Consequences of shrub expansion in the boreal forest

In Alaska’s Arctic tundra, changes in permafrost, soil and plant growth due to climate change have been well documented. However, according to University of Alaska Fairbanks researcher Samuel Dempster, similar changes in the boreal forest are often overlooked.

Dempster’s goal is to see how alder physiology in the boreal forest responds to changing environmental conditions. The goal is to better understand how expansion of small trees and shrubs will affect large-scale processes in the North.

Dempster studied a stand of alders near Fairbanks in a nonpermafrost area where the small trees are spreading.

“I was looking at them from breakup all the way to the first snow,” Dempster said. He gathered weekly measurements of stem and leaf water content, photosynthesis and transpiration, along with other related variables.

Dempster said another question he asked was “Are (the alders) looking good where all of the other trees are not doing that great?” Summer 2022 in Interior Alaska was hot and dry. The alders responded to the conditions with higher transpiration rates and lower photosynthesis rates overall. However, the trees maintained a stem water content of around 50%, suggesting they were able to regulate some physiological processes to cope with the hot, dry conditions.

That indicates alders may tolerate seasonal drought conditions, which may let them expand in areas with climate change.

UAF’s Jessie Young-Robertson also contributed to the study.