Study on site selection and density control technology of cultivating large diameter Chinese fir wood in Jiangxi Province

<bold>Objective</bold> The site and density effects of large-diameter timber cultivation of Chinese fir（<italic>Cunninghamia lanceolata</italic>（Lamb.）Hook）under the whole cycle were studied，and the suitable density of stand under different site indexes in the process of large-diameter timber cultivation of Chinese fir was determined，which provided theoretical and practical basis for large-diameter timber cultivation technology of Chinese fir. <bold>Method</bold> The 30-year-old and 50-year-old existing Chinese fir forests in Guanshan Forestry Station with different site indexes and retention densities were chosen as research material.The data of the site index of 14-22 and different retention densities were investigated，and the site and density effects of large-diameter timber cultivation were analyzed. <bold>Result</bold> Under the same density of 30 a and 50 a Chinese fir plantations，there was a positive correlation between the status index and the greater the total stock，total timber yield，large diameter timber yield and the rate of large-diameter timber.As the density increases，the total stand stock，total timber yield and large diameter timber yield increased first and then decreased，while the proportion of large diameter timber，the proportion of large diameter timber volume，and the rate of large diameter timber output show a downward trend. <bold>Conclusion</bold> After comprehensive consideration，the site with a site index of more than 14 should be selected to cultivate large-diameter timber in the 50-year cultivation cycle.When the site index is 12，it is not suitable for cultivating large-diameter wood.When the site index is 14 and 16，the stand retention density of Chinese fir is 1 200 trees/hm² when the stand is 30 years old，the stand can be thinned to 900 trees/hm² when the stand is 50 years old，the stand stock is 460-500 m³/hm²，and the rate of large diameter timber can reach more than 55%.When the site index is above 18 and the stand is 30 years old，the stand retention density is 900 trees/hm².The stand can be shortened to 600 trees/hm² when the stand is 50 years old，the stand stock is 500-560 m³/hm²，and the rate of large diameter timber is above 70%.