Floodplain forests and climate change: silvicultural recommendations for floodplain-forest management with regard to climate protection, biodiversity and economy

  • Contact:

    Mareike Roeder

  • Funding:

    Bundesanstalt für Landwirtschaft und Ernährung

  • Startdate: 02/2018
  • Enddate: 12/2020

Forestry in floodplains is presently confronted with a multitude of challenges. In floodplain habitats, in which forestry management is not unproblematic, the spectrum of tree species is by nature restricted. In the past, a focus has often been placed on the establishment of ash forest stands and non-natural monocultures of hybrid and balsam poplars. The development and distribution of ash, a riparian tree species, is currently massively endangered due to ash dieback disease. This is reminiscent of Dutch elm disease in the last century and of the black alder, which has been strongly decimated in the last 20 years by a new pathogen (alder Phytospora), especially along watercourses. For these species, new
"replacement” species must be found, either native or foreign, which fulfill the same natureconservation and economic requirements. Native oak would be a candidate, but its natural rejuvenation is difficult in floodplains and its artificial rejuvenation expensive. Therefore, forest owners and managers often see the establishment of poplar cultures as the only economically viable option. However, the cultivation of non-native poplar and hybrid poplar monocultures in floodplain habitats has been criticized from a nature conservation point of view, since these monocultures negatively affect biodiversity due to the predominant age similarity, structural poverty, short rotation times, and - in the case of balsam poplar - poorly decomposable litter of such forest stands. Thereby, floodplains and riparian forests, which are strongly affected by loss of area, are hotspots of biodiversity and of paramount importance for the conservation of countless species and numerous habitat types. This is reflected in the large-scale protection and conservation of German floodplains (Natura 2000 areas, Nature Protection Areas).

Besides these fundamental problems, uncertainties also exist concerning the future suitability of tree species for floodplain areas especially affected by climate change. At the same time, near-natural floodplain ecosystems are especially suited as carbon sinks. It may be possible to even increase this
effect through a near-natural floodplain forest management with regular tree removal to bind carbon in long-lasting wood products. Preventive flood protection also calls for more area along watercourses in order to absorb floodwater. Floodplain forests can thereby reduce flow velocities and protect soils from floodwater erosion. These floodplain functions are of particular importance since severe precipitation events are very likely to increase due to climate change. This all requires rethinking floodplain forest management and developing new concepts (forest development types) that on the one hand take the interests of forest services (economy) into account, while considering the needs and demands of climate and nature protection on the other. The definition of such forest development types is the overarching goal of this project.

Different forest management variants (including withdrawal from active use) will be studied in active and former floodplains in five forestry operational areas on the rivers Danube, Lech and Rhine. These will be assessed concerning their economical, ecological and climate-protection value. Concurrently, observation areas will be set up in the participating forest services to appraise the practicability of different forest management concepts (i.e. group selection felling) in floodplains. Based on literature studies, prognoses of the impacts of climate change on floodplain forestry (altered site conditions and tree species suitability) will be developed. The role of soil organisms in the carbon cycles of the studied floodplain forests will be assessed. The results of the survey will be analyzed in the context of the expected climate changes, and adaptation options identified. The scientific findings as well as the experience gained in the practical studies will be integrated in the definition of forest development types. The project results will be prepared into a user-friendly leaflet and information brochure to aid the practical implementation by forest owners. Based on the experience gained during the survey phase,an indication system and monitoring concept will be developed that will allow the assessment of the state of a floodplain forest site and of the impacts of forest management measures regarding biodiversity, climate protection and economy.