Effects of seasonal prescribed burns on understory vegetation in a Mediterranean mixed pine forest

Prescribed burning is a widely used fire management tool in Mediterranean forests, yet its seasonal effects on vegetation remain poorly understood. This study investigates the impact of prescribed burns in spring, summer, and autumn on understory vegetation in Mediterranean pine forests. We assess variations in total vegetation cover, alpha diversity indices, Raunkiaer life forms, post-fire regeneration strategies, and species composition. Results indicate no significant overall reduction in vegetation cover, but burns at different seasons influenced diversity and species dominance. Spring and autumn burn reduced species evenness and increased dominance by a few taxa, emphasising the influence of fire seasonality on understory community structure. Nanophanerophytes showed significant seasonal declines under pre-burned conditions in spring and summer (p < 0.001), whereas geophytes showed a significant positive response to burning in pre-burn plots (p < 0.05), indicating a more resilient baseline presence before treatment. Post-fire responses varied by season and regeneration strategy: all strategies—seeder, resprouter, and seeder-resprouter—showed significantly higher cover in pre-burned plots during autumn. Spring burns led to a non-significant increase in seeder cover and an emergence of seeder-resprouter species, suggesting potential functional plasticity. In contrast, summer burns resulted in a marked decline in both seeders and resprouters, likely due to extreme thermal and hydric stress. NMDS and SIMPER analyses revealed post-burn shifts in community composition, with notable reductions in dominant grasses and shrubs post-fire. These findings underscore the need for seasonally tailored prescribed burn strategies to balance fire risk reduction with biodiversity conservation. This research provides evidence-based insights to refine prescribed fire policies, ensuring sustainable fire management in Mediterranean landscapes under increasing climate pressures. • Changes in vegetation after prescribed burn seasonality in the Mediterranean basin. • Decrease in vegetation diversity after low-intensity prescribed burns. • Changes in life-form vegetation after seasonal burns in a black pine forest. • Increase in resprouting species after low-intensity prescribed burns. • Summer prescribed burning generates the most changes in vegetation response.