Lichens are globally distributed and are key contributors to ecosystem function, constituting a major portion of the ground-layer biomass in forest, desert, and tundra ecosystems. Recent analyses of vegetation change have found that in many ecosystems, lichens are declining in response to ongoing anthropogenic climate change. Despite their ecological importance and their sensitivity to global change, the mechanisms driving lichen community structure are poorly understood. Here we investigated how abiotic and biotic factors jointly influence terricolous lichen cover and diversity in the alpine tundra. In 88 long-term vegetation survey plots at the Niwot Ridge LTER, Colorado, we quantified terricolous lichen species composition using visual estimates of percent cover. We then linked these data with existing plot-level topographic, hydrologic, and plant trait datasets to construct separate spatially-explicit linear models for lichen cover, richness, and diversity. Each model allowed us to evaluate these responses as a function of aspect, slope, elevation, snow depth, net primary productivity, and plant functional traits associated with the leaf economic spectrum in order to jointly evaluate the abiotic and biotic factors that influence terricolous lichen biodiversity patterns in alpine tundra.
Results/Conclusions
We found that terricolous lichen composition varied across the 88 plots we surveyed and that abiotic and biotic factors jointly influence lichen biodiversity in the alpine tundra. In plant communities with more resource acquisitive functional traits (i.e., taller plants with higher specific leaf area), we found decreased lichen richness and diversity, an effect that is independent of plant community biomass (e.g. NPP). Additionally, while we found higher lichen cover in plots with less snow, we found no effect of variable snow depth across the landscape on lichen richness or diversity. Taken together, our results suggest that terricolous lichens may be less sensitive to anthropogenic changes to snow depth, but more sensitive to changes in plant functional composition, where long-term trends including increasing plant height, leaf area, and resource acquisitive strategies will negatively impact lichen biodiversity.