Radial thinning: Not as beneficial as hoped
In a 16-year study, Rocky Mountain Research Station Research Ecologist Sharon Hood and her colleagues assessed three types of radial thinning to determine whether they would improve the growth and survival of sugar pines, a species of white pine, in southwest Oregon on sites located in the Umpqua National Forest and Bureau of Land Management Roseburg District. In addition to evaluating a control group, the researchers examined three kinds of treatments in which trees and shrubs were removed around sugar pines to 3 m (10 ft); 7.6 m (25 ft), while retaining large trees with diameters greater than 64 cm (2 ft); or 7.6 m (25 ft). Though some of the radial thinning strategies seemed promising at the 9-year mark, the radial thinning did not improve sugar pine survival at the end of the study (year 16), as compared to the control group. The extended (7.6 m) radial thinning with complete tree removal treatment did increase tree growth for sugar pine that survived, but the level of tree mortality was similar regardless of whether trees had radial thinning or not. Most tree mortality was due to the native mountain pine beetle.