Urban Reconciliation Ecology: the Potential of Living Roofs and Walls

Journal of Environmental Management 92 (2011) 1429e1437

Contents lists available at ScienceDirect

Journal of Environmental Management

journal homepage: www.elsevier.com/locate/jenvman

Review Urban reconciliation ecology: The potential of living roofs and walls

Robert A. Francis*, Jamie Lorimer

Department of Geography, King’s College London, Strand, London WC2R 2LS, UK article info abstract

Article history: Reconciling human and non-human use of urban regions to support biological conservation represents Received 1 September 2009 a major challenge for the 21st century. The concept of reconciliation ecology, by which the anthropogenic Received in revised form environment may be modiﬁed to encourage non-human use and biodiversity preservation without 3 September 2010 compromising societal utilization, potentially represents an appropriate paradigm for urban conserva- Accepted 7 January 2011 tion given the generally poor opportunities that exist for reserve establishment and ecological restora- Available online 9 February 2011 tion in urban areas. Two habitat improvement techniques with great potential for reconciliation ecology in urban areas are the installation of living roofs and walls, which have been shown to support a range of Keywords: Reconciliation ecology taxa at local scales. This paper evaluates the reconciliation potential of living roofs and walls, in particular Living roof highlighting both ecological and societal limitations that need to be overcome for application at the living wall landscape scale. We further consider that successful utilization of living roofs and walls for urban green roof reconciliation ecology will rely heavily on the participation of urban citizens, and that a ‘citizen science’ urban ecosystem model is needed to facilitate public participation and support and to create an evidence base to deter- Citizen science mine their effectiveness. Living roofs and walls are just one aspect of urban reconciliation ecology, but are particularly important ‘bottom-up’ techniques for improving urban biodiversity that can be performed directly by the citizenry. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction prevent the forthcoming (or indeed current) extinction cascade (see also Rosenzweig, 1995; Dodds, 2009). ‘Unless one merely thinks man was intended to be an all- As a more realistic and practical solution, Rosenzweig (2003a, conquering and sterilizing power in the world, there must be. 2003b) proposed a ‘third strand’ of conservation (alongside some wise principle of coexistence between man and nature, even if reserves and restoration) termed ‘reconciliation ecology’.Thisisthe it has to be a modified kind of man and a modified kind of nature. modification and diversification of anthropogenic habitats to support This is what I understand by conservation’ (Elton, 1958; p. 145). a greater range of species, without compromising the land use. This Charles Elton’s ‘wise principle of coexistence’ is above all one of approach is different from ‘setting aside’ land that is associated with practicality: how to live well in and with the non-human world. The some forms of ‘ecologically friendly’ land use, for example the necessity of biodiversity for the continuance of our species is well conservation buffers and headlands of agricultural landscapes (e.g. established, as is our reluctance to reduce land and resource use at Dover, 1997); and separate from ecological restoration or rehabilita- scales that would significantly retard biodiversity loss (Tilman, 2000; tion as it does not attempt to re-create or simulate a previous Gaston and Spicer, 2004; Balvanera et al., 2006). Biological conser- ecosystem state or condition (see Francis, 2009). vation still largely focuses on ‘non-use’ land (Redford and Richter, The application of reconciliation ecology is particularly relevant 1999; Andelman and Willig, 2003), which consists of areas set to cities, which: exhibit highly modified and cosmopolitan biodi- aside for preservation from development or direct use (‘reserves’), versity that is often (though not always) lower than the pre-urban and the restoration or rehabilitation of degraded ecosystems (e.g. ecosystem (e.g. Soulé, 1990; Kuhn and Klotz, 2006; Pauchard et al., Dobson et al., 1997; Andelman and Willig, 2003). Rosenzweig 2006); contain the majority of the human population and are (2003a, 2003b) has demonstrated that the global land area avail- therefore where most people interact with the non-human envi- able for reservation and restoration, by itself, is insufficient to ronment (Miller, 2005); and are the centres of national and international political, economic and cultural power. Lundholm and Richardson (in press) have recently argued for greater consideration of artificial urban habitats such as walls and pavement as * þ Corresponding author. Tel.: 44 20 7848 1233/1372. ‘analogue’ habitats that can support species from comparable natural E-mail addresses: [email protected] (R.A. Francis), [email protected] (J. Lorimer). habitats (in this case rock pavements and cliffs), but that may not be

We also consider that successful utilization of living roofs and walls for urban reconciliation ecology will rely heavily on the participation of urban citizens, and outline a ‘citizen science’ model to create an evidence base to determine their effectiveness.

