Aridity and coexistence with vascular plants determine the dynamics of coastal dune bryophyte communities

The bryophyte communities of Atlantic coastal dunes help stabilising these habitats by promoting nutrient fixation, contributing to soil consolidation and enhancing water retention. Because of climate change and sea level rise, negative impacts on this dune vegetation have already been recorded, including habitat loss, shifts in species distribution and the spread of invasive bryophyte species. Moreover, in this stressful environment, biotic interactions may play a key in shaping plant diversity at these scales. We characterised coastal dune vegetation in 32 sampling sites along a latitudinal aridity gradient across the western Iberian Atlantic. We aimed to assess the potential interactions among moss species and between mosses and vascular plants, and analyse their relationship with abiotic factors to explain the community dynamics of dune bryophytes, and forecast how these communities may respond to climate change. Our results showed that the moss community is mainly influenced by aridity and temperature, with biotic interactions playing a minor, yet significant, role. As aridity increases, moss cover in these dune environments will decrease, and interactions with other plants are unlikely to compensate for this decline, thus in a climate change scenario we expect a decrease in coastal bryophyte community as well as the ecosystem services they provide; simultaneously the spread of the alien moss species Campylopus introflexus , linked to lower aridity, may also slow down. Consequently, the changing climate will shift optimal conditions for moss species to higher latitudes, pushing competition further north