Global warming could rapidly escalate the expansion of forests into tundra landscapes in Canada's North and force out indigenous species such as caribou, according to a group of Canadian researchers.

Rising air temperatures and soil temperatures are expected to have an impact on the ecosystem in the North, pushing the treeline, the boundary between white spruce forests and tundra, farther north.

The growth of forests in former tundra locations could have an adverse effect on the habitat of caribou.
(Canadian Press)

And if the expansion of forest in the first-half of the 20th century is any indication, in the future it will occur faster than previously thought, said Ryan Danby, a biology professor at the University of Alberta .

"Conventional wisdom suggests the advance of the treeline would creep along in colder climates, but our look at the growth of the forests during warmer temperatures between 1925 and 1950 showed quite a rapid advance," he told CBC News Online.

Danby and David Hik from the University of Alberta examined tree rings in the Kluane Wildlife Sanctuary in southwest Yukon to precisely date the year each tree was established and died to accurately map the changes in vegetation in the region. The study is published in this month's issue of the Journal of Ecology.

Danby suggests rapid growth during an earlier time of warmer temperatures does not bode well for the North amid rising evidence of global warming.

On a local level the forest growth is changing the habitat for species including caribou and wild sheep, animals that thrive in the tundra environment, Danby said.

Tundra in decline

"Animals like caribou require these places to live, and there are First Nations people who require these animals to live," he said.

The spread of forests to higher elevations is also squeezing tundra ecosystems to higher, more isolated elevations, fragmenting populations of indigenous species.

On a global level, Danby says, the darker canopy of forests would absorb sunlight at a greater rate than tundra landscapes and re-emit the absorbed light as heat, which could add to atmospheric warming.

This would cause a feedback-loop similar to the one associated with the rapidly decaying Arctic ice cap: Warmer temperatures would lead to an increase in northern forests, which in turn would lead to warmer temperatures.

Danby said he and colleagues at the University of Alberta, Simon Fraser University and the University of British Columbia are working on developing a model of the changing landscape in the North.

As part of the International Polar Year project, he will also be working with scientists studying similar northern treeline expansion in Scandinavia and Russia.