Impact of climate change on horticultural species, with special emphasis on West Africa

Food security is a major issue in West Africa (WA), and currently horticultural crops are grown mostly under rain-fed conditions. However, as the climate changes, increases in temperature and shifts in precipitation will have major ramifications for which crops can be grown in the region. The overarching aim of this thesis is to assess the likely effects of climate change on production of horticultural crops of major importance in WA, thereby helping policy-makers to identify key threats that climate change presents to food security and formulate management options to reduce risks. My thesis consists of three experimental data chapters as well as a review. First, I present a review chapter titled “What is the future of rain-fed horticultural production in a changing West African climate?”. I synthesise knowledge of the responses of key types of horticultural crops – vegetables, plantations, roots and tubers, and fruit – to climate change, and discuss options for adaptation. Two of the data chapters’ detail glasshouse experiments investigating the effects of heat and moisture stress on tomatoes, an important horticultural crop in WA. I hypothesize that (1) heatwaves will have a negative influence on the eco-physiological responses of the crops, causing a reduction in yield, (2) the effect of moisture stress combined ‘sequentially’ or ‘additively’ with heatwaves will be more severe than either of these impacts alone, and will cause a significant reduction in yield and biomass accumulation, and (3) that seasonally adapted varieties of tomato will respond differently to the stresses, with the varieties adapted for warmer regions having higher yield than varieties from cooler regions. The results demonstrate that the three tomatoes varieties experienced significant declines in yield as a consequence of the stresses, with plants unable to recover fully when both stresses co-occur. The third data chapter utilised a common habitat suitability model, Maxent, to project likely changes in suitable conditions for six economically important rain-fed horticultural crops under current and future climate conditions. From the models, I identified likely changes in areas suitability. The results show that suitable habitat for cashew is likely to be relatively stable for the future whereas the total area suitable for okra, sweet potato, and taro may decline by 2050’s to 2070’s. As such, my thesis provides guidance for the future of horticultural crops growing under rain-fed conditions in WA.