Rainforests

Introduction

Australia is largely considered to be an arid continent. There are, however, a few pockets of humid forests called rainforests. Rainforests are forests where evergreen trees grow and that receive high rainfall. There are three kinds of rainforests found in Australia, tropical rainforest, sub-tropical rainforest and temperate rainforest. Tropical rainforests are found in warmer areas in Queensland, subtropical rainforests are found in slightly cooler areas in New South Wales and Queensland, and temperate rainforests are found in New South Wales, Victoria and Tasmania. These rainforests are remnants of prehistoric rainforests that were once found all over Australia and even parts of Antarctica.

What is it like in a rainforest?

The rainforest is an immensely diverse environment. Scientists estimate that one-third of the Earth's plant and animal species live in tropical rainforests. Within one hectare (10 000 square metres) of rainforest, there can be between 50 and 200 different tree species alone. In contrast, there are 700 different tree species in the whole of the United States and Canada.

For a person walking on the floor of a rainforest, the view is very different from what might be expected. Instead of the popular image of an impassable, dense undergrowth of vines and shrubs, the forest floor of a rainforest is relatively clear of plant life. This is because the leaves of the trees above are so dense that they block any sunlight from reaching the forest floor. As a result, it is dark. Most plants on the forest floor cannot get enough light to perform photosynthesis, which is how plants make food out of water, carbon dioxide and sunlight. This is not to say there is no life on the forest floor, of course. Fungi, insects, worms and other small animals live in the litter, or debris, such as leaves, dropped to the floor by plants and animals. Large animals also live on the forest floor. When there is a clearing in the forest due to a tree falling down, however, plants grow more thickly because light can reach the ground. This also occurs at the edge of the rainforest.

Travelling up the trees brings us to the next layer, which is called the understorey. This layer is between ten and 15 metres above the ground. The understorey is also damp and dark, and there are branches and vines on which animals can move about. Some trees, such as palm trees, have their tops at this level. They have broad leaves to soak up as much sunlight as they can. Many birds and snakes live in the understorey and insects are also abundant at this level. Flowers in the understorey are brightly coloured to attract animals through the darkness.

The next level of the rainforest is called the canopy. Although it is found 20 to 30 metres above the ground, it has the most abundant life of any of the layers. This is where many animals, including amphibians, birds, bats and insects live. Many of these animals never even see the forest floor. The tops of the trees at this level are tightly packed, making a continuous level of leaves and branches, called a canopy. Often, a hazy mist collects over the top of the canopy as trees transpire.

Finally, towering above the canopy are the emergent trees, which are extremely tall trees that are between 35 and 70 metres tall. These trees are home to some birds that are similar to those found in the canopy. Above the emergent trees, clouds form from the moisture transpired by the trees, continuing the cycle of high rainfall. See image 1

Plants and animals in tropical and sub-tropical rainforests

Tropical and sub-tropical rainforests are highly diverse. In the Daintree Rainforest of northern Queensland, for example, 70 animal species and 700 tree species that are endemic to north-eastern Queensland are found. The Daintree contains 30 percent of Australia's frog, marsupial and reptile species, 65 percent of Australia's bat and butterfly species and 20 percent of Australia's bird species. See image 2

One example of a plant endemic to this type of rainforest is the scaly tree fern. Scaly tree ferns are very primitive plants. Unlike other trees, they grow only from the top - in other words, they do not grow in girth. These trees can grow to 12 metres. Many other plants grow in tropical and sub-tropical rainforests as well. These include epiphytes (plants that attach themselves to tree branches in the canopy), vines and palm trees.

An example of an animal endemic to the tropical and sub-tropical rainforests is the Bennett's tree kangaroo. This animal is very small and lives in trees. It has large, sturdy claws that are used to climb trees. Bennett's tree kangaroos are found only in Queensland, although another type of tree kangaroo can be found in New Guinea. Many other animals are found in the tropical and sub-tropical rainforest - from all parts of the animal kingdom. See image 3

Plants and animals in temperate rainforests

Plants similar to those found in the tropical and sub-tropical rainforests grow in Australian temperate rainforests. Ferns, including tree ferns and evergreen trees are common. Plants like palm trees and vines, however, are not found in temperate rainforests. This is because the temperatures do not become warm enough. Temperate rainforests are not quite as biologically diverse as tropical and sub-tropical rainforests but they still have a large number of living organisms. See image 4

An example of an endemic temperate rainforest animal is the spotted-tail quoll. This animal is found in Tasmania and parts of the eastern Australian mainland. This animal is unusual because it is a carnivorous marsupial. It hunts animals like rats, possums, small wallabies, reptiles and insects.

A living legacy

Australian rainforests are remnants of ancient rainforests that once existed across Australia and Antarctica when the two continents were still connected, forming the super-continent Gondwanaland. Since Australia is so isolated, many of the species present in the Australian rainforests have been able to survive undisturbed. Conserving Australian rainforests is important because these places provide an insight into how many modern-day plants and animals may have evolved.