USDA Forest Service

Fire and Environmental Research Applications Team


Fire and Environmental Research Applications Team
Pacific Wildland Fire Sciences Laboratory

400 N 34th Street, Suite 201
Seattle, WA 98103

(206) 732-7800

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Icon of magnifying glassLandscape Analysis of Fuel Treatment Longevity and Effectiveness in the 2006 Tripod Complex Fires

Icon of magnifying glassDo 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 tree mortality following a large wildfire event in recent thin-only, thin and prescribed burn (thin-Rx) units. Of the trees that died within the first 3 years, most died in the first year regardless of treatment. First-year mortality was much higher in control and thin-only units (65 and 52%) than in thin-Rx units (37%). Cumulative third-year mortality followed a similar trend (78 and 64% in control and thin-only units) v. 43% in thin-Rx units. Percentage crown scorch is a strong predictor of mortality and is highly dependent on fuel treatment. Across all treatments, Pinus ponderosa had a lower probability of post-fire mortality than did Pseudotsuga menziesii. Finally, the probability of beetle attack on surviving trees was 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. We also present evidence that a combination of thinning and prescribed burning is associated with lower incidence of post-fire bark beetle attack.

Prichard, S.J.; Kennedy, M.C. 2012. Fuel treatment effects on postfire tree mortality and beetle attack in dry mixed conifer forests, Washington State, USA. International Journal of Wildland Fire. 21(8): 1004-1013.

Link to complete paper

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

Final Report [.pdf 2.16 MB]

Northern Rockies Fire Science Network Review [.pdf 2 MB]

Northwest Fire Science Consortium Brief [.pdf 1.35 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.


arrowFuel Treatments and Landform Modify Landscape Patterns of Burn Severity in an Extreme Fire Event

Under a rapidly warming climate, a critical management issue in semiarid forests of western North America is how to increase forest resilience to wildfire. We evaluated relationships between fuel reduction treatments and burn severity in the 2006 Tripod Complex fires, which burned over 70 000 ha of mixed-conifer forests in the North Cascades range of Washington State and involved 387 past harvest and fuel treatment units. A secondary objective was to investigate other drivers of burn severity including landform, weather, vegetation characteristics, and a recent mountain pine beetle outbreak. We used sequential autoregression (SAR) to evaluate drivers of burn severity, represented by the relative differenced Normalized Burn Ratio index, in two study areas that are centered on early progressions of the wildfire complex. Significant predictor variables include treatment type, landform (elevation), fire weather (minimum relative humidity and maximum temperature), and vegetation characteristics, including canopy closure, cover type, and mountain pine beetle attack. Recent mountain pine beetle damage was a statistically significant predictor variable with red and mixed classes of beetle attack associated with higher burn severity. Treatment age and size were only weakly correlated with burn severity and may be partly explained by the lack of treatments older than 30 years and the low rates of fuel succession in these semiarid forests. Even during extreme weather, fuel conditions and landform strongly influenced patterns of burn severity. Fuel treatments that included recent prescribed burning of surface fuels were particularly effective at mitigating burn severity. Although surface and canopy fuel treatments are unlikely to substantially reduce the area burned in regional fire years, recent research, including this study, suggests that they can be an effective management strategy for increasing forest landscape resilience to wildfires.

Susan J. Prichard and Maureen C. Kennedy 2014. Fuel treatments and landform modify landscape patterns of burn severity in an extreme fire event. Ecological Applications 24:571–590

Link to complete paper


Northwest Fire Science Consortium. 2014. Influences on wildfire burn severity: treatment and landscape drivers in an extreme event. Research Brief 5. Corvallis, OR: Oregon State University. 2 p.

Link to complete paper


Team Lead: Susan Prichard



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