The newest data on the advance of northern, or boreal, forests come from the eastern slopes of Siberia’s Ural Mountains. Here, north of the Arctic Circle, relatively flat mats of compressed, frozen plant matter — tundra — are the norm. This ecosystem hosts a cover of reflective snow most of the year, a feature that helps maintain the region’s chilly temperatures. Throughout the past century, however, the leading edges of conifer forests have creeped some 20 to 60 meters up the mountains and begun overrunning tundra, scientists report in an upcoming Global Change Biology, now available online.
Conifers here now reside where no living tree has grown in some 1,000 years, points out ecologist Frank Hagedorn of the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf.
Ecologists and climatologists are concerned because the emerging forest data suggest that the albedo, or reflectivity, of large regions across the Arctic could change. Most sunlight hitting snow and ice bounces back into space. But convert a white landscape to open sea water or boreal forest, and the surface suddenly becomes a great collector of solar energy.
Sea-surface ice already is melting in the Arctic and polar ice sheets are thinning. Warming threatens to further degrade these solar reflectors. So does the advance of boreal forests, Chapin says.
EDIT
http://www.sciencenews.org/view/generic/id/32207/title/Boreal_forests_shift_north