ARCHIVED CONTENT: In December 2020, the CZO program was succeeded by the Critical Zone Collaborative Network (CZ Net) ×

Calhoun Critical Zone Observatory

Field Areas     


The Calhoun Critical Zone Observatory is comprised of eight research areas in the Calhoun Experimental Forest and surrounding areas in the Sumter National Forest in upstate South Carolina, including the Holcombe's Branch watershed, experimental catchments, and space-for-time (paired hardwood-pine-cultivated field) plots. The areas were chosen primarily for their wealth of historical data giving researchers an ideal platform for testing hypotheses on how critical zones evolve in response to human forcings at the landscape scale.

134 - 190 m   Elev

16 °C   Temp

1250 mm   Precip

The Calhoun CZO is mostly forested with secondary succession mixed pine-hardwood forests, with some older-growth hardwood forest, young pine stands, and some pastures and cultivated fields.

Land Use

agricultural land, forest land

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Setting & Research
Partner Organizations
  • Setting & Research

    Located in Union County, South Carolina, in the Southern Piedmont region and the heart of the Old South's cotton belt, the John C. Calhoun Experimental Forest is a 5082 acre (2057 hectare) area that has for nearly 70 years been the site of studies of land and water degradation caused by agricultural land uses.  The Calhoun was organized October 8, 1947 in response to USDA Forest Service efforts of the 1930s and 1940s that aimed to restore highly degraded soils, forests, and water of the Southern Piedmont. Shortly after World War II, the Calhoun Experimental Forest was established on land so eroded, gullied, and degraded by agriculture that they considered it "to represent poorest Piedmont conditions" (Metz, 1958). When the Calhoun Experimental Forest's laboratory with its scientific staff was abruptly closed in the early 1960s, data collection in its four experimental catchments terminated but records were archived at Coweeta Hydrologic Laboratory, holding the potential to be re-used if and when the catchments are re-instrumented. Today the Calhoun Experimental Forest is managed by the USDA Forest Service's Southern Research Station and Sumter National Forest, Enoree Ranger District.

    The Calhoun Experimental Forest warrants our interest not only because of its special 60-year history of research, but also because the history and contemporary uses of the site reflect important structures, forcings, and change ongoing in the large areas of the world not well represented among the initial six CZOs.  The Calhoun's geologic substrata, landforms, vegetation, soil conditions, and land-use history are all closely comparable to conditions across much of the southeastern North America. The Calhoun's gently rolling to moderately steep landscapes are derived from granitic-gneiss which underlies nearly half of the Southern Piedmont (Richter and Markewitz 2001).  The Calhoun has a warm temperate climate with mean annual precipitation and temperature 1300 mm and 16°C, respectively.  Annual potential evapotranspiration averages 850 mm.  Common soil series at the Calhoun include the Cecil, Pacolet, Appling, Cataula, Madison, and Chewacla, which comprise many of the region's most common soils.  These advanced weathering-stage soils are common throughout the world in non-glaciated warm temperate regions and across the lowland tropics which are experiencing land-use pressures and conversions not dissimilar to those that have already affected the Calhoun.

    For the exact locations of our research sites, see the map of Calhoun CZO Water, Soil, and Forest Sampling sites.



    Metz, L.J.  1958.  The Calhoun Experimental Forest.  USDA Forest Service Southeastern Forest Experiment Station, Asheville, NC., 24 p.

    Richter, D.D., and D. Markewitz. 2001. Understanding Soil Change: Soil Sustainability over Millennia, Centuries, and Decades. Cambridge University Press, New York. 255 p.

  • Data

    Calhoun Critical Zone Observatory - GIS/Map Data - Research Areas (2014-2018)
    3 components    Calhoun Critical Zone Observatory    All Disciplines    Brecheisen, Z.S.; Cook, Charles W.; Richter, Daniel deB.

    Calhoun CZO - GIS/Map Data, LiDAR - Canopy Height (2014)
    1 components    Calhoun Critical Zone Observatory    GIS / Remote Sensing, Biology / Ecology    Brecheisen, Zachary S.

    Enoree District, Sumter National Forest - GIS/Map Data - Land Grants, 1749-1851 (2018)
    1 components    Calhoun Critical Zone Observatory    Social Science    Coughlan, Michael R.; Nelson, Donald

    National - Air Temperature, Flux Tower, Meteorology - NADP and NOAA or other weather stations (2017)
    8 components    Boulder Creek Watershed, Calhoun Critical Zone Observatory, Jemez River Basin, Susquehanna Shale Hills Critical Zone Observatory    Climatology / Meteorology    NADP; NOAA; others

    National - LiDAR, Land Cover, GIS/Map Data - OpenTopography (2010-2017)
    18 components    Boulder Creek Watershed, Eel River Watershed, Jemez River Basin, Reynolds Creek Experimental Watershed, Susquehanna Shale Hills Critical Zone Observatory, Northeastern Puerto Rico and the Luquillo Mountains, Sangamon River Basin, Clear Creek Watershed, Calhoun Critical Zone Observatory, Providence Creek Headwater Catchments (1660 - 2115 m elevation)    Geomorphology, GIS / Remote Sensing, Hydrology, Biology / Ecology    National Center for Airborne Laser Mapping; Boulder Creek Critical Zone Observatory; Calhoun Critical Zone Observatory; University of Arizona; University of California Merced; Valles Caldera National Preserve; Bandelier National Monument; National Park Service; Jemez River Basin and Santa Catalina Mountains Critical Zone Observatory; Luquillo Critical Zone Observatory; Reynolds Creek CZO; Eel River CZO; Shale Hills CZO

    National - Streamflow / Discharge - USGS and USDA Data Resources (1985-2017)
    22 components    Boulder Creek Watershed, Santa Catalina Mountains, Jemez River Basin, Reynolds Creek Experimental Watershed, Susquehanna Shale Hills Critical Zone Observatory, Northeastern Puerto Rico and the Luquillo Mountains, Clear Creek Watershed, Sangamon River Basin, Calhoun Critical Zone Observatory, Providence Creek Headwater Catchments (1660 - 2115 m elevation)    Hydrology    USGS National Water Information System

  • Partner Organizations

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Human Impacts
  • Human Impacts

    • agricultural land
    • forest land

    The Calhoun CZO currently is mostly covered in pine and mixed pine-hardwood forests, which grew up on former agricultural land following land abandonment in the 1860s-1930s. The current landscape also includes a number of older-growth hardwood stands, some dating to the early 1800s, as well as a few pastures and agricultural fields.