Spatio-temporal Variation and its Influence Factors on Net Primary Productivity of Terrestrial Ecosystems in the Three Gorges Reservoir Area.

The carbon cycle of terrestrial ecosystems is an important element in the study of global and regional climate change and the impact of human activities. The Three Gorges Reservoir Area, as an important ecological environmental protection and restoration area in the Yangtze river basin, plays an extremely important role in global and regional carbon cycle under climate change. Therefore, based on the data of solar radiation, temperature, CO2 concentration and normalized vegetation index from 2000 to 2021, parameters were adjusted based on the C-FIX model, and a terrestrial ecosystem net primary productivity (NPP) estimation model were established in the Three Gorges Reservoir Area (Chongqing section). Quantitative analysis of the e spatial and temporal characteristics of vegetation NPP from 2000 to 2021 was conducted using the barycenter model and trend analysis methods. The relative roles of climate change and human activities in influencing NPP were quantitatively distinguished using correlation analysis methods combined with the Miami model. The results showed that: (1) NPP in the Three Gorges Reservoir Area showed a fluctuating upward trend from 2000 to 2021, and the regional mean annual NPP increased from 666.02gC·m-2·y-1 to 809.04gC·m-2·y-1 from 2000 to 2021, with an increase of 17.68%. (2) The spatial distribution of NPP in the Three Gorges Reservoir Area gradually decreased from northeast to southwest, with an average annual NPP value of 762.3gC·m-2·y-1, among which the area with NPP >800gC·m-2·y-1 accounted for 46% of the total area of the study area, and was mainly distributed in the area of 400-900m altitude. (3) The NPP center of gravity in the study area showed a trend of moving from southwest to northeast, indicating that the NPP increment and growth rate of vegetation in the northeast part of the study area were higher than that in the central and western part of the study area during this period. (4) The changes of vegetation NPP in the Three Gorges Reservoir Area were more sensitive to the effect of temperature, and the partial correlation coefficients between vegetation NPP and annual temperature range from -0.68 to 0.94, with the proportion of positively correlated areas being as high as 95.6%, and the partial correlation coefficients between vegetation NPP and annual precipitation range from -0.83 to 0.82, with the proportion of positively correlated areas being 75.7%, which were located in the majority of the areas along the north side of the Yangtze River, and the majority of the areas in Wulong and Fuling. (5) There was significant spatial heterogeneity in the relative roles of climate change and human activities on the changes of vegetation NPP in the Three Gorges Reservoir Area, and the areas in the state of vegetation recovery accounted for 93.63% of the total area, of which 45.24% were affected by climate change, and 46.72% of the areas in the state of vegetation recovery were affected by climate change and human activities. [ABSTRACT FROM AUTHOR]