Glacier extinction homogenizes functional diversity via ecological succession

Questions: The disappearance of glaciers threatens biodiversity and the functioning of ecosystems. Yet, questions remain about the response of functional diversity to glacier retreat. How does glacier retreat influence functional diversity? How does glacier retreat influence the relationship between taxonomic diversity and functional diversity? How does glacier retreat impact community mean and intraspecific trait variability (ITV) of key functional traits?. Location: Four retreating glacier ecosystems in the Italian Alps. Plant communities spanning 0 to ca 5000 years on average after glacier retreat, including a scenario of glacier extinction. Methods: We quantified functional diversity analyzing twelve plant traits associated to carbon and nitrogen cycling, resource allocation, and reproduction of 117 plant species. We addressed how functional diversity changes with glacier retreat and taxonomic diversity (i.e., plant species richness). Results: Plant functional diversity decreases with glacier extinction while increasing with species richness. The positive relationship between taxonomic and functional diversity becomes flatter, that is, less important, with glacier retreat. We document sharp changes in functional niche position and breadth with glacier retreat. Key functional traits associated with carbon cycling and resource allocation change substantially with ecological succession triggered by glacier retreat. Traits associated to nitrogen cycling show little change. We also found that flowering start shifted earlier in the season while flowering period increased with glacier retreat. Conclusion: Our results demonstrate the pervasive impact of glacier extinction on the functioning of plant communities. Changes in functional mean and functional variation indicate shifts in niche position and niche breadth which could have implications for species adaptation to changing environments