classes in the ecoregion. 

Grassland/shrubland encompassed approximately 40 percent 

of the land cover in each time period, whereas the forest class 

decreased from 58.2 percent in 1973 to 56.6 percent by 2000 

(table 3). The nonmechanically disturbed class accounted for 

1.2 percent of the land cover in 2000; mining accounted for 

1.0 percent; and the developed, barren, and agriculture classes 

made up the remaining land cover. 

The forest and nonmechanically disturbed classes experienced the greatest net change over the study period. Between 

1973 and 2000, the forest class declined by 2.7 percent, but 

the nonmechanically disturbed class increased from 0.1 percent to 1.1 percent. These changes resulted in a net decrease 

of 1,735 km2 of forest and a net increase of 1,228 km2 in 

nonmechanically disturbed land cover over the study period, 

primarily owing to fire. The remaining classes experienced 

very little net change (table 3). 

Overall net-change values can, however, mask land-cover 

dynamics that occur within the study period. Figure 5 illustrates 

the fluctuations that occurred in land-cover classes in each time 

period. The decrease in forest occurred at variable rates over 

the study period; the least amount of decrease occurred between 

1986 and 1992, and the greatest decrease occurred between 

1992 and 2000. Likewise, despite an overall increasing trend, 

figure 5 shows that the nonmechanically disturbed class had 

roughly equal gains and losses in the first two time periods, 

a small gain in the third, and a large increase in the last time 

period, a trend seen in many other forested ecoregions in the 

western United States. The overall changes in the mechanically 

disturbed class resulted in little net change (fig. 5); however, 

the gains and losses in this class did affect 1.2 percent of the 

ecoregion during the 27-year study period. These changes were 

due mainly to logging and mining activities.

The most common conversions in the Arizona/New 

Mexico Mountains Ecoregion revolved around changes to 

Figure 3. Overall spatial change in Arizona/New Mexico Mountains Ecoregion (ANMM; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial 

change in Arizona/New Mexico Mountains Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

Figure 4. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Arizona/New Mexico Mountains 

Ecoregion are represented by red bars 

in each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
116 Status and Trends of Land Change in the Western United States—1973 to 2000

the forest resulting from both mechanical and nonmechanical disturbances (table 4). These conversions, which were the 

result of both timber harvesting and wildland fires, occasionally involved grassland/shrubland as an intermediary land 

cover between the disturbance and the reforestation. Regeneration after disturbance was captured in one of two ways. If the 

disturbance was due to thinning, or to a moderate fire that did 

not destroy the majority of trees, then, in the next classification year, the land might revert directly to forest. However, 

if clearcutting or severe fire had eliminated the forest, then 

the next mapped class would usually be grassland/shrubland. 

More time would be needed for the grassland/shrubland to 

eventually revert to forest.

The main story of land-cover change in the Arizona/

New Mexico Mountains Ecoregion involves its forests and the 

changes that occurred from both natural and human-caused 

disturbances. Changes in the nonmechanically disturbed landcover class were the result of frequent fire (both lightning- and 

human-caused), which historically has been a major driver 

of change in this ecoregion (fig. 6). As of 2005, Coconino 

National Forest had averaged 501 wildfires per year (U.S. Forest Service, 2005). Dry summer thunderstorms in the forests 

of Arizona and New Mexico result in a high incidence of 

lightning strikes, causing the highest average annual number 

of lightning-caused fires in the nation (Stephens, 2005). 

Frequent, low-intensity fires that moved along the ground 

were part of the evolutionary history of ponderosa pine forests 

until the early 1900s, but the effects of heavy grazing in the 

forests, coupled with aggressive fire suppression, have resulted 

in the unnaturally high tree densities and heavy loads of 

accumulated fuels that have led to the high-risk fire conditions 

that exist today (Great Flagstaff Forests Partnership, 2009). 

These factors may have contributed to the increasing trend in 

the nonmechanically disturbed class observed in this study. 

Currently, concerns over insect infestation and catastrophic 

wildfire events have resulted in ongoing hazardous-fuel–

reduction projects (thinning and prescribed burning) throughout the national forests in the ecoregion, which will reduce 

fuel loads and promote forest health. Success of these methods 

may eventually reduce the growing number of acres lost to 

catastrophic wildland fires each year within the ecoregion. 

Timber harvesting, either through clearcutting or thinning, accounted for the majority of change in the mechanically 

disturbed land-cover class. Since 1908, the U.S. Forest Service 

has been tracking the sale of timber from forests in Arizona 

and New Mexico. The U.S. Forest Service data correlate with 

the results of this study, which show that harvests increased 

between 1973 and 1980 and between 1980 and 1986, and 

they decreased between 1982 and 1992 and between 1992 

and 2000 (Paul Fink, U.S. Forest Service, written commun., 

2009; see also, fig. 5). Harvests began to decline in 1990 

owing to changes in timber-management practices, environmental concerns, and the lack of large, profitable trees to 

cut (Kelley, 1998). In 1986, the U.S. Forest Service sold the 

rights to nearly 447 million board feet of timber in Arizona 

and New Mexico forests, which corresponded to the logging 

peak within the study period. In 2000, this number dropped to 

below 69 million board feet of timber (Paul Fink, U.S. Forest 

Service, written commun., 2009). The small towns within the 

Figure 5. Normalized average net change in Arizona/New 

Mexico Mountains Ecoregion by time period for each land-cover 

class. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. Note that not all land-cover classes 

shown in explanation may be represented in figure. See appendix 

3 for definitions of land-use/land-cover classifications.

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 6. Aftermath of fire in Coconino National Forest, north 

of Flagstaff, Arizona, which occurred between 1992 and 2000. 

Photograph taken in June 2007. 
Chapter 10—Arizona/New Mexico Mountains Ecoregion 117

ecoregion that relied on timber were severely impacted by 

these decreases, increasing the importance of tourism to their 

economies (Kelley, 1998).

Historically, logging and frequent forest fires have been 

major drivers of land-cover change within this ecoregion, and 

they will both likely continue to impact the cycle of change 

within the forests. Although the populations of the main cities 

and towns in the ecoregion continue to increase, many of these 

population centers are bounded by public lands unavailable to 

urbanization. Coupled with the fact that nearly 80 percent of 

the ecoregion is managed public and tribal lands, land-cover 

change in the Arizona/New Mexico Mountain Ecoregion is 

likely to remain low.

Table 1. Percentage of Arizona/New Mexico Mountains 

Ecoregion land cover that changed at least one time during study 

period (1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (96.5 percent), whereas 3.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 2.0 0.9 1.1 2.8 0.6 29.8

2 1.3 0.7 0.6 2.0 0.5 34.9

3 0.2 0.2 0.0 0.4 0.1 72.6

4 0.0 0.0 0.0 0.1 0.0 73.0

Overall 

spatial 

change

3.5 1.5 2.0 5.0 1.0 28.3

Table 2. Raw estimates of change in Arizona/New Mexico Mountains Ecoregion land cover, computed 

for each of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.9 0.6 0.3 1.5 0.4 46.1 0.1

1980–1986 1.3 0.7 0.5 2.0 0.5 39.2 0.2

1986–1992 1.1 0.6 0.6 1.7 0.4 34.1 0.2

1992–2000 2.0 0.9 1.1 2.9 0.6 31.1 0.3

Estimate of change, in square kilometers

1973–1980 995 676 319 1,671 459 46.1 142

1980–1986 1,373 793 581 2,166 538 39.2 229

1986–1992 1,237 622 616 1,859 422 34.1 206

1992–2000 2,171 995 1,177 3,166 676 31.1 271
118 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Arizona/New Mexico Mountains Ecoregion, calculated five 

times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.0 0.0 0.4 0.3 0.0 0.0 0.8 1.1 0.1 0.1 58.2 8.5 39.9 8.3 0.4 0.3 0.0 0.0 0.1 0.1

1980 0.1 0.1 0.4 0.3 0.1 0.1 0.8 1.2 0.1 0.1 57.7 8.5 39.7 8.3 0.5 0.4 0.0 0.0 0.5 0.6

1986 0.0 0.0 0.4 0.3 0.4 0.4 0.9 1.3 0.1 0.1 57.5 8.4 40.1 8.3 0.5 0.3 0.0 0.0 0.0 0.0

1992 0.1 0.1 0.4 0.3 0.2 0.3 0.9 1.3 0.1 0.1 57.5 8.4 40.0 8.3 0.4 0.3 0.0 0.0 0.2 0.2

2000 0.0 0.0 0.4 0.3 0.0 0.0 1.0 1.4 0.1 0.1 56.6 8.3 40.1 8.2 0.4 0.2 0.0 0.0 1.2 0.8

Net

change 0.0 0.0 0.1 0.0 0.0 0.0 0.2 0.3 0.0 0.0 −1.6 1.0 0.2 0.6 −0.1 0.1 0.0 0.0 1.1 0.8

Gross

change 0.2 0.3 0.1 0.0 1.2 1.0 0.2 0.3 0.0 0.0 3.0 1.5 1.8 0.9 0.3 0.3 0.0 0.0 2.6 1.7

Area, in square kilometers

1973 25 16 391 313 2 3 855 1,227 146 152 63,129 9,265 43,260 9,033 476 315 39 47 109 148

1980 112 107 418 314 123 124 898 1,287 149 152 62,609 9,170 43,042 9,033 557 392 34 46 490 620

1986 52 41 426 314 398 396 978 1,402 149 152 62,386 9,151 43,450 8,949 545 377 35 45 13 14

1992 79 62 448 317 268 309 1,022 1,463 156 152 62,334 9,119 43,383 8,957 482 306 49 49 211 204

2000 36 29 475 323 25 36 1,078 1,532 152 152 61,395 8,972 43,502 8,932 384 250 48 52 1,337 879

Net

change 11 17 84 50 23 36 223 306 6 7 −1,735 1,092 242 634 −92 135 9 7 1,228 896

Gross

change 231 280 84 50 1,346 1,076 223 306 33 25 3,208 1,651 1,981 1,012 277 354 29 31 2,801 1,879
Chapter 10—Arizona/New Mexico Mountains Ecoregion 119

Table 4. Principal land-cover conversions in Arizona/New Mexico Mountains Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Nonmechanically disturbed 445 563 382 0.4 44.7

Forest Mechanically disturbed 121 122 83 0.1 12.1

Grassland/Shrubland Water 83 101 68 0.1 8.4

Grassland/Shrubland Agriculture 83 110 75 0.1 8.3

Nonmechanically disturbed Grassland/Shrubland 55 71 48 0.1 5.5

Other Other 209 n/a n/a 0.2 21.0

Totals 995 0.9 100.0

1980–1986 Nonmechanically disturbed Grassland/Shrubland 485 620 421 0.4 35.3

Forest Mechanically disturbed 398 396 269 0.4 29.0

Grassland/Shrubland Forest 162 203 138 0.1 11.8

Mechanically disturbed Grassland/Shrubland 91 93 63 0.1 6.6

Grassland/Shrubland Mining 69 100 68 0.1 5.0

Other Other 169 n/a n/a 0.2 12.3

Totals 1,373 1.3 100.0

1986–1992 Mechanically disturbed Forest 306 368 250 0.3 24.7

Forest Mechanically disturbed 265 306 208 0.2 21.4

Forest Nonmechanically disturbed 207 204 138 0.2 16.7

Grassland/Shrubland Forest 120 125 85 0.1 9.7

Mechanically disturbed Grassland/Shrubland 91 117 79 0.1 7.3

Other Other 249 n/a n/a 0.2 20.1

Totals 1,237 1.1 100.0

1992–2000 Forest Nonmechanically disturbed 1,295 844 573 1.2 59.7

Mechanically disturbed Forest 262 305 207 0.2 12.1

Nonmechanically disturbed Grassland/Shrubland 168 190 129 0.2 7.7

Agriculture Grassland/Shrubland 97 123 84 0.1 4.5

Grassland/Shrubland Forest 82 105 71 0.1 3.8

Other Other 268 n/a n/a 0.2 12.3

Totals 2,171 2.0 100.0

1973–2000

(overall)

Forest Nonmechanically disturbed 1,955 1,262 857 1.8 33.8

Forest Mechanically disturbed 808 624 424 0.7 14.0

Nonmechanically disturbed Grassland/Shrubland 714 662 450 0.7 12.4

Mechanically disturbed Forest 600 548 372 0.6 10.4

Grassland/Shrubland Forest 382 336 228 0.4 6.6

Other Other 1,317 n/a n/a 1.2 22.8

Totals 5,777 5.3 100.0
120 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Arizona Game and Fish Department, 2006, Arizona-New Mexico Mountains—Arizona’s Comprehensive Wildlife Conservation Strategy; 2005-2015: Arizona Game and Fish Department, accessed February 16, 2007, at http://www.azgfd.gov/

pdfs/w_c/cwcs/downloads/Section7Arizona-NewMexico.pdf.

Daly, C., Gibson, W., and Taylor, G., 2002, 103-year highresolution precipitation climate data set for the conterminous United States: Corvallis, Oregon State University, The 

PRISM Climate Group database, accessed May 12, 2009, at 

http://www.prism.oregonstate.edu.

Freeport-McMoRan Copper and Gold, 2009, Worldwide 

operations—North America: Freeport-McMoRan Copper 

and Gold database, accessed April 29, 2009, at http://www.

fcx.com/operations/northamerica.htm. 

Greater Flagstaff Forests Partnership, 2009, History of degradation of southwestern ponderosa pine forests: Greater 

Flagstaff Forests Partnership database, accessed April 17, 

2009, at http://www.gffp.org/pine/history.htm.

Kelley, Matt, 1998, Environmental challenges, economics cut 

state logging: Tucson, Arizona, The Associated Press, in

The Arizona Daily Star, July 5, 1998. 

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Stephens, Scott L., 2005, Forest fire causes and extent on 

United States Forest Service lands: International Journal of 

Wildland Fire, v. 14, p. 213–222, accessed May 12, 2009, 

at http://www.cnr.berkeley.edu/stephens-lab/Publications/

Stephens%20USFS%20fire%20stats%20IJWF%2005.pdf.

Strom, B., and Fulé, P., 2007, Pre-wildfire fuel treatments 

affect long-term ponderosa pine forest dynamics: International Journal of Wildland Fire, v. 16, no. 1, p. 128–138.

U.S. Census Bureau, 2000, U.S. Census 2000: U.S. Department of Commerce database, accessed April 29, 2009, at 

http://factfinder.census.gov.

U.S. Environmental Protection Agency, 1997, Descriptions of level III ecological regions for the CEC report on 

ecological regions of North America: U.S. Environmental 

Protection Agency database, accessed April 12, 2006, 

at http://www.epa.gov/wed/pages/ecoregions/na_eco.

htm#Downloads.

U.S. Forest Service, Coconino National Forest, 2005, 

Coconino National Forest Fire Management Plan 2005: 

U.S. Forest Service, accessed April 17, 2009, at http://

www.fs.usda.gov/detail/coconino/landmanagement/

planning/?cid=stelprdb5334653.

U.S. Forest Service, Coconino National Forest, 2008, 2008 

Stakeholders Report: U.S. Forest Service, Coconino National 

Forest, accessed June 19, 2009, at http://www.fs.usda.gov/

Internet/FSE_DOCUMENTS/stelprdb5340530.pdf.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
Western Mountain Ranges Ecoregions

Chapter 11

Cascades Ecoregion

By Daniel G. Sorenson

Ecoregion Description

The Cascades Ecoregion (Omernik, 1987; U.S. Environmental Protection Agency, 1997) covers approximately 

46,787 km2 (18,064 mi2) in Washington, Oregon, and California (fig. 1). The main body of the ecoregion extends from Snoqualmie Pass, Washington, in the north, to Hayden Mountain, 

near State Highway 66 in southern Oregon. Also included in 

the ecoregion is a small isolated section south of Bend, Oregon, as well as a larger one around Mount Shasta, California. 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

The ecoregion is bounded on the west by the Klamath Mountains, Willamette Valley, and Puget Lowland Ecoregions; on 

the north by the North Cascades Ecoregion; and on the east by 

the Eastern Cascades Slopes and Foothills Ecoregion. 

The Cascades Ecoregion is a forested, mountainous ecoregion, and it contains a large amount of Cenozoic volcanic rock 

and many active and inactive volcanoes, especially in the east 

(McNab and Avers, 1994). Elevations range from near sea level 

at the Columbia River to 4,390 m at Mount Rainier in Washington, with most of the ecoregion between 645 and 2,258 m. The 

Figure 1. Map of Cascades Ecoregion and 

surrounding ecoregions, showing land-use/

land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); 

note that not all land-use/land-cover classes 

shown in explanation may be depicted on 

map; note also that, for this “Status and 

Trends of Land Change” study, transitional 

land-cover class was subdivided into 

mechanically disturbed and nonmechanically 

disturbed classes. Squares indicate locations 

of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic 

features mentioned in text. Abbreviations for 

Western United States ecoregions are listed 

in appendix 2. See appendix 3 for definitions of 

land-use/land-cover classifications. 

Coast Range

Klamath

Mountains

Northern Basin

and Range

Eastern Cascades

Slopes and Foothills

Willamette

Valley

BLM

PL

PL NC

CP

CLMP

CP

BLM

PACIFIC

OCEAN

122°

120°

124°

46°

44°

42°

WAS H INGTON

OREGON

CALIFORNIA

NEVADA

Portland

Weed

Ashland

Klamath Falls

Mount Shasta

C A S C A D E 

Seattle

Bend

Oakridge

Willam

et te R i ver

C o lu m bia R.

Mount Rainier

Snoqualmie Pass

Goat Rocks 

Mount St. Helens

Mount Adams

Mount Hood

Mount Jefferson

Mount Washington

Mount Thielsen

Mount Shasta

Hayden Mtn

CRATER LAKE NP

MOUNT RAINIER NP

Three Sisters 

Wilderness

R A N G E

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
124 Status and Trends of Land Change in the Western United States—1973 to 2000

west side of the ecoregion is characterized by long, steep ridges 

and wide river valleys. Subalpine meadows are present at higher 

elevations, and alpine glaciers have left till and outwash deposits 

(McNab and Avers, 1994). Precipitation in the Cascades Ecoregion ranges from 1,300 to 3,800 mm, falling mostly as rain and 

snow from October to June. Average annual temperatures range 

from –1oC to 11oC. The length of the growing season varies from 

less than 30 days to 240 days (McNab and Avers, 1994).

The dominant vegetation on the lower slopes (below 

1,000 m) is Douglas-fir (Pseudotsuga menziesii) and western 

hemlock (Tsuga heterophylla). At middle elevations (from 

about 800 to 1,280 m), Pacific silver fir (Abies amabilis) and 

noble fir (Abies procera) become prevalent. Lush wildflower 

meadows can be found in these areas. At higher elevations, 

mountain hemlock (Tsuga mertensiana), subalpine fir (Abies 

lasiocarpa), and Engelmann spruce (Picea engelmannii) are 

common. At elevations as high as 3,350 m are alpine meadows that consist of huckleberry (Vaccinium L. spp.) and heath 

(Erica L. spp.) fields, as well as barren areas.

The Cascades Ecoregion contains numerous state and 

national forests, including the Mount Baker–Snoqualmie, 

Mount Hood, Deschutes, Willamette, Umpqua, Rogue River–

Siskiyou, and Shasta–Trinity National Forests. Wilderness 

areas include the Goat Rocks, Mount Adams, Mount Hood, 

Mount Jefferson, Mount Thielsen, Mount Washington, Three 

Sisters, and Mount Shasta Wildernesses. The ecoregion also 

contains Mount Rainier and Crater Lake National Parks. Much 

of the land at middle and higher elevations is held publically 

in national forests, whereas private ownership (especially 

by the forest industry) is more common at lower elevations 

where Douglas-fir and hemlock forests dominate (Risser and 

others, 2000). Land management on public lands varies from 

intensive forestry, especially on the lower slopes, to protected 

wilderness areas (McNab and Avers, 1994). 

Before European settlement, natural disturbances, especially fire, were the dominant forces driving land-cover change 

in the Cascades Ecoregion. The southern part of the ecoregion 

is prone to frequent lightning-caused fires, having fire return 

intervals of around 55 years (Sugihara and others, 2006). In 

the north, fires are less frequent but can be more severe (Risser 

and others, 2000), with fire return intervals as long as 500 years 

around Mount Rainier (Agee, 1993). After European settlement in the mid-1800s, forest landscapes were increasingly 

influenced by anthropogenic disturbance in the form of timber 

harvesting, as well as fire suppression in the early 20th century. 

Replanting practices resulted in a more uniform, even-aged 

forest structure and greater landscape fragmentation (Wallin 

and others, 1996). Reforestation practices resulted in a simplification of species composition, with Douglas-fir replacing 

a variety of hardwoods and other softwoods (Alig and others, 

2000). These homogenous forests often lack the large trees, 

snags, downed wood, and tree-species diversity that are needed 

to promote wildlife diversity (Risser and others. 2000).

The ecoregion is sparsely populated. The largest cities are 

Mount Shasta, California (population 3,624), Oakridge, Oregon 

(3,148), and Weed, California (2,978) (U.S. Census Bureau, 

2000). With the decline of the timber industry in the Cascades 

Ecoregion, most small towns that have historically relied on a 

timber-based economy are now relying more on recreation and 

other industries to sustain their economy (Jacklet, 2009).

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the areal extent of land-use/

land-cover change (area that experienced land-cover change at 

least once in the 27-year study period) in the Cascades Ecoregion was 24.6 percent, or approximately 11,520 km2 (table1). 

Compared with other western United States ecoregions, the 

amount of change was high (fig. 2). Overall, an estimated 

4,164 km2 (8.9 percent of the total ecoregion area) changed 

in one of the time periods; 5,240 km2 (11.2 percent) changed 

Figure 2. Overall spatial change in Cascades Ecoregion (C; 

darker bars) compared with that of all 30 all Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Cascades 

Ecoregion (four time periods) labeled for clarity. See table 2 for 

years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods
Chapter 11—Cascades Ecoregion 125

during two time periods; and 2,012 km2 (4.3 percent) changed 

during three periods. Only 468 km2 (0.1 percent) changed in 

all four time periods (table 1). 

The average annual rate of land-cover change in the 

Cascades Ecoregion was 1.7 percent (795 km2) (table 2). Average annual change for successive time periods reveals a steady 

increase in rates of land-cover change over the study period for 

the first three time periods and a slight decline for the last time 

period. Between 1973 and 1980, the average rate of change 

was 1.6 percent (749 km2), increasing to 1.8 percent (833 km2) 

between 1980 and 1986. This rate continued to rise to 2.0 percent (919 km2) between 1986 and 1992, then it declined to 1.4 

percent (652 km2) between 1992 and 2000 (fig. 3; table 2). 

Forest is the dominant land-cover class in the Cascades 

Ecoregion (figs. 4,5), accounting for 82.8 percent of the ecoregion in 2000, followed by grassland/shrubland (5.6 percent), 

mechanically disturbed (3.5 percent), and agriculture (2.1 

percent) (table 3). The seven remaining land-cover classes 

accounted for 6.0 percent of the ecoregion (table 3).

The leading conversion in all time periods was from 

forest to mechanically disturbed, the result of clearcut logging 

(fig. 5). Changes associated with timber harvest and forest 

regeneration account for over 98 percent of all land-cover conversions, and they represent the top four land-cover conversions in the ecoregion throughout the study period (table 4). 

The timber-harvest-to-forest-regeneration process starts after 

the removal of trees (that is, forest to mechanically disturbed), 

after which the area is replanted with seedlings or regenerates naturally (mechanically disturbed to grassland/shrubland) 

(fig.6). The successional process continues as the seedlings 

grow tall enough (at least 2 m) to be classified as forest (grassland/shrubland to forest). In some areas, forest regeneration is 

rapid, and so the study’s six- to eight-year sampling interval 

did not capture the grassland/shrubland successional stage, 

the lack of which resulted in conversions from mechanically 

disturbed directly back to forest. 

Between 1973 and 1992, a net loss of forest occurred in 

every time period, resulting in a net decline in forest land of 

approximately 10,800 km2. This trend reversed between 1992 

Figure 5. Freshly clearcut hillside in Cascades Ecoregion. 

Logging, usually clearcutting, was leading driver of land-cover 

change in Cascades Ecoregion for all time periods. 

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

Figure 3. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Cascades Ecoregion are represented 

by red bars in each time period.

Figure 4. Forested hillsides in Cascades Ecoregion, showing 

logging roads and clearcut scars. Dominant land-cover class in 

Cascades Ecoregion is forest, which in 2000 made up almost 83 

percent of all land cover in ecoregion. 
126 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 6. Aftermath of timber harvest in Cascades Ecoregion, 

showing that most of slash is removed, burnt, or buried and 

then seedlings (wrapped in protective mesh) are planted. Some 

states, such as Washington, have laws that prescribe how soon 

to replant after tree harvesting to guard against invasive species 

(Washington State Department of Natural Resources, 2001). 

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 7. Normalized average net change in Cascades Ecoregion by time period for each land-cover class. Bars above zero 

axis represent net gain, whereas bars below zero represent net 

loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

and 2000 with an 11,050 km2 gain in forest land, suggesting 

that the losses in the early years were generally replaced by 

gains in the last time period (table 3; figs. 7,8). Types of land 

ownership and land management influenced the changes that 

occurred. Sample blocks in the Cascades Ecoregion that fell 

in protected areas experienced the least amount of change, 

whereas sample blocks in privately held land experienced the 

greatest amount of change (fig. 9). 

Several factors were involved in the decline of forest 

products from the Pacific Northwest between 1992 and 2000 

(fig.7; table 4). Lumber and wood-product exports from the 

Pacific Northwest declined in the 1990s because their main 

markets (Japan and other Asian countries) suffered economic 

downturns that reduced demand for wood-based commodities. This caused an oversupply of wood products that led to a 

collapse in prices and the amount of exports (Perez-Garcia and 

Barr, 2005). The Pacific Northwest also faced increased competition during this time from other wood-producing countries 

such as Russia, Finland, Canada, and New Zealand (Daniels, 

2005). A significant reason for the increase in Canadian exports 

was the increased harvest rate implemented to avert fires resulting from trees killed by mountain pine beetle and other pests 

(Perez-Garcia and Barr, 2005). 

Figure 8. Estimated cumulative change in Cascades Ecoregion 

for each land-cover class between 1973 and 2000. Bars above zero 

axis represent overall gain, whereas bars below zero represent 

overall loss. Mechanically disturbed class experienced largest 

decrease, while grassland/shrubland and forest classes had 

highest gains. No change was detected for ice/snow class.

−1.5

−1

−0.5

0

0.5

1

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 11—Cascades Ecoregion 127

Coast

Range

Coast

Range

Klamath

Mountains

Northern

Basin and Range

Eastern Cascades

Slopes and Foothills

ECSF

Willamette

Valley

Blue Mountains

BLM

Columbia

Plateau

CLMP

Puget

Lowland

PL North

Cascades

122°

121° 120°

124° 123°

47°

46°

45°

44°

43°

42°

0 50 100 MILES

0 50 100 KILOMETERS

Cascades Ecoregion

Other ecoregion

State boundary

Federal land-ownership class

Overall spatial change

(per 10 x 10 km sample block)

Boundaries

Wilderness Area

National Forest

National Monument or Park

Tribal lands

Other Federal lands

Other lands

EXPLANATION

0.0–10.0

10.1–20.0

20.1–30.0

30.1–50.0

50.1–70.4

In the 1990s, the Northwest Forest Plan (Espy and 

Babbitt, 1994) was developed to protect the habitat of the 

threatened Northern Spotted Owl (Strix occidentalis caurina) (Daniels, 2005). Under this plan, timber harvest was 

banned or reduced on 10 million of the 17 million acres 

(40,469 of 68,797 km2) of national forests in the Pacific 

Northwest. Before the Northwest Forest Plan, timber sales 

from these national forests were about 4 to 5 billion board 

feet per year. After 1990, sales dropped to less than a billion board feet per year (Daniels, 2005). A consequence 

of the reduced harvest in national forests in the Pacific 

Northwest was an increase in harvesting from privately 

owned land. On public land, stand replacement after 

timber harvest was 2 to 10 times more likely to occur than 

stand replacement (full or partial) as a result of wildfire 

(Alig and others, 2000).

Figure 9. Federal land ownership and cumulative landuse/land-cover change (as percent of sample-block area) 

from 1973 to 2000 in Cascades Ecoregion. Sample blocks 

that fell on wilderness areas witnessed least amount of 

change. Most sample blocks that saw highest amount of 

change fell on privately held land at lower elevations. Landownership data from National Atlas of the United States 

(2006). See appendix 2 for abbreviations for Western United 

States ecoregions.
128 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 1. Percentage of Cascades Ecoregion land cover that 

changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (75.4 percent), whereas 24.6 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 9.0 1.7 7.4 10.7 1.1 12.6

2 11.2 1.6 9.5 12.8 1.1 10.0

3 4.3 0.9 3.4 5.2 0.6 13.9

4 0.1 0.0 0.1 0.2 0.0 18.3

Overall 

spatial 

change

24.6 3.7 20.9 28.3 2.5 10.2

Table 2. Raw estimates of change in Cascades Ecoregion land cover, computed for each of four time 

periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 11.2 2.1 9.2 13.3 1.4 12.5 1.6

1980–1986 10.7 1.9 8.8 12.6 1.3 12.1 1.8

1986–1992 11.8 1.7 10.0 13.5 1.2 10.1 2.0

1992–2000 11.1 2.1 9.1 13.2 1.4 12.5 1.4

Estimate of change, in square kilometers

1973–1980 5,242 960 4,283 6,202 654 12.5 749

1980–1986 4,998 889 4,108 5,887 606 12.1 833

1986–1992 5,515 817 4,698 6,333 557 10.1 919

1992–2000 5,214 959 4,254 6,173 653 12.5 652
Chapter 11—Cascades Ecoregion 129

Table 3. Estimated area (and margin of error) of each land-cover class in Cascades Ecoregion, calculated five times between 1973 and 

2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.1 0.7 1.1 0.5 4.8 1.1 0.0 0.0 1.4 1.2 82.2 3.5 5.3 1.3 2.0 1.3 0.5 0.2 0.0 0.0

1980 1.2 0.7 1.2 0.5 4.6 1.0 0.1 0.0 1.4 1.2 81.3 3.5 6.4 1.3 2.0 1.3 0.5 0.2 0.0 0.0

1986 1.1 0.7 1.2 0.6 4.0 0.7 0.1 0.0 1.4 1.2 80.9 3.6 7.4 1.4 2.0 1.3 0.5 0.2 0.0 0.0

1992 1.1 0.7 1.3 0.6 4.8 0.8 0.1 0.0 1.4 1.2 80.5 3.6 6.8 1.3 2.0 1.3 0.5 0.2 0.0 0.0

2000 1.1 0.7 1.4 0.6 3.5 1.3 0.1 0.1 1.4 1.2 82.8 3.6 5.6 1.2 2.1 1.3 0.5 0.2 0.0 0.0

Net

change 0.0 0.0 0.3 0.1 −1.4 1.5 0.0 0.0 0.1 0.0 0.6 1.2 0.3 1.0 0.1 0.1 0.0 0.0 0.0 0.0

Gross

change 0.1 0.1 0.3 0.1 10.6 2.0 0.0 0.0 0.1 0.1 10.7 1.9 8.0 1.6 0.1 0.1 0.0 0.0 0.0 0.0

Area, in square kilometers

1973 529 338 529 240 2,254 497 21 14 641 560 38,479 1,621 2,490 603 916 601 221 94 0 0

1980 544 346 547 249 2,130 482 24 18 646 559 38,019 1,646 3,017 599 933 602 219 94 0 0

1986 527 337 570 259 1,854 341 25 18 643 560 37,828 1,667 3,465 662 949 602 220 95 0 0

1992 524 339 616 277 2,226 384 29 21 659 559 37,686 1,663 3,162 615 958 610 219 94 0 0

2000 523 340 650 287 1,620 591 31 24 666 559 38,755 1,677 2,634 577 964 616 219 95 16 17

Net

change −6 12 121 54 −634 695 11 11 25 23 276 557 144 472 48 37 −2 6 16 17

Gross

change 63 49 121 54 4,956 928 11 11 40 25 4,994 869 3,734 750 58 40 6 6 16 17
130 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Cascades Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 2,134 486 331 4.6 40.7

Mechanically disturbed Grassland/Shrubland 1,412 389 265 3.0 26.9

Mechanically disturbed Forest 975 263 179 2.1 18.6

Grassland/Shrubland Forest 710 196 134 1.5 13.5

Forest Agriculture 20 11 8 0.0 0.4

Other Other −9 n/a n/a 0.0 −0.2

Totals 5,242 11.2 100.0

1980–1986 Forest Mechanically disturbed 1,830 337 230 3.9 36.6

Mechanically disturbed Grassland/Shrubland 1,418 363 247 3.0 28.4

Grassland/Shrubland Forest 954 217 148 2.0 19.1

Mechanically disturbed Forest 716 205 139 1.5 14.3

Water Mechanically disturbed 19 24 16 0.0 0.4

Other Other 60 n/a n/a 0.1 1.2

Totals 4,998 10.7 100.0

1986–1992 Forest Mechanically disturbed 2,209 380 259 4.7 40.1

Grassland/Shrubland Forest 1,379 332 226 2.9 25.0

Mechanically disturbed Grassland/Shrubland 1,078 214 146 2.3 19.6

Mechanically disturbed Forest 745 189 129 1.6 13.5

Forest Developed 36 17 12 0.1 0.7

Other Other 68 n/a n/a 0.1 1.2

Totals 5,515 11.8 100.0

1992–2000 Forest Mechanically disturbed 1,613 592 403 3.4 30.9

Mechanically disturbed Forest 1,434 348 237 3.1 27.5

Grassland/Shrubland Forest 1,315 263 179 2.8 25.2

Mechanically disturbed Grassland/Shrubland 777 135 92 1.7 14.9

Forest Developed 29 14 10 0.1 0.6

Other Other 46 n/a n/a 0.1 0.9

Totals 5,214 11.1 100.0

1973–2000

(overall)

Forest Mechanically disturbed 7,786 1,344 915 16.6 37.1

Mechanically disturbed Grassland/Shrubland 4,686 869 592 10.0 22.3

Grassland/Shrubland Forest 4,358 775 528 9.3 20.8

Mechanically disturbed Forest 3,870 820 559 8.3 18.5

Forest Developed 98 45 30 0.2 0.5

Other Other 172 n/a n/a 0.4 0.8

Totals 20,969 44.8 100.0
Chapter 11—Cascades Ecoregion 131

References Cited

Agee, J.K., 1993, Fire ecology of Pacific Northwest forests: 

Washington, D.C., Island Press, p. 229.

Alig, Ralph J., Zheng, Daolan, Spies, Thomas A., and Butler, 

Brett J., 2000, Forest cover dynamics in the Pacific Northwest west side—Regional trends and projections: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station, Research Paper PNW-RP-522, 22 p. 

(Available at http://www.treesearch.fs.fed.us/pubs/2935.)

Daniels, J.M., 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-624.

Espy, M., and Babbitt, B., 1994, Record of decision for 

amendments to Forest Service and Bureau of Land Management planning documents within the range of the Northern 

Spotted Owl: U.S. Department of Agriculture and U.S. 

Department of the Interior Northwest Forest Plan, 74 p. 

(Available at http://www.blm.gov/or/plans/nwfpnepa/

FSEIS-1994/NWFPTitl.htm.)

Jacklet, Ben, 2009, Trouble in Timber Town—Decades after 

an industry downfall, towns still grapple with what’s next: 

Oregon Business. (Available at http://www.oregonbusiness.

com/articles/72-november-2009/2478-trouble-in-timbertown.)

McNab, W. Henry, and Avers, Peter E., 1994, Cascade mixed 

forest – Coniferous forest – Alpine meadow, in Ecological 

subregions of the United States: U.S. Department of Agriculture, Forest Service, WO-WSA-5, chap. 25. (Available at 

http://www.fs.fed.us/land/pubs/ecoregions/ch25.html.)

National Atlas of the United States, 2006, Federal Lands of the 

United States: National Atlas of the United States database, 

accessed February 19, 2006, at http://nationalatlas.gov.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, p. 118–125.

Perez-Garcia, John, and Barr, J. Kent, 2005, Forest products 

export trends update for the Pacific Northwest region: Seattle, University of Washington, College of Forest Resources, 

Northwest Environmental Forum. (Available at http://www.

nwenvironmentalforum.org/science/papers.html.)

Risser, Paul G., 2000, Cascade Mountains Ecoregion, in

Oregon State of the Environment Report 2000—Statewide 

Summary: State of the Environment Report Science Panel, 

Oregon Progress Board, chap. 4.3, accessed June 28, 2011, 

at http://www.oregon.gov/DAS/OPB/docs/SOER2000/

Ch4.3.pdf.

Sugihara, Neil G., van Wagtendonk, Jan W., Shaffer, Kevin E., 

Fites-Kaufman, JoAnn, and Thode, Andrea E., eds., 2006, 

Fire in California’s ecosystems: Berkeley, University of 

California Press, p. 215.

U.S. Census Bureau, 2000, U.S. Census, 2000: U.S. Census 

Bureau database, accessed September 28, 2009, at http://

factfinder.census.gov. 

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.

Wallin, D.O., Swanson, F.J., Marks, B., Cissel, J.H., and 

Kertis, J., 1996, Comparison of managed and pre-settlement 

landscape dynamics in forests of the Pacific Northwest, 

U.S.A.: Forest Ecology and Management, v. 85, p. 291–310.

Washington State Department of Natural Resources, 2001, 

Reforestation: Washington State Department of Natural 

Resources, Title 222 WAC - Forest practices rules, chap. 

222-34 WAC, p. 34-2.
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Chapter 12

Eastern Cascades Slopes and Foothills Ecoregion

the ecoregion to 3,000 mm in the area bordering the higher 

Cascade Range to the west. Precipitation (either rain or snow) 

falls mostly in the fall, through winter into spring. Elevations 

range from near sea level at the Columbia River to more than 

3,300 m; most of the region is between 900 and 2,000 m high. 

By Daniel G. Sorenson

Ecoregion Description

The Eastern Cascades Slopes and Foothills Ecoregion 

(Omernik, 1987; U.S. Environmental Protection Agency, 1997) 

covers approximately 57,329 km2 (22,135 mi2) in the states of 

Washington, Oregon, and California (fig. 1). The ecoregion is 

bounded on the east by the Columbia Plateau, Blue Mountains, 

and Northern Basin and Range Ecoregions; on the south by the 

Sierra Nevada Ecoregion; on the west by the Klamath Mountains and Cascades Ecoregions; and on the north by the North 

Cascades Ecoregion (fig. 1). Because the Eastern Cascades 

Slopes and Foothills Ecoregion lies within the rain shadow of 

the Cascade Range, the annual amount of precipitation varies 

greatly, from 500 mm in the eastern and southern sections of 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Eastern Cascades Slopes and Foothills 

Ecoregion and surrounding ecoregions, showing land-use/landcover classes from 1992 National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover 

classes shown in explanation may be depicted on map; note 

also that, for this “Status and Trends of Land Change” study, 

transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Map shows 

that land cover is more diverse in southern part of ecoregion. 

Squares indicate locations of 10 x 10 km sample blocks 

analyzed in study. Index map shows locations of geographic 

features mentioned in text. Abbreviations for Western United 

States ecoregions are listed in appendix 2. See appendix 3 for 

definitions of land-use/land-cover classifications. 

Cascades

Sierra Nevada

C

Northern Basin

and Range

Coast Range

Blue

Mountains

Columbia

Plateau

Willamette Valley

BLM

CR

Central Basin

and Range

Sierra Nevada

SCCCOW

NC

PL

KM

KM

PACIFIC

O

CEA

N

122°

120°

124°

46°

44°

42°

0 50 100 150 MILES

0 50 100 150 KLOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

WASHINGTON

OREGON

CALIFORNIA NEVADA

Bend

Klamath Falls

C A S C A D E R A N G E Columb ia River

Desc hutes

River

 Klamath R.
134 Status and Trends of Land Change in the Western United States—1973 to 2000

In the plateaus, elevation generally varies from 60 to 600 m 

(McNab and Avers, 1994).

The Eastern Cascades Slopes and Foothills Ecoregion 

formed from tectonic uplift with mountain ranges and valleys oriented north-to-south; it is a relatively young ecoregion 

with numerous lava flows, volcanic cones, and buttes (U.S. 

Environmental Protection Agency, 2010). Population is sparse: 

the two largest cities are Bend, Oregon, with a population of 

52,029, and Klamath Falls, Oregon, with 19,462 residents 

(U.S. Census Bureau, 2000). 

Forest is the primary land cover in the Eastern Cascades 

Slopes and Foothills Ecoregion (figs. 1,2), and fire plays an 

important role in forest composition. Ponderosa pine (Pinus 

ponderosa) is the dominant tree species, and lodgepole pine 

(Pinus contorta) is common in the drier parts of the ecoregion 

(Risser, 2000). The bark on older, larger ponderosa pines is 

thick, providing protection from fires. Ponderosa pines are usually little affected if 50 percent or less of the crown is destroyed 

by fire, giving them an advantage over less fire-tolerant tree 

species (Oliver and Ryker, 1990). Lodgepole pines have serotinous or closed cones that only open and release seeds when 

exposed to extreme heat during a fire. As a result, postfire colonization of burned areas by lodgepole pines is rapid, outpacing 

most other species (Lotan and Chritchfield, 1990). 

The northern part of the Eastern Cascades Slopes and 

Foothills Ecoregion drains into the Deschutes and Columbia Rivers. Spring-fed tributaries and snow melt provide 

most of the rivers’ water. The southern section is drained 

by the Klamath River, which is fed by a vast interior wetland. Approximately 75 percent of the historic wetlands of 

the Klamath Basin have been drained for crops. The most 

common crops grown in the Eastern Cascades Slopes and 

Foothills Ecoregion are hay, alfalfa, cereal grains, potatoes, 

onions, and sugar beets (Risser, 2000). 

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the areal extent of land-use/

land-cover change (the footprint of change, or the area that 

experienced change at least once during the 27-year study 

period) in the Eastern Cascades Slopes and Foothills Ecoregion was 12.1 percent, or 6,943 km2 (table 1). Compared 

with other western United States ecoregions, change in the 

Eastern Cascades Slopes and Foothills Ecoregion was above 

average (fig. 3). Overall, an estimated 2,637 km2 (4.6 percent) of the ecoregion changed in one time period; 3,268 km2 

Figure 2. Grassy meadow and forested hillsides in Eastern 

Cascades Slopes and Foothills Ecoregion. Dominant land-cover 

class in Eastern Cascades Slopes and Foothills Ecoregion is forest, 

although grassland/shrubland makes up about one-third of ecoregion. Forests tend to be at higher elevations, in areas with more 

precipitation, whereas grassland/shrubland areas are found mostly 

in valley bottoms and drier locations. Photograph by Terry Sohl.

Figure 3. Overall spatial change in Eastern Cascades Slopes and 

Foothills Ecoregion (ECSF; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial change 

in Eastern Cascades Slopes and Foothills Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

Change in four time periods

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods
Chapter 12—Eastern Cascades Slopes and Foothills Ecoregion 135

(5.7 percent) changed in two time periods; 1,032 km2 (1.8 

percent) changed in three periods; and less than 57 km2 (0.1 

percent) area changed in all four time periods (table 1). The 

average annual rate of change in the Eastern Cascades Slopes 

and Foothills Ecoregion between 1973 and 2000 was 0.8 

percent (table 2). Average annual change for successive time 

periods reveals a steady increase during the study period 

for the first three time periods and a slight decline for the 

last time period. Between 1973 and 1980, the annual rate of 

change was 0.5 percent (295 km2), increasing to 0.8 percent 

(486 km2) between 1980 and 1986. This rate continued to 

rise to 1.0 percent (580 km2) between 1986 and 1992 and 

then dropped slightly to 0.9 percent (489 km2) between 1992 

and 2000 (fig. 4; table 2). 

In 2000, three of the ten land-cover classes in the Eastern 

Cascades Slopes and Foothills Ecoregion dominate total 

land cover: forest (53.2 percent), grassland/shrubland (33.3 

percent), and agriculture (7.1 percent) (table 3; fig. 1). The 

remaining seven classes contained the remaining 6.5 percent 

of the classified landscape in 2000. Each of these classes alone 

represented less than 2.5 percent of the sampled area. Between 

1973 and 2000, the land-cover classes that experienced a 

measurable net change in relation to the total ecoregion area 

include net losses of forest (6.8 percent), in addition to net 

gains in grassland/shrubland (8.7 percent) and mechanically 

disturbed (7.2 percent) (table 3; fig. 5). 

The top four land-cover conversions in the ecoregion 

for all time periods (except the fourth) were associated with 

timber harvest and forest regeneration (fig. 6). The principal 

type of change in all time periods was from forest to mechanically disturbed, caused by forest logging through clearcutting. The timber harvest-to-regeneration process starts after 

the removal of trees (forest to mechanically disturbed), after 

Figure 4. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Eastern Cascades Slopes and Foothills Ecoregion are represented by red 

bars in each time period.

Figure 5. Normalized average net change in Eastern Cascades 

Slopes and Foothills Ecoregion by time period for each land-cover 

class. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. Note that not all land-cover classes 

shown in explanation may be represented in figure. See appendix 

3 for definitions of land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
136 Status and Trends of Land Change in the Western United States—1973 to 2000

which the area is replanted with tree seedlings or regenerates 

naturally (mechanically disturbed to grassland/shrubland). The 

process continues as the seedlings grow tall enough (at least 

2 m high) to be classified as trees (grassland/shrubland to forest). In some areas, forest regeneration was rapid, and so the 

six-to-eight year sampling interval missed the grassland/shrubland stage, which resulted in the apparent conversion from 

mechanically disturbed directly to forest. Forest cutting and 

regeneration accounted for almost all the change in the Eastern 

Cascades Slopes and Foothills Ecoregion, which was between 

83 and 88 percent of all periods (table 4). 

Figure 6. Clearcutting of forested area. Principal cause of 

land-cover change in Eastern Cascades Slopes and Foothills 

Ecoregion was logging and forest regenerations. Photograph by 

Terry Sohl.

Several factors were involved in the decline of forest cutting. Lumber and wood exports declined in the 1990s because 

the primary market for Pacific Northwest wood products 

(Japan and other Asian counties) experienced an economic 

downturn that reduced demand. The 1990s saw more woodproducing countries such as Russia, Canada, and New Zealand 

increase their exports. In addition, the Northwest Forest Plan 

was implemented in 1996 to protect the threatened Northern 

Spotted Owl (Strix occidentalis caurina), which prefers to 

roost in old-growth forest that has moderate to high canopy 

enclosure. Timber sales in protected areas declined from 4 to 5 

billion board feet per year to less than a billion board feet per 

year, and almost 60 percent of Pacific Northwest national forest was taken out of timber production (Daniels, 2005). 

The rate of change and dominant land cover for the sample 

blocks in California (4.5 percent) was lower than that for the 

rest of the ecoregion (12.1 percent). In 2000, the top three landcover classes in the California section of the ecoregion were 

grassland/shrubland (48.0 percent), forest (35.3 percent), and 

agriculture (10.3 percent), whereas, for the Eastern Cascades 

Slopes and Foothills Ecoregion as a whole, the percentages for 

forest, grassland/shrubland, and agriculture were 53.2 percent, 

33.3 percent, and,7.0 percent, respectively. Although 50.6 

percent of all land-cover change in the California section was 

the result of logging and forest regeneration, not all of the top 

land-cover conversions were related to logging. Fire disturbance 

and recovery (nonmechanically disturbed) was one of the top 

conversions, as was water-to-wetland conversion (table 4). 

Further research is needed to explore the cause of land-cover 

differences in this ecoregion. Possible factors might include 

elevation, annual precipitation, and varying land-use practices 

and policies in California, Oregon, and Washington.

Table 1. Percentage of Eastern Cascades Slopes and Foothills 

Ecoregion land cover that changed at least one time during study 

period (1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (87.9 percent), whereas 12.1 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 4.6 1.4 3.2 5.9 0.9 20.5

2 5.7 2.0 3.8 7.7 1.3 23.1

3 1.8 0.9 0.8 2.7 0.6 36.4

4 0.1 0.1 0.0 0.1 0.0 57.6

Overall 

spatial 

change

12.1 3.5 8.6 15.6 2.4 19.6
Chapter 12—Eastern Cascades Slopes and Foothills Ecoregion 137

Table 2. Raw estimates of change in Eastern Cascades Slopes and Foothills Ecoregion land cover, 

computed for each of four time periods between 1973 and 2000, and associated error at 85-percent 

confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 3.6 1.3 2.3 4.9 0.9 25.3 0.5

1980–1986 5.1 1.9 3.2 7.0 1.3 24.9 0.8

1986–1992 6.1 2.2 3.9 8.2 1.5 24.2 1.0

1992–2000 6.8 2.1 4.7 8.9 1.4 21.0 0.9

Estimate of change, in square kilometers

1973–1980 2,065 771 1,294 2,836 522 25.3 295

1980–1986 2,917 1,074 1,843 3,990 727 24.9 486

1986–1992 3,478 1,243 2,235 4,721 842 24.2 580

1992–2000 3,915 1,212 2,702 5,127 821 21.0 489

Table 3. Estimated area (and margin of error) of each land-cover class in Eastern Cascades Slopes and Foothills Ecoregion, calculated 

five times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.5 1.1 0.1 0.1 1.4 0.7 0.0 0.0 0.2 0.2 57.1 7.6 30.6 6.7 7.1 3.7 1.6 0.7 0.3 0.4

1980 1.5 1.2 0.1 0.1 1.5 0.7 0.0 0.0 0.2 0.2 56.2 7.4 31.7 6.5 7.2 3.7 1.6 0.7 0.0 0.0

1986 1.5 1.2 0.1 0.1 2.3 1.0 0.0 0.0 0.2 0.2 55.0 7.3 31.9 6.4 7.3 3.7 1.6 0.7 0.0 0.0

1992 1.6 1.2 0.2 0.1 2.2 0.9 0.0 0.0 0.2 0.2 54.0 7.1 33.1 6.3 7.1 3.7 1.5 0.7 0.3 0.3

2000 1.5 1.1 0.2 0.1 2.3 1.0 0.0 0.0 0.2 0.2 53.2 6.9 33.3 6.2 7.1 3.7 1.5 0.7 0.6 0.8

Net

change 0.0 0.1 0.1 0.1 1.0 1.0 0.0 0.0 0.0 0.0 −3.9 1.7 2.7 1.7 0.0 0.2 −0.1 0.1 0.2 0.9

Gross

change 0.7 0.4 0.1 0.1 6.0 1.9 0.0 0.0 0.0 0.0 6.4 2.2 6.3 2.1 0.6 0.6 0.7 0.4 1.4 1.2

Area, in square kilometers

1973 850 652 73 40 781 421 4 4 115 129 32,761 4,385 17,555 3,857 4,093 2,105 917 412 179 257

1980 856 679 78 42 843 414 4 4 115 129 32,247 4,265 18,171 3,723 4,110 2,101 904 412 0 0

1986 870 673 83 45 1,327 586 5 5 115 129 31,550 4,158 18,276 3,692 4,177 2,103 925 419 0 0

1992 889 660 90 49 1,262 541 5 5 114 128 30,930 4,042 18,990 3,583 4,057 2,122 832 383 160 161

2000 867 630 108 65 1,344 589 5 5 114 128 30,525 3,942 19,085 3,531 4,076 2,120 886 392 317 455

Net

change 17 53 35 29 563 557 1 1 −1 1 −2,236 955 1,531 986 −17 131 −31 59 138 529

Gross

change 377 218 35 29 3,442 1,076 1 1 1 1 3,643 1,281 3,587 1,191 334 336 377 231 816 696
138 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Eastern Cascades Slopes and Foothills Ecoregion, showing amount of area 

changed (and margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods 

and also during overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 835 409 277 1.5 40.4

Mechanically disturbed Grassland/Shrubland 558 343 232 1.0 27.0

Mechanically disturbed Forest 206 163 111 0.4 10.0

Nonmechanically disturbed Grassland/Shrubland 165 236 160 0.3 8.0

Grassland/Shrubland Forest 85 63 42 0.1 4.1

Other Other 216 n/a n/a 0.4 10.5

Totals 2,065 3.6 100.0

1980–1986 Forest Mechanically disturbed 1,310 582 394 2.3 44.9

Mechanically disturbed Grassland/Shrubland 594 341 231 1.0 20.4

Grassland/Shrubland Forest 378 302 204 0.7 13.0

Mechanically disturbed Forest 238 155 105 0.4 8.1

Grassland/Shrubland Agriculture 164 222 150 0.3 5.6

Other Other 233 n/a n/a 0.4 8.0

Totals 2,917 5.1 100.0

1986–1992 Forest Mechanically disturbed 1,190 538 364 2.1 34.2

Mechanically disturbed Grassland/Shrubland 1,011 500 339 1.8 29.1

Grassland/Shrubland Forest 384 219 148 0.7 11.0

Mechanically disturbed Forest 296 182 123 0.5 8.5

Agriculture Grassland/Shrubland 164 232 157 0.3 4.7

Other Other 433 n/a n/a 0.8 12.4

Totals 3,478 6.1 100.0

1992–2000 Forest Mechanically disturbed 1,309 587 398 2.3 33.4

Mechanically disturbed Grassland/Shrubland 983 484 328 1.7 25.1

Grassland/Shrubland Forest 686 432 293 1.2 17.5

Grassland/Shrubland Nonmechanically disturbed 268 384 260 0.5 6.8

Mechanically disturbed Forest 236 165 112 0.4 6.0

Other Other 432 n/a n/a 0.8 11.0

Totals 3,915 6.8 100.0

1973–2000

(overall)

Forest Mechanically disturbed 4,645 1,751 1,186 8.1 37.5

Mechanically disturbed Grassland/Shrubland 3,146 1,434 971 5.5 25.4

Grassland/Shrubland Forest 1,533 766 519 2.7 12.4

Mechanically disturbed Forest 977 591 400 1.7 7.9

Grassland/Shrubland Nonmechanically disturbed 316 387 262 0.6 2.6

Other Other 1,758 n/a n/a 3.1 14.2

Totals 12,375 21.6 100.0
Chapter 12—Eastern Cascades Slopes and Foothills Ecoregion 139

References Cited

Daniels, J.M., 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-624, 80 p.

Lotan, James E., and Critchfield, William B., 1990, Silvics of 

North America: 1 Conifers, Lodgepole Pine: U.S. Department of Agriculture, Forest Service, Agriculture Handbook 

654, v. 1, accessed June 23, 2009, at http://www.na.fs.fed.

us/spfo/pubs/silvics_manual/Volume_1/pinus/contorta.htm. 

McNab, W. Henry, and Avers, Peter E., 1994, Ecological subregions of the United States: U.S. Department of Agriculture, Forest Service, WO-WSA-5, chap. 25.

Oliver, William W., and Ryker, Russell A., 1990, Silvics of 

North America: 1 Conifers, Ponderosa Pine: U.S. Department of Agriculture, Forest Service, Agriculture Handbook 

654, v. 1, accessed June 23, 2009, at http://www.na.fs.fed.

us/spfo/pubs/silvics_manual/Volume_1/pinus/ponderosa.

htm.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, p. 118–125.

Risser, P.G., 2000, East Cascades Slope and Foothills Ecoregion, in Oregon State of the Environment Report 2000—

Statewide Summary: State of the Environment Report 

Science Panel, Oregon Progress Board, chap. 4.4, accessed 

June 23, 2009, at http://oregon.gov/DAS/OPB/docs/

SOER2000/Ch4_4.pdf.

U.S. Census Bureau, 2000, U.S. Census, 2000, accessed April 

1, 2009, at http://www.census.gov/prod/www/abs/decennial/

index.htm.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

U.S. Environmental Protection Agency, 2010, Primary distinguishing characteristics of Level III ecoregions of the 

continental United States: U.S. Environmental Protection 

Agency database, available at ftp://ftp.epa.gov/wed/ecoregions/us/Eco_Level_III_descriptions.doc.

Vogelmann, J.E., Howard, S.M., Yang L., Larson, C.R., Wylie 

B.K., and van Driel N., 2001, Completion of the 1990s 

National Land Cover Data Set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 67, p. 650–662. 
This page intentionally left blank
Chapter 13

Klamath Mountains Ecoregion

By Benjamin M. Sleeter and James P. Calzia

Ecoregion Description

The Klamath Mountains Ecoregion covers approximately 

47,791 km2 (18,452 mi2) of the Klamath and Siskiyou Mountains of northern California and southern Oregon (fig. 1) 

(Omernik, 1987; U.S. Environmental Protection Agency, 

1997). The ecoregion is flanked by the Coast Range Ecoregion 

to the west, the Southern and Central California Chaparral and 

Oak Woodlands Ecoregion to the south, the Cascades and the 

Eastern Cascades Slopes and Foothills Ecoregions to the east, 

and the Willamette Valley Ecoregion to the north. The mild 

Mediterranean climate of the ecoregion is characterized by hot, 

dry summers and wet winters; the amount of winter moisture 

varies within the ecoregion, decreasing from west to east. The 

Klamath–Siskiyou Mountains region is widely recognized as 

an important biodiversity hotspot (Whittaker, 1960; Kruckeberg, 1984; Wagner, 1997; DellaSala and others, 1999), 

containing more than 3,500 plant species, more than 200 of 

which are endemic (Sawyer, 2007). A biological assessment by 

DellaSala and others (1999) ranked the Klamath–Siskiyou 

Mountains region as the fifth richest coniferous forest in terms 

of species diversity. In addition, the International Union for the 

Conservation of Nature considers the region an area of notable 

botanical importance (Wagner, 1997). Twenty-nine different 

species of conifers can be found in the Klamath Mountains 

Ecoregion (Sawyer, 1996).

This ecoregion is underlain by belts of Paleozoic to 

Mesozoic metasedimentary and metavolcanic rocks separated 

by linear belts of serpentinite. Most of these serpentinite 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Klamath Mountains Ecoregion and surrounding 

ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note 

that not all land-use/land-cover classes shown in explanation 

may be depicted on map; note also that, for this “Status and 

Trends of Land Change” study, transitional land-cover class was 

subdivided into mechanically disturbed and nonmechanically 

disturbed classes. Squares indicate locations of 10 x 10 km 

sample blocks analyzed in study. Index map shows locations of 

geographic features mentioned in text. Abbreviations for Western 

United States ecoregions are listed in appendix 2. See appendix 3 

for definitions of land-use/land-cover classifications. 

Coast

Range

Cascades

Cascades

Sierra

Nevada

Southern and Central

California Chaparral

and Oak Woodlands

CCV

ECSF

ECSF

Willamette

Valley

PACIFIC

OCEAN

123°

122°

124°

43°

42°

41°

40°

0 50 MILES

0 50 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

OREGON

CALIFORNIA

PA C I F I C 

O C E A N

Grants Pass

Roseburg

Medford

Ashland

Yreka

Weaverville

Willits

Klamath R.

Trinit y R.

