When you return to the same forest month after month, year after year, incremental changes can become unmistakable trends. In the tropical dry forests of northwestern Costa Rica, Professor Jennifer Powers and her collaborators have been sorting what falls into litter traps every month since 2008: leaves, twigs, seeds, and, unexpectedly, caterpillar frass. In some years, the tiny pellets were so abundant that they accounted for a striking share of the material raining down from the canopy. Then, over time, the volume declined.
“We never set out to measure caterpillar poop,” Powers says. “It was just so abundant that we had to deal with it.” What began as a practical necessity has become a long-term record of dwindling insect activity, an unexpected dimension of changing forest dynamics.
Long-term observation, however, also captures sudden ruptures. In 2015, an exceptionally strong El Niño brought the lowest rainfall on record in northwestern Costa Rica. In Powers’ permanent forest plots, annual mortality rates more than doubled. In one plot, a large portion of the oaks that dominated the canopy died. “It used to be the best plot to work in,” she says. “Now it’s just this giant liana tangle.”
The observations raise questions about how particular species and the ecosystems they’re part of respond to disturbance — whether from climate change, shifting land-use, or other forces — and how those responses ripple outward over time. Answering those questions requires more than a single plot, or even a single discipline. The impact of the drought became legible in part because multiple research teams had committed to the same forest for decades. Powers’ tree censuses overlapped with monitoring by primate researchers who had been tracking tree flowering, fruiting, and vegetative patterns for years. “We were able to build this big collaborative dataset to really understand the extent of tree mortality,” Powers explains.
To understand why certain species died while others persisted, Powers turned to colleagues at the University of Tasmania who study how trees move water through their tissues. As it turned out, traits like tree size and leaf shape didn’t explain why some species survived the drought while others perished. The most telling differences lay in how much stress the tree’s internal plumbing could endure. Species with narrower margins for error were far more likely to die.
In recent years, Powers has extended that inquiry outward through large-scale collaborations such as SNAPP-MORE, which is collating long-term data on restoration outcomes to inform monitoring, and TropiRoot, a synthesis effort focused on fine roots in tropical ecosystems. A related initiative, the Tropical Roots and Disturbance (TropiRAD) project, brings together researchers across institutions and countries to understand how tropical root systems respond to disturbance. While dramatic canopy dieback captures attention aboveground, some of the most consequential responses occur below the surface.
Through TropiRAD, which Powers leads, the team worked with research librarians at the University of Minnesota to systematically review thousands of published studies, narrowing them to a curated set for quantitative analysis. The goal is to identify consistent patterns in how roots respond to disturbance and to integrate those findings into global databases used to improve ecosystem models. If Powers’ long-term observation in Costa Rica revealed the vulnerability of certain species to extreme drought, TropiRAD aims to determine whether similar principles apply more broadly, and how those belowground responses may shape the resilience of tropical forests.
Powers is a field ecologist through and through, with a particular passion for the artistry involved in observing and recording the natural world. (She’s even organized symposia on the integration of art and biology.) Yet her work increasingly unfolds in collaboration with modelers, who are developing large-scale simulations of how forests grow, die, and store carbon under shifting climate conditions. The relationship runs both ways. Field measurements refine the assumptions embedded in the models, and in turn, the models generate new questions for researchers on the ground.
Across these projects, including work she and her graduate students have conducted in the tropics of Africa and Southeast Asia, Powers’ research is united by a commitment to understanding how forests change, and how people might respond. “I didn’t come to tree mortality,” she says. “Tree mortality came to me.” In forests where change can unfold slowly — or all at once — her work circles back to a set of enduring questions: what survives, what disappears, and how those insights might guide the stewardship of tropical forests in a warming world. –Jonathan Damery