Avoiding Crown Fires
Fuels reduction thinning can help
BY GREG NAGLE, DAVE PERRY, RICH FAIRBANKS
We have serious disagreements with the Viewpoint (11/1) by Tim Hermach on fire ecology and fuels reduction with thinning. We recognize that protection of old-growth forests is necessary, since enough old growth has been clearcut — too much, in fact. Given the fact that logging reduced Oregon’s old forests by approximately 80 percent over the 20th century, people are justifiably skeptical about yet more logging in these forests.
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| An untouched pine forest (above) and a thinned and treated pine forest (below) |
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However we also fear that we may lose much of our remaining old growth to fires, especially in the mid- and low-elevation ponderosa pine zone of Eastern Oregon. With early high-grade logging and many decades in which wildfires were suppressed, forest canopies and fuel loads have changed drastically in those low- and mixed-severity fire regime areas, even in wilderness areas that have had no cutting.
In the most extreme weather conditions, little will change fire behavior, and it is likely futile to attempt large-scale fuels treatments in moister coastal and high elevation “stand replacement fire regimes” where very infrequent natural fires tend to burn everything. However, in Oregon’s drier forests with historically mixed- and low-severity regimes, fuels treatments and thinning can have a significant impact on fire behavior.
It doesn’t follow that thinning and fuels treatments guarantee a crown fire will be stopped; under severe weather conditions, almost anything will burn. The objective of such treatments is to lower the probability that a surface fire will turn into a crown fire; in other words, they are a form of insurance. There are other values at stake — water, soils, habitat — and the challenge is to reduce fire risk without compromising these.
In his column, Hermach said, “In fact, recent science demonstrates that forests that were thinned before a wildfire, including the Biscuit Fire, ended up with more dead trees than the forests that were left to nature. Not surprisingly, many of the forests around Lake Tahoe had already been ‘thinned,’ some of them up to six months before the fire, which — at best — did next to nothing to prevent the fire, and — at worst — intensified the blaze.”
The published scientific study on the Biscuit thinning Hermach talks about actually said this: “The thinned and underburned treatment was burned in fall 2001 (one year before the Biscuit Fire). The Biscuit Fire burned all around it, but stopped at the edge of the treatment.”
In fact, thinning and slash treatment have been successful in reducing severe fire in eastern Washington, Arizona, New Mexico, Tahoe, the Biscuit Fire and parts of northern California. Studies show that when the slash from thinning is treated by burning or crushing into small pieces, fires stay mostly on the ground with canopy fire reduced considerably, but without such slash treatment, fires can indeed burn hotter. Thinning opponents have sometimes singled out areas without treated slash to support their case. For example, ignoring the full range of treatment effects at Tahoe, one of Hermach’s colleagues widely distributed pictures of the one treatment area that had not had thinning slash treated, and consequently burned severely, using it to argue that thinning didn’t work.
Tahoe illustrates some of the complexities and the dangers of drawing conclusions without all the facts. There, heavy thinning treatments were less effective on very steep slopes because fire is more easily carried from the ground into canopies. In some forests, treating thinning slash alone may not be sufficient; we might also need prescribed burns to reduce small surface fuels.
Even when we disagree, we respect opponents who present evidence soberly and accurately, but we cringe when scientific literature is ignored or misrepresented. We are not contending that thinning in all locations is advised, helpful or even economical, but Hermach and others have blatantly misrepresented studies of wildfire behavior in stands thinned for fuels treatments. Whether due to sloppiness or purposeful cherry-picking to support a point of view, such distortions do a disservice to those trying to understand how to best protect our forests and rural communities.
Greg Nagle has a Ph.D. in forest science, learned field forestry as a former president of Hoedads Cooperative and works as a teacher and research scientist at Cornell University. Dave Perry is OSU professor emeritus of ecosystem studies and ecosystem management. Rich Fairbanks is the California/Nevada forest and fire program associate for The Wilderness Society.
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