Abstract:

【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.

Key words: Larix (larch) clone, superior clones, afforestation density, growth, stem form