Tropical rainforests are warm, humid places which provide shelter and sustenance for an enormous variety of animal species. Tropical rainforests are also important components in the fragile ecology of our planet, giving the oxygen we need to breath and absorbing the waste gases in the atmosphere.
This CD ROM describes the rainforests of our planet, from both the biological and environmental perspectives. You╒ll learn how rainforest ecosystems work, where the rainforests are, and what are the major threats to the integrity of the world╒s rainforests. You╒ll also find out about the wide diversity of animal and plant life in the rainforests.
There are many different types of tropical rainforest, classified according to temperature, the annual amount of rainfall, the soil type, altitude, and whether they are evergreen forest or semi-deciduous forest. This warm, wet, stable environment fosters a wealth of biological richness. Although tropical rainforests cover less than 7% of the earth's surface they are home to approximately 50% of all living things on earth. There is greater diversity, per acre, of animal and plant species here than anywhere else on earth.
Rainforests which have remained completely undisturbed for centuries are called primary rainforests. They are often also called pristine or virgin forests. Primary forests are relatively easy to walk through because very little sun reaches the forest floor thus keeping it almost clear of vegetation These true rainforest areas are now in the minority, secondary rainforests now accounting for a much greater area. Secondary forests, or 'jungles' are created by cutting down trees. The sun reaches the forest floor giving rise to thick, tangled undergrowth which makes walking through them extremely difficult.
Most botanists and biologists broadly categorise tropical rainforests as being of three different types; montane (also known as cloud) rainforest, lowland rainforest, and swamp (or mangrove) rainforest. Forests above 10,000 ft are known as subalpine forests.
Rainforest Layers
Rainforest vegetation is often divided into layers. The very top layer, the emergent layer is so called because trees emerge randomly from the main forest roof. Most of the trees at this level reach 160 ft but some reach heights of 200 feet or more. These so-called pavilion trees are able to withstand burning sun, strong winds and torrential rainshowers.
The next layer is called the canopy. The crowns of the trees in the canopy form an almost closed roof on the forest below, and the canopy is often divided into the upper and lower canopy. Because the top of the canopy basks in almost constant sunlight and can absorb light more easily, trees tend to have smaller leaves than those at a lower level. Usually trees in the canopy are very straight and reach heights of between 100 and 150 feet.
The lower canopy is the richest layer in terms of animal and plant life. Most of the mammals that live in the canopy are nocturnal. These higher levels offer a profusion of orchids, bromeliads, ferns and mosses.
The understory extends from the forest floor up to about 80 feet and contains a mix of saplings, tall shrubs, vines and palms. Leaves are often long and pointed, and their ends form 'drip tips', allowing excess water to run off quickly. Little sunlight filters into the understory, which makes it dark and humid.
The forest floor is the lowest level. Plant growth on the ground is limited, because only 1-2 percent of sunlight filters down to this level. Because the soil is so poor, trees do not send deep roots into the ground but instead they form a root mat, zig-zagging across the forest floor.
This mat immediately soaks up nutrients as they become available. The forest floor of pristine rainforest is remarkably uncluttered save for small plants, leaves and the decaying plant and animal matter which feed moulds and fungi.
Lowland rainforests
Lowland rainforests cover a greater land area than other types of rainforest ╨ the two largest such regions are in Africa and South America. Life is so abundant in lowland rainforests that a single acre may hold as many as 15,000 separate plant and animal species. Trees in lowland rainforests can grow to heights of 150 ft or more, and are often supported by enormous buttress roots.
Montane rainforests
Montane forests are given the name 'cloud' forest because they are constantly shrouded in mist. Tropical tree species at these higher elevations give way to those more commonly found in temperate forests ╨ like oak, beech and conifer.
Most animal species at the higher altitudes different from those that thrive in lowland rainforests and there is a lower density of animal species.
Custodians of the Forest
Rainforest deforestation affects each and every one of us.
We need rainforests to help stabilise our climate, to provide us with medicines, food and a host of resources, many of which remain to be discovered to this day.
This potential knowledge is in danger of being lost forever as rainforests are irreversibly destroyed. The people of the rainforests have suffered, and continue to suffer the consequences of greed, corruption, thoughtlessness, ignorance and bad management at the hands of outsiders. Interference, even some that has been well-intentioned, has cost many tribes their homes, their livelihood, their religion and their lives.
'Modernizing' indigenous people is not for the western world to decide. To retain or not to retain a traditional way of life is a decision which belongs firmly to the people of the forests. It is they who must decide their future.
This choice becomes more difficult as the food and shelter of the indigenous peoples diminishes. Tribes who are eager to adopt the technology of Western civilisations should be given time to make this transition at their own pace, without loss of dignity, without disturbance to their ecology, without loss of their culture, and without fear of exploitation.
ECOLOGY
Climate
In spring and fall, the sun is equidistant between the earth╒s poles. As winter approaches in the southern hemisphere, the earth's axis tilts so that the northern hemisphere is warmed by the summer suns rays.
As the northern hemisphere tilts further from the sun, winter approaches and summer comes to the southern hemisphere.
Because the area around the equator is almost directly under the sun throughout the year the constant rise of heated air brings moisture in from the north and the south.
The rising moisture condenses into rainclouds and falls on the rainforests, which may experience up to 400 inches of rain each year.
Photosynthesis
Plants and trees remove carbon dioxide from the atmosphere and transform it back into the oxygen our lungs need so that we can breathe. This process is known as photosynthesis.
