The alliances of
Alnion glutinosae
(alder carr) and
Alnion incanae
(floodplain forests)comprise azonal communities growing in places with a high groundwater table. The com-munities of both these alliances are widely distributed in Europe (Bodeux 1955,Oberdorfer 1953, Mucina et al. 1993, Dierßen 1996, Neuhäuslová 2000, 2003).Alder carr forests of
Alnion glutinosae
occur in localities with a high stagnant ground-water table: in most cases around fishponds, oxbows and large spring fed areas.

https://www.academia.edu/1047099/Formalized_classification_o...

A carr is a type of waterlogged, wooded terrain that, typically, represents a succession stage between the original reedy swamp and the eventual formation of forest in a sub-maritime climate.[1] The name derives from the Old Norse kjarr, meaning a swamp. The carr is one stage in a so-called hydrosere: the progression of vegetation beginning from a terrain that is submerged by fresh water along a river or lake margin. In sub-maritime regions, it begins with reed-swamp. As the reeds decay, the soil surface eventually rises above the water, creating fens that allow vegetation like sedge to grow. As this progression continues, riparian trees and bushes appear and a carr landscape is created–in effect a wooded fen in a waterlogged terrain. At this stage the pH is not too acidic and the soil is not too deficient in mineral elements. Characteristic trees include alder, willow and sallow.

http://en.wikipedia.org/wiki/Carr_(landform)#

Alder is the common name of a genus of flowering plants (Alnus) belonging to the birch family Betulaceae.

http://en.wikipedia.org/wiki/Alder#

Olsza, olcha (Alnus Mill.) – rodzaj drzew i krzewów z rodziny brzozowatych obejmujący ok. 25[2]-37[3] gatunków, spośród których typowym jest Alnus glutinosa (L.)

http://pl.wikipedia.org/wiki/Olsza#