Combining high biodiversity with high yields in tropical agroforests

Abstract

Local and landscape-scale agricultural intensification is a major driver of global biodiversity loss. Controversially discussed solutions include wildlife-friendly farming or combining high-intensity farming with land-sparing for nature. Here, we integrate biodiversity and crop productivity data for smallholder cacao in Indonesia to exemplify for tropical agroforests that there is little relationship between yield and biodiversity under current management, opening substantial opportunities for wildlife-friendly management. Species richness of trees, fungi, invertebrates, and vertebrates did not decrease with yield. Moderate shade, adequate labor, and input level can be combined with a complex habitat structure to provide high biodiversity as well as high yields. Although livelihood impacts are held up as a major obstacle for wildlife-friendly farming in the tropics, our results suggest that in some situations, agroforests can be designed to optimize both biodiversity and crop production benefits without adding pressure to convert natural habitat to farmland.

Fig. 1.

Noncrop biodiversity in smallholder cacao agroforests does not decrease with yield in (A) trees, (C) endophytic fungi, (D) butterflies, (E) ants, (F) spiders, (G) birds, (H) rats, and (I) amphibians, but decreases significantly in (B) herbs. Broken lines are intercept-only linear models. Morphospecies richness is indicated for endophytic fungi, ants and spiders. n = 43 for tree, butterfly, ant, bird, amphibian, and reptile data; n = 22 for endophytic fungi, spider, and rat data.

Fig. 2.

Endemic species richness and cacao yield do not covary. Relation between species richness of (A) butterflies and (B) birds endemic to the Sulawesi region and yield in smallholder cacao agroforestry plots. Broken lines are intercept-only linear models (regression not significant at the 95% level). n = 43 for butterfly and bird data.

Fig. 3.

Shade quantity and quality effects. (A) Expected yield based on data from the field and survey components (closed and open circles, respectively) decreases linearly with increasing percentage cover by shade trees (solid line), but maximum values conditional on shade are nonlinearly related to shade; the broken line is the simulated shade effect prediction from the SUCROS-Cocoa model (24). (B) Partitioning the negative effect of shade on yield shows most of the effect is a result of percentage cover by shade trees, with shade quality variables; that is, number of tall shade trees (>10 m height) and number of tree species, having only very small effects. (C) Bird tree species richness also benefits from the percentage cover by shade trees, but here most of the variability is explained by the above-mentioned shade-quality variables.