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Population, Land Use Change,
and Species Endangerment in the California Mojave: Alternative Futures
Lori M. Hunter,
University of Colorado at Boulder
Institute of Behavioral Science, Program on Environment and Behavior
Campus Box 468, Boulder, CO 80309
[email protected]
303-492-1006
Richard Toth
Utah State University
Landscape Architecture and Environmental Planning
Thomas C. Edwards
United States Geological Service
Department of Fisheries and Wildlife
Utah State University
Robert J. Lilieholm
Department of Forest Resources
Utah State University
DRAFT MANUSCRIPT prepared for “Population, Economy and the Environment: Modelling and
Simulating their Complex InteractionAssociation of America,” Max Planck Institute for
Demographic Research, Rostock Germany, May 19-20 2001.
The Mojave Desert Alternative Futures Project is part of a larger effort, “Analysis and
Assessment of Military and Non-military Impacts on Biodiversity in the California Mojave
Desert” funded by the DoD Strategic Environmental Research and Development Program
(SERDP) and coordinated by the Desert Research Institute (DRI). The alternative futures work is
being conducted at Utah State University.
1
Population, Land Use Change,
and Species Endangerment in the California Mojave: Alternative Futures
Abstract:
Much of the California Mojave Desert ecosystem has been negatively impacted by a variety of
human-related forces. Our research strategy is based upon the hypothesis that three main drivers
interact to produce change within the Mojave region -- sociodemographic, economic, and
biophysical factors. As an example of the interactions between these drivers, regional economic
shifts can bring population redistribution, which, in turn, impacts biodiversity through attendant
land-use change. This study makes use of this triad of cause-and-effect to model a range of
alternative futures for the California Mojave region. We make use of a GIS including
demographic, economic, and biophysical to examine of the implications of various demographic
scenarios on species diversity. Within the context of the California Mojave region, our results
suggest that high density development could reduce conflict with threatened or endangered
species habitat by over 80 percent.
2
Population, Land Use Change,
and Species Endangerment in the California Mojave: Alternative Futures
The environmental implications of population processes have been most carefully examined
within the context of developing countries. This focus can be partially justified by the fact that
much of the population within some of these regions continues to rely upon local environmental
resources for subsistence. As such, environmental change has direct and immediate implications
for local livelihoods. Yet, demographic dynamics within the context of developed nations also
have implications for the natural environment, both as a function of their relation to land-use
change, and due to their association with production and consumption processes. We examine
the former, the implications of land-use patterns as related to population dynamics, within the
context of a developed region, in particular, the California Mojave Desert ecosystem. In a
general sense, we aim to better understand the land requirements inferred by varying levels of
population growth and density, as well as the biophysical implications of those requirements. In
a more specific sense, we aim to develop and examine several plausible demographic and
biophysical future scenarios for the California Mojave, and evaluate those scenarios with an eye
toward habitat loss for currently threatened and endangered (T&E) species. These tasks are
accomplished through the creation of a spatially-explicit database reflecting demographic,
economic, and biophysical data for the region. Factors associated with past land-use patterns are
used to model possible future patterns, with the environmental implications of various plausible
futures ascertained from wildlife habitat models. It is hoped that both the process of model
development, and the results of the analysis, will be of interest to those concerned with
3
developing a better understanding of the implications of future population growth and
development patterns especially with regard to habitat loss.
Background: Fulfilling the resource requirements of a growing population ultimately
requires some form of land-use change, be it to provide for the expansion of food production
through forest clearing, to intensify production on already cultivated land, or to develop the
infrastructure necessary to support increasing human numbers. As such, it is clear that
population is associated with changes in landscape, although political forces, cultural values,
institutional histories, and other mediating factors ultimately shape the association within any
particular geographic context. A burgeoning literature examines these human dimensions of
land-use change, specifying the factors involved and modeling the processes of demographic and
environmental interactions.
