Drought impact on woody plant leaf phenology and browse availability in a semi-arid environment

Abstract

The phenology of plants is influenced by numerous environmental factors such as temperature, day length and rainfall. Droughts are characterised by below average rainfall and above average temperatures and are likely to impact plant phenology. In the semi-arid and arid environments of South Africa, droughts occur frequently but are predicted to become more common because of climate change. The impact of drought and climate change on woody plant phenology can be detrimental to wildlife and livestock that are reliant on woody plants as a food source. To determine the potential impact of drought on woody plant phenology and ultimately leaf biomass available to browsing herbivores, the leaf phenology and leaf biomass of eighteen woody species were determined over a 24-month period during a prolonged drought. It was found that drought affected all species studied as it altered periods of growth and dormancy in plants. Specifically, the drought resulted in deciduous species flushing new leaves later in the season while the dropping of leaves occurred much sooner than normal. In evergreen species total leaf carriage was reduces. Consequently, the drought also resulted in prolonged periods of reduced browse availability. The study also found that reduces rainfall over longer periods (i.e. 6 months) had the greatest effect on leave phenology. It was concluded that intense drought can result in severe food limitations. Increased drought frequencies due to climate change may therefore reduce the productivity of the Kalahari region. It is likely that land managers will have to become even more pragmatic in the management of wildlife populations, specifically focusing on stocking rates and the mix of species maintained.