Clearing the Smoke on High Intensity Fire
By Christy Sherr
Published April 29, 2015 in The Union Newspaper
The April 16 opinion piece featured a forester with Sierra Pacific Industries who discussed historical assumptions about our Sierra Nevada forests and their complex relationship with fire. His three assumptions were that high intensity fire is unnatural, that this fire is increasing because of human activities, and that mechanical thinning (i.e. logging) will fix the situation. While at first blush this may seem compelling, scientists are examining these assumptions, and finding repeatedly that these assumptions are wrong.
Instead, scientists are finding that older, even dense forests, burn at the same or lower intensity than logged or mechanically thinned forests. Older, dense forests that burn at high intensity re-burn at the same or lower intensity if left unlogged. Forests that burn at the highest intensity are those previously clear-cut in Sierra Pacific Industry fashion.
Here are four important reasons why dense, long-unburned (and unlogged) forests generally burn at lower intensity than mechanically thinned or logged forests.
Older and even very dense forests have a canopy that allows less sunlight into the forest interior, maintaining a shadier, cooler, and more humid environment. In contrast, a forest that has been mechanically thinned (logged) has a more open canopy with hotter, drier understory shrubs and chaparral.
Second, mature and dense forests self-thin. As the canopy closes, shrubs, saplings and lower branches die. The dominant trees grow taller and the crown-base height increases, the understory shrinks, and distance grows between the two layers, lessening the likelihood that fire travels into the crown. In contrast, a forest that has been logged or mechanically thinned has, within several years after thinning, an abundance of shorter, even-aged trees and pyrogenic shrubs in the understory, ripening conditions for high intensity fire.
Third, mid-flame wind speeds largely determine how fast a fire burns through a landscape, and are actually slowed down in highly dense forests. They also move more slowly through a recently burned dense forest that has not been logged. In contrast, mid-flame wind speeds are highest in forests aggressively logged and mechanically thinned.
Fourth, scientists and informed land managers agree that large wildfires are weather-driven. Fuel conditions and forest structure play a relatively minor part in whether and how a landscape burns. Weather conditions, like temperature, relative humidity, and wind speed (and topography) determine how large fires behave.
The Sierra Pacific Industries forester believes that high intensity fire injures soil and destroys seed banks. A multitude of studies find just the opposite. For example, deep within the largest high intensity fire patches in the Rim fire, a stunning carpet of wildflowers, oaks, chaparral and regenerating conifers is proliferating.
Throughout the American West, scientists are finding that private lands, like those held by SPI which are subject to the most destructive logging practices, have the most high intensity fire. Public lands that are not logged as intensively as private lands burn at lower intensity, and protected park lands and wilderness burn at lowest intensity. Reducing environmental protections and increasing mechanical thinning and post-fire logging will only create conditions for more high intensity fire, and will degrade forest ecosystems in the process.
High intensity fire is normal and natural. Historically, it comprised, on average, 10-30 percent of any given mixed intensity fire, pre-European settlement, with much higher proportions of high-intensity fire occasionally. Both the Rim fire and the King fire have high intensity fire percentages well within this norm. Moreover, while most high-intensity fire patches were smaller historically, some were thousands, or even tens of thousands, of acres in size, according to numerous scientific sources.
High intensity fire creates a very valuable wildlife habitat called Complex Early Seral Forest, which is at an extreme deficit in our forests. Species that are dependent upon or prefer CESF are largely in decline. When CESF is created, there are usually immediate plans to remove most of it. Logging this critical landscape is seen as quick revenue for our National Forest employees, who get to keep all of the proceeds. However, this practice is changing as we grow in understanding and appreciation for the important role this habitat plays in preserving biodiversity.
The SPI Forester and I do agree on one point – Californians use tons of wood products each year, and we do import too much wood. What he failed to mention is that the majority of the wood that we cut each year here in the Sierra Nevada is shipped to China and Japan.
Christy Sherr is a retired park ranger who is currently working as a wildlife biologist and outreach coordinator for the John Muir Project of the Earth Island Institute. For questions or to obtain copies of relevant scientific research, you may email her at [email protected].