Examining the impact of heathland restoration via felling on carabid diversity in the Purbeck Heaths National Nature Reserve.

Abstract

Lowland heaths have suffered considerable decline across Europe due to factors such as agricultural expansion and afforestation. The internationally significant Purbeck Heaths National Nature Reserve in Dorset has experienced substantial habitat loss, threatening numerous rare and declining species. This study aimed to evaluate how heathland restoration through conifer felling influences the species richness, composition, and functional traits of carabid assemblages. Specifically, it assessed the impact of restorative felling — the removal of planted conifers from former heathland — in the Rempstone and Godlingston areas of Purbeck Heaths. Carabid richness, abundance, and functional traits were assessed using pitfall traps across 35 sites, encompassing forested, established wet and dry heath, and restored wet and dry heath categorised by restoration age: <12 years (new) or >17 years (old). Environmental variables (ground temperature, soil moisture, and relative humidity) and vegetation characteristics were also recorded. Sampling was carried out monthly from May to August 2024, and data were analysed using generalised models (additive and linear) for species richness and abundance, and PERMANOVA to assess differences in carabid species composition, and Kruskal-Wallis tests to evaluate variation in functional traits across habitat types. A total of 354 individuals from 44 species were identified, with Abax parallelepipedus being the most abundant. Wet heath restored post-2012 exhibited the highest richness (23 species), while forested and old dry restored heath showed the lowest median richness (2 species each). Richness increased with warmer ground temperatures, highlighting the role of microclimatic conditions. The positive association between warmer ground temperatures and carabid richness suggests that thermally favourable microhabitats enhance carabid activity, underscoring the ecological importance of microclimate in driving community composition. Habitat type strongly influenced species composition, with Old Dry heath assemblages being particularly unique compared to all other habitats. Younger restorations (especially wet) showed high species turnover, while older, more established sites had more predictable communities where species were more consistently shared across sites. Functional trait analysis revealed significant habitat-specific variations: restored wet heaths favoured smaller, spring-breeding, open-habitat specialists, while forests and older dry heaths hosted larger carabids with different trait combinations, reflecting habitat structure and microclimate influences. These findings support conifer removal as beneficial for carabid diversity, while suggesting a role for retaining some mature conifers to enhance overall diversity. The study highlights the necessity of habitat-specific management, accounting for restoration age and microclimate, to maximise biodiversity conservation in restored heathlands.