WAITAKERE CITY COUNCIL Green RoofInformation · WAITAKERE CITY COUNCIL Green Roof Information INTRODUCTION • To demonstrate the range of sustainabile beneﬁ ts of green roof technology

W A I T A K E R E C I T Y C O U N C I L

Green Roof Information

W A I T A K E R E C I T Y C O U N C I L Green Roof Information

C O N T E N T

Written and compiled by Renee Davies, Waitakere City Council.

Published with assistance from the Waitakere Youth Council.

This Information pack is a collation of all the information on the Waitakere Central Civic Centre

Green Roof that might be of assistance to those investigating establishing a green roof. The

pack will be updated as new information and data becomes available. The Waitakere City

Council website will also have updated information on the green roof available for download.

www.waitakere.govt.nz

Introduction

Technical/Construction Details

Plants

Substrate/Soil

Construction Photos

Completed Green Roof photos

Viewing Area and Signage

Monitoring

Latest Updates

Articles of Interest

Waitakere City Council design team: Tony Miguel, Renee Davies,

Peter Joyce

Architects: Architectus & Athfi eld Architect

Research: Robyn Simcock,

Landcare Research

Project Management: Suresh Nagaiya, NCompass

Green Roof Advise: Logan Whitelaw

Monitoring: Landcare Research

Signage: Dallow Boss Ltd

A C K N O W L E D G E M E N T S


F U R T H E R I N F O R M A T I O N

Useful Websites

www.greenroofs.net

www.greenroofs.co.nz

www.landcareresearch.co.nz

www.livingroofs.org

www.english-nature.org.uk/pubs/publication/PDF/LivingRoofs.pdf

www.greenroofs.org

www.greenroofs.net

www.igra-world.com

Green Roof BooksGreen Roofs: Ecological Design And Construction

by Earth Pledge Foundation (Author), Leslie (FWD) Hoff man (Author), William (FWD)

McDonough (Author)

Hardcover: 158 pages

Publisher: Schiff er Publishing (February 5, 2004)

ISBN-10: 0764321897

ISBN-13: 978-0764321894

Planting Green Roofs and Living Walls

by Nigel Dunnett (Author), Noel Kingsbury (Author)


Publisher: Timber Press, Incorporated (May 1, 2004)

ISBN-10: 088192640X

ISBN-13: 978-0881926408

Green Roof: A Case Study: Design by Michael Van Valkenburgh Associates for the Headquarters

of American Society of Landscape Architects

by Christian Werthmann (Author)


Publisher: Princeton Architectural Press (July 26, 2007)

ISBN-10: 1568986858

ISBN-13: 978-1568986852

“The fi rst rule of sustainability is to align with natural forces, or at least not try to defy them”

- Paul Hawken

The Waitakere Central Civic Centre Green Roof30 October 2007

Photo: Renee Davies


I N T R O D U C T I O N

To demonstrate the range of •

sustainabile benefi ts of green roof

technology.

To create a green roof which is specifi c •

to the New Zealand situation, and at

least in part, refl ective of plant species

found in the Waitakere environment.

To create an organic patchwork of •

plants which will move and change

over the years with competition and

natural growth styles.

To provide splashes of colour variation •

through leaf colour, texture and

seasonal fl owering.

To ensure a multitude of outcomes are •

achieved for stormwater, habitat and

amenity.

To provide a robust, well-researched •

and documented process for plant

selection, including substrate make-

up, and monitoring to provide useful

and innovative input into green roof

technology specifi c to New Zealand.

G R E E N R O O F V I S I O NThis information pack provides guidance on how the Waitakere Central Civic

Centre green roof was developed and contains all the technical information

that might be of use to anyone investigating creating their own green roof.

What is a Green Roof?

Roof gardens, are not a new phenomenon, many have existed atop buildings

for decades, however, such (intensive) roof gardens are expensive to build,

and require a lot of modifi cation of roofs to support the increased weights

associated with soil and plants.

The new paradigm is for (extensive) roof systems. The principle involves

providing a very thin layer of soil over the roof structure that supports low

growing vegetation.

Extensive green roofs are the lightweight, modern versions of the sod roofs that

are a centuries-old tradition in Scandinavia. Extensive roofs do not necessarily

require fl at roofs and can be installed on roofs with slopes of up to thirty

degrees if provided with a raised grid structure to hold the growing medium in

place. They are not intended to be walked upon and generally do not feature

pedestrian access. In contrast to conventional roof gardens, that require

irrigation systems, fertilisation and frequent maintenance, extensive green roofs

require little or no irrigation or fertiliser.

Benefi ts of a Green Roof?

Green Roofs are a key Low Impact Urban Design technology to lower the

impact of stormwater runoff in urban areas with high roof coverage – the roofs

store rainfall, working like sponges to reduce and slow runoff into stormwater

pipes, cumulatively helping lower downstream impacts of fl ooding, stream

bank erosion, and stream degradation.

An example of an extensive green roof on commercial building in Boston

Photo: American Landscape Architecture

A textural mosaic of planting was anticipated for the green roofPhoto: Robyn Simcock


Other benefi ts include improving the building’s thermal insulation and reducing the urban

‘heat island’ eff ect. The vegetation on green roofs fi lters city air by absorbing carbon dioxide

and helping to reduce air pollution. Such roofs create some habitat for birds, butterfl ies and

other insects and fi nally, they have the capacity to absorb a percentage of the rain that falls on

them, thereby reducing the runoff from impervious surfaces and alleviating potential fl ooding

problems that plague many cities.

Project LocationHenderson is one of the three major town centres in Waitakere City and is recognised as a key

centre in the urban strategy. It is the city’s most centrally located town centre. It is located on

the north western rail corridor and has the largest percentage of the city’s retail fl oor-space and

community facilities.

The Waitakere Central site sits within one of the Twin Streams project catchments – the

Opanuku Catchment. The site is within close proximity of the Opanuku Stream (approximately

250 metres) at the lower part of the catchment.

The Waitakere Central Civic Centre Green Roof, as well as providing stormwater mitigation in a

key catchment within the City, provides a leading edge demonstration project of sustainable

stormwater management, habitat and amenity value.

Features of the WCC Extensive Green RoofExtensive greenroofs have a drought-tolerant plant cover growing in lightweight, thin (50 to

150 mm deep) ‘soil’ on a drainage layer and waterproof membrane.

The media used in greenroofs need to balance lightness with moisture retention and cost.

Our Green Roof PlantsPlant species chosen in the northern hemisphere for use on extensive green roofs have evolved

from choosing the most drought tolerant plants.

