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Ningxia University (2020)

Effects of Planted Shrub Encroachment on Evapotranspiration in Desert Steppe

丹杨

Titre : Effects of Planted Shrub Encroachment on Evapotranspiration in Desert Steppe

Auteur : 丹杨 ; Grade : Master’s Theses 2020

Université : Ningxia University

Résumé partiel
The ecological engineering for combating desertification in northwestern China often plant a large number of shrubs such as Caragana intermedia in arid and semi-arid desert grassland areas,which will cause the phenomenon of shrub encroachment in desert steppe.Transformation will inevitably affect the material and energy cycle processes of the ecosystem,of which the impact on the ground-gas water vapor cycle process is the most important.Evapotranspiration(ET)is an important part of the ground-air water vapor cycle,including two physical processes of evaporation and transpiration.Studying the effects of planted shrub encroachment on ecosystem evapotranspiration(ET)in desert steppe can not only reveal the mechanism how human activities change the water cycle of ecosystem in semi-arid areas,but also guide local government to implement ecological restoration and construction.To this end,taking Yanchi County as an example,based on multi-source data such as remote sensing and meteorology,combined with micro-meteorological observations,ecosystem process model simulation and remote sensing spatio-temporal analysis methods,this article studies the effect of artificial shrub encroachment on desert grassland evapotranspiration from multiple spatiotemporal scale.The main work and conclusions are as follows :(1)Using Landsat remote sensing image data and field leaf area index(LAI)data as input data,the regression model was used to estimate the LAI from 1986 to 2019 in order to study the impact of artificial shrub encroachment on vegetation.The overall fluctuation of LAI increased from 1986 to 2019 in Yanchi County,and the 67.45%regional vegetation leaf area in the county was increasing,indicating that the ecological governance project increased the regional vegetation coverage and changed the original vegetation leaf area coverage structure in the desert grassland area of Yanchi.It may cause changes in the structure and function of the ecosystem,especially the regional ground-gas water vapor cycle.(2)Based on the MODIS ET and NDVI products from 2001 to 2018,trend analysis,correlation analysis and zoning statistics were used to study the effects of artificial vegetation reconstruction on regional ecosystem evapotranspiration,take desert steppe in Yanchi county as an example ecosystem.ET increased notably after large-scale artificial vegetation reconstruction in Yanchi county,and ET and NDVI showed a significant positive correlation

Mots clés : Desert steppe; Shrub encroachment; Evapotranspiration; Ecological process model; Leaf area index; Eddy Covariance;

Présentation (CNKI)

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