Monday, August 6, 2007

PS 7-75: Survival rates of subalpine plants in a 73-year study in Yosemite National Park

Jerry J. Smith, San Jose State University

Nine small (30.5 m x 30.5 m) plots were established in a variety of subalpine habitats by Yosemite Field School students in 1933-1938.  Students and volunteers conducted restudies of the vegetation of the plots in 1953 - 2006.  Floristic composition was tallied and individual perennial plants were accurately mapped during initial and restudies, allowing determination of survival and recruitment rates. On Plot 1, on a rocky, sandy ridge at 2700 m elevation, 12 % of 1020 perennial plants mapped in 1933 survived until 1983, and 5 % survived until 2006, when they made up 3.4 % of the perennial plants present on the plot. An additional 34.7 % of perennial plants present in 2006 were at least 23 years old (first recorded in 1983); only 37.6 % of plants were less than 14 years old  Older plants had higher survival rates between census dates than younger plants, presumably because they had been “previously tested” and had the most favorable microsites.  The surprising stability of species composition and longevity of individual plants occurred despite apparent warming and drying of the plot, reflected in limited recruitment and reduction in the number of trees (n=28 in 1933 and n=16 in 2006).

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