Fires are Dynamic and Many Things Influence Fire Behavior
There have been plenty of frustrating headlines that attribute one thing for this year’s fire behavior. Predictably, the main culprit changes by the story. In some, fuel accumulation from a lack of logging is to blame. In others, the history of colonization that has removed traditional cultural burning is at fault. The truth is that there are many, many variables that influence fire behavior. We humans have better control over some (like whether homes are to be constructed out of fire-resistant materials than others (like the weather). Be careful of oversimplification!
Wildfire is a More Accurate Term than Forest Fire
Did you know that more than half of all of the acreage that burned so far this summer in California was not in forested ecosystems? Grasslands, chaparral and other ecosystem types make up the majority of lands burned. Even in a “National Forest,” many times the lands that burned are not forested, such as the fire that burned through grasslands of the Mendocino National Forest, helping to keep these prairies free from conifer encroachment.
Fire is as natural as rain for most of California’s forests, and as such, trees and ecosystems have adapted to this challenge. Some trees attempt to withstand the flames by developing thick, fire-resilient bark; others, like Lodgepole pines, have serotinous cones that require fire to open and release their seeds. Even the coastal redwoods (Sequoia sempervirens), endemic to California’s dank, moist temperate rainforests of the North Coast, are adapted to fire. Walk through an old-growth redwood forest and you’ll notice the evidence: burn scars, bearing witness to historic burns either deliberately set by humans or naturally caused. That the redwoods of Big Basin Redwoods State Park survived the fire is no surprise. They have likely been through worse.
And while forests are born to burn, in many circumstances, the forests help to temper fire conditions. The shade provided by a forest helps to cool an area and keep in moisture and retards the development of more flammable brush in the undergrowth. The trees themselves, while part fuel are also part water. That’s why even in a “megafire,” most of the time, fires tend to burn at lower severity, meaning that the trees will survive but much of the undergrowth will be removed.
But death too is a natural event, part of the cycle of life: death, decomposition, and renewal. In their death, fire-killed trees give life to others. Fire-killed trees are an important habitat component–just ask a black-backed woodpecker, a burnt forest specialist–and provide important structure to regrowing young forests.
While forests are born to burn, we have settled the landscape in ways that mean that normal burn behavior can put lives and structures at risk.
Mismanagement of Forests Affects Fire Risk
Understanding the historic and ongoing mismanagement of California’s forests is necessary to understand, in part, what is happening. Although California’s forests are born to burn, for many decades (and still to this day), we have aggressively attempted to put out every fire as soon as possible. As a result, some forests may have conditions that make high-severity fire more likely to occur: ladder fuels, dense thickets, and a pile up of undecomposed “fuel” on the forest floor. Unfortunately, the mismanagement continues. CALFIRE, and to a lesser extent the U.S. Forest Service, still prioritizes extinguishing fires instead of letting them (safely) burn. Aggressive efforts to put out fires, even when they pose little to no risk to humans, while maybe a balm to calm the nerves of a frightened public, often produces greater environmental impacts than doing nothing and furthers our fire deficit.
Similarly, we have deliberately managed forests for timber production, producing plantations more similar to midwest corn than a forest: a monoculture of densely packed trees with a uniform and unbroken canopy. If a fire is to reach a plantation, the odds are that it will burn hotter and faster than a more naturally occurring adjacent “reference” stand.
“Mega-Fires” are Weather Driven Events
While there are many factors that influence the severity of a wildfire, weather, beyond anything else, is the prime driver of large and intense fires. As a general rule, with low humidity and high winds, fire tends to burn hot and fast. The recent fires are examples of this behavior. High-winds and dry conditions whipped up the fires and caused their fast expansion. We have also seen the limits that fuels reduction efforts, such as prescribed burning and forest thinning, when fire conditions are right. Climate change also influences fire behavior both by creating drier, hotter forests and through producing more extreme weather.
Preparing for the Next Fire: What Strategies Should We Prioritize?
To briefly reiterate: fire is a natural occurrence and healthy for California forests, although it can be undesirable because of impacts to humans and property; the hottest, fastest moving and most destructive (to humans) fires are primarily weather-driven events (and humans can’t control the weather); historic mismanagement of forests and climate change have further contributed to fire effects. So what is there to do? (Especially in a world of limited funding.)
Land use plans should discourage or prohibit new development in the wildland urban interface. Just like how it is a bad idea to build housing in a floodplain in an area that receives frequent floods or hurricanes, it is likewise a bad idea to build residences and other structures in high-fire areas divorced from larger settlements. (In some areas likely to be inundated from climate change or susceptible to flooding, “managed retreat” is already being pursued.)
Where development has occurred, we need to “harden” structures. Most houses burn because of wind-blown embers, not from a moving fire. Choice of ignition resistant building materials, such as composite or metal roofing, screening of vents to prevent embers from entering the house, and an adequate water supply and infrastructure to reach all areas of your property, are the most effective way to guarantee that a structure will survive a fire.
After investing in structure hardening, spatially-limited “fuels reduction” can be useful to influence fire behavior. But as a warning: it is expensive, impactful, requires repeat treatment, and does not wholly remove the possibility of fire. (As an example, around 21% of the Hennessey Fire burned just in 2018.) That’s why fuels reduction work should be prioritized only around communities.
It is inherently costly, people and machines in the woods, chopping and grinding vegetation. It also requires repeat treatment because, obviously, plants regrow–and depending on the circumstance, fuel reduction without repeat treatments can make more aggressive fuel conditions. These “treatments” often result in significant impacts, including the taking of endangered species (who are among the supposed beneficiaries of this work).
The desire to “do something” about fire often results in bad decisions, wasted money, and degraded ecosystems. What doesn’t work is landscape-level “fuel management” to reduce vegetation to influence fire behavior. Fuel management does have a role, though. Around communities, targeted projects can influence fire intensity, allowing more time for defense or evacuation. Outside of limited work around communities, fuel reduction cannot be broadly pursued without significant cost to taxpayers and our ecosystems.