Mitigating pollinator loss in Europe: what strategies are most effective?

Flower-visiting insects provide vital pollination services to crops and wild plants. Accumulating evidence for declining populations of pollinators has increased the urgency to identify and implement measures that effectively mitigate pollinator loss. Europe has a long tradition of mitigating biodiversity loss on farmland, for example, through agri-environment schemes. Although such schemes rarely target pollinators directly, the management prescribed by these schemes can be expected to benefit pollinators. Here we present the results of a review of the effectiveness of different measures to mitigate pollinator loss, using a meta-analysis approach. All investigated mitigation measures effectively enhanced species richness and abundance of pollinators. Supplementing pollinator food resources through the establishment of sown flower strips produced the most pronounced beneficial effect and appears to be a particularly effective mitigation measure. The effects of mitigation measures were more pronounced in arable landscapes than in grassland systems. Plant species richness produced by mitigation measures furthermore influenced the effectiveness of measures. Although population-level positive effects of flower strips may be expected, the species richness and abundance data analysed in this study do not merit unambiguous conclusions about effects of flower strips on landscape-wide populations of pollinators.