Drivers of understory vegetation structure in a fire-suppressed ecosystem

Abstract Many fire-adapted ecosystems embedded in human-dominated landscapes have experienced long-term fire suppression and related shifts in vegetation structure and diversity. We examined patterns and environmental drivers (including fire history) of understory plant community composition and species richness across the Long Island Central Pine Barrens, an ecologically important fire-adapted ecosystem in northeastern United States. We asked: (1) How does understory vegetation shift across forest types with increasing time since last fire (TSLF) in this fire suppressed ecosystem? And (2) Which environmental gradients (canopy openness (CO), organic matter, basal area) best predict understory composition and richness? Vegetation and environmental data were collected on 105 permanent plots placed across six forest types using a stratified random sampling in 2019–2020. We quantified and analyzed the relationship between vegetation composition, CO, soil organic matter, and TSLF. Scrub oak ( Quercus ilicifolia ) dominated pitch pine forests understories, whereas black huckleberry ( Gaylussacia baccata ) and hillside blueberry ( Vaccinium pallidum ) were prevalent across most forest types. Together, these three species accounted for approximately 78% of all understory plants, making their responses to environmental gradients broadly representative of understory dynamics across the landscape. CO and overstory basal area were stronger predictors of understory composition than TSLF. Cover of the dominant ericaceous shrubs decreased with CO and increased with litter depth, while overall species richness was positively associated with basal area and decreased significantly with TSLF. Indicator species analysis identified plant species associations with specific forest types and fire histories. These findings suggest that forest structure, shaped by both fire history and management, currently exerts a stronger influence on understory dynamics in this fire‐suppressed landscape than direct effects of TSLF. Restoration strategies should promote light availability via prescribed fire and strategic thinning, supported by long‐term monitoring under changing climate conditions.