PAGES 601-612RANGES Improves Satellite-based Information and Land Cover Assessments in Southwest United States PAGES 601,[605][606] Because of its influence on hydrology climate, and global biogeochemical cycles, land cover change may be the most significant agent of global environmental change. Land degradation results not only from land cover conversion, but also land cover function. For example, human activities in the southwest U.S.,such as grazing regimes and fire frequency, are accel erating functional changes to fragile rangeland ecosystems, causing increased proportions of shrubs in grasslands, decreases in overall vege tation density and the introduction and spread of non-native invasive species.

No abstract

Understanding landscape conversion is vital for assessing the impacts of ecological and anthropogenic disturbances at regional and global scales. Since rangelands cover nearly half of the global land surface, and because a large part of rangelands is located in semi-arid ecosystems, they serve as critical land cover types for determining regional biodiversity, global biogeochemical cycles, and energy and gas fluxes. For such vast ecosystems, satellite imagery is often used to inventory biophysical materials and manmade features on Earth's surface. The large area coverage and frequent acquisition cycle of remotely sensed satellite images make earth observation data useful for monitoring land conversion rates at different spatial scales. Remote sensing could also be used for temporal assessment of semi-arid ecosystems by providing complimentary sets of rangeland health indicators. In this paper, temporal satellite data from multiple sensors were examined to quantify land use and land cover change, and to relate spatial configuration and composition to landscape structure and pattern. The findings were correlated with the role of fire to better understand ecological functionality and human and/or natural activities that are generating environmental stressors in a rapidly developing, semi-urban census division located in southeastern Arizona. Results indicate that conversion of a fire-suppressed native grassland area has 2 spatial components; in the rural areas, grass is being eliminated by increasingly homogeneous shrub and mesquite-dominated areas, whereas in the urban and suburban areas, grass as well shrubs and mesquite are being eliminated by a fragmented and expanding built landscape.