Objective Analyzing the responses of soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry to stand age and density in Pinus tabuliformis forest land can provide scientific evidence for sustainable management of Pinus tabuliformis plantations.
Method This study focused on Pinus tabuliformis plantations of three stand ages (30, 40 and 50 years) and three densities (1 000−1 500 tree/ha, 2 500−3 000 tree/ha, 4 000−4 500 tree/ha) in the Caijiachuan Watershed, western Shanxi Province of northern China. Soil C, N, and P contents and their stoichiometric ratios were measured and analyzed from 0 to 100 cm depth layer.
Result The two-factor interaction of stand age and density showed a significant influence on SOC, total N (TN), C∶N, C∶P, and N∶P （P < 0.05). (2) Stand age had different effects on soil TN, SOC, and chemical stoichiometric ratios in stands of different densities, plantations with high density exhibited soil fertility decline at 50 years. Plantations with older age indicated that lower density was more suitable for soil nutrient improvement. (3) Soil TN was significantly positively correlated with TP, SOC, C∶P, and N∶P (P < 0.05); SOC was significantly positively correlated with C∶N, C∶P, and N∶P (P < 0.01). C and N elements had a significant impact on soil chemical stoichiometry and stand growth (P < 0.05).
Conclusion In loess area, it is necessary to rationally adjust stand density according to different Pinus tabuliformis stand ages. For a 30-year-old stand, the recommended density was 4 000 tree/ha. The density should be reduced to 2 500−3 000 tree/ha at 40 years. For a 50-year-old stand, the optimal density range for soil nutrients was 1 000−1 500 tree/ha. The appropriate stand density can ensure that the soil nutrient status of the forest land is maintained at an optimal level, which is beneficial for the current sustainable management of the artificial forest and the continuous function of subsequent soil conservation.
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