The Cooling Trend of Canopy Temperature During the Maturation, Succession, and Recovery of Ecosystems

The maximum exergy dissipation theory provides a theoretical basis for using surface temperature to measure the status and development of ecosystems, which could provide an early warning of rapid evaluation of ecosystem degradation. In the present study, we used the radiation balance of ecosystems to demonstrate this hypothesis theoretically. Further, we used empirical data to verify whether ecosystems gain more radiation, while lowering their surface temperatures, as they develop naturally. We analyzed 12 chronosequences from the FLUXNET database using meteorological data and heat fluxes. We included age, disturbance, and successional chronosequences across six climate zones. Net radiation (R_n) and the ratio of net radiation to global radiation (R_n/R_g) were used to measure the energy gain of the ecosystems. The maximum daily air temperature above the canopy (T_max) and thermal response number (TRN) were used to analyze the surface temperature trends with ecosystem natural development. The general trends of T_max, TRN, R_n, and R_n/R_g demonstrated that ecosystems become cooler and more stable, yet gain more energy, throughout their natural development. Among the four indicators, TRN showed the most consistent trends and highest sensitivity to ecosystem growth, succession, and recovery. Moreover, TRN was not significantly influenced by precipitation or wind. We propose that TRN can be used to rapidly evaluate or warn of ecosystem disturbance, senescence, and degradation without prior knowledge of species composition, nutrient status, and complex ecosystem processes.