Impacts of climate change on bryophyte distribution: a comprehensive assessment at fine spatial resolution across Europe

Bryophytes, the second most diversified lineage of land plants after the angiosperms, play substantial ecological roles in terms of carbon and nutrient cycles, regulation of soil temperature and moisture, and as a shelter for a large array of micro-organisms. Although, due to peculiar features of their eco-physiology, bryophytes have long been identified as the canaries in the coal mine of climate change, a global assessment of climate change impacts on their distribution and diversity is still missing. Here, we compiled an expert database of more than 2,100,000 occurrences for 1476 (82%) species across Europe to calibrate species distribution models at 100 m resolution and project them to 2071–2100 climate under several scenarios of global warming from the most optimistic to the most pessimistic. Despite large differences among climate change scenarios, all models point to substantially higher median loss (12–91%) than gain (8–18%) of future suitable habitats and median northern shifts of the centroid of species habitat suitability of 65-255km. These general patterns hide contrasting impacts depending on biogeographic regions, with a median loss of 24–100% vs 2–26% of future suitable habitat in Boreo-montane vs Mediterranean regions, respectively. The regions predicted to experience the lowest (less than 10% of variation in habitat suitability) impact of future climate change are distributed along the Atlantic coast, identifying these areas as potential climatic refugia for the bryophyte flora in a warming world. Areas with the highest predicted loss of habitat suitability are concentrated in the mountain regions (Pyrenees, Alps and Tatras) and northern Scandinavia. In turn, the pixels predicted to exhibit the highest increase (more than 50%) in habitat suitability are distributed in mid-western Europe, largely corresponding to the northern shift of climatically suitable areas for Mediterranean species. The cascading effects of a future impoverishment of bryophyte floras on ecosystem functioning in Europe will be discussed.