Sustain Our Nation's Forests and Grasslands

Longleaf pine roots and carbon storage

Longleaf taproot from a 75-year-old tree on the Austin Cary Forest in Florida, cut five years prior to excavation. USDA Forest Service photo by Peter Anderson.

NORTH CAROLINA – Forest Service scientist Peter Anderson recently led a study to quantify how quickly longleaf pine roots decompose after the trees were harvested – and how that impacts the duration of belowground carbon storage. This research was part of a larger project funded by the Department of Defense to quantify carbon stocks of longleaf pine forests on military bases across the southeastern U.S.

“Longleaf roots are pretty legendary,” says Anderson. “Pines contain oleoresins, a sticky liquid mix of oil and resin (or rosin).”

Pines use their resinous sap to defend against insect pests – pitching out southern pine beetles, for example. This same substance also makes longleaf roots resistant to rot.  “There are companies today that buy and dig old taproots for rosin production,” adds Anderson.”

The research team included research plant physiologists Kurt Johnsen and John Butnor. Their findings were published in Forest Ecology and Management.

The scientists located forest stands harvested over the last 70 years selected stumps from locations across the native range of longleaf, from North Carolina to Louisiana. They dug out the stumps, removed the taproots and lateral roots, and collected soil samples. The oldest tree was cut in 1945 and estimated to have been 260 years old (with radiocarbon dating).

The researchers used these data to develop a model for estimating the amount of carbon remaining in the coarse roots systems of longleaf pines. They developed a simple model that predicts necromass, the mass of dead timber in a forest, loss based on stump diameter, years since the tree was cut, and air temperature. The model estimates necromass loss, or decomposition, for coarse root systems, as well as taproots and lateral roots.

The model predicted that 54 percent of the longleaf pine root necromass would remain after ten years and 17 percent after 60 years.

The research team found lower bulk density, higher nitrogen availability, and greater carbon content in the soil samples collected close to longleaf stumps. This suggests that decomposing roots can also benefit carbon storage by creating favorable conditions for new tree growth.

The longleaf carbon balance model is freely available through the University of Florida’s Carbon Resources Science Center, along with a user manual and video tutorial about its development and use.

Across the South, longleaf pine forests are being restored as resilient ecosystems that are able to provide wildlife habitat, clean water, sustainable wood products, and, as it turns out, long-term belowground carbon storage.