Thiago Silva: Uncovering resilience and adaptability in the Amazon’s floodplain forests 

Growing up in São Paulo, Brazil, National Geographic Explorer and scientist Thiago Silva had little exposure to dense forests and winding rivers of the Amazon wetlands. Visiting this lush tropical ecosystem for the first time during his master’s studies, he recalls, was a career-defining moment and felt like stepping “into another world.” 

“At the time, I didn’t even know what a ‘wetland’ meant,” he jokes. “The temperature, the humidity, the scale of everything— everything is enormous. This is not your regular forest or river, or anything.” 

The floodplain forests along the Amazon River and its large tributaries have been a lasting passion for Silva, who holds a doctorate in geography from the University of Victoria in Canada and now teaches environmental informatics at the University of Stirling in Scotland. He feels that the beauty of the wetlands lies in their resilience to the harsh extremes of their environment. 

“Life in the wetlands—where you really have to somehow evolve to live, from terrestrial conditions to 12 meters of water column every year and still be able to survive and reproduce,” says Silva, “that to me became a lot more fascinating [than terrestrial forests.]” 

In this massive region—which covers about 130,000 square miles of the Amazon—flooding is recurrent and intense, submerging entire forests in water. Thanks to unique characteristics adopted over time, Silva notes, the trees in this ecosystem have learned to adjust. 

“The forests are inundated by up to 10, 12 meters of water vertically every year, and of course, that requires a lot of adaptation from the trees,” he says. “The longer the flood lasts for, the harder it is for the tree to survive, and the better adapted it needs to be.”

The complexities of how these adaptations work is still somewhat of a mystery, one that Silva has spent the last decade trying to unravel. As a self-titled digital ecologist—equal parts ecologist, geoscientist, and computer scientist—he combines innovative laser scanning technology with ecological theory to identify how the wetlands respond to changing flood patterns. In the field, Silva monitors specific details ranging from the size and thickness of leaves, to an individual tree’s ability to absorb water. 

Measuring these features in a forest is not easy work, and it requires precision. That’s why Silva uses LiDAR, a remote sensing technique that produces three-dimensional models of the floodplain forests he studies, down to the individual tree. This method is faster and more accurate than traditional monitoring, which involves looking for visual indicators of flood levels on the tree itself. 

“It’s very hard to see the marks, so you never know if you’re looking at it the right way,” Silva says. “Because we have the 3D model, we [can] tell which trees are higher up, lower down – each individual tree and how long it’s flooded, with very precise measurement. That has never been done before.”

In April, Silva put this technology to work in the field. Partnering with marine ecologist and fellow Explorer Angelo Bernandino, Silva made the journey to the Amazon Delta, conducting surveys of 11 separate mangrove forests. The purpose of the study, the first to be published out of the National Geographic and Rolex Perpetual Planet Amazon Expedition, was to analyze key features of the mangroves using 3D scanning—both on the ground and from above with drones. What they found, Silva says, defied their expectations. 

“I had been to other mangroves before, and so I had this expectation in my mind of very short trees, only two, three species, very dense, very muddy,” Silva recalls. “When we got there, it was completely different.”

The Explorers observed a one-of-a-kind forest of mangroves and freshwater tree species living side-by-side in the brackish water that is typical of an Amazonian estuary. Surprisingly, the trees Silva and Bernandino studied possessed unique adaptations and structures which allowed the mangroves to survive in low-salinity conditions and freshwater ones to endure a higher-than-usual salinity level. It’s a discovery that Silva says will lead to new pathways for his research.

“What you have is this mixture of trees that creates this whole new type of forest, which is not regular mangroves. It’s not a freshwater forest [either],” says Silva. “There’s still freshwater trees, but they’re not the ones I would expect in this harder, more disturbed environment.” 

In this remote environment, threats like climate change and hydropower damming have a serious impact on flood cycles and the ecosystem they support. The risk is serious: too much or too little inundation, Silva warns, could mean the loss of several tree species in the Amazon wetlands. 

“It's still a loss of forest, but it's invisible, because if you look from satellite, the forest is still there, but the species are not the same anymore. It's like this invisible deforestation,” he says. “There's very few species that can grow all year long because of the inundation, so we will end up losing species at both extremes.” 

The wetlands fall somewhere between an aquatic and land ecosystem. This means that they fall through the cracks of conservation laws and policies, overshadowed in favor of large terrestrial forests, Silva says. Not only are the Amazon’s floodplain forests critical to the environment; the wetlands also support nearby communities for food and transportation. This is why advocating for their protection through scientific research is an impact Silva hopes to make with his work.

“There’s plenty still to be preserved, to be maintained and to support human populations, to support biodiversity,” he says. “There needs to be a serious effort in recognizing that.” 

This fall, Silva embarks on another National Geographic Expedition to the Amazon’s wetlands, where he’ll continue to study adaptations of trees in this remarkable ecosystem. Soon, he hopes to use the data he has collected to start “forecasting scenarios” for the wetlands’ changing flood cycles, preparing for irregular events before they happen. 

Silva also plans to engage the public in his research on floodplain forests through a creative virtual reality project he calls the “virtual forest.” 

“People could step into virtual reality, feel how it is to be inside the forest and see how big the trees are, see how complex the shapes are,” he says. “One thing that we definitely want to show is that when the water levels go up, how much does it mean, when you're talking about 10 meters, 12 meters of inundation?” 

As he works towards these milestones, Silva stays motivated by a deep sense of connection to his home in Brazil. 

“It doesn’t matter where I am or what location or institution I’m working in,” he says. “The Amazon is my main interest and the place I love.”

Thiago Silva is participating in the National Geographic Society Perpetual Planet Amazon Expedition—a two-year series of scientific studies spanning the entire Amazon River Basin, supported by Rolex as part of its Perpetual Planet initiative. Learn more about the expedition.

ABOUT THE WRITER
For the National Geographic Society: Elisabeth Hadjis is a 2022 intern at the Society.