南亚热带杉木林分蓄积量生长立地与密度效应

The Site and Planting Density Effects on the Wood Volume Growth of Chinese Fir Plantations in South Subtropical Area

[目的]揭示南亚热带不同密度和立地条件下杉木人工林蓄积量发育规律。[方法]以广西大青山36 a生杉木密度试验林为研究对象,分析A(1 667株·hm^-2 )、B(3 333株·hm ^-2 )、C(5 000株·hm^-2 )、D(6 667株·hm ^-2 )、E(10 000株·hm^-2 )5种初植密度杉木人工林总蓄积、活立木蓄积动态变化。[结果]初植密度与立地对林分活立木蓄积生长的影响与总蓄积一致。中幼龄阶段林分总蓄积与初植密度和立地正相关,初植密度愈高,立地指数愈大,林分蓄积生长量愈大;但15 a后中等密度林分总蓄积最大。林分蓄积连年生长高峰随密度增大而愈早;平均生长达高峰后下降,密度越大下降越早、下降趋势越明显;林分蓄积连年生长量、平均生长量大多分别在10、14 a达到高峰,林分蓄积生长率降到3%时林龄为19-25 a。[结论]随初植密度增大,立地指数对林分总蓄积的影响程度减弱。若以蓄积生长量最大为培育目标,16指数级以C密度为最适宜造林密度。南亚热带杉木林首次间伐、最后间伐、主伐时间分别为10、14、25 a;主伐林龄不宜早于19 a,且初植密度愈低主伐林龄更晚,A、B密度林分的主伐林龄可推迟到25 a。

[Objective]To provide theoretical and practical basis for the efficient cultivation of Chinese fir, the effects of site and planting density on stand wood volume growth rules of Chinese fir (Cunninghamia lanceolata) plantations in south subtropical area of China were studied.[Method] Based on 36-year positioning observation data of Chinese fir plantations in Daqingshan, Guangxi, including five planting densities, i.e. 1 667 trees·hm^-2 (A), 3 333 trees·hm ^-2 (B), 5 000 trees·hm^-2 (C), 6 667 trees·hm ^-2 (D) and 10 000 trees·hm^-2 (E), the dynamics of total wood volume and living trees wood volume were analyzed.[Result] The effects of planting density and site on the growth of total wood volume and living trees wood volume were consistent. The total wood volume was obviously positively related to stand planting density and site index during middle and young ages. The higher the planting density and the site index were, the bigger the total wood volume became, and the total wood volume of stand with medium density became much bigger than the other stands after 15 years. The mean annual increment (MAI) of total wood volume increased rapidly at first and then declined after reaching to the peak, and the higher the density was, the earlier the decline started and more obvious it became. The stand ages at which the current annual increment, and the MAI of total wood volume reached to its peaks were at the 10th and 14th years, respectively, and the growth rate of total wood volume decreased to 3% at the age of 19 25.[Conclusion] The influence of site index on total wood volume of stands with relatively low planting density is greater, but with the increasing of planting density, the influence becomes weak. If the maximum wood volume is taken as the cultivation target, density C is the most suitable planting density at the site index of 16. The first thinning, last thinning and final cutting in south subtropical area of China should be at about 10, 14, 25 years old, respectively. The final cutting should not be earlier than 19 years old, the lower the planting density is, the later the final cutting will be, and the final cutting of the stands with density A and B can be postponed to 25 years old.