Coldest of the North American ecosystems, the arctic tundra is a vast treeless region stretching across northern Alaska and Canada. Here the soil is permanently frozen except for the surface layer, thawed by the summer sun, where plants take root.
The stamp pane depicts an autumn tundra scene in the northern foothills of the majestic Brooks Range in Alaska.
In fall, animals prepare for the long arctic winter. Caribou migrate south to the forest, while tundra swans fly across the continent to the Atlantic coast. As willow ptarmigans begin molting into white plumage that conceals them in snow, singing voles build forage piles of vegetation for winter feeding. Grizzly bears and arctic ground squirrels fatten before hibernating. Arctic woolly bear caterpillars, which can live as larvae for 14 years before becoming moths, undergo the most extreme change: they freeze in winter and thaw in summer.
