The giant trees of the tropical rainforest's emergent layer live in a harsh environment, exposed to the high temperatures, strong winds and low humidity found above the canopy.

Although they began their lives in the damp shade of the understory, at maturity they live above the other trees.

The leaves that they bear when they are adults are smaller and tougher than those they have as young trees.

Their leaves often have a thick, outer waxy layer that helps reduce water loss. This is a useful for life in the dry atmosphere at the top of the tropical rainforests.

Many emergents have winged fruits that rely on the wind to carry them to new sites.

Above the canopy, air movement is at least 100 times greater than in the understory, and 10 to 20 times more than in the main canopy.

Consequently, a seed's chances of dispersal are much greater if it falls from an emergent tree than from a tree in the canopy or understory.

Asia - Shorea curtisii

Shorea curtisii, which is indigenous to Southeast Asia, belongs to the family Dipterocarpaceae, named for the two wings that support their fruits. Shorea curtisii is found throughout the Malay Peninsula, and in Sarawak, Brunei and Sabah on the island of Borneo.

A huge tree, attaining 220 feet (70m) in height and 22 feet (7m) in girth, Shorea curtisii tends to grow on ridges, mainly between 1,000 and 2,500 feet (300 and 750m) in Malaysia, but lower in Borneo.

The towering trunk may rise for 90 feet (27m) before the first branch appears, and it supports a huge cauliflowerlike crown. The grayish-brown bark is deeply fissured by vertical cracks. The leaves, which are spear-shaped with long tapering tips, have a grayish bloom on the underside. The shade of the leaves makes this dominant forest tree easily recognizable from the air.

The creamy flowers of Shorea are small, only ½ inch (1cm) across, and each is composed of five petals spreading out in a starlike pattern. The sepals grow enormously after flowering, forming the wings, which help to disperse the nut, held between them.

Shorea curtisii produces a timber similar to that of other Shorea species. Together, the woods are known as meranti and are important, valuable commercial hardwoods.

The Americas - Cavanillesia platanifolia

Although not the largest of South American emergent trees, Cavanillesia platanifolia is distinctive and impressive when in flower.

Native to Central America, from Panama south to Colombia and Peru, it is known locally as cuipo or lupuna colorada.

The trunk, slightly swollen at the base, is thick yet smooth, like the leg of a huge elephant. Small, thick buttresses and raised ridges grow around it every few feet. It supports a huge, umbrella-shaped crown.

The leaves of Cavanillesia fall once a year, and during this period, small red flowers are produced.

Each flower is only 1 inch (2.5cm) across, but they form an impressive mass.

Each fruit has a central seed with five radiating wings. The whole fruit is about 5 inches (12 cm) in diameter. Even though the tree looks strong and heavy, its wood is extremely light when dry, and has been suggested as a substitute for balsa, which is also a rainforest tree.

Africa - Triplochiton scleroxylon

Called wawa in Ghana and obeche in Nigeria, Triplochiton scleroxylon grows throughout the forests of West Africa, from Guinea to the Congo.

It is rarer in the wettest forests. Reaching 200 feet (60m) in height and 22 feet (7m) in girth, this emergent has large winglike buttresses running many feet up its trunk. The gray bark is smooth, but is fissured in old trees. The crown is frequently irregular in shape, with large maple-like leaves.

About 1 inch (2.5cm) across, the flowers have purple-based white petals. The fruits, which tend to be formed at intervals of several years, are winged and so are blown about by the wind. Seedlings seem to grow best in clearings and gaps.

The wood from this tree is soft and light, and is therefore easy to work with. Locals use it to make dugout canoes. They make doors out the trees' buttresses.