Crown construction. The crown of the tree is formed as a result of the main shoot branching. If a branch occurs at a certain height, then the trunk is formed, which can be extended vertically. If, on the other hand, a branch arises in the ground-level part, bushy forms may arise, often called natural. Thickening branches usually form limbs, and old trees with crowns set in this way are often called multi-stemmed trees.
The structure of the crown is largely determined by the way its shoots grow. There are three types of growth and branching: monopodial, sympodialny i pseudodichotomiczny. The monopodial type is the extension and continuation of the shoot from the apical bud. From the side buds on older shoots, side shoots develop in a similar way. This is how conifers and young ash trees grow and branch, clones and others.
The sympodial type is then, when the main shoot develops not from the apical but from the lateral one closest to the apical. Side shoots do not form whorls. Most species of deciduous trees exhibit sympodial growth. Linden trees are typical examples, robin and willow trees. Pseudodichotomous type (forked) it consists in the simultaneous growth of two shoots from the side buds after the apical bud has disappeared. Many tree species with dichotomous growth develop monopodial in their youth.
A natural way to grow, branching and natural crown density are not always favorable, if the tree is grown ornamental, and therefore they can be significantly modified in the process of tree care.
Leafage. The foliage density is a very important feature of the crown, which determines the shade of the environment by the tree. For heavy shade trees, so densely leafed (shadow crowns), belongs: buk, sycamore, clones, grab, linden trees, fir and spruce trees. For low shade species (luminous crowns) belongs: birch trees, poplar, modrzewie, pines and alders.
The density of foliage affects the microclimatic conditions as well as the soil under trees and the vegetation there..
The leaf is made up of three essential tissues: enveloping (epidermis), crumb (assimilation and storage) and conductive.
The leaf crumb - mesophyll - is surrounded on both sides by a skin - epidermis. It is a single-layer tissue and has protective functions. The epidermis covering the upper side of the leaf is made of dense chlorophyll-free cells, with thickened walls, usually covered with cuticle. In the epidermis of the lower side of the leaf there are respiratory stomata which enable the exchange of carbon dioxide, oxygen and water vapor with the atmosphere, which is the basis of the most important life processes of the plant. The effect of these processes is, among others. improving the composition of atmospheric air, beneficial for the environment. Due to the movements of the stomata cells, the leaf can regulate the intensity of gas exchange depending on the current light conditions, thermal and humidity. One square millimeter of the epidermis may be up to 400 respiratory stomata. Under the epidermis of the upper side of the leaf blade there is an assimilation crumb, otherwise palisade crumb, in which photosynthesis takes place most intensively. There is a spongy crumb in the lower part, with large intercellular spaces in contact with the surrounding atmosphere through the stomata.
The conductive tissues of the trunk extend through the branches to the leaves in the form of so-called veins or nerves.