The flora of the U.S. Sierra Nevada alpine zone is characterized by small, low growing, cushion and mat forming plants that can survive the harsh conditions in the high-altitude alpine zone above the timber line.Wildflowers of the Eastern Sierra and adjoining Mojave Desert Great Basin, Alpine (section), Laird R. Blackwell, 2002, Lone Pine Printing, These flora often occur in alpine fell-fields. The Sierra Nevada alpine zone lacks a dominant plant species that characterizes it, so may or may not be called a vegetation type. But it is found above the subalpine forest, which is the highest in a succession of recognized vegetation types at increasing elevations.
Botanists have ranked the Sierra Nevada alpine zone floral bloom as one of California's foremost wildflower displays, with flowers of fantastic color and abundance. Many of the alpine species are notable for large and showy flowers, which must compete for the pollinators during brief growing seasons. Botanist Philip A. Munz wrote, "These natural rock gardens are spectacular sights when in full flower." Botanist Laird R. Blackwell wrote, "Up here... the flowers seem to glow... perhaps only the flowers of the harsh desert can rival the alpine flowers for intensity."
Over 90% of California's alpine flora are perennial herbs. Annuals are not common. Depending on the elevation used to define its lower boundary, the Sierra Nevada alpine zone may have almost 600 species, about 200 of which are only found here (endemic). The flora includes plants that are descended from the plants that survived the glaciation of the last ice age (relict plants), because they were growing on mountain peaks that stood above the ice sheets like islands.
Environmental conditions influencing flora The alpine zone, or alpine fell-field, is above the tree line, generally at in the south, and to in the north. The plants are influenced by having to endure long and very cold winters, poor to no soils, constant high winds, intense sunlight, and a short cool and dry growing season in the summer, that lasts only about 6–8 weeks.
Winds are strong and constant. The constant wind makes unsheltered areas colder than sheltered spots, depositing snow in some places, while scouring the snow out of other locations. The constant wind increases loss of water from the plants to the atmosphere (transpiration). Sunlight is intense. Soils are thin and rocky, or absent. Soils are low in moisture. Rainfall is rare. Almost all of the of annual precipitation falls as snow, and growing season can be as short as just days. Annual plants must quickly grow to maturity, and all plants must quickly flower and develop mature seed.
Characteristic growth patterns and physiology Above the tree line, extreme winds preclude tree-like growth. Constant winds hitting the plants limits their size and flattens their shape. Small size or dwarfism is therefore an adaptive feature to the extremes, and most alpine plants are just a few inches tall. One botanist wrote, "Plants adapt by scrunching down close to the ground where botanists have to crawl around on their bellies with hand lenses to fully appreciate the diversity of life... Plants are mere centimeters tall, forming a mat so dense that it's hard to pick out separate species"., Another noted, "a world of miniature plants only a few inches high... leaves huddle near the ground or contour it with mats or cushions. Typically, the leaves of these plants are waxy or densely hairy - anything to protect them from the wind and intense solar radiation".
Alpine plants have many adaptations to aridity and intense sunlight in common with desert plants. Alpine plants often have gray appearance from hairs covering the leaves, which reflect the intense sunlight, and protect from winds that cause high rates of water loss through transpiration. Many Sierra Nevada alpine plants have reddish or whitish leaves to protect them from damage from intense ultraviolet radiation in the alpine zone. Fleshy roots and underground organs store food in the form of starches and sugars, allowing the plant to quickly grow when snow melts. Many plants form flower buds during the summer before the summer that they open, allowing a quick bloom for the short growing season.
Optimal temperatures for physiological processes may be lower than for lower elevation plants, and optimal light intensity for photosynthesis may be higher. Laboratory experiments showed the sierra Nevada alpine flora exhibited characteristic physiological responses. Germination best occurred at temperatures from . In the laboratory, there was strong dormancy control by short photoperiod, compared to lower elevation populations which had dormancy induced by either short or long photoperiods.
Evolutionary history and affinities The flora has developed relatively recently, on its own, from western American sources. During the glaciation of the last ice age, some peaks stood out above the ice sheet (nunataks), and thus have a high diversity of pre-ice age alpine plants (relicts), an example being the Dana Plateau at Tioga Pass. Half of all the alpine plants found in the Sierra Nevada can be found on the Dana Plateau.
Many species also occur in, or have close relatives in, the Cascade Range and Rocky Mountains, e.g., the Penstemons (Penstemon spp., and Polemoniums (Polemoneaceae spp.).
A small group of Sierra Nevada alpine plants can be found around the world in northern latitudes, which is called (circumboreal). An example is bush cinquefoil (Potentilla fruticosa), which ranges throughout arctic regions of Alaska, Labrador, and the high mountains of Eurasia.
Diversity and taxa
Broad-leaved, erect perennials constitute about 50% of the species, with perennial graminoid (grasses or grass-like plants) species next at about 21%, and plants growing as mats or cushions at about 11%. Annuals plus woody shrubs total only about 6% of the flora.
