Birch species introduced in Karelia – Betula ermanii Cham. and Betula japonica Sieb., as well as native species – Betula pendula Roth and Betula pubescens Ehrh. were compared in terms of microgametophyte fertility and vitality, pollen grain and pollen tube size. It is demonstrated that each of the species has developed its own strategy in male gametophyte formation and behaviour under certain ambient conditions. Compared to introduced species, native ones showed higher stability in formation and manifestation of pollen morphophysiological parameters, except for vitality. In introduced species, male gametophyte was more sensitive to changes in the weather and climatic conditions under which pollen formed (B. japonica) and had lower pollen fertility compensated by high vitality (B. ermanii).