Spatio-temporal Dynamics Of Vegetation Net Primary Productivity And Its Influence Factors Under The Background Of Ecological In Northwestern Guangxi

It is attached importance because vegetation as an essential ingredient of the continent ecosystem, plays an important role in the restoration of the ecosystem balance. Net primary productivity(NPP) is defined as green vegetation accumulate the organics per unit time and per unit area. It not only can reflect the production capacity of vegetation, but also is the main factor to adjust the balance of carbon source/sink in the ecological process, which is quiet significant. Therefore, it's crucial to estimate the NPP exactly, and to analyze its spatiotemporal dynamics.In the current research, our study area is the NorthwesternGuangxi, and the basic data includes the MODIS NDVI data, Landsat data and meteorological data. Applying data processing software, such as ARCGIS10.0 and ENVI5.0, and data analysis software, like SPSS and so on,adopting RS estimate model and Pearson's correlation coefficient model, to analyze the spatiotemporal dynamics of the NDVI and NPP. Meanwhile, the study explores the relationships between NDVI and NPP and its control and driving factors. The results demonstrate that:(1)The research improves the vegetation NPP estimate model, and is based on CASA model, combines with GLO-PEM model, changes the water stress index, therefore, it takes fully account of the influence that the water factor impacts on the growing of vegetation. The results of the estimate of NPP shows that the mean NPP value is between 148.63 gCm-2/a and 612.25 gCm-2/a in the research period. Compared with before carrying out the first phase engineer of controlling stony desertification,after the engineer(2005-2008), the annual average NPP increases by 73 gCm-2/a.(2)By analyzing the spatiotemporal dynamics of the NDVI and the NPP, we know that annual average NDVI and NPP rise steadily after the engineer of controlling stony desertification. The peak value of NDVI increases by 0.05, and the percentage of peak value region increases by 2.8%. According to the different vegetation types contributing to the annual average NPP, broad-leaved forest is larger than bush fallow in the research area.(3)The spatiotemporal dynamics of the NDVI and NPP are affected by the controlling factors and driving factors simultaneously. The research result shows that NDVI and NPP relate to the precipitation negatively, they relate to the temperature and solar radiation positively in the controlling factors; in the driving factors, they are related to the engineering investment of the desertification controlling positively. And they are related to the engineering area negatively in the early days, then the trend becomes positive. It shows that it has hysteresis quality when the engineering area facilitates vegetation growth. The environmental change also has some impact on the vegetation growth. In total, the first phase engineer gets certain effect, and it has a contribution to improving the ecological efficiency.