Succulent Sedums have been chosen as they have grown naturally on roofs and walls with little

substrate and have therefore adapted to extreme conditions and lack of moisture.

Waitakere City’s aim was to fi nd New Zealand native alternatives that will form a dense, weed-

resistant cover and survive in these very drought prone conditions with little watering.

The native New Zealand plants we are trialling on this green roof are:

Libertia peregrinans (NZ iris) •

Festuca coxii (Native tussock) •

Acaena microphylla (NZ bidibid) •

Pimelea prostrata (NZ daphne) •

Selliera radicans •

Disphyma australe (New Zealand iceplant) •

Coprosma acerosa (Sand coprosma) •

Leptostigma setulosa, •

Dichondra repens ‘piha’ (Mercury bay weed) •

Calystegia soldanella (Sand convolvulus) •

Muehlenbeckia complexa •

Muehlenbeckia axillaris •

Muehlenbeckia ephendroides•

Ongoing Monitoring

Waitakere City Council is going to monitor how

clean the the water run-off from the green roof is

and compare that to a normal roof. We will also be

monitoring the success of the native plants and the

habitat value of the green roof. This information will

confi rm how much benefi t there is to using a green

roof in New Zealand. This information will then be

available to others who might want to build a similar

green roof specifi cally designed for New Zealand

conditions.

A self-seeding cabbage tree on the green roof

I N T R O D U C T I O N C O N T .

Techn

ical D

etails


T E C H N I C A L D E T A I L S

A drawing showing the diff erent layers that make up the green roof.


C O N S T R U C T I O N D R A W I N G S

Not to scalePlease refer to PDF drawings on CD for A3 scaled drawing

Roof Plan of Civic Wing of Waitakere Central Civic Centre

Green Roof



C O N S T R U C T I O N D R A W I N G S C O N T .

Cross section through green roof of Waitakere Central Civic Centre



C O N S T R U C T I O N D R A W I N G S C O N T .

Roof details of green roof of Waitakere Central Civic Centre


C O S T S

The information below provides a preliminary assessment of the Civic Cetnre green roof

construction cost over and above the normal cost for the waterproofi ng and project

management for a standard concrete roof. It excludes the research and development

associated with building the fi rst green roof of this nature in Auckland. The cost also excludes

the monitoring equipment and system.

Water proofi ng memberane $30,000 (excluded as this cost is

required for any standard

concrete roof )

Drainage cell and root barrier $12,436

Growing medium - supply, cranage and installation $51,390

Plants - supply and planting $24,243

Preliminary and general (specifi c to green roof ) $9,860

Area of green roof approx. 510 square metres

Cost per square metre approx. $192/sqm for elements specifi c to the green roof

Please note that this cost is higher than would be expected due to the unkown aspects of

developing the fi rst green roof of its kind in New Zealand.

Also, note that this squre metre rate wil not be directly applicable for other projects and it is

dependent on the type of building, the structural design and system proposed for the building,

type of roof construction etc.

Example Specifi cation for Water proof

Membrane Installation

Plants


Plant species suitable for green roofs depend largely on the local climate, type and depth (the

ability to store moisture) of the substrate and maintenance expectations, in particular, whether

irrigation is available. Plant species used for green roofs need to establish a dense, weed-

resistant groundcover in a drought prone and very exposed environment.

For the Waitakere Central Civic Centre green roof, we chose to use native plant species. Trials

were undertaken prior to the fi nal choice of plant species in order to confi rm the species from

the initial list of possible plants that it was considered would best respond to the substrate and

climate conditions on the green roof.

Plant selection had the following aims:

to fi nd native plants with high survival and cover •

on the green roof in the absence of irrigation. In

addition to survival and cover, Waitakere City

specifi ed that the preferred species would also:

be sourced from those Native to New Zealand, and •

preferably the Waitakere Ecological District

be able to be used to create an aesthetically •

attractive landscape, through variety of texture,

colour and/or form and refl ect seasonal changes

through fruits, fl owers or foliage changes. This was

important as the roof is overlooked by an adjacent

wing of the building

be readily available from nurseries, so others could •

easily adopt the greenroof technology

provide habitat or food (nectar or fruits) for native •

insects and/or birds

P L A N T S E L E C T I O N A N D C O N S I D E R A T I O N S

One of the three trial

plots for the green roof

Photo: Robyn

Simcock

Plant selections were trialed over

a 3 month periodPhoto: Robyn Simcock

Planting of trial plotsPhoto: Robyn Simcock


P L A N T S E L E C T I O N A N D C O N S I D E R A T I O N S C O N T .

The native New Zealand plants we are trialling on this green roof are:

Libertia peregrinans (NZ iris)

Calystegia soldanella (sand convolvulus)

Disphyma australe (NZ iceplant)

Acaena microphylla (NZ bidibid)

Muehlenbeckia complexa Muehlenbeckia axillaris Muehlenbeckia ephendroides

Pimelea prostrata (NZ daphne)

Festuca coxii (Native tussock)

Selliera radicans

Coprosma acerosa (Sand

coprosma)

Dichondra repens ‘piha’ (Mercury Bay Weed)

Disphyma australe seedlings successfully spreading across the green roofPhoto: Robyn Simcock

Example of Planting Specifi cation for Plant Supply for Waitakere Green Roof

Scientifi c Paper Outlining Substrate and Plant Research Carried out for the Green Roof

Sub

strate/Soil


S U B S T R A T E S E L E C T I O N A N D C O N S I D E R A T I O N S

Waitakere modelled green roof runoff

(24mm storage 10 to 1500 kPa, 678 of 1298mm retained)

The graph below shows the data modelled for the runoff for the green roof, this was

used to confi rm the appropriate substrate mix from the substrate which was trialled.

The subsrate (soil) used in extensive greenroofs needs to balance:

1 The engineering requirement of light weight and rapid permeability (to prevent fl ooding).

2 The ability to store water and nutrients for plant growth.

3 Increased roof cost (structural and water proofi ng).

The substrate mix used for the Waitakere Central Civic Centre green roof was made up of a

predominantly pumice based mix made up as follows:

20% 4-8mm grade expanded clay (Hydrotech)

30% 4-8mm grade pumice

20% Perry’s garden mix or Living Earth garden mix

30% 1 to 3mm or 1 to 2mm grade pumice

The attributes of the substrate were:

Pumice-based up to 150 mm deep:

c.200 kg m-2 fully saturated•

>200 mm hour-1 infi ltration •

>15% v/v macroporosity•

store 24 to 30 mm of water•

supply major plant nutrients•

bearing strength supporting people without adverse compaction•

0

10

20

30

40

50

0 50 100 150 200 250 300 350 400Day in 2005

Rai

nfal

l, R

unof

f (m

m)


S U B S T R A T E S E L E C T I O N A N D C O N S I D E R A T I O N S C O N T .

