* Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Pandion, Alnion incanae, Salicion albae)
Riparian alluvial forests of alder and ash, and flush woods in valleys or at the foot of a slope. Featuring black alder in planar and colline situations and also grey alder at higher altitudes. Also includes softwood (Salicion albae) riparian alluvial forests which are regularly inundated, often for relatively long periods.
A special case included in this habitat type comprises alder forests on percolating mires within an area subject to river inundation.
Notes on habitat mapping
A precondition for assignment to this habitat type is a largely intact water regime (floodplains with surface inundation and upwelling subsurface water). This excludes occurrences of the stated vegetation types enclosed between or separated off by dykes that protect them from natural inundation. These may, however, count as development potential in the absence of near-natural stands. Loosely fragmented stands in which tree spacing exceeds tree height (e.g. due to overgrazing) should be classed as rows of trees and not included.
The various subtypes should be distinguished when mapping.
Willow vegetation belonging to intact floodplains is included in the habitat type as a fringe or pioneer stage of softwood alluvial forest. As softwood floodplain habitats often only survive as small residual communities without any forest proper, it may be necessary to include willow vegetation as fragments of former alluvial forest or as development potential when nominating habitats for designation.
Comments on vegetation:
The swamp forest classifications (e.g. Carici elongatae-Alnetum glutinosae and Carici laevigatae-Alnetum glutinosae) have subassociations (e.g. Cardaminetosum amarae) that are distinguished by moving groundwater and very closely resemble alluvial forest types (e.g. Carici remotae-Fraxinetum). These can be included under habitat type 91E0. If swamp forests are made a separate habitat type in a future amendment of Annex I, however, it would be more appropriate to assign the subassociations concerned to swamp forests. Depending on the physiographic conditions, swamp and alluvial forests may be closely linked and there may be transitions between the two. Willow vegetation such as Salicetum triandrae occurs at the fringes of softwood alluvial forest, but may also be a degradation (residual) stage of such forest, in some cases with scattered individual trees.