TROPICAL RAINFOREST PAGE 37-43

OBJECTIVES Describe and explain distribution of tropical rainforest. Describe the features of tropical rainforests. Describe how tropical rainforest adapt to the environment.

OVERVIEW

RAINFOREST DISTRIBUTION

Location of tropical rainforests

DISTRIBUTION Found in places between 10°N and 10°S of the Equator Mainly located in Amazon Basin, Congo Basin, and parts of Southeast Asia such as Malaysia and Indonesia.

DISTRIBUTION

Why?: high temperatures (27°C) and high rainfall (above 1500mm) throughout the year. This promotes abundant plant growth which is typical of tropical rainforests.

RAINFOREST STRUCTURE PAGE 38

STRUCTURE 5 distinct layers: Emergent, Canopy, Understorey, Shrub, Undergrowth [You are expected to label/ describe every layer in detail]

STRUCTURE Emergent: –30-50m –Tall trees (Emergent trees) –Tall, thick, straight trunks Canopy –15-30m –Wide, umbrella shaped crowns –Continuous leaf cover called canopy

STRUCTURE Understorey –6-15m –Narrower, oval-shaped crowns (?) –Young trees of canopy, emergent Shrub –5m –Tree saplings, woody plants

STRUCTURE Undergrowth –0-5m –Grasses, ferns, mosses, fungi –Sparse growth (?)

RAINFOREST CHARACTERISTICS PAGE 40-43

C#1 The undersgrowth in a tropical rainforest is sparse. This is because, little sunlight

RAINFOREST FEATURES

#1: Sparse Undergrowth There is sparse undergrowth in the forest floor of the tropical rainforest. This is because very little sunlight (about one percent) passes through the canopy and reaches the forest floor.

#2: Large Variety There is a large variety of plants in the tropical rainforest. It is estimated that rainforests may contain more than 750 species of trees and 1500 species of other plants. This is because of consistent high temperature and rainfall throughout the year that promotes plant growth.

#3: Extreme density Tropical rainforests are extremely dense due to the presence of a large variety of plant species which can grow in the tropical rainforest.

#4: Evergreen Leaves Tropical rainforests have evergreen leaves due to the consistently high rainfall throughout the year.

#5: Large & broad leaves Tropical rainforests have large and broad leaves to maximise the surface area for photosynthesis.

#6: Thin & smooth barks Tropical rainforests have developed thin and smooth barks because there is no need for protection against cold or dry conditions.

#7: Buttress Roots Some trees in the tropical rainforest have buttress roots, which are thick and spread out widely to support the great weight of trees.

RAINFOREST ADAPTATIONS

#1: Low Light The canopy layer prevents sunlight from reaching the lower layers of the tropical rainforests. Some plants such as the epiphytes and lianas have adapted to this low light condition by growing on tree branches. Furthermore, these trees have branches only on the top one-third portion of the trunks to get maximum sunlight.

#2: Bacteria Growth High temperature and high rainfall in the tropical regions promote rapid growth of bacteria. Hence, tropical rainforest have waxy leaves with drip tips to allow rainwater to drain off easily. This prevents harmful bacteria from growing and protects the plants from diseases.

#3: Still air below canopy The presence of the continuous canopy results in still air in the layers below it and this does not allow pollination to be carried out by wind. Hence, flowers and fruits in the tropical rainforest are colourful and sweet-smelling. This attracts insects for pollination and animals for seed dispersal.

#4: Rapid humus formation High temperatures and rainfall all year round causes the leaf litter to decompose and form humus rapidly. This supplies nutrients to the topsoil, which is the uppermost layer of the soil. Hence, the roots of trees in the tropical rainforest are shallow and spread widely to absorb the nutrients present in the topsoil.

RAINFOREST PLANTS

EPIPHYTES This refers to plants that grown on and use trees for physical support. Rainwater and decaying leaves provide the epiphytes with water and nutrients. Example: Bird’s Nest Fern, Orchids

LIANAS Refers to thick, woody vines that wind around tree trunks to reach for sunlight

PARASITIC PLANTS This refers to plants that compete with the host tree for space, sunlight and nutrients. These plants are common in the canopy and understorey layer of the rainforest. Example: Strangling Fig

SUMMARY Complete Review Worksheet #2