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Top Tips fom Tree Tops

The tallest known tree in the world is in Redwood National Park, a few hundred kilometres north of San Francisco, just inland from the Pacific coast. You won’t find its location marked on official hiking maps, however. That’s because the two amateur naturalists who discovered the tree in 2006 – Michael Taylor and Chris Atkins – have tried to keep its whereabouts a secret, fearing that tourists and looters might carve a mark or chisel off a chunky souvenir to take home (though you can see its approximate location on unofficial guides). They named the tree Hyperion and the intrepid climbers who measured it – using a laser and a measurement line dropped from the top – reported that this botanical titan rises about 116 m above the forest floor. That makes it a little over 1 m bigger than the second-tallest-known tree, a redwood called Helios.

Hyperion, like all trees, hides in its trunk a remarkable natural engineering process that keeps the plant hydrated and cool. Known as “transpiration”, it involves water entering the roots and travelling up the trunk before passing out via the leaves. It’s an invisible and silent process that lets a single, 90 m-high redwood shuttle about 2000 litres of water from roots to leaves in a single day – that’s more than 400 flushes of a low-volume toilet. Of course, you don’t have to bore into a redwood’s 6 m-wide trunk to find evidence of transpiration; small plants do it, too.

Details about the mechanics of transpiration were first published in 1727 by the English botanist and clergyman Stephen Hales. Water that has entered a tree via its roots flows up through the “xylem” – hardy, tubular cells in the stem that are stacked together to form a natural pipe that reaches all the way up. With thick cell walls that add structural support to the plant, xylem become useful as water carriers once they reach maturity, at which point they’re completely dead.

Read more at Physics World.