Article source: Jianshu
Super Typhoon Likima brought us to rethink the way trees were planted and planted on urban sidewalks
The choice of tree species, forcing the selection of large trees in the space, is neither economical nor ideal
The criteria for choosing street trees are strong wind resistance, good shading, less pests, seasonal flowering, rich color changes, etc., ginkgo biloba and joy trees have straight trunks and beautiful crowns, which are more street tree species used in Shaoxing.
In the past, the shading and seasonal effect functions ranked first, but according to the weather conditions of multiple winds in Shaoxing in summer and autumn, I think that wind resistance should be taken as the primary consideration in the balance between wind resistance and shade function.Especially in the streets where urban buildings have a long depth along the road layout, the valley lane effect is obvious, and it is easy to form airflow.
The U.S. Forest Service studied the wind tolerance of 150 commonly used urban tree species and found that palms are very resistant to wind (which is not very suitable for Shaoxing's climate), and other wind-resistant species include crape myrtle, holly, pond cedar, broadleaf magnolia and oak.Those that do not resist the wind include horse coat trees, pear trees, elm trees, pine trees, araucaria trees, weeping ficus, etc.
Ginkgo biloba and camptotheca acuminata are not big in shape, but their main stems are very tall, branches and even tree poles are prone to brittle fracture, and their roots are easily top-heavy. These tree species advocate matrix planting in green spaces to form small communities of trees, trees planted in groups are more resistant to typhoons. Tall trees planted on the sidewalk alone, wind resistance is not ideal.
In addition, city managers and engineering builders will encourage design units to use large trees with large breast diameters in order to pursue the effect of poles.Large chest diameter trees or old trees adapt to the surrounding environment in long-term growth, and then move, not only the top-heavy effect is obvious, but also the environmental adaptability will be poor.I think it is neither economical nor ideal to choose tall trees with large breasts in a tight space.
Rethinking the planting method, the foundation is not solid, and the best tree species are also in vain.
A tree break is only about species? It has nothing to do with the planting space provided by the city, the spatial pattern of the buildings, and the changing airflow of the city's architectural layout?
From the fallen street trees, it can be seen that most of them are high-pole ginkgo and joy trees, with small bulbs and four rods supporting but shallow burial depth.The planting does not follow the scientific laws, does not provide the necessary environment for the growth of good trees, etc.The above-ground and underground parts cannot form a good symmetrical growth, tall rods and small roots, top-heavy, and will naturally lodge when encountering strong winds.
Small planting holes, the foundation is not solid, the best tree species is also a waste. According to the photos, the root ball of ginkgo biloba is only about 60 cm, and the surrounding soil is highly consolidated (most sidewalks and roads are filled together, with high compactness and poor nutrition of filling materials) , the root system of a tree is confined in a small space and can not be fixed as it should be. Most of the roots of trees are distributed within 0.5 m of the soil layer. If they can not extend to the periphery and are confined in a very small space, they will eventually form a shallow and small root disc with very weak fixation, it can be said that the four-stroke support is carrying too much weight.
The right way is to provide enough space for trees to grow above and below ground. The standard of the above-ground space is usually determined according to the crown size of the adult tree, and it is better that the crown size of the two trees does not overlap a lot. Domestic groves are often a square or circular pit of the same size up and down. In addition to the size of the opening, there are air-permeable and water-permeable structures under the paving tile or cement pavement and extend to the periphery to meet the growth needs of tree roots.
In theory, the space for underground growth is usually 10 × 10 meters for big trees and 3 × 3 meters for small trees. This is not enough for most of us on the sidewalk. Most tree pools are only 1.5 × 1.5 meters, there were even 1.0 x 1.0 meters left. The tree ponds were already cramped. To facilitate transportation, most nurseries would make the root balls very small. The construction unit map was convenient, and it would also make up for the depth of the tree beds. The space for the underground energy root system to extend becomes limited, and most of the tree pools are close to the sidestones. The outer edge of the sidestones is the road structure. Under the 60-80 cm pavement structure layer, there is the roadbed filling layer with the compactness of more than 93% , is unfavorable to the root system to the peripheral extension. It is suggested that the tree pool should be set on the inside of the sidewalk, and the size of the tree pool should not be less than 1.5 × 1.5 meters.
Of course, in the tight urban space, many sidewalks cannot even guarantee 2 meters, and the ideal planting environment is not something that can be had.
Maintenance and management, homework done in daily life, do before typhoons
Sidewalk soil compaction is common, fertilizer water is poor, pruning should be heavier, to achieve the comprehensive effect of pruning, there must be corresponding fertilizer water management cooperation, appropriate control of irrigation and topdressing nitrogen fertilizer, timely supplementation of phosphorus and potassium fertilizer.
The above tree was broken by the wind is due to improper maintenance, the formation of parallel branches and extruded wood, the joint of the two branches is very fragile, a strong wind will be easy to split, broken.
The greening of a city is far from being as simple as digging pits and planting trees, but a work that requires the support of multiple disciplines such as biology, dendrology, soil science, ecology, mechanics, urban planning and so on.If China's urban greening only stays at a low level, it will be difficult to get out of the vicious circle of "planting and destroying, destroying and planting again, and planting and destroying again", which will cause great human, material and economic losses, and hinder us from realizing the original intention of "green mountains and green water can be seen in the city".
Author: The Fire of Mr. Fire
Source: Jane's book
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