The experimental data used for testing the applicability of the thermodynamic equations presented in the theoretical section were obtained from an ecological restoration project implemented at a manganese tailing site. Restoration of the plant community was shown to be an irreversible process characterized by spontaneous increases in its total biomass CT and total number of plant species N associated with increases in its enthalpy H, Gibbs free energy G and entropy S. Species enrichment was the cause for the decease in mass ratio xi (biomass of a species Ci divided by CT) and biomass growth potential μi (the partial derivative of Gi with respect to Ci). The increase in s/CT (s denoting the ratio of S to gas constant R) associated with decrease in f/CT (f denoting the ratio of G to RT) with increasing N confirmed that the restored plant community possessed natural trends towards increase in its species richness and evenness. The observed trends gave support to use of the thermodynamic functions for describing the productivity-biodiversity relationship. The present analysis did not fully prove the use of the Shannon form of information entropy as a biodiversity index for the investigated plant communities. Because of the presence of significant differences in individuals among species, the biodiversity of the plant community could not be uniquely determined by its individual numbers. In comparison, the entropy factor s was shown to be a suitable biodiversity index. The fact that N is the key factor that determines the changes in s/CT and f/CT makes △N > 0 a useful index for determining the direction of spontaneous changes for all open systems with continuous input of matter and energy. As a measure of disorder, s can be generally applied as a diversity index for all systems involving transformations of matter and energy.