A buzz up top - London Wildlife Trust

A buzz up top
Burrowing bee (Lasioglossum sp)
Encouraging the conservation of invertebrates
on living roofs and walls
Elevated habitats
A buzz up top aims to inspire
and encourage anyone involved
with the planning, design,
specification, installation and
management of green roofs and
living walls, to include elements
and features that benefit insects
and other invertebrates.
Ragged-robin on University College London
Green roofs and living walls are
increasingly recognised as vital
components of urban green
infrastructure. They can perform
essential ecosystem services
to help mitigate the impacts
of climate change in towns
and cities, serve to provide
more attractive and accessible
roof surfaces, and importantly
provide additional spaces to
conserve biodiversity.
The renaissance of green roofs
in Britain since the early 2000s
has in particular been driven by
the need to find viable solutions
to provide habitat for animals
and plants colonising brownfield
sites vulnerable to development.
Some of the most important
of these species are a range
of invertebrates, a remarkable
number of which, for example
solitary bees, digger wasps,
some bugs and beetles, are of
conservation interest due to
their scarcity, making the design
of living roofs to meet their
needs an imperative.
Whilst the installation of
bespoke roofs and walls should
not be seen as the only solution
to the conservation of such
species, they are a critical
contribution to the provision of
appropriate habitat that can also
serve to provide other green
infrastructure benefits, in terms
of mitigating surface water
run-off, improving cooling, and
aesthetics.
A buzz up top is the result of
the study funded by SITA Trust’s
Enriching Nature programme.
This involved a study conducted
by Dr. Gyongyver Kadas
investigating the biodiversity
potential of green roofs in an
urban environment, and the
design and installation of two
specific features to encourage
invertebrates on a number of
selected roofs.
The results of green roof
research has demonstrated
the means to encourage
invertebrates onto living
roofs and walls using simple
landscape design and
interventions. A buzz up top, a
collaboration between London
Wildlife Trust, Livingroofs.org
and the Green Roof
Consultancy, serves to whet
the appetite. More details of
specifying interventions for
invertebrates on green roofs are
signposted in the references.
Mathew Frith
London Wildlife Trust
Green - or living-roofs - are
vegetated roofs, where a
growing medium (substrate) is
isolated from the natural ground
by a man-made structure.
Green roofs can be intensive
or extensive. Intensive green
roofs (roof gardens) are
usually irrigated, tend to have
deeper, richer substrates, and
maintained in a more formal
fashion. Extensive green roofs
are low-maintenance and usually
vegetated with normally lowgrowing vegetation on shallower
substrates. Although extensive
green roofs are more likely to
be designed for biodiversity,
all green roofs can and should
where possible include habitats
and features to benefit wildlife.
For more information on green
roofs types and benefits, see
www.livingroofs.org.
Living walls (or green walls) are
exterior walls of buildings that
are vegetated. Traditionally this
involves climbing plants growing
directly onto the wall or on wires
or trellises. In recent years a
numbers of companies have
begun to supply prefabricated
irrigated, vegetated mats and
modules, which can support a
wider range of planting.
Although often overlooked,
invertebrates provide vital
ecosystem services, helping
to break down dead plant
and animal matter, pollinating
wild flowers and crops, and
providing a food source for
other wildlife, like birds and
bats. For green roofs and living
walls to meet their full potential
in conserving biodiversity,
careful attention needs to
be made to provide suitable
habitats for the full range of
invertebrates that can thrive in
urban areas, including solitary
bees, lacewings, hoverflies,
beetles, butterflies, moths, and
spiders, amongst many others.
Most species require different
features at different times during
their life cycle. For example
adult moths and butterflies
need nectar-bearing flowers,
however their caterpillars
require food plants and the
range of plant species that each
moth or butterfly caterpillar
can feed on is usually very
limited. In addition species may
have specific overwintering
requirements (like most
beetles) or special nesting
requirements (like solitary bees).
Therefore we recommend that
a roof project includes a full
spectrum of special elements
for invertebrates, including
a critical element - a locally
appropriate, species-rich sward
of wildflowers that are matched
to the substrate, aspect, and
microclimate. In addition a
green roof’s performance for
biodiversity will be improved
by having a varying depth
of substrate and mounds of
different materials as well as
untreated logs and stones.
