Rainforest composition in the canopy is dominated by a few trees like mahogany, ebony, and teak. The canopy can be continuous over hundreds of kilometers and is occasionally penetrated by taller trees. Recently, the forest canopy has been found to contain a significant portion of the forest’s biodiversity, as the canopy creates many different micro habits for innumerable forest species.
Although deciduous, rainforest trees are evergreen in habit as they continuously shed and grow leaves giving the impression of constant foliage. Rainforests have a composition of trees with an average height of 50 metres with trees of 90 metres not uncommon. They have special adaptations to their unique environment, including dark green leaves to counter excessive moisture loss at high temperatures, and many leaves in rainforests have a thickened cuticle with a waxy coating. This allows the heavy water droplets to run off to the layers below. Towards the bottom of the canopy layer, the trees have downward pointing leaves so water pours off to the roots instead of being lost by evaporation.
Trees in the rainforest usually have narrow, straight trunks with few low branches. Trees with branches close to ground level are usually juveniles attempting to grow towards the canopy. The branches of adult trees are focussed at the top as this is where they catch the most sunlight. Because of this structure, many rainforest trees can grow in a small area giving record breaking numbers of trees per unit area, and rainforests contain the highest biomass of any type of vegetation on Earth. An average 1 km2 of rainforest may contain a comparable weight of wood as 200 – 300 km2 of temperate woodland. Due to this proximity of trees, the canopy of a tropical rainforest is practically light proof with a closed network of vegetation.
Rainforest trees have neither a deep nor large root system because of the characteristic thin layer of soil. This limitation has led to the buttress root system, and usually rainforest trees have between three to ten buttresses radiating from their trunks. The buttress roots are effective at absorbing most of the falling water, but their precise function is still unknown to science.