Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture

Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
United States Department of Agriculture

                                          JANUARY 2021 • VOL. 79 • NO. 1

                           in Wildland
                           Fire Research
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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
                                                              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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JANUARY 2021 • VOL. 79 • NO. 1

Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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

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
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

Warren E. Heilman. . . . . . . . . . . . . . . . . . .  24        Nicholas F. McCarthy, Matthew P.
                                                                  Thompson, and David E. Calkin. . . . . . . . . 69

                                                                                                                                       for Contributors
Fire Management Today
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
                                                                                     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
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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;

                                                                                               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

                                                                                               appropriate spatial scales (Keane and
                                                                                               others 2012).

                                                                                               ARE THERE
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

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Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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        ( or Heather
sampling procedures; we often take             fuel sampling were better able to make      Heward (
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                                             
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
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
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
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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
Developments in Wildland Fire Research - JANUARY 2021 VOL. 79 NO. 1 United States Department of Agriculture
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. 1
Research 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. 1
Figure 1—Goat perched on snag (top)
                                                                                     browsing a dogwood on the Mark Twain
                                                                                     National Forest in Missouri.
                                                                                     Photo: Gina Beebe.

                                                                                     TESTING TARGETED
                                                                                     “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

                                                                                     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. 1
Goats 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.
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. 1
Bark 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. 1
Table 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. 1
Fettig 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, 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. 1
and 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. 1
 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

 Fire Management Today                                            18                                      JANUARY 2021 • VOL. 79 • NO. 1
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