The tropics cover less than one-third of the Earth’s surface, but are home to more than half of all known species. Forests, savannas, grasslands, deserts: a vast array of environments stretches along the planet’s equatorial belt. This diversity, however, is not static. It is the result of millions of years of changes that have reshaped the tropical landscape time and again.
Our team at the Remote Sensing Center at the Federal University of Minas Gerais (UFMG) in Brazil reconstructed the distribution of tropical vegetation over the past 3.3 million years and projected how it may experience further changes due to climate change by 2050. The study was published in the Journal of Biogeography.
The research combined satellite data, paleoclimate records, and machine learning algorithms to map how forests, savannas, and deserts have redistributed themselves across the tropics over eleven large time periods, from the end of the Pliocene to the present. It showed that current climate change could, within a few decades, cause impacts on tropical vegetation similar to those of 3 million years of the planet’s history.
A landscape that changed slowly
The results reveal profound transformations. About 3.2 million years ago, when Earth was nearly four degrees Celsius warmer than today, tropical forests reached their smallest extent throughout the entire period analyzed. The Amazon Forest covered less than half the area we know today. The Atlantic Forest was reduced to less than five percent of its potential extent. Savannas dominated landscapes that are now covered by dense forests.
In Africa — the tropical continent that changed the most over the study period — forests were always scarce, and savannas dominated almost entirely. The Sahara, which is now the world’s largest hot desert, was not always that way. During the Pliocene, it was home to mosaics of shrubs and sparse vegetation.
With the glacial cycles of the last 2 million years, the forests fluctuated. They advanced during warmer periods and retreated during colder ones. Twenty-one thousand years ago, at the height of the last ice age, the Amazon lost nearly a third of its area but retained a continuous core. It never fragmented completely. The Atlantic Forest, on the other hand, split into two blocks separated by hundreds of kilometers of open vegetation.
In Southeast Asia, on the other hand, something different happened. Nearly one-third of the Malay Archipelago kept its forests intact for more than 3 million years, making the region the most stable tropical area on the planet.
About 22% of the tropics remained climatically and vegetationally stable throughout the entire period analyzed. These areas functioned as refuges, accumulating biodiversity over millions of years. Many species living in these refuges exist nowhere else.
These transformations
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