Effect of continuous grazing in the Dohne Sourveld on species composition and basal cover.

Abstract

In a grazing trial conducted at the Dohne Agricultural Research Station, natural grassland was grazed continuously for 36 years with cattle. In a second investigation conducted on similar grassland, paddocks were grazed or rested, in all combinations of the four seasons of the year, over a ten year period. Changes in botanical composition and cover of the sward were monitored at regular intervals. The results of these investigations indicate that under a regime of non-selective grazing the composition of Dohne Sourveld is remarkably stable. After 36 years of continuous grazing the species composition of the sward was largely maintained. Floristically Dohne Sourveld is dominated by a small number of grass species of which Andropogon appendiculatus, Elionurus muticus, Heteropogon contortus, Sporobolus africanus, Themeda triandra and Tristachya leucothrix are the most important. These species react differently to under-utilisation or increasingly severe defoliation, enabling them to be classified into decreaser or increaser categories. Severe defoliation resulted in a marked decrease in basal cover but only small changes in relative species composition. As the intensity of defoliation increases, decrease in grass cover is associated with an increase of forbs, such as Senecio retrorsus.

Keywords: andropogon appendiculatus; basal cover; botanical composition; continuous grazing; defoliation; disturbance history; dohne sourveld; elionurus muticus; grass cover; grasses; grassland; grazing; heteropogon contortus; non-selective grazing; plant succession; senecio retrorsus; species composition; sporobolus africanus; themeda triandra; tristachya leucothrix; veld condition

Journal of the Grassland Society of Southern Africa.