Diversity of Alnus glutinosa dominated swamp forests in Estonia

The Alnus glutinosa swamps are the most species-rich forest communities in the Fennoscandian hemiboreal zone. Considering the species abundance in different layers and their indicator values, in Estonia these stands can be classified into ten community types: 1) Calliergonella cuspidate–Carex acutiformis–Thelypteris palustris–Alnus glutinosa; 2) Brachythecium rutabulum–Scutellaria galericulata–Rubus caesius–Alnus glutinosa; 3) Brachythecium rutabulum–Urtica dioica–Aegopodium podagraria–Alnus glutinosa; 4) Plagiomnium elatum–Galeobdolon luteum–Oxalis acetosella–Alnus glutinosa; 5) Sphagnum fallax–Filipendula ulmaria–Phragmites australis–Alnus glutinosa; 6) Sphagnum riparium–Vaccinium myrtillus–Impatiens noli-tangere–Alnus glutinosa; 7) Calliergon cordifolium–Lysimachia thyrsiflora–Carex elongate–Alnus glutinosa; 8) Calliergonella cuspidate–Deschampsia cespitosa–Filipendula ulmaria–Alnus glutinosa; 9) Climacium dendroides–Calamagrostis canescens–Athyrium filix-femina–Alnus glutinosa; 10) Calypogeia integristipula–Filipendula ulmaria–Ulmus laevis–Alnus glutinosa. The species composition of the communities is determined mainly by the soil reaction and nitrogen content in the soil of their habitats. Key words: community types, indicator species, Ellenberg’s indicator values, habitats’ reaction gradient, nitrogen content gradient.