Forests play a crucial role in the global water cycle. However, only a few studies have investigated post-damage radiative forcing of evapotranspiration and its underlying processes in forests.

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences recently investigated the water flux recovery of the forest in the Ailaoshan Mountain National Nature Reserve, a mountainous water catchment area for the Lancang River basin and a subtropical ecological conservation area in SW China.

In 2015, a heavy snowfall happened in the subtropical forest in this area and caused significant damage to the vegetation. The resilience of evapotranspiration and its partitioning in the forest to such events remains highly uncertain.

Researchers focused on how the water fluxes of subtropical forests responded to extreme weather disturbances, and the recovery process over several years after a disaster.

Using eddy covariance data from 2010 to 2019, they assessed the impact of extreme snow disasters on forest water fluxes and their subsequent recovery processes.

They quantified the impact of the disasters on the forest water cycle and tracked the recovery dynamics by comparing changes in parameters such as evapotranspiration, transpiration, evaporation, and canopy conductance before and after the extreme snow disaster event in the Ailaoshan subtropical forest.

Their results showed asynchronous responses of different water flux processes, evaporation and transpiration, to an extreme snow event during the post-damage period in an old-growth subtropical forest in Ailaoshan Mountains.

The leaf area index (LAI) decreased by 49% compared with the pre-disaster level in the snow disaster year, their study found. Severe vegetation damage led to decreases in evapotranspiration, transpiration, evaporation, and canopy conductance by 35%, 36%, 23%, and 33%, respectively, compared with the pre-disaster levels.

Transpiration recovered rapidly in 2016 due to understory vegetation growth, while evaporation and canopy conductance recovered only until 2018. The reduced ET resulted in a strong positive radiative forcing of evapotranspiration, which reduced the forest's evaporative cooling and resilience.

The results suggested that delayed evaporation recovery in subtropical forests helped water storage in the ecosystem to support rapid growth of understory vegetation through transpiration, thus enhancing ecosystem resilience to disturbance.

“Our finding has important implications for understanding the adaptive capacity and stability of forest ecosystems when facing future climate change challenges,” said SONG Qinghai of XTBG, corresponding author of the study.

Results of their study were published in Journal of Hydrology: Regional Studies, entitled “Asynchronous recovery of evaporation and transpiration following extreme snow damage in a subtropical forest”.