2. Living roofs and walls in urban landscapes

2.1. Background and deﬁnitions

The planting of vegetation on the roofs of buildings has taken place since antiquity as an architectural and horticultural practice (Oberndorfer et al., 2007; Dunnett and Kingsbury, 2008), but it is only recently that such designs have been used to attempt to mitigate the loss of species from urban regions (Brenneissen, 2006; Oberndorfer et al., 2007), and that scientific analyses of living roofs have taken place (e.g. Grant, 2006; Schrader and Böning, 2006; Orberndorfer et al., 2007). Living roofs (see Table 1 for clarification of terminology) are usually constructed on pre-existing roofs, though Fig. 1. The potential for top-down (led by local/regional government) and bottom-up many new buildings incorporate them into their design. They usually (led by conservation citizenry) reconciliation efforts. Habitat enhancement of urban consist of (1) a root resistant membrane that runs over the surface of infrastructure and public parks requires action by local or regional authorities responsible for the management of such landscape elements, while living roofs/walls the roof material to prevent root damage; (2) a drainage layer, which and domestic gardens can be enhanced by conservation-minded citizens on an indi- may or may not also act as a water reservoir for plant use; (3) a filter vidual basis. Enhancement of infrastructure and parks (driven by government or membrane, which prevents fine sediments from infiltrating into the landowners) also present higher potential for landscape co-ordination, as opposed to drainage layer and being removed from the substrate; (4) a sediment roofs/walls and gardens (driven by individuals or organisations). Likewise, a gradient layer varying in material and depth, composed of inorganic material of resource investment exists, from high for infrastructure and parks, through medium for individual living roofs/walls, to low investment in domestic gardens. with some (usually <20%) organic matter; and (5) a surface vegetation layer that can be seeded, planted, turfed, left to colonise naturally, or any combination of these options (Bates, AJ, pers. com). able to colonise such habitats because of limits to their dispersal Much of the environmental and ecological variation found in living capabilities. These habitats may also be improved using ecological roofs depends on the type of substrate used (along with type of engineering techniques, of which living roofs and walls are key planting, roof age and roof size; Schrader and Böning, 2006), and examples. Living roofs and walls have demonstrated varied envi- a wide range of options exists that can be tailored to specific habitat ronmental benefits, including the capacity to support a range of requirements (Dunnett et al., 2008). species (Grant, 2006; Kadas, 2006; Köhler, 2008; Dunnett et al., Green facades (see Table 1) have historically been used mainly 2008), though spatial parameters such as habitat size and configu- for ornamental or horticultural purposes, and involve the estab- ration are generally not considered (Oberndorfer et al., 2007). lishment of climbing vegetation which is rooted in the ground or Conservation in cities has been integrated into urban planning for planters, and which is then trained to grow directly on wall surfaces decades, and has demonstrated the need for spatially-explicit or on an overlying wire or trellis framework (Dunnett and approaches to habitat creation (e.g. Colding, 2007). The planning and Kingsbury, 2008; Köhler, 2008). Living walls are distinct from management of, for example, urban greenways (connected vege- green facades in that they support vegetation that is either rooted tated or ‘environmentally pleasant’ landscape corridors; see Imam, on the walls or in substrate attached the wall itself, rather than 2006), requires a top-down approach made possible only by the being rooted at the base of the wall, and as a consequence have cooperation of politicians, urban planners, ecologists and landscape been likened more to vertical living roofs (Dunnett and Kingsbury, engineers. Although some reconciliation (habitat enhancement) 2008; Köhler, 2008). The walls of buildings are most suited to living techniques may also be top-down (e.g. the creation of habitats in wall systems that use hydroponic technology to support plants that public parks and recreational spaces, the planting of vegetation along are kept physically separate from the wall, for example a drip-feed urban infrastructure), reconciliationwill rely much more on localised irrigation system that keeps moist a growing medium placed on the and coordinated efforts of a large number of people and organisa- wall but kept separate from the construction material by a water- tions with high levels of spatial, social and economic diversity, for proof membrane (Dunnett and Kingsbury, 2008), and thereby example the installation of living roofs and walls (Fig. 1). These are maintains the integrity of the wall structure. These are sometimes valid reconciliation techniques as they do not prevent (indeed may constructed on indoor walls (termed ‘biowalls’; Table 1) for enhance) human use of the space, but also encourage use by other aesthetic and horticultural purposes (Dunnett and Kingsbury, species. It has been demonstrated that such efforts can encourage 2008). This kind of living wall technology is often modular, allow- the use of habitats by species at local scales (e.g. Grant, 2006; ing plants to be grown on individual sections before mounting, and Schrader and Böning, 2006; Valtonen et al., 2007), though a central facilitating easy replacement if necessary. Alongside the modular question for biological conservation is whether such efforts will design, an alternate design is the use of a thin (1 cm) layer of PVC support species populations at the landscape scale, allow pop- and felt applied to a light metal frame on the wall surface supplied ulations to remain resilient in the face of disturbance and stochastic with water, which represents a lightweight cover that is also change, and therefore achieve the reduction of biodiversity loss that separate from the wall and therefore prevents roots penetrating is the aim of reconciliation (Collinge, 1996; Rosenzweig, 2003b; wall surfaces; this is demonstrated in the ‘Vertical Garden’ walls Colding, 2007; Lindenmayer, 2009). In this paper we review the pioneered by Blanc (2010). Köhler (2008) notes that living wall potential biodiversity benefits of living roofs and walls, highlighting systems do not rely on a limited range of climbing flora to the same research gaps that relate to reconciliation ecology at the landscape extent as green facades, and allow a far greater range of species to scale, before discussing socioeconomic limitations that may prevent be planted on the wall surface; this increases the potential for the installation of living roofs and walls within the urban landscape. utilising living walls for reconciliation, as species may be planted to R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 1431

Table 1 Deﬁnitions of terminology relating to living roofs and walls. Compiled from information found in Oberndorfer et al. (2007); Dunnett and Kingsbury, 2008; Emilsson, 2008; and Köhler, 2008.

Terminology Deﬁnition Green roof Usually refers to a planted living roof and is the most common term applied, though sometimes confusion has arisen when ‘green’ is used in the environmental sense, such as a roof with solar panels may be considered ‘green’ due to its energy saving capability.

Brown roof Extensive green roofs that attempt to simulate brownﬁeld conditions and use often use resource-poor substrates such as gravel or rubble to encourage the establishment of species that are often displaced by more competitive species.

Ecoroof An alternative for both ‘green roof’ and ‘brown roof’ generally used to refer to roofs that have been planted as extensive roofs for ecological (rather than aesthetic or recreational) purposes. Often used to avoid the idea that green roofs are in fact green and covered with lush vegetation (which many are not, but still provide habitat).

Living roof Any vegetated roof system; a generic term for roofs designed to promote natural or planted vegetation, and used to avoid the use of the term ‘green’ or ‘brown’. Sometimes simply referred to as a ‘vegetated roof’.

Intensive living/green roof A ‘roof garden’ where the purpose is mainly recreation or aesthetics in the same way as an ordinary garden. Such roofs will have deeper soils, be frequently used and require regular maintenance, and may support a wide range of horticultural plants.

Extensive living/green roof A roof mainly created for supporting biodiversity or providing other environmental beneﬁts, and which is not intended to be used frequently by humans. Usually contains a thinner layer of soil or substrate and after initial construction requires minimal maintenance and is essentially left to its own devices (including natural plant colonisation).

Green façade Mainly refers to climbing plants such as ivy that are encouraged to grow up and along the walls of buildings (mainly on a wire or trellis framework) to form a green covering, though the roots of the plants are contained in substrate at the base of the wall.

Living wall A wall that incorporates vegetation in its structure or on its surface, and which does not require the plants to be rooted in substrate at the base of the wall as in a green façade. Most living wall systems are modular and consist of an encased growing medium placed onto the wall surface but kept separate from the wall material via a waterproof membrane, and which is watered using a drip-feed system. Natural living walls may be seen where vegetation has become integral to the wall and may help in supporting its structure, such as on some retaining walls. Sometimes living walls are bioengineered so that plant roots are purposefully used as a reinforcing mechanism within the wall structure.

