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Does burn severity affect plant community diversity and composition in mixed conifer forests of the United States Intermountain West one decade post fire?

Author(s): Eva K. Strand, K.L. Satterberg, Andrew T. Hudak, John C. Byrne, Azad Henareh Khalyani, Alistair M. S. Smith
Year Published: 2019
Description:

Background: Wildfire is an important ecological process in mixed conifer forests of the Intermountain West region of the USA. However, researchers and managers are concerned because climate warming has led to increased fire activity in recent decades. More area burned will result in larger land areas in early successional stages and will potentially limit tree establishment; therefore, evaluating long-term forest understory response to fire is important. We evaluate the impact of burn severity, overstory canopy cover, topography, and climate on understory plant community diversity and composition in seven wildfires, 9 to 12 years post fire, along a broad climate gradient from dry to moist mixed conifer forests in Idaho, Montana, and Washington, USA.

Results: Climate was the most important driver for species diversity and composition, but a burn severity gradient was detectable in the species data one decade post fire. A strong overlap in species composition between burn severity levels was documented, but dispersion was lower for high burn severity sites, indicating that those sites are still recovering. Local species richness and diversity had a nonlinear relationship with the burn severity index dNBR, with a maximum at low to moderate burn severity; the relationship was stronger in moist climates. Functional trait analysis revealed higher grass and forb cover in high-severity burns, higher cover of tree seedlings, residual and off-site colonizers in burned areas, and more shade-tolerant species in unburned areas. Of the 270 species recorded, 10% were introduced; however, only three were of noxious status and two were invasive annual grasses, generally occurring on dry sites.

Conclusions: The understory plant community was not fundamentally altered by these fires and fire contributed to increased species diversity both locally and regionally, suggesting that low to moderate burn severity fire is a treatment that contributes to long-term maintenance of a diverse and productive understory. Individual species traits were significant drivers of understory species assemblages and, as future change in climate and fire regimes leads to shifts in species composition, anticipation of consequences will be important. Although invasive species occurred at low cover levels, noxious weeds and invasive annual grasses will continue to be management challenges, particularly in dry regions of mixed conifer forests.

Citation: Strand, Eva K.; Satterberg, Kevin L.; Hudak, Andrew T.; Byrne, John C.; Khalyani, Azad Henareh; Smith, Alistair M. S. 2019. Does burn severity affect plant community diversity and composition in mixed conifer forests of the United States Intermountain West one decade post fire? Fire Ecology 15:25.
Topic(s): Fire Ecology, Ecosystem Changes, Successional Changes, Early Successional, Fire Effects, Ecological - Second Order, Invasive Species, Vegetation
Ecosystem(s): None
Document Type: Book or Chapter or Journal Article
NRFSN number: 19868
FRAMES RCS number: 58332
Record updated: Aug 6, 2019