First, the role of urban greening
1, purifying air
All kinds of green spaces and trees in cities and towns, with their huge leaf area and dense branches and leaves, can block, filter and absorb dust and floating dust in the air, and at the same time, they can also intercept, disperse and absorb various toxic gases in the air, thus purifying the air.
Step 2 adjust the climate
Landscaping can adjust the temperature, which is warm in winter and cool in summer. In hot summer, the huge leaf area of trees can shade the sun, which can effectively reflect solar radiation and greatly reduce the direct sunlight on the ground. Trees can reduce their own temperature and increase the humidity of the nearby air by evaporating water through their leaves. Therefore, the temperature of green space in summer is 3 ~ 5℃ lower than that of non-green space. Therefore, the large area and high coverage of urban green space can effectively improve the microclimate of residential areas.
Step 3 reduce noise
Noise pollution in modern cities is becoming more and more serious. Noise not only affects people's normal life, but also seriously harms people's health, affects people's central nervous system and mental reaction, and causes people to have symptoms such as listlessness, fatigue and hypertension [1]. Noise can be absorbed and isolated by using the huge crown and branches of trees. According to the measurement, the noise intensity of the street with high-rise buildings and no trees is more than five times higher than that of the street with trees on both sides.
Step 4 beautify the environment
Garden plants are an important part of urban landscape. The beautiful shapes of plants enrich the spatial changes of the environment. The height of trees is strewn at random, and the difference of tree species and crown size breaks the plane and monotony of buildings and becomes lively, thus deepening the sense of space and hierarchy of urban environment. With the change of seasons, various plants show different seasonal colors. For example, the autumn leaves of five-pointed maple, triangle maple and other tree species turn red, and the colors of flowers are even more colorful. Therefore, reasonable greening of the city can make the city colorful, full of vitality and beautiful living environment pleasing to the eye [2].
5, disaster prevention and mitigation
Many landscaping trees have strong fire resistance and outstanding fire prevention function. For example, conifers with dense and uniform leaves can block about 95% of radiant heat from passing through, and coral trees can block 83% ~ 93% of heat from passing through, which is comparable to a firewall. Planting trees and grass on the banks of rivers and lakes can conserve water, purify water, protect soil and revetment, reduce soil erosion, pollution and sediment deposition. Greening can reduce the content of bacteria in the air, and many garden plants can inhibit and kill a variety of bacteria scattered in the air. The roots, stems, leaves, flowers and other organs of these plants can secrete some volatile substances, which can kill or inhibit the development of various microorganisms or germs. People call this substance "phytoncide". Such as pine, cypress, poplar, honeysuckle, etc. all contain certain fungicides.
Step 6 purify water sources
Green plants can purify air, protect water quality and prevent downstream water and soil pollution. For example, when sewage containing Escherichia coli flows through a pine forest with a width of 30 ~ 40m, the number of bacteria can be reduced to1/8; In the water flowing from the mixed forest of oak, Fraxinus mandshurica and Robinia pseudoacacia, the Escherichia coli is only1/23 of the control value; If water passes through a 50m-wide 30-year-old poplar-birch forest, the number of bacteria can be reduced by more than 9/ 10. After sewage enters the soil, it can be purified to a great extent through the absorption of green plants, the degradation of soil microorganisms, the adsorption, precipitation, ion exchange and the fixation of clay minerals.
Second, the strategy of urban greening
1, promoting the original ecological greening design concept.
In the design of urban landscaping, according to the local topographical features, the original mountains, natural vegetation and water resources should be fully preserved, so that nature can exist in the most "natural" way. In the construction of greening projects, we should avoid large-scale topographic transformation, try our best to maintain the original landform characteristics of the site, balance the earthwork on the spot, make full use of the original topsoil of the site as backfill planting soil, and reduce the use of foreign soil. In addition, the concept of urban greening should be renewed, and exotic tree species should not be introduced on a large scale, because exotic tree species are easy to cause acclimatization and high cost. Urban greening should make full use of local wild vegetation, give full play to the ecological function of local wild crops, and promote the original ecological greening design concept.
