Effects of fire recurrence and severity on Mediterranean vegetation dynamics: Implications for structure and composition in southern Spain

Most Mediterranean ecosystems have been profoundly shaped by wildfires, driving the evolution of plant species. Through photo interpretation and field inventories, this research assessed vegetation dynamics from 1984 to 2021, examining how fire severity and recurrence, key fire regime variables, influenced changes in structure and woody species diversity. Using two burn scars (1988 and 2006), we identified four scenarios dominated by Pinus pinea tree species: control (unburned), areas burned once (either in 1988 or 2006), and twice (in both 1988 and 2006). Areas affected by two high-severity fires experienced the most pronounced expansion of dense shrubland. However, when fire severity was moderate, wildfires led to a significant decline in understory cover in dense and open forests. Pinus pinea regeneration was influenced by fire severity and recurrence. It was absent in areas burned twice with at least one high-severity fire but showed an increased compared to control areas in areas burned with moderate fire severity without recurrence. Wildfires increased biodiversity, particularly in areas burned with high severity. The Sørensen and Jaccard indices showed the highest species diversity recovery in dense forest understory after a single moderate-severity fire in 1988. This study offers a novel approach by considering both fire recurrence and severity, along with a medium-term timeframe, in contrast to most studies focusing on short-term vegetation dynamics after single fires. Monitoring spatio-temporal dynamics is crucial for guiding ecological restoration and wildfire prevention strategies.