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.
Open Building Manufacturing: Core Concepts and Industrial Requirements
Investigation of native plants in Jogasaki coast for semi-extensive green roofs in JapanAyako Nagase, Chiba University, Graduate School of Engineering, Japan, firstname.lastname@example.orgYurika Tashiro, Chiba University, Graduate school of Horticulture, JapanAbstractMany 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.
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.
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 facilitys 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.
2.1 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 1517C 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.
Fig. 1 Location of the study site on the Izu peninsula in Japan.
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 20C) for one week and then kept in a refrigerator at 3C. 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 20C (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.
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 3.07.3 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 (1.07.3 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.
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 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
Winter collection1)Spring collection2)
Number of collected plantsNumber of surviving plantsSurvival rate
(%)Number of collected plantsNumber of surviving plantsSurvival rate
Carex meridian 15746.7 201575.0
Carex oshimensis251768.0 5360.0