A brief history of development Ancient gardens were mainly owned by royalty, nobles, monks and the rich, and a few were used for entertainment and hunting. Large-scale gardens are mostly distributed in the outer edge of the city, with a small number and uneven distribution, which has little impact on the urban environment. After the industrial revolution, the urban population in industrial countries has been increasing and the environment has been deteriorating. In this situation, the British royal family first opened some royal gardens for the public to enjoy. 1858, new york, USA established one of the earliest parks in the world-Central Park. Some well-known social reformers, activists, scientists and engineers who are enthusiastic about public welfare have been engaged in activities to improve the urban environment. They all regard the development of urban garden green space as a means to transform the urban material environment, and advocate increasing the area of green space and forming a system to make the city have an idyllic and beautiful environment. 1892, F.L. olmsted, an American landscape architect, made a plan for the Boston urban garden and green space system, connecting parks, riverside green spaces and boulevards. 1898, Howard of Britain put forward the theory of "garden city". Under the influence of Howard's thought, the theory of new town and green belt appeared later (see new town construction movement, green belt and wedge-shaped green space). Scientists have also studied the role of plants in environmental protection, laying a scientific foundation for the theory of urban garden green space system.
From the perspective of ecology, environmental psychology and environmental aesthetics, green space has two main functions.
Purify the air and improve the environmental quality. Plants can absorb carbon dioxide in the air and release oxygen through photosynthesis, which can increase the oxygen content in the air. The roots of plants absorb water and evaporate it into the air through leaves, which can improve the humidity of the air. Some plants can absorb harmful gases emitted by factories, thus reducing the content of harmful substances in the air. Some plants can secrete bactericidal substances, which helps to reduce the bacterial content in the air. Plant branches and leaves can retain and filter dust particles in the air and play a role in purifying the air. Plants covered by shade absorb part of the solar radiation heat and reduce the ground thermal radiation, resulting in low temperature in local areas and high temperature in surrounding areas, which will form air convection due to temperature difference and improve the microclimate. Forest belts can also reduce noise.
Beautify the environment and meet spiritual needs. The urban space environment with various buildings as the main body makes people feel monotonous. With its numerous varieties, colors, lines and shapes, plants enrich the urban landscape and help to relieve people's psychological pressure. Placing all kinds of plants between and around buildings can not only dilute the monotonous and boring artificial atmosphere, but also set off the personality of buildings, forming a space environment in which man and nature blend.
Planning Content China began in the early 1950s, and took the planning of urban gardens and green space systems as the content of the overall urban planning. At that time, the planning practice was to make full use of natural rivers and lakes, and to arrange all kinds of parks, green spaces and avenues in a balanced way, so as to form a complete garden green space system with other green spaces and green belts in the city. The focus of planning is to calculate and arrange all kinds of public green space.
Classification and public green space Urban green space can be divided into public green space (parks and boulevards), residential green space, special green space, protective green space and suburban scenic green space according to their functions. The quota index of urban public green space refers to the total number of tourists in the city and the park green space area that each tourist should occupy during the peak hours (such as the peak hours when tourists are concentrated on holidays). According to the investigation in 1950s, under the general climatic conditions, the number of tourists entering the urban park green space during peak hours accounts for about 10% of the urban population, and the park green space area occupied by each tourist should not be less than 60 square meters. Therefore, it is determined that the long-term planning index of urban public green space is not less than 6 square meters per person. The Interim Provisions on Urban Planning Quota Index issued by China National Capital Construction Committee 1980 stipulates that the quota of urban public green space is 3-5 square meters per person in the near future and 7- 1 1 square meter in the long term. There are no legal indicators for other green spaces other than public green spaces.
Greening Coverage Since 1970s, the international research on environmental science has gradually deepened. China also began to pay attention to the role of plants in environmental protection and conduct research. China's academic circles put forward a new supplementary green space index-urban green coverage rate, which is considered to be not less than 30% in general.
Layout of China In the 1950s and 1970s, the planning of urban garden green space system generally followed the principle of evenly arranging all public green spaces, so that every urban resident could enjoy the nearby green spaces. The main body of public green space is various types of parks. The park scale of the whole city is more than 10 hectare, which requires relatively perfect facilities; The scale of the park is 5 ~ 8 hectares; Parks or small gardens at residential level are about 1 hectare. According to the size and layout of the city, there should be one or more parks in the city, which require moderate location and convenient transportation. The service radius of the park shall not exceed 1 km. The service radius of parks and small parks at the residential area level shall not exceed 500 meters. Generally, in the planning of urban garden green space system, according to the above requirements, the location and layout of all kinds of parks are selected, and combined with the natural terrain of the city to reflect the characteristics of the city, such as using urban rivers, hills and other green belts to connect all kinds of parks and green spaces into one. Hefei city uses the demolished wall foundation and moat to arrange a circular green belt, which is very distinctive. Xi also uses parks, boulevards and factory shelterbelts around the city to connect scattered parks.
New trends In recent 20 years, a new theory about the layout structure of big cities has emerged: the traditional single-center city has been replaced by multi-center, group-like urban agglomerations or belt-like cities. This new urban layout structure may be interspersed with forests, farmland and pastures between groups, so that the city and nature can be closely combined. This can greatly improve the quality of urban environment.