Fig. 1: Floodplain at the Elz River.
With the expansion of the Rhine, local conditions within the Rhine floodplain have fundamentally changed regarding water regime. In what are known as ponds along the Rhine floodplain between Breisach and Iffezheim, there were large water level fluctuations during springtime of approximately 2 m above and below mean water level. Today, the floodplain through the canalised Rhine is in a static state, with large areas no longer flooded ("former floodplain"). The groundwater level is fixed by reservoirs and varies only slightly. Moreover, flood waters arrive faster with greater eutrophic water, and sometimes with higher levels than previously. Due to the impact of these revised growth conditions, the FVA, in close collaboration with the Regional Authority of Freiburg, has recently revised the site-related principles underlying the water regime on approximately 6,000 out of a total of about 7,200 ha of forested area along the Rhine.
Today, on about four-fifths of these areas, the forest is growing on sites where there is no more flooding. We class these areas as "former floodplain". Alternatively, this means that approximately 20% of the floodplain forest area consists of places that are at least periodically flooded. Nutrient-rich silt deposits ensure high levels of forest growth on almost two-thirds of the newly classed area, meaning that sites with high growth rates are far more common now than in the dynamic historic Rhine floodplain.
Fig. 2: "Old" Rhine floodplain Taubergießen.
Under today's conditions, naturally occurring primary tree species of floodplain forests are ash, sycamore maple, hornbeam, European beech, and on the wet, but increasingly silted sites also the relict white willow. It is becoming apparent that, locally, conditions are moving towards a terrestrial ecosystem.
Local conditions are changing once again as a result of retention areas for flood water that are in operation or under construction at thirteen locations along the Upper Rhine. These retention areas will control flooding and create habitats similar to those found on floodplains. Site-related fine mapping and modelling of floodplain forest levels expected under the new water regime are the basis for planning how to deal with the forest in the future.
Fig. 3: Ash dieback.
Today, the main tree species in the current population of the floodplain is ash, followed by sycamore maple, poplar species and willow species. The elm that shaped the forest until the 1970’s has largely disappeared as a result of Dutch elm disease. Due to a new fungal disease, ash has also experienced a massive dieback recently and this can lead to entire portions of the forest dying off. This is an ominous development for forest owners whose communities are adjacent to the Rhine. For example, ash trees in the city forest of Kehl represent 20% of the population and cover more than 40% of forest area across 350 ha. Once ash disappears, we cannot expect any immediate natural forest regeneration of these populations with other tree species suitable for the location. Consequently a long-lasting shrub stage with clematis is likely to inhabit these sites in the future.
Floodplain forests of the Upper Rhine are still home to numerous rare and endangered animal and plant species in localized areas. The vast majority of the Rhine floodplains are subject to the special protection of a nature conservation law. Out of 7,200 ha of floodplain forests, over 6,300 ha are protected under nature conservation requirements. The aim is to restore habitat conditions typical of floodplains wherever possible and to allow the environment to develop in a way that is characteristic of floodplains, i.e. to allow flooding. On the one hand, communities of species typical of floodplain forests should be able to develop within the largest possible undisturbed habitats; but on the other hand, a high structural diversity with correspondingly rare structures can only be produced and maintained by human intervention, especially in locations in the "former floodplain". It is important to also create opportunities for species to develop that are dependent on undisturbed habitats. The concept of combining rare structures and locally adapted old and dead wood that uses protected individual trees, habitat tree groups and specially designated forest refuge areas allows for a type of species protection that is adapted to the small dimensions of the floodplain.
A model for a floodplain forest management system designed for the future and underpinned by nature conservation can be based on meaningful scientific site-related findings that incorporate the requirements and the dynamics of tree species, e.g., in the case of oak, based on the results of genetic tests. In many cases, forests on the floodplain can be used and habitats preserved using an integrated approach. Light-demanding tree species in floodplain forests, especially in the "former floodplain", must in many cases be favoured through forestry operations if they are not to be shaded over during the coming decades.
Nature conservation goals can and should be met through management, especially when it comes to conserving oak forests. It is important here to align the management of oak forests with the conservation objectives of the respective FFH area. Sometimes, forest-owning communities are willing to pay the high investments for oak cultures needed to establish new oak-rich forests. Especially with oak forests, intervention measures are justified for silvicultural reasons, which especially benefit oak, and can prevent any deterioration of the situation regarding nature conservation. These measures are used to create and maintain rare forest structures that are key to nature conservation.
The conservation objectives of the FFH management plans can/must determine the extent to which oak forests of the Upper Rhine are to be preserved overall. The objective for municipalities is that forest habitat types and habitats are to be preserved at least "in their current scope and previous quality". For a municipality, this means that the conservation objectives of the FFH management plan will have to be adapted to the communal forest when developing a model. Certainly, opportunities to promote oak cultures will play a major role when a local council decides how much oak cover can be re-established. In forest management planning, nature conservation requirements must therefore be weighed against the interests of the timber industry, fishing and recreation, as well as the supply of firewood, which also assumes a very important role in many community forests.