W A I T A K E R E
C I T Y
C O U N C I L
Green Roof Information
CONTENT
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
ACKNOWLEDGEMENTS
Viewing Area and Signage Waitakere City Council design team: Monitoring Latest Updates Articles of Interest
Architects: Research: Project Management: Green Roof Advise: Monitoring: Signage:
Tony Miguel, Renee Davies, Peter Joyce Architectus & Athfield Architect Robyn Simcock, Landcare Research Suresh Nagaiya, NCompass Logan Whitelaw Landcare Research Dallow Boss Ltd
Written and compiled by Renee Davies, Waitakere City Council. Published with assistance from the Waitakere Youth Council.
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Green Roof Information
F U R T H E R I N F O R M AT I O N
Useful Websites
Green Roof Books Green Roofs: Ecological Design And Construction by Earth Pledge Foundation (Author), Leslie (FWD) Hoffman (Author), William (FWD) McDonough (Author) Hardcover: 158 pages Publisher: Schiffer Publishing (February 5, 2004) ISBN-10: 0764321897 ISBN-13: 978-0764321894 Planting Green Roofs and Living Walls by Nigel Dunnett (Author), Noel Kingsbury (Author) Hardcover: 256 pages Publisher: Timber Press, Incorporated (May 1, 2004) ISBN-10: 088192640X ISBN-13: 978-0881926408
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: A Case Study: Design by Michael Van Valkenburgh Associates for the Headquarters of American Society of Landscape Architects by Christian Werthmann (Author) Hardcover: 160 pages Publisher: Princeton Architectural Press (July 26, 2007) ISBN-10: 1568986858 ISBN-13: 978-1568986852
“The first 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 Roof 30 October 2007 Photo: Renee Davies
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Green Roof Information
INTRODUCTION
GREEN ROOF VISION • To demonstrate the range of sustainabile benefits of green roof technology. • To create a green roof which is specific to the New Zealand situation, and at least in part, reflective 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 flowering. • 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 makeup, and monitoring to provide useful and innovative input into green roof technology specific to New Zealand.
This 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 modification 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 flat 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.
An example of an extensive green roof on commercial building in Boston Photo: American Landscape Architecture
Benefits 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 flooding, stream bank erosion, and stream degradation.
A textural mosaic of planting was anticipated for the green roof Photo: Robyn Simcock
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Green Roof Information
INTRODUCTION
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Other benefits include improving the building’s thermal insulation and reducing the urban ‘heat island’ effect. The vegetation on green roofs filters city air by absorbing carbon dioxide and helping to reduce air pollution. Such roofs create some habitat for birds, butterflies and other insects and finally, 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 flooding problems that plague many cities.
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)
Project Location Henderson 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 floor-space and community facilities.
• Selliera radicans • Disphyma australe (New Zealand iceplant) • Coprosma acerosa (Sand coprosma) • Leptostigma setulosa,
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 Roof Extensive 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 Plants Plant 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 find New Zealand native alternatives that will form a dense, weedresistant cover and survive in these very drought prone conditions with little watering.
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Green Roof Information
• 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 confirm how much benefit 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 specifically designed for New Zealand conditions. A self-seeding cabbage tree on the green roof
Technical Details
TECHNIC AL DETAILS
A drawing showing the different layers that make up the green roof.
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Green Roof Information
CONSTRUCTION DRAWINGS Roof Plan of Civic Wing of Waitakere Central Civic Centre
Green Roof
Not to scale Please refer to PDF drawings on CD for A3 scaled drawing
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Green Roof Information
CONSTRUCTION DRAWINGS
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Cross section through green roof of Waitakere Central Civic Centre
Not to scale Please refer to PDF drawings on CD for A3 scaled drawing
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Green Roof Information
CONSTRUCTION DRAWINGS
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Roof details of green roof of Waitakere Central Civic Centre
Not to scale Please refer to PDF drawings on CD for A3 scaled drawing
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Green Roof Information
COSTS
The information below provides a preliminary assessment of the Civic Cetnre green roof construction cost over and above the normal cost for the waterproofing and project management for a standard concrete roof. It excludes the research and development associated with building the first green roof of this nature in Auckland. The cost also excludes the monitoring equipment and system. Water proofing memberane
$30,000
Drainage cell and root barrier
$12,436
Growing medium - supply, cranage and installation
$51,390
Plants - supply and planting
$24,243
Preliminary and general (specific to green roof )
$9,860
(excluded as this cost is required for any standard concrete roof )
Area of green roof approx.
