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Beierkuhnlein, C; Gräsle, W: The influence of light regime and water chemistry on the structure of forest spring vegetation in Botosaneanu, L: Crenobiology, Backhuys Publishers, Leiden, 9-22 (1998)

The vegetation structures and dominant species of 23 forest springs in the area of Frankenwald in Northeastern Bavaria were compared in relation to the hydrochemical and microclimatical characteristics of the spring sites. The structure of the vegetation is dicussed with regard to the strategies of resource utilization of the dominant species.

The pH-value of the spring waters has an important influence on the respective plant communities. At acidified springs with pH < 4.5 Sphagnum fallax Klinggr. dominates and those spring communities which are naturally typically for the prevailing altitudes are absent.

The vegetation at spring sites with higher water pH-values (pH > 5) is differentiated mainly on the basis of light availability. Shaded springs (with less than 5 % of relative light supply) are dominated by the evergreen perennial Chrysosplenium oppositifolium L. This species profits from the constant temperature regime of the spring sites, as it grows close to the surface. The shaded springs exhibit one low ground layer. If the light supply becomes more favorable (5 to 10 %), the annual Impatiens noli-tangere L. joins and forms a second layer. The permanent disturbance of the substrate caused by the spring water always generates areas of open soil suitable for germination. Perennial tall herbs such as Chaerophyllum hirsutum L. succeed in forming a second layer only if the light supply reaches more than 10 % of the value of the open land.

The exceptional cases of predominance of other species are due to either restrictions in the mechanisms of dispersal of the species (Petasites hybridus (L.) G., M., Sch.) or adaptations of the species to seasonal fluctuations of soil moisture (Petasites albus (L.) Gaertn.).

Under the perspective of the differentiation of vegetation structure the mutual influence of different strata is discussed on the basis of common models for competition strategies. Four types of strategy are differentiated and related to the use of light and nutrient supply and to adaptations on the specific microclimate of springs.
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