The cumulative drought exert disruptive effects on tropical rainforests in the northern edge of Asia - Based on decadal dendrometric measurements and eddy covariance method

Abstract

Studies on the effects of drought on tropical rainforests have revealed their sensitivity on multiple levels, for example, decreased photosynthetic capacity and increased mortality. However, studies on the impact of occasional drought on the rainforests are not enough as they tend to recover from such droughts within a few years. In the present study, the Xishuangbanna rainforest, located at the northern edge of Asia, witnessed extensive damage after six years of a field drought treatment (30 m × 30 m plot; ∼35% through-fall reduction): the plant carbon pool decreased at the rate of 13.71 T ha−1 yr−1 (amount to 23% loss of plant carbon in the 10th year compared to the 7th), although soil carbon accumulated at the rate of 2.68 T ha−1 yr−1. The radial growth rate of the surviving tagged trees was not constrained by drought. Additionally, drought reduced the number of seedlings per unit area by 61% compared to the control plot. The residual analysis indicates that the net ecosystem carbon exchange (NEE) of eddy covariance (EC) flux site was insensitive to soil drought on annual scale, while regression analyses showed that photosynthetic light response parameters were inhibited by drought on decalal scale. The results of both drought experiment and flux data analysis showed that the impact of drought on the rainforest will be highly apparent on long-term scale. In order to predict the fate of forests more accurately in response to prolonged drought, it is worth reassessing the long-term drought sensitivity of forest ecosystems.