The Analysis Of Temporal And Spatial Variation Characteristics Of Vegetation Net Primary Productivity And Its Influencing Factors In Lancang-mekong River Basin From 2001 To 2020

The Lancang-Mekong River Basin is one of the regions with the richest biodiversity on land.How to make the harmonious and sustainable coexistence between humans and nature in the basin has become an urgent problem.Net Primary Productivity(NPP)of vegetation refers to the remaining part after deducting the energy consumed by autotrophic respiration from the total amount of organic matter produced by green vegetation under photosynthesis in unit time and unit area,which is the structure of vegetation itself.It is the result of the interaction between the structural characteristics of vegetation itself and the external environment and it is an important indicator to evaluate the ecological security of land system and measure the carbon storage capacity of vegetation.Therefore,it has important theoretical and practical significance to estimate vegetation NPP in the study area,accurately monitor the temporal and spatial variation characteristics of vegetation NPP,and analyze its influencing factors for scientific evaluation of regional ecosystem and formulating strategic planning of regional sustainable development.Based on vegetation index data,solar radiation data,temperature data,vegetation coverage types and other data,this article estimated the vegetation NPP in the Lancang-Mekong River Basin from 2001 to 2020 based on the optimized CASA model,and analyzed the temporal and spatial variation characteristics of vegetation NPP during 20years,and its relationship with climate change,land-use change,topographic factors,population density,and carbon dioxide concentration.The main conclusions were as follows:(1)Analysis of temporal and spatial variation characteristics of vegetation NPP in the Lancang-Mekong River Basin.a)From the time change,the change of vegetation NPP from 2001 to 2020 showed a trend of decreasing fluctuation as a whole.Total vegetation NPP in the watershed showed seasonal variation with vegetation growth;the month-to-month variation of vegetation NPP in the watershed was characterized by a bimodal pattern with its peaks in May and July.b)From the perspective of the spatial pattern,the vegetation NPP had obvious spatial difference from 2001 to 2020.The vegetation NPP in the central region was high,and it decreased toward the north and southwest,showing different characteristics with seasonal changes.The spatial difference of vegetation NPP in spring,autumn and winter was obvious.c)From the changing trend,the area of Lancang-Mekong Basin with significant NPP changes accounted for 11.30%of the total area,mainly distributed in the Korat Plateau,Mekong Delta and other regions,and the area with a significant decrease accounted for 10.32%of the total area,mainly in the northern mountainous area,the Annamite Mountains and the Tonle Sap Basin.(2)Analysis of the impact of vegetation NPP based on climate-driven zoning.The change of vegetation NPP in the Lancang-Mekong River Basin was significantly driven by temperature and precipitation.The area affected by temperature and precipitation together accounted for 2.06%of the total area.The area with temperature as the main driving force accounted for 9.88%,the area with precipitation as the main driving force accounts for 3.02%of the total area,and the area with weak temperature and precipitation as the driving force accounted for 1.31%of the total area.(3)Analysis of the impact of land use on vegetation NPP in the Lancang-Mekong River basin based on the profit and loss method.The relationship between land use transition and vegetation NPP in the Lancang-Mekong River Basin was mainly positive increase and negative loss.The mutual conversion of forest land and cultivated land in the Lancang-Mekong River Basin was the main factor causing the conversion of vegetation NPP.The loss of vegetation NPP was from forest land to other land use types,and the increase was mainly from grassland to forest land.(4)Analysis of the influence of other factors on vegetation NPP in the Lancang-Mekong River Basin.Influenced by terrain factors,vegetation growth and distribution in the Lancang-Mekong River Basin presented obvious spatial differentiation characteristics in vertical zonality.The proportion of areas where vegetation NPP changes were positively and negatively correlated with population density were 20.15%and 37.72%respectively.The areas with negative correlations were mainly distributed in the Nakhon Ratchasima Plateau and the Tonle Sap Basin,and the areas with positive correlations were mainly distributed in the Qinghai-Tibet Plateau and northern highlands.There was a negative correlation between vegetation NPP and CO₂concentration in 32.10%of the area,which was mainly distributed in the southern part of the northern highlands,the Annan Mountains,the Tonle Sap Lake Basin and the Qinghai-Tibet Plateau.There was a positive correlation between vegetation NPP and population density in 31.34%of the area,where was mainly distributed in the lower reaches of the Lancang River,the Nakhon Ratchasima Plateau and the Mekong Delta.