Poplar clones reach a big advantage over other forest tree species in the production of large amounts of above-ground biomass in a relatively short time. To increase the efficiency of production during their short life cycle, it is necessary to optimize age of their felling maturity. It should be carried out in the stands age when its average production is highest. Mathematical models of yield tables were used to derive this production. Above-ground biomass production was expressed in natural units, volume (m³ ha⁻¹) and the capacity of calorific value (GJ ha⁻¹), but also in financial yield (€ ha⁻¹) from the sale of timber assortments including energy chips from smallwood. In terms of financial yield, Robusta stands are mature between 23 and 35 years and I-214 stands between 18 and 32 years. Main financial yield per year, on average 200–1900 € ha⁻¹, is expected from the production of assortments designed for classic industrial processing. Its increase by 50 to 100 € ha⁻¹ is expected to be achieved by supplemental smallwood processing to energy chips. In terms of volume production and capacity of combustion heat, stands are mature about 5–7 years earlier.