IGNATIEVA, Maria; STEWART, Glenn H; MEURK, C. (2010). Planning and design of ecological networks in urban areas

Selim Abdel CASTRO SALGADO, M. Arq. //Doctorado en Arquitectura y Urbanismo

Ficha de lectura

IGNATIEVA, Maria (2010): Planning and design of ecological networks in urban áreas

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Abstract

Urban ecological networks are defined differently in ecology, urban planning and landscape ecology, but they all have linearity and linkage in common. Early urban representations evolved from the constraints of deep ecological structure in the landscape to built elements that must work around natural linear obstacles—rivers, coast-lines, dunes, cliffs, hills and valley swamps. Village commons were linked by roads (…) Grafted onto this visual connectivity has been an awakened ecological understanding of spatial dynamics. The emergent notion of ecological corridor functionality provided support for green linear features, although initially this was based on untested theory. The idea of organisms moving along green highways seemed logical,but only recently has unequivocal empirical evidence emerged that demonstrates this functionality. Nevertheless, the main role of corridors may be to provide habitat rather than to act as connectors of nodal habitats.

Introduction

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(…) From a landscape ecology point of view, urban and rural ecological networks are especially important because, in these fragmented cultural landscapes, they may provide the only opportunity for corridors, connectivity and wildlife movement. Higher quality linkages between habitat patches or stepping stones can achieve this (Dramstad et al. 1996). Urban ecological networks, from urban planning and design angles, establish physical, visual and ecological connectivity between built-up areas of the city and surrounding natural areas and greenspaces

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(…) A variety of terminology is employed to describe Green areas. In urban planning and design, terms such as ‘‘urban open space’’, ‘‘urban green space’’ and ‘‘public open space’’ are very common. These include green áreas (playing fields, parks, gardens, etc.) as well as streets and squares. In landscape architecture literature, urban open space is seen as an integral part of urban frameworks and networks. (…)

Historical aspects

In the beginning there were clusters of dwellings, and then villages and pathways between them and the fields or woods where the villagers hunted or gathered. These embryonic urban settlements were much more constrained by natural features than today’s towns and cities. Thus, open space and especially wet, steep, unstable or rocky ground defined the locations of shelters and tracks. Open space was the matrix.

(…)

With the rise in population and technology, culminating in the Enlightenment and the Industrial Revolution, nature was almost swept aside and only the most intractable ground escaped development. This included rivers, coasts, cliffs, dunes and valley wet-lands. Industrial, commercial and urban built structures became the matrix and green space was reduced to disconnected threads. Sometimes commons or woods ended up enclosed within urban sprawl, and later these were formalised as parks, gardens, market squares and cemeteries; (…)

Early European visions

The history of creating, understanding and interpreting ecological networks goes back several centuries. Historically, urban green areas provided an early, perhaps serendipitous, focus on the design of what have become ecological networks. In early urban examples, they were expressed as explicitly visual and intuitively ecological improvements. In the sixteenth to eighteenth centuries, the generally understood function of green areas was the‘‘beautification’’ of cities and the associated improvement of urban spaces and public sanitation.

One of the first deliberate attempts at the directional design of green areas dates back to the sixteenth century in France, where Henry IV campaigned to improve Paris’s appearance, address issues of public sanitation and créate new green public spaces such as squares, gardens and alleys of trees. The principles of Baroque urban planning in eighteenth century Europe saw green areas (first of all private gardens of nobility and boulevards) as an important part of Baroque cityscape grandeur. The main emphasis was given to visual connection—the creation of axes and vistas. For example, the plan for the ‘‘urban renewal’’ of Rome (1585–1590), designed for Pope Sixtus V by Domenico Fontana, demonstrated quite clearly this penchant for strong axial organisation and street connectors.

In many other cities around the world, parks and gardens of royalty and nobility were planted in tree groves or with specimen trees in urban public squares, and these became important spatial as well as ecological nodes. Alleys of trees along main urban axes and some waterways can be also seen as prototypes of modern ecological corridors. For example, tree-lined alleys were a major contribution derived

from French formal gardens, and they subsequently provided a model for street tree planting and also the ‘‘socialisation of urban space’’ (Rogers 2001). Urban Parisian squares also contained important ‘‘green’’ spaces and served as significant convergences for urban life. Formal tree groves and park promenades created in seventeenth century Paris were inspirational for many European and later New World cities.

Here we can talk primarily about the visual connections that were the intended purpose of the constructed urban corridor-vistas and axes, allowing palace gardens to be connected and grandeur to be achieved through spatially unified urban ensembles. The most influential 3-km corridor-vista was developed by the French gardener Andre LeNotre in Versailles.

