Climate Change 2001: Mitigation

4.2.2.2 Driving Forces for Land-Use Change

Box 4.2. Disturbance, Age-class Distribution, and their Implications for Forest Carbon Dynamics

At the stand scale, disturbance events (both natural and anthropogenic) have three main impacts on the carbon budget (Apps and Kurz, 1993). First, they redistribute the existing carbon by transferring carbon from living material, above and below ground, to the dead organic matter pools. Second, they transfer some of the carbon out of the ecosystem (e.g., into the atmosphere as combustion products, in the case of fire, and/or into the forest product sector as raw feedstock, in the case of harvest). Third, by opening the forest canopy, the disturbance changes the site micro-environment and restarts the successional cycle for new stand development.

At the scale of forests (typically comprising many stands), the disturbance regime determines the age-class structure (e.g., the even-age structure associated with stand-replacing disturbance regimes or the uneven-age structures associated with individual tree mortality and gap-phase replacement), and age-class structure of stands and trees making up the forest. The C stocks in a forest landscape, and the changes in these stocks over time, are strongly influenced by the age-class distribution (Kurz et al., 1995b; Turner et al., 1995; MacLaren, 1996; Apps et al., 2000; Bhatti et al., 2001). In managed plantation forests, the age-class distribution is controlled by the management regime and harvest cycle (Heath and Birdsey, 1993; MacLaren, 1996), while in natural forests other mortality agents play a major role. See Heath et al. (1996) and Kurz et al. (1995a) for examples.

Land management decisions are influenced by many factors. In the temperate zone, and in the European parts of the boreal zone, these are mainly technological and economic. Agricultural production is, for example, heavily influenced by evolving technologies, economic opportunities, subsidies, and restrictions on international trade. Forestry practices are similarly influenced by economic returns, trade, and pressures from society (Clawson, 1979; Waggoner, 1994; Wernick et al., 1998). It is within these pressures and opportunities that carbon mitigation possibilities may be found, and preferably they would be region specific. Table 4.2 gives an overview of some of the specific issues of importance in the temperate and boreal zone of the world.

Competition for land between forestry and agriculture has become less severe. Forest area is increasing in many regions of the boreal and temperate zone, partly because agricultural yields have improved or because the profitability of marginal agriculture has declined. The ability to produce agricultural goods has grown faster than demand, resulting in a downwards trend in prices (Alig et al., 1990; Waggoner, 1994). Much abandoned agricultural land has reverted to forest, either naturally or through deliberate planting. Superimposed over these land conversions is a transition in forestry from a foraging and gathering operation, dependent upon primary forest, through a stage of more intensively managed forest, to total forest ecosystem management. The latter occurs when urbanized societies press for nature-oriented forest management. Continuously improving technologies allow low-cost establishment and higher productivity from planted and plantation forests (Sedjo, 1983; 1999a). In agriculture, also, practices are changing towards maintaining site fertility or decreasing the risk of erosion.

Silvicultural practices have increased forest growth in many boreal and temperate regions. The increasing concentration of atmospheric CO₂ may also have contributed to the enhanced growth of forests.

Incentives for planting forests are provided by a combination of market factors and public policy. Remaining wild forests, such as the public forests in the US National Forest System and in British Columbia, are becoming less accessible and have increased harvesting restrictions. Subsidies to harvesting of natural forests are also being withdrawn elsewhere. For example, large subsidies for harvesting Russian forests were prevalent during the Soviet era, largely through subsidized transportation, but have now disappeared. The economic structures are in transition and industrial production has declined. As a result, harvests have fallen dramatically in Russia since the 1990s (Nilsson and Shvidenko 1998).

Market forces, reflecting industrial needs for wood, have provided
financial incentives for expansion of commercial forests (Sedjo and Lyon, 1990). This is a trend expected to continue, because of growing demand for industrial wood and low profitability in agriculture (Sohngen et al., 1999). Early analyses suggested that economic returns from plantations (in the tropics as well as in the temperate and boreal zone) justify investment in a number of regions (Sedjo, 1983). Recent studies confirm that forest plantations are
being established at a rate of 600,000ha/yr (Pandey, 1992; Postel and Heise, 1988; UN-ECE/FAO, 2000). However, industrial plantation forestry is new in many tropical areas and yields vary considerably across ecosystems. In many locations where plantations have only recently been established, little is known about the potential capabilities for increasing productivity as well as the potential problems that may limit yields.

Box 4.3. The Reduced Impact Logging Project, Carbon Sequestration Through Reduced Impact Logging

The RIL (reduced impact logging) project developed by Innoprise, a Malaysian company with forestry activities, and the New England Power Company, USA, aims to save CO₂ already stored in forest biomass by reducing damage to vegetation and soils during harvesting. The hope is to reduce damage by 50% compared to that of conventional harvesting. The techniques employed are modifications of conventional bulldozer harvesting techniques; including pre-felling climber cutting, directional felling, skid trail design, and post harvest operations such as rehabilitation of log landings. Today the total project area amounts to 2,400 ha. The pilot research project has quantified the carbon implications and costs on 1,415ha. They found that avoided emissions amounted to 65–90MgC/ha and that the associated costs were US$3.55/MgC (Wan Razali and Tay, 2000).

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