The proportion of trees with high density wood is higher in forests with elephants.
Elephants are among the most iconic animals on Earth, yet despite being a mainstay of both folklore and popular culture worldwide the giant pachyderms are losing out to loggers, farmers and poachers. And if we drive elephants extinct, not only will we suffer the consequences but so too will their environment.
The giant herbivores serve a key ecological role in their habitats. Forest-dwelling elephants aid fruit-bearing plants by spreading their seeds (in elephant dung) far and wide. By plowing their way through thick vegetation, the jumbos also help shape their environment by knocking down some trees and plants, which enables others to grow in their place.
But there’s more, says a team of biologists from Saint Louis University. Elephant herds that dwell in forests also help sequester more atmospheric CO2. They do so by feeding on fast-growing plants in more open spaces, which facilitates the spread of slow-growing trees with higher wood density. These latter plants are better at sequestering carbon from the air.
In other words, through their feeding habits elephants contribute to improved carbon sequestration of the forests that they inhabit. Stephen Blake, an assistant professor of biology at Saint Louis University, and his colleagues realized this after analyzing data on forest structures and species compositions in the Nouabalé-Ndoki Forest of Congo in central Africa.
The researchers, who have published their findings in a paper, found that forest elephants’ preference for fast-growing plant species results in high levels of damage and mortality to these species, which benefits slow-growing plants with higher wood density.
“[A]s we look at numbers of elephants in a forest and we look at the composition of forest over time, we find that the proportion of trees with high density wood is higher in forests with elephants,” Blake notes. “[Our] simulation found that the slow-growing plant species survive better when elephants are present. These species aren’t eaten by elephants and, over time, the forest becomes dominated by these slow-growing species,” he adds.
“Wood (lignin) has a carbon backbone, meaning it has a large number of carbon molecules in it. Slow growing high wood density species contain more carbon molecules per unit volume than fast growing low wood density species,” Blake elucidates. “As the elephants ‘thin’ the forest, they increase the number of slow-growing trees and the forest is capable of storing more carbon.”
The flipside is that more and more forest-dwelling elephants are facing grave threats to their continued existence. And if their populations collapse, the result will likely be that fast-growing plants will begin to thrive at the expense of slower-growing woody plants. These forests will in turn lose some of their ability to capture more carbon from the atmosphere, even as effective carbon capture is becoming ever more urgent in the face of the ravages of climate change.
“The sad reality is that humanity is doing its best to rid the planet of elephants as quickly as it can,” Blake says. “Forest elephants are rapidly declining and facing extinction. From a climate perspective, all of their positive effect on carbon and their myriad other ecological roles as forest gardeners and engineers will be lost.”
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