Imagine you’re in a hot air balloon flying over an African savanna in the late growing season. Below, you can see herds of wildebeests, elephants, wildebeests, and rhinos in a mosaic landscape of lonesome trees, woodland, and yellow-brown grass. The herbivores who are hungry and rambunctious are eating and trampling the vegetation which stores carbon and prevents the atmosphere from heating.
You’d be forgiven for thinking that their voracious appetites and blundering steps might be disturbing and releasing the carbon stored in this ecosystem in much the same way wildfires do. Amazingly, herbivores actually help the ecosystem lock up more carbon in long-lasting stores that are hard to reach. In a new reviewWe compiled evidence from many different studies to show how large herbivores can help slow climate change.
The ultimate container for carbon storage is often the forest. The carbon found in the bark and leaves can be easily logged, harmed by pests, or burned. This can lead to decades of carbon accumulation. Even in healthy forests, the majority of carbon in vegetation above ground is lost and recycled into the atmosphere as greenhouse gases. less than a century.
In the meantime, carbon can be protected by the soil beneath savannas. tens of thousands of yearsIn underground pools that are difficult to reach. How is that possible?
Research from 2009The Serengeti savanna in east Africa, where wildebeests had been forced to return after a virus decimated their populations, saw fewer devastating wildfires. Because the wildebeests trampled and ate the vegetation that had been fuelling the fires in their absence, their return in the 1960s allowed the plants to gradually reestablish and recover their pre-epidemic abundance, along with the carbon the landscape’s soil was storing.
Although it may seem counterintuitive, large herbivores as well as seasonal fires are essential elements of grassland ecosystems. Small fires can become huge blazes if wildebeests are not there to provide the fuel.
But does it really matter if the vegetation is consumed by herbivores and fires? If you assume that 100% of the carbon in vegetation is released to the atmosphere as greenhouse gasses from fires or elephant digestion, then it shouldn’t.
But this isn’t what really happens. One reason is that the soil’s residual carbon from a fire is resistant and can be decomposed by microbes. This is sometimes called black carbon.
Large herbivores consume up to half the plant material as dung and urine. This is easier than plant litter such as dead leaves or fallen logs for soil decomposers (such as earthworms, fungi, and bacteria). Scientists used to believe that plant material consumed by animals or microbes was lost from the soil. Recent discoveries show that this view is far from simple.
While some of what’s eaten by decomposers is released as CO₂ to the atmosphere, most of it enters persistent soil pools of carbon. A good way to create long-term underground carbon storage is to feed the soil easily decomposable material.
Large animals seem to be adept at organizing carbon storage sites and redirecting a greater percentage towards stable and persistent underground reservoirs. This is a sign of how important intact wildlife communities are, and should prompt us to preserve the few remaining herbivore rich ecosystems on Earth such as the African Savanna. We may restore so much more by restoring nature’s four-legged ecosystem engineers in the places they have been lost.