USA: Even California’s mighty oaks are dying from drought

The ongoing California drought has killed more than 100 million trees, according to a recent U.S. Forest Service estimate. Many of these, it turns out, are very old oaks – trees that are known to be drought resilient and have survived numerous droughts in the past.

So what happened to these oak trees?

Todd Dawson, a biology professor at U.C. Berkeley, and several colleagues investigated that issue at three sites in Central California over the past couple of years. They found that these stately, mature oak trees fell victim to severe groundwater depletion.

In short, even the very deep roots of ancient oak trees could no longer reach the aquifers that have sustained them for centuries. That’s because the groundwater shrank amid a combination of historic rainfall deficits, high temperatures and unprecedented groundwater pumping by urban and agricultural Californians.

[...]