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Fire Chronicle #20
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Laura McCarthy, Forest Trust
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Jun 30, 2003 11:30 PDT
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FIRE CHRONICLE: Stories of the National Fire Plan
Number 20
June 30, 2003
NEW REPORT EVALUATES EFFICACY OF FUEL REDUCTION TREATMENTS
The hypothesis that fuel reduction treatments will lessen the size and
severity of wildfires is a central premise of the National Fire Plan.
The hypothesis is based on the assumption that reversing the
well-documented 20th-century buildup of forest fuels will restore
less-hazardous pre-settlement fire regimes. This increase in fuel –-
brought about by more than a century of logging, intensive livestock
grazing, and comprehensive fire suppression -- is estimated by the
Forest Service to have put 39 million acres of western forests at high
risk of catastrophic fire. The National Fire Plan addresses this problem
with a program of vegetation treatments, collectively called hazardous
fuel reduction. The administration and many Congressional leaders are
currently trying to expedite the fuel reduction program through the
President’s Healthy Forests Initiative.
A new study by the Southwest Community Forestry Research Center of the
Forest Trust examined the evidence for the hypothesis that fuel
reduction treatments change wildfire behavior. The authors, Henry Carey
and Martha Schumann, reviewed more than 250 of the most current
scientific studies about fire behavior, fire effects, and forest
structure. The primary findings of the study, “Modifying Wildfire
Behavior: The Effectiveness of Fuel Reduction Treatments,” are as
follows:
-- The scientific literature is, in general, inconclusive with respect
to the effectiveness of mechanical thinning in changing wildfire
behavior; study methods and research results vary greatly, and only one
quantitative empirical study has been completed.
-- Many studies clearly demonstrate the effectiveness of prescribed
burning in changing post-treatment wildfire behavior.
-- The limited number of studies that investigated the effectiveness of
thinning and prescribed burning in combination produced equivocal
results; more research is needed before firm conclusions can be reached.
-- There is no published scientific research on the positive effects of
commercial logging on post-treatment fire behavior.
-- A significant investment is needed in primary and applied research to
provide a credible scientific basis for the design, implementation, and
evaluation of alternative treatment methods.
One of the study’s key findings is that research on the effectiveness of
fuel treatments has employed a wide variety of methodologies, making it
difficult to compare study results. The four kinds of studies that Carey
and Schumann found in the literature were qualitative observations, case
studies, simulation models, and quantitative empirical studies. The
empirical studies generated the most rigorous data and provided the
strongest basis for evaluating treatments. The case studies investigated
the effects of fuel treatments at a single site, but lacked an
experimental design and were not replicable. The studies using models
simulated climate, fuel load, and forest structure variables to predict
fire behavior under various circumstances. The personal observations
communicated the experiences of forest managers and fire fighters, but
provided the least defensible data and the weakest basis for evaluating
treatments.
Thinning Treatments
Thinning, the selective removal of individual trees from a stand, is a
traditional forestry practice used to reduce tree density in order to
stimulate increased growth and vigor in the remaining trees. Thinning is
also used in fuel reduction treatments, although in this context the
purpose is to reduce tree density and to alter the spatial arrangement
of trees to inhibit sustained fire in the forest canopy.
In planning such treatments, forest managers assume that, if a stand
contains fewer trees, and if the tree crowns are further apart, fire
behavior will change. However, the published scientific literature
provides only tenuous support for this hypothesis.
Only 16 of the studies evaluated the effectiveness of thinning
treatments. Of these, 1 was a quantitative empirical study, 1 was a case
study, 4 were based on qualitative observation, and 10 used simulation
models. The results of the modeling studies were highly variable. Three
studies suggested that thinning reduced the incidence of crown fire and
area burned. Three other studies suggested that thinning reduced scorch
height and flame length. The remaining studies using simulation models
suggested that thinning exacerbates fire behavior, depending on the
treatment of the thinning slash. The result of the one empirical study
did not correlate tree density with reduced fire severity.
The literature confirms that fuel treatments can modify fire behavior,
yet it makes clear that tree density is only one of several factors
affecting fire behavior. The distance from the ground to the base of the
tree crown, and the amount and arrangement of surface vegetation and
dead materials, also play important roles. Research has not yet fully
explained how the relationship among these factors alters fire behavior.
Fuels management mirrors this gap in our understanding: some thinning
prescriptions do not include specifications for modifying crown base
height, surface vegetation, or dead materials.
