Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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United States Department of Agriculture
JANUARY 2021 • VOL. 79 • NO. 1
Developments
in Wildland
Fire Research
Fire Management Today is published by the Forest Service, an agency in the U.S. Department of Agriculture, Washington, DC. The purpose
of Fire Management Today is to share information related to wildland fire management for the benefit of the wildland fire community. Fire
Management Today is available on the World Wide Web at https://www.fs.usda.gov/managing-land/fire/fire-management-today.
Victoria Christiansen, Chief
Forest Service
Patricia Grantham, Acting Director Kaari Carpenter, General Manager • Hutch Brown, Editor
Fire and Aviation Management Daniel Dey, Ph.D., Issue Coordinator
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The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute
an official endorsement of any product or service by the U.S. Department of Agriculture. Individual authors are responsible for the technical
accuracy of the material presented in Fire Management Today.
JANUARY 2021 • VOL. 79 • NO. 1
www.fs.fed.us #forestservice
On the Cover:
Cross-section of a shortleaf pine
(Pinus echinata) that grew in the
Missouri Ozarks from 1577 to 1934.
Shortleaf pine requires frequent
fire for regeneration and survival,
and land managers commonly
use controlled burning to manage
shortleaf pine ecosystems. Old
fire-scarred trees like this give
researchers valuable information
about how forests, fire, climate, and
people have interacted through time.
IN THIS JANUARY 2021 • VOL. 79 • NO. 1
ISSUE
Anchor Point: Science You Can Use Indigenous Fire Stewardship: Federal/Tribal
Shawna A. Legarza.. . . . . . . . . . . . . . . . . . 4 Partnerships for Wildland Fire Research
and Management
The Photoload Technique for Sampling Frank Kanawha Lake. . . . . . . . . . . . . . . . . 30
Surface Fuel Loadings
Robert E. Keane, Heather Heward, Past to Present Human Influences
and Chris Stalling. . . . . . . . . . . . . . . . . . . . . 5 on Fire Regimes: Lessons Learned
From Missouri
The Prescribed Fire Science Consortium Michael C. Stambaugh and
Nicholas Skowronski, Bret Butler, Daniel C. Dey. . . . . . . . . . . . . . . . . . . . . . . 40
J. Kevin Hiers, Joseph O’Brien, and
J. Morgan Varner. . . . . . . . . . . . . . . . . . . . 10 Coproducing Science on Prescribed Fire,
Thinning, and Vegetation Dynamics on a
Can Targeted Browsing Be a Useful National Forest in Alabama
Surrogate for Prescribed Burning? Callie Schweitzer and Daniel Dey. . . . . . . 43
Gina Beebe, Lauren S. Pile, Michael
Stambaugh, Brian Davidson, and
Daniel Dey. . . . . . . . . . . . . . . . . . . . . . . . . 12
Learning To Live With Fire: Managing the
Impacts of Prescribed Burning on Eastern
Hardwood Value
Firefighter
Bark Beetle and Fire Interactions in Western
Coniferous Forests: Research Findings
Christopher J. Fettig, Sharon M. Hood,
Daniel C. Dey, Michael C. Stambaugh, and
Callie Schweitzer. . . . . . . . . . . . . . . . . . . . . 52 and public
Justin B. Runyon, and Chris M. Stalling. . 14
Atmospheric Turbulence in Wildland
Data and Dialogue: Assessing Forest
Service Risk Management Assistance safety is
our first
Chad Kooistra and Courtney Schultz. . . . . 61
Fire Environments: Implications for Fire
Behavior and Smoke Dispersion Moneyball for Fire
priority.
Warren E. Heilman. . . . . . . . . . . . . . . . . . . 24 Nicholas F. McCarthy, Matthew P.
Thompson, and David E. Calkin. . . . . . . . . 69
GUIDELINES
for Contributors
Fire Management Today
3
ANCHOR POINT
Interest in the evolution of fire regimes in
the United States in tandem with Tribal
cultures has long been growing, and two
Science You articles explore some of the implications.
Indigenous knowledge can help identify
Can Use trigger points, thresholds, and indicators
for ecosystems, habitats, and resources
of interest; one article is a primer that
id you know that Gifford nonindigenous fire managers can use for
D Pinchot, the founder of the
Forest Service, was one of
our earliest fire researchers? In 1899,
thoughtful and respectful engagement
with Tribal communities.
Prescribed fire is of tremendous and
Pinchot published an article on “the
growing importance for the Forest Service
relation of forests and forest fires” By Shawna A. Legarza, Psy.D. in improving forest conditions across the
(Pinchot 1899). That was well before Former Director, Fire
Nation. Several articles explore fire-related
the Nation’s forest reserves were and Aviation Management
USDA Forest Service issues in Alabama and Missouri, with
transferred to USDA in 1905 to become
useful findings for fire managers across
the National Forest System. The Bureau
many Southern and Eastern States.
of Forestry—the Forest Service’s Management. The Forest Service’s
predecessor organization in USDA, land management and wildland All articles in this issue reflect the
headed by Pinchot—had a vigorous fire management have always been spirit of “Science you can use,” the
research program devoted to forestry interdependent with our Research slogan of Forest Service Research and
and conservation, and Pinchot himself and Development mission area. It’s a Development. Researchers and fire
was a contributor. longstanding relationship and a classic managers have long been strengthening
case of interdependence as a core value their ties. Increasingly, they are designing
So it is no surprise that Forest Service
for the Forest Service. projects together, achieving outcomes
Research and Development is so deeply
together, and opening new opportunities
ingrained in the mission of the Forest In this issue of Fire Management Today, for collaborative projects in both fire
Service—and so intertwined with you can see that interdependence research and wildland fire management.
our programs for Fire and Aviation in various ways. Wind and weather
effects have long complicated wildland In the spirit of “Science you can use,”
fire management, and you can read I am pleased and proud to present the
Prescribed fire is about the implications for both fire developments in wildland fire science
behavior and smoke dispersion of contained in this issue.
of tremendous and
atmospheric turbulence in wildland
growing importance fire environments. New techniques LITERATURE CITED
for the Forest Service for sampling fuel loadings will help Pinchot, G. 1899 [reprinted 1999]. The relation
of forests and forest fires. Forest History
in improving forest fire managers anticipate fire behavior
Today. Spring: 29–32.
conditions across and severity. Another article explores
the implications for wildland fire ■
the Nation. management of forest dieoff in the West
due to bark beetle epidemics.
