Sources of Variation in the Self-Thinning Boundary Line for Three Species with Varying Levels of Shade Tolerance
Sources of Variation in the Self-Thinning Boundary Line for Three Species with Varying Levels of Shade Tolerance
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DOI：
10.1093/forestscience/55.1.84
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发表时间：
2009-02
期刊：
影响因子：
1.4
通讯作者：
A. Weiskittel;P. Gould;H. Temesgen
中科院分区：
文献类型：
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作者：
A. Weiskittel;P. Gould;H. Temesgen
物种自疏边界线已被广泛分析与各种统计技术。在林业文献中的大多数以前的研究报告说，这种关系并没有在一系列的立场和网站的因素不同，但这些研究主要使用的统计技术，使模型拟合主观或解释协变量的显着性困难。越来越多的证据表明，使用随机前沿分析是一种有效的统计手段，客观拟合物种自疏边界线，提供了机会来测试额外的协变量的影响。利用广泛的同龄沿海花旗松（Pseudotsuga menziesii var. menziesii [Mirb.] Franco）、西部铁杉（Tsuga heterophylla）和红桤木（Alnus rubra Bong.）在太平洋西北部的数据集，我们检查了假设的截距和斜率的物种自疏边界线是不敏感的林分和网站的因素。李克比检验表明，网站指数，林分原产地（自然与种植），和纯度（在主要物种的断面积的比例）显着影响的物种自疏边界线截取本研究中检查的每个物种。在花旗松和西部铁杉，自疏边界的斜率也取决于林分的起源，以及现场指数的情况下，花旗松。施肥并没有显着影响的物种的自疏线道格拉斯冷杉和西部铁杉的截距或斜率。此外，列入网站方面和干燥指数略有改善的红色桤木模型的自疏，但无论是网站土壤还是气候变量改善模型西部铁杉和道格拉斯冷杉。因此，物种自疏边界线可以在不同的林分之间变化很大，它的变化是由几个不同的因素驱动的;随机前沿分析是识别这些因素的有效工具。
The species self-thinning boundary line has been widely analyzed with a variety of statistical techniques. Most previous studies in the forestry literature have reported that the relationship does not differ across a range of stand and site factors, but these studies have primarily used statistical techniques that make model fitting subjective or interpretation of covariate significance difficult. There is growing evidence that the use of stochastic frontier analysis is an effective statistical means for objectively fitting the species self-thinning boundary line, offering the opportunity to test the influence of additional covariates. Using extensive even-aged coastal Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco), western hemlock (Tsuga heterophylla), and red alder (Alnus rubra Bong.) data sets in the Pacific Northwest, we examined the assumption that the intercept and slope of the species self-thinning boundary line are insensitive to stand and site factors. Likelihood ratio tests indicated that site index, stand origin (natural versus planted), and purity (proportion of basal area in the primary species) significantly influenced the species self-thinning boundary line intercept for each of the species examined in this study. In Douglas-fir and western hemlock, the slope of the self-thinning boundary was also dependent on stand origin as well as site index in the case of Douglas-fir. Fertilization did not significantly influence the intercept or slope of the species self-thinning line for Douglas-fir and western hemlock. In addition, the inclusion of site aspect and dryness index marginally improved the red alder model of self-thinning, but neither site soil nor climatic variables improved the models for western hemlock and Douglas-fir. Thus, the species self-thinning boundary line can vary significantly among stands, and its variation is driven by several distinct factors; stochastic frontier analysis is an effective tool for identifying these factors.