Epiphytic lichens, nitrogen deposition and climate in the US northern Rocky Mountain states

Abstract

Forested ecosystems in the NW Interior Mountains (NWIM) of the United States are jeopardized by degrading air quality and changes in climate regimes. Monitoring and tracking changes in air quality and climate through instrumentation alone can be an expensive and challenging task. Biomonitors offer a cost-effective way to maximize monitoring resolution. This thesis explored the utility of lichens as biomonitors across three sections of the NWIM. First, in the Wind River Range, WY, nitrogen concentrations (%N) in lichen thalli were calibrated with measurements of canopy throughfall N deposition. A strong correlation verified % N as a useful metric to estimate N deposition. Nitrogen deposition in the Boulder drainage, closest in proximity to large natural gas drilling operations, was clearly elevated above estimated background conditions and measurements from other drainages. Degraded lichen communities were observed at deposition levels of 4.0 kg N ha -¹year -¹. The second study used lichen community composition, elemental analysis, and lichen functional groups to analyze the importance of nitrogen deposition and climate on lichen communities along the northern Rocky Mountains. Temperature and relative humidity were the most important climatic influences on community structure. A nitrogen pollution signal was independent of climate. The relationship between % N in lichen thalli and throughfall N (study 1) was used to estimate N deposition along the northern Rocky Mountains. Eutroph (N-tolerant) and oligotroph (N-sensitive) functional group indices were correlated with both N deposition and climate. Elevated N deposition (twice background conditions) was most notable around Bozeman, MT and Pinedale, WY. The final study stratified plots across the NWIM by latitude and longitude and found precipitation, dew point, and temperature were important variables to lichen community composition. Eutroph and oligotroph distributions were partially accounted for by climate; unfortunately no N data were available for comparison to lichen communities. The models created can be utilized for monitoring changes in lichen communities over time and to predict N deposition and climate conditions for new plots. Additionally, these models can be used to address management and conservation questions related to individual lichen species, lichen communities, forest health, air quality, and climate conditions.