Lichen populations on arid soil crusts around sheep watering places in South Australia

Lichen populations, which encrust and stabilize soil surfaces in much of arid Australia, were studied around sheep watering places in two large paddocks near Whyalla, South Australia. In quadrat studies twenty-four taxa of lichen were found to occur on the soil surface. Frequency data for many species reflected the relative intensity of stocking pressure at different distances from the watering place. Influence Analysis, a technique derived from Association Analysis, showed that many significant interactions existed in the distribution of species in the quadrats. The spatial distribution of the interacting species showed that many of them were influenced in similar ways by stocking pressure and watercourse conditions. Others, while effected by stocking pressure, were not influenced by watercourse conditions. Stocking pressure caused differential destruction of species populations near the watering places. Unlike the higher vegetation, the soil crust lichen vegetation has no species which are stimulated to greater population development by intense stocking pressure. On destruction of the original lichen crust the soil surface is therefore left bare.