The demographic structure of the populations of woody plants was analysed at both woodland sites (Table 3). The site WR is an approximately 40-year-old stand that is still dominated by European birch (Betula pendula) as a pioneer species. Some late-successional species indicate the future direction of succession. Most common is the shade-tolerant sycamore maple (Acer pseudoplatanus) which is already established under the canopy of birch (Fig. 4). Other tree species occur in the herb layer (Acer campestre, A. platanoides, Carpinus betulus, Crataegus x macrocarpa, Prunus serotina, Quercus robur). In the herb layer, typical early – successional species are still present (Agrostis stolonifera, Cerastium holosteoides, Epilobium ciliatum), but woodland species indicate the further development of the stand (Dryopteris filix-mas, D. carthusiana, Deschampsia flexuosa). The moss Mnium hornum is indicative of the strongly acidic soil conditions.
At the second woodland plot (WZ), the North American black locust (Robinia pseudoacacia) had been used for recultivation purposes. Within the 80- to 90-year-old stand, a strong natural dynamic is apparent. The black locust is still dominant, but no increase in height occurs in diameter classes above 30 cm (Fig. 5). Instead, some trees are already beginning to die. Gap formation enhances the regeneration of both black locust and other trees. Black locust still predominates in the shrub layer. Due to the poor decomposition of its litter, a thick raw humus layer has accumulated. The herb layer mainly consists of Rubus spp. (R. elegantispinosus, R. nemorosoides) and fern species (Dryopteris dilatata, Athyrium filix – femina).
Table 3. Demographic analysis of urban-industrial woodlands. Site WR 40-year – old stand dominated by birch, site WZ 80-year-old stand dominated by Robinia. Only saplings with a height of more than 1 m are considered. K 1 refers to the Kraft classification “superior” trees, K > 4 to “overtopped” trees, asterisks indicate data that were not analysed
Fig. 4. Height versus diameter at breast height of Betula pendula (Bp) and Acer pseudoplatanus (Ap) in a 40-year-old birch stand at site WR