Vegetation Restoration Status And Its Driving Forces In The Loess Plateau Since 2000

The terrestrial ecosystem relies heavily on vegetation.The vegetation on the Loess Plateau has greatly improved since the ecological building project was completed.Analyzing regional vegetation change and the elements that drive it can give a scientific foundation for determining the responsive relationship between vegetation,climate,and human activities.Based on SPOT VEGETATION NDVI and meteorological data of the Loess Plateau from 2000 to 2019,The temporal and spatial variations in plant cover and climate parameters were analyzed using trend analysis.The response law between vegetation and climate was studied using correlation analysis.Residual analysis was used to analyze the impact of human activities on regional vegetation restoration.Yan’an city,a typical area of returning farmland to forest and grassland in loess Plateau,was selected to compare and analyze the intensity of vegetation restoration and its influencing factors at different spatial scales.The results show that:(1)From 2000 to 2019,NDVI on the Loess Plateau showed the spatial distribution characteristics of high in the southeast and low in the northwest.NDVI increased significantly,with a linear trend of 0.04/10 a and 0.06/10 a in the growing season.The area with increased NDVI accounted for 91.70%.The average NDVI in four seasons showed an increasing trend,with the largest increasing trend in summer.The annual variation is also obvious.The maximum value of NDVI appears in July and August,which has a certain periodicity and regularity in space.(2)In this region of the Loess Plateau,the climate showed a warming and humidifying trend.The annual precipitation increased at a rate of 43.38mm/10 a,in growing season is 49.17mm/10 a.The annual average temperature rise rate is 0.24℃/10 a,in growing season is 0.20℃/10 a.on the seasonal scale,except for a slight decrease in precipitation in winter,there were different increases in all seasons.The temperature in all seasons showed increasing trend.The monthly average precipitation and temperature change more obviously,with obvious characteristics of continental climate.(3)The correlation between NDVI and annual precipitation in the time series is 0.78 and achieves a very significant level(P < 0.01).The correlation between it and annual mean temperature is 0.25,which has no significant correlation.In space distribution,86.84% of the Loess Plateau vegetation NDVI is positively correlated with annual precipitation,and about 38% is significantly correlated.64.70% of the regions have a positive correlation with the average annual temperature,and only about 10% of the regions have a significant positive correlation.The vegetation recovery in the study area was generally influenced by both climate change and human activities,among which human activities dominated.Human activities played a positive role in vegetation cover change in 71.72% of the areas.(4)In Yan’an City,a typical area for grain for green,the NDVI of vegetation shows a spatial distribution of high in the south and low in the north,declining from south to north.During the study period,the change trend of NDVI is-0.02～0.03.More than 90% of the regional vegetation NDVI showed an upward trend.In the time series,the rising trend of NDVI in Yan’an City reached 0.07/10 a.The correlation between NDVI and precipitation for the whole region is 0.10,of which the area with positive correlation accounts for89.57% of the whole region.The correlation between NDVI and annual average temperature is 0.09,and the area with positive correlation accounts for 64.46% of the whole region.In 94.11% of the area,human activities played a positive role in the change of vegetation NDVI.Vegetation recoveries in this region is more obvious compared to the whole Loess Plateau area,and ecological construction projects led by human activities have achieved great success.