西南桦优树选择的研究

通过对西南桦Betula alnoides 分布区的调查, 实测了25 个县261 株西南桦候选优树的数量性状、质量性状及环境因子, 对候选优树9 个性状进行相关分析后选择出材积和通直度作为西南桦选优的主要性状。采用数量化回归的方法来制定优树选择的指标, 建立了各立地因子、林分类型和树龄与材积的多元数量化模型, 其复相关系数达0.920 815 。西南桦材积实测值与理论值间差值的频率分布呈正态分布, 以其差值作为西南桦优树选择的选择指标Ii , 以I 0.5 作为分级依据, 结合通直度制定出西南桦优树选择的标准为①Ⅰ级优树:通直度为Ⅰ级, 同时Ii 0.381 257 。②Ⅱ级优树:通直度为Ⅰ级或Ⅱ级, -0.381 257 Ii 0.381 257 。③一般林木(Ⅲ级木):Ii -0.381 257 。用此标准筛选出西南桦I 级优树46 株,占候选优树的17.62 %, Ⅱ级优树145 株, 占候选优树的55.56 %。图2 表2 参11

Selection of superior trees of Betula alnoides

The quantitative properties , qualitative properties and environmental factors of 261 candidate Betula alnoides trees in 25 counties were measured .The correlation analysis of 9 properties of these candidate trees showed that volume and straightness of stem could be used as the main indexes for selection of superior trees of B . alnoides .The indexes of tree-selection were defined by quantity regression .The multiple entry quantity model was established for different locality factors , stand types and ages of tree with volume .Its multiple correlation coefficient was 0.920 815 .There was a difference between theoretical and realistic volume ;the frequency of difference was in normal distribtuion .The difference was the selection index Ii for superior trees selection and I 0.5 was the foundation of classification .The superior tree selection standards were as follows :(1)Class Ⅰ superior tree :Class Ⅰ straightness of stem , Ii 0.381 257 .(2)Class Ⅱ superior tree :Class Ⅰ orⅡ straightness of stem, -0.381 257 Ii 0.381 257 .(3)Class Ⅲ superior tree (normal tree):Ii -0.381 257 .The 46 class Ⅰsuperior trees and 145 class Ⅱ superior trees were selected by the standards .They accounted for 17.62 % and 55.56 % in all candidate superior trees respectively .[ Ch , 2 fig .2 tab .11 ref .]