Climate, Not Fuels, Drives Big Wildfires

Recently U.S. Forest Service researcher Dr. Paul Hessburg presented his “mega-fire” lecture in Jackson, Wyoming. Although Hessburg made some good points that are worth reiterating, such as the need for allowing more wildfires to burn and less building in the wildlands urban interface, he also misrepresents some finer points of fire ecology.

Basically he promotes the notion that fuels resulting from “fire suppression” are what drives large wildfires, which he pejoratively calls “mega-fires.” The pejorative language is found throughout his presentation with terms like “destructive wildfires,” “unhealthy” forests and so forth, all of which are questionable from an ecological perspective and countered by other scientists.

The main problem with Hessburg’s presentation is that he promotes the idea in many direct, as well as subtle, ways that fuels are the reason we are experiencing large wildfires, while extreme fire climate/weather is the main driver of large wildfires.

A misleading idea perpetuated in Hessburg’s talk is that fire suppression has created “unnatural” fuel buildups. However, throughout the period between the late 1930s and late 1980s the climate of the West was dominated by cool, moist conditions.

Under such conditions fire suppression had little effect since ignitions simply self-extinguish. Plus, you have higher seedling survival and, as a consequence, denser forests.

However, beginning in the late 1980s the overall climate has shifted to warmer and drier conditions, likely exacerbated by human-caused climate warming. Record droughts have been recorded in the West. Those droughts, more than fuels, are responsible for the increase in large wildfires.

Under such climate conditions, large fires like the 1988 Yellowstone blazes that kill a high proportion of trees are completely normal. Even the death of trees from bark beetles is “natural” and “normal” under drought.

Persistent drought, low humidity, high temperatures and, most importantly, high winds create the conditions favorable to fire spread. If you have these conditions you will have a fast-moving and usually large wildfire.

Aspen, lodgepole pine, spruce and fir dominate the land around Jackson. The fire rotation in such forests is often hundreds of years. Where and when a fire will occur is impossible to predict. Since you cannot predict where a fire will burn, but you can predict that you don’t want a house to burn, fuel treatments should be done in the immediate area around homes to reduce their flammability, while the majority of wildfires should be permitted to burn.

Another misleading idea in Hessburg’s talk is that wildfire-induced tree mortality is “destructive.” Fires that kill a high proportion of trees are critical to “healthy” forest ecosystems. For instance, some two-thirds of all wildlife depends on dead trees for some portion of their life cycle. Many plants are found only on dead trees. Indeed, the snag forests that result from a major wildfire have the second highest biodiversity after old growth forests.

For many plants and animals it is not wildfire or bark beetles they fear, but the green forests with little tree mortality.

If we are to live with wildfire we must learn to live with the inevitable large fires that are responsible for creating much of the dead snags and down wood critical to healthy ecosystems.

George Wuerthner has published 36 books including Wildfire: A Century of Failed Forest Policy