REPORT ON THE INEFFECTIVENESS OF FOREST WILDFIRE MITIGATION MEASURES: INSIGHTS FROM THE 'BOOTLEG FIRE' AND SCIENTIFIC PRINCIPALS
- William Simpson II
- Aug 1
- 6 min read
Updated: Aug 7
By: William E. Simpson II - © 2025 – All Rights Reserved
Executive Summary
This report provides a synthesis based on fundamental scientific principles of fire behavior, particularly the fire triangle (fuel, oxygen, and heat), which governs combustion chemistry and energy release in wildfires. While the original analysis from the Los Padres ForestWatch article on the 2021 Bootleg Fire highlighted failures of mitigation measures like thinning, prescribed fire, and fuel breaks, it and quoted experts inaccurately emphasized weather and climate as primary drivers without acknowledging that only combustible fuels (such as grass, brush, and understory vegetation) provide the material necessary for fire ignition and sustenance. Wind and climate do not supply fuel; they influence fire spread and intensity by affecting oxygen supply, fuel moisture, and ignition conditions, but without sufficient fuel, no fire can occur or release significant heat energy per physics and thermodynamics. Key findings reaffirm mitigation inefficacy in the Bootleg Fire, where treated areas burned rapidly due to inadequate fuel reduction, but stress that true effectiveness requires comprehensive fuel management to prevent accumulation and regrowth. This update incorporates the critical role of natural herbivory by deer, elk, and wild horses in managing fine fuels (1-hour fuels like grass and brush) on a continuous, landscape-scale basis, including in areas inaccessible to human methods. Population declines in these herbivores—such as California's deer dropping from a peak of about 2 million to around 450,000-500,000 over recent decades, and similar reductions in cervids and wild horses in adjacent states—have contributed to fuel buildup and more intense wildfires, as evidenced by scientific studies. Recommendations prioritize targeted fuel reduction near communities, alongside home hardening and efforts to restore herbivore populations, over broad-scale interventions that may inadvertently increase fine fuels.
Introduction: The Bootleg Fire Context and Scientific Corrections
The Bootleg Fire, starting July 6, 2021, in southern Oregon's Fremont-Winema National Forest and merging with the Log Fire on July 19, burned approximately 413,765 acres. The Los Padres ForestWatch analysis documented rapid spread through tens of thousands of acres treated with thinning, prescribed fire, fuel breaks, and other management under projects like the 2012 Black Hills and 2018 East Hills initiatives. Despite these, the fire exhibited extreme behavior, growing to 200,000 acres quickly.
However, the article's attribution of fire drivers primarily to wind, hot-dry conditions, and climate change overlooks core wildfire science. The fire triangle requires fuel (combustible material like vegetation), oxygen (from air), and heat (ignition source) for combustion; without fuel, no chemical reaction releases energy. Wind supplies oxygen and spreads embers but does not create fuel; it accelerates spread by preheating and drying existing fuels. Climate change exacerbates fuel aridity through hotter, drier conditions, lengthening fire seasons and increasing lightning ignitions, but it does not generate fuel—it modifies the flammability of existing vegetation. Statements in the article suggesting fires are driven mainly by weather and climate, not fuels, conflict with evidence that fuel load and continuity are critical for intensity and spread. Dense forests can retain moisture, but excessive understory fuels (grass, brush) enable high-severity burns when ignited.
Broader evidence balances perspectives: While weather modulates behavior, fuel management is essential, as untreated fuel accumulation from fire suppression has heightened risks.
Ineffectiveness of Cited Mitigation Measures
Mitigation strategies aim to reduce fuels but proved ineffective in the Bootleg Fire, where fire spread faster through managed lands (3.4 miles per day) than unmanaged areas (2.1 miles per day), likely due to incomplete fuel removal allowing regrowth and fine fuels to persist. Without eliminating understory grass and brush—the primary combustible materials—treatments fail to prevent combustion energy release.
Key Evidence of Ineffectiveness
Rapid Spread Through Treated Areas: The fire traversed 25,000 acres of treated national forest in the first six days, plus additional logged areas, indicating treatments did not sufficiently reduce fuel loads to halt ignition and spread under available oxygen and heat.
Comparative Spread Rates: Higher rates in managed zones suggest treatments may have opened canopies, increasing wind penetration and fuel drying, thus enhancing spread without addressing core fuels.
Scientific Critiques: Claims that thinning creates hotter conditions are valid if it exposes fuels to drying, but the root issue is persistent understory fuels enabling combustion. Studies confirm fuel accumulation drives severity, with ladder fuels (vertical continuity from ground to canopy) predicting high-intensity burns more than weather alone.
