Investigation of native plants in Jogasaki coast for semi-extensive green roofs in Japan

Investigation of native plants in Jogasaki coast for semi-extensive green roofs in Japan Ayako Nagase, Chiba University, Graduate School of Engineering, Japan, a-nagase@faculty.chiba-u.jp Yurika Tashiro, Chiba University, Graduate school of Horticulture, Japan

Abstract Many species of coastal plants are endangered because of urban development, however, green roofs using such plants could help conserve local plant communities. Coastal plants may be suitable for green roofs because the maritime environment is similar to that found on roofs, such as very free draining soils and strong wind. However, there have been few studies on coastal plants for green roofs. This study investigated the suitability of plants found on the Jogasaki coast for green roofs in Japan. Aboveground of sixteen plant species and seeds of five plant species were collected from the Jogasaki coast in 2011, and appropriate propagation methods for each plant were investigated. The results showed that two species Lysimachia mauritima and Peucedanum japonicum showed high germination rate and were appropriate for direct sowing, whereas division and cutting were appropriate for other species, especially Chrisanthemum pacificum, Crepidiastrum keiskeanum, Sedum oryzifolium and Tetragonia tetragonioides. Secondly, the performance of nine plant species on semi-extensive green roofs was investigated. The Jogasaki coastal environment was recreated on volcanic rocks and three kinds of substrate, commercial green roof substrate, crushed roof tiles and pumice. It was shown that overall plants grew fast in commercial green roof substrate.

Authors’ Biographies

Ayako Nagase is an assistant professor in the Graduate school of Engineering in Chiba University, Japan. Her research interest is plant selection for green roofs and biodiversity in urban landscapes.

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1. Introduction

The use of native plants on green roofs has recently attracted considerable attention (Bulter et al., 2012). Conservation is an important driving force behind this trend, since green roofs help to conserve local plant communities. For example, in Wollishofen, Zurich, the biological diversity of species-rich wet meadows surrounding a water filtration plant was conserved on the facility’s roofs after much of the habitat disappeared due to agricultural development (Brenneisen, 2006). Coastal plants, which are endangered by urban development, may be suitable for green roofs because the maritime environment is similar to that found on roofs in terms of free-draining soil and strong wind. Moreover, coastal plants have the advantage of less competition with other plants on green roofs; most coastal plants are difficult to establish in the presence of naturally emerging inland plants (Yura, 2003). Although there is one previous study on the use of coastal plants for extensive green roofs (MaIvor and Lundholm, 2011), the plants were selected from a wide range of coastal areas in Atlantic Canada rather than from native plant communities.

Currently, the definition of native species is not clear; native species have been defined as ranging from a building site to a country (Bulter et al., 2012). Native plants found on many green roofs often originate from a wide area; for example, some plants come from the mountains and others from the coast. Another concern is where the seeds of native plant species come from and where they are propagated. A recent study showed that the performance of some native Japanese plants differed from that of native plants from Japan (Abe et al., 2004). However, most commercial Japanese native plant seeds are produced overseas and it is very difficult to find ones produced in Japan. Ideally, plants would be obtained and propagated locally. The present study examined whether it is possible to recreate a local herbaceous plant community on a roof, by studying the natural habitats of seacoast plants, and their propagation and performance on a semi-extensive green roof.

2. Methods 2.1 Investigation of seacoast plants The Izu peninsula was chosen as the study site because of its proximity to Tokyo (200 km) and abundance of endemic plant species. The climate is relatively mild, with a mean annual temperature of 15–17°C and annual precipitation of 2000 mm. We investigated six coastal areas of the peninsula: Akazawa, Jogasaki, Kawana, Kawazu, Manazuru and Shiofuki (Fig. 1). A vegetation study was carried out in seven times, on August 11, September 5, October 4, November 3, and December 4 in 2011, and on February 27 and April 29 in 2012.

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Fig. 1 Location of the study site on the Izu peninsula in Japan.

2.2 Propagation Ripe seeds of five species were collected from the natural vegetation in Jogasaki between August and December 2011. The plant species were Crepidiastrum keiskeanum, Lysimachia mauritiana, Peucedanum japonicum, Hemerocallis fulva var. littorea and Rosa luciae. The collected seeds were dried at room temperature (about 20째C) for one week and then kept in a refrigerator at 3째C. Fifty seeds of each plant species were placed in a petri dish on 9-cm filter paper moistened with distilled water. On December 28, 2011, they were placed in an incubator at 20째C (12 h light, 12 h dark). There were three replications for each plant species. Germinated seeds were counted daily.

On February 27, 2011 and April 29, 2012, sixteen species of plants were collected from Jogasaki and Kawazu. The collected species and number of plants are shown in Table 1. Most of the species were growing roots between rocks and were difficult to remove with the roots (Fig. 2).

Therefore, only the aboveground part was removed for most species. After being taken from their natural habitat, the plants were cut to an appropriate size for each species and planted in 9-cm pots filled with soil for propagation. The potted plants were kept in a greenhouse in Matsudo, Chiba and were watered daily.

