What’s the smartest tree on Earth?
That’s not a question that I’ve ever heard anyone ask before, but I believe I can answer it.
I submit to you the Acacia trees of Africa, an astounding breed that not only has developed a way of communicating with its family members, it even developed its own burglar alarm!
The most iconic plant of the savannah is surely the umbrella tree (shown above), the picturesque silhouette you always see in sunset photos of the African bush. Though the genus Acacia has over a thousand species across the world (commonly known as “wattle”) which range from shrubs to shade trees, the umbrella thorn acacia (Vachellia tortilis), makes a case for being the “smartest” of them all.
We all learned in school the theory of why giraffes have such long necks. Darwin said it himself:
“The giraffe, by its lofty stature, much elongated neck, forelegs, head and tongue, has its whole frame beautifully adapted for browsing on the higher branches of trees. It can thus obtain food beyond the reach of the other … hoofed animals inhabiting the same country; and this must be a great advantage to it.”— Charles Darwin, “Origin of the Species”
It makes sense. Their necks give them an advantage over short-necked creatures, as they can reach the berries on the tallest trees. This appears to be borne out by the fact that giraffes’ favorite food is the acacia berry which grows on the tall umbrella trees.
The bit we never realized is that the acacia trees don’t like that!
Yeah, they started fighting back.
They started by growing thorns, which deters many animals, but didn’t stop the giraffes.
Then came the tannin, a toxic chemical the trees produce that can poison predators. It works well … over time. If an animal eats it for about two weeks, it will ruin their livers. Meanwhile, it tastes terrible, which deters all but the hungriest animals in the area. Unfortunately for the acacia, this tannin can only be produced in small bursts, or else it damages the tree itself. So the acacias have learned to use it sparingly, like a can of mace on an attacker.
This is where an organic burglar alarm comes in handy. And wouldn’t you know, these amazing trees invented one!
In the 1990s, a biologist/zoologist named Wouter Van Hoven discovered how they did it. He noticed that when one plant emitted the tannin, the giraffes foraging that tree did not move on to the tree next to it. No, instead they moved more than 50 feet away before trying it again.
At the same time the acacias release their tannin to save themselves, they also warn all of their close relatives by emitting a chemical compound called ethylene. All the trees within 50 feet downwind of this sense the ethylene and immediately do both steps themselves – they start producing both tannin and ethylene. This great game of telephone actually works, resulting in a huge circle of trees that suddenly taste pretty unappetizing to the predators.
Score one for the trees!
But don’t the trees depend on the animals to disperse the seeds?
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