Data from: Shock and stabilisation following long-term drought in tropical forest from 15 years of litterfall dynamics

Litterfall dynamics in tropical forests are a good indicator of overall tropical forest function, indicative of carbon invested in both photosynthesising tissues and reproductive organs such as flowers and fruits. These dynamics are sensitive to changes in climate, such as drought, but little is known about the long-term responses of tropical forest litterfall dynamics to extended drought stress.
We present a 15-year dataset of litterfall (leaf, flower and fruit, and twigs) from the world's only long-running drought experiment in tropical forest. This dataset comprises one of the longest published litterfall time series in natural forest, which allows the long-term effects of drought on forest reproduction and canopy investment to be explored.
Over the first 4 years of the experiment, the experimental soil moisture deficit created only a small decline in total litterfall and leaf fall (12% and 13%, respectively), but a very strong initial decline in reproductive litterfall (flowers and fruits) of 54%. This loss of flowering and fruiting was accompanied by a de-coupling of all litterfall patterns from seasonal climate variables. However, following >10 years of the experimental drought, flower and fruiting re-stabilised at levels greater than in the control plot, despite high tree mortality in the drought plot. Litterfall relationships with atmospheric drivers were re-established alongside a strong new apparent trade-off between litterfall and tree growth.
Synthesis. We demonstrate that this tropical forest went through an initial shock response during the first 4 years of intense drought, where reproductive effort was arrested and seasonal litterfall patterns were lost. However, following >10 years of experimental drought, this system appears to be re-stabilising at a new functional state where reproduction is substantially elevated on a per tree basis; and there is a new strong trade-off between investment in canopy production and wood production.

热带森林凋落物（litterfall）动态是反映热带森林整体功能的良好指标，可体现分配于光合组织以及花、果实等生殖器官的碳储量。该动态对干旱等气候变化极为敏感，但目前学界对热带森林凋落物动态在长期干旱胁迫（drought stress）下的响应仍知之甚少。

本研究公开了一套基于全球唯一热带森林长期干旱实验的15年凋落物数据集，涵盖叶、花、果实以及细枝的凋落物数据。该数据集是目前已发表的天然林最长凋落物时间序列之一，可用于探究干旱对森林生殖过程以及冠层碳投入的长期影响。

实验前4年，干旱处理样地的土壤水分亏缺（soil moisture deficit）仅导致总凋落物量和落叶量小幅下降（分别下降12%和13%），但生殖类凋落物（花和果实）出现了极为显著的初始下降，降幅达54%。开花与结实量的这种减少，伴随着所有凋落物动态与季节气候变量间关联的解耦。然而，在经历超过10年的实验性干旱后，尽管干旱样地内树木死亡率较高，但花、果实的凋落量已重新稳定在高于对照样地（control plot）的水平。同时，凋落物与大气驱动因子间的关联得以重建，且凋落物生成与树木生长之间出现了新的显著权衡（trade-off）关系。

综合分析。本研究表明，该热带森林在强干旱的前4年经历了初始冲击响应：生殖投入被抑制，季节性凋落物动态规律消失。但在经历超过10年的实验性干旱后，该森林生态系统似乎已重新稳定在一种新的功能状态：单株树木的生殖产出大幅提升，且冠层碳投入与木材生产之间出现了新的显著权衡关系。