One very striking example was the plan of St. Petersburg (founded in 1703 by Peter the Great), where green areas in private gardens of the nobility created significant green ‘‘rings’’ along the Fontanka and Moika rivers (Dubyago 1963). Peter the Great was not only influenced by French urban examples but by Dutch ones as well, as especially seen in the series of concentric canals bordered by tree-lined promenades. Interestingly, Russian cities of the thirteenth to seventeenth centuries tended to have green areas within city boundaries due to the urban planning fashion of preserving a distinctive ‘‘village’’ character, where private houses always had adjacent gardens, and where there were open areas next to churches and quite extended areas of common meadows. Many European cities also incorporated the idea of creating tree-planted corridors that accentuate natural features, for example walkways along riversides in Renaissance Italian cities. Walkways and public promenades along rivers and canals in St. Petersburg and Amsterdam created important urban corridor systems (Searns 1995).

In Japanese cities, green areas next to temples and shrines were quite an important part of urban infrastructure, and were accessible to the common people. These areas had important religious significance and symbolic sacred meaning (Sorensen 2002). In modern Japanese cities, green areas of shrines and royal palaces have been revisited and newly interpreted as making a valuable contribution to planned ecological networks and the promotion of urban biodiversity.

All early urban green areas can be characterised as having a simple structure of tree and grass layers and a correspondingly limited number of species. Remnants of indigenous urban forests were commonly incorporated in the green infrastructure of many cities and towns (such as the oak woods in Moscow’s Botanical Gardens and Hampstead Heath in London). This was more a matter of accommodating something that was there and was not going away, rather than deliberately planning for such assets. While stressing the visual improvements afforded by green arteries and spaces, the fortuitous retention of ecological values and the evolution of an intuitive understanding or the adoption of natural history values of green areas should not be forgotten. These notions were gradually reinforced by mass-circulated literature and art that lovingly depicted these natural objects. One famous example of taking ecological and health values of green areas into consideration was Elizabeth I of England, who, in 1580, prohibited the construction of new buildings in a 3 mile wide belt around the City of London in an attempt to halt the spread of The Great Plague.

A significant development in the evolution of a modern vision of urban green areas and green works was the picturesque model for parks and gardens that arose in the eighteenth century: single trees, groups of trees, and groves scattered across broad expanses of mown or grazed meadow (Ignatieva and Stewart 2009).

This simplified ecological structure (allowing no natural regeneration or shrub layers) was declared to be ‘‘natural’’ and ‘‘ideal’’. The Picturesque landscape era was also influential in creating a new city model in England such as ‘‘rus in urbe’’ (country in the city), where parks, gardens, landscaped squares and promenade plantings along streets were used as a ‘‘softener’’ for hard cityscapes in the creation of ‘‘greener’’ cities. Urban green areas were visually and physically connected by systems of open grazed areas, gardens and road plantings. Out of this pre-existing functional farm structure arose the popular modern expression of the ‘‘lungs of the city’’. This supported new city design ideas and the preservation of large green areas in fast growing urban centres (Rogers 2001).

The democratisation of society during the Industrial Age of the nineteenth century resulted in the introduction of public parks as a crucial component of urban green areas. The science of urban planning was trying to solve severe problems associated with water and sewage supply and disposal and to accommodate pedestrian circulation. The era of the modern city began. Urban settlements were shaped according to new stricter regulations and planning codes brought about by the need to maintain liveable conditions for citizens and workers. Redesigning old cities by interpolating boulevard systems, planting miles of street trees, and connecting them to new landscaped public squares and old green areas or ‘‘openings’’ were done to improve the health and appearance of cities and fortuitously their ecological function. Baron Georges-Eugene Haussmann’s plan for the redevelopment of Paris literally revolutionized urban planning. The French term ‘‘boulevard’’ has been adopted as one of the most important concepts in the urban network vocabulary. The first boulevards—radiating from city bastion fortifications—were built in the seventeenth century, and this concept was subsequently transferred to peacetime roads that were specially designed for promenading and vehicular movements, giving a sense of power to both old and new world cities (cf. Meurk and Palang 2005 on the power of plants).

Some modern landscape ecology authors reinterpret and appreciate the essential ‘‘linkage’’ and movement functions of early urban axes and boulevards. They identify at least three main functions of such ‘‘grand corridors’’: movement, use and visual experience (…)

US parkways

By the end of the nineteenth century, the influence of Frederick Law Olmsted had spread through American cities and initiated the concept of parkways connecting different urban parks by systems of landscaped boulevards and roads with tree lines, sidewalks and bordering lawns (e.g. the Park and parkway systems in Buffalo, New York Stat and Riverside, California, Chicago’s park system in Illinois, Boston’s Emerald Necklace, and such systems in Denver and Portland; Beverage and Rocheleau 1995). A strong influence of the English Picturesque ideology on Olmsted also resulted in the connection of urban landscapes with rural scenery due to the rapid loss of countryside landscapes during urbanisation. This progressive aspect of Olmsted’s parkways was an attempt to reintroduce nature into the city.

