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Article

Author(s): Julien Prinet (ONF)
Editorial office: FVA, Germany
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Alder Forests and Alder-Ash Forests in Montane Areas of the Vosges and the Alsatian Jura

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Alder and alder-ash forests are so called "azonal" forest communities. This means that the soil has a larger influence than the climate. These forests are common in the bottom of valleys, at lower slopes and in swales with permanent rivulets and lateral rivulets. They can be found in areas with moist to wet soils.

Black Alder (Alnus glutinosa) and Common Ash (Fraxinus excelsior) are the predominant tree species.

Two different soil types are specified:

  1. communities dependent on the dynamic of the stream and/or influenced by the groundwater
  2. communities on swamps almost completely waterlogged

Alder-ash forests are normally stream-accompanying forests. The tree and herbaceous layer acts as the connection between land and water.

This article of the ONF describes the forest communities of the alder-forests and the alder-ash-forests of the Vosges, the ecological functions of these forests and the threats posed by human impacts. Some recommendations for the management of these forests are also given.

Occurrence in the Vosges

Schwarzerlen Auewald (Netzenbach vallée de la Bruche – Elsass) Erlenwald im unteren Abhang (Schirmeck – Elsass)
Fig. 1: Black Alder riparian forest (Netzenbach vallée de la Bruche – Alsace). Fig. 2: Alder forest on the lower slopes (Schirmeck – Alsace). (Fotos: ONF)

Alder or alder-ash forests occur over the entire Vosges (Bunt-sandstone, crystalline rock, Alsatian Jurassic rock) from colline level up to more than 1000 meters.

Their presence differs depending on the type of substrate and the type of water supply (flooding, high water, stream or standing water).

Following a survey of wet lands and streams in the public forest of the Vosges it was possible to quantify the frequency of occurrence:

  • present along 13% of water bodies (almost 188 km streams)
  • more than 350 ha, i.e. 48 % of the surveyed wet lands are alder- or alder-ash forests, with or without dependence on the stream dynamic

Ecological Functions

  • filter-function and self-clarification of surface waters and groundwater-supplying waters
  • flood control
  • disposal of organic substances and production of biomass, which supports the development of aquatic life
  • ecological corridor, ecotone and internal boundary zone
  • in areas at risk of heavy erosion: stabilisation and preservation of the bank
  • in addition to the listed ecological functions these forests have very important natural heritage values

Threats

  • every change to the management system and water body function
  • change of structure through stand transformation (plantation of coniferous trees, poplar etc.)
  • compaction and disturbance of the topsoil (mechanical utilisation, traditional skidding etc.)
  • change in the physical-chemical characteristics of the water (pollution, eutrophication etc.)
  • construction, aggradation or other impacts which might support the spread of invasive species (Japanese knotweed, Himalayan balsam etc.)

Recommendations for Management

The defined objective is the preservation of the alder and alder-ash forests as well as the regeneration of damaged habitats. Production is secondary in such forest communities.

Three measures have to be supported:

  1. systematic removal of unsuitable tree species (coniferous trees etc.) and non site specific species (within and surrounding the area)
  2. operations at the boundary of the area which support the desired tree species and their spread
  3. allowing typical deciduous trees to fulfil their role as seed trees so the forest community can develop

Plant Sociology Classification

Moor-Erlenwald (Nordvogesen – Elsass)
Fig. 3: Swamp-Alder Forest (Northern Vosges – Alsace). (Foto: ONF)

The classification of the alder and alder-ash forest can, depending on the water supply, be carried out based on their function. The forests are very complex and multifaceted forest communities. So far no detailed descriptions of their appearance are available (work in progress: summary of the forest types of the Alsace + identification key). In montane areas they occur only in small areas in non-specific associations closely connected to nearby forest communities.

Leaflets about the Plant Sociology Classification can be downloaded as PDF documents via the following links:

Some special plant species that can be found in alder-ash forests and are listed in the Alsatian Red List

Purple Small Reed Calamagrostis canescens (Swamp-Alder Forest, Swamp…)
Bog Arum Calla palustris (Swamp-Alder Forest)
Small Enchanter's Nightshade Circaea alpina (Alder-Ash Forest)
Royal Fern Osmunda regalis (Swamp-Alder Forest)
European White Elm Ulmus laevis (Alder-Ash Forest)
Crested Wood Fern Dryopteris cristata
Remote Wood Fern Dryopteris remota
Marsh Fern Thelypteris palustris
Yellow Star-of-Bethlehem Gagea lutea
Spring-Snowflake Leucojum vernum
Ostrich Fern Matteuccia struthipteris (montane Alder-Ash Forest)

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