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Have you ever seen a tree growing out of a rock? It’s an amazing sight because rocks are so hard. They don’t seem like good places for a tree’s roots to find food or water.

Trees need water to survive. A long dry spell will kill them. In the state of California, dry weather between 2010 and 2015 killed more than 100 million trees.

A recent study by scientists from The University of Texas at Austin and University of California, Berkeley found that an underground layer of rock — known as bedrock — found in mountains can hold a lot of water. The rock layer can store enough water to keep trees alive during long stretches of dry weather, known as drought, even after the soil dries up.

The water is hidden in tiny cracks and holes in the rock. The researchers found that those holes and cracks could hold about a quarter of all of the rain that falls in the mountains during a year.

To figure out how much water was in the bedrock, the researchers used large drills to create deep holes. Then they placed a scientific instrument called a neutron probe in the holes to measure the amount of water.

They found that the rock layer built up a supply of 4 to 21 inches of water during the winter wet season, depending on the well. The maximum amount of rock moisture in each well stayed about the same throughout the study period, which included a drought year. The results showed that it didn’t matter if it rained a little or a lot during the drier part of the winter, the total rainfall amount did not affect the rock moisture levels.

That’s surprising considering that a big pine tree can drink up to 100 gallons of water a day. Bathtubs hold anywhere from 80 to 110 gallons. From all of the water that a tree drinks, it will create enough oxygen for four people for one day. That’s just one reason trees are so important.

— Brett French,

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