False heartwood in beech Fagus sylvatica, birch Betula pendula, B. papyrifera and ash Fraxinus excelsior - an overview

This overview compares false heartwood in beech, birch and ash with normal heartwood, discusses its induction, the impact it has on wood quality and utilization, and considers whether it is possible to avoid the formation of false heartwood by appropriate silvicultural practices. Normal heartwood forms in trees under the control of endogenous, hereditary factors. In contrast, the formation of false heartwood is induced by diverse exogenous factors, including various kinds of injuries or stresses that damage the tree, triggering a succession of processes. The extent of both normal and false heartwood increase as the tree ages. A common cause of stress is drought; others include breakage of branches which create openings in trees or stem injuries, thereby exposing injured cells to atmospheric conditions. In all cases similar reactions to those that occur when normal heartwood is formed are triggered, e.g. cells of the inner parts of the stem are emptied of their living contents and energy reserves, vessels and tracheids are plugged and conductive capacity is diminished. Initial chemical changes occur at this time, which may result in discoloration of the wood. Microorganisms such as bacteria and non-decay fungi may subsequently invade, causing further alterations. The induced colorations can be explained by oxidation reactions of the phenolic substances catalyzed by various enzymes produced by the microbes present in the affected area. In that stage, only the aesthetical qualities of wood are affected, which are mainly considered as defects when grading wood, resulting in considerable price reductions, partly due to difficulties in visually distinguishing altered wood from rotten wood. Shorter rotations reduce the incidence of false heartwood. Hence, appropriate silvicultural measures should be applied to ensure that trees reach valuable dimensions at an early age in order to minimize the formation of false heartwood in commercially grown stands