| Sierra Nevada forests | |
|---|---|
.jpg) Subalpine forest at the base ofTemple Crag | |
 | |
| Ecology | |
| Realm | Nearctic |
| Biome | Temperate coniferous forests |
| Bird species | 197[1] |
| Mammal species | 103[1] |
| Geography | |
| Country | United States of America |
| State | California,Nevada |
| Conservation | |
| Global 200 | Yes |
| Habitat loss | 1.0785%[1] |
| Protected | 72.55%[1] |
Theecology of the Sierra Nevada, located in theU.S. states ofCalifornia andNevada, is diverse and complex. The combination ofclimate,topography,moisture, andsoils influences the distribution ofecological communities across an elevation gradient from 500 to 14,500 feet (200 to 4,400 m).Biotic zones range fromscrub andchaparral communities at lower elevations, tosubalpine forests andalpine meadows at the higher elevations. Particular ecoregions that follow elevation contours are often described as a series of belts that follow the length of the Sierra Nevada.[2] There are manyhiking trails, paved and unpaved roads, and vastpublic lands in the Sierra Nevada for exploring the many differentbiomes andecosystems.[3]
The western and eastern Sierra Nevada have substantially different species of plants and animals, because the east lies in the rain shadow of the crest. The plants and animals in the east are thus adapted to much drier conditions.[4]
The altitudes listed for the biotic zones are for the central Sierra Nevada. The climate across the north–south axis of the range varies somewhat: the boundary elevations of the biotic zones move by as much as 1,000 ft (300 m) from the north end to the south end of the range.[4]
The lowest-elevation biotic zone in the Sierra Nevada is found along the boundarywith theCentral Valley.[5] This zone, stretching in elevation from 500 to 3,500 feet (150 to 1,070 m), is thefoothill woodland zone, an area that is hot and dry in the summer with very little or no snow in the winter.[5] The foothills are vegetated with grasslands of mostly non-native grasses, mixed grasslands and woodlandssavanna, afoothill woodland community ofblue oak andgray pine, andchaparral. Many of the plant communities are similar to those found on the innerCalifornia Coast Ranges.[6] Animals typical of this zone includeblack bear,ringtail cat,coyote,gray squirrel,bobcat,California mule deer, andskunk.[4] In the foothills of the northern portion of the Sierra Nevada,toyon andchamise often co-dominate certain openserpentine chaparral communities.[7]
Beginning near the 3,000 ft (900 m) elevation, the hot, dry summers and cool, moist winters of theMediterranean climate give rise to the lowermontane forest zone. This zone is also known as theyellow pine forest zone. The accumulation of several feet ofsnow during the winter is not uncommon and can stay on the ground for several months. The diversity oftree species found in this zone make this a beautiful and interesting forest to explore. Theindicator species for the lower montane forest are theponderosa pine and theJeffrey pine: the ponderosa pine generally occurs on the west side of the Sierra, while the Jeffrey pine occurs on the east.[4] The lower montane forests also include trees such asCalifornia black oak,sugar pine,incense-cedar, andwhite fir.[3] Animals that may be found in this zone include thedark-eyed junco,mountain chickadee,western gray squirrel,mule deer, andAmerican black bear.[4] The endangeredYosemite toad is found in montane forests of the central Sierra Nevada, at elevations of 4,790 to 11,910 ft (1,460 to 3,630 m).[8]
The character of the Lower Montane Forest changes with latitude. North ofGrass Valley, the lower montane forest ranges from 2,000 to 4,000 ft (600 to 1,200 m), with less ponderosa pine and moreDouglas-fir.[9] In the middle Sierra, south to theMerced River, the lower montane forest has the same elevation, but precipitation decreases and the forest mixes with chaparral.[9] In the southern Sierra, the lower montane forest occurs between 3,000 to 5,000 ft (900 to 1,500 m), but can range as high as 6,000 ft (1,800 m), with ponderosa pine dominating the landscape. Unlike further north, the geology of the southern lower montane forest is dominated by granite.[9]
The mid-montane forest grows on the western slopes of the Sierra Nevada at moderate elevations. North ofLake Tahoe, the mid-montane forest occurs from 3,000 to 6,000 feet (900 to 1,800 m). Between Tahoe and Yosemite, the forest ranges from 4,000 to 6,000 ft (1,200 to 1,800 m), while south of Yosemite, it occurs between 5,000 to 7,000 ft (1,500 to 2,100 m). The mid-montane zone has a mixed forest ofwhite fir,coast Douglas-fir,ponderosa pine,Jeffrey pine,live oak,black oak, andtanoak, depending on location.[9]
North of Tahoe, the mid-montane forest has more white fir and Douglas-fir, and less ponderosa pine than further south. Jeffrey pine occurs onultramafic lava soils.[9] In Yosemite and points south,giant sequoia occurs in wetter locations.[9]
Theupper montane forest begins at higher elevations near 7,000 ft (2,100 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 6 ft (1.8 m) and remain until June. Pure stands ofred fir andlodgepole pine (the indicator species)[4] are typical of this forest.Jeffrey pine, which hasbark that smells likevanilla, and the picturesquewestern juniper can also be found in this zone.Wildflowers bloom in meadows from June through August.[3] Common animals in this zone include thehermit thrush,dusky grouse (Dendragapus obscurus),great grey owl,golden-mantled ground squirrel, and (more rarely) themarten.[4] Upper montane forests may be viewed from theTioga Pass Road east ofCrane Flat,Glacier Point Road, andState Route 108.