Prescribed Fire
Numerous studies examined the effectiveness of prescribed fire at
modifying subsequent wildfire behavior. Findings were consistent among
all four types of studies: prescribed fire generally reduces fire
severity. One interesting difference between simple thinning, as
conducted in these studies, and prescribed fire is that prescribed fire
is effective at increasing crown base height and reducing surface fuels
and dead materials, while thinning usually addresses tree density.
Another interesting finding in one of the case studies was that a single
prescribed fire treatment did not reduce the density of fuels to
sufficiently change fire behavior. This finding implies that treatment
objectives may not be achieved in one application of prescribed fire.
Thinning and Burning In Combination
A 1996 Forest Service General Technical Report recommends using thinning
and prescribed fire in combination to reduce fire hazard in ponderosa
pine forests, yet only a half dozen studies addressed the effectiveness
of such combination treatments in moderating wildfire behavior. The
results of these studies varied, depending on the treatment of thinning
slash prior to burning. Again, crown base height appeared to be as
important a factor as tree density. Additional research is needed to
document the effects of this widely used treatment combination.
Commercial Logging
In their extensive review of the literature, Carey and Schumann found no
scientific studies that tested the effectiveness of commercial logging
in moderating fire behavior. The literature therefore neither supports
nor undermines the hypothesis that commercial logging can moderate
wildfire behavior.
Conclusion
The authors of this report conclude that systematic field research in
combination with synthesis of existing knowledge is essential to provide
a sound scientific basis for evaluating and designing fuel reduction
treatments. They suggest that the notion that mechanical thinning, or a
combination of thinning and prescribed fire, reduces the likelihood of
catastrophic fire should be viewed as a working hypothesis. To best
assist forest managers, they believe that specific combinations of
treatments need to be tested through experimentation using site- and
weather-specific data. The Joint Fire Sciences Program is funding some
quantitative empirical studies, but the results are not yet available.
In 2000, the United States embarked on an emergency $1.6 billion program
to reduce fuels on millions of acres. The Western Governors Association
calls for sustaining this level of investment over the next ten years.
Based on the findings of this paper, a comparable investment must also
be made in primary and applied research to provide a credible scientific
basis for the design, implementation and evaluation of alternative
treatments. Priority should be given to locating fuel treatments in
areas that include a well-constructed, experimentally driven design, so
that agencies can optimize their ability to learn, to provide a higher
return on fuel reduction investments, and to set the stage for adaptive
management.
FOR MORE INFORMATION: The executive summary and full report of
“Modifying Wildfire Behavior: The Effectiveness of Fuel Reduction
Treatments” can be downloaded from www.theforesttrust.org. The authors,
Henry Carey and Martha Schumann, may be contacted via the website or at
505-983-8992.
FIRE CHRONICLE is edited by the Forest Trust. Laura McCarthy, Forest
Protection Program Director, wrote this issue. The Forest Trust welcomes
your comments, stories, and observations about how the national fire
plan is being implemented (just send a reply message and it will go to
the list moderator). To subscribe to FIRE CHRONICLE go to
http://www.topica.com/lists/firechronicles/ or send an email message to
lau-@theforesttrust.org.
PAST ISSUES OF FIRE CHRONICLE can be downloaded from
http://www.theforesttrust/forest_protection.html#fire
1. 2002 Fire Plan Appropriations will Benefit from 2001 Experience
2. Wildland-Urban Interface Definition a Barrier to Accountability
3. Stewardship Blocks: Innovative Tool Brings Fire Plan Benefits into
Community
4. Youth Training Needed for Fire Plan to Benefit Local Workforce
5. Grants Get National Fire Plan Money into Communities
6. Collaborative Forest Restoration Program Creates New Solution to
Gridlock
7. Permits Regulate Prescribed Burning on Private Land
8. Accountability Remains a Key Issue for National Fire Plan
9. National Partnership Advances Landscape-Scale Forest Restoration
10. Poor Communities Most Threatened By Wildfire
11. A New Model to Fire-Proof Forest Homes
12. Consensus Over Fuel Reduction Treatment Dissolves
13. Wildland Urban Interface Definition Needed for Effective Policy
14. Funding Gaps Prevent Completion of Hazardous Fuel Reduction
15. Agencies Propose to Streamline Environmental Review for Hazardous
Fuel Reduction Treatments
16. National Fire Plan Provides Economic Opportunity for Rural Residents
17. Bark Beetles Heighten Wildfire Concerns
18. Small And Local Businesses Cite Barriers To Reaching National Fire
Plan Goals
19. Federal Report Fuels Public Debate Over Healthy Forests Act
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