Kazuhito Ishimatsu, Keitaro Ito, Yasunori Mitani

景観生態学 17（2）31 - 41 ．2012 総 説

Developing urban green spaces for : a review

Kazuhito Ishimatsu 1*・Keitaro Ito 1・Yasunori Mitani 2

1Department of Civil Engineering, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu-shi, Fukuoka, 804-8550, Japan 2Department of Electrical Engineering and Electronics, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu-shi, Fukuoka, 804-8550, Japan

生物多様性保全を目的とした都市緑化

石松 一仁 1*・伊東 啓太郎 1・三谷 康範 2

1 九州工業大学大学院工学府建設社会工学系 〒 804-8550 福岡県北九州市戸畑区仙水町 1-1 2 九州工業大学大学院工学府電気電子工学系 〒 804-8550 福岡県北九州市戸畑区仙水町 1-1

Abstract: Urban green spaces, which are important for human and wildlife in the , have changed into man-made spaces. Increased urbanisation has had and continues to have a negative impact on urban green spaces, and affects the urban microclimate as represented by‘ (UHI)’ phenomena. Especially, habitat fragmentation can be extreme within urban ecosystems, and fragments of natural vegetation may be too small or even too isolated to support some species. Therefore, the networks, which offer habitats and corridors that help conserve biodiversity, are also important to maintain the ecological services of a sustainable urban landscape, as well as total green area. However, there are rarely enough open spaces due to urban densification. This is why rooftops of , which had not previously been regarded as spaces for planting for vegetation, have been utilised as a type of open space, and so green roofing has become one of the gradually developing fields of urban ecological engineering. This present paper aims to explore the potential of rooftops as habitats of comparing cases in Japan and UK, and pave the way for a preservation of urban biodiversity under restricted urban environmental conditions. As a result, it was suggested that Japanese industries consider the concept of brown/biodiverse roofs instead of extensive roofs with sedum or lawn. At the same time, intensive roofs should be efficiently installed to provide‘ stepping stone’ in urban areas not having enough open space. If possible, however, to create habitats on the ground is more preferable than on the rooftop due to accessibility. Finally, if impervious spaces (e.g., and asphalt) are replaced with pervious spaces (e.g., green area or brownfield), it is significant for not only urban biodiversity but also UHI.

Key Words: Urban area, Green space, Biodiversity, Green roof, Brown/biodiverse roof

要旨：生物多様性だけでなく我々の生活の豊かさを保つために極めて重要な都市緑地は，人工的な空間に置き換えられている．その 最大の原因である急速な都市化は，都市緑地に悪影響を及ぼし続け，ヒートアイランド現象に代表される局所的な気候変動まで引き 起こしている．さらに，都市域において野生動植物の生息地の断片化・孤立化は深刻であり，この変化に適応できない生物種は絶滅 に追いやられている．そのため，単に緑地の総面積を増やすだけでなく，残存する緑地間のネットワーク性強化が，弱体化した生態 系サービスを復元する有効な手法であると考えられる．しかしながら，都市の過密化により緑地を創出するためのスペースはほとん ど残されていない．以前は緑化空間として見なされていなかった建物の屋上に近年注目が集まり，景観生態学・緑化工学分野におい て屋上緑化技術は次第に発展してきている．本総説は，我が国と英国の屋上緑化の事例を比較しながら今後の屋上空間の可能性につ いて調査すると同時に，生物にとって厳しい条件下で生物多様性を保全するための緑化手法を提案することを目的とした．その結果， 我が国のセダムやシバによる単一植栽による粗放型屋上緑化は，生態学的価値が低いだけでなく期待されている室内熱環境改善効果 も大きくないため，英国で普及しているブラウンルーフに切り替えた方が，生物多様性保全や室内熱環境の観点から，より有益であ

* 連絡先：[email protected] 受付：2012 年 10 月 14 日／受理：2012 年 10 月 29 日

－ 31 － Developing urban green spaces for biodiversity

ることが示唆された．さらに，集約型屋上緑化は残存する緑地間に飛び石のように配置することで，ネットワーク性を強化すること ができると考えられた．しかしながら，屋上空間に到達できない生物種が存在する等の理由から，屋上と地上の緑地を同等に評価す ることは難しい．また，地上を覆っているアスファルトやコンクリートなどの不透水層をブラウンフィールドのような透水層に切り 替えることができれば，生物多様性保全とヒートアイランド現象緩和の両方に大きく貢献できると考えられた．

