This OSU study by Johnston et al. is interesting because it suggests that mechanical thinning can be useful in reducing without follow-up prescribed burning, at least for a while, at least in NE Oregon.
Mechanical thinning alone can calm the intensity of future wildfires for many years, and prescribed burns lengthen thinning’s effectiveness, according to Oregon State University research involving a seasonally dry ponderosa pine forest in northeastern Oregon.
Findings of the study, led by OSU research associate James Johnston and published in Forest Ecology and Management, are important because reducing accumulated fuels on federal forestland has been a congressional priority for nearly two decades; research such as this helps determine which techniques work.
Johnston’s team looked at years of data for multiple forest parcels – mechanically thinned stands and unthinned control stands – and used computer modeling to predict the behavior of future fires. The collaboration included his Oregon State College of Forestry colleagues Julia Olszewski, Becky Miller and Micah Schmidt, plus Lisa Ellsworth of the OSU College of Agricultural Sciences and Michael Vernon of Blue Mountains Forest Partners.
“Most of the studies that have been published so far suggest mechanical thinning that isn’t followed by prescribed fire is not as good for moderating fire severity than thinning combined with prescribed fire,” Johnston said. “Some studies have even suggested that thinning without prescribed fire can increase wildfire severity by adding to the buildup of fine fuels on the forest floor.”
Mechanical thinning refers to the use of commercial equipment such as a feller-buncher, which cuts and stacks whole trees, or a cut-to-length harvester and forwarder that results in logs of specific lengths being sent to the mill. In the study areas, all trees up to 53 centimeters in diameter at breast height were removed, and hand crews cut down trees too small for commercial use.
“Our work shows that mechanical thinning can moderate fire behavior even in the absence of prescribed fire,” Johnston said. “That’s good news since prescribed fire on national forests has remained flat over the last 20 years because of shortfalls in U.S. Forest Service capacity, a risk-averse agency culture and regulatory constraints on smoke.”
I guess I always thought “mechanical thinning” was cutting trees and removing them however you wanted, including hand piling and burning.
It’s interesting what Johnston ascribes the difficulties with PB to a “risk-averse agency culture” later he adds a few:
“Less than one-fifth of the area treated with mechanical thinning in the southern Blues has also been treated with prescribed fire,” Johnston said. “Prescribed fire has been significantly slowed by budget constraints, local opposition to fire use, and restrictions imposed by COVID-19 response measures.”