Researching Amazonia

By Marielle Smith + Ty Taylor

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Stories From the Field

 
Ty: I leaned back in my harness, secured by a lanyard around the tree’s trunk and my legs woven through a tangle of branches and vines. Raindrops pelted my eyes as I surveyed the top of the tree, looking for waterlogged branches that could fall on me from above. Water poured over my snake-proof gators and dropped, traversing some fifty feet of air between my perch and the forest floor. From this crow’s nest, I wrestled my pole pruner—fully extended to thirty feet—into the crown of a neighboring tree. Yanking the cord, the pulley-driven pruner bit hard into the branch I was after, and my sample fell, tumbling and brushing vines on its way to the ground. I had collected all I needed. I prepped for rappel—so happy, loving the rain and the breeze that demanded such alertness at the top of a tree.

Ty climbs the 65 m tower.
Marielle: I was driving back from the field after trying to fix yet another malfunctioning piece of equipment. Trees fall across that dirt road all the time, and as I rounded each corner I felt an increasing sense of
hope that I might escape without facing any obstructions. It was New Year’s Eve, and I was already running late. Sure enough, I came around the last bend and found the trunk of a newly fallen tree barring my way. I wasn’t getting to the party anytime soon! I’d been nervous going into the forest on my own; I could chop through small trunks with my machete, but would need help carving up a tree this size. Luckily, I was only a quarter-mile from the guard station, which protects the entrance to the national forest. After some laborious repairs to the guards’ vintage chainsaw, we made quick work of clearing the road. Ty and I made it to the local beach town in time for champagne.

These memories come from a five-month field research campaign in the eastern Brazilian Amazon in 2012. The Amazon—a paragon of tropical wilderness—has long held great allure for both of us. And how did we come to find ourselves together in this beautiful, sweaty, chigger-infested forest? We met in a rainforest in Costa Rica in 2007. Ty had escaped the biting air of the Alaskan winter to work in the tropical forest canopy. He was studying a symbiotic interaction between plants and fungi among a unique set of plants—called epiphytes—that live on the branches of tropical trees. Marielle came from her home in England to work with then PhD-student Stephen Whitfield on the causes of amphibian and reptile population declines.

Marielle levels a light sensor.

Inspired by free time spent together on late-night puma and frog hunting expeditions, we decided to follow each other around for a while. Marielle was introduced to vast boreal forests and dynamic mountain ranges during packrafting trips in Alaska, and Ty tasted the culture of civilization among 800-year-old buildings in Marielle’s hometown of Cambridge, England. In 2010, we were fortunate enough to be accepted into the Ecology and Evolutionary Biology department at the University of Arizona, where we are both working towards PhDs with the same advisor, Dr. Scott Saleska, and where we are now part of Dr. Saleska’s Amazon PIRE (Partnership in International Research and Education) research group, a project funded by the National Science Foundation, consisting of an international network of researchers and students studying the future of Amazonian forests under climate change.

 

Every year, the Amazon forest processes (through photosynthesis and respiration) twice the amount of carbon dioxide than is emitted by anthropogenic fossil fuel emissions. Climate change is expected to hit the Amazon with higher temperatures and more severe droughts. Given the scale of the Amazon basin and its importance for global carbon and water cycling, the responses of this enormous forest to climatic changes are predicted to in turn alter the global climate. The aim of our research group is to better understand how the forest interacts with the climate now, so we might better predict how the forest will react to climate change in the coming decades.

Research tower above the canopy.

Our 2012 campaign took place in the Tapajós National Forest near Santarém, Brazil, one of the driest parts of the Amazon, where a 65-meter tower lined with instrumentation provided us with a puzzle to resolve: the tower told us that the forest photosynthesizes more during the driest period of the year. Collaborating with two other students to figure out what drives this counter-intuitive behavior, Marielle tested the hypothesis that the forest photosynthesizes more because it increases its leaf area during the dry season. If this is the case, then the forest may be more limited by light than water, and is taking advantage of increased light during the dry season when there are fewer clouds. To test this hypothesis, Marielle employed a special instrument, called LiDAR (light detection and ranging), which shoots high frequency laser pulses up into the forest canopy to map leaf distributions.

Marielle: Measuring forest structure using the LiDAR required me to walk at a slow pace through the forest. Each measurement meant walking eight km of trails, which I did every two weeks, so I was able to really observe how the forest changed through the dry season; each time, I would encounter new flowers and smells. This was also the perfect way to see life in the forest, most commonly howler monkeys, agoutis (large rodents), snakes, and tortoises. Walking so many hours with my local field assistant also gave me time to practice my Portuguese. He taught me how the locals use the forest—for example, how they use a particular vine to tie poles between trunks in order to string their hammocks up high, out of reach of jaguars.

