Heartwood zone and its formation process

This paper reviews the literature on heartwood and its formation process. The factors involved in the process of heartwood formation are described, with particular attention paid to molecular, intercellular, organismal and environmental ones. The spatial distribution of heartwood along longitudinal and radial axes of the stem as well as biochemical changes in the heartwood and durability of this zone are also presented. Based on the literature data, it turns out that the heart−wood formation is neither clearly studied, nor fully understood. It seems that this part of wood can not only play a significant role from the point of view of tree biomechanics, but also is of great importance in their immune responses. In the era of observed dying processes of forest−forming trees, knowledge about the role of heartwood in these responses seems desirable