Modelling processes

A range of tools and models have been created to assist with the process of evaluating and creating habitat networks.  These can be divided into two categories:

• tools which focus on landscape structure (i.e. the shape and arrangement of different parts of a landscape);
• and tools which look at landscape function (i.e. the way in which the different parts of a landscape can be used by particular species).

Landscape structure tools

Some tools are designed to analyse landscape structure. They evaluate the physical characteristics of areas of habitat and the way in which habitat patches are arranged within the wider landscape.

This analysis is sometimes referred to as landscape characterisation or landscape metrics.  In this process, areas can be allocated as core areas, potential movement routes, stepping stones etc.  The landscape is then assessed in terms of its overall connectivity. 

However, you should remember that this only assesses structural connectivity - by looking at the arrangement of the landscape features and assessing where there are physical connections between different features. I t doesn't provide an assessment of the functional connectivity of the landscape - as we've already seen, just because there isn't a physical connection there, it doesn't necessarily mean a particular species is unable to move across the landscape.

Within Europe, a number of countries have identified networks based on this sort of analysis of landscape structure e.g. the Dutch and Flemish habitat networks. You can find further information on this type of approach on the Flemish network case study page. 

Landscape function tools

Other tools and computer models are designed to assess the functional connectivity of a landscape. This approach looks at more than just the physical linkages between core areas, and includes the extent to which areas are connected in practice for different species.  The suite of GIS modelling tools known as 'BEETLE  ' falls within this category.

By assessing the use and value of a landscape for different species, the positives and negatives of changes in land management can be assessed.  Decisions can then be made about the best way to manage a landscape, depending on which species we want to protect or encourage.

One landscape function model evaluates the connectivity of the landscape for a particular focal species.  A focal species is chosen to represent a range of species and can be a real species or a hypothetical one.  Information is added to the model about its requirements for habitat area (i.e. how much habitat does it need to support a viable population) and its ability to disperse.  The model also requires data about the landscape, including the location and distribution of core areas of habitat.

If information is known (or can be estimated), about how easily a plant or animal can travel through different land uses, then it is possible to work out the easiest way for them to travel from one core area to another. For example, a species may be able to disperse a long way through an area of scrubby woodland, but only a short distance through an urban area.

Different land uses will have a different 'resistance' for the focal species, so the 'path of least resistance' or the route that requires the least effort for an individual plant or animal can be established. This is known as the 'least cost pathway' and it may be very different from the direct, as-the-crow-flies, pathway between two patches.

By establishing these potential pathways between habitat areas, models can be used to work out where there are obvious gaps or where movement between them is very difficult. These areas can then be targeted for habitat creation or changes in land management to create a more effective network. Sometimes this will involve trade-offs between different species and so the results of models need to be carefully evaluated. You can see an example of this type of model on the forest habitat network case study page.  

Modelling green networks - If you're seeking to create a green network and achieve social and economic objectives as well, then your model will need to incorporate these.  So you might want to know about how far people will walk in certain areas or where there are existing paths that they can use. This information should be included in the network modelling and mapping process, so that the final network delivers a range of objectives.  See, for example, how habitat networks and people's access to greenspace were modelled in the Urban Networks for People and Biodiversity   project.