Map the green space

George Wu (1999) cho rằng không gian xanh ám chỉ những khu đất được bao phủ bởi thảm thực vật tự nhiên hoặc nhân tạo trong khu vực xây dựng và các khu vực quy hoạch. Bayram Cemil Bilgili and Ercan Gökyer (2012) đã định nghĩa không gian xanh từ một gốc độ khác, có tính đến các tác động của con người vào tự nhiên, Không gian xanh được định nghĩa là những khu vực đô thị nơi xảy ra sự chuyển đổi các hệ sinh thái tự nhiên hoặc bán tự nhiên thành không gian đô thị dưới các hoạt động của con người. Từ gốc độ quy hoạch cảnh quan và thiết kế đô thị, Ling Zhang (2001) đã định nghĩa không gian xanh gần như là tất cả các khu vực trong thành phố và các khu vực xung quanh nó, cho phép mọi người hòa mình vào với thiên nhiên.

Landscape and Urban Planning 998 (2003) 1–22 Comprehensive greenspace planning based on landscape ecology principles in compact Nanjing city, China C.Y Jim a,∗ , Sophia S Chen b a b Department of Geography, University of Hong Kong, Pokfulam Road, Hong Kong, China Institute of Geography and Limnology, Chinese Academy of Sciences, Beijing East Road, Nanjing, China Received 12 July 2002; received in revised form 30 October 2002; accepted November 2002 Abstract Urban greenspaces are universally valued as amenity-recreation venues, wildlife refuges and essential livable-city ingredients Western strategies of urban greenspace provision are difficult to implement or retrofit in most Asian cities, commonly constrained by a high-density compact form With recent rapid urbanization and associated brown and green field developments, ample opportunities arise to overhaul greenspace standards and patterns The case study of the ancient city of Nanjing in China permits planning for an integrated greenspace network, aiming at flexibility for future urban expansion, green field acquisition, recreational functions, wildlife habitats and environmental benefits It consists of green wedges, greenways and green extensions that incorporate urban green areas at three landscape scales At the metropolis scale, through normative and substantive analyses of urban form and urban expansion, and assessment of suburban uplands, five green wedges are demarcated to generate a star urban form The green wedges link the extensive countryside to the central city, and define elongated finger-like spaces between them for urban expansion to avoid conflicts with green fields At the city scale, three major greenways, including city-wall circular greenway, Inner-Qinhuai River greenway, and canopy-road greenway, are designed as a permeating framework to guide new greenspace location, configuration and continuity, and to link existing parks These greenways are equipped with a comprehensive trail system to foster pedestrian and cycling movements that are preferred by the public and the government At the neighborhood scale, a greenspace organization, consisting of residential public open spaces, shaded sidewalks and riparian strips, conforms to the network geometry As well-connected entities, these small proximate enclaves provide opportunities for residents to have day-to-day contact with nature They also serve to resist undue urban influences and intrusions Overall, the three-tiered greenspace system provides an alternative mode for urban development to the conventional transport-dominated one, to usher substantial improvement in landscape-environmental quality and to augment the sustainable-city notion © 2003 Elsevier Science B.V All rights reserved Keywords: Greenspace; Greenway; Green network; Compact city; Landscape ecology; Planning; Nanjing; China Introduction ∗ Corresponding author Tel.: +852-2859-2835; fax: +852-2559-8994 E-mail address: hragjcy@hkucc.hku.hk (C.Y Jim) 0169-2046/03/$20.00 © 2003 Elsevier Science B.V All rights reserved doi:10.1016/S0169-2046(02)00244-X Greenspaces in cities exist mainly as semi-natural areas, managed parks and gardens, supplemented by scattered vegetated pockets associated with roads and incidental locations Embodying the garden city ideal advocated by Ebenezer Howard (1898) and the large C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 urban park idea expounded by Frederick Law Olmsted in the US (Wilson, 1989), public greenspaces have been increasingly designated in cities since the 1880s to counteract environmental impacts of urban expansion and intensification Plants, notably trees, usher a wide range of environmental benefits and functions, and urban greenspaces often accommodate varied assemblages of flora and small animals, providing readily accessible sites with natural ingredients or surrogates of nature for the enjoyment of inhabitants who are otherwise detached from nature The compact city has been suggested as a sustainable urban form to contain the impacts of urbanization on remnant natural areas (Beatley, 2000) Engulfing and fragmenting natural areas especially in the peri-urban countryside are to be minimized (Swenson and Franklin, 2000) The high-density development mode, however, often lacks greenspaces (Jim, 2002a) Similar to compact European cities, most Chinese cities are intensively developed with a tight plan Chinese planners have attempted to conserve and create city greenspaces in response to rapid urbanization since the 1980s Most cities have augmented greening programs since the 1990s, resulting