Urban Landscapes and Green Infrastructure
Summary and Keywords
Urban green infrastructure (GI) has been promoted as an approach to respond to major urban environmental and social challenges such as reducing the ecological footprint, improving human health and well-being, and adapting to climate change. Various definitions of GI have been proposed since its emergence more than two decades ago. This article aims to provide an overview of the concept of GI as a strategic planning approach that is based on certain principles.
A variety of green space types exist in urban areas, including remnants of natural areas, farmland on the fringe, designed green spaces, and derelict land where successional vegetation has established itself. These green spaces, and especially components such as trees, can cover significant proportions of urban areas. However, their uneven distribution raises issues of social and environmental justice. Moreover, the diverse range of public, institutional, and private landowners of urban green spaces poses particular challenges to GI planning. Urban GI planning must consider processes of urban change, especially pressures on green spaces from urban sprawl and infill development, while derelict land may offer opportunities for creating new, biodiverse green spaces within densely built areas.
Based on ample evidence from the research literature, it is suggested that urban GI planning can make a major contribution to conserving and enhancing biodiversity, improving environmental quality and reducing the ecological footprint, adapting cities to climate change, and promoting social cohesion. In addition, GI planning may support the shift toward a green economy.
The benefits derived from urban green spaces via the provision of ecosystem services are key to meeting these challenges. The text argues that urban GI planning should build on seven principles to unlock its full potential. Four of these are treated in more detail: green-gray integration, multifunctionality, connectivity, and socially inclusive planning. Considering these principles in concert is what makes GI planning a distinct planning approach. Results from a major European research project indicate that the principles of urban GI planning have been applied to different degrees. In particular, green-gray integration and approaches to socially inclusive planning offer scope for further improvement
In conclusion, urban GI is considered to hold much potential for the transition toward more sustainable and resilient pathways of urban development. While the approach has developed in the context of the Western world, its application to the rapidly developing cities of the Global South should be a priority.
Green Infrastructure (GI): Background and Definition
In the 21st century, for the first time in human history, more than 50% of the human population is living in urban areas (UN, 2010), compared to only 13% at the turn of the 20th century (UN, 2006). This figure is projected to rise to over 70% by 2050 (UN, 2010), corresponding to an increase of 2.8 billion people. More than 90% of the global gross domestic product (GDP) is generated in urban areas (UN, 2011).
Consequently, cities account for approximately 70%–80% of global energy demands and greenhouse gas emissions, and thus they are a major contributor to global warming (IEA, 2008). At the same time, urban areas are particularly vulnerable to the impacts of climate change, as often they are located in areas exposed to natural hazards such as coasts and river valleys, as well as having a high concentration of people and goods (EEA, 2012; Revi et al., 2014). Replacement of vegetation by built and hard surfaces and the consequent modification of natural processes in urban areas increase cities’ risks of suffering from climate change impacts (Lindley, Handley, Theuray, Peet, & Mcevoy, 2006). Pollution of air, soil, and water, heat stress from increased air temperatures, and noise are some of the environmental problems that can create serious threats to human health and well-being (Douglas, 1983; Bridgeman, Warner, & Dodson, 1995).
Urban form is a focal area of concern in this context. In particular, the low density and discontinuous and dispersed expansion of urban areas, also termed urban sprawl (EEA, 2006; Bruegmann, 2008), is responsible for the consumption of valuable farmland and natural areas, inefficient energy consumption such as increased transport demand, and expanded infrastructure service (Gayda et al., 2004). Compact city development has been widely discussed as an approach to counter these trends and promote sustainability (Jenks, Burton, & Williams, 1996; Häußermann & Haila, 2004; Westerink et al., 2012). However, the loss of vegetated and water surfaces through ongoing densification can further impair natural processes, consequently worsening environmental conditions and reducing the capacity of cities to adapt to climate change (Pauleit, Golding, & Ennos, 2005; Gill, Handley, Ennos, & Pauleit, 2007; Lemonsu, Viguié,Daniel, & Masson, 2015; also see Figure 1).
Green infrastructure (GI), a concept that emerged in the 1990s (Firehock, 2010), is considered as a promising approach to address these challenges (Benedict & McMahon, 2002; Ahern, 2007; Mell, 2009; Pauleit, Liu, Ahern, & Kazmierczak, 2011). The concept has its antecedents, such as green structure planning (Werquin et al., 2005) and greenway planning in the United States (e.g., Ahern, 1995; Walmsley, 2006). The roots of GI planning can be traced back even to the early 20th century and projects such as the Boston Fenways by F. L. Olmsted (Eisenman, 2013). Benedict and McMahon (2002, p. 6) define GI as “an interconnected network of green space that conserves natural ecosystem values and functions and provides associated benefits to human populations.” Furthermore, GI is considered a strategic approach to land conservation that “differs from conventional approaches to open space planning because it looks at conservation values and actions in concert with land development, growth management, and built infrastructure planning” (Benedict & McMahon, 2002).
Since its inception, the GI concept has been interpreted in different ways and applied at spatial scales ranging from national and transnational ecological networks, city-regional green structure networks, and local sustainable urban drainage systems (e.g., Lafortezza, Davies, Sanesi, & Konijnendijk, 2013; Rouse & Bunster-Ossa, 2013). In Europe, GI is promoted by European Union (EU) policy for both rural and urban areas (EC, 2013). Despite different understandings, GI basically aims to create multifunctional networks of green spaces. By providing multiple environmental, social, and even economic benefits to a limited space in urban areas, GI is envisaged as being able to compensate for the negative effects of urban density while contributing to quality of life and helping adapt cities to climate change. In Box 1, a definition of urban GI planning is presented that serves as the basis for the remainder of this article.
Box 1. Definition of Urban Green Infrastructure (GI) According to the EU-Funded Research Project Green Surge
Urban GI planning is understood as a strategic planning approach that aims at developing networks of green and blue spaces in urban areas that are designed and managed to deliver a wide range of ecosystem services.
Interlinked with GI planning on a landscape scale, urban GI planning aims at creating multifunctional networks on different spatial levels, from urban regional to city and neighborhood planning.
Due to its integrative, multifunctional approach, urban GI planning is capable of considering and contributing to a broad range of policy objectives related to urban green spaces, such as conservation of biodiversity, adaptation to climate change, and supporting the green economy.
Source: Davies et al. (2015).
The text will first consider urban landscapes as the object of GI planning. The potential of GI to achieve major aims of sustainable and climate resilient urban development will be explored in the following section. Next, core principles for the planning of urban GI will be presented. Finally, conclusions will be drawn for the further advancement of GI planning.
Planning of Urban Landscapes
Urban GI planning is concerned with the entire urban area and—on the city regional scale—it even includes natural areas, farmland, and forests between settlements. Understanding the character and dynamics of these urban and regional landscapes is a prerequisite for GI planning. Every urban landscape is unique, but three general points of relevance for urban GI planning shall be highlighted, as explored next.
Urban Green and Blue Spaces Can Cover a Significant Proportion of Urban Areas
The proportionate cover of discrete green spaces larger than 25 ha spanned from 2% to nearly 50% in 386 European cities in 2000 (Fuller & Gaston, 2009). The overall green cover can be still significantly higher when smaller green spaces are included as well. For instance, the total cover of vegetated and water surfaces reached 72% in the Greater Manchester, United Kingdom, conurbation, and it was still 59% when farmland on the fringe was discounted (Gill et al., 2008). This high green cover in urban areas is perhaps surprising as buildings and paved spaces often predominate visually.
