The Influence of Slope Aspect on the Spatial Heterogeneity of Soil Nutrients and Seedling Regeneration in Pinus sylvestris var. mongolica Plantation Forests

In the fields of forestry, ecology, and pedology, different slope aspects exhibit significantly different microenvironments and soil conditions, which ultimately lead to disparities in seedling regeneration. Therefore, studying the effects of soil nutrients on seedling regeneration under different microenvironmental conditions can provide critical data for the artificial promotion of natural regeneration. In July 2021, the seedling regeneration status in 900 m2 artificial Pinus sylvestris var. mongolica forests with different slope aspects was investigated. Soil nutrient indices were obtained through the collection and measurement of soil samples. Geostatistics were used to quantify the spatial heterogeneity of soil nutrients at a small scale. Soil nutrient information from the seedling growth locations was acquired by combining geographic information system (GIS) technology and laboratory experiments to analyze the effects of soil nutrients on seedling regeneration. The spatial heterogeneity of soil nutrients and their effects on seedling regeneration change with different slope aspects. Even at a small scale (3 m), spatial heterogeneity remains evident. Shaded slopes are more prone to supporting biennial seedlings and older saplings, while seedlings on sunny slopes exhibit superior growth indicators (height and ground diameter). The correlation calculations and redundancy analysis (RDA) of the relationship between soil nutrients and seedling regeneration show that although the soil nutrient content inhibits seedling quantity, they can enhance seedling growth indicators, among which soil organic matter plays the most critical role. Different slope aspects affect soil nutrients and seedling spatial patterns, and increased soil nutrients can promote the natural regeneration of Pinus sylvestris var. mongolica seedlings.