U.S. Department of the Interior

U.S. Geological Survey

Geographic Analysis and Monitoring Program

Land-Cover Trends in the Sierra Nevada Ecoregion, 1973-2000

By Christian G. Raumann and Christopher E. Soulard

Scientific Investigations Report 2007–5011
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

Produced in the Western Region, Menlo Park, California

Manuscript approved for publication, January 23, 2007

Text edited by James W. Hendley II

Layout and design by Judy Weathers

U.S. Geological Survey, Reston, Virginia: 2007

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FRONT COVER

Photograph of a recently clear-cut area in Plumas National Forest, Plumas County, Calif.
iii

Foreword

The U.S Geological Survey (USGS) Land Cover Trends research project is focused on understanding the amounts, rates, 

trends, causes, and implications of contemporary land-use and land-cover change in the United States. The project is supported 

by the USGS Geographic Analysis and Monitoring Program in cooperation with the U.S. Environmental Protection Agency 

(EPA) and the National Aeronautics and Space Administration (NASA).

Land-use and land-cover (LU/LC) change is a pervasive environmental process that modifies landscape characteristics and 

affects a broad range of socio-economic, biologic, and hydrologic systems. Understanding the impacts of LU/LC change on 

environmental systems requires an understanding of the rates, patterns, and driving forces of past, present, and future LU/LC 

change. The objectives of the Land Cover Trends project are to (1) describe the amount, rates, and trends of contemporary LU/

LC change by ecoregion for the period 1973-2000 for the conterminous United States, (2) document the causes, driving forces, 

and implications of change, and (3) synthesize individual ecoregion results into a national assessment of LU/LC change.

The Land Cover Trends research team includes staff from the USGS National Center for Earth Resources Observation and 

Science (EROS), Rocky Mountain Geographic Science Center, Eastern Geographic Science Center, Mid-Continent Geographic 

Science Center, and Western Geographic Science Center. Other partners include researchers at South Dakota State University, 

University of Southern Mississippi, and State University of New York College of Environmental Science and Forestry.
iv 

Contents

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

Abstract...........................................................................................................................................................1

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

Study Area..............................................................................................................................................1

Historical Overview of Pre-1973 Land Use and Land Cover..........................................................2

Methodology...................................................................................................................................................2

Results .............................................................................................................................................................3

Gross Change by Period .............................................................................................................3

Footprint of Change .....................................................................................................................3

Annual Rate of Change ...............................................................................................................3

Class Area and Change ..............................................................................................................3

Most Common Conversions .......................................................................................................4

Temporal Variability of Change..................................................................................................4

Discussion.......................................................................................................................................................4

Forest Disturbance ......................................................................................................................5

Fire ........................................................................................................................................5

Timber Harvest ....................................................................................................................5

Forest Regeneration...........................................................................................................5

Reservoir Drawdown ..................................................................................................................5

Development.................................................................................................................................6

Comparison to Other Ecoregion ................................................................................................6

Relationship of Change to Spatially Explicit Variables ..........................................................6

Sampling and Uncertainty Measurement................................................................................7

Implications of Change ...............................................................................................................7

Conclusion.......................................................................................................................................................7

Acknowledgments.........................................................................................................................................8

References Cited............................................................................................................................................8

Appendix 1. Definitions of land use and land cover...............................................................................11

Appendix 2. Period contingency tables ...................................................................................................12

Figures

1. Sierra Nevada and surrounding ecoregions.......................................................................................14

2. Land ownership in the Sierra Nevada ecoregion ..............................................................................15

3. A single 100-km2 sample block illustrating forest land-cover change............................................16

4. Gross change by class by period in the Sierra Nevada ecoregion.................................................17

5. Temporal variability of individual land-use/land-cover classes .....................................................18

6. Forest area changed by fire, timber harvest, and regeneration during each period...................19

7. Photo of an area undergoing succession after the Manter Fire in Sequoia National Forest.....20

8. Photo of a recently clear-cut area in Plumas National Forest.........................................................21

9. Comparison of timber harvest and land-cover change data............................................................22
 v

10. Photo of forest regeneration after seeding in Plumas National Forest........................................23

11. Photo of lowered lake levels at Courtright Reservoir in Sierra National Forest .........................23

12. Photo of new residential construction in Franktown, Nev., north of Carson City .......................24

13. Photo of commercial construction along the access road to the 

Squaw Valley resort area..............................................................................................................24

14. Average annual rates of change by period for selected ecoregions 

in the Western United States .......................................................................................................25

15. Example of extensive land-cover change within a single sample block 

caused by wildfire .........................................................................................................................26

Tables

1. Land-use/land-cover class area by date as a percent of Sierra Nevada 

ecoregion total area......................................................................................................................27

2. Most common land-use/land-cover conversions from 1973-2000 ..................................................27

3. Rates of land-use/land-cover change grouped according to general process............................28

4. Potential explanatory variables and corresponding data sources .................................................29

5. Results of multiple linear regression analysis for the response variable 

mean gross change.......................................................................................................................29

6. Gross change by period and the corresponding margins of error at an 

85-percent confidence level ........................................................................................................29
Land-Cover Trends of the Sierra Nevada Ecoregion, 

1973-2000

By Christian G. Raumann and Christopher E. Soulard

Abstract

The U.S. Geological Survey has developed and is 

implementing the Land Cover Trends project to estimate and 

describe the temporal and spatial distribution and variability 

of contemporary land-use and land-cover change in the United 

States. As part of the Land Cover Trends project, the purpose 

of this study was to assess land-use/land-cover change in the 

Sierra Nevada ecoregion for the period 1973 to 2000 using a 

probability sampling technique and satellite imagery. We randomly selected 36 100-km2 sample blocks to derive thematic 

images of land-use/land-cover for five dates of Landsat imagery (1973, 1980, 1986, 1992, 2000). We visually interpreted 

as many as 11 land-use/land-cover classes using a 60-meter 

minimum mapping unit from the five dates of imagery yielding four periods for analysis. Change-detection results from 

post-classification comparison of our mapped data showed 

that landscape disturbance from fire was the dominant change 

from 1973-2000. The second most-common change was forest disturbance resulting from harvest of timber resources by 

way of clear-cutting. The rates of forest regeneration from 

temporary fire and harvest disturbances coincided with the 

rates of disturbance from the previous period. Relatively minor 

landscape changes were caused by new development and reservoir drawdown. Multiple linear regression analysis suggests 

that land ownership and the proportion of forest and developed cover types were significant determinants of the likelihood of direct human-induced change occurring in sampling 

units. Driving forces of change include land ownership, land 

management such as fire suppression policy, and demand for 

natural resources.

Introduction

In this report we present an assessment of land-use and 

land-cover (LU/LC) change in the Sierra Nevada ecoregion for 

the period 1973-2000. The Sierra Nevada ecoregion is one of 

84 Level-III ecoregions defined by the Environmental Protection Agency (EPA, 1999; Omernik, 1987). Ecoregions have 

been designed to serve as a spatial framework for environmental resource management and denote areas that contain a 

geographically distinct assemblage of biotic and abiotic phenomena including geology, physiography, vegetation, climate, 

soils, land use, wildlife, and hydrology (Gallant and others, 

2004). We used the established Land Cover Trends methodology (Loveland and others, 2002) to estimate LU/LC change 

using a probability sampling approach and change-detection 

analysis of thematic LU/LC images derived from Landsat 

satellite imagery.

