You've probably heard the financial advice that a diversified portfolio is better in turbulent times? Well that same wisdom may hold true for our stocks of trees. Because ecologists say forests with a diversity of trees are better at weathering drought. The reason: 

"There's a huge difference and a huge diversity of water transport strategies in trees." William Anderegg is an ecologist at the University of Utah. "It's everything from having deeper roots or shallower roots, to having these pipes that are incredibly well armored to withstand drought or incredibly weak in the face of drought."

Anderegg and his team studied droughts in 40 forests around the world. And the forests with diverse tree populations, with a mix of water-management strategies, did better than forests made up of just one or a few species. Could be a couple reasons for that.

"One is that there are other forces that are acting on the ecosystem at the same time. Other stressors like insect attack, or other things they're competing for, competing for light and for nutrients, and this is why a more diverse forest is going to be more functional. It'll be more resilient to drought but maybe also have higher carbon uptake rates over the long term." 

The second possibility, he says, is that a monoculture of drought-ready trees may look really resilient to drought. "Up until the drought is severe enough that a whole bunch of the trees shut down or even die. That threshold cliff response you would get in a one species forest and you may not get in a diverse forest." The full report is in the journal Nature. [William R. L. Anderegg et al., Hydraulic diversity of forests regulates ecosystem resilience during drought]

The lesson for land managers, he says, is that forest restoration efforts following wildfires and disease outbreaks might want to focus on planting a diverse portfolio of tree species. So that even if water plummets, tree stocks will, hopefully, remain stable.

—Christopher Intagliata

[The above text is a transcript of this podcast.]