Vegetation zoning in relation to site and soil properties : A case study in the Darling Range, south-western Australia

In this paper, we describe, using multivariate analysis, the distribution of plant species at three valley-floor sites in the Northern Jarrah Forest, south-western Australia. At each site, plant species are distributed along a topographic gradient in communities that broadly parallel the valley floor, resulting in a conspicuously zoned vegetation pattern. Soils are arranged in a similar pattern, with a clear distinction between upland sandy soils, sandy loams on the footslope and silty loams on the flat valley floor, as reflected by changes in field texture, gravel content, electrical conductivity (EC) and major element concentrations. We found that the predominant influences on plant distribution were waterlogging and gradient, indicating a direct relationship between vegetation and topography. However, the relationship between vegetation and soil was less pronounced. There were moderate correlations between species distribution and the soil properties Texture, Gravel Content and Electrical Conductivity, and weak correlations with soil concentrations of Fe, C and Mn. We speculate that soil properties at these sites developed in response to the same seasonal conditions of desiccation and waterlogging that currently control plant distribution, albeit at substantially different timescales. Thus, the relationship between vegetation and soil is an indirect one, reflecting the dominant influence of hydrology on the distributions of both plants and soil.