Stand stage affects wild bee communities in working pine forests

Abstract
Wild bees provide critical pollination services to both crops and native forest plants. Evidence suggests that wild bees are declining due to factors such as habitat loss, disease, pesticide use, and climate change. Privately owned, working loblolly pine (Pinus taeda L.) forest landscapes cover a large area in the southeastern U.S. and may be important for wild bee conservation. However, there is little research on wild bees in private, working forests. Hence, our research objectives were to compare wild bee populations and communities among different stages within working, loblolly pine forest landscapes and assess stand structure and composition effects on wild bees. We sampled bees and forest attributes in four stages [0–3 years (recently established), 4–7 years (pre-thinned, closing canopy), 8–13 years (pre-thinned, closed canopy), and 14–20 years (post-thinned)] of privately owned, working pine forests in the Southeastern Plains Ecoregion of Georgia. We collected 5,933 bees from 88 species in two years. Wild bees were 2–5 times more abundant in recently established stages, and more diverse in recently established and post-thinned stages. Functional dispersion, a measure of beta diversity, was also greater in recently established and post-thinned stages. Canopy openness, percent of plants flowering, and percent cover of minimally decayed woody debris were important variables driving the bee community composition in recently established stages. Number of snags and litter layer depth were important variables driving the bee community composition in older stages with a closing or closed canopy. Working pine forests support a diverse community of wild bees and have high conservation value for these pollinators. Overall, wild bees appear to benefit from various stand stages, especially open canopy stands with a diverse structure. Promoting and maintaining open canopy conditions in managed pine landscapes may assist with conserving wild bee communities in this region. This can be achieved by planting trees at wider spacing, thinning as early as possible, and supporting fewer trees per hectare or a lower basal area.

Keywords
Forest Management, Forest Sustainability, Georgia, Loblolly pine, Native bees, Pinus taeda, Pollinators, Southeastern United States, Working Forests