Eel River

Sacramento River

Siskiy ou Moun t ain s K L A M A T H M O U N T A I N S 

TRINITY ALPS

WILDERNESS

5

5

Coffee Cr.
142 Status and Trends of Land Change in the Western United States—1973 to 2000

belts are intruded by Mesozoic granitic rocks and (or) overlain by late Mesozoic sedimentary rocks. All of these rocks 

are overlain by gravel and alluvial deposits of Cenozoic age 

(Irwin, 1966; Snoke and Barnes, 2006). Soils developed on 

serpentinite, which are toxic and nutrient poor, are characterized by high levels of magnesium, nickel, and chromium and 

low levels of calcium. Seventy endemic species of plants are 

associated only with serpentinite extrusions in the Siskiyou 

Mountains, outnumbering those associated with any other serpentinite outcrop in North America (Coleman and Kruckeberg, 

1999; Sawyer, 2007).

Forests, which cover approximately three-quarters of the 

Klamath Mountains Ecoregion, are generally organized along 

elevation and longitudinal gradients, whereas grasslands and 

shrubs account for approximately 15 percent of the ecoregion 

(Homer and others, 2007). Redwood (Sequoia sempervirens) 

forests that dominate the coastal parts of the ecoregion give 

way to Douglas-fir (Pseudotsuga menziesii), tanoak (Lithocarpus densiflorus), Pacific madrone (Arbutus menziesii), and 

canyon live oak (Quercus chrysolepis) further inland, as well 

as Douglas-fir and ponderosa pine (Pinus ponderosa) in the 

eastern parts of the ecoregion (Sawyer, 1996). White fir (Abies 

concolor) and Shasta fir (Abies magnifica) can be found at 

higher elevations, and Mountain hemlock (Tsuga mertensiana) is common at subalpine elevations (Sawyer, 1996). Oak 

Klamath Mountains Ecoregion

Other ecoregion

State boundary

Federal land-ownership class

Overall spatial change

(per 10 x 10 km sample block)

Boundaries

Wilderness Area

National Forest

Tribal lands

Other Federal lands

Other lands

EXPLANATION

0.0–2.0

2.1–8.0

8.1–12.0

12.1–20.0

20.1–39.4

0 25 50 75 MILES

0 25 50 75 KILOMETERS

Coast Range

Cascades

C

Sierra

Nevada

Cascades

ECSF

ECSF

Southern and Central

California Chaparral

and Oak Woodlands

Central

California

Valley

Willamette

Valley

PACIFIC

OCEAN

123°

122°

125° 124°

43°

42°

41°

40°

39°

Figure 2. Federal land ownership and cumulative land-use/land-cover change (as percent of sample-block area) from 1973 to 2000 in 

Klamath Mountains Ecoregion. Land-ownership data from National Atlas of the United States (2006). See appendix 2 for abbreviations 

for Western United States ecoregions.
Chapter 13—Klamath Mountains Ecoregion 143

(Quercus spp.) woodlands are common in foothills of the Eel, 

Trinity, and Sacramento Rivers’ watersheds. 

Agriculture and developed landscapes make up much 

of the remainder of the Klamath Mountains Ecoregion. The 

major land uses within the ecoregion include forestry, farming, 

grazing, tourism, and mining. Approximately 83 percent of the 

ecoregion is managed by the Federal Government, mostly for 

public use and recreation (figs. 2,3). The U.S. Forest Service 

manages 12 wilderness areas and 8 national forests, accounting 

for the majority of public lands in the ecoregion. Other federal 

landholders include the Bureau of Land Management, National 

Park Service, and Bureau of Reclamation. In addition, several 

tribal lands are located across the ecoregion. Protected lands 

(Conservation Biology Institute, 2003), which limit permanent 

anthropogenic conversion and are managed for natural ecosystem values,1

 make up 17.3 percent of the ecoregion.

Farming is limited and is generally confined to the larger 

alluvial valleys. One of the more productive agricultural locations in the ecoregion exists in a corridor between Ashland, 

Medford, and Grants Pass, Oregon. Developed land uses are 

sparse. Medford and Grants Pass in Oregon are the two largest 

urban areas, with 2000 population estimates of 63,154 and 

23,003, respectively (U.S. Census Bureau, 2008). Other urban 

areas include Roseburg and Ashland in Oregon and Willits and 

Yreka in California.

1

 Protected lands, which are classified as having either GAP protection 

status code 1 or 2, are lands managed for different levels of biodiversity protection (Scott and others, 1993; DellaSala and others, 2001). GAP protection 

status codes are defined as follows: status code 1 is an area having permanent 

protection from conversion of natural land cover and a mandated management 

plan in operation to maintain a natural state within which disturbance events 

(of natural type, frequency, intensity, and legacy) are allowed to proceed 

without interference or are mimicked through management; status code 2 is an 

area having permanent protection from conversion of natural land cover and a 

mandated management plan in operation to maintain a primarily natural state, 

but it may receive uses or management practices that degrade the quality of 

existing natural communities, including suppression of natural disturbance.

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change in the Klamath Mountains 

Ecoregion (that is, the amount of area that changed at least 

one time between 1973 and 2000) was 8.5 percent (4,929 km2) 

(table 1). Compared to other western United States ecoregions, 

the Klamath Mountains Ecoregion experienced a modest 

amount of change, although the rate was substantially lower 

than other forested ecoregions in the Pacific Northwest (fig. 4). 

An estimated 5.2 percent of the ecoregion experienced change 

in more than one time period, indicating a cyclic pattern that is 

consistent with the changes associated with forestry. Change 

within the four individual time periods ranged from a low of 

3.0 percent between 1980 and 1986 to a high of 4.2 percent 

between 1986 and 1992 and between 1992 and 2000 (table 

2). When the change estimates are normalized to an average 

Figure 4. Overall spatial change in Klamath Mountains Ecoregion (KM; darker bars) compared with that of all Western United 

States Ecoregions (lighter bars). Each horizontal set of bars shows 

proportion of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Klamath 

Mountains Ecoregion (four time periods) labeled for clarity. See 

table 2 for years covered by each time period. See appendix 2 for 

key to ecoregion abbreviations.

Figure 3. White-water rafting along Klamath River in Klamath 

Mountains Ecoregion. 

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods
144 Status and Trends of Land Change in the Western United States—1973 to 2000

annual rate to compensate for the varying lengths of time 

periods, the time period between 1986 and 1992 experienced 

the highest rate of change, at 0.7 percent per year (fig. 5). 

The other three time periods were fairly stable, at approximately 0.5 percent per year (table 2). Staus and others (2002) 

found similar rates of forest disturbance between 1972 and 

1992 in the Klamath–Siskiyou Mountains region. The fact 

that land-cover change in the Klamath Mountains Ecoregion 

was substantially lower than that of the adjacent Coast Range 

Ecoregion is explained, in part, by the Klamath Mountains 

Ecoregion’s larger percentage of public lands, particularly 

areas of high protection (for example, wilderness areas; fig. 6), 

that either minimize, or severely restrict, timber harvest. Table 

3 provides estimates of net forest change, public land ownership, and protected lands for forest-dominated ecoregions in 

the western United States. The Klamath Mountains Ecoregion 

had the lowest net loss of forest land cover in the Pacific 

Northwest over the 27-year study period (594 km2), with the 

exception of the Cascades Ecoregion (tables 3,4; fig. 7), and it 

ranked behind only the Sierra Nevada Ecoregion in terms of 

the proportion of public lands found within the ecoregion.

Forest covered an estimated 76.6 percent of the ecoregion in 1973 and declined to 75.3 percent by 2000, a loss 

of 1.6 percent (fig. 8). The only time period to experience a 

net increase in forest was between 1980 and 1986, with an 

increase of 73 km2

. Grassland/shrubland, which accounted for 

an estimated 14.3 percent of the ecoregion in 1973, increased 

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions (gray 

bars). Estimates of change for Klamath 

Mountains Ecoregion are represented 

by red bars in each time period.

Figure 6. Wilderness area along Coffee Creek in Trinity Alps 

Wilderness, Klamath Mountains, California.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−6

−4

−2

0

2

4

6

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 7. Gross change (area gained and lost) in Klamath 

Mountains Ecoregion by time period for each land-cover class. 

Bars above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.
Chapter 13—Klamath Mountains Ecoregion 145

focused around existing cities in Oregon such as Roseburg, as 

well as along the Interstate 5 corridor between Grants Pass and 

Medford (fig. 10). The ecoregion’s only urban areas in California are Yreka, Weaverville, and Willits. 

As expected, the leading land-cover conversions were 

associated with timber harvesting (table 5; fig. 11). Changes 

associated with logging accounted for most of the change in 

each time period, ranging from a high of nearly 95 percent 

between 1973 and 1980 to 72 percent between 1992 and 2000. 

Changes between forest, mechanically disturbed, and grassland/shrubland are closely linked and, when combined, represent the cyclical nature of logging. During the last two time 

periods, fire (classified as nonmechanical disturbance) took on 

a larger role as an agent for land change; nonmechanically disturbed land accounted for an estimated 189 km2

 between 1986 

and 1992 and 206 km2 between 1992 and 2000 (table 5).

Drivers of land-cover change in the Klamath Mountains 

Ecoregion were numerous and diverse. Private-forest-management policies controlled much of the change associated 

with logging; however, in later years, state and federal 

environmental policies have taken on increasing importance. 

The collapse of the Asian log-export market in the 1990s, the 

listing of the Northern Spotted Owl (Strix occidentalis 

caurina) on the endangered species list in 1990, and the 

to 15.5 percent in 2000, a net increase of 598 km2

 over 27 

years. Furthermore, it is estimated that, between 1973 and 

1980, regrowth of forest, often captured as grassland/shrubland in the earliest stages of regeneration (fig. 9), outpaced 

logging by approximately 74 km2 per year. Logging accelerated in the 1980s and early 1990s (Daniels, 2005), resulting 

in a deficit of 43 km2

 per year between 1986 and 1992. The 

1990s saw a shift back to trends witnessed during the 1970s 

when regrowth outpaced cutting at a rate of approximately 

26 km2 per year. These trends are consistent with findings 

from Cohen and others (2002), who investigated forest disturbance in western Oregon. Changes in land-cover classes over 

the four time periods can be found in table 4.

Agriculture, which was the third most common land 

cover in the Klamath Mountains Ecoregion, was generally 

confined to the eastern and northern parts of the ecoregion. 

Farmland remained stable throughout the study period, at 

approximately 4.5 percent of the ecoregion. 

Changes associated with new development were relatively minor in the Klamath Mountains Ecoregion. It is estimated that developed land increased by 24 percent over the 

entire 27-year study, an increase of approximately 205 km2

. 

Developed land was estimated at 1.8 percent of the ecoregion 

in 1973, increasing to 2.2 percent by 2000. New development 

Figure 9. Forested hillside regenerating after clearcut in Klamath 

Mountains Ecoregion.

Figure 10. New home construction and development in Grants 

Pass, Oregon.

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 8. Normalized average net change in Klamath Mountains 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.
146 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 11. Lumber mill in Roseburg, Oregon.

Northwest Forest Plan of 1994 (Espy and Babbitt, 1994) all 

are likely drivers of land-cover change in the ecoregion, the 

most direct result being a decrease of timber production to 

approximately 25 percent of 1980s levels (Daniels, 2005). 

Decades of fire suppression and climate change have likely 

contributed to the more recent emergence of fire as a major 

land-cover conversion. Fires over this period are typified by 

more frequent, high-intensity, stand-replacing burns in 

northern California (Westerling and others, 2006).

Table 1. Percentage of Klamath Mountains Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (91.5 percent), whereas 8.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.3 1.0 2.3 4.3 0.7 20.5

2 4.3 1.3 3.0 5.6 0.9 20.2

3 0.8 0.4 0.4 1.3 0.3 36.9

4 0.1 0.1 0.0 0.1 0.0 53.3

Overall 

spatial 

change

8.5 2.3 6.3 10.8 1.5 17.9

Table 2. Raw estimates of change in Klamath Mountains Ecoregion land cover, computed for each of 

four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 3.3 1.1 2.1 4.4 0.8 23.2 0.5

1980–1986 3.0 1.0 2.1 4.0 0.6 21.4 0.5

1986–1992 4.2 1.2 3.0 5.4 0.8 19.9 0.7

1992–2000 4.2 1.3 2.9 5.5 0.9 21.1 0.5

Estimate of change, in square kilometers

1973–1980 1,554 533 1,022 2,087 361 23.2 222

1980–1986 1,449 457 992 1,906 310 21.4 242

1986–1992 2,011 592 1,419 2,603 401 19.9 335

1992–2000 2,017 627 1,390 2,644 425 21.1 252
Chapter 13—Klamath Mountains Ecoregion 147

Table 4. Estimated area (and margin of error) of each land-cover class in Klamath Mountains Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.3 0.1 1.8 1.3 2.0 0.9 0.1 0.1 0.2 0.1 76.6 4.2 14.3 3.7 4.5 1.9 0.1 0.1 0.1 0.1

1980 0.3 0.1 1.9 1.3 0.9 0.3 0.1 0.1 0.2 0.1 76.4 4.2 15.5 3.5 4.5 2.0 0.1 0.1 0.0 0.1

1986 0.3 0.1 1.9 1.4 1.1 0.4 0.1 0.1 0.2 0.1 76.5 4.3 15.2 3.6 4.5 2.0 0.1 0.1 0.0 0.0

1992 0.3 0.1 2.1 1.6 1.6 0.6 0.1 0.1 0.2 0.1 75.8 4.3 14.9 3.6 4.4 2.0 0.1 0.1 0.4 0.4

2000 0.3 0.1 2.2 1.6 1.2 0.4 0.1 0.1 0.2 0.1 75.3 4.3 15.5 3.5 4.4 2.0 0.1 0.1 0.6 0.5

Net

change 0.0 0.0 0.4 0.4 −0.9 0.6 0.0 0.0 0.0 0.0 −1.2 1.0 1.3 0.9 −0.1 0.2 0.0 0.0 0.6 0.5

Gross

change 0.0 0.0 0.4 0.4 4.3 1.3 0.0 0.0 0.0 0.0 4.4 1.1 4.3 1.3 0.3 0.2 0.0 0.0 1.1 0.8

Area, in square kilometers

1973 132 61 851 608 962 413 39 35 112 38 36,600 2,030 6,814 1,786 2,171 931 72 41 38 46

1980 128 57 892 639 449 164 42 37 112 38 36,499 2,009 7,417 1,691 2,162 935 70 39 19 27

1986 127 57 926 670 504 187 43 37 112 38 36,572 2,032 7,285 1,710 2,153 935 70 39 1 1

1992 133 61 1,001 741 764 277 43 37 113 38 36,229 2,039 7,131 1,724 2,115 933 69 38 193 211

2000 133 60 1,056 786 551 211 47 38 113 38 36,006 2,065 7,412 1,685 2,100 932 70 40 302 232

Net

change 2 4 205 193 −412 305 7 6 0 1 −594 489 598 410 −70 106 −1 2 264 238

Gross

change 17 16 205 193 2,071 633 10 8 0 1 2,111 543 2,045 638 134 103 4 5 510 386

Table 3. Comparison of areas of forest change, protected lands, and publicly held lands in Klamath Mountains Ecoregion with 

that of other forested ecoregions in western United States. 

Ecoregion

Ecoregion 

area 

Forest area in 

2000 

Change in forest area 

in 2000

Protected lands 

(GAP codes 1,2)1 Publicly held lands

(km2) (% of

ecoregion) (km2

) (% of

ecoregion) (km2

) (% of

ecoregion) (km2

) (% of

ecoregion)

Coast Range 53,986 72.4 −2,051 −5.2 6,531 12.1 13,359 24.7

Puget Lowland 16,454 48.4 −1,662 −20.8 83 0.5 567 3.4

Willamette Valley 14,883 33.5 −625 −12.5 156 1 561 3.8

Cascades 46,416 82.3 232 0.6 13,500 29.1 30,952 66.7

Sierra Nevada 52,872 70.1 −1,851 −4.9 15,143 28.6 42,166 79.8

Klamath Mountains 48,537 75.3 −594 −1.6 8,393 17.3 34,678 71.4

1 Protected lands, classified as having either GAP protection status code 1 or 2, are lands managed for different levels of biodiversity protection (Scott 

and others, 1993; DellaSala and others, 2001). GAP protection status codes are defined as follows: status code 1 is area having permanent protection 

from conversion of natural land cover and a mandated management plan in operation to maintain natural state within which disturbance events (of natural type, frequency, intensity, and legacy) are allowed to proceed without interference or are mimicked through management; status code 2 is area having 

permanent protection from conversion of natural land cover and a mandated management plan in operation to maintain primarily natural state, but it may 

receive uses or management practices that degrade quality of existing natural communities, including suppression of natural disturbance.
148 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 5. Principal land-cover conversions in Klamath Mountains Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Mechanically disturbed Grassland/Shrubland 631 267 181 1.3 40.6

Forest Mechanically disturbed 434 164 111 0.9 27.9

Mechanically disturbed Forest 323 240 162 0.7 20.8

Grassland/Shrubland Forest 30 25 17 0.1 1.9

Agriculture Developed 24 24 16 0.1 1.6

Other Other 113 n/a n/a 0.2 7.3

Totals 1,554 3.3 100.0

1980–1986 Forest Mechanically disturbed 487 184 125 1.0 33.6

Grassland/Shrubland Forest 446 207 140 0.9 30.8

Mechanically disturbed Grassland/Shrubland 325 159 108 0.7 22.4

Mechanically disturbed Forest 115 49 33 0.2 7.9

Agriculture Developed 16 20 13 0.0 1.1

Other Other 61 n/a n/a 0.1 4.2

Totals 1,449 3.0 100.0

1986–1992 Forest Mechanically disturbed 753 276 187 1.6 37.4

Grassland/Shrubland Forest 449 220 149 0.9 22.3

Mechanically disturbed Grassland/Shrubland 306 156 105 0.6 15.2

Mechanically disturbed Forest 190 102 69 0.4 9.5

Forest Nonmechanically disturbed 189 208 141 0.4 9.4

Other Other 124 n/a n/a 0.3 6.2

Totals 2,011 4.2 100.0

1992–2000 Forest Mechanically disturbed 549 211 143 1.1 27.2

Mechanically disturbed Grassland/Shrubland 442 235 159 0.9 21.9

Mechanically disturbed Forest 313 157 107 0.7 15.5

Forest Nonmechanically disturbed 206 164 111 0.4 10.2

Grassland/Shrubland Forest 166 75 51 0.3 8.2

Other Other 341 n/a n/a 0.7 16.9

Totals 2,017 4.2 100.0

1973–2000

(overall)

Forest Mechanically disturbed 2,222 687 466 4.6 31.6

Mechanically disturbed Grassland/Shrubland 1,704 656 444 3.6 24.2

Grassland/Shrubland Forest 1,091 430 291 2.3 15.5

Mechanically disturbed Forest 941 452 306 2.0 13.4

Forest Nonmechanically disturbed 415 373 253 0.9 5.9

Other Other 659 n/a n/a 1.4 9.4

Totals 7,032 14.7 100.0
Chapter 13—Klamath Mountains Ecoregion 149

References Cited

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Maiersperger, T.K., and Fiorella, M., 2002, Characterizing 

23 years (1972-95) of stand replacement disturbance in 

Western Oregon forests with Landsat imagery: Ecosystems, 

v. 5, p. 122–137.

Coleman, R.G., and Kruckeberg, A.R., 1999, Geology and 

plant life of the Klamath-Siskiyou Mountain region: Natural 

Areas Journal, v. 19, no. 4, p. 320–340.

Conservation Biology Institute, 2003, Protected areas GIS data 

layer: Corvallis, Oregon, Conservation Biology Institute, 

accessed September, 2008, at http://consbio.org.

Daniels, J.M., 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Forest Service, Pacific Northwest 

Research Station, General Technical Report PNWGTR-624, 88 p.

DellaSala, D.A., Reid, S.B., Frest, T.J., Strittholt, J.R., and 

Olson, D.M., 1999, A global perspective on the biodiversity 

of the Klamath-Siskiyou ecoregion: Natural Areas Journal,

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DellaSala, D.A., Staus, N.L., Strittholt, J.R., Hackman, A., and 

Iacobelli, A., 2001, An updated protected areas database for 

the United States and Canada: Natural Areas Journal, v. 21, 

no. 2, p. 124–135.

Espy, M., and Babbitt, B., 1994, Record of decision for 

amendments to Forest Service and Bureau of Land 

Management planning documents within the range of the 

Northern Spotted Owl: U.S. Department of Agriculture and 

U.S. Department of the Interior Northwest Forest Plan, 74 

p. (Available at http://www.blm.gov/or/plans/nwfpnepa/

FSEIS-1994/NWFPTitl.htm.)

Homer, C., Dewitz, J., Fry, J., Coan, M., Hossain, N., 

Larson, C., Herold, N., McKerrow, A., VanDriel, J.N., 

and Wickham, J., 2007, Completion of the 2001 National 

Land Cover Database for the conterminous United States: 

Photogrammetric Engineering and Remote Sensing, v. 73, 

no. 4, p. 337–341.

Irwin, Porter, 1966, Geology of the Klamath Mountains 

province, in Bailey, E.H., ed., Geology of Northern 

California: California Division Mines and Geology Bulletin 

190, p. 19–39.

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vegetation, geology, soils and management problems: 

Berkeley, University of California Press, 180 p.

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States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Sawyer, J.O., 1996, Northern California, in Kirk, R., ed., The 

enduring forests: Northern California, Oregon, Washington, 

British Columbia and Southwest Alaska: Seattle, Wash., The 

Mountaineers Press, p. 22–41.

Sawyer, J.O., 2007, Why are the Klamath Mountains and 

adjacent north coast floristically diverse?: Fremontia, v. 35, 

no. 3, p. 3–11.

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1993, Gap analysis: a geographic approach to protection of 

biological diversity: Wildlife Monographs, v. 123, p. 1–41.

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in the Klamath Mountains province, California and Oregon: 

Geological Society of America Special Paper 410, 505 p. 

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R., 2002, Rate and pattern of forest disturbance in the 

Klamath-Siskiyou ecoregion, USA between 1972 and 1992: 

Landscape Ecology, v. 17, p. 455–470.

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Oregon: U.S. Census Bureau database, accessed February 28, 

2008, at http://quickfacts.census.gov/qfd/states/41000.html.

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level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

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B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data Set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 67, p. 650–662.

Wagner, D.H., 1997, Klamath-Siskiyou region, California and 

Oregon, USA, in Davis, S.D., Heywood, V.H., HerreraMacBryde, O., Villa-Lobos, J., and Hamilton, A.C., eds., 

Centres of Plant Diversity, a guide and strategy for their 

conservation—Vol. 3, the Americas: New York, New York, 

USA, World Wildlife Fund for Nature and IUCN (World 

Conservation Union), p. 74–76. (Available at http://botany.

si.edu/projects/cpd/na/na16c.htm.)

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T.W., 2006, Warming and earlier spring increase Western 

U.S. forest wildfire activity: Science, v. 313, p. 940–943.

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279–338.
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Chapter 14

North Cascades Ecoregion

By Tamara S. Wilson

Ecoregion Description

The North Cascades Ecoregion (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997) covers 

approximately 30,421 km2 (11,746 mi2) of predominantly 

steep, mountainous terrain, home to peaks rising more 

than 3,000m, which are carved by valleys that drop below 

150 m elevation (fig. 1). The unique topography in this 

geographically isolated ecoregion has been shaped by glacial 

processes, and its deep drainage canyons have been further 

incised by subsequent runoff. Beautiful alpine scenery is 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of North Cascades Ecoregion and surrounding ecoregions, showing land-use/land cover classes from 

1992 National Land Cover Dataset (Vogelmann and others, 

2001); note that not all land-use/land cover classes shown in 

explanation may be depicted on map; note also that, for this 

“Status and Trends of Land Change” study, transitional landcover class was subdivided into mechanically disturbed 

and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in this 

study. Index map shows locations of geographic features 

mentioned in text. Abbreviations for Western United States 

ecoregions are listed in appendix 2. See appendix 3 for definitions of land-use/land cover classifications.

a major feature of the ecoregion, which includes several 

national forests, parks, and wilderness areas such as the 

North Cascades National Park, the Mount Baker–Snoqualmie 

National Forest, the Okanogan National Forest, and the 

Wenatchee National Forest, as well as the Pasayten Wilderness, the Glacier Peak Wilderness, the Alpine Lakes Wilderness, and the Henry M. Jackson Wilderness. 

The North Cascades Ecoregion extends north of the 

Canadian border into British Columbia; however, this study 

covers only the part that is in the United States, in northcentral Washington (fig. 1). The ecoregion is bounded on the 

Columbia

Plateau

CLMP

Cascades

ECSF

Puget

Lowland

PL

PL

Coast

Range

NRK

NRK Puget

Lowland

CANADA CANADA

120°

119°

124° 123° 122° 121°

48°

47°

49°

Ross L.

Baker L. Diablo L.

L. Chelan

Tacoma

Everett

Bellingham

North

Cascades

Scenic

Highway Darrington

Seattle

WASHINGTON

BRITISH COLUMBIA

B.C.

Mount Baker–

Snoqualmie NF

Leavenworth

Wenatchee

Skagit

R iver

 Stehekin R.

NORTH CASCADES NP

Wilderness areas

OLYMPIC

PENINSULA C A S C A D E R A N G E

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION
152 Status and Trends of Land Change in the Western United States—1973 to 2000

east by the Columbia Plateau Ecoregion; on the south by the 

Cascades Ecoregion and the Eastern Cascades Slopes and 

Foothills Ecoregion; and on the west by the Puget Lowland 

Ecoregion. Farther west, an isolated section of the ecoregion 

on the Olympic Peninsula is entirely surrounded by the Coast 

Range Ecoregion.

Climate in the North Cascades Ecoregion is remarkably 

varied. From fall to spring, most upper elevation areas are 

blanketed in snow. Strong weather systems from the Pacific 

Ocean pass over the mountain peaks, making this region 

one of the snowiest on earth (National Park Service, 2009). 

The western part of the North Cascades Ecoregion receives, 

on average, 193 cm of rain and 1,034 cm of snow annually, creating the lush, evergreen forests in this area. These 

precipitation totals are higher than in the far eastern part of 

the ecoregion (National Park Service, 2009), where conditions are markedly drier and where dense forests give way to 

more grasses and shrubland (fig. 1). Harnessing the annual 

snowmelt are the large-scale dam operations, reservoirs, and 

hydroelectric power plants at Diablo Lake (4 km2

; fig. 2), 

Ross Lake (48km2), and Baker Lake (15 km2), as well as Lake 

Chelan (247 km2), the third deepest lake in the entire United 

States at 457 m deep. 

This ecoregion is sparsely populated: its largest towns 

are Darrington (population 1,354 in 2009) and Leavenworth 

(population 2,347 in 2009), Washington (U.S. Census Bureau, 

2009). However, several cities are located not far outside the 

ecoregion boundary (for example, Seattle, Tacoma, Everett, 

Bellingham, and Wenatchee, Washington). Agriculture, which 

is a major land use along low-lying valley bottoms, consists of 

irrigated pastureland and crops such as alfalfa, wheat, corn, and 

other feed crops in the western part of the ecoregion. Apple and 

pear orchards predominate in the ecoregion’s eastern part. 

The North Cascades Ecoregion supports a diverse range 

of forests, including some of the oldest and richest tracts 

remaining in the conterminous United States. At lower elevations and along the west flank of the Cascade Range, these 

forests are composed of western red cedar (Thuja plicata), 

Figure 2. Diablo Lake, man-made reservoir along North 

Cascades Highway in North Cascades National Park, Washington.

Figure 3. Lush riparian forest and undergrowth within Mount 

Baker–Snoqualmie National Forest, Washington.

Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga 

heterophylla), red alder (Alnus rubra), and bigleaf maple 

(Acer macrophyllum) (fig. 3). Upslope, lodgepole pine (Pinus 

contorta), ponderosa pine (Pinus ponderosa), Pacific silver 

fir (Abies amabilis), Engelmann spruce (Picea engelmannii), 

western larch (Larix occidentalis), and whitebark pine (Pinus 

albicaulis) are more common (Uhler, 2007; Washington 

Department of Fish and Wildlife, 2005).

Late 20th century land-cover change in the North 

Cascades Ecoregion was associated predominantly with 

timber harvesting by means of clearcut logging (fig. 4). 

Large-scale forestry operations were established in areas of 

easiest access, where harvest-delivery options were most 

efficient. Timber harvesting, which is more common on 

private rather than public lands, is especially important along 

the ecoregion periphery at lower elevations. According to 

the National Park Service (1999), widespread logging in this 

area was not logistically possible in the 19th century given 

the rugged terrain and lack of reliable transportation. In addition, the availability of more accessible stands elsewhere in 

the area further slowed its expansion (National Park Service, 

1999). In the late 1800s to early 1900s, mills operated 

along the Stehekin River valley (upstream of Lake Chelan), 

processing logs for use as apple shipping boxes (National 

Park Service, 2009). Selective harvest of western red cedar 

also was allowed along the Skagit River in the early 20th 
Chapter 14—North Cascades Ecoregion 153

century in what today is the Mount Baker–Snoqualmie 

National Forest, but the harvest was halted by the early 

1920s (National Park Service, 1999). 

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the areal extent of land-use/

land-cover change (that is, the area that experienced change 

during at least one of the four multiyear periods within the 

27-year study period) in the North Cascades Ecoregion was 

10.5 percent (approximately 3,200 km2) (table 1). The North 

Cascades Ecoregion experienced a modest amount of change 

compared to other western United States ecoregions, although 

the rate was substantially lower than that experienced by other 

forested ecoregions in the Pacific Northwest (fig. 5). Overall, 

an estimated 3.9 percent (1,186 km2) of land experienced 

change in at least one time period, 5.1 percent (1,551 km2) 

changed in two time periods, 1.4 percent (426km2) changed in 

three periods, and 0.1 percent (30 km2) of sampled land area 

changed in all four time periods (table 1). 

The average annual rate of land-cover change in the 

North Cascades Ecoregion between 1973 and 2000 was 0.7 

percent (212.7 km2) in the 27-year study period (table 2). This 

measurement is a cumulative average of the annual average 

change values for each time period studied. A steady rate of 

annual change is observed in the first two time periods (0.6 

percent), peaking at 0.9 percent between 1986 and 1992 and 

dropping again to 0.7 percent between 1992 and 2000 (table 

2). Figure 6 shows the percent change by time period, normalized to annual rates for all western United States ecoregions. 

In 2000, an estimated 70.3 percent of the North Cascades 

Ecoregion was covered by forest, followed by grassland/shrubland (17.6 percent), barren (5.2 percent, mostly rock outcrops 

and mountaintops), and mechanically disturbed (2.0 percent) 

(table 3). An additional 2.6 percent was covered by ice/snow. 

Only 0.6 percent of the ecoregion was developed, and 1.1 

percent was devoted to agriculture (table 3). The remaining four 

land-cover classes made up less than 1 percent of the remaining 

area in the ecoregion (table 3). Between 1973 and 2000, there 

were net losses overall of forest (1.8 percent; 385 km2

) and 

mechanically disturbed (16.5 percent; 121 km2) land, as well as 

net gains in grassland/shrubland (10.4 percent; 507 km2) (fig. 7). 

Postclassification analysis of these results allowed for the 

identification of “from class–to class” land-cover conversions 

and the ranking of these conversions according to their magnitude. In the North Cascades Ecoregion, more than 97 percent 

of all land-cover conversions between 1973 and 2000 were 

related to timber harvesting (forest to mechanically disturbed) 

and successional regrowth (mechanically disturbed to grassland/

shrubland or forest, as well as grassland/shrubland to forest) 

(table 4). Overall, an estimated 2,320 km2 of forest land was 

mechanically disturbed (table 4), equating to approximately 

7.6 percent of the total ecoregion area. Of particular note is the 

Figure 4. Clearcut logging and regrowth in North Cascades 

Ecoregion, Washington.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods

Figure 5. Overall spatial change in North Cascades Ecoregion 

(NC; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during time periods 1, 2, 3, or 

4; highest level of spatial change in North Cascades Ecoregion (four 

time periods) labeled for clarity. See table 2 for years covered by 

each time period. See appendix 2 for key to ecoregion abbreviations.
154 Status and Trends of Land Change in the Western United States—1973 to 2000

doubling of timber-harvest rates between 1986 and 1992 and the 

subsequent sharp decline after 1992, although the rate remained 

above pre-1986 levels (table 4). This pattern is mirrored in 

other forest-dominated ecoregions of the western United States 

(for example, the Klamath Mountains, Coast Range, and Sierra 

Nevada Ecoregions). 

The timber industry has had a dominant influence on 

land-cover change in the North Cascades Ecoregion; however, 

external drivers of change, such as federal endangered-species 

protection and international timber markets, have helped 

dictate the amount and type of forest harvesting during the 

study period. Public lands occupy most of the North Cascades 

Ecoregion and are subject to state and federal regulation. 

The Washington State Wilderness Act of 1984 set aside more 

than a million acres of new wilderness area in the state, the 

majority within the North Cascades Ecoregion, including the 

Mount Baker Wilderness, Henry M. Jackson Wilderness, Lake 

Chelan–Sawtooth Wilderness, Pasayten Wilderness (additions), 

Boulder River Wilderness, Buckhorn Wilderness, Clearwater 

Wilderness, Glacier Peak Wilderness, and others (Arthur and 

others, 2009; U.S. Congress, 1984).

In 1990, the Northern Spotted Owl (Strix occidentalis 

caurina) was listed as “threatened” under the Endangered 

Species Act. In addition, new habitat-protection measures 

outlined by the Northwest Forest Plan in 1994 set harvesting 

limits on lands administered by the Forest Service and the 

Bureau of Land Management. Timber yields were set at 25 

percent of the 1980s baseline, which dropped the allowable 

harvest to 1 billion board feet (Espy and Babbitt, 1994). Additional timber-harvesting restrictions imposed by endangeredspecies protection led to a 30 percent decline in overall timber 

volume from 1980s levels (Daniels, 2005). These reductions, 

coupled with reductions in global timber demand, also have 

influenced the decline in logging activity since 1992 (Warren, 

1999; Daniels, 2005). In the 1990s, changes in the Japanese 

housing industry and Asia’s economic collapse significantly 

reduced the demand for lumber, along with greater competition from forest products from the southern United States and 

Canada (Daniels, 2005).

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 6. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

North Cascades Ecoregion are represented by red bars in each time period.

Figure 7. Normalized average net change in North Cascades 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.
Chapter 14—North Cascades Ecoregion 155

Table 1. Percentage of North Cascades Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

 [Most sample pixels remained unchanged (89.5 percent), whereas 10.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.9 1.5 2.4 5.4 1.0 25.4

2 5.1 1.9 3.2 7.0 1.3 25.6

3 1.4 0.7 0.8 2.1 0.4 31.4

4 0.1 0.1 0.0 0.2 0.0 47.9

Overall 

spatial 

change

10.5 3.9 6.6 14.4 2.6 25.2

Table 2. Raw estimates of change in North Cascades Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 4.0 1.9 2.1 5.9 1.3 32.1 0.6

1980–1986 3.5 1.5 2.0 5.0 1.0 28.3 0.6

1986–1992 5.7 2.2 3.5 7.8 1.5 25.8 0.9

1992–2000 5.6 2.0 3.5 7.6 1.4 24.6 0.7

Estimate of change, in square kilometers

1973–1980 1,225 581 644 1,805 393 32.1 175

1980–1986 1,065 444 621 1,510 301 28.3 178

1986–1992 1,724 656 1,069 2,380 444 25.8 287

1992–2000 1,689 614 1,076 2,303 416 24.6 211
156 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in North Cascades Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland Snow/Ice

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.3 0.1 0.5 0.5 2.4 1.3 0.0 0.0 5.1 1.7 71.6 5.2 16.0 4.5 1.2 0.9 0.2 0.1 2.6 1.5

1980 0.3 0.1 0.5 0.5 1.4 0.7 0.0 0.0 5.2 1.7 71.7 5.2 16.9 4.4 1.1 0.9 0.2 0.1 2.6 1.5

1986 0.3 0.1 0.5 0.5 1.4 0.6 0.0 0.0 5.2 1.7 71.3 5.2 17.2 4.3 1.1 0.9 0.2 0.1 2.6 1.5

1992 0.3 0.1 0.6 0.5 2.9 1.1 0.0 0.0 5.2 1.8 70.5 5.1 16.6 4.4 1.1 0.9 0.2 0.1 2.6 1.5

2000 0.3 0.1 0.6 0.5 2.0 0.9 0.0 0.0 5.2 1.8 70.3 5.1 17.6 4.3 1.1 0.9 0.2 0.1 2.6 1.5

Net

change 0.0 0.0 0.0 0.0 −0.4 1.2 0.0 0.0 0.1 0.1 −1.3 1.6 1.7 0.7 0.0 0.1 0.0 0.0 −0.1 0.1

Gross

change 0.0 0.0 0.0 0.0 6.0 2.1 0.0 0.0 0.1 0.1 6.6 2.6 4.6 2.0 0.1 0.2 0.0 0.0 0.1 0.1

Area, in square kilometers

1973 85 36 165 139 733 399 7 8 1,566 529 21,781 1,571 4,856 1,356 361 266 66 31 801 464

1980 92 43 166 139 425 211 9 9 1,572 532 21,813 1,568 5,139 1,324 343 263 66 31 795 459

1986 92 42 166 139 434 176 6 4 1,573 531 21,705 1,569 5,248 1,323 338 261 65 30 795 459

1992 94 43 169 139 886 332 4 3 1,582 533 21,432 1,553 5,057 1,343 339 261 66 31 792 456

2000 95 45 169 139 612 265 4 3 1,588 537 21,396 1,564 5,362 1,305 347 264 64 29 783 450

Net

change 10 12 4 4 −121 368 −3 8 22 17 −385 493 507 216 −14 28 −2 3 − 18 17

Gross

change 13 13 4 4 1,836 625 7 8 30 20 1,999 777 1,407 618 39 47 5 6 18 17
Chapter 14—North Cascades Ecoregion 157

Table 4. Principal land-cover conversions in North Cascades Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 420 211 143 1.4 34.3

Mechanically disturbed Forest 412 322 218 1.4 33.7

Mechanically disturbed Grassland/Shrubland 309 192 130 1.0 25.2

Grassland/Shrubland Forest 46 36 24 0.1 3.7

Agriculture Grassland/Shrubland 18 25 17 0.1 1.4

Other Other 20 n/a n/a 0.1 1.6

Totals 1,225 4.0 100.0

1980–1986 Forest Mechanically disturbed 415 176 119 1.4 39.0

Mechanically disturbed Grassland/Shrubland 314 186 126 1.0 29.5

Grassland/Shrubland Forest 217 124 84 0.7 20.4

Mechanically disturbed Forest 93 74 50 0.3 8.7

Agriculture Grassland/Shrubland 9 12 8 0.0 0.8

Other Other 17 n/a n/a 0.1 1.6

Totals 1,065 3.5 100.0

1986–1992 Forest Mechanically disturbed 876 328 222 2.9 50.8

Grassland/Shrubland Forest 388 237 161 1.3 22.5

Mechanically disturbed Forest 225 124 84 0.7 13.1

Mechanically disturbed Grassland/Shrubland 203 86 58 0.7 11.7

Forest Barren 7 7 5 0.0 0.4

Other Other 26 n/a n/a 0.1 1.5

Totals 1,724 5.7 100.0

1992–2000 Forest Mechanically disturbed 609 264 179 2.0 36.0

Mechanically disturbed Grassland/Shrubland 475 220 149 1.6 28.1

Mechanically disturbed Forest 408 260 176 1.3 24.2

Grassland/Shrubland Forest 166 79 54 0.5 9.8

Snow/Ice Barren 8 8 6 0.0 0.5

Other Other 22 n/a n/a 0.1 1.3

Totals 1,689 5.6 100.0

1973–2000

(overall)

Forest Mechanically disturbed 2,320 882 598 7.6 40.7

Mechanically disturbed Grassland/Shrubland 1,301 537 364 4.3 22.8

Mechanically disturbed Forest 1,139 703 477 3.7 20.0

Grassland/Shrubland Forest 816 391 265 2.7 14.3

Agriculture Grassland/Shrubland 26 37 25 0.1 0.5

Other Other 100 n/a n/a 0.3 1.8

Totals 5,703 18.7 100.0
158 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Arthur, B., Uniack, T., and Owen, J., 2009, The gift of wilderness for the people of Washington: The Seattle Times, 

accessed July 2, 2009, at http://seattletimes.nwsource.com/

html/opinion/2009413013_guests03owen.html.

Daniels, J.M., 2005, The rise and fall of the Pacific Northwest 

log export market: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station, General Technical Report PNW-GTR-624.

Espy, M., and Babbitt, B., 1994, Record of decision for 

amendments to Forest Service and Bureau of Land Management planning documents within the range of the Northern 

Spotted Owl: U.S. Department of Agriculture and U.S. 

Department of the Interior Northwest Forest Plan, 74 p. 

(Available at http://www.blm.gov/or/plans/nwfpnepa/

FSEIS-1994/NWFPTitl.htm.)

National Park Service, 1999, Loggers, in North Cascades 

National Park, Washington: National Park Service database, 

accessed March 27, 2012, at http://www.nps.gov/noca/

historyculture/loggers.htm. 

National Park Service, 2009, North Cascades National Park, 

Washington: National Park Service database, accessed 

March 27, 2012, at http://www.nps.gov/noca/index.htm.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p.118–125.

Uhler, J.W., 2007, North Cascades National Park information 

page: North Cascades National Park Information, accessed 

July 1, 2009, at http://www.north.cascades.national-park.

com/info.htm#bio.

U.S. Census Bureau, 2009, Population estimates—Places 

in Washington listed alphabetically, in State and County 

QuickFacts—Washington QuickLinks: U.S. Census Bureau 

database, accessed at http://quickfacts.census.gov/qfd/

states/53000lk.html.

U.S. Congress, 1984, Washington State Wilderness Act of 

1984—An act to designate certain National Forest System lands in the State of Washington for inclusion in the 

National Wilderness Preservation System, and for other 

purposes: U.S. Congress, 98th, Public Law 98–339, 9 p. 

(Available at http://www.wilderness.net/NWPS/documents/

publiclaws/PDF/98-339.pdf.)

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.

Warren, D.D., 1999, Production, prices, employment, and trade 

in Northwest forest industries, fourth quarter 1997: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest 

Research Station, Resource Bulletin PNW-RB-230, 130 p.

Washington Department of Fish and Wildlife, 2005, Ecoregions—Washington’s Ecoregional Conservation Strategy, 

chapter VI in Washington’s Comprehensive Wildlife 

Conservation Strategy: Washington Department of Fish and 

Wildlife report, vol. 1, p. 257–555, accessed at http://wdfw.

wa.gov/conservation/cwcs/cwcs.html.
Chapter 15

Sierra Nevada Ecoregion

By Christian G. Raumann and Christopher E. Soulard

This chapter has been modified from original material 

published in Raumann and Soulard (2007), entitled “Land-cover 

trends of the Sierra Nevada Ecoregion, 1973–2000” (U.S. Geological Survey Scientific Investigations Report 2007–5011).

Ecoregion Description

The Sierra Nevada Ecoregion covers approximately 53,413 

km2 (20,623 mi2) with the majority of the area (98 percent) 

in California and the remainder in Nevada (fig. 1) (Omernik, 

1987; U.S. Environmental Protection Agency, 1997). The Sierra 

Nevada Ecoregion is generally oriented north-south and is 

essentially defined by the Sierra Nevada physiographic province, 

which separates California’s Central Valley to the west from 

the Great Basin to the east. It is bounded by 

seven other ecoregions: Southern and Central California Chaparral and Oak Woodlands 

Ecoregion on the west; Klamath Mountains 

and Eastern Cascades Slopes and Foothills 

Ecoregions on the north; Southern California 

Mountains Ecoregion on the south; and Northern Basin and Range, Central Basin and Range, 

and Mojave Basin and Range Ecoregions on 

the east (fig. 1). The Sierra Nevada range is a 

granitic batholith, much of which is exposed at 

higher elevations, with a gradual western slope 

and a generally steep eastern escarpment.

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Sierra Nevada Ecoregion and 

surrounding ecoregions, showing land-use/landcover classes from 1992 National Land Cover 

Dataset (Vogelmann and others, 2001); note that 

not all land-use/land-cover classes shown in 

explanation may be depicted on map; note also 

that, for this “Status and Trends of Land Change” 

study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate 

locations of 10 x 10 km sample blocks analyzed in 

study. Index map shows locations of geographic 

features mentioned in text. Abbreviations for 

Western United States ecoregions are listed 

in appendix 2. See appendix 3 for definitions of 

land-use/land-cover classifications. 

Central Basin

and Range

Central Basin

and Range

Central

California

Valley

Central

California

Valley

Northern Basin

and Range

ECSF KM

SCM

MBR

Southern and 

Central California

Chaparral and

Oak Woodlands

SCCCOW

120°

119° 118°

122° 121°

40°

38°

41°

37°

36°

39°

38°

37°

36°

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

S I E R R A N E V A D A

G R E A T B A S I N

C E N T R A L V A L L E Y

FRESNO 

COUNTY

TULARE

COUNTY

PLUMAS

COUNTY

PLUMAS

NATIONAL

FOREST

SEQUOIA

NATIONAL

FOREST

SIERRA

NATIONAL

FOREST

CALIFORNIA

NEVADA

Sacramento

Fresno
160 Status and Trends of Land Change in the Western United States—1973 to 2000

The climate of the Sierra Nevada Ecoregion is primarily 

Mediterranean, characterized by cool, wet winters and long, 

dry summers. Most areas of elevation above 2,100 m have 

a Boreal climate, and the highest elevations, typically above 

3,600 m, have an Alpine climate. Precipitation increases with 

elevation from west to east as storm systems moving from 

the west are subject to orographic uplift, causing rain and 

snowfall. Because most precipitation from storm systems 

falls on the western slope of the Sierra Nevada range, a strong 

rainshadow limits precipitation on the steep eastern slope. This 

climatic gradient plays a significant role in determining the 

type and distribution of ecological communities. In order to 

provide water resources for the growing populations in lowelevation areas of California and Nevada, numerous reservoirs 

on the western and eastern slopes of the Sierra Nevada range 

collect runoff from the winter snow pack.

Before the 20th century, resource use within the Sierra 

Nevada Ecoregion was largely unregulated. However, 

laws and administrative policies such as the Wilderness 

Act of 1964, National Environmental Policy Act of 1969, 

and National Forest Management Act of 1976 provided a 

mechanism for managing national forests. Furthermore, other 

environmental laws, annual appropriations legislation, and 

administrative policies relating to fire and fuels management 

have guided resource use and likely have had significant 

environmental effects in the Sierra Nevada Ecoregion (Ruth, 

1996). Today, public lands make up 74.6 percent (39,433 km2) 

of the ecoregion, with the majority (57.8 percent of the ecoregion) managed by the U.S. Forest Service as National Forests 

and Wilderness Areas.

Despite resource regulation, California’s growing urban 

population has greatly increased the demand for wood, water, 

hydroelectricity, and recreational opportunities from the Sierra 

Nevada Ecoregion. Timber harvesting surged in the 1950s to 

1970s but decreased substantially after the economic recession in the early 1980s. Water is considered the region’s most 

valuable resource, and it is controlled in nearly every major 

river basin in the region and also managed to provide municipal water supplies and hydroelectric power (Sierra Nevada 

Ecosystem Project Science Team and Special Consultants, 

1996). Major highways and ski resorts were constructed in the 

1950s and 1960s to meet the demand for year-round recreation 

(Sierra Nevada Ecosystem Project Science Team and Special 

Consultants, 1996). Over the past several decades, the demand 

for natural resources within the Sierra Nevada Ecoregion has 

altered ecological communities in the region by changing 

land-use/land-cover patterns.

In terms of nonmechanical land-cover change components, frequent fires of low to moderate intensity are an 

integral driver of change within the region’s ecological 

communities. Fires create a cycle of disturbance and succession that floral and faunal communities have adapted to and 

often require to propagate and thrive (Skinner and Chang, 

1996). By the late 20th century the regional fire regime had 

greatly changed, primarily as a result of logging during the 

settlement period of the 1950s and 1960s and effective fire 

suppression activities mandated by State and Federal policies 

since the 1920s. Consequently, fires were less frequent and 

more severe than before (Skinner and Chang, 1996). Forest 

density increased and contributed to higher tree mortality 

because of greater intertree competition, insect attack, disease, 

and storm damage (Oliver and others, 1996). These conditions 

led to an increased supply of fuel which, in turn, resulted in 

an increased fire hazard, including the likelihood of highseverity fire (Manley and others, 2000). A shift to a warmer 

and moister climate may also have contributed to this altered 

fire regime by reducing winter severity and providing a longer 

growing season (McKelvey and others, 1996; Stine, 1996). 

Contemporary Land-Cover Change 

(1973 to 2000)

The overall areal extent, or “footprint,” of land-cover 

change between 1973 and 2000 was 5.0 percent (2,645 km2), 

which means that 5.0 percent of the Sierra Nevada Ecoregion underwent change over at least one of the four time 

periods that make up the entire 27-year study period. Areas 

totaling 3.1 percent of the ecoregion changed during only 

one period, 1.6 percent changed during two periods, and 0.3 

percent changed during three periods (table 1). This footprint 

of change in the Sierra Nevada Ecoregion was low to moderate when compared to other ecoregions in the western United 

States (fig. 2).

The estimated average annual rate of land-cover change 

is calculated by normalizing each period’s gross change by 

the number of years in that period. Normalizing gross change 

by year allows comparison of the amount of change in each 

period when periods are of varying length. It is important to 

note that the resulting rates of change, although presented as 

per-year rates, are only an estimate and should be viewed as a 

description of the period and not of the individual years within 

the period. The estimated average annual rate of change for 

the entire 27-year study period between 1973 and 2000 was 

0.3 percent/year, which means that on average 0.3 percent (or 

roughly 144 km2) of the Sierra Nevada Ecoregion changed 

each year. However, the annual rate of change has not been 

constant during the 27-year study period, as shown by the 

estimated average annual rates for the four periods. Between 

1973 and1980 and between 1980 and 1986, change occurred 

at 0.1 percent/year. The annual rate of change increased to 0.3 

percent/year between 1986 and 1992 and continued to increase 

to 0.5 percent/year between 1992 and 2000 (table 2; fig. 3).

Results show that in 2000 the Sierra Nevada Ecoregion 

was dominated by forest (70.1 percent), with grassland/shrubland (20.4 percent), barren (2.7 percent), nonmechanically 

disturbed (2.4 percent), wetland (2.2 percent), and water (1.1 

percent) making up almost all the remainder of land cover 

(table 3). Developed, mining, agriculture, ice/snow, and 

mechanically disturbed classes each made up less than one 

percent of the region (table 3). Land-use/land-cover classes 
Chapter 15—Sierra Nevada Ecoregion 161

that underwent the greatest net change (that is, total area 

gained minus total area lost) in relation to their area in 1973 

were forest (4.7 percent decrease), grassland/shrubland (6.0 

percent increase), and nonmechanically disturbed (which 

accounted for 0.2 percent or less of the ecoregion’s area in 

each year between 1973 and 1992 but increased to 2.4 percent 

of the classified area in 2000). Although the developed and 

agriculture classes each made up less than 1 percent of the 

Sierra Nevada Ecoregion, the developed class underwent the 

greatest relative increase in area (16.6 percent), and agriculture 

underwent the greatest relative decrease in area (5.2 percent). 

However, it is important to note that considerable uncertainty 

is associated with estimates for very rare land-cover classes.

The net change values as a percentage of ecoregion area at 

the beginning (1973) and end (2000) dates of the study period in 

table 3 show little variability and may seem to indicate stability 

(fig. 4). Net change values, however, often mask land-use/landcover dynamics. For example, a class may gain 100 km2 and 

at the same time lose 100 km2, which would yield a net change 

of 0 km2. Reporting the net change value of 0 km2 misses 

much of the story of landscape change. However, analysis of 

gross change (that is, area gained and area lost) by individual 

land-cover classes by period shows that classes have fluctuated 

throughout the 27-year study period to a greater degree than 

net change values may indicate. Figure 5 shows that the forest, 

grassland/shrubland, mechanically disturbed, and nonmechanically disturbed classes were the most dynamic between 1973 

and 2000. The transitional characteristic of the mechanically 

disturbed class is also illustrated by the fact that area gained 

(809 km2) nearly equals area lost (753 km2) between 1973 and 

2000. Land-cover change was clearly at its peak during the 

period between 1992 and 2000 when gains and losses were 

generally greatest for the four most dynamic classes.

All individual land-cover conversions between classes 

were ranked by summing the total area changed during 

each of the four periods. Each conversion documents land 

changing from one class to another (for example, forest to 

Figure 2. Overall spatial change in Sierra Nevada Ecoregion 

(SN; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, or 

four time periods; highest level of spatial change in Sierra Nevada 

Ecoregion (four time periods) labeled for clarity. See table 2 for 

years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

Figure 3. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Sierra Nevada Ecoregion are represented by red bars in each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
162 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 4. Normalized average net change in Sierra Nevada 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

Figure 5. Gross change (area gained and lost) in Sierra Nevada 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

developed) and shows the direction of change. Table 4 shows 

the individual conversions ranked from greatest to least 

area converted. The most common individual conversions 

describe the disturbance of forest land by mechanical (that 

is, clearcuts) and nonmechanical (that is, fire) means. 

Overall, the most common conversion was that of 1,404 

km2 of forest to the nonmechanically disturbed class, which 

accounted for 37.1 percent of all conversions (fig. 6). The 

second most common conversion was that of 784 km2 of 

forest to the mechanically disturbed class, accounting for 

20.7 percent of all changes (fig. 7). Conversion of mechanically and nonmechanically disturbed land to the grassland/

shrubland class (753 km2 and 307 km2, respectively) were 

the two next most common conversions and represented 

the process of vegetation regeneration after clearcutting or 

fire (fig. 8). Similarly, conversion of grassland/shrubland to 

forest (303 km2) represented the final stage of the regeneration cycle. A much less common but noteworthy conversion was that of water to mechanically disturbed (26 km2), 

which accounted for 0.7 percent of all individual conversions 

(fig. 9). This conversion indicates surface-level fluctuations 

of reservoirs in the ecoregion.

More insight can be provided by aggregating the conversions listed in table 4 to identify how a single land-use class 

was affected. Between 1973 and 2000, 1,540 km2 of vegetation (forest, grassland/shrubland, and wetland) area was converted to the nonmechanically disturbed class. Fire caused all 

of these conversions, and almost all of this change (1,302km2) 

took place between 1992 and 2000. Regeneration after disturbance was captured as the conversion of nonmechanically 

disturbed land to vegetation classes (forest and grassland/

shrubland) and conversion of mechanically disturbed land to 

vegetation classes (forest and grassland/shrubland) for aggregated totals of 307 km2 and 753 km2, respectively. 

The land-use/land-cover change patterns measured in the 

Sierra Nevada Ecoregion between 1973 and 2000 are consistent with information in the literature. Much of the clearcutting and reservoir water-level change in the region has been 

driven by the demand for wood, water, hydroelectricity, and 

recreational opportunities associated with California’s growing 

urban population. As for fires, many of the severe contemporary fires in the Sierra Nevada Ecoregion are likely the result 

of a fuel buildup caused by fire suppression activities mandated by State and Federal policies since the 1920s.

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 15—Sierra Nevada Ecoregion 163

Figure 6. September 2004 appearance of area (intermediate 

background slopes) undergoing regeneration following Manter 

Fire at southern end of Sierra Nevada Ecoregion in Sequoia 

National Forest, Tulare County, California. Manter Fire ignited on 

July 22, 2000, and burned about 300 km2. Land-cover types shown 

are forest, grassland/shrubland, and wetland.

Figure 7. Recently clearcut area near northern end of Sierra 

Nevada Ecoregion in Plumas National Forest, Plumas County, 

California. Land-cover types shown are forest and mechanically 

disturbed.

Figure 8. Forest regeneration after seeding, Plumas National 

Forest, near northern end of Sierra Nevada Ecoregion. Land-cover 

types shown are forest and grassland/shrubland.

Figure 9. Courtright Reservoir in Sierra National Forest, Fresno 

County, California, in southern part of Sierra Nevada Ecoregion, 

showing lowered surface levels in late summer (September 2004). 

Land-cover types shown are forest, barren, and mechanically 

disturbed (latter is due to reservoir drawdown).
164 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 1. Percentage of Sierra Nevada Ecoregion land cover that 

changed at least one time during study period (1973-2000) and 

associated statistical error.

