If you’ve looked at the sheet on the living world you’ll now be well versed on biomes. Now we’re going to look at one in more detail: the rainforest.
The tropical rainforest ecosystem is located in a band either side of the equator. This means that it is hot throughout the year, with temperatures ranging between 25 and 30oC. There is also a massive level of precipitation, usually between 2000 and 3000mm each year. Most afternoons experience a heavy downpour, which helps to keep the rainforest moist.
Rainforest soils are called latasols. They have a very thick litter layer, which decomposes rapidly in the hot, moist conditions to create thick humus, full of nutrients. This produces a soil, which acts as if it is very fertile. However that is not actually the case and if the vegetation is removed the soil rapidly becomes very infertile. Rapid leaching occurs to remove minerals and nutrients from the humus layer.
The vegetation of tropical rainforests can be divided into five simple layers, from the canopy to the forest floor, where you will see distinctive types of vegetation. The top layer is called the emergent layer. This is where a few of the largest trees have managed to grow higher than the main canopy to try to capture as much light and rainwater as possible. Examples include mahogany trees. Birds and insects would be expected to be seen in this layer.
The canopy layer is the layer at approximately 30m created by the many tall trees of the rainforest. The canopy virtually blocks out all the light for the vegetation below and is the home for birds and monkeys. The under canopy is the layer between 10 and 20 metres where there are few trees, but mainly lianas and other vines which hang down from the taller trees that they are using to climb up to the light.
The shrub layer is the fourth rainforest layer. These plants are between 5 and 10m in height and consist of small trees and other plants waiting for a tree fall to create a gap in the canopy to allow them the light to grow. The forest floor is the final layer, where there are ferns and other plants as well as the massive tree roots.
The main factor in the rainforest vegetation is the fight for light. Thus when a tree falls, creating a gap in the canopy, there are a number of fast growing species that will rapidly grow to try to capture all the available light.
Most of the tall trees have wide shallow roots, as the majority of the water and nutrients are found in the very top layer of the soil.
To prevent them from toppling over most of the tall trees have grown large buttress roots, which act to gather as much water infiltrating into the ground as possible by spreading out before they even reach the ground.
Rainforest trees have straight trunks, with their leaves and branches concentrated right at the top to trap available light.
So there was a whole load of information on the rainforest, and if you’ve never been it’s a pretty awesome place!
However, it’s not all fun and games in the rainforest, and this is sadly down to humans.
Tropical rainforests have a lot of human uses, which have in the past often been very damaging to the ecosystem. These include logging (as most rainforest trees are valuable hardwoods), ranching (clearance of vegetation for cattle ranching), damming (flooding areas to provide power for industries), and mining (often rainforest areas are extremely rich in minerals).
Forest clearance can have several negative impacts on a variety of scales, especially in tropical rainforests. This includes the loss of nutrients from the nutrient cycle, an increase in greenhouse gases in the atmosphere, and damaging effects to biodiversity.
Forest clearance also has a negative impact on the nutrient cycle. Normally, the vegetation will input most of the nutrients (which are then re-used). Leaves that have fallen will then quickly decompose in a hot and humid climate, creating a deep and nutrient-rich humus layer. However, without the input of nutrients that follows after clearing, the soil soon loses the nutrients through runoff and leaching.
This is all without mentioning the negative impact clearing is having on the atmosphere. Trees absorb carbon dioxide and store it as carbohydrate, ready for animals to consume. By chopping down large areas of both the rainforests and deciduous woodlands, less carbon dioxide can be absorbed, thus there is more in the atmosphere.
However, the areas are also used for subsistence farming by indigenous tribes and so these come into conflict with companies destroying rainforest areas. Therefore, rainforest areas are now often the focus of sustainable development schemes.
In fact woodlands and forests throughout the world are under threat from being cut down for a variety of reasons. Therefore management is becoming increasingly important. Well managed forests are managed in a sustainable way; a system known as silviculture.
This means that the forests are used, but in a way which does not affect their long-term growth. Workers carefully harvest the trees and their resources. The trees that have been harvested may then be replaced by more than one new tree. It is all too easy for governments to allow their forests to be exploited to gain foreign cash but if the exploitation is unsustainable then the country will ultimately run out of this resource.
It is therefore essential that the governments of the countries where there are still large areas of forest be persuaded not to allow them to be cut down.