Project Shows Low Value Tamarack Is a Marketable Product

Matt Aro, NRRI senior researcher, stands in front of pilot-scale thermal modification kiln supplied by American Wood Technology.
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By June Breneman for the Natural Resources Research Institute

From wildfires to drought, U.S. forests face multiple threats. In Minnesota, where the forest products industry ranks as one of the top five manufacturing sectors, climate change and the Eastern larch beetle are teaming up as an especially challenging duo to one particular forest type.

Over fifty percent of Minnesota’s tamarack forests – some 440,000 acres and growing – have been infested by the Eastern larch beetle. Many of these trees will die, leaving the state with increased volumes of fire tinder and unmerchantable timber. The warming climate has also lengthened the growing season and warmed Minnesota’s winters, which have increased the beetle spread and risk of future large-scale infestations.

The Natural Resources Research Institute in Duluth, an applied research arm of the University of Minnesota, is looking for better outcomes. Namely, markets for underutilized wood, like tamarack, and valuable products with important environmental benefits.

Matt Aro, NRRI senior researcher, is demonstrating that low-value tamarack can be harvested and used in marketable products. He, along with several project partners, received funding in 2019 to build a boardwalk in Minnesota’s Sax-Zim Bog, a public natural area, out of thermally-modified tamarack to show that the modified wood can be used for outdoor applications. The boardwalk demonstration project was funded by the U.S. Forest Service Wood Innovations Grant program in partnership with the Friends of Sax-Zim Bog.

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The Natural Resources Research Institute received funding in 2019 to build a boardwalk in Minnesota’s Sax-Zim Bog out of thermally-modified tamarack showing that the modified wood can be used for outdoor applications.

Thermal modification is a chemical-free heat-treatment process that can add value to Eastern larch and other wood species by increasing its dimensional stability and its resistance to moisture and decay. This technology, however, suffers from low awareness and relatively few real-world demonstrations.

NRRI houses one of the few pilot-scale thermal modification kilns in North America. The technology– supplied by American Wood Technology – equips NRRI to research, develop and demonstrate thermally modified wood in a range of new applications. Low value trees species are being tested under a variety of modification ‘recipes,’ and specifications are tested for use in a wide range of products – from siding to flooring to windows and doors.

“The Sax-Zim Bog is giving us a great opportunity to demonstrate how well thermally-modified tamarack holds up in outdoor applications,” said Aro. “And, of course, we hope visitors will enjoy getting closer to the birds and nature while avoiding the bog’s sensitive and damp areas.”

The Sax-Zim Bog is a 300 square-mile expanse of bogs, rivers, lakes, meadows and farms in northern Minnesota that is home to a diverse range of wildlife, attracting bird-watchers and naturalists from around the world. It is primarily a black spruce and tamarack bog, but it also includes areas of upland aspen, floodplain forest, pine stands and aquatic systems.

Northern Minnesota’s climate is warming significantly, and that impacts many natural systems that tamarack stands depend upon. While the statewide average annual temperature is about three degrees Fahrenheit warmer than at the end of the 1800s, northern Minnesota’s winter low temperatures have warmed by over seven degrees from 1895-2019, according to University of Minnesota Climate Scientist Heidi Roop.

The eastern larch beetle is a native bark beetle that feeds on a vital part of the tamarack bark, and its proliferation through Minnesota’s forests is expected to increase. “Most significantly, those cold, cold winter days that are signature climate features of northern climates are happening less and less,” said Roop. “In the absence of those cold snaps, pests like beetles have a better chance of winter survival and will thrive.”

Add drought conditions to the mix, which are expected to become more frequent in the future, and the dead, small diameter tamarack stands may pose significant wildfire concern.

Much of Aro’s career has been focused on identifying opportunities for Minnesota’s underutilized wood resources. Expanding the market value of tamarack is reaching ‘mission critical’ as the current trends unfold.

Future needs include developing performance standards and/or certification for thermally modified wood. If successful, this would give potential manufacturers and end-users confidence in the products’ performance for specific applications.

“The goals of this project are not small,” said Aro. “We want to improve forest health and reduce wildfire hazards while supporting the regional forest products industry. If we can increase production, sales and use of thermally modified tamarack, we’ll take a huge step in that direction.”

More information about the boardwalk research project can be found at, or contact Matt Aro at