キーワード：都市域，緑地，生物多様性，屋上緑化，ブラウンルーフ

Introduction wildlife (Attwell 2000). In the past two decades, landscape ecology has become Urban green spaces can be important elements one of the most rapidly developing ecological fields contributing to urban (Esbah et al. 2009) worldwide (Kong et al. 2007), because increased urbanisation and ecosystem services, because they can contribute to the has had and continues to have a negative impact on urban reduction of various types of , the improvement green spaces (Kong and Nakagoshi 2006), and affects the of microclimate conditions, the absorption of stormwaters, urban microclimate (Georgi and Dimitriou 2010) as and the prevention of flooding (Georgi and Dimitriou represented by ‘Urban Heat Island (UHI)’ phenomena. 2010). In particular, in cases where urban green space Unfortunately, urban green spaces, which are important for includes not only grass but also trees, the contributions to human and wildlife in the urban area, have largely been the above functions of urban green spaces increase. For changed into man-made spaces. In other words, urban green example, in terms of the improvement of the microclimate spaces are increasingly heavily managed and used by people in urban spaces, deciduous trees offer shade during the for recreation, such that the potential for biodiversity is summer and as Georgi and Dimitriou (2010) note, the reduced. In addition, open spaces are increasingly covered suitable selection of the right species can enhance cooling with hard surfaces rather than left green spaces. Thus, the through evapotranspiration reducing the temperature by absence of green spaces is characteristic of most up to 3.1 degrees C. Evapotranspiration creates pockets of contemporary globally (Georgi and Dimitriou 2010). In lower temperature in an urban environment, known as the addition, loss and isolation of habitats due to urbanisation ‘phenomenon of oases’. Conversely, it permits the sun to threaten biodiversity and warrant limits on development shine through the branches during the winter. (Kong et al. 2010). If these areas become separated from one Furthermore, the spaces are an effective way of another by barriers such as large expanses of buildings and protecting significant features and scenic views, as well as other human structures, species extinction may occur (Esbah providing buffers for differing land uses and valuable et al. 2009), because the majority of the remnant urban spaces for urban wildlife (Esbah et al. 2009). They shelter wildlife is located in small fragments of indigenous the native flora and fauna and help maintain native vegetation that have been set aside during development (Rudd biodiversity (Esbah et al. 2009), and offer important et al. 2002). These fragments are commonly subject to high harbours for remnant urban wildlife (Kong et al. 2010). levels of disturbance, due to the nature of human activities Some species cope with, and survive in, urban areas better undertaken within or adjacent to these areas (Fernandez- than others (Wood and Pullin 2002); for example, Sattler Juricic 2000; Marzluff and Ewing 2001). Therefore the et al. (2010) note that urban areas host many arthropod networks, which offer habitats and corridors that help species and cannot be regarded as species-poor conserve biodiversity (Kong et al. 2010), are also important environments. Green spaces can obviously provide to maintain the ecological components of a sustainable urban vegetation and‘ unsealed’ surfaces, and ameliorate the landscape (Sandström et al. 2006), as well as total green area. detrimental effects of urbanisation on species assemblages Because of this, rapid urbanisation makes people more aware by preserving or creating habitat, or by maintaining of urban green space, and there is an increasing realisation corridors for movement through the urban matrix that it is difficult to live without some contact with nature (González-García et al. 2009; Smith et al. 2006). Although (Kong and Nakagoshi 2006). urban areas are among the most modified and complex of However, there are rarely enough open spaces due to landscape, they still maintain a significant diversity of urban densification. This is why rooftops of buildings,

