Leaf Adaptations in Rainforests

Coping with Heavy Rainfall

• The large amount of rainfall that the rainforest receives is essential for plants to thrive but can also pose problems. For example, branches can snap under the weight of water collected on the leaves. Water on leaves can also cause mold to grow on a plant. In the rainforest, many leaves have adaptation that help them to avoid this problems by having waxy, waterproof surfaces and drip tips, which act like spouts in allowing water to run off the tip of a leaf.

Capturing Light

• Leaves tend to become larger and broader in the lower levels of the rainforest. This is because most of the sunlight is blocked out by vegetation in the upper layers. Broad leaves give a plant the best chance of collecting any sunlight available to it for photosynthesis. Some leaves have stalks that move the leaf to point in the direction of the sun. Leaves in the upper levels of the rainforest are smaller as more light is available to them. In the emergent layer, where a few trees rise above the dense vegetation below, leaves are very small and narrow.

Chemical Defense

• Some rainforest plants are able to defend themselves from the many plant-eating animals with leaves containing harmful chemical substances. For example, some leaves substances called alkaloids which taste bitter and can cause damage to organs such as the liver.

Climbing Vines

• Vines climb up other trees in the rainforest so that their leaves can have access to the maximum amount of sunlight possible. To reach these heights, some vines grow leaves with spikes underneath. These spikes grip onto the trees that they use for support, helping the vine to reach the top layers of the rainforest where sunlight is the most available.

Exposed Leaves

• Trees that reach above the dense roof of the rainforest have adaptations that allow them to deal with the dangers that they are exposed to. One of the problems for these trees is the danger of excess evaporation from the leaves that can be caused by direct sunlight. Exposure to wind at this level can also cause leaves to dry. A thick, waxy coating and small surface area reduce these risks.