It comes as no surprise to learn that among the plants which flourish in the tropical rain forests, trees are the most abundant. The climate of the equatorial regions provides all the necessary ingredients for rapid plant growth, and it is not uncommon for trees to attain heights of up to and sometimes over 40 metres. Such immense plants require an extremely large leaf area in order to harness enough sunlight for photosynthesis, and the combined crowns of these enormous trees form an almost continuous canopy. Occasionally an exceptionally large tree pushes its way through the leaf cover, dominating the landscape. These trees are known as emergents, and form the uppermost layer of the rain forest's complex canopy structure.

Beneath the main canopy grow smaller trees which are either young or slow-growing, and these tend to have more elongated crowns than their taller counterparts. Together with various large herbs and shrubs, these form a third canopy layer. These three layers or strata together make up an almost impenetrable cover, and under normal conditions very little light - sometimes as little as 2 per cent - is able to filter through to the forest floor. Even when a large tree falls there is little respite because there are plenty of younger trees beneath just waiting for the opportunity to take advantage of the extra sunlight and join their fellows in the canopy.

All this makes for somewhat unfavorable growing conditions on the forest floor, and the result of this is that vegetation here is sparse. The exception to this rule occurs where rivers flow through the forests, and along their banks undergrowth flourishes, making the forest thick and impenetrable. This is the typical image of the tropical rain forest, fuelled perhaps by the fact that many people's first impression is from a boat.

Exploration | Tropical rain forests |  The canopy  | On the Line home page