The effect of pruning on the growth of trees and shrubs

Even at the beginning of the previous century it was considered, that pruning has only beneficial effects on the growth of trees and their fruiting. Such a view prevailed during the period, when European horticulture developed under the influence of the art of gardening from the nineteenth-century palace gardens. When the first experiments with cutting fruit trees were made in the twenties, it turned out, that it gives not only good, but also bad results.

One of the first scientific works on apple pruning was done in America by Gardner, Bradford and Hooker, and then by Chandler. These works showed, that trees cut in the winter dormancy period or in spring grow stronger, but despite their stronger growth, they remain smaller than uncut trees. The above statement is valid so far, although the knowledge of the effects of pruning on trees has expanded significantly since then. Cut trees and shrubs try to rebuild the removed aboveground parts by creating new ones, numerous and long shoots. Rarely, these shoots are long enough, so that they can compensate for the loss caused by cutting and give such increments as at that time provided by the uncut trees. Differences can be easily identified by measuring annual shoot increments and tree crown sizes. Cut trees have more shoots and they are longer than those that are not cut, yet the size of the crowns of the former are smaller (Tab. 1).

Table 1. The effect of cutting young apple trees on shoot growth, the thickness of the trunk and the size of the crown

	Way cut	The sum of the lengths of annual increments in m	Average length of annual increments in cm	Surface cross section
Variety				trunk after six years in cm	crowns after six years in
	shoots annually shortened by 1/3	57	43	70,7	8,2
Mclntosh	shoots not shortened	34	40	71,8	14,1
	shoots annually shortened by 1/3	76	45	59,4	9,9
Jonathan	shoots not shortened	58	36	64,6	14,1

If the cut is moderate, then the differences in the size of the crowns between cut and non-cut trees disappear around 10 year of life of trees, when they enter the period of abundant fruiting. Uncut trees generally bear more fruit. Abundant fruiting inhibits crown growth and therefore cut trees can then grow to the size of uncut trees..

If the cut is intense, it can permanently inhibit the enlargement of the crowns and keep them in a constant size for many years. This is the case today in many densely planted intensive orchards. In these orchards, apple trees over a dozen years old have crowns not exceeding 4 m in diameter and 3 m in height. Due to the cut, these crowns do not enlarge. Apple trees of the same age growing freely, in a loose spacing and poorly cut, they have crowns extending to the 7 m in diameter and 6 m in height. They continue to expand in size.

To visualize how much we reduce the size of trees in cultivated orchards by cutting, you have to look at old apple trees and never cut pears, which can be found in farm yards. They are real giants compared to the equally old trees in orchards. Pieniążek in the book "Around the orchard of the world" describes a 60-year-old apple tree found in China with a height 6,5 m and the diameter of the crown 13 m annually yielding an average of almost a ton of fruit. In place of one such large apple tree, we now have at least in orchards 6 trees kept in the same dimensions for many years by pruning.

Pruning offers great possibilities to regulate the size of climbing shrubs, for example grapevines. In Italy, you can see ancient plantations of heavily cut shrubs with a bed just a few meters high, while poorly cut the flocks by the houses are several hundred meters long.

Cutting usually involves shortening and removing the shoots, branches or boughs. Shortening the shoots causes significant changes in the nature of their growth. First of all, the natural dominance of the apical bud on the shoot is canceled, which exists in the conditions of its natural growth. Domination is there, that one, and sometimes two or three apical buds per shoot, they gain an advantage over other buds early in the spring and, by developing very intensively, they inhibit the development of lower-lying buds. This process is regulated by natural growth regulators (hormones) produced in buds and growing tops. Under these conditions, a maximum of three long growths are formed at the top of the shoot, while the remaining buds develop as shoots. If the top buds are removed during cutting, along with the section of the shoot, then the apical dominance is abolished. Many more buds shoot into long increments.

Table 2. The effect of cutting young apple trees on the number of long shoots and short shoots developed in two-year increments

	Way cut	Number		Ratio
Variety		long shoots	short shoots	long shoots for shoots
Mclntosh	shoots annually shortened by 1/3	4,6	5,7	1:1,2
	shoots not shortened	2,4	13,8	1:5,8
	shoots annually shortened by 1/3	4,6	6,8	1:1,5
Jonathan	shoots not shortened	2,4	13,1	1:5,5

Table 3. Increase in the area of ​​leaves on cut and uncut 2-year Melba apple trees (according to A. Mica, M. Grochowska, A. Karaszewska)

	The surface of the leaves		in dm2 on tree
The way of cutting	1 June	29 June	26 July	3 October
Shoots shortened in spring by o 1/3 length.	10,2	34,6	88,8	113,4
Stems not shortened	26,2	67,9	90,8	119,9

As a result of pruning, the proportion between the various types of shoots in the crown of the tree changes. Young, uncut apple trees have five times more shoots than long shoots each year. With intensive pruning, the number of incongruent shoots in relation to long shoots varies depending on the variety 1:1,2 the 1:1,5 (Tab. 2).

Cutting changes the structure of the crown, as well as the habit of trees. Young trees not cut form a loose crown, their limbs are long and slender, hanging shoots. Young cut trees create a compact and dense crown, their limbs are stocky, stiff shoots .

Until the end of the 1940's, there was a view in Europe, that shoots of young trees need to be shortened in order to obtain stiff and strong branches. Was considered, that you must first take care of your strength

crown structure, and only later, when the tree is ok 10 years, it can be allowed to bear fruit.

In the early 1950s, Preston in England showed a great loss in yield from shortening the shoots. This treatment has been gradually restricted in most orchards in Europe, but it is still used in some regions in America, in Australia and China.

Cutting causes significant changes not only within the crown, but also throughout the tree. If the cut is made in the spring, it is in the first half of the growing season that trees have a smaller leaf area than comparable uncut trees, these differences are shown in tab. 3. Stronger shoot growth of cut trees gradually compensates for this difference, but not earlier than the beginning of August. If the trees are cut in summer, the foliage area also diminishes. In both cases, there are fewer assimilations, which are produced in the leaves. Cut trees have limited stockpiling capacity, and therefore stem and root growth are reduced. Differences in the growth of the trunk and roots between cut and non-cut trees show sharply in young trees. In older trees, the differences caused by pruning may be blurred due to the more abundant fruiting of uncut trees.