- Climate change, deforestation and habitat loss are favouring the dominance of fast-growing tree species.
- As native trees are displaced, biodiversity declines, disease resistance decreases and forests lose their capacity to store CO₂.
Eucalyptus is an example of a fast-growing tree species. (Pixabay)
Trees play a central role in life on Earth: they store carbon, provide habitats, stabilise soils and regulate water cycles. However, the world’s forests are entering a new era marked by homogenisation, biodiversity loss and the weakening of their ecological functioning.
This is shown by a major international study published in Nature Plants, led by East China Normal University and involving the Botanical Institute of Barcelona (IBB, CSIC-CMCNB). The research team analysed more than 31,000 tree species worldwide to provide a global picture of how forests may change in the coming decades in terms of composition, resilience and ecological functions.
The results indicate that forests are likely to become dominated by fast-growing species, while slow-growing and more specialised species — often native — face a high risk of disappearing. According to Jens-Christian Svenning, professor and director of the Center for Ecological Dynamics in a Novel Biosphere at Aarhus University and one of the study’s lead authors, this trend is particularly worrying for species with very restricted geographic distributions.
“We are talking about highly unique species, mainly concentrated in tropical and subtropical regions. When these species disappear, they leave ecological gaps that alien species rarely manage to fill, even if they grow quickly and disperse easily,” explains Svenning.
The backbone of forests is under threat
The most threatened species are typically slow-growing specialist trees with thick leaves, dense wood and long lifespans. These trees form the backbone of forest ecosystems. They are essential for forest stability, carbon storage and resilience to environmental change.
If current trends in climate change, logging and human disturbance continue, forests will increasingly be dominated by nature’s so-called “sprinters”: species with light leaves and low-density wood that enable rapid short-term growth. These include various acacias, eucalypts, poplars and pines.
Despite their ability to establish and grow quickly, these trees are often more vulnerable to droughts, storms, pests and other climate shocks. As a result, the forests they dominate may be less stable and less efficient at storing carbon in the long term.
The study also shows that nearly 41% of naturalised tree species — those growing wild outside their native range — display traits associated with rapid growth. While these characteristics make them competitive in disturbed environments, they rarely replace the ecological functions of native species.
Moreover, in landscapes subject to current and future disturbances, these species may intensify competition for light, water and nutrients, further threatening native trees.
Tropical species are particularly vulnerable
Forest homogenisation will particularly affect tropical and subtropical regions, where much of the world’s tree diversity is concentrated and where extinction risks are expected to rise significantly. Human activities are the main driver of these changes.
According to Wen-Yong Guo, first author of the study and professor at East China Normal University, many slow-growing tropical species have very limited distribution ranges. “This makes them extremely vulnerable: if their habitats are destroyed or occupied by fast-growing species, they may disappear entirely,” he explains.
Active ecosystem management is essential
Using models that simulate future scenarios, the study indicates that already naturalised species are likely to become even more dominant in the coming decades if no action is taken. The authors highlight the urgent need to halt the loss of slow-growing species through more active forest management and ecosystem restoration strategies that prioritise functional diversity.
In this context, Josep Serra-Diaz, Ramón y Cajal researcher at the Botanical Institute of Barcelona (IBB, CSIC-CMCNB), emphasises:
“The study shows that conserving tree species is not only a matter of biodiversity, but is essential for forest ecosystems to continue functioning in an increasingly warmer climate with greater risks.
It is very likely that the naturalisation of tree species will continue in the coming years, but we must assess which species, in the medium term and under a changing climate, could make our forests more unstable. We must ensure that forests remain diverse in order to face different risks.”
Access to the study
The study, Global functional shifts in trees driven by alien naturalization and native extinction, published in Nature Plants, is available here.