Pollinator habitat is good, but not quite the bee’s knees

Above, an American bumble bee, Bombus pensylvanicus on purple thistle, Cirsium horridulum. (Credit: Mary Keim/Flickr)

Introducing pollinator habitat can improve bee abundance and diversity, but the quality of that habitat matters, research finds.

An examination of the program’s effectiveness shows that the quality of the habitat played a key role in positive effects, and that management of the area could affect habitat quality over time.

North Carolina State University researchers studied the effects of a NC Department of Agriculture program that installed pollinator-friendly flowers on 16 agricultural research stations from the mountains to the coast in 2016-18. Mixtures of planted bee-friendly flowers were evaluated for their effectiveness in supporting bee populations—with the goal of increasing the abundance and diversity of bees.

Honey bee specialist David Tarpy, an extension apiculturist at NC State and a coauthor of a paper in Frontiers in Ecology and Evolution on the research, recalls thinking that the program was a unique opportunity to study government-led conservation efforts. “We should get in on the ground floor and measure this and see if it has an effect from day 0, not after the fact,” he recalls.

“We didn’t want to let that ‘natural laboratory’ opportunity pass without actually recording the data,” adds Hannah Levenson, a postdoctoral research scholar and corresponding author of the paper.

Researchers visited all 16 sites four times each year and caught bees in nets and in cups—called bee bowls—that were painted to mimic the UV reflection of flowers. In all, the researchers collected more than 16,000 bees from 128 different bee species.

Results showed bee abundance increased over time, with more bees collected in 2018 than in 2016. Meanwhile, the diversity of species increased in 2017 and then dropped slightly in 2018, although both years showed large improvement over 2016.

“We were really happy to see increases in the abundance and number of bee species found over time,” Levenson says. “It was also exciting to see how many species we documented, especially for studying one kind of habitat. This study was limited to agricultural areas but we still found nearly 130 bee species.”

The study also shows, though, that the quality of flowers was a key driver of bee abundance and diversity, with areas of higher flower quality attracting more bees and more bee species. Poorly maintained areas with degraded flowers, weeds, and grasses lagged behind in bee collection.

“North Carolina has 564 species of bees and they have very different life cycles from each other,” Levenson says. “Some are active in early spring when flowers are just starting to come up. Other species are active in summer. The end of summer is when most bee species are active but have the fewest resources available—it’s called the dearth. So it’s important to develop seed mixes that bloom across the seasons so we can support as many of North Carolina’s bees as possible.”

Levenson says there were a few surprising findings, including a few bee species showing up in unexpected areas.

“We found some specialist bees in places you wouldn’t expect,” Levenson says. “There were no squash plants in our plots, but we found squash bees. It is encouraging that these planted habitats can provide some level of support to specialist species such as this that are economically important pollinators.

“We also found a particular bumble bee—Bombus pensylvanicus—that is under review for potential addition to the endangered species list,” she adds. “We found a high abundance of them, so it’s possible that they’re attracted to agricultural areas more than other areas. We submitted the data to Fish and Wildlife so it can be used to help make the decision on whether it should be listed as endangered or not.”

Levenson says that the program examining the effects of adding pollinator habitat at scale was prescient.

“I want to give credit to the NCDA. To our knowledge it was the first government organization to do test plots like these, and hopefully what we found could encourage more government programs to take actions to protect the environment,” she says. “Even though the habitats weren’t perfect, they still made a difference.”

The researchers hope that further studies like this one can be performed in different types of habitats, like forests or urban areas, to capture a wider sense of bee populations in North Carolina.

“No matter the landscape, we’ve shown that maintenance and monitoring are important to efforts like these,” Tarpy says.

Funding came from the NC Department of Agriculture, the NC Beekeepers Association, and NC State.

Source: NC State