The Tropical Equatorial Rainforest

Tropical Equatorial Rainforest

Tropical equatorial rainforests (TER) lie within the tropic of Cancer and Capricorn, for example the Amazon and the Gabon rainforest. They are the most productive ecosystem and rely on insolation, moisture and nutrients to develop. Several vegetation layers (stratification) characterise the TER as well as the tropical climate, latosol soil and a diverse range of animal species.

Soil ::

In an undistrubed biome, the underlying soil will have developed naturally over a long period of time and be in balance with its natural environment. It is a mature soil and its characteristics strongly reflect the climate and vegetation.

A latosol is a zonal soil type associated with the TER. Ferralitisation may occur here which is a process by which bedrock is broken down into clay minerals by chemical weathering. 

The top of the latosol shows a thick humus layer made up of decaying leaves and animals. Nutrients for vegetation come from here thus vegetation has shallow roots. As break down continues a humus layer is created. Many active biota can be found here such as ants and worms.

Eluviation or leaching is common due to the high amount of rainfall and percolation. Mainly the leaching is of silica and dissolved salts. There is a build up of iron and aluminium oxides thus turning the soil red in colour. As silica becomes left behind a yellow tone will be given tot he soil.

Soil begins to get more clay-like further down the horizons. The parent material lies at the bottom where ferralitisation occurs.

Vegetation ::

The emergent layer is the top layer with trees around 30-40m high such as Mahogany and Ebony. The trunks are thin to allow for movement in harsh winds. Evaporation is rapid here since these trees have the most contact with the sun, to cope with this, the trees here have non-drip tip leaves so to retain water instead of lose it. There is nearly continuous cover here and since there is a year round growing season, an evergreen appearance is given to the rainforest. 

The canopy layer is the most productive and absorbs 25% of the available energy. There is a thin nutrient layer in rainforest soil and so deep roots are not required. Therefore buttress roots help to stabilise the tall and slender trees. The trees have huge crowns so to absorb as much sunlight as possible via a larger surface area. Leaves can often become saturated here so leaves have developed drip tip leaves to shed water quickly and efficiently.

The under canopy is where less substantial trees are found that are taller than the shrub layer and are far more tolerant of the shade than those above them. The vegetation here only gets a glimpse of sun and often has interlocking spindly branches that allow lightweight animals to travel along them,. The growth of under storey trees is restricted to several metres below the base of the canopy and so a prominent gap can be seen. 

The shrub layer is made up of woody plants and young trees. The lower layers receive around 10% of the available energy and 1% sunlight thus there is little shrub and forest floor vegetation. However ferns and Pygmy trees may be present. There is a layer of rotting leaves and dead animals called litter. This decomposes quickly (within 6 weeks) due to the humidity. Fungi and decomposers therefore thrive here and create a humus layer that is rich in nutrients. Down here the buttress roots themselves can be seen.

Climate ::

The rainforest has a low dijurnal temperature range. The average temperature being 28 degrees celcius daily falling to around 22 degrees celcius at night. Overlying clouds restrict temperatures to around 32 degrees celcious. Rain falls all year round at the equator becuase of the inter-tropical convergence zone (ITCZ) which dominates the conditions. The ITCZ consists of the NE and SE trade winds which meet and force winds to be uplifted at the equator. Evapotranspiration is rapid die to humid conditions and low pressure above the rainforest. This allows air to be uplifted rapidly and large cumulonimbus clouds form from the condensation. Cumulonimbus clouds are the biggest rain clouds and allow for heavy rainfall.

Vegetation and Animal adaptations ::

A tropical equatorial rainforest, such as the Amazon in Brazil, is home to more than 80% of the world’s population of insects as well as hundreds of species of fauna. Some examples include the Crab spider, Orangutan, Gliding Leaf frog and the Colugo. Their moist and humid climates also contain 750 different species of vegetation per hectare; some examples of flora include pitcher plants, fig trees and orchids.

Each of the above examples has adapted amazingly to life in the jungle. 

Crab spiders and pitcher plants have a symbiotic relationship, in which the crab spider feeds off the

pitcher plant’s own prey and still leaves enough nutrients for the plant itself. The pitcher plant has acclimatised to live within infertile soil conditions by arranging a snare. Its flower has a sticky surface to catch passing insects that are attracted to its brightly coloured petals.  The enzymes within the water-filled pitcher digest trapped insects. The crab spider, having adapted the ability to enter and leave the pitcher via its silk thread, can feed off the dying insects also without taking the whole of the available nutrients provided.

Orchids are epiphytes and grow off the surrounding trees of the rainforest. They have a non-parasitic relationship with their host and intend only to survive with assistance from their host. When the epiphytes are higher up, there is more energy available from the sun and they are more likely to flourish compared to if they were on the forest floor.

Some fungi have a parasitic relationship with their host, for example cordyceps. These deadly fungi grow within a host insect, maybe an ant or and prevent a species from becoming too dominant. They drug the insect from within and control their brain. With an ant, the cordycep forces it to climb high where it shall die attached to a vine of a tree. Spores then grow out of the corpse’s head which help to spread the cordyceps' ability to infect other insects.

Fig trees fruit all year round within the tropical rainforest; they are feeding ground for many species of monkey such as the spider monkey and gibbon. They often have buttress roots to stabilise them since the soil in a rainforest is often lacking sufficient nutrients and so buttress roots help to extend the area over which a tree can absorb nutrients from. 

Pictures sourced from ::

buzzle.com

latosols-rendzinas.wikispaces.com

warrenphotographic.co.uk

carnivorous--plants.com

gorgeouswall.com

tnhsprgteam.blogspot.co.uk