The literature examining population and land-use change within developing regions
demonstrates various aspects of the relationship between population and land-use. In Rwanda,
high population densities have been linked to the conversion of marginal lands, such as steep
hillsides, to agricultural use (May, 1995). Similar conclusions have been reached in Zaire
(Shapiro, 1995). The influence of mediating factors on the association between population and
land use change is evident in Honduras, where research suggests that environmental destruction
is due more to inequality of resource distribution and patterns of economic development than to
population pressures per se (DeWalt, Stonich, and Hamilton, 1993). Demonstrating the influence
of political forces, government-sponsored transmigration projects have resulted in the
deforestation of at least 750,000 hectares per year in Indonesia (Fearnside, 1997). Finally, in
South America, a mixture of policy, poverty, and demographic pressures has been found
responsible for much of the deforestation of the Brazilian Amazon (Moran, 1992).
4
Varying significantly from nations in early phases of modernization, land-use change
within many industrialized countries occurs within a framework constrained by environmental
regulations and planning restrictions. As examples of the association between human population
and land-use change within these contexts, Cowen and Jensen (1998) model urban expansion of
Columbia, South Carolina, making use of remotely-sensed imagery and aerial photographs.
Patterns of future development are inferred from the intersections of socioeconomic data and
characteristics related to developable land.
Similar to Cowen and Jensen’s work, and especially relevant to the present project, landuse models developed within the California Urban Futures Project projected growth in the 15county greater-San Francisco Bay area and estimated land use impacts under different
development scenarios (Landis, 1995). Determination of the relative impacts allows evaluation
of alternative agricultural protection and zoning policies at various policy-relevant geographic
levels (e.g., county, region). As an example, simulations suggest that by 2010, “business-asusual” development patterns would require an additional 162,964 acres, representing an increase
of 17 percent in land area developed during the period 1990-2010. Just over 36 percent of the
potential newly developed land is characterized as agriculturally sensitive, meaning that it
represents prime agricultural land, unique agriculture land, or agricultural land of state
importance. As a contrast, future development pattern characterized by compact cities and
contiguous development forms would require an additional 116,726 acres, 27 percent of which is
characterized as agriculturally sensitive (Landis, 1995). A related project examined urban
growth and farmland conversion in the California Central Valley, estimating that by 2040, high
density developments would require approximately half of the farmland conversion necessitated
5
by low density urban sprawl (474,000 acres versus 1,035,000 acres) (Bradshaw and Muller,
1998).
It is these studies which most relate to that presented here, as we examine the spatial
characteristics related to development patterns within the California context. Portions of the
California Mojave Desert ecosystem have been negatively impacted by a variety of humanrelated forces. These include factors related urbanization, off-highway vehicle use, overgrazing,
agriculture, military training exercises, the introduction of exotic plants, and anthropogenicinduced fire. Important characteristics related to land-use change include proximity to existing
development, infrastructure availability, and topographical factors such as slope. Our research
contributes to the work on human dimensions of land-use change as we explore one dimension of
the myriad environmental implications of development patterns, namely habitat loss as related to
population growth and development patterns.
Research Setting: The study region is the California portion of the Mojave Desert,
encompassing approximately 7,400,000 hectares (see Figure 1), bounded by the Great Basin to
the north, the Colorado Desert to the south, and the Sierra Nevada to the west. The region is
characterized by basin and range topography, a primarily flat landscape punctuated by numerous
compact mountain ranges. It is a land of extreme contrasts, containing the lowest point in the
United States at Badwater in Death Valley National Park, adjacent to the highest point in the 48
contiguous states, the peak of Mt. Whitney. While the Mojave is home to thousands of species
of plants and animals, it is perhaps best known as Joshua Tree habitat. It is a land of little rain,
consequently, vegetation is sparse and slow to recover from disturbances. The area contains
more than 250 vertebrate species, over 450,000 people, many commute to greater Los Angeles,
and has an economy based on recreation, resource extraction, and military training.
