The species composition of the floras of four insular forests was identified and alien fractions were analyzed. In the Krasnosamarsky pine forest the share of alien species is 12 %, in the Buzuluksky pine forest it is 14 %, in the Khrenovsky pine forest it is 15 %, in the Usmansky pine forest it is 20 %. The proportion of monospecific families with alien taxa in the floras of pine forests located in the steppe zone (Buzuluksky and Krasnosamarsky) is two times lower than in the floras of pine forests in the forest-steppe zone (Usmansky and Khrenovsky). The proportion of monospecific genera represented by alien species varies from 17.6 % to 23.5 % relative to their total number in the floras and from 45.1 % to 51.4 % relative to genera of the alien fraction. The high percentage of monospecific genera in the alien fraction and calculations based on the indicator of autonomy of the flora development are indicative of allochthonous developmental pathway of the floras of Khrenovsky and Krasnosamarsky forests.

N.O. Kin