[♪ INTRO] When you hear the expression “it looks like  a herd of elephants came through here,” you probably don’t visualize a healthy and prosperous forest with a lot of upright trees.

After all, elephants are huge and stampy and it’s somewhat easy to think of them  as destroyers rather than caretakers. But some populations of elephants  are adapted to forest life.

And not only do those forests generally  remain standing, but those elephants, and their picky taste buds, are doing a favor for not just the forest, but the entire planet. The reason is carbon sequestration. Carbon sequestration is one of the best  tools we have for fighting climate change, and the term can mean a  couple of different things.

Often, it refers to machines used to  remove carbon dioxide from the air. This is a technology engineers  have been trying to develop, though it is still in its infancy. But there’s also natural carbon sequestration.

That’s when ecosystems remove carbon  from the air through natural processes. Soil stores a lot of carbon. In fact, a lot of what's in soil is  carbon from decayed plant matter, microorganisms, and other sources.

And forests are also pretty  good at sequestering carbon, what with all the tree-growing incorporating carbon dioxide into wood and other plant matter. You might picture elephants reversing  that process to some extent, what with all the stomping. After all, even though forest elephants  are adapted to living in forests, they are under no evolutionary obligation  to help the forest lock up carbon.

But they do lock up carbon. A 2023 study in the Proceedings of  the National Academy of Sciences looked specifically at African forest elephants, which are not the same as the  elephants you’ve probably seen thundering around the savanna  in National Geographic. Savanna elephants eat an eclectic diet of  grass, bark, leaves, fruit, and foliage; basically whatever they can find out there.

African forest elephants, on the  other hand, mostly eat leaves. And, like humans, they prefer  leaves that taste good. Typically, the leaves they eat are  less fibrous than the ones they avoid, and they don’t contain unpleasant  chemicals like tannins.

Now, some humans love tannins  because they make wine "dry" and distinctively bitter, but other animals  don’t really appreciate them in the same way. And that’s because tannins  are a defensive chemical; we're not supposed to like them. And elephants avoid them.

Because they’re smarter than you. The more palatable leaves that elephants prefer come from trees that have low wood density. These trees aren’t very good at storing carbon.

The wood is less dense, so there’s  literally less carbon in it by volume. Which means the elephants are toppling, eating, and ultimately thinning the trees that  are less efficient at carbon capture, and leaving those that are more efficient. But there’s more.

Forest elephants also like to snack on fruit. The fruit they prefer grows on different  trees: ones that have higher wood density. And when elephants eat fruit from those trees, it helps to spread their seeds around, which ultimately increases the number  of dense-wood trees in the forest.

And that helps increase carbon  storage in a second way. It’s a subtle balance, and we  can’t really slap a number on how much climate change elephants might  be stopping just by living their lives. But the authors suggest the effect on  high-wood density trees alone could mean that a forest without any elephants might  store up to 9% less carbon in its trees.

Elephants also aren’t the  only large herbivores that can have this kind of impact on carbon stocks. The presence of any kind of large, wild  herbivore seems to contribute positively to soil carbon, not just in  forests, but also in grasslands. But megaherbivores are not as  abundant as they used to be.

During the late Pleistocene there were  at least 50 different species worldwide. And while all those Pleistocene  megaherbivores ate a lot of plants, they also helped spread seeds  around, cycle nutrients, and make ecosystems less susceptible to fire. And it seems likely they  contributed to carbon storage, too, in much the same way elephants do.

Today there are only a handful  of megaherbivores left, including three kinds of elephants, hippos,  rhinos, giraffes, and bovines like bison. Carbon storage might be kind of  a selfish reason to protect them, but honestly, I’ll take any reason they give us. For more on elephants, we also  have a SciShow video on the secret language of elephants which is very good and I think that you should watch it. [♪ OUTRO]