Plant functional responses to drought in the Fynbos of South Africa

Background/Question/Methods

Climate change is predicted to cause increases in the duration and intensity of drought in the Fynbos Biome of southern Africa, a global biodiversity hotspot, yet there is limited experimental data to validate model predictions about the impacts on the flora. In a field experiment, we investigated the drought sensitivity of the key plant functional types of the Fynbos, to determine whether a simple functional approach could help to categorize drought responses in this flora. Using rainout shelters, we imposed two successive 6-month summer droughts (over two full years), in a mountain Fynbos shrubland. Natural rainfall was reduced by > 50% as a result. We monitored a suite of physical and physiological parameters in seven very different species comprising the three dominant growth forms (deep-rooted Proteoid shrubs, shallow-rooted Ericoid shrubs, and grass-like Restioids). 

Results/Conclusions

There was considerable variation in the measured drought response between the growth forms. The shallow-rooted, anisohydric Erica shrubs all suffered considerable reductions in growth and flowering and increased mortality. In contrast, the shallow-rooted, isohydric Restioids and deep-rooted, isohydric, Proteoid shrubs were largely unaffected by the experimental drought. The diverse functional responses indicate a range of functional response to drought in this biodiverse region, and these are currently not captured in the simple bioclimatic models being used to predict plant responses to future climate changes in Southern Africa. A consideration of rooting depth and hydraulic strategy that includes stomatal regulation of water under stress, cavitation resistance and repair in response to soil water deficit, carbon fixation and storage that impact the ability of a species to respond to new rain events, and allocation behaviour to growth vs. reproduction all allow a first-order functional classification of drought response as well as risk of species losses that we believe can aid predictions and help mitigate impacts in this biodiverse region.