Once a patch of tropical forest is razed, it isn’t necessarily gone forever. Trees and wildlife often return, if given a chance. As trees grow, the forest resumes its role as an air filter, drawing planet-warming carbon dioxide out of the atmosphere and storing it.
That recovery process carries with it both hope and unanswered questions. “Can we help mitigate climate change by restoring tropical forests?” asks Justin Becknell, assistant professor of environmental studies. “If so, by how much, and how fast?”
Becknell’s research aims to answer those questions.
Humans are destroying tropical forests at a breakneck pace for logging, agriculture, and real estate. But when loggers move on, or markets fall out, new plant growth filters back in, creating what are known as secondary forests. Becknell has surveyed such forests in Costa Rica and Brazil, measuring how much carbon they are on track to sequester.
His findings were included in a broad analysis, published in the journal Nature in 2016, concluding that secondary forests in Latin America can accumulate 90 percent of the carbon that a mature forest would have, and do so within 66 years.
Sixty-six years “is a great number, because it says that these forests grow back really, really quickly,” Becknell said. “That’s a cool finding that kind of surprised us all as we put all of that data together.”
Becknell grew up in Minnesota, where regular father-son getaways to the state’s northern wilderness areas fostered an early love of the woods. Later, as a science-interested undergrad at the University of Minnesota, he said, “my ears would always perk up when we started talking about forest ecosystems.”
While pursuing his Ph.D. in ecology, evolution, and behavior at the University of Minnesota, he worked as a research assistant in Costa Rica on evaluations of forest land recovering from conversion to beef pasture. He was energized both by the scientific questions surrounding secondary forests and their potential role as a solution in the quest to manage climate change.
His fieldwork typically has two modes. On the ground, he measures trees from plot to plot of forest, using that inventory to estimate carbon storage across a region. In the air, he uses LIDAR—which stands for Light Detection and Ranging, a form of remote sensing using laser light—to conduct landscape-scale surveys.
Becknell, who joined Colby’s environmental studies faculty in the summer of 2017, plans to study Maine’s forests as well, to see how forest management practices relate to carbon absorption. He also wants to experiment with different uses of LIDAR. One involves mounting a sensor on a drone, which can fly lower than a plane would and collect data at a higher density, while the other involves using LIDAR from a tripod under the canopy. Both are complicated, relatively new approaches in forest ecology, he said.
“My early work was mostly measuring tapes and shovels,” Becknell said, “but now I do a lot more laser beams and writing computer programs.”
The stakes are higher than you might think. Between 50 and 60 percent of the world’s tropical forests are recovering from some kind of human disturbance, Becknell estimates. And as the human population grows, the pressure on forests will continue.
“We’re continuing to log the whole world,” he said. Because of that, “the forests of the future are really going to be the secondary forests.”
Portrait by Heather Perry ‘93