Adopting a modern ecological view of the metropolitan ... · Adopting a modern ecological view of the metropolitan landscape: the case of a greenspace ... d Regional Plan ... traditionally

Ž .Landscape and Urban Planning 39 1998 295–308

Adopting a modern ecological view of the metropolitanlandscape: the case of a greenspace system for the

New York City region

Alejandro Flores a,), Steward T.A. Pickett b, Wayne C. Zipperer c,Richard V. Pouyat c, Robert Pirani d

a School of Forestry and EnÕironmental Studies, Yale UniÕersity, 205 Prospect Street, New HaÕen, CT 06511, USAb ( )Institute of Ecosystem Studies, Box AB Route 44A , Millbrook, NY 12545, USA

c USDA Forest SerÕice, Northeastern Experiment Station, cro SUNY-CESF, 5 Moon Library, Syracuse, NY 13210, USAd Regional Plan Association, 61 Broadway 11th Floor, New York, NY 10006, USA

Received 27 January 1997; received in revised form 16 October 1997; accepted 16 October 1997

Abstract

Concern about environmental quality and the long-term livability of urban areas is now a driving paradigm for planningprofessionals. Although a modern ecological framework exists, inappropriate or outdated concepts continue to be used in thecontext of land-use decision making. These classical concepts emphasize a static view of the landscape and focus on shortterm planing of single sites. The modern framework emphasizes a dynamic view of a biologically rich urban environmentwith a focus on interactions among multiple sites across temporal scales. We summarize this framework by presenting fivekey ecological principles—content, context, dynamics, heterogeneity and hierarchy—and use the New York City Metropoli-tan Area as a case study to illustrate how these principles might be applied to achieve specific planning goals. Weadditionally use the case study as reference in providing some guidelines to more effectively incorporate the modernecological framework in future planning. q 1998 Elsevier Science B.V.

Keywords: Land-use planning; Ecology; Urban landscape; Environmental benefits; New York City Metropolitan Area

1. Introduction

The transformation of the urban landscape hasprofound social and ecological consequences for both

Žurban and rural residents Turner et al., 1990; Meyer.and Turner, 1994 . Concern about environmental

quality and the long-term livability of major urban

) Corresponding author: Tel.: q1-301-654-2436; fax: q1-203-432-3817; e-mail: [email protected]

areas is now a driving paradigm for planning profes-sionals. Within this paradigm, the incorporation ofecological knowledge is regarded as strategic to pro-tect and restore the availability of a wide array ofcritical environmental resources. The considerationof ecological understanding in planning, however, isnot new. Its roots in the United States can be tracedto seminal regional planners such as Patrick Geddesand Benton MacKaye in the early twentieth centuryŽ .e.g., MacKaye, 1928 . The ecological approach was

0169-2046r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.Ž .PII S0169-2046 97 00084-4

( )A. Flores et al.rLandscape and Urban Planning 39 1998 295–308296

Ž .later developed by Ian McHarg 1969 in his Designwith Nature, and continues to be nourished in the

Žwork of subsequent authors e.g., Fabos, 1973; Hen-drix et al., 1988; Ahern, 1991; Baschak and Brown,

.1995 . Still, the incorporation of ecological thinkingin mainstream planning at times seems more in tune

Žwith environmentalism than ecological science see.Daniels, 1988 . Moreover, the seminal period of well

known ecological paradigms in the planning profes-sion occurred during the 1960s, however, ecologicalprinciples have evolved and consolidated signifi-

Ž .cantly since then e.g., Botkin, 1990; Barbour, 1995 .This paper presents a framework for the incorpo-

ration of modern ecological thinking into the re-gional planning of urban landscapes. We summarizethis framework by presenting five key ecologicalprinciples—content, context, dynamics, heterogene-ity and hierarchies—and use the third regional plan

Ž .of the New York City Metropolitan Area NYCMAŽ .Yaro and Hiss, 1996 as a case study to illustrate

how these principles can be applied in practice. Theprimary purpose in discussing the NYCMA plan isto illustrate how the framework can be used toachieve specific planning goals. The NYCMA casestudy, however, also serves as reference in providingsome recommendations to more effectively incorpo-rate the modern ecological framework in future plan-ning. These recommendations are presented as theplan’s key strengths and weaknesses are highlightedin Section 4 of the paper.

2. A regional plan for the NYCMA and ecologicalknowledge

The NYCMA is a 41,000 km2 region composedof 31 counties in three neighboring states—NewYork, New Jersey, and Connecticut—and has a pop-

Ž .ulation of over 20 million individuals Fig. 1 . Whilelarger and more complex, this region exhibits the

Fig. 1. The New York City Metropolitan Area, composed of 31 counties in the three neighboring states of New York, New Jersey andConnecticut.

