U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007-5235

Land-Cover Trends of the Southern California Mountains 

Ecoregion
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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Suggested citation:

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 Investigation Report 2007-5235.

Manuscript approved for publication, September 10, 2007

Text edited by James W. Hendley II

Layout by Luis Menoyo

FRONT COVER

Photograph of development in the foothills of Banning, 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. This project is supported by the USGS Geographic 

Analysis and Monitoring Program in cooperation with the U.S. Environmental Protection 

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

Land-use and land-cover (LU/LC) change is a pervasive process that modifies landscape characteristics and affects a broad range of socioeconomic, biologic, and hydrologic 

systems. Understanding the impacts and feedbacks 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) determine and 

describe the amount, rates, and trends of contemporary LU/LC change by ecoregion for the 

period 1973-2001 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 USGS staff from the National Center 

for Earth Resources Observation and Science (EROS), Rocky Mountain Geographic Science 

Center, Eastern Geographic Science Center, Mid-Continent Geographic Science Center, and the 

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

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

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

Historical Context.............................................................................................................................2

Methods...........................................................................................................................................................2

Results. .............................................................................................................................................................2

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

Average Annual Change .................................................................................................................3

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

Common Conversions......................................................................................................................3

Temporal-Change Characteristics.................................................................................................3

Change Precision .............................................................................................................................4

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

Nonmechanical Disturbance .........................................................................................................4

Suburban Development...................................................................................................................5

Conclusion.......................................................................................................................................................6

References Cited............................................................................................................................................6

Appendix A. Definitions of Land Use and Land Cover.............................................................................9

Figures

1. Location map of the Southern California Mountains Ecoregion......................................................10

2. Map illustrating the major roads of the Southern California Mountains Ecoregion ....................11

3. Land-use/land-cover maps and corresponding Landsat scenes for five dates ..........................12

4. Graph illustrating gross change by class over the study period .....................................................13

5. Field photo of area undergoing vegetation reestablishment after a fire........................................14

6. Field photo of new home development ...............................................................................................15

Tables

1. Percent total land area by class over the study period ....................................................................16

2. Most common land-cover conversions over the study period ........................................................16

3. Average annual gains and losses by class .........................................................................................17

4. Rates of change related to nonmechanical disturbance..................................................................18

5. Gross change and margin of error by period......................................................................................18
Introduction

This report presents an assessment of land-use and 

land-cover (LU/LC) change in the Southern California Mountains ecoregion (fig. 1) for the period 1973-2001. The Southern California Mountains is one of 84 Level-III ecoregions as 

defined by the U.S. Environmental Protection Agency (EPA) 

(Environmental Protection Agency, 1999; Omernik, 1987). 

Ecoregions have served as a spatial framework for environmental resource management, denoting areas that contain a 

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

soils, land use, wildlife, and hydrology. The established Land 

Cover Trends methodology generates estimates of change for 

ecoregions using a probability sampling approach and changedetection analysis of thematic land-cover images derived from 

Landsat satellite imagery.

Study Area

The Southern California Mountains ecoregion 

(SCME) strata encompasses 17,800 km2 of land bordered 

to the north by the Central Valley and Sierra Nevada Mountains, to the east by the Mojave Desert, to the southeast by the 

Sonoran Desert, and to the west by the Los Angeles and San 

Diego Basins. The SCME is located entirely within the State 

of California and includes many of the 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 ranges are 

primarily composed of Mesozoic granitic rock, with a few 

sedimentary and metamorphic exceptions. Additionally, most 

of the mountains in the SCME are quite fractured and transverse in nature (oriented east to west), due to the San Andreas 

Fault and associated thrust faults that underlie the region. 

The mountains of Southern California 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 topographical gradient of rolling hills 

to mountains, not only dictates regional land-use patterns, but 

also influences the patterns of land cover. In terms of land use, 

the majority of urban lands and agricultural development (for 

example, irrigated pasture, hay fields, and orchards) occurs at 

lower elevations in more temperate parts of the SCME. Much 

of this land use is also connected to the suburban growth 

occurring in adjacent ecoregions; cities along the periphery 

of the SCME — specifically, the cities of Pasadena, Santa 

Clarita, and Palmdale — have caused a spillover in development into the SCME’s foothills. At higher elevations, development is primarily associated with recreation activities and their 

supporting infrastructure (for example, campgrounds, vacation 

homes, and ski resorts). 

Although the SCME is generally sparsely populated, the 

largest population concentration in the SCME is located in the 

northwest coastal part of the region in a stretch of lowlands 

along Highway 101. Populated areas generally reside along 

the edge of the SCME and along the numerous highways that 

run through the SCME — namely, Interstates 5 and 10 — 

between larger cities in other ecoregions (for example, Los 

Angeles, San Diego, Palm Springs, and Bakersfield). In 2000, 

the largest SCME cities in terms of population were Santa 

Barbara (pop. 92,325), Goleta (pop. 55,204), Yucaipa (pop. 