Weight of the substrate - Figure 1

Depth varies across the roof•

50 to 130 mm, mean 113 mm•

Along parapet 70 to 160 mm, mostly 100 to 140 mm•

Saturated weight below target of 200 kg/m2•

Infi ltration of the substrate - Figure 2

Mean 2000 mm/hr•

Range 600 to 3600 mm/hr•

Well above minimum acceptable of 200 mm/hr•

Infi ltration is increasing as plants ameliorate (break up) compaction

Infi ltration monitoring on the green roof.Photo: Robyn Simcock

Photo showing root growth of Libertia breaking up the substrate (ameliorating compaction).Photo: Robyn Simcock

Infiltration

0

1000

2000

3000

4000

mm

pe

r h

ou

r

FIGURE 2

Roof loading

Media depth (mm)

75 100 125

Ld

(k/

)

0

20

40

60

80

100

120

140

160

180

200

Saturated load "Operational" load

FIGURE 1

KG

PER

M2


S U B S T R A T E S E L E C T I O N A N D C O N S I D E R A T I O N S C O N T .

Expanded Clay

Expanded clay was selected as the major inorganic component of the Waitakere Civic Centre

green roof growing medium due to its proven performance both overseas and in the test trial

plots that were located on the Civic Centre roof from November 2005 to February 2006.

“The ideal substrate has to achieve the seemingly miraculous combination of being highly

effi cient at absorbing and retaining water while at the same time having free draining

properties” (Dunnet & Kingsbury, 2004). It also needs to be able to store and supply nutrients

over time and provide a stable base for plant roots to attach to.

Expanded clay is widely used as a large component of growing media for greenroofs

throughout North America and Germany due to its light weight, ability to store and provide

nutrients for plants, ability to retain moisture while also being free draining and its durability. In

all of these functions it out performs scoria as a suitable component for a potential greenroof

substrate. It would seem that expanded clay is the perfect inorganic component for the use in

greenroof growing media.

Scoria is a naturally occurring aggregate that is quarried in New Zealand while expanded clay

is a man-made product that is created by kiln fi ring clay pellets at over 1000 degrees Celsius.

A large amount of energy is consumed in this process resulting in expanded clay being much

higher in embodied energy than scoria.

This raised the question whether expanded clay should be used despite its high embodied

energy? Much advice from individuals from both New Zealand and internationally was

gathered on this issue. Many believed that it was a chance to set a precedent in New Zealand

greenroofi ng by not using this material due to its less sustainable nature. They believed if

we did not use expanded clay, future projects would not be likely to use it as alternatives

would have been shown to work. On the other hand, experts that had used expanded clay in

successful projects encouraged WCC to include it in any potential mix due to its unsurpassed

performance as an inorganic component.

It was felt that it would be unwise not to use expanded clay as a component of a potential

substrate due to its impressive performance in overseas greenroofs. The priority is that the roof

performs well and provides the anticipated environmental benefi ts. By using expanded clay

as opposed to scoria, or any other inorganic component, the risk of the roof not performing as

eff ectively as hoped is reduced. It makes sense to use what is regarded by many in the overseas

greenroof industry as the highest quality inorganic substrate component. It was considered that

a successful demonstration model would provide more cumulative benefi cial environmental

eff ects than the use of a more sustainable substrate component on this roof. However, research

should be undertaken in the future to identify locally available natural aggregates than can be

used eff ectively in greenroof applications in New Zealand. This should allow a more long term

sustainable selection of inorganic substrate components to be identifi ed.

Overall, expanded clay was deemed to be the most suitable organic material to be used in

the growing medium due to its proven performance in greenroof systems. The use of this

component will ensure that the growing medium provides the most favourable growing

conditions for the vegetation whilst still being light

enough to be accommodated on the roof structure.

Hydroton expanded clay: 4/8 mm grade

Example of the Contract Specifi cation for the Substrate used on the Green Roof

Scientifi c Paper from Landcare Research on Results of Substrate and Plant Selection Trials for the Waitakere Central Green Roof

Co

nstru

ction

p

ho

tos


P H O T O S D U R I N G C O N S T R U C T I O N

The Waitakere roof was divided into four zones, each with a diff erent planting plan: the parapet edge with a high proportion of screening plants; upstands with plants tolerant

of foot traffi c; pergola edge containing Muelenbeckai complexa; and bulk planting. Photo: Renee Davies

The water-proofi ng layer of the Green Roof is applied.Photo: Robyn Simcock


P H O T O S D U R I N G C O N S T R U C T I O N C O N T .

Drainage layer laid on top of water-proofi ng 2006

Photo: Renee Davies

Filter & root barrier fabric laid over drainage layer 2006

Photo: Renee Davies

The roof ready for substrate 2006Photo: Renee Davies

A crane delivers substrate in bags weighing about 1 tonne each to

the Waitakere Civic Centre RoofPhoto: Robyn Simcock

Substrate must be unloaded without bags resting on the roof (the

bags are too heavy). In the foreground interlocking

sections of a rigid drainage board can be

seen. An overlying fi lter cloth protects ensures

substrate does not block up the drainage board.

Photo: Robyn Simcock

Co

mp

leted

Green

Roo

f p

ho

tos


P H O T O S O F C O M P L E T E D G R E E N R O O F

Photos taken September 2006Photo: Larnie Nicolson


P H O T O S O F C O M P L E T E D G R E E N R O O F C O N T .

Photos taken July 2007 showing the growth and spread of plants

Photo: Renee Davies

Photos taken November 2006Photo: Robin Symcock



Photos taken November 2007Photos taken November 2007



Photos taken November 2007 Photos taken November 2007

View

ing

Area

and

Sign

age


P H O T O S O F G R E E N R O O F V I E W I N G A R E A A T W A I T A K E R E C I T Y C O U N C I L

Model and sign in green roof viewing areaPhoto: Renee Davies

Sign explaining green roof

Model showing green roof layers and actual materials usedPhoto: Renee Davies

Mo

nito

ring


M O N I T O R I N G

Logs (refugia) used for monitoring wildlife on the green roofPhoto: Robin Symcock

Monitoring And Trials

The green roof project provides the opportunity to undertake trials of New Zealand native plant

species for use on extensive green roof systems. Such trials and monitoring of success of native

species on green roofs has not been undertaken in New Zealand before.

