307LEB99.db V

egetation change in the American W est has been a subject of concern throughout the twentieth century

. Although many of the changes have been recorded qualitatively through the use of comparative photography and historical reports, little quantitative information has been available on the regional or watershed scale. It is currently possible to measure change over large areas and determine trends in ecological and hydrological condition using advanced space-based technologies. Specifically , this is being tested in the Upper San Pedro W atershed using a system of landscape pattern measurements derived from satellite remote sensing, spatial statistics, process modelling, and geographic information systems technology

. These technologies provide the basis for developing landscape composition and pattern indicators as sensitive measures of large-scale environmental change and thus, may provide an ef fective and economical method for evaluating watershed condition related to disturbance from human and natural stresses. Land managers in the Southwest have traditionally been interested in status and trend in environmental conditions. The principal degradation processes that have occurred throughout the western rangelands involves 1) changes of vegetative cover which result in the introduction of exotic annual species or woody shrubs and trees, and 2) acceleration of water and wind erosion processes which result in soil loss and decrease water infiltration and storage potential. Historically , these have been linked to livestock grazing and short-term drought. However , rapid urbanization in the arid and semi-arid Southwest within the last 25 years has become an important anthropogenic factor in altering land cover composition and pattern.

Land cover has been derived from a multi-date satellite imagery database which incorporates Landsat Multi-Spectral Scanner (MSS) imagery from the early 1970s, mid 1980s, and early 1990s and Landsat Thematic Mapper (TM) imagery from 1997. The MSS imagery has been remapped and projected to Universal T ransverse Mercator ground coordinates at 60 meter resolution; the 30 meter TM imagery has been resampled and mapped at 60 meter resolution for comparison. The land cover has been generated in a 10- class system using a modification of the Brown, Lowe, and Pase (BLP) hierarchical vegetation classification nomenclature. All vegetation has been classed to the BLP Formation level and an urban cover class has been added. The four land cover images represent a quarter century of change across the watershed (5 June 1973, 10 June 1986, 2 June 1992, and 8 June 1997). The painted relief map was developed from 30 meter digital elevation model data and depicts the dramatic dif ferences in topographical relief present in the watershed. Elevations vary from 900 to 2,900 meters and annual rainfall ranges from 300 to 750 mm. The total area of the upper watershed encompasses nearly 7,600 km 2 (5,800 km 2 in Arizona and 1,800 km 2 in Sonora) and represents one of the most ecologically diverse areas in the United States and northern Mexico.
Landsat observations have evolved from an experimental system in the 1970s to a required capability to ensure our ability to explore, characterize, monitor, manage, and understand changes in the Earth's land surface. Landscape ecology is a relatively new science which helps place the changes and pattern of land cover into perspective relative to their impact on important ecological and hydrological processes.

Produced by the U.S. Environmental Protection Agency
, Of

fice of Research and Development, National Exposure Research Laboratory , Las V egas, Nevada, USA Published by the U.S. Bureau of Land Management, Arizona State Of fice, Phoenix, Arizona, USA GULF OF CALIFORNIA BAJA CALIFORNIA NOR TE SONORA CHIHUAHUA

077LEB99.dc UNITED ST A

TES MEXICO NEW MEXICO COLORADO WYOMING
CALIFORNIA IDAHO

NEV ADA UT AH

ARIZONA 

# 1 986 1 997 1 992 1 973

W illiam G. Kepner 1 

# , Christopher J. W atts 2 

# , Curtis M. Edmonds 1 

# , Rick D. V an Remortel 3 

# , and Matthew E. Hamilton 3 

## 1 U.S. Environmental Protection Agency , Office of Research and Development, P .O. Box 93478, Las V egas, NV 89193-3478 2 Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora, Reyes y Aquascalientes Esq., Colonia San Benito, Hermosillo, Sonora, Mexico 83190 3 Lockheed Martin Environmental Services, 980 Kelly Johnson Drive, Las V egas, NV 891 19 

# T he Changing W a ter shed: A 25-Y ear Histor y of Land Co v er Change in the San P edr o Riv er , an American Semi-arid Bior egion T he Changing W a ter shed: A 25-Y ear Histor y of Land Co v er Change in the San P edr o Riv er , an American Semi-arid Bior e gion he Changing W shed: A 25-Y ear Histor Land Co er Change in the San P , an American Semi-arid Bior

Instituto del Medio Ambiente y el Desarr ollo Sustentable del Estado de Sonora 

# LOCKHEED MAR **TIN En**  **vir onmental Ser**  **vices**



# Forest Oak W oodland Mesquite W oodland Grassland Desertscrub Riparian Agriculture Urban W ater Barren Clouds ('92 and '97 only) 

# Land Cover Legend