Synecological differentiation of the scree vegetation of the Polish Tatra Mountains

A vegetation survey was carried out on the screes of the Polish Tatra Mountains, between 1992 and 1995. In order to study differentiation of communities, 157 releves have been made. With 75 releves from literature this number resulted in the total of 232 samples taken into consideration. All the releves were subjected to cluster analysis, in which the average linkage procedure was applied and both presence/absence (Jaccard formula) data and cover-abundance values (Ruzicka formula) were used. Community types were distinguished on the basis of two dendrograms obtained. Fifteen main types of communities were distinguished, belonging to 4 phytosociological classes: Thlaspietea rotundifolii - true scree and snow bed communities (5 communities), Seslerietea albicantis - alpine grasslands on limestone (2), Caricetea cur-vulae- alpine grasslands on siliceous rocks (3) and Betulo-Adenostyletea - tall-grass and tall-herb communities (3). The results partly confirmed previous syntaxonomical divisions of alpine vegetation in the Tatras (performed with the use of traditional method), although, some alterations are proposed here. Several new syntaxa were distinguished, such as: Oxyrio-Saxifragetum aconitetosum firmi (on moist and fertile scree, advanced succession stage towards tall-herb communities) and five subassociations of Luzuletum alpino-pilosae - the most common community on screes in the Tatras differing mostly in soil fertility and soil moisture requirements. A new association, Poo-Arabidetum alpinae (on moist montane limestone screes), was found, already known from other parts of the Carpathians and from the Alps. Substrate, altitude and soil moisture are the main habitat factors which account for the differentiation of scree communities in the Tatras. Scree flora and vegetation in the Tatras turned out to be poorer than it is in the Alps. However, the scree vegetation of the Tatras has got some unique features owing to the presence of endemic species which are usually the character taxa of scree associations, e.g. Saxifraga wahlenbergii (Saxifragetum wahlenbergii), Delphinium oxysepalum (Cerastio-Papaveretum), Saxifraga carpatica and Cardaminopsis neglecta (Oxyrio-Saxifragetum carpaticae).