Spontaneous and initiated succession on unvegetated slopes in the abandoned lignite-mining area of Goitsche, Germany

In this study, we examined the colonization of unvegetated, dry slopes in the lignite-mining area of Goitsche, Germany. The plots, characterized by different habitat conditions, were studied from 1994-2000. The vegetation development on treated plots was compared to untreated plots showing spontaneous succession. For initial treatments we used fresh plant clippings from a species-rich sandy grassland (Armerion elongatae) mowed at the end of July. Soil seed bank samples, taken at the beginning of the experiments and cultivated for 18 months, confirmed that the vegetation development on the slopes started with primary succession. Because seed rain is considered to be an important factor in primary succession, we also studied the diaspore input during the First year. The hospitable Quaternary substrate of Site I (pH = 4.1-4.7, 92% sand) supports fast vegetation development on treated and untreated plots. On treated plots, we have identified plant assemblages similar to initial stages of the Armerion elongatae community. On control plots, Coryne-phorion communities have established spontaneously. At Site 11 (mixed Quaternary and Tertiary substrate, pH = 3.0-3.5, 40% sand) the total cover and number of psammophytic species was low. Treated plots showed development towards ruderal sandy grassland, but the establishment of Calamagrostis epigejos would eventually lead to monodominant stands. Untreated control plots showed basically the same pattern, however the development was slower. At Site III (pH = 1.8-2.8, 34% sand), the hostile Tertiary substrate impeded the succession on both treated and untreated plots because low pH and therefore high amounts of Al3+ produced elemental toxicity to plants. The application of plant clippings accelerated the vegetation development in sites with a pH exceeding 3. On plots with the initial treatment, vegetation cover and total number of species were higher than on untreated plots. The application of fresh plant clippings from areas with similar habitat conditions appears to be a viable alternative to traditional restoration methods.