Climate change is on track to shift key tree species like beech and Norway spruce north: European forests will be completely changed by the year 2100
In just a few decades, the climate in many of the world’s forests will be so changed that many trees will have difficulty surviving, according to new research from Aarhus University.
The tall, slender beech trees with their dark green, dense crowns – the very symbol of the temperate forests in Europe – may have disappear from many landscapes by the turn of the next century.
Today, the beech thrives in the temperate deciduous forest zone, which stretches from southern Sweden to central France. But in the future, the beech – like many other tree species – will face increasing exposure to climatic conditions beyond the conditions in the climate zone they occupy today.
This is shown by a new global study, led by Aarhus University and Wageningen University in the Netherlands. For beech, this means that in the future, summers in much of lowland Central Europe will be warmer, drier and reminiscent of the Mediterranean climate – conditions that the beech tree will have difficulty coping with.
This is according to Jens-Christian Svenning, professor of biology and Director of the Danish National Research Foundation’s Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus University. He is one of the researchers behind the ECONOVO research study, which has been published in the scientific journal PNAS.
“Denmark – in the northern part of the temperate deciduous forest zone - is in a better position than many other countries, but we need to think carefully when planting trees as part of reforestation and restoration efforts or for forestry. It would be a bad idea to plant too many trees from the cool and humid part of the temperate climate zone – such as Norway spruce and beech – because they may not thrive. Instead, we should focus on a broad mix of native species – e.g., pedunculate oak, European hornbeam, wild cherry, and Scots pine – and species that are currently found south of Denmark, such as sweet chestnut, walnut, Turkish hazel, Turkey oak, and wild pear. Generally speaking, diversity is the safest choice,” he says.
The study can contribute useful knowledge to the implementation of the green tripartite agreement. An agreement that, among other things, involves replacing Danish agricultural land with more forest.
“Taking a long-term view is absolutely essential when it comes to planting trees, both as part of forestry operations and from a biodiversity perspective. When planting new trees, we need to factor in our future climate,” he says.
He emphasises that it is important to look at what is being done elsewhere in the world.
“In Austria, they are now planting trees such as Turkish hazel – which conventionally is only considered native further south, notably the Balkans – because the resident native trees that are there are suffering drought stress.”
Population loss for thousands of species
The research team has analysed the current distribution of more than 32,000 tree species worldwide and assessed how they will much they will be exposed to future climates markedly outside the climates they currently thrive under.
“Under a realistic climate scenario, 69% of species in at least 10% of their current geographic range are predicted to be exposed to climatic conditions that differ significantly from current conditions,” says Jens-Christian Svenning.
In these areas, there is a high risk of tree species extinction.
“We’re already seeing this in Germany, for example, where Norway spruce is dying as a result of heat and drought stressing the trees. This makes them vulnerable to diseases and attacks by pests,” says Jens-Christian Svenning.
Fortunately, according to the researchers, there will still be areas left for each individual tree species which the climate should remain suitable. These areas can be considered as climate refugia and can become crucial for the survival of each individual tree species.
Widespread risk of forest death
But even though a majority of tree species likely will be able to survive in such refugia, from a forest ecosystem perspective the news is less positive.
“The study also points to dramatic consequences for large areas of northern forest (for example, taiga) as well as key tropical forests such as the Amazon. Here, large proportions of tree species in many areas will be exposed to unprecedented high heat with a substantial risk of these forests collapsing. Such collapses will not only affect biodiversity, but also accelerate climate change due to the release of large amounts of stored carbon,” says Jens-Christian Svenning.
In the past, biodiversity strategies have focused on expanding the number of protected natural sites. But according to Jens-Christian Svenning, it is clearly not enough if the climate in these areas changes so that the species can no longer survive.
“For forests on the edge of a climate zone, the change can be catastrophic for the majority of the trees, for example if the climate changes from a Mediterranean climate to a desert zone, as is currently happening in parts of southern Europe. Therefore, we must think long-term and in terms of assisted migration of tree species – otherwise we risk major species losses and ecosystem collapses. And at the same time, we must protect the forests that are not exposed to as severe climate pressure.”
Unfortunately, we need to act quickly, adds Jens-Christian Svenning.
“In southern Europe, for example, wildfires are becoming increasingly frequent and severe. Such fires can quickly ravage trees in large areas, and recovery may be difficult due to shifts towards more stressful climates.”
Coline C. F. Boonman – now a docent at Wageningen University in the Netherlands, who was responsible for the analyses, adds:
“Our research maps ‘exposure hotspots’ – i.e. areas where the highest proportion of the local tree species will be most exposed to significantly different climatic conditions. At the same time, we identify areas where relatively few tree species will be exposed to novel climatic conditions. These areas can serve as climate refugia for the world’s tree species in a rapidly changing world. It’s important that we protect these areas from destruction from deforestation and logging, so that they can become true refugia for the endangered tree species,” says Coline C.F. Boonman.
