This video segment from ZOOM compares and contrasts some of the more interesting climatic and ecological characteristics of the Death Valley desert with those ...
Auditory, Textual, Visual
©2002 WGBH Educational Foundation. All rights reserved. ZOOM and the ZOOM words and related indicia are trademarks of the WGBH Educational Foundation. Used with permission.
The Earth supports an astounding diversity of plant and animal life. Move from one continent to another, change latitude by 10 or 20 degrees in either direction, or ascend or descend a mere 2,000 feet in elevation, and you're likely to find groups of plants and animals that are dramatically different from the ones you left behind. In comparing the ecological communities in different geographical regions, scientists have found that various life forms are not scattered randomly around the earth, but are instead arranged in obvious patterns. Not surprisingly, these patterns closely mirror precipitation and temperature patterns. For example, hot, dry areas are characterized by certain types of plants and animals, while locations that are cool and wet host an entirely different set of organisms.
Scientists often refer to large geographical areas that have their own distinct set of plants, animals, and climatic conditions as biomes. There are four major terrestrial, or land, biomes: forest, grassland, tundra, and desert. And ecologists usually divide these further into what they call biome subtypes. There are, for example, several subtypes of the forest biome. Some, like tropical rainforests, grow very near the equator; others, like the taiga (boreal) forests of Canada and Eurasia, are found just below the Arctic Circle.
While no two biomes or biome subtypes are identical, few are as different from one another as the desert of Death Valley and the temperate rainforest of the Pacific Northwest. Separated by only 1,000 miles, or about 10 degrees in latitude, these two locations are a world apart. In the Pacific Northwest rainforest, rainfall is measured in feet (about 12 feet each year), while in Death Valley, one of the driest places on earth, it rains less than two inches each year. Temperatures also differ wildly in these two locations. In the summer, Death Valley may reach 130 degrees Fahrenheit -- as much as 60 degrees warmer than the average daytime high in the temperate rainforest.
As in other biomes, plant types reflect the climatic conditions. Desert plants have evolved a wide variety of structural characteristics that limit the amount of water they lose to the atmosphere -- from dense clusters of spines on some cactuses that create shade for the plant underneath, to waxy coatings on the surfaces of leaves. Temperate rainforest plants receive plenty of water and thus don't require physical traits that help them limit water loss. Sunlight, however, is less plentiful, especially on the forest floor. Consequently, plants that grow in temperate rainforests have the ability to carry out photosynthesis at very low light levels. They also have the ability to grow quite rapidly when the opportunity presents itself, such as when a nearby tree falls and creates a break in the canopy.