Scot Martin, the Gordon McKay Professor of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), visualized an innovative drone-based chemical monitoring system in 2017.
His aim was to monitor Amazon’s health in view of the global climate change as well as deforestation and burning caused by humans.
Plants tend to emit chemical signals called volatile organic compounds (VOCs). The project would track these compounds, which aid plants to interrelate with the organisms around them. A different VOC signature—like a fingerprint—is emitted by each species of plant. This signature can change depending on the season or if the plant is stressed by flood or drought, for instance.
Tracking and translating these chemical signals can show how forest ecosystems react to stress induced by climate change. Historically, this type of monitoring has been performed from massive platform towers rising above the forest canopy.
The Amazon contains thousands of small ecosystems, each with their own biodiversity and VOC signals. 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.
Jianhuai Ye, Postdoctoral Fellow, John A. Paulson School of Engineering and Applied Sciences, Harvard University
Martin, Ye, and the remaining group, which includes partners from the Amazonas State Research Support Foundation (FAPEAM) and Amazonas State University (UEA), believed that drones may give more precise information on the forest ecosystem. The researchers’ initial mission showed they were precisely right.
In summer 2018, following many years of prototyping, the scientists finally mapped the chemical signature of two varied ecosystems in central Amazonia by using their exclusively designed drones.
But the researchers’ findings overturned most of the current biosphere emissions models, which believed that adjacent ecosystems had the same level of emissions. The study has been reported in the Proceedings of the National Academy of Sciences.
Plants and insects often communicate via chemical signaling, rather than visual or vocal signaling more common among animals. 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.
Scot Martin, Gordon McKay Professor of Environmental Science and Engineering, John A. Paulson School of Engineering and Applied Sciences, Harvard University
Sloping hills in the central Amazon give rise to water-logged valleys as well as plateaus, divided by rivers and streams. Each ecosystem—that is, the forests in the valleys and on the plateaus, the forests on the hillsides, and the vegetation along the edges of water—has a varied chemical fingerprint.
When the researchers flew drones over slope forests and plateau forests, they observed that the concentrations of a VOC known as isoprene were over 50% higher in the plateau forest when compared to those in the slope forest. They subsequently used this data to create a model which indicated that among these different sub-types of forests, isoprene emissions have increased considerably, that is, from double to triple. However, earlier emission models did not assume any difference because of the absence of measurements.
“This research highlights how little we understood forest heterogeneity,” added 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.”
In fall 2019, the scientists are planning to sample the ecosystems along the rivers and in water-logged valleys. They would use a boat in the middle of the river as a platform to launch and retrieve the drones. The team is also planning to test a three-drone fleet that would be operated simultaneously.
The study was co-authored by Carla E. Batista, Igor O. Ribeiro, Patricia C. Guimarães, Adan S. S. Medeiros, Rafael G. Barbosa, Rafael L. Oliveira, Sergio Duvoisin Jr., Kolby J. Jardine, Dasa Gu, Alex B. Guenther, Karena A. McKinney, Leila D. Martins, and Rodrigo A. F. Souza.
The work was supported by the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), the Harvard Climate Change Solutions Fund, the Brazilian National Council for Scientific and Technological Development (CNPq), a Senior Visitor Research Grant of the Amazonas State Research Foundation (FAPEAM), the Postdoctoral Program in Environmental Chemistry of the Dreyfus Foundation, and the Division of Atmospheric and Geospace Sciences of the National Science Foundation.
(Video credit: Harvard SEAS)