Switzerland's Forest in a Changing Climate: Who Gains, Who Loses – and What Must Be Done

clarus.news | Analysis | 17 May 2026

By Thierry Leserf, with analytical support from Claude Opus (Anthropic)

Correction note (23 June 2026): This version was revised following expert feedback from the Swiss Federal Research Institute WSL. The title, lead and conclusion were amended, as were the climate baselines (now Climate CH2025 instead of the older A1B projections) and the statements on non-native tree species. We thank the WSL for its input.

The 2025 Forest Report by the FOEN and WSL paints a sobering picture: spruce, beech and ash – three of the most important tree species – are losing ground markedly in Switzerland's low and mid-elevation forests. Behind the direct climate effects, two amplifiers are at work that experts watch with concern: imported pathogens and nitrogen from agriculture. With the Integrated Forest and Timber Strategy 2050, the federal government has set clear signposts – the task now is to implement the measures consistently.

2.9 Degrees – and Only the Beginning

Since November 2025, the Climate CH2025 scenarios produced by MeteoSwiss and ETH Zurich have formed the current national baseline. They show that Switzerland had already warmed by roughly 2.9 degrees above pre-industrial levels by 2024 – more than twice the global average of about 1.3 degrees. CH2025 lists the main consequences for Switzerland as more frequent and intense heat, drier summers, more frequent and heavier extreme precipitation, and less snow. For the first time, it also addresses forest-fire danger, which could roughly double in many regions in a world three degrees warmer globally.

The forest-specific projections underpinning the sections below come from the FOEN/WSL research programme "Forests and Climate Change" (2016/2017) and rest on the "medium" A1B scenario of that time. They remain the best available basis for the question of which species shift where – and CH2025 confirms, and tends to sharpen, the direction of change. More decisive for the forest than mean warming, however, is the seasonality of precipitation: while annual rainfall declines only slightly, summer rain collapses – by 24 per cent in north-western Switzerland and 23 per cent in the south by the end of the century under the "medium" scenario. Prolonged droughts become the norm. The ratio of actual to potential evapotranspiration – the key measure of water availability – falls below the critical value of 0.8 on the Plateau and in Ticino, the point at which trees close their stomata and must halt photosynthesis.

The Losers: Spruce, Beech, Fir, Ash

Spruce, at 37 per cent, is by far the most common tree in the Swiss forest – and it loses the most. While almost the entire forested area suits it today, WSL researchers led by Niklaus Zimmermann model a retreat for the second half of the century confined to the higher elevations of the Alps, Pre-Alps, Jura and Ticino. At lower elevations, spruce already shows declining stand growth. An amplifier compounds this: the spruce bark beetle, the most important pest in the Swiss forest, benefits directly from rising temperatures. On the Plateau, three beetle generations per year are expected by the end of the century – a figure reached so far only during the 2003 heatwave summer.

Beech (18 per cent of the stock) is hit especially hard on the Plateau. Models predict a climate there under which beech grows nowhere in Switzerland or neighbouring countries today. Silver fir (11 per cent) shows a similar picture, though the research may be too pessimistic here: a few thousand years ago, silver fir grew under warmer and drier conditions and is thought to have vanished from many forests largely because of human-caused fires.

The most dramatic case is ash. Fifteen years ago it was Switzerland's second most common broadleaf; today it ranks third. This has nothing to do with climate directly, however, but with ash dieback (see below). Sweet chestnut in Ticino and Scots pine in the dry valleys of Valais and Graubünden likewise already show elevated drought-related mortality.

The Winners: Oaks and Drought Specialists

Sessile oak and other oak species are clear climate winners. More drought-tolerant, they can advance to higher elevations as temperatures rise. The Italian maple (Acer opalus), found in the Jura arc, should also expand its range. The colline vegetation belt – today almost confined to the Geneva–Lausanne area and the lower Rhône valley – is spreading above all on the Plateau. It is mainly the submontane belt that should expand strongly, pushing far into the Pre-Alpine zone and almost entirely covering the Jura ridges by the end of the century.

Non-native tree species are also being discussed as a possible complement. The 2025 Forest Report holds that non-native species can be an option – but deliberately names none, since suitability depends heavily on the site and must be assessed case by case. Blanket recommendations are out of place: eastern white pine, for instance, has little future owing to a fungal infection (white pine blister rust).

The Indirect Drivers: Nitrogen, Fungi, Global Trade

Describing the Swiss forest only as a victim of climate change misses two structural burdens that the FOEN names clearly in the 2025 Forest Report: nitrogen deposition and invasive harmful organisms.

Nitrogen deposition comes mainly from agriculture, supplemented by traffic. It weakens root growth and thus tree stability. Nitrogen-loving plants such as brambles overrun the forest floor, hamper tending and impede regeneration. Critical loads are exceeded across large parts of the Swiss forest – a finding known for years that has remained without political consequence. Ozone, too, presents a misleading picture: peak concentrations have fallen since 1980, but the mean burden tends to rise. The highest ozone values in Switzerland are measured in Ticino.

The second indirect driver is global trade. With it, invasive fungi, beetles and plants enter Switzerland where they face no natural antagonists. The list is long: ash dieback, red band needle blight of pine, tree of heaven, Asian longhorn beetle. For wood packaging, the international standard ISPM 15 prescribes heat or gas treatment – yet this has not truly stopped introductions.

