The Calhoun Experimental Forest

Long-term research on restoring soil on wasted lands

The Calhoun in the 1940s, after almost a century of soil degradation. Photo by U.S. Forest Service.

Until the middle of the 20th century, forest researchers were mostly concerned with what could be done above the ground — growing trees, protecting them from insects and diseases, maximizing productivity, and regenerating stands after harvesting. It was not until 1947, when the Calhoun Experimental Forest (Calhoun) was established on the Sumter National Forest in the Piedmont of South Carolina, that soil studies began in earnest.

The 2,078-acre site for the Calhoun was chosen because it represented the poorest Piedmont conditions, the “worst of the worst.” The hope was that studies at the Calhoun could inform efforts to reforest ruined lands across the Piedmont and the South.

Under Louis Metz, the first director of the experimental forest, and with later guidance from Carol Wells, the Calhoun staff began a program of work aimed at soil improvement. According to Metz, their goal was “to find the cheapest, quickest, most effective ways of speeding tree growth, increasing plant nutrients, and improving soil structure so that the land stores water for plant use.”

To that end, they installed the Calhoun Long-Term Soil Ecosystem Experiment, regarded by many as one of the finest long-term ecological studies in the world. Started in 1957 by Metz and expanded by Wells in the 1960s, the versatility of the study has allowed scientists to address a series of important issues. At first, the experiment consisted of planting pine seedlings at different densities to determine how best to grow pine forests on soil exhausted by farming, with the aim of providing the information needed to improve soil and watersheds across the South. Later, as the stands grew, they provided long-term data that informed new studies of tree and stand dynamics, biomass, and ecosystem productivity.

The soil sample archives kept since the first experiments on the Calhoun make it one of the few sites in the world where chemical changes in soil over decades can be directly observed. In the 1980s, data from the Calhoun provided direct evidence of acid rain effects on soil. Today the same resource is providing data on carbon sequestration from over 40 years of direct observation of plant biomass, forest floor, and mineral soil.

The Calhoun is now managed collaboratively by Duke University and the Southern Research Station (SRS). SRS research ecologist and science team leader Mac Callaham works with Duke soil scientist Daniel Richter to coordinate studies on a site that provides a rare opportunity for long-term observations on soil response to degradation, restoration, and sustainability.

Read about the next phase of research at the Calhoun, the Calhoun Critical Zone Observatory established with a National Science Foundation grant.

For more information, email Mac Callaham at

SRS maintains 19 experimental forests located on National Forest System lands and uses these sites for long-term and contemporary research on water, climate, and forest resources. SRS is currently working with research partners to develop a framework for networking these 19 forests, in order to answer the critical science questions of the 21st century. For more information.



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