Key Maintenance and Management Techniques for Ginkgo and Camphor Trees in Shanghai

Introduction to knowledge related to ginkgo maintenance and camphor tree maintenance in Shanghai:

First, ginkgo is a deciduous tree, and the best season for transplanting is after leaf fall in autumn and winter, before bud break in spring. Your transplanting in May and June, that is, after leaf emergence, is off-season transplanting. For off-season transplanted trees, various technical measures such as shading and misting generally need to be taken according to weather conditions. If the technical measures are not in place, the trees may very likely face death.

Second, camphor tree is an evergreen tree, and the best season for transplanting is in its early budding stage (about early to mid-April), and during transplanting attention should be paid to minimizing root damage, keeping the soil ball, and appropriately thinning out about 1/3 of the branches and leaves. Your transplanting in May and June is, on the one hand, past the best transplanting time, and on the other hand, because temperatures in Shanghai in May and June are rather high, other technical measures such as misting are also needed. You said “the leaves of the large camphor trees have not yet grown out.” This sentence is hard to understand, because camphor tree is an evergreen tree and is transplanted with branches and leaves. As long as the branches and leaves have not withered and yellowed and are hanging on the tree body, it means they are not dead.

In addition, white magnolia and purple magnolia are both deciduous trees, and transplanting in May and June is off-season transplanting, which requires corresponding technical measures. If the techniques are inappropriate or not in place, the trees will die. The buds that newly planted trees first sprout come from the nutrients stored in the tree body itself; if the buds later wither and die, it indicates that the root system has not absorbed the water it needs in the new environment.

Answers to questions on ginkgo maintenance and camphor tree maintenance in Shanghai

On the Shaping and Pruning of Street Trees

Abstract:This article mainly describes pruning seasons, methods, pruning techniques, existing problems, solutions and precautions, and explains that pruning plays a decisive role in the uniform neatness of street tree appearance, beautiful tree form, and robust growth. Through pruning, the combination of branches can be adjusted, ventilation and light transmission can be improved, which is conducive to the growth of street trees; diseased and pest-infested branches can be cut off, reducing conditions for the hiding and spread of diseases and pests; it can also reduce interference between street trees and public utility facilities, and weaken the impact of typhoon attacks.

Keywords:Street trees, pruning season, methods, shaping and pruning techniques, existing problems, solutions

1. Overview

Street trees refer to trees planted in neat rows on both sides of roads. In cities, street trees mainly function as road shade, and at the same time have effects such as dust prevention, temperature reduction, mitigation of motor vehicle exhaust pollution, and beautification of the road environment. The environment in which street trees are located is relatively complex. First, they are mostly related to vehicle traffic, and some are affected by street orientation, width, building height, etc. In urban areas and old urban districts, they often conflict with overhead lines. On the premise that the selected tree species are suitable, these conflicts must be resolved through pruning to achieve the effect of a large crown and dense shade.

2. Pruning Season   

Pruning of deciduous street trees is generally carried out after leaf fall in winter or before germination in spring. In the Shanghai area, this is generally from mid to late December to March of the following year, because pruning during the dormant period in winter can readjust the combination of branches, so that the stored nutrients in the tree body can be reasonably distributed after germination in the following spring, and the newly grown branches can have appropriate space to obtain sunlight for photosynthesis, promoting tree growth, thereby realizing the shading and cooling functions of street trees, and giving street trees a uniform and neat tree form to achieve a neat and beautiful effect.

In addition to winter pruning, street trees must also undergo 2-3 rounds of bud removal each year from May to June. In addition, some diseased and pest-infested branches and branches that interfere with overhead lines must also be pruned at any time, and some new branches sprouting from winter pruning cuts, such as dense clusters, must also be appropriately thinned.

Evergreen street trees are generally best pruned before the first growth peak in spring and after the last growth peak in autumn. In the Shanghai area, this is generally early spring from March to April and autumn from October to November.

