This study advances our understanding of how extreme weather events associated with global warming impact high-altitude species’ growth and distribution limits. In particular, it highlights the vulnerability of early spring phenological phases to frost events. Despite elevated precipitation levels, we observed a markedly earlier and faster reduction in snow cover during late winter 2024 compared to previous years. The winter season was also exceptionally warm, with mean air temperatures from January to April exceeding the 1961–1990 climatological norm by 3.7 °C (minimum), 3.8 °C (mean), and 4.4 °C (maximum).

Under these conditions, bud development in Swiss pine (Pinus cembra) and bilberry (Vaccinium myrtillus) commenced over a month earlier than usual. However, an 11-day cold spell that started on April 16 interrupted this early development, with daily average temperatures falling to –2.0 °C, average minimum temperatures reaching –5.3 °C, and maximum temperatures remaining below 0 °C on three days. This frost event coincided with sensitive developmental stages, resulting in substantial bud damage.

In bilberry, frost injury was evident immediately, while in Swiss pine, it manifested later during flowering, with approximately 50% of the flowers remaining undeveloped and failing to produce pollen. Such events can have significant consequences for plant growth, reproductive success, and distribution boundaries, as well as for the trophic interactions of specialized alpine consumers.