GIS MAPPING AND MODELLING

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GIS MAPPING AND MODELLING CARRIE HOWARD The GIS component of the Suffolk Coast and Heaths Lifescapes project was undertaken using MapInfo v7, a windows based desk top GIS application.

Extensive use was made of digital environmental base layers provided by Suffolk County Council including extensive use of their aerial photography, without which the effectiveness of the work would have been seriously reduced. The mapping and modelling work also benefited from the advice and guidance of a whole range of individuals (including national specialists) and local partners, to whom we are also very grateful.

There were two main phases to the work which was initially planned to run over a two-year period. The first of these concentrated on identifying and mapping specific habitat types throughout the study area and digitising these into the GIS as polygons. A habitat polygon was simply a geo-referenced digital outline of the habitat to which information could then be attached in a database. The second phase of the project involved devising ways of identifying where it could be both feasible and desirable to create lost habitat in the wider countryside.

Habitats were identified using a range of sources, but relied foremost on the interpretation of aerial photography. This was available at a high resolution for the whole of the study area and could be zoomed in to highlight specific areas of interest. Many habitats are highly distinctive from their hue, or from the texture or pattern of the vegetation that they contain. Areas that then met strict criteria (using guidance material developed by English Nature on identifying BAP habitats) were digitised and assigned as a specific BAP habitat type. A range of metadata was then associated with each polygon such as: the source used to locate the habitat (what led us to believe that it may be present), what scale the polygon was digitised at, and how sure we were of the determination. In some cases aerial photography was less reliable at determining habitats and so certain areas were supplemented with an element of ground truthing; where this was the case this was again recorded in the metadata. Extensive use was also made of the species records held at the SBRC database to identify habitat types since many habitat types are characterised by the species they contain. Individual and groups of species records could be laid over the aerial photography and used as a means for ‘homing in’ on likely habitat. Once all the habitat digitising was complete the second stage of the work could begin.

Before individual habitat potential could be identified it was necessary to determine what the basic environmental requirements were in order to establish any given habitat. For example, to establish heathland a certain type of sandy soil is preferred, while grazing marsh can only really be established at below 10m elevation. The next stage was to develop a base layer of field polygons for the wider countryside where there was not currently any habitat (the majority of which was farmland or forestry). This involved digitising thousands of field boundaries so that the model we were constructing could apply a series of ‘rules’ to each field.

Trans. Suffolk Nat. Soc. 40 (2004)

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A range of environmental base layers such as soil type, floodplain extent, land profile etc. were then fed into the system and fields selected that met the basic environmental requirements prior-identified for each habitat. This gave us all the fields that could feasibly be turned into the habitats that we wished to then model for. This yielded many hundreds of fields since, of course, until relatively recently, semi-natural habitat once covered much of the area and the basic environmental requirements are the same today as they were then. Since there is high competition for available funds to undertake habitat restoration in the wider landscape (largely through agri-environment schemes), it was necessary for us to refine our selection of potential sites to select those that made the highest contribution towards enhancing existing biodiversity. This was achieved by devising a rule-based additive factorial model. The model relied on calculating the relationship between our ‘potential’ habitat polygons and the habitat that currently exists today, together with the movement restrictions (mobility) of the species that they contain. These factors included: Proximity to existing habitat Proximity to designated sites (SSSIs or County Wildlife Sites) Ability of the ‘potential’ habitat to link two or more existing habitats Time since loss of habitat (to aid this a number of historical maps were interpreted and the past extent of habitat determined for various time periods) Current land use Proximity to BAP species with restricted mobility The model then applied the rules that we set to the fields that met the basic requirements for a habitat type, and each one received a score for each factor ranging from 0–10. These scores could then be added up for each factor giving an additive score. A range of maps could then be produced to illustrate which areas could be prioritised for habitat restoration. Plate 3 illustrates an example of this for heathland potential.

It is important to note that the rules and scores were changeable according to the ecological assumptions you wished to make, and what factors you felt were important. For example, should you decide that you wanted to prioritise heathland creation on sites where it was lost in the last 40 years you could boost the score for this factor, or if you only wanted to prioritise only sites that linked existing habitats this too was possible. Therefore, all factors could be changed depending on how much they were felt to be valuable, thus giving a number of possible maps. This was felt to be a significant advance on other modelling exercises where one final map was produced and it was no longer possible to challenge the underlying assumptions of the model re-run it. The model also had advantages in that when any of the base environmental layers or habitat layers were updated, it could simply be re-run using these new layers to provide an updated output.

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The outputs that the model provides should be considered as initial guidance only on the potential for habitat creation in the area, and would always be supplemented by detailed information on the ground. No attempt was made in the model to decide which habitat should be created in any given area if it proved suitable for more than one habitat type. ‘What habitat where’ will in the end be determined by factors such as the available funding sources, preferences of the land owner and in the longer term factors such as climate change. It was therefore not felt useful to be overly prescriptive in this sense, but only to show that a range of biodiversity outcomes were possible. There proved to be hundreds of potential configurations of habitat in the landscape.

The difficult part of the modelling proved not to be showing where you could create habitat but rather why you wanted to do it, and what sort of landscape you ultimately wanted to see in the future. This certainly provoked some discussion!

The model provided outputs that will hopefully be used to guide both longterm and short-term strategic habitat creation throughout the area. This work is currently ongoing and will hopefully become more sophisticated and widely applicable in time. It is hoped that the outputs will make a significant contribution towards safeguarding the long term viability of the habitats and species that this wonderful area currently contains.

Carrie Howard Suffolk Biological Records Centre Ipswich Museum High Street Ipswich Suffolk IP1 3QH

Trans. Suffolk Nat. Soc. 40 (2004)

Plate 3: Lifescapes Heathland Potential, map of Suffolk Coast and Heaths area showing additive scores for potential heathland polygons (p. 10).