The Amazon rainforest covers 2.7 million square miles, an area roughly 87% as large as the continental United States. As the world’s most biologically diverse ecosystem, it’s increasingly viewed as a lynchpin in the health of the planet. Over the coming decades, climate change will beget an Amazon rainforest that’s hotter and drier than at any previous point in human history. Those changes could have implications for all of us, and today, our understanding of them is rudimentary at best.
A small group of university researchers is working to change that. They spend weeks at a time encamped deep in the forest, on a three-year project funded by the National Science Foundation. Their ultimate goal is to build a model of the Amazon’s inner workings that’s unprecedented in size and scope.
Among them are University of Michigan engineering professor Valeriy Ivanov and graduate student Elizabeth Agee. They’re working to install and maintain a network of custom-built sap flow sensors that will help predict how the forest’s plant life will respond to a changing climate.
Follow them deep into the Amazon to learn how the data they’re collecting day by day, tree by tree, could ultimately drive a better understanding of the Earth’s climate future.
Where the sensors are
A network of hand-built sensors is the first step in revealing the inner workings of the Amazon.
This is one of the dozens of custom-built sap flow sensors that dot trees throughout the research forest. It’s the source of the data that could help unlock the inner workings of the Amazon’s plant life. Running for months at a time, the sensors keep a running log of how much water is flowing through a tree as sap at any given time.
When Ivanov and Agee began their work in the Amazon, it quickly became apparent that off-the-shelf sap flow sensors wouldn’t cut it in the harsh conditions of the forest. Their “weather-proof” boxes quickly filled with humidity and became homes for ants and termites. Their electronics couldn’t stand up to the heat, and hungry ants snipped their delicate probe wires.
So Agee and the rest of the team in Ivanov’s research lab found a better way. They collaborated with electrical engineer and U-M alum Yuriy Goykhman, who volunteered to design a sensor that could stand up to the rigors of the forest. Built by Agee and her husband in the basement of their Ann Arbor apartment, they cost a fraction of pre-built sensors and are far more durable.
The secret math of trees
The sensors’ data reveals a web of survival strategies that’s more complex than anyone imagined.
By matching sap flow data to temperature, light, humidity and other data from the forest’s weather tower, the team can see how individual trees manage water in response to changes in their environment. They’re finding that those management strategies are more complex than anyone imagined, with each species staking out a unique strategy for success.
“In the past, researchers looked at vegetation like people with different-colored skin—they may look different on the outside but they’re basically the same underneath,” Ivanov said. “As it turns out, different species function very differently, and we want to move away from classifying plants according to outward appearance and toward classifying them according to how they function. Because once you understand how they function, you can predict how they will behave as the climate changes.”
Trees release water vapor to the atmosphere through tiny valves on the undersides of their leaves. These valves, called stomata, can be opened or closed to either hold onto water or release it. But there’s a catch—when a tree closes its stomata, it can’t photosynthesize.
Each species strikes a different balance between conserving water and producing food. Some trees shut down in times of drought, while others live more dangerously, photosynthesizing right through the dry spell to take advantage of the sunny days. The data from the sap flow sensors is key to decoding each species’ strategy.
A tree trunk is a complex system that, in addition to supporting the tree, serves as a pipeline to carry food down from the leaves and bring water up from the ground. Ivanov and Agee are most interested in a part of the trunk called the xylem—this is the layer just inside the tree's inner bark that carries water." The sap flow sensors’ probes are sized so that they penetrate the trees’ xylem.
Beneath the researchers’ feet, a web of tree roots is locked in a silent battle to wring water from the soil. And, as in the crown, each species has its own strategy. Some trees use wide, shallow roots to quickly soak up rainwater while others go deep, taking advantage of the more consistent water levels deep underground. That much is known.
But Ivanov and others have calculated that the roots don’t take in enough moisture to account for the massive amount of water vapor the trees release into the atmosphere. Nobody knows where the extra water comes from. The answer to that question and others may help researchers predict how the forest will respond as climate change brings more frequent droughts.
The forest’s voices
In the air and on the ground, a team of researchers is revealing how the world’s last great forest works.
High in the canopy, on the forest floor and in pits dug deep underground, the team is gathering information about leaf respiration, stem water content, soil temperature, humidity and other data points that, in the past, simply didn’t exist. While more temperate forests have been studied in great detail, the Amazon has always been too big, too remote, too inhospitable. As a consequence, Amazon research has often relied on simplistic models that draw sweeping conclusions from a paucity of data. By collecting an unprecedented level of data about the forest and finding new ways to analyze it, Ivanov and the rest of the team are working to change that.
