Forests and woodlands2 provide many goods and services that society values, including food, marketable timber and non-wood products (fuel, fiber, construction material), medicines, biodiversity, regulation of biogeochemical cycles, soil and water conservation (e.g., erosion prevention), carbon reservoirs, recreation, research opportunities, and spiritual and cultural values. Forests play a key role in the functioning of the biospherefor example, through carbon and water cycles (the latter is discussed in Chapter 4)and hence indirectly affect the provision of many other goods and services (Woodwell and MacKenzie, 1995). Changes in global climate and atmospheric composition are likely to have an impact on most of these goods and services, with significant impacts on socioeconomic systems (Winnett, 1998).
Since the SAR, many studies have dealt with changes in the structure, composition, and spatial patterns of forests (e.g., VEMAP Members, 1995; Smith et al., 1996a; Bugmann, 1997; Shriner et al., 1998). The biogeochemical literature has focused on the carbon cycle (e.g., Apps and Price, 1996; Fan et al., 1998; Steffen et al., 1998; Tian et al., 1998; IPCC, 2000; Schimel et al., 2000). There is an expectation that directed land-management practices can either increase or retain carbon stocks in forests, thereby helping to mitigate increases in atmospheric CO2 levels; this is discussed elsewhere (IPCC, 2000; see also TAR WGIII Chapter 4 and TAR WGI Chapter 3).
The influence of climate change on forests and associated goods and services is difficult to separate from the influence of other global change pressures such as atmospheric changes, land use, and land-use change resulting from human activities. The State-Pressure-Impacts approach outlined in Section 5.1 is used here as a framework to examine interrelated responses to global change and expected changes in supply of services from forests and woodlands (see Table 5-1). In this section, the focus is on some of the important pressures, impacts, and responses for three goods and services provided by forests and woodland ecosystems: carbon, timber, and non-wood goods and services. The impact on biodiversity in forests is covered in Sections 5.2 and 5.4. The state of the sector and the pressures acting on it, as well as possible responses, impacts, and adaptation opportunities, will differ among the regions of the world; here the focus is on global commonality.
This section presents an overview of the current status and trends for forests in general; specific regional trends are presented in some of the regional chapters (Chapters 10-17).
The world's forests cover approximately 3,500 Mha (FAO, 1997a), or about 30% of the total land area (excluding Greenland and Antarctica). About 57% of the world's forests, mostly tropical, are located in developing countries. About 60% are located in seven countries (in order): the Russian Federation, Brazil, Canada, the United States, China, Indonesia, and the Democratic Republic of Congo.
In 1995, plantation forests were estimated to cover 81 Mha (2.3% of total estimated cover) in developing countries and about 80-100 Mha in developed countries (FAO, 1997a). They play an important role, particularly in the production of industrial roundwood and fuelwood, restoration of degraded lands, and provision of non-wood products (FAO, 1997a). Some countries obtain 50-95% of their industrial roundwood production from plantations that cover 1-17% of their total forest area (Sedjo, 1999). In many developing countries, plantations often occur as community woodlots, farm forests, and agroforestry operations.
Between 1980 and 1995, the area of the world's forests decreased by about 180 Mha (5% loss of total forest area in 15 years) as a result of human activities (FAO, 1997a). About 200 Mha were converted to agriculture (subsistence agriculture, cash crops, and ranching), but this loss was partially offset by about 40 Mha increase in plantations. In developed countries, forests increased over the same period by about 20 Mha through afforestation and natural regeneration on land no longer in use by agriculture, despite losses of forests to urbanization and infrastructure development. Loss of native forest in developing countries (tropical and nontropical) appears to have slowed during 1990-1995, with an overall loss of about 65 Mha (FAO, 1997a). However, other changes such as fragmentation, nonsustainable logging of mature forests, degradation, and development of infrastructureall leading to losses of biomasshave occurred over large areas. Of about 92 Mha of tropical closed forest that underwent a change in cover class during 1980-1990, 10% became fragmented forest and 20% was converted to open forest or extended forest fallow (FAO, 1996). There are no global estimates of forest degradation, but data from specific areas give an indication of the extent of degradation. Logging practices damage and degrade more than 1 Mha yr-1 of forest in the Brazilian Amazon; surface fires (e.g., those in 1998) may burn large areas of standing forest in these regions (Cochrane et al., 1999; Nepstad et al., 1999; see also Chapter 14). These authors conclude that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each yearand even less during years of severe drought. In the boreal zone, there has been continuing encroachment by agriculture and development of infrastructure (roads, survey lines, wellheads, etc.) that open access to primary forests. Preliminary estimates of these effects for Canada, for example, indicate a net loss of 54,000-81,000 ha yr-1 of forest over the period 1990-1998 as a result of various activities (Robinson et al., 1999).
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