Professor
Jens-Christian Svenning with a specimen of the species Aspidosperma polyneuron
in Argentina. The tree is an example of one of the "slow" species
that are declining despite their high ecological value. Credit: Jens-Christian
Svenning
Trees
play a central role in life on Earth. They store CO₂, provide habitats for animals, fungi, and insects,
stabilize soils, regulate water cycles, and supply resources that humans rely
on—from timber and food to recreation and shade on a hot day.
But the world's forests are entering a
new era, characterized by homogenization, biodiversity loss, and weakened
ecosystems. This is shown by a comprehensive international study published in Nature Plants.
The researchers analyzed more than
31,000 tree species worldwide and provided a global picture of how forests are
likely to change—in terms of composition, resilience, and ecological
functioning.
According to the study, forests will
increasingly be dominated by fast-growing tree types, while slow-growing and
more specialized species are at risk of disappearing.
This is a worrying development,
according to Jens-Christian Svenning, Professor and Director of the Danish
National Research Foundation's Center for Ecological Dynamics in a Novel
Biosphere (ECONOVO) at the Department of Biology, Aarhus University, and one of
the leading authors of the study.
He warns particularly against the loss
of tree species that occur only in very limited areas of the world.
"We are talking about highly unique
species, especially concentrated in tropical and subtropical regions, where
biodiversity is high and ecosystems are tightly interconnected. When
specialized, native species disappear, they leave gaps in ecosystems that alien
species rarely fill, even if those species are fast-growing and highly
dispersive," says Svenning.
Functional
and environmental spaces of tree species. Credit: Nature Plants (2026). DOI: 10.1038/s41477-025-02207-2
The backbone of forests is under threat
The most threatened species are
often slow-growing specialists, as Svenning describes them. These are trees
with thick leaves, dense wood, and long lifespans, often associated with stable
environments—particularly moist tropical and subtropical forests.
"They form the backbone of
forest ecosystems and contribute to stability, carbon storage, and resilience
to change," says Svenning.
If current trends in climate change
and forest exploitation continue, forests will increasingly be dominated by
nature's "sprinters": trees with light leaves and low wood density
that allow rapid growth in the short term. Examples include various species of
acacia, eucalyptus, poplar, and pine.
"Although these species
establish and grow well, they are more vulnerable to drought, storms, pests, and climatic shocks. This makes
forests less stable and less effective at storing carbon over the long
term," says Svenning.
The study also shows that nearly
41% of so-called naturalized tree species—species that do not naturally occur
in a given area but now grow wild there—possess traits such as fast growth and
small leaves. This makes them well-suited to disturbed environments, but they
rarely perform the same ecological roles as native species, says Svenning.
"Moreover, in landscapes
affected by today's and tomorrow's disturbances, naturalized species can make
it even harder for native trees to survive, because competition for light,
water, and nutrients intensifies," he adds.
Tropical species are particularly vulnerable
Forest homogenization hits the
tropics and subtropics particularly hard, with future rises in tree species
endangerment concentrated in these regions.
"This is where many
slow-growing tree species with naturally small ranges occur. Because they are
confined to very limited areas, these species are especially vulnerable and
risk disappearing entirely if their habitats are destroyed or taken over by
fast-growing species," explains the study's first author, young professor
Wen-Yong Guo from the School of Ecological and Environmental Sciences, East
China Normal University, Shanghai.
"At the same time, we forecast
rising number of naturalized and fast-growing tree species adapted to
increasing disturbance throughout the world. Hence, in the colder parts of the
Northern Hemisphere, the likely dominant dynamic is the invasion of such
species," says Wen-Yong Guo.
According to the researchers, human
activities are the primary drivers of changes in forest composition.
"Human-driven climate
change,
deforestation for infrastructure, intensive forestry, logging, and global trade
in tree species all play a role. Fast-growing trees are often actively promoted
because they produce timber or biomass quickly. But ecologically, they are
often fragile and more prone to disease," explains Wen-Yong Guo.
Active ecosystem management is essential
In the study, the researchers
modeled how tree species are likely to spread or disappear under future
scenarios. The results clearly indicate that already naturalized species are
expected to become even more dominant in forests in the coming decades.
This makes it urgent to halt the
loss of slow-growing tree species, says Svenning. This can be achieved by
giving them greater priority in forest management and through more active
ecosystem restoration.
"When establishing new
forests, far more emphasis should be placed on slow-growing and rare tree
species. This would make forests more diverse and resilient. These species
should also be actively promoted in conservation and restoration efforts, where
they often interact positively with the recovery of richer communities of large
animals, which themselves are also important for future ecosystem
functioning," concludes Svenning.
Provided by Aarhus University
by Aarhus University
edited
by Sadie
Harley, reviewed by Robert Egan
Source: Fast-growing
trees are taking over the forests of the future and putting biodiversity,
climate resilience under pressure
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