Ecological impact assessment and brownfield land

13th October 2016

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  • Business & Industry ,
  • Built environment ,
  • Planning ,
  • Management


Vikki Bird

Bill Wadsworth, senior associate at Chris Blandford Associates highlights some challenges for assessing the ecological impacts of brownfield land development

Contrary to general misconceptions, brownfield land can often have high ecological value despite the apparent limited environmental interest and neglected appearance of such sites. A core principle in the National Planning Policy Framework (NPPF) for England is to encourage the effective use of land by reusing that which has been previously developed (brownfield land), provided that it is not of high environmental value. This means that planning needs to take account of issues such as the biodiversity value which may be present on a brownfield site before decisions are taken.

The government’s recent consultation on proposed changes to national planning policy in England includes the proposal to prioritise ‘the effective use of brownfield land in driving up housing supply…provided it is not of high environmental value’. The consultation proposes to ‘…make clearer in national policy that substantial weight should be given to the benefits of using brownfield land for housing - in effect, a form of ‘presumption’ in favour of brownfield land'.

This presents a challenge for decision makers in balancing the economic and social benefits of using brownfield land for housing with the potential ecological harm of developing such sites.

Subject to specific criteria, the ecological value of brownfield land is recognised as a discrete Biodiversity Action Plan (BAP) priority habitat type called ‘open mosaic habitats on previously developed land’. The ecological value of this habitat type lies in the variety of undisturbed and usually nutrient poor substrates, topography and, in some cases, permanent or ephemeral wetlands.

Mosaics of bare ground, exposed rock faces and sparsely vegetated landforms are of particular value as they can support rare plant and invertebrate species that are not present in more mature and densely vegetated habitats. Such sites are also suitable for reptiles, as well as supporting some of the UK’s rarer bird species, and can also be of biodiversity value as reservoirs for species dispersal within urban settings. As a BAP priority habitat, the impact of development on sites identified as open mosaic habitats is a material consideration in the planning process.

For example, the Thames Gateway regeneration corridor extending from East London into south Essex and north Kent is particularly well known for its network of brownfield sites, many of which are of high ecological value. In addition to their ecological value, brownfield sites in the Thames Gateway and elsewhere in the country can also function as informal areas of semi-natural green spaces, providing much needed access to nature for local communities in otherwise densely built up urban areas.

Commitment five of the IEMA EIA Quality Mark scheme requires practitioners to undertake assessment and transparent evaluation of impact significance. To meet this commitment demands expert knowledge in assessing the ecological value of open mosaic habitats due to the variability of their site-specific characteristics, and their locational and spatial relationships with other sites of ecological value. For this reason, assessing the ecological value and associated impacts of development proposals on brownfield sites can be a complex process.

Commitment five also requires practitioners to provide ‘an effective description of measures designed to monitor and manage significant effects’. For example, opportunities to incorporate landscape features that mimic the characteristics of the brownfield site prior to its development should be considered as part of the site masterplanning and design process.

Of particular value is the inclusion of extensive biodiverse green roofs for buildings, using similar substrates, topographical features and aspect that will provide a mosaic of flower-rich, sparsely vegetated and bare ground habitats analogous with the existing conditions. While green roofs are suitable for many invertebrates, other interventions, such as the carefully designed creation of areas incorporating sands, gravels, bare earth and shingle as part of a scheme’s landscaping strategy, can help enable the long-term retention of a site’s inherent ecological value within the completed development.

Overall, increased pressures for promoting economic growth through development will see a corresponding increase in pressure to use ever-decreasing brownfield sites. An important aim of the NPPF is to prevent harm to biodiversity assets from development by delivering at least no net loss of biodiversity and a net gain in biodiversity wherever possible.

To retain the ecological value of brownfield sites selected for development, it is crucial that high quality surveys and robust assessments are undertaken by experts to inform appropriate mitigation measures through the project design process. This is in line with the principles set out in Commitment five.


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