When developing promising assortments of forest woody plants, it is important to take into account not only their growth and survival in some particular environment, but also their respond to change in growing conditions. In this regard, the purpose of this work is to evaluate the ecological plasticity and stability of some poplar varieties promising for the southeastern part of European Russia and Ukraine using the Eberhart and Russell method. The research was carried out on three testing sites: upland environment of the forest-steppe zone of the Voronezh region; floodplain environment of the dry steppe zone of the Volgograd region; and floodplain environment of the steppe zone of the Donetsk region. Five promising poplar varieties were identified and studied at each of the experimental sites. The indices of survival, growth in height and diameter, trunk volumes, and productivity by wood stocks and average increments are presented for each variety. Due to the average increments change with age, the ontogeny period from 21 to 30 years was chosen for the study, during which the average survival of poplars varies slightly. It was found that Regenerata, which is characterized by average plasticity and the lowest stability, was the most productive of the studied poplar varieties. It can perform high productivity only in the favorable environment. The poplar variety Pioneer demonstrated the least plasticity. Its productivity did not vary too much with change in growth conditions at average ecological stability. The highest plasticity at average ecological stability was observed in the Vernirubens variety. Average plasticity and stability were observed in poplar E.s.-38. The poplar variety Marilandica was also characterized by average plasticity, and high ecological stability. The research results allow using of the studied varieties more rational in different growing conditions, with regard to their environmental characteristics.