Geoscience Reference
In-Depth Information
Global
warming
Higher temperatures &
more severe and
extended droughts
Fire exclusion
Ozone
High stand
densities
Bark beetles
and defoliators
Disturbance
interactions
are central
but not the
only factor.
Fuel
accumulation
Ponderosa and
Jeffrey pine
mortality
Large severe fires
Changes in species composition (including exotics)
FIGURE 8.4
Stress. complex. in. Sierra. Nevada. and. southern. Californian. mixed-conifer.
forests.. The. effects. of. disturbance. regimes. (insects. and. ire). and. ire. exclusion. are. exacer-
bated. by. global. warming.. Stand-replacing. ires. and. drought-induced. mortality. contribute.
to. changes. in. species. composition. including. increased. abundance. of. exotic. species.. (From.
McKenzie,.D.,.D.L..Peterson,.and.J.S..Littell..2009..Global.warming.and.stress.complexes.in.
forests.of.western.North.America..In.
Wildland ires and air pollution
,.Eds..A..Bytnerowicz,.
M..Arbaugh,.A..Riebau,.and.C..Anderson..Amsterdam:.Elsevier.Science,.319-37.).
WMI. researchers. have. begun. to. document. disturbance. interactions,. and. how.
these. in. turn. affect. ecosystem. process,. by. building. conceptual. models. of. “stress.
complexes”.(Allen.2007;.McKenzie.et.al..2009).and.convening.a.structured.work-
shop. to. establish. a. research. agenda. for. this. dificult. but. key. problem. area.. Early.
results. include. conceptual. frameworks. for. linking. global. warming. to. disturbance.
interactions. in. WMI. bioregions. (Figure 8.4). and. guidelines. for. landscape. distur-
bance.modeling.under.climatic.change.(Cushman.et.al..2007).
s
imulaTing
e
CosysTem
r
esponse
To
C
limaTiC
C
hange
The. response. of. hydrologic. and. ecological. processes. of. Western. US. mountains. to.
historical.climatic.extremes.provides.insight.on.how.these.systems.may.vary.in.their.
responses.to.future.climates.(Baron.et.al..2000a)..The.climates.of.Western.mountain.
catchments. vary. by. their. location. in. maritime,. continental,. windward,. or. leeward.
locations,.as.well.as.by.latitude.and.elevation..We.used.RHESSys,.a.spatially.dis-
tributed,.dynamic.process.model.of.water,.carbon,.and.nitrogen.luxes,.to.compare.
measures.of.net.primary.production,.evapotranspiration,.soil.moisture,.and.stream.
low.across.sites.in.response.to.climatic.extremes..The.ive.highest.and.lowest.pre-
cipitation,. snow. depth,. and. temperature. years. when. compared. with. their. 47-year.