The Parkway movement was closely related to the City Beautiful Movement, with its new boulevard systems, public green spaces with heroic sculptures and noble architecture. This movement clearly demonstrated the need for united park systems where natural landscapes played an important role. (…)

Greenbelt concept

The Garden City movements in England (at the end of the nineteenth century) and in Russia (1930s) were concerned with social and philosophical factors and were initially a socialist approach to the creation of a new generation of cities where all citizens had an equal opportunity to Access green areas (Ignatieva and Golosova 2009). Garden City models incorporated greenbelts and rings of green open spaces, carefully arranged green areas and recreational facilities as core considerations for achieving a new generation of urban settlements and healthy citizens. One of the very progressive outcomes of the Garden City movement was planned green areas and connectivity between urban, rural and natural landscapes.

Letchworth, England was the world’s first Garden City founded in 1903 by Ebenezer Howard. The planned Australian capital, Canberra, could be viewed as one of the largest cities designed and inspired by the Garden City movement. It incorporates so many green areas that it is often referred to as the ‘‘bush capital’’. The greenbelt idea which was pronounced so clearly in the ‘‘Garden City’’ concept was actually a continuation of Olmsted’s idea of buffering urban development. The concept of greenbelts as zones of green spaces surrounding the urban core, buffering and separating them from the countryside, was clearly expressed in Ebenezer Howard’s Garden Cities and London plan. His 5 mile strip of rural land was designed to limit the area of the city and protect valuable rural lands.

In the Soviet Union from 1917 to 1991, the concept of Garden Cities was developed further into Science Towns and the Ecopolis concept (Ignatieva 2002). The ideology behind these movements was the creation of comfortable conditions for living and to promote the creative activities of Soviet scientists, citizens and workers. Ecologically designed networks of green areas that were connected to and protected natural plant communities were a feature of these planned cities. A policy of providing máximum protection to existing vegetation, especially trees, was a core feature of the Ecopolis programme (Ignatieva 2002).

In contrast, urban grid schemes dominated the planned development of cities in the New World (Ignatieva and Stewart 2009). In the USA and New Zealand, the city grid model was improved by including special places for green squares and some public parks. For example in Christchurch, New Zealand, large open spaces in the centre of the city were dedicated to the development of green squares and a large public park with an associated botanical garden (Mihova and Ignatieva 2001; Faggi and Ignatieva 2009). Melbourne and Adelaide in Australia achieved similar inner city assets.

After World War II, redevelopment of the urban core and the rapid growth of suburbia characterised Western cities. Rapid technological development led to environmental crises, losses of valuable natural habitats, increased air and soil pollution, and soil sealing (Breuste 2007). The growth of ecology as a science (including urban ecology) and the reaction against urban environmental degradation resulted in a new vision for the planning and design of green areas as a whole system. Ian McHarg’s Design with Nature (1969) explored the opportunities provided by natural ecosystems to inform urban land planning strategies. This was furthered via the environmental movement of the 1970s to 1980s in Western countries, where the introduction of concepts of sustainability and Green urbanism (‘‘cities that are green and designed with functions in ways analogous to nature’’) called for new approaches to green urban infrastructure (Beatley 2000).

Many cities adopted the greenbelt idea. Citizens of cities such as Ottawa (Canada) (Taylor et al. 1995), St. Petersburg (Russia) (Kuznetsov and Ignatieva 2003), Portland (OR, USA), Adelaide (Australia), Milton Keynes and other new towns in Britain, as well as Dunedin (New Zealand) are proud of their extended greenbelts, which today comprise core areas for ecological networks and avenues for nature within the urban environment.

Some cities have developed green wedges or fingers which penetrate into or along the edge of the urban core,

for example Helsinki, Copenhagen, Stockholm and Christchurch. Greenbelts and green wedges have been

adopted in many Asian cities such as Beijing (Yang and Jinxing 2007), Shanghai (Zhang 1990) and Seoul (Bengston and Yeo-Chang 2005). More recently, greenbelts and similar concepts have been incorporated within a broader vision that includes all greenspaces, such as existing natural woodlands and other types of open green spaces (meadows, wetlands and farmlands, hedges, gardens, parks, boulevards, streams, rivers, canals, highways and railways, and street plantings).

