New research suggests that a climate change has contributed to a decline in white spruce tree growth in Interior Alaska.

Researchers at the University of Paris found that warming summer temperatures across Alaska has declined to record low levels in Interior Alaska, while the same species in Western Alaska is growing better than ever measured before.

"For the first time across a major forest region, we have real data showing that biome shift has started," researcher Glenn Juday said in a statement. "This is not a scenario model, or a might, or a maybe. The boreal forest in Interior Alaska is very near dying from unsuitably warm temperatures. The area in Western Alaska where the forest transitions to tundra is now the productive heart of the boreal forest."

For the 10-year study, researchers gathered white pruce tree cores and disks from 540 trees in 36 stands along the Yukon, Tanana and Kuskokwim rivers. They took two measurements from each annual growth ring of the 100 to 250-year-old trees, and then analyzed the nearly quarter-million measurements to determine how much the trees grew each year. They then compared that growth to temperature data from eastern, Interior and Western Alaska historical records and weather stations. In addition, they drew on previous scientists' work chronicling tree growth and temperature back more than two centuries.

They found that in Interior Alaska, as summer temperatures rose, the growth of the trees slowed. Meanwhile, in Western Alaska, which is also warming, the trees are growing more rapidly.

"One aspect of the study that makes the results especially clear is that the trees were all growing in the same environment along the big rivers," Juday said. "In many transect studies, lots of variables change across the area studied. In ours, the main thing that changed was the climate, from the hot, dry summers of the Interior, to the cooler, wetter climate near the coast."

Researchers note that the findings don't mean the boreal forest is going away. It's simply shifting away from lowlands in Interior Alaska to higher elevations and the western part of the state.

"The movement of an entire biome is often hypothesized in models of probable future climate, but the Alaska boreal forest is actually shifting today, and the process is well underway," Juday said.

The findings are detailed in the journal Forest Ecology and Management.