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Title: Let's mix it up! The benefits of variable-density thinning

Author: Harrington, Connie.;

Date: 2009

Source: Science Findings 112. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.

Publication Series: Science Findings

Description: Can management of 40- to 80-year- old forests on the Olympic Peninsula accelerate the development of stand structures and plant and animal communities associated with much older forests? The Olympic Habitat Development Study, a cooperative project between the Pacific Northwest Research Station and the Olympic National Forest, began in 1994 to examine this question. It uses a novel type of variable-density thinning called thinning with skips and gaps. Ten percent of the study area was left unthinned, while 15 percent was cleared to create openings in the forest canopy. These gaps also yielded most of the merchantable timber. The remaining 75 percent of the area received a light thinning that removed mostly the smaller trees of the most common tree species. Five years after treatment, there was a noticeable difference in growth rates throughout the study area. In thinned areas, average growth was nearly 26 percent greater than in the unthinned areas. Tree growth was greatest around the gaps. Understory vegetation increased, and the presence of nonnative species was low, with most of the nonnatives found in the gaps. Wind damage was low and predictable. The treatments were easy to apply, and these findings suggest that greater diversity in stand structures and plant communities can be accelerated by thinning with skips and gaps.

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Harrington, Connie. 2009. Let's mix it up! The benefits of variable-density thinning. Science Findings 112. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.


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