The socio-environmental impacts of tropical crop expansion on a global scale: A case study in cashew

Tropical crops like cashew (Anacardium occidentale) receive limited socio-ecological research attention despite expansion in regions of high biodiversity. We investigated how cashew plantations affected biodiversity and livelihoods globally by conducting a systematic literature review and modelling the potential overlaps between cashew land suitability and threatened vertebrates. Nine studies on the effects of cashew on biodiversity from India, Guinea- Bissau and Nigeria showed four to 84 % species richness reductions for fungi, plants, butterflies, birds, and terrestrial mammals across cashew and ‘reference habitats’ such as forests, woodlands, coffee plantations and sand dunes. Three studies reported that cashew harboured a subset of generalist butterfly and bird species when compared to woodlands, coffee, and forests with no evidence of forest-dependent species in cashew. Preliminary studies (n = 3) showed that the potential for facilitative coexistence among humans and wildlife in cashew land use, although further research is necessary to evaluate this. Livelihood effects of cashew farms from 29 studies across the tropics showed that cashew farms are dominated by smallholders who rely increasingly on cultivar cashew. Latin American and Asian countries showed spatial overlaps between land suitable for cashew and areas of threatened vertebrate species richness. FAO data showed that land area under cashew is expanding in African and Asian countries, but not in Latin American countries. Our study highlights the importance of studying tropical crops that lack large, apparent land-use footprints but affect biodiverse regions through steady, small-scale expansion.