Study Area

The Sierra Nevada ecoregion covers approximately 

52,872 square kilometers (km2) with the majority of area 

(98 percent) in California and a small portion (2 percent) in 

Nevada (fig. 1). The Sierra Nevada ecoregion (SNE) is generally orientated from north to south and is in essence defined 

by the Sierra Nevada physiographic province, which separates 

the California Central Valley to the west from the Great Basin 

to the east. The Sierra Nevada is a granitic batholith, much of 

which is exposed at higher elevations, with a gradual western 

slope and a generally steep eastern escarpment.

The climate of the SNE is primarily Mediterranean characterized by cool, wet winters and long, dry summers. Most 

areas of elevation above 2,100 meters have a Boreal climate, 

and the highest elevations, typically above 3,600 meters, 

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. As the 

western slope of the SNE extracts precipitation from storm 

systems, a strong rainshadow results and limits precipitation 

on the steep eastern slope. This climatic gradient plays a significant role in determining type and distribution of ecological communities. In order to provide water resources for the 

growing populations in arid, low-elevation areas of California 

and Nevada, numerous reservoirs on the western and eastern 

slopes of the SNE collect runoff from the winter snow pack.

The general Sierra Nevada region, which is slightly larger 

than the SNE proper, is home to more than 3,000 native plant 

species, of which 405 are endemic, 218 are rare and endemic, 

and 168 are rare and not endemic (Shevock, 1996). Climate, 

elevation, and soil type greatly influence the diversity and 

distribution of vegetation that makes up forests, meadows, 

chaparral, and alpine land-cover types. The western and eastern boundaries of the SNE are marked in part by the appear-
ance of the broad conifer zone. Moving up in elevation on 

the western slope, ponderosa pine mixed with black oak and 

other hardwoods appear first giving way to the commercially 

valuable mixed-conifer forest, which transitions into white 

and then red fir forests as elevation increases. Pinon pine 

and juniper woodlands are found at the base of the eastern 

slope of the SNE, replaced by mixed pine forests at higher 

elevations. The subalpine zone is a mixture of pine, hemlock, 

and juniper species. Above the subalpine is the cold and dry 

alpine zone characterized by low shrubs and cushion plants 

(SNEP Science Team and Special Consultants, 1996a).

The largest city in the SNE is South Lake Tahoe (2005 

pop. 24,059), which is located on the shore of the largest 

alpine lake in North America. The next largest municipalities 

are Susanville (2005 pop. 18,324), Grass Valley (2005 pop. 

13,006), Mammoth Lakes (2005 pop. 7,617), and numerous smaller rural communities located throughout (State of 

California, Department of Finance, 2005). Economies of these 

cities and towns largely depend on a steady flow of tourists.

Public lands make up 84.5 percent (444,677 km2) of the 

SNE with the majority (68.3 percent) managed by the U.S. 

Forest Service (USFS) as National Forests, with 21.8 percent 

of these USFS lands designated as wilderness (fig. 2). The 

National Park Service (NPS) manages 13.0 percent of the 

SNE as Yosemite, Sequoia, Kings Canyon, and Lassen Volcanic National Parks. Land holdings by the Bureaus of Land 

Management, Reclamation, and Indian Affairs cumulatively 

account for 2.4 percent of the SNE. In addition to federal 

lands, the State of California manages 0.7 percent (3,701 km2) 

of the SNE along with smaller holdings (less than 0.5 percent) 

by the State of Nevada and local cities and counties. Privately 

owned lands make up 15.5 percent (8,195 km2) of the SNE.

Historical Overview of Pre-1973 Land Use and 

Land Cover

European settlers began immigrating to the SNE in the 

early 1800s, ushering in a period of industrial resource use that 

affected land-cover conditions to varying degrees. The history 

of resource use can be followed through the land-use patterns 

related to gold and mineral extraction, grazing and agriculture, timber harvests, water diversions, and recreational and 

residential development. Starting with the discovery of gold 

in 1848 in the Sierra Nevada foothills west of the SNE, many 

of the periods of resource use in and around the Sierra Nevada 

can be described as boom-and-bust cycles. Throughout the 

late 1880s the demands of gold mining activities as well as 

residential and commercial development in the Central Valley 

and San Francisco area resulted in the harvest of thousands of 

acres of lower-elevation SNE timber each year for construction (SNEP Science Team and Special Consultants, 1996b). 

The 20th century marked a new phase of SNE history in 

which resource use became increasingly regulated. Forest and 

rangelands were protected through creation and expansion of 

national forests and parks. Laws and administrative policies 

such as the Wilderness Act of 1964, National Environmental 

Policy Act of 1969 (NEPA), and National Forest Management 

Act of 1976 (NFMA) provided a mechanism to manage national 

forests. Furthermore, other environmental laws, annual appropriations legislation, and administrative policies relating to fire 

and fuels guide resource use and likely have significant environmental effects in the SNE (Ruth 1996).

By the 1950s, California’s growing urban population 

greatly increased the demand for wood, water, hydroelectricity, 

and recreational opportunities from the SNE. Timber harvesting 

surged and continued until the economic recession in the early 

1980s. Water is considered the SNE’s most valuable resource 

(SNEP Science Team and Special Consultants, 1996b). Eighty 

percent of present reservoir capacity was completed after 1950. 

Concrete dams and the associated reservoirs control the flow 

of water in nearly every major river basin in the SNE and are 

managed to provide municipal water supplies and hydroelectric 

power. Major highways and ski resorts were constructed in the 

1950s and 1960s to meet the demand for year-round recreation 

(SNEP Science Team and Special Consultants, 1996b). 

Frequent fires of low to moderate intensity were an integral component of the preindustrial development of SNE ecological communities. Fires created 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 twentieth century the regional fire regime 

had greatly changed primarily due to logging during the settlement period and effective fire suppression activities mandated 

by State and Federal policy since the 1920s. As a result, fires 

were less frequent and more severe (Skinner and Chang, 

1996). Forest density increased and contributed to higher tree 

mortality due to greater intertree competition, insect attack, 

disease, and storm damage (Oliver and others 1996). These 

conditions contribute to fuels and increased fire hazard as 

well as the likelihood of high-severity fire (Manley and others 2000). A shift to a warmer and moister climate may have 

also contributed to this altered fire regime by reducing winter 

severity and providing a longer growing season (McKelvey 

and others, 1996; Stine, 1996). Furthermore, some SNE shrub 

communities, such as montane chaparral, require recurring 

high-severity fire for continued establishment and persistence. 

Fire suppression facilitated conifer encroachment into chaparral stands, leading to eventual replacement of chaparral by 

forest (Nagel and Taylor, 2005).

Methodology

We estimated the amount and rates of LU/LC change in the 

SNE using a random sample of 36 100-km2 (10-km by 10-km) 

blocks allocated across the SNE (fig. 1). We visually classified up to 11 classes of LU/LC (for example, water, developed, 

forest; see appendix 1) from five dates (1973, 1980, 1986, 1992, 

and 2000) of archived Landsat Multispectral Scanner (MSS), 

Thematic Mapper (TM), and Enhanced Thematic Mapper Plus 

(ETM+) satellite imagery using a 360-m2 (60-m x 60-m cell 

   Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Results   

size) minimum mapping unit (MMU). In addition to on-screen 

visual interpretation techniques, we used historical aerial 

photographs, topographic maps, and various ancillary data to 

aid in image interpretation. Our LU/LC mapping effort yielded 

five individual dates and four discrete periods for analysis. We 

then used post-classification comparison (that is, change detection) of the five dates of thematic LU/LC data for each sample 

block to estimate the amount of area changed and the context 

of change for the entire SNE along with corresponding margins 

of error at an 85 percent confidence level to describe sampling 

accuracy. A full explanation of Land Cover Trends project 

methodology is provided by Loveland and others (2002).

