The Amazon rainforest is such a rich repository of fascinating wildlife and plant species that scientists are still in the process of discovering what it contains and how it all fits together. Because of its massive size, the forest could only be studied piece by piece- so there was no way of knowing which tree species were the most common, and the most threatened, throughout the region. But researchers studying this topic recently made a startling discovery- of the thousands of tree species in the Amazon, the rainforest is dominated by just a few dozen.

From LiveScience:

To help shed light on this giant rain forest’s tree composition, more than 120 scientists catalogued any trees with stems thicker than 3.9 inches (10 centimeters) at 1,170 different locations throughout Amazonia, the 2.3-million-square-mile area (6 million square kilometers) surrounding the Amazon River. They found that approximately 16,000 tree species made up this region.

Of these 16,000 tree species, scientists unexpectedly discovered that only 227 species, or 1.4 percent of all the types of trees in Amazonia, made up half of the nearly 400 billion total trees estimated to live there.

“That’s a much smaller number than anyone anticipated,” study lead author Hans ter Steege, a tropical forest ecologist at the Naturalis Biodiversity Center in Leiden, Netherlands, said in a statement.

Hardly any of these “hyperdominant” species, as the researchers call them, are consistently common across the Amazon. Each usually specializes in certain habitats — one or two types of forest, such as swamps or white-sand forests.

It remains unclear what makes any given species hyperdominant. One possibility is that hyperdominant species are unusually resistant to disease and herbivores.

The discovery could also provide fuel for the fascinating debate over how much impact ancient indigenous agriculture had on the makeup of the rainforest. And now that they have a better picture of tree populations, scientists say, they’re better equipped to predict and mitigate the effects of deforestation and conservation in this important ecosystem. Even the plants of the Amazon have a story to tell.