Seed yield structure in taiga and sub-settlement Siberian stone pine forests: level, and nature of differences

. On the example of Siberian stone pine, seed productivity was analysed in two stands that differed in origin and formation conditions. The cone yield was analysed in years with different levels of seed production in the period from 2016 to 2019. In terms of the number of cones per tree, the sub-settlement Siberian stone pine forest was 2-3 times superior to the taiga Siberian stone pine forest. The level of individual variability in the number of cones in the near-settlement Siberian stone pine forest was significantly lower than in the taiga forest. There is reason to believe that the high level of variability is likely related to a more pronounced differentiation of the stand by crown size. The number of dead ovules in the Siberian stone pine forest in settlement is 60-70% higher than in the taiga forest. Due to high "mortality" of ovules and high variability of this trait, the number of filled seeds in the near-settlement Siberian stone pine forest is much lower, and variability in the number of complete seeds is much higher than in taiga Siberian stone pine forest. When there are few filled seeds in a cone, the size of each of them increases. Therefore, the average weight of one filled seed is higher in the subsettlement Siberian stone pine forest than in the taiga forest. Thus, the quality of the cones in the years of average and especially high yield in the near-settlement Siberian stone pine forest is much lower, and the level of variability of the traits that characterise it is much higher, and the distribution of the traits is characterised by a pronounced negative kurtosis. Obviously, these peculiarities of the near-settlement Siberian stone pine forest are related to human interference in the course of its development, which disturbed the course of natural selection and deformed the genotypic composition of the population.


Introduction
Siberian stone pine (Pinus sibirica Du Tour) is a cone-bearing species with outstanding nutritious seeds, health-supporting properties, and nut oil.In the south of the West Siberian Plain, this species is not an edifier of vegetation cover, as the southern border of its range is located here, and Siberian stone pine cannot compete with forest trees better adapted to the lack of soil moisture, such as common pine and Siberian larch.At the same time, the high level of economic development of the territory has led to a wide spread of stone pine forests near settlements.These forests are located near old villages on fertile lands.Thanks to human intervention, Siberian stone pine here occupies a dominant position among other forest trees.The traditional Siberian attitude to Siberian stone pine as a "feeding" tree excluded it from felling, and its seedlings were given the opportunity to grow young under conditions of good light and excessive soil richness, which are unusual for Siberian stone pine.As a result, cultivated and sparse stand were formed -near-settlement Siberian stone pine forests, in all respects completely different from natural taiga forests [1].
The main purpose of village pine forests is to produce high quality nuts.The creation of such pine forests is traditionally considered a positive example of human impact on nature.Even recommendations have been developed to expand their areas.However, analyses of the current state of the sub-settlement pine forests have shown that they are degrading [2].Human interference in the development of plant communities disrupts the course of natural selection, therefore, changes the structure of diversity, deforms the genotypic composition of populations, thereby reducing their adaptive potential [3].Indeed, seed productivity in nearsettlement siberian stone pine forests is significantly higher than in taiga forests [4], but seed quality, on the contrary, is significantly lower [5], which we assume is related to the low level of natural selection in artificial forests.
The purpose of this work is to carry out a comparative analysis of seed productivity and individual variability of cone production in taiga and sub-settlement Siberian stone pine forests, to establish the level, nature and nature of differences.

Object of study
Both taiga and settlement Siberian stone pine forests are located in the south of the West Siberian Plain, between the Ob and Tom rivers.The taiga Siberian stone pine forest is located near the village of Botalino.Botalino (56º11' n.l., 84º25' e.l., 159 m above sea level).This is a typical southern taiga Siberian stone pine forest with small shrubs and green moss in the ground cover.The share of Siberian stone pine from other forest trees is 70 per cent.Siberian stone pine is 170 years old, average height 23 m, average trunk diameter 34 cm.A subsettlement Siberian stone pine forest is located near Nizhne-Sechenovo village.Nizhne-Sechenovo (56º30' n.l., 84º39' e.l., 119 m above sea level).This is a typical near-settlement Siberian stone pine forest with herbaceous ground cover.The share of Siberian stone pine is 95% age 160-180 years, average height 22 m, average trunk diameter 53 cm.
The cone yield in both pine forests was analysed using the same methodology, during 3 years when the yield was high (2019), medium (2016), and low (2017).The number of cones was counted on 40 trees, and 15 cones were collected from each tree to analyse their quality, which was determined based on literature on seed development in 5-needle stone pines [6].Four traits were used to characterise the quality of the crop: (1) initial ovule number, (2) seed efficiency, (3) filled seed number, and (4) seed weight.Full-grown seeds were studied by Xray analysis [7].The potential seed production, i.e., initial ovule number, was determined as double the scale number from the medial zone of cone [5].Filled seeds were selected by Xray and weighed with an accuracy of 1 mg.Seed efficiency was calculated as the percentage of filled seeds from the initial ovule number.

