Forests are not adapting fast enough to climate change

Forests hold our climate together. They store carbon, balance rainfall, and shelter more life than we can count. Among them, the Amazon and Andes stand out. These vast forests feed rivers, shape weather, and anchor communities of plants, animals, and people.

But they are now falling behind. A new study by Wake Forest University and international partners shows that tree communities in the region are not adjusting fast enough to rising temperatures.

Decades of monitoring reveal that while some forests near the cloud base shift slightly, most remain stuck. That slow pace threatens not just biodiversity, but also the services humans rely on every day.

“These forests are simply not keeping up with climate change,” said lead author William Farfan-Rios of Wake Forest University. “The result is a growing climatic debt that threatens the integrity and functioning of the most diverse forests on Earth.”

Forests lag behind climate change

The team followed 66,000 trees across 2,500 species for more than 40 years. They expected to see warm-adapted species slowly replacing those suited to cooler conditions – a process known as thermophilization. But the forests told a different story.

From the low Amazon basin to the high Andes, tree communities showed almost no sign of this shift. Trees grew, died, and recruited, yet the overall balance barely moved.

Scientists call this gap between climate warming and ecological response a climatic debt. If that debt builds, forests risk crossing thresholds that they cannot recover from.

Stress at the cloud base

The clearest signs of strain appeared in mid-elevation forests between 1,200 and 2,000 meters. Here, mortality of cool-adapted trees rose sharply. These cloud-base forests seem to carry the heaviest burden of warming.

The Amazon lowlands, by contrast, showed little consistent movement at all. On the surface, that looks stable. In reality, it signals trouble ahead.

Heat stress and drought will hit harder in the coming decades, and these forests have no hotter-adapted species waiting to take over.

Forests must change with climate

The Amazon and Andes together hold the greatest variety of life on Earth. They also act as giant carbon sponges, slowing the buildup of greenhouse gases.

If their tree communities fail to adapt, the consequences will spread far beyond South America. Carbon storage will shrink, species will vanish, and ecosystems could unravel.

“You have to be there for long periods of time to understand how these forests change,” said co-author Miles Silman of Wake Forest University.

“If we lose these climate observatories, these natural labs, we blind ourselves to our future. What we found is that forests are changing, but they’re not changing in the ways that make them resilient to climate change.”

Limits of forest adaptation

Tree communities simply cannot keep pace with today’s speed of warming. Individual trees die within decades, but species turnover takes centuries.

On top of that, forests need dispersers and pollinators to expand into new ranges. Yet many of these animals are disappearing as habitats shrink.

“They also need the full complement of animal dispersers and pollinators to help expand their range – and loss of habitat is shrinking their ranks,” noted Silman.

“If you look at the magnitude of changes happening in the Andes-Amazon, the forest communities likely are not going to keep up. That’s why research like this is important.”

Decades of data serve as a warning

Tropical species face sharper limits than temperate ones. They tolerate only narrow temperature ranges, and they often have nowhere warmer to move. In the lowlands, for example, no hotter-adapted species exist to take over. That leaves communities locked in place.

This study, authored by more than 20 scientists across the Americas and Europe, draws on decades of collaboration.

Networks like ABERG, RAINFOR, and ForestPlots.net made it possible to track forests over long stretches of time. The collective data show that the tropics, once thought resilient, may be less able to adjust than forests in temperate zones.

The message is stark. The world’s most diverse forests are changing, but too slowly to match the heat. If this pattern continues, the Andes and Amazon could face tipping points that threaten both ecosystems and people.

For now, continued monitoring remains vital. These forests act as early warning systems, showing us how nature responds to climate stress. Without them, we lose both knowledge and time.

The study is published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–