－ 32 － Kazuhito Ishimatsu, Keitaro Ito, Yasunori Mitani which had not previously been regarded as spaces for substrate base, offering between 25 and 100 mm deep root planting for vegetation, have been utilised as a type of zones due to restrictions on weight loading on the open space, and so green roofing has become one of the ’s structure. However, because of the thin gradually developing fields of urban ecological substrate layer, the extensive roof environment is a harsh engineering. Even so, regarding objectives for installing one for plant growth; limited water availability, wide green roofing there are big differences between countries temperature fluctuations, and high exposure to wind and due to various backgrounds. Especially, it should be noted solar radiation create high stress. As a result, a relatively that the UK has moved brownfield’s ecosystems to small range of plant species is normally used for extensive rooftops of buildings for enhancing urban biodiversity green roofs. Sedum is a common and very suitable plant over the last decade. This paper aims to explore the for use on extensive green roofing (Castleton et al. 2010; potential of rooftops as habitats of urban wildlife Oberndorfer et al. 2007). While ensuring some degree of comparing cases in Japan and UK, and pave the way for a success under stressful growing conditions, widespread preservation of urban biodiversity under restricted urban use of sedum-only green roofs also has the disadvantages environmental conditions. typical of any ecological system with limited species diversity. Misunderstanding functions of green roofs in Japan According to Ministry of Land, Infrastructure, Transport and Tourism (2009), the total green roof area in Green roofs are mainly divided into two types: intensive Japan has been increasing steadily during the past decade and extensive (Molineux et al. 2009; Nagase and Dunnett (Fig. 1). Almost all of these green roofs aim to improve 2010; Schrader and Böning 2006; Wilkinson and Reed indoor thermal environment of midsummer (Iijima 2008), 2009). Intensive green roofs are characterised by a thick and about half of these roofs are extensive roofs with lawn layer (more than 200 mm) of growing medium or grass or sedum (Ministry of Land, Infrastructure, substrate, in which a wide range of plants and vegetation Transport and Tourism 2009). However, it has been can be grown, particularly if irrigation is available. reported that evapotranspiration velocity from area However, the relatively heavy weight of the substrate without any plants is similar to one from lawn grass or requires additional structural support by the building, and sedum areas, therefore in terms of cooling irrigated-soil therefore only a limited range of buildings can be used for may be key, regardless of plants (Ferrante and installing intensive green roofing. On the other hand, Mihalakakou 2001; Ohno et al. 2006). Furthermore, extensive green roofs are generally substrate based with a regarding not only sedum but also all plants, the process vegetated layer or a sedum mat, either on its own with a of evapotranspiration takes place in the plants’ leaves sponge membrane for moisture retention or with a rather than in the soil, drawing energy from the

2,500

2,000

1,500

1,000

Total green roof areas (ha) Total 500

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 Time (year)

Fig. 1 ProcessFig. 1 ofProcess total of green total green roof roof areas areas in in Japan Japan (M(Ministryinistry of Land,of Land, Infrastructure Infrastructure and Tourism and 2009) Tourism 2009)

－ 33 － Developing urban green spaces for biodiversity

environment and not directly from the soil-covered but has, to differing degrees, been abandoned and building (Pearlmutter and Rosenfeld 2008). In contrast, recolonised by different ecological assemblages (Lorimer the watered-soil layer on a roof can indeed be used as an 2008; Schadek et al. 2009). effective means of evaporative cooling and has the How did brownfield sites appear? Firstly, many particular benefit of producing this cooling during the buildings destroyed by bombing raids during World War II hottest hours (Al-Turki et al. 1995; Pearlmutter and were not immediately rebuilt, and these vacant sites were Rosenfeld 2008). In addition, plants in green roofs prevent colonised by wildlife (Grant 2006). Secondly, the process watered-soil from evaporating for cooling. In terms of of industrial change has resulted in the creation of cooling purposes, the role of plants on roofs is for shading brownfields across Europe, particularly in urban areas (Ferrante and Mihalakakou 2001; Palomo and Barrio (Grimski and Ferber 2001). As 's industry and 1998). Therefore, it has been suggested that cover- docks declined, other sites were cleared and subsequently materials other than plants could provide the wetted soil colonised by diverse vegetation (Grant 2006). While surface with substantial shading, without limiting the and come to mind as obvious refuges for nature, potential for cooling by evaporation, that is to say, the plants and animals are often more adventurous with regard possible ways of reducing this energetic liability is to to the places they colonise and use (Kadas 2006). As our “eliminate” the exposed roof by shading the roof area world becomes increasingly developed, many species of with some structures like tight weave mesh or in some wildlife adapt in unpredictable ways (Brack Jr. 2006). way sheltering it with a substantially thick layer of soil While brownfield is typically considered to have no or (Pearlmutter and Rosenfeld 2008). negative economic value, recent research suggests that Although the environmental functions of green roofs there are many ecosystem services provided by such (e.g., reducing UHI, mitigation of rainwater runoff, and so habitats (Robinson and Lundholm 2012). Brownfields on) are often promoted, the cost-effectiveness is not provide habitat conditions similar to more natural habitats, superior to alternatives due to the fact that installation and and they may help maintain populations of some rare maintenance costs are so expensive (Ishimatsu and Ito species (Eyre et al. 2003). Furthermore, compared with 2011). There are a number of inexpensive ways to achieve lawns and , the brownfield site showed higher similar environmental aims. It should be noted that green levels of ecosystem service provision for indicators of roof becomes essential only in the case of rehabilitating habitat provision, both plant species and invertebrate urban biodiversity under the condition that open space in diversity (Robinson and Lundholm 2012). In the UK, urban area is usually small (Ishimatsu et al. 2010). brownfields include some of the most species-diverse habitats left (Kadas 2006), and are thought to support a How did rooftops of buildings become habitats for minimum of 12-15% of Britain’s nationally rare urban wildlife in the UK

