Tropical Rainforest

Characteristics of tropical rainforests

A forest is an area that is dominated by trees. There are many different types of forests, often defined by climate and the types of trees that can be found in them. One prominent type of forest is the tropical rainforest.

To put it simply, tropical rainforests are hot, humid, and dense!

Climate of tropical rainforests

As we mentioned above, tropical rainforests are characterized by high temperatures, high rainfall, and high humidity. This climate is what enables the existence of tropical rainforests; the humidity, sunlight, and rain are very good conditions for thick plant growth, though soil quality in tropical rainforests can often be poor since excessive rain tends to wash away the nutrients.

Tropical rainforests experience temperatures of at least 18°C every month, while annual precipitation is usually no less than 1700mm (on average, about 142mm per month). These are minimums; many, if not most, tropical rainforests experience much higher temperatures and greater rainfall throughout the year.

Fig. 1 - Did we mention that it rains in a tropical rainforest?

Tropical rainforests do experience seasonality, but not in the way you may be used to in a temperate climate! Forget spring, summer, autumn, and winter; tropical rainforests are defined by a wet season and a dry season.

During the wet season, tropical rainforests will experience the heaviest rainfall and the hottest temperatures. Rainfall may drop all the way down to 60mm per month during the dry season – but that is still not all that dry compared to other climates. For that reason, some climatologists have suggested that tropical rainforests do not experience a "true" dry season.

Tropical rainforest location

Tropical rainforests are mostly located in, well, the tropics!

The vast majority of tropical rainforests are located around the equator (0° latitude) between the Tropic of Cancer (∼23.44° north latitude) and the Tropic of Capricorn (∼23.44° south latitude). This region of the Earth is known as the tropics, which is why the forests here are dubbed "tropical."

Fig. 2 - The tropics are around the equator in between the Tropic of Cancer and the Tropic of Capricorn

One of the reasons the tropics are so warm is that they receive more direct (concentrated) sunlight than other regions of the Earth. This is because of the way the Earth is titled on its axis. This sunlight, as heat, causes bodies of water to evaporate more readily, leading to greater humidity and precipitation.

Perhaps the most prominent tropical rainforest in the world is the Amazon Rainforest, located in South America (mostly in Brazil).

Tropical rainforest biomes

A biome is a globe-spanning distinct type of biological community. A biome also takes into account physical geography, including climate. The tropical rainforest biome includes all of the different tropical rainforests in the world.

Biogeographers, who study the spatial distribution of living organisms, do not always agree on the number of biomes. It is not uncommon to see the tropical rainforest biome combined into a more general "rainforest biome" (which can include temperate/subtropical rainforests) or even a generic "forest biome" (which includes all of the forests in the world).

Fig. 3 - The tropical rainforest biome is in dark green; the temperate/subtropical rainforest biome is in light green

Tropical rainforest plants

Biodiversity is a measure of how many unique living organisms are endemic (native) to an area – and tropical rainforests are the reigning champs of biodiversity on land. There are around 400,000 different species of plants around the world; almost half of these species (around 170,000 to 200,000) are endemic to tropical rainforests. Even then, new plant species are being discovered all the time. Who knows what's waiting around the next bend of the forest?

The Amazon Rainforest in particular is a hotbed for biodiversity, and plant life is no exception. Some of the plants endemic to the Amazon Rainforest include the cacao tree (Theobroma cacao), the mahogany tree (Swietenia macrophylla), giant water lilies (Victoria amazonica), several species of orchid, the rubber tree (Hevea brasiliensis), and several species of passion flowers. Other iconic rainforest plants include the corpse flower (Amorphophallus titanium) in Sumatra, ebony trees in the Congo, and coffee plants in Africa and Asia.

Animals of the tropical rainforest

Tropical rainforest biodiversity does not end with plants – there are countless different types of animals in tropical rainforests as well! Enabled by the density of plant life in tropical rainforests, many animal species have adapted to their little corner of the forest and are found nowhere else on earth. In other words, tropical rainforests are home to many tiny little amphibians, mammals, birds, and insects with very small ranges. This includes the many species of poison dart frogs in South and Central America, the red-eyed tree frog (Agalychnis callidryas) in Central America, and two species of pygmy marmoset ("finger monkey"), the world's smallest monkeys.

Fig. 4 - Finger monkeys are native to tropical rainforests in South America

Thanks to the abundance of fruits and insects, tropical rainforests are also a hotspot for birds, including iconic species like toucans in the Americas, birds of paradise in Oceania and Southeast Asia, and the harpy eagle (Harpia harpyja) in South and Central America.

Animals that are relatively large and capture our cultural imagination are called charismatic megafauna, and tropical rainforests are home to many. The tropical rainforests of Sumatra in southeast Asia are home to orangutans, rhinos, and tigers. In the Congolese Rainforests of Africa, charismatic megafauna includes forest elephants (Loxodonta cyclotis), gorillas, chimpanzees, bonobos, and okapis, while rainforests in the Americas include jaguars, tapirs, and caimans. And who could forget about the sloth?

All animals living in tropical rainforests need to be able to adapt to high humidity, hot weather, high precipitation, and dense plant growth. A polar bear, for example, would not be very comfortable in a tropical rainforest!

Tropical rainforest facts

Since you're such an awesome student, here is some 'bonus' facts about tropical rainforests!

Growing Season

People who live in and around tropical rainforests may clear a section of it to make space for agriculture. Because soil quality can often be poor, farmers may practice slash-and-burn agriculture, wherein they burn down a section of the forest; the charred plant matter adds nutrients to the soil. Once this new crop field has been used, farmers will leave and allow it to re-wild, moving along to a different section of the forest.

Because tropical rainforests are warm year-round, there really is no set growing season. However, it may be more difficult to plant crops if it is raining too much, so some farmers may plant during a rainforest's dry season.

Nature's Medicine Cabinet

Medical professionals and researchers have turned to tropical rainforest plants as potential sources of medicine. In fact, Amazon Rainforest plants have so frequently been used in medicine that it has sometimes been called 'Nature's Medicine Cabinet.' Plants have been used to treat everything from malaria to leukaemia. If you've ever had your mouth numbed at the dentist, you have the Amazon Rainforest to thank!

Lungs of the Earth?

It is sometimes claimed that the Amazon Rainforest acts as 'the lungs of the Earth' and is responsible for 20% of the oxygen in the Earth's atmosphere and/or 20% of the oxygen we breathe. While the Amazon Rainforest plays a very large role in the Earth's daily photosynthetic processes, almost all of the oxygen it releases is, one way or another, re-absorbed right back into the Amazon Rainforest itself!