Neophyten in Buchen- und Fichtenwäldern des Sollings

405 Neophyten in Buchen- und Fichtenwaldern des Sollings* Wolfgang Schmidt, Steffi Heinrichs, Martin Weckesser, Luise Ebrecht und Bernadett Lambertz Abstract: Non-native plant species in beech and Norway spruce forests of the Solling Hills The proportion of alien plant species in the ground vegetation of beech forests and Norway spruce stands on acidic soils was investigated by comparing vegetation releves in the Solling Hills (Lower Saxony) obtained from different research projects during four decades. In general, the proportion of non-indigenous plant species is rather low. In species-poor closed beech stands 4.4 % (on average 1.3 %) of the maximum species number and 7.3 % (on average 1.9 %) of the maximum coverage of the sparsely covered herbaceous layer belong to alien plant species. In the Norway spruce stands with a more species-rich and more densely covered herbaceous layer, the proportion of alien species is 2.8 % (on average 1.4 %, species number) and 4.7 % (on average 1.7 %, coverage) at maximum, respectively. In 1966-1968, no alien plant species were recorded in managed beech and Norway spruce forests. In contrast, vegetation releves recorded 30 years later on the same site showed an increase in the number of alien species up to 1.3 % of the mean number of species. The mean cover of non-native species increased to 0.2 % (beech) and 4.7 % (Norway spruce) of the total herbaceous layer coverage, respectively. Non-indigenous plant species are still lacking completely in the unmanaged beech forest nature reserve. Silvicultural treatments like group selection felling in beech stands or girth-limit felling and clear-cutting in Norway spruce stands were not followed by a significant increase of alien species according to the disturbance gradient. By the creation and use of skid trails in forests there was no shortterm increase of non-native species. Only on heavily or repeatedly disturbed parts of compacted forest roads and skid trails, such as wheel tracks or mid-line in Norway spruce stands did aliens increase significantly. The most important non-native herbs of beech and Norway spruce stands in the Solling Hills are Impatiens parviflora and Epilobium ciliatum. Until now, E. ciliatum was missing in the beech forests mainly due to the low light availability. Rare occurrences of spontaneous tree regeneration of introduced Pseudotsuga menziesii, Larix decidua and Quercus rubra result from near-by forest plantations and indicate that the most important impact on vegetation is coming from the plantation of exotic tree species rather than the spontaneous establishment of herbaceous neophytes. Other alien woody species as well as adventative ornamental plants which are fully established in the flora of the Solling Hills today, are presently not found in the herbaceous layer of the forests. Most of these species can be found in open landscapes or urban areas with gardens and parks. Accordingly the whole Solling landscape including the open and ruderal outskirts has a higher proportion of non-native plant species than the nearly completely forested central part of the research area (11.1 % versus 7.6 % of the flora).