Results

This section presents the results of post-classification 

comparison of the multidate LU/LC data. We report these estimates of LU/LC change in the context of the entire SNE area 

based on the sampled data. Figure 3 illustrates an example of 

mapped LU/LC change for one sample block in the SNE.

Gross Change by Period

Gross change describes the total amount of land that 

underwent any type of change during a single multi-year 

period and is perhaps the most general statistic resulting from 

post-classification comparison of thematic LU/LC data. The 

greatest amount of gross change occurred from 1992-2000, as 

3.9 percent of the SNE (2,051 km2) underwent LU/LC change 

during this period. Gross change for the remaining three 

period was as follows: 1.6 percent (864 km2) from 1986-1992, 

0.8 percent (399 km2) from 1980-1986, and 0.9 percent (452 

km2) from 1972-1980.

Footprint of Change

The overall areal extent, or “footprint,” of LU/LC change 

from 1973-2000 was 4.9 percent (2,591 km2), which means 

that 4.9 percent of the SNE underwent LU/LC change during at least one of the four multiyear periods that make up the 

entire 27-year (yr) study period. Of this 4.9 percent footprint, 

3.2 percent of the SNE changed during only one period, 1.5 

percent changed during two periods, and 0.3 percent change 

during three periods.

Annual Rate of Change

The estimated average annual rate of LU/LC change is calculated by normalizing each period’s gross change by the number of years in that period. Normalizing gross change by year 

effectively allows comparison of the amount of change in each 

period when periods are of varying duration (6, 7, or 8 years). 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 

LU/LC change for the entire 27-yr study period from 1973-2000 

was 0.3 percent/yr, which means that on average 0.3 percent of 

the SNE changed each year. However, the annual rate of change 

has not been constant during the 27-yr study period as shown 

by the estimated average annual rates for the four periods. From 

1973-1980 and from 1980-1986, change occurred at identical 

rates of 0.1 percent/yr. The annual rate of change increased to 

0.3 percent/yr from 1986-1992 and continued to increase to 0.5 

percent/yr from 1992-2000.

Class Area and Change

Our results show that in 2000 the SNE was dominated 

by forest cover (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 the remainder of land cover (table 1). Developed, mining, 

agriculture, snow/ice, and mechanically disturbed LU/LC types 

each made up less than one percent of the SNE. Land-use/landcover classes that underwent the greatest net change (that is, 

total area gained minus total area lost) in relation to total SNE 

area since 1973 were forest (3.4 percent decrease), grass/shrubland (1.1 percent increase), and nonmechanically disturbed 

(2.3 percent increase). Although the developed and agriculture classes each makeup less than 1 percent of the SNE, the 

developed class underwent the greatest increase in area (16.6 

percent) and agriculture underwent the greatest decrease in area 

(5.5 percent) in relation to their respective total class area not 

considering the transitional nonmechanically disturbed class.

The net change values as a percentage of SNE area at the 

beginning (1973) and end (2000) dates of the study period in 

table 1 show little variability and may seem to indicate stability. Net change values often serve to effectively mask LU/LC 

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 lost) by individual LU/LC 

classes by period shows classes have fluctuated throughout the 

27-yr study period to a greater degree than net change values 

may indicate. Figure 4 shows that the forest, grass/shrubland, 

mechanically disturbed, and nonmechanically disturbed classes 

were the most dynamic from 1973-2000. The transitional characteristic of the mechanically disturbed class is also illustrated 

as area gained (810 km2) and nearly equals area lost (787 km2) 

from 1973-2000. Land-cover change was clearly at its peak 

during the period from 1992-2000 when gains and losses were 

generally greatest for the four most dynamic classes.

Figure 5 shows another technique to illustrate the temporal variability of individual LU/LC classes. Each graph shows 

the dynamics of a class measured along an annual scale. The 

cumulative area gained by a class shows the amount of land that 

is converted to that class from any other class. The cumulative 
area lost by a class shows the amount of land that is converted from that class to any other class. As the next section 

will show, breaking down LU/LC change into contextual 

conversions is an even more effective way to illustrate LU/

LC dynamics.

Most Common Conversions

All individual LU/LC conversions between classes were 

ranked by summing the total area changed during each of the 

four periods:

Ranking value = 

Area∆1973 to 1980 + Area∆1980 to 1986 + Area∆1986 to 1992 + Area∆1992 to 2000 

Each conversion documents land changing from one class 

to another (for example, forest to developed) and shows the 

direction of change. Table 2 shows each individual conversion ranked from greatest to least area converted. The most 

common individual conversions describe the disturbance of 

forested lands by mechanical (that is, clear-cuts) and nonmechanical (that is, fire) means. The most common conversion 

was that of 1404.3 km2 of forest to the nonmechanically disturbed class which accounted for 37.1 percent of all conversions. The second most common conversion was that of 783 

km2 forest to the mechanically disturbed class accounting 

for 20.7 percent of all changes. Conversion of mechanically 

and nonmechanically disturbed lands to the grass/shrubland 

class (753 km2 and 307 km2, respectively) were the two next 

most common conversions and represented the process of 

vegetation regeneration after clear-cutting or fire. Similarly, 

conversion of grass/shrubland to forest (303 km2) represented 

an intermediate 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. This conversion of 

indicates surface-level fluctuations of reservoirs in the SNE.

Table 2 also provides a summary of similar conversions 

that were aggregated based on how a single to or from class 

was affected. From 1973-2000 1,545 km2 of vegetation class 

(forest, grass/shrubland, and wetland) area was converted to 

the nonmechanically disturbed class. Fire caused these conversions. Total vegetation regeneration after disturbance is 

shown by the conversion of nonmechanically disturbed lands 

to vegetation classes (forest and grass/shrubland) and conversion of mechanically disturbed lands to vegetation classes 

(forest and grass/shrubland) for aggregated totals of 787 km2 

and 317 km2, respectively. Several classes were converted to 

the developed class for an aggregated total of 21 km2.

Temporal Variability of Change

Rates of LU/LC change throughout the 27-yr study period 

fluctuated (table 3). The rate of disturbance from burning as 

represented by the conversion of vegetated lands to the nonmechanically disturbed class was 14 km2/yr averaged from 

1973-1980, decreasing to less than 1 km2/yr from 1980-1986, 

and increasing to 21 km2/yr during the 1986-1992 period. 

During the final period from 1992-2000, the rate greatly 

increased to an average of 163 km2/yr. Of all lands burned 

between 1973 and 2000, 91 percent were forested and 9 

percent were covered by grass/shrubland. The rate of vegetation regeneration after fire represented by the conversion of 

land from nonmechanical disturbance to vegetation classes 

reflects the rate of fire disturbance. Regeneration increased 

during the period following a period of higher rates of fire 

disturbance and decreased after a period of lower rates of 

fire disturbance. Between 1973 and 2000, lands disturbed by 

fire changed to grass/shrubland 97 percent of the time and 

to forest 3 percent of the time during the period immediately 

following disturbance.

