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Developing Biodiverse Green Roofs for Japan: Arthropod and Colonizer Plant Diversity on Harappa and Biotope Roofs
Ayako Nagase, Yoriyuki Yamada, Tadataka Aoki, and Masashi Nomura

Urban Naturalist, Special Issue No. 1 (2018): 16–38

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Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 16 URBAN NATURALIST 2018 Special Issue No. 1:16–38 Developing Biodiverse Green Roofs for Japan: Arthropod and Colonizer Plant Diversity on Harappa and Biotope Roofs Ayako Nagase1,*, Yoriyuki Yamada2, Tadataka Aoki2, and Masashi Nomura3 Abstract - Urban biodiversity is an important ecological goal that drives green-roof installation. We studied 2 kinds of green roofs designed to optimize biodiversity benefits: the Harappa (extensive) roof and the Biotope (intensive) roof. The Harappa roof mimics vacant-lot vegetation. It is relatively inexpensive, is made from recycled materials, and features community participation in the processes of design, construction, and maintenance. The Biotope roof includes mainly native and host plant species for arthropods, as well as water features and stones to create a wide range of habitats. This study is the first to showcase the Harappa roof and to compare biodiversity on Harappa and Biotope roofs. Arthropod species richness was significantly greater on the Biotope roof. The Harappa roof had dynamic seasonal changes in vegetation and mainly provided habitats for grassland fauna. In contrast, the Biotope roof provided stable habitats for various arthropods. Herein, we outline a set of testable hypotheses for future comparison of these different types of green roofs aimed at supporting urban biodiversity. Introduction Rapid urban growth and associated anthropogenic environmental change have been identified as major threats to biodiversity at a global scale (Grimm et al. 2008, Güneralp and Seto 2013). Green roofs can partially compensate for the loss of green areas by replacing impervious rooftop surfaces and thus, contribute to urban biodiversity (Brenneisen 2006). Green roofs can support arthropods (Hwang and Yue 2015, Kadas 2006, MacIvor and Lundholm 2011, MacIvor et al. 2015, Madre et al. 2013, Nagase and Nomura 2014), including both common and rare species (Brenneisen 2006, Grant 2006). In order to optimize biodiversity benefits, biodiverse roofs in Switzerland and the UK have focused on particular species of concern; e.g., Phoenicurus ochruros Gmelin (Black Redstart), which relies on old vacant lots and brownfield sites (Gedge 2003). Biodiverse roofs are designed to recreate such habitats by using urban substrates such as brick rubble, crushed concrete, sands and gravels, and minimal vegetation. Some cities (e.g., Basel, Switzerland; Toronto, Canada; and London, UK) have green-roof policies that include biodiversity objectives (Williams et al. 2014). Furthermore, a number of different roof styles have emerged to target specific taxa and to mimic local habitats (Lundholm 2006). 1College of Liberal Arts and Sciences, Chiba University, Chiba, Japan. 2Green Infrastructure Group, Kajima Corporation, Tokyo, Japan. 3Graduate School of Horticulture, Chiba University, Chiba, Japan. *Corresponding author - anagase@chiba-u.jp. Manuscript Editor: Sylvio Codella Green Roofs and Urban Biodiversity Urban Naturalist 17 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Although the number of biodiverse roofs is increasing in some European countries, few examples exist in Japan (Ishimatsu and Ito 2013, Yamada et al. 2013), where there seem to be several cultural and political barriers. First, in the UK, a brownfield site is defined as “previously developed land” that has the potential for repurposing. In contrast, a brownfield site in the USA refers to industrial land that has been abandoned and is contaminated with low levels of hazardous waste and pollutants (Gray 2015). Brownfield sites also have a negative connotation in Japan; therefore, it has been difficult to promote the concept there. Second, the Japanese perception is that green roofs should be kept green; therefore Sedum spp. (stonecrops) are frequently used. However, it is very difficult to keep such plantings in good condition in Japan without irrigation and intensive maintenance (MLITT 2009). Finally, green-roof regulations vary among cities, and many local Japanese authorities encourage the installment of intensive (thick substrate; require both regular maintenance and an irrigation system) rather than extensive green roofs (thin substrate; require little maintenance/irrigation). Subsidies to install green roofs are often contingent on selecting the intensive option (Organization for Landscape and Urban Infrastructure 2016). In Japan, 54% of local jurisdictions cannot provide subsidies for biodiverse roofs and a further 33% have reduced subsidies for biodiverse roofs that do not fulfill depth and/or irrigation requirements ( Yamada et al. 2013). In Japan, the number of green roofs has increased, with at least 413 ha installed between 2001 and 2014 (MLITT 2014). Methods to construct inexpensive, lightweight, extensive