Fig. 2 Jogasaki seacoast.

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2.3 Substrate and plant performance on the green roof A semi-extensive green roof was installed on the top of the ninth floor of a building, which was surrounded by a parapet 1.2 m in height. The area of the green roof was 3.0Ă&#x2014;7.3 m. The green roof was framed with timbers, and consisted of a root protection layer, 10 cm of pumice for drainage and 20 cm of one of three types of substrate: commercial green roof substrate (Kusabanameijin), pumice with 10% volume of peat moss, and roof tile with 10% volume of straw. The materials were obtained from Suikenkurieito (Tokyo), Hibia Amenis (Tokyo) and Nihoniringyohiryo (Tokyo). The green roof was divided into three plots by type of substrate (1.0Ă&#x2014;7.3 m). On May 25, 2012, successfully propagated plants were randomly planted on the green roof, then volcanic rocks (about 10 cm in diameter) were placed as mulch to create a similar landscape to that of the plant community. An installed drip irrigation system was programmed for automatic watering three times a week. Plant height was measured every two weeks. Significance of differences in substrate was determined using one-way ANOVA (Minitab Release 14) at a probability level of P < 0.05.

Fig. 3 Overview of experimental site.

3. Results and Discussion 3.1 Seacoast plants in the Izu peninsula The plant species that were observed in the studied natural habitats are shown in the Appendix. The highest number of plant species, thirty-four, was observed in Jogasaki, followed in order by twelve in Kawana, nine in Akazawa, six in Shiofuki, five in Kawazu and four in Manazuru. Yura et al. (2008) studied the vegetation in 1308 seacoast areas in Japan, and found that the average number of seacoast plant species was only six; the decrease in seacoast plants is a serious problem in Japan. They also found that the number of plants was related to the seacoast environment such as the presence of concrete structures (e.g. embankment), human activity, maintenance such as weeding, and frequency of natural disasters. Their findings agree with the results of our study; in Jogasaki, there are no concrete structures near the sea and the area is not used for activities such as swimming, whereas the other areas have embankments and most places are used for swimming.

3.2 Propagation Among the five plant species, L. mauritiana and P. japonicum showed a germination rate of more than 70%. Therefore, chilling is not necessary for these two species, which readily germinated with the appropriate temperature and water. However, the other species did not World Green Roof Congress, 19-20 September 2012, Copenhagen Page

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germinate at all, showing that these species are difficult to germinate or may require lengthy chilling to break dormancy.

Fig. 4 Change in germination rate over time.

The success rate for the cuttings is shown in Table 1. It was possible to propagate most plants from cuttings. Succulent-type plant species such as C. keisukeanum, S. oryzifolium and T. tetragonioides showed a high survival rate. Moreover, Carex spp. C. pacificum and L. mauritiana were also successful. However, some species such as C. soldanella, E. jolkinii, L. japonicus, L. maculatum and R. luciae were difficult to propagate. E. jolkinii was not successful probably because it contains latex, although the cuttings were washed before propagation. Woody plants such as R. luciae showed a low percentage of late survival and it may be beneficial to use root-inducing hormones.

Table 1 Success rate for cuttings World Green Roof Congress, 19-20 September 2012, Copenhagen Page

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Winter collection1)

Spring collection2)

Number of collected plants

Number of surviving plants

Survival rate

Number of collected plants

Number of surviving plants

Survival rate

Calystegia soldanella

3

0

0

n/a

n/a

n/a

Carex meridian

15

7

46.7

20

15

75.0

Carex oshimensis

25

17

68.0

5

3

60.0

Chrysanthemum pacificum

23

18

78.3

21

14

66.7

Crepidiastrum keiskeanum

16

9

56.3

32

25

78.1

Cytomium fortunei

18

8

44.4

20

4

20.0

Euonymus japonicus var. litoralis

15

5

33.3

20

4

20.0

Euphorbia jolkiniiă&#x20AC;&#x20AC;

42

3

7.1

30

3

10.0

Farfugium japonicum

12

7

58.3

n/a

n/a

n/a

Hemerocallis fulva var. littorea

13

5

38.5

31

15

48.4

Lathyrus japonicus

15

0

0

n/a

n/a

n/a

Lilium maculatum

n/a

n/a

n/a

13

0

0

Lysimachia mauritiana

18

12

66.7

n/a

n/a

n/a

uncountable

all

100

n/a

n/a

n/a

Tetragonia tetragonioides

3

3

100

n/a

n/a

n/a

Rosa luciae

24

5

20.8

27

3

11.1

Sedum oryzifolium

(%)

(%)

1) Winter collection: Plants were collected on February 27, 2012 and surviving plants were measured on April 23, 2012.

2) Spring collection: Plants were collected on April 29, 2012 and surviving plants were measured on May 9, 2012.

