A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle.
The soils derived from ultramafic bedrock give rise to unusual and sparse associations of edaphic (and often endemic) plants that are tolerant of extreme soil conditions, including:
These plants are commonly called serpentine endemics, if they grow only on these soils. Serpentinite is composed of the mineral serpentine, but the two terms are often both used to mean the rock, not its mineral composition.
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Excellent examples of serpentine soils and the distinctive ecologic communities associated with them have been described in western North America.[2]
For instance, in areas where these ultramafic rocks are patchy, such as the Klamath Basin region of northern California, the areas of serpentine soil can be clearly seen as sparsely covered areas bounded by forest on the normal soils.
Areas of serpentine soil are also home to diverse wildflowers, many of which are rare or endangered species such as Acanthomintha duttonii, Pentachaeta bellidiflora, and Phlox hirsuta. In California, shrubs such as leather oak (Quercus durata) and coast whiteleaf manzanita (Arctostaphylos viscida ssp. pulchella) are typical of serpentine soils.
Serpentine-rich rock or serpentinite has a mottled, greenish-gray color with a waxy feel to it. These rocks form by the reaction of olivine-rich rock, peridotite, with water.
It forms in oceanic crust near the surface of the earth, particularly where water circulates in cooling rock near mid-ocean ridges: masses of the resulting ultramafic rock are found in ophiolites incorporated in continental crust near present and past plate tectonic boundaries.
Serpentine soils are widely distributed on Earth, in part mirroring the distribution of ophiolites. Although it covers only about 1 percent of the state's surface, the state rock of California is serpentine. One such area in California is the Edgewood Park and Natural Preserve.[3] Serpentine soils also are present in small but widely distributed areas within the Appalachian mountains of eastern North America.[4]
The unique plants that survive in serpentine soils have been used in the process of phytoremediation. As those plants developed specialized processes to exist in a metal-saturated environment, the process (also known as bioremediation) utilizes them to treat environmental problems by consuming those minerals from polluted soil.[5]
Serpentine barrens are a unique ecosystem found in parts of the United States in small but widely-distributed areas of the Appalachian Mountains and the Coast Ranges of California, Oregon, and Washington.[6] The barrens occur on outcrops of altered ultramafic ophiolites.
They are named for minerals of the serpentine group, resulting in serpentine soils, with unusually high concentrations of iron, chromium, nickel and cobalt. Serpentine barrens often consist of grassland or savannas in areas where the climate would normally lead to the growth of forests.[7]
The ecology of serpentine barrens is poorly understood: the evolution of plants adapted to such areas and the relationship between the soil geology and ecology, particularly the ways in which plants handle high concentrations of metals such as nickel, is largely unexplored.[8]
Rock Springs Nature Preserve in Lancaster County, PA is a 176-acre (0.71 km2) property conserved by the Lancaster County Conservancy that is a prime example of a serpentine barren. It was originally a grassland, but fire suppression led to the conversion of the area to forest. This barren contains the rare serpentine aster, as well as a number of rare species of moth and skippers.[9]
In Chester County, PA, the Nottingham Park Serpentine Barrens was recommended by UMCES as deserving of National Natural Landmark designation, on numerous grounds, including supporting a number of rare and endemic species, an intact population of pitch pine, and also the site having historic significance.[7]