近百年全球草地生态系统净初级生产力时空动态对气候变化的响应

摘要

气候变化是影响生态系统空间地理分布、结构和功能的主要因素。为了从长时间序列大空间尺度上了解气候变化对草地生态系统的影响及其反馈机制，本研究利用综合顺序分类法及分段模型分别模拟了1911－2010年间全球草地生态系统及净初级生产力（NPP）的时空动态，并通过相关性分析揭示草地 NPP 对不同气候因子的响应。结果表明，在过去的百年间，全球草地面积从1920s 的5175．73万 km2下降到1990s 的5102．16万 km2，其中冻原与高山草地类组的面积下降最多，为192．35万 km2，荒漠草地类组、典型草地类组和温带湿润草地类组的面积分别下降了14．31、34．15和70．81万 km2，而热带萨王纳类组的面积增加了238．06万 km2。在气候变化的影响下，大多数草地类组的重心均向北方移动，在北半球尤为明显。全球草地 NPP 从1920s 的25．93 Pg DW／年增加到1990s 的26．67 Pg DW／年。就各草地类组而言，冻原与高山草地类组、荒漠草地类组、典型草地类组、温带湿润草地类组的 NPP 均呈现下降趋势，分别下降了709．57、24．98、115．74和291．56 Tg DW／年，而热带萨王纳类组的NPP 则增加了1887．37 Tg DW／年。从全球尺度来看，降水是影响草地 NPP 的主要气候因子。总的来说，近百年气候变化对全球草地生态系统产生了深刻的影响，尽管草地 NPP 呈现增加的趋势，但暖湿化的气候变化对草地生态系统的结构和空间分布产生了不利的影响。%Climate change has a significant effect on the spatial distribution,structure and function of ecosys-tems.To understand the effects and feedback mechanisms of climate change on a large spatial and temporal scale,the distribution,shift ranges and net primary production (NPP)of grassland ecosystems across the globe from 1911 to 2010 have been simulated using the Comprehensive Sequential Classification System (CSCS) and a segmentation model.Correlation analysis was also conducted to reveal the responses of grassland types to different climate variables.The results showed that the total global area of grassland ecosystems declined from 5175.73×104 km2 in the 1920s to 5102.16×104 km2 in the 1990s.The largest decrease,192.35×104 km2 ,oc-curred in tundra & alpine steppe ecosystems.The areas of desert grassland,typical grassland and temperate humid grassland decreased by 14.31,34.15 and 70.81×104 km2 respectively,while tropical savanna expanded by 238.06×104 km2 .Climate warming forced most grasslands to shift northwards,particularly in the northern hemisphere.Global grassland NPP increased from 25.93 Pg DW/yr in the 1920s to 26.67 Pg DW/yr in the 1990s.In terms of each grassland type,the NPP of the tundra and alpine steppe,desert grassland,typical grassland and temperate humid grassland decreased by 709.57,24.98,115.74 and 291.56 Tg DW/yr respec-tively.The NPP of tropical savanna increased by 1887.37 Tg DW/yr.At the global scale,precipitation was the dominant factor affecting grassland NPP.In general,grassland ecosystems have been substantially affected by climate change over the past 100 years.Although the global grassland NPP showed an overall increasing trend, the structure and distribution of particular grassland ecosystems had been adversely affected by the warmer and wetter climate.