Fire and Environmental Research Applications Team

Landscape Analysis of Fuel Treatment Longevity and Effectiveness in the 2006 Tripod Complex Fires	Do Fuel Treatments Reduce Fire Severity? Evaluating Treatment Effectiveness in the 2006 Tripod Complex Fires
We acknowledge funding from the Joint Fire Science Program under Project #09-1-01-19.	We acknowledge funding from the Joint Fire Science Program under Project #07-1-2-13.

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

Final Report [.pdf 8.72 MB]

Joint Fire Science Program Science Brief [.pdf 446 kb]

Fuel Treatments Reduce the Severity of Wildfire Effects in Dry Mixed Conifer Forest, Washington, USA.

Abstract: To address hazardous fuel accumulations, many fuel treatments are being implemented in dry forests, but there  have been few opportunities to evaluate treatment efficacy in wildfires. We documented the effectiveness of thinning and  prescribed burning in the 2006 Tripod Complex fires. Recent fuel treatments burned in the wildfires and offered an opportunity to evaluate if two treatments (thin only and thin and prescribed burn) mitigated fire severity. Fire severity was markedly different between the two treatments. Over 57% of trees survived in thin and prescribed burn (thinRx) units versus 19% in thin only (thin) and 14% in control units. Considering only large-diameter trees (>20 cm diameter at breast height), 73% survived in thinRx units versus 36% and 29% in thin and control units, respectively. Logistic regression modeling demonstrates significant reductions in the log-odds probability of tree death under both treatments with a much greater reduction in thinRx units. Other severity measures, including percent crown scorch and burn severity index, are significantly lower in thinRx units than in thin and control units. This study provides strong quantitative evidence that thinning alone does not reduce wildfire severity but that thinning followed by prescribed burning is effective at mitigating wildfire severity in dry western forests.

Prichard, S.J., Peterson, D.L., Jacobson, K. 2010. Fuel treatments reduce the severity of wildfire effects in dry mixed conifer forest, Washington, USA. Canadian Journal of Forest Research. 40: 1615-1626.

Link to complete paper

Fuel Treatment Effects on Postfire Tree Mortality and Beetle Attack in Dry Mixed Conifer Forests, Washington State, USA

Abstract: Fuel reduction treatments are increasingly used to mitigate future wildfire severity in dry forests, but few opportunities exist to assess their effectiveness.  We evaluated the influence of fuel treatment, tree size and species on direct and delayed tree mortality following a large wildfire event that involved recent thin-only and thin and prescribed burn (thin-Rx) units.  In thin-only and unmanaged control units, most trees died the first year following fire (65% and 52%, respectively) versus 37% in thin-Rx units.  Third-year mortality followed a similar trend (79% and 73% in thin-only and control units) versus 51% in thin-Rx units.  Percent crown scorch is a strong predictor of mortality and is highly dependent on fuel treatment.  Based on continuation ratio modeling, first-year mortality is predominantly in small diameter trees but lowest for thin-Rx units.  For trees that survived to the third year postfire, the probability of subsequent tree mortality is low across all treatments but slightly higher for large diameter trees in control and thin-only units. Across all treatments, Pinus ponderosa has a lower probability of mortality following fire than Pseudotsuga menziesii.  Finally, log-odds probability of beetle attack on surviving trees is highest in large diameter trees within thin-only treatments and lowest within thin-Rx treatments.  This study contributes further evidence supporting the effectiveness of thinning and prescribed burning on mitigating post-fire tree mortality.  Our sampling design in treated and untreated fuels enabled us to evaluate models using pre-wildfire stand data.  This approach may assist in the development of operational models that use variables collected prior to a wildfire event to estimate potential tree mortality.  We also present evidence that a combination of thinning and prescribed burning is associated with lower incidence of bark beetle attack.

Prichard, S.J.; Kennedy, M.C. In review. Fuel treatment effects on postfire tree mortality and beetle attack in dry mixed conifer forests, Washington State, USA. International Journal of Wildland Fire.

Landscape Analysis of Fuel Treatment Longevity and Effectiveness in the 2006 Tripod Complex Fires

Final Report [.pdf 2.16 MB]

To successfully implement fuel reduction projects, local fire and fuel managers need information about the relative effectiveness and longevity of fuel treatments at small to large spatial scales.  In the initial study we determined whether recent fuel treatments mitigated fire severity following the 2006 Tripod Complex wildfires.  A unique opportunity then existed to extend this research to a landscape analysis of 277 fuel treatments that were involved in the wildfires and span a range forest types, treatments, and time since treatment.

Geospatial, harvest, and prescribed burn records werer available for all fuel treatments.  Past harvests include clearcuts, shelterwood cuts, and thins.  Many units were broadcast burned following harvest. In this study, we:

• Validated the geospatial records of past fuel treatments and ground-truth existing fire severity maps
• Analyzed and model the relative effects of treatment type, size and time since treatment on fire severity
• Compared actual landscape patterns of fire severity to modeled fire severity.

Abstract for submitted article

GIS Data Layers Used

• Tripod data layers, summarized geodatabase
• Firefighting records

Team Lead: Susan Prichard