510 square metres
Cost per square metre
approx. $192/sqm for elements specific to the green roof
Please note that this cost is higher than would be expected due to the unkown aspects of developing the first 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.
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Green Roof Information
Example Specification for Water proof Membrane Installation
Plants
PLANT
S E L E C T I O N A N D CO N S I D E R AT I O N S
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, weedresistant 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 final choice of plant species in order to confirm 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 find native plants with high survival and cover on the green roof in the absence of irrigation. In addition to survival and cover, Waitakere City specified that the preferred species would also:
One of the three trial plots for the green roof
• be sourced from those Native to New Zealand, and preferably the Waitakere Ecological District
Photo: Robyn Simcock
• be able to be used to create an aesthetically attractive landscape, through variety of texture, colour and/or form and reflect seasonal changes through fruits, flowers 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
Planting of trial plots
Plant selections were trialed over a 3 month period
Photo: Robyn Simcock
Photo: Robyn Simcock
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Green Roof Information
P L A N T S E L E C T I O N A N D CO N S I D E R AT I O N S
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The native New Zealand plants we are trialling on this green roof are: Libertia peregrinans (NZ iris)
Disphyma australe (NZ iceplant)
Muehlenbeckia complexa Muehlenbeckia axillaris Muehlenbeckia ephendroides
Dichondra repens ‘piha’ (Mercury Bay Weed)
Disphyma australe seedlings successfully spreading across the green roof Photo: Robyn Simcock
Selliera radicans
Calystegia soldanella (sand convolvulus)
Acaena microphylla (NZ bidibid)
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Green Roof Information
Festuca coxii (Native tussock)
Coprosma acerosa (Sand coprosma)
Pimelea prostrata (NZ daphne)
Example of Planting Specification for Plant Supply for Waitakere Green Roof
Scientific Paper Outlining Substrate and Plant Research Carried out for the Green Roof
Substrate/Soil
S U B S T R AT E S E L E C T I O N A N D CO N S I D E R AT 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 confirm 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 flooding).
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The ability to store water and nutrients for plant growth.
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Increased roof cost (structural and water proofing).
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:
50
20% 4-8mm grade expanded clay (Hydrotech)
Rainfall, Runoff (mm)
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30% 4-8mm grade pumice 20% Perry’s garden mix or Living Earth garden mix
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30% 1 to 3mm or 1 to 2mm grade pumice The attributes of the substrate were: Pumice-based up to 150 mm deep:
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• c.200 kg m-2 fully saturated
10
• >200 mm hour-1 infiltration • >15% v/v macroporosity
0 0
50
100
150
200
Day in 2005
250
300
350
400
• store 24 to 30 mm of water • supply major plant nutrients • bearing strength supporting people without adverse compaction
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Green Roof Information
S U B S T R AT E S E L E C T I O N A N D CO N S I D E R AT I O N S
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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 Infiltration of the substrate - Figure 2 • Mean 2000 mm/hr • Range 600 to 3600 mm/hr • Well above minimum acceptable of 200 mm/hr
Infiltration monitoring on the green roof. Photo: Robyn Simcock
Infiltration is increasing as plants ameliorate (break up) compaction
FIGURE 1
FIGURE 2
Roof loading
Infiltration
200 180
4000 Saturated load "Operational" load
160
3000
120
mm per hour
)
KG PER M2
140
100 80
L d (k /
60 40
2000
1000
20 0 75
100
Media depth (mm)
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125
0
Photo showing root growth of Libertia breaking up the substrate (ameliorating compaction). Photo: Robyn Simcock
Green Roof Information
S U B S T R AT E S E L E C T I O N A N D CO N S I D E R AT I O N S
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 efficient 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 firing 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
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greenroofing 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 benefits. By using expanded clay as opposed to scoria, or any other inorganic component, the risk of the roof not performing as effectively 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 beneficial environmental effects 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 effectively in greenroof applications in New Zealand. This should allow a more long term sustainable selection of inorganic substrate components to be identified. 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
