Changes of the mountain grassland vegetation after abandonment and colonization by norway spruce

Changes of herb and moss vegetation during the colonization of abandoned meadows by Norway spruce on the Polana Mts were studied within a 20 x 170 m belt transect. It includes transition from the opened grassland with scarcely scattered young spruces and junipers to a 40 to 50-years-old spruce stand adjoined to a planted spruce forest edge. Vegetation changes started after the cessation of mowing, establishing of irregular grazing and subsequent spruce colonisation. We identified and differentiated 9 types of vegetation in the transect [characterised by specific species combination and species dominance; Trifolium medium-Brachypodium pinnatum type of vegetation (A), Antennaria dioica-Nardus stricta (B), Phyteuma spicatum-Agrostis capillaris (C), Knautia arvensis-Avenula sp. (D), Prunella vulgaris-Ajuga reptans (E), Platanthera bifolia-Avenella flexuosa (F), Vaccinium myrtillus (G), Hylocomium splendens (H) and Jungermannia leiantha-Plagiomnium affine agg. (I)] using the Twinspan and DCA methods. The first two DCA axes can be interpreted as alight and temporal gradient (axis 1) and a trophic gradient (axis 2). We differentiated two parallel successive paths (variants of the same succession series) - a mesotrophic (Agrostis capillaris comm. C E I) and an oligotrophic (Anthoxantho-Agrostietum tenuis nardetosum BFGHI) variant. Common are the initial type of vegetation of mowed meadows and the final phase of a pure spruce stand with poor moss vegetation (type I), but a course within both variants is different. In addition to this basic divergence several modifications mostly determined by strong competitive grass species were observed within both variants. There is only limited species turnover during this short period of successional development. Cover and number of herb species decline gradually. Moss layer reaches the highest cover within the E, F and G types, where the herb layer cover is reduced and the shrub and tree layer is not closed yet. In these types of field layer vegetation, there is the highest diversity of seedlings and juvenile woody species.