Bioenergy Production from Southern Forests

Bioenergy products from southern forests are among a large number of goods and services that can be produced using sustainable forest management practices. Bioenergy products have historically come from woody materials that have not been economically usable for the manufacture of lumber, pulp, paper, and other timber products. Most of the bioenergy products are expected to come from residues harvested after cutting for stand regeneration and from trees cut during stand improvement, but with low market values for other purposes. Mill residues, which are currently widely used by the industry for energy, are not discussed here as they do not directly impact forest management.

This section of The Encylopedia of Southern Bioenergy synthesizes knowledge on the management of forest stands to provide biomass that can be used for bioenergy or bio-based products. In some management circumstances, bioenergy will be the only material harvested from the forest stand, but more typically, bioenergy will be an additional product produced during the traditional harvesting of timber or pulpwood. The emphasis is on how, when, and where bioenergy production can be integrated into silviculture, while ensuring the long-term sustainability of the forest ecosystem. An example of an integrated approach is given at Integrating Bioenergy Harvesting with Silviculture - A California Example.

Silviculture is the science and art of managing forest stands and woodlands for the desired needs and values of landowners and society on a sustainable basis (Helms 1998). These goals or objectives can include the production of timber products (of which biomass for bioenergy is one of several possibilities), soil and water conservation, amenity values, recreation, hunting and fishing, agroforestry or range, nature preservation, biodiversity, and providing lifestyle attributes. Often forest owners have multiple goals. Although alternative forest products are important to industrial forest owners, the primary focus is on the sustainable production of saleable timber and a financial return on their investments. In many national forests and often with non-industrial private forest (NIPF) owners, the main objectives are the production of a variety of forest resources, of which timber products may be a component. Clearly it is important to define the goals of management in order to develop silvicultural plans compatible with these goals. Nevertheless, even where the goal is not for industrial products, providing biomass for bioenergy can often assist the owner in achieving the major objectives, provided this can be done within economic and other constraints.

Because of their long-lived nature, forests should be managed through carefully written plans. Most national and industrial forests have such plans that detail management objectives, the characteristics of the forest, the flow of products from the forest, monitoring systems, etc. Forest management is described in detail elsewhere (Young and Giese 2002; Davis and others 2001). However, since many small NIPF owners often do not have management plans, a section on goal setting and management planning for their particular circumstances, including how to incorporate bioenergy production can be found in Forest Management Issues for Bioenergy Production by NIPFs.

The optimum silvicultural system for a particular situation is the integration of the owners objectives, the forest type and its current state, site characteristics, ecosystem processes, market opportunities, infrastructure, and other resource opportunities. In addition, economics, environmental sustainability, and social issues must also be considered. Most of these variables are discussed in this module although some, such as economics, social, and sustainability issues, are covered in more depth elsewhere.

The potential for the production of bioenergy from Southern forests is currently constrained by the lack of developed markets in many areas of the South. Biomass for bioenergy is a low value product compared to sawlogs, but given improvements in the relative economics could compete with pulpwood and other low value products. Unlike pulpwood, the inclusion of crown material and bark, which are generally left as harvest residue, is generally not a hindrance to its use as an energy source. Apart from short rotation crops grown primarily for energy, most of the bioenergy potential is from residues or currently unutilized biomass. The following main stand condition classes can be distinguished in relation to bioenergy potential:

• Naturally managed hardwood or softwood forests with high valued timber where harvesting residues and and low-value trees are possible sources of bioenergy.
• Stands where biomass harvesting can assist other goals such as timber stand improvement, reduction of hazard and risk from fire, insects, or disease, improving amenity, or wildlife habitat.
• Degraded, low-value forests that could be utilized for bioenergy as part of the process of improving the stands or replacing them with plantations.
• Industrial plantations grown for timber or fiber and where harvesting residues and thinned trees, currently left in the woods to rot, are utilized for bioenergy.
• Short-rotation hardwoods or combinations of trees with other bioenergy-specific crops that are grown primarily as a source of energy.

Despite the largely secondary nature of biomass for bioenergy it can be integrated into silviculture and harvesting practices to obtain overall benefits to the forest owner and wider community. However, in doing so it is important to ensure sustainability and that other forest values are not compromised. More in-depth discussion of the production of biomass for bioenergy can be found at:

• Favorable Stand Attributes for Bioenergy Production
• Forest Management and Silviculture for Bioenergy Production