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made probabilistically (Intergovernmental
Panel on Climate Change 2007).
Downscaling climate models to finer
spatial resolution, whether dynamically
or statistically, increases uncertainties,
and reaches a limit between ~ 4 to 12
kilometers (2.4 to 7.4 miles) resolution
below which projections are known to
be less accurate than at coarser scales
(Salathé et al. 2007). Climate projections
for individual wilderness areas or
parks do not carry much confidence,
therefore, because future microclimates
depend on fine-scale relationships
between the atmosphere and the land
surface, which are as yet not well captured
by climate models.
Similarly, fire dynamics are most
complex and least predictable at intermediate
scales (McKenzie et al. 2011).
At the scales of forest stands or inventory
plots, fire behavior and fire effects
models function reasonably well, given
accurate representation of local weather
conditions. At regional to continental
scales, aggregate statistics (e.g., annual
area burned) can be modeled as a function
of climate variables with reasonable
success (Littell et al. 2009, 2010). The
coupled uncertainties of climate and
fire dynamics at “landscape” scales
have confounded all but the most
rudimentary attempts to project future
fire regimes (Cushman et al. 2007,
Keane et al. in press). Furthermore,
none of these initial efforts has incorporated
the nonconstant water-balance/
fire associations that we discuss above.
Fire, Other Disturbances,
and Cascading Effects
In the American West, and in much of
the rest of the world, fire is an integral
ecosystem process more than just an
external perturbation. Fire acts at different
spatial and temporal scales from
other processes (including other disturbances),
however. In particular, its
pulsed nature contrasts with the rela-
tively continuous processes of
vegetation growth and succession, or
the longer pulses (annual to multiannual)
of insect outbreaks, making the
analysis of interactions problematic
(McKenzie et al. 2011). For example,
the timing of bark beetle outbreaks
vis-à-vis wildfire in lodgepole pine
(Pinus contorta var. latifolia) forests of
western North America determines
whether fires are more or less severe
than they would have been without
insect disturbance (see figure 3). Dead
needles that are still in the canopy
provide a short pulse of very flammable
fuels, increasing the intensity of
crown fires (figure 3). Once these
needles drop, fine surface fuels increase
but canopy fuels decrease. Differential
regeneration associated with cone
serotiny and varying light levels in the
understory from tree mortality, and
Figures 3a and 3b—Fire severity on the Tripod Complex Fire of 2006, north-central Washington State,
United States, depends on previous insect disturbance. Photo 3a shows the stand unaffected by mountain
pine beetle (Dendroctonus ponderosae) before fire, and 3b shows the stand with significant
beetle-caused mortality before fire. Photos courtesy of C. Lyons-Tinsley.
APRIL 2011 VOLUME 17, NUMBER 1 International Journal of Wilderness 25