Trees as one element of green spaces were estimated to cover 35% for all areas classified as urban in the contiguous United States (Nowak & Greenfield, 2012a). On average, their crown projected cover was found to be as low as 10% for all urban areas of the state of Nevada and as high as 67% for the state of Connecticut. However, the amount of green spaces does not only differ between cities, but they usually are also unevenly distributed within urban areas. In the case of Greater Manchester, United Kingdom, the proportionate cover of green and blue areas could be as low as 20% on average in densely built town centers and as high as 60% in low-density housing areas (Gill, 2006; also see Figure 2). This has also been confirmed by other studies (e.g., Escobedo et al., 2006; Davies et al., 2008; Landry & Chakraborty, 2009; Lindley & Gill, 2013; Krafft & Fryd, 2016). As will be shown in the following sections, both the quantity and the character of green spaces [e.g., the number of trees (species and individuals) and vegetation structure] matter in terms of their biodiversity potential and the provision of ecosystem services.
Urban Landscapes Are Heterogeneous
Urban landscapes comprise a diverse mosaic of patches that are distinguishable by their heterogeneous composition of built and green spaces and highly diverse use and management patterns. Consequently, a variety of green spaces can be found within the urban fabric (e.g., Swanwick, Dunnett, & Woolley, 2003; Cvejić et al., 2015). These range from green on buildings such as balconies, green roofs, and walls; to green near built structures, such as street greening, railway banks, house gardens, playgrounds, different types of parks, institutional green spaces, cemeteries, sports facilities, and allotments and community gardens; to more open kinds of green space like farmland and horticulture, woodlands and shrublands, abandoned lands, quarries, and dunes. Also included are different kinds of blue spaces such as lakes, ponds, rivers, canals, and the sea coast, which can also be found within the administrative boundaries of urban areas. This variation implies that green networks may be a slightly deceptive term; just how different types of green spaces are connected and interact is far from fully understood.
Overall, urban green is thus much more than public green space, even if the latter may be very important for a city’s administration and its citizens. Sometimes green space can be the result of citizen activism or a community project such as urban farming or a restoration project (Buijs et al., 2016). Urban areas are also highly heterogeneous in terms of the variety of public, institutional, and private landowners. For five English cities and towns, it was estimated that between 22% and 27% of all green spaces comprised private gardens (Loram, Tratalos, Warren, & Gaston, 2007). Moreover, not all green spaces have been created intentionally, but these spaces are often remnants of the landscape that has been there before or are a by-product of urban dynamics (e.g., forests, wetlands, or open rocks). Also, management can create many differences between superficially similar areas, such as cemeteries and parks (Andersson, Barthel, & Ahrné, 2007).
From an ecological perspective, it has been shown to be useful to group urban green and blue spaces into four broad categories according to their origin: remnants of (a) natural and (b) cultural landscapes, both of which can consist of woodlands, river corridors, arable land, and hay meadows; (c) designed green spaces such as parks and gardens; and (d) derelict land where successional vegetation has established itself (i.e., urban wilderness; Kowarik, 2005; also see Figure 3).
Large variations in land uses and green spaces offers potential for GI planning to support (and even increase) biodiversity, to fulfill various environmental functions, and to meet specific human demands. On the other hand, it also brings many challenges, since approaches to the development of urban GI strategies need to account for diverse landownership, a variety of stakeholders, and legal and institutional complexity.
Urban Areas Are Dynamic
Current urban development includes processes of urban expansion, densification within already built areas via infill development, and population decline or restructuring leading to land abandonment, which sometimes occur simultaneously in different areas of the same city (e.g., Kabisch & Haase, 2012). These dynamics result in complex, sometimes unpredictable changes in the cover and composition of green space.
Expansion of urban areas, for example, has led to a major loss of farmland and natural areas between 1990 and 2000 in the countries of the European Union (EEA, 2006), while the same period saw no significant change in the average cover of green spaces larger than 25 ha within 202 urban areas (Kabisch & Haase, 2012). However, the proportion of green spaces of this size declined in cities with a dwindling population. Interestingly, residential areas grew regardless of population increase or decline, with the increase of small households being an important driver (Kabisch & Haase, 2012). Yet population loss may also lead to land abandonment within urban areas and create opportunities for new green spaces (Haase, 2008).
Green space dynamics can also be observed on a finer scale. A study of tree cover change in 20 cities of the contiguous United States showed that all but 1 of the cities had seen reductions in the cover of trees and large shrubs, regardless of whether their population had grown or declined (Nowak & Greenfield, 2012b). Sometimes the process of change follows socioeconomic boundaries: in Merseyside, United Kingdom, with Liverpool at its center, loss rates were highest in affluent areas because of infill densification (Pauleit et al., 2005).
Changes in green space are thus caused not only by broad trends such as urban growth, but also by small changes that, in sum, can lead to significant alterations of the physical makeup of green space and its distribution in urban areas. Moreover, the management of green spaces may change their appearance and functionality due to changing values, preferences, and resources. These characteristics and dynamics need to be understood if we are to identify windows of opportunity for GI planning and develop approaches that can respond to the specific challenges of urban expansion, densification, and decline.
Aims for Urban Green Infrastructure Planning
This section explores how GI can contribute to meeting major aims for sustainable urban development within four main fields of concern that can contribute to human well-being: (a) urban biodiversity; (b) environmental quality, the ecological footprint, and climate change; (c) social cohesion; and (d) the green economy (Figure 4). For instance, urban GI promotes citizens’ physical and mental well-being (e.g., Fuller, Irvine, Devine-Wright, Warren, & Gaston, 2007; Tzoulas et al., 2007; Coutts & Hahn, 2015; Coutts, 2016) via the provision of four types of ecosystem services (see Braat, 2017 for urban ecosystem services, see, e.g., Bolund & Hunhammar, 1999; Tratalos, Fuller, Warren, Davies, & Gaston, 2007; Tzoulas et al., 2007; Fryd, Pauleit, & Bühler, 2011; Roy, Byrne, & Pickering, 2012; Gómez-Baggethun et al., 2013). They include supporting (e.g., nutrient cycles), provisioning (e.g., food, timber), regulating (e.g., climate moderation), and cultural (e.g., recreation) services.
Conserving Urban Biodiversity
Urban expansion is considered to be one of the key drivers for the loss of native biodiversity (McKinney, 2002), particularly when it takes place close to (or even in) global biodiversity hot spots and protected areas (McDonald et al., 2009; Seto, Güneralp, & Hutyra, 2012; Seto, Parnell, & Elmqvist, 2013). Habitat destruction, as well as the fragmentation and degradation of remaining habitats, are main causes. Nonnative species introduced to urban areas have been associated with risks such as threats to native biodiversity in the surrounding countryside, biotic homogenization, and negative human health impacts, such as producing toxic pollen (see overview in Kowarik, 2011, p. 1980, table 4). At the same time, it is also increasingly recognized that biodiversity within urban areas can be high and exceed that of intensively farmed countryside in the surrounding area (Müller, Ignatieva, Nilon, Werner, & Zipperer, 2013). In some cases, this is because even dense cities contain seldom-visited areas that can offer refuge for sensitive species (e.g., rooftops, railway banks, and gaps between buildings), but cities may also offer alternative habitats for rare and threatened species (Sushinsky, Rhodes, Possingham, Gill, & Fuller, 2013). An abundance of urban biodiversity provides an opportunity for citizens to get into contact with nature as a source of well-being and health (Coutts & Hahn, 2015).
