Evaluation of cone and seed quality of Siberian stone pine (Pinus sibirica Du Tour) for plus-tree selection

Siberian stone pine (Pinus sibirica Du Tour) is a cone-bearing species with outstanding nutritious seeds, health-supporting properties, and nut oil. Currently, the main volume of pine nuts is harvested in natural forests, which causes damage to ecosystems. The best solution to this problem would be harvesting nuts on special pine nut plantations established on the basis of high-seeding clones. However, it is hampered by the low efficiency of the existing methods for assessing plus-tree productivity. This work focused on cone analysis in two sites used for plus-tree selection: a 42-year-old sparse forest plantation and a 186-224-year-old closed natural forest. The quality of cones and seeds was assessed for 20 traits characterizing the sequence of crop maturation, from the differentiation of the cone to seed ripening. The differences between the sites for most quality traits, except the number of developed and filled seeds, were insignificant. This means that both sites were equally promising for seed quality selection. An index of kernel weight per 1 m(2) of crown area was proposed to be used for the initial selection of plus-trees that combine a narrow crown with a large mass of kernels. Such trees can produce a greater yield from a smaller plantation area. In closed stands, the cone number per tree was strongly correlated with crown size; thus, this index can only be used for sparse forests or plantations.