Tropical Rainforests

Distribution of Tropical Rainforests vedi cgse bitesize

Tropical rainforests are found on or near the Equator (roughly between 28 degrees north and south). The main concentrations of tropical rainforests are:
  • The Congo Basin in central and west Africa
  • The Amazon in Brazil, Peru, Bolivia and Ecuador
  • SE Asia (Malaysia, Thailand, Vietnam, Indonesia and the Philippines)
  • Madagascar
  • North east Australia
  • Southern India and Sri Lanka
  • Central America
Tropical Rainforest Climate
Because tropical rainforests are close to the equator, they have very similar climates all year around. Their temperature is constant at between 25 and 30 degrees Celsius. They also receive rainfall all year around, although the monthly amounts may vary slightly (scarsamente).
  • Tropical rainforests normally experience convectional rainfall. Convectional rainfall is a type of rainfall formed when the sun heats the earth causing warm air to rise, cooling and condensing in the atmosphere to form clouds which fall as rain. The condensing water vapour forms cumulonimbus clouds and the rainfall is accompanied by thunder and lightning. Convectional rainfall usually occurs mostly in the tropics where it is hot.
  • This is because they are close to the equator where temperatures are hot.
  • The hot temperatures warm up the land, causing evaporation and transpiration and then convection (convezione la prof di matematica vi spiegherà cos’è!).
  • Not only is the weather similar between months, it is also very similar between days.
  • Days will start of warm and then the temperature and humidity will build up.
  • By the afternoon the air is saturated and tropical rainforest normally experience intense rainstorms.
  • Because tropical rainforests are near to the equator the hot air rises causing low pressure.
The graph shows average rainfall and temperature in Manaus, Brazil, in the Amazon rainforest. The rainy season is from December to May. Notice how much the rainfall varies over the year - the highest monthly rainfall is in March with over 300mm, while the lowest is in August with less than 50mm. Over the year, the temperature only varies by 2°C.

Rainforest ecosystems are characterised by heavy convectional rainfall, high humidity, lushness (rigoglosità) of vegetation and nutrient-rich but shallow soil. These factors give rise to a unique water and nutrient cycle.
Tropical Rainforest Vegetation and Adaptation
Rainforests are the Earth's oldest living ecosystems.

The graphic shows the levels of rainforest vegetation and the relative amount of sunlight that each one receives.

Adapting to rainforest life

The vegetation in the rainforest has evolved characteristics which help it to survive in this unique environment.
Emergents (Kapok, Ebany): Emergents are tall trees that grow above the canopy layer in order to reach sunlight. Emergents can grow in excess of 50 metres.The tallest trees are the emergents, towering as much as 200 feet above the forest floor with trunks that measure up to 16 feet around. Most of these trees are broad-leaved, hardwood evergreens. Sunlight is plentiful up here. Animals found are eagles, monkeys, bats and butterflies.
Main Canopy: The canopy layer contains about 50% of the rainforests wildlife. The canopy layer is extremely thick and sits at between 25 and 35 metres. It is the Jungle. This is the primary layer of the forest and forms a roof over the two remaining layers. Most canopy trees have smooth, oval leaves that come to a point. It's a maze of leaves and branches. Many animals live in this area since food is abundant. Those animals include: snakes, toucans and treefrogs.
Understory (lower canopy)-Level of trees between the rainforest floor and the upper canopy. The understory is the layer of the rainforest between the canopy and the forest floor. Here, the leaves of trees and plants are broad and large so that they can capture what little light gets through the canopy. The understory is dark and humid, and has a large amount of insect life.
The understory is hot, damp, and the air is still. This part of the rainforest is under the leaves but above the ground. The understory is a tangle of shrubs, young trees, palms and woody plants that can grow in the shade of the taller trees. The small amount of light in the understory encourages the plants to think of smart ways to survive.The leaves of many of the plants are very large, so that they can absorb or soak in as much sunlight as possible. The plants in this layer of the forest hardly ever grow higher than twelve feet.Many houseplants (piante da appartamento) are found in this part of the rainforest (philodendrons, prayer plant, zebra plants, and peace lily, for example). These plants can live in your living room as well as the understory because both places get little sunlight. Plants in the canopy include thick, snake-like vines and epiphytes ("air plants") like mosses, lichens, and orchids (which grow on trees).
Shrub Layer: The shrub layer is near the forest floor and is also extremely dense. Because the canopy is so thick the shrub layer has to adapt to survive in less light.
Forest floor It's very dark down here. Almost no plants grow in this area, as a result. Since hardly any sun reaches the forest floor things begin to decay quickly. A leaf that might take one year to decompose in a regular climate will disappear in 6 weeks. Giant anteaters (formichiere) live in this layer.
Humus Layer: Rainforest soils are fairly infertile and dependent on the humus layer (decaying biological matte (materia bilogica in decomposizione)). If the source of humus is removed through deforestation then soils degrade very quickly.Soils are red due to the high iron and aluminium content. There is a thick layer of leaf litter and decomposing organic matter on the surface.
Kinds of plants in rainforest
Competition at ground level for light and food has lead to evolution of plants which live on the branches of other plants, or even strangle large trees to fight for survival.
Lianas: These are woody vines (rampicanti) that climb up other trees to try and get into the canopy and capture sunlight.They begin life on the forest floor but depend on trees for support as they climb upwards towards the sunlight they need for survival. They do this by attaching themselves to trees with sucker roots or tendrils and growing with the young sapling, or they climb by winding themselves round the tree's trunk. When they reach the top of the canopy they often spread to other trees or wrap themselves around other lianas. This network of vines gives support against strong winds to the shallow-rooted, top-heavy trees. However, when one tree falls several others may be pulled down also.

