Fire significantly influences beetle diversity in natural wetland forests but the effects vary by forest type and insect species

Wildfires are major ecological disturbances, with increasing intensity worldwide. In Central and Northern Europe, research on wildfire impacts on biodiversity has primarily focused on dry and semi-dry coniferous habitats, while the effects of fire in wet and broad-leaved environments remain poorly understood. We investigated the impact of a large wildfire that occurred in 2020 in Biebrza National Park (Poland) on the biodiversity of beetles in wet birch, wet alder, and in dry-mesic oak forests. Beetles were sampled between 2020 and 2022 using purple 12-funnel traps placed in paired burned and unburned forest fragments. The analysis revealed significant differences in beetle communities between burned and unburned sites across all forest types. Indicator species analysis identified 12 beetle species that were associated with burned sites, primarily in oak forest, 15 species that were indicators of unburned sites, mainly in birch and alder forests, and one species whose response was dependent on forest type. Furthermore, we analyzed changes in the abundance of individual indicator species over the three years following the fire and discussed potential factors influencing the observed patterns of abundance dynamics. Our findings demonstrate that fire can have both positive and negative effects on beetle diversity, with the impact varying depending on forest type and insect species. Conservation strategies should account for differential fire effects across forest types. Given the variability in beetle species responses, we recommend a species-specific approach when assessing the effects of fire on insect communities.