Rising temperatures and shifting precipitation patterns are changing the geographic areas where mammals, birds, insects, and plants that live on land can survive—and are affecting the timing of lifecycle events, such as bud bursts, leaf drop from trees, pollination, reproduction, and bird migration.
Forced migrations and extinctions. Plants and animals are migrating to higher altitudes and latitudes. Land-based species that already live in extreme habitats—such as plants and animals found only in alpine regions—may become extinct because they literally have no place to go, while other shrubs and boreal trees encroach on the warming tundra. Plant-hardiness zones are shifting as formerly low-latitude plants survive at higher latitudes.
• Increase in agricultural pests. Agricultural pests formerly constrained to low-latitude locales are moving to higher latitudes as those regions warm. And some pests are reproducing more often as warm seasons last longer. In the now beetle-infested forests of the Kenai Peninsula of Alaska, for example, the pine bark beetle often completes two or three reproduction cycles per year instead of only one.
• Desynchronization of life-cycle events. Many formerly synchronized life-cycle events are now out of whack. For example, bird migrations timed to seasonal changes or temperatures may begin earlier. And these birds may find that the insects and other creatures on which they feed along migration routes are not available. Meanwhile warmer temperatures in late winter may force flowers to bud early, leaving them vulnerable to late-season frost.
• Changing woodlands. Many tree species are adapted to particular temperature and moisture conditions. As these conditions change, habitats become unsuitable for saplings to grow, and species attempt to migrate. Because trees are so long-lived, the effects may not be noticeable for many years. However, species that now grow only in certain areas—such as the sugar maple, now found in parts of the United States and Canada—may be quite rare in their southern range by the end of this century.
• Increase in allergens and noxious plants. Rising concentrations of CO2 in the atmosphere act as fertilizer to many plants. These changes may stimulate growth in certain crops, trees, and weeds—at least under moderate temperature increases as the climate warms. Some potent allergens and noxious plants, such as poison ivy—to which roughly 80 percent of people are allergic—seem to especially thrive in warm and CO2-rich conditions.
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