( )A. Flores et al.rLandscape and Urban Planning 39 1998 295–308 297

basic urban form that characterize metropolitan areasin North America; high density central cities thathave been losing their regional share of populationand economic activity, surrounded by expandingrings of suburbs of considerably lower housing den-sity and high per capita rates of resource consump-tion.

Regional plans for the NYCMA have been devel-oped in 1929, 1968, and 1996 by the Regional PlanAssociation, a non-profit organization located in New

Ž .York City Yaro and Hiss, 1996 . Like its predeces-sors, the 1996 plan formulates a comprehensive ap-proach that addresses the interrelationships amongthe economy, social equity, and the environment.The 1996 plan’s proposal for a regional open spacesystem—Metropolitan Greensward—is an attempt toaddress these overall concerns through the use of

Ž .open space greenspace planning and improved nat-

ural resource management. By linking urbangreenspaces with large-scale regional natural re-

Ž .serves into a single greenspace system Fig. 2 , theproposal calls for the protection and restoration ofenvironmental life support systems for the region’scities, suburbs, and rural hamlets alike.

Implicit in the rationale for this greenspace-plan-ning effort is the desire to create a spatial andinstitutional context for managing landscape ecologi-cal processes at the regional scale. Land-use plannersin urban, suburban and rural areas have long soughtto understand and address a multitude of regionalforces in developing local plans and ordinances orreviewing site level development proposals. Com-mon examples include population growth, commut-ing patterns, and market demand for residential orcommercial development. However, an understand-ing of regional ecological processes, and, especially,

Fig. 2. The 11 regional reserves and the numerous greenspaces within the urban matrix of the NYCMA represent the core of open space ofŽ .the proposed Metropolitan Greensward adapted from Yaro and Hiss, 1996 . A network of greenways is envisioned to link these two key

features of the landscape into a single regional greenspace system.


the spatial significance of those processes, has nottraditionally been part of the planner’s lexicon. Thefive key ecological principles described in Sections2.1, 2.2, 2.3, 2.4 and 2.5—ecological content, con-text, dynamics, heterogeneity and hierarchies—arepresented as the theoretical basis for incorporatingsuch understanding into the planner’s tool box.

2.1. Ecological content

An ecological principle of prime importance toŽplanners is the concept of the ecosystem Trepel,

.1995 . An ecosystem is defined as an area containingorganisms, a physical environment, and the interac-tions and exchanges among the organisms and the

Ž .environment Likens, 1992 . The ecosystem conceptemphasizes that organisms and physical environ-ments are linked functionally regardless of whether

Žlands are ‘wild’, built or intensively managed Mc-.Donnell and Pickett, 1990; Pickett et al., 1992 .

Hence, all land units regarded as greenspaces may beviewed as ecosystems, for all of them invariablyharbor a community of organisms which is activelyengaged in the exchange of energy and materialswith its physical environment.

All ecosystems have structure and function. Struc-ture refers to the physical arrangement of biologicaland non-biological components of the system,whereas function refers to the way the componentsinteract with one another. These two aspects ofecosystems cannot be effectively separated. How asystem is built is one side of the coin, while how itworks is the other. Examples of physical structureinclude the presence of a forest canopy and the sizeand age distribution of street or park trees. Func-tional relationships include the transformation of so-lar energy into biological matter, siltation and degra-dation of water quality through removal of canopycover, the cycling and the absorption of heavy metalsfrom air pollution into the soil and water and theirsubsequent transfer to some organisms including hu-mans, and the maintenance or control of certain

Ž .wildlife species Vandurff et al., 1995 .Of particular importance are the numerous envi-

ronmental resources sustained by these ecosystemsŽ .Table 1 . For convenience and because of the inter-active nature of ecological processes and human

Ž .values Harte, 1997 , we refer to all these resources

Table 1Examples of environmental benefits sustained by urbangreenspaces

Biological benefits:Refuge for threatened and endangered speciesIncreased biodiversityHabitat for flora and faunaStorage and cycling of nutrientsEcosystemrcommunity representativeness

Social benefits:Recreational opportunitiesEnhancement of property valueCommunity cohesionAesthetic enhancementSource of knowledge

Physical benefits:Flood controlReduction of erosionModulation of temperatureRemoval of air pollutionProtection of water quality

as environmental benefits. These benefits reflect awide spectrum of ecosystem functions, functions thatare strongly linked to ecosystem structure.