Fire Management Today 4 JANUARY 2021 • VOL. 79 • NO. 1
conducted countless fuel loading
inventories using only three to five
transects, all less than 30 meters (100
The Photoload
feet) long. We knew there were problems
with planar intersect sampling:
z It concerns only down dead woody fuels;
Technique
z It is difficult to repeat across samplers;
z It can’t easily be meshed with
other fixed-area plot sampling
procedures; and
for Sampling
z It doesn’t provide a visual reference
for loading in the field (so you need to
convert intersects to loading later on,
after leaving the field).
Surface Fuel But we didn’t know that the planar
intersect technique failed to capture the
variability of fuel loadings across the
Loadings
appropriate spatial scales (Keane and
others 2012).
ARE THERE
ALTERNATIVES?
Robert E. Keane, Heather Heward, and Chris Stalling The high sampling intensity demanded
by planar intersect sampling, coupled
with its other shortcomings, certainly
ow many miles of Brown’s enormous number of transects—
H (1971) transects have you done
in your lifetime? Collectively,
we estimate that we’ve established
corresponding to long transect lengths—
for a realistic estimate of fuel variability.
New research has found that surface
begs the question: Are there viable
alternatives to this “tried-and-true”
sampling method?
over 500 miles (800 km) of transects fuel components vary at different scales Destructive methods, such as clipping
in our careers—a distance from Salt (Keane and others 2012; Vakili and and weighing, are too time intensive for
Lake City, UT, to Denver, CO. If you others 2016), and because the planar most operational applications (Keane
have also sampled great distances using intersect technique samples in only 2015). Measuring fuels onsite based
planar intersect sampling, then this will one dimension, it misses much of the on cover, height, length, and width
really depress you: most operational variability of fuel loading in a stand or is also time consuming and often no
field sampling efforts probably did not landscape. As a result, more than 800 better than planar intersect methods
sample at the appropriate intensities to meters (2,600 feet) of transect might (Keane and Gray 2013). Some believe
obtain a useful estimate of fuel loadings be needed to realistically quantify fine that photo series, the most common
using planar intersect techniques. woody fuel loadings in an area of less method of estimating loadings, is a
than a hectare (2.4 acres) (Sikkink and good alternative. But many photo series
PROBLEMS WITH PLANAR Keane 2008; Keane and Gray 2013). loadings were measured using planar
INTERSECT SAMPLING intersects, and the loadings of fine fuels
This realization completely rocked are rarely visible in the oblique photos
Although the Brown (1971) method our world because we had ignorantly
is not wrong, you would need an in the photo series guides (Maxwell and
Ward 1980; Sikkink and Keane 2008).
New research Is there a fuel sampling alternative
Robert Keane is a research ecologist for the has found that to planar intersect sampling that not
Forest Service, Rocky Mountain Research
planar intersect only allows accurate estimates of fuel
Station, Missoula Fire Sciences Laboratory,
sampling might be loadings but also assesses more than
Missoula, MT; Heather Heward is a senior
down dead woody fuel components,
instructor at the University of Idaho, inappropriate for meshes well with other vegetation
Moscow, ID; and Chris Stalling is a fire many operational inventory techniques, and is repeatable?
ecologist for the Forest Service, Rocky
Mountain Research Station, Missoula Fire sampling efforts. More than a decade ago, Keane and
Sciences Laboratory, Missoula, MT. Dickinson (2007b) developed a visual
Fire Management Today 5 JANUARY 2021 • VOL. 79 • NO. 1
technique to assess fuel loadings from and Dickinson (2007a) created this new
a series of photographs representing sampling method as an alternative to New research has
the gradient of loadings in the field. planar intercept sampling for research
Unlike photo series photographs, the and operational applications. This found that wildland
photoload technique uses downward- article describes the photoload technique fuel components vary
facing photographs of known fuel and its recent improvements for more at different spatial and
loadings measured prior to taking the robust and scale-appropriate surface fuel temporal scales.
photo (fig. 1). Recent studies have found loading sampling.
that this technique is comparable and
sometimes superior to planar intersect THE PHOTOLOAD with the corresponding conditions in a
techniques, given the same level of TECHNIQUE set of photographs of known loadings
sampling effort (Sikkink and Keane The photoload technique involves (fig. 1). You start with the photograph
2008; Keane and Gray 2013). Keane matching conditions on the ground showing the lowest loading for that
fuel component and compare it to
conditions on the ground. If they don’t
match, you move on to the next photo
(and so on) until you find the photo
showing more than the fuel loading on
the ground. Then you visually compare
the loading on the ground with that
photo and the previous photo, and
you estimate a loading value that is
somewhere in between.
If the fuel component is shrub or
herbaceous, then another step is required.
You measure or visually estimate the
height of the shrub or herbaceous layer
and then divide the height by the height
in the photo within the photoload
sequences (fig. 2). You then multiply the
estimated fuel loading by this ratio to
adjust for the size of the plants.
Estimating loadings for logs (1,000-
hour down dead woody fuels) is a bit
more complicated. Manipulating log
loading in a studio or other controlled
environment was impossible because
of the immense weight of the logs
(Keane and Dickinson 2007a), so
we created the original photoload
sequences with 6-inch (15-cm) and
10-inch (25-cm) tubes painted brown
(fig. 3). The weight of each “log” was
calculated as the volume of the tube
Figure 2—A herbaceous fuelbed photo in
Figure 1—A sample of photoload loadings for 1-hour down dead woody fuels (woody fuels the photoload series. Source: Keane and
with diameters less than ¼ inch (7 mm)). Source: Keane and Dickinson (2007b). Dickinson (2007b).
