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Using Tree Rings to Reconstruct Guatemala's Climate

Doctoral student's research has implications for coffee growers

Diego Pons just might have it all. He gets to undertake fieldwork on remote mountaintops in Guatemala, give back to his country, mentor the next generation of students, and — not to be overlooked — drink some of the world’s finest coffee in the process.

A doctoral candidate in DU’s Department of Geography and the Environment, Pons will defend his dissertation in May. His research ties together climate change, coffee production and community engagement in Guatemala, a country heavily dependent on subsistence agriculture and highly vulnerable to climate change.

“As a Guatemalan, I’m very passionate about my country,” Pons says. “Because coffee production supports a lot of families, I feel responsible for trying to bring something back that will help rural communities.”

A paper he recently published in the Annals of the American Association of Geographers does exactly that. By employing dendroclimatology — the use of tree rings to determine past climate — Pons and his colleagues lay the groundwork for providing coffee growers with valuable climate information. The research was supported by DU, the National Science Foundation, American Association of Geographers and National Geographic Society.

Guatemala’s population is heavily dependent upon cash crops that are themselves dependent upon the timing and quantity of rainfall. Coffee is especially finicky, requiring highly specific climate conditions. A lack of weather stations throughout the country, particularly in remote areas, has resulted in a dearth of knowledge about local climate. Such information is crucial for helping farmers — many of whom live in poverty — grapple with the hotter, drier conditions expected to result in Guatemala as the planet heats up.

This is where Pons’ fieldwork comes in. Collaborating with a research team that includes his advisor, geography professor Matthew Taylor, he has successfully used tree rings to produce a climate record stretching back to the late 17th century. This historic data will serve as a benchmark for assessing present and future climate in Guatemala’s mountainous regions.

The researchers accumulated tree ring samples by hiking throughout the mountains in search of elusive, old-growth Guatemalan fir and mountain pine trees. From the trunks of these, they collected slivers of wood that they analyzed in a lab at the Universidad del Valle de Guatemala. There, they used dendrochronology methods to determine past climate based on properties in the tree rings.

Along the way, they learned that, in Guatemala, it takes a village to find a tree. Tropical fieldwork is challenging enough even before factoring in the country’s 23 distinct languages, land-distribution inequities, ambiguous rights over communal territories, and history of indigenous repression that often triggers distrust of outsiders. It was only through reaching out to local community leaders and engaging them in the search for trees that the team’s reconnaissance and tree sampling were possible.

This community engagement also provided valuable perspectives sometimes lacking in scientific research. For example, indigenous Guatemalans in mountainous regions refer to old pine and fir trees as “the wise ancient trees,” a description whose symbolism wasn’t lost on researchers searching for arboreal archives of historic climate information.

“Our science matches their beliefs,” Pons says. “Something that I love about this research is incorporating traditional knowledge.”

The next step for Pons is to transform the data into locally relevant climate information and communicate it to agricultural communities in a way that directly benefits them. The Guatemalan National Coffee Association, which represents more than 90,000 growers, has already expressed interest.

“The goal is to bridge the gap between what we know and what we need to do to make communities more resilient to climate change,” Pons says.

Taylor, who has conducted field research in Latin America for more than 20 years, emphasizes the connections linking climate change, agriculture, and human migration in the region.

“Hundreds of thousands of people rely on the coffee sector in Guatemala,” he says. “If it goes belly up because of climate change, we will see many more rural people on the migration road to Guatemala’s cities and, beyond that, to North America.”

“Diego’s research will permit policy makers at all levels to better prepare for climate change and its impact on Guatemala’s agricultural sector,” Taylor adds. “This is especially crucial for a country that is so dependent upon agriculture.”

As for Pons, he’ll soon hold a doctorate from DU. Having discovered that his enthusiasm for teaching matches his enthusiasm for fieldwork, he plans to stay in academia. At DU, he has worked closely with undergraduates in the geography department’s dendrochronology lab. He currently mentors students in the lab at Universidad del Valle de Guatemala, where he received his undergraduate degree.

“I really love integrating young students, working with undergrads, and bringing them into the lab,” he says. “I want to engage more people in this research.”

A core mission of DU’s Division of Natural Sciences and Mathematics is to offer students unprecedented access to research opportunities. By working alongside distinguished faculty mentors in state-of-the-art facilities, undergraduate and graduate students are able to apply their knowledge to research that changes lives and challenges ideas.