Broader Studies: Meta-analyses show thinning alone reduces severity modestly (28-40%), but without ongoing fuel maintenance, regrowth negates benefits. Fuel-focused views highlight that vegetation type and load dictate spread, with grass-dominated areas enabling rapid fires.
Counterpoints and Partial Effectiveness
Combined treatments (thinning plus prescribed fire) can reduce severity by up to 72% by targeting fuels, but effectiveness diminishes over time and under wind-driven oxygen supply. In Bootleg, some areas showed lower severity, but overall failure underscores incomplete fuel elimination.
Treatment Type Reported Effectiveness in Reducing Severity Limitations/Noted Ineffectiveness Example from Bootleg Fire
Thinning Alone 28-40% reduction by removing some fuels Fails to address understory regrowth; increases drying High-severity (68%) in thinned areas due to persistent grass/brush
Prescribed Fire Alone Up to 62% reduction in accumulated fuels Limited to prior-year fuels; no effect on spring growth Burned through without halting spread, as new fuels ignited
Thinning + Prescribed Fire 72% reduction via fuel load decrease Wanes after 10 years; ineffective if fuels regrow Mitigated locally but fire advanced rapidly overall
Fuel Breaks Variable; interrupts fuel continuity Bypassed by embers; requires maintenance Failed to stop 37-mile drive, as winds spread over breaks
Prescribed Fire: Limitations Due to Winter Timing and Spring Vegetation Growth
Prescribed fires, often in winter, target accumulated dead fuels but cannot prevent spring regrowth of fine fuels (grass, shrubs) that become highly combustible in summer. This regrowth provides fresh fuel for current-year fires, enabling combustion once ignited.
Mechanism of Limitation: Winter burns clear legacy fuels but allow rapid herbaceous regrowth, which dries and fuels fires without intervention. In Bootleg's 40,000 acres of grassland/shrub steppe, grazed and burned areas still burned due to annual fuels.
Evidence from Bootleg and Beyond: Treatments did not abate spread, as spring fuels carried flames; research shows prescribed fire shifts to herbaceous dominance without annual follow-up.
The Role of Natural Herbivory in Fuel Management
In contrast to human mitigation methods, natural herbivory by deer, elk, and wild horses provides an effective, continuous mechanism for managing 1-hour fuels (fine fuels such as grass and brush) to nominal levels across vast landscapes, including remote and inaccessible areas where techniques like mulching or mowing are impractical. These herbivores graze and browse on a 24/7 basis, reducing flammable biomass and interrupting fuel continuity, which can decrease wildfire intensity and spread. For instance, wild horses can consume large volumes of grass and brush, creating natural firebreaks and mitigating soil overheating during fires. Deer and elk similarly target understory vegetation, preferring brushy growth that follows grassland stages.
However, significant population declines in these species have led to unchecked fuel accumulation, exacerbating wildfire risks. In California, deer populations have plummeted from a peak of about 2 million around 1960 to approximately 450,000-500,000 in recent years, with a drop of over 300,000 since 1999 alone. Adjacent states like Oregon and Nevada have seen similar trends in cervids, with Oregon's mule deer declining since a 1981 peak to about 162,600 in 2022, and Nevada experiencing ongoing mule deer reductions due to habitat loss. Wild horse populations in the western U.S. have also faced management-driven reductions, with removals of about 50,000 animals between 2020 and 2023, contributing to overall declines from peaks exceeding 95,000. These reductions, totaling in the realm of hundreds of thousands for cervids and wild horses across regions, have ecological consequences, as outlined in William J. Ripple's 2015 paper "Collapse of the world's largest herbivores," which links herbivore declines to altered vegetation dynamics and increased fire susceptibility. Scientific evidence indicates that without these herbivores, wildfires become more dangerously intense and widespread due to excess fuel buildup.
Conclusion and Recommendations
The Bootleg Fire demonstrates mitigation failures stem from not fully reducing understory fuels essential for combustion, with wind and climate merely influencing conditions rather than providing fuel. Substantiated by the fire triangle and empirical studies, this corrects overemphasis on non-fuel factors. The loss of natural herbivory exacerbates these issues, as declining populations of deer, elk, and wild horses allow fine fuels to accumulate unchecked. Shift investments to fuel reduction near homes, home hardening, and defensible space for effective protection, while addressing climate's role in fuel drying through broader emissions reductions. Additionally, policies should support the restoration of herbivore populations to leverage their natural, cost-effective role in ubiquitous fuel management across diverse landscapes.
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