Plants appear to produce an excess of leaves, stems and roots beyond what would provide the most efficient harvest of available resources. One way to understand this over-production of tissues is that excess tissue production provides a competitive advantage. Indeed, game theoretic models predict over-production of all tissues compared to non-game theoretic models because they explicitly account for this indirect competitive benefit. Here, I will describe a simple game-theoretic model of plants simultaneously competing to harvest carbon and nitrogen. In the model, a plant’s fitness is influenced by its own leaf, stem and root production, and the tissue production of others which produces a triple tragedy of the commons. The model is extremely simple and can be implemented with just 4 parameters that describe basic physiological processes. The model is parameterized from first principals using physiological rates reported in the literature, and then compared to the FLUXNET and MOD17 data sets of global NPP. We also ask whether the model can predict the distribution of whittaker’s biome types and the physiognomy of the plant functional types found in each biome. Finally we ask whether the model accurately predicts ecosystem responses to resource limitation such as progressive nitrogen limitation.
Results/Conclusions
Given the simplicity of the model, it is remarkably powerful. (1) It accurately predicts total net primary production when compared to both FLUXNET and MOD17 as well as either dataset predicts the other. (2) It also predicts both the absolute and relative allocation to leaf, stem and root tissue pools in the FLUXNET data. (3) When we compare the output to the global distribution of Whittaker’s biome types and the plant physiognomy found within each biome, the model also seems to predict these from first principals. (4) Finally, the model accurately forecasts ecosystem responses to nitrogen or carbon fertilization. This is both the simplest and most accurately vegetation model that we are aware of. Not only does it accurately predict global NPP but the game theoretic approach removes the need to define allocation or vegetation type a priori but instead lets these emerge from the model as evolutionarily stable strategies. We expect this model to be the starting point for new models of vegetation dynamics.