Hurricane Maria May Help Scientists Predict How Rainforests Respond to Climate Change

Devastation of Hurricane Maria surrounding National Forest sign with CLOSED tape over the entrance.

The storm that devastated Puerto Rico became an unexpected variable in the world’s first tropical forest warming experiment

Story by Shannon Kelleher

In the early hours of September 20, 2017, Tana Wood hunkered down at her home in Luquillo, Puerto Rico as Hurricane Maria came barreling towards her. At 6:15 am, the storm made landfall, pummeling Yabucoa Harbor with 155 mile per hour winds and dousing parts of the island in 30 inches of rain. By the time Maria exited the U.S. territory near the city of Arecibo, swooping northward to plunder the Turks and Caicos Islands, lives were lost (the exact death toll remains, as of yet, undetermined) and entire neighborhoods were torn to pieces. Electrical blackouts plunged Puerto Ricans into darkness that would last for months.

As soon as it was safe to come out, Wood, a research ecologist with the USDA Forest Service’s International Institute of Tropical Forestry (IITF), jumped in her car and set out for El Yunque National Forest. She was rattled by the storm, but even in the wake of a natural disaster her scientist brain was whirring. Wood wanted to know if her team’s tropical forest climate warming experiment was still standing. She was especially curious whether the canopy observation tower, a tall metal structure used to study nutrient cycling in the treetops, had managed to fare the storm. As she approached the project site, she found the forest unrecognizable.

“The forest canopy was completely defoliated,” Wood says. “I mean, It was like this sheet was pulled back and you could suddenly see all these houses and landforms, structures you had never seen before.”

One story behind El Yunque’s name is that the indigenous Taino people called the forest “Yuke” or “white lands,” referring to the way its mountaintops disappear into the clouds. After the storm, the description seemed to take on a new meaning. Now, all of the leaves had been stripped from trees like flesh from bone, leaving behind a mess of pale, spindly trunks where dense foliage existed hours before. The trunks jutted blankly from the soil—skeletal remains of the only tropical rainforest in the U.S. National Forest System.

But there was one forest fixture the hurricane couldn’t destroy. Wood rounded a bend, and to her shock, there was the canopy access tower. Somehow it was still standing, rooted in place among the wreckage of trees that had once concealed it from view.

The World’s First Tropical Field Warming Experiment

view looking up from the bottom of the TRACE canopy tower, tall metal structure Three years before Hurricane Maria hit El Yunque, Wood and her team began constructing an elaborate experiment to measure how climate change might alter the forest’s physiology, information which could help global modelers improve their predictions. They called it the Tropical Response to Altered Climate Experiment (TRACE), and it would become the first study of its kind.

“There have been no field warming experiments in any tropical ecosystems,” Wood says. “So there is a gap of knowledge in our understanding of how systems respond to warming at this end of the temperature spectrum.”

Wood thinks one reason for that knowledge gap is a long-held belief that ecosystems in already warm environments won’t be as affected as colder regions when temperatures climb a little higher. Mounting concerns about the future of the Arctic tundra, northern grasslands, and temperate forests—regions where there are distinct differences in seasonal temperatures—have manifested in northern warming research. But Wood and her team believe climate change offers plenty of risk for tropical forest ecosystems, too.

“There is evidence to suggest that tropical forests could be near high-temperature threshold,” she says. Wood worries that as the climate warms, forests like El Yunque may have reduced capacity to provide important services to the planet, like storing carbon and supporting an enormous quantity of diverse organisms.

Dr. Tana E. Wood, USFS Research Ecologist, standing in front of one of the TRACE control plots 8 months after Hurricane Maria. Equipment and dense understory visible in background.However, there is another reason scientists have been hesitant to undertake similar forest warming projects—a rainforest is just about the worst place on Earth for high voltage equipment, and this is electricity-intensive work. “We have 480 volt electricity going into a forest that receives three and a half meters of rainfall a year, and 100% humidity in warm temperatures,” Wood says. “Which is the perfect environment for mold and fungus to grow, and for arc flashes with the equipment. [And] I start thinking about if I was going to do this in Costa Rica where they have venomous snakes,” she adds. “Some of them climb trees.”

So for Wood and her team, El Yunque seemed like the perfect place for a tropical forest warming experiment. Its location in a U.S. territory with a Forest Service research institute meant infrastructure benefits—they could access the reliable electrical power and staffing resources needed to maintain an ambitious experimental design. Plus, most of the snakes are harmless.

One of the TRACE experimental warming plots in 2015, before the experiment fully started. There was much more forest canopy and foliage in this site before the hurricanes hit in 2017.The experiment they constructed consisted of six different land plots, each measuring four meters in diameter, with three as the control group and three warmed to the test temperature. Within each plot sat an array of six infrared heaters arranged in a hexagon, each angled inwards 45 degree and connected to a central control panel which would regulate the heating elements.

Soil moisture and temperature sensors were buried 50 centimeters underground to determine if the warming could also have a drying effect, and automated chambers were installed to measure soil CO2 emissions every hour. Clear plastic tubes were fixed in the soil, with plans for a PhD student to probe them with a small camera every two weeks so that root growth could be compared from the photographs. Soil samplings were planned, with designated researchers to inspect biogeochemistry and analyze microbial DNA. “We’re thinking about everything from the roots to the microbes,” Wood says.

But before getting started, Wood and her team consulted with experts to ensure the setup would not harm local wildlife and carefully scoped out any snags that could alter their data. The control groups were outfitted with the exact same equipment, to account for shade provided by the posts and panels. Arrangements were made to average all three control plot thermometer readings before determining the proper test plot temperature. The heaters were even built so they could be lowered and raised, allowing the experiment to grow with the surrounding vegetation.
In September 2016, with the entire setup in place, the team began warming their test plots to four degrees Celsius above the control plot temperature. “The projection for the tropics over the next twenty years is that we’ll see between four and six degrees warming, so we picked a midpoint,” Wood says. “The goal wasn’t necessarily to simulate a specific future scenario, because we can’t know the future.”