Ash Dieback: When Globalisation Devours the Forest

The most dramatic case is ash dieback, caused by the East Asian fungus Hymenoscyphus fraxineus. Genetic analyses suggest that only two or three genotypes reached Poland with imported Asian ash in the early 1990s. In 2008 the fungus was first detected in the Basel region; by 2015 it was present throughout Switzerland. Today, according to the FOEN, between 90 and 95 per cent of Swiss ash trees are infected.

WSL researchers Valentin Queloz and Michael Eisenring have spent years searching for resistant ash genotypes. Five particularly tolerant trees from the cantons of Graubünden, St. Gallen, Schwyz and Thurgau are regarded as carriers of hope. But a new adversary is already at the door: the emerald ash borer (Agrilus planipennis), introduced near Moscow in 2003, has already crossed Ukraine and Belarus. Its larvae sever the trees' water supply.

The structural lesson: a single introduced pathogen can reduce a tree species by 90 per cent within one generation. Climate adaptation without biosecurity is only half the job.

What the FOEN and WSL Call For

The 2025 Forest Report – presented on 18 March 2025 at the Galmwald (FR) by FOEN Director Katrin Schneeberger – sets out the need for political action in five points:

• Promoting climate-adapted, future-fit species through targeted silvicultural intervention and, where needed, planting rather than mere natural regeneration.
• Increasing species, structural and genetic diversity, plus a possible shortening of rotation periods for climate-sensitive stands.
• Reducing browsing damage through more consistent regulation of game populations – a point where forest and hunting policy clash at cantonal level.
• Reducing stress factors: greenhouse-gas emissions, nitrogen deposition, forest fires, harmful organisms.
• Preserving the forest area in its spatial distribution – the statutory forest-conservation requirement is to be maintained.

Protective-forest management – 49 per cent of Swiss forests, or some 585,000 hectares, perform a protective function – is highly cost-effective: tending one hectare of protective forest costs around CHF 40,000 over a century, against CHF 1 million for an avalanche barrier of equivalent effect. Twenty-five times more. The economic benefit of Switzerland's protective forest is estimated at CHF 4 billion a year, while public authorities invest some CHF 150 million annually.

The area of forest reserves was expanded over the past decade from 5 to 7 per cent of the forested area – with a 2030 target of 10 per cent. Biodiversity is developing cautiously positively, above all thanks to increasing deadwood. Yet 13 per cent of forest plants and almost half of all wood-dwelling beetle species remain threatened.

Conclusion: A Generational Task

The Swiss forest is "under pressure as never before," writes the FOEN. The WSL calls the forest's adaptive capacity the country's greatest forestry challenge. One fact stands out: climate change is already transforming the Swiss forest today. Drought, heat, storms, pests and fires place many stands under mounting pressure. At the same time, there is no simple list of "winners" and "losers": whether a tree thrives in future always depends, too, on the site, the soil and local climate development.

Production horizons in the forest are long, and foresters must act under great uncertainty – about how strong climate change and its effects will be, how adaptable existing species are, or whether new pests will arrive. Many decisions will show their effects only after decades.

Climate adaptation requires diverse, site-appropriate and resilient forests. The greater the diversity of species and forest structures, the better the forest can cope with an uncertain future and continue to supply timber, provide habitat and protect people from natural hazards.

Adapting the forest is a generational task that has already begun. The challenge now is to continue it consistently, over the long term and on a sufficient scale. With the Integrated Forest and Timber Strategy 2050, the NaiS protective-forest guidelines and the current climate scenarios, the essential foundations exist. What matters now is to apply these instruments consistently, appropriately to the site, and in a verifiable way.

This analysis draws on the 2025 Forest Report by the FOEN and WSL, the WSL practitioner notice no. 59 "The Swiss Forest in a Changing Climate" (Allgaier Leuch, Streit, Brang, 2017), the FOEN overview "Forest and Timber: Key Facts" (2022), the waldwissen.net dossier, and published NZZ background articles on protective forest and forest condition.

Sources:

• FOEN / WSL: "2025 Forest Report. Development, Condition and Use of the Swiss Forest," 18 March 2025 – bafu.admin.ch
• MeteoSwiss / ETH Zurich (NCCS): "Climate CH2025 – Swiss Climate Scenarios," 4 November 2025 – nccs.admin.ch
• FOEN: "Integrated Forest and Timber Strategy 2050 (IWHS 2050)" – strategy report, indicator report and action plan 2025–2032
• FOEN: "Sustainability and Success Monitoring in Protective Forests (NaiS)" – implementation aid
• WSL press release "2025 Forest Report: Swiss Forest Under Adaptation Pressure," 18 March 2025
• Allgaier Leuch, B.; Streit, K.; Brang, P. (2017): The Swiss Forest in a Changing Climate. Practitioner notice 59, WSL Birmensdorf
• Pluess, A.R.; Augustin, S.; Brang, P. (eds., 2016): Forests in a Changing Climate. Foundations for Adaptation Strategies. FOEN/WSL, Haupt
• FOEN: "Forest and Timber: Key Facts," 20 December 2022
• FOEN: "Ash Dieback" – factsheet
• NZZ: "Mehr Vielfalt im Wald" (M. Hofmann, 28.08.2015) and "Schutzwälder brauchen Verjüngungskur" (P. Schneeberger, 13.08.2016)

Tags: #ForestReport2025 #ClimateChange #SwissForest #Spruce #Beech #Oak #Ash #AshDieback #Nitrogen #ProtectiveForest #Biodiversity #FOEN #WSL #InvasiveSpecies