Abstract
Snow-bed and marble-scree plant communities (Salicetea herblaceae and Thlaspietea rotundifolii) studied in a glacial circle of the Great Kazan, Pirin Planina Mts., Bulgaria, were ordinated in order to reveal the dominating ecological factors responsible for differentiation of vegetation types. The Salicetea relevés were separated from the Thlaspietea relevés along a diagonal interpreted in terms of duration of snow cover. Separation along the other diagonal indicated the importance of controlling effects of exposure (aspect) within the Thlaspietea rotundifolii, and habitat moisture within the Salicetea herbaceae.