LOBLOLLY AND SHORTLEAF PINE: THE SOUTH
The loblolly and shortleaf pine is the largest tree species association in the eastern U.S. and extends from Maryland to Texas. Most forest communities of this type have developed from abandoned farm land.
The Southern Experience
Longleaf pine (pinus palustris) once covered nearly 70 million acres of the southeastern coastal plain of the United States. Today, less than 5 million acres of this important southern pine forest type remain. Despite recent concerns expressed over the recent declines of temperate and tropical rainforests, a far greater percentage (99.9%) of original longleaf pine forest has been lost. Longleaf pine forests are among the most fire dependent forest types in the world; naturally occurring fire regimes regularly burned most original longleaf forests on a frequency of 2-7 years.The natural structure of longleaf stands resembles a classic, open canopy park-like forest maintained by fire.
Many of the remnant stands of longleaf suffer from midstory hardwood encroachment. Additionally, endemic vertebrates such as the red-cockaded woodpecker have suffered widespread decline as a function of fire suppression and type conversion in longleaf pine.
FIRE ECOLOGY OR ADAPTATIONS :
Longleaf pine is classified as fire-resistant. It is ideally suited to a high-frequency, low-severity surface fire regime. The natural fire interval is every year to every 5 to 10 years . Most natural fires are caused by lightning and occur in late spring and summer.
Longleaf pine has many adaptations to fire. The grass-stage seedling is resistant to fire. If top-killed, it sprouts from the root collar. Once the terminal bud develops, it is protected by a moist, dense tuft of needles. As the tuft burns towards the bud from the needle tips, water is vaporized. The steam reflects heat away from the bud and extinguishes the fire. The bud also has scales for protection and a silvery pubescence that probably reflects heat.
During the grass-stage, the seedling invests heavily in a taproot and in root collar size. When height growth is initiated, often the year after a fire, the seedling uses its stored reserves to quickly grow a straight stem with no branches. After one growing season, the terminal bud is usuallyabove the level of the next surface fire.
The bark becomes thick with age and insulates the cambium from heat. The scaly bark dissipates heat by flaking off as it burns .
In addition to fire resistant adaptations, longleaf pine has a pyrogenic strategy. Spring and summer fires are beneficial because they reduce competition and expose the mineral soil necessary for seed germination in the fall. Long, resin-filled needles have short persistence and form a highly flammable, well-aerated litter. Resin is also concentrated in the bole and roots of older trees and snags. These trees act as lightning receptors. A smoldering tree can ignite the ground several days or weeks later when the ground litter has dried out. Longleaf pine communities often have a grass understory that readily ignites. Because of openstands and high and open crowns, crown fires are rare.