The variety of built and green spaces that can be found in urban areas is a main reason for urban biodiversity. Novel habitats (i.e., habitats that do not have a precedent in nonurban landscapes, such as developing communities on abandoned industrial land) may particularly enrich and add to the distinctiveness of urban biodiversity (Kowarik, 2011; Bonthoux, Brun, Di Pietro, Greulich, & Bouché-Pillon, 2014). The location of cities in biodiversity-rich areas; altered environmental conditions such as increased temperatures, which may favor the survival of species outside their natural range; the introduction of species from other regions; a lack of hunting; and sometimes abundant food and other resources can further explain this overall species diversity (Gilbert, 1989; Kühn, Brandl, & Klotz, 2004; Kowarik, 2011). The response of species groups (plants, birds, invertebrates, reptiles, etc.) and individual species to urbanization can vary, though (McKinney, 2008; Faeth, Bang, & Saari, 2011).
Considering the dynamic nature of natural ecosystems, urban biodiversity cannot be protected only by the preservation of remnants of them. Connectivity with similar habitats and the complementarity of the surrounding areas, as well as distance from the urban fringe, are factors at the city level that can influence biodiversity (Zerbe, Maurer, Schmitz, & Sukopp, 2003; Angold et al., 2006; Sandström, Angelstam, & Mikusinski, 2006; Colding, 2007; Kowarik, 2011; Matthies, Rüter, Prasse, & Schaarschmidt, 2015). However, at the city level, overall cover of vegetated areas may be more important for biodiversity than green space connectivity (Turrini & Knop, 2015), and many species may respond more to the quality of individual green spaces (Angold et al., 2006). At the site level, the size, form, composition, and management of green spaces are important factors influencing biodiversity (Gilbert, 1989; Angold et al., 2006; Knapp, Kühn, Mosbrugger, & Klotz, 2008; Matthies et al., 2015).
Especially under conditions of urban growth, biodiversity conservation needs to be mainstreamed into urban GI planning for all kinds of seminatural and artificial green spaces. For this purpose, multiscale planning and management of urban GI—from the city regional to the site level—is required to account for the scales at which species and ecological communities operate (Hostetler, 1999; Melles, Glenn, & Martin, 2003). Here, a major challenge lies in the fact that administrative boundaries rarely coincide with the boundaries of ecological systems (Borgström, Elmqvist, Angelstam, & Norodom-Alfsen, 2006). However, some cities are able to help counter this challenge through leadership by intergovernmental task forces or nonprofit organizations, for example, which can influence change on special issues (Buizer et al., 2015).
Improving Environmental Quality, Reducing the Urban Ecological Footprint, and Climate Change Adaptation
The capacity of green and blue areas to moderate urban climates has become of particular interest in the face of climate change (Bowler, Buyung-Ali, Knight, & Pullin, 2010; Fryd et al., 2011). On average, annual air temperatures in urban areas are already elevated by 1–3°C compared to the surrounding landscapes. On warm summer days, the difference can be as high as 5–12°C (Oke, 1987). This urban heat island (UHI) effect is due to changes in the radiative energy balance that are mainly caused by a changed albedo, increased heat reradiation from built and paved spaces, and a higher heat storage capacity (Oke, 2011). Heat release from combustion processes also adds to the UHI effect. More frequent and intense heat waves caused by climate change will have particularly negative consequences for human health and well-being in urban areas due to the UHI (Gabriel & Endlicher, 2011). Moreover, air quality may deteriorate when it gets hotter in cities (USEPA, 2001). Vegetation can reduce these effects mainly by evapotranspiration and shading.
Air temperatures in large urban parks can be similar to a situation outside the city; i.e., they can be 1–3°C lower than their surrounding built environment (see Bowler et al., 2010, figure 1). They are thus cool islands for urban dwellers on hot summer days. Moreover, their cooling effect extends to the nearby built-up areas (Upmanis, Eliasson, & Linqvist, 1998; Bowler et al., 2010). Both effects are related to park size. While cooling effects may extend to more than 1 km for large parks, they are mostly restricted to a much narrower zone for smaller parks, depending on the topography and porosity of surrounding built-up areas. Therefore, cooling by a dense network of medium-sized and smaller green spaces that permeate built areas may be more effective than a single large park. The importance of overall vegetation cover and volume for urban cooling has been supported by studies based on modeling, remote sensing, or both (Huang, Akbari, Taha, & Rosenfeld, 1987; Li, Zhou, Ouyang, Xu, & Zheng, 2012). Moreover, results from a modeling study for the Greater Manchester (United Kingdom) conurbation suggest that the overall cover of green and blue spaces, including that of private spaces, is decisive for moderating projected temperature increases under climate change (Gill et al., 2007).
Besides mitigating heat, green spaces can also reduce stormwater runoff. The overall cover of green areas, but also specific features such as vegetation structure and tree cover, need to be taken into account (Xiao & McPherson, 2002, Wang, Endreny, & Nowak, 2008; Liu, Chen, & Peng, 2014). Two species of eucalyptus in Melbourne, Australia, reduced the annual amount of rainfall reaching the ground surface by up to 45% (Livesley, Baudinette, & Glover, 2014), while the reduction was 27% for an evergreen oak tree in California, United States (Xiao, McPherson, Ustin, Grismer, & Simpson, 2000). The capacity for stormwater management can also be effectively enhanced by integrating sustainable urban drainage systems such as swales, infiltration trenches, and rain gardens into green spaces (Villarreal et al., 2004; Dietz, 2007).
Other research has assessed the capacity of green spaces to sequester and store carbon and thus contribute to climate change mitigation (e.g., Nowak, 2002; Strohbach & Haase, 2012; Velasco, Roth, Norford, & Molina, 2016) or the filtering of air pollutants (Nowak, 2002). However, these effects appear to be quite limited when compared to overall emission levels of greenhouse gases and air pollutants (e.g., Nowak, 2002; Setälä, Viippola, Rantalainen, Pennanen, & Yli-Pelkonen, 2013; Russo, Escobedo, Timilsina, & Zerbe, 2015). For instance, the overall amount of carbon sequestered by urban trees has been estimated to be at 1%–3% of annual greenhouse gas emissions of cities (Nowak, 2002; Escobedo, Varela, Zhao, Wagner, & Zipperer, 2010; Crawford & Christen, 2015). Concerning the filtering of air pollutants, evidence points to a similar direction (e.g., Nowak, 2002). However, the capacity of woody vegetation to absorb different types of air pollutants via deposition or stomatal uptake depends greatly on a number of features such as vegetation structure and species traits such as evergreen or deciduous, leaf area, leaf surface and form, and physiology (Grote et al., 2016). It should be noted that trees can also become emitters of air pollutants (Calfapietra et al., 2013; Grote et al., 2016; see also “Concluding Remarks”).
