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Snag hazard to firefighters persists long after the smoke has cleared

Date: September 24, 2019

New tools to map snag hazard after fire can improve firefighter safety


A forester in a green coat and orange safety helmet stands in a burnt forest section cutting a tree with a chainsaw.
Ex-firefighter and current researcher fells fire-killed snags to evaluate the effects of decay on snag fall and breakage.

Past fire scars are often used by fire managers to limit the severity and spread of active wildfires, however there has been little work to characterize the unique hazards posed to fire responders in these recently burned environments. Snags continue to pose an ever-present hazard to responders, and recent increases in fire activity have resulted in an accumulation of these hazards across forested landscapes of the American West. Developing tools to spatially quantify this hazard can help protect the fire management service as it strives to meet societal needs.


Through a combination of remote sensing, field based estimates of mortality and snag fall rates, and analytics, researchers developed a series of statistical models of snag dynamics for common tree species in dry conifer forests of the America West. These models were then applied to six recently burned landscapes to develop maps that summarize 50 years of projected fire responder exposure to snag hazards. Starting conditions for modeling after each fire were strongly influenced by fire severity, where snag density in high-severity patches was more than double that of low-severity patches. Larger fires also tended to have larger patches of high-severity fire with increased snag hazard.

To characterize risk to fire responders, the model results were summarized by snag height and density to produce a simple index of responder exposure through time. Logical next steps for this work include incorporating non-fire causes of tree mortality and probability of reburn, and additional evaluation by and integration with fire management operations. 

A matrix showing hazard level as it corresponds to density and medlan height has photos of snags that fall under each level of hazard.
Snag density and height (potential reach) influence the exposure of responders to snags, but can be highly variable following fire and post-fire management activities. (Photo by: Christopher J. Dunn, 2008)















Key Findings

  • A forester kneels amid burned trees to collect data for snag research.
    Recent fire is important for reducing responder exposure to fire. Snag density and heights may preclude future engagement when reburn occurs, as demonstrated by this photo following high-severity 2009 Tumblebug Fire (Photo: Christipher J. Dunn, 2008)
    Snag hazard maps have the potential to improve the safety and effectiveness of fire management operations
  • The magnitude and spatial pattern of fire severity have long-lasting impacts on responder exposure to snags in future engagements
  • Snag hazard begins declining significantly after 10 years, but can persist for decades after a fire
  • Better aligning land and fire management goals and objectives can help mitigate responder exposure

Featured Publications

Dunn, Christopher J. ; O'Connor, Christopher D. ; Reilly, Matthew J. ; Calkin, Dave E. ; Thompson, Matthew P. , 2019

Principal Investigators - External: 
Christopher J. Dunn - Oregon State University
Matthew J. Reilly - Oregon State University
Forest Service Partners: 
Deschutes National Forest
Research Location: