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.

*Table 4.2:* Overview of biological carbon mitigation issues and opportunities in selected countries/regions (Based, in part, on Sedjo and Lyon, 1990; Fujimori, 1997; Nilsson and Shvidenko, 1998; De Camino et al., 1999; Sohngen et al., 1999; Zhang, 1996)

Region	Issues	Options to store carbon arising from the issues

USA/Canada	Primary forest based forestry and second rotation forestry High tech forest industry Fierce environmental debates Large impacts of natural disturbances Agriculture under pressure that restore soil C (excess agricultural land)	Fire management Afforestation Efficient use of wood products Bioenergy Farming practices (e.g., reduced tillage)

Europe	Agriculture under pressure, afforestation of agricultural lands Changing ownership Forest health problems Move towards nature-oriented forest management High tech forest industry In eastern Europe, privatization of forest ownership that restore soil C	Nature-oriented forest management Nature reserves Afforestation Efficient use of wood products Bioenergy Farming practices (e.g., reduced tillage)

Russia	Transition to market economy Bad financial situation of forest service Large impacts of natural disturbances Low levels of fellings	Natural regeneration on abandoned agricultural land Fire management Capacity building Farming practices that restore soil C

Japan	Plantation-based forestry and managed secondary forestry High tech forest industry Forest health problems Move towards nature-oriented management	Efficient use of wood Nature-oriented forests Reserves Bioenergy

China	Transition to market economy Transition from non-wood fibre sources to using wood fibre Floods resulting from loss of forest	Afforestation with plantations Protecting primary forests Flood protection Farming practices (e.g., reduced tillage) that restore soil C

Australia/ New Zealand	Plantation-based forestry and some primary forest based forestry High tech forest industry Afforestation of agricultural lands	Fire management Afforestation with plantations Efficient use of wood products Bioenergy Halting deforestation Farming practices (e.g., more forages) that enhance soil C

Argentina, Chile, Brazil	Plantation-based forestry and some primary forest based forestry High tech forest industry developing Plantations are not able to reduce deforestation because they provide different set of products	Afforestation with plantations Efficient use of wood products Bioenergy Halting deforestation Farming practices (e.g., reduced tillage) that and services. enhance soil C

Mexico	Forestry largely based on native forests Large deforestation rates Economic incentives favour agriculture/cattle over forestry Afforestation of degraded lands mostly for restoration	Halting deforestation Sustainable forest management of native forests Social forestry Afforestation with local species Bioenergy

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