Of particular concern to botanists, as well as others, are the global warming effects that are producing a shift in climate zones. For example, the warming of the Arctic regions is a threat to polar bears that need sea ice as a platform for their hunting, but it is also a threat to plants that are adapted to colder temperatures and are disappearing because of global warming. As global temperatures rise, plants in the latitudes away from the equator are affected. Many will spread northward or southward as temperatures rise; however, many species do not migrate well. This is especially true of plants (and animals that feed on them) that are located in mountainous areas. Adapted to cold temperatures in high elevation, global warming pushes them ever higher up the mountain sides until, for some, there is literally no place to go.
The changing temperatures are also affecting the hardiness zones used by farmers and gardeners to decide which plants to grow. However, global warming is not bringing a simple northward or southward movement away from the equator. The shifting flows of energy in the planetary weather patterns are making some places drier, some colder, others warmer, and others wetter.
Some botanists have hypothesized that if global warming continues, areas that have been agricultural zones for growing wheat, corn, or other crops may be lost and not easily replaced by other sufficiently warm, but less fertile, regions.
Many scientists are concerned that climate zones as they are currently known will vanish entirely by 2100. Using greenhouse gas emissions scenarios that range from low to high, it is possible that enough climate change will occur to cause major ecological transformations. Entire plant species will disappear, pine forests would become grasslands, and rainforests would become savanna. In places like Wyoming, grasslands would disappear. Higher temperatures would cause places such as Wyoming's grasslands to be much drier in the summer and to be much more threatened by fires. Researchers estimate that existing climates will disappear from almost half of the planet. New climates will develop in about 40 percent of the of the Earth's land mass. The places hardest hit will be the tropics, which have the most biodiversity.
Duke University has conducted a study of the central plains of the United States in the areas where the plains have changed from grasslands and forest because of climate change in the geologic past. After the last ice age, periods of warming and cooling caused the grasslands and the forest areas to radically change. The grasslands would expand eastward into the eastern forests. Tree mortality would be affected by seed-eating predators and the ways in which seed dispersal affects biodiversity.
Botanical evidence of global warming is accumulating at a rapid rate. Botanists in Boston have found that plants are blooming over a week earlier than they did a century ago. The plants studied are in arboretums where long-lived plants or descendants of the same species of plants provide a standard of comparison. The flowers of living plants can be compared with museum specimens that were gathered at specific dates. These plants and dates have been compared to determine that plant life is showing evidence of global warming.
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