Patterns of within-stem variations in wood specific gravity and water content for five temperate tree species
• Key message
Intensive measurements of basic specific gravity and relative water content of lumens show that within-stem variations strongly depend on species and cannot be summarised through the typical patterns reported in the literature; breast height measurements are not always representative of the whole stem.
Knowledge of the distribution of wood properties within the tree is essential for understanding tree physiology as well as for biomass estimations and for assessing the quality of wood products.
The radial and vertical variations of basic specific gravity (BSG) and relative water content of lumens (RWC L ) were studied for five species: Quercus petraea/robur, Fagus sylvatica, Acer pseudoplatanus, Abies alba and Pseudotsuga menziesii. The observations were compared with typical patterns of variations reported in the literature.
Wood discs were sampled regularly along tree stems and X-rayed in their fresh and oven-dry states.
At breast height, BSG was found to clearly increase radially (pith to bark) for two species and to decrease for one species. For F. sylvatica and A. alba, the radial variations of BSG were rather U-shaped, with in particular inner wood areas showing respectively lower and higher BSG than the corresponding mature wood. RWC L increased generally from inner to outer area but wet sapwood was clearly distinguishable only for the coniferous species. Vertical variations of BSG and RWC L were strongly dependant on the species with usually non-linear patterns.
The observed variations of BSG were only partially in agreement with the reported typical radial patterns. Despite the vertical variations, the mean BSG of a cross-section at breast height appeared to be a good estimator of the mean BSG of the whole stem (although the difference was statistically significant for coniferous species), whereas breast height measurement of RWC L was not representative of the whole stem.
KeywordsBasic density Relative water content Degree of lumen saturation Sapwood Radial and vertical variations
We thank all the people involved in this project, especially those who contributed to field measurements and CT scanning.
Compliance with Ethical Standards
A part of the data used in this work was collected within the frame of the Modelfor 2012-2015 joint project between INRA and ONF and the research project EMERGE funded by the French National Research Agency (ANR) through its Bioenergy program. The Douglas fir data were issued from the long-term experimental network managed by the French data cooperative on forest growth (Gis-Coop). The UMR 1092 LERFoB is supported by a grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” program (ANR-11-LABX-0002-01, Lab of Excellence ARBRE).
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