Midcanopy growth following thinning in young-growth conifer forests on the Olympic Peninsula, western Washington

Abstract

Midcanopy layers are essential structures in "old-growth" forests on the Olympic Peninsula. Little is known about which stand and tree factors influence the ability of midcanopy trees in young-growth forests to respond to release; however, this information is important to managers interested in accelerating development of late-successional structural characteristics. We examined basal area growth response of midcanopy trees following variable-density thinning in an effort to determine the effect of thinning and local environment on the release of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata ex. D. Don) on the Olympic Peninsula in western Washington. Release was measured as the difference between average annual basal area growth over the 5-year prior to thinning and the 3-to-6 year period following thinning. Results indicate that while growth rates were similar prior to thinning, midcanopy trees retained in a uniformly thinned matrix grew significantly more than those in unthinned patches for western hemlock and for western redcedar. Crown fullness and crown crowding affected the release of western hemlock in the thinned matrix. Initial tree size, relative age, local crowding and measures of crown size and vigor affected the release of western redcedar in the thinned matrix. Our results indicate that midcanopy western hemlock and western redcedar retain the ability to respond rapidly with increased growth when overstory competition is reduced and the magnitude of response is related to neighborhood variables, thus suggest that variable-density thinning can be an effective tool to create variability in the growth of mid canopy trees in young-growth stands.

Citation

Comfort, Emily J.; Roberts, Scott D.; Harrington, Constance A. 2010. Midcanopy growth following thinning in young-growth conifer forests on the Olympic Peninsula western Washington. Forest Ecology and Management. 259: 1606-1614.