Sunny walls can be fitted with
untreated timbers which have
been drilled to provide nesting
holes for solitary bees. Shadier
walls can include crannies
where spiders, lacewings and
moths can shelter.
Another consideration is that
the habitats provided should
be appropriate to the locality,
complementing and extending
habitat that may already be
in existence or part of an
overall plan to create stepping
stones that are part of a wider
ecological network. Your local
biological records centre and
county Wildlife Trust will be
able to provide valuable advice
on the bioregion in which
your project occurs, and the
ecological characteristics of the
neighbourhood.
There is considerable interest
in establishing beehives on
rooftops. Whilst the keeping of
honeybees and the production
of honey is a worthwhile and
rewarding experience, of itself
beekeeping does not replace
nature conservation efforts,
which involve the provision of
habitat. For beehives to be
successful, foraging habitat
is required, and if foraging
opportunities for honeybees,
in the form of wildflowers, can
be provided, then it will benefit
other invertebrates, which can
be as important for pollination.
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Comb-footed spider
Comb-footed spider
Common blue
Rooftop invertebrates
Bees and wasps
A study has found 77 species
of bee from 10 different genera
on Swiss roofs. More casual
observations of bees on green
roofs in London have recorded
21 species.
Ectemnius sexcinctus
The most commonly encountered species on roofs is the
honeybee, however bumblebees
(Bombus sp), burrowing bees
(Lasioglossum sp), sand bees
(Andrena sp) and digger wasps
(Sphecidae sp) also occur.
Flower-rich roofs are particularly
valuable for foraging bees and
wasps. Sedum provides nectar
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for bees, however the flowering
season is limited to a threeweek period in June, so it is
advantageous for green roofs or
living walls to include sedum as
part of a range of species that
flower throughout the season.
Burrowing bees and sand
bees benefit from mounds
and shallowscrapes of sand
and other loose material being
added in sunny locations on
roofs. Several species of
solitary mason bee (Osmia spp)
nest in hollow stems or holes in
wood, that in natural conditions
are made by beetle larvae and
other wood boring insects.
Holes drilled in untreated timber
can be mounted on south facing
walls to attract these bees.
Most species use holes with a
diameter of between 6-8 mm
however other species use
smaller and larger holes, so a
range of hole sizes between 2
and 10mm should be provided.
Bombus pascuorum
Flies
A range of flies will be found on
green roofs, mostly as incidental
travelers of the urban skies.
Flies generally prefer dense
vegetation and deeper damp
soils to ensure successful
breeding cycles. However,
hoverflies in particular are key
pollinators and can be attracted
to biodiverse roofs that form
part of a wider network of
flower-rich open spaces. These
can include the marmalade fly
(Episyrphus balteatus) and the
larger Volucella hoverflies which
are strong flyers.
Volucella inanis
Beetles and bugs
Roofs designed for biodiversity
support more ground beetles,
smut beetles and ladybirds
than other types of beetles.
Relatively few beetles occur
on sedum, although large
numbers of individual ladybirds
and their larvae can occur on
sedum roofs. More species of
beetle are attracted to areas
with deeper substrate and
thicker vegetation (the majority
of beetles feed on vegetation or
decaying plant matter). A higher
diversity of wildflowers will
attract more species of beetle,
because some are faithful to a
limited number of species.
Untreated hardwood logs,
especially where they are in
contact with soil, provide habitat
for beetle larvae. Beetles and
many other invertebrates can
also find refuge in cold or dry
conditions under stones.
Chlamydatus evanescens
‘True’ bugs including
leafhoppers, plant bugs, and
aphids, and predatory species,
such as assassin bugs, prefer
denser vegetation, although
many of these are common and
incidental visitors to roofs.
Moths and butterflies
Butterflies and moths are
attracted to the nectar provided
on green roofs. Flowers of
the composite family including
ox-eye daisy, yarrow and
hawkbits, are frequently visited
by butterflies. Several species
of butterfly (including common
blue) use legumes like bird’sfoot trefoil as food plants so it is
good to include these on green
roofs and in living walls.
Moths (in common with some
long-tongued species of
bumblebee) draw nectar from
long-tubed flowers, notably
species in the campion family.