Waitakere City Council has partnered with Landcare Research to undertake both pre-roof plant

species and substrate trials and also scientifi c monitoring of the implemented green roof.

Monitoring requirements (ie. equipment installation) was incorporated into the design of the

green roof. The equipment has been predominantly located in the mechanical plant room for

the building which is directly adjacent to the green roof.

Monitoring of Plant Success:

The scientifi c monitoring includes a range of the following;

Grid plots•

Photographic point surveys•

Substrate temperature•

Water in substrate•

Rainfall •

Water analysis at runoff catchpoints•

UV (light intensity)•

Air temperature above roof at diff erent points•

Seasonal Variations•


There is a small but growing body of evidence from around the world that indicates green roofs

can provide valuable wildlife habitat. Green roofs can support a range of plants and animals

and this sort of building-integrated habitat design may well play a vital and important role in

the biodiversity of towns and cities.

The green roof at the Waitakere Central Civic Centre is being monitored to see if there is habitat

created that enables a range of wildlife species to survive on the roof.

To date the results of the monitoring have been positive and show that the green roof is

providing habitat. Observations have identifi ed:

Steatoda & hunting spiders, seasonal molluscs•

Bees, bumblebees (• Selliera & pimelea fl .), butterfl ies

Hunting spiders also living in plant bases & gravel •

Weeds on the green roof have been limited. Observations have identifi ed:

Legumes & common groundsel initially the most common adventive weed between plants•

Oxalis• spp & Epilobium ciliatum which arrived on plants from nursery – these being the most

common plant weeds

Common weeds that are similar to English greenroofs (weeds of pastures)•

The green roof is also showing signs of colonisation by adventive native plants such as:

Bird-dispersed species: • Coprosma robusta, Cordyline australis

Wind dispersed: grasses, rushes, pohutakawa (1)•

Unknown source (akeake (1))•

Senecio vulgaris - a common weed on the green roof

Photo: Robyn Simcock

Discovery of a self-seeded onion leaf orchid on the green roof

Photo: Danielle Hancock

M O N I T O R I N G C O N T .

Examples of invertebratesfound in fi rst year

Waitakere Greenroof invertebrate sampling Landcare Research

We want to quantify the development of invertebrate fauna on two greenroofs in Auckland as the roofs mature to 3.5 years-old, as international research indicates plant cover tends to stabilize when a complete cover has been through one or two summers – at this stage the least competitive species are self-thinned and annual weeds find it difficult to establish. We want to know:

the role extensive, ‘wild’ (low disturbance and low maintenance) roofs can have in creating invertebrate habitat.

where the invertebrates are likely to come from – how they got to the roof the potential to use extensive greenroofs to support native invertebrate and

vertebrate species (e.g. skinks, geckos) the best methods for quantifying invertebrates on extensive greenroofs

This means we need to use methods that allow comparison with international and New Zealand literature, while also ensuring we capture the range of invertebrates likely to be on the roof by using a range of methods.

Invertebrates on greenroofs

Overseas literature on greenroof invertebrates is nearly all post 2000. The most comprehensive has been done by Dr Stephan Brenneisen of 'Dozent Hochschule Wadenswil (University of Basel)' and postgraduate students at Royal Hollaway college, University of London working with Mr Dusty Gedge, Director, Livingroofs.org. I visited both Stephan and Dusty in 2007, and saw some of their key research sites. Most of the European invertebrate monitoring has been done using pitfall traps (often uncovered). In contrast, US studies have tended to use vacuuming or sweep netting – but these have usually been one-off studies.

There is no NZ literature, however, relevant NZ studies include those investigating invertebrate colonization of minesites with non-vegetated gravel overburdens and rehabilitated areas (Richard Toft, Carol Curtis). Recent monitoring of invasive ants (Darren Ward and Richard Toft) using baits can also provide comparative data. We need to search literature on invertebrates of urban wastelands. Based on the

international greenroof and NZ we are expecting spiders (in refugia and gravels), flying insects that are blown across the roof (moths, butterflies, bees, flies, flying ants) and animals brought in on plant material (slugs and snails).

Proposed Methods

We are quantifying the invertebrate fauna of two extensive roofs constructed in winter and spring 2006 in Auckland; the Waitakere Civic Centre greenroof and the research greenroof on the School of Engineering building. The Waitakere greenroof was planted entirely with native species and tops a 3-storey building on Henderson Valley Road about 200 m from the Opunuku Stream which has extensive native and exotic vegetation. The Auckland Unviersity greenroof was planted with native and exotic sedum species and covers a 12 storey building on Symonds Street – native and exotic vegetation is present as plantings along the sides of the Grafton Gully motorway, Auckland Domain and mature street trees (London Plane trees).

Monitoring extensive roofs requires methods that are resistant to high winds and require minimal anchoring, as pegs or stakes cannot be used – this ruled out Malaise traps. Because the roofs have not reached 100% vegetation cover we also excluded suction sampling (blowervac), as the pumice and expanded clay substrates are so light they would probably be sucked into the blower. Beating or sweep netting was also rejected as relatively inefficient with low vegetation established on these roofs – most of the plants are less than 150 mm tall. It is also difficult to quantify and replicate the effort involved in beating or sweep netting. Five monitoring methods were considered suitable for the two sites.

Refugia. Wooden discs of radiata pine were put onto the Waitakere greenroof and adjacent conventional roof in November 2006 – these act as shelters or refugia for invertebrates (photo above). The rounds are lifted quarterly and their occupants counted, photographed and identified. This technique is non-destructive, non-invasive and rapid, however, because insects are not captured, identification to species level is often not possible, and what lies under the refugia is unlikely to be representative of the general invertebrate community because they are enhanced habitat. The refugia have also sometimes been moved by roof visitors (creating uneven data)

Notes from Landcare Research Outlining Aims of Habitat Monitoring for the Waitakere Central Green Roof

Lycosa (wolf spider, native) and Steadoda (false katipo, South African spider) found under wooden rounds in winter 2007

Emergence traps. These cover a defined area1, of the roof and capture insects emerge that crawl of fly towards the light and into the collection tube (photograph on page 1). Their cunning design means they don’t need anchoring against high winds. The traps are emptied weekly over a 4 week trapping period in summer, when insects are most abundant and active. Insects are preserved and later sorted and identified depending on the resources ($) available. In 2007 8 emergence traps were placed on the Waitakere greenroof, starting in the last week of November.

