Removing Privet Helps Restore Native Bee Populations

Chinese privet (Ligustrum sinense). Photo by Ted Bodner, courtesy of Bugwood.org.

When plants travel the world, they escape the checks and balances of their ancestral ecosystems and can multiply without bounds, competing with native plants for light, nutrients, and water. Do non-native invasive plants also disrupt native bee populations?

Jim Hanula, research entomologist with the SRS Insects, Diseases and Invasive Plants unit, explored this question by comparing bee diversity and abundance in forests where Chinese privet had been removed, had never invaded, and where it still dominated the shrubby layer. Hanula found that removing Chinese privet provided immediate benefits for native pollinators, even when there were no specific efforts to restore native plant communities.

Native bee, genus Halictus in the family Halictidae. Photo by Jim Hanula.

Chinese privet (Ligustrum sinense), first brought to the United States as an ornamental shrub, now infests over 2.5 million acres of public land across 12 southern states and countless more acres of privately owned land, roadsides, and forested urban areas. Hanula and his team removed privet from study sites in the Piedmont area of Georgia using chainsaws, mulching, and herbicides. They found that within a year, bee populations were larger and more diverse. In fact, areas where privet had been removed by mulching hosted average bee populations of 418 per plot, while areas where privet had not been removed had average populations of only 35 bees per plot. The bee populations in treated plots continued to soar, and by 2007, bee abundance and diversity in all the treated sites was similar to that in forests that had never been invaded by privet.

Removing privet allowed more sunlight to reach the forest floor, where flowering plants such as pokeweed, wingstem, violets and others began to flourish. Flowering plants and pollinators depend on each other, and mature healthy forests have diverse and abundant bee-supporting plants that are almost completely excluded when native plants are crowded out by non-native invasive plants such as Chinese privet. Hanula concluded that removing Chinese privet benefits native forest pollinators such as bees even without further restoration of native plant communities.

Read the full study at http://www.srs.fs.usda.gov/pubs/39743

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