Study of vegetation net primary productivity in Gannan based on light use efficiency model

As an important index reflecting ecological process, the dynamic changes in vegetation net primary productivity (NPP) play an important role in understanding the carbon cycle of ecosystems and global climatie change. By using RS and GIS techniques, an improved light use efficiency model was used to estimate the vegetation NPP in Gannan from 2011 to 2014. In addition, the connections between the spatial and temporal distribution patterns of vegetation NPP and primary terrain factors were discussed in this study. The results showed that the improved light use efficiency model provided a better simulation of the vegetation NPP in Gannan and that it also could be used in large-areas and for long-term simulations. The average annual vegetation NPP from 2011 to 2014 was 478.26 g C·(m²·a)^–1. Over a year the daily mean NPP of vegetation increased first and then decreased, reaching a maximum value in July; the accumulative NPP increased quickly from May and tended to be stable in October. With regard to the spatial distribution mean NPP was large in the southeast mountain area and small in the northern agricultural and farming-pastoral area and in the southwest high altitude area. As the altitude increased both the average NPP and accumulative NPP increased at first and then reduced; Over all the aspects of the slope NPP was highest on the north slope, and lowest on the south slope.