Background/Question/Methods 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. Results of individual studies examining the impact of biodiversity mitigation on pollinator abundance and species richness produce, however, contrasting results. Here we present the results of a review of the effectiveness of different measures to mitigate pollinator loss, using a meta-analysis approach. We ask which type of mitigation is most effective in enhancing pollinators on farmland and what factors affect the effectiveness of mitigation measures. Results/Conclusions 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 and the number of pollinator species that were present without mitigation (the ‘species pool’) furthermore influenced the effectiveness of measures. Although population-level positive effects of flower strips may be expected, the species richness and abundance data analyzed in this study do not merit unambiguous conclusions about effects of flower strips on landscape-wide populations of pollinators.
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