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

Status
Completed
Start Date
June, 2007
Recently thinned unit that was subsequently burned in the Tripod Complex fires.

We measured the relative effect of two common fuel treatments: (1) mechanical thinning only, and (2) mechanical thinning followed by prescribed burning.

Fire severity was markedly different between the two treatments. There was strong evidence that, without treatment of surface fuels, thinning alone is not a viable surrogate for prescribed fire in these dry, mixed-conifer forests. In contrast, thinning followed by prescribed burning to reduce surface fuels appears to be an effective strategy for mitigating wildfire severity.

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

Project Description

The 2006 Tripod Complex fires in Washington state offered a rare opportunity to evaluate how a large number of well-documented fuel treatments affected fire severity (e.g., tree mortality) and supported 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-Wenatchee National Forest.

Of the many fuel treatments the Methow Valley Ranger District had conducted over the previous 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 were available for the fuel treatment units.

In this study, we (1) measured how effective fuel treatments were in reducing fire severity, (2) assessed the value of past treatments and past fires as points of defensibility for fire suppression, and (3) compared actual measures of fire severity with predictions made in the Fire and Fuels Extension of the Forest Vegetation Simulator (FFE-FVS).

Results provided useful 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.

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

Purpose and Scope

Evaluate differences in wildfire severity in forests with thin treatments, thin-and-prescribed-burning treatments, and no treatment within the Tripod Complex fires of north-central Washington state.

Methods

  • Twenty-four units were selected for the study
    • Eight thinned units
    • Eight units thinned and, subsequently, treated with prescribed fire
    • Eight units with no record of tree harvest
  • The history of burning, thinning, and harvesting was collected for each site
  • Sites were marked with a permanent stake, and sampled within circular plots along a systematic grid.

Key Findings

  • Tree mortality and other fire-severity measures are significantly different between thin and prescribed burn units and other treatments (thin-only units and controls). Results are significant even when comparing large-diameter trees.
  • There is no significant difference in tree mortality and other severity measures between thin units and control units.
  • Unit size does not appear to be a factor in treatment effectiveness.

Project Deliverables

Final Report to the Joint Fire Science Program (2010)

Project Deliverables

Publications

Last updated January 18, 2024
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