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Fire and Environmental Research Applications Team
Pacific Wildland Fire Sciences Laboratory

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Abstracts

Linking Recent Historical and Current Forest Vegetation Patterns to Smoke and Crown Fire in the Interior Columbia River Basin

Little information is available on how shifts in forest composition and structure over time resulting from natural succession, disturbance, and human intervention have changed landscapes with respect to fuel build-up, wildfire and prescribed fire smoke production, and vulnerability to crown fires. This study compares the fuel loading, modeled smoke production, and crown fire of recent historical and current time periods based on vegetative attributes in 337 subwatersheds on all ownerships within the Interior Columbia River basin. Vegetation cover and structure, and management disturbance features were continuously delineated from recent historical (1930s to 1960s) and current period (1985-1993) aerial photographs of the sampled subwatersheds. Results of change analyses were reported for 13 province-scale Ecological Reporting Units (ERU) and for selected subwatersheds.

Fuel loading increased over the sample period in 8 of the 13 ERUs; 6 of the changes were significant (P> or equal to 0.2). The largest mean difference was a fuel loading increase of 10.8 megagrams/hectare on the Lower Clark Fork ERU. In general, fuel loading increase was positively correlated with forest vegetation composition shifts from open patches of seral species such as ponderosa pine and western larch to dense patches of mixed coniferous forests. Decreases in fuel loading were positively correlated with recent wildfires or human activities such as logging followed by fuels treatment. Fuel loading increase was responsible for noted increases in modeled smoke production by wildfires and vulnerability to crown fires. Under current conditions, modeled PM 10 smoke production from wildfire was two to four times the amount from a prescribed fire.

Individual subwatersheds displayed much larger changes over time than at the ERU scale. Change at the subwatershed scale was typically related to wildfires, human management activity, or natural succession. For example, the Upper Coeur d' Alene subwatershed 0501, one of 5 subwatersheds that receive special GIS analysis in this study, displayed a large increase in fuel loading over time, with a corresponding large increase in modeled smoke production and crown fire vulnerability. The subwatershed was partially burned by major wildfires in the early 1900s, with a stand of grand fir, Douglas-fir, and ponderosa pine regenerating during the 1920s and 1930s. Under a fire-exclusion policy, forests matured to predominately understory reinitiation and young, multi-story structures resulting in the noted fuel loading increase.

Ottmar, Roger D.; Alvarado, Ernesto; Hessburg, Paul F. 1998. Linking recent historical and current forest vegetation patterns to smoke and crown fire in the Interior Columbia River Basin. In: Weber, R, Chair. Proceedings 13th Conference on Fire and Forest Meteorology. Moran, WY: International Association of Wildland Fire.

U.S. Forest Service - PNW- FERA
Last Modified: Monday, 16 December 2013 at 14:18:40 CST


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