Guide to variable-density thinning using skips and gaps

Abstract

In recent years, many forest managers have become interested in managing forests for a wider range of objectives than previously. As an initial or intermediate treatment, variable-density thinning (VDT) can help meet objectives such as improving wildlife and plant habitats, increasing structural and compositional diversity, and enhancing aesthetic values in stands that are currently lacking spatial variability. The “skips and gaps” method of VDT is flexible, allowing for the preservation of existing desirable features. Areas that are not thinned (“skips”) will protect existing features that are best preserved by being within an area where logging equipment is excluded. “Gaps” can be created to closely approximate natural disturbance regimes through harvest of small groups or patches of trees. Gaps can increase growth and crown lengths of neighboring trees. Furthermore, gaps can be created that favor underrepresented tree species that are either already present or are planted after treatment. Areas that are not within skips or gaps (the “matrix”), are thinned to encourage growth of the overstory trees and the development of understory plants. This publication demonstrates the steps necessary to implement this type of VDT based on lessons learned from eight sites on the Olympic Habitat Development Study and two western Washington state parks.

Citation

Brodie, Leslie C.; Harrington, Constance A. 2020. Guide to variable-density thinning using skips and gaps. Gen. Tech. Rep. PNW-GTR-989. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 37 p.