Over the last decade, it has been thought that rooftop spaces can be habitats for urban wildlife in the UK, especially in London. It is called“ brown/biodiverse roof”. This section reveals the process of introducing brown/ biodiverse roof, as explaining why brownfields are important for urban biodiversity. In urban areas, the origin of brownfields (Fig. 2) is principally demolished buildings ( and factories), although the definition also includes landfills, sand or gravel pits, industrial dumps, former collieries and railway Fig. 2 Brownfield in the of London. These areas are quite important for urban wildlife (after Fig. 2 Brownfield in the City of London. These areas lands (Small et al. 2003). To sum up, brownfield refers to Ishimatsu and Ito 2011). are quite important for urban wildlife (after land that was previously developed for housing or industry Ishimatsu and Ito 2011).

－ 34 － Kazuhito Ishimatsu, Keitaro Ito, Yasunori Mitani invertebrate (Small et al. 2003). Eyre et al. (2003) by slowing the pace of redevelopment and by not hurrying surveyed a total of 78 brownfields for beetles between to tidy up and redevelop brownfields. 1991 and 2001 throughout England, as a result generating One of the most successful strategies that has been a total of 182 records of 46 nationally rare species (16 employed by the third constituency in its efforts to campaign ground, 10 rove and 20 phytophagous species). A number for urban biodiversity and brownfield conservation has been of these species are more usually associated with other, to compromise with developers of brownfields and to more natural habitats such as riverine sediments, sandy persuade them to install wildlife-friendly mitigation heaths and chalk grasslands. They note, brownfields are technologies on roofs of buildings (Lorimer 2008). This is important habitats for beetles, and there is evidence that why rooftops of buildings have been regarded as installment the situation is similar for other invertebrate groups. sites of threatened brownfields. Wasteland habitats associated with urban brownfields are of intrinsic importance, relying on the codification of these Brown/biodiverse roof habitats as distinctive habitats characterised by suits of species and abiotic conditions that fulfill a range of This is brown/biodiverse roof (Fig. 3), which is usually scientific criteria (Harrison and Davies 2002). constructed for habitat mitigation in the UK, especially in From the 1980s to the present day, however, with UK London, as the only mitigation obliging constructors to government policy encouraging reuse of abandoned sites install brown/biodiverse roofs comes from conservation of such as brownfields, these sanctuaries for nature have a rare bird species, the black redstart (Molineux et al. been increasingly redeveloped (Grant 2006). The UK 2009). The black redstart is listed as a priority species for government has set a target of building 60% of new the London Biodiversity Action Plan sponsored by the dwellings on previously developed land (Lorimer 2008). London Biodiversity Partnership, as a Bird of conservation Redevelopment of brownfields is widely acknowledged as concern, and a Red Data Book species (London Wildlife one of the major tools to achieve sustainable development Trust 2001). They are reliant on old vacant lots and (Grimski and Ferber 2001). Because one of the reasons for brownfields and are thus now under threat from emergence of brownfields is economic structural change regeneration of much of their breeding ground (Gedge and the decline of traditional industries, they are 2003; London Wildlife Trust 2001). frequently coupled with severe loss of jobs and, as a direct The roof membrane for each section is generally made of consequence, decline of the neighbourhoods around butyl rubber and protected by a nonwoven polypropylene derelict sites or even of whole cities. Although new parks geotextile fleece supported by a plywood deck (Grant 2006). and green spaces have occasionally been created within To promote biodiversity, a variety of substrates are used, redeveloped sites, these are, unfortunately, nearly always including a chalk and subsoil mixture, loamy topsoil, and ecologically impoverished, lacking the diversity provided by the original vacant sites (Grant 2006). Due to this, the amount of brownfields with value in Britain is set to decrease dramatically under current home-building and regeneration policies (Harrison and Davies 2002; Small et al. 2003). Huge swathes of industrial brownfield along the Thames Estuary are slated for redevelopment, and this will have an immense impact on wildlife (Kadas 2006). A challenge that faced brownfield conservationists in East London was to persuade local residents and policy makers that valuable species and ecological assemblages could be found inhabiting brownfield Fig. 3 Brown/biodiverse roof at Royal Holloway, University of London (after Ishimatsu and Ito Fig. 3 Brown/biodiverse roof at Royal Holloway, sites in the city (Lorimer 2008). Angold et al. (2006) suggest 2011). University of London (after Ishimatsu and Ito that planners can have a positive impact on urban biodiversity 2011).

