Future Climate Change Will Affect Land Based Ecosystems in a Variety of Ways

Both the amount and rate of warming will influence the ability of plants and animals to adapt. In addition, temperature changes will interact with changes in CO2, precipitation, pests, soil characteristics, and other factors. Tree species, for example, are expected to shift their ranges northward or upslope, with some current forest types such as oak-hickory expanding, others such as maple-beech contracting, and still others such as spruce-fir disappearing from the United States altogether (Figure 2.7). Experimental and modeling studies indicate that exposure to elevated CO2 and temperatures can lead to increases in photosynthesis and growth rates in many plant species, although at higher temperatures this trend may reverse. Projections suggest that forest productivity will increase with elevated CO2 and climate warming, especially in young forests on fertile soils where water is adequate. Where water is scarce and drought is expected to increase, or where pests increase in response to warming, however, forest productivity is projected to decrease.

Some analyses have indicated the possibility of major changes in ecosystems due to the combined effects of changes in temperature and precipitation, potentially affect-

1960-1990

Hadley scenario 2070-2100

Canadian scenario 2070-2100

1960-1990

Hadley scenario 2070-2100

Canadian scenario 2070-2100

FIGURE 2.7 Potential changes in the geographic ranges of the dominant forest types in the eastern United States under projections of future climate change. Many forest types shift their ranges northward or shrink in areas, while some expand their areas. For further details see Figure 9.2. SOURCE: USGCRP (2001).

U White-Red-Jack Pine

0 Spruce-Fir

1 Longleaf-Slaeh Pine I Loblolly-Shortleaf Pine y Oak-Pine

Oak-Hickory Oak-Gum-Cypress y ElnvAsh-Cottorivrood B Maple-Beech-Birch j Aspen-Birch D No Data

FIGURE 2.7 Potential changes in the geographic ranges of the dominant forest types in the eastern United States under projections of future climate change. Many forest types shift their ranges northward or shrink in areas, while some expand their areas. For further details see Figure 9.2. SOURCE: USGCRP (2001).

Co ing ecosystem productivity, carbon cycling, and the composition of plant communities. For example, drier conditions in the Amazon could potentially lead to increased susceptibility to fire, lower productivity, and shifts from forest to savanna systems in that region. The strong warming observed across the Arctic is already leading to poleward shifts of boreal forests into regions formerly covered in tundra, and these shifts are expected to continue.

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