Ripisylve

The bordering forest , riverine or ripisylve (étymologiquement of Latin the '' scraped '' the bank and the '' sylva '' the “Forêt”) is the whole of the wooded formations present on banks of a River.

Concept of bank indicating the extent of the major bed of the river not submerged with the low water level.

The ripisylves are generally linear formations spread out along small rivers, over a width from 25 to 30 meters, or less (If the vegetation extends over a width from easily flooded ground more important, one will speak rather about alluvial forest or easily flooded or flooded forest.

Function of maintenance of the banks

Trees isolated and high would quickly be exposed by the current. Banks only covered with herbaceous are dug by the lower part, and collapse by whole pieces. It is the multiplicity of the gasolines, of the types of plants and roots which makes the ripisylves so resistant.

To ensure a maximum protection of the banks against the erosion, the ripisylve must be broad at least 6 meters, on each bank. It must be dense and balanced and dominated by the bushes to preserve 15 to 20% of illumination. “ Équilibrée ” means that it must be made up of trees of all the ages and 3 layers:

arborescent with for example: Alder, Ash, Sycamore,…
shrubby, with for example: Willow, Hawthorn, Hazel tree,…
herbaceous, with for example: Two-handed hammer, Snap ring, Laîche, Poacées.

The association of the systems racinaires of the riverine plants maintains in this case in an optimal way the ground of the banks on all the scales: The graminaceous ones stabilize the ground on a lump of earth scale thanks to their roots, the shrubs fixing of small portions of banks thanks to their roots and rootlets, the trees stabilizing the whole by sections of several meters of banks.

Function Corridor

The ripisylve is a biological corridor, and has important functions of shelter and source of food for a great number of animals (insects, birds, mammals) which colonize it, or depend on it for their food. Certain species take refuge there during important floods.

Function of habitat

For the inhabitants of the river (fish, insects), cavities, roots and rootlets offer many shelters (with respect to the current and of predatory) and sometimes of support of laying. In addition, the shadow on the river seems reassuring for many species which reduce their activity in full light (species Lucifuge S). It also makes it possible to keep rather fresh water in summer (essential for salmonidés) and to limit the filling of spawning grounds by algae.

It is a écotone in particular appreciated kingfishers, otters, or beavers (which modify it and maintain the spots of lights there - where they did not disappear, or where they were reintroduced).

Purifying functions

The system racinaire of the ripisylve, and the fonge and the bacteria which are associated (symbions or not) there also constitute a purifying pump for certain pollutants (Phosphate S and Nitrate S of agricultural or urban origin, radionuclides, etc).

Inertial function

The ripisylve plays also an important role of speed reducer of the wave of rising, contributing also to the normal retention of sediments (decreasing the risk of overdeepening of the rivers which can involve a fall of the tablecloth).
Si it is source of materials (branches, sheets) being likely to make Embâcle downstream, it blocks others of them coming from the upstream, very effectively in the case of the ripisylves which push on “hairy ” of river (systems also known as in braids ).

Potential of restoration

In many areas, important linear of ripisylve could be reconquered or qualitatively improved.
For example, Wallonia had into 2006 of 18.000 kilometers rivers, made up to 80% of small rivers (less than 5 meters broad) of good quality because located in forest for more than one third of this linear. JB Schneider estimates that approximately 40% of the Walloon ripisylve are however too artificial (inadequate species and structure). The settlements of coniferous tree (acidification, dense shade) are in question, but also the shade of the too dense settlements monospecific which harms the low layers which fix also the banks and the biodiversity. Where there are no more beavers and large herbivores, the ripisylves are not cleared up any more and where the horses and cows are densément present, they eat all the growths before they open out.

Evaluation of the quality of the ripisylve

An evaluation can be required for example at the time of agro-environmental Mesures, or in the application of the Parent directive on water or of the development or evaluation of a green Trame or a ecological Réseau.

The qualitative and quantitative evaluation can in particular relate to:

its structure (vertical layers)
its importance compared to the linear one of bank
the diversity of the gasolines, and the Biodiversity which it shelters
its Naturalité (including the conservation of spaces of divagation of the dead Bras, , river Méandre S S, etc absence of dam, walls, banks of Palplanche S, Tunage S, etc)
its character of biological Continuum
its thickness and its opacity (according to the season)
its fauna associated (fish, Loutre, Beaver, Kingfisher, etc)
its state, and the state of water and banks (signs of erosion by the cattle, etc)
its degree of protection or vulnerability to the cut
its capacity to preserve the water of the Manure, Pesticide S or others Pollutant S of the area catchment

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