Greenways become ecological networks

Grafted onto the visual connectivity and recreational value ascribed to green networks up until the last few decades has been the awakened ecological understanding of spatial dynamics. This resulted in the uncritical application of an ecological corridor concept. The idea of organisms moving along green highways seemed attractive and logical, but it has been difficult to prove this functionality.

A very significant contribution to the development of urban ecological networks has been the greenway movement in the USA and Canada and the green corridors movement in some European countries in the 1990s. Most proponents of these movements saw the greenbelt concept of the Garden City of Howard and the parkways vision of Olmstead as predecessors of the twentieth century vision of greenways (Zube 1995; Searns 1995). From the late 1960s to the early 1970s, greenways began to be used in the USA by cyclists and pedestrians as alternative trails to automobile-congested roads and highways. By 1995, there were more than 500 greenways in the USA that provided  access to open space and linked rural and urban spaces. Many greenways followed waterways, and this gave rise to greenways and ‘‘blueways’’. (…)

Modern US greenways employ various landscape ecology features (corridors, patches, matrix, and connectivity), landscape planning concepts (greenways at different spatial scales), landscape architecture principles (design structure, species composition, pedestrian, and bicycle circulation) and conservation biology theory. The essential unifying feature of greenways is their linear character; they are corridors of ‘‘various widths, linked together in a network’’ (Fabos 1995). Greenways are viewed as being important for the development of urban ecological networks, and, together with greenbelts and greenspaces, provide a comprehensive green infrastructure (Walmsley 1995)—or ecostructure—that underpins cities. The English landscape architect Tom Turner (1995) argued for special purpose greenways: parkways, blueways, paveways, glazeways, skyways, ecoways and cycleways.

The typical urban American green infrastructure is ‘‘...considered to comprise all natural, seminatural and artificial networks of multi-functional ecological systems within, around and between urban areas, at all spatial scales’’ (Tzoulas et al. 2007). The development of this new ecological networking vision was mainly a reaction to US urban sprawl and the dramatic loss of natural areas. It has been an approach that has especially highlighted the importance of the natural environment in urban land use planning decisions. The most recent Seattle greenspace programmes are aimed at designing integrated and connected green infrastructure (Open Space Seattle 2100 Project 2006). These programmes are based on recent sustainable urban practices such as low-impact development (LID), which incorporates swales, rain and green roof gardens, pervious surfaces and compact development practices.

Twenty-first century vision and outlook for urban ecological networks

The planning and design of ecological networks at the beginning of the twenty-first century is seen as multidisciplinary, involving all kinds of ‘‘potential’’ ecological spaces within the city. Remnants of the original natural vegetation are always prioritised in this networking as a unique source of native biodiversity and local identity (Florga ̈rd 2009; Swaffield et al. 2009). Planted urban woodlands, public parks and gardens, golf courses, cemeteries, waterways, wetlands, motorways and railways continue to be a focus for urban planners and landscape architects in their work on ecological networks and green infrastructure at a variety of scales. Residential private gardens, street plantings and cemeteries are increasingly viewed from the angle of core patches and sources of biodiversity in urban green mosaics. Neglected lands such as wastelands and industrial sites with spontaneous vegetation and brownfields (highly disturbed and usually toxic waste sites or derelict land) with contaminated soils are also included today as potentially valuable ‘‘stepping stones’’ in ecological networks (Hough 1995). There is growing interest in novel design solutions for sustainable cities, such as green roofs, living walls, and pervious pavements (Dunnett and Kingsbury 2004, Ignatieva et al. 2008a). These types of green space are also valuable elements in ecological networking, providing healthy environments and additional habitats for urban wildlife.

(…)

Private gardens can be very important stepping stones in an ecological network. They can enhance native biodiver-sity by minimising the sterile nature of conventional lawns and using native plants and ‘‘spontaneous’’ controlled wild vegetation (…) New models of urban ecological networks should respect, conserve and enhance natural processes. They will improve biodiversity, aesthetics, and cultural identity and be an important framework for creating sustainable cities (Ignatieva et al. 2008b).

(…) At the moment, developing countries are in the process of searching for their own approaches to creating green infrastructure and ecological networking that address their own local ecologies and cultural histories. They may also gain inspiration from developed countries that have long and rich histories of ecological network planning and design and can now provide well-established models.

IGNATIEVA, Maria; STEWART, Glenn H; MEURK, C. (2010). Planning and design of ecological networks in urban areas. Landscape and Ecological Engineering, (7), 17–25. https://doi.org/10.1007/s11355-010-0143-y