Document: NAT-3-9-3

Altered disturbance regimes: fire, fuels, and forest structure

STEPHENSON, N.L.* ¹, T.W.SWETNAM ² and T.T.VEBLEN ³

USGS Western Ecological Research Center, Sequoia and Kings Canyon Field Station, Three Rivers, CA USA ¹
University of Arizona, Tucson, AZ USA ²
University of Colorado, Boulder, CO USA ³

Abstract:
A century of fire suppression has had a greater effect on western montane forests than the preceding several centuries, or even millennia, of changing climate and disturbance regimes. In many areas, fire suppression has resulted in denser forests, shifts in species composition, increased fuel loads, and a consequent increase in the occurrence of abnormally severe wildfires. Layered upon these changes will be further changes induced by rapid climatic change in the near future. In the short term, climatic change will affect the quantity and nature of forest fuels through changes in primary production and mortality rates. In the long term, fuels also will be affected by changes in species composition. Paleoecological records suggest that a warming climate may lead to a propensity for fires that are more frequent, smaller, and that collectively burn more total area than in the past. Forests in which present-year climate is overwhelmingly the most important determinant of fire occurrence may change so that the preceding few years of climate also become important. However, direct human influences on fire regimes change somewhat unpredictably through time, complicating the prediction of future forest conditions.

Keywords: climate change, disturbance, fire, forest structure

This abstract is being presented at: 9:00 AM in session:
Symposium # 2: Stressors in Western Mountain Ecosystems: Detecting Change and Its Consequences.