The Regional Impacts of Climate Change

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3.3.3. Terrestrial Ecological Systems

Climate change will affect terrestrial ecological systems through changes in permafrost as well as direct climatic changes, including changes in precipitation, snow cover, and temperature. Terrestrial ecoystems are likely to change from tundra to boreal forests, although vegetative changes are likely to lag climatic change. Vegetational ecosystem models suggest that the tundra will decrease by as much as one- to two-thirds of its present size (see Annex C). Climate change is expected to occur at a rapid rate relative to the speed at which forest species grow, reproduce, and reestablish themselves or to their ability to develop appropriate soils. The boreal forest covers approximately 17% of the world's land surface in a circumpolar complex of forested and partially forested ecosystems in northern Eurasia and North America (IPCC 1996, WG II, Section 1.6.1). If there is warming, the greatest forest changes are expected in high latitudes. Polar projections of this region's terrestrial ecological changes (Figure 3-3) derived from two different models' depictions of the future climate reinforce this conclusion, showing significant reduction in the tundra and taiga biomes and expansion of the boreal forest.

Figure 3-3: Ecological shifts derived from the MAPSS model in response to changes projected by two GCM simulations of future climate.

A poleward migration of the northern tree line would decrease winter albedo because the tree canopy has much lower albedo than exposed snow surfaces, affecting local climate through increased absorption of the sun's incoming energy (IPCC 1996, WG II, Chapter 6). Large losses are projected in the area of boreal forests despite their encroachment into current tundra. Shrinkage in total area because of the geographically limited poleward shift leads to a net loss of about 25% in boreal coverage (IPCC 1996, WG II, Section 1.3.4). On the other hand, vegetative ecosystem modeling suggests an expansion in the boreal forest ranging from 108% to 133% of the present size (see Annex C). The species composition of forests is likely to change; entire forest types may disappear, while new assemblages of species, and hence new ecosystems, may be established (IPCC 1996, WG II, Section 3.1). The rate of migration is critical, and it is likely that the loss from the southern margin will be greater than the gain in the northern margin. Projections for habitat changes are presented in Table 3-1.

By 1995, the Arctic contained 285 protected areas covering 2.1 million km² (UNEP, 1997). There will be considerable impacts of climate change on resource management in the tundra (IPCC 1996, WG II, Section 7.5). There is likely to be a change in the migration patterns of polar bears and numbers of caribou, along with other biological impacts (IPCC 1996, WG II, Section 7.5). High-arctic Peary caribou and musk-oxen may become extinct, and barren-ground caribou and musk-oxen elsewhere may be reduced (Gunn, 1995). Arctic island caribou migrate seasonally across the sea ice between many of the arctic islands in late spring and fall; changes in sea ice would disrupt those migrations, with unforeseen consequences to population survival and gene flow.

It is also anticipated that small mammals, from lemmings to aquatic furbearers (muskrats, beavers, mink), will face ecosystem alterations that will change their abundance and distribution. Amphibians and reptiles can be expected to increase their range, and the distribution and abundance of hundreds of arthropod species will alter. Changes in the timing and abundance of forage availability and parasite infestations may accumulate-driving populations into decline, with serious consequences for people still depending on them (Jefferies, 1992). Increased incidences of forest fires and insect outbreaks are likely, such as already observed in Alaska.

Indirect temperature effects associated with changes in tundra thaw depth, nutrient availability, and vegetation will cause substantial changes in Arctic species composition, litter quality, and nutrient availability. Increased nutrient availability increases shrub abundance and decreases the abundance of mosses, an important soil insulator (IPCC 1996, WG II, Section 2.7.3).

Some alpine and tundra plants have no photoperiod requirements for initiating growth and therefore are affected by spring frosts. For example, in northern Sweden, increased length of the growing season and increased summer temperature will have a significant impact on reproduction and population dynamics in Arctic and alpine plants (IPCC 1996, WG II, Section 5.2.3.1). Experimental doubling of CO₂ concentration has relatively little multiyear effect on plant growth in Arctic tundra, presumably because of constraints of low nutrient supply (IPCC 1996, WG II, Section 2.2.2).

Major shifts in biomes will be associated with changes in microbiological (bacteria, algae, etc.) and insect communities. As a consequence, some may diminish while others prosper. All microbiologically facilitated processes are strongly affected by moisture and temperature. Annual soil respiration rates are likely to increase because of the lengthened season for breakdown of plant material and because increasing temperature strongly stimulates organic-matter decomposition, especially in Arctic regions subject to permafrost (IPCC 1996, WG II, Section A.3.1).

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