Rainforests are incredibly biodiverse ecosystems that are mostly populated with evergreen trees and receive abundant amounts of rainfall. They can be found in all of the world’s continents, save for Antarctica. Tropical rainforests are also our planet’s oldest ecosystems, some have even existed the same as their present form for at least 70 million years. Although they only make up 6% of the Earth’s surface, they are inhabited by more than half of the world’s plant and animal species.
The largest rainforests on our planet are located near the Amazon River in South America, and the Congo River in Africa. They can also be found in the islands of Southeast Asia and some parts of Australia. Temperate rainforests exist in the forms of evergreen forests, such as those in North America and Europe.
Why “rain” forests
Rainforests have earned this name because they are partly self-watering. Through the process of transpiration, the many plants in the rainforest release water into the atmosphere. This moisture contributes in creating the thick, almost ever-present, cloud cover that floats atop rainforests. These clouds keep rainforests warm and humid, even without the advent of rain.
Types of Rainforests
Rainforests can be classified according to two types: tropical rainforests and temperate rainforests.
As the name suggests, tropical rainforests are found in the tropics. More specifically, they lie between the latitudes of 25.5°N (The Tropic of Cancer) and 23.5°S (The Tropic of Capricorn). Tropical rainforests are located in Southeast Asia, western India, Australia, western and central Africa, Central and South America, and New Guinea.
The tropics are particularly hot and humid environments, in large thanks to the amount of sunlight that hits it almost directly. Temperatures usually stay within the range of 21 to 30 degrees celsius. These high temperatures also keep the air hot and humid. The average humidity within these regions range between 77% to 88%. The tropics experience high and frequent amounts of rainfall, ranging between 200-1000 centimetres in a year. Tropical rainforests are so abundant in moisture that up to 75% of their rain is produced by their own transpiration and evaporation.
Tropical rainforests are the planet’s most biodiverse terrestrial ecosystems. A prime example is the Amazon rainforest. As the Earth’s largest tropical rainforest, it houses a plethora of the world’s species. An estimate of 40,000 plant species, 427 species of mammal, 1,300 bird species, 3,000 species of fish, and 2.5 million distinct insect species call this rainforest home.
Located in the mid-latitudes or temperate zones, temperate rainforests thrive where temperatures are not as hot as the tropics. Temperate rainforests are much cooler than tropical ones, with average temperatures ranging between 10°C and 21°C. They receive significantly less sunlight and rainfall. In a year, a temperate rainforest may receive only 150-200 centimetres of rain.
Temperate rainforests are often found near coastal and mountainous areas. These areas make high amounts of rainfall possible. However this is still considerably less than the rainfall received by tropical rainforests. Rainfall in temperate rainforests is created by nearby mountains capturing warm, moisture filled air moving in from the coast.
Although they are not as biologically diverse as their tropical counterparts, temperate rainforests still have immense amounts of biological productivity. Cooler temperatures and more stable climate contribute to the reduced decomposition rate and the amassing of more biological material. This also allows many species of plants, such as redwood trees, to grow for extensive periods of time.
Temperate rainforests can store up to 500-2000 metric tonnes of wood, leaves, and other organic matter per hectare. For example, the North American Pacific Northwest’s old-growth forests produce biomass three times the amount of tropical rainforests.
Temperate rainforests can be located in the United Kingdom, the coasts of the Pacific Northwest in North America, Japan, Chile, Norway, southern Australia, and New Zealand.
Tropical Rainforest Structure
Rainforests are typically structured into four important layers: emergent, upper canopy or simply canopy, understory, and forest floor. Each layer has its own distinct characteristics that depend on variations in sunlight, air circulation, and water levels. Although each layer has a unique mix of these abiotic factors, they all belong to an interdependent system. This means that the different processes and species present in one layer can affect the others.
The emergent layer is the top layer of the rainforest. Trees grow far apart and rise as tall as 60 metres, reaching far beyond the trees of the canopy. Due to the intense amounts of sunlight, these plants are meant to thrive in dry conditions. The foliage is sparse on their trunks, but greatly expands in the upper layer, where they absorb and photosynthesise sunlight. In order to avoid losing water during the drier seasons, their leaves are small and waxy. The trees in this layer rely on the wind to promulgate their lightweight seeds.
