This post is part of the LTER’s Short Stories About Long-Term Research (SSALTER) Blog, a graduate student driven blog about research, life in the field, and more. For more information, including submission guidelines, see lternet.edu/SSALTER
By Jon Gewirtzman (PhD Student at Yale University; Harvard Forest Graduate Student Researcher) and Hannah Burrows (Undergraduate Student at Harvard University; Harvard Forest 2023 REU Alum)
Trees are widely recognized for their role in carbon cycling, but did you know they also emit methane, a potent greenhouse gas? Understanding this lesser-known process requires exploring methane emissions across different environments and layers of the forest, from the ground to the canopy. Our research, based at the Harvard Forest LTER site, delves into these dimensions to get a clearer picture of how trees contribute to methane emissions across space and time.
Working in 2D: Exploring the Transition Zones
Our work begins in the transition zones between uplands and wetlands—areas that often go unnoticed but are crucial for understanding how trees respond to varying moisture conditions. The “soggy side” of the forest might not be the typical postcard image, but it’s vital for capturing methane dynamics. And these areas, rich with ancient trees, mosses, and ferns, have a beauty of their own when you stop to look.
As in much of ecology, our toolkit is a blend of high-tech and low-tech. We use high-precision, laser-based gas analyzers to measure methane, but the chambers we use to capture the gasses are made from Tupperware or PVC and stuck onto trees with caulk or clay. It’s a hands-on, practical approach—one that requires getting our boots wet while trying to keep the sensitive equipment dry! Setting up these experiments in wetlands is no small task, but the insights we gain from these challenging environments are invaluable.
Credit: Ben Goulet-Scott, CC BY-SA 4.0.
Adding a Third Dimension: Heading Up to the Canopy
Of course, there’s a whole lot more of the tree above us, where it’s harder to reach and measure. Trees are tall, complex organisms, and their emissions can vary throughout their height. So, we’ve expanded our research to include the full vertical profile, from the ground to the canopy. By measuring emissions along the entire height of the tree, we gain a more complete picture of how trees emit gasses throughout their structure—and it literally gives us a new perspective on the forest.
Credit: Ben Goulet-Scott, CC BY-SA 4.0.
Canopy work presents its own challenges, but at Harvard Forest, we’re fortunate to have access to a bucket lift. Even so, swaying in the wind 100 feet above the forest floor is not for the faint of heart. Yet, when the wind dies down and we take a moment to look away from the analyzer screens, we’re immersed in the canopy’s vibrant life—surrounded by shimmering leaves, lichens, and the calls of birds that feel distant from the forest floor.
Credit: Jon Gewirtzman
Moving to 4D: Seasonal and Diurnal Changes
In addition to examining spatial variations, we’re also exploring how methane emissions shift over time—adding a fourth dimension to our work. This includes both daily fluctuations from morning to night and seasonal changes from summer to winter.
Winter adds some complications to our typical methods, navigating wetlands now frozen and maintaining sensitive equipment in cold, wet conditions. However, it’s important to cover any possible source of variation we do or do not expect. You’ll never know what you’ll find unless you look! As difficult as winter fieldwork can seem, it allows for the opportunity to observe the forest in a new light with fresh snow covering the treetops and a soft quiet behind the thrum of the gas analyzer. Winter may be cold and silent, but the forest is never truly sleeping. And the cold was never too bothersome, especially when we could take a break to join the soup club.
Credit: Annabelle Rayson, CC BY-SA 4.0.
Measuring methane fluxes over a 24-hour period poses its own challenges. Trees “wake up” with the rising sun as sap begins to flow, and this daily restart of water and gas transport may play a key role in methane transport. To capture this, we conducted an around-the-clock measurement campaign, camping overnight with the help of some generous collaborators—and plenty of coffee and pizza. Hourly measurements over a full day and night offered a unique opportunity to observe another side of the forest and time to experience its quiet stillness (with the occasional jump at mysterious noises in the dark).
Credit: Jon Gewirtzman, CC BY-SA 4.0.
(Photo: Jon Gewirtzman. Measuring fluxes in the Harvard Forest black gum swamp at 3 AM)
Reflections
Hannah: I first came to Harvard Forest as a bright-eyed first year with no prior research experience—but I did have experience being curious about the natural world around me, the only prerequisite I needed to get involved with the LTER. Through my summer there as an REU student, I’ve discovered an entire community of students, professors, and researchers built from this forest that I’ve learned and grown so much from. They have supported me endlessly as I take the first steps in my research career, during and after my program. After my summer, I’ve returned to the forest several times and even presented a poster at ESA 2024 where I was able to reunite with some of my REU cohort and the amazing scientists from the Harvard Forest LTER.
Jon: Mentoring REU students has been one of the most rewarding aspects of my work at LTER sites. These long-term research programs give students the chance to engage in hands-on science that goes far beyond the classroom. Watching them grow from fieldwork novices to confident researchers has been incredibly fulfilling. Their contributions have been invaluable, and I’m excited to see how their future research interests evolve.
Our work at Harvard Forest has only scratched the surface of understanding how trees contribute to methane emissions. As we continue exploring the forest’s hidden dynamics, we are reminded of how much there is still to learn, and with each new discovery, we gain a deeper appreciation for its complexity and the role it plays in the global climate. We’re excited to keep learning from the forest and see where it leads us next.
