Of the 545 square kilometres of the Mecsek microregion, 335 km2 is mountainous. The mountain range can be divided morphologically into three parts, the East-Mecsek, the Middle-Mecsek, and the West-Mecsek, and geologi-cally into two halves, the West-Mecsek, and the East-Mecsek which is rich in minerals - especially limestone, coal, and uranium ore. It is bordered to the south by the Pécs plain, to the northeast by the Völgység, and to the west by the Zselic. The alder forest with a fresh, moist character that has developed in the stream valleys of the Hungarian moun-tains and hills where Alnus glutinosa dominates the canopy. The average width of this forest type is 10–15 m. Few coenological records and tables have been published so far on our Hungarian alder forests. In the late 1970s, the au-thor started a detailed survey of the alder forests in the Mecsek Mountains. The coenological recordings were made using the traditional quadrat method of the Zurich-Montpellier School of Plant Cenology. The alder forests of the Mecsek Mountains (Carici pendulae-Alnetum) in south-western Hungary have not yet been studied in detail. This publication describes this sub-Mediterranean floodplain forest community based on the results of fifty vegetation surveys. The forest stands in the Mecsek Mountains of this association differ from the alder floodplains of the Hun-garian Central Uplands (Aegopodio-Alnetum) by the followings – mostly sub-Mediterranean and Balkan – plant spe-cies: Asperula taurina, Carex strigosa, Helleborus odorus, Lathyrus venetus, Ruscus aculeatus, Scrophularia scopolii, Stachys alpina, Tamus communis, Tilia tomentosa. The geological structure of the East Mecsek is relatively diverse. It is primarily composed of Jurassic limestone and sandstone, with trachidolerite, phonolite and rarely andesite in small-er parts, while the foothills are covered by loess in several places. In the East Mecsek area, alder groves in the lower reaches of valleys or along the foothills narrowly border the streams. In the cool and humid microclimates of the mountain range, the bedrock is formed by the fragments of these rocks. The stands studied are found at altitudes be-tween 170 and 310 m above sea level on wet, gravelly, cast soils. The dominant watercourse of the eastern Mecsek water system is the Völgység stream, which originates in the Komló area of Baranya County, flows eastwards, and enters Tolna county at Máza. It turns north below Bonyhád, then turns east again at Kakasd and finally flows into the Sió. The total catchment area of the Völgység stream is about 600 km2, of which the Tolna county part is about 400 km2 and the catchment area of the Lajvér stream in the Völgység about 90 km2. The average annual rainfall in the East Mecsek is 711 millimetres, mainly in the form of summer showers. Based on previous research, we know that the Alder Forests of South Transdanubia differ from the Aegopodio-Alnetum of Slovakia, the Hungarian Central High-lands and Western Transdanubia, due to the presence of several sub-Mediterranean and Balkan plant species. Mediter-ranean and Balkan plant species.