My Science School

If trees were asked to play the hero characters in the movie called ‘Rainforest’, then pitcher plants should rightly be assigned the role of the ruthless villains! Seemingly innocent and quiet, these vicious plant carnivores cunningly set the death trap for their innocent victims.

Pitcher plants modify their leaves into a vase-like structure called ‘pitcher’ with a raised lid that prevents rain from gushing in. These brightly coloured ‘traps’ give out a pungent odour that insects find attractive. As soon as these innocent nectar seekers set their foot inside the slippery neck of the pitcher, there is no way back. The doomed insect can only watch itself slip down into the ‘deathly hallows’ that are filled with a liquid of digestive enzymes! All efforts to pull their wet bodies out of the ‘sticky situation’ go in vain and they end up as nutrient-rich ‘food’ to the plant. Large flies and other little animals also end up on these ‘plates’.

Remarkably, a few adaptive insect varieties have evolved resistance against these corrosive enzymes.

For instance, a particular pitcher variety spotted in Malaysia was found to have about 27 insect species, including mosquito larvae, happily swimming and living inside these insectivores! How cool is that!

These vegetable carnivores thrive on the forest floor and other supportive plants within the swampy peat forests of Southeast Asia, Australia, Sri Lanka, and few others.

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Climbers are plants that cling around stronger structures - rocks, soil, trees; buildings - to support their body mass and raise their leaves higher in search of sunlight.

Climbers can either be vines or lianas. Vines are mostly green-stemmed, trailing plants of a short lifespan. Examples would be the passion flower, morning glory, and few cucumber species.

Lianas, on the other hand, are longer-lived, woody varieties. Both these groups are not closely related to each other but come from different families.

As you know, trees form the basic framework of any forest. Trees are defined by their strong trunks, interlocked branches, and outstretched leafy network. Climbers use these natural scaffoldings as support structures to trail heights within and above the canopied roof.

The huge energy required to develop strong, woody trunks is thus saved and reinvested in growing leaves. It is believed that almost 90 per cent of the world’s total climber species find their origin in these rainforests. Indeed, a heaven on Earth for them!

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Tarzan, the fictional ape-man, raised in the African jungles, used the liana vines as his mode of transport. Remember the famous war-cry ‘Kreegah, Bundalo’ he makes while grabbing onto these vines and effortlessly gliding from one tree to another?

Liana vines are long-stemmed, woody plants that root in the soil. They utilize trees and other vertical structures as physical support to rise above the forest canopy for sunlight. Upon reaching the top of the overhang, these climbers extend large foliage of fast-growing shoots and leaves in all directions, filling the gaps between trees and causing unwanted shade to the plant community underneath. It might be interesting to know that a massive climber plant that was once spotted in Panama, Central America, had spanned the width and breadth of almost 65 trees!

The strong stems of the liana vines are amazingly flexible. Some of them look like looped cables, while some appear like flattened ribbons or braided threads. Animals and predators often find these structures easy ‘natural ladders’ to scale and move across the great canopy heights.

Wide tube-like channels within the stems store large amounts of water. So, if ever you get stranded inside a thick forest, and run out of drinking water, you only have to walk up to a liana vine, cut a length out of it, and quench your thirst!

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The best-known examples of epiphytes are the famous ornamental plants, the orchids. You probably might have noticed how they grow by wrapping their roots around tree trunks and other surfaces.

An epiphyte, sometimes known as an air plant, is, therefore, a plant that grows on a host plant. They are not parasitic and for that reason, do not feed by draining the nutrients from the supporting plants on which they grow. Instead, they feed on nutrient-rich air, rain, and organic waste. Since they grow and climb on other tall plants, it is easy to get sunlight.

It is calculated that there are over 30,000 varieties of epiphytes, belonging to 83 families in all, the most common types being the tropical ferns, orchids, cacti and bromeliads, and the temperate lichens and mosses.

Epiphytes add richness to the entire biomass of the ecosystem.