While the direct effects of carbon sequestration may be small, indirect effects can be of greater importance. For example, a modeling study showed that trees can reduce the energy demands of houses in the United States by 10%–15% annual cooling demand (McPherson & Rowntree, 1993) when trees are optimally located. In addition, and perhaps even more important, may be energy savings made by switching from car based transport to more sustainable modes of mobility such a walking and cycling. In the City of Copenhagen, Denmark, 45% of all journeys made to work and education are made by bicycles. Strong investment into green corridors for walking and cycling in an attractive environment play a crucial role in this strategy (City of Copenhagen, 2014).
The generation of provisioning ecosystem services by urban GI offers further potential for reducing the ecological footprint; e.g., via local provision of food from urban agriculture, by composting of biowaste from green space maintenance, or by water supply (Barthel, Parker, & Ernstson, 2013; Mettepenningen, Koopmans, & Van Huylenbroeck, 2014; Rodríguez-Rodríguez, Kain, Haase,Baró, & Kaczorowska, 2015). As with many of the other services discussed here, climate change mitigation highlights that not only quantity and quality of green spaces matter; their location and the overall spatial configuration of GI also strongly influence the magnitude of the services.
Promoting Social Cohesion
The term social cohesion means the extent to which a community shares values, cooperates and interacts (Beckley, 1994). Although more research is needed on the subject, green spaces can potentially enhance social cohesion by providing places for increased social interactions. These can range from observing to active engagement of different green-space visitors in a diverse range of activities (Gobster, 1998; Kuo, Sullivan, Coley, & Brunson, 1998; Kweon, Sullivan, & Wiley, 1998; Kazmierczak, 2013; Krellenberg, Welz, & Reyes-Päcke, 2014; Peters, Elands, & Buijs, 2010). They can also strengthen the sense of place and community identity (Peters et al., 2010). Not least, public parks can facilitate intercultural/interethnic exchange and thus provide an important tool for supporting the integration of immigrants, as a study of five parks in the Netherlands has shown (Peters et al., 2010). However, nature areas outside the city were hardly visited by people of non-Dutch origin. Thus, the type and location of green spaces are important considerations with regard to social cohesion.
Proximity to where people live and accessibility, including free access and inexpensive and reliable public transport, facilitates green-space use, and hence social cohesion. Moreover, green spaces should offer diverse facilities and allow a variety of experiences. Visits are longer and contacts more intense in larger, higher-quality green spaces that offer multiple events, activities, and other reasons for contact, such as shared amenities (Peters et al., 2010; Kaźmierczak, 2013; Kemperman & Timmermans, 2014). However, small green spaces “on the doorstep” are also very important for daily outdoor activities. There is broad evidence (for instance, see Coutts, 2016; Coutts & Hahn, 2015) that regular exposure to green space improves physical and mental health. Therefore, urban dwellers should have access to quality green spaces in a distance that can be reached within approximately 5 minutes’ walking distance from home (i.e., about 300 m) (e.g., Coles & Bussey, 2000). While citizens may prefer to visit larger and higher-quality green spaces somewhat farther from nearby green spaces (Schipperijn, Stigsdotter, Randrup, & Troelsen, 2010), this distance rule still provides an important target for urban GI planning.
Not least, green spaces should be well maintained and free from vandalism and other signs of neglect that may make visitors feel unsafe (Kuo et al., 1998; Rall & Haase, 2011). Green spaces that invite active, diverse uses and leave room for self-organization and creative activities increase the likelihood that people will take ownership of spaces and feel safe, as well as enhancing human well-being (Mean & Tims, 2005; Colding & Barthel, 2013). Activities such as urban gardening that bring people together for a common purpose offer particular potential for strong interaction across cultural and ethnic backgrounds (Colding & Barthel, 2013; Leikkilä, Faehnle, & Galanakis, 2013).
Making the Shift Toward a Green Economy
From the early days of green-space planning in the industrial city of the 19th century, the economic dimensions of urban green space have been recognized (e.g., Taylor, 2000). Today, there is widespread evidence demonstrating the relationship between prices of land, homes, and rents and proximity to green spaces (Brander & Koetse, 2011; Sunderland, 2012). For instance, a study of house transactions in three Dutch cities established that houses were up to 28% more expensive when they offered a pleasant view of water or open spaces (Luttik, 2000). In Finland, on the other hand, increase of distance to the nearest forest area by 1 km led to an average decrease in the market price of a dwelling by 6% (Tyrväinen & Miettinen, 2000). Based on a meta-analysis of 20 contingent-valuation studies, Brander and Koetse (2011) established an even stronger decline of house prices of 0.1% with a 10-m increase in distance from a park. A systematic review by Konijnendijk, Annerstedt, Nielsen, and Maruthaveeran (2013) presents results from further studies of this kind. Interestingly, they also report on studies where proximity to green spaces resulted in a decline of house prices because of elevated crime rates (e.g., Troy & Grove, 2008) or noise and unruly behavior by users (Chen & Jim, 2010). However, such results are highly context sensitive, and confounding variables make it difficult to establish clearly causal relationships between the provision of green space and property values.
The overall image of green and clean cities and neighborhoods increases their competitiveness (Jiang & Shen, 2010). In green city branding and awards such as the European Green Capital Award, the provision of green space is one of the dimensions. In the draft strategy for urban GI of the Greater Manchester conurbation, this economic role of green networks is clearly recognized (TEP, 2008) by aligning investments into being green with the designation of economic growth hubs. In an increasing number of business improvement districts (BIDs), especially in North America and the United Kingdom, business-led greening initiatives have been initiated. However, a recent study in Denmark and Singapore showed that green city branding is a biproduct of global neoliberal discourses and selectively presents images of the city’s social and green character (Gulsrud, 2015).
Green space can generate direct economic benefits, such as by providing food and timber, as a destination for tourism (e.g., to visit a garden exhibition or a spectacular new park such as the High Line in New York), or by providing attractive locations for enterprises (e.g., cafés) (Watkins & Wright, 2007; Saarev, 2012; Cianga & Popescu, 2013; Pribadi & Pauleit, 2016). Green space may also lay the groundwork for cooperatives and foundations that are not only interested in financial gains, but also in developing human resources to engage with wider social and environmental problems (Desa, 2012; Battilana, Lee, Walker, & Dorsey, 2012).
Green space also contributes to the economy by saving costs. Improved health from regular contact with green spaces in cities reduces costs in the health sector. Physical activity in parks was estimated to reduce costs of health care by $4 million, to $69.4 million per year, in 10 U.S. cities and counties (Wolf & Robbins, 2015). Regulation of local climate, not least mitigation of the increasingly frequent heat waves, has a direct bearing on health and well-being (Carter et al., 2015).
Green space can reduce the risks of damage, such as from natural hazards such as riverine flooding by storing the water in functional floodplains or by securing availability of food from urban agriculture in times of crisis. These “insurance values” (Gómez-Baggethun & Barton, 2013; Green, Kronenberg, Andersson, Elmqvist, & Gómez-Baggethun, 2016) are particularly important in the rapidly growing cities of the Global South, characterized by a high degree of poverty and informality on the one hand and weak institutional capacities on the other (Herslund et al., 2016). However, as Hurricane Katrina and Superstorm Sandy have shown in the United States, this is a very real risk, with potentially massive economic impact in the Global North as well (e.g., Temmerman et al., 2013).
