Fuel Reduction and Forest Restoration Treatments: Once Is Not Enough

PNW Pacific Northwest Research Station I NSIDE Fire and Fire Surrogates ..................................... 2 Restoring the Blue Mountains ............................. 3 A First Step Toward Forest Restoration ............ 4 One Step at a Time ................................................ 5 FINDINGS issue one hundred six / september 2008 “Science affects the way we think together.” Lewis Thomas FUEL REDUCTION AND FOREST RESTORATION TREATMENTS: ONCE IS NOT ENOUGH IN S UMMA R Y Frequent, low-intensity fires were historically a common feature in many dry forests of the United States. Today, largely owing to Andrew Youngblood fire exclusion and past management practices, many of these fire-dependent forests contain significantly more small trees and fewer large trees than occurred under the natural fire regime. These altered conditions increase the probability of unnaturally severe wildfires, sus- ceptibility to uncharacteristic insect outbreaks, and drought-related mortality. Restoration of these forests is a priority for forest managers throughout the country. Unfortunately, little information exists about the effectiveness or ecological consequences of commonly used fuel reduction and forest restoration strategies. In response, a national research project called Although they are the most difficult and expensive to implement, restoration treatments that use the Fire and Fire Surrogates Study is conduct- both thinning and burning move forest stands closest to the restoration goals of the Fire and Fire ing operational-scale experiments to evaluate Surrogates study. restoration treatments at 13 sites across the country. “Keep in mind that fire is a ecosystems. Indeed, wildfire may be the As part of this study, researchers working in natural part of the environ- single most important agent of change in forests worldwide. It’s just that the dry, low-elevation forests in northeastern Ore- ment, about as important as character of wildfire is changing. gon evaluated several fuel reduction and forest rain and sunshine… fire has restoration treatments: a commercial thin, a always been here and every- Historically, fire burned through forests prescribed burn, and a combination of the two. in drier climates quite frequently—every Thinning and the combination of thinning and thing good has evolved with it.” couple of decades or less. These are the burning reduced the density of live overstory —Harold Biswell so-called fire-dependent forests. Because trees, and burning and the combination of thin- woody vegetation never had much time to eports of “catastrophic wildfires ning and burning reduced the density of small- accumulate between burns, fires were not raging through tinder-dry forests” diameter trees. Overall, the treatments failed very intense and typically remained on the seem to take up a larger portion to completely meet the objective of restoring R surface, only occasionally torching into stands to historical conditions, yet each treat- of the evening news with each passing tree canopies. The product of repeated, summer. And although it is true, there ment successfully modified stand density, likely low-severity fire was forests of large, is a trend toward larger and more severe reducing the risk of high-severity fire. The widely spaced trees. Open canopies allowed wildfires, it is also true that fire has been results suggest that repeated treatment over ample sunlight to reach the forest floor, a ubiquitous component of many forest time will be necessary to mitigate the impact where grasses and low shrubs dominated of a century of fire suppression. the understory. K E Y FINDIN G S Kerry Metlen • Thinning and the combination of thinning and burning reduced the density of live overstory trees, whereas burning and the combination of thinning and burning reduced the density of small-diameter trees. • No treatment fully met the restoration goals; the combined thin and burn was the only treatment that reduced tree density below the threshold where serious mortality from bark beetles might be expected. • No single application of prescribed burn or thinning treatments fully restored ecosystem structure and function within the dry forests of this study that had Fire suppression and past logging practices have been removed from their natural fire regime over the past century. resulted in unnaturally high tree densities, which has increased the probability of severe wildfires, insect outbreaks, and drought-related mortality. “Collectively, these altered conditions “There is no single right treatment,” says may contribute to increased probability of Youngblood. “While historical information Today, largely owing to a century of fire sup- unnaturally severe wildfires, susceptibil- offers insight into one resilient forest condi- pression and past logging practices, many ity to uncharacteristic insect outbreaks, and tion, there may be other equally resilient fire-dependent forests are shadows of their drought-related mortality,” explains Andy targets that managers may choose, particu- former selves. Large trees typically remain, Youngblood, research forester at the PNW larly given the fact that the future climate but they are inundated by young trees and Research Station in La Grande, Oregon. may not resemble the past.” woody shrubs that have established in the “There is broad agreement that some form absence of fire. These small trees create a Youngblood recently completed the first of restoration is needed to move stands from continuous ladder of woody vegetation from phase of a long-term experiment in the their current structure and developmental the ground to the treetops and dramatically Blue Mountains of northeastern Oregon. trajectory to conditions that more closely increase competition for water, nutrients, and He made a side-by-side comparison of incorporate historical fire regimes that light. In many cases throughout the West, the several approaches to forest restoration existed before Euro-American influences.” absence of fire in dry forests has led to a shift in dry ponderosa pine- and Douglas-fir- in tree species from fire-resistant ponderosa Although it may be clear that something must dominated forests. pine and Douglas-fir to grand fir and other be done, exactly what the best path to restora- species intolerant of fire. tion looks like remains an open question. Fire and Fire Surrogates ottom line: dry forest restoration entirely, which can have ecological benefits,” structure, but it is fundamentally different means lowering the density of trees. he says. “The downside to using fire as a from fire and may produce different eco- B Certainly there are other important restoration tool is that it lacks precision. logical responses.” components, but if dry forests are to be resil- Once we ignite a treatment unit, it’s impos- ient to future fire and other stressors, there sible to know which trees will be killed and must be fewer trees. Ideally, only the largest how well we’ll meet our density targets. Purpose of PNW Science Findings trees will remain. The obvious question, then, Prescribed fire also has the big drawback of To provide scientific information to people is how best to remove the small trees: fire, producing smoke. There are huge social and who make and influence decisions about chain saw, or some combination of the two? legal constraints associated with producing managing land. smoke and reducing air quality, which Fire is the oldest tool in the forester’s tool- impedes the widespread use of burning.” PNW Science Findings is published box. Long before there were chain saws, long monthly by: before there were axes even, fire was used to Mechanical thinning is the other common Pacific Northwest Research Station manage forests. And today, prescribed fire approach to fuel reduction and forest restora- USDA Forest Service remains a popular and effective way to elimi- tion. “From a managerial perspective, thin- P.O. Box 3890 nate low vegetation under a controlled setting. ning is easy to design, and there is a high Portland, Oregon 97208 degree of precision regarding what is retained According to Youngblood, there are several and what is removed. Thinning also can pro- Send new subscriptions and change advantages to using fire. “Fire is a natural duce some revenue, which can offset some of of address information to process in these systems. It stimulates the costs of restoration,” says Youngblood. [email protected] plant species that are adapted to fire, while “However, timber sales often become com- eliminating those that are not. Prescribed fire Rhonda Mazza, editor plicated and time-consuming on federal land. also creates a diversity of conditions, burning [email protected] Also, when used as a surrogate for fire, thin- hotter in some areas while missing others ning may achieve some of the desired stand Keith Routman, layout [email protected] Science Findings is online at: http://www.fs.fed.us/pnw/ United States Forest The site includes Science Update—scientific knowledge for pressing decisions Department Service of Agriculture about controversial natural resource and environmental issues. 2 “We have a wealth of knowledge about under- The FFS Study is a network of 13 sites “We measured the same variables with the burning, thinning, and other silvicultural spanning central Florida to the Pacific same protocols across the whole network. treatments. We’ve been doing these things for Northwest. At each site, the same commonly We calculated small-mammal abundance; years,” he says. “But there is little informa-

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