Forests rely on animals to help fight climate change

We hear a lot about how climate change affects animals – but what if the reverse is also true?

New research suggests that when animals disappear from forests, the forests lose one of their key tools for fighting climate change. That connection between animals and climate may be even stronger than we thought.

Scientists at the Massachusetts Institute of Technology have found that tropical forests regrow much more effectively when they still have healthy populations of seed-dispersing animals.

In fact, they can absorb up to four times more carbon than similar forests where those animals are missing or declining.

Forests need wildlife to function

Tropical forests are the planet’s biggest land-based carbon sinks. That means they absorb and store more carbon than any other type of ecosystem.

So, understanding what keeps those forests functioning isn’t just an ecological question – it’s a climate question.

Evan Fricke, a research scientist in the MIT Department of Civil and Environmental Engineering, is the lead author of the new study.

“The results underscore the importance of animals in maintaining healthy, carbon-rich tropical forests,” said Fricke. “When seed-dispersing animals decline, we risk weakening the climate-mitigating power of tropical forests.”

Animals are nature’s forest planters

If you’ve ever watched a monkey munch on fruit or a bird fly off with a berry, you’ve seen nature’s version of forest management in action.

When these animals eat fruit and later defecate the seeds elsewhere, they help forests regenerate. In tropical regions, over 75 percent of tree species depend on animals to disperse their seeds.

Without those animals, seeds don’t travel far, germinate less often, and forests grow back more slowly – if at all.

Fricke has spent nearly 15 years studying this process. He’s shown in past work that animal seed dispersal helps trees survive and adapt. Now, his team is thinking more broadly about what that means for the planet.

“We’re now thinking more about the roles that animals might play in affecting the climate through seed dispersal,” Fricke said.

“We know that in tropical forests, where more than three-quarters of trees rely on animals for seed dispersal, the decline of seed dispersal could affect not just the biodiversity of forests, but how they bounce back from deforestation. We also know that all around the world, animal populations are declining.”

The impact of missing animals

To find out just how big an impact this has, the MIT researchers pulled together massive datasets – on biodiversity, animal movement, seed dispersal, and carbon storage. They studied 17,000 plots, tracking animals’ locations, movements, and the seeds they dispersed.

The team also factored in human pressures. In areas with heavy human activity, animals didn’t travel as far or scatter seeds as widely. The team built an index to measure how much seed dispersal had been disrupted and compared that to how much carbon forests in those areas could store.

“It was a big task to bring data from thousands of field studies together into a map of the disruption of seed dispersal,” Fricke said. “But it lets us go beyond just asking what animals are there to actually quantifying the ecological roles those animals are playing and understanding how human pressures affect them.”

What they found was striking. Forests lost 1.8 metric tons of carbon per hectare yearly where seed-dispersing animals had declined. That’s a 57 percent drop in regrowth potential.

The finding that disrupted seed dispersal leads to a fourfold drop in carbon absorption highlights seed dispersers as a key driver of tropical forest carbon.

Animals make climate solutions work

Not all forests are equally positioned for regrowth. The team found that some landscapes are more promising than others – especially those near intact forests or with lots of tree cover.

In these places, animal populations are more stable, which helps forests bounce back naturally.

“In the discussion around planting trees versus allowing trees to regrow naturally, regrowth is basically free, whereas planting trees costs money, and it also leads to less diverse forests,” said Professor César Terrer.

“With these results… we can understand where natural regrowth can happen effectively because there are animals planting the seeds for free.”

This research adds a new layer to climate modeling. If seed-dispersing animals are missing, regrowth estimates may be too optimistic. If animals are thriving, some areas may have more regrowth potential than previously thought.

Saving forests means saving animals

The researchers suggest several ways to support seed-dispersing animals. These include restoring habitats, building wildlife corridors, and limiting activities like wildlife trade.

In some cases, reintroducing missing species or planting trees that attract them could help restore these lost relationships.

It’s also about getting the science right. Future studies may examine whether the decline in tropical forests’ carbon-absorbing power is linked more to extreme weather or to the loss of these animal-plant partnerships.

“Forests provide a huge climate subsidy by sequestering about a third of all human carbon emissions,” Terrer said. “Tropical forests are by far the most important carbon sink globally, but in the last few decades, their ability to sequester carbon has been declining.”

The team will next investigate whether the decline is driven more by extreme droughts and fires or by reduced animal seed dispersal.

Losing wildlife worsens warming

Ultimately, the findings point to a deeper truth. Climate and biodiversity aren’t separate problems – they’re intertwined.

“It’s been clear that climate change threatens biodiversity, and now this study shows how biodiversity losses can exacerbate climate change,” said Fricke. “These are challenges we need to tackle in tandem.”

“When we lose our animals, we’re losing the ecological infrastructure that keeps our tropical forests healthy and resilient.”

The full study was published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–