Pollinator communities vary with vegetation structure and time since management within regenerating timber harvests of the Central Appalachian Mountains

Native pollinator populations across the United States are increasingly threatened by a multitude of ecological stressors. Although the drivers behind pollinator population declines are varied, habitat loss/degradation remains one of the most important threats. Forested landscapes, where the impacts of habitat loss/degradation are minimized, are known to support robust pollinator populations in eastern North America. Within heavily forested landscapes, timber management is already implemented as a means for improving forest health and enhancing wildlife habitat, however, little is known regarding the characteristics within regenerating timber harvests that affect forest pollinator populations. In 2018 and 2019, we monitored insect pollinators in 143 regenerating (<= 9 growing seasons post-harvest) timber harvest sites across Pennsylvania. During 1129 survey events, we observed over 9100 bees and butterflies, 220 blooming plant taxa, and collected over 2200 pollinator specimens. Bee and butterfly abundance were positively associated with season-wide floral abundance and negatively associated with dense vegetation that inhibits the growth of understory floral resources. Particularly in late summer, few pollinators were observed in stands >6 years post-harvest, with models predicting five times more bees in 1-year-old harvests than in 9-year-old harvests. Pollinator species diversity was positively associated with floral diversity and percent forb cover, and negatively associated with percent tall (>1 m) sapling cover. These results suggest that regenerating timber harvests promote abundant and diverse pollinator communities in the Appalachian Mountains, though pollinator abundance declined quickly as woody stems regenerated. Ultimately, our findings contribute to a growing body of literature suggesting that dynamic forest management producing a mix of age classes would benefit forest pollinator populations in the Central Appalachian Mountains.

Automated summary

In regenerating timber harvest sites in Pennsylvania, the abundance of bees and butterflies is positively correlated with floral abundance and negatively correlated with dense vegetation. Pollinator species diversity is positively correlated with floral diversity and forb cover, and negatively correlated with tall sapling cover. The results suggest that regenerating timber harvests promote abundant and diverse pollinator communities in the Appalachian Mountains, but pollinator abundance declines quickly as woody stems regenerate.