"Off-site" Upland Hardwoods
Many longleaf sites become occupied by hardwood species if clear-cut or other heavy harvest is followed by fire suppression and no attempts are made at longleaf regeneration. Typically, light seeded species like sweet gum and loblolly pine are the first tree species to colonize the site. Without disturbance, particularly fire, more shade tolerant hardwood tree species come to dominate the site, in the process providing enough shade to preclude regeneration by the residual pines. These hardwood species in the longleaf region typically include oaks of various species, hickories, and maples. Without further disturbance, the site will soon be crowded with woody brush and hardwood regeneration, resulting in a shaded forest floor with little or no herbaceous vegetation, with, over time, an overstory of mixed hardwoods.
On mesic sites, this can be a fairly rich mix of species. On xeric or very dry sites, the dominant species are typically scrub oaks like turkey oak, bluejack oak, post oak and blackjack oak. The effect, if left undisturbed for long periods, is similar. No pines in the overstory or understory, a mixed woody midstory and understory, and very few grasses or forbs. Restoring longleaf pine and longleaf function to this forest type is slow, but can be accomplished. Longleaf pine restoration can only be accomplished by artificial means, i.e. planting.
If the hardwood on the site is of commercial size, the first step is to remove it with a timber harvest. Careful examination of the site after harvest to determine the presence of desirable understory components should be the next step before proceeding with site preparation. If there is no significant desirable native vegetation on the cutover site, site preparation can proceed. Because hardwoods are vigorous re-sprouters, it is usually desirable to control re-growth with an herbicide. These chemicals can be applied aerially, with ground-mounted sprayers, or by hand with backpack sprayers. The chemical may be broadcast, banded, or directed at sprout clumps. It is usually recommended that the site lay out for one growing season after harvest to allow sufficient re-sprouting to translocate the chemical to the rootstocks.
Choice of chemical should be based on species to be controlled as well as species to favor. Herbicides differ in how they work and which species they control. For instance, chemicals whose active ingredients include glyphosphate (e.g. Roundup or Accord) are only foliar active and affect only the plants they are sprayed directly on. They control grasses and forbs as well as woody plants, but are much less effective on waxy leafed plants. Products containing hexazinone as an active ingredient, on the other hand, are soil active. That is, they are taken up through the plant's root system and work internally in the plant. Hexazinone products, like Velpar, Pronone, and ULW are ineffective on many grasses like the common Andropogon species (broomsedge, bluestems, etc.) and wiregrasses (Aristida spp, Muhlenbergia spp. etc.) at low rates. American beautyberry and many Vaccinium species (blueberry, sparkleberry, huckleberry, etc.) are also tolerant of hexazinone. Products like Arsenal or Chopper, which contain imazypyr as an active ingredient, afford broad scale control of many species, but have little effect on legumes, nitrogen-fixing plants which can also provide important food for many wildlife species. Tank mixes of herbicides afford broader spectra of control, but care should be taken to ensure that they are compatible.
In short, prescriptions for herbicides should be tailored carefully to fit both what species are to be controlled as well as what species are to be spared. In the case of mesic off-site hardwood conversion, there is likely to be little desirable vegetation under the stand to protect and the choice of site preparation method is more likely to depend on what species are to be controlled prior to planting. Herbicide labels are a good source of information on efficacy of the chemical on target species. It is advisable to obtain professional assistance, however, before choosing and applying an herbicide.
Appendix II contains a summary of some common herbicides, how they work, which species they are likely to control, which species are tolerant or resistant, and recommended methods of application.
Herbicides are not the only site preparation method available for off-site hardwood conversion. Mechanical site preparation in combination with fire is another effective choice. Shearing, raking and piling woody debris in preparation for planting is effective as is the three-in-one or Savannah plow. Both of these techniques, however, are likely to severely disrupt any existing native groundcover and can make re-establishment more difficult. Chopping with a drum chopper is effective where debris is fairly light and one-pass chopping can be done without completely destroying any native understory. These mechanical treatments typically result in many hardwood sprouts from roots and stumps and may threaten the survival and growth of longleaf seedlings unless controlled.
In the case of scrub oaks on xeric sites, chopping used in combination with fire or fire alone will often stimulate vegetative growth by desirable grasses and forbs. Before longleaf can be re-established, however, the site must be made accessible for the planters and the scrub oaks must be reduced in number to minimize competition with longleaf seedlings and allow the development of herbaceous fuels to carry later fires. These oaks are fairly fire tolerant and are best killed with an herbicide. Choices include a hexazinone product applied as a broadcast or banded treatment, directed or broadcast treatment with an imazypr product, or stems injection with a variety of chemicals. Again, choices should be based on existing competition and desirable vegetation and prescriptions should be prepared by knowledgeable professionals. Planting with containerized or baretroot longleaf seedlings can then usually proceed. Native vegetation typically recovers without further assistance beyond prescribed fire on these sites, but depleted seed banks may require planting desired species as noted earlier.
For patient landowners, mesic sites occupied by vigorous hardwood forests might be converted in two steps. After clearing the hardwoods through harvest and controlling the sprouts and other woody competitors with chemicals, a "nurse crop" of loblolly or slash pine might be planted and fire introduced as early as possible in the rotation, usually between ages 8 and 12, and kept in the system until final harvest of the pines, either as pulpwood in 12-15 years or as solid wood products, with thinning at 25-30 years. Keeping fire in the system on a 2-4 year rotation, with occasional growing season fires as part of the mix, should prepare the site for planting with longleaf and encourage any native species to assert themselves prior to establishment of the pines.