Тhe Phyllitido-Aceretum association described in the Ukrainian part of Roztocze is a rare variant of mountain sycamore forests, unique for the region. This type of forest phytocenosis is also rare in Europe and is protected in the system of the Natura 2000. The Phyllitido-Aceretum phytocenosis is characterized by a peculiar structure, a wealth of species, pronounced fluctuation, which indicates its natural origin. On the territory of Ukraine Phyllitido-Aceretum is found only in the Carpathians, while its location in the Ukrainian part of Roztocze is the only one in the region and the easternmost locality of the range. Long-term phytosociological studies proved that human activity provokes its transformation into phytocenoses of the Dentario glandulosae-Fagetum W. Mat. 1964 et Guzikowa et Kornaś 1969. Exploitation of the forest and felling of trees lead to an increase in the intensity of illumination of the forest floor, degradation of Phyllitido-Aceretum phytocenoses and development of phytocenoses Dentario glandulosae-Fagetum association.