Sequencing stepping stones: a raster-based GIS model for routing a connectivity corridor through a fragmented landscape

Although its effectiveness (or cost-effectiveness) remains debated, connecting habitat remnants through conservation corridors is an approach to mitigate negative effects of wildlife habitat loss and fragmentation on biodiversity. However, multiple subjective and uncertain factors are often involved in conservation corridor planning and decision-making, ranging from environmental and economic to social and political. These can limit corridor continuity, leading to corridors consisting of isolated habitat fragments that act as “stepping stones” for species movement. To provide computational support for planning such “stepping stones” corridors, we design and implement a raster-based GIS model that characterizes and searches for an optimal sequence of isolated patches across a mosaic of land cover types. The model is unique in two key aspects. First, it simultaneously selects the stepping stones and a path traversing them, which collectively form a corridor. This representation is useful for spatial planning actions engaging organisms to follow a corridor, such as identifying locations for planting or restoration. Second, unlike existing least-cost path models, no quantification of land cover types in terms of suitability (or cost) is required; their rank-ordering is used instead. While subjectivity and uncertainty may remain, they are substantially reduced. We apply the model to a conservation project in Rwanda aimed at enhancing connectivity between two national parks through the establishment of a hedgerow of native plants supporting pollinator birds’ dispersal. The results suggest that the model enables rapid initial delineation of candidate routes for stepping stone corridors and facilitates early exploratory stages of conservation planning.