Certain epiphytes are miniature ecosystems of their own! The tank bromeliads, for instance. Their leaves are stiff, pointed upwards, and closely arranged, within which rainwater gets stored in large quantities. These water reservoirs not only nourish the bromeliads during droughts but also function as habitats for salamanders, frogs, insects, and larvae. Epiphytes are so abundant that certain tropical trees can have as many as 2000 epiphytes growing within them!

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Nutrient-rich soil and water availability are both crucial for the growth of plants. Harsh conditions within forest canopies often result in uneven or scarce distribution of these vital elements.

As a means of survival, epiphytes have developed commendable adaptive methods. Their physical structure, food habits, and symbiotic relationships with other organisms speak volumes of their adaptability.

Most epiphytes wrap their roots around tree trunks and absorb vitals from the atmosphere; leaves are arranged to trap falling plant debris rich in nutrients.

Orchids conserve water by growing thick stems and leaf hairs. These hairs close the stomata during dry weather, preventing water loss through transpiration.

Leaves of tank bromeliads develop a ‘tank’ like structure that stores large amounts of rainwater for long periods, forming ideal habitats for various organisms. Bromeliads get their nourishment from the excrement of these organisms making the symbiosis complete.

As for seeds, they may be present in thousands in a single epiphytic fruit. These seeds have flying structures that help them get dispersed over great distances. The Mistletoe, an aerial epiphyte, produces laxative coated berries with sticky seeds inside. This adaptation helps the fruit to easily pass down the digestive system of birds, and eventually stick on to the tail feathers when they excrete. Birds perch on distant trees, automatically placing these seeds in the right environment to grow.

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Rainforests, as we know, are home to millions of plant species. Let us begin with the tallest of them all, the trees.

A 25-acre plot of the Borneo Rainforest alone is estimated to have around seven hundred species of tree variants which is more than what can be found in the whole of the North American continent! So much for its tree diversity!

Have you ever heard of the Kapok tree? Known as the biggest of all Central and South American rainforest trees, they can astonishingly gain a height of four metres every year!

The kapok is a multi-purpose tree too! Its fruit fibre is used to stuff mattresses, seed oil to make soaps and its lightweight trunks are widely used to make canoes. So, you can literally travel, bathe and then sleep with the help of a kapok tree!

The strangler fig tree, another type, strangles its vines around other trees in search of sunlight. It is a favourite among monkeys and parrots for its sweet fruit.

The bamboos of Asian rainforests are real friends of nature. They help prevent floods by sucking up large amounts of excess rainwater! These structures can soar up to a height of 24 m and a width of 8 m in diameter and are widely used in furniture, paper, and fishing rod manufacturing.

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Have you heard of the saying, ‘eat, drink and be merry’? Imagine a few days without food, water, or shelter. Unthinkable, isn’t it? The same holds good for all plant and animal species. The wellness and survival of any living organism are largely dependent on the environment in which it lives. A favourable climate, healthy and abundant food supplies and protective shelter is very essential for the overall well-being of all species.

The abundance of warmth from the sunlight and proper humidity from wet weather together forms a very conducive climate for organic life to thrive in the rainforests.

Plants act as battery chargers for the entire ecosystem. They trap sunlight through a process called photosynthesis and convert it into energy which is stored in their leaves and other parts. When animals feed on these plants or other plant-eating animals, this stored energy gets automatically transferred and widely spread across the system.

The thick canopies of the tropical rainforests are a good hiding place from predators and also provide a wide variety of habitat choices for the different species to live and interact with. The bromeliads, for example, is a plant variety found in these canopies. Their leaves store water which is used by frogs either to lay eggs or as their ‘hunting grounds’.

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The Daintree River is a very popular natural attraction in Australia.

It flows through the heart of the mesmerizing Daintree tropical forest in the state of Queensland. This major life-giving water body originates from the slopes of the Great Dividing Mountain Ranges of the Daintree National Park, at an elevation of 1,270 metres. The path of flow of the Daintree River is noteworthy.

