Effects of Stand Structure and Soil Depth on Soil Properties in Cryptomeria japonica Plantations

Laicong Luo Kang Lin Chao Luo Jianming Wang Tianze Duan Lingjian Tao Peng Li Xiaobin Fu Siqin Guo Yuanqiu Liu ^*

• College of Forestry, Jiangxi Agricultural University, Nanchang, China

Stand structure plays a key role in forest management, directly influencing the physicochemical properties of forest floor soil, which in turn affects forest health and productivity. Cryptomeria japonica plantations are extensively distributed across the mountainous regions of Japan and China and serve a vital role in this ecosystem. In this study, stand structures were classified as good, medium, or poor based on canopy closure (<0.5, 0.5–0.7, >0.7), understory vegetation cover (>0.8, 0.6–0.8, <0.5), and stand density (<650, 650–900, >900 trees/ha), respectively. These classifications reflect critical structural features that enhance ecosystem services, such as low canopy closure promoting light penetration and understory growth, high understory vegetation cover facilitating organic matter input, and moderate stand density reducing soil compaction. This study investigates the effects of varying stand structures and soil depths on the physicochemical properties of soil in C. japonica plantations on Mount Lu. Stand plots with varying stand structures (good, medium, poor) were selected, and soil samples from different depths (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm) were analyzed for bulk density, porosity, water-holding capacity, as well as carbon (C), nitrogen (N), phosphorus (P), and stoichiometric ratios. The results show that both stand structure and soil depth significantly affect soil physical properties and chemical stoichiometric characteristics. Compared to poor stand structures, well-structured stands significantly reduce soil bulk density, increase porosity, and enhance water-holding capacity. Soil organic carbon and total nitrogen content are higher in well-structured stands, particularly in the surface soil layer, while C:N, C:P, and N:P ratios gradually decrease with increasing soil depth. Our results indicate that maintaining optimal stand structures (low canopy closure, high understory cover, moderate density) significantly improves soil porosity, water retention, and nutrient cycling efficiency. These findings directly support sustainable forest management by guiding structural adjustments to enhance soil health.