The objective of the study was to characterize forage species composition and abundance in rangeland invaded by Opuntia humifusa. The creeping cactus invaded about 7% and 13% of the cattle and sheep grazing areas. The affected rangeland had distinct zones of new invasion (NI) < 3 colonies, heavily invaded zone (HI >30 colonies) and transitional zone (5 – 20 colonies, TI). Species composition and distribution were determined using the transect and point survey methods. Twenty-nine plant species were recorded, 11 families were unpalatable species; and 15 woody species were identified. Unpalatable shrubs (Penzia calcarea and Zygophyllum incrustatum), disturbance indicator grasses (Aristida, Chloris virgate and Cyanodon) and intermediate species (Eragrostis and Heteropogon contortus) were dominant. Disturbance indicator grasses constituted 86%, 10% intermediate grasses and 4% were dwarf shrubs. Only three palatable grasses were recorded-Themeda triandra, Stipagrostis uniplumis and Schmiditia pappophoroides. There were no palatable grasses in Cattle HI. Sheep HI zone had 15 palatable plants/m2 relative to NI (223 plants/m2) and TI (123 plants/m2). Vegetation composition was typical of Nama-Karoo biome with western Upper Karoo veld type except for the high Opuntia density. Invasion by Opuntia affected rangeland species composition, which may influence nutrition of cattle grazing the South Western rangeland of South Africa.

Keywords: Nama-Karoo Biome; Veld nutrition; Invasive alien species; Climate change; Palatable grasses; Disturbance indicators