Ecology of the Sierra Nevada

Foothill Woodland and Chaparral Zone The lowest-elevation biotic zone in the Sierra Nevada is found along the boundary with the Central Valley. This zone, stretching in elevation from , is the foothill woodland zone, an area that is hot and dry in the summer with very little or no snow in the winter. Animals typical of this zone include black bear, ringtail cat, coyote, gray squirrel, bobcat, California mule deer, and skunk. Lower Montane Forest is in the Lower Montane Forest. Beginning near the elevation, the hot, dry summers and cool, moist winters of the Mediterranean climate give rise to the lower montane forest zone. This zone is also known as the yellow pine forest zone. The accumulation of several feet of snow during the winter is not uncommon and can stay on the ground for several months. The diversity of tree species found in this zone make this a beautiful and interesting forest to explore. The indicator species for the lower montane forest are the ponderosa pine and the Jeffrey pine: the ponderosa pine generally occurs on the west side of the Sierra, while the Jeffrey pine occurs on the east. The character of the Lower Montane Forest changes with latitude. North of Grass Valley, the lower montane forest ranges from , with less ponderosa pine and more Douglas-fir. In the middle Sierra, south to the Merced River, the lower montane forest has the same elevation, but precipitation decreases and the forest mixes with chaparral. In addition, soils are thin and nutrient-poor. Due to these harsh conditions, vegetation grows slowly and at low temperatures. In addition, the stressful environment suppress species competition and promotes mutualism. South of Bridgeport, the subalpine forest ranges from of elevation and contains foxtail pines, while to the north, the subalpine forest ranges from and the foxtail pine is absent. Some animal species that are adapted to this zone include the American pika, Belding's ground squirrel, the yellow-bellied marmot, and the endangered Sierra Nevada bighorn sheep. This zone can be viewed up close by hiking or climbing into the high elevations of the Sierra. ==Eastern biotic zones==

The four highest eastern biotic zones are the same as the western zones, but at a higher elevation, due to less precipitation. The elevation of these zones in the Central Sierra are: • Alpine zone: and above • Subalpine forest: • Upper montane forest: • Lower montane forest: (heavily dominated by Jeffrey pines). In the Owens Valley, the Foothill woodland zone is replaced by a Pinyon–juniper woodland zone, characterized by single-leaf pinyon pines and sierra junipers. The underbrush contains big sagebrush (Artemisia tridentata) and blackbrush (Coleogyne ramosissima). Jeffrey pines may occur along streams. Notable animals in this zone include the pinyon jay and the desert bighorn sheep. The Pinyon–Juniper woodland zone extends down to elevation. Below , there is not enough precipitation to support trees. The zones below this elevation are the Sagebrush Scrub Zone, Saltbush Scrub Zone, and the Alkali Sink Zone. These zones are distinguished by soil salinity. ==Threats==

Exotic Plants in Yosemite National Park Yosemite National Park has documented more than 130 non-native plant species within park boundaries. These non-native plants were introduced into Yosemite following the migration of early settlers in the late 1850s. Natural and human-caused disturbances, such as wildland fires and construction activities, have contributed to a rapid increase in the spread of non-native plants. A number of these species aggressively invade and displace the native plant communities, resulting in impacts on the park's resources. Non-native plants can bring about significant changes in park ecosystems by altering the native plant communities and the processes that support them. Some non-native species may cause an increase in the fire frequency of an area or increase the available nitrogen in the soil that may allow more non-native plants to become established. Many non-native species, such as yellow starthistle (Centaurea solstitialis), are able to produce a long tap root that allows them to out-compete the native plants for available water. Bull thistle (Cirsium vulgare), common mullein (Verbascum thapsus), and Klamath weed (Hypericum perforatum) have been identified as noxious pests in Yosemite since the 1940s. Additional species that have been recognized more recently as aggressive and requiring control are yellow starthistle, sweet clovers (Melilotus spp.), Himalayan blackberry (Rubus discolor), cut-leaved blackberry (Rubus laciniatus) and periwinkle (Vinca major). Extensive stands of "ghost forest" and jackstraw trees are still conspicuous throughout Sierra Nevada. Annual monitoring of lodgepole needle miner density began in 1966, and 28 permanent plots are scattered north of the Cathedral Range. The current outbreak began in 1973 and has been sweeping around the south side of the Cathedral Range, arriving at Sunrise High Sierra Camp in 2001. The Ghost Forest which was evident at the crest between Tenaya Lake and Tuolumne Meadows in the late 1970s was noticeably reforested by 2000. Lodgepole needle miner defoliation currently extends over approximately , with nearly of low to high mortality each year. While lightning fires are frequent in lodgepole pine communities, they usually remain small, with estimated fire return intervals at Yosemite National Park that are long (relative to most other forest types). Thus, fire suppression activities are thought to have had little influence upon species composition, structure, fuels, and natural processes in lodgepole forests. Also, in comparison with Rocky Mountains lodgepole pine forests, fire plays a smaller role, and so the needle miner assumes greater importance in lodgepole pine forest population dynamics in the Sierra Nevada. However, Rocky Mountain lodgepole forest dynamics are also heavily influenced by insect outbreaks, primarily bark beetles. ==Special-status species==