41.207), Banning (pop. 23,562), and Tehachapi (pop. 10,957) 

(National Atlas of the United States, 2005a) (fig. 2). Overall, 

the SCME has a total population around 500,000 (U.S. Census 

Bureau, 2000). 

The wide range of topographic and climatic conditions 

within the SCME has led to a wide variety of vegetation 

zonation and, therefore, natural land-cover patterns. Grasses, 

chaparral shrublands and oak woodlands are found at lower, 

drier elevations. Vegetation at this elevation grades towards 

white pine, ponderosa pine, Jeffrey pine, sugar pine, and 

lodgepole pine at higher, moister elevations. The Mediterranean climate of winter-wet, summer-dry conditions sets the 

stage for the annual fire season, occurring from late summer to 

early fall. Dry conditions on the ground coupled with strong, 

seasonal Santa Ana winds, created from pressure systems that 

develop between the coast and the desert, have persistently 

fueled region-wide, large-scale fires for more than 500 years 

(Mensing and others, 1999). As a result of this long fire history, many plant species here are fire-adapted. Some conebearing species require fire for cones to open and seeds to 

Land-Cover Trends of the Southern California Mountains 

Ecoregion

By Christopher E. Soulard, Christian G. Raumann, and Tamara S. Wilson
2 Land-Cover Trends of the Southern California Mountains Ecoregion

disperse. Oak species have a thick, fire-resistant bark and can 

sprout new growth from their trunks. 

Regional vegetation diversity contributes to the large faunal diversity in the region. In all, 476 vertebrate species reside 

within the mountains and coastal areas of Southern California 

(Veirs and others, 1998). Although anthropogenic land use can 

pose a threat to animal life, many of the species that reside in 

the SCME are protected to some degree by the presence of 

Federal land.

Federal lands are 72.5 percent of the SCME, with the 

majority (65.9 percent) managed by the U.S. Forest Service 

(USFS). USFS lands include the Angeles National Forest, 

Cleveland National Forest, Los Padres National Forest, San 

Bernardino National Forest, and Sequoia National Forest. 

Other Federal land agencies include the Bureau of Land 

Management (BLM) (4.4 percent of the SCME), Department 

of Defense (DOD) (0.3 percent of the SCME) and the Fish 

and Wildlife Service (FWS) (0.2 percent of the SCME). DOD 

lands are limited to U.S. Army Corps of Engineer management of Lake Isabella, whereas FWS holdings include a small 

portion of Bitter Creek National Wildlife Refuge. Native 

American lands are concentrated in the southern portion of the 

SCME, with 12 different tribes controlling 0.2 percent of the 

region (National Atlas of the United States, 2005b).

Historical Context

Despite limited modern tribal influence, Native 

Americans were ubiquitous throughout habitable portions of 

the ecoregion prior to European settlement. Arrival of Spanish missionaries in the late 1700s marked the first instance of 

European settlement. Cattle and sheep grazing commenced 

and soon became an economic staple for local tribes, such as 

the Cahuilla Indians (Leadabrand, 1965). Spanish and American inhabitation of the area not only led to a decline in tribal 

autonomy, but also contributed to a shift in Native American 

land use from low intensity farming to more intensive cattle 

grazing.

Livestock grazing expanded in the SCME following 

the California Gold Rush of 1848, but the logging industry 

was responsible for the first road construction in the ecoregion. 

Paulino Weaver guided the first logging efforts in the San Gorgonio Pass in the 1840s, and Mormon settlers constructed the 

first sawmill in 1852 (Leadabrand, 1965; Minnich, 1988). The 

logging industry flourished between 1880 and 1910, primarily 

because of the railroads’ demand for timber for new railroad 

ties and firewood for fuel. Timber also aided in the construction of larger communities in the Los Angeles Basin and resort 

communities in the SCME (for example, Strawberry Valley 

and Idyllwild) (Leadabrand, 1966). 

The second half of the 19th century also marked the 

advent of mining exploration and dam construction within the 

SCME. Historic gold mining (gold was first discovered in Holcomb Valley in 1860) was extensive throughout the ecoregion, 

but unsuccessful in most cases. Perhaps the most successful of 

these endeavors was the gold rush in Julian, which lasted from 

1869 to1880 (Leaderbrand, 1965). Despite the lack of success 

in gold mining, miners found better success mining for gemstones and limestone (for example, in the Lucerne Valley). The 

limestone was initially used in regional steel mills, but later 

used to manufacture cement (Leaderbrand, 1966). 

The growth in each major sector of the economy 

ultimately led to a population increase in the SCME, which 

placed greater demand for water resources. As a result, dam 

construction began in the late 1800s to provide irrigation 

water to regional farmers. Dams at Lake Hemet (constructed 

1890-95) and Lake Arrowhead (1893-1908) marked the first 

such endeavors, although Lake Arrowhead became a recreation-oriented lake soon after its construction (Leadabrand, 

1966). Although many reservoirs were constructed throughout 

the SCME to meet multipurpose resource-use agendas, in current years a greater emphasis has been placed on the recreational needs of the large metropolitan populations in the Los 

Angeles and San Diego Basins to the west of the SCME. 

