State and development of phytocenoses on research plots in the Krkonoše Mts. forest stands.

The paper assesses the state and development of phytocenoses in beech, mixed and spruce stands on permanent research plots (PRP) 1-32 in the Krkonose (Giant) Mts. in the years 1980-2005, i.e. during the air-pollution calamity and afterwards. Dynamics (the extent of change) of the vegetation structure has been expressed as the over- all change of species composition in comparison with the year 1980. The change was quantified using the Euclidean distance or as the change of the several first ordination axes (DCA 1-DCA 4). Species composition was significantly changing on all 32 PRP stands in the period 1980-2005; some species completely disappeared (e.g. Cicerbita alpina, Lamium maculatum, Phyteuma spicatum, Viola biflora) or their ratio was reduced (e.g. Blechnum spicant, Dentaria enneaphyllos, Homogyne alpina). From the viewpoint of diversity, the most significant change is the reduction of spe- cies in the moss layer, which was observed in all types of stands; in beech and mixed forests the average number of species dropped from 4.8 to 2.7 (44%), in non-declining spruce stands the number fell from 11.6 to 5.5 (53%), and in declining spruce stands it dropped from 10.4 to 3.3 (68%). The overall reduction of species diversity ranged between 31% and 43%; the highest reduction was recorded at species with lower representation. The most significant factors influencing the species composition were altitude and exposition of plot.