UW Climate Impacts Group
http://www.yakima.net/
Climate change, fire,
insects, and disturbance
interactions: adaptation
challenges in the West
Don McKenzie
Pacific Wildland Fire Sciences Lab
U.S. Forest Service
Hypotheses about ecosystem change in the West
• Increasing moisture limits will alter (tree and other) species
composition and productivity by
• locally favoring more xeric species.
• exacerbating episodes of vegetation dieback.
• altering mortality and turnover rates.
• Underlying ecological mechanism = large-scale shift to a
negative water balance.
• Disturbance will be the principal agent of ecosystem change
• Late 20th-century trends such as increasing insect mortality or
fire area burned may be replaced by more abrupt changes.
• Disturbance interactions produce complex nonlinear behavior,
operate at multiple scales, and may be constrained by physical
limits.
Western Mountain Initiative (WMI) 2008
Disturbance drives ecosystem changes
Climatic change
warmer temperatures
more severe and extended droughts
New fire regimes
More frequent fire
More extreme events
Greater area burned
Much of the same logic
applies to insect outbreaks
Fire resets
succession,
temporal scale
associated with
fire rotation.
The disturbance pathway is quicker
Species responses
Fire-sensitive species
Annuals & weedy species
Specialists with restricted ranges
Deciduous and sprouting species
Mature trees buffer against
effects of warmer climate,
temporal scale associated
with species longevity.
Habitat changes
Broad-scale homogeneity
Truncated succession
Loss of forest cover
Loss of refugia
Fire-adapted species
Climate and fire area burned, 1977-2003:
an ecologically based study in the American West
• Generalized linear models to
scale area-burned statistics to
ecoprovinces.
• Predictive models of fire area
burned based on climatology.
• Potential for ecologically
meaningful future projections.
Littell et al. (2008)
At the scale of ecoprovinces
Fuel moisture associated with
current climate is the limiting
factor.
Fuel abundance and
continuity associated with
previous climate is the limiting
factor.
Northern mountain provinces, regional fire
episodes, and climatic change
MODIS
• As temperature increases, the
atmosphere evaporates more
water from the landscape and
plant tissues.
• This produces larger than normal
areas of depleted fuel moisture
during the fire season.
• Regional synchronization of fires
occurs.
Northern Rockies, July 2003
Arid Southwestern provinces, regional fire
synchrony, and climatic change
• Increasingly severe and
prolonged droughts are expected.
• But interannual cycles, e.g.,
ENSO, can maintain the pattern
of fuel continuity.
• Invasives like cheatgrass and
buffelgrass could change
everything.
Rapid climatic change may send ecosystems
across disturbance thresholds
For example
Drastic increase in
fire severity
Mountain pine beetle
Doubling of insect
reproductive cycles
Pandora moth
Why temperature increase releases
mountain pine beetle populations
• Population synchronized by
temperature (onset of
spring).
• Rate of generation turnover
increases with temperature
increase.
• Mountains were a barrier
until recently; limitation is
now forest extent and
continuity.
Figure courtesy Allan Carroll
MPB outbreaks in high-elevation whitebark pine
Railroad Ridge, ID
Eastern WA
Photo by J. Logan
July 2005, Railroad Ridge, ID
Quickbird Satellite Imagery
Threshold behavior is complex
For example
Mountain pine beetle
If insect population cycles are
not synchronized with seasons,
outbreaks are not likely.
Pinus contorta (lodgepole pine)
Hicke et al., J. Geophys. Res.-Biogeosciences, 2006
But challenges for adaptation are at the “landscape scale”
Yosemite NP fires >40 ha
and <40 ha
Yellowstone NP fires and mountain pine beetle
Severity
Lutz 2008
Simard 2008
Patch structures from mixed-severity fire
Tripod fire, north-central Washington, 2006
Stress complexes: synergistic
effects on ecosystems
McKenzie, D., D.L. Peterson, & J.S. Littell. In press. Global warming and stress
complexes in forests of western North America. In “Forest Fires and Air Pollution Issues”,
eds. A. Bytnerowicz, M. Arbaugh, C. Andersen, & A. Riebau. Elsevier Science, Ltd.
Mixed conifer
(Sierra Nevada,
southern California)
Ozone and particulate pollution
Fire exclusion high stand densities
Extended warm period insects
Ponderosa pine, Jeffrey pine, white fir die
Fuels accumulate severe fires
Exotic plants increase where fires do occur.
Sierra Nevada mixed conifer
Global
warming
Higher temperatures &
more severe and
extended droughts
Bark beetles
and defoliators
Fire exclusion
Ozone
High stand
densities
Fuel
accumulation
Ponderosa and
Jeffrey pine
mortality
Large severe fires
Changes in species composition (including exotics)
Sierra Nevada mixed conifer
Global
warming
Higher temperatures &
more severe and
extended droughts
Disturbance
interactions
are central
but not the
only factor.
Bark beetles
and defoliators
Fire exclusion
Ozone
High stand
densities
Fuel
accumulation
Ponderosa and
Jeffrey pine
mortality
Large severe fires
Changes in species composition (including exotics)
Lodgepole pine
Extended warm period, insects, pines die, fuels
accumulate, sets up for large fires. Vulnerable
age classes.
Interior lodgepole pine
Global
warming
Higher temperatures & more
severe and extended droughts
Bark beetles
and defoliators
Stand-replacing
fire regime
Extensive mature
cohorts (70-80 yrs)
Lodgepole pine mortality
Large severe fires
Fuel
accumulation
Salvage logging
Changes in species composition (including exotics)
Interior lodgepole pine
Global
warming
Higher temperatures & more
severe and extended droughts
Bark beetles
and defoliators
Here too: note
context of standreplacing fire.
Stand-replacing
fire regime
Extensive mature
cohorts (70-80 yrs)
Lodgepole pine mortality
Large severe fires
Fuel
accumulation
Salvage logging
Changes in species composition (including exotics)
Disturbance interactions
Timing of wildfires and insect
outbreaks can produce positive or
negative feedbacks.
Thresholds can be reached via
cumulative effects or one big event.
Spatial pattern matters.
Adaptation strategies
Connie Millar
Nate Stephenson
Scott Stephens
Ecol. Appl. 17:2145-2151, 2007
Create resistance to change
Promote resilience to change
Enable forests to respond to
change
Increasing precipitation
Energy-limited
ecosystems
Adaptation options change as
global warming continues
Resistance
Resilience
Responding
(high-elevation forests)
?
Water-limited
ecosystems
(eastside & low-elevation
westside forests)
Increasing temperature
Adaptation strategies
• Anticipate big surprises
Expect mega-droughts, larger fires,
vegetation dieback, species
extirpations, etc.
Incorporate these expectations in
planning.
CCSP 2008
Empirical work, synthesis, and modeling to inform adaptation (WMI 2008-2013)
Stehekin
Lake McDonald
RHESSys watersheds
Coupled modeling of mountain hydrology,
forest vegetation, and disturbance
Merced River
Frijolito
Snake River
Thanks!
Craig Allen
Allan Carroll
Ellen Eberhardt
Jeff Hicke
Jeremy Littell
Jim Lutz
Connie Millar
Dave Peterson
Martin Simard
Scott Stephens
Nate Stephenson
(anyone I forgot)