FAIRBANKS -- A newly published scientific study concludes Alaska's boreal forests are experiencing a widespread shift as they adapt to warming conditions.
The study, which includes extensive work by University of Alaska Fairbanks researchers, appears in the new issue of the scientific journal Ecology Letters. It supports what scientists and foresters have suspected for years -- that warming northern temperatures are forcing rapid changes in Alaska's forests.
The study combined satellite data and tree-ring information to determine that growth has recently been stunted among spruce trees in much of the boreal forest. At the same time, trees on some of the coldest fringes of the forest are experiencing faster growth than previously.
It's an indication that the forest could shift as its ideal temperature zones move into previously colder areas. The study is the first to combine both satellite and ground-level data to examine that theory.
"They're cold-climate species," said Glenn Juday, a UAF professor of forest ecology, of the spruce trees that populate the boreal forest. "Everything is adapted to certain climates, and that's their niche."
For more than 30 years, scientists have studied samples from tree rings to try to gauge changing growth patterns in Alaska spruce trees. The process seemed to indicate the increasingly warm summers are affecting tree growth, but Juday said he always felt those results needed to be part of a bigger picture.
"You can never sample enough -- Alaska is just too big," he said. "You're always left with the nagging problem: Was it only happening in one spot?"
Other researchers had come to the same conclusions about boreal forest growth by using satellite images that detect photosynthesis by analyzing reflected light. Those results needed some ground-level confirmation because of the detached nature of the high-altitude images.
"By putting the two together, we got the strength of both of them without the weaknesses," Juday said.
Scott Goetz, a senior scientist at Woods Hole Research Center in Massachusetts, proposed the joint study and co-authored the article with Juday.
Juday said the tree-ring samplings, which included 627 white spruce trees and 212 black spruce trees, were collected from throughout Alaska's boreal forests.
The project began with trees along the Tanana River and continued down the watershed toward the lower Yukon River. Samples were also taken in the White Mountains north of Fairbanks and in Southwest Alaska near King Salmon and Dillingham.
Juday concluded that summer temperatures in the central Interior have become nearly too warm for white spruce. Meanwhile, spruce trees in the colder parts of the boreal forest in Southwest are growing better.
Juday said a typical year in the Interior is still fine for most trees in a boreal forest. But unusually warm summers are now occurring several times each decade, which is causing stresses that leave spruce trees vulnerable.
"As the whole floor moves up, it's going to be harder for them to survive," Juday said.