UBC Reports | Vol. 50 | No. 6 | Jun. 3, 2004

Fighting Fire with Fire

Controlled burns bring back native plants

By Michelle Cook

As British Columbians brace for another summer of high forest fire risk, UBC researcher Andrew MacDougall is preparing to deliberately set alight some patches of the Cowichan Garry Oak Preserve south of Duncan to study fire's power to restore native plants.

This summer will mark the fifth year that MacDougall has conducted controlled burn experiments in the preserve to examine whether low-intensity fires will help native plants regenerate in the rare ecosystem. The goals of the project are to better understand the causes and consequences of plant invasion on native species, as well as examine possible strategies for managing the ecosystem through the re-introduction of controlled burning that had traditionally been done by First Nations people.

"The area is a hot spot for biodiversity in Canada," says MacDougall, who recently completed a PhD thesis on his work in the Garry oak preserve under the supervision of botany professor Roy Turkington. "It hasn't seen fire in more than 150 years, and invasive grasses and other introduced species have come in and choked out the native plants. They also generate large amounts of highly combustible plant litter, increasing the risk of forest fire."

In Canada, Garry oak ecosystems are found only on Vancouver Island, the nearby Gulf Islands and in the Fraser Valley. They support 91 species that have been designated at risk in B.C. or nationally.

The 18-hectare Cowichan preserve, owned by the Nature Conservancy of Canada, is the most intact remaining example of the ecosystem in the country. It is home to five endangered or threatened species: the yellow prairie violet, white-top aster, Howell's tritelaia, the Propertius dusky wing butterfly and the barn owl.

Historical records, researched by MacDougall and colleagues at the University of Victoria, show that prior to European settlement, First Nations people in the area used planned burns to manage the land and cultivate a supply of indigenous camas bulbs. Camas, a lily plant that produces a potato-like tuber, was an important food source for many Coastal tribes. The under-burning also encouraged the growth of native grasses, presumably to attract deer and elk to the area to graze.

The one-square-metre patches of ground that MacDougall burned in past years have begun to produce results.

Earlier this spring, colourful purple-flowered camas plants and native prairie violets were thriving in meadows amid the stately oaks. MacDougall says it has been interesting to watch the ecosystem respond to fire management techniques.

"We've noticed significant increases in the growth and reproduction of many native plants. Prairie violet has tripled in cover," MacDougall says. "The other good news is we've gotten rid of the invasive grasses. We'll never have the fuel loads that we did before we began the burning experiments." He says the experiment also produced some unexpected results.

"At first glance, the high abundance of invasive plants suggests that they drive biodiversity decline," MacDougall says. "However, our research has also revealed a hidden but significant impact of habitat fragmentation on the ability of native species to re-colonize invaded areas. Because exotics [introduced species] thrive in our highly developed, contemporary landscapes, they can dominate by default rather than by competition even though their dominance suggests otherwise."

Tim Ennis, the Nature Conservancy's director of land stewardship for the B.C. region, says the UBC research will not only help people doing conservation in other parts of Canada, it will help the Conservancy to make management decisions for the Maple Bay property.

"When dealing with the invasive species, they are difficult to control because they grow in among the native plants," Ennis says. "We needed to find more efficient strategies for management, and Andrew's results have given us the tools we need to handle them. We're taking the same treatments he has succeeded with and are applying them on a larger area."

The Nature Conservancy is currently using a combination of controlled burning, mowing and seeding to transform the Garry oak landscape in the years to come.

"Rather than a carpet of exotic grasses punctuated by one wildflower, what we want to achieve is a carpet of native wildflowers," Ennis says.

MacDougall says it remains to be seen whether some of the rarer native plants will be able to make a comeback, and the study is expected to continue for at least another five years. But the initial results have proven that larger scale, rotational controlled burns are a conservation option that could also help to lower the risk of forest fires.

"Invasive [introduced] grasses are fuel for fires and we need to get a handle on these fuel loads. Low intensity fires can greatly reduce the hazard of larger, destructive wildfires. Controlled burning would have the benefit of protecting an area from damage in the event of a forest fire," MacDougall says.

As for the oaks themselves, MacDougall says they love fire. "Unless they are very small, it doesn't harm them."