Structure of crown and viability of generative organs of Siberian fir were studied in disturbed forest ecosystems near Baikal Lake. The crown structure changes in damaged trees: a zone of subapical drying appears and apical dominance is lost. Needle chlorosis and necrosis appear and proceed in sprouts of male sexualization. The tree top including the female generative organs does not show degradation symptoms during about 30 years and produces seed cones. Processes of degradation in male generative zone greatly influence on fir tree pollen. Pollen viability of fir trees varied from year to year in different trees but always pollen quality of trees growing in the Khamar-Daban Mts in the air pollution zone was more poor in comparison with the pollen of trees at the Baikal Lake shore. Tree pollen growing in the Khamar-Daban Mts germinates in vitro but pollen tubes arc formed short and not viable. Seed quality of fir trees is very low. A lot of seeds are sterile. Empty seeds prevail. The formation of empty seeds was caused by the low pollen germination in ovules and as a whole absence of pollen in ovules. The high sterility of generative organs and especially of Abies sibirica pollen can limit gametic selection and decrease fir diversity in forest ecosystems near Baikal Lake.