REMOTE-SENSING-BASED CONDITION ASSESSMENT FOR NONEQUILIBRIUM RANGELANDS UNDER LARGE-SCALE COMMERCIAL GRAZING

Range condition assessment procedures that rely on field-collected bot anical data face major problems in nonequilibrium rangelands, which ar e spatially variable and extensively grazed. These problems include th e difficulty of interpreting changes in plant species composition and the logistics of obtaining representative data for large areas. Consid eration of ecosystem behavior through time and in space shows that cer tain spatial and temporal patterns exist that may be used to isolate t he impact of grazing from other processes. The patterns also make it p ossible to distinguish between temporary changes and those that are mo re long term. All relevant patterns may be expressed in terms of total plant cover and may be monitored from remote sensing satellites. It i s therefore possible to derive a set of range condition indicators tha t may be measured and monitored from space. These indicators use trend s in average vegetation cover with distance from water at the end of v ery wet periods, trends in cover variance with distance from water, an d the magnitude of observed vegetation response at individual points i n the landscape compared with that which is expected when vegetation r ecovers fully from grazing. It is also possible to use spatial variabi lity in the rate of cover depletion after rainfall to infer relative d ifferences in the amount of forage present. When used in combination, the methods offer a realistic alternative to field-based assessment an d are capable of detecting many types of rangeland degradation. They a re also considerably cheaper to use.