3. Pruning Methods

3.1 Thinning

Cut off all dead branches, diseased and pest-infested branches, crossing branches, and overly dense branches on the tree at the base of the branches, so as to improve ventilation and light transmission conditions within the crown and avoid or reduce the phenomenon of bare branches inside the crown. When thinning, the cut must be close to the node, and the cut should be on the opposite side of the bud at the cut, inclined at 45 degrees, and the cut should be smooth. If clustered branches and whorled branches need to be completely removed, this should be done in stages to avoid too many wounds affecting tree growth.

3.2 Heading Back

Mainly cutting off a portion of the branch tips at the end of the branches, to promote lateral branches and prevent excessive elongation of branches. During the growing season, light pruning is generally done; during the dormant period, heavy pruning is generally done.

3.3 Trunk Truncation

Cutting off relatively thick main branches and framework branches; this method has the effect of promoting tree renewal and rejuvenation. To reduce the wound, saw diagonally downward from above the branch point, retaining the raised part below the branch point, so that the wound is smallest and easy to heal. To prevent the wound from rotting due to water evaporation or invasion by diseases and pests, apply a protective agent at the wound or seal the wound with wax, or wrap it with plastic film and other protective measures to promote healing.

4. Commonly Used Shaping and Pruning Techniques

4.1 Cup-shaped Pruning

Cup-shaped pruning is mostly used under overhead lines and has a typical “three limbs, six forks, twelve branches” crown structure. The trunk height is 2.5-4 m. That is, after trunk determination, select and retain 3 main branches in suitable directions (the angle between adjacent main branches is 120º, and about 45º with the trunk). Then on each side of each main branch, select and retain 2 slanting branches nearly in the same plane, and then similarly select and retain 2 branches on each secondary branch. This process must be completed over several years before a cup-shaped crown can be formed. For street trees using cup-shaped training, changes may be made according to circumstances and tree species.

After the framework is formed, the crown expands quickly. Thin out dense branches and upright branches, and promote lateral branches. Branches inside the crown may be appropriately retained to increase the shading effect. Where there are overhead lines above, the branches must never touch the lines, and a safe distance must always be maintained. The safe distance between street tree branches and overhead lines includes horizontal spacing and vertical spacing, varying according to the type of line. Under normal circumstances, the safe distance for power lines below 1 kV is 1 m, for lines of 1—20 kV it is 3 m, for high-voltage lines of 30—110 kV it is 4 m, and for extra-high-voltage lines of 150—220 kV it is required to reach 5 m. The safe distance between branches and open communication wires is 2 m, and the safe distance from communication cables is 0.5 m. For street trees on the side near buildings, in order to prevent branches from sweeping tiles, blocking doors, and blocking windows, and affecting indoor lighting and safety, overly long branches should be headed back and pruned at any time.

During the growing season, bud rubbing must be carried out frequently. When rubbing buds, do not tear the bark or leave residual branches. During winter pruning, cut off crossing branches, twin branches, drooping branches, dead branches, damaged branches, and upright branches on the upper side.

4.2  Open-center Pruning

This is an improved form of the cup shape. The difference is only that the branch point is relatively lower than that of the cup shape, the inner crown is not empty, and the distribution of the three main branches has a certain interval. It is mostly used for tree species without a central leader or whose terminal buds can self-prune, and the crown naturally opens out. In the Shanghai area, for example, for silk tree, when planting, leave the trunk at 2—2.5 m, with the maximum not exceeding 3 m, or truncate the trunk; the branch point on the side near the express lane may be slightly higher. After germination in spring, retain 3 to 5 lateral branches located in different directions and evenly distributed for pruning, promoting the branches to grow into main branches, and remove all the rest. For street trees on the same road or an adjacent section of road, the tops of the main branches should be leveled. If it is determined to prune them evenly at a certain number of meters above the ground, then main branches with higher branching should be cut more, while main branches with lower branching should be cut less. In the growing season, retain only 3 to 5 lateral buds in suitable directions on the main branches. After germination the following year, select and retain 6 to 10 lateral branches, carry out heading back, and promote secondary lateral branches, so that the crown shape is full and symmetrical.

