Following Carbon’s Trail in Longleaf Pines

SRS researchers dig up whole root systems to validate findings from GPR methods. Photo by John Butnor.

Once covering some 90 million acres in the South, longleaf pine forests were the largest temperate forest type in the United States, but have been in decline for decades because of land clearing for crops and pastures, logging, and other land use changes. Longleaf pine ecosystems are some of the most diverse in the nation; nearly two-thirds of all threatened or endangered species in the Southeast call them home.

The U.S. Department of Defense (DOD) hopes to use the longleaf pine forests on their lands to sequester carbon while protecting biodiversity and restoring ecosystems. Funded by DOD, SRS plant physiologist Kurt Johnsen and his Southern Institute of Forest Ecosystems Biology team are working with university researchers to measure the carbon stored in longleaf pine ecosystems and construct a model that shows how carbon moves through young stands (0 to 50 years old) and older stands (40 to over 200 years old). DOD will use the model to evaluate different forest management strategies on three military bases in the South where they manage and restore longleaf pine forests: Fort Polk, LA; Fort Benning, GA; and Camp Lejeune, NC.

Lisa Samuelson, director of Auburn University’s  Center for Longleaf Pine Ecosystems, directs the overall project and leads efforts to measure carbon in aboveground and taproot biomass while Tim Martin, director of the University of Florida’s Carbon Resources Science Center, and his team are putting together data from the research project and other literature to develop the carbon model and management tools. Johnsen and his team study belowground carbon to understand how it moves from living roots to soils.

To analyze and quantify the movement of carbon below ground, Johnsen’s team uses the ground-penetrating radar (GPR) techniques they’ve developed for measuring tree root biomass. GPR is a nondestructive tool that allows researchers to visualize belowground root systems, which can account for 15 to 45 percent of pine stand biomass. Johnsen and his crew also dig up whole root systems that have been dead for known periods of time to measure the remaining carbon. “By comparing these quantities to carbon present in living root systems, we can determine decomposition rates for the roots,” says Johnsen. “Longleaf pines have large taproots and are long lived, so they may store lots of carbon underground.”

For the DOD project, Johnsen’s team is also looking at belowground black carbon, the sooty charcoal residue leftover from incomplete burning from wild and prescribed fires. Johnsen’s team uses lab techniques to separate the black carbon in soil from other forms of carbon, providing data for the model of carbons belowground cycle while quantifying the role of black carbon in removing carbon from the atmosphere.

The carbon cycle model developed by project collaborators will support DOD’s continuing transition towards an ecological forestry model that protects habitat and offsets carbon emissions while sustaining military operations. Funded by DOD through the Strategic Environmental Research and Development Program, the research project is the most expansive and thorough carbon assessment ever conducted on southern military bases.

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