Animals that live in this layer usually move about by means of flight or gliding. In the example of the Amazon rainforest, such animals include bats, birds, gliders, and butterflies. The emergent layer’s apex predators include large raptors such as eagles and hawks. Animals that can’t fly are commonly small in size, as their weight needs to be light enough for the thinner upper branches to support them.
Notably, bats are the most diverse mammal species found in tropical rainforests. These animals fly between the three upper layers of the rainforest.
The upper canopy, or simply canopy, is the second highest layer in the rainforest. Trees and other plants that belong to this layer reach a height of 30-45 metres tall. Unlike the emergent layer, the canopy is rich in vegetation, all in all roughly amassing to a thickness of 6 metres. The canopy acts as a roof above the rainforest. Its dense network of leaves block out sunlight, rainfall, and wind.
This keeps the rainforest below dark and humid. The trees in this damp environment have evolved to have glossy leaves that repel water. With the absence of wind, trees in the canopy layer keep their seeds in their fruit. Animals would eat the sweet fruit and later deposit the seeds on the forest floor through their droppings.
Aside from housing the majority of the rainforest’s plant species, the canopy layer is also home to most of its animal species as well. Animals enjoy the canopy’s great abundance of food. In order to pierce through the muffling veil of the canopy’s leaves, different animals have adapted to using raucous, repetitive calls. Reptiles feast on the canopy’s thousands of insect species. Some creatures that live in the canopy never set foot on the forest floor.
Resting several metres under the canopy, the understory is a layer darker, stiller, and even more humid than the layer above. The understory is more open than the canopy, most of its dense vegetation lies beside rivers and areas where sunlight can peek through. Shorter plants with large leaves, such as palms and philodendrons, have adapted to these low-light conditions.
The large surface areas of their leaves allow them to catch the minimal sunlight that seeps through the canopy. The plants of this layer make their flowers eye-catching and attention-grabbing. Flowers are large and are clearly visible, and some even produce strong aromas to entice pollinators.
The many animal species that live in the understory take advantage of its dimly lit environment through camouflage. Many species have developed specific patterns, colours, and markings on their bodies that allow them to blend in with the rainforest’s surroundings. An example of this is the jaguar, which has spots that its prey could confuse to be leaves or specks of light. In the Congo, the green mamba is nearly indistinguishable from the surrounding foliage.
Other animals prefer the understory for other reasons. Amphibians like the vibrantly colorful tree frogs are kept moist by the understory layer’s humidity. Flying animals such as birds, bats, and insects maximise the additional airspace the understory has to offer.
The forest floor is where the rainforest is at its darkest. The lack of sunlight makes it very difficult for plants to grow. The forest floor is littered with fallen leaves, dead animals, and other decaying organic material. Decomposers are surrounded by an opulence of dead organic matter and flourish in these conditions. They quickly break down the rotting material from the upper layers into nutrients. In around 6 weeks, they will have created a thin layer of humus rich in nutrients. The shallow roots of rainforest trees and other flora absorb these nutrients from the rich soil below.
When a tree falls, an opening is created in the canopy above, and light shines through. The forest floor teems with competition, young plants quickly race to grow and take advantage of the sunlight. After some time, these plants will fill in the gap left by the fallen tree.
Decomposers such as insects are consumed by animals that roam the forest floor. Anteaters, armadillos, and wild pigs scrounge the decomposing brush for these critters. In turn, these animals will be prey to larger predators such as big cats.
Benefits of Rainforaests
The rainforests’ incredible amounts of biodiversity are essential to both human well-being and the well-being of the environment. Rainforests play critical roles in regulating climate and providing us with products necessary for our daily lives.
Rainforests are critical components and contributors to the well-being of our planet. All 1.2 billion hectares of the world’s rainforests are essential in maintaining many biotic and abiotic processes necessary for all forms of life.
