Context

Given current energy concerns, governments are committed to reducing the consumption of fossil fuels and expanding the renewable energy market to reduce CO2 emissions and to compensate for the reduction in fossil fuel resources. The use of biomass (from forests, biofuel crops and agricultural by-products) is the main means of achieving this target of expanding the renewable market. This would, therefore, entail increasing the amount of wood harvested: an additional harvest of 10 million m3 was proposed by the French national forest programme. This increased use of wood may lead to more intensive harvesting and a change in forestry practices. One of the sources of forest biomass, still not of commercial value for other wood users, is the slashes and harvesting residues. These constitute a potential resource not currently included in the volumes harvested but removing them from the forest may decrease soil fertility.

Objectives

the objectives of this network to study the effect of exporting harvesting residues on the sustainability of the fertility of soils and their biodiversity. It has been set out to answer the following questions: (i) what are the effects of increased export of forest residues on biogeochemical fluxes and soil biodiversity?; (ii) how resilient are forest ecosystems to more intensive export of biomass?, (iii) what ecosystem functions can be restored by returning the ash?, (iv) is there a point of no return in the equilibrium of the fluxes or a threshold for the microbial richness below which the equilibrium can no longer be restored?

Network description:

three species are considered: beech (Fagus sylvatica L.), pedunculate or sessile oak (Quercus robur L. or Quercus petraea Liebl.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco.). These species constitute a major part of the timber used for woodworking and building in France. Beech and oak are the most concerned by changes in the management of forest residues after the timber has been harvested, whereas Douglas fir has a high potential for plantations specifically for the production of biomass, in addition to current usages. The network includes 6 experimental sites for each tree species, a total of 18 sites, in publicly and privately owned forests with as wide a range of fertility and climatic conditions as possible in lowland sites. At the start of the study, the stands have been chosen to be at the development phase near the maximum growth rate (high needs in nutrients and stands mature enough to provide wood for energy).

Experimental design and monitoring:

Each site is divided into plots with one of four treatments: (i) control (normal forestry practices), (ii) export of harvesting residues only, (iii) export of harvesting residues and all litter, (iv) returning ash to compensate for the export of the harvesting residues. Three replicates have been set up for each treatment, giving a total of 12 plots each of 1600 m2, within each experimental site of 2 hectares (see Akroume et al. 2016 for details). Monitoring of tree growth (aboveground and belowground), stand structure, soil fertility (chemical and physical component) and soil biodiversity (micro-, meso, macro-fauna). Use of the advanced tools of the mobile platform M-POETE (NIR, T-LIDAR, A-LIDAR and multispectral cameras on drones, etc..). For some sites, automatic meteorological stations have been set up, as well as soil moisture monitoring at different depths.

Running multidisciplinary projects on the network:

ANAEE-F (ANR - Infrastructure), RESPIRE (ADEME), INSENSE (ADEME), BRIDGE (Labex ARBRE)

Project investigators

Bernd Zeller (INRA BEF), Emila Akroume (INRA BEF, ONF), Marc Buée (INRA- IaM); Laurent Saint-André (INRA-BEF) – CONTACTS: ZELLER@NANCY.INRA.FR  OR STANDRE@NANCY.INRA.FR

Contributors:

Michaël Aubert (University of Rouen), Lucie Vincenot (University of Rouen), Joseph Levillain (INRA-EEF), Dominique Gérant (INRA-EEF), Cyril Rathgeber (INRA-LERFOB),  Cyril Bach (INRA-IaM), François Elie (University of Rouen), François Maillard (INRA-IaM), Claudine Richter (ONF), Marine Leblanc (UCFF)

Funding:

ONF, LHOIST Society, Parc Régional Morvan