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Green Roof Information
Example of the Contract Specification for the Substrate used on the Green Roof
Scientific Paper from Landcare Research on Results of Substrate and Plant Selection Trials for the Waitakere Central Green Roof
Construction photos
PHOTOS DURING CONSTRUCTION
The Waitakere roof was divided into four zones, each with a different planting plan: the parapet edge with a high proportion of screening plants; upstands with plants tolerant of foot traffic; pergola edge containing Muelenbeckai complexa; and bulk planting. Photo: Renee Davies
The water-proofing layer of the Green Roof is applied. Photo: Robyn Simcock
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PHOTOS DURING CONSTRUCTION
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Drainage layer laid on top of water-proofing 2006
Filter & root barrier fabric laid over drainage layer 2006
Photo: Renee Davies
Photo: Renee Davies
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The roof ready for substrate 2006 Photo: Renee Davies
A crane delivers substrate in bags weighing about 1 tonne each to the Waitakere Civic Centre Roof
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 filter cloth protects ensures substrate does not block up the drainage board.
Photo: Robyn Simcock
Photo: Robyn Simcock
Green Roof Information
Completed Green Roof photos
PHOTOS OF COMPLETED GREEN ROOF
Photos taken September 2006 Photo: Larnie Nicolson
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PHOTOS OF COMPLETED GREEN ROOF
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Photos taken July 2007 showing the growth and spread of plants Photo: Renee Davies
Photos taken November 2006 Photo: Robin Symcock
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PHOTOS OF COMPLETED GREEN ROOF
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Photos taken November 2007
Photos taken November 2007
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Green Roof Information
PHOTOS OF COMPLETED GREEN ROOF
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Photos taken November 2007
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Green Roof Information
Photos taken November 2007
Viewing Area and Signage
P H OTO S O F G R E E N R O O F V I E W I N G A R E A AT WA I TA K E R E C I T Y CO U N C I L
Model and sign in green roof viewing area
Model showing green roof layers and actual materials used
Photo: Renee Davies
Photo: Renee Davies
Sign explaining green roof
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Monitoring
MONITORING
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 scientific 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 scientific 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 different points • Seasonal Variations
Logs (refugia) used for monitoring wildlife on the green roof Photo: Robin Symcock
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MONITORING
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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 identified: • Steatoda & hunting spiders, seasonal molluscs • Bees, bumblebees (Selliera & pimelea fl.), butterflies
Examples of invertebrates found in first year
• Hunting spiders also living in plant bases & gravel Weeds on the green roof have been limited. Observations have identified: • 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))
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Discovery of a self-seeded onion leaf orchid on the green roof
Senecio vulgaris - a common weed on the green roof
Photo: Danielle Hancock
Photo: Robyn Simcock
Notes from Landcare Research Outlining Aims of Habitat Monitoring for the Waitakere Central Green Roof 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: x the role extensive, ‘wild’ (low disturbance and low maintenance) roofs can have in creating invertebrate habitat. x where the invertebrates are likely to come from – how they got to the roof x the potential to use extensive greenroofs to support native invertebrate and vertebrate species (e.g. skinks, geckos) x 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. x
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 nondestructive, 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)
Lycosa (wolf spider, native) and Steadoda (false katipo, South African spider) found under wooden rounds in winter 2007
x
x
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.
x
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!)
x
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.
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 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.
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.
