The increasing frequency of forest fires in Canada's boreal forest may be permanently changing one of the largest remaining intact ecosystems on Earth, research suggests.
"We feel very confident that these effects will persist," said Ellen Whitman, a forest ecologist with Natural Resources Canada and the University of Alberta.
Whitman is a co-author of a recently published article examining what happens when boreal forests – the huge green belt that stretches along the northernmost part of most Canadian provinces – are burned more often as a result of climate change.
She and her colleagues combined forest areas with similar weather and soil conditions that had been burned for the last time by the same fire. One half had been previously burned no more than 17 years earlier, while the other half's last fire had been at least 30 years ago.
The differences were striking.
The short-range stands were much more open with fewer trees. Poplars trembled instead of conifers. Growth under the trees – shrubs and grasses that cover a normal forest floor – was much less lush with far fewer species. Areas of exposed mineral soil, where all organic material had been burned, were larger and more common.
They felt completely different.
"You have a landscape in which you are surrounded by short, stunted trees," Whitman said. "You have a lichen crust or some sparse herbs. It's almost like crossing the edge of a prairie where you are moving from a pasture to a forest edge.
"In many long-range locations, you have fairly dense conifers, closer. You have ground moss, flowers, and shrubs. It's more like a young forest."
The boreal forest evolved into fire. Many of your tree species need it to germinate.
Typically, fires do not occur more often than every 30 years and usually for much longer. The lack of fuel in recently burned stations helps regulate this frequency.
Climate change is breaking these rules, Whitman said.
"We are facing warmer, drier days – the main trigger for big years of fire. As more years experience extreme weather conditions, the flames can overcome the resistance that recently burned places have."
Nor are park areas likely to evolve into a conventional boreal forest. Previous studies have found that the appearance of a forest is defined shortly after a fire.
"Immediate post-fire conditions are a strong predictor of what support will look like later," Whitman said.
Whitman emphasizes that the short intervals in his research are still small and most of the boreal forest patches burned in recent forest fires are recovering normally. Wetlands are also less affected by short-range fires than drier regions.
She said the forest industry is unlikely to be affected anytime soon – though forest-dependent animals such as caribou and singing birds will have impacts.
And these impacts are growing.
"With a longer fire season, larger fires, more of the landscape burning each year, the likelihood of finding a recently burned area increases. We are experiencing a shortening of the frequency of fire in the boreal forest."
This report from The Canadian Press was first published on January 12, 2010.