Diversity of the hybrid forms between Siberian stone pine and Siberian dwarf pine

Abstract

Siberian stone pine (Pinus sibirica) and Siberian dwarf pine (P. pumila) are Russian five-needle pines withdifferent life forms, namely upright tree and prostrate tree, respectively. Hybridization of the species was considered in thepaper from the point of view of the habitus of their natural hybrids. In early studies, it was always noted that the hybridswere intermediate in comparison with the parental species. Crown structure in hybrids are largely determined by twomain factors. These are deflection of the tree stem from the vertical axis and the selectivity of apical dominance. Hybridsgrowing in open places under full lighting conditions are characterized by strictly intermediate growth form. In a forestwhere there is no enough light, hybrid reaches for sun but gradually deviates to the side, which ultimately leads to a branchbreak or even the roots of the entire tree being upturned from the soil. In the mountains, hybrids can form uniform trunkbranches, forming a cup-shaped crown, similar to how it happens in Siberian dwarf pine. Thus, the previously notedintermediate morphology of hybrids represents a series of forms, from almost vertical multi-stemmed trees to pumila-likeones with a cup-shaped crown.