Page 697 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 20 Terrestrial Biomes 661
about 1850 to 1900 due to competition with livestock for food and water, as well as exposure to parasites and disease. In an effort to reestablish bighorn popula- tions, several states are transplanting the animals to their former ranges.
Other representative desert animals are the ring- tailed cat, kangaroo rat, lizards, scorpions, and snakes. Most of these animals become active only at night, when temperatures are lower. In addition, various birds have adapted to desert conditions and available food sources— for example, roadrunners, thrashers, ravens, wrens, hawks, grouse, and nighthawks.
Arctic and Alpine Tundra
The arctic tundra biome is located in the extreme northern area of North America and Russia, bordering the Arctic Ocean and generally north of the 10°C iso- therm for the warmest month. Daylength varies greatly throughout the year, seasonally changing from almost continuous day to continuous night. The region, except for a few portions of Alaska and Siberia, was covered by ice during all of the Pleistocene glaciations. With re- cent climate change, these regions have been warming at more than twice the rate of the rest of the planet over the past few decades.
This biome corresponds to the tundra climates; winters are cold and long; summers are cool and brief. A growing season of sorts lasts only 60–80 days, and even then frosts can occur at any time. Soils are poorly developed periglacial surfaces that are underlain by per- mafrost. In the summer months, the surface horizons thaw, thus producing a mucky surface of poor drainage (Figure 20.20a). Roots can penetrate only to the depth of thawed ground, usually about a metre.
(a) Tundra mosses with a glacially eroded roche moutonnée in the background (shape denotes glacial movement from left to right).
Arctic tundra vegetation consists of low, ground- hugging herbaceous plants such as sedges, mosses, arc- tic meadow grass, and snow lichen and some woody species such as dwarf willow (Figure 20.20b). Owing to the short growing season, some perennials form flower buds one summer and open them for pollination the next. Animals of the tundra biome include musk ox, caribou, reindeer, rabbit, ptarmigan, lemming, and other small rodents, which are important food for the larger carnivores—the wolf, fox, weasel, Snowy Owl, polar bear, and, of course, mosquito. The tundra is an important breeding ground for geese, swans, and other waterfowl.
Alpine tundra is similar to arctic tundra, but it can occur at lower latitudes because it is associated with high elevations. This biome usually occurs above the treeline (the elevation above which trees cannot grow), which shifts to higher elevations closer to the equator. Alpine tundra communities occur in the Andes near the equa- tor, the White Mountains and Sierra of California, the American and Canadian Rockies, the Alps, and Mount Kilimanjaro of equatorial Africa as well as in mountains from the Middle East to Asia.
Alpine tundra features grasses, herbaceous annu- als (small plants), and low-growing shrubs, such as willows and heaths. Because alpine locations are fre- quently windy sites, many plants there have forms that are shaped by the wind. Alpine tundra can experience permafrost conditions. Characteristic fauna include mountain goats, Rocky Mountain bighorn sheep, elk, and voles (Figure 20.21).
Vegetation of the tundra biome is slow-growing, has low productivity, and is easily disturbed. Hydro- electric projects, mineral exploitation, and even tire tracks leave marks on the landscape that persist for
▲Figure 20.20 Arctic tundra. [Bobbé Christopherson.]
(b) Grasses, mosses, and dwarf willow flourish in the cold high-latitude climates.