Strong density differences were observed between stem wood at 1.30 m and other tree components (stem wood, stem bark, knots, branch stumps and branches). The difference, up to 40% depending on the component, should be taken into account when estimating the biomass available for industrial uses, mainly fuelwood and wood for chemistry. Basic density is a major variable in the calculation of tree biomass. However, it is usually measured on stem wood only and at breast height. The objectives of this study were to compare basic density of stem wood at 1.30 m with other tree components and assess the impact of differences on biomass. Three softwood species were studied: Abies alba Mill., Picea abies (L.) H. Karst., Pseudotsuga menziesii (Mirb.) Franco. X-Ray computed tomography was used to measure density. Large differences were observed between components. Basic density of components was little influenced by tree size and stand density. Overall, bark, knot and branch biomasses were highly underestimated by using basic density measured at 1.30 m. Using available wood density databases mainly based on breast height measurements would lead to important biases (up to more than 40%) on biomass estimates for some tree components. Further work is necessary to complete available databases.

中文翻译：

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通过考虑树木成分之间的密度变化来改进地上生物量估计

在 1.30 m 处的茎木与其他树木成分（茎木、茎皮、树节、树枝树桩和树枝）之间观察到强烈的密度差异。在估算可用于工业用途的生物质（主要是薪材和用于化学用途的木材）时，应考虑这种差异，取决于组件，最高可达 40%。基本密度是计算树木生物量的主要变量。然而，它通常仅在茎木和胸高处测量。本研究的目的是比较 1.30 m 处的茎木与其他树木成分的基本密度，并评估差异对生物量的影响。研究了三种软木树种：Abies alba Mill.、Picea abies (L.) H. Karst.、Pseudotsuga menziesii (Mirb.) Franco。X 射线计算机断层扫描用于测量密度。在组件之间观察到很大差异。组分的基本密度受树木大小和林分密度的影响很小。总体而言，通过使用在 1.30 m 处测量的基本密度，树皮、结和树枝生物量被高度低估。使用主要基于胸高测量的可用木材密度数据库会导致对某些树木成分的生物量估计产生重要偏差（高达 40% 以上）。需要进一步的工作来完成可用的数据库。使用主要基于胸高测量的可用木材密度数据库会导致对某些树木成分的生物量估计产生重要偏差（高达 40% 以上）。需要进一步的工作来完成可用的数据库。使用主要基于胸高测量的可用木材密度数据库会导致对某些树木成分的生物量估计产生重要偏差（高达 40% 以上）。需要进一步的工作来完成可用的数据库。