Dark Island heath (Ninety-mile Plain, South Australia). II. The effects of microtopography on climate, soils, and vegetation

Abstract

The topography of the experimental area at Dark Island is described as a series of crescentic sand dunes formed under the influence of westerly winds and separated by undulating sandplain. Variation in the heath vegetation of the area in relation to topography was described by means of the varying densities of 12 representative species. These densities indicated the individual growth tolerances of the vegetation components. One hundred and twenty-six quadrats sampled from different topographical positions were sorted into homogeneous groups by the method of positive interspecific correlation. The four resultant vegetation communities were located respectively on eastern dune slopes, western dune slopes, sandplain, and in scattered sites. Examination of soil texture, rainfall incidence, and average daily hours of direct sunlight in relation to topography showed that three microhabitats can be separated: namely, eastern and western dune slopes and the sandplain. Eastern dune slopes have the most favourable growth conditions, western the least favourable. Neither the vegetation communities nor the microhabitats could be sharply delimited. The gradual changes of soil and microclimate produced a varying but continuous vegetation pattern. This pattern depended on the growth tolerances of different species and probably also on interspecific competition for the more favourable growth sites.