Establishment of an annual meadow on extensive green roofs in the UK by Landscape, University of Sheffield

Landscape and Urban Planning 112 (2013) 50–62

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Research paper

Establishment of an annual meadow on extensive green roofs in the UK Ayako Nagase a,∗ , Nigel Dunnett b,1 a b

Chiba University, Graduate School of Engineering, Division of Design Science, 1-33 Yayoicho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan University of Sheffield, Department of Landscape, Arts Tower, Western Bank, Sheffield S10 2TN, UK

h i g h l i g h t s ! ! ! ! !

Establishment of an annual meadow in an extensive green roof is investigated in Sheffield, UK. It is possible to establish a long flowering annual meadow without irrigation at 7 cm depth of substrate in the extensive green roof. A low sowing rate results in better conditions for individual plant growth when enough water is available. A high sowing rate is necessary to ensure a sufficient plant number when water resources are not abundant. Watering improves growth in most annual plant species.

a r t i c l e

i n f o

Article history: Received 11 December 2011 Received in revised form 12 December 2012 Accepted 16 December 2012 Keywords: Urban landscape Seed mixture Irrigation Germination Competition Long flowering

a b s t r a c t This study investigated the establishment of annual meadow including native and non-native species in an extensive green roof in Sheffield, UK. The study aimed to determine the feasibility of establishing annual plant species from a seed mixture and to determine the appropriate sowing rate as well as the necessity of watering during the first growing season from June to November 2006. A 22-species seed mixture was sown on an experimental green roof with a substrate depth of 7 cm using two sowing rates (2 g/m2 and 4 g/m2 ) and two watering regimes (with and without watering). The watering regime consisted of application of water four times over the course of the experiment. Each combination of sowing and watering regime yielded a successful aesthetic annual meadow green roof. Results showed that a low sowing rate resulted in better conditions for individual plant growth when enough water was available. On the other hand, a high sowing rate was necessary to ensure a sufficient number of plants when water resources were not abundant. The watering regime improved growth in most species; however, it was determined that an annual seed mixture could perform well without watering at the study site. The annual meadow possessed an abundance of flowering plants for an extended period of time; plants started flowering one month after sowing and continued until the end of October. Successful species during the first growing season included Alyssum maritimum, Echium plantagineum ‘Blue Bedder’, Gypsophila muralis, Iberis amara, Iberis umbellata ‘Fairy’, Linaria elegans and Linaria maroccana. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Although the installation of green roofs has taken place for many years (e.g. Derry and Toms, London, 1938), relevant peer reviewed research has only recently been published (Dvorak & Volder, 2010; Francis & Lorimer, 2011; Lundholm, 2006; Oberndorfer et al., 2007). Extensive green roofs are the most commonly deployed type of green roof system and are characterized by the use of a shallow substrate (depth <20 cm), low costs and low maintenance (Dunnett & Kingsbury, 2008). Growth environments of green

∗ Corresponding author. Tel.: +81 043 290 3113; fax: +81 043 290 3121. E-mail addresses: a-nagase@faculty.chiba-u.jp (A. Nagase), n.dunnett@sheffield.ac.uk (N. Dunnett). 1 Tel.: +44 0114 222 0611; fax: +44 0114 275 4176. 0169-2046/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.landurbplan.2012.12.007

roofs are considered severe due to limited water availability, wide temperature fluctuations, and high exposure to wind and solar radiation (Dunnett & Kingsbury, 2008; Oberndorfer et al., 2007). Selecting plants capable of surviving under these conditions is a critical step in successful green roof implementation. One of the most intensively investigated taxa is Sedum, since these plants have shallow root systems and are able to efficiently utilize water, making them ideal candidates for tolerating the extreme conditions found on rooftops (Emilsson, 2008; Rowe, Getter, & Durhman, 2012). Recently, alternative approaches that recognize green roofs as dynamic ecosystems and employ a diversity of species have garnered the attention of researchers (Cook-Patton & Bauerle, 2012). Some studies have examined the effects of plant mixtures as opposed to monocultures on green roof performance and have stressed that green roof performance could be improved through greater diversity of plant life forms in terms of climate change

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mitigation and adaptation strategies (Lundholm, Maclvor, MacDougall, & Ranalli, 2010; Nagase & Dunnett, 2010; Wolf & Lundholm, 2008). Annual meadows that include both native and non-native plant species have great plant diversity and they may be able to tolerate the harsh environments in extensive green roofs. Some annual plants have adapted to the brief growing seasons in steppe and desert regions around the world and some grow at the first stages of the vegetal succession in mild climate. Plant species in annual meadows germinate, grow and flower under favourable conditions and they lie dormant as seeds during periods of harsh conditions (Barber, 1954). There are a number of advantages to using annual plant meadows on extensive green roofs. First advantage is a reduction of cost and maintenance. Establishment of an annual meadow can lead to reductions in management cost due to lower levels of imposed management practice (Bretzel, Pezzarossa, Benvenuti, Bravi, & Malorgio, 2009). Implementation of annual meadows can also be achieved using direct sowing, a simple method capable of covering large areas at a low cost. For example, covering a square metre of garden with herbaceous plants may cost around £20–25, while the cost of seeds needed in order to cover the same area through direct sowing may be just 20–50p (Dunnett & Hitchmough, 2001). A seed-grown annual meadow is also sustainable, as appropriately selected species may be re-seeded from year to year (Kircher, 2004). Furthermore, very little fertilizer and herbicide are required in the cultivation of an annual meadow (Diboll, 2004). Second advantage is biodiversity benefit. Annual meadows may play a crucial role in the maintenance of biodiversity. In previous fauna studies, biodiverse roofs, which recreate brownfields on roofs in order to maximize biodiversity and comprised of meadows that include annuals and perennials, tend to be used. Biodiverse roofs were able to support populations of spiders, beetles, wasps, ants and bees and they also contained rare invertebrate taxa from the above-mentioned groups, including some with very specialized niches within the UK (Francis & Lorimer, 2011; Grant, 2006; Kadas, 2006). Kadas (2006) studied three diverse invertebrate groups, Araneae, Coleoptera, and Hymenoptera, in biodiverse roofs in London and found that at least 10% of all species collected were designated nationally rare or scarce in accordance with criteria established by the intergovernmental agency, Natural England. Annual meadows can be particularly useful in supporting both bees and butterflies as they contain many flowers with long flowering periods. Positive correlations have been identified between bee abundance and floral abundance (Banaszak, 1996; Heithaus, 1974) as well as butterfly diversity and floral abundance (Steffan-Dewenter & Tscharntke, 1997). It has also been determined that bumblebees perform better within diverse plant communities containing species that flower at different times, as these communities provide more stable nectar and pollen resources (Cook-Patton & Bauerle, 2012; Menz et al., 2011). Non-native species in particular extend the flowering season of annual meadows since plants native to UK meadows cease flowering by mid-summer (Hitchmough, de la Fleur, & Findlay, 2004). Third advantage is aesthetic. Annual meadows including various colour of flowers and many previous studies showed that people are attracted to flowers (e.g. Jorgensen, Hitchmough, & Calvert, 2002; Todorva, Asakawa, & Aikoh, 2004). Swiss study showed that annual meadows had the advantage of being aesthetically pleasing as many annual plants display bright colours, a trait that has been shown to be preferentially selected for by humans (Lindemann-Matthiens & Bose, 2007). Another Swiss study showed that plant diversity in itself is attractive to humans because species-rich communities are more likely to contain a species perceived as particularly beautiful which might increase overall appreciation (LindemannMatthies, Junge, & Matthies, 2010). In Sheffield, UK, Özgüner and Kendle (2006) studied public attitudes towards naturalistic versus

