The study led by James Johnston of the OSU College of Forestry involved long-term monitoring and research partnerships between OSU, the U.S. Forest Service and local groups in Oregon's Blue Mountains., the findings illustrate the collaboration's success in"securing federal investment and delivering science products that measure forest treatments' effectiveness," Johnston said.
In 2014 and 2015, the study area was thinned in an effort to increase resilience to fire while facilitating the return of episodic low-severity fire, Johnson said. Fire dynamics in the area, and throughout seasonally dry forests of the interior Pacific Northwest, changed drastically starting in the last decades of the 19th century, he noted.
By the late 20th century, dense stands and shaded understories were resulting in high-severity wildfire, uncharacteristically severe drought-related mortality and susceptibility to bark beetles. Generally speaking, the forests were no longer nearly as resilient as they were when they had consisted of open stands of widely spaced, shade-intolerant, fire-resistant trees.
"We also investigated the responses of understory vegetation—the grasses, forbs and shrubs that influence fire behavior and forest resilience," he said."We saw an increase inand diversity within thinned stands three to four years after thinning, which stimulated the growth of vegetation that supports low-intensity fire regimes and is suppressed under a closed-canopy forest."