Phenological development, viability, and visual tree assessment of Pinus sibirica du tour beyond the Arctic circle

The study was performed on the Kola Peninsula and aimed to assess the impact of climatic factors on Pinus sibirica’s phenological development beyond the Arctic Circle in particular. Eight phenological parameters were analyzed, including vegetative bud swelling and breaking, initiation and cessation of annual linear shoot growth, full lignification of shoots, cessation of needle elongation and maturation, duration of linear lateral shoot growth, and needle growth period. Additionally, correlations between the onset of phenophases and temperature parameters, including average monthly and ten-day temperatures, the dates of the stable transition through the thresholds of 0, 5, and 10°C, sums of active temperatures above 0, 5, and 10°C for phenological phases and periods, monthly and ten-day sums of active temperatures, and monthly and ten-day cumulative sums of active temperatures starting from April, were investigated. Viability assessment involved evaluating the degree of annual shoot lignification, winter hardiness, habitus preservation, shoot-forming capacity, vertical shoot growth, generative reproduction, and reproduction in cultivation. Tree health categories were established based on examinations of root, butt, trunk, crown base, primary branches, and crown for indications of hollows, cracks, decay and fungal fruiting bodies, damage, wounds, weak forks, and dead branches. The onset dates of the phenophases occurring in the beginning of the vegetation period and full shoot lignification correlated with the dates of transition through the thresholds of 0 and 5°C. In contrast, the onset dates of the phenophases occurring in the middle of the vegetation period and duration of phenological periods correlated with accumulated temperatures above 0 and 5°C. The date of transition through 10°C and its associated parameters yielded uninformative results. The onset dates of all phenophases exhibit negative correlations with the following parameters: (1) average temperatures in April and May, (2) the sums of active temperatures (SATs) exceeding 0 and 5°C in May, (3) cumulative SATs above the thresholds of 0 and 5°C from April to May and June, and (4) cumulative ten-day SATs above the thresholds of 0 and 5°C before the onset of a phenophase. Pinus sibirica at Polar-Alpine Botanical Garden-Institute (PABGI) exhibited winter hardiness, maintained species-typical life form, and reached the generative stage of development. They were categorized as healthy or weakened. Visual inspection revealed no restrictions to root system growth. They displayed monocormic, unimucronate or bimucronate forms, with dense crowns and well-developed apical and lateral shoots. Some instances of reduced lateral shoot growth and V-shaped trunk forks were observed. Recommendations for regular monitoring, sanitary pruning and other agrotechnical measures have been formulated for the investigated tree individuals.