Heterogeneity of suburban landscape and urban ecological construction?

Because modern cities, especially megacities, all include their surrounding suburbs, overall planning of urban areas and suburbs is the main content of urban ecological construction. According to the principles and methods of landscape ecology, the spatial structure of suburban landscape should be rationally planned, so that the number and spatial distribution of landscape elements such as corridors, patches and substrates are reasonable, and the information flow, logistics and energy flow between urban areas, suburbs and suburbs can be smoothly circulated. It has certain aesthetic value to make the suburban landscape conform to the ecological principle. Introducing natural elements into urban planning and construction makes urban landscape diversified. This is the goal of urban ecological construction at home and abroad. For example, in view of Beijing's ecological environment construction, relevant experts put forward the requirements of "2 1 Century Beijing Green Ecological Construction": "Protect the primary ecosystem and vigorously promote the restoration and reconstruction of the secondary ecosystem; Let more secondary forests become the original deciduous broad-leaved forest; Protected areas, scenic spots and forest parks are classified according to the World Conservation Union, and the classification system is incorporated into the unified leadership protection network. According to the ecosystem theory, Beijing should establish three green ecological circles. Namely, mountain water conservation ecosystem, windbreak and sand fixation-agriculture, forestry and fruit production ecosystem, urban air conditioning, pollution prevention and beautification ecosystem. Obviously, the goal of Beijing's ecological construction planning depends on the principle of landscape ecology to implement and complete. According to the principle of landscape heterogeneity, it is a meaningful practice to establish a well-developed suburban landscape pattern, improve diversity, maintain heterogeneity and promote urban sustainable development. This paper makes a preliminary discussion on this issue. 1 heterogeneity and its scale The city is a landscape that has been completely transformed by human beings. In the process of expanding urbanization, the urban areas and suburbs of modern cities have become a whole. It is the goal of human beings to have a reasonable landscape structure and a smooth urban landscape. The highly heterogeneous landscape is the basis for the good development of suburbs. Japanese scholar Sun Lang Maruyama put forward the theory of heterogeneity from the perspective of biological cybernetics. The theory holds that increasing heterogeneity, negative entropy and negative feedback of information can explain the self-organization principle in the process of biological development. The longest living creature in nature is not the strongest creature, but the creature that can co-evolve with other creatures and the environment. Heterogeneity is the fundamental attribute of landscape, or the essence of landscape is heterogeneity, which is absolute and homogeneity is relative. Landscape heterogeneity first comes from the original differences between systems and system elements, such as time differences (evolutionary degree), spatial differences (evolutionary niche and niche), poor quality, poor quantity, poor morphological structure, poor function and poor information, which are collectively called system differences. Secondly, heterogeneity also comes from the imbalance between real movement and external interference, especially the interference of human wrong ecological behavior, which mainly comes from three aspects: natural interference, human activities and endogenous succession of vegetation or dynamic changes of population. The structure, function, nature and position of landscape ecosystem mainly depend on its heterogeneity. As far as landscape ecology is concerned, we should understand heterogeneity from the following aspects: ① Two kinds of heterogeneity in time and space. Generally speaking, heterogeneity refers to spatial heterogeneity, that is, spatial distribution heterogeneity. In fact, the sections and units of time are also different from each other. Therefore, there are two kinds of heterogeneity: spatial heterogeneity and temporal heterogeneity. ② Multidimensional spatial heterogeneity. Usually, spatial heterogeneity refers to two-dimensional plane heterogeneity. In addition, there are vertical spatial heterogeneity and three-dimensional spatial heterogeneity composed of them. ③ Spatial-temporal coupling heterogeneity. In modern science, simultaneous spatio-temporal coupling represents the unified motion of matter in time and space, and can also be used to represent the unified four-dimensional motion of two kinds of heterogeneity in time and space. ④ Heterogeneity of edge effect. Spatial heterogeneity often has the nature of edge effect. Spatial heterogeneity is the research content of suburban landscape heterogeneity at present. At the landscape level, spatial heterogeneity has three components: spatial composition (namely, ecosystem type, quantity and area ratio); Spatial type (i.e. the spatial distribution of each ecosystem, patch size, landscape contrast and landscape connectivity); Spatial correlation (that is, the spatial correlation degree, spatial gradient and trend degree of each ecosystem, etc. ). Scale is the scale effect, and spatial scale usually refers to the spatial resolution of the object or process observed or studied. From the ecological point of view, spatial scale refers to the size of the study area. The larger the scale, the larger the research area, and the heterogeneity is related to the scale. For example, a landscape unit is heterogeneous on a small scale, but it becomes homogeneous on a large scale. Correct selection of scale is the guarantee for scientific research on landscape and accurate and objective conclusion. Due to the progress of aviation, aerospace and remote sensing, the research scale has increased, but not arbitrarily. Generally, the research scope of landscape ecology is defined in the mesoscale area of several kilometers to several hundred kilometers. 