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.

Comprehensive greenspace planning based on landscape

ecology principles in compact Nanjing city, China

C.Y Jima,∗, Sophia S Chenb

aDepartment of Geography, University of Hong Kong, Pokfulam Road, Hong Kong, China

bInstitute 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 3 November 2002

Abstract

Urban greenspaces are universally valued as amenity-recreation venues, wildlife refuges and essential livable-city ents Western strategies of urban greenspace provision are difficult to implement or retrofit in most Asian cities, commonlyconstrained by a high-density compact form With recent rapid urbanization and associated brown and green field develop-ments, ample opportunities arise to overhaul greenspace standards and patterns The case study of the ancient city of Nanjing

ingredi-in Chingredi-ina permits planningredi-ing for an ingredi-integrated greenspace network, aimingredi-ing at flexibility for future urban expansion, green fieldacquisition, recreational functions, wildlife habitats and environmental benefits It consists of green wedges, greenways andgreen extensions that incorporate urban green areas at three landscape scales At the metropolis scale, through normativeand substantive analyses of urban form and urban expansion, and assessment of suburban uplands, five green wedges aredemarcated to generate a star urban form The green wedges link the extensive countryside to the central city, and define elon-gated finger-like spaces between them for urban expansion to avoid conflicts with green fields At the city scale, three majorgreenways, 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 Thesegreenways 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 publicopen spaces, shaded sidewalks and riparian strips, conforms to the network geometry As well-connected entities, these smallproximate enclaves provide opportunities for residents to have day-to-day contact with nature They also serve to resist undueurban influences and intrusions Overall, the three-tiered greenspace system provides an alternative mode for urban develop-ment 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

∗Corresponding author Tel.:+852-2859-2835;

doi:10.1016/S0169-2046(02)00244-X

urban park idea expounded by Frederick Law

Olm-sted 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

func-tions, and urban greenspaces often accommodate

var-ied assemblages of flora and small animals, providing

readily accessible sites with natural ingredients or

sur-rogates of nature for the enjoyment of inhabitants who

are otherwise detached from nature

The compact city has been suggested as a

sustain-able urban form to contain the impacts of urbanization

on remnant natural areas (Beatley, 2000)

Engulf-ing and fragmentEngulf-ing 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

Chi-nese 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

congru-ence 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

biogeogra-phy (MacArthur and Wilson, 1967) In essence, large

patch, high connectivity and propinquity foster species

diversity and ecosystem functions Such spatial

con-cepts have been widely adopted in urban landscape

ar-chitecture and landscape planning projects (Goldstein

et al., 1982/1983) Various studies have proposed a

landscape mosaic composed of linear elements to

aug-ment 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

move-ment (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 prehensive greenspace planning in the context ofhigh-density development (Jim, 2002b) Introducinggreenspaces with connectivity into a heavily built-upmilieu demands detailed studies and dedicated so-lutions Nanjing, an ancient city in east China, isselected as a study case for its generous tree cover,potential greenway sites within the urban fabric, andextensive mature forests at its fringe This research at-tempts to answer the following questions (1) How toprotect urban fringe greenspaces from encroachment?(2) How to effect the penetration of greenspaces intothe high-density inner-city? (3) How to establish ade-quate home-juxtaposed greenspaces for residents? (4)How to establish an actionable greenspace plan at themetropolis (built-up area and the near suburb), city(built-up area) and neighborhood scales? (5) How todevise an acceptable urban development within thisgreen framework?

com-2 Study area

Nanjing is located at 32◦03N in the pical climatic zone with well-defined seasons and amean annual temperature of 15◦C The maximumsummer temperature exceeds 40◦C, dropping to aminimum of −14◦C in winter Rainfall averages

north-subtro-1033 mm per annum, occurring mainly in summer.Typhoon may strike once or twice annually mostly inAugust, but wind damage on trees or buildings is lessserious compared with coastal cities The zonal naturalvegetation is a mixed broadleaf evergreen and decidu-ous 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

ac-erifolia, Juniperus chinensis and Ligustrum lucidum.