Biowall A living wall or green facade that is situated indoors, primarily to enhance the atmosphere and indoor environment of, for example, shopping centres. address specific functions that may be missing in the urban envi- The extent of suitable sites for living roofs and walls is likely to ronment, for example the planting of herbs such as thyme (Thymus vary notably between urban regions based on commercial and spp.) to support key pollinators. However, despite observations that cultural differences in building design, relative density of urban living walls support a range of fauna, this is mainly anecdotal and development, and the sizes of individual buildings (e.g. Akbari has not been investigated in any depth (Köhler, 2008; Weinmaster, et al., 2003). This may vary at three broad spatial scales: 1) at the 2009). overall city scale, there is often, for example, a tendency for the densest built environment to be present in the core of the city, with 2.2. Availability of space for living roofs and walls this reducing with increasing distance from the centre and into the suburbs, with a consequent increase in e.g. vegetated habitat As living roofs and walls essentially create habitat on land that is (Peiser, 1989; Bradley, 1995); 2) within the city, density of different being directly used by humans as living space, they are a good building types changes according to the use of a given area (e.g. for example of the practice of reconciliation ecology. Their contribu- industry, business, residences; Akbari et al., 2003; Baker and Harris, tion may be particularly valuable as roof surfaces can represent up 2007); 3) within specific zones (e.g. residential) there will be to 32% of the 2D horizontal surface in some urban locations notable difference in housing density, relating to the patch sizes of (Ferguson, 2005), though of course not all roofs are flat or indeed buildings and associated features such as gardens. These are very suitable for supporting substrate and vegetation. In the Greater simplified, general patterns and will vary substantially between London (UK) urban region for example, Grant (2006) estimates that different cities (and relate to socioeconomic factors as noted roofs cover 240 km2, or 16% of the 2D land surface, while in Sac- below), but nevertheless illustrate the level of spatial complexity ramento (USA) roofs cover a total area of 150 km2, and between 19 present in city landscapes. In particular, the potential may exist for and 23% of the 2D land surface depending on urban land use walls to be used in combination with roofs to encourage 3D (Akbari et al., 2003). Vertical built surfaces within urban regions connectivity across urban landscapes, for example allowing inver- may also cover a substantial area, far greater than that of roof alone tebrate species to access roofs via wall surface foliage. or the underlying land surface, though this varies with building Roof and wall availability will also depend on spatial socioeco- dimensions and densities (e.g. Grimmond and Oke, 1999). For nomic patterns within urban regions. Socioeconomic status may be example, Darlington (1981) estimates that 0.01 km2 of wall surface a key indicator of reconciliation potential as this is correlated to exists for every 0.1 km2 of urban land surface within the UK. Along important factors such as housing density, willingness to pay for the 32 km of the River Thames through central London, 0.28 km2 of environmental improvements, patterns of home ownership and contiguous wall surface exists, much of which is colonised naturally other social factors such as level of education (e.g. Jargowsky, 1996; by vegetation (Francis and Hoggart, 2008, 2009). Consequently, Li and Wu, 2006; Troy et al., 2007). As Kinzig et al. (2005) note, there may be substantial potential for their utilisation to support groups with higher economic status can devote more resources to living walls and encourage urban biodiversity. ‘creating their ecological ideal’ (p.2). Some cities may have more 1432 R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 spatially-explicit disparities between socioeconomic status than Kadas, 2006). Invertebrate diversity can be particularly high; for others, for example those that maintain informal housing created example Kadas (2006) found over 200 species when sampling only by high levels of immigration (Forman, 2008; United Nations Araneae, aculeate Hymenoptera and Coleoptera on living roofs in Human Settlements Programme, 2008). Such areas may be London, UK. densely housed with little infrastructure, taking up less land area Species that do not disperse easily or are not vagile are less likely but also limiting roof and wall reconciliation options. In contrast, to benefit from living roofs unless they are deliberately introduced. more affluent areas (e.g. N America) may be (or have been) subject For example, living roofs do not generally support earthworms to greater sprawl, or the urbanisation of land with low-building within their soil fauna as they are unable to colonise naturally and density areas, which fragment natural habitat, but offer more most substrates are too shallow to support them (a substrate of less opportunities for reconciliation. Relationships between socioeco- than 12 cm is considered unsuitable; Schrader and Böning, 2006), nomic status and general receptivity to conservation have yet to be with the result that other soil organisms become more populous, established, though Gaston et al. (2007) for example found that such as Collembolans (Schrader and Böning, 2006). Brenneisen socioeconomic status (those employed in professional, business (2006) also notes that although living roofs may support many and administrative employment vs. those not) did not affect trends species of spider, the European members of the Atypus genus were of wildlife gardening in the UK. not found on roofs in Switzerland as opposed to terrestrial habitats, presumably due to restricted vagility. Larger organisms (including 2.3. Biodiversity benefits and limitations of living roofs and walls those that move around the landscape easily) are less likely to nest or breed on living roofs, though they may use the habitat tempo- Much of the scientific assessment of living roofs and walls has rarily, for example during foraging (Baumann, 2006). One high- focused on the benefits they provide to the urban microclimate, profile use of living roofs has been to provide habitat for bird including storm water management, cooling buildings and their species that are rare in the urban environment, such as little ringed environs, and removing pollutants from water and air (e.g. plover (Charadrius dubius) and northern lapwing (Vanellus vanellus) Oberndorfer et al., 2007; Köhler, 2008) though they can be designed in Switzerland, and black redstarts (Phoenicurus ochruros) in the UK to support particular species of conservation concern (Grant, 2006), (Grant, 2006). However, although there is evidence that such bird and to provide habitat for biodiversity in general (Getter and Rowe, species utilise living roofs as nesting as well as foraging habitat, 2006; Oberndorfer et al., 2007). As an ecological engineering tech- there is so far limited evidence that they act as successful breeding nique most extensive living roofs (those designed to support biodi- sites (Baumann, 2006), though monitoring has often not taken versity) are essentially designed to simulate brownfield ecosystems, place for very long and so breeding potential cannot be accurately which have proven of notable ecological value in recent years determined. (Wheater,1999; Jones, 2003; Schadek et al., 2009). Some are covered in Sedum mats, others may be sown with wildflower seeds after 2.4. Ecological engineering of living roofs and walls for installation, or may experience direct planting; such vegetation may reconciliation ecology remain on the roof indefinitely and is often selected to cope with the particular roof environment, e.g. stress-tolerating species that can Most living roof design is based on the Forschungsgesellschaft cope with dry, nutrient-poor substrate (Emilsson, 2008). However, Landschaftsentwicklung Landschaftsbau (FLL) Guidelines (Guide- a substantial benefit of living roofs to urban biodiversity comes from lines for the Planning, Execution and Upkeep of Green Roof Sites; FLL, their capacity to act as habitat for colonising species. There are 2002), which advises on substrate type, depth and planting regimes, relatively few investigations of spontaneous colonisation of plant among other aspects of design. Advances in living roof design are species on living roofs over both short and long timescales, though creating wider possibilities for reconciliation ecology. The use of Dunnett et al. (2008) documented 35 colonising species on a single varying substrate materials to provide different pH values, moisture experimental living roof in Sheffield, UK, over 2004e5, with greatest availability and particle size distributions, alongside additions of abundance and diversity of colonists being found on sections of the organic matter and mycorrhizal inoculations (Molineux, 2010)or roof with a substrate depth of 10 cm. Most of the species found were moisture-retaining fabrics (Dvorak and Volder, 2010), may increase agricultural weeds or ruderals common to disturbed sites, all resource availability and habitat heterogeneity and facilitate the dispersed either by anemochory or zoochory (e.g. via birds); a trend colonisation of roofs by a wider range of organisms, as well as that may be anticipated for urban living roofs in general, though this (to some extent) the replication of natural or semi-natural habitat. does not lower their biodiversity and functional potential. Interest- Molineux et al. (2009) for example found an average pH value of 8.5 ingly, a wide range of growth forms were found in the colonists, from for a substrate of clay pellets compared to 11.8 for carbonated annual and perennial herbs to grasses, shrubs and trees. Although limestone quarry waste pellets, and that addition of 25% organics plants with larger morphologies and resource requirements such as (50:50 conifer bark compost and soil) was optimum to support