in both congruence and conflicts between greenspace establishment and urban development Landscape ecology offers insights on optimization of space use vis-à-vis environmental conservation and improvement (Forman and Godron, 1986; Dramstad et al., 1996) It furnishes principles of greenspace organization related to the theory of island biogeography (MacArthur and Wilson, 1967) In essence, large patch, high connectivity and propinquity foster species diversity and ecosystem functions Such spatial concepts have been widely adopted in urban landscape architecture and landscape planning projects (Goldstein et al., 1982/1983) Various studies have proposed a landscape mosaic composed of linear elements to augment the connectedness of the otherwise isolated and often small urban habitats (Ahern, 1991; Walmsley, 1995; Mazzotti and Morgenstern, 1997; Quayle and Lieck, 1997; Flores et al., 1998; Schrijnen, 2000) In some American cities, greenways have been designed as corridors for wildlife and human movement (Little, 1990; Flink and Searns, 1993) Similarly, linkages for parks and community gardens at the neighborhood scale have been realized in Singapore, Canada and the United States (Francis et al., 1984; McCormick, 1992; Pedersen, 1999; Meeus, 2000; Foo, 2001) Scant research has been conducted on comprehensive greenspace planning in the context of high-density development (Jim, 2002b) Introducing greenspaces with connectivity into a heavily built-up milieu demands detailed studies and dedicated solutions Nanjing, an ancient city in east China, is selected as a study case for its generous tree cover, potential greenway sites within the urban fabric, and extensive mature forests at its fringe This research attempts to answer the following questions (1) How to protect urban fringe greenspaces from encroachment? (2) How to effect the penetration of greenspaces into the high-density inner-city? (3) How to establish adequate home-juxtaposed greenspaces for residents? (4) How to establish an actionable greenspace plan at the metropolis (built-up area and the near suburb), city (built-up area) and neighborhood scales? (5) How to devise an acceptable urban development within this green framework? Study area Nanjing is located at 32◦ 03 N in the north-subtropical climatic zone with well-defined seasons and a mean annual temperature of 15 ◦ C The maximum summer temperature exceeds 40 ◦ C, dropping to a minimum of −14 ◦ C in winter Rainfall averages 1033 mm per annum, occurring mainly in summer Typhoon may strike once or twice annually mostly in August, but wind damage on trees or buildings is less serious compared with coastal cities The zonal natural vegetation is a mixed broadleaf evergreen and deciduous forest The authors’ sampling survey of urban trees in 1998 yielded an evergreen:deciduous trees ratio of about 1:3, and the top three species were Platanus acerifolia, Juniperus chinensis and Ligustrum lucidum The city’s varied topography comprises mountains, low hills, low terraces, plains and rivers (Fig 1) The Yangtze River runs in the northwest, and the Qinhui River runs southeast to the northwest through the city to join Yangtze Fringe mountains surround the city, extending as low hills into built-up areas The Purple Mountain at its eastern fringe, rising to 448 m, has the largest green cover of 29.7 km2 of semi-natural forest C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 Fig Major landform features, main roads and old city-wall of Nanjing Nanjing has nearly 2000 years of development history The old core lies in the south near the Inner-Qinhuai River The Capital Plan implemented in 1928 extended the city significantly to the north, but expansion until the 1950s was confined mainly within the 14th-century Ming Dynasty city-wall Thereafter, large factories were established along the Yangtze River They triggered additional population and urban growth outside the wall towards north and south The Reform and Open Policy initiated in the 1980s brought another phase of rapid urbanization and further encroachment into the surrounding countryside The built-up areas increased 60% from 1986 to 2000, covering 194 km2 and accommodating 2.47 million population with a density of 12,700 persons/km2 (State Statistics Bureau, 1987–2001) In the last years, areas outside the east and west sides of the city-wall witnessed two large new residential precincts The Nanjing Planning Bureau has proposed new towns around the main city in its 1991–2010 Masterplan (Nanjing Planning Bureau, 1998; Fig 2; hereinafter referred to as the Masterplan) Study of green wedges at the metropolis scale 3.1 Ideal city configuration in relation to greenspace Howard (1898) pioneered consideration of the green dimension of urban forms, besides traditional functions such as employment, transport and housing His garden city concept included a compact group of cities with intervening green areas A rapid transit system was to connect the ancillary cities with the central one The notion of greenspaces encircling a central city has been translated into the planning instrument of green belt to confine unbridled urban sprawl in England (Toft, 1995) and other places It serves as a buffer between city and countryside, limiting urban extension and safeguarding farmlands from encroachment, whilst