Predicting ecological connectivity in urbanizing landscapes

Nearly half the world's population lives in urban centers, and these areas are increasingly important components of regional and global land cover. However, their ecological attributes are often overlooked, despite the presence of species, ecosystem services, and risks associated with the spread of pests or threatening processes such as fire. Movement and dispersal of organisms contribute to species persistence in urban landscapes; however, landscape patterns that promote ecological connectivity may also facilitate the spread of undesirable organisms or processes. I investigate how urban form can be used to predict ecological connectivity and assist in prioritizing urban landscapes for conservation activities and risk management. I examine the value of qualitative and quantitative descriptions of urban morphology as predictors of ecological connectivity by comparing sixty-six cities in the USA. Results show that qualitative categories are not adequate for describing ecological connectivity; multivariate descriptions are much better predictors, with urban area, number of urban patches, urban patch extent, level of aggregation, and perimeter area fractal dimension composing the significant synthetic variables. The dominance of area as a differentiating variable led to the development of a new urban connectivity index using a combination of urban area and state population size. This metric, based on readily available aspatial data, explains 78% of variation in ecological connectivity. These results provide a simple but novel tool for beginning to understand the role of urban morphology in promoting desirable environmental outcomes and managing environmental risks in urbanizing landscapes.