Fire Management Today 6 JANUARY 2021 • VOL. 79 • NO. 1
multiplied by the density of Douglas- fir wood (380 kg m-3). Moreover, because logs vary at spatial scales much more than does fine woody debris, Keane and Dickinson (2007a) used a 100-square-meter plot that was designed to be easily photographed. In subsequent testing of this method using the brown tubes, we found it useful; but there was a great deal of uncertainty in the visual estimates, and it was difficult to obtain consistent results across multiple users (Sikkink and Keane 2008). Therefore, we developed a companion tabular approach as an alternative to photo comparisons: a series of tables where rows are diameters, columns are lengths, and cells are loadings (Keane and Dickinson 2007a). You visually estimate or actually measure the average diameter and length of all logs in a 100-square-meter area and find the right loading value in the table, then reduce it for rot, if needed. The tables are the better option for estimating log loading because the method is highly scalable: you can use the method to compute the weight of each log, a set of similar logs, or all logs in the 100-square-meter area, and you can estimate lengths and diameters by eye, by pacing, or by actually measuring. Photoload techniques are best used when sampling experience is low and sampling time is limited (Sikkink and Keane 2008). The method is relatively quick and inexpensive, and it allows for moderately precise and reasonably accurate estimates of fuel loadings, especially during operational sampling. The photoload technique is not intended Figure 3—A sample of photoload loadings for 1,000-hour down dead woody fuels (woody fuels to replace previous protocols and with diameters greater than 3 inches (8 cm)). Source: Keane and Dickinson (2007b). methods but as a viable alternative when the objectives of sampling and the resources available match the The photoload technique is being used little complex equipment, the photoload design characteristics of the photoload around the world for a multitude of technique is often used by graduate technique (Keane and Dickinson 2007b; reasons. It is most often used to estimate students, foresters, and interested Sikkink and Keane 2008). The technique fuel loadings for many purposes, citizens. The photoload methodology is perfect for monitoring because it does including estimating smoke emissions, has been integrated into sampling not alter fuelbed characteristics, and fire intensity, and fire hazard. Other uses systems, such as FFI (Lutes and others it can be a valuable research sampling have included estimating plant species 2009), for estimating surface fuel in technique when paired with double biomass for forage potential, carbon wildlands and the wildland–urban sampling to create correction factors pools, and wildlife habitat. And because interface, and it is also being included as (Catchpole and Wheeler 1992). it is easy to learn and use and requires a fuel sampling method in the National Fire Management Today 7 JANUARY 2021 • VOL. 79 • NO. 1
Aeronautics and Space Administration’s directly influences wood density, which
Globe program for citizen science. then affects the accuracy of loading
estimates. Currently, most sampling
PHOTOLOAD LIMITATIONS techniques for fuel loading use wood Are You Interested
A few limitations need mention.
First, like the Brown (1974) protocols,
densities for sound logs; reduction
factors should be developed to account
in Photoload
photoloads cannot be used for for loss of mass due to decomposition. Sampling?
estimating litter and duff surface fuel The photoload method includes a way
The following is a list of websites for
loadings, which must still be sampled by to reduce loading to account for rot, but
downloading photoload reference
measuring the depth of each layer and the reduction factors are not based on
materials and taking a peek at them.
multiplying by the layer bulk densities. comprehensive research findings.
We conduct anywhere from 3 to 11
The depth of the litter and especially workshops per year at conferences,
the duff is not entirely evident in PHOTOLOAD
local offices, universities, and
downward-facing photographs, so the IMPROVEMENTS nongovernmental organizations (fig.
photoload approach is inappropriate. During the initial testing and use of 4). If you are interested in conducting a
However, depth measurements are photoloads, Sikkink and Keane (2008) workshop, please contact Chris Stalling
easily integrated into photoload found that people with experience in (chris.stalling@usda.gov) or Heather
sampling procedures; we often take fuel sampling were better able to make Heward (hheward@uidaho.edu).
depth measurements at the corners accurate visual estimates of loading
than novice samplers. Subsequent trials The sampling manual: https://www.
of the microplot frame used for fine fs.usda.gov/treesearch/pubs/26755
fuels. To estimate bulk densities, we are revealed that photoload users could
developing a photo guide for selecting more accurately estimate loadings if The development methods: https://
the most appropriate bulk densities for they were given rudimentary training—a www.fs.usda.gov/treesearch/pubs/26757
the sample site. 1- to 2-hour training session (fig. 4).
Accordingly, the Holley and Keane The training guide: https://www.
Another limitation is that there are (2010) training tool was created to give fs.usda.gov/treesearch/pubs/36328
photoload series for only six shrub and novice users a quick way to improve
four herbaceous species. Moreover, the accuracy of their visual estimation VIDEO: Introduction to the photoload
these species are primarily found in using photographs of fuelbeds where sampling technique
the northern Rocky Mountains in the the loadings were measured afterwards A zip file with presentations and
United States. using destructive techniques. reference materials is also available.
Both logs and fine woody debris pose Despite the popularity of photoload
a challenge for fuel sampling because methods, many have recognized that
woody particles are often in different the original photoload photographic
stages of decay and the degree of rot sequences were taken for a small set of
Training crews on photoload sampling.
Photos: Heather Heward, University of
Figure 4—Teaching photoload techniques to Forest Service employees at the Wildland Fire Idaho (2019).
Academy in Sacramento, CA. Basic training in the use of photoload techniques improves
estimates of fuel loadings. Photo: Heather Heward, University of Idaho (2019).
Fire Management Today 8 JANUARY 2021 • VOL. 79 • NO. 1
Lutes, D.C.; Benson, N.C.; Keifer, M. [and
others]. 2009. FFI: a software tool for
The photoload technique allows you to quickly and ecological monitoring. International Journal
accurately sample loadings of most surface fuel of Wildland Fire. 18: 310–314.
Maxwell, W.G.; Ward, F.R. 1980. Photo series
components at the appropriate spatial scales. for quantifying natural forest residues in
common vegetation types of the Pacific
Northwest. Gen. Tech. Rep. PNW–
fuel components found only in the U.S. Catchpole, W.R.; Wheeler, C.J. 1992. Estimating GTR–105. Portland, OR: USDA Forest
northern Rocky Mountains (Tinkham plant biomass: a review of techniques. Service, Pacific Northwest Forest and Range
Australian Journal of Ecology. 17(2): Experiment Station. 229 p.
and others 2016). Applying the Keane 121–131.
and Dickinson (2007b) limited set McColl-Gausden, S.; Penman, T. 2017. Visual
Harmon, M.E.; Woodall, C.W.; Fasth, B.; assessment of surface fuel loads does not
of reference photos to fuel sampling Sexton, J. 2008. Woody detritus density and align with destructively sampled surface
in other ecosystems or geographic density reduction factors for tree species in fuels. Forests. 8: 408.
areas could result in higher errors due the United States: a synthesis. Gen. Tech.
Russell, M.B.; Woodall, C.W.; Fraver, S.;
to major differences in fuelbed and Rep. NRS–29. Newtown Square, PA: USDA
D’Amato, A.W. 2013. Estimates of downed
Forest Service, Northern Research Station.
plant morphology (McColl-Gausden woody debris decay class transitions for
84 p.
and Penman 2017). Down woody forests across the eastern United States.
Holley, V.J.; Keane, R.E. 2010. A visual training Ecological Modelling. 251: 22–31.
fuel particle diameter and density tool for the photoload sampling technique.
distributions, for example, vary greatly Sikkink, P.G.; Keane, R.E. 2008. A comparison
Gen. Tech. Rep. RMRS–GTR–242. Fort
of five sampling techniques to estimate
across species, ecosystems, biophysical Collins, CO: USDA Forest Service, Rocky
surface fuel loading in montane forests.
settings, and times since disturbance Mountain Research Station. 234 p.
