Kristy Ferraro, '24 PhD
A study led by YSE doctoral candidate Kristy Ferraro demonstrates how plant-fungal associations in ecosystems can mitigate the impact of calving animals in nitrogen cycling.
In the expanding field of zoogeochemistry, which examines how animals interact with nutrient cycles, Kristy Ferraro had a novel idea. The Yale School of the Environment doctoral candidate developed a field experiment that would look at how plant-fungal ecology interacted with the nutrients introduced by calving animals — white tail deer — during spring green-up.
“Animals interact with ecosystems in so many different ways. They are constantly impacting, and are impacted by, the environments they live in,” Ferraro said. “Untangling the ways in which animals are supporting ecosystems or contributing to ecosystem function is important because it helps us understand their role. While we know that carcasses and waste can accelerate nutrient cycles and create nutrient hotspots, for large mammals, there hasn’t been much work on the role of placenta and natal fluid in ecosystem functions. There also hasn’t been any work on the interactive effects of animal inputs and the underlying plant-fungal associations. The research really extends beyond the question of how animals impact ecosystems to how ecosystems are modulating that impact.”
This groundbreaking interdisciplinary research, which was published in 2023 in the Journal of Animal Ecology, earned Ferraro the 2024 F. Herbert Bormann Prize. The award honors a YSE doctoral student whose work best exemplifies the legacy of Bormann, a plant ecologist who taught at YSE from 1966-1993 and whose research called the world’s attention to the threat of acid rain. Ferraro received the award at the 40th annual Research Day held at YSE April 12.
For the study, Ferraro and a team of YSE researchers placed animal placentas and simulated natal fluid at Yale-Myers Forest in plots dominated by one of two different plant-fungal associations common in northern forests — ericoid mycorrhizal (ErM) or ectomycorrhizal (EcM). They returned to the sites three months later to record nutrient concentrations in the vegetation in the plots, as well as the cycling of nutrients in the soil. They found that the calving materials act as fertilizers and create nutrient hotspots that ultimately create more nutritious plants for animals to eat. They also discovered that while the nutrients introduced by the calving did accelerate nitrogen cycling, in some cases the underlying plant-fungal associations mitigated the effects by slowing it down.
“Our study highlights one newly discovered piece of an infinite feedback loop between animals and ecosystems … Specifically, the underlying plant-fungal association can mediate the impacts of calving inputs,” Ferraro said.
The study was co-authored by Oswald Schmitz, Oastler Professor of Population and Community Ecology; Mark Bradford, professor of soils and ecosystem ecology; Les Welker ’22,’24 MESc; and Eli Ward ’18 MFS, ’23 PhD.
Ferraro said she was thrilled to receive the Bormann prize for the research.
From left: Les Welker ’22, ’24 MESc; Eli Ward '18 MFS, ’23 PhD; and Kristy Ferraro ’24 PhD conduct field research at Yale-Myers Forest examining how calving animals impact the nutrient cycle and how those impacts can be modulated by plant-fungal associations.
“What is special about the Bormann prize is the legacy it represents. Professor Bormann not only did interdisciplinary work, but he also did impactful work … and that’s the sort of work I want to do. I want to do work that not only brings disciplines together and helps us better understand conservation and ecology, but also makes us do better conservation and ecology,” she said.
Ferraro first had set her sights on studying caribou in Canada, but when the COVID-19 pandemic hit, she restructured her research and worked with Ward, a forest ecologist at the Connecticut Agricultural Experiment Station, to add the component of investigating plant-fungal interactions with zoogeochemistry at a site closer to home.
It wasn’t easy getting the materials for the study, Ferraro noted. Instead of white-tail deer placenta and natal fluid, the team substituted lamb placentas because it was easier to obtain. To get those, she had to call farmers around the state and ask them to freeze the placentas so she could obtain them and place them at the forest sites.
“We called about 50 sheep farmers around Connecticut to ask them to keep the materials, and we got a lot of varied responses. Some were like, ‘Absolutely not. That’s weird.’ But we ultimately found three really wonderful farmers who were super interested in the research and were really engaged,” she said.
After picking up the placentas from the farmers, sometimes out of buckets, the team then placed the placenta and simulated natal fluid in crab traps at the Yale-Myers plots that had the two different fungal associations (ErM and EcM).
“Not everyone has the stomach for it. I barely had the stomach for it. So that was the first hurdle,” Ferraro said.
They also set up camera traps to record animal interactions. The cameras revealed that some placentas were stolen by animals to nourish themselves.
“Turns out possums are really good at sticking their little hands into the cages,” Ferraro said, adding that racoons, coyotes, and turkeys also helped themselves to the placentas.
Despite the scavenging by animals, they found that the natal fluid itself had enough of an impact to bump up nutrient cycling and create nutrition hotspots in the surrounding plant material, but the impact was mediated by both plant-fungal associations, with ErM plant-fungal associations having a slower nutrient cycle compared to EcM.
The findings have important implications. As shrubs move north and spread due to climate change, the ErM plant-fungal associations that are underlyng shrub communities could mute the nutrient hotspots animals create as they did at Yale-Myers Forest, Ferraro said.
“Kristy’s research fits well with the spirit of the Bormann Award. Herb Bormann pioneered the use of experiments at scale to evaluate how human impacts, such as forest harvesting, leads to alterations of biogeochemical cycling across the landscape. Kristy also reports on an experiment, at scale, to evaluate effects of another human impact — forest management that supports deer populations — in boosting biogeochemical cycling. The work gives holistic insight into an animal species’ impact on biogeochemical processes in ecosystems,” Schmitz said.
Other Research Day award winners include doctoral students Destiny Treloar, who earned the Schmitz Prize for best oral presentation for her research on “Exploring the Relationship Between Sociodemographic Characteristics, Food Access, and Food Assistance Participation During the COVID-19 Pandemic in a Predominantly Hispanic/Latino City: Hialeah, Florida; Lachlan Byrnes, for Best Poster on “Contrasting patterns of mortality in an Amazon-Cerrado forest edge during exceptional drought”; and Ananya Rao ’25 MESc, who received the Master’s Student Oral Presentation Prize for her research on “Leveraging Community Forest Resources Rights to augment NTFP-based livelihoods in Central India.”
