Abstract
The spatial distribution of trees in forests can be described and modelled by point processes where the points are given by the locations (coordinates) of the trees. Further properties of a tree like height or mean crown radius can be interpreted as so called marks of the considered point process characterising the points or trees in some way. The so called mark correlation function describes the spatial correlation of these marks in the observed point pattern. In this paper we introduce a special mark, the overlapping or crown index. We show that mark correlation functions for the considered marks help to understand interaction effects of forest trees.