2.2. Ecological context

Ecosystems, as evident from the discussion above,contain webs of interacting organisms, materials,energy and substrates. Ecosystem function, however,is not only driven by internal interactions but also isinfluenced by processes, organisms, and materials

Žthat originate outside their boundaries Forman andGodron, 1986; Hansen and di Castri, 1992; Pickett

.and Cadenasso, 1995 . While boundaries on mapsmay depict greenspaces as delimited, isolated landunits, these ecosystems often are rather stronglyaffected by the external landscape providing a spe-cific context to each site.

Context consists of three elements: location, adja-Ž .cency and neighborhood Forman, 1995 . Location

refers to the place where the site occurs relative tothe rest of the landscape. Adjacency and neighbor-hood, on the other hand, respectively refer to theland units that are in direct contact with the site andthose adjacent or nearby units linked to it by active

Ž .interactions Fig. 3 . The combination of adjacency,


Fig. 3. Landscape context influences the movement of energy,material, and species into and out of a greenspace. The structure

Ž .and function of greenspace or ecosystem A is often stronglyŽ .influenced by those land units adjacent to it B and C . Greenspace

Ž . Ž .A , however, is also significantly influenced broken arrows byŽ .the other land units within its neighborhood D, E, F .

neighborhood and location results in considerablevariability in the kind of ecological context specificto each site.

In addition to context, the size and shape of landunits play a key role in the way ecosystem function

Ž .is influenced by external interactions Weins, 1997 .For instance, a greenspace with a high edge to

Ž .interior ratio circumferencerarea may be consider-

ably more sensitive to external factors than one witha smaller ratio sharing a similar ecological contextŽ . Ž .Forman, 1995 Fig. 4 . A higher degree of sensitiv-ity to external forces not only has important implica-tions for ecosystem function but, ultimately, for theenvironmental benefits that can be derived and themanagement objectives needed to obtain these bene-fits. For example, a greenspace with a high edge tointerior ratio may not have sufficient interior forestto provide habitat for wildlife that avoids the forestedge. Moreover, even in the case of having sufficienthabitat, a greenspace with greater exposure to exter-nal factors, such as vandalism, would likely demandgreater managerial investment to maintain the viabil-ity of such wildlife.

2.3. Ecological dynamics

Ž .Ecological systems are dynamic Meyer, 1997 .Their structure and function are in constant flux.Ecosystem dynamics results from two major ecologi-

Žcal concepts, succession and disturbance Pickett and.White, 1985 . Succession is the change through time

of community structure or species composition, e.g.,the change of a farmer’s field to a forest. Distur-bance, on the other hand, either generated naturallyor by people, may alter the resource base, structureor composition and may act as catalyst to successionif it is severe enough to alter an established biotic

Ž .community Pickett and White, 1985 . Examples of

Fig. 4. The size and shape of land units play a key role in determining the way ecosystem structure and function is influenced by externalŽ .factors. Greenspace A, having a higher edge to interior or circumference to area ratio, is likely to be considerably more sensitive to

external factors when compared to greenspace B with a smaller edge to interior ratio.


disturbance include windstorms blowing over largetrees, floods altering streams, and fire killing suscep-tible plants.

With structural changes, ecosystem function alsochanges. For instance, as the plant community in avacant lot changes from being predominantly agrassland to being predominantly a forest, water andenergy transfers between vegetation and the atmo-sphere change, and the capacity of the vacant lot tomodulate microclimate extremes is altered. Hence,derived environmental benefits sustained by a givengreenspace are dynamic. Even if the socioeconomiclandscape remains relatively constant, environmentalbenefits sustained are likely to be altered due tobiotic changes even in the absence of management.To ensure that the continued availability of environ-mental benefits is not interrupted, at least at thecitywide scale, representative successional stages indifferent urban contexts should be planned and man-aged for. Likewise, when establishing large regionalreserves, these reserves should be of a sufficient sizeto withstand the impact of different disturbances

Žwithout disrupting its main functions Pickett and.Thompson, 1978 .