Baiting. Flying ants were noted on sticky traps in a trial in 2007, and under some refugia so we know ants are present. Recent research in Auckland monitoring ants has provided useful comparative data and a standard methodology that involves using sugar and protein baits to attract ants into pottles (collecting after a few hours) and onto cards (monitoring visitors after 30 minutes). Baiting will be done once or twice concurrently with emergence and pitfall trapping, at about the same density as the pitfall traps and with 3 controls on the conventional roof.

A pitfall trap is covered with a lid to exclude rain and a stone to keep the lid on in this very windy environment. An Australian immigrant, the darkling beetle (Tenebrionidae) found its way into the traps.

1 They are therefore one of the few techniques that give an absolute estimate of invertebrate abundance

Pitfall traps. Pitfalls are the most common method used to monitor invertebrates in greenroof studies. They are part-filled with a preservative and lined with a slippery paint to increase capture rates. Like emergence traps, pitfalls are employed over 4 week trapping period over summer and are emptied weekly. Pitfalls on the conventional (control) roofs had to be built with ramps. 10 pitfalls were deployed on the Waitakere greenroof (approx 1 per 20m2) and 2 on the adjacent conventional roof – the latter were installed by building a ‘sandcastle’ around the pitfall (it couldn’t be sunk into the roof surface!)

Sticky traps. Sticky traps catch near-ground and above-ground flying insects. Two heights allow separation of insects blowing across the roof (vagrants) and insects likely to be emerging from the greenroof plants and substrate. These were trialled and proved effective, but a lack of resources meant they were unable to be deployed in summer 2007. If deployed, they would be serviced weekly over the same 4 week trapping period as pitfall and emergence traps. Servicing consists of wrapping glad wrap around sticky bottles, removing them to a freezer for later identificaiton and counting.

Available resources and the number of insects caught will determine to what extent the samples collected in summer 2007 can be sorted, and hence the richness of information we can get from the data. In early 2008, we will compile a list of options and resource costs and present these to our research partner, Waitakere City Council.

A caterpillar (wooly bear) and adult Magpie moth, Nyctemera amica/annulata (Arctiidae) in spring 2007. This is a hybrid between the native annulata and the Australian amica. These caterpillars were feeding on the Senecio, a weed on the roof. – their other favourite foods are ragwort and cineraria.

Latest U

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ates

Example of Site Specifi c Recommendations and Techniques for Weed Control on Waitakere Central Green Roof

Weeding the Waitakere Central Green Roof

AIMTo remove all adventive species. The main adventive species (except grasses) are on the attached photo list, which is updated as new species are identifi ed. If resources are limited the most important weeds to remove are legumes, fl atweeds and grasses.

WHY?To retain dominance of native perennial plants and attractive look of the roof. Many of the weed species, other than grasses and rushes, are annuals that die back and are also easily recognizable as weeds so detract from the roof. Some weeds, such as many of the legumes and grasses, are able to smother the low-growing native plants.

HOW?Preference is for the maintenance to be undertaken by fully trained teams in order to address the specifi c conditions of working on the roof site.

Technique will involve as little disturbance to the soil surface as possible – there are many native seedlings (iceplant mainly, but also Muehlenbeckia and runners of sellieria, mercury bay weed, bidibid and nertera) with small root systems that will die if the soil is disturbed (e.g., iceplant). Also disturbed soil brings more weed seeds to the surface and creates more sites for weeds to grow.

Weeding should be by hand. Pull out the weed if it has a small root mass, with one hand at the base of the plant pressing down on the surface to make sure very little soil is brought to the surface. If the weed is between native plants cut the base of the weed under the surface of the soil before pulling. Grasses tend to have a high root mass – and need cutting and special care to avoid disturbing adjacent native plants. Clovers, lotus, oxalis and pearlwort have creepers that run along just under the soil surface and can intertwine with native plants – work should be undertaken from the outside of the plant towards the centre releasing the creeping stems before removing the plant. Place weeds as pulled straight into a plastic bag ensuring any seed heads are in the bottom of the bag - this prevents the seeds blowing out (weeds should not be piled up and then the piles removed as this can distribute weed seeds).

Weeds occur mainly within 5 m of the parapet (long edge of the building with muehlenbeckia) and along the edge by the carpark/road.

The iceplant in particular is easily squashed – care should be taken not to skuff toes or boots on the surface.

A record of how many actual hours each month are spent on the roof weeding is required as this will provide useful information on the maintenance requirements for the green roof.

BEFORE GOING ON THE ROOFInduct all individuals: Go through safety plan and key hazards:

Key hazards: slipping – the clay balls on the surface are very smooth and easy to slip on. •Where fl at-surfaced shoes/boots and always walk with short strides. Keep off the upstand bases (the row of steel hooks that runs across the roof surface) as these can be very slippery when balls sit on them.

To minimise risk of falling off the roof (parapets are low), crouch or kneel when within 2 m of •the roof edge and don’t ever lean on the edge of the roofWear high visibility jackets so people can clearly identify the weed/maintenance team.•No more than 3 people working on the roof at one time… more people just means more •damage & trampling, and more potential distractionsThere is a c. 5m long cable running from the corner of the housing about parallel with the •parapet that has a probe on the end monitoring temperatureStay on the greenroof – do not go off the roof onto other surfaces.•The roof is windier and hotter than the ground. Best to work in the morning and avoid windy •days. Take water if weeding on hot days – there is very little shade on the roof (especially since the section round the corner is off-limits)Bees visit fl owers on the roof – if you are allergic to bees make sure you have your kit.•Lock the door behind you when going onto the roof (don’t let any unauthorized person onto •the roof).

Identify areas not to disturb:The sectioned-off area round the corner closest to the railway station that contains the metal fl ume (Fig 1.) – this will be weeded by the scientist monitoring the roof.Do not lift or move the wooden rounds.

The weather station (on the pole in the centre of the roof) and rain gauge (the cylinder next to the weather station) should not be touched – the weather station contains a microphone that ‘hears’ raindrops so no please don’t shout near it!

Identify the target plants and the native plants – show the contractors the native plants (on the poster immediately inside the door to the green roof), and show them the attached document with the main weeds.

HOW OFTEN?Probably 1-2 days for 2 people in October, and again in about 4 weeks (early November), then half a day for 2 people in late December, and the same low level of weeding (max of one day for one person) in February and/or March (depending on how dry it gets), then monthly once rain begins in autumn. In the fi rst year there was very little weed growth over summer (January to March) as it was too dry.

It is expected that the native vegetation cover to be approaching 80-100% over most of the roof by spring 2008, which should reduce the weeding requirement further, so best to arrange to revisit the contract in July 2008 to check it can be dropped to a two-monthly visit.

