EarthDate

How Trees Lift Water


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Think about this: a tree could be 100, 200, more than 300 feet tall, yet can lift water from deep underground all the way to the leaves of its highest branches. Each day it could move hundreds of gallons, several tons of water this way.

This gravity-defying feat is made possible not so much by the tree but by the properties of water itself.

Trees perform photosynthesis in their leaves, which requires water. The hydrogen in water goes to form carbohydrates—sugar, the food for the tree. The oxygen is exhaled through pores in the leaves.

Water also evaporates, or transpires, through these pores. It’s this transpiration from the leaves that pulls water up the trunk and branches to them.

Now, that’s a long way to lift it, so the water itself helps. Water molecules have properties of both cohesion—they want to stick together—and adhesion—they want to stick to other things.

You can see this in a water droplet on a windowpane: Cohesion holds it together. Adhesion sticks it to the glass.

Water wants to stick to the insides of the tree’s vascular system. And it wants to stay connected in an unbroken column of water, advancing ever upward, until it evaporates from the leaves.

Even if you don’t consider yourself a tree hugger, you can’t help but admire a tree’s incredible natural abilities.

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EarthDateBy Switch Energy Alliance