2.4. Ecological heterogeneity

ŽThe natural world is heterogeneous Turner, 1987;.Kolasa and Pickett, 1991 . Planners readily acknowl-

edge the fact that the socioeconomic fabric of themetropolitan landscape is heterogeneous. Similarly,the ecological fabric within a site and across anurban landscape is heterogeneous. Heterogeneity iscrucial to the functioning and maintenance of naturalsystems to provide environmental benefits. For ex-ample, within a park, tree cover may look similar

Ž .from an aerial perspective Fig. 5 . However, from aground view, a tree-covered area with grassy under-story may provide recreational opportunities for fam-ilies and limited wildlife habitat. In contrast, areaswith tree cover and an understory of small trees,shrubs, and herbs may provide critical habitat forwildlife, but marginal opportunities for family recre-ation. Each type of tree cover is likely to be neededto provide for a wide array of environmental benefitswithin an urban landscape.

Species richness within an area is one feature thatensures the functioning of ecosystems during envi-

Ž .ronmental changes Thompson, 1997 , and hetero-

Fig. 5. A representation of one aspect of greenspace heterogeneity. Both land units A and B are similar from an aerial perspective. However,their vertical structures are quite dissimilar. This difference will require different management objectives and will yield differentenvironmental benefits.


geneity aids in maintaining species richness. Specieshave evolved to exploit the heterogeneity of environ-mental conditions that exist from place to place. Therichness of species and genetic types within speciesare in part a response to the range of environmentalheterogeneity they have been exposed to. In turn,that richness acts as insurance against changing con-

Ž .ditions in the future Huston, 1994 . Hence, hetero-geneity acts as opportunity and constraint, whilebiological richness or species diversity serve as prod-uct and insurance. Maintaining such richness withinan area is one way that planners can ensure function-ing ecosystems with changing conditions or environ-ments, such as global change.

The key element of maintaining environmentalbenefits is maintaining healthy ecosystems that canpersist and adjust to future changes. Health consti-tutes the continued capacity of ecosystems to gener-

Ž .ate and respond to novelty Haskell et al., 1992 , andto sustain processes as environmental change occursŽ .Norton, 1992 . In that regard, ecosystems need notbe pristine, only flexible, connected, and diversewith complement of species to generate the genetic,biological, and biogeochemical capacity to adapt andrespond to a changing environment. This is theessence and foundation of sustainability. Heterogene-ity, diversity and connectivity within and among thecomponents of greenspaces contributes powerfully tothe features and processes for which people andinstitutions value them.

2.5. Ecological hierarchies

Ecological dynamics and heterogeneity are mani-Žfested at different nested hierarchical levels O’Neill

et al., 1986; Meentemeyer and Box, 1987; Allen and.Hoekstra, 1991 . Hierarchical approaches help man-

age ecological complexity by organizing it into dis-crete functional components operating at different

Ž .scales O’Neill et al., 1986; Urban et al., 1987 .Within a metropolitan region, these components maybe represented by a greenspace site, the neighbor-hood in which the site is located, the section of thecity in which the neighborhood occurs, and the entire

Žurban landscape within the metropolitan region Fig..6 . By dividing the metropolitan areas into functional

components, planners have the opportunity to view

Fig. 6. A generalized hierarchical system of an urban area. Level 1represents the interactions of neighborhood components. Level 2represents the interactions among neighborhoods. Level 3 repre-sents the city, a composite of neighborhoods. Thick arrows indi-cate strong interactions; broken arrows indicate weak interactionsŽ .adapted from Urban et al., 1987 .

the ways components at different scales are relatedŽ .to one another Urban et al., 1987 .

Spatial and temporal scales are familiar to plan-ners. It is important to emphasize, however, that agiven spatial or temporal scale is not defined by a

Žsingle dimension but rather by two dimensions Al-. Ž .len and Hoekstra, 1991 : 1 grain—the smallestŽ . Ž .addressable unit of space or time and 2 extent—

Ž .the largest addressable unit of space or time . Forinstance, the spatial scale of a long term planningeffort for a given county may involve a grain of 1

2 Žkm area of the smallest recognized land-use unit. 2such as a neighborhood and an extent of 2500 km

Ž .size of the entire county . Similarly, its temporalŽscale may be defined by a grain of 1 yr length of the

. Žsmallest fiscal period and an extent of 25 yr length.of planning horizon .

Two critical aspects of scale need to be placed ina planning framework. First, the particular ecological


patterns revealed by observations depend on thespatial and temporal scales adopted. Some spatialand temporal scales will, therefore, be more appro-priate than others in managing environmental bene-fits. For example, planning often neglects large-scaledisturbances, such as fire and floods. These events,having specific intensity and timing, often are neces-sary to maintain certain biological communities butpose a serious threat to development. Second, under-standing the ecological processes that sustain envi-ronmental benefits are likely to demand a focus onmultiple scales—some of which may be unconven-tional to planning. For instance, the management of agreenspace or a large forest preserve must not onlyaccount for the ecological content and dynamicsaffecting the site, but also how the ecological contextmay change the site over time and subsequentlyaffect the site.

