Life Stages of the Longleaf Pine
Longleaf pine is the longest lived of the southern pine species. Throughout most of its range, individual longleaf pines can reach 250 years in age (with trees in excess of 450 years old having been documented). To reach that point of old age the life history of longleaf pine can be described in several stages. However, due to the large occurrence of small scale disturbances, the forest as a whole is at all times transitioning through at least one of these stages of growth simultaneously. Research has shown that although a longleaf forest looks like and is defined as an "old-growth" stand (i.e., large, scattered, old trees) it still has approximately 2/3 of its trees less than 50 years old.
The Seed Stage
After falling from the tree in October to late November, winged seeds whirl to the forest floor and await adequate moisture before germination. In heavy mast years, a rain shortly after seed fall will yield a green blanket of germinants on the forest floor. Seeds either germinate within a few weeks after falling or they die. Although seeds will germinate almost anywhere (on rocks, logs, forest mulch), they generally need to land on mineral soil to survive subsequent droughty periods. During this first stage, the seedlings are very susceptible to fire, drought and predation and will take upwards to a year to reach the next life stage.
The Grass Stage
This stage is an inconspicuous yet unique stage of a longleaf pine's life history where the seedling resembles a clump of grass more than a tree, hence the name. During the grass stage, the growing tip (bud) of the tree is protected under a thick arrangement of needles at ground level. When fires sweep through, the needles may burn but the tip of the bud remains protected. New needles quickly replace those that were burned off. During the grass stage, longleaf pine seedlings are virtually immune to fire. At this stage, although the tree will not be growing upwards, the seedling will be putting down an impressive root system underground. Also during this stage, longleaf may become infected with a fungus called brown spot needle blight. Brown spot causes the needles to brown, fall off, and hamper growth. Repeated defoliation will cause the seedling to die. The grass stage may last anywhere from one to seven years depending on the degree of competition with other plants for resources. Rare instances of 20 years have been documented.
The Bottlebrush Stage
When the diameter of the root collar (that area right at ground level) reaches 1-inch, the longleaf grass stage will begin to initiate height growth. Beginning in about late February to mid-March, a single, white growing tip will emerge upwards from the protective sheath of needles. This white tip, called a candle, may grow a few feet in just a few months. By about late May, green needles begin to emerge from the candle and the candle begins to turn scaly and brown as bark begins to form. At this point, the longleaf is growing proportionally more in height then it is in diameter. There are no branches spreading out horizontally during this time causing the tree to look like a three to four-foot bottlebrush. By growing rapidly in a short period of time, the seedling is able to secure an advantageous position to gather sunlight and to get its growing tip above the frequent fires. However, during this stage of growth, longleaf pine trees are slightly more vulnerable to fire. It may take a year or so before the bark thickens enough to withstand most fires. The longleaf may remain in this stage for a couple of years.
The Sapling Stage
When the longleaf reaches about 6 to 10 feet in height, lateral branches begin to emerge and signal the beginning of the sapling stage. Diameter increases and bark thickens modestly, but the tree continues to grow in height at upwards of 3 feet per year. Around late February to mid-March white growing tips can be seen extending upwards from the tufted needles at the end of the branches. As the tree grows taller and the bark becomes thicker, the longleaf becomes less susceptible to fire. After the tree reaches 8 feet in height and about 2 inches in diameter at ground level, it becomes very robust and is rarely killed by fire. The tree will remain in this stage for several years.
The Mature Stage
Somewhere around 30 years after height growth initiation, trees begin to produce cones with fertile seeds. As the forest begins to mature, lower limbs may be shed or pruned off by fire. The trunk of the tree begins to fill out into a straight, relatively branch free tree that resembles a living telephone pole (in fact, many longleaf pines are sold for telephone poles). On more fertile soils, the tree may continue to grow in height up to 110 feet. On poorer soils, the tree may only grow to 60 feet. After about 70 -100 years longleaf essentially ceases height growth. During the later stages of this period, trees may begin to show signs of decay and rot. In particular, longleaf pine reaching 80 years in age may become infected with a fungus called red heart that causes the otherwise dense heart of the tree to become punky, soft, sappy and full of small channels.
During this period most trees have reached a steady state. Large diameter trees with flat-topped crowns dominate the forest. Historical accounts describe longleaf pines in excess of 120 feet tall and 3 feet in diameter. Conventional wisdom suggests that old-growth longleaf pine trees stop growing in size at these advanced ages. However, many instances exist where old-growth longleaf pine trees have actually increased growth rates at 200 years (+) when resources became available. At older ages, more and more trees begin to show signs of internal rot from red-heart fungus. In some localities, as many as half the trees per acre can be affected with red-heart in the crowns.
In a landscape that sees lightning, tornadoes, wildfires, drought, hurricanes, or even ice storms on a regular occurrence, it is really quite remarkable for a longleaf pine to die from old age. After 300 years, trees that survive everything that Mother Nature has to throw at them will eventually weaken and begin to lose the ability to fend off forest pests like black turpentine or southern pine beetles. Slowly the trees begin to die off. The initial signs of this weakening include a thinning of green needles in the tree crown, followed by signs of beetle activity on the bark, then wilting of needles and finally by complete defoliation.
Usually when we think of the contribution of an organism (like a longleaf pine) to an ecosystem, we focus merely on the living organism. However, a longleaf pine is perhaps just as significant to the ecosystem after the tree is dead as when it is alive. Once the tree dies, its bark quickly sloughs off or is torn off by foraging woodpeckers. What remains is the white skeleton of the tree; known as a snag. Snags that don't fall will typically remain for only a few years. Without the protective bark in place, the resinous inner wood of the longleaf is exposed and often causes the snag to ignite during a forest fire and burn to the ground.