In the Pacific Northwest, clearcutting is the preferred method for harvesting wood products from Douglas-fir plantations because it’s economical and mimics a large-scale disturbance. Following a clearcut, Douglas-fir seedlings are planted throughout the recovering native plant community. Yet the newly planted seedlings and native plants aren’t the only vegetation claiming the open ground. Invasive plant species, such as Scotch broom and sweet vernalgrass, can also colonize the site and compete with the seedlings for water, nutrients, and light.
Eradicating Scotch broom requires repeated herbicide applications, but even this approach might not fully control the infestation. Tim Harrington and David Peter, both researchers with the U.S. Forest Service Pacific Northwest Research Station, conducted a 5-year study near Matlock, Washington, to test if logging debris, in combination with herbicide applications, could reduce the spread of Scotch broom and other invasive plants; thereby improving regeneration of Douglas-fir.
They found that leaving logging debris reduced the spread of invasive plants and encouraged the development of the native plant community. Douglas-fir seedlings on these sites also grew faster and had higher survival rates than seedlings on sites where logging debris was removed. These results suggest that retaining logging debris offers a potentially cost-effective and beneficial long-term solution for managing invasive plants.
Watts, Andrea; Harrington, Tim; Peter, Dave; Slesak, Robert. 2019. Managing competing vegetation in Douglas-Fir plantations: The benefits of forest floor complexity. Science Findings 220. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.