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Dryad

Spatiotemporal patterns of forest pollinator diversity across the southeastern United States

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May 03, 2024 version files 295.92 KB

Abstract

Efforts to understand how pollinating insect diversity is distributed across large geographic areas are rare despite the importance of such work for conserving regional diversity. We sought to relate the diversity of bees (Hymenoptera: Apoidea), hoverflies (Diptera: Syrphidae), and butterflies (Lepidoptera) to the ecoregion, landscape context, canopy openness, and forest composition across southeastern U.S. forests. We established 5-7 plots in each experimental forest. In each, we sampled pollinators monthly (March-September) using colored pan traps, and collected data on local forest characteristics. We used the National Land Cover Database (NLCD) to quantify surrounding land cover at different spatial scales. Bee richness was negatively correlated with both the amount of conifer forest and the extent of wetlands in the surrounding landscape but was positively correlated with canopy openness. Hoverflies and butterflies were less sensitive to landscape context and stand conditions. Pollinator communities differed considerably among ecoregions, with those of the Central Appalachian and Coastal Plain ecoregions being particularly distinct. Bee richness and abundance peaked two months earlier in Central Appalachia than in the Coastal Plain and Southeastern Mixed Forest ecoregions. Our findings reveal ecoregional differences in pollinator communities across the southeastern U.S. and highlight the importance of landscape context and local forest conditions to this diverse fauna. The closed broadleaf forests of Appalachia and the open conifer-dominated forests of the Coastal Plain support particularly distinct pollinator communities with contrasting seasonality. Our results suggest pine forests may reduce pollinator diversity in regions historically dominated by broadleaf forests. However, efforts to create more open canopies can help improve conditions for pollinators in planted pine forests. Research exploring associations between forest pollinators and different broadleaf tree taxa is needed to better anticipate how they will be impacted by various management activities.