plant trees are unlikely to establish or survive over long periods (Emilsson, growth and reduce shrinkage of the substrate. Variations in particle 2008), the presence of a wide range of different functional typologies size, pH, moisture storage, substrate depth and micro-topography in the urban seed rain means that the potential spontaneous biodi- are likely to reflect differences in the plants and invertebrates that versity of urban roofs may be quite high, if appropriate roof habitat will colonise roofs and therefore the types of species that will be can be engineered. supported via such reconciliation techniques. Living roof habitats, probably due to their limited size, primarily Recently there have been suggestions that living roofs could be benefit organisms with small body sizes, that have the capacity to used to replicate ecosystems (or a subset of species from such disperse easily, and either have low resource requirements that ecosystems) of priority concern for biodiversity conservation, mean they can complete their life cycles on the roof (e.g. drought within a given region (e.g. Sheffield Local Biodiversity Action tolerant flora), or have more general resource requirements that Partnership, 2010). Examples within the UK include lowland mean they can utilise the habitat as part of their wider range (e.g. heathland and lowland dry acid grassland, while Dvorak and Volder bees and wasps). Living roofs are well documented for their support (2010) note that living roofs may be used to support species lost of spiders, beetles, wasps, ants and bees, and several studies note from natural grassland habitats within agricultural areas in North that rare invertebrate taxa from the above groups can be found on America. In some cases the preservation of viable populations of roofs, including some with very specialised niches (Grant, 2006; such species may not be feasible; despite the intention to replicate R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 1433 heathland on living roofs in the UK for example, many typical need to be evaluated before their potential benefits as a technique heather species (Erica spp., Calluna spp.) require acidic conditions for reconciliation ecology can be properly assessed and appropri- (3e4 pH; Grime et al., 2007), while the UK industry red-brick ately refined. standard is alkaline (9.7), and the addition of organic matter to lower pH is unlikely to result in conditions suitable for the wide- 2.5. Socioeconomic barriers to the installation of living roofs and spread maintenance of these species, though some establishment is walls certainly possible (Köhler, 2006). Low (c.4.5) pH values have for example been found on living roofs in Germany in locations prone Alongside the structural considerations noted above, potential to acid rain (Emilsson, 2008), though most roofs tend towards socioeconomic barriers to the utilisation of living roofs and walls for neutral values over time (for example Emilsson (2008) notes that reconciliation ecology exist. First, they require some monetary gravel roofs built in the nineteenth century maintain approxi- investment, usually up to £100 (c.$150) per m2 (The Green Roof mately neutral values). This is also reflected in the FLL guidelines, Centre, 2010) for retrofitting of living roofs, for example. Although which recommend neutral conditions (6.0e8.5). this is not a prohibitive cost, it does require the roof owners to value Engineering roofs to support a specific threatened or declining the potential roof benefits enough to make this initial outlay. This species or suite of species can be achieved, but may require very may frequently not be driven by biodiversity concerns but rather the specific use of substrate, depth, planting regimes and management. potential benefits to roof materials by, for example, protecting the This raises an interesting point: whether living roofs should be waterproofing membrane from weather and ultra-violet radiation. engineered to replicate ‘natural’ or semi-natural habitats at all, or Where living roofs are incorporated into building design there is whether they should be used as a tool to create spontaneous, novel greater potential for a more coordinated reconciliation effort. Some ‘recombinant’ assemblages (Hinchliffe and Whatmore, 2006)that countries and localised governmental regions are very proactive in are common in urban ecosystems. To follow the principle of encouraging the use of living roofs; Carter and Fowler (2008) review reconciliation ecology as opposed to the traditional preservation or locations where technological standards require that certain types, restoration paradigms, engineering the roof ecosystem so that sizes or proportions of new buildings are required or encouraged to anon-specific but varied and functional assemblage of species can install living roofs, sometimes including direct or indirect financial colonise is perhaps the best approach, particularly given the incentives. Living walls may have higher costs (around £260 or increasing acknowledgement of novel ecosystems (Hobbs et al., $390 per m2) and potentially require more maintenance, which may 2006) and the limitations of trying to hold onto a culturally con- be one reason why they are less common than living roofs. structed idea of what has been (or is being) lost. Lorimer (2008) for Cultural perceptions of urban nature have also proved chal- example notes that urban conservationists utilising living roofs lenging to the construction of both living roofs and walls. For have much greater ‘room for experimentation than is generally example, although many people may be supportive of living roofs granted to rural conservationists, and can tailor their hybrid on buildings, the initial terminology of ‘green roofs’ is now being coconstructions to create novel spaces’ (p. 2049). Exploration of the downplayed as people were responding negatively to the reality of possibilities of living roofs should not be constrained by conven- such roofs. In their extensive (and often more biodiverse) forms tional conservation paradigms. these roofs often do not have a lush green appearance, but are in Living roofs are of course highly variable in their sizes, eleva- fact similar to brownfield sites (Dunnett and Kingsbury, 2008). tions, shapes, and styles of construction, all of which are likely to There is a danger that visible and accessible living roofs and walls influence their capacity to support biodiversity (Oberndorfer et al., get ‘green-washed’ in order to comply with public expectations of 2007; Emilsson, 2008). The importance of the species/area rela- urban nature (Lorimer, 2008). This tendency is demonstrated in an tionship in determining the capacity for living roofs to support example from Islington, London (Blunden, 2010) where a living biodiversity has been noted by Oberndorfer et al. (2007), and wall installed on a children’s centre received very negative press studies have noted the importance of construction style (substrate, when irregular maintenance of a water pump led to the wall plantings) on the biodiversity and communities found on living becoming sparsely vegetated 4 years after installation. It was roofs (e.g. Emilsson, 2008). Quantification of these effects remains consequently regarded as an eyesore and a failure. Although this is an important research gap for urban reconciliation ecology. an example on a public building paid for by public money, the same Certainly at the local scale, some of the benefits of living roofs have issues relating to perception of the wall and the level of success may been determined, and Bates et al. (2009) recommend that ecolog- well emerge on private buildings, particularly as such walls are very ically-designed living roofs should contain low nutrient levels to prominent within urban environments (e.g. Weinmaster, 2009). If prevent competitive dominance, diverse substrate types and living roofs and walls are well constructed and maintained depths, areas of bare or sparsely vegetated substrate, areas of coarse however, they may enhance the perception and use of the host substrate and disturbance refugia such as wood or stone piles. building by people, by providing contact with non-humans that These are sound recommendations, but it is important to deter- may be psychologically beneficial (Weinmaster, 2009). Further- mine the limitations of the support that living roofs can offer to more, living roofs are frequently inhabited by obscure and biodiversity, in terms of 1) the taxa that they can support given the uncharismatic species and conservationists must devise creative limitations of design and structure (e.g. limits on substrate depth); strategies to identify flagship species for their conservation. Here 2) the limitations of their size, i.e. whether the ‘patch size’ of such some success has been achieved by linking living roofs to the roofs will generally be below a threshold that precludes some taxa habitats of rare birds such as northern lapwings (Vanellus vanellus) from using them; 3) whether the spatial patterning of living roofs and black redstarts (Phoenicurus ochruros)(Baumann, 2006; Grant, within the urban matrix may enable metapopulations to exchange 2006). A particular challenge for reconciliation ecology is in gaining individuals and therefore colonise roofs in which species have been support for the notion that the character and value of biodiversity extirpated, and 4) whether metapopulations are resilient and may cannot always be readily discerned or demonstrated, and may be therefore be persistent within the urban region, so that living roofs counter-intuitive; and that unpleasant, untidy or ‘annoying’ biodi- may genuinely support the species indefinitely (Oberndorfer et al., versity may result from reconciliation. Increased education and 2007). Living walls may possibly be linked to roof developments to public awareness of this is likely to be crucial in facilitating provide a supplementary role, as they too suffer from limitations of, reconciliation efforts, but this issue needs more detailed for example, substrate depth. These aspects of living roofs and walls investigation. 1434 R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437

