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Biodiversity net gain rules are now in force for major sites, meaning architects need to design with nature in mind, leaving a site’s biodiversity in a better state than when it was developed.We outline what you need to consider
Biodiversity Net Gain (BNG) is the biggest change to the nature planning system in a generation. Defra has confirmed the launch date for mandatory BNGs for major developments is today (12 February 2024) and 2 April for smaller sites. But what does this mean for architects?
BNG will not only impact ecologists and planning authorities, but will also be a game changer for architects, landscape architects, designers and developers. Why?Because that means we need to design and Naturally, leaving biodiversity in a better state at the end of development. Architects need to work with experienced ecologists to inform the design process from the beginning so that we avoid the best places for nature and improve the most deprived places. In fact, BNG is defined as “an approach to development that leaves biological diversity in a significantly better state than before development.”
Measurable improvements (or “net benefits”) get a lot of air time, with government metrics clarifying the area and quality of habitat we need to create or enhance in order to provide BNG. A mandatory requirement in England is a minimum 10% increase in BNG, which applies to almost all development proposals requiring permission under the Town and Country Planning Act 1990 (with a few exceptions).
The best way to achieve 10% BNG is to minimize the loss of high-value habitat. This can be achieved through careful selection of development sites. Architects are strongly advised to work with experienced ecologists and development partners to guide site selection, preferably completing a desk study or Ecological Baseline Survey (UKHAB) during Stage 0-1 of the RIBA Work Plan to confirm the site’s higher and Lower value. This screening effort can save considerable time and money, as developing sites with high-value biodiversity baselines may require very large offsets.
During the second phase of the RIBA work programme, a preliminary BNG assessment of master planning options will serve as an information tool for development designers. Although the Master Plan outline does not provide the level of detail needed to accurately determine the precise extent of the proposed habitat or BNG, a broad indicative assessment of unit gains and losses may help determine the preferred option. For example, if grazing pasture on a site is classified as otherwise neutral grassland (moderate distinctiveness habitat), it can be determined at a very early stage that if the site is overexploited, the 10% BNG. Site boundaries.
As a further consideration, the BNG assessment only considers impacts, mitigation and offsets associated with regional and linear habitats. It does not include enhancements like bats or bird boxes. Regional habitat, hedgerows and waterways are all treated separately in the metric tool, so architects should not assume that they can compensate for the loss of scrub habitat (regional habitat) by, for example, planting hedgerows (linear habitat). There are also trading rules within the metric designed to offset the loss of habitat at a site by creating or enhancing habitat of the same habitat type or of greater distinctiveness, thereby maintaining ecosystem function and landscape character. This ensures that ecological functions are maintained.
Overlaying (doubling) BNG with other project mitigation measures such as EIA compensation or suitable alternative natural green space (SANG) will also have an impact on the net benefit assessment. For example, you can use habitat created through SANG provisions in your calculations, but you can only achieve no net loss in an indicator (where the post-development score in the indicator is equal to the baseline score) whose primary indicator role is to protect a special protected area (SPA). This means you need to have an additional 10% BNG delivered elsewhere (onsite or offsite).
Providing 10% BNG can vary significantly between rural and urban settings. Rural areas often have higher value baseline habitat but more space to provide BNG at or near the site. Urban areas, on the other hand, may have lower-value baseline habitat but little scope to achieve the required net benefits. However, urban land is not always less valuable. If it is a brownfield site, there is the potential for an open mosaic of habitat (high uniqueness), especially if established infrastructure has been removed and the land has been abandoned for a long time.
An increase in green space is usually required to achieve 10% BNG compared to the existing site. Therefore, developing brownfield land may be more complex than developing low baseline value arable land, which has better scope to provide higher value habitat within the proposed open space. This does not change the fact that if the site is a wildlife-rich prairie or grassland in a rural area, achieving 10% BNG will be very challenging without finding a suitable off-site location to create similar habitat .
As you can see from the example above, delivery of 10% BNG can be complex. However, a simple set of master plan design guidelines can include:
- Development should seek to preserve areas of higher habitat value, as losses in these areas are more difficult to replace.
- Retention and enhancement of habitat provide higher unit benefits than habitat loss and recreation.
- Avoid loss of habitat (e.g. woodland) due to longer creation times.
- Avoid impacts to high-quality habitat first, then prioritize the restoration, creation and enhancement of on-site habitat.
Finally, the delivery of 10% BNG must also adhere to the “Biodiversity Gain Level”. For example, if the project cannot provide BNG on-site (within the red line boundary), then you will need to enhance or create habitat through a combination of on-site and off-site measures (or completely off-site), or in some cases, through Statutory biodiversity credits.
The hierarchy of net biodiversity benefits is as follows:
- Enhance and restore on-site biodiversity (within development site red lines).
- If you can only achieve part of the BNG on-site, you can deliver it through a mix of on-site and off-site. You can earn off-site biodiversity benefits on your own land outside the development site, or you can purchase off-site biodiversity units on the market.
- If you are unable to achieve on-site or off-site BNG, you must purchase statutory biodiversity credits from the government. This must be a last resort. The government will use the revenue to invest in habitat development in England.
All three options can be combined, but you must perform the steps in order.
Obviously, the BNG process is not simple. The evaluation and delivery of 10% BNG is often a complex process. It requires the input of professional ecological consultants with extensive experience in a range of sites and habitats. Early engagement is crucial and interdisciplinary collaboration will support the best outcomes for development and biodiversity.
Jenni Reid is Founder and Director of Burton Reid Associates; Alex Leishman is Senior Ecologist at Burton Reid Associates; Tom Butterworth is Arup Nature Group Head and Director of the UK Business and Biodiversity Forum.All three are members of the Chartered Institute of Ecology and Environmental Management
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