Catherine Cardelús Climbs into the Canopy, Uncovers Insights about Epiphytes

The summer after Catherine Cardelús graduated from Barnard College in 1996, she found herself about 30 meters above the forest floor exploring the rainforest canopy for the first time at La Selva.

“It was magnificent,” she said. “When you’re just peeking your eyes over the branch, you’re looking under all of these plants, and there’s so much life there.”

Cardelús hasn’t stopped climbing. She received a prestigious NSF Graduate Research Fellowship and her doctorate from the University of Connecticut. Now, as a Professor of Biology & Environmental Studies at Colgate University, one of Cardelús’ main research interests is to better understand how epiphytes (commonly described as plants that live on other plants) in the rainforest canopy function under changing conditions.

Since her first trip to La Selva in 1996, Cardelús has returned most every year to the research station to collect data in the canopy or to teach her tropical ecology course, mentoring a cadre of students in tropical ecology along the way.“I spent two months there (La Selva) after college, and that was it,” she said. “I was hooked and never going to leave again.”

As a tropical biologist, Cardelús is particularly interested in how epiphytes acquire nutrients and how their ability to do so may shift with climate change. This question is a complex one, especially given the diversity of epiphytes present in the canopy. When climbing her first tree, Cardelus was struck by the variety of plants living on each tree branch.

“I can have 60 species on a 3-meter branch, whereas on the forest floor, in 3 meters, you don’t get 60 plant species,” she said.

Diversity isn’t the only characteristic separating ground-dwelling from canopy-living plants. While plants on the forest floor have roots that dig into a thick layer of soil, epiphytes in the canopy do not have this option. What they do have, however, is closer access to the air – including rain – as well as a thin layer of soil.

So, epiphytes use what they have available to them.

Cardelús explained three different successful strategies present among canopy plants in the rainforest. For example, some bromeliads utilize leaves, instead of roots, to absorb water. They have a “special cell” in their leaves enabling them to do so. Other bromeliads have a tank where they catch rainwater. This tank often serves as a handy home for frogs to lay eggs and spiders to hunt while the base of the tank is home to mutualistic ant colonies.

Bromeliads aren’t the only epiphyte to leverage canopy resources. Aroids have a different strategy, using aerial roots that “hang in the air” to absorb nutrients when they are wet, Cardelús explained. Other epiphytes, such as ferns, have roots that burrow into the canopy soil. This soil layer is much thinner than soil on the forest floor – about 2 to 6 centimeters.

This soil layer may be thin, but it is popular. Cardelús said canopy soil is home to a variety of organisms’ roots that are “intertwined.” To illustrate, when conducting field work and sampling the canopy soil, Cardelús said, “It takes hours to shake off the soil and take off the root systems from it, so it’s a very complex, intricate system.”

Although many of these diverse canopy plants are competing for the same limited resources in the canopy, Cardelús said they tend to coexist with one another.

“I always think of this as the greatest example of niche partitioning,” she said. “All of these plants are living on top of each other, and they’re avoiding competition. They take up nutrients differently and have different light demands.”

Epiphytes aren’t the only organism living in a rare spot and working closely with one another. So, too, do scientists at OTS who are working and living in a remote research station and uncovering scientific insights.

At OTS, Cardelús said she has found a strong community filled with like-minded “quirky, lovers of nature.” Cardelús’ research community also includes the students she has trained in canopy biology at La Selva and field assistants who know the forest well.

Exploring the canopy is hard and rewarding work, according to Cardelús. Each person carries around 30 pounds of equipment to the study tree, including about three liters of water. Once the team has walked approximately an hour, they then begin to climb the tree. Reaching the top of the canopy can take anywhere between 15 to 45 minutes, depending on the day and the tree.

And that’s only the beginning of the field day.

“It’s really gorgeous, but it’s exhausting (to climb),” Cardelús said. “And once you get there, then you’ve got to start working.”

Cardelús and the students begin tagging plants and collecting leaf samples. For example, one of her recent studies focuses on how epiphytes respond to varying nutrient and water levels – an important topic as climate change’s impacts accelerate. While Cardelús is currently working with her collaborators to publish the findings for this study, she shared some big-picture insight about what could be happening among epiphytes in the canopy.

“We’re disrupting millions of years of evolution in a habitat that will likely see a loss of species richness,” she said.

These samples that the team collects in the canopy are integral to better understanding which epiphytes will be “winners” and which ones will be “losers” in a shifting environment. But the work doesn’t stop with climbing the tree. Back at La Selva – after a shower and some food, of course – the team then works to process the plants right away.