3. Citizen science and urban reconciliation using living roofs can be effective at the local scale and over short timeframes, and and walls ‘citizen scientists’ have been used for the collection of good quality data relating to, for example, invasive species (Delaney et al., 2008) 3.1. Post-normal science and the role of citizens and urban birds (McCaffrey, 2005). These models have been successful because they have involved some level of citizen training Conservation (of which reconciliation is one strand) is a post- in appropriate skills, have used simplified techniques for data normal science (see Funtowicz and Ravetz, 1993), in that its ‘crisis’ collection (e.g. species identification), paired citizens with profes- nature means that decisions have to be taken before much rigorous sional scientists or facilitated informal checks to verify data quality, scientific investigation can be performed. Much of the decision- and have ensured that citizens feel appropriately valued and making and application of techniques relies on practitioners who are involved within the process. All of these techniques would be not scientific experts or scientifically trained (Haila, 1999; Francis important for a citizen conservation model for urban reconciliation and Goodman, 2010). As Rosenzweig (2003b) notes, there is ‘no ecology using living roofs and walls. In this case, a citizen conser- other branch of biological science that so involves laypeople in its vation model is needed such as the ‘Adaptive Citizen Science front lines’ (p.101). Although this can lead to problems of knowledge Research Model’ proposed by Cooper et al. (2007) for residential transfer within such an ‘extended peer community’ (Francis and areas. This involves nested scales of action from local to regional Goodman, 2010), the availability of a potentially substantial volun- (fine to broad) that incorporate individuals, community groups and teer force in urban regions (Clarkson et al., 2007) makes bottom-up professionals. Their actions involve the collection of both ecological approaches to reconciliation distinctly possible (Fig. 1). There is and sociological data and the adaptive management of habitats. A a growing recognition of this potential amongst important public research-led citizen science model is most appropriate, as infor- and nongovernmental organisations (Cohn, 2008), e.g. the promo- mation on the likely success of reconciliation strategies is lacking, tion of ‘Backyard Habitats’ in the USA and the encouragement of and there is a great need to develop a robust evidence base for future wildlife gardening and reporting in the UK (Bormann et al., 1993; application. Rosenzweig, 2003b; Ryall and Hatherell, 2003; Gaston et al., Fig. 2 outlines an adaptive citizen science model for living roofs 2005a; Thompson, 2007; Goddard et al., 2009). and walls within an urban landscape. In this model, academic As noted above, research gaps exist regarding the design of researchers may provide advice for the ecological design of roof and living roofs and walls and also their landscape scale benefits and wall systems, train citizens in sampling and recording methods and interactions. A landscape scale focus is likely to be key for recon- species ID, and may be responsible for the analysis, processing ciliation ecology: Goddard et al. (2009) acknowledge this in their and publication of data so that the evidence base is of use to the call for a more coordinated landscape scale approach to wildlife international community. Citizens (individually or perhaps as gardening, noting that despite a move to ‘community-based’ organisations, e.g. employees of a company) provide the physical conservation in many developed regions, lack of biodiversity resources for the roofs and walls, and may play the most important experience, conservation knowledge and co-ordination of action role of monitoring the biodiversity on the roofs over time, and for between garden owners can lead to ineffective conservation efforts data/knowledge exchange between members of the network. or, in the worst case, decisions that are detrimental to biodiversity Consultants may be responsible for installing the roofs and walls, overall but may be perceived to be beneficial (such as those based and advising on design, though some consultants may also be on ‘extended facts’ with no scientific validation; see Francis and active in monitoring or data analysis efforts. Governmental Goodman, 2010). To improve the implementation of reconcilia- agencies have a role in the network by providing suitable incentives tion ecology, these research gaps might best be addressed using the and funding for both retrofitting and construction of new living application of citizen science, linked explicitly to researcher and roofs and walls. Some ‘citizen-based’ organisations exist to promote consultant expertise. the widespread establishment of living roofs, for example Living Roofs in London, UK (LivingRoofs, 2010), or Green Roofs for Healthy 3.2. Developing a citizen science model for living roofs and walls Cities (GRHC, 2010) in North America. These organisations have been successful in promoting living roof installation but also the In urban areas, the advantages of citizen science models for identification of research gaps and the sharing and publicising of reconciliation ecology are that 1) there is a substantial local human information, and may represent a useful focus around which citizen resource base to address reconciliation at varying levels, from the conservation models may be constructed. initial enhancement of habitat (e.g. living roofs) to monitoring them, to collating data, and general knowledge exchange between 3.3. Challenges and limitations for citizen science participants; 2) universities and professional scientists are often located in urban areas, adding a further locally-accessible essential Citizen science models do have several disadvantages that need resource required to some extent for the design, analysis and to be considered for reconciliation: 1) some level of (possibly quite validation of reconciliation efforts, as well as international publi- technical or specific) education and training is required, for essential cation of findings so that the global community can benefit from aspects such as species identification, the practical application of the research; and 3) efforts are more likely to be noticed by the habitat enhancement techniques and developing an understanding populace, further expanding interest in the area and promoting of experiment design and the kinds of data required to allow valid environmental education, which is a key element of citizen science statistical analyses to be performed and appropriate conclusions and potentially a key strength of reconciliation ecology, in that even drawn; 2) often further incentives above the preservation of biodi- if species are not preserved, the raising of public awareness of the versity will be required to encourage active and continued partici- importance of biodiversity and the possibility of living alongside pation in most cases, especially at scales required to make species even in cities represents at least a minor victory. a difference for species populations as noted above; otherwise, it is Citizen conservation based around ecological monitoring and likely that only a relative few very committed individuals will be assessment has been successfully linked to adaptive management taking part. Goddard et al. (2009) note the problems in encouraging decisions (see Araya et al., 2009), but so far there has been relatively broad-scale wildlife gardening, concluding that top-down incen- limited progress in coordinating local action for habitat enhance- tivisation or penalisation may work but is difficult to facilitate and ment into a broader network. Evidence has shown that such efforts does not change underlying social values, understanding and R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 1435