Professor of ecology and evolutionary biology, The University of Arizona
Saleska has been coming to this forest for decades. On a series of projects, he has played a key role in building the infrastructure that makes it possible to conduct science in one of the most inhospitable places on Earth. Over the years, he has overseen the construction of the basecamp, the installation of an intricate network of elevated catwalks, and the building of the 200-foot tall eddy flux tower that gathers detailed heat flux and CO2 exchange data.
PhD candidate, Universidade Federal do Oeste do Pará (UFOPA)
Penha works high in the forest canopy, where she uses an instrument called a porometer to measure leaf respiration. Originally from Óbidos, a small town on the other side of the Amazon river, Penha began interning with the crew as an undergraduate, stepping into the forest for the first time at age 23. She fell in love with ecology, and working toward her PhD has only made her more curious.
Assistant professor, forest-atmosphere interactions, Michigan State University
Stark is charged with weaving the project’s disparate streams of data into a Bayesian process model framework that will provide a sophisticated, multidimensional picture of the forest. By combining measurements of individual species traits with broader ecosystem-level data, the model will uncover connections and interrelationships that can’t be directly observed.
Data meets policy
The data the researchers are gathering could help save the forest. But will it?
A better model of the Amazon’s inner workings could help scientists accurately predict how resilient it will be in the face of climate change—and how deforestation will affect the viability of its ecosystem. That, in turn, could drive better policy decisions about how to manage the forest responsibly and balance interests like logging, mining and agriculture with the need to maintain a healthy forest.
But the intersection of science and policy can be a dangerous one, and that’s certainly the case in Brazil. Until recently, Brazil had been more proactive and successful than any other country in the area of forest management, dramatically reducing the rate of Amazon deforestation from its peak in the early 2000s.
In a worrying trend, deforestation has spiked again since president Jair Bolsonaro swept into office in 2018. He has worked to roll back forest protections and silence those who are drawing attention to the increased deforestation rates; Ivanov and the rest of the research team have found it increasingly difficult to get access to the research forest.
In response, the team is working to broaden and strengthen the research community—particularly in the Amazon region, which is far from Brazil’s power centers in the south of the country.
“When people come to Santarém, they think they’re going to see jaguars and snakes in the streets,” says Raphael Tapajos, an assistant professor in the four-year-old meteorology program at the Federal University of Western Pará (UFOPA).
Tapajos sees the meteorology program as an opportunity to pursue a more research-oriented future for UFOPA, driving a better understanding of the forest and its role in the Earth’s climate.
“We need to develop technology to manage and adapt to the climate, and I think it’s important for people who are from here to play a role,” he said. “We’re in the middle of the forest and we need to understand it, to apply our knowledge. The people I teach here will eventually teach others.”
Teaching others—particularly Brazilians—may be a key to keeping the project alive. Ivanov and Tapajos are working together to build a pipeline of UFOPA students who are interested in moving the research forward, sidestepping the onerous visa requirements and building a broader base of support inside the country.
Given the current political climate in Brazil, however, that’s likely to be an uphill battle. The country is feeling the effects of a 2016 austerity bill that’s perhaps the world’s most extreme. It freezes government spending at inflation-adjusted 2016 levels until 2036, with no provisions for population growth, recession or other possible eventualities.
Healthy Amazon, healthy world
We all have a stake in the forest’s future.
The Amazon absorbs a massive amount of the carbon we humans pump into the air—an estimated five percent of global carbon emissions, or two billion tons every year. That’s roughly equivalent to the amount by which the European Union has pledged to reduce its carbon emissions by 2030.
A large die-off in the Amazon could turn it into a net emitter of carbon rather than a sink for excess carbon, throwing a wrench into future climate projections. And right now, the likelihood of such a die-off is very much in debate. Some researchers believe that hotter, drier weather, combined with increased exploitation of the forest, may tip it into a die-off, while others believe it’s more resilient.
The amount of carbon absored by the Amazon each year is:
More than the carbon emitted by every car, truck, plane, boat and train in the United States.
US transportation emitted
“The modeling of biogeochemical feedbacks is still in its infancy,” explains Mark Flanner, a U-M professor of climate and space sciences and engineering. “How will the land and the ocean’s ability to absorb carbon change as the temperature and the amount of carbon dioxide in the air rise? We know, for example, that elevated carbon dioxide can enhance photosynthesis, but that can only occur if plants have adequate amounts of soil, nutrients, water and light. And of course at some point plants simply get too hot for their chemistry to function properly. Each species has its own set of thresholds, so it’s an enormously complicated process.”
That’s where the new data comes in. The forest model the research team creates could be a key to reducing that uncertainty and, ultimately getting a clearer picture of where the planet’s climate is headed.