There are now 66 million dead trees in California's forests due to several years of drought and native bark beetles, creating a "catastrophic" wildfire threat—or so claims U.S. Secretary of Agriculture Tom Vilsack. While Vilsack's assertion may resonate with many in the general public because it makes intuitive sense, it simply isn't true.
Among scientists, there is an overwhelming consensus that weather (hot, dry, windy conditions) determines how wildland fires behave, not the density of dead trees or "snags."
Trees larger than just a few inches in diameter are not consumed in fires — only the outer bark layer and the needles actually burn up — so the great majority of the dead trees in the forest do not significantly influence fire behavior, even if they are dry. Besides, once trees die, the combustible oils in the needles quickly begin to dissipate and the needles fall, making it more — not less — difficult for flames to spread through the forest canopy.
As it happens, numerous empirical scientific studies have been conducted on this very issue. Last year, a study published in Proceedings of the National Academy of Sciences found that high snag levels had no effect on the rate of fire spread in conifer forests of the Western U.S., including California. In 2016, another group of researchers found that forests with high snag levels actually tend to burn less intensely than other forests.
Secretary Vilsack is well aware of this research, but it does not fit with his political and economic objectives. On June 22, he argued that large-scale "tree die-offs" put "property and lives at risk," and urged Congress to act. Specifically, he recommended passage of a bill backed by the timber industry that would fund a large expansion of the federal wildland fire suppression program, and increase commercial logging on federal public lands — all in the name of removing supposedly dangerous dead trees.
Notably, the Agriculture Department has a direct financial interest in this legislation. It can sell dead trees, as well as trees the department claims are dying, to private logging companies from our national forests and other federal lands, and keep 100% of the revenue through the Salvage Sale Fund. The more logging Congress allows, the more money the Department makes.
Environmental groups and ecologists widely oppose the legislation because it would direct most fire suppression funds to remote, backcountry forests — rather than the ones that border human communities. It would also damage these forests' health.
When trees die naturally due to drought, native beetles or fire, the snags and downed logs contribute to forest rejuvenation and become microhabitats for wildlife. Birds, mammals, amphibians, reptiles and fish all use snags and logs for food, nesting or shelter. The logging Vilsack wants to encourage, on the other hand, will leave behind only stumps, which produce none of these benefits. In the long term, then, the proposed legislation will degrade our forests and, in a cruel twist, lead to even more tree deaths.
Ignorance and shameless economic opportunism will destroy our forest ecosystems if we are not careful.
Chad Hanson is a research ecologist with the John Muir Project and is the co-author and co-editor of the recent book, "The Ecological Importance of Mixed-Severity Fires: Nature's Phoenix."