Methods 

Our interpretation team estimated the amount and 

rate of LU/LC change in the SCME using a stratified random 

sampling of 30 100-km2 (10 km by 10 km) blocks from the 

178 blocks allocated across the ecoregion (fig. 1). We manually interpreted up to 11 classes of LU/LC (appendix A) from 

five dates (1973, 1980, 1985, 1992, and 2001) of archived 

Landsat Multispectral Scanner (MSS), Thematic Mapper 

(TM), and Enhanced Thematic Mapper Plus (ETM+) satellite 

imagery using a 60-meter minimum mapping unit (Anderson 

and others, 1976) (fig. 3). In addition to manual interpretation 

of satellite imagery, we used historical aerial photographs, 

topographic maps, and other ancillary data sources to aid our 

interpretation. Our LU/LC mapping effort yielded results for 

five individual dates and four discrete periods for analysis. We 

then conducted a post-classification comparison of the five 

dates of thematic LU/LC data for each sample block to generate estimates of LU/LC change for the entire SCME with corresponding margins of error at an 85-percent confidence level. 

For a more detailed description of Land Cover Trends project 

methodology, see Loveland and others (2002).

Results

The following section describes the results of the post 

classification comparison applied to the five core dates (1973, 

1980, 1985, 1992, and 2001) for the 30 100-km2 sample 

blocks within the SCME. We created estimates for the SCME 

by scaling our sampling results up to the entire ecoregion 

strata (17,800 km2).
Results 3

Footprint of Change

Between 1973 and 2001, the footprint (overall areal 

extent) of LU/LC change in the SCME was 5.0 percent, or 

885 km2. This change can be interpreted as the amount of the 

SCME that experienced LU/LC change during at least one of 

the four multi-year periods that make up the entire 28-year 

study period. This footprint of change translates to 498 km2 

that changed during one period, 284 km2 that changed during 

two periods, 103 km2 that changed during three periods, and 

less than 1 km2 that changed throughout all four periods. 

Average Annual Change

The average annual rate of LU/LC change in the 

SCME from 1973 to 2001 was 0.3 percent per year. This 

measurement, which normalizes the results for each period to 

an annual scale, means that the region averaged 0.3 percent 

(50 km2) of change each year in the 28-year study period. 

However, this annual change varied between each of the four 

periods. Between 1973 and 1980, the annual rate of change in 

the SCME was 0.2 percent per year, while the annual rate of 

change increased to 0.4 percent per year from 1980 to 1985. 

The normalized annual rate dropped from 1985 to 1992 to 0.3 

percent per year, while the final period spanning from 1992 to 

2001 experienced a greater drop, down to 0.2 percent per year.

Class Area and Change

In 2001, our results illustrate the estimated dominance of four of the eleven LU/LC classes (appendix A) in 

the SCME: grassland/shrubland (65.9 percent), forest (27.5 

percent), developed (2.6 percent), and agriculture (1.5 percent). Although six other LU/LC classes cumulatively made 

up the remaining 2.5 percent of the SCME landscape in 2001, 

each of these classes made up less than one percent of the 

ecoregion (table 1). Between 1973 and 2001, the LU/LC types 

that experienced a measurable net change in relation to the 

total SCME area include, in descending order, developed (0.8 

percent increase), grassland/shrubland (0.7 percent decrease), 

and nonmechanically disturbed (0.2 percent decrease). 

However, net change may not necessarily be the best 

indicator of within class variability for those classes experiencing spatio-temporal fluctuations. The net change metric 

often serves to mask LU/LC dynamics, while analysis of gross 

change (area gained and lost) by individual LU/LC classes 

by period shows that classes have fluctuated throughout the 

28-year study period to a greater degree than net change 

values may indicate (Raumann and others, 2007) (fig. 4). For 

example, the water class may have only experienced a net loss 

of less than 0.1 percent from 1973 to 2001, but instances of 

open water experienced 0.4 percent gross change in the SCME 

over the same 28-year period. Moreover, the same nonmechanically disturbed class that experienced a 0.2 percent net 

decrease between 1973 and 2001 underwent 3.5 percent gross 

change during the 28-year study period. Figure 4 illustrates the 

dynamic nature of LU/LC change in the SCME from 1973 to 

2001.

Common Conversions

The “from-to” information afforded by a post classification comparison allowed us to identify LU/LC class conversions and rank these conversions according to their magnitude:

Ranking value = AreaΔ1973 to 1980 + AreaΔ1980 to 1985 

+ AreaΔ1985 to 1992 + AreaΔ1992 to 2001

Table 2 illustrates the most frequent conversions from 

1973 to 2001 in the SCME. Five of the top ten most prominent 

conversions are connected to 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 land-cover loss. However, much of this land experienced ecological succession, or 

regrowth, after each disturbance event. This regrowth accounts 

for 531 km2 of vegetated land-cover gain (areas that were 

disturbed in consecutive periods account for an additional 21 

km2 of change). The transitions to the developed class represent other common conversions in the SCME during the study 

period (146 km2). Less common conversions consisted of the 

transitions to and from the water class and shifts in agricultural 

land use. 