－ 35 － Developing urban green spaces for biodiversity gravel. In addition, crushed brick favours ruderal presence of spiders would suggest a varied invertebrate vegetation and can thus be used to replicate the brownfield fauna present at the survey site. At Royal Holloway, biodiversity that was in place before development began University of London, moss forests, which provide cover (Lorimer 2008). The brown/biodiverse roof aims to for thousands of microscopic animals and habitat for other provide vegetal and animal species with habitats while invertebrates (Natural England 2007), can be seen on somehow managing to grow vegetation without any brown/biodiverse roofing (Fig. 5). In addition, it was irrigation system or . reported that ground-nesting birds utilised brown/ biodiverse roofs as a nesting location (Brenneisen 2006), Techniques to enhance biodiversity on extensive roofs though this example is from Switzerland. Unfortunately, however, there is still a lack of Firstly, from associated brownfields and other valuable information about wildlife on brown/biodiverse roofs due vegetated areas, the top 150 mm of substrate must be to the fact they do not have a very long history. Brown/ carefully removed and appropriately stored so that some biodiverse roofing needs more time to be investigated of the existing vegetation, seed bank and soil organisms because of its dependence on successions. In the presence can be conserved (if suitable) for subsequent use on of soil, rainfall and sunlight, whether on rooftops or not, extensive roofs (Brenneisen 2006); for example, white and successions suitable for each environment will take place biting stonecrops have some of the most spectacular over time. flowering displays and are very attractive to bees, butterflies and other insects (Natural England 2007). In addition, adaptation of spider and beetle fauna to natural soil and other substrates such as sand and gravel from riverbanks seemed to be a factor for successful colonisation (Brenneisen 2006). Secondly, small logs laid across the substrate will not only provide shelter for insects but also create nesting sites for many small bees and wasps that burrow into dead timber (Natural England 2007; Robinson and Lundholm 2012). Thirdly, designing brown/biodiverse roofs so that they Fig. 4 Typical cross-section of a brown/biodiverse roof (after Ishimatsu and Ito 2011). have varying substrate depths and drainage regimes Fig. 4 Typical cross-section of a brown/biodiverse roof (after Ishimatsu and Ito 2011). creates a mosaic of microhabitats on and below the soil surface and can facilitate colonisation by a more diverse flora and fauna (Brenneisen 2006). There is increasing use of locally derived lightweight granular waste materials as sustainable sources for roof substrates (Oberndorfer et al. 2007). Lastly, Fig. 4 is a diagram of a typical cross-section of a brown/biodiverse roof, showing use of diverse soil surfaces and substrates to create a mosaic of wildlife habitats for colonisation by a more diverse flora and fauna. In fact, it was reported that spiders, beetles, bees, wasps, ants and so on, which can be seen at brownfields, were found on Laban Dance Centre (brown/biodiverse) Fig. 5 Unplanted mosses at brown/biodiverse roof at Royal Holloway, University of London (after roof in London (Kadas 2006). As spiders are predatory, Fig.Ishimatsu 5 Unplanted and Ito 2011). mosses at brown/biodiverse roof at Royal Holloway, University of London (after they occupy a mid trophic level in the food chain. The Ishimatsu and Ito 2011).