The city’s varied topography comprises mountains,low hills, low terraces, plains and rivers (Fig 1) TheYangtze River runs in the northwest, and the QinhuiRiver 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 PurpleMountain at its eastern fringe, rising to 448 m, hasthe largest green cover of 29.7 km2 of semi-naturalforest

Fig 1 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

urbaniza-tion and further encroachment into the surrounding

countryside The built-up areas increased 60% from

1986 to 2000, covering 194 km2 and

accommodat-ing 2.47 million population with a density of 12,700

persons/km2 (State Statistics Bureau, 1987–2001) In

the last 5 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)

3 Study of green wedges at the metropolis scale

3.1 Ideal city configuration in relation

to greenspace

Howard (1898)pioneered consideration of the greendimension of urban forms, besides traditional func-tions such as employment, transport and housing Hisgarden city concept included a compact group of citieswith intervening green areas A rapid transit systemwas to connect the ancillary cities with the centralone The notion of greenspaces encircling a centralcity has been translated into the planning instrument

of green belt to confine unbridled urban sprawl in land (Toft, 1995) and other places It serves as a bufferbetween city and countryside, limiting urban exten-sion and safeguarding farmlands from encroachment,whilst also providing open spaces with easy access

Eng-It is, however, often difficult to sequester future citydevelopment by a girdle The somewhat rigid greenbelt has been widely breached by leap-frog growth

Fig 2 The official Masterplan of Nanjing city for 1991–2010 (Nanjing Planning Bureau, 1998).

(Frey, 2000) and sprawling into productive farmland

beyond it

The idea of sustainable development, introduced in

the 1980s, ushered the adoption of ecological

con-cepts in urban planning Landscape ecology seeks to

explain landscape structure based on three

fundamen-tal spatial concepts, namely matrix, patch and

corri-dor, with reference to flows of energy, materials and

organisms The matrix is the most extensive and

dom-inating landscape element At the regional scale, the

ideal landscape configuration is city patches

encom-passed within a greenspace matrix with diversified

habitats to foster biodiversity The greenspace–city

in-terface should preferably be convoluted and

curvilin-ear (Fig 3) to facilitate nature’s penetration into

ur-ban 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

envi-rons 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 3 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 cityform could have one dominant center with severalradial fingers The compact center facilitates effi-cient land-use, and the fingers support flexible urbangrowth based on public transport The developmentalong the length of concentric rings, which interruptgreen wedges, is not encouraged

3.2 Analysis of urban form and expansion

Three archetypal urban forms defined by geometricshapes can be identified: linear, centralized and grid-iron cities The linear form has a major transport axislinking key facilities Linear cities could grow spon-taneously in two directions along the axis The highlycentralized city is dominated by a central public space,with extensions along radial roads to form urban fin-gers connected by ring roads This geometry leads to ahighly compact center, whereas away from the centerlow-density development is possible with penetration

by green wedges The gridiron form is common inAmerican and Asian cities The chessboard layoutadopted 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 ratherautonomous parts Expansion occurs by adding par-allel roads to the existing lattice to maintain a regulargrowth 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 tual in fulfilling compact city objectives (Moughtin,

ineffec-1996)

The real-world city form is often a hybrid of thebasic types, echoing imprints of physical and culturalinfluences through time For Nanjing, the inner-citycore enclosed within the Ming Dynasty (1368–1644)city-wall has a gridiron system of four north–southmain roads intersecting four east–west ones Outsidethe wall, the regularity is interrupted by the surround-ing hills Several radial urban fingers with major trans-port lines have penetrated between the uplands ThusNanjing blends three basic urban forms: gridiron ofthe compact core, linear of urban fingers extendingradially from the core, and complex centralized form

as aggregate of both elements The uplands betweenthe fingers constitute green wedges, suggesting that amodel of green wedges associated with urban fingers

