Drought diminishes aboveground biomass accumulation rate during secondary succession in a tropical forest on Hainan Island, China

Abstract

With rising temperatures and altered annual precipitation patterns, climatic factors are likely to play an increasingly important role in controlling the biomass accumulation rate of tropical secondary forests. However, the relative importance of biotic and abiotic factors and demographic progresses (growth, mortality, and recruitment) driving biomass dynamics in these ecosystems remain largely unclear, especially in tropical Asia. We explored aboveground biomass (AGB) dynamics in old-growth and secondary tropical forests on Hainan Island, China, across two consecutive five-year intervals (2010–2020). Drought frequency was higher in the second vegetation census interval. We studied the relationships of AGB and its three demographic components with drought frequency, tree diversity, soil nutrient and microorganismal abundance, and successional stage. We found that AGB accumulation rate decreased as AGB increased gradually during secondary succession. The different drought frequency between the two intervals was the dominant factor predicting the net change of AGB. With high-frequency droughts, the loss of AGB intensified and the increment rate of AGB decreased, especially in old-growth forests during second interval (2015–2020). Considering the impact of the three demographic progresses on net change in AGB, the relative influence of mortality was the largest (61.1%), followed by growth (38.3%) and recruitment (0.6%). Successional stage was another major factor affecting AGB and its dynamics, showing a positive relationship with AGB stock and a negative relationship with net AGB change. Species richness and fungal richness had a significant positive association with AGB, while soil available nutrient had a significant negative relationship. Overall, our results show that drought frequency had a strong impact on AGB dynamics, and that the resilience of AGB accumulation to drought decreased in later successional stages. Thus, with the intensification of global climate change, the effects of high-frequency drought events should be taken into account when studying the factors affecting AGB recovery in tropical secondary forests.