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Vegetation Overview
The plants of Yosemite National Park are diverse and complex and are a significant part of the exquisite beauty and biological diversity of the park. The combination of climate, topography, moisture, and soils influence the distribution of plant communities across an elevation gradient from 1,800 feet (549 m) to over 13,000 feet (3,900 m). Vegetation zones (see map) range from scrub and chaparral communities at lower elevations, to subalpine forests and alpine meadows at the higher elevations. There are 800 miles of trails in Yosemite, which provide access for exploring the different vegetation zones. Foothill Woodland Zone The lowest elevations in Yosemite are found on the western boundary of the park at the El Portal Administrative Site, which is at approximately 1,800 feet (549 m). This is the foothill woodland zone, an area that is hot and dry in the summer with very little or no snow in the winter. Plants within this zone include chamise, ceanothus, manzanita, blue oak, interior live oak, and gray pine. These plant communities can also be found near Hetch Hetchy Reservoir. Lower Montane Forest Beginning near the 3,000 foot (900 m) elevation, the hot, dry summers and cool, moist winters of the Mediterranean climate give rise to the lower montane 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 lower montane forests are found along the western boundary of the park and include trees such as California black oak, ponderosa pine, incense-cedar, and white fir. Yosemite’s giant sequoia groves including the Mariposa, Merced, and the Tuolumne Groves are also found within this vegetation zone. The lower montane forest encompasses 166,000 acres (87,200 ha) and can be seen in Yosemite Valley and along the Wawona, Hetch Hetchy, and Big Oak Flat Roads. Upper Montane Forest The upper montane forest begins at higher elevations near 6,000 feet (1800 m), where the montane climate is characterized by short, moist, cool summers and cold, wet winters. Snow begins to fall in November and may accumulate to depths up to six feet and remain until June. Pure stands of red fir and lodgepole pine are typical of this forest. Jeffrey pine, which has bark that smells like vanilla, and the picturesque western juniper can also be found in this zone. Beautiful wildflowers bloom in meadows from June through August. Upper montane forests encompass 216,000 acres (87,000 ha) and may be viewed from the Tioga Road east of Crane Flat, and in areas north and south of Yosemite Valley, such as along the Glacier Point Road. Subalpine Forest The upper montane forest is replaced by the subalpine forest near 8,000 feet (2450 m), where the climate is cooler with an even shorter growing season due to long, cold, and snowy winters. Accumulations of three to nine feet of snow are typical. The western white pine, mountain hemlock, and lodgepole pine are found in this forest with many subalpine meadows that flower from July through August. This zone can be seen from the Tuolumne Meadows area east to Tioga Pass and encompasses 297,000 acres (120,000 ha). Alpine Zone The alpine zone of Yosemite begins near the 9,500 foot (2,900 m) elevation and is easily distinguished as it is above tree line. No trees grow in this zone due to the harsh climatic conditions. Short, cool summers with long, cold, and snowy winters are typical at these elevations. Many exposed granitic outcroppings, talus slopes, and boulder fields limit the amount of vegetation that grows here. The herbaceous plants need to flower and produce their seeds quickly during the short, frost-free period of summer. This zone covers 54,362 acres (22,000 ha) in Yosemite and is only viewed up close by hiking or climbing into the high elevations of Yosemite’s wilderness. Exotic Plants 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 Euro-American 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 star thistle (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 star thistle (Centaurea solstitialis), sweet clovers (Melilotus spp.), Himalayan blackberry (Rubus discolor), cut-leaved blackberry (Rubus laciniatus) and periwinkle (Vinca major). Lodgepole Needle Miner The lodgepole needle miner (Coleotechnites milleri) is a rather unique insect, endemic to the upper Tuolumne and Merced River watersheds of Yosemite National Park and one small headwaters drainage of the San Joaquin River (Sierra National Forest). It lives mostly within the needles of lodgepole pine for two years, emerging as a little gray moth for a few weeks in July of odd-numbered years. This keeps any predators from becoming effective control agents and allows populations to escalate rapidly. While regular prehistoric outbreaks of lodgepole needle miners have been confirmed through dendrochronology, historic records document outbreaks from 1903 to 1921, 1933 to 1941, and 1947 to 1963. Extensive stands of "Ghost Forest" and jackstrawed trees are still conspicuous throughout Yosemite National Park and the 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. Lodgepole needle miner defoliation currently extends over approximately 40,000 acres, with nearly 10,000 acres of low to high mortality each year. The lodgepole pine forest community is by far the largest vegetation type in the park, covering over 150,000 acres. While lightning fires are frequent in lodgepole pine communities, they usually remain small, with a resulting fire return interval at Yosemite estimated up to 764 years. Thus, fire suppression activities