green roofs must be developed in order to facilitate further installation and retro-fitting. Although intensive roofs may provide habitats that promote biodiversity, the potential advantages of extensive roofs suggest that further investigations are warranted. Our research group has adapted European extensive green-roof design to Japanese culture. We developed a region-specific design: the Harappa Roof. “Harappa” is a Japanese word that describes vacant lots or open fields, including grasslands frequently found in residential areas (Fig. 1). These lots are important play areas for children and have been valuable habitats for grassland fauna since the Showa era (1926–1989; Shuowen 2006). We developed the Harappa style to sidestep the negative image of brownfield. Although the community structure of brownfields and Harappa is similar, the public perception is quite different. Many people have childhood experiences playing in Harappa, and thus there is nostalgia for such sites in many Japanese cities (Nagase et al. 2015). To promote biodiversity benefits, the Biotope Roof has also been developed and installed in Japan. Biotope roofs are intensive roofs planted with various species, including native trees and shrubs, which serve as hosts and nectar sources for arthropods. These roofs can also include water features, stones, and other structural elements, to create diverse habitats. They require careful maintenance to avoid colonization by invasive plant species (Nagase and Nomura 2014). In this paper we introduce the Harappa roof and encourage green-roof practicioners outside Japan to explore its local possibilities (Lundholm 2006). We present Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 18 empirical data on differences in arthropod diversity between the extensive Harappa and the intensive Biotope designs. We use this comparison to generate hypotheses for further testing. Previous studies in Europe have compared arthropod taxa on different types of extensive green roofs (e.g., Baumann 2006, Brenneisen 2006, Grant, 2006, Kadas 2006), but little research has compared extensive and intensive roofs (e.g., Coffman and Davis 2005, Coffman and Waite 2010). Our ultimate goal is to increase the number of green roofs in Japan that will support biodiversity. Field-site Description We installed a Biotope roof and a Harappa roof on the Nishichiba campus of Chiba University, Chiba City, Chiba Prefecture, Japan (Table 1). Chiba has a humid, subtropical climate, with hot summers and mild winters (Fig. 2). We installed the Harappa roof (180 m2) during winter 2012 on a 4-story building (Fig. 3), where it received full sunlight throughout the day. We used recycled materials whenever possible (at Harappa sites, previous construction materials, such as large pipes, tend to remain in situ; these materials are then repurposed for children’s imaginative play). Therefore, we collected recycled materials from the surrounding neighborhoods to replicate Harappa conditions and to be more environmentally friendly than conventional green roofs. To construct the roof we placed a drainage layer, substrate material, and vegetation. Materials used Figure 1. Typical Harappa roof in an urban area. Urban Naturalist 19 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 included straw from replacement of thatched roofs, bamboo, old clothes (fleece), plastic bottle caps, crushed concrete, and roof tiles. The Harrapa roof substrates also included topsoil with vegetation and seeds collected from ground-level Harappa habitat and spread over the crushed concrete and roof tiles. The substrate depth varied from 5 cm to 20 cm. Table 1. Summary of Harappa roof and biotope roof at Chiba University. Initial costs include materials, shipping, labor, and facilities such as irrigation systems for green roofs. Spec. Harappa roof (extensive) Biotope roof (intensive) Initial cost 8000 yen/m2 40,000 yen/m2 Depth of substrate 5–20 cm 50 cm Drainage layer and Straw, bamboo, old clothes (fleece), Commercial plastic drainage layer moisture retention mat caps of PET bottles and moisture retention mat Substrate Crushed brick, concrete, natural soil Commercial green roof substrate Plants From neighborhood: transplanting, From nursery: mainly native spontaneous vegetation plants including trees, shrubs and forbs; spontaneous vegetation Irrigation system No irrigation Drip irrigation system Maintenance Little maintenance Once a month regular maintenance Water feature Temporary pond Circulated pond Structures for biodiversity Temporary pond, piles of stones, Pond, piles of stones empty flower pots, dead branches User involvement Design, collecting materials, Survey construction, survey Figure 2. Mean monthly temperature and rainfall change (average of 3 years from 2013 to 2015) in Chiba, Japan (Japan Meteorological Agency 2016). Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 20 Initially, we planted 11 species (20 plants for each plant species) in 9-cm pots. Characteristics of planted flora on the Harappa roof are shown in Table 2. We identified all plant species and employed the ACFOR scale (A = abundant, C = common, Figure 3. Harappa green roof, Chiba University, 10 July 2015. Table 2. Characteristics of planted floral species on Harappa roo f at Chiba University. Family Species Distribution Asparagaceae Barnardia japonica (Thunb.) Schult. et Schult.f. Japan, China, Korea (Japanese Jacinth) Asteraceae Aster microcephalus (Miq.) Franch. et Sav. var. ovatus Japan (Franch. et Sav.) Soejima et Mot.Ito Aster yomena (Kitam.) Honda var. dentatus (Kitam.) Japan H. Hara Campanulaceae Platycodon grandiflorus (Jacq.) (Balloon Flower) Japan, China, Korea, East Siberia Caryophyllaceae Dianthus superbus L. var. longicalycinus (Maxim.) Japan, China, Korea, Williams Taiwan Lythraceae Lythrum anceps (Koehne) Makino (Spiked Loosestrife) Japan, Korea Orchidaceae Spiranthes sinensis (Pers.) Ames (Austral Ladies’ Japan, Chiba, Siberia Tresses) Rosaceae Potentilla hebiichigo Yonek. et H. Ohashi Japan, China, Korea, East Asia Rutaceae Zanthoxylum piperitum (L.) DC. (Japanese Pepper) Japan, Korea Verbenaceae Phyla nodiflora (L.) Greene (Capeweed) Tropical and subtropical country Violaceae Viola mandshurica W. Becker (Sumire) Japan, China, Siberia Urban Naturalist 21 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 F = frequent, O = occasional, or R = rare within the given area; Louette, et al. 2007) to classify abundance. We convened workshops so that local residents could be involved in the design process, including collection of materials and construction. Neither irrigation nor maintenance was conducted. We set out 3 recycled wash bowls to provide temporary water-capture stations and added piles of stones, empty flower pots, dead branches, and 4 substrate-filled tires to creat e wildlife habitat. The Biotope roof (150 m2) was installed in spring 2002 on a 9-story building (Fig. 4). The roof was framed by a concrete-block retaining wall. The roof design consisted of a barrier membrane, a drainage layer (Qanat mat®), and a substrate (Laputa soil Ecola®) with a depth of 50 cm. The substrate was composed of crushed, autoclaved, aerated concrete mixed with 20% by volume of organic matter content; most of the species planted were native. All green-roof materials were obtained from Hibiya Amenis Corporation (Chiba, Japan). A pond (12 m2, 50 cm deep) was installed and planted with Typha latifolia L. (Common Cattail). The Biotope roof received full sunlight in the morning but was shaded in the afternoon. Repairs, such as additional plantings and removal of stressed plants, were carried out in spring 2012, for a total of 12 species of trees, 18 species of shrubs, and 8 species of forbs planted (Table 3). An irrigation system was installed in 2012. Weeding of invasive species was carried out once monthly. Nagase and Nomura (2014) described the previous planting scheme of this roof and the evaluation of plant development and arthropod colonization. Methods We sampled arthropods from 2013 to 2015 between 0900 h and 1300 h on 17 occasions (2013: 23 August, 10 September, 5 November, 16 December; 2014: Figure 4. Biotope green roof, Chiba University,10 July 2015. Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 22 Table 3. Characteristics of cultivated plant species on biotope roof in Chiba University. [Table continued on next page.] Family Species Distribution Adoxaceae Viburnum dilatatum Thunb. (Linden Arrowwood) Japan Aquifoliaceae Ilex crenata Thunb. (Japanese Holly) China Ilex integra Thunb. (The Mochi Tree) Japan, China, Taiwan Araliaceae Fatsia japonica (Thunb.) Decne. et Planch. (Glossy-leaf Japan, Korea Paper Plant) Asparagaceae Hosta sp. Japan, East Asia Liriope muscari (Decne.) L.H.Bailey (Big Blue Lilyturf) Japan, East Asia Ophiopogon japonicas (Thunb.) Ker Gawl. (Dwarf Japan, East Asia Lilyturf) Asteraceae Eupatorium fortunei Thunb. Japan, China, Korea Farfugium japonicum (L.) Kitamura (Leopard Plant) Japan, China, Korea, Taiwan Aucubaceae Aucuba japonica Thunb. (Japanese Aucuba) Japan, China, Korea Berberidaceae Nandina domestica Thunb. (Heavenly Bamboo) China Calycanthaceae Chimonanthus praecox (L.) Link (Wintersweet) China Caprifoliaceae Abelia × grandiflora (André) Rehd. (Glossy Abelia) Cultivar Clusiaceae Hypericum chinense L. China Cornaceae Cornus kousa F. Buerger ex Hance (Korean Dogwood) Japan, East Asia Cyperaceae Carex kobomugi Ohwi (Japanese Sedge) Japan, China, Korea, Taiwan Equisetaceae Equisetum hyemale L. (Rough Horsetail) Japan Ericaceae Enkianthus perulatus C.K. Schneid. (White Enkianthus) Japan Rhododendron indicum (L.) Sweet (Azalia) Cultivar Fabaceae Lespedeza bicolor Turcz. (Shrubby Bushclover) Japan, China, Korea Quercus serrata Thunb. (Konara) Japan, China, Korea Quercus glauca Thunb. (Ring-cupped Oak) Japan, China, Taiwan Quercus phylliraeoides A. Gray (Ubamegashi) Japan, China Hamamelidaceae Loropetalum chinense var. rubra (R. Brown) Oliver Japan, China, India (Chinese Fringe Flower) Hydrangeaceae Hydrangea macrophylla (Thunb.) Ser. (Bigleaf Cultivar Hydrangea) Hydrangea macrophylla f. normalis (Thunb.) Ser. Japan Hydrangea paniculata Sieb. et Zucc. (Panicled Japan Hydrangea) Hypericaceae Hypericum monogynum L. (St John’s Wort) China Iridaceae Iris japonica Thunb. (Fringed Iris) China Lauraceae