Fire and Environmental Research Applications Team

Do Fuel Treatments Reduce Fire Severity? Evaluating Treatment Effectiveness in the 2006 Tripod Complex Fire

The 2006 Tripod Complex fires in the northern Washington offer a rare opportunity to evaluate how a large number of well-documented fuel treatments affected fire severity and facilitated operational aspects of fire suppression. The wildfires initiated as two lightning strikes and spread over 175,000 acres of mixed conifer forest in the Okanogan National Forest.

Of the many fuel treatments the Methow Valley Ranger District conducted over the past 10 years, several were used for burnout operations near the town of Winthrop, Washington. An additional 19 thinned units and 10 thinned and prescribed-burn units were involved in the wildfire. Woody fuel loading, duff depths, and forest stand characteristics are available for the fuel treatment units.

This study will:

• Quantify how effective fuel treatments were in reducing fire severity
• Compare actual measures of fire severity with predictions made in the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS).

Additional funding has been provided by the Pacific Northwest Research Station to:

• Evaluate fire severity patterns in managed forest within the area burned during the Tripod Fire in 2006.
• Evaluate wildfires effect on regeneration in the area burned by the Tripod Fire, near Winthrop.
• Produce a camera-ready manuscript
• Assess the effectiveness of fuel treatments in modifying fire behavior and fire severity in the 2006 Tripod Complex fire.

Retrospective fire behavior will be modeled using real-time fire weather data and daily fire progression maps to provide a context for observed and modeled fire effects.

This study will provide critical information on the effectiveness of fuel treatments in modifying fire behavior and fire severity, and will inform the design of effective fuel treatment strategies and prescriptions as a component of adaptive management in dry interior forests.

Companion Study Considers Severity in Regenerating Stands

Studies have shown significant relationships between fire severity and fuel treatment residue, but have focused on forest types with mixed-severity and low fire regimes that are not typical of all dry forest systems in the West.

The Okanogan-Wenatchee National Forest on the east side of the Cascade Range in Washington has implemented silvicultural treatments to increase regeneration and reduce fire risk, including several fuel reduction strategies to alter fire behavior: thinning, prescribed fire, and small clearcuts.Clearcuts, also called regeneration cuts, coupled with prescribed fire, were implemented specifically to promote regeneration of tree species, including ponderosa pine, Douglas-fir, subalpine fir, Engelmann spruce, and western larch.

In 2006, the 80,000-ha Tripod Complex Fire burned through many of these fuel-treatment and regeneration cut areas, providing an opportunity to analyze the relationship between forest management and wildfire dynamics.

University of Washington graduate student Christina Lyons-Tinsley, along with FERA's field crew, is analyzing fire severity in regenerating stands to determine how fuels and other factors contributed to surface fire intensity and spread.

Specifically, we will:

• Compare fire severity between regeneration cuts, the surrounding matrix, and thinned units
• Analyze fire severity among regeneration units including the relationship between fire effects and stand structure.

Preliminary results indicate that regeneration units greatly modified fire behavior and minimized mortality in young trees, resulting in "green islands" in landscapes that were otherwise burned with high severity.

Team Lead: Susan Prichard

We acknowledge funding from the Joint Fire Science Program under Project JFSP 07-1-2-13.