Like all living beins, trees go through different stages over the course of their long life.
Since they are continuously growing organisms, their ability to survive depends on the possibility of regulating their mass according to the energy available, which they procure through the processes of photosynthesis that take place in the leaves.
Trees live and continue to grow, that is, to increase their mass, until the generation of new parts in new positions exceeds the processes of decay of old parts.
It is precisely the relationship between the energy that trees are able to produce as autotrophic beings (that is, which create their own nourishment) and their body mass that determines the age of a tree.
When a tree is young the decay processes are very limited and the ratio between the dynamic mass (i.e. the living parts of the tree) and the available energy is clearly in favor of energy.
The elements collecting energy (green foliage, photosynthesizing) are a large prt of the tree and can also include the trunk: growth is therefore fast and the possible removal of even high quantities of living parts does not involve large energy imbalances.
On a young tree you can therefore make even intense pruning, as long as it is carried out correctly and aimed at the correct breeding of the tree.
In an adult tree, on the other hand, there was a large increase in dynamic mass. The root system widens and gets closer to surface, while the foliage cap tends to round off due to the lower apical dominance (that physiological plant phenomenon in which the vegetative apex inhibits and controls the development of the lateral buds, thus regulating the shape of the plant itself).
In addition, the energy available for growth stored in reserved components of the tree, decreases over time as it is required for numerous other processes such as reproduction, defense against adversity, etc.
In this case the relationship between energy and dynamic mass approaches the equilibrium and energy becomes a limiting factor for growth.
The removal of even limited portions of the canopy of the adult tree can therefore seriously damage it: doing so, in fact, removes both the deposit of reserve energy stored in the wood in the form of starch, and the components devoted to the production of the energy, the leaves.
On an adult tree, provided it is properly bred and therefore not in need of corrective interventions, pruning must therefore be limited to slight adjustments of the crown and the disposal of dead parts.
Old trees, on the other hand, can no longer produce enough energy to keep all their active mass alive.
For this reason they begin to isolate parts of their organism and let them die, starting from the basal branches which, due to their position, provide less contribution to photosynthesis.
A senescent tree will therefore have an umbrella type foliage concentrated in the upper end, while the rest will be subject to desiccation. The root system will also begins to deteriorate.
Pruning of young trees
Breeding pruning is carried out to correctly set the growth of young trees or to correct structural defects on trees that have not previously undergone such an operation. If properly bred, the trees develop a balanced foliage and, having reached maturity, need less corrective action.
In the early stages of growth of a tree, breeding pruning is therefore aimed above all at developing a trunk with a strong central apex by eliminating or pruning the branches that can compete with it and that would therefore make the tree assume a non “natural” posture.
In fact, young trees should tend to develop quickly upwards to achieve exposure to sunlight, the source of their life. Therefore, they should not prematurely acquire the adult shape characterized by a more rounded and balanced crown.
On the other hand, when breeding a young tree it is necessary to keep half of the foliage of the tree on the branches that develop in the lower 2/3 of the tree itself. This favors the diametrical (conical) development of the trunk and a better distribution of weight and wind stresses along the entire structure.
Pruning of adult trees
When the tree becomes an adult, it tends to no longer have a strong vigor in the apical part and the crown tends to round off.
The technique of pruning trees that reached this stage, basically consists in trying to decrease the ramifications of equal vigor to avoid excessive density that would force the internal parts of the crown to lose foliage while keeping the foliage only in the outermost parts.
A thinning pruning is then carried out to affect only the number of branches and not the overall volume of the tree.
The thinning of the foliage consists in the removal of dead and sick branches, the ones in strong competition with others, branches poorly inserted, with weak hairline or with little vegetative vigor.
A selection of branches can be carried out in order to favor better light penetration and air circulation. An increase in brightness and ventilation stimulates and maintains the development of the foliage even in the innermost parts of the crown, while thinning reduces the effects of the wind on the leaf mass and relieves the weight of the most loaded branches.
The cleansing of the tree from the dry, on the other hand, consists in the elimination of the dead, weak or decaying parts of the plant.
If it is necessary to reduce the crown of a tree in height or width for aesthetic or space reasons, ‘crown reduction pruning’ technique is used instead.
The crown reduction pruning should preferably be carried out when the tree is young, blocking the growth in the desired size or in any case on young parts of the tree, to avoid large wounds and excessive removal of the foliage.
In any case, in all pruning techniques it is necessary to avoid removing more than 30% of the foliage in a single season. More drastic interventions risk putting the plant under stress, due to the reduction of photosynthetic activity.
In addition, trees and branches with thin bark may be prone to burns of the barks due to sudden exposure to the sun.
Pruning of senescent trees
Senescent tree specimens will not be subjected to pruning interventions, except for those with safety purposes.
Given the low energy level available, with the progress of the aging of the tree the intensity of pruning decreases until it is limited to the elimination of dry parts and to the lightening of the parts that might become unstable.
More than with pruning interventions, in the case of old tree specimens it will therefore be necessary to act to guarantee structural stability and ensure steady living conditions, to not compromise a situation of already precarious balance as much as possible
So it is important to know how to evaluate the stage of development of each plant and to know how to meet their requirements based on the typical needs of each of them.
Only by knowing the needs of trees at all ages and by applying the correct intervention techniques it is possible to take care of what are true assets for our communities.