Biological age from the viewpoint of the thermodynamic theory of ecological systems

Not all ecosystems are in a steady-state or approaching it. Some of them merely pass through the life-cycle stages. The best example is the forest ecosystems formed by even-aged forest stands, where ecosystem properties and functions are related to the stand age. The relationship is not strict, however, and so the stand age is not a general measure of ecosystem state. We propose and theoretically justify a thermodynamic measure for ecosystem state, which is named here as ecosystem biological age and defined as the period of time that some reference ecosystem needs to accumulate the same amount of exergy as the ecosystem under concern. The use of the concept is illustrated by analyzing the 30-year observations of larch stands growth.