EDMONTON – New research suggests that climate change is threatening to turn Alberta’s huge northern wetlands into vast expanses of bush and shrub, altering the province’s freshwater cycle and releasing large amounts of greenhouse gases into the atmosphere.
“You are losing a really important landscape,” said Nick Kettridge of the University of Birmingham, lead author of the paper published Tuesday in Nature.
Kettridge and his co-authors took advantage of a ready-made controlled experiment in northern Alberta’s boreal forest.
In 1983, a fen — a type of peat wetland that covers thousands of square kilometres in the province’s north — was partly drained to encourage forestry. The amount of drainage roughly corresponded to the amount of drying expected to occur as warming temperatures increase evaporation from the landscape.
Then, in 2001, a wildfire burned through the area, which affected both drained and undrained parts of the fen. Ten years after the fire, the undrained fen was recovering nicely. Peat burned in the fire was being replaced, storing carbon and offsetting the carbon released in the fire.
The drained part of the fen, however, took a completely different path.
The amount of water-storing moss was down by 77 per cent. The water table was more than 20 centimetres lower. The entire site had been overgrown with willow and poplar bush, further restricting the growth of moss by shading the ground and covering it with shedded leaves.
The two areas had less than 10 per cent of their vegetation in common.
That shift to a shrub ecosytem, spread out over a large area, would completely change how the landscape reacted to wildfire.
Healthy fens, because they store so much water, slow a fire’s progress and limit its ferocity. Willows and poplars present no such inhibitions.
That creates a feedback loop likely to speed up the conversion of fen to scrub forest, releasing millions of tonnes of carbon, said Kettridge.
Wildfires are expected to increase as climate change takes increasing hold of the boreal forest. The annual area burned in the boreal doubled between 1960 and 1990 and is expected to double again by 2100.
Although his study didn’t look specifically at the issue, Kettridge said the drying out of the Peace-Athabasca delta from upstream dams could be adding to the climate change effect.
“If you’ve got land management, climate change and wildfire on top of that, there’s a potential for a triple effect.”
Kettridge said the study suggests authorities should try to manage the landscape in ways that don’t cause further drying. He said they could also try to limit the impact of wildfires through firefighting or using controlled burns to limit the amount of available fuel.
Wetlands are vital, not only for carbon storage, but other ecological services, Kettridge said.
They buffer and stabilize river levels and filter surface water. They prevent erosion and provide habitat and nutrients for animals. Some ecologist liken them to the earth’s kidneys.
“We’re investing huge amounts of money within the U.K. to reclaim and restore these systems,” Kettridge said.
“This is one study, one unique opportunity to see the potential response. But it has implications for our understanding about how a broad range of these fen systems and peatland systems are likely to respond into the future.”