Nature’s lesser-known carbon player

A closer look at the role animals play in the world of carbon cycling and carbon capture

Grazing Newfoundland moose doing their part to contribute to nature’s carbon cycle. Photo courtesy of Kristy Ferraro

While trees are often seen as the poster child for natural carbon capture, a researcher has set out across Newfoundland to compare the ways other areas of nature contribute to this system – specifically, how large animals store carbon and cycle both carbon and nutrients through our ecosystems.

Carbon cycling, which explores how carbon moves in and out of our atmosphere, has been a longtime fascination for Yale University’s Kristy Ferraro and a wider network of scientists who seek to better understand and harness the way animals interact with carbon as a nature-based climate solution.

Ferraro, a Banting Postdoctoral Fellow who grew up around moose in New Hampshire, is spending two years studying the relationships they and caribou have with carbon in Terra Nova National Park and on Fogo Island.

For Ferraro, it means understanding how large herbivores are intrinsically valuable to ecosystems.

“The question that really drove me was this migration of caribou,” she says. “Why were they going back to these areas to have their calves in the same place over millennia?”

Ferraro is investigating whether caribou return to the same place as a way to benefit from the end result of depositing natal fluid nutrients during calving, which in turn helps plants grow, creating more forage for their herd later on. In theory, their migration could store and move substantial amounts of carbon in each herds’ biomass, in addition to the biomass of the plant life their nutrients support.

Oswald Schmitz, one of Ferraro’s postdoctoral advisors, led a 2018 study that found that animals “play an important role by mediating and balancing carbon exchange between ecosystems and the atmosphere.”

This balance happens as the animals consume and redistribute carbon-storing plant biomass, trample soil, (and in so doing, influence how much sun exposure an area gets for growing more plants) while also changing the chemical makeup of the soil by contributing nutrients from their feces.

The challenge, Ferraro notes, is that climate change, overhunting, and habitat loss have shrunk populations of large mammals, reducing their biomass and carbon cycling effect.

Another element to consider is how moose and caribou interact with carbon stored underground.

Memorial University’s Shawn Leroux, who has spent a decade studying moose in Terra Nova and elsewhere and is now a research supervisor for Ferraro, has brought large herbivores into the spotlight for their overlooked carbon value.

Carbon leaves soil and plants through being eaten by moose — eventually being released into the atmosphere through respiration; getting reabsorbed back into ecosystems through roots, soil, and newly-grown trees that are nourished by moose droppings.

“What we don’t know is the timeframe over which these processes are playing out,” Leroux says. “Maybe over a five-to-ten-year timeframe, a certain animal can have a positive effect, but then that effect might switch.”

Growing populations of large herbivores, he says, might cause more carbon to be released from plant biomass, while fluctuating predator populations might influence where and how much herbivores are eating plants, depositing nutrients, and changing soil conditions.

Considering large mammals as nature-based solutions, called trophic rewilding, is a conservation method of reintroducing animals to ecosystems that Leroux says “makes a lot of sense, as long as we’re not creating new ecosystems by putting animals in areas where they previously weren’t found.”

And it doesn’t stop at herbivores. Schmitz co-published a 2016 study that found wolves benefit carbon cycling by hunting and spreading out herbivores and called for more research into the role of large carnivores in carbon cycling.

Elizabeth Forbes, who’s studied large herbivores in Kenya, is part of a research group that has even designed a robot for measuring animal carbon cycling.

She’s also applied the technology in Newfoundland’s Gros Morne National Park, where moose play an important role moving nutrients between boreal forests and meadows. Forbes explains that what largely helps these animals to cycle carbon between ecosystems and the atmosphere are plant roots and the soil microbes around them.

Simply put, soil absorbs carbon as part of its energy cycle and using robots to help us understand the relationship between herbivores and soil microbes in storing carbon and cycling nutrients could offer insight into how to pull even more carbon from the atmosphere to be stowed underground.

Though Forbes says the science on animal carbon cycling is still fresh, difficult to consistently measure, and not a silver bullet, “it’s an arrow in the quiver of climate change solutions that we’re going to need to look into.”

Along with being tested species by species, animal-carbon relationships must also be studied ecosystem by ecosystem, she says.

For his part, Leroux says he’s excited to get a clearer picture of whether there’s a “universal law” by which animals impact carbon cycling, based on population density, body size, and feeding habitats.

Climate Stories Atlantic is an initiative of Climate Focus, a non-profit organization dedicated to covering stories about community-driven climate solutions.