Oleaceae, Ligustrum. Evergreen trees, with a height of 15m, are often shrubby. The bark is smooth and gray. The leaves are crisp, oval, dark green and shiny. It blooms in June with white flowers and large terminal panicles. The fruit ripens in11~ 65438+February, and the drupe is blue-black and covered with white powder when it ripens. Native to China and Japan, it is cultivated in Qinling and Huaihe River basins in the north, Guangdong and Guangxi in the south, Yunnan, Guizhou and Sichuan in the southwest, Shanxi, Hebei and southern Shandong. Like light, a little tolerant of shadows. Like warm and humid environment, not cold-resistant. Suitable for slightly acidic to slightly alkaline wet soil. Strong resistance to sulfur dioxide, suffering within 50 meters from the pollution source, but growing; 100 meters away without symptoms of victimization. 1 kg dry leaves contain 4 ~ 7 grams of sulfur and are not harmed. The resistance to chlorine gas is also very strong. The dry leaves of 1 kg contain 6 ~ 10 g of chlorine, and have no injury symptoms. Strong resistance to hydrogen fluoride, and it can grow normally at a distance of 100 meters from the pollution source. Can absorb lead vapor. Measured at a distance of 200 ~ 300 meters from the pollution source in the cement plant, the blades can absorb 6 grams of dust per square meter. Ligustrum lucidum has the advantages of fast growth, high germination rate, pruning resistance and easy molding. The crown is broad and full, with good shade. It is easy to survive, resistant to extensive management, and its price is relatively low among evergreen broad-leaved trees, so it is widely used as street trees on both sides of streets and suburban roads in small towns. It can also be used as a high hedge for tree walls, with good concealment effect.

2. Populus tomentosa

Salicaceae, Populus. Deciduous trees, trees up to 40 meters high. The trunk is straight and the crown is blunt and conical. Bark is gray when it is young, with obvious lenticels, dark brown in winter and longitudinal cracking. Long branches and leaves are triangular and heart-shaped, and the back is densely covered with white hair; Short branches and leaves triangular-ovoid. Flowers in March, dioecious, and male plants are selected for landscaping seedlings. Strong cold tolerance, widely distributed. Liaoning and Inner Mongolia in the north, Jiangsu and Zhejiang in the south and Yunnan and Guizhou in the southwest. The middle and lower reaches of the Yellow River are all suitable areas. Bark often freezes in areas where the temperature difference is too high in early spring; Diseases and pests are prone to occur in high temperature and rainy areas, and the growth is poor. Strong positive tree species, salt and alkali tolerance, like deep, fertile and moist soil, water and humidity resistance, strong resistance to smoke and toxic gases. Populus tomentosa is a tree species with branches as the main axis, with high height and thick leaves. It is suitable to be planted as a street tree on both sides of the road without overhead lines, and is also an excellent shade tree and a peripheral tree species of farmland forest network, and can also be used as a windbreak forest. Among the same tree species, Populus canadensis (cold-resistant), Populus italica (cold-resistant, suitable for southern areas) and Populus davidiana (not resistant to damp and heat, suitable for northern areas) are also selected for application.

3. weeping willows

Salicaceae, Salix. Deciduous tree with gray-black bark and irregular cracks. Branchlets slender, gently drooping. Leaf blade is long and narrow, narrowly lanceolate. Catkin blooms from March to April. When using dioecious plants in cities and densely populated areas, male plants should be selected to avoid catkins produced by female plants in spring, which will lead to respiratory allergies in some people. Mainly distributed in the Yangtze River valley, south to Guangdong, southwest to Yunnan, all cultivated. Likes light, warm and humid climate, is resistant to water and humidity, and does not adapt to drought or cohesive soil. It is the main greening tree species in low-humidity beaches and an important revetment tree species for soil and water conservation. Weeping willows are swaying, beautiful and natural, and are planted in rivers, lakes and Chi Pan. They often plant peaches and purple leaf peaches. They are pink and green, and they are beautiful in spring. The reflection of the hanging branches is full of beautiful water waves. Planting landscape trees and relying on pavilion rocks are both rigid and flexible, which is more graceful and charming. Planting street trees in the sparsely populated suburbs, the willow branches are gentle and natural. Bai Juyi famously said, "A tree with a thousand branches of spring breeze is tender than golden spring and softer than silk", which vividly outlined the graceful posture of weeping willows in spring. Because weeping willows germinate earlier, in order to avoid the threat of cold and low temperature in spring, they should be planted after defoliation in autumn. Weeping willows have a short life cycle and are prone to aging. In cultivation, head pruning is usually used to update and update them.

