John Stella

Floodplain forests that line river corridors provide critical functions such as flood protection, nutrient filtration, and habitat for wildlife. These areas, called riparian zones, are far more important beyond the small proportion of land area they occupy. Most large European rivers, including the Rhône River in southeastern France, have been greatly altered by agricultural development, riverbank engineering for navigation, and dams that strongly modify natural flow conditions. Over several centuries, these cumulative impacts have severely reduced the extent of riparian zones and have confined them to highly altered river margins. As we understand more about how these critical ecosystems function, and we repurpose river margins as zones of recreation and aesthetic appreciation, we are challenged to restore ecological function while maintaining the economic values that rivers provide.

During my fellowship year with IAS and the Collegium de Lyon, I am investigating the ecological status and management options for the remnant floodplain forests that line the Rhône River. All along its length from Lyon to the Mediterranean Sea, the river’s banks remain highly altered by 19th century navigation walls that trap sediment and now support narrow ribbons of floodplain forest. This is an area of particular conservation value to many stakeholders in the Rhône Basin, including the Compagnie Nationale du Rhône (CNR), EDF, and l’Agence de l’Eau. In collaboration with Hervé Piégay (CNRS) and others at the École Normale Supérieure (Lyon), I am studying these floodplain forests using an approach adapted from my long-term research on the Sacramento River in California (USA), which like the Rhône is highly modified and drains a populated, water-limited region. In both systems I am conducting forest inventories of tree species present, their sizes and ages, and relation to environmental factors such as flooding to understand how the forest is developing in response to both natural and human controls on the river’s flow regime. With this information we plan to work with river managers to identify options that would maximize the forest’s ecological values while maintaining important functions such as flood control, navigation and water for irrigation and hydropower generation.

Beyond the scope of these two rivers, this study presents an opportunity to synthesize larger lessons for river management. How have the very different histories of river development in France and the U.S. manifested as human impacts on the ecosystem? And despite these separate histories and management contexts, are there common ecological principles and goals that we can apply to other large, regulated rivers? Finally how in these scenarios do we account for the accelerated climate changes taking place in both study regions and many others globally?