Why Tropical Forests Contain Half the World's Species in 7% of Its Land

Tropical rainforests cover approximately 7% of Earth's land surface. They contain an estimated 50% of all terrestrial species — more than all other terrestrial ecosystems combined. A single hectare of tropical rainforest may contain over 400 tree species, 1,000 insect species, hundreds of bird species, and dozens of mammal, reptile, and amphibian species. Understanding why tropical forests are so extraordinarily biodiverse is not merely an academic question — it is essential to understanding what is at stake when they are cleared.

Why Are Tropical Forests So Biodiverse?

Several interlocking factors explain tropical forest biodiversity. Climate stability is paramount: tropical forests have experienced relatively stable temperatures and high rainfall for millions of years — allowing species to accumulate through speciation without the periodic mass extinctions caused by glaciation in higher latitudes. The year-round growing season allows species to partition resources across time in ways impossible in seasonal environments. The structural complexity of the multi-layered forest creates an extraordinary number of ecological niches — microhabitats ranging from the canopy exposed to full sunlight to the perpetually dark forest floor — each supporting its own suite of adapted species.

Endemic Species — Found Nowhere Else

Many tropical forest species are endemic — found in one location and nowhere else on Earth. Biodiversity hotspots like the Atlantic Forest of Brazil, the forests of Madagascar, the Philippines, and the Western Ghats of India are characterised by extraordinary concentrations of endemic species that evolved in isolation over millions of years. When these forests are cleared, their endemic species have nowhere to go. Madagascar, which has lost approximately 90% of its original forest cover, has seen population declines in virtually all of its 107 lemur species — 98% of which are endemic to the island.