Forest ThreatNet

EFETAC scientist delves into how natural disturbances impact forest carbon sequestration

Global change is today’s hot topic – and Hurricanes Katrina and Rita have elevated carbon emission discussions to new heights. Why? Because according to recent reports, those hurricanes alone caused one of the greatest forestry disasters on record in the Nation. As a result, the more than 300 million trees killed or damaged in Mississippi and Louisiana will release a tremendous amount of carbon into the air, contributing to an already increased buildup of greenhouse gases nationally.

Left: Damaged forests in the Pearl River Basin along the Louisiana-Mississippi border were photographed from the air in 2005. (Photo credit: Louisiana State University Hurricane Katrina & Rita Cooperative)

Steve McNulty, EFETAC’s Southern Global Change Program (SGCP) team leader, seeks to track Katrina and Rita’s carbon footprint, in addition to prints left by other natural disturbances. In a recent interview with National Public Radio, calculations of forest carbon loss using field surveys and aerial photography were highlighted as methods to assess carbon dioxide released from damaged and dying trees.

"The U.S. is the largest emitter of carbon dioxide in the world, but it’s difficult to measure all damage from public and private lands that causes these emissions," says McNulty, whose carbon loss estimates are likely conservative relative to actual amounts of forest carbon loss. "Links between increased atmospheric carbon dioxide and global warming have prompted forest managers to consider using increased forest carbon sequestration as one way to partially offset these gross carbon emissions."

McNulty’s research focuses on estimating potential changes in forest carbon sequestration due to impacts from three major disturbances—hurricanes, wildfires, and insects—which should result in more accurate estimations of U.S. forest carbon sequestration in the future. "Increasing forest carbon sequestration is part of the solution for reducing greenhouse gas buildup in the atmosphere, but natural disturbances such as insect outbreaks, wildfires, and hurricanes can significantly reduce a forest’s carbon sequestration potential," he says.

During the past 50 years, wildfires have significantly reduced forest carbon sequestration. Forest carbon losses from all forms of disturbance are on the rise, with the southern U.S. witnessing a reduction in carbon sequestration due to an increase in hurricane severity and frequency. The amount of hurricane caused forest carbon loss has increased steadily since the 1950’s. However, the amount of carbon loss is highly variable each year. A single storm such as Katrina or Rita can alone destroy over 40 teragrams (e.g., 10¹²g) of forest carbon—with one teragram equal to the combined weight of 150,000 adult bull African Elephants!

Global warming will very likely continue to increase the amount of annual forest carbon lost across the U.S. in future decades. McNulty’s research will assist land managers to develop new and innovative ways for managing forests in this increasingly dynamic environment.

Above right: The carbon cycle at work... (Image credit: National Center for Atmospheric Research)