Summer 2009
Serpentine Soils—Abundant Beauty in a Natural Laboratory
- If you were lucky enough to observe the ridges of Rancho San Vicente this spring, you would have seen waves of low-growing blue, pink, white and yellow flowers spreading among ancient rocks. These native flowers and grasses are evidence of underlying serpentine soils, a rare geologic formation found where the earth’s giant tectonic plates collide. Beauty and scarcity make serpentine outcrops worthy of protection, and their abundance on 506 of the 966 acres of Rancho San Vicente is one of the reasons this land is worth saving.
- “There are those in the scientific community who argue that serpentine grasslands are similar to native California grasslands before the arrival of Europeans,” says Philippe Cohen, administrative director of Jasper Ridge Biological Preserve at Stanford University. “Just how similar is a matter of debate, but at least serpentine grasslands are composed of native plants. They’re much closer to native grasslands than anything else we have left out there.”
- Earthquake Connection
- Serpentine soils result from the presence of peridotite on the earth’s surface. The slippery, green rock with a snake-like, mottled appearance gets forced up by underground slippages when oceanic plates subduct under a continental plate. Serpentine can be seen in road cuts along Highway 280, at Edgewood County Park, at Stanford’s Jasper Ridge and at Coyote Ridge, east of Highway 101 in San Jose.
- Serpentine soils differ from ordinary dirt in that they are often high in metals such as nickel, chrome and magnesium—toxic to most plants—and low in soluble calcium and nitrogen—minerals needed for healthy growth. In addition, serpentine soils are poor at holding water. Native plants are better adapted to these conditions than exotic annual grasses. Plants that
adapt to serpentine conditions are generally small in stature compared with their relatives in other habitats.
- Approximately 20 rare, threatened or endangered plants and arthropods are associated with the Bay Area’s serpentine grasslands. The list of native plants found on serpentine grasslands at Rancho San Vicente includes purple needle grass, California brome, blue dicks, owl’s clover, tidy tips, California poppy, the Metcalf Canyon jewel flower and dwarf plantain, the
most important food of the endangered Bay checkerspot butterfly in its larval stage.
- Serpentine Science
- Scientists have used serpentine soils and their associated plants as a baseline for the study of how healthy systems respond to climate change. They have also tested plants for their response to high levels of toxic minerals. In addition, there have been studies on the interaction between native pollinators—bees, butterflies, beetles and certain flies—and the serpentine floral community.
- Urban development has been the greatest threat to serpentine grasslands in California. POST is proud to have saved a significant remnant at Rancho San Vicente as well as at other properties in our region.
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