Mac A. Callaham, Jr.

Team Leader/Research Ecologist
320 Green Street
Athens, GA 30602-2044
Phone: 706-559-4321

Current Research

I am interested in soil ecosystem responses to natural disturbances (fire, wind, and flood), forest management practices which seek to simulate disturbances (prescribed fire, thinning, harvesting), and anthropogenic disturbances (e.g. invasive species).  I am particularly interested in responses of soil biota (e.g. earthworms, herbivorous insects, soil microbes, etc.) to these disturbances and land management practices, and how changes in invertebrate assemblages may lead to changes in other components of forest systems (e.g. nutrient relationships, plant-herbivore relationships).  In addition to pure soil biology, I am also interested in elemental dynamics, and specifically the effects of prescribed fire on soil organic matter and toxics (soil carbon, nitrogen, and mercury).


Ph.D. in Biology, 2000
Kansas State University
M.S. in Agronomy, 1996
University of Georgia
B.A. in English, 1994
University of Georgia
B.S. in Zoology, 1994
University of Georgia

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Research Highlights

Earthworms, Millipedes, and Soil Carbon in the Eastern U.S. (2016)
SRS-2016-77 Earthworms, millipedes, and other soil invertebrates directly contribute to forest soil processes such as leaf litter decomposition and soil organic matter formation. There is relatively little known about how the composition of soil macroinvertebrate communities varies across temperature and moisture gradients in eastern deciduous forests. Forest Service scientists found that non-native earthworms were associated with declines in other important groups of detritivores (invertebrates that eat decaying plant matter), such as millipedes, as well as with much faster decomposition rates of leaf litter in the forest floor.

Invasive earthworms have unexpected effects on other soil organisms (2017)
SRS-2017-165 Invasive earthworms alter the structure and function of soil. Forest Service scientists show that these earthworms decrease the abundance of springtails, but act as a food source for centipedes. These changes are likely to alter the communities of other soil-dwelling organisms, with potential rippling effects on the forest soil food web.

Prescribed Fire to Stem the Tide of Earthworm Invasion (2015)
SRS-2015-213 Asian earthworms are currently invading eastern deciduous forests from Georgia to Vermont. Because these earthworms eat leaf litter in the forest floor, Forest Service scientists and collaborators hypothesized that applying some heat and removing some of this food source with prescribed fire might slow or repel these invaders. In a controlled experiment, the scientists found that fire resulted in much lower reproductive success for the invasive earthworms. This may have application in controlling invasions in the field.

Short-circuiting an Invasional Meltdown (2014)
SRS-2014-132 Chinese privet is an invasive plant species in flood plain forests of the southeastern U.S., in some cases occupying up to 80 percent of available riparian floodplain forest habitat. Non-native invasive earthworm species are found in the same soils where Chinese privet is abundant. In this study, Forest Service scientists showed that five years after removal of the plant, there were lower numbers of certain invasive earthworm species, and a simultaneous recovery in numbers of native species.

Soil fauna are of vital importance to soil processes and deserve attention (2017)
SRS-2017-136 Although soil fauna are critically important for many ecosystem services, they are often neglected by researchers. Scientists at the Forest Service and the University of Georgia discuss reasons for this in their review of how disturbance affects these organisms.