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    Author(s): P.W. Rundel; C.I. Millar
    Date: 2016
    Source: In: Zavaleta, E.; Mooney, H., eds. Ecosystems of California. Berkeley, California: University of California Press: 613-634. Chapter 29.
    Publication Series: Book Chapter
    PDF: View PDF  (2.0 MB)

    Description

    Alpine ecosystems are typically defined as those areas occurring above treeline, while recognizing that alpine ecosystems at a local scale may be found below this boundary for reasons including geology, geomorphology, and microclimate. The lower limit of the alpine ecosystems, the climatic treeline, varies with latitude across California, ranging from about 3500 m in the southern California mountains and southern Sierra Nevada to 3200 m in the Yosemite region, 3000 m near Donner Pass, 2800 m at Lassen Peak, and finally 2700 m on Mount Shasta. Alpine ecosystems extend beyond the typically envisioned high-elevation open slopes and summits of cold-adapted shrubs and herbs to include as well lithic environments of cliffs, talus fields, boulder fields and rock glaciers; permanent and persistent snow and icefields, including glaciers; and various water bodies such as streams, tarns, and large lakes. Alpine ecosystems provide severe physiological stresses for both animal and plant populations. These environmental stresses in California include low winter temperatures, short growing season, low nutrient availability, high winds, low partial pressures of CO2, high UV irradiance, and limited water availability under summer drought. The alpine regions of California typically experience a mediterranean-type climate regime with dry summers and precipitation heavily centered on the winter months. This regime differs significantly from that present in most of the continental alpine habitats of the world where summer precipitation predominates. At the upper treeline in the Sierra Nevada about 95% of annual precipitation falls as winter snow, with much of this accumulating during regular winter during a very small number of storms separated by long, dry intervals. This pattern produces extreme interannual variability in precipitation and water availability. Alpine plant communities are dominated by herbaceous perennials (broad-leaved herbaceous perennials, mats and cushions, graminoids, and geophytes) which form the dominant community cover. Also present with lower species richness are low shrubs and semi-woody subshrubs. Other plant life forms such as taller woody shrubs and annuals are rare. Alpine ecosystems support a low diversity of resident mammal species, but many others use the alpine environment occasionally or seasonally. Notable are large herbivores such as mule deer and desert and Sierra Nevada bighorn sheep that forage in the alpine zone in summer. Many more small and mid-sized mammals occur in the alpine zone, with yellow-bellied marmots and pikas commonly seen in such habitats. Alpine ecosystems are predicted to experience strong levels of temperature increase from global warming globally, but will likely be most impacted by indirect effects such as declining snowpack, earlier spring runoff, and earlier growth and flowering phenology.

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    Citation

    Rundel, P.W.; Millar, C.I. 2016. Alpine ecosystems. In: Zavaleta, E.; Mooney, H., eds. Ecosystems of California. Berkeley, California: University of California Press: 613-634. Chapter 29.

    Keywords

    alpine ecosystems, Sierra Nevada, Cascade Mountains, snowpack, glaciers

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