1984, Jiangsu Academy of Forestry crossed weeping willow (S.balylonica) with Bai Liu, and bred a hybrid yellow willow with golden branches and green leaves, which was particularly enchanting and widely adaptable. There are also the same species: ① Salix matsubana (S.matsubana), with straight trunk and upward branches, is mostly used as a street tree in rural roads and general highways. It has strong cold tolerance and can be distributed in cold areas north of the Yellow River Basin. (2) River willow (S.chaenomeloides), with wide branchlets, water resistance and moisture resistance, can reach the age of 100 years.

(3) S.chienii, a small shrubby tree with spreading branchlets, nearly rectangular leaves and silvery white hairs on the back.

(4) Pinus bungeana, a shrub, 2-3 meters high, with sparse branches, green-brown branches and a blush. The winter buds are reddish purple and shiny. The leaves are oval, dark green, with white hairs on the back and semi-leathery. Male inflorescences are oval and cylindrical, and open in front of leaves in early spring. At the beginning of flowering, the bud scales spread and wrapped around the base of inflorescence, red and shiny; When in full bloom, it is covered with silvery white silk wool, which is extremely beautiful and is a popular flower arrangement material during the Spring Festival.

4. Sophora japonica

Papilionaceae, Sophora. Deciduous trees, the height of which can reach 30 meters. Bark is gray-black, rough and longitudinal, without terminal buds. Branchlets are green, with obvious lenticels and odd pinnate compound leaves. Flowering from April to May, racemes or panicles are terminal, and corollas are yellow and white. The fruiting period is 9-65438+ 10 month, the pods are beaded, the meat quality is not cracked, and it will not fall after winter. Sophora japonica has a round crown, beautiful posture, lush green shade, both flowers and fruits, and strong ability to resist air pollution and smoke. It has been planted as a street tree and a shade tree, and it is also an excellent nectar source plant. Like light, it has a wide adaptability to soil pH, but it is not resistant to stagnant water, and it is not strict with climatic and ecological factors, and it is widely distributed, so it can be planted in both north and south. It grows faster and has strong germination. When applying, bare roots should be planted in spring, and the crown should be cut off again or cut off. Planting holes should be deep, fertilization should be appropriate, and the crown should be strengthened. The cultivated variety is Sophora japonica, with drooping branchlets and elegant posture. It is usually planted in front of buildings or at the entrance of roads as a landscape tree.

5. Robinia pseudoacacia

Sophora japonica, Papilionaceae. Deciduous trees, the height of which can reach 25 meters. Bark is brown, deep and longitudinal, without terminal buds and odd pinnate compound leaves. Flowering from April to May, the raceme droops, and the corolla is white and fragrant. The fruiting period is 9 ~ 10 month, and the pods are strip-shaped with narrow wings in the abdomen. Originated in North America, it has strong climate adaptability, introduced into China and cultivated in a wide area south of Tieling, Liaoning. I like light, but I don't like shadows. Drought-tolerant and barren, it grows well in calcareous soil, but it is not resistant to water stains. Robinia pseudoacacia has strong germination ability, lush foliage, stretched crown, both flowers and fruits, strong smoking and pollution resistance, and can be planted as street trees and shade trees. It is also a pioneer tree species for afforestation in barren hills, and is suitable for building windbreak and sand-fixing forests and revetment forests. Robinia pseudoacacia flower is a kind of high-quality honey source, which can extract aromatic oil, and can be widely used to combine suburban landscaping and farmland forest network transformation to increase economic benefits.

6. Taxodium ascendens

Taxodiaceae, Taxodium. Deciduous trees, trees up to 25 meters high. The base of the trunk expands and becomes a knee-shaped respiratory root, especially in low wetland areas. Bark is grayish brown, longitudinally split and long strip falls off. Branches extend upward, and the crown is often narrow and pointed. Annual branchlets are green, slender and slightly bent downward; 2-year-old branches are reddish brown. Leaves subulate, slightly curved and spirally extended. A cone is spherical. Originally from North America, China introduced Jiangsu, Zhejiang, Hubei, Jiangxi, Guangdong and other places for cultivation in the 20th century. Sexual preference for light acidic soil, yellowing phenomenon when planted in soil above pH7.2, drought resistance, waterlogging resistance, strong germination and good wind resistance. Chifir trees are beautiful, branches and leaves are beautiful, and autumn colors are in full bloom. The planting effect of street trees in water network area is good, especially suitable for afforestation in tidal flat wetland.

7.Metasequoia glyptostroboides

Metasequoia glyptostroboides. There is only 1 species, which is endemic to China among Quaternary glacial relic plants. Deciduous trees, the height of which can reach 35 meters. The bark is grayish brown, cracked longitudinally and peeled off in strips. The young crown is steeple-shaped, gradually becoming round and muddy, and the base of the trunk expands. Large branches rotate irregularly, branchlets are opposite, pinnate leaves are opposite, and turn red in autumn. Originated in Hubei, Sichuan and other places. Sex is bright. Cold tolerance, strong adaptability, can be planted in Beijing open field for winter. Like acidic soil, it grows normally in slightly alkaline soil. Not resistant to drought, nor to water and humidity. Strong resistance to sulfur dioxide, chlorine, hydrogen chloride and other toxic gases, less pests and diseases. It is an important garden tree species in suburbs, scenic spots, factories, mining areas, roads and farmland forest networks. Metasequoia is graceful and towering into the sky; Beautiful leaves, green in summer and red in autumn. It can be used as street trees, landscape trees and scenic forests, and can be planted separately, in rows and in groups.

