The dieback process of European ash affects the disappearance of the species from the typical ash sites such as floodplain forests or alder-ash forests. The species occurs more often in moist broadleaved forests and fresh broadleaved forests. Therefore, the main aim of our study was to determine the influence of ash age and the forest site type on the chosen biometric features of dominant and codominant trees. We also aimed to compare the sizes of European ash growing in optimal forest site types with less fertile ones where it does not occur as the main species. We collected the empirical material from 25 plots representing 4 forest site types: fresh broadleaved forest, moist broadleaved forest, floodplain forest, and alder-ash forest. The research plots were located in the Babki, Konstantynowo, and Łopuchówko Forest Dis- tricts, western Poland. The age of ash varied from 52 to 144 years. On each plot, we measured a tree height and a diameter at breast height of 15 dominant and codominant ash trees. Subsequently, we used measured features to calculate the volume of each tree. We carried out the analysis of covariance of diameter at breast height, height, and volume. The analysis showed the strong relationship of examined features with the age of the species and the forest site type. Furthermore, our results indicated the underestimation of the growth possibilities of European ash in fresh broadleaved forest and moist broadleaved forest. In these sites, ash achieved similar sizes in comparison to optimal forest site types i.e. floodplain forest and alder-ash forest. This result cannot be omitted in forestry practice, especially in silviculture, which should aim to support the natural regeneration of European ash in differentiated site conditions.

Keywords: European ash, forest site type, age of a tree, biometric feature