初植密度对4个落叶松无性系生长与干形的影响

目的 探究落叶松优良无性系生长、干形与初植密度的关系,为落叶松无性系人工林的合理经营提供科学依据,促进落叶松良种的推广与应用。方法 以辽宁清原大孤家林场2006年营造的4个落叶松优良无性系3种初植密度(A.2.0 m×3.0 m;B.2.0 m×2.0 m;C.2.0 m×1.5 m)的试验林为研究对象,基于连年测定的树高、胸径、冠幅、树干通直度和圆满度等数据,分析遗传和密度效应对生长和干形特征的影响。结果 4个无性系的胸径、冠幅和单株材积生长量受初植密度影响显著,随密度的减小而增大,13年生时各无性系在低密度A林分比高密度C林分的胸径、单株材积和冠幅分别提高16.4%、28.8%和19.0%;而蓄积量和高径比则表现出相反的规律,蓄积量降低了29.3%。树高、树干通直度和圆满度受初植密度的影响较小。生长特征受遗传效应影响显著,在不同密度下从大到小均为无性系2>无性系1>无性系3>无性系4,在密度A林分中无性系2的胸径、冠幅、单株材积生长量和蓄积量分别比无性系4高出24.5%、21.2%、47.8%和42.8%。无性系间的生长和干形特征受密度影响不同,胸径、单株材积和高径比的分化均随着初植密度增大而加剧,而树高生长、树干通直度和圆满度在无性系间的差异较弱,无性系2在生长和干形变异上综合表现较为稳定。4个无性系在3种密度下抚育间伐起始期均不同,在密度A下无性系1、2、3、4的起始间伐期分别为7、9、11、11 a,在密度B下分别为7、9、9、11 a,在密度C下均为7 a。结论 遗传和密度效应对树木生长和干形均有显著影响,但交互作用不显著。生长比干形特征更易受到遗传和密度效应的影响,在树木生长前期遗传效应大于密度效应。遗传改良林分提早了抚育间伐期,需针对该林分制订相应的经营措施。4个无性系中无性系1和2属于速生型无性系,无性系3和4属于匀速型无性系,若培育大径材,无性系1和2适宜匹配A密度(2.0 m×3.0 m)营造人工林;若培育纸浆材,无性系2和4适宜匹配C密度(2.0 m×1.5 m)营造人工林,无性系3受造林密度影响较小,适宜匹配B密度(2.0 m×2.0 m)营造人工林。综合生长和干形特征来看,无性系2(日永8×长混4-14)由于其速生性和稳定性较好可在辽东山区大力推广造林,将能收获最大的林分蓄积量。

Effects of initial planting density on growth and stem form of four Larix clones

【Objective】 The objective of this study was to investigate the relationships between the growth and stem form of larch clones based on the initial planting density. This findings of the study would provide a scientific basis for the rational management of larch clone plantations and will be beneficial for promoting the application of larch superior clones. 【Method】 Studies were conducted in the Dagujia Forest Farm of Qingyuan, Liaoning. Experiment forests were established in the year 2006 with four excellent larch clones and three initial planting densities (A. 2.0 m × 3.0 m; B. 2.0 m × 2.0 m; C. 2.0 m × 1.5 m). The effects of genetic factors and densities on growth traits and stem form characteristics were analyzed based on the data on tree height, diameter at breast height (DBH), crown width, stem straightness and stem fullness measured over successive years. 【Result】 The DBH, crown width and individual volume of the four clones were significantly affected by the initial planting density and increased with the decreasing density. For 13-years-old clone plantations, the DBH, individual volume and crown width in the low-density forest (A) were 16.4%, 28.8% and 19.0% higher than those in the high-density forest (C). However, the stand volume and height-diameter ratio showed an opposite trend, and the stand volume decreased by 29.3%. Tree height, stem straightness, and stem fullness were less affected by the initial planting density. Growth properties were significantly influenced by genetic factors, and showed the same orders at different densities as follows: Clone 2 > Clone 1 > Clone 3 > Clone 4. In forest stands of density A, the DBH, crown width, individual volume increased and the stand volume of Clone 2 was 24.5%, 21.2%, 47.8% and 42.8% higher than those of Clone 4, respectively. Growth traits and stem form characteristics of clones were affected differentially by densities. The differentiation of DBH, individual volume and height-diameter ratio of clones increased with the increasing initial planting density, while the differences in tree height, stem straightness and stem fullness were marginal among clones, and Clone 2 was more stable in growth and stem shape variations. The four clones had different beginning periods of tending and thinning at the three densities. The initial thinning stages of Clones 1, 2, 3 and 4 were 7, 9, 11 and 11 a, respectively, under density A, 7, 9, 9 and 11 a, respectively, under density B, and 7 a under density C. 【Conclusion】 Both genetic factors and densities had significant effects on the tree growth and stem shape, but the interaction between genetic factors and densities was not significant. Growth traits were more susceptible to genetic factors and densities than stem shape, and the genetic effect was greater than the density effect in the early stage of tree growth. The beginning time of tending and intermediate cutting of the genetically modified stand was earlier; thus, the corresponding management measures should be implemented. Clone 1 and Clone 2 were of a rapid-type, while Clone 3 and Clone 4 were of the uniform type. To cultivate the large-diameter timber, artificial forest could be established by matching Clone 1 or Clone 2 with density A. To cultivate the pulp material, artificial forests could be established by matching Clone 2 or Clone 4 with density C or by matching Clone 3 with density B. Considering the growth traits and stem shape characteristics, Clone 2 could be widely used in the mountainous area of east Liaodong because of its fast growth and stability, and would obtain the largest stand stock. This study clarified the reasonable initial planting density of different larch genotypes and revealed the matching of superior varieties with suitable methods. It is critical to improve the directional cultivation technology of larch and improve the yield and quality of larch plantations in China.