Study On The Change Of Vegetation Productivity In The Upper Reaches Of The Minjiang River And Its Relationship With Climate And Human Activities

Net primary productivity?NPP?is an important parameter of terrestrial ecosystem function.Researching on NPP dynamic and its relationship with climate and human activitiesis of great significance for the restoration,reconstruction and protection of ecological environment in fragile mountain areas.The upper reaches of the Minjiang River characterizes by complex terrain,significant vertical differentiation of climate and vegetation.Basedon the remote sensing data,meteorological data and DEM data,using CASA model to estimate actual net primary productivity and potential net primary productivity in the upper reaches of Minjiang River,on this basis,a human activities relative influence contribution index?RICI?was established by residual method,then analyzed the space differentiation and dynamic variation ruleof RICI.Through correlation analysis of precipitation,temperature and NPP,the relationship betweenNPP changes and climate change was analyzed from different time scales.In the end,quantitativelyevaluating theeffectsof humanactivitiesonNPP from the two aspects of hydropower station exploitationandlandusechangein the upper reaches of Minjiang Riverwas carried out.The main conclusions were as follows:?1?For estimating the NPP data of long time series,based on GIMMS NDVI data,adopting a linear regression method to simulate and extend the data of MODIS NDVI by different vegetation types.The simulation data was compared with the real MODIS NDVI data,thedifference was consistent with normal distribution,and the fitting results were reliable.Based on the CASA model and the NDVI data set constructed,the estimation results of the ANPP and PNPP since 1982 were reflected.in the upper reaches of Minjiang River,the ANPP and PNPP had shown a trend of increasing fluctuation.The maximum value ofANPP and PNPP were 502.12gC·m^-2in 2014 and 555.02gC·m^-2 in 2013,and the lowest values were 374.08gC·m^-2 in1988 and 441.48gC·m^-2 in 1989,influenced by human activities,the average annual loss of NPP was 63.09gC·m^-2.74.72%of the annual average ANPP was between 200and 600gC·m^-2·a^-1,88.87%of annual average PNPP was between 200 and800gC·m^-2·a^-1.The ANPP decreased in the northeast of SongPan county,the north of LiXian county,the west of WenChuan county and in the arid valley.And thePNPP increased in the southwest region of SongPan county and WenChuan county.?2?The correlation analysis between meteorological factors and vegetation NPP showedthatprecipitationhadobviousinfluenceonNPPandthe correlationcoefficient was 0.5.In 1991-2005,the effect of NPP on precipitation had certain hysteresis effect.NPP was negatively correlated with annual mean temperature,with correlation coefficients of 0.277 and 0.348 respectively.The NPP in SongPan county had the lowest correlation with annual cumulative precipitation and annual average temperature,and the highest in WenChuan county.In June,July,August and October,the changes on NPP showed a lag of 1-2 months in response to precipitation.In June,August and October,changes on NPP showed a lag of 1-2months in response to temperature.?3?Since 1982,the human activities relative influence contribution index had a trend of increase.The average value for years was 0.0858,the lowest value was0.037 in 1986,and the highest value was 0.157 in 2012,it showed that the human activities had a negative impact on NPP in the upper reaches of Minjiang River.Among,the regions with RICI value greater than 0.2 were mainly concentrated in the southeast of WenChuan county and MaoXian county,the northern part of SongPan county and the boundary,and dry hot valley areas.37.02%of RICI values decreased,located in the northwest of SongPan county,northern and southeast of MaoXian county,the north of HeiShui county,the south of WenChuan county,and the junction of LiXian county and WenChuan county.21.76%of RICI values increased,located in the east of SongPan county,west of HeiShui county,west of WenChuan county and arid valley.?4?Cascade hydropower station exploitationin the Shay valley river of basin the upper reaches of Minjiang River had a certain impact on the NPP,and there were spatial differences.The statistical results of NPP in the 10km buffer area on both sides of the Straits showed a consistent variation tendency.The increase of the distance between the two sides of cascade hydropower station,the NPP decreased gradually.During the exploitation of the Lixian hydropower station,NPP was the highest.But during the exploitation of other cascade hydropower stations,NPP was lower than before and after exploitation.However,in the initial stage of exploitation and exploitation of cascade hydropower stations?1982-1999 years?,NPP on the left bank was higher than that on the right bank;after 2000,NPP on the left bank was lower than that on the right bank.Changes in landscape types caused by changes in human landuse patternsalso had an affect on NPP changes.In research area,the transformation from natural landscape to semi natural and semi artificial landscape,and semi natural semi artificial landscape into natural landscape could increase NPP by two ways.However,thetransformation from natural landscape to artificial landscape leaded to the decrease of NPP.