Presence of tanoak reduces Douglas-fir mortality from black-stain root disease
As part of a study on the effects of tanoak competition on Douglas-fir, a scientist with the Pacific Northwest Research Station discovered that where tanoaks and other hardwood had been retained in the stand, there was less mortality from the root disease in 20- to 24-year-old Douglas-fir compared to stands where all tanoaks had been removed when the stand was 2 years old.
The Forest Service scientist hypothesized that the presence of hardwood roots may have slowed conifer root growth and served as a physical barrier to the spread of disease. On public lands in southwestern Oregon where this study took place, forest managers are already retaining low to moderate densities of hardwoods to increase biodiversity and provide wildlife habitat; such practices should also reduce the spread of black stain.
Forest Service Partners