Cinnamomum camphora (L.) J. Presl (Camphor Tree) China Taiwan, Vietnam Liliaceae Tricyrtis hirta (Thunb.) Hook (Japanese Toad Lily) Japan, Korea, Taiwan Magnoliaceae Michelia figo (Lour.) DC. (Port Wine Magnolia) China Malvaceae Hibiscus syriacus L. (Rose Mallow) China Myricaceae Myrica rubra Siebold et Zucc. (Japanese Bayberry) Japan, China Urban Naturalist 23 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 16 April, 23 May, 20 June, 18 July, 29 August, 30 September, 3 November; 2015: 14 May, 17 June, 10 July, 7 August, 11 September, and 22 October). We divided the 2 roofs into 14 quadrats (3 m × 3 m) in which we swept an insect net 20 times. All specimens were released after we employed a hand-held 10x magnifier and several publications (Enjyu 2013, Morimoto and Hayashi 2007, Tomokuni et al. 1993) to identify all of those collected to species or morphospecies. On the Table 3, continued. Family Species Distribution Oleaceae Forsythia suspensa (Thunb.) Vahl (Weeping Forsythia) China Ligustrum obtusifolium Siebold et Zucc. (Border Privet) Japan, Korea Osmanthus fragrans var. aurantiacus Lour. (Kinmokusei) China Orchidaceae Bletilla striata (Thunb.) Rchb.f. (Hyacinth Orchid) Japan, China, Taiwan Calanthe discolor Lindl. (Ebine) Japan, China, Korea Oxalidaceae Oxalis debilis Kunth subsp. corymbosa (DC.) O. Bolos South America et Vigo (Large-flowered Pink-sorrel) Pentaphylacaceae Cleyera japonica Thunb. (Sakaki) Japan, China, Korea, Taiwan Rosaceae Cotoneaster holizontalis Decne. (Rockspray Cotoneaster) China Photinia × fraseri W.J. Dress ‘Red Robin’ (Christmas Cultivar Berry) Photinia glabra (Thunb.) Franch. & Sav. (Japanese Japan Photinia) Rhaphiolepis umbellata (Thunb.) Makino (Indian Japan, Korea, Hawthorn) Taiwan Spiraea thunbergii Siebold ex Blume (Thunberg’s Japan Meadowsweet) Rubiaceae Gardenia jasminoides Ellis (Cape Jasmine) Japan, East Asia Serisa japonica (Thunb.) Thunb. (Snowbush) Japan, East Asia Rutaceae Citrus unshiu (Swingle) Marcow. (Unshu Mikan) Japan, China Citrus junos (Makino) Siebold ex Tanaka (Yuzu) China Poncirus trifoliata L. (Japanese Bitter-orange) China, Korea Zanthoxylum piperitum (L.) DC. (Japanese Pepper Tree) Japan, Korea Scrophulariaceae Buddleja davidii Franch. (Butterfly-bush) Japan, China Theaceae Camellia japonica L. (Japanese Camellia) Japan, China, Korea, Taiwan Camellia sasanqua Thunb. (Sasanqua Camellia) Japan, China Eurya japonica Thunb. (East Asian Eurya) Japan, China, Korea Thymelaeaceae Daphne odora Thunb. (Winter Daphne) China Typhaceae Typha latifolia L. (Broadleaf Cattail) Japan, North and South America, Europe, Eurasia, Africa Valerianaceae Patrinia scabiosifolia Fisch. ex Trevir. (Patrinia) Japan, China, East Siberia Verbenaceae Callicarpa dichotoma (Lour.) K. Koch (Purple Japan, China, Korea, Beautyberry) Vietnam Xanthorrhoeaceae Hemerocallis hybrid (Hort.) (daylily) Japan, East Asia Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 24 Harappa roof, we carried out surveys of spontaneously colonizing plant species and arthropods on the same day. We collected for later identification all specimens that were impossible to identify on-site. Although our study focused on arthropods, we also observed and identified vertebrates. In order to compare arthropod diversity between the Biotope and Harappa roofs, we used species richness and abundance data to calculate Simpson’s diversity index (D) and the Shannon–Wiener index (H'). The analysis was carried out using Excel 2016. We employed a t-test (P < 0.05; Minitab v16) to examine whether species richness was significantly different between the Biotope and Harappa roofs over time. Results Overall, the arthropods collected on both roof types were species commonly observed in urban areas, and we observed no endangered species in this study. Richness (orders, species, individuals), diversity indices (Shannon–Wiener, Simpson), and temporal patterns are shown in Table 4. Over the study period, we observed 71 species (16 orders) and 93 species (13 orders) on the Harappa and Biotope roofs, respectively (Table 4, Appendices 1, 2). On the Harappa roof, 40 species were grassland specialists, as opposed to 30 species on the Biotope roof. Seven species of exotic fauna were observed on the Harappa roof vs. 8 species on the Biotope roof. Some, including the Orthopterans Patanga japonica Bolívar, Ornebius kanetataki Matsumura, Phaneroptera falcata Redtenbacher, and Euconocephalus thunbergi Montrouzier (all Hexapoda) were observed to spend their entire life-cycle on the Biotope roof. Diversity indices were high on both roof types (Table 4), and species richness varied among arthropod groups (Table 5). The most abundant taxa were Hemiptera (e.g., Plautia stali Scott [a stink bug], aphids, and leafhoppers), Coleoptera (e.g., Harmonia axyridis Pallas [a lady beetle] and Gonocephalum japanum Motschulsky [a darkling beetle]) and Lepidoptera (e.g., Papilio xuthus L. [Common Swallowtail] and Mamestra brassicae L. [a noctuid moth]) on both roofs. Table 4. The number of faunal taxa (orders, species, and individuals), biodiversity indices (Shannon– Wiener, Simpson), mean number of faunal species on each sampling