Journal
Proceedings of the National Academy of Sciences
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
High tree diversity exposed to unprecedented macroclimatic conditions even under minimal anthropogenic climate change
UNC-Chapel Hill study uncovers global rules shaping the treeline under climate change
University of North Carolina at Chapel Hill
image:
Pictured is a section of the Picea schrenkiana treeline ecotone (43.5°N, 90.1°E, 2600 m a.s.l.) in Jiangbulake Scenic Are, Eastern Tianshan Mountains, Xinjiang, China.
view moreCredit: Yuyang Xie
A new study from researchers at the University of North Carolina at Chapel Hill has revealed the key factors that determine where trees can grow at the highest elevations across the globe. By compiling the most comprehensive dataset of alpine treelines to date, more than 2,000 records worldwide, the research team uncovered a dual control system that explains why treelines form where they do, and which tree species dominate them.
The study shows that cold temperatures act as a universal ceiling that limits where all tree species can survive. Once temperatures dip more than 35% below a species’ thermal comfort zone, it can no longer establish as a “tree” beyond that point. However, water availability acts as a filter, determining which species are able to grow at those upper limits.
“This study reveals how heat and moisture shape the treeline, offering new insights into alpine ecosystems under climate change,” said Yuyang Xie, postdoctoral researcher in the department of biology at UNC-Chapel Hill and first author of the study.
To better forecast how treelines will shift as the climate warms, the researchers developed a new tool called the Relative Distance to Optimum (RDO) index. Unlike past models, the RDO index accounts for species-specific differences and measures how far plants are living from their optimal environmental conditions. This breakthrough will allow scientists to more accurately predict treeline shifts worldwide.
“Identifying the environmental limits of tree species helps accurately predict how alpine ecosystems will respond to warming,” said Xiao Feng, senior author and assistant professor in the department of biology at UNC-Chapel Hill. “These findings are crucial for guiding conservation in mountain regions under climate change.”
The research not only advances fundamental understanding of treeline formation but also has direct applications for conservation. By predicting where treelines will move in the future, scientists and policymakers can better prepare for changes in mountain biodiversity and protect vulnerable habitats.
“This study greatly advances our understanding of the complex drivers of treeline formation at the global scale,” Xie added. “It gives us the tools to anticipate how alpine ecosystems will shift in response to climate change.”
The study is available online in the journal PNAS at: https://doi.org/10.1073/pnas.2504685122
Journal
Proceedings of the National Academy of Sciences
Article Title
Keys to the global treeline formation: Thermal limit for its position and moisture for the taxon-specific variation
Article Publication Date
12-Aug-2025
Heat-stressed Australian forests are thinning fast, producing carbon emissions
image:
Heat-stressed Mountain Ash forest
view moreCredit: University of Melbourne
Heat-stressed Victorian mountain ash forests are thinning fast, turning from carbon sinks to carbon sources, new research reveals.
Published in Nature Communications, the research shows forests will lose a quarter of their trees by 2080 due to global warning.
Mountain ash forests are currently one of Earth’s most effective ecosystems for storing carbon – they store more carbon per hectare than the Amazon.
But researchers say these forests will store less carbon in the future as warming causes more trees to die and decompose.
Scientists from the Universities of Melbourne and New Hampshire (USA) analysed almost 50 years’ data from Australian forest monitoring plots.
The researchers found that increasing temperatures are thinning mountain ash forests rapidly, threatening their long-term potential to store carbon and slow global warming.
Lead researcher, University of Melbourne Dr Raphael Trouve, explained that the forests’ natural thinning response to temperature stress means that the ability of large-scale tree-planting initiatives to reduce atmospheric carbon levels may decline over the coming decades.
“Australia’s mountain ash forests are one of the Earth's most carbon-dense ecosystems, but our study reveals how climate warming could turn them from carbon sinks into carbon emitters as excess tree deaths and decomposition release stored carbon,” Dr Trouve said.
“Data collected in forest studies since 1947 shows that warming is intensifying competition amongst trees for limited resources – mainly water – and causing around nine per cent tree loss in mountain ash forests for every degree of warming.”
A projected rise of three degrees Celsius by 2080 could reduce tree density in these forests by 24 per cent. Making up for this carbon loss would require establishing hundreds of thousands of hectares of new forests.
“As more trees die and decompose, they will emit carbon dioxide, with an impact equivalent to driving a million cars 10,000km per year for 75 years,” Dr Trouve said. “This predicted forest loss does not include the impact of bushfires, which is also increasing.
