D Zhang, Auburn University, Auburn, AL, USA J Stanturf, Center for Forest Disturbance Science, Athens, GA, USA © 2008 Elsevier B.V. All rights reserved.
An Overview and Economic Explanation of Global Forest Plantations and Conservation of Natural Forests
Forest Plantation Development Direct Ecological Effects of Forest Plantation
Factors Influencing Forest Plantation Development Further Reading
Between the extremes of afforestation and unaided natural regeneration of natural forests, there is a range of forest conditions in which human intervention occurs. Previously, forest plantations were defined as those forest stands established by planting and/or seeding in the process of afforestation or reforestation. Within plantations, there is a gradient in conditions. At one extreme is the traditional forest plantation concept of a single introduced or indigenous species, planted at uniform density and managed as a single age class (the so-called monoculture). At the other extreme is the planted or seeded mixture of native species, managed for noncon-sumptive uses such as biodiversity enhancement. To further complicate matters, many forests established as plantations come to be regarded as secondary or semina-tural forests and no longer are classed as plantations. For example, European forests have long traditions of human intervention in site preparation, tree establishment, silviculture, and protection; yet they are not always defined as forest plantations.
Further refinement of the plantation concept is necessary in order to encompass the full range of actual conditions. A useful typology is based on purpose, stand structure, and composition of plantations. Thus, an industrial plantation is established to provide marketable products, which can include timber, biomass feedstock, food, or other products such as rubber. Industrial plantations usually are regularly spaced with even age classes. Home and farm plantations are managed forests but at a smaller scale than industrial plantations, producing fuelwood, fodder, orchard, and garden products but still with regular spacing and even age classes. A wide range of agroforestry systems exist, distinguishable as a complex of treed areas within a dominantly agricultural matrix. Environmental plantations are established to stabilize or improve degraded areas (commonly due to soil erosion, salinization, or dune movement) or to capture amenity values. Environmental plantations differ from industrial plantations by virtue of their purpose; they may still be characterized as regularly spaced with even age classes. Efforts to restore forest ecosystems are increasing and often utilize the technology ofplantation establishment, at least initially.
Recently, FAO defined 'planted forests' as forests in which trees have been established through planting or seeding by human intervention. This definition is broader than plantations and includes some seminatural forests that are established through assisted natural regeneration, planting or seeding (as many planted forests in Europe that resembled natural forests of the same species mix) and all forest plantations which are established through planting or seeding. Planted forests of native species are classified as forest plantations if characterized by few species, straight, regularly spaced rows, and/or even-aged stands. Forest plantations may be established for different purposes and were divided by FAO into two classes: protective forest plantations which are typically unavailable for wood supply (or at least having wood production as a secondary objective only) and often consist of a mix of species managed on long rotations or under continuous cover; and productive plantation forests which are primarily for timber production purposes.
Figure 1 shows that, in 2005, some 36% of global forests (about 4 billion ha, covering 30% of total global land area)
□ Primary forest
□ Modified natural forest
□ Seminatural forest
□ Productive forest plantation
□ Protective forest plantation
Figure 1 Global forest characteristics 2005. Modified from FAO (2005) Global forest resources assessment 2005. FAO Forestry Paper 147. Rome, Italy.
are natural forests, 53% are modified natural forests, 7% are seminatural forests, and the remaining 4% are forest plantations. Of these forest plantations, productive forest plantations account for 78% and protective forest plantations account for 22%. While natural forests and modified natural forests declined between 1990 and 2005, seminatural forests and forest plantations increased (Figure 2).
This article provides an overview and economic explanation of global forest plantation development. It also presents factors influencing global forest plantation development and lists the usefulness of forest plantations, including their roles in the conservation of natural forests. Finally, it summarizes the impact of forest plantations on biodiversity and other ecological functions.
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