Patterns of beta-diversity along elevational gradients inform epiphyte conservation in alpine forests under a climate change scenario

We explored the patterns of beta-diversity of forest epiphytic bryophytes and lichens along elevational gradients to elucidate the potential impact of climate change on these functionally relevant components of the forest biota of the Alps. Eight elevational gradients were selected from a regional forest database matching the requirement of hosting spruce-dominated forests within the whole elevational range of this forest type (900-1900 m). We calculated the decay of species compositional similarity along the gradients, considering the beta diversity components, turnover and richness difference. We then assessed the importance of temperature in explaining variation in these components of beta diversity along the elevational gradients by using a distance-based redundancy analysis. Our results warn against the impact of climate change on epiphytic bryophyte and lichen communities in alpine spruce forests. This impact could be more rapid (higher rate of similarity decay) and severe for lichens, triggering species loss with temperature warming. In contrast, temperature warming is expected to cause relevant shifts in species composition to bryophyte communities, despite allowing to maintain species richness through species replacement. The contrasting mechanisms (species loss vs species replacement) by which climate influences bryophyte and lichen communities, suggest that conservation strategies should be tailored to each organism group. In particular, for bryophytes conservation efforts should be assigned to forests at each band of the elevation gradient which hosts peculiar assemblages. In contrast, for lichens priority for conservation should be assigned to forests at higher elevation that currently host the largest species pool. In this context, forest management is the primary tool available to mitigate the effect of climate change and to give a chance to delay the local extinction of several species.