As a child of the sixties, I listened intently as Smoky the Bear shared the message that “only you can prevent forest fires”. It made perfect sense. But not all fires are bad as we have learned over the past half century, especially in the fire-adapted, pine forests of the southeastern U.S. It turns out that small, periodic fires help keep the forest healthy and safe from destruction that we often see in western forests. Here is the story.
The pine forest of the southeast has evolved to depend on frequent natural fires to reduce the chances of a catastrophic fire that destroys the entire canopy. Before humans interrupted this cycle, our upland Longleaf Forest consisted of large, long-lived Longleaf Pines (200 plus years) rising above a grass-dominated prairie. Our Wet Pine Savannas had fewer and smaller Longleaf Pines dispersed across a wetland prairie. Few if any hardwoods or shrubs were present in either.
In this region of the country, enough dead grass and pine needles accumulated every 3-5 years to allowed lightning-sparked fires to burn off this relatively small amount of fuel, but not reach the tops of the trees or destroy the roots and tubers of the natural vegetation. The 200 plus species of native plants found in upland forest and the 350 species of plants that live in Wet Pine Savannas are also fire-adapted. The dry leaves burn well, but the fire never reaches the intensity to harm the underground roots and tubers, that fuel their rapid regrowth.
In fact, fire serves three key roles in supporting the health and diversity of these habitats. First, fire burns off carbon that dominates the biomass (about 90%), while leaving behind ash that consist of nutrients needed for healthy plant growth. These forests and savannas occur on soils that are limited in these nutrients, so the fires release them back into the soil when dead leaves and needles burn. Plants in these habitats bloom profusely after a fire because the nutrients that were locked up in the dead parts of the plants once again become available.
Secondly, by burning off the vegetation, pine seeds fall on open, ash-covered ground that facilitates their germination and the rapid growth of pine seedlings. The fire also kills off the less fire-adapted hardwoods and shrubs that, if left to grow, will shade out grassland species, ultimately reducing the diversity of plants.
But the hero of this story is Longleaf Pine that has evolved to survive and thrive with fire. The length of their needles is a clue, especially for the young trees that hug the ground in the first 3-5 years of their lives in what is called its grass stage – looking much like a clump of grass. During this time, the plant produces a deep and thick tap root that will fuel rapid growth when it does reach for the sky.
But when fires occur in these early years, the long needles prevent the short-lived, low intensity fires from reaching the central growing tip. As with all pines, needles are fire-resistant, only burning under an open flame. The long needles help these young trees survive. Once the small trees begin to grow taller, the thick trunk, with fire-resistant bark, protects them from fire. Small Slash and Loblolly Pines have much smaller trunks that do not survive.
So, not all forest fires are bad, especially under natural conditions. But we pesky humans have interrupted these natural cycles, giving rise to catastrophic fires. To combat this, forest managers use prescribed fires that are set when weather conditions facilitate smoke that rises high and away from people and limits the intensity of the fire, preserving the forest.
So, a few years ago, ole Smoky changed his message with a single word. The phrase “forest fire” was changed to wildfire. Words are important. Now you know.
Hope to see you in our great outdoors!