－ 36 － Kazuhito Ishimatsu, Keitaro Ito, Yasunori Mitani

Adaptation and limitation of habitats on rooftops on the outskirts of cities and beyond (Schrader and Böning 2006). Those roofs are only a method to delay the It should be noted that green roof industries consider the weakening of urban biodiversity. It should be noted that to concept of brown /biodiverse roofs. It is not always true restore urban green spaces on the ground is controversially that a soil layer without any plants has no ecological the most effective method for enhancing urban biodiversity. value; for example, there are some invertebrates which favour areas beneth stones or logs as their habitats. If Conclusions budgets allocated for creating extensive roofs with lawn and sedum can be used for brown/biodiverse roofs, there Land and conservation management is increasingly will be much more ecological areas in urban area. concerned with regional-scale habitat analyses (Bunn et In urban environments, vegetation has largely been al. 2000) due to the fact that high-density development replaced by dark and impervious surfaces (Oberndorfer et and rapid urban sprawl have affected the urban al. 2007). Many of the well-known urban environmental vegetation’s composition and biodiversity (Kong et al. problems are caused by loss of biodiversity and natural 2010). As a result urban areas, unfortunately, provide an habitats, mainly as a result of surface sealing through excellent opportunity to study the effects of habitat construction measures, increased loads of heavy metals fragmentation, because urban green areas are typically and organics, and emission of greenhouse gases (Schrader surrounded by completely hostile man-made matrix, even and Böning 2006). Those problems can be partially though gardens in suburban areas may provide additional mitigated by altering the buildings’ surficial properties resources for some organisms (Öckinger et al. 2009). For (Oberndorfer et al. 2007). The first step to avoid these example, Sandström et al. (2006) note there is a clear problems is to increase the amount of open spaces and increase in the number of bird species as well as individuals permeable surfaces as much as possible (Ferrante and from centre to the surroundings of the city in south-central Mihalakakou 2001). Sweden. This fact visibly indicates that urban forests are an On the other hand, intensive roofs should be efficiently important component of the urban landscape in terms of at installed to provide“ stepping stone” in urban areas not least bird species diversity. having enough open scape. They can support more Habitat fragmentation caused by urbanisation can be complicated biodiversity than brown/biodiverse roofs by extreme within urban ecosystems, and fragments of offering valuable wildlife sanctuaries and providing better natural vegetation may be too small or even too isolated to connectivity between existing habitats (Kim 2004). Some support some species (Savard et al. 2000). If they become water areas should also be simultaneously installed, isolated, small populations can lose genetic variation coupled with them if possible, because the combination of through inbreeding and genetic drift, and will become water and vegetation provides greater habitat diversity increasingly prone to extinction (Rouquette and Thompson (Hunter and Hunter 2008). Despite the fact that intensive 2007). In other words, as sites become more isolated, roofs are more beneficial for the urban environment, cost dispersing individuals become less likely to find suitable problems still remain, unfortunately. Because of this, it is habitat (Rouquette and Thompson 2007). Thus, seed quite important to combine brown/biodiverse roofs with dispersal and wildlife movements have a potentially intensive roofs. profound effect on the population dynamics and constitute However, some animals cannot reach the rooftop areas an essential survival process in patchy habitats (Angelibert due to their restricted mobility, and earthworms are unable and Giani 2003; Keller et al. 2010; Rouquette and to survive on extensive roofs due to the limited substrate Thompson 2007; Rudd et al. 2002). depth; they perish during high temperatures in summer Dispersal of wildlife is usually risky, and there will because they cannot migrate to deeper and cooler regions always be a balance of risk between living longer in an of the soil (Brenneisen 2006). Thus, brown/biodiverse already occupied habitat and risking resources in an act of roofs or intensive roofs should never be considered a colonisation (Angelibert and Giani 2003). Dispersal will justification for destroying natural or semi-natural habitats be efficient if the benefits of reaching a better site exceed