Water from the two minor tributaries joins into one single river body. This then courses through the highly saline mangrove swamps of Cairns Marine Park and eventually pours itself out into the Coral Sea.

It seems to crisscross almost aimlessly through the wilderness; sometimes flowing up north, then south, and then taking an eastward course. It also serves as a great habitat for aquatic life and other diverse wildlife as well.

The Daintree River, along with its surrounding wet tropics of Queensland, has been listed by the UNESCO World Heritage in recognition of its outstanding natural universal value, representing the major stages of the Earth’s evolutionary history. For this reason, the Daintree ecosystem has become a landmark of tourist significance and value.

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The Congo River in Central Africa was once known as the Zaire River. This mighty river and its surrounding dark forests have, for centuries, been synonymous with the land of pygmies, mysterious animals, untold secrets and stories of colonial violence. Joseph Conrad, in his novella of the same name, rightly calls it ‘The Heart of Darkness’.

The Congo River is unique and you should know how!

It is the world’s most powerful river and the deepest. It is also the second-longest river in Africa, spanning a length of approximately 4700 kilometres! Every second, the river mouth throws out water into the Atlantic Ocean that has an estimated volume of more than 13 Olympic-sized swimming pools!

The Congo Basin spans across nine African countries and is home to the world’s second-largest tropical rainforest. The Congo River Basin is like a beautiful canvas painting with splashes of forests, savannahs, swamps, rivers, and organic life.

The river starts to flow peacefully in the savannahs situated south of Lake Tanganyika. It gradually gains speed and volume, turning into rapid currents. After passing the canyon called ‘Gates of Hell’, the river gains its normal flow back again and then passes peacefully through the tropical forests. In the course of its journey, it crosses the equator twice. The Congo River passes through diverse terrains and landscapes, covering hundreds and hundreds of kilometres, before it drains out into the Atlantic Ocean.

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The Amazon River is undisputedly the largest and the longest of all the rivers flowing across the globe! Want to know why?

This wonder river takes its origin from the Mantaro River in Peru, and is as voluminous as eleven Mississippi Rivers put together! Another mind-boggling fact about it is that, during rainy seasons, the river mouth can be as wide as 483 km, gushing out up to 500 billion cubic feet of water per day into the Atlantic Ocean! The force of the freshwater current is so immense that it flows continuously for about 201 km out into the sea, before getting mixed with the salty seawater! That is, you could be kilometres out in the sea and yet drink freshwater from it!

As for its length, the Amazon is estimated to be around 7000 km long, crisscrossing across countries like Brazil, Peru, and Columbia. The Amazon branches out into over 1,100 tributaries; the Purus, the Jurua and the Madeira being just a few of the longest ones.

Every day, tons of suspended sediment, which make the Amazon water muddy and turbid, gets carried along with its water current. This sediment gets deposited as silt at the river mouth. The Majuro Island, the world’s largest river island, was formed by this silt deposit. It is as big as Switzerland!

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Clearwater Rivers or Bluewater rivers are bodies of clear water that are commonly found in high rocky regions, usually flowing as creeks and streams. It is rare to sight these rivers in lowland rainforests. The best-known example of a clearwater river is the Xingu River in Brazil.

Bluewater Rivers are rapid moving. The rivers gain momentum as the water falls across these elevated rocky heights, giving rise to rapid currents. The ancient rocks have eroded so much over the years that the amount of sediment deposit washed away with the current is also minimal. Hence, the river water is clear almost all the time.

Clearwater Rivers are not acidic and are rich in dissolved minerals. Plants and animals thrive well because of this high nutrient content and lesser acidic composition. Algae too, grow in abundance on these rocky masses which forms a major source of nourishment for the aquatic sucker-mouth catfish.

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Rivers that have deep brown or black-coloured water are called Blackwater Rivers. Here again, the name could be pretty much misleading. If you thought that these waters are polluted and undrinkable, you are wrong!

