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    利用混合模型模拟树冠特征对兴安落叶松树干干形的影响

    Modeling effects of crown characteristics on stem taper of dahurian larch using mixed model.

    • 摘要: 以黑龙江省七台河市林业局金沙林场114 株人工兴安落叶松树干干形数据为例,利用非线性混合模型技术 拟合Max鄄Burkhart 分段削度方程。结果表明:当利用SAS 软件的PROC NLMIXED 模块对Max-Burkhart 模型进行拟 合时,引入随机参数b1 、b2 、b3 时模型拟合最好;随机参数b1 与冠长率和冠长呈负相关,与树冠高度呈正相关;随机 参数b2 与冠长率和冠长呈正相关,与树冠高度呈负相关;随机参数b3 与冠长率、冠长、树冠高度没有显示出相关 性。利用随机参数b1 、b2 、b3 与树冠特征的相关性构建了含有冠长率、冠长和树冠高度变量的3 个模型,并且所有 模型的参数估计值都是显著的,这充分说明冠长率、冠长和树冠高度对兴安落叶松干形的变化有显著影响。用含 有冠长率的削度模型模拟干曲线,结果表明:冠长率越大,树干削度变化越大, 干形质量越差。

       

      Abstract: In this study, the sample data was based on 114 sample trees from dahurian larch plantations located in Qitaihe Forest Bureau in Heilongjiang Province, northeastern China. The Max and Burkhart (1976) segmented taper equation was fitted using nonlinear mixed-effects modeling techniques. The results showed that Max and Burkhart's model with random parameters b1, b2, b3 showed the best performance when the model was fitted using PROC NLMIXED module in SAS. Random parameter b1 showed negative correlation with crown ratio and crown length, and positive correlation with crown height. Random parameter b2 showed positive correlation with crown ratio and crown length, and negative correlation with crown height. Random parameter b3 did not show any correlation with crown ratio, crown length and crown height. Three taper equations including crown ratio, crown length and crown height variables were developed based on these correlations. Significant test of parameter estimates indicated that crown ratio, crown length and crown height had significant effects on stem taper. A series of taper curves were generated based on the stem taper equation with crown ratio. It shows that trees of the same relative size but with a larger crown ratio generally have a bigger stem taper, lower stem profile quality.

       

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