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Wild impact

Biologist publishes research on animal influence on the carbon cycle


By Kelly Foss

Animals influence carbon cycling across landscapes in ways that could impact climate change.

That’s the finding of a new paper published today in Science magazine.

Moose eat 10 kilograms of dry matter a day and have the potential to alter forest carbon storage.
Photo: Eric Lebel

Dr. Shawn Leroux, an associate professor in the Department of Biology, Faculty of Science, co-authored the paper with researchers from the United States and Brazil.

Terrestrial and aquatic ecosystems

While predicting and managing the global carbon cycle requires an understanding of the ecosystem processes that control carbon uptake and storage, the researchers say current models focus on the exchange between plant and soil pools and the atmosphere, and don’t account for the role wild animals can play.

“In our paper, we synthesized the growing literature showing the effects animals can have on carbon flow in terrestrial and aquatic ecosystems,” Dr. Leroux said. “For example, in Newfoundland and Labrador’s boreal ecosystem, one moose can eat 10 kilograms of dry matter a day and deposit a lot of feces.

Moose in the forest
Browsing by moose following a spruce budworm outbreak in Cape Breton, N.S., has led to failed regeneration of balsam fir forests. They are being replaced with open grassland-spruce meadows, which store much less carbon.
Photo: Eric Lebel

“By selectively feeding on their favourite plants, moose can prevent forests from regenerating, which can have a huge impact on carbon storage,” he continued. “In some cases, forests that would be a carbon sink, or something that pulls carbon from the atmosphere and retains it in plant biomass, is actually becoming a carbon source and contributing to climate change.”

Dr. Leroux says animal impacts on the carbon cycle are being felt worldwide.

“With these movements, animals are transferring carbon across ecosystem boundaries.” — Dr. Shawn Leroux

The team’s research included examples from marine and freshwater systems and boreal, tundra, tropical and savannah ecosystems. Animal species such as sharks, sea otters, caribou and geese, among others, were included in their analysis.

“Some of these animals have huge migration patterns, ranging over thousands of kilometers, so they can influence the distribution of carbon over large areas,” said Dr. Leroux. “Some also use multiple ecosystems. Salmon migrate between ocean and freshwater ecosystems, moose feed in ponds and rivers on aquatic vegetation, but reside in terrestrial ecosystems.

“With these movements, animals are transferring carbon across ecosystem boundaries and these movements should be incorporated into our carbon cycling models and our understanding of climate change.”

Future predictions

However, predicting and measuring carbon cycling under such variability is a challenge.

Animals roaming across vast areas means studying these animals through fieldwork can be demanding, so mathematical modelling and spatial analysis are important. That’s the expertise Dr. Leroux brings to the table.

Dr. Shawn Leroux
Photo: David Howells

“Important impacts of animals on the carbon cycle have been demonstrated empirically, in field studies and experiments. But in order to fully understand it, we need to develop mathematical models which would allow us to make predictions for different ecosystems into the future.”

Over the next few years, Dr. Leroux hopes to develop models taking the abundance, diversity and movement of animal species across landscapes, as well as different animal traits, to decipher a handful of key factors driving animal impacts on carbon cycling.

“I think the tools that exist and are rapidly emerging will allow us to remotely measure animal impacts better.” — Dr. Shawn Leroux

He particularly wants to know: Can the impact of animals on carbon cycling be described by looking at the size of that animal? Does the animal’s size dictate its impact?

Dr. Leroux says his role going forward will be to come up with some general patterns to simplify a complex problem to a few key parts. He also hopes to encourage other people to go out and study the subject.

“The more examples we have, the better we can understand their role.”

Technological advances

Dr. Leroux believes one of the ways researchers will be collecting data will be through advances in remote-sensing technology.

These devices can provide opportunities to accurately measure the global distribution of carbon held in biomass within ecosystems but may also be able to provide information on the animals that live in these areas.

Dr. Shawn Leroux in the field.
Photo: David Howells

“Today’s remote sensing tools are phenomenal for detecting the amount of carbon in a forest patch,” he said. “We’re also starting to be able to identify some animals, like polar bears from space via high resolution images. So, I think the tools that exist and are rapidly emerging will allow us to remotely measure animal impacts better.”

Ultimately, the team believes managing large animal populations could be an important way to contribute to climate change mitigation.

“Our review offers a way for deciding when and how conserving or managing a diversity of animal species could, in fact, enhance ecosystem carbon uptake and storage.”

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