date in Harappa roof and Biotope roof in Chiba University. Means (± SE) with the different letter differ significantly from each other (t = 7.2, df = 23, P < 0.01). Differences in mean number of fauna species Harappa roof and Biotope roof were recorded on each sampling date over the survey period. Harappa roof Biotope roof Statistic (extensive) (intensive) Total number of orders 16 13 Total number of species 71 93 Total number of individuals 330 1003 Total number of grassland species 40 30 Total number of exotic species 7 8 Shannon–Wiener diversity index 3.62 3.79 Simpson diversity index 0.95 0.97 Mean number of faunal species on each sampling date 8.32 ± 0.79b* 23.26 ± 1.94a Urban Naturalist 25 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Temporal changes also varied between roofs (Fig. 5). The Biotope roof showed significantly greater mean faunal abundance (t = 7.2, df = 23, P < 0.01). The maximum richness for a single sampling event was 14 species (both June 2014 and June Table 5. The number of faunal species (n) and percentage of total (%) of each order on a Harappa roof and a Biotope roof in Chiba University. Harappa roof Biotope roof Order n % n % Odonata 3 4.2 3 3.2 Orthoptera 4 5.6 11 11.8 Blattodea 1 1.4 0 0.0 Mantodea 1 1.4 1 1.1 Psocodea 0 0.0 1 1.1 Thysanoptera 1 1.4 0 0.0 Hemiptera 16 22.5 18 19.4 Neuroptera 0 0.0 1 1.1 Coleoptera 11 15.5 16 17.2 Diptera 7 9.9 7 7.5 Lepidoptera 16 22.5 16 17.2 Hymenoptera 5 7.0 10 10.8 Araneae 4 5.6 7 7.5 Acari 1 1.4 1 1.1 Isopoda 1 1.4 1 1.1 Total 71 100.0 93 100.0 Figure 5. Change in number of arthropod species over time on Harappa and Biotope roofs. Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 26 2015) for the Harappa roof and 43 species (May 2014) for the Biotope roof. The minimum number was 3 (both December 2013 and August 2015) for the Harappa and 14 (December 2013) for the Biotope roof. Native and exotic species were equally represented, as were annual and perennial life forms (Table 6; Appendix 3). The most abundant species were Vicia sativa L. (Common Vetch), Plantago lanceolata L. (English Platain), and Setaria viridis (L.) P. Beauv. (Foxtail Millet). The arrival rate of colonizing plant species varied over time on the Harappa roof (Fig. 6). We documented the fewest arrivals in August of each year, when temperatures were high and rainfall was low. The number of plant species was highest (>15 species) in spring and autumn. Discussion The arthropods collected from both roofs in this study were common to urban areas. The results of previous studies have been varied in this regard. Hwang and Table 6. Native or exotic species and plant life-cycle of spontaneously colonizing plant species on a Harappa roof in Chiba University. Native or exotic n % Plant life cycle n % Native species 26 55.3 Annual or biennial species 26 55.3 Exotic species 21 44.7 Perennial species 21 44.7 Total 47 100.0 Total 47 100.0 Figure 6. Change in number of spontaneously colonizing plant species over time on a Harappa roof in Chiba University. Urban Naturalist 27 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Yue (2015) studied green-roof fauna in Singapore and found mostly bees, hornets, and wasps and no endangered species. Other surveys have found that green roofs support uncommon arthropod species (Brenneisen 2006, Kadas 2006, Majka and MacIvor 2009). This result may be partly related to different sampling protocols employed; those studies used pitfall traps, while we used sweep nets. We found that the Biotope roof had greater species richness and higher abundance than the Harappa roof. This result was supported by previous studies, which also compared diversity on extensive and intensive roofs (Coffman 2007, Madre et al. 2013). The Biotope roof might provide a more consistent environment for fauna and flora because of their stable planted vegetation (including trees), thick substrate (50 cm), and irrigation systems. However, with a comparison of only a single example of each roof type, we cannot generalize based on the other differences between the 2 roof sites. The building height and age of the green roofs also differed, making direct faunal comparisons difficult. In contrast, the Harappa roof type has unstable vegetation because of a thin substrate and the lack of summer irrigation. The Harappa roof became completely brown during the summer, and we found few arthropods during that period. One month later, both vegetation and arthropods recolonized. This finding suggests that the Harappa roof was used as a temporary habitat. Braaker et al. (2014) studied habitat connectivity of arthropod communities and demonstrated their movement between green roofs and ground sites. Such an exchange between communities is especially crucial on green roofs because well-connected communities are predicted to be more resilient to stochastic disturbance events, and thus, have a higher chance of persistence (Fahring and Merriam 1994). Previous work has shown that roof age affects arthropod community composition (Iwasaki et al. 2005) and that roof height affects nesting activity of bees and wasps (MacIvor 2016). Further study is necessary to examine