You're walking through the woods when you come to an open area, with shrubs, grasses, and a sheen of water here and there. The ground gets wetter and wetter, until suddenly you sink over your boots in black mire. The dog, who's been romping ahead, returns covered in black muck to the shoulder.

You -- and the dog -- have found a peatland.

The wet black muck is what defines a peatland. It's organic matter, generations of plants that have died, decomposed, and compacted over time, forming a soggy, carbon-rich layer that might be up to six metres deep.

In the southern and central Yukon, peatlands are generally much shallower than that, says Dennis Gignac, a biologist at the University of Alberta. Gignac has studied peatlands in Alberta, the Mackenzie basin, and parts of the Yukon.

Peatlands form where water can pool and collect, contributing to the breakdown of organic matter and insulating it from the air. The Yukon's dry climate and mountainous landscape limit the number of suitable sites for peat.

"In much of the Yukon, it's too precipitous a terrain for peatlands to form," Gignac says. "It's too well drained."

There are pockets of peat scattered across the south and central Yukon. For example, Gignac found a pocket near the Whitehorse airport, with peat about a metre and a half deep. The largest Yukon peatlands Gignac found, in a road-based survey, lie southeast of Watson Lake and in the Burwash/Beaver Creek areas. However, they are dwarfed by peatlands in places like northern Alberta where a peat bog covering nine square kilometres would not be unusual, Gignac says.

Peat is an important player in the global climate. It's a "carbon sink" -- a place where carbon dioxide is stored. Carbon dioxide is a greenhouse gas and a major contributor to global warming.

Living plants absorb carbon dioxide. When they die and decay, the carbon dioxide is released back into the atmosphere. However, in a peatland the decaying plants are surrounded by water, which isolates them from the atmosphere and traps the carbon dioxide.

One of the possible effects predicted for Canada due to global warming is generally drier conditions, which could have dramatic effects on peatlands and on the carbon dioxide stored in them.

When the water table drops and a peatland begins to dry, the decayed organic matter is exposed to the air and the carbon dioxide trapped in it is released into the atmosphere. Carbon dioxide from drying peatlands could add even further to the greenhouse effect, Gignac says.

In places like northern Alberta and parts of the Mackenzie Basin, where peatlands occupy huge areas, the drying of peatlands could also have a major impact on plant and animal life. As the ground dries in a peatland, forest plants begin to take over from wetland plants and, gradually, the former peatland becomes forest. Forest animals move into the new habitat, and the plants and animals dependant on the peatland move out.

At the same time, warmer temperatures would mean a longer growing season and some melting of permafrost further north, resulting in larger and richer peatlands there, perhaps all the way to the Arctic Ocean. Plants and animals that depend on drier peatlands and tundra would be displaced by the inhabitants of wetter peatlands.

Gignac and several other scientists have developed a method for predicting the change in peatland distribution within the Mackenzie Basin under the conditions of global warming expected in the next couple of generations. However, the method won't work for the Yukon, he says.

"I think the impacts of climate change in the Yukon are very unpredictable, basically because of the mountains," says Gignac. Because much of the Yukon lies in the rain shadow of the coastal and St. Elias mountain ranges, its climate is much more variable and difficult to model than a continental area like the Mackenzie Basin, he explains.

In the few locations where the Yukon supports reasonably large peatlands, he predicts some noticeable change, particularly between Burwash and the Alaska border where the peatlands occur together with permafrost.

"There's an extreme likelihood of permafrost degradation in those areas," he says. "We do not know what the effect of that will be -- whether peatlands will remain as sinks for carbon or release carbon."

For more information about peatlands and climate change, contact Environment Canada in Whitehorse or e-mail dennis.gignac@ualberta.ca.