Dynamics of Siberian stone pine (Pinus sibirica Du Tour) growth and seed production: cyclicity or acyclic oscillation?

The paper is based on the analysis of 18-year-old series of seed production dynamics in Siberian stone pine which was first obtained by direct counting the number of cones, as well as the number and mass of full seeds. The aim of the study was the comparative analysis of the dynamics of growth and seed production in Siberian stone pine, as well as revealing the nature of the differences between them. We collected the material in the southeastern part of the West Siberian Plain, in the south of the southern taiga, in the Tom-Ob interfluve, 20 km south-west of Tomsk, and in Nizhne-Sechenovsky near-settlement cembretum. We recorded the crop and collected cones annually between 1990 and 2007. We used from 25 to 100 trees in different years. We determined the crop by climbing into the crown, shaking the cones and counting them on the ground. The sample volume was 10-15 cones. The number of full seeds was determined by radiography. The width of the annual rings was measured in 15 trees. We used two cores from each tree from the opposite sides of the trunk. In the series of variability of the annual ring width, only cyclic fluctuations are presented, the age trend is absent. The average width of the annual ring of xylem over the past 18 years was 1.97 ± 0.92 мм (С = 16.3%). The minimum quantity of the characteristic is approximately 50% of the maximum. A 4-6 year cycles are clearly visible (See Fig.). Therefore, there is a significant autocorrelation of growth: according to the data for the last 40 years, the increase in the current year is positively related to the increase in the previous year (r = 0.41, p = 0.05). The average number of cones per tree during the observation period was 369 ± 71 pieces with the fluctuations from 10 to 740 pieces (С = 69%). The distribution of the feature is clearly depressive: a single year with a cone crop in the range of 193 to 391 pieces was not noted during 18 years. In the series of seed production dynamics, no regularity was found. Thus, two low crops were twice recorded in a row and once between two low crops there was an interval of three years. Two middle crops were twice recorded in a row but once between two middle crops there was an interval of six years. Finally, the interval between high crops ranged from 1 to 3 years. Autocorrelations within a seeding series are not significant. The weak tendency to negative correlation decreases with the increasing interval between years: r = - 0.39 between current and subsequent, r = - 0.24 between current and subsequent + 1, r = 0.07 between current and subsequent + 2. The analysis of information from the scientific literature has shown that in the dynamics of conifer seed production the dominance of rather long (up to 10-14 years) cycles is possible, presumably associated with climatic cycles of the same duration (mainly in Pinus). Very short cycles presumably of endogenous origin (for example, in Abies) are possible, too. There are reasons to believe that a fundamentally different variant is also possible: non-cyclic (random) dynamics of seeding. Described in the present work for the Siberian stone pine, and also in some other publications related to the genus Pinus, it implies a complete absence of autocorrelations within series and exactly the same, accidental, character of the long-term dynamics of external factors affecting the seed production. The article contains 1 Figure, 65 References.

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