Forest Fuel Reduction

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Published: Dec 26, 2021

Author: C. Michael Hogan

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Forest fuel reduction is a key strategy for lessening risk of severe wildfires. The concept has only become discussed increasingly n the last two decades, with the expanding human population, and more people residing in the Wilderness Urban Interface (WUI). The basic techniques of fuel reduction are: (1) removal of dead wood and slash; (2) thinning of tree density; (3) increasing distance from ground surface to bottom of tree crowns; (4) use of prescribed burns; and (5) creating overt fire breaks. It is important to note that current frequency and intensity of wildfires is similar to historic records, (Pyne, 1910)(Show &Koto, 1929)(Swetnam & Baisan, C.H., 1996) and through proxy studies not dissimilar to patterns of millennia ago.

Need for Forest Fuel Reduction

Although frequency of wildfires has not actually increased in modern times, there is a greater need for prevention due to a much larger human population residing in the Wildland Urban Interface. The matter is exacerbated by increasingly aggressive fire suppression. Although well intentioned, this fire suppression has created vast expanses of forest in North America and Europe, which forests have high accumulations of dead wood, which would have otherwise been reduced by natural cycles of forest wildfires. (Agee & Skinner, 2005} In addition, governmental policies have often been driven by well-meaning concepts of preserving all trees. While this sounded like a noble "environmental" goal in the 1960s, it turned out to run counter to long term forest management (Weatherspoon & Skinner, 1996) and to prevention of large-scale wildfires.

Removal of Dead Wood and Slash

The simplest form of forest fuel reduction is simply the collection of dead wood on the forest floor or pruning of dead branches. Analysis by transect methods shows that in many western USA forests, this fuel load represents a large proportion of excess forest fuel. This task is particularly easy to address, since many of the forests contain highly combustible and nonnative trees such as the Douglas Fir invasions of oak woodlands in California.

Thinning of Tree Density

This strategy is similar to selective tree harvesting. A major method of reducing wildfire spread is to decrease tree density in a forest. This not only reduces fire fuel, but also impedes spead of wildfire via crown to crown transmission. The strategy is particularly important when numerous small trees are present; such density of small trees will actually limit the viability of the forest to achieve full heights of mature trees, due to light and nutrient starvation. (Skinner et al, 2004)

Decreasing Torching

When flames from grass or shrub understory leap upward to tree canopies, the phenomenon is termed "torching" or "laddering". Mitigation of this type of wildfire spread is achieved by trimming or removing high understory grasses and shrubs, (Rothermel, 1991) and also by pruning lower branches of the tree canopy, particularly dead branches. (Agee and Skinner, 2005) These measures will mitigate the rapid spread of crown fires, where considerable fuel ignites and propagates from one tree canopy to another. (Van Wagner, 1977)

Prescribed Burns

Intentionally setting controlled burns is an efficient technique to reduce risk of substantial wildfires. (Pollet & Omi, 2002). This method can be used to create an expansive fire break, a backburn or merely to reduce the amount of active fire fuel, especially where massive amounts of dead wood are present in a forest. (Agee & Skinner, 2005) It is important to conduct these burns in seasons of lowest risk for wildfire spread and air quality concerns, and with ample advice to nearby residents.

Geographic and Governmental Factors

The risks of wildfires have been compounded by the alarming rate of arson wildfires and homeless forest encampment wildfires beginning in the early 21st century; moreover, some states such as California have encouraged serial arsonists by reducing penalties for arsonists and reducing bail for such offenders. A staggering forty percent of acres burned in the USA in recent years are in California, as well as all of the top ten costliest wildfires in US history. Two of the largest USA wildfires of the 2020-2021 years were the Caldor and Dolan Fires, (Wright, 2020) both in California and both set by arsonists. A series of seven wildfires were set in Mendocino County by a serial arsonist. Acreage in many of these major California wildfires had been identified as lands in need of forest fuel reduction, but the State of California failed to commit funds and programs to reduce such fuels. California incurs added risks by its widespread use of sanctuary city policies, where non-citizens can avoid detention for federal level felonies such as arson and homicide from arson.


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C. Michael Hogan (2021) Forest Fuel Reduction. Encyclopedia of Earth. National Council for Science and Environment. Washington DC.