The effect of organic farming on butterfly diversity depends on landscape context.
Abstract
The recent dramatic decline in farmland biodiversity is often attributed to agricultural intensification and structural changes in the agricultural landscape. One suggested farm practice seen to benefit biodiversity and reverse declines is organic farming. Because organic farming is viewed as a more sustainable form of agriculture it is currently subsidized by European agri-environment schemes. However, the efficiency of agri-environment schemes to preserve biodiversity has recently been questioned, partly because their uptake has been highest in extensively farmed more heterogeneous landscapes. The effect of farming practice was studied on lepidopteran species richness and abundance along cereal field headlands and margins on 12 matched pairs of organic and conventional farms in contrasting landscapes (homogeneous and heterogeneous landscape diversity) in Sweden. Both organic farming and landscape heterogeneity significantly increased lepidopteran species richness and abundance. There was also a significant interaction between farming practice and landscape heterogeneity, because organic farming only significantly increased lepidopteran species richness and abundance in homogeneous rather than heterogeneous landscapes. An analysis of the distribution of organic farming in Sweden in relation to productivity of the arable land (yield of spring barley; kg/ha) indicated that the distribution of organic farms was skewed towards extensively farmed agricultural areas. The lepidopteran species richness and abundance can be enhanced by actions aimed at both promoting organic farming and increasing landscape heterogeneity. However, the beneficial effect of organic farming was only evident in intensively farmed homogeneous landscapes. Currently, the majority of organic arable land in Sweden is located in heterogeneous landscapes where changing the type of farming practice adds little to the existing biodiversity. It was proposed that the interaction between landscape heterogeneity and farming practice must be considered when promoting farmland biodiversity, for example in Europe, by developing context-based agri-environment schemes to increase the amount of organic farming in intensively farmed landscapes and that, in homogeneous agricultural landscapes, organic farming could be used as a more efficient tool to restore landscape heterogeneity if the creation of semi-natural landscape elements was mandatory in the regulations associated with organic agri-environment schemes.