[Effects of litter thickness on natural regeneration of Larix principis-rupprechtii plantations].

In this study, we explored the thickness influence of undecomposed litter layer and semi-decomposed litter layer on the natural regeneration in an artificial pure forest of Larix principis-rupprechtii in the forest area of Guandi Mountain. We divided the litter into an undecomposed layer and a semi-decomposed layer, which was further divided into eight groups based on the thickness. The results showed that when the thickness of undecomposed layer was 0.32-0.83 cm, and that of semi-decomposed layer was 0.18-0.89 cm, the regeneration index was larger (≥0.15), and the regeneration was better. When the thickness of undecomposed layer was more than 1.1 cm and that of semi-decomposed layer was more than 0.5 cm, the regeneration index was smaller (≤0.07), and the rege-neration of understory was worse. Results of redundancy analysis showed that the undecomposed layer thickness of litter had a high and stable explanatory ability for natural regeneration, with a contribution rate of 38.7%, while the semi-decomposed layer thickness had no significant effect on natural regeneration. Structural equation modeling revealed that the thickness of undecomposed layer of litter increased the mechanical resistance to seed germination which had a negative direct effect on natural regeneration (-0.617), and a positive indirect effect on natural rege-neration by influencing the content of alkali-hydrolyzed nitrogen and available phosphorus (+0.178). The combined effects (-0.439) showed an inhibitory effect on the natural regeneration. In conclusion, the thickness of undecomposed layer of litter under L. principis-rupprechtii was most closely related to natural regeneration, and the thickness of semi-decomposed layer had a minimal effect on natural regeneration.