(Peer-Reviewed) Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China
Yuhang Dai ¹ ², Fanxi Gong ² ³ ⁴, Xueqin Yang ² ⁴, Xiuzhi Chen 陈修治 ² ⁵, Yongxian Su 苏泳娴 ⁴, Liyang Liu 刘礼杨 ⁴, Jianping Wu 吴建平 ⁴, Xiaodong Liu 刘效东 ¹, Qingling Sun 孙庆龄 ² ⁴
¹ College of forestry and landscape architecture, South China Agricultural University, Guangzhou, China
中国 广州 华南农业大学林学与风景园林学院
² Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China
中国 珠海 中山大学大气科学学院广东省气候变化与自然灾害研究重点实验室
³ College of Earth Sciences, Chengdu University of Technology, Chengdu, China
中国 成都 成都理工大学地球科学学院
⁴ Key Lab of Guangdong for Utilization of Remote Sensing and Geographical Information System, Guangdong Open Laboratory of Geospatial Information Technology and Application, Guangzhou Institute of Geography, Guangdong Academy of Sciences, Guangzhou, China
中国 广州 广东省科学院广州地理研究所 广东省地理空间信息技术与应用公共实验室 广东省遥感与地理信息系统应用重点实验室
⁵ Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
中国 珠海 南方海洋科学与工程广东省实验室（珠海）
Tropical and subtropical evergreen broad-leaved forests (EBF) and needle-leaved forests (ENF) in China exhibit complex leaf shedding strategies in responses to soil water availability, vapor pressure deficits (VPD) and sunlight availability. However, the seasonal variations and triggers of litterfall differ significantly in tropical/subtropical forests, and there are still many uncertainties. Herein, we aim to explore the distinct climatic factors of seasonal litterfall in a climate-phenology correlation framework.
We collected seasonal litterfall data from 85 sites across tropical/subtropical China and used linear correlation coefficients between sunlight and rainfall to partition synchronous/asynchronous climates. Additional phase analysis and structural equation model analysis were conducted to model the climatic triggers of tropical phenology.
Results indicated two types of tropical litterfall phenology under two types of climates. In synchronous climates, where seasonal sunlight and rainfall are positively correlated, the litterfall peak of the unimodal phenology and the first litterfall peak of the bimodal phenology both happen at the end of dry season. The second litterfall peak of the bimodal phenology occurs at the end of rainy season due to water stress. In asynchronous climates, where seasonal sunlight and rainfall are negatively correlated, VPD shows consistent seasonal variations with incoming sunlight. The leaf senescence is accelerated at the end of dry season by higher VPD; while soil water deficit is in anti-phase with sunlight and mainly controls the second litterfall peak of the bimodal phenology in EBF. Our findings provide an important reference for modeling tropical phenology in Earth system models.