Fire Severity and Habitat Type Determine Vegetation Change and Regeneration Time Following Wildfires in Scottish Uplands

Wildfire is an increasingly significant disturbance in temperate uplands, yet its long-term impacts on vegetation remain poorly understood. In Scotland, UK, where blanket bogs and heathlands dominated by Calluna vulgaris are widespread, we investigated how wildfire affects vegetation composition and diversity, what the recovery time scales are, and which taxa are most vulnerable. To address these questions, we conducted a space-for-time substitution survey across 27 wildfire sites, spanning 2-24 years since fire. Cover of individual plant species and lichens and 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 Canonical Correspondence Analysis (CCA) and Non-Metric Multidimensional Scaling (NMDS). Our results indicate that wildfire severity and habitat play 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. Wildfire reduced Shannon diversity in dry moorland but increased it in wet moorland, with no effect of time since fire. Plot heterogeneity increased with fire severity and also showed no temporal trend. 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, whereas graminoids and acrocarpous mosses were abundant in recently burnt areas. 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.