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. While numerous results have been produced on the associations of species in annual cropping systems, comprehensive assessments of ecological interactions in mixed species FP are lacking. The project will propose innovative alternatives to FP monocultures (mixtures of non-fixing trees with fixing trees or fixing herbaceous species). These techniques should provide a high and sustainable level of wood production with reduced chemical fertilizer applications.They should 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 3 FP schemes on 4 sites selected in France and in the tropics (Brazil, Congo) to cover an appropriate range of ecological conditions, NFS types and silvicultural practices, as well as technical and socio-economic issues that may arise in FP combined with NFS. 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.