Integrating visibility graph analysis (VGA) with connectivity analysis in landscape ecology

Paper in proceeding, 2017

Interest in urban green areas has rapidly increased in recent years as the world becomes increasingly urbanized (see e.g., McDonald, 2008, UN-habitat, 2016). This brings new demands for a deeper understanding of the morphology of green areas in cities that provide us with a range of important ecosystem services (ESS) such as evaporative cooling, water purification, micro climate regulation, recreation and even pollination (MA 2005; Andersson et al., 2007). If we also are to support or even enhance such services, we need to make this knowledge accessible for professionals in urban planning and design. In both regards we see the need to bring the fields of landscape ecology and urban morphology closer to each other. This papers addresses this, taking the ESS pollination as point of departure. It has been acknowledged that besides the amount of green, also connectivity between green areas is important for most of these ESS (Alberti, 2008; Kindleman et al., 2008). The critical issue remains how connections are represented. In this paper we propose an alternative approach inspired by space syntax where we introduce a method to capture urban form and their impact on movement behaviour of bumble bees. A first attempt to do so was discussed by Marcus et al. (2014) but instead of drawing connections using space syntax, we here propose to define the resistance to movement using visibility graph analysis (VGA). The level of visual integration can then be calculated based on the number of visual steps it takes to get from one point to any other point within the system. For species that navigate by sight this can be a rather simple and effective way to measure the cost or resistance to move through an urban landscape. To test the method, observation data on bumble bees collected in 16 sites in Stockholm (Ahrné et al., 2009) are used.