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Wood Energy as a Tool for Forest Restoration

Wood & Biomass Utilization Specialist, U.S. Forest Service
October 18th, 2017 at 11:15AM

A photo of a wood energy power plant
Wood energy power plants like this facility at Rio Bravo Fresno, California use combustion and gasification technologies to convert woody material into energy. USDA Forest Service photo by Marcus Taylor.

As we celebrate National Bioenergy Day on 18 October, part of National Forest Products Week, we can appreciate the role that wood energy plays in helping to restore forests across the country. Wood energy represents an innovative market for forest material that often cannot find another use.

Many forests in the United States are in need of restoration, especially fire-adapted forests that historically saw many low-intensity fires throughout their existence. These low-intensity fires removed small trees and saplings but left large, healthy trees intact. However, as a result of the aggressive fire suppression policies put in place during the last century, many forests are now overstocked with woody debris and small diameter trees.

The size of the tree is an important consideration when evaluating fuel loads. Small-diameter trees, like saplings and young trees, dry out more quickly than mature, large-diameter trees. They ignite and burn faster, posing a greater risk of serving as fuel for a wildfire that can make its way into the forest canopy and ignite the larger trees. Because large-diameter material typically chars on the outside and protects its interior wood from fire, it does not serve as a good fuel source. A 30-inch log is very difficult to burn completely. An eight-inch sapling, even when still alive, will burn much more easily.

As the United States comes to the end of a particularly devastating wildfire season, forest managers and ecologists have identified a need across many forests to remove small diameter trees and debris and leave larger material that is more resilient to fire. However, removing that smaller material requires site planning and preparation, cutting, stacking, and transportation.  Without a purchaser of the wood, it is difficult to fund the restoration work that removes hazardous fuels and produces a forest well adapted to the fires that inevitably start in the summer season. Hazardous fuels, including small logs and branches, need a market.

Wood energy represents an important market for small diameter material. Wood energy power plants use combustion and gasification technologies to convert woody material into useful products like electricity, steam, synthesis gas, and renewable biodiesel. These facilities can take small trees, branches, tree tops, and other unmerchantable woody material like beetle- or drought-killed wood.

Wood energy represents an important piece to the puzzle of how we can restore our forests to a state that is more fire resilient while also finding value in the small diameter logs and woody material removed from the forest.

A photo of beetle or drought killed wood
Bioenergy facilities can convert beetle-or drought-killed wood, like that on the Sequoia and Sierra National Forests shown here, into usable energy. USDA Forest Service photo.
A photo of a truck removing smaller materials
Removing that smaller material requires site planning and preparation, cutting, stacking, and transportation. Small-diameter timber harvesting and chipping for bioenergy on Apache-Sitgreaves National Forest, Arizona. USDA Forest Service photo by Nate Anderson.