Roadsides may not look like wildlife habitat, but a few simple changes to how they are maintained could turn them into much better places for pollinators.
A new uOttawa-led study found that reducing mowing and herbicide use along rural roadsides led to a 45 percent jump in pollinator numbers and a 23 percent increase in the number of species found there.
"Roadsides aren't places most people think of as wildlife habitat, but they add up to a huge amount of land across the country," explains Jessica Forrest , full professor in the Department of Biology at uOttawa's Faculty of Science and the study's principal investigator. "What surprised us wasn't that management mattered; it was how much difference two modest changes made."
Comparing Ottawa area roadsides
Researchers compared rural roadsides in neighbouring jurisdictions around Ottawa that use different maintenance practices.
Lanark County mows twice a year and only spot-treats invasive plants like wild parsnip. Ottawa and Leeds & Grenville County mow up to four times a year and spray herbicide more broadly. Because these jurisdictions sit side by side, the team could compare otherwise similar roadsides and isolate the effect of management alone.
"We found that sites managed with this low-intensity approach had far more bees and flower flies, and more species of both, than sites managed conventionally," says Professor Forrest. "And this wasn't a dramatic overhaul of how roadsides are managed, just mowing a bit less and using herbicide more precisely."
Over 3,700 pollinators identified
Over two summers, lead author Gil Miranda, a former postdoctoral researcher in Forrest's lab now with Agriculture and Agri-Food Canada, netted and identified 3,773 specimens from 31 sites, totalling 153 species: 100 bees and 53 flower flies. Low-intensity roadsides averaged 27 species per site across the study; conventionally managed ones averaged 22.
A collaborative research effort
The NSERC Alliance-funded project relied on a partnership between the University of Ottawa , Agriculture and Agri-Food Canada , and the Canadian Wildlife Federation , where Carolyn Callaghan, Tracey Etwell, and Vincent Fyson helped conceive and fund the study as part of their Rights-of Way as Habitat program. They also pinpointed site pairs that shared similar surrounding landscape but fell under different mowing regimes. Sophie Cardinal of Agriculture and Agri-Food Canada led the DNA barcoding used to confirm species identifications. The research was conducted with the support and cooperation of the City of Ottawa, Lanark County and United Counties of Leeds and Grenville.
A practical response to pollinator decline
"Roads still need to be safe to drive, and invasive species still need to be managed," adds Professor Forrest. "But our results suggest land managers don't have to choose between that and supporting pollinators. Mowing less often and spraying herbicide only where it's actually needed rather than across a whole roadside, gets you most of the way there."
The findings arrive as bee and flower fly populations face mounting pressure across North America; a recent continental assessment found more than one-fifth of native pollinator species are now at elevated risk of extinction. Forrest believes that the roadside results offer a rare bit of good news: a low-cost change within reach of any municipality or county maintaining rights-of-way.
"You don't need to plant anything new or spend more money to see a benefit," Professor Forrest concludes. "You just need to let the roadside be a little less tidy."
The study, " Roadside pollinator populations and the negative impact of intensive roadside vegetation maintenance ", is published in the Insect Conservation and Diversity journal.
Authorship: Gil Miranda, Tracey Etwell, Vincent Fyson, Sophie Cardinal, Carolyn Callaghan, Jessica Forrest. DOI: https://doi.org/10.1111/icad.70144
