The maximum exergy dissipation theory (MEDT) states that ecosystems tend to gain more solar radiation, while lowering their surface temperature as they grow and develop. The theory could provide an early warning of rapid evaluation of ecosystem degradation. However, it remains unclear whether ecosystem thermal characteristics change consistently with maturation or recovery across biomes and climate zones.

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences used the radiation balance of ecosystems to test whether ecosystems tend to gain more radiation while becoming cooler during maturation or recovery. They also wanted to identify an appropriate indicator to warn of or evaluate ecosystem degradation.

The researchers selected 39 sites comprising 12 chronosequences distributed in tropical, subtropical, Mediterranean, semi-arid, humid continental, and subarctic climate zones from the global FLUXNET database.

They used air temperature at the canopy level (Ta) to represent the surface temperature of the ecosystem, and the maximum daily Ta (Tmax) to compare the surface temperature difference among the sites.

They calculated the energy gain of the ecosystem by dividing the net radiation by the global radiation (Rn/Rg). They analyzed the surface temperature trends with ecosystem natural development by using the maximum daily temperature above the canopy and the thermal response number (TRN).

They found that the maximum daily air temperature at the canopy level decreased, energy gain, net radiation, and thermal response number increased with vegetation growth, succession, and recovery.

The results support the hypothesis that terrestrial ecosystems tend to gain more solar radiation, while maintaining lower and more stable surface temperature, during their natural development.

The study empirically verified the MEDT across multiple chronosequences in different climate zones.

The study entitled “The Cooling Trend of Canopy Temperature During the Maturation, Succession, and Recovery of Ecosystems” has been published online in Ecosystems.