How severe wildfires and climate change could drive post-fire recovery of low-elevation vegetation: data from the first field campaign of a monitoring survey in the Karts (North-East Iatly)

Wildfires are a major ecological factor shaping vegetation and landscape, and their impacts are projected to escalate due to global warming: the intensity, frequency and extent of fires are increasing all over the world, with dramatic consequences on habitats. In summer 2022, severe fires burnt over 4000 hectares of the western Karst between Italy and Slovenia, a submediterranean low-hilly area near the coast. In spring 2023, we started a survey to analyze the consequences of the 2022 fires on plant communities and to monitor post-fire vegetation dynamics. This study aims to investigate the possible effects of interactions of severe fires, climate change and alien species on the floristic composition of habitats and on the typical processes of post-fire vegetation recovery in a low-elevated area. The study was focused on 4 major habitats of the western Karst, 3 of which dynamically related: the thermophilous karst grassland Centaureo cristatae-Chrysopogonetum grylli, the thermophilous shrubland Pruno mahaleb-Paliuretum spina-christi, and the karst downy oak wood Aristolochio luteae-Quercetum pubescentis. Black pine plantations were also included due to their large extent. Permanent plots were installed in the most intensively burnt areas mapped by satellite remote sensing data using a stratified random sampling, by placing 7 x 7 m2 squared-plots in the four major habitat types identified on the basis of available habitat maps and photo-interpretation. In each plot the percent cover of total vegetation, bare soil and of all species was recorded. At the habitat level, the highest total species richness and the lowest one for alien species were both found in the dry karst grassland, which also exhibited excellent quantitative and qualitative recovery, confirming itself as a highly resilient habitat. Shrubland showed a strong recovery of native shrub species, a rather high number of total species and alien species compared to the investigated habitats, however with alien species occurring with low cover values. The downy oak woodland had similar species richness values to shrubland, but higher abundance of alien species, esp. Robinia pseudoacacia and Ailanthus altissima, and of native ruderal species: therefore strong modifications of the floristic structure with deviations from the typical secondary succession are possible. Black pine plantations were found to be characterized by the lowest total species richness, the highest number of native ruderal and alien species, poor recovery of native species and unclear dynamic trajectories. The study is meant to provide information i) to identify interventions to support and eventually correct the post-fire recovery of habitats, ii) to support land management policies to enhance the resilience and resistance of the Karst landscape to wildfires.