Drought as a driver of vegetation change in Succulent Karoo rangelands, South Africa

Abstract

We document changes in rangeland during a prolonged drought in the arid Karoo. Rangeland in this arid region is species-rich and dominated by a mixture of long-lived succulent and non-succulent shrubs. Ranching has led to the domination of vegetation by less palatable species, and resting does little to restore diversity because most species are long-lived. Between 2015 and 2020, a combination of rising temperatures and low rainfall reduced vegetation cover and grazing potential throughout the Karoo. Mortality varied among species, habitat and with predrought rangeland condition, but appeared independent of size class. Growth form was not a good predictor of drought survival, although vegetation dominated by non-succulent shrub species before the drought was dominated by a succulent shrub species toward the end of the drought. Dieback was greater on deep soil than in drainage lines and on stony rises. Historically degraded landscapes lost relatively more vegetation cover and grazing capacity than areas protected from grazing. By reducing dominant, long-lived, non-forage shrub species, drought appears to be changing the composition of the vegetation to a state that may have higher grazing potential, particularly if livestock numbers are reduced and reseeding is carried out during the recovery period.