The late quaternary palaeoecology of a floristic kingdom: the southwestern Cape South Africa

Abstract

The southwestern Cape Province of South Africa is the core region of the Cape Floristic Kingdom, one of six such large-scale phytogeographical units and by far the smallest. The region possesses one of the richest plant communities in the world when measured in terms of plant species numbers per unit area and many different hypotheses have been advanced in order to explain this prolific diversity. Historical processes and evolutionary development through time are frequently invoked as explanations, but remarkably little is known of the historical biogeography of the region and fossil-bearing sediments have yielded only a fragmented picture of the temporal development of the flora. Late Quaternary terrestrial sediments offer an opportunity to investigate the more recent history of the flora, although here too there exist several constraints which limit the precision of palaeoecological and palaeoenvironmental reconstructions. For the moment, knowledge of late Quaternary vegetation history is restricted to upland sites of organic sediment accumulation, although an increasingly detailed picture of vegetation development against a backdrop of environmental changes is emerging. This paper reviews the evidence from several fossil pollen-bearing sediments in the mountains of the southwestern Cape and presents a vegetation history for the last 14,500 years. We draw the somewhat surprising conclusion of relative vegetation stability during the time of marked climatic and environmental dynamism elsewhere. The hypothesis that assumed limited vegetation change could be a consequence of high species richness coupled with low pollen identification resolution is tested using multiple-discriminant analysis. It is argued that apparently subtle shifts in vegetation community patterns did indeed prevail during the late Quaternary. This possibly has some important implications for the evolution and maintenance of high plant species diversity in the Cape Floristic Region.