have had little influence upon species composition, structure, fuels, or natural processes. With natural fire playing such a small role in Sierra Nevada lodgepole pine forests in comparison with Rocky Mountain lodgepole pine forests, the lodgepole needle miner plays a key role in lodgepole pine forest succession and regeneration at Yosemite. National Park Service Management Policies direct managers to allow native pests to function unimpeded except where control is desirable for specific cited reasons, including conserving plants in developed areas. Special-Status Plants The vegetation in Yosemite contains at least 1,374 vascular plant species along with numerous bryophytes and lichens. A total of 109 plant species have status as either a federal species of concern, listed as rare by the State of California, or listed by the park as rare. There are six federal species of concern - three-bracted onion (Allium tribracteatum), Yosemite woolly sunflower (Eriophyllum nubigenum), Congdon’s lomatium (Lomatium congdonii), Tiehm’s rock-cress (Arabis tiehmii), slender-stemmed monkeyflower (Mimulus filicaulis), and Bolander’s clover (Trifolium bolanderi) - that are former Category 2 species under the Federal Endangered Species Act. Although Category 2 was abolished in 1996, species of concern is an informal term that 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 species - Yosemite Onion (Allium yosemitense), Tompkin’s sedge (Carex tompkinsii), Congdon’s wooly sunflower (Eriophyllum congdonii), and Congdon’s lewisia (Lewisia congdonii) - 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. The remaining species on this list are classified by the park as rare. These species are rare in the park but have no other status (either state or federal). Many of these species have extremely limited distributions in the park and may represent relict populations from past climatic or topographic conditions, while other species may be at the extreme extent of their range in the park or represent changes in species genetics. Tree Hazard Management Diseases, insects, soil moisture, wind, fire, and snow combine with human activities to create tree hazards, especially in natural areas like Yosemite. The National Park Service defines tree hazard as any tree, either alive or dead, which due to outwardly visible defects could fall down (in part or entirety) and strike a person or property within any designated portion of a development zone. Forestry workers in Yosemite balance protecting people and property with conserving unimpaired the natural and cultural resources of the park. Crews accomplish this through regularly scheduled surveillance and special surveys after severe storms, fires, or other disturbances. At that time, trees requiring hazard abatement are identified. Crews then post warnings or site closures, or proceed with hazard mitigation by pruning or tree removal. Tree debris is left on the ground in places where practicable, but often must be removed. Unfortunately, trees without apparent defects also fail, and tree hazards cannot always be immediately identified and abated or mitigated. Catastrophic tree failures in Yosemite have killed eight people since 1963, seriously injured many more, and caused $1 million worth of property damage. Wetlands Wetlands are areas that are saturated with surface water or near-surface groundwater for much of the year. They usually have no clearly defined ecological boundaries, but are a gradient between deepwater habitats, such as lakes and rivers, and upland terrestrial ecosystems, such as conifer forests. Wetlands are differentiated from deepwater habitats by the presence of rooted emergent plants, and distinguished from uplands by nearly continuous soil saturation and the presence of water-tolerant (hydrophytic) vegetation communities and characteristically textured and colored wetland (hydric) soils. These wet soils may have rust colored mottling or be very black in appearance. Wetlands in Yosemite occur in valley bottoms throughout the park, and are often hydrologically linked to nearby lakes and rivers through seasonal flooding and groundwater movement. Meadow habitats, distributed at elevations from 3,000 feet to 11,000 feet in the park, are generally wetlands, as are the riparian habitats found on the banks of Yosemite’s numerous streams and rivers. Wetland Types The park contains three major types of wetland: Riverine, Lacustrine, and Palustrine These wetland types are described below and are also discussed on the U.S. Fish and Wildlife's National Wetlands Inventory Web Site. 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 relatively rare in the park, 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. Protection and Restoration Since the 1970s the United States has made substantial progress toward protecting and restoring wetland habitats. Yosemite National Park complies with a 1990 Presidential Executive Order that mandates 'no net loss' of wetlands on federally-managed lands, and requires federal agencies to map and protect all existing wetlands. In 1996 the National Fish and Wildlife Service delineated and classified Yosemite’s wetlands, through analysis of aerial photographs and topographic maps, as a part of the National Wetlands Inventory Web Site (NWI). Although the NWI maps cover the entire park, they have not been rigorously ground-truthed and only delineate wetlands larger than five acres in size. The park 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. |
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