COS 97-1 - Assessing nitrogen deposition in mountainous regions using epiphytic lichen communities

Abstract: Anthropogenic nitrogen (N) deposition (N_dep) disrupts nutrient and carbon cycling, ecosystem function, biodiversity, and community composition across the globe. Ecosystems located in mountainous regions are potentially sensitive to nutrient enrichment from anthropogenic N_dep as they are often nutrient-limited and receive high amounts of precipitation. Epiphytic lichen community composition can indicate atmospheric N_dep because certain species are more sensitive to N than others. Increasing N inputs can cause the loss of oligotrophic N-sensitive lichens, along with an increase of eutrophic N-tolerant species. Lichen community-based airscores are a metric for estimating N_dep that reflects the proportion of eutrophic versus oligotrophic species. The goals of this study were to determine what is driving epiphytic lichen diversity and community composition in two mountainous regions in the Pacific Northwest, USA – North Cascades National Park and Olympic National Park – and to determine if lichen communities in these regions are being affected by N_dep. Our approach was to survey epiphytic lichen communities across these regions, analyze patterns of lichen α- and β-diversity, and calculate lichen community-based airscores. Climate and deposition variables accounted for 46% of observed variation in lichen communities based on variation partitioning. Community-based airscores indicate that these regions had fairly low, background levels of N_dep. This study suggests that epiphytic lichen communities can be useful indicators to assess N_dep in mountainous regions.