Principles of Urban Green Infrastructure Planning
To successfully plan and implement a high-performing urban GI capable of delivering multiple benefits, adoption of a set of principles is key. Despite variations in the literature, commonly presented principles are shown in Table 1 (adapted from Davies et al., 2015). Four of the presented principles relate to the content of planning, while the other three principles refer to the planning process.
Table 1. Principles of Urban GI Planning
Principles of Planning Content
▪ Network/connectivity: Urban GI planning aims for added values derived from interlinking green spaces functionally and physically.
▪ Multifunctionality: Represents the ability of urban GI to provide several ecological, sociocultural, and economic benefits concurrently. It means that multiple ecological, social, and economic functions, goods, and services shall be explicitly considered instead of being a product of chance. Urban GI planning aims at intertwining or combining different functions to enhance the capacity of urban green space to deliver valuable goods and services. The ecosystem services concept is suggested for operationalizing multifunctionality.
▪ Gray-green integration: Urban GI planning considers urban green as a kind of infrastructure and seeks the integration and coordination of urban green with other urban infrastructures in terms of physical and functional relations (e.g., built-up structure, transport infrastructure, water management system).
▪ Multiscale: Urban GI planning can be considered for different spatial levels ranging from city-regions to local projects. Urban GI planning aims at linking different spatial scales within and above city-regions.
Principles of the Planning Process
▪ Strategic: Urban GI planning is based on long-term spatial visions supplemented by actions and means for implementation, but it remains flexible over time. The process is usually led by the public sector, but that does not mean that nonstate actors are excluded (see The “Socially inclusive” point).
▪ Interdisciplinary and transdisciplinary: Urban GI planning aims at linkages between disciplines, as well as between science, policy, and practice. It integrates knowledge and demands from different disciplines such as landscape ecology, urban and regional planning, and landscape architecture, and it is developed in partnership with different local authorities and stakeholders.
▪ Socially inclusive: Urban GI planning aims for collaborative, socially inclusive processes.
In the following discussion, four of these principles at the core of urban GI planning will be further explored. As can be seen from Table 2, these four principles contribute in different ways to addressing the main policy challenges presented previously.
Table 2. Urban GI Principles Each Contribute to a Variety of Urban Challenges
Urban GI Planning Principles
Habitat provision;, promotion of native plants as one of the cobenefits of green-gray solutions
Ecological functions and habitat provision as integral part of planning for multifunctionality
Networks for ecological connectivity
Fostering awareness for biodiversity values
Environmental, Ecological Footprint and Climate Change Adaptation
Green-gray measures for, e.g., flood retention, urban cooling, and reduction of energy consumption
Regulating services that improve quality of air, water, and soils; enhance climate change adaptation
Connected green structures that enhance natural ventilation and cooling and environment-friendly mobility
Inclusion of vulnerable groups in urban GI planning
Consideration of usability and amenity values of integrated urban GI measures to promote social cohesion
Urban GI provision for different demands and needs
Provision of equitable access to urban green spaces
Empowerment of citizens through collaborative urban GI planning; securing the needs and demands of vulnerable and less vocal groups are considered
Reduced costs of gray infrastructure management through combined green-gray systems; avoided costs through mitigation of environmental hazards
Cost-effective urban GI solutions by providing multiple benefits in the same space
Promotion of sustainable transport systems and green corridors (walkability and bikeability)
Promotion of a social and green economy, cocreation and management of urban green
Source: Hansen et al. (2016, adapted).
The principle of green-gray integration requires that planning of the urban GI is integrated and coordinated with other urban infrastructures in terms of physical and functional relations (Hansen, Rall, & Pauleit, 2014). Especially in relation to climate change adaptation, GI can play an important role in enhancing and improving conventional monofunctional infrastructures such as a centralized sewage system. Pressure on conventional sewage systems can be alleviated by local retention, purification, and infiltration of stormwater runoff (Wang, Eckelman, & Zimmerman, 2013; Tao, Bays, Meyer, Smardon, & Levy, 2014). Bioswales, raingardens, and retention basins, but also roof gardens and permeable pavements, are elements that are part of sustainable urban drainage systems (Hoyer, Dickhaut, Kronawitter, & Weber, 2011; Imran, Akib, & Karim, 2013). These techniques also offer the potential for increasing usability, aesthetic, and habitat values of urban green space (Backhaus & Fryd, 2013; Loperfido, Noe, Jarnagin, & Hogan, 2014). They may thus contribute to meeting the objectives of biodiversity protection and social cohesion (Box 2).
Importantly, results from economic evaluation suggest that implementing approaches of local stormwater management via sustainable urban drainage systems (SUDS) can be more cost-effective than conventional “gray” solutions (Montalto et al., 2007; Spatari, Yu, & Montalto, 2011; Odefey et al., 2012). In the United States, GI for stormwater retention has experienced a boost after introduction of Phase II of the National Pollutant Discharge Elimination (NPDES) permit program in 1999 to meet federal Water Quality Act (1987) requirements. Led by front-runner cities such as Seattle (Pauleit et al., 2011; Hansen et al., 2014), more and more cities have implemented green stormwater infrastructure. For instance, for the U.S. city of Philadelphia, it was estimated that expanding the conventional sewage system would have cost $6 billion to comply with the new legal requirements, while implementation of GI for stormwater management would cost only $1.2 billion over 25 years (Green, 2013). In addition to reducing costs for stormwater treatment, Philadelphia’s GI will provide additional benefits (e.g., carbon sequestration, air quality improvement, and excessive urban heat reduction). Not least, greening is estimated to increase property values by $390 million over 45 years. In addition, construction of green roofs and other measures would create 250 jobs (Green, 2013).
Stormwater management is the most prominent example, but there are also other fields for the integration of gray and green infrastructure, such as bike paths in green corridors, developing habitat corridors along power lines or green corridors for natural ventilation of cities, and green façades and roofs for cooling of buildings and simultaneous power generation via solar panels (Oberndorfer et al., 2007; Wise, 2008; Dill et al., 2010). Moreover, integration of public health and GI planning is an emerging issue (Penny, 2014; Coutts & Hahn, 2015; Coutts, 2016). Integrating and aligning different infrastructures also may reduce to some extent the risk of these systems running perpendicular to each other and creating issues such as fragmentation.
Box 2. Green-Gray Integration for Stormwater Management—The Case of Malmo, Sweden
Malmo is Sweden’s third-largest city, with 300,000 inhabitants. The city has successfully gone through a transition from a harbor and industrial town to a service-based economy. Recent growth has led to an increase of built and paved spaces, which generates more stormwater.
As there have been incidents of severe local flooding, GI development for stormwater management has become an important topic for the City of Malmo. The Malmo Water Plan, which is currently in progress, can build on experiences at the project level and stormwater policies since the late 1980s (Stahre, 2008).
The conversion of the former Western Harbour into the new residential neighborhood Bo01 during the building exhibition in 2001 and the retrofitting of the then-rundown housing area of Augustenborg (Figure 5) have become well-known examples for integration of sustainable urban drainage systems into green spaces (Stahre, 2008). While most GI for stormwater management is implemented in urban extensions, the Augustenborg example shows that it can also be an important tool for upgrading of built areas.
