Effects of different management modes on soil characteristics and wood species structure of Cunninghamia lanceolata large-diameter timber plantation

The effects of different management modes on soil characteristics and wood species structure of Cunninghamia lanceolata large-diameter timber stand were explored theoretically, which provided a theoretical reference for long-term efficient cultivation of C. lanceolata large-diameter timber and maintenance of forest productivity. The 43-year-old C. lanceolata large-diameter timber stand was taken as the research object, and three different management modes were set up: selective cutting and intercropping with Castanopsis hystrix (T1), selective cutting only (T2), and no selective cutting and no intercropping (T3). The differences in soil physical and chemical properties, enzyme activities and wood species structure among different modes were compared, and the correlation between soil properties and wood species yield was analyzed. The soil bulk density of the three treatments was proportional to the soil depth (0-60 cm). The water content and the contents of organic carbon, total nitrogen, available nitrogen and available potassium decreased with the increase of soil depth. The content of available phosphorus did not show a significant change trend. The soil bulk density of each soil layer was T2 > T1 > T3; the water content is T3 > T1 > T2; The T1 treatment exhibited the highest levels of organic carbon and total nitrogen, whereas the T3 treatment showed the lowest concentrations of total phosphorus and total potassium.The average soil sucrase activity was the highest in T1 treatment and the lowest in T2 treatment. The activities of urease and cellulase were the highest in T1 treatment and the lowest in T3 treatment. The catalase activity was the highest in T3 treatment and the lowest in T2 treatment. The output of C. lanceolata wood species in the three treatments was mainly large-diameter wood. The output and output rate of medium and small-diameter wood were the highest in T3 treatment and the lowest in T1 treatment. The output and output rate of large-diameter wood were the highest in T1 treatment, which were 336.11 m³·hm⁻² and 75.82 %, respectively. There was a strong negative correlation between the yield of medium and small diameter timber and the urease activity in 0 ～ 10 cm soil layer, and there was a significant positive correlation between the yield of large diameter timber and the soil moisture content in 40～60 cm soil layer (P < 0.01). There is a strong negative correlation with bulk density and total potassium content. The comprehensive index of soil quality from large to small is T1 ( 2.428 ), T2 ( -1.017 ), T3 (-1.411). In summary, The improvement effect of T1 treatment on the soil characteristics of C. lanceolata large-diameter timber stand was better, and it was more conducive to the improvement of the output and output rate of large-diameter C. lanceolata.