Spatial Distribution of Timbered Soil Physicochemical Properties and Their Effects on the Vegetation Indices in Tongzhou, Beijing

Tongzhou District is designated as a city sub-center with 33.3% forest cover, representing significant ecological value for Beijing. However, this extensive forest area has lacked detailed conservation measures, leading to inefficient resource utilization over the years. Therefore, determining the various maintenance measures for the different areas is very important. This study focused on exploring the relationship between the soil nutrient structure and vegetation indices in the area to develop a more precise plan for forest maintenance. This study collected 163 sample points in the four zones of Tongzhou district, including electrical conductivity, acidity and alkalinity, bulk density, soil organic matter, total nitrogen, available nitrogen, total phosphorus, total potassium, available potassium, available phosphorus, as well as vegetation characteristics such as richness, coverage, and height. The normalized difference vegetation index, difference vegetation index, ratio vegetation index, green light vegetation index, and soil-adjusted vegetation index were calculated by remote sensing images. To test the spatial distribution of soil nutrient construction and the relationship between soil and vegetation indices using the spatial interpolation method and Pearson correlation analysis, the results showed that: (1) The soil organic matter and total nitrogen were extremely low (1.282 and 0.461 g/kg). In contrast, the available and total potassium was extremely high (227.994 mg/kg and 16.866 g/kg); (2) High-value areas of available and total potassium are in the northern area, the available and total phosphorus in the central area, and the pH in the northeast area, with overall neutral-to-alkaline conditions; (3) The mean of coverage is 72.120, with high-value areas concentrated in northern parts of the central areas. While the overall coverage is extensive, height varies significantly (3.300–479.867), and high-density vegetation is limited to the northern part of the central area; (4) Vegetation height shows a significant negative correlation with total potassium and a significant positive correlation with pH values. We suggest that it is necessary to properly retain fallen leaves and dead grass in the forest to increase the organic matter content of the soil, apply more organic fertilizers, and supplement nitrogen fertilizers. In Tongzhou District, potassium fertilizer application should be reduced, particularly in the northeast and northern areas, to prevent excess fertility. In the central area, phosphorus fertilizer application should also be controlled, while in alkaline areas, fertilizer use should be optimized, and lime should be added to improve pH. Compost or humic acid can improve the soil’s ability to absorb and release phosphorus, thereby enhancing plant phosphorus uptake and increasing vegetation height and coverage. This study only analyzed spatial changes without further examining soil layer differences at varying depths and the effects of soil microorganisms. In the future, soil fertility in various depths and the functionality and diversity of soil microorganisms are worth further exploring.