The elevation of the upper montane zone shifts with latitude: it occurs from 6,000 to 8,000 feet (1,800 to 2,400 m) north of Yosemite, and 7,000 to 9,000 ft (2,100 to 2,700 m) to the south.[9]
The upper montane forest is replaced by thesubalpine forest near 9,000 ft (2,700 m),where the climate is cooler with an even shorter growing season due to long, cold, and snowy winters. Accumulations of 3 to 9 ft (1 to 2.5 m) of snow are typical. The most common tree in the subalpine forest is thewhitebark pine.[10] Thewestern white pine,mountain hemlock, and lodgepole pine are also found in this forest with manysubalpine meadows thatflower from July through August.[3] Many species live in, or are transient in, this zone, includingClark's nutcracker.[4] The vegetation and ecology is determined by the harsh climate, with extensive snow and wind.[11] In addition, soils are thin and nutrient-poor.[10] Due to these harsh conditions, vegetation grows slowly and at low temperatures. In addition, the stressful environment suppress species competition and promotesmutualism.[11] The marginal conditions make the Sierra Nevada subalpine zone sensitive to environmental changes, such asclimate change andpollution.[12]
South ofBridgeport, the subalpine forest ranges from 9,000 to 11,000 ft (2,700 to 3,400 m) of elevation and containsfoxtail pines, while to the north, the subalpine forest ranges from 8,000 to 10,000 ft (2,400 to 3,000 m) and the foxtail pine is absent.[9]
Thealpine zone begins near 10,500 ft (3,200 m) elevation (in the southern Sierra) and near 9,000 ft (2,700 m) (in the north).[9] This zone is easily distinguished as it is above thetree 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 theseelevations. Many exposedgranitic outcroppings, talus slopes, and boulder fields limit the amount of vegetation that grows here. The herbaceous plants need to flower and produce theirseeds quickly during the short, frost-free period of summer.[3] Flora includescushion plants, grasses, willows, andsedges.[9] Themacrolichen flora in the Sierra Nevada alpine zone is not well developed as compared to neighboring alpine zones in theRocky Mountains and mountains of thePacific Northwest.[13][14] Some animal species that are adapted to this zone include theAmerican pika,Belding's ground squirrel, theyellow-bellied marmot, and the endangeredSierra Nevada bighorn sheep.[4] This zone can be viewed up close byhiking or climbing into the high elevations of the Sierra.