3. The use of modern ecological principles inachieving the Greensward campaign

We return to the important issue of the relation-ship between ecological principles and planning inthe metropolitan region by placing the objectives ofthe Greensward campaign into the ecological frame-work outlined above. The Greensward campaign has

Ž .three primary objectives Yaro and Hiss, 1996 .Ž .1 ‘Create regional reserves to conserve the wa-

terways and broad working landscapes that providethe region with fresh drinking water, harbor thearea’s most significant ecosystems, constitute ourbest recreation, and delimit the outward expansion ofthe region’s urbanized core.’

Ž .2 ‘A full-scale reinvestment in urban parks,public spaces and natural resources to improve theenvironmental quality of our cities, provide a fairshare of park land to urban residents, and help citiesattract businesses and residents.’

Ž .3 ‘Create a network of greenways to connectand nurture our cities, suburbs, and protected land-scapes.’

Given that ecological interactions are often intri-cate, inconspicuous, and involve temporal and spatiallags, the task of protecting and restoring environmen-tal benefits for a Metropolitan area is a challenging

Ž .one Godde et al., 1995 . The Greensward proposal¨

provides a useful framework for approaching thischallenge by addressing three key landscape featuresof the New York City Region and other metropolitan

Ž .landscapes: a the urban matrix at the metropolitancore where greenspaces exist only as artifacts or

Ž .highly managed parkland; b the large unfragmentedŽ .‘natural’ landscapes in ex-urban hinterlands; and c

the corridors of greenspace that run throughout theurban, suburban, and rural communities.

3.1. ObjectiÕe 1: creating regional reserÕes

Concerned with land consumption by urbansprawl, the Greensward campaign identifies 11 Re-

Ž .gional Reserves Fig. 2 to be safeguarded within themetropolitan area with the purpose of ensuring arepresentation of critical ecosystems and sustainedenvironmental benefits. The targeted reserves includeboth terrestrial and aquatic systems and representlarge areas of contiguous forest cover, productiveagricultural lands, unique geomorphological features,and critical waterways and estuaries. The conserva-tion of these areas is seen as a means to create aseries of urban growth boundaries in the region—aplace ‘where pavement ends and nature begins’.However, establishing reserves is more than justsetting aside land; it also assumes that natural sys-

Žtems and processes will be protected Noss, 1987;.Meyer, 1997 . In light of the ecological principles

discussed above, the Appalachian Highlands Reservewill be used to illustrate how the conservation ofregional reserves in the area can be addressed withinsuch ecological framework.

The Appalachian Highlands extend from Pennsyl-vania to Connecticut, encompassing over one millionacres of land of which over 60% is forested. Only10% of the area is owned by federal or state agen-cies. The value of this landscape is evident from thecritical environmental benefits it sustains. The High-lands supply water for over 3 million people inNYCMA and are known for offering exceptionalrecreational opportunities. However, the rationale forprotecting ecosystem functions in this landscapeshould extend well beyond issues of recreation andclean water. Less tangible, and often lesser known,environmental benefits include: soil erosion control,removal of air pollution, temperature modulation,enhanced aesthetics and the provision of wildlife

Ž .habitat Harte, 1997; Meyer, 1997 .


The strategic importance of preserving the High-lands landscape in the NYCMA becomes especiallyapparent when considering its context. As comparedto adjacent and neighboring landscapes, the High-lands contain rather special ecological features. Forinstance, unlike the landscape in the cities and sub-urbs adjacent to the east, the ridges and valleys ofthe Highlands are distinguished by large, contiguousforested areas unbroken by roads, urban land-uses,

Ž .and other clearings. Richard Lathrop 1995 found26 such patches greater than 1000 ha, covering

Ž .one-third of the Highlands area Fig. 7 . Moreover,the Highlands contain unique forest, grassland andaquatic habitats inhabited by threatened and endan-gered species. The conservation of these habitats is

essential to the survival of a variety of species,notably interior nesting neo-tropical migrant song-birds. Furthermore, the Highlands contain a highdegree of ecological heterogeneity created from thejuxtaposition and interspersion of habitats and suc-cessional states of these habitats. Finally, the reserveis sufficiently large to sustain and yet recover fromnatural disturbances, thereby creating a dynamic mo-saic of both ephemeral habitats and mature forestsacross the area.

