Brown leaves in August as Swiss forests face the test of summer 2026

Brown leaves in mid-August and branches already bare: the scorching summer of 2026 has left visible marks on Swiss forests. "We have never experienced anything like it," says Arthur Gessler, a researcher at the Federal Institute for Forest, Snow and Landscape Research.

The comparison with 2018, the year that had served as the benchmark for forest drought, no longer holds. Early yellowing then affected around five per cent of beech trees. This year the share is far higher and it appears earlier in the season. "It shows us what lies ahead," Gessler adds.

What strikes the researchers most is not the average but the difference from one place to another. Thirty kilometres separate Grenchen from the Thal region in the canton of Solothurn: in the first the woodland shows extensive damage, in the second the situation is much less serious. The variables at play are aspect, soil depth, water retention capacity and the composition of the stands.

What the forest will look like

"In future the forest will look different," says Andri Baltensweiler, also of the WSL. Research is focusing on species able to withstand hotter and drier summers, and on mixtures that allow a stand to hold up when one of its species fails.

The Grenchen forester Patrick Mosimann works on this ground every day. Decisions on felling and regeneration have to be taken now for woodland that will mature in eighty or a hundred years, under a climate nobody can describe precisely. Frank Krumm, also of the WSL, warns against automatic answers: "Forestry that rigidly follows the manuals is not a good idea."

Swiss woodland covers about a third of the country and more than half of Ticino. Besides producing timber it protects against avalanches, rockfall and debris flows, a service the Alpine cantons value at hundreds of millions of francs in protective works avoided. A weakened forest protects less.

Gessler closes on a point that belongs to climate policy more than to forestry: "Every tenth of a degree helps us preserve the forest." The difference between warming scenarios translates, in other words, directly into species that stay on the slopes and species that disappear from them.