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Soil Science

Editor’s note: For this year’s Soil Science Highlights, Staff Writer Naomi Lubick takes a look at a recent report on endangered soils.

Just as a house without a foundation will fall, an ecosystem built on a specific soil type may die once the soil is destroyed. New analyses of the distribution of soils across the United States show a significant loss of certain soil types, and that slightly less than 5 percent of the rarest soils in the country are facing possible extinction.

Agriculture and urban land use, seen together in this vineyard in central California, not only change the landscape, but also change the soil. Courtesy of Ronald Amundson.

The report, published last October in Ecosystems, finds that agriculture and urban development have disrupted soil profiles across the nation. Regions in the Midwest and California in particular have lost more than half their original soils, and in some places, up to 80 percent of the rare soils have been disturbed.

Using GIS, the researchers mapped the distribution of soil series at the state and local scale, using the U.S. Department of Agriculture (USDA) soil taxonomy system. Soil series are comparable to biological species, representing the most specific level of identification according to soil characteristics.

Randall Schaetzl, a soil geographer at Michigan State University in East Lansing who was not involved in the study, calls the cataloging innovative and exciting. “No one’s ever thought of it before,” he says. Because the work is based on the USDA’s most broad-brush datasets, Schaetzl says that the current study “actually forewarns us that with a better [smaller scale] database that will soon be available from the USDA, we will find even more such endangered soils.” The added value of the report, Schaetzl says, is the connection the researchers make between soil and ecosystems biodiversity.

“The soil and geology provide the real underpinnings to the landscape,” says Ronald Amundson of the University of California at Berkeley, lead author of the report. In the Midwest, Amundson and his co-workers have found endangered soils preserved only in pioneer cemetery plots, with tiny slices of prairie grasses that have all but disappeared. In the San Joaquin Valley in California, the state’s major agricultural center, the vernal pools — ephemeral ponds fed by spring rain — are disappearing because of agriculture and urbanization. These land uses destroy the soil type, known as the San Joaquin series, that supports the ponds.

That series, which is California’s state soil, contains a layer of cemented silica that serves as a barrier to water percolating down from the surface. “Farmers destroy that hardpan in order to use that soil,” says Michael Singer, a soil scientist at the University of California at Davis, who sometimes teaches with Amundson in the field. The presence of such a water barrier creates vernal ponds, which support a variety of plants and animals, from the endangered alkali milkvetch to the California tiger salamander.

Though most people would not rank soils with redwood trees or endangered animal species, soil is as necessary to preserve as any of those things, Singer says. “In these soil ecosystems, there may be the same kind of great potential for discovery that people claim for the rainforests.”

Naomi Lubick

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