Main weed species to target:All fl atweeds, legumes (clover, lotus), grasses and daisies (sowthistle) etc.Milkweed, epilobium and bittercress(attached fi le)

SPECIAL NOTEIt hasn’t been decided yet if it is cost effective to remove oxalis and Pearlwort.

Shortly after planting, spring 2006

2 November 2006

17 January 2006

2007 Waitakere greenroof diary

Assessment on 17 January

There has been an increase in invertebrate abundance and species diversity under the wooden rounds, with spiders now most common, followed by beetles and millipedes. There has been a crash in the number of slugs and snails (only 1 large snail found) – presumably they have been killed by dessication. Hunting spiders are living away from the rounds in the base of plants and in coarse gravel edging. Bumblebees were visiting Selliera radicans flowers, sand dune convolvulus was also in flower, and fruits are starting to ripen on sand dune coprosma. Overall plant cover ranges from 25 to 40%. Visually impressive species remain tussocks and NZ iris (see photos). Weed species remain the same, with the exception of white clover which has been the major inter-plant weed in the past, but now is rare. The main interplant weed is now an oxalis. Weeds were relatively sparse and weeding took less than an hour.

Plants are generally in good health showing fresh growth where substrate depth is c100 mm or more. Best performing plants w.r.t. growth rate are iceplant (although in some areas plants have significant dieback) and Mercury bay weed. Along the parapet Muelenbeckia complexa has sent out shoots and tendrils 50 to 70 cm long that are resting against the parapet sides; some shoot tips of this species and sand dune coprosma show dieback – due to rubbing against the soil surface and/or moisture stress (where substrates are thin). Several seedlings of cabbage tree and karamu have established. NZ iceplant and Selliera are notable for establishing from fragments. A few NZ iris are have sent up new shoots from rhizomes, as has Muehlenbeckia axillaris.

The two areas where substrate is thinnest (50 to 70 mm depth) contain some dead plants and stressed plants with tip or part-plant dieback. The species with highest mortality and dieback are Leptonella (prev. Nertera), Selliera radicans and Muehlenbeckia axillaris; species that are most tolerant of the thin areas are NZ iceplant, small Fescues, NZ iris and sand dune coprosma. The two stressed areas are a wedge about 8 m long at the opposite corner of the greenroof from the viewing window, and a small area near the viewing window adjacent to the copper dome.

Recommended actions nowObservation of the two thin areas to trigger watering through summer (look for wilting and colour change of mercury bay weed as an indicator) using tubing on overcast days and preferably early in the morning applying at least 10mm/session (use pot plant trays to assess irrigation depth) Start collecting stormwater and met station data. Complete characterization of substrate depth, infiltration and moisture holding, as installed and soil chemical test

Possible Autumn Actions to discuss Light fertiliser (low rate of slow release N and P) based on soil chemical test results Manual loosening of substrate using forks, particularly in the area where substrate is thin. Addition of material to the two thin areas (??) or installation of a permanent dripper irrigation system just to cover these areas. Irrigation of the far end of the greenroof will not affect stormwater monitoring. Weeding continuing; invertebrate round monitoring.

Extract from the Landcare Research Diary on Green Roof Progress

Green Roof Diary June 2007 Landcare Research

John and I had a successful few days on your roof last week; the infiltration rate was measured at 8 randonly-selected sites (photo) and is excellant, mean of 2000 mm per hour and no site below about 600 mm/hour. This indicates the ponding observed on occasion was either transient or/and small, isolated spots. We have taken cores from 6 of the sites to quantify the amount of moisture held in the substrate, and the maximum saturated weights, now that the roof will have stabilised (i.e. any mobile fines washed out).

I quantified plant cover and species presence/absence using random quadrats and the permanent tagged plots that run down the upstands; also checked out the little logs to find the two spider species (Steotoda or false katipos and Lycosa or wolf spiders-photo) still dominant and slugs have again appeared. One worm. I will not be able to crunch the plant data until next month, but I'm confident we've exceeded the vegetation cover criteria of >60% after 18 months as identified by the FLL greenroof standards (Germany). Nertera/Leptinella and Mercury bay weed in particular have rocketed back over autumn, and many of the Coprosma, Pimelea and Selliera I thought had died in February, have resprouted. You both mentioned the plethora of tiny iceplant seedlings in many areas (photo).

TWO ACTION POINTS: 1. I talked with Chris re the weed seedlings that he'd noted have also enjoyed the warm autumn weather. The numbers need a team of careful people to weed - probably a day for 4 people.I spent a couple of hours weeding examples of the different areas and species, and ensuring hte area around the door was free of weeds. Its important that the weeds are removed with minimal surface disruption, i.e. we don't want any soil to be seen at the surface, just clay balls, as soil is a great site for weeds to exploit and germinate in. Most of hte weeds can be removed without surface disturbance by pushing gently down on the soil around the base of each weed, while pulling the weed out with the other hand. The larger oxalis has developed runners that can be gently lifted up before the centre of the plant is removed. Flatweeds tended to have a large root mass so I cut these under the soil surface, leaving most of the roots behind. The weeders need to be able to differentiate iceplant seedlings and Calystegia regrowth from the weeds.

2. I suggest the interplanting two areas where high plant mortality has occured (adjacent to the copper dome near the entrance, and to the Japanese side of the air conditioning vents). These are the areas with the thinnest substrates - 55 to 65 mm depth rather than the 90-100 mm across the rest of the roof. Iceplant seedlings are common in these areas, so I think planting should concentrate on Festuca and Coprosma - the most drought tolerant of the species on the roof.

Extract from the Landcare Research Diary on Green Roof Progress

Article o

f In

terest

Article from Commercial Horticulture September 2007

Article from Urbis Landscapes Nov 2006

Article from Roofl ink Spring 2006

Article from Trends Ideas 2006

1

“Cliff s are places to fi nd plants suitable for greenroofs”

Disphyma australe at Bethels Beach, Auckland

2

potential nz native plants for

extensive greenroofs

Greenroof plants must have high tolerance of drought

by having low moisture requirements, not extensive

root systems or bulky root storage organs – extensive

greenroofs usually have 50 to 150 mm deep mm

substrates with available water capacity of only 6 to 18

mm (2 to 5 days water supply in summer for pasture).

Features of drought-tolerant plants include very small

leaves (Coprosma acerosa and Carmichaelia) or thick,

succulent leaves with waxy cuticles as (Disphyma australe), or the specialized photosynthetic cycle found

in the Crassulaceae which enables them to close their

stomata during daylight hours, thus reducing moisture

loss. Orchids, e.g., Microtis and Th elymitra longifolia, and

Lycopodiums have been excluded, as have mosses and

lichens – the bryophytes have been reported as being

particularly susceptible to damage by foraging and nest-

building birds. Images of many of the plants are on the

New Zealand Plant Conservation Network website

(www.nzpcn.org.nz).

