Contrasting Responses of Land Surface Temperature and Soil Temperature to Forest Expansion During the Dormant Season on the Qinghai-Tibet Plateau

As one of the important ecological responses of ecosystem to global climate change, forest expansion can alter land surface energy budget and local microclimate. Land surface temperature (LST) and soil temperature (ST) indicate the above- and below-ground thermal state, respectively. However, the lack of studies on the relationships between LST and ST changes after forest expansion hinders our understanding of the vegetation-microclimate interactions, especially during the dormant season. We quantified the change of LST ( increment LST) and ST ( increment ST) after forest expansion in the dormant season on the Qinghai-Tibet Plateau (QTP), and then explored their differences and linkages. The results showed that forest expansion significantly decreased LST by 0.75 +/- 0.20 degrees C, while significantly increased ST in three layers (0-7, 7-28, and 28-100 cm) by 0.31 +/- 0.06, 0.29 +/- 0.05, and 0.20 +/- 0.04 degrees C, respectively. The decreased LST was conducive to the preservation of snow, leading to larger snow depth, larger fractional snow cover and more snow cover days in forests than grasslands, which further promoted the increased ST through enhanced thermal insulation. Furthermore, it is suggested that the cooling impact of forest expansion on LST and warming impact on ST would both be stronger at humid sites than at dry sites. These findings will contribute to understand the vegetation-microclimate-snow interactions and the decoupling phenomenon between LST and ST in the dormant season influenced by vegetation change. Forest expansion is happening almost all over the world, altering land surface energy cycle. However, it is unclear that whether the temperature above ground and below ground are changing similarly or divergently. Land surface temperature (LST) and soil temperature (ST) indicate the above- and below-ground thermal state, respectively. In this work, we quantified the change of these two temperatures after forest expansion in the dormant season on the Qinghai-Tibet Plateau, and then explored their relationships. The results showed that forest expansion significantly decreased LST by 0.75 +/- 0.20 degrees C, while significantly increased ST in three layers (0-7, 7-28, and 28-100 cm) by 0.31 +/- 0.06, 0.29 +/- 0.05, and 0.20 +/- 0.04 degrees C, respectively. Cooler land surface was conducive to the preservation of snow, leading to deeper, wider, and longer lasting snow cover in forests than grasslands, which further promoted the warmer soil through enhanced thermal insulation. Furthermore, it is suggested that humid environmental conditions would cause stronger contrasting temperature responses above and below ground after forest expansion. These findings will contribute to understand the temperature decoupling phenomenon influenced by vegetation change. Land surface temperature (LST) and soil temperature (ST) were decoupled after forest expansion in the dormant season The decrease of LST and increase of ST were associated through snow cover change The contrasting temperature responses were more prominent at humid sites than at dry sites