Katarina Zimmer writes:

As we hang far above the ground on a sunny October day, it would be easy to focus on the blue crests of hills and the small towns tucked in between. But Richard Peters, who’s with me inside a metal gondola mounted onto the maneuverable arm of a crane, points me instead to the tree canopy below, flushed with the gold and copper shades of fall. “That guy is definitely on his way to die,” he says of one tree.

We hover over the leafless, barren branches of a beech tree that lost its crown due to drought, a spruce with a tip stripped bare of needles and, in the distance, we see the bald skeletons of conifers ravaged by bark beetles.

Peters yells instructions and the man operating the crane steers the 50-meter-long arm around in a circle, allowing the gondola to glide over the forest roof as a breeze gently tickles the leaves. It’s a surreal way to view the forest canopy, and for Peters and the other scientists who work here, it’s a lot more than that. They regularly visit this grove in Switzerland’s Hölstein area in the Jura Mountains to take meticulous measurements from roughly 80 of the 480 trees, right in the zone where they breathe.

Some 14 European tree species, mostly beech and spruce, grow here, the subject of a long-term study led by plant ecologist and physiologist Ansgar Kahmen of the University of Basel. When the project was launched in 2018, the goal was to simulate the effects of drought by building roofs just above the forest floor to intercept the rain. But that summer and early fall, the weather itself set up the experiment, with rainfall slashed nearly in half and temperatures three degrees higher than usual as part of the worst drought to sweep central Europe in 250 years.

Many trees were wiped out; 10 spruce succumbed at the two-hectare site (about five acres). Countless other trees were tested to their limits that year and in the years since.

Forest scientists around the globe are alarmed to see droughts, often exacerbated by fire and infestations of bark beetles, cull trees at scales they have never seen before — from massive swaths of American woodland, to dry forests in Australia where roots can reach down some 50 meters (more than 160 feet), to temperate regions and moist tropical forests where such events were long deemed unthinkable. “Even people who are really knowledgeable and who have a lot of experience out in the field were surprised to see how fast these forests were going down the drain,” says Henrik Hartmann, an ecophysiologist at the Julius Kühn Institute Federal Research Centre for Cultivated Plants in Germany and lead author of an overview of forest die-offs in the 2022 Annual Review of Plant Biology. [Continue reading…]