Effect of early girdling on standing trees on growth stresses and sawing deformations of two species of Eucalyptus

Longitudinal growth strain (LGS), which is an intrinsic property of wood, can explain the considerable internal effort - generally known as "growth stresses" - sustained by wood of standing trees. These stresses are released during processing operations (from felling to log conversion) and can damage the wood by causing end splits, warping and broken boards. The effect of early girdling, done months before felling to dry the tree on the stump, was tested by some researchers and many end-users in order to reduce the adverse effects of growth stresses. For example killing the tree on the stump months before felling seems to have been a traditional activity in Northern part of Spain where this technique was applied on previously chosen trees of Eucalyptus globulus species destined for construction wood. In this study two species of Eucalyptus from Morocco were tested: Eucalyptus grandis and Eucalyptus gomphocephala. Three trees per species were girdled for each of the four periods between girdling and felling tested (4, 6, 12 months). Three control trees were selected per species. LGS was measured on each tree initially and just before felling. Samples for physical and mechanical trials were collected on butt log. The latter was sawn and the deformation of the sawings were measured. The results obtained show important decreases in the initial values of the growth stresses. The differences between controls and girdled trees on physical and mechanical properties are discussed. The stability of the lumbers were improved. The major problem of the method is the insect attack. It could be overcome by specific solutions. (Texte intégral)