„Arche Noah“ für Pflanzen? Zur Bedeutung von Altwaldresten für die Wiederbesiedlungsprozesse im Tagebaugebiet Goitsche

Abstract

BENKWITZ, S.; TISCHEW, S.; LEBENDER, A.: „Noah’s arc“ for plants? The importance of remaining woodlots for recolonization processes in the lignite mining area Goitsche. - Hercynia N. F. 35: 181-214.Since 2000, the water level in the northern part of the former lignite mining area Goitsche (Sachsen- Anhalt, Germany) is rising. In this part of the mining area, three hills are situated, each approximately 1 km apart. Two are remnants of the former cultural landscape containing fragments of deciduous forests. They were surrounded by surface-mined land. In 1961, a tip site was built. On this site, a pioneer forest has developed spontaneously. With elapsing time, these three hill sites will become islands. The persistence ability of the herb layer and the woody species of the remnants were analyzed. The depression of the groundwater table over decades led to a reduction of the vitality of woody species. On the other hand, the herb layer was only slightly affected by the withdrawal of the groundwater. The vegetational composition of pioneer forests was used for conclusions about re-colonization processes and the dispersal abilities of selected species groups. The flora of the remnant woodlands was compared with pioneer forests. In a pioneer forest adjacent to one of the remnant woodlands, more wind-dispersed woody species of later successional stages (Carpinus betulus, Acer ssp.) could be oberserved. Whereas in the pioneer forest of the tip site, mostly bird-dispersed woody species of later successional stages (e.g. Quercus ssp., Sorbus aucuparia) immigrated. The efficiency of the dispersal mechanism is decisive for the colonization ability of woody species. A comparison of woodland species in the herb layer showed that 2/3 of this species group of the remnant woodland could be found in the adjacent pioneer forest. On the same site, adjacent grassland contained 1/3 of this species group. In the herb layer of the pioneer forest on the tip site only 1/5 of the woodland species from the remnant woodlands occurred. Forest herbs often lack long-distance dispersal mechanism. The combination of ineffective dispersal with unfavorable site conditions on the tip site hampered colonization and establishment of this species group. Spontaneously colonized pioneer forests in surface-mined land are of high conservational value. In the course of succession, rare and endangered species found refuges and new colonization areas. A comparison between the spontaneously developed pioneer forest on the tip site and the surrounding landscape outside the mining area showed that the pioneer forest led to a distinctive increase of the species diversity. In the paper, we further discuss the active introduction of forest herbs. The acceleration of the successional progress in mining areas should be restricted to recreational areas. Otherwise, the development of woodland should result from process conservation. The preservation of remnant woodland in mining areas proved to be a successful strategy. Essential potentials of woodland ecosystems remained during the mining activities. The woodlands are able to regenerate. They act as seed sources for the re-colonization of the surrounding mining sites. Long-term monitoring of the further development is necessary and can be based on our results.