Extractives in Douglas firs (Pseudotsuga menziesii (Mirb.) Franco) from three sites in south-west Germany and potential opportunities for valorization

Owing to favorable wood properties and its resilience to the effects of climate change, Douglas fir (Pseudotsuga menziesii) is a promising tree species in Central Europe. Its wood and bark extractives could also serve as feedstock for the production of bio-based materials and platform chemicals. In this study, sapwood, heartwood, knotwood and bark extractives of Douglas firs originating from three differently aged stands in south-west Germany were investigated. Two different extraction methods with organic solvents were compared: a mixture of cyclohexane/ethanol and a successive method using petroleum ether, acetone and methanol. Extraction yields obtained with the successive method were higher, however one-step extraction was very efficient considering the number of samples that could be extracted and is therefore useful for a fast screening. At all sites, extract yields from sapwood, heartwood and bark were highest close to the tree top, while at the two older sites, an additional maximum was found at 1.3 m height. Knotwood extractives tended to decline with increasing tree height. The most abundant substance with economic importance was taxifolin, yielding up to 13% of dry weight in bark, whereas knotwood contained high amounts of resin acids and the lignan nortrachelogenin. Contrary to other studies, the present study found no evidence of a significant site effect on yield and composition of extracts. Overall, many different compounds for future bio-economic applications were found so that the preferential utilization of extractive-rich bark and crown material could foster an integral valorization of trees, supplementing with existing high grade timber production.