Black spruce needle nitrogen concentration from 5 stands in 1999

We collected black spruce needle from several sites located near Fairbanks Ak, and Delta, Ak in August 1999 (Sites designated here as S1, S2, and S3) were located in Fairbanks (64o40?N, 148o15?W), Alaska (S1: 64o52.164? N, 147o51.462? W; S2: 64o52.058? N, 147o51.378? W; S3: 64o51.603? N, 147o52.789? W) with 2 additional sites (S4, S5) in Delta, Alaska (64010? N, 145030? W). In each stand, 30 trees were randomly selected for sampling. Within each tree, five shoots were collected from the southern aspect of the mid-canopy height from each of the following age classes: 0-, 1-, 4-, 9-, and 19-years old. In two of the Fairbanks stands (S2, S3), 19-year old needles were not present. A total of 690 samples over the five stands include 150 samples per stand in three stands (S1, S4, S5) and 120 samples per stand in the other two stands (S2, S3). Needles were returned to the lab and nitrogen content was determined. We used a three-factor nested analysis of variance (ANOVA) to evaluate differences in needle N concentration among the ages of needles on a tree, among trees nested within a stand, and among stands. Ages and stands were treated as fixed factors and tree was treated as a random factor. The ANOVA and means testing for these differences used Proc GLM in the SAS statistical package with needle N content as the dependent variable and needle age, tree, and stand as independent variables. The GLM procedure handled the problem of missing treatment combinations within the ANOVA. Type III sum of squares was used to test the effects of factors without interactions

1999年8月，我们于阿拉斯加州费尔班克斯（Fairbanks）及德尔塔（Delta）周边的多个样地采集黑云杉（black spruce）针叶。本次研究共设置5个样地：S1、S2、S3位于费尔班克斯（基准坐标：北纬64°40′，西经148°15′），具体采样坐标分别为S1：64°52.164′N，147°51.462′W；S2：64°52.058′N，147°51.378′W；S3：64°51.603′N，147°52.789′W；另有S4、S5两个样地位于阿拉斯加州德尔塔（基准坐标：北纬64°10′，西经145°30′）。在每个林分中，随机选取30棵树木开展采样。每棵树从中层林冠的南侧方位采集5根枝条，分别获取0年生、1年生、4年生、9年生及19年生的针叶。其中费尔班克斯的S2、S3两个林分未发现19年生针叶。五个林分共计获得690份样本：其中S1、S4、S5三个林分各150份，S2、S3两个林分各120份。采集的针叶被带回实验室后，测定其氮含量。我们采用三因素嵌套方差分析（ANOVA），分别评估单株树体内部不同龄级针叶的氮浓度差异、林分内不同树体间的差异以及不同林分间的差异。其中，针叶年龄与林分设为固定因子，树体设为随机因子。本次方差分析及差异均值检验借助SAS统计软件的Proc GLM过程完成，以针叶氮含量为因变量，以针叶年龄、树体及林分为自变量。GLM过程可妥善处理方差分析中存在的处理组合缺失问题，本次分析采用第三类平方和（Type III sum of squares）检验无交互作用的因子主效应。