International Journal of Wildland Fire. 17:
(Harmon and others 2008; Woodall Keane, R.E. 2015. Wildland fuel fundamentals 363–379.
and applications. New York: Springer. 191 p.
and Monleon 2010; Russell and others Tinkham, W.T.; Hoffman, C.M.; Canfield, J.M.
Keane, R.E.; Dickinson, L.J. 2007a. [and others]. 2016. Using the photoload
2013). More importantly, the species
Development and evaluation of the technique with double sampling to improve
that comprise shrub and herbaceous photoload sampling technique. Res. Pap. surface fuel loading estimates. International
fuels differ across ecosystems. We have RMRS–RP–61. Fort Collins, CO: USDA Journal of Wildland Fire. 25: 224–228.
recently written a comprehensive guide Forest Service, Rocky Mountain Research
Vakili, E.; Hoffman, C.M.; Keane, R.E. [and
to quickly, easily, and economically Station. 29 p.
others]. 2016. Spatial variability of surface
create a set of photoload sequences to Keane, R.E.; Dickinson, L.J. 2007b. The fuels in treated and untreated ponderosa pine
photoload sampling technique: estimating
represent surface fuel components for forests of the southern Rocky Mountains.
surface fuel loadings using downward International Journal of Wildland Fire. 25:
local applications, to be published some looking photographs. Gen. Tech. Rep. 1156–1168.
time in 2020. RMRS–GTR–190. Fort Collins, CO: USDA
Woodall, C.W.; Monleon, V.J. 2010. Estimating
Forest Service, Rocky Mountain Research
the quadratic mean diameters of fine woody
ACKNOWLEDGMENT Station. 44 p.
debris in forests of the United States. Forest
Many photoload efforts were funded by Keane, R.E.; Gray, K.; Bacciu, V.; Leirfallom, Ecology and Management. 260: 1088–1093.
S. 2012. Spatial scaling of wildland fuels
the National Fire Plan. ■
for six forest and rangeland ecosystems
of the northern Rocky Mountains, USA.
LITERATURE CITED Landscape Ecology. 27: 1213–1234.
Brown, J.K. 1971. A planar intersect method Keane, R.E.; Gray, K. 2013. Comparing three
for sampling fuel volume and surface area. sampling techniques for estimating fine
Forest Science. 17(1): 96–102. woody down dead biomass. International
Brown, J.K. 1970. A method for inventorying Journal of Wildland Fire. 22: 1093–1107.
downed woody fuel. General Technical
Report INT?16, USDA Forest Service. 24 p.
Fire Management Today 9 JANUARY 2021 • VOL. 79 • NO. 1
Scientists taking measurements during an event at Tall
Timbers Research Station in Florida. The Prescribed Fire
Science Consortium focuses on integrated fuels, fire behavior,
and fire effects measurements and prioritizes coproduction
of actionable science working closely with land managers.
The Prescribed Fire
Science Consortium
Nicholas Skowronski, Bret Butler, J. Kevin Hiers, Joseph O’Brien, and J. Morgan Varner
rescribed fire is used on more In response, the Prescribed Fire Science the Nation, including representatives
P than 12 million acres (4.9
million hectares) in the United
States annually. It is a critical strategic
Consortium (PFSC) was formed in
2016 by a group of multidisciplinary
fire scientists and managers with a focus
from each Forest Service research
station, the Tall Timbers Research
Station, the Los Alamos National
management tool for hazardous fuels on the modernization of science, with Laboratory, and numerous academic
reduction and the resilience of fire- specific applicability to safe and effective institutions. In addition, the PFSC is
adapted landscapes. In recognition of its application of prescribed fire. guided and assisted by land managers
value, the President’s Budget for fiscal from the Forest Service and State
year 2020 called for $450 million in agencies like the New Jersey Forest
funding for hazardous fuels reduction Fire Service and the Florida Division
for USDA alone.
The consortium’s of Forestry as well as by private land
coproduction events managers and landowners.
RATIONALE are increasing the
Because managers intentionally pace and scale of
choose to introduce fire onto a land
management unit for a specific objective
prescribed fire across
Nicholas Skowronski is a research forester for
or set of objectives, science-based the United States. the Forest Service, Northern Research Station,
decision making is essential. However, Morgantown, WV; Bret Butler is a research
the lion’s share of national research mechanical engineer for the Forest Service,
investment in fire science has focused Rocky Mountain Research Station, Missoula,
on wildfires and suppression needs, MT; J. Kevin Hiers is a wildland fire scientist
The PFSC takes a coproduction
neglecting the field of prescribed fire for Tall Timbers Research, Inc., Tallahassee,
approach to prescribed fire science,
science and leading to a relative paucity FL; Joseph O’Brien is a team leader and
with science discovery and delivery as
of tools for modeling prescribed fire research ecologist for the Forest Service,
closely aligned with operational needs
behavior and effects in ways that Southern Research Station, Athens, GA; and J.
as possible. The consortium comprises
managers need to safely increase the Morgan Varner is the director of fire research for
an ensemble of scientists from across
pace and scale of treatments. Tall Timbers Research, Inc., Tallahassee, FL.
Fire Management Today 10 JANUARY 2021 • VOL. 79 • NO. 1Research and Development Program. SCIENCE/MANAGEMENT
The PFSC is one of Broadly, their work advances prescribed COLLABORATION
fire research by:
several models for The PFSC is one of several models
developing scientist/ 1. Supporting the next generation of for developing scientist/manager
fire dynamics modeling, coproduction of actionable science. The
manager coproduction of consortium’s events featuring “elbow-
actionable science. 2. Improving scientific understanding to-elbow” interactions between fire
and modeling of the fluid dynamics scientists and fire managers are doing
of surface fire regimes, much to increase the pace and scale of
3. Improving scientific understanding prescribed fire across the United States.
ACTIVITIES An often-overlooked benefit from the
of how fire/atmospheric feedbacks
The PFSC has sponsored coproduction determine smoke and emissions PFSC is building rapport and breaking
events in Florida and Montana that production and transport, and down barriers between fire practitioners
spanned several days and included both and fire scientists. Fire science and
experimental and operational prescribed 4. Developing advanced understanding management share a responsibility for
burning. These events served to deepen of fire effects and responses. encouraging and collectively supporting
scientist/manager relationships, conduct the consortium and similar activities.
fireline experimentation for a variety of Managers have been involved at every
objectives, and set the stage for future step of the process and will continue ■
work. The next coproduction event is to play a critical role in operational
planned in the New Jersey Pinelands for applications of the science. The
September 2020. collaboration of researchers and
managers through the PFSC has gained
The PFSC has aggregated successful international interest and likely represents
prescribed fire research from across the largest combined investment in fire
the country, building on previous science currently underway.
investments in projects at Eglin
Air Force Base, in the New Jersey
Pinelands, and at other locations to
create new soft-funding opportunities.
