Examination of Human Impacts on the Biodiversity and Ecology of Lichen and Moss Communities

Abstract

Globally, more than half of the world's population is now living in urban areas and it is well accepted that human activities (e.g. climate warming, pollution, landscape homogenization) pose a multitude of threats to ecosystems. Largely, human-related impacts on biodiversity will hold consequences for larger ecological processes, and research looking into human impacts on sensitive epiphytic lichen and moss communities is an emerging area of research. While seemingly small, lichen and moss communities exist on nearly every terrestrial ecosystem on Earth and contribute largely to wholesystem processes (e.g. hydrology, mineral cycling, food web energetics) worldwide. To further examine human impacts on epiphytic communities, I conducted three studies examining urbanization and climate warming effects on epiphytic lichen and moss biodiversity and ecology.The first study I revisited a historic urban lichen community study to assess how urban lichen communities have responded to regional air quality changes occurring over the last nearly two decades. I further investigated, for the first time, the biodiversity of urban tree canopy-dwelling lichen communities in a native coniferous tree species, Pseudotsuga menziesii, at sites within the larger urban study. I found that urban parks and forested areas harbor a species rich community of lichens epiphytes. Further, I found evidence for the distinct homogenization of urban epiphytic lichen communities, suggesting that expanding beyond simplistic measures of biodiversity to consider community composition and functional biodiversity may be necessary when assessing the ecology and potential ecosystem services of epiphyte communites within urbanizing landscapes.ii Next, I present the first tall tree canopy study across a regional gradient of urbanization near Portland, Oregon, USA. I found that tall tree canopy epiphyte communities change dramatically along gradients of increasing urbanization, most notably by the transitioning of species functional groups from sensitive, oligotrophic species to a dominance of urban-tolerant, eutrophic species, tracking with published results from regional ground-based studies. The implications these dramatic shifts in species composition have on essential PNW ecosystem processes, like N-fixation and canopy microclimate regulation, is still not well understood and difficult to conduct ecosystem-scale projects to formally evaluate. However, we find strong evidence that native conifer trees in urban areas may provide a diversity of essential ecosystem services, including providing stratified habitat for epiphyte communities and their associated microarthropod communities and the scavenging of excess atmospherically deposited nutrients. Future work is needed to understand how losses in canopy N fixation and species with large biomass (both lichens and bryophytes) will affect nutrient and hydrologic cycling in the PNW region, which continue to undergo rapid growth and urbanization. The final chapter investigates the impacts of passive warming by O...