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.
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.
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.