Climatic and biotic factors influencing regional declines and recovery of tropical forest biomass from the 2015/16 El Niño

Abstract:

The 2015/16 El Niño brought severe drought and record-breaking temperature in the tropics. Here, using satellite-based L-band microwave vegetation optical depth, we mapped changes of above-ground biomass (AGB) during the drought and in subsequent years up to 2019. Over more than 60% of drought-affected intact forests, AGB reduced during the drought, except in wet central Amazon where AGB declined one year after. By 2019, only 44% of the AGB-reduced intact forests have fully recovered to the pre-drought level. Using random forest models, we found that AGB losses during the drought were mainly associated with soil water deficit and soil clay content. For the AGB recovery, we found the strong influences of the previous AGB losses and vertical forest canopy structure. Based on canopy structure information derived from Lidar waveform data, we separated forests into two categories: forests with high dominant understory closing the top of the canopy, and forests with low understory. The first category forests tend to have a stronger capacity to recover, compared to the second ones mainly distributed near the intact forest edges. This highlights the importance of forest structure responding to drought when predicting the consequences of future drought stress.