is an appropriate green development pattern

4 Study of green network at the city scale

4.1 Objectives and approach

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

com-prehensive greenway system which furnishes an

alter-native municipal green infrastructure Endowed with

natural amenities and a path, a greenway serves

multi-ple 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,

cul-tural features or historic relics, and often follows

nat-ural 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

loca-tions 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

con-nections 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

de-signed to improve accessibility of greenspaces with

footpaths, footbridges and underpasses

4.2 Physical landform assessment

In a mature compact city, usually few notablelandform features are spared from development,such as rivers and hills which are ideal for green-way use Nanjing incorporates diversified landformfeatures in the city A series of hills (Fugui, Ji-uhua, Beijige, and Gulou, Wutai, Qingliang) stretchfrom east to west, forming the watershed betweenJinchuan River valley and Qinhuai River valley inthe urban area; Gupin and Shizi Hills run fromsouth to north inside and along the city-wall Onthese uplands, parks of 3–30 ha have been built,conserving semi-natural to natural areas within thecity

Two lakes and two rivers define the drainage tem Xuanwu Lake (3.7 km2) west of Purple Mountainand Muchou Lake (0.37 km2) west of the city-wallhave been developed into municipal parks QinhuaiRiver runs through the city from southeast to north-west to join the Yangtze River It bifurcates into acluster of tributaries that spread in the south city Themain branch that runs along city-wall perimeter intoYangtze River is labeled Outer-Qinhuai In ancienttimes it served as the city’s major transport route(Nanjing Freeway Administration Department, 1988)

sys-At present only a small section near Yangtze is igated (Nanjing Gazetteer Editorial Office, 1994a).The other stream, named Inner-Qinhuai, bifurcatesinto two tributaries after flowing through the city-wall

nav-at the Tongji Gnav-ate In the north city, Jinchuan Riverruns through the city from the south to the north intoYangtze River, with a canal connecting to XuanwuLake

In Nanjing’s long history, many canals were structed to connect the districts with water traffic Thenotable ones include Qingxi, Yundu and Chaogoubuilt in a.d 240 (Nanjing Freeway AdministrationDepartment, 1988) Also, moats were built at differ-ent locations to defend the city In the last 1800 years,most canals and moats were clogged or filled, leavingintermittent sections They have since lost their trans-port and military functions, but remain as stormwaterand sewage channels As most sections juxtaposepresent roads, some water-edges have been devel-oped into roadside gardens (such as Zhenzhu Gardenalong North Taiping Road) If the water quality could

con-be improved, the drainage system could allow linear

greenspaces to penetrate into the congested urban

fabric

4.3 Urban context analysis

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

con-gestion The north city has more institutional lands

such as government agencies and colleges The

resi-dential neighborhoods there, mostly developed after

1949 in the closed-yard style (Wu, 1993), have a lower

built-up density with greenspaces interspersed

be-tween 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

de-velopment 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

na-tional ordinance stipulates 25% of urban land for

greening, furnishing a statutory basis for a

compre-hensive greenway system

Upgrading the urban transport system could also

incorporate greenways In Nanjing’s old city, the

gridiron urban form has bequeathed a lattice

trans-port 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

maxi-mize accessibility and connectivity of the greenways

Table 1 Major greenspace categories of NanjingaArea (ha) Number Green

cover (%)

Notable features Park 100–3000 7 70–99

1–100 30 55–97 Entry fee is charged

Active reactional facilities

<1 3 50–70 Plaza 0.1–7 34 40–100 Dominated by lawn

Scant woody vegetation Garden 0.2–2 22 40–90 Small enclaves

beside roads

<0.2 22 50–100

a This table is calculated from data of urban environment hancement in Nanjing, edited by The Administrative Bureau of Landscape and Gardening of Nanjing (1998).

en-4.4 Conservation elements assessment

The conservation elements include existing openspaces, cultural relics, historic sites, rare species, andvaluable ecological habitats They are scattered in thecity, separated by roads or buildings, and could be in-corporated into the greenway system

