Experimental reintroduction and restoration outplantings from 2003-2006 have included the greenhouse propagation of Tahoe yellow cress and the planting of over 7,500 container-grown plants at 11 sites around the lake. During that time, Lake Tahoe had gone from a low lake elevation of 6,222.6ft [LTD] (Lake Tahoe Datum) in the fall of 2004 to the maximum legal limit of 6,229.1 ft in July, 2006. This tremendous fluctuation has made ideal research conditions for investigating the effects of lake level on many aspects of Tahoe yellow cress demography and habitat characteristics.
What we are Finding
Not all sites are equal. In the conservation strategy published in 2002, site were ranked into priorities from core sites to high, medium, low, and unranked sites. Overall site suitability tended to support this site ranking. Performance at Core and High Priority Restoration Sites (Avalanche, UTE, Tallac, Taylor, Nevada) exceeded that at Medium, Low and Unranked Priority sites (D.L. Bliss, Ebright, Hidden Beach, Pope, Sand Harbor).
Plant performance also varies depending on the elevation above Lake Tahoe. In general, lower elevation microhabitats (those closer to the shoreline) supported better plant performance than did high elevation microhabitats.
Outplantings in 2003 to 2005 may have successfully created new populations and enhanced existing ones. However, high lake level in 2006 inundated all of the persisting two and three year-old outplanted individuals. Observations during 2007 suggest that plants from the submerged cohorts may have reappeared at 2 of the 8 sites that experienced inundation. Although it’s not possible to determine the exact mechanism for a site, the reappearances could be from:
Estimated annual seed production in the outplanting from 2003 to 2006 suggest that these cohorts produced nearly 1.4 million seed over the last four years. A lack of information on the seed bank dynamics of the species makes it impossible to speculate on the fate of these seeds, but the sheer numbers suggest that the outplantings must have made some significant contribution to the persistence of local subpopulations.
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