Forest fuel treatments and wildfire risk

by The Forest Advocate       Aug 6, 2020

Does thinning and burning our forests reduce wildfire risk?

The answer depends on where fuel treatments such as thinning and burning are done, and a thorough cost/benefit analysis is required.

It has been demonstrated through research by multiple scientists, including now retired US Forest Service scientist Jack Cohen, that fuel treatments out in the forest do not protect structures and communities from fire. It is very important to fire-proof the 100-200 foot radius around homes and structures, and that includes selective thinning of trees and removing flammable debris from the ground. Also structures themselves must be fire-hardened, meaning no shake roofs or wooden decks, and vents and the areas under porches must be screened so embers cannot encroach on the structure.

La Cueva Block A, 2019. Photo: Lyra Barron.

Any fuel treatments outside of the 100-200 foot radius of homes do not keep homes safer from fire.

It is also important that the area adjacent to egresses from forest communities be kept reasonably clear, so residents can escape if a fire occurs.

So what about fuel treatments in the forest away from structures and infrastructure? Do such treatments keep anyone safer from fire, or does it keep the forest itself safer from fire? That is where the serious cost/benefit analysis is needed. Forest and fire ecology science indicates that in some situations, especially when fire is of low or medium intensity, there is a window of around a decade in which fuel treatments out in the forest can slow the spread of fire.

However, research also shows that the probability that any particular fuel treatment will actually moderate a fire before vegetation starts to substantially return is extremely low, typically about 1% per year.

Fuel treatments have been shown to do little good during the very high intensity fires that occur during hot, dry and windy weather. Embers can fly for miles and spread fires during “fire weather.” Also, in some cases the openness resulting from removing the majority of trees from large areas of forest can allow the wind to blow more freely and actually cause a fire to burn hotter. Additionally, thinned and open forests tend to be drier and possibly more flammable.

In 2016, three forest and fire ecology researchers, Bradley, Hanson and DellaSala, did a large scale study of forests across the West, including our dry southwestern forests. They found that forests that were not logged and did not receive fuel treatments burned less often and less severely than forests that were were logged and/or did receive fuel treatments. This study indicates that overall fuel treatments were not beneficial for reducing the amount and intensity of fire out in forests.

Forest fuel treatments cause much ecological damage such as disruption of wildlife habitat, erosion, soil compaction, and damage to the trees that are left standing, including risk of bark beetle attack. Because thinned areas are subsequently treated with prescribed fire at regular intervals, the understory is not allowed to substantially return. This leaves forest that is barren, dried out and ecologically dysfunctional. This has to be a part of the cost/benefit analysis, along with the health effects of frequent prescribed burn smoke on the public.

Our forests have evolved through fire, and fire of all intensities are a natural part of forest ecology. Fire promotes ecological diversity and helps forests to renew themselves. This includes even high intensity fire, although clearly no one wants high intensity fire to occur anywhere near communities, or to be very widespread.

La Cueva Block A, 2018. Photo: Lyra Barron

Whether areas of forest should receive fuel treatments or not should be a site-specific determination. This requires a multi-faceted analysis, and likely the amount of forest landscape where it would be beneficial to do fuel treatments in the cost/benefit analysis will be very small. But we won’t know until the analysis has been done, which includes utilizing a broad range of scientific research. This has not been done for the Santa Fe National Forest. Full analysis, and an environmental impact statement, is essential for large-scale fuel treatment projects in order to do this comprehensive and site-specific cost/benefit analysis.

Please read an excellent overview of the issue of fuel treatments and wildfire risk by ecologist George Wuerthner.

The Forest Advocate
Santa Fe, New Mexico