Some tree lineages in the Amazon have deep evolutionary roots, dating back to the time of the dinosaurs, while others evolved much more recently. A newly published study has found that such tree diversity is strongly associated with local environmental conditions, like soil type.
Scientists have long sought to better understand the origins of the Amazon’s ancient tree diversity. To find answers, a team of more than 100 scientists investigated how Amazon trees diversified and colonized the region based on local environmental conditions.
They examined more than 5,000 tree species in nearly 2,000 plots representing four types of forests: upland forests that don’t flood, seasonally flooded forests, permanently flooded forests, and white sands forests.
The study found that permanently flooded forests and white sands forests are each home to the same dominant species of trees regardless of their location in the vast Amazon Basin. For example, star apple trees (genus Chrysophyllum) are widely found in white sands forests across the Amazon. In contrast, the kinds of trees found in upland forests and seasonally flooded forests vary from east to west across the Amazon.
The difference likely stems from the fact that permanently flooded forests and white sands forests present more difficult growing conditions than upland or seasonally flooded forests. Not many tree species can thrive in permanently submerged swamps or sandy soil lacking nutrients and water, Bruno Garcia Luize told Mongabay by phone. Luize is the first author of the study and a biologist with the State University of Campinas in Brazil.
“It is too hard to be a jack of all trades,” Luize told Mongabay in an email. Instead, the research suggests some trees have evolved to master just one.
The study also found that many tree species were quite selective when choosing what part of the Amazon to colonize. Roughly 20% of tree lineages are regionally specific to the central Amazon. In the southern Amazon, that number drops to just 5%, Luize said.
Some species, like the ice cream bean tree (Inga edulis), so named for its sweet fruit, evolved during the Plio-Pleistocene roughly 5 million years ago, Luize said. That was a time when mammoths dominated the north and giant ground sloths foraged in the Amazon. Other tree families like nutmeg (Myristicaceae) were growing in the lush jungles of the region more than 66 million years ago when dinosaurs dominated the landscape.
“The evolutionary process is not something that stopped,” Luize added. “The dinosaurs have changed and now we see them flying in our cities. The forest is still evolving.”
However, Luize went on to question whether the Amazon Rainforest will survive the human pressures of deforestation, mining and climate change. “Will they survive the seventh mass extinction event our livelihoods are causing?” he asked.
Banner image: White sands forest of the Amazon. Image by Rhett A. Butler/ Mongabay
Credits