Th is document lists native groundcovers, grasses and

ferns, in alphabetical order, that could be used on

extensive greenroofs. Th e plants are mainly sourced

from a list of NZ plants identifi ed by Colin Meurk as

suitable for dry lawns and rock gardens with growth

forms up to 150 mm tall. It includes some additional

plants from a related ‘rock garden’ list, and observations

of plants in rocky, exposed environments (e.g., old

stone walls) as suggested by Mark Smale and Colin

Meurk. Th e list is not exclusive or exhaustive. It list

includes many species that are not readily available

from nurseries, however, the plants that a bolded are

being trialed on two extensive greenroofs in Auckland

on substrates ranging from 50 to 125 mm depth, and

most of these plants are readily available from native

plant nurseries. A list of the native species on each roof,

photo, and indicative results after the fi rst year of the

trials is included. In 2008 the performance of a wider

range of native plants and some exotic species, will be

trialed on substrate depths up to 150 mm, allowing us

to recommend specifi c plants suited to the Auckland

environment.

Note that within species there are growth forms and

varieties of plants that are better adapted to greenroofs,

for example, Selliera radicans varies greatly in leaf size and

shape depending on source; Coprosma acerosa varies from

a fairly open upright form which can be susceptible to

collar-rock on greenroofs, to a more successful, extremely

prostrate form with shorter internodes. Th is list does not

include plant varieties or cultivars that may be suitable

for greenroofs, e.g. Coprosmas and Libertias.

Lava fl ows and rock rubble also support

possible greenroof plants ‘the scoria boulders

in Mount Wellington crater support native

bidibid, Acaena microphylla

3

Old rock walls support likely greenroof plants’ - Th is dry-stone

wall of scoria in Cornwall Park, Auckland has been colonised

by the leathery fern Pyrossia serpens, and native succulent

Crassula sieberiana.

4

Bidibid - Acaena microphylla ‘purpurea’

Everlasting fl ower - Anaphalioides bellidioides

5

1. Potential groundcovers for New Zealand greenroofs

Species Height (mm) Natural habitat Flowers & ecological services

Acaena microphyllaBidibid or scarlet piripiri

50 to 100 Grassland and river terrace, gravelly riverbeds*1

Rhizomatous mat-forming perennial. Attractive, massed red-pink ‘spiky’ fruit in summer (Nov-Jan)

Anaphalioides bellidioides2

Everlasting fl ower50 Grassland and open

shrubland, lowland to montane

Main stems prostrate and rooting White conspicuous daisy in summer

Calysteia soldanella Sand convolvulus or shore bindweed

100 to 150 Coastal sandy habitats behind beaches (dunes)

Perennial ground vine with creeping rhizome. Large pale pink to mauve fl owers in spring to summer (Oct to March) provide necta

Coprosma acerosa 300 Coastal sands and rocks throughout NZ

Shrub with interlacing branches forming a cushion up to 2 m diameter. Pale blue berries c. 7mm diameter. Will hang.

Coprosma petriei 100 Short turf grasslands; stream margins, rocky places

Sub-shrub with creeping and rooting branches forming dense mats up to 2 m diameter. Red to pale blue fruit, 6-8 mm diameter

Crassula sieberiana 10 Rocks, cliff s and coastal open ground

Yellowy-green herb forming dense patches rooting along the ground. Insignifi cant fl owers (Aug to Dec)

Cyathodes fraseriLeucopogon

50 to 150 Coastal dunes, rocks, open grassland, frostfl ats

Prostrate to low growing shrub forming dense patches, 8 to 9 mm long orange to yellow fruit

Dichondra repensMercury bay weed

10 to 20 Short turf, coastal cliff s & ledges to montane forest clearings

Prostrate herb forming creeping mats to 2 m

Disphyma australeNZ ice plant

100 Coastal banks, rocks and cliffs

Trailing open herb with large (20 to 60 mm diameter) white to deep pink to mauve fl owers in early summer (Oct to Jan)

Elymus solandri 200 Coastal cliff s, inland grasslands and riverbeds to 1500 m

Open grass rooting and shooting at nodes with blue-grey foliage

1 Var. pauciglochidiata is found on coastal gravels and sands.

2 Formerly known as Helichrysum bellidioides

6

Species Height (mm) Natural habitat Flowers & ecological services

Fuchsia procumbens 100 Sandy, gravelly or rocky places and beaches

Creeping shrub with 12 to 20 mm long tubular nectar-producing fl owers in summer and large oblong (20 mm) pink to bright red berries.

Leptostigma setulosa3 50 to 100 Short turf, open scrub, frost fl ats

Pale green leaves create slight mounds. Red fruit inconspicuous.

Libertia peregrinans*NZ iris

300 to 400 Sandy, peaty and pumice soils from sea level to 1000 m

Fans emerging from spreading rhizomes, copper colour in full sun, White c. 20 mm diameter fl owers on short spikes and brown capsules with orange fruit

Muehlenbeckia axillaris4

Creeping pohuehue150 Coast sands to riverbeds

and open rocky placesInterlacing branches forming tangled insect habitat, small white fl owers in summer, fl eshy opaque fruits

Pimelea prostrata5 NZ daphne, pinatoro

100 to 150 Coastal to subalpine gravels, riverbeds terraces, open shrubland

Prostrate to sprawling shrub with grey foliage and small white fl owers and berries (2mm) spring to autumn

Peperomia urvilleana Wharanui

150 Coastal rocky places & forest, often epiphytic

Slowly spreading succulent herb. Nil

Samolus repensMaakoako

150 Damp saltmarsh and rocky places

Perennial herb with prostrate branches rooting at nodes. White 6 to 7 mm long white fl owers in spring

Scirpus nodosus6 Leafl ess sedge

300 Sand dunes and from sea level to 600m

Brown composite fruit

Scleranthus bifl orus 50 to 100 Coastal rocks and grassland

Perennial close-branched herb forming relatively loose, bright green mounds Nil

Selliera radicans 50 Coastal mud, sands and rocky places; inland stream margins to 1000 m

Herb with long creeping stems rooting at nodes forming mats up to 5 m diameter. Small (7 to 10 mm) white to pale blue scented fl owers. Wide range in form and size.