Statistical analysis
The differences between samples were estimated using the ANOVA F-test.Statistical data processing was carried out using the program Statistica 6.0.

Results and discussion
In terms of the number of cones per tree, the near-settlement Siberian stone pine forest is 2-3 times higher than the taiga Siberian stone pine forest (Fig. 1).The differences between them are somewhat less in the relative yield indicator -the number of cones per 1 dm 2 barrel crosssectional area.The level of individual variability in the number of cones in the near-settlement Siberian stone pine forest is much lower than in the taiga forest.There are reasons to believe that in the latter case the high level of variability is most likely related to a more pronounced differentiation of the stand by crown size.This is a common phenomenon in natural forests and is caused by the diversity of external conditions rather than genotypic diversity [8].This is evidenced, in particular, by the close relationship between tree size (trunk diameter) and the number of cones on it (in years of medium and high yields r = 0.91 and r = 0.96, respectively).In the near-settlement Siberian stone pine forest, oppressed trees are practically absent, so similar correlation coefficients are incomparably lower (r = 0.46 and r = 0.51, respectively), which demonstrates a high degree of genotypic conditioning of the number of cones on the tree.The number of cones per 1 dm 2 the level of individual variability in both stands is approximately the same and not as high as for the number of cones per tree (Fig. 2).At the same average value, the level of variability of initial ovule number in the settlement Siberian stone pine forest is much higher than in the taiga Siberian stone pine forest.Fullgrown seeds are not formed from all ovules.Some of them die at different stages of development (Table 1).Bold font shows statistically significant differences between stands at p≤0.05

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In the sub-settlement Siberian stone pine forest, the number of dead ovules is significantly higher (by 60-70%) than in the taiga Siberian stone pine forest, so the differences in individual variability of this trait are even greater: it is 2-3 times higher in the sub-settlement Siberian stone pine forest.Due to high "mortality" of ovules and high variability of this trait, the number of filled seeds is lower in the near-settlement Siberian stone pine forest, and the variability in the number of filled seeds is much higher than in the taiga forest.When there are few filled seeds in a cone, the size of each of them increases.Therefore, the average mass of one filled seed is higher in the near-settlement Siberian stone pine forest than in the taiga forest; the variability of this trait is also slightly higher, mainly due to the upper limit (presence of trees with abnormally high value of the trait) (Table 2).Bold font shows statistically significant differences between stands at p≤0.05 Thus, the quality of cones in the years of average and especially high yield in the nearsettlement Siberian stone pine forest is much lower, and the level of variability of the traits characterising it is much higher, and the distribution of traits is characterised by a pronounced negative excess (increased proportion of very high and very low values).Obviously, these features of the near-settlement Siberian stone pine forest are associated with human interference in the course of its development, in particular, with thinning, which disturbed the course of natural selection and deformed the genotypic composition of the population.
Sub-settlement Siberian stone pine forests can hardly be regarded as an unambiguously positive example of human impact on nature, and excessive expansion of their areas should hardly be recommended.At the same time, near-settlement pine forests are a valuable source of source material for selection for seed productivity.The most expedient way to create nutbearing plantations of Siberian pine is to establish grafting plantations on a breeding basis using clone varieties developed, including those based on the best genotypes from subsettlement Siberian stone pine forests.

Fig. 1 .
Fig. 1.Number of cones on the tree.Red, green and blue colours show years of low, medium and high seed yield.Differences between groups by years are statistically significant at p≤0.05

2 .
Conferences 462, 02030 (2023) AFE-2023 https://doi.org/10.1051/e3sconf/202346202030Number of cones per 1 dm 2 of the trunk cross-sectional area.Red, green and blue colours show years of low, medium and high seed yield.Differences between groups by years are statistically significant at p≤0.05

Table 1 .
Initial number of ovules and their losses

Table 2 .
Quality characteristics of seed yield in near-settlement and taiga stone pine forests