The four highest eastern biotic zones are the same as the western zones, but at a higher elevation, due to lessprecipitation. The elevation of these zones in the Central Sierra are:[4]: 92
In theOwens Valley, theFoothill woodland zone is replaced by aPinyon–juniper woodland zone, characterized bysingle-leaf pinyon pines and sierrajunipers. The underbrush containsbig sagebrush (Artemisia tridentata) andblackbrush (Coleogyne ramosissima).Jeffrey pines may occur along streams. Notable animals in this zone include thepinyon jay and thedesert bighorn sheep. The Pinyon–Juniper woodland zone extends down to 5,000 ft (1,500 m) elevation.[4]
Below 5,000 feet (1,500 m), there is not enough precipitation to supporttrees. The zones below this elevation are the Sagebrush Scrub Zone,Saltbush Scrub Zone, and the Alkali Sink Zone. These zones aredistinguished bysoil salinity.[4]
Yosemite National Park has documented more than 130 non-native plantspecies within park boundaries. These non-native plants were introduced into Yosemite following the migration of early settlers in the late 1850s. Natural andhuman-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 asyellow starthistle (Centaurea solstitialis), are able to produce a longtap root that allows them to out-compete the native plants for available water.[15]
Bull thistle (Cirsium vulgare),common mullein (Verbascum thapsus), andKlamath 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).[15]
The lodgepole needle miner (Coleotechnites milleri) is aninsect, endemic to the upperTuolumne andMerced River watersheds of Yosemite National Park and one small headwaters drainage of theSan Joaquin River (Sierra National Forest). It lives mostly within the needles of lodgepole pine for two years, emerging as a little graymoth for a few weeks in July of odd-numbered years. This keeps anypredators from becoming effective control agents and allows populations to escalate rapidly. While regular prehistoric outbreaks of lodgepole needle miners have been confirmed throughdendrochronology, historic records document outbreaks from 1903 to 1921, 1933 to 1941, and 1947 to 1963.[16]
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 theCathedral 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 40,000 acres (160 km2), with nearly 10,000 acres (40 km2) of low to high mortality each year.[16]
Whilelightning fires are frequent in lodgepole pine communities, they usually remain small, with estimatedfire 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 uponspecies composition, structure, fuels, and natural processes in lodgepole forests. Also, in comparison withRocky 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.[16]
There are at least 1,300vascular plant species in the Sierra Nevada, along with numerousbryophytes andlichens. 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[17]
Plants that are Federal species of concern (former Category 2 species) under the FederalEndangered Species Act include:
| Image | Scientific name |
|---|---|
 | Three-bracted onion (Allium tribracteatum) |
 | Yosemite woolly sunflower (Eriophyllum nubigenum) |
 | Congdon's lomatium (Lomatium congdonii), |
.jpg) | Tiehm's rock-cress (Boechera tiehmii), |
 | Slender-stemmed monkeyflower (Erythranthe filicaulis) |
 | Bolander's clover (Trifolium bolanderi). |
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.[18]
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:
Endangered or threatened species of animals that occur in the Sierra Nevada include:[19]
Wetlands in the Sierra Nevada occur invalley bottoms throughout the range, and are often hydrologically linked to nearbylakes andrivers through seasonalflooding andgroundwater movement.Meadowhabitats, distributed at elevations from 3,000 to 11,000 feet (910 to 3,350 m), are generally wetlands, as are theriparian habitats found on the banks of numerous streams and rivers.[26]
The Sierra contains three major types of wetland:
Each of these types of wetlands varies in geographic distribution, duration of saturation, vegetation community, and overallecosystem function. All three types of wetlands provide rich habitat for plant and animal species, delay and store seasonal floodwaters, minimize downstreamerosion, and improvewater quality.[26]
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 aswillows, and aquatic animals such astadpoles and immaturefish.[26]
Lacustrine wetlands generally occur on riverfloodplains 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.[26]
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 includeswet meadows, densely vegetated riparian habitats, and shallowponds. They provide cover and forage for wildlife traveling between upland and aquatic habitats.[26]
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.[26]
In 1996 theU.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 ofaerial photographs andtopographic maps, as a part of theNational Wetlands Inventory Web Site (NWI). The NWI maps have not been rigorously ground-truthed and only delineate wetlands larger than 5 acres (2 ha) in size.
TheNational 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.[26]
This article incorporatespublic domain material from"Vegetation Overview".Yosemite National Park.National Park Service. Retrieved2009-10-25. This article incorporatespublic domain material from"Exotic Plants".Yosemite National Park.National Park Service. Retrieved2009-05-14. This article incorporatespublic domain material from"Lodgepole Needle Miner".Yosemite National Park.National Park Service. Retrieved2009-10-27. This article incorporatespublic domain material from"Special Status Plants".Yosemite National Park.National Park Service. Retrieved2009-10-26. This article incorporatespublic domain material from"Wetlands".Yosemite National Park.National Park Service. Retrieved2010-04-19.