4.3 Natural-form Pruning

Under the condition of not affecting traffic and other public facilities, street trees may adopt natural crown forms, such as tower shape, oval shape, and so on.

4.3.1 Street Trees with a Central Leader

For all tree species with an obvious main axis, the height of the branch point is determined according to the characteristics of the tree species and the tree specifications. During cultivation and pruning, attention should be paid to protecting the terminal bud so that it grows upright. If the top of the trunk is damaged, a branch growing upright should be selected, or it should be headed back at a strong bud, and the lateral buds below it should be rubbed off, so that an upright branch is drawn out to replace it, avoiding the formation of multiple leaders. Such tree species in the Shanghai area include deodar cedar, poplar, and so on.

For conifers, branches at the base that hang down to the ground should be cut off. As the tree grows, the branch point may be gradually raised as needed, and the main tip should be protected to grow upright.

For broadleaf tree species such as Chinese white poplar, which are not tolerant of heavy pollarding or heavy truncation, winter thinning should be the main method. During pruning, an appropriate ratio between crown and trunk should be maintained. Generally, the crown height accounts for 3/5, and the trunk height (below the branch point) accounts for 2/5. Beside the express lane, the branch point height should be at least 2.8 m or more. Note that the upper and lower positions of the lowest three main branches should be staggered, with even directions and suitable angles. The lateral branches on the three main branches that are closest to the trunk at the base should be cut off in time, and the branches above the three main branches should be well selected and retained so that they are arranged spirally upward, forming a conical crown after sprouting.

For ginkgo, branches are headed back every year, and the lower branches should be left longer than the upper branches, forming a conical crown after sprouting. After the form is established, mainly only dead and diseased branches and overly dense branches are thinned, and the pruning amount is generally not large.

4.3.2 Street Trees without a Central Leader

For selected tree species with weak trunk dominance, such as Hankow willow, elm, goldenrain tree, Japanese pagoda tree, and so on, the branch point height is generally 2-3 m. Near the branch point, retain 5—6 main branches, with short spacing between the main branches of each layer, so that they naturally grow into an oval or oblate crown. The main targets of annual pruning are dense branches, dead branches, diseased and pest-infested branches, and damaged branches, and so on.

5. Common Problems in Current Street Tree Pruning and Solutions

5.1 Some Street Trees Are Pruned by a Single Method

In the Shanghai area, for example, plane trees are mostly pruned in “cup shape” or “open-center shape” to avoid overhead wires and so on. With the improvement of road conditions in recent years, overhead lines on many roads have been placed underground, greatly easing the conflict between the natural growth of street trees and overhead lines, and also making plane tree pruning no longer limited to the above two methods. Areas with good spatial conditions can completely adopt “natural-form” pruning.

5.2 Heavy Pruning to Control Height of Street Trees

At present, many street tree maintenance units in the Shanghai area, seeking convenience, use the simple one-step “height control” technique to prune street trees. The reasons for using this method are nothing more than the following aspects: First, street trees are located in busy downtown areas and are old trees that have never been pruned. Such street trees are often more than 10 m tall and require mechanical operations to complete pruning. The pruning process is relatively prolonged, and the geographical location involves multiple factors such as traffic and residents, making the project enormous. As a result, the maintenance department has kept delaying pruning under the condition of not affecting overhead lines, residents' lighting, and so on, and when pruning must be done, it has no choice but to adopt one-step “height control” to complete the pruning task. Second, current street tree maintenance mostly belongs to various maintenance contracting units. To reduce maintenance costs, maintenance units may adopt pruning every other year, and pruning is also limited to the parts that are truly unsightly. When the maintenance period is about to expire and they do not plan to continue contracting, they use the one-step height control technique before handover to complete pruning in one go, and so on and so forth……

Although this method may be used under special circumstances, it will cause the green volume of street trees to decrease rapidly and is quite damaging to street trees. Therefore, for street tree pruning, standardized operations are still advocated. Whether it is “cup-shaped,” “open-center,” or “natural-form” pruning, all should be gradually brought into a fixed form. Unless renewal is needed, simple height-control heavy truncation and heavy pruning methods should not be adopted.

