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Stream Salamanders and Urbanization

September 2006

Location of the Davidson, North Carolina study area (star symbol) within the Piedmont region (orange-shaded area) of the eastern United States. Davidson is among the fastest-growing urban areas in the country.

Urbanization is occurring at a rapid pace in some parts of the United States, and represents a significant threat to animal populations. Stream salamanders may be particularly vulnerable when their environment is altered by urban development. They live in very small streams that often lack legal protection, and are sensitive to changes in water quality, hydrology (how water cycles through the system), and land use. Unfortunately, because long-term information is scarce for stream salamanders, scientists know little about how they have fared in urbanized areas.

Recently, researchers from Davidson College conducted a field study of two species of stream salamanders near Davidson, North Carolina. Located in the Piedmont region, Davidson is among the fastest growing urban areas in the country. The study identified a relation between the abundance of salamanders and the percent of forest cover in watersheds. Researchers found the most salamanders in watersheds that were completely forested, but salamanders dramatically decreased in abundance with increasing amounts of forest removal.

Northern dusky salamander (Desmognathus fuscus). The range of this species intersects some of the most densely (human) populated areas in the Nation. Photo by Kristen Cecala.

To study the effects that several decades of urbanization may have had on stream salamanders, the Davidson researchers teamed up with scientists from the U.S. Geological Survey (USGS) to take advantage of information from the Survey’s Landsat satellite data archive. USGS scientists had already been using the satellite data to study the types and rates of land cover change across the country, and were able to provide information on forest changes from 1972-2000 for the area around Davidson.

The satellite data showed that approximately eight percent of the forest cover had been replaced by urbanization. The data also showed that this type of conversion was happening at a variable rate throughout the Piedmont. Although some parts of the Piedmont were being converted with comparable rapidity to the Davidson area, much of the region was being converted at a slower rate. Overall, there was about a five percent reduction in forest area and a 4.5 percent increase in urban area throughout the Piedmont during the study period.

Landsat Satellite Images of the Davidson Study Area in 1992

These Landsat satellite images show a portion of the Davidson study area in 1992 (left image) and 2000 (right image). Yellow circles highlight many areas that were developed during that period. Most of the conversion was from forest to urban, though some agricultural land was also developed. Area shown is approximately four miles (6,350 m) across.

What has this meant for amphibians?

The forest conversion around Davidson has meant that the abundance of southern two-lined salamander (Eurycea cirrigera) populations has probably decreased 32 to 44 percent during 1972-2000, while abundance of northern dusky salamanders (Desmognathus fuscus) has probably decreased 21 to 30 percent. The results from this study suggest that the conversion of forest to urban land has likely been responsible for a substantial decline of populations of stream salamanders, and that this could have serious effects on stream ecosystems. Salamanders are often the dominant vertebrate in streams, serving as important predators of stream invertebrates and as prey for birds, mammals, reptiles, fish, large invertebrates, and other amphibians.

Southern two-lined salamander (Eurycea cirrigera). Loss of habitat has very likely reduced the abundance of this species. Photo by Pierson Hill.

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Last Update: March 7, 2006
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