Anderegg and his colleagues collected data on the flow of heat, water, and carbon at 40 sites around the world, from Canada to Zambia, Denmark, Russia, and Australia. They then compared those measurements with the tree species prevalent in each location to see what traits were associated with intensified droughts.
The group also found that sites with a greater variety of trees better buffered drought conditions. “That suggests it’s not just the dominant trees that matter, but having a diversity of tree species,” Anderegg says. “It would be like having a portfolio of investments.” Current large-scale climate models factor in whether a region is covered by deciduous, coniferous, or tropical forest, for example—but only in broad strokes. “That grouping by biome is going to miss a lot of really important nuances,” he says.