Abstract
Aspalathus linearis (Burm. f.) R. Dahlgren (rooibos) is endemic to the Fynbos Biome of South Africa, which is an internationally recognized biodiversity hot spot. Rooibos is both an invaluable wild resource and commercially cultivated crop in suitable areas. Climate change predictions for the region indicate a significant warming scenario coupled with a decline in winter rainfall. First estimates of possible consequences for biodiversity point to species extinctions of 23% in the long term in the Fynbos Biome. Bioclimatic modelling using the maximum entropy method was used to develop an estimate of the realized niche of wild rooibos and the current geographic distribution of areas suitable for commercially production. The distribution modelling provided a good match to the known distribution and production area of A. linearis. An ensemble of global climate models that assume the A2 emissions scenario of high energy requirements was applied to develop possible scenarios of range/suitability shift under future climate conditions. When these were extrapolated to a future climate (2041–2070) both wild and cultivated tea exhibited substantial range contraction with some range shifts southeastwards and upslope. Most of the areas where range expansion was indicated are located in existing conservation areas or include conservation worthy vegetation. These findings will be critical in directing conservation efforts as well as developing strategies for farmers to cope with and adapt to climate change.
Highlights
There is compelling evidence of climate change induced impacts on species diversity through among others, species composition changes (Bertrand et al 2011; RuizLabourdette et al 2013), range shifts (Bertin 2008; Colwell et al 2008), and altered phenology (Cleland et al 2007; Prieto et al 2009; Hulme 2011)
The objectives of the study were to (1) identify the environmental factors limiting or determining the natural distribution; (2) use this to develop a first estimate of the realized niche and potential geographic distribution of wild rooibos and the current geographic distribution of areas suitable for commercially production; (3) inform the location and design of field experiments to assess its ability to survive under different climatic conditions; and (4) develop possible scenarios of range/suitability shift under future climate conditions
The strong influence of land types indicates that the sandy, infertile soils derived from Table Mountain sandstone origin are required for rooibos production
Summary
There is compelling evidence of climate change induced impacts on species diversity through among others, species composition changes (Bertrand et al 2011; RuizLabourdette et al 2013), range shifts (Bertin 2008; Colwell et al 2008), and altered phenology (Cleland et al 2007; Prieto et al 2009; Hulme 2011). Increasing attention has, been focussed on implementing a proactive approach through developing plausible scenarios of future climate change and modelling the associated species range and ecosystem shifts Decision tools such as correlative spatial distribution models (SDMs) have become key in assessing biodiversity responses to climate change (Midgley et al 2003; Guisan and Thuiller 2005; Heikkinen et al 2006; Araujo et al 2011; Rodrıguez-Castan~eda et al 2012). These include mechanistic models, climatic envelope methods, and machine learning techniques (Yates et al 2010) All of these methods estimate a species actual or potential geographic range through relating field observations of species occurrences to environmental and climatic variables. This relationship can be used to assess species’ range shifts under different climate scenarios to undertake risk assessments in specific focal areas
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