is one of a number of rare plants in the Sierra Nevada There are at least 1,300 vascular plant species in the Sierra Nevada, along with numerous bryophytes and lichens. There are at least 450 species of vertebrate animals. A total of 135 plant species in the Sierra Nevada have status as Threatened, Endangered, or Sensitive Plants that are Federal species of concern (former Category 2 species) under the Federal Endangered Species Act include: Although Category 2 was abolished in 1996, species of concern refers to those species that might be declining or be in need of concentrated conservation actions to prevent decline. Therefore, these six species continue to be evaluated and managed by the National Park Service. Four state-listed rare plant species are considered restricted and limited throughout all or a significant portion of their range, and may represent disjunct populations at the extreme end of their range: • Yosemite onion (Allium yosemitense), • Tompkin's sedge (Carex tompkinsii), • Congdon's woolly sunflower (Eriophyllum congdonii), and • Congdon's lewisia (Lewisia congdonii). • Sierra Nevada bighorn sheep (Ovis canadensis sierrae), endangered (2000) • California condor (Gymnogyps californianus), endangered (1967) • Southwestern willow flycatcher (Empidonax traillii extimus), endangered (1995) • Paiute cutthroat trout (Oncorhynchus clarki seleniris), threatened (1975) • Lahontan cutthroat trout (Oncorhynchus clarki henshawi), threatened (1975) • Owens Tui chub (Gila bicolor snyderi), endangered (1985) ==Wetlands==

Wetlands in the Sierra Nevada occur in valley bottoms throughout the range, and are often hydrologically linked to nearby lakes and rivers through seasonal flooding and groundwater movement. Meadow habitats, distributed at elevations from , are generally wetlands, as are the riparian habitats found on the banks of numerous streams and rivers. The Sierra contains three major types of wetland: • Riverine, • Lacustrine, and • Palustrine Each of these types of wetlands varies in geographic distribution, duration of saturation, vegetation community, and overall ecosystem function. All three types of wetlands provide rich habitat for plant and animal species, delay and store seasonal floodwaters, minimize downstream erosion, and improve water quality. Riverine wetlands are found within river and stream channels and are strongly influenced by seasonal runoff patterns. When inundated, riverine wetlands provide habitat for water-tolerant plants such as willows, and aquatic animals such as tadpoles and immature fish. Lacustrine wetlands generally occur on river floodplains and along lakeshores and are influenced by seasonal variations in groundwater levels. These wetlands are rare in the mountain range, but support an abundance of warm-water loving plant and animal species. Palustrine wetlands are typically distinguished from riverine and lacustrine systems by the presence of very dense covers of trees, shrubs, or emergent plants. This wetland type includes wet meadows, densely vegetated riparian habitats, and shallow ponds. They provide cover and forage for wildlife traveling between upland and aquatic habitats. Since the 1970s the United States has made substantial progress toward protecting and restoring wetland habitats. All federal land in the Sierra Nevada complies with a 1990 Presidential Executive Order that mandates 'no net loss' of wetlands, and requires federal agencies to map and protect all existing wetlands. In 1996 the U.S. Fish and Wildlife Service delineated and classified some of the wetlands of the Sierra Nevada, including all of Yosemite National Park. This was performed through an analysis of aerial photographs and topographic maps, as a part of the National Wetlands Inventory Web Site (NWI). The NWI maps have not been rigorously ground-truthed and only delineate wetlands larger than in size. The National Park Service restores to natural conditions wetlands that have been drained or filled in the past. Most recently in Yosemite Valley, the Cook's Meadow restoration project involved filling old drainage ditches that were draining the meadow and removing an old roadbed that was inhibiting water flow. These actions are currently being monitored with vegetation transects and mapping of surface water to determine how successful the project was in restoring the wetland. ==References==