Restoring longleaf pine forests to enhance water resources
A new study by USDA Forest Service researchers shows that restoring longleaf pine forests can enhance water resources in the South.
New research shows that longleaf pine, in addition to their other benefits, use less water than loblolly pine forests.
The South is considered water-rich, but water shortages are becoming more common due to more frequent and severe drought, declining water quality, and increased water consumption from population growth and agriculture – which includes planted pine stands. Managers are searching for nature-based solutions to increase water yields and drought resiliency in forests.
More than 95% of original longleaf pine forests, which once dominated 90 million acres, have been replaced by other land uses, including planted loblolly pine. This longleaf habitat loss has severely affected plants and animals that depend on the longleaf pine ecosystem, including endangered and threatened species like the gopher tortoise, Louisiana pine snake, and red-cockaded woodpecker.
The new research shows that in addition to the other benefits of longleaf forests, they also use significantly less water than fast growing loblolly pine forests.
“Most of the public aren’t aware how forest management matters to water resources,” says Ge Sun, Forest Service research hydrologist and study coauthor. “No one is restoring the forests solely to save water, but at a regional forest level, using less water is always a good thing, especially in areas that are at risk of water shortages.”
Loblolly pine is the primary planted species on southern timberland. It accounts for 71% of all the South’s planted forests. These timber forests are planted at high densities that use more water than natural forests.
Longleaf pine, however, is managed with open canopy conditions and frequent prescribed fire. The species tolerates fire and drought better than loblolly, partially because of its unique characteristics, like dense needle clusters and a deep root system.
An eddy flux tower, as seen on the Santee Experimental Forest, is used to measure gas exchange between vegetation and the atmosphere.
To conduct the study, researchers used remote sensing, eddy flux measurements, and various models to compare evapotranspiration rates of longleaf and loblolly pine forests. The researchers also analyzed site characteristics that might affect evapotranspiration rates, like fire history, soil properties, amount of overstory and understory vegetation, and sunlight reflectance and surface temperature of the stands.
The results showed that all year round, longleaf pine stands used less water than loblolly pine. The difference was minor during winter, but very significant during the peak summer growing months. While this study did not compare longleaf and loblolly pines at the individual tree level, at the stand level, the results are clear: longleaf pine stands use far less water.
By restoring longleaf pine forests with lower tree density and prescribed burn regimes, southern landowners may be able to reduce water use and increase water yield. A forest that uses less water may have healthier aquatic ecosystems, more biodiversity, and more resilience to future droughts.
“Everybody is excited. After a hundred years of longleaf pine removal, we need to show that restoration will be worth it, and that requires understanding what the hydrology there is supposed to look like,” says Sun.
For more information, email Ge Sun at ge.sun@usda.gov.