Abstract
The article presents the results of a long-term study on an experimental plantation of four poplar cultivars (‘Canadian-Balsamic’, ‘Druzhba’, ‘Tronko’, and ‘Strilopodibna’) at 7, 9, and 15 years of age. The plantation was established near Ternopil, the city in western Ukraine. Under conditions of natural thinning, the average survival rate of the poplar cultivars decreased linearly (R2 = 0.995) from 83.5% on a 7-year-old plantation to 32.5% on a 15-year-old plantation. The average stem wood stock of all poplar cultivars on the plantation increased over the 8-year period (from 7 to 15 years), rising from 108.3 to 134.5 m3·ha−1. However, the growth dynamics of individual cultivars varied. At 7 years of age, the Strilopodibna poplar exhibited slightly lower growth rates in both height and diameter than the other cultivars and had the smallest stem wood stock (93 m3·ha−1). However, due to a lower natural tree loss rate, it ranked first in productivity by the age of 15, nearly doubling its stem wood stock to 171 m3·ha−1 over the 8-year period. The study has also shown that all poplar cultivars on the experimental plantation have a high potential for generating various ecosystem services, including CO2 sequestration, oxygen production, and energy biomass generation. However, the trends in both average annual values and current changes in the provision of these ecosystem services vary among cultivars. Similar to the trends observed in stem wood accumulation, the average annual volumes of ecosystem services for the poplar cultivar ‘Strilopodibna’ declined at a significantly lower rate than those of ‘Druzhba’, ‘Canadian-Balsamic’, and ‘Tronko’. At the same time, the current change in ecosystem service provision for ‘Strilopodibna’ at ages 9 and 15 remained positive and relatively high, whereas for the other cultivars, it was low and often negative. Based on these findings, the results of the study suggest that the optimal maturity age of the analyzed poplar cultivars, based on their maximum efficiency in ecosystem service generation, is less than 7 years.