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In the lignite mining area of the Rhineland (Germany) some wet forests, valuable from the point of view of ecology and nature conservation, have been affected by the drainage caused by the large and deep mining pits. In order to restore these drained forests and to protect others from drainage, an irrigation project was started in 1987. Preliminary investigations had begun in 1982. The aims of the total project were to document the changes in vegetation and soil caused by drainage, to test the suitability of different methods of irrigation in order to restore forests affected by drainage, and to document and evaluate the development of the forests under the influence of irrigation. The drainage of the different Alno-Ulmion communities and of the Carici elongatae-Alnetum, all typical for undrained areas, leads to Alnus glutinosa-forests dominated by Deschampsia cespitosa, by Urtica dioica or by Rubus fruticosus agg. In some cases Betulo-Quercetum alnetosum is the final result, in other cases Alnus glutinosa-forest with a Carpinion-like herb layer. Seepage of water at the edge of the valley has proved to be an adequate method to re-transform drained alder forests into wet alder forests. However, the habitat conditions achieved up to now by irrigation seem to support the development of riparian forest (Alno-Ulmion) more than alder swamp (Carici elongatae-Alnetum).

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