[NDVI Changes and Influencing Factors of Different Soil and Water Conservation Zones in Shandong Province]

Exploring the characteristics of vegetation change and its influencing factors is essential to construct an ecological environment. Based on the NDVI dataset from 2000 to 2020, this study analyzed the spatial temporal attributes of NDVI changes in Shandong Province using the Sen trend analysis and the gravity center migration model. Furthermore, the spatial heterogeneity of NDVI and its influencing factors within the whole study area and different soil and water conservation zones were investigated using a Geo-detector model, considering population, hydrological, topographic, soil types, and vegetation types. The results were as follows： ① The NDVI in Shandong Province from 2000 to 2020 showed a fluctuating upward trend with significant seasonal characteristics that varied from different zones. The annual NDVI change showed a trend of single-peak in the Ⅲ-4-2t, Ⅲ-4-1xt, and Ⅲ-5-2w but showed a trend of double-peak in the Ⅲ-5-3fn. ② Regarding the spatial distribution, the NDVI was higher in the west-north and west-south areas and lower in the north and coastal areas. During the 21 years, the primary type of NDVI change was "medium-high coverage → high coverage," especially in the northeastern part of the soil conservation area of the Ⅲ-4-2t, the western part of the Ⅲ-4-1xt, and the ecological maintenance area of the Ⅲ-5-2w. Overall, 61.47% of the area had a positive trend of NDVI change with the gravity center of high coverage mitigating to the northeast, and the ecological environment was improved. ③ Soil types and population density were the dominant factors affecting NDVI in Shandong Province, with q values of 0.174 and 0.130, respectively. The chief factor in the Ⅲ-5-3fn, Ⅲ-4-2t, and Ⅲ-4-1xt was population density, with q values higher than 0.22, and the dominant factors in the Ⅲ-5-2w were soil types and vegetation types, with q values of 0.326 and 0.227, respectively. The interaction of the two factors enhanced the influence of the single factor, and the relationship between the influencing factors showed two-factor enhancement and nonlinear enhancement. The q-value of population density ∩ relative humidity was the highest, with a value of 0.257 in the Ⅲ-5-3fn. The q-value of population density ∩ soil types was the highest in the Ⅲ-4-2t and Ⅲ-4-1xt, reaching 0.297 and 0.378, respectively. The q-value of soil types ∩ vegetation types was the highest, with a value of 0.444 in the Ⅲ-5-2w. The results are expected to provide valuable references for improving the ecological environment of Shandong Province and lay a scientific foundation to make different conservation strategies for the individual soil and water conservation zones.