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Home Water Aquatic Species and Communities

Hell Hole

Status and Trend

Interpretation and Commentary

Status: At or Somewhat Better Than Target
Trend: Little or No Change
Confidence: Moderate

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  • Relevance - Hell Hole is one of five distinct fens located within the Hell Hole Critical Aquatic Refuge (CAR; a USFS designation), which lies at the western base of Freel Peak (see above Map). At 15 acres, Hell Hole is the largest fen in the CAR and is home to the only known Tahoe Basin population of mountain yellow-legged frogs (Rana mucosa), a candidate for listing under state and federal Endangered Species Acts (Sikes et al. 2011). Fens are peat-forming wetlands that rely on groundwater input rather than precipitation. They are important sites of groundwater discharge, and may serve as indicators of shallow aquifers (Cooper 1990). Fens form slowly over thousands of years; thus, they are not easily restored once destroyed (Cooper et al. 1998). Fenshave been identified by the U.S. Forest Service (SNEP 1996; USDA 2004) and in the Tahoe Science Plan (Hymanson and Collopy 2010) asamong the most sensitive habitat types in the Sierra Nevada.Fens are hotspots of biodiversity that support rare plants, insects, and small and large mammals. Vegetation in all wetland types including fens, marshes and meadows plays an important role in recycling nutrients, trapping eroding soil, and filtering pollutants such as nitrates (Cooper and Wolf 2006). In addition, fens figure prominently in nearly all scenarios of carbon dioxide-induced global climate change because they are major sinks for atmospheric carbon (Chimner and Cooper 2002).
  • Adopted Standards - Provide for the non-degradation of the natural qualities of any plant community that is uncommon in the Basin, or of exceptional scientific, ecological, or scenic value. The Threshold Standard shall apply, but not be limited to, 1) the deep-water plants of Lake Tahoe, 2) Grass Lake, 3) Osgood Swamp, 4) Hell Hole, 5) Upper Truckee Marsh, 6) Taylor Creek Marsh, 7) Freel Peak Cushion Plant Community, and 8) Pope Marsh.
  • Indicator - The status and trend determination was based on a qualitative assessment of the natural qualities of a plant community. The natural qualities of a plant community include the current plant species assemblage, the health, age and ecological condition of those plant species, and the condition of the hydrologic regime.
  • Status – Hell Hole is not accessible by road, and the wet conditions and unstable sphagnum substrate deter hikers and cyclists. LTBMU management actions have focused on the installation of vegetation monitoring plots but the data is not yet available (Shana Gross, personal communication). Grazing was eliminated in the area in 2001 (TRPA 2007c). Recent Threshold Evaluations have assessed the status of Hell Hole as in attainment based on the low level of recreation, and minimal potentially degrading threats (TRPA 2001; TRPA 2007c). Aquantitative system for ranking the ecological integrity and quality of fens in the Sierra Nevada has recently become available (Sikes et al. 2011),and was used to assess the attainment status of the Hell Hole fen. In the 2010 Lake Tahoe Basin Fen Assessment, Hell Hole received a Conservation Significance score of 24 out of 40. Elements that contributed positively to the ranking include the presence of rare plants, animals, and vegetation associations, high physical diversity, and a high likelihood of persistence due to its size and proximity to other fens. Elements that reduced the score include its lack of unique features (relative to other fens in the area), relatively homogeneous vegetation, and the presence of the chytrid fungus (Batrachochytrium dendrobatidis), which is detrimental to rare amphibians. While chytrid fungus may be present at other fens in the Tahoe Basin, Hell Hole is the only site where presence has been confirmed (Sikes et al. 2011).A Conservation Significance ranking of 24 is midway between the highest (30) and lowest (18) score assigned to fens in the Tahoe Basin. While this is not a particularly high score, the elements that reduced the score (lack of uniqueness, homogeneous vegetation) are not indicative of compromised qualities, and the impact of the fungus on the vegetation quality is unknown. The elements that contributed positively to the ranking, especially the presence of rare species and the high viability, do indicate that the natural qualities of the site are being maintained and that the threshold is “at or better than target.”