In fact, rainforest Blackwater Rivers are considered the clearest and cleanest of all natural river bodies. They are so clear that you can actually see the bottom of the river bed! Then why are they black?

Certain living plants produce certain toxins in their body to protect themselves from leaf-eating insects and other predators. When these plants decay or leaves fall, the toxin-rich plant debris is carried along with the river current. This decaying plant matter deposited beneath the water gives it a dirty black appearance.

Blackwaters are relatively softer in terms of water hardness but are more acidic than white-water rivers. This explains why the two tributaries of the Amazon River, the blackwaters of the Rio Negro River and the white waters of the Solimones River, do not mix when the two water channels combine. They flow next to each other, dark on one side and light on the other!

This high acidity level also makes it impossible for microbes and parasites to survive. Hence, the water is sterile and as good as distilled water. Hence, only a few plant and tree species thrive in these unfavourable forest conditions and this considerably lowers insect varieties and animal species too.

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You probably know that the human body is made up of a complex network of thousands of veins and capillaries. What do they do? They bring nutrient-rich blood to each cell and organ of the body, making it healthy and strong.

The thousand little streams, creeks, waterfalls, and lakes of the tropical rainforests function more or less the same way! Found in every nook and corner within the darkest of its interiors, these forest water resources nourish the millions of plant and animal species of the ecosystem and also form the backbone of larger water bodies such as rivers and their tributaries.

Since tropical areas receive tremendous rainfall throughout the year, some of the biggest rivers in the world are also found in these rainforest ecosystems. The world’s biggest river, the Amazon, is one such mega river that is unique in many amazing ways.

Thousands of kilometres long, experts opine that it is at least eleven times bigger than the Mississippi River and voluminous enough to meet the needs of New York City for nine years in a row!

Amazonian rivers fall into three main categories based on their chemistry, sediments and water colour. They are white water, black water and clear water rivers.

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Forests that grow on heaths are called heath forests, or kerangas. Heaths are uncultivated areas that have acidic and sandy soil. The Sundaland heath forest (also known as Kerangas forest) is one such forest, found on the Borneo Island lying between Indonesia, Brunei, and Malaysia and also, on the Belitung and Banka islands of Indonesia.

The availability of vital nutrients that is required for the normal growth of plants and other species is meagre because of this acidic soil.

Heath forests differ from lowland rainforests in terms of species composition, structure, texture, and colour. The trees are short and stunted in growth because of the difficulty in extracting essentials from the soil. However, to compensate for the loss, the trees grow a mat of roots above the soil surface and scavenge nutrients from decaying matter. The leaves are the cleverest of all! They shield themselves from the attack of leaf-eating insects by producing certain chemicals. Insects don’t find this tasty at all!

Heath forests are characterized by these short and slender trunked trees which form a low, uniform forest canopy. Vegetation that can nourish their growth from the available minimal source of soil nutrients are able to survive here. The under-brush beneath the canopy is therefore, thick and abundant with moss, epiphytes and a few other plant types.

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The white-water rivers have a highly deceiving name. A first-time visitor could walk up to the river to quench his thirst only to realize that the ‘white-water’ is actually murky and muddy!

What could be the reason?

The water in these rivers flow great distances from their origin and pass through myriads of landscapes like mountains, riverbanks, rocks, and plains Tons of heavy sediment also get carried along with these water currents. Heavy rains and deforestation increase the amount of soil and sediment that get washed away. This is why they have a ‘cafe-au-lait’ (coffee in hot milk) appearance.

These white waters are soft in terms of water hardness and slightly acidic. The softness is because of the low mineral content and acidity because of a pH level just below 7. The best known whitewater rivers are Amazonian.

An aquatic variety that thrives well in this water environment is the river dolphin. River dolphins have poor eyesight. But they can easily navigate and hunt through the muddy waters using their sound navigation and ranging (sonar) skills. These human-friendly creatures are mostly found in large, open river channels and sometimes, deep inside such whitewater rivers.

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