Distribution of introduced North American ash species and their role in lowland forest management in Croatia

North American ash species were introduced 100 years ago in the lowland regions in Croatia to afforestation sites where the native narrow-leaved ash could not survive. Presence and distribution of these species were obtained on the basis of forest management plans. A total number of 1,917 subcompartments (16,970 ha) showing the presence of these species as pure stands, partial stands, groups of trees, or individual trees were established. Gauss-Krüger coordinates of subcompartment center points and a Universal Transverse Mercator (UTM) 100 × 100-km grid were used for mapping the distribution of introduced ash species. The total standing volume of North American ash in the surveyed area is estimated to be 181,500 m3. In 90 randomly selected localities, the presence of green ash was confirmed, whereas white ash was not found. In the management of lowland forests in Croatia to date, the pioneer and ameliorative role of green ash in the preparation of habitat for the arrival and survival of narrow-leaved ash has been emphasized, though its economic function is not substantial. This North American ash will continue to have a minor but useful role in forest management on wet sites in Croatia.