Biomass yield and energy balance of a short-rotation poplar coppice with multiple clones on degraded land during 16 years

Although poplar short-rotation coppice (SRC) systems as an alternative to fossil fuels have been intensively studied, little is known about their biomass potential during several consecutive harvest cycles. For the very first time, this study reports on aboveground biomass yield and energy balance of a 16-year-old poplar SRC with a mixture of 17 pure species and hybrid Populus spp. clones. The plantation established on degraded land in Boom, Belgium, was maintained as a low-energy input system, i.e. no irrigation, no fertilizers and no fungicides were applied. The average dry biomass yield during the fourth rotation was 4.3 ± 3.4 ton ha−1 year−1 across all clones, but the most productive clones yielded up to 10.5 ton ha−1 year−1. After 16 years, stool survival ranged from 6 to 91% among clones. Our results demonstrated the sustained biomass potential and resprouting capacity after a severe leaf rust attack and after several harvests of the studied Populus nigra and Populus trichocarpa clones as opposed to hybrids between Populus deltoides and P. trichocarpa which hardly survived the fourth rotation. These findings suggest that pure species might perform better than hybrids under suboptimal conditions, e.g. on degraded lands, throughout several harvest cycles and/or after leaf rust infestations. Despite the relatively low yields, the investigated system on degraded land had a positive energy balance producing 7.9 times more energy than it consumed from cradle to plant gate.