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Discovering Tropical Rainforests

Forests in the tropics can be considered ‘biodiversity hotspots’.  As well as supporting a vast array of vegetation, they provide shelter and nourishment for a wealth of wildlife.   Depending on the area of land covered, forests can even affect the local and regional climate – cooling and refreshing the tropical atmosphere.

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Rainforests have a clearly identifiable structure – and each vertical layer has a distinctly different type of vegetation and wildlife associated with it.  The ‘bushy’ leafy tree level of the forest is known as the ‘canopy’.  This is where birds and primates predominantly live.  Occasionally huge trees pierce through the canopy, extending towards the sunlight; and these occupy the ‘emergent layer’.

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In the understory layer beneath the canopy there are smaller trees such as tree ferns and lianas, which are long-stemmed, climbing woody vines. Lianas use the tree trunks for support as they climb to reach the sunlight they need to survive. They coil around and between the trees and often appear to hang like long ropes.

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Other tropical plants can actually strangle the host tree, taking over their trunks until eventually the tree dies.  Indonesia has some spectacular banyan fig trees that have even enveloped not only trees; but entire buildings with their dramatic ‘aerial prop roots.’

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But other plants live on trees too – such as flowering orchids, which are ‘epiphytes’.  These plants simply use the trees for support and to receive more sunlight away from the forest floor.  They do not sap the trees of nutrients and can often be found in indentations in the big gnarly trunks where pools of water gather.

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At ground level it is much cooler and darker and this area is home to a multitude of insects, invertebrates, reptiles and amphibians.  Due to the bushy canopy, little sunlight gets to the forest floor and there is great competition between plants for sunlight.  At ground level there are lots of shade-loving ferns and fungi.   Beautiful seed cases and petals drift down to the forest floor from the canopy.  

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Also at ground level there are some rather incredible tree trunks and root systems.  To support the huge tropical trees, many trunks have ‘buttress roots’ jutting out in different directions.  Tropical root systems can be both above and below ground.

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When trees fall to the ground, they leave a gap for sunlight to come flooding down to the forest floor.  

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This area quickly becomes popular with insects such as butterflies wanting to warm their wings; and any fruit and seeds that have fallen can begin to germinate into saplings.

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The forest floor is covered with a thick leaf litter from the continual fall of leaves and this makes the soils rich and fertile.  However, this is exactly why – following tropical deforestation – the newly exposed land becomes too poor for agriculture in just a few years.  Without the continual fall of leaf litter, the nutrients within the soils are quickly exhausted.  So once a rainforest has gone, sadly it has gone forever.  The complex structure that supports such a rich biodiversity cannot be replanted or replicated.

Written by Sarah Rees

Environmental Scientist, presenter and keen wildlife photographer; Sarah is also a Fellow of the Royal Geographical Society. With a background in television production, she launched her online Forestwatch videos to celebrate the diversity of woodland wildlife and ancient trees.

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