Drones Perform Amazon Health Check
By Christina Phillis
The Amazon rainforest is a vast and difficult-to-traverse region, so observing its health can be a challenge. It spans eight different countries and accounts for half the planet’s remaining tropical forests. That’s why a team of scientists at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) turned to high-flying drones to track the well-being of this important resource.
A Planet Under Duress
The health of the planet and the Amazon rainforest is invariably linked. As deforestation continues, more harmful carbon dioxide stays in the atmosphere instead of being converted into oxygen. This only aggravates the effects of climate change, and in turn, causes further harm to the rainforest.
One way to track how these plants are responding to climate change is by monitoring their chemical signals. Each species of plant emits unique volatile organic compounds (VOCs) that help them interact with other organisms. When a plant is responding to stress, these signals can change.
“Plants and insects often communicate via chemical signaling, rather than visual or vocal signaling more common among animals,” said Scot Martin, the Gordon McKay Professor of Environmental Science and Engineering at SEAS. “With our chemical sensors, we can better understand the current functioning of the forest and how it is changing with shifting regional climate, including a more frequent occurrence of fires in recent years in the central part of the Amazon.”
Even trees from colder regions of the world have been found to emit higher levels of terpenes as temperatures rise. When VOCs from plants enter the atmosphere, they can react with existing chemicals to form aerosols, further contributing to air pollution. Increased air pollution leads to higher-than-average temperatures and plants that are under stress emitting VOCs. It’s a vicious cycle.
Up until this point, monitoring the health of the Amazon has been accomplished using large platform towers that rise above the forest.
“The Amazon contains thousands of small ecosystems, each with their own biodiversity and VOC signals,” said Jianhuai Ye, a postdoctoral fellow at SEAS. “Yet, there are less than 10 of these towers in the entire forest and they are all built in similar ecosystems where the soil can support large structures. As you can imagine, this leads to a lot of bias in the data.”
The team, which included collaborators from Amazonas State University (UEA) and the Amazonas State Research Support Foundation (FAPEAM), believed they could get more accurate data using a drone-based chemical monitoring system. The drone could collect samples of VOCs at various altitudes and specific points. Utilizing lightweight materials, it could withstand the heat and humidity of the jungle.
Taking to the Skies
In the summer of 2018, the team used their specially designed drones to map the chemical fingerprint of two different ecosystems in central Amazonia. Their findings, published in the Proceedings of the National Academy of Sciences, challenged most present-day models, which assumed nearby ecosystems had the same emissions.
"This research highlights how little we understood forest heterogeneity."
Researchers flew drones over plateau forests and slope forests and found a significant difference in the VOCs of these two locations. The plateau forest had 50 percent higher concentrations of isoprene than the slope forest. The model they developed based on this data suggested isoprene emissions doubled to tripled among these forest sub-types. Prior emission models assumed no difference.
“This research highlights how little we understood forest heterogeneity,” said Martin. “But drone-assisted technologies can help us understand and quantify VOC emissions in different, nearby ecosystems in order to better represent them in climate and air quality model simulations.”
The team continued their research in Fall 2019, this time observing the valleys and rivers of the Amazon. In the future, they plan on testing a three-drone fleet operated in unison. As climate change remains an issue, this technology will only help us truly understand its far-reaching effects.