Habitat quality and disturbance drive lichen species richness in a temperate biodiversity hotspot

The impacts of disturbance on biodiversity and distributions have been studied in many systems. Yet, comparatively less is known about how lichens-obligate symbiotic organisms-respond to disturbance. Successful establishment and development of lichens require a minimum of two compatible yet usually unrelated species to be present in an environment, suggesting disturbance might be particularly detrimental. To address this gap, we focused on lichens, which are obligate symbiotic organisms that function as hubs of trophic interactions. Our investigation was conducted in the southern Appalachian Mountains, USA. We conducted complete biodiversity inventories of lichens (all growth forms, reproductive modes, substrates) across 47, 1-ha plots to test classic models of responses to disturbance (e.g., linear, unimodal). Disturbance was quantified in each plot using a standardized suite of habitat quality variables. We additionally quantified woody plant diversity, forest density, rock density, as well as environmental factors (elevation, temperature, precipitation, net primary productivity, slope, aspect) and analyzed their impacts on lichen biodiversity. Our analyses recovered a strong, positive, linear relationship between lichen biodiversity and habitat quality: lower levels of disturbance correlate to higher species diversity. With few exceptions, additional variables failed to significantly explain variation in diversity among plots for the 509 total lichen species, but we caution that total variation in some of these variables was limited in our study area. Strong, detrimental impacts of disturbance on lichen biodiversity raises concerns about conservation and land management practices that fail to incorporate complete estimates of biodiversity, especially from ecologically important organisms such as lichens.