Treeline is the northernmost place where trees can grow — a transition zone where boreal forest meets tundra. Patrick Sullivan has studied the treeline in the Northwest Arctic for nearly two decades, focusing on vegetation changes along the Agashashok River, which locals call the Agi.
One of Sullivan’s findings is that increased precipitation and snowpack in the Northwest Arctic may be encouraging the growth of white spruce trees, causing a northern migration of the treeline.
As part of his research, Sullivan and his team constructed fences along the treeline on the Agi that capture snow drifts. The fences were built six years ago and are about five feet tall, set up around individual trees at several locations in wet, normal and dry soils. The idea behind the snow fences is to mimic increased snowpacks that may be becoming more common for the region.
“There are indications that winter precipitation has been increasing in Northwest Alaska, and our snow fence experiment is very realistic,” Sullivan said.
This winter, Kotzebue set several precipitation records.
Sullivan said his team’s research on snowpack will help predict whether trees will be able to grow further north.
“The reason that we're really interested in snow is that we've found that years later, the deeper snowpacks are followed by years with much greater tree growth,” he said.
Sullivan says a heavy blanket of snow keeps the soil warmer and encourages increased mycorrhizal, or fungal, growth under the surface. That makes more nutrients available to the tree, which in turn could be increasing seed production in white spruce.
Sullivan said that more snow, along with warming arctic temperatures, could have other significant environmental effects, too.
“As scientists, we try not to make value judgments to what's going on and in ecosystems, but I think that from a climate perspective, the advance of the treeline is generally expected to lead to greater carbon uptake from the atmosphere,” he said.
While the spruce’s ability to sequester carbon might be seen as a positive aspect of the advancing treeline, Sullivan said it's not so simple.
“The assemblage of species that live in forested ecosystems is very different from what you see in tundra,” he said.
Sullivan said the advancing treeline could have a dynamic effect on the Arctic ecosystem, hurting caribou habitat. Caribou tend to avoid forested areas and primarily eat small shrubs and lichens.
Sullivan, whose work is largely funded by the National Science Foundation is working on several more treeline projects besides the snow fences. Last summer, working with a 10-person crew, he conducted tree growth measurements along the Brooks Range, working from west to east. He’s also been studying the bark in Northwest Arctic spruce for evidence of spruce bark beetle infestations,which was not previously documented.
Sullivan plans to continue his research on spruce trees this summer and hopes to continue the snow fence experiment for a few more years.
