Wildfires

DEFINITION: Fires that occur in wilderness or open country in various vegetation types, generally characterized by large size, rapid flame spread, intensity of heat and smoke, and difficulty of predicting or controlling their behavior. Also known as forest fires or bush fires.

Throughout history, the definition of "wild" fire has evolved as increasing human control of fire has led to the intensification of the human relationship with, and responsibility for, fire in the environment. These changes in definition are themselves reflective of fire-mediated alteration and modification of the preexisting environment by humans.

For more than 450 million years, all fires on Earth were both “natural” and “wild.” Naturally occurring fires can be ignited in various ways, including lightning strikes, volcanic eruptions, and spontaneous combustion. They tend to be more common in areas such as forests and grasslands with extensive vegetation, which serves as combustible fuel. While wildfires are by nature destructive forces, they also can be ecologically beneficial by returning nutrients from plants to the soil and increasing habitat diversity. Indeed, some ecosystems and organisms evolved to not only cope with but even depend on fire.

Only after early humans learned to control fire—which most researchers suggest began about 1 million years ago—do the concepts of “natural fire” and “wildfire” come into play, to distinguish from the intentional, controlled burning of vegetation. Particularly during the past twenty thousand years, the control (meaning both use and suppression) of fire by humans changed the character of many ecosystems and the human cultures sustained by them, with tremendous consequences. In general, humans have sought to prevent and mitigate wildfires due to their significant potential threat to life and property. Yet ironically, human activity—including controlled uses of fire such as slash-and-burn agriculture as well as broader trends leading to climate change—has led to increases in the number, intensity, and duration of wildfire events in the twenty-first century. For instance, in 2024, the New York Times reported on a study that found the occurrence of extreme wildfires had doubled between 2003 and 2023. The researchers attributed the increase to global warming and climate change. As a result, perspectives on wildfires and how to manage them have also evolved.

Use and Suppression of Fire

Although wildfires occur on every continent except Antarctica, the consequences of the use and the suppression of fire are best seen in four regions: Amazonia, equatorial Africa, Australia, and western North America. An understanding of the dynamics of use and suppression in regard to wildfire requires expansion of the traditional “fire triangle”—consisting of ignition source, combustible material, and oxygen—into a “wildfire hexagon” through the addition of three more key factors: topography (the “shape” of the landscape), climate or weather (particularly in regard to the effects of drought on fuel moisture and strong winds on fire behavior), and human interaction (both in shorter-term responses to individual fire events and in longer-term transformation of fire-prone environments).

Weather, topography, and the presence of atmospheric oxygen are not easily altered on large scales within short time frames, so only three elements of the wildfire hexagon—ignition source, combustible material, and human interaction—can be readily affected by short-term human activity. Fire has long been a tool useful in clearing the land for subsequent agricultural production. People around the world continued to practice slash-and-burn agriculture, especially in developing countries. Yet fire has also been widely perceived as a threat to valuable timber, homes, and other property. Therefore, in many areas people intervene to suppress natural fire cycles by reducing ignition sources and combustible materials where possible or, once a fire has been ignited, attempting to reduce the combustibility or availability of fuels through firefighting activities.

Problems with these strategies of use and suppression arise when the use becomes too careless or the suppression too careful. Fire that is used to clear land in Amazonia and equatorial Africa often ends up making its way into surrounding rainforest, where it becomes wildfire. Decades of too-careful fire suppression in western North America and Australia resulted in thickety forests so overburdened with ladder fuels—leading from flashy fuels such as grass and duff along the ground through a middle level of shrubs and younger trees and then, finally, to the topmost canopy of mature trees—that once a fire got started in such a forest, it was much more prone to become a catastrophically destructive burn. Although “natural” and “controlled” are usually seen as opposites, human control of fire in both the use and the suppression situations outlined above has separated “natural” from “wild” such that the resulting wildfires are both uncontrolled and unnatural.

