Chemical products from temperate forest tree species—Developing strategies for exploitation

Forest trees are integral to the landscape and rural economy. Unfortunately, the economic returns from timber production have declined significantly across Europe. Only 25% of felled wood is converted to timber, the remaining material is a rich composite of primary and secondary metabolites and plant fibres, a relatively unexplored and unexploited resource for potentially novel products that could compliment revenue from traditional market outlets. Wood from temperate forest trees has traditionally been used as a source of tannins, terpenes, rosins and aromatic phenolic compounds. Existing information on such chemical groups, and other secondary metabolites was collated for a range of temperate forest tree species including, alder (Alnus glutinosa L. Gaertn.), ash (Fraxinus excelsior L.), aspen (Populus tremula L.), beech (Fagus sylvatica L.), birch (Betula pendula Roth., Betula pubescens Ehrh.), cherry (Prunus avium L.), Corsican pine (Pinus nigra Arnold), Douglas fir (Pseudotsuga menziesii Mirib. Franco), larch (Larix deciduas Mill., Larix kaempferi Sarg.), oak (Quercus robur L., Quercus petraea Mattuschka, Liebl), poplar (Populus nigra L., Populus gileadensis Rouleau, Populus alba L., Populus canescens Ait. Sm.), Scots pine (Pinus sylvestris L.), sitka spruce (Picea sitchensis Bong. Carr.) and willow (Salix alba L., Salix fragilis L.).Over 37,000 records were extracted from phytochemical databases, research papers, conference proceedings, books, unpublished reports and company literature, covering identified metabolites, the tissues from which they were extracted (e.g., bark, leaves, heartwood, roots), reported yields, properties and hazards. Very little data exists on the yield or variability of individual metabolites limiting the ability to assess economic potential. The information sourced is collated in a database, available to view at http://tree-chemicals.csl.gov.uk.Traditional and new markets for exploitation of tree metabolites are reviewed along with possible methods of extraction. Computer-aided Quantitative-Structure Activity Relationship Modelling (QSAR) augmented the search for novel applications for the tree metabolites. By this method, monoterpenes with useful anti-microbial properties were identified. Application of green chemical technologies also show promise in adding value to tree metabolites including the modification of cellulose and the benign extraction of valuable chemical products. Opportunities for possible future routes of exploitation of wood biomass are presented and discussed.