Temporal-Change Characteristics

We measured significant temporal variability in 

certain LU/LC classes in the SCME throughout the 28-year 

study period. In certain instances, LU/LC changes tended to 

be unidirectional in nature, changing rather consistently in 

each of the four periods. Developed land not only represents 

the only land use that had a significant increase between 1973 

and 2001, but also stands alone as the only land-use class that 

did not experience any decline in each of the four periods. 

Between 1973 and 1980, the developed class averaged a net 

annual increase of 5.9 km2 per year. During the next two periods, development in the SCME averaged an annual increase 

of 7.2 km2 per year (1980-1985) and 6.2 km2 per year (1985-

1992). During the final period from 1992 to 2001, developed 

land continued to increase, but at a lower rate of 2.9 km2 per 

year (table 3).

Although expansion of anthropogenic land uses such 

as development had an inverse and a measurable influence 

on background land-cover types, nonmechanical disturbance 

events (exclusively in the form of fire) had the most significant impact on the temporal variability of grass/shrubland 

and forest changes in the SCME throughout the study period. 

The average areal extent of fire disturbance, as represented 

by the conversion of vegetated lands to the nonmechanically 

disturbed class, was 7.0 km2 per year averaged from 1973-
4 Land-Cover Trends of the Southern California Mountains Ecoregion

1980, with an increase to 53.9 km2 per year from 1980-1985. 

During the 1985-1992 and 1992-2001 periods, the conversion 

to nonmechanically disturbed lands decreased to 9.5 km2 per 

year and 15.4 km2 per year, respectively. The rate of vegetation 

regeneration after fire, represented by the conversion of land 

from nonmechanical disturbance to vegetation classes, mirrors 

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 

(Raumann and others, 2007) (table 4). In the SCME, 89 

percent of this regeneration occurred as conversion to grass/

shrubland, whereas the remaining 11 percent occurred as a 

conversion to forest. 

Change Precision

LU/LC change estimates for each of the four time 

periods (1973-1980, 1980-1985, 1985-1992, and 1992-2001) 

are stated by a margin of error at an 85-percent confidence 

interval (table 5). Only one of the four periods had a margin 

of error within +/- one percent at an 85 percent confidence. 

These larger errors are directly related to the high amount and 

uneven distribution of gross change across the SCME (1,410 

km2). In terms of change distribution, ecoregions with uneven 

pockets of change require a greater sampling density to reduce 

uncertainty in change estimates. Therefore, increasing the 

number of sample blocks in the SCME would likely reduce 

the region’s margin of error. A more complete explanation of 

Land Cover Trends sampling design and sampling uncertainty 

is provided by Stehman and others (2003) and Loveland and 

others (2002).

Discussion

Changes and overall LU/LC trends in the SCME can be 

attributed to various driving forces. Here, we explain these 

possible drivers based on both existing literature and direct 

field observation. In some cases, drivers of change are unique 

to a given landscape. However, we will also explore how 

certain drivers may influence change in multiple LU/LC types. 

In addition, we will examine how changes in one LU/LC class 

may influence change in another. Understanding both the 

positive and negative feedback mechanisms driving change 

within and among LU/LC classes will illustrate the overall 

interdependence of land dynamics within the ecoregion. On 

the basis of our change estimates, we can make some generalizations about the possible drivers of change and the potential 

implications of these changes in the future.

Nonmechanical Disturbance

The most dynamic LU/LC conversions in terms 

of area changed throughout the 28-year study period were 

conversions pertaining to the nonmechanical disturbance class. 

Nonmechanical landscape disturbance, which was entirely 

attributed to fire, typically involved changes from grassland/

shrubland, forest, and previously disturbed lands to the 

nonmechanically disturbed class. The majority of this change 

occurred in grassland and chaparral sites at lower elevations, 

with less change occurring in higher elevation forests of the 

SCME. In terms of vegetation recovery after a nonmechanical disturbance event, the burnt area either transitioned back 

to its original land-cover class in the following time period or 

to an intermediate successional state. Although the latter was 

masked in shrubland environments due to the generalization 

of the grassland/shrubland class, the establishment of grasses 

in some forested areas following a fire illustrated these early 

stages of secondary succession (table 4).