Multifunctionality refers to the ability of urban GI to provide several ecological, sociocultural, and economic benefits (Kambites & Owen, 2006; Ahern, 2011; Pauleit et al., 2011; Madureira & Andresen, 2013; Sussams, Sheate, & Eales, 2015). The notion of multifunctional green space is not new; it mostly has been related to social functions, such as providing for different recreational uses. The concept of ecosystem services is one approach to systematically considering a broad range of services (Ahern, Cilliers, & Niemelä, 2014; Hansen, Rall, & Pauleit, 2014) and thus developing urban GI that concurrently contributes to a diversity of aims, including biodiversity conservation, climate change adaptation, and social cohesion. Multifunctionality, however, extends beyond the idea that green space inherently provides a multitude of ecosystem services in an optimal combination.
Skillfully combining different functions or services in both space and time is a key to creating a well-performing GI in densely built urban areas, and is likewise a key idea underlying the concept of multifunctionality (Hansen & Pauleit, 2014). For instance, several functions may be provided on one green space at the same time, such as a green space being a place for recreation, serving as a habitat, and providing a cool island in an otherwise hot city. Also, different green spaces with different functions may interact in a green-space network to provide multiple functions (Barker, 1997; Landscape Institute, 2009). A green space may have a particular function at a certain time (e.g., as a sports playground while serving as stormwater retention during strong rains). Urban GI planning aims to increase these different benefits while avoiding trade-offs and disservices. An example of the latter would be the conflict between biodiversity conservation and human recreation (Chace & Walsh, 2006; Marzluff & Rodewald, 2008).
Tools and indicators have been developed for multifunctionality assessment. For instance, in Liverpool’s GI strategy, 28 functions were assessed for 18 green-space types (LCC, 2010). These functions relate to regulating ecosystem services such as water interception and storage or carbon sequestration to cultural services such as recreation and aesthetic and educational functions. Overlaying provision and demand allowed one to identify areas where needs were well met, as opposed to areas in deficit.
Planning for multifunctionality needs to build on an understanding of different human demands, and it should strive for universal access to multiple green-space services, regardless of socioeconomic status. Groups and individuals will have different preferences, and multifunctionality is one way of making sure that these needs are met. Otherwise, GI planning may rather reinforce environmental injustice in cities (Wolch, Byrne, & Newell, 2014; Krafft & Fryd, 2016 and thus be counterproductive for the aim of contributing to social cohesion.
Hansen and Pauleit (2014) and Ahern et al. (2014) suggested stepwise approaches for multifunctional and adaptive planning of urban GI, respectively. In both frameworks, ecosystem services play a central role in assessing and monitoring the capacity of green space and networks as GI components to provide multiple benefits and balance the provision of ecosystem services with human demand, in so doing providing information for setting priorities and defining actions in urban GI planning. Both approaches stress the need to broadly consider stakeholder preferences in ecosystem services assessment, whether for GI planning or adaptive management of its components.
Connectivity aims to link individual green spaces spatially and/or functionally. Green corridors and green rings have already been implemented in urban planning since the early 20th century (in cities such as Hamburg, Cologne, and Copenhagen, to give just a few examples). The purpose was mainly to define clear boundaries for urban growth, to provide access to and enhance movement within green spaces for recreational purposes, but also to provide ventilation for inner cities to improve air quality (e.g., Warsaw, as discussed in Szulczewska & Kaliszuk, 2005). Landscape ecology, on the other hand, stresses the need to improve connectivity between habitats so that the movement and dispersal of plant and animal species via corridors and a network of “stepping stones” and “core areas” is facilitated (Jongman, Külvik, & Kristiansen, 2004; Crooks & Sanjayan, 2006). Such connecting structures should counter the negative effects of habitat loss, fragmentation, and consequent isolation in otherwise intensively used landscapes. Another aspect in connectivity is to look for how various ecosystem functions and services (e.g., pollination) depend on connectivity in urban landscapes (Colding, 2007). The “Patch-Corridor-Matrix” model has been very influential in shaping this view on structural and functional relationships in landscapes, also in urban areas (Baudry & Merriam, 1988; Forman, 1995).
Ecological connectivity may be achieved by adopting a whole-landscape perspective (Taylor, Fahrig, & With, 2006). For instance, dense stands of old trees in private gardens and street trees can enhance the dispersal of birds (Goddard, Dougill, & Benton, 2010). A multiple-scale perspective needs to be introduced here as well, in order to account for activity ranges of different animal species and their relations in food webs (Hostetler, 1999). Different green space types offer different resources; through strategic planning of different combinations of green spaces in a well-conceived GI, both greater biodiversity and stronger functional linkages between the spaces can be supported.
Similarly, social connectivity for humans has been stressed (Box 3). Green-space networks offer a greater number and variety of different recreational opportunities (Tzoulas & James, 2010). In the United States, greenways are strategically planned for multiple human benefits (e.g., Bryant, 2006). Such greenways may include diverse landscapes with scenic quality, and they may even affect people living at a distance due to their visual qualities. Also, connectivity between public green spaces and everyday surroundings of where people are living may positively influence social relations between neighbors and thus contribute to social cohesion as a primary aim of urban GI planning (Shafer, Lee, & Turner, 2000).
The role of distance to green spaces for their use is well-established (e.g., Gobster, 1998; Coles & Bussey, 2000; Van Herzele & Wiedemann, 2003; Moseley, Marzanoa, Chetcutia, & Watts, 2013) and has resulted in standards and guidance on travel distance to public green spaces (Moseley et al., 2013). However, ease of access, attractiveness of the park and of the travel route (e.g., whether it is well greened and free from barriers and environmental pollution), and the destination are also important determinants of green-space use (e.g., Giles-Corti et al., 2005; Schipperijn et al., 2010; Sarkar et al., 2015). Therefore, a well-connected path network that allows mobility by bike and walking away from busy roads is also considered to promote environmental friendly mobility.
Box 3. The Role of Connectivity in Berlin’s “Landscape Programme”
The “Landscape Programme” for the City of Berlin (Senatsverwaltung für Stadtentwicklung und Umwelt, 2016) is a strategic instrument for the integration of ecological goals into urban development. The programme aims for a well-connected green structure that should serve as a habitat network, moderate the urban climate, and create corridors for human use. The recent update of the habitat network plan is now based on a scientific study including target species. Existing and potential habitats for these species were mapped by local experts.
For increasing connectivity of Berlin’s green structure, the General Urban Mitigation Plan identifies priority areas in which measures to compensate for urban development projects according to the German Federal Nature Conservation Law are concentrated (Figure 6).
Source: Adapted from Hansen et al. (2016).
Participation and Social Inclusion
GI planning that includes public and private land and aims at providing multiple benefits needs to involve a large range of stakeholders in planning and implementation. Planning approaches that have been called participatory, collaborative, or communicative are needed for this purpose (Healey, 1997). For instance, adopting novel approaches for the local management of stormwater in densely built environments requires cooperation from different sectors of the public administration, but also the private sector (e.g., landowners, local residents, and green-space users that should benefit from such measures). Therefore, the themes of green-gray integration and social inclusion are clearly connected.
