Basel's Forests Face a Dry Reckoning

There is a certain sobriety in measuring the decline of a forest. In the woodlands above Muttenz, near Basel, forestry engineers are engaged in what they call “taking the temperature” of the trees. The diagnosis is not encouraging. While the rest of the country may still cling to idyllic images of its natural landscapes, here the evidence points to a system under severe stress.

The work itself is a curious mix of modern science and old-fashioned detective work. Engineers Maria Oesch and Raphael Hähner navigate the undergrowth, searching for trees marked for observation decades ago. A metal detector, an unusual tool in forestry, helps locate the metal pipes driven into the ground in 1990 to mark the subjects of this long-term study. It is a meticulous, typically Swiss approach to cataloguing a crisis.

Occasionally, there is good news. One particularly robust beech, estimated at 140 years old, has grown five centimetres in circumference since the last measurement. With a trunk over 80 centimetres thick, it is a rare survivor. But such specimens are becoming historical artefacts rather than a sign of health. The very trees that define these forests, the large beeches, are struggling most.

Their vulnerability is a simple matter of biology. A mature beech requires between 400 and 600 litres of water a day, a demand that a warming climate can no longer reliably meet. The Basel region, situated in the rain shadow of the Jura, Vosges, and Black Forest, is proving to be a canary in the coal mine for the rest of the country. According to Luzius Fischer of the cantonal forest office, the effects of prolonged dry spells became apparent here sooner than elsewhere.

The consequences are quantifiable and stark. Data from another nearby forest shows that the standing timber stock has collapsed from 300 cubic metres per hectare to just 180 in the space of 15 years. This is not a subtle shift; it is a radical thinning. A glance up at the canopy confirms the numbers, revealing sparse crowns and significant gaps between trees where a dense roof once stood.

This grim accounting, however, is not merely an academic exercise in documenting decline. The data collected by Oesch and Hähner is fundamental to planning the forest of the future. The measurements reveal not only which species are failing but also which are proving more resilient to heat and drought.

Consequently, forest management is shifting its focus. The goal now, as Fischer explains, is to actively promote species better equipped for the new reality. Trees such as oaks, lindens, and pines are being favoured in the hope they can withstand the climate extremes to come. It is an admission that the forest of the past is gone, and what replaces it will be a landscape shaped more by necessity than by nature.

Written by Thorben Thiede thorben.thiede@alpineweekly.com