Swiss Forests in Climate Change: Who Benefits, Who Loses – and What Politics is Missing

clarus.news | Analysis | May 17, 2026

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

The 2025 Forest Report from FOEN and WSL paints a picture that Switzerland reluctantly hears: Spruce, beech, fir, and ash – four of the most important tree species – are losing their climatic habitat in low and medium elevations. Oak benefits, sweet chestnut in Ticino and Scots pine in Valais are dying out. Behind the immediate climate impacts work two amplifiers that hardly anyone has on their radar: imported pests and nitrogen from agriculture. France has been discussing the strategic importance of forests for years. Switzerland publishes reports – and leaves implementation to the cantons.

1.8 Degrees – and That's Just the Beginning

Switzerland has warmed by around 1.8 degrees since the beginning of MeteoSwiss recordings in 1864 – about twice as much as the global average. In the decade 2011 to 2020, the average temperature was already 2.5 degrees above pre-industrial levels. Under the medium A1B-emission scenario on which FOEN and WSL base their forest projections, a further 3.3 degrees compared to 1980–2009 is expected by the end of the century. Summer temperatures rise particularly strongly: In the "Alps West" region, scientists model summer warming of 4.5 degrees.

More decisive for forests than average warming, however, is the seasonality of precipitation. While annual precipitation in Switzerland is likely to decrease only slightly, summer rains collapse: minus 24 percent in northwest Switzerland, minus 23 percent in southern Switzerland by the end of the century. Longer dry periods become normal. The ratio of actual to potential evapotranspiration – the decisive measure for water availability – falls below the critical value of 0.8 in the Central Plateau and Ticino, below which trees must close their stomata and stop photosynthesis.

The Losers: Spruce, Beech, Fir, Ash

Spruce is by far the most common tree species in Swiss forests at 37 percent – and it loses the most. While almost the entire forest-capable Switzerland serves as its habitat today, WSL researchers around Niklaus Zimmermann model a retreat area for the second half of the century that remains limited to the higher elevations of the Alps, Pre-Alps, Jura, and Ticino. In lower elevations, spruce already shows declining stand growth today. An amplifier is added: The European spruce bark beetle, the most important pest insect in Swiss forests, benefits directly from rising temperatures. In the Central Plateau, three beetle generations per year will be expected by the end of the century – a value previously reached only in the century summer of 2003.

Beech (18 percent stand share) is hit particularly hard in the Central Plateau. The modeling predicts a climate for the Swiss Central Plateau under which beech grows nowhere in Switzerland or nearby abroad today. Fir (11 percent) shows a similar picture, though research here might be too pessimistic: A few thousand years ago, silver fir grew under warmer and drier conditions and likely disappeared from many forests only due to human-caused fires.

The most dramatic case is ash. It was still the second most common deciduous tree species in Switzerland 15 years ago – today it ranks third. However, this has nothing directly to do with climate, but with ash dieback (see below). Sweet chestnut in Ticino and Scots pine in the Valais and Graubünden dry valleys also already show increased drought-related mortality today.

The Winners: Oaks and Drought Specialists

Sessile oak and other oak species are among the clear climate winners. They are more drought-tolerant and can advance to greater heights with rising temperatures. The field maple (Acer opalus) occurring in the Jura arc is also likely to expand its range. The colline vegetation zone – today found almost only in the Geneva–Lausanne area and the Rhone valley – spreads mainly in the Central Plateau. The submontane zone will expand strongly, likely advancing far into the pre-Alpine region and almost completely spanning the Jura ridges by the end of the century.

Additionally, non-invasive non-native tree species come into focus. The 2025 Forest Report explicitly names Austrian pine, Douglas fir, red oak, and Eastern white pine as options for forestry adaptation. Their share is small today, but it is likely to increase.

The Indirect Drivers: Nitrogen, Fungi, Global Trade

Anyone describing Swiss forests only as victims of climate change overlooks two structural stresses that FOEN clearly identifies in the 2025 Forest Report: nitrogen inputs and invasive pest organisms.

Nitrogen inputs come mainly from agriculture, supplemented by traffic. They weaken root growth of trees and thus their stability. Nitrogen-loving plants like blackberry overgrow the forest floor, complicate management, and hinder regeneration. Critical load limits are exceeded in large parts of Swiss forests – a finding that has been known for years and remains politically without consequence. Ozone also shows a misleading picture: peak concentrations have been falling since 1980, but average exposure tends to increase. The highest ozone values in Switzerland are measured in Ticino.

The second indirect driver is global trade. With it, invasive fungi, beetles, and plants reach Switzerland that have no natural opponents here. The list is long: ash dieback, red band needle blight, tree of heaven, Asian longhorn beetle. For wood packaging, the international standard ISPM 15 prescribes heat or gas treatment – but this hasn't really stopped introduction.

