Why Green Roofs are Vital Components of Urban Biodiversity
As our towns and cities expand, the need for sustainable urban planning becomes increasingly critical. One innovative solution playing a pivotal role in this development is the installation of green roofs. These structures are not just visually appealing; they are ecological powerhouses that offer enhanced biodiversity, reduce urban heat island effects, and improve stormwater management. In particular, green roofs can replicate rare natural habitats that are crucial for specialised species, such as those found on coastal vegetated shingles.
The Unique Ecology of Green Roofs
Vegetated shingle/shell at Pūkorokoro / Miranda on North Island, New Zealand (Photo: Dusty Gedge)
Coastal vegetated shingles and shells are unique ecosystems found only on certain coastlines where vegetation grows amidst pebbles or shell fragments, providing valuable habitats for rare and highly specialised species due to their unique conditions. These habitats, found mostly in Northwest Europe (the United Kingdom), Japan, and New Zealand, are somewhat rare globally. The vegetation in these areas must endure constant exposure to sun and wind, and they typically lack fresh water and rich soil, making them remarkably resilient and specialised.
Such environments provide valuable habitats for rare and highly specialised species and are threatened by human activity, emphasising the urgent need for their protection. Experts on green roofs see these coastal habitats as ideal models for low-maintenance green roofs in urban settings. They require minimal upkeep and, if designed correctly, can replicate these rare conditions on rooftops, significantly enhancing urban biodiversity.
Additionally, the method used to evaluate low-maintenance green roofs is based on studies from Switzerland in the late 1990s. These studies showed that by imitating the gravel beds found in rivers, we can create rooftop environments that support diverse insects and other small wildlife typically found in undisturbed lands. This Swiss approach was also used to design artificial riverbeds on the ground that provide homes for endangered species, such as the Wall Lizard (Podarcis muralis) and various other insects.
The success of this research in Switzerland inspired similar initiatives in London in the early 2000s, subsequently becoming the basis for how green roofs are assessed in terms of biodiversity in England’s Biodiversity Net Gain metric (BNG), which is now a required feature for new developments in England. As a result, these environmentally beneficial roofs are becoming more common in urban areas across the country.
Case Study: Green Roofs in Japan
The roof of the Morigasaki Water Reclamation Center West during installation in 2012 (Photo: Ayako Nagase)
In Japan, the rooftop of Morigasaki Water Reclamation Center West in Tokyo's coastal area has become a crucial nesting ground for Little Terns. The industrialization and urbanisation of Tokyo led to the degradation of their natural coastal habitats. When it was discovered that these birds were laying eggs on the building's concrete roof and struggling, a mixture of small gravel and sea shells was installed to create a more natural nesting environment, supporting the hatching of thousands of Little Terns since 2002.
The mixture of gravel and sea shells on the roof of the Morigasaki Water Reclamation Center West (Photo: Ayako Nagase)
To further explore the concept of sustainable green roofs, Professor Ayako Nagase from Chiba University introduced "Harappa" roofs in Japan, inspired by extensive green roof designs from the UK and Switzerland. The term "Harappa" refers to vacant lots or open fields, common in Japanese residential areas, and evokes a sense of nostalgia. These roofs are not only low-maintenance—remaining in good condition for over a decade without intervention—but also provide valuable habitats for insects and birds, enhancing urban biodiversity.
While some might view Harappa roofs as less visually appealing compared to meticulously maintained green roofs, it's important to consider their ecological value. Such green roofs may appear beautiful at first, they often require ongoing maintenance to preserve their appearance, whereas nature thrives and remains effortlessly beautiful without constant intervention.
By recreating extensive green roofs using vegetation from similar natural landscapes, it's possible to strike a balance between beauty and sustainability. Perhaps the key lies in spending more time in nature, observing its dynamic changes, and replicating these patterns to create biodiverse and resilient urban green spaces.
The Broader Impact of Green Roofs
Example summary of a green roof survey by Gentian
While some countries like England actively consider biodiversity in their policies, it remains challenging for investors and decision-makers to prioritise species protection. However, green roofs offer not only biodiversity benefits but also contribute to urban resilience. They mitigate the urban heat island effect, assist with stormwater management, and cool the buildings they adorn. Moreover, the deeper the substrate, the better it supports biodiversity and water storage, enhancing stormwater management and cooling capabilities.
Gentian's habitat mapping software plays a pivotal role by identifying potential roofs for greening and mapping existing green roofs as important assets in the urban green network. Conducting comprehensive studies on how the functions for biodiversity and resilience can be integrated can inform innovative and beneficial green roof designs.
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Are you interested in exploring how green roofs can transform your urban environment? Contact us to learn more about our services or to discuss potential collaborations. We believe in a greener, more resilient urban future, and we invite you to join us in this journey.