The ecological richness of our alluvial forests

Background

The alluvial forests contain an exceptional diversity of habitats, with a wide range of environmental conditions that offer an "ecological niche" for a large number of species of fauna and flora. The natural habitats and forestland are considered to be of high environmental value, although the considerable changes that have been made in and around the Rhine over the past decades have brought about a modification of this very special environment, which is threatening certain habitats and species.

Unique to Strasbourg

Strasbourg is the only European city with alluvial forests round its outskirts. Various tree-planting operations (beech, spruce, sycamore maple and walnut) have been carried out over the years, but there are still old forest stands and sectors which have seen no woodcutting since 1984.

An ancient and luxurious forest

The three great forest areas (Neuhof, Robertsau and Rohrschollen) contain about 70 to 80 woody species (trees, shrubs and lianas), some of which are rare and even threatened, such as the White Elm and Wild Pear and Wild Apple trees. Lianas such as ivy, clematis, hops and the rare, protected wild vine, and the richness of the flora help give the forest the luxurious vegetation reminiscent of a tropical forest. Ivy is a creeper which does no harm to its host tree, which it uses only to climb up to the light.

As there has been no woodcutting in certain parts of the forest since the 1980s, old trees can still be found there with trunk diameters that sometimes exceed 200 cm (mainly oak trees), along with a significant amount of dead wood left lying on the ground, which encourages the natural recycling process. Some sectors contain the remains of natural alluvial forests, with ash, oak and lime trees.

Forest birdlife

The Rhine alluvial forest is home to a number of nesting forest birds (54 species in the natural reserve of the island of Rohrschollen), including 6 species of woodpecker – the Black Woodpecker, the Green Woodpecker, the Grey Headed Woodpecker, the Great Spotted Woodpecker, the Middle Spotted Woodpecker and the Lesser Spotted Woodpecker – and the Short Toed Treecreeper, a species which is normally only seen in coniferous mountain forests, but which can be spotted in the forests of the Robertsau and Rohrschollen.

Fauna and flora of the waterways and wetlands

A vast number of amphibians and remarkable plant species are to be found in and around the internal waterways, wetlands and ponds of the alluvial forests.

Among the rare or protected species to be found there is the weird and wonderful carnivorous Utricularia australis, which feeds on microorganisms in the water.

The three forests are home to 10 species of amphibians, including the very rare Crested Newt in the Robertsau and Rohrschollen and large populations of the Common Frog and Common Toad.

A number of Libellulidae can be seen along the fast flowing Altenheimerkopf waterway in the forest of Neuhof, including the protected Southern Damselfly, the Small Pincertail, the Keeled Skimmer and the Southern Skimmer, and, since 2011, the Golden Ringed dragonfly.

The ponds, wetlands and slower-flowing waterways of the Robertsau and Rohrschollen forests are home to many species of nesting waterbirds, including a number of rare ones such as the Tufted Duck and the Little Grebe, whose nest is a floating raft made of plant debris. Other species include the Mallard, Mute Swan and the Eurasian Coot, while the Black Kite can sometimes be spotted flying overhead searching for the dead fish floating on the surface of the water which make up much of its diet.

The waterways also contain a rich fish population, which includes eels, pike and the Spined Loach, which is only to be found in the Natural Reserve of the island of Rohrschollen.

Flora, butterflies, grasshoppers and crickets

The meadowland at the edges of the forests is wet in some sections and dry in others and contains a wide variety of fauna and flora.

Some of the meadows have up to 70 or 80 plant species spread over just a few hundred square metres. Five protected species have been found in the meadows so far, along with other remarkable species including orchids. The wet meadows can be home to the Early Marsh Orchid and the Large Pink, while the Bee Orchid, Pyramidal Orchid and Burnt-tip Orchid can be found in the dry sections.

The Entomofauna includes 29 species of orthoptera (grasshoppers and crickets) as well as 48 species of diurnal Lepidoptera (butterflies) including a number of remarkable and protected species such as the Dryad, Old World Swallowtail, the Grey Bush Cricket, the Tessellated Shieldback, the Blue Winged Grasshopper and the Sphingonotus caerulans locust, which are to be found in the dry meadows, and on the rare gravel banks of the Natural Reserve of the island of Rohrschollen.

The protected Large Copper and Dusky Large Blue butterflies, the Large Marsh Grasshopper and Leek Grasshopper are more likely to be found in wet meadowland, especially in the Robertsau forest or occasionally in the Rohrschollen and Neuhof forests.

Facts and figures

• 13 locally or nationally protected plant species
• Robertsau forest:
  • 33 species of Lepidoptera and 20 species of Orthoptera recorded since 2008
  • 48 species of nesting birds, including 39 forest species and 9 waterbirds
  • 3 species of reptiles and 6 species of amphibians in 2011
• Neuhof forest:
  • 32 species of Libellulidae, 17 species of Orthoptera and 31 species of Lepidoptera recorded since 2008
  • 4 species of reptiles and 5 species of amphibians in 2011
  • 18 species of fish recorded from 1995 to 2007
• Natural Reserve of the island of Rohrschollen :
  • 54 species of forest-nesting birds and 30 species of meadow-nesting birds
  • 10 species of amphibians and 4 species of reptiles recorded
  • 45 species of Lepidoptera and 27 species of Orthoptera recorded in the meadowland
  • 22 species of fish in the internal waterways on the island and the Vieux Rhin
  • 10 species of Chiroptera recorded, including 2 species which still need confirmation.