迄今为止，越来越多的人投入到对植被生态系统总初级生产力的研究中去，总初级生产力（ GPP）影响着全球气候、地表系统的物质循环，也是碳循环的重要组成因素，是大气中 CO2 进入陆地生态系统的起点和重要分量，对于碳循环的研究有着重要的意义。
2000-2016 Changes in GPP Based on MODIS Data and Its Influencing Factors
So far, more and more people have invested in the study of the Gross Primary Productivity of the vegetation ecosystem. It affects the global climate, the material cycle of the surface system, and the gross primary productivity (GPP) of terrestrial ecosystems is also an important component of the carbon cycle. It is the starting point and important component of CO2 in Atmospheric entering the terrestrial ecosystem. It is of great significance for the study of the carbon cycle.
In this study, the Beijing-Tianjin-Hebei area was selected as the research site, and the GPP data, land-use type data, and climate data of MODIS from 2000-2016 in the area were collected. Using the mean method and correlation analysis method, the space distribution, space distribution changes and time distribution of GPP in the past 17 years were obtained as well as land-use types and climatic factors influence the changes in GPP.
In this study, the following conclusions were obtained.
(1) In terms of spatial distribution, from 2000 to 2015, although the land using situation kept changing during the 16 years, the overall framework was at a relatively stable stage. Through the sorting of land using types (farmland, forest land, grassland, city, and water), it was found that the area of use of farmland has remained at the top, followed by forest land, grassland, and finally cities and water, Which has a major guiding role in the development of land using types in the Beijing-Tianjin-Hebei region. The areas with high GPP are mainly concentrated in Chengde, Hebei, southwest of Zhangjiakou, and northern Beijing (these areas are mainly forest land). The lower area of GPP is mainly in the north of Zhangjiakou.
(2) In terms of spatial changes, from a regional point of view, the northern part of Hebei Province is basically in a substantially increasing state, the southwestern part near the provincial boundary increases more, and the smaller one is mainly focus on the city and the water. The highest value is in Chengde City, and the lowest value is in the coastal area of Tangshan City. From the perspective of land use. With the city as the center, almost only the GPP around the town are in a state of reduction, while the forest land, grassland, farmland, and GPP are all in an increasing state. Among them, the GPP increases the fastest in terms of forest land and grassland, followed by farmland.
(3) In spite of fluctuations in the time, the GPP in 2006 and 2009 had a significant decline. However, there is an overall upward trend. The results show that the ecological environment (grassland, forest land, farmland) was obtained in the Beijing-Tianjin-Hebei area, which represents very good protection and development.
(4) Within the study area, GPP is mainly related to temperature and precipitation mainly in low degree correlation. Among them, precipitation has a greater impact on the annual average GPP for many years, while the change in temperature is almost nothing to do with the GPP in the Beijing-Tianjin-Hebei area
(5) Therefore, in the Beijing-Tianjin-Hebei area, it is necessary to increase forest land and grassland construction, properly plan urban land using and cultivated area, effectively protect the environment, and make the ecological environment in a dynamic and balanced state.
Key words: Beijing-Tianjin-Hebei Area; Gross Primary Productivity (GPP); Spatio-temporal Evolution; Influencing Factors