Development of generic crop models for simulation of multi-species plant communities in mown grasslands

Plant diversity supports the high aptitude of grassland covers to provide fodder production for animal feedingand contribute to the storage of carbon, while also granting pollination and aesthetics of landscapes. This abilitydepends on the management intensity of the grassland system, physical constraints and climatic characteristics.Most of current grassland models simulating the impact of weather conditions, soil fertility and the intensity ofuse of grassland systems (by grazing and/or mowing) on fodder production and carbon-nitrogenfluxes inheriteco-physiological and biophysical details from crop models without considering explicitly temporal changes intaxonomic and functional composition. The dynamic grassland model CoSMo (COmmunity Simulation MOdel)includes a set of rules to simulate explicitly seasonal changes in species composition of managed grasslandsunder various soil, climate and management drivers, and it is consistent with the degree of complexity of themost generic crop simulators. The incorporation of CoSMo functionalities into the standalone crop simulatorsCropSyst and WOFOST is proposed as a way to: (i) reduce the uncertainty in estimations of harvested above-ground biomass (AGB) and (ii) simulate dynamically the relative abundance of species (for respectively thewhole community and individual species). Considering three mixtures of grassland species (with increasingcomplexity from Mix 1 to Mix 3) in a mown hay meadow in central Italy (Massa Marittima, 43° 03′N, 10° 53′E,380 m a.s.l.), we show that CoSMo overall improved the model ability to reproduce observed AGB in Mix 1 and 2(e.g. with CropSyst in Mix 2 relative root mean square error [RRMSE] lowered from 35.01 to 25.27%) while themodel performance for Mix 3 appeared as not unambiguously linked to considering plant diversity. An assess-ment of the relative abundance estimates for the whole community indicates 30% <RRMSE< 40% with bothCoSMo-coupled CropSyst and WOFOST in Mix 1 and Mix 2, while it increases up to∼60% in Mix 3. Theconsequences of explicitly accounting for plant diversity for simulated grassland outputs depend on the con-ditions evaluated, which require further studies. However, our results suggest that grassland modelling omittingplant diversity dynamics are likely over- or underestimating harvested biomass of the plant community, thusbiasing projections of future fodder production and estimates of animal feed supplies. This work proves for thefirst time that CoSMo can support the simulation of grassland systems beyond its theoretical framework