Patchwork use of broadcast burning in wildland—by hunters to stampede game, by pastoralists to open up grazing lands, and by agriculturalists to prepare land for planting—originated many tens of thousands of years ago. Systematic, widespread suppression of fire in US wildland arguably began only in response to the Great Fire of 1910, which burned approximately three million acres in the northwestern United States. With the continued unprecedented growth in human population over the past three centuries, however, the increasing number of wildfires stemming from both fire use and fire suppression has resulted in many negative effects on the environment, from the physical (increased erosion, landslides, mudflows, flash flooding, and altered water quality) to the biological (loss of species habitat, introduction of invasive species, and decreased biodiversity).

Increases in population and demographic changes have meant that more and more land that was formerly wild has become increasingly bordered and penetrated by housing tracts along the wildland-urban interface, or intermix (WUI). The upshot has been still more property at risk, with consequent pressures to suppress fire more thoroughly in naturally fire-prone but increasingly populated and economically valuable areas—with the result that more fuels build up year upon year until, when ignition finally comes, the result is too often a devastating wildfire.

Wildfires affect not only physical, biological, and economic aspects of landscapes and watersheds but also the atmosphere. Smoke, soot, ash, ozone, greenhouse gases (such as carbon dioxide), and other fire by-products are lofted by wildfire not only throughout the troposphere (the lowest layer of the atmosphere) but also as high as the lower stratosphere, where their influence on climate and human health can be global. In addition, the smoke from wildfires have shown to have both short-term and long-term effects on health. Short-term effects include issues with the respiratory system—like coughing, difficulty breathing, and increased risk of asthma exacerbation—and the cardiovascular system—like heart failure and stroke. Long-term effects include increased risk of respiratory disease, cardiovascular disease, and certain cancers, among other physical and mental health issues.

Striking a New Balance

Growing awareness that too-careless use and too-careful suppression of fire in wildlands have both led to increases in the number, duration, and intensity of wildfires—with cascading local, regional, and global ecological and economic effects—has led fire experts to reevaluate approaches to wildfires. This reevaluation is based on an increasingly nuanced ecological understanding of the roles of natural fire, fire cycles, weather patterns, and fire-dependent, fire-tolerant, and fire-intolerant plant adaptations.

The recognition that many natural landscapes contain plants that are fire-dependent or fire-tolerant, not only in western North American and Australian wildlands but also in Southeast Asia and southern Africa, has called into question policies of too-careful or complete fire suppression, particularly when such policies have resulted in the increased presence of both flashy, fire-intolerant vegetation and higher fuel loads generally. Because lower-intensity fires can reduce fuel loads and reduce or eliminate often invasive fire-intolerant vegetation, fire has been selectively allowed back into these wildlands. Fires that have been naturally caused—most often by lightning, but also at times by volcanic eruptions or meteor strikes—are allowed to burn so that they can fulfill their ecological role, while being carefully monitored against escape to higher-value locations.

Controlled burning (also referred to as prescribed burning) is a fire-management strategy in which wildland fires are purposely ignited under favorable weather conditions, with the goal of creating lower-intensity fires that help clean out accumulated fuels, foster higher levels of species diversity, and reduce the future risks of intense, long-lived wildfires. The goal of such “allowed fire” strategies is to emulate natural fire through the use of controlled fire of the right type, in the right place, and at the right time.

Just as too-careful fire suppression has had to give way to some controlled use of fire in an attempt to emulate natural fire, so too has too-careless fire use had to be curbed through prevention of ignition, again in an attempt to emulate natural fire. Because slash-and-burn agricultural practices damage fire-resistant rain forests and encourage the growth of flammable brush (and, as a result, the more frequent occurrence of future wildfires), those wishing to curtail careless fire use in rain-forest areas—whether neighboring landowners with flammable tree crops and orchards or environmentalists wishing to preserve rain-forest species diversity—have had to exert pressure on slash-and-burn agriculturalists to be more circumspect in igniting, more careful in monitoring, and more thorough in suppressing fires lit to clear land.

Because human interaction can change both the fuel and the ignition factors in the wildfire hexagon, the fastest and most powerful way to affect the risk of future wildfire is to change the way humans interact with their environments. Those who in the past suppressed fire in order to further their interests now find they must at times incorporate fire use in their approach, and those who in the past used fire to further their own interests now find they must also at times incorporate fire suppression.

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