Fires in grassland, shrubland, and forest landscapes 

presented a unique suite of problems in terms of manually 

mapping fire. We integrated a historical fire-perimeters dataset 

from California Department of Forestry/Fire and Resource 

Assessment Program (CDF/FRAP) into our manual interpretation to help interpret the Landsat imagery. The CDF/

FRAP database not only contains fire location information 

from 1910-2001, but also provides ancillary attributes such as 

ignition date, tracking agency, and cause (California Department of Forestry, 2006). Our detection of fires was consistent 

with the CDF/FRAP fires database in that each of our mapped 

fires were included in the database. However, the CDF/FRAP 

database had many fires mapped within the 28-year study 

period that we did not map in our study. Factors such as fire 

intensity/severity, ignition date, and burn area may explain this 

discrepancy. For example, a grassland/shrubland area many 

have burned immediately following one of our imagery dates 

and fully recovered to pre-burn conditions by our next Landsat 

imagery date (or burned multiple times). As for forested areas, 

many of the prescribed burns used to thin forested lands may 

not have been large enough or severe enough to map with our 

60-meter mapping unit. 

The former fire cycle under which plant and animal species evolved has changed with increasing human populations 

and implementation of fire suppression efforts in the 20th century. In the past, natural ignition sources such as lightning and 

wind dictated fire behavior in the SCME, but today most of the 

fires are human-caused and are located at or near the interface 

between human development and wild lands (U.S. Department of Agriculture, 2005) (fig. 3). Although debate still 

exists regarding whether or not fire suppression efforts have 

offset the effects of human caused fires on a whole within the 

SCME, existing research clearly indicates that humans have 

changed the nature of these fires in terms of frequency, size, 

and location (Minnich and others, 1995; Keeley and others, 

1999; Stephenson and others, 1999; California Department 

of Fish and Game, 2006). According to Keeley and others 

(1999), increasing encroachment of human populations into 

wildlands is highly correlated with increased fire frequency 

and decreased fire return intervals. For example, the addition 

of the human element has increased the frequency of fires by 
Discussion 5

increasing artificial ignitions, while suppression efforts have 

kept many of these fires small in size. As a result, the SCME’s 

landscape appears to have more of a patchwork appearance 

compared to areas with limited human presence or without 

suppression programs (for example, Baja California, Mexico; 

see Minnich, 1983). Suppression efforts have led to the reduction of fires in montane woodlands, while the presence of 

the urban interface has increased the frequency of fires in the 

grassland/shrubland land cover at lower elevations, shifting the 

actual location of where fires occur (fig. 5). 

Although the human element plays a pivotal role in the 

occurrence of fire in the SCME, the cyclic ecoregion-wide 

signal of fire occurrence followed by grassland regeneration 

also follows the well documented cyclic process of interannual 

climate variability associated with El Niño. The influence of 

El Niño is well established for Southern California. In general, El Niño events bring higher than normal winter rainfall 

with the southern displacement of the jet stream, whereas 

La Niña events are associated with anomalously dry winters. 

Higher than normal rainfall during an El Niño winter increases 

available fuel load, whereas the subsequent dry years deplete 

vegetation fuel moisture, creating optimal fire conditions. 

Antecedent wet years followed by subsequent dry years have 

already been shown to increase fire occurrence in southwestern forests (Swetnam and others, 1990; Swetnam and others, 

1999). Historic dendrochronological records from Northern 

Baja California also indicate large fires occurring in anomalously dry years (Stephens and others, 2003). Occurring the 

year after our core date of 1992 and 1 year after a significant 

El Nino winter, the 1993 fire season greatly impacted the 

region at an estimated cost of 1.3 billion dollars (Lott and others, 2006). The most recent occurrence of this sort occurred in 

late 2003, when more than 700,000 acres burned in the SCME 

following 5 years of drier than normal conditions. Estimated 

costs of this latest disaster alone were 2.5 billion dollars (Lott 

and others, 2006).

Economic losses are not the only consequence of fire in 

SCME. Changes in the historical fire regime can also threaten 

ecological diversity in the area by creating a more fragmented 

landscape that may effectively inhibit the dispersal mechanisms of some species, while enabling the rapid encroachment of others. For example, the closed-coned Tecate cypress 

(Cupressus forbesii) requires fire to release seeds from the 

cone, but increased fire frequency can wipe out local sapling 

populations before they are mature enough to produce seed 

(White and others, 1995). Conversely, seedling establishment 

in Coulter pines (Pinus coulteri) is prolific following a fire, as 

seedlings flourish in full sun (U.S. Department of Agriculture, 

2005). At lower elevations, a different story emerges. The 

most dramatic fire-induced changes here occur in coastal sage 

and buckwheat scrub communities where frequent fires have 

been shown to significantly degrade habitat quality (Stephenson and others, 1999). Loss of shrub cover creates opportunities for the invasion of nonnative annual grasses, such as 

cheatgrass, which inhibit future reestablishment of scrubland 

vegetation. 

Changes in plant cover and abundance will invariably 

lead to changes in faunal distribution. Recent declines in 

California spotted owl populations have been attributed to fires 

that eliminate tree stands as well as the lack of riparian corridors linking SCME’s discontinuous mountain ranges (White 

and others, 1995). Other endangered species whose habitats 

have recently suffered fire-associated habitat decline include 

the Quino checkerspot butterfly (Euphydryas editha quino), 

coastal California gnatcatcher (Polioptila californica californica), Least Bell’s vireo (Vireo bellii pusillus), and mountain 

yellow-legged frog (Rana muscosa) (Center for Biological 

Diversity, 2007). 

