Any injury to a tree that exposes the wood becomes a threat to its entire mass. Organic substances on the surface of the wood in the place of damage undergo various changes due to the influence of weather conditions. These substances in a very short time become a medium that enables the development of various microorganisms. Each wound is a site of the development of many species of bacteria and fungi competing in the control of such a substrate. In the first phase of infection, due to the natural resistance barrier of the wood at the site of the injury, bacteria and fungi only work on the surface. At this stage, the wood changes color most often. In the later phase, however, only some of the mushrooms, and above all, various species of hub, they are able to penetrate their mycelium deep into the wood. This is possible not only due to the properties of these species, but also as a result of increasingly deeper effects of weather conditions and - in many cases - wood-eating insects. The rate at which infection progresses depends greatly on the overall viability of the tree, quality of wood, the state of humidity and air access.
Any untreated wounds are the site of a potential threat to wood - its infection and decay. Very often, trunk or limb wood infection occurs as a result of dieback, and then breaking even small twigs inside the crown. Such infection is extremely dangerous and occurs very easily in sapwood trees, such as linden trees, poplars and others. In trees of these species already at the age of 30-50 years, due to the existence of numerous primary outbreaks of infection, the trunks completely rot.
Wood affected by fungi and brought to the state of decomposition of cellulose and lignin loses its mechanical strength. Places that show this condition in the trunk or limb wood mass are called cavities. As a result of further decomposition, such wood turns into rot. Such a place is often referred to as scorch.
Drawing. A closed place of progressive decay and wood loss on an oak trunk (Quercus robur); The decay of the wood is evidenced by the fruiting bodies of the fire hubs visible on the bark surface (Phellinus igniarius).
If the infection has occurred at the wound site, before the wound surface is covered with healing tissue, out of careful care, wood decomposition can proceed very quickly. The tissue that is unfolded is then closed. In other cases of large wounds, a thin layer of healthy wood may remain on the surface of decaying wood, under which decay proceeds. This is easy enough to say, because in such cases a characteristic noise is heard when tapping. Cavities masked in this way are most often formed in places of large wounds caused by tearing the bark of trees with hard wood. The easy drying of the surface of such exposed wood allows it to remain in the form of a screen for a long time, masking progressive decay and scorch.
In trees with soft and easily absorbable wood, its decomposition, especially in the places of cutting, occurs much faster, causing decay already visible on the surface. This creates distinct open cavity sites. In the early stages of decomposition, the cavity sites may only be shallow depressions, lasting for many years. The slow decomposition of wood occurs only because of this, that such places are not damp with rainwater, flowing directly into or flowing from the surface of the bark to the inside. This is determined by the location of the wound on the surface of the trunk or limb (drawing).
Drawing. The location of the wound may make it easier for water to enter the decomposed wood, which determines the speed of decomposition.
If water enters the cavity area, wood decomposition progresses much faster. The persistence of water is favored by the large water capacity of the resulting humus and its porous structure, also facilitating the access of air. Such places, even in the period of prolonged drought, they often maintain very high humidity for a long time. Water flowing to the bottom causes, that decomposition progresses faster downward, creating characteristic pocket defects. The decay of the wood is also progressing upwards, but much slower. The decomposition sites that begin at the bifurcation of the branches are the most dangerous. Intensive water supply causes, that the decay of wood in certain tree species, for example in linden, it can cover the entire trunk within 2-3 years and lead to complete destruction of its interior. Very often, intensive decomposition of trunk wood may proceed from the ground level, after damage to the bark or roots. A factor contributing to decomposition in such places is high humidity due to direct contact with the soil, often by capillary infiltration.
Based on the observation of a wide variety of wood damage, it can be stated, that the size of the wound as a site of initiation of infection and decay is generally not indicative of the size or extent of internal damage.