Abstract: Net primary productivity (NPP) is an important factor to judge the quality of ecosystem and carbon sink, and reflects the production capacity and ecological process of plant community, which is of great significance for regulating global carbon balance and enhancing ecological services. Based on MODIS satellite remote sensing data and improved CASA model, the dynamic changes of forest vegetation NPP in Yichun and the main affecting factors such as temperature, precipitation, and human activities were analyzed by using MOD17A3HGF NPP annual data and meteorological data from 2000 to 2019. The results showed that, from 2000 to 2019, the average NPP of forests in Yichun was 477.76 g C·m^-2·a^-1, and the NPP was mainly in the range of 400-500 g C·m^-2·a^-1, accounting for 83.30% of the total in Yichun, showing the distribution characteristics of partly high in the north and south, average in the middle, and lowest in Jiayin and Tieli Plain. The deciduous broad-leaved forest in Yichun had the highest contribution to the area with high NPP value, followed by evergreen coniferous forest. The main NPP value of coniferous and broad-leaved mixed forest was at the average level of NPP in Yichun, while the area of deciduous coniferous forest and evergreen deciduous forest was relatively small. From 2000 to 2019, the interannual NPP of forests in Yichun showed a fluctuation but overall increasing trend, among which the extremely significant increasing trend was the main one, accounting for 81.43% of the total area. On the interannual scale, there was a close correlation between annual precipitation and annual average NPP in Yichun, but a low correlation between mean annual temperature and annual average NPP. On the monthly scale, vegetation was significantly affected by temperature and less affected by precipitation, especially in the high-altitude areas such as the mountains at the junction of Yimei District, and the Korean pine concentrated area such as the southern part of Tangwang County, Fenglin Nature Reserve, Wuying National Forest Park. In the plain and low altitude areas, NPP was affected by both temperature and precipitation. Ecological projects, such as the Yichun Natural Forest Protection Project and various conservation measures, played an important role in promoting the ecological restoration of vegetation.

Key words: net primary productivity, MOD17A3HGF, CASA model, meteorology, state-owned forest area.