Wildfires are essential to the health of a boreal forest

Scientists of the International Boreal Conservation Campaign have identified Canada's boreal forest "as the largest intact forest and wetland ecosystem remaining on earth.

by Erling Friis-Baastad

Scientists of the International Boreal Conservation Campaign have identified Canada’s boreal forest “as the largest intact forest and wetland ecosystem remaining on earth.” Biologist Jill Johnstone has devoted her professional life to that forest in an attempt to understand how climate change is affecting it.

Johnstone directs the Northern Plant Ecology Lab at the University of Saskatchewan. Along with her graduate students, she spends much of her lab and field time trying to determine how changes in climate affect growing season conditions and weather extremes, and also how wildfires affect northern ecosystems.

“One of the primary mechanisms by which climate is going to affect the boreal forests is indirectly through its impact on the fire regime,” she says. “I’m very interested in how forest composition in both the Yukon and the interior of Alaska might change with changes in climate.”

‘Fire regime’ refers to many factors: how big the fires are, how frequently an area is burned, and how fire behaviour affects the severity of the burn, or how much vegetation is consumed and how much of the organic layer is burned away. These factors all determine how an ecosystem recovers.

If climate change is affecting a fire regime, those changes will be evident in processes of forest regeneration. Much of Johnstone’s Yukon study of these processes has concentrated on spruce-dominated ecosystems such as the Fox Lake area that burned in 1998. There’s also the Little Salmon area that burned in the same year, as well as the region near Minto where a landscape that burned in 1969, burned again in 1995. Those overlapping areas, the “fire complex,” can reveal essential data about the effects of fire frequency.

“One of the things we’ve learned after long-term monitoring of a forest … is that a system really reorganizes itself within the first decade after a fire,” says Johnstone. “Think of fire coming in as shuffling a deck of cards and then immediately after the fire the cards are dealt – and that’s the hand the ecosystem has to play over the coming century.”

When Johnstone and her students put their boots on the ground in a burned-over area such as the one north of Fox Lake on the North Klondike Highway, they can perform a variety of tasks and experiments. They observe the quality of regeneration that occurs on cool north-facing slopes and warmer south-facing slopes. The ever-present shovel sees plenty of use when it comes to determining how much of the organic upper soil remains intact. Determining soil acidity from pH readings can tell much about nutrients available on a site. Moisture content is important, as are drainage characteristics.

Many graduate-student projects last about three years. Such longer-term studies allow researchers to observe the results of planting seeds and greenhouse-raised seedlings. “Sometimes a tree species isn’t present in a location simply because no seeds got there. That’s a really different constraint than seedlings not being there because there were seeds and they wouldn’t grow,” says Johnstone.

Were conditions unsuitable for germination? Or were they suitable for germination but not for subsequent growth? Some basic silviculture can provide the answers.

Johnstone is also a research associate at the Institute of Arctic Biology at the University of Alaska Fairbanks, and both the U.S. and Canada help fund her wildfire studies. The dual position helps facilitate the sharing of information between the experts of both countries.

The general public has an obvious stake in all this research and data too. “The boreal forest provides a whole bunch of what we call ecosystem services,” says Johnstone. Most obviously, the forest cover can determine what kinds of wildlife live in a region. Not only does vegetation provide food for moose, elk, caribou and other megafauna, but it also provides thickets in which animals can hide from predators, including humans.

Fire gives some species opportunities to flourish that they wouldn’t have otherwise enjoyed. Consider fireweed, says Johnstone. It grows sparsely in thick old-growth forest, but flourishes when a forest is opened up by fire – only to diminish again as a forest matures and other types of plants thrive. As for smaller animals, burned-over areas attract their own “specialists,” such as woodpeckers that show up to feed on larvae growing in dead trees.

The type of vegetation that dominates a particular ecosystem can affect how that region contributes to important feedback mechanisms. For instance, says Johnstone, if the cover type after a forest fire shifts from being predominantly black spruce to predominantly aspen, the change affects how much carbon is returned to the atmosphere and where it is stored.

The water-cycling dynamic is affected as well. “Broadleaf species like aspen transpire a lot more – take moisture from the ground and put it in the atmosphere,” she says. Changes in that dynamic affect how much water enters streams and lakes.

“A lot of people are really afraid of fire and wish that fire were gone from the landscape,” says Johnstone. “It’s really important to understand that if we had a landscape without fire, it would be completely different.” Without a periodic fire cleanse, forests likely wouldn’t host as many different species over time as they do.

“We need to understand fire. We need to understand how things we are doing – like changing climate – are going to affect fire.”

For Johnstone, the key message is: “Fire is part of the dynamic system of the boreal forest, just like breathing in and breathing out is an essential component of being alive.”

Keeping tabs on, and adapting to, changes in the fire regimes, is an urgent task in an age beset by climate change, and one Johnstone would gladly share with many more researchers. “I’m just one of a small handful of people working on these dynamics,” she says. “I think it’s an area where we could use ten times more research than we have right now.”

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.yukoncollege.yk.ca/research