Biomass and nutrient changes in the herbaceous layer of two central Australian mulga shrublands after unusually high rainfall

The amount of standing plant material in the ground storey and its botanical composition are compared for two central Australian mulga communities, one with a predominantly annual understorey and the other with a predominantly perennial understorey. Amounts of litter and nutrient levels in standing plant material, litter and soils are also compared. The number of species, particularly forbs, was greater in the annual community and differences in botanical composition are unlikely to have been caused by cattle grazing. The differences may be attributable in part to the greater proximity of the annual community to sources of alluvial material, and thus to better supplies of nutrients. For the 13 1/2 month study period following exceptional summer rain, the weight of herbage in the perennial community generally exceeded that in the annual community, whereas the weight of litter was less in the perennial community. Of a large number of plant and soil nutrients, phosphorus, calcium and magnesium were lower in the perennial community; these three nutrients, together with nitrogen, may be deficient for either plant growth or cattle diet in that community. The amount of sulphur was lower in the annual community but was unlikely to be deficient.