also providing open spaces with easy access It is, however, often difficult to sequester future city development by a girdle The somewhat rigid green belt has been widely breached by leap-frog growth C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 Fig The official Masterplan of Nanjing city for 1991–2010 (Nanjing Planning Bureau, 1998) C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 (Frey, 2000) and sprawling into productive farmland beyond it The idea of sustainable development, introduced in the 1980s, ushered the adoption of ecological concepts in urban planning Landscape ecology seeks to explain landscape structure based on three fundamental spatial concepts, namely matrix, patch and corridor, with reference to flows of energy, materials and organisms The matrix is the most extensive and dominating landscape element At the regional scale, the ideal landscape configuration is city patches encompassed within a greenspace matrix with diversified habitats to foster biodiversity The greenspace–city interface should preferably be convoluted and curvilinear (Fig 3) to facilitate nature’s penetration into urban areas (Forman and Godron, 1986) The resulting green wedges serve as natural corridors linking the inner-city with the extensive countryside matrix A city patch should have a high perimeter-to-area ratio to maximize exchanges with the matrix environs The edge effect can enhance habitat and species diversity and population abundance An elongated patch with a longer border allows more interactions with the surrounding matrix Thus linear greenspaces should be incorporated into urban areas to maximize edge effects, such as line, ring, or star with radials Fig A star-shaped configuration of the city–countryside interface with a curvilinear and convoluted outline that provides a long contact boundary and generous penetration of nature into urban areas (Blumenfeld, 1949; Moughtin, 1996) An ideal city form could have one dominant center with several radial fingers The compact center facilitates efficient land-use, and the fingers support flexible urban growth based on public transport The development along the length of concentric rings, which interrupt green wedges, is not encouraged 3.2 Analysis of urban form and expansion Three archetypal urban forms defined by geometric shapes can be identified: linear, centralized and gridiron cities The linear form has a major transport axis linking key facilities Linear cities could grow spontaneously in two directions along the axis The highly centralized city is dominated by a central public space, with extensions along radial roads to form urban fingers connected by ring roads This geometry leads to a highly compact center, whereas away from the center low-density development is possible with penetration by green wedges The gridiron form is common in American and Asian cities The chessboard layout adopted since the Western Zhou Dynasty (1028-771 b.c.) has a lingering influence on city form in China (Wu, 1993) Gridiron cities can comprise several rather autonomous parts Expansion occurs by adding parallel roads to the existing lattice to maintain a regular growth pattern If developed to a high-density, it tends to exclude greenspaces If developed at a low-density, it caters mainly to private traffic and is ineffectual in fulfilling compact city objectives (Moughtin, 1996) The real-world city form is often a hybrid of the basic types, echoing imprints of physical and cultural influences through time For Nanjing, the inner-city core enclosed within the Ming Dynasty (1368–1644) city-wall has a gridiron system of four north–south main roads intersecting four east–west ones Outside the wall, the regularity is interrupted by the surrounding hills Several radial urban fingers with major transport lines have penetrated between the uplands Thus Nanjing blends three basic urban forms: gridiron of the compact core, linear of urban fingers extending radially from the core, and complex centralized form as aggregate of both elements The uplands between the fingers constitute green wedges, suggesting that a model of green wedges associated with urban fingers is an appropriate green development pattern 6 C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 Study of green network at the city scale 4.2 Physical landform assessment 4.1 Objectives and approach In a mature compact city, usually few notable landform features are spared from development, such as rivers and hills which are ideal for greenway use Nanjing incorporates diversified landform features in the city A series of hills (Fugui, Jiuhua, Beijige, and Gulou, Wutai, Qingliang) stretch from east to west, forming the watershed between Jinchuan River valley and Qinhuai River valley in the urban area; Gupin and Shizi Hills run from south to north inside and along the city-wall On these uplands, parks of 3–30 have been built, conserving semi-natural to natural areas within the city Two lakes and two rivers define the drainage system Xuanwu Lake (3.7 km2 ) west of Purple Mountain and Muchou Lake (0.37 km2 ) west of the city-wall have been developed into municipal parks Qinhuai River runs through the city from southeast to northwest to join the Yangtze River It bifurcates into a cluster of tributaries that spread in the south city The main branch