Existing open spaces in Nanjing mainly include ditional urban parks, recently built plazas and smallgardens beside streets In 2000, 24 of the 40 parks(Table 1) are located in the main city Most parksare associated with natural landform or historical fea-tures that can act as key nodes in the greenway sys-tem Since 1996, nine new plazas each covering over

tra-1 ha have been established in the main city They arelargely situated at main-road intersections, dominated

by lawns and ornamental pavement, to serve port, recreation and landscape functions In addition,small gardens each of 0.02–2 ha have been establishedbeside secondary roads, usually densely covered bytree canopies for passive amenity Some were included

trans-in houstrans-ing developments as residential greenspaces.Others were developed from derelict edges of canalsand moats in tandem with road widening As increase

in human density shifts habitat value from the urbanground level to the overhead canopy, artificial cavitiesand other measures could be created on trees to aug-ment their habitat value to a variety of animals andamenity value to humans

Greenspaces and cultural heritages serve synergistic

recreation functions, with the latter adding interesting

and knowledge-based ingredients With a 2000-year

history and as the capital of ten dynasties, Nanjing

has 142 protected items of national, provincial or

mu-nicipal cultural relics, including cemeteries, temples,

notable buildings and historical sites Private,

pub-lic or royal buildings and historical repub-lics dominate

the inner-city sites, with potential to enrich the

at-traction of greenways The Ming Dynasty city-wall is

the most prominent feature (with a 34 km perimeter,

over 14 m height, 14 m base width and 7 m top width;

Nanjing Freeway Administration Department, 1988)

A city-wall landscape belt has been incorporated in

the Masterplan However, the existing gridiron road

system frustrates this green ribbon concept Existing

or planned main roads going through the green

rib-Fig 4 Streets with existing large mature trees and roadside amenity strips in Nanjing.

bon should be reduced, and unavoidable intersectionsshould be treated sympathetically to facilitate conti-nuity and accessibility of greenspaces

Champion trees constitute a living cultural itage of the city, and they are protected from fellingand transplanting by national ordinances In Nan-jing, 1132 trees, including many large ones over 70years old, have been officially designated since 1982(Nanjing Greening Committee, 2000) They are scat-tered in residential, government, industrial and parklands, and many are potential landmark features forgreenways Large trees grace parkways that link themajor commercial centers (such as Zhongshan, NorthZhongshan, South Zhongshan, East Zhongshan andHanzhong Roads;Fig 4) Unfortunately, some havebeen felled since 1993 to widen roads, and the re-mainder are threatened by rapid urbanization Such

her-sylvan parkways need to be protected, and their

pedestrian-movement function reinforced in crowded

Small greenspaces at the neighborhood scale cater

to daily needs for contact with nature Burgess et al

(1988)found that the most valued open areas are the

intimate and familiar ones that play a part in peoples’

daily lives, rather than the distant ones The demand

for home-juxtaposed greenspaces calls for distance to

homes within 400 m or 10 min of walking

Quantita-tive criteria have been adopted in some countries to

foster penetration of greenspaces into crowded areas

For instance, Singapore’s facility planning standards

for new towns suggest one local garden (at least

0.2 ha) for 3000 dwelling units (Foo, 2001) Similar

greenspace standards in China stipulate not less than

1 m2per person for a neighborhood with 7000–15,000

people (State Technology Supervision Bureau and

Construction Ministry, 1994)

Detailed design of greenspaces could attend to the

need to attract patronage, such as easy accessibility

by most users and catering to neighborhood

resi-dent activities Friendly entrances to the greenspaces

and comfortable connecting footpaths are suggested

(Taylor, 1978; Hough, 1989) Marcus et al (1990)

