| Vegetation is an important part of the ecosystem,and its coverage has an important impact on the quality of the ecological environment.Net Primary Productivity?NPP?as an important indicator of vegetation growth has become an indispensable indicator and content in the study of terrestrial ecosystems.It is not only an important factor for evaluating carbon balance,but also an important indicator for measuring the ecological quality of vegetation and evaluating the function and structure of ecosystems.The factors affecting vegetation cover are complex and diverse,among which climate change and human activities are the more important factors.The LPJ Model?Lund-Potsdam-Jena Model?was used to assess NPP in the Yangtze River basin and to study the temporal and spatial dynamic change of the NPP and its influencing factors from1982 to 2013,which can provide a reference for vegetation monitoring and ecological construction in the Yangtze River basin.Based on the residual analysis method,the relative effects of human activities and climate to vegetation were discussed by combining modis data and simulation data of NPP vegetation from 2000 to 2013,which can provide a theoretical basis for the sustainable development of the ecological environment,economy and society in the Yangtze River basin.The main conclusions are as follows:?1?The spatial distribution of vegetation NPP in the Yangtze River basin was heterogeneous.From 1982 to 2013,NPP declined from southeast to northwest.The annual average NPP value of vegetation was 475.76 gC·m-2·y-1.The order of annual mean NPP in three areas of the Yangtze River is as follows:lower Yangtze River>middle Yangtze River>upper Yangtze River.The order of the total amount of NPP in three areas of the Yangtze River is as follows:upper Yangtze River>middle Yangtze River>lower Yangtze River.The NPP of different types of vegetation in the Yangtze River basin fluctuated and increased in time.NPP fluctuated with elevation.?2?Climatic factors have an important influence on NPP change.From the perspective of time scale,the average annual NPP of vegetation in the Yangtze River basin during 1982-2013exhibited a significant positive correlation with temperature,while a weak negative correlation with precipitation.Spatially,the correlation between NPP and temperature and precipitation was positive in more than 70%of the study area.The proportion of different vegetation types NPP positively correlated with temperature is ranked as follows:grassland>shrubs>forests>farmland.The proportion of positively correlated area with precipitation is ranked as follows:farmland>forests>shrubs>grassland.Extreme floods and droughts led to NPP reduction in some areas of the Yangtze River,so large-scale extreme weather events may lead to NPP reduction.The upper,middle and lower reaches of the Yangtze River were sensitive to temperature and precipitation,but have a strong sensitivity to temperature,but not a strong sensitivity to precipitation.?3?From 2000 to 2013,the increase of NPP in the Yangtze River was mainly distributed in the middle and east of the upper reaches of the Yangtze River,the west of Dongting Lake and the north of the lower Yangtze.NPPres?residual NPP?was positive,and human activities played a positive role.Human activities led to the decrease of NPP and negative NPPres in areas from southern Qinghai province to northwestern Sichuan,Hanjiang River basin,eastern Dongting Lake and Jiangxi province.From 2002 to 2008,human activities had a positive impact on NPP change.Moreover,after 2000,the growth rate of NDVI in Poyang Lake,Dongting Lake,Jinsha River,Jialing River,Wujiang River and Han River was higher than the simulated value of NPP,indicating that major ecological restoration projects increased the vegetation coverage.?4?From 2000 to 2013,the improvement area accounted for 60.42%of the total change area,and the degraded area accounted for 39.58%of the total change area in the study area.Human activity as the dominant factor has the greatest influence on vegetation improvement and degradation.The increase of NPP in farmland and forests was mainly affected by human activities,however,the increase of NPP in grassland and shrubs was mainly affected by climate change,and the degradation of four cropping types was mainly affected by human activities.?5?The spatial distribution of the contribution rate of climate change and human activities in the Yangtze River from 2000 to 2013 was different.The relative contribution of human activities to the NPP change of the Yangtze River was higher than that of the climate to a certain extent.Therefore,human activity was the main factor of the NPP change in the Yangtze River. |
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