tahoemonitoring.org

  • Increase font size
  • Default font size
  • Decrease font size
Home Land Upland Species and Communities

Tahoe Yellow Cress (Rorippa subumbellata)

Status and Trend

Interpretation and Commentary

TAHOE YELLOW CRESS


Click to interpret this icon

Status: Considerably Better Than Target
Trend: Moderate Improvement
Confidence: High

 

  • Relevance - Tahoe yellow cress (Rorippa subumbellata) is a small perennial plant in the Brassicaceae (Mustard) family. The species has small yellow flowers and is characterized by fleshy leaves and a spreading growth form (Ferreira 1987). Tahoe yellow cress occurs on the sandy shores of Lake Tahoe and nowhere else in the world (CNPS 2010).The species is listed as Endangered in California, Critically Endangered in Nevada, and has been a candidate species for listing under the federal Endangered Species Act since 1999. This high level of protection is the greatest of any plant occurring in the Basin. In response to near extinction of the species in the late 1990s, a Conservation Strategy for Tahoe Yellow Cress was completed in 2002. Thirteen stakeholders, including TRPA, signed a Memorandum of Understanding agreeing to implement the strategy (Pavlik et al. 2002).
  • Adopted Standards  - Maintain 26 Tahoe yellow cress population sites.
  • Indicator - The total number of population sites that are maintained as suitable habitat as determined by a qualified expert.

Click here for more information...

  • Status – The current Threshold Standard of 26 population sites was established in 1982 when the survey record for Tahoe yellow cress had only three years of data (TRPA 2007c). Since then, standardized surveys for Tahoe yellow cress have been conducted in the first week of Septemberat up to 62 population sites around Lake Tahoe (Stanton and Pavlik 2010). These monitoring sites are distributed around the entire Lake shoreline, and each site is known to have supported Tahoe yellow cress at some point since the species was first described in 1941. In 2002, the Conservation Strategy illustrated that the distribution and abundance of Tahoe yellow cress in any given year is closely linked to the water elevation of Lake Tahoe; the greatest number of sites is occupied when Lake elevation is low (Pavlik et al. 2002).Lake Tahoe is regulated between the natural rim at 6,223 feet (Lake Tahoe Datum, LTD) and the maximum legal limit set at 6,229.1 feet LTD. Tahoe yellow cress habitat occurs solely on sandy beaches within this zone. With respect to Tahoe yellow cress, the Lake is considered low (6,223-6224 ft.), in transition (6,225-6226 ft.), or high (>6226 ft.) as measured in the first week of September when the surveys are conducted. The current dataset from 1979 to 2011 includes 26 years where >50% of the known population sites were monitored, and is balanced with a nearly equal number of years of low (10) and high (11) Lake level years, with five transition years. During this period the average number of occupied sites at low Lake levels was 36.8, in transition years it was 28.8, and at high Lake levels only 14.5 sites were occupied. This long-term dataset reveals that the current Threshold Standard is not likely to be met under high Lake levels, but that it is attainable at most other Lake levels. Over four of the last five years (no survey was conducted in 2010)the number of sites occupied by Tahoe yellow cress ranged from a low of 25 in 2011 to a high of 46 sites in 2009 (see above figure). During this three-year period, the average number of population sites occupied by Tahoe yellow cress was 34, which is considerably more than the target of 26. The Threshold Standard is in attainment, calculated at 131% of the Threshold Standard over the last five years. The indicator was determined to be “considerably better than target.”
  • Trend – The trend for the species in any given period varies with Lake level. Over the last five years Lake level has fluctuated from high to low and back to high again, while the number of population sites occupied by Tahoe yellow cress fluctuated from 24 to 46 and back down to 25 (see above figure). In the previous five-year period, the number of occupied sites fluctuated between 29 and 47, so the short-term trend of Tahoe yellow cress has not changed. In contrast, the trend for Tahoe yellow cress since the adoption of the Conservation Strategy in 2002 has shown rapid improvement. During the period from 1979 to 2001, an average of 39 sites was surveyed each year and 19 of those sites were occupied. From 2002 to 2011, the average number of surveyed sites climbed to 59, and 39 of those were occupied. Some of this increase may be due to an increase in survey effort and because there were fewer high Lake level years from 2002-2011 than in the previous survey period. Since there was no change in the short-term, but a rapid improvement in the longer term, the overall trend for Tahoe yellow cress was determined to be “moderate improvement.”
  • Confidence  - There is a high degree of confidence in the status and trend based on the longevity of the monitoring program and the quality of the data collected.
  • Human and Environmental Drivers - High levels of recreational activities that can cause trampling of plants on both public and private beaches pose a significant threat to Tahoe yellow cress (Stanton and Pavlik 2011).Beach raking to remove debris and vegetation, and construction of piers, jetties, and other structures can directly destroy plants and decrease the amount of suitable habitat (Pavlik et al. 2002). These human-caused impacts are intensified when the level of Lake Tahoe is high (>6,226 ft. LTD), and less sandy beach habitat is available due to the geometry of the filling basin (Pavlik et al. 2002). Successive years of high Lake level have the potential to seriously reduce the presence and abundance of Tahoe yellow cress; between 1995 and 2000, the number of occupied Tahoe yellow cress sites declined from 37 in 1993, to only 9 in 1995-96, prompting concerns of imminent extinction of the species (Pavlik et al. 2002). Climate change may also adversely affect Tahoe yellow cress populations through altered levels of runoff into the Lake.
  • Monitoring Approach – Quantitative monitoring of Tahoe yellow cress began in 1979 (Knapp 1979). Survey effort has varied over the years, but the number of regularly surveyed locations has expanded during that time from 38 to 62 population sites (Stanton and Pavlik 2010). At occupied sites, the abundance of Tahoe yellow cress is recorded as stem counts, and notes are taken regarding land use and potential or actual impacts to the species. In 2010, the Tahoe yellow cress Adaptive Management Working Group (AMWG) shifted from an annual survey to an adaptive survey strategy where the Lake-wide monitoring effort is now linked to Lake level (Stanton and Pavlik 2011). Surveys are conducted every year that the Lake is at or above 6,226 ft. LTD, and every other year when the Lake is lower.
  • Monitoring Partners – Monitoring is implemented by the AMWG. Members include resource staff from the following entities: TRPA, U.S. Forest Service, US Fish and Wildlife Service, US Bureau of Reclamation, California State Parks, California Tahoe Conservancy, California Department of Fish and Game, California State Lands Commission, Nevada Division of State Lands, Nevada Division of Forestry, Nevada Natural Heritage Program, Natural Resources Conservation Service, Tahoe Resource Conservation District, Nevada Tahoe Conservation District, and Tahoe Lakefront Owner’s Association.

Links

 

Map

 

 

 

click map for larger image

Trend Charts

Chart data not available at this time.
 

Additional Info

References

  1.  
  2.  
  3.  

Additional Information

  1.  
  2.  
  3. Conceptual Model:
  4. Monitoring Plan:
Last Updated on Tuesday, 13 November 2012 11:50