ABSTRACT

Taper models, which describe the shape of tree stems, are central to estimating stem volume. Literature provides both taper- and volume models for the three main species in Norway, Norway spruce, Scots pine, and birch. These models, however, were mainly developed using approaches established over 50 years ago, and without consistency between taper and volume. We tested eleven equations for taper and six equations for bark thickness. The models were fitted and evaluated using a large dataset covering all forested regions in Norway. The selected models were converted into volume functions using numerical integration, providing both with- and without-bark volumes and compared to the volume functions in operational use. Taper models resulted in root mean squared error (RMSE) of 7.2, 7.9, and 9.0 mm for spruce, pine, and birch respectively. Bark thickness models resulted in RMSE of 2.5, 6.1, and 4.1 mm, for spruce, pine, and birch respectively. Validation of volume models with bark resulted in RMSE of 12.7%, 13.0%, and 19.7% for spruce, pine, and birch respectively. Additional variables, tree age, site index, elevation, and live crown proportion, were tested without resulting in any strong increase in predictive power.

摘要

锥度模型描述树干的形状，是估计树干体积的核心。文献提供了挪威三种主要树种：挪威云杉、欧洲赤松和桦树的锥度模型和体积模型。然而，这些模型主要是使用 50 多年前建立的方法开发的，锥度和体积之间没有一致性。我们测试了十一个锥度方程和六个树皮厚度方程。使用覆盖挪威所有森林地区的大型数据集对模型进行拟合和评估。使用数值积分将所选模型转换为体积函数，提供带树皮和不带树皮的体积，并与操作使用中的体积函数进行比较。锥度模型导致云杉、松木和桦木的均方根误差 (RMSE) 分别为 7.2、7.9 和 9.0 毫米。树皮厚度模型得出的云杉、松树和桦树的 RMSE 分别为 2.5、6.1 和 4.1 毫米。使用树皮验证体积模型，云杉、松树和桦树的 RMSE 分别为 12.7%、13.0% 和 19.7%。对其他变量、树龄、立地指数、海拔和活树冠比例进行了测试，但预测能力没有明显提高。