Encouraging citizens to play a more active role as the stewards of green spaces is also required on the one hand due to the diminishing budgets in many cities (e.g., Davies et al., 2015). This may also include public-private partnerships. On the other hand, citizens are increasingly demanding to be more deeply involved in the creation and the management of green spaces, as the urban gardening movement shows. Cocreation, codesign, and comanagement have been coined as terms to denote this trend (Bodin & Crona, 2009; Graham & Ernstson, 2012), and offer an opportunity to reduce the disconnection of urban dwellers from their natural environment (Krasny & Tidball, 2012). There is evidence that this may increase not only the citizens’ quality of life (e.g., Dallimer et al., 2012), but also the interest in global issues like biodiversity conservation and environmental protection (Dunn, Gavin, & Sanchez, 2006).
Social inclusion in planning means involving a wider range of social groups, not least the vulnerable ones that are often not well represented in decision-making (Cornwall & Jewkes, 1995; Baker & Eckerberg, 2008; Tosics, 2015) (Box 4). The latter may include, for instance, extremely poor, homeless, unemployed, migrants, or ethnic minorities. Research has shown that access to, perception, and use of green spaces differ between socially and culturally different groups (e.g., Barbosa et al., 2007; Gidlow & Ellis, 2011; Kabisch & Haase, 2014). Lack of socially inclusive planning, therefore, may result in an urban GI that does not meet the requirements of the different sectors of urban society well, thus intensifying social inequalities rather than promoting social cohesion.
Box 4. The Challenges of Social Inclusion in the Regeneration of an Urban Neighborhood in Aarhus, Denmark
Aarhus is Denmark’s second-largest city. The Gellerup neighborhood was built between 1968 and 1972. It is a large social housing area with approximately 2,400 flats and 7,000 residents in 30 blocks of multistory housing. Due to its extremely high share of residents which were unemployed, had a criminal record, low education and income levels or a migrant background, the areas was declared a “ghetto” in 2000 by the Danish state.
Upgrading the green spaces was an important element in the overall master plan for regenerating the neighborhood. Local authorities went beyond conventional forms of planning consultation. Instead, a participatory process was designed so that all residential groups could voice their concerns. Different forms of communication and engagement with the residents were employed for this purpose. These included, among others, participatory workshops and visits to inspirational projects in places in Denmark that helped to incite discussion for the vision for Gellerup. Special attention was paid to involving women from different ethnic groups with respect to safety issues in public spaces, as well as representatives from youth associations. The municipality has also employed 10 so-called leisure time workers representing ethnic minorities to facilitate the link to the local residents.
These measures were important for developing the master plan and devising concrete plans. Experience to date shows that despite the ample measures taken, it still has proved difficult to involve all ethnic groups due to cultural and language barriers.
Source: Adapted from Hansen et al. (2016).
GI Planning as a Holistic Approach
The preceding sections emphasized GI planning as a strategic approach, which has the integration of gray and green infrastructures, multifunctionality, connectivity, and social inclusion as its key principles. However, strategic planning, interdisciplinary and transdisciplinary partnerships, and multiscale planning are important additional principles to consider, as they can help achieve a more quickly implemented and successful, long-lasting GI system.
Establishing a long-range vision can be a cohesive force for both government agencies and nongovernmental actors to work toward a more sustainable future, but strategic planning is most successful when defined targets and implementation measures are put forth. Considering the level of integration and complex requirements required, urban GI should also build on sound knowledge from engineering, landscape ecology, the social sciences, and planning. This calls for interdisciplinary and transdisciplinary approaches involving actors from different disciplines and sectors (i.e., public, private, voluntary). Finally, recognizing that socioecological systems and processes occur across administrative boundaries, GI planning must include actors from different scales in order to reach consensus and define action plans that can target and improve GI. Developing governance arrangements that enable such approaches will be key for strategic urban GI planning and implementation.
While each of the given principles for GI planning are important on their own, the real art in developing a GI will lie in considering them together, in a holistic approach, to address several planning aims simultaneously. In a sense, this may not be as challenging as it might at first seem. For one, as is clearly evident from the preceding sections, many objects of GI planning are clearly interrelated, and integrated planning naturally requires planning from different disciplines and sectors at different spatial levels. In addition, since GI aims and principles are closely correlated, addressing or applying one of them will mean that there are many connections to the others, where synergies can be sought and at least unnecessary trade-offs avoided. For example, aligning green and gray infrastructure may simultaneously support climate change mitigation, improve the value of the gray infrastructure, support multifunctionality, and avoid the fragmentation of GI that is one of the major impediments to urban biodiversity conservation. Furthermore, since many green-space benefits are shared across different sectors, there is ample opportunity for public-private partnerships, as well as other forms of partnerships among the public, private, and voluntary sectors that can greatly increase the level of funding, knowledge, and resources available for GI projects. Particular potential has been noted for public-voluntary partnerships, including innovative approaches to the creation and management of green space by grass-roots movements (Buijs et al., 2016). In any case, with its many connections and interdependencies, urban GI must be planned with an understanding the dynamics of the urban system resulting in urban growth, shrinkage, and restructuring.
Application of the Urban GI Approach
Cities across the developed world seem to be starting to pay more attention to various aspects of the GI approach. For instance, the integration of green and gray infrastructures became an important solution for stormwater management in the United States. While this is one approach to implement urban GI, the City of New York shows how this may be expanded to tackle wider challenges of climate change adaptation. After experiencing the disastrous consequences of Superstorm Sandy, New York adopted a plan called “A Stronger, More Resilient New York” (NYC.gov, 2013), an ambitious strategy to increase its climate resilience by combining engineering with GI to provide multiple social and environmental benefits. In Europe, cities such as Barcelona, Spain, are now noted for equally ambitious strategies that put emphasis, for example, on increasing connectivity (Box 5). If successfully implemented, New York and Barcelona might serve as front runners for demonstrating how urban GI can effectively address big challenges of urbanization in very densely built cities.
Other cities have adopted strategic green-space planning under different names. A survey of 20 European urban areas showed that all municipalities had some kind of strategic green-space planning in place (Davies et al., 2015). Analysis of their plans and further documents, as well as interviews with city officials, revealed that the principles of GI planning are already known to different degrees. However, how they are adopted in planning varies widely in both the breadth and the depth of their uptake. While multifunctionality is recognized as being important, in most cases, the number of functions mentioned was limited and biased toward the more traditional recreational functions and biodiversity conservation. Moreover, multifunctionality often appeared to be taken as a given characteristic of urban green spaces rather than an outcome of careful planning and design.
Similar limitations of current green-space planning could be observed with regard to other GI planning principles. Notably, social inclusion appeared to offer much room for expansion and further innovation. City administrations in northern and western Europe were already more open to experimenting with participatory approaches toward planning, while such efforts were less frequent in the Mediterranean countries (see also Buijs et al., 2016). There is also still ample scope for further development of governance approaches to join forces between government-led planning and other players in developing UGI, not least grass-roots initiatives (Buijs et al., 2016). Many community-led initiatives centered around green-space development and management already exist in Europe’s urban areas, and a number of these have been identified as good practices (Buijs et al., 2016). These initiatives are often developed by local organizations that are rarely supported by government but nevertheless often provide a number of public benefits. Moreover, urban authorities increasingly aim to enhance urban GI but tend to ignore initiatives at the grass-roots level with which partnerships could be formed. To improve this situation, better interfaces between the public sector and civil society need to be developed (see Franklin & Marsden, 2015 for examples of sustainability initiatives in the United Kingdom).
