Rapid Change and Thermophilization of Summit Plant Communities in the Central Eastern Alps (Italy)

Prepared by Friederike Westrich

Mountain ecosystems are among the environments most strongly affected by climate warming. Plants growing at high elevations are adapted to cold conditions and often live close to their environmental limits. As temperatures rise, plant species that normally occur lower down the mountains move uphill. This increases the number of plant species found on mountain summits, but it may also threaten species that depend on very cold conditions, which are not strong competitors and have nowhere higher to go.

In this study, we investigated how plant communities on four mountain summits, from the lower alpine to the nival zone in the Texel Group in northern Italy, have changed over the last 21 years. We repeatedly surveyed vegetation from 2003 to 2024 and compared these changes with long-term soil temperature measurements.

We found clear signs that alpine vegetation in the Texel Group is changing in response to warming. Overall, the number of plant species increased by 13% over the last 21 years. Most newcomers are usually found at lower elevations and are adapted to warmer conditions. At the same time, species adapted to very cold environments are declining. This shift towards communities dominated by warm-adapted species is known as thermophilization.

Particularly striking was the highest summit at 3287 m a.s.l., where species richness increased by 75% during the last seven years alone. Until recently, this zone had remained relatively stable despite ongoing climate warming. This rapid increase coincided with warmer soil temperature and a longer snow-free growing season, giving plants more time to establish and grow. Our data suggest that this ecosystem may have crossed an ecological threshold: soil temperatures during the growing season exceeded an average of 4.9 °C, a soil temperature associated with the development of dense alpine grassland. Once such thresholds are crossed, ecosystem change may accelerate.

At the same time, cold-adapted species are facing increasing habitat loss as suitable areas become smaller and more isolated. Cooler north-facing slopes may temporarily provide small refuges where these cold-adapted species can persist, but their long-term survival remains uncertain as climate warming continues. Therefore, our results highlight the importance of protecting high-elevation refugia and explicitly integrating retreating nival habitats into alpine biodiversity policy.

Reference:

• Pauli, H., M. Gottfried, A. Lamprecht, S. Niessner, S. Rumpf, M. Winkler et al. 2015. “The GLORIA Field Manual—Standard Multi-Summit Approach, Supplementary Methods and Extraapproaches (5th Ed.).” GLORIA-Coordination, Austrian Academy of Sciences & University of Natural Resources and Life Sciences.

This is a plain language summary of the paper by Westrich et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.70158).