Population dynamics in a 6-year old coppice culture of poplar. I. Clonal differences in stool mortality, shoot dynamics and shoot diameter distribution in relation to biomass production

Poplar trees have the capacity to regrow a number of shoots after being coppiced. In April 1996, a high density field trial with 17 different poplar (Populus) clones was established in Boom (Belgium) on a former waste disposal site. At the end of the establishment year (December 1996), all plants were cut back to a height of 5 cm to create a coppice culture. Four years after the first coppicing in January 2001, the stand was cut back again. During 6 years (1996-2001), shoot diameters and number of stools and shoots were assessed every year for all clones. Before the second coppicing, biomass production of all clones was estimated. Significant clonal differences were found in stool mortality, number of shoots per stool and biomass production. After 6 years (December 2001), stool mortality averaged 7-65%. After the first coppicing (1997), the average number of shoots ranged between three and seven shoots per stool; after the second coppicing, the average number of shoots ranged between 8 and 19 shoots per stool. During the 4 years following the first coppicing, shoot density decreased exponentially, leaving mostly one or two dominant shoots per stool by the end of 2000. The other shoots had no significant influence on stool dry mass, since most of the surviving shoots were suppressed and small and made little contribution to total dry mass. The diameter of the dominant shoot(s) was the most important determinant of stool dry mass. Mean annual biomass production ranged from 2 to 11 Mg ha-1