There are over 500 floral species above , and almost 400 above . Almost 100 species reach elevations of , and more than 25 reach .
Six plant families encompass more than 50% of the alpine zone species. The sunflower family (Asteraceae) is represented by about 55 species, there are almost 40 species from the grass family (Poaceae), the mustard family (Brassicaceae) has 34 species, and sedges (Cyperaceae) have over 30 species represented.
The largest genus is Carex, the "true sedge", with about 50 species above , followed by Draba in the mustard family, then Lupinus in the legume family (Fabaceae) with about 10 species.
Almost 70 species (about 17% of the flora) can be found in both subalpine and alpine habitats. Over 25% range from the alpine zone all the way to foothill habitats below . Nine species are only found in the alpine zone (obligate) above .
In a transectional study running from the desert near Bishop, California (elevation ), to Piute Pass (elevation ), perennials dominated, but also present were several annual species. Annuals are also rare in other alpine floras, including arctic.
Transpiration rates are of importance in determining local distribution patterns of flora of the Sierra Nevada alpine zone.
Annuals
Annuals plus woody shrubs constitute only about 6% of the number of Sierra Nevada alpine floral species.
Sierra gentian (Gentianopsis holopetala), in the gentian family (Gentianaceae), is an erect or sprawling annual or perennial, growing in wet meadows from elevation.
Toothed owl's clover (Orthocarpus cuspidatus) is not a true clover, but is in the broomrape family (Orobanche).
Low growing pussypaws (Cistanthe umbellata), in the purslane family (Portulacaceae), usually grows in damp, partially shaded areas, and can be found up to as high as elevation. It grows in a basal rosette, radiating leaf bearing and flower-head bearing stems that hug the ground. When the ground warms, the stems lying on the ground rise, to a steep angle, lifting the flower heads.
Perennials Characteristic perennials are low growing, small, and may be erect or form mats or cushions. Broad-leaved, erect perennials constitute 50% of the diversity of Sierra Nevada alpine species, with mats and cushions 11%.
Swamp onion (Allium validum) is a perennial bulb in the onion family (Alliaceae) found in alpine wetlands to . The low-growing head of flowers of red sierra onion (Allium obtusum) appears to sit on the ground.
In the carrot family (Apiaceae), Clemen's mountain parsley (Oreonana clementis) forms a dense mat of tiny plants with tiny leave that might cover several square yards the area like a blanket. Sierra podistera (Podistera nevadensis) is compact, stemless, and found only above the timberline to .
Sunflower family (Asteraceae) perennials include western snakeroot (Ageratina occidentalis), an erect perennial to subshrub in the sunflower family that is found up to . Flat-topped pussytoes (Antennaria corymbosa) is a small (to ), mat-forming perennial herb, spreading via a tangled network of stolons. In the same genus are rosy pussytoes (A. rosea) and the mat forming Alpine Everlasting (A. media). Alpine aster (Aster alpigenus) stems may be lying on the ground (decumbent) or erect, and can be found up to elevations. Dusty maidens (Chaenactis douglasii var. alpina), also called pincushion plant, is a sunflower family plant with cobwebby stems, and leaves and stems like a miniaturized version of its cousin, dusty maidens (var. douglasii). Yellow rabbitbrush (Chrysothamnus viscidiflorus) grows on dry, open slopes to , and Parry's rabbitbrush (C. parryi) on mountainsides and flats to .
Alpine fleabanes, or daisies, are sunflower family members. They include dwarf mountain fleabane, or cut-leaf daisy (Erigeron compositus), typifies the dwarfed growth pattern of the alpine zone, with disproportionately large flower heads compared to body size (1/4 to 1/2 the height of the flower stem). It grows as a mat or cushion on rocky slopes, talus, and rock ledges, to elevation. Also growing to elevation is the shorter rambling fleabane (E. vagus), which grows in talus and only gets tall. dwarf daisy, (E. pygmaeus), grows from a woody taproot as a compact, cushion forming plant that can be found on rocky slopes and flats from . It provides some of the most vivid color in the alpine zone, with flowers sometimes blooming in such profusion that they cover the leaves and rocky sloes and flats below. Glacial daisy (E. glacialis) grows to , often in large colonies. Alpine daisy, or loose daisy (E. vagus) grows in rocky scree and in rock crevices, from to as high as .
Golden yarrow, or wooly sunflower (Eriophyllum lanatum), found to , is not a true yarrow, but another member of the sunflower family, and is sometimes an annual. Prickly hawkweed (Hieracium horridum) is hairy and grows in rocky places and crevices. Foul smelling alpine gold (Hulsea algida) occurs only on talus (the pile of rocks at the bottom of cliffs), and rocky peaks as high as . It is unusually "tall" for an alpine zone plant, with stems reaching . At higher eleveations above the timber line, is a dwarf variety of pumice hulsea (H. vestita subsp. pygmaea) growing to .