Across North America, forest managers are increasingly tasked with managing forests for multiple goals: protecting biodiversity, sustaining timber production, combating invasive species, and buffering the effects of climate change, among others. In eastern North American forests, that challenge has become especially pressing as the eastern hemlock succumbs to the invasive hemlock woolly adelgid, and native pollinators vanish from the landscape. But new research suggests that a single silvicultural action – cutting small canopy gaps in the trees to let in sunlight – may simultaneously improve hemlock health and boost the diversity of native forest bees.
Eastern hemlock is a foundational species throughout its range, impacting both ecosystem structure and function. The loss of hemlocks from forests can have cascading effects that negatively impact carbon storage, alter hydrological and nutrient cycling, and decrease avian and amphibian diversity. The hemlock woolly adelgid, an insect within the “true bug” order of Hemiptera, feeds on the sap of hemlocks and can kill trees within a few years of infestation. Accidentally introduced from Japan more than 70 years ago, it now ranges from Georgia to Nova Scotia in eastern North America.
In the article “Two for One: Canopy Gaps that Improve the Health of Adelgid-Infested Eastern Hemlock also Favor Bee Diversity and Abundance,” published in the Journal of Forestry in August 2025, a research team from the U.S. Forest Service and North Carolina State University tested whether creating small canopy gaps could meet both forest health and pollinator conservation goals. Conducted at eight sites in western North Carolina and southwestern Virginia, the experiment built on previous work by members of the research team showing that more light helps hemlocks resist adelgid damage. The researchers asked whether these same canopy openings could also create favorable conditions for bees, which are declining globally but remain critical for forest and agricultural ecosystems.
In 2017, researchers created experimental gaps around hemlock trees at sites within mature, closed-canopy, mixed species forests in two areas of southern Appalachia: one at Jefferson National Forest in Virginia, and the other at Green River Game Lands in North Carolina. Researchers paired each gap – averaging 0.06 hectares (0.15 acres) – with a nearby intact control plot. In spring 2020, scientists collected bees at both locations and simultaneously monitored hemlock health through measures of foliage transparency, crown density, and new shoot growth to calculate a composite health index.
Hemlocks benefited from the experimental treatment; their crowns remained denser, and they produced more new shoots over three years, while those in shaded plots steadily declined. Extra sunlight likely improved photosynthesis rates and helped trees tolerate adelgid stress. Bees also benefitted from the treatment; bee diversity was 78 percent higher and abundance 60 percent greater in canopy gaps than in control plots, and three species – Osmia taurus, O. pumila, and Bombus bimaculatus – occurred almost exclusively in gaps. The same boost of sunlight that appears to help hemlocks also fueled the growth of flowering understory plants and shrubs, providing pollen and nectar for foraging bees. Trees felled to create the experimental gaps were left on-site and provided nesting material for wood- and stem-nesting bee species, further enhancing habitat quality.
These findings align with other studies showing that small canopy openings – whether created by natural events or selective cutting – can enhance pollinator diversity without degrading forest integrity. Here, a single silvicultural treatment served a two-for-one purpose, supporting both hemlock resilience and native bee communities.