Bush clump succession in grassland in the Kei Road region of the Eastern Cape, South Africa

Abstract

Bush encroachment is a vegetation dynamic of global interest. This study describes the pattern of succession of bush clumps in the Eastern Cape, South Africa, using a space-for-time substitution. Clumps formed following establishment of mainly Acacia karroo in grassland through nucleation via animal dispersal. A total of 49 tree or shrub species were recorded in 40 clumps. With increasing clump size, there was a corresponding increase in woody basal area, species richness and diversity, but not evenness. Correspondence analysis showed that the pattern of compositional variation was closely related to clump size; differences resulting from clump establishment disappeared as clumps developed. Population size structure of 20 (of 21) species was dominated by small individuals, indicating that regeneration has increased over time. Coddia rudis was prolific on a clump periphery; Scutia myrtina and A. karroo were dominant within clumps. Seven shrub and nine tree species were encountered more frequently within a clump than on its periphery. All species other than A. karroo had fruits suited to dispersal by birds or mammals. The overall pattern of bush clump succession shows close parallels with that initiated by invasion of Prosopis glandulosa into grassland in Texas, USA.

Keywords: Acacia karroo, bush encroachment, plant diversity, savanna, woody invasion

African Journal of Range & Forage Science 2012, 29(3): 133–146