Limitations to crop diversification for enhancing the resilience of rain-fed subsistence agriculture to drought

Diversification of agricultural systems is a standard suggestion for increasing the resilience of rain-fed subsistence farming to drought. However, grain crops share many physiological characteristics, potentially forming a plant functional type (PFT), a term ecologists apply to groups of species that respond in functionally similar ways to environmental variation. Here we test whether grain crops are a PFT, and whether diversification between grain crops, to other crops or livestock that feed on natural plants results in sufficient variation in water-use physiology to form a diversified agricultural portfolio. To this end, we simulated the response of crops and natural PFT’s to rainfall variation using a simple plant growth model. We then predicted subsistence farmer allocation with a safety-first economic analysis and compared these to observed allocations at 78 sites across a rainfall gradient in South Africa. We demonstrate that there are shifts from crop to livestock farming with aridity, and that this is correlated with the extant natural PFT’s. That is, as the simulated probability of crop failure diverges from that of the natural vegetation, there is a shift to livestock farming. Diversifying within grain crops would lead to little increase in resilience due to limited physiological variation – an indication that grain crops are one PFT – while other crops had some potential for greater diversification advantages, and livestock feeding on natural plants the greatest. Thus, a plant functional type approach is vital in understanding the developmental economics of subsistence farmer diversification with the goal of increasing resilience to drought.