8/15/2012 8:35:37 PM

Forest Fires Sweep Polar Bear Denning Area

There's no arguing that the expansive fires sparked by unusually warm and dry conditions have created massive destruction to the American West this summer. NOAA has reported that July 2012 was the hottest month in the contiguous U.S. since record keeping began in 1895, and much of North America remains in a deep drought

But the devastation has reached a rather unexpected ecosystem, too.

Unusually hot, dry conditions in Manitoba, Canada, have sparked forest fires in a prime polar bear denning area along Western Hudson Bay, a rare occurrence in permafrost areas. Hotter temperatures are thawing the permafrost, and drier conditions allow fires to kill the trees. 

Manitoba Conservation Officer Daryll Hedman said several fires sighted in July in a wildlife management area along the Deer River could well have affected known polar bear maternal den sites. Female polar bears in the Western Hudson Bay population den under the root crowns of small, slow-growing spruce trees that occur in permafrost soils along the banks of rivers and lakes, often reusing dens for generations.

"Not only is the permafrost no longer permanent, tree roots needed to stabilize the den structure are disappearing," said Dr. Steven C. Amstrup, chief scientist for Polar Bears International. "In other words, the kinds of habitats where mother polar bears in this area give birth to their cubs are simply disappearing as the world warms." 

In addition to the existing issue of declining sea ice, disappearing denning grounds will create a greater challenge to sustainable polar bear populations, accentuating the need for a reduction in greenhouse gas emission.

A study funded several years ago by PBI on the effect of forest fires on permafrost denning habitat predicted such an outcome. The study was conducted by Evan Richardson, a student at the time of Dr. Ian Stirling.

The major destruction produced by these recent natural disasters could be just the incentive for this type of change. It certainly provides yet another reminder of the global reach of human-caused warming.

"A warmer world will guarantee more fires, and those fires will continue to hit both people and polar bears close to home," Amstrup said. 

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