Fire severity and habitat type determine vegetation change and regeneration time following wildfires in Scottish uplands

Questions: How does wildfire impact vegetation composition and diversity in Scottish blanket bogs and heathlands dominated by Calluna vulgaris? What are the recovery time scales, and which taxa are most vulnerable? Location: Blanket bog and heathland sites in Scotland, UK. Methods: We conducted a space-for-time-substitution survey of 27 wildfire sites, spanning 2-24 years since wildfire. Cover of individual plant species and lichens alongside data on soil carbon, nitrogen and pH were collected in burnt and adjacent unburnt areas, with fire severity assessed using remote sensing. Regression models were used to examine Shannon diversity, heterogeneity, and compositional dissimilarity between burnt and unburnt areas over time. Effects on community composition were assessed using CCA and NMDS. Results: Wildfire severity and habitat played crucial roles in shaping post-fire vegetation dynamics. Blanket bog and wet heathland displayed resistance to severe burning, with mild effects on vegetation composition. Dry heathland experienced stronger initial impacts but demonstrated significant recovery over time. Vegetation composition resembled adjacent unburnt areas in approximately 20-25 years following low severity fire, and higher severity fires prolonged regeneration times. We found no effect of time since fire on diversity. Sphagnum abundance showed little relationship with time since fire and may contribute to the resilience of wet moorlands to severe fire. Lichens and pleurocarpous mosses were reduced in cover, whilst graminoids and acrocarpous mosses were abundant in recently burnt areas. Conclusions: Wet moors were more resistant to severe burning whilst dry moors showed strong initial effects but exhibited recovery over time. Higher severity fires led to greater vegetation change and longer recovery times. The increased risks and consequences of wildfire under climate change may be most severely felt on dry moorland habitats. Although wet moorlands are currently resilient, ongoing management is crucial as future conditions may increase their susceptibility to fire and vegetation change.