"It's a very severe problem," Ullsten told Reuters ahead of a conference in Winnipeg attended by timber industry representatives and environmentalists.

"If you want to illustrate the environmental dilemma the world is in, I think what has happened to the boreal forest in Manitoba, or you can probably take some other provinces as well, is a very good or tragic example of what might happen if actions aren't taken."

Boreal, or northern, forests are a belt of mostly coniferous trees running through much of Canada, the United States, Russia, Scandinavia and parts of Mongolia and China. They make up about one-third of the Earth's forests and form the basis for the global timber industry.

Trees found there, including aspen, spruce, fir and pine, are uniquely adapted to cold northern climates, and experts say they are far more sensitive to temperature fluctuations than temperate or tropical species.

Ullsten said that the main way to combat the threat is to reduce the burning of fossil fuels, one of the main contributors to global atmospheric warming, and focus on alternative energy sources.

"When you think about what is likely to be done to make a real difference, then you have to turn to governments and then ask them, what do they want to do and what do they dare to, and then you get more pessimistic," said Ullsten.

He said many scientists believe that a winter temperature rise of as little as three degrees Celsius (five degrees Fahrenheit) over the next half century could destroy half the world's boreal forests.