Suburban Development

Mid 20th century development in the SCME primarily consisted of recreational development — campgrounds, 

resort communities (for example, Lake Arrowhead), and 

vacation homes. This type of development provided a temporary getaway for tourists from adjacent areas. However, the 

SCME’s rugged terrain deterred most people from taking up 

permanent residence. Recreational development continues to 

thrive throughout the SCME (for example, Mountain High Ski 

Resort and Pine Mountain Club), but a suite of driving forces 

has contributed to new development in the region. 

Development in the basin just west of the SCME consists 

of Los Angeles and San Diego, two of the most populated 

metropolitan areas in the Untied States. Additionally, Bakersfield borders the SCME to the north and Palm Springs flanks 

the SCME to the east. The SCME not only acts as a thoroughfare between these cities (with an extensive and ever-changing 

road network) but also represents a location for suburban 

expansion to accommodate a nearly fivefold increase in population in surrounding areas since 1940 (California Department 

of Finance, 2004; Southern California Association of Governments, 2006) (fig. 6). In recent decades, suburban development 

along the ecoregion — specifically, the cities of Pasadena, 

Santa Clarita, and Palmdale — has caused a spillover in 

development into the SCME’s foothills (fig. 3). This spillover 

accounts for a large part of the urban change that we detected 

between 1973 and 2001. Although this increase in population may contribute 

to economic benefits such as increased tourism and commerce, 

these changes do not come without an environmental cost. The 

consequences of development are often the same as fire in the 

SCME, such as the eradication of floral and faunal habitat. For 

instance, both development and fire tend to occur in the lower 

elevations of the SCME, a landscape where grass/shrubland is 

the primary land cover. The loss of approximately 80 percent 

of coastal sage scrub has been attributed to development in 

the coastal basins. This land cover is also the primary habitat 

of the California gnatcatcher and other endangered species 

(Stephenson and others, 1999). Loss of grass/shrubland 

pushes some species to marginal habitat and may contribute to 

the creation of disjunct populations and habitat fragmentation. 
6 Land-Cover Trends of the Southern California Mountains Ecoregion

Continued development will place additional limits on range 

size, continuity, and connectivity (Kattan and others, 1994; 

Knick and others, 1995).

LU/LC conversions may also indirectly affect quality of 

animal life by increasing water and air pollution. For example, 

development adds to the impervious surface area of the landscape through roads, structures, dams, and other manmade 

features. This, in turn, changes surface and ground-water 

hydrology, including increased surface water temperatures, 

higher flood frequency, increased erosion potential, and water 

pollution concentrations (for example, sediments, metals, 

fertilizers, and pesticides) (Raumann and others, 2007; Jones 

and others, 2001; Barnes and others, 2000). These changes 

not only impact wildlife, but also pose a threat to humans by 

increasing the toxicity of drinking water and the potential of 

hazardous events. Regional development also facilitates heavy 

vehicle use within and around the SCME, producing high concentrations of ozone and nitrogen in the region’s atmosphere 

(Lee and others, 2003). These pollutants cause increased 

tree mortality, alter species dynamics, and eventually runoff 

into streams (causing increased water nitrate concentrations) 

(Takemoto and others, 2001; Stephenson and others, 1999).

Conclusion

The SCME is a geographically unique place, nearly surrounded at lower elevations by human development with few 

natural corridors linking its composite mountain ranges. Population expansion and contact with wildland areas are changing 

the historical fire regime. These anthropogenic changes make 

predictions of future ecosystem health difficult as threats and 

outcomes cannot be measured against historical conditions. 

Topographic isolation coupled with increased fragmentation of 

habitat by fire pose significant threats to existing diversity and 

may ultimately drive species turnover in SCME. Protection of 

this designated biodiversity hotspot will become increasingly 

difficult given current LU/LC trends (Myers and others, 2000). 

On Federal lands, many agencies have had to adopt multiscale 

integrated planning and management activities in an attempt 

to deal with these ecological processes within their given management unit (Hann and others, 2001). However, the consequences of LU/LC trends for nonmechanical disturbance, loss 

of grass/shrubland, and development do not necessarily follow 

managerial boundaries. 

Our description of contemporary LU/LC change trends 

in the SCME illustrates the benefit of multi-temporal analysis 

and reinforces the interconnection between regional land use 

and land cover. As the Land Cover Trends team continues to 

interpret change for other ecoregions within the United States, 

we are exploring methods to refine our change estimates and 

the corresponding margin of error with tools such as regression estimators and post-stratification techniques (Stehman and others, 2003). Additionally, completing additional 

ecoregions will provide the opportunity to compare change 

estimates between ecoregions in an attempt to learn about 

the variability of change between different landscapes and 

will allow results to be merged to create estimates for larger 

geographic assemblages, such as California, or the Western 

United States. 

