The tropical rainforest is dominated by the tall trees of the emergent layer

The entire crowns of these trees often clear the canopy.

While they are extremely tall, they are not the tallest trees in the world.

Within the tropical rainforests, particularly those of Africa and South America, trees more than 200 feet tall are rare.

In comparison, the tallest species of tree overall is the coast redwood, The tallest one of these measured was about 370 feet tall.

The tall trees of the tropical rainforest have trunks that hardly taper until the first branches are reached.

The trunks then break up immediately into a number of huge limbs which support a dome-shaped crown.

In Malaya, a Balanocarpus heimii tree had a girth of 27 feet 6 inches at 4 feet above the gournd and a girth of 23 feet at 88 feet above the ground, where the branches began.

It is difficult to tell how old these huge trees are. In temperate regions trees grow quickly during the summer, but slowly during the winter. Their wood is marked by a series of rings, each representing a

year's growth. The number of rings reveal the tree's age.

In the tropics, growth is either continuous or, if periodic, the growth periods do not necessarily occur once a year.

If the girth of a tree is measured regularly, however, it is possible to rind out the average annual increase. To estimate age, the girth of a mature tree is divided by its average annual increase.

Growth probably does not continue at the same rate throughout the years, however, and so ages obtained by this method are likely to be underestimates.

Balanocarpus heimii, according to calculations based on this method, can reach 1,400 years of age.

Another way to determine age is to date the heartwood of the tree by radiocarbon analysis.

Shorea curtisii, another tall Malayan tree, has been shown by this method to be at least 800 years old.

In comparison, there are bristlecone pines, found in the California mountains, which are over 4000 years old.