Introduction to the Pine and Mixed-Pine Hardwood Forests
In the last half of the 20th century, the practice of silviculture in southern pine (Pinus spp.) stands has focused on one silvicultural system—clearcutting and planting. This focus has been made possible by two great advances during that time: (1) the development of genetically improved planting stock and (2) the advent of herbicide technology for control of unwanted vegetation in planted stands. The silvicultural system of clearcutting, planting, and associated herbicide treatments has come to define intensive forest management. Forest industry, nonindustrial private forest (NIPF) landowners, and Government agencies have all employed variations of this prescription, and as a result the area in plantations in the South has gone from virtually none to roughly 12.5 million ha (31 million acres) in the last 50 years. In 1995, plantations occupied 15 percent of the forest land in the South but provided 35 percent of the harvested volume (Wear and Greis 2002). By 2040, pine plantations will occupy approximately 20 million ha (50 million acres), or 25 percent of the southern forest area. This will represent roughly half of the projected pine-dominated forest area at that time (Wear and Greis 2002).
This silvicultural system has become popular because of the large total merchantable volume of wood and wood fiber that can be obtained. The estimated average annual growth rates in natural stands are lower than those of planted pine stands, which range approximately 109 cubic feet per acre to 183 cubic feet per acre per year (Siry 2002). FIA-based empirical yields indicate that average annual growth rates for natural pine across all sites can be as high as 86 cubic feet per acre per year, followed by oak-pine forests with 54 cubic feet per acre per year, upland hardwood forests with 47 cubic feet per acre per year, and bottomland hardwood forests with 44 cubic feet per acre per year (Abt and others 2001, Siry and others 1999).
On the other hand, these data also imply that by 2040, 75 percent of the South’s forest land will not be in plantations, but rather in stands of naturally regenerated origin. Currently more than half of the area in the South’s pine-dominated forest types is managed by methods other than intensive plantation culture. Some of this area will not be managed at all in a professional sense; it will simply be allowed to grow as it will and will be high-graded when an operable commercial harvest becomes feasible. But other areas are, and will continue to be, managed using classical silvicultural practices that establish and maintain naturally regenerated pine stands. Specifically, these include even-aged reproduction cutting methods, such as the seed tree and shelterwood methods, and uneven-aged reproduction cutting methods, such as the group selection and single tree selection methods.
Management of naturally regenerated stands will have four prominent areas of application in the decades to come. The first of these is in management of the forest land owned by NIPF landowners. Many NIPF landowners choose not to employ clearcutting on their land, because clearcutting requires a large capital investment in stand establishment. Plantation establishment costs can quickly exceed $500/ha ($200 per acre), especially if intensive site preparation includes applications of chemicals and fertilizer (Dubois and others 2001). While such costs are easily borne by large companies, they are often difficult for NIPF owners of small properties to justify. Management prescriptions that rely on natural regeneration can be adapted to make stand establishment costs very low, although the tradeoff is that it takes longer to develop trees of merchantable size. However, many NIPF landowners find this acceptable, especially in light of the multiple management objectives they often seek, within which the aesthetic disadvantages associated with clearcutting do not fit.
The second prominent area of application is in management of large-diameter pine trees and the higher unit value that sawtimber brings relative to pulpwood when trees are harvested. For example, during the past 10 years in Louisiana, prices of softwood sawtimber averaged from 3.2 to 5.4 times those of pine pulpwood on an equivalent weight basis (Louisiana Department of Agriculture and Forestry 2002). In multiple-use settings, management of stands to large tree size can produce aesthetic, wildlife, and other benefits sought by a landowner. Finally, a part of the South’s forest industry will continue to concentrate on the manufacture of high-quality dimension lumber, the best source of which is high-quality trees of sawtimber size.
The third area of application is within streamside management zones (SMZ), often among the most productive sites in a forested ownership. Clearcutting is generally avoided in SMZs, because it has adverse effects on water quality and aquatic systems. High-grading or selective cutting is often used to capture standing volume of desired species found in SMZs, but experience shows that such practices are neither sustainable nor grounded in sound silvicultural practice. One sensible approach to the management of SMZs is to employ management prescriptions that naturally regenerate desired species while maintaining forest cover within the SMZs.
Finally managers of public forest land in the South, especially those who manage national forest lands, are increasingly seeking alternatives to clearcutting (Guldin and Loewenstein 1999). This trend has its origins in the fact that the public does not like the appearance of clearcutting on public lands. But it also is seen in modern approaches to management of Government lands by means of silvicultural prescriptions designed to retain or restore forest stand conditions that benefit underrepresented plant and animal communities, such as the pine-bluestem habitat restoration in the western Ouachita Mountains (Stanturf and others 2004).
Research and practical experience suggest that both even-aged and uneven-aged reproduction cutting methods can be used in southern forest stands, depending on forest type, prevailing economic and ecological conditions, and ownership (Burns 1983). It is likely that the range of potential applications will grow wider rather than narrower as a wider variety of practitioners employ a wider variety of these methods on a wider variety of ownerships.
Encyclopedia ID: p1086
