The most remarkable habitat, protected by the reserve, is without doubt the alluvial forest. It provides optimal conditions for the development of its species and is also referred to as a "gallery forest" owing to the density of the shrublayer and the presence of numerous climbing plants.

The alluvial forest

The forest's dynamic begins with the colonisation of areas cleared during flooding: the open habitats then gradually make room for the forest if development is uninterrupted and the forest is composed of all of its successive stages at the same time. At Rohrschollen, the visitor can therefore observe the pioneer or softwood forest stage, the terminal or hardwood forest stage and the mixed forest, the transitional stage between the two:

The softwood forest, the pioneer stage in the forest dynamic, is made up of willow and poplar. It can be picked out by its typical bluish grey colouring caused by the abundance of white willow and rosemary willow.

As these are light-loving species, this afforestation colonises the places stripped bare by flooding: along the water courses, on the newly formed banks of gravel, among windfall in the forest. Canalisation of the Rhine has given man total control over flooding. Therefore, on Rohrschollen Island, this softwood forest is not widely represented as flooding has not altered the habitat since the 1970s. This typical habitat can be seen in the former car park, a place that has been considerably damaged by human activity. Over the last ten years, nature has been reasserting its rights and trees are recolonising this area and forming a softwood forest. The well lit banks of the Bauerngrundwasser, stripped bare during the most recent floods, are creating areas conducive to this biotope.

The mixed forest is a mature willow/poplar plantation, which is beginning to be replaced by hardwood species (oak and ash). It occupies a large part of the forest in the north of Rohrschollen, along the internal water course. It is making the transition between the softwood forest bordering the Giessen and the hardwood forest.

The hardwood forest covers almost half of the island and represents the natural state of the mature forest: it is the final development of the Rhine forest.

Its deepest part is barely affected by the encroachment of man and is composed largely of oak forest with elm and ash. Owing to its luxuriant vegetation, it can be said to resemble the Amazon rainforest with the presence of numerous climbing plants (hop, clematis…) and trees of impressive size.

Scientific survey

The Rohrschollen forest massif benefits from long-term surveys of the spontaneous dynamic of alluvial forests. This survey, carried out every 10 years, was set up by the France Nature Reserves network, which proposes a strict, standardised protocol for all fluvial reserves wishing to undertake surveys, and therefore enables comparisons between reserves.

Its objective is to describe the current state of the alluvial forests and assess their dynamic over the long term. A network of permanent sample plots covers the entire forest massif.

A sample plot is a delimited, precisely located area in which vegetation inventories are made. The permanent sample plots enable long-term surveys of the development of vegetation. The size and shape of the sample plot varies depending on the purpose of the study.

For each sample plot, the readings taken concern data on the trees present (species, diameter, presence of cavities, health…) as well as a floristic survey of the herbaceous plant species present on the sample plot and a pedological survey (a soil core sample is extracted using a auger). These surveys help the managing authority to come to a better understanding of the possible development of the forest and its state of health.