Ghent University, Department of Forest and Water Management, Faculty of Bioscience Engineering, Coupure Links 653, 9000 Ghent, Belgium.
Ann Bot. 2011 Feb;107(2):293-302. doi: 10.1093/aob/mcq224. Epub 2010 Dec 3.
Density is a crucial variable in forest and wood science and is evaluated by a multitude of methods. Direct gravimetric methods are mostly destructive and time-consuming. Therefore, faster and semi- to non-destructive indirect methods have been developed.
Profiles of wood density variations with a resolution of approx. 50 µm were derived from one-dimensional resistance drillings, two-dimensional neutron scans, and three-dimensional neutron and X-ray scans. All methods were applied on Terminalia superba Engl. & Diels, an African pioneer species which sometimes exhibits a brown heart (limba noir).
The use of X-ray tomography combined with a reference material permitted direct estimates of wood density. These X-ray-derived densities overestimated gravimetrically determined densities non-significantly and showed high correlation (linear regression, R(2) = 0·995). When comparing X-ray densities with the attenuation coefficients of neutron scans and the amplitude of drilling resistance, a significant linear relation was found with the neutron attenuation coefficient (R(2) = 0·986) yet a weak relation with drilling resistance (R(2) = 0·243). When density patterns are compared, all three methods are capable of revealing the same trends. Differences are mainly due to the orientation of tree rings and the different characteristics of the indirect methods.
High-resolution X-ray computed tomography is a promising technique for research on wood cores and will be explored further on other temperate and tropical species. Further study on limba noir is necessary to reveal the causes of density variations and to determine how resistance drillings can be further refined.
密度是森林和木材科学中的一个关键变量，可通过多种方法进行评估。直接重量法大多具有破坏性且耗时。因此，已经开发出更快且半破坏性或非破坏性的间接方法。
从一维电阻钻孔、二维中子扫描以及三维中子和 X 射线扫描中得出了具有约 50 µm 分辨率的木材密度变化曲线。所有方法都应用于非洲先锋树种 Terminalia superba Engl. & Diels 上，该树种有时会出现棕色心材（黑木 Limba）。
使用 X 射线断层扫描并结合参考材料，可以直接估算木材密度。这些 X 射线衍生的密度与称重法确定的密度无显著差异，相关性很高（线性回归，R²=0.995）。当将 X 射线密度与中子扫描的衰减系数和钻孔阻力的幅度进行比较时，发现与中子衰减系数呈显著线性关系（R²=0.986），而与钻孔阻力呈弱相关（R²=0.243）。当比较密度模式时，所有三种方法都能够揭示相同的趋势。差异主要归因于树木年轮的方向以及间接方法的不同特征。
高分辨率 X 射线计算机断层扫描是研究木材芯材的有前途的技术，将在其他温带和热带物种上进一步探索。需要进一步研究黑木，以揭示密度变化的原因，并确定如何进一步改进电阻钻孔。
