Erfolgskontrollen der Renaturierungsmaßnahmen auf der Brockenkuppe im Nationalpark Harz

Abstract

Hünig, C.; Tischew S.; Karste, G.: Evaluation of restoration measures on top of the mountain Brocken in the Harz National Park. – Hercynia N.F. 41 (2008): 201-217.Since 1990 great efforts have been done to restore the former military area on top of the mountain Brocken into the Harz National Park. The restoration measures aimed to establish mosaics of the former natural vegetation with subalpine Calluna-heathland and meadow vegetation as well as to support endangered plant species like Pulsatilla alpina subsp. alba. Moreover, effective management to control the increasing dominance of grasses (e.g. Calamagrostis villosa) caused by a tremendous input of atmospheric nitrogen should be developed. Since 1991 small-scale heathland restoration experiments were performed using two different methods (sod cutting in different depths and mowing). In the same year deconstruction of the military infrastructure has been started and experiments with application of different substrates have been executed to counteract effects of the soil sealing. On half of the plots seeding of target species was performed. Important results of the heathland restoration measures were that (1) continuous mowing successfully reduced the dominance of Calamagrostis villosa, (2) only complete removal of the duff supported the rejuvenation of Calluna vulgaris and of other target species as well as it restricted the re-colonization of Calamagrostis villosa, (3) adjacent vegetation strongly influenced the colonization of the areas where sod cutting took place, and (4) re-colonization of these areas was accelerated by seeding of target species. The small-scale experiments after deconstruction of the military infrastructure showed best results after application of granite gravel and seeding target species. However, Calluna vulgaris very slowly developed full-grown individuals in the course of all experiments caused by the unfavourable conditions on top of the mountain Brocken. In 1996 large-scale destruction of the military infrastructure was finished and granite gravel and granite rocks were put on the surface. Vegetation development was continuously monitored on permanent plots subsequently. Accordingly to the goals of the National Park Harz vegetation developed spontaneously. In some parts of that area subalpine heathlands emerged, but large parts were colonized by Deschampsia cespitosa. Therefore these restoration areas should be necessarily monitored for the next years. Overall the sum of the restoration measures led to an increasing number of Pulsatilla alpina subsp. alba individuals on top of the Brocken. To stabilize that positive trend in population dynamics the management and restoration of the subalpine heathland communities on the Brocken must be continued. At the moment deep sod cutting and planting of Calluna vulgaris- and Pulsatilla alpina subsp. alba-individuals are performed as well as mowing of the grass-dominated heathlands on 25% of the area on top of the Brocken. Without these measures endangered and poor competitive species such as Pulsatilla alpina subsp. alba would be seriously endangered because there is no evidence that the input of atmospheric nitrogen will decrease noticeably in the future.