One decade of monitoring the consequences of different forest management alternatives on ecosystem functioning in young plantations | Une décennie de monitoring des conséquences de différentes sylvicultures sur le fonctionnement des écosystèmes dans de jeunes plantations

The global demand for wood biomass is increasing, therefore it is necessary to develop forest management alternatives that can, simultaneously, produce large amounts of biomass and maintain ecosystem functions and services in a sustainable way. However, assessing the consequences of silviculture is challenging, as forest ecosystems function slowly over long periods of time. Therefore, in this study, an experimental platform was set up to monitor the long-term effects of several forest management alternatives (FMA) on ecosystem functioning in a pine forest in a temperate region characterised by oligotrophic conditions. In practice, we monitored three contrasting FMA over a decade: (i) wood biomass production (WBP), designed using an approach of very intense forestry (high stand density; seed lot of pines selected to growth fast), (ii) combined objective management (COM; low stand density), aimed at improving pine growth by alleviating any competition by spontaneous vegetation, and (iii) nutrient management (NuM; medium stand density), designed to improve tree nutrition using N-fixers in the stand furrows. Overall, although FMA showed contrasting stand growth and structures, they had modest effects on forest biogeochemistry over a decade of monitoring: FMA showed similar trends regarding atmospheric deposition, soil solution chemistry and water table-ditch chemistry. The main difference observed was a more important role of dissolved organic matter in NuM biogeochemical functioning. Conversely to their effects on biogeochemistry, the FMA appeared to influence the biophysical properties of stands. The WBP management (with high stand density) was shown to be shadier, cooler and wetter than the other FMA. This trend was fairly clear during the summer periods although differences were observed all year-long. An important result regarding biophysical effects was that, in addition to being observed in the topsoil layers, they were also evident in deeper soil layers and in the water table. All in all, our results indicated that contrasting FMA have tended to influence the ecosystem functioning, in particular its biophysical component, but showed no early sign of unsustainable biogeochemical functioning. Nonetheless, this latter result should be confirmed in the long-term through further monitoring.