Disturbance from clear-cutting as represented by the conversion of forest to the mechanically disturbed class occurred 

at an average rate of 24 km2/yr from 1973-1980. Clear-cutting 

slightly increased to an average rate of 25 km2/yr from 1980-

1986, although for a shorter period of time (6 years rather than 

7). Change continued increasing to 70 km2/yr from 1986 to 

1992 and then decreased to 32 km2/yr from 1992-2000. The 

rate of vegetation regeneration reflects the rate of clear-cutting, increasing after a period of higher rates of clear-cutting 

and decreasing after a period of lower rates of clear-cutting. 

Between 1973 and 2000, clear-cut lands changed to grass/

shrubland 96 percent of the time and to forest 4 percent of the 

time during the period immediately following disturbance. An 

intermediate stage of forest regeneration represented by grass/

shrubland changing to forest occurred at varying rates with an 

average of 11 km2/yr from 1973-2000. Figure 6 shows the rates 

of disturbance from fire and clear-cutting and the corresponding 

rates of regeneration from each process.

The rate of conversion of area classified as water to the 

mechanically disturbed class varied between periods with the 

highest average rate during the period 1986-1992 (2 km2/yr). 

We did not detect any land-cover conversions to the developed class during the 1973-1980 and 1980-1986 periods. 

From 1986-1992, conversions to developed occurred at an 

average rate less than 1 km2/yr, and from 1992-2000 they 

occurred at a rate of 3 km2/yr.

Discussion

In this section we discuss LU/LC dynamics in the SNE 

based on the aforementioned estimates of the amounts and 

rates of LU/LC change, existing literature, and knowledge of 

the SNE based on observations made during field reconnaissance. The causes of the LU/LC changes and trends form the 

framework for discussing these changes. When possible, we 

have identified the likely driving forces of change and compared LU/LC change estimates with independent data sources 

when available and appropriate.

 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Discussion 

Forest Disturbance

Fire

Landscape disturbance from fire was represented by 

lands classified as forest, grass/shrubland, or disturbed changing to nonmechanically disturbed lands and was the dominant 

change that we detected throughout the 27-yr study period 

(fig. 7). These burned areas are typical of the fire regime during the study period of low-frequency, high-severity fires that 

overwhelm suppression efforts and result in stand replacement. 

High-severity fires result in the mortality of small and subcanopy trees as well as many to most overstory trees (Skinner and 

Chang, 1996). Low- and moderate-severity fires that usually 

do not kill large trees would likely not be mappable because 

the resulting level of disturbance does not meet criteria for 

classifying a forested area as nonmechanically disturbed 

(appendix 1) and/or may not be visible in the satellite imagery. 

We used a dataset of fire perimeters developed by California Department of Forestry/Fire and Resource Assessment 

Program (CDF/FRAP) with contributions from the USFS, 

BLM, and NPS to help interpret the Landsat imagery. This 

dataset contains regions (polygons) representing fire perimeters from 1898-2000 and includes fire name, tracking agency, 

cause, and date of ignition. All of the fires we detected generally coincided spatially with fire locations and temporally 

with ignition dates from the CDF/FRAP dataset. Furthermore, 

although the fires we detected appear in the CDF/FRAP dataset, we did not detect all fires identified by the CDF/FRAP 

dataset occurring within our samples in the imagery for the 

study period. Due to the variety of fire characteristics, including burn-area size and severity of disturbance, not all fires in 

the CDF/FRAP dataset were visible in the imagery or met our 

mapping criteria.

Timber Harvest

All instances of forest cover changing to mechanically disturbed lands represent areas harvested by clear-cutting (fig. 8). 

Our study period begins at the same time as the implementation 

of the CDF’s Z’berg-Nejedly Forest Practice Act (1973) that 

introduced improved silviculture standards with mechanisms 

for inspection and enforcement (Helms and Tappeiner, 1996). 

Figure 9 compares our LU/LC change data documenting timber 

harvest with California timber harvest statistics from USFS and 

tax data. The USFS and tax harvest data includes all counties 

with area in the Sierra Nevada and is a slightly larger than the 

full extent of the SNE. The temporal trends of the two separate 

timber harvest indicators are similar for each ownership class 

as well as for the combined total. Between 1980 and 1986, both 

the amount of timber (fig. 9A) and the amount of land-cover 

change directly resulting from timber harvest (fig. 9B) decline 

probably due to a shift in the harvest pattern shifting from old 

growth to young growth stands as old growth harvesting restrictions increased and young growth stands matured (Stewart, 

1996). Both timber harvest indicators showed an increasing 

trend from 1986-1992 as demand and prices increased for lower 

grade timber that was once considered economically unfeasible 

to harvest. In general, private timber lands are at lower elevations and of higher site quality whereas USFS timber lands are 

at higher elevations and usually of lower site quality (that is, 

primarily lower soil productivity) (Stewart, 1996). This elevation-related ownership distribution may explain the disparity in 

figure 9 between private timber harvest area shown by the two 

indicators, as many privately owned timber sites included in the 

tax data may fall outside of the SNE boundary. As a result, our 

land-cover change data represents less private timber harvest 

than the tax data.

Forest Regeneration

Burned and clear-cut areas are temporary land-cover 

types that transition to various vegetation land-cover classes 

at differing rates in the absence of other disturbances. Burned 

areas usually changed to grass/shrubland and represented 

the early stages of secondary succession. This is the LU/LC 

conversion observed most commonly during the period immediately following fire disturbance. In a few cases, nonmechanically disturbed lands changed to forest rather than grass/shrubland in the period following the disturbance. These cases may 

indicate faster regeneration rates due to more favorable site 

quality, varying fire severity, or forest management policies. 

These cases may also be a function of the varying lengths (that 

is, 6 to 8 years) of the study periods. 

Forest regeneration was likely driven by management 

activities that influenced the natural dynamics of succession. 

Land managers in the SNE usually used seed to regenerate 

forest stands after clear-cutting (fig. 10), although replanting 

may have been used when prompt regeneration was required. 

Private landowners commonly relied on natural regeneration 

(Helms and Tappeiner, 1996). In most cases, Federal and State 

regulations require that sites cleared for timber production must 

be stocked with seedlings within 3 to 5 years of stand removal, 

and so managers often choose to plant in order to ensure 

compliance. Managers also plant rather than seed sites after 

high-severity fires when pine seed is not available and competition with shrubs and shade-tolerant tree species would prevent 

natural regeneration of pine species. Rapid establishment of 

grasses, herbs, and shrubs usually follows disturbance from fire 

or logging and often must be controlled in order for conifers to 

successfully regenerate (Tappeiner and McDonald, 1996).

Reservoir Drawdown

We classified barren shorelands that were exposed due 

to reservoir drawdown as mechanically disturbed because the 

lowering process was primarily driven by human forces (water 

and hydroelectric power demands), although environmental 

conditions such as drought may have influenced where the 

responsible utility companies set the height of reservoir water 
levels. SNE reservoirs’ surface levels vary seasonally because 

winter snowmelt fills reservoirs during the late spring and 

early summer months. Numerous reservoirs were captured 

within our sample blocks, and evidence of reservoir drawdown was apparent in southern Sierra Nevada reservoirs, such 

as Florence Lake, Mammoth Pool Reservoir, and Courtright 

Reservoir (fig. 11).

Reservoir storage data from the California Department 

of Water Resources Data Exchange Center (CDEC) provide 

insight into the temporal variability of reservoir drawdown. 

