Abstract:
In a companion paper we showed that degraded rangelands in central Australia could rarely be rehabilitated economically with mechanical treatments like pitting and opposed discing. In this paper we devise a set of environmental indicators to guide the selection of areas which might respond to treatment, by exploring the relationships between a wide variety of environmental attributes, the types of treatment and the responses of different groups of plants. The best response of palatable perennials to these mechanical treatments was likely on soils with no more clay than a sandy clay loam, and where average annual rainfall was at least 280 mm. Well developed micro-relief in the soil surface and a crust that was reasonably penetrable when dry and stable when wet were also useful though less important as indicators of likely plant response. Generally, land with these attributes in central Australia is unlikely to be severely degraded. Treatment structures do not persist in soils of high clay content. Buffel grass (Cenchrus ciliaris L.), an exotic species commonly introduced with treatment, does not thrive in clayey soils, and can invade untreated, better potential areas. The alternatives of larger-scale water ponding or harvesting, and the use of native species, should be considered for degraded soils. Rapid comparative assessments of the response of plants to treatment can be made by counting all perennials with a basal diameter of 25 cm within a standard area.