Managing Longleaf Pine with Prescribed Fire

Frequent fire is essential for maintaining longleaf pine woodlands and savannas in a healthy condition. In the modern landscape of the southeastern US the only practical way of accomplishing this objective is prescribed burning. Because plants and animals will be adapted to the historic fire regime, the specified prescribed burn regime should conform closely to the best guess historic burn regime for the particular location.

Southeastern US habitats dominated by longleaf pine have declined precipitously in area and extent (Frost 1993). Consequently, restoration of such habitats is now a high priority for conservation. Re-initiation of frequent prescribed burning is an absolutely critical first step in restoration of longleaf pine woodlands and savannas. Almost any fire is likely to have some positive effects (Provencher et al. 2001b). However, prescribed fire alone may not be sufficient for restoration (Provencher et al. 2001b). There are two reasons why this may be the case. First, long periods of fire exclusion lead to structural changes in the plant community that may not be reversible with prescribed burning (see: Effects of Fire Suppression). Tree species other than longleaf pine can become established and reach a fire resistant size during long fire free intervals. Overly dense stands of trees decrease light and nutrient availability and consequently inhibit recovery of herbaceous-dominated ground layer plant communities. Hardwood tree species, in particular, can also modify the local environment in such a way as to reduce the likelihood of ignition and subsequent fire spread (Williamson and Black 1981, Streng and Harcombe 1982). It may be necessary to remove undesirable tree species and to thin overly dense pine stands in order to restore a more appropriate stand structure before reinitiating a prescribed burn program.

The second reason why fire alone may be insufficient for restoration is that certain plant and animal species that historically occurred on a site may no longer be present. Loss of species may occur as a consequence of prolonged fire exclusion (Lemon 1949, Abrahamson and Abrahamson 1996, Maliakal et al. 2000) or a history of intensive soil disturbance due to agriculture or forestry. The missing species may include longleaf pine itself as well as many of the typical ground layer plants and arthropods. Selective cutting and reintroduction of fire may create the appropriate environmental framework to support populations of these characteristic longleaf species but this will be of little use if they are not actually present at the site. It may therefore be necessary to reintroduce missing species. A variety of approaches are available to accomplish this objective, including direct seeding, nursery propagation and out-planting, and translocation of mature plants (Glitzenstein et al. 2001). Results to date indicate that most longleaf ground layer plants are relatively easy to propagate. Consequently, re-initiation of new populations is not particularly difficult if a stand is managed appropriately with frequent prescribed fire (Seamon 1998, Glitzenstein et al. 2001) and competition from canopy trees is not too great (Mulligan et al. 2002).

Management Considerations for Wildlife

The surest method for maintaining the characteristic fauna of longleaf pine ecosystems is to maintain the appropriate historical burn regime and overall site integrity (Engstrom 1993, Guyer and Bailey 1993, Folkerts 1993, Means et al. 1996, James et al. 2001, Provencher et al. 2001b). Site integrity includes the micro-topographical, hydrological and floristic components of the site. Activities that destroy these components, e.g. agricultural usage, ditching, bedding, intense mechanical site preparation, and some broadcast herbicides, can permanently damage the habitat for many species of animals and plants. Restoration of some or all of these components will improve habitat suitability and some animal species, particularly mammals and birds, may respond rather quickly (Engstrom et al. 1984, Provencher et al. 2001b). Insects, herpetofauna, and some of the rarer birds tend to perceive the environment on a finer scale, and these groups may be more difficult to restore. Insects and smaller herps may also be dispersal limited, and, like plants will need to be reintroduced. Despite these concerns it is worth noting that restoration science is still in its infancy, and promising studies for a number of groups of organisms are just now being initiated (Colby 2000, Provencher et al. 2001b).

See also: Using Prescribed Fire to Manage Wildlife Habitat

Using Prescribed Fire to Control Insects and Diseases

Although wildfires can increase insect infestations, some authors have suggested that typical low intensity prescribed fires may help to limit populations of damaging insects (Brennan and Hermann 1994). For example fires in early spring may kill bark beetle larvae that are in diapause within the forest litter at that time.

See also: Using Prescribed Fire to Control Insects and Disease

Key Issues in the Implementation of Prescribed Burning

Compared to ecosystems adapted to longer fire return intervals, prescribed burning of longleaf pine is a relatively simple matter. For example, a five-person burn crew with two drip torches and a pumper truck for backup can burn 1000 hectares or more per day of healthy longleaf with an herbaceous dominated understory. Aerial ignition via helicopter, an increasingly common method, allows for prescribed burns this large or larger in a few hours time. Fires administered at the proper high frequency are low in intensity and relatively easy to control.

With some caveats discussed below, implementation issues pertain not so much to the practicalities of how to carry out the fires, but to research questions related to effects of different fire regimes. Pending further work, the historic fire regimes inferred by Frost (1998) may serve as the best guide for prescribed fire as well, with the caveat that fire frequency goals should take precedence over fire season goals when the two are in conflict (Glitzenstein et al. 2003).

Without doubt, keeping prescribed fire as an important land management tool is the most critical issue relating to conservation and management of the longleaf pine ecosystem. Unfortunately, spreading suburbia increasingly hampers use of this critical management tool. According to Wade (1993, p. 352),

“The longleaf pine ecosystem is currently facing another crisis. The land base of this once vast ecosystem is disappearing at an alarming rate (less than 4% of the original 60 to 90 million acres remains in longleaf). Since at least the early 1970’s immigration to Florida has averaged more than 1000 people a day. A seeming insatiable demand for single family homes in the suburbs and the attendant network of highways has displaced the natural landscape. Moreover, fire and smoke generally are not welcomed along the urban-wildland (WUI) interface or along transportation corridors. This, in turn, makes it much more difficult to perpetuate remaining fire-dependent wildland areas.”

Wade (1993) suggests that sensitivity on the part of fire managers to public concerns, along with education about the importance of prescribed fire, may allow managers to continue to use prescribed fire even in WUI areas. One important potential limitation to continued use of prescribed fire is the 1970 Federal Clean Air Act (renewed in 1990)(Achtemeier et al. 1998). This law mandates regional limits on various types of air pollutants including particulate matter and carbon monoxide, two of the main components of smoke. Whereas smoke from woods fires is generally considered a minor source of these pollutants, reducing smoke may be more expedient politically than regulating other sources of these pollutants. Furthermore, heavy local concentrations of prescribed fires can exceed recommended local air quality standards. Recent rule changes by the federal Environmental Protection Agency (EPA), the agency charged with administration of the Clean Air Act, do take into account the need (and legal obligations) for prescribed burns in natural resource management. The rules allow for development of burn plans by land management agencies that are then reviewed by EPA. The latter is then allowed some discretion in not designating the land management agency as “in violation” during periods when prescribed fires contribute significantly to fine particulate (PM 2.5 and PM 10 loads). Despite these efforts at accommodation, air pollution concerns significantly complicate the lives of burn managers and likely lead to fewer prescribed fires.