Determinants of lichen diversity and community assembly along elevational gradients in Central Argentine mountains

The distinctive features of alpine ecosystems, along with complex evolutionary and migration patterns, contribute significantly to the remarkable species richness found within these environments. This study aimed to investigate the environmental effects of elevation and microsite characteristics on the diversity and community structure of saxicolous lichens in mountain ecosystems. We also explored the hypothesis that lichen species may migrate to more sheltered microsites in response to climate change. We surveyed 406 plots across seven elevation levels (900 to 2700 m a.s.l.), documenting saxicolous lichen species richness and community composition. Microsite factors such as rock aspect, inclination, and sun exposure were recorded. Statistical analyses included generalized linear mixed models (GLMMs) for richness and community weighted mean trait (CWM) by growth form, as well as multivariate analyses (CCA and NMS) to assess the influence of environmental variables on lichen community composition. We identified 195 lichen species, with significantly lower richness at 900 m a.s.l. compared to higher elevations. Richness was also greater on steep and south-facing rocks. Crustose CWM varied significantly with rock aspect, while foliose and fruticose CWMs were influenced by rock inclination. Multivariate analyses indicated that elevation, rock inclination, rock aspect, and sun exposure significantly shaped the community structure. The study highlights the combined influence of macro- and micro-environmental factors on lichen diversity. Crustose species tolerate harsher conditions, while foliose and fruticose lichens prefer steeper, south-facing microsites. These findings underscore the importance of considering both scales of environmental variation when analyzing the assembly and biodiversity of lichen communities, especially under scenarios of climate change.