The importance of vertically stratified, multi-year sampling for understanding native bee assemblages in southeastern temperate deciduous forests

Authors: SELDEN, VERONICA - Auburn University; Campbell, Joshua; BENEDUCI, ZACHARY - Auburn University; ABBATE, ANTHONY - Auburn University

Submitted to: Biodiversity and Conservation Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2025
Publication Date: 10/10/2025
Citation: Selden, V.L., Campbell, J.W., Beneduci, Z.J., Abbate, A.P. 2025. The importance of vertically stratified, multi-year sampling for understanding native bee assemblages in southeastern temperate deciduous forests. Biodiversity and Conservation Journal. 34:4359-4381. https://doi.org/10.1007/s10531-025-03146-2.
DOI: https://doi.org/10.1007/s10531-025-03146-2

Interpretive Summary: Native bees are important pollinators and are often found in forests. However, how native bees use forest canopies is largely unknown and most knowledge on bees in forests is from the understory. We collected bees from the Tuskegee National Forest in Alabama by placing blue vane traps in the understory and within the canopy. Overall we captured nearly 1500 bees that comprised 38 different taxa. Seventy percent of the bees captured were from traps placed within the canopy of the forests. These data elucidate the importance forest canopies may be for native bee foraging and nesting resources.

Technical Abstract: Bees are highly effective pollinators, making global declines observed in bee populations a cause for concern. We need a better understanding of our existing native bee assemblages to preserve them. Recent studies have shown that bee assemblages are vertically stratified in forested habitats, but our understanding of how that translates to the southeastern United States is lacking. Most of our knowledge is restricted to how bees utilize the forest understory, potentially biasing monitoring efforts. We sampled and compared the bee assemblages of a temperate deciduous forest (Tuskegee National Forest, Tuskegee, Alabama, USA) in both canopy and understory from April-October 2021 and March-October 2022. Blue vane traps were deployed at four sites across Tuskegee National Forest with four replicates per site. Each replicate had a blue vane in the understory (1m) and in the upper canopy (20 m average). In total, we captured 1,494 bees representing 38 taxa belonging to 15 genera and 5 families (Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae). Abundance varied seasonally and by year. The canopy traps produced 70% of all captures and there were almost three times as many bees in the canopy as in the understory. The four most commonly captured species (Lasioglossum bruneri, Melissodes bimaculatus, Augochlora pura, and Bombus impatiens) were present in significantly higher abundances in the canopy. We found no significant differences in species richness between the canopy and understory, but found that Simpson diversity was significantly different between strata. Interestingly, while overall and in 2021 Simpson diversity was higher in the canopy, in 2022 it was higher in the understory. Based on our findings, we suggest multi-year, multi-strata sampling when surveying for bees in forested environments.