Forests are important in our warming world. As we burn fossil fuels—such as coal, gas and oil—and cut down and burn forests for agricultural fields, the released carbon dioxide spreads across the planet. That, in turn, captures and traps the solar heat that would otherwise be radiated out into space, and our Earth heats up.
Finding solutions for slowing down and reversing this trend involves understanding the natural processes that lead to carbon sequestration. Before the start of the Industrial Revolution, our planet was more in balance with CO2 emissions. As carbon dioxide was released into the atmosphere, similar amounts were absorbed by carbon sinks (anything that takes in more carbon than it releases) or carbon sequesters (anything that traps carbon in a certain form for a long period of time).
Luckily, our still-intact forests are able to store some of that excess carbon dioxide. Even our cities—when they’re smartly constructed—can help in taking CO2 out of the air we breathe.
But now, there’s an exciting new study from California’s Stanford University, published in October 2017 in the journal Nature: Ecology and Evolution, which shows that large animals in the wild also play an important role in sequestering carbon—and the more species in an area the better. It’s the first to suggest the importance of animal biodiversity rather than just animal numbers in the carbon cycle.
Amazon ambles result in astronomical carbon captures
According to a press release issued by Stanford, a conversation during a biology department happy hour provided the inspiration for this work.
Scientists have long known that an ecosystem with more species generally functions better, leading to the assumption that it has something to do with the carbon cycle: animals breathing, ingesting, digesting and decomposing. Traditionally, however, it was the plant biologists who investigated questions about carbon stocks, and plants were the most acceptable subjects for experiments. So, proving the relationship between animal diversity and carbon was not going to be easy. The economic resources, logistics and time involved in testing vertebrates in the real world were unprecedented—especially in the Amazon, chosen for its very biodiverse ecosystems.
In order to find technicians who had the skills to walk into and detect animals in remote, often mountainous or swampy, tropical rain forests, the researchers hired more than 300 indigenous people from the Makushi, Waiwai and Wapishana nations. They trekked through the Amazon, noting the number, diversity and potential carbon storage of trees (by using size and rainfall estimates) and the presence and activities of vertebrate animals, including large mammals, amphibians, birds and reptiles. Over a three-year period, they saw 132,995 individual vertebrate animals and recorded signs of an additional 190,369, representing 218 species. There was evidence of 43,448 feeding events; and for each one of them, technicians recorded what was eaten. These data sets were then cross-referenced with carbon levels that came from 825 soil samples taken in the final six months of the fieldwork.
By analyzing more than a million records of animal sightings and activity, the researchers found that soil stored the highest concentrations of carbon in places that had not just the most animals but the highest animal biodiversity.
When they looked for a mechanism to explain the finding, it turned out that the areas with the highest animal diversity had the highest frequency of feeding interactions, such as animals preying on other animals or eating fruit, which results in organic material left on and in the ground. These meal remnants increased the diversity and abundance of soil microbes, which convert the remains into stored carbon. In other words, more mammal species means more carbon ending up in the soil or in the bodies of trees.
Bigger biodiversity means abundant breathable air
While we don’t know exactly how much extra carbon a mammal-rich forest might store versus one devoid of mammals, scientists offer this rough estimate: a forest with 30 mammal species probably sequesters an extra 10,000 kilograms per hectare in aboveground tree biomass alone. Extrapolated to the entire Amazon, that translates to some 5.5 billion metric tons of carbon, roughly equivalent to U.S. emissions in 2017—and that doesn’t even account for soil-bound carbon, which would make the total much higher.
Once again, it’s clear that nature is telling us that every part of an ecosystem matters to the functioning of the whole—and to the operating system of the entire planet. Large vertebrates are not just the beneficiaries of healthy ecosystems or the victims of degraded ones but are integral to the carbon cycle. Not only does their abundance matter in sequestering carbon but also the diversity among them. It matters a great deal.
And it could just be that when we rid ourselves of the large predators among us, such as bears and wolves, we’re also extinguishing some of the air we breathe.
Here’s to finding your true places and natural habitats,
Will policy makers use this output as one more good reason to protect large predators as bears and wolves?