Study finds biomass harvesting techniques with minimal impacts

By USDA Forest Service Rocky Mountain Research Station | October 07, 2016

A set of newly published studies evaluated nearly 40 years of data on the impacts of biomass utilization on soil, tree, and plant recovery and found minimal impact using certain forest harvesting techniques.

The experiments, initiated in 1974, were conducted by scientists from the USDA Forest Service Rocky Mountain Research Station on the Coram Experimental Forest, located in Northwestern Montana. In order to evaluate the ecological consequences of large-scale biomass harvesting, scientists implemented three different tree removal techniques on the landscape—group selection (remove small groups of trees), clearcut (remove all timber), and shelterwood (retain some trees for shade and structure)—all using cable logging. On all three sites the soil was left relatively undisturbed from the harvesting and varying amounts of down wood were left to promote soil organic matter and wildlife habitat. For some sites, prescribed fire was applied to reduce fuels and fire danger. Scientists then tracked these sites over 38 years to provide a contemporary look at the long-term impacts of biomass utilization on forest productivity (e.g., tree growth).

“In the early 1970’s there was a growing concern that high levels of biomass removal would deplete these ecosystems of vital nutrients and organic matter and negatively impact the long-term health of forests—that is what fueled this research,” said Deborah Page-Dumroese, lead scientist on the study from the U.S. Forest Service Rocky Mountain Research Station.

“We did not find any clear evidence that intensive biomass removal negatively impacted these sites, nearly forty years later these sites were healthy and had minimal observable impact,” said. Woongsoon Jang, a research scientist on the study from the University of Montana.

These findings are important because of the renewed focus on the potential for biomass energy to be a big contributor to the growing green economy. They also reveal the importance of long-term forest research. Initial differences in the soils and shrub communities disappeared as these forests matured, a fact that could be determined only with the passage of time.

The studies show that with proper use of low-impact logging techniques, intensive biomass utilization from forests can be done with few long-term impacts to the site. “This is great news for those interested in the green economy and the ability of forest biomass to contribute as a low-carbon alternative,” said Christopher Keyes, a lead scientist on the study from the University of Montana. “In moist-cool forests like these, using low-impact harvesting techniques, we can extract forest biomass, reduce fire hazard and promote the local economy, with few long-term impacts.”