Rocks Give Their Hidden Moisture to Trees in Times of Drought

CC BY 2.0. Wikimedia Commons

Researchers find that water in bedrock can sustain trees through dry periods, even after the soil has become parched.

Below the point where trees meet the soil, below the soil itself, a little-studied layer of rock could be working to give forests a watery assist when they need it the most. Often overlooked when scientists are studying hydrologic processes, a new study reveals that the water contained in the fractures and pores of this rock could be an important part of the water cycle.

"There are significant hydrologic dynamics in weathered bedrock environments, but traditionally they are not investigated because they are hard to access," says lead author of the study, Daniella Rempe, a geoscientist at UT Austin. "Our study was designed to investigate this region."

The study specifically looked at the water stored in bedrock beneath the soils in mountain forest ecosystems; they discovered that it varied from location to location. Remarkably, at one field site in California, they found that up to 27 percent of annual rainfall was stored as "rock moisture," the water clinging to cracks and pores within the bedrock.

The researchers explain that this could likely be the reason that these trees in particular fared so well during the state’s severe drought from 2010 to 2015. Throughout the state, some 100 million trees did not survive.

"How trees can survive extended periods of severe drought has been a mystery," said Richard Yuretich, director of NSF's Critical Zone Observatory program. "This study reveals a significant reservoir of trapped water that had gone unnoticed in the past," he says. "Research of this kind can help greatly in managing natural resources during times of environmental stress."

They say you can't get water out of a stone ... the trees might disagree.