Alaska’s forests stressed by warming

Alaska’s forests stressed by warming

11June 2008

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One result: Trees weakened by insects and fires

BONANZA CREEK EXPERIMENTAL FOREST, Alaska — The answer to what’s in store for Alaska’s trees could be somewhere amid the flora of a two-acre experimental forest.

The living laboratory has been the domain of Glenn Juday, a forest ecology professor at the University of Alaska-Fairbanks, for three decades.

Every seedling here, every fallen log and every tree, some 200 years old, has been mapped and monitored. The rules here, intended to keep the tract as natural as possible, are simple: no leaning on trees, and no urinating.

As he walks gingerly through the forest, Juday explains how warming has hurt some of Alaska’s trees. Insects are flourishing because they can reproduce faster, and trees stressed by drought are struggling to defend themselves against the onslaught of bugs.

As a result, many of Alaska’s white spruce trees are growing at half the rate they used to.

Ironically, warming also has led to heavier snow in winter, causing more tree branches to snap and creating more openings for insects. “These are really serious effects, and they can result in the death of the forest,” Juday says.

Fighting fires
Alaska’s forests also face another, more immediate threat tied to warming: fires.

Juday says warming has paralleled bad fire seasons in Alaska, especially in 2004 and 2005 – the worst and third-worst on record.

The fires blackened one-third of northeast Alaska’s landscape, an area bigger than any state except Texas. When the smoke cleared, forests had been wiped out from “horizon to horizon,” Juday says. Some fires smoldered into the fall, even under snow.

Forest fires release carbon dioxide, pumping more of the greenhouse gas into the atmosphere. And when they burn peat, which is pretty common in Alaska, mercury is released at a rate 15 times greater than previously estimated. Much of the mercury goes into lakes and rivers, where it becomes a threat to wildlife and eventually to humans who eat fish and fowl.

Migrating to survive
The stress on forests has also accelerated the natural process of trees migrating to remain in their preferred climate. Birds and other animals migrating for the same reason take seeds with them, building forests in their new homes.

In Alaska, forests are heading for cooler climes to the north, crowding out Arctic tundra, which is projected to shrink to its smallest size in at least 21,000 years.

Now some scientists worry about extinctions. Caribou, which search out the moist lichen and moss found on the tundra, could starve to death as shrubs, a staple for moose, move in.

A shrubbier Arctic could compound warming over time. At first, the plants would trap snow. But eventually, as temperatures rose and the tundra’s snow-free seasons became longer, the shrubs would absorb more heat, warming the earth beneath them.

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