Abstract
Responses to climate change are often measured in relation to summer heat or drought. An equally important phenomenon is winter climate change. Climate change can cause warmer winters, the lack of an insulating snow cover and increased winter precipitation. In cold adapted communities at high latitudes communities, this can have severe detrimental effects. One assumption is that disturbance by winter climate change causes spatial biotic homogenization by favoring widespread generalist species over locally adapted specialists. We here test this hypothesis in leaf litter communities of fungi and arthropods in temperature European beech forests, making use of a winter climate change experiment. The experiment compared three treatments: snow exclusion combined with additional winter precipitation, in which snowfall was artificially removed (RnoS), additional winter precipitation with natural snow cover (RS), and an untreated reference (Ref). We characterized fungal and arthropod communities using eDNA metabarcoding right after the experiment in spring and in summer. The snow exclusion with additional rain experiment led to considerable biotic homogenization across the transect. Interestingly, our analysis suggests that not a lack of insulating snow cover, but actual winter warming due to the experimental set up caused the observed homogenization. The homogenization was stronger for fungi than arthropods. Despite pronounced taxonomic change in the plots, functional diversity remained largely unchanged, species replacements were functionally redundant. Biotic homogenization was found in spring, while the effect had disappeared in summer, suggesting temporal resilience against winter climate change. Our results provide a clear link between warmer winters and widespread biotic homogenization, a phenomenon described in many ecosystems, which is still not well understood.