6
(Figure 1: Study Context)
The study region includes approximately 30 municipalities located within portions of 3
counties (Kern, Los Angeles, San Bernadino). The largest of the cities is Lancaster with a 1990
population of 97,291, located just south of Edwards Air Force Base in the extreme southwestern
portion of the study region. Other settlements of substantial size include Palmdale (68,842),
Hesperia (50,418), Apple Valley (46,674), Victorville (40,674), Ridgecrest (27,725), and
Barstow (21,472).1 As is apparent from Figure 2, many of these communities lie nearby military
bases, suggesting the central role of the military in the region’s economy. Indeed, China Lake
Weapons Center, Fort Irwin National Training Center, TwentyNine Palms Marine Corp Base,
and Edwards Air Force Base all fall within the study’s boundaries. Also noteworthy is the large
portion of the study region which is public property; Death Valley National Park, Mojave
National Preserve, and Joshua Tree National Park are within the study region, in addition to
thousands of acres of Forest Service and Bureau of Land Management property.
(Figure 2: Primary Cities and Land Ownership in Study Region)
Research Objectives, Data, and Methods: As mentioned above, our general aim
is to develop a more detailed understanding of the environmental implications of various landuse patterns within the California Mojave Desert ecoregion. To this end, we merge spatiallyexplicit information on socioeconomic and biophysical systems with an eye toward Objective 1:
1
1990 Population as recorded by the U.S. Bureau of the Census.
7
Develop several plausible scenarios reflecting future patterns of development. In particular, we
ask, for the period 1990-2020, What is the scale of future landscape change implied by current
population projections and current levels of population density?
In order to estimate the scale of landscape change within the region between 1990-2020,
we estimate the projected population growth based upon county-level projections developed by
the California Department of Finance (1998). The following steps are taken to apply county
projections to the study area:
1. Determine the proportion of county population that resided in study area cities for the
years 1970, 1980, and 1990.
2. Project the proportion of county population that will reside in study area cities for the
years 2000, 2010, and 2020. Here we assume the linear change in proportion
exhibited by the historical data will continue through projection years.
3. To calculate the projected population for the study area, apply the projected
proportions to the projected county populations obtained from the California
Department of Finance.
According to historial population data, the Mojave region’s population has experienced
staggering growth over the past several decades. During the period from 1970-1990, the
population of incorporated cities within our study area grew by over 350 percent, increasing from
nearly 70,000 in 1970 to over 300,000 in 1990. As such, human population represents a key
driver of environmental change within the area. If trends continue, the study region’s population
is projected to increase by nearly 900,000 people during the period 1990-2020, representing a
200 percent increase (see Figure 3).
(Figure 3: Actual and Projected Population, Study Region, 1970-2020).
8
A region-wide, spatially-explicit database was created to examine potential for future
development; the units of analysis represent 1,542,337 grid cells each 1-hectare square. Urban
expansion during the period 1970-1990 was discerned from remotely sensed imagery (see Figure
4; Cablk, 2000), with each analytical unit not already developed in 1970 assigned a development
value of either 1 = developed during period 1970-1990 or 0 = not developed during period 19701990. Each grid cell is also assigned a value for the following factors associated with
development:
♦
♦
♦
♦
♦
♦
proximity to existing development
percentage of surrounding cells which are developed
presence within city boundary
distance to primary road
distance to secondary road
slope
(Figure 4: Extent of Urbanization, Study Region, 1970 and 1990).
A logistic regression model is estimated predicting development during the period 19701990 as a function of the above factors. The parameters of this model are then applied to the
analytical units remaining undeveloped in 1990 to estimate future probabilities of development
(Gonzalez, 2000).
To create various scenarios of future land-use, each of the undeveloped grid cells are
“populated” according to their level of development probability and according to regional
population figures. Within this paper, we present two scenarios: 1) projected population at
current density levels (876,985 persons at 3.76 persons/hectare), 2) projected population with
high density development (876,985 persons at 20 persons/hectare). Here we aim to demonstrate
change in habitat conflict implied by current development density vis-à-vis a focus on high
9
density land-uses; varying levels of landscape change are implied by respective levels of
population density. Obviously, these two scenarios represent only a small portion the myriad
scenarios which could be created reflecting various permutations of population size and
densities, each scenario representing their respective levels of human-induced landscape change
to 2020.
