ENVIRONMENTAL CORRELATES OF VEGETATION PATTERNS AND SPECIES RICHNESS IN THE NORTHERN GRAMPIANS, VICTORIA

Plant species cover-abundance and density data were collected for 94 s ample plots across a gradient from rocky uplands to sandy outwash plai ns in the northern part of Grampians (Gariwerd) National Park in weste rn Victoria. Detrended correspondence analysis (DCA) was used to ident ify dominant gradients in species composition. A range of static (e.g. substrate type, soil depth, microclimate indicators) and dynamic (e.g . elapsed time since last fire) environmental variables were measured. Correlations were sought between these variables and vegetation patte rns including those for richness (R) and Shannon-Weiner diversity (H') . The dominant gradient of vegetation change identified by DCA separat ed rocky sites and sites near ephemeral streams, from well-drained, sa ndy sites. Secondary gradients identified time since last fire as impo rtant for sandy sites, and altitude and aspect-related microclimate fo r rocky sites. Diversity was highest in the first 2 years after fire b ut showed no further decline in older sites. Overall, R and H' were ne gatively correlated with soil nutrient concentrations. On sandy sites R was high, but was low on rocky sites and near streams. Within the ro cky sites, R was highest on cool, moist south and east slopes, and low est on hot, dry north and west slopes. Explanations of diversity patte rns based on inhibition of competitive exclusion due to stress and rec urrent disturbance best fit the results presented here.