Quantifying deforestation and forest degradation with thermal response

Deforestation and forest degradation cause the deterioration of resources and ecosystem services. However, there are still no operational indicators to measure forest status, especially for forest degradation. In the present study, we analysed the thermal response (TRN, calculated by total net radiation divided by daily temperature range) of 163 sites including mature forests, disturbed forests, planted forests, shrublands, grasslands, savanna or woody savanna vegetation and croplands. The regression fit of TRN against latitude differed among vegetation types. Mature forests are important for thermal buffering, and had significantly higher TRN than the disturbed and planted forests. Except for the shrublands, there was a clear boundary between TRNs of the non-forest vegetation (i.e. grasslands and savanna vegetation) and forests. According to the statistical results, we propose to take the TRN of the mature forest as the local optimal TRN (TRNopt), forest with 83% of TRNopt as indicative of significantly disturbed forest, and 73% of TRNopt as the threshold for deforestation that can be used as an early warning point. Our results revealed the difference in thermal response among vegetation types, which emphasized the irreplaceable thermal buffering capacity of mature forests without artificial fertilizer input. The criteria derived by TRN are applicable for assessing forest degradation and can give warnings of deforestation.