CLIMATE, MOUNTAIN ECOSYSTEMS, AND DISTURBANCE ACROSS SCALES:
CHALLENGES FOR THE NEXT CENTURY
MCKENZIE, DON
USDA Forest Service, Pacific Wildland Fire Sciences Lab, US Forest Service, Seattle, WA
With input from: Craig Allen, Sam Cushman, Paul Hessburg, Lara Kellogg, Jeremy Littell, Carol
Miller, Bruce Milne, Dave Peterson, Nate Stephenson, and others
Global warming ensures that mountain ecosystems are driven by non-equilibrium dynamics.
Non-stationary climate forcing and dominance of disturbance regimes, particularly fire, by
extreme events are two factors that limit our ability to understand and predict ecosystem change.
Land-use changes and other pressures on mountain resources make non-reversible changes
more likely and landscapes more vulnerable, while making accurate predictions more urgent. I
present three challenges to researchers studying climate, mountain ecosystems, disturbance,
and their interactions. These issues do not appear to be tractable using current methodology,
given limited resources, and may require new conceptual advances and thinking outside the box.
1) understanding the biophysical controls on species distribution, abundance, and migration, with
emphasis on limiting factors. I focus on tree species of western mountains and energy and water
as canonical limiting factors. 2) understanding fire regimes in the context of climatic variability. I
focus on a multivariate approach with particular attention to fire severity. 3) Linking drivers and
responses across scales: scaling laws and scale invariance vs. the need for transfer functions. I
use this issue to inform challenges 1 and 2, in that their solutions most likely involve analyses at
multiple scales. As climatic change continues and possibly accelerates, the demand for quick
simple answers will intensify, whereas their likelihood will diminish. One response to this
conundrum is to focus on issues and methods that will identify potential surprises and abrupt or
non-reversible changes in mountain landscapes.