Influence of late spring light frosts on Siberian stone pine (Pinus sibirica Du Tour) seed production in changing climate

The dynamics of Siberian stone pine cone bearing for the period from 1990 to 2023 has been considered to establish the influence of weather conditions in the spring period during the pollination year on the subsequent cone crop. It has been found that over the past two decades, the average annual level of the mature cones number has decreased by almost a quarter of the level that was at stable climate. The amplitude of fluctuations in cone crops has also changed, as the alternation of high and low yields characteristic of the previous climate was replaced by an alternation of medium and low ones. It has been suggested that one of the reasons for a negative trend in the seeding dynamics is late spring frosts, which remained within the same time frame despite climate warming. The number of mature cones in the crown largely depended on the spring weather in the pollination year and negatively correlated with the sum of active temperatures above +5°C accumulated before the onset of late spring frost. The value of this indicator was determined by the April temperature. In years when late spring frost occurred at low active temperatures (less than 100 °C), the cone crop was large. In contrast, when 300 °C or more accumulated before freezing, cone crop was minimal. Changes in the timing of the last spring-summer frosts were also noted; on average, there is a tendency for the timing of the last frosts to shift to later dates. It is assumed that with further climate warming, the onset of spring development of reproductive structures will occur at an earlier date, therefore reproductive structures will be more damaged by late spring frosts, since the latter remain within the same time frame. Abundant crops of Siberian stone pine can be formed only in some years with late spring and/or in the absence of late spring frosts.