Our second research objective is to evaluate the extent of habitat loss for threatened and
endangered species implied by the various future development patterns. The study region of the
California Mojave provides habitat for 12 Federal or State threatened, endangered, or protected
terrestrial vertebrate species (1 reptile, 1 amphibian, 5 mammals, and 5 birds).2 The total number
of vertebrate species predicted to occur in the desert, not including non-natives, is 266 (7
amphibians, 44 reptiles, 62 mammals, and 153 birds).
An understanding of the habitat requirements of these species is developed making use of
natural history information contained in the 3 volumes of California’s Wildlife published by the
State of California, Department of Fish and Game (DFG). The original wildlife habitat
relationship models developed by the DFG were further refined using information from
California’s Wildlife. Specific land form, elevation, and hydrological habitat requirements of the
species were compared with the original habitat models, and areas in which species were not
predicted to occur were removed from the original distributions -- the result being refined species
distributions (see Figure 5).
(Figure 5: Threatened and Endangered Species Habitat, Study Region).
2
In the conflict analysis presented here, 3 bird species are not considered since predicted new development does not
conflict with their predicted distributions.
10
Each of the alternative development patterns implied by the two scenarios above is
evaluated with regard to the percentage of habitat lost for the 9 threatened and endangered
species under consideration. The refined species distribution models were overlaid with the
areas of predicted development to calculate the area of habitat that would be lost to growth under
each scenario’s respective assumptions.
Results: The study results are presented spatially in Figures 6 through 9, with Scenarios
1 and 2 also associated with a table reflecting land-use change required to accommodate the
various demographic projections.
Figure 6 displays projected development under the revised regional population
projections at current density levels. As apparent from the figure, substantially expanded
projected population concentrations characterize the southwestern portion of the study region,
particularly to the southwest and southeast of Edwards Air Force Base within and around
Lancaster, Palmdale, and Victorville. In addition, Ridgecrest and Barstow, and their respective
environs, experience noticeable projected growth. Finally, the primary road to the south of
TwentyNine Palms Marine Corps Base drives that area’s projected pattern of development.
(Figure 6: Scenario One, Population and Development Trend, 2020)
The conflict between this scenario’s projected development and habitat requirements for
the California Mojave’s threatened and endangered species is presented by Figure 7. Analytical
units which are classified as habitat for at least 3 T&E species represent the conflict criteria (total
criteria habitat area on private land = 840,510 hectares); green areas represent habitat with no
11
projected development conflict, while red represent areas where projected land-use change and
important T&E habitat overlap. Within this scenario, 233,075 additional hectares are projected
as developed, 162,542 (69.73%) of which are characterized as habitat for at least 3 threatened
and endangered species. As apparent from the figure, the projected development surrounding
Lancaster, Palmdale, Victorville, and Ridgecrest all pose potential habitat conflicts.
(Figure 7: Scenario One, Threatened and Endangered Species Conflicts)
In order to examine the habitat implications of different development criteria, Scenario
Two in Figure 8 represents equivalent population projections distributed across the probability of
development surface at higher densities (20 persons/hectare). The narrowed land-use
requirements are especially apparent around the region’s primary population centers, those noted
above. In all, new development under this scenario would entail land-use change of 43,860
hectares, representing only 18.82% of that required under the first scenario.
(Figure 8: Scenario Two, High Density Development, 2020)
T&E habitat conflict is greatly diminished under Scenario Two; 31,126 hectares of
critical habitat are projected to undergo human-induced change within this scenario (19.15% of
the critical habitat conflict suggested by Scenario One). Nonetheless, the conflict identified by
this scenario further demonstrates the near-inevitability of habitat loss; although the scale of
landscape change is diminished, a full 70.97% of the change projected falls within areas
identified as habitat for at least 3 threatened or endangered species.
12
(Figure 9: Scenario Two, Threatened and Endangered Species Conflicts)
To further examine the habitat implications of these land-use change scenarios, Table 1
provides the habitat implications of the projected new development for each T&E species. For
each species, hectares of habitat in conflict with projected development are presented for each
scenario, as well as the percentage of habitat within the study area which is represented by this
projected conflict. For instance, under Scenario One, 944 hectares of Arroyo Toad habitat
(32.6% of Arroyo Toad habitat within the study area) are projected to conflict with future
development under this scenario’s assumptions. This is in contrast to the 298 hectares of Arroyo
Toad habitat which conflicts with projected development under Scenario Two. The habitat of the
White-Tailed Kite is also projected to significantly conflict with future development under
Scenario One, with projected growth under Scenario One conflicting with 21.2% of this species
habitat. In all, as would be expected, high density development patterns lead to substantially
reduced habitat conflict for nearly all of the region’s T&E species.
