During the summer of 1981 we determined the age of trees, mainly of the following species: Alnus glutinosa, Betula sp., Crataegus monogyna, Acer pseudoplatanus, Euonymus europaeus, Fagus sylvatica, Frangula alnus, Fraxinus excelsior, Populus tremula, Quercus robur, Rhamnus catharticus, Salix sp., Sambucus nigra and Viburnum opulus. The best method of age-determination, when the exact ages are needed, is to use the increment borer and then cut off one side of the core perpendicular to the xylem vessels. Then the annual rings can be counted with the help of a binocular microscope.