The practical application of street trees should be based on the road construction standards and the specific circumstances of the surrounding environment, taking the convenience of passers-by and vehicles as the first criterion, and combining with the requirements of landscape effect, determine the appropriate tree species and varieties, and select the appropriate tree body and tree shape. If there are restrictions such as power and communication lines above the planned planting belt, trees whose final growth height is lower than the elevation of overhead lines should be selected to save the cost of regular pruning. If there are enough funds, equipment and pruning technicians to maintain a high level of requirements for tree maintenance, we can choose tall trees, adopt correct pruning methods and avoid the restrictions of lines, so as to obtain satisfactory use results. In addition, when planting plastic, the branches of trees should be high enough so as not to hinder the normal walking of passers-by and vehicles, and not to block the sight of pedestrians and drivers, so as to avoid accidents. Especially in areas with small turning radius and poor line of sight when turning, more attention should be paid. The selection of tree size should be appropriate and should not exceed the requirements of the proportion with the architectural landscape on both sides of the street. Its size and growth form should meet the specific requirements of design and stand the test of time.

The crown shape of street trees is determined by the environment where they are planted. On the main road where overhead lines pass, regular crown shapes can be adopted to trim trees into cups or open hearts. General highway trunk roads or narrow carriageways can be dominated by natural crowns. The street trees with cup-shaped pruning have a typical crown shape of "3 strands and 6 branches 12 branches", and the height of the branch point of the trunk should be below the overhead line, which does not hinder the passage of pedestrians and vehicles, generally 2 ~ 3 meters. Every year, we should adjust the growth direction of the lateral branches of the crown in time, keep the crown shape uniform and tidy, eliminate the interference to overhead lines, and take care of the safety and lighting of adjacent buildings. The safe distance between street tree branches and overhead lines (including horizontal spacing and vertical spacing) varies with the type of road in sight. In general, the safe spacing of power lines below 1 KV is 1 m, 3 m for1~ 20kV lines, and 4 m for 30 ~10kV high voltage lines,150 ~ 220kV lines. The safe distance between the branch and the communication open wire is 2m, and the safe distance between the branch and the communication cable is 0.5m..

Open-heart pruning evolved from cup-shaped pruning, which is mostly used for self-pruning trees without spindle or terminal buds. When pruning, choose 3 ~ 5 main branches with different directions and uniform distribution at the branch point, and choose 2 ~ 3 side branches on each main branch. The crown develops naturally, and the crown is full, but the cavity is empty.

Natural pruning should be treated separately according to whether the tree species have the central leadership or not. Any tree species with central leadership, such as poplar, oleander, Metasequoia glyptostroboides, Taxodium ascendens, etc. The height of lateral branches should be more than 2.5 ~ 3 meters, and the lower skirt branches should be thinned according to the situation, especially in the sections with poor traffic sight such as bends and forks, and more attention should be paid to broadening the horizons to avoid traffic accidents. Tree species without central leadership, such as willow, elm, locust tree, camphor tree, privet, camphor tree, etc. The height of the branch point should be controlled at 2 ~ 3 meters, and the crown naturally forms a sphere.

The height of street trees on the same main road should be relatively consistent, and it should be more than 3 ~ 3.5 meters in the area where the road surface is narrow or large vehicles notice. In the pedestrian street area where the sidewalk is wide or only pedestrians are allowed to announce, it can be reduced to 2.5 ~ 3.0 meters, and the tree species with small branching angle can be appropriately reduced, but not less than 2 meters. The size of the tree should be as neat and uniform as possible to avoid the aesthetic effect and management inconvenience caused by uneven height and different sizes and thicknesses. The planting spacing of street trees is generally 8 ~ 10 m in urban areas and 6 ~ 8 m in suburban areas. In seedling size, DBH is 7 ~ 8cm and 3 ~ 4cm, respectively, to achieve early shading. Fixed after planting to improve the survival rate of transplanting. In order to ensure the normal growth of street trees planted in urban streets with large traffic, a suitable tree pool (1.0m× 1.0m) should be built. In order to prevent the soil in the tree pond from being trampled by pedestrians, it is best to have kerbs 10 cm above the ground, or lay through-hole cast iron or cement cover plates flush with the ground.

When planting street trees, pay attention to the horizontal distance between trees and adjacent buildings, underground engineering pipelines and sidewalk edges (table).

Minimum horizontal distance between trees and buildings (structures)