The effects of light and soil conditions on the species richness of the ground vegetation of deciduous forests in northern Germany (Schleswig-Holstein)

This paper reports a study carried out in 91 deciduous forests to investigate the influence of light and soil conditions on the species richness of the ground vegetation (vascular plants, bryophytes, lichens). To examine the relationships between the species richness and environmental factors all data were evaluated using univariate and multivariate (principle component analysis) methods. At all the stands investigated, the conditions of soil and light have a vegetation type specific effect on the species richness of the ground vegetation. In moist forests (alder-ash forests of the alliance Alno-Ulmion), species richness has a close positive correlation with soil moisture, whilst light conditions and nutrient supply have in the main no effect on species richness. On the other hand, in meso- to eutrophic beech forests (beech forests of the alliance Fagion sylvaticae), species richness is closely correlated with soil activity and with the base and nitrogen supply. Improving the light conditions for the ground vegetation does not increase the number of typical woodland species as most of these are shade tolerant and have very limited light requirements. Species richness in acidophytic beech and mixed beech–oak forests (beech and mixed beech–oak forests on acid soils of the order Quercetalia roboris) is affected mainly by the canopy closure and the interior light conditions. Soil moisture, nutrient supply and light availability must therefore be evaluated differently for their effect on the number of species of the ground vegetation and with regard to individual forest communities as they are distinguishable according to their site conditions. If the relation between species richness and environmental factors like soil conditions is analysed not with reference to individual forest communities but rather with reference to the totality of central European forests, relationships may be found which are not helpful for an explanation of the species richness of a certain forest community and thus they are only of restricted usefulness for appropriate recommendations for forest management. The consequences of the results for the effects of silvicultural treatment on deciduous forest ecosystems of the central European lowlands are discussed.