The tropical r ainforest is a unique biome with a constant temperature and a high rainfall. The level of humidity and denseness of the vegetation give the ecosystem a unique water and nutrient cycle. Rainforests around the world are threatened by the expansion of man.
In general, tropical rainforests have hot and humid climates, where it rains virtually everyday. At some parts of the year the rainfall is extremely heavy, while in other parts of the year it will rain a lot less. Temperatures vary through the year - but much less than the rainfall. The graphic shows average rainfall and temperature in Manaus, Brazil, in the Amazon rainforest. Total rainfall is 2104mm per year, most of it during the rainy season 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 November with less than 50mm. Meanwhile the temperature only varies by 2°C.
The shrub layer is at ground level in a tropical forest. It is dark and gloomy with very little vegetation between the trees. During heavier rainfalls this area can get flooded. The Under canopy is the second level up. There is limited sunlight. Saplings wait here for larger plants and trees to die, leaving a gap in the canopy into which they can grow. Woody climbers called lianas av oid having to wait for gaps by rooting in the ground and climbing up trees to get to the sunlight. The Canopy is where the upper parts of most of the trees are found. The canopy is typically about 65 to 130 feet (20 to 40 metres) tall. This leafy environment is full of life such as insects, arachnids, birds and some mammals. Emergents are the tops of the tallest trees in the rainforest. These are much higher, and give the trees an advantage (in terms of light) than the average trees that populate the forest canopy.
Vegetation in the rainforest has evolved characteristics which help it survive in this unique environment. Here are some examples:- Fan Palms Fan palms have large, fan-shaped leaves that are good for catching sunshine and water. The leaves are segmented, which allows excess water to drain away.
Buttress Roots Rainforests have a shallow layer of fertile soil, so trees only need shallow roots to reach the nutrients. However shallow roots aren't great for supporting huge rainforest trees, so many tropical trees have developed huge buttress roots . These stretch from the ground to two meters or more up the trunk, which help anchor the tree to the ground.
Lianas Lianas are woody vines that start at ground level, and use trees to climb up the canopy where they will spread from tree to tree to get as much light as possible.
Strangler Figs Strangler figs start at the top and work down. The seed is dropped in a nook at the top of a tree where it starts to grow, using the debris collected there. 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, the aerial roots will criss-cross the trunk and start to strangle. Meanwhile the figs branches will grow taller, dominating the sunlight, while invasive roots rob the host of nutrients. Eventually the host will die and decompose leaving the hollow, but sturdy trunk of the strangler fig.
Rainforest water and nutrient cycles Rainforest ecosystems are characterised by heavy convectional rainfall , high humidity and lushness of vegetation, and nutrient-rich but shallow soil. These factors give rise to a unique water cycle and nutrient cycle .
<ul><ul><ul><li>Rainforest water cycle </li></ul></ul></ul><ul><li>The rainforest climate is very humid. The vegetation is very lush as water is taken up by the roots and rain is intercepted as it falls - much of it at the canopy level. The next day, as the rainforest heats up, the water given off by the plants and trees evaporates into the atmosphere - where it forms into clouds to make the next day's rain. This is called convectional rainfall. </li></ul>
<ul><ul><ul><li>Rainforest nutrient cycle </li></ul></ul></ul><ul><li>Plenty of dead plant material and the hot, damp conditions on the forest floor allow rapid decomposition. This provides plentiful nutrients that are easily absorbed by plant roots. But because these nutrients are in very high demand from the rainforest's many fast-growing plants, they do not remain in the soil long, and remain close to the surface of the soil. </li></ul><ul><li>This means that if the rainforest is cleared for agriculture it will not make very good farm land as the soil is not rich in nutrients. Also once the trees (with their roots) are removed the soil can be easily washed away. </li></ul>
Humans intervene in tropical rainforests in order to bring real or imagined benefits to themselves or the local population. The short-term benefits of clearing rainforest areas usually include: · land for agriculture, houses and roads · jobs for local workers in road building, logging agriculture, extractive mining, building etc · The generation of income (often in valuable foreign currency) for the LEDC where the rainforest is located, when wood, minerals, and other resources are sold. · Scientific investigation into the rainforest plants may provide new food sources and medicines. These benefits, however, come at a heavy cost. Clearing rainforest threatens the survival of many plant and animal species and can lead to serious environmental degradation. Widespread deforestation damages the whole biosphere - the balance of living and non-living things on planet Earth - with serious long-term consequences for humans.
Positive impacts of human intervention · Improving transportation by building roads and airports provides jobs and benefits local people who use the roads. · Transportation improves access to raw materials like minerals and timber. Rainforest resources can be transported away and sold. · Profits from selling resources can be used to bring more development to a relatively poor country. For example, the tax a country raises from the sale of rainforest resources can be used to build schools and hospitals. · Selling raw materials , f or example tropical hardwoods such as ebony and mahogany, are valuable resources that can be sold for a good price abroad, bringing in foreign currency. People in MEDC's such as those in Europe and North America use hardwoods for garden furniture and hardwood flooring, for example. · Mineral deposits in the Amazon include bauxite (the main constituent of aluminium), iron ore, manganese, gold, silver and diamonds. Minerals can be sold with profits benefiting the LEDCs. · Infrastructure , hospitals and education can be improved from the money gained from selling natural resources. · Large-scale farming is another important way to bring money into a poor country, and to provide food for the country's growing population. Large-scale farming also employs local workers. · Small-scale farming is important for providing food for rainforest communities and landless poor of Brazil. Often these people have been displace from land in other parts of the country and have no other land to live on to produce the food they need to survive.
Problems of human intervention · Roads divide up parts of the rainforest and can cut off connections between different biotic and abiotic systems. For example, a road can stop monkeys such as the Golden Lion Tamarin from travelling to gather food and, in turn, distribute seeds to re-sow plants in the forest. · Land clearance for farming, transportation and mining can lead to deforestation . Hardwood trees take many years to grow, so can be difficult to replace. · Farming is estimated to be responsible for 25 percent of the Amazon forest being cleared. · Fertile soils that make farming possible are quickly washed away when the forest is cleared for farming, mining or transportation. · Loss of animal habitat occurs when trees are cut down and animals that live in them have to find somewhere else to live. Hence, deforestation can result in endangering animals and plant life, or even causing them to become extinct. · Profits from large-scale farming and selling resources often go back to MEDCs or large companies and don't benefit rainforest communities.