Skip to main content
Author(s):
Michelle Coppoletta, Brandon M. Collins, Scott H. Markwith, Kyle E. Merriam
Year Published:

Cataloging Information

Topic(s):
Fire Behavior
Fire Regime
Mapping
Fuels
Recovery after fire
Restoration

NRFSN number: 22235
FRAMES RCS number: 62056
Record updated:

In the face of changing climatic regimes and increases in extreme fire events, many western forests are poised to burn, not only once but multiple times, sometimes in short succession. As such, land managers have limited opportunities to effectively alter post-fire vegetation and fuels to make them more resilient to future disturbances like fire. In this study, we took advantage of a unique opportunity to examine vegetation and fuels development after successive fires, and in doing so identified several management-relevant pathways by which post-fire vegetation structure and fuels influence the severity and ecological outcomes of a subsequent wildfire. We analyzed three datasets, collected at multiple spatial and temporal scales, from three overlapping fires in northern California. First, we collected and analyzed data from 134 field plots, established after an initial mixed severity fire and remeasured after a subsequent reburn. Second, we used repeat LiDAR data, collected over the same time period, to expand our analysis to a larger spatial scale. Finally, we used high-resolution aerial orthoimagery to assess how post-fire vegetation and fuel development influence fire severity patterns in a reburn. Our results suggest that resistance to high-severity reburn is contingent on a combination of factors, including topography, fire weather, vegetation structure, and woody fuels. In our study fires, areas with more variable and mesic terrain were less likely to reburn at high severity. In stands that burned at lower initial severities, high relative humidity and low wind speeds during the reburn also reduced the likelihood of high-severity fire effects. In areas that initially burned at high severity, high densities of snags and down woody fuels were associated with high-severity effects in the second fire. Variability and density of vegetation also played an important role in moderating reburn severity. In early-seral habitats (i.e. those that burned initially at high severity), areas with relatively sparse understory and variable sub-canopy were most likely to avoid repeat high-severity fire. Forests that burned initially at low to moderate severity were most likely to resist high-severity fire if they supported sparse understories and relatively dense but heterogeneous vegetation in the upper strata (> 2 m in height). Following the reburn, areas impacted by successive high-severity fires had little to no live conifer overstory, retained high cover of shrubs in the understory, and had little to no conifer regeneration. In contrast, successive low to moderate severity fires significantly reduced tree density, increased tree regeneration, and in some severity combinations (e.g. low followed by moderate severity) promoted colonization by shrubs. In our study, multiple low to moderate severity fires did not shift forest composition toward dominance of more fire tolerant or shade intolerant species. Taken together, the results of our study suggest that post-fire vegetation structure and woody fuels play an important role in subsequent fire severity patterns and ultimately influence the resilience of post-fire landscapes to future fire. In areas where high-severity reburn is undesirable, managers should consider treatments that reduce the density and continuity of vegetation, standing snags, and large woody surface fuels. In areas where proactive reforestation is necessary, planting in areas that are in rough or mesic terrain may reduce the likelihood of high-severity reburn. The results of our study also suggest that active post-fire management may be necessary in areas that have burned at low to moderate severity in order to maintain or promote the restorative benefits of an initial fire or to restore the dominance of fire resilient tree species.

Citation

Coppoletta, Michelle; Collins, Brandon; Markwith, Scott; Merriam, Kyle. 2020. Effects of post-fire management on vegetation and fuels following successive wildfires in mixed conifer forests - Final Report to the Joint Fire Science Program. JFSP Project ID: 16-1-05-13. USDA Forest Service, Pacific Southwest Region. 34 p.

Access this Document