Aspen for short rotation coppice plantations on agricultural sites in Germany: Effects of spacing and rotation time on growth and biomass production of aspen progenies

The suitability of agricultural sites for the production of woody biomass using fast-growing trees in short-rotation coppice plantations is being investigated in a joint multi-discipline project. The basis of this project are two trial plantations, one in Bavaria (south Germany) and the other in Hesse (central Germany). At the trial plantation in Bavaria (Abbachhof), six aspen progenies were planted in 1983 and tested for their suitability in different short-rotation periods (5 and 10 years) and three different spacings. At the other location in Hesse (Canstein), 14 aspen progenies were planted in 1986 and tested in a 10-year rotation period at one spacing. The progenies tested resulted from cross-pollinations of selected trees of European (Populus tremula L.) and American aspen (P. tremuloides Michx.). The trials show that hybrid aspen have a higher biomass production in short-rotations than progenies from European or American aspen. This is due to a lower mortality rate as well as to a higher growth rate. Even on sites low in nutrients and only average water availability hybrid aspen are capable of producing biomass on an average of 100 t/ha (wood and bark including branches, absolutely dry) within a 10-year rotation period. The results show that the harvesting should be more than 10 years in order to achieve a maximum average biomass-production per year.