Deforestation and forest degradation are global environmental problems. Deforestation implies the transformation of a forest into another land cover type, whereas degraded forest has lost some of the ability to provide ecosystem services and resources. Both of these processes cause the deterioration of resources and ecosystem services. However, there are still no operational indicators to measure forest status, especially for forest degradation. 

Together with her collaborators, Dr. LIN Hua from Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study aiming to find criteria that can quantitatively distinguish deforestation and forest degradation. They used long-term meteorological data to analyze the thermal response to radiation of different vegetation types. 

The researchers analyzed the thermal response number (TRN, defined as the amount of net radiation required to change one unit of surface temperature; calculated by daily total net radiation divided by daily temperature range) of 163 sites including mature forest, disturbed forest, planted forest, shrubland, grassland, savanna vegetation and cropland. 

They found that the thermal response number (TRN) linearly decreased with increasing latitude, except in grasslands and croplands. TRNs of the mature forests were significantly higher than those of other vegetation types across all latitudes, except for those of shrublands, whose TRN overlapped with those of forest vegetation. TRNs of the grasslands and savannas showed the lowest level. 

There were no significant differences in the slopes of the regression lines of TRN of the mature forests, the disturbed forests against latitude and the lines separating forest and non-forest vegetation. 

Statistical results showed that the average TRN of the disturbed forests was 75% of the optimal TRN and 66% of the optimal TRN was the critical transition point from forest to non-forest at 40° latitude (shrublands excluded).

The researchers therefore recommended using 75% of the local optimal TRN as the baseline for forest disturbance, and 66% as the early warning of deforestation within the absolute latitude from 30° to 55°. 

The results emphasized the irreplaceable thermal buffer capacity of mature forest. TRN is an operational indicator capable of quantifying forest status and applicable for identifying forest degradation and for providing an early warning of incipient deforestation.  It can be regarded as a valuable tool in the effort to protect forests and prevent deforestation. 

The study entitled "Quantifying deforestation and forest degradation with thermal response" has been published online in Science of The Total Environment.