Bummer: "The Arctic tundra may soon feel much like the doomed Macbeth with an army of trees (and invading species) closing in."

Birnam Wood in the 21st Century: northern forest invading Arctic tundra as world warms

The Arctic tundra may soon feel much like the doomed Macbeth with an army of trees (and invading species) closing in.
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Summer temperatures in central Interior Alaska are now almost too warm for white spruce to survive," explained co-author Glenn Juday, professor of forest ecology at the University of Alaska Fairbanks.

White Spruce Vs. Norway Spruce | eHow.com

According to the American Horticultural Society's heat zone designations, white spruce is best where summers provide no more than 60 days of high temperatures above 86 degrees F.