VEGETATION-ENVIRONMENT RELATIONSHIPS ON A SPECIES-RICH COASTAL MOUNTAIN-RANGE IN THE FYNBOS BIOME (SOUTH-AFRICA)

The species-rich fynbos of the southern Langeberg Mountains, South Afr ica was studied along three transects (a) to evaluate the compatibilit y of a floristic classification of the southern Langeberg vegetation w ith a fynbos biome-wide structural classification of mountain vegetati on, (b) to describe the environmental gradients to which the vegetatio n responds and (c) to investigate the relationship between the vegetat ion and the abiotic environmental variables which determine the patter n of distribution of the fynbos communities on the southern Langeberg. Principal Components Analysis (PCA) was used to determine correlation s between environmental variables independent of vegetation data. Simi larities between the 46 communities (determined by floristics) from th e three transects were determined using cluster analysis and grouped i nto 14 higher-level units. Detrended Correspondence Analysis (DCA) was then used for indirect gradient analysis after which Canonical Corres pondence Analysis (CCA) was used in a direct gradient analysis of the vegetation with the environmental variables. Compatibility between the floristic and structural classification of the vegetation was analyse d. The PCA principal gradient was defined as one from sites with high rock cover, shallow soils and north aspects to those with low rock cov er, deeper soils and south aspects. The second gradient is most strong ly positively correlated with percentage organic carbon and most stron gly negatively correlated with soil clay content. In contrast to the P CA, the DCA showed that the principal gradient is a precipitation grad ient, with the response of the vegetation dominated by the change from wet to dry conditions and from low to high winter incoming radiation. The CCA showed that the variation in the mountain habitats to which t he vegetation responds can be predicted from a combination of a few en vironmental variables. The principal gradient was one of change from h igh to low mean annual precipitation with an opposite change in winter incoming radiation. The second gradient was described by percentage s urface rock cover and soil clay content. A simple model using the envi ronmental factors selected in the CCA was proposed for predicting the distribution of floristically determined community groups in the fynbo s vegetation of the Langeberg and the southern Cape coastal mountains in general.