Monday, 10 July 2006

Management of Forest Soils on Disturbed Grounds.

Wolfgang Schaaf and Reinhard F. Hüttl. Brandenburg Univ of Technology, Chair of Soil Protection and Recultivation, Konrad-Wachsmann-Allee 6, Cottbus, 03044, Germany

The spoil substrates of the Lusatian lignite mining district in eastern Germany (80.000 ha) are composed of a mixture sediments forming the parent material for newly developing soils. These soils contain varying amounts of pyrite and lignitic fragments throughout the solum resulting in specific features. Forestry is the dominating land use in the post-mining landscape. These forest ecosystems start at xpoint zerox, especially with regard to soil processes, plant-soil interactions, and biogeochemical cycles. Afforestation of these sites requires specific strategies. Severe acidification due to pyrite oxidation and poor water and nutrient holding capacities of the young mine soils call for comprehensive amelioration efforts. Up to 190 t CaO ha-1 in form of lime or fly ash are incorporated into the topsoil layer to allow root growth under reduced phytotoxic conditions. To study soil and stand development at these sites a chronosequence of pine stands covering a period of 60 years was used. The initial soil chemical status is influenced by pyrite oxidation, internal (and management induced) buffering, and formation of secondary minerals such as gypsum. Soil solution chemistry and element fluxes are controlled by these primary and secondary minerals. In the ameliorated top layers pH values are clearly elevated, whereas the unameliorated subsoils remain very acid (pH 2.5 – 2.9) showing extremely high ion concentrations. Geogenic organic matter contents, i.e. lignitic particles, increase the cation exchange capacity of the sandy substrates considerably. Despite unfavorable soil chemical conditions, the growth and nutritional status of the pine stands at these mine sites is surprisingly good. The content of lignitic fragments and secondary minerals in the soils seems to play an important role for the element cycling and nutritional status of the established forest ecosystems. However, the disturbance impact by mining operations presents a long-term effect.

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