Studies on structure in plant communities. V. Pattern in Atriplex vesicaria communities in South-Eastern Australia

Abstract

The distribution pattern of Atriplex vesicaria (perennial saltbush) was examined in a number of locations extending from Hay in western New South Wales to Koonamore Station in South Australia. The populations sampled were from a range of locations exhibiting a variety of topographical, edaphic, and effective rainfall conditions. The scales and intensities of pattern varied considerably between sites, but in all sites there was evidence of contagion on at least two scales (both larger than could be attributed to the morphology of the individual plants) and in no instance was there evidence of uniform (underdispersed) distribution. The two major scales of pattern were attributable to the development of gregariousness and either the patchiness of nodulated limestone (or gypsum) in the soils or the development of gilgai relief. It was demonstrated for one site that drought stress had brought about an apparent decrease in the stocking density of A. vesicaria; this reduction of density was associated with a decline in pattern intensity, although the scales of pattern present in the original vegetation were maintained in the residual population.