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Forests worldwide are filling with fast-growing trees and becoming weaker and more vulnerable as slow, long-lived species rapidly vanish.
Swapping fast growth trees for long, stable lifetimes favors the timber industry and quick recovery after wildfires, but it puts forests at much greater risk when facing changing climates.
Across a global analysis of 31,001 tree species, scientists at Aarhus University mapped where fast-growth traits are taking over.
Using those maps, Jens-Christian Svenning showed slow, specialized trees losing ground to fast generalist species.
In tropical and subtropical regions, Svenning flagged many small-range trees as most likely to disappear as disturbances multiply.
Once fast growers dominate a stand, storms, drought, and pests can knock larger portions of that forest down at once.
Forests, fires, and fast-growth trees
Logging, road building, and stronger fires leave open, sunny gaps where fast-growing trees take over quickly.
Lighter leaves and softer wood let these trees grow fast, even when drought or heat makes water scarce. Low wood density, how heavy wood is for its size, also made trunks easier to break and dry out.
Over decades, stands packed with light-wood trees can snap or dry faster, making die-offs more likely during extreme years.
Long-lived trees grew slowly, yet their deep roots and sturdy trunks held a forest together when weather turned harsh.
Denser wood and tougher leaves helped them resist drought and pests, and a recent report tied that durability to climate protection.
“They form the backbone of forest ecosystems and contribute to stability, carbon storage, and resilience to change,” said Svenning.
Losing those steady species leaves more open space for short-lived trees, and the forest can swing harder with each disturbance.
When outsiders take hold
Across ports, nurseries, and plantations, humans moved trees far beyond their native ranges, and some now spread without help.
Nearly 41 percent of naturalized, able to reproduce in the wild outside its home range, tree species showed fast growth and small leaves.
As storms, logging, and heat disturb forests more often, these outsiders can crowd native seedlings for light, water, and nutrients.
That pressure can push rare local trees closer to extinction, even when the newcomers look healthy and grow quickly.
Tropical forests lose rare trees
Tropical forests pack many tree species into small areas, so losing even a few can thin entire food webs quickly.
Many threatened trees there are endemic, living only in one region, and they depend on stable heat and moisture.
Conservation groups use the IUCN Red List, the global system for extinction risk categories, to rank many of them.
After logging or heat pushes conditions outside that narrow comfort zone, a local population can vanish for good.
Northern forests face invasions
Farther north, warming winters and heavier land use create new openings where imported trees can gain a foothold.
In colder regions, many native trees already live near their frost limits, so newcomers that handle swings spread faster.
Trade and landscaping often move hardy, fast-growing species between continents, and repeated planting gives them multiple chances to escape.
Over time, that spread can make distant forests look more alike, and losses can add up for local species.
Wildlife and forest tree loss
Globally, forests still act as a carbon sink, removing more carbon than they release. Slow, dense-wood trees locked carbon into trunks for decades, because each inch of solid wood held more material.
Fast growers often died younger and built lighter trunks, so storms and decay returned that stored carbon to air sooner.
“This makes forests less stable and less effective at storing carbon over the long term,” said Svenning.
Wildlife depends on particular trees for food and shelter, so removing one species can ripple through a forest community.
Some slow-growing trees flowered or fruited on schedules that local animals followed, and their loss can break those routines.
Seed dispersers and pollinators often matched the timing of those trees, so replacements with different cycles can leave animals hungry.
Without the right tree partners, forests can lose birds and mammals that spread seeds, slowing recovery after storms or fire.
Planting for resilience
Forest managers often favor fast-growing trees for quick harvests, but long-term resilience improves when plantings include slower species too.
Choosing a wider mix protects rare genetics, and it keeps old-growth traits in the forest as climate stress rises.
Limiting repeated disturbance, and stopping aggressive naturalized trees early, can give native seedlings enough light and water.
Because slow-growing trees take decades to mature, today’s choices can lock in either stability or fragility for a long time.
Overall, forests seem set to grow quicker while losing the slow trees that keep ecosystems steady and diverse.
Future planning can treat those slow species as essential infrastructure, and it can test which restoration mixes hold up under extremes.
The study is published in the journal Nature.
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