3 Formerly Nertera, probably better suited to areas with some shade

4 NZ Flora notes “a complicated aggregate of forms is included under the name M. complexa”. It is probable that hybridism is one reason for this variety of forms, for example botanists have noted hybrids of M. complexa

with M. axillaris, M. australis and M. ephredioides. 5 NZ Flora notes a great complex of forms, including some that are genotypic (breed true to form) but others that are habitat modifi cations, with evidence of hydrids with other species.

6 Fomerly Isolepis nodosa and Holoschoenus nodosus

Leptostigma setulosa

NZ daphne – Pimelea prostrata

7 8

Other potential groundcover species

• Brachyglottis bellidioides7

• Carmichaelia corrugate & C. unifl ora, prostrate

brooms, nitrogen fi xing shrubs

• Colobanthus species, about 8 species, see www.

nzpcn.org.nz

• Coprosma atropurpurea, very low spreading cushion

• Epilobium species, New Zealand willowherbs,

comprising 37 species difficult to tell apart

and tend to hydridise so may impact local

populations?). Some willowherbs resemble

sedums, e.g., E. pycnostachyum

• Geranium, 6 native species

• Gonocarpus aggregatus

• Haloragis depressa

• Helichrysum fi licaule, everlasting daisy

• Lepidium species

• Leptinella serrulata

• Leucopogon fraseri

• Luzula celata, woodrush

• Mazus pumilo, probably for shadier areas

• Muehlenbeckia ephredroides, threatened prostrate vine

• Neopaxia australasica, montia, shadier areas

• Lagnifera species, L. pumila is probably the most

drought resistant

• Raoulia, cushion plants

• Stackhousia minima, tiny herb with outsized tubular

red fl owers – maybe too small

• Wahlenbergia albomarginata, New Zealand bluebell

“Flowers attract bees!”

Mazus pumilo

Selliera radicans

7 Also known as Senecio bellidioides

9

• Austrofestuca littoralis (sand tussock)

• Agrostis species (NZ bentgrass)

• Carex resectans, sedge

• Festuca actae, F. coxii

• Lachnagrostis species, e.g., Lachnogrostis fi liformis/billardierei

• Microlaena stipoides (Auckland)

• Poa imbecilla, P. lindsayi, P. maniototo

• Pyrrhanthera exigua (mountain twitch)

• Rytidosperma species

• Zoysia minima (sand twitch or prickly couch)

• Cheilanthes (growing on soil veneer over rock on

Tiritiri matangi Island)

• Ophioglossum coriaceum (adder’s tongue fern, sand

dune hollows8 )

• Pellaea rotundifolia (chainfern)

• Phymatosoros pustulatus (hounds tongue fern)

• Pleurosoros rutifolius (hot rock fern)

• Psilotum nudum

• Pyrrosia eleagnifolia = P. serpens (ngarara wehi, rock

walls in Auckland)

3.Potential ferns for New Zealand greenroofs

2. Potential grasses and monocots for New Zealand greenroofs

Festuca coxii

Rock wall with Pyrrosia eleagnifolia,

lichens and Crassula sieberiana

8 www.sbs.auckland.ac.nz

10

• Acaena microphylla – bidibid

• Coprosma acerosa ‘Hawera’ - a prostrate

variety of sand dune coprosma

• Cotula australis

• Crassula sieberiana - succulent sourced

from scoria rock walls

• Disphyma australe - New Zealand iceplant

• Festuca coxii – a type of tussock grass

• Libertia peregrinans – New Zealand iris

• Mazus pumilo

• Pyrrosia eleagnifolia - sourced from scoria

rock walls, planted in the second winter

• Selliera radicans

Native plant section of Plot one, spring 2007, about one year after establishment, showing Crassula sieberiana (right and background) with iceplant (light green succulent in foreground), NZ iris (orange spikey foliage on left) and fescue (blue tussock grass in the centre). Two sedum species have invaded the plot (bright yellow Sedum mexicanum upper left and a variety of Sedum album – the blue succulent within iceplant in centre foreground and left)

University of Auckland, School of Engineering Greenroof Plants

Th e greenroof was constructed in late spring 2006. After

one year Disphyma australe and Crassula sieberiana have

established large numbers of new seedlings across most

of the roof, including areas where they were not originally

planted. Crassula may not provide year-round cover.

We wait to see if the new iceplant seedlings will survive

summer. Vegetation data quantifying performance after

the fi rst year has yet to be analysed, however, species that

have highest survival are iceplant, crassula, fescue, sand-

dune coprosma and NZ iris. Some individuals of all

plant species survive on the roof – no species has failed

entirely, however, survival appears to be highest on areas

with more shade and deeper substrate (plots are either

50 or 75 mm depth).

case study

NZ Iris – Libertia peregrinans

Sedum alba

11

case study

Waitakere greenroof in spring 2007, just over one year after establishment. A 1 to 2 m wide strip of deeper substrate along the left hand side is planted in Muehlenbeckia species, white-fl owering NZ daphne (Pimelia) and rounded mounds of Leptinella. Th e remainder of the roof is visually dominated by the tall spikey fescues (blue tussocks) and NZ iris (orange), and lime-green iceplant.

Waitakere Civic Centre Greenroof Plants

About 50% of the plants were the following three species

• Disphyma australe* – New Zealand iceplant

• Coprosma acerosa* – sand dune coprosma (prostrate

and upright forms)

• Libertia peregrinans – New Zealand iris

Smaller proportion:

• Calystegia soldanella* – sand dune convolvulus

• Dichondra repens* – Mercury Bay weed

• Selliera radicans*

• Leptostigma setulosa

• Acaena microphylla – bidibid (green form)

• Pimelea prostrata – New Zealand daphne

• Festuca coxii

• Muelenbeckia axillaris and M. complexa (in an area

with substrate to 200 mm depth)(* = sourced from the Waitakere Ecological District source):

Th e greenroof was constructed in winter 2006. After one

year Disphyma australe has established large numbers of

new seedlings. Vegetation data quantifying performance

after the fi rst year has yet to be analysed, however, species

that have highest survival are iceplant, fescue, sand-dune

coprosma and NZ iris. Some individuals of all plant

species survive on the roof, however, the diversity and cover

of plants is highest on areas with deeper substrate (100

to 150 mm depth); two areas with thin substrates (c.70

mm depth) have had moderate to high plant mortality.

Mercury bay weed, Selliera and Leptostigma died back in

summer but have spread dramatically since autumn rains

have fallen – these species may be best suited to deeper

substrates or areas with afternoon shade.

case study

Convolvulus – Calystegia saldanella

Selleria with Disphyma

For further information contactthe call centre on 839 0400

or visit www.waitakere.govt.nz

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