In light of the points discussed above, inclusion ofregional reserves in land-use decision making needsto consider both the ecological content of these land

Žunits and the context in which they occur see Duever.and Noss, 1990 . Indeed, the ability of land-use

ŽFig. 7. The ten largest blocks of contiguous forest cover in NY–NJ Highlands courtesy of Richard Lathrop and John Bognar, Center for.Remote Sensing and Spatial Analysis, Rutgers University, New Brunswick, NJ .


planners to guide urbanization or evaluate specificdevelopment proposals in relation to regional re-serves like the Highlands may require a greater-than-local planning framework. Regional regulatorypowers or land acquisition may well be the onlyviable policies for planners to consider. Local zon-ing, subdivision and site plan controls can be em-ployed only given a planning framework that effec-tively clusters new urban uses across several parcelsor municipalities.

3.2. ObjectiÕe 2: inÕigorating existing greenspacesin highly urbanized enÕironments

The importance of establishing reserves to safe-guard regional ecosystems is evident from an ecolog-ical, social and economic perspective. Of equal im-portance are the numerous greenspaces within the

Ž .complex urban matrix Fig. 2 . At the local scale,greenspaces collectively play a critical role in pro-viding environmental benefits such as removing airpollution, creating opportunities for recreation, fos-tering community cohesion, reducing noise, and pro-viding wildlife habitat. In NYCMA, protection andmanagement of these benefits is seen by the Re-gional Plan Association as a means of improving thequality of life in urban areas, and stemming the flowof jobs and residents to new suburbs in the reserveareas.

In contrast to the NYCMA regional reserves,however, the ecological content of the inner citygreenspaces is likely to be highly altered from its

Žpre-development state McDonnell and Pickett, 1990;.Cramer, 1993; Zipperer and Pouyat, 1995 . For in-

stance, even greenspaces that may otherwise looknatural may experience dramatic alterations to thestructure and composition of their biotic community.A study of an old growth, remnant forest at the NewYork Botanical Garden, Bronx, NY revealed thatnon-native species make up to 80% of the seed poolŽ .Rudnicky and McDonnell, 1989 . Moreover, theecological dynamics of greenspaces also havechanged considerably such as the suppression orenhancement of pre-development disturbance fre-

Žquency Rudnicky and McDonnell, 1989; Cramer,.1993 .

The structure and function of inner citygreenspaces are delimited by a mix of both natural

and human processes internally and externally. Whilethe context of a highly urbanized matrix has longexposed the inner city greenspaces of NYCMA tohighly modified ecological conditions, caution shouldbe taken in dismissing or generalizing a rich array ofecosystem functions present in these sites. The waythese land units are formed or transformed becauseof varied pre-existing conditions and exposure to adiverse and ever changing urban context, has re-sulted in markedly different types of greenspaces. Ahigh heterogeneity in the content and context ofgreenspaces immediately suggests two planning con-siderations. First, it is unlikely that all urbangreenspaces are equally able to sustain various envi-ronmental benefits. Second, the prospect of restor-ing, maintaining or enhancing some of these benefitsmay require different planning and managementstrategies for different greenspaces. Selecting theoptimum use of a site depends not only on manage-ment policies but also on community involvement asthese inner city sites often galvanize residentialneighborhoods to improve the quality of their envi-

Žronment through ecological stewardship Burch and.Grove, 1993 . This last point shows how application

of ecological principles must recognize and interactwith social and political constraints.

Inner city greenspace management is often frag-mented among public agencies and private landown-ers. For example, urban forestry can be the responsi-bility of a parks department, a transportation depart-

Ž .ment for street trees , and many small privatelandowners. A city-wide or region wide spatial scalecan yield insights into how best to optimize environ-mental benefits for the entire greenspace network.Since all greenspaces are not the same, selection formanagement practices needs to be prioritized basedon well-defined goals. Hence, cleaning the groundand planting trees on derelict sites may have agreater net effect on providing environmental bene-fits than planting additional trees in a well managedpark. Similarly, planning decisions can only be madethrough an integrative management program that in-volves the different city agencies responsible formanagement, a comprehensive classification systemof greenspaces to account for their heterogeneity,and an ecological understanding of how modifyingstructure affects function and, hence, the expectedbenefits derived from management. The environmen-


tal benefits that can be derived from these urbangreenspaces are only now being truly understoodŽ .e.g., McPherson et al., 1994 . Until planners canbetter and more rationally account for the complexland and management costs associated with greeningurban open space, it will be difficult to institutional-ize the urban ecosystem management envisionedhere.

