L. Lőkös szerk.: Studia Botanica Hungarica 25. 1994 (Budapest, 1994)

Szerdahelyi, Tibor: Gallery forest fragments in the Szigetköz Protected Area (Hungary)

associations have retarded, its species composition has been changing. The drastic decrease of the forest areas and the appearence of monocultures cause the invasion of several adventive and neophyte species. We wanted to describe the rate of similarity of the sites by using cluster analisis based on the species composition of the stands broken into pieces. Within the protected area sample sites were selected in nearly native forest stands. This Fraxino pannonicae-Ulmetum area takes up a place on a little bit higher region beside the lateral river branches. In the title the "fragments" not only means spatialism, but the character of this association {Fraxinopannonicae-Ulmetum) as well. In the results the examined spots correspond to several subassociations of Fraxino pannonicae-Ulmetum, but really they are in [some case extremely] modified conditions of the Fraxino pannonicae-Ulmetum, now. The species list and the cover values are in Table 1. The Braun-Blanquet values were transformed according to the van der Maarel method (MAAREL 1979) for numerical analysis. Values of the sample plots were analysed with the Syn-Tax III program package (PODANI 1988). The NCLAS2A program was used for cluster analysis and PRINCOOR to perform a principal coordinate analysis. The species names and their parameters (coenological characters, TWR-values, floral elements etc.) correspond with those of the HUNGPLANT database (DOBOLYI etal. 1994). RESULTS Running for the cluster analysis we used the Czekanowski's index. The result can be seen in Fig. 1. We have got 7 (from A to G) markant sample groups at the 0.66 similarity level. These sample groups were compared with each other according to their coenological characters, floral elements and ecological parameters (TWR). The division of the floral elements of the sample groups shown in Fig. 3. The European and the Eurasian elements dominate, while the Mediterranean and Submediterranean elements are characteristic, too. The Circumpolar, Pontic and Balkan-Pannonian elements are of less value, but these groups are still characteristic of the Fraxino pannonicae-Ulmetum. The F and G sample groups quite differ from the others. The F group contains the "Ásványráró" sample plots, while the G is formed by the "Lóvári erdő" sample plots. The distribution of the coenological characters of sample groups are shown in Fig. 4. The Fagetalia and the Querco-Fagetea elements dominate almost in all groups. The quantities of these elements in F and G sample groups (Ásványráró and Lóvári erdő) differ from the others. Here the quantities of Alno-Padion and Prunion spinosae species are higher than in the other sample groups. Concerning the "Derék-erdő" ZÓLYOMI pointed out that this forest is a typical example of "plain Carpinetum association" (ZÓLYOMI 1937). Really it may be a variant of the Carpinetum associ-