Adaptation to frequent fires

Figure 3. Longleaf pines are resistant to the effects of frequent fire. (Photograph by the author. More about the photograph)

In addition to fire-resistant bark, longleaf pines have a number of other adaptations to their frequent-fire habitat other than their fire resistant bark. For example, their seedlings have a growth cycle that helps them escape fires. After seeds are shed from the cones, they sprout rapidly and form the ground hugging “grass stage” that lives below the height of the hottest fires. This stage lasts several years while the seedling develops a deep tap root to assure access to water in the well drained sandy soils, and stores energy for a remarkable growth spurt that takes the seedling to a height of three to four feet in a single summer. Both the grass stage and post growth spurt saplings can be seen in Figure 3.

The growth spurt puts the needles and buds above the height of the hottest fires. In the wake of this spurt, the saplings are quite resistant to normal fires, although both they and the older trees can be destroyed by the hot fires fueled by years of accumulated vegetation. As a result, good management of these forests mimics the natural fire regime in which frequent cool fires repeatedly remove developing vegetation before it can accumulate to levels that would pose a threat to the survival of the forest if it were to burn all at once. Usually this means a fire every two to four years, but scientific management uses the accumulation rate of fuel as the basis for setting fire regimes.

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