Studies and Monitoring

Ongoing research in Joshua Tree NP, California:

Nitrogen & Sulfur Impacts

Joshua Tree National Park receives high levels of nitrogen deposition from air pollution that originate mainly from urban areas and automobiles to the west (Sullivan et al. 2001 [pdf, 6.3 MB]; Fenn et al. 2003). Elevated nitrogen has promoted growth of invasive and non-native grasses, reducing the diversity of native plant species (Allen et al. 2009). This is a particular concern for rare species such as the Joshua tree. Extensive areas of weedy grasses have also increased fire risk in the park. Fire risk increases exponentially when nitrogen deposition reaches 3–4 kilograms per hectare per year, the critical load for increased fire frequency. This critical load is currently exceeded in many areas of the park (Rao et al. 2010). Fires alter park ecosystems by reducing the diversity and density of native shrubs. Greenhouse and field experiments are being used to evaluate the impacts of nitrogen deposition on native plant species, and the extent to which the response of invasive species to nitrogen is promoting vegetation type conversion at the park.

Ground-Level Ozone Impacts

Ground-level ozone at Joshua Tree NP often exceed standards set by the U.S. Environmental Protection Agency to protect public health and vegetation. The high ground-level ozone levels at the park are a result of emissions from vehicles and urban areas in the nearby Los Angeles air basin (Sullivan et al. 2001 [pdf, 6.3 MB]; Fenn et al. 2003). While there are several ozone-sensitive plants in the park, limited assessments have not documented ozone injury to vegetation growing naturally in the field (Temple 1989). However, a park biomonitoring plot demonstrated that under irrigated conditions the ozone-sensitive skunkbush sumac showed typical ozone injury symptoms (Temple 1989). Earlier work showed ozone damage to native plants growing naturally in the desert outside of Joshua Tree NP (Bytnerowicz et al. 1988). This finding suggests that ozone uptake in even the arid, desert ecosystems of the park may occur in wet years, resulting in plant injury.

Air quality monitoring information and data access:

Abbreviations in the above table:

CASTNet: EPA Clean Air Status and Trends Network
GPMP: Gaseous Pollutant Monitoring Program
IMPROVE: Interagency Monitoring of Protected Visual Environments
MDN: Mercury Deposition Network
NADP: National Atmospheric Deposition Program
NPS: National Park Service
NTN: National Trends Network
VIEWS: Visibility Information Exchange Web System

For more information regarding monitoring and data assessments conducted by the National Park Service, link to the NPS Air Quality Monitoring Program or to the NPS Air Quality Monitoring History Database for a history of active and inactive monitoring sites at Joshua Tree NP.

Key air quality related references from Joshua Tree NP, California:

Allen, E. B., Rao, L. E., Steers, R. J., Bytnerowicz, A., and Fenn, M. E. 2009. Impacts of atmospheric nitrogen deposition on vegetation and soils in Joshua Tree National Park. Pages 78–100 in R. H. Webb, L. F. Fenstermaker, J. S. Heaton, D. L. Hughson, E. V. McDonald, and D. M. Miller, eds. The Mojave Desert: Ecosystem Processes and Sustainability. University of Nevada Press, Las Vegas.

Bytnerowicz, A., Olszyk, D. M., Fox, C. A., Dawson, P. J., Kats, G., Morrison, C. L., and Wolf, J. 1988. Responses of desert annual plants to ozone and water stress in an in situ experiment. Journal of Air Pollution Control Association 38: 1145–1151.

Fenn, M. E., Haeuber, G. S., Tonnesen, J. S., Baron, J. S., Grossman-Clarke, S., Hope, D., Jaffe, D. A., Copeland, S., Geiser, L., Rueth, H. M., and Sickman, J. O. 2003. Nitrogen emissions, deposition and monitoring in the western United States. Bioscience 53: 391–403.

[IMPROVE] Interagency Monitoring of Protected Visual Environments. 2010. Improve Summary Data. Available at http://vista.cira.colostate.edu/improve/Data/IMPROVE/summary_data.htm.

Rao L. E., Allen E. B., Meixner T. 2010. Risk-based determination of critical nitrogen deposition loads for fire spread in southern California deserts. Ecological Applications 20 (5): 1320–1335.

Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at www.nature.nps.gov/air/permits/aris/networks/n-sensitivity.cfm.

Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Mojave Desert Network (MODN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/330. National Park Service, Denver, Colorado. Available at http://www.nature.nps.gov/air/Pubs/pdf/n-sensitivity/mojn_n_sensitivity_2011-02.pdf (pdf, 7.4 MB).

Sullivan, T. J., Peterson, D. L., Blanchard, C. L. 2001. Assessment of Air Quality and Air Pollutant Impacts in Class I National Parks of California. National Park Service. 421 pp. Available at http://nature.nps.gov/air/Pubs/pdf/reviews/ca/CAreport.pdf (pdf, 6.3 KB).

Temple, P. J. 1989. Oxidant air pollution effects on plants of Joshua Tree National Monument. Environ. Pollut. 57: 35–47.