High-resolution proxies for wood density variations in Terminalia superba.
OBJECTIVE
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.


METHODS
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).


RESULTS
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.


CONCLUSIONS
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.
Ghent University, Department of Forest and Water Management, Faculty of Bioscience Engineering, Coupure Links 653, 9000 Ghent, Belgium.
Maaike
M
De Ridder
Jan
J
Van den Bulcke
Dries
D
Vansteenkiste
Denis
D
Van Loo
Manuel
M
Dierick
Bert
B
Masschaele
Yoni
Y
De Witte
David
D
Mannes
Eberhard
E
Lehmann
Hans
H
Beeckman
Luc
L
Van Hoorebeke
Joris
J
Van Acker
D001696:Biomechanical Phenomena; D003247:Conservation of Natural Resources; D003720:Densitometry; D029766:Terminalia / Q000254:growth & development*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014197:Trees / Q000254:growth & development*; D014934:Wood / Q000254:growth & development