A methodological framework for the use of landscape graphs in land-use planning

• The use of landscape graphs is investigated through routine land-planning issues.
• Landscape graphs can help to identify optimal locations for increasing connectivity.
• Mitigation of a barrier effect may be guided by landscape-graph analysis.
• Diachronic analysis of graphs is useful for including landscape connectivity in impact assessment.

Landscape graphs are now widely used for representing and analysing ecological networks. Although several studies have provided methodological syntheses of how to use these tools to quantify functional connectivity, it is still unclear how landscape graphs can be used for decision support in land planning. This paper outlines the different types of application that may provide relevant responses to the main questions arising in land planning about ecological networks. Three approaches are distinguished according to their objective: (1) to support prioritisation within an ecological network from a conservationist perspective; (2) to increase connectivity by identifying the best locations for adding new elements to the network, either when starting from the current state of the network or when seeking to mitigate the barrier effect engendered by a development project; (3) to assess the potential impact of a development project in terms of decreased connectivity. The computations based on connectivity metrics are explained for each of these three approaches. Then each approach is illustrated in the context of a pond network near the town of Belfort, in eastern France. The results show how the same connectivity metric used in the different approaches may serve different purposes. This emphasises the potential value of landscape graphs for the land-planning decision-support process and not just for conservation purposes (i.e. prioritisation).