How past riparian management practices can affect composition and structure of vegetation for headwater ecological restoration projects
Résumé
Ecological restoration of river networks, especially of headwaters, is a key issue to improve water ecological, chemical and physical qualities and ecological functioning of aquatic ecosystems. Ecological restoration of degraded riparian vegetation is commonly considered as an efficient way to improve headwater habitats. This study aims to describe past management dynamics and their effect on current riparian vegetation structure and composition. We focused on two headwater brooks surrounded by traditional pasture in the rural catchment of the river Oir, a salmonid nursery of the river Selune, Normandy, France. Historical riparian vegetation dynamic has been characterized thanks to interpretation of ortho-photographs from 1947 to 2010. GIS analyses allowed us to distinguish five types of management practices from stable vegetation (maintained open or maintained woody) to heterogeneous dynamic vegetation ( alternation of clear-cutting, coppice management and recolonization by ligneous species). To measure their impact on the riparian ecosystem, past management practices were linked with field data describing current structure and composition of riparian vegetation. Results show that structure of riparian plant communities depends mainly on recent management practices, while floristic composition depends both on recent and past management practices. Knowledge of the past dynamics of riparian landscapes proves to be a relevant indicator of the ecological status of headwater ecosystems that could be used to improve ecological restoration instead of classical management practices of riparian vegetation.