Canadian Forest Service Publications
Black spruce trees from fire-origin stands have higher wood mechanical properties than those from older, irregular stands. 2014. Paes Torquato, L.; Auty, D.; Hernandez, R.E.; Duchesne, I.; Pothier, D.; Achim, A. Can. J. For. Res. 44:118-127.
Issued by: Laurentian Forestry Centre
Catalog ID: 35356
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In the eastern Canadian boreal forest, long fire return intervals lead to over 60% of stands having an irregular, uneven-aged structure, which is associated with slower growth. The aim of this study was to examine the effect of stand structure on the clear wood mechanical properties of black spruce (Picea mariana (Mill.) B.S.P.). A total of 128 trees were destructively sampled from stands of regular and irregular structure across Quebec, Canada. Nonlinear mixed-effects models were developed for each stand type to describe the variation in modulus of elasticity (MOE) and modulus of rupture (MOR) in small defect-free samples as functions of cambial age and annual ring width. Mechanical properties were strongly related to cambial age, with a smaller influence of ring width. After accounting for these variables, both MOE and MOR were higher in samples from stands of regular structure, although differences were less pronounced in the upper stem compared with breast height. The fixed effects of the models explained between 34% and 53% of the variation in mechanical properties. A higher incidence of mild compression wood in trees of layer origin may explain the observed differences between stand structures.
Plain Language Summary
This study demonstrates that the wood of black spruce trees from fire origin stands has mechanical properties superior to those of black spruce trees from older, irregular stands. In the boreal forests of Eastern Canada, the long intervals between fires ensure that 60% of stands are made up of trees of various ages. This forest dynamic creates an irregular structure and is associated with slow growth.
The objective of this study was to examine the effect of stand structure on the clear wood mechanical properties of black spruce. A total of 128 trees were sampled from stands of regular and irregular structure across Quebec. Models were then developed for each stand type to describe the variation in modulus of elasticity1 and modulus of rupture2 as functions of cambial age (the cambium is the living part located between the wood and the bark) and annual ring width.
Mechanical properties were strongly related to cambial age, and to a lesser degree to ring width. The modulus of elasticity and the modulus of rupture were higher in samples from stands of regular structure, which are characteristics sought after by the forest industry.
The modulus of elasticity is a measurement of wood rigidity when the wood is placed under increasingly constrained conditions without causing the wood to be permanently deformed.
The modulus of rupture is a measurement of the maximum force that a piece of wood can withstand before breaking.