－ 37 － Developing urban green spaces for biodiversity the cost from the risk of death during dispersal (Angelibert This present paper suggests that rooftop space can and Giani 2003). Furthermore, whether or not patches can contribute to enhance urban biodiversity. If possible, be recolonised depends on the availability of dispersing however, to create habitats on the ground is more individuals and the ease with which these individuals can preferable than on the rooftop due to accessibility. move about within the landscape (Kindlmann and Burel Moreover, if impervious spaces (e.g., concrete and 2008). Due to this, new habitat should be created between asphalt) are replaced with pervious spaces (e.g., green area the existing sites to reconnect the extant populations, and and brownfield), it is significant for not only urban connectivity should be a key component of all management biodiversity but also UHI. Even so, the character of habitat planning (Rouquette and Thompson 2007). In particular, it in urban areas desired for biodiversity is not completely is often said that greenways (corridors) provide an compatible with the needs for a secure human environment opportunity to reduce the impacts of habitat fragmentation (e.g., juvenile crime). As a consequence, the directives in (Linehan et al. 1995). Given that the primary function of management plans aim to remove potentially dangerous greenways is to provide linkages, they represent one of the places (e.g., shrub on urban green spaces). Another most effective tools in preventing fragmentation and conflict between biodiversity and people is the risk of perhaps species loss at the regional level. However, it is falling trees or branches from large old trees, and difficult to implement it, as of today, because a lot of accordingly insurance implications that can force the buildings have occupied urban areas. That means there is removal of standing dead wood. To deal with the planning no open space. Therefore, rooftop spaces on buildings can dilemma between social security and biodiversity support a development of green areas and ecological maintenance, one solution may be small-scale networks in urban areas. planning in parks to create vegetated zones with different Yet, landscape connectivity changes with the choice of characteristics in urban green spaces (Sandström et al. measures. For example, connectivity measures based on 2006). Understanding the ecological interactions between distances may be appropriate for birds as the matrix and built and natural areas within urban areas can help us corridors may not be of great importance in this case. manage and plan urban environments to promote diversity Measures based on the amount of corridors in the and ecological function (Newbound et al. 2010). landscape may be appropriate for small mammals (e.g., In conclusion, an important aspect in dealing with carabid beetles) whose movement is affected by matrix biodiversity is that not all species are equal. Species vary permeability. Furthermore, road and railway lines are in size, shape, abundance, distribution, trophic position, considered to be barriers against the movement of animals ecological function feeding habitats and desirability moving on the ground (Kamada 2005). Evidently, each of (Savard et al. 2000). Some species may play important these measures will give us a different connectivity for the roles in the community, so their absence would same landscape (Kindlmann and Burel 2008). Another significantly affect several other species (Savard et al. very important component of network planning is the 2000). For example, insect pollination is a vital ecosystem consideration of private and unprotected areas (e.g., function in terrestrial systems (Robinson and Lundholm brownfield). Those habitats can be an invaluable food and 2012). At the same time, it can be predicted that it will be habitat source for a wide range of urban species and are quite important to pay attention to brownfield wildlife in essential in developing the matrix that supports the large the near future, in countries facing severe population numbers of corridors required for connectivity. Public decline, especially Japan and Republic of Korea, where education on with native plants and providing there is a possibility that brownfields will increase proper habitats is another tool to enhance the connectivity (Ishimatsu and Ito 2011). Conservation planners, therefore, of the region and improve the viability of the corridors. have to consider the quality of urban green spaces with Conservation planners should be concerned with how to their aesthetic value. Öckinger et al. (2009) found that invest resources wisely to realise the greatest return, in traditional parks had the lowest number of butterfly terms of protected or enhanced biodiversity (Kadoya species because the parks usually lack most of the features 2009). that constitute suitable butterfly habitat. Typically, they