the importance of connectivity and proximity among green roofs, as well as the influence of groundlevel biodiversity (Hwang and Yue 2015, MacIvor and Lundholm 2011). Although the Harappa roof had less richness than the Biotope roof, it provided habitats, particularly for grassland specialists. In Japan, there was 1.2 million ha of grassland habitat in the 1960s, but this area declined to 0.4 million ha in the 2010s (Ogura 2006). Grasslands are primarily lost through urban development; however, trees are often saved and/or added due to their frequent role in urban greening (MLITT 2009). Thus, grassland conservation is critical (Ishii and Nakamura 2012), and Harappa roofs could play a role in the conservation of grassland specialists. The Harappa roof supported 47 spontaneously colonizing plant species, but none of these was endangered or rare. The dominant plant species were Vicia sativa L. (Common vetch; native), Plantago lanceolata L.(Foxtail Millet) (English Plantain; non-native) and Setaria viridis (L.) P. Beauv (Wild Foxtail Millet; native); richness was highest in the Poaceae (grass family). In previous long-term research of green roofs in Germany (Catalano et al. 2016, Köhler and Poll 2010), Poaceae was the most commonly observed family as well. In a previous study of Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 28 spontaneous plant colonizers on a Biotope roof, Solidago altissima L. (Tall Goldenrod) and Miscanthus sinensis Andersson (Zebra Grass) (both invasive) were the most abundant species (Nagase and Nomura 2014). However, we observed few of these specimens on the Harappa roof during this study. Their colonization was likely prevented by the Harappa roof’s thin substrate because these are largebodied plants (Dunnett and Kingsbury 2008). There was concern that dense brush might develop on Harappa roofs, which would require frequent cutting; however, the vegetation was short, and no maintenance was needed over the study period. These results suggest that it is possible to control the amount of vegetation using different depths of substrate. The new concept of the Harappa roof was established successfully, and it provides a unique opportunity for participatory design and maintenance. Harappa roof development can lead to important opportunities for environmental education, cost reduction, and positive public opinion. These roofs can be made completely from recycled materials. Green roofs are expected to improve urban environments. Plastic materials are frequently used for root barriers, drainage mats, and other purposes; thus, using recycled materials can reduce the life-cycle cost of a green roof. Harappa roofs are also much cheaper than Biotope roofs (at least 25% less in initial cost), and it was easy for citizens to get involved in the design process and in construction. In Japan and around the world, there are still too few examples of public participation in green-roof creation. Successful implementation of green roofs for urban biodiversity depends on participation of urban citizens, and a “citizen scientist” model is needed to facilitate public participation in green roof design (Francis and Lorimer 2011). Conclusion It is clear that biotope roofs encourage urban biodiversity. However, the results of this study suggest that Harappa roofs might be able to provide habitats, particularly for grassland fauna, without maintenance or irrigation. Future research should test several hypotheses using multiple examples of each type of biodiversity roof. First, greater structural diversity and standing biomass should make Biotope roofs a more stable habitat, resulting in more consistent faunal diversity and abundance over time. Harappa roofs would represent temporary habitats due to large changes in vegetation cover and biomass during the growing season. Second, we predict that Harappa roofs will preferentially support arthropod species from grassland habitats due to the similarity of their vegetation to ground-level grasslands. Third, aggressively invasive plant species are likely to be less common on Harappa roofs, because low-fertility soils and frequent drought should limit their ability to colonize and spread on Harappa roofs. To further develop green roofs for biodiversity, it is necessary to study them from both the natural (e.g., long-term research, regional variation) and social science perspective (e.g., citizen involvement, psychological effects). Detailed guidelines must be made available in order to set standards for green–roof design and biodiversity optimization. Urban Naturalist 29 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Acknowledgments This work was supported by JSPS KAKENHI Grant Number JP 26750001 and Campus Asia Program Inter University Exchange Program (2010–2014, 2016–2021) ( Ministry of Education, Culture, Sports, Science and Technology). We thank Dr. Scott MacIvor (University of Toronto), Dr. Olyssa Starry (Portland State University), Dr. Jeremy Lundholm (St. Mary's University), and 2 anonymous reviewers for providing helpful comments on our manuscript. Literature Cited Baumann, N. 2006. Ground-nesting birds on green roofs in Switzerland: Preliminary observations. Urban Habitats 4:37–44. Baumann, N., and F. Kasten. 