The Natural Resource Condition Assessment (NRCA) Program aims to provide documentation about current conditions of important park natural resources through a spatially explicit, multi-disciplinary synthesis of existing scientific data and knowledge. For a given NPS unit, NRCAs evaluate conditions for a representative subset of natural resources and resource indicators, reporting where possible on trends in resource condition. They also identify critical information gaps, and characterize a general level of confidence in study findings. The resources and indicators emphasized in a given NRCA project depend on the park’s resource setting, status of resource stewardship planning and science in identifying high-priority indicators, and availability of data and expertise to assess current conditions for a variety of potential study resources and indicators.
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Great Basin National Park was established as a national park in 1986 providing a high quality and characteristic representation of the basin and range region. Such characteristic features include the gradient of cold desert shrubland to montane forests and woodlands to alpine environments. Ancient bristlecone pine woodland occurs up along the alpine fringe of the park. Given its relatively remote location, high air quality, visibility, and brilliant night skies are also featured. The park encompassed the Lehman Caves National Monument which was created in 1922 to preserve its outstanding cave resources. The NRCA for Great Basin National Park began in 2012 and 16 focal natural resources and ecological stressors were chosen for assessment. These assessments were arranged into four categories including landscape resources, upland resources and ecological integrity, aquatic resources and ecological integrity, and future landscape conditions. This project used a structured ecological integrity assessment framework to evaluate conditions of ecological resources. The framework applies most directly to two of the four thematic resources categories – upland resources and aquatic resources – because these are categories of ecological resources. Primary steps to apply this framework include: identifying the key ecological attributes for each focal resource on which to further focus assessment and subsequent management, identifying indicators for each key attribute for each resource, identifying an expected or reference range of variation for each indicator for each resource, and documenting the status and trends of each focal resource based on indicator data, comparing measured conditions to expected or reference conditions.
The landscape resources selected for assessment included air quality, viewsheds, night sky, and rock glaciers. Current conditions for air quality, viewsheds, and night skies at the park are some of the best in the country. Dark night skies and expansive vistas in and around the park draw many visitors annually. Their excellent condition results largely from the park’s location in the Great Basin – a region with generally little urban and industrial development and few sources of light or air pollution. Great Basin NP has a well-established, long-term monitoring program in place for air quality; and recent measurements by the Night Sky Program scientists provide excellent baseline data for future monitoring of night sky conditions.
However air quality is of some concern due to the sensitivity of the park’s ecosystems to pollutants; in particular nitrogen and sulfur deposition and elevated ozone levels. Regional haze affects long-distance views and has reduced the visual range. Views from the west-side of the park are affected by the Spring Valley Wind Farm, which contrasts with views of the surrounding rural landscape. Rock glaciers are another landscape resource in need of monitoring to detect potential effects of climate change. Increasing ambient temperatures could result in changes to the shape and size of these alpine glacial features.
Upland Resources and Ecological Integrity
Assessed upland resources and indicators included wildfire regime, aspen-mixed conifer forest, sagebrush steppe, and bighorn sheep. Introduced animals and plants, including wild turkey and invasive annual grasses, were also assessed. Upland resources vary in their condition and ecological integrity across the park and surrounding landscape. Current conditions reflect a long history of land use, where past grazing and fire suppression have had lasting effects on upland vegetation, including promoting or allowing the colonization of the park by non-native species. In most native plant communities, late successional vegetation stages are over-represented relative to earlier stages as a result of past suppression of natural wildfire. This condition has many cascading effects, such as limited tree species regeneration in aspen communities, or encroachment of other tree species into sagebrush communities. These effects limit the suitability of habitat for species such as bighorn sheep, likely limiting population viability. Introduced plant species, such as annual cheatgrass, can severely alter vegetation composition and fire regime, especially given the naturally great extent of sagebrush vegetation at lower elevations within and surrounding the park. Wild turkeys, introduced nearby for sport hunting, may be an increasing cause of concern for their effects on park resources. Reintroduction of historically characteristic fire regimes across most park vegetation represents one management response, and can be advanced in places through the safe use of prescribed burning. Challenges to the safe and effective management of fire within the park are many and significant, but taking actions to address the need for a more natural fire regime in the park will remain an important priority into the future.
