低密度造林对杉木生长、形质和材种结构的影响

【目的】对江西大岗山地区低密度杉木人工林自然稀疏进程、林木生长进程、形质特征、材种结构和经济效益动态变化特征进行调查分析,为杉木低密度造林调控管理提供科学依据。【方法】以2 500株/hm²传统造林密度为对照,对设立在江西省分宜县初植密度为1 111、1 667株/hm²的2种低密度杉木试验林生长发育规律进行了25 a动态监测分析。【结果】林分平均树高、平均胸径、枝下高和蓄积量均随林龄增加而增加,随密度的减小而递增;19~25年生时不同造林密度林分的平均胸径差异达显著水平,8~19年生和22~25年生时分别为枝下高和蓄积量增加最快的时期,但二者受林分密度的影响均不明显;累积枯损率和林木自然分化程度随林龄的增加而增加,随密度的降低而减小,25年生时不同造林密度林分累积枯损率差异达显著水平;林木平均冠幅随年龄增加呈先上升后下降再缓慢上升的趋势,19年生时不同密度的冠幅间差异达显著水平;年均自然稀疏率和林冠重叠度随林龄的增加呈先上升再缓慢下降的趋势,年均自然稀疏率22年生时达最大值,林冠重叠度8年生时达最大值,此时不同密度的林冠重叠度间差异达显著性水平。25年生时,造林密度为1 111和1 667株/hm²林木的胸高形率、心材占比高于造林密度为2 500株/hm²的指标,断梢率、高径比和幼/成龄材比率低于造林密度为2 500 株/hm²的指标,其中高径比密度间差异达显著水平;19~25年生近成熟龄期,林分大径木比例和大径材出材量均随造林密度降低而增加,该时期1 111和1 667株/hm²低密度林分总蓄积量、总出材量和经济材出材量逐渐与造林密度为2 500株/hm²接近,25年生时造林密度为1 667株/hm²的总蓄积量、总出材量和经济材出材量均超越造林密度为2 500株/hm²的指标。经济效益分析表明,造林密度1 667株/hm²林分的纯收入和净现值最大,比2 500株/hm²林分的提高了1.09倍和1.10倍,而造林密度为1 111株/hm²的效益成本比和内部收益率最高,分别为7.35和30.20%。【结论】初植造林密度1 111和1 667株/hm²较适宜在江西大岗山地区杉木人工林造林中选择应用。

Effects of low stand density afforestation on the growth,stem-form and timber assortment structure of Cunninghamia lanceolata plantations

【Objective】 The goal of this study was to clarify the growth process, shape, quality characteristics, timber species structure and dynamic change characteristics of the economic benefits of low-density Cunninghamia lanceolata plantations in the Dagangshan area of Jiangxi Province. 【Method】 Using the traditional planting density of 2 500 individuals/hm ² as the control, the growth and development of two low-density Chinese fir experimental forests with an initial planting density of 1 111 and 1 667 individuals per hectare in Fenyi County of Jiangxi Province were monitored and analyzed for 25 years. 【Result】 The average tree height, average diameter at breast height (DBH), under branch height, and stock volume increased with stand age and decreasing densities. The average DBH of different stand densities at 19-25 years of age differed significantly, and the height under branches and volume increased the fastest at 8-19 years and 22-25 years of age, respectively. The results showed that the degree of natural differentiation increased with an increase in forest age and decreased with a decrease in densities. The cumulative withering rate was 25 years, and the difference between densities was significant. The average crown width of trees first increased, then decreased, and then increased slowly with an increase in age, and reached significant differences among densities at 19 years old. The annual average sparse rate and degree of crown overlap of natural lines first increased and then decreased slowly with an increase in forest age; the annual average natural sparsity rate reached a maximum value at 22 years of age, and the canopy overlap degree reached a maximum value at 8 years of age. The difference between the densities was significant. At 25 years, the breast height form ratio and heartwood ratio of 1 111 individuals per hectare and 1 667 individuals per hectare were higher than 2 500 individuals per hectare , and the rate of broken shoots, ratio of height to diameter, and young-adult wood ratio were lower than 2 500 individuals per hectare , and the difference in the height diameter ratio density was significant. At the near mature age of 19-25 years, the proportion of large diameter trees and volume of large-diameter timber increased with the decrease in stand densities, and 1 111 individuals per hectare and 1 667 individuals per hectare occurred in this period. The results showed that the total volume, total timber output, and economic timber output of the low-density stands were close to 2 500 individuals per hectare , and the total volume, total timber output, and economic timber output of 1 667 individuals per hectare stand exceeded 2 500 individuals per hectare at 25 years, respectively. The economic benefit analysis showed that the net income and net present value of the 1 667 individuals per hectare stand were the highest, which were 1.09 and 1.10 times higher than those of the 2 500 individuals per hectare , respectively, whereas 1 111 individuals per hectare had the highest benefit-cost ratio and internal rate of return, which were 7.35 and 30.20%, respectively. 【Conclusion】 The initial planting density of 1 111 individuals per hectare and 1 667 individuals per hectare can be selected and applied in the plantations of Cunninghamia lanceolata in the Dagangshan area of the Jiangxi Province.