Basics
Tahoe Yellow Cress (Rorippa Subumbellata)
Tahoe Yellow Cress
Action
Program
Each Unit (number)
No
Tahoe Yellow Cress (Rorippa Subumbellata)
The number of population sites that are maintained as suitable habitat for sensitive plant species (as determined by a qualified expert).
This Indicator is reported in the following LT Info areas:
Accomplishments

No Subcategories for this Indicator.

Program Tahoe Yellow Cress Monitoring

Approach

Knowledge of TYC distribution has been developed through shorezone surveys since 1979. Before 2000, surveys followed a general protocol and were completed at various times during the summer. Since 2001, surveys are conducted the first week of September following a standardized protocol. During the first survey in 1979, 32 TYC sites were surveyed; this has since grown to 55 sites. A survey “site” is defined as a stretch of public beach, adjacent private parcels, or adjacent parcels under a combination of private and public ownership. Surveys include stem count estimates as a measure of TYC abundance because clonal growth makes it impossible to distinguish individuals. The amount of available shorezone habitat for TYC fluctuates widely with changes in lake level, with high lake levels leaving little habitat. On average, over 70% of surveyed sites are occupied when the lake is below 6,225 ft. in September, but less than 40% are occupied when the lake level is above 6,228 ft.

To download all of the Tahoe yellow cress data on this page please see Tahoe Open Data.

Partners

Associated Programs data not provided.

Tahoe Yellow Cress (Rorippa Subumbellata) is include in the Threshold Dashboard. Threshold Indicators are evaluated against Threshold Standards every 4 years. Thresholds are environmental goals and standards for the Lake Tahoe Basin that indirectly define the capacity of the Region to accommodate additional land development.

2011 Evaluation

Status
Considerably Better Than Target
Trend
Moderate Improvement
Confidence
High

2015 Evaluation

Status
Considerably Better Than Target
Trend
Moderate Improvement
Confidence
High

2019 Evaluation

The 2019 Threshold Indicator evaluation is not available yet. Check back soon for updates.
Key Messages
About the Threshold
Vegetation Preservation
Sensitive Plants
Tahoe yellow cress (TYC, Rorippa subumbellata) is a small perennial plant in the mustard family (Brassicaceae) known only from the shores of Lake Tahoe in California and Nevada. Impacts from recreation and development led to conservation concerns as early as 1974 (Smithsonian Institute 1974). In 1982, TYC was listed as endangered by the State of California and as critically endangered by the State of Nevada. Those levels of protection are the highest of any plant species in the Lake Tahoe Region. TYC is also a U.S. Forest Service Sensitive Species. The U.S. Fish and Wildlife Service (USFWS) placed TYC on the candidate list under the Endangered Species Act several times. The first was in 1980, but the USFWS removed TYC from the candidate list in 1996 after a prolonged regional drought exposed large expanses of shoreline habitat and lake-wide surveys indicated high rates of site occupancy. In 1999, after a period of sustained high lake levels in which TYC habitat was inundated and occupied sites declined, USFWS again placed TYC on the candidate list. In October 2015, the USFWS announced a “not warranted” finding and removed TYC from the federal candidate list due to the successful implementation of the Tahoe Yellow Cress Conservation Strategy (Pavlik et al. 2002, Stanton et al. 2015).
Knowledge of TYC distribution has been developed through systematic lake-wide surveys that have been completed in targeted parts of the Lake Tahoe shorezone since 1979 (Knapp 1980, CSLC 1994, Pavlik et al. 2002, Stanton et al. 2015). The primary driver of TYC distribution and abundance is the level of Lake Tahoe. The amount of available shorezone habitat for TYC fluctuates widely with changes in lake level such that large amounts of shorezone habitat are exposed at the lowest lake levels, and as Lake Tahoe rises, these areas are inundated due to the geometry of the filling Region (Pavlik et al. 2002). The natural rim of Lake Tahoe occurs at 6,223.0 feet (1,896.8 meters) and the high water line at 6,229.1 feet (1,898.6 meters) Lake Tahoe Datum (LTD). TYC has been found at elevations lower than the natural rim, but occurrences above the high water line are rare (Stanton and TYCAMWG, 2015). Although lake level is controlled in part by the operation of the dam at the outlet of Lake Tahoe in Tahoe City, California, lake level is primarily controlled by environmental factors that increase water input (tributary stream discharge and precipitation) or cause water loss (evaporation and outflow to the Truckee River) (Reuter and Miller 2000). Successive years of high lake levels have the potential to seriously reduce the presence and abundance of TYC as was observed between 1995 and 2000 when the number of occupied Tahoe yellow cress sites declined from 35 in 1993 to only eight in 1995-96, prompting concerns of imminent extinction of the species (Pavlik et al., 2002). The effect of climate change on TYC depends on how climate changes affect the level of Lake Tahoe. The climate-related scenario with the greatest threat to TYC would be a drought-induced period of sustained low lake level followed by a rapid rise in lake level which inundates TYC plants across the entire elevation range of the species (Stanton and TYCAMWG, 2015). If this occurred, species viability would depend entirely on recruitment from the seedbank and re-sprouting of submerged rootstocks after the lake receded. Recreation and land management practices on the beaches of Lake Tahoe are the primary human drivers of TYC distribution and abundance and constitute the greatest manageable threat to TYC and its habitat (Stanton and TYCAMWG, 2015). Trampling from human foot traffic and dogs may directly destroy plants, roots, and/or seeds and inhibit germination and recruitment of seedlings. Beach raking to remove debris and vegetation can directly destroy plants and decrease the amount of suitable habitat. These human-caused impacts are intensified when the level of Lake Tahoe is high (greater than 6,226 feet) and use is concentrated on smaller amounts of shoreline. Although significant development in the shorezone occurred prior to the adoption of the TRPA Regional Plan in 1987, current TRPA regulations strongly limit the types and amount of development that can occur in the shorezone of Lake Tahoe and the threat to TYC from future development of additional boat launch facilities in the shorezone is expected to remain relatively small (Stanton and TYCAMWG, 2015).
Standards
Numeric
Rorippa subumbellata – Tahoe yellow cress (26)