Managing Forests with Fire Maintains Pollinator Diversity across the Southeast
Forest with open pine condition on the coastal plain at the Santee Experimental Forest.
An expansive study reveals the diversity of pollinator communities throughout the entire Southeast.
The study is the first of its kind and was conducted across 19 experimental forests of the Southern Research Station. Most of these research sites are located on national forest lands and were established decades ago.
“These experimental forests provide a good representation of major forest types typical of the southeastern U.S.,” says Michael Ulyshen, USDA Forest Service research entomologist and lead author of the study. A separate study confirms that the network represents southern forests relatively well.
The network of experimental forests was ideal for learning about patterns of pollinator diversity across the region and how forest conditions affect these important creatures.
The study was conducted in 2021 and documented in a short video. Three days each month, from March to September, researchers and technicians at each experimental forest set out colored pan traps to capture pollinators in a soapy solution. The bees, butterflies, and hoverflies were then shipped to Ulyshen who identified, pinned, and cataloged them.
The analysis showed that across the entire region, canopy openness was associated with higher bee richness – the number of species present. Open canopied forests have become uncommon over the past century, with previous research suggesting that canopy closure contributed to pollinator declines.
“Two conservation goals of the early 20th century, extensive reforestation and reduced wildfire through fire exclusion, may have contributed to declining pollinator abundance as forests became denser and shrub covered.”
The researchers also found bee diversity to be lower when pine was more dominant in the surrounding landscape, especially on the piedmont. A study shows that pine-dominated systems need to be managed for open canopies to best benefit pollinators while canopy openness may be less critical in hardwood forests that provide resources in the canopy. This reflects both the value of flowering tree species to native bees, as shown in previous research as well as the importance of frequent prescribed fire, especially in pine forests.
Open pine forests require fire. Without frequent fires, other tree species have the growth advantage. By themselves, pine trees do not provide much to pollinators – wind carries pollen amongst the pines and this pollen is largely ignored by bees. In an open pine ecosystem, the forest floor gets enough sun for grasses and flowers to flourish, providing bees with nectar and pollen. Open pine forests were once very common on the Coastal Plain.
“We also detected distinct pollinator communities in the Central Appalachian and Coastal Plain ecoregions,” says Ulyshen. “Differences in forest structure and composition likely drove many of the differences we observed.”
The team documented 266 species of pollinators. Forests play key roles in supporting pollinator diversity, as previous research has shown.
For more information, email Michael Ulyshen at michael.ulyshen@usda.gov
The study was published in the journal Diversity and Distribution.
Bumblebee collects pollen from and pollinates wingstem.