Maintenance of the banks of small streams in the South Channel bocage: responses of herbaceous vegetation to ecological and agricultural processes

Abstract

Within an Observatory of Research in Environment on the catchment area of the Oir river, in south-Manche, a research project applied to the maintenance of salmon's rivers in an agricultural context (installation of fences and feeding troughs to limit the access of the cattle to the brook), is studying the importance of parameters, which structure the riparian vegetation. A small brook of watershed's head is used in preliminary study. We processed the various information, and then we used a method of multivariate analysis to treat on a hierarchical basis the factors, which determine the composition of the riparian vegetation. The principal factors that differentiate the riparian vegetation seem to be related to the recent anthropic impacts (pasture, with the trampling of banks by animals) and old ones (bocage structure: woodlands and hedges). The secondary factors are related to aspects of hydromorphology and the longitudinal gradient, which would be extended to other small brooks of this type. After a long time, these installations will strongly contribute to create a connectivity of the woody elements on the brook that did not exist (from 21 % of disconnected hedges, one passes to 3 %), but that will require a regular maintenance of the riparian vegetation. Agriculture impact and bocage connection are determinant for herbaceous vegetation composition, parameters unusually considered in riparian management, where focus are done on the hydraulic functioning.