Bee community composition and vegetation across a suite of restoration conditions in a longleaf pine savanna
There is growing concern about population declines in several North American pollinator species, and loss of appropriate native habitat for some pollinators may be a contributing factor. While interest in restoring pollinator habitat extends to the species rich, fire-maintained longleaf pine (Pinus palustris Mill.) ecosystem in the southeastern United States, little is known about the response of the bee communities to such restoration efforts or how restoration sites should be monitored to determine effectiveness over time. Longleaf pine savannas historically covered the majority of the southeastern Coastal Plain of the US, but most of this ecosystem has been lost because of fire suppression, land conversion, and urbanization. We investigated the effects of fire and forest cover on bee communities in a suite of restoration conditions. Specifically, we measured bee community composition in reference longleaf savannas, fire suppressed longleaf forests, young longleaf plantations with and without ground cover reintroduction, and mature slash pine (Pinus elliottii Engelm.) forests that are being converted to longleaf pine. Bee sampling was conducted using a combination of pan trapping and standardized netting transects. We also assessed how factors such as plant community characteristics, habitat availability, and forest structure affect bee assemblages.
Preliminary analysis indicates that bee and plant communities found in 75 year old frequently burned slash pine stands were most similar to those found in longleaf reference sites because of the similarities in percent canopy cover and ground cover composition. Bee abundance was highest in young longleaf pine plantations likely due to absence of canopy cover. Although bee species richness in young planted pine stands was similar to that of reference longleaf pine savannas, the assemblage of species was quite variable from site to site in the planted stands, and fewer oligolectic bees (diet specialists) were found, indicating that the plant-pollinator communities in these sites had not reached a reference condition.
Bee species richness and abundance and plant species richness were higher in longleaf savannas which were burned less than two years ago compared to longleaf stands which have not been burned for 10 or more years. Flower production is greater the same year of burn in reference sites and is associated with abundance of bees. These results suggest frequent fire plays an important role in maintaining plant-pollinator relationships in this ecosystem.