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

Abstract Bryophyte communities play a vital functional role in Atlantic coastal dune ecosystems, where they contribute to soil stability, moisture retention, and nutrient cycling. However, these habitats are increasingly affected by climate change and sea level rise, with reported consequences including habitat degradation, shifts in species distributions, and the proliferation of invasive bryophyte species. To assess how bryophyte communities might respond to future climate conditions, 32 coastal dunes were studied along a latitudinal gradient on the western Atlantic coast of the Iberian Peninsula. We investigated (i) how abiotic factors related to aridity influence bryophyte cover and species composition, (ii) whether patterns of co-occurrence with vascular plants (annuals and perennials) and lichens could mitigate climate impacts, and (iii) the role of interactions between the invasive moss Campylopus introflexus and native species along the gradient. Our results showed that the moss community is mainly influenced by aridity and annual mean temperature (as defined in the WorldClim database), with biotic interactions playing a minor, yet significant, role. As aridity increases, total moss cover declines noticeably with no consistent patterns of facilitation or competition observed across sites. Based on these findings, we suggest that under future climate scenarios, coastal bryophyte communities are likely to suffer reductions in cover and associated ecosystem functions, with limited buffering potential through plant interactions and a northward shift in species distributions. At the same time, the spread of the exotic moss species Campylopus introflexus , associated with lower aridity, could also slow down. Further research is needed to better understand how these changes will affect the ecological integrity of coastal dunes, habitats already recognised as priorities for conservation.