Does fire-induced bud mortality reduce phenotypic variability?

Abstract Background and Aims For plants that resprout after fire, burning creates a strong before–after contrast in which lost biomass must be rebuilt under altered environmental conditions. In species that regenerate through protected belowground buds (basal resprouters), postfire resprouting may lead to increases in subindividual variability through the activation of dormant buds. In contrast, in species where regeneration depends on the survival of stem buds (aerial resprouters), fire might impose a filter favoring well protected buds that might lead to a reduction in variability. We tested whether frequent low-severity fires act as a phenotypic filter in apical resprouters, reducing variability in bud protection and associated leaf traits. Methods We studied the shrub Palicourea rigida Kunth (Rubiaceae) in the Brazilian Cerrado, and sampled three populations with contrasting fire histories. We quantified bud mortality, bud protection (using terminal stem diameter and height above ground), and leaf phenotype (leaf area, dry mass, moisture content and specific leaf area), and assessed fire-driven changes in phenotypic variability at subindividual and population scales. Key Results In high fire frequency populations, bud mortality strongly depended on terminal stem diameter; while in the fire-excluded population it depended solely on bud height. These patterns were associated with reduced variability in stem diameter and leaf traits under frequent fires at both population and subindividual scales. Leaf phenotypes also differed between fire histories, with frequently burned populations showing more conservative leaf traits. Conclusions Frequent low-severity fires can reduce subindividual phenotypic variability in aerial resprouters by selectively removing poorly protected buds. This contrasts with the increased subindividual variability reported for basal resprouters and highlights that fire modifies plant variability and that the direction of change depends on resprouting strategy, and ultimately, on fire regime. Incorporating subindividual variability into fire ecology provides new insights into how disturbance shapes plant form, function and resilience.