Page 684 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

648 part IV Soils, Ecosystems, and Biomes
Rain forests feature ecological niches that are distributed vertically rather than horizontally because of the competition for light. The canopy is filled with a rich vari- ety of plants and animals. Lianas (woody vines that are rooted in the soil) stretch from tree to tree, entwining them with cords that can reach 20 cm in diameter. Epiphytes flourish there, too; these plants, such as orchids, bromeliads, and ferns, live entirely aboveground, supported physi- cally, but not nutritionally, by the struc- tures of other plants. On the forest floor, the smooth, slender trunks of rainforest trees are covered with thin bark and but- tressed by large, wall-like flanks that grow out from the trees to brace the trunks. These buttresses form angular hollows that are ready habitat for various animals. Branches are usually absent on at least the lower two-thirds of the tree trunks.
The animal and insect life of the rain forest is diverse, ranging from animals liv- ing exclusively in the upper stories of the trees to decomposers (bacteria) working the ground surface. Arboreal (from the Latin word meaning “tree”) species, those dwell- ing in the trees, include sloths, monkeys, lemurs, parrots, and snakes. Throughout the canopy are multicoloured birds, tree frogs, lizards, bats, and a rich insect com- munity that includes more than 500 species of butterflies. On the forest floor, animals include pigs (the bushpig and giant forest hog in Africa, wild boar and bearded pig in Asia, and peccary in South America), small antelope, and mammalian predators (the tiger in Asia, jaguar in South America, and leopard in Africa and Asia).
0°
10°
20°
30°
40°
80°
ARCTIC OCEAN
70° 70°
60°
50°
40°
30°
Tropic of Cancer
Tropical seasonal forest and scrub Tropical savanna
Midlatitude broadleaf and mixed forest Boreal and montane forest
Temperate rain forest Mediterranean shrubland
20° 20°
Tall grass
Short grass
Midla3t0it°ude grasslands 30°
Warm desert and semidesert
Cold desert and semidesert
Arctic tundra
Alpine tundra
40°
10° 10°
Deserts Arctic and alpine tundra
50° 50°
Polar desert
50°
Tropic of
Capricorn
ATLANTIC
60°
OCEAN
50°
40°
30°
20°
10°
PACIFIC
OCEAN
160°
20°
10°
Tropical rain forest
140° 130° 120° 110° 100°
Equator
20°
30°
40°
Deforestation of the Tropics More than
half of Earth’s old-growth tropical rain for-
est is gone, cleared for pasture, timber, fuel
wood, and farming. Tropical deforestation
is threatening native rainforest species, and in the bigger picture of global systems and societies, is jeopardizing an important recycling system for atmospheric carbon dioxide, as well as potential sources of valuable pharma- ceuticals and new foods—so much is still unknown and undiscovered.
rain forests is for pulpwood production, which consumes all species.
Fires are used to clear forested lands for agriculture, which is intended to feed the domestic population as well as to produce accelerating cash exports of beef, soy- beans, rubber, coffee, palm oil, and other commodities. When orbiting astronauts look down on the rain forests at night, they see thousands of human-set fires. During the day, the lower atmosphere in these regions is choked with the smoke. Forest clearing and burning release mil- lions of tonnes of carbon into the atmosphere each year.
Because of the poor soil fertility, intensive farm- ing quickly exhausts the productivity of cleared lands, which are then generally abandoned in favour of newly burned lands (unless fertility is maintained artificially by chemical fertilizers). The dominant trees require from
Worldwide, an area greater in size than the three Mari- time provinces, is cleared each year (169000 km2), and about a third more is disrupted by selective cutting of can- opy trees that occurs along the edges of deforested areas. The economically valuable varieties of trees include ma- hogany, ebony, and rosewood. Selective cutting required for species-specific logging is difficult because individual species are widely scattered; a species may occur only once or twice per square kilometre. As a result, most logging in
▲Figure 20.7 (a) The 10 major global terrestrial biomes. (b) Inset map contains more detail for Canada. Biomes are described in Table 20.1. [(b) Adapted with permission of Natural resources Canada, 2012, Courtesy of the National Atlas of Canada.]
(a)