Provenance variability of black alder in Poland

European black alder (Alnus glutinosa (L.) Gaertn.) is a widespread tree species associated with wetlands and riparian ecosystems, thus it plays an important ecological role. Due to its fast growth and favorable wood properties it also has a potential to satisfy a growing demand for wood and fiber. However, its growth potential is not fully realized in Poland. In this study we investigated variation in growth traits, productivity, and stem straightness among 11 populations of European black alder originating from the lowland distribution of the species in Poland. The common-garden experiment located in 1968 in Kornik (mid-western Poland) has been so far the only provenance experiment with this species in our country. We measured height and diameter of all trees at the site, assessed stem straightness in a 5-step scale (1-crooked; 5-straight), and calculated productivity at age of 50 years, which should be considered close to the rotation age. We found significant variation among populations in all investigated traits. The difference in productivity between the best and the worst provenance reached 75%. Using published and unpublished data from previous measurements at this site we also analyzed a trend in provenance ranking through time. The best and worst provenance could be identified at age 16 years, but many ranking shifts took place afterwards at the intermediate rank positions. We conclude that growth, productivity and stem quality of black alder could be improved through selection of favorable provenances within the species. Selection decisions can be made at the age below the half the rotation age, although decisions at 3/4 of rotation age would be more precise.