"A prescribed burn cycle approaching five years should balance the conflicting needs of amphibians and longleaf pines without placing the entire community in danger of catastrophic fire," say Jamie Schurbon and John Fauth in the October issue of Conservation Biology. Schurbon and Fauth did this work while at the College of Charleston in South Carolina, and are now at the Anoka Conservation District in Ham Lake, Minnesota, and the University of Central Florida in Orlando, respectively.
To keep the pine savannahs from being replaced by hardwoods, the U.S. Forest Service burns sections of South Carolina's Francis Marion National Forest every two-to-three years. While prescribed burns appear to have little effect on amphibians in some ecosystems, the effects of fire on amphibians in pine savannahs are unknown. Fire could drive amphibians out by making the soil hotter and drier, and by reducing the leaf litter that provides cool, moist refuges.
To test whether prescribed burning affects amphibians in southeast U.S. pine savannahs, Schurbon and Fauth determined the diversity and abundance of 25 amphibian species in 15 temporary ponds in areas that were burned 0-12 years ago in the Francis Marion National Forest. Pine savannahs are home to several sensitive species (including the flatwoods salamander and the Carolina gopher frog) and have among the greatest amphibian diversity in the U.S., with 31 species in the Francis Marion National Forest alone. "A single pond can easily harbor more species of frogs than inhabit entire states in the northern and western U.S.," says Fauth.
Schurbon and Fauth found that amphibian diversity and abundance was far lower in areas that had been burned more recently. An analysis correcting for variations in environmental factors (such as leaf litter and pond pH) suggests that there are roughly twice as many species per pond in areas burned 10 years ago than in those burned three years ago. Similarly, the analysis suggests that there are about 50% more amphibians per pond in areas burned 12 years ago than in those burned three years ago.
While pine savannah amphibians do better with less frequent fires, longleaf pines do better with more frequent fires. To compromise, Schurbon and Fauth recommend increasing the prescribed burn cycle from every two-to-three years to about every five years. The researchers also recommend shifting the prescribed burns from the winter to the summer, which is when the pine savannahs burned historically. This shift would benefit both the amphibians and the longleaf pines: summer fires have the ecological advantages of not interrupting amphibian breeding and of controlling hardwoods more effectively.
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