Impact of the 'Grain for Green' project on the spatial and temporal pattern of habitat quality in Yan'an City, China

In an attempt to alleviate increasing pressure caused by human activities on the environment, numerous ecological restoration projects have been implemented around the world. The 'Grain for Green' project in China is currently the largest and most extensive ecological restoration project globally. Research indicates the substantial investment given to this project has achieved significant ecological benefits. Habitat quality is an important indicator of the ability of an ecosystem to provide sustainable conditions for persistence of individuals and populations. Accordingly, this study aimed to investigate the temporal and spatial patterns of habitat quality in Yan'an City, the piloted research area of the 'Grain for Green' project, to identify the impact of the restoration project on the city. Research into the impacts of this project are of great significance for successful implementation of ecological restoration projects moving forward, as well as expanding knowledge on regional ecosystems, and on socio-economic sustainable development. Land use/land cover data of Yan'an City in 2000, 2008, and 2015 were evaluated for the study. The habitat quality index of Yan'an City in 2000, 2008, and 2015 was estimated based on the ArcGIS platform and the InVEST model. The temporal and spatial evolution pattern of habitat quality and its driving factor and spatial clustering characteristics were discussed by using the exploratory spatial data analysis. Our results showed that the main feature of land use change in Yan'an City from 2000 to 2015, driven by the 'Grain for Green' project was the conversion of cultivated land to woodland and grassland; the area of woodland and grassland increased significantly in the city during the study period. The habitat quality of Yan'an City in 2015 was relatively good, demonstrating a pattern of high habitat quality in the south, low habitat quality in the north. The habitat quality index showed an upward trend during the study period; the regional average habitat quality index increased from 0.69 in 2000 to 0.71 in 2015. Additionally, habitat quality of the study area as a whole showed significant positive global spatial autocorrelation, and habitat quality, as well as its spatial variation, indicated obvious spatial clustering differentiation characteristics. Forest-rich areas, such as Huangling County and Huanglong County in the south, exhibited predominately high-high agglomeration characteristics highlighting the need for these areas to remain the focus of ecological protection measures. Conversely, low-low and high-low agglomeration areas were found interspersed, and concentrated in the north (i.e., Baota County, Zichang County, Ansai County, Wuqi County, and in other counties as well as agricultural areas of this region); accordingly, ecological restoration in northern areas should be strengthened and consolidated. Our results indicate that the 'Grain for Green' project will likely affect the processes and functions of the Yan'an City ecosystem by changing land use patterns and structure. In particular, the increase of forestland and grassland in this area will significantly promote the improvement of regional habitat quality. Therefore, by optimizing land use pattern and structure (in particular forest and grassland habitats) will assist in the development of a more coordinated and balanced policy for ecological protection and economic development in response to regional ecological problems, while systematically improving regional habitat quality and ecosystem stability.