The tundra biome is characterized by climatic extremes and complex interrelationships between organisms and their environment. The world of any one species is an intricate web of land and ice conditions, seasonal changes, and interdependencies on other plants and animals. Changes that affect even a small part of this structure can have far-reaching effects on the ecosystem as a whole.
Ice shapes the landscape of the tundra biome and, somewhat paradoxically, allows for far more plant life to grow in this environment than would otherwise be possible. Precipitation levels in the Arctic (six to ten inches annually) are equivalent to those found in the world's deserts. Thus, water, even in summer, is at a premium. However, because of a permanently frozen underground layer called permafrost, water that falls to the ground as precipitation collects on the surface, rather than moving quickly through the soil and out of reach. This allows a wealth of plants to exist even in the driest parts of the Arctic.
There are about seventeen hundred species of plants in the Arctic, including grasses, mosses, herbaceous plants, and shrubs. All of these have shallow root systems, tend to grow low to the ground, and generally reproduce by budding rather than with flowers and seeds. This last characteristic causes many tundra biome plants to grow in clumps and, in some cases, to become reproductively isolated from related clumps growing nearby.
Indeed, scientists have found significant genetic variation between members of the same species of plant growing within a mile of one another. It is thought that these variations -- which probably correspond to differences in microclimate -- provide a long-term survival benefit, equipping the species as a whole with adaptations that allow at least some individuals to withstand dramatic climate shifts.