Wildfire impacts on seedbank and vegetation dynamics in Calluna heath

Abstract

Moorlands dominated by Calluna vulgaris (hereafter Calluna) are globally rare and under increasing threat of wildfires due to climate change. The soil seedbank is important for community resilience, but research on its contribution to regenerating vegetation after moorland fires has, to date, focused on prescribed fire or on the short‐term (≤ 2 year) impacts of wildfire. To address the role of the seedbank in long‐term vegetation regeneration, we studied a chronosequence of six wildfire sites within a Scottish moorland catchment, ranging from 2 to 64 years since burning. We recorded vegetation composition and sampled the seedbank. Calluna and Erica spp. comprised 66 and 27% of germinated seeds, respectively, and the majority of vegetation species were not represented in the seedbank. Canonical correspondence analysis (CCA) revealed that time since fire was a strong predictor of vegetation species composition, but it had no effect on seedbank composition, suggesting that the same species dominate the seedbank regardless of burning. Whilst total seed density was not affected by time since wildfire, the effect on the non‐Calluna seedbank was more notable. The proportion of non‐Calluna species decreased with time in both vegetation and seedbank as Calluna cover was re‐established and the seedbank of other species became gradually depleted. Whilst relative non‐Calluna cover in the vegetation was at a maximum in recently burnt areas and declined with time since fire, the species richness and proportion of non‐Calluna in the seedbank followed a unimodal pattern after fire and reached a peak after approximately 35 years. Our results contribute to the knowledge of how moorland ecosystems regenerate after severe disturbances, which are likely to become more common as the climate changes.