Soil-vegetation relationships on the Agulhas Plain, South Africa

Abstract

Broad correlations can be drawn between soil-based land systems and an independently derived vegetation classification in the Agulhas Plain at the extreme southern tip of Africa. The Agulhas Plain is an area of low climatic and topographic diversity where Cenozoic geomorphic processes have produced a diversity of erosional and depositional landscapes, mantled largely by soils of low fertility. A multivariate analysis of soil pit data from 20 sites indicates three major soil groups (alkaline-neutral sands, acid sands, acid loams) in the area, each supporting distinct groups of vegetation types. Within land systems site variation, which is distinguished by changes in soil type and variable slope processes along toposequences, is associated with abrupt changes in plant composition. This results in high beta diversity (compositional turnover) of the vegetational component. It is suggested that the high gamma diversity (species richness) of the area's flora (ca. 1700 species) results from site specialization both on a local scale within land systems and on a regional scale between land systems. Variation in soil nutrient status appears to be more influential than soil moisture at the regional level owing to the variety of lithospheric material.