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, coauthored by 15 scientists from eight countries, illustrates how rewilding can help keep the global average temperature increase below 1.5°C. 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 has 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 are not a quick solution to the climate crisis.
Indeed, there is plenty of evidence to suggest that we are not actually thinking through trees properly. One study found that 50 percent of them died within five years in tropical and subtropical forest restoration efforts. In the UK, National Highways planted 850,000 saplings along one 34km stretch of road. Three years later, 75 percent 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 cobenefits, store less carbon and are more vulnerable to pests and disease.
In our laser-eyed focus on trees, we have developed a static understanding of the carbon cycle: They absorb carbon dioxide, end of story. The reality is that trees do not thrive alone. They exist within complex communities, helped along by each other as well as the animals they coexist with. We have also forgotten that woodland is not nature’s only carbon sink: Grasslands, oceans and tundra also contribute to negative emissions — and rely on a healthy amount of biodiversity.
That is what the paper, published in Nature’s climate change journal, wants to get across. Coauthor Oswald Schmitz, a professor of ecology at Yale University, said that 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 48,000km2 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 is 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.
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 show that protecting or restoring populations of just nine animal species and groups — fish, whales, sharks, gray wolves, wildebeest, sea otters, musk oxen, African forest elephants and American bison — could collectively remove about 5.8 billion tonnes of carbon dioxide from the atmosphere annually. That is more than 95 percent of the annual amount needed to eliminate 450 billion tonnes of carbon dioxide from the atmosphere by 2100.
That is why it is frustrating that efforts to protect biodiversity and halt climate change are treated separately.
Schmitz says that 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,” he says.
There are other benefits to rewilding. In West Blean Forest in Kent, England, European bison were introduced to a 50-hectare area of woodland in July last year.
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 last year.
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 UN 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 that animals should factor into the design of REDD+ projects.
I would 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 would also discourage grim, monoculture plantations. Those are not forests; they are deserts.
Likewise, the UN Global Biodiversity Framework and its 30x30 target — in which participating nations pledge to protect 30 percent of their land and oceans by 2030 — is an excellent start for rewilding.
However, they fail to recognize the role that rewilding involving plants and animals could play in mitigating climate change. Those animated carbon cycles will not happen if protected areas are too small or disconnected for animals to thrive and fulfill their roles in the environment.
Of course, rewilding is not 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.
However, the message is clear: We need a full picture — with trees and animals — to harness nature’s full potential.
Lara Williams is a Bloomberg Opinion columnist covering climate change.
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