Black alder forests (type 91E0* Natura 2000 type E.2.1.9. NHC) in the Plitvice Lakes National Park

Abstract

The paper presents the first results of monitoring Natura 2000 habitat type 91E0*in the Plitvice Lakes National Park (Croatia). This type is represented in black alder forests (Alnus glutinosa /L./ Gaertn.) on an area of 44 ha. There, following the Braun-Blanquet method (1964), 25 plots were set up and relevés made, with 175 species of higher plant species recorded. Their environmental and sociological features suggest wetland and periodically flooded habitats with high ground water levels throughout the year, hence hygrophytes are decisive for the community structure. In addition, there is a moderate share of mesophilic species that are not present in the wetland black alder forests along the Sava and Drava rivers in the lowland part of northern Croatia. A comparison of black alder forests of the Plitvice Lakes NP with other black alder syntaxa in Croatia (Figure 2, Table 3) demonstrates that, together with other alder stands in the Dinaric region of Croatia, they belong to the group of wetland forests of the alliance Alnion glutinosae. Their differentiating species with regard to other syntaxa of the alliances Alnion glutinosae and Alnion incanae in Croatia are Fraxinus excelsior, Daphne mezereum, Viburnum lantana, Cirsium oleraceum, Crepis paludosa, Equisetum arvense, Paris quadrifolia, Thalictrum aquilegifolium, Valeriana dioica, Veratrum album, Acer pseudoplatanus, Chaerophyllum hirsutum, Lonicera xylosteum, Filipendula ulmaria, Knautia drymeia, Cruciata glabra. In addition, the researched stands in the Plitvice Lakes NP demonstrate individuality with regard to other stands of the Croatian Dinarides through the differentiating species of Phalaris arundinacea, Dactylorhiza maculata, Cirsium arvense, Primula vulgaris, Listera ovata, Carex acutiformis, C. paniculata, Succisa pratensis, Gentiana asclepiadea. Black alder forests in the Plitvice Lakes NP were created by successive processes in non-forest areas after their fall out of use (Figure 1). They grow by watercourses in karst depressions with occasionally stagnant surface water. Here the river courses are slowed down and distanced from the slopes and surrounding massifs, hence zonal forests do not have a dominant influence on the floral composition. The researched forests are classified in the class Alnetea glutinosae Br.-Bl. et Tx. 1943, order Alnetalia glutinosae Tx. 1937, and alliance Alnion glutinosae Malcuit 1929. They exhibit greatest similarity to the Central European association Carici acutiformis-Alnetum glutinosae. However, these results should not be generalized for the entire Dinaric region of Croatia. Detailed studies of black alder forests in the Dinarides are pending and their results will determine their nomenclature and syntaxonomic character.