Overview
Some natural pine stands in the longleaf range contain a significant longleaf component in the overstory. Some of these stands offer the option of regenerating longleaf naturally if there is an adequate seed source and that seed source is well distributed. Longleaf seeds are the heaviest of the southern pine seeds and do not disperse very far from the parent tree, usually not much more than the height of the tree. Consequently, it is recommended that no fewer than 20 seed trees per acre greater than 16" diameter at breast height (DBH) be present for adequate coverage of the area with seed. The only way to determine if this is true is a good ground inventory or "cruise". Plot tallies should be kept separately because an average "trees per acre" figure is of limited use if the trees are not well distributed.
If there is an evenly distributed and adequate longleaf seed source available, then it might be possible to regenerate the stand with longleaf naturally via some form of the shelterwood method. In the classic shelterwood method used in longleaf systems, a preparatory cut is made to obtain a Basal Area of approximately 60 ft2 /acre to allow the crowns of potential seed trees to expand, therefore producing more cones. When the crowns have expanded to fill the canopy gaps, a second cut is made to reduce BA to approximately 30 ft2 /acre, favoring good cone producers well distributed across the site. Fire is used throughout this process to control competing vegetation, particularly woody brush, and to encourage a desirable grasses and forbs understory.
Once the desired stocking level is obtained, the cone crop must be monitored in anticipation of a good seed year. Longleaf produces good seed sporadically, on the average of every six years across most of it range. Prescribed fire is necessary while waiting on a good seed crop to retain control of the understory. Because longleaf is a "two-year" cone, inventory of the potential seed crop can begin in the year previous to seedfall. Binocular counts of female flowers are an index of the coming seed crop. In the spring and summer of the next year, binocular surveys of tree crowns can be conducted using a systematic method described by Bill Boyer. When the seed trees have an average of 30 cones per tree, or 1000 cones per acre, a burn should be performed to prepare a seedbed. This burn should take the form or a late winter or early spring burn (March-April) to control vegetation and reduce the duff layer, allowing the seed to fall on mineral soil. Sufficient time should be allowed for litter and vegetation re-growth to cover the soil and conceal the seed from hungry birds and small mammals until it can germinate. Longleaf seed typically falls in October and November and germinates as soon as it encounters adequate moisture. If it falls on heavy litter, it may germinate but suffers from May droughts and the seedlings are often killed in the first fire because their roots are not in mineral soil.
Shelterwoods are usually even-aged systems, and the seed trees are removed when an adequately stocked new stand is achieved. The seed trees may be retained, at the owner's discretion, to create a two-aged stand. There is evidence that the retention of as little as 10 ft 2 of BA can significantly retard growth of seedlings, however. If the stand is a mixed species pine stand with longleaf as a minor component, it may be necessary to use fire or other means to control seedlings of the other species while the shelterwood process is underway. It will probably be necessary to leave some trees of other pine species in the first shelterwood cut to provide fuel and shade to control invading woody brush. In the second cut, however, it is unwise to leave any loblolly or other pines to provide seed to compete with the longleaf seedlings. Because these species are annual and prolific producers of easily and widely dispersed seed, they are excellent colonizers of unoccupied sites. It is preferable to leave larger gaps in the stand than to retain loblolly seed trees. Once loblolly seedlings attain 6 feet or more in height, typically in 3 or 4 years, they are tolerant of fire and are difficult to control in that manner.
There is always the option in the above situation to clear-cut and plant with longleaf after establishing a burning regime and controlling the woody understory. This is a more reliable and quicker way to re-establish the longleaf component in these stands, but sacrifices the appearance of the forest for the short term and creates an even-aged stand. The new stand should still be managed with fire as described below, with caution advised when the seedlings are most vulnerable.
Mixed Pine Stands with at least 20 square feet of Basal Area of Longleaf per Acre in the Ovestory and No Recent Fire History
Fire must be a part of the restoration process, but must be re-introduced very carefully if it has been long excluded. Excessive fuel build-up can result in damaging or lethal fires, even in mature stands. In stands with a pine overstory other than longleaf, forest floor fuel depths may not be as great, because loblolly and slash pine needles are shorter and decay more rapidly than do longleaf needles. Still, if fuel accumulations are very deep, feeder roots may have grown up into the duff and can be damaged or killed by a hot fire. In addition, litter buildups around the base of the boles of standing timber can smolder for long periods of time, damaging the cambium where the bark is thin. In addition, long-term fire exclusion usually results in a woody mid- and understory. These fuels can feed hot fires, especially if needles drape on vines and shrubs and "ladder" flames up into the canopy.
The first fire in a situation like this should be as cool as possible, burning on a cold, breezy day with moderate humidity and fuel moisture. In extreme cases, fuel treatments such as mowing or raking around the boles of overstory trees might be employed. If longleaf is to be favored in these stands, special attention should be paid to the bases of existing longleaf trees. Raking or wetting the fuel around the trees might lessen the danger of damage from fire if scale of operation allows. Strip headfires move the heat through the stand relatively quickly without allowing intensity to build to dangerous levels and are good options.
The second fire might also be a dormant season strip headfire to further reduce fuel loads, push longleaf surface roots deeper, and consume or topple woody shrubs top-killed by the first fire. The interval between the first and second fires should be no more than 3 years. Subsequent fires should take place on two or three-year intervals, depending on fuel conditions. The third or fourth fires should be a growing season fire, ideally in late March through early May. From this point on, at least every third burn should be a growing season burn, extending the window into early summer. As fuel loads are reduced, hotter fires can be safely used. For more information on this subject click here.
The understory should begin to respond following the first growing season fire and continue to develop with successive burns. If this is not the case, the process might be "jump-started" by planting or seeding desired species.