Critical load of atmospheric nitrogen deposition in French forests: modelling soil and vegetation response in a context of climate change

Anthropogenic activities highly contributed to increased nitrogen and sulfur atmospheric emissions since 1880. Nitrogen deposition is known to severely impact ecosystem functioning by infl uencing soil biogeochemistry, nutrient balance, and consequently tree growth, forest health, and biodiversity. Since the 1980s, within the Geneva Convention on Long-Range Transboundary Air Pollution, European countries have joined their efforts to abate atmospheric pollution. The concept of N critical loads was developed to mitigate the impacts of N deposition. Moreover, because climate greatly infl uences soil processes, climate change and atmospheric deposition must be jointly taken into account to assess the evolution of forest ecosystem status over time. The purpose of this study was to predict forest vegetation response to the combined effects of nitrogen atmospheric deposition and climate change by using a dynamic coupled biogeochemical-ecological model (ForSAFE). We ran this model for various climatic and deposition scenarios on several temperate French forest sites, from today to 2100. The outputs of the biogeochemical model were used as inputs to a vegetation table compiling reference ecological parameters for more than 450 species. We present the results of the biogeochemical response, namely the changes in soil parameters, and illustrate the response of the vegetation groups regarding vegetation cover