A global increase in the demand for wood products has been observed worldwide during the last decades. This trend is expected to continue in the future as a consequence of population growth. Additionally, the need for wood is augmented by the increasing substitution of fossil energy by wood biomass-based energy to mitigate greenhouse gas emissions. This demand will not be satisfied by natural and naturally regenerated forests: they are threatened by high deforestation rates and forest degradation mainly in the tropics and the costs of wood mobilization in the temperate zones is a concern. Forest plantations (FP) are therefore expected to provide a large part of the global wood supply. Their ability to meet wood demand is limited by competing land uses. Higher stand yields must be obtained on soils that may not necessarily support such intensification especially as nitrogen (N) and phosphorus (P) exportations by biomass removal are generally not offset by fertilization. Therefore, FP sustainability is currently a major concern, particularly with regard to serious long-term N and P deficits. Innovative FP management schemes, and attractive to the stakeholders must be then deployed. The Intens&Fix project will deal with the ecological intensification of FP through the association of N2-fixing species (NFS) with the goal to increase stand production as, in particular, a result of better N and P availability in the soil. These systems hould combine positive environmental impacts while ensuring social-economical improvement of livelihood for smallholders or performances for commercial companies. The project will develop an experimental approach on various and complementary FP with associated NFS, both in France (Juglans sp. and Alnus cordata or herbaceous NFS in Languedoc, Populus sp + Robinia pseudoacacia. in North-Est of France) and in the Tropics (mixed-species plantations of Eucalyptus grandis and Acacia mangium in Brazil and Congo). An integrated biophysical model will be developed for the simulation of mixed species in FP. Outputs of virtual experiments performed with the biophysical model will feed a plantation-level model allowing to assess the economical feasibility and to test decision rules for the management of FP with NFS. Crossing models outputs and a survey of stakeholders’ innovation process concerning the use of NFS will entitle us to assess the potential development of these systems. The approach will be multidisciplinary and involve scientists working in ecophysiology, biogeochemistry, soil science, microbiology, silviculture, socio-economics, and modelling. This project will contribute to the production of innovative results i.e. refined methodological techniques for estimation of N transfer, documentation of mechanisms of competition/ facilitation for N and P bioavailability, model coupling water, N and C functioning adapted to mixed-species forests and practices (species, density…) to manage NFS in FP, and socio-economical assessment of these new management schemes. The results will be valorised through publications in high level scientific journals, as well as in R/D journals and participation to international conferences. More generally the involvement of a top resource partner in farm forestry and agroforestry, the participative approach deployed, and the strong partnership developed with producer organisations in France, Brazil and Congo will warrant a large and efficient dissemination of the Intens&Fix results. From an operational view point, the Intens&Fix project will provide tools of ecological intensification to significantly improve FP management with specific targets in eucalyptus plantations in Congo and Brazil (several millions ha), Very Short Rotation Coppices, and high value timber in agroforestry systems (potential of several millions ha in Europe).

In the current context of climate change and a staggering increase in the world’s population, urgent solutions are required to ensure both ecological integrity and optimal productivity of any agricultural/forested site. The FAO has estimated that more than 10 Mha of the world’s cultivated land suffers from degradation, particularly soil erosion and mass movement on hillslopes; soil loss in turn compromising the quantity of carbon (C) that can be sequestered in the soil. There is also a pressing need to improve non-irrigated agriculture upon which the world's poorest populations depend. Understanding the hydrological interactions between plant roots and the soil profile is thus a priority. Although ecological intensification is currently being studied in many projects worldwide, largely with regard to e.g. production scenarios for increasing yield, the ‘hidden half’ of a plant, i.e. the root system, is still neglected in many studies or is limited to those processes occurring in the upper soil layers. In Ecosfix, we propose to investigate the influence of root structure and function on physical and biological processes, from the soil surface to the deep horizons. This new paradigm will permit us to evaluate the ecosystem services provided by plant root functioning throughout the soil profile, with specific reference to soil erosion, mass movement, C sequestration and hydraulic redistribution. Ecosfix is a highly multidisciplinary project uniting practitioners from a socio-economic context with scientists from (agro)forestry, soil science, ecology, mechanical engineering and hydrology. Beginning with a better quantitative description of the structure and function of roots at different depths within the soil profile, we will seek to define spatial and temporal dynamics of root growth in different complex (agro)forest structures. These forest structures are representative of different types of food and fibre production in a range of climates. Root growth in complex communities has found to increase compared to monocultures, thus having major implications for mixed crops and agroforestry. We will measure root traits with soil depth at the individual and community level within each forest structure examined. As fine roots are major conduits for C into the soil, sequestration is a major service that roots provide. We will determine the fate of root-related C into the soil profile using isotopic chemistry. Monitoring of hydraulic redistribution within the soil profile will be carried out using isotopic tracers and results will provide information concerning hydraulic redistribution by plant roots within a community. By carrying out experiments on soil cohesion and aggregate stability, we will determine the role that roots play in modifying soil structure, and hence erosion and mass movement processes. Through integrated modelling and the analysis of patterns among root system traits and functions, ecosystem services can be assigned to different suites of root traits. The trade-offs between traits and services will be investigated and a set of criteria will be proposed related to site effects. A major milestone of this project is the production of a decision support tool and guidelines for end users. Our research will be performed within the carefully defined socio-economic context of local end-user requirements. The relations between researchers and managers/stakeholders are at the forefront of the work to be carried out and will be facilitated through the participation of a partnering agroforestry association, a NGO and a training/research centre.