Wildfire contributes greatly to the function and assembly of many forest ecosystems. Features of the post-fire environment and species interactions influence system recovery and by extension shape understory plant communities, but post-fire characteristics are not homogenous throughout a burned landscape. While a wildfire burns, variations in weather, fuel loading and topography define the intensity of the fire and by extension determine the magnitude of ecological effect, or fire severity, at a post-fire site. How plant species respond to variations in fire severity is somewhat poorly understood, but there is observational evidence that shrubs quickly germinate and dominate sites of high post-fire severity. Research in the temperate forests of the Sierra Nevada has found that high severity fire is becoming more frequent and high severity patches are larger than historic fire regimes. This implies that sites dominated by shrubs (in the Sierra Nevada species of Ceanothus and Arctostaphylos) could also be more common and larger. This has meaningful implications for system function and biodiversity after wildfire. Shrubs can shade out the understory and soak up important resources, and therefore act as a competitive biotic influence. Restoration efforts, especially in USDA Forest Service sites throughout the Sierra Nevada, have used herbicides and other strategies to knock down shrub cover to benefit conifer regeneration. However, little work has been done to quantify how shrub cover varies by fire severity type, the effect that these plant forms can have on understory plant diversity, and the growth tactics they employ in response to the post-fire environment. We cataloged understory plant communities across sites of varying fire severity and shrub cover to understand the influence of these plant species on understory biodiversity and collected functional trait data from these shrubs to better understand their economic strategies in post-fire environments. We surveyed 116 sites across the fire severity spectrum of a fire that burned in mixed-conifer forest in the Sierra Nevada.
Results/Conclusions
We confirmed prior observational data of high shrub cover in high severity sites, and we found decreases in understory diversity with increasing shrub cover. Shrubs in this system also operated in more resource-acquisitive manners in high severity sites and employed more conservative strategies in sites of low post-fire severity. Our results may be most useful to land managers seeking to moderate shrub growth and improve biodiversity after disturbance.