Burn severity and pre-fire seral state interact to shape vegetation responses to fire in a young, western Cascade Range forest

Wildfire size and frequency are increasing across the western U.S., affecting large areas of young, second-growth forest originating after logging burning. Despite their prevalence in Cascade landscape, we have a poor understanding how these young stands respond to fire or responses differ from older, undisturbed forests, which well studied. We explore questions using pre- early post-fire data (<30-year-old), naturally regenerating Oregon that was burned preemptively limit spread 2018 Terwilliger Fire. exploit natural variation initial vegetation behavior test pre-fire seral state (relative abundance early-seral vs. forest-generalist species) burn severity interact shape short-term fire. Drawing disturbance theory studies older forests hypothesized would mediate compositional change functional-group cover richness through regenerative clonal traits available species. Two years fire, found greater with severity, although effect weaker where species dominated prior Species unaffected by as gains were balanced loss In contrast, diversity (Hill’s N1) evenness declined, reflecting shift dominance structure understory, dominant, Pteridium aquilinum, expanding further, generalists declining. Among plant functional groups, both annuals perennials responded positively but remained sparse (<1% herbaceous cover), stark contrast forests. Increasing enhanced herbs. However, it reduced most other including shrubs, herbs, shrubs. Within varied type depth burial perennating structures potential for growth. Our results underscore importance conditions shaping understory they do Legacies past species’ adaptions clearly favor herbs over residual Further study is needed determine whether recurrence during stages stand development simply resets succession alters its longer-term trajectory.