Habitat-based biodiversity responses to macroclimate and edaphic factors in European fen ecosystems.

Understanding large-scale drivers of biodiversity in palustrine wetlands is challenging due to the combined effects of macroclimate and local edaphic conditions. In boreal and temperate fen ecosystems, the influence of macroclimate on biodiversity is modulated by hydrological settings across habitats, making it difficult to assess their vulnerability to climate change. Here, we investigate the influence of macroclimate and edaphic factors on three Essential Biodiversity Variables across eight ecologically defined habitats that align with ecosystem classifications and red lists. We used 27,555 vegetation plot samples from European fens to assess the influence of macroclimate and groundwater pH predictors on the geographic distribution of each habitat type. Additionally, we modeled the relative influence of macroclimate, water pH, and water table depth on community species richness and composition, focusing on 309 plant specialists. Our models reveal strong effects of mean annual temperature, diurnal thermal range, and summer temperature on biodiversity variables, with contrasting differences among habitats. While macroclimatic factors primarily shape geographic distributions and species richness, edaphic factors emerge as the primary drivers of composition for vascular plants and bryophytes. Annual precipitation exhibits non-linear effects on fen biodiversity, with varying impact across habitats with different hydrological characteristics, suggesting a minimum requirement of 600 mm of annual precipitation for the occurrence of fen ecosystems. Our results anticipate potential impacts of climate warming on European fens, with predictable changes among habitat types and geographic regions. Moreover, we provide evidence that the drivers of biodiversity in boreal and temperate fens are closely tied to the ecological characteristics of each habitat type and the dispersal abilities of bryophytes and vascular plants. Given that the influence of macroclimate and edaphic factors on fen ecosystems is habitat specific, climate change research and conservation actions should consider ecological differentiation within functional IUCN ecosystems at continental and regional scales.