Linear growth of lateral shoots of plants belonging to the genus Crataegus L. and the influence of the temperature factor during introduction in the Arctic zone of the Russian Federation (Kola Peninsula)

This study is devoted to assessing the patterns of seasonal growth of lateral shoots of introduced Crataegus L. species beyond the Arctic Circle (using the example of the Kola Peninsula). The paper presents the timing of the onset and end of the linear growth of shoots, the duration of the shoots growth, the influence of the thermal regime on the duration and intensity of the growth of shoots belonging to some species of hawthorn. The beginning of linear growth of shoots in introduced hawthorn species on average occurs on June 1. The sequential series of hawthorn species according to the timing of the onset of linear growth of shoots from early to late is as follows: C. sanguinea, C. flabellata, C. maximowiczii, C. laevigata, C. dahurica, C. russanovii. The average duration of shoot growth for 2018–2020 was 38 days. The shortest increase was observed in 2019 for C. russanovii, the maximum increase was recorded for C. maximowiczii plants in 2018. The differences in the annual growth of shoots of the studied hawthorn species are due to the intensity, not the duration of growth. C. sanguinea, C. maximowiczii belong to the group of species with the highest requirements for heat accumulated by the end of the shoot growth period, C. dahurica plants were characterized by the least accumulation of positive temperatures.