Species richness increases income in agroforestry systems of eastern Amazonia

Biodiversity is believed to reduce risks (resistance and resilience against perturbations), to increase productivity via niche expansion, and possibly also to improve resource efficiency via mutually benefic species interactions. Agroforestry has been postulated as an ideal pathway of maintaining or restoring biodiversity in a socioeconomically sustainable manner. This study tests the relevance of agroforestry species diversity and richness on socioeconomic performance in a wide range of agroforestry systems in 38 farms aggregated in four clusters of sites in eastern Amazonia. We cover both commercial and subsistence agroforestry, ranging from simply structured plantations to diverse systems (enriched fallows, multi-strata home gardens), as well as pastures and shifting cultivation for comparisons. We quantify (i) all cultivated species, classifying them economically into species with commercial value, primarily subsistence purpose species or 'non-productive' species, and (ii) socioeconomic system variables (costs, monetary/non-monetary income, degree of satisfaction). Land-use intensity (per-hectare costs and income) was highest in commercial agroforestry and subsistence home gardens, and lowest in enriched fallows and pastures. All agroforestry systems resulted in higher income:cost ratios and greater satisfaction than pastures and shifting cultivation. Net income, non-monetary income and income:cost ratio were maximum in home gardens. Total species richness was negatively related with costs and monetary income, but not with non-monetary income, due to occupation of space by 'non-productive' species (juveniles or species providing ecosystem services). By contrast, productive (combining commercial and subsistence) species richness was positively related with (mainly non-monetary) income, net income and income:cost ratio. According to GLM, both productive species richness and Shannon-Wiener diversity positively affected net income. Future efforts for food security and poverty reduction need to focus more on species-rich agroforestry systems, both in terms of applied research and of extension service programs. Notably, the ubiquitous and successful home gardens merit far more attention.