Vegetation and vegetation-environment relationships at Grootbos Nature Reserve, Western Cape, South Africa

Abstract

The private Grootbos Nature Reserve is located at the Western edge of the Agulhas Plain in the Cape Floristic Region of South Africa, an area characterized by high habitat and floristic diversity. The Reserve is covered in near-natural fynbos shrublands with a few patches of forest and wetland. The main objective of this study was to classify the vegetation into discrete units and relate them to the prevailing environmental conditions. The vegetation was analysed by numerical means (TWINSPAN, DCA, CCA) and mapped on GIS. At the vegetation type level, Forest & Thicket and Fynbos formed distinctive clusters, whereas the wetland relevés were intermixed, but without relationships to one of these units. Fire incidence served as the major determinant of the forest-fynbos boundary. The Forest & Thicket grouping was separated into Thicket (as transitional to fynbos), Afromontane Forest and Milkwood Scrub Forest. Two broad complexes were distinguished within the Fynbos grouping, the Alkaline Sand Fynbos Complex corresponding to Coastal Fynbos, and the Acid Sand Fynbos Complex corresponding to Mountain Fynbos. They discriminated along gradients of pH, soil depth and rock cover. The complexes were further subdivided into formations by using one or a few subjectively chosen dominant species as indicators. The transitions between these formations were rather continuous than discrete. The vegetation type and complex levels correspond well to existing fynbos-wide classifications. Comparing the formations to the results of other vegetation studies is problematic even on the scale of the Agulhas Plain, due to the high regional plant diversity in the Fynbos Biome.