The study’s findings show a strong connection between rooting depth and local soil and water conditions. In well-drained uplands, tree roots can reach the level of infiltration by rainwater and snowmelt. In flooded lowlands, roots remain shallow.

In between, high growth rates and drought can cause roots to deepen many meters into the saturated zone just above the water table.

Reinfelder said the findings have important implications for the question of whether trees and other plants can adapt and survive changing climate conditions this century and beyond. Overall, the odds seem favorable. Plants are often adaptable, and those with deeper roots will have a greater advantage.

“Plants may be more resourceful and resilient to environmental stress and climate change than we previously thought, but only to a certain extent,” she said. “They can withstand periods of drought. But if the drought continues for a century, they won’t be able to cope.”

She notes that plants can transition from unfavorable environments by moving downhill, where there is more water. They do so by shedding seeds, of which those that make it wetter at lower altitudes survive.

The global study led by Reinfelder included 2,200 observations of roots of more than 1,000 species in all major plant groups, including trees, grasses, shrubs, herbaceous plants and succulents.

The next step, Reinfelder said, is to research and predict the drought resilience of the world’s largest forest – the Amazon rainforest – by the end of this century, thanks to the trees’ deep roots.

“We need to invest in understanding the underground half of the ecosystem,” she said. “It’s dark. It’s not clear, but it holds the key to many questions and the scientific community needs to unravel it.”