James Johnston

BURNS, Ore. — Mechanical thinning is helping to improve the health and resiliency of seasonally dry forests in Eastern Oregon, according to research by Oregon State University.

For the last decade, a team of scientists led by James Johnston, assistant professor in the College of Forestry at OSU, has trekked into a rugged area of the Malheur National Forest north of Burns to study the environmental effects of one thinning project.

What they found was that cutting down some younger trees resulted in greater biodiversity and made older, larger trees more resistant to drought and disease, Johnston said. 

Their findings were recently published in the scientific journal Forest Ecology and Management.

The Malheur National Forest in the southern Blue Mountains is one of 23 “priority landscapes” identified by the U.S. Forest Service for accelerated restoration under the Collaborative Forest Landscape Restoration Program, or CFLRP.

Conditions in the forest have changed drastically over time, Johnston said. Much of the landscape was overgrazed a century ago, and unsustainable logging practices targeted old-growth ponderosa pine. The Forest Service also began extinguishing every wildfire in the woods regardless of location or size — a practice known as “fire exclusion.” 

That has led to a buildup of vegetation fueling larger, more destructive wildfires and making older trees more susceptible to drought, insects and disease.

“In a word, we’ve made every bad (management) decision you can make over the last 100 years,” Johnston said. 

The CFLRP was created to speed up restoration work in these priority forests and rehabilitate them to their historical conditions.

In late 2014 and early 2015, the Forest Service thinned several thousand acres in the Malheur National Forest, part of the Marshall Devine Hazardous Fuel Reduction Project. Johnston and his team have collected 10 years of data, both pre- and post-thinning, examining the project’s impact.

By reducing the number of younger and smaller trees, Johnston said the older, more fire-resilient ponderosa pines grew larger after about three years since they were no longer competing as much for water and nutrients. 

The trees left standing were also able to build up greater defenses against insects, disease, drought and fire, Johnston said. 

Meanwhile, thinning had another effect on the forest understory. Fewer trees meant more water and sunshine was available for hundreds of species of forbs and grasses, Johnston said, creating a “ripple effect” throughout the system for native plants and animals. 

“If you like flowers, these thinned stands are a good place to visit,” he said.

Johnston’s study was done in partnership with the Forest Service and Blue Mountains Forest Partners, a coalition whose members include local city and county officials, loggers, millworkers, ranchers and environmental advocates.

While legal and logistical hurdles remain for accelerating forest management, Johnston said he hopes this research will show scientifically how thinning can be beneficial.

“I think that the scientific results that we published this week show that these forest restoration treatments work, that we are creating better outcomes for old-growth trees and native biodiversity by these selective thinning operations in dry forests of Eastern Oregon,” he said.