Start of reproduction and allozyme heterozygosity in Pinus sibirica under different techniques of artificial forest stand establishment

Siberian stone pine (Pinus sibirica Du Tour) is one of the main forest-forming tree species in boreal forests of Eurasia. Large edibleseeds of this species have an important resource value because of their high nutritious properties. Development of approaches toestablishment of early cone producing Siberian stone pine stands including utilization of corresponding genetic background is one of the priorities of forest resource management. The goal of our study was to evaluate the effect of stand density on the differentiation of trees bythe age of first reproduction and the relationship of allozyme heterozygosity and morphological traits variability in Siberian stone pine.Morphological and allozyme variability in artificial Pinus sibirica stands with high and low density was investigated. In the high-densitystand the distance between trees was 0.7 and 3 meters (4080 trees per ha) while in the lowdensity stand it was 8 and 8 meters (144 treesper ha). Age of formation of first male and female cones was evaluated by retrospective method based on analysis of tracks of cones ona shoot bark. Tree height, diameter and number of male, female and vegetative shoots in a crown of model trees were measured.Genotypes of the trees were determined by 29 isozyme loci coding for 16 enzymes (ADH, FDH, FEST, GDH, GOT, IDH, LAP, MDH, MNR, PEPCA, 6-PGD, PGI, PGM, SDH, SKDH, SOD). In the low-density stand, the portion of generative trees was higher and differentiation of trees by age of reproduction starting was lower in spite of the smaller age of trees as compared to the high-density stand. Inboth samples, the age of formation of first generative organs was related negatively with stem height, stem diameter and number offemale shoots. In the high-density stand, positive relation of age of first reproduction with total number of shoots and number ofmale shoots was found. In both samples nonreproductive trees were less heterozygous at isozyme loci as compared to trees starting coneproduction. Allozyme heterozygosity correlated positively with the age of first cone production in the high-density stand only. Weconclude that the degree of competition between trees due to different stand density determined age and timing of first reproductionand development of tree crowns. The relationship of allozyme heterozygosity and the age of first reproduction was expressed more in the high-density stand of Siberian stone pine.