For one year, the scientists gathered data from these curated plots of land, taking the pulse of a warming world until the day the hurricane hit.

Picking up the Pieces

During her post-hurricane reconnaissance trip, Wood discovered that most of the equipment at the field site had miraculously survived. Aside from an understory weather station crushed by falling trees, the experiment was safe. Her team had even managed to swing by a few days before the storm hit, removing some equipment and taking last-minute samples, which were hastily overnighted to a collaborator in Moab, Utah. And in a somewhat surreal display of technological fortitude, many of the data sensors had kept right on documenting soil conditions while Hurricane Maria pummeled the island.
One of the TRACE experimental warming plots, after cleaning up the debris and logs that fell on top of the infrastructure during Hurricane Maria.
It seemed, despite everything, that the experiment had fared well. And as community members learned about the project when they saw the unconcealed canopy tower for the first time, many offered to lend the scientists a hand. Residents of Luquillo worked alongside Forest Service interns, technicians, and seasonal hires to sort roots, clear a path through the forest, and put the pieces of the warming experiment back together. “It feels like it’s not just a Forest Service project,” Wood says. “It’s like something owned and invested in by a large group of people here in Puerto Rico.”

But as Wood soon realized, getting the forest warming experiment up and running in post-hurricane Puerto Rico—not to mention simply meeting her own basic needs—would not be easy. It would be two weeks until she could make it to the IITF headquarters to call friends and loved ones, and she wouldn’t regain cellular service at her home until November. “We had no form of communication at all after the storm,” Wood says. “Thankfully, the Forest Service had a radio, so I gave them the phone number to my Mom to tell her I was OK.”

TRACE intern Tessaliz Quiles-Delgado is collecting soil pore water to analyze for nutrients. In those first most difficult weeks of the aftermath, she would travel to a wireless Liberty Cablevision hotspot, often arriving at 4am just to send an email before the building became overcrowded with hundreds of people trying to make calls. “In the midst of all that, trying to facilitate repairing the experiment, talking to our collaborators and thinking about what our next steps were going to be was a challenge,” Wood says.

She and her team tried to adapt. When Wood went to the headquarters, she would take messages back to the field station, often leaving hand-written notes in an effort to keep their work going. But as the weeks wore on, Wood struggled with new way of life forced on the entire island by Hurricane Maria. It was nerve-wracking watching basic goods dwindle, and the effort required to get things she needed was exhausting. “I planned for a week without food,” Wood says. “I didn’t plan for how long we were going to go without having grocery stores that had food in them. There were hour long lines to get into Walgreens if you needed medication or milk or bread. The stores were empty.”

But Wood felt fortunate for the assistance she received from her colleagues and the Forest Service. A colleague flew in to Puerto Rico with supplies, ordinary objects that suddenly became precious—solar lights, a mosquito net, a battery-operated fan. And there was a generator in the field station, so Wood and the other researchers could go there to charge their phones. Even better, the field station provided clean water and ice, as well as a camp stove and a backup battery she could take home. “If it hadn’t been for the field station, I don’t know if I could have made it,” Wood says.
post hurricane house, surrounded by debris, broken tress, and down power lines
All around her, Puerto Ricans found themselves forced to make do with much less. Many lost their running water and had to bathe and wash clothes in rivers. Many others lost their jobs. “There was this career fair for people in the community to get these temporary jobs at the Forest Service,” Wood says. “Probably a thousand people came looking for work. We were looking for volunteers to help with the warming experiment, and [this woman] was like ‘I’ll do anything. My whole family lost their jobs. We have no way to get money.’ Afterwards, I just started crying. [There were] people who were educators or architects, very skilled, educated people that had no source of income and were looking for anything they could do in order to survive.”

Looking to El Yunque’s Hotter Future

Puerto Ricans would continue to face an uphill battle for months to come. But meanwhile, something in El Yunque was stirring. Less than two weeks after the storm, new leaves sprang to life all up and down the barren tree trunks, giving them a hopeful adolescent appearance that reminded Wood of bottle brushes. The understory soon grew thick with vegetation, uninhibited by the canopy that blocked out sunlight before the storm. Come December, seedlings were popping up all over the forest floor, fertilized by fallen leaves.

One of the TRACE experimental warming plots, 6 months after the impacts of Hurricanes Irma and Maria. Seedlings and herbaceous plants have been growing rapidly due to increased sunlight reaching the understory.As the forest continues to heal, Wood and her team are now working to analyze the pre-hurricane results from their first year of data collection. So far, one finding stands out—while carbon levels stayed the same at both baseline and elevated temperatures, available phosphorus in the warmed soil plummeted. The team is still trying to understand why, but they believe lower levels of this key nutrient could affect microbial communities and stunt plant growth.

After they finish analyzing the pre-hurricane data, Wood and her team will begin warming the plots again—this time to understand what a natural disaster like Hurricane Maria could mean for a hotter El Yunque. “Our question going forward is, in the face of a warmer climate following a disturbance like this, are we going to see a different trajectory of recovery?” says Wood. “[Are warmer temperatures] going to affect the community composition? Does [warming] exacerbate changes to microclimate, nutrient cycling, and plant physiology?”

Despite everything she and her team have experienced over the past months, Wood sees an invaluable silver lining in the chance to answer questions like these. “We’re going to be the only project in the world that has the opportunity to look at interactions of hurricane and increased temperature,” she says. “And that’s probably going to be a reality we face.”

Shannon Kelleher