fonoitacilbuP r fonoitisiuqca+stluse egdelwonk Pebu utaretildehsil sabecnedive/er

iuqcA s fonoiti egdelwonk

eR raes Ihc utitsn snoit snoitasinagrOlatnemnrevoG

gdelwonkfoetatS e Pr jo ec isedt g fn or rppA rpo lopetai i yc itnecnI ev s/ dnuf ing weiver llocatad noitce eldna talsig noi

seR ear l-hc e cerd o licn i ta oi n ane ct tnem Mo tin ro in ag n add at lloc ect noi S cep ai tsil dnalaicnaniF wonk el egd , .e .g T cinhce al Lo silac ed syhp i lac sp ce i DIse exp re esit e g. . know egdel ser uo secr fonoitallatsni li iv n sfoorg P efor s is ano l oC nsul nat st Cit snezi

noisivorpataD

adilavataD t sylana,noi i as n ftcejorpd eed kcab

Fig. 2. Key flows of information between different components of an adaptive research citizen science reconciliation model based on living roofs and walls. Citizens effectively drive the model, with professional consultants, research institutions and governmental agencies providing key knowledge, advice, services and incentives. Two key outputs exist: as well as the reconciliation enactment itself, the publication of an evidence base is essential for furthering reconciliation efforts in other locations. This literature filters back into enactment mainly via researchers and governmental agents. attitudes; while bottom-up approaches that utilise local residence of the concept (Lundholm and Richardson, in press). Living roofs and organisations or horticultural societies would probably produce walls represent ecological engineering techniques with notable more effective results, but are unlikely to include many people or potential for reconciliation ecology, either by replicating urban operate at scales sufficient to make a difference. Motivation for (brownfield) or non-urban natural and semi-natural ecosystems conservation (as discussed above) remains a major obstacle to (e.g. xeric grassland); or preferably by allowing spontaneous overcome; 3) data collected by citizen scientists needs to be verified urban assemblages to form. Varied, heterogeneous designs and and of sufficient quality and quantity, which may require a landscape scale approach may both serve to maximise the a substantial amount of ‘auditing’ by academics or environmental biodiversity potential of roofs and walls and make urban recon- professionals; 4) initiatives such as reconciliation that focus on ciliation ecology successful. Such landscape scale approaches are maintaining populations of species necessitates a sustained interest difficult in urban areas due to the spatial complexity of both the and commitment, which can be especially hard to maintain in physical and social landscapes, both of which are important in dynamic urban societies; 5) data collection by volunteers may not determining whether living roofs and walls are likely to be be as possible as in other citizen science models, as volunteers may installed, and whether they are likely to be successful. This is not have easy and ready access to roofs and walls; 6) the large particularly true for bottom-up reconciliation efforts instigated number of actors involved in such schemes requires notable orga- largely by the citizenry (though with some governmental support) nisation, and establishing responsibility and commitment to this as in the case of living roofs and walls. Co-ordination of action at may be problematic; and 7) the model needs to be adaptive and the landscape scale is likely to rely on citizen science due to the responsive as information becomes available, meaning that partic- amount of work involved and the timescales under consideration ipants must be willing to change or adapt their resources and (e.g. for species colonisation, population monitoring), which activities accordingly. would be beyond the scope of a typical team of academic Despite these limitations, citizen science models offer a useful researchers. The success of citizen science initiatives in other areas base for developing evidence-based reconciliation activities using suggests that this is real possibility, and initial efforts at devel- roofs and walls in cities at scales that are most likely to mitigate the oping living roof communities in various parts of the world have current and future loss of biodiversity. Much of the variability in the clearly made steps in this direction. likely success of reconciliation ecology, via the implementation of Living roofs and walls do not represent the only techniques for such a model, lies not just with the physical and ecological urban urban reconciliation ecology however, and should be considered template upon which habitat may be enhanced, but also in the alongside enhancement of remnant or introduced recreational socioeconomic and cultural differences found within the citizenry. habitat, including private gardens, allotments and public parks; and The extent to which these create a dynamic spatial landscape of enhancement of infrastructure, such as road and railway buffers attitudes and responses to reconciliation is an important area for and the planting of urban trees. Though we do not review these further investigation. possibilities here, they too form part of the urban landscape that may be utilised to support biodiversity, and a coherent, integrated 4. Concluding remarks approach is something for urban ecologists, sociologists and planners to strive for. We urge a management of expectations though, The practice of reconciliation ecology is not of course limited to and encourage citizens to consider that the biodiversity that urban areas, but they do represent key ecosystems for the application emerges is likely to be in untidy, unexpected and non-traditional 1436 R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 forms. We consider that many aspects of Elton’s vision of conser- Francis, R.A., 2009. Perspectives on the potential for reconciliation ecology in urban vation as ‘a modified kind of man and a modified kind of nature’ riverscapes. CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources 4, 73. will emerge from an engagement with reconciliation ecology in Francis, R.A., Hoggart, S.P.G., 2008. Waste not, want not: the need to utilize existing urban ecosystems. artificial structures for habitat improvement along urban rivers. Restoration Ecology 16, 373e381. Francis, R.A., Hoggart, S.P.G., 2009. Urban river wall habitat and vegetation: References observations from the River Thames through central London. Urban Ecosystems 12, 468e485. Akbari, H., Rose, S.L., Taha, H., 2003. Analyzing the land cover of an urban envi- Francis, R.A., Goodman, M.K., 2010. Post-normal science and the art of nature ronment using high-resolution orthophotos. Landscape and Urban Planning 63, conservation. Journal for Nature Conservation 18, 89e105. 1e14. Funtowicz, S.O., Ravetz, J.R., 1993. Science for the post-normal age. Futures 25, Andelman, S.J., Willig, M.R., 2003. Present patterns and future prospects for 739e755. biodiversity in the Western Hemisphere. Ecology Letters 6 (9), 818e824. Gaston, K.J., Spicer, J.I., 2004. Biodiversity: An Introduction, second ed. Blackwell, Araya, Y.N., Schmiedel, U., von Witt, C., 2009. Linking ‘citizen scientists’ to profes- Oxford. sionals in ecological research, examples from Namibia and South Africa. Gaston, K.J., Smith, R.M., Thompson, K., Warren, P.H., 2005a. Urban domestic Conservation Evidence 6, 11e17. gardens (II): experimental tests of methods for increasing biodiversity. Biodi- Baker, P.J., Harris, S., 2007. Urban mammals: what does the future hold? An analysis versity and Conservation 14, 395e413. of the factors affecting patterns of use of residential gardens in Great Britain. Gaston, K.J., Fuller, R.A., Loram, A., MacDonald, C., Power, S., Dempsey, N., 2007. Mammal Review 37 (4), 297e315. Urban domestic gardens (XI): variation in urban wildlife gardening in the Balvanera, P., Pfisterer, A.B., Buchmann, N., He, J.