How to apply thermodynamic optimality principles to co-evolved soil-vegetation systems

Optimality in the co-evolved soil-vegetation system has been a highly debated topic by researchers for over a century. Widely accepted conceptual models in the biogeosciences such as Jenny's model of soil development and Holdridge life zones have hypothesised the co-evolution of soils, vegetation and climate, highlighting systematic functional patterns across climate gradients. Modelling of these systems has significant complexity due to the feedbacks between the abiotic and biotic sub-systems and the variance in temporal and spatial scales that they operate. This often results in the under-representation of soil development and its constraint on system evolution, dynamics and fluxes. Thermodynamic optimality principles (TOP) in the form of maximum power and entropy production have been proposed as a modelling approach to explain natural system trajectories. However, to date there has been minimal work utilising these approaches and highlighting its benefits and limitations in modelling the co-evolved soil-vegetation system. We believe this is in part due to three main issues which will be addressed in this work: 1) The lack of a clear case being made for why TOP is an applicable approach, 2) Inconsistency in the methodology surrounding the application of TOP when modelling energy, water and mass dynamics, and, 3) The spatial and temporal scales that adhere to TOP, capturing gradients, feedbacks and boundaries has not been critically evaluated for the soil-vegetation system. By addressing these current knowledge gaps within the literature, we clarify the benefits and limitations of utilising TOP in the modelling of these complex systems, creating a path forward for modelling trajectories of these systems within a thermodynamic framework which can be critically assessed and compared to real world observations.