Interpreting the shifts in forest structure, plant community composition, diversity, and functional identity by using remote sensing-derived wildfire severity

We conducted an observational study in the Karst forests one year after the large wildfire which affected the area in 2022 through 35 field plots (200 m2 each) distributed among different fire severity classes assessed using the Normalized Burn Ratio (dNBR) calculated from satellite images. In each plot, tree species, diameter, vitality, resprouting capacity and seedling density were measured. As well, herb species richness (taxonomical diversity) was quantified and plant cover visually estimated.

Functional diversity was also assessed considering six functional traits retrieved by existing trait database. Results Our results highlight the vulnerability of the forest stands to an increase in wildfire severity, resulting in significant mortality and changes in tree community structure. Some tree species (i.e., Quercus pubescens) showed an higher resistance to the fire, while other showed a higher resilience (i.e. recovery after fire through resprouting or seedlings).

The transition to a shrub-dominated community (i.e., Cotinus coggygria) where fire severity was the highest underlines the dynamic nature of the post-fire succession. We also detected a significant shift in herbaceous plant community composition, diversity and functional identity with fire severity: high-fire severity areas exhibited higher species richness compared to low-severity or unburned areas. Total non-native plant cover increased with fire severity while native cover remained constant.

We also found shifts in species and functional composition, particularly for traits related to germination potential and growth strategy. Conclusions This study contributes to the understanding of ecological processes after wildfires in temperate forests, emphasizing the need for conservation strategies aimed at limiting fire damages while increasing prevention.