[Most sample pixels remained unchanged (95.0 percent), whereas 5.0 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.1 2.5 0.6 5.6 1.7 55.1

2 1.6 0.5 1.1 2.1 0.4 22.2

3 0.3 0.3 0.0 0.5 0.2 77.6

4 0.0 0.0 0.0 0.0 0.0 90.3

Overall 

spatial 

change

5.0 2.5 2.4 7.5 1.7 34.9

Table 2. Raw estimates of change in Sierra Nevada Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.9 0.5 0.4 1.3 0.3 36.0 0.1

1980–1986 0.7 0.4 0.4 1.1 0.2 33.2 0.1

1986–1992 1.6 0.5 1.1 2.1 0.4 21.6 0.3

1992–2000 3.9 2.5 1.3 6.4 1.7 44.3 0.5

Estimate of change, in square kilometers

1973–1980 454 241 213 695 164 36.0 65

1980–1986 400 196 205 596 133 33.2 67

1986–1992 868 276 592 1,144 188 21.6 145

1992–2000 2,059 1,344 715 3,404 913 44.3 257
Chapter 15—Sierra Nevada Ecoregion 165

Table 3. Estimated area (and margin of error) of each land-cover class in Sierra Nevada Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.1 0.5 0.2 0.3 0.4 0.3 0.1 0.2 2.7 1.5 73.5 4.6 19.2 4.0 0.3 0.4 2.2 1.2 0.2 0.0

1980 1.1 0.5 0.2 0.3 0.1 0.1 0.1 0.2 2.7 1.5 73.2 4.6 19.7 3.9 0.3 0.4 2.2 1.2 0.2 0.0

1986 1.1 0.5 0.2 0.3 0.3 0.2 0.1 0.2 2.7 1.5 73.1 4.6 19.9 3.9 0.3 0.4 2.2 1.2 0.0 0.2

1992 1.1 0.5 0.2 0.3 0.8 0.3 0.1 0.2 2.7 1.5 72.5 4.5 19.8 3.9 0.3 0.4 2.2 1.2 0.2 0.3

2000 1.1 0.5 0.3 0.3 0.4 0.2 0.1 0.2 2.7 1.5 70.1 4.6 20.4 3.8 0.3 0.4 2.2 1.2 2.4 0.1

Net

change 0.0 0.1 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 -3.5 2.3 1.1 0.6 0.0 0.0 0.0 0.0 2.3 0.1

Gross

change 0.0 0.1 0.0 0.0 1.9 0.7 0.0 0.0 0.0 0.0 4.5 2.3 2.6 0.9 0.0 0.0 0.0 0.0 3.2 0.8

Area, in square kilometers

1973 612 288 127 134 191 144 73 100 1,446 799 39,274 2,477 10,259 2,143 160 223 1,176 666 84 109

1980 606 287 127 134 65 39 73 100 1,446 799 39,104 2,466 10,534 2,093 160 223 1,175 665 114 152

1986 606 287 127 134 153 89 73 100 1,446 799 39,046 2,455 10,616 2,074 160 223 1,176 666 0 1

1992 592 287 129 137 411 156 73 100 1,446 799 38,741 2,384 10,550 2,093 160 223 1,176 666 125 127

2000 586 287 148 150 215 106 73 100 1,446 799 37,427 2,477 10,872 2,043 152 212 1,176 666 1,307 1,345

Net

change −26 30 21 23 23 129 0 0 0 0 −1,847 1,241 613 319 −8 12 0 0 1,223 1,354

Gross

change 26 30 21 23 1,016 368 0 0 0 0 2,412 1,249 1,367 468 8 12 3 3 1,690 1,362
166 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Sierra Nevada Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Mechanically disturbed Grassland/Shrubland 191 144 98 0.4 42.1

Forest Nonmechanically disturbed 112 152 103 0.2 24.6

Nonmechanically disturbed Grassland/Shrubland 84 109 74 0.2 18.6

Forest Mechanically disturbed 58 38 26 0.1 12.9

Water Mechanically disturbed 6 9 6 0.0 1.4

Other Other 2 n/a n/a 0.0 0.5

Totals 454 0.9 100.0

1980–1986 Forest Mechanically disturbed 146 89 60 0.3 36.5

Nonmechanically disturbed Grassland/Shrubland 110 152 103 0.2 27.4

Grassland/Shrubland Forest 81 78 53 0.2 20.3

Mechanically disturbed Grassland/Shrubland 54 37 25 0.1 13.5

Mechanically disturbed Forest 4 6 4 0.0 1.0

Other Other 4 n/a n/a 0.0 1.1

Totals 400 0.7 100.0

1986–1992 Forest Mechanically disturbed 391 154 105 0.7 45.1

Grassland/Shrubland Forest 190 171 116 0.4 21.9

Mechanically disturbed Grassland/Shrubland 146 89 60 0.3 16.8

Forest Nonmechanically disturbed 102 96 65 0.2 11.8

Grassland/Shrubland Nonmechanically disturbed 23 32 22 0.0 2.6

Other Other 16 n/a n/a 0.0 1.8

Totals 868 1.6 100.0

1992–2000 Forest Nonmechanically disturbed 1,190 1,230 835 2.2 57.8

Mechanically disturbed Grassland/Shrubland 361 135 92 0.7 17.6

Forest Mechanically disturbed 188 104 71 0.4 9.1

Nonmechanically disturbed Grassland/Shrubland 112 119 81 0.2 5.4

Grassland/Shrubland Nonmechanically disturbed 112 116 79 0.2 5.4

Other Other 96 n/a n/a 0.2 4.7

Totals 2,059 3.9 100.0

1973–2000

(overall)

Forest Nonmechanically disturbed 1,404 1,244 845 2.6 37.1

Forest Mechanically disturbed 784 299 203 1.5 20.7

Mechanically disturbed Grassland/Shrubland 753 323 219 1.4 19.9

Nonmechanically disturbed Grassland/Shrubland 307 214 145 0.6 8.1

Grassland/Shrubland Forest 303 195 132 0.6 8.0

Other Other 231 n/a n/a 0.4 6.1

Totals 3,782 7.1 100.0
Chapter 15—Sierra Nevada Ecoregion 167

References Cited

Manley, P.N., Fites-Kaufman, J.A., Barbour, M.G., 

Schlesinger, M.D., and Rizzo, D.M., 2000, Biological 

integrity, in Murphy, D.D., and Knopp, C.M., eds., Lake 

Tahoe watershed assessment: U.S. Forest Service Pacific 

Southwest Research Station, Albany, Calif., Gen. Tech. Rep. 

PSW-GTR-175, v. 1, chap. 5, p. 403–598.

McKelvey, K.S., Skinner, C.N., Chang, C., Erman, D.C., 

Husari, S.J., Parsons, D.J., van Wagtendonk, J.W., and 

Weatherspoon, C.P., 1996, An overview of fire in the Sierra 

Nevada, in Sierra Nevada Ecosystem Project final report 

to Congress, vol. II, Assessments and scientific basis for 

management options: Davis, University of California, 

Centers for Water and Wildlands Research, v. 2, chap. 37, p. 

1,033–1,040.

Oliver, W.W., Ferrell, G.T., and Tappeiner, J.C., 1996, Density 

management of Sierra Forests, in Sierra Nevada Ecosystem Project final report to Congress, vol. III, Assessments, 

commissioned reports, and background information: Davis, 

University of California, Centers for Water and Wildlands 

Research, v. 3, chap. 11, p. 217–276.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Raumann, C.G., and Soulard, C.E., 2007, Land-cover trends of 

the Sierra Nevada Ecoregion, 1973-2000: U.S. Geological 

Survey Scientific Investigations Report 2007–5011, available at http://pubs.usgs.gov/sir/2007/5011/.

Ruth, L., 1996, Conservation and controversy—national forest 

management, 1960-95, in Sierra Nevada Ecosystem Project 

final report to Congress, vol. II, Assessments and scientific 

basis for management options: Davis, University of California, Centers for Water and Wildlands Research, v. 2, chap. 

7, p. 145–162.

Sierra Nevada Ecosystem Project Science Team and Special Consultants, 1996, People and resource use, in Sierra 

Nevada Ecosystem Project final report to Congress, vol. I, 

Assessment summaries and management strategies: Davis, 

University of California, Centers for Water and Wildlands 

Research, v. 1, chap. 2, p. 17–45.

Skinner, C.N., and Chang, C., 1996, Fire regimes, past and 

present, in Sierra Nevada Ecosystem Project final report 

to Congress, vol. II, Assessments and scientific basis for 

management options: Davis, University of California, 

Centers for Water and Wildlands Research, v. 2, chap. 38, p. 

1,041–1,069.

Stine, S., 1996, Climate, 1650-1850, in Sierra Nevada Ecosystem Project final report to Congress, vol. II, Assessments and scientific basis for management options: Davis, 

University of California, Centers for Water and Wildlands 

Research, v. 2, chap. 2, p. 25–30.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
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Chapter 16

Blue Mountains Ecoregion

Quaternary-age volcanoes, distinguish the Blue Mountains from 

the adjacent Cascade Range (Thorson and others, 2003). 

The Cascade Range to the west creates a rain-shadow 

effect in the Blue Mountains Ecoregion, which receives much 

less rain relative to the Cascade Range and the marine forests 

of the Pacific Northwest. The rain shadow is most dramatic 

in the southern reach of the Blue Mountains Ecoregion; the 

northern part of the ecoregion receives more moisture-bearing 

air, which passes across the Cascade Range by way of the 

Columbia Gorge (Heyerdahl and others, 2001). This interregional precipitation gradient contributes to significant vegetation variability across the Blue Mountains Ecoregion. In the 

northern part of the ecoregion, grasslands thrive at low elevations, and dense forests persist in moist ash soils at high elevations. Much of the southern part of the ecoregion is covered 

By Christopher E. Soulard

Ecoregion Description

The Blue Mountains Ecoregion encompasses approximately 65,461 km2 (25,275 mi2) of land bordered on the north 

by the Columbia Plateau Ecoregion, on the east by the Northern 

Rockies Ecoregion, on the south by the Snake River Basin and 

the Northern Basin and Range Ecoregions, and on the west by 

the Cascades and the Eastern Cascades Slopes and Foothills 

Ecoregions (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). Most of the Blue Mountains Ecoregion is 

located within Oregon (83.5 percent); 13.8 percent is in Idaho, 

and 2.7 percent is in Washington. The Blue Mountains are 

composed of primarily Paleozoic volcanic rocks, with minor 

sedimentary, metamorphic, and granitic rocks. Lower mountains and numerous basin-and-range areas, as well as the lack of 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Blue Mountains Ecoregion and surrounding ecoregions, showing 

land-use/land-cover classes from 1992 National Land Cover Dataset (Vogelmann and 

others, 2001); note that not all land-use/land-cover classes shown in explanation may 

be depicted on map; note also that, for this “Status and Trends of Land Change” study, 

transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks 

analyzed in study. Index map shows locations of geographic features mentioned in 

text. Abbreviations for Western United States ecoregions are listed in appendix 2. See 

appendix 3 for definitions of land-use/land-cover classifications. 

Columbia Plateau ECSF

C

ECSF

ECSF Northern Basin and Range

Snake

River

Basin

Northern

Rockies

NRK

120° 119° 118° 117° 116°

121°

45° 46°

44°

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

WASH INGTON

OREGON IDAHO

Columbia

River

Columbia

 Gorge

C A S C A D E R A N G E

Snake

Riv e r Spokane

Portland

Bend

Richland

Yakima

B L U E M T N S
170 Status and Trends of Land Change in the Western United States—1973 to 2000

by drought-tolerant sagebrush (Artemisia spp.), shrubland, and 

juniper woodland (Juniperus spp.).

The variety of land covers across the Blue Mountains 

Ecoregion drives a wide range of land-use patterns in the 

region. Fertile grasslands support large hay and livestock 

operations in the northern Blue Mountains Ecoregion where 

windblown silt has created thick soils. Smaller agricultural 

operations persist in the dry southern reach of region where 

soils are less developed (Busacca, 1991). Another contrast is 

the difference in anthropogenic land disturbances between the 

northern and southern parts of the Blue Mountains Ecoregion. 

All mechanical disturbances in the northern forests resulted 

from logging, but clearings in the southern Blue Mountains 

Ecoregion resulted primarily from the removal of juniper to 

improve rangeland. Perhaps the most consistent pattern of 

land-cover change across the Blue Mountains Ecoregion is that 

which is caused by nonmechanical disturbances such as fire. 

Fire has an established history in the Blue Mountains Ecoregion owing to the region’s low-to-moderate precipitation and 

abundant fuel sources (Heyerdahl and others, 2001). However, 

fire now poses a larger threat in the Blue Mountains Ecoregion 

(and in the greater western United States) because of vegetation 

build-up following decades of fire suppression (McCullough 

and others, 1998). Prescribed burning and forest thinning 

became increasingly common within much of the Blue Mountains Ecoregion in the latter part of the 20th century to remove 

dense vegetation and neutralize the threat of large, unmanageable fires that jeopardize wildlife and human habitats.

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the footprint (overall areal 

extent) of land-use/land-cover change in the Blue Mountains 

Ecoregion was 6.5 percent, or 4,275 km2. The footprint of 

change can be interpreted as the area that experienced change 

during at least one of the four time periods that make up the 

27-year study period. Of the total change, 2,476 km2 (3.8 

percent) of the ecoregion changed during one period, 1,367 

km2 (2.1 percent) changed during two periods, 425 km2 (0.6 

percent) changed during three periods, and roughly 5 km2 (less 

than 0.1 percent) changed throughout all four periods (table 1). 

Overall, this level of spatial change is lower than that of most 

of the western United States ecoregions (fig. 2). 

Between 1973 and 2000, the average annual rate of 

change in the Blue Mountains Ecoregion was roughly 0.4 

percent. This measurement, which normalizes the results for 

each period to an annual scale, indicates that the region averaged roughly 0.4 percent (241 km2) of change each year in the 

27-year study period (table 2). However, this annual change 

varied between each of the four time periods (fig. 3). Between 

1973 and 1980, the annual rate of change in the Blue Mountains Ecoregion was 0.1 percent. The annual rate of change 

steadily increased in each of the following periods, to 0.3 

Figure 2. Overall spatial change in Blue Mountains Ecoregion 

(BLM; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, or 

four time periods; highest level of spatial change in Blue Mountains Ecoregion (four time periods) labeled for clarity. See table 2 

for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

percent between 1980 and 1986, to 0.4 percent between 1986 

and 1992, and to 0.6 percent between 1992 and 2000 (table 2).

The results of this study illustrate the estimated dominance 

of four of the eleven land-use/land-cover classes in the Blue 

Mountains Ecoregion in 2000: forest (48.4 percent), grassland/shrubland (42.1 percent), agriculture (4.1 percent), and 

nonmechanically disturbed (2.4 percent). Although six other 

classes cumulatively made up the remaining 3.0 percent of the 

Blue Mountains Ecoregion landscape in 2000, each of these 

classes made up less than one percent of the ecoregion (table 

3). Between 1973 and 2000, the land-use/land-cover classes 

that experienced a noteworthy net change in relation to the total 

Blue Mountains Ecoregion area include, in descending order, 

forest (7.9 percent decrease), grassland/shrubland (3.3 percent 

increase), and nonmechanically disturbed, which occupied no 

land in 1973 and only 0.2 percent of the total area in 1992 but 

expanded to 2.4 percent of the sampled area in 2000 (fig. 4). 

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four

time periods
Chapter 16—Blue Mountains Ecoregion 171

Figure 3. Estimates of land-cover change per time period, normalized to annual rates 

of change for all 30 Western United States ecoregions (gray bars). Estimates of change 

for Blue Mountains Ecoregion are represented by red bars in each time period.

Figure 4. Normalized average net change in Blue Mountains 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications. 

Figure 5. Gross change (as percent of ecoregion) in Blue Mountains Ecoregion by time period for each land-cover class. Diagram 

illustrates how net change can mask within-class fluctuations in 

each period and for entire 27-year study period. Bars above zero 

axis represent area gained, whereas bars below zero represent 

area lost. Note that not all land-cover classes shown in explanation may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

−6

−4

−2

0

2

4

6

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
172 Status and Trends of Land Change in the Western United States—1973 to 2000

Net change, however, may not necessarily be the best 

indicator of within-class variability for those classes experiencing spatiotemporal fluctuations. The net-change metric 

often masks dynamics of land-use/land-cover change, whereas 

analysis of gross change (area gained or lost) by individual 

land-use/land-cover classes by time period shows that classes 

have fluctuated throughout the 27-year study period to a 

greater degree than net-change values may indicate (Raumann 

and others, 2007) (fig. 5). In addition, land-cover classes may 

experience gains and losses in area both within and between 

time periods (fig. 5). For example, the mechanically disturbed 

class increased by more than 600 percent between 1973 and 

2000, but gross change relating to mechanical disturbance 

affected an area greater than 40 times the size of the 1973 

classification area. Figure 5 illustrates the dynamic nature of 

land-use/land-cover change in the Blue Mountains Ecoregion 

between 1973 and 2000.

The land-use/land-cover change information for each of 

the four time periods afforded by a postclassification comparison allowed the identification of land-use/land-cover class 

conversions and the ranking of these conversions according to 

their magnitude. Table 4 illustrates the most frequent conversions in the Blue Mountains Ecoregion between 1973 and 

2000. The largest overall conversion and the largest conversion in each of the first three time periods represented the 

mechanical disturbance of forest by logging and rangeland 

improvement (fig. 6). Additionally, the second most common 

overall conversion and a major conversion in each of the last 

two time periods were connected to nonmechanical disturbance of forest by fire and to a significantly lesser degree, to 

insect damage from the Douglas-fir tussock moth (Orgyia 

pseudotsugata McDunnough), the western spruce budworm 

(Choristoneura occidentalis Freeman), and the mountain 

pine beetle (Dendroctonus ponderosae) (Wickman, 1992) 

(fig. 7). Insect damage to forest land cannot be separated out 

from other nonmechanical disturbances in the present study; 

however, it must be stressed that insect-caused declines in 

forest health are known to exacerbate the effects, spread, and 

intensity of wildfires (Wickman, 1992). The effect of mechanical disturbance on forest resulted in an estimated 1,663 km2 

of land-cover loss, whereas the impact of nonmechanical 

disturbance on grassland/shrubland and forest resulted in an 

estimated 1,760 km2 of vegetated land-cover loss. 

Most mechanical disturbances (74.1 percent) occurred 

between 1980 and 1992, and these changes declined significantly between 1992 and 2000. This decline coincided with 

the decline in timber harvest in Oregon in the 1990s, when 

a shift towards forest conservation caused the federal share 

of Oregon’s timber harvest to decrease from approximately 

50 percent in 1989 to 10 percent by 2000 (Brandt and others, 

2006). Although mechanical forest clearing declined between 

1992 and 2000, over 90 percent of all nonmechanical disturbances took place during this period. 

Mechanical and nonmechanical disturbances are transitional by definition, so many of these disturbed areas 

experienced ecological succession, or regrowth, after each 

Figure 6. Young stand of trees in formerly cleared part of Blue 

Mountains Ecoregion. Standing snags provide nesting and 

roosting sites for avian species. Land-use/land-cover classes 

shown are forest and grassland/shrubland.

Figure 7. Cut trees in Blue Mountains Ecoregion during 

precommercial thinning. Land-use/land-cover classes shown are 

mechanically disturbed and forest.

disturbance event. The cumulative regrowth following 

mechanical and nonmechanical disturbances accounts for 

1,555 km2 of vegetated land-cover gain through 2000; on 

the basis of field observations, disturbances that occurred in 

2000 would also convert to one of the vegetation land-cover 

classes if mapping efforts had been extended to include a 2007 

date. Conversions to and from the agriculture class represent 

another conversion in the Blue Mountains Ecoregion during 

the study period. Between 1973 and 2000, 273 km2 converted 

from agriculture to grassland/shrubland and 219 km2 converted from grassland/shrubland to agriculture. 

The mechanical removal of forest in the Blue Mountains 

Ecoregion between 1973 and 2000 occurred in over half of the 

sample-block locations. Most of these conversions were associated with silviculture. Considerable research has been conducted, and policy has been implemented, to establish improved 
Chapter 16—Blue Mountains Ecoregion 173

forestry practices such as sustainable stocking levels, thinning 

practices, and snag preservation (Cochran and others, 1994; 

Parker and others, 2006; U.S. Department of Agriculture, 1979) 

(figs. 6,8). The goal of many of these practices has been to replicate old-growth forest conditions and remedy the detrimental 

effects of logging on forest fauna. For example, protecting tree 

snags and select trees while cutting is intended to preserve nest 

and roost sites vital for breeding and winter survival of many 

avian species (Zarnowitz and Manuwal, 1985; Bryce, 2006; 

U.S. Department of Agriculture, 1979).

Nonmechanical disturbances, although comparable to 

mechanical disturbances in terms of the overall footprint of 

change across the Blue Mountains Ecoregion, were much less 

frequent than the mapped instances of forest cutting. Despite 

this lower frequency, nonmechanical disturbances caused by fire 

had a much larger patch size. Larger fires have become much 

more common in the Blue Mountains Ecoregion and can be 

largely attributed to fire-suppression practices that took place 

over much of 20th century. Fires not only pose an immediate 

threat to wildlife and human habitats, but they also contribute to 

future fires by altering forest composition and making damaged 

Figure 8. Forested area in early-stage succession (regrowth) 

following fire. Although grasses and shrubs tend to reestablish 

themselves quite soon after fire, trees take much longer to recover. 

Land-cover classes shown are grassland/shrubland and forest.

Figure 9. Forested area during prescribed fire, showing warning 

sign (A) and scattered smoldering logs (B). Prescribed fires 

remove undergrowth and prevent large, unmanageable fires 

from occurring. Land-cover classes shown are nonmechanically 

disturbed and forest.

trees more vulnerable to insect pests (McCullough and others, 

1998). In an effort to reduce the threat of forest fires, prescribed 

fires are being applied more regularly to remove built-up fuels 

and excess understory growth within the Blue Mountains Ecoregion (Mutch and others, 1993) (fig. 9).

A

B
174 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 1. Percentage of Blue Mountains Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (93.5 percent), whereas 6.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.8 1.9 1.8 5.7 1.3 34.7

2 2.1 0.8 1.3 2.9 0.5 25.8

3 0.6 0.4 0.3 1.0 0.2 38.3

4 0.0 0.0 0.0 0.0 0.0 67.8

Overall 

spatial 

change

6.5 2.2 4.3 8.8 1.5 23.0

Table 2. Raw estimates of change in Blue Mountains Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence levels.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.6 0.2 0.4 0.8 0.1 18.1 0.1

1980–1986 1.7 0.7 1.0 2.4 0.5 28.0 0.3

1986–1992 2.6 1.1 1.5 3.7 0.8 28.7 0.4

1992–2000 5.0 2.1 3.0 7.1 1.4 27.7 0.6

Estimate of change, in square kilometers

1973–1980 399 107 292 506 72 18.1 57

1980–1986 1,094 453 641 1,548 306 28.0 182

1986–1992 1,714 727 988 2,441 491 28.7 286

1992–2000 3,300 1,353 1,947 4,653 915 27.7 413
Chapter 16—Blue Mountains Ecoregion 175

Table 3. Estimated area (and margin of error) of each land-cover class in Blue Mountains Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.4 0.3 0.2 0.2 0.1 0.0 0.0 0.0 0.8 0.6 52.5 7.8 40.8 7.6 4.1 2.1 1.0 0.5 0.0 0.0

1980 0.4 0.3 0.2 0.2 0.2 0.1 0.0 0.0 0.8 0.6 52.3 7.7 40.8 7.6 4.1 2.1 0.9 0.5 0.0 0.0

1986 0.4 0.3 0.2 0.2 0.9 0.6 0.0 0.0 0.8 0.6 51.4 7.4 40.9 7.5 4.2 2.1 1.0 0.5 0.0 0.1

1992 0.4 0.3 0.2 0.2 1.0 0.5 0.0 0.0 0.8 0.6 50.3 7.3 41.8 7.3 4.1 2.0 1.0 0.5 0.2 0.2

2000 0.4 0.3 0.3 0.2 0.4 0.2 0.0 0.0 0.8 0.6 48.4 7.0 42.1 7.3 4.1 2.0 0.9 0.5 2.4 2.0

Net

change 0.1 0.1 0.0 0.0 0.4 0.2 0.0 0.0 0.0 0.0 −4.2 1.9 1.3 0.7 0.0 0.2 0.0 0.1 2.4 2.0

Gross

change 0.2 0.2 0.0 0.0 2.5 1.2 0.0 0.0 0.1 0.1 5.1 2.1 2.5 0.8 0.5 0.3 0.3 0.2 2.9 2.0

Area, in square kilometers

1973 250 205 144 99 40 21 26 22 539 420 34,399 5,076 26,677 4,958 2,694 1,360 639 316 0 0

1980 282 212 149 103 153 67 25 21 530 420 34,262 5,046 26,685 4,961 2,704 1,367 612 318 5 7

1986 285 212 157 106 580 404 25 21 530 420 33,626 4,876 26,799 4,892 2,750 1,364 625 325 31 44

1992 236 203 162 110 661 339 26 22 521 420 32,953 4,758 27,337 4,787 2,696 1,299 675 333 140 163

2000 284 210 168 114 284 137 29 27 539 420 31,671 4,573 27,546 4,780 2,667 1,285 618 321 1,602 1,281

Net

change 33 34 24 18 244 132 4 4 0 0 −2,728 1,239 868 435 −27 155 −20 36 1,602 1,281

Gross

change 140 121 25 18 1,604 811 7 7 36 52 3,363 1,395 1,646 533 329 166 166 112 1,888 1,299
176 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Blue Mountains Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Mechanically disturbed 152 67 45 0.2 38.0

Agriculture Grassland/Shrubland 52 47 32 0.1 13.1

Grassland/Shrubland Agriculture 51 49 33 0.1 12.9

Wetland Water 31 32 22 0.0 7.7

Mechanically disturbed Grassland/Shrubland 30 18 12 0.0 7.4

Other Other 83 n/a n/a 0.1 20.9

Totals 399 0.6 100.0

1980–1986 Forest Mechanically disturbed 579 404 273 0.9 52.9

Mechanically disturbed Grassland/Shrubland 118 53 36 0.2 10.8

Grassland/Shrubland Agriculture 91 64 43 0.1 8.4

Forest Grassland/Shrubland 75 107 72 0.1 6.9

Agriculture Grassland/Shrubland 63 56 38 0.1 5.8

Other Other 168 n/a n/a 0.3 15.3

Totals 1,094 1.7 100.0

1986–1992 Forest Mechanically disturbed 653 340 230 1.0 38.1

Mechanically disturbed Grassland/Shrubland 527 363 246 0.8 30.7

Forest Nonmechanically disturbed 139 163 110 0.2 8.1

Grassland/Shrubland Forest 96 78 53 0.1 5.6

Agriculture Grassland/Shrubland 90 111 75 0.1 5.2

Other Other 210 n/a n/a 0.3 12.3

Totals 1,714 2.6 100.0

1992–2000 Forest Nonmechanically disturbed 1,471 1,170 791 2.2 44.6

Mechanically disturbed Grassland/Shrubland 566 293 198 0.9 17.1

Grassland/Shrubland Forest 397 251 170 0.6 12.0

Forest Mechanically disturbed 279 137 93 0.4 8.5

Grassland/Shrubland Nonmechanically disturbed 125 114 77 0.2 3.8

Other Other 462 n/a n/a 0.7 14.0

Totals 3,300 5.0 100.0

1973–2000

(overall)

Forest Mechanically disturbed 1,663 809 547 2.5 25.5

Forest Nonmechanically disturbed 1,632 1,178 797 2.5 25.1

Mechanically disturbed Grassland/Shrubland 1,240 630 426 1.9 19.0

Grassland/Shrubland Forest 554 293 198 0.8 8.5

Agriculture Grassland/Shrubland 273 247 167 0.4 4.2

Other Other 1,146 n/a n/a 1.8 17.6

Totals 6,508 9.9 100.0
Chapter 16—Blue Mountains Ecoregion 177

References Cited

Brandt, J.P., Morgan, T.A., Dillon, T., Lettman, G.J., Keegan, 

C.E., and Azuma, D.L., 2006, Oregon’s forest products 

industry and timber harvest, 2003: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 

General Technical Report PNW-GTR-681. (Available at 

www.fs.fed.us/pnw/pubs/pnw_gtr681.pdf.)

Bryce, S.A., 2006, Development of a Bird Integrity Index; 

Measuring avian response to disturbance in the Blue Mountains of Oregon, USA: Environmental Management, v. 38, 

no. 3, p. 470–486.

Busacca, A.J., 1991, Loess deposits and soils of the Palouse 

and vicinity, in Baker, V.R., ed., Quaternary geology of the 

Columbia Plateau, in Morrison, R.B., ed., Quaternary nonglacial geology—conterminous U.S.: Geological Society of 

America, Decade of North American Geology, DNAG, v. 

K–2, p. 216–228.

Cochran, P.H., Geist, J.M., Clemens, D.L., Clausnitzer, R.R., 

and Powell, D.C., 1994, Suggested stocking levels for forest 

stands in northeastern Oregon and southeastern Washington: U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Region Research Note PNW-RN-513. (Available 

at http://www.treesearch.fs.fed.us/pubs/25113.)

Heyerdahl, E.K., Brubaker, L.B., and Agee, J.K., 2001, Spatial 

controls of historical fire regimes; A multiscale example 

from the Interior West, USA: Ecology, v. 82, no. 3, p. 

660–678.

McCullough, D.G., Werner, R.A., and Newmann, D., 1998, Fire 

and insects in northern and boreal forest ecosystems of North 

America: Annual Review of Entomology, v. 43, p. 107–127.

Mutch, R.W., Arno, S.F., Brown, J.K., Carlson, C.E., Ottmar, 

R.D., and Peterson, J.L., 1993, Forest health in the Blue 

Mountains; A management strategy for fire-adapted ecosystems: U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Region General Technical Report PNW-GTR-310. 

(Available at http://www.treesearch.fs.fed.us/pubs/9056.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Parker, T.J., Clancy, K.M., and Mathiase, R.L., 2006, Interactions among fire, insects and pathogens in coniferous forests 

of the interior western United States and Canada: Agricultural and Forest Entomology, v. 8, p. 167–189.

Raumann, C.G., and Soulard, C.E., 2007, Land-cover trends of 

the Sierra Nevada Ecoregion, 1973–2000: U.S. Geological 

Survey Scientific Investigations Report 2007–5011, 29 p. 

(Available at http://pubs.usgs.gov/sir/2007/5011/.)

Thorson, T.D., Bryce, S.A., Lammers, D.A., Woods, A.J., 

Omernik, J.M., Kagan, J., Pater, D.E., and Comstock, 

J.A., 2003, Ecoregions of Oregon: U.S. Geological Survey 

Ecoregion Map Series, scale 1:1,500,000. (Available at 

http://www.epa.gov/wed/pages/ecoregions/or_eco.htm.)

U.S. Department of Agriculture, 1979, Wildlife habitats in 

managed areas; The Blue Mountains of Oregon and Washington: U.S. Department of Agriculture, Forest Service, 

Agriculture Handbook No. 553, 512 p.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.

Wickman, B.E., 1992, Forest health in the Blue Mountains; 

The influence of insects and disease: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research 

Station, General Technical Report PNW-GTR-295. (Available at http://www.treesearch.fs.fed.us/pubs/9032.)

Zarnowitz, J.E., and Manuwal, D.A., 1985, The effects of 

forest management on cavity-nesting birds in northwestern 

Washington: The Journal of Wildlife Management, v. 49, 

no. 1, p. 255–263.
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Mediterranean California Ecoregions

38°

Sierra Nevada

Sierra Nevada

CBR

MBR

Southern and 

Central California

Chaparral and

Oak Woodlands

SCCCOW

SCM

Coast Range

KM NBR

PACIFIC

OCEAN

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

122° 120°

40°

38°

36°

36°

S I E R R A N E V A D A

San 

Francisco 

Bay

Fresno

Bakersfield

Stockton

Sacramento

Los Angeles

C O A S T R A N G E S

C E N T R A L V A L L E Y

PA

C I F I C

O

C E A N

CALIFORNIA

Chapter 17

Central California Valley Ecoregion

Ecoregion Description

The Central California Valley Ecoregion, which covers approximately 45,983 km2

 (17,754 mi2), is an elongated 

basin extending approximately 650 km north to south through 

central California (fig. 1) (Omernik, 1987; U.S. Environmental Protection Agency, 1997). The ecoregion is surrounded 

entirely by the Southern and Central California Chaparral and 

Oak Woodlands Ecoregion, which includes parts of the Coast 

Ranges to the west and which is bounded by the Sierra Nevada 

to the east. The Central California Valley Ecoregion accounts 

for more than half of California’s agricultural production value 

and is one of the most important agricultural regions in the 

country, with flat terrain, fertile soils, a favorable climate, and 

nearly 70 percent of its land in cultivation (Kuminoff and others, 2000; Sumner and others, 2003). Commodities produced 

in the region include milk and dairy, cattle and calves, cotton, 

almonds, citrus, and grapes, among others (U.S. Department 

of Agriculture, 2004; Johnston and McCalla, 2004; Kuminoff and others, 2000) (figs. 2A,B,C). Six of the top eight 

agricultural-producing counties in California are located at 

least partly within the Central California Valley Ecoregion 

(Kuminoff and others, 2000) (table 1). The Central California Valley Ecoregion is also home to nearly 5 million people 

spread throughout the region, including the major cities of 

Sacramento (state capital), Fresno, Bakersfield, and Stockton, 

California (U.S. Census Bureau, 2000) (fig. 1). 

By Benjamin M. Sleeter

Status and Trends of Land Change in the Western United States—1973 to 2000 

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Central California Valley Ecoregion and 

surrounding ecoregions, showing land-use/land-cover classes 

from 1992 National Land Cover Dataset (Vogelmann and others, 

2001); note that not all land-use/land-cover classes shown 

in explanation may be depicted on map; note also that, for 

this “Status and Trends of Land Change” study, transitional 

land-cover class was subdivided into mechanically disturbed 

and nonmechanically disturbed classes. Squares indicate 

locations of 10 x 10 km sample blocks analyzed in study. Index 

map shows locations of geographic features mentioned in text. 

Abbreviations for Western United States ecoregions are listed 

in appendix 2. See appendix 3 for definitions of land-use/landcover classifications. 
182 Status and Trends of Land Change in the Western United States—1973 to 2000

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change in the Central California 

Valley Ecoregion (the percentage of area that changed at 

least one time between 1973 and 2000) was estimated at 12.9 

percent (±3.1 percent at 85-percent confidence level) (table 2). 

Compared to other western ecoregions, change in the Central California Valley Ecoregion was above average (fig.3). 

Total estimated change was highest in the first time period 

(1973–1980), when 5.7 percent of the ecoregion changed from 

one land cover to another (table 3). When change estimates 

are normalized to account for the varying lengths of the time 

periods, change is also highest in the first time period (at 0.8 

percent per year) and then constant for the following three 

time periods at just greater than 0.5 percent per year (fig. 4).

The largest change in any one land-cover class between 

1973 and 2000 was the loss of 1,782 km2

 of grassland/shrubland (20.2 percent of the area it occupied in 1973, table 4). 

The second largest change was the addition of 1,129 km2 of 

developed land cover (an increase of 37.7 percent), increasing from 6.5 to 9.0 percent of the ecoregion area. Agricultural 

lands, which accounted for more than 70 percent of the Central California Valley Ecoregion, remained relatively stable 

throughout the study period with a net increase of 358 km2

(1.1 percent increase). Estimates of percent cover for all landcover classes by time period are found in table 4, and estimates of average annual change by class are found in figure 5.

The dominant land-cover conversion that occurred in 

the Central California Valley Ecoregion was from grassland/

shrubland to agriculture. This conversion was most common 

near the ecoregion boundary (fig. 6), because historically open 

grazing lands were brought into agricultural production to 

Figure 2. Agriculture in Central California Valley Ecoregion. A, 

Newly planted field. B, Young orchard. C, Tomato field. 

A

B

C

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

Change in four time periods

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Figure 3. Overall spatial change in Central California Valley 

Ecoregion (CCV; darker bars) compared with that of all 30 Western 

United States ecoregions (lighter bars). Each horizontal set of 

bars shows proportions of ecoregion that changed during one, 

two, three, or four time periods; highest level of spatial change 

in Central California Valley Ecoregion (four time periods) labeled 

for clarity. See table 3 for years covered by each time period. See 

appendix 2 for key to ecoregion abbreviations.
Chapter 17—Central California Valley Ecoregion 183

grow grapes, nut crops, and citrus. This change may also be 

attributed to the tilling cycle, when farmers allow parcels of 

land to revert to natural vegetation before eventually being 

returned to production. This particular conversion (grassland/

shrubland to agriculture) accounted for 45.0 percent of all 

change in the ecoregion. The second most common conversion 

was from agriculture to grassland/shrubland (26.5 percent of 

all change). Again, a portion of this change can be attributed 

to the cycling of cropland into and out of production (fig. 7), 

although this conversion was also commonly observed at the 

edge of urban areas and new development. As urban areas 

expand, agricultural land is converted to developed land. In 

many instances, farmland converts to grassland/shrubland 

before being developed. The third and fourth most common 

conversions were from agriculture and grassland/shrubland 

to developed land (9.2 and 4.9 percent of ecoregion change, 

respectively). Combined, the top four conversions account for 

88 percent of all land-cover change in the Central California 

Valley Ecoregion between 1973 and 2000. A detailed description of the most common land-cover conversions for the 

Central California Valley Ecoregion is found in table 5.

A major driver of change in the ecoregion is population growth. Population growth in the San Francisco Bay 

area and Los Angeles, as well as in the Central Valley itself, 

has resulted in a high demand for land for urban uses (figs. 

8A,B). Within the ecoregion, as new development adjacent 

to existing urban areas converts agricultural land to homes, 

businesses, and other urban uses, farms are relocating to the 

ecoregion periphery and then converting traditional grazing 

lands (grassland/shrubland) into new agricultural uses. Annual 

climatic variability may also play a role in the conversion rates 

and, more importantly, in the types of land-cover conversions 

that occurred in the ecoregion. In all but the 1986 to 1992 

period, the leading conversion was from grassland/shrubland 

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 4. Estimates of land-cover change per time period, normalized to annual rates 

of change for all 30 Western United States ecoregions (gray bars). Estimates of change 

for Central California Valley Ecoregion are represented by red bars in each time period.

Figure 5. Normalized average net change in Central California 

Valley Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.
Figure 9. Irrigation systems in Central California Valley Ecoregion. A, Section of Delta-Mendota Canal, which runs 188 km 

through ecoregion. B, Single-field irrigation ditch. 

184 Status and Trends of Land Change in the Western United States—1973 to 2000

to agriculture, and the second most common conversion was 

from agriculture to grassland/shrubland. This pattern was 

reversed during the 1986 to 1992 period, which also corresponded to a period of prolonged drought in California. During this period, irrigation-water-supply (figs. 9A,B) shortages 

coupled with increased cost and conservation efforts led to 

decreased production in some of the Central California Valley’s primary crops, such as cotton and rice (U.S. Department 

of Agriculture, 1991). In response to the reduced surfacewater supplies, producers who normally relied on irrigation 

increased groundwater usage, idled some land, sought to 

minimize waste, and shifted water to the production of higher 

value crops (U.S. Department of Agriculture, 1991). In 1991, 

conservation efforts alone resulted in widespread declines in 

irrigated lands, including 56,500 acres of corn, 36,000 acres 

of wheat, 12,600 acres of pasture, 9,200 acres of alfalfa, and 

Figure 6. New asparagus fields planted along Central California 

Valley Ecoregion boundary. 

Figure 7. Abandoned agricultural field near Kern National 

Wildlife Refuge, Kern County, California.

Figure 8. Development in Central California Valley Ecoregion. A, 

New home construction. B, New subdivision for-sale signs in a 

Fresno, California, suburb. 

A

B

A

B
“Status and Trends of Land Change”

study period (1973–2000)

Year

Farmland, in millions of acres

0

2

4

6

8

10

12

1950 1954 1959 1964 1969 1974 1978 1982 1989 1992 1997

Total crops

Pasture

Irrigated crops

Orchard

Chapter 17—Central California Valley Ecoregion 185

9,100 acres of sugar beets, while surface water shortages 

resulted in an estimated 14-percent decrease in cotton production and a 23-percent decrease in rice production (U.S. Department of Agriculture, 1991). 

The loss of farmland to urban uses is often assumed to 

be the single greatest threat to the Central California Valley 

Ecoregion (Hart, 2003). While significant amounts of high 

quality farmland are being converted to permanent urban uses 

(an estimated 684 km2 between 1973 and 2000), agriculture is 

evolving and, in fact, increasing in scale (Hart, 2003; Johnston and McCalla, 2004; Sleeter, 2008). Farmers continue to 

make use of advances in irrigation technologies, such as drip 

systems, in an effort to cultivate lands once considered marginal for traditional crops (Charbonneau and Kondolf, 1993). 

Central California Valley Ecoregion agriculture continues its 

adaptation through investments in higher value, higher risk 

crops, such as almonds and grapes, instead of traditional field 

crops, such as alfalfa and grains (U.S. Department of Agriculture, 2004; Johnston and McCalla, 2004) (fig. 10). This is 

possible because these higher value crops can be successfully 

cultivated on slopes at the ecoregion periphery and on soils 

of significantly lower quality than those found on the fertile 

valley floor.

California has led the nation in agricultural cash receipts 

in every year since 1948 and, in 1999, recorded nearly $25 

billion; California farmers have increased their national share 

from 9.5 percent in 1960 to 13.1 percent in 1999 (Kuminoff 

and others, 2000). For comparison, Australia and Canada 

each had approximately $18.5 billion in agricultural cash 

receipts in 1999 (Kuminoff and others, 2000). Due to the 

ecoregion’s economic importance, consequences of landcover change are a significant concern at multiple scales and 

will require detailed analysis. As California’s population 

continues to increase, additional demands will be placed on 

the Central California Valley Ecoregion to support people 

and the agricultural complex they depend on, which will 

result in the continued evolution of the nation’s most diverse 

agricultural region.

Figure 10. Changes in California agriculture (total crops, irrigated crops, 

pasture, and orchards) between 1950 and 1997 (U.S. Department of Agriculture, 2004).
186 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 2. Percentage of Central California Valley Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

 [Most sample pixels remained unchanged (87.1 percent), whereas 12.9 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 9.7 2.0 7.7 11.7 1.4 14.4

2 2.4 1.1 1.3 3.6 0.8 31.7

3 0.7 0.3 0.4 0.9 0.2 26.7

4 0.1 0.0 0.0 0.1 0.0 48.8

Overall 

spatial 

change

12.9 3.1 9.7 16.0 2.1 16.6

Table 1. Gross value of agricultural production in 1999 by county in Central California Valley Ecoregion (California Agricultural 

Statistics Service, 2001; modified from Kuminoff and others, 2000).

California 

county rank 

(1999)

County1

Value of 

production2

(millions of dollars)

Top commodities3

1 Fresno 3,559 Grapes, Poultry, Cotton, Tomatoes, Milk

2 Tulare 3,075 Milk, Grapes, Navel and Valencia Oranges, Cattle and Calves, Plums

4 Kern 2,128 Grapes, Cotton and Processed Cottonseed, Citrus, Milk, Almonds and By-Products

5 Merced 1,534 Milk, Chickens, Almonds, Tomatoes, Cotton

6 San Joaquin 1,352 Grapes, Milk, Tomatoes, Cherries, Almond Meats

8 Stanislaus 1,210 Milk, Almonds, Chickens, Cattle and Calves, Tomatoes

12 Kings 901 Milk, Cotton, Cattle and Calves, Turkeys, Alfalfa Hay

14 Madera 700 Grapes, Milk, Almonds, Pistachios, Nursery Stock

18 Colusa 351 Rice, Processing Tomatoes, Almond Meats, Cucumber Seed, Rice Seed

19 Sutter 347 Rice, Prunes, Peaches, Tomatoes, Walnuts

21 Yolo 339 Processing Tomatoes, Winegrapes, Seed Crops, Rice, Alfalfa

22 Sacramento 293 Winegrapes, Milk, Bartlett Pears, Processing Tomatoes, Ornamental Nursery Stock

23 Butte 257 Milling Rice, Almonds, Prunes, Walnuts, Kiwifruit

24 Glenn 253 Rice Paddy, Dairy Products, Almonds, Prunes, Cattle and Calves

28 Solano 195 Processing Tomatoes, Nursery Stock, Alfalfa Hay, Winegrapes, Cattle and Calves

34 Yuba 108 Rice, Peaches, Walnuts, Cattle and Calves, Prunes

35 Tehama 97 Cattle and Calves, Walnuts, Prunes, Milk, Olives

37 Contra Costa 86 Bedding Plants, All Milk, All Tomatoes, Grapes, Sweet Corn

39 Placer 58 Rice, Cattle and Calves, Nursery, Chickens, Pasture and Range, Walnuts

47 Amador 19 Winegrapes, Cattle and Calves, Pasture and Range, Grain Hay, Alfalfa Hay

49 Mariposa 18 Cattle and Calves, Range, Misc. Livestock/Poultry Products, All Poultry

51 Calaveras 15 Cattle and Calves, Winegrapes, Poultry, Livestock and Poultry Products, Walnuts

1

Counties in California that intersect the boundary of Central California Valley Ecoregion (Omernik, 1987; U.S. Environmental Protection Agency, 1997).

2

Gross value of production includes all farm production, whether sold into usual marketing channels or used on farm where produced.

3

Information reported by agricultural commissioners of each county. Level of detail reported differs by county. For example, some may report grapes 

(table, raisin, and wine) as an aggregate category, whereas others may report them as distinct categories.
Chapter 17—Central California Valley Ecoregion 187

Table 3. Raw estimates of change in Central California Valley Ecoregion land cover, computed for each 

of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 5.7 1.4 4.3 7.1 1.0 17.1 0.8

1980–1986 3.3 0.8 2.4 4.1 0.6 17.6 0.5

1986–1992 3.0 1.2 1.8 4.3 0.8 27.5 0.5

1992–2000 4.1 1.3 2.7 5.4 0.9 22.4 0.5

Estimate of change, in square kilometers

1973–1980 2,624 656 1,968 3,279 448 17.1 375

1980–1986 1,504 387 1,116 1,891 265 17.6 251

1986–1992 1,395 562 833 1,957 384 27.5 232

1992–2000 1,879 615 1,264 2,494 420 22.4 235

Table 4. Estimated area (and margin of error) of each land-cover class in Central California Valley Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.7 0.3 6.5 3.1 0.0 0.0 0.2 0.1 0.0 0.0 0.3 0.1 19.2 5.1 71.6 5.8 1.4 1.0 0.0 0.0

1980 0.7 0.3 7.2 3.4 0.1 0.0 0.2 0.1 0.0 0.0 0.3 0.1 17.7 4.9 72.3 5.7 1.6 1.1 0.0 0.0

1986 0.8 0.5 7.6 3.5 0.1 0.0 0.2 0.2 0.0 0.0 0.3 0.1 16.7 4.7 72.8 5.6 1.7 1.2 0.0 0.0

1992 0.7 0.3 8.2 3.7 0.1 0.1 0.2 0.2 0.0 0.0 0.3 0.1 17.3 5.0 71.5 5.8 1.7 1.2 0.0 0.0

2000 0.9 0.5 9.0 3.8 0.2 0.1 0.2 0.2 0.0 0.0 0.3 0.1 15.4 4.4 72.4 5.6 1.7 1.2 0.0 0.0

Net

change 0.2 0.2 2.5 1.0 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 −3.9 1.9 0.8 2.3 0.3 0.5 0.0 0.0

Gross

change 0.9 0.5 2.5 1.0 0.3 0.2 0.1 0.1 0.0 0.0 0.1 0.0 8.7 2.8 10.3 2.8 0.6 0.5 0.0 0.0

Area, in square kilometers

1973 300 146 2,996 1,446 17 14 80 65 2 2 156 64 8,841 2,359 32,934 2,678 658 464 0 0

1980 330 153 3,293 1,562 29 22 87 66 2 2 147 60 8,129 2,231 33,249 2,610 718 503 0 0

1986 359 209 3,475 1,611 24 16 86 69 2 3 146 60 7,671 2,160 33,457 2,560 761 539 0 0

1992 323 159 3,755 1,688 36 30 91 76 3 5 145 59 7,965 2,288 32,895 2,681 771 549 0 0

2000 413 217 4,124 1,751 74 39 96 82 2 3 142 58 7,060 2,044 33,292 2,564 780 564 0 0

Net

change 112 101 1,129 455 57 37 16 18 0 0 −14 11 −1,782 860 358 1,039 122 214 0 0

Gross

change 391 222 1,129 455 160 76 29 25 3 5 26 15 4,020 1,302 4,747 1,307 253 217 0 0
188 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 5. Principal land-cover conversions in Central California Valley Ecoregion, showing amount of area changed (and margin 

of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent 

of all 

(km2

) (+/− km2) (km2) changes

1973–1980 Grassland/Shrubland Agriculture 1,305 462 316 2.8 49.7

Agriculture Grassland/Shrubland 748 351 240 1.6 28.5

Agriculture Developed 177 94 64 0.4 6.7

Grassland/Shrubland Developed 106 75 51 0.2 4.0

Agriculture Wetland 71 92 63 0.2 2.7

Other Other 217 n/a n/a 0.5 8.3

Totals 2,624 5.7 100.0

1980–1986 Grassland/Shrubland Agriculture 734 275 188 1.6 48.8

Agriculture Grassland/Shrubland 316 179 122 0.7 21.0

Agriculture Developed 98 52 35 0.2 6.5

Grassland/Shrubland Developed 71 43 29 0.2 4.7

Agriculture Water 57 68 47 0.1 3.8

Other Other 227 n/a n/a 0.5 15.1

Totals 1,504 3.3 100.0

1986–1992 Agriculture Grassland/Shrubland 675 460 314 1.5 48.4

Grassland/Shrubland Agriculture 271 119 81 0.6 19.5

Agriculture Developed 160 77 53 0.3 11.5

Grassland/Shrubland Developed 101 49 33 0.2 7.2

Water Agriculture 44 58 39 0.1 3.1

Other Other 144 n/a n/a 0.3 10.3

Totals 1,395 3.0 100.0

1992–2000 Grassland/Shrubland Agriculture 1,024 536 366 2.2 54.5

Agriculture Developed 249 146 99 0.5 13.2

Agriculture Grassland/Shrubland 225 101 69 0.5 12.0

Grassland/Shrubland Developed 89 46 32 0.2 4.7

Agriculture Mechanically disturbed 62 37 26 0.1 3.3

Other Other 231 n/a n/a 0.5 12.3

Totals 1,879 4.1 100.0

1973–2000

(overall)

Grassland/Shrubland Agriculture 3,334 1,160 792 7.3 45.0

Agriculture Grassland/Shrubland 1,965 960 656 4.3 26.5

Agriculture Developed 684 289 198 1.5 9.2

Grassland/Shrubland Developed 366 181 123 0.8 5.0

Agriculture Wetland 165 213 145 0.4 2.2

Other Other 887 n/a n/a 1.9 12.0

Totals 7,401 16.1 100.0
Chapter 17—Central California Valley Ecoregion 189

References Cited

California Agricultural Statistics Service, 2001, 2000 County 

Agricultural Commissioners’ Data: Sacramento, CA, California Agricultural Statistics Service, 76 p. (Available at 

http://www.nass.usda.gov/ca.)

Charbonneau, R., and Kondolf, G.M., 1993, Land use change 

in California, USA: Nonpoint source water quality impacts: 

Environmental Management, v. 17, no. 4, p. 453–460.

Hart, J.F., 2003, Specialty cropland in California: Geographical Review, v. 93, no. 2, p. 153–170.

Johnston, W.E., and McCalla, A.F., 2004, Whither California 

agriculture: Up, down or out? Some thoughts about the 

future: University of California, Agriculture and Natural 

Resources, Giannini Foundation Special Report 04-1.

Kuminoff, N.V., Sumner, D.A., and Goldman, G., 2000, The 

measure of California Agriculture: University of California, 

Agricultural Issues Center. (Available at http://aic.ucdavis.

edu/pubs/moca.html.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Sleeter, B.M., 2008, Late 20th century land change in the Central California Valley Ecoregion: Geographical Society, The 

California Geographer, v. 48, p. 27–60. 

Sumner, D., Bervejillo, J.E., and Kuminoff, N.V., 2003, The 

measure of California agriculture and its importance in the 

state’s economy, in Siebert, Jerry, ed., California Agriculture 

Dimensions and Issues: Davis, University of California, 

Giannini Foundation Information Series 03-1. (Available at 

http://giannini.ucop.edu/CalAgbook.htm.)

U.S. Census Bureau, 2000, U.S. Census Bureau database, 

accessed at http://www.census.gov/prod/www/abs/decennial/index.htm.

U.S. Department of Agriculture, 1991, California drought persists—includes related article—U.S. Dept. of Agriculture, 

Economic Research Service report: Agricultural Outlook, 

accessed June 11, 2007, at http://findarticles.com/p/articles/

mi_m3778/is_1991_July/ai_12034691.

U.S. Department of Agriculture, 2004, Census of agriculture, 

1987, 1992, 1997: Ithaca, N.Y., Cornell University, Mann 

Library. (Available at http://agcensus.mannlib.cornell.edu/

AgCensus/homepage.do.)

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
This page intentionally left blank
Chapter 18

Southern California Mountains Ecoregion

approximately 17,871 km2 (6,900 mi2) of land located entirely 

within California. The ecoregion is bounded on the far north 

by the Sierra Nevada Ecoregion, on the east by the Mojave 

Basin and Range Ecoregion, on the southeast by the Sonoran 

Basin and Range Ecoregion, and on the west and north by 

Southern and Central California Chaparral and Oak Woodlands Ecoregion. In addition, the northern part of the ecoregion is separated from the Central California Valley Ecoregion 

by a narrow strip of the Southern and Central California 

Chaparral and Oak Woodlands Ecoregion (fig.1). 

By Christopher E. Soulard, Christian G. Raumann, and Tamara S. Wilson

This chapter has been modified from original material 

published in Soulard and others (2007), entitled “Land-cover 

trends of the Southern California Mountains ecoregion” (U.S. 

Geological Survey Scientific Investigations Report 2007–5235).

Ecoregion Description

The Southern California Mountains Ecoregion (Omernik, 

1987; U.S. Environmental Protection Agency, 1997) encompasses 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Southern California Mountains Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 

1992 National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation 

may be depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided 

into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed 

in study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are 

listed in appendix 2. See appendix 3 for definitions of land-use/land-cover classifications. 

Mojave Basin

and Range

Sierra Nevada

Southern and Central

California Chaparral

and Oak Woodlands

Central

California Valley

SBR

Southern and Central

California Chaparral

and Oak Woodlands

Southern and

Central California

Chaparral

and

Oak Woodlands

120° 119° 118° 117°

35°

36°

34°

33°

PA C I F I C

O C E A N

CALIFORNIA

Los Angeles

San Diego

PA C I F I C

O C E A N

Pasadena

Palmdale

Santa Clarita

Silverwood Lake

Castaic

San Fernando Valley

San Andreas Fault

San Gabriel

Valley

SANTA YNEZ 

MTNS

SAN GABRIEL

MTNS

SAN JACINTO

MTNS

SANTA ROSA

MTNS

SAN BERNARDINO 

MTNS

TEHACHAPI

MTNS 5

Map 

area

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
192 Status and Trends of Land Change in the Western United States—1973 to 2000

The Southern California Mountains Ecoregion includes 

several Pacific Coast mountain ranges. From northwest to 

southeast, these are the Santa Ynez Mountains, the Tehachapi 

Mountains, the San Gabriel Mountains, the San Bernardino 

Mountains, the San Jacinto Mountains, and the Santa Rosa 

Mountains. These mountain ranges are composed primarily 

of Mesozoic granitic and metamorphic rocks, in addition to 

Tertiary sedimentary rocks. The mountains are fractured and 

discontinuous, owing to movement on the San Andreas Fault 

and also the associated thrust faults that underlie the region. 

Additionally, the Santa Ynez Mountains, San Gabriel Mountains, and San Bernardino Mountains make up part of the geologic province known informally as the “Transverse Ranges 

Province,” so-named because of its atypical east-west orientation, which differs from the more typical northwest-southeast 

orientation (roughly parallel to the San Andreas Fault) of most 

mountain ranges and valleys elsewhere in California.

The mountains of the Southern California Mountains 

Ecoregion act as a barrier between a coastal Mediterranean 

climate to the west and a dry desert climate to the east. This 

physiographic-barrier effect, along with the topographic 

gradient of rolling hills to mountains, plays a large role in 

dictating regional land-use patterns. For example, most urban 

and agricultural development (for example, irrigated pasture, 

hay fields, orchards) occurs at lower elevations in the more 

temperate parts of the ecoregion. Much of this land use is also 

connected to the suburban growth occurring in adjacent ecoregions; population pressure from cities along the periphery of 

the Southern California Mountains ecoregion—specifically, 

the San Fernando and San Gabriel Valleys in the greater Los 

Angeles, California, area, as well as the cities of Pasadena, 

Santa Clarita, and Palmdale, California —has caused a spillover in development into the Southern California Mountains 

Ecoregion’s foothills. At higher elevations, development is 

less dense and is primarily associated with recreational activities and their supporting infrastructure (for example, campgrounds, vacation homes, ski resorts). 

The physiographic barrier between the coastal and desert 

climates also sets the stage for the annual fire season, which 

occurs from late summer to early fall. Dry conditions on the 

ground, coupled with the seasonal strong, offshore Santa Ana 

winds (created from steep pressure gradients that develop 

between the desert and the coast), have fueled frequent major 

wildfires throughout the region for more than 500 years (Mensing 

and others, 1999). The increase in contemporary development, 

coupled with the long fire history, makes human populations in 

the region susceptible to fire hazards on a regular basis.

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the footprint (overall areal 

extent) of land-use/land-cover change in the Southern California Mountains Ecoregion was 5.1 percent, or 906 km2. The 

footprint of change can be interpreted as the area that experienced land-cover change during at least one of the four multiyear time periods that make up the 27-year study period. Of 

the total change, 518 km2 changed during one period, 268 km2 

changed during two periods, 107 km2 changed during three 

periods, and less than 1 km2 changed during all four periods 

(table 1). Compared to other western United States ecoregions, 

overall change was low (fig. 2).

The average annual rate of land-cover change in the 

Southern California Mountains Ecoregion between 1973 and 

2000 was roughly 0.3 percent per year. This measurement, 

which normalizes the results for each period to an annual 

scale, means that the ecoregion averaged roughly 0.3 percent 

(50 km2) of change each year in the 27-year study period. 

However, this annual change varied between each of the four 

time periods (fig. 3). Between 1973 and 1980, the annual rate 

of change in the Southern California Mountains Ecoregion 

Figure 2. Overall spatial change in Southern California Mountains Ecoregion (SCM; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial 

change in Southern California Mountains Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods
Chapter 18—Southern California Mountains Ecoregion 193

was 0.2 percent per year, increasing to 0.3 percent per year 

between 1980 and 1986 and 0.4 percent per year between 

1986 and 1992. The normalized annual rate dropped to 0.2 

percent per year between 1992 and 2000 (table 2).

In 2000, 4 of the 11 land-cover classes occupied most 

of the Southern California Mountains Ecoregion: grassland/

shrubland (65.9 percent), forest (27.5 percent), developed (2.6 

percent), and agriculture (1.5 percent). Six other land-cover 

classes cumulatively made up the remaining 2.5 percent of the 

ecoregion in 2000, each making up less than 1.0 percent of the 

ecoregion (table 3). 

Between 1973 and 2000, the land-cover classes that experienced a measurable net change in relation to the total Southern California Mountains Ecoregion area were, in descending 

order, developed (44.6 percent increase) and grassland/shrubland (1.1 percent decrease) (fig. 4). However, net change may 

not necessarily be the best indicator of change for individual 

land-cover classes as it can mask more complex land-use/landcover dynamics. Analysis of gross change (that is, area gained 

or lost) by individual land-cover classes by time period shows 

that classes have fluctuated throughout the 27-year study 

period to a greater degree than net change values may indicate 

(fig. 5). Figure 5 illustrates how land-cover classes may experience gains and losses in area both within and between time 

periods. For example, the water class had no significant net 

change but experienced a gross change of nearly half its 1973 

value. The nonmechanically disturbed class, which fluctuated 

greatly over the study period. underwent gross change totaling 

more than four times its original value. 

The “from class–to class” information afforded by a 

postclassification comparison allows the identification of 

land-use/land-cover class conversions and the ranking of these 

conversions according to their magnitude. Table 4 illustrates 

the most frequent conversions between 1973 and 2000 in the 

Southern California Mountains Ecoregion. Five of the top ten 

Figure 3. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Southern California Mountains Ecoregion are represented by red bars in 

each time period.

Figure 4. Normalized average net change in Southern California 

Mountains Ecoregion by time period for each land-cover class. 

Bars above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
194 Status and Trends of Land Change in the Western United States—1973 to 2000

most prominent conversions are connected to the nonmechanical disturbance of land cover by fire. Cumulatively, the effect 

of nonmechanical disturbance on grassland/shrubland and 

forest resulted in an estimated 501 km2 of vegetated landcover loss. However, much of this land experienced ecological 

succession, or regrowth, after each disturbance event (fig. 6). 

