Abstract This study evaluates the impacts of the 2015/2016 El Nino event on the phenology and carbon dioxide (CO2) exchange in a secondary dry dipterocarp forest (DDF). In western Thailand, El Nino events significantly reduced rainfall and increased air temperature, leading to prolonged dry season with low soil water content and high vapor pressure deficit (VPD). During 2014–2017, leaf phenology was monitored and CO2 exchanges in this forest were measured by an eddy covariance method. During El Nino year, dry dipterocarp species were shed their leaves earlier when compared to neutral years (i.e. with no El Nino event). The species Shorea siamensis Miq. and Sindora siamensis Teijsm.&Miq. showed complete deciduousness during the dry season 2015/2016 as typically observed for these species, but the leafless period was longer than during non-El Nino years. Shorea roxburghii G.Don and Shorea obtusa Wall. showed untypically complete deciduousness during the El Nino year. For the species Sindora siamensis, however, the timing of first leaf expansion was not affected by the strong El Nino. In addition, El Nino resulted in a decline of the annual gross primary productivity (GPP) and evapotranspiration (ET) by 9.6 and 14.1%, respectively. The net ecosystem productivity (NEP) was only affected by El Nino during the dry months, but not during the following wet season therefore the total annual NEP was not significantly affected. Our result demonstrates that El Nino events have a strong impact on canopy duration of DDF ecosystem. However, our study suggests that the carbon loss during this prolonged dry season of 2015/2016 can be compensated in this young secondary DDF during the following wet season, leading to increased NEP on a yearly basis.

中文翻译：

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强厄尔尼诺事件对次生干燥龙脑香林叶片物候和二氧化碳交换的影响

摘要 本研究评估了 2015/2016 年厄尔尼诺事件对次生干燥龙脑香林 (DDF) 物候和二氧化碳 (CO2) 交换的影响。在泰国西部，厄尔尼诺现象显着减少降雨量和升高气温，导致旱季延长，土壤含水量低，蒸汽压差 (VPD) 高。2014-2017 年期间，监测了叶片物候，并通过涡度协方差方法测量了该森林中的 CO2 交换。在厄尔尼诺年，与中性年（即没有厄尔尼诺事件）相比，干燥的龙脑香属植物更早脱落叶子。物种 Shorea siamensis Miq。和 Sindora siamensis Teijsm.&Miq。在 2015/2016 年旱季表现出完全的落叶性，正如这些物种通常观察到的那样，但无叶期比非厄尔尼诺年长。Shorea roxburghii G.Don 和 Shorea obtusa Wall。在厄尔尼诺年期间表现出非典型的完全落叶。然而，对于Sindora siamensis 物种，第一次叶片扩张的时间不受强厄尔尼诺现象的影响。此外，厄尔尼诺现象导致年度总初级生产力（GPP）和蒸散量（ET）分别下降 9.6% 和 14.1%。净生态系统生产力（NEP）仅在旱季受到厄尔尼诺现象的影响，而在接下来的雨季不受厄尔尼诺现象的影响，因此全年的净生态系统生产力没有受到显着影响。我们的结果表明厄尔尼诺事件对 DDF 生态系统的冠层持续时间有很大的影响。然而，