Download April 2011 PDF - International Journal of Wilderness

SCIENCE and RESEARCH
Climate Change and
Wilderness Fire Regimes
BY DONALD McKENZIE and JEREMY S. LITTELL
Abstract: A major challenge to maintaining the integrity of wilderness areas in a warming world will
be adapting to changing disturbance regimes. Projections from both simulation models and empirical
studies suggest that fire extent and probably fire severity will increase under the warmer drier
conditions predicted by most global climate models. Projections are limited, however, not only
simply because burnable area is finite, but also because water-balance dynamics may decouple
existing relationships between drought and area burned across many landscapes, particularly forested
wilderness areas. Disturbance interactions, and interactions between global warming and
human-caused stresses such as air pollution, may compromise the ability of wilderness areas to
respond to climate change. Adaptive strategies must be creative and flexible, especially considering
the limited acceptability of active manipulations, such as assisted migration and fuel treatments, in
protected areas.
Introduction
A major challenge to maintaining the integrity of wilderness
areas in a warming world will be adapting to changing disturbance
regimes. Projections from both simulation models
and empirical studies suggest that fire extent and probably
fire severity will increase under the warmer drier conditions
predicted by most global climate models (Flannigan et al.
2001; Gillett et al. 2004; McKenzie et al. 2004). Outbreaks
of cambium-feeding insects may also increase as insect life
cycles accelerate (Logan and Powell 2001; Hicke et al. 2006)
and host species become more vulnerable from drought
stress (Oneil 2006). Disturbances are likely to act synergistically
and be further affected by human-caused factors such
as air pollution, extraction of resources, and land-use change
(McKenzie et al. 2009). Wilderness areas will feel the effects
of natural and human disturbances that originated outside
their boundaries. For example, in the American West,
regional haze inside park and wilderness areas often comes
from sources hundreds of kilometers upwind (McKenzie et
al. 2006).
It is essential that we understand the limits to projections
of future fire. In the late 20th century, climate was the
principal top-down control on the extent and spatial pat-
PEER REVIEWED
22 International Journal of Wilderness APRIL 2011 VOLUME 17, NUMBER 1
terns of wildfire (Gedalof et al. 2005; Littell et al. 2009;
Gedalof 2011). Climate drivers will continue to be important
through the 21st century, but the quantitative
relationships that are apparent from recent models, whether
they be simulation based or empirically based, may change
or be superseded by other controls. For example, annual area
burned by fire cannot increase indefinitely into the future,
even as warmer drier weather increases in both frequency
and magnitude. Eventually there would not be the available
biomass to sustain a perpetual monotonic increase.
In this article we briefly review model projections of
future fire regimes and identify one particular limitation to
projections that is based on the relationship of fire to broadscale
water relations. We also highlight uncertainties in models
that are a result of a scale mismatch between the models and
their application to wilderness landscapes. We focus on
western North America, giving an example from four national
parks, because this is the geographic area of our expertise,
while suggesting that the water-balance dynamics have global
application. We also briefly identify interactions of fire with
other disturbances and give two examples of feedbacks and
cascading effects. We conclude by examining contrasting
strategies for adapting to changing fire regimes.