The Olympic National Forest is comprised of more than 200,000 acres of young-growth forest, established primarily through past tree planting efforts after clear-cut timber harvesting. These tree plantations were initially created on the forest to maximize wood fiber production. However, the focus shifted from fiber production to ecological restoration on the forest with the inception of the 1994 Northwest Forest Plan. Today forest managers work with multiple partners to help Olympic National Forestlands regain natural ecological functions and processes.
Variable-density thinning (VDT) is the primary commercial thinning method we use to accomplish restoration goals within forested stands. It entails increasing the variation of tree spacing to promote structural complexity, increase plant community diversity, and create a mosaic of habitat conditions. An area treated with VDT will have both “skips,” untreated areas, and “gaps,” where some trees were removed to create small canopy openings, usually less than a quarter acre.
Managers on the Olympic National Forest typically apply Variable Density Thinning treatments to stands that are 40 to 80 years old in order to accelerate the development of old-growth forest characteristics such as large diameter trees, long live tree crowns, and continuous vegetative canopies. Many of the plantations on the Olympic National Forest require more than a single thinning entry to achieve restoration objectives, and we currently treat a very small portion of them, less than 0.5 percent each year.
Pacific Northwest Research Station - For more information about variable-density thinning and the Olympic National Forest visit the Pacific Northwest Research Station website, http://www.fs.fed.us/pnw/olympia/silv/ohds/.