Evaluation Of Ecological Effects For The Grain For Green Project In The Farming-pastoral Ecotone Of Northern China

The farming-pastoral ecotone of northern China is an ecologically fragile zone,and the restoration and reconstruction of ecological environment was an important but difficult task in the last hundred years.Since the Grain for Green project in 2000,the vegetation restoration,ecological environment change and the effect of returning farmland to forest have become the focus of regional and national ecological environment construction.Theore,this paper proposes the evaluation of the ecological effects of Grain for Green project,as well as its influencing factors,taking the central part of the northern ecotone—Ulanqab city as a research case,analyzing the ecological effect evaluation and its influencing factors of the project.The main research findings and results are as follows:(1)The theoretical framework of ecological effect evaluation of returning farmland to forest in the northern agro-pastoral Ecotone is constructed.Based on the analysis of ecological effect evaluation theory of land use change and land cover change,this paper analyzes the ecological mechanism of returning farmland to forest from two aspects of land use and land cover change,and then puts forward the internal and external reasons that affecting the effect of returning farmland to forest from the perspective of farmers.(2)Ecological effects evaluation of returning farmland to forestry based on land use change.By increasing the function of regional ecosystem services,reducing the production of sloping arable land and high altitude arable land,promoting the reconstruction of landscape pattern,the.project promots regional ecological environment to be better.Over the past 15 years,the area of forest and grassland in the study area has been increased by 205765.7hm2,and especially focus on the range of slope below 6° and elevation between 1300m and 1500m of the study area,the proportion of the cultivated land within the range of slope above 15° and elevation of more than 1600m are 17.22%and 0.07%respectively.Under the background of Grain for Green project,the proportion of returning farmland to forest is 36.62%of the total change of regional land use,and there are three ways of farmland intensity,farmland retreatment and farmland abandonment in the area without the program,and their changes account for 49.38%.Within the range of slope above 10°and elevation of more than 1500m,human activities are mainly concentrated on farmland abandonment.Compared with the above three kinds of human activities,returning farmland to forest has great influence on landscape reconstruction,which makes regional landscape fragmentation intensified,landscape diversity increased and landscape structure more stable.(3)Ecological effects evaluation of returning farmland to forest based on vegetation cover change.Since the implementation of returning farmland to forest,the trend of the vegetation coverage in the area of farmland conversion and research area has been improved.At the same time,agricultural intensification" strengthening" the ecological effect of the project,while the abandoned cultivated land"weakening" the ecological effect of the project.The vegetation improvement is concentrated in the Front region of the study area,while vegetation degradation is concentrated on the Back region of the study area.Under the comprehensive influence of human activities and climate,the significantly increased area(20.18%)of NDVI is much larger than significantly decreased area(3.13%)in the project area.Among them,the proportion of increased area of NDVI in the region in front of mountain is much larger than that in the region behind the mountain.After removing the climate influence,NDVI has a similar pattern of change in the project area.Overall,returning farmland to forest is the major land use change that contributes to regional vegetation restoration.In the area of total land use change in the research area,the contribution of returning farmland to the regional vegetation restoration(36.41%)is greater than that of farmland intensity(31.53%).Otherwise,in vegetation degradation area,both returning farmland to forest and farmland abandonment cause regional vegetation degradation,and the effect of returning farmland(30.33%)is greater than that of farmland abandonment(20.73%).(4)Analysis of influencing factors for ecological effect of returning farmland to forest based on farmers.Sloping farmland is the main choice of farmer's farmland conversion.There is still a large number of flat farmland converted to forest,flat farmland conversion results in low target efficiency of the project,and the proportion of sloping farmland conversion in Front region is lower than that in Back region.The low level of management behavior such as improper selection of planting grass and grass,secretly grazing,irrigation,scarcity of management and protection measures causes low survival of trees and poor regional vegetation growth.Therefore,the low target efficiency of the region and the low level of management of farmers are the internal reasons of reducing the ecological effect of returning farmland to forest by affecting the implementation and subsequent vegetation growth.In the non-afforested areas,the low efficiency of the implementation has promoted the farmland abandonment,and the lower target efficiency,the greater probability the degree of abandonment.The good conditions of rural water conservancy facilities,the good quality of cultivated land and sufficient agricultural labor are the external reasons to promote farmland intensity and "enhance" the ecological effect;otherwise poor quality of cultivated land and deficient agricultural labor force are the external reasons to cause farmland abandonment and "weaken" the ecological effect of returning farmland to forest.