The consortium takes a coproduction approach, with science
Over the past several years, consortium discovery and delivery as closely aligned with operational
teams have made 10 successful research needs as possible.
proposals to the U.S. Department
of Defense Strategic Environmental
Fire Management Today 11 JANUARY 2021 • VOL. 79 • NO. 1Figure 1—Goat perched on snag (top)
browsing a dogwood on the Mark Twain
National Forest in Missouri.
Photo: Gina Beebe.
TESTING TARGETED
BROWSING
“Targeted browsing” is the use of
browsing livestock at predetermined
levels of intensity and seasonality to
achieve desired land management
objectives. In the oak and pine
woodlands of the Missouri Ozarks,
we are testing targeted browsing as a
management tool to meet restoration
objectives and fuel targets on the Mark
Twain National Forest (figs. 1, 2).
Can Targeted
Silvicultural prescriptions for woodland
restoration require lowering overstory
stocking levels and removing the
midstory to increase sunlight reaching
Browsing Be a the forest floor. However, this often
results in vigorous sprouting by oaks
and hickories as well as less desirable
Useful Surrogate
species such as red maple. Furthermore,
it can increase the abundance of woody
shrubs, including fragrant sumac
and blackberry, which compete with
for Prescribed
herbaceous plants.
This aggressive woody ingrowth into the
midstory could be managed effectively
Burning?
with frequent low-intensity surface fire.
However, maintaining such levels of
disturbance can be complicated on some
sites, resulting in the need for other or a
Gina Beebe, Lauren S. Pile, Michael Stambaugh, Brian Davidson, combination of approaches. Specifically:
and Daniel Dey
he limitations on prescribed
T burning are numerous, but
fire’s ecological role in shaping
the health and integrity of our forests
In the oak and
pine woodlands
Gina Beebe is a graduate student in the School
of Natural Resources, University of Missouri,
Columbia, MO; Lauren Pile is a research
is incredibly important. Browsers, of the Missouri
such as domesticated goats, prefer to ecologist at the Northern Research Station,
consume woody species. People can Ozarks, we are USDA Forest Service, Columbia, MO; Michael
use goats and other browsers to help testing targeted Stambaugh is an associate research professor in
manage ecological communities that are browsing as a the School of Natural Resources, University of
degraded by nonnative invasive shrubs Missouri, Columbia, MO; Brian Davidson is a
management tool. botany and invasive species program manager
and vines or located in the wildland–
urban interface or where smoke impacts for the Mark Twain National Forest, USDA
are considerable. Furthermore, browsers Forest Service, Rolla, MO; and Daniel Dey
Browsers can constitute an additional is a research forester and project leader at the
could supplement prescribed burning
and accessible tool in managing fire- Northern Research Station, USDA Forest
by treating forest stands in “off years”or
maintained landscapes. Service, Columbia, MO.
outside of typical burn windows.
Fire Management Today 12 JANUARY 2021 • VOL. 79 • NO. 1Goats and other browsers
can constitute an
additional and accessible
tool in managing fire-
maintained landscapes.
Targeted goat browsing has a notable
impact on litter, 1-hour fuels, and 10-
hour fuels. In a study by Tsiouvaras and
others (1989), a herd of 113 goats per
acre reduced 1-hour dead fuels by 58.3
percent and average litter depth by 27.4
percent in 3 days. Goats’ capacity to
reduce fine dead fuels is mainly through
trampling as the fuels are crushed and
incorporated into soils.
Figure 2—Browsed (left) and nonbrowsed (right) plots. Photo: Gina Beebe. To learn more about this project, please
visit our project website: https://www.
nrs.fs.fed.us/sustaining_forests/conserve_
We are interested in the combined effects of targeted enhance/biodiversity/goats-fire-woodlands/
browsing and prescribed burning in meeting our LITERATURE CITED
restoration objectives. Tsiouvaras, C.N.; Havlik, N.A.; Bartolome,
J.W. 1989. Effects of goats on understory
vegetation and fire hazard reduction in a
coastal forest in California. Forest Science.
1. We are investigating browsing season Finally, we will examine the effects of 35(4): 1125–1131.
(late winter, spring, and late summer) targeted browsing on fuels, a topic of ■
to determine when we can maximize rising interest to many land managers.
the impact of browsing on the growth Past declines in fire use have led to
of woody stems while minimizing its an accrual of surface fuels, reaching
impact on ground flora; levels of management concern. Surface
fuels play a critical role in fire spread,
2. We are interested in how targeted and their removal greatly reduces the
browsing might stimulate the likelihood of fire hazard and stand-
available seedbank by reducing replacing crown fires as well as the need
midstory vegetation (such as for recurrent prescribed burns.
dogwoods) and thereby increasing
sunlight reaching the forest floor and RESULTS
exposing bare mineral soil through
Although examples are limited, targeted
trampling; and
browsing has been demonstrated to
3. We are interested in the combined supplement prescribed fire as a fuels
effects of targeted browsing and management technique. Goat browsing,
prescribed burning in meeting our in particular, can be a highly effective
restoration objectives—that is, a fuels reduction treatment due to the
two-layer (ground and canopy) ability of goats to consume a wide
open woodland with a diverse forb- variety of plants and to remove shrubs
and grass-dominated ground layer up to 6 feet (2 m) high, reducing both
that provides critical habitat for vertical and horizontal fuel continuity.
important wildlife species.
Fire Management Today 13 JANUARY 2021 • VOL. 79 • NO. 1Bark Beetle and Fire
Interactions in Western
Coniferous Forests:
Research Findings
Christopher J. Fettig, Sharon M. Hood, Justin B. Runyon, and Chris M. Stalling
ative bark beetles and wildfires Figure 1—Tree mortality following a bark beetle outbreak in the Sierra Nevada in California.
N are important disturbances
in western coniferous forests.
