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Photo by Kelly Reynolds.
Jessie Young-Robertson on the ҹɫ���� Troth Yeddha' Campus

By Laura Weingartner

Trees are central to the story of how water moves through an ecosystem. They absorb it through their roots, move it upward through straw-like tissues called xylem, and release it back into the atmosphere through their leaves or needles in a process known as transpiration. Roughly 25–50% of a living tree is water, and scientists estimate that about 10% of atmospheric moisture originates from transpiring trees. In that sense, forests don’t just respond to weather, they help create it.

Jessie Young-Robertson, research associate professor of forest ecology at the University of Fairbanks Alaska Institute of Agriculture, Natural Sciences and Extension, studies this relationship between water and forests, a field known as ecohydrology. When she arrived in Fairbanks from Tucson, Arizona, in 2009, the discipline wasn’t widely discussed in Alaska.

“I felt like that field was mainly a desert thing,” she said.

Seventeen years later, ecohydrology has become part of the conversation in the boreal forest. Young-Robertson now builds detailed datasets to understand how trees use, store and move water under shifting conditions such as drought, permafrost and insect outbreaks.

At research sites across Interior Alaska, she and her team collect a wide range of measurements to understand tree physiology and the environments in which trees live. In some locations, they run controlled experiments to examine how trees respond to stressors like aspen leaf miner or spruce beetle infestations.

“We have paired trees, some treated with insecticide and some not, so we can clearly see the effects of leaf minor on aspen,” she said.

Her team has also developed sensors that measure water pressure inside trees in real time. In spring, as snowmelt begins, they watch pressure build as trees start pumping water upward — higher pressure during the day when meltwater is flowing, lower at night as temperatures drop.

“They fill with water almost like a pump,” she said. “The second the leaves come out, the pressure drops, and then they go into negative pressure.”

That negative pressure is created as water is pulled out through tiny pores in the leaves called stomata, creating tension within the tree. Monitoring these subtle changes reveals patterns that aren’t visible from the outside, such as when birch trees put themselves to bed, even in Alaska’s light-filled summer. 

“They have a strong circadian rhythm, and they'll go to sleep at five or six p.m.,” she said.

At night, when photosynthesis stops and stomata close, trees shift to growing and repairing cells, using sugars produced during the day. Water is no longer escaping through the leaves, but since the trees are still under negative pressure, they continue to pull water in. Young-Robertson, who has stayed out all night monitoring this phenomenon, can watch the water content go up.

“They're rehydrating at night, and then in the morning you can see exactly when they wake up because [the water content] starts to go down again,” she said.

Collecting this level of detail is labor-intensive. Over the summer, Young-Robertson and her team visit 16 sites weekly. To streamline the process, she’s searching for key indicators — measurements that can capture long-term trends with fewer data points. She compares it to measuring a person’s blood glucose every week, or using a single test, called an A1C test, once every few months. 

“A1C tells you how your blood glucose has been over three months,” she said. “Whereas blood glucose is, right now, in this moment.”

Underlying all of this work is a larger goal: to understand the fundamental processes shaping the forest so that changes, whether from climate, insects or human activity, can be better interpreted.

“We are trying to put a puzzle together, but we don’t know what the picture on the box is,” she said.

When Young-Robertson thought about how her work shows up in people's everyday lives, the picture on the box took the form of firewood stacked in a woodshed. So she designed a study to determine the best time to harvest firewood for faster drying. She found that timing mattered less than conditions: wood exposed to hot, dry weather early in the drying process lost moisture much faster. In one case, a cord of white spruce cut and stacked in late spring lost 175 gallons of water in its first month.

The strong public interest in that study encouraged her to think more broadly about how her research could serve the community, from practical guidelines for homeowners to a deeper understanding of how trees, water and infrastructure intersect.

Outside the lab, Young-Robertson’s interests are expansive. She has always been an artist and even encourages her employees to find interesting ways to share science through art.

“It’s a big part of who I am,” she said. “It’s just fun.”

She is also pursuing her master’s in counseling and started taking classes after work because she has always been interested in mental and behavioral health.

“I practiced as a counselor for a while outside of work, and I think it helped me overcome burnout,” she said. “I could use a really different part of my brain.” 

The juggling of jobs in seemingly opposite directions isn’t new for Young-Robertson. Before arriving in Alaska, she worked on bird studies across the Lower 48, took a job in a genomics lab to gain research experience, and even taught aerobics, despite never having taken a class herself. 

Throughout her myriad jobs, she knew she wanted to come to Alaska and even had a stuffed penguin she named Fairbanks when she was nine. 

“Wrong animal, wrong whatever,” she said, acknowledging the lack of penguins in Alaska. 

After arriving for a postdoctoral fellowship in 2009, she spent years, as she puts it, “stumbling uphill,” before finding her footing in the Fairbanks research community. Collaborating with hydrologist Bob Bolton helped her recognize a gap between hydrology and plant physiology — one her work now helps bridge.

Young-Robertson’s fascination with water began when a friend in college casually mentioned that all biological reactions occur in water. It nudged her toward studying biology and a career built around understanding how water moves through living systems, which she continues to research to find an answer to what fundamentally shapes the boreal forest.