River Dikes in Agricultural Landscapes: The Importance of Secondary Habitats in Maintaining Landscape-Scale Diversity

摘要

Lowland rivers and their floodplains have changed markedly over the last centuries. River dikes have become among the most extensive secondary habitats of former floodplains. Our main question was, what role do secondary habitats on river dikes play in harbouring plant species and maintaining plant diversity of lowland landscapes dominated by agricultural areas? We compared historical maps and current habitat maps to understand the effects of landscape changes on the vegetation pattern of the study region, in southern Hungary. Dikes and primary vegetation of the landscape were selected for intensive vegetation sampling. We compared the floristic similarity and the Shannon diversity of the vegetation types. We used ordinations to visualize relationships among the vegetation types and among dike vegetation and environmental variables. Our results indicated that profound changes have been brought about in the vegetation during the last 150 years, resulting in a transition from marshland to agricultural land. The species composition and pattern of dike vegetation strongly depended on their relative position to the river and their aspect. We conclude that dikes can harbour many vascular plants that are absent or rare in the surrounding habitats and therefore play a decisive role in maintaining plant diversity in agricultural landscapes.