不同修枝方法对杨树人工林生长、光合叶面积和主干饱满度的影响

【目的】杨树是我国长江中下游平原地区种植面积最大、木材产量最高的速生工业用材树种之一,如何在适地适无性系的基础上提高无节良材的出材率,是生产中需要解决的关键技术问题。研究不同修枝方法对杨树人工林生长、光合叶面积和主干饱满度的影响,旨在为杨树人工林的产量和质量提升提供依据。【方法】选择两种密度的无性系I-69杨人工林为研究对象,设计4种修枝处理方法,通过测量胸径、树高、枝下高、主干不同高度的直径、光合叶面积,分析不同处理对杨树胸径年均生长量、树高年均生长量、枝下高、单株材积年均生长量、叶面积指数、不同高度主干分段饱满度变化的影响,再用改进层次分析法对不同处理的修枝成效进行综合评价。【结果】3年的研究结果表明,两种密度的I-69杨林分对4种修枝方法的响应存在差异:修枝处理1(T1)和处理2(T2)有利于株行距为3 m×6 m林分胸径、树高和单株材积的生长,而对株行距为6 m×6 m的I-69杨林分生长的影响差异不显著;与对照(T4)相比,修枝显著提高了林木枝下高,并降低杨树单株叶面积和林分叶面积指数;修枝对I-69杨主干不同高度区分段饱满度影响不显著,但修枝处理2有利于提高两种密度林分主干的饱满度。【结论】综合评价分析得出,采用处理2的修枝方法第1年4月上旬不修枝,第2年3月下旬修除冠层Ⅰ的枝条(枝龄4 a),第3年3月下旬修除冠层Ⅱ的枝条(枝龄4 a)]对I-69杨人工林的效果最好,更有利于培育通直、饱满、无节的优质胶合板材。

Effects of pruning methods on growth,photosynthetic leaf area and plumpness of trunk segment in poplar plantations

【Objective】Poplar is one of the tree species with the highest yield, the largest planting areas and the most suitability in the middle and lower reaches of the Yangtze River of China. However, how to improve the plantation yield and wood quality is the key issue to be solved in the practices.【Method】In this paper, the plantations of poplar clone I-69(Populus deltoides cv. I-69/55)with planting spacings of 3 m × 6 m and 6 m × 6 m were taken as the research object, and four pruning treatments were designed. Based on the measurements of diameter at breast height (DBH), tree height, height under branch, trunk diameter at different height and photosynthetic leaves area, the effects of different treatments on the average annual growth of DBH, the average annual growth of tree height, the height under branch, the average annual growth of tree volume, the leaf area index and the plumpness of trunk segments at different height were analyzed, while the pruning effectiveness of different treatments was comprehensively evaluated using the improved analytic hierarchy process.【Result】Based on the 3-year investigation, the results showed that the response of the two plantations with various planting spacings to the pruning treatments was different. Pruning treatments one and two could improve the plantation growth of DBH, tree height and tree volume in the 3 m × 6 m spacing, whereas no significant effect on growth was observed among the 4 pruning treatments in the 6 m × 6 m spacing. Compared with CK, pruning treatments significantly increased the height under branches, and decreased the leaf area and leaf area index. Although pruning treatments did not significantly affect the trunk plumpness, the pruning treatment two was favorable to the trunk plumpness for the plantations of two planting spacings.【Conclusion】In term of the comprehensive assesment, the pruning way of the treatment two would achieve the best effects for P. deltoides plantations, which is more beneficial to cultivating high quality plywood timber with straightness, large plumpness and no knots.