False spring disrupted the life cycles of Pinus cembra and Vaccinium myrtillus at the alpine treeline ecotone in the High Tatras (Western Carpathians)

Abstract This study examines the impact of extreme weather events driven by global warming on the growth and distribution limits of high-elevation vegetation by analysing the effects of frost following an exceptionally early onset of spring phenological phases. Climate data from the Skalnaté Pleso Observatory in the High Tatras indicate that the winter of 2023/24 was unusually warm, with January–April temperatures exceeding the 1961–1990 climate normal by 3.8 K for average temperature and 4.4 K for maximum. Despite increased winter precipitation, snowmelt in 2024 occurred significantly earlier and more rapidly than in previous years. Consequently, bud development in Pinus cembra and Vaccinium myrtillus , as well as leafing in Calluna vulgaris , began unusually early. This early onset of phenophases was interrupted by an 11-day cold spell, with minimum temperatures reaching as low as −8.3 °C and an average daily air temperature of −2.0 °C. This episode led to the frost damage of buds during the sensitive development stages, indicating a so-called false spring. V. myrtillus buds were visibly damaged immediately. In P. cembra , needle yellowing and defoliation appeared in the next weeks, while reproductive organs damage became evident later during flowering when male flowers were undeveloped and did not pollinate. Frost damage to high-elevation vegetation can disrupt plant growth, competition, and food chains, especially when phenological advances outpace the retreat of late spring frosts.