Disjunctions and Distribution Limits of Forest Species in the Southern Cape

SYNOPSIS

A total of 206 species reach their distribution limits within the southern Cape forests, or have disjunct distributions within this area and wider distributions outside. Biological variables (growth form, dispersal type) and habitat variables (forest type, moisture tolerance) are not significantly correlated with the drop-out of species, but all distribution variables (spread and abundance in study area, geographic origin) are. Species with a western distribution limit are concentrated in the Mossel Bay-George area. It is suggested that these western limits and the disjunctions west of Gouritz River and in the Knysna and Tsitsikamma forests relate to the major forest decline with the onset of the Late Pliocene marine regression. Species tolerant of drier conditions are concentrated in disjunct localities of dry high or scrub forest in the drier valleys around Mossel Bay and Plettenberg Bay, at Nature's Valley, on the dunes around Sedgefield, and in the coastal areas of eastern Tsitsikamma. This pattern is attributed to the elimination of coastal dune forest and eastern Cape subtropical transitional thicket on the Agulhas Bank during the marine transgression after the Last Glacial Maximum.