[Spatio-temporal variation of NPP from 1999 to 2015 in Zoige grassland wetland, China]

Abstract

Net primary productivity (NPP) is one of the core components of the grassland wetland ecosystem carbon balance and climate change. Based on data of vegetation index, meteorology (precipitation and temperature), and vegetation type, we used the CASA (Carnegie-Ames-Stanford Approach) model to estimate NPP of the Zoige grassland wetland from 1999 to 2015. The spatial and temporal patterns of NPP in the Zoige grassland wetland ecological function area and its relationship with precipitation and temperature were examined. The results showed that the measured values of NPP were close to the simulated values, with the root mean square error being 120.3 g C·m^-2 and a R² of 0.78. The annual mean and the growth season (April-September) mean of NPP of the study area were 329.0 and 229.4 g C·m^-2·a^-1, respectively, with obvious inter-annual fluctuations, with a weak trend of decline (2.3, 1.6 g C·m^-2·a^-1). The inter-annual fluctuations of NPP in different vegetation types were basically consistent with the overall fluctuations of NPP of the whole study area. The slope of NPP in annual and growing seasons was from -21.3 to 18.7, -31.5 to 23.1 g C·m^-2·a^-1. The area with significant increase (mainly distributed in forest coverage area and wetland ecological compensation area) only accouned for 0.3% and 0.7% of the total area, and the area with significant decline (mainly distributed in areas where human activities were concentrated) only accounted for 1.4% and 6.4% of the total area, respectively. The carbon sequestration capacity of different vegetation types was different, among which the forest was the strongest, the grassland was the second, and the wetland vegetation was the weakest. Precipitation was the dominant climatic factor affecting NPP in grassland wetland.

Keywords: Zoige; climate response; net primary productivity (NPP); spatio-temporal variation characteristics.