Context

Environment Systems was commissioned by ECUS Ltd. on behalf of Wealdon District Council to create a detailed habitat map of the Ashdown Forest Special Area of Conservation and Special Protection Areas. The Council is keen to understand the impact of nitrogen deposition on biodiversity in the area so that it can be monitored and mitigated if necessary in the future. The Ashdown Forest is also designated a Site of Specific Scientific Interest so the emphasis is on ensuring that future management is sustainable.

The Ashdown Forest is an ancient area of open heathland occupying the highest ridge of the High Weald in East Sussex

What we did

Environment Systems used EO (Earth Observation) analysis together with a field validation survey conducted by ECUS to build on the existing biodiversity information for the area. This project used a robust and repeatable approach to obtaining habitat spatial extents, to provide a baseline for further modelling and monitoring. Creating a habitat map of an area of this size lends itself to the use of satellite remote sensing because large areas can be analysed relatively quickly; it is also an Environment Systems specialism.

In this case Spot 5 and WorldView 2 satellite imagery was used to produce the map. With ‘object-based’ analysis the satellite image is segmented into objects based on size and similar spectral characteristics.  This enables the whole area to be classified using rules developed by ecological experts.

Additional datasets, such as topography, are also important considerations for producing the accurate habitat extents. Results generated by the initial output were verified by ECUS ground surveys, which provided further guidance to known locations of particular wet and dry heath habitats. By using these ground truth samples, results were adjusted to provide a more accurate and detailed map of the habitats and estimated area coverage.

Results

The results of the updated map show that the extent of wet and dry heath is fragmented with a high proportion of bracken coverage. This enabled the separation and identification of different species communities, as well as quantifying other biophysical features, such as vegetation productivity and degradation.

By establishing a robust workflow comprising remote sensing software, accurate rule sets and enhanced ecological knowledge, the maps can be updated more easily than conventional methods. Satellite imagery can be processed more quickly and cost effectively to monitor the region over time, either by using future imagery as it becomes available, or by processing past imagery to create a historical record of habitat change.