Regrowth accounted for 531 km2 of vegetated land-cover gain; 

areas that were disturbed in consecutive periods account for an 

additional 21 km2. 

Conversions to the developed class also were common in 

the Southern California Mountains Ecoregion during the study 

period (146 km2) (fig. 7). The ecoregion is a geographically 

unique place, surrounded at lower elevations by human development and having few natural corridors that link its multiple 

mountain ranges. In the past, natural ignition sources such as 

lightning and wind dictated fire behavior in the Southern California Mountains Ecoregion, but today most of the fires are 

human-caused and are located at or near the interface between 

human development and wildlands (U.S. Department of Agriculture, 2005). These anthropogenic changes make predictions 

of future ecosystem health difficult as threats and outcomes 

Figure 5. Gross change (area gained and lost) in Southern California Mountains Ecoregion by time period for each land-cover 

class. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. Note that not all land-cover classes 

shown in explanation may be represented in figure. See appendix 

3 for definitions of land-use/land-cover classifications. Diagram 

illustrates that net change can mask within-class fluctuations 

within each time period and during entire 27-year study period.

Figure 6. Photograph taken in April 2005 of Silverwood Lake, 

California, and its surroundings, showing area undergoing 

regeneration following fire. Although grasses and shrubs tend 

to reestablish themselves quite soon after fire, trees take much 

longer to recover. Land-cover classes shown are grassland/

shrubland and water.

Figure 7. Photograph taken in April 2005 of new homes in Castaic, 

California, an unincorporated community in Los Angeles County 

located alongside Interstate 5. Land-use/land-cover classes shown 

are grassland/shrubland, forest, developed, and water.

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 18—Southern California Mountains Ecoregion 195

cannot be measured against historical conditions. Topographic 

isolation, coupled with increased fragmentation of habitat 

by fire, poses significant threats to existing diversity and 

may ultimately drive species turnover in Southern California 

Mountains Ecoregion (Center for Biological Diversity, 2007). 

Protection of this designated biodiversity hotspot will become 

increasingly difficult given current land-use/land-cover trends 

(Myers and others, 2000). The consequences of land-use/landcover change caused by nonmechanical disturbance and development, as well as the general loss of grassland/shrubland, 

do not necessarily follow managerial boundaries. On Federal 

lands, many agencies have adopted multiscale, integrated 

planning and management activities in an attempt to deal with 

these ecological processes within and across management 

units (Hann and Bunnell, 2001). 

Table 1. Percentage of Southern California Mountains Ecoregion 

land cover that changed at least one time during study period 

(1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (94.9 percent), whereas 5.1 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 2.4 1.3 1.5 4.2 0.9 31.6

2 1.1 1.6 0.0 3.1 1.1 68.8

3 0.6 0.7 −0.1 1.4 0.5 78.1

4 0.0 0.0 0.0 0.0 0.0 52.2

Overall 

spatial 

change

5.1 2.5 2.6 7.5 1.7 32.8

Table 2. Raw estimates of change in Southern California Mountains Ecoregion land cover, computed for 

each of four time periods, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 1.6 1.0 0.6 2.6 0.7 41.6 0.2

1980–1986 2.1 1.5 0.6 3.5 1.0 47.4 0.3

1986–1992 2.3 1.6 0.6 3.9 1.1 48.4 0.4

1992–2000 1.9 1.1 0.8 3.0 0.7 38.4 0.2

Estimate of change, in square kilometers

1973–1980 289 178 111 467 120 41.6 41

1980–1986 371 260 111 632 176 47.4 62

1986–1992 407 291 116 698 197 48.4 68

1992–2000 346 196 149 542 133 38.4 43
196 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Southern California Mountains Ecoregion, calculated five 

times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.8 0.6 1.8 0.8 0.1 0.2 0.1 0.0 0.5 0.2 27.4 5.3 66.6 5.0 1.6 1.2 0.2 0.2 0.9 0.8

1980 1.0 0.7 2.1 0.9 0.0 0.0 0.1 0.1 0.5 0.2 27.7 5.3 66.7 5.0 1.5 1.2 0.2 0.2 0.3 0.2

1986 0.9 0.7 2.3 0.9 0.0 0.0 0.1 0.1 0.5 0.2 27.0 5.0 65.9 4.9 1.5 1.2 0.2 0.2 1.5 1.3

1992 0.8 0.6 2.5 1.0 0.1 0.1 0.1 0.1 0.5 0.2 27.0 5.0 66.9 4.8 1.5 1.2 0.2 0.2 0.4 0.4

2000 0.8 0.6 2.6 1.1 0.1 0.1 0.1 0.1 0.5 0.2 27.5 5.3 65.9 5.0 1.5 1.2 0.2 0.2 0.8 0.6

Net

change 0.0 0.2 0.8 0.3 −0.1 0.2 0.0 0.0 0.0 0.0 0.1 0.3 −0.7 0.8 −0.1 0.2 0.0 0.0 −0.2 1.0

Gross

change 0.4 0.3 0.8 0.3 0.3 0.2 0.0 0.0 0.0 0.0 1.6 1.5 4.6 2.4 0.2 0.2 0.0 0.0 4.1 2.4

Area, in square kilometers

1973 143 100 327 146 26 28 11 7 92 44 4,893 940 11,902 897 279 214 30 29 169 143

1980 175 120 368 159 3 4 13 10 92 44 4,943 941 11,924 892 274 210 30 29 49 43

1986 167 119 404 167 7 5 14 10 92 44 4,830 886 11,781 884 276 209 31 29 269 234

1992 147 101 448 185 14 13 17 12 92 44 4,831 888 11,958 849 267 207 31 30 66 80

2000 151 102 473 194 16 14 19 14 92 44 4,916 939 11,769 892 265 207 31 29 139 106

Net

change 8 32 146 62 −10 31 8 7 0 0 24 58 −133 148 −13 30 1 1 −30 172

Gross

change 70 46 146 62 55 36 8 7 0 0 291 266 814 426 32 29 2 2 741 431
Chapter 18—Southern California Mountains Ecoregion 197

Table 4. Principal land-cover conversions in Southern California Mountains Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Nonmechanically disturbed Grassland/Shrubland 98 89 60 0.5 33.7

Nonmechanically disturbed Forest 53 51 34 0.3 18.2

Grassland/Shrubland Nonmechanically disturbed 31 37 25 0.2 10.7

Grassland/Shrubland Developed 31 19 13 0.2 10.7

Grassland/Shrubland Water 24 20 13 0.1 8.4

Other Other 53 n/a n/a 0.3 18.3

Totals 289 1.6 100.0

1980–1986 Grassland/Shrubland Nonmechanically disturbed 166 183 124 0.9 44.7

Forest Nonmechanically disturbed 103 132 89 0.6 27.9

Nonmechanically disturbed Grassland/Shrubland 48 43 29 0.3 12.8

Grassland/Shrubland Developed 21 9 6 0.1 5.8

Forest Developed 10 11 7 0.1 2.8

Other Other 23 n/a n/a 0.1 6.1

Totals 371 2.1 100.0

1986–1992 Nonmechanically disturbed Grassland/Shrubland 262 232 157 1.5 64.3

Grassland/Shrubland Nonmechanically disturbed 62 76 51 0.3 15.3

Grassland/Shrubland Developed 30 14 9 0.2 7.3

Water Grassland/Shrubland 11 14 9 0.1 2.8

Agriculture Developed 10 13 9 0.1 2.3

Other Other 32 n/a n/a 0.2 7.9

Totals 407 2.3 100.0

1992–2000 Grassland/Shrubland Nonmechanically disturbed 122 93 63 0.7 35.4

Grassland/Shrubland Forest 98 132 90 0.5 28.4

Nonmechanically disturbed Grassland/Shrubland 64 79 53 0.4 18.5

Grassland/Shrubland Developed 22 10 7 0.1 6.5

Forest Nonmechanically disturbed 14 19 13 0.1 4.1

Other Other 24 n/a n/a 0.1 7.0

Totals 346 1.9 100.0

1973–2000

(overall)

Nonmechanically disturbed Grassland/Shrubland 471 377 255 2.6 33.3

Grassland/Shrubland Nonmechanically disturbed 382 344 233 2.1 27.0

Forest Nonmechanically disturbed 119 133 90 0.7 8.4

Grassland/Shrubland Developed 104 41 28 0.6 7.4

Grassland/Shrubland Forest 101 132 89 0.6 7.2

Other Other 236 n/a n/a 1.3 16.7

Totals 1,413 7.9 100.0
198 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Center for Biological Diversity, 2007, Impacts of the 2003 

Southern California wildfires on four species listed as 

threatened or endangered under the Federal Endangered 

Species Act—Quino checkerspot butterfly, Mountain 

yellow-legged frog, Coastal California gnatcatcher, 

Least Bell’s vireo: Tucson, Ariz., Center for Biological 

Diversity, 46 p., last accessed June 18, 2007, at www.

biologicaldiversity.org/publications/papers/report-2003.pdf.

Hann, W.J., and Bunnell, D.L., 2001, Fire and land management 

planning and implementation across multiple scales: 

International Journal of Wildland Fire, v. 10, p. 389–403.

Mensing, S.A., Michaelson, J., and Byrne, R., 1999, A 

560-year record of Santa Ana fires reconstructed from 

charcoal deposited in the Santa Barbara Basin, California: 

Quaternary Research, v. 51, p. 295–305.

Myers, N., Mittermeier, R.A., Mittermeier, C.G., da Fonseca, 

G.A.B., and Kent, J., 2000, Biodiversity hotspots for 

conservation priorities: Nature, v. 403, p. 853–858.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Soulard, C.E., Raumann, C.G., and Wilson, T.S., 2007, 

Land-cover trends of the Southern California Mountains 

ecoregion: U.S. Geological Survey Scientific Investigations 

Report 2007–5235, 22 p., available at http://pubs.usgs.gov/

sir/2007/5235/.

U.S. Department of Agriculture, 2005, Final environmental 

impact statement, volume 1, Land management plans—

Angeles National Forest, Cleveland National Forest, Los 

Padres National Forest, San Bernardino National Forest: 

United States Department of Agriculture, Forest Service, 

Pacific Southwest Region, R5-MB-074-A.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
Chapter 19

Southern and Central California Chaparral and 

Oak Woodlands Ecoregion

By Darrell E. Napton

Ecoregion Description

The Southern and Central California Chaparral and Oak 

Woodlands Ecoregion, which covers approximately 102,110 

km2 (39,425 mi2), is characterized by a Mediterranean climate 

with cool, moist winters and hot, dry summers (Omernik, 

1987; U.S. Environmental Protection Agency, 1997). Natural 

vegetation includes chaparral (for example, manzanita, Arctostaphylos spp.) and oak (Quercus spp.) woodlands with extensive grassland and shrubland cover. The low mountains and 

foothills of the ecoregion border or parallel the Pacific Ocean 

from Mexico to Point Reyes, California, and continue inland 

surrounding the Central California Valley Ecoregion (fig. 1). 

These mountains and hills are interrupted by limited areas of 

flat land generally used for development or agriculture. The 

largest developed area in the ecoregion is the Los Angeles 

Basin, followed by the San Francisco Bay area and the San 

Diego metropolitan area (fig. 1). The largest agricultural area 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Southern and Central California Chaparral and 

Oak Woodlands Ecoregion and surrounding ecoregions, showing 

land-use/land-cover classes from 1992 National Land Cover 

Dataset (Vogelmann and others, 2001); note that not all land-use/

land-cover classes shown in explanation may be depicted on 

map; note also that, for this “Status and Trends of Land Change” 

study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares 

indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned 

in text. Abbreviations for Western United States ecoregions are 

listed in appendix 2. See appendix 3 for definitions of land-use/

land-cover classifications. 

118°

Sierra

Nevada

Klamath

Mountains

CR

CR

Central

Basin

and

Range

Central 

California

Valley

Mojave Basin

and Range

Northern

Basin

and

Range

SCM

SBR

Eastern Cascades

Slopes and Foothills

PACIFIC

OCEAN

MEXICO

120°

118° 116°

124° 122°

40°

38°

36°

34°

32° 0 50 100 150 MILES

0 50 100 150 KILOMETERS Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

S I E R R A N E V A D A

CALIFORNIA

Los Angeles

C O A S T R A N G E S

San Diego

San Francisco

Monterey

Salinas

Salinas R.

PA

C I F I C

O C E A N

Point

Reyes

NEVADA

C E N T R A L V

A L L E Y
200 Status and Trends of Land Change in the Western United States—1973 to 2000

is the Salinas River valley south of Monterey, California. Most 

of the ecoregion consists of rangelands classified as grassland/

shrubland and forest land covers (figs. 1,2).

Contemporary Land-Cover Change

(1973 to 2000)

The overall spatial change (that is, the percentage of area 

that changed at least one time between 1973 and 2000) in the 

ecoregion was estimated at 9.7 percent (table 1). The amount 

of change in the Southern and Central California Chaparral and 

Oak Woodlands Ecoregion was close to the median among the 

western United States ecoregions (fig. 3). Nearly seventy percent 

of the converted landscape changed land-cover class only one 

time, whereas thirty percent changed land cover twice (table 1). 

Fire, which produces a landscape classified as nonmechanically 

Figure 2. Typical Southern and Central California Chaparral and 

Oak Woodlands Ecoregion landscape, consisting of grassland/

shrubland or forest land cover. 

Figure 3. Overall spatial change in Southern and Central California Chaparral and Oak Woodlands Ecoregion (SCCCOW; darker 

bars) compared with that of all 30 Western United States ecoregions (lighter bars). Each horizontal set of bars shows proportions 

of ecoregion that changed during one, two, three, or four time 

periods; highest level of spatial change in Southern and Central 

California Chaparral and Oak Woodlands Ecoregion (four time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.

Figure 4. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Southern and Central California Chaparral and Oak Woodlands Ecoregion 

are represented by red bars in each 

time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
Chapter 19—Southern and Central California Chaparral and Oak Woodlands Ecoregion 201

disturbed, was the primary cause of land-cover change in areas 

that experienced two or more changes during the study period. 

Land-conversion rates varied temporally with the fastest annual 

rates occurring between 1992 and 2000 (at 0.6 percent) and slowest rate between 1986 and 1992 (at 0.3 percent) (table 2; fig.4). 

Figure 5 provides an overview of the net land-cover 

change by time period. Forest and grassland/shrubland losses 

were associated with net increases in nonmechanical disturbances, a conversion normally attributed to fire, which is a 

major presence in the Southern and Central California Chaparral and Oak Woodlands Ecoregion. Cool, wet winters bring a 

growth of annual grasses providing the necessary fuel load for 

fires to spread during the ecoregion’s hot, dry summers. Many 

of the endemic chaparral plant species here are adapted to 

survive low-frequency fires, and some species even depend on 

fire as part of their life-cycle strategy (fig. 6; see also, Halsey, 

2005). Developed land cover increased throughout the study 

period and accounted for virtually all of the net change occurring between 1986 and 1992. A net loss of agriculture occurred 

during each time period in the study. As agriculture here typically occurs on flat, easily developed land, agriculture lands 

are often best suited for urban expansion (fig. 7). 

Figure 5. Normalized average net change in Southern and 

Central California Chaparral and Oak Woodlands Ecoregion by 

time period for each land-cover class. Bars above zero axis 

represent net gain, whereas bars below zero represent net loss. 

Note that not all land-cover classes shown in explanation may be 

represented in figure. See appendix 3 for definitions of land-use/

land-cover classifications.

Figure 6. Grassland/shrubland and forest in Southern and 

Central California Chaparral and Oak Woodlands Ecoregion, two 

land-cover classes that are prone to fires during dry summers 

associated with Mediterranean climate of ecoregion. 

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Figure 7. Conversion of grassland/shrubland to agriculture was 

most common nonfire land-cover change in Southern and Central 

California Chaparral and Oak Woodlands Ecoregion during study 

period. 

Figure 8. Conversions of grassland/shrubland and agriculture 

to developed land were two common land-cover changes in 

Southern and Central California Chaparral and Oak Woodlands 

Ecoregion during study period.
202 Status and Trends of Land Change in the Western United States—1973 to 2000

Grassland/shrubland land cover makes up the largest share of this ecoregion, followed by forest, agriculture, 

and developed lands (table 3). These four land-cover classes 

accounted for 96 percent of the ecoregion in 1973 but only 

93.2 percent in 2000, largely because of the net increase in 

nonmechanically disturbed land cover coupled with a decrease 

in forest and grassland/shrubland land covers. Developed land 

increased 33 percent during the study period as population in 

the Southern and Central California Chaparral and Oak Woodlands Ecoregion increased from 14.5 to 22.2 million between 

1970 and 2000 (U.S. Census Bureau, 2000). More than half of 

the land converted to developed land cover came from agriculture, and nearly thirty percent was converted from grassland/

shrubland (figs. 8, 9). 

Between 1973 and 2000, the five most common land 

conversions accounted for 73 percent (by area) of the change in 

the ecoregion (table 4). The most common land-cover conversion was grassland/shrubland to nonmechanically disturbed, 

accounting for nearly one-quarter of all area converted, whereas 

forest to nonmechanically disturbed accounted for an additional 

19 percent. These conversions largely represent the impact of 

wildfire in the ecoregion. The third and fifth most common 

conversions (nonmechanically disturbed back to grassland/

shrubland and nonmechanically disturbed back to forest) reflect 

the cyclic nature of landscape changes associated with wildfire 

and postfire vegetation recovery. The numbers do not balance 

because there is a lag time between fire occurrence and the 

conversion back to the original land cover, especially in the case 

of forests where an intermediate, successional vegetation cover 

is likely to occur. The conversion of agriculture to developed 

land was the fourth most common conversion and accounted for 

nearly 10 percent of the land-cover change in the ecoregion.

The Southern and Central California Chaparral and Oak 

Woodlands Ecoregion is the most populous of the nation’s 

ecoregions. Many people find the ecoregion’s Mediterranean 

climate desirable, but little accessible, flat land suitable for 

affordable housing is available. Additionally, water shortages 

and drought are common, and much of the ecoregion’s water 

is imported from other ecoregions. Consequently, most of 

the ecoregion’s landscape remains open rangeland with land 

covers of grassland/shrubland mixed with oak forest. The 

region’s limited farmland is used for specialty crops such as 

wine grapes, table grapes, and strawberries. New development 

has resulted in the conversion of some agricultural land, but 

the largest driver of land-cover change has been the periodic 

burning of grassland/shrubland and forested land during the 

ecoregion’s long, hot, and dry summers.

Figure 9. Areal percentages of sources of developed land in 

Southern and Central California Chaparral and Oak Woodlands 

Ecoregion during study period.

55.1% 28.9%

13.5%

1.4% (Forest)

0.8% (Wetland) 0.3% (Water)

Agriculture

Grassland/Shrubland

Mechanically Disturbed

Forest

Wetland

Water

EXPLANATION

SOURCE LAND-USE/LAND-COVER CLASS
Chapter 19—Southern and Central California Chaparral and Oak Woodlands Ecoregion 203

Table 1. Percentage of Southern and Central California Chaparral 

and Oak Woodlands Ecoregion that changed at least one time 

during study period (1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (90.3 percent), whereas 9.7 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 6.7 2.3 4.4 9.0 1.5 23.1

2 2.9 1.6 1.3 4.5 1.1 37.9

3 0.1 0.1 0.0 0.1 0.0 50.5

4 0.0 0.0 0.0 0.0 0.0 87.5

Overall 

spatial 

change

9.7 2.9 6.7 12.6 2.0 20.8

Table 2. Raw estimates of change in Southern and Central California Chaparral and Oak Woodland. 

land cover, computed for each of four time periods between 1973 and 2000, and associated error at 

85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 3.1 1.7 1.5 4.8 1.1 36.1 0.4

1980–1986 3.1 1.6 1.5 4.7 1.1 35.8 0.5

1986–1992 2.0 0.9 1.1 2.9 0.6 29.6 0.3

1992–2000 4.5 2.2 2.3 6.8 1.5 33.8 0.6

Estimate of change, in square kilometers

1973–1980 3,216 1,704 1,512 4,921 1,161 36.1 459

1980–1986 3,149 1,653 1,496 4,802 1,126 35.8 525

1986–1992 2,037 . 885 1,151 2,922 . 603 29.6 339

1992–2000 4,607 2,286 2,321 6,893 1,557 33.8 576
204 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Southern and Central California Chaparral and Oak 

Woodlands Ecoregion, calculated five times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 2.5 1.7 6.6 3.6 0.1 0.1 0.2 0.2 0.3 0.3 21.3 4.2 58.0 5.7 10.1 3.1 0.6 0.4 0.3 0.2

1980 2.5 1.7 7.3 4.0 0.1 0.1 0.2 0.2 0.3 0.3 20.5 4.0 57.0 5.7 9.9 3.1 0.6 0.4 1.6 1.6

1986 2.5 1.7 7.7 4.0 0.2 0.1 0.2 0.2 0.3 0.3 21.1 4.1 57.2 5.6 9.7 3.0 0.6 0.4 0.6 0.6

1992 2.4 1.7 8.3 4.2 0.2 0.1 0.2 0.2 0.3 0.3 21.0 4.0 57.2 5.7 9.4 3.0 0.6 0.4 0.3 0.2

2000 2.5 1.7 8.8 4.4 0.1 0.1 0.2 0.2 0.3 0.3 19.8 3.5 55.3 5.6 9.3 3.0 0.6 0.4 3.1 2.1

Net

change 0.0 0.1 2.2 1.4 0.0 0.1 0.0 0.1 0.0 0.0 −1.5 1.6 −2.7 1.3 −0.8 1.1 0.0 0.0 2.8 2.0

Gross

change 0.4 0.3 2.2 1.4 0.6 0.3 0.1 0.1 0.0 0.0 3.2 2.4 6.1 2.2 2.3 1.1 0.1 0.1 7.5 3.8

Area, in square kilometers

1,973 2,507 1,776 6,743 3,650 140 112 199 234 339 291 21,741 4,296 59,216 5,777 10,340 3,200 627 424 257 212

1,980 2,601 1,773 7,417 4,039 62 71 188 220 338 291 20,924 41,20 58,220 5,783 10,121 3,170 644 440 1,595 1,586

1,986 2,505 1,770 7,836 4,101 155 93 187 220 338 291 21,520 4,216 58,408 5,763 9,905 3,103 654 428 602 598

1,992 2,455 1,772 8,456 4,279 216 140 168 161 337 291 21,491 4,133 58,447 5816 9,563 3,069 663 432 315 221

2,000 2,502 1,773 8,977 4,443 116 71 214 169 346 291 20,234 3,611 56,471 5,707 9,478 3,043 626 416 3,146 2,097

Net

change −5 55 2,234 1,381 −25 99 15 88 7 15 −1,506 1,677 −2,746 1,326 −862 1,170 −1 31 2,889 2,057

Gross

change 447 278 2,234 1,381 612 314 135 91 13 15 3,305 2,499 6,221 2,247 2,346 1,076 116 80 7,620 3,843
Chapter 19—Southern and Central California Chaparral and Oak Woodlands Ecoregion 205

Table 4. Principal land-cover conversions in Southern and Central California Chaparral and Oak Woodlands Ecoregion, showing 

amount of area changed (and margin of error, calculated at 85-percent confidence level) for each conversion during each of four 

time periods and also during overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Forest Nonmechanically disturbed 825 990 674 0.8 25.6

Grassland/Shrubland Nonmechanically disturbed 755 803 547 0.7 23.5

Agriculture Developed 481 437 298 0.5 14.9

Grassland/Shrubland Agriculture 409 306 209 0.4 12.7

Nonmechanically disturbed Grassland/Shrubland 226 186 127 0.2 7.0

Other Other 520 n/a n/a 0.5 16.2

Totals 3,216 3.1 100.0

1980–1986 Nonmechanically disturbed Grassland/Shrubland 810 841 573 0.8 25.7

Nonmechanically disturbed Forest 769 926 631 0.8 24.4

Grassland/Shrubland Nonmechanically disturbed 448 523 357 0.4 14.2

Agriculture Developed 210 184 125 0.2 6.7

Agriculture Grassland/Shrubland 156 141 96 0.2 5.0

Other Other 756 n/a n/a 0.7 24.0

Totals 3,149 3.1 100.0

1986–1992 Nonmechanically disturbed Grassland/Shrubland 485 526 358 0.5 23.8

Agriculture Developed 327 328 224 0.3 16.1

Grassland/Shrubland Developed 210 124 85 0.2 10.3

Grassland/Shrubland Nonmechanically disturbed 169 123 84 0.2 8.3

Forest Nonmechanically disturbed 134 170 116 0.1 6.6

Other Other 712 n/a n/a 0.7 34.9

Totals 2,037 2.0 100.0

1992–2000 Grassland/Shrubland Nonmechanically disturbed 1,771 1,230 838 1.7 38.4

Forest Nonmechanically disturbed 1,353 1,589 1,082 1.3 29.4

Grassland/Shrubland Agriculture 261 174 119 0.3 5.7

Agriculture Developed 213 147 100 0.2 4.6

Grassland/Shrubland Developed 183 107 73 0.2 4.0

Other Other 826 n/a n/a 0.8 17.9

Totals 4,607 4.5 100.0

1973–2000

(overall)

Grassland/Shrubland Nonmechanically disturbed 3,144 1,643 1,119 3.1 24.2

Forest Nonmechanically disturbed 2,442 2,018 1,375 2.4 18.8

Nonmechanically disturbed Grassland/Shrubland 1,680 1,080 736 1.6 12.9

Agriculture Developed 1,230 931 634 1.2 9.5

Nonmechanically disturbed Forest 1,007 939 640 1.0 7.7

Other Other 3,506 n/a n/a 3.4 27.0

Totals 13,009 12.7 100.0
206 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Halsey, R.W., 2005, Fire, chaparral, and survival in southern 

California, San Diego, CA: Sunbelt Publications. 

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

U.S. Census Bureau, 2000, Census of population 1970 

through 2000: U.S. Census Bureau database, accessed at 

http://www.census.gov/prod/www/abs/decennial/index.htm. 

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
Cold Deserts Ecoregions

120° 118° 116° 114° 112°

42°

40°

38°

36°

Northern Basin

and Range

Snake River Basin

Colorado

Plateaus

WUM

Mojave

Basin and Range

Sierra

Nevada

ANMP

ECSF

MRK

WB

CCV

SCCCOW

SCM

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

Salt

Lake

City

Ogden

Lockwood Tooele

Reno Sparks

Truckee River

Walker Lake

Humboldt R iver Carson River

Walker River

80

IDAHO

OREGON

CALIFORNIA

UTAH

N E VA D A

GREAT

BASIN

DESERT SIERRA NEVADA

Chapter 20

Central Basin and Range Ecoregion

Wasatch and Uinta Mountains Ecoregion, on the north by the 

Northern Basin and Range and the Snake River Basin Ecoregions, and on the south by the Mojave Basin and Range and 

the Colorado Plateaus Ecoregions (fig. 1). Most of the Central 

Basin and Range Ecoregion is located in Nevada (65.4 percent) 

and Utah (25.1 percent), but small segments are also located 

in Idaho (5.6 percent), California (3.7 percent), and Oregon 

(0.2 percent). Basin-and-range topography characterizes the 

Central Basin and Range Ecoregion: wide desert valleys are 

bordered by parallel mountain ranges generally oriented northsouth. There are more than 33 peaks within the Central Basin 

and Range Ecoregion that have summits higher than 3,000 m 

By Christopher E. Soulard

This chapter has been modified from original material 

published in Soulard (2006), entitled “Land-cover trends of 

the Central Basin and Range Ecoregion” (U.S. Geological 

Survey Scientific Investigations Report 2006–5288).

Ecoregion Description

The Central Basin and Range Ecoregion (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997) encompasses 

approximately 343,169 km2 (132,498 mi2) of land bordered on 

the west by the Sierra Nevada Ecoregion, on the east by the 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Central Basin and Range Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted on 

map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map 

shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. See 

appendix 3 for definitions of land-use/land-cover classifications. 
0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in three time periods

210 Status and Trends of Land Change in the Western United States—1973 to 2000

(10,000 ft), but valleys in the ecoregion are also high, most having elevations above 1,200 m (4,000 ft) (Grayson, 1993). 

The Central Basin and Range Ecoregion’s high elevation and location between mountain ranges influences regional 

climate. The Sierra Nevada to the west produces a rain shadow 

effect that blocks moisture from the Pacific Ocean, and the 

Rocky Mountains to the east creates a barrier effect that restricts 

moisture from the Gulf of Mexico (Rogers, 1982). This lack of 

moisture creates the Great Basin Desert (encompassed within the 

Central Basin and Range Ecoregion), which is one of the four 

biologically distinct deserts in North America, along with the 

Mojave, Sonoran, and Chihuahuan Deserts (Grayson, 1993). The 

Great Basin has the coldest climate of these deserts. As opposed 

to the other North American deserts, precipitation within the 

Great Basin regularly falls in winter as snow (Mac and others, 

1998). Because no natural drainages exist within the Central 

Basin and Range Ecoregion, the little precipitation that does fall 

either drains to ephemeral or saline lakes by means of streams or 

disappears through evaporation and (or) absorption into the soil 

(Grayson, 1993).

Inhospitable conditions, such as harsh climate, infertile 

soils, and lack of viable resources, have been a formidable barrier to human land use in the Central Basin and Range Ecoregion. These conditions also restrict ecoregion resilience, which 

results in lasting impacts from most land-use practices. This 

ecoregion is very sensitive to those land-use changes that do 

occur (Mac and others, 1998; Pellant and others, 2004; Chambers and Miller, 2004). Much as with the historical land-use 

legacies of the ecoregion, factors that have driven contemporary 

change in the ecoregion have the potential to produce long-term 

consequences. For example, the poor soil quality and low rainfall 

characteristic of the ecoregion make successful farming difficult. 

As a way to overcome these obstacles, farmers either establish 

irrigation-dependent crops near rare riparian segments or rely on 

groundwater pumping and water diversions. Water diversions 

from the Carson, Humboldt, Truckee, and Walker Rivers have 

shifted to accommodate irrigation demand (particularly to support the ranching industry), municipal-water demand in regional 

cities (for example, Reno, Nevada), and government-mandated 

water conservation. Shifts in agricultural land use across the 

Central Basin and Range Ecoregion degrade ecosystems vital to 

the fitness of many vertebrates and invertebrates. This degradation is manifested as livestock trampling of native vegetation (in 

wetlands and grasslands) and lowered water tables in places like 

Walker Lake (Mac and others, 1998).

The arid climate and abundance of dry fuel sources also 

make the ecoregion naturally susceptible to fire. This susceptibility has been magnified since European settlement in the late 

1800s. Early settlers changed the composition of grasslands and 

shrublands by introducing livestock grazing and fire-suppression 

practices within the sagebrush-dominated landscape. Grazing 

and fire suppression have continued to the present day and have 

shaped the grassland/shrubland landscape by degrading sagebrush plant communities and enabling nonnative annual grasses 

to invade much of the ecoregion (Miller and others, 2001). These 

grasses, most notably cheatgrass (Bromus tectorum), not only 

contribute to a rise in fire susceptibility across the ecoregion by 

increasing dry fuel sources but also reestablish themselves more 

easily than native plants following fires, thereby perpetuating and 

magnifying the cycle of fires (Pellant and others, 2004). Historical and contemporary land-use practices have produced lasting 

impacts in the Central Basin and Range Ecoregion by changing 

the fire regime and making the ecoregion more susceptible to 

fire. The increased probability of fire poses long-term risks for 

human and natural systems.

Contemporary Land-Cover Change 

(1973 to 2000)

Land-use/land-cover change between 1973 and 2000 

that was discernable using a 60-m mapping unit was minimal, 

especially when compared to other ecoregions of the western 

Figure 2. Overall spatial change in Central Basin and Range 

Ecoregion (CBR; darker bars) compared with that of all 30 Western 

United States ecoregions (lighter bars). Each horizontal set of 

bars shows proportions of ecoregion that changed during one, 

two, three, or four time periods; highest level of spatial change in 

Central Basin and Range Ecoregion (three time periods) labeled 

for clarity. See table 2 for years covered by each time period. See 

appendix 2 for key to ecoregion abbreviations.
0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−1

−0.5

0

0.5

1

1973–1980 1980–1986 1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Time period

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Chapter 20—Central Basin and Range Ecoregion 211

Figure 3. Estimates of land-cover change per time period, normalized to annual rates of 

change for all 30 Western United States ecoregions (gray bars). Estimates of change for 

Central Basin and Range Ecoregion are represented by red bars in each time period.

Figure 4. Normalized average net change in Central Basin and 

Range Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 2 for 

definitions of land-use/land-cover classifications.

United States (fig. 2). Between 1973 and 2000, the footprint 

(overall areal extent) of land-cover change in the Central Basin 

and Range Ecoregion was only 1.5 percent, or 4,979km2. 

The footprint of change can be interpreted as the area in the 

Central Basin and Range Ecoregion that experienced change 

during at least one of the four multiyear periods that make up 

the 27-year study period; it does not account for the frequency 

of change in any given location. This overall spatial change 

translates to 4,461 km2 that changed in one period, 343 km2 

that changed in two periods, and 166 km2 that changed in three 

periods (table 1). 

The normalized annual rate of land-cover change in the 

Central Basin and Range Ecoregion between 1973 and 2000 

was less than 0.1 percent per year. This means that the ecoregion averaged less than 0.1 percent (206 km2) of change each 

year in the 27-year study period. Between 1973 and 1980, the 

annual rate of change in the Central Basin and Range Ecoregion was less than 0.1 percent per year, while the annual rate of 

change increased to about 0.1 percent per year between 1980 

and 1986, 1986 and 1992, and 1992 and 2000 (table 2; fig. 3). 

Of the 11 land-use/land-cover classes, 4 dominated the 

landscape of the Central Basin and Range Ecoregion in 2000: 

grassland/shrubland (75.4 percent), forest (15.3 percent), barren 

(3.9 percent), and agriculture (2.9 percent). The remaining seven 

classes cumulatively made up the remaining 2.5 percent of the 

Central Basin and Range Ecoregion landscape in 2000 (table 3). 

Between 1973 and 2000, the land-cover classes that experienced a measurable net change include grassland/shrubland 

(0.8 percent decrease), forest (1.9 percent decrease), developed 

(43 percent increase), wetland (12.2 percent decrease), mining 

(159 percent increase, but still representing just 0.2 percent 

of the ecoregion), and nonmechanically disturbed (which was 

not present until the 2000 classification, when it occupied 0.5 

percent of the sampled area). Net change by temporal period is 

illustrated in figure 4. 
Figure 6. Instances of agriculture in Central Basin and Range 

Ecoregion. A, Livestock grazing on rangeland. B, Irrigated fields 

growing livestock feed.

−1

−0.5

0

0.5

1

1973–1980 1980–1986 1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Time period

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

212 Status and Trends of Land Change in the Western United States—1973 to 2000

Net change, however, is not necessarily the best indicator of within-class variability for those classes experiencing 

spatio-temporal fluctuations (fig. 5). For instance, areas classified as water fluctuated wildly between 259 km2

 (1980) and 

1,168 km2

 (1986) because of the ephemeral nature of desert 

lakes. Between 1973 and 2000, a net areal gain of 172 percent 

(518 km2) in water was measured, but gross change over the 

entire study period reached 1,420 km2, nearly five times the 

area that water occupied in 1973. 

The “from class–to class” information afforded by a 

postclassification comparison was used to identify landcover class conversions and rank them according to their 

magnitude. Table 4 illustrates the most frequent conversions 

for each individual time period and also between 1973 and 

2000. Although fieldwork confirmed the presence of many 

of the conversions listed in table 4, the ability to report these 

changes on the basis of interpretations was accomplished 

with varying degrees of uncertainty (as illustrated by the 

statistical error values in the table). In general, higher uncertainty arose where sampled changes were clustered within 

certain parts of the ecoregion rather than distributed evenly 

across the ecoregion. 

The two most prominent conversions reflect the natural, or nonmechanical, disturbance of natural land cover by 

fire. Cumulatively, the effect of nonmechanical disturbance 

on grassland/shrubland and forest resulted in 1,872 km2 

(32.5 percent of all changes) loss of vegetated land cover. As 

discussed earlier, the increase in fire seen within the Central 

Basin and Range Ecoregion is largely attributable to the invasion of annual grasses like cheatgrass (Bromus tectorum), which 

has increased dry fuels on the landscape. The changes in the 

agriculture and water classes represent other common conversions. Prominent changes in agricultural lands include 527 km2 

of conversion from grassland/shrubland to agriculture and 503 

km2 from agriculture to grassland/shrubland (fig. 3). Similarly, 

the water class experienced a variety of conversions within the 

Central Basin and Range Ecoregion, including 640 km2 from 

wetland to water, 255 km2 from water to grassland/shrubland, 

222 km2 from grassland/shrubland to water, and 178 km2 from 

water to wetland (note that water conversions account for 

changes in both natural and manmade water bodies). Ultimately, 

these land-use dynamics vary across the ecoregion and, as 

noted earlier, are associated with irrigation demand (to support 

the ranching industry), municipal-water demand in cities (for 

Figure 5. Gross change (area gained and lost) in Central Basin 

and Range Ecoregion by time period for each land-cover class. 

Area gained is shown by positive values, and area lost is shown 

by negative values. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 2 for 

definitions of land-use/land-cover classifications.

A

B
Figure 7. Hillside municipal-waste facility (A) and its downhill 

stream drainage (B) near Lockwood, Nevada.

Chapter 20—Central Basin and Range Ecoregion 213

example, Reno, Nevada), and government-mandated water conservation. Changes from grassland/shrubland to both developed 

(538 km2) and mining (526 km2) were predominantly unidirectional and permanent (figs. 6,7,8). 

Contemporary land-use/land-cover change has been 

minimal throughout the Central Basin and Range Ecoregion. 

However, landscape changes that result from increased fire 

frequency, rising demand for water and mineral resources, 

and growing highway development can have far-reaching 

consequences despite the small spatial extent of change. 

For example, increased fire frequency in the Central Basin 

and Range Ecoregion has ultimately contributed to the loss 

of sagebrush plant communities in favor of invasive annual 

grasses (Miller and others, 2001), resulting in possible impacts 

on biological diversity and human health. Much of the wildlife 

that depends on this vegetated landscape may become more 

vulnerable as a result of loss of habitat following a fire. Fire 

also directly threatens human communities and indirectly 

affects humans by jeopardizing traditional ranging practices 

(U.S. Geological Survey, 2003). Agricultural and developed 

land-use changes also have possible impacts, including pollution from agricultural and municipal sources as well as 

mechanical disturbances associated with water and mineralresource use. Although wildlife has proven to be resilient to 

anthropogenic land use, the loss of natural vegetation resulting 

A

B

Figure 8. Different elements of mining in Central Basin and 

Range Ecoregion. A, Gravel-extraction site near Tooele, Utah. 

B, Piles of gravel aggregate awaiting transport. C, Mineralprocessing facility along Interstate 80 near Reno, Nevada. D, Old 

tailings pile undergoing reestablishment of vegetation.

A

B

C

D
214 Status and Trends of Land Change in the Western United States—1973 to 2000

from the afore-mentioned changes has both eliminated and 

polluted ecosystems used by endangered species such as the 

Greater Sage Grouse (Centrocercus urophasianus). 

The growth of human populations in the Reno–Sparks 

and Salt Lake City–Ogden metropolitan areas will likely 

dictate the rate of future land-use conversions in the Central 

Basin and Range Ecoregion. The findings from the present 

study can be used in conjunction with existing literature to 

explore how, and to what extent, current land-use/land-cover 

trends will affect the Central Basin and Range Ecoregion into 

the future, and they also can provide insights into how policy 

change may alter current landscape conditions.

Table 1. Percentage of Central Basin and Range Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

[Most sample pixels remained unchanged (98.5 percent), whereas 1.5 percent 

changed at least once throughout study period. Two dashes (--) indicate that, 

because zero pixels changed four times during study period, relative error is 

not calculable] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.3 0.7 0.6 1.9 0.4 35.0

2 0.1 0.1 0.0 0.2 0.1 59.7

3 0.0 0.0 0.0 0.1 0.0 65.9

4 0.0 0.0 0.0 0.0 0.0 --

Overall 

spatial 

change

1.5 0.7 0.7 2.2 0.5 34.2

Table 2. Raw estimates of change in Central Basin and Range Ecoregion land cover, computed for each 

of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.2 0.1 0.1 0.3 0.1 48.2 0.0

1980–1986 0.3 0.3 0.0 0.7 0.2 69.5 0.1

1986–1992 0.4 0.2 0.2 0.5 0.1 34.1 0.1

1992–2000 0.8 0.6 0.2 1.3 0.4 49.4 0.1

Estimate of change, in square kilometers

1973–1980 698 495 202 1,193 337 48.2 100

1980–1986 1,163 1,190 −27 2,354 808 69.5 194

1986–1992 1,254 629 624 1,883 428 34.1 209

1992–2000 2,638 1,918 721 4,556 1,303 49.4 330
Chapter 20—Central Basin and Range Ecoregion 215

Table 3. Estimated area (and margin of error) of each land-cover class in Central Basin and Range Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed

Mechanically disturbed

Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.1 0.1 0.4 0.4 0.0 0.0 0.1 0.1 3.9 3.6 15.6 5.1 75.9 5.7 2.9 2.1 1.0 0.7 0.0 0.0

1980 0.1 0.1 0.4 0.4 0.0 0.0 0.1 0.1 3.9 3.6 15.6 5.1 75.8 5.7 3.0 2.2 1.0 0.7 0.0 0.0

1986 0.3 0.4 0.5 0.4 0.0 0.0 0.1 0.1 3.9 3.6 15.6 5.1 75.8 5.7 3.0 2.2 0.8 0.7 0.0 0.0

1992 0.2 0.3 0.6 0.4 0.0 0.0 0.1 0.1 3.9 3.6 15.6 5.1 75.8 5.7 2.9 2.1 0.9 0.7 0.0 0.0

2000 0.2 0.3 0.6 0.4 0.0 0.0 0.2 0.2 3.9 3.6 15.3 4.8 75.4 5.6 2.9 2.1 0.9 0.7 0.5 0.6

Net

change 0.2 0.3 0.2 0.1 0.0 0.0 0.1 0.1 0.0 0.0 −0.3 0.4 −0.6 0.5 0.0 0.1 −0.1 0.2 0.5 0.6

Gross

change 0.4 0.5 0.2 0.1 0.0 0.1 0.2 0.1 0.0 0.0 0.3 0.4 1.0 0.5 0.3 0.2 0.2 0.3 0.5 0.6

Area, in square kilometers

1973 302 278 1,510 1,256 0 0 312 317 13,320 12,282 53,407 17,337 260,616 19,717 10,060 7,371 3,509 2,405 0 0

1980 259 246 1,530 1,261 0 0 345 307 13,323 12,282 53,407 17,337 260,266 19,706 10,401 7,401 3,506 2,403 0 0

1986 1,168 1,219 1,581 1,262 61 89 336 280 13,323 12,282 53,384 17,341 259,975 19,699 10,302 7,396 2,906 2,281 0 0

1992 847 968 1,922 1,308 0 0 454 328 13,323 12,282 53,400 17,343 260,129 19,580 9,905 7,150 3,055 2,281 0 0

2000 820 930 2,159 1,368 12 18 806 520 13,323 12,282 52,366 16,615 258,664 19,382 9,932 7,131 3,082 2,283 1,872 1,916

Net

change 518 925 649 484 12 18 494 349 3 5 −1,041 1,471 −1,952 1,580 −128 434 −428 628 1,872 1,916

Gross

change 1,420 1,575 649 484 134 179 570 375 3 5 1,074 1,470 3,311 1,578 1,150 629 782 1,133 1,872 1,916
216 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Central Basin and Range Ecoregion, showing amount of area changed (and margin 

of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 352 353 240 0.1 50.5

Water Grassland/Shrubland 101 148 101 0.0 14.5

Grassland/Shrubland Mining 62 51 34 0.0 8.9

Wetland Water 39 57 38 0.0 5.5

Grassland/Shrubland Wetland 37 55 37 0.0 5.3

Other Other 106 n/a n/a 0.0 15.2

Totals 698 0.2 100.0

1980–1986 Wetland Water 600 874 594 0.2 51.6

Grassland/Shrubland Water 202 234 159 0.1 17.3

Agriculture Water 108 158 107 0.0 9.3

Grassland/Shrubland Agriculture 55 57 39 0.0 4.8

Grassland/Shrubland Developed 51 46 31 0.0 4.4

Other Other 147 n/a n/a 0.0 12.7

Totals 1,163 0.3 100.0

1986–1992 Agriculture Grassland/Shrubland 399 320 218 0.1 31.8

Grassland/Shrubland Developed 243 193 131 0.1 19.4

Water Grassland/Shrubland 154 225 153 0.0 12.3

Water Wetland 149 214 145 0.0 11.9

Grassland/Shrubland Mining 126 117 79 0.0 10.1

Other Other 182 n/a n/a 0.1 14.5

Totals 1,254 0.4 100.0

1992–2000 Forest Nonmechanically disturbed 1,005 1,471 1,000 0.3 38.1

Grassland/Shrubland Nonmechanically disturbed 867 1,269 862 0.3 32.9

Grassland/Shrubland Mining 328 252 171 0.1 12.4

Grassland/Shrubland Developed 224 198 135 0.1 8.5

Grassland/Shrubland Agriculture 85 124 84 0.0 3.2

Other Other 130 n/a n/a 0.0 4.9

Totals 2,638 0.8 100.0

1973–2000

(overall)

Forest Nonmechanically disturbed 1,005 1,471 1,000 0.3 17.5

Grassland/Shrubland Nonmechanically disturbed 867 1,269 862 0.3 15.1

Wetland Water 640 932 633 0.2 11.1

Grassland/Shrubland Developed 538 386 262 0.2 9.4

Grassland/Shrubland Agriculture 527 413 281 0.2 9.2

Other Other 2,177 n/a n/a 0.6 37.8

Totals 5,753 1.7 100.0
Chapter 20—Central Basin and Range Ecoregion 217

References Cited

Chambers, J.C., and Miller, J.R., 2004, Great Basin riparian 

areas; ecology, management, and restoration: Washington, 

D.C., Society for Ecological Restoration International, 

Island Press, 303 p.

Grayson, D.K., 1993, The desert’s past; a natural prehistory of 

the Great Basin: Washington, D.C., Smithsonian Institute 

Press, 356 p.

Mac, M.J., Opler, P.A., Puckett Haecker, C.E., and Doran, 

P.D., 1998, Status and trends of the nation’s biological 

resources, v. 2: Reston, Va., U.S. Geological Survey, p. 

437–964. (Available at www.nwrc.usgs.gov/sandt/SNT.pdf.)

Miller, R., Baisan, C., Rose, J., and Pacioretty, D., 2001, Preand post-settlement fire regime in mountain big sagebrush 

steppe and aspen; the northwestern Great Basin: Corvallis, 

Oregon, National Interagency Fire Center.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Pellant, M., Abbey, B., and Karl, S., 2004, Restoring the Great 

Basin Desert, U.S.A.; integrating science, management, and 

people: Environmental Modeling and Assessment, v. 99, p. 

169–179.

Rogers, G.F., 1982, Then and now; a photographic history of 

vegetation change in the central Great Basin desert: Salt 

Lake City, University of Utah Press.

Soulard, C.S., 2006, Land-cover trends of the Central Basin 

and Range Ecoregion: U.S. Geological Survey Scientific 

Investigations Report 2006–5288, 20 p., available at http://

pubs.usgs.gov/sir/2006/5288/. 

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

U.S. Geological Survey, 2003, Biological science in the Great 

Basin: Seattle, Washington, U.S. Geological Survey Forest 

and Rangeland Ecosystem Science Center, Western Region 

Briefing Paper, 2 p.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
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Chapter 21

Colorado Plateaus Ecoregion

Ecoregions in Colorado and on the northwest by the Wasatch 

and Uinta Mountains Ecoregion in northern and central Utah. 

To the south, the ecoregion borders the Arizona/New Mexico 

Plateau Ecoregion, which has a higher elevation and more 

grasslands than the Colorado Plateaus Ecoregion (Omernik, 

1987; U.S. Environmental Protection Agency, 1997).

The climate in the ecoregion is arid to semiarid, with only 

15 to 40 cm of annual precipitation. Higher elevation areas 

such as the La Sal Mountains receive more precipitation and 

support a mixed forest of ponderosa pine (Pinus ponderosa), 

Douglas-fir (Pseudotsuga menziesii), 

quaking aspen (Populus tremuloides), 

and Engelmann spruce (Picea engelmannii). Most other locations of the 

ecoregion are covered by an extensive 

woodland zone, which is dominated by 

a “pygmy forest” of pinyon pine (Pinus 

edulis) and several species of juniper 

(Juniperus spp.; fig. 3). The ground 

between these trees is sparsely covered 

by blue grama (Bouteloua gracilis), 

shrubs such as big sagebrush (Artemisia 

tridentata) and alderleaf cercocarpus 

(Cercocarpus montanus), and various herbs (McGinley, 2007). Grassland/shrubland land cover accounts 

for approximately 63 percent of the 

By Michael P. Stier

Ecoregion Description

The Colorado Plateaus Ecoregion covers approximately 

129,617 km2 (50,045 mi2) within southern and eastern Utah, 

western Colorado, and the extreme northern part of Arizona 

(fig. 1). The terrain of this ecoregion is characterized by broad 

plateaus, ancient volcanoes, and deeply dissected canyons 

(Booth and others, 1999; fig. 2). The ecoregion is bounded 

on the east by the Wyoming Basin and Southern Rockies 

Figure 1. Map of Colorado Plateaus Ecoregion and surrounding 

ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note 

that not all land-use/land-cover classes shown in explanation may 

be depicted on map; note also that, for this “Status and Trends of 

Land Change” study, transitional land-cover class was subdivided 

into mechanically disturbed and nonmechanically disturbed 

classes. Squares indicate locations of 10 x 10 km sample blocks 

analyzed in study. Index map shows locations of geographic 

features mentioned in text. Abbreviations for Western United States 

ecoregions are listed in appendix 2. See appendix 3 for definitions 

of land-use/land-cover classifications.

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

LA SAL

MTNS

ABAJO

MTNS

HENRY

MTNS

COLORADO

NV

WY

NEW MEXICO

UTAH

ARIZONA

Page

Moab

Grand Junction

Saint George

Cedar City BRYCE CANYON NP

ZION NP

Redlands

Fruita Rifle

G

Parachute reen

River

White River

S an Juan River

C o l o r a d o

R i v e r

Glen Canyon Dam

70

15

112° 110° 108°

114°

114°

40°

38°

Central

Basin and Range

Southern

Rockies

ANMP

Wasatch and Uinta

Mountains Wyoming

Basin

ANMM ANMM

MBR

CBR

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
220 Status and Trends of Land Change in the Western United States—1973 to 2000

ecoregion, whereas the remainder is covered by forest (25 

percent), agriculture (6 percent), barren (4 percent), developed 

(1 percent), water (0.5 percent), wetland (0.4 percent), and 

mining (0.1 percent). The land-cover makeup of the ecoregion 

is summarized in table 3, which shows the percent land cover 

by type in the year 2000 (see appendix 3 for definitions of 

land-cover classifications).

From the Paleozoic into the Mesozoic era (600 to 300 

million years ago), thick layers of limestone, sandstone, 

siltstone, and shale were deposited in shallow marine waters 

and then overlain by eolian deposits. Layers of sediment 

accumulated for millions of years on a thick crustal block that 

became the foundation of the Colorado Plateaus Ecoregion. As 

the plateau started to rise because of tectonic activity about 10 

million years ago, streams that would become the present-day 

Colorado and Green Rivers carved down through the colorful 

(reds, purples, and oranges, stained by iron and other minerals) sedimentary rocks (Booth and others, 1999). Erosional 

processes created the arroyos, canyons, mesas, buttes, monuments, towers, and cliffs that make up the dramatic landscape 

we see today (fig. 4). 

Because the Colorado Plateaus Ecoregion has been 

stable geologically (in other words, little rock deformation by 

faulting and folding) within the last 500 million years, conditions were ideal to create, preserve, and then reveal the unique 

rock formations and landforms (Wheeler, 1990). As a result of 

extensive conservation efforts, numerous U.S. National Parks, 

Forests, and Monuments have been established to protect, and 

preserve access to, these unique features. These extensive federal lands, coupled with Bureau of Land Management rangelands, account for nearly 55 percent of the ecoregion area. 

The remaining public land in the ecoregion is tribal land (24 

percent) or held by state and local governments (6 percent). 

Private lands account for an estimated 15 percent of the entire 

ecoregion (Booth and others, 1999).

Today (2012), with the easy access provided by Interstate 

Highways 15 and 70 and secondary roads through the ecoregion to numerous wilderness areas and National Parks and 

Monuments, the area has become a tourist mecca. National 

Park visits increased 94 percent between 1981 and 1994, and 

recreation and tourism has become one of the ecoregion’s largest industries (Hecox and Ack, 1996). Other major economic 

activities include ranching, farming, timber harvesting, and 

mining. From the late 1800s to the 1950s, gold, silver, and uranium mining were the major economic drivers in the region. 

Since the 1970s, increased demands have made coal, oil, and 

Figure 2. Shrubland plateau dissected by canyons in Colorado 

Plateaus Ecoregion.

Figure 3. Mix of junipers and pinyon pine in eastern part of 

Colorado Plateaus Ecoregion.

Figure 4. Mesas, towers, and monuments just east of Moab, Utah.

Figure 5. Coal power plant in eastern part of Colorado Plateaus 

Ecoregion near Grand Junction, Colorado.
Chapter 21—Colorado Plateaus Ecoregion 221

gas the primary targets of mining and energy exploration in 

the Colorado Plateaus Ecoregion (fig. 5). 

As the tourism and energy-exploration industries grew, 

the number of new jobs increased 225 percent between 1970 

and 2000, 140 percent faster than the national average (van 

Riper and Mattson, 2005). Approximately 95 percent of all 

new jobs were service based. Resource-based employment 

in farming and mining only made up 2 percent of this growth 

(8,728 jobs), whereas manufacturing provided the remaining 3 

percent (14,038 jobs) during this period (van Riper and Mattson, 2005). Service-based employment accounted for nearly 

90 percent of all jobs within the Colorado Plateaus Ecoregion 

by 2000. All these factors indicate a rapid conversion from 

resource-extractive to service-based industries in the ecoregion 

during the study period. 

Contemporary Land-Cover Change

(1973 to 2000)

An estimated 2.6 percent of the land cover in the Colorado Plateaus Ecoregion changed at least once between 1973 

and 2000 (table 1). Overall, the ecoregion experienced a low 

amount of land-cover conversion when compared to other 

western ecoregions (fig. 6). An estimated 0.6 percent of the 

ecoregion experienced change in more than one of the four 

time periods analyzed (table 2). Much of the land-cover 

change involved the expansion of developed land that accompanied employment increases and population growth. Change 

within the four individual time periods ranged from a low of 

0.6 percent between 1980 and 1986 to a high of 1.1 percent 

between 1973 and 1980 (table 2). When the estimates are normalized to an annual average, accounting for varying lengths 

of study periods, the period between 1973 and 1980 experienced the highest normalized annual rate of change, at 0.15 

percent (196 km2; fig. 7). The other three time periods were 

relatively stable, at approximately 0.1 percent change per year. 

Figure 6. Overall spatial change in Colorado Plateaus Ecoregion 

(CLRP; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Colorado 

Plateaus Ecoregion (three time periods) labeled for clarity. See 

table 2 for years covered by each time period. See appendix 2 for 

key to ecoregion abbreviations.

Figure 7. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions (gray 

bars). Estimates of change for Colorado 

Plateaus Ecoregion are represented by 

red bars in each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

Change in three time periods

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
222 Status and Trends of Land Change in the Western United States—1973 to 2000

The largest amounts of net change that occurred over the 

entire study period (1973–2000) were an estimated 430 percent 

(1,408 km2) increase in developed land and a 1.3 percent (1,121 

km2) decrease in grassland/shrubland (table 3). The largest net 

change in developed land occurred between 1973 and 1980 

(fig.8), almost all new developed land resulting from losses in 

either agriculture (756 km2) or grassland/shrubland (644 km2; 

table 4).

Although developed land only accounted for a small 

percentage of the ecoregion, nearly 43 percent of the land that 

changed became new developed land. Developed land is estimated to account for 0.3 percent (326 km2

) of the ecoregion in 

1973, increasing to just over 1.3 percent (1,735 km2) by 2000 

(table 3). New developed land primarily was found near the 

ecoregion’s urban centers of Saint George, Utah, and Grand 

Junction, Colorado, which had respective population estimates 

of 49,663 and 41,986 in 2000 (U.S. Census Bureau, 2000). 

Both of these cities have seen substantial population increases 

because of flourishing tourism and energy-mining industries. 

For example, Saint George’s population increased 600 percent, 

from 7,097 in 1970 to 49,728 in 2000, whereas Grand Junction’s increased 108 percent, from 20,170 in 1970 to 41,986 

in 2000 (U.S. Census Bureau, 2000). The Interstate 15 and 

70 corridors near these two cities also attracted new development, especially north from Saint George along Interstate 

15 to Cedar City, Utah, and west from Grand Junction along 

Interstate 70 to Fruita, Colorado (fig. 9).

The grassland/shrubland land-cover class had the largest net loss in the ecoregion, decreasing by approximately 

1,121 km2. New developed land accounted for most of this 

decline, but land-cover conversions between agriculture and 

grassland/shrubland between 1973 and 2000 also affected 

the net change of grassland/shrubland. Considerable areas of 

land fluctuated between these two classes in all time periods 

between 1973 and 2000 (table 4). The overall trend from 1973 

to 1992 indicated that more grassland/shrubland converted to 

agriculture than agriculture to grassland/shrubland. As a result, 

a net loss of grassland/shrubland to agriculture of approximately 327 km2

 occurred between 1973 and 1992. Irrigation 

needed to grow crops in the Colorado Plateaus Ecoregion’s 

arid and relatively warm climate expanded in the counties 

of southeastern Utah and southwestern Colorado, causing 

agricultural lands to increase at the expense of grassland/

shrubland. Irrigation water was drawn from the Dakota–Glen 

Canyon aquifer and the Colorado, White, San Juan, and Green 

Rivers to grow corn, wheat, barley, dry beans, hay, and alfalfa 

(U.S. Department of Agriculture, 2002). From 1992 to 2000, 

the exchange between grassland/shrubland and agricultural 

lands was balanced.

Even though agricultural lands increased at the expense 

of grassland/shrubland, the increase was not enough to offset 

agricultural lands lost to new developed land and mining 

between 1973 and 2000. As a result, agricultural lands in 

the Colorado Plateaus Ecoregion had a net decrease of 5.6 

percent. Agricultural lands were estimated to account for 6.2 

percent (8,004 km2) of the ecoregion in 1973, decreasing to 

5.8 percent (7,555 km2) by 2000 (table 3). The largest net 

loss in agricultural lands occurred between 1992 and 2000, at 

321 km2, most of which went to developed land and grassland/

shrubland (table 3). Increased municipal-water demands, as 

well as water scarcity in the arid Colorado Plateaus Ecoregion, 

may leave limited water available to farmers growing irrigated 

Figure 8. Normalized average net change in Colorado Plateaus 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

Figure 9. Development in Redlands, between Fruita and Grand 

Junction, Colorado. 

