Structural relationships between the epicormic formations on the trunk surface and defects induced in the wood of Quercus petraea

Abstract

Timber quality and value could be reduced by the emergence and persistence of epicormic formations in Quercus petraea. Apart from epicormic branches, little information is available on other epicormic formations such as clusters of buds and burrs. We propose a classification based on a description of epicormic formations' shape and the dimensions of traces developed in the wood. This enabled us to understand their ontogeny and their relationships, and to evaluate defects formed in the wood. The final classification contains four types: (1) type b characterised by a shoot stump with a diameter less than 15 mm, either bearing or not bearing buds; (2) type g comprising thin epicormic shoots (diameter <15 mm) without epicormic buds at their base; (3) type bt comprising a group of thin epicormic shoots (<5 mm diameter) and epicormic buds borne either by a small shoot stump or directly from the trunk; and (4) type gt comprising thick epicormic shoots (diameter >15 mm) bearing buds and/or epicormic shoots at their base. We propose the following relationship between the different types of epicormic formations: an epicormic bud develops into a thin shoot (type g), the shoot can either partially die and induce a cluster of buds (type b) which then give rise to type bt, or survive and form an epicormic branch (type gt). In parallel, we show that defects increase from type g to type gt. Type g induces minor defects since the knots in the wood are small, sound and single, whereas type gt produces major defects with knots that are generally large, rotten and grouped.