Transiently Richer but Profoundly Changed: Fire Regime Triggers Physiognomic Changes in Sub‐Mediterranean Vegetation

ABSTRACT Questions Which components of the fire regime affect plant species diversity? Does pre‐fire vegetation physiognomy influence the effect of the fire regime? Which species are favoured by different fire regimes? Location Natural Reserve of Monte Catillo (central Italy). Methods We sampled vegetation in 58 units across areas that underwent different fire regimes and were originally occupied by different vegetation physiognomies. We used plot‐level species diversity calculated through Hill numbers in (generalised) linear models with components of fire regimes (time since the last fire, fire frequency and severity) and pre‐fire physiognomy as explanatory variables. We identified species related to different levels of fire frequency, severity and time since the last fire through indicator species analysis. Results Species richness ( q = 0) was negatively related to time since last fire, while Shannon ( q = 1) and Simpson ( q = 2) diversity were influenced by the severity of last fire, with positive and negative relationships, respectively. Shrubland pre‐fire vegetation interacted significantly with severity effects on diversity. All components of fire regimes favoured annual and chamaephytic species with a Mediterranean distribution, while areas subjected to older, less severe and less frequent fires were characterised by tree species, including deciduous ones, and paleotemperate herb species. Conclusions Recent fires increase vascular plant species richness, but only temporarily. Severe fires determine relevant shifts in community dominance. Frequent and severe fires favour the spread of Mediterranean herb species in areas potentially occupied by thermophilous forests dominated by a mix of deciduous and evergreen tree species.