Tree-Planting Is No Solution Without Animals

Trees have become a mascot for nature’s role in the climate fight. But what if I told you that the part could have as easily been filled by wolves, or wildebeests, or whales?

A new paper, co-authored by 15 scientists from eight countries, illustrates how rewilding can help keep the global average temperature increase below 1.5C. It also makes the case for a more holistic approach to the biodiversity and climate crises, which are currently treated separately by intergovernmental bodies.

Tree-planting — the main so-called “nature-based solution” intended to help draw down carbon dioxide from the atmosphere — has become a synonym for climate action. Governments and companies make forestry promises that spring up like eager saplings. That’s become a convenient way to assuage consumer and corporate guilt: Brands like sustainable fashion label tentree and search engine Ecosia pledge to plant trees in return for our patronage. Trees are wonderful, but they’re not a quick solution to the climate crisis.

Indeed, there’s plenty of evidence to suggest that we’re not actually thinking through trees properly. One study found that 50% of them died within five years in tropical and sub-tropical forest restoration efforts. In the UK, National Highways planted 850,000 saplings along one 21-mile stretch of road. Three years later, 75% of them had perished. The carbon offset market also arguably incentivizes single-species plantations that are fast and cheap to grow but come with little ecological co-benefit, store less carbon and are more vulnerable to pests and disease.

In our laser-eyed focus on trees, we’ve developed a static understanding of the carbon cycle: They absorb carbon dioxide, end of story. The reality is that trees don’t thrive alone. They exist within complex communities, helped along by each other as well as the animals they coexist with. We’ve also forgotten that woodland isn’t nature’s only carbon sink: Grasslands, oceans and tundra also contribute to negative emissions — and rely on a healthy amount of biodiversity.

That’s what the paper, published in Nature’s climate change journal, wants to get across. Co-author Oswald J. Schmitz, a professor of ecology at Yale University, said trees might not be able to do their carbon-uptake job efficiently without the right animals in their ecosystem. For example, a study sampled 650 plots over 48,000 square-kilometers of tropical forest in Guyana. Tree and soil carbon storage increased by about four times as arboreal species in the 100m2 plots went from 10 to 70. However, carbon storage in those same plots was about five times higher when the types of mammals present increased from five to 35.

That’s because animals “animate the carbon cycle” — in the words of the paper — through their behavior and roles in the ecosystem. That goes far beyond forests. Take wildebeests. They turn the Serengeti into a carbon sink by grazing, which reduces wildfire risk. Their waste, which contains carbon from the vegetation, is then buried in the soil by insects. In tundra, herds of musk oxen compact the snow, which keeps the soil frozen, therefore reducing methane emissions and increasing albedo — or the ability to reflect sunlight, which cools the local environment. Whales and other large ocean creatures take their embodied carbon to the bottom of the sea when they die, as I discussed here. Other animals, like tapirs or elephants, engineer landscapes through their diet, which reduces plant competition, spreads seeds and enhances soil nutrition.

Data in the paper shows that protecting or restoring populations of just nine animal species and groups — fish, whales, sharks, grey wolves, wildebeest, sea otters, musk oxen, African forest elephants and American bison – could collectively remove an additional 6.41 billion tons of CO2 from the atmosphere annually. That’s more than 95% of the annual amount needed to eliminate 500 billion tons of CO2 from the atmosphere by 2100. 

That’s why it’s frustrating that efforts to protect biodiversity and halt climate change are treated separately. Schmitz says people should start thinking holistically: “By expanding the dimensions of the problem, we can arrive at solutions that are beneficial for both biodiversity and climate.”

There are other benefits to rewilding. In West Blean Forest in Kent, England, European bison were introduced to a 50-hectare area of woodland last July. A spokesperson for Kent Wildlife Trust told me that the five animals have opened corridors in the forest and brought light to its floor to encourage new plant growth. The bison also helped tackle common rhododendron — an invasive species that has crowded out native vegetation and cost the UK millions of pounds between 2015 and 2022 . The small herd tramples and breaks the bushes to create a natural insect repellant that shoos bugs away from the herd.

Tackling biodiversity and the climate crisis separately hinders progress for both endeavors. The REDD+ program of the United Nations Framework Convention on Climate Change aims to avoid emissions and manage tropical forests for conservation and carbon storage in developing countries. Yet the populations of animals in those habitats continue to be depleted by hunting. That runs the risk of projects not reaching their goals.

The paper says animals should factor into the design of REDD+ projects. I’d go even further: If biodiversity is built into the monitoring, reporting and verification of all forestry-related carbon offsets, it might encourage more efficient and holistic projects. It’d also discourage grim, monoculture plantations. Those aren’t forests; they’re deserts.

Likewise, the UN Global Biodiversity Framework and its 30×30 target — in which participating nations pledge to protect 30% of their land and oceans by 2030 — is an excellent start for rewilding. However, they fail to recognize the role that rewilding involving both plants and animals could play in mitigating climate change. Those animated carbon cycles won’t happen if protected areas are too small or disconnected for animals to thrive and fulfill their roles in the environment.

Of course, rewilding isn’t a one-stop-solution. To maintain a diverse and healthy planet, we also need to stop polluting. Rewilding also requires approaches tailored to unique species, environments and local communities, and more research is required to fill in the gaps in our knowledge. But the message is clear: We need a full picture — with both trees and animals — to harness nature’s full potential.

More From Bloomberg Opinion:

This Ocean Monster Offers a Potential Climate Solution: Lara Williams

California’s Drought Is Over. Its Water Problems Aren’t: Mark Gongloff

Wind’s Future Is Looking More Turbulent Than Ever: David Fickling

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Lara Williams is a Bloomberg Opinion columnist covering climate change.

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