Successive large mixed-severity wildfires and vegetation and fuel dynamics in the Sierra Nevada, CA

Authors: Scott Markwith*, Florida Atlantic University, Asha Paudel, Florida Atlantic University, Michelle Coppoletta, US Forest Service, Kyle Merriam, US Forest Service, Brandon Collins, US Forest Service
Topics: Biogeography, Environment, Mountain Environments
Keywords: reburn, mixed conifers, repeated sampling, national forests, Sierra Nevada
Session Type: Paper
Day: 4/4/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Regency Ballroom, Omni, West
Presentation File: No File Uploaded

Increasing incidence of successive large high severity wildfires across the western U.S. has raised awareness of potential large-scale and long-term vegetation state changes. In the Sierra Nevada mountains, California, these shifts are manifested as large shrub patches replacing mixed conifer stands in large high severity patches with little conifer regeneration and large residual fuel loads. High severity fire effects in an initial fire can create conditions, such as standing and fallen snags and dense shrub vegetation, that promote high severity fire effects in subsequent reburns. This feedback trajectory with subsequent fires (i.e. extensive stand-replacing fire will promote more stand-replacing fire) has the potential for long-term state change. In this study, the following hypotheses are tested: 1) in mixed conifer forests affected by fire suppression, successive high severity fires create a positive feedback that promotes shrub dominance, and homogenization of vegetation structure across the landscape, and 2) multiple low to moderate intensity fires in mixed conifer forests result in a stabilizing negative feedback by reducing surface fuels and small tree density, while maintaining larger overstory trees and promoting landscape-scale forest heterogeneity and diversity. Our study area is located in the northern Sierra Nevada, California in Plumas and Lassen National Forests. We resampled field plots that were established after the 2000 Storrie and 2008 Rich fires, and reburned by the 2012 Chips Fire. Our intent is to provide managers with critical information for managing post-fire landscapes before long-term vegetation and fuels trajectories establish as a result of successive, high severity fires.

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