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Although the area of potential distribution of temperate forests in Temperate Asia is, to a large extent, cleared and used for intensive agriculture, global warming can be considered sufficient to trigger structural changes in remaining temperate forests. The nature and magnitude of these changes depend on associated changes in water availability, as well as in water-use efficiency. Shifts in temperature and precipitation in temperate rangelands may result in altered growing seasons and boundary shifts among grasslands, forests, and shrublands (IPCC 1996, WGII, Sections 1.5 and 2.6).
According to simulation results of potential vegetation change by Neilson (see Annex C), temperate mixed forest areas, temperate evergreen forest, and grassland areas would expand in Temperate Asia under 2xCO2 equilibrium scenario conditions. However, there would be practically no change in the leaf area index (LAI) in almost all parts of the region (see Figures C-2 and C-4 of Annex C). Uncertainty remains about the time lag between climate change and migration of forest species at high latitudes.
For boreal forests, which are mainly concentrated in the Russian Federation, climate models (UKMO-H3, GFDL-A2) suggest large shifts in distribution (area reductions of up to 50%) and productivity (Dixon et al., 1996). All components of boreal forest ecosystems would be affected, including water resources, soil systems, and wildlife, and the combined effect could be even stronger as a result of interacting factors.
Grasslands and shrublands in boreal regions may expand significantly, whereas the tundra zone may decrease by up to 50%, according to model projections. Climatic warming also would increase the release of methane from deep peat deposits, particularly from tundra soils, because they would become wetter. It is expected that the release of CO2 would increase, though not by more than 25% of its present level (IPCC 1996, WG II, Section 7.4.2).
The most widely distributed coniferous forests in Siberia are the larch forests: West of the Yenissei River, Larix russica predominates; to the east, Larix gmelini prevails. The latter grows in the north of eastern Siberia, where the annual temperature range reaches about 100�C (-64�C to +38�C), as shown by mean long-term meteorological data from 1937 to the present from Yakutsk weather station. Larix gmelini has a specialized root system: Its apex central root dies off at the permafrost border, and a root system develops in the upper soil layers. The larch is vulnerable to damage by fires and insects, which may occur more frequently under global warming. Increased steppe area also may be expected in the southern part of eastern Siberia (Kobak et al., 1996).
The biomass densities of larch (Larix sibirica), scotch pine (Pinus silvestris), Siberian pine (Pinus sibirica), and birch (Betula platyphylla) are projected to decrease by 27.7, 4.3, 28.5, and 2.6 t/ha, respectively, under a 2xCO2 equilibrium scenario (Ulziisaikhan, 1996). Such decreases seem to be caused by warming air temperature and reduced rainfall during the summer season. Gobi and steppe areas in Mongolia would therefore expand.
The numbers of all known and endemic species of mammals, birds, and flowering
plants in Temperate Asia are shown in Table 10-3. Existing
factors causing the loss of biodiversity include natural factors, such as storms
and floods; population pressure; soil erosion and desertification; deforestation
and timber cutting; and overcollection of wild plant resources (Davis et al.,
1995; Heywood, 1995). Although global warming will play an important role in
future changes in biodiversity, human influences also may have the potential
to affect the climate system (Mooney et al., 1995). Such influences have taken
the form of rapid, large, and frequent changes in land and resource use; increased
frequency of biotic invasions; reductions in species numbers; creation of novel
stresses; and the potential for change in the climate system.
Climate change may affect the biodiversity in boreal forests of Temperate Asia
through a myriad of processes and effects: local mortality of boreal species
and replacement by northern hardwoods or prairies, depending on locale and soil
type; migration of boreal species northward and coastward, also depending on
locale and soil type; increased probability of fire; increased or decreased
soil nutrient availability, depending on permafrost, soil water-holding capability,
and locale; increased emissions of greenhouse gases-particularly methane-from
wetlands; and increased probability of outbreaks of pests, particularly insects,
to drought-stressed trees (Pastor et al., 1996).
Changes in local vegetation zones as a result of global warming could be important in marginal areas of the region. For example, in the Kamtchatka Peninsula, five ecological zones may be classified (Kojima, 1992): the Larix Kamtchatka zone, the Picea ajanensis zone, the Betula ermanii zone, the Pinus pumila zone, and the alpine tundra zone. These zones coincide with the division by continentality (or oceanity) defined by types of seasonal change, annual range, and other characteristics of air temperature. The first three zones are boreal forest, under three different climate types: subhumid continental, humid continental, and superhumid maritime, respectively. The fourth zone is subalpine, corresponding to a humid maritime climate zone. Under global warming, the most vulnerable region would be the Larix Kamtchatka zone because of the increasing aridity of soils or increasing frequency of forest fires. Major alterations in vegetation could be expected, especially in the mountains of the northern boreal subzone and the subarctic forest-tundra ecotone in northeast Siberia. In the middle and southern boreal subzones, vegetation changes may be more limited because of more-resistant species interaction in the forest communities of the continental area and the isolated islands of the Kuril, Shantar, and Kommander groups (Grishin, 1995).
Plant phenology is an important indicator of vegetation change. It also is quite useful and necessary for farmers of intensively cultivated small-hold rice fields in this region because their cultivation calendar depends on the year-to-year change of seasons, which is reflected in local plant phenology. For example, the flowering of cherry blossoms in spring begins about 3-4 days earlier per 1�C increase in the mean temperature in March (Yoshino and Ono, 1996). Leaf-color-change dates of Ginko biloba and Acer palmatum in autumn are delayed for 2-7 days per 1�C increase in monthly mean temperature (Kai et al., 1996).
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