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Arctic treeline advance not as fast as previously believed

Carey RestinoThe Arctic Sounder

A study released this month by Cambridge University indicates the advance of the treeline in the Arctic is moving slower than previously predicted.

The study, which was released March 17 by Gareth Rees, a researcher with the university’s Scott Polar Research Institute, says the relationship between climate change and tree growth is more complicated than initially thought.

“To generalize our results, the tree line is definitely moving north on average but we do not see any evidence for rates as big as 2 kilometers per year anywhere along the Arctic rim,” he said in a news release. “Where we have the most detailed information, our results suggest that a rate of around 100 meters per year is more realistic. In some places, the tree line is actually moving south. The predictions of a loss of 40 percent of the tundra by the end of the century is probably far too alarming.”

According to the report, Earth’s surface temperature has risen an average of 1.3 degrees F, but the average is greater in the far north. Rees’ study coordinated experts from across various Arctic nations, primarily in northern Europe. But Canada, Alaska, Russia and Scandinavia also participated.

“What we are saying is that when you take the step from a climate model to a vegetation model, we may be doing that in a way that exaggerates what is actually happening,” he said. “Furthermore, the response around the Arctic rim is by no means uniform.”

In addition to temperature, other conditions must be considered -- suitable soil, the absence of animals that destroy saplings, and the ability of trees to produce viable seeds.

Scientists are paying close attention to the Arctic tree line for several reasons. Trees impact the earth’s climate in several ways – they are darker than tundra and therefore absorb sunlight and increase temperature. Trees also transpire more than small plants, having an impact on the hydrological cycle of the earth.

“We understand a bit about what’s going on, but definitely not enough,” Rees said.

Click here for more on the study.

In a similar story that came out last November, scientists at Columbia University’s Lamont-Doherty Earth Observatory noted that the white spruce of Alaska’s boreal forest have been growing faster in recent decades, boosted by warming temperatures.

The findings, based on an extensive analysis of growth rings and wood density going back almost 1,000 years in trees at the tundra edge along Alaska's Firth River are in dramatic contrast to the ailing Interior forests, where warmer temperatures and drought have cut growth rates, increased forest fires and triggered insect outbreaks.

"I was expecting to see trees stressed from the warmer temperatures," said lead author Laia Andreu-Hayles, a tree ring scientist at Lamont-Doherty. "What we found was a surprise."

The study, published in Environmental Research Letters, is part of a broader effort to track the ecological impact of climate change through dendrochronology -- the study of the growth rings inside trees.

As anyone who has ever counted the concentric lines etched into an old stump knows, the quality and intensity of each growing season in a tree’s life gets recorded year by year. "In warm years, trees tend to produce wider, denser rings and in cool years, the rings are typically narrower and less dense," explains this story about the project. 

Alaska Dispatch reporter Doug O'Harra contributed to this report.