CARTON

Forests play a major role in climate change mitigation. By performing photosynthesis, trees incorporate carbon from atmospheric CO2 into their tissues. Subsequently, dead plant debris (litterfalls, senescent fine roots) enrich the soil with organic carbon. In soils, once stabilised, organic carbon can be sequestered for up millennia. In addition to their carbon sequestration function, forests also play a positive role in the global carbon budget via substitution effects. Indeed, using wood instead of carbon-based fossil fuels, or materials that require a lot of these polluting energies, reduces the net CO2 emissions because the carbon of the wood was previously fixed by trees. However, optimising the carbon sinks role of forests is the subject of intense debates involving scientists and decision-makers: is it better to promote the effects of carbon substitution, or the effects of carbon sequestration? This project aims to solve this dilemma by optimising both biomass production and soil organic C sequestration. In practice, the CARTON project aims to (i) identify the characteristics of trees (notion of "functional traits") that are involved in rapid biomass growth, (ii) identify the functional traits that influence soil organic carbon sequestration, and (iii) evaluate to which extent these two groups of functional traits are compatible within the same tree species. To do this, we will study the functional traits of many species in sites where they were planted at the same time (the so-called "arboretum" sites). The link between growth and functional traits will be evaluated using a meta-analysis carried out at the global scale. The link between soil organic carbon storage and functional traits will be studied in 20 mature arboretums in contrasting contexts, along a European latitudinal gradient. Once these two groups of traits have been identified, we will study their relationships within tree species, using a database of functional traits. In particular, we will investigate what values optimise both growth in biomass and sequestration of organic carbon in soils. The final objective of this project is to indicate some species that optimise both carbon substitution (through a rapid growth in biomass) and carbon sequestration (through an efficient organic carbon storage in soils).