Bark beetles can colonize and kill trees
California experienced a severe drought from 2012 to 2015, stimulating a large bark beetle
outbreak in the central and southern Sierra Nevada. Most tree mortality was caused by western
pine beetle (Dendroctonus brevicomis), which readily colonizes drought-stressed ponderosa
of all species, ages, and sizes, but each pine (Pinus ponderosa), but other tree and shrub species were also affected. About 89 percent
species exhibits unique host preferences of the ponderosa pines in the three largest diameter classes were killed (Fettig and others 2019),
and impacts. Some bark beetles cause representing the loss of an important structural component of these forests. Mortality of
extensive levels of tree mortality (table sugar pine (Pinus lambertiana), caused primarily by mountain pine beetle (Dendroctonus
1), as demonstrated by mountain ponderosae), was also substantial (48 percent). In total, 49 percent of the trees died between
pine beetle (Dendroctonus ponderosae) 2014 and 2017. Photo: C. Fettig, USDA Forest Service.
in several pines, western pine beetle
(Dendroctonus brevicomis) in ponderosa
pine (Pinus ponderosa), Douglas-fir beetle In general, bark beetles require
(Dendroctonus pseudotsugae) in Douglas- living phloem (the layer of cells
fir (Pseudotsuga menziesii), and spruce Christopher Fettig is a research entomologist
within the inner bark that transports for the Forest Service, Pacific Southwest
beetle (Dendroctonus rufipennis) in several photosynthates (sugars) within the
spruces. Other bark beetles are secondary Research Station, Davis, CA; Sharon Hood is
tree) to reproduce. When bark beetle a research ecologist for the Forest Service, Rocky
agents that colonize stressed, dead, populations are low, the beetles create
or dying trees. The impacts of these Mountain Research Station, Missoula, MT;
small gaps in the forest canopy by Justin Runyon is a research entomologist for
secondary agents often go unnoticed, colonizing and killing trees stressed by
while the former occasionally drive the Forest Service, Rocky Mountain Research
age or other factors. During bark beetle Station, Bozeman, MT; and Chris Stalling is a
headlines in large newspapers. outbreaks, large numbers of trees can be biologist for the Forest Service, Rocky Mountain
Research Station, Missoula, MT.
Fire Management Today 14 JANUARY 2021 • VOL. 79 • NO. 1Table 1—Bark beetles recognized as causing substantial levels of tree mortality during outbreaks in the Western United States.
Current knowledge of effects on
Common name Scientific name Common host(s)
wildfire behavior and severitya
Lodgepole pine, sugar pine,
California fivespined ips Ips paraconfusus Low
ponderosa pine
Douglas-fir beetle Dendroctonus pseudotsugae Douglas-fir Moderate
White fir, grand fir, California
Fir engraver Scolytus ventralis Low
red fir
Jeffrey pine beetle Dendroctonus jeffreyi Jeffrey pine Low
Whitebark pine, lodgepole pine,
Mountain pine beetle Dendroctonus ponderosae limber pine, sugar pine, western High
white pine, ponderosa pine
Northern spruce engraver Ips perturbatus White spruce, Lutz spruce Low
Lodgepole pine, Jeffrey pine,
Pine engraver Ips pini Low
sugar pine, ponderosa pine
Pinyon ips Ips confusus Pinyon pine(s) Low
Engelmann spruce, white
Spruce beetle Dendroctonus rufipennis Moderate
spruce, Lutz spruce
Western balsam bark beetle Dryocoetes confusus Subalpine fir Low
Western pine beetle Dendroctonus brevicomis Ponderosa pine, Coulter pine Low
a. Level (low, moderate, or high) defined in relation to knowledge of the effects imposed by mountain pine beetle outbreaks, which have been most intensively studied.
killed over extensive areas (fig. 1), often to repel beetle attack (Kolb and others In this article, we consider two common
adversely affecting timber and wood 2016). Accordingly, recent bark beetle interactions between bark beetles and
fiber production, water quality and outbreaks have been correlated with wildland fires:
quantity, fish and wildlife populations, shifts in temperature and precipitation
opportunities for outdoor recreation, caused by climate change. In some 1. The effects of fuel reduction
and biodiversity and carbon storage, forests, increases in tree density have treatments (prescribed fire and
among other ecological goods and exacerbated the effect by providing an mechanical thinning) and wildfires
services (Morris and others 2018). abundance of hosts and by increasing on bark beetles; and
competition among hosts for limited 2. The effects of bark beetle outbreaks
HISTORIC OUTBREAK LEVELS resources, making trees more vulnerable and associated levels of tree
The amount of tree mortality caused to beetle attacks. mortality on fuels and wildfire
by bark beetles in the Western United behavior and severity.
Wildfires have sculpted many western
States has exceeded that caused by
forests for millennia, reducing the We briefly describe the current state
wildfires in the last 3 decades (Hicke
quantity and continuity of fuels, of knowledge and identify gaps in
and others 2016), and several recent
discouraging establishment of fire- knowledge needed to make informed
outbreaks are considered the most
intolerant tree species, and influencing management decisions.
severe in history. Since 2000, for
the susceptibility of forests to bark
example, about 25.5 million acres (10.3
beetle outbreaks and other disturbances. EFFECTS OF FUEL
million ha) in the Western United
Climate change is increasing the REDUCTION TREATMENTS
States have been affected by mountain
number of large wildfires (fires greater
pine beetle. Activity peaked in 2009, ON BARK BEETLES
than 1,000 acres (400 ha) in size), the
with 8,842,698 acres (3,578,513 ha) Tens of millions of acres of forest in the
frequency of wildfires, the length of
affected in that year alone. Western United States are classified as
the wildfire season (by up to 90 days
Bark beetles are cold-blooded in some locations), and the cumulative having moderate to high fire hazards.
organisms highly sensitive to changes area burned (Vose and others 2018). Efforts to lower hazards focus on
in temperature, which influence their Suppression costs and risks to homes reducing surface fuels, increasing
survival and population growth (Bentz and other infrastructure are also the height to live crowns, decreasing
and others 2010). Drought stress increasing (Flannigan and others 2006). crown bulk density, and retaining large
adversely affects the ability of conifers trees of fire-resistant species such as
Fire Management Today 15 JANUARY 2021 • VOL. 79 • NO. 1Fettig and McKelvey (2014) monitored
A common management concern is that bark beetles the effects of fuel reduction treatments
on levels of tree mortality at Blacks
might colonize and kill trees injured by prescribed fire. Mountain Experimental Forest in
California over a 10-year period. Twelve
experimental plots (ranging from
190 to 356 acres (76–142 ha)) were
ponderosa pine (Agee and Skinner and others (2006) showed that chipping established to create two distinct forest
2005). When applied under prescription, submerchantable and unmerchantable structural types: midseral stage (with
planned ignitions and their mechanical ponderosa pines and depositing the low structural diversity) and late-seral
surrogates (such as thinning from below) chips back into treated stands increases stage (with high structural diversity).
are generally effective in meeting fuel the risk of infestation by several species Following harvesting, half of each plot
reduction goals (McIver and others of bark beetles in the Southwestern was treated with prescribed fire.
