Decades of climate change have not left Europe's mountain vegetation unscathed. However, the changes observed do not always match expectations. As a new international study by a research team led by researchers from the University of Vienna, the Austrian Academy of Sciences and the BOKU University shows, alpine vegetation has shifted significantly towards warmth-associated species. However, the direct link between this so-called thermophilisation and local warming is surprisingly weak. The study has recently been published in the prestigious journal Nature Ecology and Evolution.

For the study, the international research team analysed data from 724 long-term monitoring plots on 53 mountain summits, spread across all major European mountain regions. These plots were surveyed a total of four times over a period of 21 years as part of the global GLORIA monitoring network, the most comprehensive monitoring programme to date on the effects of climate change on mountain summit vegetation.

The results show that warmth-associated plant species are now more common in many places than they were at the beginning of the monitoring program. At the same time, temperatures on the summits studied have risen. Surprisingly, however, the extent of thermophilisation at a monitoring plot could only be poorly explained by the warming measured there.

"Our data clearly show that vegetation on European mountain summits is changing and that warmth-associated species are becoming more common," explains biodiversity researcher Johannes Hausharter from the University of Vienna, the study's lead author. "However, the rate of these changes does not appear to depend solely on rising temperatures."

The study thus provides new insights into the complex mechanisms driving changes in alpine vegetation and shows that the consequences of climate change, even in sensitive ecosystems such as those of Europe's high mountains, are more nuanced than has often been assumed.

Local conditions override the effect of climate

The researchers compared the observed changes in vegetation with a whole series of different temperature-related climate indicators from various data sources. Despite this exceptionally comprehensive dataset, the link between rising temperatures and changes in vegetation remained limited at the local level.

The integration of the monitoring plots within the surrounding vegetation proved to be particularly important. “How alpine vegetation responds to climate change depends not only on how many degrees warmer it gets, but also on whether other warmth-associated species are already present,” says project leader Stefan Dullinger from the University of Vienna.

Climate change remains the overarching driver

Despite the complex local dynamics, the researchers emphasise that climate change is the primary cause of the observed changes. This becomes clear when the data from the individual monitoring plots are aggregated. "If you summarise the data on a larger spatial scale, it becomes clear that in mountain ranges that have warmed more significantly, summit vegetation also shows, on average, a greater shift towards warmth-associated species," explains Hausharter, "in other words, more warming tends to mean more warmth-associated species, but each summit reacts slightly differently."

Long-term monitoring remains essential

According to the research team, the findings underscore the great value of long-term monitoring programmes. Predictions for individual mountain summits or other landscapes are of great importance for effective nature conservation, but require a better understanding of the interplay between climate change and other influencing factors, based on long-term and wide-ranging data collection.

"Long-term monitoring programmes provide indispensable insights into the understanding of Alpine ecosystems and their vegetation," emphasises Harald Pauli, head of the GLORIA network at the Austrian Academy of Sciences and BOKU University: "In order to better predict the future of biodiversity in Europe's high mountains, we must continue these programmes and also expand their scope so that the various, often interrelated factors can be better assessed."

Summary:

• To measure the effects of climate change on vegetation in Europe's mountains, data from 724 long-term monitoring plots on 53 summits across Europe were analysed over a period of 21 years.
• The results show that warmth-associated plant species are now more common in many places than they were at the start of the studies.
• Surprisingly, the link between rising temperatures and changes in vegetation remained limited at the local level.
• Another decisive factor was whether other warmth-associated species were already present in the surrounding area. Where this was the case, the proportion of warmth-associated species on the monitoring plots also increased more strongly.
• The study thus reveals a thoroughly complex set of dynamics. The researchers emphasise, however, that climate change is a key driver of these changes.

About the University of Vienna:

For over 650 years the University of Vienna has stood for education, research and innovation. Today, it is ranked among the top 100 and thus the top four per cent of all universities worldwide and is globally connected.
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