Most of our imagery and field photographs were acquired in 

mid to late summer, so we analyzed reservoir storage data for 

the month of September. Storage data for 1983 and 2000 for 

reservoirs in the Upper San Joaquin River watershed (southern SNE) show a drop in storage from 63 percent of capacity 

in 1983 to 50 percent of capacity in 2000. CDEC storage 

data do not account for year-to-year fluctuations, but the 

general trend of decreasing September storage agrees with 

our results, which show a detectable drop from 1986-1992 

and from 1992-2000.

Development

We detected little new development in the SNE between 

1973 and 2000. Although Duane (1996) states that the population of the Sierra Nevada doubled between 1970 and 1990, 

most of this documented new development occurred near the 

historical centers of the gold rush in towns that lie to the west 

and outside of the SNE boundary in the Southern and Central 

California Chaparral and Oak Woodland ecoregion. In the case 

of the Lake Tahoe basin, which contains the most urbanized 

areas of the SNE, the footprint of development was established 

by 1969 prior to our study period. After 1969, development 

has greatly slowed due to the constraints of increased public 

ownership through intensive State and Federal land acquisition 

programs, as well as stringent regulations on new development 

aimed at alleviating adverse environmental impacts in the 

Lake Tahoe basin. Most of the small amount of new development we detected in the SNE occurred along the western and 

eastern boundary (fig. 12) of the ecoregion in the form of commercial development to support tourism (fig. 13). 

Comparison to Other Ecoregions

In comparison with the rates of LU/LC change for other 

ecoregions in the Western United States that have undergone 

Land Cover Trends analysis as of January 2006 (fig. 14), the 

SNE is distinctive in that it is the only ecoregion that exhibited a significant trend of increasing rate of change throughout the entire study period. Rates as well as footprints of 

change were significantly greater in the Coast Range and 

Puget Lowland ecoregions, which were both dominated by 

extensive timber harvest and some urban development. In 

comparison to these other ecoregions, change in the SNE can 

be described as low to moderate. 

Relationship of Change to Spatially Explicit 

Variables

We used multiple linear regression analysis to explore 

what spatially explicit environmental and human variables 

may have a statistically significant relationship to LU/LC 

change in the SNE. The dependent response variable in our 

model was mean gross change for each of the 36 sample 

blocks, which was derived by calculating the average of the 

gross change results for each of the four multi-year periods 

that make up the entire 27-yr study period. The potential 

explanatory variables, which were derived from multiple 

sources, are listed in table 4. We selected these variables 

based on knowledge of the SNE and data availability.

Initial multiple regression analysis testing of all eight 

explanatory variables showed a weak relationship to mean 

gross change values that included all changes with the coefficient of determination (R2) being less than 0.10. However, 

eliminating the change resulting from fire and including only 

changes from directly human-induced changes (primarily 

timber harvest, relatively small amounts of reservoir drawdown and development) in the mean gross change values saw 

a strengthening in the relationship between the independent 

variables and mean gross change (R2=0.40). Removing the 

inherently random wildfire events in the SNE may explain 

the improvement in goodness of fit. The t-value for each 

independent variable from the initial regression showed that 

many of these variables do not have a significant influence 

on LU/LC change. A combination of three variables, percent 

private ownership, average percent forest cover, and average 

developed cover, provided the best model which accounted 

for 58 percent (R2=0.58) of the variability of human-induced 

mean gross change (table 5). 

Although there is a great deal of variation evident in 

this analysis, proportion of forest cover, developed cover, 

and land ownership appear to be determinants of the likelihood of direct human-induced change within sample blocks 

located throughout the SNE. Percent private ownership is 

the variable with the highest degree of influence on the mean 

gross change in the model (t-value of 5.18). It is possible that 

these regression results do not necessarily indicate that direct 

human-induced changes occur mostly on private lands, but 

may suggest that these changes are more likely to occur on 

Federally owned lands that are located in close proximity to 

private lands or exhibit a patchwork pattern of ownership. 

The average percent forest and developed cover variables 

have similar degrees of influence (t-values of 2.34 and −2.01, 

respectively) with forest cover having a positive correlation 

and developed cover having a negative correlation to mean 

gross change. Because timber harvesting is the dominant 

change measured by the mean gross change values, it seems 

reasonable that areas with a greater amount of forest cover 

are more likely to undergo change. The inverse relationship 

of developed cover to change in the SNE may show that 

change, such as timber harvest, is more likely to occur away 

from developed areas.

 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Conclusion   

Results of this simple statistical analysis suggest that 

specific spatially explicit variables have a unique relationship 

to LU/LC change in the SNE. We will pursue further quantitative analysis of determinants and driving forces of LU/LC 

change in the SNE and other ecoregions in the Western 

United States. We would like to expand our analysis to link 

metrics of LU/LC change to spatially as well as nonspatially 

explicit variables related to management and policy, economics, and environmental conditions. Furthermore, analysis on a 

cell-by-cell basis within each sample block will allow a more 

detailed examination of change.

Sampling and Uncertainty Measurement

The Land Cover Trends project uses a probability sampling design to provide estimates of LU/LC change for four 

time periods. The precision of our estimates for gross change 

by period (that is, percent area of the ecoregion that underwent any type of change between two dates) is described by a 

margin of error at an 85 percent confidence level (table 6). For 

the SNE, all periods had a margin of error equal to or less than 

+/- 0.5 percent, except for the period 1992-2000, which had a 

margin of error of +/- 2.5 percent. The relatively high margin of 

error from 1992-2000 is likely the result of inadequate sampling density given the spatial distribution of change within the 

SNE. More specifically, most of the gross change during this 

period can be attributed to high amounts of fire occurrence, 

which was not evenly distributed throughout the SNE (fig. 15). 

In general, ecoregions with evenly distributed change require 

fewer sample blocks, while ecoregions with clustered and 

clumped areas of change require more sample blocks to reduce 

sampling uncertainty. We are currently examining methods for 

improving the precision of our estimates, including post-stratified and regression estimation. For additional information on 

the Land Cover Trends sampling design and the inherent uncertainties of sampling estimates, see Stehman and others (2003) 

and Loveland and others (2002).

Implications of Change

Fires that cause land-cover change alter landscape structure by promoting a relatively coarse-grained landscape pattern, increasing soil erosion, affecting nutrient cycling, and 

stimulating plant growth, which benefits faunal communities 

(Chang, 1996). Furthermore, fire can have physical, chemical, and biological effects on soils including loss of soil 

structure, loss of nutrients, and mortality of soil organisms 

(Poff, 1996). Areas affected by high-intensity fires are often 

characterized by increased adverse effects due to greater burn 

intensity (DeBano, 1979 as cited in Poff, 1996).

Soil productivity in areas of land-cover change resulting 

from timber harvest may be affected through erosion, displacement, compaction, biomass export, and leaching (Poff, 1996). 

Additionally, these effects are likely to be greater in areas of 

detectable land-cover change that result from clear-cutting 

in comparison to areas harvested through partial removal of 

forest stands (Poff, 1996). After an area undergoes timber harvest, land managers often apply a variety of practices to prepare the site for regeneration, such as piling slash by mechanical means and burning slash piles. Long-term soil productivity 

is potentially impacted during the preparation period through 

manipulation of the forest floor, especially after clear-cutting 

operations (Poff, 1996). 

