Early seral pathways of vegetation change following repeated short-interval, high-severity wildfire in a low-elevation, mixed conifer – hardwood forest landscape of the Klamath Mountains, California

Abstract

We compared early seral development between stands subject to single and repeated high-severity wildfire in low-elevation, mixed conifer – hardwood forests in the Klamath Mountains, California, USA. We used a before–after, control–impact (BACI) approach to assess changes in the density of conifer regeneration and the cover of multiple components of vegetation structure (conifers, hardwoods, shrubs, forbs, and graminoids) and compare pathways of seral development between plots that burned once and plots that burned twice. Fifty-three field plots were established 6 years following a high-severity fire in 2004. Nineteen of these plots experienced a second high-severity wildfire 11 years later (2015), and all plots were remeasured in 2016–2017. Conifer regeneration was abundant following the first fire but was greatly reduced by the second fire. Plots that did not reburn increased in conifer, hardwood, and shrub cover, whereas plots that reburned increased in forb cover and decreased in shrub, hardwood, and conifer cover. Despite conifer loss, we found little evidence of shifts to nonforested states following repeated fire due to resilience of resprouting hardwoods. Our results indicate that repeated high-severity fire has the potential to protract early seral development and catalyze transitions from mixed conifer – hardwood forest to hardwood-dominated early seral conditions.