## 1 Introduction
### Existing Forest Ecosystem Model Intercomparison Projects  
Existing forest model intercomparison projects, or MIPs, in Europe include the stand-level Intersectoral Impact MIP (ISMIP) regional forests sector [51] and the landscape-level Comparison of Forest Landscape Models (CoFoLaMo) [52] through ISMIP, both conducted under the European Union Cooperation on Science and Technology (COST) Action FP1304 \"Towards robust projections of European forests under climate change\" (PROFOUND). Previous MIP efforts in the United States are limited and include the Throughfall Displacement Experiment (TDE) Ecosystem MIP at Walker Branch Watershed in Oak Ridge, Tennessee [53; 54]. The TDE MIP involved a large-scale manipulation experiment to assess ecosystem responses to changes in precipitation, utilizing a total of 13 models. The MIP included an array of monthly, daily, and hourly temporal resolution models. Notable models compared include PnET-II [55], SPA [56], Biome-BGC [57], LINKAGES [58], and MAESTRO/MAESTRA [59], in addition to nine other models. Perhaps unsurprisingly, they found that no single model was ideal for predicting a variety of variables while there was substantial disagreement between models in the C response of vegetation to soil water changes. They also found that more mechanistic models operating at shorter temporal resolution generally showed higher fitness [54]. While the TDE MIP provided a thorough model intercomparison using a variety of model structures, it was limited to a single location and was completed nearly two decades ago. ISMIP is a protocol that provides a framework for projecting the impacts of climate change across different sectors. The recent ISMIP2 biome sector MIP involved the following simulation models: CARAIB [60], DLEM [61], JULES [62; 63], LPJ-GUESS [64], LPJmL [65], ORCHIDEE [66], VEGAS [67], and VISIT [68]. These models were used to simulate carbon cycling in terrestrial ecosystem in response to climate change and increased atmospheric CO\({}_{2}\)[69]. Shared forcing data was provided at daily temporal and 0.5\({}^{\circ}\) spatial resolution. The ISMIP2 simulation protocol called for model spin-up followed by a transient run forced by historical climate, CO\({}_{2}\) concentration, and land-use [69; 70]. ISMIP2 also involved a regional forests sector, the ISMIP2/PROFOUND model intercomparison, which included the following models: 3D-CMCC FEM [71; 72], 3D-CMCC-CNR-BGC [73], 3-PG [33], 4C or FORESEE [74], ANAFORE [75], BASFOR [76], CARAIB [60], ED2 [43; 44], ForClim [20], FORMIND [77], GO+ [78], GOTILWA+ [79], Landscape-DNDC [80], LPJ-GUESS [64], PnET-BGC [81], and PRELES [82]. ISMIP2/PROFOUND resulted in the release of a database of harmonized data for model intercomparisons, as well as a wrapper library in the R language for statistical computing [83], yet to be released at the time of this writing. For the ISMIP regional forest model intercomparison, sites were selected in COST Action FP1304 PROFOUND that provide simplified forest model initialization. Modeling experiments mostly encompassed managed forests. Long time-series data from forest inventories and FLUXNET sites were used in model intercomparisons. Meanwhile, CoFoLaMo involved a comparison of the following forest ecosystem models through the ISMIP framework [52]: LandClim [84], ForHyCS [85], TreeMig [86], LANDIS-II [87], and iLand [50]. Rather than being driven by climate data at 0.5\({}^{\circ}\) spatial resolution, temperature and precipitation drivers were downscaled to 100 m resolution in CoFoLaMo. Forest models were compared with respect to their scales, processes, interactions, drivers, disturbances, uncertainties, and implementation details such as data requirements. For model spin-up, the models used observed climate data hindcast to 1600 A.D., while model forecasts used Representative Concentration Pathways (RCPs) from ISMIP [52]. Given extensive model intercomparison efforts currently underway in Europe, the question remains, is a forest biogeochemistry MIP necessary for North America?