YOSEMITE Vegetational Changes in Yosemite Valley NPS Occasional Paper No. 5

Yosemite Valley in California's central Sierra Nevada has been used primarily as a recreational site since its discovery in 1851. Recreational facilities needed to make the valley accessible and to enhance or maintain its beautiful setting have impacted upon the vegetation, animals, and soil in many ways. Crops, planted pastures, haymaking, horses, dairy animals, corrals, a slaughter house, and fencing preceded automobiles and refrigeration. Roads, campgrounds, a garbage dump, a sewage plant, barrow pits, drainage tiles, buildings, walkways, water developments, and utility lines, enhanced the safety, comfort, and pleasure of visitors. Subtle control occurred in populations of tree seedlings in the meadows, weeds, deer, bear, and forest insects. Removal of trees for building sites, firewood, safety, and vista clearing as well as other ecological influences continues today. It is a necessary situation with more than two million visitors per year in Yosemite Valley.

Despite these disturbances, Yosemite Valley has a healthy vegetational cover. Several conclusions were reached after analysis of photographs (some over 100 years old), written materials in park files, age structure of forest stands, botanical composition in relation to soil development, and vegetational measurements over a 10-year period. Forest stands have thickened with the continuous establishment of trees over the last 100 years. Half of the area that was meadow in the late 1800s is now forest. All of the meadows might have disappeared without the intentional and unintentional control of trees. All the soil types in the valley support trees and many sites are excellent for tree growth. Plant succession on a bare area proceeds rapidly from annual broadleaved plants through annual grasses, perennial grasses, and sedges to dominance by a mixed coniferous forest. Introduced plant species altered botanic composition in all stages of grassland succession, but overall meadow views remain essentially unchanged. Young trees must be removed continually from the meadows to maintain the vistas of waterfalls, granite cliffs, and mountain spires. Suggestions for vegetational management are given.