(Table 1: Scenarios 1 and 2, Conflict Details)
Conclusions: Human-induced landscape change is a key factor in species decline. As
such, developing a more detailed understanding of the landscape implications of various
development patterns should be useful to policymakers interested in lessening developmentrelated habitat loss. Our analysis demonstrates the increased habitat pressures brought to bear
upon the natural landscape as a result of population growth, densities, and related development
13
patterns. In particular, higher density development implies significantly more habitat conflict.
Within the context of the California Mojave region, our results suggest that high density
development could reduce conflict with threatened or endangered species habitat by over 80
percent.
In the case of development conflict with T&E species habitat, alternative development
areas or mitigation strategies may need to be considered in the face of future landscape change.
In part, the flexibility of the scenario generation process demonstrated here was designed
specifically for these situations. As an example, the sensitive habitat can be “removed” from
areas representing potential development regions, and the predicted growth then redirected to the
remaining available private lands. The habitat implications of various development scenarios
can then be evaluated relative to each other, therefore clarifying the disparities in costs of the
human dimensions of land-use and planning decisions. In addition to these alternative scenarios,
myriad evaluation metrics could be used; the focus within this paper on threatened and
endangered species is only one such approach. Other work may examine overall habitat
implications through the lens of mammal richness, measures of endemism, or other important
ecological indicators.
The scenarios presented here have been developed to demonstrate linkages between
socioeconomic and biophysical dimensions; it is hoped that both the process and the outcomes
are of interest to both policymakers involved in land-use planning and researchers interested in
the human dimensions of landscape change, particularly as related to the environmental
implications of future development patterns.
14
References
Bradshaw, Ted K. and Brian Muller. 1998. “Impacts of Rapid Urban Growth on Farmland
Conversion: Application of New Regional Land Use Policy Models and Geographical
Information Systems.” Rural Sociology. Vol. 63. No. 1: 1-25.
Cablk, Mary. 1999. Ongoing work at Oregon State University and Desert Research Institute.
California State Department of Finance. 1998 (December). County Population Projections with
Race/Ethnic Detail, Estimated July 1, 1990-1996 and Projections for 1997 through 2040.
Sacramento, CA. Downloaded from
http://www.dof.ca.gov/html/Demograph/Proj_race.html December, 1999.
Cowen, David J. and John R. Jensen. 1998. “Extraction and Modeling of Urban Attributes Using
Remote Sensing Technology.” People and Pixels: Linking Remote Sensing and Social
Science. National Academy Press: Washington DC.
DeWalt, Billie R., Susan C. Stonich, and Sarah L. Hamilton. 1993. “Honduras: Population,
Inequality, and Resource Destruction.” in Carole L. Jolly and Barbara Boyle Torrey, eds.,
Population and Land Use in Developing Countries, Committee on Population,
Commission on Behavioral and Social Sciences and Education. Washington DC:
National Research Council, National Academy Press. Fearnside, Philip M. 1997.
“Transmigration in Indonesia: Lessons from its Environmental and Social Impacts,”
Environmental Management, Vol. 21, No. 4: 553-570.
Gonzalez, Manuel. 2000. “Land Use Futures in the California Mojave.” Ph.D. Dissertation.
Forest Resources, Utah State University: Logan, Utah.
Landis, John D. 1995. “Imagining Land Use Futures: Applying the California Urban Futures
Model.” Journal of the American Planning Association. 61: 438-457.
May, John. 1995. “Policies on Population, Land Use, and Environment in Rwanda,” Population
and Environment: A Journal of Interdisciplinary Studies, Vol. 16, No. 4: 321-334.
Moran, Emilio F. 1992. Deforestation in the Brazilian Amazon, Occassional Paper No. 10, Series
on Environment and Development, Indiana University, Bloomington.