2013; Stephens and others 2012). For United States. The effect was due
example, the effectiveness of prescribed to large amounts of monoterpenes A total of 16,473 trees (9 percent of all
fire for treating surface and ladder being released during chipping, which trees) died. Mortality was concentrated:
fuels to reduce the incidence of passive enhanced attraction to bark beetles.
z On plots with high structural diversity
crown fire (that is, the torching of small Impacts were greater from chipping
(64 percent);
groups of trees) is well supported by in spring (April–May) than in late
modeling of predicted fire behaviors summer (August–September) because z On burned-split plots (61 percent);
(Stephens and others 2009) and by spring is the time of peak flight activity z Within the two smallest diameter
empirical research (Ritchie and others for several species of bark beetles in classes (87 percent); and
2007). Furthermore, results from the the Southwestern United States as
z During the second sample period (3 to
National Fire and Fire Surrogate Study, they search for new hosts. If possible,
5 years after prescribed burns).
the largest study of its kind (www. chipping should be conducted in fall to
frames.gov/ffs/about), indicate that the minimize tree losses to bark beetles if Most mortality was caused by bark
incidence of active crown fire is best the chips will remain onsite. beetles (65 percent), notably fir
reduced by combining prescribed fire engraver (Scolytus ventralis) in white
with mechanical fuel treatments (McIver PRESCRIBED FIRE fir (Abies concolor) and mountain pine
and others 2013). Following fire, tree mortality can be beetle, western pine beetle, and pine
immediate due to consumption of engraver (Ips pini) in ponderosa pine.
The type of fuel reduction treatments The authors concluded that this level
living tissue or heating of critical plant
and their manner of implementation of tree mortality did not interfere
tissues; or it can be delayed, occurring
have different effects on the fuel matrix, with management objectives aimed at
over the course of a few years as a
which can influence the susceptibility of increasing overall forest resilience.
result of fire injuries to the crown, bole,
forests to bark beetles in different ways
or roots (Hood and others 2018a). Similarly, Douglas-fir beetle, pine
(Fettig and others 2007). For example,
Levels of delayed tree mortality caused engraver, and western pine beetle caused
prescribed fire can affect the health
by bark beetles depend on numerous some tree mortality following prescribed
and vigor of residual trees; the size,
factors, including tree species; tree size; fires in western Montana. Mortality
distribution, and abundance of preferred
tree phenology; degree of fire-caused occurred shortly after prescribed fires,
bark beetle hosts; and the physical
injuries; initial and postfire levels of tree and unburned plots were unaffected.
environment within forests. Associated
vigor; the postfire environment; and However, following a regional mountain
reductions in tree density can alter
the scale, severity, and composition of pine beetle outbreak that started about 5
microclimates, affecting beetle fecundity
bark beetle populations and other tree years after treatments were completed,
(the ability to produce offspring) and
mortality agents in the area. 50 percent of ponderosa pines in control
fitness as well as the phenology (timing
of life cycle events) and voltinism A common management concern is that (untreated) plots and 39 percent in
(number of generations per unit of time) bark beetles might colonize and kill trees prescribe-burned plots were colonized
of bark beetles and their predators, that were injured by prescribed fire and
parasites, and competitors. Tree density otherwise would have survived. These
reductions can also disrupt pheromone trees may then serve as a source of It is reasonable to
plumes that attract bark beetles to a tree beetles and attractive semiochemicals as
during initial colonization. host volatiles are released by the boring assume that bark
activity of bark beetles. In addition to beetles and wildfires will
Volatiles (volatile organic compounds)
host volatiles, the pheromones produced increasingly interact to
released from trees are known to
by bark beetles might attract other shape western forests.
influence the behavior of many bark
beetles and result in additional levels of
beetles (Seybold and others 2006). Fettig
tree mortality over time.
Fire Management Today 16 JANUARY 2021 • VOL. 79 • NO. 1and killed. Almost no trees were killed that unburned areas do not benefit from 2006). Six and others (2002) showed that
by mountain pine beetle in thinned the positive effects of prescribed fire pine engravers are unable to colonize
plots and thinned-and-prescribe-burned (such as increased growing space due to and reproduce in chips. Moreover,
plots (Hood and others 2016). Thinning reduced tree density), which affect tree slash can be managed to minimize
treatments, with or without prescribed vigor and susceptibility to colonization colonization of residual trees by bark
fire, dramatically increased tree growth by bark beetles. Notable infestations in beetles (DeGomez and others 2015).
rates and production of resin ducts adjacent unburned areas are uncommon
(a measure of conifer defense against but can occur and should be watched EFFECTS OF WILDFIRES ON
bark beetles) relative to the control and for in case additional management is BARK BEETLES
prescribed fire treatments. warranted to limit tree losses (Fettig and Factors that influence tree mortality
Hilszczański 2015). caused by bark beetles are the same
In some cases, concerns about
maintaining large-diameter trees after wildfires as after prescribed fires.
MECHANICAL FUEL Our distinction is based not on ignition
following prescribed fire have been
justified. For example, Fettig and
TREATMENTS type but largely on differences in fire
McKelvey (2014) reported that most Factors such as stand density, host intensity and fire severity: most wildfires
tree mortality (78 percent) in the largest density, and average tree diameter are are higher in intensity and severity than
diameter class occurred during the first strong predictors of the severity of bark prescribed fires (though not always).
