ABSTRACT
Arid and semi-arid landscapes are fragile ecosystems, sensitive to degradation and desertification. Loss of productivity results from complex interactions between climate impacts and unsustainable land use practices. The United Nations Conference on Envi ronment and Development (UNCED, 1992) estimates 70% of all drylands, totaling about 3.6 B ha or 25% of the Earth’s land surface, are affected by desertification. North America and Spain have the largest percentage of deteriorating arid lands, with 90% of arid lands in North America moderately to severely desertified (Dregne, 1986). Dregne (1986) identifies three processes that promote desertification: 1) deterioration of vegetation cover from overgrazing, wood cutting and burning; 2) wind and water erosion from improper land management; and 3) salinization from improper irrigation management. The U.S. National Research Council (1994) identified three criteria for defining rangeland health: soil stability and watershed function, integrity of nutrient cycles and energy flow, and presence of functioning recovery mechanisms. Land managers need new techniques to identify and map locations of environmental problems within their management units to develop effective plans for sustainability. Human activities create disturbances at all spatial scales, making it difficult to develop consistent management decisions, especially over the extended periods necessary to reverse environmental degradation.