3.3. ObjectiÕe 3: creating a regional network ofgreenspaces

Within the highly fragmented landscapes of ametropolitan region, maintaining connectivity amonggreenspaces is paramount in that it may ensure theflow of energy, species and matter. Without connec-tivity, sites become isolated and their ability to sus-tain themselves and to produce environmental bene-fits may diminish. A regional network of greenwaysin NYCMA is being envisioned by RPA to serve asa pathway for both species and human movementsacross the region.

Within the ecological literature, there is an ongo-ing debate about the value of corridors or greenwaysin the landscape. Narrow corridors can be costly tomaintain because of their edge to interior ratios; theymay serve as avenues for the spread of pathogens,non-native species and disturbances; and they may

Žbe detrimental to some species Simberloff et al.,.1992 . However, increasing width of corridors can

reduce many of the negative effects and managementŽ .can compensate for other effects Forman, 1995 . In

the urban environment, benefits to humans may out-weigh the costs of corridors and increased connect-edness. In the NYCMA greenways can connectneighboring communities and commercial centers,provide forms of recreation, connect communitiespoor in greenspaces to those rich in greenspaces, andprovide a focus point for environmental education

Ž .and citizen efforts Yaro and Hiss, 1996 . Ecologi-cally, greenways may additionally maintain geneticfitness of species populations by reducing isolationand enable species to migrate with environmentalchanges and to new sites created by disturbances.

In designing and managing a regional greenwaysystem for a metropolitan area like the NYCMA, two

Žinsights are particularly useful Huston, 1994; For-.man, 1995 . First, connectedness in greenway sys-

tems is hierarchical. The ecological processes thatsustain any environmental benefit are likely to oper-ate at multiple spatial and temporal scales; the rangeof spatial and temporal scales will depend on thebenefit. Second, of special interest to the planning ofgreenway networks is the ecological content andheterogeneity of greenspaces as a whole. No degreeof connectivity between greenspaces may suffice toovercome critical deficiencies in their combined eco-logical content. This is especially evident for thepurpose of maintaining regional ecological diversitywith a system of reserves and parks that is skewedtowards protecting a narrow range of ecosystemtypes at the expense of others. Because of ecologicaldynamics, it is important to maintain a representativecollection of ecosystems within the greenway net-work to ensure the sustainability of a wide array ofenvironmental benefits.

4. Conclusion and recommendations

ŽThe NYCMA third regional plan Yaro and Hiss,.1996 testifies to the openness of contemporary plan-

ners to the consideration of ecological aspects in theregional planning of metropolitan areas. Overall, theobjectives and the initiatives the third plan delineatesfor the NYCMA greenspace system are consistentwith the modern ecological framework and the eco-logical principles can certainly be used to guide theplan’s implementation efforts. The full strengths of-fered by the ecological principles, however, are notbeing realized by the plan. Sections 4.1, 4.2, 4.3, 4.4and 4.5 offer specific recommendations to moreeffectively incorporate the framework in future plan-ning efforts while highlighting the plan’s keystrengths and weaknesses. These are organized byecological principle. Each one is discussed in turn.

4.1. Content

A wide variety of open spaces in the NYCMAhave been regarded as part of the plan’s greenspacesystem. Included in the greenspace system, for ex-ample, are small and intensively managed inner cityparks and non-vegetated ‘land’ units such as theLong Island sound. This conceptualization representsan important step forward from that of other plans


that reserve their consideration of greenspaces to‘pristine’ and vegetated land units in rural areas.While not explicit in the plan, the notion persistshowever that non-greenspace land units are some-how devoid of living systems. Based on the principleof ecological content, the next step in incorporatingthe modern framework is to consider, or at leastacknowledge, the potential role of the vast number ofcommunities of organisms harbored in the rest ofland units not classified as greenspaces. Of course,the complete roster of structural components in theseecosystems would include much more than onlybiotic elements. Indeed, in addition to the naturalsubstrate, many ecosystems in urban areas will in-clude civil infrastructure as well.

4.2. Context

This principle states that ecosystems often arestrongly affected by the external landscape providinga specific context to each site. Greenspaces in theNYCMA plan, as in most other plans, continue to bethought of as discretely delimited, highly isolatedland units. This represents an important strategic

Žlimitation for context both socioeconomic and eco-.logical is often highly influential in shaping a site’s

ecological processes and, ultimately, the inputs re-quired by them and the kinds of benefits beingderived from them. Perhaps a rather practical way todiscourage the old way of thinking from persisting isto use less discrete boundaries or even buffer zonesŽ .areas of influence to depict greenspaces on maps.

