尾叶桉、巨桉优树选择标准的建立

尾叶桉、巨桉是华南地区引种成功及重点改良的2种桉树，以往选优基本上是围绕短周期纸浆纤维材改良目标而进行，选优林分的林龄小于15 a，多为6 a以下。本文以林龄16 a以上的尾叶桉、巨桉林分进行选优，以期为中大径材桉树培育提供改良用的优树材料。采用三株优势木对比法和配对T检验法确定优树生长量临界值，并兼顾干形质量指标进行选优。通过对25株候选优树和75株优势木生长量、分枝与干形分值的分析，建立了尾叶桉、巨桉优树选择标准：优树的单株材积≥3株优势木平均单株材积的1.35倍，胸径≥3株优势木平均胸径的1.15倍或树高≥3株优势木平均树高的1.03倍，分枝＋干形得分≥7。在候选的25株优树中有17株符合标准被评为优树，入选率为68%。

Establishing Optimal Selection Criteria for Eucalyptus urophylla and E. grandis

Eucalyptus urophylla and E. grandis have been highly successful as exotic forest plantation species in southern China. In the past, the goal of selection for improvement of both species was to improve wood pulp fiber yield for trees grown on rotations of 15 years or less, and mostly for rotations of less than 6 years. In this paper, plantation grown E. urophylla and E. grandis trees of more than 16-year-old were studied to understand the optimal selection method for improving production of large-diameter timber trees of both E. urophylla and E. grandis. Selection methods for single plus trees and groups of 3 plus tree were compared using paired t-tests to determine the critical value of plus tree growth taking into account quality indicators of stem form. The growth, branch and stem form score of the 25 candidate plus trees and 75 dominant trees were analyzed to establish the optimal selection criteria for E. urophylla and E. grandis：individual volume of plus tree ≥ 1.35 times average individual volume of 3 plus trees, DBH ≥ 1.15 times average DBH of 3 plus trees or height ≥ 1.03 times average height of 3 plus trees, the score of branching＋stem form ≥ 7. In this study, 17 trees were selected by the standard from 25 candidate plus trees providing a selection ratio of 68%.