designed landscapes and determined that naturalistic landscapes, such as meadows, were associated with greater senses of naturalness and feelings of freedom and were perceived as better places to socialize. Currently, studies to the performance of meadows on green roofs have been limited. Two studies investigated changes in species composition in rooftop grass and wildflower meadows located in the U.S. (Dewey, Johnson, & Kjelgren, 2004) and Germany (Köhler, 2006) while another examined the effect of adding the seeds of annual species to a Sedum green roof in Bernburg, Germany (Kircher, 2004). Information currently available is not sufficient to encourage people to implement meadows in extensive green roofs. This study was carried out in order to investigate the performance of annual meadows grown from a seed mixture on an extensive green roof. The first goal was to investigate the feasibility of establishing annual plant species from a seed mixture. Appropriate establishment is important for successful use of annual meadows on extensive green roofs because seed germination performance plays a major role in the persistence and dynamics of annual plants ˇ Velasco Hernández, & Zavala-Hurtado, (Rivas-Arancibia, Montana, 2006). The second goal was to evaluate successfully established species in terms of emergence, growth and flowering and to determine an appropriate sowing rate and watering regime for use in the first growing season. Determination of an appropriate sowing rate for extensive green roofs is necessary since the environment on the rooftop is harsher than it is on the ground. In particular, differences in water availability may affect plant emergence in green roof annual meadows. It has been hypothesized that irrigation has a significant effect on the performance of annual plant communities located in extensive green roofs. It has also been hypothesized that it is possible to create an annual meadow without irrigation in the UK due to the presence of a generally mild climate, the UK typically having relatively warm winters and a high likelihood of regular rainfall throughout the summer (Dunnett, 2004).

2. Methods This study was carried out on the roof of a four storey commercial building located in the city centre of Sheffield, UK. An extensive green roof was installed on the roof of the building (approximately 150 m2 ), which was surrounded by a parapet 0.345 m in height. The green roof was flamed by timber (5.5 m × 6.0 m × 0.1 m) and had a build-up that consisted of a root protection layer, geotextile made of polypropylene, with fleece backing for green roof drainage (SSM 45), a drainage layer (Floradrain FD 25/25-E) and 7 cm of commercial green roof substrate (Zinco semi-intensive: granules <0.063 mm in diameter ≤15%, salt content ≤2.5%, porosity 64%, pH 7.8, dry weight 940 kg/m3 , saturated weight 1360 kg/m3 , maximum water capacity 42%, air content at maximum water capacity 22%, water permeability ≥0.064 cm/s) (Alumasc Exterior Building Products, 2006). All materials were obtained from Alumasc (Northamptonshire, UK). Sowing rates of 2 g/m2 and 4 g/m2 were selected for use in this study because a sowing rate of 3–5 g/m2 had been used previously to establish annual meadows at ground level (Dunnett, 1999). This study employed a split-plot experimental design (Fig. 1). Three main plots with timber fames (2.2 m × 1.0 m) were established for both the watering regime and the non-watering regime. Each of the six plots was divided into two sub-plots, which varied with respect to sowing rate, giving twelve plots in total (1.1 m × 1.0 m). Plots were located 1 m apart in order to prevent water from travelling between plots. The seed mixture employed in this study was comprised of equal proportions (by weight) of 22 annual species. The species used were Adonis aestivalis, Anagallis arvensis, Alyssum maritimum, Centaurea cyanus, Chrysanthemum segetum, Consolida regalis, Convolvulus

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Fig. 1. Layout of study plots and sample configuration of seedling emergence quadrats within plots.

Table 1 Characteristics of species used in this study. Species

Family

UK native

Native

Habitat

Adonis aestivalis

Ranunculaceae

Non-native

Cornfields and waste grounds

Anagallis arvensis

Primulaceae

Native

Alyssum maritimum Centaurea cyanus Chrysanthemum segetum Convolvulus tricolor Consolida regalis

Brassicaceae Asteraceae Asteraceae

Non-native Native Native

Convolvulaceae Ranunculaceae

Non-native Non-native

Coreopsis tinctoria

Asteraceae

Non-native

Echium plantagineum ‘Blue Bedder’ Eschscholzia californica

Boraginaceae

Cultivar

Europe from France and Spain eastwards to the Caucasus, Syria and Iran Europe and Asia eastwards to Iraq and Afghanistan Europe – Mediterranean. Naturalized in Britain Europe, Turkey East Mediterranean, North Africa, Europe as far north and west as Scotland and Ireland Portugal and Mediterranean Southeast Europe, eastwards to Iran and Turkmenia North America, from Saskatchewan and Minnesota to Louisiana, Texas and Arizona n/a

Papaveraceae

Non-native

Geranium molle

Geraniaceae

Native

Gypsophila muralis

Caryophyllaceae

Non-native

Iberis amara

Brassicaceae

Native

Iberis umbellata ‘Fairy’ Linaria elegans

Brassicaceae Scrophulariaceae

Cultivar Non-native

Much of central Europe (not the Mediterranean), the Caucasus and Siberia, and naturalized in eastern North America West Europe from Southeast England and Germany and Italy n/a North and central Spain and North Portugal

Linaria maroccana Linum grandiflorum var. rubrum Linum usitatissimum Papaver rhoeas

Scrophulariaceae Linaceae

Non-native Non-native

Morocco and North America North Africa, California

Linaceae Papaveraceae

Non-native Native

Reseda odorata

Resedaceae

Non-native

Tripleurospermum maritimum Viola tricolor

Asteraceae

Native

Not known as wild plant Europe and North Africa, east across Asia to Northwest China, throughout temperate world Egypt, naturalized in the Mediterranean and California Eurasia, North Africa, North America

Violaceae

Native

Adapted from Phillips and Rix (2002).

