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The beech is the most common deciduous tree in Switzerland. <\/p>\n
Keystone \/ Christian Beutler <\/p>\n
This year\u2019s exceptional drought is causing irreversible damage to Swiss forests. But trees\u2019 health is being undermined by more than just the lack of rainfall.\n<\/p>\n
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This content was published on <\/p>\n
September 5, 2026 – 10:20\n<\/p>\n
With yellow treetops visible as early as July, the sight of Swiss forests this summer is unusual even for someone who has studied them for decades. \u201cI knew this scenario would eventually occur. But I did not expect it to happen this year, nor with such intensity,\u201d Ansgar Kahmen, professor of physiological plant ecology at the University of Basel, told Swissinfo.<\/p>\n
The early drying and shedding of leaves is not merely a temporary defense mechanism against water shortages, Kahmen explains. It signals deep and irreversible damage to tree tissues.<\/p>\n
For the researcher, 2026 is a turning point for Swiss forests. \u201cThe extent of the damage is such that we believe many of the trees that have already lost their foliage will die either immediately or in the coming years,\u201d he says.<\/p>\n
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Climate adaptation\n <\/p>\n
Drought in Switzerland: Europe\u2019s \u2018water tower\u2019 runs dry <\/p>\n
This content was published on <\/p>\n
Aug 21, 2026 <\/p>\n
Rivers reduced to trickles, scorched landscapes and forests taking on autumn colours weeks ahead of schedule: such scenes highlight the severity of a drought unmatched in Switzerland for decades. <\/p>\n
<\/p>\n Read more: Drought in Switzerland: Europe\u2019s \u2018water tower\u2019 runs dry Rising tree mortality, driven by increasingly hot and dry conditions, could weaken the protective role of Alpine forests against avalanches, landslides, and other natural hazards. It also reduces forests\u2019 ability to absorb carbon dioxide (CO2), a powerful greenhouse gas, and to help mitigate climate change. Water stress further makes trees more vulnerable to pests and diseases.<\/p>\n Swiss forests will not disappear, Kahmen emphasises. \u201cBut the forests we grew up with, which hold strong emotional value for people in Switzerland and Central Europe, will no longer exist.\u201d<\/p>\n No new buds on drought-affected beech trees<\/p>\n This summer recalls 2018, when around 5% of Switzerland\u2019s beech forest areas experienced premature yellowing. Beech trees account for approximately 19% of all trees found in Swiss forests. \u00a0Many forest ecology experts initially suggested that the trees were simply undergoing leaf senescence, the natural aging process of leaves that normally occurs in autumn.<\/p>\n The following spring, however, many beeches failed to produce new buds, indicating that they had suffered severe and lasting damage. This was also confirmed by a recent studyExternal link<\/a> conducted by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).<\/p>\n Drought particularly affects the meristem, the tissue from which trees generate new leaves and shoots, Kahmen explains. Research carried out in Switzerland, including Kahmen\u2019s own work in an experimental forest in the canton of Basel Country, indicates that many trees, especially beeches, struggle to recover after episodes of severe water stress.<\/p>\n Kahmen says it has been surprising to discover just how vulnerable some Swiss tree species are. The explanation ultimately comes down to one simple factor: access to water. Trees with roots deep enough to reach still-moist soil layers, or with more extensive root systems, are generally better able to withstand drought.<\/p>\n Some trees in this beech forest in the canton of Jura are showing signs of premature yellowing of their leaves, 29 July 2026. <\/p>\n Keystone \/ Jean-Christophe Bott <\/p>\n The \u2018thirst of the air\u2019 drains water from plants<\/p>\n Between 2018 and 2022, the number of dead and damaged trees increased in Switzerland, rising by around 50% in some regions, accordingExternal link<\/a> to the National Forest Inventory. Tree mortality in 2018 exceeded levels recorded during the so-called \u201cheatwave summer of the century\u201d in 2003.<\/p>\n The succession of extreme drought episodes in recent years has contributed to increased mortality in Swiss forests. However, low summer rainfall and reduced soil moisture are not the only explanations.<\/p>\n Kahmen points out another factor: the \u201cwater thirst of the air,\u201d known scientifically as vapour pressure deficit (VPD). As temperatures rise, the atmosphere can hold greater amounts of water vapour and therefore becomes \u201cthirstier\u201d for moisture. As a result, it extracts more water from leaves and from the soil.<\/p>\n These conditions put many plants in an impossible situation. They need to keep the tiny pores on the surface of their leaves, known as stomata, open to absorb the CO2 necessary for photosynthesis and growth. But in such dry conditions, plants also must close the stomata to reduce water loss. \u201cFor every molecule of CO2 absorbed, a plant loses about a thousand molecules of water,\u201d Kahmen explains.<\/p>\n VPD increases exponentially with temperature. During a heatwave, when air temperatures rise from 25\u00b0C to 35\u00b0C, an increase of 40%, VPD rises by around 80%. According to a WSL studyExternal link<\/a>, in the last four centuries, Europe\u2019s atmosphere has never been as dry as it is today.<\/p>\n \u201cI believe that declining atmospheric humidity has even greater effects on vegetation than rising temperatures, although the two phenomena are linked,\u201d Kahmen says. With the same amount of rainfall, he adds, ecosystems dry out much faster today than they did twenty or thirty years ago.<\/p>\n \n More<\/p>\n More <\/p>\n Climate solutions\n <\/p>\n Swiss experiment targets forest drought, a driver of climate change <\/p>\n This content was published on <\/p>\n Oct 9, 2024 <\/p>\n Climate change and droughts are transforming forests and reducing their ability to absorb CO2. Which tree species are suitable for the climate of the future? A unique Swiss experiment is seeking answers. <\/p>\n
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