[EXCLUSIVE] Study: Thinning Forests for Bioenergy Can Worsen Climate

– by Josh Schlossberg, The Biomass Monitor

A new study out of the Geos Institute in Ashland, Oregon concludes that selectively logging or “thinning” forests for bioenergy can increase the amount of carbon dioxide in the atmosphere and exacerbate climate change.

The study, “Thinning Combined With Biomass Energy Production May Increase, Rather Than Reduce, Greenhouse Gas Emissions,” by D.A. DellaSala and M. Koopman, challenges bioenergy and timber industry assertions that logging forests will aid in the fight against climate change.

DellaSala and Koopman also refute assumptions that wildfires are bigger or more severe than in the past, citing multiple studies showing that the occurrence of wildfire has actually “changed little from historical (early European settlement) times.”

The Western Governor’s Association has stated that 10.6 million acres of western forests are available for “hazardous fuel reduction.” Yet, instead of instead of the build up of “fuel” (aka small trees and understory plants) being the main driver of large wildfire, the study authors blame climate, namely drought and high temperatures, explaining that, “during severe weather events, even thinned sites will burn.”

Instead of preventing large wildfires, the study argues that thinning can increase the chance of severe fire by opening the forest canopy which can dry out the forest, leaving flammable slash piles on the ground, and allowing winds to penetrate the previously sheltered stands, potentially spreading wildfire. Post-fire “salvage” logging is also thought to increase the risk of a re-burn.

Carbon emissions from wildfire have long been an argument to log forests, in an effort to harness energy from trees that may burn at some point anyway. Yet findings show that after a fire the majority of the carbon remains in dead trees, with severe fires that kill most trees in the area emitting 5-30% of stored carbon. Severe fires account for 12-14% of the area burned in large fires.

Even in the cases where thinning would be effective at stopping wildfire–typically small fires of limited threat to public safety–the study cites computer simulations estimating a 5-8% chance of a thinned parcel experiencing fire within the first twenty years, when fuels are lowest. The chance of encountering severe fire is 2%.

DellaSala and Koopman also urge an accurate carbon accounting of forest bioenergy, cautioning that the amount of carbon dioxide released from burning woody biomass is “often comparable to coal and much larger than that of oil and natural gas due to inefficiencies in burning wood for fuel compared to more energy- dense fossil fuels.”

In the rare cases in which a thinned forest is allowed to grow back without repeated logging, the several decades over which forests could reabsorb carbon “conflicts with current policy imperatives requiring drastic cuts in emissions over the near term.”

The study warns about “large-scale clearing of forests” at a time when natural forests are needed to buffer the planet against runaway climate change.

“Woody biomass,” said DellaSalla in a December 17 phone interview with The Biomass Monitor, “almost never pencils out as an efficient renewable energy source.”


  • It is obvious that biomass burning is horrible for the environment. Below is a old letter of mine on the subject.

    Use solar, wind, not biomass Eugene Weekly ( a few years ago)
    Seneca Sustainable Energy, with the approval of the state of Oregon, wants to continue the practice of burning the chips, wood debris and even whole trees from the site of former clearcuts. That we allow non-sustainable logging to take place is bad enough. To take away for any reason the matter, which when decomposed with the help of fungi, insects and microorganisms, will be the foundation upon which the forest will re-grow is lack of foresight. Without abundant vegetation to photosynthesize oxygen and consume carbon dioxide, this planet will die, and burning cellulose produces more greenhouse gases than burning coal.
    Some local politicians call this method of producing electricity green or clean, including Eugene Mayor Kitty Piercy, Rep. Peter DeFazio, Sen. Ron Wyden and Gov. John Kitzhaber. Others, too, refer vaguely to the economy, but biomass provides less jobs than truly sustainable forestry and energy production. To use the power of the sun in a variety of ways, including wind and geothermal, will get civilization simultaneously out of the energy crisis, climate change, wars over resources and a weak economy.
    Putting solar collectors on every rooftop and spreading windmills out evenly to account for loss of power during transportation is the way to go. In this manner, we would have our energy needs met and wouldn’t have to worry about destroying our forests.
    Dave Ivan Piccioni


    • Thanks for your comment and for being engaged enough on that issue that you’d submit a letter to your local newspaper.

      Obviously, every energy source has health and environmental impacts, including solar and wind. The goal of The Biomass Monitor is to ensure that people understand both the pros and the cons of bioenergy, and make their energy decisions accordingly.


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