Less is better

Roadside mowing not necessary to combat invasive species

Todd McLeish

URI graduate student Sara Wigginton poses by a Rhode Island roadside
during her research on roadside mowing and invasive species.
(Photo courtesy of Sara Wigginton)

A University of Rhode Island graduate student studying the varying mowing practices used along Rhode Island roadsides has found that a reduction in mowing does not result in a proliferation of invasive species, as some researchers have previously suggested.

“There is a national trend to reduce the amount of mowing that occurs on rscioadsides because it’s expensive and takes a lot of effort,” said Sara Wigginton, a doctoral student from Glendale, Ky, who completed the research as part of her studies for a master’s degree. 

“But there have been worries that decreased mowing will make invasive species proliferate and get to the point where we can’t do anything about them.”

Her research, funded by the Rhode Island Department of Transportation, was published this month in the journal Ecological Restoration.

According to Wigginton, Rhode Island reduced its roadside mowing regime about six years ago, as did dozens of other states. 

In some areas, transportation workers still mow from 3 to 6 times per year; in others, which Wigginton calls passive restoration sites, mowing only occurs in a narrow strip closest to the road to ensure driver visibility; and elsewhere mowing has been stopped completely and the sites have become forested.

Working with URI Professor Laura Meyerson, Wigginton identified 15 roadsides along limited-access highways, including Interstates 95 and 295 and Route 138, with each of the three mowing schedules represented. 

In plots at each site, she identified the plants and estimated their density, and she determined whether each plant species was native to Rhode Island, introduced or invasive.

“Our main conclusion was that there was no difference between the mowed and restored sites,” Wigginton said. 

“The sites that were mowed like a lawn had no difference in terms of native, introduced or invasive species than the sites undergoing passive restoration. The two ecosystems aren’t behaving any differently.”

That means, she added, that the Department of Transportation can proceed with its reduced mowing plan without any concern that invasive species will become a nuisance.

Previous research elsewhere found that some invasive species, especially shrubby species like multiflora rose and Asiatic bittersweet, must be mowed regularly to ensure they are kept under control. 

But while Wigginton did detect those species in slightly higher abundance in the forested sites, she found that they were not a problem in the passive restoration sites.

“Our recommendation to the Department of Transportation is to stop mowing,” she said. “About half of the states are moving toward a sustainable vegetation management plan, and all include the reduction or elimination of mowing. We’re in good company.”

While the main focus of Wigginton’s research was on the effect of reduced mowing on invasive species growth, she also found that reducing or eliminating roadside mowing would also save about $30,000 in fuel costs. It would also reduce greenhouse gas emissions by eliminating the 230,000 kilograms of carbon dioxide emitted each year by the mowers.

“And there is the potential to increase the ecosystem services provided by roadsides, which has an economic value, including erosion control, carbon sequestration, and wildlife habitat,” said Wigginton. “We didn’t observe any rare plants in our surveys, though previous studies by URI Professor Rebecca Brown found evidence of some.”

She also recommends that the Department of Transportation consider a plan that would involve mowing every few years on a rotating basis to provide habitat diversity for local wildlife. Such a plan may require the involvement of wildlife biologists to ensure that wildlife – and people – are not put at risk, Wigginton added.