Climatic impacts on managed forests: projecting the future from the past

Forests are one of the most vulnerable ecosystem under the coming climate changeand a growing concern arise about their capacity to maintain ecosystem services suchas production of timber, fiber and energy, climate and hydrological regulations, or soil and biodiversity protection. Climate effects are significant not only at a short timescale, but also on the temporal horizon of a forest life cycle, e.g. through continuous shifts in atmospheric CO2 concentration, air temperature and precipitation regimes induced by the enhanced greenhouse effect. This will affect not only the functioning of forests in situ but also the range and geographical distribution of forest trees pecies and therefore the spatial distribution of ecosystem services and production across countries and continents. The long term sustainable management of European forests must account for thesedynamic changes and the interactions between climate and forests. Observations of forest functioning growth and distribution for the last decades provide a rich information about forest response to climatic shifts and extreme events and the way management interplays with these impacts. We present in this communication how two modeling approaches for predicting the future of managed forest at country scale might optimize past observations to streng then their likelihood and reduce uncertainty of their projections. In situ observation networks such as flux tower networks (FLUXNET, ICOS), ICP forest network and National Forest Inventories are the main data sources used. The climate niche modeling predicts the potential distribution of forest species in the geographic domain using past observations of climate and water balance and presence/absence of tree species. Results show an expected poleward shift of forest biomes or species due to global warming and water balance changes that may reach several 10s to 100s of km during the 21st century. Similarly, a process based modelcan be calibrated and evaluated using past observations to predict forest functioning as forced by climate scenarios. The energy balance and the carbon and water cycles in the soil-plant-atmosphere system are modeled at an hourly scale and integrated over an annual basis. As one of the main disturbance in the temperate forests,management is integrated through practices such as ploughing, thinning or clearcutting. Long time series of flux measurements in monospecific forest stands are used tocalibrate the model while adjusting parameters. In a second step, models have been run in various ecological conditions and we have compared the outputs to long time series of observed data from forest inventories or monitoring networks to model predictions. Last, we use climate projections derived from RCP scenarios until 2100 at8x8 km grid to force the models. This work is conducted across the French metropolitan area for 3 of the main European forest species: Maritime Pine, common Beech and Douglas-fir. Our results provide an evaluation of the ecosystem services (carbon sequestration, wood supply, water regulation) taking into account climate change. Based on these results we will discuss about the way to manage/optimize these French forests in the future. To enhance cooperation between researchers and stakeholders, a panel of managers and decision makers has been involved to implement various forest management scenarios in the model