An analysis of long-term survey data revealed that the level of Lake Tahoe is one of the most important determinants of TYC presence around Lake Tahoe. Although it reflects the form and amount of annual precipitation, the upper 6 feet of Lake Tahoe is actively managed as a reservoir with a natural sill at 6 223 feet Lake Tahoe Datum (LTD) and a legal maximum of 6 229.1 feet LTD that was established by Federal Court decree in 1941. The survey period from 1979 to 2006 encompassed two complete cycles of lake level fluctuations.

Obtain technical reports on the lake-wide annual survey from the TYC Virtual Library.

The number of Tahoe yellow cress occurrences around the lake correlates directly with fluctuating lake levels. Wide expanses of beach are available for colonization and the number of occupied sites is generally high when the lake is low. When the lake rises, less habitat is available and the number of occupied sites declines. As the amount of available habitat declines pressure from recreation intensifies in the remaining beach habitat. It is this recurrent combination of artificially high lake levels imposed by dam operations and increased trampling from recreational beach use that pose a continued threat to TYC.

As a result of the biological meta-analysis, the Conservation Strategy proposed a mainland –island metapopulation model for TYC. This model of metapopulation dynamics refers to spatio-temporal changes in distribution and abundance where “mainland” subpopulations persist over long periods of time while other “island” subpopulations come and go through the processes of local colonization and extirpation. Thus, the species can persist in sandy beach habitat around Lake Tahoe despite periodic high water levels and human-related impacts. The overall intent of the TYC Conservation Strategy is to preclude the need to list Tahoe yellow cress under the Endangered Species Act (ESA) through restoration of a self-sustaining metapopulation dynamic.

The number of occupied sites around Lake Tahoe dipped perilously low in 1995 and 1996 to only 9 sites. In response to this near extinction event, a Technical Advisory Group (TAG) was formed to develop and implement a conservation strategy for the species. Development of the Conservation Strategy began with the synthesis of a 22-year monitoring dataset in an attempt to clarify the stressors to the species its habitat at Lake Tahoe. Existing populations were then prioritized for conservation with a ranking system based on the abundance, persistence, and variability of each subpopulation. The site rankings formed the foundation for the specific goals and objectives of the Conservation Strategy. An adaptive management framework was developed for structuring information flow and making management decisions. An Imminent Extinction Contingency Plan was devised defining the types and degree of actions to be taken when the number of populations and/or the sizes of populations become critically low, so that the level of effort and resource commitment was acknowledged by all stakeholders in advance. Another year was spent reviewing, discussing and revising the draft strategy by all potential stakeholders, including the general public. After external review the strategy was formally adopted in 2002 through a memorandum of understanding / conservation agreement (MOU/CA).