-S., Nakashizuka, T., Raffaelli, D., United Kingdom. Biodiversity and Conservation 16 (11), 3227e3238. Schmid, B., 2006. Quantifying the evidence for biodiversity effects on ecosystem Getter, K.L., Rowe, D.B., 2006. The role of extensive green roofs in sustainable functioning and services. Ecology Letters 9 (10), 1146e1156. development. HortScience 41, 1276e1285. Bates, A.J., Mackay, R., Greswell, R.B., Sadler, J.P., 2009. SWITCH in Birmingham, UK: Goddard, M.A., Dougill, A.J., Benton, T.G., 2009. Scaling up from gardens: biodi- experimental investigation of the ecological and hydrological performance of versity conservation in urban environments. Trends in Ecology and Evolution extensive green roofs. Reviews in Environmental Science and Biotechnology 8, 25 (2), 90e98. 295e300. Grant, G., 2006. Extensive green roofs in London. Urban Habitats 4, 51e65. Baumann, N., 2006. Ground-nesting birds on green roofs in Switzerland: prelimi- Green Roofs for Healthy Cities, 2010. http://www.greenroofs.org/. nary observations. Urban Habitats 4, 37e50. Grime, J.P., Hodgson, J.G., Hunt, R., 2007. Comparative Plant Ecology: A Functional Blanc, P., 2010. The Vertical Garden, from Nature to Cities. http://www. Approach to Common British Species, second ed. Castlepoint Press, Colvend, verticalgardenpatrickblanc.com/mainen/. UK. Blunden, M, Council spends another £130,000 on living wall after the first one died. Grimmond, C.S.B., Oke, T.R., 1999. Aerodynamic properties of urban areas derived London Evening Standard, 23rd April 2010. http://www.thisislondon.co.uk/ from analysis of surface form. Journal of Applied Meteorology 38, 1262e1292. standard/article-23827300-council-spends-another-pound-130000-on-living- Haila, Y., 1999. Biodiversity and the divide between culture and nature. Biodiversity wall-after-the-first-one-died.do. and Conservation 8, 165e181. Bormann, H., Balmori, D., Geballe, G., 1993. Redesigning the American Lawn. Yale Hinchliffe, S., Whatmore, S., 2006. Living cities: towards a politics of conviviality. University Press, New Haven, CT. Science and Culture 15, 123e138. Bradley, G., 1995. Urban forest landscapes: integrating multidisciplinary perspec- Hobbs, R.J., Arico, S., Aronson, J., Baron, J.S., Bridgewater, P., Cramer, V.A., tives. In: Bradley, G.A. (Ed.), Urban Forest Landscapes: Integrating Multidisci- Epstein, P.R., Ewel, J.J., Klink, C.A., Lugo, A.E., Norton, D., Ojima, D., plinary Perspectives. University of Washington Press Publisher, Washington, Richardson, D.M., Sanderson, E.W., Valladares, F., Vila, M., Zamora, R., Zobel, M., pp. 1e11. 2006. Novel ecosystems: theoretical and management aspects of the new Brenneisen, S., 2006. Space for urban wildlife: designing green roofs as habitats in ecological world order. Global Ecology and Biogeography 15, 1e7. Switzerland. Urban Habitats 4, 27e36. Imam, K.Z.E.A., 2006. Role of urban greenway systems in planning residential Carter, T., Fowler, L., 2008. Establishing green roof infrastructure through environ- communities: a case study from Egypt. Landscape and Urban Planning 76, mental policy instruments. Environmental Management 42 (1), 151e164. 192e209. Clarkson, B.D., Wehi, P.M., Brabyn, L.K., 2007. A spatial analysis of indigenous cover Jargowsky, P.A., 1996. Take the money and run: economic segregation in US patterns and implications for ecological restoration in urban centres, New metropolitan areas. American Sociological Review 61 (6), 984e998. Zealand. Urban Ecosystems 10, 441e457. Jones, R., 2003. A celebration of urban entomology. British Journal of Entomology Cohn, J.P., 2008. Citizen science: can volunteers do real research? BioScience 58 (3), and Natural History 16, 109e121. 192e197. Kadas, G., 2006. Rare invertebrates colonizing green roofs in London. Urban Habi- Colding, J., 2007. ‘Ecological land-use complementation’ for building resilience in tats 4, 66e86. urban ecosystems. Landscape and Urban Planning 81, 46e55. Kinzig, A.P., Warren, P., Martin, C., Hope, D., Katti, M., 2005. The effects of human Collinge, S.K., 1996. Ecological consequences of habitat fragmentation: implications socioeconomic status and cultural characteristics on urban patterns of biodi- for landscape architecture and planning. Landscape and Urban Planning 36, versity. Ecology and Society 10 (1), 23. 59e77. Köhler, M., 2006. Long-term vegetation research on two extensive green roofs in Cooper, C.B., Dickinson, J., Phillips, T., Bonney, R., 2007. Citizen science as a tool for Berlin. Urban Habitats 4, 3e26. conservation in residential ecosystems. Ecology and Society 12 (2), 11. Köhler, M., 2008. Green facades e a view back and some visions. Urban Ecosystems Darlington, A., 1981. Ecology of Walls. Heinemann Educational Books, London. 11, 423e436. Delaney, D.G., Sperling, C.D., Adams, C.S., Leung, B., 2008. Marine invasive species: Kuhn, I., Klotz, S., 2006. Urbanization and homogenization - Comparing the floras of validation of citizen science and implications for national monitoring networks. urban and rural areas in Germany. Biological Conservation 127 (3), 292e300. Biological Invasions 10, 117e128. Li, Z.G., Wu, F.L., 2006. Socio-spatial differentiation and residential inequalities in Dobson, A.P., Bradshaw, A.D., Baker, A.J.M., 1997. Hopes for the future: restoration Shanghai: a case study of three neighbourhoods. Housing Studies 21 (5), ecology and conservation biology. Science 277 (5325), 515e522. 695e717. Dodds, W.K., 2009. Laws, Theories and Patterns in Ecology. University of California Lindenmayer, D.B., 2009. Large-scale Landscape Experiments: Lessons from Tumut. Press, Los Angeles. Cambridge University Press, Cambridge. Dover, J.W., 1997. Conservation headlands: effects on butterfly distribution and LivingRoofs, 2010. http://www.livingroofs.org/. behavior. Agriculture, Ecosystems and Environment 63 (1), 31e49. Lorimer, J., 2008. Living roofs and brownfield wildlife: towards a fluid biogeography Dunnett, N., Kingsbury, N., 2008. Planting Green Roofs and Living Walls. Timber of UK nature conservation. Environment and Planning A 40 (9), 2042e2060. Press, London. Lundholm, J.T., Richardson, R.J., Habitat analogues for reconciliation ecology in Dunnett, N., Nagase, A., Hallam, A., 2008. The dynamics of planted and colonising urban and industrial environments. Journal of Applied Ecology, in press. species on a green roof over six growing seasons 2001e2006: influence of McCaffrey, R.E., 2005. Using citizen science in urban bird studies. Urban Habitats substrate depth. Urban Ecosystems 11, 373e384. 3 (1), 70e86. Dvorak, B., Volder, A., 2010. Green roof vegetation for North American ecoregions: Miller, J.R., 2005. Biodiversity conservation and the extinction of experience. Trends a literature review. Landscape and Urban Planning 96, 197e213. in Ecology and Evolution 20, 430e434. Elton, C.S., 1958. The Ecology of Invasions by Animals and Plants. University of Molineux, C.J., 2010. Development of suitable growing media for effective green Chicago Press, Chicago. roofs. PhD thesis, Royal Holloway University, Egham, UK. Emilsson, T., 2008. Vegetation development on extensive vegetated green roofs: Molineux, C.J., Fentiman, C.H., Gange, A.C., 2009. Characterising alternative recycled influence of substrate composition, establishment method and species mix. waste materials for use as green roof growing media in the UK. Ecological Ecological Engineering 33, 265e277. Engineering 35 (10), 1507e1513. Ferguson, B.K., 2005. Porous Pavements. CRC Press, Boca Raton, Florida. Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R.R., Doshi, H., Dunnett, N., Forman, R.T.T., 2008. Urban Regions: Ecology and Planning beyond the City. Gaffin, S., Köhler, M., Liu, K.K.Y., Rowe, B., 2007. Green roofs as urban ecosys- Cambridge University Press, Cambridge. tems: ecological structures, functions and services. BioScience 57, 823e833. Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau (FLL), 2002. Pauchard, A., Aguayo, M., Pena, E., Urrutia, R., 2006. Multiple effects of urbanization Guidelines for the Planning, Execution and Upkeep of Green Roof Sites (English on the biodiversity of developing countries: the case of a fast-growing metro- ed.). Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau. politan area (Concepcion, Chile). Biological Conservation 127 (3), 272e281. R.A. Francis, J. Lorimer / Journal of Environmental Management 92 (2011) 1429e1437 1437

