Spatial-temporal distribution of vegetation net primary productivity and its driving factors from 2000 to 2015 in Shaanxi, China.

Abstract

Using MOD17A3 NPP time series data, surface cover type data, weather data, MOD16 evapotranspiration products and terrain data, the temporal and spatial variability of vegetation net primary productivity (NPP) in Shaanxi Province from 2000 to 2015 was analyzed, and its response to each influencing factor were discussed. The results showed that the NPP of Shaanxi had a significant upward trend in the past 16 years with a slope of 5.02 g C·m-2·a-1. The annual average of NPP was 344 g C·m-2·a-1 with a range from 247 to 390 g C·m-2·a-1. The NPP at 61.2% area of Shaanxi Province showed a significant increasing trend, which were mainly distributed at northern part of Shaanxi, Weibei area and western part of Qinba Mountain. There was a decrease trend of NPP for the area around Xi'an and Baoji City, accounting for only 2.5% of the whole province. During the study period, the variation of annual mean temperature and annual precipitation in Shaanxi showed no significance. The temperature showed a increase trend and the precipitation showed a decrease trend, implying a drier and warmer climate trend in Shaanxi Province. The areas with significant correlation between NPP and precipitation and temperature accounted for 9.4% and 1.5% of the total area of the province. The frequent intervention of human activities reduced the impact of climate on the changes of NPP, so human activity had gradually become the dominant factor. NPP in northern Shaanxi and Guanzhong areas was significantly correlated with evapotranspiration. The increases of NPP in these areas would have great influence on the water and heat balance. The average NPP at different land cover was farmland > forestland > grassland > garden, increasing rate of NPP at different land cover was garden > grassland > forestland > farmland, and proportional changes of NPP was grassland > garden > forestland > farmland. The increasing percentage of NPP at three gradient ranges were 14.6% (0°-5°), 25.7% (5°-25°) and 35.9% (>25°), respectively.