Overview
Obviously, overstory conversion is not needed in these situations. However, there are several options for regeneration and maintenance of these stands. If the stand is even-aged, it can be maintained in an even-aged condition by regenerating via the clear-cut and replant or shelterwood methods. Of course, the current stand may be retained for some time, given longleaf's long life. On the other hand, if the landowner desires an uneven- or all-aged forest, there are several techniques available.
Creating gaps in the canopy of an even-aged mature longleaf forest allows longleaf regeneration to occur when seed crops are available. If the gaps are created prior to a seed crop, fire must necessarily be used to keep those gaps from becoming occupied with woody brush or hardwoods like turkey oak or water oak. Another approach includes creating gaps just prior to seed fall in a seed year and opening up holes in the canopy after new seedlings have established themselves, giving them space to grow into.
Size of the gaps is a subject of some discussion, but there are some generally accepted tradeoffs. As gaps grow smaller, seedling survival and growth are poorer. Single tree removal works with longleaf systems if the stand is fairly open in nature already and growth rates are not particularly important. Small group cuts to open gaps of ¼ acre to ½ acre in size are adequate to start regeneration on its way. Typically, subsequent cuts are used to expand these openings in anticipation of new seedlings and perpetuating the range of age classes of an all-aged forest. "Domes" of young longleaf are created, with the oldest and tallest saplings in the center of the gaps and the height and age decreasing with distance from the center.
Eventually, the gaps merge into each other and a forest with trees representing many seed years scattered across the entire stand in clumps. This stand structure is considered typical of much of the pre-settlement longleaf forest. Patch size undoubtedly varied in pre-settlement forests, because natural forces of varying intensity created them. Recurring fires probably kept invading species at bay, while the longleaf gradually reoccupied large areas from seed and seedlings in place and residual seed trees that survived the catastrophic event.
Stands that are Predominately Longleaf Pine and No Recent Fire History
Longleaf forests are more likely than other pine forests to accumulate high levels of forest floor litter. Longleaf needles are larger and more decay resistant than those of other pines and can build up litter depths of 12 inches or more. Fire must be reintroduced into these situations very cautiously. Fuel treatments such as raking around existing trees, wetting areas immediately around existing trees, and mowing or otherwise removing standing fuels might be necessary to avoid or reduce mortality of the overstory. Longleaf is fire-tolerant, not fire-proof.
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Feeder roots frequently grow into the duff layer in long unburned stands and can be severely damaged by even moderately hot surface fires. It is common for fuel to accumulate around the base of large longleaf in fire-excluded situations. Fires in these situations can smolder in these duff piles for long periods, damaging the cambium layer of the bole at a location where the insulating bark is often thin to begin with. High mortality levels in mature longleaf are not uncommon when fire is incautiously applied in long unburned stands.
If scale permits, extraordinary efforts are warranted to prevent this mortality. If it does not, the first fires should be conducted on cool or cold days, with moderate humidity and moderate to high fuel moisture levels. Wind speeds should be moderate (e.g., 5 - 7 mph) and steady. Strip headfires are recommended, with strips a chain (66 feet) or less apart. This allows the fires to move fairly rapidly through the fuel without building excessive intensity. As the fuel is gradually reduced with successive fires, more latitude with fire intensity and season is allowed.
Eventually, as feeder roots are forced down into the mineral soil and the fuel load is reduced, growing season fires may be introduced into the fire regime to encourage the herbaceous understory typical of longleaf forests. When regenerating longleaf stands naturally, it is important to remember that longleaf seed should fall on mineral soil or very light litter to achieve best germination and survival and fires should be timed accordingly. It is equally important to remember that longleaf seedlings are extremely vulnerable to fire in the first year after germination and mortality is high on seedlings with root collar diameters (the diameter right at the groundline) of less than ¼ inch. Once seedlings start height growth, fires should be applied cautiously or withheld when a majority of the seedlings are between 6 inches to 4 feet in height, as this size class is vulnerable to fire, particularly when the terminal bud is in the "candle" stage.