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Producción Científica, Adapting forests to climate change is a critical issue for forest management. It requires an understanding of climate effects on forest systems and the ability to forecast how these effects may change over time. We used Spanish Second National Forest Inventory data and the SIMANFOR platform to simulate the evolution of CO2 stock (CO2 Mg · ha−1) and accumulation rates (CO2 Mg · ha−1 · year−1) for the 2000–2100 period in pure and mixed stands managed under different Shared Socioeconomic Pathways (SSPs) in Spain. We hypothesized that (1) the more optimistic climate scenarios (SSP1 > > SSP5) would have higher CO2 stock and accumulation rates; (2) mixed stands would have higher CO2 stock and accumulation rates than pure stands; and (3) the behavior of both variables would vary based on forest composition (conifer–conifer vs. conifer–broadleaf). We focused on Pinus sylvestris L., and its main mixtures with Pinus nigra, Pinus pinaster, Fagus sylvatica and Quercus pyrenaica. The SSP scenarios had correlating CO2 stock values in which SSP1 > SSP2 > SSP3 > SSP5, ranging from the most optimistic (SSP1) to the most pessimistic (SSP5). Though pure stands had higher CO2 stock at the beginning, differences with regard to mixed stands were drastically reduced at the end of the simulation period. We also found an increase in the aboveground CO2 proportion compared to belowground in conifer–broadleaf mixtures, while the opposite trend occurred in conifer–conifer mixtures. Overall CO2 accumulation rates decreased significantly from the beginning to the end of the simulation period, but our results indicated that this decline would be less drastic in mixed stands than in pure ones. At the end of the simulation period, CO2 accumulation rates were higher in mixed stands than in pure stands for all mixtures, fractions (aboveground and belowground) and SSPs. Knowing the evolution of mixed forests in different climate scenarios is relevant for developing useful silvicultural guidelines in the Mediterranean region and optimizing forestry adaptation strategies. Better understanding can also inform the design of management measures for transitioning from pure stands to more resource efficient, resistant and resilient mixed stands, in efforts to reduce forest vulnerability in the face of climate change. This work highlights the importance and benefits of mixed stands in terms of CO2 accumulation, stand productivity and species diversity., Ministerio de Economía y Competitividad (proyecto de investigación de Doctorado Industrial - [Beca DI-15–07722]), Programa Torres Quevedo (Beca PTQ-12–05409)., Publicación en abierto financiada por el Consorcio de Bibliotecas Universitarias de Castilla y León (BUCLE), con cargo al Programa Operativo 2014ES16RFOP009 FEDER 2014-2020 DE CASTILLA Y LEÓN, Actuación:20007-CL - Apoyo Consorcio BUCLE

International audience; Coarse woody debris (CWD) plays a substantial role in several ecological processes in forest ecosystems, providing a habitat for many organisms and participating in biogeochemical fluxes. Understanding CWD dynamics is important to classify adequate density, size and amount into different decay classes and to make decisions that include biodiversity and the carbon budget in practical forestry.* A two-step model has been developed to quantify CWD in Pinus spp. plantations in Northern Spain. The two-step approach was composed of a logistic model to predict the probability of CWD occurrence and linear models to quantify the two components considered, basal area of snags and volume of logs.* Site conditions, and climatic and stand variables were included in the models as independent variables. Good performance of the two-step model (R2snag = 39.9%, R2log = 62.8%) was observed.* Modelling CWD is a useful tool for simulating future scenarios in the current context of climate change. Models inform stakeholders properly about defining the best silvicultural options for the distribution of CWD under sustainable forest management.