Weather Conditionality of Siberian Stone Pine (Pinus sibirica Du Tour) Seeding

Abstract

The dynamics of Siberian stone pine sexual reproduction in the South-Eastern part of the West Siberian Plain was studied by 13-year stationary observations. The stand age was 160–180 years, the average tree height was 22 m, and the average diameter of the trunk at breast height was 53 cm. On average, 50–60 trees were analyzed annually (in different years from 25 to 100). Cones were counted and samples were collected annually from August 10 to August 20. The resercher (usually the author of this paper) climbed each tree, knocked down the cones with operating tools (a bat and a rod), and then their number was counted on the ground. A sample of 10–15 cones was taken from each tree. Afterwards, a complete morphological analysis was performed: the number of sterile and fertile scales, and underdeveloped and developed seeds were counted. Developed seeds were analyzed by the X-ray method. To determine the weight, only perfectly full seeds selected by the X-ray pattern were used. Information on weather conditions was used according to data from the Tomsk station of Roshydromet. The main factor in the cone initiation was the amount of precipitation during 2 years before the start of this process: with an increase in the amount of precipitation, the number of cones increases. However, the final seed productivity depends to a greater extent not on the number of initiated cones, but on the success of their further development. The most important stage in the cone development was spring in the year of pollination and the main negative factor was late frosts. The degree of their negative impact is determined by the sum of the effective (above 5 °C) mean daily temperatures at which the return of frost with temperature from –3 to –4 °C occurred. Complete abortion of cones occurred only when the sum of effective temperatures was 150–180 °C. The same frost at the accumulated temperature sum of 100–150 °C killed a significant part of the cones, and the rest strongly disrupted the development. When the sum of accumulated temperature was about 50 °C, a strong frost significantly increased the loss of seedbuds at all stages of their development, thereby reducing the number of full seeds. The average temperature of September in the pollination year was an important factor in seed production. The loss of seedbuds increased significantly with its increase. The only important trait that is formed in the year of cone maturity is the weight of full seeds: it increases with the amount of precipitation from April to June of the current year.