Do the Math
In 1963, from his work on the Escambia Experimental Forest (Escambia), U.S. Forest Service research forester (now emeritus) Bill Boyer developed the formula for longleaf pine seed dispersal that became one of the foundations for the natural regeneration of the species.
Natural regeneration—literally allowing seedlings to sprout wherever seeds fall— seems the intuitive choice for replanting longleaf pine, but compared to other pines, longleaf ranks very low when it comes to producing seed. It takes 3 years for seed to develop after the tree flowers, and seed crops adequate enough to regenerate a stand may come once every 5 or 7 years.
In 1997, after more than 40 years of working with longleaf, Boyer wrote of longleaf pine cone crops:
“Longleaf cone crops are highly variable from year to year, and also from place to place. Given a receptive seedbed, 360 cones per acre are needed, on average, just to obtain the first seedling. A minimum of 750 cones per acre is usually needed for acceptable regeneration. Given 25 residual seed trees per acre in a shelterwood stand, it takes an average of 30 cones per tree to reach this minimum. Cone crops of this size or larger are uncommon throughout much of the longleaf region, and are erratic in their occurrence. In most years, cone crops will average less than 10 cones per mature seed tree.” For marginal stands, this can mean little or no regeneration.
In 1966, Boyer helped set up a regionwide study that still continues to monitor flowering and count cones and seeds from mature longleaf pine trees on sites ranging from North Carolina to Louisiana, and on the Escambia. Yearly cone reports are still issued from this study, with Dale Brockway, research forester with the Forest Service Southern Research Station Restoring Longleaf Pine Ecosystems unit, serving as point of contact.
The 47-year regional cone production average for longleaf pine is 27.5 cones per tree. The best cone crop occurred in 1996 and averaged 115 cones per tree. Fair or better cone crops have occurred during 51 percnet of all years since 1966, with an increasing frequency since 1983. The reason for this increasing frequency is not known.