Tropical forests store about 70% of the total living biomass on land and yet very little is known about changes in this vital carbon reservoir. Changes in their biomass stock, determined by changes in carbon input (i.e., net primary production [NPP]) and carbon turnover time (τ), are critical to the global carbon sink. In this study, we calculated transient τ in tropical forest biomass using satellite‐based biomass and moderate‐resolution imaging spectroradiometer (MODIS) NPP and analyzed the trends of τ and NPP from 2001 to 2012. Results show that τ and NPP generally have opposite trends across the tropics. Increasing NPP and decreasing τ (“N+T−”) mainly distribute in central Africa and the northeast region of South America, while decreasing NPP and increasing τ (“N−T+”) prevail in Southeast Asia and western Amazon forests. Most of the N+T− tropical forest areas are associated with mean annual precipitation (MAP) below 2,000 mm·y⁻¹ and most N−T+ tropical forests with MAP above 2,000 mm·y⁻¹. The τ and NPP trends in the N+T− region are statistically associated with radiation, precipitation and vapor pressure deficit (VPD), while the τ and NPP trends in the N−T+ region are mainly associated with temperature and VPD. Our results inherit the uncertainties from the satellite‐based datasets and largely depend on the carbon use efficiency from MODIS. We thus systematically assessed the robustness of the findings. Our study reveals regional patterns and potential drivers of biomass turnover time and NPP changes and provides valuable insights into the tropical forest carbon dynamics.

中文翻译：

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2001年至2012年热带森林生物量周转时间的变化及其环境驱动因素

热带森林将约70％的生物量存储在陆地上，但对该重要碳库的变化知之甚少。由碳输入（即净初级生产[NPP]）和碳周转时间（τ）的变化确定的生物量库的变化对全球碳汇至关重要。在这项研究中，我们使用基于卫星的生物量和中分辨率成像光谱仪（MODIS）NPP计算了热带森林生物量的瞬时τ，并分析了2001年至2012年τ和NPP的趋势。结果表明，τ和NPP总体上具有相反的趋势在整个热带地区。NPP增加，τ减小（“ N + T-”）主要分布在中部非洲和南美洲东北部地区，而NPP的降低和τ（“ NT +”）的增加在东南亚和西部亚马逊森林中普遍存在。大多数N + T-热带森林面积与2,000 mm·y ^-1以下的年平均降水量（MAP）相关，而大多数N + T +热带森林的MAP高于2,000 mm·y ^-1。N + T-区域的τ和NPP趋势在统计上与辐射，降水和蒸气压亏缺（VPD）相关，而τN T +区域的NPP趋势主要与温度和VPD有关。我们的结果继承了基于卫星的数据集的不确定性，并且很大程度上取决于MODIS的碳使用效率。因此，我们系统地评估了结果的稳健性。我们的研究揭示了区域格局以及生物量周转时间和NPP变化的潜在驱动因素，并提供了对热带森林碳动态的宝贵见解。