Identification of key grass species under grazing in the Highland Sourveld of Natal

Abstract

Relative abundances of rangeland species have for many years been used to index trends in range condition following the impact of grazing. All species recorded in a botanical survey are usually classified according to their assumed reaction to grazing using the increaser and decreaser groups. We used a gradient analysis of 216 sample sites to show that only certain species in the Highland Sourveld of Natal, South Africa, were responsive to the grazing impact. We therefore recommend that non-responsive species should not be used to monitor trends in range condition. Three categories of grass species were defined for interpretive purposes in a monitoring programme, viz. decreaser, increaser and invader species, based on their reaction to the grazing impact. Eight grass species in the Highland Sourveld of Natal showed clear responses along a gradient of grazing intensity, and were abundant over at least a portion of this gradient. These species were selected as key species and were recommended for monitoring range condition in this vegetation type.

Keywords: botany; categories; decreaser species; gradient analysis; grasses; grazing impact; grazing intensity; highland sourveld; increaser species; invader species; key species; monitoring; natal; ordination; range condition; rangeland; relative abundance; south africa; species responses; vegetation type

African Journal of Range & Forage Science, 10(2): pp. 96-102