渭河流域长时间序列NPP估算及时空变化特征分析

Estimation and Spatial-Temporal Dynamics of Long Time Sequenced Vegetation Net Primary Productivity in the Weihe River Basin

植被净初级生产力(net primary production,NPP)是生态系统碳循环及能量流动的关键参数,也是生态系统可持续发展的重要生态指标,分析植被NPP的时空变化特征对于区域碳循环研究具有重要意义。利用MODIS反射率数据(MOD09A1)、MODIS NDVI数据(MOD13A3),基于CASA模型估算2001-2018年渭河流域植被NPP,分析植被NPP的时空变化特征,并探讨不同植被类型间NPP的差异性以及高程变化对植被NPP的影响。研究表明:1)2001-2018年,渭河流域植被NPP总体呈波动式增加趋势,年均NPP处于292.59~444.90 gC·m^2,年际增加速率为6.23 gC·m^2;流域植被NPP具有明显的空间异质性,表现为中东部的六盘山、子午岭和南部秦岭等地区较高,西部和北部的黄土高原地区较低。2)18 a来,除常绿针叶林外,其余植被类型NPP均呈增加趋势。不同植被类型的年均NPP的差异表现为落叶阔叶林(625.70 gC·m^2)>常绿针叶林(390.16 gC·m^2)>草地(368.49 gC·m^2)>农田(344.65 gC·m^2)>灌丛(340.17 gC·m^2)。3)不同地形条件下植被NPP具有一定差异性,在900~1 300 m(农田、山地落叶小叶林),植被NPP最高;1 700~1 900 m及3 500 m以上区域(稀树灌木草原、灌木),植被NPP最低。

Net primary production(NPP)of vegetation is a key parameter of carbon cycle and energy flow of ecosystem,and also an important ecological index of sustainable development of ecosystem.It is of great significance to analyze the temporal and spatial characteristics of vegetation NPP for the study of regional carbon cycle.Based on MODIS reflectance data(MOD09A1),MODIS NDVI data(MOD13A3),spatialtemporal variations of the vegetation NPP in the Weihe River Basin from 2001 to 2018 was simulated by using CASA model.Besides,the difference of NPP over different vegetation types and the impact of elevation change on vegetation NPP were also analyzed.The results showed that 1)NPP of vegetation in the Weihe River Basin increased with fluctuations from 2001 to 2018,with mean annual value between 292.59-444.90 gC·m2.Vegetation NPP increased at a rate of 6.23 gC·m2.The vegetation NPP in the basin exhibited obvious spatial heterogeneity,which was shown by the relatively higher values observed in Liupan-Ziwuling Mountains in the Middle East of the basin as well as in the south of Qinling Mountains,and the lower values were observed in the western and Northern Loess Plateau.2)In the past 18 years,NPP of all vegetation types increased except evergreen coniferous forest.The difference of annual NPP over different vegetation types ranked as deciduous broad-leaved forest(625.70 gC·m2)>evergreen coniferous forest(390.16 gC·m2)>grassland(368.49 gC·m2)>farmland(344.65 gC·m2)>shrub(340.17 gC·m2).3)Vegetation NPP under different terrain conditions presented certain differences.In 900-1300 m(farmland,mountain deciduous forest),NPP of vegetation was the highest.In 1700-1900 m and above 3500 m(sparse shrub grassland,shrub),NPP of vegetation was the lowest.