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    Author(s): C.I. Millar; P.W. Rundel
    Date: 2016
    Source: In: Zavaleta, E.; Mooney, H., eds. Ecosystems of California. Berkeley, California: University of California Press: 579-611. Chapter 28.
    Publication Series: Book Chapter
    PDF: Download Publication  (2.0 MB)

    Description

    The subalpine forests of California comprise the highest elevation ecosystems that are dominated by upright trees. They are defined as a zone influenced primarily by abiotic controls, including persistent snowpack, desiccating winds, acute and chronic extreme temperatures, soil moisture and evapotranspirative stresses, and short growing seasons. Bounded at the upper elevation by the forest-alpine treeline ecotone, the forests persist under conditions of deep snows and exposure to severe winds and high solar radiation. Disturbances such as fire and biotic interactions are less important than in lower-elevation montane forests. Most subalpine forests in California are sparse woodlands, with short statured individuals, and wide spacing of young as well as old trees, commonly interrupted by areas of exposed rock, dry upland slopes, meadows, and lakes. Subalpine forest ecosystems extend across California in the highest mountains, including several ranges in the Klamath Mountains, the southern Cascades, especially around Mts. Shasta and Lassen. They dominate the upper elevations of the Sierra Nevada extend across the Great Basin ranges such as the Warner Mountains, Carson Range, Sweetwater Mountains, White-Inyo Range, and Panamint Range, and also cap the highest elevations of the Transverse Range and mountains of southern California, including the San Gabriel, San Bernardino, and San Jacinto Mountains. The conifer forest types are diverse and characterized by iconic and charismatic species such as bristlecone pine, whitebark pine, mountain hemlock, foxtail pine, limber pine, western white pine, and Sierra juniper. Broadleaf subalpine ecosystems include those associated with high soil moisture, such as quaking aspen and water birch, as well as evergreen species on dry uplands such as mountain mahogany. Subalpine forests have existed in California for more than 20 million years, although species diversity, ecosystem function, and mountain climates have changed drastically during that time. Unique adaptations have evolved among species of the subalpine forests to cope with extreme climates, including individual longevity, long needle retention, stripbark growth habit, and high fecundity. A remarkable co-adaptation for seed dispersal and planting is exemplified in the dependency of Clark's nutcracker and whitebark pine for each other, whereby the indehiscent seed cones of the pine must be opened by birds, and birds in turn depend on seeds for their sustenance. In planting pine nuts for later harvest, the birds' abundance over their needs ensures pine regeneration in the thin and desiccating soils of the subalpine zone. Minimal anthropogenic effects disturb subalpine ecosystems, as much of the area of these forests lie in remote locations under federal administration with limited recreational and grazing uses. Subalpine forests in California have an uncertain future under changing climates, with some projections showing very high losses if species move upslope and off mountain summits with warming while others suggesting that environmental heterogeneity could afford adequate refugia for long term species persistence.

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    Citation

    Millar, C.I.; Rundel, P.W. 2016. Subalpine forests. In: Zavaleta, E.; Mooney, H., eds. Ecosystems of California. Berkeley, California: University of California Press: 579-611. Chapter 28.

    Keywords

    subalpine forests, Sierra Nevada, Cascade Mountains, Klamath Mountains, whitebark pine

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