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Treeline Advances in Canada’s Arctic

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In a widely recognized painting by Tom Thomson, a bent and lonely tree hunches on a rocky ledge overlooking a windswept lake and distant snowy peaks. The misshapen tree remains so emblematic of the beauty and harshness of Canada’s climate that it is part of the permanent collection at the National Art Gallery in Ottawa.

Fast forward 100 years after the tree first sparked the painter’s imagination and climate change is a global concern. It’s timely to consider how trees are faring on the highest mountain slopes and at the northern treeline. In such extreme environments, oddly contorted forms of pine, spruce, birch and fir are created by blasting winds and inhospitable soils. These ‘Krumholz’ – stunted trees that look more like shrubs – are markers that will enable scientists to assess the impact of climate change.

Adjunct Professor at Halifax's Dalhousie University, Karen Harper is an expert in the dynamics of plant communities and has previously studied the forest edge along clearcuts, lakeshores and wildfires. She attempts to understand how the forest edges forward into the treeless tundra. Dr. Harper became intimately acquainted with the harsh realities of this habitat during field work for her doctoral studies on Canadian boreal forests.

“The flies! Don’t even think about it,” says Dr. Harper, shaking her head.

At one point in northern Alberta, a cloud of mosquitoes, midges and blackflies found her inventing ways to escape the onslaught. A bug jacket with an enclosed mesh hood provided the first line of defense. Next, as her hands and feet became the insects’ favored target, she added gloves and thick socks. Still when she moved, flies would razor in on a thin line between gloves and jacket. Finally, in desperation, she began cutting up her socks to slide over her arms for an extra layer of protection. All that clothing added to the ambience of hiking in 30 degree Celsius weather.

This perseverance and passion provided the background necessary to become the project leader for an extensive study of the Arctic Treeline Advance. Funded through the Government of Canada during the International Polar Year 2007-2009, her team is collaborating with researchers around the globe. This participation resulted from her efforts to recruit and convince Canadian researchers to contribute to the international project by focusing on the Arctic treeline, specifically how the boreal forest transitions into tundra. Field researchers look at patterns and ecological processes, including changes in growth and reproduction in tree species like White Spruce, Black Spruce, Balsam Fir and Eastern Larch. The socio-economic impact of this changing landscape for communities will include an assessment of changes in the food supply.

“What does that transition zone look like? Is it an abrupt change to less abundance, like you would see on alpine Rockie mountain slopes? Are ‘islands’ of trees and shrubs found ‘floating’ within the tundra? Or, is it a mosaic of forest, wetlands and tundra, all with associated plant communities?” she asks.

As an adjunct professor with Dalhousie's School for Resource and Environmental Studies, and the Department of Biology, she supervises both undergraduate and graduate students participating in this ambitious project.

Brian Starzomski, a post-doc researcher, is focusing on White Spruce growing beyond the treeline in the Yukon. He’s also monitoring how bird communities change as they move across the treeline in Labrador.

Environmental science student Stephanie Daley is looking at the effects of sheltering from the wind on the growth and establishment of a strange growth-form of Balsam Fir and White Spruce called ‘Krummholz.’

Another environmental student, Julie Pelton, and biology student Elisabeth Oakham are based in Churchill, Manitoba. Danielle Defields, a SRES graduate student, is looking at spatial patterns of vegetation at the treeline in the Yukon and in Labrador.

“The general expectation is increased growth and reproduction as a result of warming climate that causes the treeline to simply expand beyond where it is currently found, both further north, and higher up on mountains,” says Dr. Starzomski. “So, the treeline expands. Darker trees absorb more solar radiation, leading to more warming. This leads to further expansion and the creation of a positive feedback cycle.”

There is often beauty in the midst of a harsh landscape, as painter Tom Thomson recognized and preserved for posterity.

Dr. Harper recalls an unforgettable moment that happened near the treeline at the MacMillan Pass in the Mackenzie Mountains. A large group of caribou gradually grazed their way over the crest of a hill toward her, ending up passing only about 20 metres away from where she was standing.

“I was so mesmerized, I forgot to take a photo,” she laughs.

With perseverance and insight, these studies will generate knowledge that provides a clear picture of what will transpire within this fragile ecosystem in the years ahead.

Charles Crosby | Quelle: Newswise Science News
Weitere Informationen: www.dal.ca

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