Proximity to forest mediates trade-offs between yields and biodiversity of birds in oil palm smallholdings

There is much debate about how best to mitigate the effects of
agricultural expansion on biodiversity, especially in the tropics. Recent
studies have emphasised that proximity to natural habitats can enhance
farmland biodiversity, yet few studies have examined whether or not such
proximity mediates local trade-offs between yields and biodiversity, and
hence alters conclusions about the ecological benefits of alternative
farming strategies. Here we examine yield-biodiversity trade-offs,
focusing on birds in oil palm smallholdings at different distances from
remaining areas of forest, including a large forest reserve, in Ghana. We
found significantly fewer birds on higher-yielding than lower-yielding
farms, in terms of both species richness and abundance. For forest
specialist birds (likely to be highly vulnerable to conversion of land to
agriculture) we also found a greater trade-off (i.e. lower richness and
abundance for a given yield) at farms further from forest, to the extent
that increasing distance to the nearest forest from 1 to 10 km had a
similar effect as a 3- to 5-fold increase in fruit yield brought about by
increased intensification. Our study highlights the importance of
accounting for the effects of natural forest in the landscape when
considering agricultural policies for biodiversity protection, underlining
the importance of a landscape-scale approach to conservation.