(The Center Square) – Forest thinning efforts have benefitted the robustness of older trees and enhanced native biodiversity on federal lands in eastern Oregon, research by Oregon State University revealed.
James Johnston of the OSU College of Forestry led a study coming to this conclusion. His study involved long-term monitoring and research partnerships between OSU, the U.S. Forest Service, and local groups in the state’s Blue Mountains region.
The Oregon Department of Forestry estimated the state had spent more than $20 million fighting wildfires as of mid-August 2023, according to Axios.
The findings show the collaboration’s success in “securing federal investment and delivering science products that measure forest treatments’ effectiveness,” Johnston said in a news release issued by OSU.
“Ecological restoration of seasonally dry, fire-prone forests has been a key goal of Forest Service managers for more than two decades,” Johnson said in the release. “Our study shows that thinning aids in bringing back tree and understory vegetation conditions associated with the ability to bounce back in the face of disturbance. And thinning doesn’t just help managers mitigate fire risk – it restores a range of ecological functions that over time make forests more resilient.”
Researchers studied a 2,900-hectare area in the Malheur National Forest. The study area included ponderosa pine forests of the southern Blue Mountains; the area has “priority landscape” status and receives money from the Forest Service’s Collaborative Forest Landscape Restoration Program.
Between 2014 and 2015, this area was thinned in hopes of improving its fire resiliency “while facilitating the return of episodic low-severity fire,” according to OSU.
Fire dynamics in the interior of the Pacific Northwest began changing in the last half of the 19th century, according to Johnston.
“The late 1800s and early 1900s were unusually cool and moist,” he said in the release. “On top of that, European settlement changed how Indigenous people used fire on the landscape – i.e., the settlers did not want fire on the land, and early forest rangers aggressively extinguished fire starts in the name of sustained yield timber harvest. Also, there was extensive unregulated grazing that removed the fuel that carried low-severity surface fire.”
In the late 20th century, dense stands and shaded understories caused “high-severity wildfire, uncharacteristically severe drought-related mortality, and susceptibility to bark beetles,” according to the release. That said, forests were less resilient than they had been previously.
Johnston and his research team quantified how much thinning can restore forest resilience. They looked at overstory tree attributes, including radial growth, resin production, abundance of non-structural carbohydrates, and leaf area.
“We also investigated the responses of understory vegetation – the grasses, forbs, and shrubs that influence fire behavior and forest resilience,” Johnston said. “We saw an increase in species richness and 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.”
Researchers found that tree radial growth was higher in thinned stands three years after thinning began. They also found that glucose and fructose presence was lower in treated stands, “suggesting trees were using carbon reserves for leaf and wood production,” according to the release.
“And while our study area was not treated with prescribed fire, we see the reintroduction of fire as an important management tool that can restore historical fire regimes and achieve additional management goals,” Johnston said in the release.
The study received funding from the Forest Service thanks to the Collaborative Forest Landscape Restoration Program, the National Institute of Food and Agriculture, and the Blue Mountain Forest Partners.
