Soil and vegetation changes across a Succulent Karoo grazing gradient

Abstract

This study describes soil and vegetation changes radiating out from a central watering point on a livestock farm in the Succulent Ceres Karoo (Tanqua). The aim was to identify possible relationships between long-term grazing pressure, and soil and vegetation properties. There are indications that continuous high-intensity defoliation of Succulent Karoo vegetation leads to a decline in species richness and perennial plant cover with a consequent loss of fertile topsoil. Over-grazed areas close to the watering point had shallow soils with a greater potential for crusting and therefore poorer water capacity. Mainly short-lived succulents (Mesembryanthemaceae) were recorded here, while under-utilised veld far from the watering point was identified by plant groupings dominated by Antimima hantamensis and Ruschia spinosa. Malephora crassa and Rhinephyllum macradenium are two key species which could be useful in veld condition assessment since they showed strong relationships with distance from the watering point. The results also have implications for restoration of degraded veld. Soils from degraded areas have been altered almost permanently and simply resting from livestock grazing may not achieve the desired vegetation recovery.