proposed that certain park areas should be left for

spontaneous plant growth or to be designed by park

users, aiming to maximize the diversity of

pleasur-able experiences Physical arrangement of facilities

for special user groups could meet the varied needs

of the neighborhood Unsuitable design might

re-sult in low usage of neighborhood parks even in the

crowded metropolis Joardar (1989) studied 14 local

parks in Calcutta, and found that poor visual

qual-ity and facilqual-ity accounted for low popularqual-ity Some

well-maintained public spaces might be shunned if

they ignore inhabitants’ needs

As a public place, the neighborhood greenspaces

could encourage informal community meetings

Comfortable seats at suitable locations could be

de-signed for people to meet, view and converse withother residents These places might become tangiblereminders of childhood and community life, withplants playing a key role in forging the communitysense Willeke (1989)observed that for most Amer-icans, home is where the trees are In China, treesare also commonly related with the hometown Apublic place with vigorous trees of well-selectedspecies presents an attractive vista and serves as asymbolic community image.Meeus (2000)suggestedthat public gardens with unique designs could bestow

on each district a recognizable character and furnishsignature sites Inhabitants have varied expectations

of neighborhood greenspaces, ranging from contactwith people to nature Based on local physical andcultural conditions, designers could provide a mix-ture of opportunities with varied environmental fea-tures and leisure facilities A green connection withgreenspaces is a good measure to present users withmore choices Connection increases habitat diversityand capability to support flora and fauna, which inturn enhance amenity value to humans Such func-tions are increasingly valuable as human densityrises, accompanied by more isolation from functionalgreen

5.2 Ecological benefits and design implications

Plants especially trees in the city can improvethe environment by shading, intercepting pollutants,attenuating noise, absorbing carbon dioxide and emit-ting oxygen At the neighborhood scale, trees canreduce building energy consumption due to coolingand windbreak effects (Rudie and Dewers, 1984;Davey Resource Group, 1993; Simpson andMcPherson, 1996) For air pollutant interception,conifers are commonly suggested due to the high sur-face area, evergreen growth habit and effectiveness(Dochinger, 1980; Mao et al., 1993) More vegetationespecially trees should be brought into urban areasindividually or in groups to maximize their ecologicalbenefits

Abundance and diversity of wildlife indicateecosystem stability, which depends partly on habi-tat diversity Within the urban fabric dominated byartificial surfaces and structures, greenspaces act asrefuges for wildlife They can also sustain some

uncommon and rare plant species that are vanishing

in nature Measures to enhance wildlife increase the

attraction of greenspace to humans For the white

pine in the USA,Neuenschwander et al (1999)

sug-gested planting them on neighborhood streets, parks

and backyards to revive the declining species In

ad-dition, more native species should be introduced into

urban forests to counter the domination by exotics

(Rowntree, 1984; Jim, 1991)

The remnant natural habitats in cities, with

lim-ited human interference, provide valuable sites for

diversified wildlife They form unique urban

com-munities that differ from the countryside ones

An-thropogenic and synanthropic species thriving under

semi-natural conditions have been reported byGilbert

(1991)at a small discarded site in Sheffield, England

Remnant natural habitats provide proximate

ecologi-cal education opportunities compared to remote

coun-tryside locations In addition, the edges of a river, lake,

stream, creek, canal or pond have particular value for

wildlife.Cook and Lier (1994)identified seven

ecolog-ical zones at a canal cross-section to support different

life forms The unmanaged vegetation at path verges

provide habitat for insects and food for seed-eating

birds Some abandoned industrial sites or unused lands

within large factories have been commonly claimed

as semi-natural habitats by wildlife (Hough, 1989,

1994)