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Appendix A. Definitions of Land Use and Land Cover 9

The following are the general land-cover definitions that 

will be used in the project. To the extent possible, the definitions reflect the original Anderson and others (1976) level-I 

definitions so that land-cover data developed through the 

Land Cover Trends project are consistent with those produced 

through other programs and projects. A minimum mapping 

unit of 60 meters will used to determine land-cover.

Developed – Areas of intensive use with much of the land 

covered with structures (for example, high density residential, 

commercial, industrial, or transportation) or less intensive 

uses where the land-cover matrix includes both vegetation and 

structures (for example, low density residential, recreational 

facilities, cemeteries, or transportation and utility corridors), 

including any land functionally related to the developed or 

built-up activity.

Cropland and Pasture – 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 as forests or 

woodlands regardless of the use of the wood products.

Forests and Woodland – Tree-covered land where the 

tree-cover density is greater than 10 percent. Note that cleared 

forest land (for example, clearcuts) will be mapped according to current cover (for example, disturbed or transitional, 

shrubland/grassland).

Shrubland/Grassland – Land predominately covered with 

grasses or shrubs. The vegetated cover must be at least 10 

percent of the area.

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.

Water Bodies – Areas persistently covered with water, 

such as streams, canals, lakes, reservoirs, bays, or oceans.

Snow and Ice – Land where the accumulation of snow 

and ice does not completely melt during the summer period.

Barren – Land comprised of natural occurrences of 

soils, sand, or rocks where less than 10 percent of the area is 

vegetated.

Mining – Areas with extractive mining activities that have 

a significant surface expression. This includes (to the extent 

that these features can be detected) mine buildings, quarry 

pits, overburden, leach, evaporative, tailing, or other related 

components.

Mechanical Disturbed or Transitional – Land in an 

altered unvegetated state that, due to disturbances by mechanical means, is in transition from one cover type to another. 

Mechanical disturbances including forest clear cutting, earthmoving, scraping, chaining, reservoir draw down, or other 

related human-induced changes.

Nonmechanical Disturbed or Transitional – Land in an 

altered unvegetated state that, due to disturbances by nonmechanical means, is in transition from cover type to another. 

Nonmechanical disturbances include wind, floods, fire, animals, and other related sources.

Appendix A. Definitions of Land Use and Land Cover
Figure 1. Southern California Mountains ecoregion and surrounding ecoregions. Information shown includes land-use/land-cover data National Land Cover Dataset (Vogelmann and others, 2001) and the 30 randomly selected 100 km2 blocks discussed in text.
Figure 2. Southern California Mountains ecoregion and surrounding ecoregions. Information shown includes partial road and city data National Atlas (National Atlas, 2005c).
Figure 3. A single 100-km2 sample block located in the foothills of the Southern California Mountains ecoregion. Dominant land-use/land-cover expansion of development into agriculture and grass/shrubland and conversions to/from nonmechanically disturbed land, which illustrates the firegeneration process. [Mech., mechanically; Nonmech., nonmechanically]
Figures and Tables 13

Gains and Losses by Land-Use/Land-Cover Class

-800

-600

-400

-200

0

200

400

600

Water

Developed

Mech. Disturbed

Mining

Barren

Forest

Grass/Shrub

Agriculture

Wetland

Nonmech. Disturbed

1992-2001 

1985-1992

1980-1985 

1973-1980 

Figure 4. Gross change in land use/land cover for each of the four periods studied. This diagram illustrates 

how net change can mask within class fluctuations within each period and for the entire 28-year study period. 

[Mech., mechanically; Nonmech., nonmechanically]
14 Land-Cover Trends of the Southern California Mountains Ecoregion

Figure 5. Field photo taken April 2005 of an area by Silverwood Lake, Calif., undergoing 

regeneration following a fire. Although grasses and shrubland tend to reestablish quite soon after 

a fire, trees take much longer to recover. Land-cover types shown are grass/shrubland and water.
Figures and Tables 15

Figure 6. Field photo taken April 2005 of new homes in Castaic, Calif. Castaic is an unincorporated community 

in Los Angeles County that is located along Interstate 5. Land-use/land-cover types shown are grass/shrubland, 

forest, developed, and water.
16 Land-Cover Trends of the Southern California Mountains Ecoregion

Table 1. Land-use/land-cover class area as a percentage of the Southern California Mountains ecoregion strata area (17,800 km2).

