Quantifying the urban gradient: A practical method for broad measurements

Abstract

The process of habitat urbanization has intense and manifold effects on the biota that we need to better understand. The urbanization gradient approach is increasingly used in ecological research to study the responses of communities and populations of plants and animals to different degrees of landscape urbanization. However, the methods used for quantifying the urbanization gradient are heterogeneous. Here, first we validate a manual method designed for broad measures of landscape urbanization, based on major land-cover characteristics calculated from aerial images, that has been applied in former studies, and compare its results to measurements taken with a widely accepted geoinformatics software. Second, on the basis of this manual scoring method we introduce a recently developed, easily feasible, semi-automated method of measuring degree of urbanization, which uses only freely and worldwide accessible satellite imagery. Finally, we compare the results obtained by the three methods and the conclusions they yield within the framework of an ecological study conducted on birds. Our results show that the three methods quantify the urbanization gradient similarly, as the ‘urbanization scores’ they provide are strongly correlated and the results of the ecological analyses are highly repeatable across the three approaches. Since the semi-automated method grants this performance at far the lowest cost of time, we propose it as a useful tool for broad measurements of urbanization and its application can promote greater integrity between studies of urbanization effects on wildlife around the world. We also provide a download link to the free application of our semi-automated method.