Street trees are the skeleton of urban greening. Generally, tall tree species are used, and the trunk height is required to be between 2.5 meters and 6 meters. After planting street trees, they should be pruned every year to enlarge the crown, adjust the extension direction of branches, increase the shading effect, and consider the use and lighting of buildings.
Deciduous trees are mainly pruned in dormancy period, supplemented by pruning in growth period, because there are enough nutrients stored in dormancy period, and the branches and buds are reduced after pruning on the ground, which can intensively use the stored nutrients and promote the growth of new shoots; In the growing season, trees store less nutrients, so pruning will reduce the leaf area, but the same amount of pruning will have a greater inhibitory effect on the growth of trees. Most evergreen trees have no real dormancy period, and their roots, branches and leaves are active all year round, but pruning in late spring is better, because most newly pruned wounds heal before the end of the growing season, and tree bleeding seriously weakens the tree vigor and affects the normal growth of trees.
The following briefly introduces several plastic methods.
1. Cup crown
In the street with overhead lines, in order to solve the contradiction between trees and lines, a cup-shaped shape can be adopted. Cup-shaped street trees have a typical crown shape of three forks, six strands and twelve branches, and the trunk height is 2.5 meters to 4 meters. Plastic surgery was completed within five to six years after colonization.
2. The crown shape of happiness
It is mostly used for trees with no central spindle or self-shearing terminal buds, and the crown naturally develops. When planting, leave the trunk 3 meters or cut it off. After germination in spring, leave 3 ~ 5 evenly distributed lateral branches in different directions for pruning, so as to promote the branches to grow into main branches, and erase all others. In the growing season, only 3-5 lateral buds with suitable directions are left on the main branches, and after germination in the second year, 6- 10 lateral branches are selected for short cutting to promote the secondary lateral branches to make the crown plump and symmetrical.
3. Natural crown shape
Under the condition that traffic and other public facilities are not hindered, when trees have any growth conditions, street trees often adopt natural crown shapes, such as tower, oval, oblate and so on.
Street trees with main branches in the middle, such as poplar, cedar and Pterocarya stenoptera. The height of the branching point depends on the characteristics and specifications of the tree species, and the terminal buds should be protected from growing upward during cultivation. If the top of the trunk is damaged, the branches that have been growing vertically should be selected or cut short at the strong buds, and the lower lateral buds should be erased, and the upright branches should be taken out to avoid the phenomenon of multiple heads.
Street trees without middle main branches, such as willow, elm, etc. , generally 2 meters to 3 meters high, leaving 5 to 6 main branches to naturally form an oval or oblate crown. The objects of pruning every year are dense branches, dead branches, diseased branches and residual branches.