Due to climate change, high-altitude plants are going extinct at an increasing rate on European mountaintops

Due to climate change, plant biodiversity on European mountaintops has increased in recent decades. While this may seem like good news, a new study in Science reveals that local plant species, which are specifically adapted to life at high altitudes, are simultaneously becoming extinct at an increasing rate. “Here, for the first time, we demonstrate the actual, accelerating extinction of high-altitude species due to climate change, rather than just the shifts that usually precede it,” says co-author and Utrecht University biodiversity researcher Jonas Lembrechts.

Over the past few decades, temperatures on mountaintops have risen. As a result, plant species adapted to the cold mountain climate have increasingly been joined by species that previously only occurred lower down the mountain, leading to an overall increase in plant biodiversity on mountaintops.

However, new research, carried out on 62 European mountaintops that were monitored four times between 2001 and 2022, now shows for the first time that it is precisely the specialist high-altitude species on these peaks that are disappearing, and that this has been happening at an increasing rate over the last 20 years.

As species move further up the mountain, the species that were already at the top are being pushed off.

Pushed off the mountain

“We had been observing shifts in distribution and increases in numbers on mountaintops for some time, but the actual extinction remained difficult to prove, as many species respond to climate change with a significant delay,” explains Lembrechts. “Now, at last, there is enough data spanning a sufficient number of years to reveal local extinction as well: as species move further up the mountain, the species that were already at the top are being pushed off.”

Climate change is the cause

In other locations, factors like nitrogen deposition and other forms of human disturbance often contribute to species loss, sometimes even more so than climate change itself. This makes it difficult to isolate climate change’s role in those areas. On mountaintops, however, such disturbances play hardly any role, meaning local extinctions there can in fact be directly attributed to climate change. 

“The data clearly show that species were more likely to disappear from summits which experienced stronger warming,” says lead author Johannes Wessely of the University of Vienna.

It is becoming increasingly clear that climate change, on top of existing pressures, is rapidly gaining in significance.

Increasingly clear

According to Lembrechts, this study is part of a growing body of research showing just how significant climate change’s impact on nature has now become. “Land-use change and nitrogen deposition remain, for the time being, the main culprits behind local biodiversity loss; this study does not change that,” Lembrechts points out. “But it is becoming increasingly clear that climate change, on top of these existing pressures, is rapidly gaining in significance. We have been seeing this in the oceans for much longer: species’ ranges have been shifting there for decades, and the bleaching of coral reefs is a well-known and unmistakable sign of this very same problem.” 

“Extinction debt”

Typical high-altitude mountain plants are often hardy and long-lived, which is why it was not immediately apparent that climate change was affecting them. The current higher rate of extinction could therefore be a response to changes that occurred, or at least began, decades ago.

According to the researchers, it is not inconceivable that even more locally adapted plant species will disappear from the mountaintops. “The results could indicate that an extinction debt starts to be paid off,” says Stefan Dullinger of the University of Vienna, who coordinated the research project. “However, whether this interpretation holds true needs further investigation.”

In the Netherlands too?

According to Lembrechts, it is quite conceivable that, in the coming years, we will see more reports attributing species loss in the Netherlands to climate change. 
“Unlike on mountaintops, it is difficult to attribute species loss here directly to climate change, given the significant role played by nitrogen and other human-induced disturbances,” he explains. “But there are early indications: for example, among dragonflies, we are seeing a decline in cold-loving species compared to heat-loving ones, although multiple stressors are at play here as well.”