Phytochorology and Vegetation History in the South-Eastern Cape, South Africa

Abstract

Using the results of a descriptive and an historical approach, hypotheses are presented on vegetation history during a glacial-interglacial sequence in the chorologically complex south-eastern Cape. In the descriptive approach 879 taxa from fynbos, renosterveld, subtropical thicket and Afromontane forest communities are classified into phytochorological groups according to their distribution relative to major African phytochoria. The relative occurrence of these phytochorological groups in the different communities are determined. Taxa typical of the Cape phytochorion predominated in fynbos communities, particularly in Mountain Fynbos; there was a strong CapeAfromontane linking element in Grassy Fynbos and Cape-Tongaland-Pondoland linking element in Dune Fynbos. Phytochorological spectra of renosterveld communities were complex and dominated by Cape linking elements. Afromontane endemics predominated in Afromontane forests while the spectra of subtropical thicket communities were dominated by taxa characteristic of the Tongaland-Pondoland Region. In mesic thicket there was a strong Afromontane component whereas karroid taxa were conspicuous in the drier succulent thicket. Levels of endemism were highest for Cape taxa in fynbos, and succulent karroid taxa in dry thicket. Very few subtropical and Afromontane endemics were recorded. In an historical approach, the palaeoenvironment of the Cape coastal region during the last glacial maximum to Holocene sequence is discussed briefly as a model for predicting vegetation change. Available data on phylogeny, speciation and endemism of taxa characteristic of S.E. Cape phytochoria are discussed in their historical perspective. From a consideration of the descriptive and historical components of the study the following hypotheses on vegetation history are generated. Cape fynbos has had a long history in the S.E. Cape and elsewhere in the Cape Region. Its distribution on edaphic 'islands' associated with infertile soils derived from quartzites and sandstones of the mountains would not have been disrupted to any extent, during a glacial-interglacial cycle. Renosterveld is a chorologically complex vegetation type whose distribution on the moderately fertile soils in the Cape Region would have fluctuated dramatically depending on prevailing climatic conditions. Subtropical thicket and grassland and Afromontane forest would have been largely displaced from the Cape Region during the last glacial and would have only become established on certain edaphic sites in the area, with the onset of a warmer, wetter Holocene climate. Karroid taxa have had a lengthy history in the S.L. Cape and during drier glacial times karroid communities would have occupied much of the terrain presently supporting renosterveld and thicket. *Present address: School of Biology, Western Australian Institute of Technology, Bentley 6102, Western Australia.