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Longleafs and Fire

Natural Fires

We can, of course, only speculate on the nature of those fires which occurred in the southeast before the arrival of the first humans, some 10,000 years ago.  Lightning certainly caused some fires and it is generally accepted that once they arrived, Indians deliberately set fires to create clearings both for agriculture and to attract wild game to the new succulent growth after a fire.  So fire in the region has been important for a very long time, and during that long time, longleafs have adapted to fire.

The adaptations of longleafs may most easily be seen in young trees.  Instead of growing straight up as do most saplings, longleafs stay close to the ground in what is known as the “grass stage” for anywhere from two to ten or more years.  During this time they grow a long taproot which stores energy and reaches far down to moisture; when they are ready to begin height growth, these essential items are available to quickly fuel it.  In the meantime, should a fire occur, it will sweep over the top of the seedling.  The needles burn, but in doing so release moisture, lowering the temperature of the flames.  By the time they reach the center where the critical growing tip is located, they are flickering out and do no harm.

Pines seedling

At the end of a longleaf grass stage seedling’s last winter, it quickly bolts upward two or three feet.  By late spring, when most lightning-caused fires occur, the growing tip may already be above the height of the flames.  And it is still protected by a thick tuft of needles.  The following growing season, the young longleaf will grow several more feet, often with no side branches; producing side branches would drain off some energy and keep that important growing tip closer to the ground.  The bark on the main trunk will begin to thicken, offering further protection from ground fire.

Young longleaf

For the most part other southern pines lack these adaptations.  They begin height growth immediately, usually an advantage, but not if there’s a fire.  Then their thin vulnerable bark is girdled and they are killed.  These other pines remain susceptible to fire damage for many years.  Should they be fortunate enough to avoid fires for a long time, that is not necessarily a good thing, as fuel on the forest floor will build up during that time and make any fire even hotter and more lethal when it does occur.

Another adaptation of longleafs is found in their seeds, but here the adaptation does not so much protect them from the effects of fire, as it makes them dependent on it.  Longleaf seeds are larger and heavier than those of other southern pines.  That gives them an advantage in that the seeds contain a greater store of nutrients and energy.  But because of their size, they cannot penetrate a thick litter of needles and other debris on the ground.  If the ground has not been cleared by a fire, they will not touch the bare soil and will not germinate.  Instead they will lie where they fall until the are no longer viable or are eaten by forest creatures.  On the other hand, if they do reach bare mineral soil, they quickly germinate and avoid being eaten.

Longleaf sprouts

Prescribed Fires

While we have no written records of pre-settlement fires, it’s not difficult to imagine that once a fire got started, it would burn for miles and miles, as there we no roads or other man-made obstacles to stop it.  Summer thunderstorms, accompanied by lightning, are frequent across the range of the longleaf pine and no doubt caused many fires each year.  Someplace that was burned one year might not have had sufficient fuel for a fire the following year, but within a year or two, it could burn again, although any fire might be somewhat spotty.  Accordingly, the natural fire regime of the southeast might be characterized as frequent, but of low intensity.
Now that natural lightning-caused fires are contained by roads, fields, and other obstacles, and are quickly suppressed to protect homes and towns, land managers wishing to mimic natural fires must resort to prescribed burning.


Copyright 2010.