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They are therefore one of the few techniques that give an absolute estimate of invertebrate abundance
Latest Updates
Example of Site Specific Recommendations and Techniques for Weed Control on Waitakere Central Green Roof Weeding the Waitakere Central Green Roof
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AIM To remove all adventive species. The main adventive species (except grasses) are on the attached photo list, which is updated as new species are identified. If resources are limited the most important weeds to remove are legumes, flatweeds and grasses.
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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.
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HOW? Preference is for the maintenance to be undertaken by fully trained teams in order to address the specific 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 ROOF Induct 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 flat-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.
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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 roof Wear 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 distractions There 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 temperature Stay 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 flowers 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 flume (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 first 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 flatweeds, legumes (clover, lotus), grasses and daisies (sowthistle) etc. Milkweed, epilobium and bittercress (attached file) SPECIAL NOTE It hasn’t been decided yet if it is cost effective to remove oxalis and Pearlwort.
Extract from the Landcare Research Diary on Green Roof Progress
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.
Shortly after planting, spring 2006
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 now x Observation 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) x Start collecting stormwater and met station data. x Complete characterization of substrate depth, infiltration and moisture holding, as installed and soil chemical test
2 November 2006
Possible Autumn Actions to discuss x Light fertiliser (low rate of slow release N and P) based on soil chemical test results x Manual loosening of substrate using forks, particularly in the area where substrate is thin. x 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. x Weeding continuing; invertebrate round monitoring. 17 January 2006
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.
Article of Interest
Article from Commercial Horticulture September 2007
Article from Urbis Landscapes Nov 2006
Article from Rooflink Spring 2006
Article from Trends Ideas 2006
Lava flows and rock rubble also support possible greenroof plants ‘the scoria boulders in Mount Wellington crater support native bidibid, Acaena microphylla
Disphyma australe at Bethels Beach, Auckland
potential nz native plants for extensive greenroofs
“Cliffs are places to find plants suitable for greenroofs”
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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 Thelymitra 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 nestbuilding birds. Images of many of the plants are on the New Zealand Plant Conservation Network website (www.nzpcn.org.nz). This document lists native groundcovers, grasses and ferns, in alphabetical order, that could be used on extensive greenroofs. The plants are mainly sourced from a list of NZ plants identified by Colin Meurk as suitable for dry lawns and rock gardens with growth forms up to 150 mm tall. It includes some additional 2
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. The 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 first 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 specific 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. This list does not include plant varieties or cultivars that may be suitable for greenroofs, e.g. Coprosmas and Libertias.
Bidibid - Acaena microphylla ‘purpurea’ Everlasting flower - Anaphalioides bellidioides
Old rock walls support likely greenroof plants’ - This dry-stone wall of scoria in Cornwall Park, Auckland has been colonised by the leathery fern Pyrossia serpens, and native succulent Crassula sieberiana.
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NZ daphne – Pimelea prostrata
1. Potential groundcovers for New Zealand greenroofs Species
Height (mm)
Natural habitat
Flowers & ecological services
Species
Height (mm)
Natural habitat
Flowers & ecological services
Acaena microphylla Bidibid 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)
Fuchsia procumbens
100
Sandy, gravelly or rocky places and beaches
Creeping shrub with 12 to 20 mm long tubular nectarproducing flowers in summer and large oblong (20 mm) pink to bright red berries.
Anaphalioides bellidioides2 Everlasting flower
50
Grassland and open shrubland, lowland to montane
Main stems prostrate and rooting White conspicuous daisy in summer
Leptostigma setulosa3
50 to 100
Short turf, open scrub, frost flats
Pale green leaves create slight mounds. Red fruit inconspicuous.
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 flowers in spring to summer (Oct to March) provide necta
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 flowers on short spikes and brown capsules with orange fruit
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.