Strangler Figs (detti strangolatori):in Spanish they are known as matapalo - 'killer tree'.Strangler figs (famiglia dei ficus) grow around the outside of other trees taking their light and nutrients and slowly killing the host tree. However, when the host tree collapses so does the strangler fig.start at the top of a tree and work down. The seed is dropped in a nook (nicchia) at the top of a tree and starts to grow, using the debris (detriti) collected there as nourishment. Gradually the fig sends aerial roots down the trunk of the host, until they reach the ground and take root. As it matures, the fig will gradually surround the host, criss-cross its roots around the trunk and start to strangle. The figs branches will grow taller to catch the sunlight and invasive roots rob the host of nutrients. Eventually the host will die and decompose leaving the hollow (cavo) but sturdy (solido) trunk of the strangler fig.
By using an adult tree as its host, the strangler fig avoids competition for light and nutrients at ground level.

Buttress Roots: (esempio mangrovie) Very long roots that are designed to support tall trees and to suck up the maximum amount of nutrients in fairly nutrient poor soil. Rainforests have a shallow layer of fertile soil, so trees only need shallow roots to reach the nutrients. However, shallow roots can't support huge rainforest trees, so many tropical trees have developed huge buttress roots. These stretch from the ground to two metres or more up the trunk and help to anchor the tree to the ground.


Fan Palms: Huge wide leaved plants that aim to capture as much sunlight and rainfall as possible.
Evergreen: Most vegetation in rainforests does shed (fare la muta) its leaves once a year. However, because the climate of rainforests is similar all year, they shed their leaves at different times providing a constant source of biological matter and keeping the rainforest green.
Drip tip leaves (foglie con estremità a gocciolatoio) : A lot of vegetation have leaves designed for rainfall to travel over them and drip to the ground. This is because the vegetation does not wanted to be damaged by large quantities of water.

Rainforest water and nutrient cycles

Rainforest ecosystems are characterised by heavy convectional rainfall, high humidity, lushness of vegetation and nutrient-rich but shallow soil. These factors give rise to a unique water and nutrient cycle.

Rainforest water cycle

The roots of plants take up water from the ground and the rain is intercepted as it falls - much of it at the canopy level. As the rainforest heats up, the water evaporates into the atmosphere and forms clouds to make the next day's rain. This is convectional rainfall.
The rainforest nutrient cycling is rapid. The hot, damp (umido) conditions on the forest floor allow for the rapid decomposition of dead plant material. This provides plentiful nutrients that are easily absorbed by plant roots. However, as these nutrients are in high demand from the rainforest's many fast-growing plants, they do not remain in the soil for long and stay close to the surface of the soil. If vegetation is removed, the soils quickly become infertile and vulnerable to erosion. If the rainforest is cleared for agriculture it will not make very good farmland, as the soil will not be rich in nutrients.

