Roselière

A roselière or phragmitaie is a zone in edge of lakes, ponds, marsh or dead arms of river where pushes mainly reeds.

Description

Among the various vegetable belts which constitutes the frontier zone between the dry land and stagnant waters, the first area supralittorale names the Cariçaie, the roselière is the first littoral belt itself, formed by emergent watery plants. This zone goes from not very deep water until 1,5 meters. The following zone, that of the Water lily S and the Potamot S consists of plants which live only in water.

One finds in the roselière:

the common Reed ( Reeds communis ) mainly;
the Two-handed hammer (kind Typha );
the Snap ring (kind Juncus );
the lake Scirpe ( Scirpus lacustris );

the Prêle (kind Equisetum );
the Ribbon (kind Sparganium );
the Plaintain of water ( Water-plantain plantago );
the yellow Iris ( Iris pseudacorus ).

Roles

Animal protection

It allows the animals and in particular birds of the marshes which populate it to be nourished, to protect themselves from predatory and also to raise their small there. The crested grèbes nest there so of the interior lagoons are present and if the roselière is sufficiently large and calm. Some cyprinidés can clear interior water levels so there are maintained.

Purification of water

She plays a part in the cleanliness of the lake or the pond, the made-to-order of a Purification plant: she filters the matters and allow their decantation. Moreover, the plants as the Roseau X assimilate in their fabrics of the pollutants like the Phosphore, the Nitrate, but also the Cyanure or of the Hydrocarbure S. the Scirpe S metabolize the phenol.

Natural evolution of the roselière

The plants of the roselière form thick networks of rhizomes which contribute to the progressive filling of the medium. In particular in the eutrophic or polluted mediums, which accelerate the vegetative development. Gradually the level of water decrease and the medium is colonized by the Carex (the Cypéracée S). The phragmithes go, they, to approach the center of the water level.

The long-term evolution continues then towards the Tourbière or the Forêt. This phenomenon of filling of a water level names “alluvial deposit”.

Ecological threats

The man accelerates the phenomena of Eutrophisation by massive use of manure and alluvial deposit per contribution of alluvia.

To be able to reach a water level, the man did not hesitate to destroy the roselière who makes the access too difficult. On the big lakes, the existing roselières are very often protected.

The regulation of the levels of the lakes or the ponds also seems to have weakened the roselières. Formerly, natural marling made it possible to dissipate the energy of the waves on a greater portion of littoral.

Technical measures

To stop the erosion of the lake faces of roselières, there exist many techniques resulting from the biological genius which allow, in the medium term, to form a protection against the negative action of the waves. For example: piles of wood in which faggots of branches of willows are inserted. It is also possible artificially to recreate the favorable conditions with the development of the reed where it is not or more present. With this intention, it is necessary to exploit the slope, the substrate brought, and to take account of the exposure to the waves, the dominant winds and the Bathymétrie.

See too

Lake Annecy

Sources

Gerard Lacroix, Lakes and rivers: alive mediums , Bordered, 1991.

Mauchamp A., Sinnassamy J. Mr., Roselières functional and patrimonial management , Technical Workshops of Natural spaces (ATEN), Natural reserves of France and Ornithological Station of the Tower of Valat, Technical Books N°63, 2001.

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