2010. Green roofs: Urban habitats for ground-nesting birds and plants. Pp. 348–362, In N. Muller, P. Werner, and J.G. Kelcy (Eds). Urban Biodiversity and Design. John Wiley and Sons, Chichester, UK. 648 pp. Braaker, S., J., Ghazoul, M.K. Obrist, and M. Moretti. 2014. Habitat connectivity shapes urban arthropod communities: The key role of green roofs. Ecology 95:1010–1021. Brenneisen, S. 2006. Space for urban wildlife: Designing Green roofs as Habitats in Switzerland, Urban Habitats 4:27–36. Catalano, C., C., Marcenò, V.A. Laudicina, and R. Guarino. 2016. 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List of fauna species on Harappa roof in Chiba University. Grassland Native or Class/ Order Species species Exotic Aves Passeriformes Corvus macrorhynchos Wagler Native Hypsipetes amaurotis Temminck Native Motacilla alba lugens Gloger Exotic Passer montanus L. Native Columbiformes Columba livia Gmelin Exotic Reptilia Squamata Plestiodon japonicas Peters ○ Native Insecta Odonata Ischnura senegalensis Rambur Native Pantala flavescens Fabricius Native Sympetrum frequens Sélys Exotic Orthoptera Dianemobius nigrofasciatus Matsumura ○ Native Oedaleus infernalis Sauss ○ Native Patanga japonica Bolívar ○ Native Teleogryllus emma Ohmachi & Matsuura ○ Native Blattodea Periplaneta fuliginosa Serville Native Mantodea Hierodula patellifera Serville Native Thysanoptera Thysanoptera sp. - Hemiptera Aphidoidea sp. - Cicadellidae sp. - Delphacidae sp. ○ - Dolycoris baccarum L. ○ Native Geocoris proteus Distant ○ Native Getomus pygmaeus Dallas ○ Native Lygaeoidea sp. ○ Native Nabis kinbergii Reuter ○ Native Orius sp. ○ - Pachygrontha antennata Uhler ○ Native Phyrrhocoris sinuaticollis Reuter ○ Native Plautia stali Scott ○ Native Riptortus pedestris Trusted ○ Native Trigonotylus caelestialium Kirkaldy ○ Native Typhlocybinae sp. Native Yemma exilis Horváth ○ Native Coleoptera Cheilomenes sexmaculata Fabricius Native Coccinella septempunctata L. Native Curculionoidae sp. - Gonocephalum japanum Motschulsky ○ Native Halticinae sp. ○ Native Urban Naturalist 33 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Grassland Native or Class/ Order Species species Exotic Harmonia axyridis Pallas Native Histeridae sp. Native Hypera postica Gyllenhal ○ Exotic Illeis koebelei Timberlake Native Paederus fuscipes Curtis ○ Native Staphylinidae sp. Native Diptera Chironomidae sp. Native Drosophilidae sp. Native Sphaerophoria philanthus Meigen ○ Native Episyrphus balteatus De Geer ○ Native Syrphinae sp. Native Tephritidae sp. - Tipulidae sp. Native Lepidoptera Argyreus hyperbius L. ○ Exotic Agrotis segetum Denis & Schiffermüller Native Crambidae sp. ○ Native Helicoverpa armigera armigera Hübner ○ Native Mamestra brassicae L. ○ Native Noctuidae sp. - Palpita nigropunctalis Bremer Native Papilio xuthus L. Native Parnara guttata Bremer & Grey ○ Native Potanthus flavum Murray ○ Native Pediasia teterrellus Zincken ○ Native Pieris rapae L. ○ Exotic Pyralidae sp. Native Lycaena phlaeas L. ○ Native Oncocera sp. ○ Native Zizeeria maha Kollar ○ Native Hymenoptera Camponotus japonicus Mayr ○ Native Apis mellifera L. Exotic Campsomeriella annulata Fabricius Native Formica japonica Motschoulsky ○ Native Tetramorium tsushimae Emery ○ Native Arachnida Araneae Lycosidae sp. Native Misumenops tricuspidatus Fabricius ○ Native Salticidae sp. Native Thomisidae sp. ○ Native Acari Balaustium murorum Hermann Native Malacostraca Isopoda Armadillidium vulgare Latreille Exotic Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 34 Appendix 2. List of fauna species on a Biotope roof in Chiba University. Grassland Native or Class/ Order Species species Exotic Aves Passeriformes Corvus macrorhynchos Wagler - Native Motacilla alba lugens Gloger - Native Columbiformes Columba livia Gmelin - Exotic Insecta Odonata Lestes sponsa Hansemann - Native Orthetrum albistylum speciosum Uhler - Native Pantala flavescens Fabricius - Native Orthoptera Acrida cinerea Thunberg ○ Native Atractomorpha lata Mochulsky ○ Native Euconocephalus thunbergi Montrouzier ○ Native Oecanthus euryelytra Ichikawa ○ Native Ornebius kanetataki Matsumura - Native Patanga japonica Bolívar ○ Native Phaneroptera falcata Redtenbacher ○ Native Polionemobius micado Shiraki ○ Native Teleogryllus emma Ohmachi & Matsuura ○ Native Tettigonia orientalis Uvarov - Native Velarifictorus micado Saussure - Native Mantodea Tenodera aridifolia Stoll ○ Native Neuroptera Chrysopidae sp. - Native Hemiptera Anisops ogasawarensis Walker - Native Ceroplastes ceriferus Fabricius - Native Ceroplastes rubens Maskell - Exotic Coccoidea sp. - - Corythucha marmorata Uhler ○ Exotic Dulinius conchatus Distant ○ Exotic Geisha distinctissima Walker - Native Gerris lacustris latiabdominis Miyamoto - Native Graptopsaltria nigrofuscata Motschulsky - Native Kallitaxilla sinica Walker - Native Meimuna opalifera Walker - Native Microvelia douglasi Scott - Native Nipponaphis distyliicola Monzen - Native Nippolachnus piri Matsumura - Native Ossoides lineatus Bierman ○ Native Plautia stali Scott - Native Riptortus pedestris Trusted ○ Native