Longleaf Pine's Adaptations to Fire

The longleaf pine forest is considered a fire subclimax type that has developed and maintained itself in close association with periodic fires. The species is resistant to fire. It is also very sensitive to competition, especially as seedlings. This has restricted longleaf largely to sites that have been periodically burned and to poor sites supporting only a sparse cover of competing vegetation. Longleaf pine is a pioneer species that, given an adequate seed source, can invade abandoned fields or areas cleared by a catastrophic event such as blowdown or severe wildfires (Boyer 1979, Eyre 1980).

Once established, longleaf pine tends to perpetuate itself in areas where fires occur frequently. Needle litter from overstory pines support hot surface fires. These fires slow or prevent the encroachment of hardwoods and other pines; they also provide a favorable seedbed by removing accumulated litter and exposing mineral soil.

Grass-stage longleaf seedlings are highly resistant to fire and can even tolerate growing season fires in the open or under light pine overstories. But under medium to heavy pine overstories, most seedlings cannot survive the combination of slow growth resulting from overstory competition plus hot fires fueled by abundant needle litter. Therefore, longleaf pine usually originates in openings or under light parent overstories where less intense fires still suppress hardwoods but do little harm to vigorous longleaf seedlings.

Reduction in the frequency or exclusion of fire leads to substantial changes in the longleaf pine ecosystem. The open, park-like longleaf forests, with an understory comprised mainly of grasses and forbs, is invaded and eventually superceded by hardwoods as succession on these upland sites moves through pine-hardwood types toward eventual dominance by climax hardwoods. Dominance by other pines may precede hardwoods where presence of a slash pine (Pinus elliottii Engelm.) or loblolly pine (P. taeda L.) seed source permits these species to gain a foothold on longleaf uplands. In the absence of fire, the grass-stage of longleaf pine seedlings gives them a great competitive disadvantage in the presence of the fast-growing seedlings of other pines and hardwoods.