Negative effects of false spring on P. cembra in the alpine treeline ecotone of the High Tatras, Slovakia

Trees growing in mountain regions have evolved adaptations to withstand extreme winter conditions, primarily through dormancy and frost-avoidance mechanisms. However, frost events occurring after the growing season begins pose a substantial risk, as ice formation can damage newly developing tissues. A warm episode in late winter or early spring that triggers premature growth, followed by a subsequent hard freeze, is termed a false spring.

In the alpine treeline ecotone in the High Tatras, Pinus cembra, a native, long-lived mountain conifer, experienced such a false spring in 2024. Weather conditions in late winter led to an unusually early bursting of vegetative buds, which was interrupted by an 11-day cold spell. During this period, minimum air temperatures dropped to −8.3 °C, with a mean daily temperature of −2.0 °C, as recorded at the Skalnaté Pleso Observatory (1778 m a.s.l.). This freezing event occurred shortly after vegetative buds had lost their protective resin layer and begun to burst. The aim of this study was to assess the impact of this event on the life cycle of P. cembra.

In the weeks following the false spring, affected individuals exhibited pronounced needle yellowing and defoliation. While senescence and shedding of older needles typically occur between August and September, frost-induced stress led to the premature loss of approximately one-third of needles as early as May, at the beginning of the growing season. Although new shoots and needles developed normally, reproductive organs were severely affected. Cone bud formation was observed approximately two months after vegetative budburst; however, male (pollen) cones were degenerated and showed minimal pollination potential. Following the false spring, P. cembra individuals developed several seed cones, which subsequently abscised between July and August 2025. These cones were immature, small, and deformed.

Our results demonstrate that false spring events associated with ongoing climate change can disrupt the life cycles of P. cemba, substantially limiting its reproductive potential in the alpine treeline ecotone of the High Tatras.

Acknowledgement: This study was funded by the project VEGA 2/0048/25.