RESUMO
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.
Assuntos
Ecossistema , Modelos Teóricos , Desenvolvimento Vegetal , China , Clima , Plantas , TemperaturaRESUMO
We analyzed spatiotemporal changes in vegetation net primary productivity (NPP) in the Qinling-Daba Mountains based on MOD17A3 data and driving factor data from 2000 to 2015. We used trend analysis, Hurst index, and correlation analysis to examine the effects of climate change, soil type, topographic factors, vegetation type, and human activities on NPP. With respect to spatial variation, NPP was the highest in southwestern area and lowest in the northeast. The temporal trend over the 16-year period showed that NPP was increased in the northwest and decreased in the northeast. The projected trend of NPP was of continuity in northern area and anti-continuity in southern area of the Qinling-Daba Mountains. NPP was positively correlated with precipitation and temperature. NPP in areas with dark-brown earths, yellow earths, purplish soils and paddy soils were significantly higher than those with other soil types. The spatial distribution and trends of NPP differed among vegetation types. High NPP mainly occurred on slopes of 25° to 50° and altitudes of 500 to 1000 m or above 2500 m. Human activities had both positive and suppressive effects on NPP.