2 Heterogeneity of suburban landscape From the development trend of modern cities, the planning of satellite cities and suburbs of cities is unified with that of urban areas. Heterogeneity is the fundamental attribute of landscape, and so is suburban landscape. When the scale of traditional urban landscape research is enlarged, the suburbs are included, forming the so-called suburban landscape, that is, an ecosystem complex with a certain scale that shows the respective characteristics of cities and suburbs and their mutual blending. In the process of urbanization, suburban landscape is mainly disturbed by human beings. From the perspective of spatial pattern, suburban landscape includes urban areas and suburban rural areas. Are mosaics of heterogeneous units. In suburban landscape, landscape elements such as patches, corridors and substrates can be divided. Blocks, buildings, roads, roads between suburbs, shelterbelts, farmland, canals, etc. Everything in the city is formed by human activities, while rivers and some woodlands in suburbs or urban areas are formed by natural reasons. These different landscape elements form heterogeneous suburban landscape in a certain combination way. Artificial system and natural system are two kinds of ecosystems that constitute suburban landscape, of which artificial system is the main ecosystem. The heterogeneity of suburban landscape is firstly manifested as the spatial heterogeneity of two-dimensional plane. Streets, parks, water surfaces, buildings, highways, woodlands, farmland and other properties are different. Parks and green spaces in cities are mostly planted artificially, and patches with different shapes and functions are formed in green spaces due to differences in plant species and distribution areas. Roads and communication networks spread all over blocks and buildings, increasing the fragmentation of urban landscape. Roads, railways and electric wires extending in all directions between suburbs make energy flow, logistics and information flow smooth, and landscape heterogeneity increases. All kinds of artificial buildings, including roads, cover the surface of the city, which is very different from the thermal and hydrological conditions of the underlying surface such as bare open space, green space or farmland. Radiating outward from the city center, the population density decreases from large to small, the traffic volume, pollutants and suspended solids decrease, and the interference is weakened. Therefore, different landscape functional areas can be divided. Such as commercial and residential areas, cultural areas, industrial areas and so on. In the suburbs, it can also be divided into township enterprise areas and agricultural and sideline base areas. The difference of different functional effects reflects the heterogeneity of suburban landscape. As for any element of suburban landscape, there is heterogeneity within it, such as the combination of different functional plots such as water surface, lawn, trees, flowers, hardened ground and amusement facilities in the park. Street trees, non-motor vehicle lanes, motor vehicle lanes, etc. A road corridor is formed, and a wide main road has a separation belt composed of hedges and lawns. They form a corridor to realize the functions of logistics, energy flow and information flow. The suburban shelterbelt not only protects farmland, but also afforests and beautifies urban areas. The heterogeneity of suburban landscape also shows spatial heterogeneity in vertical direction. For example, the air composition in urban areas changes with the height, and the concentration of dust and suspended matter in the air near the ground is higher than that in the upper air. In addition, the height of buildings in urban areas is uneven and the vertical characteristics are not consistent. Spatial heterogeneity also leads to temporal heterogeneity, which belongs to spatio-temporal coupling heterogeneity. Uneven spatial distribution of landscape elements is heterogeneity. Time heterogeneity is dynamic change, and heterogeneity is spatial pattern. The more types of landscape elements, the greater the heterogeneity. There are many indicators to measure heterogeneity, and the following indicators can also be used to measure the heterogeneity of suburban landscape: diversity index, dominance, uniformity, minimum distance index, connectivity and so on. Among them, diversity index and evenness index are the most widely used in the study of urban landscape heterogeneity. 