fire covering the horizon of the prairie with a blue sky and clouds in the back ground
Recent prescribed burn at the Rare Charitable Research Reserve. Fire crews doing ‘backburns’ prior to setting the main fire. A kerosene drip-torch is used to set a line of fire that slowly burns forward into the wind.

A massive fire that burned up 18.5 hectares of grasslands near Cambridge, Ont., this week may have appeared disastrous, but it was just the opposite.

Protecting native plant species by burning grasslands may seem counterintuitive, but University of Guelph ecologist Dr. Andrew MacDougall has proven it works.

This week’s blaze was all part of the integrative biology professor’s ongoing research at the rare Charitable Research Reserve, where he and his research team study how prescribed burning helps to eliminate invasive plants and encourage native plants to thrive.

The stretch of prairie was planted by the MacDougall lab in collaboration with the reserve in 2010. Their first prescribed burn was in 2016; this week’s was their second.

“It’s part of the long-term study on restoration, recovery and resilience of Ontario’s tall grass prairie,” said MacDougall. “Tall grass prairie formerly covered 1,000 to 2,000 square kilometres of Ontario at the time of European settlement. There is now less than 1 per cent and it is home to more than 100 at-risk plants and animals.”

Tall grass prairie was burned annually or semi-annually by Indigenous people for centuries until Europeans arrived, MacDougall added.

Fire crews continuing to do downwind ‘backburns’ prior to setting the main fire

“As soon as you stop burning in the few prairie areas that remain, you get a conversion from grassland community to a forest, and that’s what has happened. This conversion to forest means a substantial reduction in the population sizes of hundreds of species. Conservation of this system is not simply about putting up a fence but also requires active management, especially fire.”

Fire is critical to prevent invasion by non-prairie species, especially trees and exotic grasses that were introduced by European settlers, he added.

The presence of aggressive perennial exotic grasses, such as creeping red fescue and smooth brome, is commonly associated with the displacement of native plant species such as monarda, blazing star and butterfly weed, all of which are critical for native pollinators,  he said.

Although prescribed fires might be presumed to damage all plants and not just the invasive ones, MacDougall said that’s not the case.

Almost all native plant species can tolerate burns because they are inactive during the early-spring burning season, he said.

“Many tallgrass species are what we call ‘warm-season plants,’ which don’t become active until early to mid-summer and are still setting seed in the fall. The early season burns consume last year’s plant litter, promoting vigorous and unobstructed growing conditions when the native plants finally emerge later on.”

The final burn stage when fire crews light a line of fire upwind that rapidly burns downwind toward the ‘backburn’ area that is already burned and lacking fuel. When the final burn hits the ‘backburn’ the fire puts itself out because of lack of fuel.

MacDougall has found that prescribed burning not only controls invasion by trees and exotic grasses but also eliminates accumulated plant litter, such as dead grass, needles, bark, fallen trees and branches, which reduces the risk of accidental fires.

“By regularly burning, you actually prevent big fires,” he said.

Over the years, MacDougall and his team have become experts at prescribed burns. Earlier, he conducted similar research in Vancouver Island’s Garry oak ecosystem, a biodiversity hot spot.

At the Cambridge site, the researchers plan to repeat the burn every five years.

In the weeks before the burn, the group monitors humidity and moisture levels to ensure the grassland is dry enough to ignite but not so dry that a fire would pose a hazard. The team also ensures wildlife have left the area long before the fire.

MacDougall said benefits of the burn will appear in July.

“There will be thousands of flowers and pollinators. It will be spectacular.”

Dr. Andrew MacDougall