Therefore, it appears that GI indeed is a concept that challenges current practice of green-space planning in Europe and offers a pathway for its advancement. However, this will require significant efforts to be made (Hansen et al., 2016), from developing a sound evidence base (e.g., based on the assessment of multiple ecosystem services for the different types of green and blue areas); to furthering governance approaches and citizen participation, including vulnerable groups as highlighted in the Gellerup case of Aarhus (see Box 4); to developing policies and using a suite of available planning, regulatory, and economic instruments for implementation of urban GI. Linking urban GI to pressing challenges such as issues of flooding and stormwater in the light of climate change, urban densification, or both can open windows of opportunity for urban GI. Legislation that requires or promotes urban GI, such as the Clean Water Act in the United States or the European Commission’s GI strategy, can be an important driver for developing GI, but it can also narrow the scope of urban GI to serving as technical fixes to current problems. Therefore, promoting a debate on GI and its broader aims to raise awareness of its value is important.
Box 5. Barcelona’s Green Infrastructure and Biodiversity Plan 2020
Barcelona, a thriving city of 1.6 million inhabitants in 2012 on an area of 9,458 ha, is located on the shore of the Mediterranean Sea (Hansen et al., 2015). The core is extremely densely built and deficient in green space. However, the city contains a rich heritage of natural parks on the surrounding hills and mountains (Figure 7).
In past decades, the city has made great efforts to create new open spaces and to improve existing ones as part of urban regeneration and concurrent with its strong economic development. The new “Green Infrastructure and Biodiversity Plan 2020” (Ajuntament de Barcelona, 2013) provides a strategic framework for developing the city’s GI of natural and designed green spaces for human health and well-being and biodiversity conservation. A short reference to this plan is made here because it illustrates well how planning can include GI principles that have been presented in the preceding sections:
The concept of urban GI aims to improve the quality of life in cities, as well as to increase their sustainability and resilience in the face of climate change. Urban GI needs to consider the entire urban landscape, with its diversity of open and green spaces, to address these challenges successfully. This article has provided ample evidence for the enhancement of biodiversity and provision of ecosystem services by urban GI, as well as how these services are linked to human health and well-being and a green economy. GI builds bridges between the social, engineering, and nature conservation-oriented disciplines, and it advocates a socially inclusive approach, which is important considering that it has been argued that only such approaches can achieve urban transformation toward greater sustainability (Pauleit et al., 2011; Visseren-Hamakers, Leroy, & Glasbergen, 2012; Frantzeskaki, Wittmayer, & Loorbach, 2014).
However, in the academic debate, criticisms over GI planning have been voiced. For instance, it has been argued that GI is a neoliberal approach where the value of green is mainly seen in economic terms (Thomas & Littlewood, 2010; Horwood, 2011; Lennon, 2015). Indeed, the example of the draft GI strategy for Greater Manchester showed that GI is considered in part as an important tool for attracting economic investment. Attempts at economic valuation of ecosystem services have received similar criticism (Goméz-Baggethun & Barton, 2013). Moreover, it has been argued that GI is biased toward technical rationality, whereby it is considered as another facet of traditional, expert-driven engineering approaches. Instead, it is argued that the deliberative dimension needs to be strengthened by a socially inclusive approach if GI planning should more fundamentally challenge the prevailing aims and practice of development (Lennon, 2015). On a similar note, GI is often expressed in terms that are viewed as technical and abstract to the public, instead of in terms that resonate with people and their everyday lives. Here, place-based approaches and communication strategies may be needed to maximize public participation (Metz & Weigel, 2010).
Such criticism needs to be taken seriously. It would also be naïve to propose urban GI planning as an approach that supplies plenty of benefits at no costs. Costs, for instance, are related to the maintenance of urban green spaces. There may also be disservices such as leaf litter clogging drains, damage of infrastructures (e.g., by tree roots), emission of biogenic volatile compounds, or the production of allergenic pollen by certain species of trees and grass (Nicoll & Armstrong, 1997; Lyytimäki & Sipilä, 2009; Roy et al., 2012; Calfapietra et al., 2013; Dobbs, Kendal, & Nitschke, 2014). Moreover, trade-offs between different ecosystem services need to be balanced during the planning, design, and management of green spaces (Haase, Schwarz, Strohbach, Kroll, & Seppelt, 2012; Sanon, Hein, Douvena, & Winkler, 2012). For instance, there may be trade-offs between the goal to maximize the recreational potential of green spaces, regulating functions and their biodiversity. However, comprehensive assessments of ecosystem disservices and trade-offs between different ecosystem services are still rare (Döhren & Haase, 2015). A well-planned, multifunctional GI will still require space, and there will be limits for the provision of multiple ecosystem services under conditions of urban growth and densification.
Moreover, concern is increasingly voiced over the role of green spaces in reinforcing social inequalities via gentrification (Dooling, 2009; Wolch et al., 2014). Property prices and rents may become unaffordable for less affluent people when the environment is improved through urban greening. Therefore, it has been argued that the social consequences of urban greening in different urban contexts should be carefully considered. The phrase “just enough green” has been coined to advocate for socially sensitive greening that may rather build on small-scale, modest interventions instead of realizing spectacular park projects (Wolch et al., 2014).
We would argue, though, that urban GI planning should not be dismissed on the ground of these limitations and pitfalls. Rather, it represents a novel, holistic, but demanding approach addressing multiple environmental, social, and economic aims. Following this route, urban GI planning could be more than “old wine in new bottles” (Davies et al., 2006), but make a significant contribution to the transformation of urban areas for improved quality of life, sustainability, and resilience.
Finally, it can be debated whether urban GI can serve as a universal approach to addressing the challenges of urbanization in different contexts. This article has mainly concentrated on the European situation, with some references to North America. Urban GI planning is also discussed as it applied in Australia, mostly related to combating the negative effects of climate change (e.g., Coutts, Tapper, Beringer, Loughnan, & Demuzere, 2012; Norton et al., 2013), and in Asia (e.g., Kato, 2011). Certainly, no simple transfer of knowledge, instruments, and tools from the Western world to cities like those in sub-Saharan Africa will be possible. Research on urban GI and ecosystem services is still too scarce for this and other regions of the developing world (e.g., Haase et al., 2014). However, what has been done so far has demonstrated the enormous importance of green spaces for improving the liveability of the mostly poor urban population (e.g., by providing basic food resources and alleviating urban poverty), particularly in times of economic crisis (e.g., Halloran & Magid, 2013; Cilliers, Cilliers, Lubbe, & Siebert, 2013; Pribadi & Pauleit, 2016), as well as increasing climate change resilience (e.g., Lindley et al., 2015). Protecting and further developing a functional GI in such rapidly developing cities are perhaps one of the biggest challenges for urbanization globally.
The authors greatly appreciate the careful reading and constructive comments of an anonymous reviewer and the editor. This article relies considerably on the results of the EU FP7 research project GREEN SURGE “Green Infrastructure and Urban Biodiversity for Sustainable Urban Development and the Green Economy” [grant agreement no: 603567 (www.greensurge.eu)].
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