3.3 Substrate and plant performance on the green roof The results for plant height on June 14, 2012 are shown in Fig. 5 for three representative plants (Chrysanthemum pacificum, Hemerocallis fulva var. littorea, Rosa luciae). Currently, all plants have survived and are growing well in each type of substrate. However, plants in the commercial green roof substrate are growing faster than those in the crushed roof tiles and pumice, and this tendency is more pronounced in herbaceous perennials than in woody plants.

The statistical results showed that the difference in substrate had a significant effect on the plant height of C. pacificum and H. fulva var. littorea. A previous study showed that plants with lush growth may not be able to withstand drought (Nagase and Dunnett, 2011). Further observation is necessary to confirm the plant performance on the green roof.

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Fig. 5 Plant height on June 14, 2012. n = 5. Error bars represent the standard error of mean values. P = probability. n.s. = not significant. One-way ANOVA was used to compare the values from each plant species.

Substrate type had a significant effect on plant height in Chrysanthemum pacificum and Hemerocallis fulva var. littorea.

4. Conclusion Green roofs may be ideal places for conserving coastal plant species. Moreover, the process of studying their natural habitat, propagating the plants, planting them on the roof and observing their performance would be an appropriate environmental education for understanding local plant communities. Green roofs also have potential as nurseries for growing plants and returning them to their natural seacoast habitat, where endemic plant species are decreasing.

Longer-term study is necessary to confirm the plant performance in different types of substrate.

References 1. Abe, T., Nakano, Y., Kuramoto, N., 2004. Is it possible to consider Chinese origin of Indigofera pseudotinctoria as Japanese native plants ? Journal of the Japan society Revegetation Technology 30 (1): 344-347. (in Japanese) 2. Butler, C., Butler, Orians. C.M., 2012. Native plant enthusiasm reaches new heights: Perceptions, evidence, and the future of green roofs. Urban Forestry and Urban greening 11:1-10.

3. Brenneisen,2006. Space for urban wildlife: Designing green roofs as habitats in Switzerland, Urban habitat 4 (1): 27-33.

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4. MacIvor, J.S., Lundholm, J., 2011. Performance evaluation of native plants suited to extensive green roof conditions in a maritime climate. Ecological Engineering.37,407417.

5. Nagase and Dunnett, 2011. The relationship between percentage of organic matter in substrate and plant growth in extensive green roofs, Landscape and Urban Planning 103:230-236.

6. Yura,H. 2003. Survival and growth of Chrysanthemum pacificum Naki seedlings at the inland site, Natural History Research 7 (2):107-114.

7. Yura,H. 2008. Report of investigation of coastal plants with citizens 2004-2007., The nature conservation society of Japan, available from http://www.nacsj.or.jp/project/spc/ (in Japanese)

Acknowledgements The authors would like to thank students in Laboratory of design management, Faculty of Engineering in Chiba University for helping set up the experimental site. Funding for this research was provided by the new technology development foundation.

Appendix

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Jogasaki

Kawana

Akazawa

Shiofuki

Kawazu

Manazuru

Ampelopsis brevipedunculata var. hancei

Angelica keiskei

B. biloba

A. keiskei

Calystegia soldanella

A. brevipedunculata var. hancei

Angelica japonica

A. brevipedunculata var. hancei

C.pacificum

C.soldanella

I. repens

B. biloba

Boehmeria biloba

C. pacificum

C. falcantum

C. falcantum

Lathyrus japonicus

C. soldanella

Carex meridian

C. heterocarpa japonica

C. keiskeanum

E.jolkinii

M. condensatus

T. tetragonioides

Carex oahuensis var. robusta

C. falcantum

Ixeris repens

F. japonicum

Oenothera laciniataă&#x20AC;&#x20AC;

Carex oshimensis

Dianthus japonicus

Lemmaphyllum microphyllum

P. tobira

Chrysanthemum pacificum

F. japonicum

M. condensatus

Ixeris repens

Piper kadzura

Crepidiastrum keiskeanum

Lilium maculatum

Polygonum chinese

Cyrtomium falcantum

M. condensatus

Cytomium fortunei

Raphanus sativus var. hortensis f. raphanistroides

Dioscorea tokoro

T. tetragonioides

Corydalis japonica

heterocarpa

var.

var.

Euonymus japonicus var. litoralis Euphorbia jolkiniiă&#x20AC;&#x20AC; Eurya japonica Elaeagnus rotundifolia

umbellata

var.

Farfugium japonicum Fimbristylis pacifica Hedyotis strigulosa var. parvifolia Hemerocallis fulva var. littorea Juniperus chinensis Lysimachia mauritiana Miscanthus condensatus Peucedanum japonicum Pinus thunbergii Pittosporum tobira Rhaphiolepis integerrima

umbellata

var.

Rosa luciae Rumex acetosa Sagina maxima Sedum oryzifolium Setaria viridis var. pachystachys Sphenomeris biflora Tetragonia tetragonioides 34 species

12 species

9 species

6 species

5 species

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4 species 9