Rainfall partitioning and soil water dynamics along a tree species diversity gradient in a deciduous old growth forest in Central Germany Species diversity effects have been extensively investigated in grassland ecosystems however little is known about the influence of tree species diversity on the forest water cycle. In this dissertation several hydrological processes including soil water dynamics rainfall partitioning and the related ion deposition with rainfall have been investigated along a tree species diversity gradient. In addition the results were used to model the water cycle. The studies were conducted in twelve study plots in old growth deciduous forest stands in the Hainich National Park Germany. Monospecific plots were formed by Fagus sylvatica (beech) and mixed forest plots consisted of a variable admixture of up to eleven broad leaved deciduous tree species such as Tilia spec. Fraxinus excelsior Carpinus betulus and Acer pseudoplatanus. The first part of this thesis presents the partitioning of rainfall into throughfall stemflow and interception along the tree species diversity gradient. The results demonstrated that several stand characteristics influenced rainfall partitioning ...