Reibsame, William E. 1990. “The United States Great Plains.” Chapter 34 in The Earth as
Transformed by Human Action. B.L. Turner II, W.C. Clark, R.W. Kates, J.F. Richards,
J.T. Mathews, W.B. Meyer (Eds). Cambridge University Press: Cambridge.
Reibsame, William E, W.J. Parton, K.A. Galvin, I.C. Burke, L. Bohren, R. Young, and E. Knop.
1994. “Integrated Modeling of Land Use and Cover Change.” BioScience. Vol. 44, No.
5:350-356.
15
Shapiro, David. 1995. “Population Growth, Changing Agricultural Practices, and Environmental
Degradation in Zaire,” Population and Environment: A Journal of Interdisciplinary
Studies, Vol. 16, No. 3: 221-236.
U.S. Department of Commerce, Bureau of the Census, 1970 Census of Population, Volume 1,
Characteristics of the Population, Part 6, California, Section 1, Table 6, “Population of
Places”, Issued 1973.
U.S. Department of Commerce, Bureau of the Census, 1980 Census of Population, Volume 1,
General Population Characteristics, Part 6, California, Chapter B, PC80-1-B6, Table 14,
“Summary of General Characteristics”, Issued 1982.
16
Table 1: Scenario 1, T&E Habitat Conflict Details
Scenario 1
(population projections at current density)
Scenario 2
(population projections at high density)
Percentage point
difference in habitat conflict,
Scenarios 1 and 2
Habitat Area
(hectares)
Habitat in conflict
with development
(hectares)
Percentage habitat
in conflict
Habitat in conflict
with development
(hectares)
Percentage habitat
in conflict
2.893
944
32.6%
298
10.3%
-22.3%
Elanus leucurus
Aquila chrysaetos
256.675
7.301.245
54.289
233.075
21.2%
3.2%
7.282
43.860
2.8%
0.6%
-18.3%
-2.6%
Mammals
Mojave Ground Squirrel
Ringtail
Feral Horse
Feral Ass
Nelson’s Bighorn Sheep
Spermophilus mohavensis
Bassariscus astutus
Equus caballus
Equus assinus
Ovis canadensis nelsoni
1.579.194
859.368
262.856
1.901.703
620.897
127.036
20.068
84
2.235
4.076
8.0%
2.3%
0.0%
0.1%
0.7%
46.803
4.183
0
310
938
3.0%
0.5%
0.0%
0.0%
0.2%
-5.1%
-1.8%
0.0%
-0.1%
-0.5%
Reptiles
Desert Tortoise
Xerobates (Gopherus) agassizii
5.980.684
223.980
3.7%
42.948
0.7%
-3.0%
Species
Scientific Name
Amphibians
Arroyo Toad
Bufo microscaphus californicus
Birds
White-Tailed Kite
Golden Eagle
Figure 1: Study Context
Figure 2: Primary Cities and Land Ownership in Study Region.
Figure 3: Actual and Projected Population, Study Region, 1970-2020.
1,600,000
1,400,000
1,200,000
1,000,000
800,000
600,000
400,000
200,000
0
1970
1980
1990
2000
2010
2020
Data source: Based upon population projections prepared by the California Department of Finance, 1999.
Figure 4: Extent of Urbanization, Study Region, 1970 and 1990.
Data source: Based upon analysis of remotely sensed imagery by Mary Cablk, Oregon State University (1999).
Figure 5: Threatened and Endangered Species Habitat, Study Region.
Figure 6: Scenario 1, Population and Development Trend, 2020.*
* Projected population applied to “probability of development” surface at current population density (3.76 persons per hectare).
Figure 7: Scenario 1, Threatened and Endangered Species Conflicts.*
* Areas in which projected development occurs withinT&E species habitat.
Figure 8: Scenario 2, High Density Development, 2020.*
* Projected population applied to “probability of development” surface at high population density (20 persons per hectare).
Figure 9: Scenario 2, Threatened and Endangered Species Conflicts.*
* Areas in which projected development occurs withinT&E species habitat.