Simulating C cycles in forest soils: Including the active role of micro-organisms in the ANAFORE forest model

A soil module was developed to improve on the ecosystem-scale simulations of forest models. The module includes simulations of bacteria, mycorrhizal and non-mycorrhizal fungi. The inclusion of these soil organisms allows for the simulation of several soil biological processes in a more mechanistic way. In this paper the soil module is used in combination with the forest model ANAFORE (ANAlysing Forest Ecosystems) a stand-scale forest model that simulates wood tissue development, carbon (C) and water (H2O) fluxes dynamically from physiological principles. Although the main purpose of this paper is the model description, a showcase run of the new soil model was performed using a Bayesian parameterization procedure for 16 forest sites (pedunculate oak, beech, Scots pine and poplar) on different soils in Belgium. Emphasis was on the soil organic horizons formation. The results show that one single parameter set could be used for the different forests in the study, and yielded reasonably close fits for most sites concerning pH and formation of the humus layer. Although running the Bayesian procedure to obtain good input parameter distributions was time-consuming (several months), runs using the developed parameter set are reasonably fast (days). These results are promising. However, the high uncertainty of both the input and the output of the model indicates that it is mainly useful as an experimental tool, rather than a predictive instrument.