Impact of Increased Genotype or Species Diversity in Short Rotation Coppice on Biomass Production and Wood Characteristics

Short rotation coppice (SRC) plantations are predominantly established as monocultures. Reasons include simplicity and thus efficiency in planting, homogeneous growth, and a desire to maximize yields by selecting top-performing species. However, pests and disease outbreaks generally cause much greater damage to monocultures than to mixed plantations, thus affecting yields as well as other ecosystem services. Mixed SRC with varying genotypes or even species have the potential to positively affect biodiversity and ecosystem services, however, little is known about the quantity and quality of woody biomass from mixed SRC in respect to its use for energy generation. Therefore, we tested how volume, calorific value, and ash content of woody biomass are influenced by (1) diversity in genotypes in a Salix SRC, and (2) diversity of species in a Salix, Robinia, Paulownia, and Populus SRC. Results show that increasing the number of genotypes or species in a SRC plantation does not negatively affect woody biomass, calorific value, or ash content of wood chips. On average, the plots with mixed genotypes or tree species produced more biomass compared with monocultures of the component species. We found evidence of overyielding in mixtures of poplar and robinia. Our findings are relevant for managers planning new SRC plantations and indicated that mixtures of specific tree species or genotypes should be considered. Therefore, we argue that high-diversity SRC plantations represent a valuable alternative to conventional SRC for sustainable bioenergy production.