UAF researcher studies when to harvest firewood, reducing drying time

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FAIRBANKS, Alaska (KTVF) A researcher at the University of Alaska Fairbanks has been studying the moisture content of trees and has found that in the fall, when the temperature has dropped below freezing at 32 degrees Fahrenheit for more than 24 hours, might be the best time to harvest firewood.

A researcher at the University of Alaska Fairbanks has been studying the moisture content of trees and has found that in the fall, when the temperature has dropped below freezing at 32 degrees Fahrenheit for more than 24 hours, might be the best time to harvest firewood. (Sara Tewksbury/KTVF)

Jessie Young-Robertson Research Assistant Professor at UAF says that is commonly known that trees soak up water in the spring from snowmelt, but Young-Robertson says trees also soak up rain from the summer and become saturated. Young-Robertson says they will just completely fill with water, and then when the temperature drops below freezing for more than a day, the trees will dump about 70% of their water and if the temperature goes back up above freezing, they will take water back in. Since the temperature has to be sustained below freezing, she says October and November tend to have temperatures low enough to keep the trees drier.

By harvesting after the tree has purged water, Young-Robertson says it will make the trees lighter to carry, and take less time to dry to below 20 percent moisture content.

She says they are establishing a site at UAF to be able to stream data from the trees to a website to share with the public. It will have tree water content, soil water content, and air temperature and humidity. “The intention of that website is so that people can tune in everyday to see what the water contents are, which is important for people who tap the birch for sap but also for harvesting firewood,” said Young-Robertson.

Young-Robertson says they are also going to do a drying experiment, where they will cut trees at the time they would recommend when the air temperature drops below freezing for more than 24 hours, and also when trees are wetter, and see how long the wood has to be dried to get to 20% moisture content or less.

The Fairbanks North Star Borough Air Quality Division is working with Young-Robertson to apply the findings from her research.

“The emissions from woodstoves are dependent on the willingness and the expertise of every homeowner to operate the device correctly and to use the correct fuel, and the correct fuel is dry clean wood at 20% or less moisture content, “said Nick Czarnecki, air quality manager for the Fairbanks North Star Borough.

One concern in the community when considering burning dry wood, is how to get that dry wood, how long do you have to dry it, and is their enough wood for everyone to burn dry wood. That’s why Czarnecki is interested in Young-Robertson’s research since it may show that if the wood is harvested at a certain time, it will take less time to dry, in turn, Czarnecki says, getting more dry wood into the community.

“Back in 2018 with the Air Quality Stakeholders group, we had some analysis done that showed if we could get a bigger chunk of the community to use dry wood that there is some significant emission, so it has real potential to help with the PM 2.5 issue,“ said Czarnecki.

Young-Robertson and the borough’s air quality division are partnering on two aspects, using the research to update the borough’s best practices on harvesting time, and to use the data analysis to incorporate it into their education and outreach campaign.

Young-Robertson says they were also talking to the Alaska Department of Environmental Conservation about using this information for businesses that may soon have to sell wood at 20% or less moisture content.

“It’s very important to use dry wood, it not only helps clean the air, but it saves you money in the long run, because you end up burning less wood,” said Czarnecki.

Young-Robertson says as the temperature drops lower and lower below freezing, the trees will continue to dump their water and that they don’t know the exact numbers yet, but that is something they will look at in their upcoming research.

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