The combination of carbon dioxide, water and chlorophyll, a chemical which gives leaves their green color, allows the sun's energy to be turned into the food energy plants need to grow, whilst at the same time releasing oxygen back into the air.
Soil
Temperate forests usually have a thick layer of soil which contains nutrients and minerals. Roots of temperate trees often go deep into the soil.
But tropical rainforest soil is mostly very old and impoverished.
This is because the constant rains leach important minerals from the soil. Trees in tropical rainforests often have shallow root systems.
Soil is protected by the plants and trees growing in it. In areas where trees are cut down, the heavy rains wash away the topsoil, exposing clay soil, colored red by deposits of aluminum and iron oxides
The new surface layer exposed after erosion becomes cracked and hardened and useless for any form of agriculture. This type of soil is called lateritic soil
Global warming
The air around our planet is a mix of 21 percent oxygen, 78 percent nitrogen, plus a few trace gases such as methane, ozone, carbon dioxide (CO2), nitrous oxide and chlorofluorocarbons (CFCs).
About 70% of the sun's energy reaches the earth's surface ╨ the remainder is reflected back into space.
As the energy is reflected, some of the heat is captured by the trace gases and retained in the atmosphere. This is known as 'the greenhouse effect'. Without this action, the earth would be a very cold place to live.
Burning rainforests releases huge amounts of carbon dioxide into the atmosphere adding to the greenhouse gases already present. Scientists now warn us that the increase of carbon dioxide is warming the planet up.
This may lead to melting of polar ice, causing severe flooding to coastal areas around the globe. Many big cities sited on coastlines could suffer severely from the predicted rise in sea levels of between 1-3 feet.
Biodiversity
Tropical rainforests cover only 2% of the earth's land surface area but the diversity of life here is truly overwhelming. It is estimated that nearly 50% of the world's plant and animal species live in the rainforests. Some experts say this figure could be as high as 90%.
The sheer abundance and diversity of life in the rainforests is almost impossible to imagine. Sixteen per cent of all bird species nest in the rainforests of Indonesia alone, and over 90% of the world's fern species are found in tropical rainforests. Over 300 different kinds of butterflies were found In just one square mile of African rainforest and most of the world's apes and monkeys live in the rainforest. The forests are also home to more than three fourths of all types of wild cats.
Tragically, two species of animal or plant become extinct every single hour. Unless the rainforests are protected, a potential 20 million living species face extinction during the next 25-30 years.
Who lives in the rainforests?
It is now believed that tropical rainforests could be home to as many as 500 million people, a figure that has more than doubled since 1970. Only 50 million of these are tribespeople. The rainforest provides indigenous people with food, medicine and shelter, but people too are disappearing along with the plants and animals.
Since the Second World War the destruction of our rainforests has accelerated considerably and many areas are now nothing more than barren wastelands without any chance of recovery. Primary rainforests are burned to provide grazing land for cattle, and huge tracts of forests are cleared to build highways making it easier for mining, dam building and logging activities to flourish.
Hunter-gatherers
Hunter-gatherers live deep in the forest. They often lead a nomadic existance and live in small family groups. They hunt, fish and gather fruits, nut and berries. To catch their prey, hunters often mimic the animal╒s call to draw it closer. Bows and arrows are the hunter-gatherer╒s main weapons. The arrows are dipped in poison, which comes from a variety of sources including plants, tree bark and the toxic skin of tree frogs. Another weapon used is the blow pipe. Made from bamboo, a pointed dart is forcibly ejected from the pipe by blowing hard into one end of the pipe.
Shifting cultivators
Shifting cultivators practise a type of farming which makes the best possible use of the rainforests poor soil. Small areas of forest are cleared. The vegetation is left to dry out which usually takes about one month, after which it is burned. The resulting ash contains valuable plant nutrients and serves as fertiliser. Crops are immediately planted to decrease the chances of the rains washing away the nutrient rich ash. A large variety of crops are grown to reduce the risk of loss from possible disease or pest attacks.
Rubber tappers
There are still approximately 500,000 rubber tappers in Brazil who depend on the rainforests to make a living. The majority live in Acre, near the Peruvian and Bolivian border. Rubber is a sustainable rainforest resource. Approximately one cup of latex is obtained from each tree per day and a single rubber tree can provide latex for many years during which time no harm is done to the tree.
Airplane tires are often made from 100% natural rubber because of its heat resistant quality and its elasticity.
Besides extracting rubber, tappers also gather brazil nuts for use in a variety of food items. Oil extracted from the brazil nut is used commercially in hair conditioner.
Rubber and brazil nuts are both good examples of the many renewable resources rainforest trees provide. There has been much conflict over the years between rubber tappers and cattle ranchers who burn down trees to turn the land into grazing areas for cattle. The results of such conflict have often been bloody. Several rubber tappers and their leaders have been murdered, the most notable being Chico Mendes the founder of the rubber tappers union who was murdered in 1988.
Shaman
The shaman knows how to use plants to treat many illnesses, from a simple ear infection to blood disorders. Although most healers are men, women also fulfill this role. Cures for modern day incurable illnesses such as the common cold, cancer and AIDS may well be found in tropical vegetation. But time is running out. At the current rate of deforestation, 115,000 acres a day, it is estimated that all rainforests will disappear in less than 40 years together with the extinction of a vast array of potential new disease treatments.
