Tropical Rainforests

Vegetation

A tropical rainforest has more kinds of trees than any other area in the world. The vegetation is rather dense because of the high temperatures and heavy rainfall, as it encourages a lot of growth. Scientists have counted 179 species in one 1-hectare area in South America. Most northern temperate forests have fewer than seven species. About half of the world's species of plants and animals also live in tropical rainforests. More species of amphibians, birds, insects, mammals, and reptiles live in tropical rainforests than anywhere else.

Tropical rainforests stay green throughout the year. Most trees in the forest lose old leaves and grow new ones throughout the year. But certain species of trees may lose all of their leaves for a short time during the year. Different kinds of trees bear flowers and fruit at different times of the year. Thus, some kind of tree is in bloom or in fruit at any time of the year. Some short trees bear fruit on the trunk or on large, low branches. Some tall trees bear large fruit on long, drooping, ropelike stalks. Since the seasons never really change in the rainforest, the continuous growing season with different tress shedding their leaves at a different time makes the rainforest look green all the time.

The tallest trees of a rainforest may grow as tall as 60 metres. The crowns (tops) of other trees form a covering of leaves about 30 to 45 metres above the ground. This covering is called the upper canopy. The crowns of smaller trees form one or two lower canopies. All the canopies shade the forest floor so that it receives less than 1 per cent as much sunlight as does the upper canopy. All trees need sunlight, so in their efforts to grow tall, the trees don't grow any branches and are straight.

Most areas of the forest floor receive so little light that few bushes or herbs can grow there. As a result, a person can easily walk through most parts of a tropical rainforest. Areas of dense growth called jungles occur within a tropical rainforest in areas where much sunlight reaches the ground. Most jungles grow near broad rivers or in former clearings.

In a tropical rainforest, many plants grow on tree branches, where they receive more sunlight than they would on the ground. Such plants, called epiphytes or air plants, include ferns, mosses, orchids, and bromeliads. Climbing plants called lianas twine around tree trunks and branches. Some lianas form loops and knots as they grow toward the sunlight.

In a tropical rainforest, most plant nutrients are locked up in the living vegetation. Small amounts of nutrients are stored in a thin layer of soil near the surface, where decaying vegetation mixes with the soil. The roots of most rainforest trees remain close to the supply of nutrients near the surface. In some species, the roots form large growths called buttresses that extend between the roots and the trunk. The buttresses may help keep the trees upright.

A tropical rainforest has no dominant species of trees. Most kinds of trees are widely scattered throughout the forest and depend on animals for pollination. A tropical rainforest has millions of species of trees; plants and animals.