Historical State of Ecosystem

Yosemite National Park is located within Yosemite Valley, a glaciated landscape in the Sierra Nevada Mountains.  Rock fall is responsible for creating Yosemite's scenery-- more than six hundred rock falls have occurred in the park during the past 150 years.  (Colten, 2011)  Glaciation has created U-shaped canyons, rounded domes like Half Dome, waterfalls like Bridal Veil Falls and Vernal Falls, and jagged peaks.  Two glaciers still remain at Mount Maclure and Mount Lyell.  Spring floods from river channels redistribute rock, soil, silt, and sand.  The ecosystem lacks water in the summer, and some thirsty plants must go dormant in order to survive.  3% of Yosemite's area is meadows, which act like sponges as they absorb and hold water when snowpack melts.  ("Yosemite National Park", 2011) Meadows contain one third of all plant species found in the park, and a large portion of the park's animals depend on meadow for habitat or food. When Euro-American settlers discovered Yosemite's meadows in the 1850's, they were surrounded by open conifer forests and woodlands.  Conditions changed when pioneers transported cattle and sheep onto Yosemite Valley Meadows and planted non-native species for grazing.  In the 1860's, grazing increased because of droughts in the Central Valley-- during the peak of the wool industry after the decline of the Gold Rush.  Use of these meadows decreased in the 1900s.  American Indians used to burn these meadows, but settlers stopped anthropogenic burning.  Fire might have promoted meadow stability by reducing the encroachment of the surrounding forests, but there is not enough evidence to make this claim for all meadows.