Identifying state and transition models in the mitchell grasslands

Abstract

The Mitchell grasslands are the most extensive and productive native pastures of semi -arid western Queensland. The grasslands are dominated by the long -lived perennial Astrebla spp. (Mitchell grasses). Rainfall is highly variable, leading to fluctuations in both pasture yield and composition, particularly of annual and ephemeral species growing between these perennial tussocks (Orr and Holmes 1984). These fluctuations create problems when attempting to assess rangeland condition and trend which is often based upon single, or short term, data. Furthermore, Everist and Webb (1975) concluded "the extrapolation from observations made at any one time can be misleading and inaccurate". This paper summarises an approach by which State and Transition theory (Westoby et al. 1989) and the Degradation Gradient Method (Bosch and Kellner 1991) were used to develop models of vegetation change which were able to account for this inherent variability.