Annals of Forest Research (Sep 2008)
Ecological and morphological studies in the hybrid zone between Pinus sibirica and Pinus pumila
Abstract
In the Baikal Region, there is no phenological isolation between Siberian stone pine (P. sibirica Du Tour) and Siberian dwarf stone pine (P. pumila (Pall.)Regel) since the timing of their 'flowering' coincides. Morphologically intermediate individuals, supposedly natural hybrids,occur not very often. In the west half ofStanovoye upland area four regions were investigated: Barguzinskiy, Baikalskiy, Verchneangarskiy and the Severo-Myiskiy mountain ridges. Interspecific natural hybridization was found to take place in several overlapping regions of the species' ranges; however there are some differences in frequency of natural hybrid occurrencebetween regions as well as within each region. Great numbers of natural hybrids arefound only in a specific habitat which occurs rarely and occupies a relatively small area. At the north-east coast of Lake Baikal the lakeside zone is occupied by Siberianstone pine forests with moderate participation of Siberian dwarf stone pine in theundergrowth. The natural hybrid are widespread everywhere. The ratio of fructiferousSiberian stone pine, Siberian dwarf stone pine and natural hybrid was found tobe approximately 300:10:1. About 90% of the examined natural hybrids took anintermediate position between the two parental species by most features (structure ofneedles, shoots, and crown), i.e. representing putatively the first generation hybrids.Therefore, in contrast to the parental species they are subjected to the destructiveeffect of snowbreak (broken off or dislocated from part of the root system). Like theSiberian dwarf stone pine the natural hybrid has specific root sources forming fromlatent buds. Therefore, the hybrids are not subjected to ageing, as well as have nointernal limitation of age and size. Siberian dwarf stone pine, Siberian stone pine andtheir natural hybrid grow together in the Upper Angara delta in the bog regions. Inthe most productive sites the ratio of fructiferous Siberian dwarf stone pine, Siberianstone pine and natural hybrid amounts approximately to 60:3:1. The ratio of fructiferousSiberian dwarf stone pine and natural hybrid reaches about 20:1 in the lessproductive sites where Siberian stone pine is sterile. Analysis of cone structureshowed that the natural hybrid have substantially increased in comparison with thespecies' mortality and aplasia of reproductive structures at all stages of the generativecycle, from differentiation of the seed-bearing scales to differentiation of the embryo.The portion of the ovules, which develop into the valuable seed with differentiatedembryo, amounted in Siberian dwarf stone pine to 69%, in Siberian stone pine to44%, and in natural hybrid to 25%. Thus, the fertility of natural hybrid in the UpperAngara Delta substantially decreased in comparison with the pure species; however,it was demonstrated that natural hybridization between Siberian dwarf stone pine andSiberian stone pine species occurred.