Tropical Rainforest Animals

Tropical rainforests have a huge amount of biodiversity within them - some estimates suggest that up to 50% of the earth's biodiversity live there (flora and fauna). The are many big famous mammals like tigers in SE Asia, jaguars in Central and South America and leopards in Africa. However, there are also much smaller mammals like sloths and primates like lemurs that live in rainforests. All mammals and primates have adapted in different ways to survive in the rainforest e.g. camouflage. As well as mammals and primates there are many other animals like birds, amphibians, reptiles and insects. Many rainforest animals are under threats. Threats include:
  • Habitat loss (deforestation)
  • Climate change (reduction in rainfall or increases in temperature)
  • Pollution (especially reptiles and amphibians)
  • Hunting (food food, skins and parts for Chinese medicine)
  • Cross breeding with domestic animals
  • Diseases (bird flu)

Deforestation rates vary massively, one reason is the inaccessibility of many of the forests and the way people classify deforestation. However, it is claimed that now only about 5% of the earth's surface is covered in tropical rainforests, compared to nearly 15% 50 years ago. Many people believe that tropical rainforests could disappear this century. /

Deforestation: The removal (cutting down) of trees.

Logging: disboscamento
Reforestation: The replanting of trees once they have been cut down.
Afforestation: Planting trees in an area that previously did not have trees.

PEOPLE OF THE RAINFOREST

We often overlook the millions of people that live in the rain forests. Did you know that there are about 50,000,000 tribal people living in world's rainforests? These people depend on the forests for their food and shelter. As we cut more and more trees and destroy more and more of the forests, we are also killing people. Many native tribes have been exterminated already because their governments failed to protect them from logging companies, the mining companies and the slash and burn farmers.
Mbuti and Baka Pygmies live in the rainforests of Central Africa. Traditionally they live by hunting and gathering food.
The Huli are one of the many tribes that live in the remote highland forests of Papua New Guniea. They live by hunting, gathering plants and growing crops. Men and women live seperately, in large group houses. The men decorate their bodies with colored clay and wear elaborate headdresses for ceremonies.

Rainforests are the source of many items that we all use in our own homes!
We eat several foods from the rainforest and many medicines are made from ingredients found only in these areas.

/ Some of the common products we
know of include:
  • chocolate
  • sugar
  • cinnamon
  • rubber (gomma, caucciù)
  • medicine
  • pineapples

