&EPA
CMW
San Pedro River
A Landscape Approach to Community-
Based Environmental Protection
Office of Research and
Development
National Exposure
Research Laboratory
Environmental Sciences
Division
Landscape Ecology
Branch
For More Information
Contact:
William Kepner
kepner.william@epa.gov
Website:
http://www.epa.gov/
nerlesd1/land-sci/
san-pedro.htm
In 1992, the U.S. Environmental Protection Agency
(EPA) developed a national framework for
conducting ecological risk assessment to
evaluate vulnerability of ecological
resources to environmental stres-
sors (EPA/630/R-92/001). Sub-
sequently, the EPA National Exposure
Research Laboratory implemented a
landscape analysis research program
to test the concept of using landscape
composition and pattern indicators as
sensitive measures of large-scale environ-
mental change. The purpose of a land-
scape analysis approach is to provide an
effective and economical method for evalu-
ating watershed and ecological condition
related to disturbance from human and
natural stresses.
Landscape pattern indicators
are derived from remote sensing
data, process models, spatial
statistics, and geographic informa-
tion system technology. They are
used to estimate current status, trend, and
changes of condition in regard to selected
environmental endpoints, such as water-
shed condition, sustainability of ecologi-
cal goods and services, and habitat
condition.
This process is currently being tested in
a small community-based watershed in
southeast Arizona and northern Sonora,
Mexico under a regional interagency research
initiative entitled Semi-Arid Land-Surface-
Atmosphere (SALSA) program. SALSA is a collaborative research proj-
ect composed of international scientists committed to the study of
land degradation processes in semi-arid areas using space-based
technologies. The research is sponsored by EPA, other federal agen-
cies such as the USDA Agricultural Research Service, and other
national research institutes such as IMADES and IRD (the Mexican
and French scientific research institutes for sustainable development,
respectively)
The current research is focused on the upper San Pedro River
basin which originates in Sonora, Mexico and flows north into south-
eastern Arizona. It is an international basin with significantly differ-
ent cross border legal and land use practices. The watershed embod-
ies a variety of characteristics which make it an exceptional outdoor
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San Pedro River - A Landscape Approach to
Community-Based Environmental Protection
laboratory for addressing a large
number of scientific questions in
arid and semi-arid hydrology,
ecology, meteorology, and the
social and policy sciences. The
upper basin represents a transi-
tion area between the Sonoran
and Chihuahuan deserts with sig-
nificant topographic and vegeta-
tion diversity, and a highly vari-
able climate. Elevation ranges
from 900 - 2,900 m and annual
rainfall ranges from 300 to 750
mm. Biome types include
desertscrub, grasslands, oak
woodland-savannah, mesquite
woodland, riparian forest, conifer-
ous forest, and agriculture. The
upper watershed encompasses an area of approxi-
mately 7,600 km2 (5,800 km2 in Arizona and 1,800
km2 in Sonora, Mexico) and represents one of the
most ecologically diverse areas in the United
States and northern Mexico. The riparian zone in
Arizona has been Congressionally designated as a
National Conservation Area and is managed by the
U.S. Department of the Interior.
Landscape research in the upper San Pedro
River basin has focused on the influence of land
cover composition, connectivity, patch size, and
patch abundance to evaluate ecosystem resilience,
watershed condition, and wildlife habitat suitabili-
ty. It utilizes a series of images derived from
Landsat orbiting satellites equipped with the
Multi-Spectral Scanner (MSS). The MSS imagery
has been obtained from three periods (5 June
1973, 10 June 1986, and 2 June 1992) and
remapped and projected to UTM coordinates at
60-m pixel resolution. The derivative products
include digital land cover maps which can be
interfaced with other relevant biophysical data and
ecological and hydrological process models to
assess the trend and consequences of landscape
change on sustainable resources. Additionally, an
8 June 1997 Landsat Thematic Mapper (TM)
image has been added to the database.
Preliminary results about changes in land cover
for the study period indicate that extensive, highly
connected grassland and desertscrub areas are
the most vulnerable ecosystems to fragmentation
and actual loss due to encroachment of xerophytic
mesquite woodland. In the study period, grass-
lands and desertscrub not only decreased in
extent but also became more fragmented. That is,
the number of grassland and desertscrub patches
increased and their average patch sizes decreased.
In stark contrast, the mesquite woodland patches
increased in size, number, and connectivity.
These changes have important impact for the
hydrology of the region, since the energy and
water balance characteristics for these cover types
are significantly different.
While primary anthropogenic stressors in the
project area include urbanization and livestock
grazing, they differ in their magnitude and distri-
bution throughout the watershed. The prelimi-
nary results from this project indicate that the
approach provides a useful methodology to 1)
measure landscape change over large geographic
areas and 2) determine 25-year trends in ecologi-
cal and hydrological condition using advanced
space-based technologies (especially in regard to
land degradation in arid and semi-arid regions of
the United States and Mexico).
For further information contact:
William Kepner
US EPA, National Exposure Research Laboratory
P.O. Box 93478
Las Vegas, NV 89193-3478
http: / /www. epa. gov/ nerlesd 1 / land-sci/ san-pedro. htm
Also, see:
http://www.tucson.ars.ag.gov/salsa/salsahome.html
WEBSITE ANNOUNCEMENT
AUGUST 2001 - 2851eb01
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