Thinning won’t protect forests from wildfire

Thinning won’t protect forests from wildfire

05 November 2015

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USA–   One of the assumptions behind federal legislation like the Resilient Federal Forest Act supported by Congressman Zinke is that more thinning of our forests will halt or significantly reduce large wildfires. Yet the scientific evidence for such a conclusion is ambiguous at best.

Any number of studies have found that thinning usually fails under severe fire conditions.

A large percentage of fires in the Rockies are burning through forests of lodgepole pine, subalpine fir, Douglas fir and other forest types that tend to burn at long rotations of 50-500 years or more.

Large fires are the norm in these forest types, not a consequence of “fire suppression” as falsely asserted. These forest types, when they burn, commonly burn as “mixed severity” to “high severity” fires.

However, most fuel reductions have limited value under mixed to high severity fire conditions.

Even if they did work to some degree under high severity fire weather conditions — an unproven assumption — the chances that a fire will encounter a fuel reduction during the time when it is effective is very small. Because of the naturally long fire rotations in these forest types, most fuel reductions will simply grow back into forest before any fire touches them.

Under severe fire conditions which includes low humidity, high temps, drought, and high winds you usually cannot stop a blaze. If you have those ingredients, very few thinned fuel reductions work. According to a number of review studies as well as lots of anecdotal evidence, most of these fuel reductions fail — again under severe fire weather conditions.

Why is that important? Nearly all of the acreage burned annually is the result of a few large fires burning under severe weather/climate conditions. So even if fuel reductions were effective — a questionable assumption — they do little to halt the very large fires that pose the greatest threat to homes and communities.

When the wind blows, burning embers land miles in front of a fire front, starting new spot fires. The wind also fans flames to greater rates of burn (heat release). That is why fires regularly burn through clearcuts, jump across 16 lane freeways and other situations where there is virtually no fuels.

So here’s a few quotes from various studies that come to similar conclusions:

“Fuel treatments … cannot realistically be expected to eliminate large area burned in severe fire weather years,” from “Atmospheric, climatic and ecological controls on extreme wildfire years in the northwestern United States”by Ze’ev Gedalof, David L. Peterson, and Nathan J. Mantua.

“Extreme environmental conditions … overwhelmed most fuel treatment effects. … This included almost all treatment methods including prescribed burning and thinning. … Suppression efforts had little benefit from fuel modifications,” from “Objectives and considerations for wildland fuel treatment in forested ecosystems of the interior western United States,” by Elizabeth D. Reinhardt, Robert E. Keane, David E. Calkin, Jack D. Cohen at the Rocky Mountain Research Station, Fire Science Laboratory in Missoula.

“Although there are many examples of fuel treatments reducing fire behavior when conditions are not extreme, recently treated forests can experience a stand-replacing crown fire when wind speeds exceed 30 km h and when fuel moisture is low. When the probability of fire occurring in a particular area is relatively low, the odds of a fuel treatment influencing the behavior of a wildfire there, within the time frame that treatments are effective, is also low,” from the article “Learning to coexist with wildfire” published in the journal Nature in 2014.

Finally Jack Cohen at the Missoula Fire Lab concludes: “Wildland fuel reduction may be inefficient and ineffective for reducing home losses, for extensive wildland fuel reduction on public lands does not effectively reduce home ignitability on private lands.”

The one thing that almost all researchers agree upon is that if you want to protect structures, start with the home ignition zone around the houses and work outward. Second, stop building homes in the woods.

I might also emphasize that even if we could stop these large fires, we should not as they are critical to healthy forest ecosystems. Dead trees are very important as biological legacy and large wildfires are the primary means of input into forest ecosystems.

We need large fires to create important snag and down wood habitat critical for healthy forest function.

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