4.3. Dynamics

This principle states that the structure and func-tion of ecosystems are in constant flux. Obviously,important chronological changes in the landscape arenoted in the plan. Yet, it is evident that a somewhatstatic view of the landscape and particularly of thegreenspace system is retained. The more dynamicview of greenspaces within the modern frameworkhas important implications for both planning andmanagement. For instance, to ensure that the contin-ued availability of environmental benefits is not in-terrupted, at least at the citywide scale, representa-tive successional stages in greenspaces at differenturban contexts should be planned for. At the same

time it is important to realize that the prospect ofrestoring, maintaining or enhancing some benefitsmay require different management strategies for eachsuccessional stage.

4.4. Heterogeneity

The plan acknowledges the most obvious ecologi-cal differences amongst NYCMA’s set ofgreenspaces: that between the regional reserves onthe one hand, and the inner city greenspaces, on theother. The plan also acknowledges the marked differ-ences between the 11 regional reserves themselves,which include terrestrial and aquatic systems setaside for a wide variety of reasons. Marked differ-ences within inner city greenspaces, however, are notgiven due consideration. Moreover, the whole issueof vertical heterogeneity between greenspaces is notaddressed. It is highly recommended that ecologicalheterogeneity be noted not only amongst large pro-tected areas but also amongst inner city greenspaces,not only in a horizontal plane but also in a verticalplane, and, finally, not only in a site’s content butalso in its context.

4.5. Hierarchies

The plan’s Greensward proposal is one of the firstattempts to conceptualize such a large, connectedsystem of greenspace. Its three main components—the regional reserves, urban greenspaces, and green-ways—set a fitting spatial framework that is usefulfor land-use planners in NYCMA considering thecompelling ecological aspects of open space and itsinfluence on the well-being of more than 20 millionpeople residing in the area. Indeed, understandingthe ecological processes that sustain the wide arrayof environmental benefits in metropolitan areas de-mands a focus on multiple scales. It is important tonote, however, that successful understanding of eco-logical processes and their management also requiresthe incorporation of a complementary set of temporalscales not considered in the plan. Moreover, whenconsidering the issue of ecological scale it is highly

Ž .recommended to note that: a the particular ecologi-cal patterns revealed by observations depend on the

Ž .specific spatial and temporal scales adopted; and bthat the specific spatial or temporal scales are notonly defined by their extent but also by their grain.


Through its metropolitan Greensward proposal,the third NYCMA regional plan explicitly exploresthe connection between ecological process and qual-ity of life. Less explicit is the notion, however, thatsuch connection be made well beyond publicizedissues of recreation, clean water, and wildlife habitatto include other less tangible benefits like soil ero-sion control, removal of air pollution, and tempera-ture modulation. Success in incorporating ecologicalknowledge to establish such connections in a plan-ning context, however, is often limited by the avail-ability of ecological information on the systems andfunctions of interest. For instance, importantsubject-matter, taxonomic and geographic gaps re-main to be addressed in the ecological literature of

Ž .the NYCMA Flores et al., in review . On the otherhand, the NYCMA ecological literature also providesevidence to a long and rich history of biologicalscholarship in some North American urban areas thatis often glossed-over or underutilized in planningefforts.

Undoubtedly, the formulation of objectives toachieve planning goals in NYCMA and othermetropolitan areas can be guided by ecological prin-ciples and benefit from ecological perspectives. Yet,benefits are often not fully realized due to the contin-ued adoption of a now outdated ecological perspec-tive. Indeed, from a modern ecological point ofview, the metropolitan landscape looks much more‘alive’ than land-use maps or the older ecologicalframework would suggest. This landscape appears asa dynamic mosaic of highly interactive and heteroge-neous land units functionally linked at multiple scalesby the continued interplay of physical, social andbiological processes. These functional links sustainthe often differential, yet always limited availabilityof critical environmental benefits to residentsthroughout metropolitan areas. This paper has pre-sented and illustrated the application of five keyecological principles that can help planners addressthese functional links while striving to make oururban areas a more livable place for current andfuture generations to come.

Acknowledgements

The authors would like to acknowledge the Re-Ž .gional Plan Association New York, NY for our

research on the ecological aspects of planning in theNew York City Region and the Institute of Ecosys-

Ž .tem Studies Millbrook, NY for providing a highlyproductive environment for scholarly discussions onthe topic. Drs. J.M. Grove and R. Neville of theUSDA Forest Service’s Northeast Experimental Sta-tion, Durham, NH, offered valuable advice whilereviewing earlier drafts of this manuscript.

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