中国草地净初级生产力时空格局及其影响因素

Spatiotemporal dynamics of China ’s grassland NPP and its driving factors

基于光能利用效率模型(Carnegie-Ames-Stanford Approach,CASA),结合MODIS系列遥感数据、植被数据和气象数据等,对2000—2015年中国草地的NPP进行估算,运用趋势分析法、变异系数及Hurst指数法对中国草地NPP时空动态、稳定性及持续性进行分析,并对中国草地NPP变化的主影响因素进行探讨。结果表明:(1)2000—2015年中国草地NPP呈现显著增加的变化趋势,平均变化率为1.53 g C·m-2·a-1,NPP变化趋势在2011年之后发生了突变,增加趋势更为明显。(2)空间上,草地NPP呈现西北低而东南高的分布格局,NPP低值区集中分布在青藏高原的大部分地区和内蒙古中部。草地NPP增加的区域占草地总面积的81.21%,主要分布在青藏高原中部地区和黄土高原大部分地区。草地NPP变化稳定的区域主要集中在甘肃省甘南地区和青海省东部的大部分地区,而不稳定区域则主要分布在青藏高原的大部分地区以及内蒙古的中部地区和呼伦贝尔等地。Hurst指数分析表明,新疆北部、黄土高原的大部分地区草地NPP将持续增加或减少,而青海省南部、内蒙古中部和黑龙江省等地的草地NPP未来变化具有反持续性。(3)不同草地类型的NPP均值有很大差异,其中高山亚高山草甸及草甸的平均NPP值较高,分别为578.8和565.31 g C·m-2·a-1,而荒漠草地的NPP平均值最低,仅为122.61 g C·m-2·a-1。(4)中国大多数地区草地NPP的增加主要受降水控制,而气温的升高对草地NPP具有一定的抑制。人类活动如过度放牧状况的改善以及退耕还草的实施对于近年来草地NPP的增加具有重要作用。

Grassland NPP in China from 2000 to 2015 was simulated based on the CASA model,incorporated with MODIS and meteorological data.Trend analysis,coefficient of variation and Hurst index were used to examine the temporal and spatial dynamics,stability and persistence of grassland NPP.The main influencing factors of grassland NPP change in China were identified.The results showed that grassland NPP increased significantly from 2000 to 2015,with an average change rate of 1.53 g C·m-2·a-1.Grassland NPP changed abruptly after 2011,with an obvious increase trend.Grassland NPP showed spatial heterogeneity,being lower in Northwest and higher in Southeast China.Areas with low NPP value were concentrated in most areas of Tibet Plateau and central Inner Mongolia.The area with increased grassland NPP accounted for 81.21%of the total grassland area,mainly distributed in the central region of Tibet Plateau and most areas of Loess Plateau.The regions with stable grassland NPP were mainly concentrated in Gannan region of Gansu Province and most of eastern Qinghai Province,while the unstable regions were mainly distributed in most areas of Tibet Plateau,central part and Hulunbuir of Inner Mongolia.The result of Hurst index analysis showed that grassland NPP in northern Xinjiang and most regions of Loess Plateau would continue to increase or decrease,while the future change of grassland NPP in southern Qinghai,central Inner Mongolia and Heilongjiang would be anti-sustainable.The average NPP values of alpine and subalpine meadow and meadow were 578.8 and 565.31 g C·m-2·a-1,respectively,while that of desert grassland was 122.61 g C·m-2·a-1.The increase in grassland NPP in most areas of China is mainly controlled by precipitation,while the increased temperature has a certain inhibition on grassland NPP.Human activities such as the reduction of overgrazing and the implementation of returning farmland to grassland exert important influence over the increases of grassland NPP.