that runs along city-wall perimeter into Yangtze River is labeled Outer-Qinhuai In ancient times it served as the city’s major transport route (Nanjing Freeway Administration Department, 1988) At present only a small section near Yangtze is navigated (Nanjing Gazetteer Editorial Office, 1994a) The other stream, named Inner-Qinhuai, bifurcates into two tributaries after flowing through the city-wall at the Tongji Gate In the north city, Jinchuan River runs through the city from the south to the north into Yangtze River, with a canal connecting to Xuanwu Lake In Nanjing’s long history, many canals were constructed to connect the districts with water traffic The notable ones include Qingxi, Yundu and Chaogou built in a.d 240 (Nanjing Freeway Administration Department, 1988) Also, moats were built at different locations to defend the city In the last 1800 years, most canals and moats were clogged or filled, leaving intermittent sections They have since lost their transport and military functions, but remain as stormwater and sewage channels As most sections juxtapose present roads, some water-edges have been developed into roadside gardens (such as Zhenzhu Garden along North Taiping Road) If the water quality could be improved, the drainage system could allow linear An ideal greenspace layout calls for a green network embedded within urban areas (Forman and Godron, 1986) It separates urban areas, enhances landscape impacts, and facilitates environmental and ecological functions The green network is materialized as a comprehensive greenway system which furnishes an alternative municipal green infrastructure Endowed with natural amenities and a path, a greenway serves multiple functions, such as protecting and enhancing natural heritage and cultural relics, and providing open space for passive recreation (Flink and Searns, 1993) It is widely embraced by municipal governments, planners, ecologists and the public The greenway form could be flexibly molded to connect parks, nature reserves, cultural features or historic relics, and often follows natural landform alignment such as riverbank, valley and ridgeline Each greenway could be uniquely designed to match local conditions, rendering the approach quite amenable for mature cities It should be stressed that a chlorophyll continuum alone does not imply a habitat connection For some sites, ecological attributes need to be modified or created for habitat optimization to enhance the natural functions of the greenways The network configuration furnishes a practical framework for greenspace planning in Chinese cities Firstly, its linearity suits the compact urban form In China, urban land is limited and congested, at merely 70–100 m2 per capita, with scant greenspaces The greenway network could use derelict or unused lands such as water-edges and slopes to minimize conflicts with development Secondly, new greenspaces can be planned at greenway intersections and strategic locations to connect isolated green pockets The linked and integrated greenway system can act as a catalyst to preserve existing greenspaces and generate new ones It reduces some common conflicts in Chinese cities, such as road widening versus street trees, and housing development versus green fields The connections between the green enclaves can stem the tendency to eliminate small and isolated greenspaces, which are the most common form of greenspaces in Chinese cities Thirdly, the network can be designed to improve accessibility of greenspaces with footpaths, footbridges and underpasses C.Y Jim, S.S Chen / Landscape and Urban Planning 998 (2003) 1–22 greenspaces to penetrate into the congested urban fabric Table Major greenspace categories of Nanjinga Area (ha) 4.3 Urban context analysis Park South Nanjing is more densely-populated than the north, accommodating the original urban core with dense packing of buildings separated by narrow streets and scant open spaces The three southern districts, Qinhuai, Jianye and Baixia, have a built-up population density reaching about 30,000 persons/km2 The south city, especially the old downtown along Inner-Qinhuai River, urgently needs greenspaces to relieve the congestion The north city has more institutional lands such as government agencies and colleges The residential neighborhoods there, mostly developed after 1949 in the closed-yard style (Wu, 1993), have a lower built-up density with greenspaces interspersed between buildings (Nanjing Gazetteer Editorial Office, 1994b) Urban planning could guide future land-use and population distribution with influence on greenway location The Masterplan has earmarked farmlands between Yangtze and Outer-Qinhuai Rivers for a new residential district of over 100,000 inhabitants (Nanjing Planning Bureau, 1998) A greenway system could extend into this area to forestall excessive development and to preserve adequate recreational land The Masterplan includes redevelopment projects, such as improving the old city core and rebuilding poor-quality housing in the old downtown These schemes bring ample opportunities for greenways through town-plan re-structuring The relevant national ordinance stipulates 25% of urban land for greening, furnishing a statutory basis for a comprehensive greenway system Upgrading the urban transport system could also incorporate greenways In Nanjing’s old city, the gridiron urban form has bequeathed a lattice transport system Greenways can be established along selected roads equipped with widened amenity strips and roadside trees The criss-crossing primary roads, however, break greenway continuity which needs footbridges and underpasses for uninterrupted pedestrian-movement Such links could be planned comprehensively in conjunction with the underground railway system, which is under construction, to maximize accessibility and connectivity of the greenways Number Green cover (%) Notable features 100–3000 1–100 30 70–99 55–97 [...]