Green roof advocate Dusty Gedge on boosting urban biodiversity

Dusty Gedge, from South East London in the UK, is an internationally recognised expert on green roofs.

Gedge was one of the keynote speakers at the World Green Infrastructure Congress held at Waipapa Taumata Rau from 3-5 September. The event, MCed by Mike McRoberts (Ngāti Kahungunu) and organised by the Faculty of Creative Arts and Industries, featured hundreds of local and international sustainability and green infrastructure experts converging on campus to share their ideas with companies, institutions, public authorities and scientists. The goal was to examine and catalyse nature-based solutions to create sustainable urban environments.

Gedge, the president of the European Federation of Green Roof Associations and founder of Livingroofs.org, delivered an engaging and insightful talk that explored the importance of green roofs and the types of plants best suited for them.

With more than two decades of experience, Gedge has a deep understanding of how urban ecology and green roofs can contribute to a sustainable future, particularly in cities like London. He has challenged conventional wisdom about green spaces, advocating for a future where cities are not just concrete jungles but vibrant, living ecosystems integrated into every level of the urban fabric of a city.

Green roofs, according to Gedge, are not just about aesthetics or superficial greening. Instead, they are an ecological response to urban environments. He stressed the need to think ahead, designing landscapes that are resilient to future environmental conditions, especially given the growing challenges posed by climate change.

Improvements to biodiversity in central London are being driven in part by the financial institutions, real estate agents and legal offices whose buildings dominate the area. Many are taking on board the advice of the global Taskforce on Nature-related Financial Disclosures (TNFD). The TNFD developed a set of recommendations and guidance to encourage business and finance to assess, report and act on their nature-related dependencies, impacts, risks and opportunities. One such opportunity has been green roofs and biosolar green roofs.

One of the key takeaways from Gedge’s talk was the idea of replication rather than restoration. Restoration often implies returning a landscape to a previous state, but as Gedge points out, that’s not always practical or desirable, especially in cities like London that have been profoundly altered by human activity for more than two millennia.

Instead of trying to bring back ancient ecosystems, Gedge advocates for creating new habitats that replicate successful elements of nature. He emphasises the importance of understanding the natural history of an area, as this informs which plants and ecological strategies will thrive on a green roof.

“Since the central city companies took these ideas on board, there are probably more wild flowers in central London now than there are in many of the counties in the countryside, because of intensive agriculture in those areas.”

Gedge discussed his experience working on brownfield sites – former industrial areas that have developed unique ecosystems due to their man-made nature. These areas often serve as critical refuges for rare species of invertebrates, and Gedge sees them as complementary to green roof design.

When it comes to the types of plants used on green roofs, Gedge suggests a mix of native species and plants that are well adapted to the specific conditions of urban environments. Resilient plants that require minimal nutrients and thrive in stressful conditions, such as those found on rooftops, are ideal. He also highlights the importance of using plants that can withstand drought and low-nutrient soils, as these are common challenges for green roofs.

A key principle Gedge advocates for, not just on rooftops, but in the average garden in areas prone to drying out, is keeping nutrient levels low.

While many landscape architects and gardeners in general might instinctively want to use rich topsoil, Gedge warns against this.

“I'm so fed up with topsoil. It's so depressing. Topsoil is about performance, making it all nutrient-rich, making everything grow fast, and then when the drought comes, what happens? Everything dies.”

Instead, he recommends using substrates with just 10 percent nutrients. This creates stress in the plants, which, paradoxically, makes them hardier and more resilient over time. The result is a landscape that may look sparse initially but grows into a rich, biodiverse ecosystem.

Gedge’s designs are also shaped by his fascination with open mosaic habitats – urban landscapes that have evolved on their own, often in post-industrial sites. These habitats, which combine different ecological elements in a mosaic of plant life, are more complex and valuable than simple lawns or manicured gardens. Gedge explains that these areas are critical for biodiversity, especially in urban environments where traditional green spaces are limited.

As an ornithologist, he has been particularly fascinated by the impact of green roofs on bird life. He cited the linnet bird which has been in decline. Gedge proudly displayed a photo of a linnet hanging out on a roof-top garden in London. “There it is, in the garden with more than 148 species of plants. There are now more linnets in central London, because of green roofs. So in my life, I’ve helped a bird,” he said proudly.

Another critical element of Gedge’s green roofs is the creation of conditions that mimic coastal habitats. In the United Kingdom, as well as in countries like New Zealand and Japan, coastal areas are often rich in biodiversity. Gedge believes these habitats offer valuable lessons for green roof design, particularly in terms of plant selection and soil management. He refers to a project in Berlin where the ecology between old runways at Tempelhof Airfield created a highly biodiverse environment, demonstrating the power of post-industrial landscapes to support rich ecosystems.

Ultimately, Gedge’s vision for green roofs is one that balances aesthetics with ecology. His designs aren’t just about putting plants on rooftops; they’re about creating resilient, biodiverse ecosystems that can thrive in urban environments and adapt to future climatic conditions.

As Gedge says, "It’s not about culture; it’s about nature." In this sense, green roofs are more than just a way to beautify buildings and tick a few sustainability boxes. They are a critical part of the urban ecology of the future.