Pollinator and floral 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, primarily the loss of habitat. 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 and floral communities in 143 regenerating (≤ 9 growing seasons post-harvest) timber harvest sites across Pennsylvania. During 1,129 survey events, we observed over 9,100 bees and butterflies, 220 blooming plant taxa (over 1.5 million individual flowers) and collected over 2,200 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 (fern and saplings). 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 diversity was positively associated with floral diversity and forb cover and negatively associated with tall ( >1m) sapling cover. Early in the growing season, more flowers bloomed in older regenerating stands (e.g., > 5 yr old) but this pattern reversed by the end of the growing season. These results suggest that regenerating timber harvests promote abundant and diverse pollinator communities in the Appalachian Mountains, though pollinator abundance and floral resource availability declined quickly as woody stems regenerated.