The Effect of Agri-environment Schemes on Farmland Bee Populations

Abstract

Over the past century there have been substantial declines in farmland biodiversity as a result of the intensification of agricultural practice. Concerns over these declines have led to the development of agri-environment schemes designed to mitigate the effects of intensive agriculture and to benefit biodiversity. Prior to commencing this thesis it was not clear if flower-rich, pollinator-focused agri-environment schemes had a population level impact on wild bees on farmland. Whilst previous work has shown that the creation of flower-rich habitat can provide suitable foraging resources for bumblebees, little was known about the impact of this management on bumblebee population sizes and even less on whether these resources were used by and benefited solitary bees. This thesis compares bee populations between farms with and without flower-rich, pollinator-focused agri-environment schemes in Hampshire and West Sussex, UK. Using genetic techniques to estimate colony density, and hence population size, farms implementing targeted schemes had a significantly higher density of bumblebee nests for the four species studied (212 nests/km² against 112 nests/km²). However, there was no difference in the species richness of bees between these different farm types. When assessing pollen use by solitary bees, flowering plants sown as part of pollinator-focused agri-environment schemes were not widely used, representing 27% of pollen foraging observations and 23% of pollen collected by volume. Only 35% of solitary bee species were found to use sown plants for pollen to a meaningful extent, with most pollen collected from plants persisting in the wider environment. The creation of flower-rich habitat significantly increased resource availability, but did not increase resource diversity. These results indicate that if diverse bee populations are to be maintained on farmland then agri-environment schemes must be developed that effectively increase the number of flowering plant species present at the farm scale.