Ash Dieback: When Globalization Devours the Forest

The most dramatic case is ash dieback, caused by the fungus Hymenoscyphus fraxineus ("False White Stalk Cup") originating from East Asia. Genetic studies suggest that only two to three fungal genotypes arrived in Poland with imported Asian ash trees – in the early 1990s. In 2008, the fungus was first detected in the Basel region. By 2015, it was detectable throughout Switzerland. Today, according to FOEN, between 90 and 95 percent of Swiss ash trees are infected.

WSL researchers Valentin Queloz and Michael Eisenring have been searching for resistant ash genotypes for years. Five particularly tolerant trees from the cantons of Graubünden, St. Gallen, Schwyz, and Thurgau are considered promising. But a new enemy is already at the door: The emerald ash borer (Agrilus planipennis), introduced in the Moscow region in 2003, has already crossed Ukraine and Belarus. It cuts off the water supply to trees through larval feeding.

The structural lesson: A single introduced pest can reduce a tree species by 90 percent in one generation. Climate adaptation without biosecurity is half-hearted.

What FOEN and WSL Demand

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

• Promotion of future-viable, climate-adapted tree species through targeted silvicultural interventions and – where necessary – planting instead of mere natural regeneration.
• Increasing tree species, structural, and genetic diversity as well as possible shortening of rotation periods for climate-sensitive stands.
• Reduction of wildlife browsing through more consistent regulation of wildlife populations – a point where forest policy and hunting policy clash at the cantonal level.
• Reduction of stress factors: greenhouse gas emissions, nitrogen inputs, forest fires, pest organisms.
• Preservation of forest area in its spatial distribution – the legal forest conservation requirement should be maintained.

Protection forest management – 49 percent of Swiss forests or around 585,000 hectares fulfill a protective function – is economically highly efficient: managing one hectare of protection forest costs around 40,000 francs over 100 years, while technical avalanche barriers with the same effect cost 1 million francs. 25 times more. The economic benefit of Swiss protection forests is estimated at 4 billion francs per year, while public authorities invest around 150 million francs annually.

Forest reserve area was expanded from 5 to 7 percent of forest area in the last decade – the goal by 2030 is 10 percent. Biodiversity is developing cautiously positively, mainly thanks to increasing deadwood. However, 13 percent of forest plants and almost half of wood-dwelling beetle species remain endangered.

Conclusion: A Generational Task Without Pace

Swiss forests are "under pressure like never before," writes FOEN. WSL describes the forest's adaptability as Switzerland's greatest forestry challenge. Both are correct – and both are not enough.

What the 2025 Forest Report lacks is a binding roadmap with deadlines. Adapting tree species composition takes decades – a newly planted tree needs 80 to 120 years until it's ready for harvest. The climatic conditions we adapt to today are the conditions our grandchildren will experience. Those who don't plant in 2026 will have no protection forest in 2100.

The silence on a structural weakness is striking: forest policy is primarily organized at the cantonal level, the federal government defines framework conditions. In climate change, this federalism leads to 26 different speeds – while bark beetles know no cantonal borders. A central office that demands migration plans across departments, as France has in digital policy with DINUM, doesn't exist for forests.

The loser tree species won't die tomorrow. They die over decades. This is exactly what makes political inaction so dangerous: it becomes visible only when it's too late.

This article is based on the 2025 Forest Report by FOEN and WSL, WSL Practice Guide No. 59 "Swiss Forests in Climate Change" (Allgaier Leuch, Streit, Brang, 2017), FOEN overview "Forest and Wood: The Most Important in Brief" (2022), the waldwissen.net dossier on Swiss forests in climate change, and published NZZ background articles on protection forests and forest conditions.

Sources:

• FOEN / WSL: "Forest Report 2025. Development, Condition and Use of Swiss Forests," March 18, 2025 – bafu.admin.ch/waldbericht-2025
• WSL press release "Forest Report 2025: Swiss Forest Under Adaptation Pressure," March 18, 2025
• Allgaier Leuch, B.; Streit, K.; Brang, P. (2017): Swiss Forests in Climate Change: What Developments Are Coming? Practice Guide 59, WSL Birmensdorf
• Pluess, A.R.; Augustin, S.; Brang, P. (Eds., 2016): Forest in Climate Change. Foundations for Adaptation Strategies. FOEN/WSL, Haupt Verlag
• FOEN: "Forest and Wood: The Most Important in Brief," December 20, 2022
• FOEN: "Ash Dieback" – Fact sheet on invasive alien fungal disease
• waldwissen.net: "Swiss Forest in Climate Change" and "Research on the Future of Ash" (V. Queloz, M. Eisenring)
• NZZ: "More Diversity in the Forest" (M. Hofmann, 28.08.2015) and "Protection Forests Need Rejuvenation" (P. Schneeberger, 13.08.2016)
• Forest Practice: "Swiss Forest in Climate Change – Forest Report 2025" (A. Gröning, March 23, 2025)

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