Tropical Rain Forest Canopy and the Life Below it
A rain forest's second layer is called the canopy layer or roof. This layer is formed by flat-crowned trees generally between 65 and 100 feet (19.5 and 30 m) tall. The network of branches and leaves from these trees forms an umbrella-like covering over the forest, allowing very little of the sunlight that strikes the top of the canopy trees to penetrate to the layer beneath. Like the emergent trees (see the previous section), the tops of these trees are also exposed, so they experience changing temperatures, humidity, and winds.
Below the canopy layer is the subcanopy or understory. The trees here are short, growing to a height of about 15 feet (4.5 m). If a canopy tree dies, it creates an opening in the canopy that allows more sunlight to reach the subcanopy layer. Then, one or more of the shorter subcanopy trees can then quickly grow to replace the fallen one. Part of this layer is made of shrubs (short, woody plants with several main stems instead of one main supportive stem called a trunk) that are shorter than the trees. Many of the plants in this layer have large leaves that help them catch almost every ray of sunlight that reaches them.
The forest floor layer, the bottom layer, in contrast to the canopy layer, is still and dark. The temperature and humidity there is always high and relatively constant. People sometimes assume that a tropical rain forest is filled with the remains of fallen trees, branches, and leaves. But the truth is that the floor of a tropical rain forest is basically open and uncluttered. This is because so little sunlight reaches the floor that only a few small plants can survive, and when any plant dies it quickly decomposes on the dark, damp forest floor. Only along open areas, such as where the forests have been cut or along a riverbank, is the undergrowth so thick that it is like a jungle.
To determine how tree leaf size affects sunlight on a forest's floor.
- Sheet of green construction paper
- 2 green pipe cleaners (found at craft stores)
- Desk lamp
- Fold the paper in half by placing the short ends together, then unfold it. Cut along the fold.
- On one of the pieces of paper, draw a picture of a leaf as big as possible with a point at one end, as shown. Cut out the leaf.
- Fold the other piece of paper in half two times, first from top to bottom then from side to side.
- Draw two leaves on the folded paper. Cut out the leaves, cutting through all four layers.
- Make a model of a canopy tree stem with one leaf by taping the large leaf to the end of one of the pipe cleaners.
- Make a model of a stem from an emergent tree by taping one small leaf to one end of the remaining pipe cleaner. Tape the other small leaves along the sides of the pipe cleaner, as shown.
- Hold the stem models side by side under the light of the desk lamp. Observe how much light hits the desk under each model.
There is a large shadow beneath the stem with one large leaf, and small shadows with light showing among them beneath the stem with eight small leaves.