Bees Prefer Open Habitats

How managers can help conserve pollinators

A forest road with dense stands on both sides shades the road edge (left), while a road with wider edges annd thinned stands (right) allows in more light for plants and pollinators. Photo by U.S. Forest.
A forest road with dense stands on both sides shades the road edge (left), while a road with wider edges annd thinned stands (right) allows in more light for plants and pollinators. Photo by U.S. Forest.

Bees are a critical part of many flowering plants’ reproductive cycles. “By some estimates, nearly 90 percent of the world’s flowering plants are pollinated by bees, butterflies, beetles, or other pollinators,” says U.S. Forest Service research entomologist Michael Ulyshen. “There is also growing evidence that many pollinators are declining.”

In the U.S., there are approximately 4,000 species of native bees. Some are declining, but it is difficult to determine which. Some scientists have suggested that one of our 46 bumble bee species is already extinct – and half the other species may be threatened. Meanwhile, 24 butterfly species are listed as federally endangered, and, at some locations, the number of bee species may have fallen by half over the last 120 years.

Unfortunately, the alarm is tempered by a lack of data. “There is not enough information available to assess the conservation status of most species,” says Ulyshen. “However, there is clear evidence that bees prefer open habitats.”

Ulyshen recently coauthored a review article about pollinator conservation and forest management. The review was led by emeritus Forest Service scientist James Hanula, and published in the Natural Areas Journal.

“The data clearly show that bee and butterfly communities benefit from more open forest conditions,” says Ulyshen. “The positive effect on pollinators is seen in all forest types and geographic regions.” A number of common management techniques used for other purposes also help create pollinator-friendly conditions, including prescribed fire, harvesting or thinning, shrub removal, or some combination.

Open forests are less susceptible to pests and disease, so creating pollinator habitat and protecting forest health are goals that can be accomplished simultaneously. Over the past century, forests have changed dramatically and many have shifted towards closed canopies, resulting in less light reaching the forest floor. The changes have affected the herbaceous plant community and the bees, butterflies, and other pollinators who depend on flowering plants. Hanula and others recently addressed these issues in a separate study.

In some cases, nonnative flowers are a useful source of nectar, pollen, and larval food. However, when nonnative plants crowd out natives, the results are almost always negative. Herbaceous plants are pollinators’ primary source of food. When shrubs proliferate on the forest floor, they often prevent herbaceous plants from growing and blooming. “Dense non-native shrub layers beneath forest canopies negatively impact herbaceous plant cover and diversity as well as pollinators,” says Ulyshen.

The network of roads that crisscross the U.S. also provides opportunities for creating pollinator habitat. “By creating wider edges and thinning stands near the road, managers can allow more light in for plants and pollinators,” says Ulyshen. “Mowing in these areas should be minimal, and in some cases, managers may want to plant native flowering plants along the edges.” There are approximately 350,000 miles of forest roads in the U.S., and the low speeds and relatively low traffic on these roads makes them safer for pollinators than highways.

Road edges and powerline clearings can also provide pollinator habitat and corridors for movement. Some scientists have found that powerline corridors support a number of butterfly species, including some that are very rare. Unlike roads, which are usually cleared each year, powerline corridors are cleared about every four years. “Mowing powerline corridors less frequently, and only during the dormant season may help minimize negative impacts on butterflies,” says Ulyshen.

“The needs of specialist species and vulnerable, declining species should also be considered,” says Ulyshen. “Pollinator conservation in forests is important for many forest plant species, and forests may also serve as reservoirs of pollinators that can benefit surrounding habitats.”

Read the full text of the article.

For more information, email Michael Ulyshen at mulyshen@fs.fed.us.

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