−1

−0.5

0

0.5

1

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 21—Colorado Plateaus Ecoregion 223

crops, further contributing to this decline. Additionally, 

because of cyclic changes in the extent of grassland/shrubland 

and agricultural lands, the gross land-cover change for agriculture and grassland/shrubland were the greatest among the 

other land-cover categories, totaling 1.2 percent (1,606 km2) 

and 1.7 percent (2,204 km2) of the ecoregion, respectively 

(table 3).

Periodic wildfires (classified as nonmechanically disturbed) affected nearly 1 percent (983 km2

) of the ecoregion’s 

land between from 1973 and 2000 (table 3). These fires created common land-cover conversions involving forest and 

grassland/shrubland categories, especially between 1980 and 

1986 and between 1986 and 1992. Between 1980 and 1986, 

conversion from forest to nonmechanically disturbed was the 

second greatest land change, whereas conversion from grassland/shrubland to nonmechanically disturbed was the top landcover change between 1986 and 1992 (table 4). As burned 

areas recovered, land-cover conversion from nonmechanically 

disturbed to grassland/shrubland was common. For example, 

between 1986 and 1992, approximately 253 km2 of grassland/

shrubland burned, becoming nonmechanically disturbed, and 

then, by 2000, returned to grassland/shrubland. Because of this 

sequence of events, the return of nonmechanically disturbed 

lands to grassland/shrubland was the fifth most common 

conversion between 1973 and 2000, at 434 km2 (table 4). As 

some burned areas have recovered by 2000, nonmechanically 

disturbed lands covered an estimated 115 km2 of the ecoregion 

in 2000 (table 3). 

Forest, the second most common land-cover class at 

approximately 25 percent of the Colorado Plateaus Ecoregion, 

generally was confined to the higher elevations of the ecoregion in the La Sal, Abajo, and Henry Mountains. Changes 

associated with forests were relatively small in the Colorado 

Plateaus Ecoregion. Forests had a small net decrease of 132 

km2 between 1973 and 2000 (table 3). Much of the forest loss 

is attributed to wildfires that occurred between 1980 and 1986, 

which caused an estimated loss of 178 km2 in forest land to 

nonmechanically disturbed. Forest areas did expand in some 

locations of the ecoregion between 1980 and 1986 but not 

enough to make up for losses caused by wildfires. Slight forest 

gains in the ecoregion may be a result of the forest-management practice of fire suppression, as well as the dissemination 

of juniper seeds by grazing cattle while they simultaneously 

remove the competing grasses that inhibit juniper expansion 

(Allen, 1998). Both factors caused grasses to decline, whereas 

dense woodlands of pinyon pine and juniper expanded. 

Other land-cover classes that changed very little are 

water, mining, and mechanically disturbed. Gross and net land 

change between 1973 and 2000 for each of these land categories affected no more than 0.1 percent (approximately 100 

km2

) of the ecoregion. Mining lands had a net increase of 91 

km2 between 1973 and 2000 (table 3).

In Grand Junction and in many locations of the western 

slope of Colorado, new development expanded at a brisk pace, 

especially between 1973 and the early 1980s as people came 

to work in the energy-exploration business. An economic 

boom occurred during this time as major oil companies began 

investing large sums of money in the oil-shale industry (Gulliford, 2003). Grand Junction had its largest population increase 

(approximately 39 percent) between 1970 and 1980 (U.S. Census Bureau, 2000). This increase likely contributed to the large 

expansion of developed land in Colorado Plateaus Ecoregion 

between 1973 and 1980 (table 2).

As oil and gas exploration increased in the eastern part 

of the Colorado Plateaus Ecoregion during the energy crisis 

of the mid-1970s, the amount of new mining land increased 

between 1973 and 1992 (71 km2

 to 175 km2, respectively; 

table 3). Mining of aggregate for the new Interstate 70 also 

accelerated mining land expansion in the 1970s. Nearly 78 

percent of all new mining land was converted from grassland/

shrubland. After 1982, however, the energy industry declined 

dramatically as the value of oil, coal, and uranium decreased, 

causing a “bust” economic condition in many small communities (notably, the towns of Rifle and Parachute, Colorado) that 

relied on the energy industry in the Colorado Plateaus Ecoregion (Gulliford, 2003). Mining land stabilized between 1986 

and 1992 before decreasing from 175 km2 in 1992 to 162 km2

in 2000 (table 3). 

Population gains continued in the Grand Junction area 

following the departure of major oil companies, causing a continuation of new developed lands. The economy in this part of 

the ecoregion became more diversified as a stable health care 

industry, tourism, agriculture (orchards and vineyards), livestock, and oil-and-gas extraction became major economic contributors. As oil and natural-gas prices increased in the 1990s, 

major energy companies once again invested large amounts 

of money into the area (van Riper and Mattson, 2005). In the 

1990s, many Americans, especially well-educated retirees, 

were attracted to the western slope area of Colorado near 

Grand Junction because of outdoor amenities such as access 

to public lands and high mountain meadows. New developed 

land expanded as numerous second homes were built for the 

retirees (Gulliford, 2003). 

The Saint George, Utah, area (known informally as 

“Utah’s Dixie”) also expanded for similar reasons. Outdoor 

recreational areas and nearby Zion and Bryce Canyon National 

Parks helped the tourism and recreation industry to grow there, 

attracting workers. The mild climate, access to high-quality 

health care, and natural amenities in the Saint George area 

attracted numerous retirees from other parts of the country. In 

addition, some large corporations such as SkyWest Airlines 

and Intermountain Health Care made their home in Saint 

George (Hecox and Ack, 1996). All these factors played an 

important role in expanding developed lands within the Colorado Plateaus Ecoregion.

Consequences of land change within the Colorado Plateaus 

Ecoregion became especially apparent between 1973 and 2000. 

Many agents of change are related to population growth in the 

ecoregion. As new development, tourism, mining, and heavy 

grazing increased, habitats that support wildlife and native 

plants have been greatly degraded. Approximately 85 percent 

of the ecoregion’s habitat has been altered by human activity 
224 Status and Trends of Land Change in the Western United States—1973 to 2000

(McGinley, 2007). Hardest-hit areas include riparian ecosystems 

and areas where mineral resources have been extracted. Habitat 

destruction caused by dam building (fig. 10) and other forms of 

development threaten native fish, including the humpback chub 

(Gila cypha), bluehead sucker (Catostomus discobolus), and the 

Colorado pikeminnow (Ptychocheilus lucius) (McGinley, 2007). 

Demand for water by growing municipalities also is having an 

effect on riparian areas as the water needs of wildlife, vegetation, and riparian systems become secondary (Booth and others, 

1999). Today (2012), land managers are charged with accommodating land uses that can be sustained without degrading the 

health of the land and water. As a result, timber harvesting, mining, and livestock grazing all have been reduced in the ecoregion (Booth and others, 1999). Land managers increasingly are 

relying on science to balance commodity extraction and public 

recreation use while, at the same time, protecting ecosystem 

health within the Colorado Plateaus Ecoregion.

Figure 10. Glen Canyon Dam in southwestern part of Colorado 

Plateaus Ecoregion, near Page, Arizona.

Table 2. Raw estimates of change in Colorado Plateaus Ecoregion land cover, computed for each of 

four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 1.1 1.2 −0.2 2.3 0.8 78.4 0.2

1980–1986 0.6 0.3 0.3 0.9 0.2 37.0 0.1

1986–1992 0.8 0.5 0.4 1.3 0.3 37.5 0.1

1992–2000 0.9 0.7 0.1 1.6 0.5 56.2 0.1

Estimate of change, in square kilometers

1973–1980 1,369 1,589 −219 2,958 1,074 78.4 196

1980–1986 738 404 334 1,142 273 37.0 123

1986–1992 1,053 584 469 1,637 395 37.5 175

1992–2000 1,135 943 191 2,078 638 56.2 142

Table 1. Percentage of Colorado Plateaus Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (97.4 percent), whereas 2.6 percent 

changed at least once throughout study period. Two dashes (--) indicate that, 

because zero pixels changed four times during study period, relative error is 

not calculable] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 2.0 1.7 0.2 3.7 1.2 59.2

2 0.6 0.4 0.2 1.1 0.3 47.6

3 0.0 0.0 0.0 0.0 0.0 82.3

4 0.0 0.0 0.0 0.0 0.0 --

Overall 

spatial 

change

2.6 2.1 0.6 4.7 1.4 53.2
Chapter 21—Colorado Plateaus Ecoregion 225

Table 3. Estimated area (and margin of error) of each land-cover class in Colorado Plateaus Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.4 0.3 0.3 0.3 0.0 0.0 0.1 0.1 4.3 2.5 24.9 6.8 63.5 7.5 6.2 3.7 0.4 0.2 0.0 0.0

1980 0.4 0.3 0.8 1.0 0.0 0.0 0.1 0.1 4.3 2.5 24.9 6.8 63.1 7.5 6.0 3.5 0.4 0.2 0.0 0.0

1986 0.4 0.3 0.9 1.1 0.0 0.0 0.1 0.1 4.3 2.5 24.8 6.7 62.8 7.6 6.1 3.6 0.4 0.2 0.1 0.2

1992 0.4 0.3 1.0 1.2 0.0 0.0 0.1 0.1 4.3 2.5 24.8 6.7 62.6 7.6 6.1 3.6 0.4 0.2 0.2 0.3

2000 0.5 0.3 1.3 1.7 0.0 0.0 0.1 0.1 4.3 2.5 24.8 6.7 62.6 7.7 5.8 3.5 0.4 0.2 0.1 0.1

Net

Change 0.0 0.0 1.1 1.4 0.0 0.0 0.1 0.1 0.0 0.0 −0.1 0.3 -0.9 0.6 −0.3 1.2 0.0 0.0 0.1 0.1

Gross

Change 0.1 0.1 1.1 1.4 0.1 0.1 0.1 0.1 0.0 0.0 0.3 0.2 1.7 0.8 1.2 1.1 0.0 0.0 0.8 0.8

Area, in square kilometers

1973 547 389 326 394 0 0 71 72 5,545 3,186 32,302 8,771 82,281 9,680 8,004 4,750 541 268 0 0

1980 547 387 1,011 1,360 2 3 135 127 5,542 3,186 32,306 8,767 81,815 9,754 7,718 4,524 541 271 0 0

1986 546 386 1,155 1,450 2 3 175 163 5,544 3,186 32,173 8,702 81,437 9,837 7,859 4,650 546 275 181 265

1992 561 390 1,319 1,612 43 40 175 188 5,544 3,186 32,194 8,698 81,097 9,888 7,876 4,696 555 281 253 370

2000 589 409 1,735 2,189 18 27 162 169 5,544 3,186 32,170 8,689 81,161 9,928 7,555 4,599 568 281 115 168

Net 

Change 42 54 1,408 1,795 18 27 91 97 −1 5 −132 328 −1,121 840 −449 1,513 27 23 115 168

Gross 

Change 69 71 1,408 1,795 112 82 168 148 9 8 332 318 2,204 1,091 1,606 1,456 42 22 983 999
226 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Colorado Plateaus Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Developed 343 478 323 0.3 25.0

Agriculture Developed 342 489 331 0.3 24.9

Grassland/Shrubland Agriculture 305 198 134 0.2 22.3

Agriculture Grassland/Shrubland 246 349 236 0.2 18.0

Grassland/Shrubland Mining 57 52 35 0.0 4.1

Other Other 77 n/a n/a 0.1 5.7

Totals 1,369 1.1 100.0

1980–1986 Grassland/Shrubland Agriculture 235 202 136 0.2 31.8

Forest Nonmechanically disturbed 178 0 0 0.1 24.1

Grassland/Shrubland Developed 92 82 56 0.1 12.4

Grassland/Shrubland Forest 50 69 47 0.0 6.7

Agriculture Developed 50 65 44 0.0 6.7

Other Other 138 n/a n/a 0.1 18.8

Totals 738 0.6 100.0

1986–1992 Grassland/Shrubland Nonmechanically disturbed 253 266 180 0.2 24.1

Nonmechanically disturbed Grassland/Shrubland 181 265 179 0.1 17.2

Grassland/Shrubland Agriculture 162 153 103 0.1 15.4

Grassland/Shrubland Developed 102 95 65 0.1 9.7

Agriculture Grassland/Shrubland 76 71 48 0.1 7.3

Other Other 278 n/a n/a 0.2 26.4

Totals 1,053 0.8 100.0

1992–2000 Agriculture Developed 305 445 301 0.2 26.9

Nonmechanically disturbed Grassland/Shrubland 253 370 250 0.2 22.3

Grassland/Shrubland Developed 108 130 88 0.1 9.5

Agriculture Grassland/Shrubland 98 103 70 0.1 8.6

Grassland/Shrubland Agriculture 90 83 56 0.1 8.0

Other Other 280 n/a n/a 0.2 24.7

Totals 1,135 0.9 100.0

1973–2000

(overall)

Grassland/Shrubland Agriculture 793 534 361 0.6 18.5

Agriculture Developed 756 1,085 733 0.6 17.6

Grassland/Shrubland Developed 644 711 481 0.5 15.0

Agriculture Grassland/Shrubland 466 533 360 0.4 10.9

Nonmechanically disturbed Grassland/Shrubland 434 448 303 0.3 10.1

Other Other 1,201 n/a n/a 0.9 28.0

Totals 4,295 3.3 100.0
Chapter 21—Colorado Plateaus Ecoregion 227

References Cited

Allen, C.D., 1998, Where have all the grasslands gone?: Quivera Coalition Newsletter, Spring/Summer.

Booth, B., Fischman, S., and Smith, S., 1999, The Colorado 

Plateau: High, Wide, and Windswept: Bureau of Land Management, accessed December 04, 2009, at http://www.blm.

gov/wo/st/en/res/Education_in_BLM/Learning_Landscapes/

For_Teachers/science_and_children/colplateau/index.html.

Gulliford, A., 2003, Boomtown Blues: Colorado Oil Shale, 

1885–1985 (2d ed.): Niwot, Colo., University Press of 

Colorado, p. 8–13, 229–240.

Hecox, W.E., and Ack, B.L., 1996, Charting the Colorado 

Plateau: An Economic and Demographic Exploration: Flagstaff, Ariz., Grand Canyon Trust.

McGinley, M., 2007, Colorado Plateau shrublands [Content 

Partner: World Wildlife Fund], in Cleveland, C.J., ed., 

Encyclopedia of Earth: Washington, D.C, Environmental 

Information Coalition, National Council for Science and the 

Environment, available at http://www.eoearth.org/article/

Colorado_Plateau_shrublands?topic=58071. 

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

U.S. Census Bureau, 2000, U.S. Census, 2000: U.S. Census 

Bureau database, accessed April 2, 2010, at http://www.

census.gov/prod/www/abs/decennial/index.htm.

U.S. Department of Agriculture, 2002, 1997 Census of Agriculture: U.S. Department of Agriculture database, accessed 

February 24, 2010, at http://www.agcensus.usda.gov/Publications/1997/County_Profiles/index.asp.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

van Riper, C., III, and Mattson, D.J., 2005, The Colorado Plateau II: Biophysical, Socioeconomic, and Cultural Research: 

Tucson, Ariz., University of Arizona Press, p. 13–23.

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., Wylie, 

B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data Set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 61, p. 650–662.

Wheeler, Ray, 1990, The Colorado Plateau Region, in Wilderness at the Edge: a citizen proposal to protect Utah’s canyons and deserts: Salt Lake City, Utah Wilderness Coalition, 

p. 97–104.
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Chapter 22

Columbia Plateau Ecoregion

Ecoregion (and to the west of it, the Cascades Ecoregion); to 

the south, the Blue Mountains Ecoregion; and to the east, the 

Northern Rockies Ecoregion (fig. 1) (Omernik, 1987; U.S. 

Environmental Protection Agency, 1997). The climate is Mediterranean, with cool wet winters and hot dry summers. 

The ecoregion was formed by Miocene (17 to 6 million 

year old) flood basalts covering approximately 200,000 km2 in 

what is currently central and eastern Washington, northern Oregon, and western Idaho (Hooper, 1982). Other notable processes 

By Benjamin M. Sleeter

Ecoregion Description

Located in eastern Washington and northern Oregon, the 

Columbia Plateau Ecoregion is characterized by sagebrush 

steppe and grasslands with extensive areas of dryland farming 

and irrigated agriculture. The ecoregion, which is approximately 90,059 km2

 (34,772 mi2), is surrounded on all sides 

by mountainous ecoregions: to the west, the North Cascades 

Ecoregion and the Eastern Cascades Slopes and Foothills 

Figure 1. Map of Columbia Plateau Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in 

appendix 2. See appendix 3 for definitions of land-use/land-cover classifications.

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Northern

Rockies

North

Cascades

Blue

Mountains

BLM

Cascades

Puget

Lowland

Eastern Cascades

Slopes and Foothills

PL

NBR

BLM

CANADA

118°

116°

122° 120°

48°

46°

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

Lake

Pend

Oreille 

Glacial Lake

Missoula 

Palouse

Grand Coulee Dam

Moro

Naches R. Spokane

Tieton

WASH INGTON

OREGON IDAHO

MONTANA

Colum b i a River

Yakima R.

Toppenish
230 Status and Trends of Land Change in the Western United States—1973 to 2000

that shaped the Columbia Plateau Ecoregion were the great Missoula floods caused by catastrophic failures of glacial dams that 

blocked Montana’s Glacial Lake Missoula 10 to 15 thousand 

years ago. Massive amounts of water rushing westward from 

the vicinity of the present-day east end of Lake Pend Oreille, 

Idaho, transformed a dendritic preglacial drainage pattern into 

the channeled scablands of today (Bretz, 1969; Smith, 2006). 

The great floods resulted in the loss of loess soils that covered 

much of the region. The only areas spared were those not in the 

path of flood waters or that had high enough elevations, such as 

the fertile Palouse region in eastern Washington. Today (2012) 

these areas support vast amounts of grain farming. 

Since European settlement in the mid-19th century, the 

region has been heavily used for agricultural production. 

Much of the Columbia Plateau Ecoregion is used for dryland 

winter wheat production (fig. 2), the typical pattern being 

winter-wheat, followed by summer-fallow, cultivation. Soil 

moisture is accumulated throughout the winter; most growth 

occurs in the spring, and the harvest takes place in the summer. The hot and dry summer climate is ideal for maturation of 

dryland grains and cereals, but without irrigation little else can 

flourish (Schillinger and Papendick, 2008).

The Columbia Basin Project, a large engineered irrigation network serving eastern Washington, began in the 

1930s with the construction of Grand Coulee Dam, originally 

designed to provide irrigation to the region’s farmers. World 

War II caused the project to shift its focus to providing hydroelectric power; the irrigation component was not functional 

again until the 1950s. In 2009 alone, water from the Columbia Basin Project irrigated approximately 670,000 acres of 

crops valued at over $600 million annually (U.S. Bureau of 

Reclamation, 2009) (fig. 3).

Development in the Columbia Plateau Ecoregion generally 

is rural with only a few major urban areas. Population growth 

was slow in the 1980s, increasing only 4.9 percent. In the 1990s 

the ecoregion population increased by 20 percent to just under 

one million people (U.S. Census Bureau, 2000) (table 1). 

Contemporary Land-Cover Change 

(1973 to 2000)

An estimated 9.2 percent of the Columbia Plateau 

Ecoregion land cover changed at least once between 1973 and 

2000 (table 2). Compared to other ecoregions, change in the 

Figure 2. Wheat fields near Moro, Oregon (A) and outside of 

Spokane, Washington (B).

Figure 3. Hops planted in Yakima Valley, Washington (A) and 

corn field near Toppenish, Washington (B).

A

B

A

B
Chapter 22—Columbia Plateau Ecoregion 231

Columbia Plateau Ecoregion is considered modest (fig. 4). Of 

the total area, 2.3 percent changed in more than one of the four 

time periods analyzed (table 3), mostly a result of farmland 

cycling in and out of production. Changes to ecoregion land 

cover were not spread evenly throughout the entire 27-year 

study period. As is the case in many other agricultural regions, 

the period between 1986 and 1992 experienced the greatest 

amount of change, owing, in large part, to the conversion of 

marginal agricultural lands to grassland/shrubland (see appendix 3 for definitions of land-cover classes). The average annual 

rate of change during this period was 0.7 percent, whereas the 

other three periods experienced rates roughly one-half that 

amount (table 3; fig. 5).

Agricultural lands made up approximately 48.8 percent 

of the ecoregion in 1973 (table 4). By 1986 the agriculture 

land-cover class had increased an estimated 1,475 km2 to 

make up 50.4 percent of the ecoregion. Between 1986 and 

1992, agricultural lands declined by an estimated 1,531 km2

(fig. 6), decreasing to approximately 48.7 percent of total 

ecoregion land cover. By 2000, agriculture had once again 

increased to account for 49.4 percent of the ecoregion (table 

4). The Conservation Reserve Program (CRP), a federal policy 

to encourage landowners to convert marginal farmlands to 

native vegetation, played an important role in the Columbia Plateau Ecoregion. After the onset of the program, the 

ecoregion reversed the prior trend of increasing agricultural 

land use, and by 1997 enrollment in the CRP program totaled 

3,311 km2 (U.S. Department of Agriculture, 1999). Expiration 

of 10-year CRP contracts in the late 1990s contributed to 0.6 

percent of the ecoregion converting back into agricultural land 

use by 2000. During the study period, dryland wheat farming 

experienced a sharp decline, whereas other areas of agriculture 

intensified with the addition of new irrigated lands. Historical 

levels of dryland wheat, irrigated cropland, and CRP enrollments are summarized in figure 7. 

Trends in grassland/shrubland mirrored those of the 

agriculture class. Grassland/shrubland made up 41.0 percent 

of the ecoregion in 1973 and 39.9 percent in 2000, a net 

Figure 4. Overall spatial change in Columbia Plateau Ecoregion 

(CLMP; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Columbia 

Plateau Ecoregion (four time periods) labeled for clarity. See table 

3 for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions (gray 

bars). Estimates of change for Columbia 

Plateau Ecoregion are represented by 

red bars in each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
232 Status and Trends of Land Change in the Western United States—1973 to 2000

loss of 973 km2. Developed land accounted for a very small 

proportion of the ecoregion (about 1.0 percent), an estimated 

net increase of approximately 284 km2 over the 27-year 

period. All other land-cover classes remained relatively 

stable (table 4).

As expected, the most common land-cover conversions were between the agriculture and grassland/shrubland 

classes. In all four time periods, these were the two most 

common land-cover conversions. In three of the four periods, 

increases in conversions from agriculture to grassland/shrubland outpaced losses. The exception was between 1986 and 

1992, when 2,342 km2 changed from agriculture to grassland/shrubland, and only 886 km2

 converted from grassland/

shrubland to agriculture. Other conversions of note were 

grassland/shrubland to nonmechanically disturbed (by fire) 

and agriculture to developed (table 5).

Irrigation technology, infrastructure development, federal conservation efforts, and population growth all acted as 

drivers of change on Columbia Plateau Ecoregion land cover. 

In the 1960s and 1970s, the spread of center-pivot irrigation technology enhanced the ability to bring marginal lands 

into agricultural production. The spread of irrigation was 

facilitated by the expansion and utilization of water-delivery 

infrastructure from the Columbia Basin Project, designed to 

irrigate more than 1 million acres of marginal lands. Estimates indicate that this period resulted in the greatest rate of 

change from sagebrush steppe (grassland/shrubland class) 

to new agriculture, adding an average of 290 km2 per year 

between 1973 and 1980. 

Whereas new lands were being added to the Columbia 

Plateau Ecoregion’s agriculture mosaic in each time period, 

in only one period, 1986 to 1992, were these additions outpaced by the reversion back to natural vegetative conditions, 

largely as a result of the CRP (fig. 8). In the western United 

States, CRP had its most substantial effect in the Columbia 

Plateau Ecoregion. Estimates reveal that this period (1986–

1992) experienced the only net decline in agriculture land 

cover during the 27-year land-cover study.

Figure 6. Normalized average net change in Columbia Plateau 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

Figure 7. Historical trends in acreage for irrigated agriculture, 

dryland wheat, and Conservation Reserve Program enrollments 

(CRP). Total annual values were summed for all counties that 

have their centroid within Columbia Plateau Ecoregion. Data from 

United States Department of Agriculture’s agriculture census (U.S. 

Department of Agriculture, 1999).

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

1950 1955 1960 1965 1970 1975

Year

1980 1985 1990 1995 2000

1.0

0

2.0

3.0

4.0 Wheat

EXPLANATION

Irrigated

CRP

Farmland, in millions of acres

Figure 8. Agricultural land converted to grassland/shrubland 

under Conservation Reserve Program.
Chapter 22—Columbia Plateau Ecoregion 233

Regional population growth also has had an effect on 

regional land-cover change. Although developed land-cover 

areas accounted for approximately 1 percent of the total 

ecoregion area, a measured increase in developed lands of 

approximately 32 percent occurred between 1973 and 2000. 

Demand for new housing and infrastructure to support an 

additional 200,000 people resulted in the conversion of a 

relatively small amount of agricultural land and, to a lesser 

extent, grassland/shrubland to new developed uses (fig. 9).

Figure 9. New home construction and orchard near Naches 

River and town of Tieton, Washington.

Table 1. Columbia Plateau Ecoregion population estimates by 

state for 1980, 1990, and 2000 censuses (U.S. Census Bureau, 

2000). Population estimates are calculated using census tracts 

that have their centroid within ecoregion. Total population 

estimates are sums of all three states for each year. 

[--, no significant change]

Census year State Population

Percent change 

from previous 

decade

1980 Total 777,166

Oregon 90,051

Washington 618,055

Idaho 69,060

1990 Total 814,979 +4.9

Oregon 90,861 --

Washington 654,062 +5.8

Idaho 70,056 +1.4

2000 Total 978,069 +20.0

Oregon 107,212 +18.0

Washington 792,260 +21.1

Idaho 78,597 +12.2

Table 2. Percentage of Columbia Plateau Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

 [Most sample pixels remained unchanged (90.8 percent), whereas 9.2 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 7.0 2.3 4.8 9.3 1.6 22.2

2 1.7 0.6 1.2 2.3 0.4 22.2

3 0.4 0.2 0.2 0.5 0.1 32.0

4 0.0 0.1 0.0 0.1 0.0 84.6

Overall 

spatial 

change

9.2 2.7 6.3 11.9 1.8 20.4

Table 3. Raw estimates of change in Columbia Plateau Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 2.9 1.4 1.5 4.3 1.0 32.8 0.4

1980–1986 2.3 0.6 1.7 3.0 0.4 18.9 0.4

1986–1992 4.1 1.4 2.7 5.5 0.9 23.0 0.7

1992–2000 2.4 0.7 1.7 3.2 0.5 21.0 0.3

Estimate of change, in square kilometers

1973–1980 2,641 1,275 1,366 3,915 866 32.8 377

1980–1986 2,080 579 1,501 2,659 393 18.9 347

1986–1992 3,702 1,251 2,451 4,954 850 23.0 617

1992–2000 2,174 671 1,504 2,845 456 21.0 272
234 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Estimated area (and margin of error) of each land-cover class in Columbia Plateau Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed

Mechanically disturbed

Mining Barren Forest Grassland/

Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.8 0.4 1.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 7.6 3.1 41.0 6.4 48.8 7.4 0.9 0.3 0.0 0.0

1980 0.8 0.4 1.1 0.7 0.0 0.1 0.0 0.0 0.0 0.0 7.6 3.0 39.2 6.1 50.4 7.3 0.9 0.3 0.0 0.0

1986 0.8 0.4 1.1 0.7 0.0 0.0 0.0 0.1 0.0 0.0 7.7 3.1 38.9 5.9 50.4 7.1 0.9 0.3 0.1 0.2

1992 0.8 0.4 1.2 0.8 0.0 0.0 0.0 0.0 0.0 0.0 7.6 3.0 40.5 6.1 48.7 7.2 0.9 0.3 0.1 0.2

2000 0.8 0.4 1.3 0.8 0.0 0.0 0.0 0.0 0.0 0.0 7.6 3.0 39.9 6.1 49.4 7.2 0.9 0.3 0.0 0.0

Net

change 0.1 0.1 0.3 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 −1.1 2.5 0.6 2.5 0.1 0.1 0.0 0.0

Gross

change 0.1 0.1 0.3 0.2 0.1 0.1 0.1 0.1 0.0 0.0 0.4 0.4 7.6 2.4 7.3 2.4 0.1 0.1 0.5 0.5

Area, in square kilometers

1973 680 360 878 580 0 0 7 8 1 1 6,836 2,754 36,943 5,742 43,946 6,674 768 291 0 0

1980 730 390 967 612 41 59 18 18 0 1 6,817 2,728 35,331 5,455 45,387 6,532 768 288 0 0

1986 738 394 1,025 647 0 0 40 46 1 2 6,894 2,779 35,068 5,350 45,421 6,435 775 288 96 139

1992 718 387 1,095 682 8 9 36 43 1 1 6,847 2,679 36,495 5,464 43,889 6,447 840 291 131 189

2000 740 388 1,162 734 5 5 29 28 4 5 6,843 2,678 35,970 5,486 44,480 6,525 826 289 0 0

Net

change 61 71 284 172 5 5 21 25 3 4 7 224 -973 2,270 534 2,223 58 63 0 0

Gross

change 113 83 284 172 94 118 57 61 5 7 381 325 6,881 2,166 6,561 2,144 111 74 455 463
Chapter 22—Columbia Plateau Ecoregion 235

Table 5. Principal land-cover conversions in Columbia Plateau Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 1,960 1,139 774 2.2 74.2

Agriculture Grassland/Shrubland 440 301 204 0.5 16.7

Agriculture Developed 61 50 34 0.1 2.3

Grassland/Shrubland Water 51 73 50 0.1 1.9

Forest Mechanically disturbed 41 59 40 0.0 1.5

Other Other 88 n/a n/a 0.1 3.3

Totals 2,641 2.9 100.0

1980–1986 Grassland/Shrubland Agriculture 944 363 246 1.0 45.4

Agriculture Grassland/Shrubland 822 419 285 0.9 39.5

Grassland/Shrubland Nonmechanically disturbed 94 135 92 0.1 4.5

Agriculture Developed 47 37 25 0.1 2.3

Agriculture Forest 42 60 41 0.0 2.0

Other Other 132 n/a n/a 0.1 6.3

Totals 2,080 2.3 100.0

1986–1992 Agriculture Grassland/Shrubland 2,342 1,155 785 2.6 63.3

Grassland/Shrubland Agriculture 880 470 319 1.0 23.8

Forest Nonmechanically disturbed 131 189 129 0.1 3.5

Nonmechanically disturbed Grassland/Shrubland 96 138 94 0.1 2.6

Grassland/Shrubland Forest 89 76 52 0.1 2.4

Other Other 165 n/a n/a 0.2 4.5

Totals 3,702 4.1 100.0

1992–2000 Grassland/Shrubland Agriculture 1,276 527 358 1.4 58.7

Agriculture Grassland/Shrubland 634 313 212 0.7 29.1

Nonmechanically disturbed Grassland/Shrubland 131 188 128 0.1 6.0

Agriculture Developed 49 44 30 0.1 2.3

Wetland Water 19 20 14 0.0 0.9

Other Other 66 n/a n/a 0.1 3.0

Totals 2,174 2.4 100.0

1973–2000

(overall)

Grassland/Shrubland Agriculture 5,060 2,075 1,410 5.6 47.7

Agriculture Grassland/Shrubland 4,238 1,621 1,101 4.7 40.0

Nonmechanically disturbed Grassland/Shrubland 226 230 156 0.3 2.1

Agriculture Developed 211 149 102 0.2 2.0

Forest Nonmechanically disturbed 134 189 129 0.1 1.3

Other Other 729 n/a n/a 0.8 6.9

Totals 10,597 11.8 100.0
236 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Bretz, J.H., 1969, The Lake Missoula floods and the channeled 

scabland: Journal of Geology, v. 77, p. 505–543. 

Hooper, P.R., 1982, The Columbia River basalts: Science, v. 

215, no. 4539, p. 1,463–1,468.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Schillinger, W.F., and Papendick, R.I., 2008, Then and now—

125 years of dryland wheat farming in the inland Pacific 

Northwest: Agronomy Journal, v. 100, p. 166–182.

Smith, L.N., 2006, Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, 

Montana, USA: Quaternary Research, v. 66, p. 311–322.

U.S. Bureau of Reclamation, 2009, The story of the Columbia 

Basin Project – Washington: U.S. Bureau of Reclamation 

database, accessed July 16, 2009, at http://www.usbr.gov/

pn/project/columbia_index.html#.

U.S. Census Bureau, 2000, U.S. Census, 2000: U.S. Census 

Bureau database, accessed July 16, 2009, at http://www.

census.gov/prod/www/abs/decennial/index.htm.

U.S. Department of Agriculture, 1999, 1997 Census of agriculture—agricultural atlas of the United States v. 2, subject 

series, part 1: Washington, D.C., U.S. Government Printing 

Office, 163 p.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662. 
Chapter 23

Northern Basin and Range Ecoregion

the Sierra Nevada Ecoregions, on the north by the Blue Mountains and the Snake River Basin Ecoregions, and on the south 

by the Central Basin and Range Ecoregion (fig. 1). Much like 

the other Basin and Range ecoregions in the western United 

States (for example, Central Basin and Range, Mojave Basin and 

Range, and Sonoran Basin and Range Ecoregions), the Northern 

Basin and Range Ecoregion is characterized by basin-and-range 

topography. The ecoregion contains several wide basins bordered 

by scattered low mountains. Big sagebrush (Artemisia tridentata), the predominant vegetation, is intermixed with grasslands. 

Despite regional aridity, natural springs and spring-fed wetlands 

By Christopher E. Soulard

Ecoregion Description

The Northern Basin and Range Ecoregion (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997) is located in 

eastern Oregon (58.7 percent), northern Nevada (20.6 percent), 

southwestern Idaho (14.8 percent), and northeastern California 

(5.9 percent), encompassing the northern extent of the hydrographic Great Basin (Grayson, 1993). The ecoregion, which covers approximately 110,039 km2 (42,486 mi2

) of land, is bordered 

on the west by the Eastern Cascades Slopes and Foothills and 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Northern Basin and Range Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be 

depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into 

mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in 

study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are 

listed in appendix 2. See appendix 3 for definitions of land-use/land-cover classifications.

Blue Mountains

BLM

Central

Basin and Range

Northern

Rockies

Snake River

Basin

C

CLMP

CLMP

Eastern Cascades

Slopes and

Foothills

SN

116°

114°

122° 120° 118°

44°

42°

40°

C

0 50 100 150 MILES

0 50 100 150 KILOMETERS Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

Boise

OREGON

IDAHO

N E VA D A

CA

GREAT BASIN

Bend
238 Status and Trends of Land Change in the Western United States—1973 to 2000

are scattered around the landscape, sustaining much of the 

region’s wildlife (Oregon Department of State Lands, 2000).

Because most of the Northern Basin and Range Ecoregion is arid and soil development generally is poor, viable 

economic land uses are limited. Livestock (cattle and sheep) 

grazing, the predominant land use, occurs mostly in the 

grassland/shrubland landscapes (fig. 2). Some agriculture 

(mostly hay farming) occurs where reservoirs have been 

constructed along regional waterways. Mining and recreation also account for small fragments of local economy. 

Ultimately, the scarcity of economic activity explains the 

absence of any large municipalities and the general lack of 

developed land across the ecoregion’s landscape.

Land-cover change in the ecoregion is caused primarily by livestock grazing. Grazing activity has effectively 

modified the contemporary fire regime, contributing to the 

loss of native-plant communities in the region (Miller and 

others, 2001) (fig. 3). Historical land-management practices 

of unregulated grazing and fire suppression have led to 

increased fuel loads and nonnative-species invasion of 

rangelands (Oregon Department of State Lands, 2000). The 

most notable of these invasive species is cheatgrass (Bromus 

tectorum), which was introduced by settlers intending to feed 

domestic livestock by seeding areas devoid of native vegetation (Pellant and others, 2004). Cheatgrass and other introduced annuals not only outcompete native plants but also 

alter the fire regime by providing a denser, more continuous 

fuel source, which can extend the fire season (Pyke, 2002). 

Increased fire frequency eliminates native sagebrush in the 

short term, as the highly prolific seed-production capability 

of cheatgrass allows it to reestablish before sagebrush can 

take hold (Keeley, 2006; Pellant and others, 2004). Cheatgrass has ultimately created a positive-feedback mechanism 

for its own colonization, quickly expanding its range owing 

to frequent fires and its early reestablishment success in 

burned landscapes formerly occupied by sagebrush.

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, the footprint (overall areal 

extent) of land-use/land-cover change in the Northern Basin 

and Range Ecoregion was 5.8 percent, or 6,430 km2. This 

can be interpreted as the amount of land that experienced 

change during at least one of the four time periods that make 

up the entire 27-year study period. This footprint of change 

translates to an estimated 3,631 km2 of land that changed 

during one time period, 2,421 km2 that changed during 

two time periods, 110 km2 that changed during three time 

periods, and 220 km2 that changed throughout all four time 

periods (table 1; fig. 4). 

The average annual rate of change between 1973 and 

2000 was 0.3 percent per year. This measurement, which normalizes the results for the 27-year study period to an annual 

scale, means that the region averaged 363 km2 of change 

each year between 1973 and 2000 (table 2); however, this 

annual change varied between each of the four time periods. 

Between 1973 and 1980, the annual rate of change was 0.1 

percent per year; this rate increased to 0.3 percent annually 

between 1980 and 1986 and 0.6 percent annually between 

1986 and 1992. The normalized annual rate dropped back to 

0.3 percent between 1992 and 2000 (table 2). Compared to 

the other ecoregions in the western United States, land-cover 

change in the Northern Basin and Range Ecoregion was 

relatively low (fig. 5).

In 2000, five of the eleven land-use/land-cover classes 

made up the majority of the Northern Basin and Range 

Ecoregion: grassland/shrubland (89.3 percent), forest (3.7 

percent), nonmechanically disturbed (2.5 percent), agriculture 

(2.3 percent), and wetland (1.1 percent). Five other classes 

cumulatively made up the remaining 1 percent of the Northern Basin and Range Ecoregion landscape in 2000 (table 3). 

Figure 3. Shrubland being used as open rangeland for cattle in 

Northern Basin and Range Ecoregion. Charred shrubs illustrate 

nonmechanical disturbance of land cover by fire. Land-use/landcover classes shown are grassland/shrubland and nonmechanically disturbed. 

Figure 2. Area undergoing livestock grazing and hay farming 

in Northern Basin and Range Ecoregion. Land-use/land-cover 

classes shown are grassland/shrubland and agriculture.
Chapter 23—Northern Basin and Range Ecoregion 239

Between 1973 and 2000, the land-cover classes that experienced a measurable net change in relation to total ecoregion 

area include grassland/shrubland (2.6 percent decrease) and 

nonmechanically disturbed (which occupied 194 km2 in 1973 

and 2,713km2 in 2000, owing to fires) (fig. 6).

The “from class–to class” information afforded by a 

postclassification comparison was used to identify land-cover 

class conversions and to rank these conversions from highest to lowest (table 4). Although fieldwork confirmed the 

presence of many of the conversions listed in table 4, the 

ability to report these changes on the basis of interpretations 

was accomplished with varying degrees of uncertainty (as 

illustrated by the statistical error values in the table). In general, higher uncertainty arose where sampled changes were 

clustered spatially within the ecoregion rather than distributed 

evenly across the ecoregion. 

Four of the top ten most prominent conversions are connected to nonmechanical disturbance of land cover by fire 

(fig. 7). Cumulatively, nonmechanical disturbance of grassland/shrubland resulted in the loss of an estimated 5,016 km2; 

however, much of this land experienced ecological succession, 

or regrowth, and by the end of the study period, 2,530 km2 had 

converted back to grassland/shrubland (fig. 7; table 4). Areas 

that experienced fires in consecutive periods accounted for an 

additional 1,491 km2 (table 4). The conversions to and from 

the water class also were common in the Northern Basin and 

Range Ecoregion (1,016 km2 of gross change). Less common 

were the conversions from grassland/shrubland to agriculture 

and to mining. Figure 4. Overall spatial change in Northern Basin and Range 

Ecoregion (NBR; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

time periods 1, 2, 3, or 4; highest level of spatial change in 

Northern Basin and Range Ecoregion (four time periods) labeled 

for clarity. See table 2 for years covered by each time period. See 

appendix 2 for key to ecoregion abbreviations.

Figure 5. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Northern Basin and Range Ecoregion 

are represented by red bars in each 

time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
240 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 6. Normalized average net change in Northern Basin and 

Range Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

Figure 7. Area experiencing active nonmechanical disturbance 

of land cover by fire in Northern Basin and Range Ecoregion. 

Land-use/land-cover classes shown are grassland/shrubland, 

forest, and nonmechanically disturbed.

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

Table 1. Percentage of Northern Basin and Range Ecoregion 

land cover that changed at least one time during study period 

(1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (94.2 percent), whereas 5.8 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 3.3 3.2 0.0 6.5 2.2 67.0

2 2.2 2.1 0.1 4.4 1.5 65.3

3 0.1 0.1 0.0 0.3 0.1 52.7

4 0.2 0.3 −0.1 0.5 0.2 97.7

Overall 

spatial 

change

5.8 3.9 2.0 9.7 2.6 44.7
Chapter 23—Northern Basin and Range Ecoregion 241

Table 2. Raw estimates of change in Northern Basin and Range Ecoregion land cover, computed for 

each of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.8 0.5 0.3 1.2 0.3 42.8 0.1

1980–1986 1.6 1.0 0.6 2.6 0.7 43.3 0.3

1986–1992 3.9 2.7 1.2 6.5 1.8 47.2 0.6

1992–2000 2.8 2.1 0.7 4.8 1.4 50.2 0.3

Estimate of change, in square kilometers

1973–1980 828 523 305 1,351 354 42.8 118

1980–1986 1,727 1,104 624 2,831 748 43.3 288

1986–1992 4,249 2,957 1,292 7,207 2,004 47.2 708

1992–2000 3,055 2,263 792 5,319 1,533 50.2 382

Table 3. Estimated area (and margin of error) of each land-cover class in Northern Basin and Range Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.5 0.4 0.1 0.0 0.1 0.1 0.1 0.1 0.4 0.2 3.8 2.5 91.9 2.6 2.0 0.9 1.0 0.5 0.2 0.3

1980 0.3 0.2 0.1 0.0 0.2 0.3 0.1 0.1 0.4 0.2 3.8 2.5 91.9 2.7 2.2 1.0 1.0 0.5 0.0 0.0

1986 0.6 0.4 0.1 0.0 0.0 0.0 0.1 0.1 0.4 0.2 3.8 2.5 90.7 2.7 2.3 1.0 1.0 0.5 1.1 1.0

1992 0.3 0.2 0.1 0.0 0.3 0.3 0.2 0.1 0.4 0.2 3.8 2.5 89.4 3.2 2.2 1.0 1.0 0.5 2.3 2.4

2000 0.3 0.2 0.1 0.1 0.0 0.0 0.2 0.1 0.4 0.2 3.7 2.5 89.3 3.9 2.3 1.1 1.1 0.5 2.5 3.2

Net

change −0.2 0.3 0.0 0.0 0.0 0.1 0.1 0.1 0.0 0.0 0.0 0.1 −2.6 3.3 0.3 0.3 0.1 0.2 2.3 3.3

Gross

change 0.9 0.9 0.0 0.0 1.2 1.2 0.1 0.1 0.0 0.0 0.0 0.1 6.7 4.5 0.4 0.3 0.3 0.4 6.1 4.6

Area, in square kilometers

1973 551 401 62 49 59 84 73 57 463 183 4,156 2,792 101,150 2,908 2,177 964 1,152 526 194 282

1980 374 223 64 50 267 342 79 58 461 182 4,158 2,792 101,139 2,947 2,401 1,070 1,091 524 5 8

1986 619 386 68 53 1 1 97 65 458 182 4,157 2,791 99,752 2,974 2,492 1,132 1,145 523 1,250 1,060

1992 307 215 69 53 372 337 188 118 449 181 4,157 2,790 98,361 3,527 2,474 1,127 1,078 523 2,584 2,616

2000 378 229 80 65 30 25 219 133 451 181 4,111 2,783 98,309 4,301 2,538 1,178 1,210 548 2,713 3,571

Net

change −173 356 18 16 −29 89 146 116 −12 10 −45 60 −2,841 3,589 361 348 58 179 2,519 3,582

Gross

change 1,016 997 18 16 1,305 1,340 152 116 28 21 48 60 7,387 4,965 444 342 381 404 6,670 5,066
242 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Northern Basin and Range Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Water Mechanically disturbed 256 341 231 0.2 30.9

Grassland/Shrubland Agriculture 226 183 124 0.2 27.2

Nonmechanically disturbed Grassland/Shrubland 193 280 190 0.2 23.3

Mechanically disturbed Water 59 84 57 0.1 7.2

Wetland Grassland/Shrubland 44 50 34 0.0 5.3

Other Other 51 n/a n/a 0.0 6.1

Totals 828 0.8 100.0

1980–1986 Grassland/Shrubland Nonmechanically disturbed 1,250 1,060 718 1.1 72.4

Mechanically disturbed Water 237 315 213 0.2 13.7

Grassland/Shrubland Agriculture 95 96 65 0.1 5.5

Grassland/Shrubland Wetland 34 40 27 0.0 2.0

Grassland/Shrubland Mining 21 28 19 0.0 1.2

Other Other 90 n/a n/a 0.1 5.2

Totals 1,727 1.6 100.0

1986–1992 Grassland/Shrubland Nonmechanically disturbed 2,482 2,528 1,713 2.3 58.4

Nonmechanically disturbed Grassland/Shrubland 1,139 961 651 1.0 26.8

Water Mechanically disturbed 313 330 224 0.3 7.4

Wetland Grassland/Shrubland 70 68 46 0.1 1.6

Grassland/Shrubland Mechanically disturbed 49 72 49 0.0 1.2

Other Other 195 n/a n/a 0.2 4.6

Totals 4,249 3.9 100.0

1992–2000 Grassland/Shrubland Nonmechanically disturbed 1,279 1,558 1,055 1.2 41.9

Nonmechanically disturbed Grassland/Shrubland 1,193 1,669 1,131 1.1 39.0

Mechanically disturbed Wetland 152 220 149 0.1 5.0

Mechanically disturbed Grassland/Shrubland 144 127 86 0.1 4.7

Grassland/Shrubland Agriculture 73 104 70 0.1 2.4

Other Other 215 n/a n/a 0.2 7.0

Totals 3,055 2.8 100.0

1973–2000

(overall)

Grassland/Shrubland Nonmechanically disturbed 5,016 4,243 2,875 4.6 50.9

Nonmechanically disturbed Grassland/Shrubland 2,530 2,450 1,660 2.3 25.7

Water Mechanically disturbed 569 662 449 0.5 5.8

Grassland/Shrubland Agriculture 407 345 234 0.4 4.1

Mechanically disturbed Water 354 345 234 0.3 3.6

Other Other 983 n/a n/a 0.9 10.0

Totals 9,860 9.0 100.0
Chapter 23—Northern Basin and Range Ecoregion 243

References Cited

Grayson, D.K., 1993, The desert’s past; a natural prehistory of 

the Great Basin: Washington, D.C., Smithsonian Institution 

Press, 356 p.

Keeley, J.E., 2006, Fire management impacts on invasive 

plants species in the Western United States: Conservation 

Biology, v. 20, p. 375–384.

Miller, R., Baisan, C., Rose, J., and Pacioretty, D., 2001, Preand post-settlement fire regimes in mountain big sagebrush 

steppe and aspen: the northwestern Great Basin: Corvallis, 

Oregon, National Interagency Fire Center, 28 p. (Available 

at http://fresc.usgs.gov/products/papers/fr-nifc.pdf.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, p. 118–125.

Oregon Department of State Lands, 2000, Northern Basin and 

Range Ecoregion, Chapter 4.8, in Oregon State of the Environment Report: Oregon Department of State Lands, 

p. 201–205, accessed January 3, 2008, at http://egov.oregon.

gov/DAS/OPB/docs/SOER2000/Ch4_8.pdf. 

Pellant, M., Abbey, B., and Karl, S., 2004, Restoring the Great 

Basin Desert, U.S.A.; integrating science, management, and 

people: Environmental Modeling and Assessment, v. 99, 

p. 169–179.

Pyke, D.A., 2002, Born of fire—restoring sagebrush steppe: 

U.S. Geological Survey Fact Sheet FS–126–02, 2 p. (Available at http://pubs.er.usgs.gov/publication/fs12602.)

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
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Chapter 24

Snake River Basin Ecoregion

precipitation occurs in the high elevations of the dissected plateaus and Teton Basin along the eastern edge of the ecoregion. 

Mean January temperatures range from –14 to 4°C, with mean 

July temperatures ranging from 8 to 32°C.

 Land cover in the Snake River Basin Ecoregion is dominated by grassland/shrubland, which covered approximately 

two-thirds of the landscape in 2000 (fig. 2). The sagebrushsteppe ecosystems of the Snake River Plain consist of a mosaic 

of sagebrush and perennial grass species, including Wyoming 

big sagebrush (Artemisia tridentata), bluebunch wheatgrass 

(Pseudoroegneria spicata), basin wildrye (Leymus cinereus), 

rabbitbrush (Chrysothamnus viscidiflorus), Thurber needlegrass (Achnatherum thurberianum), Idaho fescue (Festuca 

By Benjamin M. Sleeter

Ecoregion Description

Located in south-central Idaho, the Snake River Basin 

Ecoregion spans 66,063 km2 (25,507 mi2) of mostly sagebrushsteppe (Artemisia tridentata) with some areas of saltbushgreasewood (Atriplex spp. and Sarcobatus spp.) and barren lava 

fields (fig. 1) (Omernik, 1987; U.S. Environmental Protection 

Agency, 1997). The Snake River is the dominant hydrographic 

feature extending the full length (east to west) of the ecoregion. 

Elevation ranges from approximately 640 m in the “Treasure 

Valley” (Canyon County, near Nampa, Idaho) to 2,000 m in the 

semiarid foothills and eastern Snake River Plain. Mean annual 

precipitation ranges from 15 to 50 cm annually, and highest 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Snake River Basin Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map 

shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. 

See appendix 3 for definitions of land-use/land-cover classifications. 

116° 114° 112°

44°

42°

42°

Northern

Rockies

Northern Basin

and Range

Blue

Mountains

Central

Basin and Range CBR

Middle

Rockies

Montana Valley

and Foothill

Prairies

WB

WUM

NRK

MRK

NRK NRK

NRK

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

Twin Falls

Nampa Boise

Pocatello TETON RA.

Hells Cyn 

Idaho

Falls

OREGON

IDAHO

NEVADA UTAH

MONTANA

WYOMING

S n a k e

Ri v e r

CRATERS

OF THE

MOON NM

YELLOWSTONE NP

Teton

Basin COLUMBIA

PLATEAU

Snake River Plain
246 Status and Trends of Land Change in the Western United States—1973 to 2000

cover an additional 1.9 percent. Developed lands accounted for 

only 0.5 percent of the Snake River Basin Ecoregion. Whereas 

developed lands were limited, five of Idaho’s largest cities are 

found within the Snake River Basin Ecoregion, including Boise 

(population 185,787), Nampa (population 51,867), Pocatello 

(population 51,466), Idaho Falls (population 50,730), and Twin 

Falls (population 34,469) (U.S. Census Bureau, 2010). 

The high-elevation mountains surrounding the eastern 

Snake River Basin Ecoregion provide abundant high-quality 

water to the region. The absence of large settlements and industry contribute to the high quality of the water entering the basin. 

The Snake River derives as much as 50 percent of its annual 

flow from natural spring discharge (Miller and others, 2003). 

Surface water feeds the Snake River Basin aquifer, which is as 

much as 400 m thick, underlies 26,000 km2 of the ecoregion, 

and contains about 1.23 x 1012 m3 (100 million acre-ft) of water 

(Smith, 2004). Johnson and Cosgrove (1997) estimated that 

total groundwater storage declined on average about 350,000 

acre-ft per year between 1975 and 1995, a cumulative decrease 

of 7 million acre-ft. Drought conditions caused declines in 

spring discharge and subsequent declines in groundwater levels 

as recharge capability dropped while withdrawals continued 

(Kjelstrom, 1986). However, in certain areas of the ecoregion, 

declines may be predominantly the result of a single factor 

(Idaho Department of Water Resources, 1999). For example, 

groundwater declines of 10 ft or more in Minidoka County 

were attributed to increased groundwater pumping in that area 

(Lindholm and others, 1988). Agricultural activities, urban 

runoff, and historical disposal practices at the Idaho National 

Engineering and Environmental Laboratory are major threats to 

groundwater quality (Smith, 2004).

Base flow of the Snake River was reduced, in part, owing 

to the introduction of more efficient irrigation technologies 

and a conversion from surface water to groundwater irrigation 

sources (Idaho Department of Water Resources, 1999; Miller 

and others, 2003). The net effect of efficiency improvements 

and pumpage by 1992 was an annual decrease in aquifer 

recharge of more than 2.1 million acre-ft, leading to groundwater-level and springflow declines (Idaho Department of Water 

Resources, 1999). Demands for Snake River water are diverse 

and include competition among agriculture, municipal users, 

industry, hydroelectric-power-generating utilities, recreation, 

and fish and wildlife. Federal and state management agencies 

are attempting to adjust to changing values while maintaining 

most of the traditional demands (Miller and others, 2003).

Contemporary Land-Cover Change 

(1973 to 2000)

Overall spatial change in the Snake River Basin Ecoregion, or the area that changed at least one time between 1973 

and 2000, was 8.5 percent (5,604 km2) (table 1). Compared 

to other western ecoregions, the Snake River Basin Ecoregion experienced a modest amount of change (fig. 6). Of the 

Figure 2. Sagebrush steppe, which characterizes Snake River 

Basin Ecoregion.

idahoensis), threetip sagebrush (Artemisia tripartita), Gardner’s saltbush (Atriplex gardneri), black greasewood (Sarcobatus vermiculatus), Indian ricegrass (Achnatherum hymenoides), 

fourwing saltbush (Atriplex canescens), crested wheatgrass 

(Agropyron cristatum), alkali sagebrush (Artemisia longiloba), 

and cheatgrass (Bromus tectorum) (McGrath and others, 2001). 

Disturbance from fire occurs at relatively long periods with low 

severity burns most common. However, due to the introduction 

of exotic species, such as cheatgrass, and managed burns to 

clear sagebrush for rangeland improvements, fire regimes have 

been altered, resulting in decreased fire-return periods with 

higher severity (fig. 3). Whisenant (1990) found fire-return 

periods had decreased from more than 75 years to as little as 

5 to 10 years in some areas. The result on the landscape is a 

reduced ability of sagebrush species to recover postdisturbance, 

which may impact the long-term viability of sage-dependent 

species (Knick and Rotenberry, 1995).

Agriculture was the second most common land-use/landcover type, accounting for approximately one-quarter of the 

ecoregion’s area (fig. 4). Barren lands, primarily volcanic basalt 

flows, cover 2.6 percent of the ecoregion (fig. 5), and wetlands 

Figure 3. Road serving as fire break in Snake River Basin Ecoregion. Area on right recently burned and has been revegetated with 

grasslands. Area to left of road was not burned and is dominated 

by sagebrush steppe.
Chapter 24—Snake River Basin Ecoregion 247

total area that changed, 6.6 percent of the ecoregion changed 

in only one time period, while 1.8 percent of the ecoregion 

changed in two periods. Changes in multiple dates are primarily attributed to fire disturbance and subsequent revegetation 

in following periods.

Change by time period ranged from 1.0 percent to 5.0 

percent (table 2). When the time periods are normalized to 

account for the varying lengths of time, the highest rate of 

change was an estimated 411 km2

 of change per year between 

1992 and 2000. The second highest rate of change was 343 

km2 per year between 1986 and 1992. The first two periods 

(1973–1980, 1980–1986) were relatively stable at an estimated 0.2 percent change per year. Rates of overall land-cover 

change in the Snake River Basin Ecoregion are unique from 

surrounding ecoregions (fig. 7). Ecoregions to the north are 

characterized by changes associated with forest disturbance 

from both natural and anthropogenic sources, whereas to 

the south change was relatively low in the basin-and-range 

ecoregions. The Snake River Basin Ecoregion contains a mix 

of land-cover changes that are generally associated with three 

themes: rangeland fire, agricultural expansion and contraction, 

and urbanization.

Grassland/shrubland declined 2.3 percent over the 

27-year period, from 66.3 percent of the ecoregion in 1973 to 

64.8 percent of the ecoregion in 2000. This amounts to a loss 

of 988 km2. The period of greatest decline was between 1992 

and 2000—an estimated loss of 1,232 km2 over the 8-year 

period. The first three time periods were relatively stable in 

terms of net changes in grassland/shrubland (table 3; fig. 8). 

The large loss of grassland/shrubland between 1992 and 2000 

was primarily a result of fire disturbance. During that period, 

an estimated 1,907 km2 of grassland/shrubland were disturbed 

by fire, whereas 500 km2 converted from a disturbed state back 

to grassland/shrubland (table 4).

The Snake River Basin Ecoregion is one of five key agricultural regions in the western United States along with the 

Columbia Plateau, Willamette Valley, Central California Valley, and Southern and Central California Chaparral and Oak 

Woodlands Ecoregions. Compared to these other agricultural 

Figure 4. Irrigated potato field near Twin Falls, Idaho.

Figure 5. Lava field at Craters of the Moon National Monument 

and Preserve, Idaho.

Figure 6. Overall spatial change in Snake River Basin Ecoregion 

(SRB; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, or 

four time periods; highest level of spatial change in Snake River 

Basin Ecoregion (four time periods) labeled for clarity. See table 2 

for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

Change in four time periods

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods
248 Status and Trends of Land Change in the Western United States—1973 to 2000

ecoregions, the Snake River Basin Ecoregion had the lowest 

overall spatial change but lost the largest amount of agriculture over the 27-year period (table 5).

The 1973 to 1980 period was the only period that realized a net increase (153 km2

) of agricultural land. Following 

1980, agriculture began to decline and reached its largest 

period of loss between 1986 and 1992—a net loss of 773 

km2. Between 1992 and 2000, there was a net decline of 260 

km2 of agriculture. Driving the high amount of net loss in 

agriculture between 1986 and 1992 was the establishment of 

the Conservation Reserve Program (CRP). CRP enrollments 

began in 1986 and provided incentives for landowners to 

convert marginal and highly erodible croplands into natural 

vegetation. Based on county data from the U.S. Department 

of Agriculture (1999), counties in the Snake River Basin 

Ecoregion enrolled a total of 147,787 acres (598 km2) into 

CRP by 1992. The main counties in Idaho that contributed to 

the program were Clark, Elmore, Madison, Teton, Bingham, 

and Twin Falls. Combined, they accounted for over threequarters of all Snake River Basin Ecoregion CRP enrollments in 1992 (fig. 9).

