When insect scourges run rampant through forested ecosystems they can leave behind entire stands of dead and dying trees – especially if that scourge is the spruce budworm. In the Upper Midwest, where the spruce budworm infests forests on a cyclic 30-50 year pattern, forest managers oftentimes use salvaged logs from the dead and dying trees to produce low-value wood products, such as wood pulp, or merely count the dead trees as a loss and leave them standing.
But Forest Products Laboratory (FPL) researchers developed ways to evaluate the quality of salvaged wood and sort out the higher-quality wood for production of cross-laminated timber (CLT) – a high-value wood product that can increase forest revenues. “We’re at the point of demonstrating commercially available technologies,” said FPL engineer Robert Ross, “and the idea that we can take high-grade material out [of dead tree stands].”
Ross and Xiping Wang, also a forest products technologist at FPL, are embarking on a research project with partners from Michigan Technological University to demonstrate how effective new technologies are at allowing forest managers to distinguish between low-quality and high-quality wood in dead or dying stands. For years, Ross and Wang collaborated with members of numerous Forest Service research stations, regions, and departments, along with local state universities, to establish a scientific baseline that led to the development of these quality-detecting technologies.
In the ongoing research project, Ross and Wang will evaluate three technologies: longitudinal acoustic waves, single-path stress wave timing and resistance drilling. The first two technologies function similar to low-resolution dental X-rays, but with sound waves instead of X-rays. By measuring how long it takes for a sound wave to travel through a dead tree trunk, either perpendicular or parallel to the trunk depending on the method, they can determine if the interior of a tree is low-quality wood riddled with rot and decay or if it’s in better condition and of higher quality. In the third method, resistance drilling, researchers or managers use a very fine drill bit to drill across the tree trunk. They can identify if a dead tree contains weak and decayed wood by how much resistance the drill meets; some drills can even measure the voltage used and relate that to the quality of wood.
“Wood quality” might bring to mind density, but density isn’t the sole determinant of the quality of wood. What these technologies test and evaluate is the density, growth rate (fast versus slow growth), reaction wood, and if the wood is dried and decayed or not. All of those factors together determine whether wood from a dead or dying tree is low- or high-quality.
Once the team determines the quality of sample salvage logs, collected from three to five predetermined stands, they’ll separate the collected wood by quality and then make them into CLT panels, which Ross describes as “plywood on steroids.” These panels will be evaluated for structural performance to further demonstrate how identifying high-quality salvage wood can lead to the production of high-value wood products that increase forest revenues and money-making opportunities.
For more information on this project, see the related Research In Progress report.
Blog post by Cody Sullivan