5.3 Inadequate Prevention and Control of Diseases and Pests, Resulting in Renewal and Heavy Pruning of Street Trees as a Last Resort

If diseases and pests are not controlled in time and thoroughly during routine maintenance of street trees, then after trunks and branches are hollowed out by borers, there is no choice but to renew and heavily prune them, replacing prevention with pruning, which greatly affects the landscape and tree vigor. In ordinary times, disease and pest control should be strengthened. Once diseases and pests are found, they should be controlled early, with prevention as the main approach. If prevention fails, they must still be treated early, while small, and thoroughly. Diseased and pest-infested branches that affect appearance should be cut off in time, to prevent reaching a point where heavy pruning is required to salvage the situation once they are discovered.

6. Pruning of Several Common Street Trees in the Shanghai Area

6.1 Plane Tree

Plane tree is a tree species with terminal buds and monopodial growth. There are two pruning methods: sympodial trunk-form pruning and cup-shaped pruning. In the Shanghai area, cup-shaped pruning is more common. Cup-shaped pruning requires cutting the top and determining the trunk above a certain height. This will promote the buds below the cut to sprout and grow branches. At this time, the method of bud removal and branch thinning in stages may be adopted, selecting and retaining 3-5 strong buds or main branches. During the growing season, pinching may be carried out continuously to strengthen the lateral branches (buds) above them. After growth stops in winter, select 2 lateral branches on each main branch and head them back. In this way, a cup shape of “three limbs, six forks, twelve branches” is initially formed. Then remove the original upright branches and crossing branches. Thereafter, every winter cut off 1/3 of the main branches, appropriately retain weak small branches as auxiliary nurturing branches, and cut away overly dense lateral branches so that lateral branches grow alternately, but their length should not exceed that of the main branches. For strong branches, retrenchment pruning should be carried out in time to prevent the crown from becoming too large and the leaf layer from becoming too sparse. At the same time, diseased and pest-infested branches, crossing branches, overlapping branches, and upright branches should also be cut off in time. For large trees after the form is established, pruning may be done once every 2 years, which can prevent seed hair pollution.

Sympodial trunk-form pruning of plane trees requires protecting strong terminal buds and upright buds, developing robust branches at all levels, and allowing the crown to continue expanding.

In recent years, natural-form pruning of plane trees has been advocated in the Shanghai area. For naturally pruned plane trees, after cultivating the first- and second-level framework and expanding the shade, the upper part is allowed to grow naturally. Daily pruning focuses on bud rubbing, pruning diseased and pest-infested branches, water sprouts, rotten heads, and so on, retaining as many healthy branches as possible to increase green volume.

6.2 Silk Tree

In the Shanghai area, silk tree is mainly pruned in the natural open-center form. When the trunk reaches 2-2.5 m or more, trunk determination pruning may be carried out, selecting staggered lateral branches as main branches. Never choose lateral branches at the same base point as main branches, so as to avoid excessive force on one part of the trunk. In winter, head back the three main branches, and then cultivate several lateral branches on each main branch, distributed in a staggered manner and occupying a certain space. If the crown expands too far, retrenchment pruning and head changing should be carried out in time, selecting several robust buds lower down to gradually replace them, and when they sprout the following spring, a new trunk can be formed. Repeating this cycle can form a natural open-center crown, like a large sunshade umbrella, fully displaying the unique function of street trees. At ordinary times, pay attention to cutting off dead branches, diseased and pest-infested branches, overly dense branches, crossing branches, and so on.

