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Collaboration Looks to Maximize Value from Thinning Operations in the West

by Rebecca Wallace
Public Affairs Specialist

A recent focus of research at the U.S. Department of Agriculture (USDA) Forest Products Laboratory (FPL) has been finding high-value uses for forest thinnings to offset the cost of expensive, but necessary, treatments that improve forest health and decrease the risk of catastrophic wildfires.

Ironically, the availability of pulpwood from public and private lands in the western United States is diminishing, and the pulp and paper industry has become increasingly reliant on the availability of residuals from sawmill operations.

A team of FPL researchers may have found a way to simultaneously address both of these forestry-related issues: Their results have shown that small-diameter, thinned trees, once thought to be inferior, are in fact suitable for both lumber and pulp production. The team has discovered compelling evidence indicating that fibers produced from thinned forests are at least equivalent to those from traditional wood supplies. Initial research showed that small-diameter (suppressed-growth) trees have narrower annual rings, more uniform fiber cell structure within the rings, and a higher volume fraction of mature wood. These factors should improve pulp properties in the production of thermomechanical pulp (TMP).

Pulping trials undertaken by FPL in an industrial pilot-scale facility confirmed these findings. Furthermore, less refining energy was required to produce pulp from forest thinnings than conventional wood supplies. However, to convince the pulp and paper industry that thinnings are a good alternative source of wood fiber, researchers needed to demonstrate their findings at an industrial-scale pulp and paper mill. “We needed to find a way to bring years of laboratory research into a mill environment,” said FPL research general engineer Junyong Zhu. “We were able to accomplish this through a partnership with interested parties from both the forest health and forest products sides of the issue.”

The diverse partnership consisted of representatives from FPL, University of Idaho (Moscow), USDA Forest Service Pacific Northwest Research Station (PNW), Colville National Forest, Ponderay Newsprint Company (PNC), and Ponderay Valley Fiber (PVF). Bringing these institutions together helped to ensure that issues were being addressed from all angles and possible solutions were feasible in every arena.

University of Idaho professor Lou Edwards said the key to success for this project was the various expertise that different partners brought to the table. “FPL’s extensive testing of wood, fiber, and paper products was essential to the success of this project,” said Edwards. “The University of Idaho and the commercial companies involved don’t have the comprehensive testing capability, but we can provide the necessary familiarity with the local infrastructure that FPL researchers do not have. Bringing these two different, but equally valuable, areas of knowledge together is a big part of what made partnership so successful.”

The first step in the research project was to identify an appropriate site for a thinning operation to provide lumber and chips for the trial. Forest Service personnel from Colville National Forest in Washington selected a 70-acre site at East LeClerc, near Usk, Washington.

“The Colville [Forest] was chosen because it has a large number of overstocked small-diameter stagnant stands that need treatment,” said Ed Maffei, Timber Management Assistant and Contracting Officer for Colville National Forest. The site was then evaluated by members of PNW’s Ecologically Sustainable Production of Forest Resources team to determine species distribution, stem densities, and available log sizes. “Our expertise is on solid-wood recovery, so we focused our efforts on that part of the study,” said Dennis Dykstra, research forest products technologist at PNW in Portland, Oregon. “We selected the sample trees to be harvested and were on hand during the harvesting operation to tag all the logs with identity markers so we would know the individual tree from which each log was derived.” Trees were selectively harvested by PVF with Reynolds Logging using a cut-to-length harvester and forwarder according to Forest Service regulations and project specifications. The logs were then hauled to PVF, where they were sorted by species. For the sawmill trial, all logs with defects (heart rot, checks, and distortion) and those with minimum diameters less than 4.1 inches (typically tree tops) were segregated from saw logs and chipped as whole logs. Saw logs were then processed through the HewSaw (Veisto Ltd., Mäntyharju, Finland) at PVF. Residual chips produced from the sawing operation were collected separately. Both whole-log and residual chips were shipped to PNC for pulping trials.

Preliminary results based on visual inspection by PVF indicated that lumber produced from thinned trees meets their product specifications. This is a critical component to the success of future thinning operations. “If products can be obtained from the thinnings that have structural and quality characteristics that make them attractive in markets, the national forests could extend their treatments over much larger areas,” said Dykstra. “Currently, the national forests have very limited budgets to undertake this type of work, so hazardous fuels are slowly increasing in forests throughout the West.” Dykstra said producing lumber from thinnings would be beneficial to the health of the forests, the safety of people who live in and around forests, and the economies of local communities where wood-processing facilities are located.

Two separate pulping trials were then conducted at PNC. The first trial was an evaluation of pulping characteristics of whole-log chips when added to the mill’s conventional blend. This portion of the study was of particular interest to PNC and the paper industry because, although a large quantity of this material is available, only a small fraction (about 20%) is typically used due to problems with chip quality (such as species, color, moisture, degradation). For these trials, a 44% whole-log blend (30% from thinnings) was used without a noticeable loss of pulp quality, and the blend required less energy to refine. For the residual chip trial, up to 50% of the chip blend evaluated was from thinning residuals. FPL researchers were mainly interested in studying pulp properties, such as fiber length and freeness, and how they changed as the ratio of thinned chips to traditional pulp mill chips was altered. Again, no loss of pulp quality was apparent, and refining energy requirements were similar. Chips generated from forest thinnings as either whole logs or sawmill residuals produced commercial-quality TMP for newsprint, and the newsprint produced meets market specifications. Researchers continue to analyze the data but predict that mills may be more willing to use thinning materials in the future as a result of this study. “Wood chips are getting harder and harder to come by these days,” said Robert Grace, pulping manager at PNC. “If there is an opportunity out there for us to improve our raw fiber supply, we need to look at it, and if further trials prove to be successful, we will consider consuming more of this type of wood chips in the future.”

Originally published in Newsline, Volume 5, Issue 3, Summer 2006