tropical zone

Australian plant life is distributed in three main zones—the Tropical, Temperate, and Eremian—a pattern that reflects overall climatic conditions. The Tropical Zone, which arcs east and west across the northern margin of the continent and extends halfway down the eastern seaboard, has a mainly dry monsoonal climate, with some wet regions. The Temperate Zone, with a cool-to-warm...

The climate of the Caribbean generally is tropical, but there are great local variations, depending on mountain elevation, water currents, and the trade winds. Rainfall varies from about 10 inches (25 cm) per year on the island of Bonaire off the coast of Venezuela to some 350 inches (900 cm) annually in parts of Dominica. The northeast trade winds dominate the region with an average velocity...

Tropical regions are dominated by dense vegetative cover and deep weathering profiles. In continuously humid tropical zones, fluvial activity is facilitated by intense rainfall but inhibited by the protective effect of rainforests. The lateritic soils of these regions, however, do not promote deep root penetration, and the vegetative cover may be undermined by fluvial erosion or mass movement....

There is no sharp line of demarcation between the tropics and the subtropics. Just as many tropical plants can be cultivated in the subtropics, so also many subtropical and even temperate plants can be grown satisfactorily in the tropics. Elevation is a determining factor. For example, the scarlet runner bean, a common plant in temperate regions, grows, flowers, and develops pods normally on...

...latitude. In the extreme conditions at the poles, plankton populations crash during the constant darkness of winter and bloom in summer with long hours of light and the retreat of the ice field. In tropical waters, variation in sunlight and temperature is slight, nutrients are present in low concentrations, and planktonic assemblages do not undergo large fluctuations in abundance. There are,...

In the tropics, however, little opportunity for similar overland movement of cold-adapted biota was possible because vast forestland in the tropical lowlands formed a barrier to migration. The organisms therefore have been isolated more completely from those of other cold environments. Despite this situation, colonization of tropical high mountains has occurred. Birds are particularly mobile,...

In the tropics, by contrast, species-diverse forests that can be described as stunted evergreen rainforests typically grow as far as the uppermost limits of tree growth. This is the case in New Guinea, Southeast Asia, and East Africa; however, in parts of the tropical Andes, single species of Polylepis (of the rose family) often grow at altitudes above all other trees, especially on...

Parrots are primarily birds of the tropics. Their distribution encompasses the tropical and southern temperate regions of the world, including Madagascar, many Pacific Islands, and the West Indies. In Asia they occur throughout almost all of India but extend northward only to the Himalayas and southern China. They are absent from Europe. In North America one species, the thick-billed parrot...

Water conditions favourable to the growth of reefs exist in tropical or near-tropical surface waters. Regional differences may result from the presence or absence of upwelling currents of colder waters or from the varying relation of precipitation to evaporation.