An international study published in Science, which included the involvement of Pau Carnicero, lecturer in the Department of Animal Biology, Plant Biology and Ecology at the UAB, finds that the increase in the number of species masks an ever-increasing loss of high-mountain specialist plants on European summits.
Decades of warming have mitigated the limitations of low temperatures on the distribution of mountain plants, leading to an increase in the number of species on summits. Now, an international research team led by scientists from Vienna and involving the Universitat Autònoma de Barcelona shows that these changes are also resulting in an increasing number of casualties. The disappearance of plants from summits can take decades, but it has accelerated over the past twenty years. The increase in biodiversity is, therefore, only part of the story and conceals an important aspect of the recent dynamics of summit vegetation.
Until a few decades ago, short growing seasons, low temperatures, and the risk of frost throughout the year made alpine landscapes difficult for many European plant species to colonise. However, accelerating global warming has mitigated these limitations. Consequently, species have begun to expand to higher elevations, and the number of plant species on summits has increased.
However, the research team demonstrates that this apparent success story also has a dark side: while the total number of species is increasing, the rate of extinction is also rising, and the losses mainly affect specialist species in high-mountain ecosystems.
Scientists have analysed the vegetation of 62 European summits four times between 2001 and 2022 as part of the global monitoring initiative GLORIA. The data show that the percentage of species that were not re-detected increased with each new sampling campaign. Species that were mainly distributed above the summit studied were overrepresented among the species that had disappeared.
Extinction rate rises with global warming
The study results suggest that rising temperatures are the primary driver of these local extinctions. "The data clearly show that the species most likely to disappear were those on summits that had experienced the most intense warming. This correlation was even stronger than the temporal trend," explains the study's lead author, Johannes Wessely of the University of Vienna. Furthermore, the probability of local extinction increases as we approach the lower altitudinal limit of the species' current distribution. "In other words, when species are already growing in locations that are warmer than average, they become more sensitive to any further rise in temperature," clarifies Harald Pauli, GLORIA coordinator at the Austrian Academy of Sciences and BOKU University.
Is this an extinction debt?
Specialist species in high-mountain areas tend to be particularly tolerant of environmental stress and are long-lived. For this reason, local extinction may occur long after the onset of the environmental changes that triggered it. This phenomenon leads to the accumulation of an extinction debt within biological communities.
It had already been suggested that these time lags might be a primary reason why, to date, colonisations by new species have been documented more frequently than extinctions of pre-existing species in alpine vegetation. The results of this study are consistent with this interpretation: local extinctions are often preceded by long periods of population decline. This implies that the current extinction rate could be a response to environmental changes that occurred—or at least began—decades ago. "Consequently, this could indicate that an extinction debt is beginning to be paid. However, further research is needed to confirm whether this interpretation is correct," emphasises project coordinator Stefan Dullinger.
This work has been funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 883669).
Original article: Wessely, J., Dullinger, S., et al. Rising plant extinction rates on European mountain summits. Science. DOI: 10.1126/science.aed2974
