BIODIVERSITY
Summary
This page expands on the topics raised in the ‘Biodiversity Loss‘ section of the Sustainability page, using the Natural England Biodiversity Metrics formulas (JP029) to provide the calculations behind the numbers .
In the UK, on average, a typical modern housing development would result in a 49% reduction in biodiversity (assuming the development was on a typical agricultural field – if a it was on a natural landscape this loss would be a 87%-91% reduction).
The Deeping Project development would increase the site Biodiversity by over 300%.
Blueprint Biodiversity Levels
The conceptual site can be divided into four biodiversity classifications:
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- Minimal (16%) – the site roads would be non-adopted, grass covered ‘green lanes’ (grass grown in a thin layer of soil sprinkled over a geotextile membrane on top of Type 1 sub-base – they would stay mainly green subject to traffic levels and be completely free draining so would not require storm drains, gullies or soakaways) but would not support any significant quantity of plant or animal life. The areas with photovoltaic panels would similarly support limited life.
- Low (12%) – the lawns and amenity area will allow some vegetation, invertebrates and animal feeding areas.
- Agricultural (7%) – the allotments will provide more biodiversity than the lawns and roads but not by fully available to nature.
- Full (65%) – the rest of the development, the roofs of the buildings, the bunds and surrounding areas would be left to nature to grow unmanaged. Some trees would be planted to ensure that desirable native species like oak, for example, take hold and to provide fruit and nut trees to augment local food production. Otherwise all that is required, as shown by rewilding elsewhere, is for some of the ground to be disturbed/tuned over occasionally to allow the local wind driven spores and pollen to get a hold.
Most modern housing developments would only have ‘minimal’ and ‘low’ classification areas of biodiversity. On this blueprint housing development these classifications would make up less than a quarter of the site.
On an ideal site a significant area would be put aside for trees providing canopy coverage to a minimum of 15% of the site. This does mean that house density is an issue, more land does have to be allowed for nature to flourish.
Natural England Biodiversity Metrics 2.0 (JP029)
The biodiversity change that will occur with the development of a site can be calculated using Natural England’s Biodiversity Metrics 2.0 (JP029) methodology . The spreadsheet tool that accompanies the methodology calculates the existing biodiversity and then the biodiversity that will result from the site’s change of use, immediately and over time.
The full calculations for the blueprint site were made using the spreadsheet tool and the key outputs are provided here. No off-site mitigations have been used.
Site Habitat Baseline
The initial baseline figures for undeveloped site are detailed in the following table:
‘Accelerated Succession’ is a specific process where habitat such as woodland is created from existing habitats. In this case the intention is that 15% of the site will become woodland and so 0.963 hectares is reserved for this purpose.
The Habitat Unit figure is a simple indicator of biodiversity. The tool user guide states under Principle 3 that ‘The metric’s biodiversity units are only a proxy for biodiversity. While it is underpinned by ecological evidence the metric is only a proxy for biodiversity and to be of practical use has been kept deliberately simple. The numerical values generated by the metric represent relative, not absolute, values.’
Site Habitat Creation
The habitats that will be created on our ideal site are detailed in the following table:
The habitat unit figures given reflect the habitat value immediately created. Some habitats cannot be created quickly, so for example, while Wetland Reed-beds are an immensely biodiverse resource they will not reach maximum biodiversity for many years (the tool allows 15 years in this case) and so the initial score is low.
Site Habitat Accelerated Succession
The part of the site that will be under Habitat Accelerated Succession (for creating woodland) is detailed in the following table:
The tool gives a time to target habitat maturity of 30+ years for growing trees.
Calculation Results
The following tool results show a total net biodiversity improvement of 323%:
Comparison with a traditional build
A traditionally built housing development has less green space and utilises construction materials that are inimical to wildlife. There is very little that can get a toe hold on tiled roofs or tarmacked roads. Against the same baseline above the typical development would work out as follows.
Site Habitat Creation
The area below were calculated by uploading a satellite photo from the ‘Abbotswood’ development in Romsey to a suitable CAD package (approximate postcode SO51 0BX).
Results of Traditional build
Based on the above the net change is a reduction in biodiversity of 49%. This is the change against an agricultural field. If the original site was:
- Natural grassland (‘Grassland – Bracken’) then the biodiversity loss would be 87.3%.
- Woodland (‘Woodland and forest – Lowland mixed deciduous woodland’) then the biodiversity loss would be 91.53%.
Mitigations
There are some simple changes to construction methods that would dramatically change the biodiversity outcome.
- If the roofs of the buildings were changed to Sedum covered roofs (‘Urban – Intensive green roof’) then the site’s biodiversity would actually increase by 11.04% (agricultural fields are not very biodiverse).
- If the roofs of the buildings were changed to more extensive green roofs, that use planting mediums of a greater depth that allow the growth of larger plants, then biodiversity would increase by 37.5%.
Other mitigations would be to use ‘green lanes’ instead of Tarmac and to include areas for tree growth.