Campions can be grown on
green roofs and in living walls,
where they may be combined
with honeysuckle, another
species visited by moths.
Spiders
Fifty species of spider have
been collected from green
roofs in London. This study
revealed both common and
widespread species as well
as many rarities. Sedum roofs
support hunting spiders which
favour open habitats, however
once taller tussocky vegetation
is able to establish on green
roofs web-forming species like
the comb-footed spiders are
able to colonise, so for a higher
diversity of spiders it is better
to have a range of vegetation
including shorter and bare areas
combined with tussocks or
taller plants. Tussocks and taller
plants can become established
on mounds or areas of deeper
substrate or may benefit from
microclimates created by logs
or large stones.
Jumping spider
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holes for
solitary
bees
grasses
wildflowers
pebble
perimeter
Lacewing
yarrow
Wool carder
bee
sandy
scrapes
ox-eye daisy
viper’s bugloss
bird’s-foot trefoil
hawkbits
logs
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dead wood
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Hoverfly
Case studies
Laban Dance Centre,
Deptford
This is the original ‘rubble’ or
‘brown’ roof. It was conceived
as part of the action plan to
benefit black redstart and
installed in 2000. It consists of
unscreened crushed concrete
and other site waste between
50mm and 200mm in depth.
It was left to self colonise but
vegetation was slow to establish
and so was subsequently sown
with wildflower seed obtained
commercially and collected
locally. A number of habitat
features were added included
logs. In addition, sand boxes
for nesting bees were added as
part of the SITA-funded project.
This roof has become rich in
plant and invertebrate species
diversity, however the crushed
concrete substrate, which
absorbs little water, means that
the roof suffers from severe
water stress during drought.
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FC4 Building,
Canary Wharf
This roof has a sedum blanket
laid onto a 20mm layer of
horticultural rockwool. It was
installed in 1999 as part of
a programme to improve the
appearance of roofs on the
Canary Wharf estate. High
on a 12 storey building, it is
exposed to wind and is drought
stressed. Around the drainage
outlets, where the substrate is
wetter, plant diversity is higher
and taller vegetation occurs.
Basic sedum roofs like these
are species-poor however
they support some interesting
species, including in this case,
the rare spider Philodromus
albidus.
Green roof research station
B1 Texaco Building
B1 (Texaco) Building,
Canary Wharf
This roof was established as a
green roof research station in
2004. Consisting of a series
of plots with varied substrate
depths from 20mm to 150mm,
it was originally seeded with
the London Livingroofs mix and
over time has developed into a
species-rich dry grassland in
the areas with a substrate depth
over 80mm. In the shallower
areas sedums have colonised
and spread. Species that are
doing particularly well are bird’sfoot trefoil, kidney vetch, hare’s
foot clover and viper’s bugloss.
Komodo Dragon House
Green roof London
Komodo Dragon House,
London Zoo
Completed in 2004, this sloping
green roof has a substrate
of crushed brick and soil in
varying blends, complemented
by a veins of stones which
help to dissipate the energy
of water coming from a gutter.
The substrate depth varies
between 65mm and 150mm
and was planted with drought
tolerant native species. The
technique of varying substrate
depth, developed by Stephan
Brenneisen in Switzerland, was
used to promote diversity of
vegetation and plants cover and
therefore invertebrates.
Laban Dance Centre
Roots and Shoots,
Lambeth
This roof was originally
conceived as a ‘brown’
or rubble roof (see Laban
Dance Centre) and installed
in 2005. The roof was
covered with approximately
70mm of screened crushed
concrete and brick with no
organic material. Over time a
series of mounds have been
added, some consisting of
sand and others brick-based
extensive roof substrate. In
2009 sand bees and cuckoo
bees were observed nesting
in the mounds. The roof was
originally left to self-colonise
but vegetation establishment
was slow, so the roof has been
seeded with wildflowers and
planted with bulbs in order to
provide a nectar source.
175-185 Grays Inn Road,
Holborn
This roof was established in
2006. The intention was to
promote diversity by using a
range of substrates, including
fired sewage pellets, glass
sand and crushed brick and
concrete. There are also a
number of untreated logs and
timber ‘paviours’. The roof
was seeded with the London
Livingroofs wildflower mix.
