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Post-fire burn severity and vegetation response following eight large wildfires across the western United States

Author(s): Leigh B. Lentile, Penelope Morgan, Andrew T. Hudak, Michael J. Bobbitt, Sarah A. Lewis, Alistair M. S. Smith, Peter R. Robichaud
Year Published: 2007
Description:

Vegetation response and burn severity were examined following eight large wildfires that burned in 2003 and 2004: two wildfires in California chaparral, two each in dry and moist mixed-conifer forests in Montana, and two in boreal forests in interior Alaska. Our research objectives were: 1) to characterize one year post-fire vegetation recovery relative to initial fire effects on the soil surface that could potentially serve as indicators of vegetation response (and thus, ultimately longerterm post-fire ecosystem recovery), and 2) to use a remotely-sensed indicator of burn severity to describe landscape patterns in fire effects. We correlated one-year post-fire plant species richness and percent canopy cover to burn severity and to soil surface cover immediately after the fires. For all eight wildfires, plant canopy cover and species richness were low and highly variable one year post-fire. We found a greater number of forbs when compared to other plant life forms, independent of burn severity. Plant cover was dominated by grasses in chaparral systems, by forbs in mixed-conifer forests, and by shrubs in boreal forests, similar to the unburned vegetation. Finescale variability in post-fire effects on soils, the diversity of pre-fire vegetation, and the resilience of plants to fire likely explain the high variation observed in post-fire vegetation responses across sites and burn severities. On most low and moderate burn severity sites, >30% of the soil surface was covered with organic material immediately post-fire, and one year later, the canopy cover of understory vegetation averaged 10% or more, suggesting low risk to post-fire erosion. In California chaparral and the two Montana mixed conifer sites, 5% or less of the area within the fire perimeter burned with high severity, while in Alaska, 58% was mapped as high burn severity; we think this is characteristic in Alaska, but uncharacteristic of chaparral fires, especially given the high proportion of non-native species post-fire in our chaparral sites. All fires had a mosaic of different burn severities (as indicated by delta Normalized Burn Ratio, dNBR) with highly variable patch size (mean 1.3 ha to 14.4 ha, range from <1 ha to over 100,000 ha).

Citation: Lentile, Leigh B.; Morgan, Penelope; Hudak, Andrew T.; Bobbitt, Michael J.; Lewis, Sarah A.; Smith, Alistair M. S.; Robichaud, Peter R. 2007. Post-fire burn severity and vegetation response following eight large wildfires across the western United States. Fire ecology. 3(1): 91-108.
Topic(s): Fire Effects, Ecological - First Order, Ecological - Second Order, Soils, Vegetation, Fire Regime, Fire Intensity / Burn Severity, Fire and Landscape Mosaics, Patch Size
Ecosystem(s): Montane wet mixed-conifer forest, Montane dry mixed-conifer forest
Document Type: Book or Chapter or Journal Article
NRFSN number: 8168
FRAMES RCS number: 7321
Record updated: Sep 11, 2018