Muehlenbeckia axillaris4 Creeping pohuehue
150
Coast sands to riverbeds and open rocky places
Interlacing branches forming tangled insect habitat, small white flowers in summer, fleshy opaque fruits
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
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 flowers and berries (2mm) spring to autumn
Rocks, cliffs and coastal open ground
Yellowy-green herb forming dense patches rooting along the ground. Insignificant flowers (Aug to Dec)
Peperomia urvilleana Wharanui
150
Coastal rocky places & forest, often epiphytic
Slowly spreading succulent herb. Nil
Samolus repens Maakoako
150
Damp saltmarsh and rocky places
Perennial herb with prostrate branches rooting at nodes. White 6 to 7 mm long white flowers in spring
Scirpus nodosus6 Leafless sedge
300
Sand dunes and from sea level to 600m
Brown composite fruit
Scleranthus biflorus
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 flowers. Wide range in form and size.
Coprosma petriei
Crassula sieberiana
100
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Cyathodes fraseri Leucopogon
50 to 150
Coastal dunes, rocks, open grassland, frostflats
Prostrate to low growing shrub forming dense patches, 8 to 9 mm long orange to yellow fruit
Dichondra repens Mercury bay weed
10 to 20
Short turf, coastal cliffs & ledges to montane forest clearings
Prostrate herb forming creeping mats to 2 m
Disphyma australe NZ ice plant
100
Coastal banks, rocks and cliffs
Trailing open herb with large (20 to 60 mm diameter) white to deep pink to mauve flowers in early summer (Oct to Jan)
Elymus solandri
200
Coastal cliffs, 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
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 modifications, with evidence of hydrids with other species. 6 Fomerly Isolepis nodosa and Holoschoenus nodosus
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Leptostigma setulosa
Other potential groundcover species • Brachyglottis bellidioides7 • Carmichaelia corrugate & C. uniflora, prostrate brooms, nitrogen fixing shrubs
• Raoulia, cushion plants
• Colobanthus species, about 8 species, see www. nzpcn.org.nz
• Stackhousia minima, tiny herb with outsized tubular red flowers – maybe too small
• Coprosma atropurpurea, very low spreading cushion
• Wahlenbergia albomarginata, New Zealand bluebell
• 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 filicaule, 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
7 Also known as Senecio bellidioides
Mazus pumilo
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• Lagnifera species, L. pumila is probably the most drought resistant
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“Flowers attract bees!” Selliera radicans
case study 2. Potential grasses and monocots for New Zealand greenroofs • Austrofestuca littoralis (sand tussock)
• Microlaena stipoides (Auckland)
• Agrostis species (NZ bentgrass)
• Poa imbecilla, P. lindsayi, P. maniototo
• Carex resectans, sedge
• Pyrrhanthera exigua (mountain twitch)
• Festuca actae, F. coxii
• Rytidosperma species
• Lachnagrostis species, e.g., Lachnogrostis filiformis/ billardierei
• Zoysia minima (sand twitch or prickly couch)
NZ Iris – Libertia peregrinans Rock wall with Pyrrosia eleagnifolia, lichens and Crassula sieberiana
Sedum alba
University of Auckland, School of Engineering Greenroof Plants • 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
Festuca coxii
• Pyrrosia eleagnifolia - sourced from scoria rock walls, planted in the second winter • Selliera radicans
The 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 first year has yet to be analysed, however, species that have highest survival are iceplant, crassula, fescue, sanddune 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).
3.Potential ferns for New Zealand greenroofs 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)
• 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) 8 www.sbs.auckland.ac.nz
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case study case study
Convolvulus – Calystegia saldanella Selleria with Disphyma
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)
The greenroof was constructed in winter 2006. After one year Disphyma australe has established large numbers of new seedlings. Vegetation data quantifying performance after the first 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. (* = sourced from the Waitakere Ecological District source):
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-flowering NZ daphne (Pimelia) and rounded mounds of Leptinella. The remainder of the roof is visually dominated by the tall spikey fescues (blue tussocks) and NZ iris (orange), and lime-green iceplant.
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For further information contact the call centre on 839 0400 or visit www.waitakere.govt.nz PRINTED ON RECYCLED PAPER