Peiser, R.B., 1989. Density and urban sprawl. Land Economics 65 (3), 193e204. Soulé, M.E., 1990. The onslaught of alien species, and other challenges in the coming Redford, K.H., Richter, B.D., 1999. Conservation of biodiversity in a world of use. decades. Conservation Biology 4 (3), 233e239. Conservation Biology 13 (6), 1246e1256. The Green Roof Centre, 2010. Frequently asked questions: how much does a green Rosenzweig, M.L., 1995. Species Diversity in Space and Time. Cambridge University roof cost?. http://www.thegreenroofcentre.co.uk/pages/faq.html. Press, Cambridge. Thompson, K., 2007. No Nettles Required: The Truth about Wildlife Gardening. Rosenzweig, M.L., 2003a. Reconciliation ecology and the future of species diversity. Transworld Publishers, London. Oryx 37, 194e205. Tilman, D., 2000. Causes, consequences and ethics of biodiversity. Nature 405, 208e211. Rosenzweig, M.L., 2003b. Win-win Ecology: How the Earth’s Species Can Survive in Troy, A.R., Grove, J.M., O’Neil-Dunne, J.P.M., Pickett, S.T.A., Cadenasso, M.L., 2007. the Midst of Human Enterprise. Oxford University Press, Oxford. Predicting opportunities for greening and patterns of vegetation on private Ryall, C., Hatherell, P., 2003. A survey of strategies adopted by UK Wildlife Trusts in urban lands. Environmental Management 40 (3), 394e412. the promotion of gardening for wildlife. The Environmentalist 23, 81e87. United Nations Human Settlements Programme, 2008. State of the World’s Cities Schadek, U., Strauss, B., Biedermann, R., Kleyer, M., 2009. Plant species richness, 2008/9: Harmonious Cities. Earthscan, London. vegetation structure and soil resources of urban brownfield sites linked to Valtonen, A., Saarinen, K., Jantunen, J., 2007. Intersection reservations as habitats for successional age. Urban Ecosystems 12 (2), 115e126. meadow butterflies and diurnal moths: guidelines for planning and manage- Schrader, S., Böning, M., 2006. Soil formation on green roofs and its contribution to ment. Landscape and Urban Planning 79, 201e209. urban biodiversity with emphasis on Collembolans. Pedobiologia 50, 347e356. Weinmaster, M., 2009. Are green walls as “green” as they look? An introduction to Sheffield Local Biodiversity Action Partnership, 2010. Habitat Action Plan: Green Roofs. the various technologies and ecological benefits of green walls. Journal of Green http://www.thegreenroofcentre.co.uk/Library/Default/Documents/Sheffield% Building 4 (4), 3e18. 20Green%20Roof%20HAP%20Feb%202010_634159246532552600.pdf. Wheater, C.P., 1999. Urban Habitats. Routledge, London.