What is a rainforest?
A forest called a rainforest must be permanently green. It must get at least 2,000 mm (2 metres) of rain per year. That is four times as much rain as Skåne gets in a year! For it to count as a rainforest, it must rain regularly for 9 months of the year. There are places in the rainforest that get 8,500 mm of rainfall in a year!
Rainforests are often called the lungs of the earth, because they produce much of the oxygen in our atmosphere, and clean the air. The water sucked up by the root systems is purified, and the forest stores huge amounts of carbon dioxide as it grows.
For a forest to be called a rainforest, it must get at least 2 meters of rain per year.
Photo: Andreas-Tollkotter-CC-BY-SA
The canopy of a rainforest in Australia.
Photo: CSIRO-CC-BY
The canopy in a rainforest is often so dense that the supply of light is very low on the ground. The competition for light is very big in the rainforest.
Photo: Jaygayani-CC-BY-SA
Roof of tree tops
In the rainforest, trees grow so densely that the tops form what is known as a canopy. Very little grows on the ground, as the canopy stops sunlight from reaching that far down. As soon as a tree falls in the rainforest, many different plants compete for the light that becomes available. The trees grow rapidly in height, trying to be the first to access the precious light. Between the dark ground and the canopy, there is a layer where the leaves are at their largest, and the greatest number of insect species live.
About half of the earth's animal and plant species live in the rainforest. All parts of a rainforest are full of life, and all surfaces are used by someone or something.
The plant bromeliad thrives in the rainforest, and grows on tree branches. In the middle of bromeliad plants is a small puddle of water, where small frogs thrive.
Photo: Geoff-Gallice-CC-BY
The Sri Lankan junglefowl - a relative of the hens we raise for meat and eggs - lives in the rainforest. So do the ancestors of domestic chickens.
Photo: Asif-N-Khan-CC-BY-SA
The African forest elephant lives in the Congolian rainforest.
Photo: dsg-photo.com-CC-BY-SA
The helmet vanga, a rare bird that lives in the rainforests of Madagascar.
Photo: Eric-Mathieu-CC-BY-SA
The endangered orangutan depends greatly of the Indonesian rainforests.
Photo: RaiyaniM-CC-BY-SA
Insects, both small and large, live everywhere in the rainforest. Like this dragon-headed bug in Costa Rica.
Photo: Geoff-Gallice-CC-BY
The two-toed sloth also lives in the rainforest of Costa Rica.
Photo: Geoff-Gallice-CC-BY
Us humans use products that come from the rainforest on a daily basis, such as fruit, coffee, chocolate, wood, make-up and various oils.
Photo: John-Ocampo-CC-BY-SA
A hundred species in a single tree
Rainforests have existed for about 60 million years. Half of all animal and plant species – about 4.5 million – live in rainforests. A single tree can contain around 100 species of everything from mammals to invertebrates. Many mammals, reptiles, amphibians, birds, insects, plant species and fungi live only in rainforests.
Every day, people use products that originated in the rainforests. These include houseplants, perfumes, chewing gum, wood, furniture, rubber, coffee, cocoa, avocados, nuts, coconuts, mangoes, bananas, pineapples, oranges, tobacco, make-up and various vegetable oils. Much of the raw material for medicines also comes from the rainforest.
Large tropical rainforests, such as the Amazon, can create their own weather. When a lot of water evaporates in the mornings, clouds form over the forest in the afternoons which then causes the rain to fall on the forest again. The water cycle is very fast in the rainforest.
Cloud forest is the name of a type of rainforest at high altitude. They have a colder average temperature than the surrounding rainforest at lower altitudes. In cloud forests, the cloud cover is often at the height of the canopy.
Photo: Ade-javanese-CC-BY-SA
Temperate rainforests are further from the equator than tropical rainforests. They are located in coastal areas such as Chile, southern Australia, the northwest coast of North America such as Oregon in the picture, and in fact even Norway!
Photo: Sam-Beebe-CC-BY
Tropical rainforests – and rainforests in Norway!
Rainforests are found in several climates, from tropical and subtropical to temperate parts of the world. Tropical rainforests are only found in the tropics. The tropics is the name of a wide belt around the equator, taking in Central America, South America, Southeast Asia and Central Africa. The water cycle is fast in tropical rainforests. Large amounts of water evaporate in the mornings, and then rain down in the afternoons. The average temperature in the rainforest is 27°C. There are no seasons like in Sweden, the only thing that varies is the amount of rain.
Subtropical rainforests are found mostly on the Asian continent. The climate alternates in the subtropical rainforest between long, hot, rainy periods and shorter, colder, dry periods. Temperate rainforests are found in areas with moist westerly winds such as the northwest coast of North America, Alaska, southern Chile, parts of Australia and New Zealand, and even northern Spain – and actually a small part of Norway.