Description and evaluation of the process-based forest model 1 4 C at four European forest sites 2

The process-based model 4C (FORESEE) has been developed over the past twenty years. The 26 objective of this paper is to give a comprehensive description of the main features of 4C and to present an 27 evaluation of the model at four different forest sites across Europe. The evaluation was focused on growth 28 parameters, carbon, water and heat fluxes. The main data source for the evaluation was the PROFOUND 29 database. We applied different statistical metrics of evaluation and compared the inter-annual and inter-monthly 30 variability of observed and simulated carbon and water fluxes. The ability to reproduce forest growth differs 31 from site to site and is best for the pine stand site Peitz. The model’s performance in simulating carbon and water 32 fluxes was very satisfactory on daily and monthly time scales in contrast to the annual time scale. This 33 underlines the conclusion that processes that are either not represented in dependence on on mediumto long34 term dynamic influences such as allocation, or those that are not represented at all but may have a large impact at 35 specific sites – such as the dynamics of non-structural carbohydrates (NSC) and ground vegetation growth – 36 need to be elaborated for general forest growth investigations under climate change. On the other hand, 4C has 37 shown a great potential for improvement since it emphasizes the representation of boundary conditions such as 38 soil temperature at different depths. Therefore, more spatial differentiation of processes such as organ-specific 39 respiration should easily be accomplished. Nonetheless, by using the PROFOUND database we were able to 40 demonstrate the applicability and reliability of 4C. 41 Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-2 Manuscript under review for journal Geosci. Model Dev. Discussion started: 15 January 2019 c © Author(s) 2019. CC BY 4.0 License.