PLANTING NATIVE PLANTS IN RESIDENTIAL LANDSCAPES INCREASES VISITS BY WILD BEES AND OTHER IMPORTANT POLLINATORS

Abstract

1. The potential for residential landscapes to support pollinators is of great interest to conservation and agriculture yet little is known of the impacts achieved by adding native plants to residential yards. 2. We implemented landscaping improvements incorporating native flowers, shrubs, and small trees into existing designs of front yards (N = 19) and backyards (N = 11) of private residences in Ithaca, NY and encouraged the homeowners to practice sustainable management practices in their yards. All 30 treatment properties, and an additional 8 quasi-control properties, were monitored for pollinator visits to both the enhanced and unmanipulated front and back yard sections for two years (2016 and 2017). We ran generalized linear mixed effects models in R to estimate the effects of enhancement and other factors on pollinator visits and included environmental and land use data to account for additional variation. 3. Counts of pollinator visits in the most active area (“Most Active Area” method) of the yards revealed that the total N pollinator visits and N wild bee visits were greater in enhanced sections of properties than in unmanipulated sections and that wild bee visits, specifically, increased with backyard enhancements in year two (2017). Enhanced sections of yards also received more pollinator visits than quasi-control yards, but only in the second year (2017). 4. In 2017, we tested for the effect of local enhancement on pollinator visits using an identical, predetermined focal plant (false sunflower). Unlike the Most Active Area method, the Focal Plant method showed no differences in the total number of pollinator visits nor number of wild bee visits between enhanced sections of treatment yards and quasi-control yards. As area enhanced (m2) tended to be negatively associated with the number of pollinator visits using the Most Active Area method, pollinators are likely more dispersed in enhanced than unenhanced quasi-control yards. 5. Synthesis and applications. Our results indicate that modest native plant additions have positive effects on the number of pollinator visits in residential yards and suggest that the “Most Active Area” method may be more powerful for detecting these effects than using a single sunflower as a focal census plant. Our quasi-experimental design allowed for practical implementation of native plant enhancements based on homeowner preferences and local growing capabilities while providing robust results. The rural landscape surrounding the city of Ithaca may have played a large role in our results and more research is needed to examine the extent to which landscape context influences the benefits of habitat enhancements for pollinators in small towns and cities.