Uroleucon nigrotuberculatum Olive ○ Exotic Coleoptera Agrypnus binodulus Motschulsky - Native Anomala albopilosa Hope - Native Urban Naturalist 35 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Grassland Native or Class/ Order Species species Exotic Anomala cuprea Hope - Native Anomala orientalis Waterhouse - Native Argopistes coccinelliformis Motschulsky - Native Aulacophora femoralis Motschulsky ○ Native Chilocorus kuwanae Silvestri ○ Native Coccinella septempunctata L. - Native Gametis jucunda Faldermann ○ Native Gonocephalum japanum Motschulsky - Native Harmonia axyridis Pallas - Native Illeis koebelei Timberlake - Native Linaeidea aenea L. - Native Pseudocneorhinus bifasciatus Roelofs - Native Propylaea japonica Thunberg - Native Pyrrhalta humeralis Chen - Native Diptera Chironomidae sp. - Native Episyrphus balteatus De Geer ○ Native Milesiinae sp. ○ Native Sphaerophoria indiana Bigot ○ Native Sphaerophoria menthastri L. ○ Native Syrphinae sp. - Native Tipulidae sp. - Native Lepidoptera Adoxophyes honmai Yasuda - Native Crambidae sp - Native Eumeta minuscula Butler - Native Geometridae sp. - Native Glyphodes perspectalis Walker - Native Homona magnanima Diakonoff - Native Mamestra brassicae L. ○ Native Palpita nigropunctalis Bremer - Native Papilio machaon L. ○ Native Papilio xuthus L. - Native Parapediasia teterella Zincken - Exotic Parnara guttata Bremer & Grey ○ Native Pyralidae sp. - Native Pelopidas mathias Fabricius ○ Native Tortricidae sp. - Native Vanessa indica Herbst ○ Native Hymenoptera Braconidae sp. - Native Camponotus japonicus Mayr ○ Native Chalcididae sp. - - Formica japonica Motschoulsky ○ Native Icheumonidae sp. - Native Megacampsomeris schulthessi Betrem - Native Megachile sp. - Native Pristomyrmex punctatus Smith ○ Native Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 36 Grassland Native or Class/ Order Species species Exotic Tetramorium tsushimae Emery ○ Native Xylocopa appendiculata circumvolans Latreille - Native Psocodea Psocodea sp. - Native Arachnida Araneae Carrhotus xanthogramma Latreille - Native Hasarius adansoni Audouin - Native Misumenops sp. - Native Myrmarachne sp. - Exotic Nephila clavata L. Koch - Native Thomisidae sp. - Native Malacostraca Isopoda Armadillidium vulgare Latreille - Native Pholcus sp. - Native Urban Naturalist 37 A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 Appendix 3. List of spontaneously colonizing plant species on a Harappa roof in Chiba University. ACFOR: A = abundant (≥30%), C = common (20–29%), F = frequent (10–19%), O = occasional (5–9%), R = rare (1–4%). Native or Plant ACFOR Family Species Exotic life-cycle scale Amaryllidaceae Allium macrostemon Bunge Native Perennial R Apiaceae Torilis japonica (Houtt.) DC. Native Perennial R Asteraceae Bidens frondosa L. Exotic Annual R Conyza canadensis (L.) Cronquist Exotic Biennial F Conyza sumatrensis (Retz.) E. Walker Exotic Perennial F Gnaphalium japonicum Thunb Native Perennial R Solidago altissima L. Exotic Perennial R Stenactis annuus (L.) Cass. Exotic Annual C Youngia japonica (L.) DC. Native Perennial R Boraginaceae Trigonotis peduncularis (Trevir.) Benth. ex. Native Annual F Hemsl Brassicaceae Cardamine scutata Thunb. Exotic Annual O Caryophyllaceae Cerastium glomeratum Thuill. Exotic Annual F Chenopodiaceae Chenopodium album L. Exotic Annual R Convolvulaceae Calystegia japonica (Thunb.) Choisy Native Perennial R Cyperaceae Carex leucochlora Bunge Native Perennial O Cyperus microiria Steud. Native Annual O Cyperus rotundus L. Native Perennial O Euphorbiaceae Acalypha australis L. Native Annual O Euphorbia maculata L. Exotic Annual R Fabaceae Kummerowia stipulacea (Maxim.) Makino Native Annual F Trifolium pratense L. Exotic Perennial C Vicia hirsuta (L.) Gray Native Perennial C Vicia sativa L. Native Perennial A Geraniaceae Geranium carolinianum L. Exotic Annual R Iridaceae Sisyrinchium rosulatum E.P. Bicknell Exotic Annual F Lamiaceae Lamium purpureum L. Native Perennial C Oxalidaceae Oxalis corniculata L. Native Perennial C Plantaginaceae Plantago lanceolata L. Exotic Perennial A Veronica arvensis L. Exotic Annual or F Biennial Veronica persica Poir. Exotic Perennial F Poaceae Bromus catharticus Vahl Exotic Annual F Dactylis glomerata L. Exotic Perennial O Digitaria ciliaris (Retz.) Koel Native Annual F Eleusine indica (L.) Gaertn. Native Annual C Urban Naturalist A. Nagase, Y. Yamada, T. Aoki, and M. Nomura 2018 Special Issue No. 1 38 Native or Plant ACFOR Family Species Exotic life-cycle scale Elymus tsukushiensis Honda var. transiens Native Perennial O (Hack.) Osada Festuca arundinacea Schreb. Exotic Perennial O Festuca ovina L. Exotic Perennial O Setaria pumila (Poir.) Roem. & Schult. Native Annual C Setaria viridis (L.) P. Beauv. Native Annual A Zoysia japonica Steud. Native Perennial R Polygonaceae Rumex japonicus Houtt. Native Perennial O Portulacaceae Portulaca oleracea L. Native Perennial F Rubiaceae Galium spurium var. echinospermon Native Annual R (Wallr.) Hayek Solanaceae Solanum carolinense L. Exotic Perennial R Ulmaceae Zelkova serrata (Thunb.) Makino Native Perennial R Vitaceae Cayratia japonica (Thunb.) Gagnep. Native Perennial O