Forest growth and species distribution in a changing climate.

Climate change has many potential effects on plants, some detrimental to growth, others beneficial. Increasing CO(2) concentration can increase photosynthetic rates, with the greatest increases likely to be in C(3) plants growing in warm dry conditions. Increasing temperature directly affects plant growth through effects on photosynthetic and respiration rates. However, plants have a considerable ability to adapt to changing conditions and can tolerate extremely high temperatures, provided that adequate water is available. Increasing temperature may increase vapor pressure deficits of the air, and thereby increase transpiration rates from most plant canopies. Effects are likely to vary among plant communities, with forests generally experiencing greater increases in transpiration rates than grasslands. These increases in transpiration are likely to be reduced by stomatal closure in response to increasing CO(2) concentration. In many areas, precipitation will probably increase with global warming; however, these increases may be insufficient to meet the increased transpirational demand by plant canopies. Increasing temperature is likely to increase soil organic matter decomposition rates so that nutrients may be more readily mineralized and made available to plants. In highly fertile systems, this could lead to nutrient losses through leaching. For different combinations of increases in temperature and CO(2) concentration, and for systems primarily affected by water or nutrient limitations, different overall effects on plant productivity can be expected. Responses will be negative in some circumstances and positive in others, but on the whole, catastrophic changes to forest growth seem unlikely under most conditions. In contrast,ecological consequences of climate change are potentially more serious. The distribution of many species tends to be limited to a narrow range of environmental conditions. Climate conditions over much of a species' current natural range may therefore become unsuitable, leading to significant decline of forests or of particular species within forests.