Northwest America from Washington to South California Britain, Europe to the Himalayas

Most of Europe and Asia, southwards to central Turkey and eastwards to Siberia and Himalayas

Waste places, cornfields, sand dunes, rive banks Dry sunny places in the Mediterranean Pine forest, rocky slopes, cornfield Acidic, sandy soil Dry, open, grassy places Cornfields, steppe and west ground, at up to 1000 m Moist low ground roadsides and waste places n/a

Number of seeds/g 85 2500 2500 220 600 100 750 3000 250 200

Grassland, chaparral and desert up to 2000 m Dry grassland, dunes, waste places and cultivated ground Dry, sandy places

860

Chalky hills and cornfields

400

n/a Grassy roadsides and among bracken in open pine forest Open ground and sandy fields Fields and waste places

Cornfields, disturbed ground Open ground

380

430 15,000 15,000 350 300 9000 750

Common on stony ground by the sea

2000

Grassy places and arable fields

1000

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tricolor, Coreopsis tinctoria, Echium plantagineum ‘Blue Bedder’, Eschscholzia californica, Geranium molle, Gypsophila muralis, Iberis amara, Iberis umbellata ‘Fairy’, Linaria elegans, Linaria maroccana, Linum grandiflorum var. rubrum, Linum usitatissimum, Papaver rhoeas, Reseda odorata, Tripleurospermum maritimum, and Viola tricolor. It was predicted that these plants would thrive in extensive green roof conditions since their habitats, which consist of open ground, cornfields, grasslands and sandy fields, are seasonally arid. In general, selected species were also short, a trait selected for so that species could survive despite the strong winds present in rooftop environments. It was also predicted that they produce various colours, white, red, yellow, pink, purple and orange. Plant characteristics are summarized in Table 1. Seed mixture was obtained from John Chambers Wildflower Seeds (Northamptonshire, UK) and seeds were sown on June 16, 2006. Seeds were mixed with sand because they were too small to distribute over the substrate. 5000 mL of sand and 20 g of seeds were mixed thoroughly in a bucket prior to distribution. An amount of mixture composed of approximately 500 mL sand and 2 g seeds was distributed by hand within low sowing rate (2 g/m2 ) plots. For high sowing rate plots, a similar mixture was prepared using 5000 mL sand and 40 g seeds. An amount of mixture composed of approximately 500 mL sand and 4 g seeds was distributed by hand within high sowing rate (4 g/m2 ) plots. After sowing, the substrate was gently raked in order to allow the seeds to be incorporated. The surface was levelled using the edge of a rake. All plots were watered every other day from the date of sowing until July 13, 2006 to ensure seedling emergence. Irrigation treatment started in watering regime plots on July 20, 2006. Once a week prior to watering, substrate moisture was measured using a moisture sensor (SM200, Delta-T Devices, Cambridge, UK). Three measurement points were randomly chosen from each plot and a total of eighteen points were measured for each watering regime. When the mean substrate moisture of all eighteen points was less than 15%, water was applied as a fine spray to each plot using a handheld hose. Application continued until water started to drain off the plot. Between July 13 and August 11, 2006, plots were watered a total of four times (July 20, July 27, August 4, August 11). Substrate moisture levels were less than 15% during weeks in which no rainfall was observed. Non-watering regime plots received water only from natural rainfall. Mean substrate moisture in both watering regime plots and non-watering regime plots is shown in Fig. 2. Mean monthly temperature and rainfall for Sheffield during 2006 are shown in Fig. 3. June and July 2006 were typically dry, warm months. A relatively larger amount of rain was observed in August, however, recorded values of moisture content remained low until the middle of the month. Variables measured were as follows: (1) Final number of plants and shoot dry weight Harvesting took place on October 30, 2006. Total emergence of plants per plot for each species was determined at the time of harvest. Three replicates existed for each combination of sowing rate and watering regime (2 g/m2 watering, 2 g/m2 nonwatering, 4 g/m2 watering, 4 g/m2 non-watering). Harvested plants were dried in a drying oven at room temperature for a period of seven days, after which shoot dry weight was measured. It was impossible to distinguish between L. elegans and L. maroccana subsequent to flowering; therefore, these two species were measured together during determination of final number of plants and shoot dry weight. Shoot dry weight was measured using a Precisa 2200c balance, which was accurate to 0.01 g. While only three replicates were employed in these variables due to budget and time constraints, a larger number of replications is necessary in order to perform a more robust statistical analysis. (2) Seedling emergence

Fig. 2. Substrate moisture in each plot (n = 18). Error bars represent standard error of mean values. Lower case letters show significance of t-test comparison within a given day. Paired means displaying the same letter do not differ significantly from each other. Substrate moisture was measured prior to watering. Water was applied only when measured substrate moisture was below 15% and only within watering regime plots (July 20, July 27, August 4, August 11).

Since it was impossible to determine total seedling emergence of all plant species in a given plot, three quadrats (30 cm × 30 cm) in each plot were determined randomly and set up using sticks and string (Fig. 1). A total of nine quadrats for each combination of sowing rate and watering regime were established in this manner. Seedling emergence of each species in a given quadrat was determined every three weeks (July 28, August 18 and September 11, 2006). Seedling of L. elegans and L. maroccana as well as L. grandiflorum var. rubrum and L. usitatissimum were impossible to distinguish during early developmental stages and were measured together. (3) Growth (height) Growth of 5 randomly selected representative plants from each species was measured in each plot yielding a total fifteen replicates for each of the 22 plant species examined. A total of three hundred and thirty plants for each combination of sowing rate and watering regime were measured in this manner. Measurements of height were carried out on August 5, August 30 and September 28, 2006. Plants were marked by small flags to ensure that the same plant was examined for

Fig. 3. Changes in mean monthly temperature and rainfall, Sheffield, UK, 2006. Source: Met Office (2007).

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Fig. 4. Mean total shoot dry weight of all plant species per plot (n = 3). Error bars represent standard error of mean values. n.s., not significant. Two-way ANOVA determined that watering, sowing rate and interaction between the two treatments did not have a significant effect on shoot dry weight.

each measurement. Height was defined as the distance from the bottom of the plant to the highest leaf apex. (4) Number of flowers The number of flowering plants per plot was determined weekly for each species. Flowering period was determined by counting the number of weeks from the start of flowering (at least one plant of a given species was observed flowering) to the end of flowering (no plants of a given species were observed flowering). A t-test was used in order to determine significance of differences in substrate moisture between watering and non-watering regime plots (Minitab Release 14) at a probability level of P < 0.05. Significances of differences of other variables were determined using a two-way ANOVA (Minitab Release 14) at a probability level of P < 0.05. 3. Results It was shown that each combination of sowing and watering regime yielded a successful annual meadow green roof. Mean total shoot dry weight of all plant species in a given plot for each combination of sowing rate and watering regime are shown in Fig. 4. Although mean total shoot dry weight of all plant species was higher in watering regime plots than it was in non-watering regime plots, no significant effects of watering regime, sowing rate or interaction between the two treatments could be determined. Across low sowing rate plots, total shoot dry weight was higher in watering regime plots than it was in non-watering regime plots, while the same pattern was not observed across high sowing rate plots. Patterns in mean total number of plants were different from those observed in mean dry weight of plants (Fig. 5). Sowing rate appeared to have a significant effect on mean total number of plants in a given plot, while no significant effect of watering or interaction between sowing and watering treatments could be found. A larger total number of plants emerged in higher sowing rate plots. Across high sowing rate plots, total number of plants was larger in non-watering regime plots than it was in watering regime plots. The larger number of plants observed under non-watering regime conditions was likely the result of reduced competition between plants due to smaller individual plant size. The watering regime employed in this study did not significantly affect final plant emergence or shoot dry weight. In addition, individual plant growth

Fig. 5. Mean total plant number per plot (n = 3). Error bars represent standard error of mean values. P, probability. Sowing rate, sowing rate regime. Two-way ANOVA determined that sowing rate had a significant effect on total plant number.

tended to be improved in low sowing rate plots, as demonstrated by the higher dry weight of plants despite their relatively smaller numbers. The above results are illustrated in photographs of annual meadow plots representing each combination of sowing rate and watering regime (September 1) (Fig. 6). Mean final plant number and shoot dry weight of each species per plot are shown in relation to sowing rate and watering regime in Tables 2 and 3, respectively. For the majority of species, watering, sowing rate and interaction between these treatments did not have a significant effect on either mean final plant number or mean shoot dry weight. In C. cyanus, C. tinctoria, L. grandiflorum var. rubrum and T. maritimum, a significant difference existed in shoot dry weight between watering regimes. Sowing rate did not have a significant effect on shoot dry weight in any of the plant species examined. In A. maritimum, E. plantagineum â&#x20AC;&#x2DC;Blue Bedderâ&#x20AC;&#x2122;, G. muralis, I. amara and L. grandiflorum var. rubrum, sowing rate had a significant effect on mean total number of plants. In E. californica, watering regime had a significant effect on total number of plants. Under watering regime conditions, many species displayed a higher shoot dry weight in low sowing rate plots; however, the opposite was true for the non-watering regime, under which many species displayed a greater shoot weight in high sowing rate plots. In most species, a higher total number of plants emerged in high sowing rate plots. These results suggested that many of the examined species have grown better with a reduced sowing rate when cultivated under the watering regime whereas growth was reduced in plots of both sowing rates under non-watering conditions. Greater shoot dry weights were observed in higher sowing rate plots under nonwatering regime conditions due to a greater total number of plants as opposed to increased individual size. There existed considerable variation in shoot dry weight and number of plants between species. Only A. aestivalis did not germinate at all. A. maritimum, G. muralis, L. elegans and L. maroccana showed high shoot dry weights as well as large numbers of plants. Some species, such as A. arvensis, G. molle, T. maritimum and V. tricolor, produced large numbers of plants; however, their shoot dry weights were smaller than those of other species. The effects of sowing rate and watering regime on changes in mean seedling emergence of all plant species over time per quadrat are shown in Fig. 7. Changes in mean seedling emergence of individual plant species over time per quadrat are shown in Appendix 1. A large number of plant species displayed a tendency towards decreasing seedling emergence over time (A. maritimum, L. elegans, L. maroccana); however, in the majority of species, the number

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Fig. 6. Photographs of representative plots of annual meadow with low sowing rate (2 g/m2 ) and watering regime (top left), low sowing rate (2 g/m2 ) and non-watering regime (top right), high sowing rate (4 g/m2 ) and watering regime (bottom left) and high sowing rate (4 g/m2 ) and non-watering regime (bottom right) on September 1.

of plants increased over time. In each of three measurements taken, a significant effect of sowing rate on seedling emergence was observed and, with the exception of measurements taken on September 11, a significant effect of the interaction between sowing rate and watering regime was also observed. Plant emergence was higher in high sowing rate plots. In high sowing rate plots, no significant difference existed with respect to watering and non-watering regime; however, watering had a significant positive correlation with emergence in low sowing rate plots.

The effects of sowing rate and watering on changes in mean height of all plant species over time are shown in Fig. 8. Changes in mean height of individual plant species per plot over time are shown in Appendix 2. The mean height of all plant species was significantly affected by watering in all three measurements. Therefore, it was determined that watering played an important role in encouraging plant growth, especially during the early stages of annual meadow establishment. In both the watering and non-watering regimes, many species showed better growth

Table 2 Mean total shoot dry weight (g) of each species per plot (n = 3). Sowing rate

2 g/m2

4 g/m2

Irrigation

Watering

Non-watering

Watering

Non-watering

Adonis aestivalis Anagallis arvensis Alyssum maritimum Centaurea cyanus Chrysanthemum segetum Convolvulus tricolor Consolida regalis Coreopsis tinctoria Echium plantagineum ‘Blue Bedder’ Eschscholzia californica Geranium molle Gypsophila muralis Iberis amara Iberis umbellata ‘Fairy’ Linaria elegans and Linaria maroccana Linum grandiflorum var. rubrum Linum usitatissimum Papaver rhoeas Reseda odorata Tripleurospermum maritimum Viola tricolor

0 0.36 22.66 1.28 4.10 0.39 0.07 8.11 3.22 0.29 1.69 16.64 3.31 1.78 95.93 0.61 0.91 0.35 2.41 1.18 0.71

0 0.13 22.35 0.51 1.80 0.31 0.03 3.10 1.40 0.07 0.76 11.57 2.51 1.50 84.56 0.29 0.31 0.20 1.20 0.30 0.36

0 0.33 23.36 2.39 1.83 0.65 0.04 6.45 2.38 0.18 1.32 11.87 3.75 1.69 84.15 0.71 0.72 0.35 1.26 0.80 0.63

0 0.18 21.13 0.98 2.29 0.37 0.05 3.70 2.00 0.12 1.25 11.87 4.29 1.80 95.93 0.45 0.46 0.01 1.42 0.70 0.43

Probability

n/a 0.13 3.61 0.42 0.88 0.18 0.02 1.14 0.57 0.08 0.54 2.87 0.87 0.28 8.52 0.11 0.26 0.18 0.56 0.20 0.14

n/a n.s. n.s. Watering P < 0.05 n.s. n.s. n.s. Watering P < 0.01 n.s. n.s. n.s. n.s. n.s. n.s. n.s. Watering P < 0.05 n.s. n.s. n.s. Watering P < 0.05 n.s.

Two-way ANOVA was used to compare values within species. SE, standard error; n.s., not significant; P, probability; Watering, watering regime.

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Table 3 Mean total plants number of each species per plot (n = 3). Sowing rate

2 g/m2

4 g/m2

Irrigation

Watering

Non-watering

Watering

Non-watering

0 31.33 216.30 8.67 12.00 6.33 9.00 65.33 10.00 9.33 44.67 44.33 22.00 26.67 640.70 13.00 8.33 10.33 31.67 54.33 42.00

0 20.00 192.70 6.67 6.67 4.33 6.00 41.00 8.67 4.00 26.33 47.67 23.67 23.33 687.70 12.33 4.00 5.00 17.33 26.33 31.67

0 46.00 322.70 16.00 15.00 8.00 7.67 81.00 18.33 5.67 59.00 72.33 33.00 35.67 773.70 28.67 5.67 5.00 19.33 49.00 49.00

0 35.00 336.70 12.67 12.67 7.67 5.67 68.00 15.67 4.00 52.33 76.33 45.33 40.33 845.70 26.00 5.00 1.00 23.67 63.00 53.00

Probability

n/a 10.48 29.48 3.87 3.00 2.38 2.19 9.40 1.58 1.40 11.39 6.81 5.83 7.71 86.09 3.58 1.57 4.26 6.11 15.48 10.06

n/a n.s. Sowing rate P < 0.01 n.s. n.s. n.s. n.s. n.s. Sowing rate P < 0.01 Watering P < 0.05 n.s. Sowing rate P < 0.01 Sowing rate P < 0.05 n.s. n.s. Sowing rate P < 0.01 n.s. n.s. n.s. n.s. n.s.

Two-way ANOVA was used to compare values within species. SE, standard error; n.s., not significant; P, probability; Sowing rate, sowing rate regime; Watering, watering regime.

alongside a low sowing rate. A. aestivalis, C. tricolor, C. regalis, E. californica, G. molle, T. maritimum and V. tricolor were small in size and not prominent in study plots. At the beginning of August, the height of most individuals of these species was less than 15 cm. As time passed, individuals from these species could be divided into three groups: short (under 10 cm, e.g. A. maritimum), medium (between 10 and 20 cm, e.g. E. plantagineum ‘Blue Bedder’, Iberis spp.) and tall (over 20 cm, e.g. C. tinctoria, G. muralis, Linaria spp.). When selecting annual plant species for use in green roofs it is important to consider variations in height in order to achieve a more interesting visual effect. Changes in mean number of flowering plants per plot over time are shown in Fig. 9 (high number of flowering plant species) and Fig. 10 (low number of flowering plant species). Values of per plot number of emerging flowers shown are averages of all treatment regimes. A. aestivalis, E. californica and G. molle had no flowers in any of the treatment regimes. C. regalis produced only one flower, which

Fig. 7. Changes in mean seedling emergence of all plant species over time per quadrat (n = 9). Error bars represent standard error of mean values. P, probability; Sowing rate, sowing rate regime; Sowing rate × Watering, interaction between sowing rate regime and watering regime. Two-way ANOVA was used to compare values from each day. Sowing rate had a significant effect on emergence each day and interaction between sowing rate and watering had a significant effect on emergence on September 11.

had already disappeared by the time weekly measurements were taken. Species for which the average number of emerging flowers per plot was less than 1.0 (C. tricolor, L. usitatissimum and V. tricolor) were not shown. A. maritimum and L. maroccana displayed particularly large peak values of emerging flowers per plot in the middle of August and beginning of September, respectively. E. plantagineum ‘Blue Bedder’, G. muralis, I. amara, I. umbellata ‘Fairy’ and L. elegans showed relatively constant numbers of emerging flowers per plot over the course of the study. These species also had long flowering periods. C. tinctoria, C. segetum and T. maritimum showed smaller numbers of emerging flowers per plot; however, they flowered late and reached flowering peaks at the beginning of October. These species could be used to extend the term of flowering in an annual meadow green roof. Mean flowering period of each species is shown in Appendix 3. For the majority of species, no significant

Fig. 8. Changes in mean plant height of all plant species over time (n = 330). Error bars represent standard error of mean values. P, probability; Watering, watering regime; Sowing rate, sowing rate regime. Two-way ANOVA was used to compare values from each day. Watering regime had a significant effect on height each day and sowing rate had a significant effect on height on August 30.

A. Nagase, N. Dunnett / Landscape and Urban Planning 112 (2013) 50–62

Fig. 9. Changes in mean number of flowering plants per plot (high number of flowering plant species). Values shown are means taken from all treatment regimes (n = 12).

Fig. 10. Changes in mean number of flowering plants per plot (low number of flowering plant species). Values shown are averages taken from all treatment regimes (n = 12).

effect was exerted on flowering period by either watering, sowing rate or the interaction between the two treatments. 4. Discussion A limited selection of plant species (such as Sedum spp.) has been used for extensive green roofs. This has, in part, been the result of previous studies that have concluded that regular irrigation or deeper substrates (depths greater than 15 cm) are necessary for successful growth of herbaceous perennials in extensive green roofs, and that only Sedum spp. are able to survive in a thin substrate without irrigation (Monterusso, Rowe, & Rough, 2005; Wolf & Lundholm, 2008). This study demonstrated that it is possible to create colourful and long flowering green roofs using annual meadow with a substrate depth of only 7 cm and without irrigation in Sheffield, UK. Embracing these results would expand the range of options in planting design of extensive green roofs for landscape designers and urban planners. Although it is possible to install annual meadows without irrigation systems under average weather conditions in central UK, supplemental irrigation may be beneficial during dry and hot summers, since the high stress imposed on plants under these conditions has the

potential to reduce plant dry weight, number of flowers and seeds and the ability of those maintaining green roofs to re-seed, even in plants from arid regions (Goldberg, Turkington, Olsvig-Whittaker, & Dyer, 2001; Mott & McComb, 1975; Rivas-Arancibia et al., 2006; Rutledge & Holloway, 1994). In this study, plant growth was encouraged using supplemental watering and it was determined that initial watering was particularly important to improve annual plant growth. Previous studies have also addressed the importance of irrigation during the establishment stage in green roofs (Monterusso et al., 2005). Final total number of plants was significantly higher in high sowing rate plots than it was in low sowing rate plots. These results were consistent with those of previous studies (Hitchmough et al., 2004; Shaw & Antonovics, 1986). Across high sowing rate plots, a larger number of seedlings emerged in non-watering regime plots than watering regime plots. These patterns could have been the result of competition between plants. Shoot dry weight in watering regime plots was greater than it was in non-watering regime plots. Larger numbers of seeds were able to germinate under nonwatering regime conditions since most plants were relatively small and exerted less of a competitive effect on one another. The opposite effect was observed in low sowing rate plots, as plant growth was improved and exploitation competition appeared to be the primary mechanism of interaction influencing growth in the annual community (Goldberg et al., 2001; Inouye, Byers, & Brown, 1980). Therefore, it was determined that watering was an important factor influencing sufficient seedling emergence. Based on these results, it was concluded that a low sowing rate (2 g/m2 ) might be better than a high sowing rate (4 g/m2 ) when rainfall was sufficient. On the contrary, a high sowing rate was determined to be more effective in a dry environment as it would ensure a sufficient total number of plants. Under non-watering regime conditions, seedling emergence rate was low in low sowing rate plots and individual growth was not encouraged due to a lack of water. Under these conditions, a high sowing rate would likely improve the visual quality of the annual meadow due to the resulting increases in both flowering plants and total number of plants. As highlighted in the introduction, visual quality of annual meadows depends on the flowers it contains. In order to determine the potential of individual annual species for using extensive green roofs in the seed mixture used in this study, emergence, height, number of flowering plants and length of flowering periods were summarized (Table 4). To develop a successful annual seed mixture, it is necessary to choose plant species that possess a high emergence rate, good growth, high numbers of flowering and long flowering periods. In this study, A. maritimum, E. plantagineum ‘Blue Bedder’, G. muralis, I. amara, I. umbellata ‘Fairy’, L. elegans and L. maroccana fulfilled these requirements during the first growing season. These species are recommended for inclusion in seed mixtures intended for use in central UK in extensive green roofs with substrate depths similar to those used in this study. A. maritimum and L. maroccana in particular showed a large number of flowering and they formed the backbone of the annual plant mixture. The seed mixture used in this study contained amounts of seeds from each of the 22 species included that were equal with respect to weight. Linaria spp. seeds are smaller than the seeds of the other species included (Table 1) and were therefore more prevalent in the seed mixture. A. maritimum is a low-growing, creeping plant that is useful for filling gaps in a meadow. This species was also self-seeding and seedling emergence was observed just after the completion of autumn flowering. Linaria spp. are slender plants, and L. maroccana produced a mixture of white, yellow, pink and orange flowers that provided bright colours to the annual meadow extensive green roof. G. muralis plants are also slender; however, this species possesses a large flower, and stems were often broken by strong winds. C. tinctoria flowered at a later time and could be

A. Nagase, N. Dunnett / Landscape and Urban Planning 112 (2013) 50–62

Table 4 Performance summary of each species.

Adonis aestivalis Anagallis arvensis Alyssum maritimum Centaurea cyanus Chrysanthemum segetum Convolvulus tricolor Consolida regalis Coreopsis tinctoria Echium plantagineum ‘Blue Bedder’ Eschscholzia californica Geranium molle Gypsophila muralis Iberis amara Iberis umbellata ‘Fairy’ Linaria elegans Linaria maroccana Linum grandiflorum var. rubrum Linum usitatissimum Papaver rhoeas Reseda odorata Tripleurospermum maritimum Viola tricolor

Emergence

Height

Number of flowering plants

Length of flowering period

No High High Low Low Low Low High Low Low High High Medium Medium High High Medium Low Low Medium High High

No Short Short Medium Medium Low Low Tall Medium Short Short Tall Medium Medium Tall Tall Tall Medium Medium Short Short Short

No Small Large Small Small Small No Small Medium No No Medium Large Medium Large Large Small Small Small Small Small Small

No Short Long Medium Medium Short No Short Long No No Long Long Long Long Long Short Short Short Medium Short Short

Potential for annual plant seed mixture

High

High High High High High

Emergence: Mean plant number per plot at time of harvest. No emergence = 0, 0 < low ≤ 20, 20 < medium ≤ 50, 50 < high. Height: Mean plant height at the final measurement. No height = No emergence, 0 < short ≤ 10 cm, 10 cm < medium ≤ 20 cm, 20 cm < tall. Number of flowering plants: Mean number of flowering plants per plot at the peak of flowering in each plant species. No flowering plants = 0, 0 < small ≤ 5, 5 < medium ≤ 20, 20 < large. Length of flowering periods: Length of flowering period per plot. No flowering plants = 0, 0 weeks < short ≤ 5 weeks, 5 weeks < medium ≤ 9 weeks, 9 weeks < long.

used to extend the flowering season of a seed mix. E. plantagineum ‘Blue Bedder’, I. amara and I. umbellata ‘Fairy’ showed long flowering periods and possessed outstanding flowering attributes. Gypsophila spp. and Iberis spp. were successfully implemented in a previous study on annual seed mixtures for use in extensive green roofs (Kircher, 2004). Some species, such as C. cyanus and C. segetum, have provided an impressive floral display over a period of several months when grown on the ground (Dunnett, 2004); however, their flowering period was reduced in the rooftop environment. Of the 22 species used, only A. aestivalis did not germinate at all. This may have been the result of not only dormancy and low seedling emergence rate, but of low initial numbers of seeds as well, which likely resulted from the relatively large size of seeds in this species and the way in which initial seed mixture composition was determined. Growth of A. arvensis, C. regalis, E. californica, G. molle, P. rhoeas and V. tricolor was restricted and inconspicuous, and some of these plants did not produce flowers, while others had only a very small number of flowers for a short period of time. The failure of these species to establish themselves in the study plots was probably due to competition with other species or their inability to adapt to the green roof environment. Furthermore, petals of E. californica and P. rhoeas were easily broken off by strong winds. Selection of plant species that can tolerate strong wind is an important consideration for extensive green roofs. In this study, performance of non-native and cultivar species was better than that of native species. Of the successful plant species mentioned previously, I. amara was the only native species. As Hitchmough and Woudstra (1999) pointed out, the inclusion of exotic species into purposely sown native meadows allows for the addition of dramatic colours effect as well as extension of the flowering season. Despite these observations, the use of native plants on green roofs has attracted considerable attention in recent years for the following reasons: native plants provide a sense of place and blend into the natural landscape; native plants are adapted to local environments; native plants function as habitat for native fauna and serve to increase biodiversity; and native plants are

less likely to become invasive than non-native species (Butler, Butler, & Orians, 2012). Research on performance of native plant species in green roofs is limited and it is necessary for future research to examine the performance of seed mixtures containing only native plant species. Moreover, the role of chorology and optimal habitats for annual meadow green roofs was not clear in this study. Therefore, it is also interesting to study native and exotic annual plant community from various habitats to understand them. This type of annual meadow cost 60 p/m2 (2 g/m2 ) to install and spreading the seeds took less than one hour. Furthermore, since fully grown plants do not have to be transported to the roofs, money that would otherwise have been spent on transportation and planting can be saved. These factors make annual meadow particularly useful in the establishment of large area green roofs. Annual meadows on extensive green roofs also require little maintenance. During the present study, no weeds colonized the extensive green roof examined as the substrate was thin and relatively dry. Another advantage of annual meadow green roofs is the reduction of competition with spontaneous plant species resulting from initial installation of clean substrate. Seed banks of weedy plant species tend to be a serious problem when establishing annual meadows on the ground (Prentis & Norton, 1992). The primary maintenance act required for annual plant meadows in extensive green roofs is an annual mowing. According to Hitchmough (2004), annual plants are transient and even with proper management encouraging regeneration from self-sowing seeds, sowing is often required on an annual basis. Previous studies have shown that management of meadow structure and composition and the abundance and availability of plant (mainly as seeds) and invertebrate food resources for birds are inextricably linked and it is important to leave seed heads without cutting over winter (Atkinson, Buckingham, & Morris 2004; McCracken & Tallowin, 2004; Vickery et al., 2001). Francis and Lorimer (2011) demonstrated that green roofs can be used for urban reconciliation ecology, which is defined as the

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modification and diversification of anthropogenic habitats in order to support a greater range of species without compromising land use. They stressed that, in order for green roofs to be successfully utilized in urban reconciliation ecology, the participation of urban citizens is crucial. Use of annual meadow plants help to ensure the participation of urban citizens. According to a public opinion survey on wildflower mixtures, a long bloom season and multi-coloured flowers are generally seen as favourable qualities (Rutledge & Holloway, 1994). It was also determined that the communities identified as the most aesthetically pleasing were those that possessed the greatest species richness and structural diversity (Lindemann-Matthiens & Bose, 2007; Lindemann-Matthies, Junge, & Matthies, 2010). Recently, many biodiverse roofs have been installed due to the associated biodiversity benefits; however, they lack the lush green appearance of green roofs but they have a similar appearance to brownfields (Dunnett & Kingsbury, 2008). In this study, biodiversity values of the annual meadow examined were not measured; however, many bees, particularly bumblebees, were attracted to the study site due to the abundance of flowers. Especially, it was observed that bees visited E. plantagineum ‘Blue Bedder’ and Linaria spp. frequently and generally, pollen dispersal success in entomophilous plants is influenced by visitation frequency of a pollinator (Galen & Stanton, 1989). Therefore, annual meadows could be one potential alternative to biodiverse roofs in areas where aesthetics are important. In future research, assessment of aesthetic value in annual plant meadow roofs and biodiverse roofs is required. It is important to note that the appearance of annual meadow green roofs in winter should be considered, as some individuals might find them untidy if left unmanaged during that time period (Rohde & Kendle, 1997). Moreover, bare ground may become apparent during the wintertime (Dunnett, 2004). Combination of annual plants and bulbs or perennials during winter would serve an aesthetic purpose and might also help to minimize soil erosion on green roofs. Moreover, it is

required to use big aggregate of substrate to reduce soil erosion and to keep seeds into the substrate when annual meadow is used for extensive green roofs. 5. Conclusion The annual plant seed mixture used in this study was easy to install, inexpensive and quick to establish, and the majority of plant species used were drought tolerant and long flowering. Furthermore, annual meadows established using this seed mixture required little in the way of maintenance and irrigation. A low sowing rate is recommended in order to facilitate plant growth when water resources are abundant, while a high sowing rate would be ideal under drier environmental conditions in order to ensure a sufficient total number of plants. Further study of this annual mixture over a longer period is necessary to confirm the sustainability, biodiversity value and detail flower colours (e.g. chromatic spectrum) of the annual meadows produced. In addition, the assessment of aesthetic value of annual meadow is also required. Performance of resulting annual meadows must also be assessed over a range of green roof environments. This annual seed mixture might only be effective in areas with climates similar to that of the UK; therefore, research on different seed mixtures for other regional extensive green roofs is essential. Acknowledgements We express our appreciation to Almasc for providing the experimental materials, to career-support program for woman scientists in Chiba University for founding to proof our English, to Dr. Noel Kingsbury in University of Sheffield for his valuable advice, to Mr. Min-Sung Choi in University of Sheffield for helping to set up the experiment, to Dr. Shinichi Kurihara in Chiba University and Dr. Ann-Mari Fransson in Swedish University of Agricultural Science for their advice of statistical analysis.

Appendix 1. Mean emergence of each species per quadrat (n = 9) July 28

August 18

September 11

Probability

2 g/m2

4 g/m2

Probability

0 1.67 21.67 1.00 1.67 0.33 1.22

n/a 0.53 1.80 0.35 0.39 0.29 0.32

n/a Watering P < 0.05 Sowing rate P < 0.01 n.s. Sowing rate P < 0.05 n.s. Sowing rate * Watering P < 0.05 n.s. n.s.

Watering

Nonwatering

Watering

Nonwatering

0 2.44 12.22 0.78 1.00 0.44 1.22

0 0.70 12.22 0.89 0.56 0.56 0.22

0 2.56 18.78 1.00 1.56 0.67 0.78

Adonis aestivalis Anagallis arvensis Alyssum maritimum Centaurea cyanus Chrysanthemum segetum Convolvulus tricolor Consolida regalis

n/a Watering P < 0.05 n.s. n.s. Sowing rate P < 0.05 Watering P < 0.01 n.s.

n/a Watering P < 0.05 Sowing rate P < 0.01 Sowing rate P < 0.05 n.s. n.s. n.s.

Coreopsis tinctoria Echium plantagineum ‘Blue Bedder’ Eschscholzia californica

Watering P < 0.01 n.s.

n.s. n.s.

4.00 1.11

2.22 1.11

3.11 1.44

3.78 1.67

0.65 0.41

n.s.

1.00

0.11

0.33

0.44

0.23

Geranium molle Gypsophila muralis Iberis amara Iberis umbellata ‘Fairy’ Linaria elegans and Linaria maroccana Linum grandiflorum var. rubrum and Linum usitatissimum Papaver rhoeas Reseda odorata

n.s. n.s. Watering P < 0.05 Watering P < 0.01 n.s.

Watering P < 0.05 Sowing rate P < 0.01 n.s. n.s. Sowing rate P < 0.05

2.56 3.44 2.44 1.33 40.33

1.67 4.11 1.11 1.89 30.89

4.56 6.22 3.22 2.78 45.33

2.78 5.00 3.89 3.11 49.44

0.71 0.78 0.78 0.49 4.21

Sowing rate * Watering P < 0.05 Sowing rate P < 0.05 Sowing rate P < 0.05 Sowing rate P < 0.05 Sowing rate P < 0.05 Sowing rate P < 0.01

n.s.

1.33

1.56

2.22

2.00

0.43

n.s.

Watering P < 0.01 Watering P < 0.01

Sowing rate P < 0.05 Watering P < 0.01 Sowing rate * Watering < 0.05

1.44 3.22

0.44 1.67

0.33 1.22

0.33 2.00

0.43 0.59

n.s. n.s.

A. Nagase, N. Dunnett / Landscape and Urban Planning 112 (2013) 50–62

Appendix 1 (Continued) July 28

August 18

September 11

Probability

2 g/m2 Watering

4 g/m2 Nonwatering

Watering

Probability

Sowing rate * Watering P < 0.01 n.s.

Nonwatering

Tripleurospermum maritimum

Watering P < 0.01

4.56

1.44

1.67

2.44

0.57

Viola tricolor

n.s.

3.00

1.67

1.78

1.89

0.36

Two-way ANOVA was used to compare values within species. Results of the first two measurements show only the probability derived from statistical analysis. SE, standard error; n.s., not significant; P, probability; Watering, watering regime; Sowing rate, sowing rate regime; Sowing rate * Watering, interaction between sowing rate regime and watering regime.

Appendix 2. Height of each species (cm) (n = 15) August 5

August 30

September 28

Probability

2 g/m2 Watering

Adonis aestivalis Anagallis arvensis Alyssum maritimum Centaurea cyanus Chrysanthemum segetum

Convolvulus tricolor Consolida regalis Coreopsis tinctoria

Echium plantagineum ‘Blue Bedder’ Eschscholzia californica

n/a Watering P < 0.01 Watering P < 0.01 Sowing rate P < 0.05 Watering P < 0.01 Watering P < 0.05 Sowing rate P <0.05 Sowing rate * Watering P <0.01 Watering < 0.05 n.s. Watering P < 0.01 Sowing rate P < 0.05 Sowing rate * Watering P < 0.05 Watering P < 0.01

n/a Watering P < 0.01 Watering P < 0.01

4 g/m2 Nonwatering

Watering

Probability

Nonwatering

0 4.15 6.79

0 1.48 6.09

0 3.11 6.27

0 1.84 6.02

n/a 0.44 0.51

n/a Watering P < 0.01 n.s.

Watering P < 0.01 Sowing rate P < 0.05

13.19 25.39

14.17 13.29

18.72 13.89

13.37 14.37

1.73 2.38

Watering P < 0.05 n.s. Watering P < 0.05

8.11 1.53 34.36

6.77 1.56 25.52

7.20 0.96 30.72

6.65 0.71 24.57

1.12 0.38 2.06

n.s. Watering P < 0.05 Sowing rate P < 0.05 Sowing rate * Watering P < 0.05 n.s. n.s. Watering P < 0.01

Watering P < 0.01

17.32

10.98

14.79

12.32

0.97

Watering P < 0.01

6.43

3.46

3.97

3.01

0.62

Watering P < 0.01 Sowing rate P < 0.05

4.26 28.73 18.73

2.59 21.15 16.22

3.37 25.77 16.11

2.37 20.79 15.87

0.33 1.78 0.69

Watering P < 0.01 Watering P < 0.01 Sowing rate P < 0.05

14.99

9.63

11.71

10.93

0.76

Watering P < 0.01 Sowing rate * Watering P < 0.01 n.s.

Watering P < 0.01 Sowing rate P < 0.01 Sowing rate * Watering P < 0.01 Watering P < 0.01 Watering P < 0.01 Watering P < 0.01 Sowing rate * Watering P < 0.01 Watering P < 0.01

Geranium molle Gypsophila muralis Iberis amara

Watering P < 0.01 Sowing rate P < 0.01 Sowing rate * Watering P < 0.01 Watering P < 0.01 n.s. Watering P < 0.01

Iberis umbellata ‘Fairy’

Watering P < 0.01

Linaria elegans

Watering P < 0.01 Sowing rate P < 0.05 Watering P < 0.01 Watering P < 0.01 Sowing rate P < 0.01 Watering P < 0.01 Watering P < 0.01 Watering P < 0.01 Watering P < 0.01

n.s.

40.30

37.59

34.37

37.20

2.65

Watering P < 0.05 Watering P < 0.01 Sowing rate P < 0.05 Watering P < 0.01 Watering P < 0.01 Watering P < 0.05 Watering P < 0.01

27.12 26.81

27.05 18.69

26.93 26.21

28.31 16.50

2.05 n.s. 1.623 Watering P < 0.01

22.15 15.52 10.53 11.68

14.97 12.57 8.72 3.88

21.53 16.43 8.96 7.10

15.65 6.49 7.03 3.54

0.82 1.91 1.42 1.16

Watering P < 0.05

n.s.

1.63

1.65

1.79

0.99

0.40

Linaria maroccana Linum grandiflorum var. rubrum Linum usitatissimum Papaver rhoeas Reseda odorata Tripleurospermum maritimum Viola tricolor

Watering P < 0.01 Watering P < 0.01 n.s. Watering P < 0.01 Sowing rate P < 0.05 n.s.

Two-way ANOVA was used to compare values within species. Results of the first two measurements show only the probability derived from statistical analysis. SE, standard error; P, probability; n.s., not significant; Watering, watering regime; Sowing rate, sowing rate regime; Sowing rate * Watering, interaction between sowing rate regime and watering regime.

A. Nagase, N. Dunnett / Landscape and Urban Planning 112 (2013) 50–62

Appendix 3. Mean flowering period of each species per plot (week) (n = 3) Sowing rate

2 g/m2

Irrigation

Watering

Non-watering

Watering

Non-watering

Adonis aestivalis Anagallis arvensis Alyssum maritimum Centaurea cyanus Chrysanthemum segetum Convolvulus tricolor Consolida regalis Coreopsis tinctoria Echium plantagineum ‘Blue Bedder’ Eschscholzia californica Geranium molle Gypsophila muralis Iberis amara Iberis umbellata ‘Fairy’ Linaria elegans Linaria maroccana Linum grandiflorum var. rubrum Linum usitatissimum Papaver rhoeas Reseda odorata Tripleurospermum maritimum Viola tricolor

0 2.00 12.67 7.67 5.33 0.33 0 4.00 10.33 0 0 10.33 10.33 9.33 9.00 11.00 4.33 1.67 3.33 5.67 6.00 0.33

0 0 13.00 4.67 5.33 0.67 0 5.00 11.00 0 0 12.00 10.00 10.33 9.00 10.67 4.00 0 1.67 5.67 2.00 0.67

0 1.00 12.67 9.67 5.00 0.67 0 5.33 10.33 0 0 11.00 10.33 10.33 9.33 11.00 3.33 2.33 2.33 5.67 5.33 0.67

0 1.00 12.67 6.33 3.33 0.33 0 2.67 9.67 0 0 10.33 9.67 9.67 9.00 11.00 3.33 0.67 1.00 3.67 1.67 0

4 g/m2

Probability

n/a 0.65 0.29 1.20 0.71 0.44 n/a 0.62 0.91 n/a n/a 0.55 0.29 0.60 0.17 0.17 0.82 0.58 1.19 1.42 0.99 0.41

n/a n.s. n.s. Watering P < 0.05 n.s. n.s. n.s. Sowing rate * Watering P < 0.05 n.s. n/a n/a n.s. n.s. n.s. n.s. n.s. n.s. Watering P < 0.05 n.s. n.s. Watering P < 0.01 n.s.

Two-way ANOVA was used to compare values within species. SE, standard error; P, probability; n.s., not significant; Watering, watering regime; Sowing rate * Watering, interaction between sowing rate regime and watering regime.

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