3 the significance of the heterogeneity of suburban landscape in urban construction The heterogeneity of suburban landscape leads to the complexity and diversity of suburban landscape, which is conducive to its stable development. The urban landscape includes the central city and satellite towns, which is characterized by non-agricultural activities such as industry and service industry. Population, material information, production, life, entertainment, municipal administration, transportation and pollution are all concentrated in towns dominated by man-made things, which belong to cultural landscapes that have greatly changed the ecological characteristics of natural landscapes. Rural landscape, including farmland, plantations, plantations, farms, pastures and fish ponds, is characterized by agricultural activities and is a combination of natural and artificial structures established by human beings on the basis of natural structures. Suburban landscape is the combination and unity of urban landscape and rural landscape. Maintaining landscape heterogeneity is the key to promote urban construction and development. For urban landscape, we should first protect the environmentally sensitive areas in urban landscape, which are often easily affected by human activities. Environmental sensitive areas usually include ecological sensitive areas, cultural sensitive areas, resource production sensitive areas and natural disaster sensitive areas. Secondly, the existing landscape structure should be improved. Such as urban transformation, residential district construction, traffic trunk line construction and so on. These are the foundations for giving full play to the functions of cities. Only by ensuring the rationality and perfection of landscape structure can we realize the efficient display of landscape functions. In urban construction, building patches and road corridors are generally the main ones, while green patches and street tree corridors are few, and the proportion is seriously unbalanced. In order to improve the urban landscape structure, green corridors and green patches should be added and rationally distributed in the block. The construction of urban green space requires not only a large number, but also uniform distribution of large and small patches and reasonable configuration. From the perspective of landscape ecology, large vegetation patches have many important ecological functions and are beneficial to the landscape. Small vegetation patches can be used as a transit point for species migration, and protecting and planning scattered rare species or niches is conducive to improving landscape heterogeneity. Therefore, large and small plaques should exist in balance and cannot replace each other. In urban landscape ecological planning, we should adhere to the principle of diversity: supplement natural elements and coordinate landscape structure; Increase the types of greening; There are various forms of corridors and patches. This can keep the diversity of urban landscape. Shelterbelt, farmland and woodland in the suburbs are also rationally distributed, so that natural and artificial green ecosystems can play a role, with diversification and diversity as the pursuit goal. For example, Beijing's urban construction, in addition to the local transformation of the existing urban structure, aims to improve heterogeneity from the perspective of landscape. According to experts' suggestions, three green ecological circles should be established from suburban counties to urban areas to form a stable protective net. The first circle is the ecological circle of mountain water conservation, mainly in mountainous areas, accounting for 62% of the city. It includes four belts: low mountain fruit forest belt, Zhongshan water conservation forest belt, Zhongshan upper meadow belt and mountain basin reservoir. The management measures of the circle are natural forest protection, comprehensive management of small watersheds, establishment of nature reserves, construction of forest parks and development of eco-tourism. The second circle is the windbreak and sand fixation ecological circle-the agricultural and forestry fruit production belt. Mainly refers to the suburban plain area, accounting for about 32% of the city's area, including windbreak belt, sand fruit belt and basic farmland belt. The management measures are ecological agriculture, water-saving agriculture and compound agriculture. The third circle is the urban air conditioning, pollution prevention and beautification ecological circle, that is, the urban isolation area, with a total area of about 2.4 million hm ㎡. The management measures include: the construction of urban isolated forests, the construction of large-scale green spaces and parks. According to the above requirements, the overall planning of Beijing urban construction should also be based on the principle of landscape heterogeneity. According to Beijing Master Plan, the urban layout of "dispersed groups" in urban areas is planned to be separated by greening between the large group in the center of the city and ten marginal groups. The total area of the planned green isolation zone is 2.4 million hm ㎡. By 2003, the green area will be100000 square meters, and suburban green industrial parks and sports parks will be built1000, and greening will be the main task gradually. In view of the lack of urban design connection between the overall urban planning and individual planning, comprehensive greening planning should be carried out for factories, schools, government agencies, commercial areas and development zones, especially residential areas in the city. Developing three-dimensional greening is a practical way to solve the lack of green trees in the central area and should be popularized in urban areas. In the design and construction of urban green space landscape, the exquisite