Extrapolating critical loads of nitrogen for alpine vegetation and assessing exceedance in national parks based on TDep Total N from 2002–2016
McClung JJ, Bell MD, Felker-Quinn E. 2021. Extrapolating critical loads of nitrogen for alpine vegetation and assessing exceedance in national parks based on TDep Total N from 2002–2016. Natural Resource Report. NPS/NRSS/ARD/NRR—2021/2240. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/nrr-2284914
Excessive deposition of atmospheric nitrogen can have harmful impacts to vegetation and wildlife, especially within alpine ecosystems. Alpine environments receive high levels of reactive nitrogen deposition from upslope winds, but shallow soils and sparse vegetation make these ecosystems particularly susceptible to the negative impacts of nitrogen deposition. Bowman et al. (2012) established critical load thresholds, deposition levels below which harmful ecosystem effects do not occur, for preventing alpine vegetation community changes (3.0 kg-N ha-1 yr-1) and soil nitrate leaching (10 kg-N ha-1 yr-1). Critical loads give land managers and policy makers the ability to assess the amount of risk imposed by different levels of deposition and develop responsive management plans. This report compares these critical loads with the estimated total nitrogen deposited in the alpine area of national parks from 2002 and 2016 to identify national parks at risk of soil nitrate leaching or changes to their alpine vegetation. 14 National Parks contain alpine ecosystems, defined here as having any area above tree-line. 10 of the 14 parks are currently at risk to changes in their alpine vegetation communities and exceeded the alpine vegetation critical load in at least 80% of their alpine area in 2016. Eight of these parks either increased in exceedance area or remained at 100% exceedance from 2002–2016. The critical load of N for soil nitrate leaching was exceeded in two parks, Sequoia and Kings Canyon National Parks, in 2002 and by 2016, deposition levels in all alpine areas fell below the 10 kg-N ha-1 yr-1 critical load. Our results are likely most relevant in the four national parks (Glacier, Grand Teton, Rocky Mountain and Yellowstone National Parks) containing the indicator species, Carex rupestris, used to establish the alpine vegetation critical load. While the lack of the target species within the herbaceous community critical load indicates research is needed on additional alpine herbaceous communities, the consistency of herbaceous responses in low nutrient environments suggests that there are likely to be shifts in alpine community structure across all NPS units. Additionally, preliminary research in the Pacific Northwest has shown indications of soil N leaching at levels as low as 3 kg-N ha-1 yr-1 which enhances the value of this analysis to prioritize areas for follow-up research. High use or disturbed alpine areas are most likely to be impacted by community shifts, but all alpine areas above the critical load should be monitored to prevent the cascading impacts to wildlife and park visitor experience.
- Type
- Published Report
- Authors
- McClung, Jeremy; Bell, Michael; Felker-Quinn, Emmi
- Date of Issue
- 2021-03
- Publisher
- National Park Service
- DOI
- 10.36967/nrr-2284914
- Units
- ARD , GLAC , GRSA , GRTE , KICA , LAVO , MORA , NOCA , NRSS , OLYM , ROMO , SEKI , SEQU , YELL , YOSE
- Keywords
- alpine, carex rupestris, critical loads, nitrogen deposition, soil nitrogen, tdep
- Subjects
- Ecological Framework: Air and Climate | Air Quality | Wet and Dry Deposition , Ecological Framework: Geology and Soils | Soil Quality | Soil Function and Dynamics , Ecological Framework: Biological Integrity | Focal Species or Communities | Grassland/Herbaceous Communities