Distribution of three indigenous fern species along a rural–urban gradient in the city of Angers, France

The preservation of wild plants and animals in urban environments can be a good means to meet the demand for natural areas for recreational purposes. However, the impacts of urbanisation on native species distribution are poorly studied. A city environment has high impact on vegetal community dynamics, especially in terms of climate modification, level of perturbationand pattern of dispersion. We chose to study the three indigenous species of the genus Polypodium that are known to grow in a wide range of habitats, including forest and urban environments, and exhibit a priori a strong ability for dispersal. The aim of the study was to evaluate the factors involved in the Polypodium species distribution and to determine whether this distribution was influenced by the rural–urban gradient. The distribution of the three fern species was investigated in the city of Angers (France) at two levels: for a park (urban woodland) and for the whole city. A contrasted distribution of the three Polypodies has been recorded and shows a rural–urban gradient. This can be explained by the ecology of each species and some biological traits. It means that differences in the spatial structure of the city lead to particular patterns of distribution for these plants. Thus, preserved indigenous vegetation may be influenced in its species composition by the surrounding urban development.