Remote‐Sensing‐Based Condition Assessment for Nonequilibrium Rangelands Under Large‐Scale Commercial Grazing

Abstract

Range condition assessment procedures that rely on field—collected botanical data face major problems in nonequilibrium rangelands, which are spatially variable and extensively grazed. These problems include the difficulty of interpreting changes in plant species composition and the logistics of obtaining representative data for large areas. Consideration of ecosystem behavior through time and in space shows that certain spatial and temporal patterns exist that may be used to isolate the impact of grazing from other processes. The patterns also make it possible to distinguish between temporary changes and those that are more long term. All relevant patterns may be expressed in terms of total plant cover and may be monitored from remote sensing satellites. It is therefore possible to derive a set of range condition indicators that may be measured and monitored from space. These indicators use trends in average vegetation cover with distance from water at the end of very wet periods, trends in cover variance with distance from water, and the magnitude of observed vegetation response at individual points in the landscape compared with that which is expected when vegetation recovers fully from grazing. It is also possible to use spatial variability in the rate of cover depletion after rainfall to infer relative differences in the amount of forage present. When used in combination, the methods offer a realistic alternative to field—based assessment and are capable of detecting many types of rangeland degradation. They are also considerably cheaper to use.

Effects of rainfall variability and communal and semi-commercial grazing on land cover in southern African rangelands

“…Attempts to assess the extent of degradation in Botswana have been limited by a lack of data and absence of a methodology designed to cope with the characteristic spatial and temporal variations of nonequilibrium rangelands (see Pickup et al 1994 for a general discussion of these issues). Ground-based surveys have only covered limited areas and faced sampling difficulties (Tolsma 1989, Perkins & Thomas 1993, Moleele & Perkins 1998.…”

“…These methods were developed for land degradation assessment in non-equilibrium rangelands under commercial grazing in arid Australia using remotely sensed data (Bastin et al 1993, Pickup et al 1994). However, they should apply more generally.…”

Journal of Range Management, Volume 53, Number 6 (November 2000)

“…These data indicate that substantial errors may result from assuming consistent relationships between total cover and total biomass. Estimates of productivity from cover at large scales should therefore take into account measures of grass form (for example, foliage orientation) and of the proportional mass of green material (analogous to measures of greenness in satellite imagery, Pickup et al 1994). …”

Land Degradation States and Trends in the Northwestern Maghreb Drylands, 1998–2008

“…Increasing: Biomass accumulation over time, whatever the response to between-year variation in aridity; The Range class is likely to contain locations under active land use, where different responses may be expected from the vegetation cover. We adapted the principles of the ecological theory of succession to formalize an approach to land degradation in rangelands [34,35]. The hypothesis is that annual average biomass may be expected to decrease as land degradation proceeds, whilst productivity would peak at intermediate degradation states.…”