| Abstract: | Spatial analysis of vegetation and soil data collected from 64 sites in southern Western Australia suggests that both soil characteristics and geographic distance between sites are important predictors of the floristic resemblance of sites on a regional scale. These two factors are largely independent, a finding that may reflect recent, rapid speciation in the study area postulated in other studies. Spatial patterns of plant guilds suggest geographic replacement, and contingent exclusion may be an important mechanism maintaining species-richness. Existing soil and vegetation maps used to delineate reserve boundaries are found to be accurate, although the soil maps include information on vegetation patterns, independent of information on soil patterns. Within broad vegetation formations, there is some correlation of floristics in mallee stands with soil characteristics. Ordination analysis indicates a soil moisture/nutrient axis. In contrast, there are few important correlations of floristics with soil characters in kwongan (sand heath) or halophytic vegetation. Geographic distance between sites is a much more important factor. The absence of edaphic correlations implies that the observed geographic replacement of species between sites is a historical legacy, the result of recent, rapid speciation in the spatially patchy environment. It is concluded that if reserves in the region are to conserve the flora, especially rare species, the reserve system should include replicates of stands within the same broad formations and soil types at intervals less than 15 km, the minimum scale of resolution of this study. |
