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 History of Fire
You're there! In this situation, the only decisions to be made are fire regime and whether or not you need some method of regenerating the forest naturally. If the understory is still occupied by woody brush, a switch to growing season burns is probably in order to encourage the proliferation of grasses and forbs typically indicative of restored longleaf forests. The choice of regeneration method will shape the stand's structure for the future. Both even and uneven-aged conditions are natural in longleaf forests.