 Net change, 1973-2001

Land-use/cover class 1973 1980 1985 1992 2001 km2 Percent of

ecoregion

Percent of 1973 

class area

Water 0.8% 1.0% 0.9% 0.8% 0.8% 7.8 0.0% 5.5%

Developed 1.8% 2.1% 2.3% 2.5% 2.6% 145.8 0.8% 44.8%

Mechanically disturbed 0.1% 0.0% 0.0% 0.1% 0.1% -10.1 -0.1% -38.8%

Mining 0.1% 0.1% 0.1% 0.1% 0.1% 7.7 0.0% 70.3%

Barren 0.5% 0.5% 0.5% 0.5% 0.5% 0.2 0.0% 0.3%

Forest 27.4% 27.7% 27.0% 27.0% 27.5% 21.4 0.1% 0.4%

Grass/Shrubland 66.6% 66.7% 65.9% 66.9% 65.9% -130.1 -0.7% -1.1%

Agriculture 1.6% 1.5% 1.5% 1.5% 1.5% -13.4 -0.1% -4.8%

Wetland 0.2% 0.2% 0.2% 0.2% 0.2% 0.6 0.0% 2.1%

Nonmechanically disturbed 0.9% 0.3% 1.5% 0.4% 0.8% -29.9 -0.2% -17.8%

Table 2. Most common land-use/land-cover conversions in the Southern California Mountains ecoregion from 1973-2001. 

Rank From Class To Class Area Changed (km2)

1 Nonmech. Disturbed Grass/Shrubland 470

2 Grass/Shrubland Nonmech. Disturbed 382

3 Forest Nonmech. Disturbed 119

4 Grass/Shrubland Developed 104

5 Grass/Shrubland Forest 102

6 Nonmech. Disturbed Forest 60

7 Grass/Shrubland Water 27

8 Agriculture Developed 22

9 Mech. Disturbed Grass/Shrubland 21

10 Nonmech. Disturbed Nonmech. Disturbed 21

11 Forest Developed 16

12 Water Grass/Shrubland 16

Mech., mechanically; Nonmech., nonmechanically]
Figures and Tables 17

Table 3. Average annual gains and losses by land-use/land-cover class for the Southern California Mountains ecoregion.

Normalized Gains and Losses

(km2/year) 1973 1980 1985 1992 2001

Water

 Losses - - -1.6 -3.1 -0.2

 Gains - 4.5 - 0.2 0.6

Net change (gains minus losses) - 4.5 -1.6 -2.9 0.5

Developed

 Gains - 5.9 7.2 6.2 6.2

Mechanically disturbed

 Losses - -3.7 -0.6 -0.5 -0.6

 Gains - 0.4 1.3 1.7 0.8

Net change (gains minus losses) - -3.3 0.7 1.1 0.2

Nonmechanically disturbed

 Losses - -21.7 -9.7 -38.1 -7.3

 Gains - 4.5 53.9 9.1 15.4

Net change (gains minus losses) - -17.2 44.1 -29.0 8.1

Forest

 Losses - -0.7 -23.1 -0.7 -1.6

 Gains - 8.0 0.2 0.8 11.1

Net change (gains minus losses) - 7.3 -22.9 0.1 9.4

Grass/Shrubland

 Losses - -13.6 -38.8 -14.1 -28.2

 Gains - 16.7 10.7 39.3 7.3

Net change (gains minus losses) - 3.1 -28.1 25.2 -20.9

Agriculture

 Losses - -1.6 -0.7 -1.5 -0.4

 Gains - 0.9 1.1 0.3 0.2

Net change (gains minus losses) - -0.7 0.3 -1.2 -0.2

Mining

 Losses - - - - -

 Gains - 0.3 0.2 0.4 0.2

Net change (gains minus losses) - 0.3 0.2 0.4 0.2

Wetland

 Losses - - - - -0.1

 Gains - - 0.1 0.1 -

Net change (gains minus losses) - - 0.1 0.1 -0.1
18 Land-Cover Trends of the Southern California Mountains Ecoregion

Table 4. Rates of land-use/land-cover changes grouped according to the processes that the changes represent.

Land-use/land-cover class

From class To class

1973-1980

km2/yr

1980-1985

km2/yr

1985-1992

km2/yr

1992-2001 

km2/yr

1973-2001

km2/yr

Fire

Forest Nonmech. disturbed <1 20.7 <1 1.6 4.3

Grass/Shrubland Nonmech. disturbed 4.4 33.2 8.9 13.6 13.6

Nonmech. disturbed Nonmech. disturbed 2.5 - <1 <1 <1

Agriculture Nonmech. disturbed - - - <1 <1

Total 7.0 53.9 9.5 15.4 18.7

Regeneration (from fire)

Nonmech. disturbed Grass/Shrubland 13.9 9.5 37.3 7.1 16.8

Nonmech. disturbed Forest 7.5 <1 <1 <1 2.2

Nonmech. disturbed Developed <1 - - - -

Nonmech. disturbed Total 21.6 9.7 38.1 7.2 19.0

Regeneration (intermediate)

Grass/Shrubland Forest <1 - - 10.5 3.6

[Dashes (-) are used to show rates that equal zero km2/yr in order to highlight rates greater than zero. Nonmech., nonmechanically]

Table 5. Gross change and corresponding margin of error for 

each time period for the Southern California Mountains ecoregion.

Period Gross Change %

Margin of Error 

85%

Confidence Interval

1973 to 1980 1.6% +/-1.0%

1980 to 1985 2.1% +/-1.5%

1985 to 1992 2.3% +/-1.6%

1992 to 2001 1.9% +/-1.1%