Discussions about longleaf pine restoration tend to focus on replanting trees and using prescribed fire, but ecosystem restoration also involves bringing back the groundcover that makes longleaf pine forests some of the richest plant communities on Earth.
“The groundcover of the longleaf pine forest is truly extraordinary,” says Joan Walker, research plant ecologist with the U.S. Forest Service Southern Research Station Restoring and Managing Longleaf Pine Ecosystems unit. “Some longleaf pine communities have over 40 vascular plant species in a square meter, or over 200 species in 100 square meters. At these scales, the ground layers in longleaf pine woodlands are as species-rich as any area in North America.”
Longleaf pine forests now occupy less than 5 percent of an original range estimated at around 92 million acres. Sites with both old-growth longleaf pine trees – defined as more than century old – and undisturbed understory are very rare. Usually they are small fragments of land that were always too wet, too dry, or too inconvenient to farm or convert to pine plantations.
Second-growth stands (70-100 years old) with intact ground layers are more common. The largest blocks of this relatively healthy longleaf forest are found in national forests and on military installations, some managed with regular cycles of prescribed fire.
On private industry lands and military bases across the South, forest managers are expanding longleaf stands by planting seedlings in areas previously planted in loblolly or slash pine—areas where the groundcover species of the original longleaf forest may have completely disappeared.
“To restore the ecosystem and the function of fire within it, you must restore the ground layer as well as the trees,” Walker says. “This can be complicated. Unless you have an intact site nearby to use as a reference, you may not know which plants should be there.”
Fire brings out the best in these ecosystems. “Most of the plants are sun-loving perennials that re-sprout after fire, which typically stimulates flowering and seed production,” says Walker.
The most common plant families in the longleaf pine ground layer are composites, legumes, and grasses. Many of those flowering after fire are composites, plants such as asters and black-eyed Susan whose blooms are actually composed of clusters of small individual flowers.
Legumes, members of the bean family bearing pea-like flowers and pods, can be herbs, vines, or shrubs: species commonly found on longleaf sites include beggarweeds, lespedezas, goat’s rue, milkpeas, and dollar leaf.
Because grasses produce fine fuel for frequent surface fires, they are key understory plants across the range of longleaf pine, and are often the first choice for restoration. Coastal Plain grasses include wiregrass, panic grass, and bluestem, with wiregrass the most prominent in the East. From western Alabama to Texas, bluestem grasses replace the wiregrasses in longleaf pine habitats.
Though the plants that make up the grassy ground layers are exceptionally hardy, they don’t survive long without longleaf pine, whose fallen needles feed the low-intensity fires that keep the system alive.
“The longleaf pine tree is not only the most dominant tree species in the ecology, but also a keystone species upon which the others depend,” says Walker. “In areas where longleaf pine has disappeared, so have the grassy ground layers. To begin restoring the ecosystem, you need to work at both tree and ground levels.”
In eastern sand hill areas where managers are replacing loblolly and slash pine with longleaf, replanting wiregrass is a good way to start restoring the ground layer. Wiregrass seeds benefit from the same bare mineral soil that favors longleaf pine seedlings. Wiregrass also provides good fuel for the low-intensity fire needed to clear the soil to mineral and reduce competition from shrubs and small hardwoods.