北洛河上游流域植被覆盖度时空变化及其地形分异特征OA北大核心CSTPCD

[Objective]The aims of this study are to reveal the process of vegetation restoration in loess hilly and gully region before and after the implementation of the Grain for Green Project as well as its topographic differentiation effects,and to provide scientific support for formulating appropriate regional ecological construction and protection countermeasures.[Methods]Based on four Landsat images and digital elevation model data from 1990 to 2019 in the upper reaches of the Beiluo River watershed,the spatiotemporal changes of vegetation coverage and its topographic differentiation characteristics of the study area before and after the implementation of the Grain for Green project were studied using pixel dichotomy model and GIS technology.[Results](1)The spatial distribution of vegetation coverage in the watershed was high in the southeast and lower in the northwest.From 1990 to 2019,the average annual vegetation coverage of the watershed showed a continuous increasing trend,and the proportion of high-grade vegetation coverage area increased signifi-cantly after the implementation of the Grain for Green Project.The proportions of high-grade vegetation cov-erage area in 1990,2000,2010 and 2019 were 0.97%,6.96%,42.17% and 64.18%,respectively.(2)In each period of the Grain for Green Project,the vegetation coverage of the watershed improved continuously,but the vegetation degradation occurred in small parts of northwestern of the watershed.During the study period,vegetation coverage structure of the watershed significantly improved.The area with medium-high and high vegetation coverage was mainly transferred in,and the area with medium-low and low vegetation coverage was mainly transferred out.(3)Topographic factors had an obvious impact on the vegetation coverage distri-bution pattern in the watershed.The vegetation coverage tended to decrease with the increase of elevation.The vegetation coverage was positively correlated with slope,and the steeper the slope,the greater the vege-tation coverage.The vegetation coverage showed the characteristics of shady slope>half-shady slope>flat land>half-sunny slope>sunny slope.[Conclusion]The implementation of the Grain for Green Project plays a key role in increasing the vegetation coverage in the upper reaches of the Beiluo River watershed,but the vegetation degradation is serious in some areas.In the future,more attention should be paid to the impact of the urban spatial expansion and climate change on vegetation construction in the watershed,so as to cope with the challenges of sustainable development of vegetation ecosystem under the changing environment.