The Influence of Late Spring Frosts on the Reproduction of Four 5-Needle Pine Species during their Cultivation in the South of the Forest Zone of Western Siberia

As is known from the introduction theory, the two necessary conditions for complete acclimatization of a species in its new habitat are the species’ resistance and reproducibility. Late spring frosts are the most important factor that causes losses of crops of forest woody species in the south of the forest zone of Western Siberia. In particular, for the valuable local species of Siberian pine P. sibirica, the crop production periodicity is directly dependent on the impact of late spring frosts on its generative organs. To date, no similar research has been conducted on the introduction objects of exotic 5-needle pines in this region. Therefore, the present study aims to assess the influence of late spring frosts on the reproductive organs of four 5-needle exotic pine species during their introduction through the vegetative method in subtaiga and the forest zone of south taiga of Western Siberia. Methods. Grafting was performed on four-year-old
P. sibirica rootstocks, with the 3×6 m placement of trees, in nine replications. The study was carried out during seven years after the transition of grafts to the generative stage of ontogenesis.
The assessment of spring frost damage to cones was conducted using the following indicators: the average daily sum of effective temperatures, the last frost date, the sum of effective temperatures before the last frost date, the last frost date temperature, and the number of days with temperatures above +5 ºC before the last frost date. Results. Based on the timing of peak pollen shedding and cone receptivity phases, the species were placed in the order of accumulation of the necessary sum of temperatures depending on their natural habitat conditions: subarctic-subalpine P. pumila, mountain-taiga P. cembra, nemoral P. koraiensis, and P. strobus distributed in monsoonal areas of the temperate and subtropical zones. The survivability and resistance of the reproductive organs in 5-needle exotic pine species were found to be higher in the case the final spring frost occurred earlier in May and was combined with a low accumulated sum of effective temperatures along with a relatively small number of days with temperatures above +5 ºC before the last frost date. Conclusion. The species P. cembra and P. strobus were resistant to frosts, while P. pumila and P. koraiensis were less frost resistant, the latter exhibiting a wider range of resistance of its generative structures. The primary reason is related to the cone development timing. For P. pumila, the least adversely affected by spring frosts were the western continental and nemoral ecotypes, while for P. koraiensis those were ecotypes from the northern part of its native habitat. It is these ecotypes that are recommended to be used in this introduction area while conducting works on their complete acclimatization and further introduction into forestry and landscaping.