Why Some National Capital Region Parks Have Fewer Amphibian Species

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Habitat fragmentation is a major threat to amphibians: it can shift where species live and cut the number of species present. Amphibians are very sensitive to environmental change, so those in the National Capital Region parks around Washington, D.C., are especially at risk as the region becomes more urban.

Scientists from Michigan State University and the U.S. Geological Survey, working with the National Park Service's National Capital Region Inventory & Monitoring Network, studied how fragmentation and other factors shape amphibian communities in these parks — asking which landscape-scale factors set the number of species in a park, and which local factors set the number at a single wetland.

A small, mottled green spring peeper, just transformed from a tadpole, crouching on a lichen-covered rock.

What was measured

Scale	Factors
Whole park	park area; percentage of forest cover; isolation — how much of the land around the park is not potential amphibian habitat
Single wetland	wetland area; connectivity (all known wetlands, weighed against how far amphibians disperse); water conductivity (how much salt and other material, usually pollutants, is dissolved in the water); hydroperiod (how long the wetland holds water); precipitation

What was found

Parks: smaller and more isolated parks have fewer amphibian species.
Wetlands: larger wetlands and wetlands closer together have more species, because both help adults move about and breed successfully.
Wetlands with high conductivity — lots of dissolved material and poor water quality — had fewer species.
The biggest factor at the wetland level was the hydroperiod: a wetland must stay wet through the breeding season for tadpoles to complete metamorphosis into adults.

Bare tree trunks and branches reflected in the still water of a woodland vernal pool at Manassas National Battlefield Park.

Managing for amphibians

To keep the number of amphibian species up, parks could:

manage actively for larger wetlands and wetlands that stay wet longer;
avoid roads, trails and other breaks that fragment individual wetlands and clusters of wetlands;
keep roads away from wetlands to limit contaminated runoff.

The Park Service's Inventory & Monitoring scientists track natural resources from birds to forest health and water quality in parks nationwide; the National Capital Region Network serves the parks of the greater Washington area, including Antietam, Catoctin Mountain, the C&O Canal, Greenbelt Park and the George Washington Memorial Parkway.