It is important to keep in mind that even if Marielle’s hypothesis is supported, and the forest is not stressed from water limitation during a normal dry season, this does not suggest that the forest will never be drought-stressed, it just means we need a better understanding of its limits. For example, a widespread drought in Amazonia in 2005 caused increased rates of tree death across the basin. The resulting excess of wood decomposition caused a net loss of carbon from the forest to the atmosphere, increasing the amount of CO2 in the atmosphere and demonstrating the type of feedback between forest and climate that our group is trying to better understand.

An important result from the 2005 droughts was that some species were able to withstand the excess water deficit, while others were not. During this 2012 campaign, Ty worked on a project that he hopes will help us understand the species-specific responses to climate changes. Ty assessed the composition of tree species and leaf and wood characteristics in areas of the forest with hot and dry microclimates, such as the edge of the national forest along the highway. He believes forest composition in these locations portends the characteristics and activity of the Amazon in a hotter and drier future.

Chart: leaf area density by canopy height
This graph serves as an example of the sort of information LiDAR can uncover about the forest—in this instance, leaf area densities. The LiDAR instrument can estimate the amount of leaf area at different levels in the canopy; interestingly, we can see from this graph that the majority of leaf area in this forest is found in the understory.
Image courtesy Marielle Smith.

Ty: Some trends, only the data will show you. But my ability to interpret the data and ask relevant questions is enhanced by knowledge of the forest absorbed through my own eyes. On an overnight trip in the forest, Marielle and I followed our machetes off-trail for a few miles and slept in hammocks under our tarp. As we descended from the clay-soil plateau to a sandy valley, the forest shrunk, the understory opened, and giant palm fronds barred the way. The species composition was clearly different on these nutrient and water-deprived soils, but there were some groups in common with the plateau. I mused: could it be that as the climate over the Amazon warms and dries during this century, these tough species of the sandy soils will expand their ranges to dominate the landscape and maintain the functions of the forest?

 

During our time in the Amazon, we hacked through our fair share of tree-falls, endured endless troubleshooting of instruments tormented by the high humidity, and wandered for countless hours through unnamed streets—over asphalt radiating the tropical heat—to find obscure shops for spare parts and field supplies. After five months, we were dead tired.

Back in Arizona, our lives are very different. Most of our time now is spent in front of computer screens, writing scripts in command-line programs to organize and analyze our data. After the day-to-day thrills and challenges of the field, the amount of deskwork ahead of us is daunting. Still, we’re happy to be preparing to contribute our own answers to important questions about how the Amazon is responding to climate change.

As we stare at the numbers on our screens, we remember not just the hardships, but our friends who taught us which vines you can cut for a drink of water, and cold beers with our feet dipped in the old igarapé (a stream) below the camp. We recall the pitter patter of falling flowers that, on closer inspection, look like the heads of alien creatures, and the landscape of odors that sometimes compel you to follow them, like an insect, to their source. As scientists, we will always need more data, and as humans, we will always need more adventure. The Amazon will continue to draw us back for both.

 

Gallery: Researching Amazonia
Photos by Marielle Smith and Ty Taylor

Hover over an image to see its details, or click image to view in larger format and begin slideshow:

 

Post-script acknowledgements: We are indebted to our scientific collaborators and other dear friends from Santarém, Manaus, São Paulo, Campinas, Arizona, Harvard, and elsewhere for their logistical support, productive collaborations, and friendship. Without their support, none of this would have been possible.

 

Tyeen Taylor is a PhD student in ecology and evolutionary biology at the University of Arizona. His research focuses on shifts in tropical forest composition in response to climate change, and he has done extensive research in the tropical forest biome of Biosphere 2, as well as in Costa Rica and Brazil. He practices science communication through writing, movies, photography, and has appeared in interviews on radio and television, including National Geographic’s X-Ray Earth series and two Brazilian broadcasting channels. He is an enthusiast of remote backcountry trips, and of teaching and inspiring others to enjoy the natural world.

Also a PhD student in ecology and evolutionary biology at the University of Arizona, Marielle Smith is investigating how forest structure, principally leaf area, changes seasonally in tropical forests and how this influences forest productivity. She is also interested in understanding how forests regenerate following deforestation. Outside of work, Marielle enjoys mountain biking, road biking and hiking in Arizona’s beautiful desert landscapes. She also enjoys communicating her research via her blog and has had the pleasure of organizing outreach events at Biosphere 2.

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