Increasing the biomass production level of dedicated or semi-dedicated woody crops. Mains lessons learned from the SYLVABIOM project

For three species (poplar, black locust and willow) cultivated as short or very short rotation coppices (SRC/ VSRC), the project relied on monitoring growth and efficiency with which trees use water and nitrogen in a network of four experimental sites, located in contrasting stations. The relevance of DNA methylation levels as an early marker of the level of productivity was also evaluated. For short-rotation plantations (SRP), the project was based on the collection of growth and biomass data in experimental networks, to build compartmented biomass yield tables (trunk, bark, branches and leaves) for forest species for which the literature is scarce. Significant differences appear, both in SRC and VSRC, between the three species, and between intraspecific genotypes for biomass production, its phenology, architecture, leaf structure, and resource use efficiency. The pedo-climatic conditions and the planting density modulated the complex relationships between these traits. Measurement of apex or leaf DNA methylation rate may be a good predictor for the growth potential in poplar. Mean annual biomass production ranging from 7 to 13 dry tons/ha can be expected at age 20 years with fast-growing conifers grown in SRP on site types other than those used for SRC and VSRC. Moreover, very significant genetic gains on biomass production in SRP are also offered by selection of efficient genotypes. (authors)