The Spatial-temporal Changes Of NPP In Napaihai Watershed Of Northwest Yunnan Plateau

Vegetation Net Primary Productivity(NPP),an important part of terrestrial ecosystem carbon cycle,plays a vital role in global carbon balance.The Napahai wetland in the northwest of Yunnan plateau has an important carbon sink function,and it has great significance to protect the country's ecological security.During the recent years,Napahai watershed environment problems have become severer,which draws more and more attention from researchers.The research of NPP estimation for Napahai Watershed,contributing to finding out the driving factors of watershed vegetation fixing the CO2,provides reference for the watershed environment protection.Based on biomass measured data,combining the remote sensing data and climate data,the CASA(Carnegie Ames Stanford Approach)model used in this paper,to estimating the spatial-temporal distribution and changes trends of the vegetation NPP of Napahai watershed,and analyzing the driving factors causing NPP changes.The main results are as follows:(1)The annual NPP of Napahai watershed in 1995,2005,2014 were respectively 6.80×1010 gC·a-1?7.13×1010 gC·a-1?6.39×1010 gC·a-1 with a firstly increases and then decreases process.The NPP value of Napahai watershed from April to October is larger.The NPP value from April to October in Napahai watershed were respectively 5.54×1010gC?5.97×1010gC?5.13×1010gC,accounting for relatively 81.48%,83.67%,80.29%of the whole year.(2)The NPP value of the southeastern,western and central regions in Napahai watershed is higher.Southern NPP value is at a medium level.The lowest NPP is near the water in the northern Napahai watershed and the airport.(3)The NPP of grassland and forestland are the top two vegetation type in Napahai watershed areas.In 1995,2005 and 1995,the proportions of grassland NPP in the total NPP were 45.57%?64.62%and 45.57%respectively.The proportions of the forestland NPP were 33.00%,21.32%and 23.24%respectively.The change trends of NPP in the grassland and forestland as well as watershed were similar.(4)NPP is closely related to the changes of climate and vegetation types.The urban expansion and sharp increase of population also are influencing factors.From 1995 to 2005,a large moment of forest land turned into grass and bushes,farmland changed into grass,and the climate condition were almost similar,so the total NPP in 2005 increased by 3.30×109 gC·a-1 than that in 1995.From 2005 to 2014,building area in the watershed rising sharply and less rainfall in 2014 caused the total annual NPP in 2014 decreased by 0.82×107 gC·a-1 than that in 2005.In 1995-2014,the town of building area near Napahai watershed has been expanding,and the population has been increasing dramatically,which is also one of the factors influencing the spatial-temporal variation of NPP in Napahai watershed.