The possible ecological implications of the relatively 

small amount of natural land-cover conversion to residential 

and commercial development that we detected from 1973-

2000 are numerous. Direct effects of land conversion to 

development include reduction of total habitat area, reduction 

of habitat patch size, increased habitat fragmentation, and 

isolation of habitat patches by roads, structures, and fences 

(Duane, 1996). Impervious-surface area is a primary landcover component of the developed land-use class and occurs in 

the form of roads, parking lots, driveways, building footprints, 

and other manmade features. Impervious surfaces prevent 

ground percolation and effectively increase runoff velocity, 

peak flows, stream-water temperature, erosion potential, and 

non-point source pollutant concentrations (Slonecker and others, 2001, Brabec and others, 2002).

Conclusion

Land-use and land-cover change has played an important role in shaping the landscape of the SNE. The results of 

our analysis show quantified trends in LU/LC change resulting from fire, timber harvest, development, and reservoir 

drawdown for the period 1973-2000. Extensive public land 

ownership, which continues to increase in areas such as the 

Lake Tahoe basin, will almost assuredly dictate the future 

amounts and geographic distribution of directly humaninduced LU/LC change such as timber harvest and urban 

development. Additionally, fire will undoubtedly continue to 

leave its mark on the SNE landscape as it has in the past. 

The description of the trends of LU/LC change presented here highlights the benefits of multi-temporal analysis 

and, specifically, the uniqueness of the results produced 

using USGS Land Cover Trends project methodology. As 

the project team produces results for additional ecoregions 

in the Western United States, we will have an opportunity to 

conduct regional synthesis and comparison of LU/LC change 

characteristics from multiple ecoregions. Furthermore, we 

consider this study to be the first analysis in anticipation of 

future analyses and applications and this Land Cover Trends 

data, and the results from this study may be used in future 

studies requiring estimates of amounts and rates of regional 

LU/LC change. 
Acknowledgments

We would like to thank Christy Ryan for her invaluable 

assistance throughout the course of this study and Alicia Torregrosa and Nora Devoe for providing insightful comments on 

an earlier draft this report.

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Ruth, L., 1996, Conservation and controversy—national forest 

management, 1960-95, in Sierra Nevada Ecosystem Project 

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10 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000

Appendixes 1–2
Appendix 1 11

Appendix 1. Definitions of land use and land cover

The following are the land-use/land-cover (LU/LC) definitions used in the Land Cover Trends project. To the extent possible, the definitions are based on the original Anderson and others (1976) Level I definitions so that LU/LC data developed 

through this project are consistent with those produced through other programs and projects.

It is important to recognize that our ability to identify and map these LU/LC classes is limited by the technical specifications 

of Landsat MSS, TM, and ETM+ sensors and by the local and regional landscape characteristics that affect the form and contrast 

of LU/LC characteristics. Thus, consistent and accurate detection of fine-scale patterns and features will sometimes be difficult.

1. Water — Areas persistently covered with water, such as streams, canals, lakes, reservoirs, bays, or oceans.

2. Developed — Areas of intensive use with much of the land covered with structures and/or anthropogenic impervious surfaces 

(for example, high-density residential, commercial, industrial, or transportation) or less intensive uses where the land-cover 

matrix includes both vegetation and structures (e.g., low-density residential, recreational facilities, cemeteries, transportation and 

utility corridors, etc.), including any land functionally related to the developed or built-up activity.

3. Mechanically disturbed — Land in an altered and often unvegetated state that, due to disturbances by mechanical means, is in 

transition from one cover type to another. Mechanical disturbances include forest clear-cutting, earthmoving, scraping, chaining, 

reservoir drawdown, and other similar human-induced changes.

4. Mining — Areas with extractive mining activities that have a significant surface expression. This includes (to the extent that these 

features can be detected) mining buildings, quarry pits, overburden, leach, evaporative, tailing, or other related components.

5. Barren — Land comprised of soils, sand, or rocks where less than 10 percent of the area is vegetated. Barren lands are usually 

naturally occurring.

6. Forest — Tree-covered land where the tree cover density is greater than 10 percent. Note that cleared forest land (i.e., clearcuts) will be mapped according to current cover (for example, mechanically disturbed or shrubland/grassland).

7. Grassland/Shrubland — Land predominately covered with grasses, forbs, or shrubs. The vegetated cover must comprise at 

least 10 percent of the area.

8. Agriculture — Land in either a vegetated or unvegetated state used for the production of food and fiber. This includes cultivated and uncultivated croplands, hay lands, pasture, orchards, vineyards, and confined livestock operations. Note that forest 

plantations are considered forests regardless of the use of the wood products.

9. Wetland — Lands where water saturation is the determining factor in soil characteristics, vegetation types, and animal communities. Wetlands are comprised of water and vegetated cover.

10. Nonmechanically disturbed — Land in an altered and often unvegetated state that, due to disturbances by nonmechanical 

means, is in transition from one cover type to another. Nonmechanical disturbances are caused by wind, floods, fire, animals, 

and other similar phenomenon.

11. Snow/Ice — Land where the accumulation of snow and ice does not completely melt during the summer period (that is, perennial).
12 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000

Appendix 2. Period contingency tables

The following tables show matrices describing land-use/land-cover change area and direction by period. All 

of the tables and graphs describing amounts and rates of land-use/land-cover change in the Results section of this 

report can be produced using the data in these contingency tables with the exception of footprint of change.

Wat. Dev. M.Dis. Mini. N.Bar. Fore. Gr./Sh. Agri. Wetl. N.M.Di. Sn./Ice Total

Wat. 605.5 0 0 0 0 0 0 0 0 0 0 605.5

Dev. 0 126.6 0 0 0 0 0 0 0 0 0 126.6

M.Dis. 6.4 0 0 0 0 58.4 0 0 0 0 0 64.8

Mini. 0 0 0 73.5 0 0 0 0 0 0 0 73.5

N.Bar. 0 0 0 0 1446.0 0 0 0 0 0 0 1446.0

Fore. 0 0 0 0 0 39104.0 0 0 0 0 0 39104.0

Gr./Sh. 0 0 191.2 0 0 0 10258.0 0 0 84.4 0 10533.5

Agri. 0 0 0 0 0 0 0 160.1 0 0 0 160.1

Wetl. 0 0 0 0 0 0 0 0 1175.3 0 0 1175.3

N.M.Di. 0 0 0 0 0 111.7 1.0 0 1.1 0 0 113.8

Sn./Ice 0 0 0 0 0 0 0 0 0 0 9.9 9.9

Total 611.9 126.6 191.2 73.5 1446.0 39274.1 10259.0 160.1 1176.5 84.4 9.9 53413.0

1973

1980

km2

1973 to 1980:

Wat. Dev. M.Dis. Mini. N.Bar. Fore. Gr./Sh. Agri. Wetl. N.M.Di. Sn./Ice Total

Wat. 605.5 0 0 0 0 0 0 0 0 0 0 605.5

Dev. 0 126.6 0 0 0 0 0 0 0 0 0 126.6

M.Dis. 0 0 6.4 0 0 146.2 0 0 0 0 0 152.6

Mini. 0 0 0 73.5 0 0 0 0 0 0 0 73.5

N.Bar. 0 0 0 0 1446.0 0 0 0 0 0 0 1446.0

Fore. 0 0 4.2 0 0 38877.8 81.4 0 0 2.8 0 38966.2

Gr./Sh. 0 0 54.2 0 0 0 10452.2 0 0 109.9 0 10616.2

Agri. 0 0 0 0 0 0 0 160.1 0 0 0 160.1

Wetl. 0 0 0 0 0 0 0 0 1254.9 1.1 0 1256.0

N.M.Di. 0 0 0 0 0 0.5 0 0 0 0 0 0.5

Sn./Ice 0 0 0 0 0 0 0 0 0 0 9.9 9.9

Total 605.5 126.6 64.8 73.5 1446.0 39024.5 10533.5 160.1 1254.9 113.8 9.9 53413.0

