Activity indices of plant species in altitudinal zonal elements of the flora were analyzed. As a result, displacement of forest-steppe species by true steppe species in Cleistogenetea squarrosae communities was revealed. Comparison of these tendencies with those in forest vegetation in Baikal Region suggests that ridge slopes are characterized by increasing of humidity. On the contrary, aridization process is observed in basins. Both alternatively oriented trends are inspired by general climate warming. Due to temperature increase, the permafrost existing on the forested slopes is gradually melting and provides additional soil moisturing. At the same time, the steppe ecosystems suffer a loss of the soil water supply as well as air moisture affected by climate warming.Key words: flora, steppes, Cleistogenetea squarrosae, climate warming, aridization, Baikal region.