Domino effect cited in warming of boreal wilderness
HAINES JUNCTION, Yukon–A veil of smoke settled over the forest in the shadow of the St. Elias Mountains, in a wilderness whose spruce trees stood tall and gray, a deathly gray even in the greenest heart of a Yukon summer.
"As far as the eye can see, it’s all infested," forester Rob Legare said, looking out over the thick woods of the Alsek River valley.
Beetles and fire, twin plagues, are consuming northern forests in what scientists say is a preview of the future, in a century growing warmer, as the land grows drier, trees grow weaker and pests, abetted by milder winters, grow stronger.
Dying, burning forests would then only add to the warming.
It’s here in the sub-Arctic and Arctic – in Alaska, across Siberia, in northernmost Europe, and in the Yukon and elsewhere in northern Canada – that Earth’s climate is changing most rapidly.
In Russia’s frigid east, some average temperatures have risen more than 2 degrees Celsius (3.6 degrees Fahrenheit), with mid-winter mercury spiking even higher.
Along with shrinking the polar ice cap and thawing permafrost, scientists say the warming of the Arctic threatens to turn boreal forest – the vast cover of spruce, pine and other conifers blanketing these high latitudes – into less of a crucial "sink," absorbing carbon dioxide –and more of a source, as megatons of that greenhouse gas rise from dead, burning and decaying wood.
American forest ecologist Scott Green worries about a "domino effect.”
"These things may occur simultaneously," said the researcher from the University of Northern British Columbia. "If the bark beetles kill the trees, you’ll have lots of dead, dry wood that will create a really, really hot fire, and then sometimes you don’t get trees regenerating on the site.”
Dominoes may already be falling.
From Colorado to Washington state, an unprecedented, years-long epidemic of mountain pine beetle has killed 2.6 million hectares (6.5 million acres) of forest.
The insect has struck even more devastatingly to the north, in British Columbia, where clouds of beetles have laid waste to 14 million hectares (35 million acres) – twice the area of Ireland.
It is expected to kill 80 per cent of the Canadian province’s lodgepole pines before it’s finished.
Winter spells of minus-40-Celsius (minus-40-Fahrenheit) temperatures once killed off larvae, but those deep freezes now occur less often. And warmer summers enable some beetles to complete their reproductive cycle in one year instead of two, speeding up population growth. Years of summer drought, meanwhile, weakened the spruces’ ability to extrude sticky pitch to trap and expel beetles.
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