| The Loess Plateau is located in the north of central my country,in the upper and middle reaches of the Yellow River,and is the largest loess-covered area in the world.Since the beginning of the new century,with the vigorous development of the"Reverting Cropland to Forest(Grassland)Project",the level of vegetation coverage on the Loess Plateau has been improved,and vegetation net primary productivity(NPP)has increased significantly.Eco-geographical division refers to the division of the entire area into different types of ecological areas based on the similarities and differences of natural geographic conditions,regional ecological economic relations,and structural functions of agricultural ecological economic systems.The Loess Plateau has a large area with nine eco-geographical subregions,namely the desert area of Alashan and Hexi Corridor,the desert steppe area of Ordos and the western Inner Mongolia Plateau,the steppe area of eastern Inner Mongolia,the artificial vegetation area of the North China Plain,and the deciduous broad-leaved forest area of the North China mountain,Fenwei Basin,deciduous broad-leaved forests,artificial vegetation areas,grassland areas in the central and northern Loess Plateau,coniferous forests in the Qingdong Alpine Basin in Qilian,grassland areas,mixed forest areas of evergreen and deciduous broad-leaved forests in the Qinba Mountains.There are significant differences in natural factors such as temperature,precipitation,solar radiation,topography and landforms in each subregion,and the economic development status and the degree of ecological engineering construction in different regions are also very different.The inter-annual variation of NPP is not consistent with the spatial distribution characteristics.At present,the differences and driving factors of NPP changes in different ecological geographic regions of the Loess Plateau have not been studied in detail,which has affected the differential assessment of vegetation restoration levels in different ecological geographic regions and the precise implementation of ecological restoration projects.Therefore,based on the CASA(Carnegie-Ames-Stanford approach)model,this study calculated the NPP of the Loess Plateau during the 16 years from 2000 to 2015 and analyzed the Loess Plateau since the implementation of the project of returning farmland to forest(grass).The spatiotemporal changes and driving forces of the NPP of the region as a whole and its different ecological geographic regions provide support for the better implementation of accurate regional ecological restoration projects and the formulation of sustainable economic development policies.This study first collected long-term series of land cover,vegetation index,meteorological(precipitation,temperature,solar radiation)and other data.On this basis,the Loess Plateau's“returning farmland to forests and grasslands”project since 2000-2015 was calculated.NPP,and further analyzed the temporal and spatial changes of the NPP of the Loess Plateau and its ecological geographic regions.Through the land transfer matrix and correlation analysis,the driving force of the NPP changes in each region was studied.The results show:(1)The NPP of the Loess Plateau from 2000 to 2015 shows an overall upward trend in time series,from 161 g C/(m~2·a)in 2000 to 224 g C/(m~2·a)in 2015.The average growth rate is 3.93 g C/(m~2·a);from the perspective of spatial distribution,the NPP in the region shows a trend of declining from southeast to northwest,and the NPP is higher in regions with a wider distribution of water systems.(2)Based on the ecological geographical divisions proposed by Zheng Du(1999),there are nine ecological geographical divisions in the Loess Plateau.The NPP change trends of different ecological geographic regions are different:the desert area of Alashan and Hexi Corridor,the desert steppe area of Ordos and the western Inner Mongolia Plateau,and the artificial vegetation area of the North China Plain.The total NPP of vegetation mainly fluctuates with time during 2000-2005;the grassland area of eastern Inner Mongolia.,Fenwei Basin,deciduous broad-leaved forests,artificial vegetation areas,grassland areas in the central and northern Loess Plateau,and Qilian Qingdong Alpine Basin coniferous forests and grassland vegetation total NPP showed an upward trend from 2000 to 2015;North China mountain deciduous broad-leaved forest areas The total NPP of vegetation showed an upward trend and then a downward trend during 2000-2015;the total NPP of mixed evergreen broad-leaved forests in the Qinba Mountains showed an upward trend.(3)The overall NPP of the Loess Plateau is affected by human activities and climatic factors.Most of the ecological geographic regions NPP are mainly affected by climate,and a few regions are affected by the coupling effect of climate and ecological engineering construction,and the NPP changes brought about by ecological engineering construction are mainly Reflected in 2000-2010.The driving forces of NPP change in different ecological geographic regions are different:the change of NPP in the desert areas of Alashan and Hexi Corridor is mainly affected by precipitation;the NPP vegetation in the desert steppe area of Ordos and the western Inner Mongolia Plateau is mainly affected by precipitation,and is also affected by ecological restoration projects,Regional economic development and other human activities;the vegetation NPP of the eastern Inner Mongolia grassland area is affected by the coupling factors of human activities and precipitation;the NPP of the artificial vegetation area of the North China Plain and the deciduous broad-leaved forest area of the North China mountain is mainly affected by the combined effects of precipitation,temperature,radiation and other climatic factors The NPP of vegetation in the deciduous broad-leaved forests and artificial vegetation areas in the Fenwei Basin is mainly affected by human activities;the vegetation NPP in the grassland areas of the central and northern Loess Plateau is mainly affected by the coupling factors of human activities and climatic factors;the Qilian Qingdong Alpine Basin coniferous forest,The change of NPP in the grassland area is mainly affected by precipitation;the change of NPP in the mixed forest area of evergreen and deciduous broad-leaved forest in the Qinba Mountains is mainly affected by the combined effects of precipitation,temperature,radiation and other climatic factors.(4)There are differences in the types of vegetation suitable for restoration in different ecological geographic regions:In the grassland area of eastern Inner Mongolia,vegetation is suitable to be restored to grassland during the construction of ecological projects;deciduous broad-leaved forests and artificial vegetation areas in the Fenwei Basin have more cultivated land in the ecological restoration project.It is suitable to be restored to vegetation types such as grassland and shrubs;while in the middle-northern grassland area of the Loess Plateau during the construction of ecological restoration projects,the cultivated land is suitable to be restored to grassland. |
PDF Full Text Request