Over the 27-year study period, developed land increased 

47 percent. However, developed land uses make up less than 

1 percent of the total ecoregion area. In 1973, an estimated 

0.4 percent of the ecoregion was developed land, including 

the largest developed areas in the western part of the ecoregion associated with the cities of Boise and Nampa, Idaho. By 

2000, developed land had increased to account for approximately 0.5 percent of the ecoregion—a gain of 112 km2

. Over 

the same three-decade period, population of counties that 

intersect the Snake River Basin Ecoregion increased from 

561,641 in 1970 to 1,041,398 in 2000, an increase of 85 percent (U.S. Census Bureau, 2010). 

Wetlands accounted for slightly less than 2 percent 

of the ecoregion and experienced a statistically significant 

Figure 7. Estimates of land-cover change per time period normalized to annual rates 

of change for all 30 Western United States ecoregions (gray bars). Estimates of change 

for Snake River Basin Ecoregion are represented by red bars in each time period.

Figure 8. Normalized average net change in Snake River Basin 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

−4

−2

0

2

4

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
Chapter 24—Snake River Basin Ecoregion 249

increasing trend throughout the study period. In 1973, wetlands accounted for 1.7 percent of the ecoregion, and by 2000 

they accounted for 1.9 percent, an increase of 156 km2.

As with many western ecoregions, ecosystem disturbance 

played an important role in the Snake River Basin Ecoregion. 

Nonmechanical disturbance, primarily from fire, accounted for 

an estimated 2,517 km2 over the 27-year study period (table 

4). Between 1973 and 1992, fire disturbance was relatively 

low with less than one percent of the ecoregion experiencing 

a disturbance in any of the periods. However, between 1992 

and 2000, fire disturbance affected an estimated 3.0 percent of 

the ecoregion. Introduction of nonnative species and managed burns to remove sagebrush for range improvement are 

largely the cause of increased fire frequency (Pellant, 1990; 

Whisenant, 1990; Billings, 1994).

Land-cover change in the Snake River Basin Ecoregion 

generally involved land conversions into and out of the grassland/shrubland class (table 4). Conversions from grassland/

shrubland to and from agriculture were most common and 

ranked in the top five conversions in each of the four time periods. Conversion from agricultural land to grassland/shrubland 

between 1980 and 1992 were especially common and were the 

top-ranked conversion during that time. From 1973 to 1980 and 

1980 to 1986, conversion of grassland/shrubland to agriculture 

was the first and second most common conversion, respectively. 

Irrigation projects and technology advances, such as the adoption of center-pivot irrigation, likely resulted in the increase in 

agricultural land during this time. Changes associated with fire 

were most common in the last two time periods. Between 1992 

and 2000 an estimated 1,907 km2 converted from grassland/

shrubland to nonmechanically disturbed, whereas an additional 

500 km2

 of area classified as nonmechanically disturbed in the 

previous time period converted back to grassland/shrubland.

Drivers of land-cover and land-use change in the Snake 

River Basin Ecoregion are primarily associated with anthropogenic alteration of the sagebrush-steppe ecosystem. In the 

1970s, areas of new agriculture outpaced areas converted out 

of agriculture by a 2:1 margin. With the implementation of the 

federal CRP program in the late 1980s, the trend reversed and 

nearly six times as much land ceased to be used for agriculture as there was new agricultural land. Historic management 

practices and the introduction of cheatgrass have influenced 

land change by promoting a change in historic fire regimes to 

more frequent and higher intensity burns. Managed burning to 

remove sagebrush for range improvement has also contributed 

to changes in land cover.

Figure 9. Enrollments in Conservation Reserve Program (CRP) for counties in 

Idaho that intersect Snake River Basin Ecoregion.

Year

1986 1988 1990 1992 1994 1996 1998

Percentage of county land in the

Conservation Reserve Program

0

2

3

1

4

5

6

7

Payette

Clark

EXPLANATION

Note: Blaine, Butte, Canyon, 

Gooding, Jerome, and Lincoln 

Counties never had more than

0.5% of their land in CRP and 

were excluded from this chart.

Elmore

Ada

Jefferson

Madison

Teton

Bingham

Minidoka

Twin Falls

Table 1. Percentage of Snake River Basin Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated error.

 [Most sample pixels remained unchanged (91.5 percent), whereas 8.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 6.6 2.7 3.8 9.3 1.9 28.4

2 1.8 1.1 0.6 2.9 0.8 43.5

3 0.2 0.1 0.1 0.2 0.1 29.5

4 0.0 0.0 0.0 0.0 0.0 61.2

Overall 

spatial 

change

8.5 3.0 5.5 11.5 2.1 24.3
250 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 2. Raw estimates of change in Snake River Basin Ecoregion land cover, computed for each of 

four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 1.6 0.4 1.1 2.0 0.3 18.6 0.2

1980–1986 1.0 0.4 0.6 1.4 0.3 27.7 0.2

1986–1992 3.1 1.6 1.6 4.7 1.1 33.9 0.5

1992–2000 5.0 2.6 2.4 7.6 1.8 35.9 0.6

Estimate of change, in square kilometers

1973–1980 1,024 280 744 1,305 190 18.6 146

1980–1986 665 271 394 936 184 27.7 111

1986–1992 2,056 1,026 1,030 3,082 697 33.9 343

1992–2000 3,292 1,738 1,553 5,030 1,181 35.9 411

Table 3. Estimated area (and margin of error) of each land-cover class in Snake River Basin Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed

Mechanically disturbed

Mining Barren Forest Grassland/

Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 1.0 0.9 0.4 0.2 0.0 0.0 0.1 0.0 2.6 1.9 3.1 2.7 66.3 8.3 24.5 7.5 1.7 1.2 0.4 0.3

1980 1.0 0.9 0.4 0.3 0.0 0.0 0.1 0.1 2.6 1.9 3.1 2.7 66.2 8.4 24.7 7.5 1.8 1.3 0.1 0.1

1986 1.1 0.9 0.4 0.3 0.1 0.1 0.1 0.1 2.6 1.9 3.1 2.6 66.3 8.4 24.5 7.5 1.7 1.2 0.0 0.0

1992 0.7 0.5 0.5 0.3 0.3 0.3 0.1 0.1 2.6 1.9 3.1 2.6 66.6 8.2 23.3 7.3 1.9 1.4 0.9 1.1

2000 0.9 0.8 0.5 0.3 0.0 0.0 0.1 0.1 2.6 1.9 3.2 2.7 64.8 8.2 22.9 7.2 1.9 1.4 3.0 2.6

Net

change −0.1 0.1 0.2 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 −1.5 2.9 −1.5 1.5 0.2 0.2 2.7 2.4

Gross

change 1.1 0.9 0.2 0.1 0.7 0.7 0.0 0.0 0.0 0.0 0.1 0.1 7.8 3.5 3.3 1.5 0.6 0.5 5.0 3.4

Area, in square kilometers

1973 678 592 237 138 27 27 41 30 1,704 1,272 2,074 1,755 43,775 5,491 16,154 4,964 1,126 818 248 181

1980 644 591 277 166 23 20 48 35 1,698 1,269 2,072 1,752 43,764 5,561 16,307 4,981 1,191 866 42 59

1986 758 618 297 178 41 42 56 43 1,699 1,269 2,063 1,735 43,825 5,577 16,177 4,961 1,148 823 0 0

1992 429 337 329 198 206 229 51 35 1,704 1,270 2,065 1,735 44,019 5,441 15,404 4,812 1,288 925 569 711

2000 622 555 349 213 27 24 56 41 1,706 1,270 2,089 1,767 42,787 5,385 15,144 4,787 1,282 917 2,000 1,718

Net

change −56 69 112 91 1 32 15 15 2 7 15 16 −988 1,930 −1,009 1,010 156 140 1,752 1,613

Gross

change 732 568 116 90 476 450 33 29 14 14 46 57 5,160 2,299 2,154 1,016 409 343 3,319 2,256
Chapter 24—Snake River Basin Ecoregion 251

Table 4. Principal land-cover conversions in Snake River Basin Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 382 157 107 0.6 37.3

Nonmechanically disturbed Grassland/Shrubland 248 180 123 0.4 24.2

Agriculture Grassland/Shrubland 169 102 69 0.3 16.5

Water Wetland 54 54 36 0.1 5.2

Grassland/Shrubland Nonmechanically disturbed 42 59 40 0.1 4.1

Other Other 130 n/a n/a 0.2 12.7

Totals 1,024 1.6 100.0

1980–1986 Agriculture Grassland/Shrubland 200 124 84 0.3 30.1

Grassland/Shrubland Agriculture 151 83 56 0.2 22.6

Wetland Water 109 129 88 0.2 16.4

Agriculture Wetland 49 71 48 0.1 7.4

Nonmechanically disturbed Grassland/Shrubland 42 59 40 0.1 6.2

Other Other 114 n/a n/a 0.2 17.1

Totals 665 1.0 100.0

1986–1992 Agriculture Grassland/Shrubland 890 721 490 1.3 43.3

Grassland/Shrubland Nonmechanically disturbed 569 711 483 0.9 27.7

Water Mechanically disturbed 182 225 153 0.3 8.8

Grassland/Shrubland Agriculture 143 122 83 0.2 7.0

Water Wetland 138 137 93 0.2 6.7

Other Other 134 n/a n/a 0.2 6.5

Totals 2,056 3.1 100.0

1992–2000 Grassland/Shrubland Nonmechanically disturbed 1,907 1,635 1,111 2.9 57.9

Nonmechanically disturbed Grassland/Shrubland 500 706 480 0.8 15.2

Agriculture Grassland/Shrubland 375 261 177 0.6 11.4

Mechanically disturbed Water 178 225 153 0.3 5.4

Grassland/Shrubland Agriculture 173 71 48 0.3 5.3

Other Other 158 n/a n/a 0.2 4.8

Totals 3,292 5.0 100.0

1973–2000

(overall)

Grassland/Shrubland Nonmechanically disturbed 2,517 1,831 1,244 3.8 35.8

Agriculture Grassland/Shrubland 1,634 1,030 700 2.5 23.2

Grassland/Shrubland Agriculture 849 276 187 1.3 12.1

Nonmechanically disturbed Grassland/Shrubland 789 720 489 1.2 11.2

Mechanically disturbed Water 208 229 156 0.3 3.0

Other Other 1,039 n/a n/a 1.6 14.8

Totals 7,036 10.7 100.0
252 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 5. Overall spatial change and net agricultural change in five main agricultural ecoregions of western 

United States.

Ecoregion Overall spatial change 

(percent of ecoregion)

Agricultural change

(km2

)

Agricultural change

(percent ecoregion)

Snake River Basin 8.5 −1,022 −1.6

Southern and Central California 

Chaparral and Oak Woodlands

9.7 −862 −0.8

Willamette Valley 14.5 −322 −2.2

Central California Valley 12.4 +358 +0.8

Columbia Plateau 9.0 +534 +0.6

References Cited

Billings, W.D., 1994, Ecological impacts of cheatgrass and 

resultant fire on ecosystems in the western Great Basin, 

in Monsen, S.B., and Kitchen, S.G., comps., Proceedings—Ecology and management of annual rangelands, May 

18–22, 1992: Boise, ID: U.S. Department of Agriculture, 

Forest Service, Intermountain Research Station, General 

Technical Report INT-GTR-313, p. 22–30.

Idaho Department of Water Resources, 1999, Feasibility of large-scale managed recharge of the eastern Snake 

Plain Aquifer System: Boise, Idaho Department of Water 

Resources, 248 p.

Johnson, G.S., and Cosgrove, D.M., 1997, Recharge potential 

on the Snake River Plain, Idaho: A Drop in the Bucket?: 

Tempe, Arizona, Biennial Symposium on the Artificial 

Recharge of Groundwater. 

Kjelstrom, L.C., 1986, Flow characteristics of the Snake River 

and water budget for the Snake River Plain, Idaho and eastern Oregon: U.S. Geological Survey Hydrologic Investigations Atlas HA–680. 

Knick, S.T., and Rotenberry, J.T., 1995, Landscape characteristics of fragmented shrub steppe habitats and breeding passerine birds: Conservation Biology, v. 9, no. 5, p. 1,059–1,071.

Lindholm, G.F., Garabedian, S.P., Newton, G.D., and Whitehead, R.L., 1988, Configuration of the water table and depth 

to water, spring 1980, water level fluctuations and water 

movement in the Snake River Plain regional aquifer system, 

Idaho and eastern Oregon: U.S. Hydrological Investigations 

Atlas, HA–703.

McGrath, C.L., Woods, A.J., Omernik, J.M., Bryce, S.A., 

Edmondson, M., Nesser, J.A., Sheldon, J., Crawford, R.C., 

Comstock, J.A., and Plocher, M.D., 2001, Ecoregions of 

Idaho: U.S. Geological Survey Ecoregion Map Series, scale 

1:1,350,000, available at http://rockyweb.cr.usgs.gov/outreach/mapcatalog/environmental.html.

Miller, S.A., Johnson, G.S., Cosgrove, D.M., and Larson, R., 

2003, Regional scale modeling of surface and ground water 

interaction in the Snake River Basin: Journal of the American Water Resources Association, v. 39, no. 3, p. 517–528.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Pellant, Mike, 1990, The cheatgrass-wildfire cycle—Are there 

any solutions?, in McArthur, E.D., Romney, E.M., Smith, 

S.D., Tueller, P.T., comps., Proceedings—Symposium 

on cheatgrass invasion, shrub die-off, and other aspects 

of shrub biology and management, April 5–7, 1989, Las 

Vegas, NV: U.S. Department of Agriculture, Forest Service, 

Intermountain Research Station, General Technical Report 

INT–276, p. 11–17.

Pierce, K.L., Morgan, L.A., and Saltus, R.W., 2002, Yellowstone plume head: Postulated tectonic relations to the 

Vancouver slab, continental boundaries, and climate: Idaho 

Geological Survey Bulletin 30, p. 5–33.

Smith, R.P, 2004, Geologic setting of the Snake River Plain 

aquifer and vadose zone: Vadose Zone Journal, v. 3, p. 

47–58.

U.S. Census Bureau, 2010, Population estimates—Incorporated places and minor civil divisions: U.S. Census Bureau, 

accessed June 10, 2010, at http://www.census.gov/popest/

data/cities/totals/2009/index.html.

U.S. Department of Agriculture, 1999, 1997 Census of agriculture—Agricultural atlas of the United States: Washington, 

D.C., U.S. Government Printing Office, v. 2, subject series, 

pt. 1, 163 p.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.
Chapter 24—Snake River Basin Ecoregion 253

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.

Whisenant, S.G., 1990, Changing fire frequencies on Idaho’s 

Snake River plains: Ecological and management implications, in McArthur, E.D., Romney, E.M., Smith, S.D., and 

Tueller, P.T., eds., Proceedings of a symposium on cheatgrass invasion, shrub die-off, and other aspects of shrub 

biology and management, April 5–7, 1989, Las Vegas, NV: 

U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Gen. Tech. Rep. INT–276, p. 4–10.

Wood, S.H., and Clemens, D.L., 2002, Geologic and tectonic 

history of the western Snake River Plain: Idaho Geological 

Survey Bulletin 30, p. 69–103.
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Chapter 25

Wyoming Basin Ecoregion

east by the Northwestern Great Plains Ecoregion; on the south 

and east by the Southern Rockies Ecoregion; on the south by 

the Colorado Plateaus Ecoregion; on the south and west by the 

Wasatch and Uinta Mountains Ecoregion; and on the north by 

the Middle Rockies Ecoregion and parts of the Montana Valley 

and Foothill Prairies Ecoregion (fig. 1). The ecoregion generally consists of broad intermountain basins dominated by arid 

By Todd J. Hawbaker

Ecoregion Description

The Wyoming Basin Ecoregion (Omernik 1987; U.S. 

Environmental Protection Agency, 1999) covers approximately 

128,914 km2 (49,774 mi2) in Wyoming and parts of northwestern Colorado, northeastern Utah, southeastern Idaho, and 

southern Montana (fig. 1). The ecoregion is bounded on the 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper XXXX–A, 2012

Figure 1. Map of Wyoming Basin Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted on map; 

note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map 

shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. Also 

shown on map are parts of two Great Plains ecoregions: Northwestern Great Plains (NWGP) and Western High Plains (WHP). See appendix 3 

for definitions of land-use/land-cover classifications.

Middle

Rockies

Middle

Rockies

Southern

Rockies

WHP

Colorado Plateaus

Wasatch and

Uinta Mountains

Snake River

Basin

Northwestern

Great Plains

Central

Basin

and

Range

MRK

MVFP

MVFP

MRK NWGP NWGP

MVFP

110° 108° 106°

112°

42°

44°

44°

40° 0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

Green R.

WYOMING

COLORADO

MONTANA

IDAHO

UTAH

Gas

Hills

Oregon Trail

Mormon Trail

Cherokee Trail

Thermopolis

Casper

Laramie

Lander

Jeffrey City

Bairoil

Fort

Bridger Green River

Rock Springs

Cheyenne

North Platte R.
256 Status and Trends of Land Change in the Western United States—1973 to 2000

grasslands and shrublands, as well as isolated hills and low 

mountains that merge to the south into a dissected plateau.

The climate in the Wyoming Basin Ecoregion is semiarid continental, and it is drier and windier than most places 

in the United States. The average annual precipitation from 

rain is 20 cm in Green River, Wyoming, 28 cm in Thermopolis, Wyoming, and 30 cm in Casper, Wyoming. The average 

annual snowfall is 74 cm in Green River, 76 cm in Thermopolis, and 198 cm in Casper. Average maximum monthly 

temperatures range from 32°C and above in July to near 

−17°C in January (Desert Research Institute, 2011). Nearly 

surrounded by forest-covered mountains, the region is somewhat drier than the Northwestern Great Plains Ecoregion to 

the northeast. 

Vegetation consists of grasses interspersed among big 

sagebrush (Artemisia tridentata). Higher elevations harbor 

some quaking aspen (Populus tremuloides) and patches of 

coniferous forest. Open water is rare in this ecoregion, consisting mainly of reservoirs on the North Platte and Green Rivers, 

as well as on smaller rivers that traverse the area. Many minor 

waterways have been dammed to provide water for livestock. 

Stream beds are often dry in these riparian areas. Wetlands are 

especially rare and typically are riparian.

This ecoregion has a rich history in the settlement of the 

American West. Several major trails cross through the ecoregion, as it provides a low pass across the Rocky Mountains 

(fig. 1). The Oregon Trail was used by settlers heading west 

during the 1840s to 1890s. The northern route of the Cherokee 

Trail, which crosses through southern Wyoming, was used 

primarily by travelers heading west to the California gold 

fields. The Mormon Trail was used between 1846 and 1857 

by Mormons fleeing to Utah after persecution in the Midwest 

(Hill, 1987). The short-lived Pony Express also had stations 

lining an east-to-west route near the Oregon Trail (Di Certo, 

2002). Evidence of many of these old trails is still visible. 

The Pony Express and overland movement along wagon trails 

started to decline with the increase in rail travel and telegraph 

use starting in the mid- to late-1800s.

Human population in the Wyoming Basin Ecoregion is 

sparse. The largest cities in the ecoregion are Casper (population, 49,644 in 2000), Laramie (27,204), and Rock Springs 

(18,708), Wyoming (U.S. Census Bureau, 2011). Much of 

the ecoregion is used for cattle and sheep grazing, often in 

managed pastures, and ranches are common, but many areas 

lack sufficient vegetation to support grazing. Agriculture 

is limited primarily to irrigated hay, corn, and sugar beets 

along river bottoms (fig. 2). Much of the land is owned by 

the Bureau of Land Management and is leased to ranches for 

cattle grazing.

The Wyoming Basin Ecoregion has a long history of 

energy development, as it holds large reserves of minerals, 

oil, and natural gas (fig. 3). Wyoming accounts for roughly 

40 percent of all coal production in the United States, the 

most of any state (Freme, 2009). Much of the coal mined in 

Wyoming is shipped to the Midwest, producing approximately 

30 percent of the electricity consumed in the United States. 

Figure 2. Agriculture in Wyoming Basin Ecoregion. A, Irrigated 

crops. B, Hay production.

Figure 3. Energy development in south-central Wyoming.

Figure 4. Reclaimed mine in Gas Hills District of Wyoming.

A

B
Chapter 25—Wyoming Basin Ecoregion 257

Coal-fired power plants are scattered throughout the ecoregion, and large transmission lines radiate from them. Uranium 

mining once was common but decreased in the 1980s after the 

incidents at Three Mile Island and Chernobyl nuclear power 

plants. Many of those once-active mines have been reclaimed 

(fig. 4). Towns associated with uranium mining, such as Jeffrey City, Wyoming, are largely deserted. Today, uranium is 

mined in place using chemicals to dissolve the minerals before 

pumping them to the surface (Gregory, 2011).

Wyoming’s first oil well was drilled in 1885, just 

southeast of Lander, Wyoming (Roberts, 2011). As of 2006, 

Wyoming ranked second in the United States for proven 

natural-gas reserves and fourth for proven crude-oil reserves 

(fig. 5). The most recent period of energy development started 

in the late 1990s and has intensified with rising energy prices 

during the 2000s. In some places, the density of recent energy 

development has produced a nearly continuous matrix of wells 

and their associated transportation networks. There is growing concern about how intensifying energy development will 

affect the populations and migration patterns of wildlife species that use parts of the Wyoming Basin Ecoregion (Bowen 

and others, 2009).

Contemporary Land-Cover Change 

(1973 to 2000)

Between 1973 and 2000, 1.8 percent of the Wyoming 

Basin Ecoregion changed land-use/land-cover classes at 

least once (table 1; fig. 6). In 1.4 percent of the ecoregion, 

change occurred in land-use/land-cover in one time period. 

Overall, the average annual rate of land-cover change in the 

Wyoming Basin Ecoregion was very low, at only 0.1 percent 

(fig. 7; table2). Rates of change varied little among the different time periods analyzed. Even though the rate of change 

appeared low, the Wyoming Basin Ecoregion’s size meant 

that it amounted to nearly 92 to 181 km2

 per year of total 

change, depending on the time period (table 2). Overall, this 

ecoregion’s level of change was one of the lowest among 

western United States ecoregions (table 1).

The extent of agriculture increased until 1986 and 

then started to decline, although it remained at 2 percent of 

ecoregion in 2000. The extent of grassland/shrubland was 

negatively correlated to agriculture, and it was at its lowest 

point in 1986. In contrast, the amount of area classified as 

water, wetland, and mechanically disturbed (primarily reservoir drawdown) fluctuated during each time period (table 3). 

Conversions between grassland/shrubland and agriculture and 

between water, wetland, and mechanically disturbed account 

for the majority of change observed in the ecoregion (table 4). 

During the 27-year study period, the extent of urban 

developed land increased from 39 km2

 to 61 km2, with most 

expansion occurring near cities such as Cheyenne and Rock 

Springs, Wyoming. The amount of forest land decreased by 

Figure 5. Oil well near Bairoil, Wyoming, and warning sign for 

hydrogen-sulfide gas.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

Figure 6. Overall spatial change in Wyoming Basin Ecoregion 

(WB; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, 

or four time periods; highest level of spatial change in Wyoming 

Basin Ecoregion (four time periods) labeled for clarity. See table 2 

for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.
258 Status and Trends of Land Change in the Western United States—1973 to 2000

4.2 percent, from 4,205 km2 in 1973 to 4,027 km2 in 2000. 

Nonmechanical disturbances were rare (table 3; figure 8).

The area covered by energy-related development (mining 

land-cover class) also was relatively low (0.3 percent in 2000; 

table 3); however, this area increased substantially, from 301 

km2 in 1973 to 435 km2 in 2000 (table 3). Thus, a 44 percent 

increase occurred in the area impacted by energy development 

during the 27-year study period. Most of the mining increases 

took place between 1973 and 1980, during which time mining 

land cover is estimated to have increased by nearly 30 percent 

(fig. 8) following the energy boom that occurred in the 1970s.

The amount of area affected by mining may be underestimated, owing to the study’s sampling design and the random 

sample-block selection process, as well as the 60-m resolution 

of the data. Almost all of the blocks fell outside areas experiencing major energy development. Some sample blocks (143, 

533, 622) contained some energy development, but major 

oil and gas fields such as the Jonah and Pinedale fields were 

not sampled in the random selection process. Many oil- and 

gas-well pads are less than 60 m2 and, thus, did not meet the 

minimum mapping-unit size in this study. Additionally, the 

extensive transportation networks required to access the oiland gas-well pads have not been mapped. Thus, the measures 

of area in the mining and developed land-use/land-cover 

classes can be interpreted as highly conservative estimates of 

the true area affected.

Today (2012), Wyoming is in the midst of another energy 

boom. High demand and increasing prices for oil and gas since 

2000 have rapidly transformed Wyoming’s economy and landscape. Information from this project and other USGS projects 

that are examining the impacts of energy development, as well 

as from anecdotal accounts, indicates that the current rate of 

energy development is greatly outpacing past rates.

The fact that a large proportion of the Wyoming Basin 

Ecoregion is public land will constrain certain types of 

Figure 7. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Wyoming Basin Ecoregion are represented by red bars in each time period.

Figure 8. Normalized average net change in Wyoming Basin 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−1

−0.5

0

0.5

1

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 25—Wyoming Basin Ecoregion 259

land-use/land-cover change. Energy exploration and grazing 

are extensive on both public and private lands, but intensive 

agricultural and urban development is limited to private lands. 

This constraint, in addition to a harsh and dry climate, generally limits agriculture to riparian areas where water is directly 

available for irrigation. The extent of agriculture fluctuated 

during the study period and is likely to continue to fluctuate as 

demand for agricultural products changes over time.

Urban development also will be both constrained and 

driven by land-ownership patterns. On the one hand, public 

lands preclude housing and urban development. On the other 

hand, public lands provide natural amenities that often attract 

low-density-housing development. The greatest increases in 

developed land occurred between 1986 and 1992, following the energy boom of the mid-1970s, and between 1992 

and 2000 (fig. 8). Just as this study provides a conservative estimate of the area impacted by mining, it is probably 

providing a highly conservative estimate of the area impacted 

by development.

Most of the Wyoming Basin Ecoregion has not experienced 

substantial land-use/land-cover change during the past three 

decades. Large expanses of land remain largely free of development and agriculture; however, Wyoming’s mineral resources 

are abundant, and the only limit to energy development may 

be the cost of extraction. As demands for energy increase with 

population growth, energy-related landscape change in the 

Wyoming Basin Ecoregion will increase. The overall footprint 

of energy development may be small, but the impacts on wildlife 

and water quality from mines, well pads, and related transportation infrastructure may extend out for some distance. Balancing 

wildlife and habitat conservation with the economic and social 

benefits of agricultural land uses and energy development will 

become increasingly challenging as the landscape in the Wyoming Basin Ecoregion continues to change.

Table 1. Percentage of Wyoming Basin Ecoregion land cover 

that changed at least one time during study period (1973–2000) and 

associated statistical error.

[Most sample pixels remained unchanged (98.2 percent), whereas 1.8 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.4 0.7 0.6 2.1 0.5 35.6

2 0.3 0.2 0.1 0.5 0.1 41.9

3 0.0 0.0 0.0 0.0 0.0 56.4

4 0.2 0.3 −0.1 0.5 0.2 97.5

Overall 

spatial 

change

1.8 0.9 1.0 2.7 0.6 32.0

Table 2. Raw estimates of change in Wyoming Basin Ecoregion land cover, computed for each of four 

time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.8 0.4 0.4 1.2 0.3 34.7 0.1

1980–1986 0.4 0.3 0.1 0.7 0.2 47.1 0.1

1986–1992 0.8 0.7 0.2 1.5 0.5 54.0 0.1

1992–2000 0.7 0.5 0.2 1.1 0.3 46.5 0.1

Estimate of change, in square kilometers

1973–1980 1,018 523 495 1,541 354 34.7 145

1980–1986 550 383 167 933 259 47.1 92

1986–1992 1,087 868 219 1,955 587 54.0 181

1992–2000 858 591 267 1,449 399 46.5 107
260 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Wyoming Basin Ecoregion, calculated five times between 

1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.5 0.4 0.0 0.0 0.0 0.0 0.2 0.2 0.6 0.5 3.3 1.9 92.3 2.4 1.9 1.4 1.2 0.5 0.0 0.0

1980 0.3 0.2 0.0 0.0 0.1 0.2 0.3 0.3 0.6 0.5 3.3 1.9 92.0 2.5 2.2 1.5 1.2 0.5 0.0 0.0

1986 0.5 0.4 0.0 0.0 0.0 0.0 0.3 0.3 0.6 0.5 3.2 1.9 91.9 2.5 2.3 1.5 1.1 0.5 0.0 0.0

1992 0.2 0.1 0.0 0.0 0.3 0.3 0.3 0.3 0.6 0.5 3.2 1.9 92.2 2.3 2.0 1.1 1.2 0.5 0.0 0.0

2000 0.5 0.4 0.0 0.0 0.0 0.0 0.3 0.3 0.6 0.5 3.1 1.7 92.2 2.3 2.0 1.2 1.1 0.5 0.1 0.2

Net

change 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.0 0.0 −0.1 0.2 −0.1 0.7 0.1 0.7 −0.1 0.1 0.1 0.2

Gross

change 1.1 1.4 0.0 0.0 0.8 0.9 0.1 0.1 0.0 0.0 0.1 0.2 1.1 0.6 0.9 0.6 0.5 0.4 0.1 0.2

Area, in square kilometers

1973 659 576 39 40 6 9 301 289 749 581 4,205 2,426 118,962 3,124 2,511 1,812 1,483 642 0 0

1980 403 276 40 40 152 219 390 371 751 581 4,193 2,423 118,539 3,192 2,886 1,917 1,548 620 13 19

1986 638 545 42 41 1 1 397 369 755 581 4,184 2,421 118,426 3,206 3,028 1,967 1,444 608 0 0

1992 234 164 57 43 362 397 416 371 759 581 4,183 2,421 118,825 2,958 2,570 1,476 1,508 603 0 0

2000 660 566 61 44 10 7 435 380 760 581 4,027 2,229 118,822 2,947 2,595 1,498 1,388 586 157 229

Net

change 1 21 23 13 4 11 134 95 10 16 −178 230 −140 857 85 845 −96 69 157 229

Gross

change 1,412 1,769 23 13 1,033 1,221 140 101 22 16 179 231 1,422 807 1,113 831 589 560 183 231
Chapter 25—Wyoming Basin Ecoregion 261

Table 4. Principal land-cover conversions in Wyoming Basin Ecoregion, showing amount of area changed (and margin of error, 

calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall study 

period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 423 339 229 0.3 41.6

Water Mechanically disturbed 150 219 148 0.1 14.8

Water Wetland 122 170 115 0.1 11.9

Grassland/Shrubland Mining 89 84 57 0.1 8.7

Agriculture Grassland/Shrubland 82 109 74 0.1 8.1

Other Other 152 n/a n/a 0.1 14.9

Totals 1,018 0.8 100.0

1980–1986 Grassland/Shrubland Agriculture 135 88 59 0.1 24.6

Mechanically disturbed Water 133 195 132 0.1 24.3

Wetland Water 107 155 105 0.1 19.5

Grassland/Shrubland Wetland 43 41 28 0.0 7.9

Wetland Grassland/Shrubland 40 29 19 0.0 7.2

Other Other 91 n/a n/a 0.1 16.6

Totals 550 0.4 100.0

1986–1992 Agriculture Grassland/Shrubland 498 716 484 0.4 45.8

Water Mechanically disturbed 333 397 269 0.3 30.6

Water Wetland 82 113 77 0.1 7.5

Grassland/Shrubland Agriculture 39 33 22 0.0 3.6

Grassland/Shrubland Mechanically disturbed 23 32 22 0.0 2.1

Other Other 112 n/a n/a 0.1 10.3

Totals 1,087 0.8 100.0

1992–2000 Mechanically disturbed Water 336 397 268 0.3 39.2

Forest Nonmechanically disturbed 157 229 155 0.1 18.3

Wetland Water 88 121 82 0.1 10.3

Grassland/Shrubland Agriculture 77 75 50 0.1 9.0

Agriculture Grassland/Shrubland 59 54 37 0.0 6.8

Other Other 141 n/a n/a 0.1 16.5

Totals 858 0.7 100.0

1973–2000

(overall)

Grassland/Shrubland Agriculture 675 456 309 0.5 19.2

Agriculture Grassland/Shrubland 641 874 591 0.5 18.3

Water Mechanically disturbed 486 611 413 0.4 13.8

Mechanically disturbed Water 472 587 397 0.4 13.4

Wetland Water 217 277 187 0.2 6.2

Other Other 1,022 n/a n/a 0.8 29.1

Totals 3,513 2.7 100.0
262 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Bowen, Z.H., Aldridge, C.L., Anderson, P.J., Assal, T.J., Baer, 

L.A., Bristol, S., Carr, N.B., Chong, G.W., Diffendorfer, 

J.E., Fedy, B.C., Homer, S.L., Manier, D., Kauffman, M.J., 

Latysh, N., Melcher, C.P., Miller, K.A., Montag, J., Nutt, 

C.J., Potter, C., Sawyer, H., Smith, D.B., Sweat, M.J., and 

Wilson, A.B., 2009, U.S. Geological Survey science for 

the Wyoming Landscape Conservation Initiative—2008 

annual report: U.S. Geological Survey Open-File Report 

2009–1201, 83 p., accessed March 28, 2011, at http://pubs.

usgs.gov/of/2009/1201/.

Desert Research Institute, 2011, SOD USA Climate Archive, 

period of record monthly climate summary: Western 

Regional Climate Center database, accessed March 28, 

2011, at http://www.wrcc.dri.edu/summary/.

Di Certo, J.J., 2002, The saga of the Pony Express: Missoula, 

Montana, Mountain Press Publishing Company, 244 p.

Freme, F., 2009, U.S. coal supply and demand—2009 review: 

U.S. Energy Information Administration, accessed March 

28, 2011, at http://www.eia.gov/coal/review/.

Gregory, R, 2011, Uranium: Wyoming State Geological Survey, accessed March 28, 2011, at http://www.wsgs.uwyo.

edu/AboutWSGS/Uranium.aspx.

Hill, W.E., 1987, The Oregon Trail—Yesterday and today: 

Caldwell, Idaho, Caxton Press, 179 p.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, p. 118–125.

Roberts, P., 2011, History of oil in Wyoming, chap. 9 in A new 

history of Wyoming: Phil Roberts Wyoming Home Page, 

accessed March 28, 2011, at http://uwacadweb.uwyo.edu/

robertshistory/history_of_oil_in_wyoming.htm.

U.S. Census Bureau, 2011, American fact finder: U.S. Census 

Bureau database, accessed March 28, 2011, at http://factfinder2.census.gov/faces/nav/jsf/pages/index.xhtml.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E, Howard, S.M., Yang, L., Larson, C.R., Wylie, 

B.K., and van Driel, N., 2001, Completion of the 1990s 

National Land Cover Data set for the conterminous United 

States from Landsat Thematic Mapper data and ancillary 

data sources: Photogrammetric Engineering & Remote 

Sensing, v. 67, p. 650–662.
Chapter 26

Arizona/New Mexico Plateau Ecoregion

on the northeast (Southern Rockies Ecoregion) and southwest 

(Arizona/New Mexico Mountains Ecoregion). Warmer and drier 

climates exist to the south (Chihuahuan Deserts Ecoregion) and 

west (Mojave Basin and Range Ecoregion). The semiarid grasslands of the western Great Plains are to the east (Southwestern 

Tablelands Ecoregion), and the tablelands of the Colorado 

Plateau in Utah and western Colorado lie to the north (Colorado Plateaus Ecoregion). The Arizona/New Mexico Plateau 

Ecoregion occupies a significant portion of the southern half of 

the Colorado Plateau. 

By Jana Ruhlman, Leila Gass, and Barry Middleton

Ecoregion Description

Situated between ecoregions of distinctly different 

topographies and climates, the Arizona/New Mexico Plateau 

Ecoregion represents a large area of approximately 192,869 km2

(74,467 mi2) that stretches across northern Arizona, central and 

northwestern New Mexico, and parts of southwestern Colorado; 

in addition, a small part extends into southeastern Nevada (fig. 

1) (Omernik, 1987; U.S. Environmental Protection Agency, 

1997). Forested, mountainous terrain borders the ecoregion 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Arizona/New Mexico Plateau Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be 

depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into 

mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. 

Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in 

appendix 2. Also shown on map are parts of two Great Plains ecoregions: Southwestern Tablelands (SWT) and Western High Plains (WHP). 

See appendix 3 for definitions of land-use/land-cover classifications. 

Southern

Rockies

SWT

WHP

Colorado Plateaus

CLRP

Arizona/

New Mexico

Mountains

ANMM

ANMM

WHP

MA

Sonoran

Basin and

Range

Chihuahuan

Deserts

Chihuahuan

Deserts

Madrean

Archipelago

ANMM

MBR

CBR

WUM

MEXICO

106°

104°

114° 112° 110° 108°

36°

38°

34°

32°

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

ARIZONA

NV UTAH COLORADO

NEW MEXICO

Torrance Co.

Gallup Santa Fe

Rio Rancho

Durango

Farmington

Los Lunas

Estancia

Albuquerque

Chihuahuan Desert

Colorado Plateau

San Juan

River

Salt River

Rio

Gra nde

Conejos R.

PETRIFIED

FOREST NP

MESA

VERDE NP

GRAND CANYON NP

CEDAR

BREAKS NM San Luis

Valley

San Juan

Basin
264 Status and Trends of Land Change in the Western United States—1973 to 2000

The Arizona/New Mexico Plateau Ecoregion is covered 

predominantly in a mosaic of sparse semiarid grassland and 

desert-scrub species. Major washes and river courses often 

contain riparian canopies of cottonwood (Populus deltoides), 

desert willow (Chilopsis linearis), and salt cedar (Tamarix 

spp.). Juniper (Juniperus spp.) and pinyon (Pinus spp.) trees 

are located in the upland areas, with ponderosa pine (Pinus 

ponderosa) forests present at the highest elevations. The 

climate in the ecoregion is mostly semiarid, but regional 

topography causes annual precipitation to vary substantially, 

ranging from 127 to 890 mm (Daly and others, 2002). Most of 

the ecoregion, however, averages between 152 and 254 mm of 

precipitation from southwestern monsoonal summer thunderstorms and winter frontal storms. The coldest areas can dip 

below −17.8°C in winter, and the hottest summer temperatures 

can exceed 36°C (Western Regional Climate Center, 2009).

Albuquerque, New Mexico, is the largest urban area, with 

a 2000 census population of 448,607, followed by Santa Fe, 

New Mexico, with a population of 62,203. Numerous smaller 

communities exist within the ecoregion, but only five municipalities had a 2000 census count greater than 10,000: Rio Rancho, Farmington, Gallup, and Los Lunas, New Mexico, and 

Durango, Colorado (U.S. Census Bureau, 2001a, 2001b). Over 

55 percent of the ecoregion is federal land, with the majority 

occupying one of 29 different Indian reservations and pueblos. 

The largest of these tribal lands is the Navajo Nation, with 

41,562 km2 within the Arizona/New Mexico Plateau Ecoregion. The next largest federal landholders in the ecoregion are 

the Bureau of Land Management, Forest Service, and National 

Park Service. There are 15 National Park Service areas within 

the ecoregion; many of the national parks and monuments are 

dedicated to preserving the rich history and remnants from the 

Southwest’s ancient native cultures. Prominent national parks 

in the ecoregion are the Grand Canyon and the Petrified Forest 

in Arizona and Mesa Verde in Colorado.

Because of limited rainfall in the ecoregion, crop production is found primarily in close proximity to natural water 

sources such as the Rio Grande, San Juan River, and Conejos 

River. The high mountains surrounding the fertile San Luis 

Valley in south-central Colorado and northern New Mexico 

provide snowmelt, which supports extensive farming in 

that area (McNoldy and Doesken, 2007). Likewise, there is 

considerable agriculture in the closed Estancia basin region in 

Torrance County, New Mexico, which is “one of the most productive agricultural counties in the United States” (Torrance 

County, New Mexico, 2009).

With over 33 percent of the Arizona/New Mexico Plateau 

Ecoregion designated as tribal lands, sheep ranching, cattle 

ranching, and farming (dry and some irrigated) continue to be 

the primary traditional economic activities for many Native 

Americans (Grahame and Sisk, 2002). The effect of low 

regional precipitation levels that can support only scant forage 

has been exacerbated by a long-term trend toward aridity in 

this part of the ecoregion (Karl and others, 2009). Combined 

with historical overgrazing and desertification, the condition 

of the rangeland in many areas is poor. As early as 1933, the 

Bureau of Indian Affairs determined that two-thirds of the 

Navajo rangeland had been overgrazed (Grahame and Sisk, 

2002). Increases in wind erosion and sand-dune mobility that 

have resulted from current drought conditions across northeastern Arizona have further degraded rangelands (Ferguson 

and Crimmins, 2009).

Mining also contributes to local economies in parts of 

the Arizona/New Mexico Plateau Ecoregion. The San Juan 

Basin in northwestern New Mexico and southwestern Colorado was at one time the second largest natural-gas reserve 

in the United States (La Plata County Energy Council, 2009), 

having 20,000 producing wells (Ortega, 2009). Additionally, the 

Peabody Western Coal Company mines about 8.5 million tons 

of coal annually through lease agreements with the Navajo 

Nation and Hopi Tribe (U.S. Office of Surface Mining, 2008). 

As the ecoregion’s largest city, Albuquerque is also its largest 

economy. Located at the crossroads of Interstate Highways 25 

and 70, Albuquerque has a “diverse economic base consisting 

of government, services, trade, agriculture, tourism, manufacturing, and research and development” (City-Data.com, 2009). 

Kirtland Air Force Base is the largest employer in the Albuquerque metropolitan area (Albuquerque Economic Development, Inc., 2010). 

Contemporary Land-Cover Change 

(1973 to 2000)

The Arizona/New Mexico Plateau Ecoregion experienced very little land-cover change during the study period 

(fig. 2). An estimated 1.2 percent of the ecoregion (2,380 km2) 

converted to other land-cover classes during the study period. 

Estimates reveal that 1.1 percent of the ecoregion changed 

only once during the study period, and 0.1 percent changed 

twice (table 1). However, standard error is high as a proportion 

of overall spatial change, which is not unusual for an ecoregion with little change. Compared to other western United 

States ecoregions, the Arizona/New Mexico Plateau Ecoregion 

had the lowest amount of change other than the Chihuahuan 

Deserts Ecoregion and the Southern Rockies Ecoregion. Low 

estimates of land-cover change are consistent with other ecoregions in the Southwest (figs. 2, 3). 

Estimated land-cover change per time period started with 

0.2 percent between 1973 and 1980, and it increased 0.1 percent each time period thereafter, to reach 0.5 percent between 

1992 and 2000. When the change estimates are normalized to 

account for the varying lengths of time between satellite imagery dates, the average rate of change per year was less than 

100 km2 between 1973 and 1980 and between 1980 and 1986, 

131 km2 between 1986 and 1990, and 111 km2 between 1992 

and 2000 (table 2; fig. 3).

Results showed that grassland/shrubland and forest were 

the predominant land-cover classes within the ecoregion. 

Grassland/shrubland encompassed approximately 78 percent 

of the land cover in each time period, whereas forest covered 
Chapter 26—Arizona/New Mexico Plateau Ecoregion 265

19 percent (table 3). The barren class accounted for 1.7 

percent of the land cover, and the water, developed, mining, 

agriculture, wetland, and nonmechanically disturbed classes 

collectively made up the remaining land cover. 

The developed and grassland/shrubland classes had 

the greatest net change during the study period. Grassland/

shrubland declined by 0.5 percent (810 km2), from 78.0 to 

77.6 percent of the ecoregion. The developed class increased 

by 144 percent during the study period but remained only 0.7 

percent of the ecoregion in 2000. The remaining classes experienced minimal net change (table 3). 

Examination of net-change values alone can mask 

land-cover dynamics that occur within a given study period. 

Figure 4 illustrates the fluctuations that occurred in land-cover 

classes between time periods. Changes in grassland/shrubland occurred at variable rates over the study period; a slight 

increase occurred between 1986 and 1992, and the greatest 

decrease occurred between 1992 and 2000. The developed 

class increased the most between 1980 and 1986 but consistently gained over the entire study period. Mobility in active 

sand dunes was mapped during the study period, and it is 

conceivable the intense drought that began in this area in 1996 

allowed for more sand deposition and active transport than in 

previous years, possibly explaining the 80 km2 growth of the 

barren class over the study period. Research by U.S. Geological Survey scientists confirmed that drought conditions on the 

Navajo Nation Reservation have accelerated destabilization 

and mobility of sand dunes, owing to the detrimental effect on 

stabilizing vegetation (Redsteer and Block, 2004).

The most common land-cover conversions between 1973 

and 2000 involved the grassland/shrubland, agriculture, and 

developed classes (table 4). Grassland/shrubland to developed 

(533 km2) was the primary conversion between 1973 and 

2000, followed by agriculture reverting to grassland/shrubland 

(470 km2). Fire caused the next most common conversion 

of grassland/shrubland to nonmechanically disturbed, which 

occurred between 1992 and 2000 (393 km2). Agriculture to 

Figure 3. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Arizona/New Mexico Plateau Ecoregion are represented by red bars in 

each time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in three time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

Figure 2. Overall spatial change in Arizona/New Mexico Plateau 

Ecoregion (ANMP; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial 

change in Arizona/New Mexico Plateau Ecoregion (three time 

periods) labeled for clarity. See table 2 for years covered by each 

time period. See appendix 2 for key to ecoregion abbreviations.
266 Status and Trends of Land Change in the Western United States—1973 to 2000

developed was the fourth most common land-cover conversion. The overall net loss in agriculture (to grassland/shrubland and developed) was 30.8 percent of the area occupied by 

agriculture in 1973. However, although fieldwork confirmed 

the presence of many of the conversions listed in table 4, the 

margins of error in the table demonstrate the high degree of 

uncertainty derived from this study’s interpretations. 

The Arizona/New Mexico Plateau Ecoregion experienced little change in major land-cover classes between 1973 

and 2000. Except for the Albuquerque metropolitan area, the 

ecoregion is sparsely populated, consisting mainly of large 

expanses of grassland/shrubland devoted to grazing (fig. 5). 

In an ecoregion where 78 percent of the land cover is grassland/shrubland, most land-cover change would be expected to 

occur in that dominant class. Change in grassland/shrubland 

class was distributed throughout the ecoregion, occurring in 26 

out of 32 study blocks. 

Change in the agriculture class occurred mainly in study 

blocks located along the San Juan River or in or near the 

Estancia basin region of central New Mexico. The largest 

observed area of former agricultural lands had evidence of 

abandoned canals leading from the nearby river. Statistics for 

the ecoregion’s largest agricultural area, the San Luis Valley, 

indicated a small decrease (1.5 percent) in acreage devoted to 

farming between 1987 and 2002 (U.S. Department of Agriculture, 1992, 2002). 

The Albuquerque metropolitan area is the location of 

most of the growth of developed land in the ecoregion. In 

2000, Albuquerque’s population was 448,607 (U.S. Census 

Bureau, 2001b), having grown from 243,751 in 1970 (U.S. 

Census Bureau, 1973). This 84 percent growth rate is substantial; moreover, the entire Albuquerque metropolitan area 

grew 125.7 percent within this same time frame (U.S. Census 

Bureau, 1973, 2001b). This population growth is reflected in 

the continually increasing acreage devoted to urban development. A 1997 U.S. Geological Survey study that mapped urban 

land use from aerial photographs noted that the Albuquerque 

metropolitan area had grown from 49,746 to 84,889 acres 

between 1973 and 1991, a 71 percent increase in area (Braun 

and others, 1998). Growth of the Albuquerque metropolitan 

area is expected to continue, with population projected to hit 

one million by 2021 or before (Siemers, 2007).

Coal mining in the Navajo Nation and the prolific 

amount of coal-bed methane available in the San Juan Basin 

will remain important and have many potential impacts 

on the Arizona/New Mexico Plateau Ecoregion. The area 

occupied by mining more than doubled during the study 

period (although the area remained as roughly 0.1 percent of 

ecoregion area). This small reported area might be attributable to the fact that no areas of coal mining were captured in 

our study blocks, as well as the fact that the footprint of new 

oil or gas wells mapped in study blocks within the San Juan 

Basin was minimal. Increased mining activity in the future 

may cause more land-cover change in the ecoregion, especially in the San Juan Basin.

The small land-cover changes that did occur during the 

study period were mainly due to increased urbanization, at the 

expense of natural grassland/shrubland and agricultural lands, 

as well as agricultural abandonment. It is important to keep in 

mind, however, that these land-cover changes were minor, and 

they represent a small percentage of the overall land cover of 

the ecoregion. 

Figure 4. Normalized average net change in Arizona/New 

Mexico Plateau Ecoregion by time period for each land-cover 

class. Bars above zero axis represent net gain, whereas bars 

below zero represent net loss. Note that not all land-cover classes 

shown in explanation may be represented in figure. See appendix 

3 for definitions of land-use/land-cover classifications.

Figure 5. Rangeland southwest of Albuquerque, New Mexico.

−1

−0.5

0

0.5

1

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 26—Arizona/New Mexico Plateau Ecoregion 267

Table 2. Raw estimates of change in Arizona/New Mexico Plateau Ecoregion land cover, computed for 

each of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.2 0.1 0.1 0.3 0.1 40.2 0.0

1980–1986 0.3 0.3 0.0 0.5 0.2 66.4 0.0

1986–1992 0.4 0.3 0.1 0.7 0.2 44.6 0.1

1992–2000 0.5 0.3 0.1 0.8 0.2 49.2 0.1

Estimate of change, in square kilometers

1973–1980 422 250 171 672 170 40.2 60

1980–1986 513 503 10 1,016 341 66.4 85

1986–1992 789 520 269 1,308 352 44.6 131

1992–2000 891 647 245 1,538 438 49.2 111

Table 1. Percentage of Arizona/New Mexico Plateau Ecoregion 

land cover that changed at least one time during study period 

(1973–2000) and associated statistical error.

[Most sample pixels remained unchanged (98.8 percent), whereas 1.2 percent 

changed at least once throughout study period. Two dashes (--) indicate that, 

because zero pixels changed four times during study period, relative error is 

not calculable] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.1 0.6 0.5 1.8 0.4 38.9

2 0.1 0.0 0.0 0.1 0.0 34.3

3 0.0 0.0 0.0 0.0 0.0 39.2

4 0.0 0.0 0.0 0.0 0.0 --

Overall 

spatial 

change

1.2 0.7 0.6 1.9 0.5 36.9
268 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Arizona/New Mexico Plateau Ecoregion, calculated five 

times between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.1 0.0 0.3 0.2 0.0 0.0 0.1 0.0 1.7 1.6 18.8 6.1 78.0 6.0 0.8 0.8 0.3 0.3 0.0 0.0

1980 0.1 0.0 0.3 0.3 0.0 0.0 0.1 0.1 1.7 1.6 18.8 6.1 78.0 6.0 0.8 0.7 0.3 0.3 0.0 0.0

1986 0.1 0.0 0.5 0.4 0.0 0.0 0.1 0.1 1.7 1.6 18.8 6.1 77.9 6.0 0.7 0.6 0.3 0.3 0.0 0.0

1992 0.1 0.1 0.6 0.5 0.0 0.0 0.1 0.1 1.7 1.6 18.8 6.1 77.9 6.0 0.6 0.6 0.2 0.3 0.0 0.0

2000 0.1 0.0 0.7 0.6 0.0 0.0 0.1 0.1 1.7 1.6 18.8 6.1 77.6 5.9 0.5 0.6 0.2 0.3 0.2 0.3

Net

change 0.0 0.0 0.4 0.5 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 −0.4 0.5 −0.2 0.3 0.0 0.0 0.2 0.3

Gross

change 0.1 0.0 0.4 0.5 0.0 0.0 0.1 0.0 0.1 0.0 0.1 0.1 0.9 0.5 0.3 0.3 0.0 0.0 0.2 0.3

Area, in square kilometers

1973 111 83 524 463 0 0 102 93 3,289 2,999 36,322 11,852 150,513 11,487 1,523 1,447 486 529 0 0

1980 99 82 606 518 8 9 129 120 3,313 2,998 36,283 11,843 150,403 11,487 1,543 1,423 485 529 0 0

1986 104 85 934 856 3 5 147 122 3,318 2,998 36,282 11,842 150,212 11,506 1,385 1,231 484 526 0 0

1992 138 106 1,067 964 8 7 180 135 3,330 2,998 36,305 11,838 150,281 11,536 1,073 1,151 481 521 6 9

2000 116 79 1,277 1,187 3 4 212 155 3,369 2,996 36,265 11,833 149,703 11,471 1,053 1,130 475 514 396 580

Net

change 5 40 753 900 3 4 110 76 80 76 −57 68 −810 981 −470 517 −10 16 396 580

Gross

change 168 96 753 900 27 20 110 76 102 86 178 148 1685 967 590 512 13 16 409 580
Chapter 26—Arizona/New Mexico Plateau Ecoregion 269

Table 4. Principal land-cover conversions in Arizona/New Mexico Plateau Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Agriculture 104 101 68 0.1 24.7

Agriculture Grassland/Shrubland 62 66 45 0.0 14.7

Grassland/Shrubland Developed 59 73 50 0.0 14.0

Forest Grassland/Shrubland 38 53 36 0.0 9.0

Grassland/Shrubland Barren 31 33 22 0.0 7.4

Other Other 127 n/a n/a 0.1 30.1

Totals 422 0.2 100.0

1980–1986 Grassland/Shrubland Developed 172 214 145 0.1 33.6

Agriculture Developed 151 221 150 0.1 29.5

Agriculture Grassland/Shrubland 49 55 37 0.0 9.5

Grassland/Shrubland Agriculture 40 39 27 0.0 7.8

Grassland/Shrubland Water 22 12 8 0.0 4.2

Other Other 79 n/a n/a 0.0 15.4

Totals 513 0.3 100.0

1986–1992 Agriculture Grassland/Shrubland 327 445 302 0.2 41.4

Grassland/Shrubland Developed 113 116 79 0.1 14.4

Grassland/Shrubland Forest 96 133 90 0.0 12.2

Forest Grassland/Shrubland 61 83 56 0.0 7.8

Grassland/Shrubland Water 55 60 41 0.0 7.0

Other Other 137 n/a n/a 0.1 17.3

Totals 789 0.4 100.0

1992–2000 Grassland/Shrubland Nonmechanically disturbed 393 575 390 0.2 44.1

Grassland/Shrubland Developed 188 212 143 0.1 21.1

Forest Grassland/Shrubland 53 77 52 0.0 6.0

Grassland/Shrubland Barren 42 43 29 0.0 4.8

Agriculture Grassland/Shrubland 32 35 24 0.0 3.6

Other Other 182 n/a n/a 0.1 20.4

Totals 891 0.5 100.0

1973–2000

(overall)

Grassland/Shrubland Developed 533 598 405 0.3 20.4

Agriculture Grassland/Shrubland 470 467 316 0.2 18.0

Grassland/Shrubland Nonmechanically disturbed 393 575 390 0.2 15.0

Agriculture Developed 201 293 198 0.1 7.7

Grassland/Shrubland Agriculture 197 151 102 0.1 7.5

Other Other 821 n/a n/a 0.4 31.4

Totals 2,615 1.4 100.0
270 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

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employers: Albuquerque Economic Development database, 

accessed June 30, 2011, at http://www.abq.org/uploads/

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Braun, P., Chourre, M., Hughes, D., Schubert, J., Striebek, 

H., and Thorstad, R., 1998, Urban land use change in 

the Albuquerque metropolitan area, in Merideth, R.W., 

ed., Climate variability and change in the Southwest, 

Final Report of the Southwest Regional Climate Change 

Symposium and Workshop, September 3-5, 1997, Tucson, 

Arizona: Tucson, University of Arizona, Udall Center for 

Studies in Public Policy, 81 p.

City-Data.com, 2009, Albuquerque—Economy, in Cities 

of the United States–The West: City-Data.com database, 

accessed August 6, 2009, at http://www.city-data.com/

us-cities/The-West/Albuquerque-Economy.html.

Daly, C., Gibson, W., and Taylor, G., 2002, 103-year 

high-resolution precipitation climate data set for the 

conterminous United States: Corvallis, Oregon State 

University, The PRISM Climate Group database, accessed 

on August 5, 2009, at http://www.prism.oregonstate.edu.

Ferguson, D., and Crimmins, M., 2009, Who’s paying 

attention to the drought on the Colorado Plateau?: Tucson, 

University of Arizona, Southwest Climate Outlook, July 

2009, accessed August 10, 2009, at http://www.climas.

arizona.edu/feature-articles/july-2009.

Grahame, J.D., and Sisk, T.D., 2002, Canyons, culture and 

environmental change; An introduction to the land-use 

history of the Colorado Plateau: Flagstaff, Northern 

Arizona University database, accessed July 22, 2009, at 

http://www.cpluhna.nau.edu.

Karl, T.R., Melillo, J.M., and Peterson, T.C., eds., 2009, 

Global climate change impacts in the United States: 

Cambridge University Press, p. 30, accessed December 1, 

2009, at www.globalchange.gov/usimpacts.

La Plata County Energy Council, 2009, Gas facts–San Juan 

Basin map: La Plata County Energy Council database, 

accessed July 22, 2009, at www.energycouncil.org/

gasfacts/sjbmap.htm.

McNoldy, Brian, and Doesken, Nolan, 2007, Precipitation 

characteristics of the San Luis Valley during Summer 2006: 

Fort Collins, Colorado Climate Center, accessed July 20, 

2009, at http://einstein.atmos.colostate.edu/~mcnoldy/tmp/

SCF/SanLuis_Precip_Summary.pdf.

Omernik, J.M., 1987, Ecoregions of the conterminous 

United States: Annals of the Association of American 

Geographers, v. 77, no. 1, p. 118–125.

Ortega, K., 2009, History: Four Corners Oil and 

Gas Conference, accessed July 22, 2009, at www.

fourcornersoilandgas.com.

Redsteer, Margaret H., and Block, Debra, 2004, Drought 

conditions accelerate destabilization of sand dunes on the 

Navajo Nation, southern Colorado Plateau: Geological 

Society of America Abstracts with Programs, v. 66, no. 8, 

p. 171.

Siemers, Erik, 2007, Managing Albuquerque’s growth poses 

challenges with 1 million people projected for 2021: 

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Chapter 26—Arizona/New Mexico Plateau Ecoregion 271

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This page intentionally left blank
Warm Deserts Ecoregions

Chapter 27

Chihuahuan Deserts Ecoregion

is generally oriented from northwest to southeast, with the 

Madrean Archipelago Ecoregion to the west; the Arizona/New 

Mexico Mountains, Arizona/New Mexico Plateau, Southwestern Tablelands, and Western High Plains Ecoregions to 

the north; and the Edwards Plateau and Southern Texas Plains 

Ecoregions to the east (fig. 1). 

