The ability of trees to heal wounds.
Each incision wound can be healed by the healing tissue that forms on its edges – this tissue is also called scar tissue, wound or callus. How this tissue is formed was discussed in the previous articles. It is known from the practice of making various cuts of shoots and branches, that in some cases the wound heals easily and quickly, in others it is slower, it is often uneven, and sometimes there is no healing tissue production at all. These differences are most often related to the location of the cutting site in relation to the left parts of the tree crown. The formation of the healing tissue depends mainly on the supply of assimilation products. These products reach the forming tissue much easier, when the edges of the wound are adjacent to the active ethmoid tissue (with a sip), which distributes the products of assimilation from the leaves. Thus, a further condition for wound healing is the existence of assimilating organs above the cut site, ensuring the inflow of a sufficient number of assimilates. So if the cut was made in a place without the supply of these products, the wound will never heal. Cases of different positions of the cutting site preventing or impeding wound healing are shown in the figure.
Drawing. Location of the pruning sites in relation to the "routes" of assimilation flow on the unbranched one-year and perennial shoots, preventing the wound from healing; at the same time, the recommended method of cutting for the bud on the shoot is shown.
One-year and perennial shoots, unbranched, cut too far above the bud in the first growing season, they already form visible thickening of the bark on the border of the plug devoid of assimilate inflow. The location of this thickening indicates, where the cut plane should run. The tenon bark dies off in the first year, and the left plug prevents the living tissue of wood from being covered with the healing tissue (drawing).
Drawing. Inaccurately cut branches, too far from the trunk at the bottom, causes uneven overgrowing of the wood surface with healing tissue; pedunculate oak (Quercus robur).
In most trees, cutting a few years old unbranched shoot should be made above the visible or hidden bud, the so-called. sleeping, at distance 0,5-1,0 cm, sloping down, at an angle of approximately 25-30 °. Shoots of hardwood trees are cut closer to the bud, and about soft – a little higher, which protects the bud from drying out. Thicker shoots are usually cut more obliquely (closer to the "route" of assimilations), which facilitates the overgrowth of the wound with healing tissue. Determining where the cut is against a hidden bud is quite difficult in thick sections, unbranched branches, covered with thick, exfoliated bark. In such cases, the cuts should be perpendicular, and after the sprout has grown out of the awakened bud of a sleeping person, correction must be made. At the trees, from which large side branches or limbs were removed, often the position of the cutting plane is too distant and the cut is made at too sharp an angle towards the limb or trunk (Lynx. on the left).
Drawing. The influence of the method of cutting on the size of the wound, its shape and the formation of a healing tissue: first row - cutting, middle row - wound in front, bottom row - wound healing.
Such a cut should also be done like this, so that the edges of the wound are as close as possible to the “routes” assimilates. The cut should therefore be made in a plane parallel to the trunk (drawing). A rather large wound then develops, which, however, is due to the better "nourishment" of its healing tissue, it grows faster and more evenly than the wound remote from the trunk. However, some uneven growth is also observed then, when the cut plane is completely parallel and elliptical in shape. The weakest healing tissue is formed in the lower part, better at the top, preferably on the sides (drawing bottom row). To prevent this, the wound surface is extended by cutting the cortex in the upper and lower parts (Lynx. right in the middle). The side edges of the wound are then very close to the assimilation "routes", thanks to which they are intensively and evenly "fed". The length of the wound formed in this way should be at least twice its width. With this wound configuration, it is often necessary to remove the wood that protrudes above the plane defined by the wound edges. This helps heal the wound, that is, complete coverage of the internal surface with healing tissue, healthy wood (drawing).
Drawing. Completely healed wounds where the branches were cut off in the common beech (Fagus silvatica).