of the drought in Valley Karoo

the condition and carrying capacity of the veld that animals, and many people, as a result, are dependent on for their livelihoods. Droughts have the potential to degrade the vegetation to such an extent that it cannot support livestock economically.

The veld research team at the Western Cape Department of Agriculture is studying vegetation changes in the arid regions of the Western Cape over the long term. It has been decided to use the data from 14 farms in the Rainshadow Valley Karoo to determine the possible impact of the drought on plant species composition and cover. Surveys in the bioregion were done in the winter of 2016 at the onset of the drought and were repeated in the winter of 2019. Rainfall figures were also obtained from the farms.

There was a significant change in the species composition with more than 15% of the species lost during the study period. Most of these species were previously present in small numbers. More common species that showed a sharp decline in their cover over time included bitterbos (Chrysocoma ciliata), asbos (Psilocaulon junceum) and bierbos (Pteronia oblanceolata). It appears that these species are not drought tolerant. The first two species have little value from a grazing perspective and if present in high numbers, is a sign of mismanagement. However, bierbos is a highly valuable dwarf shrub that is readily browsed by livestock and game and its presence indicates veld in good condition. Their numbers are generally not high in the study area.

Succulents, dwarf shrubs and shrubs accounted for 99% of the plant cover, with succulents, as expected, the most dominant (53%). The cover of all three of these growth forms decreased significantly with the highest percentage change in the dwarf shrubs (-32,4%), followed by the succulents (-27,5%) and shrubs (-27,1%). A study by Milton and others in the Steytlerville area after the drought of 1990/91 found that succulents were much less affected by drought than the dwarf shrubs. However, since most of the succulents are not that palatable, their decrease in this study was most likely due to the drought rather than grazing. The cover of all palatability classes declined over the study period with the highly palatable species showing the greatest decrease (-67,2%). Highly palatable and palatable species accounted for 14% to 16% of the plant cover and unpalatable species 25%, where most species present in the Rainshadow Valley Karoo are unpalatable species. The total plant cover declined by 26,2%, while the cover of dead plants increased by 71,4% during the drought. The loss in plant cover allows space for new plants to establish after the drought. However, this can only be positive if there are desirable species present in the veld that can provide seed, and in the case of this bioregion it seems highly unlikely.

The drought has affected the species composition negatively with fewer, mainly less valuable forage species remaining after the drought. Therefore, the overall condition and potential agricultural productivity of the Rainshadow Valley Karoo veld have been reduced by the five-year drought. It will need several years of above-average rainfall and sound veld management practices to recover. With the long-term study underway, we might be able to predict how many years it will need to recover.

AP