Sun Kun, Sun Honggang, Lu Guobin, Fang Lejen, Wan Zhibing, Tan Zifeng
Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou, China.
College of Forestry, Beihua University, Jilin, China.
Front Plant Sci. 2023 May 9;14:1130299. doi: 10.3389/fpls.2023.1130299. eCollection 2023.
The aim of this study was to clarify the mechanism by which thinning alters stand structure and affects forest productivity by characterizing changes in stand quantitative maturity age, stand diameter distribution, structural heterogeneity, and forest productivity of Chinese fir plantations at different thinning times and intensities. Our findings provide insights into how the density of stands could be modified to enhance the yield and timber quality of Chinese fir plantations. The significance of differences in individual tree volume, stand volume, and timber merchantable volume was determined using one-way analysis of variance and Duncan tests. The stand quantitative maturity age was obtained using the Richards equation. The quantitative relationship between stand structure and productivity was determined using a generalized linear mixed model. We found that (1) the quantitative maturity age of Chinese fir plantations increased with thinning intensity, and the quantitative maturity age was much greater under commercial thinning than under pre-commercial thinning. (2) Individual tree volume and the proportion of medium-sized and large-sized timber merchantable volume increased with stand thinning intensity. Thinning promoted increases in stand diameter. pre-commercially thinned stands were dominated by medium-diameter trees when the quantitative maturity age was reached, whereas commercially thinned stands were dominated by large-diameter trees. The living trees volume will decrease immediately after thinning, and then it will gradually increase with the age of the stand. When the stand volume included both living trees volume and thinned volume, thinned stands increased stand volume compared with unthinned stands. In pre-commercial thinning stands, the greater the intensity of thinning, the greater the increase in stand volume, and the opposite was true for commercial thinning. (3) Thinning also reduced heterogeneity in stand structure, which was lower after commercial thinning than after pre-commercial thinning. The productivity of pre-commercially thinned stands increased with thinning intensity, whereas that of commercially thinned stands decreased with thinning intensity. (4) The structural heterogeneity of pre-commercially and commercially thinned stands was negatively and positively correlated with forest productivity, respectively. In the Chinese fir plantations in the hilly terrain of the northern Chinese fir production area, when pre-commercial thinning was performed in the ninth year to a residual density of 1750 trees per hectare, the stand quantitative maturity age was reached in year 30, medium-sized timber accounted for 75.2% of all trees, and the stand volume was 667.9 m per hectare. This thinning strategy is favorable for producing medium-sized Chinese fir timber. When commercial thinning was performed in year 23, the optimal residual density was 400 trees per hectare. When the stand quantitative maturity age was reached in year 31, large-sized timber accounted for 76.6% of all trees, and the stand volume was 574.5 m per hectare. This thinning strategy is favorable for producing large-sized Chinese fir timber.
本研究的目的是通过描述不同间伐时间和强度下杉木人工林林分数量成熟龄、林分直径分布、结构异质性和森林生产力的变化，阐明间伐改变林分结构并影响森林生产力的机制。我们的研究结果为如何调整林分密度以提高杉木人工林的产量和木材质量提供了见解。使用单因素方差分析和邓肯检验确定单株材积、林分材积和可销售木材材积差异的显著性。利用理查兹方程获得林分数量成熟龄。使用广义线性混合模型确定林分结构与生产力之间的定量关系。我们发现：（1）杉木人工林的数量成熟龄随间伐强度增加而增加，商业间伐下的数量成熟龄比预商业间伐下的大得多。（2）单株材积以及中、大径级可销售木材材积的比例随林分间伐强度增加而增加。间伐促进了林分直径的增加。达到数量成熟龄时，预商业间伐林分以中径级树木为主，而商业间伐林分以大径级树木为主。间伐后活立木蓄积量会立即下降，然后随林分年龄逐渐增加。当林分材积包括活立木蓄积量和间伐材积时，间伐林分的林分材积比未间伐林分增加。在预商业间伐林分中，间伐强度越大，林分材积增加越大，而商业间伐则相反。（3）间伐还降低了林分结构的异质性，商业间伐后的异质性低于预商业间伐。预商业间伐林分的生产力随间伐强度增加而增加，而商业间伐林分的生产力随间伐强度降低。（4）预商业间伐和商业间伐林分的结构异质性分别与森林生产力呈负相关和正相关。在杉木产区北部丘陵地带的杉木人工林中，第9年进行预商业间伐至每公顷保留1750株时，30年达到林分数量成熟龄，中径级木材占总株数的75.2%，林分材积为每公顷667.9立方米。这种间伐策略有利于生产中径级杉木木材。在第23年进行商业间伐时，最佳保留密度为每公顷400株。31年达到林分数量成熟龄时，大径级木材占总株数的76.6%，林分材积为每公顷574.5立方米。这种间伐策略有利于生产大径级杉木木材。
