What makes a forest a tropical rainforest?
A rainforest is not just a wet forest: it is hot and wet every single month, and it sits on the scattered pieces of an ancient supercontinent.
▶ Start the storyA forest is a tropical rainforest when it is hot all year and wet all year. Scientists are fairly strict about it: every month averages above 18 °C, even the driest month gets at least 60 mm of rain, and a typical year brings between 1,750 and 3,000 mm. There is no cold season to slow the trees down and no dry season to wait out.
18 °C+
These forests sit close to the Equator, mostly within about 10° north and south of it. Today they are found in five main regions: tropical America, Africa, Southeast Asia, Madagascar and New Guinea, with smaller patches in Australia. Most of them grow on fragments of the ancient supercontinent , which is why they are scattered across the globe. The Amazon alone holds more than half of all the rainforest left on Earth.
Not every green tropical forest qualifies. Some get plenty of rain overall but have a cooler, drier season, and some of their trees drop leaves during it: those are seasonal tropical forests. Climb high up a tropical mountain, where it is cooler, and the rainforest turns into a cloud forest.
True rainforest
- No dry season
- Every month has at least 60 mm of rain
- Warm all year, above 18 °C
Seasonal tropical forest
- High rainfall overall
- A cooler, drier season
- Some trees drop their leaves
The result is a place that covers a small part of the planet but is crowded with life. One may hold up to 807 trees of 313 species, and estimates say that 40 to 75 percent of all species on Earth live in rainforests. The same heavy rain has a catch, though: it washes nutrients out of the ground, so the soil under the world's richest forests is often poor.
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Recap
A true rainforest is hot and wet every month near the Equator, and most grow on pieces of the old supercontinent Gondwana.
💡 A trick to remember it · Think of a greenhouse with the thermostat stuck on warm and the sprinklers never switched off: no winter, no dry spell, ever.
Surprising fact · One hectare can hold up to 807 trees of 313 species.
Connects to
- 🌳 Why is a rainforest built in layers, from the forest floor to giant treetops?
- 🔄 Where does the carbon in your breath go next?
- 🌧️ Why does most of India's rain fall in just a few months?
- Nutrient cycle
- Latitudinal gradients in species diversity
Sources (2)
No source, no claim. Every fact in this lesson (14 claims) cites at least one of these.