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Home Land Upland Species and Communities

Tahoe Draba (Draba asterophora var. asterophora)

Status and Trend

Interpretation and Commentary

TAHOE DRABA


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

 

  • Relevance - Tahoe draba (Draba asterophora var.asterophora) is a small alpine perennial plant in the Brassicaceae (Mustard) family. The species has small yellow flowers and is characterized by a pincushion growth form where all the foliage grows close to the ground in a short mound or mat (Baad 1979). The worldwide distribution of Tahoe draba is limited to high elevation (>8,000 feet) peaks in the vicinity of Lake Tahoe. Within the Tahoe Basin, the species is found at Mount Rose in the north, and the Freel Peak/Jobs Sister and Monument Peak areas in the south. Although there are a few occurrences located adjacent to the Lake Tahoe Basin in the Humboldt-Toiyabe National Forest, the largest number of plants occur in the Tahoe Basin populations; thus the status of Tahoe populations is critical to the viability of the entire species.Tahoe draba has special designations by TRPA and the U.S. Forest Service, who provide the plants with increased levels of protection.
  • Adopted Standards  - Maintain five Tahoe draba population sites.
  • Indicator -  The total number of population sites that are maintained as suitable habitat as determined by a qualified expert.
  • Status –  The Tahoe draba currently exists in the Lake Tahoe Basin in three general locations near Freel Peak, Monument Peak, and Mt. Rose. Plants are mapped and tracked at these locations in a combined total of 34 population sites, which is considerably more than the target of five population sites. Therefore, the Threshold Standard is in attainment and was determined to be “considerably better than target.”
  • Trend – Quantitative monitoring of Tahoe draba began in 2004 when plants were located and counted at 22 population sites (Englehardt and Gross 2011b). An additional three sites were added in a limited survey in 2005. All sites were re-surveyed in 2009. Between 2004/05 and 2009, plant counts at 22 of the 25 population sites (88%) were stable, increased at two (8%) and one site originally identified was not found (4%). In 2009, nine new population sites were added, bringing the total number of sites to 34 (above figure). The addition of new sites may point to an increase in the abundance of Tahoe draba, or simply an increase in survey effort, but with only two data sets it is not statistically possible to assess a trend. Given the fact that plant counts at 88% of the population sites were stable over the last five years and that the high elevation cushion plant community where Tahoe draba occurs is known to be a naturally stable type, a conservative approach leads to the conclusion that there was no change in the trend of Tahoe draba.

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  • Confidence  - There is a high degree of confidence in the status based on the quality of the data collected and the robust nature of the monitoring program. However, there is low confidence in the trend determination because the trend analysis is based on data from only two sample periods in 2004/05 and 2009. Therefore, there is a “moderate” level of confidence in the status and trend.
  • Human and Environmental Drivers - Human activities that pose direct threats include recreational activities that might trample or uproot plants (e.g., camping, hiking, equestrian use, trail construction, snowmobiles) and the construction and maintenance of ski resort facilities. Freel Peak is a popular hiking destination because it is the tallest peak in the Basin, and trampling of Tahoe draba in the area has been observed (Engelhardt and Gross 2011b). Snowmobile traffic may increasingly be cause for concern at the Mount Rose and Freel Peak/Jobs Sister areas (Engelhardt and Gross 2011b). Tahoe draba is found at both Heavenly Ski Resort and Mt Rose Ski Tahoe where construction and maintenance of ski facilities have the potential to directly impact entire population sites. Preliminary results from one study indicate that grading of ski runs is correlated with lower plant densities, smaller plant sizes, and higher annual mortality rates (Smith et al. 2008). The strongest environmental driver of Tahoe draba distribution and abundance may come through changes in precipitation type, timing, and quantity associated with climate change. Decreased snowpack and/or earlier snowmelt have the potential to impact populations by altering plant community composition and species interactions, and decoupling plant flowering periods and insect pollinator visitation.
  • Monitoring Approach – A comprehensive monitoring program for Tahoe draba was initiated in 2009 when long-term plots were installed at nine population sites (Engelhardt and Gross 2011b). These populations are visited every five years, or more frequently when data suggests the population is decreasing. The monitoring objective is to provide a quantitative and consistent method for evaluating status and trend, especially at sites comprised of large numbers of plants where it is difficult to accurately count individuals. Monitoring in permanent plots allows for more repeatable and efficient surveys.
  • Monitoring Partners – Ecology and botany staff from the U.S. Forest Service – LTBMU, and the Humboldt-Toiyabe National Forest developed the long-term monitoring plan. The U.S. Forest Service is monitoring populations on both forests.

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Map

 

 

 

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Trend Charts

Chart data not available at this time.
Number of population sites of Tahoe draba where plant counts decreased, increased, were stable, or where new population sites were detected between 2004 and 2009. Source: U.S. Forest Service - LTBMU.

Additional Info

References

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Additional Information

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  3. Conceptual Model:
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Last Updated on Tuesday, 13 November 2012 11:58