The Tallest Living Thing on Earth

The story

What is the tallest living thing on Earth? Not an elephant. Not a giraffe. Not even a whale, stood on its tail. The tallest living thing on Earth is a TREE.

In a foggy forest in California grows a coast redwood that scientists measured at about one hundred and sixteen metres tall. That is like a building of more than thirty storeys, or a standard football pitch stood on end. Its very top waves about in different weather from its roots. Naturalists found it, scientists measured it, and the park that guards it does not publish its exact location, to protect its home from trampling visitors.

But the most astonishing thing about this giant is not how tall it is. It is a puzzle hiding inside the trunk. Every leaf at the top of that tree needs water. And the water is down in the ground, over a hundred metres below. Day after day, whenever the air is dry enough to draw on it, that tree lifts water higher than any fire hose could easily spray, up towards its highest twigs. And it does this with no pump, no motor, no moving parts, and it never gets tired, standing there drinking uphill century after century.

So how? The secret is a pull instead of a push, and the puller is the sky.

Inside the trunk, the wood is packed with countless tiny water pathways, finer than hairs, built from short cells joined end to end, and water passes from cell to cell through microscopic doorways on its way from roots towards leaves. The pathways are full of water. And water has a hidden talent: its tiny droplets cling to each other, holding on like a chain of hands. You have seen this yourself, when raindrops on a window reach for each other and snap together into one drop. Inside those hair-thin pathways, the water hangs together in connected chains reaching from roots towards crown.

Now for the pull. Up at the top, sun and wind slowly dry the leaves, and water at the top of the chain drifts away into the air as invisible vapour. In a working pathway, the chain of hands holds. As each droplet leaves, it tugs the chain up behind it, and that tug runs all the way down the trunk, down to the roots, which draw in fresh water from the soil. The sky dries the top, the chain gets pulled up, the roots drink at the bottom. The tree is not pushing water up at all. The weather is quietly pulling it, through the tree, all day long.

Scientists think this trick has a limit for redwoods, a little above the tallest ones alive, which may be part of why the giants stop where they do, and why redwoods love foggy coasts, where high leaves can sip extra water straight out of the mist.

So when you next stand under a tall tree, lay your hand on the bark and think of what is passing beneath it: a silent chain of water, hand in hand in hand, being drawn up towards the sky.