“A growing tree needs space and resources to survive. Under resource-limited conditions, such as water stress, a big tree will outcompete smaller, surrounding trees, causing their deaths.”
Dr Trouve said recent research has shown how natural thinning in forests changes streamflow and water yield.
“Natural thinning of the mountain ash forests will likely impact Melbourne’s water supply,” he said.
“One promising management option is reducing stand density: selectively thinning some trees to give others a better chance of survival. This would accelerate the natural self-thinning process and give the rest of the trees more water, nutrients, and space to grow.
“Decades of research around the globe has shown that thinned forests are more resilient to drought, and the trees in them grow faster and survive better during dry periods.”
Native to south-eastern Australia, soaring to over 90 metres, the mountain ash or Eucalyptus regnans is one of the tallest tree species in the world.
“The trend in natural forest thinning may depend on regional climate as well as tree species,” Dr Trouve said.
The Australian Research Council funded the research described in the paper as a Discovery Project entitled Is climate change altering the carrying capacity of the world's forests?
Journal
Nature Communications
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Global warming reduces the carrying capacity of the tallest angiosperm species (Eucalyptus regnans)
Article Publication Date
21-Aug-2025
Where plant matters: How forests adjust aerosol cooling effect in surprising ways
Science China Press
The research team, led by Professors Pingqing Fu from Tianjin University has uncovered previously unrecognized complexities in how vegetation changes influence climate through interaction with aerosol formation utilizing an advanced Earth system model. The findings demonstrate that forestation initiatives must carefully consider regional variations in atmospheric feedbacks to maximize their intended climate benefits. While tree planting has been widely promoted as a climate solution, this research reveals the mechanisms are far more nuanced than previously understood.
Reforestation and afforestation have been recognized as a crucial strategy for mitigating global warming. However, beyond assessing its "carbon sink effect," it is equally important to holistically evaluate the dual climatic effects induced by vegetation changes through alterations in both surface and atmospheric conditions: Vegetation modifications regulate radiative balance by changing surface albedo, while also disturbing near-surface aerodynamic processes through structural changes in plant cover. These biogeophysical effects can trigger cascading climate responses. Simultaneously, biogenic volatile organic compounds (BVOCs) released by vegetation undergo atmospheric oxidation to form secondary organic aerosols (BSOA), which exert cooling effects by scattering solar radiation and modulating cloud microphysical processes.
The study reveals a dual modulation mechanism governed by distinct biogeophysical processes: When vegetation changes are primarily driven by reduced surface albedo, increased forest cover enhances solar absorption, leading to localized warming that significantly stimulates BVOC emissions from trees. This in turn amplifies the radiative cooling effect of BSOA. Conversely, when vegetation changes are dominated by enhanced updraft disturbances, the moisture uplift intensified by forests promotes the formation of dense cloud layers, which reduce surface solar radiation and consequently suppress BVOC emissions. This suppression diminishes BSOA formation and weakens its radiative cooling capacity.
This bidirectional modulation stems from fundamental regional differences in dominant biogeophysical mechanisms - albedo reduction acts as a "warming engine" that activates BSOA's cooling potential, while aerodynamic disturbance functions as a "sunshade" that inhibits BSOA's cooling capability. The contrasting effects highlight the complex interplay between surface and atmospheric processes in determining the net climate impact of afforestation.
Earth system modeling reveals pronounced spatial heterogeneity in how biogeophysical processes modulate BSOA radiative effects across vegetated regions. The simulations demonstrate that biogeophysical feedback acts as an "effect amplifier" in half of global vegetated areas, intensifying BSOA radiative effect variations by up to twofold. Conversely, in the remaining half of vegetated zones, these processes function as "dampening regulators," offsetting over 50% of BSOA radiative effect changes.
The study further reveals that biogeophysical feedback can induce large-scale climatic changes which subsequently cause disproportionately large variations in BVOC emissions even in areas with relatively minor vegetation changes. Such regional feedback effects are especially prominent in densely vegetated ecosystems like the Amazon rainforest. Importantly, failure to account for this spatial heterogeneity in biogeophysical modulation may lead to significant uncertainties in evaluating and predicting BSOA radiative effects under global vegetation change scenarios.
This landmark study has for the first time systematically revealed the dual regulatory mechanism through which vegetation changes modulate aerosol radiative effects via biogeophysical processes. "Our work provides the missing piece in understanding the complex 'afforestation-climate feedback' chain," said Prof. Pingqing Fu. "We now know tree planting isn't as simple as 'plant and cool' - it requires precision design based on regional dominant biogeophysical processes."
Journal
National Science Review
Method of Research
Computational simulation/modeling
