三江源国家公园植被净初级生产力变化趋势及影响因素

Changes and influencing factors of vegetation net primary productivity in the Sanjiangyuan National Park

净初级生产力(NPP)是评估全球气候变化和人类活动下生态系统状况、过程和机制的重要指标之一。研究以中国首批国家公园之一的三江源国家公园为对象,利用GLOPEM⁃CEVSA耦合模型,以1981—2018年空间插值的气象数据和基于遥感反演的FPAR数据为输入,分别估算仅气候驱动的潜在NPP(NPP_(CL))和气候遥感共同驱动的现实NPP(NPP_(RS)),以二者之差厘定人类活动影响的NPP(NPP_(HA)),进而探究全球气候变化下人类活动的影响。结果表明:(1)三江源地区NPP_(RS)多年均值为309.70 g C m^(-2)a^(-1),占NPP_(CL)的61.65%。其中,黄河源、长江源和澜沧江源园区NPP_(RS)分别为249.88 g C m^(-2)a^(-1)、140.18 g C m^(-2)a^(-1)和330.55 g C m^(-2)a^(-1)。(2)全区NPP_(RS)以2.00 g C m^(-2)a^(-1)速率显著增加,高于NPP_(CL)(1.74 g C m^(-2)a^(-1)),其中黄河源、长江源和澜沧江源园区NPP_(RS)增长速率分别占各自NPP_(CL)增长速率的89.13%、90.23%和77.43%,澜沧江源园区整体受人类活动影响最大。(3)气候影响方面,年降水、年平均日最高气温和年平均日最低气温共同可解释全区NPP_(CL)和NPP_(RS)年际变化的51%和73%,可分别解释黄河源、长江源和澜沧江源园区的48%和58%、52%和69%、42%和50%,其中气温对NPP年际变化趋势影响更大。(4)人类活动在大部分区域呈负影响,存在西北向东南负面影响增强的空间分布特征,但2000年前后人类活动对生产力变化趋势呈负影响的面积从79.12%降低到56.34%,NPP变化量从-71.41 Tg C降低到-38.72 Tg C,作为主导因子的变化范围从18.73%增加至38.76%,三江源地区生态保护与恢复等措施促进了植被生产力增加,但需进一步实施生态保护与恢复措施,这是一项长期而艰巨的任务。

The Net Primary Productivity(NPP)is an important indicator quantifying ecosystem status,process and undying mechanisms due to global climate change and human activities.The potential NPP(NPP_(CL))and actual NPP(NPP_(RS))were estimated through GLOPEM⁃CEVSA model driven by the only interpolated climate data,and both climate and remote sensing data,respectively,for the near 40 years from 1981 to 2018.The human activities dominated NPP(NPP_(HA))was defined as the difference between NPP_(RS)and NPP_(CL).The method was applied in the Sanjiangyuan National Park,one of the first national parks in China,to explore the impacts of human activity under global climate change.The results showed that:(1)the average NPP_(RS) was 309.70 g C m^(-2)a^(-1),accounting for 61.65%of the NPP_(CL) for the whole region.For the three sub⁃parks,the NPP_(RS)were 249.88 g C m^(-2)a^(-1),140.18 g C m^(-2)a^(-1)and 330.55 g C m^(-2)a^(-1)in the Yellow River headwater,Yangtze River headwater and Lancang River headwater,respectively.(2)The NPP_(RS)was increasing significantly by a speed of 2.00 g C m^(-2)a^(-1),which was faster than the NPP_(CL)(1.74 g C m^(-2)a^(-1)).The speed ratio of NPP_(RS)to NPP_(CL) were 89.13%,90.23%and 77.43%for the three sub⁃parks by the above oder,respectively,which meant the Lancang Park was most impacted by human activities.(3)In the terms of climate impact,temperature had a stronger impact on the trend of NPP.Specifically,annual total precipitation,average annual maximum temperature and minimum temperature explained 51%and 73%of the interannual variation of NPP_(CL) and NPP_(RS)in the whole region,which can explain 48%and 58%,52%and 69%,42%and 50%of the interannual variability in the NPP timeseries in the Yellow River,Yangtze River and Lancang River sub⁃park,respectively.(4)Human activities had a negative influence over the most areas and became stronger to the southeast from the northwest.And the area showing a negative influence from human activities on the productivity changes decreased from 79.12%before 2000 to 56.34%after 2000.The total NPP over the whore negative area decreased from-71.41 Tg C to-38.72 Tg C,and the human activity as the dominant factor increased from 18.73%to 38.76%for the same two periods.It illustrated that the ecological protection and restoration of the Three⁃River Headwaters Region have contributed to an increasing vegetation productivity,but the protection and restoration measures should be further implemented.