22.214.171.124.3. Pressures from other disturbances
Additional disturbances are associated with extreme weather events such as
hurricanes, tornadoes, unexpected drought or heavy rainfall, flooding, and icestorms
that lead to extensive mortality and ecosystem change (e.g., Lugo et al., 1990;
Walker and Waide, 1991). Such events generally are highly localized and take
place in a relatively short period of time but have long-term economic impacts
(Haight et al., 1995) and effects on ecosystems (Pontailler et al., 1997). There
is some evidence of recent increases in damage from such extreme events (Berz,
1999; see also Chapters 8 and 9).
126.96.36.199. Changing Demand for Forest Goods and Services
Future demand for industrial wood products depends on income growth, population
growth, technological change, growth in human capital, changes in tastes and
preferences, and institutional and political change (Solberg et al., 1996).
Changes in other markets also can influence demand for wood products. For example,
increases in the price of substitutes, such as steel and concrete building materials,
would increase the demand for industrial timber. In light of these driving factors,
recent timber market assessments have predicted that industrial harvests will
increase by 1-2% yr-1 (Solberg et al., 1996; Brooks, 1997; FAO,
1997b; Sohngen et al., 1999). These results contrast with those in the SAR (Solomon
et al., 1996), which concluded that global demand for industrial fiber would
exceed global supply in the next century.
There is some debate about which forests are likely to be harvested in the
future. Some authors contend that most supply will come from new industrial
plantations, secondary growth forests, and enhanced management, rather than
from native forests (FAO, 1997b; Sohngen et al., 1999). The proportion of global
timber from subtropical plantations (presently 10%) may increase to 40% by 2050
(Sohngen et al., 1999). Non-native species, such as eucalypts and pines, are
favored in these regions because the costs of management and harvesting are
low compared to those in temperate and boreal forests (Sedjo and Lyon, 1990;
Sedjo, 1999). Recent estimates use global timber market models that incorporate
management responses to prices across a wide range of forests. Under most price
scenarios, subtropical plantations with 5- to 20-year rotations are a financially
attractive alternative (Sedjo, 1999). However, higher demand still may put pressures
on native forests even if plantation establishment and forest management responds
to price increases (Solberg et al., 1996; Brooks, 1997).
Policies that raise prices for substitute products, such as non-wood building
materials made from steel or plastics, may increase timber demand, increase
non-native plantation establishment, and cause additional pressures on native
forests. Substituting non-wood products for wood products could increase carbon
emissions as well (Marland and Schlamadinger, 1995; Schlamadinger et al., 1997).
Increased reliance on plantations may have positive and negative ancillary
consequences. For example, most of the plantations established for industrial
purposes involve nonindigenous species, and the environmental effects of these
plantations are not fully evident. However, most plantations have been established
on former agricultural lands, which begins the process of restoring forests
(Lugo et al., 1993). Furthermore, plantations may reduce harvest pressures on
natural forests. Despite increased reliance on plantations, however, industrial
harvests in native forests along accessible roadways are likely to continue
(Johns et al., 1996).
The relationship between income and fuelwood demand is nonlinear. As incomes
rise and infrastructure grows, households substitute alternative fuel sources
(e.g., natural gas, fuel oil). Brooks et al. (1996), for example, suggest that
fuelwood harvests will increase by 17% by 2050 under a low-GDP-growth scenario,
but only by 4% under a high-growth scenario. Fuelwood harvest depends on the
extent of substitution by alternative methods of heating and cooking. Currently,
use of wood for energy on a large scale does not appear to be cost-effective
relative to other energy sources, but if future energy prices rise, the demand
for wood as a source of energy could rise.