More important goals and types of tree cutting.
Shaping the crown. The crown of a tree has a specific arrangement of boughs and branches and forms a mutually interconnected whole. The crown must have sufficiently high mechanical strength, so that it can resist the action of the forces causing the damage. Strong winds are the most important of them, which are capable not only of breaking branches, but also trunks and uprooting trees. Very frequent damage to tree crowns is caused by snow cover, when it's falling wet snow, freezing to the branch, causes them to overload and break. The icing caused by the precipitation of frozen rain works similarly.
It is known from observations, that the most common damage to the crown as a result of the above-mentioned factors consists in breaking off large branches or limbs at the forks. This usually happens then, when two branches make a very small angle with each other, and even developed in an almost parallel arrangement. Another common cause of limbs breaking is the concentration of their bases in one construction node, which most often occurs in wireless crowns, that is, having no main stem forming the structural body.
Drawing. Improperly formed crown with branches forming very small angles.
The figure shows a poorly formed crown, found primarily in many street trees; this formation is one of the main causes of middle age tree deterioration. Damage caused by improper mechanical design of crowns is discussed in more detail in the chapter on the treatment of damage.
The task of shaping the crown of a tree is to create such an arrangement and connection with the trunk, to provide greater resistance to external forces, and even the own weight of the limbs.
The basic requirement for a mechanically strong crown is to maintain its conductive character. Many trees tend to produce many uniform shoots at a young age. Such competing conductors must be removed by appropriate cutting. The next condition is to create and maintain the first branches already in the lower part of the trunk and not to allow the formation of multi-branch branches.. Such branches can only be maintained by 2-3 patch, later, only one branch should be left. Side branches with the conductor trunk should form an angle within 45-50 °. It is definitely risky to leave very narrow forks. In certain tree species, like for example. elm trees, the bifurcation angles are very small, which forces them to open them artificially. The higher side branches should be vertically separated by at least 30-70 cm, depending on the thickness of the trunk and branches that can be achieved. Conductor branching should be uniform along its entire length. The torsional arrangement of branches and limbs on the trunk is most preferred. It provides a good distribution of the forces acting on the trunk, and at the same time prevents the formation of clusters of several branches in one place. Often it is not possible to obtain such a low-branched trunk, because in nurseries, trees are usually produced with a highly extended and cleaned conductor. Such trees should be used in a few, well-founded cases, like for example. near the road, sidewalks etc.. Planting low-branched forms (multi-stage), i.e. the so-called. natural, it is still infrequent. And even if they do, they are gardeners who are unaware of the advantages of such trees, these side branches cut quickly.
Drawing. Beneficial for the tree, the natural form of the crown with correctly spaced branches.
The figure shows the structure of a properly formed crown, ensuring high resistance to various external forces. This should always be taken into account, that the crown of each tree becomes denser with age and that the weakest ones have to be cut every few years, even thick branches, which cause excessive compaction.
When shaping the crown, pay attention to the symmetrical load on the trunk, to prevent unilateral expansion of the crown. One-sided expansion upsets the tree's statics, which in turn - especially in old trees - can cause the trunk to crack or even break. In some situations, it is deliberately allowed to expand the crown more from the side of prevailing strong winds, which, to some extent, may mitigate their effects (drawing).
Drawing. Trees with a long and unbranched trunk (on the left) are much more likely to be broken or blown over by the wind.
Shaping the crown, meeting the above-mentioned conditions, it is possible only in conditions of unrestricted spatiality, and above all – even sunlight. If there are any factors causing the distortion of tree crowns, such as in the vicinity of a building, excessive tree density, etc.. creating a crown that is structurally correct, resistant to mechanical action, is impossible.