Assessing functioning of pollinator habitat plantings for agricultural settings

Background/Question/Methods

Recent honey bee declines and evidence that native bees can provide pollination services to economically valuable crops have motivated landowners and managers nationwide to enroll substantial acreage into conservation programs that target planting of habitat to support pollinators. The success of these plantings depends on their ability to support native pollinators and other beneficial insects.  We quantified the effect of habitat enhancements on pollinator communities in California, Michigan and New Jersey, three regions of fruit and vegetable crop production heavily dependent on pollinators.  At seventeen sites per region over a three year period (5-6 per year) we compared the abundance and diversity of net-collected wild bees at habitat-enhanced sites compared to paired controls.  Control plots were located between 100 and 800 m distant from restored plots so that pollinators were choosing between the two habitat types. Each site was sampled four-six times during the active growing season to span the range of bloom times of planted restoration wildflowers.  We related insect visitation to the flower abundance of each plant species.  Differences between treatment and control site were compared separately by state using generalized linear mixed models.

Results/Conclusions

Across all regions, both abundance and species richness of wild bees was significantly higher on enhanced plots compared to controls.  Results were consistent among years.  These findings suggest pollinator enhancements can contribute to bolstering biodiversity of beneficial insects in North American agricultural landscapes.  Often particular plant species made an unusually high contribution to the benefit.  Future research will identify key plant resources that can make such habitat installations cost effective.