Risk to epiphytic lichen communities in NPS units from atmospheric nitrogen and sulfur pollution: Changes in critical load exceedances from 2001‒2016

McCoy, Kelly; Bell, Michael; Felker-Quinn, Emmi

doi:10.36967/nrr-2287254

Human caused nitrogen (N) and sulfur (S) pollutants travel from their sources (power plants, oil & gas developments, mobile emissions, and agriculture) to national park lands and cause harm to ecosystems through fertilization and acidification. Scientists have developed critical loads of N and S deposition to communicate the levels of pollution that prevent ecosystem harm. One of the ecosystem components most sensitive to air pollution are epiphytic lichen communities. Geiser et al. (2019) developed a dose-response relationship between deposition of N and S and four metrics of epiphytic lichen species communities: total species richness, N/S sensitive species richness, forage lichens abundance, and cyanolichens abundance. From each relationship they established a critical load at a 20% loss in richness. Here the critical loads are compared to current deposition to identify areas at risk of community decline. To accomplish this, we extrapolated the dose-response relationships and applied critical loads to forested areas within national park units to assess risk from current deposition levels as well as changes in conditions from 2000–2017. Within this analysis forested areas were chosen as a proxy for the presence of epiphytic lichen communities as tree trunks, branches, and boles are the most common surface for them to grow. The National Park Service (NPS) protects 423 units across the United States, preserving natural and cultural resources. At the time of this analysis, there are 280 Inventory and Monitoring Parks with significant natural resources and 169 of these areas have forested areas greater than 1 km within the contiguous United States (CONUS). Of these 168 have modeled deposition to assess risk to lichen communities. Generally, the risk to lichen communities from both N and S deposition declined across national parks between 2000–2002 (2001) and 2015–2017 (2016). The average difference in N deposition within national parks was a reduction of 2.9 kg-N ha−1 yr−1 of deposition. The average difference in S deposition within national parks was a decrease of 5.8 kg-S ha−1 yr−1. The rate of species richness loss attributed to N deposition decreased for 88% of national parks between 2001 and 2016, and yet in 2016 89% of CONUS I&M National Park Service units (149 national parks) remained above the critical load of N for a decline in species richness (CLN-SR) of 3.5 kg-N ha−1 yr−1. The total forested area in the 168 parks that was in exceedance of the CLN-SR decreased from 2001 to 2016, indicating that the health of forests is improving. There was an increase of two NPS units that had any forested area below the CLN-SR (with improving conditions at Chaco Culture National Historical Park, Curecanti National Recreation Area, and Black Canyon of the Gunnison National Park, and deteriorating conditions at Nez Perce National Historical Park). As of 2016, 95 parks are predicted to have 100% of the forested area in exceedance of the CLN-SR. Sulfur deposition decreased more dramatically between 2001 and 2016 than did nitrogen deposition, which is demonstrated by the large number of parks and total forested area trending below the critical load of S for a decline in species richness (CLS-SR) of 6.0 kg-S ha−1 yr−1. Risk to lichen species richness from S deposition decreased in 98% of CONUS I&M National Park Service units between 2001 and 2016. By 2016, there are only 6 parks that were predicted to exceed the CLS-SR and only 9 parks that had any forested area that was at or above the CLS-SR. However, all of these parks have experienced improving conditions since 2001 in regard to S deposition. The geospatial response of epiphytic lichen species richness loss and risk to forested ecosystems from N deposition against acid deposition was evaluated for 10 case study national parks: Acadia National Park, Glacier National Park, Grand Teton National Park, Great Smoky Mountains National Park, Joshua Tree National Park, North Cascades National

Risk to epiphytic lichen communities in NPS units from atmospheric nitrogen and sulfur pollution: Changes in critical load exceedances from 2001‒2016

Series

Collections