... fingers Urban fingers, in contrast to green wedges, originate from the central city and extend into the countryside Four major urban fingers can be planned for Nanjing, stretching respectively to the northeast, the east, the southeast and the southwest (Fig 8) They are shaped by sympathetic accommodation of existing greenspace layout, filling the space left by the planned green wedges to avoid land-use conflicts... parks This green framework departs from the conventional passive approach in allocating greenspaces It could coordinate the provision of a greenspace network among neighborhoods that are laid out as coordinated clusters of high-rise buildings More importantly, it can curtail the expansion of the anachronistic chessboard urban form from the old city After defining the greenspace boundaries, the plan can... For the old downtown community, these greenspaces could enhance the quality of life, the health of citizens and natural areas, and residents’ pride (Shafer et al., 2000) Moreover, the improved community ambience could attract new businesses and developments which are earnestly sought by the government 7.3.4 Greenway extensions The above three greenways constitute the primary framework of Nanjing’s greenway... between the park and the adjacent built-up areas A new park could be planned based on the existing Zhonghua Gate Park at the tip of the v-shaped river course It could serve as a node linking the riverbank greenway to the city-wall greenway, to present an alternative route for walking through the commercial center The park could be abundantly filled with trees to create an urban forest to envelop the ancient... which abundant greenspaces and outstanding trees have been identified in the 1998 field survey The existing large roadside trees can shade the pedestrian and cycling paths In adjacent institutional grounds, see-through fences could replace concrete walls to improve path-side landscape Moreover, the enclosed green enclaves could be open to the public on holidays Along the greenway, new greenspaces are proposed... building-density neighborhoods, the garden block strategy (Dekey, 1997) could be adopted Several contiguous blocks of greenspaces could serve as a green corridor with residential blocks at two sides Buildings can occupy half of a block’s width, leaving the remainder for greening (Fig 5) Such linear garden blocks function as residential greenspaces as well as green connectors for the overall green network Where... Unfortunately, like other roadside greeneries, these magnificent trees could not escape losses under urbanization pressure The four rows in the medians were felled to widen roads in 1994 The remnants are threatened with further destruction from increasing traffic demands and conflicts between trees and adjacent buildings The greenway plan aims to restore the landscape quality of the degraded parkway... Six green corridors that link the current and planned clustered development areas at the city scale are proposed for Nanjing wedges of farmland, in the southeast and southwest, can protect cultivated lands and break up the otherwise monotonously contiguous urban developments Mufu Hill in the north is an elongated belt beside the Yangtze River It is almost engulfed by the urban fabric except for the. .. corridor to the extensive countryside The Hill is an important scenic area of Nanjing and was highly appreciated by ancient poets About half of its forest canopy has been destroyed since the 1970s due to quarrying The government intends to restore the damaged forest to promote tourism Connectivity with the greenspace matrix should be conserved or rebuilt Yuhua Hill in the south provides extensive greenspaces... In selected localities of the buffer zone, some low-density dwellings could be allowed after careful planning scrutiny Secondly, the connectivity of green wedges to the countryside matrix should be ascertained Urban extension should be confined to the fingers between the wedges, and development along ring roads that cut through the green wedges must not occur The tips of the green wedges could be given ... development versus green fields The connections between the green enclaves can stem the tendency to eliminate small and isolated greenspaces, which are the most common form of greenspaces in Chinese... Moreover, the enclosed green enclaves could be open to the public on holidays Along the greenway, new greenspaces are proposed as rest gardens and connectors In the north 19 city, a greenway based... originate from the central city and extend into the countryside Four major urban fingers can be planned for Nanjing, stretching respectively to the northeast, the east, the southeast and the southwest