Dynamics of biomass production in a poplar coppice culture over three rotations (11 years)

Short rotation coppice culture systems are characterized by a high stool and shoot density, and by rotation durations between 2 and 3 years for species showing an extremely fast growth such as poplar. With the objective to study the long-term biomass production evolution and dynamic of such systems, a high-density plantation with 17 poplar (Populus) clones belonging to six parentages was established in April 1996 and coppiced in December 1996, January 2001, and February 2004. At the end of each growing season, stool survival, shoot diameter, and the number of shoots per stool were measured. Biomass production was estimated directly by harvesting a number of shoots or indirectly via allometric power equations. Stool survival rates differed among parentages and from year to year irrespective of number of rotations; the highest rates were for P. nigra and the lowest rates were for P. deltoides x P. nigra and P. deltoides x P. trichocarpa parentages. In the second and third rotations, the P. trichocarpa x P. deltoides hybrids showed very high mortality rates. The number of shoots per stool varied among rotations and parentages, and shoot elimination was parentage specific. The number of shoots per stool increased with increasing rotation number, while they decreased from year to year within each rotation. A single general allometric equation linking shoot diameter to shoot biomass could be used to estimate biomass production for most years and most clones. Exceptions were found for the year 2001 and for clone Hazendans. Biomass production differed among parentages and among rotations. The different parentages also differed in their strategy of biomass accumulation. Although P. nigra had the highest biomass production over 11 years, the parentage ranking of biomass production shifted over rotations. The P. trichocarpa x P. deltoides hybrids showed high biomass production in the first rotation, but low in the second and third rotations. Biomass production increased from year to year within one rotation, while it decreased with rotation number. Among the parentages examined, P. nigra and P. trichocarpa were the best performing ones and the best adapted to the multiple coppice rotations.