Regulation of stand density alters forest structure and soil moisture during afforestation with Robinia pseudoacacia L. and Pinus tabulaeformis Carr. On the Loess Plateau

How do forests respond to management practices designed to improve their ecological benefits? Clarifying how forest structure and soil moisture vary with the regulation of stand density can help us answer the question. Appropriate maintenance of stand density via thinning or complementary planting can optimize stand structure and increase soil moisture in low-efficiency stands. In this study, four 40 m ? 40 m sample plots (each divided into four 20 m ? 20 m subplots) were established in plantations of Robinia pseudoacacia L. (RP) and likewise those of Pinus tabulaeformis Carr. (PT) plantations. The recommended stand densities below the soil water carrying capacity for vegetation were set up, ranging from 1500 to 1800 plants?ha? 1 for RP and from 1100 to 1600 plants?ha? 1 for PT. Across the three years since stand density regulation practices were implemented, the significant dominant factors varied. Their corresponding contribution rates (CRs) were as follows: stand density, 0.766 (RP) and 0.857 (PT); canopy density, 0.814 (RP); leaf area index, 0.822 (PT); Pielou?s index of herbs, 0.908 (PT); and water retention of litter, 0.932 (PT). Furthermore, soil infiltration (0.861, RP) had significant effects on shallow and deep soil water. With consideration of the above drivers, the optimum stand density range should be further determined in future experiments. These results can provide guidance to forest managers on how to remain within the carrying capacity of stands and their water resources, which is critical for constructing highquality ecological systems on the Loess Plateau.

Automated summary

Managing forest stand density can improve ecological benefits by optimizing stand structure and increasing soil moisture. Research on Robinia pseudoacacia and Pinus tabulaeformis plantations found that factors such as stand density, canopy density, leaf area index, herb diversity, and litter water retention significantly affect soil water. Further studies are needed to determine the optimal stand density range for future experiments.