01.12.1 Habitat Functions for Rare and Near-Natural Plant Communities
Almost all soils are generally potential growth sites for plants, and hence provide a habitat function for plant communities. Differences in efficacy arise from the evaluation of the vegetation which potentially grows on that specific soil, with rare species or plant communities being evaluated more highly, primarily from the view of conservation.
Changes of the soil by excavation, land-filling and earth-moving, as well as by groundwater lowering and nutrient introduction cause far-reaching equalization of site qualities, which deprives particularly specialized plant species of their already rare habitats. A not atypical special case is that of poor and dry locations, with the comparatively rare dry meadows which take root there, the occurrence of which in the Berlin area is, however, tied to a low degree of anthropogenic influence.
In the present evaluation of the habitat function, a further continuation of the concept developed by Lahmeyer (2000), soil associations with extreme conditions of water balance and rare soil associations are primarily assessed as valuable. Rare and wet locations are identified as so-called special sites. In that way, ecologically particularly valuable locations and potentials for development, such as meadow communities, damp meadows and boglands, can be highlighted.
Extremely dry and low-nutrient dunes and anthropogenically created young soils represent potential sites for valuable dry meadows. These sections receive a medium evaluation as special natural spaces, regardless of their degree of near-naturalness.
Overall, the evaluation represents the potential of the soil to sustain certain vegetation, and is not an evaluation of the existing vegetation.
The habitat function for rare and near-natural plant communities is ascertained on the basis of the criteria near-naturalness (cf. Map 01.11.3), regional rareness of the soil association (cf. Map 01.11.1), dampness of the site (cf. Map 01.01 and 01.06.4) and nutrient supply (cf. Map 01.06.9) (cf. Figure 1). Using these criteria, so-called “special sites” are ascertained. Special sites include:
- Sections on which the site dampness is indicated as “wet”
- Sections on which the regional rareness of the soil association has been assessed as “very rare to rare”
- Sections with dry, low-nutrient soils.
As shown in Table 1, the evaluation of the habitat function for near-natural and rare plant communities is carried out according to three classes (low, medium, high), with consideration given to the degree of near-naturalness. The rare and wet classes receive a considerably higher evaluation than the dry locations, which are less sensitive because they regenerate more easily. The latter are assigned exclusively a medium potential for development, regardless of their near-naturalness. “Normal” locations obtain a medium efficacy rating only with very high near-naturalness.