As The Bee recently reported, a new study, by Malcolm North and others (2022), promotes the idea of killing and removing 80% of the trees in the forests of the Sierra Nevada through commercial logging, ostensibly as a wildfire management strategy. The North study was authored by scientists funded by the U.S. Forest Service, an agency that financially benefits from commercial logging on our public lands, and the study neglected to mention some essential information and evidence.
The North study reported that “current” tree densities are 83 to 171 trees per acre, and claimed that only 30 trees per acre existed a century ago. But the study used 2011 to represent the “current” condition of Sierra Nevada forests in the two areas that were analyzed, and failed to mention that nearly all of the forests in the two study areas have burned in wildfires since 2011, including the Rim fire of 2013 on the Stanislaus National Forest, and the Cedar fire of 2016 and French fire of 2021 on Sequoia National Forest. Why didn’t the North article mention that their two study areas have almost entirely burned since 2011?
The North study also neglected to mention that more detailed investigations of the same historical forest surveys used by the North study have found that the Forest Service scientists omitted most of the historical tree density data. When the omitted tree data were included, it turns out that historical forests had about 200 trees per acre, on average, with some areas much denser, and some less dense. This is undisputed by the Forest Service in the scientific literature. Why didn’t the North study mention this?
Similarly, why didn’t the North study mention the fact that most published research finds that denser forests tend to burn at lower intensities on average, due to the cool, shaded conditions created by higher forest canopy cover, and the windbreak effect that denser stands provide against the gusts that drive flames? Conversely, when logging occurs, including commercial thinning, it reduces the shade of the forest canopy, creating hotter, drier, and windier conditions that often increase fire intensity by changing the microclimate of the forest, as over 200 forest and climate scientists recently noted. The suggestion by the North study that removing trees from forests will consistently and reliably curb fire intensity is simply false. In the 380,000-acre Creek fire of 2020, for example, forests with previous commercial thinning burned more intensely, not less, based on the Forest Service’s own data.
The North study also promotes the notion of “overgrown” Sierra Nevada forests that are largely unmanaged and have not burned in a century or so. This too is misleading. In recent decades, vast areas of forest in the Sierra Nevada have been logged, including through commercial thinning, or have burned in big wildfires, including the Caldor fire of 2021 and the Dixie fire of 2021. Over the past decade, mixed-intensity wildfires have spanned millions of acres of Sierra Nevada forests — over 2.5 million acres in the past two years alone, in fact.
Contrary to widespread misconceptions, large Sierra Nevada wildfires are dominated by low and moderate intensity effects, where most mature trees survive, while a minor portion experiences high-intensity fire that creates “snag forest habitat” upon which many native wildlife species depend. High-intensity fire patches do not “vaporize” forests, as North inaccurately claims. Only about 2% of live tree biomass is consumed in high-intensity fire patches, and forests naturally regenerate quite well.
Again, why did the North study conceal all of this important information from the public?
Dr. Chad Hanson is a research ecologist with the John Muir Project, and is the author of the book, “ Smokescreen: Debunking Wildfire Myths to Save Our Forests and Our Climate ”.