18.104.22.168. Forests, Grasslands, and Rangelands
Most of the frontier forests in Asia are endangered today by rapid population
growth, ever-increasing demand for agricultural land, poverty, poor institutional
capacity, and lack of effective community participation in forestry activities
(Mackenzie et al., 1998). Climate change is expected to affect the boundaries
of forest types and areas, primary productivity, species populations and migration,
the occurrence of pests and diseases, and forest regeneration. The increase
in GHGs also affects species composition and the structure of ecosystems because
the environment limits the types of organisms that can thrive and the amount
of plant tissues that can be sustained (Melillo et al., 1996). Compositional
and structural changes, in turn, affect ecosystem function (Schulze, 1994).
The interaction between elevated CO2 and climate change plays an
important role in the overall response of net primary productivity to climate
change at elevated CO2 (Xiao et al., 1998).
Climate change will have a profound effect on the future distribution, productivity,
and health of forests throughout Asia (see also Section 5.6).
Because warming is expected to be particularly large at high latitudes, climate
change could have substantial impact on boreal forests (Dixon et al., 1996;
IPCC, 1996; Krankina, 1997). Global warming will decrease permafrost areas,
improve growing conditions, and decrease areas of disturbed stands and ecosystems
in a general sense, although impacts would be significantly different at various
locations within the boreal forests. Moreover, forest fire is expected to occur
more frequently in boreal Asia as a result of increased mean temperature (Valendik,
1996; Lelyakin et al., 1997). Pest activity also could increase with a rise
in temperature, depending on the age composition of the boreal forests (Alfiorov
et al., 1998).
Asia's temperate forests are a globally important resource because of
their high degree of endemism, biological diversity, ecological stability, and
production potential. About 150 Mha of forests in central China have been cleared
during the past several decades. Efforts are now underway to at least partially
restore the area under forest cover in China through reforestation, soil recovery,
and water conservation programs (Zhang et al., 1997). Studies on projected impacts
of climate change suggest that northeast China may be deprived of the conifer
forests and its habitat, and broad-leaved forests in east China may shift northward
by approximately 3° of latitude. These results are based on a 2°C increase
in annual mean temperature and a 20% increase in annual precipitation (Omasa
et al., 1996; Tsunekawa et al., 1996).
Tropical moist forests have trees with higher densities of wood and larger
proportions of branch wood relative to those in temperate forests. As many as
16 countries of tropical Asia are located within the humid tropical forest region.
These forests and woodlands are important resources that must be safeguarded,
given the heavy use of wood as fuel in some countries. Past policies in the
humid tropics have focused mainly on natural forest protection and conservation
(Skole et al., 1998). However, there is a need to shift emphasis from conservation
alone to a strategy that involves sustained development, investment performance,
and public accountability (see Section 5.6). Encouragingly,
the current annual rate of reforestation is highest in tropical Asia as a result
of relatively high investments in reforestation schemes, including social forestry.
Most semi-arid lands in Asia are classified as rangelands, with a cover of
grassland or scrublands. Although the share of land area used for agricultural
purposes is about 82% of the total area, it is mainly low-productive pastures.
With an increase in temperature of 2-3°C combined with reduced precipitation
as projected for the future in the semi-arid and arid regions of Asia, grassland
productivity is expected to decrease by as much as 40-90% (Smith et al.,
1996). Approximately 70% of pastures are facing degradation, with dramatic decreases
in fodder yield over recent decades in some parts of Mongolia (Khuldorj et al.,
1998). Rangelands in Nepal also have been subject to degradation in recent years
(NBAP, 2000). Climate change is likely to represent an additional stress to
rapid social change in many of Asia's rangelands.