Yield development of poplar, willow, aspen and black locust in two to six years rotation lengths for a total of 15 to 24 years in six different short rotation coppice long term experimental sites

The dynamics of current (CAI) and mean annual increment (MAI) of short rotation coppice (SRC) plantation gives information about the total period of use of such a cultivation system. However, SRC-yield investigations over a long period of time are rare. Therefore, practical implications regarding yield development and profitability or carbon-sink performance of coppice systems lack information base. In Germany, several SRC experiments were established in the 1990s with varying tree species and clones and observed for longer periods of time. This study presents results of the development of CAI and MAI of the Thuringian experimental sites “Dornburg”, “Langenwetzendorf” (three and five years rotation) and “Bad Salzungen” (three years rotation) with an observation period of 21 and 18 years each (“Bad Salzungen”); of the Saxonian experimental site “Kalkreuth” (three years rotation) at an observation duration of 15 years; of the Brandenburgian experimental site “Potsdam Bornim” (two and four years rotation) at an observation duration of 24 years as well as of the Mecklenburg Pomeranian experimental site "Gülzow" (three and six years rotation) at an observation duration of also 24 years. At every experimental site the plots were fully randomized and had three to four repetitions per investigated species or clone. Overall the biomass performance of the poplar clones averaged better than willow, aspen, and black locust. In particular, the clones of the “Max family” (P. maximowiczii x P. trichocarpa) showed top performances that significantly surpassed pure balsam poplar clones, especially with increasing root age. Individual willow clones - Zieverich (s. viminalis) and Tora (S. schwerinii x S. viminalis) - showed in single experiments performances equal to the strongest poplar clones. For poplar at sites with low vigor, a decrease in CAI was not observed until after 18 years root age, and first after 21 years at sites with stronger vigor. The MAI decreased only after two subsequent harvests with decreasing CAI. For willow, the decrease in CAI and MAI ocurred one or two rotations sooner than in poplar. The influence of rotation length on biomass performance was dependent of the chosen planting density. Yields were highest at sites with improved water supply. All in all, we observed that under German site conditions short rotation coppices show stable MAI, and therefore productive life, up to 20 to 25 years. We suggest validating these results with actual trials exposed to climate change conditions. (From IPS8 book of abstracts, ISBN-978-86-900741-2-9)