Tropical Forest
Tropical Forest
The worldwide equatorial belt of tropical
forests is an area of high rainfall
(more than 200 cm [80 inches] per year),
high humidity, relatively high and constant
temperatures averaging more than
17° C (63° F), and little seasonal variation
in day length. These conditions
have nurtured luxurious, uninterrupted
growth that reaches its greatest intensity
in rain forests. In sharp contrast to temperate
deciduous forests, dominated as
they are by relatively few tree species,
tropical forests contain thousands of
species, none of which is dominant. A
single hectare typically contains 50 to 70
tree species as compared with 10 to 20
tree species in an equivalent area of
hardwood forest in the eastern United
States. Climbing plants and epiphytes
are common among the trunks and
limbs. A distinctive feature of tropical
forests is stratification of life into six, and
occasionally as many as eight, feeding
strata (Figure 39-8).
Insectivorous birds and bats occupy the air above the canopy; below it birds, fruit bats, and mammals feed on leaves and fruit. In the middle zones are arboreal mammals (such as monkeys and tree sloths), numerous birds, insectivorous bats, insects, and amphibians. A middle zone of climbing animals, such as squirrels and civets, range up and down the trunks, feeding from all strata. On the ground are large mammals lacking climbing ability, such as the large rodents of South America (for example, capybara, paca, and agouti) and members of the pig family. Finally, a mixed group of small insectivorous, carnivorous, and herbivorous animals searches the litter and lower tree trunks for food. No other biome can match tropical forests in incredible variety of animal species. Food webs are intricate and notoriously difficult for ecologists to unravel.
Tropical forests, especially the enormous expanse centered in the Amazon Basin, are the most seriously threatened of forest ecosystems. Large areas are being cleared for agriculture by “slash-and-burn” methods, but, because of low soil fertility, farms are soon abandoned. It may seem paradoxical that a biome as luxuriant as a tropical forest should have poor soil. This occurs because nutrients released by decomposition are rapidly recycled by plants, leaving no reservoir of humus. In many areas, once the plants are removed, the soil rapidly becomes a hard, bricklike crust called laterite. Tropical plants cannot recolonize such areas.
 |
| Figure 39-8 Profile of tropical forest, showing stratification of animal and plant life into six strata. The animal biomass is small compared with the biomass of the trees. |
Insectivorous birds and bats occupy the air above the canopy; below it birds, fruit bats, and mammals feed on leaves and fruit. In the middle zones are arboreal mammals (such as monkeys and tree sloths), numerous birds, insectivorous bats, insects, and amphibians. A middle zone of climbing animals, such as squirrels and civets, range up and down the trunks, feeding from all strata. On the ground are large mammals lacking climbing ability, such as the large rodents of South America (for example, capybara, paca, and agouti) and members of the pig family. Finally, a mixed group of small insectivorous, carnivorous, and herbivorous animals searches the litter and lower tree trunks for food. No other biome can match tropical forests in incredible variety of animal species. Food webs are intricate and notoriously difficult for ecologists to unravel.
Tropical forests, especially the enormous expanse centered in the Amazon Basin, are the most seriously threatened of forest ecosystems. Large areas are being cleared for agriculture by “slash-and-burn” methods, but, because of low soil fertility, farms are soon abandoned. It may seem paradoxical that a biome as luxuriant as a tropical forest should have poor soil. This occurs because nutrients released by decomposition are rapidly recycled by plants, leaving no reservoir of humus. In many areas, once the plants are removed, the soil rapidly becomes a hard, bricklike crust called laterite. Tropical plants cannot recolonize such areas.
Support our developers