6.3 Goldenrain Tree

After trunk determination of goldenrain tree, in the winter of that year or the following spring, select and retain 3-5 robust, evenly distributed main branches, head them back leaving about 40 cm, and cut off the remaining branches. In order to concentrate nutrients to promote lateral branch growth, promptly remove new buds sprouting on the main branches in summer. In the first bud removal, select and retain 3-5 buds on each main branch; in the second, retain 2-3. The bud retention directions should be reasonable and the distribution should be even.

In winter, carry out branch thinning and heading back so that the lateral branches on each main branch are evenly distributed and in reasonable directions. Head back 2-3 lateral branches and cut off all the rest, with a heading-back length of about 60 cm. Heading back in this way for 3 years enlarges the crown and thickens the trunk, forming a spherical crown.

Every winter, cut off dead branches, diseased and pest-infested branches, crossing branches, thin and weak branches, and dense branches. If the extension branch of a main branch is too long, retrenchment pruning should be carried out in time, and it should continue to serve as the extending leader of the main branch. For upright water sprouts on the upper side of the main branches, cut them off from the base. Retain some small lateral branches on both sides of the main branches, so that there is space, the tree form is not disturbed, and the growth of the main branches is not affected.

6.4 Camphor Tree

For camphor tree pruning, thin out 4-6 lateral branches below the terminal bud that grow longer than the main branches, and rub off the lateral buds near the terminal bud to ensure the dominance of the terminal bud. If the lateral branches are strong and the main branch is weak, the lateral branch may also be retained, using the lateral branch to replace the main branch, and cut off the competing branches of the new main branch, remove overlapping branches on the trunk, and maintain 2-3 main branches, making them stagger vertically and gradually shorten from bottom to top. In the growing season, head back the competing branches near the extension branches of the main branches to ensure the dominance of the main branch tips. Pay attention to pruning whorled branches within the crown, trying as much as possible to make the upper and lower layers of branches stagger. For thick main branches, retrenchment pruning may be carried out to facilitate crown expansion. Because camphor tree has many branches, it also has many tender shoots, so the tender shoots need to be removed as much as possible, retaining old leaves.

7. Pruning Precautions

Pruning order. When pruning street trees, never prune randomly without order or thought. Pruning should follow the order of “from base to tip, from inside to outside,” that is, first consider what form the overall crown should be pruned into, and then prune gradually upward from the base of the main branches from inside to outside.

The branch height of street trees on the same road should be basically consistent, and the branch heights of adjacent plants should be roughly the same.

For overly thick large branches, the sectional branch-cutting method should be adopted to prevent splitting.

Because of the influence of street orientation, high-rise buildings, and underground pipelines, street trees often suffer from crown deviation, leaning, and so on. The center of gravity should be adjusted through pruning as early as possible. For branches on the weaker side of growth vigor, as long as there is no conflict with overhead lines or buildings, light pruning should be carried out to achieve the purpose of moderating tree vigor and balancing growth.

Tree climbing for pruning should comply with safe operation regulations to prevent safety accidents. Before climbing the tree, carefully check whether the ladder and safety belt are secure. At the same time, pay attention to the safety of passing pedestrians and nearby buildings.

References: 1. Lu Jianguo   Ornamental Plant Cultivation.

2. Urban Construction Division of Zhejiang Provincial Construction Department Hangzhou Blue Sky Vocational Training School   Landscape Construction Management.

3. Textbook Compilation Group of Shanghai Municipal Greening Administration   Construction and Maintenance Management of Landscape Greening Construction Projects 2000.

4. Shanghai Municipal Greening Administration  Nursery Stock Management of Landscape Greening Construction Projects  2000.

5. Hu Changlong   Handbook of Shaping and Pruning of Ornamental Flowers and Trees.

6. Hu Lü [2007] No. 0219    Notice of Shanghai Municipal Greening Administration on Standardizing the Pruning and Maintenance of Street Trees