西南桦21年生人工林生长对造林密度的响应

Response of growth to density for a 21-year-old Betula alnoides plantation

【目的】为了解西南桦人工林的生长过程,采用解析木分析其生长动态。【方法】在云南普洱市江城县,对不同非均匀密度控制(2 m×2 m×5 m、2 m×3 m×5 m、3 m×3 m×5m和2 m×2 m×10 m)造林的21 a生西南桦人工林进行调查基础上,基于每木检尺选择的12株标准木,分析不同造林密度的林木生长过程。【结果】林龄21 a时,不同造林密度的西南桦林木的平均胸径、树高和材积分别为16.82~17.52 cm、26.70~28.00 m和0.274 3~0.333 8 m^(3),林木依然属于旺盛生长阶段,未达数量成熟期。林龄1~6、1~6和6~18 a期间分别是胸径、树高和材积的速生期,其平均连年生长量最高分别达1.61 cm/a、2.67 m/a和2.807 6×10^(-2) m^(3)/a。西南桦隶属云南热区(云南热带和南亚热带的统称)大径材树种,速生期延续较长,其生长对造林密度较为敏感。及时进行密度调控的抚育采伐是培育大径级木材的必要经营措施,林分密度越高,开展抚育采伐的林龄越小。【结论】优质高效的西南桦人工林培育应选择最适宜的造林密度,并且适时开展密度的动态调控。基于单株材积生长,2 m×3 m×5 m可作为西南桦的造林密度。同时,林龄10 a左右应对西南桦人工林开展密度调控的首次抚育采伐。

【Objective】In order to understand the growth process of Betula alnoides plantation,analytical trees were employed to analyze its growth dynamics.【Method】In Jiangcheng county,Pu’er city,Yunnan province,based on the investigation for a 21-year-old B.alnoides plantation of established by different initial uneven row spacings(2 m×2 m×5 m,2 m×3 m×5 m,3 m×3 m×5 m and 2 m×2 m×10 m),the growth process of the trees with different planting densities was analyzed based upon the 12 standard trees selected from each tree measure.【Result】The mean diameters at the breast height(DBH),tree heights(TH)and timber volume of the different planting densities for 21-year-old stand trees were 16.82-17.52 cm,26.70-28.00 m和0.2743-0.3338 m^(3),respectively,and the trees were still in vigorous growth stage,in terms of the quantity of trees was not mature.The fast-growing periods of the DBH,TH and volume were presented in the ages for 1-6,1-6 and 6-18 years old with the maximum current annual increment of which 1.61 cm/a,2.67 m/a and-22.8076×10 m^(3)/a,respectively.B.alnoides belongs to tree species of large-diameter timber in the topical and south-subtropical area in Yunnan province.Tending cutting with timely density control is a necessary management measure for cultivating large-diameter timber.The higher the stand density is,the earlier the age of tending cutting.【Conclusion】Its fast-growing period lasts for a long time,and its growth is more sensitive to planting density.The most suitable planting density should be selected for establishing B.alnoides plantation with high-quality and high-efficiency,and dynamically regulate stand density in time.Based on individual timber volume growth,2 m×3 m×5 m could be applied as the planting density of B.alnoides.At the same time,the first tending cutting of density control should be carried out for the B.alnoides plantation in 10 years old.