5 years after prescribed fire and that beetle infestations in the Western United Low-severity wildfires can induce tree
66 percent was caused by bark beetles. States. High levels of beetle-caused defenses against bark beetles (Hood and
Tree protection treatments (such as tree mortality (for example, greater others 2015). Resin-duct-related defenses
insecticides and semiochemicals) than 20 percent) should be expected take about 1 year after wildfire to form;
can be selectively used to protect following fuel reduction treatments during this time, fire-injured trees can be
individual trees from colonization by
bark beetles (Fettig and Hilszczański
2015). Furthermore, methods such as Firefighters should anticipate the potential for unusual
raking litter and duff from the bases of fire behavior in beetle-affected forests and the unique
large-diameter trees have been shown suppression challenges that can result.
to reduce prescribed fire severity and
levels of tree mortality (Fowler and
others 2010; Hood 2010). Additional
research is needed to determine under that retain high residual stand densities, more susceptible to colonization by bark
what conditions large-diameter trees are regardless of treatment effects. Although beetles, which might help explain some
most susceptible to delayed mortality thinning has long been advocated as a of the near-term increases in levels of
following prescribed fire and when tree measure to reduce beetle-caused tree beetle-caused tree mortality after some
protection treatments are warranted. mortality (Fettig and others 2007), wildfires and prescribed fires (Hood and
thinning prescriptions for fuel reduction others 2015, 2016). The level of tree
The limited number of studies on the differ from prescriptions for reducing injury influences bark beetle attraction,
effects of season of burn (spring versus susceptibility to bark beetles. In the with moderately injured trees being
fall) on levels of tree mortality caused by latter, crown or selection thinning most susceptible to colonization by bark
bark beetles show mixed results. Some (that is, removal of larger trees in the beetles (see, for example, Hood and
studies show increases in certain bark dominant and codominant crown Bentz 2007; Lerch and others 2016; and
beetle species following fall treatments classes) is typically required to achieve Powell and others 2012).
(that is, when fuels are drier and burns target threshold densities and residual
are more intense); see, for example, tree spacing as well as significant High-severity wildfires generally reduce
Fettig and others (2010). Other studies reductions in the abundance of preferred susceptibility to bark beetles by killing
show stronger effects following early- hosts. Nevertheless, thinning from large numbers of host trees. For example,
season burns (that is, when bark beetles below (for fuels reduction) does release research in subalpine forests in Colorado
are more active); see, for example, growing space, reducing a stand’s shows that spruce beetle outbreaks are
Schwilk and others (2006). More susceptibility to bark beetles. reduced for decades after high-severity
research is needed to fully define these wildfires (Bebi and others 2003), the
relationships in different forest types. A common concern following dominant fire regime in these forests. As
mechanical fuel treatments is that bark with prescribed fires, bark beetles routinely
Although most of the tree mortality beetles could breed in logging residues cause additional levels of tree mortality
caused by bark beetles following (chips and/or slash) and emerge to after wildfires, but infestations in adjacent
prescribed fire occurs during the first few colonize residual trees. However, most unburned areas are uncommon (Davis
years, this pattern might differ in adjacent studies indicate that this is uncommon and others 2012; Lerch and others 2016;
untreated areas. The reason, in part, is (see, for example, Fettig and others Powell and others 2012).
Fire Management Today 17 JANUARY 2021 • VOL. 79 • NO. 1EFFECTS OF BARK BEETLE
OUTBREAKS ON FUELS
AND FIRE BEHAVIOR AND
SEVERITY
Although fuel reduction treatments
and wildfires can affect bark beetles,
the reverse is also true: bark beetles
can alter wildfire behavior by changing
fuel conditions. Of the bark beetle–
host systems to consider, the effects
of mountain pine beetle in lodgepole
pine (Pinus contorta) have been most
intensively studied (table 1), and for
good reason: mountain pine beetle alone
is responsible for almost half of the
total area affected by bark beetles in the
Western United States. All other bark
beetle–host systems have received less
attention, some little or none (table 1).
Figure 2—Bark beetles can cause dramatic changes to forest canopies in coniferous forests.
Fire behavior in beetle-affected forests For example, during and after mountain pine beetle (Dendroctonus ponderosae) outbreaks,
largely depends on the severity of lodgepole pine (Pinus contorta) canopies transition from the green-infested stage (A) to the
the outbreak (the proportion of trees red stage (B) in about 1 to 3 years and then to the gray stage (C), which lasts from about 3 to
colonized and killed) and the amount 25 years following the outbreak. The likelihood of crown and spot fires is greater during the
of time since the outbreak occurred. red stage and possibly reduced during the gray stage. Bark beetle activity frequently results in
Jenkins and others (2008, 2014) use the a mosaic of green, red, and gray trees (D) as trees are attacked and killed over several years
term “bark beetle rotation” to describe (usually 2 to 6 years for mountain pine beetle), which can complicate fire behavior prediction in
the period from the start of a bark beetle these forests. Photos: J. Runyon, USDA Forest Service.
outbreak to the next outbreak within
susceptible forests. In the “endemic trees turn red (fig. 2B). The final stage is energy required for fuels to ignite and
phase,” beetle-caused tree mortality the “gray” stage, when needles fall off burn. Trees colonized and killed by
is limited (for example, to less than 2 the trees (fig. 2C). The timing of needle bark beetles rapidly dry out and lose
trees per acre per year) and generally fade and color change varies considerably most of their water content by the first
isolated to stressed hosts. In the by tree species, bark beetle species, and summer following attack as needles
“epidemic phase,” beetles colonize and geographic location. For example, in transition from green to red (fig. 2A,
kill large numbers of susceptible hosts. the mountain pine beetle–lodgepole 2B). For example, the twigs and needles
In the “post-epidemic phase,” beetle pine system, the green-infested stage of lodgepole pine killed by mountain
populations subside and most beetle- lasts for about 1 year; the yellow and red pine beetle lose 80 to 90 percent of
killed trees fall to the forest floor. The stages last for about 1 to 3 years; and the their water content within 1 year of
endemic and post-epidemic phases can gray stage lasts for about 3 to 25 years attack (Jolly and others 2012a; Page
last for decades to centuries, whereas the (Klutsch and others 2009). It is important and others 2012). The loss of moisture
epidemic phase usually lasts from 2 to to note that, during an outbreak, trees increases flammability by shortening
10 years. are attacked and killed over several years, time to ignition, lowering temperature
Recently attacked trees are referred to and cumulative levels of tree mortality at ignition, and raising heat yields when
as “green-infested” (fig. 2A). As needles vary considerably even within the same burned (Jolly and others 2012a; Page
fade, trees enter the “yellow” stage. In bark beetle–host system. Therefore, a and others 2012). Reduction in moisture
the “red” stage, needles on beetle-killed forest often contains trees and stands content explains nearly 80 percent of the
in multiple stages and phases of a bark increase in needle flammability (Page
beetle rotation at the same time (fig. 2D). and others 2012). Similar reductions in
foliage moisture content and increases
Not surprisingly, beetle- CROWN AND CANOPY FUELS in flammability have been documented
induced changes to foliar Not surprisingly, beetle-induced changes in Engelmann spruce (Picea engelmannii)
to foliar moisture have the greatest killed by spruce beetle (Page and others
moisture have the greatest effects on flammability. This is because 2014) and Douglas-fir killed by Douglas-
effects on flammability. water is a heat sink and moisture in fir beetle (Giunta 2016).
plant tissues increases the amount of
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