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Researchers found a surprising abundance of life high in the mountains
“It’s not the easiest place to live. But these species are still there. They are incredibly resilient,” says researcher Lotta Schultz.
High above the treeline lies a world full of plants, mammals, reptiles, and birds. They have survived and adapted to extremely challenging conditions. Together, they form an ecosystem unlike any other.
Researcher Lotta Schultz has examined biodiversity in alpine regions, areas that are surprisingly full of life.
In her research group at the University of Bergen and the Bjerknes Centre for Climate Research, they study mountains as dynamic parts of the Earth system, shaped by changing climates, shifting treelines, and expanding and retreating glaciers.
The aim is to understand how these changes affect life in alpine ecosystems.
But before they can answer that question, they need to understand what animal and plant life actually looks like across the world's mountains.
“Before we can study how biodiversity changes, we need the data to describe it,” Schultz explains.
Mountains are hotspots for life
The alpine biome covers only around 3 per cent of Earth's land surface. Nevertheless, Schultz and her colleagues found that it contains 7.8 per cent of all vertebrate species worldwide.
A biome is a term used to describe different types of biological communities.
More than 10 per cent of all the world's bird and mammal species are found in alpine environments.
“Mountains in general are hotspots for biodiversity. But the alpine biome is special in a different way: There are hotspots within alpine ecosystems. Some mountain regions are incredibly biodiverse, while others have far fewer species,” says Schultz.
The clearest example is found in the tropical Andes in South America, which emerged as one of the world's great alpine biodiversity hotspots.
By comparison, mountain systems such as the Alps and the Scandinavian mountains have fewer species relative to their size.
What surprised Schultz most was not the overall richness of alpine life, but how different each mountain range turned out to be.
“I thought there would be a more obvious global pattern,” she says.
Instead, each mountain range seemed unique.
"In one region you find highly specialised birds. In another, specialised mammals. The biodiversity of each mountain system tells a story of its own,” the researcher says.
True alpine specialists
“Within a mountain, we have different life zones. As you move up a mountain, at some point the trees become shorter and more scattered, and then there are no trees anymore. That's what we call the alpine zone,” Schultz explains.
The study differentiates between species that occasionally inhabit alpine areas and species that are true alpine specialists.
Some species can thrive across a broad range of elevations. Others are restricted to life above the treeline. These specialists are often particularly vulnerable because they have no higher ground to retreat to when conditions change.
“Some species live in the mountain forest but also venture into the alpine zone, for example for breeding,” says Schultz.
She explains that others are much more closely tied to the alpine zone. One example is the rock ptarmigan, a characteristic alpine bird found above the treeline, including in Norway's mountain regions.
According to the study, 360 vertebrate species can be classified as alpine specialists. As many as 91 per cent of these species are confined to a single mountain range.
This shows how restricted many alpine species are. It also shows how different one alpine biome can be from another.
Islands in the sky
Why are there so many unique species in the high mountains?
Part of the explanation may be that mountain regions function much in the same way as islands do.
Because mountaintops are separated by valleys, forests, and lowlands, populations become isolated from one another. Over long periods of time, this isolation can drive evolution, leading to the emergence of new species.
“Alpine ecosystems are sometimes referred to as islands in the sky,” says Schultz.
Just as rising and falling sea levels can connect and separate oceanic islands, shifting climates have repeatedly connected and fragmented alpine habitats.
Glaciers expand during colder periods and forests move uphill during warmer periods.
As a result, alpine habitats either become connected or are divided into separate areas. This has happened repeatedly over thousands of years in mountain regions around the world.
“You have populations that are together at one point and then become separated,” Schultz explains.
She says this can trigger a range of ecological and evolutionary processes that may eventually lead to the emergence of new species.
Researchers sometimes describe these changing landscapes as a pump for biodiversity. As populations alternately come into contact and become isolated, and different species communities mix, new opportunities for evolution arise.
Over time, this contributes to the rich diversity of species found in the world's mountain regions today.
A global network for mountain research
Understanding alpine biodiversity on a global scale required a global research effort. Data exists for many mountain regions around the world. But it has often been collected using different methods and stored in separate databases.
This makes global comparisons difficult.
“You might have detailed data for specific regions, but for our study we needed to zoom out and use data on a larger scale in a consistent format across many different mountain regions,” says Schultz.
To build the dataset behind the study, Schultz combined information from global biodiversity databases, scientific literature, and spatial analyses.
The team also collaborated with the Global Mountain Biodiversity Assessment, a worldwide network of mountain researchers. They helped validate the compiled data.
The human impact
The same processes that shaped alpine biodiversity in the past are now being accelerated by climate change.
As temperatures rise, species adapted to cold conditions lose their habitats. Trees move uphill, while species from lower elevations move into alpine areas and compete with established communities.
“We have climate change yes, but we also have human impacts. And that plays a very important role in mountain regions around the world,” Schultz says.
Schultz grew up in the Alps, where she has witnessed these changes firsthand. Tourism infrastructure continues to expand farther into the landscape, while improved technology makes it possible for agriculture to move higher up the mountainside than ever before.
“The small paths I knew when I was younger have become large gravel roads. Machines can now reach places that were impossible only a decade or so ago,” she says.
Finding a balance between conservation and human needs is rarely straightforward. Traditional alpine farming practices have existed for centuries and remain an important part of local cultures and economies.
At the same time, Schultz believes that people need to experience mountain environments in order to appreciate them.
“If you want to protect something, people need to see its value. They need to see nature, the plants, and the animals to understand why these ecosystems matter,” she says.
The story begins above the treeline
For Schultz, perhaps the most remarkable aspect of alpine ecosystems is how much life thrives in places that many people perceive as barren and inhospitable.
Across the Himalayas, the Andes, the Alps, and the mountains of Norway, very different communities have evolved under similar environmental conditions.
“It’s not the easiest place to live. But these species are still there. They are incredibly resilient,” she says.
That resilience does not mean that alpine ecosystems are invulnerable.
As climate change and human activities continue to reshape mountain landscapes, understanding the distribution and uniqueness of alpine biodiversity becomes increasingly important.
The new global dataset developed by Schultz and her collaborators provides an important foundation for that work. It reveals a world of extraordinary diversity hidden above the treeline, where every mountain range tells a different evolutionary tale.
Reference:
Schultz et al. Contrasting patterns of alpine biodiversity across mountains and taxa worldwide, Nature Communications, 2026. DOI: 10.1038/s41467-026-75210-6
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