Have you ever wondered why the damp wood of trees doesn’t immediately begin to rot after a heavy thunderstorm? Or how aquatic plants, like mangroves, manage to thrive with their trunks and roots submerged in swamp water? And what about those pesky thorns on some plants—why do they have them, while others don’t?

Well, the answer might surprise you—it’s all about tannins!

Tannins are these amazing little compounds that many plants have, and they play a crucial role in keeping those plants safe and sound. You see, unlike animals, plants are pretty much stuck in one spot—they can’t just up and run away when something scary comes along, like fungi, bacteria, viruses, or even hungry browsers (those animals that love munching on leaves, like the ones we see at Londolozi). So, plants had to get creative with their defence strategies, and tannins are a big part of that.

Now, here’s the cool part about how plants protect themselves from being overbrowsed by animals: tannins make the leaves taste super bitter. Some plants go the thorny route to protect their yummy leaves, but others rely on tannins to keep those browsers at bay. The more an animal nibbles on the plant, the more tannins the plant pumps out, making the leaves taste even more bitter. It’s like the plant is saying, “Nope, that’s enough!”

I recently had a chat with Stoff Kane-Berman about this whole tannin story. He noticed that the nyala and bushbuck around camp would nibble on the leaves of one tree and then move on to the next pretty quickly. They never seemed to stick around on one tree for too long. I had to agree with Stoff—I’ve seen the same thing out in the field with giraffes and other browsers. And yep, you guessed it, tannins are behind this behaviour.

The dappled light falling over this Nyala bull made for a beautiful image.

But Stoff didn’t stop there. He got curious and decided to do a little experiment to see just how strong tannins really are. He broke off branches from a few different tree species and noticed something interesting: the animals seemed to prefer the brown ivory tree, but they would spend more time feeding on the broken-off branch compared to the branch that was still attached to the tree. Why? When the branch is broken off, the tannin flow stops, so the leaves don’t taste as bitter or dry anymore and the bushbuck will feed on it for longer.

Here are a few ways plants use tannins to protect themselves:

The Mycelium Network:

Now I won’t go into the vast wonders of the mycelium network here, maybe that’s a story for another blog explaining this amazing fungi. Basically, it is a network of fungi that connects plants by a stringy web through their roots (kind of like a secret underground web). This network helps plants share nutrients and information amongst the plants in a forest (for example). And, yes, it even comes into play with tannins.

Warning Signals:

When a plant is under attack, it can send out chemical signals through the mycelium network, alerting nearby plants to the danger. These plants may then ramp up their defences, like producing more tannins or other protective chemicals to ward off the threat. This form of communication enhances the survival chances of the entire plant community.

I’ve seen this happen with giraffes—they’ll start nibbling on one tree, then quickly move on to the next tree as it has already increased its tannins after receiving the distress signal from the tree next to it.

Other Ways Tannins Protect Plants

The primary job of tannins is to act as a natural shield. Their chemical makeup makes them really good at stopping harmful microorganisms like fungi and bacteria. This superpower works even in water.

When plants are stuck in damp conditions—after a storm or in waterlogged soil—tannins jump into action. They prevent the wood and other plant parts from rotting by inhibiting the growth of moisture-loving fungi and bacteria. This is why, despite the dampness, the wood remains intact, strong, and resistant to decay.

Biomimicry of Nature: How we as Humans can learn from Tannins

What’s even more remarkable is that tannins retain their protective properties even after they’ve been extracted from plants. This stability opens up a world of possibilities for their use in various applications.

For centuries, we’ve used tannins in leather tanning to treat animal hides, making them durable and resistant to rot. The same stuff that keeps plants safe can also make leather last for years. And in today’s world, we’re finding all kinds of new ways to use tannins—in medicine, where their antimicrobial properties might help fight infections, or in environmental science, where they could help purify water or stabilize soils.

A Natural Defense with Endless Potential

Tannins are a testament to the ingenuity of nature. While plants may be stationary and vulnerable in some ways, tannins provide them with a powerful defence mechanism that ensures their survival against the constant threat of pathogens. This natural protection, honed over millions of years, not only keeps plants safe but also offers humans valuable tools for a wide range of uses.

So, the next time you see a tree standing tall after a storm or admire the resilience of a mangrove forest, remember the tannins at work behind the scenes—nature’s way of ensuring that life, in all its forms, continues to thrive.