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What drives low-severity fire in the southwestern United States?

Date: May 15, 2018

How do we promote low-severity fire in the southwest US? This study provides some answers.


In the southwestern U.S. and elsewhere, there is keen interest in restoring dry conifer forests to conditions that are conducive to low-severity fire. Yet, there has been surprisingly little research evaluating factors that promote low-severity fire.  

The study was conducted in dry conifer forest in Arizona and New Mexico that historically experienced fairly frequent low-severity fire. Dominant forest types analyzed include ponderosa pine, pine-oak, and mixed conifer.

Cooler and wetter conditions for the year in which the fire burned were associated with lower-severity fire. Photo credit: NIFC.
Cooler and wetter conditions for the year in which the fire burned were associated with lower-severity fire. Photo credit: NIFC.
This study examined thirteen explanatory variables that potentially control low-severity fire; these variables were combined into four groups representing: live fuel, topography, climate (30-year normal characterizing spatial variability), and inter-annual climate variation (year-of-fire climate). Fire severity and live fuels were measured using satellite imagery, whereas topography, climate, and inter-annual climate variation were obtained from various sources. Fires from 1984 to 2015 were sampled.

The results of this study provide valuable information to land managers tasked with restoring forest structures and processes in the southwestern USA and other regions dominated by dry forest types.

Key Findings

  • Live fuel was the most influential factor driving low-severity fire: the probability of low-severity fire increased with lower fuel levels.
  • Inter-annual climate variation was the second most influential factor (although fuels influence was approximately 2.4 times greater); low-severity fire was more likely in years that were cooler and wetter than average.
  • Low temperatures and high moisture during June were especially important for facilitating low-severity fire.
  • Promoting and allowing fire in cool, wet years will reduce fuel loads and possibly decrease high-severity fire in warmer, drier years.
  • Surprisingly, topography and climate (30-year averages) had virtually no effect on prevalence of low-severity fire, although other studies show otherwise. Topography and climate have an effect on fuel levels, however, and their importance may have been minimized because this study included fuel as a separate variable 

Featured Publications

Parks, Sean A. ; Holsinger, Lisa M. ; Miller, Carol L. ; Parisien, Marc-Andre , 2018
Walker, Ryan B. ; Coop, Jonathan D. ; Parks, Sean A. ; Trader, Laura , 2018
Parks, Sean A. ; Holsinger, Lisa M. ; Panunto, Matthew H. ; Jolly, William M. ; Dobrowski, Solomon Z. ; Dillon, Gregory K. , 2018

Principal Investigators: 
Principal Investigators - External: 
Solomon Z Dobrowski - University of Montana