1986

km2 1980

Wat. Dev. M.Dis. Mini. N.Bar. Fore. Gr./Sh. Agri. Wetl. N.M.Di. Sn./Ice Total

Wat. 592.4 0 0 0 0 0 0 0 0 0 0 592.4

Dev. 0 126.6 0 0 0 2.2 0 0 0 0 0 128.8

M.Dis. 13.1 0 6.4 0 0 391.1 0 0 0 0 0 410.6

Mini. 0 0 0 73.5 0 0 0 0 0 0 0 73.5

N.Bar. 0 0 0 0 1446.0 0 0 0 0 0 0 1446.0

Fore. 0 0 0 0 0 38470.8 190.2 0 0 0 0 38661.1

Gr./Sh. 0 0 146.2 0 0 0 10403.4 0 0 0.5 0 10550.1

Agri. 0 0 0 0 0 0 0 160.1 0 0 0 160.1

Wetl. 0 0 0 0 0 0 0 0 1256.0 0 0 1256.0

N.M.Di. 0 0 0 0 0 102.0 22.6 0 0 0 0 124.6

Sn./Ice 0 0 0 0 0 0 0 0 0 0 9.9 9.9

Total 605.5 126.6 152.6 73.5 1446.0 38966.2 10616.2 160.1 1256.0 0.5 9.9 53413.0

1992

km2 1986

1980 to 1986:

 1986 to 1992:
Appendix 2 13

Appendix 2. Period contingency tables—Continued

Wat. Dev. M.Dis. Mini. N.Bar. Fore. Gr./Sh. Agri. Wetl. N.M.Di. Sn./Ice Total

Wat. 586.3 0 0.1 0 0 0 0 0 0 0 0 586.4

Dev. 0 128.8 0 0 0 3.4 5.1 10.4 0 0 0 147.6

M.Dis. 6.2 0 19.4 0 0 187.8 0.9 0 0.3 0 0 214.5

Mini. 0 0 0 73.5 0 0 0 0 0 0 0 73.5

N.Bar. 0 0 0 0 1446.0 0 0 0 0 0 0 1446.0

Fore. 0 0 29.7 0 0 37359.3 31.3 0 0 7.0 0 37427.3

Gr./Sh. 0 0 361.4 0 0 0 10398.9 0 0 112.0 0 10872.3

Agri. 0 0 0 0 0 0 2.1 149.7 0 0 0 151.8

Wetl. 0 0 0 0 0 0 0 0 1176.2 0 0 1176.2

N.M.Di. 0 0 0 0 0 1190.1 111.7 0 0 5.6 0 1307.5

Sn./Ice 0 0 0 0 0 0 0 0 0 0 9.9 9.9

Total 592.4 128.8 410.6 73.5 1446.0 38740.6 10550.1 160.1 1176.5 124.6 9.9 53413.0

km2 1992

2000

1992 to 2000:

Explanation of land-use/land-cover class abbreviations used in period contingency tables:

 Wat., Water

 Dev., Developed

 M.Dis., Mechanically disturbed

 Mini., Mining

 Bar., Barren

 Fore., Forest

 Gr./Sh., Grassland/Shrubland

 Agri., Agriculture

 Wetl., Wetland

 N.M.Di., Nonmechanically disturbed

 Sn./Ice, Snow/Ice
14  Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000

Figure 1. Sierra Nevada and surrounding ecoregions. Land-use/land-cover data 

shown for the Sierra Nevada ecoregion is from the 1992 National Land Cover Dataset 

(Vogelmann and others, 2001). The 36 100-km2 sample blocks were randomly selected.
Figures 15

Figure 2. Land ownership in the Sierra 

Nevada ecoregion for ownership groups having 

greater than 1 percent of total ecoregion 

area. Ownership data is from the California 

Resources Agency Legacy Project dated 

August 7, 2003. 
16  Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000

Figure 3. A single 100-km2 sample block illustrating land-cover change resulting from timber 

harvest, fire, and subsequent forest regeneration. Most of this sample block (90 percent) is located 

within the Eldorado National Forest in the central Sierra Nevada ecoregion.
Figures 17

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

Land-use/land-cover class

Area (km2

)

1992-2000

1986-1992

1980-1986

1973-1980

Water

Developed

Mechanically

disturbed

Nonmechanically

disturbed

Forest

Grass /Shrubland

Figure 4. Gross change (area gained and lost) by class by period in the Sierra Nevada ecoregion. Class 

area gained is shown by positive values and class area lost is shown by negative values. No changes were 

detected to the mining, snow/ice, and barren classes and consequently are not listed here.
18  Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000

Figure 5. Temporal variability of individual land-use/land-cover classes in the Sierra Nevada ecoregion 

from 1973 to 2000 shown by cumulative area gained, area lost, and net change (gains minus losses).

Forest

1970 1975 1980 1985 1990 1995 2000 2005

Year

Area changed (sq. km)

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Mechanically disturbed

1970 1975 1980 1985 1990 1995 2000 2005

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Area changed (sq. km)

Year

Nonmechanically disturbed

1970 1975 1980 1985 1990 1995 2000 2005

Year

Area changed (sq. km)

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Grass/Shrubland

1970 1975 1980 1985 1990 1995 2000 2005

Year

Area changed (sq. km)

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Developed

1970 1975 1980 1985 1990 1995 2000 2005

Year

Area changed (sq. km)

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Water

1970 1975 1980 1985 1990 1995 2000 2005

Year

Area changed (sq. km)

1600

1400

1200

1000

800

600

400

200

0

-200

-400

-600

-800

-1000

-1200

-1400

-1600

-1800

-2000

-2200

Losses

Gains

Net change
Figures 19

0

20

40

60

80

100

120

140

160

180

1973-1980 1980-1986 1986-1992 1992-2000

Period

Area changed (sq. km)

Fire

Forest regeneration (from fire)

Timber harvest

Forest regeneration (from cutting)

Figure 6. Forest area changed in the Sierra Nevada ecoregion by fire, timber harvest, and 

regeneration during each period.
Figure 7. Photo taken September 2004 of an area (background slope) undergoing regeneration that was 

burned by the Manter Fire on the southern end of the Sierra Nevada ecoregion in Sequoia National Forest, 

Tulare County, Calif. The Manter Fire ignited on July 22, 2000 and burned about 300 km2. Land-cover types shown 

are forest, grass/shrubland, and wetland.

20 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Figure 8. Recently clear-cut area in Plumas National Forest, Plumas County, 

Calif. Land-cover types shown are forest and mechanically disturbed. 

Figures 21
Figure 9. Comparison of timber harvest and land-cover change 

data for the Sierra Nevada ecoregion. A, Timber harvest data by 

year reported by the United States Forest Service and California 

State Board of Equalization for the period 1970-1995 (adapted 

from Stewart, 1996). B, Land-cover change data from analysis 

describing timber harvest (forest conversion to mechanically 

disturbed) by period for the Sierra Nevada ecoregion. 