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  • Trend Since this is the first time the status of Hell Hole has been assessed based on the Conservation Significance ranking, a trend analysis of that ranking is not possible. Recent Threshold Evaluations have assessed the trend of Hell Hole as improving after the removal of grazing in 2001 (TRPA 2007c), based on evidence that grazing is known to harm fens (Cooper and Wolf 2006). While the chytrid fungus has always been present in aquatic environments, it has only recently become pathogenic (Quinn 2005). The reason for the change is not clear but may be a result of changes in water chemistry and/or temperature. Without data, it is not possible to evaluate whether the presence of the fungus is a sign of declining conditions at Hell Hole, or whether the vegetation has in fact responded positively to the removal of grazing. There have been few changes in recreation use or management actions that have been implemented at Hell Hole in the last five years that would cause a change in the status. Therefore,the trend in the condition of Hell Hole is assessed as “little or no change.”

  • Confidence – The confidence in the status as assessed by the Conservation Significance ranking was high, but the confidence in the trend analysis was low because of insufficient data. Therefore, confidence in the status and trend at Hell Hole is determined to be “moderate.”
  • Human and Environmental Drivers - Any condition or activity that disturbs the hydrologic regime or nutrient levels of a fen, or causes drying or changes in plant composition is a threat to the function of that fen (Weixelman and Cooper 2009). Activities that threaten fens in the Sierra Nevada include timber harvest, mechanical fuel reduction treatments, road and trail construction, stock trampling, off-road vehicles, ground and surface water pumpingand water pollution (Cooper and Wolf 2006). None of these activities are present in or around Hell Hole.Hydrologic change is predicted to be the largest threat to this community, which could be exacerbated by climate change.
  • Monitoring Approach – Two different monitoring approaches have been recently implemented at Hell Hole. As part of the Region 5 Fen Assessment program, a total of 135 potential fens, including Hell Hole, have been assessed within the Lake Tahoe Basin Management Unit since 2006 (Sikes et al. 2011). Of these, a total of 47 locations have been confirmed as fens. In addition to this inventory, the Forest Service collaborated with the California Native Plant Society in 2010 to developa quantitative system for ranking the ecological integrity and quality of fens (Sikes et al. 2011).Using this ranking system, surveyors objectively score a fen on eight different criteria on a five-point scale. The criteria include such factors as rarity, biodiversity, impacts, accessibility, and uniqueness. The Conservation Significance rank is the sum of scores for each criterion and has a maximum value of 40 points. In 2010, the Conservation Significance of the 47 confirmed fens in the Tahoe Basin ranged from a low of 18 to a high of 30.

    The second monitoring approach ispart ofthe U.S. Forest Service Region 5 Range Monitoring Program designed to quantify changes in the ecological condition of wetland plant communities (Weixelman et al. 2003).The protocol is designed to classify meadows and wetlands according to dominant plant species, elevation, and site moisture characteristics, and then use a customized quantitative ecological condition scorecard for that meadow type. The user assigns an ecological condition of low, moderate, or high based on plant species composition, the presence of different plant functional groups, and other hydrogeomorphic variables. The protocol also provides information on the environmental conditions necessary to support certain rare species and the monitoring design allows for quantitatively tracking rare species abundance. In 2004, two plots and permanent photo points were established at Hell Hole (Engelhardt and Gross 2011a). Plots were re-visited in 2009/2010 but the data has not yet been analyzed. Due to the absence of any other available data, these quantitative data will likely form the basis of future Threshold Evaluations.

  • Monitoring Partners – U.S. Forest Service Lake Tahoe Basin Management Unit, California Native Plant Society


  • Monitoring Plan
  • Conceptual Model


Map of the location of fen assessment plots established at Hell Hole in 2010
(Sikes et. al 2010).

Additional Info


Additional Information

Last Updated on Wednesday, 03 October 2012 10:44