rainforest (redirected from Lower canopy)

rainforest

Lush forest, generally composed of tall, broad-leaved trees and usually found in wet tropical regions around the Equator. Despite increased awareness of the rainforests' importance during the late 20th century, they continue to be cleared. Rainforests grow mainly in South and Central America, West and Central Africa, Indonesia, parts of Southeast Asia, and tropical Australia, where the climate is relatively humid with no marked seasonal variation. Depending on the amount of annual rainfall, the trees may be evergreen or mainly deciduous. The former require more water. Temperatures are high, usually about 86 °F (30 °C) during the day and 68 °F (20 °C) at night. Soil conditions vary with location and climate, though most rainforest soils tend to be permanently moist and not very fertile, because the hot, humid weather causes organic matter to decompose rapidly and to be absorbed quickly by tree roots and fungi. Rainforests have several layers. The highest continuous layer, called the canopy, extends across the treetops at a height of 100–165 ft (30–50 m). Most animals live among the leaves and branches. Below the canopy is a thick understory filled with small trees, lianas, and epiphytes. The space directly above the ground can be occupied by tree branches, twigs, and foliage, but, contrary to popular belief, the rainforest floor is not impassable. Rather, it is bare except for a thin layer of humus and fallen leaves. Animals inhabiting this layer (e.g., gorillas, elephants, jaguars, and bears) are adapted to walking or climbing for only short distances. Burrowing animals, such as armadillos and caecilians, are found in the soil, as are microorganisms that help decompose and recycle the organic litter accumulated by other plants and animals from all layers. The climate of the ground layer is unusually stable because the upper stories of tree canopies and the lower branches filter out sunlight, retain heat, and reduce wind speeds, keeping the temperature fairly even.

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rainforest

dense forest found in tropical areas of heavy rainfall. The trees are broad-leaved and evergreen, and the vegetation tends to grow in three layers (undergrowth, intermediate trees and shrubs, and very tall trees, which form a canopy)

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rainforest [′rān‚fär·əst]

(ecology)

A forest of broad-leaved, mainly evergreen, trees found in continually moist climates in the tropics, subtropics, and some parts of the temperate zones.

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Rainforest

Forests that occur in continually wet climates with no dry season. There are relatively small areas of temperate rainforests in the Americas and Austral­asia, but most occur in the tropics and subtropics.

The most extensive tropical rainforests are in the Americas. These were originally 1.54 × 10⁶ mi² (4 × 10⁶ km²) in extent, about half the global total, and mainly in the Amazon basin. A narrow belt also occurs along the Atlantic coast of Brazil, and a third block lies on the Pacific coast of South America, extending from northern Peru to southern Mexico.

Tropical rainforests have a continuous canopy (commonly 100–120 ft or 30–36 m tall) above which stand huge emergent trees, reaching 200 ft (60 m) or taller. Within the rainforest canopy are trees of many different sizes, including pygmies, that reach only a few feet. Trees are the main life form and are often, for purposes of description and analysis, divided into strata or layers. Trees form the framework of the forest and support an abundance of climbers, orchids, and other epiphytes, adapted to the microclimatic conditions of the different zones of the canopy, from shade lovers in the gloomy, humid lower levels, to sun lovers in the brightly lit, hotter, and drier upper levels. Most trees have evergreen leaves, many of which are pinnate or palmate. These features of forest structure and appearance are found throughout the world's lowland tropical rainforests. There are other equally distinctive kinds of rainforest in the lower and upper parts of perhumid tropical mountains, and additional types on wetlands.

Rainforests occur where the monthly rainfall exceeds 4 in. (100 mm) for 9–12 months. They merge into other seasonal or monsoon forests where there is a stronger dry season (3 months or more with 2.5 in. or 60 mm of rainfall). The annual mean temperature in the lowlands is approximately 64^°F (18^°C). There is no season unfavorable for growth.

Primary rainforests are exceedingly rich in species of both plants and animals. There are usually over 100 species of trees 2.5 in. (10 cm) in diameter or bigger per 2.4 acres (1 ha). There are also numerous species of climbers and epiphytes. Flowering and fruiting occur year-round, but commonly there is a peak season; animal breeding may be linked to this. Secondary rainforests are much simpler. There are fewer tree species, less variety from location to location, and fewer epiphytes and climbers; the animals are also somewhat different. See Ecological succession

Tropical rainforests are a source of resins, dyes, drugs, latex, wild meat, honey, rattan canes, and innumerable other products essential to rural life and trade. Modern technology for extraction and for processing has given timber of numerous species monetary value, and timber has come to eclipse other forest products in importance. The industrial nations use much tropical hardwood for furniture, construction, and plywood. Rainforest timbers, however, represent only 11% of world annual industrial wood usage, a proportion that has doubled since 1950. West Africa was the first main modern source, but by the 1960s was eclipsed by Asia, where Indonesia and Malaysia are the main producers of internationally traded tropical hardwoods. Substantial logging has also developed in the neotropics. See Forest ecosystem