Yosemite

COUNTRY United States of America - California
NAME Yosemite National Park
GEOGRAPHICAL LOCATION Central portion of the Sierra Nevada in central California.

PHYSICAL FEATURES Yosemite is dominated by the Sierra Nevada which is a tilted granite area. Granite underlies most of the park and is exposed as domes, partial domes, knobs and cliffs. Glaciation has influenced the topography over most of the area including the Yosemite Valley, a 914m deep cleft carved by glaciers through a gently rolling upland. The valley is a widened portion of the prevailing narrow Merced River canyon which traverses the southern sector of the park from east to west. The massive sheer granite walls present a freshly glaciated appearance with little postglacial erosion. This area also contains many waterfalls and some 300 lakes. Other notable canyons in the park are the Grand Canyon of the Tuolumne River and the Tenaya Canyon.

CLIMATE There is considerable climatic variation with mean temperatures varying some 20°C between the valleys and mountains. Annual precipitation ranges between 1270mm and2652mm with most of the rain and snow falling at middle elevations from 1,220m to 2,743m. The crests and peaks are relatively dry and the foothills and lower slopes are semi-arid.

VEGETATION There are 27 major vegetation communities, ranging from low elevation chaparral woodland to alpine fell fields above 3,900m, the most extensive being white fir (15.18% of the park), lodgepole pine (20.45%) and red fir (12.38%) dominated. The park includes 16 major forest types with 37 tree species. Within these there are three stands of giant sequoia Sequoiadendron giganteum totalling 169ha, four meadow types and black oak Quercus kelloggii woodlands. The Mariposa, Merced and Tuolumne groves of sequoias were among the first discovered by European explorers and contain many important trees, most notably the Grizzly Giant. The lower elevations are covered with chaparral woodland with digger pine Pinus sabaniana and oak Quercus chrysolepis in the overstorey and extensive brush fields of Ceonothus spp., Arctostaphylos spp. and chamise Adenostoma fasciculatum or mixed coniferous forest with ponderosa pine Pinus ponderosa, incense-cedar Calocedrus decurrens, Douglas fir Pseudotsuga menziesii, white fir Abies concolor and California black oak Quercus kelloggii.
The next elevation zone comprises meadows of three distinct types: 'low elevation' below 1,829m, 'alpine and subalpine' and 'boggy' which both occur above 1,829m and are characterised by a very high water table in late summer or early autumn. This zone also contains areas of red fir Abies magnifica with some western juniper Juniperus occidentalis, Jeffrey pine Pinus jeffreyi, western white pine P. monticola and one of the finest virgin sugar pine stands P. lambertiana in the world. Meadows are significant due to their species diversity, as even though they constitute less than 10% of the total vegetation in the Sierra Nevada and less than 4% of the park, they contain nearly 40% of the park's flora. This diversity in turn attracts an equally diverse fauna. The threatened great grey owl is directly dependent upon several meadow systems within the park. Likewise, the park's black oak woodland communities support both a diverse flora and fauna which are presently in decline throughout California.
The subalpine zone is dominated by lodgepole pine P. contorta which is also associated at higher elevations with mountain hemlock Tsuga mertensiana and whitebark pine Pinus albicaulis.Above 3,048m there is alpine vegetation with alpine willow Salix petrophila, perennial herbs, grasses and sedges which are distinctive, sparse and low growing.
The park contains a diverse flora of more than 1,400 species of flowering plant, ferns, bryophytes and lichens. Between the park and the El Portal administration site there is one endemic species Eriophyllum nubigenum, eight threatened or endangered (Federal Register), 19 locally rare species and 18 species rare for the Sierra Nevada range.

FAUNA Some 74 species of mammals and over 230 bird species have been recorded. The most commonly seen mammals include chipmunk Eutamias spp., yellow-bellied marmot Marmota flaviventris, ground squirrel Spermophilus spp., black bear Ursus americanus, coyote Canis latrans and mule deer Odocoileus hemionus. Resident but rarely seen are pine marten Martes americana, fisher marten M. pennati, wolverine Gulo luscus, mountain lion Felis concolor and Sierra red fox Vulpes vulpes necatoc. Bighorn sheep Ovis canadensis were declared extinct in Yosemite in 1914 but were reintroduced in 1986. The avifauna includes the federally endangered southern bald eagle Haliaeetus leucocephalus and peregrine falcon Falco peregrinus which successfully breeds here. Great grey owl Strix nebulosa nests in thepark. Some ten species of amphibians and 18 reptile species are endemic. The park contains 11 fish species, six of which are endemic.

SCIENTIFIC RESEARCH AND FACILITIES A total of 63 active projects during 1988 included atmospheric research (3), biology/ecology (9), hydrology (3), geology (10), zoology and animal ecology (13), botany and plant ecology (9), sociology (7), forestry (6), physics (1), epidemiology (1) and Geographical Information Systems (1). There is a research library and a museum collection containing some 2,000 bird and mammal study skins, 2,000 insect specimens, 5,000 archaeological specimens, an herbarium with 5,000 plant specimens and over 20,000 historic photographs.

CONSERVATION MANAGEMENT The park is under strict protection, although sport fishing is permitted. The park is zoned as follows: Natural Environment Protection zone 6%, Outstanding Natural Features zone 2% and Special Use zone to accommodate two reservoirs 1%. The remaining area comprises Natural Environment, Historical, Archaeological and Development zones. The park is surrounded by four national forests which provide important buffer zones.
Fire was reintroduced into the giant sequoia ecosystem and other fire-dependent communities in 1970 to ensure their perpetuation. Yosemite's General Management Plan was approved in 1980 under which facilities and vehicle traffic will be reduced in the valley. The management plan consists of three components: natural and cultural resources management; visitor use, operations and development; and interpretive prospectus. The second sub plan identifies major threats and outlines measures to address them. The Resources Management Plan identifies numerous conservation threats including concerns about air quality, exotic plants and animals, impacts to vegetation from visitation, and programmes designed to mitigate these impacts.

MANAGEMENT CONSTRAINTS Extreme visitor pressure and development of modern accommodation facilities on a large scale have had a disturbing impact. Inappropriatedevelopment and commercial services have impacted large portions of Yosemite Valley. Two hydroelectric and water storage facilities permitted under special legislation cause significant local disturbance at Hetch Heetchy and Lake Eleanor in the north-west of the park. A major trans-Sierra road bisects the park. From 1890 to 1968 management suppressed natural fires which caused significant changes to the forests. The area was heavily grazed in the past which has resulted in changes in species composition and exotic plant introduction. Grizzly bear, California bighorn sheep and possibly grey wolf disappeared from the area in the 1800s and early 1900s. A few non-native species, such as beaver and white-tailed ptarmigan have been introduced. Black bear has been adversely affected by human contact. Studies of Yosemite's backcountry areas have identified significant impacts due to campsites, trails and high Sierra camps.