Effect of forest management on future carbon pools and fluxes: A model comparison

Currently, there is a strong demand for estimates of the current and potential future carbon sequestration in forests, the role of management practices, and the temporal duration of biotic carbon sinks. Different models, however, lead to different projections. Model comparisons allow us to assess the range of potential ecosystem responses, and they facilitate the detection of the strengths and weaknesses of particular models. In this study, the empirical, individual-based forest models MASSIMO, the semi-empirical individual-based forest models SILVA – both combined with the soil model YASSO – and the process-based, biogeochemical model Biome-BGC were used to assess the above- and belowground carbon pools and net fluxes of several forested regions in Switzerland for the next 100 years under four different management scenarios: (1) the current harvest amounts were used, (2) harvest was intensified by reducing the amount of large tree dimensions, (3) harvest was reduced to a minimum by only maintaining the protection function in mountain forests and avoiding pests and diseases, and (4) harvest was adjusted to achieve maximum sustainable growth. The results show that the three models projected similar patterns of net carbon fluxes. The models estimated that in the absence of large-scale disturbances the forest biomass and soil carbon can be increased, particularly under scenario 2, and therefore, forests can be used as carbon sinks. These sinks were estimated to last for a maximum of 100 years. Differences between the management scenarios depend on the time period considered: either net carbon fluxes are maximized at a short term (30–40 years) or at a longer term (100 years or more). In contrast to the similar carbon fluxes, some carbon pools projected by the models differed strongly. These differences in model behaviour can be attributed to model-specific responses to the strongly heterogeneous Swiss climate conditions and to different model assumptions. To find the optimum strategy in terms of not only maximizing carbon sequestration but climate protection, it is essential to account for wood-products and particularly substitution of fossil fuel in the model simulations.