Decadal nitrogen deposition impacts on forest functions and ecosystem services across the Europeanof Alps

Forests provide various ecosystem services (ES), including the delivery of natural resources, the regulation of atmosphere-land surface interactions, and the facilitation of social and cultural activities. However, the acceleration of climate change is increasingly threatening the sustainability of these ES by modifying essential ecological processes via biogeophysical-chemical determinants of critical processes such as fluxes of gases, water, energy, and nutrients. Atmospheric nitrogen deposition is a major air pollutant that affects forest ecosystems through nitrogen cycles. Across the European Alps, though the total nitrogen deposition has steadily decreased since the late 1980s, the present annual deposition remains at medium to high levels (on average 15 kg N/ha), while temperate forests are generally nitrogen-limited. How nitrogen deposition affects forests in the Alps, particularly in the context of reduced nitrogen deposition, is critical for anticipating future forest functions and ES. In addition, the promotion of some essential forest ES is inherently contradicting. For instance, timber production requires massive logs of standing trees, whereas mitigating abiotic disturbances and hazards generally necessitates retaining high biomass and biological diversity. Balancing forest multi-functions is, therefore, integral to ensuring better, more sustainable use of natural resources benefiting our societies in the context of rapid global change. Here, we focus on (i) building a framework to identify and integratively quantify various ES across 6000 Swiss National Forest Inventory plots; (ii) quantifying and comparing the impact of nitrogen deposition on various ES at the stand level since 1990 in a multivariate inference framework while explicitly taking into account potential spatial dependence and confounding factors using [YV1] a stochastics process embedded in the multivariate framework; (iii) quantifying the overall impact of two-decadal nitrogen deposition rates on forest multi-functionalities accounting for the synergies between each ES. Finally, we discuss the potential and conditions for transposing these impacts to other forest ecosystems.