Evaluating Letharia vulpina transplants for bioindication of nitrogen deposition

Abstract. The epiphytic lichen Letharia vulpina has been commonly sampled in-situ for nitrogen (N) deposition biomonitoring studies but has never before been transplanted for this purpose. In the high-elevation wilderness areas of southern California Letharia vulpina is generally uncommon, making in-situ sampling difficult. In this study, we compared thallus N accumulation between in-situ Letharia vulpina reference samples from the relatively low N deposition environment of the northern Sierra Nevada mountains and Letharia vulpina transplants that were deployed at nine plots of varying climatic and N deposition regimes in the southern Sierra Nevada mountains for 12 months. Survival of transplants was low (33%) and only occurred at the plots within the current range of Letharia vulpina. Transplant N concentrations became higher than those of the reference samples, while transplants that died had a net loss of N. Transplants that survived had strong relationships of N concentrations to N deposition and approached N concentrations of in-situ Letharia vulpina at the same plots. At the same time, reference plot N concentrations in a relatively clean environment increased substantially from early summer 2020 to 2021, presumably in response to extended exposure to smoke from huge wildfires in summer and fall of 2020.