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When the much delayed UK Environment Bill becomes law, it will be obligatory for new developments to not only to protect, but also to improve the biodiversity of the plot by 10%. This means developers need to prove so-called biodiversity net gain (BNG) to receive planning permission. The provision of habitats and food through biodiverse living walls and roofs could play a major role in helping developers prove BNG.
The Environment Bill is currently awaiting its third reading in the House of Commons. The important part of the bill from a biodiversity and planning perspective is Schedule 14. This will insert the following in the Town and Country Planning Act:
“Planning permission in England [is] subject to a condition to secure that the biodiversity gain objective is met.” This means “the biodiversity value attributable to the development exceeds the pre-development biodiversity value of the onsite habitat by at least the relevant percentage” and “the relevant percentage is 10%.”
To get planning permission the developers need to put together a compelling the biodiversity gain plan that explains how provision for species’ habitats will be at least 10% better than any habitat existing prior to the development. The developer remains responsible for the biodiversity of the site for “at least 30 years after the development is completed.”
Some local authorities already insist on 10% biodiversity net gain for new developments, see, for example, this guidance from the City of Leeds.
This article discusses the importance of biodiversity and how living roofs and walls can help developers meet BNG goals.
What is biodiversity?
The World Wildlife Fund offers the following definition of biodiversity:
“Biodiversity is all the different kinds of life you’ll find in one area—the variety of animals, plants, fungi, and even microorganisms like bacteria that make up our natural world. Each of these species and organisms work together in ecosystems, like an intricate web, to maintain balance and support life. Biodiversity supports everything in nature that we need to survive: food, clean water, medicine, and shelter.”
What is the problem with biodiversity?
Global and national studies have proven that Human activity is having a devastating impact on biodiversity, with many species facing extinction:
- The WWF’s 2018 Living Planet Report found an average 60% decline in global populations of mammals, fish, birds, reptiles, and amphibians in the last 50 years.
- The 2019 Global Assessment Report by the Intergovernmental Platform on Biodiversity and Ecosystem Services reported “1 million animal and plant species are now threatened with extinction, many within decades, more than ever before in human history.”
- Currently in the UK, 1,188 species are currently threatened with extinction according to the 2019 State of Nature Report
What is biodiversity net gain and what does it actually mean for developers?
The 2019 best practice principles for Biodiversity Net Gain, by CIEEM, IEMA and CIRIA, defines BNG thus:
“Biodiversity Net Gain is development that leaves biodiversity in a better state than before. It is also an approach where developers work with local governments, wildlife groups, land owners and other stakeholders in order to support their priorities for nature conservation.”
The overarching principle is based on Mitigation Hierarchy, which means developers should first strive to avoid impacting diversity, then minimise impact and, as a last resort, compensate where losses cannot be avoided. There also appears to be a hierarchy of habitats and species. So irreplaceable habits – such as ancient woodland should not be impacted, but it is possible to offset damage to less significant habitats by making improvements to more significant habitats.
This leaves some scope for creating new biodiverse habitats, including through living walls, living roofs.
So how do living walls, living roofs, podiums and rooftop gardens help developers with BNG?
The CIEEM principles outlines a number of measures to incorporate biodiversity features. These specifically name green roofs, brown roofs and green walls, but we have also included other measures and explained with P&P notes how these relate to living walls, roofs, podiums and rooftop gardens.
1. Green roofs with a diversity of plant species.
- P&P note: More intensive planting with a wider variety of native species (particularly those that are present prior to development), in deeper substrate is more beneficial to local wildlife than an extensive / sedum roof. See living roofs.
2. Brown roofs with a range of substrates.
- P&P note: The concept of the brown roof is to reuse or reproduce the environment of the brown-field site (which are often rich in biodiversity) on the roof of the development, and allow native plants to naturally colonise. See Brown roofs.
3. Green walls created with planting locations built in, or a planting framework added externally.
- P&P note: Similar to roofs, living walls that allow for the planting of a greater variety and size of plants, including native and those known to be beneficial to wildlife are better than walls that designed simply for visual appeal. Some walls host up to 50 plants per square metre – that’s provides a good scope for variety. See Living roof FAQ.
4. Introducing bat and bird boxes, following guidelines.
- P&P note: In the correct circumstances, bird boxes and bat boxes can be introduced to green walls, and should be used by birds and bats. However biodiverse living walls are also a valuable source of food, both in terms of edible plants and the invertebrates that live there. A 2014 study by Caroline Chiquet found that more birds were present in neighbourhoods with green walls than those without. See the Benefits of green walls for more details.
5. Rough or natural stone walls with holes for invertebrates and small birds to use.
6. Habitat creation for locally relevant wildlife habitat types.
7. Provide a range of ‘bug hotels’ with dead wood and stone piles, or purpose-made bug boxes with tubes and drill holes.
- P&P note on 5-7: Green and brown roofs are perfectly good homes for bug hotels, hives, log or stone piles and other habitats, where they can remain undisturbed for years.
8. Native wild flower mixes as an alternative to amenity grassland or verges.
9. Early flowering plants that provide a nectar source for early invertebrates such as bees.
10. Nectar-rich native planting and native species with berries in the autumn within formal landscaping.
11. Species-rich native hedgerows as boundary features.
- P&P notes on 8-11:
- Green roofs make great wildflower meadows, see the Wimbledon Grounds case study, where every one of the roofs has been seeded with a wildlife-friendly flower mix.
- Roofs with a deeper substrate can accommodate bulbs and perennials known to suit pollinators.
- The deeper substrate of landscaped podiums and roof gardens can incorporate native shrubs, even trees. See the Barbican case study.
12. Ponds (not fish stocked) with an irregular and shallow, sloping edges.
- P&P note: Landscape podiums can be designed to encorporate wildlife ponds.
13. Habitat corridors across a site to make a connection with wider habitats.
- P&P note: There have been some studies that have looked at whether living roofs and walls contribute to wildlife corridors, between wild spaces. It seems that living roofs and walls could become wildlife corridors, but there needs to be a higher concentration of living roofs and walls in a given area and these installations need to be larger with more thought given to the planting.
How is Biodiversity Net Gain measured?
The exact metrics for measuring BNG haven’t been completed yet. DEFRA is establishing a points system where the ecological nature of the site is assessed by an ecologist before development and this is compared to the impacts positive and negative of the proposed development in a report.
This will become clearer when DEFRA publishes its Biodiversity Metric 3.0 (which has been delayed until spring 2021). The criteria that ecologists are likely to take into account are explained in CIEEM’s Biodiversity Net Gain guidance.
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Pritchard and Pritchard are specialist installers of Green walls for both commercial and residential projects. We work with living wall specialists across the UK and have detailed and professional knowledge of each and every living wall system, if you have a vision for a vertical garden at your home or business premises, get in touch, we can help you every step of the way.