Importance of Tropical Rainforests / Reasons for Deforestation / Problems Caused by Deforestation
  • Biodiversity: Although rainforests cover only about 5/6% of the world's land mass, it is estimated that they could contain up to 50% of the world's biodiversity. This is potentially up to 15 million species.
  • Photosynthesis: Tropical rainforests are often referred to as the 'lungs (polmoni) of the earth'and convert large amounts of the greenhouse gas carbon dioxide back into oxygen. It is estimated that the Amazon rainforest alone produces about 20% of the earth's oxygen.
  • Flood control interception(part of the precipitation that is temporarily stored in the top layer of the forest floor and successively evaporated within a few hours or days during and after the rainfall event) transpiration: Rainforests are an excellent natural measure to reducing flooding. There is leaf cover in rainforests all year so interception continually happens, extending rivers lag time (scarto temporale). All vegetation uptakes water and transpires it.
  • Control of soil erosion: The root systems of trees and shrubs hold the very thin soil of rainforest in place. If trees are removed then both erosion of topsoil and landslides are more likely
  • Source of nutrients to humus layer in soil: The topsoil in rainforests is very thin and relies (contare su) on the nutrients provided by rotting plants and animals. Because of the rainforests climate, there is a constant supply of leaf litter.
  • Medical remedies: Rainforests have been the source of many of today's drugs, including the basic ingredients for the hormone contraceptive pill, quinine (a anti-malaria drug) and curare (a paralysing drug).
  • Cash crops and agricultural products: Yam, coffee, rubber, mango, banana, sugarcane, cocoa and avocado were all first discovered in rainforests.
  • Ecotourism: With people becoming ever more environmentally conscious and looking for increasing adventures, ecotourism to rainforests is increasing. This not only helps protect rainforests, but creates income for locals. Ecotourism is an important income to countries like Costa Rica and Belize.
  • Home to indigenous groups: Although the number of indigenous groups and people have declined rapidly since colonisation in South America, it is estimated that there are still over 200,000 people that consider the Amazon their home.
/
  • Cattle Ranching: As the world's population gets bigger and richer, the demand for meat is increasing. To rear (allevare) the cattle (bestiame) increasing tracts of the rainforest are being cleared to make pastures for grazing (pascolo).
  • Subsistence Farming: Because of the large amounts of poor people that still live in tropical areas, subsistence farming is still widespread. Because rainforest soil loses its fertility quickly after deforestation, the most common form of subsistence farming is slash and burn. With growing populations this method of farming can cause widespread deforestation.
  • HEP (global hydroelectric power): Many of the world's great rivers flow through rainforests e.g. the Amazon. These great rivers often have the most HEP potential. Unfortunately when a dam (diga) and reservoir are built it causes damage during construction, but also floods large areas.
  • Mining: With an ever increasing demand for the world's natural resources, countries and companies are looking at increasingly isolated locations, places like rainforests and Antarctica. The rainforests are believed to have many resources including metals and fossil fuels beneath their soils. Gold mining can be particular damaging as mercury is used in its extraction and often runs off into rivers.
  • Road building: Building new roads like Trans Amazon highway from Brazil to Bolivia not only causes deforestation itself, but its also opens up new areas to urbanisation, mining and farming causing further deforestation.
  • Urban growth: With the world population increasing as well as rates of urbanisation increasing many cities like Manaus in Brazil are growing rapidly causing deforestation.
  • Population growth: As populations grow, particularly in countries like Brazil, Peru, India and Vietnam that contain rainforests the demand for land increases, both to grow food and to live).
  • Plantations: Primary products are often seen as an income source for LEDCs, many of who have large areas of rainforest. At the same time with fossil fuels running out, alternative fuels sources are been searched for including biofuels e.g. Palm oil. This has lead to widespread deforestation in countries like Malaysia and Indonesia to plant cops like palm oil.
  • Timber (legname) (hardwoods): Hardwoods like mahogany and teak that take hundreds of years to grow are still in high demand to make things like furniture. The extraction of these trees can kill trees around them. Also many countries like China are also demanding large amounts of normal timber that are not always taken from sustainable sources.
  • Hunting: Hunting takes two forms, one form is for bushmeat (carne di animali selvatici) to feed families and enough the sale of animals either alive e.g. parrots (pappagalli) or dead for their skins e.g jaguars.
/
  • Flooding: Flash (improvvise) floods become more common after deforestation because there is less interception and less root uptake and transpiration. As such rainwater reaches the ground quick, saturating it and causing surface run-off and potential flooding.
  • Landslides (frane): By removing trees and vegetation, you are making the soil less stable. Combine this with saturated ground and the likelihood (probabilità)of floods increases.
  • Biodiversity loss: Because all the species that live in the rainforest are not known it is hard to calculate species loss. However, scientists believe that 1 mammal or bird extinction can be extrapolated to approximately 23,000 extinctions.
  • Reduced photosynthesis: As more and more trees are removed the rate of photosynthesis reduces, releasing more carbon dioxide into the atmosphere and contributing to the greenhouse effect.
  • Silting (riempirsi di fango)of rivers: With increased flooding and surface run-off moil soils and silt is washed into rivers, this can not only change local ecosystems (water temperature and clarity) but can also reduce the depth of rivers making navigation harder.
  • Siltingof seas and oceans: With the increased frequency of flooding and landslides more silt gets washed into the oceans. The increased amount of silts reduces the transparency of the sea reducing the light reefs receive and the temperature of the water. Increased silt can also block important shipping lanes.
  • Breaking of nutrient cycle: The top soil of rainforests is very thin an receives the majority of its nutrients from rotting flora and fauna. Be removing trees you also remove animals and therefore the source of the soils nutrients. With increased erosion the top soil (humus) layer is quickly washed away.
  • Sandification/desertification: Because rainforest soil loses its fertility very quickly after deforestation it quickly becomes hard to grow any vegetation on it, leading to sandification and possibly desertification.
  • Loss of indigenous homes: By clearing rainforests you are obviously destroying the homes of indigenous groups. But also moving close to indigenous groups can spread disease and alter local culture and traditions.
  • Reduced rainfall: Deforestation can lead to reduction in local rainfall because less water is intercepted and transpired from vegetation into the atmosphere reducing the formation of clouds and rainfall.

Problems and changes caused to rivers and drainage basins by deforestation include: