2013 pefromance of geophytes on extensive green roofs in the uk

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Urban Forestry & Urban Greening 12 (2013) 509–521

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Urban Forestry & Urban Greening

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Performance of geophytes on extensive green roofs in the UnitedKingdom

Ayako Nagasea,∗, Nigel Dunnettb,1

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

a r t i c l e i n f o

Keywords:AestheticBiodiversityCovering plantsSedumSubstrate depthUrban landscape

a b s t r a c t

Dwarf geophytes have great potential for use on extensive green roofs because they often come from aridareas and can survive dry and hot summer in a dormant state. However, there has been little researchregarding geophytes on green roofs. This experiment was conducted to study the performance of 26species of geophytes on a green roof during 2005–2006 in Sheffield, UK. The geophytes were grown attwo substrate depths (5 cm and 10 cm) of substrate on a green roof without irrigation. To investigatethe susceptibility of geophytes to competition from a covering of permanent plants, the geophytes weregrown with or without a surface vegetation layer of Sedum album. Overall, the growth, survival rate,regeneration and flowering of geophytes were more successful at a substrate depth of 10 cm than of 5 cm,probably because of improved moisture retention, fewer temperature fluctuations and the protectionfrom digging by animals. The flowering period was limited to spring, therefore, it is recommended tocombine with other plant species such as covering plants. Geophyte species did not compete muchwith S. album and Sedum cover had no significant effects on the growth, survival rate, regeneration andflowering of geophytes in most species. Iris bucharica, Muscari azureum, Tulipa clusiana var. chrysantha,Tulipa humilis, Tulipa tarda and Tulipa turkestanica had good performance at the substrate depth of 5 cm. Inaddition, Narcissus cyclamineus ‘February gold’ and Tulipa urumiensis exhibited a successful performanceat the substrate depth of 10 cm.

© 2013 Elsevier GmbH. All rights reserved.

Introduction

Green roofs have gained global acceptance as a technology withpotential to help mitigate the multifaceted and, complex environ-mental problems of urban centres (Clark et al., 2008). Extensivegreen roofs are characterized by their light weight, low mainte-nance requirements, little or no irrigation systems requirementsand thin substrate depths (2–20 cm). They are widely used becausethey are easy to install on existing buildings without structuralmodifications and they are inexpensive (Oberndorfer et al., 2007).The most commonly used species on extensive green roofs areSedum spp. because they can tolerate extreme temperatures, highwinds, low fertility and limited water supplies (Durhman et al.,2006, 2007; Van Woert et al., 2005). Recently, biodiverse roofs areoften used for extensive green roofs. This type of extensive greenroof is used to recreate conditions found in typical urban brown-field sites in order to enhance their potential biodiversity value

∗ Corresponding author. Tel.: +81 0432903113; fax: +81 0432903121.E-mail addresses: [email protected] (A. Nagase),

[email protected] (N. Dunnett).1 Tel.: +44 01142220611; fax: +44 01142754176.

(Dunnett and Kingsbury, 2008). However, both Sedum roofs andbiodiverse roofs often lack aesthetic appeal. Sedum spp. are usu-ally evergreen, however, they only flower for a limited period andchange little throughout a year (Kadas, 2006). Biodiverse roofs oftenlack the lush green appearance of green roofs and have an appear-ance similar to that of brownfields (Dunnett and Kingsbury, 2008).The visual appearance may not be a concern if the roof is generallynot visible and is installed primarily for its functional attributessuch as storm water retention (Getter and Rowe, 2006). However,aesthetics may be important if green roofs are visible and activelyused.

Geophytes are important plants species that can adapt to harshenvironment found on extensive green roofs. They are plants witha swollen storage organ, such as true bulbs, corms, tubers and rhi-zomes (Raunkiaer, 1934; Mathew and Swindells, 1994). Bulb (e.g.Narcissus, Tulipa and Lilium) has a short stem surrounded by fleshyscale leaves or leaf bases. Corm (e.g. Crocus, Colchicum and Gladi-olus) consists of a swollen stem base covered with scale leaves.Rhizome (e.g. Iris) has a continuously growing horizontal under-ground stem which puts out lateral shoots and adventitious rootsat intervals. Tuber (e.g. Begonia, Anemone and Cyclamen) has a thick-ened underground part of a stem (Oxford dictionaries, 2010). Thestructures are different, but these plants act in the same manner,

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510 A. Nagase, N. Dunnett / Urban Forestry & Urban Greening 12 (2013) 509–521

i.e. these structures all play the role of storage organs that allowplants to retreat underground for long periods of dormancy (Garrettand Dusoir, 2004). There are several benefits of using geophyteson extensive green roofs. First, their ecological characteristics areappropriate for the green roof environment. Some geophytes arehighly drought tolerant and may perform well on extensive greenroofs without irrigation in the UK. These drought-tolerant geo-phytes often come from dry climates, such as South Africa, theMediterranean basin and Central Asia (Kingsbury, 1996), wherewinters are wet and summers are hot and dry, with a short spring(Phillips and Rix, 1989). These plants can grow, flower and seedduring cool moist seasons and disappear into the comparative coolof the earth during hot summers (Kingsbury, 1996). The growingseason is short, and the plants use their stored energy to flowerand quickly set seed during spring (Blamey and Blamey, 1979).Second, they produce colourful flowers early in the season whenmany herbaceous plants have not started growing. The early flow-ering of geophytes provides colours and is also very useful forproviding nectar sources at a time of year when little else maybe flowering on a green roof. The first spring-flowering geophytesare a lifeline for overwintering insects in search of nectar after along period of dormancy (Dunnett, 2004). Third, they require lit-tle maintenance and their storage organs often act as a means ofpropagation (vegetative reproduction). Geophytes grow and flowerfor a short time after planting. After planting, geophytes usuallyrequire little maintenance while some multiply rapidly when thegrowth conditions are suitable. For example, Muscari armeniacumproliferated rapidly after appearing spontaneously on an over 30-years-old extensive grass roof in the UK (Dunnett and Kingsbury,2008).

However, there are also disadvantages of using geophytesbecause the flowering periods of individual plants are relativelyshort and they become unsightly after flowering. In addition, geo-phyte species that are potentially suitable for extensive green roofstend to exhibit winter to early summer growth. Thus, it is recom-mended that they are combined with other plants, such as likeplants that cover the ground throughout the year. Mathew (1997)discussed the benefits of using creeping or carpeting plants withgeophytes; the flower stems of geophytes receive some support andblooms are protected from soil splashes during heavy rain. How-ever, it is necessary to avoid vigorous plants for cover plants withgeophytes (Elliott, 1995). Previous studies have shown that thegrowth of geophytes was reduced because of competition with cov-ering grass (Hughes, 1986). In a study of the competition betweenAllium vineale and Lolium perenne, emergence and growth of A.vineale were affected (Lezenby, 1961). These studies were con-ducted on the ground, but, it is predicted that vigorous coveringplants may lead to nutrient removal and moisture stress (Hewsonand Roberts, 1973).

Although there has been little research on how geophytes per-form on extensive roofs, geophytes have been used on extensivegreen roofs. Allium spp. is one of the most commonly encoun-tered geophytic genus on extensive green roofs (Dunnett andKingsbury, 2008). Long-term research on extensive green roofsin Berlin showed that Allium schoenoprasum was the most dom-inant plant species throughout 20 years because of self-seeding(Köhler and Poll, 2010). Lilium auratum has been used in traditionalthatched roofs in Japan for reinforcement and for its aesthetics.Dwarf geophytes may be more appropriate for extensive greenroofs because they are more drought tolerant than large hybrids(Glattstein, 2005; Snodgrass and Snodgrass, 2006). Short speciesmay also be better at withstanding wind on green roofs, whereastall or top-heavy flowers would not withstand on a windy site (Rees,1992). Storage organs of dwarf geophytes are also small; therefore,they can tolerate a shallow planting and are expected to be betteradapted to thin substrates.

The aim of this study was to identify appropriate geophytespecies for extensive green roofs and to investigate how substratedepth and covering plants of Sedum spp. may affect the perfor-mance of geophytes on extensive green roofs. The effect of substratedepth was studied because it often limits the root growth and theavailability of water and nutrients and it may be an important factorthat affects plant performance on extensive green roofs (Dunnettet al., 2008; Olly et al., 2011; Rowe et al., 2012). Sedum spp. wereused as covering plants because they are one of the most frequentlyused species for extensive green roofs. In addition, compared withother plants, Sedum spp. are expected to offer less competition togeophytes because they are low growing plants with shallow rootsand require little water and nutrients.

Methods

Experimental setup

The experiment was initiated in December 2004 on the roof ofa four-storey commercial building near the city centre in Sheffield,UK. The green roof was framed by timbers and consisted ofroot protection barriers, drainage layers (Floradrain FD 25/25-E) and a commercial green roof substrate composed of crushedrecycled brick and 10% organic material (Zinco sedum substrateand Zinco semi-intensive substrate 1:1, ≤7–15%, in which thegranules measured <0.063 mm in diameter; salt content ≤2.5%;porosity 63–64%; pH 7.8–7.9; dry weight 940–980 kg/m3; saturatedweight 1240–1360 kg/m3; maximum water capacity 25–42%; aircontent at maximum water capacity 22–38%; water permeability≥0.064–0.1 cm/s) (Alumasc, 2006). Zinco substrate was obtainedfrom Alumasc (Northamptonshire, UK). The substrate depth (5 cmand 10 cm) and covering plants (with and without Sedum album)were the variables. We tested substrate depths of 5 cm and 10 cmbecause a depth of at least 5 cm was necessary to cover geophytes.It was estimated that the substrate depth of 5 cm depth was too thinto allow the sufficient growth of some geophytes; therefore, a sub-strate depth of10 cm depth was also tested. Half of plots were leftwithout covering plants to test whether Sedum spp. affect the per-formance of geophytes on extensive green roofs. There were threereplicates for each combination; hence, a total of 12 plots werearranged randomly (Fig. 1). These plots received similar length ofsunlight. Each plot measured 60 cm × 145 cm and was divided into30 subplots (12 cm × 24 cm) (Fig. 1). Each plot was framed by tim-bers, however, there were no partitions between each subplot. Ineach subplot, three individual geophytes from a single species wereplanted in a line. Twenty-six plant species were planted as under-ground storage organs on January 14, 2005. Storage organs weresmall; from 1.5 cm to 3.0 cm. Therefore, subplots provide enoughspace to grow geophytes. Name of plants and their characteristicsare described in Table 1. Geophytes were obtained from Dutchbulbs(Manchester, UK). They are popular plants for typical gardens andthey are easy to get and low price. These plants were expected tobe well-adapted to extensive green roofs because they naturallyin European or Asian alpine regions mainly with rocky or stonysubstrate and relatively low temperature. They tended to be shortheight, which is appropriate for green roof environment to resiststrong wind. Twenty-six subplots were used out of 30 subplots. 4subplots were left empty. The empty subplots were chosen in ran-dom. The geophytes were planted at a depth of 3 cm below thesubstrate surface using two different total substrate depths, i.e.5 cm and 10 cm (Fig. 1). S. album seeds (0.5 g) were sown in Sedumcover plots on April 30, 2005 as covering plants. The seeds wereobtained from Jelitto (Schwarmstedt, Germany). S. album seedswere too small to distribute over the plot; therefore, they weremixed with horticultural sand. It took 1 year for S. album to cover


A. Nagase, N. Dunnett / Urban Forestry & Urban Greening 12 (2013) 509–521 511

Table 1Characteristics of the geophyte species used in this study.

Family Distribution Typical habitat Flowering season Height

Allium flavum Liliaceae Southern Europe fromFrance to Greece

Dry hills July 25–30 cm

Allium karataviense ‘Ivory queen’ Liliaceae Central Asia, especiallyTurkestan

Semi-desert mountain May 15 cm

Allium ostrowskianum Liliaceae Central Asia, especially inTien Shan, the Pamir Alaiand the Ala Tau, as well aseastern Turkey and theCaucasus

Stony slopes at3000–3800 m

May–June 15 cm

Allium unifolium Liliaceae North California and southOregon in the coast ranges

Coast ranges, growing inthe moist substrates inpine or mixed evergreenforest below 1200 m

May–July 45 cm

Crocus sieberi ‘Tricolor’ Iridaceae Crete and Greece Short mountain turf oropen woodland

February–March 8 cm

Crocus tommasinianus Iridaceae Dalmatia, South Hungary,Yugoslavia and NorthBulgaria

In woods and shadyhillsides, especially onlimestone, at ground1000 m


Crocus vernus ‘Vanguard’ Iridaceae Europe from the Pyreneeseastwards to Poland andRussia, and south to Sicilyand Yugoslavia

Mountains February–June 10 cm

Iris bucharica Iridaceae Central Asia, especially thePamir Alai, Tajikistan andnortheast Afghanistan

Stony and grassy hills from800 to 2400 m

March–April 30 cm

Iris danfordiae Iridaceae Central Turkey, in theTaurus, in west Malatya,Amasya and Gümüsane

2000–3000 m, on bare,earthly hills


Iris reticulata Iridaceae Russia, Turkey, Iran, SouthTranscaucasia and Iraq

Scree and bare stony placesand among scrub from600 m to 2700 m

March–May 20 cm

Ixioliron pallasii Amaryllidaceae Western Asia from Turkey,Egypt and eastwards towestern Siberia

In fields and on hillsidesfrom 200 to 2700 m

June 30 cm

Muscari azureum Iridaceae Caucasus and northwestTurkey

High elevation March 15 cm

Narcissus cyclamineus ‘February gold’ Amaryllidaceae Northwest Portugal andnorthwest Spain

River banks and dampmountain pastures

Early March 30 cm

Puschkinia libanotica Liliaceae Caucasus, south Turkey,North Iraq and from Iran toLebanon

In scrub, in stony placesand in meadows inmountains, at up to 3000 m

March–April 15 cm

Scilla siberica Liliaceae South Russia, Caucasus andTurkey southwards toSiberia, naturalized in eastEurope

Woods, scrub and amongrocks, up to 2000 m

March–April 10 cm

Sparaxis tricolor Iridaceae South Africa Cape province June 25 cmTulipa bakeri ‘Lilac wonder’ Liliaceae Crete (Greece) Fields and rocky places March 25 cmTulipa clusiana var. chrysantha Liliaceae Iran, near Shiraz eastwards

to the Himalayas fromAfghanistan to Kumaon,and naturalized in SouthEurope

Stony mountain sides April 20 cm

Tulipa hageri ‘Splendens’ Liliaceae Greece, Crete, Bulgaria andwest Turkey

Cornfield and stony places April 20 cm

Tulipa humilis Liliaceae East Turkey, north Iraq andnorth west Iran

Stony hillside March 8–10 cm

Tulipa kolpakowskiana Liliaceae Central Asia, especially thenorthern Tien Shan andsouthern Ala Tau

Rocky slopes up to 2000 m May 15 cm

Tulipa linifolia Liliaceae Uzbekistan, north Iran andAfghanistan

Mountains Mid-May 12 cm

Tulipa saxatilis Liliaceae Crete (Greece) Fields and rocky places Early May 15 cmTulipa tarda Liliaceae Central Asia, especially

Tien ShanStony and rocky slopes April 12 cm

Tulipa turkestanica Liliaceae Central Asia, especiallyTien Shan, the Pamir Alai,and north west China

Stony slopes, by streamsand on rock ledges from1800 m to 2500 m

Early May 15 cm

Tulipa urumiensis Liliaceae Iran Not known in the wild April 10–15 cm

Adapted from Botschantzeva (1982) and Phillips and Rix (1989).



Fig. 1. Layout of the study plots and the arrangement of geophytes within the plotsand planting positions used for the geophytes at the substrate depths of 5 cm and10 cm.

fully plots of both substrate depth of 5 cm and 10 cm. All of the plotsreceived only rain water. An overview of the experimental site isshown in Fig. 2.

Data collection

In the first year, the emergence rate (the percentage ofplants exhibiting above-ground emergence) was measured 4 timesbetween March 24 and April 28, 2005. In the second year, growthwas measured 11 times (between March and July = 22 weeks). Itwas considered that recording the second year of growth would beimportant since the geophytes had overwintered on the roofs. Thefirst year of growth was largely determined by the state of the bulbbefore planting (i.e. how it was grown prior to planting). However,growth in the second year was likely to be strongly determinedby the actual growing conditions in situ. In addition, the coveringplants may have had little effect in the first year because S. albumdeveloped after the growth of geophytes was completed in the firstyear. Therefore, the emergence rate was the only variable measuredin the first year.

The parameters measured were as follows: leaf length (thelongest leaf from the proximal to the apex); total leaf num-ber (including small leaves more than 5 mm); flower height (thelongest flower stem, from the proximal to the apex); proximalshoot number (number of shoots grown by vegetative reproduc-tion); the period of above-ground growth (from emergence tocompletely drying out); flowering duration (from the opening ofthe buds to the end of flowering). Most emerged plants producedonly one proximal shoot in the first year; however, the numberincreased in the second year because of vegetative reproduction.Therefore, we treated the maximum proximal shoot number asan indicator of vegetative reproduction. These parameters were

Fig. 2. Overview of the study site.

chosen with the reference of previous studies to evaluate growthof geophytes (Lazenby, 1962; Ernst, 1979; Barkham, 1980a,b).A few weeds were colonized in these experimental plots, how-ever, they were removed when the measurements were carriedout.

Mean monthly temperature and rainfall during 2005 and 2006 inSheffield are shown in Fig. 3. Winter was mild in 2005, whereas thesummer temperature was lower than the one of average. Annualprecipitation in 2005 was higher than average. In 2006, winter wascold whereas summer was dry and warm. There was a small amountof rainfall during July in 2006.

Fig. 3. Changes in the mean monthly temperature and rainfall for Sheffield, UKduring 2005 and 2006.

Source: Met office (2007).



Fig. 4. Mean final percentages of emergence rates of all geophytes per plot dur-ing the second year (n = 3). Error bars represent the standard errors of the means.Two-way ANOVA showed that the substrate depth had a significant effect on meanemergence (P < 0.05). Means with the same letter are not significantly different.

Data analysis

T-Test was used to detect the effects of different substratedepths on emergence in the first year (Minitab Release 14). Two-way analysis of variance (ANOVA) was used to detect the effectsof different substrate depths and covering plants (with and with-out) on the other parameters measured (Minitab Release 14).This statistical analysis was carried out to compare the growthof plant within the same plant species in different treatments. Ifthere were significant differences, the means were separated usingTukey test. However, the results of two-way ANOVA and Tukeytest were sometimes contradictory, e.g. two-way ANOVA showeda significant difference, whereas Tukey test showed no significantdifference. If this was the case, the result of two-way ANOVA wasused to analyze the data. For all analyses, the threshold of signifi-cance was set at P < 0.05.

Results

Emergence

In the first year, the substrate depth had no significant effect onemergence. However, emergence was significantly higher with thedeeper substrate during the second year (P < 0.05) (Fig. 4). This sug-gests that the substrate depth was more important for the survivalrate over winter rather than emergence after a few months of plant-ing. The covering plants and the interaction between the substratedepth and covering plants had no significant effects on emergence.No significant difference was observed, however, emergence ratewas higher with Sedum than without. This trend was more obviousat the shallow substrate.

In mean percentage of emergence of individual species, theresults showed that most species exhibited better emergence withthe deep substrate (Appendix 1 for first year, Table 2 for secondyear). In the second year, the substrate depth had a significant effecton five species (A. unifolium, N. cyclamineus ‘February gold’, S. siber-ica, S. tricolor and T. turkestanica). About half of the species hadhigher emergence with Sedum. The covering plants had a significanteffect on the emergence of five species (A. flavum, A. ostrowskianum,I. reticulata, T. linifolia and T. turkestanica). Only T. linifolia had higheremergence without Sedum. A. flavum was the only species with asignificant interaction effect between the two treatments. In thisspecies, the percentage of emergence was much higher with Sedum

and the substrate depth of 5 cm than with Sedum and substratedepth of 10 cm. These results suggest that covering plants had var-ious types of effects on emergence; most species were not affectedby the Sedum cover, some species competed with Sedum and somewere encouraged by the Sedum cover.

The percentages of emergence differed among the species.Although the substrate depth was important for emergence in thesecond year, the overall percentage of emergence in the first andsecond years tended to be similar. For example, I. bucharica, M.azureum, N. cyclamineus ‘February gold’, T. clusiana var. chrysantha,T. humilis, T. turkestanica and T. urumiensis even had high emer-gence rates at the substrate depth of 5 cm in the first and secondyears. By contrast, A. karataviense ‘Ivory queen’, C. sieberi ‘Tricolor’,C. tommasinianus, C. vernus ‘Vanguard’, I. danfordiae, S. siberica, T.hageri ‘Splendens’ and T. kolpakowskiana had low emergence ratesin the first and second years.

Growth

Growth was measured 11 times (from March to July = 22 weeks)and individual species exhibited growth peaks at different times.Therefore, only the maximum leaf length, leaf number and flowerheight of individual species are shown in Table 3 (leaf length)and Appendix 2 (leaf number and flower height). Overall growthwith the deeper substrate was better; these plants exhibited longerleaf length, higher number of leaves and greater flower height.About half of the species were significantly affected by the sub-strate depth, and all of these species showed better growth withthe deeper substrate. An exception was the leaf length of A. uni-folium, which was longer at the substrate depth of 5 cm, whereaslarger number of leaves was produced at the substrate depth of10 cm.

The effect of covering plants appeared to vary among species.Similar to the results of emergence, about half of the species per-formed better with Sedum. However, more species grew betterwithout Sedum at substrate depth of 10 cm. The growth of twospecies, S. tricolor and T. turkestanica, was affected significantlyby covering plants. Sparaxis tricolor grew better without Sedum,whereas the leaf growth of T. turkestanica was increased withSedum.

Some species did not appear to exhibit sufficient growth, suchas A. karataviense ‘Ivory queen’, C. siberi ‘Tricolor’, C. tommasinianus,C. vernus ‘Vanguard’, I. danfordiae and T. hageri ‘Splendens’.

Flower performance

Similar to the results of emergence and growth, many speciesexhibited longer flowering periods with the deeper substrate(Table 4). The effect of the substrate was statistically significantfor three species (M. azureum, N. cyclamineus ‘February gold’ and S.siberica). Again, the effect of covering plants differed among species.However, most geophyte species were not significantly affected induration of flowering by the Sedum cover. Only two species weresignificantly affected by the covering plants, i.e. T. kolpakowskianaand T. turkestanica. They showed longer flowering with the Sedumcover.

Table 5 shows the flowering periods of the individual species.The flowering period was determined as the start of flowering (atleast 1 plant of a given species showed flowering) until the end offlowering (no plants of a given species showed flowering) for allplots containing individual species. The combination of geophytespecies produced over 4 months of flowering. Highest number ofspecies showed flowering from the end of April to the beginningof May. In general, the flowering season of geophytes was notlong, lasting less than 2 months. M. azureum, I. reticulata and P.libanotica had long flowering seasons because individuals flowered



Table 2Mean percentage of emergence of individual species per plot in response to substrate depth and Sedum cover in the second year (percentage, n = 3).

Substrate depth 5 cm 10 cm S.E. Probability

Sedum cover Without Sedumcover


Allium flavum 88.89 22.22 33.33 33.33 14.96 C: P < 0.05, D*C: P < 0.05Allium karataviense ‘Ivory queen’ 0 11.11 11.11 33.33 11.45 n.s.Allium ostrowskianum 77.78a 44.44a 100a 66.67a 14.16 C: P < 0.05Allium unifolium 33.33b 44.44ab 88.89a 88.89a 14.43 D: P < 0.01Crocus sieberi ‘Tricolor’ 22.22a 11.11a 22.22a 22.22a 13.89 n.s.Crocus tommasinianus 0a 11.11a 0a 0a 5.56 n.s.Crocus vernus ‘Vanguard’ 22.22a 22.22a 33.33a 11.11a 14.43 n.s.Iris bucharica 100 100 100 100 – –Iris danfordiae 0a 22.22a 0a 0a 7.35 n.s.Iris reticulata 44.44a 11.11ab 66.67b 11.11b 14.43 C: P < 0.01Ixioliron pallasii 66.67a 66.67a 55.56a 44.44a 17.12 n.s.Muscari azureum 100 100 100 100 –Narcissus cyclamineus ‘February gold’ 88.89a 66.67a 100a 100a 10.02 D: P < 0.05Puschkinia libanotica 55.56a 44.44a 66.67a 77.78a 16.67 n.s.Scilla siberica 33.33a 0b 66.67a 44.44a 14.70 D: P < 0.01Sparaxis tricolor 0b 0b 66.67a 88.89a 10.02 D: P < 0.01Tulipa bakeri ‘Lilac wonder’ 44.44a 22.22a 22.22a 11.11a 14.70 n.s.Tulipa clusiana var. chrysantha 100 100 100 100 –Tulipa hageri ‘Splendens’ 11.11a 11.11a 33.00a 0a 11.45 n.s.Tulipa humilis 88.89a 77.78a 88.89a 77.78a 13.03 n.s.Tulipa kolpakowskiana 22.22a 11.11a 44.44a 44.44a 15.47 n.s.Tulipa linifolia 33.33a 66.67a 55.56a 88.89a 15.71 C: P < 0.01Tulipa saxatilis 44.44a 44.44a 44.44a 77.78a 16.90 n.s.Tulipa tarda 66.67a 77.78a 55.56a 55.56a 16.67 n.s.Tulipa turkestanica 77.78ab 11.11b 100a 77.78ab 11.79 D: P < 0.01. C: P < 0.01Tulipa urumiensis 88.89a 100a 100a 88.89a 7.86 n.s.

Two-way ANOVA was used to compare values within a species. Means with the same letter are not significantly different. S.E. = standard error, P = probability, D = substratedepth regime, C = Sedum cover regime, D*C = interaction between the substrate depth regime and the Sedum cover regime, n.s. = not significant.

Table 3Maximum leaf length of individual species per plot in response to the substrate depth and Sedum cover (cm, n = 3).




Allium flavum May 22 4.34a 7.28a 16.88a 6.04a 3.67 n.s.Allium karataviense ‘Ivory queen’ June 6 0a 1.89a 0a 0.22a 0.62 n.s.Allium ostrowskianum April 27 4.46a 5.59a 2.28a 3.50a 1.62 n.s.Allium unifolium April 27 10.44a 11.22a 3.98a 4.21a 1.99 D: P < 0.01Crocus sieberi ‘Tricolor’ March 29 1.00a 0.37a 0.30a 0.74a 0.61 n.s.Crocus tommasinianus March 17 0a 0.24a 0a 0a 0.12 n.s.Crocus vernus ‘Vanguard’ April 27 0a 0a 2.57a 2.11a 1.36 n.s.Iris bucharica June 6 18.70c 18.36bc 24.64ab 25.50a 1.61 D: P < 0.01Iris danfordiae March 29 0a 0.7a 0a 0a 0.35 n.s.Iris reticulate May 4 1.82b 0b 11.22a 2.68ab 2.84 D: P < 0.05Ixioliron pallasii June 6 1.36a 13.42a 12.61a 6.06a 4.02 D*C: P < 0.05Muscari azureum May 22 6.78a 9.13a 10.47a 10.01a 1.08 D: P < 0.05Narcissus cyclamineus ‘February gold’ May 4 0.33b 6.08b 21.66a 18.90a 2.223 D:P < 0.01Puschkinia libanotica April 27 3.86a 1.62a 3.14a 6.12a 1.39 n.s.Scilla siberica May 22 1.14ab 0b 6.18a 4.63ab 1.49 D: P < 0.01Sparaxis tricolor May 22 0b 0b 2.88b 8.17a 1.03 D: P < 0.01

C: P < 0.05D*C: P < 0.05

Tulipa bakeri ‘Lilac wonder’ April 27 7.77a 1.50a 1.20a 0.78a 1.99 n.s.Tulipa clusiana var. chrysantha April 27 12.94a 13.81a 13.99a 14.21a 1.64 n.s.Tulipa hageri ‘Splendens’ April 13 1.68a 1.11a 3.89a 0a 1.41 n.s.Tulipa humilis April 13 6.87a 5.66a 5.88a 7.50a 1.46 n.s.Tulipa kolpakowskiana April 13 2.14a 0a 5.07a 3.26a 1.50 D: P < 0.05Tulipa linifolia April 27 1.68b 3.28ab 5.09ab 7.57a 1.45 D: P < 0.05Tulipa saxatilis March 29 5.40a 3.77a 3.03a 4.39a 1.88 n.s.Tulipa tarda April 27 5.23a 7.96a 5.16a 5.37a 1.73 n.s.Tulipa turkestanica April 27 13.66a 1.67b 18.67a 16.23a 2.67 D: P < 0.01

C: P < 0.05Tulipa urumiensis May 22 5.87ab 3.32b 10.48a 10.19a 1.38 D: P < 0.01

The date indicates the day when the maximum leaf length was recorded for an individual species. Two-way ANOVA was used to compare values within a species. Meanswith the same letter do not differ significantly. S.E. = standard error, P = probability, D = substrate depth regime, C = Sedum cover regime, D*C = interaction between substratedepth regime and Sedum cover regime, n.s. = not significant.



Table 4Mean flowering periods of individual species in response to the substrate depth and Sedum cover (week, n = 9).

Substrate depth 5 cm 10 m S.E. Probability



Allium flavum 1.56 0.67 0.22 0.89 0.45 n.s.Allium karataviense ‘Ivory queen’ 0 0 0 0.67 0.24 n.s.Allium ostrowskianum 0 0 0 0 – –Allium unifolium 0 0.44 0.44 0.22 0.24 n.s.Crocus sieberi ‘Tricolor’ 0 0 0 0 – –Crocus tommasinianus 0 0 0 0 – –Crocus vernus ‘Vanguard’ 0a 0a 0a 0.22a 0.11 n.s.Iris bucharica 2.00a 1.78a 2.22a 2.22a 0.25 n.s.Iris danfordiae 0 0 0 0 – –Iris reticulate 0.44a 0a 0.22a 0.44a 0.29 n.s.Ixioliron pallasii 0.22a 0.22a 0.22a 0.44a 0.24 n.s.Muscari azureum 2.67b 4.22ab 6.22a 5.56a 0.68 D: P < 0.01Narcissus cyclamineus ‘February gold’ 0b 0.67b 3.11a 4.00a 0.44 D: P < 0.01Puschkinia libanotica 0.67a 0.44a 0.67a 1.78a 0.48 n.s.Scilla siberica 0a 0a 0.89a 1.33a 0.44 D: P < 0.05Sparaxis tricolor 0 0 0 0 – –Tulipa bakeri ‘Lilac wonder’ 0a 0.22a 0.22a 0a 0.16 n.s.Tulipa clusiana var. chrysantha 1.78a 1.78a 1.78a 1.78a 0.32 n.s.Tulipa hageri ‘Splendens’ 0a 0.22a 0a 0a 0.11 n.s.Tulipa humilis 1.78a 1.11a 1.11a 1.56a 0.54 n.s.Tulipa kolpakowskiana 0.44a 0a 0.67a 0a 0.22 C: P < 0.05Tulipa linifolia 0.44a 0.67a 0.67a 1.11a 0.33 n.s.Tulipa saxatilis 0 0 0 0 – –Tulipa tarda 1.33a 1.56a 1.11a 1.33a 0.40 n.s.Tulipa turkestanica 2.67a 0.44b 2.89a 2.44a 0.54 C: P < 0.05Tulipa urumiensis 1.56a 1.56a 2.22a 1.78a 0.51 n.s.

Two-way ANOVA was used to compare values within a species. Means with the same letter do not differ significantly. S.E. = standard error, P = probability, D = substrate depthregime, C = Sedum cover regime, D*C = interaction between the substrate depth regime and the Sedum cover regime, n.s. = not significant.

each other in succession, although the latter two species had a lowpercentage of flowering. Interestingly, late flowering species (e.g.Allium spp., I. pallasii, S. tricolor and T. hageri ‘Splendens’) tended toflower for shorter periods. A. cernuum, A. ostrowskianum, C. sieberi‘Tricolor’, C. tommasinianus, I. danfordiae, S. tricolor and T. saxatilis

Table 5Flowering periods of individual species.

March April May June

Allium flavumAllium karataviense ‘Ivory queen’Allium ostrowskianumAllium unifoliumCrocus sieberi ‘Tricolor’ NoCrocus tommasinianus NoCrocus vernus ‘Vanguard’Iris bucharicaIris danfordiae NoIris reticulateIxioliron pallasiiMuscari azureumNarcissus cyclamineus ‘February gold’Puschkinia libanoticaScilla sibericaSparaxis tricolor NoTulipa bakeri ‘Lilac wonder’Tulipa clusiana var. chrysanthaTulipa hageri ‘Splendens’Tulipa humilisTulipa kolpakowskianaTulipa linifoliaTulipa saxatilis NoTulipa tardaTulipa turkestanicaTulipa urumiensis

Gray highlighted areas indicate flowering periods.The flowering period was defined as the start of flowering (at least 1 plant of a givenspecies showed flowering) until the end of flowering (no plants of a given speciesshowed flowering) in all plots of each species.

did not flower at all, therefore, these plants are not recommendedfor use on extensive green roofs in areas with a similar climate toSheffield, UK.

Vegetative reproduction

In the mean proximal shoot number for individual species,the results showed that many species exhibited better vegetativereproduction with a deeper substrate (Table 6). The substrate depthhad a significant effect on A. unifolium, N. cyclamineus ‘Februarygold’, S. siberica, S. tricolor and T. turkestanica. T. turkestanicaappeared to be positively affected by the covering plants becausethis species produced significantly more shoots with Sedum. Theeffects of covering plants varied according to the substrate depthfor some species. At the 5 cm depth, more species reproduced betterwith Sedum whereas the opposite effect was observed at the sub-strate depth of 10 cm. This effect was significantly for T. clusiana var.chrysantha. Good reproduction was observed in A. ostrowskianum, I.bucharica, N. cyclamineus ‘February gold’, T. clusiana var. chrysanthaand T. urumiensis.

Discussion

Effect of the substrate depth

This study showed that the deeper substrates promoted greateremergence, growth, foliage and flower performance and vegetativereproduction in most geophyte species tested. Greater emergencewith the deeper substrate in the second year suggested that thesubstrate depth might have an important effect on the survival rateover winter. It was found that some geophytes were dug out overwinter. Thus, the deeper substrate is more likely to protect geo-phytes from digging by animals such as birds. There appears to bea common problem with birds removing plants, particularly plugplants, in their search for food on extensive green roofs (Emilsson



Table 6Mean number of proximal shoots produced by individual species (n = 9).




Allium flavum 2.22a 1.22a 0.67a 1.78a 0.67 n.s.Allium karataviense ‘Ivory queen’ 0a 0.22a 0.11a 0.33a 0.15 n.sAllium ostrowskianum 1.22a 1.67a 2.89a 3.00a 0.77 n.s.Allium unifolium 0.89a 0.67a 2.67b 2.56b 0.40 D: P < 0.05Crocus sieberi ‘Tricolor’ 0.33a 0.11a 0.33a 0.67a 0.33 n.s.Crocus tommasinianus 0a 0.11a 0a 0a 0.06 n.s.Crocus vernus ‘Vanguard’ 0.89a 0.22a 0.67a 0.22a 0.39 n.s.Iris bucharica 5.00a 4.33a 4.78a 4.89a 0.46 n.s.Iris danfordiae 0.44a 0a 0a 0a 0.15 n.s.Iris reticulate 0.56a 0.22a 0.89a 0.22a 0.24 n.s.Ixioliron pallasii 0.78a 0.67a 0.56a 0.44a 0.19 n.s.Muscari azureum 1.00a 1.33 1.22 1.78 0.23 n.s.Narcissus cyclamineus ‘February gold’ 1.44b 1.33b 3.67a 3.67a 0.32 D: P < 0.01Puschkinia libanotica 0.78a 0.67a 1.00a 1.56a 0.34 n.s.Scilla siberica 0.44a 0a 0.78a 0.89a 0.28 D: P < 0.01Sparaxis tricolor 0b 0b 0.89a 1.44a 0.18 D: P < 0.01Tulipa bakeri ‘Lilac wonder’ 0.78a 0.33a 0.44a 0.33a 0.31 n.s.Tulipa clusiana var. chrysantha 2.56a 2.00a 2.11a 2.78a 0.21 D*C

P < 0.01Tulipa hageri ‘Splendens’ 0.11a 0.11a 0.67a 0a 0.23 n.s.Tulipa humilis 2.00a 2.33a 2.44a 1.89a 0.49 n.s.Tulipa kolpakowskiana 0.56a 0.11a 1.44a 0.67a 0.40 n.s.Tulipa linifolia 0.67a 1.00a 1.11a 1.89a 0.34 n.s.Tulipa saxatilis 0.67a 0.67a 0.67a 1.56a 0.33 n.s.Tulipa tarda 1.56a 1.33a 1.00a 1.00a 0.36 n.s.Tulipa turkestanica 2.11a 0.44b 3.00a 1.67ab 0.42 D: P < 0.05

C: P < 0.01Tulipa urumiensis 2.11a 1.78a 2.33a 2.44a 0.41 n.s.

Two-way ANOVA was used to compare values within a species. Means with the same letter do not differ significantly according to Tukey test. S.E. = standard error,P = probability, D = substrate depth regime, C = Sedum cover regime, D*C = interaction between the substrate depth regime and the Sedum cover regime, n.s. = not significant.

and Rolf, 2005). Although the soil temperature was not measuredin this study, it was estimated that there were also fewer tem-perature fluctuations in the deeper substrate. Boivin et al. (2001)showed that the minimum daily temperatures were significantlylower at the substrate depth of 5 cm plots (−0.4 ◦C) than at thesubstrate depths of 10 cm (0.9 ◦C) or 15 cm (1.6 ◦C) on extensivegreen roof in Quebec city Canada during October and November1995. In another study, it was found that foliage formation by tulips,hyacinths, narcissi and irises was affected detrimentally when thesubstrate depth dropped below −1 ◦C (Van der Valk, 1971). Thisresult suggested that the low temperatures in shallow substratesmight affect the survival rate and growth of geophytes. Previousstudies of plant selection for green roofs showed that plants per-formed better with deeper substrates, although perennials suchas forbs, grasses and Sedum spp. were used rather than geophytes(Dunnett, 2004; Dunnett and Nolan, 2004; Durhman et al., 2007).In general, deeper substrates provided greater moisture retentionand root protection from temperature fluctuations, while they alsogave more vertical space for plant root growth before reaching theroot barrier (Durhman et al., 2007). Moisture retention seems tobe particularly important for plant growth, and Dunnett (2004)emphasized that the main constraint for perennial plant growth onextensive roofs was water availability rather than substrate depthalone. However, it is important to note that there are differencesbetween geophyte species and other perennial species. Geophyteplants use their stored biomass and water for early shoot develop-ment; therefore, air humidity or contact with water has little effectduring the early stages of growth, whereas they are more importantduring later growth and flowering (Boeken, 1991).

In this study, clonal growth appeared to be more important thanseed reproduction. The seeds of Allium spp. germinated in the sec-ond year, although most seedlings disappeared over time. Clonalgrowth is commonly stimulated in geophytes under conditions inwhich there is a high assimilation rate (Van der Valk and Timmer,

1974). Plant growth is encouraged with deep substrate, and theassimilation rate is higher than that with shallow substrate, whichleads to greater reproduction. However, some studies have shownthat environmental stress, such as a shallow position in the sub-strate (Barkham, 1980a), or high density (Barkham, 1980b) canlead to a higher rate of vegetative reproduction in geophytes (Rees,1972; Grime, 1977). Long-term research is necessary to determinehow the rate of vegetative reproduction in geophytes changes overtime on extensive green roofs.

Effect of covering plants

Results showed that the S. album cover had no significant effectson emergence, growth, foliage and flower performance and repro-duction in most species. This suggests that geophyte species didnot compete much with Sedum. Sedum spp. require little waterbecause they possess Crassulacean Acid Metabolism (CAM), wherestomata open only at night to minimize the amount of water lostwhen carbon dioxide is converted to sugars during photosynthe-sis (Van Woert et al., 2005). They have a creeping habitat andfibrous roots, therefore, may not compete with geophytes for lightand space. However, the effect of covering plants differed amongspecies. Some species such as A. flavum, A. ostrowskianum, I. reticu-lata and T. turkestanica showed significantly better emergence withSedum, whereas the emergence of T. linifolia was restricted withSedum (Table 2). T. kolpakowskiana and T. turkestanica grew signif-icantly better with Sedum, whereas S. tricolor grew better withoutSedum (Table 3, Appendix 2). It is possible that the species thatshowed a negative response to Sedum spp., may be more sensitiveto competition with other species.

Total emergence was higher with the Sedum cover at both sub-strate depths, although statistical analysis showed that the coveringplants did not significantly affect emergence. In particular, theperformance of geophytes was better with Sedum in a shallow



Table 7Summary of the performance of individual species.

Emergence Length of the period ofabove ground growth

Length of theflowering period

Reproduction Potential for use on extensivegreen roofs

Allium flavum Medium Long Short MediumAllium karataviense ‘Ivory queen’ Low Short Short LowAllium ostrowskianum High Medium Short HighAllium unifolium Medium Long Short MediumCrocus sieberi ‘Tricolor’ Low Short No LowCrocus tommasinianus Low Short No LowCrocus vernus ‘Vanguard’ Low Short Short LowIris bucharica High Long Long High HighIris danfordiae Low Short No LowIris reticulata Low Medium Short LowIxioliron pallasii Medium Long Short LowMuscari azureum High Long Long Medium HighNarcissus cyclamineus ‘February gold’ High Long Medium High High (10 cm is recommended)Puschkinia libanotica Medium Medium Short MediumScilla siberica Medium Short Short LowSparaxis tricolor Medium Short No LowTulipa bakeri ‘Lilac wonder’ Low Short Short LowTulipa clusiana var. chrysantha High Long Medium High HighTulipa hageri ‘Splendens’ Low Short Short MediumTulipa humilis High Long Medium Medium HighTulipa kolpakowskiana Medium Short Short LowTulipa linifolia Medium Medium Short MediumTulipa saxatilis Medium Medium No LowTulipa tarda Medium Medium Medium Medium HighTulipa turkestanica Medium Long Long Medium HighTulipa urumiensis High Long Medium High High (10 cm is recommended)

Emergence: mean percentage of emergent plants per plot, i.e., 0 ≤ low ≤ 30, 30 < medium ≤ 70, 70 < high. Length of the period of above ground growth (weeks): 0 ≤ short ≤ 3,3 < medium ≤ 6, 6 < long. Length of the flowering periods (weeks): No = no flowering, 0 ≤ short ≤ 1, 1 < medium ≤ 2, 2 < long. Reproduction: mean number of proximal shoots,i.e.: 0 ≤ short ≤ 1, 1 < medium ≤ 2, 2 < high.

substrate, and this was probably because Sedum prevents moistureevaporation and digging by animals and provides some supportto the geophytes. This is in agreement with the results of pre-vious studies. Two previous studies showed that the substratemoisture levels in vegetated treatments with Sedum were typicallyhigher than in unvegetated treatments or other planting treatmentsbecause its growth form impeded evaporation from the soil sur-face (Van Woert et al., 2005; Wolf and Lundholm, 2008). Butler andOrians (2011) showed that Sedum spp. enhanced the performanceof neighbouring plants when there was a summer water deficitbecause they could reduce the plant size and make the plants lesssusceptible to subsequent drought. They also showed that coolingthe soil could decrease the abiotic stress and that Sedum spp. mayreduce water loss from the substrate.

In this study, half of plots were left without covering plantsto test whether Sedum spp. affect the performance of geophyteson extensive green roofs. However, it does not mean that onlygeophytes are used and they would be barren most of the timeexcept a short period with brief bust of geophytes in spring. Thecommon expectation of roof greening is to have evergreen in thecold or dry season so as to maximize the environmental, ecolog-ical and landscape-aesthetic contributions of the vegetation. Thisstudy showed that geophytes were good candidates to combinewith herbaceous plants for garden type of shallow substrate greenroofs (e.g. semi-extensive green roofs).

Performance of individual species

Table 7 shows the emergence, plant growth rate, length of theabove-ground growth period and flowering periods and reproduc-tion rate for the test geophytes. Mean period of above-groundgrowth for individual species is shown in Appendix 3. Geophytesgrown on extensive green roofs should have high emergenceand survival rates, adequate foliage for healthy growth, attractiveflower growth, and ideally good vegetative reproduction. In this

study, I. bucharica, M. azureum, N. cyclamineus ‘February gold’, T.clusiana var. chrysantha, T. humilis, T. tarda, T. turkestanica, and T.urumiensis showed good potential for use on extensive green roofs.In particular, I. bucharicsa, M. azureum, T. clusiana var. chrysantha,T. humilis, T. tarda and T. turkestanica showed good performanceat the substrate depth of 5 cm, although they showed bettergrowth, foliage and flowering periods with the substrate depthof 10 cm. These species are probably drought tolerant and canwithstand the high temperature fluctuations that occur in shal-low substrates. They could be very useful plants for extensivegreen roofs because only a limited number of species can survive,grow and flower at the substrate depth of 5 cm without irriga-tion.

However, N. cyclamineus ‘February gold’ and T. urumiensis mayrequire a substrate depth of 10 cm. The geophyte species, namelyA. karataviense ‘Ivory queen’, C. sieberi ‘Tricolor’, C. tommasinianus,C. vernus ‘Vanguard’, I. danfordiae, I. reticulata, S. siberica, S. tricolor,Tulipa bakeri ‘Lilac wonder’, T. hageri ‘Splendens’ and T. saxatil thatexhibited low emergence, poor growth and no flowering are notrecommended for use on extensive green roofs. Five species, i.e.,C. sieberi ‘Tricolor’, C. tommasinianus, I. danfordiae, S. tricolor andT. saxatilis never flowered. There are several possible reasons forthis failure. The geophytes might not have emerged and grownbecause of the low availability of soil water or nutrients. More-over, they did not survive or persist their summer resting stagebecause the conditions that trigger development were not met.In this study, planting was delayed until January because of thelate green roof construction. Thus, the planting season may haveaffected the growth of some geophytes because the appropriateplanting timing was October and November. Interestingly, the lateflowering species were not very successful and had short floweringperiods. This may have been due to a shortage of water before theydeveloped because the rainfall was low during May 2005 and June2006 (Fig. 3). Further study is required to confirm the reason forthis failure.



Application of geophytes on extensive green roofs

Geophytes can be useful plants for adding aesthetic value andenhancing number of plant species to not only new green roofsbut existing green roofs without any major changes to the plantingdesign. Sedum green roofs are the most commonly used exten-sive green roofs, but they have less seasonal changes and dynamicchanges compared with other vegetation types because of theirlimited flowering period and low structural diversity (Dunnettet al., 2008). Recently, the aesthetic value and higher species rich-ness of green roofs have attracted considerable attentions. Hence,there is a demand for adding these improvements to existing Sedumgreen roofs. The seasonal conditions of the vegetation, soil coverageand colour affected preferences in a previous study of the aestheticimprovement of extensive green roofs (Dagenais et al., 2010). Geo-phytes may be useful for fulfilling these requirements. Geophytesmay also be combined with biodiverse green roofs to add aestheticvalue. Hands and Brown (2002) studied the visual preferences forthe ecological rehabilitation of decommissioned industrial landin Canada. The study sites were commonly perceived as messy;however, the addition of colour in the form of bold floweringforbs significantly improved their visual preference. Although thisstudy was conducted on the ground, this can also apply to bio-diverse green roofs. It is important to reconcile aesthetics withecology when considering biodiverse green roofs, rather than rely-ing on habitat creation and restoration ecology theory, such asthe exclusive use of naive species and the use of characteristicslocal plant communities (Dunnett, 2006). However, few scientificstudies have investigated whether geophytes can provide nectarsources to wildlife and determined the species that can providebetter nectar sources, although some books have shown that geo-phytes can act as nectar sources in early spring (Beresford-Kroeger,2004; Waring, 2011). Unfortunately, the biodiversity value of geo-phytes was not measured in the present study. Therefore, furtherresearch is required to confirm the biodiversity value of geophytes.

In this study, all of them are non-native species in the UK. Some-times, people think that native species are preferable for greenroofs, especially for biodiverse roofs. However, many native geo-phytes in the UK (e.g. Hyacinthoides non-scripta, Allium ursinum)are found in relatively moist soil and shady places such as wood-lands and they may be not able to tolerate for drought and windon green roofs. Scilla verna is one of native dwarf geophyte specieswhich may be able to survive on extensive green roofs. They arenaturally found on sea coast. However, a few nurseries produceS. verna and they tend to be difficult to get this species. There-fore, it is also important to use non-native plant species to achievegreen roof benefits. For example, annual meadows can be combinedwith geophytes to extend the flowering period for aesthetic reasonsand to provide nectar sources. Nagase and Dunnett (2013) showed

that it was possible to create an annual plant meadow (mixture ofnative and non-native species) without irrigation using a substratedepth of 7 cm on an extensive green roof in Sheffield, UK. The geo-phytes start flowering early in spring, while annual plants take overthem from late spring to autumn. However, geophytes may com-pete more with annual plants than Sedum spp. Further researchis necessary to study how geophytes might perform with annualplant meadows on extensive green roofs.

Conclusion

This study showed that some dwarf geophytes, such as I. buchar-ica, M. azureum, T. clusiana var. chrysantha, T. humilis T. tarda andT. turkestanica could perform well at substrate depth of 5 cm on anextensive green roof without irrigation. Overall, the performanceof geophytes was better at the substrate depth of 10 cm depth thanof 5 cm. However, it is possible to achieve sufficient growth andflowering with carefully chosen geophytes when using the sub-strate depth of 5 cm. For many existing buildings, thin substrateis ideal not to exceed the load-bearing capacity of the buildingroof slab. Most geophytes used in this study disappeared afterMay; therefore, it is important to combine them with other plantspecies such as covering plants of Sedum spp. Geophytes may beuseful for adding aesthetic value and enhancing biodiversity forextensive green roofs including existing Sedum green roofs. In thepresent experiment, the green roof environment parameters werenot measured, however, collection of data regarding continuousmoisture and temperature data using a data logger in the substratewould have been helpful for analysing the determinants of plantgrowth. Thus, the present experiment needs to be continued tounderstand how the performance of geophytes might change overtime. In particular, the loss of nutrients from the substrate over timemay affect plant performance. A future study comparing the per-formance of geophytes with and without supplemental watering isrecommended. It is also recommended that geophytes are studiedin a climate-controlled greenhouse to identify the effect of impor-tant environmental factors such as temperature and watering.

Acknowledgements

We express our appreciation to Almasc for providing the exper-imental materials, to career-support program for woman scientistsin Chiba University for founding to proof our English, to Dr. NoelKingsbury in University of Sheffield for his valuable advice, to Dr.Min-Sung Choi in University of Sheffield for helping to set up theexperiment.

Appendix 1. Mean percentage of emergence of individualspecies per plot in response to the substrate depth duringthe first year (percentage, n = 3).

5 cm 10 cm S.E. Probability

Allium flavum 72.22a 33.33b 11.15 D: P < 0.05Allium karataviense ‘Ivory queen’ 5.56a 5.56a 5.56 n.s.Allium ostrowskianum 94.44a 83.33a 7.50 n.s.Allium unifolium 72.22a 27.78a 10.86 D: P < 0.05Crocus sieberi ‘Tricolor’ 22.22a 16.67a 9.58 n.s.Crocus tommasinianus 0 0 –Crocus vernus ‘Vanguard’ 16.67a 16.67a 9.04 n.s.Iris bucharica 94.44a 100a 3.93 n.s.Iris danfordiae 5.56a 5.56a 5.56 n.s.Iris reticulate 83.33a 44.44b 10.65 D: P < 0.05




Ixioliron pallasii 61.11a 72.22a 11.35 n.s.Muscari azureum 94.44a 100.00a 3.93 n.s.Narcissus cyclamineus ‘February gold’ 100.00 100.00 – –Puschkinia libanotica 55.56a 22.22b 11.11 D: P < 0.05Scilla siberica 16.67a 11.11a 8.36 n.s.Sparaxis tricolor 66.67a 66.67a 11.43 n.s.Tulipa bakeri ‘Lilac wonder’ 44.44a 38.89a 11.94 n.s.Tulipa clusiana var. chrysantha 94.44a 94.44a 5.56 n.s.Tulipa hageri ‘Splendens’ 27.78a 16.67a 9.99 n.s.Tulipa humilis 72.22a 66.67a 11.15 n.s.Tulipa kolpakowskiana 27.78a 5.556a 8.63 n.s.Tulipa linifolia 55.56a 77.78a 11.11 n.s.Tulipa saxatilis 50.00a 38.89a 11.98 n.s.Tulipa tarda 66.67a 66.67a 11.43 n.s.Tulipa turkestanica 94.44a 100a 3.93 n.s.Tulipa urumiensis 100 100 – –

T-Test was used to compare values within a species. Means with the same letter are not significantly different. S.E. = standard error, P = probability, D = substrate depth regime,n.s. = not significant.

Appendix 2. Maximum leaf number and flower height ofindividual species per plot in response to the substratedepth and Sedum cover (n = 3).

Plant name MaximumgrowthDate


Sedumcover

WithoutSedumcover

Sedumcover

WithoutSedumcover

Allium flavum Leaf number May 22 0.89a 4.22a 4.89a 2.89a 1.57 n.s.Flower height (cm) July 10 8.13a 4.21a 3.59a 8.04a 3.75 n.s.

Allium karataviense ‘Ivory queen’ Leaf number June 6 0a 0.3a 0a 0.22a 0.14 n.s.Flower height (cm) May 22 0a 0a 0a 3.34a 1.12 n.s.

Allium ostrowskianum Leaf number April 27 3.56a 2.67a 0.89a 1.67a 1.02 n.s.Flower height (cm) – 0 0 0 0 – –

Allium unifolium Leaf number April 27 2.78a 3.28a 10.44a 9.67a 2.24 D: P < 0.01Flower height (cm) June 6 0a 4.90a 6.23a 1.49a 2.74 n.s.

Crocus sieberi ‘Tricolor’ Leaf number March 29 1.56a 0a 2.56a 3.56a 2.32 n.s.Flower height (cm) – 0 0 0 0 – –

Crocus tommasinianus Leaf number March 17 0a 0.11a 0a 0a 0.06 n.s.Flower height (cm) – 0 0 0 0 –

Crocus vernus ‘Vanguard’ Leaf number April 27 0.89a 0.11a 1.00a 0.89a 0.81 n.s.Flower height (cm) March 17 0a 0a 0a 1.44a 0.72 n.s.

Iris bucharica Leaf number June 6 28.22a 22.44a 32.22a 30.11a 3.33 n.s.Flower height (cm) April 17 17.81b 19.05b 25.29ab 26.64a 1.96 D: P < 0.01

Iris danfordiae Leaf number March 29 0a 0.4a 0a 0a 0.22 n.s.Flower height (cm) – 0 0 0 0 – –

Iris reticulata Leaf number May 4 0.44a 0a 2.00a 0.67a 0.57 n.s.Flower height (cm) April 13 2.03a 0a 0a 0a 0.68 n.s.

Ixioliron pallasii Leaf number June 6 0.33a 3.67a 2.89a 1.67a 1.03 D*C P < 0.05Flower height (cm) June 6 0.00a 3.33a 3.58a 5.75a n.s.

Muscari azureum Leaf number May 22 2.11b 3.33ab 3.56ab 4.78a 0.63 D: P < 0.05Flower height (cm) April 27 3.09b 5.37ab 7.27ab 9.43a 1.41 D: P < 0.01

Narcissus cyclamineus ‘February gold’ Leaf number 4th May 0.78b 2.11b 8.11a 8.56a 1.24 D: P < 0.01Flower height (cm) 27th

April0b 2.65b 21.51a 21.39a 2.89 D: P < 0.01

Puschkinia libanotica Leaf number April 27 1.22a 0.78a 1.63a 2.00a 0.63 n.s.Flower height (cm) April 13 2.27a 1.13a 0.78a 4.52a 1.27 n.s.

Scilla siberica Leaf number May 22 1.44a 0a 3.11a 2.00a 1.08 n.s.Flower height (cm) April 13 0.89a 0a 1.61a 2.33a 0.93 n.s.

Sparaxis tricolor Leaf number May 22 0b 0b 1.44b 5.44a 0.68 D: P < 0.01C: P < 0.01D*C: P < 0.01

Flower height (cm) – 0 0 0 0 – –Tulipa bakeri ‘Lilac wonder’ Leaf number April 27 1.89a 0.78a 0.22a 0.33a 0.60 n.s.

Flower height (cm) April 27 0a 1.48a 0a 0a 0.74 n.s.Tulipa clusiana var. chrysantha Leaf number April 27 7.33a 6.78a 7.67a 8.78a 0.96 n.s.

Flower height (cm) May 4 14.04a 13.15a 10.91a 17.19a n.s.Tulipa hageri ‘Splendens’ Leaf number April 13 0.33a 0.33a 0.78a 0a 0.33 n.s.

Flower height (cm) May 4 0a 1.03a 0a 0a 0.52 n.s.Tulipa humilis Leaf number April 13 4.67a 5.78a 6.22a 6.11a 1.47 n.s.

Flower height (cm) April 13 3.66a 3.54a 5.96a 7.40a 1.75 n.s.Tulipa kolpakowskiana Leaf number April 13 1.56ab 0b 3.44a 0.44ab 0.89 C: P < 0.05

Flower height (cm) April 13 0a 0a 3.42a 0a 0.87 n.s.



Plant name MaximumgrowthDate


Sedumcover

WithoutSedumcover

Sedumcover

WithoutSedumcover

Tulipa linifolia Leaf number April 27 2.33a 2.56a 4.00a 6.56a 1.47 n.s.Flower height (cm) May 4 2.23a 2.77a 3.67a 5.71a 1.73 n.s.

Tulipa saxatilis Leaf number March 29 2.22a 2.00a 0.56a 0.56a 0.81 n.s.Flower height (cm) – 0 0 0 0 – –

Tulipa tarda Leaf number April 27 4.33a 4.44a 4.00a 3.56a 1.41 n.s.Flower height (cm) April 27 5.34a 7.07a 4.98a 4.66a 1.60 n.s.

Tulipa turkestanica Leaf number April 27 5.00ab 1.11b 5.44a 3.00ab 1.11 C P < 0.01Flower height (cm) April 13 13.03ab 1.89b 18.39a 14.77a 3.00 D: P < 0.01

C: P < 0.05Tulipa urumiensis Leaf number May 22 5.11a 1.89a 6.22a 6.11a 1.34 n.s.

Flower height (cm) May 4 2.71a 2.87a 5.85a 3.54a 1.50 n.s.

The date indicates the day when the maximum flower height occurred in individual species. Two-way ANOVA is used to compare values within a species. Means with thesame letter do not differ significantly from each other. S.E. = standard error, P = probability, D = substrate depth regime, C = Sedum cover regime, D*C = interaction between thesubstrate depth regime and the Sedum cover regime, n.s. = not significant.

Appendix 3. Mean period of above-ground growth forindividual species (week).

5 cm 10 cm S.E. P



Allium flavum 13.56a 4.00b 3.56b 5.33ab 2.464 D*CP < 0.05

Allium karataviense ‘Ivory queen’ 0a 1.11a 0.44a 3.11a 1.12 n.s.Allium ostrowskianum 4.00a 5.33a 7.56a 7.56a 1.74 n.s.Allium unifolium 4.44a 4.44a 10.89ab 13.33a 1.98 D: P < 0.05Crocus sieberi ‘Tricolor’ 1.78a 0.44a 0.67a 2.00a 0.96 n.s.Crocus tommasinianus 0a 0.22a 0a 0a 0.11 n.s.Crocus vernus ‘Vanguard’ 1.56a 0.67a 2.44a 1.56a 1.17 n.s.Iris bucharica 16.00a 14.67a 16.00a 16.00a 0.67 n.s.Iris danfordiae 0a 0.89a 0a 0a 0.24 n.s.Iris reticulate 2.22a 0.67a 5.56a 1.56a 1.38 n.s.Ixioliron pallasii 2.00a 7.78a 5.78a 4.00a 1.91 n.s.Muscari azureum 13.56a 15.78a 15.78a 14.89a 0.62 D*C: P < 0.05Narcissus cyclamineus ‘February gold’ 5.33b 6.67b 12.89a 13.57a 1.18 D: P < 0.05Puschkinia libanotica 4.89a 2.89a 4.89a 7.33a 1.55 n.s.Scilla siberica 3.11ab 0b 7.78a 4.89ab 1.79 D: P < 0.05Sparaxis tricolor 0c 0c 6.22b 13.11a 1.39 D: P < 0.05

C: P < 0.05D*C: P < 0.05.

Tulipa bakeri ‘Lilac wonder’ 0.89a 1.11a 1.78a 0.67a 0.97 n.s.Tulipa clusiana var. chrysantha 11.33a 12.67a 14.44a 14.67a 0.98 D: P < 0.05Tulipa hageri ‘Splendens’ 1.33a 2.00a 3.11a 0a 1.36 n.s.Tulipa humilis 7.33a 6.89a 6.44a 7.56a 1.40 n.s.Tulipa kolpakowskiana 2.67a 0.67a 5.78a 3.56a 1.65 n.s.Tulipa linifolia 3.56a 5.78a 6.22a 10.44a 1.92 n.s.Tulipa saxatilis 2.89a 2.22a 3.78a 6.44a 1.58 n.s.Tulipa tarda 6.89a 8.22a 6.67a 7.11a 2.23 n.s.Tulipa turkestanica 8.89 1.11 14.22 10.89 1.76 D: P < 0.05

C: P < 0.05Tulipa urumiensis 10.00 9.56 11.11 9.33 1.49 n.s.

Two-way ANOVA is used to compare values within a species. Means with the same letter do not differ significantly from each other. S.E. = standard error, P = probability,D = substrate depth regime, C = Sedum cover regime, D*C = interaction between the substrate depth regime and the Sedum cover regime, n.s. = not significant.

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2013 pefromance of geophytes on extensive green roofs in the uk

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tulipa humilis

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