Forest ecosystems are undergoing unprecedented changes in environmental conditions due to global change impacts. Modification of global biogeochemical cycles of carbon and nitrogen, and the subsequent climate change are affecting forest functions at different scales, from physiology and growth of individual trees to cycling of nutrients. This review summarizes the present knowledge regarding the impact of global change on forest functioning not only with respect to climate change, which is the focus of most studies, but also the influence of altered nitrogen cycle and the interactions among them. The carbon dioxide (CO₂) fertilization effect on tree growth is expected to be constrained by nutrient imbalances resulting from high N deposition rates and the counteractive effect of increasing water deficit, which interact in a complex way. At the community level, responses to global change are modified by species interactions that may lead to competition for resources and/or relaxation due to facilitation and resource partitioning processes. Thus, some species mixtures can be more resistant to drought than their respective pure forests, albeit it depends on environmental conditions and species’ functional traits. Climate change and nitrogen deposition have additional impacts on litterfall dynamics, and subsequent decomposition and nutrient mineralization processes. Elemental ratios (i.e., stoichiometry) are associated with important ecosystem traits, including trees’ adaptability to stress or decomposition rates. As stoichiometry of different ecosystem components are also influenced by global change, nutrient cycling in forests will be altered too. Therefore, a re-assessment of traditional forest management is needed in order to cope with global change. Proposed silvicultural systems emphasize the key role of diversity to assure multiple ecosystem services, and special attention has been paid to mixed-species forests. Finally, a summary of the patterns and underlying mechanisms governing the relationships between diversity and different ecosystems functions, such as productivity and stability, is provided.

Rear‐edge populations at the xeric distribution limit of tree species are particularly vulnerable to forest dieback triggered by drought. This is the case of silver fir (Abies alba) forests located in Southwestern Europe. While silver fir drought‐induced dieback patterns have been previously explored, information on the role played by nutritional impairment is lacking despite its potential interactions with tree carbon‐water balances. We performed a comparative analysis of radial growth, intrinsic water‐use efficiency (iWUE), oxygen isotopes (δ¹⁸O) and nutrient concentrations in leaves of declining (DD) and non‐declining (ND) trees in silver fir in four forests in the Spanish Pyrenees. We also evaluated the relationships among dieback predisposition, intraspecific trait variation (wood density and leaf traits) and rhizosphere soil physical–chemical properties. The onset of growth decline in DD trees occurred more than two decades ago, and they subsequently showed low growth resilience against droughts. The DD trees presented consistently lower foliar concentrations of nutrients such as P, K, Cu and Ni than ND trees. The strong effects of foliar nutrient status on growth resilience indices support the key role played by mineral nutrition in tree functioning and growth before, during and after drought. In contrast, variability in wood density and leaf morphological traits, as well as soil properties, showed weak relationships with tree nutritional status and drought performance. At the low elevation, warmer sites, DD trees showed stronger climate–growth relationships and lower δ¹⁸O than ND trees. The uncoupling between iWUE and δ¹⁸O, together with the positive correlations between P and K leaf concentrations and δ¹⁸O, point to deeper soil/bedrock water sources and vertical decoupling between nutrient and water uptake in DD trees. This study provides novel insights into the mechanisms driving silver fir dieback and highlights the need to incorporate tree nutrition into forest dieback studies.