The Chihuahuan Desert is distinguished from other hot 

deserts in the Southwest by its higher elevation and summerdominant rainfall. The terrain consists of broad basins and valleys bordered by sloping alluvial fans and terraces, along with 

isolated mesas and mountains. The alluvial fans and basins 

By Jana Ruhlman, Leila Gass, and Barry Middleton

Ecoregion Description

The Chihuahuan Desert is the largest of the North 

American deserts, extending from southern New Mexico and 

Texas deep into Mexico, with approximately 90 percent of its 

area falling south of the United States–Mexico border (Lowe, 

1964, p. 24). The Chihuahuan Deserts Ecoregion covers 

approximately 174,472 km2

 (67,364 mi2) within the United 

States, including much of west Texas, southern New Mexico, 

and a small portion of southeastern Arizona (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997). The ecoregion 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Chihuahuan Deserts Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 National 

Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be depicted 

on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into mechanically 

disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in study. Index map 

shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are listed in appendix 2. 

Also shown on map are parts of five Great Plains Ecoregions: Central Great Plains, Edwards Plateau (EP), Southern Texas Plains (STP), 

Southwestern Tablelands (SWT), and Western High Plains. See appendix 3 for definitions of land-use/land-cover classifications.

104° 102°

102°

108° 106°

34°

32°

30°

30°

Western

High

Plains

Central

Great Plains

Arizona/

New Mexico

Mountains

ANMM

Arizona/

New Mexico

Plateau

MA

SWT

EP

STP

MEXICO

SWT

NEW MEXICO

AZ

TEXAS

MEXICO

El Paso

Langtry

Comstock

Del

Rio

Las Cruces

Silver City

Deming

Sunland Park

Roswell

Artesia

Pecos

Socorro

San Elizario

Fort Stockton

Ozona

Alamogordo

Carlsbad 

Rio

Gr a n de

Holloman AFB

Amistad 

BIG BEND NP Reservoir

Pe c os R.

0 50 100 150 MILES

0 50 100 150 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION
276 Status and Trends of Land Change in the Western United States—1973 to 2000

play an important role in groundwater recharge of the alluvialbasin aquifer systems that supply water to human populations 

along the Texas–Mexico border. 

In the northern Chihuahuan Desert, annual precipitation 

averages 245 to 265 mm, with most of the precipitation falling 

in the summer (Gucker, 2006; Schmidt, 1983). Annual mean 

temperatures range from less than 12°C to greater than 20°C 

throughout the part of the Chihuahuan Desert that is north of 

the border (Daly and others, 2002). January minimum temperatures reach near or below freezing except along parts of 

the Rio Grande in Texas, where July maximum temperature. 

exceed 36°C (National Park Service, 2007).

Unique in its diversity of yucca (Yucca spp.) and agave 

(Agave spp.) species (fig. 2), the Chihuahuan Desert replaces 

the large cacti, creosote bush (Larrea tridentata), and bursage 

(Asteraceae spp.) communities of the Sonoran Desert to the 

west with large yuccas amid a sea of sparse grass and shrubs. 

Much of the Chihuahuan Deserts Ecoregion was once covered 

by healthy semidesert grasslands, but heavy livestock grazing coupled with frequent droughts during the 20th century 

transformed thousands of acres to desert shrubland, a process 

that still continues (Hoyt, 2002). Extensive areas of Chihuahuan semidesert grasslands are now dominated by creosote 

bush (Larrea tridentata), tarbush (Flourensia cernua), and 

mesquite (Prosopis spp.) (Buffington and Herbel, 1964, p. 

139). McClaran and Van Devender (1995, p. 250–251) stated 

that livestock grazing and range-management programs since 

the 1870s have “led to soil erosion, destruction of those plants 

most palatable to livestock, changes in grassland fire ecology, the spread of nonnative plants, and a steady increase in 

the density of woody shrubs and brush.” However, some have 

challenged these prevailing interpretations of influences on 

environmental degradation, highlighting the significance of 

climate variability as a catalyst and the need for a more stakeholder-driven research approach when evaluating ecological 

stewardship (West and Vásquez-León, 2008). 

Water in the ecoregion is limited, which makes its major 

rivers, the Rio Grande (fig. 3) and the Pecos River (fig. 4), 

precious resources. These river valleys create large riparian 

areas, and major pockets of development are located along 

their corridors (New Mexico State University, 2007). Most of 

the water in the Chihuahuan Deserts Ecoregion is associated 

with the Rio Grande and the Pecos River and their tributaries. 

Reservoirs on these rivers provide water for the ecoregion’s 

limited irrigated agriculture, as well as supply water for its 

major cities, including Las Cruces and Roswell, New Mexico, 

and El Paso, Texas.

Livestock, oil and gas production, and tourism are all

important to the economy of the Chihuahuan Deserts Ecoregion (Conservation History Association of Texas, 2009). The 

Natural Resources Conservation Service reported that, in the 

Chihuahuan Desert Resource Conservation and Development 

area of Texas, 89 percent of the area was rangeland, and beef 

cattle, dairy cattle, pecans, onions, and various other crops 

were the major agricultural products (U.S. Department of 

Agriculture, 2008). Wheat (mostly irrigated), hay, sorghum, 

Figure 4. View looking north over Pecos River, between Langtry 

and Comstock, Texas. This part of river contains water impounded 

by Amistad Reservoir, located farther downstream.

Figure 2. Soaptree yucca (Yucca elata) near Texas–New Mexico 

border, south of Carlsbad, New Mexico. This is one of many types 

of yuccas and agaves indigenous to Chihuahuan Deserts Ecoregion.

Figure 3. View of Rio Grande from scenic overlook in Big Bend 

National Park, looking southwest into Mexico at Santa Elena 

Mountains.
Chapter 27—Chihuahuan Deserts Ecoregion 277

cotton, and a variety of fruits, nuts, and vegetables, as well as 

livestock, are important to the economy of all New Mexico 

counties in the ecoregion (U.S. Department of Agriculture, 

2007). Farmers in the ecoregion also grow many varieties of 

chili peppers in the fertile fields along the Rio Grande in both 

New Mexico and Texas. 

Federal lands make up approximately 28 percent of the 

Chihuahuan Deserts Ecoregion, with the majority managed 

by the Bureau of Land Management and the Department of 

Defense (for example, White Sands Missile Range, Holloman Air Force Base, and Fort Bliss); these military installations are a vital part of the local economies (Las Cruces and 

Alamogordo, New Mexico, and El Paso, Texas, respectively). 

Approximately 4,460 km2 are managed by the National 

Park Service within seven park units, and these represent 

the nation’s most significant areas of preserved Chihuahuan 

Desert landscape (National Park Service, 2005). White Sands 

National Monument and Carlsbad Caverns National Park in 

New Mexico and Big Bend National Park in Texas are three of 

the more notable parks within the ecoregion.

Contemporary Land-Cover Change 

(1973 to 2000)

The Chihuahuan Deserts Ecoregion had very little landcover change during the study period (fig. 5). An estimated 

0.5 percent of the ecoregion (822 km2) was converted to other 

land-cover types (table 1). The standard error of 0.2 percent 

is high in proportion to the overall change of 0.5 percent but 

is not unusual for an ecoregion with so little change. Compared to other western ecoregions, change in the Chihuahuan 

Deserts Ecoregion was the lowest (figs. 5,6). Low change is 

consistent with that of other ecoregions in the arid Southwest. 

The estimated change in land cover was 0.2 percent between 

1980 and 1986 and between 1992 and 2000; it was 0.1 percent 

between 1973 and 1980 and between 1986 and 1992. When 

Figure 5. Overall spatial change in Chihuahuan Deserts Ecoregion (CD; darker bars) compared with that of all 30 Western United 

States ecoregions (lighter bars). Each horizontal set of bars shows 

proportions of ecoregion that changed during one, two, three, or 

four time periods; highest level of spatial change in Chihuahuan 

Deserts Ecoregion (four time periods) labeled for clarity. See table 

2 for years covered by each time period. See appendix 2 for key to 

ecoregion abbreviations.

Figure 6. Estimates of land-cover 

change per time period normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change 

for Chihuahuan Deserts Ecoregion 

are represented by red bars in each 

time period.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period
278 Status and Trends of Land Change in the Western United States—1973 to 2000

the change estimates are normalized to account for the varying 

lengths of study periods, annual change ranged from 25 km2

(1986–1992) to 57 km2 (1980–1986) (table 2).

 Grassland/shrubland was the predominant land cover, 

covering 95.6 percent of the Chihuahuan Deserts Ecoregion in 

2000 (table 3; fig. 7). Forest (both riparian and higher elevation) was the second largest land cover in 2000 (2.4 percent), 

followed by developed lands at 1.0 percent. Water, mining, 

barren land, and agriculture contributed to the remaining 1.0 

percent of the ecoregion’s land-cover types. 

Four classes changed by at least 100 km2 during the study 

period: developed, mining, grassland/shrubland, and agriculture (table 3). The other classes experienced almost no change. 

Statistically significant, increasing trends of 11.2 percent over 

the study period were observed for the developed class, and 

the mining class nearly quadrupled in size, whereas a statistically significant, decreasing trend of 0.1 percent occurred in 

the grassland/shrubland class (fig. 8). No trend was apparent 

for agriculture, which fluctuated in gains and losses throughout the study period and had a net loss of 11.2 percent (fig. 8). 

The most common conversions were grassland/shrubland to mining (217 km2

), grassland/shrubland to developed 

(187 km2), and agriculture to grassland/shrubland (158 km2) 

(table 4). The conversion from grassland/shrubland to mining, which occurred in each time period, was attributable 

to increased oil and gas extraction in the eastern part of the 

ecoregion (fig. 9). This type of conversion was evident in nine 

of the Chihuahuan Deserts Ecoregion’s study blocks, which 

are located near the eastern border of the ecoregion and which 

overlie the Permian Basin, a geological province located in 

several counties in southeastern New Mexico and western 

Texas (fig. 10). More than half of the oil and gas production 

from Texas comes from the Permian Basin, making it the 

most prolific oil-producing province in United States history 

(Bureau of Economic Geology, 2005).

Conversion from grassland/shrubland to developed also 

took place during each time period, and it was the leading 

conversion between 1986 and 1992. The majority of mapped 

development increases, which were captured in three study 

blocks, took place in or near cities and near Holloman Air 

Force Base, New Mexico. Overall, developed land is estimated to have increased by 174 km2

 between 1973 and 2000. 

Mining in the Chihuahuan Deserts Ecoregion is likely 

to continue to increase. In 2007, the U.S. Geological Survey 

estimated that 41 trillion ft3

 of undiscovered natural gas and 

1.3 billion barrels of undiscovered oil are in the Permian Basin 

Province (Schenk and others, 2008). A decision in 2005 by the 

Bureau of Land Management allowed for oil and gas leasing 

and development on public lands in southern New Mexico’s 

Sierra and Otero Counties. Publicized as one of the most 

restrictive plans ever developed for oil and gas leasing on 

federal lands, the plan provided for a variety of environmental 

protections and reclamation efforts for Chihuahuan Desert 

grasslands within the planning area (U.S. Bureau of Land 

Management, 2006).

Conversion of grassland/shrubland to developed is also 

likely to continue within the ecoregion. Areal interpolation 

of census-block data was used to obtain population totals 

for the Chihuahuan Deserts Ecoregion (U.S. Census Bureau, 

2000). Using this technique, population in the ecoregion 

Figure 7. Chihuahuan Desert grasslands south of Fort Stockton, 

Texas.

Figure 8. Normalized average net change in Chihuahuan Deserts 

Ecoregion by time period for each land-cover class. Bars above 

zero axis represent net gain, whereas bars below zero represent 

net loss. Note that not all land-cover classes shown in explanation 

may be represented in figure. See appendix 3 for definitions of 

land-use/land-cover classifications.

−1

−0.5

0

0.5

1

1973–1980 1980–1986 1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Time period

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 27—Chihuahuan Deserts Ecoregion 279

grew from 851,797 in 1980 to 1,178,626 in 2000, an increase 

of 38.4 percent. The population of the largest cities showed 

an overall increase of 67.1 percent between the 1970 and 

2000 census (table 5). 

A major concern in the Chihuahuan Deserts Ecoregion is 

the ongoing transformation of semidesert grassland into shrubland and a more desertlike ecosystem. The change in composition of the Chihuahuan grasslands has changed dramatically 

in the last century and continues to be observed (Brown, 1994, 

p. 169). Desert-scrub communities, which now make up nearly 

one half of the total vegetation in the Chihuahuan Desert, may 

have grown to their present extent through invasion of eroded 

grasslands (Chihuahuan Desert Research Institute, 2009). 

Scientists disagree, however, on the relative importance of 

factors such as livestock grazing, fire, and climate change as 

drivers of this transformation (McClaran and Van Devender, 

1995, p. 265). (Note that the desertification of the Chihuahuan 

Desert grasslands is not reflected in the statistics of this report 

because capturing change within land-cover classes is not part 

of the Status and Trends of Land Change project design.) 

Major land-cover classes changed very little in the 

Chihuahuan Deserts Ecoregion between 1973 and 2000. The 

small changes that did occur were due to increased oil and 

gas extraction and some urban growth, but these localized 

changes accounted for a small fraction of the overall ecoregion area. Except for its major cities, the ecoregion remains 

sparsely populated and consists mainly of large expanses of 

grassland and shrubland that are devoted to grazing. Little 

rainfall and a scarcity of both surface water and groundwater 

inhibit anthropogenic change in much of the ecoregion and 

will continue to be a challenge to future growth. 

Figure 9. Hydrocarbon-extraction facility southwest of Ozona, 

Texas.

Figure 10. Sample block 24-1094, located between Pecos and 

Fort Stockton, Texas, showing land-use/land-cover data in 1973 

(left) and 2000 (right). Between 1973 and 2000, oil and gas exploration and production increased in Permian Basin, part of Chihuahuan Deserts Ecoregion. Sample blocks show conversion between 

1973 and 2000 of grassland/shrubland (yellow) to mining (black) 

associated with energy production; also shown are small areas of 

grassland/shrubland converting to agriculture (orange).

1973 2000
280 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 1. Percentage of Chihuahuan Deserts Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

[Most sample pixels remained unchanged (99.5 percent), whereas 0.5 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 0.4 0.2 0.2 0.6 0.1 29.8

2 0.0 0.0 0.0 0.1 0.0 45.9

3 0.0 0.0 0.0 0.0 0.0 85.3

4 0.0 0.0 0.0 0.0 0.0 99.1

Overall 

spatial 

change

0.5 0.2 0.2 0.7 0.2 32.1

Table 2. Raw estimates of change in Chihuahuan Deserts Ecoregion land cover, computed for each of 

four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.1 0.1 0.0 0.2 0.0 38.2 0.0

1980–1986 0.2 0.1 0.1 0.3 0.1 39.7 0.0

1986–1992 0.1 0.1 0.0 0.2 0.0 51.6 0.0

1992–2000 0.2 0.1 0.1 0.3 0.1 33.6 0.0

Estimate of change, in square kilometers

1973–1980 198 112 87 310 76 38.2 28

1980–1986 341 200 141 541 135 39.7 57

1986–1992 151 115 36 266 78 51.6 25

1992–2000 299 148 151 447 100 33.6 37
Chapter 27—Chihuahuan Deserts Ecoregion 281

Table 3. Estimated area (and margin of error) of each land-cover class in Chihuahuan Deserts Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.1 0.1 0.9 1.0 0.0 0.0 0.0 0.0 0.2 0.1 2.4 1.3 95.8 2.3 0.6 0.6 0.0 0.1 0.0 0.0

1980 0.1 0.1 0.9 1.0 0.0 0.0 0.1 0.0 0.2 0.1 2.4 1.3 95.7 2.3 0.6 0.6 0.0 0.0 0.0 0.0

1986 0.1 0.1 0.9 1.0 0.0 0.0 0.1 0.1 0.2 0.1 2.4 1.3 95.7 2.3 0.6 0.5 0.0 0.0 0.0 0.0

1992 0.1 0.1 1.0 1.0 0.0 0.0 0.1 0.1 0.2 0.1 2.4 1.3 95.7 2.3 0.6 0.5 0.0 0.0 0.0 0.0

2000 0.1 0.0 1.0 1.0 0.0 0.0 0.2 0.1 0.2 0.1 2.4 1.3 95.6 2.3 0.6 0.5 0.0 0.0 0.0 0.0

Net

change 0.0 0.0 0.1 0.1 0.0 0.0 0.1 0.1 0.0 0.0 0.0 0.0 −0.1 0.1 −0.1 0.1 0.0 0.0 0.0 0.0

Gross

change 0.1 0.2 0.1 0.1 0.0 0.0 0.1 0.1 0.0 0.0 0.0 0.0 0.3 0.1 0.1 0.1 0.1 0.1 0.0 0.0

Area, in square kilometers

1973 123 122 1,553 1,659 5 7 73 38 266 205 4,159 2,316 167,127 4,034 1,084 961 81 105 0 0

1980 160 175 1,581 1,675 22 26 124 65 271 205 4,139 2,298 167,043 4,050 1,107 969 25 26 0 0

1986 114 109 1,627 1,709 11 8 201 99 271 205 4,138 2,299 167,024 4,005 1,029 925 57 70 0 0

1992 153 163 1,692 1,746 5 7 227 104 271 205 4,131 2,299 166,941 4,022 1,032 926 18 19 0 0

2000 93 79 1,727 1,752 35 29 283 124 300 210 4,127 2,297 166,879 4,014 963 909 66 83 0 0

Net

change −30 46 174 116 30 28 210 98 34 49 −33 30 −249 151 −122 110 −15 22 0 0

Gross

change 189 264 174 116 77 61 218 102 34 49 36 31 512 168 188 155 175 256 0 0
282 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 4. Principal land-cover conversions in Chihuahuan Deserts Ecoregion, showing amount of area changed (and margin of 

error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Mining 51 34 23 0.0 25.8

Wetland Water 37 54 36 0.0 18.5

Grassland/Shrubland Developed 28 24 16 0.0 14.1

Grassland/Shrubland Agriculture 23 27 18 0.0 11.9

Wetland Grassland/Shrubland 20 29 20 0.0 10.0

Other Other 39 n/a n/a 0.0 19.7

Totals 198 0.1 100.0

1980–1986 Grassland/Shrubland Mining 85 47 32 0.0 24.9

Agriculture Grassland/Shrubland 85 89 61 0.0 24.8

Grassland/Shrubland Developed 63 61 42 0.0 18.4

Water Wetland 32 47 32 0.0 9.4

Developed Grassland/Shrubland 19 28 19 0.0 5.6

Other Other 57 n/a n/a 0.0 16.8

Totals 341 0.2 100.0

1986–1992 Grassland/Shrubland Developed 62 44 30 0.0 41.1

Wetland Water 41 59 40 0.0 27.0

Grassland/Shrubland Mining 27 18 12 0.0 18.1

Forest Grassland/Shrubland 7 11 7 0.0 4.8

Mechanically disturbed Developed 3 5 3 0.0 2.1

Other Other 10 n/a n/a 0.0 6.9

Totals 151 0.1 100.0

1992–2000 Agriculture Grassland/Shrubland 71 67 46 0.0 23.8

Grassland/Shrubland Mining 53 33 23 0.0 17.8

Water Wetland 48 70 48 0.0 16.1

Grassland/Shrubland Developed 34 23 16 0.0 11.3

Grassland/Shrubland Mechanically disturbed 29 28 19 0.0 9.8

Other Other 63 n/a n/a 0.0 21.2

Totals 299 0.2 100.0

1973–2000

(overall)

Grassland/Shrubland Mining 217 101 68 0.1 21.9

Grassland/Shrubland Developed 187 134 91 0.1 18.9

Agriculture Grassland/Shrubland 158 133 90 0.1 15.9

Water Wetland 82 120 81 0.0 8.3

Wetland Water 77 113 77 0.0 7.8

Other Other 269 n/a n/a 0.2 27.2

Totals 989 n/a n/a 0.6 100.0
Chapter 27—Chihuahuan Deserts Ecoregion 283

Table 5. Populations of largest cities in Chihuahuan Deserts Ecoregion 

that had both 1970 and 2000 census data. Cities of Socorro and San Elizario, 

Texas, and Sunland Park, New Mexico, had 2000 populations greater than 

10,000, but no 1970 census data was available (U.S. Census Bureau, 2000).

City State 1970

population

2000

population County Percent increase

El Paso TX 322,261 563,662 El Paso 74.91

Las Cruces NM 37,857 74,267 Dona Ana 96.18

Roswell NM 33,908 45,293 Chaves 33.58

Alamogordo NM 23,035 35,582 Otero 54.47

Del Rio TX 21,330 33,867 Val Verde 58.78

Carlsbad NM 21,297 25,625 Eddy 20.32

Deming NM 8,343 14,116 Luna 69.20

Artesia NM 10,315 10,692 Eddy 3.65

Silver City NM 8,557 10,545 Grant 23.23

Total 486,903 813,649

Total

increase: 67.11% Average increase: 48.26%

References Cited

Brown, D.E., 1994, Biotic communities—Southwestern 

United States and northwestern Mexico: Salt Lake City, 

University of Utah Press, 342 p.

Buffington, L., and Herbel, C., 1964, Vegetational changes 

on a semidesert grassland range from 1858 to 1963: U.S. 

Department of Agriculture, Jornada Experimental Range, 

accessed June 8, 2009, at http://usda-ars.nmsu.edu/biblio/

pdf/091.pdf.

Bureau of Economic Geology, 2005, Oil and gas production 

in Texas: Bureau of Economic Geology, The University of 

Texas at Austin, accessed April 3, 2009, at http://www.beg.

utexas.edu/UTopia/images/pagesizemaps/oilgas.pdf.

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Desert—Major plant communities: Chihuahuan Desert 

Research Institute, accessed October 30, 2006, at http://cdri.

org/desert-explorer/the-chihuahuan-desert-2/major-plantcommunities/.

Conservation History Association of Texas, 2009, The Texas 

Legacy Project—An archive and documentary series: 

Conservation History Association of Texas, accessed 

March 30, 2009, at http://www.texaslegacy.org/bb/regions/

transpecos.html.

Daly, C., Gibson, W., and Taylor, G., 2002, Development of a 

103-year high-resolution climate data set for the conterminous United States: Corvallis, Oregon State University, The 

PRISM Climate Group, accessed April, 4, 2009, at http://

www.prism.oregonstate.edu.

Gucker, C.L., 2006, Agave lechuguilla, in Fire effects information system: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, Fire Sciences Laboratory database, accessed March 24, 2009, at 

http://www.fs.fed.us/database/feis/plants/shrub/agalec/all.

html#INTRODUCTORY.

Hoyt, C.A., 2002, The Chihuahuan Desert: Diversity at Risk:

Endangered Species Bulletin, v. XXVII, no. 2, accessed 

November 2, 2006, at http://www.fws.gov/Endangered/

bulletin/2002/03-06/16-17.pdf. 

Lowe, C.H., 1964, The vertebrates of Arizona: Tucson, The 

University of Arizona Press.

McClaran, M.P., and Van Devender, T.R., 1995, The desert 

grassland: Tucson, The University of Arizona Press.

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database, accessed March 26, 2009, at http://science.nature.

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accessed April 3, 2009, at http://www.wrcc.dri.edu/nps/

reports/2007_04_24_chdninventory_final.pdf.

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2009, at http://ddl.nmsu.edu/chihuahua.html.
284 Status and Trends of Land Change in the Western United States—1973 to 2000

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

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Klett, T.R., Charpentier, R.R., and Cook, H.E., 2008, 

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United States and Mexico, 20-21 October 1983: Alpine, 

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and resource management plan amendment for McGregor 

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Chapter 28

Madrean Archipelago Ecoregion

species dispersal. Nevertheless, the geographic convergence of 

these two major continental mountain ranges, as well as of the 

Chihuahuan Desert to the east and the Sonoran Desert to the 

west, forms the foundation for ecological interactions found 

nowhere else on Earth (Skroch, 2008).

A rise in elevation, from approximately 600 m in the lowlands to over 3,000 m in the mountains (Mount Graham summit, 3,267 m), is accompanied by dramatic gradients in temperature and precipitation, coinciding with at least eight distinct life 

zones (Skroch, 2008). Lower, hot and dry plains support desert 

and semiarid grasslands vegetation. Woodlands of oak (Quercus 

spp.) and juniper (Juniperus spp.) grow on lower slopes. Colder 

and wetter climates at higher elevations support ponderosa pine 

(Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), and 

Engelmann spruce (Picea engelmannii) (figs. 2–4). 

Climate summaries for 10 urban areas in the lowlands 

indicate that they average annual minimum and maximum 

By Jana Ruhlman, Leila Gass, and Barry Middleton

Ecoregion Description

The Madrean Archipelago Ecoregion (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997), also known as 

the “Madrean Sky Islands” or “Sky Islands,” covers an area 

of approximately 40,536 km2 (15,651 mi2) in southeastern 

Arizona and southwestern New Mexico (fig. 1). The ecoregion is bounded on the west by the Sonoran Basin and Range 

Ecoregion, on the east by the Chihuahuan Deserts Ecoregion, 

and on the north by the Arizona/New Mexico Mountains 

Ecoregion. This area of basin-and-range topography is one 

of the most biologically diverse in the world (Koprowski, 

2005; Skroch, 2008). Although the mountains in the ecoregion 

bridge the Rocky Mountains to the north and the Sierra Madre 

Occidental in Mexico to the south (U.S. Environmental Protection Agency, 1997), the lower elevations act as a barrier to 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Madrean Archipelago Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be 

depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into 

mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 20 x 20 km sample blocks analyzed in 

study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are 

listed in appendix 2. See appendix 3 for definitions of land-use/land-cover classifications.

Arizona/New Mexico

Mountains

Sonoran

Basin

and

Range Chihuahuan

Deserts

ANMP

MEXICO

112° 111° 110° 109°

33°

34°

32°

31°

0 50 100 MLES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

NEW

MEXICO

COCHISE CO.

ARIZONA

MEXICO

Tucson

Douglas

Morenci

Sierra Vista

Pearce

Mount Graham

Mount 

Hopkins

Nogales

Sonoran

Desert

Chihuahuan Desert

San Simon Valley

Pinaleño Mtns.

Chiricahua Mtns.

Santa Rita Mtns.

Cave Creek Cyn

G i l a

R i v er
286 Status and Trends of Land Change in the Western United States—1973 to 2000

temperatures of 7.9oC and 25.7oC, respectively (Western 

Regional Climate Center, 2009). Lowe (1964) described 

decreases in temperature of 2.2oC and increases in precipitation of 100 to 125 mm for every 305 m gain in elevation.

Estimates from the Parameter-elevation Regressions on 

Independent Slopes Model (Daly and others, 2002) indicate 

that as much as 1,118 mm of annual precipitation is received 

on mountaintops (fig. 5). The ecoregion receives a biseasonal rainfall regime, with frontal precipitation in winter and 

convective thunderstorms in summer. The large elevation and 

precipitation gradients caused by topography, coupled with 

the north-south convergence of multiple floral and faunal 

realms, are both important geographic factors that contribute 

to the high biodiversity in the Madrean Archipelago Ecoregion 

(Coblentz and Riitters, 2005).

The Madrean Archipelago Ecoregion is sparsely populated. Sierra Vista, Arizona, is the largest city in the ecoregion, 

having a 2000 census population of 37,775. Nogales and Douglas, Arizona, are the next largest cities, having populations of 

20,878 and 14,312, respectively (U.S. Census Bureau, 2000). 

Farming and ranching are the principal industries of the ecoregion (fig. 6). Primary irrigated crops are corn, wheat, grain, 

alfalfa hay, and cotton (U.S. Department of Agriculture, 2004).

Contemporary Land-Cover Change 

(1973 to 2000)

As measured by the project methodology, the Madrean 

Archipelago Ecoregion experienced little land-cover change 

during the study period. An estimated 1.4 percent (575 km2) 

of the ecoregion converted to other land-cover classes during 

the study period (table 1). The relative error is high at 33.7 

percent, which is not unusual for an ecoregion with very little 

change. Compared to other western United States ecoregions, 

change in the Madrean Archipelago Ecoregion was low (figs. 

7,8). However, change in this ecoregion is consistent with that 

of other ecoregions in the southwestern United States.

Total estimated change in land cover per time period varied 

from a high of 0.5 percent between 1973 and 1980 and between 

1980 and 1986 to a low of 0.3 percent between 1992 and 2000 

(table 2). When the total change estimates were normalized to 

account for the varying lengths of the time periods between 

satellite imagery dates, the period between 1992 and 2000 had a 

near 0 percent rate of change per year, while the other three time 

periods had 0.1 percent change per year (table 2).

A closer look at the net-change estimates reveals that 

each time period experienced a net increase for the mining 

and developed classes, although the size of the gains varied 

between time periods (fig. 9). Grassland/shrubland was the 

predominant land cover of the ecoregion (estimated at 87.9 

percent in 2000), and this class experienced the greatest 

absolute amount of net change, with a net loss of 0.7 percent 

(271km2) during the study period (table 3). Analysis of this 

Figure 2. View southeast toward San Simon Valley from Mount 

Graham, in Pinaleño Mountains in Arizona, showing diverse 

topography of Madrean Archipelago Ecoregion.

Figure 3. Whipple Observatory (elevation 2,623 m) on Mount 

Hopkins, in Santa Rita Mountains, south of Tucson, Arizona. Land 

cover includes grassland, oak woodland, and montane forest.

Figure 4. Grassland park near Cave Creek Canyon, in Chiricahua 

Mountains, Arizona.
Chapter 28—Madrean Archipelago Ecoregion 287

Figure 5. Estimated average annual precipitation in Madrean Archipelago Ecoregion between 

1971 and 2000. Highest precipitation rates (shades of green, blue, purple) on mountaintops sustain 

evergreen woodlands and montane forests, whereas more arid lowland areas are covered in 

grassland and desert vegetation.

Figure 6. Harvested cotton field in Gila River valley, Arizona.

112° 111° 110° 109°

33°

32°

0 50 100 MILES

0 50 100 KILOMETERS

Explanation

Average annual precipitation, in inches

(1971–2000)

19.1–21.0

17.1–19.0

15.1–17.0

13.1–15.0

11.1–13.0

9.0–11.0

31.1–33.0

29.1–31.0

27.1–29.0

25.1–27.0

23.1–25.0

21.1–23.0

43.1–45.0

41.1–43.0

39.1–41.0

37.1–39.0

35.1–37.0

33.1–35.0
288 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 7. Overall spatial change in Madrean Archipelago 

Ecoregion (MA; darker bars) compared with that of all 30 Western 

United States ecoregions (lighter bars). Each horizontal set of 

bars shows proportions of ecoregion that changed during one, 

two, three, or four time periods; highest level of spatial change 

in Madrean Archipelago Ecoregion (three time periods) labeled 

for clarity. See table 2 for years covered by each time period. See 

appendix 2 for key to ecoregion abbreviations.

Figure 8. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Madrean Archipelago Ecoregion are 

represented by red bars in each time 

period.

Figure 9. Normalized average net change in Madrean Archipelago Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in three time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−1

−0.5

0

0.5

1

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
Chapter 28—Madrean Archipelago Ecoregion 289

class per time period shows net losses for the first three time 

periods but a slight gain between 1992 and 2000 (fig. 9). 

The second and third most common land-cover types in 

2000 were forest (5.3 percent) and agriculture (3.9 percent), 

followed by mining (1.1 percent). Although developed land 

was estimated at just 1.0 percent in 2000, it expanded 34 percent (98 km2

) over the course of the study; its increases were 

associated with small declines in grassland/shrubland. Overall, 

no statistically significant trends were observed during the 

study period.

The two most common conversions from 1973 to 2000 

were grassland/shrubland to mining and grassland/shrubland 

to agriculture (table 4). Grassland/shrubland to developed land 

was the third most common conversion in all time periods 

except between1986 and 1992, when it ranked fourth. The 

conversion of 65 km2 from grassland/shrubland to nonmechanically disturbed between 1986 and 1992 and its reversion 

back to grassland in the following period (1992–2000) was 

probably due to a fire event, followed by quick revegetation of 

the area.

This study’s analysis clearly indicates that the Madrean 

Archipelago Ecoregion experienced very little land-cover 

change between 1973 and 2000. Reasons for this stability are 

diverse, but the principal factor is probably the sparse population of the region. Other possible contributing factors include 

the high percentage of federal land in the ecoregion (approximately 48 percent), the scarcity of water, and the mountainous 

terrain, all of which inhibit large amounts of anthropogenic 

change. The lack of statistically significant trends and the high 

levels of uncertainty prohibit drawing clear-cut conclusions, 

but each time period experienced an increase in the developed 

and mining land-cover classes. The increase in developed land 

between 1973 and 2000 is shown on fig. 10.

The steady increase in developed land may be correlated to increased population in the Madrean Archipelago 

Ecoregion. U.S. Census Bureau (2000) figures show that 

the population of the three Arizona counties that form most 

of the Madrean Archipelago Ecoregion grew an average of 

122 percent between 1970 and 2000, an increase of 97,163 

persons. Population growth is predicted to continue, both 

in the currently populated areas and in the rural parts of the 

ecoregion (Carreira, 2005). In rural Cochise County alone, 

the population increased 11.5 percent between 2000 and 2010, 

from 117,755 persons in 2000 to 131,346 persons in 2010 

(U.S. Census Bureau, 2010), likely owing to its proximity to 

a major highway, railroads, and the United States–Mexico 

border, as well as its amenable climate, cultural history, growing golf-course communities, outdoor-recreation opportunities, 

and fertile agricultural lands (Cochise County, 2012).

 The land-cover transformation from grassland/shrubland 

to mining in all four time periods was primarily attributable 

to the observed growth of the massive open-pit copper mine 

at Morenci, Arizona, one of five major copper mines located 

within the ecoregion (Arizona Department of Mines and Mineral Resources, 2008). The gains in the developed and mining 

classes all came at the expense of the grassland/shrubland 

class, but the total converted area totaled only 271 km2 over 

entire the study period.

Figure 10. Sample block 79-6, centered over Pearce, Arizona, 

showing land-use/land-cover data in 1973 (left) and 2000 (right). 

Sample blocks show expansion of developed land (red) between 

1973 and 2000, especially in Sunsites, Arizona, which is a growing, 

unincorporated retirement and golf community in northern part of 

sample block. Also shown are areas of agricultural land (orange) 

that reverted back to grassland/shrubland (yellow).

1973 2000

Table 1. Percentage of Madrean Archipelago Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

[Most sample pixels remained unchanged (98.6 percent), whereas 1.4 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.2 0.7 0.4 1.9 0.5 39.9

2 0.2 0.2 0.0 0.5 0.1 61.9

3 0.0 0.0 0.0 0.0 0.0 63.3

4 0.0 0.0 0.0 0.0 0.0 0.0

Overall 

spatial 

change

1.4 0.8 0.7 2.2 0.5 33.7
290 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Madrean Archipelago Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically disturbed Mining Barren Forest Grassland/

Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.1 0.1 0.7 0.4 0.0 0.0 0.7 1.0 0.6 0.4 5.3 2.5 88.5 4.3 3.8 2.5 0.2 0.3 0.0 0.0

1980 0.1 0.1 0.8 0.4 0.0 0.0 0.9 1.3 0.6 0.4 5.3 2.5 88.4 4.4 3.7 2.5 0.2 0.3 0.0 0.0

1986 0.1 0.1 0.9 0.4 0.0 0.0 0.9 1.4 0.6 0.4 5.3 2.5 88.2 4.5 3.8 2.7 0.2 0.3 0.0 0.0

1992 0.1 0.1 0.9 0.4 0.0 0.0 1.0 1.5 0.6 0.4 5.3 2.5 87.9 4.4 3.8 2.7 0.2 0.3 0.2 0.2

2000 0.1 0.1 1.0 0.4 0.0 0.0 1.1 1.6 0.6 0.4 5.3 2.5 87.9 4.5 3.9 2.8 0.2 0.3 0.0 0.0

Net

change 0.0 0.0 0.2 0.1 0.0 0.0 0.4 0.6 0.0 0.0 0.0 0.0 −0.7 0.7 0.1 0.4 0.0 0.0 0.0 0.0

Gross

change 0.0 0.0 0.2 0.1 0.0 0.0 0.4 0.6 0.0 0.0 0.0 0.0 1.3 0.8 0.6 0.5 0.0 0.0 0.3 0.5

Area, in square kilometers

1973 41 41 298 155 6 9 289 417 259 178 2,154 1,015 35,891 1,744 1,528 1,033 70 104 0 0

1980 40 41 319 165 6 9 364 527 255 176 2,151 1,016 35,838 1,775 1,493 1,006 70 104 0 0

1986 38 41 357 164 6 9 381 554 258 177 2,151 1,016 35,735 1,814 1,541 1,098 70 104 0 0

1992 40 41 366 164 6 9 424 616 260 177 2,144 1,018 35,615 1,791 1,546 1,099 70 104 65 97

2000 40 41 387 169 6 9 443 644 256 176 2,146 1,018 35,620 1,837 1,569 1,121 70 104 0 0

Net

change −1 3 89 59 0 0 153 227 −2 6 −8 15 −271 269 41 157 0 0 0 0

Gross

change 6 6 90 60 1 1 158 226 19 16 18 13 538 309 230 198 0 0 129 194

Table 2. Raw estimates of change in Madrean Archipelago Ecoregion land cover, computed for each of 

four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.5 0.3 0.1 0.8 0.2 47.2 0.1

1980–1986 0.5 0.3 0.2 0.9 0.2 41.8 0.1

1986–1992 0.4 0.3 0.1 0.6 0.2 46.1 0.1

1992–2000 0.3 0.2 0.1 0.6 0.1 45.4 0.0

Estimate of change, in square kilometers

1973–1980 185 137 47 322 87 47.2 26

1980–1986 210 138 72 348 88 41.8 35

1986–1992 145 105 40 251 67 46.1 24

1992–2000 132 95 38 227 60 45.4 17
Chapter 28—Madrean Archipelago Ecoregion 291

Table 4. Principal land-cover conversions in Madrean Archipelago Ecoregion, showing amount of area changed (and margin 

of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Mining 73 108 69 0.2 39.6

Agriculture Grassland/Shrubland 59 59 38 0.1 32.0

Grassland/Shrubland Developed 21 23 14 0.1 11.1

Grassland/Shrubland Agriculture 19 16 10 0.0 10.4

Barren Agriculture 4 7 4 0.0 2.4

Other Other 8 n/a n/a 0.0 4.5

Totals 185 0.5 100.0

1980–1986 Grassland/Shrubland Agriculture 92 137 87 0.2 43.8

Agriculture Grassland/Shrubland 37 42 27 0.1 17.8

Grassland/Shrubland Developed 34 32 20 0.1 16.0

Grassland/Shrubland Mining 24 34 21 0.1 11.6

Mining Grassland/Shrubland 8 9 6 0.0 4.1

Other Other 14 n/a n/a 0.0 6.8

Totals 210 0.5 100.0

1986–1992 Grassland/Shrubland Nonmechanically disturbed 65 97 61 0.2 44.6

Grassland/Shrubland Mining 39 56 36 0.1 27.1

Grassland/Shrubland Agriculture 10 10 6 0.0 6.9

Grassland/Shrubland Developed 6 7 4 0.0 4.4

Grassland/Shrubland Barren 5 7 4 0.0 3.1

Other Other 20 n/a n/a 0.0 13.9

Totals 145 0.4 100.0

1992–2000 Nonmechanically disturbed Grassland/Shrubland 65 97 61 0.2 48.9

Grassland/Shrubland Agriculture 23 27 17 0.1 17.4

Grassland/Shrubland Developed 21 13 8 0.1 15.6

Grassland/Shrubland Mining 19 28 18 0.0 14.1

Barren Grassland/Shrubland 3 5 3 0.0 2.5

Other Other 2 n/a n/a 0.0 1.5

Totals 132 0.3 100.0

1973–2000

(overall)

Grassland/Shrubland Mining 155 226 144 0.4 23.1

Grassland/Shrubland Agriculture 144 177 112 0.4 21.4

Agriculture Grassland/Shrubland 100 92 59 0.2 15.0

Grassland/Shrubland Developed 81 56 36 0.2 12.1

Grassland/Shrubland Nonmechanically disturbed 65 97 61 0.2 9.6

Other Other 126 n/a n/a 0.3 18.8

Totals 672 1.7 100.0
292 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Arizona Department of Mines and Mineral Resources, 2008, 

Arizona major mines: Arizona Department of Mines and 

Mineral Resources, accessed July 29, 2008, at http://mines.

az.gov/Info/MajorMines08.pdf.

Carreira, R., 2005, Populations projected to 2015 for Cochise, 

Santa Cruz counties, in The Indicator: Cochise College, 

Center for Economic Research, v. 8, no. 2, accessed July 30, 

2008, at http://www.cochise.edu/deptsdirs/organizations/

cer/documents/indicator/IndicatorSpring05.pdf.

Coblentz, David, and Riitters, K.H., 2005, A quantitative topographic analysis of the Sky Islands—A closer examination 

of the topography-biodiversity relationship in the Madrean 

Archipelago, in Gottfried, G.J., and others, comps., Connecting mountain islands and desert seas—Biodiversity 

and management of the Madrean Archipelago II: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station, Proceedings RMRS-P-36, p. 69–74, 

accessed July 29, 2008, at http://www.treesearch.fs.fed.us/

pubs/23173.

Cochise County, 2012, Economic Development: Cochise 

County, Arizona, accessed March 22, 2012, at http://cochise.

az.gov/cochise_economic_development.aspx?id=1584. 

Daly, C., Gibson, W., and Taylor, G., 2002, Development of a 

103-year high-resolution climate data set for the conterminous United States: Corvallis, Oregon State University, The 

PRISM Climate Group, accessed July, 22, 2008, at http://

www.prism.oregonstate.edu. 

Koprowski, J.L., Edelman, A.J., Pasch, B.S., and Buecher,

D.C., 2005, A dearth of data on the mammals of the 

Madrean Archipelago—What we think we know and 

what we actually do know, in Gottfried, G.J., and others, 

comps., Connecting mountain islands and desert seas—

Biodiversity and management of the Madrean Archipelago 

II: U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Proceedings RMRS-P-36, 

p. 412–415, available at http://www.treesearch.fs.fed.us/

pubs/21519.

Lowe, C.H., 1964, Vertebrates of Arizona: Tucson, The University of Arizona Press, p. 10, 85.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Skroch, M., 2008, Sky Islands of North America—A globally 

unique and threatened inland archipelago: Terrain.org, A 

Journal of the Built & Natural Environments, Winter/Spring 

Issue, no. 21, Islands & Archipelagos, p. 147–152. (Available at http://www.terrain.org/articles/21/skroch.htm.)

U.S. Census Bureau, 2000, State & county quickfacts: U.S. 

Census Bureau database, accessed July 29, 2008, at http://

quickfacts.census.gov/qfd/states/.

U.S. Census Bureau, 2010, State & county quickfacts: U.S. 

Census Bureau database, accessed March 22, 2012, at http://

quickfacts.census.gov/qfd/states/04/04003.html.

U.S. Department of Agriculture, 2004, 2002 census of agriculture, Arizona state and county data: U.S. Department 

of Agriculture, National Agricultural Statistics Service, 

Geographic Area Series, v. 1, pt. 3, AC-02-A-3, p. 204–207, 

accessed July 22, 2008, at http://www.agcensus.usda.gov/

Publications/2002/Volume_1,_Chapter_2_County_Level/

Arizona/st04_2_001_001.pdf.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.

Western Regional Climate Center, 2009, SOD USA climate 

archive: Desert Research Institute, Western Regional Climate Center, accessed July 22, 2008, at http://www.wrcc.

dri.edu/summary/.
Chapter 29

Mojave Basin and Range Ecoregion

includes the Mojave Desert and much of the other desert 

areas in southeastern California, as well as a large part of the 

southern Nevada desert (fig. 1). The ecoregion is bounded on 

the north by the Central Basin and Range Ecoregion, on the 

east by the Colorado Plateaus and the Arizona/New Mexico 

Plateau Ecoregions, on the south by the Sonoran Basin and 

Range Ecoregion, and on the west by the Southern California 

Mountains and the Sierra Nevada Ecoregions.

By Benjamin M. Sleeter and Christian G. Raumann

This chapter has been modified from original material 

published in Sleeter and Raumann (2006), entitled “Land-cover 

trends in the Mojave Basin and Range Ecoregion” (U.S. Geological Survey Scientific Investigations Report 2006–5098).

Ecoregion Description

The Mojave Basin and Range Ecoregion (Omernik, 1987; 

U.S. Environmental Protection Agency, 1997) covers approximately 130,922 km2

 (50,549 mi2) in the southwestern United 

States. The ecoregion, which encompasses parts of four states, 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Mojave Basin and Range Ecoregion and surrounding ecoregions, showing land-use/land-cover classes from 1992 

National Land Cover Dataset (Vogelmann and others, 2001); note that not all land-use/land-cover classes shown in explanation may be 

depicted on map; note also that, for this “Status and Trends of Land Change” study, transitional land-cover class was subdivided into 

mechanically disturbed and nonmechanically disturbed classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in 

study. Index map shows locations of geographic features mentioned in text. Abbreviations for Western United States ecoregions are 

listed in appendix 2. See appendix 3 for definitions of land-use/land-cover classifications.

Central

Basin and Range

Sonoran Basin and Range

Sierra

Nevada

Arizona/

New Mexico

Plateau

CCV

SCCCOW

SCCCOW

SCM

Colorado

Plateaus

ANMM

PACIFIC

OCEAN

118° 116° 114°

36°

38°

34°

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

EXPLANATION

ARIZONA

CALIFORNIA

NEVADA

UTAH

Las Vegas

Los Angeles

Palmdale

Henderson

Searchlight

Victorville

Lancaster

Fort Irwin

Mojave

Desert

Color ado River

Mojav e River

Lake

Mead

Red Lake playa

DEATH VALLEY NP

LAKE 

MEAD

NRA

MOJAVE

NATIONAL

PRESERVE

JOSHUA TREE NP

Clark Co.

San Bernardino Co.
294 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 2. Federal land ownership and cumulative land-use/land-cover change (as percent of sample-block area) from 1973 

to 2000 in Mojave Basin and Range Ecoregion. Land-ownership data from National Atlas of the United States (2006). See 

appendix 2 for abbreviations for Western United States ecoregions.

114°

113°

119° 118° 117° 116° 115°

37°

38°

36°

35°

34°

Central

Basin and Range

SBR

Sierra

Nevada

Arizona/

New Mexico

Plateau

CCV SCCCOW

SCCCOW

SCCCOW

SCM

SCM

Colorado

Plateaus

ANMM

PACIFIC

 OCEAN

0 50 100 MILES

0 50 100 KILOMETERS

Mojave Basin and 

Range Ecoregion

Other ecoregion

State boundary

Federal land-ownership class Overall spatial change

(per 10 x 10 km sample block)

Boundaries

Wilderness Area

National Forest

National Monument or Park

Military land

Tribal lands

Other Federal lands

Other lands

EXPLANATION

0.0–1.0

1.1–3.0

3.1–10.0

10.1–20.0

20.1–30.3
Chapter 29—Mojave Basin and Range Ecoregion 295

The Mojave Basin and Range Ecoregion is characterized 

by distinct fault-bounded mountain ranges that typically run 

northeast to southwest. The ecoregion receives very little annual 

precipitation (50–250 mm in the valleys), which, when combined with high temperatures during summer months, results in 

an ecoregion slow to recover from anthropogenic disturbances 

(Hunter and others, 2003). Federal lands constitute approximately 81 percent of the total land area (fig. 2), with major holdings under the jurisdiction of the Bureau of Land Management, 

National Park Service, and Department of Defense. Grasslands 

and shrublands dominate the ecoregion, whereas developed 

land accounts for only 1.5 percent of total land area (Vogelmann 

and others, 2001). Although developed land is limited, the two 

major urban areas found in the ecoregion are among the fastest growing locales in the western United States. Las Vegas, 

Nevada, is the major urban center within the ecoregion (fig. 3), 

although the cities of Palmdale and Lancaster, California, also 

had significant growth between 1973 and 2000. 

The Mojave Basin and Range Ecoregion has long supported human activities such as livestock grazing, mining, 

military training, and recreation, all of which have had some 

effect on the desert landscape (Lovich and Bainbridge, 1999). 

Agriculture, although not extensive, takes place along the 

Colorado and Mojave Rivers. Mining, which historically has 

been an important land-use activity, is found throughout the 

ecoregion wherever mineral resources are available (fig. 4). 

Recreation activities have become increasingly important in 

the ecoregion, with millions of people each year visiting Death 

Valley National Park, Mojave National Preserve, and Lake 

Mead National Recreation Area, as well as numerous openaccess Bureau of Land Management lands (fig. 5).

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change (that is, the percentage of 

area that changed at least one time between 1973 and 2000) 

in the Mojave Basin and Range Ecoregion is estimated at 2.7 

Figure 3. Construction of new hotel, resort, and lake (Lake Las 

Vegas) outside of Henderson, Nevada.

Figure 4. Abandoned mine shaft outside Searchlight, Nevada.

Figure 5. Staging and camping area for off-highway-vehicle 

users near Red Lake playa, Arizona, located about 30 km southeast of Lake Mead.

percent (3,474 km2), which is low when compared to other 

western United States ecoregions (fig. 6). The ecoregion also 

showed low rates of change across all time periods when 

compared to other western United States ecoregions (fig. 7). 

The period between 1986 and 1992 had the highest estimated 

rate of change, at 1.3 percent. In addition, when change 

estimates are normalized to account for the varying lengths 

of the time periods, change remained highest between 1986 

and 1992, at 0.2 percent per year, whereas the other three 

time periods (1973–1980, 1980–1986, and 1992–2000) are 

estimated at 0.07 to 0.08 percent per year (table 2). 

The largest change in any one land-cover class was the 

estimated loss of 2,387 km2

 of grassland/shrubland, a 2.0 
296 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 6. Overall spatial change in Mojave Basin and Range 

Ecoregion (MBR; darker bars) compared with that of all 30 

Western United States ecoregions (lighter bars). Each horizontal 

set of bars shows proportions of ecoregion that changed during 

one, two, three, or four time periods; highest level of spatial 

change in Mojave Basin and Range Ecoregion (three time periods) 

labeled for clarity. See table 2 for years covered by each time 

period. See appendix 2 for key to ecoregion abbreviations. 

percent decline. In 1973, grassland/shrubland is estimated to 

account for 89.2 percent of the ecoregion. In 2000, grassland/shrubland accounted for 87.4 percent of the ecoregion. 

The second largest change was the addition of 1,673 km2

of developed land, which increased from 1.5 percent of the 

ecoregion in 1973 to 2.8 percent of the ecoregion in 2000. 

Estimates of land-cover composition for all classes for each 

time period can be found in table 3. Normalized net change 

values for all classes for each time period can be found in 

figure 8. 

The dominant land-cover change that occurred in 

the Mojave Basin and Range Ecoregion was the conversion of grassland/shrubland to developed land. An estimated 1,426 km2

 of grassland/shrubland were converted to 

developed land between 1973 and 2000, with 52.7 percent 

(751 km2) converting between 1986 and 1992. Grassland/

shrubland converting to mechanically disturbed and mining, 

forest converting to mechanically disturbed, and mechanically disturbed converting to developed were the other top 

land-cover conversions between 1973 and 2000 (table 4). 

Combined, these conversions account for an estimated 78.5 

percent of all changes in the ecoregion.

Population growth in the Mojave Basin and Range 

Ecoregion, much of it spillover from the Los Angeles, 

California, metropolitan area, was the primary driver of 

change in the ecoregion. In three of the four time periods 

(1973–1980, 1980–1986, and 1986–1992), grassland/shrubland converting directly to developed land was the most 

common conversion and, between 1992 and 2000, the second 

most common conversion. New developed land was added 

to the ecoregion at an average rate of 62 km2 per year, an 

estimated total of 1,680 km2 over the 27-year study period. 

Development was not dispersed evenly across the ecoregion. 

On the basis of field observations, increases in developed 

land appeared to be concentrated in two main regions, the 

Las Vegas, Nevada, metropolitan area and the cities of Victorville, Lancaster, and Palmdale, California, in the western 

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in three

time periods

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

Figure 7. Estimates of land-cover 

change per time period, normalized 

to annual rates of change for all 30 

Western United States ecoregions 

(gray bars). Estimates of change for 

Mojave Basin and Range Ecoregion 

are represented by red bars in each 

time period.
Chapter 29—Mojave Basin and Range Ecoregion 297

Figure 8. Normalized average net change in Mojave Basin and 

Range Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

Mojave Desert; Las Vegas is one of the fastest growing cities 

in the United States, whereas Palmdale and Lancaster both 

have populations larger than 100,000 (U.S. Census Bureau, 

2001). Population statistics show that Clark County, Nevada, 

added more than 1.3 million residents between 1970 and 

2000, whereas San Bernardino County, California, has added 

more than 1.175 million people during the same time period 

(fig. 9) (U.S. Census Bureau, 2001). Figure 10 shows landuse/land-cover data for a sample site near Palmdale, California, which has experienced rapid urbanization. 

Land ownership is another driving force of land-cover 

change. As previously noted, the Federal Government owns 

a large percentage of land within the ecoregion, the largest landholder being the Bureau of Land Management, and 

each federal agency manages public lands to meet distinct 

goals and objectives. For instance, Bureau of Land Management lands are often open for public use and recreation 

such as off-highway-vehicle (OHV) activities (Lovich and 

Bainbridge, 1999). In most cases, OHV disturbances such as 

single vehicle tracks were not detected in image interpretations because of the coarse size of the minimum mapping 

unit (60m) and are, therefore, not described by the change 

estimates. However, image interpretations did identify several OHV staging areas where relatively large areas of grassland/shrubland have been gradually stripped of vegetation. 

Continued use of these areas has resulted in soil compaction, 

which has prevented the reestablishment of vegetation. The 

growth of OHV activity in the ecoregion can be attributed 

largely to the open-access policy of the Bureau of Land Management lands, as well as the close proximity of these lands 

to major urban areas (Sheridan, 1979).

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS

523,364

210,994

441,298

189,799

278,372

835,082

Year

Number of persons added per year

0

200,000

400,000

600,000

800,000

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Inyo County, California

San Bernardino County, California

Clark County, Nevada

Esmeralda County, Nevada

“Status and Trends of Land Change”

study period (1973–2000)

Figure 9. Population trends between 1910 and 2000 of selected counties in Mojave Basin 

and Range Ecoregion. Numbers of persons added to each county are from U.S. Census 

data at 10-year intervals (U.S. Census Bureau, 2001). San Bernardino County, California, and 

Clark County, Nevada, have experienced highest growth of any counties in ecoregion, each 

adding more than 175,000 persons in each decade since 1980.
298 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 10. Data for sample block 14-1009, located near Palmdale, California, illustrating urbanization taking place in Mojave Basin and 

Range Ecoregion. Left column is satellite imagery collected for each of five years analyzed in study, used to map land-use/land-cover 

change in four time periods between study years (imagery sources for study years: 1973, 1980, and 1986 are Landsat Multispectral 

Scanner (MSS) images; 1992 is Landsat Thematic Mapper (TM) image; 2000 is Landsat Enhanced Thematic Mapper (ETM) image). 

Center column is mapped land-use/land-cover data for each study year. Right column shows areas that changed (green areas) in each 

of four time periods between study years; light- and dark-gray-shaded areas do not change between study years but, rather, represent 

overall land-use/land-cover footprint throughout study period.

1973–1980

1980–1986

1986–1992

1992–2000

Agriculture

Grassland/Shrubland

Mining

Mechanically disturbed

Developed

Land-use/land-cover class

1973

Landsat images Mapped land-use/land-cover Areas of change

1980

1986

1992

2000
Chapter 29—Mojave Basin and Range Ecoregion 299

for desert soils and vegetation to recover once exposed to 

these intensive land-use practices (Prose and Wilshire, 2000; 

Steiger and Webb, 2000). This phenomenon was observe. in 

the eastern part of Fort Irwin, which was heavily used for 

tracked- and wheeled-vehicle operations training (fig. 11). 

Evidence of this destruction includes compacted and rutted 

soils, low shrub density, and stunted growth of creosote bush 

(Larrea tridentata) and other vegetation.

Unlike the Bureau of Land Management and Department of Defense, the National Park Service attempts to 

preserve natural desert lands while promoting low-impact 

public recreation such as camping, hiking, and sightseeing. The largest holding of the National Park Service within 

the ecoregion is Death Valley National Park (12,759 km2). 

Other National Park Service areas include Mojave National 

Preserve and Joshua Tree National Park. With the exception 

of small, tourism-supported development such as visitor centers, boardwalks, campgrounds, hiking trails, and 

unimproved roads, no land-cover changes were detected on 

National Park Service lands, further illustrating the significant role that land-ownership and -management goals play 

in regards to the spatial distribution of contemporary landcover change.

Results show that change between land-cover classes 

in the Mojave Basin and Range Ecoregion is relatively rare 

and highly localized. Urbanization is the primary source of 

change, although other human-use activities such as military 

training and recreation are significant contributors to change 

within the ecoregion.

Figure 11. Mechanical disturbance (vehicle tracks) observed 

at Fort Irwin National Training Center, California, site of intensive 

military training that includes live-fire exercises.

