As a result of the closure of many mines at the beginning of the 1990s after the German Reunification, there are still large areas of bare soil dumps as well as older open-cast areas. Based on the analysis of site conditions, spontaneous development of large woodlands is to be predicted for many parts of surface mines. These woodlands will show high chronological and spatial differentiation in their development due to site heterogeneity and different site advantages. This is related to different land-use potentials. Varied and continuously changing landscape structures offer ideal conditions for recreational activities in the sense of “nature tourism.” The mainly regional population uses this wilderness for walking, cycling or mushrooming. The unique potential of these sites in terms of process conservation must also be maintained for nature conservation. In general, greater proportions of abandoned lignite mining areas reserved for spontaneous succession will increase the floristic diversity in intensively used landscapes (Hadacova and Prach 2003; Tischew and Kirmer 2003). Conservation organizations and foundations are taking this chance and currently buying up large successional areas. Conservation authorities in the federal states support them. As scientists see it, these sites can be used as unique specimens for the observation of regeneration processes in large, disturbed areas. Spontaneous woodland development on these sites should also be encouraged for financial reasons: afforestation costs about € 20,000/ha and mostly can not be sold or cultivated profitably, whereas succession sites require only about € 1,400/ha (Abresch et al. 2000). Suitable methods for near-natural acceleration of vegetation development have been developed for problem areas, where vegetation development has to be accelerated because of erosion or to avoid dust emissions (Tischew et al. 2004).
Summary
We studied the spontaneous development of peri-urban woodlands on more than a hundred sample sites in eastern German open-cast lignite mining areas. The regeneration ability of the sites and the variety of developmental paths are remarkable. On hospitable substrates, pioneer birch forests can spontaneously develop within a few years if diaspore sources are available. Intermediate and climax tree species (e. g. common oak, smallleaved lime, sycamore) take root on these substrates on 30-year-old sites. They slowly displace birch after 60-80 years. Due to the variety of substrates and topography, spoil-dump woodlands are mostly of high structural diversity and aesthetically enrich post-mining landscapes. Thin birch and pine woodlands, including grasslands or heaths on less hospitable sites, are interesting examples of colonization processes after a massive turnover which was previously found to this extent only during the last ice age. Less competitive species can find refuges on these sites for longer periods. Therefore, woodlands in post-mining landscapes contribute to the maintenance of biological diversity and dynamic processes in postindustrial landscapes. Though far-reaching disturbance is the starting point of its development, a unique “nature of the fourth kind” can develop by natural colonization processes and offer various options for recreational activities for the public to experience a natural wilderness as well as potential for nature conservation.
Economical points of view are also good reasons for including spontaneous colonization processes in the design of former surface-mining areas. Spontaneous succession in surface mines therefore represents a great challenge and requires a rethinking of reclamation strategies by all people and institutions involved. More than 10,000 ha of eastern German post-mining landscapes are currently designated as sites for succession.
Acknowledgements
Investigations were funded by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as well as the Lusatian and Central German Mining Management Company (LMBV).
