The work involved assessing data originally from the National Land Use Database of Previously Developed Land, British Geological Society BRITPITS data and Environment Agency Historic Landfill data. Each feature was interpreted on aerial photography to determine whether OMH was likely to be present. Where OMH was not thought to be present the feature was removed from the inventory. Where OMH was thought to be present the feature was replaced with an accurately mapped boundary. Attributes were recorded for each retained feature detailing the sources of information, the confidence that OMH was present and notes describing the reasons for any uncertainty.

The result was the first ever inventory that separated OMH from brownfield sites more generally. In total 141,153 features were checked, but only 8,410 (32,602 hectares) of these were believed to be possible OMH and were therefore retained in the inventory. Greater London was shown to have the highest density of possible OMH, though Middlesbrough and St Austell in Cornwall were also found to be hotspots (shown above).

The process of inventory creation and the results were recorded in a rule base and project report.

Further information from Claire Lush.

Because of the biodiversity importance of OMH the habitat was identified as a Biodiversity Action Plan habitat in 2007. However, such sites are threatened by redevelopment (due to their usual status as brownfield sites), inappropriate ‘restoration’, inappropriate management or natural succession. There is very little knowledge of the distribution of OMH, as there is no data that identifies OMH sites at a national level.

exeGesIS were awarded this project in 2011, which has increased understanding of OMH in England and Wales by identifying the key features that are found within such habitats and enhancing knowledge of the distribution of such sites. This involved the development of a new survey methodology and a survey of 98 survey sites to identify OMH habitat, as well as a survey of invertebrates on 50 of the sites - the largest single survey of its kind in the UK. These surveys provided invaluable information on the importance of OMH sites to conservation and the recognition of important sites remotely and in the field.

The results of this work were:

• A handbook for the identification and survey of OMH sites.
• A provisional national inventory of OMH sites in England and Wales, along with an inventory data capture rule base.
• An integrated OMH survey website, including a map of OMH sites and survey data entry forms.
• Field survey data supplied to the NBN Gateway.

Further information from Crispin Flower.