This study includes all black alder sites (or stands) in Finland in the natural state from wet black alder swamps to fresh black alder -dominated forests. The material is based on 650 sample plots with complete descriptions of vegetation and ecology studied in altogether 200 black alder sites all over the distribution area (59°47′–66°45′N).
The a priori classification of the studied sites is based on field observations during several decades and on DCA-ordination and clustering analysis (Euclidian distance with centroid group averages and the Ward linkage method) using the Finnish “Cajanderian” forest and mire site type classification approach.
Based on this material, 14 black alder community types and several variations are described. Half of them are black alder swamps and the rest herb-rich and alluvial forests. Most of them are situated on lake and seashores where new sites are exposed continuously as a result of land elevation.
The results of the classification are compared with the phytosociology of several Northern and Central European black alder communities. Ecological factors affecting the formation and development of black alder communities in Finland are also discussed. Many of these environmental factors deviate noticeably from conditions in Central Europe and are reflecting the special features of Finnish black alder swamps and forests.