This Month in Science: The Longleaf Pine

The longleaf pine (Pinus palustris) once dominated 92 million acres of the southeast (over 150,000 square miles), stretching from eastern Texas, north to Virginia, and south to Florida. The tree is now an endangered species, existing in fragmented stands across a mere 3 million acres of land. Over the past few centuries, the forests were decimated by economic opportunity, development, and fire exclusion practices. In the Cape Fear Region and throughout eastern North Carolina, the resin of the trees was harvested and used to produce naval stores such as tar and turpentine. A lack of human understanding of the tree’s life cycle, the diverse ecosystem it anchored, and its dependence upon fire contributed mightily to this destruction. Scientific research now informs conservation and restoration efforts to protect this important species.

Longleaf pine trees grow anywhere between 60-110 feet depending on how nutrient-rich the soil is. The trees live an average of 250 years, with some up to 450 years. As its name suggests, longleaf pines have the longest needles of any southern pine species, ranging in length from 7 to 18 inches. The needles are grouped by threes and tufted at the end of branches. The trees produce cones that range in length from 5 to 12 inches. The cones contain the seeds that allow longleaf pines to reproduce. Cones open in October and November, releasing winged seeds that flutter to the ground.

About every seven years, longleaf pines have what’s called a mast period—a year where the tree produces an excess number of cones and seeds. It is thought that this phenomenon is both an adaptation to a fire-dependent ecosystem and a way to control predatory seed-eating populations. By producing more seeds at irregular intervals instead of yearly, the seeds are more likely to avoid being burned by unpredictable fire or eaten by well-fed predators.

Longleaf pines are uniquely adapted to withstand fire, and in fact, need it to survive. The pine thrives following a wildfire and suffers during periods of fire exclusion. Historically, lightning-ignited fires and use of fire by Native Americans helped the longleaf forest flourish. Fire clears the underbrush and prevents infiltration of hardwood trees, which can suppress the growth of longleaf seedlings. The longleaf itself grows a thick bark to protect the wood from fire. The green needles that are difficult to burn also serve as a protective barrier.

The life cycle of a longleaf pine involves five major stages: seedling, grass, bottle brush, sapling, and maturity. In the fall, the tree’s cones begin to open, and seeds fall to the ground. Seeds need both moisture and direct contact with the soil to germinate. While the seeds are susceptible to fire, fire is an essential part of this process. Fire clears the forest floor allowing the necessary contact with the soil for the seeds to establish roots.

Following establishment, the tree enters the grass stage and begins the process of growing a taproot. From the surface, the pine looks like a large clump of grass, but much of its growth is happening underground. The grass stage is extremely resistant to fire, with the needles protecting the growing tip from burning. After one to seven years, the young tree will enter the bottlebrush stage. A white tip emerges from the grass and begins to rapidly grow upward. The rapid growth protects the growing tip from fire. Thick bark also begins to form, protecting the wood from burning.

At around 6 to 10 feet in height, the tree becomes a sapling and starts to grow branches. As a sapling, longleaf can grow up to 3 feet in height a year. The bark thickens, becoming more immune to fire. By the time a tree reaches 8 feet, the ground level trunk diameter is around 2 inches, and the tree is almost entirely protected from death by fire. The final life stage is maturity. A longleaf pine begins to produce cones containing fertile seeds after around 30 years of growth. Between 70-100 years, the pines halt their vertical growth—anywhere between 60-110 feet depending on how nutrient-rich the soil is.

Trees older than 80 years are considered old-growth pines. Only 12,000 acres of old-growth longleaf remain, existing in fragmented stands across the southeast. It is at this stage that many trees become infected with a red-heart fungus that causes internal rot. While the fungus will ultimately lead to the death of the tree, the infection is part of a life cycle essential to other animals within the ecosystem. If a tree makes it to the ripe old age of 300, it weakens and becomes more susceptible to pests. Eventually the tree will die, but it will still serve a role in the ecosystem, providing nutrients and homes to the nearly 600 plant and animal species living in the forest.

Many efforts are currently underway to both conserve the existing forest and restore the ecosystem to protect the species that live there—many of which are currently endangered. If you want to get involved with restoring the longleaf pine forests, contact the North Carolina Longleaf Coalition, the American Longleaf Restoration Initiative or the Longleaf Alliance. If you’d like to learn more about the forest and its use in the Cape Fear Region, come to the Museum and check out Cape Fear Stories and Discovery Gallery.

Previous Columns

July 2022: Sea Turtle Season
May 2022: Ghost Trees
March 2022: Jellyfish
January 2022: Venus Flytrap
November: Citizen Science
September: Hurricane Season
July: Plastic Free July
June: All About Alligators
May: Rain Gardens
April: Bald Cypress Trees and The Climate Record
March: Ocean Waves
February: The Scientific Method
January 2021: Static Electricity

 


Longleaf pines.
Source: AmericanForests.org, Credit: Eric Sprague

Historic (purple) and current (red) range of the longleaf pine forests.
Source: Blain Cerame, et al. Adaptation to Ephemeral Habitat May Overcome Natural Barriers and Severe Habitat Fragmentation in a Fire-Dependent Species, the Bachman's Sparrow (Peucaea aestivalis). PLOS One, 2014. doi:10.1371/journal.pone.0105782.g002

Needle leaves of the longleaf pine.
Source: AmericanForests.org

Longleaf Life Stages.
Source: Longleaf Alliance
814 Market Street • Wilmington, NC 28401 • Phone 910-798-4370 • Fax 910-798-4382
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