City birds and their habitats have been closely

examined Davey Resource Group (1993) found

the highest bird density in areas with the largest

trees, greatest tree species richness and abundance

of ruderal growth Tomialojc (1998) suggested that

high bird density might be related to the absence

of main predators and availability of natural food

To maximize opportunities for wildlife, the

commu-nal greenspaces of neighborhoods could incorporate

some natural enclaves The planting palette could

em-ulate indigenous composition and biomass structure,

trigger successional changes, and create conditions

for spontaneous wildlife invasion Landscape ecology

(Forman and Godron, 1986) and island

biogeogra-phy theory (MacArthur and Wilson, 1967) provide

fundamental strategies for greenspace system design

For small neighborhood greenspaces in Nanjing, a

network of greenways and green wedges is suggested

to link isolated green patches within and without

the city

6 Patterns of green extensions at neighborhood scale

6.1 Riparian linkage for the gridiron urban fabric

The riparian network provides a natural order forpublic greenspaces at the neighborhood scale Streambanks, usually embedded in the urban fabric and oftenignored by people, are being rediscovered in Chinesecities They serve as the backbone of the greenspacenetwork, determining the location of new linear parksand giving a skeleton to green connectors The di-versified wildlife habitats at water-edges can providevarious amenities for visitors The pedestrian pathsalong the riverbank can avoid conflicts with vehiculartraffic As a natural indicator of unity and coherence,the riparian network can be creatively used in urbandesign to relieve the harshness of urban environmentand bring vitality to the downtown Cases in point in-clude the Royal Spring Park in Georgetown, Kentuckyand the Creek Front plan in Denver, Colorado (cover

story of Landscape Architecture, February, 1994), and

the Garrison Creek Linkage Plan in Toronto, Canada(Pedersen, 1999)

6.2 Pedestrian route

Based on the belief that the whole is more than thesum of the parts, the linkage system at the neighbor-hood scale aims at connecting existing isolated res-idential greenspaces with municipal parks and otherextensive greenspaces A pedestrian way can act as asubstantive connector, through which inhabitants walkfrom home directly to adjacent or more distant parks,

or even walk to the downtown Definite destinationsand landmarks associated with the route can make thelinkages attractive For example, the Creek Front plan

of Denver incorporated a series of pedestrian spacesconnecting the Denver Convention Center, LarimerSquare Historical District and with other destinations

to add vitality to the downtown

6.3 Street and streetside system

Tree-lined streets can be enlisted as green dors to provide continuity to the greenway networkwhere the drainage system cannot reach Along theroute, crosswalks, signalized intersections and transit

corri-stops could be created or relocated to ensure the

convenience, comfort and safety of pedestrians If

breaks in the green network are difficult to join due

to present structural and town-plan constraints,

conti-nuity should be proposed for the long-term For

in-stance, fences could replace concrete walls to expose

the greenery, and the streetscape quality of traffic

is-lands, underpasses and medians could be upgraded to

soften concrete dominance For high 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

connec-tors for the overall green network Where physical

constraints do not permit a better design, even alleys

could be converted into linear greenspaces

6.4 New parks

New parks could be created at nodes of the drainage

or street systems The intersections command a large

visitor catchment, and provide more route choices to

other destinations Besides, the larger water area

ad-vocated for the new parks, with appropriate treatment

to optimize habitat conditions, considering the spatial

constraints, could attract more wildlife and provides

humans with more amenities for natural contacts

Waterfront parks often have attractive natural

endow-ments to attract patronage In Denver’s Creek Front,

the drop structures to stabilize the channel act as

dra-matic water features In Royal Spring Park, a dam is

designed to hold a pool of water stocked with trout

and a deck allows fishing in the stream Both cases

are equipped with paved banks to facilitate visitors

touching the water

6.5 Planting scheme

An indigenous-species planting scheme for the

green network could attend to species diversity,

mi-croclimatic moderation and aesthetic coherence A

native vegetation composition is conducive to

provid-ing the right kind of food and shelter to native

ani-mals, the presence of which create a truly functional

green complex to augment amenity value to humans

Fig 5 Two patterns of green corridors that penetrate high building density areas at the neighborhood scale are proposed for Nanjing.

Firstly, the existing vegetation should not be clearedexcept for footpath construction Natural treatment ofriver edge could encompass a variety of plant species,texture and color, and a low-maintenance landscape.For most situations, a natural forest section could beplanned, including a main forest canopy, understorytrees, shrubs and herbs Secondly, native species could

be given priority, supported by systematic tion of suitable candidates by form, texture, growthrate, city tolerance and maintenance requirements(Jim, 1999) Thirdly, certain species could be planted