The Department of Defense has a substantially different 

mandate pertaining to its land ownership and management 

policies. The Department of Defense manages vast areas 

of the ecoregion (fig. 2) for conducting military training 

activities. The largest of the facilities that lie entirely within 

the ecoregion is Fort Irwin National Training Center, California (2,369 km2

), which is used for desert-warfare training that includes live-fire exercises. Tracked and wheeled 

vehicles, which operate throughout the facility, can have 

a major impact on the health and composition of desert 

flora and fauna (Prose and Wilshire, 2000). Recent studies 

have estimated that several hundred years will be needed 

Table 1. Percentage of Mojave Basin and Range Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

[Most sample pixels remained unchanged (97.3 percent), whereas 2.7 percent 

changed at least once throughout study period. Two dashes (--) indicate that, 

because zero pixels changed four times during study period, relative error is 

not calculable] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 2.4 1.3 1.1 3.8 0.9 37.0

2 0.2 0.1 0.1 0.3 0.1 45.9

3 0.0 0.0 0.0 0.0 0.0 98.5

4 0.0 0.0 0.0 0.0 0.0 --

Overall 

spatial 

change

2.7 1.4 1.2 4.1 1.0 36.5
300 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 2. Raw estimates of change in Mojave Basin and Range Ecoregion land cover, computed for each 

of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 0.5 0.3 0.2 0.8 0.2 37.0 0.1

1980–1986 0.5 0.2 0.2 0.7 0.2 36.4 0.1

1986–1992 1.3 0.9 0.3 2.2 0.6 50.6 0.2

1992–2000 0.6 0.5 0.2 1.1 0.3 50.5 0.1

Estimate of change, in square kilometers

1973–1980 675 366 308 1,041 250 37.0 96

1980–1986 605 323 282 928 220 36.4 101

1986–1992 1,660 1,232 428 2,892 839 50.6 277

1992–2000 841 624 217 1,466 425 50.5 105

Table 3. Estimated area (and margin of error) of each land-cover class in Mojave Basin and Range Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.9 0.9 1.5 0.9 0.1 0.1 1.1 1.2 4.7 3.9 2.0 1.6 89.2 4.6 0.2 0.2 0.3 0.3 0.0 0.0

1980 0.9 0.9 1.8 1.0 0.1 0.1 1.1 1.2 4.7 3.9 2.0 1.6 88.9 4.6 0.2 0.2 0.2 0.3 0.0 0.0

1986 0.9 0.9 2.0 1.0 0.2 0.1 1.3 1.3 4.7 3.9 1.9 1.6 88.6 4.6 0.2 0.2 0.2 0.3 0.0 0.0

1992 0.8 0.9 2.6 1.4 0.5 0.4 1.4 1.4 4.7 3.9 1.9 1.6 87.5 4.7 0.2 0.2 0.3 0.4 0.1 0.1

2000 0.9 0.9 2.8 1.5 0.7 0.6 1.4 1.4 4.7 3.9 1.7 1.5 87.4 4.7 0.2 0.2 0.3 0.4 0.0 0.0

Net

change 0.0 0.1 1.3 1.0 0.6 0.6 0.3 0.2 −0.1 0.1 −0.3 0.4 −1.8 1.3 0.0 0.0 0.0 0.0 0.0 0.0

Gross

change 0.2 0.2 1.3 1.0 0.8 0.6 0.3 0.2 0.1 0.1 0.3 0.4 2.0 1.3 0.1 0.1 0.1 0.2 0.1 0.2

Area, in square kilometers

1973 1,164 1,183 1,958 1,184 152 104 1,394 1,604 6,196 5,097 2,581 2,119 116,844 5,984 303 270 331 419 0 0

1980 1,198 1,209 2,349 1,263 124 96 1,482 1,627 6,196 5,096 2,570 2,113 116,430 6,001 277 243 296 370 0 0

1986 1,198 1,209 2,594 1,303 216 185 1,638 1,707 6,153 5,094 2,522 2,097 116,013 5,991 293 250 296 370 0 0

1992 1,108 1,123 3,386 1,784 609 587 1,776 1,777 6,123 5,093 2,520 2,106 114,622 6,096 287 250 408 530 82 118

2000 1,139 1,140 3,638 1,908 925 790 1,813 1,783 6,123 5,093 2,189 1,903 114,457 6,150 270 228 369 474 0 0

Net

change −25 106 1,680 1,329 773 745 418 281 −73 110 −392 493 −2,387 1,646 −33 50 38 55 0 0

Gross

change 224 274 1,680 1,329 1,073 785 422 281 93 109 417 528 2,611 1,649 73 67 185 267 163 236
Chapter 29—Mojave Basin and Range Ecoregion 301

Table 4. Principal land-cover conversions in Mojave Basin and Range Ecoregion, showing amount of area changed (and margin 

of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during overall 

study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin of 

error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Developed 314 241 164 0.2 46.5

Grassland/Shrubland Mining 90 94 64 0.1 13.3

Mechanically disturbed Developed 52 56 38 0.0 7.7

Wetland Water 34 50 34 0.0 5.1

Barren Grassland/Shrubland 34 49 34 0.0 5.0

Other Other 151 n/a n/a 0.1 22.4

Totals 675 0.5 100.0

1980–1986 Grassland/Shrubland Developed 202 192 131 0.2 33.3

Grassland/Shrubland Mechanically disturbed 115 132 90 0.1 19.0

Grassland/Shrubland Mining 110 103 70 0.1 18.1

Barren Mining 49 70 48 0.0 8.0

Mechanically disturbed Developed 38 35 24 0.0 6.2

Other Other 92 n/a n/a 0.1 15.3

Totals 605 0.5 100.0

1986–1992 Grassland/Shrubland Developed 751 851 580 0.6 45.2

Grassland/Shrubland Mechanically disturbed 435 421 287 0.3 26.2

Water Wetland 125 180 123 0.1 7.5

Grassland/Shrubland Mining 110 97 66 0.1 6.6

Grassland/Shrubland Nonmechanically disturbed 82 118 80 0.1 4.9

Other Other 158 n/a n/a 0.1 9.5

Totals 1,660 1.3 100.0

1992–2000 Forest Mechanically disturbed 324 467 318 0.2 38.5

Grassland/Shrubland Developed 160 183 124 0.1 19.1

Mechanically disturbed Developed 89 80 54 0.1 10.5

Nonmechanically disturbed Grassland/Shrubland 82 118 80 0.1 9.7

Grassland/Shrubland Mechanically disturbed 77 58 40 0.1 9.1

Other Other 110 n/a n/a 0.1 13.1

Totals 841 0.6 100.0

1973–2000

(overall)

Grassland/Shrubland Developed 1,426 1,191 811 1.1 37.7

Grassland/Shrubland Mechanically disturbed 651 591 403 0.5 17.2

Grassland/Shrubland Mining 345 245 167 0.3 9.1

Forest Mechanically disturbed 340 488 332 0.3 9.0

Mechanically disturbed Developed 205 138 94 0.2 5.4

Other Other 814 n/a n/a 0.6 21.5

Totals 3,781 2.9 100.0
302 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Hunter, L.M., Gonzalez, M. de J., Stevenson, M., Karish, 

K.S., Toth, R., Edwards, T.C., Lilieholm, R.J., and Cablk, 

M., 2003, Population and land use change in the California 

Mojave; natural habitat implications of alternative futures: 

Population Research and Policy Review, v. 22, p. 373–379.

Lovich, J.E., and Bainbridge, D., 1999, Anthropogenic degradation of the southern California desert ecosystem and 

prospects for natural recovery and restoration: Environmental Management, v. 24, p. 309–326.

National Atlas of the United States, 2006, Federal Lands of the 

United States: National Atlas of the United States database, 

accessed February 19, 2006, at http://nationalatlas.gov.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Prose, D.V., and Wilshire, H.G., 2000, The lasting effects 

of tank maneuvers on desert soils and intershrub flora: 

U.S. Geological Survey Open-File Report 00–512, 22 p., 

accessed at http://geopubs.wr.usgs.gov/open-file/of00-512/.

Sheridan, D., 1979, Off-road vehicles on public land: Council 

on Environmental Quality, 84 p.

Sleeter, B.M., and Raumann, C.G., 2006, Land-cover trends 

in the Mojave Basin and Range Ecoregion: U.S. Geological 

Survey Scientific Investigations Report 2006–5098, 18 p., 

accessed at http://pubs.usgs.gov/sir/2006/5098/.

Steiger, J.W., and Webb, R.H, 2000, Recovery of perennial 

vegetation in the military target sites in the eastern Mojave 

Desert, Arizona: U.S. Geological Survey Open-File Report 

00–355, 28 p., accessed at http://geopubs.wr.usgs.gov/openfile/of00-355/.

U.S. Census Bureau, 2001, American Fact Finder: U.S. Census 

Bureau database, accessed May 1, 2005, at http://factfinder.

census.gov/home/saff/main.html?_lang=en.

U.S. Environmental Protection Agency, 1997, Descriptions of 

level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection 

Agency database, accessed April 12, 2006, at http://www.

epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
Chapter 30

Sonoran Basin and Range Ecoregion

Plateaus, and the Arizona/New Mexico Mountains Ecoregions; 

and on the east by the Madrean Archipelago Ecoregion (fig.1). 

The Sonoran Basin and Range Ecoregion extends far southward 

into both mainland Mexico and northeastern Baja California 

peninsula; however, those international parts were not included 

in the present study. The largest concentrations of population in 

the ecoregion include the Palm Springs–Coachella Valley area 

(population 332,485 in 2000) in California’s Riverside County, 

as well as the Phoenix and Tucson metropolitan areas (metropolitan populations of approximately 4.2 million and 1 million, 

respectively) in Arizona (U.S. Census Bureau, 2011). 

By James P. Calzia and Tamara S. Wilson

Ecoregion Description

The Sonoran Basin and Range Ecoregion covers 

approximately 116,364 km2 (44,928 mi2) of desert landscape 

in southeastern California and southwestern Arizona (fig.1) 

(Omernik, 1987; U.S. Environmental Protection Agency, 

1997). This ecoregion is bounded on the west by the Southern 

and Central California Chaparral and Oak Woodlands and 

the Southern California Mountains Ecoregions; on the north 

by the Mojave Basin and Range, the Arizona/New Mexico 

Status and Trends of Land Change in the Western United States—1973 to 2000

Edited by Benjamin M. Sleeter, Tamara S. Wilson, and William Acevedo 

U.S. Geological Survey Professional Paper 1794–A, 2012

Figure 1. Map of Sonoran Basin and Range Ecoregion and surrounding 

ecoregions, showing land-use/land-cover classes from 1992 National Land 

Cover Dataset (Vogelmann and others, 2001); note that not all land-use/landcover classes shown in explanation may be depicted on map; note also that, 

for this “Status and Trends of Land Change” study, transitional land-cover class 

was subdivided into mechanically disturbed and nonmechanically disturbed 

classes. Squares indicate locations of 10 x 10 km sample blocks analyzed in 

study. Index map shows locations of geographic features mentioned in text. 

Abbreviations for Western United States ecoregions are listed in appendix 2. 

See appendix 3 for definitions of land-use/land-cover classifications. 

115° 114° 113° 112° 111°

110°

117° 116°

34° 35°

33°

32°

31°

Mojave Basin and Range

Madrean

Archipelago

Arizona/

New Mexico Mountains

Arizona/

New Mexico

Plateau

ANMP

SCCCOW

CCV

SCM

GULF of

CALIFORNIA

MEXICO

0 50 100 MILES

0 50 100 KILOMETERS

Ecoregion boundary

Sample block (10 x 10 km)

Land-use/land-cover class

Water

Developed

Transitional

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

EXPLANATION

ARIZONA

MEXICO

CALIFORNIA

Tucson

Palm

Springs

Phoenix

Sonoran

Desert

Salton Trough

Gila River

Salt River

Colora do

River

Salton

 Sea

BAJA

CALIFORNIA Gulf of

California

Coachella

Valley

RIVERSIDE

CO.
304 Status and Trends of Land Change in the Western United States—1973 to 2000

The geography of the Sonoran Basin and Range Ecoregion is characterized by discontinuous mountain ranges separated by wide alluvial plains. The mountains are composed 

of igneous, sedimentary, and metamorphic rocks that vary in 

age from Precambrian to Tertiary (Jennings, 1977; Arizona 

Geological Survey and Bureau of Land Management, 1993). 

Elevations range from 20 to 1,830 m. The largest rivers 

include the Colorado River along the boundary between 

California and Arizona, as well as the Gila and Salt Rivers 

in Arizona. The Salton Sea at the northern end of the Salton 

Trough is located near the ecoregion’s western border.

The Sonoran Basin and Range Ecoregion is characterized by a warm, arid climate. During winter months, daytime 

temperatures can average 21°C, and overnight temperatures 

can drop to below freezing in some low-lying desert valleys 

(Climate Assessment for the Southwest, 2010). In summer 

months, temperatures often climb above 38°C during the 

day. Daily temperature variation can exceed 15°C (Climate 

Assessment for the Southwest, 2010). Annual precipitation 

varies from 7.5 to 43 cm, with slightly more rainfall at higher 

elevations (Arizona Fish and Game Department, 2006; 

McGinnies, 1976) and a gradient of increasing precipitation 

from west to east. The western Sonoran Desert receives most 

of its precipitation in winter, whereas summer precipitation totals farther east are greater because of the influence 

of monsoon rains fed by higher temperatures and moisture 

pumped in from the Gulf of California and the Gulf of 

Mexico (Comrie and Glenn, 1998). 

The bimodal precipitation pattern contributes to the 

surprisingly diverse range of vegetation within the Sonoran 

Basin and Range Ecoregion. More than 2,500 species, 

including both annual and perennial trees and shrubs, as well 

as succulents and cacti (Turner and others, 1995), are found 

here. Vast expanses of cholla (Opuntia spp.) cactus in California are joined by the giant saguaro (Carnegia gigantea) 

cactus in Arizona. The saguaro is cold-intolerant and highly 

susceptible to winter freeze mortality; it cannot survive in 

the California part of the ecoregion (Steenbergh and Lowe, 

1977). Creosote (Larrea tridentata), white bursage (Ambrosia dumosa), ocotillo (Fouquieria splendens), and brittlebush 

(Encelia farinosa) shrubs dominate plant communities in the 

hottest, driest areas; palo verde (Parkinsonia spp.), mesquite 

(Prosopis spp.), and ironwood (Olneya tesota) trees are common on slopes and near the heads of alluvial fans. 

Land ownership in the ecoregion is primarily Federal, 

managed by the Bureau of Land Management, Department of 

Defense, and National Park Service, and some of the remainder is occupied by tribal lands. Major land uses include 

urban and rural settlement, agriculture and livestock grazing, 

mining, and military training. Agriculture was established 

where water was available, but in recent years it has given 

way to urban growth. The dry climate makes this ecoregion 

a favored destination for relocation and retirement (Arizona 

Fish and Game, 2006).

Contemporary Land-Cover Change 

(1973 to 2000)

The overall spatial change of land cover in the Sonoran 

Basin and Range Ecoregion between 1973 and 2000 was 

estimated at 2.6 percent (table 1). Although the overall change 

is small when compared to other ecoregions in the western 

United States, the amount of change is high relative to the 

adjacent Chihuahuan Deserts (0.5 percent; CD, on fig. 2) and 

Madrean Archipelago (1.4 percent; MA, on fig. 2) Ecoregions. Our estimates indicate that between 1973 and 2000, 1.3 

percent of the ecoregion changed at least once, and 1.1 percent 

changed at least two times (table 1). 

The normalized annual rates of land-cover change, which 

account for varying lengths of time between imagery dates 

(table 2), show that the rate of land-cover change in the 

0 10 20 30

Area, as percent of ecoregion

CD

SRK

ANMP

MA

CBR

WB

WUM

SBR

MBR

CLRP

ANMM

SN

SCM

NBR

BLM

CRK

MVFP

SRB

MRK

CLMP

SCCCOW

KM

NC

ECSF

CCV

NRK

WV

C

CR

PL

Ecoregion 

EXPLANATION

Change in one time period

Change in two time periods

Change in three time periods

Change in four time periods

Change in four time periods

Figure 2. Overall spatial change in Sonoran Basin and Range 

Ecoregion (SBR; darker bars) compared with that of all 30 Western 

United States ecoregions (lighter bars). Each horizontal set of 

bars shows proportions of ecoregion that changed during one, 

two, three, or four time periods; highest level of spatial change in 

Sonoran Basin and Range Ecoregion (four time periods) labeled 

for clarity. See table 2 for years covered by each time period. See 

appendix 2 for key to ecoregion abbreviations.
Chapter 30—Sonoran Basin and Range Ecoregion 305

Sonoran Basin and Range Ecoregion was very low compared to that in other ecoregions in the western United States 

(fig. 2). Within the Sonoran Basin and Range Ecoregion 

itself, the fastest rate of land-cover change occurred between 

1980 and 1986, when approximately 264 km2 changed landcover classes per year, followed closely by 221 km2

 annually between 1973 and 1980. These rates were nearly twice 

as fast as between 1986 and 1992 and were approximately 

50 percent faster than the rate of change between 1992 and 

2000. It is worth noting that, because considerable error is 

associated with these rates, they may not be significantly different (table 2).

Net change in land-cover classes per time period is 

presented in figure 4. Between 1973 and 1980, a large net 

increase in water coupled with a large net decrease in grassland/shrubland was observed, whereas between 1980 and 

1986 this trend reversed, with a large increase in grassland/

shrubland and wetland coupled with a large decrease in 

water. These changes in land cover were in response to 

short-term climate fluctuations that resulted in widely varied 

reservoir levels. Grassland/shrubland changes were also 

influenced by an increase in developed land, which expanded 

by 173 percent over the study period, from 278 to 759 km2. 

Grassland/shrubland dominates the Sonoran Basin and 

Range Ecoregion, followed distantly by agriculture. In 2000 

the grassland/shrubland class covered 92.9 percent (108,139 

km2) of the ecoregion, while agriculture covered 3.2 percent of 

the ecoregion (3,698 km2

) (table 3). Between 1973 and 1980, 

617 km2 of grassland/shrubland and 264 km2 of wetland were 

converted to water, and another 257 km2 of grassland/shrubland 

was converted to agriculture (table 4). Nearly the same area 

of water changed back to grassland/shrubland and wetland 

between 1980 and 1986. In addition, 147 km2

 of grassland/

shrubland was converted to agriculture, and 96 km2 was 

Figure 3. Estimates of land-cover change per time period, normalized to annual 

rates of change for all 30 Western United States ecoregions (gray bars). Estimates of 

change for Sonoran Basin and Range Ecoregion are represented by red bars in each 

time period.

Figure 4. Normalized average net change in Sonoran Basin and 

Range Ecoregion by time period for each land-cover class. Bars 

above zero axis represent net gain, whereas bars below zero 

represent net loss. Note that not all land-cover classes shown 

in explanation may be represented in figure. See appendix 3 for 

definitions of land-use/land-cover classifications.

0.5

0.0

1.0

1.5

2.0

2.5

1973 to 1980 1980 to 1986 1986 to 1992 1992 to 2000

Average annual change,

as percent of ecoregion

Time period

−2

−1

0

1

2

1973–1980 1980–1986 

Time period

1986–1992 1992–2000 

Area changed, as percent of ecoregion 

Water

Developed

Mechanically disturbed

Mining

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Nonmechanically disturbed

Ice/Snow

EXPLANATION

LAND-USE/LAND-COVER CLASS
306 Status and Trends of Land Change in the Western United States—1973 to 2000

reclassified as developed. These changes continued between 

1986 and 2000, during which time the Sonoran Basin and 

Range Ecoregion experienced net losses of 461 km2 of grassland/shrubland and 245 km2

 of water, as well as net gains of 244 

km2 of agricultural land and 481 km2 of developed land (fig. 4).

Estimates suggest that, between 1973 and 2000, landcover change in the Sonoran Basin and Range Ecoregion 

was small, and it also occurred at a slow rate relative to other 

ecoregions in the western United States. However, as in the 

Mojave Basin and Range Ecoregion to the north, a seemingly 

small, yet significant change was occurring in developed 

land (fig. 5). Although development is sparse, all three major 

metropolitan regions in the Sonoran Basin and Range Ecoregion experienced unprecedented rates of population growth 

both during and since the study period. Between 1990 and 

2000 alone, the population of the Coachella Valley grew at 

more than twice the rate of any other region in California. 

This growth has continued since the end of the study: between 

2000 and 2005, the population of the Coachella Valley grew 

to 410,974 (an increase of 23.6 percent) (U.S. Census Bureau, 

2011); by 2008, the Phoenix metropolitan area added nearly 

a million more people, a 31.7 percent increase since 2000. 

The greater Tucson region grew from 531,443 residents in 

Figure 6. Increased use of water (A), coupled with decreasing 

water supplies (B), has controlled, and will continue to control, 

rate of land-cover change in Sonoran Basin and Range Ecoregion.

1980 to 666,880 in 1990 (a 25.5 percent increase) and to an 

estimated 843,746 people in 2000 (a 26.5 percent increase 

since 1990) (U.S. Census, 2011). In 1990, the Sonoran Basin 

and Range Ecoregion included 6.9 million residents; by 2020, 

the population is expected to reach 12 million (U.S. Census 

Bureau, 2011). Land-cover data suggest that urbanization of 

the Sonoran Basin and Range Ecoregion comes primarily at 

the expense of grassland/shrubland. As the population grows, 

water resources may become limited as human uses draw 

down regional water tables by groundwater pumping and 

also tax the Colorado River’s finite water resources and its 

long-distance water delivery systems (for example, the Central 

Arizona Project canal) (fig. 6).

A

Figure 5. Changing landscape of Sonoran Basin and Range 

Ecoregion. A, Typical grassland/shrubland land cover within 

ecoregion. B, Result of change from grassland/shrubland to 

developed land-cover classes.

A

B

A

B
Chapter 30—Sonoran Basin and Range Ecoregion 307

Table 1. Percentage of Sonoran Basin and Range Ecoregion land 

cover that changed at least one time during study period (1973–

2000) and associated statistical error.

[Most sample pixels remained unchanged (97.4 percent), whereas 2.6 percent 

changed at least once throughout study period] 

Number

of

changes

Percent

of

ecoregion

Margin

of error

(+/− %)

Lower

bound

(%)

Upper

bound

(%)

Standard

error

(%)

Relative

error

(%)

1 1.3 0.7 0.6 2.0 0.5 35.4

2 1.1 0.8 0.2 1.9 0.6 53.1

3 0.2 0.2 0.0 0.4 0.1 84.0

4 0.0 0.0 0.0 0.0 0.0 85.9

Overall 

spatial 

change

2.6 1.4 1.2 3.9 0.9 36.4

Table 2. Raw estimates of change in Sonoran Basin and Range Ecoregion land cover, computed for 

each of four time periods between 1973 and 2000, and associated error at 85-percent confidence level.

[Estimates of change per period normalized to annual rate of change for each time period]

Period Total change

(% of ecoregion)

Margin of 

error

(+/− %)

Lower 

bound

(%)

Upper 

bound

(%)

Standard 

error

(%)

Relative 

error

(%)

Average 

rate

(% per year)

Estimate of change, in percent stratum

1973–1980 1.3 0.9 0.4 2.2 0.6 45.4 0.2

1980–1986 1.4 1.1 0.3 2.5 0.7 55.0 0.2

1986–1992 0.5 0.4 0.1 0.8 0.2 50.2 0.1

1992–2000 0.8 0.5 0.4 1.3 0.3 38.8 0.1

Estimate of change, in square kilometers

1973–1980 1,544 1,029 515 2,574 701 45.4 221

1980–1986 1,583 1,277 306 2,861 870 55.0 264

1986–1992 558 411 147 969 280 50.2 93

1992–2000 985 560 424 1,545 382 38.8 123
308 Status and Trends of Land Change in the Western United States—1973 to 2000

Table 3. Estimated area (and margin of error) of each land-cover class in Sonoran Basin and Range Ecoregion, calculated five times 

between 1973 and 2000. See appendix 3 for definitions of land-cover classifications.

Water Developed Mechanically 

disturbed Mining Barren Forest Grassland/Shrubland Agriculture Wetland

Nonmechanically 

disturbed

% +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/− % +/−

Area, in percent stratum

1973 0.3 0.3 0.2 0.1 0.0 0.0 0.0 0.0 2.1 2.9 0.8 0.4 93.3 3.4 3.0 2.0 0.2 0.3 0.0 0.0

1980 1.1 1.1 0.3 0.1 0.1 0.1 0.0 0.0 2.1 2.9 0.8 0.4 92.5 3.6 3.2 2.1 0.0 0.0 0.0 0.0

1986 0.2 0.2 0.4 0.2 0.0 0.0 0.0 0.0 2.1 2.9 0.8 0.4 92.9 3.5 3.2 2.1 0.3 0.4 0.0 0.0

1992 0.0 0.0 0.5 0.3 0.0 0.0 0.0 0.0 2.1 2.9 0.9 0.4 93.1 3.4 3.2 2.0 0.2 0.3 0.0 0.0

2000 0.1 0.0 0.7 0.4 0.0 0.0 0.0 0.0 2.1 2.9 0.8 0.3 92.9 3.5 3.2 2.1 0.2 0.3 0.1 0.1

Net

change −0.2 0.3 0.4 0.3 0.0 0.0 0.0 0.0 0.0 0.0 −0.1 0.1 −0.4 0.6 0.2 0.4 0.0 0.1 0.1 0.1

Gross

change 1.9 1.9 0.4 0.3 0.1 0.2 0.0 0.0 0.0 0.0 0.2 0.2 2.3 1.4 0.8 0.5 0.7 0.9 0.1 0.1

Area, in square kilometers

1973 308 402 278 143 8 7 8 6 2,449 3,332 981 478 108,599 4,012 3,454 2,355 280 387 0 0

1980 1,224 1,321 328 172 88 90 9 6 2,428 3,326 962 489 107,615 4,175 3,696 2,398 14 13 0 0

1986 218 224 511 257 14 11 14 9 2,431 3,324 973 490 108,115 4,033 3,724 2,388 366 511 0 0

1992 43 42 604 313 15 13 14 10 2,435 3,323 995 495 108,315 4,010 3,674 2,381 269 368 0 0

2000 62 56 759 426 20 16 19 14 2,439 3,324 876 376 108,139 4,048 3,698 2,400 239 321 113 163

Net

change −245 396 481 310 12 11 11 13 −10 9 −104 130 −461 717 244 500 −42 67 113 163

Gross

change 2,173 2,267 482 310 164 178 12 13 51 37 282 220 2,719 1,666 987 565 757 1,083 113 163
Chapter 30—Sonoran Basin and Range Ecoregion 309

Table 4. Principal land-cover conversions in Sonoran Basin and Range Ecoregion, showing amount of area changed (and 

margin of error, calculated at 85-percent confidence level) for each conversion during each of four time periods and also during 

overall study period. See appendix 3 for definitions of land-cover classifications.

[Values given for “other” class are combined totals of values for other land-cover classes not listed in that time period. Abbreviations: n/a, not applicable]

Period From class To class

Area 

changed

Margin 

of error

Standard 

error Percent of 

ecoregion

Percent of 

all changes (km2

) (+/− km2) (km2)

1973–1980 Grassland/Shrubland Water 617 608 414 0.5 40.0

Wetland Water 264 381 260 0.2 17.1

Grassland/Shrubland Agriculture 257 188 128 0.2 16.6

Grassland/Shrubland Forest 90 120 82 0.1 5.8

Grassland/Shrubland Mechanically disturbed 80 90 61 0.1 5.2

Other Other 236 n/a n/a 0.2 15.3

Totals 1,544 1.3 100.0

1980–1986 Water Grassland/Shrubland 657 738 503 0.6 41.5

Water Wetland 344 496 338 0.3 21.7

Grassland/Shrubland Agriculture 147 112 76 0.1 9.3

Grassland/Shrubland Developed 96 75 51 0.1 6.1

Agriculture Grassland/Shrubland 90 108 74 0.1 5.7

Other Other 249 n/a n/a 0.2 15.7

Totals 1,583 1.4 100.0

1986–1992 Wetland Grassland/Shrubland 158 227 155 0.1 28.3

Water Grassland/Shrubland 147 160 109 0.1 26.4

Grassland/Shrubland Developed 91 63 43 0.1 16.3

Agriculture Grassland/Shrubland 49 44 30 0.0 8.7

Grassland/Shrubland Wetland 47 67 46 0.0 8.4

Other Other 67 n/a n/a 0.1 12.0

Totals 558 0.5 100.0

1992–2000 Grassland/Shrubland Agriculture 245 264 180 0.2 24.9

Agriculture Grassland/Shrubland 207 161 110 0.2 21.0

Grassland/Shrubland Developed 135 99 68 0.1 13.7

Forest Nonmechanically disturbed 113 163 111 0.1 11.5

Wetland Grassland/Shrubland 89 128 87 0.1 9.0

Other Other 195 n/a n/a 0.2 19.8

Totals 985 0.8 100.0

1973–2000

(overall)

Water Grassland/Shrubland 833 809 551 0.7 17.8

Grassland/Shrubland Water 682 620 422 0.6 14.6

Grassland/Shrubland Agriculture 651 427 291 0.6 13.9

Agriculture Grassland/Shrubland 360 241 164 0.3 7.7

Water Wetland 358 514 350 0.3 7.7

Other Other 1,786 n/a n/a 1.5 38.2

Totals 4,671 4.0 100.0
310 Status and Trends of Land Change in the Western United States—1973 to 2000

References Cited

Arizona Fish and Game Department, 2006, Section 10: 

Sonoran Desert, in Arizona’s Comprehensive Wildlife 

Conservation Strategy: 2005-2015: Arizona Fish and Game 

Department. (Available at http://www.azgfd.gov/pdfs/w_c/

cwcs/downloads/Section10Sonoran.pdf.) 

Arizona Geologic Survey and Bureau of Land Management, 

1993, Arizona geologic map: Arizona Geological Survey 

Map 26.

Climate Assessment for the Southwest, 2010, Temperature 

and precipitation: Tucson, University of Arizona, accessed 

June 24, 2011, at http://www.climas.arizona.edu/sw-climate/

temp-precip.

Comrie, A.C., and Glenn, E.C., 1998, Principal componentsbased regionalization of precipitation regimes across the 

Southwest United States and Northern Mexico, with an 

application to monsoon precipitation variability: Climate 

Research, v. 10, p. 201–215.

Jennings, C.W., 1977, Geologic map of California: California 

Geological Survey Geologic Data Map No. 2, scale 

1: 750,000.

McGinnies, W.G., 1976, An overview of the Sonoran Desert: 

An essay developed from a paper given at the opening session of the 2nd Annual Conference of the Consortium of 

Arid Lands Institutions (CALI), February 4, 1976, in Tucson, 

Arizona: Tucson, University of Arizona, Arid Lands Information Center. (Available at http://alic.arid.arizona.edu/sonoran/

documents/mcginnies/McGinnies_overview.html.)

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers 

v. 77, no. 1, p. 118–125.

Steenbergh, W.F., and Lowe, C.H., 1977, Ecology of the 

saguaro, II—reproduction, germination, establishment, 

growth, and survival of the young plant: National Park 

Service, Scientific Monograph 8. 

Turner, R.M., Bowers, J.E., and Burgess, T.L., 1995, Sonoran 

desert plants—an ecological atlas, (2d ed.): Tucson, University of Arizona Press, 501 p.

U.S. Census Bureau, 2011, New American Fact Finder: U.S. 

Census Bureau database, accessed June 23, 2011, at http://

factfinder2.census.gov/faces/nav/jsf/pages/index.xhtml. 

U.S. Environmental Protection Agency, 1997, Descriptions of level III ecological regions for the CEC report on 

ecological regions of North America: U.S. Environmental 

Protection Agency database, accessed April 12, 2006, 

at http://www.epa.gov/wed/pages/ecoregions/na_eco.

htm#Downloads.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650–662.
Appendixes 1–4
This page intentionally left blank
Appendix 1. Map of Ecoregions in Conterminous United States 313

Appendix 1. Map of Ecoregions in Conterminous United States

This volume—U.S. Geological Survey Professional Paper 1794–A, which covers 30 ecoregions in the Western United 

States—provides an assessment of the rates and causes of land-use and land-cover change in the Western United States region 

between 1973 and 2000. The other three volumes of this Professional Paper (1794–B, 1794–C, and 1794–D) provide similar 

analyses for the Great Plains, the Midwest–South Central United States, and the Eastern United States regions, respectively.

The map contained in this appendix (fig. 1.1) shows all 84 ecoregions in the conterminous United States, as originally defined by Omernik and others (1987) and later modified by the U.S. Environmental Protection Agency (1999), in addition to the 

ecoregions that are contained in the Western United States, Great Plains, Midwest–South Central United States, and Eastern 

United States regions. Also shown are the land-use/land-cover classes from the 2001 National Land-Cover Database (Homer 

and others, 2004). 

References Cited

Homer, C., Huang, C., Yang, L., Wylie, B., and Coan, M., 2004, Development of a 2001 National Land-Cover Database for the 

United States: Photogrammetric Engineering and Remote Sensing, v. 70, 

no. 7, p. 829–840.

Omernik, J.M., 1987, Ecoregions of the conterminous United States: Annals of the Association of American Geographers, v. 77, 

no. 1, p. 118–125.

U.S. Environmental Protection Agency, 1997, Descriptions of level III ecological regions for the CEC report on ecological 

regions of North America: U.S. Environmental Protection Agency database, accessed April 12, 2006, at http://www.epa.gov/

wed/pages/ecoregions/na_eco.htm#Downloads.

Ecoregion Abbreviations Used on Map

[Map is on following pages]

ACPB Atlantic Coastal Pine Barrens Ecoregion

ANMM Arizona/New Mexico Mountains Ecoregion

CR Coast Range Ecoregion

CRK Canadian Rockies Ecoregion

EGLHL Eastern Great Lakes and Hudson Lowlands Ecoregion

HELP Huron/Erie Lake Plains Ecoregion

LPH Laurentian Plains and Hills Ecoregion

MACP Middle Atlantic Coastal Plain Ecoregion

MRK Middle Rockies Ecoregion

MVFP Montana Valley and Foothill Prairies Ecoregion

MVLP Mississippi Valley Loess Plains Ecoregion

NAPU Northern Appalachian Plateau and Uplands Ecoregion

NCA North Central Appalachians Ecoregion

NCHF North Central Hardwood Forests Ecoregion

NECZ Northeastern Coastal Zone Ecoregion

NEH Northeastern Highlands Ecoregion

NLF Northern Lakes and Forests Ecoregion

NMW Northern Minnesota Wetlands Ecoregion

PL Puget Lowland Ecoregion

SCCCOW Southern and Central California Chaparral and Oak Woodlands Ecoregion

SCM Southern California Mountains Ecoregion

SEWTP Southeastern Wisconsin Till Plains Ecoregion

SFCP Southern Florida Coastal Plain Ecoregion

TBP Texas Blackland Prairies Ecoregion

WUM Wasatch and Uinta Mountains Ecoregion

WV Willamette Valley Ecoregion
MEXICO

Pacific

 Ocean

Blue Mountains

Central Basin

and Range

Central California Valley

Columbia Plateau

Colorado

Plateaus

Coast Range

Cascades

Klamath

Mountains

Madrean

Archipelago

Mojave Basin

and Range

Middle

Rockies

MVFP

Northern Basin

and Range

Northern

Rockies

PL

Sonoran Basin

and Range

SCCCOW

SCCCOW

SCM

Sierra Nevada

Snake River Basin

Southern

Rockies

Wyoming Basin

SCCCOW

CR

MRK

ANMM

WUM

Central Great 

E

Edwards

Plateau

Nebraska Sand Hills

Northwestern Great Plains

Southern

Texas Plains

Western

High Plains

Western

High Plains

North

Cascades

Chihuahuan Deserts

Northwestern Glaciated Plains

Southwestern

Tablelands

Ce

Oklaho

Pl

CRK

WV

Eastern

Cascades

Slopes and

Foothills

MRK

110° 100° 

110° 100° 

120°

120°

50°

40°

30°

0 125 250 500 MILES

0 125 250 500 KILOMETERS

Arizona/

New Mexico

Plateau

Arizona/ 

 New Mexico

 Mountains

WESTERN UNITED STATES

GREAT 

314 Status and Trends of Land Change in the Western United States—1973 to 2000

Figure 1.1. Map 

of ecoregions in 

conterminous 

United States.
Appendix 1. Map of Ecoregions in Conterminous United States 315

CANADA

Atlantic

 Ocean

Gulf

of 

Mexico

SFCP

Southern

Coastal

Plain

Western

Allegheny

Plateau

Appalachians

Southwestern

Southeastern Plains

Northeastern

Highlands

Middle Atlantic Coastal Plain

Interior

Plateau Blue Ridge Mountains

Ridge and Valley

Northern Piedmont

ACPB

MACP

MACP

NEH

LPH

NEH

NEH

EGLHL

NAPU

NCA

NCA

Plains

East Central Texas Plains

Western Gulf Coastal Plain

TBP

Lake

Agassiz

Plain

Northern

Glaciated Plains

Western Corn Belt Plains

Central

Irregular

Plains

Boston Mountains

Central Corn

Belt Plains

Eastern Corn

Belt Plains

Erie Drift Plains

HELP

HELP

Interior

River Lowland

Northern Lakes

and Forests

NMW

Ozark Highlands

South

Central

Plains

Southern 

Michigan/

Northern 

Indiana 

Drift Plains 

NLF

Flint

Hills

Ouachita Mountains

Arkansas Valley

entral

ma/Texas

lains

TBP

MVLP

Mississippi

Alluvial

Plain

NCHF

Driftless

Area SEWTP

NECZ

 Central

Appalachians

Piedmont

70°

90° 80° 50°

90° 80°

40°

30°

EXPLANATION

Water

Developed

Barren

Forest

Grassland/Shrubland

Agriculture

Wetland

Ice/Snow

Land-use/land-cover class

PLAINS

 MIDWEST–

SOUTH CENTRAL

UNITED STATES

EASTERN UNITED STATES

Ecoregion boundary

Major ecoregion 

 group boundary
316 Status and Trends of Land Change in the Western United States—1973 to 2000

Appendix 2. Abbreviations for Western United States Ecoregions

ANMM Arizona/New Mexico Mountains Ecoregion

ANMP Arizona/New Mexico Plateau Ecoregion

BLM Blue Mountains Ecoregion

C Cascades Ecoregion

CBR Central Basin and Range Ecoregion

CCV Central California Valley Ecoregion

CD Chihuahuan Deserts Ecoregion

CLMP Columbia Plateau Ecoregion

CLRP Colorado Plateaus Ecoregion

CR Coast Range Ecoregion

CRK Canadian Rockies Ecoregion

ECSF Eastern Cascades Slopes and Foothills Ecoregion

KM Klamath Mountains Ecoregion

MA Madrean Archipelago Ecoregion

MBR Mojave Basin and Range Ecoregion

MRK Middle Rockies Ecoregion

MVFP Montana Valley and Foothill Prairies Ecoregion

NBR Northern Basin and Range Ecoregion

NC North Cascades Ecoregion

NRK Northern Rockies Ecoregion

PL Puget Lowland Ecoregion

SBR Sonoran Basin and Range Ecoregion

SCCCOW Southern and Central California Chaparral and Oak Woodlands Ecoregion

SCM Southern California Mountains Ecoregion

SN Sierra Nevada Ecoregion

SRB Snake River Basin Ecoregion

SRK Southern Rockies Ecoregion

WB Wyoming Basin Ecoregion

WUM Wasatch and Uinta Mountains Ecoregion

WV Willamette Valley Ecoregion
Appendix 3. Land-Cover Classification System Used in “Status and Trends of Land Change” Study 317

Appendix 3. Land-Cover Classification System Used in “Status and Trends of 

Land Change” Study

This analysis of land-use/land-cover change during the 

1973–2000 study period is based on land-cover classifications 

mapped for five study dates—1973, 1980, 1986, 1992, and 

2000. The use of moderate-resolution imagery—Landsat Multispectral Scanner, Thematic Mapper, and Enhanced Thematic 

Mapper Plus—necessitated a land-cover classification system 

that was fairly general in order to achieve high levels of accuracy and consistency in the interpretations. The classification 

system also needed to contain classes that could be used as 

an appropriate surrogate for land use. This classification, 

which is based on the Anderson Level I classes (Anderson 

and others, 1976), was used because the classes have been 

designed as use surrogates, but this system has been further 

modified by adding two transitional disturbance categories, 

mechanically disturbed (human induced) and nonmechanically disturbed (natural). 

The classification system used consists of the following 

11 general land-cover classes: water, developed, mechanically 

disturbed, mining, barren, forest, grassland/shrubland, agriculture, wetland, nonmechanically disturbed, and ice/snow. Classes are defined as follows:

Water—Areas that are persistently covered with water, 

such as perennial streams, canals, rivers, lakes, reservoirs, 

bays, and oceans.

Developed—Areas of intensive use, in which much of 

the land is covered with structures or other anthropogenically induced, impermeable surfaces (for example, high-density 

residential, commercial, and industrial areas, as well as 

roads, highways, and other transportation corridors), or less 

intensive use, in which the land-cover matrix includes both 

vegetation and structures (for example, low-density residential areas, recreational facilities, cemeteries, parking lots, and 

utility corridors). Land that is functionally related to urban or 

built-up environments (for example, parks and golf courses) 

is also included.

Mechanically disturbed—Land in an altered and often 

unvegetated state owing to disturbance by mechanical (that is, 

human) means. Mechanically disturbed land is in transition 

from one land-cover class to another. Processes leading to 

mechanical disturbance include forest clearcutting, earthmoving, scraping, chaining, reservoir drawdown, and other types 

of anthropogenically induced changes.

Mining—Areas of extractive mining activities that have 

significant surface expression, including mining buildings and 

apparatus, quarry pits, evaporation and leach ponds, tailings 

and overburden piles, and other components related to mining, 

to the extent that these features can be detected.

Barren—Areas of bare soil, sand, or rock, in which less 

than 10 percent of the area is vegetated. Barren lands generally 

are naturally occurring.

Forest—Tree-covered land where the tree-cover density is greater than 10 percent. Cleared forest land is mapped 

(according to land cover at the time of the imagery) as either 

mechanically disturbed or grassland/shrubland.

Grassland/Shrubland—Land that is predominately covered with grasses, forbs, or shrubs. Vegetated cover must make 

up at least 10 percent of the area.

Agriculture—Land, in either a vegetated or an unvegetated state, used for the production of food or fiber. This 

includes cultivated and uncultivated croplands, hay lands, pasture, orchards, vineyards, and confined-livestock operations. 

However, forest plantations always are classified as forest, 

regardless of how the wood products are used.

Wetland—Land where water saturation is the determining factor in soil characteristics, vegetation types, and 

animal communities. Wetlands usually contain both water and 

vegetated cover.

Nonmechanically disturbed—Land in an altered and 

often unvegetated state owing to disturbance by nonmechanical (that is, natural) means. Nonmechanically disturbed land 

is in transition from one land-cover class to another. Causes of 

nonmechanical disturbance include fire, wind, floods, animals, 

and other similar phenomena.

Ice/Snow—Land where the accumulation of snow and 

ice does not completely melt during the summer period (for 

example, alpine glaciers and perennial snowfields).

Reference Cited

Anderson, J.R., Hardy, E.E., Roach, J.T., and Witmer, R.E., 

1976, A Land Use and Land Cover Classification System 

for Use with Remote Sensor Data: U.S. Geological Survey 

Professional Paper 964, 28 p. (Available at http://pubs.usgs.

gov/pp/0964/report.pdf.)
318 Status and Trends of Land Change in the Western United States—1973 to 2000

Appendix 4. Methodology Used in “Status and Trends of Land Change” Study

This appendix describes the methodology used to 

determine the temporal and spatial rates, trends, and types 

of change documented in this “Status and Trends of Land 

Change” study. The methodology is based on a statistical 

sampling approach, manual classification of land use and 

land cover, and postclassification comparisons of land cover 

over five different study dates (Loveland and others, 2002). 

U.S. Environmental Protection Agency’s (1999) Level III 

ecoregions provided the geographic framework for regional 

land-cover change estimates, and land-use/land-cover change 

was estimated on an ecoregion-by-ecoregion basis using a 

probability sample of randomly selected blocks within each of 

84 ecoregions across the conterminous United States. For each 

sample block, five dates of Landsat imagery were interpreted 

in order to map land use and land cover, using a classification 

system that consists of 11 general land-cover classes (see 

appendix 3, entitled “Land-Cover Classification System Used 

in ‘Status and Trends of Land Change’ Study”). The resulting 

land-cover data for each sample block were used to determine 

change for four time periods, and sample-block data were used 

to calculate change estimates for each ecoregion. 

Sampling Strategy

In this study, a sampling strategy was used as a costefficient method for characterizing land-cover change in an 

area as large as the conterminous United States. The study used 

a stratified random sample of 2,688 square blocks (fig. 4.1); a 

random sample of these blocks was independently selected for 

each ecoregion analyzed. Because the study used a probability 

sample, the estimates of land-use/land-cover change that are 

derived can be considered as categorically representative of 

the population (Kish, 1987). 

The size of each sample block in this study, as well as 

the sampling density (that is, the number of sample blocks 

analyzed per ecoregion), was based on a compromise between 

two conflicting objectives: (1) estimating change in land-cover 

area, and (2) estimating change in landscape pattern. Larger 

numbers of smaller sample blocks would result in more precise 

estimates of change in land-cover area, whereas smaller 

numbers of larger sample blocks would be more desirable for 

characterizing landscape pattern. 

Size of Samples

In the initial study design, a 20 × 20 km (400 km2) sample-block size was used, and nine ecoregions were analyzed, 

each analysis consisting of 9 to 11 sample blocks. On the basis of 

results from these initial ecoregion analyses, a decision was made 

to use a higher density of smaller (10 × 10 km; 100 km2) sample 

blocks for the remainder of the ecoregion analyses in order to 

maximize the precision of the land-cover change estimates.

Sampling Density

The sampling density was determined by both the project 

requirements for precision in the change estimates and the 

expected characteristics of change within the ecoregion being 

studied. As precision requirements increase, so must the sampling density. Similarly, a greater sampling density is required 

when areas of change are expected to be less evenly distributed throughout an ecoregion.

In this study, the target precision level was to map gross 

overall change to within a ±1% margin of error at an 85% 

confidence level for each ecoregion. On the basis of this target 

precision level and the expected characteristics of change 

within all 84 ecoregions in the conterminous United States, 

it was determined that between 25 and 48 of the 10 × 10 km 

sample blocks per ecoregion would likely be needed to adequately characterize overall change in each ecoregion.

Implementation of the Sampling Strategy

The sampling strategy outlined above was fairly straightforward to implement. A regular grid of 10 × 10 km (or, in a few 

cases, 20 × 20 km) sample blocks was overlain on an ecoregion 

map of the conterminous United States. Blocks whose centers 

fell within the boundaries of an ecoregion were highlighted 

as potentially valid sample blocks for that ecoregion and then 

were assigned a unique numerical value from 1 to N. A random 

number generator was then used to select sample blocks, one at 

a time, until the desired number was reached. Thus, each sample 

block within an ecoregion had an equal probability of being 

included in the final sample analysis. 

Although the number of sample blocks selected and 

analyzed was based on both the target precision level and the 

expected characteristics of change within the ecoregion, unexpected heterogeneity in the distribution of change could still 

result in the estimates of change having levels of precision that 

are lower than desired. Should this occur, the sampling strategy allowed for the selection and interpretation of additional 

sample blocks. The inclusion of these reserve blocks allowed 

the analysis to achieve change estimates that have acceptable 

levels of precision.

Geographic Framework

A central premise of the study design was the use of a 

geographic framework to provide regional land-cover change 

estimates. Geographers have long used regional frameworks 

because they capture the essence and potential of the landscape without masking the roles of environmental, social, 

and economic forces (Turner and Meyer, 1991). This “Status 

and Trends of Land Change” study chose to use ecoregions, 

as originally defined by Omernik (1987) and later modified 
Appendix 4. Methodology Used in “Status and Trends of Land Change” Study 319

by the U.S. Environmental Protection Agency (1999), as the 

framework from which to tell the regional story of change. 

Ecoregions were chosen as the unit of analysis because 

(1) they provide a means to localize estimates of the rates 

and driving forces of change, (2) they were developed by 

synthesizing information on a wide variety of factors (for 

example, climate, geology, physiography, soils, vegetation, 

hydrology, and human influences) and, therefore, should 

reflect both current land-use and land-cover types and future 

change trajectories, and (3) they provide a framework that 

can be extended globally. 

Landsat Data

Landsat satellite imagery was the primary source of data 

used for detecting land-cover change in this study. Data from 

the Landsat Multispectral Scanner (MSS), Thematic Mapper 

(TM), and Enhanced Thematic Mapper Plus (ETM+) instruments were acquired from the Landsat data archive: Landsat 

MSS datasets are available from late-1972 through late-1992; 

Landsat TM data are available from 1982 to the present; and 

Landsat ETM+ data are available from 1999 to the present. Each of these products provided a consistent, synoptic, 

multispectral view of the land surface from which land cover 

could be interpreted for the period between 1973 and 2000. To 

analyze trends in land-use/land-cover change throughout this 

period, five target study dates spaced at semiregular intervals 

(1973, 1980, 1986, 1992, and 2000) were selected. Landsat 

imagery corresponding to each 10 × 10 km (or 20 × 20 km) 

sample block was extracted from full Landsat scenes, resulting 

in five dates of satellite imagery for each sample block. 

To reduce expenses, the initial data-acquisition strategy 

was to use existing geoprocessed Landsat datasets as the primary input data source. Four of the five dates of Landsat MSS, 

TM, and ETM+ data were available in a geocoded format as 

a result of processing done for two previous projects: (1) the 

North American Landscape Characterization (NALC) project 

produced 1973, 1986, and 1992 geocoded Landsat MSS datasets for the conterminous United States and Mexico (Lunetta 

and others, 1998), and (2) the 1992 TM and 2000 ETM+ data 

came from the Multiresolution Landscape Characterization 

initiative (Loveland and Shaw, 1996). New 1980 Landsat MSS 

acquisitions were obtained in order to maintain the six- to 

eight-year interval between the five target dates. 

The Landsat MSS, TM, and ETM+ scenes obtained were 

previously georeferenced to root-mean-square error of 1 pixel or 

less but to differing map projections. For this study, all scenes 

were translated to a common Albers equal-area projection. 

Most of the NALC MSS data had also been terrain-corrected, 

but approximately one-third of the NALC data (path and rows) 

had been processed before the implementation of terrain-correction techniques. However, this was not considered a problem 

because the early NALC scenes were located primarily in 

areas with negligible terrain variability.

Ancillary Data

Additional ancillary data were acquired to aid interpreters 

in delineating land use and land cover from the Landsat data. 

For example, aerial photography was acquired for each sample 

block to provide a high-resolution data source to help with difficult interpretations. The National Aerial Photography Program 

(NAPP) generally provided one or two dates of color-infrared 

(CIR) and (or) black-and-white aerial photographs from 1987 

to the present. The National High Altitude Photograph (NHAP) 

Program generally provided one date of CIR and (or) blackand-white aerial photographs between 1980 and 1986. Aerial 

photographs were not consistently available for dates prior to 

1980 but were acquired when available. Although the Landsat 

imagery was always used as the source material for delineating 

land use and land cover, these higher resolution aerial photographs were invaluable for assisting in the interpretation of 

the imagery. Topographic maps, census data, other electronic 

sources of aerial photographs (for example, Google Earth), and 

digital raster graphics were among the other sources of information that interpreters found useful when processing the data.

Land-Cover Classification Scheme

The analysis of land use and land cover change during 

the 1973 to 2000 study period was based on classifications of 

land cover for the five target dates mentioned previously. The 

classification system used consists of the following 11 general 

land-cover classes: water, developed, mechanically disturbed, 

mining, barren, forest, grassland/shrubland, agriculture, wetland, nonmechanically disturbed, and ice/snow. See appendix 

3, entitled “Land-Cover Classification System Used in ‘Status 

and Trends of Land Change’ Study,” for definitions of these 11 

classifications.

Two primary factors affected the design of the classification system. The first factor was recognizing that the use 

of moderate-resolution Landsat imagery would necessitate 

a land-cover classification system that was fairly general in 

order to achieve high interpretation accuracy and consistency. 

The ability to identify and map land cover would be limited 

both by the technical specifications of the Landsat MSS, TM, 

and ETM sensors and by the local and regional landscape 

characteristics that affect the form and contrast visible in satellite imagery. This would be especially true when interpreting 

Landsat MSS data. 

The second factor involved choosing land-cover classes 

that captured the land-cover changes of interest. Because the 

project’s interest was in land-use change, with land cover 

serving as a surrogate for land use, the decision was to use the 

Anderson Level I classes (Anderson and others, 1976) because 

they were designed as use surrogates. However, the Anderson 

system was selectively modified by adding two disturbance 

categories, mechanically disturbed (human induced) and nonmechanically disturbed (natural). 
320 Status and Trends of Land Change in the Western United States—1973 to 2000

Manual Land-Cover Delineation

Land-cover delineation for each sample block began with 

the creation of a baseline reference land-cover dataset. The 1992 

date usually was the starting point owing to the availability of 

the 30-m-resolution 1992 National Land Cover Data (NLCD) 

dataset (Vogelmann and others, 2001). The NLCD dataset provided a starting template after the more detailed NLCD classes 

were aggregated to match the general land-cover classification 

described above. 

The NLCD data first were manually edited on the 

computer screen, using on-screen interpretation methods, 

while using the 1992 Landsat TM data and the NAPP aerial 

photographs as interpretation aids. This cleanup procedure 

to improve the NLCD classification accuracy was carried 

out because the NLCD data were created using automated 

image-processing procedures, and they were not meant for 

use in local- or ecoregional-scale assessments. A minimum 

mapping unit of 60 m2

 was used for this study. Thus, features having ground footprints less than 60 m wide generally 

were not mapped, resulting in the exclusion of high-contrast 

features such as roads, which have a distinct spectral signature 

but have ground dimensions of less than 60 m.

To carry out the NLCD editing for a particular sample 

block, the analyst displayed the NLCD data alongside the 

1992 Landsat TM data on the computer screen. These data 

sources, along with hard-copy prints of NAPP aerial photography roughly corresponding to the 1992 date, were visually 

inspected by the analyst to determine if any corrections were 

needed in the sample block. The analyst manually delineated polygons that consisted of contiguous blocks of specific 

land-cover classes. Each of these polygons was then given a 

code value that corresponded to the land-cover classes outlined in the classification scheme in appendix 3. The process 

continued until the entire sample block was manually inspected, mapped, and coded by the analyst.

To analyze change, land-cover classes for the 1973, 1980, 

1986, and 2000 study dates were backward- or forward-classified using the 1992 land-cover dataset as the template. For example, creation of the 2000 land-cover product began by making an exact copy of the 1992 land-cover product. This copy 

served as a baseline for the 2000 land-cover product, in which 

identified changes between 1992 and 2000 were manually 

edited into the copied image. This baseline 2000 land-cover 

product was displayed on screen, along with the 1992 Landsat 

imagery and the 2000 Landsat imagery, allowing the analyst to 

pan through the entire area of the sample block while examining the 1992 and 2000 Landsat imagery and any relevant aerial 

photography for valid land-cover changes between the two 

study dates. Any identified land-cover changes were manually 

digitized on screen, and the land cover was recoded on the 

2000 land-cover product. 

Upon completion of the 2000 land-cover product, the 

same procedures were used to create the 1986, 1980, and 1973 

land-cover products. This manual process eliminated errors 

that may occur between independently created land-cover 

products that are compared in a subsequent change analysis. Because only manually identified, delineated, and coded 

land-cover changes were analyzed during this phase, classification errors were greatly reduced.

Statistical Analysis

The resulting land-cover data for each sample block was 

used in postclassification comparisons to determine change 

between study years (fig. 4.2). Sample blocks within each 

ecoregion were used to generate change statistics for all 84 

ecoregions. These statistics were used to determine the predominant types of land-cover conversions occurring within 

each ecoregion, the estimated rates of change for these conversions, and whether these types and rates of change are constant 

or variable across time. The analysis of change also involved 

looking for spatial correlations between conversion types and 

selected socioeconomic and environmental factors, such as 

timber production, agricultural yields, precipitation amounts, 

population levels, proximity to urban development, and overall economic conditions, in order to improve the understanding 

of potential drivers of change.
80°

80°

90°

90°

100°

100°

110°

120° 110°

45° 40° 35° 30° 

25° 

CANADA

MEXICO

0 200 400 600 MILES0 200 400 600 KILOMETERS

10 × 10 km20 × 20 km

Total change, as percent of ecoregion

Sample blocks

Ecoregion boundary

EXPLANATION

0 – 4.14.2 – 7.57.6 – 14.414.5 – 33.8

Figure 4.1. Map of ecoregions in conterminous United States, showing locations of 2,688 sample blocks that were used in “Status and Trends o(purple and blue squares indicate locations of 10 × 10 km and 20 × 20 km sample blocks, respectively). Also shown are amounts of total change in between 1973 and 2000, as percent of ecoregion.
322 Status and Trends of Land Change in the Western United States—1973 to 2000

1973–1980

1980–1986

1986–1992

1992–2000

Forest

Grassland/Shrubland

Mining

Water

Barren

Mechanically disturbed

Developed

Land-use/land-cover class

1973

Landsat images Mapped land-use/land-cover Areas of change

1980

1986

1992

2000

Figure 4.2. Example of data compiled for each sample block, showing sample block 14-0555 (located near 

Henderson, Nevada, in Mojave Basin and Range Ecoregion). Left column is satellite imagery collected for each 

of five years analyzed in study (imagery sources for study years: 1973, 1980, and 1986 are Landsat Multispectral 

Scanner (MSS) images; 1992 is Landsat Thematic Mapper (TM) image; 2000 is Landsat Enhanced Thematic 

Mapper (ETM) image). Center column is mapped land-use/land-cover data for each study year. Right column 

shows areas that changed (green areas) in each of four time periods between study years; light- and dark-grayshaded areas show areas of previous change and represent overall land-change footprint throughout study period.
Appendix 4. Methodology Used in “Status and Trends of Land Change” Study 323

References Cited

Anderson, J.R., Hardy, E.E., Roach, J.T., and Witmer, R.E., 

1976, A Land Use and Land Cover Classification System 

for Use with Remote Sensor Data: U.S. Geological Survey 

Professional Paper 964, 28 p. (Available at http://pubs.usgs.

gov/pp/0964/report.pdf.)

Kish, L., 1987, Statistical Design for Research: New York, 

John Wiley & Sons, Inc., 296 p.

Loveland, T.R., and Shaw, D.M., 1996, Multiresolution land 

characterization—Building collaborative partnerships, in

Scott, J.M., Tear, T.H., and Davis, F.W., eds., Gap Analysis—A landscape approach to biodiversity planning: 

Bethesda, Maryland, American Society for Photogrammetry 

and Remote Sensing, p. 17–25.

Loveland, T.R., Sohl, T.L., Stehman, S.V., Gallant, A.L., Sayler, K.L., and Napton, D.E., 2002, A strategy for estimating 

the rates of recent United States land cover changes: Photogrammetric Engineering and Remote Sensing, v. 68, no. 10, 

p. 1,091–1,099.

Lunetta, R.S., Lyon, J.G., Guindon, B., and Elvidge, C.D., 

1998, North American landscape characterization dataset 

development and data fusion issues: Photogrammetric Engineering and Remote Sensing, v. 64, no. 8, p. 821–829.

Omernik, J.M., 1987, Ecoregions of the conterminous United 

States: Annals of the Association of American Geographers, 

v. 77, no. 1, p. 118–125.

Turner, B.L., II, and Meyer, W.B., 1991, Land use and land 

cover in global environmental change—Considerations 

for study: International Social Science Journal, v. 130, p. 

669–677.

U.S. Environmental Protection Agency, 1999, Level III Ecoregions of the continental United States: U.S. Environmental 

Protection Agency National Health and Environmental 

Effects Research Laboratory, scale 1:7,500,000, available at 

ftp://ftp.epa.gov/wed/ecoregions/us/Eco_Level_III_US.pdf.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and van Driel, N., 2001, Completion of the 

1990s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering & 

Remote Sensing, v. 67, p. 650–662.
Produced in the Menlo Park Publishing Service Center, Menlo Park, California

Manuscript approved for publication November 19, 2012

Edited by Taryn A. Lindquist, Peter H. Stauffer, Jan L. Zigler, Theresa Iki, Tracey L. Suzuki, and Teri Losano

Design and layout by David R. Jones and Jeanne S. DiLeo