－ 38 － Kazuhito Ishimatsu, Keitaro Ito, Yasunori Mitani have short grass turf that is cut regularly, low numbers of 265-278. native plant species and a low structural diversity. On the Castleton, H.F., Stovin, V., Beck, S.B.M. and Davison, J.B. other hand, it was also found that brownfields had a high 2010. Green roofs: building energy savings and the value for urban biodiversity and it may be more beneficial potential for retrofit. Energy and Buildings 42: to leave brownfields unmanaged than to try to manage 1582-1591. urban and suburban parks for biodiversity. But, what kind Esbah, H., Cook, E.A. and Ewan, J. 2009. Effects of of green space do urban dwellers prefer? Mathey and Rink increasing on the ecological integrity of (2010) recognise brownfields as a new form of urban open space preserves. Environmental Management 43: nature, and recommend that urban dwellers be informed 846-862. about the biodiversity value of brownfield therewith learn Eyre, M.D., Luff, M.L. and Woodward, J.C. 2003. Beetles to accept new aesthetical paradigms, under the condition (Coleoptera) on brownfield sites in England: An of shrinking cities. From now on, this approach from both important conservation resource? Journal of Insect conservation biodiversity and landscape design will be Conservation 7: 223-231. more significant. Finally, it might be easy for some Fernandez-Juricic, E. 2000. Avifaunal use of wooded invasive alien plants to colonise there because brownfields streets in an urban landscape. Conservation Biology 14: develop due to the abandonment. It will be also necessary 513-521. to monitor colonisations of invasive alien plants at Ferrante, A. and Mihalakakou, G. 2001. The influence of brownfields. Brownfields might have a possibility to be water, green and selected passive techniques on the ideal spaces for them. rehabilitation of historical building in urban areas. Solar Energy 70: 245-253. References Gedge, D. 2003‘. …From rubble to redstarts…’ Available at: www.laneroofing.co.uk/marketingbox/documents/ Al-Turki, A.M. Gari, H.N. and Zaki, G.M. 1995. generic/682732553_10Gedge.pdf (Accessed 8 Comparative study on reduction of cooling loads by December 2010). roof gravel cover. Energy and Buildings 25: 1-5. Georgi, J.N. and Dimitriou, D. 2010. The contribution of Angelibert, S. and Giani, N. 2003. Dragonfly urban green spaces to the improvement of environment characteristics of three odonate species in a patchy in cities: Case study of Chania, Greese. Building and habitat. Ecography 26: 13-20. Environment 45: 1401-1414. Angold, P.G., Sadler, J.P., Hill, M.O., Pullin, A., Rushton, González-García, A., Belliure, J., Gómez-Sal, A. and S., Austin, K., Small, E., Wood, B., Wadsworth, R., Dávila, P. 2009. The role of urban green spaces in fauna Sanderson, R. and Thompson, K. 2006. Biodiversity in conservation: the case of the iguana (Ctenosaura urban habitat patches. Science of The Total similis) in the ‘patios’ of León city, Nicaragua, Environment 360: 196-204. Biodiversity Conservation 18: 1909-1920. Attwell, K. 2000. Urban land resources and urban Grant, G. 2006. Extensive green roofs in London. Urban planting: Case studies from Denmark. Landscape and habitats 4(1): 51-65. 75: 125-142. Grimski, D. and Ferber, U. 2001. Urban brownfields in Brack Jr., V. 2006. Short-tailed shrews (Blarina Europe. Land Contamination and Reclamation 9(1): brevicauda) exhibit unusual behavior in an urban 143-148. environment. Urban habitats 4(1): 127-132. Harrison, C. and Davies, G. 2002. Conserving biodiversity Brenneisen, S. 2006. Space for urban wildlife: designing that matters: practitioner’s perspectives on brownfield green roofs as habitats in Switzerland. Urban habitats development and urban nature conservation in London. 4(1): 27-36. Journal of Environmental Management 65: 95-108. Bunn, A.G., Urban, D.L. and Keitt, T.H. 2000. Landscape Hunter, M.R. and Hunter, M.D. 2008. Designing for connectivity: A conservation application of graph conservation of insects in the built environment. Insect theory. Journal of Environmental Management 59: Conservation and Diversity 1: 189-196.

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