Tropical Rainforests Ecosystem

Antonia Blankenberg
Note by , created almost 2 years ago

The next in our series of study notes on ecosystems looks at Tropical Rainforests, and in particular focuses on causes and effects of deforestation.

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Antonia Blankenberg
Created by Antonia Blankenberg almost 2 years ago
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Page 1

Distribution and Characteristics

Tropical rainforests take up approximately 7% of the Earth's land surface.   The main areas of tropical rainforest are the Amazon Basin, Central Africa, and South East Asia.   The Amazon Rainforest is the largest rainforest in the world.

Climate: The location of rainforests near the equator means that the climate is warm and wet.  Annual average temperatures are around 26 degrees; this temperature shows little variation throughout the year. High temperatures allow for more water vapour to be held in the air.  Rainforests receive high amounts of precipitation. Annual rainfall usually exceeds 2,500mm. Up to 50% of rainfall over tropical rainforests comes from its own evapotransiration. Plants and animals in the rainforest have adapted to these climate conditions. The trees in the canopy have small leaves to prevent water loss through transpiration. Many plants on the forest floor adapt to the low levels of sunlight that reach the floor.    Vegetation:  Tropical rainforests have very rich and diverse vegetation cover. Trees often fight to be the tallest as sunlight is sparse below the canopy. The largest trees have buttress roots to support their height. Plants adapt to the humidity by circulating water as a cooling system. There are very few limiting factors to species in the tropical rainforest, this brings the high amount of biodiversity.   Soils: Rainforest soils are usually thin and of poor quality. The nutrient cycle of the rainforest is what provides plants with nutrients due to the poor quality of soils. Most of the forest's nutrients are locked up in the biomass and plant litter. Heavy rains usually wash nutrients from the soil. This creates a hardpan deep in the soil which cannot be accessed by plants. 

Page 2

Value of the Rainforest to Humans

Tropical rainforests bring a huge variety of goods and services to the planet.    Medicines: Tropical plants have a large variation of medicinal properties which are commonly used by rainforest tribes. Recent developments in medicine have discovered the use of many rainforest plants; over 120 prescription drugs worldwide come from plants and up to 25% of medicines have rainforest plants in them.  Quinine, which is a cure for malaria, comes from the bark of the chinchona tree, and is found in South America and Africa. The chemical structure of rainforest plants is often used as a template for new medicines. For example, the blueprint for aspirin comes from the willow tree.  Madagascan rosy periwinkle has properties that cure Hodgkin's disease.   Food production: The forest provides a number of unique foods that are in demand worldwide. Bananas, coffee, and black pepper are examples of this. Palm oil is a product used in most manufactured food worldwide and derives from rainforests.   Timber and Minerals: Rainforests are often cut down for mahogany and teak extraction, particularly for use in the US and UK. Local people use timber from the rainforest for building and for fires. The Amazon rainforest in particular has a large store of gold.    Recreational Services and Tourism: River boat rides are popular with tourists as roads around the rainforest are poor. Nature trails are a common way of seeing the forest floor. These are often run by trained guides. White-water rafting is popular on the rivers that flow through the rainforest.    Environmental Protection: The plants of the rainforest are a huge carbon dioxide sink and are important for the purification of air. The rivers of the rainforest can provide hydroelectric power. The trees of the rainforest protect the poor soils from soil erosion. Without the vegetation cover, many of these soils will wash away due to heavy rainfall. Tropical rainforests have high levels of biodiversity and hold many endangered species.

Page 3

Causes of Deforestation

Deforestation is the biggest threat to rainforest ecosystems, clearing the rainforest at up to 1 hectare per second and an area the size of Poland every year.   Logging: Logging is usually the first step in clearing rainforest land for other purposes.  Selective logging is the selection of more valuable trees such as mahogany and teakwood with the purpose of reselling for the manufacture of furniture. Clear felling is the clearing of vast areas of forest in one go. Much of the clearing of the land is done using the slash and burn technique.   Mineral Extraction: Gold is a valuable commodity mined in the Amazon rainforest. In 1999, 10,000 hectacres were being mined. Today this figure is above 50,000. Bauxite, used in aluminium production is another common rainforest mineral.   Energy Development: The building of dams for hydroelectric power floods vast areas of rainforest.    Agriculture: Huge areas of land are cleared for cattle ranching and palm oil production in particular. Cattle ranching is believed to account for 80% of deforestation in Brazil. Cattle ranching quickly degrades the landscape, this means that more land is regularly cleared. Poor rainforest soils cannot support crops for long and are usually left empty after more land is cleared.   Infrastructure: Road building and population growth account for about 2% of forest clearance. The Trans-Amazonian Highway was built in 1972 and runs directly through the Amazon rainforest.

