How stag beetles enrich a rooftop ecosystem in London

Up to 70mm long and with antler-like jaws, the stag beetle Lucanus cervus is the largest beetle living in Britain and the largest land insect in Europe. Its larvae are no less impressive: they grow to 11 cm in length over a four-year period and feed on decaying trees, which play a valuable role in ecosystems by breaking down decaying material.

“They’re a showcase species to the many other creatures that help recycle and feed on dead wood,” says Andrew Salisbury, chief entomologist at the Royal Horticultural Society. “Fostering stag beetles boosts ecosystems,” he says.

Despite their seven-year lifespan, these fearsome beetles are elusive and their numbers are now in sharp decline as land development threatens their natural forest habitat. Stag beetles are protected in the UK by the Wildlife and Countryside Act 1981.

Excessive tidying up of parks and gardens also plays a role. “They’re the mascot of a whole bunch of invertebrates that rely on old dead trees – and things we’ve taken from our environment – to live on,” says Lucy Hodson, a Lancashire naturalist with 45,000 followers on Instagram as Lucy lap wing

Female stag beetle © F Martinez Clavel/Science Photo Library

Male stag beetle

Male stag beetle © F. Martinez Clavel/Science Photo Library

But there’s a surprising European stronghold for the bugs: London. Populations in the capital and the Thames Valley are among the largest in Europe.

It was these populations that inspired Harris Bugg Studio, a garden designer who has won gold medals at the Chelsea Flower Show, to include the beetles in his plans for a new program in the capital for commercial developer Fabrix.

The Roots in the Sky project – a series of terraced gardens built on top of a converted Southwark courthouse – is not due for completion before 2025. But the designers, with encouragement from their client and the environmental officers at Southwark Council, were keen to start building ecosystems from the start.

“We thought beforehand about how we’re going to develop this invertebrate life — like getting stag beetle larvae onto the roof by creating woodpiles and vertical woodpiles ahead of time,” says Charlotte Harris, co-founder of Harris Bugg. “These are erected by the landscapers well in advance off-site and in the right light and moisture conditions that allow the wood to begin the valuable process of decay.”

A representation of the Roots in the Sky project

A rendering of the Roots in the Sky project © Fabrix/Sheppard Robson

The gardens will be built on top of a blue roof system – which acts like the water table and waters the vegetation in a similar way, with the plants pulling what they need. The hope is that the development will make a small contribution to London’s biodiversity, greening and sustainability goals.

“It’s really an artificial garden and environment,” says Harris. “And while it will be colonized by invertebrates over time, the soil will be relatively inert when first installed.” The designers wanted to find ways to positively encourage these ecosystems in their plans.

While avid gardeners with an understanding of wildlife are increasingly leaving messy areas in their outdoor spaces, working with nature rather than against it, it’s still uncommon to see designated wildlife areas in public spaces or design-led private gardens.

Harris Bugg hopes to advance conversations about ecosystem design and habitat creation. “There’s a huge and growing awareness of the importance of gardening to biodiversity,” says Harris. “But we also need to make it accessible and engaging.”

At Roots in the Sky, the office floors are crowned by a communal patio with an orchard, a productive crop area, a meadow and a small forest. Other creatures Harris Bugg would like to support on the roof are moths, butterflies, stick bees, house sparrows and black redstarts. Some sections are closed to the public to protect ecosystems.

“We’re regularly checking to see if we can add more elements,” says Harris. “Can we do dead hedges or ‘hill culture’ principles? [using mounds of dead plant material to make raised garden beds] For example, works that are already a beautiful element in themselves, but contribute to improved biodiversity? And of course, measuring that effectiveness is just as important, because that way we can demonstrate results.”

The studio also follows others in the industry experimenting with habitat creation such as John Little of Grass Roof Company, Fergus Garrett of Great Dixter and Nathalie Pettorelli of the Zoological Society of London.

Although Roots in the Sky is an experiment in building a landscape and ecosystem from the ground up, this approach could be adopted in other places where wildlife is scarce and habitats have been destroyed by human activity.

A recent University College London study looking at how changes in land use and climate are affecting insect populations found that insect numbers in areas where temperature has risen due to climate change have fallen by about 50 percent has declined.

With net biodiversity gain quotas expected to come into effect in 2023 and new construction projects needing to take steps to compensate for the habitats they damage, developers can no longer ignore these issues and must incorporate them into their strategies from the start.

Popular campaigns that focus on specific groups of species — to save bees, for example — have helped people connect to a vast and otherwise confusing world of invertebrates and pollinators.

If Harris Bugg’s project shows that city developers can create ecosystems from scratch, perhaps more garden designers and landscape architects working with existing spaces will take steps to protect important habitats for stag beetles – and all the other miniature animals that work alongside us Life.

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