Fire Myths, Hanson 2018

Compendium Volume 4 Number 2 January 2021

In this podcast interview, Dr. Chad Hanson, an ecologist and fire researcher, shares his perspective on the 2018 wildfires in the American West and some myths that have circulated about fire management in their wake.

First, there is a perception that wildfires in forested regions are so devastating that they reverse the ‘carbon sink’ effect of forests, releasing the carbon of the burned biomass back into the atmosphere. Forests still sequester large amounts of carbon, even if they experience wildfires, because most of the forest remains intact even through blazes. Models that fault wildfires for turning forests into net carbon emitters rest on the assumption that all of the carbon that would usually be stored in a forest is combusted during a fire, but this is far from the reality, in which just a small fraction of a forest’s biomass is consumed. As Hanson says,

In fact, even in the most intensely burned patches where a fire kills all the trees (which in reality, even in the biggest fires, it’s only a small portion, a minor portion of the overall fire)… But even in those areas, only about two or three percent of the above ground biomass is actually consumed, in other words, ends up as carbon. The trees are still standing there [Hanson 2018].

Second, the intensity of fires has not been universally increasing in recent years. We are experiencing a lot of geographically large fires, but these are not necessarily high intensity fires. The percentage of high intensity fire today is similar to historical precedent, and overall, there is much less fire in our landscapes now than in Earth’s geological history. Further, even in the highest intensity fires, forests are never decimated past the point of no return. Trees and vegetation are reestablished after fires, and the ash left behind is dense with nutrients, promoting new growth. Even dead trees, which have long been thought to be responsible for contributing to high intensity fires, are actually not shown to drive fire intensity, according to Hanson.

This series of myths – that forest fires are raging with high intensities, that they burn up so much biomass as to make forests ineffective sources of carbon sequestration, and that the only way to manage forests to avoid these outcomes is to thin out the trees – hinder our understanding of forest management and allow false and harmful solutions to propagate. As a result of these perceptions, proponents of logging have pushed to expand logging operations, purportedly as a fire management strategy. However, according to Hanson, logging is actually linked to greater fire intensity. He explains that small materials, like twigs, are more flammable than trunks.

Tree trunks are not combustible. They really just don’t burn. Again, outer bark can burn, but the trees themselves don’t burn. What logging does is it removes noncombustible material essentially from the forest and leaves behind very combustible kindling, like slash debris – the branches and small twigs and things like that that are not possible to get up off the forest floor after the tree trunks are removed and that’s very combustible.

The other thing that logging does is that it reduces the cooling shade of the forest canopy. By removing a lot of trees, you have more sunlight reaching the forest floor, and what that does is it creates hotter and drier conditions and that means everything on the forest floor gets more dried out, more potentially combustible, and logging also spreads invasive weeds like cheatgrass, which is very, very flammable. Cheatgrass loves a lot of sunlight and so you get a lot of that after intensive logging.

And the last [problem with logging] is a little bit more technical, but basically when you have a lot more trees, it cuts down on the wind speeds that drive fires. It has a buffering effect in a sense. And when a lot of the trees are removed, that buffering effect is reduced or eliminated and fire spreads through those forests faster [Hanson 2018].

This three-fold effect of logging makes forests more vulnerable, and it is important to dispel the concept that removing trees is the best way to keep people safe from fires. Hanson criticizes the opportunism of using these fire myths to advance an agenda of logging. He cautions that when fire science and policy emerge from the U.S. Forest Service, which manages national forests and gains a good deal of revenue from logging, there is a perverse incentive to keep practicing logging as fire management. He calls for clearer and more public communication from scientists to dispel fire myths and share recent findings that have been shifting so much of what we know about fire science.

Hanson says that the best strategy to ensure the protection of homes from wildfire is to focus on the homes themselves. This can be done by using fire resistant building materials, fire-proofing roofs, erecting rain gutter guards to prevent the accumulation of small fuels like pine needles, pruning the vegetation in a 100-foot radius of a house, and removing small shrubs and branches of mature trees, while leaving those trees standing. Fire management interventions at this level are shown to be far more effective at preventing damage than attempts to control the fuel load of fires within forests.

Hanson points out the need to decouple fires that occur in remote forest ecosystems and those that rage through human settlements and urban communities, because thinning out vegetation in attempts to suppress the former do not actually protect against the latter. In fact, thinning forests undermines the ecological processes that fire serves in forest systems. When discussing fires that have devastated homes and lives, he says

I mean, where’s the forest in Malibu? There’s no forest. These are chaparral ecosystems, most of the fires that are burned homes and lives have been lost are not in forest. In fact, they’re mostly nowhere near forests. They’re in grasslands, chaparral shrub habitat, oak woodlands. But the areas that are in forest, where we’ve had tragic loss of homes and lives, these are mostly areas where we’ve had intensive logging, and it’s like I mentioned earlier, you know, more logging is typically associated with more intense fire at a faster rate of spread. [Hanson 2018]

He advocates for a greater focus on fire prevention around homes and communities themselves, in what is known as ‘defensible space.’ He points out that such measures are a great source of jobs, as well as an effective intervention curbing the destructiveness of fires. With a shift in focus from forest thinning to fire-proofing, and better understanding and communication of fire science, we can let go of some of the fire myths that have been dictating policy and failing to meet public needs.

More logging is typically associated with more intense fire at a faster rate of spread [Hanson 2018].

Hanson, Chad, Fire Myths, Podship Earth: November 25, 2018, podcast created and hosted by Jared Blumenfeld,

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 4 Number 2 January 2021