Page 4

Effects of Deforestation

The effects of deforestation can be split into local impacts and global impacts. Local impacts include soil erosion, river pollution, decline of indigenous tribes, and conflicts. On a larger scale, deforestation contributes to biodiversity loss and climate change.   Climate Change: Rainforests are a sink for carbon dioxide. Without these trees, carbon dioxide in the atmosphere is not absorbed. This contributes to the growing amount of carbon dioxide in the atmosphere and the greenhouse effect. Slash and burn deforestation releases the stored carbon dioxide from the trees into the atmosphere also.  On a local scale, deforestation disrupts the water cycle, reducing evapotranspiration and making the local climate warmer and drier.    Biodiversity Loss: Deforestation reduces the amount of global biodiversity. Species will become endangered and extinct, including many of the plants used in medicine today, and many more undiscovered species.    Soil Erosion: Once vegetation is cleared, heavy rainfall will quickly remove the topsoil. Once this is removed, nothing will grow in this area again. Soil erosion is common on bare slopes, this can contribute to the silting up of river courses and flooding. High amounts of plant litter gave the soil its little fertility, when they are removed, the soil becomes infertile and unusable.   River Pollution: Agricultural fertilisers and pesticides can be washed into local rivers due to the heavy rainfall.  The mercury that is used to separate gold from the ground is a harsh poison that can kill fish. The additional soil added to rivers because of soil erosion also plays a part in harming aquatic biota (wildlife).   Decline of Indigenous Tribes: Approximately 1 million people live in the Amazon rainforest, but this number is steadily declining. The number of rainforest tribes has been reduced to 240; this figure was 330 in 1900. Deforestation is removing the home of new tribes and even some of the measures to manage deforestation section off the land, restricting it from the tribes. Many displaced tribes have to move to larger cities and adapt to brand new lifestyles.   Conflicts: Disputes can be caused between tribes and loggers. Disputes more commonly arise between conservationists and large logging companies.        

Page 5

Management of Rainforests

Management of tropical rainforests is undertaken by actors at many different levels. This management has varying levels of effectiveness in different locations. Sustainable management means using goods and services in a way that they are still available to future generations.    International Level: Debt Reduction Many of the countries that contain tropical rainforests are in the Global South. This means that they have low income. Many of these countries are indebted to richer countries because of loans and international aid.  These countries often overexploit their resources, such as the rainforest, to attempt to pay back this money. Debt reduction programs have become more popular in recent years in an attempt to conserve the rainforest. In 2010, the USA signed an agreement to convert the Brazilian debt of $13.5 million to a fund to protect the Amazon.    International Level: NGO Programmes Non-governmental organisations such as the WWF rely on volunteers and donations to promote conservation and education. They often buy up areas of forest to create nature reserves. They provide practical help to make programmes more sustainable.   National Governments: Governments can pass laws to create protected areas and increase education about sustainability. However, few governments are willing to do this due to the slow rate of economic development. There is often a lot of corruption when it comes to rainforest management; there are a large number of illegal loggers and bribes placed around logging.   Local Level: Logging Practices Satellites and drones can be introduce to find and stop illegal logging that usually goes unnoticed. Selective logging involves the cutting down the trees only when they are fully grown. This lets smaller trees continue to grow.  Selective logging can help to prevent soil erosion and ensures that the forest does not run out. Agroforestry follows a practice where only small areas are logged at a time. The cleared areas of forest are used to combine forestry and agriculture in a way that does not degrade the soil. Replanting projects are also in place in Brazil.    Local Level: Ecotourism Ecotourism promotes the scenery and wildlife of the rainforest to tourists. The goals of ecotourism are to be sustainable and to educate those who visit. There are many eco-lodges in the Amazon, these are small scale lodges that run on little to no energy and blend in with the scenery. They contrast large hotels that require large areas of land to be cleared. Ecotourist establishments are mostly run by local communities; it provides employment and income, which helps to prevent people turning to logging activities for money.