2. Advocate conservation-oriented landscaping.
The essence of conservation-oriented city landscaping is "to choose the greening mode with the least land use, the least water consumption and the least financial allocation, which will cause the least interference to the surrounding ecological environment". Conservation-oriented city landscaping should start from three aspects: saving land, water and money.
(1) Conservation of Landscaping Land
Saving land is to improve the utilization rate of land, not to reduce the planning investment of landscaping land. Three-dimensional greening, roof greening, wall greening, vertical greening and other land-saving garden forms should be widely promoted to make every urban element green as much as possible.
(2) Water saving in landscaping
The construction of water-saving gardens should start from two aspects: open source and throttling. On the one hand, it is necessary to increase the available water sources, such as promoting air-permeable pavement on the ground, building a reservoir at the discharge port of rainwater pipes, and making full use of unconventional water such as natural precipitation and reclaimed water; On the other hand, it is necessary to reduce the consumption of water resources, advocate the use of reclaimed water for irrigation, pay attention to the water-saving design of landscape engineering, balance earthwork on the spot, make full use of the original topsoil as backfill planting soil, and reduce the use of foreign soil.
(3) saving landscaping costs
Saving money is not to reduce expenditure, but to improve the utilization rate of funds, spend the least money to build the most greening, prevent transplanting big trees and planting old trees, and resolutely stop digging big trees and transplanting old trees from deep forests to cities. Advocate the planting of large seedlings and the use of native plants, and resolutely stop blindly introducing rare plant varieties and new plant varieties that are not suitable for local climate conditions. The construction of conservation-oriented gardens follows the principle of "circular economy" to reduce the impact of various wastes on the environment. Such as "rockery" formed by using the remaining concrete in the mixer; Use the stones and gravel left by paving as garden paving, and use dead trees and branches to form garden landscape. In addition, we should also advocate and encourage the use of local inexhaustible natural energy, such as wind energy, solar energy, water power and so on. , to achieve safe and clean landscaping construction, maintenance and daily management [3].
3. Rational selection of plants
When choosing garden plants, we should choose plants with ornamental, sunshade, dustproof, sound insulation, air purification and water and soil conservation. When creating a group landscape, we should pay attention to the contrast and harmony of trees, adhere to the greening idea of giving priority to trees, combining trees, shrubs, grass, vines and flowers, planting many trees together, planting a lot of trees and planting grass moderately, and build an urban forest with tall trees as the main body and multi-layer structure of trees, shrubs, grasses and vines, and lay the foundation of urban environment with "forest" as the background. Only in this way can it help to alleviate the "heat island effect", improve air quality and fundamentally improve the ecological and living environment of the city.
4. Low-carbon garden maintenance
The construction of urban landscaping should be based on the convenience of maintenance and management, which requires reducing the investment of manpower, material resources and strength in the maintenance and management of landscaping and daily operation. According to statistics, in developed countries, the maintenance cost of 10 is equivalent to the construction cost of gardens, and the maintenance cost of gardens has become a huge burden for the government. In recent years, the cost of human resources in China has gradually increased, and the maintenance cost of landscaping will be higher and higher. If the maintenance and management problems in the later period are neglected in the construction of urban landscaping, landscaping is likely to become an unbearable burden for some local governments over time.
5, vigorously promote the roof greening design.
As a kind of building envelope, building roof consumes more heat than any external wall or ground because of its indoor and outdoor temperature difference. Therefore, it can be said that building roof is an indispensable platform to realize the concept of "low carbon and environmental protection" in civil buildings. The measured results show that roof greening can reduce the temperature of the top floor of the building, reduce the air conditioning cost by 20% ~ 50%, and greatly reduce the heating cost in winter. At the same time, roof greening can also reduce the heat island effect of big cities and reduce and utilize rainwater discharge. Planting roofs not only plays a role in thermal insulation of the roofs of buildings, but also beautifies buildings, embellishes the environment and improves the thermal environment and air quality of buildings. Radiant heat energy will be transformed into biological energy of plants and beneficial components of air, thus realizing the transformation of solar radiation resources [4].
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