Vegetation heterogeneity due to multiple wildfires in northern Sierra Nevada forests.

Keywords: disturbance, patch dynamics, landscape diversity, scale, vegetation dynamics, wildfire
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 09:40 AM (Eastern Time (US & Canada)) - 2/25/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 42

Abstract

Historically, diverse vegetation pattern has been created and maintained by wildfire in the northern Sierra Nevada, California. Interrupting this ecological process resulted to fuel accumulation and infilling of open heterogenous landscape by conifer trees that favored repeated high severity fire and created large homogenous shrub patches. However, a clear understanding of the effects of contemporary fires on landscape-scale heterogeneity is lacking. Our research question was: Does repeated fire in conifer forests reduce landscape heterogeneity when extensive high-severity fire patches convert forest to shrubland? The study area consists of a mosaic of burned and unburned patches within Lassen and Plumas National Forests. We used secondary geospatial landcover data classified by cover type before any fires from the years 1991-2000 and after multiple fires between 2000 and 2014. We calculated various landscape metrics using FRAGSTATS for comparison before and after fires. Results at the scale of burn patches showed that reburning at low- to moderate-severity nearly doubled vegetation cover type heterogeneity, but at high-severity it reduced by half. However, at the full landscape scale, including all burn severities, increased vegetation cover type heterogeneity. Fragmentation indices at vegetation class level showed that fire created larger patches of shrub and fragmented continuous conifer forest. This study provides insights concerning vegetation pattern change due to frequent large fire events suggesting that heterogeneity varies with scale of analysis. Hence, more than one scale should be considered to measure heterogeneity and vegetation pattern change before prioritizing management actions of the conifer forests of the Sierra Nevada.