Plant communities generated by fluvial dynamics are highly diversified and continually renewed by the action of erosion and flooding. This has meant that the Allier is accompanied by a wide range of natural habitats, their shapes and distribution a reminder of past courses of the river. Such are their special features and ecological abundance, that these environments are often of great interest in heritage terms.
DYNAMICS OF ENVIRONMENTS
The geomorphology of zones bordering the Allier is regularly remodelled by the dynamics of the river, creating virgin environments in which an ecological dynamic will develop in close association with the river and its water table.
Displacement of the river bed brings in its wake a whole series of natural ecosystems: at a single spot, as a function of distance from the river and the rise in soil level (by successive additions of silt), there may arise, in succession, a water-filled channel, a bare beach, stonecrop ground cover, a couch-grass meadow, undergrowth, and finally, alluvial forest. And the cycle begins again when the river at last returns after several decades – or centuries.
A PATCHWORK OF ENVIRONMENTS
Spatially, as opposed to temporally, a great variety of young and less young natural ecosystems extend either side of the river, in complex interspersion. For example, the lobe of a former meander, between the abandoned channel that has now become a backwater and the new active channel, the whole series of ecosystems mentioned above can be seen.
The mosaic forms a corridor of habitats which shifts with the river, known as the fluvial corridor.
EXCEPTIONALLY RICH ECOLOGY
With such soil and hydrology conditions, regeneration and regular flooding, the alluvial vegetation is very varied and displays many special features that greatly enrich its ecology. No less than forty-three natural plant communities are thus to be found in the Allier’s alluvial plain. Of the listed natural sites and habitats of Community Interest covered by the Natura 2000 network, 12 habitats are on the Upper Allier and 14 on the Allier plains (including alluvial forest, dry grassland, the vegetation of the river's associated ecosystems and emerged silt) out of a total of twenty. They account for 23,500 ha along the Allier in Auvergne designated in the Natura 2000 network.