22 Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Figure 10. Forest regeneration after seeding, Plumas National Forest. Land-cover types shown are forest and 

grass/shrubland. 

Figure 11. Courtright Reservoir in Sierra National Forest, Fresno County, Calif., exhibited lowered surface levels 

by late summer (Sept. 2004). Land-cover types shown are forest, barren, and mechanically disturbed. 

Figures 23
Figure 12. New residential construction in Franktown, Nev., about 1 km west of the eastern boundary of 

the Sierra Nevada ecoregion and north of Carson City. Land-cover types shown are forest, grass/shrubland, 

developed, and agriculture.

Figure 13. Commercial construction along the access road to the Squaw Valley resort area near Lake Tahoe, 

Calif. Land-cover types shown are forest and developed.

24  Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

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

Period

Average annual rate of change (%/yr)

Sierra Nevada

Mojave Basin and Range

Coast Range

Central Valley

Central Basin and Range

Puget Lowland

.Figure 14. Average annual rates of change by period for selected ecoregions in the Western 

United States. These ecoregions were chosen for comparison based on their relative proximity to 

the Sierra Nevada ecoregion and the availability of completed Land Cover Trends analysis data.

Figures 25
Figure 15. Example of extensive land-cover change within a sample block during a single period (1992-2000) caused 

by wildfire in the southern Sierra Nevada ecoregion. The two top images are Landsat Thematic Mapper false-color 

composites (bands 7-4-1) and the bottom images are the corresponding visually interpreted land-cover maps. The 

Manter Fire of July 2000 burned 56.4 percent of this 100-km2 sample block.

26  Land-Cover Trends of the Sierra Nevada Ecoregion, 1973-2000
Figures and Tables 27

Table 1. Land-use/land-cover class area by date as a percent of Sierra Nevada ecoregion total area (52,872 km2).

Table 2. Most common land-use/land-cover conversions in the Sierra Nevada ecoregion from 1973-2000 affecting 

greater than 5 km2 ranked by greatest to least area changed; changes were also aggregated based on how a single or a 

group of similar “to” or “from” classes were affected.

[Mech., mechanically; Nonmech., nonmechanically]

Percent of Percent of

Land-use/land-cover class 1973 1980 1986 1992 2000 km2 ecoregion 1973 class area

Water 1.1 1.1 1.1 1.1 1.1 -25.3 0.0 -4.2

Developed 0.2 0.2 0.2 0.2 0.3 +20.9 0.0 +16.6

Mechanically disturbed 0.4 0.1 0.3 0.8 0.4 +7.7 0.0 +3.7

Mining 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.0

Naturally barren 2.7 2.7 2.7 2.7 2.7 0.0 0.0 0.0

Forest 73.5 73.1 73.0 72.5 70.1 -1812.2 -3.4 -4.7

Grass/Shrubland 19.2 19.7 19.9 19.8 20.4 +603.8 +1.1 +5.9

Agriculture 0.3 0.3 0.3 0.3 0.3 -8.2 0.0 -5.2

Wetland 2.2 2.3 2.4 2.2 2.2 -0.3 0.0 0.0

Nonmechanically disturbed 0.2 0.2 0.0 0.2 2.4 +1210.7 +2.3 +1449.6

Net change, 1973-2000

Area converted Percent of all

Rank From class To class (km2

) conversions

1 Forest Nonmech. disturbed 1404 37.1

2 Forest Mech. disturbed 784 20.7

3 Mech. disturbed Grass/Shrubland 753 19.9

4 Nonmech. disturbed Grass/Shrubland 307 8.1

5 Grass/Shrubland Forest 303 8.0

6 Grass/Shrubland Nonmech. disturbed 135 3.6

7 Mech. disturbed Forest 34 0.9

8 Water Mech. disturbed 26 0.7

9 Agriculture Developed 10 0.3

10 Nonmech. disturbed Forest 10 0.3

11 Nonmech. disturbed Nonmech. disturbed 6 0.1

12 Forest Developed 6 0.1

13 Grass/Shrubland Developed 5 0.1

Total 3782 100.0

Aggregated:

All classes Nonmech. disturbed 1545

Mech. disturbed Vegetation classes 787

Nonmech. disturbed Vegetation classes 316

All classes Developed 21

[Net change is the difference in area between beginning and end dates of the study period (1973 and 2000) which may 

mask changes that occurred during the intermediate periods. Net change by class is shown in terms of class area (km2) 

changed, percent of ecoregion changed, and percent of a class’s 1973 area changed]
28  

Table 3. Rates of land-use/land-cover change for the Sierra Nevada ecoregion grouped according to the general process that the 

conversions and corresponding rates describe.

[Dashes (-) are used to show rates that equal zero km2/yr in order to highlight rates greater than zero. Regen., regeneration; Mech., mechanically; 

Nonmech., nonmechanically]

1972-1980 1980-1986 1986-1992 1992-2000

Cause From class To class km2

/yr km2/yr km2/yr km2/yr

Fire Forest Nonmech. disturbed 14 <1 17 149

" Grass/Shrubland Nonmech. disturbed <1 - 4 14

" Nonmech. disturbed Nonmech. disturbed - - - 1

Total for cause 14 <1 21 163

Forest regeneration Nonmech. disturbed Grass/Shrubland 11 18 <1 14

(from fire) Nonmech. disturbed Forest - <1 - 1

Total for cause 11 18 <1 15

Timber harvest Forest Mech. disturbed 24 25 70 32

Forest regeneration Mech. disturbed Grass/Shrubland 26 32 25 65

(from harvet) Mech. disturbed Forest 1 5

Total for cause 26 32 25 70

Regen. (intermediate) Grass/Shrubland Forest - 13 9 23

Land-use/land-cover class
Table 5. Results of multiple linear regression analysis for the response variable mean gross change.

Table 6. Gross change by period as a percentage of total Sierra 

Nevada ecoregion area and the corresponding margins of error at an 

85-percent confidence level.

Table 4. Potential explanatory variables and corresponding data sources to be tested in statistical analysis of land-use/landcover change.

Tables 29

Potential explanatory variable Data source

Percent private ownership California Resources Agency Legacy Project (2003)

Average percent forest cover, 1973-2000 Land Cover Trends sample block interpretations

Average percent grass/shrubland cover, 1973-2000 Land Cover Trends sample block interpretations

Average percent developed cover, 1973-2000 Land Cover Trends sample block interpretations

Latitude Map coordinates

Longitude Map coordinates

Average elevation USGS National Elevation Dataset

Average percent slope USGS National Elevation Dataset

n = 36

R2 = 0.58

F = 14.58

Residual standard error = 1.05

Model equation: 

mean gross change = (-1.37) + 0.06(perc. private ownership) + 0.02(avg. perc. forest) - 0.34(avg. perc. developed)

Explanatory variable Coefficient Standard error t-value p-value

Percent private ownership 0.06 0.01 5.18 0.00

Average percent forest cover 0.02 0.01 2.34 0.03

Average percent developed cover 0.34 0.17 2.01 0.05

Intercept 1.37 0.71 1.92 0.06

Gross Margin of error

Period change 85% conf. interval

1973-1980 0.9% +/-0.5%

1980-1986 0.7% +/-0.4%

1986-1992 1.6% +/-0.5%

1992-2000 3.9% +/-2.5%

1973-2000 1.8% +/-0.7%