Among its benefits to the world’s ecological well-being is its management of the Earth’s climate. Around 20% of the world’s oxygen is produced by rainforests. Additionally, rainforests also trap and store great amounts of carbon dioxide, reducing the impact of greenhouse gases. Rainforests also regulate the world’s temperature by absorbing tremendous amounts of solar energy.
Rainforests are also major proponents in the maintenance of the world’s water cycle. Rainforests receive a substantial amount of precipitation, and more than 50% of this water is returned to the atmosphere through evaporation and transpiration.
As previously mentioned, rainforests also house a great number of the world’s species. As centers of biodiversity, rainforests play a key role in allowing innumerable plant and animal species to thrive. Many species are yet to be discovered, catalogued, and some species are still in need of further study.
Rainforests also provide us humans with various natural resources, their products and applications. Lumber obtained from tropical wood such as teak, rosewood, mahogany, and balsa are widely used in the construction of houses. Bamboo, raffia, kapok, rattan, and other fibers are used in the making of furniture, weaving, insulation, and making ropes and cords. Many of the food products we consume originate from rainforests. A few examples are spices such as cinnamon, vanilla, ginger, and nutmeg, fruits such as bananas, mangoes, papayas, as well as cocoa and coffee beans.
Throughout the years, many plants in the rainforest have been discovered to have medicinal properties. A quarter of all natural medicines were originally found in rainforests. Rainforest plants are currently invaluable to the field of cancer treatment and cancer research. 70% of the plants deemed effective treatments against cancer had been discovered in rainforests.
Other medicinal applications of rainforest plants include steroids, insecticides, and muscle relaxants. They can also be used in the treatment and prevention of various illnesses such as asthma, arthritis, malaria, pneumonia, and heart disease. At present, only 1% of rainforest plant species have been studied for their medicinal value. This figure has grand implications on the great value rainforest plants have in medicine and public health.
Threats to Rainforests
Rainforest Loss and Deforestation
Rapid human development in the last few centuries has led to great loss and destruction of rainforests worldwide. Rainforests once occupied 14% of the world’s surface, but deforestation and other harmful human processes have reduced it to 6% at present.
Agriculture, ranching, logging, mining, are all major threats to rainforest conservation. Aside from robbing these ecosystems of their natural resources, many of these also employ harmful mechanical techniques that further harm the environment. These can lead to increased levels of erosion, destruction of natural habitats, the loss of the soil’s nutrients, and more. Unsustainable human behaviour creates near irreversible changes to the environment, making it difficult for biodiversity to return to its previous state.
In response to these immense threats to our planet’s well-being, many individuals, communities, governments, and international agencies have banded together for the protection and conservation of the world’s rainforests. The governments of countries with rainforests have recently been advocating for the sustainable use of their rainforests. Various initiatives against illegal logging, reducing carbon emissions, and promoting the sustainable use of rainforest resources, have been enacted around the globe.
Local and international conservation groups cooperate in the protection and preservation of these natural treasures. Ecotourism has particularly been effective in encouraging appreciation for rainforests. Aside from educating tourists and visitors, ecotourism also provides jobs for local communities.
In Brazil specifically, many indigenous groups have come forward and staked their claim on endangered lands. These indigenous people argue that they are better stewards of these natural habitats than national governments and large corporations.
Many efforts have also been directed towards reforestation. In an attempt to rehabilitate rainforest habitats, one project, in particular, aimed to plant 73 million trees in the Amazon.
- Rainforest . (n.d.). Retrieved from National Geographic: https://www.nationalgeographic.org/encyclopedia/rain-forest/
- Rainforests, explained. (n.d.). Retrieved from National Geographic: https://www.nationalgeographic.com/environment/habitats/rain-forests/
- Tropical rainforest. (n.d.). Retrieved from Britainnica: https://www.britannica.com/science/tropical-rainforest/Environment
- Tropical Rainforest. (n.d.). Retrieved from Internet Geography: http://www.geography.learnontheinternet.co.uk/topics/rainforest.html
- Tropical rainforest biomes. (n.d.). Retrieved from BBC: https://www.bbc.co.uk/bitesize/guides/zpmnb9q/revision/1