基于精细控制实验和理论模型法分割气候和植被覆盖变化对森林蒸散的贡献

Evapotranspiration, which is composed of transpiration and soil evaporation, consumes nearly 55~75% of the annual precipitation in the terrestrial ecosystem. It is the major way of inland water resources losing. Climate warming and vegetation cover change are recognized as two main factors influencing the forest evapotranspiration variations. So, under the present background of significant air temperature rise and large-scale afforestation, it will be a difficulty and also a focus in the forest hydrology community that how to distinguish the impact of climate and vegetation cover changes on forest evapotranspiration. The traditional time-trends studies and paired-watersheds experiments fail to strictly control the system output water, while the climate and hydrology models always need lots of other auxiliary parameters. For these, in the Dinghushan Forest Ecosystem Research Station, we have established the experimental platform of forest ecosystems transplanted down an elevation gradient, which accurately controls the hydrological process. Based on the platform, this project aims to study on the evapotranspiration changes of the typical forest types of south subtropical zone using both fine controlled experiment and theory model methods. We intend to distinguish the comprehensive impact of climate warming and vegetation cover change by comparing the evapotranspiration differences between the same forest type in different elevations, or different forest types in the same elevation, or different vegetation growth stages. In addition, we will also undertake sustainable observations to monitor the relative variations of micro-climate, vegetation, and soil properties; and then study the mechanism of subtropical forest evapotranspiration responses to climate warming and vegetation cover change. The results will be helpful for scientific forest management and future climate change tackling.

蒸散（包括蒸发和植被蒸腾）消耗约55~75%的年降水，是陆地生态系统水资源的主要消耗途径。气候变暖和植被覆盖变化被认为是影响森林蒸散的两个主要因素，如何分割两者对森林蒸散的综合影响，在当前气温明显升高和大面积植树造林的双重背景下显得尤为重要，是森林水文学的难点和热点。传统的时间序列实验和配对实验很难严格控制系统水分输出，气候/水文模型法则需要大量的辅助参数。为此我们在鼎湖山国家野外生态定位研究站设计了严格控制水循环过程的森林生态系统移位精细实验平台，本项目以此为基础选取南亚热带典型森林类型，通过对比不同海拔同一林型、同一海拔不同林型及不同生长阶段的森林蒸散差异，结合精细控制实验和理论模型法分割气候变暖和植被覆盖变化对森林蒸散的贡献，并通过持续的监测平台微气象、植被和土壤参数变化，来研究南亚热带典型森林类型蒸散对气温上升和植被覆盖变化的响应机制，以期科学合理的开展森林管理和应对未来气候变化。

气候变暖和植被覆盖变化被认为是影响森林蒸散的两个主要因素，如何分割两者对森林蒸散的综合影响，在当前气温明显升高和大面积植树造林的双重背景下显得尤为重要，是森林水文学的难点和热点。本项目基于鼎湖山国家野外生态定位研究站“森林生态系统垂直移位实验平台”， 相继利用实验和理论模型方法相结合的手段，分割、量化气候和植被覆盖变化对森林水文过程的影响。通过精细控制实验和理论模型相结合的手段，我们研究了气候变化和植被覆盖变化对森林蒸散变化的贡献量，同时也计量了森林蒸散对气候和植被覆盖的变化响应的敏感性，最后，通过监测样地气象、植物生长、生理生化、土壤理化参数以及系统水循环要素变化等，研究了森林蒸散对气温上升和植被覆盖变化的响应规律。结果表明，在海拔300m的实验样地中，山地林和混交林月均蒸散量有着明显的季节性变化规律，在湿季中山地林蒸散量显著高于混交林，而在旱季中，混交林蒸散量则显著高于山地林。山地林、混交林和季风林三种森林类型在湿季中其蒸散对植被覆盖变化敏感性显著高于对气候变化的敏感性，相反，在干季中则对气候变化的敏感性更高。植物的生长导致其冠幅和叶面积指数均有所增长，植物的遮阴作用导致土壤水分的蒸发减少，增温直接效应就是导致叶片气孔导度增大，蒸腾速率也变大；而增温的间接效应则导致植被生长加快，叶片的蒸腾面积增大，阐述了南亚热带地区森林蒸散变化的驱动机制。