Aquatic Resources and Ecological Integrity
Aquatic resources vary relatively little in their condition and ecological integrity across the park. The resources and indicators that were assessed included water quality, montane riparian woodlands, Bonneville cutthroat trout, cave and karst processes, and springs. These aquatic resources are all parts of a single hydro-ecological system shaped by the geology and topography of the South Snake Range. The dynamics of this hydro-ecological system are naturally driven by inputs of rain and snow. In turn, these dynamics are shaped by watershed cover and evapotranspiration, surface runoff and groundwater recharge from rainfall and snowmelt, groundwater flow and discharge through the park’s bedrock fracture and karst geology, and the diversity of native terrestrial, riparian, semi-aquatic, and aquatic species that have found their ways into the South Snake Range over many millennia. Changes in precipitation and air temperatures, deposition of atmospheric pollutants, chemical contamination from past land uses, alterations to watershed hydrology through surface development or changes in ground cover, surface water diversions and groundwater pumping, introductions of non-native aquatic species, and visitor traffic through caves all have the potential to alter the park’s natural hydro-ecology both above and below ground.
The assessment found some evidence of changes in hydrologic inputs or in factors that shape watershed hydrologic function that result in altered hydrology within the park. Diversions take place from four springs and from one of the park’s streams. A pipeline carries all of Snake Creek’s flow past a 3-mile (4.8-km) reach. The pipeline interrupts the natural hydrologic processes of the creek and impacts aquatic resources, including fisheries, riparian vegetation, and karst processes. Groundwater pumping in the surrounding valleys does not presently affect springs and streams within the park, but could in the future. Riparian vegetation is in good condition throughout most of the park but encroachments of woody vegetation – an issue across the park’s upland plant communities as well – is a matter of concern.
Atmospheric deposition of nitrogen and sulfur compounds, which can disrupt aquatic chemistry and nutrient cycles, has declined for decades and now meets expectations for natural background deposition. On the other hand, the park continues to experience a high rate of atmospheric deposition of mercury, although there is no evidence that the mercury is bio-accumulating in the aquatic food web to harmful levels. The frequency with which water samples exceed water quality standards for supporting aquatic life has declined over time and the few remaining occurrences may reflect the unique geochemistry of the park rather than any contamination.
Aquatic macroinvertebrate communities in the park’s streams appear to be in good condition, showing no evidence of impacts from impaired water quality or physical habitat. And the park has carried out a highly effective program to restore the native Bonneville cutthroat trout along several streams, removing non-native trout from the restored stream sections at the same time.
Finally, the processes that shape cave and karst ecology and geologic formations appear to be intact, except for possible effects from visitors through Lehman Caves. However, additional data are needed to evaluate these possible effects. Cave visitor usage varies over time and can have both direct and indirect effects on cave resource conditions, from direct damage to cave formations to changes in cave air humidity and chemistry that in turn affect cave species and geologic processes.
Future Landscape Conditions
Climate change has a number of potential effects on park resources and values that will require concentrated investment in monitoring over the upcoming decades. Climate projections indicate that in the region surrounding the park, increasing temperatures may also coincide with increasing precipitation. As compared with temperature variables, given inherent variability in precipitation patterns, interpreting past observations and future projections is much less certain. Model projections linking climate to hydrologic models indicate a slight decline in annual flow over upcoming decades. They also suggest shift to earlier snowmelt by up to 30 days, and modest change in snowpack and annual flow by the decade including 2060.
The alpine environment faces high likelihood of significant exposure to climate change effects. Monitoring of alpine vegetation sample plots should assist with detecting trends in alpine plant composition. Phenology indicators, such as rattlesnake emergence and cutthroat trout spawning times, should also provide useful indicators for signaling biological responses to a changing climate.
Results of the NRCA will assist park staff with objectives including prioritzed management actions, Resource Stewardship Strategies and other management plans, support to interpretation of park resources and issues, and engagement in landscape-scaled partnership efforts.