Keywords: current situation and countermeasures of street trees
Urban road greening is an important part of urban landscape greening. Urban roads are distributed in the city in the form of lines, which connect the scattered "points" and "areas" of garden green space in the city, thus forming a complete urban garden green space system. As the backbone tree species of urban landscaping, urban street trees play a very important role in creating beautiful urban environment and improving urban ecological environment. In recent years, with the acceleration of urban construction and the rapid development of landscaping in Ningbo, the varieties of urban street trees have been enriched. However, judging from the current situation of street trees in Ningbo, there are still problems such as single variety, low ornamental value and frequent pests and diseases. Therefore, how to choose street trees with strong adaptability, less pests and diseases and high ornamental value should become a new problem in landscaping work. 1 Selection principle of street trees Street trees are trees planted on both sides of the road in a certain way to produce shade. Because the growth of street trees is restricted by the city's extraordinary environmental conditions, such as buildings, underground pipelines, people flow, traffic and other human factors, the roots can only grow in a limited range, and the aboveground parts are also in unfavorable environmental conditions, and at the same time meet the various functional requirements of street trees, so the requirements for tree species selection are strict. Now, according to the requirements of urban street trees for the growth environment, the selection of street trees must meet the following principles: 1 can be suitable for the local growth environment.
It can adapt to tree species with extensive management, low requirements for soil, moisture and fertilizer, pruning resistance, less pests and diseases and strong stress resistance.
Tree species with straight trunk end, straight tree shape, beautiful crown, large crown and strong shading effect.
Tree species with early leaves and late leaves are required.
The requirements are tree species with deep roots, no thorns, non-toxic flowers and fruits, no odor, no flying hair and few roots and tillers.
6 to adapt to the urban ecological environment, long life, less pests and diseases, strong resistance to tobacco and wind damage. 2 Application Status of Urban Street Trees in Ningbo The old city of Ningbo is small in scale, and the original street trees are mainly Cinnamomum camphora and Fawu. Since the 1980s, with China's continuous opening to the outside world, Ningbo, as a coastal open city, has a relatively developed economy, and its urban construction is changing with each passing day. The government has paid more and more attention to landscaping. With the increasing area of green space, the varieties of street trees are becoming more and more abundant. From the original single variety to more than a dozen varieties such as Cinnamomum camphora, Ginkgo biloba, Du Ying, Luanshu, Sophora japonica, Magnolia grandiflora and Magnolia grandiflora. With the improvement of street greening level, urban greening and ecological environment have been continuously improved. However, as far as the application of street trees is concerned, it is not satisfactory and there are many problems. The single phenomenon of 1 tree species has not been fundamentally solved. Before 1980s, Ningbo, like other big cities in China, was dominated by street trees with a small amount of camphor trees. Since 1980s, Cinnamomum camphora, as a city tree in Ningbo, has gradually replaced Fraxinus fargesii as the leading variety of street trees. Although camphor tree is evergreen all the year round, its crown is tall and its growth is also very suitable for Ningbo. Because of the single tree species, pests and diseases have become more and more serious since the 1990s. Although the number of street trees has increased in recent years, due to the limitation of seedling supply, the number and specifications of other varieties of seedlings are small, and the situation of Cinnamomum camphora has not changed. There are many evergreen trees and few deciduous trees. In the choice of street trees, there are few deciduous trees in Ningbo at present because of the habitual influence. Although the landscape effect of evergreen trees in winter is good, it gives people a cold feeling because evergreen trees block the sunshine. Deciduous trees, such as Ginkgo biloba, Liriodendron chinense and Sapindus mukoraiensis, should be planted in narrow roads or busy streets. The research on the development and utilization of street trees is very weak. For a long time, Ningbo's garden scientific research work is very weak, lacking professional research institutions and specialized institutions or researchers specializing in the development and utilization of street trees, which makes the introduction, development and utilization of new street trees not included in the agenda so far. Due to the limitation of green seedlings, there are only trees and plants in the green planning, which is a bit helpless. 3 Development Prospect and Countermeasures of Urban Street Trees in Ningbo 1 Strengthen the investigation and study of existing street trees and select and apply excellent tree species. There are many tree species suitable for street trees in Ningbo. The relevant government departments should organize technical forces to investigate and study local excellent tree species and try their best to tap local native tree species, because local tree species have strong adaptability, vigorous growth and reflect local characteristics. Through investigation, scientific analysis and evaluation of the characteristics of different tree species, the street tree species suitable for Ningbo city are selected as the main tree species for urban street trees or urban greening. 2. Strengthen the introduction of street trees. Appropriately introduce street tree species from other places, introduce street tree species with high ornamental value at home and abroad in a planned way, and enrich the tree species through trial planting-selection-promotion. However, to oppose blind introduction, a large number of Italian poplars were planted in some places a few years ago, and the pests and diseases of Italian poplars have become very serious a few years later. Some places blindly introduce tropical plants at high prices, which is not suitable for the local environment, not only causing economic waste, but also losing the local characteristics of Ningbo. 3. Improve the maintenance and management level of existing street trees, enhance tree potential and prolong tree life. Because the growth environment of street trees is poor, it has certain influence on the growth of trees. The existing urban roads are generally narrow in pavement and heavily trimmed in crown; However, when building or rebuilding roads, the specifications of tree species are generally large, the trunk and roots are severely cut off, and the tree potential is weak. Therefore, it is necessary to strengthen the maintenance and management level of existing street trees and carry out scientific management of street trees, such as watering, fertilization, pruning, pest control and so on. It is necessary to adjust measures to local conditions according to different tree species and tree potentials, improve the level of conservation and management, enhance the tree potential, improve the ornamental value, prolong the life of trees, and maintain the long-term stability of urban street greening landscape.