Garage, 4 West Heath Drive,
Golders Green
This roof has a mixture of
crushed brick based substrates
laid to a depth of 100mm and
seeded with the London
Livingroofs mix. A number of
bulbs have also been planted to
provide an early nectar source
for bees including crocus,
narcissus and dwarf iris.
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Key components
A range of simple interventions
can boost the conservation
value of green roofs and living
walls for invertebrates. These
include:
Wildflowers – a wide range of
drought tolerant wildflowers
can be grown on extensive
green roofs, providing nectar
for butterflies, hoverflies, bees
and beetles and larval food
plants for moths, butterflies
and beetles. Other wildflowers
can be incorporated into living
walls, which are irrigated and
can support a range of species
more usually associated with
woodland and woodland edge
habitats. The low level of
management on extensive green
roofs means that there can be
plenty of taller plants and stems
to allow spiders to build webs
and stems for invertebrates to
overwinter in. Deeper areas and
mounds of substrate support
taller, tussocky vegetation and
provide damper soil conditions.
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The associated increase in
biomass which occurs where
soil is deeper and vegetation
thicker also means that more
insects can be available as food
for birds and bats.
Open bare ground – such area
may occur where substrate is
shallow and stressed or where
there are stones. They warm
quickly and benefit a wide range
of butterflies, bees, wasps,
beetles and spiders which enjoy
these conditions.
Deadwood – beetles and other
species burrow into or shelter
in and under logs, which should
be hardwood and untreated.
Loose mounds – sand or
other loose material set in
sunny locations may be used
by solitary bees and wasps for
their nests.
Pebbles and grasses
Wet areas – shallow water
bodies can be provided by
placing a shallow plastic
container or area of waterproof
liner. They provide drinking
opportunities for birds and
damper areas which increase
the numbers of some species,
which again means that more
food can be available for birds
and bats.
Insect hotels and habitat
walls – these can be made
from untreated timber, pallets,
canes, stems and recycled
building materials to create
areas for invertebrates to
shelter, overwinter or nest in.
South facing habitat walls may
be used by mason bees. More
shaded areas may shelter
beetles, spiders, lacewings and
other species.
Further information
Biodiverse roof in full flower
Brenneisen, S. (2006) Space for Urban Wildlife: Designing green roofs as habitat in Switzerland,
University of Applied Sciences Wädenswil. www.urbanhabitats.org/v04n01/wildlife_full.html
Gedge, D., Grant, G., Kadas, Dr. G., Dinham, C. (2012), Creating green roofs for invertebrates; a best
practice guide, Buglife, Peterborough.
www.buglife.org.uk/Resources/Buglife/GreenRoofGuide_P5.pdf
Jones, R. A. (2002), Tecticolous invertebrates; A preliminary investigation on the invertebrate fauna on
green roofs in urban London, English Nature, London.
www.livingroofs.org/images/stories/pdfs/Tecticolous%20Insects.pdf
Kadas, Dr. G. (2002), Study of green roofs; how roof design can maximise biodiversity in an urban
environment, University College London. www.urbanhabitats.org/v04n01/invertebrates_full.html
www.livingroofs.org - information on green roof types, benefits and specifications.
Acknowledgements
Text: Gary Grant, Dusty Gedge, Mathew Frith, Dr. Gyongyver Kadas and John Newton.
Thanks to Dave Perkins at Roots and Shoots for his advice on habitat walls.
Design: Metalanguage Design
Illustration: Full Circle Design
Images: livingroofs.org, Penny Frith, Tristan Bantock, Mathew Frith, Pavel Krásensky and Tony Wileman.
A buzz up top has been funded by SITA Enriching Nature through the Landfill Communities Fund.
SITA Trust is an independent funding body set up in 1997 to provide funding through the Landfill Communities
Fund. SITA Trust funding enriches nature by supporting biodiversity conservation projects in England.
www.sitatrust.org.uk
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Chicago City Hall
Protecting London’s Wildlife for the future
Skyline House, 200 Union Street, London SE1 0LW
Tel: 020 7261 0447; www.wildlondon.org.uk
London Wildlife Trust is company limited by guarantee registered in England and Wales 1600379 and registered charity number 283895