landscape design methods that used to pursue neatness and meticulous decoration were reduced or abandoned, and replaced by organic landscape design methods with overall aesthetic feeling. For example, in the square, cement laying should be reduced as much as possible, the green area should be expanded as much as possible, and potted flowers should be put in the ground for the holidays. The greening of the development zone should be based on the greening design and level to determine the valuation of property assets and develop by stages. It is worth noting that in urban construction, lawn construction should be moderate. Lawn not only has the ecological functions of absorbing carbon and oxygen, storing water and preventing surface runoff, but also has special aesthetic and landscape effects. In order to connect with the international metropolis, a large area of lawn is necessary. However, according to the principle of landscape heterogeneity, the ecological function of arbor and shrub can not be replaced by other plant materials, and it is not advisable to replace trees with lawn. As a whole, the beautification and greening of urban and suburban areas of modern cities are integrated with each other. In the three green ecological circles mentioned above, it is necessary to actively develop urban forestry, and "the forest enters the city and the garden goes to the countryside" is the development direction. The main functions of the capital forest are environmental function, scenic recreation function and economic production function. Forestry should serve urban functions. On the premise of giving full play to environmental functions, we will build and improve scenic recreational forests in key areas, enrich the composition of tree species, improve biodiversity and landscape diversity, and improve the aesthetic and ornamental functions of scenic forests. In urban areas, it is especially necessary to increase flowers in summer and green in winter, and generally improve vegetation coverage. In a word, maintaining the heterogeneity of suburban landscape is of great significance to urban construction. In urban construction, we should pay attention to the following points when applying the principle of heterogeneity: ① urban construction must be combined with ecological planning; ② Green landscape elements should be protected and supplemented in urban construction and transformation; ③ The layout of suburban landscape pattern is reasonable, and the number of green ecosystems is increasing; ④ Urban beautification, greening and suburban protection are combined, with diverse species and reasonable collocation. For Beijing's urban construction, urban forestry plays an obvious role in urban planning. There are three main measures: First, build an isolation belt between the planned urban area and the suburbs, control urban development within the isolation belt, and ensure the formation of Beijing's decentralized group layout. The second is to build broad forest belts on both sides of the main road to form a green corridor, which is not only conducive to the increase and maintenance of heterogeneity, but also has the role of protection and beautification. In recent years, more than 5 million trees have been planted on both sides of the trunk highway with a total length of 500 kilometers, which not only beautifies the environment, but also standardizes the overall layout, prevents indiscriminate reclamation and occupation, and maintains the integrity of urban landscape planning. The third is to build a forest around the city in suburban counties, which requires "seeing the forest first, then seeing the city". It not only limits the blind development of suburban counties, but also maintains the unified coordination of suburban landscapes. The scale of urban forestry requires a forest network that combines point, line and area, and the green coverage rate is large. The layout should be considered from the perspective of landscape, combining production, viewing and tourism. However, urban greening pays more attention to the specific microenvironment, emphasizing beautification and refinement. The indoor and outdoor individual greening area is limited, and the plant configuration is diverse, artificial landscaping and appreciation are emphasized. From the scale of landscape research, suburban forestry is a unified whole, including urban and suburban forestry systems. Generally, it is divided into three levels: ① urban greening, beautification, fragrance and gardening. The combination of arbor, shrub and grass constitutes the urban greening system. (2) Suburban forest belt (forest). Including suburban orchards, suburban parks, shelterbelts, etc. It has the functions of production and leisure, assisting and regulating the urban environment. ③ Outer suburb forest belt (piece). Including scenic forests, forest parks, various shelterbelts and other forest types, it has a relatively complete forest system and comprehensive forest functions, and can be used for forest tourism, recuperation, vacation, camping and exploration. Suburban forestry stratification is not necessarily obvious. Due to the different geographical location, transportation and economic conditions, sometimes it presents a seamless belt system, and sometimes it is a landscape that alternates between layers and layers. Therefore, it is of great significance to use the principle of landscape heterogeneity to guide urban construction and urban ecological environment construction.

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