Trees on Tundra’s Border Are Growing Faster in a Hotter Climate

Trees on Tundra’s Border Are Growing Faster in a Hotter Climate

Measuring Techniques Improve—But the Implications Are Not Certain

2011-11-10

Evergreen trees at the edge of Alaska’s tundra are growing faster, suggesting that at least some forests may be adapting to a rapidly warming climate, says a new study.

While forests elsewhere are thinning from wildfires, insect damage and droughts partially attributed to global warming, some white spruce trees in the far north of Alaska have grown more vigorously in the last hundred years, especially since 1950, http://iopscience.iop.org/1748-9326/6/4/045503/">the study has found. The health of forests globally is gaining attention, because trees are thought to absorb a third of all industrial carbon emissions, transferring carbon dioxide into soil and wood. The study, in the journal Environmental Research Letters, spans 1,000 years and bolsters the idea that far northern ecosystems may play a future role in the balance of planet-warming carbon dioxide that remains in the air. It also strengthens support for an alternative technique for teasing climate data from trees in the far north, sidestepping recent methodological objections from climate skeptics.

“I was expecting to see trees stressed from the warmer temperatures,” said study lead author http://www.ldeo.columbia.edu/user/lah">Laia Andreu-Hayles, a tree ring scientist at Columbia University’s Lamont-Doherty Earth Observatory. “What we found was a surprise.”

Members of the Lamont Tree-Ring Lab have traveled repeatedly to Alaska, including the Arctic National Wildlife Refuge this past summer. In an area where the northern treeline gives way to open tundra, the scientists removed cores from living white spruces, as well as long-dead partially fossilized trees preserved under the cold conditions. In warm years, trees tend to produce wider, denser rings and in cool years, the rings are typically narrower and less dense. Using this basic idea and samples from a 2002 trip to the refuge, Andreu-Hayles and her colleagues assembled a climate timeline for Alaska’s Firth River region going back to the year 1067. They discovered that both tree-ring width and density shot up starting a hundred years ago, and rose even more after 1950. Their findings match http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2011.01598.x/abstract">a separate team’s study earlier this year that used satellite imagery and tree rings to also show that trees in this region are growing faster, but that survey extended only to 1982.

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